multi scale curvature for automated identification of glaciated mountain landscapes erosion by glacial and fluvial processes shapes mountain landscapes in a long recognized and characteristic way upland valleys incised by fluvial processes typically have a v shaped cross section with uniform and moderately steep slopes whereas glacial valleys tend to have a u shaped profile with a changing slope gradient we present a novel regional approach to automatically differentiate between fluvial and glacial mountain landscapes based on the relation of multi scale curvature and drainage area sample catchments are delineated and multiple moving window sizes are used to calculate per cell curvature over a variety of scales ranging from the vicinity of the flow path at the valley bottom to catchment sections fully including valley sides single scale curvature can take similar values for glaciated and non glaciated catchments but a comparison of multi scale curvature leads to different results according to the typical cross sectional shapes to adapt these differences for automated classification of mountain landscapes into areas with v and u shaped valleys curvature values are correlated with drainage area and a new and simple morphometric parameter the difference of minimum curvature dmc is developed at three study sites in the western united states the dmc thresholds determined from catchment analysis are used to automatically identify 5 5 km quadrats of glaciated and non glaciated landscapes and the distinctions are validated by field based geological and geomorphological maps our results demonstrate that dmc is a good predictor of glacial imprint allowing automated delineation of glacially and fluvially incised mountain landscapes

stabilizing feedbacks in glacier bed erosion glaciers often erode transport and deposit sediment much more rapidly than nonglacial environments1 with implications for the evolution of glaciated mountain belts and their associated sedimentary basins but modelling such glacial processes is difficult partly because stabilizing feedbacks similar to those operating in rivers2 3 have not been identified for glacial landscapes here we combine new and existing data of glacier morphology and the processes governing glacier evolution from diverse settings to reveal such stabilizing feedbacks we find that the long profiles of beds of highly erosive glaciers tend towards steady state angles opposed to and slightly more than 50 per cent steeper than the overlying ice air surface slopes and that additional subglacial deepening must be enabled by non glacial processes climatic or glaciological perturbations of the ice air surface slope can have large transient effects on glaciofluvial sediment flux and apparent glacial erosion rate

waterfalls on the eastern side of rocky mountain national park colorado usa abstract we examined 30 waterfalls on the eastern side of rocky mountain national park in colorado usa to evaluate whether drainage area or bedrock properties as reflected in joint characteristics correlate more strongly with the location and characteristics of individual waterfalls longitudinal profiles tend to be more concave for larger drainages to have a smaller proportion of total elevation loss in waterfalls and to have vertical drops rather than angled or ramp waterfalls we interpret these trends to indicate greater overall incisional capability for larger catchments shape of individual waterfalls and height of drop correlate more strongly with bedrock properties waterfalls in bedrock lacking prominent vertical joints perpendicular to flow are more likely to have a single drop rather than multiple drops and taller waterfalls correlate with more widely spaced horizontal joints waterfalls also noticeably correspond to resistant bedrock outcrops that form steep segments along hillslopes adjacent to the channel we interpret these results to indicate that the location and characteristics of waterfalls along headwater streams in the study area reflect primarily a limited ability to incise through more resistant segments of the underlying bedrock

fission track evidence of the cenozoic thermal history of the idaho batholith abstract apatite and zircon fission track data are combined with published k ar biotite dates from the idaho batholith to outline the cenozoic thermal history of central idaho apatite apparent ages reveal that parts of the batholith have been at temperatures below 100 c for over 50 ma suggesting that much of the batholith has remained at shallow crustal levels throughout cenozoic time eocene plutonism and attendant hydrothermal circulation resulted in thermal resetting of apatite and zircon dates from near the plutons concordant zircon and biotite dates indicate that hydrothermal systems associated with eocene plutonism operated at shallow crustal levels so that cooling occurred rapidly as geothermal activity waned the calculated depth to the 105 c apatite annealing isotherm suggests that as much as 3 km of erosion has occurred in deep canyons during the last 10 ma presumably associated with final erosion of the batholith following the establishment of drainage at low elevation along the snake river plain

postglacial topographic evolution of glaciated valleys a stochastic landscape evolution model the retreat of valley glaciers has a dramatic effect on the stability of glaciated valleys and exerts a prolonged influence on the subsequent fluvial sediment transport regime we have studied the evolution of an idealized glaciated valley during the period following retreat of ice using a numerical model the model incorporates a stochastic process to represent deepseated landsliding non linear diffusion to represent shallow landsliding and an approximation of the bagnold relation to represent fluvial sediment transport it was calibrated using field data from several recent surveys within british columbia canada we present ensemble model results and compare them with results from a deterministic linear diffusion model to show that explicit representation of large landslides is necessary to reproduce the morphology and channel network structure of a typical postglacial valley our model predicts a rapid rate of fluvial sediment transport following deglaciation with a subsequent gradual decline similar to that inferred for holocene time we also describe how changes in the model parameters affect the estimated magnitude and duration of the paraglacial sediment pulse

paleovolcanic facies and exhalite geochemistry guides for selecting exploration areas in volcano sedimentary complexes about a half of the 620 000 km 2 upper proterozoic arabian shield comprises weakly meta morphosed and tectonized volcano sedimentary rocks prospecting for precious and base metals in this large area is likely to continue for some time a pilot study of a typical area around wadi abennah involved the mapping of paleovolcanic facies and the geochemical analysis of contained cherts gossans and carbonates portions of three deformed stratovolcanoes were identified one of which the iktinah paleovolcano is mineralized a characteristic feature of the iktinah paleovolcano is that the entire central facies and adjacent parts of the proximal facies contain disseminated pyrite in argillized host rocks indicating an extensive original hydrothermal core base metal occurrences are recorded immediately outside this core and associated geophysical anomalies suggest other hidden occurrences other base metal occurrences are known in the distal facies most cherts and gossans of the central facies of the iktinah paleovolcano also reflect well developed hydrothermal core geochemistry since they contain significant amounts of the precious metal pathfinder elements as sb mo bi and te such geochemistry suggests that precious metal bearing cherts and or epithermal quartz veins may also occur results of this study suggest exploration areas can be rapidly selected within extensive deformed volcano sedimentary complexes such target areas correspond to the central proximal and distal facies of paleovolcanoes with large pyritized argillized cores such as iktinah others lacking such cores are rejected as unlikely to have had well developed hydrothermal systems

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

rare earth element mobility at constant inter ree ratios in the alteration zone at the phelps dodge massive sulphide deposit matagami quebec rare earth elements ree from la to ho were mobile and enriched in hydrothermally altered rocks below the archean phelps dodge cu zn volcanogenic massive sulphide deposit in northwestern quebec largest net enrichment was in the moderately altered quartz chlorite zone where la concentration increased six fold and lanybn steepened from 1 9 to 13 0 the intensely altered chloritite zone had both minor net ree enrichment and depletion yb and lu were immobile throughout both zones the mobile ree were added and subtracted in constant chondrite normalized inter ree proportions 1 0 la 0 79 ce 0 57 nd 0 49 sm 0 01 eu 0 10 tb and 0 02 hb small additions of eu relative to generally larger additions of lree and tb produced enhanced negative eu anomalies the ree were mobilized at the hot 300 c core of the alteration system and deposited at the cooler periphery other sites of intense alteration and water rock interaction display similar ree changes indicating that selective ree enrichment at constant inter ree ratios is a widespread phenomenon

erosional unloading hillslope geometry and the height of the cascade range washington state usa peaks in the cascade range in northern washington state are on average 800 m higher than in southern washington the influences of differential valley excavation and variations in hillslope length and average slope on these altitudinal trends were tested using a 3 dimensional model for isostatic rock uplift and calculations of hillslope length and slope respectively the magnitude of isostatic peak uplift calculated by the model is highly dependent on the flexural rigidity d and the related effective elastic thickness te of the crust of this region crustal rigidity was constrained using published estimates and by estimating the depth of the seismogenic zone in the area d 1 1023 nm and te 24 km with these constraints isostatic compensation due to differential erosion added 700 m and 300 m or 25 overall of height to peaks in the northern and southern cascades respectively deeper valley incision in the northern cascades accounts for 300 m of the 800 m difference in peak altitudes between north and south similarly variation in valley spacing and slope account for 350 m of the difference in mean altitude between northern and southern regions hence at least several hundred m difference in altitude between the northern and southern regions of the cascades in washington must be due to tectonic geologic or geophysical factors rather than surficial and geomorphic effects like isostatic response to valley incision and hillslope geometry copyright 2009 john wiley sons ltd

numerical simulations of glacial valley longitudinal profile evolution glaciers shape alpine landscapes they broaden valley bottoms enhance local valley relief generate multiple steps overdeepen valley floors and cause tributary valleys to hang these distinctive glacial signatures result from 10 4 10 5 yr of erosion during which swings in climate drive advances and retreats of alpine glaciers we use a numerical model of glacial erosion to explore the development of the longitudinal profiles of glaciated valleys the model is driven by the past 400 k y of variable climate because both sliding speed which dictates abrasion rate and water pressure fluctuations which strongly modulate quarrying rate should peak at the equilibrium line altitude ela we expect the locus of most rapid erosion to follow the transient ela simulations of a single glacial valley show rapid flattening of the longitudinal profile inclusion of a tributary glacier creates a step immediately downvalley of the tributary junction that persists over multiple glaciations and commonly leaves the tributary valley hanging steps and overdeepenings result from an increase in ice discharge immediately below the tributary junction which is accommodated primarily by increased ice thickness and hence sliding rate the size of the step increases with the ratio of tributary to trunk ice discharge while the height of a hanging valley reflects the difference in the time integrated ice discharge in tributary and trunk valleys and therefore increases as the discharge ratio decreases

chemostratigraphic division of the blake river group rouyn noranda area abitibi quebec the effusive rocks of the blake river group in the abitibi volcanic belt rouyn noranda region belong to a bimodal sequence in which andesites and rhyolites clearly dominate the identification of calc alkaline and tholeiitic affinities is made upon examination of the major trace and rare earth element ree content thus the andesites 58 normalized sio2 value without volatiles of the calc alkaline units have average k 4800 ppm ba 160 ppm and rb 13 ppm values that are greater than the average k 1800 ppm ba 130 ppm and rb 3 ppm values for andesites 57 sio2 that belong to associated tholeiitic units furthermore tholeiitic andesites have distinctive average values of ti 9600 ppm and y 40 ppm that are higher than the average values of ti 6700 ppm and y 25 ppm of calc alkaline andesites an effective discrimination between the calc alkaline and tholeiitic affinities is obtained using the zr y and ti zr ratios which are respectively less than 4 and greater than 70 in andes

