role of crustal contamination in heterogeneous archean volcanics from the leonora region western australia abstract archean supracrustal volcanic successions in the leonora laverton region of the eastern goldfields province western australia are subdivided into two stratigraphic associations 1 an early succession ten km thick containing homogeneous high ti tholeiite basalts displaying nearly flat chondrite normalized incompatible lithophile element patterns with la sm n ratios ranging from 0 88 to 1 12 and 2 an unconformably overlying heterogeneous succession four km thick consisting of a early siliceous low ti tholeiites and associated intermediate calc alkaline volcanics grading to b high ti tholeiite similar to those of association 1 and c late siliceous high mg spinifex textured basalts fractionation models and trace element distribution in high ti basalts suggest that all the flows were derived from similar but not identical parental magmas and that subvolcanic gabbroic fractionation was characteristic basaltic end members of the siliceous low ti suite had identical fractionation patterns but hornblende joined the assemblage in contaminated intermediate calc alkaline members producing low hree fractionates the siliceous basalts exhibit variable enrichment in large ion lithophile lile and light rate earth lree elements with a continuum of la sm n ratios up to 2 75 they also have marked negative anomalies for nb p and ti several samples also exhibit a positive anomaly for zr on normalized distribution diagrams low sr concentrations are inconsistent with mantle enrichment processes and compositions of siliceous volcanics are explained instead by up to 30 contamination of high ti tholeiite liquids by archean crust composed of hornblende tonalite gneiss geochemistry of the volcancis is consistent with eruption in a continental back arc basin tectonic setting

evolution study of a regional groundwater system using hydrochemistry and stable isotopes in songnen plain northeast china groundwater is often a critical source of water for municipal industrial and agricultural uses especially in arid and semi arid environments songnen plain located in the central part of northeast china is such a region it being an important productive base of commodity grain in this country in the past two decades groundwater quality in the region especially salinization has deteriorated under natural changes and human activities and has become a crucial factor restricting sustainable eco environmental and socio economic development in this paper the taoer river catchment situated in the middle of the region was selected as the study area for the groundwater quality evolution study using hydrochemistry and stable isotopes to obtain a better understanding of the system fifty two groundwater samples were collected with systematic design during the low water and high water periods in 2003 a series of comprehensive quality data interpretations e g statistics ratios of ions and piper diagrams together with stable isotope data have been used to gain an insight into the spatial and temporal variations and evolution laws of groundwater hydrochemistry the following main hydrochemical processes were identified as controlling the water quality of the groundwater system weathering dissolution evaporation condensation ion exchange reactions and groundwater salinization this latter process salinization is the most important process and is caused by the leaching of superficial or near surface salts from the saline alkaline soil into shallow groundwater

significance of ferrodioritic liquids in magma mixing processes a general model to explain the various igneous associations found in mixed magma intrusives and extrusives belonging to high level volcanic centres is presented this model is based on detailed mapping in the british tertiary volcanic centre on skye which suggests that basic and acid magmas were continually available throughout its development new major and trace element data from these rocks indicate that they were co genetic and that the basic magmas which combined with acid magmas to produce hybrid magmas were ferrodioritic in composition and not basaltic as had previously been thought

hydrochemical characteristics and salinity of groundwater in the ejina basin northwestern china a hydrochemical investigation was conducted in the ejina basin to identify the hydrochemical characteristics and the salinity of groundwater the results indicate that groundwater in the area is brackish and are significantly zonation in salinity and water types from the recharge area to the discharge area the ionic ration plot and saturation index si calculation suggest that the silicate rock weathering and evaporation deposition are the dominant processes that determine the major ionic composition in the study area most of the stable isotope 18o and d compositions in the groundwater is a meteoric water feature indicating that the groundwater mainly sources from meteoric water and most groundwater undergoes a long history of evaporation based on radioactive isotope tritium 3h analysis the groundwater ages were approximately estimated in different aquifers the groundwater age ranges from less than 5 years between 5 years and 50 years and more than 50 years within 1 km of the river water influence zone the groundwater recharges from recent heihe river water and the groundwater age is about less than 5 years in shallow aquifer from 1 km to 10 km of the river water influence zone the groundwater sources from the mixture waters and the groundwater age is between 5 years and 50 years in shallow aquifer the groundwater age is more than 50 years in deep confined aquifer

stratigraphic evolution of the late holocene ganges brahmaputra lower delta plain sediment cores from the ganges brahmaputra delta in bangladesh were examined for sedimentological character clay mineralogy elemental trends c n s and 14c geochronology to develop a model for the sedimentary sequence resulting from lower delta plain progradation in the late holocene a widespread facies succession from muddy sand to interbedded mud records progradation of shoal island complexes and the transition from subtidal to intertidal conditions mangrove vegetated islands and peninsulas represent the final phase of progradation a mottled mud that is deposited by penetration of turbid coastal water into the mangroves during high water events organic matter preservation is generally low 1 toc in most of these well drained deposits that are characterized by a permeable silt dominated granulometry clay mineralogy in the cores records the relative influence of smectite and kaolinite rich ganges sediments and illite and chlorite rich brahmaputra material the lower delta plain west of the modern river mouths was deposited as a ganges dominated delta in three phases since 5000 cal years bp with brahmaputra influence confined to the meghna estuary area and to the supratidal section of western delta deposits evolution of the lower delta plain in the late holocene was influenced by regional subsidence patterns in the tectonically active bengal basin which controlled distributary channel avulsion and migration and the creation of accommodation space

hydrochemical and isotopic characteristics of groundwater in the yanqi basin of xinjiang province northwest china in this study hydrochemical and isotope investigations were conducted in the yanqi basin to determine the chemical composition and to gain insight into the groundwater recharge process in the yanqi basin it mainly used hydrochemistry environmental isotopes and a series of comprehensive data interpretation e g statistics ionic ratios and piper diagram to obtain a better understanding of the functioning of the system the following hydrochemical processes were identified as the main factors controlling the water quality of the groundwater system weathering of silicate minerals dissolution ion exchange and to a lesser extent evaporation which seemed to be more pronounced down gradient of the flow system as groundwater flows from the recharge to discharge areas chemical patterns evolve in the order of ca2 hco3 ca2 mg2 hco3 to ca2 mg2 cl so4 2 na k cl so4 2 and na cl according to lithology the environmental isotope 18o 2h 3h measurements further revealed that precipitation was the main recharge source for the groundwater system some local values indicated high levels of evaporation tritium and cfc analysis were used to estimate the ages of the different groundwater the tritium values of the groundwater samples varied from 2 82 to 29 7 tu the age of the groundwater at depths of 120 m is about 30 50 years cfc values obtained for six samples to determine groundwater age the age of the groundwater is about 20 50 years

