valley scale morphology drives differences in fluvial sediment budgets and incision rates during contrasting flow regimes abstract high resolution topographic surveys using lidar and multibeam sonar can be used to characterize and quantify fluvial change this study used repeat surveys to explore how topographic change fluvial processes sediment budgets and aggradation and incision rates vary across spatial scales and across two contrasting decadal flow regimes in a regulated gravel cobble river a novel method for quantifying digital elevation model uncertainty was developed and applied to a topographic change detection analysis from 2006 2008 to 2014 during this period which had four modest 3 5 year floods most sediment was laterally redistributed through bank erosion and channel migration erosion primarily occurred in the floodplain 97 000 m 3 terraces 80 000 m 3 and lateral bars 58 000 m 3 while deposition occurred in the adjacent pools 73 000 m 3 fast glides 48 000 m 3 and runs 36 000 m 3 in contrast significantly higher magnitude and longer duration floods from 1999 to 2006 2008 caused sediment to be displaced longitudinally with the upstream reaches exporting sediment and the downstream reaches aggrading the river maintained floodplain connectivity during both periods despite different processes dominating the type of connectivity larger floods promoted overbank scour and avulsion while smaller floods promoted bank erosion and lateral migration this study explores and illustrates how the geomorphic response to contrasting flood regimes in a nonuniform river is highly dependent on which landforms are controlling hydraulics

high resolution reflection seismic imaging of the upper crust at laxemar southeastern sweden abstract a major cost in exploring the upper 1 2 km of crystalline crust with reflection seismics is the drilling required for explosive sources by reducing the charge size to a minimum shallow inexpensive shotholes can be drilled with handheld equipment here we present results from a full scale test using small charges for high resolution seismic surveying over a nuclear waste disposal study site not an actual site two 2 2 5 km long crossing profiles were acquired in december 1999 with 10 m shot and geophone spacing in the laxemar area near oskarshamn in southeastern sweden after standard processing including dip moveout dmo several subhorizontal to moderately dipping reflections are imaged many of the dipping ones can be correlated to fracture zones observed in a ca 1700 m deep borehole where the profiles cross and or to fracture zones mapped on the surface the imaged fracture zones form a complex 3d pattern illustrating the necessity of having 3d control before interpreting seismic reflection data analyses of sonic and density logs from the borehole show that greenstones have significantly higher impedances than the more dominant granite found in the borehole granite greenstone reflection coefficient is 0 065 these greenstones may contribute to the reflectivity when associated with fracture zones in some cases where they are present as larger subhorizontal lenses they may be the dominant source of reflectivity a set of north dipping 10 reflectors at 3 3 5 km depth can be correlated to a similar set observed below the island of avro about 3 km to the east

the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

preeruption conditions and timing of dacite andesite magma mixing in the 2 2 ka eruption at mount rainier analytical field and experimental evidence demonstrate that the mount rainier tephra layer c 2 2 ka preserves a magma mixing event between an andesitic magma whole rock sio 2 content of 57 60 wt and a dacitic magma whole rock sio 2 content of 65 1 wt the end member andesite a mix of an injected and chamber andesite and dacite can be characterized on the basis of the homogeneity of the matrix glass and phenocryst rim compositions many pumices however contain mixtures of the end members the end member dacite contains a microlite free matrix glass with 74 77 wt sio 2 orthopyroxene rims of mg 57 64 clinopyroxene rims of mg 66 74 and plagioclase rim anorthite contents of an 45 65 the temperature and oxygen fugacity from fe ti oxide compositions are 930 10 c and 0 5 0 75 log units above nno the mixed andesite contains mg 73 84 orthopyroxene rims mg 73 78 clinopyroxene rims an 78 84 plagioclase rims and mg 67 74 amphibole rims the temperature from fe ti oxides hornblendeplagioclase and two pyroxene geothermometry is 1060 15 c and the oxygen fugacity is approximately one log unit above nno for the injected andesite the chamber andesite is estimated to be a magma with a 64 65 wt sio 2 melt at 980 c and a nno oxygen fugacity we conclude that the andesitic and dacitic magmas are from separate magma storage regions at 7 km and 2 4 km due to differences in the bimodal whole rock matrix glass and phenocryst compositions and the presence or absence of stable hornblende the time involved from the mixing event through the eruption is limited to a period of 4 5 days based on fe ti oxide reequilibration phenocryst growth rates and hornblende breakdown the eruption sequence is interpreted as having been initiated by an injection of the 1060 15 c andesitic magma into the 980 c 7 km andesite storage region the mixed andesitic magma then intersected a shallow 2 4 km dacitic storage system on its way toward the surface the eruption became more dacitic over time and the final products some show evidence of partial reequilibration between the andesite and dacite

landstreamer seismics and physical property measurements in the siilinjarvi open pit apatite phosphate mine central finland abstractwe tested the applicability of a newly developed broadband 0 800 hz digital based seismic landstreamer for open pit mine planning in the apatite bearing siilinjarvi mine in central finland four seismic profiles in total approximately 2 5 km long 2 4 m source and landstreamer receiver spacing two inside the pit and two on its margins were acquired in combination with wireless recorders connected to 10 hz geophones and fixed at every 10 m spacing along the seismic profiles while the streamer data were being acquired downhole logging and laboratory physical property measurements on core and rock samples were carried out to not only support the seismic interpretations but also to provide information about the possible geophysical signature of these unique types of deposits in spite of a highly noisy mining environment seismic data of high quality were acquired however reflection processing and interpretations were challenged by the geologic complexities of several generations of basic and

imaging and interpreting the shallow crystalline crust abstract in the past many tests of high resolution seismic imaging methods utilizing off the shelf technology from hydrocarbon exploration have had only limited success some problems associated with the application of seismic profiling in the shallow crystalline crust differ from those encountered in sedimentary basins perhaps the most fundamental distinction stems from differences in statistical properties of the reflection coefficient time series analysis of power spectra derived from borehole data indicates that the reflection coefficients in the crystalline crust are depleted in the seismic bandwidth relative to sedimentary basins this fundamental difference must be considered in the design of shallow crustal seismic surveys in order to achieve success to a first approximation acoustic impedance variations in sedimentary basins are controlled by velocity changes whereas velocity and density can vary independently in the crystalline crust and changes in density may be relatively more important in controlling reflectivity in certain instances density fluctuations outweigh velocity fluctuations for example physical rock property data from mining districts in the canadian shield suggest that massive fe oxide or sulphide bodies will generate strong seismic reflections

determining the three dimensional geometry of a dike swarm and its impact on later rift geometry using seismic reflection data dike swarm emplacement accommodates extension during rifting and large igneous province lip formation with ancient dike swarms serving to localize strain during later tectonic events deciphering three dimensional 3 d dike swarm geometry is critical to accurately calculating magma volumes and magma assisted crustal extension allowing syn emplacement mantle and tectonic processes to be interrogated it is also important for quantifying the influence of ancient dike swarms on post emplacement faulting however the essentially 2 d nature of earth s surface combined with the difficulties in imaging subvertical dikes in seismic reflection data and the relatively low resolution of geophysical data in areas of active diking means our understanding of dike swarm geometry at depth is limited we examine an 25 km wide 100 km long west southwest trending dike swarm imaged due to post emplacement rotation to shallower dips in high quality 2 d and 3 d seismic reflection data offshore southern norway tuned reflection packages correspond to thin 75 m thick closely spaced dikes these data provide a unique opportunity to image and map an ancient dike swarm at variable structural levels crosscutting relationships indicate emplacement occurred in the late carboniferous early permian and was linked to the formation of the ca 300 ma skagerrak centered lip dike swarm width increases with depth suggesting that magma volume and crustal extension calculations based on surface exposures are dependent on the level of erosion during the mesozoic rift related faults localized above and exploited mechanical anisotropies within the dike swarm we demonstrate that seismic reflection data are a powerful tool in understanding dike swarm geometry and the control of dikes on subsequent faulting

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

flood driven topographic changes in a gravel cobble river over segment reach and morphological unit scales regulated rivers generally incise below dams that cut off sediment supply but how that happens and what the consequences are at different spatial scales is poorly understood modern topographic mapping at meter scale resolution now enables investigation of the details of spatial processes in this study spatial segregation was applied to a meter scale raster map of topographic change from 1999 to 2008 on the gravel cobble regulated lower yuba river in california to answer specific scientific questions about how a decadal hydrograph that included a flood peak of 22 times bankfull discharge affected the river at segment reach and morphological unit scales the results show that the river preferentially eroded sediment from floodplains compared to the channel and this not only promoted valley wide sediment evacuation but also facilitated the renewal and differentiation of morphological units especially in the channel at the reach scale area of fill and mean net rate of elevational change were directly correlated with better connectivity between the channel and floodplain while the mean rate of scour in scour areas was influenced by the ratio of slope to bankfull froude number a ratio indicative of lateral migration versus vertical downcutting hierarchical segregation of topographic change rasters proved useful for understanding multiscalar geomorphic dynamics this article is protected by copyright all rights reserved

compositional and dynamic controls on mafic silicic magma interactions at continental arc volcanoes evidence from cordon el guadal tatara san pedro complex chile

a review of high resolution seismic profiling across the sudbury selbaie noranda and matagami mining camps lithoprobe high resolution seismic surveys have provided the first systematic images of the deep stratigraphy in four major canadian mining camps noranda matagami sudbury and selbaie systematic compressional wave velocity and density measurements in deep boreholes have established that lithological contacts were the main impedance contrast imaged although reflections from faults and deformation zones have also been observed the strongest reflections are attributed to mafic intrusions and some sulphides and oxides integrating seismic physical rock property measurements and geological data has resulted in the revision of several geological models with direct impact on local strategies for deep mineral exploration mining companies have shown an interest in seismic reflection methods and this has led to several follow up studies the application of seismic methods to the direct detection of massive sulphides based on physical rock property measurements has been studied through two dimensional an

