fluid inclusion petrography of sw england granites and its potential in mineral exploration fluid inclusions in granite quartz from sw england provide a record of the complex and protracted hydrothermal history of this important metallogenic province regional variations in terms of the different types of inclusions can be correlated on an inter pluton scale with both the texture of the host granite and the extent to which it is mineralized on an intra granite scale those areas where mineralization is particularly pronounced show a higher overall inclusion abundance than areas where little or no mineralization is known to occur the types of fluid inclusion most commonly related to sn w cu mineralization are halite free moderate temperature inclusions inclusions containing visible co2 at room temperature are restricted to two localities in sw england both of these contain stockwork vein swarm tungsten mineralization these regional fluid inclusion anomalies show that fluid inclusion petrography using a simple petrographic microscope has potential application in the field of mineral exploration

tourmalinite from northern guangxi china the extensive development of tourmalinite is a feature that distinguishes the northern guangxi polymetallic tin province of china from similar metallogenic provinces elsewhere two types of tourmalinite occur in the province the first type in the lower part of the early proterozoic sibao group is bedded stratiform or lenticular tourmalinite that shows well developed laminated gel and degelatinized structures its mineral assemblage is very simple and the grain size ranges from 2 to 8 m this tourmaline is relatively rich in mg with an fe fe mg ratio of 0 25 0 50 the second type of tourmalinite occurs as lodes distributed in the exocontact zone of late proterozoic biotite granite intrusions its mineral assemblage is relatively complex the tourmaline is present as euhedral or subhedral crystals ranging from 0 1 to 3 5 mm mostly from 0 5 to 1 mm this tourmaline commonly exhibits a radiating zoned structure with fe fe mg ratios of 0 64 0 79 it is suggested that the bedded tourmalinite formed by exhalation in an early proterozoic spreading ridge environment whereas the vein tourmalinite formed in a plate convergence setting genetically associated with emplacement of late proterozoic biotite granite as the tourmalinites themselves are related to mineralized rocks and orebodies their origin and the related boron cycle of the region reflect to some extent the formation and evolution of the associated polymetallic tin deposits of the region

observations of near surface currents and hydrography in the connecticut river plume with the surface current and density array it has been well established that the connecticut river forms a large plume in the vicinity of its mouth during periods of high river discharge the plume is bounded on the offshore side by a distinct front where the water color and turbidity changes rapidly and foam and detritus accumulate though there have been many observations of similar fronts throughout the world the details of the density and velocity structure in the vicinity of a plume front and the propagation velocity of the feature have not been adequately resolved to better observe the properties of these phenomena we have constructed a ship mounted array of instruments to measure the near surface currents and density scud distribution in plumes and fronts scud provides current velocity components at four levels and conductivity and temperature at five levels in the upper 3 m of the water column by using the global positioning system in differential mode to obtain position the system has a horizontal resolution of 5 m at a ship speed of 1 2 ms 1 estimates of the ground referenced water velocity components have an uncertainty of approximately 0 1 ms 1 to demonstrate the performance of the scud array we report the preliminary results of an observation program to examine the variability of the front of the connecticut river plume in the spring of 1994 several 200 m across front scud transects separated by 200 m were obtained during the mid ebb in long island sound during this period the front advanced to the west with a velocity of the order of 0 1 ms 1 in opposition to an eastward tidal current of 1 0 ms 1 a practical salinity increase of 20 in less than 10 m was observed at the front on crossing into the plume in concert the front normal velocity component decreased by 0 5 0 1 ms 1 over 10 m and the vertical shear in the front parallel component decreased dramatically the performance and potential of the instrumentation and the implication of the observations for the development theories of river plume fronts are discussed

coupled mineral fluid evolution of a basin and high kaolinization in the sw england granites in relation to the development of the plymouth basin

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

turbulence and entrainment in a buoyant surface plume in winter tidal outflow from the leschenault estuary forms a buoyant sheared stratified plume in koombana bay on each outgoing tide the turbulence in the plume and the local entrainment into the plume are examined based on measurements collected in an intensive field program coherency measurements between horizontally separated sensors are used to examine the anisotropy of the turbulence the effects of viscosity and buoyancy on the turbulence are studied using an activity diagram which is also an indicator of the mixing efficiency and total mixing the osborne cox model is tested and found to be valid in the plume

models of convective fluid flow and mineralization in south west england two notable features of the mineralization in sw england are the asymmetrical pattern of mineral lodes and the mineral zoning within this distribution despite the fact that many theories have been advanced to explain the mechanisms of mineralization qualitatively no numerical models have been produced in this paper the finite element technique is used to construct a very simple model which helps to explain general features of the pattern of mineralization the model describes the steady state convection of fluid in the environment of the cornubian batholith convection is driven by the radiothermal contrast between the granite and the host rocks results show that the locations of upward flowing hot fluids are determined by the three dimensional shape of the batholith initially upward flow was concentrated along the axis of the batholith and these regions correlate with high temperature mineralization erosion of the cover rock above the granites altered the fluid flow pattern such that the upward flow became concentrated outside the outcropping granites these regions correlate with low temperature mineralization a correlation also exists between kaolinization and areas of downward flowing fluid for present day levels of erosion

the effects of channels and shoals on exchange between the chesapeake bay and the adjacent ocean the role of bathymetric changes in determining the transport of water and salt in the lower chesapeake bay lcb was investigated using high resolution acoustic doppler current profiler adcp and conductivity temperature depth profiles a cross channel transect was repeated eight times during neap tides on october 6 7 1993 which illustrated the lateral structure of the longitudinal and transverse flow fields and the intratidal variations in the flow structure across the lcb amplitude and phase of the m2 tidal component as well as the mean flow velocity were calculated using least squares fitting at every point of a uniform grid obtained from the adcp data the results differ from the classical two layer pattern of estuarine circulation modified by coriolis effects but are consistent with recent hydrographic observations semidiurnal flow was highest over the navigational channels and lateral gradients were strongest in regions of sharp bathymetric changes the phase lag of the semidiurnal flow also showed lateral and vertical gradients that represented advances at the bottom with respect to the surface and over the shoals in relation to the channels the section of the water column measured indicated a mean outflow of 0 7 104 m3 s and a mean inflow of 1 3 104 m3 s the apparent gain of water by the estuary during the period of observation can be explained by meteorologically forced net barotropic inflow the depth averaged mean longitudinal flow consisted of inflow in the navigational channels and outflow over the shoals the mean transverse flow showed near surface convergence over the channels we propose a possible explanation for the observed flow and density structure as follows the barotropic and baroclinic forcing interact with the bathymetry to extend the inflow from the bottom to the surface thereby inducing a transverse circulation that yields near surface convergence over the channels

cross shore stratified tidal flow seaward of a mega nourishment abstract the sand engine is a 21 5 million m 3 experimental mega nourishment project that was built in 2011 along the dutch coast this intervention created a discontinuity in the previous straight sandy coastline altering the local hydrodynamics in a region that is influenced by the buoyant plume generated by the rhine river this work investigates the response of the cross shore stratified tidal flow to the coastal protrusion created by the sand engine emplacement by using a 13 h velocity and density survey observations document the development of strong baroclinic induced cross shore exchange currents dictated by the intrusion of the river plume fronts as well as the classic tidal straining which are found to extend further into the nearshore from 12 to 6 m depth otherwise believed to be a mixed zone estimates of the centrifugal acceleration directly after construction of the sand engine showed that the curvature effects were approximately 2 times stronger suggesting that the sand engine might have played a role in controlling the cross shore exchange currents during the first three years after the completion of the nourishment presently the curvature effects are minute

petroleum seepages and impregnations in great britain abstract this paper documents 173 occurrences of surface petroleum seepages and impregnations in great britain a brief description is given of the seven main areas where they are found the descriptions range from pore fillings of bitumen to steady flows of oil and gas the principal areas in which seepages are found are as follows the orcadian basin of north east scotland the midland valley of scotland the flanks of the pennines the welsh borderlands cornwall the dorset coast of the wessex basin and the south eastern weald stratigraphically the seepages range from caledonide basement to holocene peat the principal sources for the petroleum are devonian oil shales orcadian basin carboniferous shales and coals midland valley pennines welsh borderlands devon and cornwall and the liassic wessex and wealden basins several anomalous seepages are recorded from welsh and scottish basement there are three clearly defined styles in which the seepages occur many are found where permeable carrier beds unconformably overlie impermeable basement around the margins of basins orcadian basin midlands carboniferous basin others are fault related especially in the wessex and wealden basins the seepages in the cornish tin mines are best explained as sourced from the culm series and drawn by the convective flow of connate waters into the thermal chimneys of the granite intrusions

