the tertiary structural and thermal evolution of the central alps compressional and extensional structures in an orogenic belt the western alpine arc has been created during the cretaceous and the tertiary orogenies the interference patterns of the tertiary structures suggest their formation during continental collision of the european and the adriatic plates with an accompanying anticlockwise rotation of the adriatic indenter extensional structures are mainly related to ductile deformation by simple shear these structures developed at a deep tectonic level in granitic crustal rocks at depths in excess of 10 km in the early palaeogene period of the tertiary orogeny the main tertiary nappe emplacement resulted from a nw thrusting of the austroalpine penninic and helvetic nappes heating of the deep zone of the upper cretaceous and tertiary nappe stack by geothermal heat flow is responsible for the tertiary regional metamorphism reaching amphibolite facies conditions in the lepontine gneiss dome geothermal gradient 25 c km the tertiary thrusting occurred mainly during prograde metamorphic conditions with creation of a penetrative nw se oriented stretching lineation xi finite extension parallel to the direction of simple shear earliest cooling after the culmination of the tertiary metamorphism some 38 ma ago is recorded by the cooling curves of the monte rosa and mischabel nappes to the west and the suretta nappe to the east of the lepontine gneiss dome the onset of dextral transpression with a strong extension parallel to the mountain belt and the oldest s vergent backfolding took place some 35 to 30 ma ago during retrograde amphibolite facies conditions and before the intrusion of the oligocene dikes north of the periadriatic line the main updoming of the lepontine gneiss dome started some 32 30 ma ago with the intrusion of the bergell tonalites and granodiorites concomitant with s vergent backfolding and backthrusting and dextral strike slip movements along the tonale and canavese lines argand s insubric phase subsequently the center of main updoming migrated slowly to the west reaching the simplon region some 20 ma ago this was contemporaneous with the westward migration of the adriatic indenter between 20 ma and the present the western aar massif toce culmination was the center of strong uplift the youngest s vergent backfolds the glishorn anticline and the berisal syncline fold the 12 ma rb sr biotite isochron and are cut by the 11 ma old rhone simplon line the discrete rhone simplon line represents a late retrograde manifestation in the preexisting ductile simplon shear zone this fault zone is still active today the oligocene neogene dextral transpression and extension in the simplon area were concurrent with thrusting to the northwest of the helvetic nappes the prealpes 35 15 ma and with the jura thin skinned thrust 11 3 ma it was also contemporaneous with thrusting to the south of the bergamasc 35 5 ma and milan thrusts 16 5 ma the oligocene neogene dextral transpression in the central alps is of the same age as the thrusting to the west and southwest in the external french part and to the east in the internal italian part of the alpine arc of the western alps

identifying sediment sources in a gullied catchment using natural and anthropogenic radioactivity the ratio of the lithogenic nuclides 226ra and 232th indicates that the major source of sediment in transport in a gullied catchment located in the head waters of whiteheads creek new south wales australia is the gully itself this observation is supported by 7be and 137cs concentrations which indicate that the sediment is derived from erosion of either gully floor or gully wall material while subcatchment 7be and 137cs data show sheet rill and gully erosion are occurring in the upstream catchments sediment from these sources is either being trapped before entering the gully or the volume of sediment is small compared to that derived from the gully itself the differences in the 226ra to 232th ratio between the suspended solids collected on the rising stage and samples of sediment deposited during the falling stage at the outlet of the catchment indicate a change in the source of sediment during storm events the results presented here demonstrate the applicability of radionuclide tracers in providing quantitative estimates of the relative contributions of individual catchments to the sediment moving within a drainage network and in determining whether or not the sediments are mainly derived from subsoil or topsoil sources

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

the localized role of base level lowering on channel adjustment of tributary streams in the trinity river basin downstream of livingston dam texas usa the purpose of this study is to describe and explain river channel cross sectional change in tributary streams within the 60 km scour zone of the trinity river texas downstream of livingston dam this study investigates changes within the tributary systems to base level changes triggered by incision associated with scour and channel migration within the dammed trunk stream the dam represents a precise moment and place of a system perturbation and therefore represents an opportunistic geomorphic experiment geomorphological effects of the lower trinity river tributaries were investigated through three different types of data resurveys of bridge cross sections planform change as measured from aerial photographs and field mapping of changes in channel geometry using fallen trees undercut banks and other geomorphic indicators of change while field evidence of channel change was found at sites well upstream of tributary confluences with the trinity these were not consistent with responses to lower base level downcutting and lateral changes in response to lowered base level were confined to lower tributary reaches this suggests distance decay and lag times in transmission of responses upstream and or masking of dam induced effects by other processes and controls the most dynamic locations of geomorphic change are near the confluences of the tributaries with the trinity river where the response to dam induced incision is strongly influenced by local trunk stream morphology indicating a high degree of historical and geographical contingency

a novel method for determining residence times of river and lake sediments based on disequilibrium in the thorium decay series sediment fluxes in rivers have proved difficult to measure or model at timescales relevant to land and water resource management decisions determining transport rates and residence times is complicated by the intermittent movement and temporary storage of sediments in natural streams this paper presents a new tool for estimating the residence times of river borne sediments based on the observed disequilibria between the naturally occurring radionuclides 228ra and 232th in the thorium decay series disequilibrium between concentrations of 228ra half life 5 75 years and its long lived parent 232th has been observed in marine environments and in terrestrial freshwaters but has not been previously reported in fluvial sediments or soils here we report 228ra excesses in sandy stream and silty lake sediments from southeastern australia the excess is developed in hillslope soils in the catchment headwaters and begins to decay back to secular equilibrium once the sediment is finally removed from contact with the soil water the short half life of 228ra enables this process to be used to investigate fluvial sediment transfers and alluvial and lacustrine sediment storages over the past 30 years when combined with indicators of sediment source such as 226ra 232th and 230th 232th ratios observation of this excess should provide a useful new tool for examining the residence and transit times of bed load and suspended load sediments in streams and lakes

3d modeling of crustal shortening influenced by along strike lithological changes implications for continental collision in the western and central alps abstract the european alps show major along strike variations in the partitioning of crustal shortening between the upper and the lower plates either explained by lateral variation in temperature and rheology or by along strike changes in crustal scale lithology here we present the first 3d thermomechanical geodynamic model to test the potential impact of along strike lithological and associated rheological changes and lateral temperature variations on crustal shortening during continental collision in the western and central alps numerical modeling results suggest a minor impact of lateral thermal variations and lithological changes in the lower plate for the alpine orogeny in contrast lateral lithological changes in the upper plate structure defined by the presence of the buried ivrea body in the western alps should play a major role in determining the present day architecture of the alpine belt our models suggest that the ivrea body acts as a strong rigid buttress constraining crustal shortening to the lower plate promoting the formation of the jura fold and thrust belt and supporting the higher surface elevation observed in the western alps on the other hand in the central alps where the ivrea body is absent much broader distribution of crustal shortening results in lower surface elevation numerical modeling results also suggest that crustal shortening in the central alps is focused within the upper plate during the final stages of continental collision favored by the indentation of thickened upper crust of the lower plate and by detachment of the adriatic upper crust from the underlying lithosphere

3 d pn tomography reveals continental subduction at the boundaries of the adriatic microplate in the absence of a precursor oceanic slab abstract slab pull generated by subducting oceanic lithosphere is generally considered as a major trigger for the onset of continental subduction however this may be in conflict with the occurrence of uhp terranes bearing no evidence of oceanic lithospheric rocks involved in the exhumation cycle here we image the uppermost mantle p velocity structure beneath the central mediterranean suggesting the possibility that the initiation of continental subduction may not require a precursor oceanic slab we combine i a three step inverted 3 d pn tomography model of the adriatic microplate with ii available geologic constraints and palinspastic reconstructions of the africa eurasia plate boundary zone our pn tomography model reveals elongated regions with vp

determining the times and distances of particle transit in a mountain stream using fallout radionuclides abstract targeting of erosion and pollution control programs is much more effective if the time for fine particles to be transported through a watershed the travel distance the proportions of old and new sediment in suspension and the rate of erosion of the landscape can be estimated in this paper we present a novel technique for tracing suspended sediment in a mountain stream using fallout radionuclides sorbed to sediment atmospherically delivered 7 be 210 pb and 137 cs accumulate in the snowpack are released with its melting and sorb to fine particulates a portion of which are carried downslope into stream channels the half life of cosmogenic 7 be is short 53 4 days thus sediment residing on the stream bed should contain little of the radionuclide the different signatures of newly delivered sediment from the landscape with its 7 be tag and older untagged sediment from the channel is the basis for the tracing the total flux of such radionuclides compared to the inventory in the soil permits estimates of the rates of erosion of the landscape fine suspended particulates in the gold fork river id are transported downstream through the drainage in one or more steps having lengths of tens of kilometers length of the step decreases from about 60 km near the peak of the hydrograph to about 12 km near baseflow the percent of sediment in suspension that is new i e recently delivered from the landscape ranges from 96 to 12 the remaining sediment is resuspended older channel sediment residence times for particulates range from 1 6 days early in the hydrograph at the upper site to 103 days late in the hydrograph at the lowest elevation location rates of erosion of fine sediment calculated from the flux of radionuclides average 0 0023 cm year the long distance transport of fine particles suggests that delivery through the gold fork drainage to the basin outlet is fairly rapid once particles reach the channel and perhaps is also rapid in similar and smaller basins

dam to delta sediment inputs and storage in the lower trinity river texas livingston dam on the trinity river in se texas usa disrupts the transport of sediment to the lower trinity river and the trinity bay galveston bay estuary however a sediment budget of the lower basin shows that the effects of this disruption are undetectable in the lower river sediment trapped in lake livingston is partly offset by channel erosion downstream of the dam and by inputs from the lower basin most importantly however the lower coastal plain reaches of the trinity are characterized by extensive alluvial storage and are a bottleneck that buffers the bay from effects of upstream changes in sediment flux storage is so extensive that the upper trinity basin and the lowermost river reaches were essentially decoupled in the sense that very little upper basin sediment reached the lower river long before the dam was constructed whereas sediment storage in lake livingston is extensive alluvial storage on the trinity flood plain is even more extensive dam related sediment starvation effects are noted for about 52 km downstream and the sediment budget suggests that a majority of the sediment in this reach is likely derived from channel scour and bank erosion the capacious alluvial storage in the lower trinity not only limits flux to the bay but the large amount of remobilizable alluvium also allows the system to adjust to localized sediment shortages as illustrated in the dam to romayor reach internal adjustments within the lower trinity river valley thus buffer the bay from changes in sediment supply upstream

