geochronology and tectonic implications of magmatism and metamorphism southern kootenay arc and neighbouring regions southeastern british columbia part i jurassic to mid cretaceous k ar dates and u pb zircon dates define three periods of igneous activity in the southern kootenay arc 1 emplacement of late synkinematic to post kinematic granodioritic plutons in mid jurassic time 170 165 ma accompanying amphibolite facies regional metamorphism 2 emplacement of post kinematic granitic plutons in mid cretaceous time 100 ma and 3 emplacement of small bodies of syenite in eocene time 50 ma in the western part of the area micas from mid jurassic plutons that yield the oldest k ar dates 158 166 ma also yield plateau shaped 40ar 39ar age spectra age spectra for biotites younger than these but older than 125 ma reflect thermal overprinting in southeastern british columbia the kootenay arc marks the transition from the north american rocks of the cordilleran miogeocline to the tectonic collage of allochthonous terranes that have been accreted to it deformation metamorphism and plutonism recorded in rocks of the southern kootenay arc commenced in mid jurassic time as a co

the boycott effect in magma chambers 1 we investigate the plausibility of the stratified boycott effect as a source of layering in magma chambers crystal settling within the magma chamber will generate buoyant fluid near the sloping sidewalls whose vertical ascent may be limited by the ambient stratification associated with vertical gradients in sio2 the resulting flow may be marked by a layered structure each layer taking the form of a convection cell spanning the lateral extent of the magma chamber using parameters relevant to magma chambers we estimate that such convection cells would be established over a timescale of a month and have a depth on the order of 4m which is roughly consistent with field observations of strata within solidified chambers

aeration due to breaking waves part i bubble populations abstract the population of bubbles produced by breaking waves in 10 m winds of up to 12 m s 1 is analyzed using calibrated images from a vertical pencil beam sonar system placed on the seabed near the dutch coast the structure in the images is parameterized and the volumetric bubble backscatter is inverted to yield bubble concentrations data were obtained at three acoustic frequencies with inversion effected by prescribing a bubble spectrum with two free variables leaving a redundant measurement to test the robustness of the model median concentrations may in this way be obtained up to the sea surface measurements are multiply regressed on wind and dominant wave variables bubbles penetrate to a depth of about a factor of 6 1 times the significant wave height hs where is the wave age or ratio of dominant wave phase speed to wind speed the measured mean bubble radius decreases weakly with depth unless waves are gently sloping at about 5 m 1 at 0 4 m the mean radius ranges from 30 to 80

double diffusive convection in magma chambers single or multiple layers an approximate set of equations applicable to double diffusive convection in magma chambers has been solved in the steady state for a range of geologically relevant parameters no evidence for the steady state existence of layered convection for conditions appropriate to magma chambers has been found at large ratios of the thermal to chemical diffusivity lewis number le the heat transport is independent of the lewis number and equal to that found for thermal convection in a single component fluid the vertical upward transport of light component varies directly with both the rayleigh and lewis numbers nuc ra0 23 le0 37

chronology of tectonothermal activity in the western avalon zone of the newfoundland appalachians the ackley granite was intruded into variably deformed and metamorphosed rocks within the gander and avalon zones of the newfoundland appalachians biotite and hornblende from the pluton record internally concordant 40ar 39ar age spectra that define total gas dates of 352 356 ma these are similar to a previously reported 355 5 ma rb sr whole rock isochron age and indicate relatively rapid post magmatic cooling a feature consistent with the post kinematic character of the pluton in the western avalon zone recrystallized sericitic metavolcanic rocks from the late precambrian love cove and marys town groups display variably discordant whole rock 40ar 39ar age spectra however the samples yield well defined plateau ages of 353 400 ma 11 samples which are interpreted to closely date the regional metamorphism and associated deformation in the western avalon zone this chronology is similar to that of the easternmost gander zone indicating that deformation and metamorphism in the western avalon zone

