brittle frictional mountain building 2 thermal structure and heat budget this paper describes a simple thermal model of an actively deforming critically tapered fold and thrust belt the model determines the steady state temperature distribution and heat flow as well as the pressure temperature time histories of rocks that outcrop at the surface the main parameters controlling the thermal structure are the accretion and erosion rates the undisturbed geothermal gradient at the toe and the amount of frictional heating both shear heating on the decollement fault and internal strain heating within the deforming brittle wedge are incorporated in a mechanically consistent manner and they dominate the effect of radiogenic heating except in fold and thrust belts with significantly overpressured pore fluids the mean stresses temperatures and surface heat flow all increase with an increase in the basal and internal coefficients of friction and this dependence is used to constrain the level of friction on the decollement fault beneath the steady state fold and thrust belt in taiwan rocks outcropping in the core of the central mountain range of taiwan experience maximum theoretical temperatures in excess of 400 c and maximum mean pressures in excess of 500 mpa if the coefficient of basal friction is b 0 5 qualitatively these conditions are in good agreement with the observed high greenschist facies metamorphism the theoretical surface heat flow which increases from 95 mw m2 at the front of the fold and thrust belt to 240 mw m2 at the rear is in excellent agreement with the results of a recent geothermal survey of taiwan and theoretical cooling histories are in good agreement with fission track and other geochronologic studies taken together these results provide strong evidence that sliding on the basal decollement fault beneath taiwan is governed by a coefficient of friction in the range of typical laboratory measurements b 0 5 0 2 approximately 35 of the total surface heat flux of 3 gw is heat conducted into the base of the wedge from the top of the basal decollement fault and somewhat more than 30 is heat advected into the toe by accretion the remaining heat is generated internally about 25 by internal strain heating and about 10 by radiogenic heating either an increase in the coefficient of basal friction b or a reduction in the pore fluid pressure ratio b leads to an increase in the surface heat flow because of the increased frictional heating within the wedge and on the basal decollement fault the overall balance of energy in a steady state fold and thrust belt is described by the equation e w g q where is the rate at which both mechanical and heat energy are added from external sources w g is the rate at which work is performed against gravitational body forces in a reference frame attached to the overriding plate and q is the rate at which waste heat flows out of both the upper and lower boundaries the total power input into the taiwan fold and thrust belt is approximately 4 2 gw the mechanical work being done on the base and front of the fold and thrust belt accounts for 3 of these 4 2 gw in addition 0 9 gw of heat are being advected from the subducting plate into the toe by accretion the remaining 0 3 gw are being supplied by in situ radiogenic heating the outgoing energy is dominated by the 3 gw of heat conducted out the top in the surface heat flow however another 0 8 gw are conducted down beneath the rear portion of the basal decollement fault to heat the underlying subducting slab only 0 4 of the incoming 4 2 gw do useful mechanical work against gravity within the wedge the efficiency of brittle frictional mountain building in taiwan is therefore 10

path and variability of the agulhas return current the combined analysis of hydrographic kinematic and dynamic data collected during the 1997 1999 kapex cape of good hope experiments reveals a quasi stationary meandering pattern of the agulhas retroflection current east and upstream of the southwest indian ridge the current meanders between 38 s and 40 s in a spatially and temporally continuous fashion and has a core width of approximately full size image 1 k with an associated transport of full size image 1 k in the upper full size image 1 k peak surface velocities decrease from full size image 1 k near the agulhas retroflection to full size image 1 k around 32 e meander troughs northward extremes are found predominantly near 26 8 e 32 6 e and 38 9 e while crests southward extremes are located with high probability near 29 7 e 35 5 e and 42 9 e resulting in a typical wavelength of full size image 1 k cold eddies are shed along the northern boundary of the current from meander troughs into the recirculation regime between the agulhas current proper and the agulhas return current strongest cyclonic eddies are preferably shed in austral autumn the cyclonic eddies so formed propagate westward at an average phase speed of full size image 1 k with however a variability of at least the same magnitude subsequently the cyclones are absorbed by the next meander trough located upstream and to the west of the shedding trough

source scaling relationship for m 4 6 8 9 earthquakes specifically for earthquakes in the collision zone of taiwan we investigated the source scaling of earthquakes mw 4 6 8 9 mostly from the taiwan orogenic belt and made a global compilation of source parameters to examine the scaling self similarity finite fault slip models 12 dip slip and 7 strike slip using mainly dense strong motion data and teleseismic data from taiwan were utilized seven additional earthquakes m 7 were included for further ex amination of scaling of large events we determined the effective length and width for the scaling study was m0 l 2 and m0 l 3 for the events less than and larger than the seismic moment of 10 20 nm respectively regardless of the fault types suggesting a nonself similar scaling for small to moderate events and a self similar scaling for large events although the events showed variation in stress drops with the exception of three events with high stress drops most of the events had stress drops of 10 100 bars the observed bilinear relation is well explained by the derived magnitude area equation of shaw 2009 when we considered only events with stress drops of 10 100 bars and a seismogenic thickness of 35 km the bilinear feature of the regressed magnitude area scaling holds for ruptured areas up to about 1000 km 2 for our seismogenic thickness of 35 km for the events having rupture areas larger than that the average slip becomes proportional to the rupture length the distinct high stress drop events from blind faults in the western foothill of taiwan yield local high peak ground accelerations pgas when compared to the next generation attenuation model regardless of the relative small magnitudes of these events the high pgas give the region higher seismic hazard potential and thus require special attention for seismic hazard mitigation

from swallow floats to argo the development of neutrally buoyant floats neutrally buoyant floats have been a vital tool in the exploration of the global ocean circulation and now provide a central element of the in situ ocean observing system through the argo project the paper traces the development of neutrally buoyant floats from their origins in the mid 1950s to the present day and highlights areas of ocean science to which floats made significant contributions

importance of pre existing oceanic conditions to upper ocean response induced by super typhoon hai tang 1 this study investigates upper ocean response to super typhoon hai tang the most intense typhoon in 2005 in the western north pacific using multi satellite microwave data typhoon data and argo profiles sequential merged microwave sea surface temperature sst images show that hai tang induced four separately cooling responses after its trail in the western north pacific during 11 18 july comparison between upper ocean responses of cooling sst and pre typhoon sea surface height suggests that these cooling responses of the upper ocean to hai tang are closely associated with pre existing cyclonic circulation denoted by pre existing negative sea surface features furthermore applying argo profiles the physical mechanism is confirmed to be associated with pre existing cyclonic circulations provide a relatively unstable thermodynamic structure and therefore cold water would be brought up readily this paper provides the rather convincing evidence that cyclonic flow and uplifted thermocline are the pre existing conditions for intensive cooling following the typhoon passage

direct measurement of the deep circulation within the brazil basin abstract in support of the deep basin experiment part of the world ocean circulation experiment a large number of neutrally buoyant floats were released within the brazil basin during the 1990s in an attempt to measure directly the circulation in the deep ocean interior three levels corresponding to the three major subthermocline water masses were selected and results from the deeper two north atlantic deep water nadw and antarctic bottom water aabw are described at this writing processing of acquired tracking data is incomplete hence this paper reports on the progress of the observational program and gives our initial conclusions it appears that the flow in the deep brazil basin is unlike previous conjectures in which the circulation patterns can be characterized as being primarily meridional both along the western boundary and in the interior the existence of a deep western boundary current dwbc is quite clear in the float data at the nadw level but less prominent in the aabw and the interior flow is dominantly zonal with unexpectedly small meridional space scales integral time scales are long of order 20 30 days and eddy kinetic energy levels are low of order 1 cm2 s2 in spite of the low energy levels a surprising number of our floats became caught up in vortices a line of seamounts extending offshore near 20 s known as the vitoria trindade seamounts interrupts the dwbcs and is the location for eddy formation and apparent flow away from the boundary into the interior although it has been speculated that this could feed a narrow zonal current of nadw the namib col current our float trajectories suggest a return to the western boundary rather than a continuation to the east