strontium neodymium and lead isotopic compositions of deep crustal xenoliths from the snake river plain evidence for archean basement abstract xenoliths of intermediate to felsic granulites found in evolved lavas from the snake river plain have been analyzed for nd pb and sr isotopic compositions and related trace element contents overall they exhibit wide ranges in present day values of 87 sr 86 sr 0 70235 0 83011 143 nd 144 nd 0 51023 0 51148 and 206 pb 204 pb 13 43 24 65 the rb sr u pb th pb and sm nd decay schemes have been variably affected by granulite facies metamorphism and possibly by transport in the host magmas however pb pb and sm nd isochron systematics seemingly are preserved in many of the xenoliths and indicate essentially concordant metamorphic ages of about 2 8 ga nd model ages are significantly older ca 3 1 3 4 ga for many of the xenoliths precambrian metasediments exposed along the southern margin of the snake river plain have sm nd systematics similar to those of the xenoliths these results suggest that at least two significant thermal events occurred during archean evolution of the crust in this region a early ca 3 1 3 4 ga additions of mantle derived magmas to the crust and b regional metamorphism at 2 8 ga accompanied at least locally by magmatism concordance between the sm nd and pb pb ages suggests that these isotopic systems are little affected by high grade metamorphism in this case the distribution of xenoliths in snake river plain lavas supports the presence of archean crust beneath much of southern idaho although such rocks rarely are exposed at the surface thus nd and pb isotopic studies of crustal xenoliths can provide a useful means of determining the extent of crustal age provinces where surface exposures are lacking

continental basalts of the boise river group near smith prairie idaho the boise river group of late cenozoic age consists of basaltic lavas and intercalated fluvial and lacustrine sediments deposited in drainages of the boise river and boise river south fork from 1 8 to 0 2 m y basalts of the boise river group can be divided into two groups based on major and trace element chemistry boise river group 1 basalts brg 1 which comprise the three oldest flows in the smith prairie area are silica saturated olivine tholeiites characterized by low alkalis mg fe and ni high concentrations of high field strength elements hfse and enrichment in the heavy isotopes of sr nd and pb they are chemically similar to basalts of the snake river plain and both units probably derive from a similar enriched mantle lithosphere source some brg 1 flows long gulch rock creek record the affects of crustal assimilation and fractional crystallization boise river group 2 basalts brg 2 are all younger than brg 1 0 7 m y and are transitional between olivine tholeiites and alkali olivine basalts brg 2 basalts are characterized by high alkalis mg fe and ni lower hfse concentrations and isotopic compositions of sr and nd near bulk earth these lavas have distinct geochemical characteristics and are not cogenetic with the older brg 1 flows or with coeval lavas of the snake river plain chemical variations within individual flows are consistent with low pressure crystal fractionation of the observed phenocryst phases olivine plagioclase chemical variations between different flows within the same group cannot result from low pressure fractionation but can be modeled by combined high pressure pyroxene fractionation and low pressure olivine plagioclase fractionation the high mg numbers and ni of the younger brg 2 basalts are not consistent with enrichment of the light field strength elements by crustal assimilation this enrichment must reflect a mantle source region characteristic the trace element and isotopic systematics of this source region are similar but not identical to the asthenospheric source inferred for ocean island basalts in contrast chemical and isotopic systematics of the brg 1 basalts imply derivation from ancient subcontinental lithosphere which has been isolated from the asthenosphere for at least 1 5 eons the subcontinental lithosphere was affected by an early enrichment in rb sr which supported growth of high 87sr 86sr a second enrichment event resulting in fe ti metasomatism of the lithosphere occurred later in response to intrusion of partial melts from a mantle plume rooted in the underlying asthenosphere this is second enrichment event is required by the high nb rb ratios of the brg 1 lavas and of similar lavas of the snake river plain the transition from saturated olivine tholeiites of boise river group 1 to transitional alkalic lavas of brg 2 in the smith prairie region implies a time dependent change in mantle source region with early magmas derived from a shallow lithospheric source giving way to younger magmas derived from a deeper asthenospheric source the eruption of these younger lavas along the flanks of the snake river plain coeval with eruption of saturated tholeiites of the snake river group to the south further implies an axial zonation to magmatism in the snake river province the nature of this axial zonation suggests that the deeper asthenospheric melts were preferentially tapped along the margins of the snake river plain but were blocked from reaching the surface in the axial zone these time space relationships are consistent with a model in which thinned lithosphere near the rift axis undergoes extensive partial melting which overwhelms any asthenospheric melts that may attempt passage the lithosphere is too cool to melt along the rift margins where pressure release by extensional thinning is minor subsequent small volumes of asthenospheric melt are able to traverse this region more easily and erupt with little or no lithospheric contamination

crystallization and hybridism in microgranitoid enclave magmas microstructural evidence microstructural evidence indicates that many microgranitoid enclaves mafic inclusions in granitoids crystallize from globules of magma that have undergone previous magma mixing hybridism the evidence includes 1 rounded xenocrysts ocelli of quartz rimmed with fine grained aggregates of early formed minerals especially mafic minerals 2 k feldspar megacrysts commonly rimmed with plagioclase rapakivi structure and 3 corroded cores dendritic overgrowths and calcic spikes in plagioclase initial quenching of a magma globule in felsic magma involves rapid temperature equilibration which causes a high rate of nucleation of minerals precipitating from the enclave magma at the time followed by a period of slow cooling during which the nucleation and growth rates of later crystallizing minerals are similar to the much slower rates prevailing in the granitic melt this may result in markedly poikilitic microstructures involving inclusion of the earlier formed finer grained minerals in quartz and or k feldspar which are common in microgranitoid enclaves