asymmetric growth of collapsed caldera by oblique subsidence during the 2000 eruption of miyakejima japan abstract oblique development of the ring faults reflecting the structural heterogeneities inside the volcano formed many asymmetric structures of miyakejima 2000 ad caldera the asymmetry includes a offset location of the ring faults with respect to the associated shallow magma chamber b unequal outward migration of the caldera wall 600 m at the southeastern rim but only 200 m at the northwestern rim c development of tilted terrace only at the southeastern caldera margin d eruption sites and fumaroles being confined to the southern part of the caldera geophysical data including ground deformation and seismic activity indicates the offset of the location of the magma chamber about 2 km south of the caldera center on the surface the ring faults propagated from the deflating magma chamber obliquely about 30 degrees toward the summit the oblique subsidence of the cylindrical block formed a wider instable zone particularly in the southeastern side of the ring fault that enhanced the larger outward migration of the caldera rim and also caused the formation of the outer half ring fault bordering the tilting slope at the southern part ascending pass of the buoyant magma along the tilted ring faults was concentrated in the southern half of the caldera and consequently the distributions of the eruption sites and fumaroles are localized in the southern half part of the caldera the structure of the miyakejima 2000 caldera with complete development of the ring faults its high roof aspect ratio and oblique subsidence is clearly distinguishable from trapdoor type caldera the oblique development of the ring faults can be controlled by the mechanical contrast between the solidified conduits and surrounding fragile volcanic edifice asymmetric development of the miyakejima caldera shows that the collapsed calderas are potential indicators of the heterogeneous structures inside of the volcano particularly in the case of small size caldera

eruptive history of the late quaternary ciomadul csomad volcano east carpathians part i timing of lava dome activity located at the southern tip of the intra carpathian volcanic range in romania and composed of a dozen dacitic lava domes the ciomadul csomad volcanic complex is the youngest eruptive centre of the carpatho pannonian region whereas in the last decade the explosive history of ciomadul since 50 ka has been well constrained by numerous studies the chronology of the dome sequence still lacks robust chronological constraints and an extended analysis of all available data here we apply a detailed k ar dating approach to refine the chronology of the lava dome eruptions using the unspiked k ar cassignol gillot technique our dating focused on the most voluminous central part of the lava dome complex new eruption ages were determined following a strict separation of 10 g of groundmass from about 3 kg of unaltered sample rocks thereby isolating material whose cooling was contemporaneous with the eruption the newly applied methodology mainly consisting of a double full preparation first at larger grain size 0 4 mm and then at 100 m provides an appropriate procedure to separate suitable material to obtain the k ar age of the eruption i e the sample s groundmass in which there is no risk of the presence of older inherited crystals our new geochronological data set gives an improved insight into the temporal construction of the ciomadul volcanic complex where due to the method applied here all ages are younger than those from previous studies that used whole rock k ar ages our new results show that ciomadul s volcanic activity began with the construction of the south eastern peripheral domes from ca 850 ka to 440 ka after a ca 250 ky long repose period the activity resumed in the northern part at around 200 ka with subsequent domes emplaced between 200 and 130 ka aligned roughly north south in the western central part of the complex following a 30 ky long quiescence period the eastern central domes formed between 100 and 60 ka in addition to the chronological history of lava dome volcanism we also investigated the sequence of crystallization of mineral phases present in the lavas with respect to the modification of eruption ages ages obtained on pure minerals plagioclase amphibole and biotite are systematically older than those obtained on groundmass showing that most of them formed up to 1 85 myr before eruption in a long lived pre ciomadul magmatic system crystal size distribution csd data support the age contrasts between juvenile groundmass and older inherited minerals after injection of new magma and convective mixing with crystal clots ascent of the resulting mixture led to eruptions of material representing contrasting ages

seismic reflections from subvertical diabase dikes in an archean terrane a 20 km seismic reflection profile in the superior province of northwestern ontario imaged polydeformed archean terrane including the manitouwadge greenstone belt and the adjacent wawa quetico subprovince boundary in addition to reflectivity from archean lithostructural elements we recognize discrete reflections that correlate with undeformed subvertical proterozoic dikes moderately to steeply inclined linear events in the stacked section are related to matachewan dikes that intersect the seismic profile at 50 75 the reflections project to the surface at points corresponding to dike profile intersections and have apparent dips in the seismic section consistent with the intersection angles in map view subhorizontal linear to curvilinear reflections originate from marathon dikes that are subparallel to the seismic line on the basis of forward modeling studies the events occur at two way traveltimes for horizontally propagating waves we conclude that a number of dipping and subhorizontal events represent refracted waves propagated along horizontal ray paths near the surface and reflected from subvertical dikes in many other seismic profiles in crystalline crust reflections originating from subvertical dikes have likely been overlooked or misinterpreted either because the presence of dikes was not recognized or because their seismic response was not evaluated

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

high resolution seismic reflection imaging of a thin diamondiferous kimberlite dyke seismic reflection techniques are for the first time used to image a thin diamondiferous kimberlite dyke from subcrop to depths greater than 1300 m geophysical exploration for kimberlite deposits typically involves airborne potential field surveys that are well suited for detecting vertical outcropping pipes but often fail to reveal thin subhorizontal dykes and sills because seismic techniques are especially well suited for mapping structures that have shallow dips and strong impedance contrasts a feasibility study and seismic reflection survey were undertaken on the diamondiferous snap lake dyke northwest territories canada to evaluate the potential for using seismic techniques on these targets the dyke average thickness 2 3 m provides an excellent test site because a drilling program has defined the gross dyke geometry and provides core samples from the kimberlite and host rocks the feasibility study involved measuring p velocity and density of selected cores using these data reflectivit

geometric difference between non feeder and feeder dikes feeder dikes bring magma to the surface non feeder dikes become arrested and never reach the surface the differences if any between these dike types remain largely unexplored because in the field it is normally unknown if a particular dike is a feeder or non feeder here we present measurements of feeder and non feeder dikes exposed from depths of 200 m to the surface in the walls of the a d 2000 caldera collapse of the miyakejima volcano japan a typical feeder thickness reaches a maximum of 2 4 m at the surface decreases rapidly to 1 m at a depth of 20 40 m and then remains constant to the bottom of the exposure by contrast a typical non feeder thickness reaches a maximum of 1 5 2 m at 15 45 m below the tip and then decreases slowly with depth to 0 5 1 m at the bottom of the exposure we propose that free surface effects and magmatic overpressure driving pressure changes during the eruption cause the overall shape of a feeder to differ from that of a non feeder

seismic imaging of the geologic framework and structures related to volcanogenic massive sulfide deposits in the archean rouyn noranda district quebec canada two seismic reflection profiles acquired by xstrata canada in the noranda mining camp were reprocessed and interpreted with the objective of providing key information on the geologic contacts and structures associated with volcanogenic massive sulfide vms deposits at depth the amulet and ribago seismic profiles run approximately from east to west and cross the volcanic rocks of the noranda formation which host most of the ore deposits in this camp the seismic data interpretation relies strongly on a detailed three dimensional geologic model built from an extensive number of exploration boreholes available in this area and is further supported by physical rock property measurements from in situ borehole logging data some reflections observed on the amulet and ribago seismic profiles correlate with rhyolite andesite or silicified andesite andesite contacts that host the prospective exhalites of the noranda formation in particular the silicified andesite andesite contact hosting the c contact exhalite is imaged clearly down to a vertical depth of 1 100 m along the ribago profile the processing sequence included dip moveout dmo corrections and poststack migration the seismic data reprocessing allowed the identification of two diffractions that correlate with known sulfide bodies intersected in boreholes located close to the ribago profile one of these diffractions at approximately 1 200 m depth coincides with the main massive sulfide intersection of the subeconomical ribago orebody diorites cause several reflections observed within the flavrian pluton some diorite units also have sufficient acoustic impedance contrast to produce strong reflections when juxtaposed against volcanic rocks however such reflections do not predominate in the amulet and ribago profiles possibly because reflective diorite units are not so significant or have limited lateral continuity in this part of the noranda formation the reconciliation of the detailed three dimensional geologic model and two dimensional seismic data was not necessarily a straightforward task a significant complication results from the inherent limitations of two dimensional seismic imaging techniques in a complex three dimensional geologic environment nevertheless results presented in this paper indicate that seismic methods can image prospective contacts and deep seated massive sulfide mineralization and can be a valuable exploration tool in the noranda mining camp

buoyant replenishment in silicic magma reservoirs experimental approach and implications for magma dynamics crystal mush remobilization and eruption 1 we present new experiments on replenishment of rhyolite magma chambers by rhyolite magma using corn syrup water solutions we emphasize small density contrasts and show that buoyancy is the key controlling factor for whether injections will rise to the top if buoyant or pond at the base if denser during emplacement we observe little or no mixing of the injected liquid with the reservoir liquid as predicted by the fact that our injections have low reynolds numbers 10 typically at later stages the low buoyancy 1 kg m 3 injected liquid which has accumulated at the top of the reservoir undergoes mixing with the reservoir liquid which may originate by the gravitational destabilization of a thin layer of denser resident liquid trapped above the injected liquid layer the presence of a basal crystal mush modeled by acrylic beads in a corn syrup water solution matrix is also considered slightly buoyant injections entrain a small fraction of mush particles to the top of the overlying liquid layer entrainment efficiency increases dramatically for high buoyancy injections we hypothesize that the injected liquid can entrain a maximum quantity of mush particles which corresponds to the amount required for the injected liquid mush particle suspension to attain neutral buoyancy in the resident liquid hence for silicic systems a replenishing melt can entrain up to 12 5 crystals during its ascent through the mush our results have implications for rhyolites bearing crystals with disequilibrium features as they may represent mush crystals remobilized by a replenishing silicic magma

magma mixing by convective entrainment recent studies of volcanic eruptions have brought to light a puzzling sequence the ejection of dense and mixed liquids followed by a larger volume of unmixed less dense liquid1 4 although these studies have shown that the mixing is associated with the injection of basaltic liquid into a more silicic magma chamber a paradox remains basaltic magma is denser than silicic magma and should flow along the floor of the magma chamber this configuration impedes mixing of the two liquids and appears incompatible with the early eruption of basaltic liquid from the top of the chamber previously proposed mixing processes explain neither the eruption sequence nor the eruption of dense liquid during the time of lowest eruption rate1 8 we report here fluid mechanical experiments that suggest a solution a thermal plume forms over the replenishment inlet dragging basaltic liquid upward by viscous coupling and producing mixing only in a localized area without affecting the bulk of the chamber