vertical structure of dissipation in the nearshore abstract the vertical structure of the dissipation of turbulence kinetic energy was observed in the nearshore region 3 2 m mean water depth with a tripod of three acoustic doppler current meters off a sandy ocean beach surface and bottom boundary layer dissipation scaling concepts overlap in this region no depth limited wave breaking occurred at the tripod but wind induced whitecapping wave breaking did occur dissipation is maximum near the surface and minimum at middepth with a secondary maximum near the bed the observed dissipation does not follow a surfzone scaling nor does it follow a log layer surface or bottom boundary layer scaling at the upper two current meters dissipation follows a modified deep water breaking wave scaling vertical shear in the mean currents is negligible and shear production magnitude is much less than dissipation implying that the vertical diffusion of turbulence is important the increased near bed secondary dissipation maximum results from a decrease in the tu

the role of viscous particle segregation in forming chromite layers from slumped crystal slurries insights from analogue experiments the question of how the mineral layering in layered intrusions forms has been extensively debated for many decades there are many types of layering and it is of course possible that a number of mechanisms are involved of particular interest is how chromite layers form because these may contain valuable metals such as platinum group elements in addition to cr one model for the formation of these layers is that they formed through slumping of semi consolidated cumulates from the margins of the intrusion into the magma chamber during this slumping the grains are sorted by density and or size differences this study examines the viability of this process using analogue modelling starting materials beads and glycerine were scaled to match the density and size of the minerals chromite orthopyroxene and plagioclase present in layered mafic ultramafic layered intrusions and to match the density and viscosity of the silicate magma a perspex flume tank divided by a removable partition at one end was fully filled with glycerine a homogenized mixture of the beads was placed in the smaller partition of the tank representing the margins of the magma chamber the tank was then inclined between 16 and 45 the partition was removed and the beads flowed into the main part of the box the experiments were recorded by video camera allowing us to follow the dynamics of the flow during each run segregation of the beads was observed in the final deposits the larger less dense beads representing plagioclase concentrated at the top of the flow with the intermediate sized and medium density beads representing orthopyroxene in the middle and the smaller denser beads representing chromite at the bottom thus mimicking natural examples in experiments where the angle of inclination was low long thin layers formed such as those found in the bushveld complex in experiments where the angle of inclination was high thick but short layers formed a dimensionless analysis allows better understanding of the dynamics of the flow at the macroscopic scale the flow regime is strongly influenced by the viscosity of the fluid and is considered macro viscous where the role of the interstitial liquid is non negligible

40ar 39ar dating of micas from the east kemptville tin deposit yarmouth county nova scotia the east kemptville tin deposit in nova scotia the largest known tin deposit in north america lies in a greisen zone within the davis lake pluton generally considered to be part of the devonian south mountain batholith our dating of micas from within the deposit suggests that the greisenization process that accompanied mineralization took place about 295 5 ma ago that is ca 60 ma after the emplacement of the batholith hydrothermal alteration mineralization activity in southern nova scotia coincided with extensive shearing and tectonism throughout the hercynian orogen the east kemptville deposit appears to be approximately coeval with similar mineralization in southwest england the iberian peninsula and northwest africa and much younger than the devonian acadian orogeny

directional attributes of the ocean surface wind stress vector in a recent paper by geernaert 1988 it was suggested that the stress and wind vectors are rarely aligned and that the deviation of the stress vector direction from the wind vector is related to the surface heat flux it was argued that since cold air advection over the open ocean generally corresponds to upward heat flux the consequent rotation of the winds to the right with height during cold air advection could be responsible for observations of the stress vector to be to the right of the wind flow for unstable stratifications conversely observations of the stress vector to the left of the flow for stable stratifications were suggested to be associated with the turning of the wind vector to the left of the flow for warm air advection or downward heat flux in that study only 30 of the statistical variance of the angle between the wind and wind stress vectors could be explained by air sea heat flux and it was suggested that the orbital velocity spectrum of surface waves i e data unavailable in that study could be important for explaining at least part of the remaining variance in this study we report on measurements of the wind stress vector and wave directional spectrum collected during the synthetic aperture radar x band ocean nonlinearities experiment conducted on the chesapeake light tower during 1988 the experiment yielded data reported herein that provide convincing evidence that the stress vector direction during light winds and near zero air sea heat flux is governed in large part by the direction of long waves on the ocean surface further the measurements suggest that the stress vector has a direction which is a blend between the wind direction and the swell direction