extremely high energy wave deposits inside the great barrier reef australia determining the cause tsunami or tropical cyclone abstract a hydrodynamic approach is used to determine whether tsunami or cyclone generated waves were responsible for the deposition of fields of well imbricated rock boulders up to 290 tonnes along the coast of cairns inside the great barrier reef australia calculations of the overturning moments show that only tsunami are capable of moving such large boulders in this environment it is hypothesised that large tsunami 11 m have been able to penetrate the great barrier reef through wide 5 10 km 50 70 m deep passages between individual reefs three such passages each approximately 35 km apart and oriented in the same direction exist in the cairns region it is possible that these passages have funnelled and amplified palaeotsunamis the preferential location of eroded coral boulders up to 3 m in length on reef flats alongside these passages and their absence on other reefs throughout the region provide further evidence that extremely high energy waves have been able to penetrate the great barrier reef into the inner channel adjacent to the mainland carbon 14 ages of the coral boulders on these reef flats matches closely the ages of coral fragments pinned below the very large rock boulders along the coast these ages suggest that the cairns region has experienced large tsunami twice over the last millennium

comments to dawson a g and stewart i 2007 tsunami deposits in the geological record sedimentary geology 200 166 183

the dynamics and origin of groundwater salinity in the northeast hufu plain the aim of this research is to identify the dynamic characteristics and origins of groundwater salinity in the hufu plain samples of groundwater were taken from wells throughout the hufu plain geochemical analyses using integrated ionic ratios with a variety of graphical approaches saturation indices and the gis method were performed to distinguish the sources of groundwater salinity the results indicated that the groundwater can be classified into five main types the cation and anion trends were ca2 na mg2 k and hco3 so42 cl no3 respectively groundwater quality in the hufu plain is influenced by the chemical weathering of rock forming minerals the variation in saturation indices for different minerals indicated that groundwater salinization was controlled to some degree by human activities in the hufu plain groundwater salinity is not only governed by mineral weathering and dissolution such as calcite aragonite dolomite and gypsum but also significantly influenced by anthropogenic inputs such as fertilizer pesticide and sewage irrigation groundwater salinity originates mainly from the dissolving of gypsum and anhydrite and from anthropogenic inputs rather than from the weathering precipitation and dissolution of calcite dolomite and aragonite

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

origin of hybrid ferrolatite lavas from magic reservoir eruptive center snake river plain idaho the mineralogy and geochemical characteristics of intermediate composition ferrolatites and related lavas from the magic reservoir eruptive center central snake river plain have been investigated to evaluate the origin and petrologic significance of these hybrid lavas the ferrolatites are chemically uniform but contain a disequilibrium phenocryst xenocryst assemblage derived in part from mixed rhyolitic and basaltic magmas that are closely represented by extrusive units in the area the hybrid lavas also contain xenoliths of archean granulites and have high 87sr 86sr and low 143nd 144nd ratios all of which suggest significant magma crust interaction quantitative models including magma mixing minor crystal fractionation and crustal contamination very closely reproduce the observed compositions of these ferrolatites closed system fractionation and or simple bulk contamination models are not as successful and can be ruled out it appears that preexisting mafic and silicic magmas from distinct sources e g mantle and crust encounter one another in crustal level magma chambers under conditions where intimate mixing may occur despite wide differences in the physical properties of these liquids

differentiation of tholeiitic basalt to a type granite in the sept iles layered intrusion canada the undeformed 564 ma sept iles layered intrusion quebec canada is a large igneous body of c 20 000km3 from the base to the top it consists of a layered series dominated by troctolite and gabbro an anorthositic upper border series and a dominantly granitic upper series the parent magma of the layered series is inferred to be an iron rich tholeiitic basalt 48 wt sio2 15wt feot whole rock compositions from the chilled margin dykes cross cutting the layered series and silicic rocks from the upper series display continuous major and trace element geochemical trends ranging from basalts to ferroan metaluminous a type granites 77 wt sio2 initial 143nd 144nd 0 51201 0 51207 and 87sr 86sr 0 70353 0 70548 indicate a juvenile mantle source and minimal contamination by old crust 1 2 during crystallization geochemical modeling using the melts thermodynamic calculator combined with equations predicting mineral melt equilibria from experiments on tholeiitic basalts indicate that basaltic to monzonitic melt compositions are in equilibrium with the troctolites and gabbros of the layered series fe ti oxides saturate early in the layered series after 14 fractionation of plagioclase olivine cumulates further fractionation of fe ti oxide bearing gabbros drives the residual liquids toward silica enrichment and iron depletion major and trace element modeling indicates that the a type granites from the upper series were produced by protracted fractional crystallization of an iron rich basaltic parent magma at a fraction of residual liquid of only 8 the observed relative volumes of mafic cumulates and silicic rocks in the intrusion are in agreement with the calculations most of the intermediate compositions correspond to magmatic mafic enclave bearing granitoids and display geochemical evidence of hybridization intermediate compositions produced by fractional crystallization are scarce and a daly gap occurs from 57 to 67 wt sio2 this gap could result either from the fractional crystallization process or from silicate liquid immiscibility during that compositional interval

the origin of mount st helens andesites abstract mount st helens volcano has intermittently produced mainly dacitic products but occasionally erupted a more diverse suite of lavas including basalts and andesites petrogenetic relations between these magmas provide insight into the dynamics of the subjacent magma system mineralogical and geochemical features of representative lavas erupted during the past 2200 years can distinguish three basaltic and three andesitic variants the mafic lavas include a transitional olivine plagioclase basalts with low k 2 o and incompatible trace element abundances b calc alkaline olivine plagioclase clinopyroxene basalts enriched in k 2 o tio 2 and incompatible trace elements and c calc alkaline olivine plagioclase basaltic andesites with incompatible trace element contents transitional between the two basalt types intermediate lavas include a tholeiitic two pyroxene andesites b calc alkaline plagioclase two pyroxenes olivine amphibole mafic andesites 56 59 wt sio 2 and c calc alkaline plagioclase two pyroxenes amphibole high silica andesites 61 62 wt sio 2 eruption of these magmatic variants within the same eruptive phase implies the existence of different petrogenetic lineages and that the plumbing system is sufficiently complex to simultaneously isolate and preserve numerous magma batches it is unlikely that any of the andesites or dacites are derived by fractional crystallization of the recognized basaltic variants formation of the andesites simply by contamination or assimilation fractional crystallization of basaltic magma is also improbable more plausibly the andesites represent mixing between basaltic and dacitic end member magmas each of which may be somewhat heterogeneous or vary in composition with time in this model efficient mixing must occur in some parts of the magma plumbing system while some conduits or storage reservoirs must be effectively isolated

