seasonal variability of sea surface height in the south china sea observed with topex poseidon altimeter data topex poseidon altimeter measurements along 16 ground tracks in the south china sea from november 1992 to october 1997 were used to observe the seasonal variability of sea surface height ssh in winter november december january and february the ssh images are generally characterized by a sea surface tilting downward toward the east high sea levels on the western side of the sea have a little monthly change and a low minus sea level peak is centered in the northeastern deep basin in spring march and april a single high sea level peak hp centered at 14 n 114 e becomes a dominant feature in summer may june july and august the ssh images show a sea surface tilting downward toward the west the hp moves from 14 n 114 e in may to the northwest of luzon island in july low sea levels are centered in the offshore of the northern and southern vietnamese coast in fall september and october the appearance of an eastward low sea level jet in the western basin between 12 and 14 n constitutes a major feature of the ssh images these results are comparable with previous results and drifter measurements

interannual modulation of eddy kinetic energy in the northeastern south china sea as revealed by an eddy resolving ogcm interannual modulation of eddy kinetic energy eke in the northeastern south china sea ne scs is investigated based on outputs of an eddy resolving oceanic general circulation model between 1980 and 2014 the eke displays distinct interannual modulations with periods between 1 5 and 7 years the maximum peak to trough amplitude of the interannual modulation occurred during period 2004 2005 which was about 1 5 fold the time mean eke level further analysis suggested that interannual variability of eke in the ne scs is primarily modulated by the luzon strait transport lst during high eke years the lst increases corresponding to a strengthened kuroshio intrusion the strengthened kuroshio intrusion enhances the baroclinic instability of current in the ne scs and thus leads to a strong eke the reverse is true during low eke years when lst is smaller influences of enso and pacific mesoscale eddies on the interannual modulation of lst are also discussed in this study

south china sea isopycnal surface circulation this paper investigates the seasonal variabilities of the south china sea isopycnal surface circulations and of the kuroshio intrusion through the luzon strait using the u s navy s climatological temperature and salinity dataset public domain with 83 8 resolution by the p vector method the representative pattern is a persistent basin scale cyclonic circulation away from the surface and a seasonally varying circulation with a weak anticylonic gyre in the summer and a strong cyclonic gyre in the winter near the surface this pattern is consistent with a classical view of mean cyclonic circulation in large stratified lakes and semienclosed marginal seas by emery and csanady and with a recent numerical simulation using the navy s layered ocean model by metzger and hurlburt the computed monthly volume transport through the luzon strait is negative inflow all year round with a minimum value of 213 7 sv in february strongest intrusion and a maximum value of 21 4 sv in september weakest intrusion the annual mean transport is 26 5 sv intrusion

interannual variability of the kuroshio transport in response to the wind stress field over the north pacific its relation to the path variation south of japan we have investigated the interannual variability in the kuroshio transport focusing on the baroclinic response of the upper ocean to the long term variation of the wind stress field over the north pacific from 1961 to 1987 first temporal change of the kuroshio transport at the western boundary from 17 to 31 n has been estimated on the assumptions that the kuroshio is a baroclinic flow confined in the upper layer and that the effect of interior wind stress curl on the volume transport at the western boundary is transferred by nondispersive baroclinic rossby wave peak values in the estimated transport appear in its beginning region 17 21 n when or just before the kuroshio settles into a meandering state south of japan in 1975 1981 and 1986 these peaks are due to negative wind stress curl anomalies which are induced by the intensified trade winds in the central and eastern tropical north pacific on and just after an el nino event and in the western tropical north pacific months to years before the next el nino event such peaks are not found in the barotropic sverdrup transport in downstream regions i e in the east china sea and south of japan north of 23 n on the contrary the estimated transports through baroclinic and barotropic responses do not have such good correlation to the path variation temporal change in thermocline depths estimated from bathythermograph data clearly shows the westward propagations of positive anomalies by nondispersive baroclinic rossby waves at latitudes of the beginning of the kuroshio south of 21 n which is in phase with peaks of the kuroshio baroclinic transport at the western boundary on the other hand there are only the local propagations of the anomalies in the downstream regions as previous studies reported however it is emphasized that temporal change of the geostrophic transport in the east china sea 28 n is coincident with that of the baroclinic transport at the beginning of the kuroshio not with that at the same latitude a numerical experiment with a nonlinear reduced gravity model confirms that temporal changes of the transport in the east china sea and south of japan are due to the advective nonlinear effect of the kuroshio itself while the linear baroclinic response to the wind stress field is dominant in its beginning region

intraseasonal sst variations in the south china sea during boreal winter and impacts of the east asian winter monsoon present study documents the intraseasonal variability of sea surface temperature sst in the south china sea scs during boreal winter and its association with the east asian winter monsoon eawm variability in northern tropics the largest intraseasonal variability of sst during boreal winter is found in the scs with two localized regions of large standard deviation one extending westward from the luzon strait and the other extending southward from the coast of central vietnam correspondingly large intraseasonal variability in surface heat fluxes is observed in the above regions analysis shows that the formation of large intraseasonal sst anomalies in these regions is attributed largely to wind related surface latent heat flux changes with supplementary contribution from cloud related surface shortwave radiation changes wind induced ekman advection has a negative effect and the ekman upwelling pattern differs from the intraseasonal sst anomaly pattern the intraseasonal variations of sst in the scs display a close association with the east asian winter monsoon eawm change with a time lag of 3 5 days in a weak strong phase of the eawm decrease increase in surface wind speed and suppression enhancement in surface latent heat flux lead to intraseasonal sst warming cooling this intraseasonal sst signal displays a southward propagation with the sst change in northern scs leading that in southern scs by about 2 days a similar southward propagation is seen in surface wind speed and latent heat flux anomalies the southward propagation of cloud and shortwave radiation anomalies is limited to northern part of the scs

ice volume forcing of winter monsoon climate in the south china sea high resolution studies of a planktonic foraminifer core record from the south china sea scs 31kl 18 45 4 n 115 52 4 e water depth 3360 m reveal changes driven by ice volume forcings in the climate of the east asian monsoon in the western pacific marginal sea during the late quaternary the analyses of planktonic foraminifer faunal abundance data from the core indicate significant variations in the relative abundances of the dominant taxa over the past 100 000 years since the isotope stage 5 the transfer function estimates of faunal sea surface temperatures sst correlate well with a long term 104 105 years trend of global glaciation about 65 000 years ago there was an observable change in the mode of sst variability as many low latitude records have shown these findings suggest that the scs surface circulation and the east asian winter monsoon systems are mainly driven by variations in global glaciation levels the association of surface ocean cooling in the scs with global climatic events suggests that fluctuations in the strength of the east asian winter monsoon may be linked to shifts in the latitudinal position of the westerly winds and the siberian high pressure system

chronology and dynamics of a large silicic magmatic system central taupo volcanic zone new zealand the central taupo volcanic zone in new zealand is a region of intense quaternary silicic volcanism accompanying rapid extension of continental crust at least 34 caldera forming ignimbrite eruptions have produced a complex sequence of relatively short lived nested and or overlapping volcanic centers over 1 6 m y silicic volcanism at taupo is similar to the yellowstone system in size longevity thermal flux and magma output rate however taupo contrasts with yellowstone in the exceptionally high frequency but small size of caldera forming eruptions this contrast reflects the thin rifted nature of the crust which precludes the development of long term magmatic cycles at taupo 11 refs 4 figs 1 tab

unchanged nitrogen isotopic composition of organic matter in the south china sea during the last climatic cycle global implications the 15n of surface and down core sediments spanning the last 20 200 kyr from the entire south china sea scs ranges only from 3 0 to 6 5 with no correlation with discernible paleoclimatic oceanographic changes detailed profiles of the uppermost sediment column including fluff samples indicate a minor diagenetic overprint of 0 3 1 2 at the sediment water interface the absence of any correlation with reconstructed glacial interglacial changes in primary production terrigenous input and or sea level related basin configuration is attributed to a complete consumption of nitrate during primary production in this marginal basin during at least the last 140 000 years this in turn implies that the 15n of the nitrate used during primary production remained approximately constant during the last climatic cycle the proposed scenario infers an unchanged nitrogen isotopic composition of the western pacific subsurface nitrate between glacial and interglacial stages as well as during terminations and thus constrains proposed changes in the oceanic n inventory

