fatty acid composition as an indicator of the trophic position of abyssal megabenthic deposit feeders in the kuril basin of the sea of okhotsk abstract this study examines the fatty acid fa composition in eight species of deposit feeders including holothurians echiurans sipunculan polychaete and bivalve mollusc from the kuril basin of the sea of okhotsk most of the fas in the species studied have been described previously for abyssal deposit feeders but 20 2 n 12 22 4 n 8 and 22 5 n 5 were new among megabenthic invertebrates principal component analysis indicated sample separation of the deposit feeders into three groups the first group included subsurface deposit feeders and the other two consisted of surface deposit feeders all groups differed in the ratio of 20 5 n 3 to 20 4 n 6 this ratio was 0 2 0 4 in the subsurface deposit feeder molpadia musculus risso 1826 group i and 0 6 0 9 in the surface deposit feeding echiuran pseudoikedella achaeta zenkevitch 1958 and the elasipodid holothurian psychropotes raripes ludwig 1893 group ii in the second group of surface deposit feeders group iii this ratio was a little larger in the polychaete travisia sp 1 3 and was much larger 2 1 2 5 in the echiuran alomasoma nordpacificum zenkevitch 1958 the sipunculan golfingia margaritacea sars 1851 and the holothurian peniagone dubia d yakonov and savel eva in d yakonov et al 1958 unlike previous data we found that the most abundant megabenthos species in the basin are subsurface deposit feeders and two groups of surface deposit feeders

spreading structure of the troodos ophiolite cyprus some paleomagnetic constraints it has been suggested that grabens on the northern flank of the troodos ophiolite formed by listric faulting in an oceanic environment and represent axial valleys fossilized by ridge jumping this paleomagnetic survey of the solea graben was carried out to constrain the structural interpretation an analysis was devised which restores both the dikes sampled to vertical and the primary remanent magnetizations to a previously derived structurally corrected remanent magnetization direction typically two solutions for the original dike orientation and the pole and angle of net rotation are obtained for each dike sampled these solutions can be separated if a locally consistent original dike strike is assumed reasons are discussed for the selection of the solution that gives an original northwesterly dike strike results are consistent with a graben rotations are up to 78 at the sites studied rotation vectors are subhorizontal and subparallel to the original dike strike suggestive of an axial process for the development of the structure however on the basis of field observations an alternative mode of origin is proposed invoking ephemeral extreme upper crustal extension by listric faulting on the west flank of an intermediate to fast spreading axis the grabens being formed by antithetic faulting

spreading structure of the troodos ophiolite cyprus orientations of dikes within the sheeted dike complex of the troodos ophiolite reveal primary spreading structure produced at a complex ridge transform intersection three structural grabens are defined by listric and planar normal faults and rotated dikes that dip symmetrically toward graben axes faults flatten at depth into a detachment within the upper parts of the plutonic complex large exhalative massive sulfide deposits occur within the pillow sections of two of the grabens and appear to be associated with underlying altered and mineralized normal fault zones that channeled hydrothermal fluids we suggest that the grabens are fossil axial valleys produced by successive eastward jumps of an approximately north trending present coordinates slow spreading ridge crest a simple model for ridge migration indicates eastward jumps of 8 13 km changes in ridge orientation are suggested by changes in trends of dikes and graben axes comparison of the pattern of dikes near the arakapas fault zone with the structure of active ridge transform intersections suggests that the fault is a right offset sinistral transform in contrast to earlier models in which a ridge to the west of the exposed troodos complex was proposed

dynamics of sinking particles in northern japan trench in the western north pacific biogenic chemical components and fatty acids biomarkers abstract biogenic opal was predominant component and had strongly positive correlation with organic carbon in both traps the average atomic ratios of biogenic opal and calcium carbonate caco 3 were also large 7 1 and 11 in the shallow and deep trap respectively and the highest ratio was found in may 1995 when the biogenic opal proportion to the total particle flux and c org c inorg ratio increased concomitantly however transient switching of the biogenic opal and caco 3 ratios 0 6 and 0 8 was observed in winter 1995 which seems to be related to a warm core ring developed in the northwestern pacific downward fluxes of fatty acids as molecular markers were determined and compared with major biogenic chemical components in sinking particles as a diatom index of fatty acids the 16 1 n 7 16 0 ratio is positively related to biogenic opal contribution to the sinking particles in the shallow and deep traps 20 5 n 3 proportion was also correlated with opal content in sinking particles in the 1 km trap in addition a major source of sinking fatty acids in the western north pacific might be characterized by algal fatty acids as a diatom marker 16 1 n 7 comparing to a zooplankton fatty acid 18 1 n 9 in the central north pacific and fecal pellets and coccolithophores in the eastern north pacific respectively also pufa index a measure of polyunsaturated fatty acids contribution to the total fatty acids correlated well with chl a inventory in surface 0 50 m water these results suggest that undegraded diatomaceous fatty acids are present in sinking particles and the composition of fatty acids is useful to understand the origin of sinking organic particles

the joint global ocean flux study canada in the ne subarctic pacific abstract this volume of dsr ii is dedicated to the canadian joint global ocean flux study jgofs in the ne subarctic pacific this oceanic province is one of three high nitrate low chlorophyll hnlc regions in the world oceans furthermore this region is characterised by a shallow ca 100 120 m permanent pycnocline during winter which permits relatively high numbers of phytoplankton and micro grazers to subsist over winter which in turn strongly influences pelagic community structure the 5 year field study encompassed two phases phase 1 seven voyages between september 1992 and may 1995 and the intensive phase 2 six voyages between september 1995 and june 1997 each voyage transected line p from the coastal ocean westward to the open ocean in addition to the jgofs study this volume also includes analyses of long time series 20 yr data sets from ocean station papa osp 50 n 145 w and other stations in the coastal and open ocean