a gravity and magnetic interpretation of the structure of the irish midlands and its relation to ore genesis regional gravity and magnetic data from the irish midlands have been studied in an attempt to map the structures within and beneath the lower carboniferous limestones the magnetic data suggest that the precambrian crystalline basement is at a depth of 3 4 km and is overlain by ordovician volcanics of varying magnetization a fourier analysis of the gravity field has been used to construct a residual gravity map which represents principally the gravity effect of shallow sources these sources are probably the topographic variations of dense ordovician volcanics beneath a less dense succession of ordovician to carboniferous sediments the residual gravity clearly shows the presence of a series of linear volcanic blocks and sedimentary troughs trending ne sw the major mineralized zones in the area all occur close to the margins of these troughs this investigation indicates that the initial position of the midland plain was controlled by caledonide factors some of which modified the later subsidence which we attribute to hercynian plate margin processes the genesis of the major ore bodies is probably associated with de watering of the shale filled troughs the subsequent concentration of metal bearing fluids along the trough margins and their deposition in relatively unloaded carbonate host rocks on the up standing blocks

depth of emplacement fluid provenance and metallogeny in granitic terranes a comparison of western thailand with other tin belts the most important tin mineralization in thailand is associated with the late cretaceous to middle tertiary western thai granite belt a variety of deposit types are present in particular pegmatite vein and greisen styles of mineralization a feature common to most of the deposits is that they are associated with granites that were emplaced into the khang krachan group which consists of poorly sorted carbonaceous pelitic metasediments most of the deposits contain low to moderately saline aqueous fluid inclusions and aqueous carbonic inclusions with variable ch4 co2 ratios low salinity aqueous inclusions represent trapped magmatic fluid in at least one case the nong sua pegmatite based on their occurrence as primary inclusions in magmatic garnet aqueous carbonic inclusions are commonly secondary and neither the co2 nor nacl contents of these inclusions decrease in progressively younger inclusions implying that they are not magmatic in origin reduced carbon is depleted in the metasediments adjacent to granites and the d values greisen muscovites are variable but are as low as 134 per mil indicative of fluid interaction with organic graphitic material this suggests that the aqueous carbonic fluid inclusions represent fluids that were produced at least in part during contact metamorphism metasomatism by comparing the western thai belt with other sn w provinces it is evident that there is a strong correlation between fluid composition and pressure in general low to moderately saline aqueous inclusions and aqueous carbonic inclusions are characteristic of mineralization associated with relatively deep plutonic belts mineralized pegmatites are also typically of deeper plutonic belts and pegmatite hosted deposits may contain cassiterite that is magmatic crystallized from granitic melt or is orthomagmatic hydrothermal crystallized from aqueous or aqueous carbonic fluids in origin the magmatic aqueous fluids those that were exsolved from granitic melts are interpreted to have had low salinities as a consequence of the low salinities tin is partitioned in favour of the melt on vapour saturation thus with a high enough degree of fractionation the crystallization of a magmatic cassiterite or different sn phase such as wodginite is inevitable because tin is not partitioned in favour of the vapour phase upon water saturation of the granitic melts it is proposed that relatively deep vein and greisen systems tend to form by remobilization processes in addition many deeper greisen systems are hosted in part by carbonaceous pelitic metasediments and the reduced nature of the metasediments may play a key role in remobilizing tin sub volcanic systems by contrast are characterized by high temperature high salinity fluids owing to the high chlorinity tin is strongly partitioned in favour of the vapour and cassiterite mineralization can form by of orthomagmatic hydrothermal processes similar relationships between the depth of emplacement and fluid composition also appear to apply to other types of granite hosted deposits such as different types of molybdenum deposits

comparison of fluid inclusions in coexisting cogenetic wolframite cassiterite and quartz from st michael s mount and cligga head cornwall england abstract the st michael s mount occurrence and cligga head deposit are typical examples of w sn mineralization in the cornwall district in s w england mineralization consists of quartz wolframite cassiterite and various amounts of base metal sulfides in sheeted veins associated alteration includes greisenization and argillization in both areas textural evidence for contemporaneous deposition of the ore minerals wolframite and cassiterite with quartz is generally ambiguous previous studies state that the quartz and wolframite are intergrown but do not address the genetic relation between them in this study microthermometry was performed on fluid inclusions in wolframite cassiterite and quartz the inclusions in wolframite were observed using an infrared microscope and those in cassiterite and quartz were observed with visible light at st michael s mount th values for primary inclusions in quartz average 311 c and in wolframite average 369 c salinities average 7 3 eq wt nacl in quartz and 4 2 eq wt nacl in wolframite at cligga head the average th values for primary inclusions in the various minerals are cassiterite 352 c wolframite 324 c and quartz 295 c fluid inclusion salinities average 5 3 eq wt nacl in cassiterite 3 9 eq wt in wolframite and 6 0 eq wt nacl in quartz the magnitude of the changes in th measurements between minerals cannot be accounted for by post trapping changes and therefore must be due to actual differences in the temperatures of deposition these data suggest that the ore minerals wolframite and cassiterite were deposited earlier than the associated quartz even though conclusive textural evidence is lacking wolframite and cassiterite were deposited at about the same temperature at st michael s mount but at cligga head cassiterite was deposited at higher temperatures than wolframite certainly in these areas the gangue minerals do not provide reasonable estimates of the depositional conditions of the ore minerals even though they are intimately intergrown

seasonal patterns of wind stress and wind stress curl over the gulf of mexico meteorological observations from an array of stations deployed along the periphery of the gulf of mexico between 1990 and 1993 are used to describe the seasonal fluctuations in patterns of atmospheric variables from a contemporary set of measurements seasonal maps of wind stress based on these measurements resemble wind stress maps based on ship observations as published by elliott 1979 rather than maps based on analyses of numerical weather forecasts as published by rhodes et al 1989 particularly near the western boundary of the gulf seasonal maps of wind stress curl are characterized by positive curls over the western and southwestern gulf the central result of this study is to document the important role of the mountain chain which extends along the southwestern section of the gulf in channeling the wind toward the isthmus of tehuantepec

simulation of geological processes using an expert system regional geological processes may be simulated rapidly using a combination of image processing and expert system techniques rapid interactive simulations are achieved with image processing and a reduction of the problem to the two map dimensions in order to manage these multiple simulations expert system software is used to infer the optimum path through the modelling options we illustrate our approach by referring to a computer system designed to produce maps of the prospectivity of carbonate hosted pb zn f ba buried mineralization in the east midlands of england the system simulates the process of mineralization near the end of the carboniferous involving the rapid expulsion of metal rich brines from a series of small shale basins by e w compressive tectonism there is preferential migration of these fluids along reactivated basin bounding faults and deposition of the metals as sulphides within neighbouring limestone platforms computer simulation using this or similar approaches has particular potential for multidisciplinary projects in regional geology where disciplinary expertise in handling different types of data and in performing the simulation needs to be replicated

three dimensional vp and vs structural models associated with the active subduction and collision tectonics in the taiwan region summary 3 d vp and vs models for the crust and upper mantle beneath the taiwan area have been determined using selected high resolution earthquake data from an island wide seismic network and two local seismic arrays lateral structural variations in the upper crust as also evident from surface geology are responsible for the observed large traveltime residuals or station corrections prior shallow velocity information inferred from traveltime residuals and joint hypocentral determination jhd station corrections for the uppermost crust is essential to facilitate a reliable tomographic inversion a finite difference method that is efficient and accurate for a highly heterogeneous velocity structure is applied to calculate p and s wave traveltimes from the source to receiving stations all earthquakes in the taiwan central weather bureau s catalogue are then relocated using the resultant 3 d vp and vs models the depth of the moho varies significantly especially along the east west direction in the western coastal plain and western foothills the depth of the moho is around 35 km which deepens gradually eastward reaches a maximum depth of 55 km beneath the eastern central mountain range shallows up rapidly beneath the longitudinal valley and coastal range and merges with the thin philippine sea plate offshore of eastern taiwan in central taiwan the central mountain range is bounded to the east and west by two steeply westward dipping active faults from the upper crust to a depth of about 30 km therefore the uplifted and thickened central mountain range serves as a backstop for the converging eurasian and philippine sea plates the crust beneath the central mountain range is characterized by a brittle high velocity and seismically active upper crust 15 km and a ductile low velocity and aseismic mid to lower crust below 15 km most probably due to the high geothermal activity from the excess heat supplied from the hot upper mantle beneath the thin oceanic crust to the east from the surrounding hotter upper mantle beneath the thickened continental crust and from shear heating during active collision the collision zone in eastern taiwan is characterized by an active and steeply eastward dipping seismic zone along a region of low vp and high vp vs ratio near the taitung region in southeastern taiwan it transforms into an active westward steeply dipping seismic zone along a transition zone between the high vp and vs oceanic crust and the low vp and vs continental crust near hualien region in central eastern taiwan there is no apparent seismicity within many sedimentary basins imaged from the tomographic inversion however af ew basins are either bounded on one side by an active fault or are characterized by blind faults beneath the geometry of the subduction zone in northeastern taiwan can be clearly imaged from the relocated earthquake locations behind the subduction a region of low vp and high vp vs ratio at depths of 5 to 10 km can be identified beneath the tatun chilung volcano group indicating a potential magma reservoir two steeply dipping linear seismic zones in the volcano region may mark the upward escape paths of the magmatic materials in the region