intermediate and deep currents of the black sea obtained from autonomous profiling floats abstract float trajectories observed at three depths 200 750 and 1550 m in the black sea during a 1 5 yr period offer new insights on the circulation below the permanent pycnocline the float observations for the first time provided direct quantitative evidence for strong currents and a well organized flow structure at intermediate and deep layers in contrast to prior ideas of a rather sluggish deep circulation of the black sea the magnitudes of intermediate and deep currents are typically about 5 10 of the surface currents reaching as much as 5 cm s 1 at 1550 m adjacent to the steep topographic slope on the periphery the combination of float and sea level height altimeter data suggests that a well defined cyclonic circulation extends from the surface to the bottom without reversal in its direction deep currents are steered by the steep topographic slope and well correlated with surface currents at seasonal and longer time scales

lagrangian circulation of antarctic intermediate water in the subtropical south atlantic this study combines float data from different projects collected between 1991 and 2003 in the south atlantic to describe the flow of antarctic intermediate water aaiw velocity space time averages are calculated for various grid resolutions and with cells deformed to match the bathymetry f h or f h with h being the water depth and h being the thickness of the aaiw layer when judged by the degree of alignment between respective isolines and the resulting average velocity fields the best grid is based on a nominal cell size of 3o latitude by 4o longitude with cell shapes deformed according to f h using this grid objectively estimated mean currents and their associated errors as well as meridional and zonal volume transports are estimated results show an anticyclonic subtropical gyre centred near 36os and spanning from 23o 1 s to 46 1os the south atlantic current meanders from 33os to 46os and shows a mean speed of 9 6 7 8 cm s 1 8 5 sv 3 5 sv 1 sv 1 106 m3 s 1 the northern branch of the subtropical gyre is located between 22os and 32os and flows westward with a mean speed of 4 7 3 3 cm s 1 9 3 sv 3 4 sv evidence of a cyclonic tropical gyre divided in two sub cells is visible on the stream function

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

sulfide composition and microthermometry of fluid inclusions in the leg 111 sheeted dike section of ocean drilling program hole 504b costa rica rift hole 504b of the ocean drilling program is dedicated to the study of crustal structure and hydrothermal processes in 5 9 m y old oceanic basement continuing the work of previous legs hole 504b was extended 212 3 m to a total depth of 1562 3 m below seafloor bsf during leg 111 in 1986 quartz sulfide veins occur at a depth of 1369 1388 m bsf in basalts of the sheeted dike complex the ore minerals are predominantly pyrite less chalcopyrite rare corich cu fe s phases and a thiospinel linnaeite carrollite microprobe analyses yield a high co content in zoned vein pyrites 8 wt as well as in the cu fe s phases 5 wt up to 35 8 wt co was detected in the thiospinel a co ni ratio of 100 distinguishes the vein pyrite from pyrite in the basaltic wall rock and from pyrite formed as an alteration product of olivine co ni 5 the co ni ratios correlate positively with cu and negatively with as co rich nonstoichiometric cu fe s sulfides in chalcopyrite are interpreted as metastable phases which have been quenched at a high temperature and prohibited from exsolution of the stable products chalcopyrite and pyrite fluid inclusions in quartz from the quartz sulfide veins are two phase and vary from liquid to vapor dominated their salinities range from 4 2 to 7 2 wt equivalent nacl and average 5 5 wt pressure 360 bars corrected average filling temperatures vary from 271 to 408 c with a maximum of 486 c this is consistent with calculated quartz formation temperatures for a single quartz separate 4 2 18o using oxygen isotope thermometry the 18o value of the hydrothermal fluid was determined to be 1 7 the temperature data indicate fluid alteration of the sheeted dikes at about 350 to 500 c the maximum homogenization temperatures intersect the liquid vapor two phase boundary above the critical point of seawater thus phase separation could have occurred before or during the formation of the mineralized veins and the alteration of the sheeted dike sequence

thrust front zone of the precordillera argentina a thick skinned triangle zone the frontal thrust zone of the precordillera thrust belt of western argentina only superficially resembles a classical alberta style triangle zone in this thick skinned triangle zone the thrust front is the result of interaction between the eastward verging thin skinned central precordillera and the westward verging thick skinned eastern precordillera system the western boundary formed by the niquivil thrust plate has been refolded and faulted by thrust faults from the eastern precordillera at several localities the deformation is still active we divide the thick skinned triangle zone into three segments based on the system s activity independent late interfering and collision zones balanced cross sections across a thick skinned triangle zone show a uniform s ortening for the eastern precordillera 17 km the structural geometry suggests multiple reactivation of the main faults the thick skinned triangle zone began to grow after 2 6 ma and is still active episodic and alternating opposing movement is controlled by buttressing of the thin skinned thrust system against the basement structures of the eastern precordillera

seismotectonics of the loma prieta california region determined from three dimensional v p v p v s and seismicity three dimensional vp and vp vs velocity models for the loma prieta region were developed from the inversion of local travel time data 21 925 p arrivals and 1 116 s arrivals from earthquakes refraction shots and blasts recorded on 1700 stations from the northern california seismic network and numerous portable seismograph deployments the velocity and density models and microearthquake hypocenters reveal a complex structure that includes a san andreas fault extending to the base of the seismogenic layer a body with high vp extends the length of the rupture and fills the 5 km wide volume between the loma prieta mainshock rupture and the san andreas and sargent faults we suggest that this body controls both the pattern of background seismicity on the san andreas and sargent faults and the extent of rupture during the mainshock thus explaining how the background seismicity outlined the along strike and depth extent of the mainshock rupture on a different fault plane 5 km away new aftershock focal mechanisms based on three dimensional ray tracing through the velocity model support a heterogeneous postseismic stress field and can not resolve a uniform fault normal compression the subvertical or steeply dipping san andreas fault and the fault surfaces that ruptured in the 1989 loma prieta earthquake are both parts of the san andreas fault zone and this section of the fault zone does not have a single type of characteristic event

from passive continental margin to mountain belt insights from analytical and numerical models and application to taiwan abstract the physics of deformation at plate boundaries is insufficiently understood taiwan is particularly interesting in this context since geological and geophysical arguments indicate that passive margin sediments were exhumed into an active mountain belt over a relatively short period of time classically taiwan has been described as a critical wedge orogeny in which deformation is entirely restricted to the crust more recent data however indicate that deeper parts of the lithosphere also participate in deformation in order to study the physical feasibility of various endmember hypothesis we have performed two dimensional 2 d thermo mechanical numerical experiments in which both mantle lithospheric and surface processes are taken into account and in which crustal deformation evolves as a function of mantle flow our setup consists of ocean ocean subduction followed by passive continental margin deformation results indicate that in most cases the subducting slab becomes close to vertical upon arrival of continental material to the trench whereas crustal rheology deformation and surface processes do not modify mantle flow significantly they are important for crustal scale processes relatively little crustal exhumation occurs if the crust is homogeneous and erosion rates are small significant exhumation in a dome like structure is obtained if a weak lower crust and large erosion rates are present the presence of an oceanic arc in the overriding oceanic lithosphere modifies but does not control crustal deformation synthetic metamorphic facies maps and thermochronological data computed from the numerical models are in reasonable agreement with observations in southern taiwan if exhumation occurs in a dome like structure further physical insight in the doming mechanisms is obtained by a combination of analytical techniques and crustal scale numerical models this analysis indicates that the dome like exhumation mechanism can be attributed to a compressional mechanical instability facilitated by both a weak lower crust and large rates of erosion both conditions are likely to be satisfied in taiwan