origin of modal and rhythmic igneous layering by sedimentation in a convecting magma chamber experimental investigations of convecting particle laden fluids show two regimes for convection driven by cooling from above1 in very dilute suspensions convection will maintain a homogeneous distribution of particles throughout the convecting layer provided that particle fall velocities are small compared with turbulent fluid velocities above a critical concentration convection is unable to keep the particles suspended so the particles settle leaving behind a layer of convecting fluid virtually free of particles here we apply these results to cooling magma chambers in which crystallization leads to an increase in suspended crystal content with time discrete sedimentation events are predicted each time the concentration exceeds the critical value for common igneous minerals critical concentrations are very small typically 0 002 0 03 wt and layers of the order of centimetres to a few metres thick will result because minerals of different density and size have different critical concentrations and settling velocities complex fluctuations in sedimentation rate and mineral proportions can occur in a multi component melt this may lead to either regular repetitive cycles or more complex fluctuations the process is confined to low viscosity magmas such as basalts in which the crystals are able to separate from the active thermal boundary layer during convection

magma dynamics crystallization and chemical differentiation of the 1959 kilauea iki lava lake hawaii revisited abstract using constraints from an extensive database of geological and geochemical observations along with results from fluid mechanical studies of convection in magma chambers we identify the main physical processes at work during the solidification of the 1959 kilauea iki lava lakes in turn we investigate their quantitative influence on the crystallization and chemical differentiation of the magma and on the development of the internal structure of the lava lake in contrast to previous studies vigorous stirring in the magma driven predominately by the descent of dense crystal laden thermal plumes from the roof solidification front and the ascent of buoyant compositional plumes due to the in situ growth of olivine crystals at the floor is predicted to have been an inevitable consequence of very strong cooling at the roof and floor the flow is expected to have caused extensive but imperfect mixing over most of the cooling history of the magma producing minor compositional stratification at the roof and thermal stratification at the floor the efficient stirring of the large roof cooling is expected to have resulted in significant internal nucleation of olivine crystals which ultimately settled to the floor additional forcing due to either crystal sedimentation or the ascent of gas bubbles is not expected to have increased significantly the amount of mixing in addition to convection in the magma circulation driven by the convection of buoyant interstitial melt in highly permeable crystal melt mushes forming the roof and the floor of the lava lake is envisaged to have produced a net upward flow of evolved magma from the floor during solidification in the floor zone mush convection may have caused the formation of axisymmetric chimneys through which evolved magma drained from deep within the floor into the overlying magma and potentially the roof we hypothesize that the highly evolved pipe like vertical olivine rich bodies vorbs bull volcanol 43 1980 675 observed in the floor zone of the lake are fossil chimneys in the roof zone buoyant residual liquid both produced at the roof solidification front and gained from the floor as a result of incomplete convective mixing is envisaged to have percolated or leaked into the overlying highly permeable cumulate displacing less buoyant interstitial melt downward the results from rayleigh fractionation type models formulated using boundary conditions based on a quantitative understanding of the convection in the magma indicate that most of the incompatible element variation over the height of the lake can be explained as a consequence of a combination of crystal settling and the extensive but imperfect convective mixing of buoyant residual liquid released from the floor solidification front the remaining chemical variation is understood in terms of the additional influences of mush convection in the roof and floor on the vertical distribution of incompatible elements although cooling was concentrated at the roof of the lake the floor zone is found to be thicker than the roof zone implying that it grew more quickly the large growth rate of the floor is explained as a consequence of a combination of the substantial sedimentation of olivine crystals and more rapid in situ crystallization due to both a higher liquidus temperature and enhanced cooling resulting from imperfect thermal and chemical mixing