magma plumbing system of the 2000 eruption of miyakejima volcano japan during the 2000 eruption at miyakejima volcano two magmas with different compositions erupted successively from different craters magma erupted as spatter from the submarine craters on 27 june is aphyric basaltic andesite 5 vol phenocrysts 51 4 52 2 wt sio2 whereas magma issued as volcanic bombs from the summit caldera on 18 august is plagioclase phyric basalt 20 vol phenocrysts 50 8 51 3 wt sio2 the submarine spatter contains two types of crystal clots a type and a type andesitic type the phenocryst assemblages plagioclase pyroxenes and magnetite and compositions of clinopyroxene in these clots are nearly the same but only a type clots contain ca poor plagioclase an 70 we consider that the a type clots could have crystallized from a more differentiated andesitic magma than the a type clots because feo mgo is not strongly influenced during shallow andesitic differentiation the summit bombs contain only b type basaltic type crystal clots of ca rich plagioclase olivine and clinopyroxene the a type and b type clots have often coexisted in miyakejima lavas of the period 1469 1983 suggesting that the magma storage system consists of independent batches of andesitic and basaltic magmas according to the temporal variations of mineral compositions in crystal clots the andesitic magma became less evolved and the basaltic magma more evolved over the past 500 years we conclude that gradually differentiating basaltic magma has been repeatedly injected into the shallower andesitic magma over this period causing the andesitic magma to become less evolved with time the mineral chemistries in crystal clots of the submarine spatter and 18 august summit bombs of the 2000 eruption fall on the evolution trends of the a type and b type clots respectively suggesting that the shallow andesitic and deeper basaltic magmas existing since 1469 had successively erupted from different craters the 2000 summit collapse occurred due to drainage of the andesitic magma from the shallower chamber as the collapse occurred it may have caused disruption of crustal cumulates which then contaminated the ascending deeper basalt thus porphyritic basaltic magma could erupt alone without mixing with the andesitic magma from the summit caldera the historical magma plumbing system of miyakejima was probably destroyed during the 2000 eruption and a new one may now form

a morphology independent methodology for quantifying planview river change and characteristics from remotely sensed imagery abstract remotely sensed imagery of rivers has long served as a means for characterizing channel properties and detection of planview change in the last decade the dramatic increase in the availability of satellite imagery and processing tools has created the potential to greatly expand the spatial and temporal scale of our understanding of river morphology and dynamics to date the majority of gis and automated analyses of planview changes in rivers from remotely sensed data has been developed for single threaded meandering river systems these methods have limited applicability to many of the earth s rivers with complex multi channel planforms here we present the methodologies of a set of analysis algorithms collectively called spatially continuous riverbank erosion and accretion measurements scream scream analyzes planview river metrics regardless of river morphology these algorithms quantify both the erosion and accretion rates of riverbanks from binary masks of channels generated from imagery acquired at two time periods additionally the program quantifies the area of change between river channels and the surrounding floodplain and area of islands lost or formed between these two time periods to examine variations in erosion rates in relation to local channel attributes and make rate comparisons between river systems of varying sizes the program determines channel widths and bank curvature at every bank pixel scream was developed and tested on rivers with diverse and complex planform morphologies in imagery acquired from a range of observational platforms with varying spatial resolutions validation and verification of scream generated metrics against manual measurements show no significant measurement errors in determination of channel width erosion and bank aspects scream has the potential to provide data for both the quantitative examination of the controls on erosion rates and for the comparison of these rates across river systems ranging broadly in size and planform morphology

river basin organization around the main stem scale invariance in tributary branching and the incremental area function the incremental increase in contributing area along a main stem river called here the incremental area function iaf has direct relevance to the spatial heterogeneity of environmental fluxes water sediment nutrients etc entering the stream from hillslopes and side tributaries it also dictates to a large extent possible ecohydrologic discontinuities or transitions resulting from large tributary contributions mathematically the iaf directly reflects the topological and geometrical structure of the river network and maps the two dimensional landscape organization into a one dimensional function in this paper we use two approaches to investigate the spatial heterogeneity of the iaf first we implement a multithreshold decomposition on iaf to study the distribution of distances between tributaries as a function of the imposed threshold contributing area and verify the presence of a simple power law scaling relationship between the threshold and the average distance between tributaries second we use a wavelet based multiscale approach and document the presence of statistical self affinity multifractality in the iaf with a high intermittency coefficient reflecting the complex arrangement of extreme contributions of different size tributaries we propose a multiplicative cascade model parameterized in terms of basin specific properties to statistically simulate the iaf along the main stem finally we point out the relation between the iaf and the widely used width function of a basin and show how the latter can be constructed from the former via a convolution on the self similar structure of a tree

dynamics of the ca 4965 yr 14c bp ochre pumice plinian eruption of popocatepetl volcano mexico abstract the ochre pumice op plinian fallout was produced by popocatepetl volcano in central mexico during a major plinian eruption that occurred 4965 65 14 c yr bp 3700 bc the op is part of the ochre pumice sequence ops that consists of surge fall and pyroclastic flow deposits the op plinian fallout shows a bimodal grain size distribution with poor to moderate sorting that improves progressively towards the upper beds the juvenile component is mainly pumice 83 wt whereas the accidental components consist of igneous sedimentary and metamorphic clasts from the walls of the magma chamber and or conduit the vesicularity of the pumice decreases from bottom to top of the stratigraphic sequence while the crystal and glass contents increase this suggests increasing magma degassing prior and during the eruption the chemical composition of the pumice varies insignificantly at the base it is less evolved sio 2 61 wt and it becomes slightly more silicic towards the top sio 2 63 wt pumice clasts have a crystallinity index that ranges between 10 and 25 vol and display a seriate texture with phenocrysts of euhedral plagioclase pl clinopyroxene cpx orthopyroxene opx olivine ol oxide ox apatite ap the size of the maximum lithic 2 5 cm at a horizontal distance of 19 km indicates an eruption column height of 37 41 km the isopach map allows the recognition of a dispersal axis that points towards the nne where an area of 300 km 2 was covered by 6 cm of pumice and ash a minimum volume for the op plinian fallout deposit was calculated using a minimum thickness of 6 cm found at distal outcrops and was estimated at 4 9 km 3 which corresponds to 2 km 3 of dense rock equivalent dre stratigraphic relations indicate that the entire ops was emplaced during a short time interval of a few days to weeks and consisted of three main different phases phreato magmatic plinian and vulcanian it started violently with the emplacement of surges and then culminated with the eruption of the op fallout deposit as the eruption advanced discharge rates became more intermittent and the height of the column fluctuated and finally collapsed generating pumice and ash flows that were emplaced around the volcano this short but intense activity was followed during subsequent years by the growth of domes in the crater and the emplacement of block and ash flows generated by vulcanian explosions

amphibole perspective to unravel pre eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes a case study from ciomadul volcano se carpathians ciomadul is the youngest volcano in the carpathian pannonian region produced crystal rich high k dacites that contain abundant amphibole phenocrysts the amphiboles in the studied dacites are characterized by large variety of zoning patterns textures and a wide range of compositions e g 6 4 15 wt al2o3 79 821 ppm sr often in thin section scale and even in single crystals two amphibole populations were observed in the dacite low al hornblendes represent a cold 900 c mafic magma amphibole thermobarometry suggests that the silicic crystal mush was stored in an upper crustal storage 8 12 km this was also the place where the erupted dacitic magma was formed during the remobilization of upper crustal silicic crystal mush body by hot mafic magma indicated by simple zoned and composite amphiboles this includes reheating by 200 c and partial remelting of different parts of the crystal mush followed by intensive crystallization of the second mineral population including pargasites breakdown textures of amphiboles imply that they were formed by reheating in case of hornblendes suggesting that pre eruptive heating and mixing could take place within days or weeks before the eruption the decompression rim of pargasites suggests around 12 days of magma ascent in the conduit several arc volcanoes produce mixed intermediate magmas with similar bimodal amphibole cargo as the ciomadul but in our dacite the two amphibole population can be found even in a single crystal composite amphiboles our study indicates that high al pargasites form as a second generation in these magmas after the mafic replenishment into a silicic capture zone thus they cannot unambiguously indicate a deeper mafic storage zone beneath these volcanoes the simple zoned and composite amphiboles provide direct evidence that significant compositional variations of amphiboles do not necessarily mean variation in the pressure of crystallization even if the al tschermak substitution can be recognized suggesting that amphibole barometers that consider only amphibole composition may often yield unrealistic pressure variation

a review of reflection seismic investigations in three major metallogenic regions the kevitsa ni cu pge district finland witwatersrand goldfields south africa and the bathurst mining camp canada abstract effective exploration for mineral deposits depends on a sound understanding of the processes and geological structures that contributed to their formation the reflection seismic method has proven to be a powerful tool that provides a high resolution image of the subsurface and information about structural and lithological relationships that control mineral deposits the method has also become an attractive geophysical tool for deep exploration and mine planning in this paper we review the use of reflection seismic methods to obtain a better understanding of the architecture and ore forming processes of three diverse mineral regions the kevitsa ni cu pge district in finland the goldfields of the witwatersrand basin south africa and the bathurst mining camp canada seismic data both 2d and 3d from the kevitsa deposit clearly image the 3d geometry of the ore bearing intrusion and provide information about its relationship to the host rock units and nearby intrusions within a larger tectonic framework 3d seismic data from the witwatersrand basin not only provide clear images of major structures including a distinct reflection that acts as a marker horizon for the gold bearing reef but also provide information that may be useful in resolving a long standing controversy regarding the origin of the gold in the basin for example it might be possible to show that dykes formed impermeable barriers thereby falsifying the epigenetic hydrothermal models 2d and 3d seismic data from the brunswick no 6 area in the bathurst mining camp suggest that the brunswick horizon which contains the bulk of the massive sulfide and associated iron deposits occurs within a reflective package that extends down to at least 6 7 km depth

channel network extraction from high resolution topography using wavelets 1 the availability of high resolution topography from lidar offers new opportunities for objectively extracting the channels directly from a dem using local topographic information instead of inferring them indirectly based on global criteria such as area or area slope threshold relationships here we introduce the use of wavelet filtering to delineate threshold curvatures for defining valleys and threshold slope direction change for defining probable channeled portions of the valleys this approach exploits the topographic signatures uniquely found in high resolution topography and reveals the fuzzy topographic transition in which local weakly convergent areas lie at the transition between hillslopes and valleys