seasat altimeter observations of dynamic topography in the gulf stream region individual seasat altimeter profiles in the western north atlantic have been differenced with the best available geoid model to remove the gravitational component the resulting sea surface height profiles compare remarkably well with independent oceanographic observations the gulf stream is clearly apparent in each profile as a 1 to 2 m step and known positions of cyclonic and anticyclonic rings correspond with depressions and elevations respectively with amplitudes as large as 95 cm some of the most important altimeter data for analyzing the dynamic ocean signal were gathered during the last month of the mission when the same ground track was repeated every 3 days these data allow detailed examination of time varying ocean phenomena since the gravitational component is time invariant one set of collinear passes clearly shows a cyclonic ring as it moves out from underneath the spacecraft s track an event which was simultaneously observed with the aid of a satellite tracked surface buoy another striking feature seen in the altimeter data set is the apparent variability exhibited by the gulf stream on time scales of a few days surface transport indicated by the sea surface height difference across the stream varied by nearly 30 and over the entire 3 month period much larger fluctuations were observed suggesting significant changes in total mass transport altimetry may provide an effective means of determining the time and space scales associated with these variations

friction on subduction megathrust faults beyond the illite muscovite transition abstract previous experimental studies addressing subduction megathrust friction have focused on shallow fault gouges dominated by smectite illite and quartz here we aim to determine the effect of the transition to muscovite rich fault rock at depths beyond the illite dominated region of the seismogenic zone to achieve this rotary friction experiments were performed on simulated muscovite quartz 65 35 gouge at 100 600 c an effective normal stress of 170 mpa pore pressures of 100 and 200 mpa and sliding velocities of 1 100 m s we isolated the effects of muscovite by shearing pure muscovite gouge at 200 600 c under otherwise identical conditions at low shear strains 1 muscovite quartz gouge showed a friction coefficient of 0 4 0 5 while pure muscovite gouge exhibited 0 3 both gouges showed an increase in with and temperature the muscovite quartz gouge was characterised by velocity strengthening or neutral behaviour at 100 350 c velocity weakening at 350 500 c and velocity strengthening at 500 600 c in contrast pure muscovite gouge showed predominantly velocity strengthening or neutral behaviour demonstrating a key role of quartz in producing velocity weakening the velocity weakening regime in the mixed gouge extends that of 250 400 c recently reported for illite quartz gouge up to 500 c taking into account the observed effect of sliding velocity on a b the data for illite quartz and muscovite quartz together help explain the depth extent of seismogenesis on subduction megathrusts interestingly comparison with previous microphysical models suggests that the mechanism causing velocity weakening in phyllosilicate quartz gouges is one of granular flow involving competition between shear induced dilation and compaction through thermally activated quartz deformation

directly measured mid depth circulation in the northeastern north atlantic ocean the circulation of water masses in the northeastern north atlantic ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes but the ocean circulation at depths below the reach of satellite observations is difficult to measure and only recently have comprehensive direct observations of whole ocean basins been possible here we present quantitative maps of the absolute velocities at two levels in the northeastern north atlantic as obtained from acoustically tracked floats we find that most of the mean flow transported northward by the gulf stream system at the thermocline level about 600 m depth remains within the subpolar region and only relatively little enters the rockall trough or the nordic seas contrary to previous work our data indicate that warm saline water from the mediterranean sea reaches the high latitudes through a combination of narrow slope currents and mixing processes at both depths under investigation currents cross the mid atlantic ridge preferentially over deep gaps in the ridge demonstrating that sea floor topography can constrain even upper ocean circulation patterns

correlations between compressional and shear wave velocities and corresponding poisson s ratios for some common rocks and sulfide ores abstract the correlations between v p and v s and corresponding poisson s ratios are important in modeling and interpreting seismic data in terms of chemistry and lithology data from high pressure laboratory measurements of compressional and shear wave velocities v p and v s are analyzed for 12 common categories of rocks amphibolite anorthosite basalt diorite eclogite felsic gneiss gabbro diabase granite intermediate gneiss limestone mafic gneiss and peridotite and 4 types of massive sulfide ores chalcopyrite pyrite sphalerite and pyrrhotite the analysis reveals that the linear correlation provides good descriptions for the v s v p and ln v s ln v p relationships poisson s ratio is linearly correlated with v s v p shear modulus g and young s modulus e for these rocks and sulfide ores a decrease in poisson s ratio is associated with increases in v s g and e however the variation of poisson s ratio with v p depends on the logarithmic ratio r s p i e ln v s ln v p poisson s ratio increases or decreases with v p when r s p 1 r s p varies systematically with lithology 0 300 for granite 0 573 for diorite 0 602 for felsic gneiss 0 631 for intermediate gneiss 0 721 for gabbro diabase 0 768 for mafic gneiss 0 866 for eclogite 0 890 for amphibolite and 1 391 for peridotite it is suggested that r s p can be used as a proxy for the composition of the deep continental crust and the upper mantle

shear wave velocity model of the chukuo fault zone southwest taiwan from cross correlation of seismic ambient noise abstract the chia nan chiayi tainan area is in the southwestern taiwan and is located at the active deformation front of the collision of the eurasian continental plate and the philippine sea plate which causes complex folds as well as thrust fault systems in the area the chukuo fault zone is a boundary between the western foothill and the western coastal plain in the chia nan area the nature of the crustal structure beneath the fault zone especially the eastern part of the fault zone with mountain topography has not been well known in detailed due to lack of drilling data as well as its limitation in using other geophysical methods such as active source survey in this study we deployed an array with 11 broadband seismic stations to monitor the seismicity of the chukuo fault zone the array has recorded more than 1000 microearthquakes around this area it provides an opportunity to use p and s wave travel time data to investigate the both the crustal p and s velocity in the fault zone however due to the nature of the earthquake distribution the ray density is relatively low at depth between 0 and 7 km in addition the uncertainty of s wave reading for small earthquake also a limit in building precise s velocity profile thus we take the advantages of using cross correlation of seismic ambient noise to investigate crustal s velocity profile in the chukuo fault area especially in the mountain area where crustal faulting is a dominated phenomenon the results indicate that s wave velocity in the uppermost crust in the chukuo fault zone is shown to be slower than previous studies a low velocity layer exists at depth between 1 and 2 km in the east of the chukuo fault the low s velocity is related to a highly fractured upper crust due to intensive deformation caused by the orogenic process

evolution of hydrothermal fluid characteristics at the santa rita new mexico porphyry copper deposit mineralogic and fluid inclusion investigations conducted in the laboratory combined with in situ observations of temporal relationships among geologic features demonstrate that systematic changes in hydrothermal fluid characteristics occurred with time during evolution of mineralization and alteration of the granodiorite stock at the santa rita porphyry copper deposit the earliest fluids to circulate are recorded in potassically altered orthoclase and biotite stable veins as vapor rich h 2 o co 2 inclusions and hypersaline 30 70 equiv wt nacl or kcl inclusions which homogenize over a wide temperature range from 240 degrees to greater than 800 degrees c the high salinity fluid inclusions are complex chloride brines with significant concentrations of sodium potassium copper iron and sulfur but sulfide minerals are not associated with the early potassic assemblage produced by this fluid oxygen isotope ratios of quartz in the orthoclase and biotite stable veins are identical to phenocryst quartz in the intrusion 8 2ppm later solutions circulated through newly formed fractures and older reopened veins and are recorded in low salinity less than 15 equiv wt nacl fluid inclusions which homogenize primarily in the temperature range of 220 degrees to 360 degrees c these hydrothermal fluids formed two distinct alteration assemblages as they reacted with potassically altered rock chlorite is the dominant silicate gangue mineral of the earlier chalcopyrite bearing orthoclase and clay stable assemblages and sericite characterizes the later phyllic alteration assemblage with quartz and pyrite oxygen isotope ratios of quartz of the later assemblages 8 6 10 4ppm are heavier than quartz of the earlier potassic assemblages it is concluded that the earliest hydrothermal fluids to circulate within the stock localizing the orebody at santa rita could have been derived by phase separations of fluids exsolved from crystallizing magma into condensed hypersaline liquids and h 2 o co 2 vapors as these fluids moved through fractures potassic alteration of rock occurred without concomitant deposition of sulfides later solutions of dominantly meteoric origin progressively formed hypogene copper mineralization associated with chlorite stable alteration and then phyllic alteration