tides of mississippi sound and the adjacent continental shelf abstract hourly water level and current data were collected in mississippi sound and the adjacent continental shelf from april 1980 to october 1981 amplitudes and epochs of the principal tidal constituents were calculated for each location the data were used to construct cotidal charts and describe characteristics of the predominant diurnal tide the pattern of the diurnal partial tides on the shelf is explained by reflection of first class waves propagating normal to the coast the period of the k 1 tide equals the inertial period just offshore of mississippi sound the resulting diurnal shelf currents are sverdrup waves with typical speeds of 5 10 cm s 1 the tidal wave is transformed into a rectilinear shallow water wave as it enters the tidal inlets of mississippi sound the form number of the shelf currents changes from 8 5 to 2 1 in the inlets due to enhancement of the semidiurnal currents this is a result of continuity constraints which transform currents in the inlets within mississippi sound the tidal waves shoal and become increasingly progressive in response to bottom friction

integration of detrital gold microchemistry heavy mineral distribution and sediment geochemistry to clarify regional metallogeny in glaciated terrains application in the caledonides of southeast ireland regional exploration for rare and precious metal enrichment traditionally uses multielement geochemical analysis of the fines 150 m fraction of stream sediments however these data can be misleading in glaciated regions with complex geology here we compare the spatial distributions of data from sediment fines with distributions of heavy mineral concentrates including detrital gold in the same region gold grains are characterized according to abundance and morphology plus a microchemical signature from the combination of alloy analysis and systematic identification of mineral inclusions revealed in polished sections these inclusions survive indefinitely and are indicative of hypogene mineralogy whereas the metal loadings of fines may be affected by weathering or anthropogenic activity all three approaches are mutually supportive sediment fines analyses provide a basis for more labor intensive targeted gold grain studies which in turn highlight specific gold element associations useful for interpretation of geochemical data sets spatial distributions of resistate heavy mineral suites constrain the directions and extents of glacial transport which facilitates more confident interpretations of placer lode relationships from gold grain studies characterization of 2 160 gold grains from 40 localities in the auriferous region of southeast ireland provided a clear indication of proximity of gold to source and identified gold derived from different episodes of mineralization a distinction is apparent between gold in the south of the region wexford likely derived from widespread stratabound au as fe s mineralization and that in the north wicklow where the historical placer mining district of the goldmines river yielded gold with inclusions exhibiting a distinctive pb bi as association the goldmines river placers formed by the efficient accumulation and preservation of detrital gold derived from several discrete intravalley sources we recommend that a combination of classic stream sediment geochemistry heavy mineral analysis and gold grain studies is used more widely to provide additional insights on the location and nature of gold mineralization and regional metallogeny in regions of poor exposure and complex geology

detailed structures of the subducted philippine sea plate beneath northeast taiwan a new type of double seismic zone we studied the detailed structure of the subducted philippine sea plate beneath northeast taiwan where oblique subduction regional collision and back arc opening are all actively occurring simultaneous inversion for velocity structure and earthquake hypocenters are performed using the vast high quality data recorded by the taiwan seismic network we further supplement the inversion results with earthquake source parameters determined from inversion of teleseismic p and sh waveforms a critical step to define the position of plate interface and the state of strain within the subducted slab the most interesting feature is that relocated hypocenters tend to occur along a two layered structure the upper layer is located immediately below the plate interface and extends down to 70 80 km at a dip of 40 50 below approximately 100 km the dip increases dramatically to 70 80 the lower layer commences at 45 50 km and stays approximately parallel to the upper layer with a separation of 15 5 km in between down to 70 80 km below that the separation decreases and the two layers seem to gradually merge into one wadati benioff zone we propose to term the classic double seismic zones observed beneath japan and kuril as type i and that we observed as type ii respectively a global survey indicates that type ii double seismic zones are also observed in new zealand near the southernmost north island cascadia just north of the mendocino triple junction and the cook inlet area of alaska all of them are located near the termini of subducted slabs in a tectonic setting of oblique subduction we interpret the seismogenesis of type ii double seismic zones as reflecting the lateral compressive stress between the subducted plate and the adjacent lithosphere originating from oblique subduction and the downdip extension from slab pulling force the upper seismic layer represents seismicity occurring in the upper crust of a subducted plate and or along the plate interface whereas the lower layer is associated with events in the uppermost mantle

kinematic analysis of the taiwan slate belt the taiwan slate belt can be subdivided into two structural domains based on fold and cleavage geometries and finite and incremental strain histories the two belts correspond generally to two topographic ranges in taiwan the hsuehshan range and the backbone range rocks in the hsuehshan range are characterized by upright symmetric folds and a steeply se dipping axial planar pressure solution cleavage synkinematic fibers in pressure shadows are typically straight parallel to cleavage and plunge downdip indicating that the rocks experienced a coaxial strain history in contrast rocks in the backbone range are characterized by inclined asymmetric folds that verge toward the foreland and display a moderately se dipping axial planar pressure solution cleavage synkinematic fibers are straight and parallel to the downdip stretching lineation in xy sections in xz sections however the fibers typically display a clockwise curvature viewed to the ne indicating a noncoaxial strain history we propose that the different strain histories are due at least in part to differences in the original tectonostratigraphic settings of the strata in the two ranges strata in the hsuehshan range are interpreted to have been deposited in a half graben associated with an east dipping normal fault the strata of the backbone range in contrast are considered to have been deposited on the unfaulted chinese continental margin we suggest that the basement horst on the east side of the half graben functioned as a steep faced rigid backstop that concentrated pure shear deformation throughout most of the hsuehshan range shear strains were apparently limited to zones near the base of the sedimentary sequence and adjacent to the backstop the noncoaxial strains characteristic of the backbone range are interpreted to be the result of a regional scale shear zone that formed as chinese basement and its sedimentary cover were underthrust southeastward beneath the luzon arc

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

manganiferous garnet underlying the bousquet gold orebody quebec metamorphosed manganese sediment as a guide to gold ore garnet quartz muscovite rock stratigraphically underlies a volcanogenic pyritic gold orebody within bousquet township abitibi greenstone belt quebec garnet constitutes only 3 of the rock within muscovite rich layers near its east and west ends whereas the rock contains 12 of garnet near its center trails of quartz carbonate and sulphide inclusions and parallel bands of an ultrafine black opaque mineral produce a layered appearance in the garnet garnet consists of 25 mno and is zoned with maximum mno content at its center furthermore mno content is greatest in garnet near the center and stratigraphic top of the rock and decreases systematically to the east west and stratigraphic base pb zn and ba exhibit similar enrichment trends from stratigraphic base to top of the rock however ba remains abundant in the overlying orebody the interpretation is that the garnet rock was a primary mn rich sediment that accumulated near a sea floor hydrothermal vent by analogy with modern hydrothermal mn d

on the nature of the frontal zone of the choctawhatchee bay plume in the gulf of mexico river plumes often feature turbulent processes in the frontal zone and interfacial region at base of the plume which ultimately impact spreading and mixing rates with the ambient coastal ocean the degree to which these processes govern overall plume mixing is yet to be quantified with microstructure observations a field campaign was conducted in a river plume in the northeast gulf of mexico in december 2013 in order to assess mixing processes that could potentially impact transport and dispersion of surface material near coastal regions current velocity density and turbulent kinetic energy values e were obtained using an acoustic doppler current profiler adcp a conductivity temperature depth ctd profiler a vertical microstructure profiler vmp and two acoustic doppler velocimeters advs the frontal region contained e values on the order of 10 5 m2 s 3 which were markedly larger than in the ambient water beneath o 10 9 m2 s 3 an energetic wake of moderate e values o 10 6 m2 s 3 was observed trailing the frontal edge the interfacial region of an interior section of the plume featured opposing horizontal velocities and a e value on the order of 10 6 m2 s 3 a simplified mixing budget was used under significant assumptions to compare contributions from wind tides and frontal regions of the plume the results from this order of magnitude analysis indicated that frontal processes 59 dominated in overall mixing this emphasizes the importance of adequate parameterization of river plume frontal processes in coastal predictive models