some petrologic and oxygen isotopic relationships in the amulet mine noranda quebec and their bearing on the origin of archean massive sulfide deposits a concentrically zoned alteration pipe is present at the amulet a cu zn mine in the archean abitibi greenstone belt the pipe consists of a central core zone of so called dalmatianite spotted cordierite anthophyllite rock surrounded by a zone of biotite bearing grid fracture alteration study of the dalmatianite indicates that these rocks experienced two episodes of recrystallization first the original andesite was completely reconstituted during a hydrothermal event producing a quartz chlorite assemblage this transformation was associated with the formation of the massive sulfide lens and presumably took place in a submarine environment later contact metamorphism associated with the intrusion of the nearby lake dufault granodiorite resulted in partial recrystallization of the chlorite and quartz to cordierite and anthophyllite whole rock delta 18 o values decrease from about 6 to 10 in most of the abitibi belt to 5 to 7 in the country rocks surrounding the ore deposit to values as low as 3 6 in the core of the dalmatianite zone this oxygen isotopic zoning must have been produced by the hydrothermal activity because the dehydration reactions associated with contact metamorphism cannot have affected delta 18 o by more than 0 5 per mil assuming an alteration temperature of 300 degrees or 50 degrees c and a water rock ratio greater than two the hydrothermal fluid must have had delta 18 o 0 5 or 1 0 this indicates that the amulet ore deposit formed from a hydrothermal fluid that had a delta 18 o value similar both to modern seawater and to the fluids which formed the phanerozoic massive sulfide deposits of the kuroko and cyprus types the apparent constancy of delta 18 o of seawater during the precambrian and the continued importance of seawater hydrothermal processes are important constraints which must be considered in developing models of the history of the earth

cathodoluminescence characteristics of archean volcanogenic massive sulfide related quartz noranda ben nevis and matagami districts abitibi subprovince canada 1 the cathodoluminescence cl of quartz from ore stockwork veins and interstitial fillings between lava pillows from the 2 7 ga noranda ben nevis and matagami volcanogenic massive sulfide vms districts abitibi greenstone belt has been investigated using the hot cathode technique hc1 lm system to assess the potential of these various sample types to host primary seafloor vms related fluids trapped as inclusions in minerals with primary depositional morphologies the cl responses indicate that the various quartz types are of hydrothermal origin and are therefore a potential host for primary hydrothermal fluid inclusions most notable is a transient t 120 s blue cl characteristic of hydrothermal quartz observed in most samples cl characteristics are similar over 250 km indicating coherent nonrandom behavior furthermore in ore and stockwork material from the matagami and noranda districts respectively cl reveals primary concentric growth zoned quartz that predates pulses of sulfide deposition clear evidence that the quartz is undeformed and directly related to vms mineralization these growth zones are not apparent in transmitted light in addition ore and stockwork quartz commonly show a very unstable t 30 s yellow cl coincident with microfractures and grain boundaries defining areas affected by secondary hydrothermal activity in ore from matagami local zones of nontransient brown cl may reflect strain zones associated with the deformation and recrystallization of the massive sulfide mound and indicate that such modifications can be recognized and are minor in the investigated cases cl clearly reveals pseudo hexagonal apparently zoned structures in sulfide mineralized breccia pipe quartz from the ben nevis area these structures and their host quartz characterized by a very unstable t 20 s bright yellow cl are interpreted as recrystallized quartz that has undergone rapid growth from a strongly supersaturated solution and noncrystalline precursor the cl also clearly reveals colloform crustiform textures indicative of open space filling these textures are not visible optically

an evaluation of stream characteristics in glacial versus fluvial process domains in the colorado front range abstract many of the conceptual models developed for river networks emphasize progressive downstream trends in morphology and processes such models can fall short in describing the longitudinal variability associated with low order streams a more thorough understanding of the influence of local variability of process and form in low order stream channels is required to remotely and accurately predict channel geometry characteristics for management purposes and in this context designating process domains is useful we define process domains with respect to glacial versus fluvial valleys and lateral confinement of valley segments we evaluated local variability of process domains in the colorado front range by systematically following streams categorizing them into stream morphologic type and process domain and evaluating a number of channel geometry characteristics we evaluated 111 stream reaches for significant differences in channel geometry among stream types and process domains location and clustering of stream types on a slope drainage area s a plot and downstream hydraulic geometry relationships although individual channel geometry variables differed significantly between individual stream types in glacial and fluvial process domains no single channel geometry variable consistently differentiated all stream types between process domains hypothetical s a boundaries between bedrock and alluvial bed channels proposed in previous studies did not reliably divide bedrock and alluvial reaches for our study sites although downstream hydraulic geometry relationships are well defined using all reaches in the study area reaches in glacial valleys display much more variability in channel geometry characteristics than reaches in fluvial valleys less pronounced downstream hydraulic geometry relationships and greater scatter of reaches on an s a plot local spatial variability associated with process domains at the reach scale 10 1 10 3 m overrides progressive downstream relationships in low order mountain streams of the colorado front range

mineralogy and textures of the lahanos and kizilkaya massive sulphide deposits northeastern turkey and their similarity to kuroko ores a distinct vertical zonation very similar to that described for the kuroko deposits of japan is displayed by both mineralogy and textures of sulphides from the lahanos and kizilkaya massive sulphide deposits of northeastern turkey a deeper erosional level is exposed at the kizilkaya deposit so that only remnants of the massive sulphide ore zone are present the zonation is from an upper zone of massive cu and zn sulphides black and yellow ore with fine grained colloform banded framboidal and spherulitic textures downwards through an intermediate zone of low cu zn massive pyrite with transitional textures to a lower zone of stockwork and impregnated pyrite displaying euhedral zoned textures the fine grained and colloform pyrite of the upper zones is progressively overgrown by and recrystallized to the massive and euhedral pyrite of lower zones the original textures of these deposits are best preserved by pyrite the previous interpretation of these textures of sulphide deposition from colloidal solutions ponded by an impermeable pyroclastic horizon is reexamined in the light of present observations although ultra fine grained sulphides framboids and radially cracked spherules could have formed by replacement of pre existing minerals by a colloidal solution the colloform and banded textures are indicative of growth in open spaces it thus seems likely that the fine grained colloform sulphides including chalcopyrite sphalerite and tennantite as well as pyrite were initially deposited on or near the surface of the sea floor additional evidence for this interpretation is seen in the progressive recrystallization of the sulphide textures to massive much coarser pyrite in the lower zones this recrystallization may in part be due to diagenetic and hydrothermal processes operating after formation of the original layered sulphides these conclusions are in agreement with those reached for the similar but larger madenkoy deposit 100 km to the east

slope distributions threshold hillslopes and steady state topography digital elevation models of two steady state mountain ranges the olympic mountains om and oregon coast range ocr are used to examine relationships between slope distributions the development of threshold hillslopes and steady state topography plots of drainage area versus slope for these mountain ranges exhibit substantial scatter that complicates comparison of range form to analytical theories and landscape evolution models contour plots of the density of such data reveal an attractor at the scale of the transition from hillslope processes to channel processes and log bin averaging reveals trends that parallel predictions of steady state erosion laws but with different rate laws for five distinct process domains hillslopes valley heads and colluvial bedrock and alluvial valley segments slope histograms computed for 100 km2 areas defined by a 10 10 km grid throughout the om exhibit approximately normal or exponential distributions in areas of active rock uplift and depositional topography respectively local slope distributions in the ocr also tend to be normally distributed but some are left skewed in areas with gentler slopes mean slopes determined both over the above referenced grid and a 10 km diam moving window are relatively invariant in the core of the om in spite of strong contrasts in bedrock erodibility and gradients in long term rock uplift rates in contrast the mean slopes in the ocr parallel latitudinal gradients in rock uplift rates and bedrock erodibility hence the slope distributions in the om and ocr reflect distinct relationships between development of threshold bedrock and soil mantled hillslopes and steady state topography

massive sulfide deposits of the noranda area quebec ii the aldermac mine the original aldermac mine near noranda contained several cu zn massive sulfide lenses hosted by felsic to mafic volcanic rocks of the late archean blake river group the original nos 3 6 orebodies which consisted of massive pyrite with lesser magnetite pyrrhotite chalcopyrite and sphalerite contained 1 87 mt of cu zn ore that averaged 1 47 cu zn was not recovered the orebodies occurred within felsic breccias and tuffs up to 100 m thick that are stratigraphically overlain by an extensive dome of mainly massive rhyolite and rhyodacite up to 250 m thick and at least 550 m across most of the volcanic rocks that laterally flank and overlie the felsic dome are dacitic to andesitic flows breccia and tuff with minor rhyolites and associated subvolcanic sills of quartz feldspar porphyry and gabbro the new massive sulfide deposit discovered in 1988 lies 150 200 m east of the mined out orebodies at a similar stratigraphic level within altered felsic breccia and tuff the sulfides are mainly in

geochemistry of metamorphosed volcanic rocks in the neoarchean qingyuan greenstone belt north china craton implications for geodynamic evolution and vms mineralization abstract the qingyuan greenstone belt qgb situated in the northeastern section of the north china craton ncc is considered to be the unique metallogenic province in china that hosts both banded iron formations bifs and volcanogenic massive sulfide vms deposits traditionally the qgb is divided into the hunbei and hunnan terranes separated by the hunhe fault and grouped into the lower shipengzi middle hongtoushan and upper nantianmen formations which have undergone amphibolite to granulite facies metamorphism exposed supracrustal rocks are composed of plagioclase amphibolite and biotite plagioclase gneiss with minor amounts of bif marble and schist in this study detailed field and petrographic observations lithogeochemical u pb geochronological as well as whole rock sm nd isotope analyses were conducted on the metamorphosed mafic and felsic volcanic rocks i e plagioclase amphibolite and biotite plagioclase gneiss respectively in the qgb in order to discuss implications for tectonic evolution and comitant vms mineralization the supracrustal rocks of both hunbei and hunnan regions were formed synchronously from 2 57 to 2 53 ga and then had undergone 2 52 2 48 ga regional metamorphism specifically the lower section of the shipengzi formation is composed dominantly of transitional tholeiitic basalts with negative nb anomalies suggesting that they were likely generated by partial melting of a mantle source that was previously altered by variable amounts of slab derived fluids or melts in contrast the lithologic assemblages grade upward into interlayered bimodal volcanic rocks i e n morb type tholeiitic basalts and fi to fii type dacites of transitional to calc alkalic affinities representing a change in tectonic regime related to subduction from compression to extension among them all the basalts are characterized by consistently positive initial nd compositions end t 2 7 to 3 4 further indicate a depleted mantle source whereas those dacites possess negative to positive initial nd values end t 4 6 to 3 0 suggesting they were formed by partial melting of depleted mafic source likely lower mafic crust and accompanied with variable addition of old crustal material significantly vms deposits are genetically linked to this extensional event and closely associated with the fii type dacites that were generated by higher melting degree at high temperature conditions and shallow crustal level likely 10 15 km in all geochemical features e g negative nb anomalies and end value together with contamination from continental crusts for tholeiitic mafic rocks and inherited zircons from these volcanic rocks imply a continental arc setting where the qgb was evolved