the real southern basin and range mid to late cenozoic extension in mexico much of northern and central mexico underwent east northeast extension in the mid to late cenozoic this area constitutes a major but little recognized part of the basin and range province the extended region is bounded on the east by the laramide thrust front of the sierra madre oriental on the west the relatively unfaulted sierra madre occidental separates the extended area in central mexico from that around the gulf of california extension occurred as far south as what is now the trans mexican volcanic belt and in oaxaca south of the belt the basin and range province in mexico constitutes approximately half of the 19 x 10 5 km 2 of western north america that underwent mid to late cenozoic extension north northwest orientations of numerous epithermal vein systems indicate that east northeast extension began as early as 30 ma in areas north of the volcanic belt major episodes of faulting began at about 23 to 24 ma and 12 to 13 ma both in mexico and in the southwestern united states faulting was commonly accompanied by eruption of alkali basalts typical of intraplate rifting widespread quaternary fault scarps and alkali basalts indicate that extension continues to the present in the region north of the trans mexican volcanic belt in contrast the tectonics in and south of the belt are now probably related to subduction of the rivera plate contemporaneity of the 12 ma episode with early extension around the gulf of california attributed to pacific north american plate boundary reorganization suggests that extension is related predominantly to plate boundary effects the beginning of extension at 30 ma may be related to initial encroachment of the east pacific rise upon the trench that lay off western north america

nature and timing of faulting and synextensional magmatism in the southern basin and range central eastern durango mexico the nazas area in the central eastern portion of the state of durango is within the poorly studied southern half of the basin and range province in mexico at nazas high angle normal faults that cut part of the mid tertiary volcanic sequence strike between n 20 and 70 w with 40 of them between n 40 and 50 w tilting of faulted blocks varies from 5 to 35 to the northeast most commonly around 25 ne a few blocks are tilted to the southwest as much as 25 fault offsets range from 40 m to nearly 300 m the earliest faulting occurred between 31 and 29 ma before the emplacement of mid tertiary ash flow tuffs had ended the santa ines formation a widespread fanglomerate was deposited after the earliest faulting episode and is overlain by 24 to 20 ma alkalic basalt flows although not cut by faults the flows are adjacent to or cover normal faults some of the mapped faults could have been coeval with basalt eruption as is the case in trans pecos texas where alkalic basalt having similar age and composition to that in the nazas area erupted contemporaneously with normal faulting the nazas alkalic basalt also has similar age and stratigraphic position as but is compositionally distinct from the southern cordilleran basaltic andesite scorba a widespread mafic suite in southwestern north america that has been linked to regional extension

gap leaping kuroshio and blocking westward propagating rossby wave and eddy in the luzon strait 1 based on analysis of both observational data and data assimilation model product it is shown that there exists a gap leaping path of the kuroshio in the luzon strait numerical results of two sets of hybrid coordinate ocean model twin experiments indicate that bottom topography and islands in luzon strait exert control of kuroshio s gap leaping behavior especially existence of sharp northeast cape of philippine island is one of the most important factors for the gap leaping kuroshio path in model simulation corresponding to the gap leaping kuroshio there is steep westward shoaling of thermocline in luzon strait the enhanced upper layer stratification in south china sea due to westward shoaling thermocline results in strong zonal potential vorticity pv gradient one order higher than s induced planetary pv gradient and pv isolines are always parallel to the gap leaping path of the kuroshio this pv front acts as a dynamic barrier in the luzon strait blocking the westward propagating rossby waves and eddies from pacific this blocking effect is verified through sea surface height anomaly spectrum analysis radon transform based feature tracking method and eddy identification and tracking method numerical twin experiments demonstrate from another point of view that the gap leaping kuroshio can efficiently block the westward propagating rossby wave and eddy energy while the fluctuating kuroshio is less efficient for blocking

upper ocean currents around taiwan abstract current velocity measured by shipboard acoustic doppler current profiler sb adcp during 1991 2000 was used to study the upper ocean the composite and moored currents revealed a branch of the kuroshio that intruded steadily and persistently into the south china sea part of the intruded kuroshio flowed out of the south china sea through the northern luzon strait and re united with the main stream kuroshio the kuroshio had two velocity maximum cores southeast of taiwan but gradually combined into one as the kuroshio flowed north the kuroshio was deflected by the i lan ridge east of taiwan and the zonal running shelf break northeast of taiwan at the shelf break the kuroshio split with one branch intruding onto the shelf west of the luzon strait the kuroshio intruded into the south china sea some water flowed northward into the taiwan strait and re joined the kuroshio currents in the taiwan strait flowed primarily in a northward direction except for the southward current near the coast of mainland china north of the taiwan strait a branch of the northward flow followed the northern coast of taiwan to join the kuroshio the composite current varied consistently from season to season there was generally poor correlation between currents and local winds especially in the deep water regime remote forces were important in the currents around taiwan

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

basaltic volcanism and extension near the intersection of the sierra madre volcanic province and the mexican volcanic belt three groups miocene pliocene and pleistocene off oceanic type basalts associated with normal faulting have been identified in an area surrounding the city of guadalajara mexico although most basalts within these groups have compositional characteristics of an asthenospheric source each group is also associated with lavas that have subduction related traits the first group the san cristobal plateau basalts has a minimum volume of 1 800 km 3 of predominantly alkali olivine basalt and lesser basaltic andesite and fills a pre existing extensional basin of unknown configuration 10 m y ago the relatively rapid eruption of these basalts along with their volume structural association and chemistry suggest an upwelling mantle plume beneath the guadalajara region this region may be the earliest indication of the separation of the jalisco block from north america the second basalt group the guadalajara basalts consists of small volumes of porphyritic basalts and basaltic andesites 3 3 5 0 ma in age that outcrop near the northern outskirts of guadalajara and near the town of hostotip aquillo to the northwest the youngest basalts in the guadalajara area are the 0 4 1 4 ma santa rosa suite of basalts hawaiites mugearites close to the contemporary 0 2 ma andesitic central volcano v tequila these either flowed from nearby cinder cones toward the rio santiago canyon or erupted in the canyon to dam the river the flat lying tertiary 23 27 ma ash flows of the sierra madre volcanic province that lie to the north of guadalajara are faulted north northeast into horsts and grabens that in one case can be dated as being older than 21 8 ma this fault trend has been reactivated closer to guadalajara as normal faults 200 to 300 m displacement cut the miocene plateau basalts but are hidden by a cover of younger volcanic rocks close to the city also hidden by the young volcanic succession there is the north west southeast fault zone that extends to the gulf of california as the tepic zacoalco graben system faulting of this zone is well displayed in the region of the santa rosa dam in the santiago canyon northwest of guadalajara two styles of faulting are found there an older 1 ma 3 has been approximately north northeast for at least 4 m y characteristic of the mexican basin and range province

recent planktonic foraminifers and their relationships to surface ocean hydrography of the south china sea the relative abundances of recent planktonic foraminifers from surface sediments on the sea floor reveal relationships to hydrographic variables of the ocean surface to investigate whether the evect of the vertical structure of oceanic upper layer environments is important to the changes in the abundance of planktonic foraminifers a set of 173 coretop faunal data from modern south china sea scs surface sediments was compiled for comparison with direct observations of sea surface temperature sst and the depth of thermocline dot the coretops used in this study are distributed within the area of 25 n and 105 125 e with water depths ranging from 68 to 3990 m the relationships between the abundances of planktonic foraminifer species and hydrographic variables were examined using simple correlation analyses in the analyses four groups of planktonic foraminifers with diverent ecological preferences were identified group i faunas primarily reliant on dot with positive correlations n dutertrei group ii faunas reliant on both sst and dot showing negative correlations with sst and positive correlations with dot g glutinata p obliquiloculata and g bulloides group iii faunas reliant on both sst and dot showing positive correlations with sst and negative correlations with dot including g sacculifer g menardii and g aequilateralis and group iv faunas reliant on both sst and dot with positive correlations g ruber though each of these species displays selectivity of ecological controls these results indicate that in the scs correlations between faunal abundances of planktonic foraminifers and sst or dot are about equally significant this study also indicates a need for re evaluating the relationships between planktonic foraminifer abundances and many other important hydrographic variables in the upper layer of oceans on a more regional scale 1998 elsevier science b v all rights reserved