on the reactivation of extensional fault systems in terranes that have undergone substantial extension three sets of faults dominate a shallow to steep dipping commonly rotational normal faults b a really extensive shallow dipping normal detachment faults and c steep dipping transfer faults that strike at high angles to the normal faults these fault systems may extend through a large fraction of the crust reactivation of these fault systems will depend primarily on the relative strengths of the faults shear zones and their host rock and their orientation in the prevailing stress field it is concluded that reactivation is generally mechanically favoured but that it will probably only take place when the fault shear zones are in near ideal orientations consideration of the tectonic setting of extended terranes and of the limited number of well described examples suggests that reverse thrust reactivation of the normal and detachment faults and wrench reactivation of transfer faults are the most likely styles examples of these styles are described from the bass strait basins of southeastern australia because extended terranes commonly underlie sedimentary basins for example on passive continental margins reactivation of extensional faults may be a key control on the tectonic evolution of such basins i e basin inversion

understanding parafluvial exchange and degassing to better quantify groundwater inflows using 222rn the king river southeast australia 222rn is an important tracer for quantifying groundwater inflows to rivers especially where groundwater and surface water have similar major ion and stable isotope geochemistry uncertainties in the 222rn mass balance arise however from not accurately estimating the degree of degassing of 222rn to the atmosphere and the extent to which interaction within the parafluvial zone provides an additional source of 222rn this study estimates both 222rn production in the parafluvial zone and degassing along a 75km stretch of the king river australia in order to more precisely quantify groundwater inflows the contribution of 222rn from the parafluvial zone fp was estimated using 222rn emanation rates from near river sediments and assessment of the residence time of water in the parafluvial zone from 222rn activities and cl concentrations in water the alluvial sediments values of fp range from 40 400bq m day in the upper king to 8500bq m day in the lower king corresponding to differences in the mineralogy and the volume of the parafluvial zone the gas transfer coefficient k was estimated by matching groundwater inflows to observed increases in river discharge during a period of low discharge k decreases from 25day 1 in the upper king to 3day 1 in the lower king these k values are higher than those from most empirical formulations probably due to the extensive pool and riffle sections that promote degassing the king river is gaining in its upper and middle sections but several of the lower reaches are losing groundwater inflows on a reach scale are as high as 10m3 m day and cumulative inflows along the 75km stretch are up to 19 000m3 day groundwater inflows increase proportional to total flow reflecting the response of both groundwater and surface water systems to rainfall uncertainties in the calculated groundwater inflows are reduced by independently estimating k from the discharge data however calculated inflows are up to 40 higher if parafluvial flow were not taken into account predicted rn activities from emanation measurements agree with those measured in groundwater contribution of rn from parafluvial zone is assessed rn degassing is independently assessed by comparison with flow gauge data rn degassing is higher than predicted from empirical formulations due to pool and riffle sections king river transitions from gaining in upper sections to losing in lower sections

poas volcano crater lake acts as a condenser for acid metal rich brine models of formation of volcanic hosted metal deposits hypothesize that subsurface brines transport metals to sites of deposition laguna caliente in the active crater of poas volcano central costa rica consists of acid sulphate chloride brine with extreme ph 0 0 lake water sampled between 9 and 12 january 1987 at eight sites within the 40 m deep 210 m wide lake revealed temperatures between 58 and 64 c and densities measured in the laboratory at 60 c of 1 0575 0 0015g cm 3 the water s extreme acidity reflects the dominating input of acid fumaroles the presence of precipitated silica gypsum and sulphur as sediments reflects lake water equilibrium with those phases mass balance considerations require that dense brines percolate downwards from the lake into the volcano these may act as a source of metal rich brine feeding an underground ore forming hydrothermal system

ophiolite generation and emplacement by rapid subduction hinge retreat on a continent bearing plate an outstanding problem with understanding the origin and significance of many ophiolites is reconciling their are geochemical signatures with the structural evidence for extreme crustal extension a hypothesis is presented that accounts for these and other ophiolite characteristics by processes that are kinematically linked to ophiolite emplacement ophiolite emplacement particularly over passive continental margins is probably due to intra oceanic subduction dipping away from the continent where the future ophiolite is the subduction hanging wall if the continent bearing plate is kinematically linked to the plate behind the subduction related arc with a limiting case in which the continent and the rear arc oceanic plate are mutually stationary then supra subduction zone spreading may accommodate the resultant subduction hinge retreat that proceeds at the subduction rate thus extreme extension in an arc petrotectonic environment during ophiolite generation could produce the unique structure and geochemistry of ophiolites due to the plate geometry that prescribes their emplacement onto continental margins the kinematic link between the continent bearing plate and the rear arc plate could be due to both plates being a single large plate both plates being large plates that move independently of the intervening ophiolitic microplate or viscous drag beneath the continent bearing plate

solute sources and water mixing in a flashy mountainous stream pahsimeroi river u s rocky mountains implications on chemical weathering rate and groundwater surface water interaction abstract identifying solute sources and mixing processes between various water types is challenging in geologically diverse fractured rock settings where various minerals contribute to solute loads and mixing between groundwater and surface water can occur at difficult to delineate point locations in such regions chemical indicators that allow constraining characteristic mineral fingerprints of drainage lithology or aquifer end members are critical this study assesses solute sources and water mixing in the pahsimeroi river a small stream with highly variable discharge draining two heavily deformed mountain ranges of the u s rocky mountains solute inputs to the main stream were estimated using an end member mixing model with 87 sr 86 sr and na sr ratios as tracers considering that these depict the compositional variability pertaining to the various carbonate and silicate lithologies of the basin our results show that the mean solute input from carbonate dominated terrains decreases from 95 9 in the headwaters to about 36 4 in the lowlands while the corresponding inputs from volcanic and metamorphic sources increase from 3 63 to 51 0 and 0 45 to 12 6 respectively data further indicate highly variable chemical weathering rates with highest values observed in the steeper uplands calculated co 2 consumption rates mean value 0 14 mmol km 2 a 1 are lower than the reported continental average 0 21 mmol km 2 a 1 possibly due to lower than average streamflow at the time of sampling and significant input of carbonate solute enriched baseflow in the downstream sections where the basin shallows and decreases in width the herein delineated gaining stream segments are consistent with those deduced from downstream seepage runs which suggests that groundwater sustains perennial flow in the agriculturally developed lowlands