geology of the ivanhoe hg au district northern nevada influence of miocene volcanism lakes and active faulting on epithermal mineralization the mercury gold deposits of the ivanhoe mining district in northern nevada formed when middle miocene rhyolitic volcanism and high angle faulting disrupted a shallow lacustrine environment sinter and replacement mercury deposits formed at and near the paleosurface and disseminated gold deposits and high grade gold silver veins formed beneath the hot spring deposits the lacustrine environment provided abundant meteoric water the rhyolites heated the water and the faults flow units and lakebeds provided fluid pathways for the hydrothermal fluids a shallow lake began to develop in the ivanhoe area about 16 5 ma the lake progressively expanded and covered the entire area with fine grained lacustrine sediments lacustrine sedimentation continued to at least 14 4 ma and periodic fluctuations in the size and extent of the lake may have been responses to both climate and nearby volcanism the eruption of rhyolite and andesite flows and domes periodically disrupted the lacustrine environment and produced interfingered flows and lake sediments the major pulse of rhyolitic volcanism took place between 15 16 0 05 and 14 92 0 05 ma high angle faulting began in the basement about 15 2 ma penetrated to and disrupted the paleosurface after 15 10 0 06 ma and largely ceased by 14 92 0 05 ma ground motion related to both faulting and volcanism created debris flows and soft sediment deformation in the lakebeds mercury gold mineralization was coeval with rhyolite volcanism and high angle faulting and it took place about 15 2 to 14 9 ma at and near the paleosurface hydrothermal fluids migrated through tuffaceous sediments above relatively impermeable volcanic and paleozoic units creating chalcedonic cinnabar bearing replacement bodies and sinters disseminated gold was deposited in sedimentary and volcanic rocks beneath the mercury deposits although the hydrologic path between the two ore types is unclear higher grade gold silver deposits formed in massive rhyolites and paleozoic quartzites at deeper levels and these mineralized zones possibly represent the feeder zones for the higher level deposits fluctuations in the ground water table locally produced hydrothermal oxidation of the near surface mercury and disseminated gold deposits the locus of mineralization shifted with time moving south and east from its inception point in the west central part of the district thus although mineralization in the district took place during a span of 300 000 years the duration of mineralization at any one place probably was much shorter the low sulfidation deposits of the ivanhoe district formed at the same time and under similar conditions as those in the nearby midas district 15 km to the northwest which includes the large high grade ken snyder gold silver epithermal vein deposit the exposures in the ivanhoe district are interpreted to represent the near surface example of the paleosurface that originally was present above the midas mineralizing system the resulting combined ivanhoe midas model provides an exploration guide for epithermal deposits in similar geologic environments in northern nevada

chemical evolution of a gas capped deep aquifer southwest of iran the kangan aquifer ka is located below a gas reservoir in the crest of the kangan anticline southwest of iran this aquifer is composed of permo triassic limestone dolomite sandstone anhydrite and shale it is characterized by a total dissolved solid of about 332 000 mg l and na ca cl type water a previous study showed that the source of the ka waters is evaporated seawater chemical evolution of the ka is the main objective of this study the major minor and trace element concentrations of the ka waters were measured the chemical evolution of ka waters occurred by three different processes evaporation of seawater water rock and water gas interactions due to the seawater evaporation process the concentration of all ions in the ka waters increased up to saturation levels in comparison to the evaporated seawater the higher concentrations of ca li sr i mn and b and lower concentrations of mg so4 and na and no changes in concentrations of cl and k ions are observed in the ka waters based on the chemical evolution after seawater evaporation the ka waters are classified into four groups 1 no evolution cl k ions 2 water rock interaction na ca mg li and sr ions 3 water gas interaction so4 and i ions and 4 both water rock and water gas interactions mn and b ions the chemical evolution processes of the ka waters include dolomitization precipitation ion exchange and recrystallization in water rock interaction bacterial reduction and diagenesis of organic material in water gas interaction also occur a new type of chart caexcess versus mgdeficit is proposed to evaluate the dolomitization process

hydrochemical characterization of groundwater in the accra plains of ghana chemical and isotopic analyses are used to characterize and identify the relevant water rock interactions which are responsible for the poor groundwater quality in the accra plains four main water types are identified processes that singly or in combination influence the chemical composition of each water type include halite dissolution carbonate dissolution and precipitation seawater intrusion cation exchange evaporative concentration of solutes and aluminosilicates dissolution these processes contribute considerably to the concentration of major ions in the groundwater stable isotope contents of the groundwater suggest mainly direct integrative recharge a few samples plot along the meteoric seawater mix line which is coincidentally the evaporative line the cl br ratios of some of these are close to 300 confirming marine origin others probably concentrated by evaporation have their cl br ratios significantly lower than 300 groundwater is qualitatively good for drinking purposes only along the foothills of the akwapim togoland ranges