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

relative size of fluvial and glaciated valleys in central idaho quantitative comparisons of the morphometry of glaciated and fluvial valleys in central idaho were used to investigate the differences in valley relief and width in otherwise similar geologic and geomorphic settings the local relief width and cross sectional area of valleys were measured using gis software to extract information from usgs digital elevation models hillslope gradients were also measured using gis software power law relationships for local valley relief width and cross sectional area as a function of drainage area were developed local valley relief in glaciated valleys relates to drainage area with a power law exponent similar to fluvial valleys but glaciated valleys are deeper for a given drainage area local valley width in glaciated valleys is greater than in fluvial valleys but the exponent of the power law relationship to drainage area is similar in both valley types local valley cross sectional area in glaciated valleys increases with drainage area with a power law exponent similar to fluvial valleys however glacial valleys have roughly 80 greater cross sectional area steep valley walls in glaciated basins increase the potential for bedrock landsliding relative to fluvial basins both the olympic mountains of washington and valleys in central idaho show relationships in which glaciated valleys are up to 30 deeper than fluvial valleys despite differences in lithology tectonic setting and climate

trace element geochemistry of ore associated and barren felsic metavolcanic rocks in the superior province canada reply archaean felsic metavolcanic rocks in the superior province of the canadian shield may be divided into three major groups on the basis of trace element abundances and ratios 1 fi felsic metavolcanic rocks are dacites and rhyodacites characterized by steep ree patterns with weakly negative to moderately positive eu anomalies high zr y low abundances of high field strength elements e g hree y zr hf and high abundances of sr examples occur in the bowman subgroup and skead group in the abitibi belt in the kakagi lake lake of the woods shoal lake and sturgeon lake areas of the wabigoon belt and in the confederation lake area of the uchi belt none of these horizons as known hosts base metal sulphide deposits 2 fii felsic metavolcanic rocks are rhyodacites and rhyolites characterized by gently sloping ree patterns with variable eu anomalies moderate zr y and intermediate abundances of hfs elements and sr examples occur in the misema subgroup of the abitibi belt in the wabigoon lake a

positive feedbacks associated with erosion of glacial cirques and overdeepenings the principal points of water input to a glacier are the bergschrund in cirques and crevasse fields lower on the glacier crevasse fields commonly occur over convexities at the heads of overdeepenings in glacier beds the amplitude of subglacial water pressure fluctuations is large just down glacier from these points of water input erosion by quarrying is likely in such areas erosion is thus inferred to be localized on the headwalls of cirques and overdeepenings in the case of overdeepenings this leads to a positive feedback process in which a perturbation in the bed causes crevassing at the surface resulting in erosional forces that accentuate the perturbation when subglacial water flows up an adverse bed slope leading out of a cirque or overdeepening much of the viscous energy dissipated is used to warm the water to keep it at the pressure melting temperature as the ice thins and the pressure decreases in such situations subglacial conduits are maintained by high water pressures rather than by melting of conduit walls in the limit water pressures apparently become so high that water is forced out along the ice bed interface and the conduits collapse the products of erosion are then no longer flushed out and a protective till layer accumulates by limiting erosion on such adverse bed slopes this till layer controls the geometry of these overdeepened basins

numerical modeling of the development of u shaped valleys by glacial erosion the steep sided valleys and overdeepened basins of alpine landscapes are well known products of glaciation yet relatively little is known about how the dynamics of ice flow and glacial erosion interact to give rise to such landforms by linking a finite element model for ice flow through a glacier cross section with an erosion model it is possible to investigate the development of one of the most striking glacial landforms the u shaped valley in addition to providing a detailed understanding of landform development such modeling provides a way to test current understanding of the controls on glacial sliding and erosion to simulate valley development i first model flow through an initial glacier cross section and calculate the glaciological parameters that govern erosion i then numerically simulate erosion to produce a modified transverse profile for which a new flow field and erosion pattern are computed a number of iterations permits examination of the progressive transformation of cross section form which can be compared with field data model predictions of the cross section flow field are in close accord with data from the athabasca glacier and include marked lateral variations in sliding velocity with an erosion law dependent on basal velocity the model predicts the rapid transformation of a v shaped cross section into a recognizably glacial form over a time period on the order of 10 4 yr and the eventual development of a steady state quasi parabolic glacier cross section better agreement with empirical data from glaciated valleys is obtained by including temporal variations in ice discharge in order to mimic the characteristics of 100 000 yr glacial cycles the high discharge phase dominates form development and at low discharges cross section form is essentially inherited from the central part of the form that developed during the preceding high discharge phase

pleistocene plateau ice fields in the high atlas morocco large ice fields 25 km2 formed over the tazaghart and iouzagner plateaux of the high atlas morocco during the late pleistocene the plateau ice fields were drained by large valley glaciers forming a series of moraine assemblages four moraine units have been mapped and subdivided on the basis of morphostratigraphy and the degree of soil weathering soil profile development index pdi values indicate that the moraine units are widely separated in time with the oldest moraines deeply weathered and degraded whereas soils are absent on the youngest moraines the highest moraine unit was formed by a small niche glacier which was present as recently as the mid 20th century pleistocene glaciers are likely to have been associated with wetter conditions than today in addition to colder air temperatures combined with ice in neighbouring areas such as the toubkal massif the sw high atlas supported some of the largest glaciers in africa during the pleistocene the extent of glaciation with ice exploiting and breaching drainage divides has major implications for landscape development the evolution of the high atlas is therefore strongly shaped by glaciation and this is closely intertwined with tectonic fluvial and slope processes

small valley glaciers and the effectiveness of the glacial buzzsaw in the northern basin and range usa the glacial buzzsaw hypothesis suggests that efficient erosion limits topographic elevations in extensively glaciated orogens studies to date have largely focussed on regions where large glaciers tens of kilometres long have been active in light of recent studies emphasising the importance of lateral glacial erosion in lowering peaks and ridgelines we examine the effectiveness of small glaciers in limiting topography under both relatively slow and rapid rock uplift conditions four ranges in the northern basin and range idaho montana and wyoming usa were chosen for this analysis estimates of maximum pleistocene slip rates along normal faults bounding the beaverhead bitterroot mountains similar to 0 14 mm y 1 lemhi range similar to 0 3 mm y 1 and lost river range similar to 0 3 mm y 1 are an order of magnitude lower than those on the teton fault similar to 2 mm y 1 we compare the distribution of glacial erosion estimated from cirque floor elevations and last glacial maximum lgm equilibrium line altitude ela reconstructions and fault slip rate with three metrics of topography in each range the along strike maximum elevation swath profile hypsometry and slope elevation profiles in the slowly uplifting beaverhead bitterroot mountains and lemhi and lost river ranges trends in maximum elevation parallel elas independent of variations in fault slip rate maximum elevations are offset similar to 500 m from lgm elas in the lost river range lemhi range and northern beaverhead bitterroot mountains and by similar to 350 m in the southern beaverhead bitterroot mountains where glacial extents were less the offset between maximum topography and mean quaternary elas inferred from cirque floor elevations is similar to 350 m in the lost river and lemhi ranges and 200 250 m in the beaverhead bitterroot mountains additionally slope elevation profiles are flattened and hypsometry profiles show a peak in surface areas close to the ela in the lemhi range and beaverhead bitterroot mountains suggesting that small glaciers efficiently limit topography the situation in the lost river range is less clear as a glacial signature is not apparent in either slope elevation profiles or the hypsometry in the rapidly uplifting teton range the distribution of elas appears superficially to correspond to maximum topography hypsometry and slope elevations profiles with regression lines on maximum elevations offset by similar to 700 and similar to 350 m from the lgm and mean quaternary ela respectively however grand teton and mt moran represent high elevation teflon peaks that appear impervious to glacial erosion formed in the hard crystalline bedrock at the core of the range glacier size and drainage density rock uplift rate and bedrock lithology are all important considerations when assessing the ability of glaciers to limit mountain range topography in the northern basin and range it is only under exceptional circumstances in the teton range that small glaciers appear to be incapable of imposing a fully efficient glacial buzzsaw emphasising that high peaks represent an important caveat to the glacial buzzsaw hypothesis c 2008 elsevier b v all rights reserved

alteration mineralogy lithochemistry and stable isotope geochemistry of the murgul artvin ne turkey volcanic hosted massive sulfide deposit implications for the alteration age and ore forming fluids abstract the murgul artvin ne turkey massive sulfide deposit is hosted dominantly by late cretaceous calc alkaline to transitional felsic volcanics the footwall rocks are represented by dacitic flows and pyroclastics whereas the hanging wall rocks consist of epiclastic rocks chemical exhalative rocks gypsum bearing vitric tuff purple vitric tuff and dacitic flows multi element variation diagrams of the hanging wall and footwall rocks exhibit similar patterns with considerable enrichment in k rb and ba and depletion in nb sr ti and p the chondrite normalized rare earth element rees patterns of all the rocks are characterized by pronounced positive negative eu anomalies as a result of different degrees of hydrothermal alteration and the semi protected effects of plagioclase fractionation mineralogical results suggest illite illite smectite chlorite kaolinite and chlorite in the footwall rocks and illite smectite kaolinite and chlorite illite in the hanging wall rocks overall the alteration pattern is represented by silica sericite chlorite and chlorite carbonate epidote sericite and quartz albite zones increments of ishikawa alteration indexes resulting from gains in k 2 o and losses in na 2 o and the chlorite carbonate pyrite index towards to the center of the stringer zone indicate the inner parts of the alteration zones calculations of the changes in the chemical mass imply a general volume increase in the footwall rocks abnormal volume increases are explained by silica and iron enrichments and a total depletion of alkalis in silica zone relative k increments are linked to the sericitization of plagioclase and glass shards and the formation of illite smectite in the sericite zone in addition fe enrichment is always met by pyrite formation accompanied by quartz and chlorite illite is favored over chlorite smectite and kaolinite in the central part of the ore body due to the increase in the al k na ca ratio although the rees were enriched in the silicification zone light rees show depletion in the silicification zone and enrichment in the other zones in contrast to the heavy rees behavior hydrothermal alteration within the hanging wall rocks apart from the gypsum bearing vitric tuffs is primarily controlled by chloritization with proportional fe and mg enrichments and sericitization the 18 o and d values of clay minerals systematically change with increasing formation temperature from 6 6 to 8 7 and 42 to 50 for illites and 8 6 and 52 for chlorite respectively the o and h stable isotopic data imply that hydrothermal alteration processes occurred at 253 332 c for illites and 136 c for chlorite with a temperature decrease outward from the center of the deposit the positive 34 s values 20 3 to 20 4 for gypsum suggest contributions from seawater sulfate reduced by fe oxide hydroxide phases within altered volcanic units thus the hydrothermal alteration possibly formed via a dissolution precipitation mechanism that operated under acidic conditions the k ar dating 73 62 ma of the illites indicates an illitization process from the maastrichtian to early danian period

the gold content of volcanogenic massive sulfide deposits volcanogenic massive sulfide deposits contain variable amounts of gold both in terms of average grade and total gold content with some vms deposits hosting world class gold mines with more than 100 t au previous studies have identified gold rich vms as having an average gold grade expressed in g t exceeding the total abundance of base metals expressed in wt however statistically meaningful criteria for the identification of truly anomalous deposits have not been established this paper presents a more extensive analysis of gold grades and tonnages of 513 vms deposits worldwide revealing a number of important features in the distribution of the data a large proportion of deposits are characterized by a relatively low gold grade 2 g t with a gradual decrease in frequency towards maximum gold grades defining a log normal distribution in the analysis presented in this paper the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of vms deposits based on gold grade especially when comparing deposits within individual belts and districts the geometric mean gold grade of 513 vms deposits worldwide is 0 76 g t the geometric standard deviation is 2 70 g t au in this analysis deposits with more than 3 46 g t au geometric mean plus one geometric standard deviation are considered auriferous the geometric mean gold content is 4 7 t au with a geometric standard deviation of 26 3 t au deposits containing 31 t au or more geometric mean plus one geometric standard deviation are also considered to be anomalous in terms of gold content irrespective of the gold grade deposits with more than 3 46 g t au and 31 t au are considered gold rich vms a large proportion of the total gold hosted in vms worldwide is found in a relatively small number of such deposits the identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in vms at the district scale the gold rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes the gold rich vms are commonly associated with transitional to calc alkaline intermediate to felsic volcanic rocks which may reflect a particularly fertile geodynamic setting and or timing e g early arc rifting or rifting front at the deposit scale uncommon alteration assemblages e g advanced argillic aluminous strongly siliceous or potassium feldspar alteration and trace element signatures may be recognized e g au ag as sb bi hg te suggesting a direct magmatic input in some systems