bank accretion and the development of vegetated depositional surfaces along modified alluvial channels this paper describes the recovery of stable bank form and development of vegetated depositional surfaces along the banks of channelized west tennessee streams most perennial streams in west tennessee were straightened and dredged since the turn of the century patterns of fluvial ecological responses to channelization have previously been described by a six stage model dendrogeomorphic tree ring techniques allowed the determination of location timing amount and rate of bank sediment deposition channel cross sections and ecological analyses made at 101 locations along 12 streams encompassing bends and straight reaches show that channel and bank processes initially react vertically to channelization through downcutting a depositional surface forms on banks once bed degradation and heightened bank mass wasting processes have eased or slowed the formation of this depositional surface marks the beginning of bank recovery from channelization dominating lateral processes characteristic of stable or natural channels return during the formation and expansion of the depositional surface suggesting a relation with thalweg deflection point bar development and meanderloop extension characteristic woody riparian vegetation begins to grow as this depositional surface develops and becomes part of the process and form of restabilizing banks the depositional surface initially forms low on the bank and tends to maintain a slope of about 24 mean accretion rates ranges from 5 9 cm yr on inside bends to 0 cm yr on most outside bends straight reaches have a mean accretion rate of 4 2 cm yr the relatively stable convex upward depositional surface expands and ultimately attaches to the flood plain the time required for the recovery process to reach equilibrium averaged about 50 years indicative pioneer speccies of woody riparian vegetation include black willow river birch silver maple and boxelder stem densities generally decrease with time after and initial flush of about 160 stems per 100 m2 together bank accretion and vegetative regrowth appear to be the most important environmental processes involved in channel bank recovery from channelization or rejuvenation

the late archaean melita complex eastern goldfields western australia shallow submarine bimodal volcanism in a rifted arc environment abstract the melita volcanic complex is a late archaean bimodal rhyolite basalt volcanic succession within the gindalbie terrane in the eastern goldfields province of the yilgarn craton the melita complex has been dated by ion probe at 2683 3 ma 95 and forms part of a distinctive 2681 2692 ma volcanic association that records bimodal basalt rhyolite and calc alkaline intermediate silicic volcanism at several discrete volcanic centres and which locally hosts volcanic massive sulphide mineralisation teutonic bore approximately 3 km of stratigraphic thickness is exposed in the melita area the upper 1 1 5 km of the exposed succession is dominated by subaqueously resedimented volcaniclastic sandstones and breccias rhyolite flows and sills primary subaerial pyroclastic deposits including ignimbrites have not been identified in this study although subaerial explosive activity is indicated by the occurrence of accretionary lapilli and the abundance of vitric material shards and pumice fragments in resedimented deposits the lower part of the succession is dominated by pillowed to massive basalt lavas and in situ and resedimented mafic hyaloclastites mafic extrusive and intrusive rocks are tholeiitic with trace element concentrations similar to modern arc tholeiites felsic volcanic rocks at melita are dacite to high silica rhyolite they are highly enriched in incompatible elements particularly high field strength element enriched compared to other felsic associations in the eastern goldfields province representing evolved partial melts of heterogeneous intermediate arc type crust the volcanic facies and geochemistry of volcanic rocks at melita are consistent with those observed in modern intra arc or arc rift settings and the succession is interpreted to represent the initial stages of back arc rifting within a complex convergent margin

physical volcanology and geochemistry of a late archaean volcanic arc kurnalpi and gindalbie terranes eastern goldfields superterrane western australia abstract late archaean 2715 2704 ma calc alkaline volcanic complexes in the kurnalpi terrane are identical in facies and geochemistry to modern intra arc volcanic complexes preserved volcanic rocks and associated feldspathic sedimentary rocks represent proximal to medial submarine facies of submarine to locally emergent intra oceanic arc related volcanoes the least altered volcanic rocks are dominantly andesite but range from basalt and basaltic andesite to rare rhyolite and are the product of magmas similar in composition to those of modern arcs intermediate magmas were most likely derived from large ion lithophile element lile enriched mafic magmas by fractional crystallisation with or without assimilation processes the kurnalpi terrane thus provides an example of a late archaean volcanic arc in which hydrated mantle wedge melting was the main mechanism for magma genesis ttd suite volcanism derived from slab melting was either absent or played a subordinate role the adjacent gindalbie terrane contains younger 2692 2680 ma bimodal basalt rhyolite volcanic complexes with associated quartz rich sedimentary rocks and calc alkaline intermediate silicic volcanic complexes volcanosedimentary basement to the gindalbie volcanic sequences is deeply eroded equivalents of the calc alkaline volcanic complexes their associated sedimentary rocks and younger basaltic sequences found in the kurnalpi terrane gindalbie basalt rhyolite successions locally contain volcanic hosted massive cu zn mineral deposits rhyolites derived by low pressure fractional crystallisation or melting of andesites are more abundant than in the kurnalpi volcanic complexes facies associations and the local occurrence of distinctive incompatible element enriched mildly peralkaline a type rhyolites are consistent with rifting of a mature arc system the two terranes most likely represent volcanic evolution of the same late archaean volcanic arc but are different tectonic fragments that were welded together by 2660 ma

contemporaneous plutonism and strike slip faulting a case study from the tonale fault zone north of the adamello pluton italian alps 1 a field microstructural and geochronological study of contemporaneous plutonism and strike slip faulting along the eastern tonale fault zone provides new insights into the interrelationships between magmatic emplacement contact metamorphism and shearing and it places new time constraints for the periadriatic fault system although pluton emplacement and shearing were not caused by each other they mutually interacted during contact metamorphism the character of the composite tonale fault zone varies considerably with its proximity to the northern margin of the adamello pluton from a paired greenschist facies mylonite belt northern mylonite zone and cataclastic fault zone in the west to a fault zone consisting of northern mylonite zone cataclastic fault zone and a second mylonite belt southern mylonite zone formed by contemporaneous shearing and contact metamorphism in the east ongoing strike slip motion led to telescoping and advective cooling of the deforming contact aureole new u pb zircon ages for the northernmost adamello intrusions the avio at 34 6 1 0 ma and the presanella at 32 0 2 3 ma date the onset of contact metamorphism rb sr and k ar cooling ages and new zircon fission track ages provide evidence that postintrusive cooling to below 300 c was achieved rapidly i e approximately 30 myr ago being consistent with a shallow crustal emplacement at ambient temperatures of approximately 250 c cataclastic dextral strike slip faulting continued until about 20 ma when the tonale fault zone became offset by a number of minor sinistral shears and by the giudicarie fault hence dextral strike slip motion along the periadriatic fault system east of the bergell pluton lasted from approximately 35 20 myr ago

architecture of the neoarchaean jaguar vhms deposit western australia implications for prospectivity and the presence of depositional breaks abstract the duration and nature of breaks in archaean volcanosedimentary packages recently re evaluated in the abitibi greenstone belt has been assessed at jaguar an archaean cu zn rich volcanic hosted massive sulphide vhms deposit in the teutonic bore volcanic complex tbvc the eastern goldfields of the yilgarn craton western australia the deposit is hosted by coherent volcanic facies and associated volcaniclastic facies with minor non volcanic facies the hypothesis that vhms ore lies on the intersection of volcanic centres and depositional breaks is found to be valid for the jaguar deposit with the site being an active volcanic complex at footwall time with further dome development close to the final ore location at mineralised package time and then reoccurring volcanic complexes andesitic and basaltic at several points in the hangingwall succession broadly tied into the ore position at jaguar the entire stratigraphic sequence faces west with no major structural complications making it ideal for stratigraphic analysis the footwall evidences prolific volcanism with no intervening sedimentation the mineralised package mp consists of intercalated dacite breccia conglomerate sandstone and mudstone the footwall volcanic rocks and the mp dacite appear to be differentiation products from the same magma chamber a major volcanic geochemical boundary is identified between the footwall mp tholeiitic to transitional affinities and the immediate hangingwall succession calc alkaline the hangingwall package includes four distinct volcanic units intercalated with mass flow deposits and graphitic argillites vhms mineralisation occurred across a distinct change in the geochemistry of erupted volcanic facies at a time of increased volcaniclastic sedimentation and extension this break is comparable to member level hiatuses seen in the abitibi gb i e the most brief of breaks because there is no silicification of sedimentary unit tops by silicic seawater exposure and there is minimal development of black shales a third time sensitive criteria was the development of peperite on the base of hanging wall hw andesite lavas the mp closely resembles breaks within interpreted deeper water domains of the abitibi gb for instance the deloro tisdale assemblage interface south of timmins the recognition of the change in the rate of emplacement of volcanic units and particularly the change in chemistry of volcanic rocks are critical exploration lithologic guides to use in the absence of chemical sediment deposits exhalites although crustal extension and basin subsidence were factors in the shaping of the succession their effects were too subtle to use as an exploration tool a corollary of the recognition of a member level vhms bearing interval in the teutonic bore volcanic complex is that like the kidd munro assemblage stratigraphy abitibi gb where several ore bearing depositional breaks are known below the great kidd creek deposit there is scope for the discovery of further potentially larger deposits on higher formation or group level breaks in the tbvc

sediment storage and yield in an urbanized karst watershed abstract in karst watersheds sinkholes and other drainage features control the temporal and spatial pattern of sediment storage across the landscape however studies dealing with sedimentation in karst watersheds are scarce and the sediment storage function of sinkholes and caves has not been investigated using a sediment budget approach in this study we use estimates of channel erosion sinkhole sedimentation and suspended sediment yield to examine changes in sediment storage in the 9 km 2 upper pigeon roost creek fluviokarst watershed near cookeville tn the study watershed has undergone urbanization over the last 50 years and sinkholes and caves in the area show signs of recent sedimentation buried tree roots buried cultural artifacts etc while sinkholes are generally considered to be sediment sinks sinkholes examined in this study are shown to cycle between periods of net sediment storage and net sediment loss using copyright dates on trash items buried in sinkhole deposits we estimated the residence time of sinkhole stored sediment to range from 6 to 10 years however other evidence indicates that some sinkholes may store sediment for several centuries we propose that sediment storage within sinkholes is controlled by several factors including sinkhole drainage area sinkhole morphology and basin sediment yield in addition changes in sediment storage in karst watersheds are contingent upon random events such as sinkhole collapses annual sediment yield was estimated to be 111 mg km 2 year 1 for the entire study watershed and ranged from 11 to 128 mg km 2 year 1 for 3 sub watersheds sediment eroded from the watershed perhaps during historic settlement of the area is stored within a large cave system underlying the city however the results of a partial sediment budget indicate that the cave is presently a net sediment source overall the findings indicate that the sediment storage function of caves and sinkholes varies spatially and temporally and that these changes need to be incorporated into sediment budgets for karst watersheds