geochemical stratigraphy of the huronian continental volcanics at thessalon ontario contributions of two stage crustal fusion the 1500 m thick sequence of huronian continental volcanics at thessalon ontario is subdivided into 4 volcanic cycles each of which includes abundant early mafic end members central intermediate flows and late rhyolite units major and trace element concentrations are dominated by extensive gabbroic fractionation trends that ultimately produced two types of felsic flows 1 rhyolites with high light rare earth element lree and relatively low large ion lithophile element lile concentrations high lree low lile rhyolites and 2 following late separation of ree rich accessory phases rhyolites depleted in lree low lree high lile rhyolites mafic end members of individual volcanic cycle are progressively less siliceous and less enriched in lile and lree with height in the stratigraphic section ti zr ratios gradually rise from 35 in early mafic flows to stabilize at about 85 in late units while average sio2 contents decrease from 56 to about 50 and mg rises from about 48 to 52 nd values are consistently negative indicating variable degrees of pre fractionation crustal contamination of the end member magmas during their uprise through the crust mixing models are consistent with up to 50 contamination by crustal material of tonalitic hornblende gneiss composition a progressive increase in nd from about 5 0 to 0 5 upward in the volcanic succession reflects a decreasing degree of crustal contamination due to development of insulating layers along margins of the feeder system detailed stratigraphic variations suggest that successive magmas batches were intercepted by a progressively fractionating periodically replenished magma source giving rise to open system magmatism despite the prevalence of crustal assimilation in the huronian lavas la sr n ratios are too low in least contaminated end members to be explained by contamination of tholeiitic magmas the late basalts resemble instead modern island are basalts and it is suggested that the subcontinental mantle source was enriched by subduction related processes during crustal formation within individual volcanic cycles gabbroic fractionation trends systematically deviate from calculated factors toward compositions characteristic of hornblende gneiss such relations suggest that further crustal contamination of the magmas occurred simultaneous with crystal fractionation probably within undulating sills at upper crustal levels quantitative analysis suggests assimilation fractional crystallization a fc ratios of about 0 45 as a result of extensive two stage contamination rhyolites from the initial volcanic cycle incorporate a total of over 60 of crust

hydrogeochemical and isotopic evidence of groundwater salinization in a coastal aquifer a case study in jeju volcanic island korea abstract in order to identify the origin of saline groundwater in the eastern part of jeju volcanic island korea a hydrogeochemical and isotopic study has been carried out for 18 observation wells located in east and southeast coastal regions the total dissolved solid contents of groundwaters are highly variable 77 21 782 mg l oxygen hydrogen sulfur and strontium isotopic data clearly show that the saline water results from mixing of groundwater with seawater strontium isotopic compositions and br cl and i cl ratios strongly suggest that the source of salinity is modern seawater intrusion hydrogeochemical characteristics based on bivariate diagrams of major and minor ions show that changes in the chemical composition of groundwater are mainly controlled by the salinization process followed by cation exchange reactions the highly permeable aquifers at the east coastal region are characterized by low hydraulic gradient and discharge rate and high hydraulic conductivity as compared with other regions these properties enhance the salinization of groundwater observed in the study area based on the cl br and 18 o data seawater was determined to have intruded inland some 2 5 km from the coastline considering the poor correlation of sampling depth and cl concentrations observed the position of seawater freshwater interface is not uniformly distributed in the study area due to heterogeneities of the basaltic aquifers

analysis of environmental controls on tsunami deposit texture abstract tsunamis transport large amounts of sediment and can leave recognisable signatures in the landscape the form and composition of onshore tsunami deposits are a function of wave dynamics sediment availability and characteristics of the local environment the latter of which also partially controls preservation of the deposit this research reviews these relationships in a global context and assesses the connection between tsunami deposit particle size and four controlling parameters climate temperature and rainfall density of tsunami sediments degree of coastal protection and distance between tsunami source and sediment deposition an international dataset of tsunami deposit locations and texture was compiled from published literature and existing databases values for environmental variables were calculated for each location from global datasets of temperature rainfall coastline shape and tsunami source locations spearman s rank order correlation principal component analysis pca and hierarchical cluster analysis ca were used to analyse relationships between these variables pca results show an inverse relationship between particle size and sediment density climate variables and distance from source ca results support this suggesting a cluster structure controlled primarily by particle size and secondly by climate and sediment density these relationships can be explained by the influence of the environment on antecedent morphology and the composition of sediments available for tsunami transport

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

isotope geochemistry and origin of calc alkaline lavas from a caledonian continental margin volcanic arc abstract analyses for major and trace elements including ree and sr nd and pb isotopes are reported from a suite of siluro devonian lavas from fife scotland the rocks form part of a major calc alkaline igneous province developed on the scottish continental margin above a wnw dipping subduction zone within the small area ca 15 km2 considered rock types range from primitive basalts and andesites high mg ni and cr to lavas more typical of modern calc alkaline suites with less than 30 ppm ni and cr there is a marked silica gap between these rocks 74 yet the latter can be generated by fractional crystallization from the more mafic lavas in contrast variation in incompatible element concentrations and ratios in the mafic lavas can not be generated by fractional crystallization processes increasing sio2 is accompanied by increasing rb k pb u and ba relative to sr and high field strength elements increasing lree enrichment and increasing sr calculated at 410 ma and by decreasing hree eu eu sm nd and nd 410 nd and sr are roughly anticorrelated and have more radiogenic compositions than the mantle array in common with data reported elsewhere from this part of the arc the correlation extrapolates up to cross the mantle array within the composition field of the contemporary morb source and extrapolates down towards the probable compositional range of lower palaeozoic greywackes which may form the uppermost 8 km of the crust or may be supplied to the source by subduction one sample however lies within the mantle array and closely resembles lavas from northwestern parts of the arc where a mantle source with mild time integrated rb sr and lree enrichment has been inferred the lavas have relatively high initial 207pb 204pb for their 206pb 204pb a feature which has been interpreted elsewhere as the result of incorporation of a sediment component into arc magmas the systematic changes with increasing sio2 in isotopic and chemical parameters can be explained by mixing of a greywacke derived component with depleted mantle the various possible mixing mechanisms are discussed and it is considered most likely that mixing occurred in the mantle source through greywacke subduction the bulk of the rb k ba and pb in the lavas is probably recycled from the crust whereas less than some 40 of the sr and nd is recycled the calc alkaline chemical trends are solely a function of mixing with the sediment component

