microgranitoid enclave swarms in granitic plutons central sierra nevada california abstract microgranitoid enclaves are common in granitic plutons worldwide occurring individually and in homogeneous or heterogeneous swarms three plutons in the central sierra nevada batholith contain swarms with mostly heterogeneous suites of enclaves in the intermediate composition range and occur in a number of two dimensional shapes specifically as dikes small rafts lenses pipe vortices and large massive shapes swarms are characterized by various features including the nature of their boundary with the host their planar or non planar character internal geometry density of enclave packing presence or absence of schlieren and crystal aggregates and axial ratios and degree of preferred alignment of enclaves we propose that heterogeneous enclave swarms form by one or some combination of the following mechanisms 1 velocity gradient sorting parallel or normal to the flow 2 gravitational sorting or 3 break up of heterogeneous dikes common sites where enclave swarms form include pluton margins or internal viscosity walls within fractures and near the pluton roof

keeping the edge a numerical method that avoids knickpoint smearing when solving the stream power law the stream power equation is commonly used to model river incision into bedrock although specific conditions allow an analytical approach finite difference methods fdms are most frequently used to solve this equation fdms inevitably suffer from numerical smearing which may affect their suitability for transient river incision modeling we propose the use of a finite volume method fvm which is total variation diminishing tvd to simulate river incision in a more accurate way the tvd fvm is designed to simulate sharp discontinuities making it very suitable to simulate river incision pulses we show that the tvd fvm is much better capable of preserving propagating knickpoints than fdms using niagara falls as an example comparison of numerical results obtained using the tvd fvm with analytical solutions shows a very good agreement furthermore the uncertainty associated with parameter calibration is dramatically reduced when the tvd fvm is applied the high accuracy of the tvd fdm allows correct simulation of transient incision waves as a consequence of older uplift pulses this implies that the tvd fvm is much more suitable than fdms to reconstruct regional uplift histories from current river profile morphology and to simulate river incision processes in general

insights from quartz cathodoluminescence zoning into crystallization of the vinalhaven granite coastal maine the vinalhaven intrusive complex provides field and petrographic evidence for multiple replenishments of mafic and silicic magmas mingling and limited mixing and rejuvenation of granite quartz in granitic rocks preserves a record of those processes in the form of cathodoluminescence cl zoning which is related to concentration of titanium and to temperature of crystallization using the new titaniq ti in quartz geothermometer injection of mafic melts into partly crystalline vinalhaven granite resulted in partial quartz resorption followed by higher temperature growth from h2o undersaturated melt this is shown by steep rimward increases in cl intensity and ti content across discordant boundaries that truncate older growth zones quartz zoning in granite affected by mafic magmas displays large rimward jumps in ti content whereas quartz in granitic feeders and in granite far from mafic rocks typically displays broad rims with decreasing ti contents consistent with slow cooling without thermal disruptions due to mafic recharge

seasonal and interannual behaviour of groundwater catchment boundaries in a chalk aquifer groundwater catchment boundaries and their associated groundwater catchment areas are typically assumed to be fixed on a seasonal basis we investigated whether this was true for a highly permeable carbonate aquifer in england the berkshire and marlborough downs chalk aquifer using both borehole hydrograph data and a physics based distributed regional groundwater model borehole hydrograph data time series were used to construct a monthly interpolated water table surface from which was then derived a monthly groundwater catchment boundary results from field data showed that the mean annual variation in groundwater catchment area was about 20 of the mean groundwater catchment area but interannual variation can be very large with the largest estimated catchment size being approximately 80 greater than the smallest the flow in the river was also dependent on the groundwater catchment area model results corroborated those based on field data these findings have significant implications for issues such as definition of source protection zones recharge estimates based on water balance calculations and integrated conceptual modelling of surface water and groundwater systems

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

river drainage patterns in the new zealand alps primarily controlled by plate tectonic strain the persistence of dendritic drainage patterns implies that rivers reorganize after a tectonic perturbation preserving no long term record of that tectonic event numerical simulations of the evolution of drainage patterns in the southern alps new zealand however reveal rivers that resist reorganization and thus preserve a record of plate tectonic strain over 10 million years

how late are k feldspar megacrysts in granites abstract various petrologists have suggested that k feldspar megacrysts grow in granites that are extensively crystallized even at subsolidus conditions however experimental evidence indicates that though k feldspar nucleates relatively late in the crystallization history abundant liquid is available for development of large crystals a great deal of evidence involving many different factors favours a magmatic phenocrystic origin for k feldspar megacrysts in granites namely simple twinning oscillatory zoning euhedral plagioclase inclusions and concentric crystallographically controlled arrangements of inclusions in addition abundant evidence has been presented of 1 mechanical accumulation of k feldspar megacrysts in granites 2 alignment of megacrysts and megacryst concentrations in magmatic flow foliations 3 involvement of megacrysts in zones of magma mixing in granite plutons and 4 occurrence of megacrysts in some volcanic rocks implying that the megacrysts were suspended in enough liquid to be moved without fracturing or plastic deformation detailed trace element and isotopic data also indicate that megacrysts can move between coexisting felsic and more mafic magmas irregular overgrowths on megacrysts are consistent with continued magmatic growth after euhedral megacrystic growth ceased the overgrowths being impeded by simultaneously crystallizing quartz and feldspar grains

