the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part ii xenotime xenotime from a geochemically heterogeneous series of mildly to strongly peraluminous granites of the erzgebirge germany displays extended compositional variability with respect to abundances of hree y u and th with few exceptions the maximum and minimum concentrations for the lanthanides and actinides exceed those noted for this mineral from other geologic environments xenotime chemistry is dominated by the theoretical end members hree po 4 and ypo 4 90 mol in total typical xenotime grains from the erzgebirge granites and from other granites worldwide contain 70 80 mol ypo 4 and 16 25 mol hree po 4 this study documents the occurrence of xenotime abnormally rich in hree in place of y with up to 45 mol hree po 4 substitutions of thorite coffinite th u pb sio 4 brabantite ca th u po 4 2 and monazite la sm po 4 are of minor importance reaching maximum levels of 5 6 mol each with a total contribution typically th u super 4 ca super 2 the total lanthanide and actinide contents in xenotime and host granite are not strongly correlated however formation of xenotime unusually rich in hree occurs only in the a type limica granites that are strongly enriched in these elements the shapes of hree patterns of xenotime and host rock are similar which combined with mass balance calculations indicate the importance of this mineral in affecting the hree as well as y evolution of late stage granitic melts late xenotime may show strong y ho fractionation thus recording the decoupling of y and the hree which can occur in the latest stages of crystallization of evolved granites and which may be associated with deuteric alteration

identification of inherited radiogenic pb in monazite and its implications for u pb systematics the simplest interpretation of uranium lead mineral ages in igneous rocks embodies the assumption that melting of pre existing rocks leads to homogenization of the lead isotopes thus resetting the radiometric clock zircons often violate this assumption by only partially dissolving and preserving a component of lead inherited from before the melting episode but until now such behaviour has not been observed in monazite here we report u pb data for zircons and monazites from a tertiary granite from the himalayas in which zircons and monazites contain inherited radio genic lead an analysis of a single entirely igneous zircon crystal plots on concordia at 19 5 0 4 myr eight monazite fractions lie on a line from an upper intercept of 471 10 myr to the youngest fraction which plots slightly above concordia at 21 myr the presence of excess 206pb in the youngest monazite fractions indi cates that the monazite data represent a mixing line between young magmatic monazite and an older inherited component rather than a resetting of 471 myr monazites at 20 myr these data suggest a closure temperature for pb in monazite significantly higher than previously published estimates

wind and density driven circulation in a well mixed inverse estuary abstract near the ocean the residual circulation in laguna san ignacio located on the pacific coast of baja california in mexico has been shown to be driven by tides here the subtidal circulation in the portion of the lagoon farther from the ocean is shown to be driven by the wind the pressure difference between two stations one near the closed end and the other midway along the central axis is correlated well with the wind stress in the sense that sea level rises downwind where the bathymetry is relatively simple with a deep channel separating two shoal areas the flow is upwind at the deepest part of the section driven by the axial pressure gradient in areas where the bathymetry is more complex the direction of the observed flow is parallel neither to the local bathymetry nor to the applied wind stress linear theory qualitatively explains the major features of the wind driven flow including the relative strength of the pressure gradient to the wind stress the direction of the flow and t

microprobe monazite geochronology understanding geologic processes by integrating composition and chronology abstractmonazite is a light rare earth element lree bearing phosphate mineral that is present in a wide variety of rock types has an extremely variable composition reflecting host rock conditions and is a robust geochronometer that can preserve crystallization ages through a long history of geological events monazite crystals typically contain distinct compositional domains that represent successive generations of monazite which in turn can provide a detailed record of the geologic history of its host rocks the electron microprobe can be used to characterize the geometry of compositional domains analyze the composition of each domain and when carefully configured determine the u th total pb age for domains as small as 5 m in width these data allow the monazite to be linked with and place timing constraints on silicate processes in the host rocks current applications span a broad range of geologic processes in igneous metamorphic hydrothermal and sedimentary rocks

density driven exchange flow in terms of the kelvin and ekman numbers 1 the pattern of density induced flow influenced by basin s width friction and earth s rotation is investigated as a function of the ekman ek and kelvin ke numbers a semianalytical solution is used to determine the conditions under which the density induced exchange flow is vertically sheared or horizontally sheared solutions are obtained over diverse laterally varying bathymetries it is found that the exchange flow is horizontally sheared under high frictional conditions ek 1 independently of the width of the basin ke the horizontally sheared pattern describes inflow in the channel and outflow over shoals with the inflow occupying the entire water column the exchange flow pattern is also horizontally sheared under weak friction ek 0 and in wide ke 2 basins in that case however the outflow is concentrated on the left looking into the basin in the northern hemisphere portion of the cross section and inflow appears on the right also under weak friction the exchange pattern becomes more vertically sheared with outflow at surface and inflow underneath as the width of the basin becomes small ke 1 bathymetry is not very influential in the weak friction exchange patterns finally under moderate friction 0 01 ek 0 1 the exchange pattern is both horizontally and vertically sheared for all widths the horizontally sheared pattern is best defined in wide basins high ke whereas the vertically sheared pattern practically dominates in narrow basins low ke these findings allow classification of various estuaries in the ek ke parameter space

on the nature of transverse variability in a coastal plain estuary even though estuarine processes are inherently three dimensional most of the previous studies have focused primarily on the axial longitudinal and vertical variabilities recent surveys in the lower delaware bay indicate the presence of significant transverse variability in the salinity distribution and residual circulation pattern conceptual models are developed to examine the mechanisms which might explain the observed transverse structure results indicate that both the gravitational effect and wind forcing are capable of generating substantial transverse structure in drowned river valley estuaries with triangular cross sections

genesis of the xianghualing sn pb zn deposit south china a multi method zircon study abstract the xianghualing sn pb zn deposit is situated near the center of the world class nanling w sn ore belt associated with the highly evolved laiziling granite of jurassic age previous studies focused mainly on geochemical and geochronological features of the mineralization related granite whereas research on the source evolution and geochronology of the ore forming fluids has been limited we carried out precise u pb dating trace element and hf isotopic analyses on magmatic and hydrothermally altered zircons from the skarn stage and sulfide stage ores in the xianghualing deposit zircon u pb dating results from the two ore forming stages show distinct geochronological populations the skarn stage ores contain mainly magmatic and hydrothermally altered zircons in three age clusters 150 ma 220 ma and 420 ma whereas the sulfide stage ores are characterized by abundant old detrital zircons ranging from 497 to 3409 ma with a peak at 800 1000 ma this pattern may indicate that magmatic hydrothermal events in the silurian and triassic were precursors to the main sn mineralization event in the jurassic when circulation of evolved fluids through older sedimentary rocks led to pb zn mineralization the jurassic zircons exhibit high trace element contents e g hf p y nb ta th u and low ti contents eu anomalies nb ta and th u ratios which imply that the laiziling magma experienced significant plagioclase biotite and muscovite fractional crystallization and that it interacted extensively with post emplacement f rich hydrothermal fluids the positive ce anomalies of these zircons ce ce 1 0 226 indicate that the magmatic hydrothermal fluids that led to the jurassic sn mineralization event were reducing the less negative ehf t values of triassic zircons 18 7 to 2 6 compared to the silurian zircons 14 6 to 2 3 suggest more limited interaction between the mantle and the magma source region the jurassic magmatic zircons in the skarns exhibit even more negative ehf t values 30 7 to 6 7 along with tdmc model ages ranging from 1627 to 3134 ma indicating that the jurassic magma was derived from partial melting of old continental crustal basement based on the combined study of zircons in the skarns and sulfide ores we propose a three stage ore genetic model for the xianghualing sn pb zn deposit

effects of bathymetry friction and rotation on estuary ocean exchange an analytical model that includes pressure gradient friction and the earth s rotation in both components of the flow is used to study the transverse structure of estuarine exchange flows and the nature of transverse circulation in estuaries of arbitrary bathymetry analytical results are obtained for generic bathymetry and also over real depth distributions and are compared with observations this study extends previous efforts on the topic of transverse structure of density induced exchange flows in three main aspects 1 the analytical model explores any arbitrary bathymetry 2 the results reflect transverse asymmetries relative to a midchannel centerline associated with the effects of the earth s rotation and 3 the transverse circulation produced by the analytical model is examined in detail analytical results over generic bathymetry show in addition to the already reported dependence of exchange flow structure on the ekman number two new features first the transverse structure of along estuary flows shows the earth s rotation effects even in relatively narrow systems thus producing transverse asymmetries in these flows the asymmetries disappear under strongly frictional high ekman number conditions thus illustrating the previously documented pattern of inflow in channels and outflows over shoals for typical estuaries second transverse flows resemble a sideways gravitational circulation when frictional effects are apparent ekman number greater than 0 1 responding to a transverse balance between pressure gradient and friction these transverse flows reverse direction under very weak friction and reflect coriolis deflection of along estuary flows that is geostrophic dynamics all examples of observed flows are satisfactorily explained by the dynamics included in the analytical model