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

k ar and 40ar 39ar geochronology of granitoid rocks from southern nova scotia its bearing on the geological evolution of the meguma zone of the appalachians k ar and or 40ar 39ar apparent ages are reported for 28 samples of biotite and muscovite from nova scotia s south mountain batholith and associated northern satellite stocks in addition 14 mica samples from the southern satellite stocks were dated previous workers using primarily k ar and rb sr techniques have reported a spread of apparent ages ranging from 240 420 ma for these intrusive rocks the present data set is internally consistent and has been calibrated against accepted interlaboratory standards a mean age of 367 ma was obtained for the south mountain batholith and the northern stocks a value consistent with results recently obtained in an rb sr study by clarke and halliday no differences in apparent age among the various phases or clear geographic age distribution patterns were evident satellite stocks in the southern part of the province have in general younger apparent ages clustered in the range 300 320 ma we suggest that in southern areas mica argon systems record the effect

sm nd isotopic geochemistry of precambrian to paleozoic granitoid suites and the deep crustal structure of the southeast margin of the newfoundland appalachians in the eastern central mobile belt of the newfoundland appalachians late precambrian basement inliers have end from 3 to 2 but cambro ordovician metasedimentary rocks have initial end below 7

age and origin of the dover fault tectonic boundary between the gander and avalon zones of the northeastern newfoundland appalachians the dover fault forms a tectonic boundary between northern portions of the gander and avalon zones of the newfoundland appalachians a systematic geochronological investigation across the mylonitic

segregation processes in vesiculating crystallizing magmas vesiculation of crystallising magma can produce either a mobile vesicular magma or a rigid network of crystals containing vesicular liquid where partially crystallized rigid mush underlies less crystallized magma such as near the base of a lava flow or in the cumulus pile of a magma chamber evolved interstitial melt and or gas may escape into the main body of magma the consequences of this may include contamination of the overlying liquid with gas and interstitial melt or intrusion of diapirs of vesicular evolved liquids to form vertical vesicle cylinders and other segregation features found in many basaltic lava flows and sills analog experiments were used to investigate some of the phenomena that can arise during vesiculation within a crystal mush which was simulated by pumping air through a porous plate that formed the floor of a container filled with a viscous liquid floored with a layer of glass beads experiments used either a single liquid or two stably stratified liquids with a liquid interface either coincident with the top of the porous layer of beads or slightly above the porous layer for a range of liquid viscosities and air flow rates vesiculation rates individual bubbles emerged from the top of the porous layer of beads and carried a thin trail of interstitial liquid into the overlying liquid the number of bubble trains leaving the surface of the porous bed increased with decreasing liquid viscosity and flow rate and with increasing bead size and hence with increasing permeability analog vesicle cylinders composed of diapirs of bubbly interstitial liquid were produced only when a layer of buoyant bubbly liquid lay above the surface of the porous layer the relative size of the bubbles and constrictions within the porous layer are argued to control whether individual bubbles leading to bubble trains or vesicular liquid leading to vesicle cylinders leaves the porous layer and hence whether vesicle cylinders can form

geochronology and tectonic implications of magmatism and metamorphism southern kootenay arc and neighbouring regions southeastern british columbia part ii mid cretaceous to eocene a north south trending belt of amphibolite facies regional metamorphism parallels the purcell trench transects the kootenay arc and is in part fault bounded towards the axis of this belt progressively higher pressure metamorphic mineral assemblages are exposed in the contact aureoles of post kinematic mid cretaceous 100 ma plutons and in metapelites contours of k ar biotite dates for plutonic rocks 55 95 ma are regular are broadly conformable with metamorphic isograds appear to cross internal intrusive contacts of post kinematic plutons and young towards the highest pressure and temperature regional metamorphic zones within the sillimanite zone most micas yield k ar dates between 40 and 55 ma rb sr muscovite dates for deformed and undeformed pegmatites and for muscovite bearing monzogranite and granodiorite fall between 53 and 84 ma u pb zircon dates for the kaniksu batholith and nearby gneiss of uncertain origin yield a lower concordia intercept of 94 ma micas from mid jurassic and mid