igneous banding schlieren and mafic enclaves in calc alkaline granites the budduso pluton sardinia abstract this study deals with the origin of igneous layering in plutons and especially the extent layering is related to mafic silicic magma interactions the budduso pluton sardinia shows three main scales of organization i large scale lithological variations correspond to three main magmatic units with differentiation increasing from the outer hornblende bearing biotite granodiorite monzogranite to the middle biotite monzogranite and the inner leucomonzogranite units the striking homogeneity of 87 sr 86 sr initial ratios 0 7090 4 and e nd t values 5 6 0 1 strongly suggests that magma isotopic equilibration was achieved prior to emplacement whereas mixing mingling structures observed within the pluton reflect second stage processes involving broadly cogenetic components ii metre to decametre scale igneous layering may be isomodal or modally graded locally with cross layering biotite and plagioclase compositions are similar in both biotite rich and quartzofeldspathic layers as are the trace element patterns which differ only by relative abundances this precludes an origin by fractional crystallization a penetrative submagmatic fabric superimposed on the layering and corresponding mainly to flattening can be ascribed to interference between pluton growth and regional deformation iii composite layering and schlieren are commonly associated to mafic microgranular enclaves locally within synmagmatic shear zones or disrupted synplutonic dykes in that case there is a progressive shift in biotite x fe values from the core of enclave 0 65 to the host monzogranite 0 72 schlieren in the monzogranite show biotite x fe values similar to that of the host rock whereas schlieren close to mafic enclaves show lower x fe values 0 69 towards those of enclave rims these features can be ascribed to three main processes i assembly of differentiated mixed mingled magmatic pulses ii local hydrodynamic sorting related to density currents in a mush and segregation of residual melt iii mechanical disruption and chemical hybridization of mafic magmas during ascent or within the pluton related to magma dynamics none of these processes affect the whole pluton but they are limited to specific magmatic units therefore pluton growth by incremental assembly of magma batches is not incompatible with magma chamber processes

geomorphology tectonically twisted rivers tracking diffuse shearing deformation of continents is difficult numerical modelling of drainage evolution in the southern alps new zealand suggests that rivers can act as dynamic markers of tectonic deformation over geological timescales

depositional features and stratigraphic sections in granitic plutons implications for the emplacement and crystallization of granitic magma abstract many granitic plutons contain sheet like masses of dioritic to gabbroic rocks or swarms of mafic to intermediate enclaves which represent the input of higher temperature more mafic magma during crystallization of the granitic plutons small scale structures associated with these bodies e g load cast and compaction features silicic pipes extending from granitic layers into adjacent gabbroic sheets indicate that the sheets and enclave swarms were deposited on a floor of the magma chamber on granitic crystal mush and beneath crystal poor magma while the mafic magma was incompletely crystallized these structures indicate way up typically toward the interior of the intrusions and appear to indicate that packages of mafic sheets and enclave concentrations in these plutons are a record of sequential deposition hence these plutons preserve a stratigraphic history of events involved in the construction filling replenishment and crystallization of the magma chamber the distinctive features of these depositional portions of plutons allow them to be distinguished from sheeted intrusions which usually preserve mutual intrusive contacts and dike sill relations of different magma types the considerable thickness of material that can be interpreted as depositional and the evidence for replenishment suggest that magma chamber volumes at any one time were probably much less than the final size of the pluton thus magma chambers may be constructed much more slowly than presently envisaged the present steep attitudes of these structures in many plutons may have developed gradually as the floor of the chamber along with the underlying solidified granite and country rock sank during continuing episodes of magma chamber replenishment these internal magmatic structures support recent suggestions that the room problem for granites could be largely accommodated by downward movement of country rock beneath the magma chamber

connecting large scale atmospheric circulation river flow and groundwater levels in a chalk catchment in southern england summary groundwater is an important water resource and globally it represents the largest distributed store of freshwater in southern england groundwater is a major source for public water supply and many aquifers have recently experienced both extreme low and high groundwater levels in this paper we use observations of precipitation river discharge and groundwater levels 1964 2010 and an atmospheric reanalysis to explore the large scale climate patterns preceding the nine highest and lowest march river discharge and groundwater levels in the chalk catchment of the river lambourn berkshire downs southern england peak monthly precipitation is shown to occur from october to january while the highest river discharge and groundwater levels are found from february to april for high discharge groundwater levels composite anomaly patterns of the mean sea level pressure show a stronger than average pressure gradient across the north atlantic ocean with enhanced water vapour transport across southern england for the lowest discharge groundwater levels a blocking high pressure system is found across the british isles deflecting storms and precipitation to the north significantly the intra composite variability suggests that different sequences of atmospheric states may lead to high and low discharge groundwater events

quartz and feldspar zoning in the eastern erzgebirge volcano plutonic complex germany czech republic evidence of multiple magma mixing abstract zoned quartz and feldspar phenocrysts of the upper carboniferous eastern erzgebirge volcano plutonic complex were studied by cathodoluminescence and minor and trace element profiling the results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends magma mixing and recharge events and suggest that much heterogeneity in plutonic systems may be overlooked on a whole rock scale multiple resorption surfaces and zones element concentration steps in zoned quartz ti and feldspar phenocrysts anorthite content ba sr and plagioclase mantled k feldspars etc indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern erzgebirge volcano plutonic complex generally feldspar appears to be sensitive to the physicochemical changes of the melt whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas the regional distribution of mixing compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late variscan granites and associated volcanic rocks quartz phenocrysts from 14 magmatic phases of the eastern erzgebirge volcano plutonic complex provide information on the relative timing of different mixing processes storage and recharge allowing a model for the distribution of magma reservoirs in space and time at least two levels of magma storage are envisioned deep reservoirs between 24 and 17 km the crystallisation level of quartz phenocrysts and subvolcanic reservoirs between 13 and 6 km deflation of the shallow reservoirs during the extrusion of the teplice rhyolites triggered the formation of the altenberg teplice caldera above the eastern erzgebirge volcano plutonic complex the deep magma reservoir of the teplice rhyolite also has a genetic relationship to the younger mineralised a type granites as indicated by quartz phenocryst populations the pre caldera biotite granites and the rhyodacitic schonfeld volcanic rocks represent temporally and spatially separate magma sources however the deep magma reservoir of both is assumed to have been at a depth of 24 17 km the drastic chemical contrast between the pre caldera schonfeld westfalian b c and the syn caldera teplice westfalian c d volcanic rocks is related to the change from late orogenic geotectonic environment to post orogenic faulting and is considered an important chronostratigraphic marker