bias associated with detrital zircon geochronology and thermochronometry detrital studies that utilize zircon u pb geochronology and fission track ft thermochronometry are subject to a range of potential sources of bias that should be properly evaluated and minimized some of them are common to any single grain mineral analysis e g variable bedrock mineral fertility hydraulic sorting during transport selective grain loss during sample processing whereas others are intrinsic to zircon and are related to radiation damage and age discordance in this article we quantify the impact of intrinsic bias on detrital studies thanks to the analysis of modern detritus shed from the european alps and illustrate the general implications on geological interpretations we show that detrital zircon u pb age distributions based on statistically robust datasets are highly reproducible and representative of the parent bedrock ages in the catchment arbitrary or selective removal of discordant grain ages can be minimized by using the kolmogorov smirnov test to identify an appropriate cutoff level loss of metamict damaged zircon has a minor impact on data representativeness and is mainly controlled by regional metamorphism rather than by mechanical abrasion during river transport zircon ft grain age distributions were found to have poor reproducibility although age spectra are consistent with bedrock data however unlike the u pb datasets u rich zircon grains 1000 ppm are systematically missed and undatable grains may exceed 50 we identify two major sources of distribution bias specific to zircon ft datasets i sediment sources dominated by u rich zircon grains are markedly underrepresented in the detrital record because such grains often have uncountable high densities of fission tracks u concentration bias ii sediment sources that shed zircon grains with high levels of damage are underrepresented because these grains are lost during chemical etching for ft revelation etching bias in the case of multimethod dating on the same grains e g ft and u pb double dating bias affecting detrital zircon ft dating propagates to the entire dataset these effects may not impact on exhumation rate studies that utilize the youngest grain ages i e lag time approach however they represent a limiting factor for conventional provenance studies and generally preclude application of zircon ft dating to sediment budget calculations

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

deciphering the tectonic evolution of archaean greenstone belts the importance of contrasting histories to the distribution of mineralization in the yilgarn craton western australia abstract the distribution of archaean metallic mineral deposits reflects tectonic controls operating during the evolution of granitoid greenstone terranes tectonic analysis of these terranes not only allows recognition of parameters that may be important in interpreting the tectonic histories of greenstone belts but also the resultant tectonic control on mineral deposit distribution in the yilgarn craton of western australia the late archaean 2 7 ga norseman wiluna belt is most intensely mineralized with both komatiite associated ni cu deposits and epigenetic gold deposits this belt is dominated by 2 7 ga supracrustal successions and its tectonic history is that of an orogenic belt at an obliquely convergent craton or proto craton margin tectonostratigraphic associations preserved resemble younger volcanic arc and back arc basin crust and many represent the remains of a volcanic arc and back arc basin complex developed in response to westward dipping subduction these sequences were deformed metamorphosed and intruded by granitoids relatively soon 30 ma after the major period of volcanism with gold mineralization occurring late in the orogenic event possibly during uplift in contrast greenstone belts in the murchison and southern cross provinces are dominated by older supra crustal successions that contain 2 9 ga volcanosedimentary associations characterized by extensive oxide facies banded iron formations bifs bifs appear to have been deposited in shelf or platform environments in intra oceanic or passive craton margin settings komatiite associated ni cu mineralization and volcanogenic cu zn mineralization are locally hosted by favourable tectonostratigraphic associations the main period of deformation metamorphism and gold mineralization in these provinces was broadly synchronous with that in the norseman wiluna belt as was regional granitoid emplacement during this event strain was probably transmitted from the eastern margin of the craton via a yilgarn wide system of shear zones faults and fold belts gold mineralization is developed best in greenstone belts such as the meekathara mt magnet belt that contain large scale fault systems and internal granitoids similar tectonic controls on the distribution of mineral deposits can also be recognized in other archaean cratons and the heterogeneous distribution of archaean mineral deposits probably reflects a range of tectonic settings as well as different stages in the evolution of individual cratons

the recent history of erosion and sedimentation on the southern tablelands of southeastern australia sediment flux dominated by channel incision abstract as in other regions colonised from europe within the last few centuries australia s vegetation and soils have been dramatically changed by clearing cropping and grazing in southeastern australia particularly on the southern tablelands the impacts of european settlement are clearly manifested by channel incision by using stratigraphic and documentary evidence in conjunction with aerial photographs sediment budgets for the post settlement period have been constructed to define the fluxes and stores of sediment for each of the major geomorphic components of the 136 km2 catchment of jerrabomberra creek near canberra using these budgets and some plausible assumptions it has been possible to approximate the history of both the sediment delivery ratio and sediment yield for this catchment while the quantities estimated in this analysis are approximations the trends through time are credible sediment yield increased rapidly to a peak after european settlement and has returned to a level between the peak and the pre european value the delivery ratio has followed a similar trend the most general conclusion to emerge is that in this landscape both the total sediment flux and the sediment yield of the catchment have been dominated by channel erosion this result is contrary to the findings in many parts of the world where sheet and rill erosion dominates the fluxes the soil conservation implication of these results is clear to control off site effects of erosion the focus must be on the channels

deformation and recrystallization of plagioclase along a temperature gradient an example from the bergell tonalite abstract syn to post mylonitic tilting of the bergell tonalite allows investigation of the deformation and recrystallization of plagioclase grains along a temperature gradient from the lower to the upper amphibolite facies at the lowest temperatures recrystallization occurs by nucleation and growth of new grains having a different composition from the old grains in contrast at the highest temperatures recrystallization occurs by subgrain rotation associated with grain boundary migration the temperature increase is inferred to induce this transition in two ways first at higher temperatures the anorthite content of the new grains is higher and thus the comositional difference between old and new grains is lower hence the chemical driving potential is small compared with recrystallization at lower temperatures second higher temperatures facilitate climb of dislocations and thus subgrain formation as well as grain boundary mobility the temperature increase is also associated with a transition in the dominant deformation mechanism intracrystalline plasticity dominates deformation at lower temperatures whereas at higher temperatures deformation occurs primarily by diffusion accommodated grain boundary sliding as indicated by the weakening of the indicatrix preferred orientation and the formation of a mixed plagioclase biotite matrix with increasing deformation therefore the strength of the mid to lower crust may be overestimated by dislocation creep flow laws for plagioclase lower crust rheology for polyphase rocks is better approximated by constitutive relationships involving diffusion accommodated grain boundary sliding

assessment of different colour parameters for discriminating potential suspended sediment sources and provenance a multi scale study in luxembourg abstract sediment colour has recently been used successfully to estimate suspended sediment sources in small catchments using the fingerprinting approach the methodology offers opportunity for further research since it provides a rapid and cheap means for investigating sediment sources however the colour based fingerprinting approach has not yet been tested in medium and large catchments this paper aims to test whether colour parameters are capable of discriminating sediment sources in a nested system of seven sub catchments ranging from 0 7 to 247 km 2 of the attert river catchment nw luxembourg time integrated suspended sediment samples and samples of potential sediment sources land use types and channel banks were collected in all catchments sediment colour was then computed from diffuse reflectance spectrometry measurements asd fieldspec ii spectrometer 0 4 2 5 m taken over the visible wavelength range twenty four colour parameters were derived from several colour space models cie xyy cie xyz rgb munsell hvc helmholtz chromaticity cieluv and cielab and their ability to discriminate potential suspended sediment sources and provenance was evaluated and compared results demonstrated that time integrated suspended sediment samples collected in the study catchments had statistically different colour values moreover these values always represented a mixture of the colour values measured on potential suspended sediment sources in the catchment inter source colour contrasts land use types and channel banks were observed in all catchments kruskal wallis h test however although colour is able to distinguish potential sediment sources in small catchments the level of source discrimination decreases as the catchment size increases probably due to heterogeneous geology and pedology intra source variability and to source overlap nevertheless in the studied medium sized catchments ranging from 19 4 to 247 km 2 colour could differentiate between topsoil and sub surface i e channel bank material and or up to three sources types no single colour model had discrimination power across catchments instead in each catchment a different combination of colour parameters gathered from different colour space models produced optimal discrimination of potential sediment sources furthermore a colour based fingerprinting approach did not possess potential for integrating spatial provenance and source type information because colour parameters could not discriminate between contrasting geological sub areas in summary although colour parameters were not capable of discriminating the range of land use type and channel banks as potential suspended sediment sources in medium sized catchments they afford substantial information and could be integrated into the classical fingerprinting approach together with other constituents e g geochemistry radionuclides and or organic compounds

riparian vegetation and fluvial geomorphic processes abstract riparian vegetation and fluvial geomorphic processes and landforms are intimately connected parts of the bottomland landscape relations among vegetation processes and landforms are described here for representative streams of four areas of the united states high gradient streams of the humid east coastal plain streams great plains streams and stream channels of the southwestern united states vegetation patterns suggest that species distributions in the humid east are largely controlled by frequency duration and intensity of floods along channelized streams vegetation distribution is largely controlled by variation in fluvial geomorphic processes cycles of degradation and aggradation in response to increases in channel gradient associated with channelization similarly riparian vegetation of great plains streams may be controlled by fluxes in sediment deposition and erosion along braided streams patterns of riparian vegetation in semi arid regions may be most closely related to patterns of water availability unlike most other streams in more humid environments channel equilibrium conditions control stability of the coincident fluvial landform and attendant vegetation pattern throughout the continent in most situations riparian vegetation patterns are indicative of specific landforms and thus of ambient hydrogeomorphic conditions