critical taper model of fold and thrust belts and accretionary wedges the fold and thrust belts and submarine accretionary wedges that lie along compressive plate boundaries are one of the best understood deformational features of the earth s upper crust although there is considerable natural variation among the many fold and thrust belts and accretionary wedges that have been recognized and explored several features appear to be universal in cross section fold and thrust belts and accretionary wedges occupy a wedge shaped deformed region overlying a basal detachment or decollement fault the rocks or sediments beneath this fault show very little deformation the decollement fault characteristically dips toward the interior of the mountain belt or in the case of a submarine wedge toward the island arc the topography in contrast slopes toward the toe or deformation front of the wedge deformation within the wedge is generally dominated by imbricate thrust faults verging toward the toe and related fault bend folding two north american fold and thrust belts that exhibit these features are shown in figure 1 neither of these two examples is tectonically active today the southern canadian fold and thrust belt was active during the late jurassic and cretaceous 150 100 ma whereas the southern appa lachians were deformed during the late carboniferous to permian alle ghenian orogeny 300 250 ma figure 2 shows two examples that are currently active the taiwan fold and thrust belt produced by the sub duction of the eurasian plate beneath the philippine sea plate suppe 1981 1987 and the barbados accretionary wedge produced by the sub

deep convection in the labrador sea as observed by lagrangian floats abstract during the winters of 1997 and 1998 a total of 24 lagrangian floats were deployed in the labrador sea these floats were designed to match the buoyancy and compressibility of seawater they measured temperature and three dimensional position pressure for vertical position and rafos acoustic tracking for latitude and longitude as they followed water motions three dimensionally this data provides direct observation of mixed layer depth and excellent estimates of vertical velocity floats were repeatedly carried across the convecting layer by vertical velocities averaging several centimeters per second with vertical excursions of up to one kilometer in the horizontal several scales of eddy motion were resolved as was a possible float predilection toward remaining in water preconditioned for convection heat flux estimates from this data reveal entrainment and surface heat fluxes similar in magnitude the mixed layer acts as a vertical conveyor belt of temperature transporting heat from depth

chloride depletions and enrichments in seafloor hydrothermal fluids constraints from experimental basalt alteration studies na k ca cl fluid was reacted with diabase at 400 and 425 c 400 bars and fluidrock mass ratio of 0 5 to assess the relative mobility of dissolved cl fluids from the present experiments reveal relatively large time and temperature dependent decreases in cl temperature increase enhances cl removal whereas reaction progress has the opposite effect these changes are not due to boiling and or phase separation at 400 and 425 c 400 bars cl removal from solution is accompanied by ca and na fixation respectively both experiments produced mixed layer chlorite smectite clinozoisite and albite olivine was not detected by x ray diffraction or petrographic analysis of run products from either experiment however we propose that the time dependent changes in dissolved cl result from olivine replacement by an fe hydroxy chloride phase followed by hydration effects quenched and washed alteration products however did not reveal anomalous cl which suggests that the cl bearing phase is characterized by retrograde solubility this is consistent with the relative magnitude of cl fixation observed for experiments at both temperatures and from results of an isobaric cooling experiment the experiments provide evidence for the non conservative behavior of cl during hydrothermal alteration of basalt the data are particularly important in light of the cl depleted nature of some ridge crest hot spring fluids and suggest temperatures of formation for these fluids of approximately 410 c assuming sub seafloor pressure of 400 bars in addition the retrograde solubility of the cl bearing phase responsible for cl fixation during high temperature basalt alteration may help to explain cl enrichment in hot spring fluids which have conductively cooled below 350 c

joint vp and vs tomography of taiwan implications for subduction collision orogeny abstract the taiwan orogen sitting at the pre rifted eurasian margin and bracketed by two sub orthogonal subduction systems is subject to complicated geotectonics motivating numerous seismic tomographic studies in local and regional scale most of them obtained p wave velocities vp or with vp vs ratio jointly but few were for s wave velocities vs with unprecedented amount of s wave data in this study a new set of well tuned vp vs and vp vs models were determined by an elaborate joint inversion scheme integrating the data of p and s wave travel times s p times and the borehole logging data for near surface correction into one system this allowed us to revisit the subduction collision process in detail by comparing vp vs and vp vs ratio simultaneously with enhanced slab imaging of philippine sea plate psp under northeast taiwan we are able to discriminate the plausible missing luzon forearc basement along the plate boundary and propose a skateboarding edge model in which the westernmost psp rides on the east subducted forearc basement and subducts northward underneath the eurasian lithosphere the underlain forearc basement along with the psp subduction then results in the anomalous shallow double seismic zone observed only near taiwan island meanwhile at around 121 e the north subducting psp seems dipping west to collide with the deep eurasian lithosphere shaping an irregular corner wedge structure in addition we evaluate our model with previous ones by waveform modeling approach and show the current performance of travel time tomography in taiwan region

preliminary results from directly measuring middepth circulation in the tropical and south pacific as part of the world ocean circulation experiment 300 autonomous lagrangian circulation explorer floats were deployed in the tropical and south pacific to measure the general circulation at 900 m depth most floats measured average currents over 25 submerged days between ascents to the surface for locating and data relay by the end of 1997 over 12 500 observations spanning 840 float years were obtained accuracy of the average velocity is limited by variability some of which is found to arise from steady flows with spatial variations smaller than averaging scales observed 25 day velocities are serially uncorrelated except near the equator where energetic zonal variability has seasonal timescales and appears to be described by a data assimilating ocean circulation model run by the national centers for environmental prediction space time averages of float velocities disclose a general pattern of middepth flow that resembles the surface circulation with the strongest flows of o 3 cm s in the deep antarctic circumpolar current and east australian current the weaker elements of the flow including an interior subtropical circulation with o millimeters per second flows are described by an objective analysis whose accuracy is limited by sampling noise rather than uncertainty of the analysis parameters the subtropical circulation has a gyres within a gyre structure including boundary currents along australia and east of new zealand and a concentrated equatorial limb with surprising strength in the western basin this current is also involved in a tropical gyre with generally eastward flow along the equator in the western basin at least because of strong seasonal scale variability the equatorial zonal currents are not well measured yet but data are still being accumulated comparison with reid s 1997 absolute circulation shows more areas of agreement than of disagreement

magma chamber profiles from the bay of islands ophiolite complex models of the oceanic lithosphere derived from constraints imposed by the geology of ophiolite complexes require a magma chamber to produce the cumulate and other plutonic portions of the oceanic crust and upper mantle evidence from the bay of islands ophiolite complex indicates that layered plutonic rocks have not formed solely due to differential crystal settling to the horizontal floor of a magma chamber but have formed largely by heterogeneous nucleation and in situ crystallization along gently inclined as well as steeply inclined bounding surfaces of a large magma reservoir coherent well defined and systematically oriented large scale arcuate patterns described by mesoscopic igneous layering have been identified in the plutonic sections of two ophiolite massifs in the bay of islands complex these layering patterns seem to outline the shape of a large continuously evolving steady state magma chamber that extended along a ridge axis and ended at a transform fault intersection