snake river sr type volcanism at the yellowstone hotspot track distinctive products from unusual high temperature silicic super eruptions a new category of large scale volcanism here termed snake river sr type volcanism is defined with reference to a distinctive volcanic facies association displayed by miocene rocks in the central snake river plain area of southern idaho and northern nevada usa the facies association contrasts with those typical of silicic volcanism elsewhere and records unusual voluminous and particularly environmentally devastating styles of eruption that remain poorly understood it includes 1 large volume lithic poor rhyolitic ignimbrites with scarce pumice lapilli 2 extensive parallel laminated medium to coarse grained ashfall deposits with large cuspate shards crystals and a paucity of pumice lapilli many are fused to black vitrophyre 3 unusually extensive large volume rhyolite lavas 4 unusually intense welding rheomorphism and widespread development of lava like facies in the ignimbrites 5 extensive fines rich ash deposits with abundant ash aggregates pellets and accretionary lapilli 6 the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre 7 a bimodal association between the rhyolitic rocks and numerous coalescing low profile basalt lava shields and 8 widespread evidence of emplacement in lacustrine alluvial environments as revealed by intercalated lake sediments ignimbrite peperites rhyolitic and basaltic hyaloclastites basalt pillow lava deltas rhyolitic and basaltic phreatomagmatic tuffs alluvial sands and palaeosols many rhyolitic eruptions were high mass flux large volume and explosive vei 6 8 and involved h2o poor low 18o metaluminous rhyolite magmas with unusually low viscosities partly due to high magmatic temperatures 900 1 050 c sr type volcanism contrasts with silicic volcanism at many other volcanic fields where the fall deposits are typically plinian with pumice lapilli the ignimbrites are low to medium grade non welded to eutaxitic with abundant pumice lapilli or fiamme and the rhyolite extrusions are small volume silicic domes and coulees sr type volcanism seems to have occurred at numerous times in earth history because elements of the facies association occur within some other volcanic fields including trans pecos texas etendeka parana lebombo the english lake district the proterozoic keewanawan volcanics of minnesota and the yardea dacite of australia

mineralogy and geothermometry of high temperature rhyolites from the central and western snake river plain voluminous mid miocene rhyolitic ash flow tuffs and lava flows are exposed along the northern and southern margins of the central and western snake river plain these rhyolites are essentially anhydrous with the general mineral assemblage of plagioclase sanidine quartz augite pigeonite hypersthene fayalitic olivine fe ti oxides apatite zircon which provides an opportunity to compare feldspar pyroxene and fe ti oxide equilibration temperatures for the same rocks estimated pyroxene equilibration temperatures based on the geothermometers of lindsley and coworkers range from 850 to 1000 c and these are well correlated with whole rock compositions with the exception of one sample agreement between the two pyroxene thermometers tested is well within 50 c fe ti oxide geothermometers applied to fresh magnetite and ilmenite generally yield temperatures about 50 to 100 c lower than the pyroxene temperatures and erratic results are obtained if these minerals exhibit effects of subsolidus oxidation and exsolution results of feldspar thermometry are more complicated and reflect uncertainties in the thermometer calibrations as well as in the degree of attainment of equilibrium between plagioclase and sanidine in general temperatures obtained using the ghiorso 1984 and green and usdansky 1986 feldspar thermometers agree with the pyroxene temperatures within the respective uncertainties however uncertainties in the feldspar temperatures are the larger of the two and exceed 60 c for many samples the feldspar thermometer of fuhrman and lindsley 1988 produces systematically lower temperatures for many of the samples studied the estimated pyroxene temperatures are considered most representative of actual magmatic temperatures for these rhyolites this range of temperatures is significantly higher than those for rhyolites from many other suites and is consistent with the hypothesis that the snake river plain rhyolitic magmas formed by partial fusion of relatively dry e g granulitic crustal lithologies

geochemical evolution of groundwater in the quaternary aquifer of calcutta and howrah india abstract groundwater in the quaternary aquifer of the twin city calcutta and howrah occur in a confined condition coarse clastic deposits consisting of fine to coarse sand at places mixed with gravels form the aquifer above and below lie clay sequences the average thickness of the top confining clay bed is 40 m and the aquifer continues down to a depth of at least 296 m below which the bottom clay bed of pliocene age occurs during the last five decades there is a distinct lowering of piezometric head in calcutta and howrah the groundwater flow pattern changed from an open system which was from north to south in the mid 1950s to a closed one in the mid 1980s with the formation of a groundwater trough this closed flow system persisted in the 1990s with the increase in the area of the trough detailed geochemical investigation of groundwater samples n 57 along with statistical analyses viz correlation principal component and mixing analyses on these chemical data reveal i that the groundwater samples can be categorised into eight hydrochemical facies which may be assigned to the three broad types fresh blended and brackish water ii a pronounced and well defined trend of variation of chemistry of the groundwater iii modified connate water and or interaction with the aquifer matrix was possibly responsible for the evolution of the brackish water iv mixing of fresh water and brackish water in ca 48 52 proportion is presently taking place due to heavy groundwater withdrawal and v such mixing will cause deterioration in quality from fresh water to the blended variety mean tds 724 mg l

source transport and evolution of saline groundwater in a shallow holocene aquifer on the tidal deltaplain of southwest bangladesh deltaic groundwater resources are often vulnerable to degradation from seawater intrusion or through interaction with saline paleowaters the ganges brahmaputra meghna river delta in bangladesh and west bengal india is a particularly vulnerable area with an estimated 20 million coastal inhabitants directly affected by saline drinking water the shallow groundwater of the coastal regions is primarily brackish with pockets of fresher water a small scale hydrologic investigation of groundwater salinity beneath an embanked tidal channel island was undertaken to explore possible hydrogeological explanations of the distribution of water salinities in the shallow aquifer this study employs a combination of 3h and 14c dating electromagnetic subsurface mapping and a 2 d solute transport model the authors conclude that the shallow groundwater salinity can best be explained by the slow infiltration of meteoric water into paleo brackish estuarine water that was deposited during the early mid holocene

waves coastal boulder deposits and the importance of the pre transport setting the pre transport environment of a coastal boulder along with its shape size and density determines the height of wave required for it to be transported different forces act on sub aerial boulders as opposed to submerged boulders when struck by a wave boulders derived from joint bounded blocks on shore platforms predominantly experience lift force and require a wave of greater height to be transported than boulders in other environments no one equation is applicable to determine the height of palaeo waves responsible for depositing a field or ridge of imbricated coastal boulders a range of equations and their derivation is presented here which can be applied to the respective pre transport environment of a boulder such an approach is necessary when attempting to reconstruct the frequency and magnitude of past coastal wave hazards and for differentiating between tsunami and storm wave deposited boulder fields