footwall geometry and the rheology of thrust sheets abstract the inter relationships between the exact footwall geometry and the rheology of thrust sheets are investigated deviations in the thrust fault surface from an ideal plane will induce a local heterogeneous deformation the resulting deformation processes depend upon the rate of thrust sheet displacement the geometry of the feature causing heterogeneous flow the deformation conditions and the lithologies involved two classes of features are particularly important in causing heterogeneous deformation in thrust sheets the first features are small perturbations on bedding planes which may be inherited sedimentary structures or produced during layer parallel shortening the second class of features are ramps where the thrust sheet climbs up the stratigraphic section displacement over these features causes repeated cyclic straining in the hanging wall during movement the strain rates associated with deformation at perturbations ramps of different geometries and different displacement rates are estimated and used to discuss the influence of footwall geometry on the structural evolution of a thrust sheet particular attention is given to the range of fault rocks and deformation microstructures preserved after movement over a footwall with a complex geometry perturbations are suggested to be important in the localization of ramps either because they create sticking points near the fault tip during propagation or because they induce eventual failure in the hanging wall after the movement over a number of these features raises the accumulated damage to a critical level analysis of the influence of the exact geometry of ramps on deformation processes during displacement leads to two important conclusions firstly the exact geometry of ramps i e the maximum dip angle and the straining distance from a flat to this maximum angle may be used to estimate a maximum displacement rate of the thrust sheet secondly the listric geometry of ramps may be an equilibrium shape adjusted to the displacement rate and the rheology of the hanging wall adjustments towards the final geometry may involve the generation of shortcuts on either hanging or footwall which reduce the imposed deformation rate in the hanging wall during displacement

modeling of groundwater processes in a karstic aquifer of sierra madre oriental mexico abstract the sierra madre oriental smo is composed of ranges with important regional geological structures in highly fractured carbonate rocks abra formation which facilitate the recharge of aquifers at the regional scale recharge occurs in the western smo and locally in ranges such as palmillas la colmena and abra while the regional discharge is to the east in the huasteca zone intermountain valleys such as el salto are located near the regional discharge zone three end members were identified in these regions one related to local flow another to intermediate and a third to regional flow these flows define ternary mixing processes in groundwater in this paper the evolution of groundwater is studied which is important for learning the system performance and hydrogeochemical processes through vishmod virtual samples in hydrochemical modeling methodology the mixing model for the intermountain valleys indicates that many recharges occur for which local flow contributes 68 3 intermediate flow 12 3 and regional flow 19 4 the inverse modeling shows that the water rock interaction precipitation and or dissolution of calcite gypsum and dolomite are the main processes occurring in the aquifer system of the intermountain valleys

chemical and isotopic signature of old groundwater and magmatic solutes in a costa rican rain forest evidence from carbon helium and chlorine 1 c he and cl concentrations and isotopes in groundwater and surface water in a lowland costa rican rain forest are consistent with the mixing of two distinct groundwaters 1 high solute bedrock groundwater representing interbasin groundwater flow igf into the rain forest and 2 low solute local groundwater recharged in the lowlands in bedrock groundwater high 13c 4 89 low 14c 7 98 pm high r ra for he 6 88 and low 36cl cl 17 10 15 suggest that elevated tracer concentrations are derived from magmatic outgassing and or weathering of volcanic rock beneath nearby volcan barva in local groundwater the magmatic signature is absent and data suggest atmospheric sources for he and cl and a biogenic soil gas co2 source for dissolved inorganic carbon dating of 14c suggests that the age of bedrock groundwater is 2400 4000 years most likely at the lower end of the range local groundwater has 14c 100 pm indicating the presence of bomb carbon and thus ages less than 55 years overall data are consistent with a conceptual hydrologic model originally proposed on the basis of water budget and major ion data 1 large variation in solute concentrations can be explained by mixing of the two distinct groundwaters 2 bedrock groundwater is much older than local groundwater 3 elevated solute concentrations in bedrock groundwater are derived from volcanic fluids and or rock and 4 local groundwater has not interacted with volcanic rock tracers with different capabilities converge on the same hydrologic interpretation also transport of magmatic co2 into the lowland rain forest via igf seems to be significant relative to other large ecosystem level carbon fluxes

mechanisms of subduction accretion along the central aleutian trench we have used migrated 24 fold seismic records to study mechanisms of subduction accretion along the central aleutian trench two major structural units underlie the landward trench slope and are separated by an acoustically defined decollement surface that can be traced at least 20 km landward of the trench axis the upper unit consists of three to four structural blocks of deformed trench fill each block possesses a consistent internal structure and is bound by major landward dipping thrust faults the structures within the blocks include monoclinal sequences antiforms synforms and faulted folds beneath the decollement nearly undeformed trench fill 1 km thick is being under thrust along with the underlying oceanic lithosphere this basal section is an intervening unit between the offscraped sediment and the rough igneous oceanic basement and may prevent the oceanic crust from being incorporated into the subduction complex at least within 20 km of the front of the subduction zone owing to bending stresses the oceanic crust fails along normal faults beneath and at least 15 km landward of the trench axis these normal faults although poorly constrained are believed to propagate upwards producing offsets within both the subducting and the accreting sediment in addition normal faulting enhances the irregular surface of the oceanic crust structural associations imaged on all of the seismic reflection profiles although possibly fortuitous suggest that the subduction of these irregular basement highs results in the temporary displacement of the overlying fault bound sediment packets and promotes the development of the structures found within the accretionary prism tectonic riffling of the accreted sediment by the passage of the basement relief may also provide a mechanism by which underthrusting sediments are decoupled from the subducting lithosphere and underplated to the base of the aleutian accretionary complex