seismic structure of the upper mantle beneath the philippine sea from seafloor and land observation implications for mantle convection and magma genesis in the izu bonin mariana subduction zone abstract we have determined the three dimensional shear wave speed structure of the upper mantle in and around the philippine sea region using seismograms recorded by dense land based and long term broadband ocean bottom seismographic stations we used a surface wave tomography technique in which multimode phase speeds are measured and inverted for a 3 d shear wave speed structure by incorporating the effects of a finite frequency and ray bending the new ocean bottom data provided us with improved spatial resolution 300 km in the philippine sea region in the upper 120 km the shear wave speed structure is well correlated with seafloor age at depths greater than 160 km fast anomalies of the subducting pacific plate are clearly defined we also found slow speed anomalies beneath the kyushu palau ridge at depths greater than 120 km along the izu bonin ogasawara mariana arc we have detected three separate slow anomalies in the mantle wedge at depths shallower than 100 km beneath the back arc each anomaly has a width of 500 km moreover these three anomalies have a close relationship with the three groups of frontal and rear arc volcanoes having distinct sr nd and pb isotope ratios we suggest that each of the anomalies is a site of large scale flow of upper mantle into the mantle wedge and that each already contains a component from the adjacent subducting slab

constraints on crystal storage timescales in mixed magmas uranium series disequilibria in plagioclase from holocene magmas at mount hood oregon abstract uranium series crystal ages interpreted within a textural and geochemical framework can provide insight into crystal storage timescales especially in cases where crystals may derive from multiple sources we report here 230 th 226 ra model ages of two distinct populations of plagioclase from low silica dacites from mount hood oregon a volcano where previous studies show that the compositions of erupted magmas are controlled by magma recharge mixing and incorporation of plagioclase derived from mafic and silicic end member magmas we have measured trace element concentrations and 238 u 230 th 226 ra disequilibria in four plagioclase size fractions from the timberline 1500 a and old maid 215 a eruptive sequences after correction for groundmass and apatite contamination average 230 th 226 ra model ages of large 500 m plagioclase are 4 5 ka timberline and 5 5 ka old maid with ages of cores that are 10 ka in each case indicating that plagioclase derived from silicic magmas crystallized thousands of years before eruptions these model ages are longer than timescales of repose between eruptions indicating that these crystals resided in the sub surface over multiple eruptions likely stored in a silicic crystal mush zone that periodically interacts with mafic recharge magmas remobilizing a fraction of the large plagioclase crystals during each eruptive event after correction for large plagioclase contamination small 226 ra ba relative to equilibrium with liquid proxies groundmass and mafic inclusion leading to 230 th 226 ra model ages that are 230 th 226 ra disequilibria require that the majority of crystals in the separate are young 226 ra ba could potentially be explained by rapid crystallization immediately prior to and or during mixing events consistent with evidence of rapid crystallization of rims rapid crystallization of mafic intrusions may trigger eruption at mount hood by producing a partially crystalline mafic magma capable of mixing with a reheated silicic crystal mush

geochemical evolution of a shallow magma plumbing system during the last 500 years miyakejima volcano japan constraints from 238u 230th 226ra systematics abstract in order to unravel magma processes and the geochemical evolution of shallow plumbing systems beneath active volcanoes we investigated u series disequilibria of rocks erupted over the past 500 years 1469 2000 ad from miyakejima volcano izu arc japan miyakejima volcanic rocks show 238u 230th 226ra disequilibria with excess 238u and 226ra due to the addition of slab derived fluids to the mantle wedge basaltic bombs of the 2000 ad eruption have the lowest 230th 232th ratio compared to older miyakejima eruptives yielding the youngest 238u 230th model age of 2 kyr this reinforces our previous model that fluid release from the slab and subsequent magma generation in the mantle wedge beneath miyakejima occur episodically on a several kyr timescale in the last 500 years miyakejima eruptives show 1 a vertical trend in a 230th 232th 238u 232th diagram and 2 a positive linear correlation in a 226ra 230th 0 1 230th diagram which is also observed in lavas from some of the single eruptions e g 1940 1962 and 1983 ad the variations cannot be produced by simple fractional crystallization in a magma chamber with radioactive decay of 230th and 226ra but it is possibly produced by synchronous generation of melts in the mantle wedge with different upwelling rate or addition of multiple slab derived fluids a much more favorable scenario is that some basaltic magmas were intermittently supplied from deep in the mantle and injected into the crust subsequently modifying the original magma composition and producing variations in 230th 232th and 226ra 230th 0 ratios via assimilation and fractional crystallization afc the assimilant of the afc process would be a volcanic edifice of previous miyakejima magmatism due to the relatively short timescales involved the interaction between the assimilant and recent miyakejima magmatism has not been recorded by the sr nd pb isotopic systems in such cases th isotopes and 226ra 230th ratio are excellent geochemical tracers of magmatic evolution

integrated geological and geophysical studies in the sg4 borehole area tagil volcanic arc middle urals location of seismic reflectors and source of the reflectivity near vertical incidence reflection seismic data acquired in the tagil volcanic arc middle urals show the upper crust to be highly reflective two intersecting seismic lines located near the ongoing 5400 m deep sg4 borehole show that the main reflectivity strikes approximately n s and dips 35 55 to the east prominent reflections intercept the borehole at 1000 1500 2800 2900 3400 and between 4000 and 5400 m which correspond to intervals of low velocity low density low resistivity the surface projections of these reflections lie parallel to the strike of magnetic anomaly trends multioffset vertical seismic profile vsp data acquired in the sg4 borehole show a seismic response dominated by p to s reflected converted waves from the moderately east dipping reflectivity and from a set of very steep east dipping reflectors not imaged by the surface data modeling of the vsp data constrains the depth at which reflectors intercept the borehole and suggests that the p to s conversions are best explained by low velocity porous intervals rather than higher velocity mafic material the most prominent east dipping reflection on the surface seismic data is only imaged on vsp shots that sample the crust closer to the e w seismic line this discrepancy between the vsp and the surface seismic data is attributed to rapid lateral changes in the physical properties of the reflector surface and borehole data suggest that the low velocity low density low resistivity intervals are the most important source of reflectivity in the sg4 borehole area although lithological contrasts may also play a role drill cores from the these zones contain hydrothermal alteration minerals indicating interaction with fluids tectonic criteria suggest that they might represent imbricated fracture zones often bounding different lithologies and or intrusions some of them might also represent high porosity lava flows or pyroclastic units common in island arc environments

phreatomagmatic eruptions associated with the caldera collapse during the miyakejima 2000 eruption japan abstract the 2000 ad eruption of miyakejima was characterized by a series of phreatomagmatic eruptions from the subsiding caldera six major eruptive events occurred and they can be divided into the first and second periods separated by a 25 day hiatus the phreatomagmatic eruptions produced a total of 2 1010 kg of tephra which mainly comprised fine grained volcanic ash the tephra layers could be divided into six fall units corresponding to the six major eruptive events the grains of the 2000 tephra consisted mainly of accessory fragments derived from the previous edifice juvenile fragments were identified in four major units the angular and blocky shape of the juvenile fragments showed rapid cooling of magma by external water indicating the mechanical mixing of ground water and magma the removal of the load on the aquifer by caldera subsidence and the intrusion of magma into the decompressed aquifer caused a series of phreatomagmatic eruptions from the subsiding caldera the absence of surface water in the subsiding caldera during the eruption showed that groundwater participated in the phreatomagmatic eruptions rising magma along the ring faults intruded into the decompressed aquifer surrounding the caldera and caused phreatomagmatic explosions the 2000 eruption of miyakejima indicated that the fine grained tephra abundant in hydrothermally altered rock fragments is a possible indicator of the phreatomagmatic eruptions in the hydrothermal system during the caldera formation in basaltic volcanoes

reflection seismic investigations in the dannemora area central sweden insights into the geometry of polyphase deformation zones and magnetite skarn deposits the bergslagen region is one of the most ore prospective districts in sweden presented here are results from two nearly 25 km long reflection seismic profiles crossing this region in the dannemora

modeling the sharp compositional interface in the pu u ō ō magma reservoir kīlauea volcano hawai i 1 lavas from the early episodes of the pu u eruption 1983 1985 of k lauea volcano on the island of hawai i display rapid compositional variation over short periods for some episodes especially the well sampled episode 30 with 2 wt mgo variation in 4 hours little chemical variation is observed within the episode 30 lavas before or after this abrupt change suggesting a sharp compositional interface within the pu u dike like shallow reservoir cooling induced crystal fractionation in this reservoir is thought to be the main control on intraepisode compositional variation potential explanations for a sharp interface such as changing reservoir width and wall rock thermal properties are evaluated using a simple thermal model of a dike like body surrounded by wall rock with spatially variable thermal conductivity the model that best reproduces the compositional data involves a change in wall rock thermal conductivity from 2 7 to 9 w m 1 c 1 which is consistent with deep drill hole data in the east rift zone the change in thermal conductivity may indicate that fluid flow in the east rift zone is restricted to shallow depths possibly by increasing numbers of dikes acting as aquicludes and or decreasing pore space due to formation of secondary minerals results suggest that wall rock thermal gradients can strongly influence magma chemistry in shallow reservoirs