constraints on average taiwan reference moho discontinuity model receiver function analysis using bats data summary by analysing teleseismic waveform data we propose a large scale taiwan reference moho discontinuity model trmdm through coherent stacking and h analysis of receiver functions rfs tectonic structural features are determined from accurate crustal thickness h and reliable vp vs ratio consequently poisson s ratio estimations for taiwan the best estimated regional average moho depth is 33 5 2 9 km noted is a westward crustal thinning from 39 3 0 km in eastern taiwan to 30 1 5 km in southeastern china the averaged moho depth is 23 0 2 5 km in northern taiwan and increases to 33 5 2 0 km in the south the markedly thin crust and high vp vs ratio in northern taiwan are mainly associated with backarc opening and magmatic activities based on h estimations and associated seismicity patterns beneath suang long sslb and adjacent four stations we propose two moho reference models that exhibit distinctive crustal thickening in central taiwan the spatial variations of crustal thickness models show strong lateral change in the moho topography the thick crust in the south thin crust in the north and transition in central taiwan mark the different tectonic units between the subduction wedge and the collision prism onshore in view of the following list of constraints thicker crust in the south than in the north eastward crust thickening significant moho depth changes clear 9 11 s subcrustal boundaries from five stations the compelling thickening of crust and upper mantle beneath the central mountain belt seismicity patterns with the absence of mantle earthquake in the wadatibenioff zone regional geological features the occurrence of the inland chi chi earthquake the compelling low at yulb 1 58 0 13 that may extend to central taiwan at sslb 1 59 0 23 relatively thick crust at yulb 39 5 1 6 km and sslb 40 5 1 3 km or 52 5 1 5 km and finally the apparent horizontal offset between highest yu shan mountain and the deepest moho at sslb we are able to suggest that the initial subduction of the eurasian plate occurred in southern taiwan and most likely extended to the transition zone in central taiwan although the current rf study is limited by large interstation distance our analysis provides more notable constraints than previous studies to explicitly determine the characteristic features of moho discontinuity this detailed approach means that rather than treating the tectonic framework as a whole heterogeneous lithospheric feature clear moho boundary geometry variations indicate that active orogenic processes and differential tectonic stress loading create separate and complex crustal and subcrustal to upper mantle structural features caused by the arc continent collision

tourmalinization related to late proterozoic early palaeozoic lode gold mineralization in the bin yauri area nigeria three types of tourmaline occurrence have been identified in the area of bin yauri nigeria mesothermal lode gold mineralization these are 1 stratabound tourmalinites in pelitic metasediments 2 tourmaline in a hydrothermal alteration assemblage within hornfelsed wall rocks 3 tourmaline in auriferous quartz and quartz carbonate veins although the tourmaline occurrences are all within or close to the contact aureole of a granodiorite intrusion geochemical characteristics of the tourmalines are broadly similar and reflect a common metasedimentary source two stages of tourmalinization are envisaged the earlier ca 1100 ma involved syngenetic diagenetic formation of tourmalinites while the later ca 500 ma involved epigenetic hydrothermal tourmaline gold mineralization possibly derived by dehydration and devolatilization of metasedimentary sequences containing tourmaline rich rocks or tourmalinites electron microprobe analyses indicate that the tourmalines are intermediate members of the schorl dravite solid solution series plots involving feo mgo and or al2o3 from these analyses are used to constrain the sources and processes of tourmalinization two metallogenic implications are derived from this study one is that although the tourmalinites are barren of gold and base metal mineralization their occurrences nevertheless encourages exploration for syngenetic exhalative massive sulphide deposits in the region the other implication applies to the potential use of tourmaline in deciphering the physico chemical conditions of gold mineralizing fluids in the bin yauri area

the deep structure of south central taiwan illuminated by seismic tomography and earthquake hypocenter data abstract the taiwan mountain belt is generally thought to develop above a through going basal thrust confined to within the sedimentary cover of the eurasian continental margin surface geology magnetotelluric earthquake hypocenter and seismic tomography data suggest however that crustal levels below this basal thrust are also currently being involved in the deformation here we combine seismic tomography and earthquake hypocenter data to investigate the deformation that is taking place at depth beneath south central taiwan in this paper we define the basement as any pre eocene rifting rocks and use a p wave velocity of 5 2 km s as a reference for the interface between these rocks and their sedimentary cover we found that beneath the coastal plain and the western foothills clustering of hypocenters near the basement cover interface suggests that this interface is acting as a detachment this detachment is located below the basal thrust proposed from surface geology for this part of the mountain belt inherited basement faults appear to determine the geometry of this detachment and their inversion in the alishan area result in the development of a basement uplift and a lateral structure in the thrust system above them however across the shuilikeng and the chaochou faults earthquake hypocenters define steeply dipping clusters that extend to greater than 20 km depth above which higher velocity basement rocks are uplifted beneath the hsuehshan and central ranges we interpret these clusters to form a deeply penetrating east dipping ramp that joins westward with the detachment at the basement cover interface it is not possible to define a basal thrust to the east beneath the central range

tidal and nontidal exchange at a subtropical inlet destin inlet northwest florida abstract a tidal cycle study at destin inlet northwest florida investigated intratidal and residual flow structures for the first time across the inlet underway current velocity profiles were combined with hydrographic station profiles at neap tides to document the appearance of tidal fronts the distribution of tidal currents across two cross sections and the residual or non tidal flow structure at the same cross sections intratidal variations of water density and velocity showed the presence of fronts both in 1 late ebb early flood and 2 late flood early ebb tidal stages late ebb early flood tidal intrusion fronts brought about depth independent changes in water density 10 kg m 3 in

a multi disciplinary study of frontal systems in the tay estuary scotland the results of a remote sensing study of tidal mixing processes in the tay estuary have been correlated with the results of mathematical and physical models and ground sampling data in an attempt to assess the nature the spatial and temporal extent and the variability in the formation of convergent fronts in the tay estuary the application of remote sensing methods to the study of estuarine mixing processes in the tay estuary supported by ground measurements has discovered convergent front mechanisms and complex hydrodynamic processes which had not previously been recognized in the tay estuary this integrated approach has enabled the various features and mixing mechanisms found in the lower section of the estuary to be interrelated the limitations of using a two dimensional mathematical and a physical model to predict the complex mixing processes affecting water quality in the tay estuary are discussed

distribution of fluid inclusions in igneous quartz of the capitan pluton new mexico usa abstract fluid inclusions in granites have been used extensively in studies of magmatic hydrothermal processes but few studies have documented the distribution of secondary fluid inclusions within the nonmineralized main body of an intrusion previous work on fluid inclusions in th u ree quartz fluorite vein deposits in the capitan pluton suggests that these veins resulted from high temperature high salinity magmatic fluids in fractured and brecciated zones in the cooled outer carapace of the pluton petrographic examination of phenocryst quartz in forty four thin sections of granite from the capitan pluton reveals that these same fluids are found in secondary fluid inclusions fluid inclusions with daughter minerals commonly occur in the outer granophyre and aplite zones but are usually absent in the porphyritic core microthermometric data and calculated salinities from fifty eight fluid inclusions in phenocryst quartz and thirty one fluid inclusions in miarolitic quartz both samples taken from the granophyre zone also correlate fairly well with the data from the th u ree quartz fluorite vein deposits and similar types of fluid inclusions are found in all three occurrences of quartz a major difference however is that vapor rich inclusions abundant as secondary inclusions in igneous phenocryst quartz are extremely scarce in the vein quartz liquid vapor homogenization temperatures of high salinity inclusions in phenocryst quartz range from 204 509 c with an average of 384 c halite dissolution temperatures of high salinity inclusions range from 442 583 c with an average of 525 c total homogenization temperatures are not as well documented due to decrepitation of many of the high salinity inclusions before total homogenization samples of miarolitic quartz appear to contain more low salinity fluid inclusions than the phenocryst quartz but high salinity inclusions are present as well these observations suggest that the magmatic hydrothermal fluids responsible for vein mineralization were not only concentrated in the vein systems but were also widely dispersed within the outer portions of the pluton furthermore the greater abundance of fluid inclusions in the outer textural zones of the pluton suggests that the interior of the pluton had not yet fully crystallized when these fluids exsolved from the magma

primary geochemical characteristics of mineral deposits implications for exploration extract the old adage mineral exploration is like finding a needle in a haystack recaps the difficulty of finding economic mineral deposits near or beneath the surface in general two main approaches can be used to detect the presence of mineral deposits near or beneath the ground surface one employs a mineral deposit model and the other aims at the identification of a primary halo about a mineral deposit a mineral deposit model provides systematic empirical descriptive and or theoretical genetic descriptions of the essential geological geochemical and geophysical features of a type of mineral deposits cf cox and singer 1986 and roberts et al 1988 the primary halo of a mineral deposit as defined originally by safronov 1936 is an area including rock surrounding mineral deposit ore bodies and enriched elements that make up that deposit thus descriptions of primary haloes may form part of a mineral deposit model but both deposit model and primary halo approaches to mineral exploration are based on studies of primary geochemical characteristics of mineral deposits because chemical processes during mineralization are the ones that ultimately bring about metal precipitation or mineral formation however a deposit model approach to mineral exploration is apt for identifying which haystacks contain a needle whereas a primary halo approach to mineral exploration is proper for deducing where in a needle bearing haystack is the needle located