is 222rn a suitable tracer of stream groundwater interactions a case study in central italy abstract river water infiltration into an unconfined porous aquifer 73 gravels 12 sands 15 silts and clays in the petrignano d assisi plain central italy was traced combining isotopic techniques 222 rn with hydrochemical and hydrogeologic techniques in order to characterize the system under study the 222 rn gave information about the river water residence times within the aquifer and hydrochemical data in a two component mixing model which allowed estimating the extent of mixing between surface waters and groundwater in wells at increasing distances from the river the mixing measured in the well closer to the riverbank indicated a higher contribution of river water up to 99 during the groundwater recession phase and a moderate contribution up to 64 during the recharge phase a model describing 222 rn concentrations in groundwater as the result of both parent daughter nuclide equilibrium and mixing process 222 rn mixing saturation model was used to describe observed rn concentrations and mixing index trends with the aim of evaluating water mean infiltration velocities along the transect the stream bank infiltration velocities obtained by the model ranged from 1 m day 1 during groundwater recharge periods when river water infiltration is lower to 39 m day 1 during recession phases when river water infiltration is larger

geochemical and 222rn constraints on baseflow to the murray river australia and timescales for the decay of low salinity groundwater lenses the distribution of 222rn activities and major ion concentrations show that during low river flows characteristic of the recent drought conditions the middle reaches of the murray river northern victoria were a predominantly gaining system at low river levels may 2009 may 2010 and were variably gaining and losing at higher river levels november 2009 the location of gaining and losing reaches are partially governed by the position of the river with respect to the edge of its floodplain gaining reaches occur where the floodplain narrows or where the river is adjacent to the steep slopes at the floodplain margin cumulative inflows along this 350km stretch of the river estimated from 222rn activities were 320 1500m 3 day in november 2009 and 560 4300m 3 day in may 2010 the relatively large uncertainty reflects the heterogeneous and poorly constrained groundwater 222rn activities major ion variations notably cl concentrations and na ca ratios correlate with 222rn activities and may be used as indicators of groundwater inflows baseflow contributed 1 of the total water to this part of the river and consequently has little impact on river water quality nevertheless the groundwater inflows remove water from low salinity groundwater lenses that underlie the river and during the drought conditions these lenses were degrading these reaches of the river murray are an example of a system that transitioned from being dominantly losing to being variably gaining due to diminishing surface water flows

pliocene near trench magmatism in southern chile a possible manifestation of ridge collision eight shallow level intrusions and an ophiolite complex have recently been discovered in a remote region along the pacific coast of southern chile known as the taitao peninsula the magmatic rocks are found only 10 to 15 km from the buried extension of the peru chile trench the ophiolite body includes serpentinized ultramaflc rocks gabbro dikes and an interbedded sequence of volcanic and marine sedimentary rocks more regionally distributed granodiorite plutons and porphyritic stocks and sills intrude pre late jurassic basement as well as tertiary marine sequences of the south american forearc k ar ages of 3 5 to 4 0 ma of the ophiolite and other intrusions suggest that these rocks represent a short lived pulse of pliocene magmatism directly seaward of the taitao peninsula a segment of the chile rise bounded by the tres monies and taitao fracture zones collided with the chilean forearc and was subducted about 2 5 to 4 0 ma because of this good spatial and temporal correlation the magmatic activity of the taitao peninsula is likely to be a direct result of ridge subduction

behaviour of chemical solutes during a storm in a rainforested headwater catchment the aim of this study is to identify in a small catchment area located within a tropical forest the pedological compartments in which the export of nutrients and chemical erosion of solutes occur during a stormflow event the catchment area displays two types of lateral flow i overland flow at the surface of the soil in the litter and root mat and ii groundwater flow in a macroporous subsurface horizon we interpret the variations of stream water chemistry during a storm flow event using the separation of storm flow hydrograph data between overland and groundwater flow and cl as a chemical parameter characterizing the residence time of water in the soil it appears that k especially was released into the throughfall whereas ca mg and na were clearly released from the litter k disappeared rapidly from soil solution whereas ca and mg were more progressively absorbed by the vegetation the ca and mg contents in groundwater increased with increasing residence time owing to the transpiration of trees the export of h4sio4 in the overland flow was moderate i e 24 of total h4sio4 export in the stream flow as overland flow represented 39 of total runoff the subsurface horizon where active groundwater flow occurs was successively affected by chemical erosion during the storm flow peak and then by neoformation of kaolinite favoured by increasing water residence time copyright 2003 john wiley sons ltd

constraints on the structure of the east pacific rise from seismic refraction data university of washington seismic data taken during rose phase 1 have been used to study the structure of the east pacific rise in the vicinity of 12 n off axis but within 50 km of the axis we find that the oceanic crust can be modeled with a rapid change in velocity in the top 2 5 km a zone of low but uniform velocity gradient from 2 5 to about 5 5 km and a transitional zone about 1 km thick to mantle material there is also evidence for substantial anisotropy in mantle velocity gradients with a positive velocity gradient in the spreading direction and a negative velocity gradient parallel to the rise under the rise axis the data allow at most a very narrow zone of low velocity less than about 2 km wide in the crust

determination of sr and ca sources in small tropical catchments la selva costa rica a comparison of sr and ca isotopes summary a comparative study of sr and ca isotopes was conducted to assess solute sources and effects of biogeochemical processes on surface water and groundwater in four small tropical catchments located at la selva biological station costa rica variable concentrations of dissolved sr 2 and ca 2 in the catchments are related to mixing of waters from different origin three catchments are influenced by high solute bedrock groundwater while another catchment is primarily supplied by local recharge 87 sr 86 sr ratios were employed to discriminate contributions from mineral weathering and atmospheric sources solutes in bedrock groundwater have a predominant geogenic origin whereas local recharge is characterized by low solute inputs from rainwater and minor in situ weathering releases from nutrient depleted soils bedrock groundwater contributes more than 60 of dissolved sr 2 to surface discharge in the salto saltito and arboleda catchments whereas the taconazo catchment receives more than 95 of dissolved sr 2 from rainwater 44 40 ca values of dissolved ca 2 vary greatly in the catchments mainly as a result of heterogeneous ca isotope compositions of the contributing sources based on differences in 44 40 ca values two distinct bedrock groundwaters discharging at the salto and the arboleda catchments are suggested effects of biological processes in the plant soil system on solute generation in the catchments are indicated by variable ca sr ratios however these effects cannot clearly be assessed by ca isotopes due to the strong heterogeneity of 44 40 ca values of ca 2 sources and high ca 2 concentrations in bedrock groundwater