resetting of oxybarometers and oxygen isotope ratios in granulite facies orthogneisses during cooling and shearing adirondack mountains new york the petrography petrology and oxygenisotope geochemistry of granulite facies granitic and syenitic orthogneisses of the diana and stark complexes adirondack mountains new york show that the extent and nature of resetting of isotopic and mineralogic systems is highly variable there is a strong correlation between retrogression and shearing and the rocks may be divided texturally into 1 unsheared lithologies that preserve little retrogressed pyroxene or hornblendebearing peak metamorphic mineralogies and 2 sheared rocks that underwent retrogression marked by the growth of late biotite in centimetre to metre wide shear zones after the peak of metamorphism oxygen fugacities in the unsheared lithologies were estimated for reintegrated mineral compositions from magnetiteilmenite mt ilm and ferrosilite magnetic quartz fs mt qtz equilibria mt ilm yields logfo2mt ilm values of 15 9 to 17 6 0 6 to 1 3 log units below the fayalite magnetite quartz buffer fmq and temperatures of 670 745 c that agree with those from other geothermometry and phase equilibria studies these data suggest that aside from oxyexsolution of ilmenite from magnetite the fe ti system underwent only minor resetting during cooling and the fe ti oxides yield good estimates of peak metamorphic temperatures and fo2 in unsheared ilmenite magnetite orthopyroxene quartz assemblages values of logfo2mt ilm are lower than logfo2fs mt qtz by an average of 0 6 when the orthopyroxene activity model of sack and ghiorso is used minor resetting of the fe ti oxides analytical errors and errors in the placement of end member reactions probably account for this relatively small difference in fo2 values whole rock 18o values of unsheared diana and stark lithologies range from 4 0 to 10 3 reflecting pre regional metamorphic oxygen isotope ratios peak metamorphic minerals preserve high temperature oxygen isotope fractionations and in many samples the effective diffusion of oxygen in minerals ceased at higher temperatures than predicted from wet experimental diffusion data these data suggest that the rocks did not contain an aqueous fluid phase during cooling the combination of petrologic isotopic and textural data also permits a detailed study of shearing and retrogression ilmenites in the sheared lithologies underwent greater degrees of hematite loss than in the unsheared rocks resulting in logfo2mt ilm values as low as 24 1 3 1 log units below fmq and mt ilm temperatures that are up to 175 c below regional estimates sheared rocks also have higher 18o values up to 13 3 during shearing 18o values of biotite k feldspar and magnetite reset readily while the degree of isotopic resetting of quartz correlates with the intensity for recrystallization

wind modifications to density driven flows in semienclosed rotating basins abstract an analytical two dimensional model is used to describe wind induced modifications to density driven flows in a semienclosed rotating basin wind stress variations produce enhancement inversion or damping of density driven flows by altering the barotropic and baroclinic pressure gradients and by momentum transfer from wind drag the vertical structure of wind induced flows depends on h the nondimensional surface trapping layer where is the inverse of the ekman layer depth d and h is the maximum water depth for h 5 wind driven flow structures are similar to the ekman spiral for h 2 wind driven flows are unidirectional with depth the relative importance of density to wind forcing is evaluated with the wedderburn number w 1 h2d which depends on water density mean depth h a proxy of the baroclinic pressure gradient d and wind stress because d depends on and therefore on the eddy viscosity of water az wind speed and az both modify w moreover wind direction alters w by

dating iron skarn mineralization using hydrothermal allanite la u th pb isotopes by laser ablation icp ms abstract trace elements and u th pb isotopes of hydrothermal allanite from the beiminghe iron skarn deposit eastern north china craton were simultaneously analyzed using laser ablation inductively coupled plasma mass spectrometry la icpms to demonstrate the suitability and robustness of the u th pb system in this phase as a geochronometer of ore forming processes allanite grains from the beiminghe deposit typically exhibit optical and chemical zoning and are intergrown or texturally equilibrated with prograde and or retrograde skarn assemblages mainly consisting of tremolite diopside magnetite and garnet in addition they contain abundant aqueous two phase or daughter mineral bearing three phase aqueous fluid inclusions confirming their hydrothermal origin most grains have high la ce ratios 1 19 1 74 and thus are classified as allanite la a notable feature of the hydrothermal allanite la is the lack of common pb with values comparable with those of the zircon standards 91500 and gj 1 used in this study la icpms spot analyses reveal remarkable variation in ca rees rare earth elements fe al and mg within a single grain consistent with the substitution of ree3 mg fe2 for ca al fe3 in the mineral structure traverses of zoned grains show that the rims have th u ratios ranging from 0 73 to 11 55 significantly higher than the core areas 0 07 1 81 fifty nine spot analyses beam size of 32 m or 60 m on 5 allanite la grains yield reproducible 206pb 238u ages of 134 7 to 139 6 ma with a weighted mean 206pb 238u age 206pbexcess corrected 206pb 238u age of 136 1 ma 2 of these 34 analyses on allanite rims have a weighted mean 208pb 232th age of 139 2 ma 2 that is within error of the 206pb 238u age the dating results showed that an increase of beam size from 32 to 60 m significantly reduces the analytical uncertainties 2 petrographic and textural data have demonstrated that the allanite la grains formed during skarn alteration and notably have close paragenetic relationships with retrograde skarn assemblages and iron oxide minerals their u th pb ages therefore are interpreted as the timing of iron skarn mineralization at beiminghe thirteen zircon grains from the ore related diorite intrusion have a weighted mean 206pb 238u age of 136 2 ma 2 consistent with and thus confirming the reliability of the allanite la u th pb ages when interpreted as the formation age of the beiminghe iron deposit our results suggest that hydrothermal allanite with low th and u is a promising u th pb geochronometer and can provide reliable constraints on the timing of hydrothermal mineralization without requiring a matrix matched external standard the present dating results also indicate that the u pb rather than th pb isotope system is preferable for u th pb dating of low th u allanite

volatile transport in a convecting magma column implications for porphyry mo mineralization we propose that convection in a column of silicic magma allows transport of volatile components from large 50 km3 magma chambers to the sites of shallow 3 km porphyry type mo deposits using constraints from the henderson and pine grove systems we show that even at temperatures as low as 700 c a granitic magma with 30 vol phenocrysts can flow through a magma column with a 150 m radius at a rate 10 km3 yr enough magma to contribute the mo necessary to form an ore deposit in a geologically reasonable time frame this process requires an efficient mechanism for bubble separation at the top of the magma column to produce degassed magma that can descend down through the column it also requires slow rates of crystallization in the silicic magma consistent with experimental studies hydrothermal fluids released from the convecting magma column can explain many geologic features of the deposits

a long lived hydrothermal system in bushveld granites at the zaaiplaats tin mine lead isotope evidence tin mineralization at zaaiplaats is hosted in alkali feldspar granites of the lebowa granite suite which intrude the rashoop granophyre suite from the upper contact downward the alkali feldspar granites include the marginal pegmatite fine grained lease granite and the coarse grained bobbejaankop granite the major mineralization styles consist of subhorizontal tabular low grade orebodies in the lease granite a lower zone of disseminated cassiterite mineralization in the bobbejaankop granite and shallowly plunging and branching pipe orebodies in both granites fluid inclusion data show a continuous evolution of the magmatic hydrothermal system from 600 degrees to 200 degrees c with cassiterite and scheelite precipitation above 400 degrees c mineral compositions and oxygen isotope fractionations indicate reequilibration of minerals within the granites during pervasive alteration at temperatures generally between 200 degrees and 300 degrees c the emplacement age of these and other bushveld granites is ca 2050 ma yet pb pb whole rock isochron ages for the different variably mineralized granite bodies at zaaiplaats show a relatively restricted range from 961 or 129 ma for the rashoop granophyre to 1187 or 51 ma for the lease granite thus the analyzed sample suites consistently record an event approximately 1 b y after the emplacement of the granites modeling their pb isotope evolution indicates that each suite evolved independently between 2050 and ca 1100 ma suggesting that hydrothermal fluid circulation was essentially confined within each granite body and or fluid rock ratios were low and that the overall 238 u 204 pb within each suite from 2050 to ca 1100 ma was not unusually high or low for fractionated granites suggesting largely closed system behavior of u and pb within each suite during this interval the ca 1100 ma event which caused closure of the u pb systems at zaaiplaats is interpreted to reflect a blocking temperature age related to uplift and cooling of a long lived hydrothermal system and precipitation of the latest stage minerals e g galena at 200 degrees to 300 degrees c the high steady state temperature required to maintain the hydrothermal system at zaaiplaats at temperatures above 200 degrees c for ca 1 b y was provided by radioactive decay current heat production characteristics calculated from present day u th and k 2 o concentrations range from 4 2 mu w m 3 for the rashoop granophyre to 11 5 mu w m 3 for the lease granite preweathering heat production of 30 3 mu w m 3 is inferred for the mineralized bobbejaankop granite after accounting for dramatic recent losses of u and th the low level of hydrothermal fracturing combined with stable and pb isotope evidence effectively rules out convective cooling by external fluids as a significant heat loss mechanism at zaaiplaats fluid pathways within the granites were controlled dominantly by grain boundaries microfractures and vugs which allowed internal circulation and elevated subsolidus temperatures to be maintained indefinitely under a thermal blanket of an estimated 4 km of postemplacement cover uplift and erosion of the terrain caused cooling through the pb exchange blocking temperatures at ca 1100 ma