plutonic and hydrothermal events in the ackley granite southeast newfoundland as indicated by total fusion 40ar 39ar geochronology results of total fusion 40ar 39ar dating eight biotites four muscovites and one hornblende of magmatic and hydrothermal stages of the high silica chemically zoned ackley granite indicate three distinct episodes of magmatic activity viz 410 378 374 and 355 ma and that the metallogenic system w sn mo evolved synchronously with only one of the magmatic phases the oldest suite is indicated by two biotite dates at 410 4 4 4 and 392 5 7 6 ma which are themselves considered as representing partial resetting related to a tectonothermal event of acadian age thus the 410 ma age offers the best estimate of intrusion although it must be considered a minimum the main magmatic pulse for the ackley granite is indicated by dates between 378 and 374 ma with most of these phases occurring in the southern part of the complex concordant hornblende biotite ages 374 8 3 8 and 372 3 4 8 ma respectively for one of the southern phases rencontre lake granite suggests rapid cooling for this part o

new age data refine extent and duration of paleozoic and neoproterozoic plutonism at ganderia avalonia boundary newfoundland devonian and younger plutonic suites of the appalachian orogen in newfoundland form a curvilinear belt straddling the boundary between ganderia and avalonia and exhibit a general pattern of younging to the southeast however many individual plutonic suites within this belt remain undated or have ages that are poorly constrained this study reports u pb sensitive high resolution ion microprobe shrimp data from zircon and 40ar 39ar data from hornblende biotite and muscovite which collectively improve definition of post tectonic plutonic events in southeastern newfoundland but at the same time raise new questions for further study u pb zircon shrimp determinations provide valuable new geochronological information for the deadman s bay granite 390 4 ma the gander lake granite 378 4 ma the terra nova granite 384 4 ma the old woman stock 376 4 ma and the easternmost unit tolt phase of the composite ackley granite 372 4 ma the pass island granite long considered part of this

relationship between plagioclase crystallization and cooling rate in basaltic melts rock textures commonly preserve a record of the near surface crystallization history of volcanic rocks under conditions of simple cooling without convection or mixing textures will reflect sample cooling rate the temperature at which crystallization was initiated and the distribution of mineral phase precipitation across the crystallization interval compilation of plagioclase size and number density data on natural dike sill and lava lake and experimental samples suggests that 1 growth and nucleation rates of plagioclase in natural basaltic samples are a predictable function of cooling rate and 2 the observed crystallization rate dependence on cooling rate is similar to that observed in experiments initiated at subliquidus temperatures comparison of natural and experimental samples thus suggests that most basalts crystallize under conditions of heterogeneous nucleation with the number density of preexisting nucleii partially controlling textural responses to cooling rate changes time scales of crystallization and cooling in magmatic systems are intimately linked through a balance between heat removal from the system and heat evolved through crystallization evaluation of textural data in the context of recent numerical models of crystallization in simple one and two component systems provides new insight into regularities in the crystallization behavior of basaltic magmas for example the rate of change in crystal size and number density as dictated by mass balance has been used as a measure of the relative importance of time scales of crystallization and cooling in numerical models of crystallizing systems in natural samples plagioclase size scales with the length scale of cooling such that a logarithmic plot of grain size as a function of normalized distance across the dike has a slope that appears approximately independent of dike width solidification time comparison with available textural data for other phenocryst phases suggests that the same may be true for pyroxene and magnetite crystallization with each phase having a characteristic slope probably controlled by the thermodynamic properties of the crystallizing phase measured crystal size distributions are unimodal and show maximum frequencies in the smaller size classes distributions broaden and the grain size at peak frequency increases with increasing crystallization times decreasing cooling rates in contrast partially crystallized makaopuhi lava lake samples have crystal size distributions that decrease exponentially with increasing crystal size measured size distributions in dikes can be explained by late stage modification of makaopuhi type distributions through loss of small crystals possibly the consequence of growth without nucleation finally this compilation of the textural response of basaltic magmas to changes in cooling rate suggests that empirical calibrations of crystallization rate dependence on cooling rate from natural samples provide a reasonable model for plagioclase crystallization in near surface basaltic systems predicted growth rates will be slow and relatively constant 10 10 10 11 cm s for crystallization times expected in most shallow volcanic systems 1000 years