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

high resolution measurements made across a tidal intrusion front high spatial resolution current and hydrographic measurements have been made across a tidal intrusion front in the james river estuary virginia during the first few hours of flood the current measurements were made with a surface towed acoustic doppler current profiler which was used in both profile and side scan configurations the profile data show a 30 50 cm s 1 inflow of water from the chesapeake bay a time evolving across front density gradient and downward velocity beneath the front of about 15 cm s 1 the side scan observations directly measure the across front change in current and provide a view of the three dimensional character of the frontal interface the near surface horizontal strain rate a critical parameter for understanding the modulation of surface waves across the front is estimated to be about 0 04 s 1 using phillips 1984 theory as a guide fronts with such large strain rates as these should be discernible in imagery from the ers 1 c band synthetic aperture radar for wind speeds of 4 m s 1

statistical properties of low frequency earthquakes triggered by large earthquakes in southern taiwan abstract the recent discovery of triggered tremors tts and low frequency earthquakes lfes in various tectonic environments provides an opportunity for studying the fundamental properties and physical mechanisms of deep tectonic tremor here we quantify the relationship between tts and lfes beneath the central range in southern taiwan and their statistical properties during the teleseismic waves of six large distant earthquakes using waveforms of 11 lfes triggered by the 2005 m w 8 6 nias earthquake as templates we scan through 12 hours of waveform data around six mainshocks and identify a total of 783 lfes the lfes were mainly located in a compact region between 12 and 36 km in depth near the chaochou lishan fault most of lfes occurred within tt during the passage of large amplitude surface waves and the increase of the lfe rate during the surface waves is statistically significant the lfe rates do not follow an omori s type decay but rather abruptly return to the background rate immediately after the surface wave passage these findings suggest that lfes do not trigger any additional lfes at later times and are primarily driven by an external forcing our observations are consistent with the inference that tts consist of many reoccurring lfes

deformational and stratigraphic influences on mineralization in se ireland the evidence that has accumulated to date to support the thesis that deformational and stratigraphic controls are reflected in the occurrence and siting of metal deposits in se ireland is evaluated in the case of an important tungsten deposit stratigraphic influences can be seen in the geochemical and mineralogical development of wallrocks prior to crystallization of granite hosted mineralization tourmalinites confined to a definable stratigraphic interval are associated with pegmatite hosted lithium deposits though the stratigraphic control is important the tungsten and lithium deposits are in addition confined to the trace of a major deformation zone

gold antimony mineralization at loddiswell devon uk native gold in association with tetrahedrite bournonite bismuthian jamesonite antimonian bismuth chalcopyrite sphalerite gersdorffite galena covelline yarrowite and acanthite occurs in a nw se trending quartz carbonate vein which cuts folded lower devonian slates of the meadfoot group the locality 2 5 km north of the village of loddiswell lies in a belt of devonian thrust and nappe terrain with a roughly e w trend the host rocks are muddy turbiditic sediments interbedded with spilitic lavas keratophyres and tuffs together with intrusive dolerites greenstones which were deformed together during the variscan orogeny the deposit was worked briefly in the nineteenth century but little ore was raised and it is doubtful whether any gold was recovered analysis of samples collected in the present study revealed gold values of 5 10 ppm and silver values of 1000 2000 ppm the relationship between gold antimony mineralization the basic igneous rocks in the nappe sequence and their intersection by a series of major nw se fracture zones is discussed in the context of the regional metallogenic evolution of sw england the mineralization is considered to be the result of fluid extraction during shear movements on the nw se structures and shows features in common with mesothermal gold bearing sulphide veins in other palaeozoic provinces

gps observation of crustal deformation in the taiwan luzon region fifteen gps stations in the batan luzon area were surveyed three times during 1996 to 1998 in order to study crustal deformation in the taiwan luzon region the data from these annual surveys are processed together with data from 20 permanent stations in the taiwan area and igs stations in the asia pacific region we found that the chinese continental margin is moving in directions of 102 112 with rates of 11 12 mm yr relative to stable eurasia there is a significant southward increase in crustal motion with respect to eurasia along the n s trend of the luzon arc in the coastal range of taiwan the velocity is 53 mm yr in the direction 313 further south at two volcanic islands lanhsu and batan the velocities increase to 68 mm yr in the direction 306 and 81 mm yr in the direction 299 respectively in northern luzon the velocity reaches 86 mm yr in the direction 301 remarkable fault slips of 17 31 mm yr across the philippine fault system are detected

tidal and subtidal exchange flows at an inlet of the wadden sea abstract observations of underway velocity profiles during complete spring and neap tidal cycles were used to determine whether the spatial structures of tidal and subtidal flows at a tidal inlet in a multiple inlet embayment are consistent with those observed at single inlet embayments measurements were obtained at the otzumer balje one of the multiple inlets among the east frisian islands of the wadden sea the 1 5 km wide inlet displayed a bathymetric profile consisting of a channel 15 m deep flanked by

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

decrepitometry of fluid inclusions in quartz from the guadalcazar granite of mexico principles and application to mineral exploration a simple acoustic decrepitometric method with which samples of granite quartz are heated to about 600 c while the number of decrepitations are counted has been developed to study rock samples derived from the mineralized guadalcazar granite in mexico decrepitation temperatures for individual inclusions have also been determined by observing the point at which they rupture upon heating using a microscope heating stage decrepitation temperatures of individual fluid inclusions in granite quartz are influenced by a variety of factors notably size shape composition homogenization temperature and proximity to the surface there is a positive correlation between total decrepitation activity and fluid inclusion abundances determined optically using point counting methods decrepitographs show a period of low intensity decrepitation activity below 390 c followed by a period of intensive decrepitation up to 570 c the onset of massive decrepitation at around 390 c is constant for all samples but variations in decrepitation activity often occur between mineralized and barren samples these variations reflect complex differences in the fluid inclusion populations but illustrate the potential for applying simple audio decrepitometry as an aid to mineral exploration in granite terrains

salt intrusion and secondary flow in a shallow well mixed estuary observations of an axial convergence front formed within the conwy estuary north wales u k during the flood tide were indicative of density driven secondary circulations it has been proposed that these were the result of lateral density gradients established by the interaction of the lateral shear of the longitudinal currents with the axial salinity gradients through a differential advection mechanism in the present study the evolution of axial salinity gradients during a tidal cycle along the length of a shallow well mixed estuary was examined using six recording instruments deployed over a 25 day period the evolution of channel geometry and of the lateral shear of axial current speed was examined using simple models in conjunction with the observations of near bed pressure and current speed it is hypothesized that the complex interaction between these three parameters channel geometry lateral shear of axial current and axial salinity gradient results in the observed evolution of secondary flow throughout the tide which itself causes a redistribution of the density field

transient tidal circulation and momentum balances at a shallow inlet an analysis of transient momentum balances is carried out to elucidate circulation dynamics and exchange mechanisms at shallow barotropic tidal inlets circulation is computed using a depth integrated fully nonlinear time stepping finite element model with variably spaced grids having horizontal resolution down to 50 m velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance a transformation of the x y momentum terms into an s n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow the analysis is conducted for an idealized inlet and contrasted with a highly detailed model of beaufort inlet north carolina results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states near maximum ebb or flood the alongstream momentum balances are dominated by advective acceleration pressure gradient and bottom friction cross stream balances are dominated by centrifugal acceleration and pressure gradients near slack balances more closely follow linear wave dynamics with local accelerations balancing pressure gradients and to a lesser degree coriolis comparisons between the idealized inlet and beaufort inlet show broad similarities in these momentum balances however natural inlet geometry and bottom topography as well as the tidal transmission characteristics of the sounds behind beaufort inlet produce strong asymmetries moreover momentum balances are highly localized often with subkilometer length scales the dynamics are used to explain the physical mechanisms for inlet exchange in particular the results indicate that the cross stream dynamics generate a wall along the length of an inlet during the stronger phases of the tide the wall is established by opposing cross inlet pressure gradients and centrifugal forces and it poses a significant barrier to cross inlet exchange during the stronger phases of the tide but is absent near slack

