interactions between the ebb tidal delta and landward shoreline price inlet south carolina abstract patterns of erosion and deposition along the shoreline of price inlet south carolina are strongly influenced by ebb tidal delta processes the ebb delta goes through cycles of growth and decay 15 20 change in volume which last from 4 to 7 years in the growth phase large intertidal bar complexes are formed on both sides of the main ebb channel by the coalescence of landward migrating swash bars during this stage waves refracting around the southern bar complex produce a reversal in the longshore transport direction on the downdrift shoreline this results in little sediment escaping the inlet and delta system the sand trapping mechanism ceases and the delta reduces in volume when the bar complexes migrate onshore and attach to the beach the inlet shoreline also goes through cycles of 7 to 42 years duration in which its offset configuration changes the shift in shoreline alignment is controlled by the orientation of the main ebb channel and the resulting ebb tidal delta morphology when the inlet has a downdrift offset configuration the ebb tidal delta is skewed along the updrift shoreline in this position bar complexes preferentially accrete along the updrift beach causing a progradation of the shoreline at the same time the downdrift shoreline erodes due to little sediment bypassing the inlet this pattern of sedimentation eventually produces an updrift offset inlet the erosional depositional processes are reversed when the ebb flow in the channel thalweg is deflected off the prograding updrift inlet shore ine this causes a clockwise rotation of the main ebb channel and a shift in the ebb delta to a position along the downdrift shoreline in this configuration the updrift shoreline erodes and the downdrift shoreline accretes this study documents the close relationship that exists at price inlet south carolina between the ebb tidal delta and landward shoreline evidence is presented to show that this relationship may hold for other mixed energy tidal inlets as well

meso scale transfer of sand during and after storms implications for prediction of shoreline movement abstract monitoring beach volume changes of the texas coast following a major hurricane reveals the impact of storms on sand dispersal and shoreline movement at spatial and temporal scales encompassing tens of kilometers and decades beach volume histories at profile sites show the interdependence of sand exchange among adjacent sites and the spatial autocorrelation of sand movement beach volume histories also indicate periods when either longshore or cross shore transport predominate and illustrate the long term effects of coastal structures on beach mobility this study confirms that net losses of sand from updrift barriers may not be directly linked with net gains of sand on adjacent downdrift barriers instead sand dispersal within a coastal compartment may depend partly on the dynamics of shoals and temporary sand storage at the intervening tidal inlet in our study sand eroded from the updrift barrier galveston island is deposited in a terminal sand flat of the barrier whereas sand accreted to the downdrift barrier follets island is derived from the intermediate ebb tidal delta san luis pass unlike continuous sand bypassing on some microtidal wave dominated coasts sand bypassing at san luis pass is episodic event driven and inefficient and sand is not transferred directly from one barrier to the next p because storms rapidly redistribute beach sediment they can be the most important factor controlling short term

the temperature dependence of hydrogen isotope fractionation between clay minerals and water evidence from a geopressured system abstract d values of water samples from two gulf coast geopressured fields vary linearly with temperature while the d values from the coexisting clays remain constant and are independent of temperature fluid how rates on the order of millimeters per year characteristic of gulf coast geopressured systems provide adequate residence time for hydrogen isotope equilibrium to be achieved between the extant porewaters and clay minerals since equilibrium is achieved these d values are used to calculate the temperature dependence of the hydrogen isotope fractionation factor between illite smectite and water clay waterh between 0 and 150 c 1000 in clay water h 45 3 10 3 t 94 7 this equation predicts values for clay waterh at 96 c which are equal to those predicted by a similar equation derived by yeh 1980 above and below 96 c this new equation predicts values which diverge from those predicted by the equation of yeh 1980 with a difference of 9 at 150 c and 25 at 0 c the possibility is raised that the very slow upward component of flow characteristic of gulf coast geopressured sediments combined with the slow downward subsidence of the clay rich sediments can result in a system which is rock dominated with respect to hydrogen