fluvial incision into bedrock insights from morphometric analysis and numerical modeling of gorges incising glacial hanging valleys western alps france bedrock gorges incising glacial hanging valleys potentially allow measurements of fluvial bedrock incision in mountainous relief using digital elevation models topographic maps and field reconnaissance we identified and characterized 30 tributary hanging valleys incised by gorges near their confluence with trunk streams in the romanche watershed french western alps longitudinal profiles of these tributaries are all convex and have abrupt knickpoints at the upper limit of oversteepened gorge reaches we reconstructed initial glacial profiles from glacially polished bedrock knobs surrounding the gorges in order to quantify the amount of fluvial incision and knickpoint retreat from morphometric analyses we find that mean channel gradients and widths as well as knickpoint retreat rates display a drainage area dependence modulated by bedrock lithology however there appears to be no relation between horizontal retreat and vertical downwearing of knickpoints assuming a postglacial origin of these gorges our results imply high postglacial fluvial incision 0 5 15 mm yr 1 and knickpoint retreat 1 200 mm yr 1 rates that are however consistent with previous estimates numerical modeling was used to test the capacity of different fluvial incision models to predict the inferred evolution of the gorges results from simple end member models suggest transport limited behavior of the bedrock gorges a more sophisticated model including dynamic width adjustment and sediment dependent incision rates predicts present day channel geometry only if a significant supply of sediment from the gorge sidewalls 10 mm yr 1 is triggered by gorge deepening combined with pronounced inhibition of bedrock incision by sediment transport and deposition

partial least squares discriminant analysis of trace element compositions of magnetite from various vms deposit subtypes application to mineral exploration abstract the petrography and mineral chemistry of magnetite from fifteen volcanogenic massive sulfide vms deposits in canada and the lasail vms deposit in oman as well as from two vms associated banded iron formations bif austin brook new brunswick canada and izok lake nunavut canada were investigated using optical microscopy electron probe micro analyzer epma and laser ablation inductively coupled plasma mass spectrometry la icp ms the method of robust estimation for compositional data robcompositions was applied to investigate geochemical censored data among thirty seven elements analyzed by epma and or la icp ms in magnetite from the studied deposits bedrock lithologies only the results for si ca zr al mg ti zn co and ni contain pls da shows that variable compositions of magnetite slightly discriminate different studied deposits bedrock lithologies the geochemical observations suggest that the variation in magnetite chemistry from different vms settings might be sourced from differences in 1 the composition and temperature of parental magmas or hydrothermal fluids 2 the composition of host bedrocks 3 the composition of co forming minerals and 4 oxygen fugacity pls da distinguishes magnetite compositions from the studied vms deposits and bifs from that of the other ore deposit types including ni cu porphyry cu mo au iron oxide copper gold iron oxide apatite and the bayan obo ree fe nb deposit magnetite from the vms settings on average contains lower concentrations of si zr al mg ti zn co and ni relative to that from the other mineral deposit types pls da of magnetite data from vms deposits and bifs of the bathurst mining camp as well as pls da of magnetite compositions from various mineral deposit types yield discrimination models for application to mineral exploration for vms deposits using indicator minerals in quaternary lithified sedimentary rocks

volcanism and metallogenesis of axial and off axial structures on the east pacific rise near 13 degrees n a fast spreading segment 12 cm yr super 1 of the east pacific rise near 12 degrees 50 n explored in detail by surface ship and manned submersible displays intense hydrothermal activity the rise crest about 1 500 m in width with a regional depth of 2 600 m is occupied at its center by an axial graben 1 3 titania alkali enriched olivine ti k basalts with high tio 2 1 4 and high alkali content na 2 o 3 0 k 2 o 0 3 occur on the southeastern seamount the fractionated tholeiites are believed to have been derived from primitive melts during differentiation which took place within a magma reservoir asymmetrical with respect to the axis of the graben which supplied both axial and off axial lava flows the ti k enriched basalts are believed to have been produced from an alkali enriched magmatic source

depositional setting and structural evolution of the archean perseverance volcanogenic massive sulfide deposit matagami mining district quebec canada the perseverance volcanogenic massive sulfide deposit 5 1 mt at 15 8 zn 1 24 cu 29 4 g t ag 0 4 g t au matagami district abitibi greenstone belt consists of four pipelike orebodies discordant to local bedding in a shallow dipping portion of the south flank volcanic succession most of the ore is hosted by rhyolitic lavas of the watson unit 2725 9 0 8 ma and is overlain by a thinly laminated tuffaceous unit known as the key tuffite as well as by rhyodacitic lavas of the dumagami unit 2725 4 0 7 ma the presence of sulfide zones predominantly hosted in the footwall rhyolite relicts of key tuffite within the ore and intricate sulfide replacement of the laminated tuff are all features consistent with the formation of most of the deposit via subseafloor replacement the permeability of steep synvolcanic structures likely controlled the migration of metal bearing fluids and simultaneously allowed the downward infiltration of seawater causing mixing cooling and sulfide deposition in the subseafloor environment stratigraphic relationships suggest that massive sulfide formation was active at perseverance while tuffaceous sedimentation was ongoing on the seafloor progressive growth of the massive sulfides along subvertical structures was accompanied by the development of pipelike sericite chlorite talc alteration halos both the hanging wall and the footwall units are characterized by significant mgo mass gains k 2 o na 2 o mass losses and high alteration index values e g chlorite carbonate pyrite index alteration index however these geochemical changes are less intense and widespread in the hanging wall than in the footwall the record of a decreasing alteration above the orebodies was likely caused by the emplacement of the rhyodacite while massive sulfide deposition and hydrothermal activity were still ongoing primary relationships between mineralization and the host lithofacies were overprinted by intense deformation during the main event of compression induced by regional north south shortening deformation is controlled by contrasting rheologies within the sulfide assemblage and between the orebodies and their host rocks structural modifications include the transposition of sulfide ores subparallel to the main foliation the formation of piercement veins at the interface with the host rocks and the generation of a series of secondary textures within the orebodies including a vertical mineralogical banding the distribution of cu in the deposit is interpreted to be affected by the mechanical remobilization of chalcopyrite during deformation whereas the zonation of zn is likely primary hydrothermal alteration halos adjacent to the orebodies have accommodated significant strain as indicated by the presence of tight folds in the key tuffite unit and a marked schistosity strain localization in the vicinity of the deposit highlights the relative ductility of the ore assemblage with respect to the host volcanic succession and resulted in a spatial association between hydrothermal alteration and deformation despite the lack of a genetic relationship

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

the relative efficiency and influence of glacial and fluvial erosion on tibetan plateau landscapes abstract driven by climate change periods of dominating glacial and fluvial erosion have both sculpted mountain ranges during the quaternary to understand the evolution of mountain landforms there is considerable interest in knowing which erosion agent leads to more incision how glacial thermal regime impacts erosion and landscape development and whether glacial erosion can result in increased relief to investigate the relative efficiency of glacial and fluvial erosion and the influence of glacial thermal regime on topography we compare two different mountain ranges the qionglai shan monsoonal temperate glaciation and lenglongling subcontinental glaciation in western china we use a 1 d model to construct presumptive fluvial longitudinal profiles if glaciation had not occurred and compare these with the actual glacial profiles to obtain relative incision rates of fluvial and glacial erosion results demonstrate that glacial incision is smaller than fluvial incision in lenglongling and larger than fluvial incision in the qionglai shan which may be influenced by different tectonics and glacier types topographic analysis of glacial and fluvial valleys with similar drainage areas show that glacial erosion results in valley widening local valley relief increase induced by isostatic uplift and slope gradient increase in lenglongling however there is no local valley relief and slope increase observed in the qionglai shan which may reflect slope process responses to threshold hillslope limiting the height above valley bottoms

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

subglacial basins their origin and importance in glacial systems and landscapes closed topographic basins are found beneath contemporary ice masses and within the footprint of former ice masses in all glaciated regions we present the first integrated review of subglacial basin occurrence and formation and the implications of such basins for glaciological processes and the evolution of landscape our purpose is to motivate research in areas where understanding of basin origin and process significance is weak basins on the order of 10 102 m deep and 102 103 m long are produced by glacial erosion of subglacial rock and or sediment and are known as overdeepenings outlet and valley glaciers can overdeepen their beds far below sea level or local fluviatile base level larger basins typically in ice sheet contexts may have a pre glacial usually tectonic origin subglacial basins are important glaciologically because they require ice water and sediment to ascend an adverse subglacial slope in order to exit the glacial system the efficiency of which is dependent upon the gradient of the adverse slope and that of the ice surface basins thus influence subglacial drainage system morphology and transmissivity the thickness and distribution of basal ice and sediment layers and the mechanisms and dynamics of ice flow adverse gradients that exceed 11 times that of the ice surface may even permit the formation of subglacial lakes we speculate that in comparison to ice masses with few or no subglacial basins those with numerous or very large basins may respond to climatic changes with unexpected vigour in addition erosion rates and transport pathways of water and sediment through the glacial system and the expression of these processes in the sediment and landform record may be unexpectedly complex further our review shows that in a warming climate ice masses resting on adverse slopes will be vulnerable to rapid and potentially catastrophic retreat new lakes in subglacial basins exposed by mountain glacier retreat will present an increasing hazard and subglacial lakes may drain catastrophically on even longer time scales we speculate that the glacial excavation and post glacial filling of basins in mountainous regions should contribute importantly to climate related changes in isostasy and relief although the controls on overdeepening and their influence on other glacial and landscape processes remain uncertain we hypothesise that overdeepened glacial systems reflect an equilibrium ice bed geometry that maximises the efficiency of ice discharge improved understanding of overdeepening processes especially overdeepened bed hydrology is therefore necessary to understand fully the dynamic behaviour of valley and outlet glaciers and thus the fate of earth s largest ice masses

development of glacial valley cross sections under conditions of spatially variable resistance to erosion abstract a simulation model that examines the development of valley cross profiles as a result of glacial erosion has been constructed by placing a finite element model for ice flow within an iterative program that modifies channel cross section form on the basis of an erosion equation the simulation model has previously been used to examine how different flow laws erosion laws and ice discharge histories affect medium scale landform development this allows us to better understand the development of glacial landforms and also provides a critical test for erosion and flow laws within the erosion component of the simulation program it is possible to specify spatial variations in bedrock erodibility in order to examine the effect of spatially variable lithologies on form development as an initial test of form development under these conditions a central area of enhanced erodibility is placed in the valley center in this case active glacial channels develop that are narrower and deeper than those which occur with homogenous bedrock this change in form occurs as long as the weaker zone is small enough that the active channel does not eventually narrow to a stage such that it is entirely contained within the weaker material and as long as it is large enough that it continues to have a significant impact on overall discharge through the section form variation occurs because the weaker central zone enhances the lateral gradient of the erosion rate which is critical for form development a central area of more erodible bedrock changes not only the form of the active glacial channel but also the convexity of side slopes that are left above the glacier as it erodes downwards into the landscape the absence of a classic u shaped cross section should not be taken a priori to suggest either absence of glacial erosion or ineffective glacial erosion rather the combination of active glacial and hillslope processes in a landscape with spatially and temporally variable ice discharge and rock characteristics can create a diverse set of cross section forms