assimilating altimetric data into a south china sea model sea surface heights from the topex poseidon altimeter are assimilated into a three dimensional primitive equation model to derive the circulation in the south china sea with data assimilation the model resolves not only the basin wide circulation but also a dipole off vietnam and a low high feature near the luzon strait mesoscale features are missing in the simulation without data assimilation because of poor resolution in the wind field and inadequate knowledge of the transport through the luzon strait compared to the case without data assimilation data assimilation reduces the root mean square error between the simulated and observed sea surface heights by a factor of 2 3 circulation derived from data assimilation under climatological conditions is contrasted with that during el nino in the normal winter of 1993 1994 flow at 50 m depth is strong and cyclonic flow at 900 m depth is cyclonic as well the deep cyclone persists into the following summer during the 1994 1995 el nino winter features in the flow field at 50 m depth either weaken or disappear and circulation at 900 m depth is anticyclonic in the summer of 1995 the dipole and the eastward jet off vietnam at 50 m depth are missing and the anticyclonic circulation at 900 m depth persists temperature at 65 m shows significant warming from fall 1994 to summer 1995 a weakened flow field and warming in the upper ocean are consistent with findings from earlier el nino events

toward establishing a maritime proxy record of the east asian summer monsoons for the late quaternary abstract an astronomically tuned late quaternary planktic foraminiferal 18o record of site md972142 12 41 33 n 119 27 90 e 1557 m water depth in the southeastern south china sea was established the difference in 18o between md972142 and odp792 of the sulu sea is regarded as a maritime proxy of the summer monsoon intensity over the south china sea and southeast asia the profile of this maritime proxy matches well with the summer monsoon index obtained from the terrestrial record of louchuan central chinese loess plateau the amplified planktic 18o signals of the south china sea relative to the sulu sea record are partly caused by the changing intensities of the east asian monsoons at the glacial interglacial time scale throughout the late quaternary

area balance depth to detachment and strain in extension a new lost area cross section construction and validation technique is based on the area balance of a graben system formed above a detachment area balance requires that the area displaced below the original regional level of each bed in a graben the lost area be balanced by the displaced area at the boundary of the system given by the product of the displacement times the depth to detachment this relationship is a straight line on a plot of lost area versus depth the slope of the line is the displacement and the depth intercept is the depth of the detachment in general beds within the graben system undergo both visible and homogeneous layer parallel extension the homogeneous component can be determined from the width of the graben system the lost area and the depth to detachment conversely the detachment depth may be calculated from the total layer parallel extension and the lost area the techniques are illustrated by application to models and to very well constrained natural examples an earthquake induced slope failure in alaska and kilometric sized horsts and grabens in the black warrior foreland basin of alabama a half graben without footwall uplift and a full graben are the same on a lost area diagram a half graben with footwall uplift linked to the hanging wall extension requires that both the hanging wall and footwall areas be included to determine the detachment depth and displacement all the models show layer parallel extension e in the upper levels that are less than the crustal scale strain

reply to comments on nd sr isotopic compositions of lower crustal xenoliths evidence for the origin of mid tertiary felsic volcanics in mexico by k l cameron and j v robinson cameron and robinson question the meaning of model nd ages obtained by ruiz et al 1988a for xenoliths from many localities on the easternmost edge of the sierra madre occidental smo this is a legitimate concern because the age of the xenoliths has direct bearing on the genesis of the voluminous silicic ignimbrites of the smo ruiz et al 1988b the source of these volcanics is the underlying and most important issue cameron and co workers have to be congratulated for their pioneering work on the volcanics of the smo besides the careful field work and k ar dating by f w mcdowell s group at texas summarized in mcdowell and clabaugh 1979 and p e damon at arizona i e damon et al 1981 very little petrochemical data existed for this large volcanic province until cameron started working on the problem of the origin of the silicic volcanics in the late 70 s after detailed field and petrologic studies in the batopilas area bagby 1979 cameron et al 1980 lanphere et al 1980 cameron and hanson 1982 cameron and co workers concluded that most of the smo volcanic felsic in chihuahua was produced by crystal fractionation of mantle derived basalt with little or no crustal assimilation contamination or any other crustal interaction in a more recconnaissance type study of volcanic rocks from various places of the sierra madre occidental in northern mexico see figure 1 of cameron and cameron 1985 it was concluded that the parental mantle material needed to produce the silicic volcanic rocks of the smo had sr and nd isotopic values near chur as cameron and co workers admitted their studies were hampered by a complete lack of knowledge of the mexican lower crust the suggestion was however that the lower crust and upper mantle would be sufficiently different in their isotopic and some chemical compositions and therefore that any interaction between mantle derived and the lower crustal materials would be evident in the final chemical and isotopic compositions of the

mesoscale eddies cases study at xisha waters in the south china sea in 2009 2010 analyzing the observed currents at xisha 110 3899 degrees e 17 1038 degrees n during may 2009 to may 2010 it is found that the kinetic energy has significant mesoscale variability and each peak responds to large positive negative ocean surface current curl caused by mesoscale eddies compared the kinetic energy with the wind stress work and the pressure work it is also found that the barotropic pressure work which is mainly contributed by the sea surface height ssh corresponding to the mesoscale eddies behaves like the kinetic energy the contribution of the mesoscale eddies to the kinetic energy can be up to 90 sometimes and reach deep level every time using the satellite altimeter data the paths of mesoscale eddies contributing to the kinetic energy variability are traced back in the winter half of the year the mesoscale eddies propagating along the northern south china sea shelf or across the basin from the west of the philippines toward xisha arrive at xisha influencing the kinetic energy in the summer half of the year the mesoscale eddies are mainly from the south which were shed from the vietnam coast current and the cause for eddy shedding may be related to the relaxation of the ekman transport anomalies

observations of inflow of philippine sea surface water into the south china sea through the luzon strait abstract velocity observations near the surface made with argos satellite tracked drifters between 1989 and 2002 provide evidence of seasonal currents entering the south china sea from the philippine sea through the luzon strait the drifters cross the strait and reach the interior of the south china sea only between october and january with ensemble mean speeds of 0 7 0 4 m s 1 and daily mean westward speeds that can exceed 1 65 m s 1 the majority of the drifters that continued to reside in the south china sea made the entry within a westward current system located at 20 n that crossed the prevailing northward kuroshio path in other seasons the drifters looped across the strait within the kuroshio and exited along the south coast of taiwan during one intrusion event satellite altimeters indicated that directly west of the strait anticyclonic and cyclonic eddies resided respectively north and south of the entering drifter track the surface currents measured by the crossing drifters were much

lagrangian observations of surface flow patterns in the vicinity of taiwan two satellite tracked surface drifters were launched off the southwestern coast of taiwan on october 7 1997 both traveled northward along the taiwan strait ts and into the seas north of taiwan lasting 20 and 53 days respectively from the drifter trajectories their rotary spectra and satellite infrared imagery several oceanic features have been detected and are discussed in this paper our results indicate that in the southern and central portions of the ts the floats followed a northward flow with a mean speed of 30 50 cm s upon reaching the northwestern taiwan coast the trajectories were strongly affected by the semidiurnal tides and interacted with the kuroshio water in the southern east china sea the onset of the strong northeastern winter monsoon in early november decelerated the northward movement and eventually reversed the direction this process was accompanied by wind generated near inertial motion one drifter was then captured by a counterclockwise circulation of a cold dome at the continental shelf break northeast of taiwan finally the drifter was entrained by the mainstream of the kuroshio and flowed towards the northeast