contrasts in morphology and deformation offshore montserrat new insights from the sea calipso marine cruise data 1 during the december 2007 sea calipso experiment we collected seismic reflection profiles offshore of montserrat off the east coast we imaged deep fans of volcaniclastic debris from three volcanoes progressively active from 2 ma to present near shelf sedimentation rates of 8 9 cm ka are approximated following cessation of local volcanic activity the fans were deposited on sediments with apparent dips towards the ese trending montserrat havers fault system mhfs in southern montserrat the mhfs encloses the soufriere hills volcano has elevated crustal blocks at roche s bluff st georges hill and garibaldi hill and extends off the west coast off the west coast the n dip of two faults supports a n dip interpretation for a major component of mhfs the belham valley fault we propose that local deformation is affected by stress redistributions consistent with a right stepping sinistral en echelon fault system but the interplay of transtension and magmatism has resulted in complex and evolving stress regimes

andesitic water a phantom of the isotopic evolution of water silicate systems comment on isotopic shifts in waters from geothermal and volcanic systems along convergent plate boundaries and their origin by w f giggenbach on account of the low porosity of the lithosphere intracrustal fluids behave very differently from surface fluids in that they are changing their geochemical and isotopic labels according to the geological environment given a heat source meteoric waters can be supplied plentifully and their rates of throughput in geothermal systems are sufficiently high to exhaust the compositional signals of a given rock buffer in contrast fluids exsolved from magma and subducted fluids would be supplied at less than about one tenth of the meteoric rate over the life time of a system based on up to date flow models the isotopic evolution of meteoric water interacting with crustal rock follows a curved to l shaped track in the d versus 18o plot instantaneous present day tie lines between recharge and discharge are secants of such tracks and can have a range of slopes at the start of an interaction waters have d and 18o values approaching equilibrium with the original rock composition water w1 using known hydrogen isotope fractionation factors w1 values generally plot in the region of andesite or andesitic waters of various authors since the w1 waters have d values that are on average more positive and also less variable than those of the meteoric recharges most tracks and tie lines have positive slopes and the plotting of a large number of tie lines will produce a focus on the field of w1 waters regardless of the original water source

current block motions and strain accumulation on active faults in the caribbean the caribbean plate and its boundaries with north and south america marked by subduction and large intra arc strike slip faults are a natural laboratory for the study of strain partitioning and interseismic plate coupling in relation to large earthquakes here we use most of the available campaign and continuous gps measurements in the caribbean to derive a regional velocity field expressed in a consistent reference frame we use this velocity field as input to a kinematic model where surface velocities results from the rotation of rigid blocks bounded by locked faults accumulating interseismic strain while allowing for partial locking along the lesser antilles puerto rico and hispaniola subduction we test various block geometries guided by previous regional kinematic models and geological information on active faults our findings refine a number of previously established results in particular slip rates on the strike slip faults systems bounding the caribbean plate to the north and south and the kinematics of the gonave microplate our much improved gps velocity field in the lesser antilles compared to previous studies does not require the existence of a distinct northern lesser antilles block and excludes more than 3 mm yr of strain accumulation on the lesser antilles puerto rico subduction plate interface which appears essentially uncoupled the transition from a coupled to an uncoupled subduction coincides with a transition in the long term geological behavior of the caribbean plate margin from compressional hispaniola to extensional puerto rico and lesser antilles a characteristics shared with several other subduction systems