glacial valley cross profile development the influence of in situ rock stress and rock mass strength with examples from the southern alps new zealand abstract the evolution of the glacial valley cross profile form is commonly attributed primarily to the glaciological variables that control the erosion of the channel however studies in the new zealand southern alps suggest that the rock mass strength rms of the eroded rock mass is a major control on slope stability and hence on the final form of the trough rms of the slope rock will alter with time and erosional excavation and oversteepening of the valley slopes the in situ rock stress field induced by 1 the extreme topography in the axial ranges of the new zealand southern alps and 2 tectonically by collision of the australian and pacific crustal plates may play a role in valley slope development by controlling the location of rock failure and reducing rms this provides weakened rock that may provide sites for selective glacial erosion of the rock mass hence valley form evolution models should also take into account the rms and the in situ stress field acting in the eroded rock mass this study has implications for the development and modification of alpine glacial troughs in similar tectonic settings elsewhere

an oxygen isotope study of the kidd creek ontario volcanogenic massive sulfide deposits evidence for a high 18 o ore fluid the hydrothermally altered rhyolites delta 18 o 10 16ppm at the kidd creek cu zn ag pb volcanogenic massive sulfide deposit archean abitibi greenstone belt are all markedly enriched in 18 o compared to almost all other massive sulfide deposits a chalcopyrite stockwork zone forming a concordant keel stratigraphically below the massive sulfide typically has whole rock delta 18 o 10 to 12 per mil beneath the stockwork keel rhyolite delta 18 o values systematically increase stratigraphically downward for about 50 m below this level all of the footwall rhyolites in the kidd creek area display exceptionally high delta 18 o values of 13 to 16 per mil the groundmass quartz in the rhyolites ranges from 13 6 to 15 5 per mil and crosscutting quartz veins associated with the chalcopyrite stockwork mineralization have delta 18 o 11 9 per mil by contrast the postore basalts of the hanging wall are weakly altered show only modest 18 o enrichments delta 18 o 8 10ppm and are isotopically similar to the volcanic rocks in other parts of the abitibi greenstone belt petrographically all of the kidd creek footwall rhyolites are intensely altered typically containing 76 90 wt sio 2 indicating that the high 18 o characteristics are not primary magmatic features but are the result of hydrothermal alteration several disequilibrium oxygen isotope relationships are present for example volcaniclastic rhyolites consist of extremely 18 o rich chlorite rich and sericite rich clasts enclosed within a lower 18 o sericitically altered rhyolite tuff matrix this implies at least a two stage hydrothermal history involving either different temperatures of alteration or different fluid sources or both using a temperature of 300 degrees to 350 degrees c the main ore forming fluid must have had delta 18 o 6 to 9 per mil inasmuch as the associated felsic volcanic rocks were apparently erupted in a shallow subaqueous locally subaerial environment the most plausible origin of the ore fluid is evaporation and enrichment in 18 o of normal seawater in a closed basin at the western edge of the abitibi belt this would produce a strongly 18 o shifted high salinity fluid that would have been capable of transporting large amounts of metals the high 18 o signature of the kidd creek timmins volcanic rocks may constitute an exploration target that warrants further study and evaluation in other areas

effects of greenschist facies metamorphism and related deformation on the mobrun massive sulfide deposit quebec canada the mobrun zn cu ag au deposit in the noranda mining camp is hosted by archean mafic and felsic submarine volcanic rocks the deposit comprises three massive sulfide complexes the main and satellite lenses near surface and the 1100 orebody at depth the rocks have been subjected to lower greenschist facies metamorphism and related deformation which resulted in changes in ore textures development of shear zones and veins systems remobilization of gold and formation of a new mineral electrum within the orebodies both mechanical and chemical processes operated to produce secondary textures and structures resulting from brittle deformation ductile deformation and annealing the specific deformation mechanisms include brittle failure and cataclastic flow dislocation glide dislocation creep and solution precipitation creep the main and satellite lenses are characterized by excellent preservation of primary sulfides deposited from and reworked by synvolcanic hydrothermal fluids these orebodies were affected to a limited degree by mechanical processes of deformation in contrast the 1100 orebody is characterized by a higher degree of development of textures and structures related to metamorphism and deformation especially those formed by chemical processes the differences may be due to the greater depth of the 1100 orebody relative to the other lenses as regional metamorphic isograds are subhorizontal and more extensive interaction between metamorphic fluids and the 1100 lens

intraseasonal variability of the south china sea summer monsoon the objective of this study is to explore based on the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data the intraseasonal variability of the south china sea scs summer monsoon sm in terms of its structure and propagation as well as interannual variations a possible mechanism that is responsible for the origin of the 10 20 day oscillation of the scs sm is also proposed the 30 60 day hereafter the 3 6 mode and 10 20 day hereafter the 1 2 mode oscillations are found to be the two intraseasonal modes that control the behavior of the scssm activities for most of the years both the 3 6 and 1 2 modes are distinct but may not always exist simultaneously in a particular year and their contributions to the overall variations differ among different years thus the interannual variability in the intraseasonal oscillation activity of the scs sm may be categorized as follows the 3 6 category in which the 3 6 mode is more significant in terms of the percentage of variance explained than the 1 2 mode the 1 2 category in which the 1 2 mode is dominant and the dual category in which both the 3 6 and 1 2 modes are pronounced composite analyses of the 3 6 category cases indicate that the 30 60 day oscillation of the scs sm exhibits a trough ridge seesaw in which the monsoon trough and subtropical ridge exist alternatively over the scs with anomalous cyclones anticyclones along with enhanced suppressed convection migrating northward from the equator to the midlatitudes the northward migrating 3 6 mode monsoon trough ridge in the lower troposphere is coupled with the eastward propagating 3 6 mode divergence convergence in the upper troposphere it is also found that for the years in the dual category the scs sm activities are basically controlled by the 3 6 mode but modified by the 1 2 mode composite results of the 1 2 mode category cases show that the 10 20 day oscillation is manifest as an anticyclone cyclone system over the western tropical pacific propagating northwestward into the scs a close coupling also exists between the upper level convergence divergence and the low level anticyclone cyclone it is found that the 1 2 mode of the scs sm mainly originates from the equatorial central pacific although a disturbance from the northeast of the scs also contributes to this mode the flow patterns from an inactive to an active period resemble those associated with a mixed rossby gravity wave observed in previous studies

glacial landscape and paleoglaciation in terra sabaea evidence for a 3 6 ga polythermal plateau ice cap abstract in a previous study we demonstrated with a comparative morphometrical analysis the first morphometric evidence of a glacial landscape composed of glacial cirques and glacial valleys in the south of terra sabaea at an elevation 1000 m in two impact craters and one mountain the purpose of this study is to use the same method to seek other geomorphologic evidence of glacial landscapes elsewhere in terra sabaea based on a comparison between current and old glacial landscapes on earth and mars we identified 81 glacial valleys and possible evidence for a former plateau ice cap dated at 3 6 ga at the highest elevation in terra sabaea the identified glacial valleys have the same morphometric properties as terrestrial and martian glacial valleys with u shaped cross sectional profiles a v index 0 2 a length to with ratio 1 and a cross sectional area to drainage area ratio four times higher than the fluvial ones moreover these properties are different from terrestrial and martian fluvial valleys we did not find well preserved glacial cirques in this area this absence questions the origin of glacial valleys however the presence of an extensive flat plateau from which the long valleys radiate could have hosted an ancient plateau ice cap which was the source of these glacial valleys a comparison with the cantal and the shaluli shan in the southeastern tibetan plateau on earth reveals morphometrical similarities with our study area in fact long glacial valleys originating radially from a plateau at higher elevation are characteristics of an ancient plateau ice cap this analysis allowed us to propose a polythermal regime for martian glacial landscape namely a cold based ice cap except at the margin where the regime is warmed based due to the steeper topography this topography created shear stress which increased the heat at the base of the ice and created the outlet glacial valleys near the plateau the radial valleys are u shaped with a v index 0 2 but downstream to the low elevation area these valleys become more v shaped with a v index around 0 1 this hypothesis is supported by the presence of an open basin paleolake making the transition between inlet glacial valleys upstream and an outlet v shaped valley downstream so the morphometry of the radiating valleys suggests that liquid water played a role in the formation of this landscape

alpine landscape evolution dominated by cirque retreat despite the abundance in alpine terrain of glacially dissected landscapes the magnitude and geometry of glacial erosion can rarely be defined in the eastern kyrgyz range of central asia a widespread unconformity exhumed as a geomorphic surface provides a regional datum with which to calibrate erosion as tectonically driven surface uplift has progressively pushed this surface into the zone of ice accumulation glacial erosion has overprinted the landscape with as little as 500 m of incision into rocks underlying the unconformity distinctive glacial valleys display their deepest incision adjacent to cirque headwalls the expansion of north facing glacial cirques at the expense of south facing valleys has driven the drainage divide southward at rates of as much as two to three times the rate of valley incision glacial erosion rules based on ice flux incompletely explain this dominance of cirque retreat over valley incision local processes that either directly sap cirque headwalls or inhibit erosion down glacier appear to control at least initially alpine landscape evolution

plume and arc magmatism in the abitibi subprovince implications for the origin of archean continental lithospheric mantle abstract based on eclogitic mantle xenoliths that appear to be the residue of slab melts it is commonly argued that the formation of distinctive lithospheric keels beneath archean cratons occurred by the tectonic accretion of oceanic crust these models are complicated by evident buoyancy of the keels the varied compositions of the mantle xenolith suite as a whole and a compositional constraint that a large portion of the keels originated in mantle plume melting events resolution of these issues is complicated by the long development history of most cratons 100 s of m y and the multiple cycles of magmatism they represent in contrast the single 50 m y period of arc volcanism in the abitibi subprovince and the immediate onset of orogeny and craton stabilisation avoids many of these uncertainties chemical and isotopic data demonstrate that syn volcanic to syn tectonic adakitic abitibi granitoids were derived via slab melting deep seismic reflection profiles image singular slab like features along the moho these are interpreted as the remnants of oceanic slabs emplaced and torn during orogeny nonetheless their presence directly contradicts subcretion models of keel formation because they occupy regions that should correspond to the top of an earlier formed subcreted keel post adakite shoshonitic granitoids and lamprophyres also attest to the presence of a metasomatised mantle wedge throughout the entire period of abitibi arc magmatism diamond bearing lamprophyres in the abitibi and adjacent wawa subprovince are compositionally equivalent to paleoproterozoic diamondiferous rocks and characteristic of adakite generating shallow subduction rather than evidence of pre existing sub cratonic keels abitibi mantle plume and subduction related volcanism also demonstrates the continuous presence of shallow asthenospheric mantle beneath the belt over a 50 m y period komatiites and then boninites erupted along the central part of the belt halfway through its evolution and rifted arc style volcanism dominated the belt within a few m y of orogeny none of these events are consistent with the development of a progressively thickened continental lithospheric keel the geodynamic evolution of the abitibi belt demonstrates a fact recognised in some xenolith studies the characteristic association of deep keels and archean cratons was not developed gradually during greenstone belt volcanism rather it was initiated by the coupling of shallow imbricated plume and arc related crust with the buoyant residue of mantle plume melting that rose from depths of 80 km to 400 km subduction was active along the southern and eastern margin of the superior province craton before and after ascent of the abitibi plume renewal of subduction in the abitibi as marked by the occurrence of the 2716 ma boninitic volcanic suite delayed the ascent of the deep keel and its coupling to the composite crust final ascent of the plume residue occurred following orogeny and slab loss and may have included entrainment of fragmented slab residue into the rising diapir the coupling of shallow crust and deep keel occurred soon after and the keel s presence beneath the subprovince is recognised by phanerozoic diamond deposits xenolith chemistry and geophysical data