velocity field in asia inferred from quaternary fault slip rates and global positioning system observations we perform a joint inversion of quaternary strain rates and 238 global positioning system gps velocities in asia for a self consistent velocity field the reference frames for all geodetic velocity observations are determined in our inversion procedure india in moves relative to eurasia eu about a pole of rotation at 29 78 n 7 51 e 0 353 myr 1 which yields a velocity along the himalaya within india that is 73 76 of the magnitude of the in eu nuvel 1a velocity and a vector azimuth that is 8 10 clockwise of nuvel 1a in eu vector azimuth relative to eurasia south china moves at 9 11 mm yr in the direction 110 120 with a pole position 64 84 n 156 74 e 0 12 myr 1 amurian block motion has a pole position in a similar location but at a slower rate 64 61 n 158 23 e 0 077 myr 1 and most of the amurian eurasia motion is accommodated by extension across lake baikal tarim basin moves relative to eurasia about a pole of rotation at 39 24 n 98 2 e 0 539 myr 1 and 16 18 mm yr of shortening is accommodated across the west central tien shan there is distributed e w extension throughout both southern and north central tibet within southern tibet between the longitudes of 77 e to 92 e the deformation field accommodates 16 19 mm yr of e w extension we compare predicted seismic moment rates with those observed in this century in asia total observed seismic moment rates within the entire area of central and east asia 2 2 107 km2 in this century are 2 26 0 7 1020 n m yr 1 as compared with a predicted total rate of 2 03 0 066 1020 n m yr 1 comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long term seismic moment rates from a catalog of limited duration 94 years an observation period of 10 000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates inferred from the joint inversion of gps and quaternary rates of strain we show that in general a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude mb 5 0 for the period january 1 1965 to january 1 1999

topographic advection on fault bend folds inheritance of valley positions and the formation of wind gaps drainage basins formed along the flanks of any individual linear mountain range or fault block are commonly observed to be self similar in planform uniformly spaced and in some cases aligned with drainage basins on the opposing flank data from the siwalik hills nepal illustrate this organization where drainage basins and valleys are aligned across the main divide we suggest that valley alignment is a consequence of advection of topography across the divide to explore this hypothesis numerical experiments were conducted using a landscape evolution model of a fault bend fold that simulates detachment limited stream incision and linear hillslope diffusion results show that the presence of incised valleys and a lateral component of bedrock motion are necessary and sufficient conditions for advection of relief across the divide a mechanism by which wind gaps form and valley spacing on the far side of a ridge is inherited from that on the near side this topographic inheritance is promoted by low rock erodibility low precipitation rates fast bedrock velocities and or intermediate fault dips

deformation of an experimental drainage network in oblique collision in oblique collision settings parallel and perpendicular components of the relative plate motion can be partitioned into different structures of deformation and may be localized close to the plate boundary or distributed on a wider region in the southern alps of new zealand it has been proposed that one third of the regional convergence is distributed in a broad area along the southern alps orogenic wedge to better document and understand the regional dynamics of such systems reliable markers of the horizontal tectonic motion over geological time scales are needed river networks are able to record a large amount of distributed strain and they can thus be used to reconstruct the mode and rate of distribution away from major active structures to explore the controls on river resilience to deformation we develop an experimental model to investigate river pattern evolution over a doubly vergent orogenic wedge growing in a context of oblique convergence we use a rainfall system to activate erosion sediment transport and river development on the model surface at the end of the experiment the drainage network is statistically rotated clockwise confirming that rivers can record the distribution of motion along the wedge image analysis of channel time space evolution shows how the fault parallel and fault perpendicular components of motion decrease toward the fault and impose rotation to the main trunk valleys however rivers do not record the whole imposed rotation rate which suggest that the natural lateral channel dynamics can alter the capacity of rivers to act as passive markers of deformation

spatial heterogeneity of high resolution chalk groundwater geochemistry underground quarry at saint martin le noeud france chalk groundwater is an important aquifer resource in france because it accounts for a production of 12 million m3 y 1 with a large proportion reserved for drinking water processes occurring in the unsaturated zone uz and the overlying superficial formations have a high impact on chalk groundwater geochemistry and require better understanding the study site is a former underground chalk quarry located near beauvais france that extends over 1200 m in length at a depth ranging from 20 to 30 m the water table intersects the cavity creating 15 underground lake that give access to the chalk groundwater lakes geochemistry has been studied water samples were collected in july 2013 and major ion concentrations were analyzed uz and clay with flints thickness above each lake were estimated qualitatively using an electromagnetic sensor em31 and underground gps the results unexpectedly showed that groundwater quality varied widely in spatial terms for both allochthonous and autochthonous ions e g hco3 ranged from 2 03 to 4 43 meq l 1 no3 ranged from 0 21 to 1 33 meq l 1 principal component analysis indicated the impact of agricultural land use on water quality with the intake of no3 as well as so42 cl and ca2 chalk groundwater geochemistry is compared with the nature and structure of the uz we highlight correlations 1 between thick clay with flints layers and the ions mg2 and k and 2 between uz thickness and na in conclusion this paper identifies various ion sources agriculture clay with flints and chalk and demonstrates different processes in the uz dissolution ionic exchange and solute storage

present day kinematics of the eastern california shear zone from a geodetically constrained block model we use global positioning system gps data from 1993 2000 to determine horizontal velocities of 65 stations in eastern california and western nevada between 35 and 37 n we relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km the velocity of the sierra nevada block with respect to nevada is 11 1 0 3 mm yr with slip partitioned across the death valley 2 8 0 5 mm yr panamint valley 2 5 0 8 mm yr and airport lake owens valley 5 3 0 7 4 6 0 5 mm yr faults the western mojave block rotates at 2 1 0 8 my clockwise with 3 7 0 7 mm yr of left lateral motion across the western garlock fault we infer 11 2 mm yr of right lateral motion across the mojave region of the eastern california shear zone