chemical evolution of thermal springs at arenal volcano costa rica effect of volcanic activity precipitation seismic activity and earth tides arenal volcano in nw costa rica central america has been active during the last 37 years however only relatively low temperature springs have been identified on its slopes with temperatures less than around 60 c the springs are clustered on the ne and nw slopes of the volcano close to contacts between the recent and older volcanic products or at faults that intercept the volcano this volcano is located in a rain forest region with annual rainfall averaging around 5 m during the last 15 years the temperature and chemical composition of 4 hot springs and 2 cold springs have been monitored approximately every 3 months in addition two more thermal sites were identified recently and sampled as well as two boreholes located on a fault ne of the volcano scatter plots of chemical species such as cl and b suggest that the waters in these discharges belong to the same aquifer with a saline end member similar to rio tabacon at the beginning of the study period 1990 and the deeper borehole b 2 in 2004 the waters of quebrada bambu and quebrada fria represent a more dilute end member both long term over the 15 years and short term or seasonal decreases in concentration and steady or decreasing temperature are noted in nw springs springs located at the ne show increasing temperatures and ion concentrations except for bicarbonate that has decreased in concentration for all the springs this behavior is likely associated with a shallow source for the solutes and heat for this aquifer to the nw the early lavas and pyroclastic flows have been cooling down decreasing the contribution of leaching products to the infiltrating waters to the ne pyroclastic flows to the n during the last decade are contributing increasing concentrations of solutes and heat throughout water infiltration and circulation within the faults and the surficial drainage that has a ne regional trend for the short term or seasonal variations concentrations of chemical constituents decrease when precipitation increases however correlations between concentrations and the number of seismic events per month and the modeled vertical tidal acceleration are also observed the intrinsic periodic behavior of all these variables influenced by the earth s rotation can complicate the interpretation of the chemical changes at hot springs for example variations in atmospheric pressure can affect the degassing and seismic tremor of a volcano as well as the rate of precipitation frequent monitoring and understanding of these variations is essential at every volcano if we want to use the variations in chemical composition of hot springs in volcanic monitoring

the influence of alongshore and cross shore wave energy flux on large and small scale coastal erosion patterns a strong low pressure system traveled along the japanese main island honshu in october 2006 high waves and storm surge attacked the kashima coast resulting in huge erosion over the area airborne laser data measured in october 2005 and november 2006 were analyzed to estimate cross sectional changes within the subaerial zone the results of the alongshore distribution of the changes of cross sectional area indicate that the amount of erosion of the 38 km long northern and 15 km long southern parts decreased toward the south in each part and that the amount of erosion was smaller in protected areas with artificial headlands than in unprotected areas the local alongshore variation of the erosion and accretion patterns showed wavy fluctuations of several hundreds of meters the total amounts of the estimated eroded volume of the subaerial zone over the northern and southern parts were 620 000 m3 and 600 000 m3 respectively the simulating waves nearshore swan wave model was applied to estimate wave conditions along the coast during the storm the computational results were verified and then the alongshore distribution of wave energies expressed as the alongshore and cross shore components of the wave energy flux was compared with the alongshore distribution of cross sectional change the results show that the distribution of energy flux explains the distribution of erosion well the alongshore variability in the cross shore energy flux is responsible for the large scale variability in erosion and shorter scale variability is due to gradients in the alongshore energy fluxes especially for the areas without coastal works copyright 2011 john wiley sons ltd

collisional model for rapid fore arc block rotations arc curvature and episodic back arc rifting in subduction settings 1 we review geophysical and geological data from 23 active and ancient plate boundaries to document a compelling spatial and temporal relationship between collision plate boundary curvature rapid tectonic rotations and the occurrence of back arc rifting our observations support a conceptual model where the change from subduction to collision causes rapid fore arc rotation when viewed in a reference frame relative to the bounding tectonic plates leading to marked plate boundary curvature our global compilation reveals that most active back arc rifts are associated with rapidly rotating fore arcs and nearby collisions thus we propose that collision and rapid fore arc rotations play a major role in the evolution and kinematics of back arc basins we conduct numerical modeling to better understand the physical processes behind these observed rapid tectonic rotations at convergent margins our results suggest that the presence of an indentor or choke point in the subduction system e g collision can generate rapid rotation of the fore arc about a nearby pole and lead to back arc rifting the rate of fore arc rotation and back arc rifting depends on the incoming indentor velocity and can be greatly enhanced by slab rollback and the presence of a low viscosity back arc where viscosity of the back arc is low fore arc rotation dominates where back arc viscosity is high the formation of strike slip faults and tectonic escape dominates our observational and model derived results illustrate that shallow crustal forces produced by the entry of buoyant features into subduction zones are a fundamental mechanism for the generation of fore arc block rotations plate boundary curvature back arc rift evolution and tectonic escape in subduction systems rollback of the subducting slab within the mantle will certainly enhance the processes we describe but it is not the only driving force