rejuvenation of crustal magma mush a tale of multiply nested processes and timescales some relatively crystal rich silicic volcanic deposits including large volume ignimbrites preserve evidence of a history where a rheologically locked high crystallinity magma was rejuvenated unlocked through enthalpy mass exchange with newly injected recharge magma of higher specific enthalpy this is one event in a possible complex history that is the volcanic product of an eruption reflects an array of sequential and nested processes including melt formation and segregation ascent cooling crystallization crustal assimilation magma recharge unlocking shallow ascent fluid exsolution and eruption deconvolution of these these nested processes and concomitant timescales is complicated and relies on a multidisciplinary approach studies that do not clearly associate process and correlated timescale have the potential to provide misleading timescale information we report the results of thermodynamic and heat transfer calculations that document mass energy and phase equilibria constraints for the unlocking of near solidus rhyolite mush via magma mingling heat exchange only with basaltic recharge magma of higher specific enthalpy to achieve unlocking defined as the transition from near solidus to 50 percent melt of the host silicic magma phase equilibria computations provide 1 the enthalpy required to unlock mush 2 the mass ratio of recharge magma to mush mr mm when the two magmas achieve thermal equilibrium and 3 the changes in melt mineral and fluid phase masses compositions and temperatures during the approach to unlocking the behavior of trace elements is computed with knowledge of mineral fluid and melt proportions and solid fluid and solid melt partition coefficients evaluation of unlocking for relatively dry 0 5 wt h2o and wet 3 9 wt h2o rhyolitic mushy locked magma by basaltic recharge at upper crustal pressures indicates minimum values of mr mm can be significantly less than 1 assuming the mingling process is isenthalpic with no waste heat for active volcanic systems estimates of mr may be tested using geodetic data wet mush has lower energy requirements for unlocking and thus requires lower mr mm than dry mush wet rejuvenated magmas therefore may be more abundant in the volcanic rock record and unlocked dry mushes may be restricted to extensional tectonic settings with high recharge flux temperature changes in dry mush as it unlocks are pronounced greater than 150 c compared to those in wet mush which are smaller than the resolution of classical geothermometry 15 c phase equilibria calculations show that as required the net volume of crystals decreases during unlocking interestingly calculations also indicate reactive crystal growth by chemical re equilibration at the crystal size scale during unlocking may also take place in either dissolution by unidirectional resorption or reactive dissolution new growth the chemical signatures of unlocking potentially preserved in crystals or parts of crystals for example rims are predictable and hence testable independent of unlocking thermodynamics the phase equilibria and elemental consequences of isentropic magma ascent a transport event that follows unlocking can also be predicted detailed examination of several canonical cases reveals a marked contrast with isenthalpic unlocking thereby providing a means of process deconvolution unlocking timescales are estimated by two methods one that calculates the time to reach thermal equilibrium for recharge magma dispersed in mush as clumps of fixed size and the second where the required volume of recharge magma is initially a single clump and evolves to smaller size through clump stretching and folding for a range of magma volumes from 0 1 to 5000 km3 unlocking times range from 10 2 to 106 years the shorter timescales for any magma volume requires a large number of relatively small clumps n 106 which implies that large volumes of mush purported to unlock over short timescales 102 103 years and less should preserve and exhibit evidence of intimate magma mingling the key result of our analysis is that multiple timescales are operative during the potentially long and complex history of silicic mush formation rejuvenation and ascent to correctly ascribe timescales to unlocking requires a holistic understanding of the myriad processes that affect the magma before during and after enthalpy exchange in the absence of this context unlocking timescales may be incorrectly constrained which in turn may hinder eruption forecasting and associated hazard mitigation

old magma and a new intrusive trigger using diffusion chronometry to understand the rapid onset calbuco eruption april 2015 southern chile in april 2015 an unpredicted rapid onset eruption occurred at calbuco volcano southern andes of chile this event consisted of two sub plinian eruptions separated by a few hours by analysis of fe ti exchange between ilmenite and titanomagnetite crystals in samples of erupted material we determine timescales of pre eruptive heating experienced at the partially solidified chamber base and constrain the magma residence time for the bulk of the carrier magma analysis of the fe ti oxide pairs from a sample retrieved from a pyroclastic density current deposit cal 160 shows that it was affected by a significant heating event recording 70 220 c of heating while other collected samples did not record this late heating this sample is interpreted to represent a piece of crystal mush located at the bottom of a prolate ellipsoidal mush reservoir mobilised 4 days before the eruption by a triggering pulse of mafic magma considerably hotter than the typical magmatic temperature of the reservoir another two fall deposit samples lapillus cal 149tb and cal 155 of the eruption are interpreted to represent resident eruptible magmas that did not interact with any magma recharge immediately prior to or during the eruption we infer that these magmas had been at eruption temperature for some years based on their extensively equilibrated fe ti oxides

comment on the october 2005 georgian bay canada earthquake sequence mafic dykes and their role in the mechanical heterogeneity of precambrian crust by s dineva d eaton s ma and r mereu abstract it has been proposed dineva et al 2007 that the location of upper to midcrustal earthquakes in the canadian precambrian shield is related to rheological differences between mafic dykes and country rock we show that this hypothesis is critically dependent on assumed lithology strain rate and temperature and consequently is not established with any level of confidence furthermore it appears to lack self consistency because it postulates earthquakes to occur in the ductile regime

dynamics and thermodynamics of magma mixing insights from a simple exploratory model the mixing of magmas of distinct temperature bulk composition mineralogy and physical properties plays a central role in explaining the diversity of magma types on earth and in explaining the growth of continental and oceanic crust magma mixing is also of practical importance for example the mixing of distinct magmas has been cited as an important process in creation of economically important horizons in layered intrusions as well as a triggering mechanism for initiation of volcanic eruptions the motivation for better quantifying the dynamics and thermodynamics of magma mixing and its attendant plutonic and volcanic products is clear the degree of magma mixing which spans a continuum from mingling to complete hybridization depends upon initial and boundary conditions magma properties driving forces and time available for mixing magma mingling produces a heterogeneous mixture of discrete clumps of the end member magmas whereas complete hybridization involves the thermodynamic equilibration of two distinct magmas to form a third qualitatively mixing occurs via reduction in the size of compositional heterogeneities i e clumps through stretching and folding by viscous flow followed by homogenization once shear has reduced the size of compositional anomalies to diffusive length scales quantification of this process relies on two statistical measures the linear scale of segregation defined as the spatial integral of the compositional correlation function related to the size distribution of the segregated clumps within the mixture and the intensity of segregation i a measure that quantifies how much the composition at each location differs from the average the mixing dynamics of a layered system are analyzed in terms of the parameters governing mixing rayleigh lewis and buoyancy numbers and viscosity ratio to estimate how the timescale for magma hybridization h compares to solidification recharge diffusive and assimilation timescales this analysis illustrates that hybridization times can be shorter than or comparable to thermal solidification and replenishment timescales thus formation of hybridized or nearly hybridized magmas is one anticipated outcome of mixing the machinery of thermodynamics can be used to compute the hybrid magma state an exploratory model for the thermochemistry of hybridization is developed based on binary eutectic phase relations and thermodynamics eight thermodynamic parameters define the phase diagram and associated energetics and six parameters initial temperatures compositions mass ratio of mixing magmas and an enthalpy parameter are necessary and sufficient to determine the state of hybrid magma uniquely while relevant combinations of 14 thermodynamic and mixing parameters might suggest that the number of mixing outcomes i e products is too high to systematize monte carlo simulations using the exploratory model document how millions of arbitrary initial states evolve into five possible final mixed states such an analysis implies that a magma mixing taxonomy that defines possible mixed product states can be developed and tied to petrologic indicators of mixing additional insights gained from this exploratory model that are supported by independent results from a multicomponent multiphase thermodynamic model of magma mixing magma chamber simulator include 1 the proclivity of invariant point hybrid states which may explain some instances of compositionally monotonous melts associated with mixed magma eruptions 2 a surprising thermal effect such that the temperature of hybridized magma can be significantly less than the initial temperature of either of the mixing magmas this type of magma mixing may result in crystal resorption thus invalidating an assumption that resorption textures in crystals are typically the result of a magma heating event 3 illustration of the differing effects of stoped block temperature and composition on hybrid magma temperature and phase state and 4 illustration of a cessation of crystallization effect that may pertain to the morb pyroxene paradox differences between adiabatic or r hybridization and diabatic or rfc hybridization are also explored the model can be used to elucidate the thermodynamic principles underlying magma mixing in the hybridization limit these principles are of general applicability and carry over to more compositionally complicated systems

spatial discontinuity and temporal evolution of channel morphology along a mixed bedrock alluvial river upper drome river southeast france contingent responses to external and internal controls abstract the rehabilitation of degraded river channels is often guided by assumptions of continuity yet in response to spatial and temporal variations in controlling conditions rivers typically display discontinuous response in space and time this study examines the development of a 5 km reach of the drome river s e france characterised by alternating alluvial and bedrock zones that are separated by abrupt downstream transitions this reach is representative of the drome river as a whole and other rivers in the european alps where braided channel planforms have been replaced by more complex discontinuous morphologies the primary aims are to understand how this spatial complexity has developed on the drome evaluate how temporal channel changes have been affected by local factors particularly bedrock exposures and by long term catchment scale changes in sediment supply and the flood activity and consider the implications of this discontinuous geomorphology for reach management the development of geomorphological zonation is examined by documenting sequential changes in channel planform between seven periods using aerial photography 1948 2006 and by analysing change in bed elevation from profiles surveyed in 1928 2003 and 2005 between 1948 and 2001 bedrock exposed in the channel bed and along the floodplain margins defined discontinuities in sediment connectivity that were largely responsible for the configuration of channel zones the impact of floods on this system was not proportional to flood magnitude a modest flood in 1978 was an important event that by incision and avulsion at key locations defined a pattern of zonation that persisted until the end of the study in 2006 during the final 5 years of the study alluvial zones that previously responded to large floods by widening underwent narrowing despite the occurrence of a large flood and led to an overall reduction in width variance this resulted from progressive incision beneath and disconnection from formerly active channel areas in response to long term catchment scale reductions in sediment supply and flood frequency in 2006 the pattern of zonation remains distinct disguising this recent change in channel response and underlining the need for long term and sequential perspectives of channel development to fully understand the processes in operation contemporary snapshots of channel form may be misleading understanding interactions between inherent channel complexity and prevailing flow and sediment conditions and how this shapes channel response to individual floods is essential when interpreting future trajectories of channel change and likely response to management intervention

mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab slab derived fluids play an important role in heat and material transfer in subduction zones dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow nevertheless direct observations of the fluid chemistry and pressure temperature conditions of fluids are few this report describes co2 bearing saline fluid inclusions in spinel harzburgite xenoliths collected from the 1991 pinatubo pumice deposits the fluid inclusions are filled with saline solutions with 5 1 1 0 wt nacl equivalent magnesite crystals co2 bearing vapor bubbles and a talc and or chrysotile layer on the walls the xenoliths contain tremolite amphibole which is stable in temperatures lower than 830 c at the uppermost mantle the pinatubo volcano is located at the volcanic front of the luzon arc associated with subduction of warm oceanic plate the present observation suggests hydration of forearc mantle and the uppermost mantle by slab derived co2 bearing saline fluids dehydration and decarbonation take place and seawater like saline fluids migrate from the subducting slab to the mantle wedge the presence of saline fluids is important because they can dissolve more metals than pure h2o and affect the chemical evolution of the mantle wedge

floodplain width adjustments in response to rapid base level fall and knickpoint migration abstract geomorphology has long been engaged in characterizing the form and understanding the evolution of floodplains this study primarily examines floodplain width in four tributaries to the minnesota river in southern minnesota namely the maple le sueur and blue earth rivers and seven mile creek the tributary systems are relatively young having formed after retreat of the wisconsinan ice sheet and are rapidly evolving in response to a base level fall of nearly 70 m 13 400 ybp as a result the lower reaches of all four river channels are aggressively incising this study applies a new freely available open code plug in for arcgis to measure floodplain width as a function of elevation above the geomorphic top of bank systematic changes are observed in all four systems above the steep incising knickzone reaches of each of the tributaries relatively wide and mostly unconfined floodplains are observed within the knickzone floodplains progressively narrow to between 25 60 of their width above the knickzone despite the fact that sediment loads increase significantly in the downstream direction a power law relationship is consistently observed between floodplain width and the ratio of local channel slope to contributing drainage area to about the negative one third power in all four rivers this same power law relationship is observed for two other rivers that differ significantly from our study systems in climatic and tectonic environment as well as base level history

seismic images and three dimensional architecture of a proterozoic shear zone in the sudbury structure superior province canada a broad zone of intense ductile to brittle deformation transects the paleo proterozoic sudbury igneous complex and likely formed during the final stages of the penokean orogeny on the southern margin of the superior province herein we present a three dimensional image of this deformation zone derived from four seismic reflection profiles additional information from rock property measurements drill results and published structural mapping suggests that the seismic data define the three dimensional disposition of listric shear zones the seismic image of the deformation is best developed within the onaping formation however the images of the deformation zone envelope are imperfect being most clear where truncating known contacts within the sudbury igneous complex and its contact with huronian host rocks the southern edge of the seismically imaged shear zones does not extend significantly beyond the exposed sudbury igneous complex suggesting limits to the extent of deformation in the sudbury structure

geoscience impact a synthesis of studies of the sudbury structure geophysical probing results are synthesized into a three dimensional framework necessary for understanding the genesis of the sudbury structure based primarily on seismic reflection results centred on the sudbury igneous complex remnants of crustal melting from a catastrophic meteorite impact are superimposed on the juxtaposition of mid crustal rocks exhumed during the archean against deformed paleoproterozoic sedimentary rocks sedimentation metamorphism deformation and metasomatic overprints are all part of the post impact history of sudbury and tend to dominate the geophysical response of the structure pre impact deformation although certainly preserved in some aspects of sudbury geology is not clearly expressed in the geophysical data nor are any elements of impact induced deformation geophysical views of the sudbury igneous complex are thus somewhat biased in representing mostly the post impact but pre grenvillian history of the region with the exception of igneous events establishing th

remobilization of highly crystalline felsic magma by injection of mafic magma constraints from the middle sixth century eruption at haruna volcano honshu japan the latest eruption of haruna volcano at futatsudake took place in the middle of the sixth century starting with a plinian fall followed by pyroclastic flows and ending with lava dome formation gray pumices found in the first plinian phase lower fall and the dome lavas are the products of mixing between felsic andesitic magma having 50 vol phenocrysts and mafic magma the mafic magma was aphyric in the initial phase whereas it was relatively phyric during the final phase the aphyric magma is chemically equivalent to the melt part of the phyric mafic magma and probably resulted from the separation of phenocrysts at their storage depth of 15 km the major part of the felsic magma erupted as white pumice without mixing and heating prior to the eruption after the mixed magma gray pumice and heated felsic magma white pumice of the lower fall deposit although the mafic magma was injected into the felsic magma reservoir at 7 km depth part of the product lower fall ejecta preceded eruption of the felsic reservoir magma as a consequence of upward dragging by the convecting reservoir of felsic magma the mafic magma injection made the nearly rigid felsic magma erupt letting low viscosity mixed and heated magmas open the conduit and vent indeed the lower fall white pumices preserve a record of syneruptive slow ascent of magma to 2 km depth probably associated with conduit formation

a complex magma mixing origin for rocks erupted in 1915 lassen peak california the eruption of lassen peak in may 1915 produced four volcanic introduction rock types within 3 days and in the following order 1 hybrid magma mixing is an important process among interblack dacite lava containing 2 undercooled andesitic inclusions mediate magmas in volcanic arcs e g turner 3 compositionally banded pumice with dark andesite and light campbell 1986 philpotts 1990 and references therein dacite bands and 4 unbanded light dacite all types represent laboratory studies of synthetic analogs of silicate magma stages of a complex mixing process between basaltic andesite systems and mathematical modeling of mixing viscous and dacite that was interrupted by the eruption they contain liquids have suggested a range of possible mixing mechdisequilibrium phenocryst assemblages characterized by the coanisms e g cashman bergantz 1991 however use existence of magnesian olivine and quartz and by reacted and of these results to interpret magmatic systems is limited unreacted phenocrysts derived from the dacite the petrography and by the applicability of synthetic analogs to magmatic crystal chemistry of the phenocrysts and the variation in rock conditions and by the imprecise knowledge of the effective compositions indicate that basaltic andesite intruded dacite magma viscosity of silicate liquid crystal mixtures at magmatic and partially hybridized with it phenocrysts from the dacite magma temperatures and pressures if magmas mix incompletely were reacted cooling crystallization and vesiculation of the hybrid i e mingle features such as compositional banding or andesite magma converted it to a layer of mafic foam the decreased undercooled inclusions are usually apparent but if they density of the andesite magma destabilized and disrupted the foam mix completely mineralogical disequilibrium may be the blobs of foam rose into and were further cooled by the overlying dacite magma forming the andesitic inclusions disaggregation of only direct evidence for a mixing origin andesitic inclusions in the host dacite produced the black dacite and if the thermal and compositional contrasts between light dacite magmas formation of foam was a dynamic process two magmas are great and the ratio of silicic to mafic removal of foam propagated the foam layer downward into the magma is large there is little interaction between them hybrid andesite magma eventually the thermal and compositional and the mafic magma is undercooled e g bacon 1986 contrasts between the hybrid andesite and black dacite magmas were many undercooled inclusions contain reacted phereduced then they mixed directly forming the dark andesite magma nocrysts inherited from their host silicic magma heiken about 40 50 andesitic inclusions were disaggregated into the eichelberger 1980 and bacon 1986 pointed out host dacite to produce the hybrid black dacite thus disaggregation that undercooled inclusions are typically formed from of inclusions into small fragments and individual crystals can be hybrid magmas in general the formation of undercooled an efficient magma mixing process disaggregation of undercooled inclusions retards further mixing sakuyama 1984 inclusions carrying reacted host magma phenocrysts produces cothompson dungan 1985 sparks marshall 1986 existing reacted and unreacted phenocryst populations koyaguchi blake 1991 however fragmentation and or disaggregation of undercooled inclusions plays an important role in hybridization in some magma systems thompson dungan 1985 coulon et al 1986 clynne christiansen 1987 clynne 1989 linneman myers

the prevalence of plagioclase antecrysts and xenocrysts in andesite magma exemplified by lavas of the tongariro volcanic complex new zealand beneath subduction zone volcanoes the parental magmas are thoroughly blended during temporary storage in the crust via repeated heating and mixing from new inputs of magma to obtain a clearer picture of magma assembly we employed a sub crystal scale sr isotope analysis coupled with textural and geochemical data on plagioclase phenocrysts in basaltic andesite and andesite erupted from the tongariro volcanic complex new zealand deposits from two neighbouring vents were examined 1 0 3 3 4 ka lava flows of the polygenetic red crater volcano and 2 26 ka pyroclastics of the monogenetic pukeonake scoria cone despite the differences in eruptive styles and history of the two volcanoes the plagioclase growth histories are similar one common phenocryst type comprises of a resorbed core zone variously an50 70 surrounded by a sieve textured mantle rim of higher an 80 fe and mg contents other phenocrysts have resorbed calcic cores an70 90 in situ 87sr 86sr analyses reveal a wide isotopic range 0 7044 0 7060 for pre 1 8 ka red crater 0 7044 7057 for post 1 8 ka red crater 0 7047 0 7055 for pukeonake most of the values are higher than that of the host bulk rock 87sr 86sr 0 7049 0 7051 for pre 1 8 ka red crater 0 7045 0 7046 for post 1 8 ka red crater 0 7048 for pukeonake the variation within some individual phenocrysts is comparable to that of the entire population the higher 87sr 86sr ratios are related relic phenocryst cores indicating that their parental source was more radiogenic than the host magma in contrast their sieve textured mantle rim zones have lower 87sr 86sr ratios 0 7045 0 7049 similar that of their host rock these features record magma mixing less than 10 of phenocryst interiors are cognate autocrysts with the host rock based on their high 87sr 86sr ratio some phenocrysts are likely to be xenocrysts derived from the disintegration of deep crustal meta igneous rocks however based on textures consistent with growth from a melt the majority are antecrysts from intrusive forerunners and or crystal mush zones entrained during eruption or storage overall the andesites are a product of crystal poor magmas of mantle or lower crustal origin carrying phenocrysts from mostly crustal sources the magma system likely comprised of a series of semi isolated melt pods or crystal mush zones in a larger network of intrusions of various ages and states of solidification possibly hosted in country rock of various compositions resorption of the sieve textured mantle zones on the phenocrysts and growth of a normally zoned outermost rim represents a final period of fractional crystallization in the newly homogenised melt following the ascent and intrusion of mafic magma hence the final tipping point to eruption may have involved crystallization induced volatile exsolution and degassing