stratigraphy and geochronology of the comondu group near loreto baja california sur mexico abstract upper oligocene to middle miocene volcanic and sedimentary rocks in the loreto region baja california sur are widely exposed and make up the comondu group as redefined here following mcfall the comondu group is part of a volcanic arc and forearc basin that formed along the northwestern margin of mexico regional to detailed scale mapping stratigraphic analysis and geochronology in a 10 20 km wide and 70 km long belt from the gulf escarpment to the coast near loreto reveal three main units in the comondu group and a composite thickness of 1 5 2 km 1 the lower clastic unit 30 19 ma contains 200 300 m of fluvial sandstone and conglomerate with probable local eolian deposits and numerous felsic tuffs and basalt flows that accumulated in a forearc basin 2 the middle breccia and lava flow unit 19 15 ma is up to 750 m thick and consists of massive andesite breccia that was deposited as proximal debris flows interbedded with minor andesite lava flows 3 the upper lava flow and breccia unit 15 12 ma consists almost entirely of up to 600 meters of andesite lava flows a few kilometers west of loreto that are part of a composite volcano north and south of loreto for up to 25 km the unit is composed of andesite lava flows and massive andesite breccia that formed from thick debris flows near that and other volcanic centers the three units of the comondu group in the loreto area correlated with the salto pelones and ricason formations of the bahia concepcion area the lower clastic unit of this study is time equivalent to the marine san gregorio el cien and isidro formations on the western and southern baja california peninsula the middle and upper units of the loreto area are the proximal equivalent to the type section of the comondu group near the village of comondu during deposition of the lower part of the comondu group the arc lay to the east on mainland mexico in the sierra madre occidental and then migrated to the position of the gulf of california at about 25 ma at 19 ma the proximal part of the arc migrated abruptly 50 km westward to approximately the position of carmen island and at 15 ma the arc once again stepped west forming eruptive centers along the coast near loreto until 12 ma also at 15 ma the proximal forearc region changed from aggradational to neutral or erosional such that no rocks of the upper unit are preserved in the gulf escarpment

flattening of the sea floor depth age curve as a response to asthenospheric flow the flattening of sea floor depths from the age dependence predicted by considering the cooling plate as a growing thermal boundary layer is a fundamental constraint on the evolution of oceanic lithosphere1 previous explanations for the flattening have included reheating from convective instabilities that form beneath lithosphere older than 80 myr ref 2 thermal rejuvenation of lithosphere that passes over stationary hotspots3 5 or a whole mantle flow forced by two converging plates6 we suggest here that the flattening of old ocean floors can perhaps best be explained as a dynamic phenomenon reflecting flow in asthenosphere underlying the oceanic lithosphere applying the model to the pacific plate we show that a solution for flow in an asthenosphere low viscosity channel which is consumed by plate accretion and the subduction of lithosphere at trenches and replenished by near ridge upwelling and near ridge hotspots generates the observed 1 km of sea floor flattening for asthenospheric viscosities of 2 1018 pa s and an absolute pacific plate motion of 100 mm yr 1 our model can also explain the asymmetric subsidence of the south american and african plates away from the mid atlantic ridge

regional dynamics of seasonal variability in the south china sea abstract dynamics of the seasonal cycle of sea surface height ssh in the south china sea scs are studied using observations as well as numerical and theoretical models seasonal variability of the scs is interpreted in light of large scale dynamics and rossby waves it is found that the seasonal cycle over most of the scs basin is determined predominantly by the regional ocean dynamics within the scs the ssh variability is shown to be forced mainly by surface wind curl on baroclinic rossby waves annual baroclinic rossby waves cross the basin in less than a few months leaving the upper ocean in a quasi steady sverdrup balance an anomalous cyclonic anticyclonic gyre is generated in winter summer by the anomalous cyclonic anticyclonic wind curl that is associated with the northeasterly southwesterly monsoon in addition surface heat flux acts to enhance the wind generated variability the winter surface cooling warming cools warms the mixed layer especially in the central scs reducing

multidecadal variations of the surface kuroshio between 1950s and 2000s and its impacts on surrounding waters based on the analyses of 59 year 1950 2008 surface geostrophic velocities the multidecadal changes of kuroshio from the eastern luzon to the southern japan are investigated result shows that the upstream kuroshio from the east of luzon to southern east china sea suffers much more obvious multidecadal changes except for the decade of 1980 the kuroshio east of luzon possesses a multidecadal tendency opposite to that east of taiwan besides 1980s the multidecadal change of kuroshio bordering taiwan is mainly governed by the eddy activity off the eastern taiwan while the wind stress curl plays a major role in the kuroshio in the east of luzon and in the luzon strait the wind stress induced ekman transport plays a secondary role in regulating the kuroshio east of luzon in addition the multidecadal fluctuation of kuroshio east of luzon also modulates the westward intrusion in the luzon strait instead the ekman transport dominated the whole upstream kuroshio area from the eastern luzon to the vicinity of taiwan during the exceptional decade of 1980 associated changes of water properties in the northern south china sea and southern east china sea are also ascribed to the multidecadal changes of surface kuroshio in the upstream area

spatial structure and temporal variability of the zonal flow in the luzon strait one year long full depth velocity measurements were used to examine the spatial structure and temporal variability of the zonal flow in the luzon strait lszf the observation revealed a renewed mean flow structure in the upper 2000 m layers the lszf was mostly westward in the intermediate layer 500 2000 m it was dominated by an eastward flow in the south but a westward flow in the north the volume transport across the observed section between 19 8 n and 21 2 n exhibited strong seasonal and intraseasonal variability on the seasonal time scale the upper layer transport showed a clear annual cycle strongest in january and weakest in june the intermediate layer transport also showed a semiannual cycle attaining its peaks troughs in january and june april and october on the intraseasonal time scale both the upper layer and intermediate layer transports showed significant energy peaks at about 60 and 10 30 days further analysis indicated that the 60 day variability might be attributed to the impinging mesoscale eddies from the pacific while the 10 30 day variability appeared to obtain its energy from local intraseasonal wind forcing and baroclinic instability of the background current the 10 100 day upper layer and intermediate layer transport variabilities were highly anticorrelated suggesting a baroclinic nature of the intraseasonal variabilities of the lszf

water mass and throughflow transport variability in the taiwan strait 1 variability of water mass and throughflow transport in the taiwan strait are analyzed using strait wide conductivity temperature depth 1985 2003 and sectional acoustic doppler current profiler 1999 2001 data results from a cluster analysis temperature salinity diagrams and direct transport calculations indicate that the strong northeast monsoon drives the brackish mixed china coastal water into the northern strait and hinders the northward intruded saline kuroshio branch water kbw in the southeastern strait from december to january the mean throughflow transport across the central strait is about 0 1 sv southward during this period thus supporting previous observations that there is no persistent northward flowing current throughout the strait in winter the weakening of the northeast monsoon in february march however emancipates the kbw to intrude northward into the east china sea ecs in june the increase in this northward transport accompanied by the decrease in the westward intrusion of kuroshio through the luzon strait leads to the replacement of the kbw by the less saline south china sea water scsw the northward transports ranging from 1 16 to 2 34 sv between march and august yield 0 131 0 238 1015 w and 53 33 81 74 106 kg s of temperature and salt transports respectively toward the ecs the inception of the northeast monsoon in october marks both the change of water mass from fall to winter patterns and the decrease of the northward throughflow transport our results also reveal that the subsurface kbw and scsw remain consistent throughout the observation periods between 100 and 200 m and below 200 m depths respectively in the southeastern strait