caribbean intra plate deformation paleomagnetic evidence from st barthelemy island for post oligocene rotation in the lesser antilles forearc abstract as subduction zones and their related processes are often studied in 2d or cylindrical 3d sections the dynamic effects of trench curvature and its evolution through time remain under explored whereas temporal variations in trench trend may be estimated through restoring upper plate deformation we investigate the forearc deformation history of the strongly curved northern lesser antilles trench connecting the near orthogonal lesser antilles subduction zone with the motagua cayman transform plate boundary our new paleomagnetic dataset consists of 310 cores from eo oligocene magmatic rocks and limestones from st barthelemy island the limestones yielded a post folding magnetization containing a similar magnetic direction to those stored in magmatic rocks that intrude the folded carbonates both indicating a post oligocene 15 and perhaps up to 25 counterclockwise rotation of the island our results highlight that the present day trench curvature formed progressively during the cenozoic allowing us to discuss different tectonic scenarios explaining ne caribbean plate deformation and to identify key targets for future research on tectonic architecture and the potential present day activity of intra plate deformation that may pose seismic hazards

seabed texture and composition changes offshore of port royal sound south carolina before and after the dredging for beach nourishment abstract beach nourishment has been a strategy widely used to slow down coastal erosion in many beaches around the world the dredging of sand at the borrow site however can have complicated physical geological and ecological impacts our current knowledge is insufficient to make accurate predictions of sediment infilling in many dredging pits due to lack of detailed sediment data two sites in the sandy shoal southeast of port royal sound prs of south carolina usa were sampled 8 times from april 2010 to march 2013 one site defined as borrow site was 2 km offshore and used as the dredging site for beach nourishment of nearby hilton head island in beaufort county south carolina and the other site defined as reference site was 10 km offshore and not directly impacted by the dredging a total of 184 surficial sediment samples were collected randomly at two sites during 8 sampling periods most sediments were fine sand with an average grain size of 2 3 phi and an organic matter content less than 2 after the dredging in december 2011 january 2012 sediments at the borrow site became finer changing from 1 0 phi to 2 3 phi and carbonate content decreased from 10 to 4 changes in mud content and organic matter were small compared with the reference site the borrow site experienced larger variations in mud and carbonate content an additional 228 sub samples were gathered from small cores collected at 5 fixed stations in the borrow site and 1 fixed station at the reference site 0 3 6 9 and 12 months after the dredging these down core sub samples were divided into 1 cm slices and analyzed using a laser diffraction particle size analyzer most cores were uniform vertically and consisted of fine sand with well to moderately well sorting and nearly symmetrical averaged skewness based on the analysis of grain size populations 2 phi and 3 phi sized sediments were the most dynamic sand fractions in prs mud deposition on shoals offshore of prs presumably happens when offshore mud transport is prevalent and there is a following rapid sand accumulation to bury the mud however in this borrow site there was very little accumulation of mud this will allow the site to be used in future nourishment projects presuming no accumulation of mud occurs in the future

hurricane associated ebb tidal delta sediment dynamics bathymetric surveys conducted before and after the 2005 hurricane season at little pass timbalier in the mississippi river delta plain united states demonstrate that 9 1 2 4 10 6 m 3 of sediment was eroded from a 47 9 km 2 area between the two surveys hurricanes cindy katrina and rita passed within 300 km of the tidal inlet comparison of before and after bathymetric data sets shows that the distal portion of the ebb tidal delta etd was the site of 63 of the total erosion locally resulting in 400 m of shoreface retreat shoaling 0 75 1 0 m in the seawardmost portion of the ebb channel and erosion in the landward portion 1 5 m resulted in a 160 m landward shift of the inlet throat collectively these processes forced the landward migration of the entire tidal inlet and etd system there has been considerable discussion about large volumes of mineral sediment deposited on the mississippi river delta plain interior marsh surface as a result of hurricanes however the origin of this sediment is unknown we identify the distal portion of an etd as one possible sediment source and hypothesize that etd and shoreface sediment is mobilized by hurricane waves and transported landward by surge induced currents our results emphasize the role of frequent and intense hurricanes in long term coastal evolution and as a mechanism for regional sediment retention within the transgressive system beyond typical barrier overwash processes