emplacement and movement of boulders by known storm waves field evidence from the okinawa islands japan abstract field observations from previous studies of boulder movements were compiled to augment our own work on boulders that have been displaced by storm waves during recent typhoon events in the okinawa islands japan to elucidate the ability of storm waves to move boulders our observations reveal that recent storm waves displaced by sliding and overturning 100 ton boulders emplacing them on the reef or high cliff tops and that storm waves might also be capable of displacing 200 ton boulders on the reef the weights of storm wave boulders at the okinawa islands are of comparable order to those boulders displaced by historical tsunami origins consequently boulder weight alone is an inappropriate parameter to discriminate between tsunami or storm wave processes however these heavy storm wave boulders are close to the reef and cliff edges while tsunami boulders can be deposited much further inland hence horizontal displacement distance of boulders could be a useful parameter to discriminate boulders deposited by the tsunami and storm waves on the wide fringing reef the storm wave boulders were characteristically concentrated on the southeastern pacific ocean sides of each island but large boulders are rarely found on the northwestern east china sea side this is probably because the storm wave intensities are generally stronger at the southeastern side than at the northwestern side although differences of reef strength and initial condition of boulders should also be taken into account consideration of the high frequency of typhoons at the area suggests that effects of the storm waves and the consequent displacement of boulders on the reef might have contributed to the formation of the reef moat framework that typifies the okinawa islands especially if the moat is located within the transport limit of the storm wave boulders approximately 300 m from the reef edge at the islands

magma mixing the marsco suite isle of skye scotland magma mixing has been proposed as a major mechanism for the origin of a wide variety of rock suites in mid ocean basalts there are few obstacles to mixing because of the similarities in chemical and physical properties of the proposed end members however in calc alkaline rocks the proposed end members have disparate properties and these present obstacles to mixing

quantitative evaluation of fractional crystallization in bouvet island lavas abstract bouvet island situated near the southernmost end of the mid atlantic ridge is characterized by lavas ranging in composition from hawaiite through mugearite and benmoreite to rhyolite major and trace elements vary systematically throughout the sequence as do mineral compositions and geochemical modelling indicates that the compositional variations observed in the differentiated lavas can be ascribed to extensive fractional crystallization of a parental hawaiite magma following this scheme the hawaiite parent magma experienced approximately 44 fractional crystallization of plagioclase clinopyroxene olivine opaque oxides and minor apatite to give rise to the mugearite magma which in turn experienced a further 69 fractional crystallization of the same phase assemblage though with more evolved compositions to give rise to the bouvet island rhyolite extensive fractional crystallization 64 possibly separated in time of the parental hawaiite gave rise to the benmoreite magma in the latter scheme the fractionating phases are similar both in composition and proportion to those crystallizing in the passage from hawaiite to mugearite suggesting that the bouvet island hawaiites correspond in composition to a six phase plag of cpx fe ti oxide ap lq saturation surface and that the more differentiated lavas resulted from differing degrees of crystallization on this surface

the graveyard point intrusion an example of extreme differentiation of snake river plain basalt in a shallow crustal pluton the graveyard point intrusion is the only known example of a wellexposed differentiated mafic pluton associated with the late miocene pleistocene magmatism of the western snake river plain srp it is exposed in a 6 km by 4 km area adjacent to the oregon idaho border and exposures range in thickness from 20 to 160 m the thicker parts of the intrusion are strongly differentiated and contain a 25 60 m thick section of well laminated cumulus textured gabbros that grade upward into pegmatoidal ferrogabbro evolved liquids formed sheets of fe rich siliceous granophyre at least two injections of magma are indicated by abrupt discontinuities in the rock and mineral compositions and by the lack of mass balance between the bulk intrusion and its chilled borders the laminated gabbros are interpreted to have formed from a tongue of augite and plagioclase crystals that were carried in with the second pulse of magma following the final emplacement of the intrusion in situ differentiation proceeded through a two stage process the ferrogabbros are explained as interstitial liquids forced out of the crystal mush by compaction and the siliceous granophyres are interpreted to be residual liquids that migrated out of the partly crystallized ferrogabbros in response to the exsolution of volatiles because the geochemical trend inferred for the mafic to intermediate composition liquids in the graveyard point intrusion is similar to the trend for many western snake river plain lavas the pluton may be a good model for shallow sub volcanic magma chambers elsewhere in the srp however some western srp lavas contain anomalously high concentrations of p2o5 which are best explained by mixing within the active crustal mush column or with partial melts of previously formed differentiated mafic intrusions

mixing basaltic and dacitic magmas by forced convection although magma mixing is an old concept which has been applied to many magma types recent petrographic studies have revived interest in the theory by suggesting that it may account for the origin of calk alkaline magma1 6 and mid ocean ridge basalt7 9 there has been no previous experimental investigation into how two magmas with different properties can mix to form a homogeneous magma of andesitic composition or to produce textures such as observed in banded dacite we present here the results of experiments demonstrating that basaltic and dacitic magmas can be easily mixed by forced convection to form both banded dacite and homogeneous andesite in less than a few hours

sources of deep groundwater salinity in the southwestern zone of bangladesh twenty groundwater samples were collected from two different areas in satkhira sadar upazila to identify the source of salinity in deep groundwater aquifer most of the analyzed groundwater is of na cl hco3 type water the trends of anion and cation are cl hco3 no3 so4 2 and na ca2 mg2 k respectively groundwater chemistry in the study area is mainly governed by rock dissolution and ion exchange the dissolved minerals in groundwater mainly come from silicate weathering the salinity of groundwater samples varies from 1 to 5 and its source is possibly the paleo brackish water which may be entrapped during past geologic periods

salinization properties of a shallow groundwater in a coastal reclaimed area yeonggwang korea the need for more agricultural or residential land has encouraged reclamation at the coastal areas of korea since 1200 ad approximately the groundwaters of these reclaimed areas could be expected to reveal hydrogeochemical properties different from those of areas directly affected by seawater intrusion the purpose of this study therefore was to examine the salinization of shallow groundwater in a coastal reclaimed area and to identify the effect of land reclamation on groundwater quality major cations and anions iodide total organic carbon d 18o and 13c were measured to assist the hydrogeochemical analysis chloride d and 18o data clearly show that the na cl type water results from mixing of groundwater with seawater in particular the d and 18o of ca mg cl no3 type groundwaters are close to the meteoric water line but na cl type waters enriched in chloride are 18o enriched with respect to the meteoric water line meanwhile carbon isotopic data and i cl ratios strongly suggest that there are various sources of salinity the 13c values of na cl type groundwaters are generally similar to those of ca mg cl no3 type waters which are depleted in 13c with respect to seawater i cl ratios of na cl type groundwater are 10 100 times higher than that of seawater because the reclamation has incorporated a large amount of organic matter it provides optimum conditions for the occurrence of redox processes in the groundwater system therefore the salinization of groundwater in the study area seems to be controlled not only by saltwater intrusion but also by other effects such as those caused by residual salts and organic matter in the reclaimed sediments