is stoping a volumetrically significant pluton emplacement process magmatic stoping is widely called upon to explain discordant pluton contacts but several lines of evidence indicate that stoping is not volumetrically significant in the emplacement of most plutons first xenoliths rarely make up more than a few percent of most plutons this sparseness even on well exposed pluton floors argues that few xenoliths make it into plutons second piles of rock fragments have sufficiently high porosities 50 that a significant accumulation of stoped blocks on the floor of a magma chamber would trap much if not all of the available magma producing pluton scale magmatic breccias that are not observed third although settling calculations show that large meter scale or larger xenoliths could sink rapidly in magma natural fragmentation processes are likely to produce a fractal distribution of particle sizes with small particles far more abundant than large ones the absence of small xenoliths at pluton contacts where magma cools most rapidly thus argues against stoping fourth although contamination of magmas by anatectic liquids derived from wall rocks and xenoliths is common geochemical data from many plutons clearly rule out significant bulk assimilation of local wall rocks finally there is growing evidence that at least some large plutons never were large molten bodies of magma but grew incrementally stoping cannot be volumetrically important in incrementally emplaced plutons because blocks can only fall through the volume that is molten at any given time where xenoliths are abundant in plutons they may commonly represent isolation of wall rock bodies between successive intrusive increments rather than wall rock fragments that were engulfed by magma however even xenoliths that were engulfed by magma did not necessarily sink from the roof of a magma chamber although stoping undoubtedly occurs during the emplacement of some plutons it is unlikely to be a volumetrically significant process

plagioclase zonation styles in hornblende gabbro inclusions from little glass mountain medicine lake volcano california implications for fractionation mechanisms and the formation of composition gaps the rhyolite of little glass mountain 73 74 sio2 is a single eruptive unit that contains inclusions of quenched andesite liquid 54 61 sio2 and partially crystalline cumulate hornblende gabbro 53 55 sio2 based on previous studies the quenched andesite inclusions and host rhyolite lava are related to one another through fractional crystallization and represent an example of a fractionation generated composition gap the hornblende gabbros represent the cumulate residue associated with the rhyolite producing and composition gap forming fractionation event this study combines textural nomarski differential interference contrast ndic imaging major element an content and trace element mg fe sr k ti ba data on the style of zonation of plagioclase crystals from representative andesite and gabbro inclusions to assess the physical environment in which the fractionation event and composition gap formation took place the andesite inclusions 54 61 sio2 are sparsely phyric with phenocrysts of plagioclase augite and fe oxide olivine orthopyroxene hornblende set within a glassy to crystalline matrix the gabbro cumulates 53 55 sio2 consist of an interconnected framework of plagioclase augite olivine orthopyroxene hornblende and fe oxide along with highly vesicular interstitial glass 70 74 sio2 the gabbros record a two stage crystallization history of plagioclase olivine augite stage i followed by plagioclase orthopyroxene hornblende fe oxide stage ii texturally the plagioclase crystals in the andesite inclusions are characterized by complex fine scale oscillatory zonation and abundant dissolution surfaces compositionally an content the crystals are essentially unzoned from core to rim these features indicate growth within a dynamic convecting reservoir of andesite magma in contrast the plagioclase crystals in the gabbros are texturally smooth and featureless with strong normal zonation from an74 at the core to around an30 k and ba abundances increase and mg abundances decrease steadily towards the rim ti fe and sr abundances increase and then decrease towards the rim the trace element variations are fully consistent with the two stage crystallization sequence inferred from the gabbro mineralogy these results indicate progressive closed system in situ crystallization in a quiescent magmatic boundary layer environment located along the margins of the andesite magma body the fractional crystallization that generated the host rhyolite lava is one of inward solidification of a crystallizing boundary layer followed by melt extraction and accumulation of highly evolved interstitial liquid this mechanism explains the formation of the composition gap between parental andesite and rhyolite magma compositions

direct observation of deformation processes in crystal mushes isothermal microstructural development in deforming melt bearing crystal mushes is studied using synkinematic microscopy and a polyphase thiocyanate system the aim of the work is to contribute to the basis for understanding the origin of microstructures in rocks which have undergone melt present deformation during high strain rate pure shearing experiments microstructures indicating crystal plasticity and dynamic recrystallization are observed during low strain rate pure shearing experiments a pressure solution like process called contact melting is active resulting in optically strain free crystals crystal boundary sliding is active in both regimes framework scale processes such as filter pressing grain flow and development of a micro shear zone are illustrated some of these processes are cryptic microstructurally and may be difficult or impossible to recognize in rocks the validity of the experimental system as an analog for magmatic systems is discussed we conclude that the experiments can serve as a source of ideas to test against the evidence from rocks but that no direct analogy to the behavior of natural crystal mushes has been or will readily be established

magmatic stratigraphy of the tilted tottabetsu plutonic complex hokkaido north japan magma chamber dynamics and pluton construction abstract the steeply tilted tottabetsu plutonic complex tpc provides an exceptional cross sectional view of a frozen felsic magma chamber the entire pluton is apparently cylindrical in shape but the active magma chamber at any one time was much thinner tabular in shape the pluton is stratified with a topmost granitic unit zone iii an underlying dioritic unit zone ii and a lowermost gabbroic unit zone i field petrographic and geochemical data suggest that zones i and ii developed at the aggrading floor of a felsic magma chamber only part of zone iii appears to have crystallized from the roof successive stoping events recorded as included country rock blocks in zones i and ii apparently prohibited growth of the roof solidification zone the complex record of hotter replenishments and fractional crystallization is preserved in the stratigraphy of zones i and ii as either alternating comagmatic sheets and cumulate layers or an upward fractionation trend with a major compositional reversa

distorted drainage basins as markers of crustal strain east of the himalaya extensive lithospheric deformation on the eastern margin of the india eurasia collision has brought three major rivers into exceptionally close proximity for over 300 km the salween mekong and yangtze rivers are only tens of kilometers apart 10 times closer than rivers of comparable length elsewhere in the world we view deeply incised river valleys as displacement markers that move with the underlying crust over time scales of at least tens of millions of years accordingly the close spacing of these major rivers and their nearly parallel trends reflect the large crustal strains near the eastern himalayan syntaxis these river characteristics are consistent with two primary phases of deformation in this tectonic setting ne sw shortening of 0 5 oriented radially from the eastern syntaxis followed by dextral shear strain of 6 1 along a north trending zone pervasive shearing of this magnitude throughout the 150 km wide region of anomalous drainage would account for 1000 km of northward motion of india relative to southern china directly east of this region another 1000 km of northward motion is likely to have been accommodated by pervasive shearing through a zone hundreds of kilometers wide finally we draw attention to the remarkable accord between the arcuate paths of each of the three great rivers in the broader southeastern tibet region and small circles that curve around the eastern himalayan syntaxis