tectonic evolution and mantle structure of the caribbean we investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic p wave velocity structure under the caribbean region in the upper mantle positive seismic anomalies are imaged under the lesser antilles and puerto rico these anomalies are interpreted as remnants of atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the lesser antilles island arc during the past 45 myr the imaged lesser antilles slab consists of a northern and southern anomaly separated by a low velocity anomaly across most of the upper mantle which we interpret as the subducted north america south america plate boundary the southern edge of the imaged lesser antilles slab agrees with vertical tearing of south america lithosphere the northern lesser antilles slab is continuous with the puerto rico slab along the northeastern plate boundary this results in an amphitheater shaped slab and it is interpreted as westward subducting north america lithosphere that remained attached to the surface along the northeastern boundary of the caribbean plate at the muertos trough however material is imaged until a depth of only 100 km suggesting a small amount of subduction the location and length of the imaged south caribbean slab agrees with proposed subduction of caribbean lithosphere under the northern south america plate an anomaly related to proposed oligocene subduction at the nicaragua rise is absent in the tomographic model beneath panama a subduction window exists across the upper mantle which is related to the cessation of subduction of the nazca plate under panama since 9 5 ma and possibly the preceding subduction of the extinct cocos nazca spreading center in the lower mantle two large anomaly patterns are imaged the westernmost anomaly agrees with the subduction of farallon lithosphere the second lower mantle anomaly is found east of the farallon anomaly and is interpreted as a remnant of the late mesozoic subduction of north and south america oceanic lithosphere at the greater antilles aves ridge and leeward antilles the imaged mantle structure does not allow us to discriminate between an intra americas origin and a pacific origin of the caribbean plate key points tectonic reconstructions for the caribbean validated by seismic tomography cenozoic lesser antilles and mesozoic greater antilles subduction confirmed tomography gives insight into geodynamics of lesser antilles

transport mechanisms by fluid flow in metamorphic rocks oxygen and strontium decoupling in the trois seigneurs massif a consequence of kinetic dispersion

stable isotopes evidence of recycled subduction fluids in the hydrothermal volcanic activity across nicaragua and costa rica abstract the central america volcanic front provides a unique opportunity to study hydrothermal inputs and their interaction and mixing with modern meteoric waters the objectives of this study were to a characterize the isotopic composition 18 o 2 h d excess and lc excess of hydrothermal volcanic systems b analyze the influence of kinetic fractionation and meteoric water inputs in the isotopic composition of hydrothermal waters and c estimate the andesitic water contribution recycled subduction fluids within the volcanic front of nicaragua and costa rica hydrothermal evaporation lines are described as 2 h 4 7 18 o 13 0 costa rica and 2 h 2 7 18 o 31 6 nicaragua these regressions are significantly p 2 h 7 6 18 o 7 4 costa rica and 2 h 7 4 18 o 5 2 nicaragua the greater rainfall inputs in costa rica with respect to nicaragua resulted in the attenuation of the evaporative effect as observed in the strong bimodal distribution of the hydrothermal waters which can be divided in fluids a isotopically close to meteoric conditions and b isotopically altered by the interaction with recycled subduction fluids and kinetic fractionation the latter is clearly depicted in the significantly p d excess and lc excess median values between costa rica 5 10 5 25 and nicaragua 2 42 10 65 respectively poor correlations between 18 o 2 h and the elevation gradient emphasize that the contribution of recycled subduction fluids and subsequent surface kinetic fractionation are the main drivers of the isotopic departure from the orographic distillation trend captured in the rainfall isoscapes end member mixing calculations resulted in a significant difference p 2 he contributions across the volcanic front of nicaragua and costa rica