origin and tectonic interpretation of multiple fault patterns abstract it is shown that in two dimensional and three dimensional deformation accommodated by fracture the symmetry of the fault patterns is an intrinsic attribute because it reflects the symmetry of either stress or strain tensors the deformation accommodated by sliding along pre existing planes when there is kinematic interaction between that planes forms multiple fault pattern and multiple slickenline sets during a single deformation event these fault patterns have no restrictions with respect to symmetry number of fault sets or fault orientation the kinematic analysis developed here shows that an interacting system is formed by two cross cutting faults and three slickenlines one slickenline must be parallel to the intersection line between the planes also it is demonstrated that the slickenlines generally do not correspond to the shear stress solution on the planes thus the interaction between planes does not satisfy the assumption of parallelism between shear stress and slip vector we conclude that the inversion methods to calculate paleostress tensors can lead to erroneous interpretations in structurally complex zones with many pre existing planes of weakness we propose four possibilities to form multiple fault patterns 1 two or more events of faulting obeying coulomb s law with a change of orientation of the principal stresses in each event 2 reactivation of non interacting planes according to the bott 1959 model 3 one three dimensional strain event that obeys the slip model this mechanism will form an orthorhombic four fault pattern and two slickenline sets in a single strain event and 4 one or more events obeying the interacting block model proposed here with or without rotation of the principal stresses we propose the last origin as the most common in continental regions

plate interactions control middle late miocene proto gulf and basin and range extension in the southern basin and range middle late miocene proto gulf 12 6 ma extension around the gulf of california gulf extensional province is commonly interpreted as resulting from partitioning of oblique pacific north american plate motion into strike slip displacement along the margin and east northeast extension perpendicular to the margin within the north american plate we propose that this mechanism also applies to kinematically similar predominantly east northeast extension that occurred at the same time throughout the southern basin and range province from southern arizona and new mexico to the trans mexican volcanic belt new field and 40ar 39ar data in sinaloa and durango confirm that this episode of extension occurred on the mainland side of the gulf and in the basin and range east of the sierra madre occidental which is generally considered the eastern margin of the gulf extensional province published data indicate the middle late miocene episode also occurred across the northern and southern ends of the sierra madre where the gulf extensional province connects with the basin and range 1 from central sonora into southern arizona and new mexico and 2 from nayarit into central mexico north of the trans mexican volcanic belt this episode appears to have avected an area that continues to the eastern edge of the basin and range province in texas and san luis potosi recognition that this episode of extension avected the entire southern basin and range resolves the discrepancy between the amount of extension calculated based on plate reconstructions and that based on field data within the gulf extensional province alone published plate reconstructions require 160 to 110 km of east northeast extension between 12 and 6 ma if taken up solely within the gulf extensional province this would have generated 66 to 78 extension which is much greater than observed spread across the entire southern basin and range it requires only 20 total extension which is more consistent with observations of cumulative extension between 12 and 6 ma extension was partitioned into the gulf extensional province because 1 it lies between two stable batholith belts mesozoic peninsular ranges on the west and mid tertiary sierra madre occidental on the east that resisted extension and 2 the gulf was thermally weakened by immediately preceding arc magmatism extension in the main basin and range province in part probably avoided the relatively strong batholithic crust of the sierra madre occidental 2000 elsevier science b v all rights reserved

groundwater seawater interactions off the coast of southern taiwan evidence from environmental isotopes abstract we have conducted detailed hydrochemical surveys off the pingtung plain coast sw taiwan using environmental isotope compositions d 18 o 13 c dic tritium and 14 c as the main tracers to investigate groundwater seawater interactions in the region the 18 o values of seawater in this area show significant variability with heavy isotope enrichment relatively to groundwater the d and 18 o data also confirmed that submarine groundwater discharge sgd originated from meteoric water and were mixed with seawater due to an overdraft of groundwater seawater has intruded inwardly through the offshore outcrops for both the unconfined and confined aquifers at a depth of 300 m however 18 o depleted layer is found along deep parts of kaoping canyon this result provides evidence for sgd in this region this phenomenon is also reflected in depleted 13 c dic and lower 14 c values in deep canyon water than in adjacent seawater and indicating that the discharge zone extends over a considerable distance to the offshore area 25 km based on these three parameters 18 o 13 c dic and 14 c we used two end member mixing model to estimate that fresh submarine groundwater constitute the submarine fresh groundwater contributed about 3 and the estimated submarine fresh groundwater discharge was calculated as 4 5 10 9 m 3 per year this result is comparable with groundwater annual loss in the pingtung plain as documented by the isotopic composition of the collected samples detailed results show that sgd in the pingtung coastal zone raises a potential environmental concern and provides implication for the management of groundwater resource in the region

do microplates in subduction zones leave a geological record active microplate boundaries in ocean continent subduction zones may induce deformation of the overlying plate and spatial or geochemical variations in the volcanic arc we discuss two modern cases the first is the south gorda juan de fuca plate boundary in the cascadia subduction zone where there is little or no effect on the overriding plate and the oceanic plate takes up much of the deformation the second case is the cocos rivera plate boundary in the middle america trench where the overlying colima graben contains substantial deformation in a zone extending from the trench to the volcanic arc and the sub duction related volcanism is spatially and geochemically complex we apply these observations to boundaries of the arguello monterey guadalupe and magdalena microplates which existed in the subduction zone west of baja california at various times from 20 to 12 5 ma the past positions of these boundaries relative to baja california are constrained by global plate reconstructions closure of the gulf of california and an estimate of extension in the mexican basin and range province existing regional mapping and our additional reconnaissance mapping show that paleocene to eocene fluvial and marine sedimentary rocks south of ensenada along the western baja california peninsula and eastward to the mid miocene volcanic arc are undeformed limited available data reveal no major spatial or geochemical variations in the mid miocene volcanic arc that might correlate with the past positions of the microplate boundaries thus these microplate boundaries had little to no effect on the overriding continental plate the nature of guadalupe and magdalena interactions with north america may have been closer to the south gorda juan de fuca example with possible internal deformation of the microplates the monterey and arguello microplates may have behaved like the modern explorer plate with largely strike slip motion relative to north america during their last stages of existence tectonic patterns similar to these examples may be expected from other plate boundaries where a plate is fragmenting as it enters a subduction zone e g the aluk plate in the trench beneath west antarctica in early tertiary time whether these microplates subsequently become attached to the overriding continental plate or to a larger oceanic plate and whether this causes deformation in the region of the former subduction zone may depend on the velocities of the nearby major plates and the relative orientations of the microplate boundaries

ignimbrite flare up and deformation in the southern sierra madre occidental western mexico implications for the late subduction history of the farallon plate geologic mapping and structural data for the southern part of the smo demonstrating that most of this volcanic province was built in two episodes of ignimbrite flare up in oligocene 31 5 28 ma and early miocene 23 5 20 ma time and that extensional deformation occurred mostly before the transfer of baja california to the pacific plate extensive ignimbrite successions with 40 ar 39 ar ages clustering at 23 and 21 ma cover most of the southern smo thus correlating in age with ignimbrites exposed in southern baja california and central mexico grabens with a 020 to n s orientation developed in the east almost concurrently with this volcanic episode half grabens and nnw striking listric normal fault systems formed at the end of middle miocene as far as 150 km from the present coast a belt of left lateral transpressional structures formed along the southern boundary of the smo during the same period we link these magmatic and tectonic events to the evolution and dynamics of the farallon and north america plates during the miocene particularly we propose that a first detachment of the lower part of the farallon plate in early miocene time produced a transient thermal event and partial melting of the crust via mafic underplating middle miocene extension would be related to a second detachment event resulting from the slowing subduction that preceded the final capture of the magdalena microplate by the pacific plate at 12 5 ma transpression at the southernmost end of the smo occurred along the inland projection of the magdalenacocos plate boundary and may be explained by a difference in subduction rate and by a temporal convergence between the two plates in the eve of the end of subduction of the magdalena plate index terms 5480 planetology solid surface planets volcanism 8450 8150 tectonophysics evolution of the earth plate boundary general 3040 8109 tectonophysics continental tectonics extensional 0905 keywords ignimbrite flare up sierra madre occidental western mexico extensional tectonics slab detachment