seismic reflection imaging over the south portuguese zone fold and thrust belt sw iberia 1 we reprocessed an 35 km long part of the ibesreis seismic reflection profile which runs over the iberian pyrite belt section of the south portuguese zone sw iberia with the goal to image the upper crust 15 km depth the applied processing sequence enhanced numerous prominent reflections and diffraction patterns within the uppermost 5 s travel time relative to high amplitude source generated noise a complex subsurface characterized by conflicting dips and a survey following winding roads require a crooked line prestack migration scheme for coherent imaging to interpret sources of diffracted energy we additionally employed a diffraction imaging scheme which enhances diffractions at the expense of reflections the final seismic images show south vergent imbricate fold and thrust tectonics documenting the contractive deformation that the south portuguese zone experienced during the variscan orogeny based on surface geological information we correlate a low reflective unit with the shallow upper carboniferous flysch group a highly reflective unit ranging in depth from 2 to 4 km with the middle carboniferous volcano sedimentary complex group which hosts massive sulfide deposits and a moderately reflective unit with the upper devonian phyllite quartzite group below these units another low reflective facies is present which may represent older paleozoic metasediments in addition the seismic and diffraction images reveal bands of high reflectivity and distinct diffraction patterns that were interpreted as extensive layered mafic intrusions these proposed mafic bodies may be related to the same event that triggered a huge hydrothermal activity assumed in early carbonifereous times

insights into magmatic evolution and recharge history in capraia volcano italy from chemical and isotopic zoning in plagioclase phenocrysts plagioclase phenocrysts in dacites from the high k calc alkaline capraia volcano were investigated for major trace element and sr isotope variations in order to gain better insight into the proposed open system behaviour of the volcano repeated dissolution zones in plagioclases from the early erupted monte castello mc and later monte rucitello mr dacitic units are associated with a sharp increase in an content and variation in isotopic compositions 87sr 86sr 0 70872 0 71004 which argue for repeated magma mixing in particular petrographic and mineralogical evidence suggest that recharge with hot basaltic magma occurred repeatedly during the lifetime of the capraia volcanic system we attempted to correlate shared crystallization and resorption histories using chemical mol an fe and sr isotopic zoning in plagioclase in this correlation framework the observed mismatch between chemical and isotopic data in some phenocrysts is interpreted to reflect either growth of phenocrysts in a separate magma chamber or compositional zoning within a single magma chamber a minor role of crustal contamination is inferred instead the intra crystal variations in isotopic composition in plagioclase reflect the existence of distinct components that may have thoroughly mixed at the end of the mc plagioclase growth history the dominant radiogenic component is similar to lamproites occurring in tuscany recharge with this component occurred throughout the genesis of the mr dacites but was restricted to the early growth history of the mc dacites the mr plagioclases are inferred to have crystallized from separate more differentiated batches of magma that were likely to have evolved at the top of a zoned magma reservoir decrease in the an content after most dissolution zones in all phenocrysts and low temperature estimates from zircon saturation thermometry 800 c also emphasize the importance of crystal fractionation during the evolution of the volcano in agreement with the occurrence of a significant amount of rhyolitic material thus it is inferred that a rather large magma chamber may have existed during the first cycle of eruptive activity

seismic methods in mineral exploration and mine planning a general overview of past and present case histories and a look into the future abstractdue to high metal prices and increased difficulties in finding shallower deposits the exploration for and exploitation of mineral resources is expected to move to greater depths consequently seismic methods will become a more important tool to help unravel structures hosting mineral deposits at great depth for mine planning and exploration these methods also can be used with varying degrees of success to directly target mineral deposits at depth we review important contributions that have been made in developing these techniques for the mining industry with focus on four main regions australia europe canada and south africa a wide range of case studies are covered including some that are published in the special issue accompanying this article from surface to borehole seismic methods as well as petrophysical data and seismic modeling of mineral deposits at present high resolution 2d surveys mostly are performed in mining areas but there is a general increasing trend in the use of 3

petrological architecture of a magmatic shear zone a multidisciplinary investigation of strain localisation during magma ascent at unzen volcano japan shearing of magma during ascent can promote strain localisation near the conduit margins anymechanical and thermal discontinuities associated with such events may alter the chemical physicaland rheological stability of the magma and thus its propensity to erupt lava spines can record suchprocesses preserving a range of macroscopic and microscopic deformation textures attributed toshearing and friction as magma ascends through the viscous brittle transition here we use a multi disciplinary approach combining petrology microstructures crystallography magnetics and experi mentation to assess the evidence role and extent of shearing across a marginal shear zone of the1994 1995 lava spine at unzen volcano japan our results show that crystals can effectively moni tor stress conditions during magma ascent with viscous remobilisation crystal plasticity and com minution all systematically increasing towards the spine margin accompanying this we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex tural variations across the shear zone from symplectitic to granular rims towards the spine margin in addition the compaction of pores chemical and textural alteration of interstitial glass and mag netic variations all change systematically with shear intensity the strong correlation between thedegree of shearing crystal deformation and disequilibrium features together with distinct magneticproperties implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent this was accompanied by late stage or post emplacement fluid andgas induced alteration of the gouge as well as oxidation and glass devitrification understandingand recognising evidence for strain localisation during magma ascent may therefore be vital whenassessing factors that regulate the style of volcanic eruptions which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava domes

crustal signature of late archaean tectonic episodes in the yilgarn craton western australia evidence from deep seismic sounding abstract deformation in the greenstone supracrustal rocks of the eastern goldfields province of the archaean yilgarn craton in western australia is delaminated from the underlying basement along a regional detachment surface presently at 3 7 km depth this might suggest that the history of crustal deformation cannot be inferred with any certainty from that of the greenstones however seismic images of the crust below the greenstones show structures that can be interpreted in terms of a series of tectonic events similar to those within the greenstones the upper crust below and to the west of the greenstones is largely unreflective with interpreted west dipping reverse faults the middle crust is reflective with reflector geometry implying thickening by west directed thrust stacking and the lower crust has a fabric indicative of ductile deformation these reflection fabrics imply crustal shortening probably during the late archaean regional d2 ene wsw shortening event they were subsequently overprinted and disrupted by structures consistent with regional nnw sse strike slip d3 faulting and probably younger more localised d4 faulting the seismic images of the crust therefore show that the crust suffered tectonic events in which both the order and direction of deformation are similar to those of the greenstones this is evidence that the whole crust deformed when the greenstones deformed however the scale and style of deformation vary with depth through the crust and include thrusting and probably folding in the upper crust thrust stacking in the middle crust and ductile deformation in the lower crust the length scale wavelength of structures in the middle and lower crust is greater than that in the greenstones

synthetic river valleys creating prescribed topography for form process inquiry and river rehabilitation design abstract the synthesis of artificial landforms is complementary to geomorphic analysis because it affords a reflection on both the characteristics and intrinsic formative processes of real world conditions moreover the applied terminus of geomorphic theory is commonly manifested in the engineering and rehabilitation of riverine landforms where the goal is to create specific processes associated with specific morphology to date the synthesis of river topography has been explored outside of geomorphology through artistic renderings computer science applications and river rehabilitation design while within geomorphology it has been explored using morphodynamic modeling such as one dimensional simulation of river reach profiles two dimensional simulation of river networks and three dimensional simulation of subreach scale river morphology to date no approach allows geomorphologists engineers or river rehabilitation practitioners to create landforms of prescribed conditions in this paper a method for creating topography of synthetic river valleys is introduced that utilizes a theoretical framework that draws from fluvial geomorphology computer science and geometric modeling such a method would be valuable to geomorphologists in understanding form process linkages as well as to engineers and river rehabilitation practitioners in developing design surfaces that can be rapidly iterated the method introduced herein relies on the discretization of river valley topography into geometric elements associated with overlapping and orthogonal two dimensional planes such as the planform profile and cross section that are represented by mathematical functions termed geometric element equations topographic surfaces can be parameterized independently or dependently using a geomorphic covariance structure between the spatial series of geometric element equations to illustrate the approach and overall model flexibility examples are provided that are associated with mountain lowland and hybrid synthetic river valleys to conclude recommended advances such as multithread channels are discussed along with potential applications

isotopic characteristics of neogene quaternary tephra from iodp site u1438 a record of explosive volcanic activity in the kyushu ryukyu arc a m acknowledges support from the swiss national science foundation grant 200020 135511 to othmar muntener and grant p2lap2 171819 to a m and swiss iodp this work was also supported by grants to g m y and m b from nsf oce 1537135 and iodp

partition coefficients for iron between plagioclase and basalt as a function of oxygen fugacity implications for archean and lunar anorthosites abstract experimental studies were undertaken to determine d for feot between plagioclase and melt as a function of oxygen fugacity for a basaltic composition that occurs as matrices for plagioclase megacrysts that are similar to those in calcic anorthosites at liquidus conditions the d for feot between calcic plagioclase and tholeiitic basalt changes very little from 0 030 to 0 044 between the very low o 2 of the iron wustite buffer and that of the quartz fayalite magnetite qfm buffer at fugacities above qfm the value for d increases rapidly to 0 14 at the magnetite hematite buffer and 0 36 in air the increase in d results from the fact that nearly all of the fe is in the fe2 state at o 2 below qfm and the fe 3 fe 2 ratio in the melt increases rapidly above qfm causing more fe to enter the plagioclase which accepts fe3 more readily than fe2 there is essentially no change in values of d over cooling rates that vary by two orders of magnitude the d for feot of 0 030 at iron wustite is in good agreement with earlier studies at low o2 terrestrial calcic plagioclase matrix pairs display ds of about 0 043 in excellent agreement with the experimental value of 0 044 at qfm which is the accepted fugacity for terrestrial tholeiitic basalts application of the ds for feot and other components to terrestrial calcic anorthosites indicates that the anorthosites were in equilibrium with nearby coeval tholeiitic basalts at qfm as was expected lunar anorthosites however have anomalously low contents of feot as well as mgo and would be in equilibrium with melts that are several times lower in these components than expected the low values of feot and mgo in the plagioclase of lunar anorthosites are a result of subsolidus reequilibration with pyroxene olivine and other fe mg bearing phases during high temperature metamorphism as is the case in terrestrial anorthosites that have undergone granulite grade metamorphism the ds for k2o mgo and tio2 were determined as 0 21 0 044 and 0 033 respectively and show no variation with o 2 the value for k2o is in good agreement with natural assemblages the values for mgo and tio2 however are lower in natural assemblages but the high degree of mobility of mg and the very low contents of tio2 in plagioclase makes the reliability of the natural values rather low also the d for tio2 may be affected by rate of cooling attempts to determine the d for cr2o3 as a function of o 2 were made difficult by the low levels of cr2o3 300 to 500 ppm in the melt when saturation with a cr spinel occurred because the cr concentrations in plagioclase are nearly 100 times less than those in the melt it was not possible to obtain reliable analyses for plagioclase these uncertainties constrain the d for cr to be less than 0 07 at the qfm buffer