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

tracking adria indentation beneath the alps by detrital zircon u pb geochronology implications for the oligocene miocene dynamics of the adriatic microplate the adriatic microplate is a key player in the western mediterranean tectonic puzzle but its oligocene miocene dynamics are not yet fully understood in fact even though the timing and magnitude of adriatic slab rollback and backarc extension in the apennines have long been established the timing of progressive adria indentation beneath the central alps and major strike slip motion along the insubric fault are still poorly constrained here we tackle these issues by utilizing detrital zircon u pb geochronology on adriatic foredeep turbidites i e by comparing the geochronologic fingerprints of the exhuming tectonic domes of the central alps ticino and toce subdomes with those of the oligocene miocene turbidites chiefly derived from their erosion we analyzed 11 sandstone samples ranging in age from 32 to 18 ma the ratio between variscan and caledonian zircon grains which are dominant in the toce and ticino subdomes respectively sharply increases at ca 24 23 ma this major provenance change marks the westward shift of the adriatic indenter beneath the central alps and the associated right lateral activity of the insubric fault the coexistence of strike slip motion at the northern boundary of the adriatic microplate at ca 24 23 ma and trench retreat during scissor type backarc opening to the west requires a near vertical rotation axis located at the northern tip of the ligurian provencal basin we propose that the rotation axis position was controlled by the interaction between the european and the adriatic slabs which may have collided at depth by the end of the oligocene triggering the westward shift of the adriatic indenter beneath the central alps

multiple sulfur isotope analyses support a magmatic model for the volcanogenic massive sulfide deposits of the teutonic bore volcanic complex yilgarn craton western australia we report sensitive high mass resolution ion microprobe stable isotopes shrimp si multiple sulfur isotope analyses 32s 33s 34s to constrain the sources of sulfur in three archean vms deposits teutonic bore bentley and jaguar from the teutonic bore volcanic complex of the yilgarn craton western australia together with sedimentary pyrites from associated black shales and interpillow pyrites the pyrites from vms mineralization are dominated by mantle sulfur but include a small amount of slightly negative mass independent fractionation mif anomalies whereas sulfur from the pyrites in the sedimentary rocks has pronounced positive mif with 33s values that lie between 0 19 and 6 20 with one outlier at 1 62 the wall rocks to the mineralization include sedimentary rocks that have contributed no detectable positive mif sulfur to the vms deposits which is difficult to reconcile with the leaching model for the formation of these deposits the sulfur isotope data are best explained by mixing between sulfur derived from a magmatic hydrothermal fluid and seawater sulfur as represented by the interpillow pyrites the massive sulfide lens pyrites have a weighted mean 33s value of 0 27 0 05 mswd 1 6 nearly identical with 0 31 0 08 mswd 2 4 for pyrites from the stringer zone which requires mixing to have occurred below the sea floor we employed a two component mixing model to estimate the contribution of seawater sulfur to the total sulfur budget of the two teutonic bore volcanic complex vms deposits the results are 15 to 18 for both teutonic bore and bentley much higher than the 3 obtained by jamieson et al 2013 for the giant kidd creek deposit similar calculations carried out for other neoarchean vms deposits give value between 2 and 30 which are similar to modern hydrothermal vms deposits we suggest that multiple sulfur isotope analyses may be used to predict the size of archean vms deposits and to provide a vector to ore deposit but further studies are needed to test these suggestions

burial and exhumation across the alps apennines junction zone constrained by fission track analysis on modern river sands terra nova 24 221 226 2012 abstract we applied fission track analysis on modern river sands to constrain the cenozoic evolution of the alps apennines junction zone west of the villalvernia varzi ottone fault samples yielded major peaks at 33 36 and 62 65 ma showing that apatites in the eroded wedge top successions were largely unreset to the east samples yielded prominent peaks at 4 0 4 7 6 5 6 7 and 19 ma probably formed by reset ages our results indicate that the alpine orogenic wedge originally tapered out to the south the northern apennines were buried beneath a thick and widespread epiligurian cover now almost completely eroded and experienced major uplift and erosional exhumation since early pliocene times at average rates of 1 km ma 1 a large amount of alpine derived detritus previously stored on top of the orogenic wedge was transferred into the po plain sediment recycling thus overwhelmed any eventual effect of climate change on plio quaternary sedimentation rates south of the alps

revealing exhumation of the central alps during the early oligocene by detrital zircon u pb age and fission track double dating in the taveyannaz formation

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

chemical weathering of fluvial sediments during alluvial storage the macuapanim island point bar solimoes river brazil abstract modification of sediment composition by chemical weathering depends both on the overall intensity of weathering and on its duration at macuapanim island solimboes river amazon main channel brazil a number of alluvial deposits have been exposed to intense tropical weathering for differing lengths of time in the very fine sand fraction the detrital component shows a steady and marked increase in compositional maturity with increasing sediment age immature sands of arkosic to litharenitic composition show a progressive loss of lithic fragments feldspars and accessory minerals with a concomitant enrichment in quartz this process produces first cycle sands whose detrital component is of quartz arenite composition among the salts quartz is enriched over time relative to more nstable phases particularly plagioclase this enrichment is probably largely caused by the destruction of plagioclase through chemical weathering but silt size quartz may also be produced through the breakdown of sedimentary and metasedimentary lithic fragments in the sand fraction in the clay fraction an increase in the relative abundance of smectite accompanies the breakdown of volcanic lithic fragments in the sand fraction and probably reflects the degradation of volcanic glass the clay fractions of the oldest samples examined contain less smectite somewhat more kaolinite and markedly more vermiculite as compared to younger samples but an extensively leached cation poor clay fraction analogous to the quartz dominated silts and sands is never attained the compositional mat rity of the clay fraction is everywhere lower than that of associated silts and sands perhaps because of a continual influx into the clay fraction of immature cation rich clays derived from the physical breakdown of lithic fragments in coarser size fractions this effect is enhanced by the translocation of fines whereby younger less weathered fine material is juxtaposed with older more mature coarse material in the lower levels of the alluvial stratigraphy reworking of floodplains during channel migration results in the reincorporation of older material stored on the floodplains into the sediment load if sediments have been intensely weathered during storage on the floodplain then the result will be a net dilution and replacement of younger relatively immature sands transported by the river by older more mature material from the floodplain the relative proportion of the older sands in the bedload will increase downstream resulting in a progressive downstream increase in the compositional maturity of the bedload of the river

emplacement related deformation of granitoid magmas southern adamello massif italy the lago della vacca suite in the tertiary adamello massif italian alps is a small 10 km 2 crudely zoned granitoid pluton emplaced at a pressure of 3 5 kbar into folded mesozoic sediments and precursor intrusive rocks field relations and detailed mapping reveal a temporal evolution in the style of emplacement from early passive stoping by the mafic to intermediate composition marginal units to later forceful emplacement of the more silicic core marginal units of the pluton have highly discordant stoped outer contacts against folded triassic carbonates and precursor mafic ultramafic rocks in contrast the core units have steeply inward dipping contacts against these marginal units magmatic foliations defined by the planar alignment of plagioclase amphibole and biotite and by mafic enclaves are well developed in all units they describe steeply inward dipping concentric trajectories that approximately parallel unit contacts and in general increase in intensity toward the pluton margin lineations are rarely present the most intensely foliated rocks occur in the marginal units as anastomosing sinuous bands that wrap around lenses of less intensely foliated granitoid three dimensional strain analysis using mafic enclaves from throughout the pluton indicates that these bands represent zones of very high strain strain ellipsoids are weakly prolate within the core of the pluton becoming increasingly oblate as strain increases toward the pluton margin the short axis z of the strain ellipsoid is uniformly subnormal to the foliation suggestive of radial flattening textures of the marginal rocks which record high strain coupled with amphibole plagioclase thermometry indicate that deformation occurred in the magmatic or submagmatic state 650 780 c and was accompanied by significant migration of interstitial melt the documented transition from passive to forceful emplacement and final geometry of the suite resulted from temporal changes in the rheology of both the magma and adjacent country rocks pulses of low density hydrous magma were initially emplaced by stoping denser country rocks on cooling and solidification these magmas contracted by 15 20 creating an unpressured volume which allowed subsequent magma pulses to be emplaced into the pluton core these pulses distended and flattened their partially molten carapace and those parts of the aureole that had been thermally softened by intrusion of earlier magmas emplacement of the lago della vacca suite was therefore the product of several internal or magma related processes an interaction between stoping radial expansion and volume contraction on solidification of the hydrous magmas the heterogeneous distribution of strain in the marginal units reflects local variations in temperature and most importantly in the distribution of interstitial melt during emplacement

the role of strain localization in the segregation and ascent of anatectic melts namaqualand south africa granulite facies gneisses of the late proterozoic okiep copper district of the namaqua province in south africa preserve evidence of a range of anatectic melt features that reflect the initial stages of segregation and ascent of crustally derived magmas during high grade metamorphism these melt bodies include both in situ and sharply transgressive subvertical pipe like bodies that show vertical dimensions of several hundreds of metres and horizontal dimensions of tens to hundreds of metres migmatite bodies are spatially closely linked with narrow upright zones characterized by intense high strain fabrics locally referred to as steep structures they display a progressive textural development from diktyonitic textures in in situ bodies via schollen and raft textures to largely homogeneous intrusive granites that have migrated vertically for distances of several hundreds of metres or more the intimate association of the migmatite bodies with the steep structures reflects strain induced melt segregation facilitated by increased permeabilities in these ductile deformation zones and migration of melts into sites of strain incompatibility at the intersections between the regional subhorizontal gneissosity and the superimposed high strain zones subsequent melt migration was focused along the network of subvertical structural anisotropies provided by the steep structures melt migration was controlled by a combination of buoyancy shear enhanced melt compaction during ongoing deformation melt compaction due to the settling of wall rock fragments from higher stratigraphiclevels and subordinate brittle fracturing the unusual geometry of the steep structures and the intensely heterogeneous nature of the strain and the absence of similar strain features and voluminous melt bodies elsewhere in the granulite facies terrane suggest a positive feed back mechanism between melt generation and strain localization in steep structures the structural development of the migmatite bodies illustrates that the efficiency of melt segregation and migration in a mid crustal segment is dependent not only on the fertility of its lithologies but also on its deformational style

slope channel decoupling in wolumla catchment new south wales australia the changing nature of sediment sources following european settlement within a few decades of european settlement channel incision transformed discontinuous river courses throughout wolumla catchment on the south coast of new south wales australia the development of continuous channels greatly increased sediment delivery from the catchment this paper documents the character timing and proportion of sediment sourced from upland valley fills channel expansion sites and gully networks volumes of material transferred from these sources are compared with estimates of sediment eroded from hillslopes and the movement of sediment off the slopes to the valley floor is assessed although disturbance of slopes resulted in significant movement of materials most of this material has been stored on slope in trapped tributary fills and along lower order drainage lines the slopes are effectively decoupled from the channel sediment accumulation in farm dams over the past few decades has been negligible around 75 of the total volume of material released from creeks in wolumla catchment since 1865 i e 5500 103 m3 has been derived from channel incision into valley fills at the base of the escarpment sediment flushing occurred within a few decades of catchment disturbance bedrock confinement in the middle and lower catchment resulted in very efficient downstream transfer of materials although gully networks and channel expansion sites have released a relatively small volume of material these sources are the greatest contemporary source of sediment in wolumla catchment

the building of the central swiss alps an experimental approach abstract a kinematic model explaining the building of the central swiss alps is proposed from a review of various kind of data including structural geophysical petrological and geochronological data the eo alpine event is taken into account in order to determine the thermo mechanical evolution from the cretaceous to the late tertiary the stacking process of crustal wedges which took place during cretaceous time has led to the formation of a thickened crust with a very low geothermal gradient high pressure low temperature metamorphism this period was followed by a lull in tectonic activity during which thermal relaxation took place the major tertiary deformation is thought to result from horizontal compression of a thickened crust having a geothermal gradient higher than the average horizontal surface forces are due to the adriatic sub plate acting as a rigid indenter the model explaining the present day structure of the swiss alps emphasizes vertical extrusion and horizontal intrusion of the deepest highly ductile basement units several scale model experiments have been carried out in order to test this basic kinematic idea they display quite similar structures to those identified for the swiss alps striking features of the swiss alps such as their metamorphic and uplift history are discussed and compared with the timing of the tectonic evolution we conclude that the general process of vertical extrusion and horizontal intrusion can possibly explain the overall structure of the central swiss alps external crystalline massifs and the penninic zone