sediment accretion subduction and dewatering at the base of the trench slope off costa rica a seismic reflection view of the decollement sea beam bathymetric and water gun seismic reflection data off the west coast of costa rica image the base of the trench slope its underlying structure and the behavior of a decollement surface in the presence of relief on the subducting plate a low angle landward dipping reflection marks the master decollement above which only about 80 m of a 350 m oceanic sedimentary section is offscraped and accreted to the lower trench slope a small horst block at least 9 km long 1 5 km wide and 300 m high is being obliquely subducted beneath the landward trench slope on five seismic lines the decollement rises over the horst and then descends into the next incoming graben as the fault zone maintains a specific stratigraphic level the undulating geometry of the decollement implies that the subducting grabens are not sites for sediment entrapment and subduction and that the horsts are not causing tectonic erosion of the landward trench wall substantial dewatering within the subducting sediments is documented within about 4 km of the deformation front the dewatering may favor development of bedding parallel zones of low shear strength within the subducting sediments and the master decollement may seek one of these zones

chemical mixing model of streamflow generation at la selva biological station costa rica abstract la selva biological station occupies an area of lowland tropical rainforest in central costa rica sodium and chloride data were used to quantify the mixing proportions of local runoff and geothermal groundwater at several sites throughout the stream channel system in late april at the end of the dry season the fraction of streamflow accounted for by geothermal groundwater varied spatially between 0 and 0 85 indicating a significant contribution to streamflow and to stream solute loads from geothermal groundwater at some sites in general higher inputs of geothermal groundwater were found at lower elevations over half the flow from one basin the salto was due to geothermal groundwater suggesting a minimum annual runoff of about 0 7 m of geothermal groundwater from this basin a plot of na cl vs fraction of geothermal groundwater revealed watershed scale chemical differences between the two major drainage systems the sura and the salto differences that were not apparent from a traditional two solute plot of cl vs na concentration a small 21 mm storm produced relatively little change in mixing proportions as most throughfall was apparently retained in the relatively dry soils

subduction of a late cretaceous seamount of the louisville ridge at the tonga trench a model of normal and accelerated tectonic erosion the hotspot generated louisville ridge is a 4000 km chain of seamounts typically 2 2 5 km high and 10 40 km in diameter and an underlying crustal swell 1 5 km high and 100 km wide trending nnw across the southwestern pacific the northwest end of the ridge collides with the north trending tonga trench 26 s which just north of that point is exceptionally deep 10 8 km and lacks both a turbidite wedge and a bordering accretionary complex the collision zone is moving rapidly southward multichannel seismic reflection data in the collision zone show a west dipping subsurface platform 2 3 km beneath the lower western trench slope which is interpreted as the flat summit of a subducted guyot motuku of the louisville chain projected eastward the summit plain passes 1 2 km above the trench floor dredging of the nearby inner trench wall recovered uppermost cretaceous maestrichtian oceanic pelagic sediments interpreted to be fragments of the sedimentary mantle of a subducted louisville seamount the principal effects of hotspot ridge collision with a sediment starved trench are 1 the impacting seamounts are subducted rather than accreted and 2 although some seamount rocks are temporarily accreted the inner trench wall is tectonically eroded arcward at rates possibly as high as 50 km m y accelerated tectonic erosion is related to 1 fracturing shearing and general weakening of arc substrate rocks as they are lifted by the swell penetrated by impacting seamounts and left to collapse as the ridge moves away 2 a more effective removal of weakened rock in underthrusting grabens which are larger in the crustal swell 3 a possible elevation of the subduction decollement to account for the removal of as much as 30 000 km of material from a 400 km sector of the trench in 1 million years and 4 a reduction in supply of arc derived debris resulting from the gap in arc volcanism accompanying subduction of the ridge normal tectonic erosion in the tonga trench is apparently minor and we conclude that the bulk of the 37 000 km of material which fills subducting grabens each million years is arc derived volcanic and pelagic sediment

ridge collision at convergent margins implications for archean and post archean crustal growth abstract growth of continental crust today occurs dominantly at convergent plate margins through magmatic addition and tectonic accretion lateral and vertical related to 1 1 steady state subduction 2 2 non steady state episodic processes ridge forearc collision is one episodic process that can cause significant highly diachronous thermal and tectonic effects when a buoyant bathymetrically high and thermally active oceanic spreading ridge approaches collides with and potentially subducts below a continental margin near field effects within 100 km of collision site in the forearc may include anomalous heat anomalous magmatism ophiolite obduction forearc deformation and tectonic erosion of the base of the forearc far field effects generally postdate collision and may include changes in the thermal structure of the continent changes in the composition of arc magmas a reduction or hiatus in arc magmatism uplift and or subsidence of the continental margin marginal basin formation underplating of subducted slabs and intraplate deformation effects of ridge collision can vary depending on the triple junction geometry the chile margin triple junction cmtj where the actively spreading chile ridge is colliding with the south american forearc is the best modern example of ridge collision near field effects of pliocene recent ridge collisions near the cmtj include 1 1 emplacement of the pliocene taitao ophiolite less than 15 km from the trench 2 2 intrusion of pliocene granitic plutons and 3 3 forearc deformation formation of a pull apart basin on the continental shelf and late tertiary recent movement on a major fault along the arc forearc boundary far field effects include reduction in subduction related seismicity and volcanism chemical changes in arc magmatism and possibly uplift and or subsidence ridge collison features in southern chile are similar to features of archean greenstone belts suggesting that some greenstone sequences may have formed in a ridge collision setting and that ridge collision may have been an important process in archean crustal growth these features include granitic rocks closely associated with ophiolitic rocks formed near a continental margin mafic ultramafic section overlain by basaltic to andesitic volcanic rocks of mixed calc alkaline and morb character intercalated with volcaniclastic sedimentary rocks differences between archean and phanerozoic tectonic processes mainly related to higher heat production in the past probably have affected the nature and importance of ridge collision in archean crustal growth during the archean greater ridge length and smaller plates probably resulted in more ridge collisions and related processes contributing to a higher continental growth rate in particular underplating of subducted slabs and direct slab melting may have been important processes in archean continental growth but are of relatively minor importance today

