trace element distributions in the chalcopyrite wall of a black smoker chimney insights from laser ablation inductively coupled plasma mass spectrometry la icp ms abstract the thin walls of young black smoker chimneys experience steep physico chemical gradients during active venting of hydrothermal fluid and these gradients control trace element precipitation within those walls here we utilise a combination of high sensitivity icpms and uv laser ablation resolution of better than 30 m to demonstrate the existence of non random v ag in te ba au pb and u distributions within the chalcopyrite wall of an immature black smoker chimney the data are the first of their kind to be produced for black smoker chimney walls distributions of in and te are attributed to preferential incorporation into lattices at elevated temperature enrichments of u and v derived from seawater are the product of redox immobilisation on sulphide surfaces the distributions of au ag pb and ba may be related to interactions at the hydrothermal fluid seawater mixing front however comparison of distribution data with reaction transport models of chimney walls suggest a possible ph control on precipitation these data illustrate the power of the la icp ms method and such spatially resolved data have the potential to constrain models of element precipitation both in chimneys and in associated mounds

recognition of active strike slip faulting from high resolution marine seismic reflection profiles eastern marlborough fault system new zealand major strike slip faults within the eastern part of the marlborough fault system of new zealand extend offshore beneath the continental shelf into the southern end of the hikurangi margin six major submarine faults each tens of kilometers in length and exhibiting the three dimensional structural characteristics typical of strike slip deformation zones are mapped in detail using closely spaced high resolution seismic reflection profiles each fault displaces late quaternary sediments that have been interpreted within the framework of the sequence stratigraphic model and the established history of glacio eustatic sea level cyclicity some of the faults are associated with strike slip microearthquake focal mechanisms the faults are within a complex structural high that underlies much of the outer continental shelf and within the flaxbourne basin between the structural high and the coast the plan view pattern of faulting recorded in the quaternary sediments reflects only the major surface traces that have propagated upsection as contemporaneous sedimentation has blanketed most of the evolving structures regionally the late quaternary faults compose two groups that bound blocks with rhomboid surface areas on a scale of tens of square kilometers to hundreds of square kilometers one group strikes typically between 023 and 057 i e 22 56 from the plate motion vector 079 and includes dextral oblique slip thrust faults as well as inherited steeply dipping pre pliocene strike slip faults that bound thick sedimentary basins the second group comprises possibly young 1 ma steeply dipping strike slip faults that commonly exhibit normal slip separation and strike between 067 and 085 subparallel to the azimuth of the instantaneous pacific australian plate motion vector

late quaternary transpressional earthquakes on a long lived intraplate fault a case study of the southern yangsan fault se korea abstract the nne ssw striking yangsan fault in southeastern korea has been regarded as one of the most prominent seismogenic structures in the korean peninsula on the basis of instrumental and historical seismicity and paleoseismic records along the fault zone its seismic behavior is however still uncertain due to long recurrence intervals of strong earthquakes and insufficient historical and geologic records we conducted a detailed paleoseismic investigation including an 8 m deep excavation in order to understand recent earthquake faulting events along the southern yangsan fault our observations indicate that at least two and possibly four dominantly strike slip surface faulting events have occurred along a subsidiary fault in the eastern boundary of the fault valley since the late pleistocene stratigraphic features and osl ages of the stratigraphy exposed in the trenches indicate that the most recent rupture s occurred after 29 2 1 4 ka and the timing of earlier ruptures are constrained to between 70 0 3 7 ka and 29 2 1 4 ka using a contact of the oldest dated unit that has at least 7 5 m of vertical separation we calculate a minimum vertical slip rate during the late quaternary of 0 11 mm yr the minimum horizontal slip rate is presumed to be two times that of the vertical slip rate based on striations observed on clasts next to the fault core we also propose that the late quaternary earthquake faulting kinematics along the yangsan fault expressed as contractional dextral slip with east side up geometry is strongly dependent on a pre existing fault zone architecture with a strike of n10 20 e that dips to the east and the direction of neotectonic maximum horizontal stress ene wsw to e w

mineralogy sulphur isotope geochemistry and the development of sulphide structures at the broken spur hydrothermal vent site 29 10 n mid atlantic ridge a large collection of hydrothermal sulphides from the broken spur hydrothermal vent site including representative samples of mound sulphide materials has been characterized using optical mineralogy and sulphur isotope analysis young mound sulphides from broken spur have a pyrrhotite dominated mineralogy unusual for bare ridge vent systems however pyrrhotite is metastable and is ultimately converted to iron disulphides mature sulphides are indurated recrystallized and contain abundant quartz sulphide mound materials are developed by three major processes i coalescing of chimney structures ii accumulation of talus from mass wasting and iii precipitation and growth in response to hydrothermal flow progressive maturation of mound materials is by modification of primary textures development of mineralogical zoning and replacement of metastable phases sulphur isotope analysis of 35 mineral separates returned 34 s values of 0 5 to 3 2 these values are similar to those previously measured for broken spur and snakepit but are distinctly 32 s enriched compared to the tag active mound and some pacific sites seawater entrainment and sulphate reduction within the subsurface feeder zone below broken spur mounds do not appear to be important processes at broken spur in contrast to the tag active mound