modelling the effects of climate change and its uncertainty on uk chalk groundwater resources from an ensemble of global climate model projections projections of climate for the 2080s from an ensemble of global climate models gcms run under a medium high a2 emissions scenario are used to simulate changes in groundwater resources of a chalk aquifer in central southern england few studies that have investigated the impacts of climate change on groundwater resources have addressed uncertainty in this paper the uncertainty associated with use of a suite of gcm outputs in catchment scale impact studies is quantified a range of predictions is obtained by applying precipitation and temperature change factors derived from thirteen gcms to a distributed recharge model and a groundwater flow model of the chalk aquifer of the marlborough and berkshire downs and south west chilterns in the uk the ensemble average suggests there will be a 4 9 reduction in annual potential groundwater recharge across the study area although this is not statistically significant at the 95 confidence level the spread of results for simulated changes in annual potential groundwater recharge range from a 26 decrease to a 31 increase by the 2080s with ten predicting a decrease and three an increase whilst annual recharge is not found to change significantly the multi model results suggest that the seasonal variation in the groundwater resource will be greater with higher recharge rates during a reduced period of time in winter the spread of predictions for changes in river baseflow at the bottom of the largest river sub catchment is from 16 to 33 in march and from 68 to 56 in october the effects of climate change are shown to depend significantly on the type of land use it is concluded that further research is required to quantify the effect of different vegetation types on chalk covered by different thicknesses of soil and their response to a changing climate

contrasting stratified plutons exposed in tilt blocks eldorado mountains colorado river rift nv usa abstract roof to floor exposures of mid miocene plutons in tilt blocks south of las vegas nv reveal distinct but strongly contrasting magma chamber statigraphy the searchlight and aztec wash plutons are well exposed stratified intrusions that show a similar broad range in composition from 45 75 wt sio 2 homogeneous granites that comprise about one third of each intrusion are virtually identical in texture and elemental and isotopic chemistry mafic rocks that are present in both plutons document basaltic input into felsic magma chambers isotopic compositions suggest that mafic magmas were derived from enriched lithospheric mantle with minor crustal contamination whereas more felsic rocks are hybrids that are either juvenile basaltic magma crustal melt mixtures or products of anatexis of ancient crust young mesozoic or miocene mafic intraplate despite general similarities the two plutons differ markedly in dimensions and lithologic stratigraphy the searchlight pluton is much thicker 10 vs 3 km and has thick quartz monzonite zones at its roof and floor that are absent in the aztec wash pluton isotopic and elemental data from searchlight pluton suggest that the upper and lower zones are cogenetic with the granite we interpret the finer grained slightly more felsic upper zone to represent a downward migrating solidification front and the lower zone to be cumulate in contrast the upper part of the aztec wash pluton is granite and a heterogeneous mafic rich injection zone with distinct isotopic chemistry forms the lower two thirds of the intrusion similar mafic rocks are relatively sparse in searchlight pluton and do not appear to have played a central role in construction of the pluton large felsic and composite dikes that attest to repeated recharging and intrachamber magma transfer are common in the aztec wash pluton but absent in the searchlight pluton thus although both intrusions were filled by similar magmas and both developed internal stratification the two intrusions evolved very differently the distinctions may be attributable to scale and resulting longevity and or to subtle differences in tectonic setting

structural criteria for identifying granitic cumulates abstractcumulates are igneous rocks that reflect relative concentration of crystals and or loss of melt and that therefore did not crystallize entirely from a magma of their current whole rock composition however this definition does not help to identify cumulates and so the problem is to determine whether the current whole rock composition reflects cumulate processes which is where structural criteria can be useful identification of cumulates in granitoids can be difficult especially in the absence of major whole rock compositional differences between cumulate and host structural and structural mineralogical criteria diagnostic of or at least consistent with granitic cumulates include 1 locally high concentrations of particular minerals relative to concentrations in the bulk of the intrusion 2 abundant euhedral crystals in contact at least with regard to cores that touched before any overgrowths and consequent molding of minerals about each other occurred 3 abundant antecrysts or mantle

how extensive are subsolidus grain shape changes in cooling granites abstract the hypothesis that granites sensu lato commonly undergo extensive grain shape changes recrystallization during cooling is not supported by microstructural evidence especially the abundance of non truncated zoning patterns in mineral grains regional metamorphic felsic gneisses that have undergone extensive neocrystallization recrystallization at amphibolite facies conditions which some have suggested are equivalent to those in slowly cooling granites typically lose igneous microstructures including oscillatory zoning and are characterized by polygonal to irregularly xenoblastic grains of quartz and feldspar as well as by rounded inclusions of quartz in feldspar and vice versa in contrast granites typically show oscillatory zoning especially in plagioclase elongate euhedral to subhedral feldspar grains and euhedral plagioclase inclusions in quartz and k feldspar the contrast between these two situations is probably the result of felsic gneisses undergoing chemical reactions and regional deformation especially in the presence of water released pervasively from dehydration reactions which are strong driving forces for the production of new grains whereas the minerals in cooling granites are chemically compatible without strong deformation and so do not react with each other or recrystallize therefore massive granites without solid state foliations generally do not undergo grain shape changes owing to inadequate driving forces as well as to decreasing temperature an important implication of this conclusion is that internal structures formed during chamber construction and magmatic flow in granite plutons are not likely to be removed by subsolidus intergranular microstructural changes

geomorphic constraints on the active tectonics of southern taiwan summary taiwan is a region of rapid active tectonics yet the study of the tectonic processes that shape the interior of the island is difficult due to the high rates of erosion and dense vegetation we use digital topography to look for indications of active deformation preserved in the local geomorphology in particular anomalies in the regional pattern of drainage are used to infer zones of enhanced tectonic activity the apparent anticlockwise rotation of major river systems in plan view indicates the presence of a diffuse zone of left lateral shear running down the southeastern side of taiwan asymmetries in the catchments of individual drainage basins show the influence of varying rates of uplift across southern taiwan with the most rapid uplift close to taitung at the indentation point of the luzon arc with the chinese continental margin our interpretations though based predominantly on remote sensing observations are consistent with the available field evidence this study demonstrates the usefulness of drainage basins as tectonic markers in the quantification of regional strain and uplift which may have wider applicability in other deforming parts of the world