the effect of a topographic high on the morphological stability of a two inlet bay system abstract the cross sectional stability of two tidal inlets connecting the same back barrier lagoon to the ocean is investigated the condition for equilibrium is the cross sectional area tidal prism relationship in an earlier study van de kreeke j 1990 can multiple inlets be stable estuarine coastal and shelf science 30 261 273 using the same equilibrium condition it was concluded that where two inlets connect the same basin to the ocean ultimately one inlet will close one of the major assumptions in that study was that the water level in the basin fluctuated uniformly in hindsight this assumption might be too restrictive for example in the wadden sea the back barrier lagoon consists of a series of basins rather than one single basin separated by topographic highs these topographic highs limit but do not exclude the exchange of water between the sub basins for this reason in the present study a topographic high in the form of a weir was added separating the back barrier lagoon in two sub basins the water level in the sub basins rather than in the back barrier as a whole is assumed to fluctuate uniformly for this schematization the hydrodynamic equations are solved using a finite difference method the results together with the equilibrium condition yield the equilibrium flow curve for each of the inlets the intersections of the two equilibrium flow curves represent combinations of cross sectional areas for which both inlets are in equilibrium the stability of the equilibriums was investigated using a non linear stability analysis resulting in a flow diagram calculations were carried out for different inlet and weir characteristics sinussoidal tides were the same for both inlets the results show that for relatively large wetted cross sectional areas over the topographic high approaching the situation of a single basin there are no combinations of inlet cross sectional areas for which both inlets are in a stable equilibrium this supports the conclusion in the earlier study for relatively small wetted cross sectional areas over the topographic high there is one set of stable equilibriums in that case the two inlet bay system approaches that of two single inlet bay systems

tidal and subtidal variability in delaware s inland bays abstract sea level observations made during a three month period in late 1984 at four stations in and near delaware s inland bays are used for the examination of tidal and subtidal variability in the bays five tidal constituents are found to be active in the bays with m2 being the most important one the inland bays with their narrow inlets and shallow depths behave like low pass filters for oceanic disturbances propagating into the interior of the bays overall tidal variance decreases sharply inside the bays with the semidiurnal tides suffering significantly higher attenuation than the diurnal tides at subtidal frequencies sea level fluctuations in the interior of the bays are primarily forced by coastal sea level fluctuations generated by atmospheric forcing on the adjacent shelf local wind forcing within the bays appears to play only a secondary role in modifying the coastally forced sea level the active subtidal sea level fluctuations induced by the bay shelf coupling effect experience no a

channel curvature effects on estuarine circulation in a highly stratified tropical estuary the sao francisco river estuary brazil abstract the effects of the channel curvature on estuarine circulation were assessed in the sao francisco river estuary this estuary is a deltaic front system with a highly stratified salinity distribution the assessment was based on field experiments where currents and salinity and temperature were monitored during a semi diurnal tidal cycle in two cross sections with distinct curvatures radii of 2 and 8 km the least squares method was used to determine the mean velocity residual velocity and the tidal velocity amplitude and phase for the m2 harmonic the results for the m2 harmonic were compared to an analytical solution that considers a simplified momentum balance between barotropic pressure gradient and bottom friction the model skill for these two results was 0 44 and 0 63 for sections a and b respectively the differences between these results indicate that there are other dynamically influential forces for the longitudinal momentum balance besides those included in the analytical solution the baroclinic pressure gradient presented values two orders of magnitude greater than the bottom friction demonstrating the dynamic importance of this force although centrifugal acceleration is a component of the lateral momentum balance it also plays a role in the distribution of longitudinal currents in the cross section displacing the maximum currents towards the exit of the curve in addition to the channel curvature effect the influence of the bathymetry was also observed on the tidal amplitude in the cross sections and on the depth averaged residual longitudinal velocities along the sections with the highest average speed in the shallowest areas of each section

transition from oblique subduction to collision in the northern luzon arc taiwan region constraints from bathymetry and seismic observations we systematically study the detailed bathymetry seismicity and source parameters of large and moderate sized earthquakes that occurred in the northern luzon arc taiwan region between 1964 and 1996 the purpose is to characterize the transition from oblique subduction to regional collision in terms of the distribution of morphological features the characteristics of seismogenic structures and the corresponding state of strain to the south of 21 5 n the existence of a subduction zone is clearly shown by both bathymetry and seismicity the subducted eurasia slab reaches a maximum depth of 200 km and the depth decreases sharply as it approaches taiwan focal mechanisms indicate that the subducted slab is in downdip extension for depths 150 km but switches to downdip compression at greater depths to the north of 23 n collision is clearly the predominant process with broad deformation on both sides of the suture in between the transition is accommodated by a distributed thrust deformation zone in the frontal portion of the accretionary prism closure of the forearc basin and the right lateral ne sw striking taitung canyon fault zone tcfz these structures resolve the differential movements between the subduction and collision zones and will repeatedly change their positions as the collision propagates southwestward the present day plate boundary follows the axis of the manila trench in the south broadens significantly in the zone of transition and finally becomes a zone of several tens of kilometers in width across eastern taiwan the deformation front on the other hand is located between the western foothills and coastal plain in taiwan then connects to the manila trench to the south seismic strain tensors indicate that the region to the north of tcfz has a compression rate 15 times larger than that to the south the northern luzon arc shows characteristics of oblique subduction but the effects of collision are not as significant within the subducted eurasian lithosphere as comparing to the subducted philippine sea plate beneath the southernmost ryukyu arc

remote triggering of non volcanic tremor around taiwan summary we perform a systematic survey of triggered deep non volcanic tremor beneath the central range cr in taiwan for 45 teleseismic earthquakes from 1998 to 2009 with mw 7 5 and epicentral distance 1000 km to the broad band station tpub triggered tremors are visually identified as bursts of high frequency 2 8 hz non impulsive and long duration seismic energy that are coherent among many seismic stations and modulated by the teleseismic surface waves out of the 45 earthquakes we identified nine teleseismic events associated with nine tremor sources in the southern and five in the northern cr most of the tremor sources are located within the depth range of 15 25 km in the lower crust above the moho we find that the amplitudes of the surface waves play an important role in determining the triggering potential and the apparent triggering threshold is 0 1 cm s 1 or 7 8 kpa however such threshold is partially controlled by the background noise level which could prevent weaker tremor triggered by surface waves with smaller amplitudes from being identified the amplitudes of the triggered tremor show a positive correlation with the amplitudes of the triggering surface waves consistent with the predictions by the clock advance model in addition to amplitudes other factors such as frequency contents and incidence angles also affect the triggering potential we find that intermediate period 30 10 s surface waves could trigger modulate tremors suggesting that long period 30 s surface waves are not always required in long range triggering tremors appear to be triggered by both love and rayleigh waves when the incidence angles are parallel to the strike of the cr all six events triggered tremor primarily during the rayleigh waves for strike normal incidence only the 2001 mw7 8 kunlun earthquake showed predominant love wave triggering this observation can be qualitatively explained by a simple coulomb failure for a left lateral shear on the low angle detachment fault beneath the southern cr

tidal fronts in estuaries abstract three estuaries in wales were carefully surveyed during flood conditions they are characterized by the intrusion of a tidal front in one estuary the front retreats after maximum flood velocities and stratification persists during the whole tidal cycle in the other estuaries the flood erases the initial stratification causing partially or totally mixed situations a tidal froude number is employed to characterize the evolution of stratification during the flood it is shown that gravity current theory approximately holds under well stratified conditions in a region near to but not too close to the head of the front

u pb geochronology of tin deposits associated with the cornubian batholith of southwest england direct dating of cassiterite by in situ la icpms the cornwall and devon vein and greisen type copper and tin deposits of southwest england are spatially and genetically related to shallow seated granitic intrusions these late variscan intrusions collectively known as the cornubian batholith extend over 200 km and form a continuous granitic spine from the isles of scilly granite in the west to the dartmoor granite in the east the granitic plutons of the cornubian batholith were intruded from 295 to 270 ma without a major hiatus twelve samples of cassiterite sno2 were obtained from tin deposits associated with seven different plutons within the cornubian batholith for in situ la icpms u pb dating this study of cassiterite was undertaken to obtain the first results of direct dating of ore mineral to refine the geochronology of tin mineralization in this region of the cassiterite samples analyzed the oldest ages were determined within the kit hill and hingston gunnislake granites in the central part of the cornubian batholith the hingston gunnislake cassiterite from drakewalls mine was the oldest sample dated at 291 8 3 4 ma the next oldest dates 290 5 2 8 and 288 5 2 9 ma were from two cassiterite samples extracted from the adjacent kit hill consolidated mines within the kit hill granite at the eastern end of the study area two cassiterite samples within the dartmoor granite produced ages of 286 0 1 8 and 284 1 1 3 ma the youngest sample from this study 275 4 1 6 ma is from the balleswidden mine within the westernmost land s end granite the cassiterite dates do not reveal any readily observable relationship between ore ages and geographic relationship from west to east throughout the cornubian batholith incorporating the associated errors the geochronology does indicate continuous mineralization within the granites for 21 million years from ca 295 to 274 ma this span falls within the established period of granitic magmatism of ca 295 to 270 ma for the cornubian batholith and further confirms the reliability of in situ la icpms u pb dating of cassiterite