sea level rise and coastal marsh sustainability geological and ecological factors in the mississippi delta plain chronostratigraphic approaches to coastal geomorphology frequently include consideration of salt marsh deposits as indicators of past sea level positions continuous horizons of such deposits can be used to infer that salt marshes were keeping pace with local rates of relative sea level rise rslr rates of past accumulation estimated using dating techniques are then used to hindcast the rate of sea level rise in that area estimates of contemporary sea level rise rates are often derived from tide gauge records this approach allows identification of subdecadal variations in mean water level accumulation rates of both organic and inorganic sediments can also be derived at these time scales and studies from many coastal marshes demonstrate the episodic nature of inorganic sediment deposition the frequency and spacing of these events does not necessarily coincide with periods of increased local sea level in addition short term increases in sea level could result in marsh deterioration as soils become excessively waterlogged a conceptual model of changes in geomorphic and ecological processes contributing to marsh sustainability during the holocene has been developed for the mississippi delta plain mdp the survival of some marshes in this area despite high rates of subsidence indicates that the combined effect of organic and inorganic accumulation processes can be adequate to sustain coastal marshes in the face of sea level rise

do storms cause long term beach erosion along the u s east barrier coast abstract in a few hours or days scores of meters of beach width can be lost due to a severe storm however newly available shoreline data from the u s east coast show that beaches recover after storms to positions consistent with their long term 100 yr trend even the largest storms such as the ash wednesday storm of 1962 considered to be the most damaging in the twentieth century appear to have had little effect on the long term trend the gradual recession of beaches along the u s east coast is mainly controlled by other factors such as sea level rise and variations of sediment supply therefore it follows that barrier beaches in a coastal plain setting would not experience long term erosion in response to storm impact if the sea were to stop rising and sediment supply did not change

fluid flow and chemical reaction kinetics in metamorphic systems the treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow diffusion and thermal evolution the interplay of fluid flow and surface reaction rates the distinction between steady state and equilibrium and the possible overstepping of metamorphic reactions are discussed using a simple analytic model this model serves as an introduction to the second part of the paper which develops a reaction model that solves the coupled temperature fluid flow chemical composition differential equations relevant to metamorphic processes consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole a general numerical scheme is discussed to handle the solution of the model the results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event 41 refs 19 figs 5 tabs

the generation and preservation of multiple hurricane beds in the northern gulf of mexico abstract cores collected from mississippi sound and the inner shelf of the northeast gulf of mexico have been examined using 210 pb and 137 cs geochronology x radiography granulometry and a multi sensor core logger the results indicate that widespread event layers were probably produced by an unnamed hurricane in 1947 and by hurricane camille in 1969 physical and biological post depositional processes have reworked the event layers producing regional discontinuities and localized truncation and resulting in an imperfect and biased record of sedimentary processes during the storms the oceanographic and sedimentological processes that produced these event beds have been simulated using a suite of numerical models 1 a parametric cyclone wind model 2 the swan third generation wave model 3 the adcirc 2d finite element hydrodynamic model 4 the princeton ocean model 5 a coupled wave current bottom boundary layer sedimentation model and 6 a model for bed preservation potential as a function of burial rate and bioturbation rate simulated cores from the mississippi sound region are consistent with the observed stratigraphy and geochronology on both the landward and seaward sides of the barrier islands

stable isotope evidence for a magmatic component in fumarole condensates from augustine volcano cook inlet alaska u s a abstract d h and 18 o 16 o ratios have been determined for fumarole condensates from augustine volcano an active calc alkaline stratovolcano in lower cook inlet alaska the isotopic data for the condensates form a linear d 18 o array from low temperature fluids d 150 18 o 19 to high temperature 450 c fluids collected at the volcano summit which are enriched in both d and 18 o d 35 18 o 3 5 several lines of evidence suggest that the d and 18 o rich condensates likely are magmatic fluids released into the hydrothermal system during and immediately after the 1976 eruption prior to 1976 the augustine hydrothermal system was dominated completely by local meteoric waters between 1976 and 1982 fumarole condensates were observed to be variable mixtures of the magmatic fluid and meteoric water with the proportion of the former systematically decreasing as the hydrothermal system cooled following the 1976 eruption