deep water circulation in the luzon strait deep water circulation in the luzon strait which connects the pacific deep circulation with the south china sea throughflow is investigated using a set of oceanographic observations combined with results from three numerical experiments both the in situ observations and the model show a deep water overflow in the luzon strait their results suggest that the deep pacific water first flows into the luzon strait through the bashi channel 1 2 sv 1 sv 1 106 m3 s 1 and the taltung canyon 0 4 sv then turns southward along the luzon trough and finally enters the south china sea primarily through two gaps in the heng chun ridge overall the mean transport of the luzon strait overflow is about 1 5 sv results from numerical experiments suggest that strong diapycnal mixing in the south china sea and luzon strait which sustains the baroclinic pressure gradient across the luzon strait is the primary driving mechanism of the deep circulation in the luzon strait

sr and nd isotopic evidence for petrogenesis of mid tertiary felsic volcanism in the mineral district of zacatecas zac sierra madre occidental mexico abstract twelve samples of mid tertiary felsic volcanic rocks from zacatecas and san luis potosi both belonging to the sierra madre occidental and one sample of lower tertiary porphyritic andesite from zacatecas are analyzed for 87 sr 86 sr k rb and sr eight selected samples are also analyzed for 143 nd 144 nd a linear regression of the present day 87 sr 86 sr and 87 rb 86 sr of the felsic volcanic rocks in zacatecas gives an approximate date of 30 8 ma the initial 87 sr 86 sr ratios are high and widely distributed from 0 705 to 0 712 or higher whereas the initial 143 nd 144 nd ratios are somewhat low and show a narrow range 0 5125 0 5127 the available isotopic and trace element data are best explained in terms of a binary mixing model in which the magmas derived from a slightly depleted mantle fractionate and mix with varying proportions of the overlying middle upper continental crust and undergo further shallow level fractional crystallization before eruption this model is also compatible with the trace element and sr isotopic data published from other areas of the sierra madre occidental for which a purely mantle origin has been proposed

earthquake rate analysis abstract earthquake rate analysis explores the quantitative relationship between earthquake occurrence rates and geological deformation rates one application is the estimation of tectonic deformation rates from seismicity for comparison with tectonic models another application is the use of geological models to help quantify seismic hazards seismicity is described by a catalog of the largest earthquakes in the region the contribution of small earthquakes towards causing geological deformation is insignificant although the occurrence rate of small events may be predictable from the occurrence rate of large events by a b value relationship the critical information about each earthquake is its seismic moment or better still its seismic moment tensor when moment is not available directly it can be estimated from the earthquake magnitude although this increases uncertainties considerably the average annual moment from all the earthquakes in the catalog is the seismic moment rate uncertainties in seismic estimates of moment rate arise from the short time period of observations from the magnitude moment relationship from the shape of the distribution function giving number of earthquakes as a function of magnitude and from uncertainties in the physical properties of the earth near the source geological models for deformation rates are described by slip rates on individual faults or by regional strain rates a regional strain rate can be derived as a limiting case where there are numerous individual faults such a strain rate is a particularly useful concept where information about each of the faults is limited in the case of either faulting or regional strain the average seismic moment rate is proportional to the deformation rate geological uncertainties arise from difficulties in estimating slip rates or strain rates from fault creep and other aseismic deformation from uncertainty in the part of the fault that fails during earthquakes and boundaries of the deforming region and from uncertainty about the earth s physical properties the seismic moment rate is the critical factor for relating the earthquake occurrence rate and the geological deformation rate using this intermediate parameter one can infer earthquake occurrence rates from deformation rates or infer deformation rates from earthquake occurrence rates generally it is found that deformation rates and earthquake occurrence rates are consistent within uncertainties where both are well constrained they are generally consistent within a factor of two or three

the seasonal variation of the intrusion of the philippine sea water into the south china sea the seasonal variation of the intrusion of the philippine sea water into the south china sea was studied by analyzing the historical hydrographic station data in the northern south china sea and the philippine sea water masses at 150 200 and 250 m were classified by discriminant analysis according to their temperature salinity characteristics at each depth most water in the study region was classified into two groups representing the philippine sea water and the south china sea water respectively the geographic distribution of water masses in the south china sea shows that the philippine sea water was present along the continental margin south of china between october and january a westward current in the northern south china sea in winter was inferred from the distribution of the intrusion water

miocene shearing along the northern boundary of the jalisco block and the opening of the southern gulf of california new geologic and structural mapping in western mexico shows that the tectonic boundary between the eocene early miocene sierra madre occidental volcanic province and the cretaceous paleocene jalisco block was reactivated as a transfer zone accommodating a limited amount of lateral motion in middle and late miocene time transpressional folding left lateral strike slip faulting and minor thrusting occurred between 14 5 and 11 5 ma during initial rifting at the mouth of the gulf of california inferred right lateral transtension between 12 and 9 ma took place concurrently with widespread alkaline volcanism and east west extension at the gulf mouth and east of the jalisco block these events can be explained in light of the long extensional history that led to the separation of baja california from mainland mexico since the birth of the magdalena microplate about 14 5 ma left lateral shearing at the sierra madre occidental jalisco block boundary indicates that initial 14 12 ma rifting at the mouth of the gulf was accomplished mainly by east southeast motion of the block this was caused by differential stresses applied to the north america plate at the two sides of the subducting magdalena cocos plate boundary as a consequence of the waning of subduction of the magdalena plate subsequent right lateral transtension at the sierra madre occidental jalisco block boundary and extension to the east imply a limited west northwest motion of the block which possibly accounts for the discrepancy between slow rifting at the mouth of the gulf and fast northwest motion of baja california

the eddy mean flow interaction and the intrusion of western boundary current into the south china sea type basin in an idealized model abstractin this paper an ideal model of the role of mesoscale eddies in the kuroshio intruding into the south china sea scs is developed which represents the northwestern pacific and the scs as two rectangular basins connected by a gap in the case of considering only intrinsic ocean variability a time dependent western boundary current wbc driven by steady wind is modeled under both eddy resolving and noneddy resolving resolutions almost all simulated wbcs intrude into the adjacent sea in the form of the loop current with multiple state transitions and eddy shedding processes which have aperiodic variations on intraseasonal or interannual scales determined by the eddy induced wbc variation for the parameters considered in this paper the wbc intrusion exhibits a 30 90 day cycle in the presence of the subgrid scale eddy forcing ssef but a 300 500 day cycle in the absence of ssef moreover the roles of the grid scale and subgrid scale eddies in the wbc intrusion are studied by using the dynam

the separation of the yucatan current from the campeche bank and the intrusion of the loop current into the gulf of mexico data collected in the eastern gulf of mexico during 1974 1975 and 1976 show that the penetration of the loop current into the gulf is strongly correlated with the location of the yucatan current on the campeche bank the loop does not penetrate far into the gulf when the yucatan current separates from the bank in the vicinity of the catoche tongue i e the eastern campeche bank deep loop penetrations are correlated with separations farther west on the bank the angle of the yucatan current at separation is also correlated with the location of separation i e smaller angles relative to due east are correlated with separations from farther east on the bank thus small angles at separation are correlated with shallow intrusions of the loop historical temperature data collected in the eastern gulf are reviewed and support these correlations simple conservation of potential vorticity considerations can explain the correlation between the angle at separation and the penetration of the loop