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

origin of a foreland dipping seismogenic zone and its basal decollement in southwestern taiwan abstract an unusual foreland dipping seismicity band has been identified at a depth between 7 and 25 km beneath the coastal plain a foreland basin in southwestern taiwan this seismogenic zone is closely associated with abrupt changes in vp vs based on our new high resolution seismic tomography rocks with high vp vs ratios of up to 1 84 were found directly above the inclined seismicity band below it the vp vs ratio dramatically drops to about 1 72 1 78 we found that this change may result from illite bearing slates transforming to muscovite bearing phyllite mica schist previous studies suggested that the frictional instability regime for illite quartz gouge and muscovite quartz gouge falls in the range of 250 500 c we calculated the isotherms based on regional heat flow data and found that the foreland dipping seismicity band can well be bounded between the 250 c and 500 c isotherms in addition in the same temperature range wet illite hydromuscovite would transform to muscovite and release water this dehydration may elevate pore pressure and facilitate the formation of an incipient decollement at the base of the seismicity band in front of the mountain belt the hypothesis that such a decollement exists is supported by the existence of a corresponding zone of low resistivity and also by the geometry of the earthquake of october 22 1999 the latter clearly shows a fault branched off the basal decollement with an angle about 45 this finding implies that the effective friction coefficient of the basal decollement is at least 23 less than that of the overlying rocks

earthquake nucleation in weak subducted carbonates ocean floor carbonate and clay rich sediments form major inputs to subduction zones especially at low latitude convergent plate margins therefore knowledge of their frictional behaviour is fundamental for understanding plate boundary earthquakes here we report results of mechanical tests performed on simulated fault gouges prepared from ocean floor carbonates and clays cored during iodp drilling offshore costa rica clay rich gouges show internal friction coefficients that is the slope of linearized shear stress versus normal stress data of int 0 44 0 56 irrespective of temperature and pore fluid pressure pf by contrast int for the carbonate gouge strongly depends on temperature and pore fluid pressure with int decreasing dramatically from 0 84 at room temperature and pf 20 mpa to 0 27 at t 140 c and pf 120 mpa this effect provides a fundamental mechanism of shear localization and earthquake generation in subduction zones and makes carbonates likely nucleation sites for plate boundary earthquakes our results imply that rupture nucleation is prompted by a combination of temperature controlled frictional instability and temperature and pore pressure dependent weakening of calcareous fault gouges

significant rotations related to cover substratum decoupling example of the dome de barrot southwestern alps france the barrot area presents an important contrast of deformation between a foliated faulted and non rotated permian substratum and a folded and strongly rotated meso cenozoic sedimentary cover the permian substratum and the sedimentary cover are separated by a decollement level of triassic gypsum while numerous studies have been done on the dome de barrot i e the permian substratum we focused our work on the deformed meso cenozoic sedimentary cover around the dome de barrot where we measured and analyzed both the magnetic susceptibility fabrics and the paleomagnetic directions our results highlight an arcuate pattern of the directions of shortening trajectories revealed by type ii iii fabrics of anisotropy of magnetic susceptibility which predates the folding and a later syn or post folding anticlockwise rotation of large amplitude 64 14 for the sedimentary cover the arcuate pattern of the directions of shortening and the different rotations between the permian substratum and the sedimentary cover can be partly explained after restoring the paleogeographic location of the sedimentary cover before the oligocene alpine compression event we tend to interpret the remaining 30 anticlockwise rotation as a result of the high efficiency of the triassic gypsum decollement surface a nearby regional left lateral shear zone rdfz and a possible near field gravitational sliding near the later exhumed dome de barrot

magnetotelluric imaging beneath the taiwan orogen an arc continent collision 1 the taiwan orogen has formed since the late miocene by oblique collision between the luzon volcanic arc on the philippine sea plate and the eurasian continental margin this oblique collision has produced an orogen that decreases in age from north to south and permits study of the temporal evolution of an arc continent collision these factors make taiwan a favorable location to study the process of arc continent collision the first long period magnetotelluric mt measurements were recorded in taiwan as part of the taiwan integrated geodynamics research taiger project in 2006 7 measurements were made at 82 sites on three transects across south central and north taiwan that span the breadth of the orogen and cross all major tectonic boundaries robust remote reference processing of the mt time series data resulted in high quality soundings that were modeled in both 2 and 3 dimensions these mt models support predictions of lithospheric deformation i e thick skinned tectonics beneath the central ranges in south and central taiwan but are inconsistent with predictions of orogen scale thin skinned models the mt resistivity model for northern taiwan is consistent with dewatering of the subducting philippine slab and with deformation described by the subducting indenter tectonic model modeling the taiger mt data has definitively shown that conductive and seismically active crustal structures exist to 30 km beneath the orogen these conductive regions interpreted as interconnected fluid map pervasive zones of collisional deformation that are lithospheric in scale

active detachment of taiwan illuminated by small earthquakes and its control of first order topography we use 110 000 small earthquakes to locate and map active faults in three dimensions within the taiwan arc continent collision the structure is dominated by a nearly horizontal band of small earthquakes at 10 km depth that is interpreted to seismically illuminate the main detachment zone of the mountain belt with other illuminated fault zones abutting the detachment zone the zone steepens below eastern taiwan to 30 90 and reaches depths of 30 60 km the three dimensional shape of the detachment zone in relation to topography allows a new test of critical taper wedge mechanics and suggests that the reversal of topographic slope across taiwan is controlled by the shape of the detachment

effects of temperature and sliding rate on frictional strength of granite layers of artificial granite gouge have been deformed on saw cut granite surfaces inclined 30 to the sample axes samples were deformed at a constant confining pressure of 250 mpa and temperatures of 22 to 845 c the velocity dependence of the steady state coefficient of friction ss was determined by comparing sliding strengths at different sliding rates the results of these measurements are consistent with those reported bysolberg andbyerlee 1984 at room temperature andstesky 1975 between 300 and 400 c stesky found that the slip rate dependence of ss increased above 400 c in the present study however the velocity dependence of ss was nearly independent of temperature

influence of subduction zone conditions and gouge composition on frictional slip stability of megathrust faults to understand the temperature depth distribution of destructive earthquakes in subduction megathrusts and the mechanisms of nucleation of these events data on the frictional behaviour of phyllosilicate quartz rich megathrust fault gouges under in situ conditions are needed we performed rotary shear friction experiments at effective normal stresses of 25 200 mpa pore fluid pressures of 50 200 mpa at 140 600 c and sliding velocities of 1 100 m s using gouge mixtures with an illite quartz ratio between 65 35 and zero experiments on 65 35 mixtures deformed at an effective normal stress neff of 170 mpa a pore fluid pressure pf of 100 mpa and 150 500 c provided a reference dataset this showed three temperature dependent slip stability regimes with potentially unstable velocity weakening behaviour at 250 400 c and velocity strengthening at lower and higher temperatures the velocity weakening regime was found to shift towards higher temperatures with decreasing neff being located at 350 600 c at 50 mpa increasing quartz content and decreasing sliding velocity also displaced the velocity weakening regime towards lower temperatures increasing pf increased a b at all temperatures narrowing the temperature extent of the velocity weakening regime we explain our results qualitatively in terms of a microphysical model in which changes in friction coefficient and a b with velocity and temperature are brought about by changes in the relative importance of deformation of the clast phase by thermally activated stress corrosion cracking and pressure solution versus athermal granular flow of the mixture accompanied by dilatation our results imply that the depth extent of the seismogenic zone on subduction megathrusts depends not only on temperature and that to predict its location it is essential to have well constrained depth profiles for pore fluid pressure and effective normal stress