cathodoluminescence and micro structural evidence for crystallisation and deformation processes of granites in the eastern lachlan fold belt se australia trace elements al k ti fe growth and deformation pattern in quartz of the multiple deformed carcoar barry and sunset hills granites were investi gated by electron micro probe and cathodolumines cence zoned quartz phenocrysts with high ti concentrations 70 ppm that show blue cathodolu minescence originated from the early stage of magma crystallisation multiple deformation of quartz causes the redistribution of al and k in the quartz lattice which results in the accumulation of these elements in submicroscopic inclusions 0 5 lm of muscovite like composition in contrast structural ti in quartz is mostly kept in the lattice common halos of defect poor secondary quartz around fluid inclusions result from re equilibration of fluid inclusions because of differences between fluid pressure and lithostatic pressure e g duringuplift isothermal decompression and or a b transition of quartz duringhealing defect poor sec ondary quartz grows at the cost of the host quartz and releases or replaces defect centres the results of micro structural investigations combined with al in horn blende thermobarometry allow the reconstruction of regional processes carcoar and barry granodiorites and sunset hills granite were intruded in the late ordovi cian early silurian at depths of 4 8 6 and 10 12 km respectively in contrast to the continuous crystallisation of the granodiorite magmas the magma of the sunset hills granite ascended in a stepwise fashion causing multiple quartz nucleation the two granodiorites were multiple post magmatically deformed first during early devonian under more brittle conditions at temperatures of 350 400 c whereas the sunset hills granite experienced more ductile deformation at tem peratures of around 550 c

shape and microstructure of microgranitoid enclaves indicators of magma mingling and flow abstract at tarandore point 328 km south of sydney new south wales australia two tonalite phases are in contact with a gabbroic diorite all belonging to the moruya batholith lobate to crenulate contacts pillowing of the more mafic phase in the more felsic phase net veining of the more mafic phase by the more felsic local chilling of the more mafic phase against the more felsic and an abundance of rounded to elongate microgranitoid enclaves all suggest mingling of magmas at the site of emplacement therefore all phases were emplaced before the others solidified and an order of intrusion cannot be determined the variety of microgranitoid enclaves suggests that repeated magma mingling has occurred linear geochemical trends indicate either magma mixing or restite unmixing as a prime cause of variation in the members of the moruya suite of granitoids direct evidence of mixing is not present but evidence that the magmas were substantially liquid at the time of emplacement sugests that mixing is possible restite unmixing is unlikely to be the prime process because near minimum melts which would occur in all granitoid phases according to that model should mix easily rather than mingling in fact mingling has occurred between tonalite phases of very similar composition which would not be expected if the liquid parts of enclaves were minimum melts available experimental and theoretical data on mixing in both magma chambers and conduits cannot be applied directly to the occurrence at tarandore point owing to inadequately constrained parameters but mixing generally should be favoured by higher temperatures which is consistent with our inference that relatively high proportions of melt were present in the granitoid phases at the time of emplacement conduit mixing may be reflected in a local zone of strong to extreme elongation of enclaves in which the distortion has been accomplished by magmatic flow without solid state deformation as evidenced by strong dimensional preferred orientations coupled with a lack of microstructural evidence of intragranular plastic strain this suggests that elongate enclaves should not be used as indicators of solid state deformation or as tectonic strain markers without microstructural evidence that suitably strong intracrystalline plastic deformation has taken place

provenance interpretation of quartz by scanning electron microscope cathodoluminescence fabric analysis we used a cathodoluminescence cl detector attached to a scanning electron microscope sem to study patterns of variable intensity cl in quartz grains from a variety of igneous metamorphic sedimentary and shock deformed meteorite impact rocks distinctive fabrics in quartz grains revealed by sem imaged differential cl include zoning healed fractures complex shears planar features shocked quartz dark cl streaks and patches indistinct mottled texture and nondifferential low contrast cl zoning is common in volcanic quartz and some plutonic quartz zoned plutonic quartz is distinguished from volcanic quartz by the presence of closed fractures and dark cl streaks and patches metamorphic quartz displays either an indistinct mottled texture or nearly uniform nondifferential cl quartz from rocks severely deformed by tectonism displays a complex pattern of multiple small scale shears quartz from meteorite impact sites and some system boundaries is characterized by intricate patterns of planar features presumably created by shock metamorphism thus the sem cl fabric analysis technique provides a rapid method for distinguishing quartz from a variety of source rocks

long term holocene groundwater fluctuations in a chalk catchment evidence from rock eval pyrolysis of riparian peats he depositional history of peat dominated wetlands can be used to understand palaeoclimate and palaeohydrology and also constrain the impacts of future climate change however in chalkland valleys seasonal water table fluctuations and a high alkalinity have diminished key environment indicators such as pollen and there is a need for alternative investigative techniques the method of rock eval pyrolysis can track changes in organic matter source and degradation potentially relating to historic changes in vegetation cover this is the first rock eval on cores from a groundwater dependent riparian chalk valley wetland combined with radiocarbon dating the dating showed that the cores represented approximately 4000 years of depositional history changes in hydrocarbon chemistry including normal alkane composition of the peat indicated shifts of around 500 to 1000 years between terrestrial and more aquatic species relating to periods of climate wetness these climatic shifts are broadly consistent with other evidence from ombrotrophic peatland and lacustrine sediments across northwest europe however the connection between climate wetness and groundwater dependent chalkland wetlands is complicated by external anthropogenically driven factors relating to land use and vegetation cover changes in the catchment nonetheless this study suggests that rock eval pyrolysis is a useful and cost effective tool that can provide evidence for long term holocene groundwater fluctuations