behavior of dissolved inorganic arsenic in the yellow sea and east china sea abstract the yellow sea and east china sea are strongly affected by input from freshwater discharge e g from the changjiang yangtze river in the west and the kuroshio incursion in the east the r v dong fang hong 2 carried out two cruises in september of 2002 and 2003 to understand the behavior of arsenic in the yellow sea and east china sea arsenic species total dissolved inorganic arsenic and arsenite were determined by selective hydride generation atomic fluorescence spectrometry high concentrations of total dissolved inorganic arsenic species tdias as v as iii appeared near the changjiang estuary and at the bottom of the shelf break in the east china sea where the incursion of the kuroshio reaches the shelf tdias were moderately depleted in the surface water and enriched in the deep water the distribution of arsenite aso33 as iii was opposite that of arsenate aso43 as v in seawater but was positively correlated with that of chlorophyll a the as iii tdias ratio at the surface of coastal stations was lower than 0 3 in the summer of 2002 and as high as 0 5 in the summer of 2003 a limited effect from the changjiang discharge in september 2003 according to the salinity profile and or high phytoplankton conversion in the study area was hypothesized for the observed interannual variation the stoichiometric ratio of as to p in the biological assimilation was estimated to be about 2 10 3 at the pn section a southeast transect from the changjiang estuary to the ryukyu islands of the east china sea in the summer a preliminary box model was established to estimate the water mass balance and arsenic budgets for the east china sea shelf in the summer compared with other areas in the world the concentration of dissolved inorganic arsenic in the yellow sea and east china sea remained at natural levels

kuroshio intrusion into the south china sea a review the kuroshio carrying the northwestern pacific water intrudes into the south china sea scs through the luzon strait significantly affecting the temperature salinity circulation and eddy generation in the scs thus the kuroshio intrusion makes important contributions to the momentum heat and salt budgets in the scs in the past decades much work has been done on the kuroshio intrusion this paper reviews past efforts and summarizes our current understanding of the kuroshio intruding processes from observational evidence laboratory results theoretical analyses and a range of numerical model simulations in addition discrepancies between results simulated by models as well as those between simulations and observations are presented specifically this paper addresses the following topics 1 different types of the kuroshio intrusion into the scs and their identification 2 vertical structure of the kuroshio in the luzon strait 3 an overview of the luzon strait transport resulting from observations and numerical model simulations 4 seasonal and interannual variations of the kuroshio intrusion as well as eddy generation due to the kuroshio path variation and 5 dynamical mechanisms e g wind forcing interbasin pressure gradient beta effect and hysteresis potential vorticity eddy activity controlling the kuroshio intrusion into the scs finally several future research topics for gaining a better understanding of the kuroshio intruding processes are suggested c 2014 the authors published by elsevier ltd

post laramide removal of the farallon slab western united states i propose that post laramide removal of the subhorizontally subducting farallon slab occurred by buckling downward along an approximately east northeast trending axis this process was accomplished by a tearing or necking separation of the subducted slab near the northern and southern boundaries of the united states and propagation of the separated edges toward the central axis of downwelling accompanied by aesthenosphic upwelling behind the trailing edges initial buckling probably began near 50 ma and slab removal was complete by 20 ma this model is based primarily on the space time evolution of the ignimbrite flare up a major mid tertiary igneous event of mantle origin which involved two propagating fronts of initiation of volcanism that followed the proposed motions of the separated slab edges as they converged on central nevada from the north and southeast post laramide uplift extension establishment of the cascadia subduction zone and active magmatism may be consequences of lithosphere scale modifications caused by the laramide removal of the slab and the resulting asthenospheric upwelling

the forcing mechanism leading to the kuroshio intrusion into the south china sea 1 we use a high resolution numerical model to examine the forcing mechanism responsible for kuroshio intrusion into the south china sea scs the collective wisdom is that variations in kuroshio intrusion are closely related to the wind inside or outside the scs a series of experiments was performed to identify the wind related forcing regulating the intrusion the experiments demonstrated that the importance of wind inside the scs is greater than that outside the scs furthermore the northwestward ekman drift due to northeasterly wind in winter intensifies the upstream kuroshio in the luzon strait enhancing the kuroshio intrusion into the scs in particular the wind stress curl wsc off southwest taiwan is chiefly responsible for the kuroshio intrusion both the wsc and intrusion show both seasonal and intraseasonal variation as the negative wsc off southwest taiwan becomes stronger it contributes to anticyclonic circulation the enhanced anticyclonic circulation helps the development of the kuroshio intrusion the consistency between wsc variability and the intrusion suggests that the wsc off southwest taiwan is essential to the kuroshio intrusion variability

influence of intermediate water in the western okinawa trough by the outflow from the south china sea although the kuroshio and the south china sea scs waters flow in and out of the luzon strait near surface the scs water mainly flows out of the scs at mid depth between 350 and 1350 m in all seasons and years that we studied the eastward flowing scs intermediate water is blocked by and joins the northward flowing kuroshio at about 122 e thus the kuroshio intermediate water kiw is composed of the west philippine sea wps proper water on the east centered at 600 m depth because the ridge east of taiwan separating the okinawa trough from the wps is mostly shallower than 600 m the eastern portion of the kiw is largely blocked by the ridge and is forced to turn eastward this water does not enter the okinawa trough freely until it reaches a deep gap in the ryukyu ridge farther north subsequently forming the eastern portion of the intermediate water in the trough the western portion of the kiw is the mixed water of scs and wps the nutrient rich scs intermediate water centered at 500 m is less influenced by the ridge and is able to flow into the okinawa trough the scs intermediate water thus retains its signature in the southern and western okinawa trough upwells onto the east china sea shelf and becomes a major source of nutrients to the shelf water

interannual modulation of the pacific decadal oscillation pdo on the low latitude western north pacific to investigate the interannual variability in the northwestern pacific an empirical mode decomposition emd was applied to 17 year absolute dynamic topography adt data west of luzon island the philippines the mean sea surface height in this area is an appropriate index for the kuroshio intrusion into the south china sea scs significant interannual fluctuations were extracted by the emd the interannual variability was strongly correlated with the pacific decadal oscillation pdo index but not the el nino southern oscillation enso this indicated the potential impact of the pdo on the circulation in the area in the warm phase of the pdo positive index a southerly anomalous wind off the philippines causes a northward shift of the north equatorial current bifurcation latitude necbl this leads to a weakened kuroshio off luzon favoring kuroshio intrusion into the scs the northward migration of the necbl also results in a weakened kuroshio off southeast taiwan and a larger kuroshio transport off northeast taiwan the abundant westward propagating eddies impinging on the kuroshio in the subtropical countercurrent region increases this transport although the enso has little effect on monsoonal winds during the warm pdo phase it has a strong impact on the monsoon and meridional migration of the necbl during the cold phase of the pdo therefore necbl variations only show a close correspondence with the enso during the cold pdo phase because the influence of the enso is not stationary the impact of the pdo should be taken into account when examining interannual variability in the low latitude western north pacific

large magnitude oligo miocene extension in southern sonora implications for the tectonic evolution of northwest mexico new structural and 40ar 39ar data from the santa rosa area southeastern sonora shed light on the magnitude and timing of extensional tectonism episodic magmatic activity from the late cretaceous to the miocene is recorded by a 3 4 km thick structural stratigraphic section that includes a composite laramide granodiorite batholith and its andesitic wall rocks early to middle tertiary rhyolite ignimbrites and silicic domes and late oligocene to middle miocene mafic lavas interbedded with tuffaceous sediment and fanglomerate the older units are complexly faulted and steeply tilted by several generations of normal faults palinspastic reconstructions indicate cumulative extension of 90 early gently dipping nw striking normal faults document major extension oriented n50 e angular unconformities and growth fault relations within oligo miocene sequences bracket this extension between 26 and 20 ma younger widely spaced ns to nnw trending high angle normal faults cut the previously faulted and tilted sections and produced modest 10 15 e w extension that is largely bracketed between 20 and 17 ma the magnitude of neogene extension in this region is greater and the timing is older than previously recognized reconnaissance of other areas between the sierra madre occidental and the coast at this latitude suggests that most extension in sonora occurred between 27 and 12 ma while remnants of the farallon plate were still being subducted plate tectonic models that predict substantial extension in sonora during proto gulf 10 5 ma transtensional deformation may need to be reevaluated an alternative model presented here is that baja california began moving with pacific plate motion shortly after the 11 ma termination of subduction and that northwest motion of baja relative to mainland mexico might total 500 km distributed across the previously extended oligo miocene magmatic arc