2 7 ga plume associated vhms mineralization in the eastern goldfields superterrane yilgarn craton insights from the low temperature and shallow water ag zn au nimbus deposit economic volcanic hosted massive sulfide vhms deposits of the archaean yilgarn craton of western australia are restricted to zones of juvenile crust as revealed through regional nd pb and hf isotopic variations and the geochemistry of felsic volcanic rocks interpreted as archaean paleo rift zones one of these runs n s through the eastern goldfields superterrane broadly coincident with the kurnalpi terrane and is associated with the high grade ca 2690 ma teutonic bore jaguar and bentley deposits plus sub economic vhms mineralization further south to date only small historic cu occurrences e g anaconda and barren pyritic lenses have been recognized in the older 2 7 ga plume dominated lower stratigraphy of the eastern goldfields superterrane the nimbus ag zn au deposit 12 1 mt at 52 g t ag 0 9 zn and 0 2 g t au is located approximately 10 km east of kalgoorlie near the margin of the kurnalpi terrane its origin has been contentious for a number of years with previous models favouring seafloor sub seafloor vhms mineralization or a high sulfidation fault hosted system we present a detailed account of the deposit its host stratigraphy and associated hydrothermal alteration plus two new shrimp u pb zircon ages pb isotope galena and o isotope zircon constraints compared to other vhms occurrences in the yilgarn craton the nimbus deposit is unusual in terms of its tectono stratigraphic position the geochemistry of its host sequence i e fi affinity felsic volcanic rocks ocean plateau like low th basalts mineralogy e g abundance of ag sb pb as bearing sulfosalts high hg low cu and quartz carbonate sericite dominated alteration assemblages classification of nimbus as a shallow water and low temperature vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit is consistent with its position near the margin of the kurnalpi paleo rift zone and radiogenic 238u 204pb values the recognition that the nimbus deposit is associated with c 2705 ma plume magmatism opens new areas for vhms exploration in the eastern goldfields superterrane over a strike length exceeding 500 km

magnetic fabric and pluton emplacement in a transpressive shear zone system the itaporanga porphyritic granitic pluton northeast brazil the itaporanga granitic pluton intruded into the lithological contact separating neoproterozoic pelitic metasediments from meso to paleoproterozoic rocks that constitute the cachoeirinha belt of northeastern brazil an aureole of pelitic gneisses containing sillimanite and andalusite indicates that emplacement occurred at 12 15 km depth the objective of this work is a detailed study of its magmatic structures mainly by means of anisotropy of magnetic susceptibility ams regularly spaced sampling 61 stations yielded a magnetic fabric map which shows two domains 1 a western lobe which has lineations close to vertical and e trending foliations that merge southwestward as the transcurrent igarassi shear zone is approached isz and 2 an eastern lobe showing se trending lineations associated with inward dipping magmatic foliation situated in the center of the lobe the magnetic fabric is mostly paramagnetic in origin i e related to crystallographic preferred orientation of biotite and hornblende a low susceptibility magnitude 0 4 10 3 si typically of the ilmenite series granites is found in porphyritic granites diorites or their hybrid products hysteresis data indicate that the ferrimagnetic contribution to the bulk susceptibility does not reach 30 the magma was emplaced into a chamber developed by local wnw ese extension induced by an overall n s shortening melt ascent may have been facilitated by the pre existence of a steep fault zone bounding crustal discontinuities the magma must have ponded along a mechanical barrier formed by the contact between phyllitic metapelites and its gneissic basement which controlled the final emplacement structures of the pluton

geologic setting of the teutonic bore massive sulfide deposit archean yilgarn block western australia the teutonic bore massive sulfide deposit occurs in a sequence of archean mafic and felsic volcanic rocks in the northeastern yilgarn block western australia felsic volcanic rocks form part of a regionally continuous linear belt consisting of locally emergent volcanic centers separated by interbedded aquagene tuffs and water lain epiclastic sedimentary rocks mafic and felsic rocks in the area have been extensively intruded by gabbro and subsequently by high level granitoids believed to be cogenetic with the rhyolitic rocks regionally the deposit lies in a linear zone of complex structure and lithology characterized by repeated periods of extensional tectonism rhyolite and cogenetic granitoids are related to earlier phases of extension whereas subsequent activity led to the formation of a suite of saturated to undersaturated syenites and fault bounded units of polymictic conglomerate derived largely from the rhyolite and high level granitoids the teutonic bore deposit consists of one relatively small steeply dipping lens of predominantly banded massive sulfides mainly pyrite sphalerite chalcopyrite and galena underlain by concordant and discordant stringer mineralization the mineralization occurs within a sequence of pillowed basalt and tuffaceous sediment 0 to 150 m stratigraphically above rhyolitic volcanic and volcaniclastic rocks primary textures within the massive sulfides and underlying chert indicate depositional instability active growth faulting controlled the deposition of felsic epiclastic sedimentary rocks subsequent basaltic rocks and the development of the third order basin which provided the site for deposition of massive sulfides the faults probably provided the conduits for hydrothermal solutions these fluids spread laterally and vertically prior to exhaling at the rock seawater interface during a volcanic hiatus features within the local environment are compatible with regional extension regional extension resulted in bimodal magmatism and the associated rifting formed basins suitable for the deposition of extensive epiclastic sedimentary rocks the bimodal volcano plutonic host at teutonic is similar to many examples from the archean of canada but the style of felsic volcanism the carbonate rich alteration and the lead and silver enriched ore are most similar to deposits in the sturgeon lake area

chemical remobilization of contaminant metals within floodplain sediments in an incising river system implications for dating and chemostratigraphy metals such as pb zn cd and cu from historical mining activity have been used as stratigraphic markers for dating and provenancing vertically accreted fine grained floodplain overbank deposits this study presents evidence for chemical remobilization of these metals within overbank sediments in the tyne basin uk the evidence includes breakdown of metal bearing minerals sulphides carbonates iron and manganese oxyhydroxides shifts of chemical fractions within zones of relatively low ph towards more soluble and reactive phases and accumulation of secondary iron and manganese oxyhydroxides at levels related to fluctuating water table levels or to the breakdown of organic matter all of this suggests that fine centimetre scale chemostratigraphy using metal concentrations and ratios is unlikely to provide reliable data in river systems that have experienced or are experiencing major changes in water table levels or pedogenesis coarse tens of centimetre to metre scale chemostratigraphy when applied with caution may still provide a means of delineating contaminated units

subsea floor replacement in volcanic hosted massive sulfide deposits abstract recent research on volcanic hosted massive sulfide vms deposits indicates that syngenetic subsea floor replacement ores form an important component of many deposits in the context of vms deposits subsea floor replacement can be defined as the syn volcanic formation of sulfide minerals within pre existing volcanic or sedimentary deposits by infiltration and precipitation in open spaces fractures inter and intra granular porosity as well as replacement of solid materials there are five criteria for distinguishing subsea floor replacement in massive sulfide deposits 1 mineralized intervals are enclosed within rapidly emplaced volcanic or sedimentary facies lavas intrusions subaqueous mass flow deposits pyroclastic fallout 2 relics of the host facies occur within the mineral deposit 3 replacement fronts occur between the mineral deposit and the host lithofacies 4 the mineral deposit is discordant to bedding and 5 strong hydrothermal alteration continues into the hanging wall without an abrupt break in intensity criteria 1 3 are diagnostic of replacement whereas criteria 4 and 5 may suggest replacement but are not alone diagnostic because clastic sulfide ores contain accessory rock fragments collected by the parent sediment gravity flow s during transport criteria 2 can only be applied to massive semi massive disseminated or vein style deposits and not clastic ores the spectrum of vms deposit types includes deposits that have accumulated largely subsea floor and others in which sedimentation and volcanism were synchronous with hydrothermal activity and precipitation of sulfides occurred at and below the sea floor over the life of the hydrothermal system deposits that formed largely subsea floor are mainly hosted by syn eruptive or post eruptive volcaniclastic facies gravity flow deposits water settled fall autoclastic breccia however some subsea floor replacement vms deposits are hosted by lavas and syn volcanic intrusions sills domes cryptodomes burial of sea floor massive sulfide by lavas or sediment gravity flow deposits can interrupt sea floor mineralization and promote subsea floor replacement and zone refining the distance below the sea floor at which infiltration and replacement took place is rarely well constrained with published estimates ranging from less than 1 to more than 500 m but mainly in the range 10 200 m the upper few tens to hundreds of metres in the volcano sedimentary pile are the favoured position for replacement as clastic facies are wet porous and poorly consolidated in this zone and at greater depths become progressively more compacted dewatered altered and less amenable to large scale infiltration and replacement by hydrothermal fluids furthermore sustained mixing between the upwelling hydrothermal fluid and cold seawater is regarded as a major cause of sulfide precipitation in vms systems and this mixing process generally becomes less effective with increasing depth in the volcanic pile the relative importance of subsea floor replacement in vms systems is related principally to four factors the permeability and porosity patterns of host lithofacies sedimentation rate the relative ease of replacement of host lithofacies especially glassy materials and early formed alteration minerals during hydrothermal attack and physiochemical characteristics of the hydrothermal fluid

apparent polar wander path for adria extended by new jurassic paleomagnetic results from its stable core tectonic implications abstract as a continuation of a systematic paleomagnetic research in the northern part of stable adria which provided a well defined apparent polar wander apw path for the cretaceous eocene we present new paleomagnetic results for the jurassic these new data were obtained from 15 geographically distributed localities from the trento platform eastern southern alps using standard paleomagnetic approach the lower jurassic shallow water carbonates are not considered for tectonic interpretation due to inconsistent inclinations the middle and upper jurassic rosso ammonitico provided excellent kinematic constraints with the new jurassic results an apw is now defined for adria for the 167 40 ma interval it is well constrained for timing of important changes like the speed and the sense of rotations this apw suggests that the cw rotation and southward shift changed to the opposite at 155 1 5 3 ma signifying a dramatic change in the life of the neo tethys from opening to closing the latter is manifested in fast ccw rotation and northward movement of adria up to 102 9 2 4 ma and moderate displacements in the same manner in post 103 ma times combined data sets from stable istria and the foreland of the southern alps point to an approximately 15 cw rotation with respect to africa at the end of the cretaceous and an about 25 in the ccw sense after the eocene