observed directional characteristics of the wind wind stress and surface waves on the open ocean sonic anemometer data were taken during the surface waves processes program swapp in march 1990 in the north pacific measurements of the wind stress vector span several strong wind events significant angles between the wind stress vector and the mean wind vector are seen simultaneous measurements of the directional wave field were made with a surface scanning doppler sonar the data suggest that the wind stress direction is influenced by the direction of the surface waves especially for stronger winds overall the stress vector lies between the mean wind and the mean wave directions at the higher wind speeds over 8 6 m s there is a nonzero correlation between the variations in wave directions and stress directions as well finally the stress and wave component directions have similar frequency dependence over the frequency band where wave energy is nonnegligible suggesting a dynamic link

replenished magma chambers effects of compositional zonation and input rates several recent publications have reported investigations of the dynamical effects and geological consequences of the replenishment of a homogeneous magma chamber by the rapidinjection of hot relatively dense fresh magma the new magmaforms a separate layer at the base of the chamber whereit cools and crystallizes until the density of the residual liquid in the lower layer becomes equal to that of the upperlayer at which time the fluid in the two layers becomes intimately mixed the fluid dynamical aspects of this modelwere confirmed by laboratory experiments using aqueous solutions this paper reports three experimental variations on the basic theme which examine the effects of the rate of injection into homogeneous and compositionally stratified chambers first the rapid injection of a hot dense layer beneath a fluid with a lower temperature and a vertical compositional gradient is considered a series of layers gradually builds up from the base of the upper gradient region while the lower layer cools crystallizes and finally overturns in this situation however the rise of the lower layer fluid is restrained by the density gradient and mixing takes place with only part of the upper fluid second the slow influx of a hot dense liquid beneath a cold less dense homogeneous layer is considered a considerable quantity of the input fluid coolsand crystallizes immediately releasing some lighter fluid to mix with the fluid in the homogeneous layer with time some dense input fluid spreads along the bottom so that locally the situation is the same as the one considered in the previous studies with a local overturning occurring when the density of the lower fluid has decreased sufficiently the deposition of crystals continues and some rather fine chimney like structures can develop which bear a resemblance to the black smokers recently discovered on the sea floor third a combination of the first two variations is studied by the consideration of the slow influx of hot dense liquid beneath a uniformly cooler fluid with a vertical compositional gradient the input fluid is constrained in its rise by the density gradient as the influx continues the additional thermal energy is also confined and causes the crystals to redissolve and build up a lower layer as was observed in the case of a rapid injection beneath a compositional gradient

geochemical trends in the ackley granite southeast newfoundland their relevance to magmatic metallogenic processes in high silica granitoid systems the ackley granite occupying an area of approximately 2700 km2 was intruded at about 355 ma across the boundary between the avalon and gander tectonic terranes of southeast newfoundland it is dominated by k feldspar megacristic and equigranular biotite bearing granite with subordinate granodiorite but 10 separate phases have been recognized also including hornblende and muscovite bearing varieties small aplite pegmatite type molybdenite deposits occur in a southwest lobe and cassiterite wolframite bearing quartz topaz greisens are found as steeply dipping veins and pods within a south central lobe of the pluton a geochemical study of 357 rock samples randomly distributed on a grid of 2 km spacing shows systematic geographic variation in the concentrations of a range of elements the concentrations of silica and some other elements show a relatively abrupt change approximately 10 15 km west of the projected boundary between the avalon and gander terranes indicating that the different terranes ha