mass change calculations in altered rock series a technique is presented whereby precursors of altered rocks in a fractionated rock series can be identified and changes in chemical components mass and volume accurately calculated the procedure utilizes elements with high degrees of immobility in hydrothermal and associated interactive water rock systems igneous rock series and sedimentary and metamorphic rocks with primary continuity of chemical composition are amenable to this treatment in the procedure for igneous rocks best fit fractionation lines are established for an immobile igneous compatible incompatible element pair the latter element functioning as the fractionation monitor alteration paths are linear and pass through the origin intersections of the fractionation and alteration lines yield the immobile element concentrations in the precursors to the altered rocks mobile components are determined from fractionation lines and monitor values total mass changes are proportional to the displacement of altered samples from the fractionation line masses of other elements in an altered sample reconstructed values are recalculated to the concentration of the monitor element in the precursor chemical changes are the differences between the calculated precursor compositions and the reconstructed altered rock compositions errors are mainly a function of the positioning of the fractionation lines

latest pleistocene alpine glacier advances in the sawtooth mountains idaho usa reflections of midlatitude moisture transport at the close of the last glaciation mountain glaciers in the sawtooth mountains responded strongly to reinvigorated atmospheric moisture transport following the last ice sheet maximum the glaciers constructed an extensive moraine belt in the southeastern sawtooth mountains allowing determination of a detailed radiocarbon chronology from lake and marsh cores moraine morphometry and soil data indicate construction of seven to nine moraines in each of four valleys during two main late pleistocene ice advances a basal radiocarbon date from marsh cores in the alturas valley documents that the maximum advance during marine oxygen isotope stage 2 occurred shortly before ca 16 900 calibrated cal yr b p minimum limiting dates on glacial lacustrine sediment in lake and marsh cores from three valleys clustered around 13 950 cal yr b p document the maintenance or reestablishment of extensive ice volume during early late glacial time the ca 16 900 cal yr b p advance postdates the last ice sheet maximum by 4000 yr and is broadly correlative with maximum advances of the north yellowstone outlet glacier and the puget lobe of the cordilleran ice sheet and a near maximum advance of wallowa mountain glaciers these synchronous advances indicate response of a variety of ice systems to reinvigorated moisture transport following the ice sheet maximum as does the subsequent sawtooth advance during early late glacial time together these responses indicate strong sensitivity of certain ice systems to moisture delivery fluctuations

volcanic and structural reconstruction of the deformed and metamorphosed ming volcanogenic massive sulfide deposit canada implications for ore zone geometry and metal distribution

influence of a glacial buzzsaw on the height and morphology of the cascade range in central washington state usa abstract analysis of climatic and topographic evidence from the cascade range of washington state indicates that glacial erosion limits the height and controls the morphology of this range glacial erosion linked to long term spatial gradients in the ela created a tilted planar zone of 373 cirques across the central part of the range peaks and ridges now rise 600 m above this zone hypsometric analysis of the region shows that the proportion of land area above the cirques drops sharply and mean slopes 30 indicate that the areas above the cirques may be at or near threshold steepness the mean plus 1 relief of individual cirque basins 570 m corresponds to the 600 m envelope above which peaks rarely rise the summit altitudes are set by a combination of higher rates of glacial and paraglacial erosion above the ela and enhanced hillslope processes due to the creation of steep topography on the high precipitation western flank of the cascades the dominance of glacial and hillslope erosion at altitudes at and above the ela may explain the lack of a correspondence between stream power erosion models and measured exhumation rates from apatite u th he thermochronometry

mass volume and chemical changes in the alteration zone at the norbec mine noranda quebec a funnel shaped alteration pipe in archean rhyolite and andesite below massive sulphide zn cu ores at the norbec mine in northwestern quebec was outlined from drill core samples geochemical parameters and normative alteration mineralogy the pipe has a mass of 37 9 million tonnes giving a volume of 13 106 m3 which represents volume increase of 10 relative to the unaltered host volcanic rocks a bulk chemical composition was calculated using weighting procedures for volumes of influence for the samples net mobile mass change or chemical flux for the alteration pipe was 5 8 106 tonnes inclusion of the massive ore lens yields a flux of 9 6 106 tonnes for the whole hydrothermal system the largest additions to the system in millions of tonnes were feo 4 2 sio2 3 8 s 1 8 k2o 0 55 and mgo 0 5 the only depletions were na2o 1 4 and cao 0 44 base and precious metals accounted for 3 4 of the total element flux

the mattagami lake mine archean zn cu sulfide deposit quebec hydrothermal coprecipitation of talc and sulfides in a sea floor brine pool evidence from geochemistry 18 o 16 o and mineral chemistry orebody 2 is 21 million metric tons grading 10 5 percent zn 0 17 percent cu and 0 014 oz au plus 1 15 oz ag per short ton quartz in the orebody has a delta 18 o of 10 to 11 9 per mil or approximately 2 per mil heavier than footwall quartz signifying precipitation temperatures 250 degrees to 280 degrees c this is corroborated by filling temperatures of primary fluid inclusions within gangue quartz t f 240 degrees 270 degrees c both isotopic and fluid inclusion temperatures signify a broad thermal zonation from approximately 270 degrees c at the base to approximately 240 degrees c at the top of the orebody minimum water depths of 300 m are indicated from nonboiling hydrothermal fluids of 3 to 5 weight percent nacl equivalent at approximately 250 degrees c a approximately 50 degrees c cooling of fluids during passage from the footwall to a suggested sea floor brine pool above the ore zone may have been induced by turbulent mixing of approximately 20 percent pristine archean marine bottom water at approximately 70 degrees c downward into the brine pool chert in the overlying key tuffite has delta 18 o of 10 to 12 per mil probably representing equilibrium precipitation from brine pool fluids at 200 degrees to 250 degrees c spreading laterally across the sea floor in a gravitationally stable boundary layer modified journal abstract

massive sulfide deposits of the noranda area quebec iv the mobrun mine the corbet deposit is located in the upper part of the flavrian andesite the lowest volcanic formation within cycle iii of the noranda central mine sequence the deposit consisted of one main lens of massive sulfides and several smaller lenses and contained 2 7 106 t of mineable ore at 2 92 cu 1 98 zn 20 6 g t ag and 1 0 g t au the orebody had a massive pyrrhotite chalcopyrite core which passed laterally into massive pyrite sphalerite the northwestern part of the ore body is overlain by 50 100 m of flavrian andesite whereas the southeastern portion is overlain by northwest rhyolite lavas within the flavrian andesite and the lower northwest rhyolite are low in k2o 0 5 and are partly of tholeiitic affinity and partly of transitional affinity the tholeiitic volcanic series has zr y ratios of 2 8 to 4 5 whereas the transitional series has zr y ratios of 4 5 to 7 1 the two series are also distinct in plots of nb zr yb zr nb y and the rare earth elements these data indicate that two s

geological setting of the rapu rapu gold rich volcanogenic massive sulfide deposits albay province philippines gold rich fe cu zn volcanogenic massive sulfide deposits occur within strata of probable jurassic age on rapu rapu island in albay province philippines massive sulfides at the ungay malobago and hixbar deposits are spatially associated with dacitic volcanic rocks within a highly deformed sequence of mafic volcanic and quartzofeldspathic sedimentary rocks the massive sulfide deposits formed at the stratigraphic contact between footwall dacites and hangingwall mafic volcanic and quartzofeldspathic rocks the deposits and their host strata have undergone regional metamorphism with strong penetrative deformation metamorphic mineral assemblages and textural evidence suggest that peak metamorphism was upper greenschist to lower amphibolite grade and syn d1 deformation based on the age of regional metamorphism deformation is inferred to be mid tertiary in age deformation at rapu rapu resulted in reorientation of the strata into a broad antiform with strong shallow plunging elongation fabrics overturning of the volcanic sequence that hosts the ungay malobago deposit and complex folding of the mineralized zones the present highly linear form of the ungay malobago deposit is mainly a product of this ductile strain

erosion rates during rapid deglaciation in icy bay alaska 1 contemporary glacial erosion rates based on sediment yields in southeast alaska merit considerable attention because they are unsurpassed worldwide and they significantly exceed long term exhumation rates in the region two issues are likely to contribute to these high rates contemporary sediment yields in fjords 1 have generally been overestimated by failing to account for the considerable input of subaerially derived material and 2 are exceptionally high because tidewater glaciers in southeast alaska have been anomalously dynamic and erosive during the past century of rapid retreat to investigate these influences and to quantify the rate at which tyndall glacier erodes its basin we present seismic data defining the volume of sediments in taan fjord icy bay we subtract the contribution of subaerially derived sediments from the fjord sediment package to determine the sediment yield directly from tyndall glacier during the most recent period of retreat 1962 1999 using a numerical model of proglacial glacimarine sedimentation we then calculate the annual sediment yield from and the corresponding erosion rate of tyndall glacier during this period which averages 28 5 mma 1 a strong correlation emerges between glacial retreat rates and glacial sediment yields implying that most contemporary sediment yield data from retreating tidewater glaciers may correspond to contemporary erosion rates that are a factor of 3 5 1 5 higher than in the long term hence we estimate the long term erosion rate for tyndall glacier to be 9 2 mma 1

glacial sequence near mccall idaho weathering rinds soil development morphology and other relative age criteria abstract the sequence of glacial deposits near mccall idaho previously assigned to the pinedale and bull lake glaciations contains deposits of four different ages these ages are defined by multiple relative age criteria including weathering rinds soil development surface rock weathering morainal morphology and loess stratigraphy the thickness of weathering rinds on basaltic clasts is statistically representative and reproducible and can be used to estimate numerical ages following in order of decreasing relation to age are soil development surface rock weathering and moraine morphology the glacial deposits near mccall appear to correspond to times of high worldwide ice volume indicated by the marine oxygen isotope record pilgrim cove and mccall deposits both assigned to the pinedale glaciation are late wisconsin in age perhaps 14 000 and 20 000 years respectively they represent a rare case in which deposits of pinedale age can be separated by relative age data timber ridge deposits assigned to the bull lake glaciation have subdued but well preserved morainal morphology relative age data indicate that they are pre wisconsin in age probably about 140 000 150 000 years old although we cannot exclude an older age williams creek deposits are clearly distinct from and intermediate in age between mccall and timber ridge deposits weathering rinds and the inferred ages of the other deposits suggest an early wisconsin age for williams creek deposits