mafic injections in situ hybridization and crystal accumulation in the pyramid peak granite california located in the northern sierra nevada the middle jurassic pyramid peak granite and associated dioritic rocks display superbly exposed interlayered sheets of mafic felsic and hybrid rocks the mafic hybrid layers show a consistent asymmetry sharply chilled on one side and gradational through hybrids to granite on the other and dip to the southwest load casts and silicic pipes along the chilled mafic northeastern margins of the sheets indicate that depositional way up is to the southwest and that the adjacent mount tallac roof pendant was the original floor of the intrusion orientations of the pipes indicate that the layers were tilted after deposition and solidification we interpret the sheets to be intramagmatic flows that formed by injections of mafic magma into a silicic magma chamber followed by flow across the crystal rich base of that chamber the granitic and hybrid rocks interlayered with the mafic sheets represent material that accumulated on the chamber floor between episodes of mafic replenishment most contamination of the mafic sheets probably occurred because of flow front instabilities generated as the mafic magma entered and spread across the chamber floor the upward gradation from diorite to granite with decreasing abundance and size of mafic enclaves can best be explained by convective stirring at the upper boundaries of the dioritic replenishments the pyramid peak granite was probably initiated as a thin concordant sheet intruding into gently dipping jurassic supracrustal rocks the pluton was constructed incrementally with many replenishments of felsic and mafic magma and dominantly solidified by accumulation of crystals on the floor of the chamber the present steep dips of the layers suggest that downward warping of the chamber floor may have been a factor in accommodating the incrementally constructed pluton

the spatial distribution of groundwater flooding in a chalk catchment in southern england groundwater flooding occurred in the upper parts of many chalk rivers in the uk during the exceptionally wet winter of 2000 01 this provided a rare opportunity to investigate the spatial distribution of groundwater discharge and flooding along the normally dry intermittent headwaters of a chalk catchment the extent of flooding along the river pang upstream of the seasonal head was mapped using aerial photography and point measurements of flow and water temperature were used to identify the contributing reaches of the river the results are discussed in the context of the geological and groundwater conditions the occurrence of flooding can largely be explained by the regional groundwater flow directions but increased flow in some locations may be as a result of preferential groundwater flow along lines of geological structure published by john wiley sons ltd

grain scale processes in actively deforming magma mushes new insights from electron backscatter diffraction ebsd analysis of biotite schlieren in the jizera granite bohemian massif abstract in the porphyritic jizera granite bohemian massif three distinct types of lattice preferred orientations of biotite grains were revealed in schlieren delineated magmatic structures using the electron backscatter diffraction ebsd method 1 biotite basal planes 001 reorient from schlieren subparallel near the schlieren base to schlieren perpendicular in the upper part of the schlieren both orientations share subhorizontal n s to nne ssw trending a axes 2 in some domains the a axes are steep and at a high angle to the schlieren plane while the c axes plunge shallowly and rotate around an ill defined a axis 3 in other domains the ebsd coincides with background magnetic fabric of the host granite revealed using the anisotropy of magnetic susceptibility ams method that is the a axes plunge shallowly to the se or nw while the c axes are subhorizontal and cluster around the ne sw trend these multiple biotite orientations in the schlieren are interpreted to reflect 1 velocity gradient in laminar magma flow along channel like conduits localized within the high strength host phenocryst framework 2 grain scale gravity driven constrictional deformation of the magma mush and 3 overprinting background tectonic deformation transmitted across large parts of the magma chamber prior to its final crystallization the grain scale mechanisms of biotite fabric acquisition in the schlieren presumably involved rotation of biotite crystals during flow with the biotite alignment reflecting the flow geometry and kinematics replaced after flow cessation by melt aided grain boundary sliding of those biotite crystals still enclosed in melt pockets within otherwise static highly crystallized magma mush the latter process was sufficient to reorient biotite grains but not to cause destruction of the schlieren using the jizera granite as a case example we argue that the lattice preferred orientation of mineral grains in mafic schlieren is highly sensitive to reorient in response to processes both associated with the schlieren formation e g localized magma flow and those that occur later and are superimposed onto the effectively solid high strength magma mush

the origin of laminated and massive anorthosite sept iles layered intrusion quebec canada well laminated plagioclase rich rocks anorthosite occur as layers in mineralogically similar but massive rocks in the sept iles intrusion several phases of crystallization of poikilitic clinopyroxene have preserved the intermediate stages in the production of these rocks plagioclase nucleated and initially grew in random orientations in the stationary part of the boundary layer there in the absence of other events crystallization produced the massive anorthosite the laminated anorthosite may have been produced by episodic increases in the velocity of the magma adjacent to the boundarylayer induced by magmatic density currents such currents would have caused the zone of simple shear of the boundary layer to migrate outwards into the previously stationary part this simple shear would then have rotated the existing plagioclase crystals as well as crystals that nucleated at that time towards the shear plane some rocks show evidence of several periods of enhanced flow velocities the production of the lamination may have weakened the crystal mush and enabled slumping to occur producing folds and contorted layers finally compaction liberated large quantities of intercumulus magma of which some was trapped as granophyric segregations and some escaped by overturing and churning the crystal pile earlier formed granophyric segregations and laminated layers were disrupted during this process to produce a range of more complex rocks including igneous breccias