sediment yield determination using uranium series radionuclides the case of the wash and fenland drainage basin eastern england abstract water and sediment samples were collected from the fenland drainage basin to assess the fluvial contribution to the sediment budget of the wash on the east coast of england using the uranium series disequilibrium found in the products of the weathering system river sediment and water the ratio of material carried in solid form to that dissolved u s u w was assessed and the total flux of weathered material sediment yield was quantified the results show that the u s u w ratio is controlled to a degree by catchment geology and hydrology and that there is a marginal seasonal increase from between 3 28 3 95 and 4 60 0 44 summer mean and weighted mean to between 5 35 3 05 and 6 07 0 63 winter mean and weighted mean the best estimate of annual sediment flux from the fenland to the wash is between 2800 and 17 700 tonnes yr 1 equivalent to a rate of 0 22 1 42 tonnes km 2 yr 1 this is lower than previous estimates for the region but reinforces the argument that sediment reworking within the wash and erosion of the adjacent coasts and sea beds are important sources of sediment for the intertidal flats and salt marshes

emplacement origins of coarsely crystalline mafic rocks hosted in greenstone belts examples from the 2 7 ga yilgarn craton western australia coarsely crystalline mafic rocks commonly referred to as dolerite and diabase make up a substantial proportion of archean greenstone belts and are hosts to major orogenic gold deposits yet their internal architecture and contact relationships remain poorly documented and their emplacement origins are assumed rather than supported with evidence we present results from drill core logging of several late archean coarsely crystalline packages from the eastern goldfields superterrane of the yilgarn craton western australia including the golden mile dolerite these large mafic bodies comprise mostly medium to coarsely crystalline mafic rocks but also include a variety of other products of differentiation the bodies range from 75 to 460 m thick and extend for tens of kilometers are primarily hosted in mudstones and basalt and appear to be concordant to stratigraphy as such this study excludes mafic dykes and extremely thick and internally complex bodies such as the bushveld complex from base to top the internal stratigraphy generally consists of a lower unit of aphyric basalt dolerite gabbro and peridotite pyroxenite then a voluminous middle dolerite gabbro and an upper quartz dolerite gabbro and a topmost aphyric basalt granophyric veins and domains are common in the upper third of the mafic body contacts are gradational between all lithofacies with the exception of granophric veins which have sharp contacts within this overall stratigraphic framework there is variability in the relative thickness of lithofacies number of lithofacies as well as repetition of some lithofacies several examples also include basalt in the interior in well exposed examples the key evidence for distinguishing intrusions from extrusions is provided by the top contact however the top contact from these examples is ambiguous to overcome this gap we review the character of well studied thick ponded lavas from the literature most aspects of the internal character are not unique to intrusions although the maximum groundmass grain size excluding granophyric veins of the archean examples 3 mm is significantly coarser than that for any known ponded lavas 1 mm the ability to distinguish intrusions from extrusions has important implications for reconstructing archean greenstone stratigraphy and mineral exploration

detrital zircon u pb ages and hf isotopic constraints on the terrigenous sediments of the western alps and their paleogeographic implications detrital zircons from cretaceous micaschist late eocene earliest oligocene sandstone and early oligocene siltstone of the western alps fall into three main separable age clusters at 610 540 ma 490 430 ma and 340 280 ma that correspond to the cadomian neoproterozoic ordovician and variscan carboniferous events widespread in western and central europe hf isotopic results indicate that these three magmatic and tectonic episodes did not give rise to significant production of juvenile crust a distinguishable group of triassic zircons around 250 200 ma which is considered to derive from the southern alps has been detected in the early oligocene schistes a blocs formation and the brianconnais flysch noir in contrast this age group is absent in late eocene earliest oligocene sandstones in agreement with sedimentological studies our results show that the main source areas of the eocene sandstone were probably located in the european continent the arrival of detritus from the internal zone occurred in early oligocene coeval with the tectonic rotation from northwestward to westward in the propagation of allochthonous units based on previous studies and our new data we argue that the the brianconnais zone was likely a paleorelief since the middle eocene that accounts for the lack of detritus from the adriatic units contemporary sediments were accumulated in the foredeep of the adriatic plate from oligocene time onwards the blockage was cut through after a regional uplifting and thus the internal zone started to provide detritus into the western flexural basins

residence time of alluvium in an aggrading fluvial system relationships between the surface area and age of alluvial deposits were used to estimate the residence time of alluvium in the 2205 km2 waipaoa river basin new zealand the contemporary waipaoa river is an efficient transporter of sediment to the continental shelf but the basin has been characterized by rapid channel and valley aggradation in the historic period and by extensive mid to late holocene alluvial storage in the lower reaches the area weighted mean age of alluvial deposits in the lower part of the river basin is 4400 yr these deposits comprise terrace remnants isolated by downcutting and holocene to recent sediments that are potentially remobilizable by the modern river even though the amount of storage is small relative to downstream transport the majority of the potentially remobilizable alluvium is likely to remain in storage for 100 yr and its half life time for 50 per cent removal is 2000 yr within the confines of the flfloodplain the apparent loss of older deposits is due primarily to burial but losses of the most recent deposits are due almost entirely to remobilization 30 40 per cent with the remainder preserved in the alluvial record for at least 104 yr most of this sediment is likely to remain in storage until there is a shift to a degradational state copyright 2006 john wiley sons ltd

continuity of the alpine slab unraveled by high resolution p wave tomography the question of lateral and or vertical continuity of subducted slabs in active orogens is a hot topic partly due to poorly resolved tomographic data the complex slab structure beneath the alpine region is only partly resolved by available geophysical data leaving many geological and geodynamical issues widely open based upon a finite frequency kernel method we present a new high resolution tomography model using p wave data from 527 broadband seismic stations both from permanent networks and temporary experiments this model provides an improved image of the slab structure in the alpine region and fundamental pinpoints for the analysis of cenozoic magmatism u hp metamorphism and alpine topography our results document the lateral continuity of the european slab from the western alps to the central alps and the downdip slab continuity beneath the central alps ruling out the hypothesis of slab break off to explain cenozoic alpine magmatism a low velocity anomaly is observed in the upper mantle beneath the core of the western alps pointing to dynamic topography effects a ne dipping adriatic slab consistent with dinaric subduction is possibly observed beneath the eastern alps whereas the laterally continuous adriatic slab of the northern apennines shows major gaps at the boundary with the southern apennines and becomes near vertical in the alps apennines transition zone tear faults accommodating opposite dipping subductions during alpine convergence may represent reactivated lithospheric faults inherited from tethyan extension our results suggest that the interpretations of previous tomography results that include successive slab break offs along the alpine zagros himalaya orogenic belt might be proficiently reconsidered

active and fossil mantle flows in the western alpine region unravelled by seismic anisotropy analysis and high resolution p wave tomography abstract the anisotropy of seismic velocities in the mantle when integrated with high resolution tomographic models and geologic information can be used to detect active mantle flows in complex plate boundary areas providing new insights on the impact of mantle processes on the topography of mountain belts here we use a densely spaced array of temporary broadband seismic stations to analyze the seismic anisotropy pattern of the western alpine region at the boundary between the alpine and apenninic slabs our results are supportive of a polyphase development of anisotropic mantle fabrics possibly starting from the jurassic to present geophysical data presented in this work and geologic evidence taken from the literature indicate that i fossil fabrics formed during tethyan rifting may be still preserved within the alpine and apenninic slabs ii mantle deformation during apenninic slab rollback is not compensated by a complete toroidal flow around the northern tip of the retreating slab iii the previously observed continuous trend of anisotropy fast axes near parallel to the western alpine arc is confirmed we observe that this arc parallel trend of fast axes is located in correspondence to a low velocity anomaly in the european upper mantle beneath regions of the western and ligurian alps showing the highest uplift rates we propose that the progressive rollback of the apenninic slab in the absence of a counterclockwise toroidal flow at its northern tip induced a suction effect at the scale of the supraslab mantle the resulting mantle flow pattern was characterized by an asthenospheric counterflow at the rear of the unbroken western alps slab and around its southern tip and by an asthenospheric upwelling mirrored by low p wave velocities that would have favored the topographic uplift of the alpine belt from the mont blanc to the mediterranean sea

styles of crustal deformation in compressional orogens caused by subduction of the underlying lithosphere abstract crustal scale deformation is calculated for models in which the driving mechanism corresponds to the asymmetric detachment and underthrusting of the underlying mantle lithosphere the plane strain finite element model results provide indications of the styles of deformation to be expected in small compressional orogens in particular these styles occur where shortening of the mantle lithosphere is achieved by the nearly rigid convergence between lithospheric mantles and the subduction of one mantle beneath the other the crust is modelled using coulomb plastic frictional and thermally activated power law viscous rheologies and the effects of compositional layering and variable geothermal gradients are included results are presented for a range of models in which the strength of the coupling between the model crust and its basal boundary surface denudation partial and total subduction of the crust and compositional layering are examined the results show the development of inclined step up shear zones which are a consequence of conjugate thrusting in regions of coulomb controlled rheology these zones link to sub horizontal shear zones which occur where composition and temperature render the crust viscously weak the model strain fields are interpreted in terms of deformation on discrete planes and the seismic reflectivity fabric that may be associated with this discrete deformation finally we ask whether similar seismic reflectivity fabric can be recognized in observations from small compressional orogens

reconciling plate tectonic reconstructions of alpine tethys with the geological geophysical record of spreading and subduction in the alps article a new reconstruction of alpine tethys combines plate kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution from sea floor spreading through subduction to collision in the alps unlike previous models which relate the fate of alpine tethys solely to relative motions of africa iberia and europe during opening of the atlantic our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record the motions of these microplates adria iberia alcapia alkapecia and tiszia relative to both africa and europe during late cretaceous to cenozoic time involved the subduction of remnant tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces 1 131 84 ma intra oceanic subduction of the ligurian part of alpine tethys attached to iberia coincided with eo alpine orogenesis in the alcapia microplate north of africa these events were triggered primarily by foundering of the older 170 131 ma neotethyan subduction slab along the ne margin of the composite african adriatic plate subduction was linked by a sinistral transform system to e w opening of the valais part of alpine tethys 2 84 35 ma subduction of primarily the piemont and valais parts of alpine tethys which were then attached to the european plate beneath the overriding african and later adriatic plates nw translation of adria with respect to africa was accommodated primarily by slow widening of the ionian sea 3 35 ma recent rollback subduction of the ligurian part of alpine tethys coincided with western alpine orogenesis and involved the formation of the gibraltar and calabrian arcs rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable retreating adriatic and african slabs during slow convergence of africa and europe the upper european iberian plate stretched to accommodate this slab retreat in a very mobile fashion while the continental core of the adriatic microplate acted as a rigid indenter within the alpine collisional zone the subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the alps and apennines as well as beneath parts of the pannonian basin the adriatic sea the ligurian sea and the western mediterranean the predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10 30 indicating that parts of slabs may be superposed within the mantle transition zone and or that some of this subducted lithosphere became seismically transparent