investigating the lithospheric velocity structures beneath the taiwan region by nonlinear joint inversion of local and teleseismic p wave data slab continuity and deflection the interaction between two flipping subduction systems shapes the complicated lithospheric structures and dynamics around the taiwan region whether and in what form the eurasian plate subducts deforms under taiwan island is critical to the debate of tectonic models although an east dipping high velocity anomaly down to a depth below 200 km has been reported previously its detailed morphology remains uncertain and leads to different interpretations with a two step strategy of nonlinear joint inversion the slab images of the eurasian plate were retrieved in a geometry that is hyperthin in the south becoming massive and steeper in the central and severely deformed in the north the possible depth and dimension of a slab break were also investigated through synthetic tests of whether the slab had torn moreover the slab deflection found at 23 2 n latitude seems to correspond to where the nonvolcanic tremors and recent nw se striking structures have occurred in southern taiwan

north atlantic subtropical gyre sofar floats tracked by moored listening stations in 1980 sofar sound fixing and ranging floats were tracked acoustically in the western north atlantic entirely by means of moored autonomous listening stations during a 5 month period 17 float trajectories were obtained in the eastern 45 degrees to 65 degrees w gulf stream and subtropical gyre interior at depths of 700 and 2000 meters these mid depth trajectories suggest a time varying gulf stream with instances of both a narrow swift westward recirculation south of the stream and a northeastward penetration into the newfoundland basin a hundredfold increase of eddy kinetic energy was observed at 2000 meters from the gyre interior south of 30 degrees n to the gulf stream

chemical controls on the composition of vent fluids at 13 11 n and 21 n east pacific rise six vent fields sampled at 13 11 n east pacific rise epr in may 1984 exhibit large interfield variations and a much wider range of chemical compositions than previously observed at 21 n measured ph at 25 c are acidic ranging from 3 1 to 3 7 sodium and chloride vary from 40 lower to 30 higher than seawater iron concentrations range from 2 to 10 mmol kg compared with 0 7 2 5 mmol kg at 21 n other sulfide forming metals cu zn cd and pb are generally lower at 11 13 n than at 21 n reliable temperature measurements were obtained at only two of the six vents and both were 350 5 c the vent fields at 21 n epr were resampled in august 1985 thus extending to almost 6 years the time period over which they have been monitored previous expeditions were made in november 1979 and november 1981 campbell et al this issue have shown that the chemistry of the hydrothermal fluids from these fields has been very stable over the period of repeated observation equilibrium calculations for the fluids from the fields at 13 n and 21 n using a greatly improved thermodynamic data base are described in this report they indicate that the chemistry is rock buffered and that the stability of these systems over time is a result of equilibrium control with respect to a greenschist type mineral assemblage at depth calculated high temperature ph of the fluids range from 4 1 to 4 7 with those from 13 11 n at the more acidic end of the range calculated affinities show that the fluids are close to or at saturation with respect to quartz albite muscovite smectite chlorite epidote and pyrrhotite the computations imply that lower temperature vents such as national geographic smoker ngs 273 c may have their silica concentrations controlled by equilibrium with respect to a phase other than quartz a comparison of fluid chemistry between ngs and vent 5 at 11 n suggests that the latter vent may also have a temperature 300 c while the fluid chemistry of a given field is compositionally stable the compositions themselves are unique for a particular field and cover a wide range between fields the processes controlling this variability probably include the depth of reaction i e pressure which is difficult to treat thermodynamically at present in addition increasing depth in the crust may be accompanied by decreasing permeability and hence a probable decrease in the water rock ratio it may be difficult to separate these two effects if the age differences between the fields at present unknown are of the order of decades then their temporal histories may have an important influence on their particular chemistries

thick skinned and thin skinned thrusting in the la ramada fold and thrust belt crustal evolution of the high andes of san juan argentina 32 sl abstract the cenozoic structural evolution of the la ramada fold and thrust belt in the high andes of argentina between 32 00 s and 32 30 s shows in time and space the interaction of thin skinned and thick skinned deformations based on geometric and kinematic constraints three different deformation stages have been recognized the first began with thin skinned nnw trending structures detached in upper jurassic gypsum in the second stage the basement was involved by tectonic inversion of triassic normal faults producing a thick skinned fold and thrust belt this inversion combined with the ductile rheology of the jurassic gypsum resulted in refolding of older structures the uplift of the basement by high angle reverse faults at the ramada espinacito massif produced a sticking point in the foreland propagation of the thrust belt this was responsible for the third stage of deformation characterized by thin skinned nnw out of sequence thrusts developed in the westernmost sector the total andean shortening calculated in the area was 21 24 km near 30 the structure of the la ramada fold and thrust belt was integrated into a crustal scale cross section at 32 s latitude based on gravimetric models and surface geology a crustal model is proposed for the andes of chile and argentina a shortening of 180 km was calculated between the chile trench and the sierra de pie de palo this implies a mean deformation rate of 2 8 mm year 1 during cenozoic times an initial crustal thickness of ca 33 km was computed a two layer model with a middle detachment level is proposed to explain the spatial decoupling between maximum shortening at the surface and maximum crustal thickening the upper layer was balanced based on surface structural information the lower layer is interpreted to have been constructed by an imbricate thrust system controlled by the mercedario rift master shear and the precordillera chilenia suture

the isopycnal swallow float a simple device for tracking water parcels in the ocean abstract a standard swallow float can be converted into a passive isopycnal follower by the addition of a compressee a spring backed piston in a cylinder designed to give the float the compressibility of seawater thus no archimedian buoyancy is created due to changes in depth in addition the float must have a coefficient of thermal expansion significantly smaller than that of seawater an instrument meeting these requirements ballasted to a chosen isopycnal will approximately follow that isopycnal on time scales longer than the local buoyancy period two preliminary field experiments were conducted in the upper main thermocline near the north wall of the gulf stream during august 1981 a spherical glass float was deployed 200 km downstream from cape hatteras and was tracked for approximately 100 km neutrally buoyant in the oxygen minimum near 380 m the float tracked the t 27 12 0 01 as determined from ctd data during its passage through a mini meander during september 1982 a cylindrical float was tracked for approximately 100 km east of cape hatteras deployed in the gulf stream near the 250 m level the float tracked the t 26 74 0 01 isopyncal surface during a gradual descent and cross stream motion over the 24 hr sampling period thus the floats tracked nearly isopycnally in both field tests clusters of these instruments used in concert with hydrographic surveys have the potential for unique studies of mixing entrainment and topographic effects

fault stability inferred from granite sliding experiments at hydrothermal conditions seismicity on crustal faults is concentrated in the depth interval 1 3 to 12 15km tse and rice 1986 suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening destabilizing to velocity strengthening stabilizing friction they inferred this transition from friction data for dry granite however pore fluids exist at elevated temperatures throughout the crust and may strongly influence strength and sliding behavior we present new data from sliding experiments on granite at elevated t 23 to 600 plus elevated ph2o 100 mpa our results show velocity strengthening at room temperature but velocity weakening from 100 to 350 c except at 250 from 350 to 600 there are systematic trends from velocity weakening to strong velocity strengthening and from high to low friction neither trend was seen in tests on dry granite the velocity dependence data imply the potential for unstable slip in the interval 100 to 350 using a geotherm to map temperature to depth this interval closely matches the observed earthquake distribution