what drives microplate motion and deformation in the northeastern caribbean plate boundary region the north caribbean plate boundary zone is a broad deformation zone with several fault systems and tectonic blocks that move with different velocities the indentation by the bahamas platform the bahamas collision is generally invoked as a cause of this fragmentation we propose that a second driver of deformation is the western edge of the south dipping puerto rico slab moving sideways with the north america plate the westward motion of the slab edge results in a push on the caribbean plate farther west we refer to this second mechanism for deformation as slab edge push the motion of the north america plate relative to the caribbean plate causes both drivers to migrate from east to west the bahamas collision and slab edge push have been operating simultaneously since the miocene the question is the relative importance of the two mechanisms we use mechanical finite element models that represent the two mechanisms from the late oligocene 30 ma to the present for the present both models successfully reproduce observed deformation implying that both models are viable back in time the slab edge push mechanism better reproduces observations neither mechanism successfully reproduces the observed miocene counterclockwise rotation of puerto rico we use this rotation to tune a final model that includes fractional contributions of both mechanisms we find that the slab edge push was the dominant driver of deformation in the north caribbean plate boundary zone since 30 ma

recent investigations of the 0 5 ma geomagnetic field recorded by lava flows we present a synthesis of 0 5 ma paleomagnetic directional data collected from 17 different locations under the collaborative time averaged geomagnetic field initiative tafi when combined with regional compilations from the northwest united states the southwest united states japan new zealand hawaii mexico south pacific and the indian ocean a data set of over 2000 sites with high quality stable polarity and declination and inclination measurements is obtained this is a more than sevenfold increase over similar quality data in the existing paleosecular variation of recent lavas psvrl data set and has greatly improved spatial sampling the new data set spans 78 s to 53 n and has sufficient temporal and spatial sampling to allow characterization of latitudinal variations in the time averaged field taf and paleosecular variation psv for the brunhes and matuyama chrons and for the 0 5 ma interval combined the brunhes and matuyama chrons exhibit different taf geometries notably smaller departures from a geocentric axial dipole field during the brunhes consistent with higher dipole strength observed from paleointensity data geographical variations in psv are also different for the brunhes and matuyama given the high quality of our data set polarity asymmetries in psv and the taf cannot be attributed to viscous overprints but suggest different underlying field behavior perhaps related to the influence of long lived core mantle boundary conditions on core flow psv as measured by dispersion of virtual geomagnetic poles shows less latitudinal variation than predicted by current statistical psv models or by previous data sets in particular the brunhes data reported here are compatible with a wide range of models from those that predict constant dispersion as a function of latitude to those that predict an increase in dispersion with latitude discriminating among such models could be helped by increased numbers of low latitude data and new high northern latitude sites tests with other data sets and with simulations indicate that some of the latitudinal signature previously observed in vgp dispersion can be attributed to the inclusion of low quality insufficiently cleaned data with too few samples per site our matuyama data show a stronger dependence of dispersion on latitude than the brunhes data the taf is examined using the variation of inclination anomaly with latitude best fit two parameter models have axial quadrupole contributions of 2 4 of the axial dipole term and axial octupole contributions of 1 5 approximately 2 of the octupole signature is likely the result of bias incurred by averaging unit vectors

isotope shift data and the natural evolution of geothermal systems abstract oxygen is a major component of rocks and of hydrous solutions and interacting rock and water of initially arbitrary compositions always set up a potential for isotope exchange that in time leads to mutual isotope shifts regardless of kinetic factors exchanged rocks may be viewed as exhausted isotope shifting capacities that correspond to equivalent quantities of exchanged fluid since most of the actual isotope exchange in geothermal systems takes place in reaction zones with a relatively narrow temperature range a zeroeth order mixed model is considered which consists of batches of water passing through a fixed rock reservoir the model provides an estimate of the cumulative water throughput or hydrological maturity of geothermal systems in terms of the measurable isotope shifts of present day throughput and the overall isotope shifting potential the assumption of discrete batches of throughput partially simulates the inefficiency of natural water rock interaction while the continuous process with vanishing batch size sets a lower limit for the required fluid throughput hydrogen and strontium isotopes respectively could provide better sensitivity at very early and very late stages of evolution several examples of geothermal systems are discussed and placed into a tentative order of maturity