thermohaline circulation in the deep south china sea basin inferred from oxygen distributions 1 on the basis of the historical oxygen data available distributions of dissolved oxygen were analyzed in detail to investigate the thermohaline circulation in the south china sea scs the analyses confirmed the existence of a layer of minimal oxygen content at intermediate depths of the basin which shows a low oxygen 1 6 ml l 1 core in the southern basin with water ages shorter than 100 years after entering the scs and which appears isolated from its counterpart of the western philippine sea north to the core along the northern slope there is a band of oxygen rich water in both upper and intermediate layers above 700 m the band can be attributed to the intrusion of high oxygen water through the luzon strait while vertical flux appears to be responsible between 700 and 1500 m the oxygen distribution provides additional evidence for a sandwiched vertical structure in transports through the luzon strait with outflows in the intermediate layer and inflows above and below while the abyssal water of the scs is being replenished by the deep inflows an abrupt change of water properties was observed in both upper and intermediate layers across the luzon strait suggesting possible domination of local vertical mixing over horizontal spreading of inflows in the northern scs a four cell conceptual model was proposed for the thermohaline circulation which consists of a three layer cross basin exchange cell in the luzon strait an active ventilation cell in the upper and intermediate layers along the northern slope an abyssal replenishment cell in the deep and a cyclonic recirculation cell in the interior basin

pre miocene palaeogeography of the los cabos block baja california sur geochronological and palaeomagnetic constraints the los cabos block lcb is located at the southern end of the baja california peninsula and is composed mainly of intrusive rocks that were emplaced into pre cretaceous heterogeneous metasediments and are partly covered by miocene volcanic and volcaniclastic rocks field observations provide evidence that the undeformed homogeneous gabbronorite of the sierra el novillo in the ne part of the lcb is the oldest crystalline unit which is intruded by undeformed to slightly deformed tonalitic quartz dioritic granitoids for these rocks an rb sr intrusion age of 129 15 ma and a biotite whole rock cooling age of 116 2 ma were obtained low initial 87sr 86sr and high e nd values of about 0 7036 and 5t o 6 respectively characterise the intrusives as primitive mantle derived granites further to the southeast and south granitoids are more silicic with abundant deformed sequences orthogneisses diatexites and migmatites among others from the southern part of the lcb an rb sr intrusion age for the undeformed granites of 115 4 ma and a biotite cooling age of 90 2 ma were determined initial 87sr 86sr was determined to be 0 7054 and e nd values fall between 2 and 0 the isotopic data do not clearly allow us to characterise the deformed granitoids of the lcb as being intruded by the undeformed unit deformation could have been partly due to syn intrusive tectonics palaeomagnetic data suggest minor if any northward displacement of the lcb with respect to continental mexico corresponding to the rifting in the gulf of california since the late miocene and significant 35 45 clockwise rotations possible tilting evects which may have occurred given the dip of tertiary volcanics on top of the intrusives would modify these values for rotation and to a lesser degree of northward displacement geochemical isotopic and palaeomagnetic results and the cooling history of the lcb are similar to those from the puerto vallarta batholith whereas other mexican continental margin plutons further to the se display lower intrusion ages more rapid cooling rates and generally more primitive magma compositions in the light of the data presented a common magmatic evolution of the lcb and the puerto vallarta batholith is strongly suggested 2000 elsevier science b v all rights reserved

the intrusion of water masses into the sea southwest of taiwan characteristics of water masses were analyzed to study the kuroshio intrusion into the sea southwest of taiwan hydrographic data were obtained from ctd conductivity temperature and depth casts during two cruises in may and august 1986 in may remnants of water intruding from the kuroshio were found on the continental slope south of the penghu channel by august these were replaced by water from the south china sea during this period water from the kuroshio also appeared near the southern tip of taiwan the intrusion current reached a depth of at least 500 m and was probably part of a cyclonic circulation in the northern south china sea the results support the hypothesis of a seasonal pattern of the intrusion process intrusion of water from the kuroshio begins in late summer intensifies in winter and ceases by late spring when south china sea waters again enter this region

calderas of the sierra madre occidental volcanic field western mexico approximately 296 000 km2 of western mexico is covered by a volcanic sequence that has an average thickness of 1 km and is mostly ash flow tuff although some 350 calderas are suggested by this tremendous volume only a few have been located or described in the state of durango the only well documented examples are in the 30 ma old chupaderos caldera complex near durango city although the complex is mostly covered by quaternary basalt and sediment the exposed portion reveals nested calderas that produced two major rhyolitic ash flow tuffs a third major tuff appears to have been erupted from the complex but no caldera has yet been found the caldera formed by the first eruption contains a resurgent dome and a thick sequence of moat sedimentary rocks and lava flows that are hosts for significant iron and tin deposits other possible durango calderas exist at el salto west of durango city at temoaya south of durango city and in the sierra de la silla to the north calderas in chihuahua have beep described from mountain ranges in the central part of the state and from the sierra madre occidental to the west a composite resurgent caldefa 35 ma old and approximately 22 km in diameter has been de scribed from the sierra pastorias immediately south of chihuahua city the main erupted unit is well exposed in the caldera s resurgent dome and a second tuff found outside the caldera was emplaced from a trap door structure nested in the caldera s northwest corner the area also contains a younger smaller resurgentiy domed caldera other possible calderas include a relatively large 35 km in diameter structure in the sierra del nido 75 km north of chihuahua city and a poorly defined structure related to a sequence f older 45 ma silicic volcanic rocks at cerro jesus maria 25 km northwest of chihuahua city calderas in the sierra madre plateau have been described from the tomochic and ocampo areas of western chihuahua the tomochic area records volcanic activity from 34 5 to 28 9 ma and contains at least three calderas these include the tomochic caldera a strikingly well preserved resurgent caldera approximately 20 by 25 km in diameter the north structural margin of the tomochic caldera cuts the intracaldera facies of an ash flow tuff related to the older las varas caldera epithermal precious metal fissure veins are located where the tomochic structural margin cuts this older unit a third structure the corallitos caldera is located only a few kilometers to the northeast reconnaissance studies in far western chihuahua indicate the existence of a large 40 km resurgent caldera centered on the village of ocampo landsat imagery shows a well developed arcuate drainage pattern and maps of the area show a distribution of lithologies that is consistent with the caldera interpretation gold and silver deposits hosted almost exclusively in precaldera rocks are best developed where the older rocks are cut by faults of the caldera s ring fracture zone and resurgent dome in general the calderas thus far mapped in western mexico follow the valles type resurgent caldera model variations however of the ideal caldera cycle are common as are repetitions of the cycle to form caldera complexes all of the better known calderas have associated mineral deposits although they may be best developed in precaldera rocks

an updated examination of the luzon strait transport 1 despite numerous previous estimates of luzon strait transport lst we attempt an update using a fine resolution model with these improvements the circulation in and around luzon strait shows up rather realistically intrusion of a kuroshio meander into the south china sea scs is seasonally varying the lst especially in the upper ocean caused by a small difference between the large meander inflow and outflow is also seasonally varying and subject to large standard deviation the annual mean lst is estimated to be westward 4 0 5 1 sv along 120 75 e we have also conducted process of elimination experiments to assess the relative importance of open ocean inflow outflow wind stress and surface heat flux in regulating lst and its seasonality the east asian monsoon winds stand out as the predominant forcing without it the upper ocean lst changes from westward to eastward ranging up to 4 sv and with misaligned seasonality triggering an inflow from the mindoro strait to the scs to replenish the water mass loss discounting monsoon winds sea level in the sulu sea is generally higher because it receives the indonesian throughflow before the scs which causes an inflow from the sulu sea to the scs on the other hand the annual mean wind from the northeast invites outflow from the scs to the sulu sea or inflow from the luzon strait weighing the two competing factors together we see the cessation of northeast monsoon as a condition favorable for the luzon strait outflow or the mindoro strait inflow