velocity weakening behavior of plagioclase and pyroxene gouges and stabilizing effect of small amounts of quartz under hydrothermal conditions 1 we investigated properties of frictional sliding of plagioclase pyroxene and their mixture gouges with a small amount of hornblende biotite and quartz as accessory minerals under hydrothermal conditions with an effective normal stress of 200 mpa pore pressure of 30 mpa and temperatures from 100 c to 600 c axial loading rate was stepped between 0 001 and 0 0001 mm s to acquire the rate dependence both plagioclase and pyroxene gouges showed velocity weakening behavior in the whole temperature range except the velocity strengthening behavior of pyroxene at 200 c for temperatures above 400 c both plagioclase and pyroxene gouges showed oscillatory slips as a result of small dc values of 3 4 m which make the critical stiffness rise remarkably and approach the system stiffness above 300 c the direct effect of plagioclase shows an increasing trend with temperature indicating control of the deformation process by thermally activated mechanisms as the difference of a and b values here are only 20 at most this trend also applies to the evolution effect our analytical derivation based on the theory of pressure solution shows a log linear contact area growth with time that corresponds to an evolution effect and estimations based on this encompass the plagioclase data though the identification of actual mechanisms is not easy finally it is found that a little quartz 3 5 added to the plagioclase 60 62 pyroxene 35 mixture has a strong stabilizing effect leading to a transition from velocity weakening to velocity strengthening these results may help constrain the depth range of seismic slips on deep faults in the lower crust of gabbroic composition

rheology and strength of the eurasian continental lithosphere in the foreland of the taiwan collision belt constraints from seismicity flexure and structural styles 1 deformation in western taiwan is characterized by variable depth frequency distribution of crustal earthquakes which are closely connected with along strike variations of tectonic styles thin or thick skinned around the peikang high a major inherited feature of the chinese margin to fit the calculated high crustal geotherm and the observed distribution of the crustal seismic activity a qz diorite and granulite composition for the upper and the lower crust is proposed we then model the plate flexure through te estimates using brittle elastic ductile plate rheology flexure modeling shows that the best fit combination of te boundary condition is for thrust loads acting at the belt front the calculated te vary in the range of 15 20 km these values are primarily a reflection of the thermal state of the rifted chinese margin inherited from the oligocene spreading in the south china sea however other mechanical properties such as the degree of crust mantle coupling and the thickness of the mechanically competent crust and mantle are considered south of the peikang high flexure modeling reveals lower te associated with thinner mechanically strong layers variable stress strain distribution associated with a higher degree of crust mantle decoupling is examined to explain plate weakening we first show that plate curvature cannot easily explain strength reduction and observed seismic activity additional plate boundary forces arising from the strong coupling induced by more frontal subduction of a buoyant crustal asperity i e the peikang high with the overriding plate are required favorably oriented inherited features in the adjacent tainan basin produce acceleration of strain rates in the upper crust and hence facilitate the crust mantle decoupling as attested by high seismic activity and thick skinned deformation the relative weakening of the lower crust and mantle then leads to weaken the lithosphere by contrast to the north more oblique collision and the lack of inherited features keep the lithosphere stronger this study suggests that when the eurasian plate enters the taiwan collision tectonic inheritance of the continental margin exerts a strong control on the plate deformation by modifying its strength

variability of the mixed layer heat budget in the eastern equatorial atlantic during 2005 2007 as inferred using argo floats we examine the variability of the sea surface temperatures in the eastern equatorial atlantic during 2005 2007 by using argo profiling floats prediction and research moored array in the atlantic buoys and satellite in situ and atmospheric data sets the eastern equatorial atlantic characterized by shallow mixed layers all yearlong is divided into nine boxes of nearly equal surface area with respect to the dynamics and thermodynamics in this region monthly mixed layer heat budgets are computed in each box from 10 day argo profiles in all the boxes the net surface heat flux is one of the main causes of the seasonal evolution of sea surface temperatures for the 3 studied years the amount of short wave radiation penetrating through the base of the mixed layer and horizontal heat advection may locally contribute to the temperature variability while entrainment has a weaker contribution to balance the heat budget a residual term exists which includes all processes that cannot be calculated with observations as well as the possible errors in the other terms this residual is more intense in the cold tongue and the northern region and exhibits a clear seasonal cycle with minimum negative values in boreal summer and maximum values in winter this residual compares well with available observations of vertical turbulent mixing collected during etude de la circulation oceanique et des echanges ocean atmosphere dans le golfe de guinee campaigns 2005 2007 in the eastern equatorial atlantic when assuming that the residual is mostly associated with vertical turbulent mixing it can be conjectured that turbulent mixing is a significant cooling source in the cold tongue and north of the equator

metal depleted root zones of the troodos ore forming hydrothermal systems cyprus the cupriferous pyrite deposits of cyprus were precipitated from hydrothermal solutions derived by interaction of contemporaneous seawater with hot mafic rock at the ancient troodos spreading centre here we identify the zones in which this interaction took place the zones occur in the lower part of the sheeted dyke complex and within them 30 50 of the rock is made up of epidosite an epidote quartz rock replacing the dykes as sheets and pipes the epidosites contain abundant fluid inclusions which give trapping temperatures of 350 400 c or even higher and contain water normally near seawater in salinity zones of epidosite are elongate parallel to the strike of the sheeted dykes and are up to 1 km wide the rocks throughout these zones are strongly depleted in cu and zn and the metals removed are sufficient to supply the ore deposits in fact several large ore deposits lie along strike from zones of epidosite all of these features support the identification of the epidosites as the hydrothermal reaction zones the location of the epidosite zones immediately above the gabbros of the plutonic complex supports the hypothesis that the heat to drive the ore forming systems came from the underlying magma as is also likely for modern black smoker springs

the intermediate depth circulation of the western south atlantic the subsurface oceanic circulation is an important part of the earth climate system subsurface currents traditionally are inferred indirectly from distributions of temperature and dissolved substances occasionally supplemented by current meter measurements neutrally buoyant floats however now enable us to obtain for the first time directly measured intermediate depth velocity fields over large areas such as the western south atlantic here our combined data set provides unprecedented observations and quantification of key flow patterns such as the subtropical gyre return flow 12 sv 1 sverdrup 10 6 m 3 s 1 its bifurcation near the santos plateau and the resulting continuous narrow and swift northward intermediate western boundary current 4 sv this northward flowing water passes through complex equatorial flows and finally enters into the north atlantic

salinity of oceanic hydrothermal fluids a fluid inclusion study abstract an extensive microthermometric study of quartz epidote plagioclase anhydrite and sphalerite hosted fluid inclusions from ophiolitic semail oman and trinity california ophiolites and oceanic east pacific rise hydrothermal vents gorringe bank odp leg 111 hole 504b crust has been carried out in order to constrain a model accounting for wide salinity variations measured in the oceanic hydrothermal fluids recorded salinities in fluid inclusions vary between 0 3 and 52 wt nacl eq however more than 60 of the mean standard deviation salinities of the samples are within the range 3 2 0 3wt nacl eq microthermometric error and the mean salinity of all fluid inclusions without the brines is 4 0 wt nacl eq with a standard deviation of 1 6 wt nacl eq whereas most samples display slightly higher salinities than seawater several samples exhibit very high salinities more than two times that of seawater these high salinities are restricted to the plagiogranites semail and trinity ophiolites which mark the top of the fossil magma chamber in the transition zone between the plutonic sequence and the sheeted dyke complex the fluid inclusion population studied in the plagiogranites is characterized by the occurrence of four major fluid inclusion families 1 low to medium salinity liquid vapor fluid inclusions which homogenize into the liquid phase 2 low salinity liquid vapor fluid inclusions with pseudocritical homogenization 3 low to medium salinity liquid vapor fluid inclusions which homogenize into the vapor phase and 4 high salinity liquid vapor halite fluid inclusions which homogenize into the liquid phase by halite dissolution and exhibit salinities as high as 52 wt nacl eq these fluid inclusion families are interpreted as resulting from phase separation occurring in hydrothermal or magmatic fluids within the transition zone between the hydrothermal system and the magma chamber at temperatures higher than 500 c very low salinities less than half that of seawater have been found only in one dioritic sample from the gorringe bank mineralogical and petrological data from the semail ophiolite shows the absence of cl rich minerals furthermore hydration of the crust although very important cannot account for the large salinity variations thus the large salinity variations measured are interpreted as resulting from phase separation and generation of brine rich fluids at the top of the magma chamber this phase separation and subsequent phase segregation and brine accumulation may result in a double diffusive convection of the fluids in the hydrothermal system