field chemical and physical constraints on mafic felsic magma interaction in the lamarck granodiorite sierra nevada california evidence of magma interactions resulting in both hybridization and mingling are preserved in a diverse suite of gabbroic to intermediate rocks associated with the compositionally zoned hornblende biotite lamarck granodiorite of the eastern sierra nevada california ellipsoidal mafic enclaves were formed by quenching of small amounts of high alumina basaltic magma upon injection into and dispersal through granodiorite magma early in its crystallization synplutonic intrusions of hornblende gabbro through hybridized mafic granodiorite represent injection of mafic magma at a later stage of crystallization of the granodiorite as they crosscut regional trends in foliation and compositional zoning in the host pluton where compositional contrasts between intrusion and host granodiorite are large contacts are sharp and abundant enclaves derived from the mafic intrusion are present in the granodiorite where the host is relatively mafic or where the local scale proportion of mafic magma is large contacts are zones of extensive hybridization that contain both enclaves and hybrid schlieren uncontaminated mafic intrusions have high alumina basaltic compositions whereas hybridized intrusions have silica contents as high as 63 5 mafic intrusions locally contain coarse grained cumulus gabbro inclusions mafic schlieren in granodiorite far from mafic intrusions represent localized accumulations of hornblende fe ti oxides and biotite from the granodiorite intrusion of late mafic dikes mobilized and entrained granitic residue from the granodiorite and formed composite dikes of aplite and pillowed diorite whether interacting magmas mix or mingle is a function of the heat contents and mass fractions of the end members calculations that account for compositions heats of fusion heat capacities of liquids and crystals and a range of initial temperatures crystallinities crystal sizes and magma water contents indicate that in most circumstances the basalt end member quenches the resulting large viscosity contrast between the end members prevents hybridization homogenization is likely only if the compositional difference between host and injected mafic magma is less than 10 sio2 or if the mass fraction of mafic magma is greater than 0 5 resulting mixtures have the composition of tonalite or mafic granodiorite thus the more silicic rocks of the granodiorite pluton must represent differentiation products rather than direct hybrids of mafic or intermediate magma and felsic magma

right lateral shear and rotation as the explanation for strike slip faulting in eastern tibet the convergence of two continents can be accommodated by crustal thickening and by lateral transport of crust out of the path of the converging continents1 3 the principal features suggesting that lateral transport is important are major strike slip faults striking roughly orthogonally to the orientation of convergence between the continents displacement on such faults is imagined to allow lateral transport of material with respect to the converging continents possibly accounting for a large fraction of the convergence between the two continents the most spectacular example of such strike slip faulting is in the eastern part of the tibetan plateau where three major left lateral faults with slip rates of 10 mm yr 1 and several smaller roughly parallel faults dominate the regional strain field2 3 cobbold and davy4 suggested that these faults may be rotating in a clockwise fashion here we put bounds on that rate of rotation and conclude that the image of lateral transport on such faults2 known also as continental escape extrusion or expulsion is an illusion and that instead the left lateral slip on east striking planes in eastern tibet is a manifestation of north striking right lateral simple shear if this conclusion is correct the east striking left lateral faults and the crustal blocks between them are rotating clockwise at 1 2 myr 1 the east west dimension of eastern tibet is shortening at 10 20 mm yr 1 and little material is moving eastward out of india s path into eurasia by left lateral simple shear

hydrological processes in the chalk unsaturated zone insights from an intensive field monitoring programme as part of the nerc lowland catchment research programme locar the pang lambourn catchments berkshire uk have been extensively instrumented to provide an improved understanding of the hydrological processes in the unsaturated zone of the chalk a subject of much debate over the past 30 years to quantify the movement of water through the unsaturated zone it is necessary to measure matric potential and water content as well as input and output fluxes from precipitation evapotranspiration and groundwater recharge previous studies have indicated the need for fine temporal resolution data to monitor this system effectively due to the challenges faced in meeting this objective a monitoring scheme was designed that combines a variety of instrumentation to provide the required range accuracy and spatial and temporal resolution of data this paper firstly presents an overview of the monitoring programme and a critical discussion of the instrumentation used subsequently the field data are used to characterise the hydrological properties of the unsaturated zone and to gain insight into recharge processes the interpretation of the data presented in this paper indicate that in the chalk unsaturated zone at west ilsley matrix flow is the dominant recharge mechanism

pyroxene oikocrysts in troctolitic cumulates evidence for supercooled crystallisation and postcumulus modification studies of pyroxene oikocrysts in plagioclase olivine cumulates crystallised from high alumina olivine tholeiite magmas in layered intrusions inferred to represent periodically replenished magma chambers show that small plagioclases enclosed within the oikocrysts differ significantly from plagioclases in the host rock plagioclases within oikocrysts are very elongate with a high surface area show extensive mutual attachment at high angles resembling skeletal growth and tend to be randomly orientated some are rounded and embayed are reversely zoned and more sodic by an 5 10 than some of the plagioclase in the host rock plagioclase crystal centres tend to be closer spaced in the oikocrysts than in the host rock in contrast plagioclases in the host rock are discrete coarser grained less elongate strongly aligned and locally polygonised

basaltic pillow mounds in the vinalhaven intrusion maine the vinalhaven intrusion is a dominantly granitic pluton of probable devonian age located on vinalhaven island and adjacent islands maine it consists of four main units coarse grained granite fine grained granite a gabbro diorite unit consisting of interlayered mafic hybrid and granitic rocks and a heterogeneous granitic unit the gabbro diorite unit occurs along the south and east coast of the island as a sheet like body hundreds of meters to more than 1 km thick that dips beneath the central granitic units and rests on heterogeneous granitic rocks that form the base of the intrusion and are exposed on islands to the southeast load cast and pipe structures at the bases of mafic sheets indicate that the gabbro diorite unit represents a sequence of basaltic injections that ponded on crystal rich mush at the base of a silicic magma chamber and variably interacted with overlying crystal poor granitic magma the pluton therefore represents a fossilized silicic magma chamber that was periodically replenished by basaltic magma near the base of the gabbro diorite unit some basaltic injections produced large mounds up to more than 10 m high and 100 m wide of tightly packed meter scale chilled basaltic pillows tubes and sheets in a granitic matrix the mounds appear to represent flow fronts of basaltic injections that entered and ponded on the floor of a silicic magma chamber although physical conditions differ significantly these plutonic pillow mounds appear to share many characteristics with submarine pillow basalts and lava flows

factors governing the textural development of skaergaard gabbros a review abstract recent work has shown that the nomenclature and earlier interpretations of cumulates no longer provide an adequate conceptual framework for understanding basic plutonic rocks most of the rocks have undergone extensive recrystallization and no longer preserve their original textures compositions or modal proportions depending on the conditions governing these metasomatic changes they can produce a wide variety of effects we still have much to learn but with the abundant evidence available in well studies bodies like the skaergaard intrusion it should be possible to reach a better understanding of the late stage processes that have had such pervasive effects on mafic layered intrusions