zircon inheritance in an igneous rock suite from the southern adamello batholith italian alps zircons from a suite of basic to acidic calcalkaline igneous rocks from the southern adamello batholith s ab southern alps n italy display complex u pb isotopic patterns which are mainly due to the presence of variable amounts of isotopically heterogeneous inherited radiogenic pb and to minor postmagmatic loss of pb inherited pb is mainly composed of 1 a 1100 ma pb component located in zircons devoid of visible cores and 2 a 450 ma component associated with conspicuous bubble rich turbid cores in concordia representation the data points conform to lower intercept ages of 40 ma a linear fit of three samples devoid of visible cores from the granodiorite defines an intrusion age of 39 3 ma u pb systematics of zircon in particular u content and crystal morphology are clearly related zircons of type g1 which form relatively late in the zircon crystallization sequence consistently show the highest u contents in each zircon population these late zircons however are not devoid of inherited radiogenic lead in a population from a granodiorite cores are randomly distributed throughout the morphological spectrum the presence of old inherited zircon components in all investigated samples furnishes proof for involvement of crustal material in the genesis of the s ab rocks samples characterized by crustal nd and sr values usually show enhanced zircon inheritance inheritance varies with differentiation and reaches a maximum for intermediate to acidic members these compositions show the highest zr saturation temperatures calculated for the rock spectrum studied textural relations between zircon and major phases indicate that the magmas of the leucocratic rocks were saturated with zr at an early stage of crystallization on the other hand zr solubilities and textural relations consistently show that melts of basic to intermediate rocks were not saturated with zr extension of the zr solubility model to mineral melt mixtures of tonalitic bulk composition demonstrates that zr solubility in the residual melt is drastically reduced by crystallization of plagioclase and amphibole survival of xenocrystic zircons in the mafic to intermediate rocks of the s ab can best be explained in terms of dissolution kinetics since temperature and h2o content of these zr undersaturated melts were favourable for relatively rapid zircon dissolution inherited zircons in particular trace element rich unstable cores cannot have been exposed to such conditions over extended time periods therefore the tonalitic or more basic magmas of the s ab cannot have been derived from crustal sources by slow processes such as burial metamorphism

u th pb and 230th 238u disequilibrium isotope systematics precise accessory mineral chronology and melt evolution tracing in the alpine bergell intrusion in order to investigate the potential of combined th u pb isotope and 230th 238u disequilibrium systematics for tracing magmatic crystallization and melt evolution conventional high resolution single crystal tims techniques have been applied to zircon titanite and fragments of geochemically characterized growth zones of allanite these minerals were extracted from a single tonalite specimen collected from the feeder zone of the tertiary bergell pluton southern steep belt s switzerland n italy the isotopic results document an extended history of crystallization and melt evolution of at least 5 ma with well resolved zircon ages defining an early interval of 33 0 to 32 0 ma followed by crystallization of zoned allanite from 32 0 to 28 0 ma and formation of magmatic epidote possibly as late as 26 ma trace and major element patterns in zoned allanite closely mirror melt evolution characterized by increase of u concentration and sharp decrease of th and lree reflecting early crystallization of phases low in u and in particular the dominating control by allanite precipitation preservation of substantial quantities of excess 206pb derived from initial excess 230th in all analyzed allanite grains indicates that their isotopic systems have not been reset by loss of radiogenic pb during prolonged residence at magmatic conditions and regional metamorphic cooling and that the measured sequence of 208pb 232th dates translates into a real age sequence major loss of radiogenic pb from compositionally zoned allanite by volume diffusion would have resulted in a data pattern grossly different from the observed one as demonstrated by numerical modeling of 232th 208pb 238u 230th 206pb isotopic evolution the results therefore suggest closure temperatures 700 c for magmatic allanite quantification of 230th 238u disequilibrium relationships reveals a smooth initially steep decrease of th u in the magma from values of 2 9 at 32 0 ma to 0 1 at 28 0 ma in equilibrium with sequential allanite zoning comparison of calculated th u magma with measured total rock th u 0 79 requires fractional crystallization of allanite at an early stage this process of removal of allanite and thus th from the melt was operative at least until 31 5 ma providing an upper limit for the time of emplacement of the studied magma batch the fact that bulk zircon and a large part of allanite crystallization predate emplacement cautions against equating ages determined on refractory minerals from deep seated plutons with intrusion ages the persistence of magmatic conditions over a period of 5 ma concentrated in a narrow collision zone between the european and the african plate has been a major controlling factor for the oligocene evolution of the adjacent insubric fault the main tectonic lineament of the alps being active from late cretaceous to miocene times

u th pb systematics of morphologically characterized zircon and allanite a high resolution isotopic study of the alpine rensen pluton northern italy abstract the rensen pluton is a typical member of the tertiary calc alkaline plutonic suite structurally connected to the periadriatic lineament it intrudes the austroalpine polymetamorphic basement of the eastern alps southwest of the tauern window northern italy zircons and allanites from tonalitic quartz dioritic and monzogranitic lithologies were studied systematically on the basis of refined grain by grain microanalytical techniques high resolution isotope analyses show that morphology and u pb systematics of zircon are highly correlated with magma evolution zircons from the main tonalitic part of the intrusion display a gradual increase of u content from early stage s type morphology to late stage g1 type morphology most of the zircon crystals include premagmatic seeds derived from old crustal sources unevolved s type zircons contain inherited components of late proterozoic early paleozoic apparent age whereas late stage g1 type zircons show inheritance of early proterozoic apparent age both types of inherited components are present in zircons from a fine grained tonalitic domain located at the center of the pluton which shows restitic structures the crustal affinity of this rock is corroborated by its relatively low e nd value 6 0 as compared to values obtained for the main tonalite 3 9 and the quartz diorite 3 5 the accuracy of cainozoic zircon ages is affected by initial radioactive disequilibrium in the u pb decay chains particularly uncertain is the fractionation behavior of protactinium which could be enriched in zircon due to the high stability of the pa 5 oxidation state because the th pb system is devoid of long lived intermediate radioactive nuclides the best approximation to the emplacement age of the rensen pluton is given by allanite th pb ages of 31 70 0 25ma 95 c l for the main tonalite and by a slightly younger age of 31 09 0 32ma for quartz diorite

trace element and nd isotope systematics in detrital apatite of the po river catchment implications for provenance discrimination and the lag time approach to detrital thermochronology abstract detrital thermochronology is often employed to assess the evolutionary stage of an entire orogenic belt using the lag time approach i e the difference between the cooling and depositional ages of detrital mineral grains preserved in a stratigraphic succession the impact of different eroding sources to the final sediment sink is controlled by several factors including the short term erosion rate and the mineral fertility of eroded bedrock here we use apatite fertility data and cosmogenic derived erosion rates in the po river catchment alps apennines to calculate the expected percentage of apatite grains supplied to the modern po delta from the major alpine and apenninic eroding sources we test these predictions by using a cutting edge dataset of trace element and nd isotope signatures on 871 apatite grains from 14 modern sand samples and we use apatite fission track data to validate our geochemical approach to provenance discrimination we found that apatite grains shed from different sources are geochemically distinct apatites from the lepontine dome in the central alps show relative hree enrichment lower concentrations in ce and u and higher 147 sm 144 nd ratios compared to apatites derived from the external massifs derived provenance budgets point to a dominant apatite contribution to the po delta from the high fertility lepontine dome consistent with the range independently predicted from cosmonuclide and mineral fertility data our results demonstrate that the single mineral record in the final sediment sink can be largely determined by high fertility source rocks exposed in rapidly eroding areas within the drainage this implies that the detrital thermochronology record may reflect processes affecting relatively small parts of the orogenic system under consideration a reliable approach to lag time analysis would thus benefit from an independent provenance discrimination of dated mineral grains which may allow to proficiently reconsider many previous interpretations of detrital thermochronology datasets in terms of orogenic wide steady state

european impacts on downstream sediment transfer and bank erosion in cobargo catchment new south wales australia abstract upland valley fills in cobargo catchment on the south coast of new south wales represent substantial sediment source zones contemporary channels within these fills are up to 8 m deep and 50 m wide for catchment areas 2 virtually all banks are eroding downstream of this sediment source zone sediment transfer zones are characterised by sinuous channels that are partially choked by sands released from upland valley fills coarse sands stored in point bars deflect flow to outer banks where colluvial footslopes are eroded approximately 50 of banks are eroding in this section of the catchment other than the 10 km river reach upstream of the river mouth the remainder of the catchment is a bedrock confined sediment throughput zone characterised by fluctuations in channel bed elevation the downstream 10 km of the catchment is a sediment accumulation zone in which erosion is restricted to occasional concave banks prior to european settlement of cobargo catchment upland valley fills were largely unincised and middle transfer reaches of the catchment comprised swamps vegetation clearance along with disturbance and drainage of swamps transformed discontinuous water courses into continuous channels working from a base point of intact upland valley fills almost 50 of available material has been removed from the upper catchment sediment source zone contributing 2 9 10 6 m 3 of material to the lower catchment of this roughly 65 has been stored along the channel bed and floodplain this gives a total sediment contribution to the delta of 1 0 10 6 m 3 sufficient materials are stored in transient storage units along transfer zones to maintain current rates of sediment throughput to the delta for several decades cobargo catchment experienced dramatic acceleration of channel incision and bank erosion processes within a few decades following european settlement of the catchment i e around 1830 transition in landscape form and associated sediment delivery were rapid with a negligible lag interval i e within a few decades of disturbance however given the extensive volume of sediment released from upland valley fills landscape recovery i e refilling of upland valleys will likely take thousands of years