permo triassic accretionary subduction complex southwestern klamath mountains northern california the western paleozoic and triassic subprovince of the southwestern klamath mountains has previously been subdivided into three relatively steeply dipping fault bounded litho tectonic terranes in descending structural order from east to west these terranes are 1 the north fork terrane 2 the hayfork terrane and 3 the rattlesnake creek terrane in a general fashion each of these terranes exhibits its own particular set of lithologic structural and temporal relationships that sets it apart from adjacent terranes this threefold subdivision of the southwestern klamath mountains needs modification only as far as the hayfork terrane is concerned the hayfork terrane is actually a composite terrane consisting of a structurally lower assemblage of predominantly basaltic metavolcaniclastic rocks and a structurally higher assemblage of chaotically disrupted metasedimentary rocks juxtaposed along a previously unrecognized major regional thrust these two lithologically and structurally distinct assemblages have been elevated to the status of a terrane in this report and are herein referred to as the western hayfork terrane structurally lower metavolcaniclastic assemblage and the eastern hayfork terrane structurally overlying metasedimentary assemblage and the fault which juxtaposes these two terranes is herein referred to as the wilson point thrust this paper will focus on the eastern hayfork and north fork terranes and their relationship to other roughly coeval tectonic elements of the klamath mountain province the eastern hayfork terrane is best described as a tectono stratigraphic unit consisting of a complex chert argillite and quartzose sandstone melange and broken formation that contains radiolarian cherts as young as late triassic in age scattered throughout this terrane are various types of blocks some of which are clearly exotic metachert is by far the most common type of metamorphic block and these blocks appear to have been derived via sedimentary processes from the paleozoic central metamorphic belt and or the mesozoic stuart fork formation shallow water permian limestone blocks are also plentiful and are interpreted as reefal accumulations which flanked seamounts that became incorporated into the melange and broken formation as proto pacific ocean floor was subducted beneath the western margin of north america during at least the permo triassic to early jurassic the north fork terrane has at its base basaltic rocks tentatively interpreted as an oceanic crustal remnant generated within an open ocean ridge setting that was removed from any appreciable source of continental or volcanic arc derived detritus overlying the basaltic rocks is a sequence of pelagic hemipelagic terrigenous and tuffaceous metasedimentary rocks that have yielded a late triassic and early or middle jurassic radiolarian fauna the metasedimentary rocks of the north fork terrane are lithologically very similar to those of the eastern hayfork terrane both terranes consist predominantly of chert and argillite contain blocks of metamorphic rock and permian limestone and are at least in part of overlapping age however the metasedimentary rocks of the north fork terrane are structurally coherent unlike the chaotic melange and broken formation of the eastern hayfork terrane taken together the north fork and eastern hayfork terranes bear remarkable similarities to both modern and ancient rock assemblages that occupy sites within zones of lithospheric plate convergence and are interpreted as tectonic elements of an underthrust plate margin developed oceanward of a volcanic arc represented by the permo triassic to middle jurassic volcanic strata of the eastern klamath belt

tracing stream leakage towards an alluvial aquifer in a mountain basin using environmental isotopes abstract stream aquifer relationships in mountain basins are of great relevance because they control the water balance and with it the amount of resources whether surface water or ground water available for ecological and human demands in this paper this relationship is studied using environmental isotopes 18 o and d to identify the occurrence of stream recharge in the arbucies river basin ne spain isotopic data from 51 natural springs define the local altitudinal gradient this function is weighted by the proportional area above each point given by the hypsometric curve in order to estimate the isotopic stream water content as the contribution of runoff from incremental elevations stream water isotopes from two surveys are compared with hypsometrically averaged isotopic values to check for the appropriateness of this approach results show that it is more suitable when subsurface flows from surface formations such as alluvial deposits are the main contributors to stream discharge than when it derives from a single rainfall event the characterization of stream isotope values is used as a key factor in identifying stream leakage to an unconfined alluvial aquifer in the lower reach of the arbucies river

distribution of biogenic silica and quartz in recent deep sea sediments all available quartz and biogenic silica concentrations from deep sea surface sediments were intercalibrated plotted and contoured on a calcium carbonate free basis the maps show highest concentrations of biogenic silica opal along the west african coast along equatorial divergences in all oceans and at the polar front in the southern indian ocean these are all areas where upwelling is strong and there is high biological productivity quartz in pelagic sediments deposited far from land is generally eolian in origin its distribution reflects dominant wind systems in the pacific but in much of the atlantic and indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes

thickening of fault zones a mechanism of melange formation in accreting sediments sediments accreted at subduction zones undergo stratal disruption and form a type of melange the thickness of the disrupted zones grows with progressive deformation this suggests that initial fault surfaces are abandoned and deformation propagates into adjacent undeformed sediment factors causing the abandonment of fault surfaces during continuing deformation include 1 strengthening owing to porosity loss during consolidation 2 localized drops in fluid pressure on fault surfaces that act as dewaterinig conduits and 3 reorientation of fault surfaces the disruptive processes occurring in accretionary prisms result principally from the deformation of a consolidating sediment mass