granulite formation is driven by magmatic processes in the deep crust abstract known examples of granulite facies metamorphism span at least 3 5 b y of earth history mineralogic geobarometry indicates that such metamorphism has occurred in the deep crust typically at 20 30 km 6 9 kbar geothermometry indicates that peak t 700 900 c and therefore that t was elevated by at least 200 c over an anorogenic geotherm of 15 20 c km 1 commonly invoked sources of heat include rising magmas radioactive decay insulated by continent continent collision mantle volatiles or crustal thinning present day crustal thicknesses are normal beneath exposed granulite terranes and the common absence of evidence for post metamorphic underplating suggests synmetamorphic thicknesses of 60 80 km thus granulites form in tectonically active regions of thickened crust and elevated geotherm xenolith suites suggest that granulite facies mineralogy persists in the deepest crust after tectonism in spite of declining temperature to greenshist amphibolite facies conditions

u pb geochronology of hydrothermal zircons from the early cretaceous iron skarn deposits in the handan xingtai district north china craton the handan xingtai district in the north china craton is one of the most important concentrations of iron skarn deposits in china with proven reserves of 900 to 1 000 mt at an average of 40 to 55 wt fe the iron mineralization occurs predominantly along contact zones between early cretaceous intermediate silicic intrusions and middle ordovician marine carbonates intercalated with numerous evaporite beds in this paper we present textural features and laser ablation icp ms u pb dating results of hydrothermal zircon from five major iron skarn deposits to place tight constraints on the timing and duration of the district scale iron mineralization zircon grains from the mineralized skarns are anhedral to subhedral crystals and euhedral tetragonal bipyramids they are closely intergrown or texturally associated with diopside garnet epidote calcite albite and phlogopite other common minerals in the skarn assemblages include f rich hornblende wilkeite f f apatite and fluorite zircon grains typically contain abundant inclusions of skarn minerals and daughter mineral rich mostly magnetite halite and sylvite fluid inclusions compositionally these zircon grains have moderately to extremely high th 518 7 477 ppm and u 109 25 610 ppm contents with highly variable th u ratios ranging from 0 01 to 5 23 the morphological textural and geochemical features of the zircons confirm their hydrothermal origin and indicate that they most likely precipitated from high temperature f rich magmatic derived ore forming fluids the hydrothermal zircon grains yield well defined concordant u pb ages for the five studied iron skarn deposits with weighted mean 206 pb 238 u dates ranging from 133 6 0 9 to 128 5 1 4 ma 2 these ages are remarkably consistent with u pb ages 134 1 1 2 to 128 5 0 9 ma 2 of magmatic zircon grains from the ore related intrusions in each deposit demonstrating that iron skarn mineralization was genetically related to the coeval magmatism our new geochronological data when combined with existing isotopic ages indicate that iron mineralization and associated magmatism in the handan xingtai district took place mainly at the ca 137 133 and 131 128 ma intervals iron skarn deposits of similar ages also occur widely in other parts of the eastern north china craton forming the only known giant mesozoic iron skarn province in a cratonic block on the earth the formation of these iron skarn deposits and associated intrusions coincided in time with lithospheric thinning or destruction of the north china craton strongly suggesting a causal link between the two processes

wind driven lateral circulation in a stratified estuary and its effects on the along channel flow 1 in the stratified rotating estuary of chesapeake bay the ekman transport drives a counterclockwise lateral circulation under down estuary winds and a clockwise lateral circulation under up estuary winds looking into estuary the clockwise circulation is about twice as strong as the counterclockwise circulation analysis of the streamwise vorticity equation reveals a balance among three terms titling of the planetary vorticity by vertical shear in the along channel current baroclinic forcing due to sloping isopycnals at cross channel sections and turbulent diffusion the baroclinic forcing is highly asymmetric between the down and up estuary winds while the counter clockwise lateral circulation tilts isopycnals vertically and creates lateral barolinic pressure gradient to oppose the ekman transport under the down estuary wind the clockwise circulation initially flattens the isopycnals and the baroclinic forcing reinforces the ekman transport under the up estuary wind the coriolis acceleration associated with the lateral flows is of the first order importance in the along channel momentum balance it has a sign opposite to the stress divergence in the surface layer and the pressure gradient in the bottom layer thereby reducing the shear in the along channel current compared with the non rotating system the shear reduction is about 30 40 two summary diagrams are constructed to show how the averaged streamwise vorticity and along channel current shear vary with the wedderburn w and kelvin ke numbers

scapolite phase equilibria and carbon isotopes constraints on the nature and distribution of co2 in the lower continental crust abstract recent applications of scapolite phase equilibria and carbon isotopes are reviewed in order to evaluate the role played by co2 in the genesis of granulites in the lowermost crust scapolite occurs mainly in mafic granulites from exposed high grade terranes most of which have had a prior upper crustal history before equilibration at 9 10 kbar and in high pressure 11 15 kbar xenoliths and orthogneisses which likely represent mantle derived material that has not interacted with supracrustal lithologies calculated equilibrium co2 activities are sufficiently high 0 7 to be consistent with the presence of a co2 rich fluid phase accounting for the low h2o activities in scapolite bearing granulites and some xenoliths co2 activities less than ca 0 5 or the absence of scapolite are consistent with fluid absent metamorphism the measured isotopic composition of carbon 13cpdb in scapolite is only a tight constraint on the source of carbon in scapolite for mafic xenoliths and high pressure orthogneisses carbon isotope values for these lithologies 7 to 2 overlap the range of values for co2 dissolved in or exsolved from basalts and are consistent with a magmatic origin for the co2 the carbon isotope composition of scapolite in granulites from exposed terranes 10 to 4 is more equivocal and may instead be related to pregranulite facies carbonate present in the rock minimum values of volumetric fluid rock calculated to account for the modal abundance and composition of scapolite in granulites on the order of 0 001 to 0 1 are much lower than those required for the desiccation of amphibolites to granulites 0 1 to 0 5 thus scapolite should form in response to infiltration of such large volumes of co2 if p t and bulk compositional constraints are met however only seven of twenty granulite occurrences contain primary carbonate bearing scapolite in mafic granulites it appears that co2 occurs in the lower crust only locally in a co2 rich fluid phase or dissolved in mafic melts and not on a pervasive scale or at the high volumetric fluid rock required the model of carbonic metamorphism

a fluid inclusion investigation of ore formation in a tin mineralized granite new england new south wales primary fluid inclusions have filling temperatures from 550 degrees to more than 620 degrees c and salt contents of 54 to 65 wt percent daughter crystals in multiphase inclusions were mostly halite and other chlorides above a temperature of 400 degrees c the hydrothermal solutions were two phase fluid inclusion measurements and chemical analyses indicate two stages of hydrothermal activity in stage one in which heat was dispersed but not dissolved salts the temperature decreased by 200 degrees c while the salt content increased in stage two dissolved salts were dispersed more rapidly than heat and fluid inclusion evidence indicates a decreasing incidence of vapor in the hydrothermal system formation of major fractures occurred at the transition from stage one to stage two of hydrothermal activity fracturing accelerated condensation of vapor and mixing of magmatic brine and ground water most of the tin and tungsten ores were precipitated during the decrease in salt content of the concentrated brine modified journal abstract

the new england batholith eastern australia geochemical variations in time and space the new england batholith australia is part of the upper paleozoic new england fold belt with most plutons intruded into the deformed trench complex metasedimetary rocks in the southeast part of the fold belt the batholith was emplaced in two major periods of plutonism the first during the upper carboniferous and the second during the upper permian and triassic with a major phase of metamorphism and deformation including westward overthrusting of the trench complex sedimentary rocks between the two periods on the basis of petrography geochemistry and isotopic characteristics the granitoids of the batholith are subdivided into five named intrusive suites and a group of leucoadamellites the differences between the six groups are considered to reflect differences in their source rock types the carboniferous granitoids are peraluminous s type and are divided into the bundarra plutonic suite a belt of very coarse grained adamellites with cordierite garnet and the hillgrove plutonic suite a belt of biotite rich garnet deformed adamellites and granodiorites both suites have 18o greater than 10 negative 34s 87sr 86sr initial ratios about 0 706 are ilmenite bearing and have low feo3 ratios the bundarra plutonic suite however is consistently sio2 rich greater than 70 contains cordierite and has higher 18o than the hillgrove plutonic suite the two s type suites are inferred to have formed by partial melting of the deepest parts of a wedge of trench complex sedimentary rocks oceanwards of an andean volcanic chain to the west analagous to the lower tertiary s type plutons of the sanak baranof plutonic belt of southern alaska of the remaining four groups of plutons emplaced during the upper permian and triassic two are metaluminous i type granitoids one the clarence river plutonic suite new name a group of k poor granodiorites and tonalites with low 87sr 86sr initial ratios average 0 7035 and the other the moonbi plutonic suite a group of k rich adamellites with low 87sr 86sr initial ratios average 0 7045 18o less than 10 and 34s positive the clarence river plutonic suite is inferred to have formed from the partial melting of a large ion lithophile element poor gabbro source region and the moonbi plutonic suite from a large ion lithophile element rich shoshonite source region a third group the uralla plutonic suite is less metaluminous has higher 87sr 86sr initial ratios average 0 706 18o only just less than 10 and negative 34s and is considered to have formed in a region containing a physical mixture of metaluminous and peraluminous source rocks gabbro and metasedimentary rocks plutons of the fourth group are leucoadamellites largely emplaced after the other suites with low 18o indicating an i type source it is argued that this group has resulted from low degrees of dry partial metling of an i type source region that had undergone an earlier melting event these four groups of plutons are largely confined to a narrow belt parallel to but 100 km west of the present rifted margin of australia their origin may be related to crustal thickening attendant on the overthrusting that occurred early in the permian and or a temperature increase in the lower crust due to the recovery of normal continental geotherms following the cessation of subduction