influence of structural inheritance on foreland foredeep system evolution an example from the po valley region northern italy understanding the development of foreland foredeep systems and the influence exerted by pre existing structures on their evolution is an important step for defining the key factors that control long term basin and lithosphere dynamics comprehending the associated seismic hazard and assessing their economic potential in the domain of hydrocarbon exploration the po valley is a rather unique foreland basin for two major reasons a it developed intermittently at the front of two different mountain chains the northern apennines and the southern alps progressively converging one towards the other b the inherited structures mainly derived from the mesozoic extensional tectonics are oriented at high angle to the advancing belts the coexistence of these two factors and their various implications make the po valley basin a complex case study that deserves attention taking advantage of the recent building of a 3d structural model across the region we reconstructed the possible geometry and migration pattern of the tertiary basins that developed at the front of the northern apennines and the southern alps as part of the po valley tectonic evolution in addition a number of sections sliced from the 3d model across selected domains have then been used to restore the present day structural units to their pre compressional setting while highlighting the key stages of their geological history results from the model analysis show that the mesozoic extension related tectonics and the associated carbonate facies geometry and distribution localized and constrained the alpine structures inside around the basin their control on the cenozoic deformation and sedimentation is evident during the paleogene and the miocene whereas it becomes more subtle during the plio pleistocene when lithospheric scale mechanisms need to be invoked notwithstanding the model uncertainties and its explicit regional significance our results may be taken as reference for any foreland foredeep setting worldwide especially in complex systems where tectono sedimentary inhomogeneity is spatially and temporally dominant

the 4d evolution of the teutonic bore camp vhms deposits yilgarn craton western australia abstract the teutonic bore camp comprised of the teutonic bore jaguar and bentley deposits is one of the most significant volcanic hosted massive sulphide vhms camps in western australia despite being extensively studied only recently there have been advances in the understanding of the mechanism that drove the formation of mineralisation it has been recognized by recent studies that the volcanic hosted deposits from the teutonic bore camp represent replacement type vhms systems with significant input of fluids and metals from a magmatic source this paper tests the existing hypothesis that the nearby penzance granite acted as the metals source and or thermal engine driving the development of these ore deposits new age constraints on the formation of the host volcanic sequence at the bentley deposit and the crystallization of the penzance granite allows for the construction of a 4d evolutionary model for the ore system a new u pb shrimp monazite age of 2681 9 4 5 ma indicates that the penzance granite post dates the host stratigraphy at bentley ca 2693 ma and is probably coeval with mineralisation all zircons penzance bentley units i and iii have very similar hf i with most values between 1 and 6 slightly higher than the hf i of zircons from other granites and volcanics within the kurnalpi terrain and indicative of juvenile sources the mean th u ratios are 0 7 and 0 6 for the penzance and bentley zircons respectively all zircons have similar ce nd cn ratios the chemical similarities between the zircons from the granite and the volcanic rocks at bentley support a shared magmatic source between the penzance and the teutonic bore camp sequence the penzance granite is the likely source of heat and potentially metals which drove the vhms mineralisation at the teutonic bore camp

residence times of alluvium in an east texas stream as indicated by sediment color abstract the relationships between sediment production storage and transport in fluvial systems are complex and variable key issues in addressing these relationships are the residence times of sediment delivered to the channel and the proportion derived from recent upland erosion as opposed to remobilized alluvium the systematic changes in iron geochemistry often experienced by sediments deposited in an anaerobic environment such as a stream channel or waterlogged floodplain are used here as an indicator of residence time over contemporary time scales in areas such as east texas where upland soils are high in iron oxide content these changes are reflected in soil color alluvium with red yellow or brown colors indicating ferric oxidized iron and sufficient organic matter for reduction to occur indicates a short 1 year sediments with the longest residence times in alluvial environments 1 year will not oxidize on exposure to the atmosphere due to the loss of iron while those with ferrous iron remaining will experience oxidation and color change on exposure in loco bayou texas these indicators of residence time are shown to be generally consistent with other field evidence of erosion and sedimentation further the color indicators correctly indicate the residence time in several cases where the latter is known from field observations

sources of alluvium in a coastal plain stream based on radionuclide signatures from the 238u and 232th decay series ratios 226 ra 232 th 226 ra 230 th and 230 th 232 th channel alluvium indicates a transition from interfluve surface to subsoil sources during flood subsoil 34 to 91 over about 8 km and bank full stages subsoil 9 to 74 over about 12 km with distance downstream these results indicate strong coupling between hillslope and channel processes reflecting land use change from forested to agricultural concentrated in lower loco bayou this methodology shows that sediment sources can be differentiated based upon landscape placement where lithologic contrast is absent the geochemistry long halflives and fractionation of 238 u and 232 th decay series radionuclides during pedogenic and fluvial processes in humid climates suggest that these methods are applicable in a wide variety of fluvial systems index terms 1040 geochemistry isotopic composition chemistry 1803 hydrology anthropogenic effects 1815 hydrology erosion and sedimentation 1824 hydrology geomorphology 1625 keywords natural radionuclides fingerprinting alluvium source apportioning

geochemistry of the adamello massif northern italy the tertiary adamello massif outcropping over an area of more than 550 km2 in the southern alps northern italy is composed mainly of granitoid rocks granodiorite tonalite quartz diorite with minor amounts of diorite and gabbro the major and trace element composition of these rocks is comparable to calc alkaline volcanic rocks of continental margins the granitoid rocks display spatial and temporal variations in their composition particularly in na p sr la nb and y contents and 87sr 86sr ratios the variations were probably produced by concurrent contamination wall rock assimilation and fractional crystallization of high alumina basaltic magma

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

detrital geochronology of unroofing magmatic complexes and the slow erosion of oligocene volcanoes in the alps abstract tectonic reconstructions and quantitative models of landscape evolution are increasingly based on detailed analysis of detrital systems since the definition of closure temperature in the 1960s mineral ages of low temperature geochronometers are traditionally interpreted as the result of cooling induced by erosion whose rate is a simple unique function of age patterns such an approach can lead to infer paradoxically high erosion rates that conflict with compelling geological evidence from sediment thickness in basins this indicates that tectonic and landscape models that solely interpret mineral ages as due to cooling during exhumation may not be valid here we propose a new approach that takes into account the effects of both crystallization and exhumational cooling on geochronometers from u pb on zircon to fission tracks on apatite we first model the mechanical erosion of an unroofing magmatic complex and the resulting accumulation and burial of the eroded units in reverse order in the basin detrital mineral ages follow a regular pattern downsection some mineral ages such as e g u pb ages of zircons cluster around the magmatic age i e the crystallization of the magma its value is constant along the stratigraphic column in the sedimentary basin we refer to this behavior as stationary age peak some other mineral ages such as e g apatite fission track ages are often younger than the magmatic age when they vary smoothly with depth they define a moving age peak which is the only possible effect of undisturbed cooling during overburden removal and can therefore be used to calculate an erosion rate the predictions of our model were tested in detail on the extremely well studied bregaglia bergell orogenic pluton in the alps and on the sedimentary succession derived from its erosion the gonfolite group the consistency between predicted and observed age patterns validates the model our results resolve a long standing paradox in quantitative modelling of erosion sedimentation namely the scarcity of sediment during apparently fast erosion starved basins are the observational baseline and modelling must be tuned to include a correct analysis of detrital mineral geochronology in order to reconcile perceived discrepancies between stratigraphical and geochronological information in addition our data demonstrate that volcanoes were active on top of the growing oligocene alps this study illustrates rigorous criteria for detrital mineral geochronology that are applicable to any geological setting including magmatic arcs and collision orogens and provides fundamental interpretive keys to solve complex puzzles and apparent paradoxes in geological reconstructions

is there a close spatial relationship between faults and plutons abstract using spatial relationships between individual plutons and faults to support genetic correlations between faulting and magmatism is meaningless since even random magmatic or tectonic processes will result in some plutons adjacent to faults our initial analyses of populations of faults and carboniferous plutons in the armorican massif france and faults and alleghanian plutons in the southern appalachians usa indicate that plutons have broad distributions with respect to faults but with a tendency for plutons to occur away from faults maxima of integrated pluton areas occur at 1 4 appalachians and 1 2 armorican of the distance between the average fault spacing in these orogens although there is a great need for statistical evaluations of relationships between populations of igneous bodies and structures in a wide variety of settings and crustal depths our initial studies suggest that faults do not preferentially channel magma during ascent or emplacement and that these are relatively unfocused processes within orogenic belts

restoring the source to sink relationships in the paleogene foreland basins in the central and southern alps switzerland italy france a detrital zircon study approach late paleogene syn tectonic magmatic products are known from sandstones contained in the north alpine nafb and south alpine safb foreland basins and in the south alpine pelagic trento basin the generally turbiditic and mass flow deposits grade up from marly hemipelagic deeper water series the source and amount of the reworked volcanic materials have been in debate for a long time as a proxy for the magma derived input we use the u pb geochronology and geochemistry 176hf 177hf t and eu eu ratios of detrital zircons and evaluate their temporal and genetic relationships with potential volcanic sources in the periadriatic magmatic systems adamello bergell biella the oldest volcanic sources lutetian priabonian we identify are in the trento basin and glarus nafb during most rupelian bergell and biella volcaniclastics were delivered to the nafb in the glarus alpe de taveyanne and haute savoie bergell and minor adamello magmatic material were supplied to the villa olmo conglomerate in the safb during late rupelian chattian in the entire nafb the influx of paleogene volcanic material faded out at the same time in the safb the como conglomerate shows mixed input from biella and bergell high numbers of old zircons 90 in the nafb document the asymmetry of the early alpine orogenic wedge exposing large basement areas to the north of the periadriatic intrusions the syn sedimentary right lateral movement along the periadriatic fault system is identified as the main driver of magmatic activity uplift and exposure to erosion and transport to the basins on this base the dynamics of the early alpine drainage systems are reconstructed with new accuracy

some methodological developments in the analysis of sediment transport processes using age distribution of floodplain deposits abstract floodplain areas are primary storage sites for river sediment in the saru river ages of floodplain surfaces were examined by tree ring analysis and vertical and horizontal configurations of floodplain deposits were measured by field and aerial photo surveying a flood in 1992 provided a good opportunity to examine depositional and erosional processes of floodplain sediment before and after the flood predominant disturbances were observed in the unconstrained wide reaches where floodplains develop this event indicated that eroded areas of floodplain deposits in each age class linearly increased with sediment volume and that the proportion of the total area eroded decreased exponentially with increase in the age of sediment we constructed basic equations expressing continuity of age distribution in order to analyze river sedimentation in a time series according to the results of the 1992 flood the floodplain disturbance rates determined by this analysis showed similar temporal changes with sediment transport rates monitored at the iwachishi reservoir a sharp increase in sediment discharge was seen after 1962 associated with the historical maximum rainfall in the temporal analysis of floodplain sediment the time series approach presented here is useful for evaluating the speed of sediment waves and the cumulative impact of sedimentation in a river basin