hydrochemical characteristic and interaction process of surface and groundwater in mid lower reach of hanjiang river china hanjiang river the largest tributary of yangtze faces environmental pressures from south to north water transfer project and anthropogenic influences in order to reveal the chemical characteristics of river and contribution of groundwater to the river along mid lower reaches of hanjiang river field works have been conducted in wet and dry seasons the major ion compositions are characterized by the dominance of ca2 and hco3 in surface water and groundwater as a result calcite weathering is a dominant process for surface water and groundwater additionally dolomite weathering also contributes to hydrochemical evolution in the groundwater of the basin stable isotopes 18o d show that both surface and groundwater most probably originate from present day precipitation isotopic of both surface water and groundwater can provide greater confidence in identifying the weathering and extent of interaction processes it was found that river water was mainly recharged by tributaries in wet season while recharged by groundwater in dry season dissolved solute flux from tributaries and groundwater to the river was estimated by water balance budget model and environmental tracer mass balance approach tributaries and groundwater contribute to mid lower reach of hanjiang river in wet season and dry season respectively from section h1 to h9 there were 455 4 kg s of total dissolved solute tds transferred from tributaries to the main channel and 99 8 kg s of tds fluxed from groundwater to river water in dry season

single channel seismic reflection data from the east pacific rise axis between latitude 11 50 and 12 54 n two single channel seismic profiles were recorded in 1981 during a cruise of r v jean charcot along the axis of the east pacific rise between lat 11 50 n and 12 54 n the seismic source was a 1 3 1 80 in 3 water gun the ship9s track was kept on the rise axis by using the real time mapping capabilities of the seabeam echo sounder the seismic data were recorded in analog form and no signal processing was performed the seismic sections revealed the existence of segments of 7 to 30 km long coherent arrivals located at about 0 6 s two way traveltime below the sea floor reflection the same time difference observed for the water borne multiple of these arrivals is a strong indication that these segments of reflection are not side echoes but vertical incidence reflections originating from the subbottom the correlation between the seismic data and some geologic observations in the area near lat 12 13 n indicates that the observed reflections are probably associated with the roof of discontinuous magma chambers situated at an average depth of about 1 5 km below the sea floor

organic carbon fluxes degradation and accumulation in an anoxic basin sediment trap results from the cariaco basin organic carbon fluxes were measured in the anoxic water column of the cariaco basin under varying levels of primary productivity our results indicate that water column degradation of fresh organic matter in this anoxic setting is similar to what has been previously observed in the open ocean additionally the rate at which carbon is consumed increases as primary productivity increases these findings support the hypothesis that sulfate reduction is as efficient as aerobic respiration in degrading labile organic matter and that an anoxic water column does not necessarily result in an enhanced delivery of organic carbon to the sea floor we estimate that 1 2 of the organic carbon produced at the surface reaches the seafloor and that approximately 50 of this is preserved in the sediments this burial efficiency is comparable to that previously reported for both oxic and anoxic settings and with sedimentation rates similar to that in cariaco basin

basement slivers within the new britain accretionary wedge implications for the emplacement of some ophiolitic slivers using multichannel seismic data from the western solomon sea we have imaged several 2 5 to 3 km thick oceanic basement slivers within the new britain accretionary wedge which may serve as a modern analogue for the detachment of some ophiolitic slivers the most recently accreted basement sliver is located just over 5 km from the thrust front an approximate area balance indicates the subjacent section of the downgoing plate from which this sliver originated is between 11 km and 15 km arcward of its present position though we have not imaged the basement ramp sedimentary strata beneath the basement sliver pinch out between 9 and 12 km from its seaward edge suggesting that detachment occurred in that vicinity normal faults reactivated in response to the flexural bending of the downgoing oceanic plate are a prominent feature of this region significantly almost all basement normal faults near the recently accreted basement sliver including those imaged beneath the toe of the wedge dip arcward based on these data we suggest that small 1 3 km thick basement slivers are decoupled along favorably oriented preexisting zones of weakness formed by normal fault detachments within the oceanic basement

comments on the growth of accretionary wedges uplift within accretionary foreland wedges has been explained by the development of duplexes which provides a mechanism for underplating in submarine accretionary wedges with little deformation in the upper part of the wedge we interpret duplex development beneath the costa rica forearc a zone widely considered to be a prime example of nonaccretion because of the apparent absence of an imbricate fan of thrusts at the toe of the wedge large scale structural geometry of accretionary wedges is compatible with low angle trenchward dipping backstops in centrist to reverse angle backstops used commonly in models of return flow within wedges which have been invoked to explain the presence of high p t metamorphic rocks we suggest that emplacement of high p t metamorphic rocks are better explained in a collisional setting where known uplift rates are high than by flow within noncollisional accretionary wedges

landward vergence in accretionary prisms the role of the backstop and thermal history the accretionary histories recorded along the convergent margins in southwest alaska and southwest japan are punctuated by two anomalous events near trench magmatism closely associated in time and space with landward structural vergence in both areas the near trench magmatism is believed to be related to the subduction of an active spreading center it is postulated that these anomalous thermal events caused the backstop i e mechanical boundary within the prism to be reoriented to a seaward instead of a landward dip this seaward dipping backstop resulted in the development of landward verging structures for the only time in the almost 100 m y history of these two margins a modern analog may be the washington convergent margin these examples illustrate the potential importance of thermal history and the dip of the backstop in controlling the style of accretion in submarine wedges

tectonic rotations in extensional regimes and their paleomagnetic consequences for oceanic basalts paleomagnetic samples of many deep sea drilling project dsdp basalts have shallower inclinations than would be inferred from the paleolatitude at which the basalts were extruded at mid ocean ridges rather than arising from peculiarities of the geomagnetic field the anomalous magnetic directions may result from tectonic rotations along the listric normal faults which often characterize extensional tectonic regimes several lines of evidence support this conclusion observations of the basin and range province an extensional tectonic regime occurring in continental crust observations of the troodos complex cyprus an oceanic extensional tectonic regime now exposed on land and analysis of possible fault patterns associated with the magma chambers postulated to occur at some mid oceanic ridges the tectonic rotations resulting from movement along the listric normal faults occur about a horizontal axis generally perpendicular to the extension direction and typically amount to 30 to 50 although rotations as large as 70 to 90 are not uncommon the paleomagnetic consequences of these rotations can be calculated for dsdp basalts if the original strike and latitude of a ridge are known at four dsdp sites for which adequate data are available namely sites 319 332 410 and 417 rotations ranging from 50 to 70 are required to explain the paleomagnetic results if the original strike and location of the ridge are not known as is the case for most of the older parts of the pacific ocean the paleomagnetic data and the inferred rotation determine a relationship between possible ridge strikes and locations this information combined with a similar but independent relationship derived from the marine magnetic anomalies puts severe constraints on the original strike and location of the ridge