basalt vesicularity as a measure of atmospheric pressure and palaeoelevation the pressure in and thus the size of a bubble in a lava flow is determined by the atmospheric pressure and the hydrostatic pressure of the overlying lava if atmospheric sea level pressure is known or assumed vesicle size distributions in basalt flows can thus be used as an indicator of the palaeoelevation of emplacement1 here we show by analysis of the vesicle size distribution of basalt samples collected from the summit and base of mauna loa volcano in hawaii that the technique provides estimates of ambient pressure that are accurate to within 0 1 bar and thus estimates of elevation with a resolution of about 1 400m this palaeoaltimetric technique should find useful application in palaeogeographical reconstruction2 for times when sea level pressure was similar to the present value conversely if the elevation of emplacement is known our technique should be able to provide a measure of sea level palaeopressure unlike palaeo botanical methods for estimating elevations3 6 this method does not have to assume a relationship between temperature and altitude on the other hand its use is restricted to lava flows that have had a simple emplacement history

alongshore momentum balances in the nearshore the one dimensional time averaged over many wave periods along shore momentum balance between forcing by wind and breaking waves and the bottom stress is examined with field observations spanning a wide range of con ditions on a barred beach near bottom horizontal currents were measured for 2 months at 15 locations along a cross shore transect extending 750 m from the shoreline to 8 m water depth the hourly averaged bottom stress was estimated from observed currents using a quadratic drag law the wave radiation stress was estimated in 8 m depth from an array of pressure sensors and the wind stress was estimated from an anemometer at the seaward end of a nearby pier the combined wind and wave forcing integrated over the entire cross shore transect is balanced by the integrated bottom stress the wind stress contributes about one third of the forcing over the transect analysis of the momentum balances in different cross shore regions shows that in the surf zone wave forcing is much larger than wind forcing and that the bottom drag coefficient is larger in the surf zone than farther seaward consistent with earlier studies

evidence for volatile influenced differentiation in a layered alkali basalt flow penghu islands taiwan an approximately 20 m thick alkali basalt flow on the penghu islands contains 20 cm thick horizontally continuous 50 m vesicular layers separated by 1 5 m of massive basalt in its upper 8 5 m the three layers contain ocelli like vesicles filled with nepheline and igneous carbonate they are coarse grained and enriched in incompatible elements relative to the massive basalt with which they form sharp contacts these vesicular layers segregation veins formed when residual liquid in the underlying crystal mush was forced gas filter pressing or siphoned into three thermally induced horizontal cracks that opened successively in the advancing crystal mush of the flow s upper crust most vesicular layer trace elements can be modelled by residual melt extraction after 25 40 fractional crystallization of massive basalt underlying each layer sulphur cl as zn pb k na rb and sr show large concentration changes between the top middle and bottom layers with each vesicular and underlying massive basalt forming a chemically distinct pair the large changes between layers are difficult to account for by crystal fractionation alone because other incompatible elements e g la sm yb zr nb and the major elements change little the association of these elements s cl etc with fluids in various geologic environments suggests that volatiles influenced differentiation perhaps by moving alkali alkaline earth and chalcophile elements as magma dissolved volatile complexes volatiles may have also led to large grain sizes in the segregation veins by lowering melt viscosities and raising diffusion rates the chemical variability between layers indicates that a convection and concentration mechanism acted within the flow the specific process cannot be determined but different rates of vesicle plume rise through the flow and or accumulation in the upper crust s crystal mush might account for the chemical pairing and extreme variations in cl s as and c this study emphasizes the importance of sampling vesicular rocks in flows it also suggests that volatiles play important physical and chemical roles in rapidly differentiating mafic magmas in processes decoupled from crystal fractionation

some evidence of colinear wind stress and wave breaking abstract data collected during the surface waves and processes program are employed to investigate a possible interrelation between wind stress and surface wave breaking from comparison of data from 15 half hour long time segments the directions of the wind stress and the whitecap motion are observed to be generally colinear with both lying between the mean wind and the swell as well a nondimensionalized whitecap speed is found to correlate with the drag coefficient these results suggest that the magnitude and direction of the wind stress might be estimated from wave breaking information