a two dimensional analytic tidal model for a narrow estuary of arbitrary lateral depth variation the intratidal motion an innovative method is introduced to solve a two dimensional depth averaged analytic model for narrow estuaries or tidal channels with arbitrary lateral depth variations the solution is valid if the lateral variation of the amplitude of tidal elevation a is small i e a a where a is the amplitude of the tidal elevation this assumption is supported by a 60 day observation of elevation in the james river estuary using pressure sensors at both sides of a cross section of the estuary the error introduced by the solution is of the order of a a which has a maximum of 5 in the james river estuary the propagation of the tidal wave elevation is therefore essentially one dimensional along the estuary regardless of the depth distribution whereas tidal velocity has a strong transverse shear and is three dimensional in general dozens of depth functions in six groups of various forms are used to calculate the solution the tidal velocity is highly correlated with the bathymetry the largest amplitude of the along channel velocity is in the deepest water the phase of the along channel velocity in the shallow water leads that in deep water causing a delay in time of flood or ebb in the deep water the transverse velocity is generally small in the middle of a channel but reaches its maximum over the edges of bottom slopes the depth function has a significant effect on the ellipticity and the sense of rotation of the tidal ellipses by fitting the observed phase of semidiurnal tide in the james river estuary to the phase of the momentum equation we have obtained optimal values of the drag coefficient 1 5 10 3 and 1 8 10 3 for the spring and neap tides respectively then we apply these values of the drag coefficient and the model to the james river estuary using the real bathymetry results show remarkable agreement between the observations and the model along the transects for both spring and neap tides the cross channel phase difference of the along channel velocity between the channel and the shoal is found to be 1 hour a value consistent with that from the model the model estimated lateral variation of elevation is 2 5 of the tidal amplitude which is slightly smaller than the observed value

axial convergence in a well mixed estuary abstract transverse secondary circulations involving surface convergence observed in a well mixed estuary in north wales are made visible by the collection of surface material along an axial line which extends continuously for many kilometres through the estuary the circulation and axial convergence however are seen only during the flood phase of the tide and no similar behaviour has been observed during the ebb phase convergent circulations in the estuary are associated with small but steady transverse density gradients in the cross section produced by non uniform advection of the longitudinal gradient through the channel a diagnostic model using measured mean distributions of cross sectional density indicates surface transverse velocities 0 1 ms 1 similar to those observed in the estuary the model further predicts appreciable transverse divergent currents at a fractional depth of 0 75 a prediction which has been tested in the estuary using a vertical array of accurately resolving current direction indicators

three dimensional wind driven flow in an elongated rotating basin abstract the wind driven circulation in lakes lagoons estuaries or coastal embayments is described with a linear steady three dimensional barotropic model in an elongated basin of arbitrary depth distribution on an f plane with rotation the vertically averaged velocity scales with the ekman depth rather than the maximum depth h0 as in the case without rotation near the closed ends of the basin the flow turns in viscous boundary layers because the length of the turning areas depends on the sign of the bottom slope and on the ratio of the ekman depth to h0 there is a striking contrast between the turning areas on either side of an observer looking toward the end of the basin in the northern hemisphere the turning area on the left is broad of order 1b where b is the basin half width the turning area on the right is narrow of order b and dynamically equivalent to the western boundary current in models of the wind driven ocean circulation ekman solutions are used to describe the ve

effects of winds on stratification and circulation in a partially mixed estuary 1 numerical experiments are conducted to investigate how axial winds affect stratification and circulation in the partially mixed estuary of chesapeake bay in the absence of rotational effects stratification in the estuary decreases following both down estuary and up estuary winds but stratification experiences larger reduction and takes longer to recover under up estuary winds in the presence of rotational effects wind driven lateral circulations cause the lateral straining of density field and weaken the shear in the along channel flows under the down estuary winds a counterclockwise lateral circulation steepens isopycnals in the cross channel sections while the coriolis force acting on it decelerates the downwind current in the surface layer and the upwind directed current in the bottom layer under the up estuary winds a clockwise lateral circulation flattens isopycnals in the cross channel sections and reduces the shear between the surface and bottom currents hence in the presence of rotational effects the lateral straining offsets the effects of longitudinal straining such that the asymmetry in stratification reduction is significantly reduced between the down estuary and up estuary winds regime diagrams based on wedderburn w and kelvin ke numbers are constructed to summarize the net effects of winds on estuarine stratification during both wind perturbation and postwind adjustment periods

the influence of lateral advection on the residual estuarine circulation a numerical modeling study of the hudson river estuary abstract in most estuarine systems it is assumed that the dominant along channel momentum balance is between the integrated pressure gradient and bed stress scaling the amplitude of the estuarine circulation based on this balance has been shown to have predictive skill however a number of authors recently highlighted important nonlinear processes that contribute to the subtidal dynamics at leading order in this study a previously validated numerical model of the hudson river estuary is used to examine the forces driving the residual estuarine circulation and to test the predictive skill of two linear scaling relationships results demonstrate that the nonlinear advective acceleration terms contribute to the subtidal along channel momentum balance at leading order the contribution of these nonlinear terms is driven largely by secondary lateral flows under a range of forcing conditions in the model runs the advective acceleration terms nearly always act in concert with the baroclinic pressure gradie

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

the lateral density distribution in a partially mixed estuary abstract the density distribution across the york river is characterized by distinct inhomogeneities especially in the upper 2 m of the water column the pattern of variability is repetitive and closely correlated with the semi diurnal tidal cycle and water depth in the shallow areas the water column remains vertically well mixed at all times the density differences are greatest at times of minimum currents at slack before flood the least dense water is located in a lens over the main channel towards the end of the flood cycle and at slack before ebb this is reversed with the least dense water situated over the shoals these density differences result in horizontal pressure gradients which at times may be of sufficient strength to generate localized lateral circulations such circulation patterns would form zones of convergence or divergence across the estuary depending on the particular density distribution

electron microprobe dating of monazites from high grade gneisses and pegmatites of the kerala khondalite belt southern india monazites of five samples one leptynitic garnet biotite gneiss one khondalite one augen gneiss and two pegmatites from the central and northern part ponmudi unit of the kerala khondalite belt kkb in southern india were analyzed with the electron microprobe dating technique monazites in the augen gneiss and the pegmatites yield grain sizes between 200 800 m th abundances are rather low 10 wt and the distribution of th u and pb within single grains is fairly homogeneous contrasting to this monazites in the leptynitic gneiss and the khondalite are small 150 m they often display very complex th u pb patterns and contain high th concentrations up to 20 wt the statistical treatment of individual ages from the investigated samples revealed three populations of lower proterozoic 1 9 ga upper proterozoic 580 ma and ordovician age 470 ma as well as mid proterozoic ages between 0 8 1 7 ga which are not regarded to be of geological significance lower proterozoic ages are preserved in the cores of monazites from leptynitic gneisses and khondalites they fairly agree with sm nd model ages for similar rocks of the kkb and give a minimum age for first monazite growth or complete homogenization the prominent pan african population with mean values between 540 and 580 ma is present in the leptynitic gneiss the khondalite and the augen gneiss and in line with published isotope ages for the kkb the ordovician population finally marks the emplacement of granitic pegmatites subsequent to the pan african high grade metamorphic event there is an obvious discrepancy between khondalites and leptynitic gneisses on the one hand and augen gneisses on the other concerning the presence of lower proterozoic ages while these are abundant in the former often rimmed by upper proterozoic ages they are completely absent in the latter it appears unlikely that lower proterozoic ages were completely reset during a pan african event exclusively in the augen gneisses while they were preserved in leptynitic gneisses and khondalites it is further concluded that the augen gneisses are of magmatic origin and were derived from porphyritic granites thus the upper proterozoic age of 605 37 ma calculated for the investigated sample approximates the time of magma emplacement which slightly precedes the peak stage of pan african high grade metamorphism in the kkb and of monazite crystallization from the granitic melt a characteristic feature of the investigated monazites is the resetting of lower proterozoic and pan african ages to significantly younger values due to partial pb loss monazites not shielded by other minerals e g garnet suffered selective mobilization of pb along fractures or at their rims while th and u concentrations remained almost unchanged the results presented in this study indicate that this was mainly due to fluid rock interaction it is concluded that thermal diffusion of pb even at the suggested temperatures of 900 c only had minor influence on the th u pb composition in monazite and that the closure temperature for this system must be significantly higher than previously assumed 750 c