use of radon 222 and calcium as tracers in a three end member mixing model for streamflow generation on the west fork of walker branch watershed genereux d p hemond h f and mulholland p j 1993 use of radon 222 and calcium as tracers in a three end member mixing model for streamflow generation on the west fork of walker branch watershed j hydrol 142 167 211 measurements of naturally occurring radon 222 222 rn and calcium ca in surface and subsurface waters on the west fork ef walker branch suggest that a simple three end member mixing model provides a realistic and useful framework for streamflow generation over a wide range of flow conditions the three end members are vadose zone water soil groundwater and bedrock groundwater bedrock groundwater was distinguished from the soil end members on the basis of its high ca content 222 rn concentration was the basis for the distinction between vadose zone water low 222 rn and soil groundwater high 222 rn the behavior of the end members with changing flow was consistent with a wide variety of environmental observations including temperature and flow variations at springs water table responses the general lack of saturated zones on hillslopes and even near the stream in some places and the importance of water movemen t through bedrock variability in the chemistry of the end members precluded using other solutes na k and so4 to test the mixing fractions derived from 222 rn and ca data during those times of year when the soil temperature is most different from that of the underlying bedrock late summer and late winter temperature may be a useful tracer for distinguishing between water from the soil end members and that from bedrock the mixing model provides a simple framework for analyzing the essential features of streamflow generation in this highly heterogeneous terrain

a forward modeling strategy for balancing cross sections 1 a strategy to balance cross sections of complex structures is documented and illustrated by the interpretation of a compressional structure in the deep water gulf of mexico the strategy is applicable to structures formed in sedimentary rocks under low temperatures in both compressional and extensional environments and involves the comparison of the observed structure with simple balanced forward models forward models generated using fault related fold theory help in understanding the processes and kinematics involved in the deformation further forward models are completely constrained and easy to balance whereas it is difficult to balance data therefore forward models are useful in evaluating ideas without completely solving the structure models are constructed assuming parallel behavior preservation of layer thickness no net distortion where layers are horizontal and conservation of bed length unmetamorphosed sedimentary rocks are generally observed to deform obeying the assumptions of parallel behavior in field map well and seismic data

evolution of an ophiolitic tectonic melange marble mountains northern california klamath mountains the marble mountain terrane of northern california constitutes a metamorphosed ophiolitic tectonic melange occupying the lowest structural levels of the western paleozoic and triassic belt of the klamath mountains province on the basis of lithology and structural position it probably represents the metamorphosed equivalent of the rattlesnake creek terrane the marble mountain terrane consists of sedimentary oceanic mafic volcanic and ultramafic rocks and is structurally and probably stratigraphically overlain by arc derived meta volcanic and volcaniclastic rocks of the western hayfork terrane the contact between the two terranes is interpreted to be a zone of tectonic and stratigraphic interlayering but superimposed metamorphism has largely obscured its original character metamorphism of the assembled melange and overlying western hayfork terrane took place under low pressure amphibolite facies conditions a conclusion based primarily on the presence of prograde andalusite in pelitic rocks metamorphism was accompanied by penetrative deformation which produced two generations of northeast trending subhorizontal isoclinal recumbent folds and associated axial planar foliation mineral and stretching lineations also formed at this time these events preceded the intrusion of the 162 2 ma wooley creek batholith a later episode of deformation and recrystallization locally produced north northeast trending upright folds and steeply dipping crenulation cleavage greenschist to lower amphibolite facies metamarphic assemblages that were developed at this time overprint the earlier structures the latter deformational event may reflect the westward thrusting of the western paleozoic and triassic belt over the subjacent western jurassic belt during late jurassic time the marble mountain rattlesnake creek terranes probably represent oceanic crust which lay to the west of an active subduction zone along the western margin of north america during late triassic and early jurassic time and which was trapped in the forearc region when subduction stepped westward in earliest middle jurassic time newly initiated subduction led to the inception of the western hayfork arc which was built upon the marble mountain rattlesnake creek oceanic basement the melange may have been formed by imbrication of the oceanic lithosphere trapped between the new trench and the magmatic axis of the incipient arc continued convergence led to juxtaposition of oceanic and arc derived rocks to regional metamorphism and to deformation of the melange and overlying volcaniclastic rocks the low pressure character of the metamorphism supports an arc setting rather than a subduction zone regime for this tectonism

compositions and transport of lipid biomarkers through the water column and surficial sediments of the equatorial pacific ocean abstract a systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the u s jgofs egpac transect from l2 n to l5 s at 140 w fluxes of lipids out of the euphotic zone varied spatially and temporally ranging from 0 20 0 6 mmol lipid c m 2 day 1 lipid fluxes were greatly attenuated with increasing water column depth dropping to 0 002 0 06 mmol lipid c m 2 day 1 in deep water sediment traps sediment accumulation rates for lipids were 0 0002 0 00003 mmol lipid c m 2 day 1 lipids comprised 11 23 of corg in net plankton 10 30 in particles exiting the euphotic zone 2 4 particles in the deep egpac and 0 1 1 in sediments lipids were in general selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids fatty acids were the most labile compounds with polyunsaturated fatty acids pufas being quickly lost from particles branchedchain c15 and c17 fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment indicating inputs of organic matter from bacteria long chain c39 alkenones of marine origin and long chain c20 c30 fatty acids alcohols and hydrocarbons derived from land plants were selectively preserved in sediments compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds and hence of organic matter as a whole a thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is thus essential for using the sediment record for reconstructing past oceanic environments