non magmatic fracture controlled hydrothermal systems in the idaho batholith south fork payette geothermal system abstract non magmatic fracture controlled hydrothermal systems located within and near the idaho batholith have been examined and evaluated for potential application as natural analogues to high level nuclear waste repositories detailed geochemical petrologic and structural studies of hot springs along the south fork of the payette river sfpr in central idaho usa have been combined to assess the nature of a hydrothermal aquifer system along a major brittle shear zone geochemical modeling of thermal spring water chemistry with solveq reed m h 1992 solveq users manual unpublished report dept of geological sciences university of oregon eugene or indicates reservoir temperatures of 85 c to 160 c and an alteration assemblage consisting of several clays chlorite serpentinites quartz albite microcline and micas geothermometry calculations coupled with independent estimates of geothermal gradients based on heat flow and regional geology allow estimation of reservoir depths ranging from 2 4 to 6 7 km comparison of trace element rare earth element and solveq alteration assemblages supports the hypothesis that waters equilibrated with granitic rocks at depth and ascended to the surface in a short time span stable isotope data d 138 4 to 148 4 and 18 o 17 5 to 19 4 indicate that thermal waters of meteoric origin have interacted with country rocks at a very high water rock w r ratio systematic variations in d values and the amount of 18 o shift for thermal waters suggest that recharge probably occurs at much higher elevations than discharge fracture orientations petrologic relations and geochemical differences between adjacent springs delineate separate hydrothermal systems along the major structure defining the course of the sfpr hydrothermal systems along the sfpr exist primarily as small circulation cells which are probably influenced by minor changes in geothermal gradients associated with different rock types these subsystems are dependent on periodic seismic or microseismic activity to maintain flowpaths a working model of deep fracture controlled hydrothermal convection systems based on the sfpr geothermal system may be used to evaluate the long term behavior of artificial hydrothermal systems associated with high level nuclear waste repositories

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

hillslope asymmetry maps reveal widespread multi scale organization 1 hillslope asymmetry is the condition in which oppositely facing hillslopes within an area have differing average slope angles and indicates aspect related variability in hillslope evolution as such the presence orientation and magnitude of asymmetry may be a useful diagnostic for understanding process dominance we present a new method for quantifying and mapping the spatial distribution of hillslope asymmetry across large areas resulting maps for the american cordillera of the western hemisphere and the western united states reveal that hillslope asymmetry is widespread with distinct trends at continental to drainage scales spatial patterns of asymmetry correlate with latitude along the american cordillera mountain range orientation for many ranges in the western united states and elevation in the idaho batholith of the northern rocky mountains spatial organization suggests that non stochastic process driven controls cause these patterns the hillslope asymmetry metric objectively captures previously documented extents and frequencies of valley asymmetry for the gabilan mesa of the central california coast range broad scale maps of hillslope asymmetry are of interest to a wide range of disciplines as spatial patterns may reflect the influence of tectonics atmospheric circulation topoclimate geomorphology hydrology soils and ecology on landscape evolution these maps identify trends and regions of hillslope asymmetry allow possible drivers to be spatially constrained and facilitate the extrapolation of site specific results to broader regions

morphometric evidence of 3 6 ga glacial valleys and glacial cirques in martian highlands south of terra sabaea abstract the climate of early mars remains unclear and the debate is topical recently climatic models have suggested a cold climate during the noachian early hesperian on mars which goes against the wet and warm climate often put forward the purpose of this study is to seek geomorphologic evidence of this early cold climate to achieve this a step by step study of the geometry and morphology of several martian valleys has been done in the southern highlands the analysis highlights the morphometric properties which enable the identification of martian glacial landscapes we identified 100 cirques and 83 glacial valleys in two craters and on one mountain in the southern part of terra sabaea the studied morphologies have the same morphometric characteristics and trends as terrestrial and martian glacial valleys and glacial cirques in contrary these trends are very different from those observed in fluvial valleys on earth and on mars 1 the martian glacial valleys are u shaped with a large flat floor and a v index 0 20 while martian and terrestrial fluvial valleys are v shaped with a v index 1 while for fluvial valleys this ratio is 1 3 finally the cross sectional area and the elevation are higher for the glacial valleys compared to the fluvial ones these glacial valleys often originate with a topographic hollow which have the same properties than terrestrial glacial cirque the glacial landscapes identified in southern terra sabaea are restricted to elevations 1000 m and are dated by crater counting to be 3 6 ga this study strongly supports glacial processes as the origin of these valleys and cirques and is the first morphometric evidence of glacial valleys associated with glacial cirques in the southern highlands in agreement with the climatic models we propose that the martian climate during the late noachian early hesperian was characterized by glaciated highlands at elevations 1500 m and at lower elevations where fluvial valley network has been identified

potential effects of subglacial water pressure fluctuations on quarrying water pressure fluctuations beneath glaciers may accelerate rock fracture by redistributing stresses on subglacial bedrock and changing the pressure of water in bedrock cracks to study the potential influence of water pressure fluctuations on the fracture of subglacial bedrock ice flow over a small bedrock step with a water filled cavity in its lee is numerically modeled and stresses on the bedrock surface are calculated as a function of transient water pressures in the cavity stresses on the bed are then used to calculate principal stress differences within the step rapid reductions in cavity water pressure increase principal stress differences in the bed increasing the likelihood of crack growth in the step and the formation of predominantly vertical fractures relatively impermeable bedrock may be most susceptible to fracturing during water pressure reductions because high water pressure in cracks within the rock can be maintained as water pressure decreases in cavities these results when considered in conjunction with the strong likelihood that increases in water pressure accelerate the removal of rock fragments loosened from the bed suggest that in zones of ice bed separation where water pressure fluctuations typically are large rates of quarrying may be higher than along other parts of glacier beds

geochemistry and origin of archean felsic metavolcanic rocks central noranda area quebec canada felsic magma petrogenesis was studied by analyzing 24 stratigraphically controlled archean andesite to rhyolite lava flows of both tholeiitic and calc alkalic affinity from the upper noranda subgroup quebec using instrumental neutron activation and x ray fluorescence techniques the lavas have moderate values of la yb n 0 9 3 8 and low values of 100 th zr 1 according to calculations following batch partial melting and rayleigh fractional crystallization models both the calc alkalic and tholeiitic felsic volcanic rocks are probably products of shallow level fractional crystallization of mafic parental magmas formed respectively by lower 7 for calc alkalic and higher 14 for tholeiitic degrees of partial melting of a primitive mantle source contribution to the magma genesis from plausible crustal materials was negligible a back arc type diapirism is geochemically suggested for the tectonic model of origin of noranda felsic magmas in conformity with geological observations felsic volca

morphological and chemical characteristics of soil catenas on pinedale and bull lake moraine slopes in the salmon river mountains idaho abstract morphological and chemical properties of soils developed on moraines of granitic composition and forested with lodgepole pine in bear valley idaho change significantly with age and slope position soil development on pinedale and bull lake moraine slopes of similar curvature and steepness was assessed at the summits shoulders backslopes and footslopes of both catenas and at the toeslope of the bull lake catena many soil properties show trends in development with both age and slope position these properties include clay content clay film development color plagioclase weathering and dithionite citrate extractable iron fed the degree of development of all these properties is greater on the bull lake catena relative to that on the pinedale catena this trend reflects increased soil development with age on both catenas development of soil properties is commonly highest at the footslope or toeslope sites and minimum at the backslope site downslope changes are attributed to both colluviation and pedogenic processes including sorting of sediments during downslope transport greater accumulation of eolian materials transported to downslope sites by surface processes and greater in situ weathering of mineral grains at the footslope and toeslope sites

contribution of deep seated bedrock landslides to erosion of a glaciated basin in southern alaska landslides represent a key component of catchment scale denudation though their relative contribution to the erosion of glaciated basins is not well known bedrock landslide contribution was investigated on the surface of one of eleven glaciers on a glaciated ridge in the chugach st elias range of southern alaska where the debris from four major landslides is easily distinguished from moraines and other supraglacial material a series of aerial and satellite photos from 1972 to 2000 and field observations in 2001 and 2002 indicate that three of four landslides have fallen onto the surface of the glacier since about 1978 the landslides which originated from the steeply dipping 60 70 bedrock walls were deposited onto the glacier in the ablation zone and are currently being transported downstream supraglacially individual glacial valleys with topographic relief of 400 m are cut into highgrade metamorphic rock characterized by a steep north dipping foliation and fractured by numerous large joints measurements of landslide area and average thickness obtained from high resolution survey data indicate a total landslide volume of 2 3 10 5 m 3 this volume suggests a basin averaged erosion rate from landslides of 0 48 mm a 1 an overall basin scale erosion rate of 0 7 to 1 7 mm a 1 can be inferred but depends on the percentage of the totalbasin sediment yield contributed by supraglacial sources a mean rockwall retreat rate of 6 7 mm a 1 is calculated and is considerably higher than published rates which range from 0 04 to 4 0 mm a 1 controls on landslide generation include seismicity freeze thaw processes topography rock strength and debuttressing it is likely all of these factors contribute to failure although the primary controls for the landslides in this study are thought to be rock strength and topography the absence of landslides on ten of the eleven glaciers on this ridge is attributed to landslide magnitude frequency relationships and short temporal scale of this study large volume bedrock landslides 100 000 m 3 may have low frequency occurring less than once in a 55 year time frame copyright 2005 john wiley sons ltd

surface reconstruction and derivation of erosion rates over several glaciations 1 ma in an alpine setting sinks canyon wyoming usa at middle to high latitudes many alpine valleys have been shaped by glaciers associated with periods of pleistocene glaciation present glaciated valleys are characterised by broadened valley floors and u shaped cross sections continuously formed by glacial activity from initially v shaped fluvial cross sections sinks canyon wind river range usa is a glaciated valley characterised by a typical u shaped cross section containing till from several glacial advances over a range of at least 1 ma the morphostratigraphic records indicate a fourfold difference in ice surface elevation between the youngest and oldest glacial periods which is not easily explained by the present day valley topography to assess possible evolution scenarios of sinks canyon we modelled the palaeovalley topography using a geographic information system gis filtering technique in combination with temporal reference points from relative and numerically dated glacial deposits ice thicknesses were calculated using the shallow ice approximation in our model the valley became shallower and the topography smoother with increasing years back in time the results suggest that valley topography with ages between 640 and 1000 ka can clearly be distinguished from the present day topography surfaces with ages of 130 200 ka attributable to mis 6 bull lake glaciation still could be discerned from present day topography but with relatively high uncertainties the method did not work for topography less than 100 ka or older than 1 ma erosion depths were calculated using the differences between present day elevation and the modelled surfaces calculated erosion rates were within the range of reference values for glacial erosion 0 001 to 1 mm a 1 glacial erosion appears to have removed 0 52 to 0 72 mm a 1 of rock within a time frame of 1 ma assuming 200 ka of aggregated glacial flow if the glacial occupation was longer or the impact of fluvial erosion was not negligible as assumed then the calculated rate is lower if the model assumes a less extended time of glacial flow 100 ka the rate exceeds 1 mm a 1 the method used for surface reconstruction and erosion rates calculation is highly dependent on i the reliability of the temporal anchor points and ii the assumption of physical glacier conditions basal shear stress