mafic enclaves in the wilson ridge pluton northwestern arizona implications for the generation of a calc alkaline intermediate pluton in an extensional environment the wilson ridge pluton is an epizonal calc alkaline pluton that formed about 13 5 ma during a period of mid miocene extension faulting and erosional dissection provide a cross section of the pluton the apex of the pluton in the boulder wash area nevada is composed of hypabyssal quartz monzonite and dacite the base of the pluton is 20 km to the south where quartz monzodiorite monzodiorite and diorite are in low angle intrusive contact with precambrian basement the pluton was separated from cogenetic volcanic rocks in the river mountains by movement along the saddle island detachment fault at about 13 4 ma the river mountains now lie 20 km to the west of the pluton the wilson ridge pluton is composed of the teakettle pass suite consisting of foliated monzodiorite and quartz monzodiorite and unfoliated quartz monzonite and the older horsethief canyon diorite rocks of the pluton contain 2 4 modal percent sphene intermediate rocks of the teakettle pass suite contain abundant basaltic and diorite enclaves basaltic enclaves are lensoidal and pillow like and commonly have crenulate and fine grained margins enclaves are chemically similar to mafic dikes of the wilson ridge pluton and to cogenetic alkali basalt flows in the river mountains they probably represent blobs of mafic liquid that commingled and mechanically mixed with felsic magma to produce the intermediate rocks of the pluton basaltic enclaves commonly occur as inclusion rich zones that represent synplutonic mafic dikes that were injected into a quartz monzonite host mafic magma was entrained and mechanically broken down by magmatic flow shear a continuum in shape exists from enclaves that are bulbous and ellipsoidal to those that are thin tabular mafic selvages and schlieren and ultimately to the mafic component in foliated quartz monzodiorite and monzodiorite diorite enclaves have angular contacts with host rocks and are interpreted as xenoliths field evidence and major and trace element models suggest that the intermediate rocks of the pluton were produced by the commingling of a large volume of mafic magma with a smaller volume of felsic magma a mafic felsic ratio of about 70 30 as well as fractional crystallization similar open system processes may be responsible for the production of calc alkaline intermediate rocks in other parts of the great basin

intermediate composition magma production in an intracontinental setting unusual andesites and dacites of the mid miocene santa rosa calico volcanic field northern nevada abstract the mid miocene santa rosa calico volcanic field sc of northern nevada provides an outstanding example of the role open system magmatic processes play in producing calc alkaline and tholeiitic andesite dacite magmas in an intracontinental setting sc volcanism commenced at 16 7 ma and is associated with the initial manifestations of the yellowstone hotspot the columbia river steens flood basalt event s and the formation of the northern nevada rift locally a diverse package of magmatic products ranging from tholeiitic basalt to high si rhyolite was produced during an 2 myr duration within this package are the products of at least four distinct intermediate composition magmatic systems that may represent as much as 40 of the sc volcanic pile these help differentiate the sc from contemporaneous oregon plateau volcanic fields e g mcdermitt lake owyhee northwest nevada that are dominated by bimodal basalt rhyolite assemblages all sc intermediate units are characterized by textural and mineralogic complexities including xenoliths and xenocrysts of local crust and crystal clots of plagioclase clinopyroxene orthopyroxene oxide sc intermediate units are dominantly tholeiitic but include lava flows with transitional to calc alkaline affinities relative to locally erupted steens basalt sc intermediate lava flows have similar elemental enrichments and depletions but dissimilar sr and nd isotopic compositions these isotopic differences coupled with the abundant disequilibrium features and variable incompatible element ratios indicate that open system magmatic processes played a major role in the genesis of the intermediate units sc silicic magmas were produced primarily via upper crustal melting of chemically and isotopically heterogeneous cretaceous granitoid interaction between fractionating mafic steens flood basalt magmas and the more evolved crustal melts assimilation of local upper crust provides a general template for the generation of sc tholeiitic and calc alkaline intermediate magmas between system heterogeneities primarily reflect magma versus assimilation dominated mixing these complex processes and the resulting production and eruption of sc intermediate composition melts were stimulated by incipient focused lithospheric extension and driven by the virtually continuous local availability of upwelling steens basalt over at least a 2 myr duration these results demonstrate that at least some of the mid miocene and younger calc alkaline magmas that are found across the pacific northwest and are unrelated to subduction processes were formed as a direct result of open system processes affecting regional flood basalt magmas rather than just melting of previously enriched via subduction lithospheric mantle as suggested by previous workers

rocky coasts their role as depositional environments abstract the role of rocky coasts as depositional environments has been generally neglected by rock and depositional coast workers although rock coasts can be hostile sedimentary environments they frequently host a variety of deposits consisting of mixes of boulders and megaclasts to sand and cobbles these deposits include pockets of sand and pebble trapped in topographic depressions or at the foot of scarps and cliffs isolated boulders pocket beaches trapped between headlands and sand to boulder beaches in shallow bays exposed to strong wave action the tectonic setting which is reflected in the degree of geological heterogeneity alongshore together with the wave regime and other elements of the morphogenic environment help to determine the amount and mobility of the sediment and consequently whether it plays an essentially abrasional or protectional role many beaches have a resistant rock foundation which will modulate their response to rising sea level and possibly increased storminess during this century wave refraction and temporal and spatial changes in sediment abrasional and protectional efficacy influence the development of crenulated planforms on coasts with a high degree of geological heterogeneity and possibly on more geologically homogeneous coasts with longshore variations in cliff height or in the amount of sediment theory suggests that these coasts may develop equilibrium planforms with uniform rates of erosion in bays and on headlands or they may undergo a series of cyclical transformations involving alternating increases and decreases in the depth of the bays relative to the headlands