lithogeochemical studies of aureoles around the panasqueira tin tungsten deposit portugal multi element lithogeochemical surveys of aureoles surrounding tin tungsten bearing quartz vein systems have been utilized infrequently in exploring for these deposits at panasqueira beira beixa portugal a wrich quartz vein mineralization occurs in the beira schists surrounding a greisenized cupola and offers a suitable test case for such lithogeochemical studies therefore shale samples were collected at a density of about 6 samples per km2 pronounced anomalies of tin and tungsten have been detected in these samples together with those of other elements coeval with the mineralizing processes

stable isotope studies of sulphide mineralisation on the leinster granite margin and some observations on its relationship to coticule and tourmalinite rocks in the aureole galena and sphalerite occur in brecciated veins along the eastern margin of the caledonian leinster granite in south east ireland this mineralisation is spatially related to the occurrance of spessartine quartzites coticules in the aureole rocks tourmalinites are closely associated with these coticules a decrease in the temperature of mineralisation from about 500 c in the northern unit i to 250 c in the central unit iii to possibly less than 200 c in the southern unit v of the intrusion is suggested by decreasing sulphide 34s values increasing sulphate 34s values and sulphide sulphate fractionation values sulphur carbon and oxygen isotope data suggest the involvement in the vein mineralisation of sulphur carbon and mineralising fluids at least partially derived from the coticule and tourmaline bearing aureole schists

trace element compositions and br cl ratios of fluid inclusions in the tsushima granite japan significance for formation of granite derived fluids abstract fluid inclusions in quartz samples from a miarolitic cavity two quartz veins and a hydrothermal ore vein in the tsushima granite japan were analyzed by particle induced x ray emission to examine the chemistry and process of formation of hydrothermal fluids in an island arc granite most of the inclusions were polyphase or vapor and there were smaller numbers of two phase aqueous inclusions the inclusions contained cl k ca ti mn fe cu zn ge br rb sr ba and pb for each inclusion there was a strong positive correlation between cl content and contents of other elements identified concentration ranges for most elements other than rb and ge in polyphase inclusions from the miarolitic cavity were comparable to those from cavities in alkaline granites those from the ore vein were comparable to large scale continental hydrothermal ore deposits the lower rb and higher ge contents in the polyphase inclusions of the tsushima granite may be characteristic of hydrothermal fluids from calc alkaline granites in an island arc setting br cl ratios by weight for the vapor and two phase inclusions were 0 0013 0 0030 and differed among the three geological settings br cl ratios of polyphase inclusions increased with increasing cl content in single crystal and polycrystalline quartz and high values of more than 0 0100 were found the high br cl ratios and the differences among the geological settings sampled may be due to pressure dependences of partitioning of cl and br between fluid and magma during fluid segregation and between liquid and vapor during boiling using a simple model based on these dependences we calculated br cl ratios greater than 0 01 in brine generated at pressures

significant crustal structural variation across the chaochou fault southern taiwan new tectonic implications for convergent plate boundary abstract the chaochou fault a major geological boundary in southern taiwan is considered to be a part of the convergent plate boundary between the eurasia plate and the philippine sea plate we applied the common conversion point stacking technique to teleseismic radial receiver functions and obtained moho variation and crustal structure across the chaochou fault in the eurasia plate to its west the moho depth is about 37 km and the crust is subducting to the east beneath the philippine sea plate with a dip angle of about 30 between the backbone belt and the tananao schist in the philippine sea plate the moho depth is about 17 km the longitudinal valley marks the collision boundary between the eurasia plate and the philippine sea plate the results suggest that the depth extent of the chaochou fault is about 30 35 km and the fault becomes a shallow angle thrust fault at depth the common conversion point image also shows several bending interfaces of velocity contrast in the crust we proposed a simple model to explain the philippine sea plate and eurasia plate collision process and the observed crustal deformations

dinantian dolomites from east fife hydrothermal overprinting of early mixing zone stable isotopic and fe mn compositions thin marine limestones from the dinantian of the st monans syncline east fife are extensively dolomitized they occur within a deltaic sequence cut by upper carboniferous volcanic rocks the volcanic rocks have been extensively modified by co 2 enriched hydrothermal fluids the dolomite is ferroan and nonluminescent stable isotope compositions for groundmass dolomite range from 18 o 4 76 to 0 47 and 13 c 3 29 to 0 60 later void filling dolomite falls into two groups the first is 18 o depleted with 18 o as low as 10 6 while the second is 18 o enriched 18 o 2 8 to 1 2 despite almost homogeneous staining characteristics backscattered sem imaging shows the dolomites to be chemically extremely heterogeneous dolomitization was a multistage process in which an early mixed water component was variably remobilized to form the matrix dolomite biomolds and other vuggy post early dolomite porosity are filled by dolomite precipitated within a volcanically driven hydrothermal system the chemistry of the later dolomite reflects the mixing of upward moving hydrothermal fluids modified by interaction with volcanic material with downward moving seawater feeding the hydrothermal system in addition material released during normal processes of siliciclastic diagenesis added a further component to the late stage dolomitization only two of the limestones escaped complete dolomitization and appear to have undergone early post depositional diagenesis within meteoric porefluids they contain early meteoric calcite cements and later post compaction calcite cements dolomite and siderite one of the implications of this study is that the interpretation of dolomite geochemical data can be vastly enhanced by the use of back scattered electron microscopy to reveal otherwise hidden compositional heterogeneity

3 d numerical modelling of the conductive heat flow of sw england summary the effect of 3 d geology on conductive heat flow was investigated using the finite element technique on two models from sw england one a regional model centred on the comubian batholith as a whole and the other a more detailed model centred on the cammenellis pluton only two rock types granite and country rock were used to represent the geology of the region and yet good agreement between modelled and observed data was obtained provided that the granite was assumed to be highly homogeneous with surface heat production values persisting throughout its depth and the base of the batholith was assumed to be flat at a depth of 15 km the results show that the surface heat flow pattern is dominated by the 3 d shape of the batholith which controls the relative importance of the two opposing effects that operate at its margins heat refraction due to conductivity contrasts enhancing heat flow in the granite and lateral flow of heat caused by heat production contrasts diminishing it the highest heat flows occur at the boundaries of outcrops facing the axis of the batholith where there is significant heat refraction but little lateral loss a high degree of correlation between mineralized zones and areas of very high heat flow in both granite and country rock is also noticeable the temperature field at any depth displays wide ranging lateral variations over relatively short distances the highest values occurring in areas of granite which are covered by insulating country rock and which lie towards the centre of the batholith regions of highest heat flow are not necessarily the regions where the highest sub surface temperatures are likely to be found and it is shown that the hot dry rock geothermal test project at rosemanowes is not optimally sited from temperature considerations when the constraints on the physical parameters of the model are sufficiently reliable as they are in sw england the heat flow and temperature predictions from 3 d numerical models can be of enormous value in the assessment of the geothermal potential of a region

the effect of channel length on the residual circulation in tidally dominated channels with an analytic model this paper describes the subtidal circulation in tidally dominated channels of different lengths with arbitrary lateral depth variations the focus is on an important parameter associated with the reversal of the exchange flows this parameter is defined as the ratio between the channel length and one quarter of the tidal wavelength which is determined by water depth and tidal frequency in this study a standard bottom drag coefficient cd 0 0025 is used for a channel with smaller than 0 6 0 7 short channels the exchange flow at the open end has an inward transport in deep water and an outward transport in shallow water this situation is just the opposite of channels with a value larger than 0 6 0 7 long channels for a channel with a value of about 0 35 0 5 the exchange flow at the open end reaches the maximum of a short channel for a channel with a value of about 0 85 1 0 the exchange flow at the open end reaches the maximum of a long channel with the inward flux of water occurring over the shoal area and the outward flow in the deep water area however near the closed end of a long channel the exchange flow appears as that in a short channel that is the exchange flow changes direction along the channel from the head to the open end of the channel for a channel with a value of about 0 6 0 7 the tidally induced subtidal exchange flow at the open end reaches its minimum when there is little flow across the open end and the water residence time reaches its maximum the mean sea level increases toward the closed end for all values however the spatial gradient of the mean sea level in a short channel is much smaller than that of a long channel the differences between short and long channels are caused by a shift in dynamical balance of momentum or equivalently a change in tidal wave characteristics from a progressive wave to a standing wave