pleistocene relief production in laramide mountain ranges western united states gently sloped summits and ridges collectively referred to as summit flats are abundant in many laramide ranges in the western united states the erosion rate of summit flats is 10 m m y on the basis of the concentrations of cosmogenic radionuclides because erosion rates in valleys between summit flats are an order of magnitude faster relief within these ranges is currently increasing by about 100 m m y if summit flat erosion is slower than rock uplift driven by the isostatic response to valley erosion then this relief production could result in increased summit elevations the mean depth of material eroded from a smooth surface fit to existing summit flats varies from 280 to 340 m in four laramide ranges based on geographic information system gis analyses of digital elevation models this erosion would result in a maximum of 250 300 m of rock uplift assuming airy isostasy however because the laramide ranges examined here are narrow relative to the flexural wavelength of the lithosphere erosionally driven rock uplift is limited to 50 100 m over the past several million years summit erosion would approximately offset this rock uplift therefore we conclude that summit elevations have remained essentially constant even though several hundred meters of relief has been produced on the basis of valley and summit erosion rates and the average depth of erosion we estimate that relief production in laramide ranges began at ca 3 ma we hypothesize that this relief production was climatically driven and was associated with the onset or enhancement of alpine glaciation in these ranges

three dimensional visualization of the archean horne and quemont au bearing volcanogenic massive sulfide hydrothermal systems blake river group quebec the hydrothermal system architecture related to the formation of the contemporaneous au bearing horne and quemont volcanogenic massive sulfide vms deposits was visualized by employing kriging methods to map whole rock oxygen isotope compositions zones of silica addition and loss and water contents in two and three dimension zones of alteration were mapped in three dimensions in the vicinity of the steeply dipping horne deposit to depths of as much as 2 km in all nearly 300 samples were analyzed for oxygen isotopes and supplemented by previously published whole rock analyses contents of sio2 h2o mgo al2o3 and s from chemical analyses of nearly 5 000 samples within the two and three dimensional study regions were used separately and in combination with the oxygen isotope data for modeling and hydrothermal mapping purposes the horne and quemont deposits formed within a similar time frame but in different magmatic hydrothermal systems distinguished by their mapped hydrothermal architecture the quemont deposit appears to be centered on the powell pluton which intruded late into an apparent volcanic filled rift graben structure although structural complexities are apparent we infer mineralizing high temperature upflow in the footwall of the quemont deposit to have emanated from a reaction zone above the powell pluton and its precursors beneath a zone of extensive silicification faulting on the andesite fault and horne creek faults plus erosion has removed evidence of the upflow zone in the hydrothermal system of the horne deposit areas of silicification correspond in general with isotopic evidence of lower temperature alteration such alteration east of the quemont deposit signaled the waning of hydrothermal activity the suggested cooling for the most part promoted the precipitation of silica in the case of the horne deposit mixing of metalliferous hydrothermal fluid with cold seawater in the permeable footwall rocks in an apparently relatively stratigraphically stable and long lived hydrothermal system evidently led to marked footwall silicification the silicified footwall may have contributed to an increased efficiency of sulfide precipitation in the horne deposit continued intrusion and some post vms hydrothermal activity is recorded in the hanging wall section to the horne deposit our data suggest that deposition of the 10 million ounces moz of au within the horne deposit was syngenetic and not the product of subsequent hydrothermal activity

synvolcanic and younger plutonic rocks from the blake river group implications for regional metallogenesis the blake river group of the abitibi greenstone belt is host to the well known volcanogenic massive sulfide vms deposits of the noranda camp quebec canada in the noranda camp massive sulfide deposits are spatially associated with the coeval flavrian powell intrusive complex which is interpreted to have driven hydrothermal circulation that formed the deposits in the camp in the western blake river group in ontario there are also abundant intrusive rocks yet relatively insignificant accumulations of vms deposits these intrusive rocks are younger 2686 9 1 2 and 2688 5 2 3 ma and are associated with porphyry style cu mo au mineralization with re os molybdenite ages of 2682 4 5 ma the intrusions are also smaller in areal extent and do not have a temporally extended polyphase history like the flavrian powell intrusive complex the intrusions of the western blake river group can also be distinguished by lithogeochemical attributes and a distinct petrological history compared to the flavrian powell intrusive complex they have lower total y yb th hfse and ree with higher zr y la yb sm yb al2o3 yb and la smucn ratios and lower zr nb zr th zr la zr tio2 and nb thucn ratios petrologic modeling is consistent with the western blake river group intrusive rocks being generated as relatively low temperature melts 40 km in the crust where garnet is stable in the residue e g garnet amphibolite residue in contrast modeling of the flavrian powell intrusive complex is consistent with melting at shallower levels in the crust e g 800o to 850oc the occurrence of high temperature magmatism at high levels within this crust that is coeval with volcanic activity explains the occurrence of numerous vms deposits with the flavrian powell intrusive complex as this intrusive complex would have generated abundant heat at high levels in the crust to drive hydrothermal circulation in contrast the intrusions of the western blake river group were generated at depth and at lower temperature increasing the probability of heat loss upon emplacement from depth hence decreasing the probability of hydrothermal circulation at high levels in the crust and likely explaining the paucity of vms mineralization associated with these intrusive rocks the petrological attributes of the flavrian powell intrusive complex and western blake river group may be useful in delineating potentially fertile versus less prospective intrusive complexes in greenfields exploration areas notably the western blake river group intrusions have geochemical features similar to some phanerozoic porphyry cu mo au associated intrusive systems consistent with the observed mineralization and highlighting the potential of porphyry cu mo au systems of late archean age elsewhere in the abitibi

processes rates and time scales of fluvial response in an ancient postglacial landscape of the northwest indian himalaya both glacial and fluvial processes are key elements in molding landscapes in high mountain environments glaciers are highly efficient erosional agents and producers of sediment but are restricted spatially while rivers can transmit such signals through landscapes and flush this sediment out of mountain belts and into sedimentary basins however little research has focused on the manner in which these two agents of landscape change interact especially on longer time scales we analyze a suite of catchments that drain the previously glaciated ladakh batholith in the northwest indian himalaya which preserve the oldest known moraine succession in this mountain chain we describe and quantify the rates processes and time scales of postglacial recovery of the fluvial system across a previously unstudied time interval of 105 106 yr we demonstrate that glacial modification of the upper reaches of a catchment can have profound first order influence on the hydraulic scaling of the channel downstream where increasing degree of glacial modification systematically and nonlinearly elevates the channel concavities of downstream reaches above the expected value range of 0 3 0 6 we also demonstrate that the response time of these systems as they recover must exceed 500 k y which is longer than any previously reported estimate for recovery times from glaciations but is comparable with estimates from many tectonically perturbed landscapes

the gamburtsev mountains and the origin and early evolution of the antarctic ice sheet the manner in which the antarctic ice sheet first formed at a time of rapid global climate change about 34 million years ago has been the subject of considerable speculation several lines of evidence point to central antarctic mountain ranges as the site of the initial ice sheet but our knowledge of the present ice sheet topography is highly restricted in the very zone where ice sheet initiation is most likely along the subglacial gamburtsev mountain range at the centre of the present ice sheet now a detailed survey and analysis of the morphology of the gamburtsev mountains has been performed based on an ice penetrating radar study conducted over two seasons the data reveal a mountain landscape initially incised by rivers then over deepened by ice movement the topography beneath up to 3 000 metres of ice resembles an exploded version of classic alpine valley topography and seems to have developed more than 34 million years ago when mean summer temperatures were about 3 c the nature of initial glaciation on antarctica about 34 million years ago is a mystery results from an intensive radar survey now show that the gamburtsev mountains at dome a at the centre of the present ice sheet were initially incised by rivers and then subsequently overdeepened by ice movement this is suggestive of topographical development before 34 million years ago when mean summer temperatures were about 3 c ice sheet development in antarctica was a result of significant and rapid global climate change about 34 million years ago1 ice sheet and climate modelling suggest reductions in atmospheric carbon dioxide less than three times the pre industrial level of 280 parts per million by volume that in conjunction with the development of the antarctic circumpolar current led to cooling and glaciation paced by changes in earth s orbit2 based on the present subglacial topography numerical models point to ice sheet genesis on mountain massifs of antarctica including the gamburtsev mountains at dome a the centre of the present ice sheet2 3 our lack of knowledge of the present day topography of the gamburtsev mountains4 means however that the nature of early glaciation and subsequent development of a continental sized ice sheet are uncertain here we present radar information about the base of the ice at dome a revealing classic alpine topography with pre existing river valleys overdeepened by valley glaciers formed when the mean summer surface temperature was around 3 c this landscape is likely to have developed during the initial phases of antarctic glaciation according to antarctic climate history estimated from offshore sediment records the gamburtsev mountains are probably older than 34 million years and were the main centre for ice sheet growth moreover the landscape has most probably been preserved beneath the present ice sheet for around 14 million years

geochemistry of the alteration pipe at the amulet upper a deposit noranda quebec the amulet upper a orebody is a stratiform pyritiferous copper zinc deposit situated within a sequence of andesitic pillow lavas underlying the massive sulphides is a cylindrical alteration pipe c

geochemistry of hydrothermally altered rocks at the horne mine noranda quebec low k rhyolites of the archean blake river group that host the horne volcanogenic massive sulfide deposit are altered to quartz sericite chlorite albite quartz sericite zone and chlorite or quartz chlorite zone assemblages the quartz sericite zone accounts for approximately 90 percent of the 5 km 3 of the altered hanging wall and footwall rocks chlorite zone alteration is limited to portions of the footwall and flanks of the cu rich h orebodies clusters of gold bearing chlorite quartz veinlets crosscut large volumes of the quartz sericite zone rocks alteration has added an average of 13 wt percent sio 2 2 3 wt percent k 2 o 430 ppm ba and 46 ppm rb to the system and leached 3 6 wt percent na 2 o 2 2 wt percent cao and 41 ppm sr middle and light ree were increasingly mobile from yb to la they were leached from the chlorite zone rocks and added to quartz sericite zone rocks chlorite was more fe rich fe fe mg 0 65 0 85 in the chlorite zone rocks than in other altered lithologies fe fe mg 0 2 0 5 sulfur isotope values for massive ores are in the range delta 34 s 2 1 to 1 9 per mil mineral separates from altered rocks yielded delta 18 o values of 10 2 to 12 1 per mil for quartz 7 2 to 9 5 per mil for calcite 2 2 to 3 0 per mil for chlorite and 0 1 to 1 0 per mil for magnetite oxygen and sulfur isotope fractionation between coexisting minerals suggests formation from fluids having delta 18 o 3 to 4 per mil at temperatures between 275 degrees to 380 degrees c oxygen isotope compositions of host rocks are delta 18 o 8 or 1 per mil for freshest rhyolite delta 18 o 6 6 to 11 6 per mil for quartz sericite zone rocks and delta 18 o 3 9 to 4 4 per mil for chlorite zone rocks these measured values compare closely to estimated whole rock delta 18 o values based on mass balance considerations using normative mineralogies alteration of wall rocks encompassing the massive sulfide orebodies is characterized by intense sericitization a high degree of silicification and a marked positive delta 18 o anomaly calculations based on sio 2 solubilities and probable k contents of the hydrothermal fluids suggest a water rock mass ratio of 50 to 300 during the mineralization event