oxygen isotope evidence for the mixing of magmatic and meteoric waters during tin mineralization in the mole granite new south wales australia oxygen isotope measurements of quartz in the tin mineralized permian mole granite new south wales support a model of progressive mixing of magmatic water and surface derived water of meteoric origin in mineralizing hydrothermal circulation systems the magmatic water observed as multiphase fluid inclusions in hydrothermal quartz biotite orthoclase topaz bearing pegmatites had a high temperature 550 degrees c high salinity 55 75 wt and a delta 18 o smow value of about 8 7 per mil the initial magmatic delta 18 o smow value of the granite is estimated to be about 9 per mil the meteoric water observed as liquid rich fluid inclusions in quartz from late veins of quartz sphalerite galena had a low temperature 250 degrees c low salinity 3 5 wt and a delta 18 o smow value of 15 per mil permian meteoric water is expected to be light isotopically owing to a near polar 70 degrees palcolatitude for the new england fold belt quartz from cassiterite quartz chlorite sericite ores has a wide range of delta 18 o values from 2 8 to 6 7 per mil this is intermediate between the values for quartz deposited from magmatic and from meteoric waters the fluid inclusions in these samples have homogenization temperatures of about 300 degrees c and a wide range of salinities 25 35 wt the variation in isotopic composition observed for quartz is attributed to a fluctuating isotopic composition of the hydrothermal solutions resulting from variable degrees of mixing of magmatic and meteoric water cassiterite has a narrow range of delta 18 o 5 9 7 2ppm which suggests precipitation of cassiterite over a narrow range of mixing of the hydrothermal fluids three cassiterite quartz mineral pairs with textures indicating synchronous crystallization imply cassiterite water fractionations of 2 2 per mil at 300 degrees c and 4 1 per mil at 370 degrees c hydrogen isotope data are less systematic due to postcrystallization isotopic exchange of hydrous minerals and the presence of younger fluids in secondary fluid inclusions in quartz

petrology and geochemistry of the neoproterozoic guaxupe granulite facies terrain southeastern brazil abstract geochemical and oxygen isotopic data on the neoproterozoic granulite facies rocks enderbites charnockite and charnokitic augen gneisses of guaxupe brazil are assembled geochemical discrimination function calculations show an igneous origin for majority of the rock types in the area major and trace element data especially ree are similar to tonalite and granodiorite oxygen isotope composition for charnockitic gneisses and mafic granulites yield 18o values in the range of 8 8 to 11 and fall in the range of quartzofeldspathic rocks of medium to high grade terrains elsewhere a small scale variation of 18o values compatible with the chemical data imply the preservation of pre metamorphic oxygen isotope compositions minimum peak pressure temperature conditions are 8 5 kbar and 850 c the high grade metamorphism did not appear to have altered significantly the geochemical and oxygen isotope compositions of the protoliths approximately 2 5 kbar of pressure decrease accompanied by 200 c cooling has been recorded for a portion of the cooling path the p t path is consistent with a single event namely the formation and uplift of the guaxupenappe in the neoproterozoic brasiliano cycle

mixed layer dynamics in a lake exposed to a spatially variable wind field1 field measurements are described detailing the formation of frontal structures in the surface mixed layer near the entrance of an embayment in a medium sized lake the observed evolution of the fronts is interpreted in terms of three well defined dynamical regimes the first differential heating is defined as the variable heat capture due to decreased surface heat losses and warmer surface water in the sheltered embayments the second variable deepening of the mixed layer is induced by a sudden increase in wind speed in the open central areas of the lake with only minimal mixing in the sheltered parts of the lake the third is the horizontal gravitational motion driven by the horizontal density gradients set up by the active deepening of the mixed layer in the exposed parts of the lake although detailed wind data were not available observations of the temperature and salinity fields show the existence of fronts in lakes and strongly suggest the importance of the above mechanisms in determining the horizontal variability of these fields in the surface mixed layer of medium sized lakes

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

post metamorphic co2 rich fluid inclusions in granulites in granulite facies samples from the adirondack mountains ny estimates of peak metamorphic co2 fugacities based on mineral equilibria are not consistent with estimates based on data for high density co2 rich fluid inclusions of the 21 adirondack samples investigated for this study all contain co2 rich inclusions inclusions occur in quartz apatite and garnet they range in size from 3 to 50 m and are without visible h2o in a few of the inclusions freezing point determinations and preliminary laser raman spectroscopy show the presence of small amounts 3 of other fluids n2 and h2s co2 liquid vapor homogenization temperatures are between 46 and 31 c corresponding to densities between 1 14 and 0 5 gm cc some of these densities are consistent with peak metamorphic entrapment 1 06 to 1 1 gm cc

stratified ekman layers under fair weather conditions the time averaged wind driven current forms a spiral in which the current vector decays and turns clockwise with increasing depth these spirals resemble classical ekman spirals they differ in that their rotation depth scale exceeds the e folding depth of the speed by a factor of 2 to 4 and they are compressed in the downwind direction a related property is that the time averaged stress is evidently not parallel to the time averaged vertical shear we develop the hypothesis that the flat spiral structure may be a consequence of the temporal variability of stratification within the upper 10 20 m of the water column this variability is associated primarily with the diurnal cycle and can be treated by a time dependent diffusion model or a mixed layer model the latter can be simplified to yield a closed solution that gives an explicit account of stratified spirals and reasonable hindcasts of midlatitude cases at middle and higher latitudes the wind driven transport is found to be trapped mainly within the upper part of the ekman layer the diurnal warm layer at tropical latitudes the effects of diurnal cycling are in some ways less important and ekman layer currents are likely to be significant to much greater depths in that event the lower part of the ekman layer is likely to be affected by stratification variability that may be nonlocal

formation of the trimouns talc chlorite deposit pyrenees from persistent hydrothermal activity between 112 and 97 ma for many economically important deposits precise duration and age of hydrothermal ore formation are poorly known we tackle these questions for the large trimouns talc chlorite deposit by u pb analyses of xenotime and monazite which crystallized within cm size geodes in the hanging wall dolostones formation of geodes and ree minerals occurred in relation to 300 350 c 0 2 0 3 gpa metasomatism along a host shear zone sixteen xenotime fragments broken off from four single euhedral grains define an age range from 112 to 97 myr and a monazite age of 99 myr some ages of individual fragments are grain specific whereas others show the same range of dates given the analytical uncertainties on individual fragments about 1 myr the absence of inherited components and the fact that no thermal event has affected these crystals after their formation these ages are interpreted to record continuous crystallization between 112 and 97 ma this means that the trimouns deposit was produced by hydrothermal activity lasting for at least 16 million years occurring along a shear zone through which fluids continuously or episodically circulated to allow ion transport from the country gneisses to the deposit locality persistent deformation and high heat flow related to the transtensional regime that opened the bay of biscay seems to be the most likely tectonic scenario to explain this activity

modeling the lateral circulation in straight stratified estuaries the dynamics of lateral circulation in an idealized straight estuary under varying stratification conditions is investigated using a three dimensional hydrostatic primitive equation model in order to determine the importance of lateral circulation to the momentum budget within the estuary for all model runs lateral circulation is about 4 times as strong during flood tides as during ebbs this flood ebb asymmetry is due to a feedback between the lateral circulation and the along channel tidal currents as well as to time varying stratification over a tidal cycle as the stratification is increased the lateral circulation is significantly reduced because of the adverse pressure gradient set up by isopycnals being tilted by the lateral flow itself when rotation is included a timedependent cross channel ekman circulation is driven and the tidally averaged bottom lateral circulation is enhanced toward the right bank when looking toward the ocean in the northern hemisphere this asymmetry in the tidally averaged bottom lateral circulation may lead to asymmetric sediment transport leading to asymmetric channel profiles in straight estuaries for the weakly stratified model run advection due to lateral currents is a dominant term in both the along channel and cross channel momentum equations over a tidal cycle and for the tidally averaged momentum equations in the tidally averaged along channel momentum equation lateral advection acts as a driving term for the estuarine exchange flow and can be larger than the along channel pressure gradient therefore it should not be ignored when estimating momentum budgets in estuaries

influence of lateral advection on residual currents in microtidal estuaries abstract the influence of nonlinear lateral advection on estuarine exchange flow is examined with a scaling analysis and eight groups of idealized numerical experiments nonlinear lateral advection is related to the linkage between lateral circulation and the lateral shear of the along estuary flow the relative contribution of lateral advection to the overall dynamics of a microtidal estuary is found to be a function of width and depth and of vertical mixing lateral advection is dynamically important in narrow and deep estuaries particularly under relatively weak vertical mixing the relative importance of lateral advection and the earth s rotation on estuarine dynamics can be evaluated in terms of the nondimensional rossby and ekman numbers ro and ek lateral advection is most effective at large ro and small ek and is negligible at small ro and large ek as expected the earth s rotation is most significant at small ro and ek and is negligible at large ro and ek under the influence of lateral adv

observed flow variability along the thalweg and on the coastal slopes of the gulf of finland baltic sea abstract bottom mounted adcp measurements from 10 installations collected between 2009 and 2014 and each lasting several months are analysed in order to distinguish between different flow regimes and to detect variability a along the thalweg of the elongated basin with different regimes in summer and in winter and b on the coastal slopes in the deep thalweg area the mean flow speed amounts to 6 13 cm s 1 whereas the maximum speeds appear in winter near the bottom of the basin and in summer within the halocline around 70 m depth the mean zonal flow component reveals a nearly depth uniform inflow during winter and a layered inflow outflow during summer in years where up estuary w to sw winds are stronger during the summer inflow dominates in upper layers and anti estuarine outflow dominates in deeper layers this causes the export of a salt wedge and the weakening of haline stratification infra low frequency zonal currents i e excluding topographic waves etc with periods of less than 10 days have a structure which is uniform with depth for 53 of the time in winter in summer a layered structure is present 65 of the time however during both periods the reversed estuarine flow inflow in upper layers and outflow in the bottom layer appears on average for 30 of the time the deep flow zonal component is well correlated with westward winds during summer r 0 84 and south westward winds during winter r 0 77 on the coastal slopes the speed of the currents are lower than in the thalweg region and they decay with depth in the vertical the flow exhibits a layered structure in both the winter and summer seasons

post granulite facies fluid infiltration in the adirondack mountains granulite facies lithologies from the adirondack mountains of new york contain alteration assemblages composed dominantly of calcite chlorite sericite these assemblages document fluid infiltration at middle to upper crustal levels cathodoluminescence of samples from the marcy anorthosite massif indicates that the late fluid infiltration is more widespread than initially indicated by transmitted light petrography alone samples that appear unaltered in transmitted light show extensive anastomosing veins of calcite 0 05 mm wide along grain boundaries in crosscutting fractures and along mineral cleavages the presence of the retrograde calcite documents paleopermeability in crystalline rocks and is related to the formation of high density co sub 2 rich fluid inclusions recognition of this process has important implications for studies of granulite genesis and the geophysical properties of the crust

from andesitic volcanism to the formation of a porphyry cu au mineralizing magma chamber the farallon negro volcanic complex northwestern argentina abstract the geological relations and geochemical composition of extrusive and subvolcanic intrusive rocks of the upper miocene farallon negro volcanic complex nw argentina were studied to reconstruct the evolution of a deeply eroded andesitic volcano over most its life history of some 3 5 my this paper is part of an integrated study of the processes that generate magmatic hydrothermal fluids responsible for the formation of porphyry cu au deposits here we present new data on bulk rock chemical and nd sr and pb isotopic compositions of unaltered volcanic and subvolcanic intrusive rocks for which geological relations and ages are constrained by field based stratigraphy and extensive ar ar geochronology the combined results indicate that voluminous volcanism started at ca 9 7 ma with the eruption of basaltic andesite to andesite lava flows and pyroclastic deposits this basic to intermediate volcanism persisted until 7 5 ma and was followed at 7 35 ma by the eruption of dacites as the last recorded major extrusive event the oldest andesitic intrusions emplaced at 9 0 ma were followed by hypabyssal intrusions of basaltic andesite andesite and dacite composition which intruded the volcanic sequence between 8 3 and 6 1 ma intrusions at 6 8 0 2 ma led to the formation of over 800 mt of porphyry cu au ore at bajo de la alumbrera it was formed by a large flux of magmatic hydrothermal fluids channeled through several phases of fractured dacitic porphyry which together with immediately following barren andesitic intrusions make up a composite stock after this magmatic hydrothermal event only minor rhyodacitic to rhyolitic intrusions were emplaced until magmatic activity ceased at 6 1 ma geochemical data for the magmatic rocks indicate that the evolution of the system was dominated by mixing of a mafic magma with a felsic magma that contained a component of crustal material as indicated by linear compositional correlations between compatible and incompatible elements initial strontium isotopic ratios vary between 0 7047 and 0 7118 while 143nd 144nd range from 0 5127 to 0 5124 and both isotopic variations correlate with each other and with sio2 content of the rocks after 8 5 ma a continuous increase in the silica content of intrusive rocks suggests the gradual formation of a magma chamber a substantial magma reservoir 7 km3 must have been established by the time of porphyry cu au mineralization to allow rapid release of a large volume of ore forming magmatic brine as a result of wholesale crystallization and de volatilization of the magma chamber

wind induced circulation in semienclosed homogeneous rotating basins the wind induced circulation over laterally varying bathymetry was investigated in homogeneous systems using the three dimensional regional ocean model system roms the investigation focused on the influence of the earth s rotation on the lateral distribution of the flow with particular emphasis on the transverse circulation along basin wind stress with no rotation caused a circulation dominated by an axially symmetric transverse structure consisting of downwind flow over the shoals and upwind flow in the channel along the whole domain transverse circulation was important only at the head of the system where the water sank and reversed direction to move toward the mouth the wind induced flow pattern under the effects of the earth s rotation depended on the ratio of the maximum basin s depth h to the ekman depth d the solution tended to that described in a nonrotating system as h d remained equal to or below 1 for higher values of h d the longitudinal flow was axially asymmetric maximum downwind flow was located over the right shoal in the northern hemisphere looking downwind the transverse component of velocity described three gyres the main gyre was clockwise looking downwind and occupied the entire basin cross section as expected from the earth s rotation and the presence of channel walls the other two gyres were small and localized and were linked to the lateral distribution of the along channel velocity component which in turn was dictated by bathymetry these results compared favorably with a limited set of observations and are expected to motivate future measurements

dynamics of wind driven circulation in a shallow lagoon with strong horizontal density gradient 1 albemarle pamlico sound aps is a shallow lagoonal estuary with weak stratification but strong horizontal density gradient idealized and realistic model simulations are conducted to examine the dynamics of wind driven circulation in aps two dimensionless parameters the ekman ek and wedderburn w numbers are found to be two key parameters in controlling the flow pattern and dynamics circulation in albemarle sound and northern pamlico sound is primarily driven by wind forcing and shows laterally sheared flows withek approaching 1 and wexceeding 1 analysis of the along channel momentum equation shows a balance among the wind stress barotropic pressure gradient due to sea level setup and bottom friction while the vertical vorticity is primarily determined by the balance between the wind stress curl and bottom stress curl in contrast circulation in southern pamlico sound is driven by both wind and gravitational forces and shows vertically sheared two layer flows with lowek and waround 1 both baroclinic and barotropic pressure gradients act against the wind stress to drive the two layer flows a regime diagram in the parameter space ofek and w is used to summarize variability of circulation pattern on the seasonal time scale northern pamlico sound is characterized by high ek and high w values and laterally sheared currents southern pamlico sound is usually characterized by low ek and low w values and vertically sheared flows but featuring laterally sheared flows during the fall when ek averages to over 0 5

textural and geochemical discrimination between xenotime of different origin in the archaean witwatersrand basin south africa abstract xenotime ypo4 of detrital diagenetic and hydrothermal origin within siliciclastic rocks of the archaean witwatersrand basin south africa has been identified on the basis of petrography and in situ ion microprobe shrimp age data the chemical composition of xenotime determined by in situ electron microprobe analysis can be correlated with its origin this allows the origin of any xenotime grain to be assessed by a non destructive microanalytical method prior to ion microprobe geochronology the main chemical discriminators are mree hree abundance normalised hree slope and eu anomaly and in some cases u and th contents igneous detrital xenotime 2800 ma is distinguished from diagenetic 2780 ma and hydrothermal

causes for large scale metal zonation around mineralized plutons fluid inclusion la icp ms evidence from the mole granite australia detailed reconstruction of the fluid evolution in several ore deposits associated with the sn w and base metal mineralized mole granite shows that multiple factors contributed to the zonal metal distribution around this intrusion information about the mechanism of ore formation was obtained from field relationships detailed petrographic studies and laser ablation inductively coupled plasma mass spectrometry la icp ms microanalysis of single fluid inclusions premineralization fluid inclusions in sn deposits are characterized by high sn w ratios whereas early fluid inclusions from w deposits contain higher w concentrations and comparatively low sn w ratios this indicates that the metal ratio in these deposits already was predefined by the composition of the magmatic input fluid however in both types of deposits the input fluid actually contained much higher concentrations of base metals pb zn cu etc than sn and w demonstrating that metal precipitation was highly selective the metal zonation around the mole granite therefore reflects both a compositional variation of the source fluid as well as sequential metal precipitation from it an additional process contributing to metal fractionation occurred by phase separation of the hydrothermal fluid into saline brine and low density vapor whereby cu b li as s ag la preferentially partitioned into the vapor phase analyses on six assemblages of unambiguously coexisting vapor and brine inclusions allowed direct determination of vapor brine distribution coefficients for 24 elements

assessment of the ore forming process of the gejiu tin district south china abstract the gejiu tin district of southern china is the largest tin polymetallic ore district in the world even though the mining operation has lasted more than 2000 years in this area the metallogenic mechanism of this gigantic tin mineralization is still controversial based on petrographic geochemical and zirconological information from this study we present a particular model of the magma evolution and tin mineralization for the gejiu tin district the ore forming processes involved both a batholithic biotite monzogranite bmg emplaced at 94 ma and a satellitic muscovite alkali feldspar granite mag emplaced at 72 ma the bmg and the mag were produced from a long lived magma chamber by two stages of magmatic activity during intracontinental orogeny in the youjiang block the hiatus between the two magmatic stages indicates that the deep seated magma chamber persisted during the dominant phase of the orogeny progressive fractional crystallization of the magma caused the extreme enrichment of incompatible elements which include ore forming components such as tin aqueous fluids and other volatiles in the residual magma when the regional tectonic environment evolved into the extensional regime at 72 ma the highly fractionated residual magma ascended and once emplaced it formed the highly evolved mag with a mean zircon crystallization age of 71 8 1 2 ma the mag is temporally and spatially associated with cassiterite bearing quartz vein cqv with a mean zircon crystallization age of 72 6 1 6 ma this metallogenic model of the bmg mag cqv association is generally applicable to other granite related metallic deposits in south china southeast asia and elsewhere australia bolivia brazil usa etc the recognition of this bmg mag cqv association in regional geological survey may facilitate the future exploration for this type of deposit

diachronous and independent histories of plutonism and mineralization in the cornubian batholith southwest england concordant u pb dates of magmatic monazites in the dominant coarse grained biotite muscovite granites of the late variscan cornubian batholith demonstrate that the emplacement of the six main plutons was diachronous ranging from 293 1 1 3 ma carnmenellis to 274 5 1 4 ma land9s end southern lobe 40 ar 39 ar age spectra for magmatic muscovites confirm that cooling to about 320 c at the present level of exposure was accomplished within 4 to 5 ma in each intrusion moreover age spectra for hydrothermal muscovites show that development of the major sn cu lodes of the south crofty mine commenced before 286 ma only 2 to 3 ma after cooling of the hosting cam brea granite a satellite of the carnmenellis pluton the older plutons had therefore approached ambient temperatures and had even experienced intense hydrothermal activity before emplacement of the youngest

u pb lu hf and trace element characteristics of zircon from the felbertal scheelite deposit austria new constraints on timing and source of w mineralization abstract combined in situ u pb lu hf and trace element la icp ms analyses were performed on zircons from the w mineralized k1 k3 orthogneiss and associated aplite gneiss from the felbertal scheelite deposit the textural and trace element characteristics suggest the presence of magmatic and hydrothermal zircon magmatic zircons have low concentrations of w 0 108 3 77 ppm nb 5 04 48 ppm u 691 3079 ppm b 0 26 6 57 ppm and ree y 640 4576 ppm and form euhedral cl bright cores with distinct oscillatory zoning zone a saturation of p in the granitic melt causing apatite crystallization explains the presence of two sub types of cl bright zircon cores distinguished by distinct p and ca concentrations and variable positive ce anomalies higher trace element abundances and lower zr hf ratios occur in cl dark zircons with weak oscillatory zoning zone b overgrowing the zircon cores and in granular textured zircons restricted to the aplite gneiss the increase in trace elements in zircon can be linked to the differentiation of the granitic melt and prolonged zircon crystallization during the transition from the late magmatic to the hydrothermal stage cl dark unzoned texture less domains zone b in k1 k3 orthogneiss zircons and granular textured zircons from the aplite gneiss have supra chondritic y ho ratios 29 62 indicating zircon growth in the presence of f rich hydrothermal fluids exsolved from the evolved k1 k3 melt zone b zircons have the highest concentrations of w 4 3 11 4 ppm nb 63 405 ppm b 7 3 135 ppm ree y 0 31 1 87 mass and u 1 23 5 56 mass they are interpreted as hydrothermal and related to w mineralizing fluids magmatic and hydrothermal zircon has identical u pb and lu hf isotopic signature indicating the same source the in situ u pb concordia ages of zircons of four k1 k3 orthogneisses and one aplite gneiss confine the emplacement period of this granitic series between 341 0 ma and 336 2 ma the initial hf t values ranging from 7 6 to 4 3 indicate a crustal protolith the felbertauern augengneiss is similar it yielded a u pb concordia age of 338 5 1 3 ma and initial hf t between 6 8 and 5 3 on the contrary zircons from the granatspitz gneiss yielded discordant u pb ages late carboniferous to early permian and the hf t values scatter between 3 1 and 2 5 excluding any relation with the k1 k3 orthogneiss our new la icp ms data corroborate the genetic relationship of the w mineralization at felbertal with the early carboniferous k1 k3 orthogneiss series the k1 k3 orthogneiss was part of a larger magmatic suite that developed during the variscan orogeny in the pre alpine basement of the tauern window in the visean

hydrothermal zircon geochronology age constraint on nanling range tungsten mineralization southeast china abstract the nanling range southeast china is well known for its wolframite bearing quartz vein wqv tungsten deposit this study focuses on the geochemistry and geochronology of zircons from the wqv and challenges the current view of the tungsten mineralization in the nanling range the features of the wqv zircons include 1 pale brown murky brown or orange red color and translucence under microscope 2 110 101 type crystal form 3 weak cathodoluminescence 4 enrichment of hf ranging from 1 97 to 7 83 wt hfo2 u ranging from 0 02 to 3 97 wt uo2 th ranging from 0 to 0 65 wt tho2 and p ranging from 0 to 1 82 wt p2o5 and 5 presence of solid hydrothermal and ore minerals and fluid inclusions these features indicate that the wqv zircons crystallized from hydrothermal fluids during tungsten mineralization the in situ la icpms u pb results of the wqv zircons from five different tungsten deposits in the nanling range yield similar ages ranging from 134 4 1 9 ma to 132 9 1 5 ma approximately 20 million years younger than proposed tungsten ore ages 155 5 ma several mineralization characteristics and field observations also cast doubt on the current model nanling range tungsten ore is the result of orthomagmatic processes the zircon characterization method provided in this study could be applied to tungsten metallogenic research in other parts of the world

solutions for subtidal flow in channels and estuaries under different integral constraints this study builds on huntley and ryan 2018 and related prior works on channels and estuaries by considering solutions for the same subtidal dynamics but with alternative integral flow constraints

rejuvenation of the fish canyon magma body a window into the evolution of large volume silicic magma systems voluminous unzoned phenocryst rich pyroclastic deposits considered as erupted batholiths provide a unique opportunity to investigate magmatic processes in silicic magmas the fish canyon tuff a well documented example of these monotonous ignimbrites displays evidence for simultaneous dissolution of feldspars 1 quartz and crystallization of hydrous phases during gradual near isobaric reheating from 720 to 760 8c these observations along with a high crystallinity 45 and near solidus mineral assemblage suggest that the fish canyon magma cooled to a rigid crystal mush before being partly remelted prior to eruption rejuvenation was triggered by intrusion of water rich mafic magmas at the base of the fish canyon mush but the mechanisms of heat transfer remain poorly understood the growth of amphibole during reheating requires addition of mafic components but the absence of any measurable gradients and the paucity of mafic enclaves in the fish canyon magma rule out a reheating event dominated by convective mixing with a mafic magma closed system processes such as heat conduction and convective self mixing could not account for the transport of externally derived mafic components we performed numerical simulations of upward percolation of a hot low density h2o co2 fluid phase gas sparging through a crystalline framework saturated with rhyolitic melt to assess the efficiency of such a process in rejuvenating silicic mushes in open systems sparging by 20 40 km 3 of gas extracted from 3000 km 3 of mafic magma is capable of reheating 7500 km 3 of silicic crystal mush by 40 8c in 150 200 k y moreover the vertical thermal gradient after 150 k y in most of the mush is small 25 8c in the upper 65 gas sparging also produces an increase in the internal pressure of silicic crystal mushes and may lead to the formation of crystal poor rhyolites by expelling interstitial melt however our simulations predict that filter pressing driven by sparging of externally derived gas could not solely account for the generation of the most voluminous rhyolites

understanding geologic processes with xenotime composition chronology and a protocol for electron probe microanalysis abstract xenotime ypo 4 is iso structural with zircon group minerals and lies at one end of a compositional solid solution with monazite as with monazite and zircon naturally occurring xenotime may accommodate significant concentrations of rare earth elements as well as th and u making it an important repository for these valuable geochemical marker elements and a potential geochronometer xenotime grows in sediments during diagenesis in low to granulite grade metamorphic rocks in migmatites and is common in peraluminous igneous rocks xenotime can be a complement or indeed an alternative to monazite and or zircon in geochemical and geochronological studies to maximise the petrographic potential of xenotime a complete understanding of its composition and relationship to rock forming assemblages is essential electron beam techniques provide micron scale resolution of compositional and textural variation and yield precise dates for individual micro volumes in multi domain grains methods for collecting trace element data by electron probe microanalysis differ from those routinely employed to collect major element concentrations careful characterisation of background curvature and background interferences around the th u and pb peaks is required to avoid large overlap correction for y l 2 3 on pb m analysis of pb is made on the m peak a broad array of geochemical and geochronological applications can take advantage of the links between xenotime composition and texture and the evolution of silicate mineral assemblages in a diversity of environments one example of metasomatised xenotime from a pegmatite in sw norway demonstrates a practical application to dating geologic processes as well as the potential limitations that arise in compositionally heterogeneous xenotime

response of a large stratified estuary to wind events observations simulations and theory for long island sound abstractthe response to wind events in the long island sound lis a large macrotidal estuary influenced by rotation and stratification is studied using long term ferry based current observations near the mouth unstratified and stratified numerical simulations forced with along estuary winds and analytic solutions based on linear barotropic theory the observed wind event velocity anomalies for down estuary winds have surface intensified downwind flows flanking a deeper central upwind flow response to up estuary wind events has a weaker magnitude and a broader and thicker downwind flow the downwind and upwind flows are more laterally aligned than vertically layered as determined by a newly defined dimensionless lateral alignment index simulation results and analytic solutions share the gross spatial patterns of the observed response though statistical measures indicate weak agreement along estuary variations in the simulation results and analytic solutions follow similar trends and are strongly

fluid heterogeneity during granulite facies metamorphism in the adirondacks stable isotope evidence the preservation of premetamorphic whole rock oxygen isotope ratios in adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived hot co2 h2o fluids during granulite facies metamorphism this conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations the data suggest that these rocks were not an open system during metamorphism that fluid rock ratios were in many instances between 0 0 and 0 1 that externally derived fluids as well as fluids derived by metamorphic volatilization rose along localized channels and were not pervasive and thus that no single generalization can be applied to metamorphic fluid conditions in the adirondacks

effect of the earth s rotation on the circulation in regions of freshwater influence recent surveys in various regions of freshwater influence have shown considerably different flow patterns in each region an analytical model including viscous effects and the earth s rotation is proposed to examine the along channel flow pattern and to explain the differences model results show that the flow pattern is strongly dependent on the ekman number e with a large ekman number e 1 the system is governed by gravitational circulation and thus horizontal density gradients in along channel direction are important the whole water column is in the ekman layer and consequent jet inflow penetrates the surface over a deep depression if the bottom topography varies in a cross channel direction with an intermediate ekman number e 0 1 this jet inflow concentrates in the lower layer in which the viscosity still plays an important role the flow in the upper layer is on the other hand determined by the geostrophic balance the contribution by the geostrophic flow becomes larger so that the cross channel density gradients are important when die ekman number is small e 0 01 since the ekman layer is clung to the bottom the jet inflow exists only in the thin bottom layer the hydrographic and acoustic doppler current profiler surveys were conducted in ise bay japan both the density structure and the flow pattern were different from those observed in many drowned river valleys a strong jet inflow existed in the lower layer over the depression while the flow in the upper layer suggested anticyclonic circulation the estimated ekman number is 0 07 in the bay and thus the observed pattern is consistent with the model result when e 0 1

mineral equilibria and zircon garnet and titanite u pb ages constraining the ptt path of granite related hydrothermal systems at the big bell gold deposit western australia the big bell deposit 75 t gold is located in a narrow spur of the meekatharra greenstone belt yilgarn craton western australia two ore bodies are located in a calcic potassic contact alteration zone overprinting lineated granodiorite dykes and amphibolite almandine cummingtonite hornblende skarn 1 3 g t au 1700 g t as 330 g t w and the muscovite microcline gneiss 3 5 g t au 580 g t sb 620 g t w of the main lode genetic models vary from pre to post metamorphic replacement hornblende plagioclase pairs in amphibolite constrain peak metamorphic temperature to 670 50 c in contrast garnet biotite thermometry provides estimates of 578 50 and 608 50 c for garnet cordierite biotite schist bordering the skarn and enveloping the main lode garnet cordierite and garnet hornblende pairs extend the range of fluid temperature to 540 65 c well below peak metamorphic temperature at 540 600 c the alteration assemblage andalusite sillimanite constrains pressure to 300 400 mpa corresponding to 11 14 km crustal depth published u pb ages indicate that metamorphism took place in the aureole of the southeast granodiorite tonalite batholith 2740 2700 ma followed by gold mineralization at 2662 5 ma and by the emplacement of biotite granite and sn ta nb granite pegmatite dykes at 2625 2610 ma amphibolite xenoliths in granite northwest of the deposit record the lowest temperature 628 50 c suggesting it lacks a metamorphic aureole the rare metal dykes are spatially associated with epidote albite and andradite diopside skarns 1 5 g t au mined where enriched in the weathered zone we analysed hydrothermal zircon intergrown with andradite concordant u pb ages of 2612 7 and 2609 10 ma confirm the presence of a second granite related system the zircons display oscillatory zoning and have low th u ratios 0 05 0 08 low th titanite from an albite granite dyke has a concordant but reset u pb age of 2577 7 ma

geochemical characterisation of xenotime formation environments using u th abstract xenotime ypo4 is a trace component in many metasedimentary and some igneous rocks altered rocks and many hydrothermal ore assemblages where it forms in response to a range of different processes from igneous crystallisation to low temperature early diagenesis due to its wide range of formation temperatures its suitability and isotopic robustness for reliable u pb geochronology dissolution precipitation characteristics during overprint events and widespread occurrence it is one of the most valuable minerals for u pb geochronology leading to four dimensional 4d studies of many terranes the formation environment of xenotime can be deduced from careful petrography and reliable u pb in situ geochronology within a 4d framework further xenotime is a physically robust mineral during sediment transport and may carry distinctive geochemical fingerprints including age to secondary environments from published works we review the u th contents of well characterised examples of xenotime formation to provide chemical fingerprints which assist in identifying the xenotime formation environment although the u th characteristics of xenotime from all formation environments show considerable overlap we make the following observations which may be distinctive of some ore formation environments i hydrothermal xenotime formed from low salinity ore fluids e g iron ore and orogenic gold deposits trend to have the lowest u contents 10 iii diagenetic xenotime has the most variable and highest u th whereas iv xenotime from precambrian orogenic gold deposits has the least variable and lowest u th petrogenetic inferences from these observations for ore deposit research and exploration include i support for the homogenising effect of the crustal scale of the fluid system in precambrian orogenic gold deposits and ii the potential for distinctive u th geochemical fingerprints for u ores and some au ores these characteristics may be reflected in detrital xenotime grains recovered from routine exploration sampling programs

magmatic to hydrothermal crystallization in the w sn mineralized mole granite nsw australia part i crystallization of zircon and ree phosphates over three million years a geochemical and u pb geochronological study abstract zircon monazite and xenotime crystallized over a temperature interval of several hundred degrees at the magmatic to hydrothermal transition of the sn and w mineralized mole granite magmatic zircon and monazite thought to have crystallized from hydrous silicate melt were dated by conventional u pb techniques at an age of 247 6 0 4 and 247 7 0 5 ma respectively xenotime occurring in hydrothermal quartz is found to be significantly younger at 246 2 0 5 ma and is interpreted to represent hydrothermal growth from associated fluid inclusions it is concluded that it precipitated from a hydrothermal brine 600 c which is below the accepted closure temperature for u pb in this mineral these data are compatible with a two stage crystallization process precipitation of zircon and monazite as magmatic liquidus phases in deep crustal magma followed by complete crystallization and intimately associated sn w mineralization after intrusion of the shallow sill like body of the mole granite later hydrothermal formation of monazite in a biotite fluorite topaz reaction rim around a mineralized vein was dated at 244 4 1 4 ma which distinctly postdates the mole granite and is possibly related to a younger hidden intrusion and its hydrothermal fluid system obtaining precise age data for magmatic and hydrothermal minerals of the mole granite is hampered by uncertainties introduced by different corrections required for multiple highly radiogenic minerals crystallising from evolved hydrous granites including 230 th disequilibrium due to th u fractionation during monazite and possibly xenotime crystallization variable th u ratios of the fluids from which xenotime was precipitating elevated contents of common lead and post crystallization lead loss in zircon enhanced by the fluid saturated environment the data imply that monazite can also survive as a liquidus phase in protracted magmatic systems over periods of 10 6 years the outlined model is in agreement with prominent chemical core rim variation of the zircon

rare earth elements ree minerals in the silius fluorite vein system sardinia italy publisher elsevier articletitle rare earth elements ree minerals in the silius fluorite vein system sardinia italy journaltitle ore geology reviews articlelink http dx doi org 10 1016 j oregeorev 2015 11 016 content type article copyright copyright 2015 elsevier b v all rights reserved