crustal structure across the san andreas fault southern california from teleseismic converted waves crustal structure along a 140 km long profile across the san andreas fault saf in southern california was imaged by stacking teleseismic p s converted phases recorded by a dense short period seismic array the crust mantle discontinuity moho is visible as a continuous feature at a depth around 30 km but is offset 6 to 8 km beneath the saf a small moho disruption can also be seen under the eastern california shear zone ecsz these results suggest that the saf and ecsz extend through the entire crust the moho upwarp under the san gabriel mountains indicates that the mountain ranges were lifted en masse as a result of crustal buckling under horizontal compression

lateral entrapment of sediment in tidal estuaries an idealized model study two physical mechanisms leading to lateral accumulation of sediment in tidally dominated estuaries are investigated involving coriolis forcing and lateral density gradients an idealized model is used that consists of the three dimensional shallow water equations and sediment mass balance conditions are assumed to be uniform in the along estuary direction a semidiurnal tidal discharge and tidally averaged density gradients are prescribed the erosional sediment flux at the bed depends both on the bed shear stress and on the amount of sediment available in mud reaches for resuspension the distribution of mud reaches over the bed is selected such that sediment transport is in morphodynamic equilibrium that is tidally averaged erosion and deposition of sediment at the bed balance analytical solutions are obtained by using perturbation analysis results suggest that in most estuaries lateral density gradients induce more sediment transport than coriolis forcing when frictional forces are small ekman number e 0 02 the lateral density gradient mechanism dominates and entraps sediment in areas with fresher water results also show that the lateral sediment transport induced by the semidiurnal tidal flow is significant when frictional forces are small e 0 02 model predictions are in good agreement with observations from the james river estuary

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

geological setting and genesis of coticules spessartine metapelites in the lower ordovician of the stavelot massif belgium the lower ordovician in the caledonian stavelot massif belgium contains a coticule member probably arenig in age composed of red hematite rich shales alternating with thin yellowish coticule beds these coticules are fine grained highly manganiferous metamorphic rocks mainly composed of spessartine garnet mica and quartz similar rocks of about the same age occur in several localities along the appalachian and caledonian fold belts the belgian coticules are thought to have originated from marly sediments which had been deposited rapidly probably by density currents and in which caco 3 had been diagenetically replaced by mnco 3 during metamorphism spessartine garnets were formed from this mnco 3 and mica manganese and iron are thought to have originated from volcanic exhalative processes

tourmalinites from the golden dyke dome northern australia tourmalinites occur at five stratigraphic levels within the low metamorphic grade multiply deformed lower proterozoic metasediments and metavolcanics of the golden dyke dome the geological setting exhalite associations sedimentary structures and tourmaline chemistry all preclude a granitic origin tourmalinite derived from the isochemical metamorphism of an exhalite comprising silica and tourmaline tourmalinite and other exhalites are hosted by carbonaceous pelitic metasediments and were deposited in deeper basinal areas the ore fluid was probably dolerite heated seawater which leached a thick pile of argillaceous sediments and acquired metals and boron by leaching the first and second increase in geothermal gradient produced tourmalinite the third produced auriferous tourmalinite and iron formations with tourmalinite and exhalative pb zn deposits forming during the period of maximum geothermal gradient more tourmalinite formed during the subsequent decline in geothermal gradient tourmalinites are regarded as b rich iron formations which can be the host for or associated with exhalative deposits of au and base metals

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

spatial temporal evolution of early aftershocks following the 2010 ml 6 4 jiashian earthquake in southern taiwan chi chia tang 1 2 cheng horng lin2 and zhigang peng3 1hubei subsurface multi scale imaging lab institute of geophysics and geomatics china university of geosciences 388 lumo rd wuhan hubei 430074 p r china e mail iori897 gmail com 2institute of earth sciences academia sinica 128 sec 2 academia rd nangang taipei 11529 taiwan 3school of earth and atmospheric sciences georgia institute of technology 311 ferst drive atlanta ga 30332 usa

deciphering fluid flow at the magmatic hydrothermal transition a case study from the world class panasqueira w sn cu ore deposit portugal abstract deciphering the behavior of fluid flow at the magmatic hydrothermal transition is crucial to understanding the physical processes leading to the formation of intrusion related ore deposits and hence to predicting the locations of mineralized bodies however the hydrodynamics direction and velocity of the hydrothermal fluid flows related to this transitional stage remains poorly constrained here we present a coupled textural and chemical study performed on tourmaline growth bands to constrain fluid flow during the initiation of the hydrothermal system of the panasqueira w sn cu deposit this exceptional deposit consists of a dense network of flat wolframite and cassiterite bearing quartz veins intensely developed above a well known but hidden greisen cupola the w sn mineralization is preceded by a tourmalinization stage occurring as metasomatic halos around veins and as selvages developed along the vein wall rocks contacts results emphasize the key role of the greisen cupola in fluid focusing and the role of fluid overpressure during vein opening velocity values highlight an efficient transport of metals in veins largely dominated by advective processes 10 4 to 10 3 m s 1 whereas fluid flow in the altered wall rocks is slow and pervasive 10 6 to 10 5 m s 1 suggesting that element transport through the metasedimentary host rock was low and limited to the alteration haloes la icp ms analyses of tourmaline growth bands reveal that fluids coming from the cupola are enriched in na k li sr and sn emphasizing the contribution of magmatic fluids during vein formation and the metasomatic alteration of the wall rocks more generally this study demonstrates that the apical portions of granite bodies act as emanative centers of mineralizing fluids and highlights the usefulness of mineral growth band analysis in the search for intrusion related mineralization

the influence of inherited continental margin structures on the stress and strain fields of the south central taiwan fold and thrust belt in this paper we test whether or not structural and morphological features inherited from the eurasian continental margin are affecting the contemporary stress and strain fields in south central ta

the crust and upper mantle structure beneath southeastern china we analyzed teleseismic waveforms recorded by 44 stations in the fujian and taiwan provinces of china and obtained 5344 high quality receiver functions the crustal thickness h and average crustal vp vs ratio k beneath every station were estimated using the h k stacking method crustal thicknesses near the fujian province range from 28 3 to 32 8 km with an average of 31 1 km and the corresponding vp vs ratios vary from 1 70 to 1 84 with a mean of 1 76 from inland to offshore of the fujian province the crustal thicknesses decrease and poisson s ratios increase these may indicate decreasing sio2 and increasing calcalkaline contents in the crust the discontinuity structures such as the moho subducting slab the 410 and 660 km discontinuities hereafter we call them the 410 and the 660 are also studied using common converted point ccp stacking of receiver functions along two nw se lines of central and northern taiwan the ccp stacking results show a western dipping structure at depths above 50 km suggesting that the philippine sea plate is probably subducting beneath the eurasian continent plate near the central and northern taiwan the ccp stacking results show sharp and flat 410 and 660 km discontinuities and the transition zone thickness tzt is the same as that of ambient mantle beneath fujian and taiwan strait but thickens in the east of taiwan these results suggest that 1 the subducting eurasian continent plate is confined to the depths above 410 km beneath fujian and taiwan strait and 2 the south china sea slab may reach the transition zone beneath the east of taiwan 2007 elsevier b v all rights reserved

tourmalinite as a potential host rock for gold in the caledonides of southeast ireland initial investigations designed to test the potential for gold in a series of lithologies associated with tourmalinites and coticules in the neighbourhood of the caledonian leinster granite of southeast ireland are reported the results of geological mapping geochemical analyses and panning of stream sediments indicate that significant levels of gold are associated with some tourmalinite zones the possible exploration implication of this work is that tourmalinites have potential as target indicators although secondary controls on mineralization are also important

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

seismic tomography of taiwan improved constraints from a dense network of strong motion stations in this study a large collection of 41 141 s p times from the untapped records of the taiwan strong motion instrumentation program tsmip network is combined with the p and s wave arrival times from the taiwan central weather bureau seismic network cwbsn to image the v p and v p v s structures beneath taiwan the records from the 680 tsmip stations throughout taiwan in the past 15 years enhance the path coverage and the resolution in the tomography inversions tremendously our result for the v p structure largely confirms previous studies but brings better constraint on the v p v s structure the colliding luzon volcanic arc is characterized by a belt of high v p and high v p v s with high seismicity that includes the offshore islands of lutao and lanyu and the coastal ranges in eastern taiwan at the depth between about 13 and 25 km this high v p v s belt can be traced to the subduction zone in the region between hualian and ilan in the deeper portion the shallow portions of the southwestern coastal plain and the pingtung region are also characterized by a belt of high v p v s with lower seismicity most of the events occurred at the base of the high v p v s zones we suggest that material strength in those regions may be too low to accumulate stress which may indicate water saturated young sediments finally the central range region is characterized by a low v p v s belt