structure and paleoearthquake records of active submarine faults cook strait new zealand implications for fault interactions stress loading and seismic hazard 1 a new interpretation of active faulting in central cook strait new zealand reveals tectonic structures associated with the spatial transition from subduction to continental transform faulting marine seismic reflection profiles and multibeam bathymetric data indicate that there are no throughgoing crustal faults connecting the north island dextral fault belt and the marlborough fault system in south island the major faults terminate offshore associated with 5 20 km wide step overs and a change in regional fault strike this structure implies that propagation of strike slip earthquake ruptures across the strait is not probable faulted sedimentary sequences in the wairau basin marlborough shelf correlated to glacioeustatic sea level cycles provide a stratigraphic framework for fault analysis a high resolution study of the postglacial 20 ka vertical displacement history of the cloudy and vernon faults reveals up to six and five paleoearthquakes since 18 ka respectively these long timescale records indicate variable recurrence intervals and possibly variable stress drop thus conforming to the variable slip model of earthquake behavior integration of these data with other submarine and terrestrial paleoearthquake records indicates the presence of clustered earthquake sequences involving multiple faults different sequences do not always involve the same faults it appears that earthquake clustering is driven by fault interactions that lead to specific loading conditions favoring the triggering of earthquakes on major faults in relatively short time intervals present day regional coulomb stress distribution has been calculated in two scenarios considered to represent minimum and maximum loading conditions the models incorporating secular tectonic loading and stress changes associated with major crustal earthquakes indicate high stress loading in a large part of central cook strait these conditions may favor the triggering of future damaging earthquakes in this region

an expression of philippine sea plate rotation the parece vela and shikoku basins abstract the philippine sea plate located between the pacific eurasian and australian plates is the world s largest marginal basin plate the motion of the philippine sea plate through time is poorly understood as it is almost entirely surrounded by subduction zones and hence previous studies have relied on palaeomagnetic analysis to constrain its rotation we present a comprehensive analysis of geophysical data within the parece vela and shikoku basins two oligocene to miocene back arc basins which provide independent constraints on the rotational history of the philippine sea plate by means of their seafloor spreading record we have created a detailed plate model for the opening of the parece vela and shikoku basins based on an analysis of all available magnetic gravity and bathymetric data in the region subduction along the izu bonin mariana trench led to trench roll back arc rupture and back arc rifting in the parece vela and shikoku basins at 30 ma seafloor spreading in both basins developed by chron 9o 28 ma and possibly by chron 10o 29 ma as a northward and southward propagating rift respectively the spreading orientation in the parece vela basin was e w as opposed to ene wsw in the shikoku basin the spreading ridges joined by chron 6by 23 ma and formed a r r r triple junction to accommodate the difference in spreading orientations in both basins at chron 6no 20 ma the spreading direction in the parece vela basin changed from e w to ne sw at chron 5ey 19 ma the spreading direction in the shikoku basin changed from ene wsw to ne sw this change was accompanied by a marked decrease in spreading rate cessation of back arc opening occurred at 15 ma a time of regional plate reorganisation in se asia we interpret the dramatic change in spreading rate and direction from e w to ne sw at 20 1 3 ma as an expression of philippine sea plate rotation and is constrained by the spacing between our magnetic anomaly identifications and the curvature of the fracture zones this rotation was previously thought to have begun at 25 ma as a result of a global change in plate motions our results suggest that the philippine sea plate rotated clockwise by about 4 between 20 and 15 ma about a pole located 35 n 84 e this implies that the majority of the 34 clockwise rotation inferred to have occurred between 25 and 5 ma from paleomagnetic data may have in fact been confined to the period between 15 and 5 ma

distributions of hydrothermal activity along the mid atlantic ridge interplay of magmatic and tectonic controls abstract hydrothermal activity has been investigated along three different sections of the slow spreading mid atlantic ridge mar 11 20 30 n 36 38 n and the reykjanes ridge 57 45 63 06 n when considered in total the incidence of venting along these three sections of the mar compares well with the predictions of a model in which frequency of venting is linearly related to ridge crest spreading rate at the scale of individual study areas however departure from the model is observed by up to an order of magnitude venting is anomalously rare along the reykjanes ridge but anomalously abundant along the mar 36 38 n whilst such variability may be within the error of the linear spreading rate model we note that the interplay between magmatic and tectonic processes also differs between the three study areas in the case of the reykjanes ridge we propose that the low incidence of venting reported may reflect a limitation of the sampling investigative strategy because the style of venting which predominates may not give rise to conventional black smoker hydrothermal plumes along the oblique and broadly segmented mar 36 38 n we propose that vigorous hydrothermal venting in broad segment end non transform discontinuities may be focussed along deeply penetrating active faults with the requisite heat supply being supported through some combination of along axis magmatic intrusions and thermal release associated with the serpentinisation of crustal peridotites

geometric model of conjugate faulting in the gyeongsang basin southeast korea 1 the nne trending dextral yangsan fault system and the wnw trending sinistral gaum fault system comprise a conjugate set that cuts the cretaceous gyeongsang basin along the se margin of the korean peninsula these faults evidently formed under compressional stress accompanied by a progressive 12 block rotation calculated from a geometric model incorporating angles between conjugate fault sets widths of fault domains and measured fault displacements the angle between paleomagnetic declinations in the set of conjugate fault domains increases with age suggesting incremental block rotation that included overall rotation of the entire gyeongsang basin or the korean peninsula with respect to eurasia the model accounts for yucheon group volcanism subsequent caldera subsidence in the uiseong subbasin and volcanism in the miryang subbasin all produced by regional tension the tectonic regime of the gyeongsang basin apparently evolved from compression to extension at 50 ma reflecting india eurasia collision and opening of the sea of japan east sea

broad trends in geomagnetic paleointensity on hawaii during holocene time paleointensity determinations have been obtained from 22 basaltic lava flows on the island of hawaii using the thelliers method radiocarbon dating indicates that these flows erupted at intervals ranging from about 200 to 1000 years and results of the experiments provide an estimate of broad trends in geomagnetic paleointensity during holocene time in the vicinity of hawaii most of the samples were obtained from quickly cooled flow margins and as a consequence typically contain two titanomagnetite populations only two of the 79 samples analyzed failed to yield an estimate of the paleofield demonstrating that paleointensities can be obtained from such samples if carefully selected virtual dipole moments calculated for the flows are compared with a published curve of dipole field intensity that was constructed using worldwide archeomagnetic data the large nondipole fields that were previously postulated for the vicinity of hawaii are confirmed and the present data indicate that they were present from about 5000 years b p to perhaps as recently as the past 200 years the data indicate however that these nondipole sources must have been virtually absent between about 12 000 and 5000 years b p as they are at the present time

crustal structure of the continental margin of korea in the east sea japan sea from deep seismic sounding data evidence for rifting affected by the hotter than normal mantle abstract despite the various opening models of the southwestern part of the east sea japan sea between the korean peninsula and the japan arc the continental margin of the korean peninsula remains unknown in crustal structure as a result continental rifting and subsequent seafloor spreading processes to explain the opening of the east sea have not been adequately addressed we investigated crustal and sedimentary velocity structures across the korean margin into the adjacent ulleung basin from multichannel seismic mcs reflection and ocean bottom seismometer obs data the ulleung basin shows crustal velocity structure typical of oceanic although its crustal thickness of about 10 km is greater than normal the continental margin documents rapid transition from continental to oceanic crust exhibiting a remarkable decrease in crustal thickness accompanied by shallowing of moho over a distance of about 50 km the crustal model of the margin is characterized by a high velocity up to 7 4 km s lower crustal hvlc layer that is thicker than 10 km under the slope base and pinches out seawards the hvlc layer is interpreted as magmatic underplating emplaced during continental rifting in response to high upper mantle temperature the acoustic basement of the slope base shows an igneous stratigraphy developed by massive volcanic eruption these features suggest that the evolution of the korean margin can be explained by the processes occurring at volcanic rifted margins global earthquake tomography supports our interpretation by defining the abnormally hot upper mantle across the korean margin and in the ulleung basin

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

faulting and extension rate over the last 20 000 years in the offshore whakatane graben new zealand continental shelf oblique rifting in the offshore taupo volcanic zone new zealand is expressed in widely distributed active normal faulting in the 20 km wide whakatane graben active faults are identified along seafloor scarps and displacements of the post last glacial transgressive ravinement surface 400 faults we derive an extension rate at seismogenic depths 6 10 km across the graben of 13 6 mm yr by summing surface measurements assuming an average crustal fault dip of 45 15o and correcting for the discrepancies between surface and deep crustal extension estimates structural and kinematic data implies an extension direction 20o oblique to the rift axis resulting in up to 4 6 2 1 mm yr of dextral motion parallel to the rift axis the strike slip motion is accommodated by dip slip displacements on oblique faults in the centre of the graben and oblique slip faulting along the rift margins pure dip slip in the graben centre represents 50 of the total slip with the rangitaiki fault accommodating 25 of the total extension in the graben

an absolute palaeointensity record from soh1 lava core hawaii using the microwave technique absolute palaeointensity results were obtained from 392 samples 166 of 241 flows from the upper 779 m of the scientific observation hole 1 soh1 basalt core kilauea volcano hawaii using the microwave palaeointensity technique based on k ar dates and a previously published age model this covers the last 45 ka thus giving a high resolution record of geomagnetic intensity in hawaii comparisons with other hawaiian absolute palaeointensity data show similar trend of higher intensity than present day for the last 3 ka and then a general decrease in intensity over the last 45 ka though this study reports consistently lower palaeointensity values direct comparison with previous thellier data from the soh1 core shows some discrepancies between the two methods with the thellier data yielding generally higher palaeointensity estimates than the microwave data in view of these discrepancies between the two methods the introduction of raw palaeointensity data into the public domain is suggested

back arc rifting in the korea plateau in the east sea japan sea and the separation of the southwestern japan arc from the korean margin abstract the south korea plateau is a remnant of continental crust in the middle of the eastern korean margin that was deformed by extension in association with back arc rifting and separation of the southwestern japan arc in the cenozoic multichannel seismic profiles show that the south korea plateau preserves structure of rift basins flanked by uplifted footwall blocks rift basins in the plateau are filled with distinct syn and post rift sequences separated by a prominent breakup unconformity resulting from uplift the crustal and upper mantle structures computed by ambient noise tomography indicate that the south korea plateau defines the seaward limit of rifted continental crust in addition rifting occurred with vigorous asthenospheric upwelling induced along the korean margin and depth dependent stretching therefore the south korea plateau underwent the entire sequence of tectonic events typical of a passive continental margin encompassing rifting with subsidence uplift erosion and breakup prior to the separation of the southwestern japan arc breakup at the korean margin may substantiate successive episodes of back arc spreading which migrated toward the arc in response to trench retreat we suggest that the southwestern japan arc moved to its present location from the southern part of the korean margin with a significant amount of clockwise rotation during back arc spreading

estimation of possible maximum earthquake magnitudes of quaternary faults in the southern korean peninsula the korean peninsula is located in the intraplate regime of the eurasian plate and numerous historical and instrumental earthquakes have been recorded among these the largest earthquakes were recorded in and around the gyeongju and ulsan areas in the southeastern part of the korean peninsula we recently reexamined faults in jinhyun and jintee part of the ulsan fault swarm to clarify the average slip rate and the maximum potential magnitude of future earthquakes the jinhyun fault extends to the tabgol fault j t fault and the jintee fault extends to the singye s j fault the faults cut through alluvial fans and are covered by unconsolidated granite washes on tertiary granite all of these faults show reverse sense of motion such that the tertiary granite has been moved upward with a high angle relative to the quaternary sediments most sediment samples from the jinhyun and jintee faults showed quartz osl ages of ca 40 60 ka the calculated vertical slip rate for the jinhyun and jintee faults is in the range of 0 18 0 28 mm y based on maximum earthquake magnitudes calculated from geological survey results as well as historical and instrumental earthquake information the maximum potential magnitudes of future earthquakes in the gyeongju area are estimated to range from 4 6 to 5 6 this suggests that the potential maximum magnitude in the southern korean peninsula is presumably not more than 6

a laboratory analog study of the surface morphology of lava flows extruded from point and line sources abstract in laboratory experiments designed to model lava flow processes liquid polyethylene glycol wax is forced through either a small hole or a long narrow slit onto the base of a tank of cold water where it spreads laterally while cooling and solidifying at its surface we observe the surface structure of the flow and its dependence on the flow rate thermal conditions and basal roughness in each case solidification of a crust during spreading gives rise to a number of different surface morphologies each of which forms under a restricted range of conditions the dominant morphologies referred to as pillows rifts transverse folds and marginal levees correspond to features observed on natural lava flows results for radial spreading over a rough base and for spreading in two directions from the line source over both smooth and rough bases complement those reported earlier for radial spreading of solidifying wax from a point source on a smooth base together they indicate a robust dependence of morphology on the distance from the vent at which solid crust begins to form this distance is in turn determined by the extrusion rate the rheology of the liquid wax or magma the reduced gravity the magnitude of the surface heat flux and the amount of cooling required to solidify the flow surface the results also indicate factors influencing the distribution of crust and its deformation and may provide a means by which observations of surface morphology can be used to place constraints on the emplacement conditions of lava flows

the offshore yangsan fault activity in the quaternary se korea analysis of high resolution seismic profiles abstract the nne trending dextral yangsan fault is a 190 km long structure in the korean peninsula traced to the southeastern coast the scarcity of quaternary deposits onland precludes any detailed investigation of the quaternary activity and structure of the yangsan fault using seismic reflection profiling we acquired offshore high resolution seismic profiles to investigate the extension of the yangsan fault and constrain its quaternary activity using stratigraphic markers the seismic profiles reveal a nne trending fault system consisting of a main fault and an array of subsidiary faults that displaced quaternary sequences stratigraphic analysis of seismic profiles indicates that the offshore faults were activated repeatedly in the quaternary the up to the east sense of throw on the main fault and plan view pattern of the fault system are explained by dextral strike slip faulting the main fault when projected toward the korean peninsula along its strike aligns well with the yangsan fault we suggest that the offshore fault system is a continuation of the yangsan fault and has spatial correlation with weak but ongoing seismicity

characteristics of magma driven hydrothermal systems at oceanic spreading centers 1 we use one and two limb single pass models to de termine vent field characteristics such as mass flow rate q bulk permeability in the discharge zone kd thickness of the conductive boundary layer at the base of the system magma replenishment rate and residence time in the discharge zone data on vent temperature vent field area heat output and the surface area and depth of the subaxial magma chamber amc constrain the models the results give q 100 kg s kd 10 13 m2 and 10 m essentially independent of spreading rate and detailed characteristics of the amc in addition we find no correlation between heat output at individual vent fields and spreading rate or depth to the amc we conclude that high temperature hydrothermal systems are driven by local magma supply rates in excess of that needed for steady state crustal production and that crustal permeability enables hydrothermal circulation to tap magmatic heat regardless of amc depth using data on partitioning of heat flow between focused and diffuse flow we find that 80 90 of the hydrothermal heat output is derived from high temperature fluid even though much of the heat output discharges as low temperature fluid in some cases diffuse flow fluids may exhibit considerable conductive cooling or heating by assuming conservative mixing of diffuse flow fluids at east pacific rise 9 50 n we find that most transport of metals such as fe and mn occurs in diffuse flow and that co2 h2 and ch4 are taken up by microbial activity

seismic characteristics and identification of negative flower structures positive flower structures and positive structural inversion negative and positive flower structures and positive inverted structures imply specific modes of formation and their distinctive characteristics make them important criteria for the identification of certain structural styles a negative flower structure from the andaman sea consists of a shallow synform bounded by upward spreading strands of a wrench fault that have mostly normal separations paralleling monoclines and oblique en echelon normal faults flank the divergent wrench fault a positive flower structure from the ardmore basin oklahoma consists of a shallow antiform displaced by the upward diverging strands of a wrench fault that have mostly reverse separations en echelon folds are present on either side of this convergent wrench fault flower structures may resemble extensional or contractional fault blocks on individual seismic profiles flower structures are identified by their unique internal fault and fold architecture by their association with a straight and throughgoing zone of deformation and by their lack of a consistent sense of separation or regional upthrown side positive structural inversion at the rambutan oil field south sumatra basin has formed a shallow anticlinorium and has partly uplifted the underlying graben deeper fault segments bounding the graben have retained their normal fault profiles but at shallow levels some of these faults have reverse separations similar changes of separation with depth may be produced by strike slip but sets of faults with listric profiles and nearby blocklike trend patterns identify the inversion as a dip slip event where correlation of reflections is uncertain or deep control is unobtainable positive inverted structures may also resemble contrational fault blocks detached normal fault assemblages and certain negative inverted structures

structural evolution of the southwestern margin of the ulleung basin east sea japan sea and tectonic implications abstract structural mapping and restoration of depth converted seismic profiles from the southwestern ulleung basin in the east sea japan sea back arc basin reveal the structural evolution of the area since the middle miocene the back arc closure began in the earliest middle miocene ca 15 ma and caused compressional deformation that has propagated southwestward from the dolgorae to the gorae structures and further to the unnamed inversion structure immediately adjacent to se korea the accelerated convergence of the young

evidence for hydrothermal venting and sediment volcanism discharged after recent short lived volcanic eruptions at deception island bransfield strait antarctica abstract the results of a combined geophysical and geochemical research programme on deception island an active volcano at 62 43 s 60 57 w in bransfield strait antarctica are presented ultrahigh resolution acoustic data obtained with a topas topographic parameter sonar system and multibeam bathymetry simrad em1000 allow a detailed analysis of submarine vents in port foster the submerged caldera of deception island the data show three different types of seafloor structures low relief mounds high relief mounds wasp nest like and spire like structures we interpret these structures as products of sediment volcanism and seeps caused by heating and boiling of pore fluids in gas charged sediments and related to recent short lived volcanic events possibly those that occurred in 1967 1969 and 1970 in addition subsurface vertical disturbed zones formed by increased amplitude and phase inverse reflectors beneath the mounds suggest the presence of fluidised and brecciated sediments within hydrofracture systems a key finding of this study is that there appears to be a close relationship between the submarine mounds detected by our ultrahigh resolution seismic study geochemical haloes fault pathways and present day thermal anomalies in surface waters we suggest that seafloor hydrofracture systems and subsurface pipes can be re used as fluid migration pathways resulting in hydrothermal seeps and vents on the seafloor possibly up to decades after coeval volcanic eruptions

sources and fluxes of hydrothermal heat chemicals and biology within a segment of the mid atlantic ridge we have conducted a segment wide study of the chemical biological and thermal effects of hydrothermal activity in a bathymetrically enclosed 50 km long segment of the mid atlantic ridge at 29 n our study involved long term monitoring of bottom current speeds and temperatures coupled with snap shot surveys of the concentrations of hydrothermal shrimp manganese and particulate plumes occupying the water column enclosed by the axial valley these data are combined with the calculated volume transport rates for the segment and the results compared with the heat and manganese flux from the broken spur vent field located in the center of the segment our current meter data show that the basin like bathymetry acts to restrict and control flow of water warm and shallow water exported from the segment is replaced by colder and deeper water water column profiles showed an increase in temperature of the water within the broken spur segment compared with background stations located outside the ridge axis the average refresh rate for the water column enclosed by the segment was found to be about 262 days from these data we calculate that the segment wide flux of juvenile shrimp is 20 106 individuals per year we show that the flux of manganese exported at a rate of 5 6 mol s is matched by input from high temperature effluent discharge at the broken spur vent field we also calculate that the minimum average heat flux exported from the segment is about 275 mw of this more than 90 is pervasively dissipated throughout the segment floor by conductively heated sea water or simple thermal conduction that carries little or no manganese to the water column the remaining 10 or less of the heat flux results from localized manganese rich high temperature hydrothermal venting

esr dating of the subsidiary faults in the yangsan fault system korea abstract the yangsan fault system is located near heavy industrial complexes and nuclear power plants in the korean peninsula we carried out esr dating of fault rocks from the wonwonsa and ihwa faults two subsidiary faults of the yangsan fault system esr ages are divided into three groups in order of decreasing confidence multiple plateau esr ages single plateau esr ages and maximum esr ages the wonwonsa fault was reactivated at least 4 times and the ihwa fault at least 2 times within the quaternary period long term cyclic fault activity of some subsidiary faults of the yangsan fault system occurred in the pleistocene and suggests the possibility of continued activity on this fault system

hydrothermal plumes above the east scotia ridge an isolated high latitude back arc spreading centre we have identified first evidence for the presence of submarine hydrothermal activity along the east scotia ridge an isolated back arc spreading centre located at 55 60 s in the atlantic sector of the southern ocean using a combination of in situ optical light scattering sensor data and total dissolvable mn concentrations we demonstrate the existence of hydrothermal plumes overlying two segments of this 500 km ridge crest both segments exhibit anomalous topography and at least one segment is also underlain by an axial magma chamber seismic reflector future investigation of the fauna that inhabit these remote hydrothermal environments may provide an important missing link between the distinct biogeographical provinces delimited from previous investigation of northern atlantic versus eastern pacific vent sites

geomagnetic intensity and inclination variations at hawaii for the past 98 kyr from core soh 4 big island a new study and a comparison with existing contemporary data abstract reliable thellier thellier paleointensity determinations were obtained from 321 out of 766 examined samples from the upper 200 units 675 m of core soh 4 drilled in the kilauea volcano the main trend of the soh 4 record is a marked decrease from values higher than present in the last 4 kyr to values about 40 smaller from about 20 kyr to the bottom of the sampled interval three main lows coinciding with shallow or negative inclinations observed in the record were identified with an excursion previously documented in hawaii and the mono lake and laschamps events for the last 15 kyr the soh 4 intensities are largely in agreement with the worldwide distribution of volcanic data in the 15 75 kyr interval the general lack of volcanic data makes comparison with the soh 4 data difficult the soh 4 record is similar to a composite record of paleointensity largely based on a recent north atlantic sedimentary paleointensity stack napis 75 the soh 4 record is also generally consistent with a record of geomagnetic field intensity obtained from a study of 36 cl in the grip ice core calculated with the assumption that the production rate of 36 cl is controlled only by the geomagnetic field one pronounced discrepancy between the different records is observed around 50 kyr bp when the sedimentary and cosmogenic based records document high intensities which are not observed in soh 4 these high intensities are also absent in a recent record based on the analyses of sea floor magnetic anomalies the histogram of vadms obtained from soh 4 is different from that obtained from the sedimentary or 36 cl based records and is more skewed than the distribution given by kono and tanaka for the last 2 5 million years

quantifying tectonic strain and magmatic accretion at a slow spreading ridge segment mid atlantic ridge 29 n high resolution deep towed side scan sonar data are used to characterize faulting and variations in tectonic strain along a segment of the slow spreading mid atlantic ridge near 29 n sonar data allow us to identify individual fault scarps to measure fault widths and spacing and to calculate horizontal fault displacements heave and tectonic strain we find that over long periods of time 1 myr on average tectonic strain is 10 on average and does not vary significantly along axis there is a marked asymmetry in tectonic strain that appears to be linked to asymmetric accretion along the whole segment indicated by 50 lower tectonic strain on the east flank than on the west flank these variations in tectonic strain do not correlate directly with changes in fault spacing and heave fault spacing and heave increase from the center of the segment toward the end inside corner on the west flank and from the outside to the inside corner across the axis these parameters remain relatively constant along the segment on the east flank and across the axis at the segment center tectonic strain appears to be decoupled from magmatic accretion at timescales 1 myr as the decrease in magma supply from the segment center toward the end inferred from variations in crustal thickness along the axis is not correlated with a complementary increase in tectonic strain instead tectonic strain remains relatively constant along the axis at 7 on the east flank and at 15 on the west flank these results indicate that variations in fault development and geometry may reflect spatial differences in the rheology of the lithosphere and not changes in tectonic strain or magma supply along axis

relationships between hydrothermal activity and axial magma chamber distribution depth and melt content 1 hydrothermal activity especially high temperature discharge is commonly thought to require the presence of an axial magma chamber amc but this association has not been examined systematically the availability of six lengthy 170 560 km ridge sections with continuous surveys of both amcs and hydrothermal plumes now makes it possible to quantitatively compare the distribution and intensity of hydrothermal activity to amc extent depth and at a few locations melt content these six ridge sections span spreading rates from 55 to 145 mm a and total 20 second order segments at the section multisegment scale the linear incidence of hydrothermal plumes increases with amc incidence amci r2 0 64 excluding the hot spot affected galapagos spreading center for all six sections plume incidence increases as amc depth below the seafloor decreases amcz r2 0 66 at the second order segment scale plume incidence is poorly correlated with both amci r2 0 12 and amcz r2 0 25 finally at the subsegment or local scale 0 75 km long bins plume intensity increases as amcz shallows r2 0 85 of bins where plumes are most intense and thus closest to their seafloor sources 68 13 lie directly over an amc as do at least 37 of the 40 known high temperature vent fields the data also allow tests of other hypotheses linking amc properties and hydrothermal activity existing data though still sparse do not support the hypothesis that lenses of melt rich magma preferentially support vigorous long lasting venting also the suggestion that increased hydrothermal cooling within a segment locally depresses amcz finds no support within any ridge section evidence for magma bodies is much scarcer on slow spreading ridges but the data are nevertheless consistent with those from faster ridges observations from all spreading rates thus demonstrate that high temperature vent fields are almost universally associated with the presence or inference of magma hot rock or other nonmagmatic heat sources are insufficient

geomagnetic field intensity at hawaii for the last 420 kyr from the hawaii scientific drilling project core big island hawaii four hundred twenty five new paleointensity thellier thellier determinations out of 545 analyzed samples have been obtained from core hsdp which penetrates about 1000 meters 208 flows of the mauna loa and mauna kea volcanic series encompassing the last 420 kyr rock magnetic investigations identify pseudo single domain magnetite as the main magnetic mineral inclinations are shallower than expected from a geocentric dipole field but are consistent with data from other geographical regions at the same latitude the inclination record reveals three episodes of negative inclination whose interpolated age correlates well with that of known geomagnetic events the paleointensity record from the mauna loa sequence is not very detailed and does not allow precise comparison with other data in the 0 50 kyr interval the record from the mauna kea sequence on the contrary is very detailed and documents relatively short lived episodes of low and high field strength from 15 to 60 t the average virtual dipole moment 8 7 3 0 10 22 a m 2 is not significantly different from the value reported by kono and tanaka 1995 for the last 2 5 myr a comparison with other data from hawaii and other geographical regions is described in detail there are no drastic changes in paleointensity with the inclination anomaly in agreement with previous results from hawaii but in contrast with most published results which however consider data from polarity transition spectral analysis of a particularly detailed portion of the record between 420 and 326 kyr documents significant periodicities at 36 8 5 and 4 ka in the inclination record but not in the intensity record suggesting that changes in time of the inclination are to a certain extent independent from those of the intensity

quaternary normal faulting in southeastern sicily italy a seismic source for the 1693 large earthquake summary we present geological and morphological data combined with an analysis of seismic reflection lines across the ionian ovshore zone and information on historical earthquakes in order to yield new constraints on active faulting in southeastern sicily this region one of the most seismically active of the mediterranean is avected by wnw ese regional extension producing normal faulting of the southern edge of the siculo calabrian rift zone our data describe two systems of quaternary normal faults characterized by diverent ages and related to distinct tectonic processes the older nw se trending normal fault segments developed up to 400 kyr ago and striking perpendicular to the main front of the maghrebian thrust belt bound the small basins occurring along the eastern coast of the hyblean plateau the younger fault system is represented by prominent nnw sse trending normal fault segments and extends along the ionian ovshore zone following the ne sw trending avola and rosolini ispica normal faults these faults are characterized by vertical slip rates of 0 7 3 3 mm yr 1 and might be associated with the large seismic events of january 1693 we suggest that the main shock of the january 1693 earthquakes m 7 could be related to a 45 km long normal fault with a right lateral component of motion a long term net slip rate of about 3 7 mm yr 1 is calculated and a recurrence interval of about 550 50 yr is proposed for large events similar to that of january 1693

the geochemical controls on vent fluids from the lucky strike vent field mid atlantic ridge abstract hydrothermal vent fluids were collected from the lucky strike site at 37 17 n on the mid atlantic ridge in both 1993 and 1996 seven vents were sampled with the dsv alvin in 1993 and six vents were sampled in 1996 using the rov jason during the lustre 96 cruise as three of the vents were sampled in both 1993 and in 1996 a time series of vent fluid chemistry is also reported measured temperatures ranged from 202 to 333 c at the 1618 1726 m depth of the vent field which is located on lucky strike seamount these fluids are either equal to or less than the local bottom seawater in chlorinity while the range in fluid compositions at lucky strike is generally within that observed elsewhere the unusual aspects of the fluid chemistries are the relatively high ph and low fe mn li and zn we attribute this as well as an usually low sr ca ratio to reaction with a highly altered substrate the high si and cu contents suggest a deep as well as hot source for these fluids the fluid compositions therefore suggest formation by super critical phase separation at a depth not less than 1300 m below the seafloor and reaction with a relatively oxic and previously altered substrate there is temporal variability in some of the vent fluid compositions as li k ca and fe concentrations have increased in some of the vents as has the fe mn molar ratio although the chlorinities have remained essentially constant from 1993 to 1996 while there is not a simple relationship between vent fluid compositions or temperatures and distance from the lava lake at the summit of the seamount the vent fluids from many of the vents can be shown to be related to others often at distances 200 m the most southeasterly vents eiffel tower and the marker mounds vents are distinct in chlorinity and other chemical parameters from the rest of the vents although closely related to each other within the southeastern area similarly all of the vents not in this one area appear closely related to each other this suggests one or two source fluids for many of the vents as is also inferred to be the case at tag but which is in contrast to observations on faster spreading ridges this may suggest inherently different plumbing for hydrothermal systems at slower versus faster spreading ridges

geotectonic setting of hydrothermal activity on the summit of lucky strike seamount 37 17 n mid atlantic ridge we have investigated the relations between volcanic tectonic and hydrothermal activity on lucky strike seamount 37 17 n mid atlantic ridge using a nested survey strategy involving collection of data from different deep sea mapping systems the highly tectonized seamount summit consists of three volcanic cones surrounding a relatively flat depression with a young lava lake in its center hydrothermal activity is focused mainly within the summit depression with most of the vents located proximal to the lava lake isolated active and inactive chimneys and mounds are widespread throughout the summit depression and occur on both volcanic pillow lava and hydrothermal sulfide rubble and hydrothermally cemented breccias substrates the large volume of sulfide rubble together with the nature of the sulfide structures indicates that hydrothermal activity has been episodic but ongoing for a long period of time hundreds to thousands of years on the basis of the distribution of hydrothermal deposits we propose a model of alternation between tectonic and volcanic control on hydrothermalism at lucky strike seamount midsegment melt focusing produces a spatially and temporally stable heat source that sustains focused high temperature hydrothermal activity over long time periods during periods of amagmatic extension active faulting within the summit depression provides multiple near surface fluid flow pathways for discharge of high temperature fluids and widespread deposition of massive sulfides during eruptive events rapid effusion of very hot lava creates a lava lake and hyaloclastite deposits the new sheet flows form a cap on the hydrothermal system and fluid upflow is reorganized discharge of high temperature fluids is restricted to isolated sites with relatively high permeability for example the edges of the lava lake much of the upwelling hydrothermal fluid pools in the subsurface conductively cools and mixes with entrained seawater before discharging as widespread low temperature diffuse flow hyaloclastites become cemented further augmenting the sealing of the system present day activity at lucky strike seamount represents this locally volcanically controlled phase of activity despite the segment as a whole being dominantly amagmatic

fault slip analysis of quaternary faults in southeastern korea abstract the quaternary stress field has been reconstructed for southeast korea using sets of fault data the subhorizontal direction of the maximum principal stress 1 trended ene and the direction of the minimum principal stress 3 was nearly vertical the stress ratio 2 3 1 3 value was 0 65 two possible interpretations for the stress field can be made in the framework of eastern asian tectonics 1 the hmax trajectory for southeast korea fits well with the fan shaped radial pattern of maximum principal stress induced by the india eurasia collision thus we suggest that the main source for this recent stress field in southeast korea is related to the remote india eurasia continental collision 2 the stress field in korea shows a pattern similar to that in southwestern japan the origin for the e w trending hmax in japan is known to be related to the mantle upwelling in the east china sea thus it is possible that quaternary stress field in korea has evolved synchronously with that in japan we suggest further studies gps and in situ stress measurement to test these hypotheses

stratigraphic architecture and spatio temporal variability of high frequency milankovitch depositional cycles on modern continental margins an overview abstract this study is a review of quaternary milankovitch cycles as recorded on modern continental shelves worldwide on the background of the many existing examples we focus on selected case studies from mediterranean adriatic and tyrrhenian seas and atlantic gulfs of mexico and cadiz margins that represent general and peculiar characters of middle upper pleistocene sequences forming under the control of composite 100 and 20 ka milankovitch cycles the most pervasive stratigraphic pattern displayed by shelf deposits is referred to the 100 ka sea level cycle and consists of fairly uniform depositional sequences mostly composed by regressive deposits forming during the falling limb of the sea level curve these are generally classified as falling stage systems tract fsst and display a regressive facies architecture reflecting the dominant control of sea level on many margins fsst units may show slight though significant differences with respect to highstand systems tract hst and lowstand systems tract lst regressive units more closely reflecting environmental changes and the local variability of depositional systems in contrast with the theoretical and overall scale independent model developed to predict composite stratigraphic cycles and sequences the middle upper pleistocene stratigraphic record from numerous shelf settings shows a subdued signature of the higher frequency 20 ka milankovitch cyclicity however when detectable the 20 ka architectural pattern is characterized by a relatively greater spatial and temporal variability compared to 100 ka sequences this fact likely reflects the increasing importance of factors controlling the depositional environment e g seafloor morphology oceanographic regime sediment input and dispersal etc with respect to sea level change during the shorter intervals encompassed by 20 ka cycles on this basis two end member cases have been distinguished depending on the generation or not of high frequency sequence boundaries a prerequisite to qualify the higher frequency motifs as depositional sequences these two end members are comprehensive of the highly variable patterns displayed by middle upper pleistocene shelf sequences which in turn reflect the interplay between the geological setting the dominant sea level control and the effective response of sedimentary systems the variable stratigraphic patterns of milankovitch cycles represent conceptual and practical constraints as to the classification of high frequency quaternary sequences under the general schemes of the standard sequence stratigraphy model

late quaternary inner shelf deposits in response to late pleistocene holocene sea level changes nakdong river se korea abstract the high resolution seismic profiles from the inner shelf off the nakdong river in se korea can be directly correlated with the lithologic characteristics in the borehole data these correlations offer an opportunity to document the evolution of the inner shelf deposits with sediment supplies in response to the late quaternary sea level changes the inner shelf sequence in this area consists of four sedimentary units which comprise a set of lowstand transgressive and highstand systems tracts deposited since the last glacial maximum incised channel fill su1 estuary su2 sand veneer su3 and subaqueous delta su4 the lowermost unit su1 which overlies the sequence boundary is interpreted as fluvial deposits formed during the last glacial period and the early stage of transgression and belongs to the lowstand to transgressive systems tract the lower middle unit su2 lying below the ravinement surface represents a paralic component that consists of estuarine sandy mud or muddy sand developed between approximately 13 and 8 cal ka bp whereas the upper middle unit su3 above the ravinement surface corresponds to a marine component that consists of sand veneer produced by the shelf erosion during the ensuing sea level rise these two units su2 and su3 belong to the transgressive deposits the uppermost unit su4 regarded as the highstand systems tract formed the nakdong subaqueous delta including the proximal and distal systems developed after the highstand sea level at approximately 6 cal ka bp the lateral transition from the proximal to distal facies suggests a prograding delta system in the nakdong river

hydrothermal exploration of mid ocean ridges where might the largest sulfide deposits be forming highlights black smokers on slow spreading ridges can host larger seafloor massive sulfide sms deposits than on fast ridges the largest slow ridge sms deposits are typically associated with long lived tectonic fractures sustained fluid flow ultramafic tectonic hosted sites exhibit high average cu 10wt and au 3ppm contents in their surface sms samples hydrothermal plume surveys are consistent with equal abundances of magmatic vs tectonic vent control along ultraslow ridges the first black smokers on any ultraslow ridges exhibit high cu au sms contents at both magmatic and tectonic vent sites abstract here we review the relationship between the distribution of modern day seafloor hydrothermal activity along the global mid ocean ridge crest and the nature of the mineral deposits being formed at those sites since the first discovery of seafloor venting a sustained body of exploration has now prospected for one form of hydrothermal activity in particular high temperature black smoker venting along 30 of the global mid ocean ridge crest while that still leaves most of that 60 000 km continuous network to be explored some important trends have already emerged first it is now known that submarine venting can occur along all mid ocean ridges regardless of spreading rate and in all ocean basins further to a first approximation the abundance of currently active venting as deduced from water column plume signals can be scaled linearly with seafloor spreading rate a simple proxy for magmatic heat flux what can also be recognized however is that there is an excess of high temperature venting along slow and ultra slow spreading ridges when compared to what was originally predicted from seafloor spreading magmatic heat budget models an examination of hydrothermal systems tracked to source on the slow spreading mid atlantic ridge reveals that no more than half of the sites responsible for the black smoker plume signals observed in the overlying water column are associated with magmatic systems comparable to those known from fast spreading ridges the other half of all currently known active high temperature submarine systems on the mid atlantic ridge are hosted under tectonic control these systems appear both to be longer lived than and to give rise to much larger sulfide deposits than their magmatic counterparts presumably as a result of sustained fluid flow a majority of these tectonic hosted systems also involve water rock interaction with ultramafic sources importantly from a mineral resource perspective this subset of tectonic hosted vent sites also represents the only actively forming seafloor massive sulfide deposits on mid ocean ridges that exhibit high concentrations of cu and au in their surface samples 10 wt average cu content and 3 ppm average au along ultraslow spreading ridges first detailed examinations of hydrothermally active sites suggest that sulfide deposit formation at those sites may depart even further from the spreading rate model than slow spreading ridges do hydrothermal plume distributions along ultraslow ridges follow the same 50 50 distribution of black smoker plume signals between magmatic and tectonic settings as the slow spreading mar however the first three black smoker sites tracked to source on any ultra slow ridges have all revealed high temperature vent sites that host large polymetallic sulfide deposits in both magmatic as well as tectonic settings further deposits in both types of setting have now been revealed to exhibit moderate to high concentrations of cu and au respectively an important implication is that ultra slow ridges may represent the strongest mineral resource potential for the global ridge crest despite being host to the lowest magmatic heat budget

high resolution imagery of active faulting offshore al hoceima northern morocco abstract two recent destructive earthquakes in 1994 and 2004 near al hoceima highlight that the northern moroccan margin is one of the most seismically active regions of the western mediterranean area despite onshore geodetic seismological and tectonic field studies the onshore offshore location and extent of the main active faults remain poorly constrained offshore al hoceima high resolution seismic reflection and swath bathymetry have been recently acquired during the marlboro 2 cruise these data at shallow water depth close to the coast allow us to describe the location continuity and geometry of three active faults bounding the offshore nekor basin the well expressed normal left lateral onshore trougout fault can be followed offshore during several kilometers with a n171 e 3 trend westward the bousekkour aghbal normal left lateral onshore fault is expressed offshore with a n020 e 4 trending fault the n030 e 2 bokkoya fault corresponds to the western boundary of the plio quaternary offshore nekor basin in the al hoceima bay and seems to define an en echelon tectonic pattern with the bousekkour aghbal fault we propose that these three faults are part of the complex transtensional system between the nekor fault and the al idrissi fault zone our characterization of the offshore expression of active faulting in the al hoceima region is consistent with the geometry and nature of the active fault planes deduced from onshore geomorphological and morphotectonic analyses as well as seismological geodetic and geodynamic data