transient modulation of kuroshio upper layer flow by directly impinging typhoon morakot in east of taiwan in 2009 this study deals with the modulation of the kuroshio upper layer flow kulf in response to the passage of typhoon morakot in 2009 using regional oceanic modeling system roms and in situ measurements from argos drifters and argo floats the analysis of the simulated current fields near the typhoon track revealed an intermittency phenomenon of the kulf which was almost shut down for at least 6 hours the process begun 2 days prior to the approach of typhoon center due to blockage of the kulf by the steadily northerly winds and lasted for more than 2 days simultaneously shifting the kuroshio main stream kms path when the morakot gradually moved closely to the kuroshio the kms shifted vertically from the surface layer to deeper layer of 50 100 m depth and the maximum current speed in the kms decreased from more than 1 3 m s 1 to less than 1 1 m s 1 when the morakot center approached about 100 km to the original position of the kuroshio the kulf spread eastward for 1 5 degrees at 24 n when the morakot center moved to the original position of the kms the kuroshio abruptly rushed with a maximum speed near 1 4 m s 1 meanwhile an offshore cool jet originating from southeastern tip of taiwan was generated and extended northward along the kuroshio in the cool jet the lowest temperature reached about 5 c lower than the ambient waters modeled current variations and the cool jet during the morakot passage were validated by in situ measurements

observations of open ocean deep convection in the labrador sea from subsurface floats abstract the occurrence and extent of deep convection in the labrador sea in winters 1996 97 and 1997 98 is investigated from measurements of over 200 neutrally buoyant subsurface profiling autonomous lagrangian circulation explorer palace and sounding oceanographic lagrangian observer solo floats in addition to providing drift velocity data and vertical profiles of temperature and salinity 55 floats are equipped with vertical current meters vcms time series of vertical velocity derived from measured pressure and vertical flow past the float and temperature are obtained from the vcm floats mixed layer depths estimated from profile measurements indicate that convection reached depths greater than 1300 m in 1997 but no deeper than 1000 m in 1998 deep mixed layers were concentrated in the western basin although a number of deep mixed layers were observed southwest of cape farewell and also north of 60 n the highest variance in vertical velocity and the lowest mean temperatures were found in t

deep cross equatorial flow in the atlantic measured with sofar floats neutrally buoyant sofar floats at nominal depths of 800 1800 and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the atlantic near 6 n and at several sites near 11 n as well as along the equator trajectories at 1800 m show a swift 50 cm s narrow 100 km wide southward flowing deep western boundary current dwbc extending from 7 n to the equator the average transport per unit depth in the dwbc was estimated to be 13 8 103 m2 s coupling this value with mean velocities measured in the dwbc by current meters gave a volume transport of 15 106 m3 s between depths of 900 m and 2800 m approximately 6 106 m3 s recirculated northward between the dwbc and the mid atlantic ridge leaving 9 106 m3 s as cross equatorial transport no obvious dwbc nor swift equatorial current was observed by the 3300 m floats a low mean velocity at this depth lay between f 11 and higher velocity cores above and below the 1800 m trajectories also suggest that at times february march 1989 the north atlantic deep water in the dwbc turned eastward and flowed along the equator and at other times august september 1990 the dwbc crossed the equator and continued southward the velocity near the equator calculated by grouping floats in a box along the equator was eastward at 4 1 cm s from february 1989 to february 1990 and westward at 4 6 cm s from march 1990 to november 1990 thus the amount of cross equatorial flow in the dwbc appeared to be linked to low frequency variability of the structure of the equatorial current system floats in antarctic intermediate water at 800 m revealed a northwestward western boundary current although flow patterns were complicated three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm s six 800 m floats drifted eastward along the equator between 5 s and 6 n at a mean velocity of 11 cm s one reached 5 w in the gulf of guinea suggesting that the equatorial currents at this depth extended at least 35 40 along the equator three of these floats reversed direction near the end of the tracking period

formation of an active thrust triangle zone associated with structural inversion in a subduction setting eastern new zealand 1 we analyze a thrust triangle zone which underlies the continental shelf of hawke bay eastern new zealand within the hikurangi subduction margin this triangle zone differs from many other examples in that it is active 90 km from the leading edge of the overriding plate and formed due to polyphase deformation involving opposed dipping thrust duplex and backthrust with the later structure forming in response to inversion of an extensional graben the component structures of the zone mainly developed sequentially rather than synchronously high quality marine seismic reflection lines tied to well and seabed samples reveal the three dimensional structure of the zone together with its 25 myr evolution and late quaternary activity the triangle zone occurs in the lateral overlap between a stack of nw dipping blind thrusts and a principal backthrust the kidnappers fault the nw dipping thrusts initiated in the early middle miocene during the early stages of subduction with subsequent thrust duplex formation producing major uplift and erosion in the late miocene early pliocene the active backthrust formed during the late miocene to early pliocene as a thin skinned listric extensional fault confined to the cover sequence structural inversion of the extensional fault commenced in the early middle pliocene produced the backthrust and marks the formation of the thrust triangle zone the thrust duplex and backthrust accrued strain following inversion however the later structure accommodated most of the surface deformation in the quaternary section balancing of the triangle zone together with a detailed analysis of reverse displacements along the backthrust reveal spatial and temporal variations of strain accumulation on the two principal components of the zone although the formation of the triangle zone is strongly influenced by regional tectonics of the subduction system these variations may also in part reflect local fault interaction for example high quaternary displacement rates on the backthrust accounts for 70 of the displacement loss that occurs on the southern segments of the overlapping lachlan fault understanding the tectonic evolution of such complex polyphase thrust triangle zones requires the preservation of growth strata that record sequential deformation history in the absence of such data synchroneity of opposed dipping thrusts in triangle zones cannot be assumed

processes of brine generation and circulation in the oceanic crust fluid inclusion evidence from the troodos ophiolite cyprus detailed temporal thermal and compositional data on aqueous fluid inclusions from a suite of plutonic and diabase samples from the troodos ophiolite cyprus provide the first documentation that generation of high temperature brines may be common at depth in the oceanic crust anastomosing arrays of fluid inclusions in rocks of the upper intrusive sequence record episodic fracturing events the earliest fracturing event at temperatures 450 600 c resulted in entrapment of brine rich aqueous fluids with salinities of 36 61 wt nacl equivalent homogenization of the brine inclusions by haute dissolution the virtual absence of vaporrich fluid inclusions throughout the upper level plutonic sequence and the restriction of brine inclusions to the most evolved plutonic rocks suggests that exsolution of brines off of the late stage gabbro and plagiogranite melts played a significant role in generating the quartz hosted high salinity inclusions cooling of the fluids during pulses of fluid migration associated with episodic fracturing events resulted in entrapment of the brines in the deep seated high temperature portion of the hydrothermal system in localized areas the high temperature brines nacl kcl cacl2 caused extreme alteration of the plagiogranite bodies and in the formation of podiform epidosites arrays of low temperature low salinity fluid inclusions which in some samples crosscut fractures dominated by brine inclusions indicate downward propagation of a cracking front subsequent to collapse of the high temperature magmatic system resulting in penetration of seawaterlike fluids into the plutonic sequence at temperatures 200 400 c hydration reactions under greenschist facies conditions or limited mixing with brine rich fluids may have resulted in salinity variations from 70 below to 200 above seawater concentrations temperatures and compositions of the low salinity inclusions are similar to those found in stockwork systems beneath troodos ore deposits and to those of fluids exiting active submarine hydrothermal vents at mid ocean ridge spreading centers the low temperature fracture networks may represent an extensive deep seated feeder system which coalesced to form zones of concentrated hydrothermal upflow