gently dipping fracture zones in paleoproterozoic metagranite sweden evidence from reflection seismic and cored borehole data and implications for the disposal of nuclear waste 1 the svecokarelian orogen in the coastal area north of stockholm central sweden is characterized by a complex deformation belt in this belt bedrock domains strike wnw nw dip steeply and are affected by high ductile strain these domains anastomose around tectonic lenses that are up to a few tens of kilometers in length and are a few kilometers wide the bedrock within the lenses is folded and in general affected by lower ductile strain site investigations for the disposal of highly radioactive nuclear waste are presently in progress within one of these lenses approximately 16 km of high resolution 10 m source and receiver spacing 100 channels seismic data were acquired in 2002 along five separate profiles 2 to 5 km in length within this lens in the southeast reflection orientations are well determined where profiles cross one another here there is a nearly one to one correlation of distinct reflections on the seismic sections with hydraulically conductive fracture zones in cored boreholes indicating that these fracture zones control the reflectivity however smaller lenses of amphibolite within the fracture zones may enhance the reflectivity the reflections dip gently to the sse and se and the zones in the boreholes are dominated by fractures that show the same dip direction or are subhorizontal a working hypothesis for the gently dipping fracture zones suggests that these structures formed as minor thrust faults during the later stages of the svecokarelian orogeny mineral fillings and coatings along fractures in these zones indicate later reactivation the current stress field a high intensity of fractures in the zones at a high angle to 3 high in situ stresses in the bedrock and rapid glacial unloading with the development of high differential stresses may explain the large volume of groundwater in these zones the reflection seismic data in combination with the verifying work presented in the cored borehole data have steered the subsequent focus in geoscientific studies to the northwestern part of the candidate area

scaling in river corridor widths depicts organization in valley morphology landscapes have been shown to exhibit numerous scaling laws from horton s laws to more sophisticated scaling in topography heights rivernetworktopology andpower lawsinseveralgeomorphicattributes inthispaper weproposeadifferent wayof examining landscape organization by introducing the river corridor width lateral distance from the centerline of the river to the left and right valley walls at a fixed height above the water surface as one moves downstream we establish that the river corridor width series extracted from 1 m lidar topography of a mountainous river exhibit a rich multiscale statistical structure anomalous scaling which varies distinctlyacross physicalboundaries e g bedrockversusalluvialvalleys we postulatethatsuchananalysis inconjunctionwith field observations and physical modeling has the potential to quantitatively relate mechanistic laws of valley formation to the statistical signature that underlying processes leave on the landscape such relations can be useful in guiding field work by identifying physically distinct regimes from statistically distinct regimes and advancing process understanding and hypothesis testing 2007 elsevier b v all rights reserved

revisiting scaling laws in river basins new considerations across hillslope and fluvial regimes 1 increasing availability of high resolution 1 m topography data and enhanced computational processing power present new opportunities to study landscape organization at a detail not possible before here we propose the use of directed distance from the divide as the scale parameter instead of horton s stream order or upstream contributing area for performing detailed probabilistic analysis of landscapes over a broad range of scales this scale parameter offers several advantages for applications in hydrology geomorphology and ecology in that it can be directly related to length scale dependent processes it can be applied seamlessly across the hillslope and fluvial regimes and it is a continuous parameter allowing accurate statistical characterization higher order statistical moments across scales application of this scaling formalism to three basins in california demonstrates the emergence of three distinct geomorphic regimes of divergent highly convergent and moderately convergent fluvial pathways with notable differences in their scaling relationships and in the variability or spatial heterogeneity of topographic attributes in each regime we show that topographic attributes such as slopes and curvatures conditional on directed distance from the divide exhibit less variability than those same attributes conditional on upstream contributing area thus affording a sharper identification of regime transitions and increased accuracy in the scaling analysis

crustal structure beneath the western canada sedimentary basin constraints from gravity and magnetic modelling regional gravity and magnetic anomalies that originate from crystalline basement rocks extend over many parts of the western canada sedimentary basin although these potential field anomalies provide a basis for tectonic subdivisions of the basement crust most previous interpretations of these features have been largely qualitative in nature this study focuses on numerical simulation and quantitative interpretation of five regional potential field anomalies in alberta canada for which independent constraints on crustal structure are available from lithoprobe seismic and electromagnetic studies the kimiwan high 55 n 116 w is a roughly 250 km long linear magnetic high seismic profiles across this anomaly provide evidence for a crustal scale extensional fault system that offsets the winagami reflection sequence a series of mid crustal sills we find that the magnetic anomaly can be modelled as either a 15 40 km wide zone of moderate positive susceptibility 4 5 10 3 si units in the hanging wall

linking fluid dynamics and olivine crystal scale zoning during simulated magma intrusion the compositional zoning styles of natural crystals produced during magma intrusion can be used to investigate the structure of magmatic plumbing systems and its relation to expressions of volcanic unrest seismic deformation volatiles however magma intrusion is a progressive dynamic process and yields non monotonic heterogeneities in physio chemical variables such as complex spatial variations in temperature and liquid composition with time such changes in variables are difficult to incorporate in models of crystal zoning in natural systems here we take another approach by integrating the results of a numerical multiphase simulation of melt arrival in an olivine rich reservoir with models of chemical re equilibration of olivine we evaluate the diversity of chemical zoning styles and the inferred time scales using fe mg diffusion in olivine for a limited range of system geometries and time composition temperature values although our models are still a large simplification of the processes that may occur in natural systems we find several time dependent and systematic relations between variables that can be used to better interpret natural data the proportions of zoned and unzoned crystals the zoning length scales and the calculated diffusion times from the crystals vary with time and the initial position of the crystal in the reservoir these relationships can be used for example to better constrain the plumbing structure and dynamics of mafic eruptions from monogenetic volcanoes by detailed studies of changes in the zoning of the crystal cargo with eruptive sequence moreover we also find that the time scales obtained from modeling of crystals at a single temperature and boundary condition tend to be shorter about 25 than the residence time which could also be tested in natural studies by combining crystal time scale records with monitoring datasets

shift and rotation of composition trends by magma mixing 1983 eruption at miyake jima volcano japan levels of ascent of the fountain in the host andesite magma analysis of compositional zoning in titanomagnetite crystals revealed that the eruption of the 1983 magmas was initiated soon after the replenishment of the basaltic magma in the 1kbar magma chamber

the october 2005 georgian bay canada earthquake sequence mafic dykes and their role in the mechanical heterogeneity of precambrian crust on 20 october 2005 at 21 16 utc a moderate earthquake mn 4 3 occurred in an area of low seismicity within georgian bay approximately 12 km north of thornbury ontario 44 67 n 80 46 w despite its moderate magnitude it was exceptionally well recorded and is of particular interest because of its location 90 km from a proposed long term storage facility for low and medium level nuclear waste no damage was reported but ground shaking was felt to a distance of 100 km within 24 hours after the mainshock four portable seismograph systems were in stalled in the epicentral region in total eight events were recorded over a 4 day period including a foreshock and six aftershocks the unusually rich dataset from this moderate earthquake sequence enabled robust determination of hypocentral pa rameters including well constrained focal depths for most events for the mainshock we estimated a seismic moment of m0 4 5 10 14 n m and corner frequency of 3 7 hz based on a spectral fit using brune s source model least squares waveform inversion of p and s phases yielded a double couple focal mechanism with a reverse sense of slip and northwest striking nodal planes the reverse mechanism and mid crustal focal depths 10 12 km are characteristic in general of more abundant seismicity located 200 km northeast of this event in the western quebec seismic zone these parameters differ however from shallow 2 6 km earthquakes with predominantly strike slip mechanisms observed near lake erie 200 km to the south we attribute this north south change in rupture mechanism to variations in crustal stress induced by postglacial isostatic rebound aeromagnetic data in and around the epicentral region reveal prominent northwest striking lineations caused by precam brian mafic dykes under midcrustal conditions the dyke material is mechanically stronger than generally more felsic upper crustal host rocks we propose that where large dykes are favorably oriented with respect to the stress field they may strongly influence the locations of intraplate earthquake rupture in shield regions

reflection seismic imaging and physical properties of base metal and associated iron deposits in the bathurst mining camp new brunswick canada the bathurst mining camp northern new brunswick canada is a major base metal producing region that includes the brunswick no 12 and smaller past producing brunswick no 6 deposit sustaining mining activity in the camp requires exploration of orebodies near and adjacent to existing mines in this paper we recovered re processed modeled and interpreted a 2d high resolution reflection seismic profile in the vicinity of the brunswick no 6 open pit with the aim of providing key information on the geological structures associated with mineral deposits at depth the seismic data quality is good to excellent with numerous strong reflections in raw shot gathers resulting from a careful survey design that included test shots and a priori considerations for the geological environment physical properties of lithological units and mineralized zones including gamma gamma conductivity magnetic susceptibility density and sonic data were studied from borehole geophysical measurements conducted near the mine this helped to correlate seismic data and shows that the brunswick horizon a key ore prospecting horizon and associated lithological contacts are strongly reflective the results demonstrate that reflection seismic imaging has been particularly effective for imaging steeply dipping structures of the brunswick no 6 deposit many of which intersect the surface and thus allow for correlation with surface geology massive sulfides and iron formation of the brunswick horizon are identifiable locally within a distinctive reflective package that can be used as a broad guide in the region for the exploration of deep base metal deposits in several locations a change from highly reflective to semi transparent seismic character is explained by the presence of faults that juxtapose highly reflective lithological units with seismically transparent lithologies

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient