local atmospheric forcing during the coastal ocean dynamics experiment 1 a description of the marine boundary layer and atmospheric conditions over a northern california upwelling region as part of the coastal ocean dynamics experiment code meteorological instruments were deployed on buoys and at coastal stations and instrumented aircraft flights and coastal soundings were made to study the three dimensional structure of the marine boundary layer over the continental shelf off northern california during the 1981 and 1982 upwelling seasons these measurements show that after the atmospheric spring transition the airflow in the marine layer is dominated by the north pacific high and the surface wind field over the shelf is characterized by periods of strong 7 15 m s upwelling favorable alongshelf winds lasting for up to 30 days interrupted by shorter periods of much weaker winds directed either equatorward or poleward these periods of weak or reversed winds typically last several days and are called wind relaxations even though they are primarily associated with coastally trapped perturbations of the marine layer along the central and northern california coast and not with a large scale weakening of the north pacific high the atmospheric boundary layer measurements made in code suggest a simple conceptual model which can explain much of the physiology or structure of the marine layer and associated surface wind field during periods of persistent upwelling favorable winds during these periods which represent the quasi steady state regime during the upwelling season the inversion base of the marine layer drops eastward toward the coast until it intersects the coastal mountain range at a height of several hundred meters and the associated thermal wind produces an alongshelf wind jet which has a maximum speed just below the inversion base turbulent mixing tends to homogenize any stratification in the marine layer beneath the jet and couple the jet to the ocean surface producing strong upwelling favorable winds over the shelf day night heating cooling over the narrow coastal strip beneath the marine layer generates a weak cross coast secondary circulation which causes the core of the alongshelf jet to drop in elevation and shift onshore this diurnal change in the marine layer structure explains both the daytime acceleration of the surface winds observed over and near the coast and its offshore decay and the associated offshore increase in the subdiurnal alongshelf wind thus the quasi steady component of the wind stress has a significant curl over the inner shelf during periods of active upwelling this mean summer atmospheric boundary layer regime is occasionally interrupted by synoptic and or mesoscale events or anomalous conditions analysis of the code observations suggests five types of events two primarily synoptic scale conditions which lead to stronger than normal upwelling favorable winds over the shelf and three primarily mesoscale events which lead to wind relaxation about half of the wind relaxation events observed in 1981 and 1982 are believed to be associated with either coastal trapped gravity currents or internal kelvin waves which propagate north ward in the marine layer along the central and northern california coastal mountain range

moored wind temperature and current observations made during coastal ocean dynamics experiments 1 and 2 over the northern california continental shelf and upper slope moored observations of winds currents and temperature made over the northern california shelf and upper slope during the 1981 and 1982 upwelling seasons as part of the coastal ocean dynamics experiment code are described in both field experiments code 1 and code 2 the onset of the upwelling season is triggered by the strengthening of the north pacific high off northern california and signalled by the presence of water colder than 9 c near the bottom over the shelf vertical temperature stratification over the shelf is reduced during active upwelling local winds and subtidal currents over the shelf are strongly polarized in the alongshelf direction and the mean wind stress is directed equatorward response of alongshelf currents to wind forcing is similar at all depths over the shelf the response of the cross shelf current is more complex in the surface layer offshelf flow is significantly and positively correlated with the upwelling favorable alongshelf wind stress beneath this layer a weak return flow exists the thickness of the upper mixed layer varies greatly reaching 60 m during upwelling events thus direct wind forcing affects a substantial fraction of the water over the shelf low frequency wind stress current and temperature fields are adequately described by a few energetic empirical orthogonal functions with simple spatial structure the most energetic mode typically accounts for 75 or more of the variance of wind stress and temperature over the middle and inner shelf the most energetic current mode accounts for 90 or more of the variance is dominated by he alongshelf component and veers to the left with depth the low frequency alongshelf flow fluctuations are quasi barotropic with some vertical shear but no reversal with depth vertical shear in alongshelf current and the cross shelf density gradient obey the thermal wind relation the simple structure of the subdiurnal currents allow estimation of the alongshelf volume transport between the 60 and 130 m isobaths through three cross shelf transects in code 2 volume transport over the shelf is often nearly two dimensional but occasional large differences indicate significant mass exchange between the shelf and the adjacent upper slope correlation of low frequency currents and alongshelf wind stress shows the response of alongshelf current to be maximum near the surface and near midshelf where a 15 cm 1 alongshelf flow lags a 1 dyn cm 2 alongshelf wind stress by the order of 10 hours currents over the upper slope are not significantly correlated with local wind alongshelf transport over the shelf is highly correlated with local wind stress explaining 80 of the variance in the low frequency transport during code 2 volume transport is best correlated with wind stress approximately 30 km to the south winds in the code area during spring and summer are characterized by strong and persistent upwelling favorable winds interrupted by shorter periods of weak winds regression analysis indicates that in the absence of wind a poleward barotropic current jet exists over the shelf with a maximum amplitude over the inner shelf in the code area an upwelling favorable wind counters this jet over the shelf so that the alongshore flow is everywhere equator ward during strong wind events since the maximum response to wind forcing is found at midshelf and near surface the mean current over the upwelling season is strongly sheared in both the vertical and cross shelf directions mean flow over the outer shelf is surface intensified and is directed offshelf and equatorward while the deeper flow at midshelf and through most of the water column over the inner shelf is directed poleward

upwelling in the alaskan beaufort sea atmospheric forcing and local versus non local response abstract the spin up and relaxation of an autumn upwelling event on the beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models the event occurred in november 2002 and was driven by an aleutian low storm the wind field was strongly influenced by the pack ice distribution resulting in enhanced winds over the open water of the chukchi sea flow distortion due to the brooks mountain range was also evident mooring observations east of barrow canyon show that the beaufort shelfbreak jet reversed to the west under strong easterly winds followed by upwelling of atlantic water onto the shelf after the winds subsided a deep eastward jet of atlantic water developed centered at 250 m depth an idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm the disparity in wave speeds between the sea surface height signal traveling at the fast barotropic shelf wave speed versus the interior density signal traveling at the slow baroclinic wave speed leads to the deep eastward jet the broad scale response to the storm over the chukchi sea is investigated using a regional numerical model the strong gradient in windspeed at the ice edge results in convergence of the offshore ekman transport leading to the establishment of an anti cyclonic gyre in the northern chukchi sea accordingly the chukchi shelfbreak jet accelerates to the east into the wind during the storm and no upwelling occurs west of barrow canyon hence the storm response is fundamentally different on the beaufort slope upwelling versus the chukchi slope no upwelling the regional numerical model results are supported by additional mooring data in the chukchi sea

circulation in the santa maria basin california during 1998 1 moored observations and numerical model results are used to describe the circulation during 1998 in santa maria basin smb and santa barbara channel sbc located to the northwest and southeast respectively of a bend in the southern california coastline singular value decomposition svd analysis of observed wind stress and currents yields a first mode that represents large scale alongshore flow variability that appears to be wind driven and a second mode which mostly represents flow variability in sbc and appears coherent with wind stress shear there a three dimensional numerical ocean circulation model is used to simulate the flow the model derived surface heat flux is most similar to observation derived values in summer and least similar in winter and more similar in smb than in sbc empirical orthogonal function eof analysis of the coriolis and pressure gradient terms for modeled near surface currents supports the hypothesis that the large scale flow variability of the first mode is wind driven it further suggests that an alongshore pressure gradient drives the poleward flow along sbc s northern shelf wind stress curl of which the shear along sbc is a part or its gradient may govern such a pressure gradient although this could not be ascertained modeled and observed currents are similar in their directions but both the annual mean and variance tend to be smaller for modeled flow svd analysis shows that modeled and observed flows have similar modes of variability remotely driven flow may play a role in smb especially in summer

mantle discontinuities and temperature under the north american continental keel a ubiquitous feature of upper mantle seismic velocity models has been the presence of high velocity keels beneath stable continental interiors1 2 3 4 5 uncertainty remains however regarding the maximum depth to which continental keels extend the degree to which they have cooled the mantle that surrounds them and their role in mantle flow here we investigate thermal anomalies across the eastern margin of the north american continental keel by imaging the seismic discontinuities at depths of 410 and 660 km with compressional to shear converted waves recorded by a 1 500 km long seismometer deployment in the eastern united states the thickness of the transition zone the region nominally between depths of 410 and 660 km and the depth to the 410 km discontinuity indicate that cold keel material and sub keel downwellings must be largely confined to the upper mantle and may impinge on the transition zone only in localized regions and with thermal anomalies of less than 150 k a 20 km depression of the 660 km discontinuity to the south of the westernmost stations coincides with a region of fast velocity in the deep transition zone2 and may be associated with the remnants of the subducted farallon plate1 2 4

tectonic and sedimentary evolution of a cretaceous continental arc backarc system in the korean peninsula new view abstract this paper focuses on the tectonic and sedimentary evolution of the cretaceous volcanic rocks and nonmarine successions in the southeastern part of the korean peninsula which constitute an ancient continental arc system the arc system gyeongsang arc system comprising an arc platform gyeongsang volcanic arc and a backarc basin gyeongsang backarc basin was a southwestward extension of the japanese arc formed by oblique northward subduction of the proto pacific izanagi plate under the asian continent the backarc basin was initiated in the southeastern part of the korean peninsula in the early cretaceous as a narrow ns trending trough the basin was bounded by a major fault in the northern part of the basin from which sediments largely emanated sediments were deposited in streamflow dominated alluvial fans adjacent to the fault bounded basin margin in the north and low gradient fluvial systems of braided channels that extended southward and southeastward for tens of kilometers sediments were also derived from the western highland margin draining precambrian to jurassic basement rocks the initially narrow trough progressively expanded toward the east resulting in eastward migration of depocenters that eventually generated a broad fluvio lacustrine plain fringing the volcanic arc platform the arc platform played an important role for the derivation of volcanogenic materials and accreted sediments into the backarc basin via extensive fluvial network pyroclastic density currents and landslides which originated from the arc platform also entered the basin in addition extrusion of basaltic volcanic rocks was continual within the basin during basin expansion the resultant succession of mixed sedimentary and volcanogenic rocks is generally indicative of a temporal increase in volcanic activity in the arc platform and in subsidence rate of the basin in the late cretaceous andesitic to rhyolitic volcanism became climactic in the arc platform producing a number of calderas or volcanotectonic depressions volcaniclastic aprons fringing the arc platform encroached upon the basin fill intraarc basins produced by sinistral shearing of the arc platform received sediments from active volcanoes and footwalls of contemporaneous faults forming small scale streamflow dominated alluvial fans and floodplains with later development of a deep lake overall the gyeongsang arc system formed under an extensional or transtensional sinistral strike slip stress regime suggesting that the subducting and the overriding plates were not strongly coupled both the volcanic arc and the backarc basin ceased to develop as volcanic activities shifted progressively eastward in the paleogene accompanied with rollback of the subduction of the izanagi plate

temporal changes in the subduction of the paleo pacific plate beneath eurasia during the late mesozoic geochronological and geochemical evidence from cretaceous volcanic rocks in eastern ne china abstract subduction of the paleo pacific plate played an important role in the evolution of the eastern margin of the eurasian continent however the details of the processes of subduction during the late mesozoic remain poorly constrained here we examine the geochronology and geochemistry of cretaceous volcanic rocks from eastern ne china with the aim of understanding the variation of subduction process cretaceous volcanism in the region mainly occurs in the raohe mishan suifenhe wangqing and jiamusi jixi areas in eastern jilin and heilongjiang provinces as well as in the lesser xing an range where volcanism extends from the continental margin farther inland the cretaceous volcanic rocks in the raohe mishan suifenhe wangqing rmsw area are composed of basalts basaltic andesites andesites dacites and rhyolites with late early cretaceous 122 106 ma ages and dacites that yield early late cretaceous 96 93 ma ages a mixed source of compositionally heterogeneous mantle and crustal rocks is assumed based on the compositional range of volcanic rocks adakitic andesites 114 110 ma were derived from a mantle source modified by slab derived melt that infiltrated the mantle wedge adakitic dacites 122 106 and 96 93 ma were produced by partial melting of thickened lower crust that formed in response to earlier subduction of the paleo pacific plate beneath eurasia the rhyolites and dacites that lack adakitic signatures were derived from partial melting of a depleted lower crustal block that was accreted during the neoproterozoic in particular the late early cretaceous 106 ma basalt was derived from a depleted lithospheric mantle that was metasomatized by slab derived fluids and subsequently by asthenospheric melts at a relatively shallow depths implying rollrback of the subducted paleo pacific plate the cretaceous volcanism in the jiamusi jixi area formed during the late early cretaceous 124 110 ma and shows a bimodal distribution of compositions with a prominent daly gap the mafic members were generated by re melting of depleted lithospheric mantle that was modified by subduction related fluids and underwent fractional crystallization the coeval felsic end members with or without a type characteristics were generated by partial melting of juvenile crustal material consistent with an extensional environment related to subduction of the paleo pacific plate cretaceous volcanism in the lesser xing an range shows a bimodal compositional distribution of volcanic rocks with a daly gap and a period without volcanism at 108 97 ma andesites with and without adakitic signatures were derived from partial melting of mantle that was hybridized by slab derived melts and metasomatized by a fluid rich subduction component in contrast the coeval a type rhyolites were generated by partial melting of juvenile crust implying the migration of the extensional environment the formation of and spatio temporal relationships between cretaceous volcanic rocks in ne china combined with the regional geological data suggest a transition from low angle subduction to slab rollback and subsequent changes in the direction of motion of the paleo pacific plate during the late early cretaceous to the late cretaceous

early paleozoic amalgamation of the songnen zhangguangcai range and jiamusi massifs in the eastern segment of the central asian orogenic belt geochronological and geochemical evidence from granitoids and rhyolites abstract to constrain the early paleozoic tectonic evolution of the songnen zhangguangcai range and jiamusi massifs we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic igneous rocks in the lesser xing an zhangguangcai range of eastern heilongjiang province ne china the zircons from one diorite two rhyolites and four granitoids are euhedral subhedral and display fine scale oscillatory growth zoning indicating a magmatic origin la icp ms zircon u pb age data indicate the occurrence of magmatic events in the late ordovician 443 451 ma and middle silurian 424 430 ma the late ordovician igneous rocks are composed mainly of diorite tonalite and rhyolite whereas the middle silurian igneous rocks consist mainly of monzogranites the early paleozoic igneous rocks have sio2 59 65 76 11 wt mgo 0 13 1 23 wt and na2o k2o 4 68 7 77 wt and are chemically a calc alkaline series they are characterized by enrichment in light rare earth elements and large ion lithophile elements and depletion in heavy rare earth elements and high field strength elements such as nb ta and ti consistent with the chemistry of igneous rocks from an active continental margin setting in situ hf analyses of zircons show that ehf t values of zircons that formed in the early ordovician captured and inherited zircons in late ordovician igneous rocks range from 0 1 to 7 1 those of zircons that formed in the late ordovician including captured and inherited zircons in middle silurian monzogranite vary from 2 6 to 5 6 and those of zircons that formed in the middle silurian vary from 3 0 to 3 2 the progressive decrease in zircon ehf t values from the early ordovician to the middle silurian suggests an increasing involvement of ancient crust in the magma sources corresponding to the transition from subduction to collision take together these data suggest that the formation of late ordovician diorite tonalite and rhyolite in the zhangguangcai range adjacent to the mudanjiang fault may have been related to the westward subduction of an oceanic plate between the songnen zhangguangcai range and jiamusi massifs in contrast coeval rhyolites from the lesser xing an range located far from the mudanjiang fault may have formed in the supra subduction zone the occurrence of a middle silurian monzogranite association combined with geochronological data for detrital zircons from early devonian sedimentary rocks in eastern heilongjiang province suggests that the amalgamation between the songnen zhangguangcai range and jiamusi massifs occurred in the middle silurian

early cretaceous adakitic granites in the northern dabie complex central china implications for partial melting and delamination of thickened lower crust abstract to date few adakitic rocks have been reported in direct association with contemporary intra continental extensional structures which has cast doubt on genetic models involving partial melting of the lower crust this study presents early cretaceous 143 129 ma new sensitive high resolution ion microprobe shrimp zircon u pb ages adakitic granites which are directly associated with a contemporary metamorphic core complex i e the northern dabie complex in the dabie area these granites exhibit relatively high sr contents negligible to positive eu and sr anomalies high la yb and sr y ratios but very low yb and y contents similar to subducted oceanic crust derived adakites they are also characterized however by very low mgo or mg and ni values and nd sr isotope compositions end t 14 6 to 19 4 and 87sr 86sr i 0 7067 0 7087 similar to triassic continent derived eclogites subducted in the dabie sulu orogen additionally late granitic dikes in the adakitic intrusions exhibit low sr contents clearly negative eu and sr anomalies low la yb and sr y ratios but relatively high yb and y contents similar to 118 105 ma granites in the northern dabie complex based on composition and geochronology data of neoproterozoic amphibolites and orthogneisses triassic high to ultra high pressure metamorphic rocks and early cretaceous mafic ultramafic intrusive rocks and the constraints provided by experimental melt data for tonalites metabasaltic rocks and eclogites we suggest that the adakitic granites were most probably generated by partial melting of thickened amphibole or rutile bearing eclogitic lower crust as a consequence of triassic middle jurassic subduction and thrusting the late dikes probably originated from plagioclase bearing intermediate granulites moreover we suggest that late mesozoic delamination or foundering of thickened eclogitic lower crust is also a more plausible mechanism for the petrogenesis of early cretaceous mafic ultramafic intrusive rocks in the dabie area and probably involved partial melting of a mixed source comprising eclogitic lower crust that had delaminated or foundered into upper lithospheric or asthenospheric mantle peridotite asthenospheric upwelling in response to post collisional delamination of lithospheric mantle was likely to have provided the heat source for the cretaceous magmatism

petrogenesis of late carboniferous a type granites and early cretaceous adakites of the songnen block ne china implications for the geodynamic evolution of the paleo asian and paleo pacific oceans abstract the petrogenesis of late carboniferous a type granites and early cretaceous adakites in ne china offers new insights into the geodynamic evolution of the paleo asian and paleo pacific oceans this study reports new la icp ms zircon u pb ages geochemical data and zircon hf isotopic compositions of syenogranites and quartz diorite porphyries exposed on the northern margin of the songnen block ne china zircon u pb age data indicate that the syenogranites and quartz diorite porphyries were emplaced at ca 319 and 120 ma respectively the syenogranites have high k2o contents of 4 15 4 79 wt and k2o na2o cao ratios of 33 102 and low mgo 0 06 0 20 wt and p2o5 0 01 0 02 wt contents their remarkably high hree contents and y nb ratios 2 07 2 40 significantly negative eu anomalies eu eu 0 15 0 28 and low sr contents 29 7 85 8 ppm indicate that the syenogranites are a type granites they have positive zircon ehf t values of 8 4 12 1 and neoproterozoic hf tdm2 ages of 795 561 ma suggesting a juvenile lower crustal source the quartz diorite porphyries have relatively high na2o and mgo and moderate k2o contents their a cnk values 0 95 1 18 indicate a transition from being metaluminous to weakly peraluminous they are enriched in liles e g rb k and ba and depleted in hfses e g nb ta ti and p their low y 11 1 14 4 ppm and yb 0 98 1 34 ppm contents and high sr 589 1131 ppm cr and ni contents and sr y ratios indicate that they were generated by partial melting of oceanic crust based on these data and regional geological investigations we propose that the syenogranites on the northern margin of the songnen block were formed in a post collision extensional setting likely due to closure of the paleo asian ocean between the xing an and songnen blocks formation of the early cretaceous quartz diorite porphyries may have been triggered by partial melting of the paleo pacific flat slab apart from rollback of the paleo pacific oceanic slab the main reason for the eastward migration of magmatism during the cretaceous was the trench ward dehydration eclogitization and sinking of the residual paleo pacific flat slab

the physical environment of the peruvian upwelling system abstract knowledge of the characteristics of the physical environment of the peru coastal upwelling zone has increased greatly during the past decade observations made during 1976 and 1977 many made as part of the coastal upwelling ecosystem analysis joint ii expedition provide the basis for an interpretative description of the physical processes and phenomena occurring in peru coastal waters four important phenomena are discussed wind driven upwelling the poleward undercurrent surface mixed layer deepening and low frequency coastal trapped waves the coastal winds were invariably favorable for coastal upwelling even during the 1976 el nino the agreement between the offshore transport in the relatively shallow 30 m surface layer and the ekman transport deduced from the local wind was good for both the mean and variable state the agreement with the deeper onshore transport was less good consistent with the marked three dimensionally and spatial variability of the upwelling the poleward undercurrent was apparently continuous from 5 s to at least 15 s flowing just below the surface layer over the continental shelf and slope and supplying the upwelling water the variability in the alongshore velocity field was dominated by baroclinic free coastal trapped waves with periods of 5 20 days although there is appreciable temporal and spatial variability in the peru coastal upwelling system the upwelling the undercurrent and the low frequency coastal trapped waves were ubiquitous

3d numerical modeling of mantle flow crustal dynamics and magma genesis associated with slab roll back and tearing the eastern mediterranean case interactions between subduction dynamics and magma genesis have been intensely investigated resulting in several conceptual models derived from geological geochemical and geophysical data to provide physico chemical constraints on these conceptual models self consistent numerical simulations containing testable thermo mechanical parameters are required especially considering the three dimensional 3d natural complexity of subduction systems here we use a 3d high resolution petrological and thermo mechanical numerical model to quantify the relative contribution of oceanic and continental subduction collision slab roll back and tearing to magma genesis and transport processes our modeling results suggest that the space and time distribution and composition of magmas in the overriding plate is controlled by the 3d slab dynamics and related asthenospheric flow moreover the decrease of the bulk lithospheric strength induced by mantle and crust derived magmas promotes the propagation of strike slip and extensional fault zones through the overriding crust as response to slab roll back and continental collision reduction of the lithosphere asthenosphere rheological contrast by lithospheric weakening also favors the transmission of velocities from the flowing mantle to the crust similarities between our modeling results and the late cenozoic tectonic and magmatic evolution across the eastern mediterranean region suggest an efficient control of mantle flow on the magmatic activity in this region which in turn promotes lithospheric deformation by mantle drag via melt induced weakening effects

observations of mixed layer restratification by onshore surface transport following wind reversal in a coastal upwelling region 1 observations from the oregon continental shelf describe the slumping of a coastal upwelling front in response to a reversal of winds from upwelling to downwelling favorable initially the front outcropped in a surface mixed layer of depth 10 20 m with a pronounced cross shelf density gradient following wind reversal both the unbalanced cross shelf pressure gradient and wind driven ekman transport drove a rapid onshore movement of near surface water causing the mixed layer to restratify at the surface the cross shelf density gradient steepened to become a discontinuous front which propagated onshore at 0 43 0 60 m s 1 as the head of a buoyant gravity current internal waves were driven ahead of the front on the base of the former mixed layer an injected dye tracer revealed that surface water from inshore of the strongest frontal gradient detached from the surface as the gravity current passed over the top of it this water largely retained the low potential vorticity signature that it had taken on in the mixed layer as it spread across the shelf in a weakly stratified subsurface layer restratification and frontogenesis were most likely gravity driven in the first hours following wind reversal with the contribution from ekman transport becoming increasingly significant

the seismic 8 discontinuity and partial melting in continental mantle strong scattered reflections beyond 8 degrees 8 offset are characteristic features of all high resolution seismic sections from the continents the reflections identify a low velocity zone below approximately 100 kilometers depth beneath generally stratified mantle this zone may be caused by partial melting globally initiated at equal depth in the continental mantle solid state is again attained at the lehmann discontinuity in cold stable areas whereas the zone extends to near the 400 kilometer discontinuity in hot tectonically active areas thus the depth to the lehmann discontinuity may be an indicator of the thermal state of the continental mantle

high sr y and la yb ratios the meaning of the adakitic signature abstract the name of adakite is used to describe a far too large group of rocks whose sole common feature is high sr y and la yb ratios however such a signature can be achieved via different processes melting of a high sr y and la yb source deep melting with abundant residual garnet fractional crystallization or afc or interactions of felsic melts with the mantle causing selective enrichment in lree and sr over hree a database of the compositions of adakitic rocks including high silica and low silica adakites martin h smithies r h rapp r p moyen j f champion d c 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 2 1 24 continental adakites and archaean adakites was assembled geochemical modeling of the potential processes is used to interpret it and reveals that 1 the classical model of slab melting provides the best explanation for the genesis of high silica adakites 2 low silica adakites are explained by garnet present melting of an adakite metasomatized mantle i e at depths greater than 2 5 gpa 3 continental adakites is a term encompassing a huge range of rocks with a corresponding diversity of petrogenetic processes and most of them are different from both low and high silica adakites 4 archaean adakites show a bimodal composition range with some very high sr y examples similar to part of the ttg suite reflecting deep melting 2 0 gpa of a basaltic source with a relatively high sr y while lower sr y rocks formed by shallower 1 0 gpa melting of similar sources comparison with the archaean ttg suite highlights the heterogeneity of the ttgs whose composition spreads the whole combined range of hsa and archaean adakites pointing to a diversity of sources and processes contributing to the ttg suite

final amalgamation of the central asian orogenic belt in ne china paleo asian ocean closure versus paleo pacific plate subduction a review of the evidence abstract the central asian orogenic belt caob evolved through complex closure of the paleo asian ocean from the neoproterozoic to the late phanerozoic this caused the chinese cratons to collide with eurasia and led to the formation of the world s largest phanerozoic orogenic belt ocean closure commenced in the west and was completed in the east near changchun closure of the paleo asian ocean in ne china was along the solonker xar moron changchun yanji suture and this was likely completed in the late permian although associated activity continued into the triassic there was an overlap in the latest permian early triassic between terminal activity associated with paleo asian ocean closure and the onset of tectonism associated with subduction of the paleo pacific plate this switch in geodynamic setting occurred at 260 250 ma and is reflected by a relaxing of north south directed compression and the onset of east west directed processes related to paleo pacific subduction by the early jurassic events associated with the westward advance of the paleo pacific plate dominated leading to extensive development of i type granites as far inland as the great xing an range from 140 ma the paleo pacific plate retreated eastward resulting in an extensional setting in the early cretaceous the effects of which were enhanced by regional thinning of the lithosphere commonly attributed to delamination throughout this period the eastern asian margin was tectonically complex the north south oriented jiamusi khanka bureya block was rifted away from the eastern margin of the caob in the late triassic but was then re united in the jurassic by westward advancing subduction that affected both the western and eastern margins of the block accretionary complexes continued to evolve in the cretaceous along the whole eastern margin of asia with final accretion of the nadanhada terrane part of the sikhote alin accretionary terrane with the caob at 130 ma followed by the emplacement of s type granites

efficient calculation of complete differential seismograms for laterally homogeneous earth models summary differential seismograms the sensitivity of the seismogram to perturbations of parameters of the earth model are essential for waveform modelling with iterative non linear optimization techniques the growing number of broad band highdynamic range fixed and portable stations provide a rich data set of regional distance events with accurate locations and source mechanisms that are ideal for modelling lithospheric structure an efficient technique for calculating differential seismograms for complete synthetic seismograms in laterally homogeneous earth models will significantly decrease the computational burden of seismic waveform inverse modelling the technique we present here is equivalent to computing three synthetic seismograms in multilayered models contrasted with n 1 seismograms for a typical brute force approach which reduces the work to 3 n 1 or about a 90 per cent saving for 30 layers the lateral homogeneity requirement will yield path averaged structures which may form the basis for later tomographic studies to resolve lateral variations

numerical model simulations of continental shelf flows off northern california abstract the three dimensional circulation on the continental shelf off northern california in the wind events and shelf transport west experiment region during summer 2001 is studied using the primitive equation regional ocean modeling system roms the simulations are performed with realistic topography and initial stratification in a limited area domain with a high resolution grid forcing consists of measured wind stress and heat flux values obtained from a west surface buoy the general response shows a southward coastal upwelling jet of up to 1 m s 1 and a weakening or reversal of currents inshore of the jet when upwelling winds relax model results are compared to west moored velocity and temperature measurements at five locations to codar surface current observations between pt reyes and bodega bay and to hydrographic measurements along shipboard survey lines the model performs reasonably well with the highest depth averaged velocity correlation 0 81 at the inshore mooring 40 m water depth and lowest correlation 0 68 at the mid depth mooring 90 m depth the model shows generally stronger velocities than those observed especially at the inshore moorings and a lack in complete reversal of southward velocities observed when upwelling winds relax the comparison of surface velocities with codar measurements shows good agreement of the mean and the dominant mode of variability the hydrography compares closely at the southern and northern edges of the survey region correlation coefficients between 0 90 and 0 97 with weaker correlations at the three interior survey lines correlation coefficients between 0 44 and 0 76 mean model fields over the summer upwelling period show slight coastal jet separation off pt arena and significant separation off pt reyes the cape regions also experience relatively strong bottom velocities and nonlinearity in the surface flow across shelf velocity sections examined along the shelf reveal a double jet structure that appears just north of bodega bay and shows the offshore jet strengthening to the south we examine the dynamics during an upwelling and subsequent relaxation event in may 2001 in which the west measurements show evidence of a strong flow response the alongshelf variability in the upwelling and relaxation response introduced by pt reyes is evident analysis of term balances from the depth averaged momentum equations helps to clarify the event dynamics in different regions over the shelf a clear pattern in the nonlinear advection term is due to the spatial acceleration of the southward jet around the capes of pt arena and pt reyes during upwelling results from a three dimensional lagrangian analysis of water parcel displacement show significant southward displacement in the coastal jet region including a strong signal from the double jet alongshelf variability in parcel displacements and upwelling source waters due to the presence of pt arena and pt reyes is also apparent from the lagrangian fields a cyclonic eddy like recirculation feature offshore of pt arena prior to the upwelling event causes large patches of onshore displaced parcels additionally across shelf variability in the response of water parcels along the d line includes decreased vertical displacement and increased alongshelf displacement in the offshore direction

spatiotemporal variations of jurassic cretaceous magmatism in eastern asia tan lu fault to sw japan evidence for flat slab subduction and slab rollback here we examine spatiotemporal variations of jurassic cretaceous magmatism along a c 1000 km transect across eastern asia including sw japan the korean jiaodong and liaodong peninsulas and eastern jilin province integration of tectonic regime data with age data from igneous rocks in eastern asia from the tan lu fault to sw japan suggests a shallowing of the subduction angle and subsequent flat slab subduction during the jurassic and slab rollback during the early cretaceous the combination of a subducting plateau and root enhanced suction provides the best explanation for the flat slab subduction in the final stage albian of slab rollback the geotectonic setting changed from subduction accretion to a continental arc in the area close to the ancient trench i e the inner zone of sw japan

cross shelf transport causes recruitment to intertidal populations in central california the control of recruitment to intertidal barnacle populations along the central california coast was examined from april to mid october 1988 four recruitment pulses occurred during periods of relaxation in alongshore winds and cessation of coastal upwelling in each case recruitment ended when strong equatorward winds reappeared and upwelling resumed data on sst salinity adjusted sea level and satellite avhrr images revealed alternating periods of onshore and offshore transport of the surface water layer the onset ofthe largest recruitment pulse was associated with the advection of warm clear low salinity water into the nearshore region this oceanic water mass also contained a different zooplankton assemblage than the water mass it replaced

thermo mechanical controls of flat subduction insights from numerical modeling this study was supported by national basic research program of china 2014cb440901 the strategic priority research program b of cas xdb18020104 national science foundation of china 41190073 41372198 and 41304071 and nerc grant ne j021822 1

lehmann discontinuity as the base of an anisotropic layer beneath continents long period surface wave r 1 g 1 body wave s ss sss and scs reverberation data have been inverted to obtain anisotropic structures along seismic corridors that sample australia and the western pacific these models support the proposal that the lehmann discontinuity beneath stable continents represents a transition from an anisotropic lithosphere to a more isotropic material in the lower part of the continental tectosphere

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

shear wave splitting continental keels and patterns of mantle flow in this study we investigated the origin of seismic anisotropy in the mantle beneath north america in particular we evaluated whether shear wave splitting patterns in eastern north america are better explained by anisotropy caused by lithospheric deformation anisotropy due to mantle flow beneath the lithosphere or a combination of both we examined new measurements of shear wave splitting from the missouri to massachusetts broadband seismometer array moma the north american mantle anisotropy and discontinuity experiment nomad as well as splitting parameters from several previous studies we developed a simple finite difference model that approximates mantle flow around a complex three dimensional continental lithospheric keel to evaluate potential anisotropy from mantle flow beneath the lithosphere in eastern north america we compared shear wave splitting observations to predicted splitting parameters calculated using this mantle flow model our results indicate that a significant portion of observed shear wave splitting in eastern north america can be explained by mantle flow around the continental keel however shear wave splitting patterns in a few regions of eastern north america indicate that a component of lithospheric anisotropy must exist particularly in regions containing the largest keel thicknesses for eastern north america as well as for splitting observations in australia europe and south america we favor a model in which anisotropy is controlled by a combination of both lithospheric deformation and subcontinental mantle flow

early jurassic mafic magmatism in the lesser xing an zhangguangcai range ne china and its tectonic implications constraints from zircon u pb chronology and geochemistry abstract la icp ms zircon u pb dating and geochemical data have been obtained from five representative mafic ultramafic intrusions in the lesser xing an zhangguangcai range ne china with the aim of improving our understanding of the mesozoic tectonic evolution in the region and in particular determining the time of initiation of the circum pacific tectonic system the selected zircons exhibit striped absorption in cathodoluminescence cl images and have high th u ratios 0 20 3 16 indicating a magmatic origin the zircon u pb dates indicate that most of these magmatic zircons other than a few relics that were captured and entrained in the magma formed in the late early jurassic 186 182 ma and not as previously supposed in the middle caledonian the five mafic ultramafic plutons are composed of olivine gabbro hornblendite gabbro hornblende gabbro and gabbro diorite the olivine gabbro and hornblendite display cumulate textures implying that fractional crystallization of olivine and plagioclase took place during magma evolution these mafic ultramafic igneous rocks have sio2 37 3 55 7 mgo 3 05 13 3 al2o3 11 8 23 8 mg 42 69 mg 100mg mg fe2 total and eu 0 88 1 32 and they display three types of rare earth element ree distribution patterns right slipped flat patterns or dome like the trace element spider diagrams show that the rocks are enriched in large ion lithophile elements liles such as ba k and sr and depleted in high field strength elements hfses such as nb ta zr and hf the zircons have ehf 186 182 ma 2 7 to 12 0 and tdm1 366 732 ma the geochemical data indicate that the early jurassic mafic magma originated in an extensional environment from the partial melting of a depleted mantle wedge that had been metasomatized by fluids released from a fossil subducted slab these data combined with information on the spatial variation of coeval igneous rocks indicate that the formation of the early jurassic mafic ultramafic rocks in the lesser xing an zhangguangcai range was related to the subduction of the paleo pacific plate beneath the eurasian continent and this event would mark the beginning of the circum pacific tectonic system

possible role of gravity currents in northern california s coastal summer wind reversals north winds along the northern california coast in the summer of 1982 were interrupted by six events with southerly winds four of these events occurred under similar circumstances one of these four events is presented in detail at the start of this event the marine layer is thickened in the southern california bight a couple of days later the marine layer thickens from point conception to monterey then the marine layer thickness increase surges to the north along the coast to point arena where progression stopped and an eddy formed in this surging stage winds switched to southerlies as the leading edge of the event passed a day later the leading edge surged further to the north inshore winds were southerly and the lifted marine layer extended to cape blanco in oregon this event is interpreted as a gravity current surging up the coast the basic reservoir is the thickened marine layer in the southern california bight northerly progression is interrupted by a blocking wave near point arena where an eddy forms it is hypothesized that most of the major wind reversals along the northern california coast during the summer are gravity currents or kelvin waves in the marine layer that are formed to the south

wind relaxations and poleward flow events in a coastal upwelling system on the central california coast 1 when upwelling favorable winds weaken or relax in coastal upwelling systems prevailing equatorward currents often weaken and then reverse to form propagating poleward currents here the statistics of wind relaxations and poleward flow events along the south central california coast are derived using meteorological and oceanographic times series during 2000 2006 over the 7 year record 169 wind relaxations were observed about 1 every 2 weeks and 127 of these were followed by poleward flow events thermistor moorings and current profilers along the 15 m isobath at alegria point arguello point purisima and point sal recorded the poleward flows the poleward flows propagate northward at 10 30 km d 1 and appear as sequential temperature increases at the moorings wind relaxations occur throughout the year but are most frequent in september and least frequent in april when upwelling winds are strong and persistent poleward flows follow wind relaxations frequently during may through november and rarely in december and january sea level differences between santa monica and port san luis california decreased as winds relaxed consistent with forcing by alongshore pressure gradients temperature distributions at point arguello point purisima and point sal were skewed toward higher values because of the poleward flows the alongshore distance traveled by the poleward flows increased with duration of the wind relaxations and magnitudes of alongshore temperature and sea level differences prior to the relaxations

evidence of kelvin waves in california s marine layer and related eddy generation abstract evidence suggests that an internal solitary kelvin wave exists in the marine layer along california the marine layer is lifted over the central coast by a weak cyclonic circulation this bump initially 850 m high moves to the north along the coast at 6 m s 1 the undisturbed layer depth is 100 200 m thick the crest height of the wave decreases to 500 m farther north winds under the raised marine layer are southerly the leading edge of the wave is easily followed by satellite as the thickened marine layer is marked by overcast stratus a greatly curved offshore leading edge indicates that nonlinear effects are important offshore scale in the overcast is about 300 km in the south and 50 km in the north surface pressure gradient alongshore is closely related to the marine layer depth the surface wind shifts when the leading and trailing edge of the wave passes northerly wave progression ceases at the sharp bend formed by cape mendocino at this time a vortex is formed in the marine laye

shear wave splitting in refracted waves returned from the upper mantle transition zone beneath northern australia the broadband recording site at warramunga wra in the northern territory of australia provides good coverage of seismic wave propagation through the upper mantle for sources in the earthquake belt through indonesia and new guinea waves recorded on the radial v and tangential sh components are of comparable quality because the hard rock recording site minimizes the influence of coupling to p on the radial component refracted waves from the upper mantle transition zone show a clear advance of h wave arrivals compared with v eleven polarization analyses of waves returned from the transition zone yield an average time shift of 2 3 s with the fast direction scattered about the transverse direction nine polarization measurements of waves returned from the top of the lower mantle yield an average time shift of 1 7 s again with the fast direction near the transverse no appreciable time differences are observed between the radial and transverse polarizations for paths refracted within the lithospheric lid because the observations of shear wave splitting in waves passing through the low velocity zone he transition zone and the top of the lower mantle are not coherent in their absolute polarization the cause cannot lie in azimuthal anisotropy at shallow depths under the wra station the most plausible exphnation is transverse isotropy in shear within the low velocity zone under the unusually thick mantle lid under australia a possible contribution may come from anisotroly in olivine at the top of the upper mantle transition zone transverse isotropy in the 200 kin thick layer below the lithosphere down to the transition zone with a 1 faster shear wave speeds for horizontal polarization compared with vertical polarization will explain the splitting data for this asthenospheric region the level of anisotropy is quite reasonable and the polarization is consistent with lateral flow the geometry of the available paths for waves propagating within the mmltle lid inot sufficient to place constraints on the anisotropic properties of this heterogeneous a nd low loss region

the anisotropic seismic structure of the east european platform 1 we present models for the p and s velocity structure of the upper mantle beneath the east european platform including measurements of radial anisotropy the models were obtained by full waveform inversion of 3 component broadband seismograms from strike slip earthquakes located near the edge of the platform and recorded in russia and europe we used direct and multiply reflected body wave arrivals s ss p pp combined with fundamental mode love and rayleigh waves at source receiver distances between 15 and 50 to resolve mantle structure down to the 410 km discontinuity the platform is underlain by a radially anisotropic mantle lid extending to a depth of 200 km with a largely isotropic mantle below the model has a positive velocity gradient from 41 km to 100 km depth and a relatively uniform velocity structure from 100 km to 200 km depth with high sh and ph velocities 4 77 km s 8 45 km s shear anisotropy is uniform at 5 h v from 41 to 200 km depth drops to 2 from 200 to 250 km and is isotropic below that the average shear velocity from 100 to 250 km is also uniform at 4 65 km s and the drop in anisotropy is matched by a drop in h to 4 70 km s combined with an increase in v to 4 60 km s below 250 km there is a positive velocity gradient in both p and s velocity down to 410 km p anisotropy is not well resolved but p structure mimics the sh velocity structure suggesting that p is also anisotropic within the lid

generation of oceanic island basalt type volcanism in the western trans mexican volcanic belt by slab rollback asthenosphere infiltration and variable flux melting mantle plumes or decompression melting of a heterogeneous mantle have been proposed to explain oceanic island basalt oib type lavas found in the western trans mexican volcanic belt we show that mantle plumes cannot account for several geologic observations whereas decompression melting is unrealistic given the low extension rate in the volcanic arc on the basis of new geologic and geochemical studies we propose an alternative model that reconciles geologic data plate tectonic history and petrology since 8 5 ma the volcanic front has migrated trenchward 80 km and oib began to be emplaced in the rear half of the arc after a period of stalled subduction of the rivera plate between 7 2 and 4 8 ma as a whole oib accounts for 5 of the total volume of volcanism their trace element signatures require an enriched mantle source akin to the deep asthenosphere but also indicate a minor involvement of a subduction component we propose that during the period of very low convergence at the end of the miocene the leading edge of the rivera slab started to sink into the mantle and continued rolling back until it reached the present dip of 45 the sinking of the slab may have induced small amounts of asthenosphere to flow laterally into the opening mantle wedge from the gulf of california rift on the west and through the subducted rivera cocos plate boundary on the east this mechanism would produce veins of relatively enriched mantle which would be able to produce melts with an oib composition once the flux of fluids released from the subducted slab resumed

ore forming fluids and ore genesis of the large bayanbaolege ag polymetallic deposit southern great xing an range ne china abstract the large bayanbaolege ag polymetallic deposit is one of the newly discovered deposits in the tuquan linxi fe sn cu pb zn ag nb ta metallogenic belt of the southern great xing an range ne china its major ore bodies sulfide quartz veins are distributed within granodiorite porphyry and in adjacent late permian strata according to ore forming geological conditions mineralization and alternation characteristics source and features of ore forming fluid as well as metallogenic depth 2 o co 2 nacl system with medium temperatures mean temperatures stage i 368 c stage ii 286 c stage iii 206 c and medium low salinities mean salinities stage i 2 1 7 6 wt nacl equivalent stage ii 1 6 11 6 wt nacl equivalent stage iii 1 2 8 4 wt nacl equivalent c h o isotope data indicate that ore forming fluid was derived largely from magmatic fluid with the addition of meteoric water in the later stage

inversion of far regional broadband p waves for the estimation of source parameters from shallow depth earthquakes 1 attempts in separating the earthquake source effect from complex upper mantle wave propagation effects have been unsuccessful due to band limited world wide standardized seismograph network data and limitations in the computation of accurate seismograms in this study we examine the potential for estimating source parameters using broadband p waves observed between distances of 10 and 30 we used the reflectivity method which retains all of the rays to compute synthetic green s functions from the earth flattened global ak135 and regional t7 isotropic velocity models we applied the moment tensor inversion and iterative dislocation grid search methods to estimate seismic moment moment tensor focal mechanism and focal depth for three example seismic events the 1995 m w 5 7 west texas 1999 m w 5 6 scotty s junction nevada and 1999 southern iran m w 4 8 earthquakes the west texas and scotty s junction earthquakes were well recorded and they had independently established source parameters independent estimates from different data sets and agencies were used to validate the inversion results we selected the southern iran earthquake to show the utility of the method at lower magnitudes selected vertical and radial component seismograms were windowed about the p wave arrival corrected for instrument response and converted to velocity preserving the absolute amplitudes and periods within approximately 0 5 to 100 s both inverse methods were successful in separating the source effect with the use of the ak135 velocity model the inversion results using the t7 model appear slightly biased and had worse waveform fits compared to ak135 more importantly the use of two different velocity models resulted in biases in focal depths that were less than 2 km thereby providing a robust inverse method for focal depth utilizing far regional p waves would be most useful for remote earthquakes not adequately recorded locally and too small in magnitude to be recorded beyond epicentral distances of 30 for teleseismic analysis

orographically trapped coastal wind events in the pacific northwest and their oceanic response three ageostrophic orographically trapped wind events in the coastal zone of the pacific northwest are examined time series of wind speed wind direction air temperature sea level pressure ocean currents and ocean temperature are utilized to establish the general features of these events and to characterize the oceanic response it is suggested that these atmospheric events are highly nonlinear bores or gravity currents rather than quasi linear kelvin waves observed oceanic responses include a drop in sea surface temperature sst of 1 3 c offshore to approximately 150 km approximately the atmospheric rossby radius and a rise in sst of similar magnitude within 15 km of the shore a set of reduced gravity fully nonlinear single layer models is utilized to investigate the dynamics of the atmospheric features and their oceanic response and a possible air sea interaction the models reproduce several of the first order features of the air and sea phenomena such as the development of the atmospheric front and the wake of near inertial waves in the ocean

seasonal renewal of the california current the spring transition off california 1 a pair of high resolution oceanographic surveys in march and april 1995 revealed a large and rapid transition from late winter to spring conditions in the coastal zone off central and southern california these data are unique in capturing the detailed three dimensional physical structure of and biological response to the spring transition in the southern california current system ccs changes associated with the transition included a strong tilting of isopycnals which lifted by up to 60 m near the coast and dropped 20 40 m offshore a subsequent increase in cross shore density gradients the development of a strong nearshore equatorward jet and an increase in net equatorward transport from the shelf break out to 300 km offshore the most dramatic physical changes were confined to the shoreward 150 km and extended at least to the depth of the core of the california undercurrent 300 m in response to these physical changes there was an apparent strong increase in primary productivity as indicated by changes in nearshore vertically integrated fluorescence and beam attenuation coefficient atmospheric and oceanic conditions in the ccs were near seasonal norms in the winter and spring of 1995 implying that a transition of the magnitude and rapidity observed here may be an annual event furthermore the development of the coastal upwelling jet was independent of the winter manifestation of the main core of the california current which was maintained well off shore this suggests that the california current is regenerated seasonally through the development and offshore evolution of the coastal upwelling jet it is not known whether the new jet joins and strengthens or replaces the offshore core of the previous winter

upper mantle shear and compressional velocity structure of the central us craton shear wave low velocity zone and anisotropy one dimensional upper mantle velocity structure is estimated by modeling p sv and sh body waveforms sampling the central united states the resulting model features a thick mantle lid with a positive velocity gradient a significant shear wave low velocity zone 6 velocity reduction is required below the lid however the compressional velocities are not reduced the paths studied lie along the fast axes of teleseismic shear wave splitting measurements and absolute plate motion we observe splitting of upper mantle refracted shear waves with the transverse component slow relative to the radial component in order to fit the shear wave arrivals and satisfy teleseismic shear wave splitting observations we infer azimuthal anisotropy maximum 1 6 distributed throughout the mantle lid and low velocity zone with increasing anisotropy with depth

boninite like volcanic rocks in the 3 7 3 8 ga isua greenstone belt west greenland geochemical evidence for intra oceanic subduction zone processes in the early earth abstract the 3 7 3 8 ga isua greenstone belt of southwest greenland is characterized by variably metamorphosed metasomatised and deformed lithotectonic successions of volcanic and sedimentary rocks the voluminous mafic volcanic rocks are composed primarily of pillow basalts intercalated with ultramafic units the sedimentary rocks consist mainly of banded iron formation cherts conglomerates and siliciclastic turbidites the least altered metavolcanic amphibolites the garbenschiefer unit from the central tectonic domain of the isua greenstone belt are characterized by high mg number 0 60 0 80 mgo 7 18 wt al2o3 14 20 wt ni 60 645 ppm and cr 60 1920 ppm contents but low tio2 0 20 0 40 wt zr 12 30 ppm y 6 14 ppm and rare earth element ree concentrations these compositional features collectively represent a coherent mafic to ultramafic suite chondrite normalized ree patterns are concave upward on the primitive mantle normalized extended trace element diagrams they are characterized by relative depletion of nb but with an enrichment of zr relative to neighboring rees alteration deformation and crustal contamination can be ruled out as the cause of the distinct and coherent composition the average initial end value of these metavolcanic rocks is 2 collectively these geochemical characteristics are comparable to those of phanerozoic boninites given the observation that in the tertiary boninites are exclusively associated with intra oceanic subduction environments e g izu bonin mariana subduction system this suggests that intra oceanic subduction zone like geodynamic processes were operating as early as 3 7 3 8 ga

petrogenesis of adakitic porphyries in an extensional tectonic setting dexing south china implications for the genesis of porphyry copper mineralization the dexing adakitic porphyries quartz diorite granodiorite porphyries associated with giant porphyry cu deposits are located in the interior of a continent south china they exhibit relatively high mgo cr ni and sr contents high la yb and sr y ratios but low yb and y contents similar to adakites produced by slab melting associated with subduction however they are characterized by bulk earth like nd sr isotope compositions end t 1 14 to 1 80 and 87 sr 86 sr i 0 7044 0 7047 and high th 12 6 27 2ppm contents and th ce 0 19 0 94 ratios which are different from those of cenozoic slab derived adakites sensitive high resolution ion microprobe shrimp geochronology studies of zircons reveal that the dexing adakitic porphyries have a crystallization age of 171 3ma this age is contemporaneous with middle jurassic extension within the shi han rift zone and within plate magmatism elsewhere in south china indicating that the dexing adakitic porphyries were probably formed in an extensional tectonic regime in the interior of the continent rather than in an arc setting their high th contents and th ce ratios and middle jurassic age argue against an origin from a neoproterozoic 1000ma stalled slab in the mantle taking into account available data for the regional metamorphic magmatic rocks and the present day crustal thickness 31km in the area we suggest that the dexing adakitic porphyries were most probably generated by partial melting of delaminated lower crust which was possibly triggered by upwelling of the asthenospheric mantle due to the activity of the shi hang rift zone moreover the dexing adakitic magmas must have interacted with the surrounding mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity fo2 of the mantle the high fo2 could have induced oxidation of metallic sulfides in the mantle and mobilization of chalcophile elements which are required to produce associated cu mineralization therefore the cu metallogenesis associated with the dexing adakitic porphyries is probably related to partial melting of delaminated lower crust similar to the metallogenesis accompanying slab melting

a surface wave analysis of seismic anisotropy beneath eastern north america summary the nature of upper mantle seismic anisotropy beneath central and eastern north america has been evaluated using the phase velocities of surface waves traversing the length of the missouri to massachusetts moma broad band array frequency dependent phase delays of fundamental mode love and rayleigh waves measured across the array using a cross correlation procedure require the presence of anisotropy in the upper mantle 2 d radially anisotropic structures obtained via linearized inversion of these data contain shear anisotropy with a magnitude of 3 per cent between the moho and at least 180 km depth models in which the mantle lithosphere is isotropic cannot satisfy the data this anisotropy is approximately constant across the tectonic transition from the craton to the atlantic margin forward models consisting of a shallow lithospheric layer of azimuthal anisotropy derived from previous shear wave splitting observations fail to satisfy the surface wave delay times the combined surface wave and splitting results suggest the presence of two layers of anisotropy a lithospheric layer that produces the phase delay differences observed in love and rayleigh waves but is transparent to vertically propagating shear body waves and a deeper presumably asthenospheric layer that generates the shear wave splitting one plausible model is that the lithosphere is characterized by vertically heterogeneous anisotropic fabric which would produce minimal splitting in vertical shear waves such fabric has been hypothesized for regions of weak and complex splitting such as south africa and australia the results here imply that it may be appropriate for north america as well

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

relaxation from upwelling in the coastal ocean dynamics experiment a relaxation of the upwelling system on the northern california shelf occurs when upwelling favorable winds decay or reverse observations from the coastal ocean dynamics experiment are used to investigate this process with emphasis on the near surface temperature evolution models of relaxation warming are tested for the surface layer 0 30 m over midshelf with the result that the surface heat flux and poleward alongshelf advection can account for the observed temperature behavior onshore advection of the upwelled isopycnal field is a relatively unimportant contribution the warming patterns that are observed and which provide the gradients for the advective process have wedgelike shapes warmest inshore and in the south of the experimental area these patterns appear to be related to a topographic influence of point reyes possibly through the generation of gradients in the wind field remote advection of warm water from as far south as san francisco occasionally occurs as well the nature of the relaxation mechanism has general implications a new warm saline nutrient rich water mass may be formed in the surface layer since the warming processes are not the reverse of the cooling an important asymmetry is present it causes time variable upwelling to generate conditions very different from steady upwelling a new upwelling front is created during each event with upwelled water seaward of it and reversed alongshelf flow contributes to the warming and exchange mechanisms the system cannot be described or understood without the irreversible processes during upwelling and relaxation or without a mixed layer

petrogenesis of an alkali syenite granite rhyolite suite in the yanshan fold and thrust belt eastern north china craton geochronological geochemical and nd sr hf isotopic evidence for lithospheric thinning the yanshan fold and thrust belt in eastern china has been intruded by a series of alkalic igneous rocks ranging in composition from granite and rhyolite to syenite and trachyte laser ablation inductively coupled plasma mass spectrometry u pb analyses of zircon from three alkaline suites yield early cretaceous ages of 130 117ma three groups of rocks have been identified based on their mineralogical geochemical and sr nd hf isotope characteristics the alkali granites and rhyolites are ferroan and have low al2o3 mgo cao sr ba and eu concentrations and high sio2 total fe2o3 k2o nb ga ta th and heavy rare earth element abundances and ga al ratios geochemical data and sr ndand zircon hf isotopic compositions sr sr i1 4 0 7050 0 7164 end t 1 4 8 4 to 13 6 and ehf t 1 4 5 7 to 16 8 indicate that they were probably generated by shallow dehydration melting of biotiteor hornblende bearing granitoid crustal source rocks and then mixed with contemporaneous magma from a mantle and or lower crustal source ferroan syenites have distinct geochemical features from those of the alkaline granites and rhyolites suggesting that they were produced by clinopyroxene and plagioclase fractionation of melt derived from an enriched mantle source mixed with lower and upper crustal derived magmas the magnesian syenites and trachytes have sr ndand zircon hf isotopic compositions that are distinct from those of the ferroan syenites they were mainly derived from partial melting of lower crustal materials mixed with enriched mantle derived alkali basaltic magma the emplacement of an alkali syenite granite rhyolite suite coeval with the formation of metamorphic core complexes and pull apart basins in eastern china indicates they formed in an extensional setting possibly as a result of lithospheric thinning

emergence of burrowing urchins from california continental shelf sediments a response to alongshore current reversals abstract two sequences of bottom photographs taken every two or four hours for two months during the coastal ocean dynamics experiment code off the russian river california reveal the dynamic nature of interations between the water column the sediments and benthic organisms in the mid shelf silt deposit time lapse photographs taken between late spring and early summer in 1981 and 1982 show that the subsurface dwelling urchin brisaster latifrons one of the largest invertebrates found in shelf depth fine sediment off the u s pacific coast occasionally emerged from the sediment plowed the sediment surface during the course of a few hours to several days then buried themselves again frame by frame study of the film sequences shows that the urchins typically emerged following relaxation of coastal upwelling periods characterized by current direction reversals and increases in bottom water turbidity among the possible causes of the emergence of urchins and the consequent bioturbation of the upper few cm of sediment a response to an enhanced food supply seems most plausible circumstantial evidence suggests the possibility that phytoplankton sedimentation during periods of upwelling relaxation could provide a new source of food at the sediment surface

dynamics of wind driven upwelling and relaxation between monterey bay and point arena local regional and gyre scale controls 1 in north and central california equatorward winds drive equatorward flows and the upwelling of cold dense water over the shelf during the midspring and summer upwelling season when the winds temporarily weaken the upwelling flows between point reyes and point arena relax becoming strongly poleward over the shelf analytical and numerical models are used to describe the effect of alongshore variability of winds bathymetry and basin scale pressure gradients on the strength of upwelling and its relaxation alongshore winds weaken to the south of point reyes and the shelf becomes narrower from point reyes to monterey bay both of these lead to reduced upwelling at and to the north of point reyes causing an alongshore gradient of temperature and density on the shelf these alongshore gradients lead to an along isobath pressure gradient over the shelf that drive the relaxation flows a simple analytical model is used to explain the dynamics magnitude and structure of the relaxation flows the modeling also suggests that the depth of origin of the upwelled waters and thus their temperature is controlled by the along isobath pressure gradient that exists over the continental slope this along slope pressure gradient is also responsible for the california undercurrent in this region this pressure gradient is not generated in a model of the californian coast extending from 32 n to 42 n and integrated for several months suggesting it is caused by dynamics whose spatial or temporal scales are larger than the californian coast and or longer than several months

early cretaceous bimodal magmatism related epithermal mineralization a case study of the gaosongshan gold deposit in the northern lesser xing an range ne china abstract low sulfidation ls gold mineralization is partially associated with bimodal volcanism in origin sources of ore mineralized fluids and relevant dynamic processes remain poorly understood to better understand these issues a study including deposit geology petrology zircon u pb dating and element and sr nd hf isotope geochemistry of bimodal volcanic rocks at gaosongshan was conducted the bimodal volcanic rocks are composed of andesitic rocks basalt andesite andesite trachyandesite andesitic pyroclastic of the meifeng formation and overlying rhyolite lava of the fuminhe formation cut by equivalent porphyry stocks which contain pyrite bearing granular textured quartz cavity with a sugary appearance with trapped single phase magmatic fluids the andesitic suite formed at approximately 106 108 ma prior to eruption of the younger rhyolitic magmas 105 6 1 7 ma n 13 mswd 1 2 the andesites show calc alkaline affinities which is a subduction related characteristic and show moderate la ybn 7 91 11 36 and weakly negative europium anomalies 0 80 1 02 indicating a source in the asthenospheric mantle with varying contamination by both subduction and continental materials a type rhyolitic rocks are geochemically comparable to the andesitic suite and their higher la ybn 13 01 30 05 and lower eu eu 0 66 0 73 indicate evolved products of andesitic magmas the estimated oxygen fugacity of dry 1 2 water rhyolite lava is fmq 1 87 whereas rhyolite porphyry is more oxidized fmq 0 12 and water rich 2 5 2 8 with probably being water saturated at 2 0 2 4 km depths therefore it is assumed that the essential constraints of bimodal magmatism on epithermal gold mineralization are sequential processes from ascending and gradual differentiation of crustal level mantle derived basaltic magmas to releases of hydrothermal solutions from the silica rich magma reservoir at shallower levels most importantly the oxygen fugacity of and the fluid fluxes from dry rhyolitic melts are critical restricting parameters for the limited reserves at gaosongshan thus this research contributes objective evidence for investigations of deposit genesis and prospecting targets

lithospheric structure of the qiangtang terrane northern tibetan plateau from complete regional waveform modeling evidence for partial melt we report models of p and s wave velocity and attenuation for the the crust and uppermost mantle of the qiangtang terrane northern tibetan plateau inferred by fitting reflectivity synthetic seismograms to observed complete regional waveforms the data are three component broadband seismograms recorded by the 1991 1992 iris passcal incorporated research institutions for seismology program for array seismic studies of the continental lithosphere tibetan plateau experiment and global seismic network stations in the region the qiangtang terrane has thick crust 65 5 km with p and s wave velocities of 6 1 6 3 and 3 34 3 43 km s respectively yielding an anomalously high crustal poisson s ratio of 0 29 0 02 seismic velocities of the upper mantle of the qiangtang terrane are normal for p waves and slow for s waves 8 10 and 4 35 4 41 km s respectively with a high mantle poisson s ratio of 0 29 0 01 attenuation in the crust and upper mantle is high qp 100 200 and qs 44 89 modeling of the broadband p waveforms suggests that a decrease in mantle velocity occurs at about 160 km depth in the mantle however this is not unambiguously supported by the data and modeling the crust and uppermost mantle of the qiangtang terrane probably contains partial melt based on the high poisson s ratio low shear wave velocities and low q the absence of high frequency sn and the presence of volcanism of mantle lithospheric origin support the presence of partial melt crustal and uppermost mantle structure in the qiangtang terrane is different from that for the lhasa terrane immediately to the south based on results of our previous studies the average crustal p and s wave velocities are 4 faster and 2 slower respectively in the qiangtang terrane relative to the lhasa terrane this yields a significant difference in the crustal poisson s ratio with values of 0 29 for the qiangtang terrane and 0 25 for the lhasa terrane differences in the uppermost mantle p and s wave velocities and poisson s ratios of these two adjacent terranes cannot be explained by temperature differences alone using the mantle temperature estimates of mcnamara et al 1997 we suggest that partial melt of an ultramafic composition beneath the qiangtang terrane fits the velocity and poisson s ratio estimates

cross shore variation of wind driven flows on the inner shelf in long bay south carolina united states and exceeded 0 1 n m 2 vertical mixing occurred the two layered flow pattern disappeared and currents were directed alongshore with the wind at all sites and throughout the water column in the fall near bed flows close to the shore water depth 7 m were often reduced compared to or opposed those measured farther offshore under southwestward winds a simplified analysis of the depth averaged alongshore momentum balance illustrates that the alongshore pressure gradient approached or exceeded the magnitude of the alongshore wind stress at the same time that the nearshore alongshore current opposed the wind stress and alongshore currents farther offshore in addition the analysis suggests that the wind stress is reduced closer to shore so that the alongshore pressure gradient is large enough to drive the flow against the wind

surface circulation in the gulf of california in summer from surface drifters and satellite images 2004 2006 surface drifters released in the gulf of california between june 2004 and august 2006 are used to describe the surface circulation in late spring and summer in the june to september mean there was a poleward coastal current on the shelf and slope of the mainland side of the gulf with mean speed 0 3 m s it reached the northern gulf and joined the cyclonic circulation typical of this zone in summer in the western half of the southern gulf the drifters presented recirculating currents that are due to mesoscale eddies that appear to dominate the surface circulation in summer in june 2004 the coastal current presented an enhancement event with mean speed around 0 60 m s and maximum 0 80 m s it took 20 days for a particular drifter to travel the 1000 km from the gulf entrance to the head this strengthening of the coastal current was apparent in chlorophyll a and sst satellite images the drifters following closely the intrusion of warm chlorophyll poor surface water from outside the gulf the drifters and the satellite images suggest that the current enhancement event lasted less than a month this mesoscale event was linked with a mesoscale remote forcing in the tropical pacific coast and with a mesoscale local forcing of the wind these events seem to occur every year and are probably important in carrying organisms and properties from the entrance to the whole length of the gulf

on the lehmann discontinuity the lehmann discontinuity 200km in the upper mantle is proposed to result from a change in the preferred orientation of olivine as a result of a change in deformation mechanism in the shallow upper mantle deformation is due to dislocation creep and results in an anisotropic structure whereas in the deeper upper mantle diffusion creep becomes dominant due to a smaller activation volume resulting in an isotropic structure for anisotropy due to dislocation glide corresponding to a horizontal flow the resultant anisotropy will yield vsh vsv and vph vpv thus for waves propagating nearly vertically e g scs waves there will be discontinuous jumps in the s and p wave velocities at this discontinuity in this model the depth of the lehmann discontinuity depends on the deformation conditions such as stress level geotherm water fugacity and grain size giving a natural explanation for its observed variation with tectonic setting

large scale structure in wind forcing over the california current system in summer abstractthe wind that drives oceanic eastern boundary upwelling systems is highly variable in many locations the standard deviation of wind velocity on time scales of days to weeks is larger than the mean in the 1600 km long california current system ccs the spatial decorrelation scale of the wind fluctuations is 400 800 km suggesting wind fluctuations in the north and south ends of the system are not related yet there is also the suggestion in the literature of a larger scale structure in the fluctuations here empirical orthogonal function eof analysis of buoy and satellite wind velocities confirms the existence of that structure this analysis covers a larger spatial domain than previous eof studies in the ccs and to allow for propagation of the wind fluctuations includes an approach for calculating hilbert eofs from time series with gaps the large scale structure in the wind fluctuations is a quasi dipole pattern spanning the coastline from washington through california it accounts f

tracing magma mixing in granite genesis in situ u pb dating and hf isotope analysis of zircons in situ zircon u pb and hf isotopic data have been determined for mafic microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china in order to constrain the sources and petrogenesis of granites the zircon u pb age of the enclaves 120 1 ma is identical to that of the host monzogranite 120 1 ma establishing that the mafic and felsic magmas were coeval the hf isotopic composition of the enclaves ehf t 4 5 to 6 2 is distinct from the host monzogranite ehf t 15 1 to 25 4 indicating that both depleted mantle and crustal sources contributed to their origin the depleted mantle component was not previously revealed by geochemical and nd and sr isotopic studies showing that zircon hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information some wall rock contamination is indicated by inherited zircons with considerably older u pb ages and low initial hf isotopic compositions hafnium isotopic variations in early cretaceous zircons rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data

upper mantle s velocity structure of north america we have inverted fundamental and higher mode rayleigh waveforms from 685 vertical component broadband seismograms with wave paths over north america to obtain an image of the upper mantle s velocity structure down to 660 km among the well resolved features of the new model are 1 a high velocity root beneath the north american craton which extends no deeper than 250 km except near the archean core of the craton where depths of 350 km are reached 2 a weak band of low velocity along the eastern margin of the north american craton which reaches into the transition zone 3 a low velocity slab window beneath the western united states down to a depth of 300 km 4 areas of low uppermost mantle velocity beneath the cascade volcanoes the yellowstone hotspot track the colorado plateau the sierra madre occidental and the grabens bordering the jalisco block and 5 a pronounced band of high velocities in the transition zone coinciding with the expected location of the subducted trailing fragments of the farallon plate we introduce several improvements to the method of partitioned waveform inversion which was used to compute the new model rather than to correct for an estimated depth to the mohorovicic discontinuity we leave the crustal thickness as a free though yet poorly resolved parameter in the inversion we also improve the windowing and filtering operator used to select uncontaminated waveforms

late cretaceous genesis of the kula plate abstract we propose that the pacific kula ridge began spreading approximately 85 m y b p during late cretaceous time extrapolation of the great magnetic bight backwards in time results in an implausible ridge configuration this implies that plate velocity vectors for the pacific kula and farallon plates were not constant during this interval evidence for splitting of the kula plate from the pacific plate along the chinook trough is the relationship between the north striking amlia and adak fracture zones the chinook and emperor troughs and the magnetic lineations south of the aleutian trench if this hypothesis is correct it will require that mesozoic reconstructions of the pacific basin and their relation to cenozoic reconstructions be re examined a previously unrecognized mesozoic plate may be required we propose calling this the izanagi plate

mesozoic strike slip movement of the dunhua mishan fault zone in ne china a response to oceanic plate subduction abstract the ne striking dunhua mishan fault zone dmfz is one of two branches of the continental scale sinistral tan lu fault zone in ne china the field data presented here indicate that the ca 1000 km long dmfz records two phases of sinistral faulting the structures produced by these two phases of faulting include ne sw striking ductile shear belts and brittle faults respectively mylonite hosted microstructures and quartz c axis fabrics suggest deformation temperatures of 450 c 500 c for the ductile shear belts combining new zircon u pb dates for 14 igneous rock samples analyzed during this study with the geology of this region indicates these shear belts formed during the earliest early cretaceous this phase of sinistral displacement represents the initial formation of the dmfz in response to the northward propagation of the tan lu fault zone into ne china a phase of early cretaceous rifting was followed by a second phase of sinistral faulting at 102 96 ma as evidenced by our new u pb ages for associated igneous rocks combining our new data with the results of previous research indicates that the dfmz records a four stage cretaceous evolutionary history where initial sinistral faulting at the beginning of the early cretaceous gave way to rifting during the rest of the early cretaceous this was followed by a second phase of sinistral faulting at the beginning of the late cretaceous and a second phase of local rifting during the rest of the late cretaceous the cretaceous evolution of the dmfz records the synchronous tectonic evolution of the ne china continent bordering the pacific ocean two phases of regional n s compression generated the two phases of sinistral faulting within the dmfz whereas two stage regional extension generated the two phases of rifting the two compressive events were the result of the rapid low angle subduction of the izanagi and pacific plates whereas the two stage extension was caused by the roll back of these respective plates the final closure of the mongol okhotsk ocean at the beginning of the early cretaceous intensified the synchronous compression in ne china causing the northward propagation of the tan lu fault zone

dynamic buckling of subducting slabs reconciles geological and geophysical observations abstract ever since the early days of the development of plate tectonic theory subduction zones have been engrained in geological thinking as the place where steady linear slabs descend into the mantle at a constant uniform dip angle beneath volcanic arcs however growing evidence from geological and geophysical observations as well as analog and numerical modeling indicates that subducting slabs buckle in a time dependent manner in contrast to the steady state linear cartoons that dominate the literature to evaluate the implication of time dependent slab buckling of geological events we conduct a series of 2 d numerical dynamic kinematic subduction experiments by varying the viscosity increase across the 660 km discontinuity and the strength of the subducting slab our results show that slab buckling is a universal figure in all the experiments when rate of the trench migration vtrench is relatively slow vtrench the slab buckling behavior in our experiments explains a variety of puzzling geological and geophysical observations first the period of slab buckling is consistent with short periodic variations 25 myr in the motions of the oceanic plates that are anchored by subduction zones second the scattered distributions of slab dips from 20 to 90 in the upper mantle are snapshots of time dependent slab dip third the current compressional and extensional stress environments in back arcs are well correlated with shallowing and steeping slab dip resulting from slab buckling fourth the temporal evolution of stress environments in the andes is well correlated with alternate slab dip these correlations indicate that time dependent slab buckling is a major factor controlling subduction zone dynamics

satellite derived sea surface temperature variability off california during the upwelling season abstract an empirical orthogonal function analysis of an advanced very high resolution radiometer sea surface temperature data set encompassing the spring summer period during 1991 1993 was used to examine patterns of temperature variability off northern and central california this analysis decomposed the spatial variability of remotely sensed sea surface temperature in 124 images that covered an offshore distance of 200 km and an alongshore distance of 500 km the first mode empirical orthogonal function described 65 of the spatial variability in the data set the spatial amplitude pattern of the first mode which closely resembled the mean of all the images revealed a strong cross shore gradient with much cooler water nearshore and warmer water offshore these areas of cool waters were associated with known upwelling locales and the large scale temperature structure compared favorably to that derived from historical california cooperative oceanographic fisheries investigation calcofi climatology the mode 1 temporal amplitude function representing the temporal modulation of this spatial pattern was coupled with changes in the alongshore component of the coastal wind field interannual variations in the timing of the spring transition were reflected in this temporal amplitude time series the second mode empirical orthogonal function described 11 of the variability in the data set the spatial pattern revealed a north south structure that appeared to be related to regional spatial variations in the strength of upwelling favorable wind the third empirical orthogonal function described only 3 of the data variability and the spatial structure suggested a meandering of the coastal surface flow the results of this investigation indicate that the empirical orthogonal function method was effective at characterizing from the satellite data the dominant nearshore surface properties of the california current system related to upwelling and wind and by extension suggest that it is a suitable approach for remotely investigating other less well known eastern boundary current systems

spatial temporal relationships of mesozoic volcanic rocks in ne china constraints on tectonic overprinting and transformations between multiple tectonic regimes abstract la icp ms zircon u pb ages and geochemical data are presented for the mesozoic volcanic rocks in northeast china with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the paleo asian ocean mongol okhotsk and circum pacific tectonic regimes the new ages together with other available age data from the literature indicate that mesozoic volcanism in ne china can be subdivided into six episodes late triassic 228 201 ma early middle jurassic 190 173 ma middle late jurassic 166 155 ma early early cretaceous 145 138 ma late early cretaceous 133 106 ma and late cretaceous 97 88 ma the late triassic volcanic rocks occur in the lesser xing an zhangguangcai ranges where the volcanic rocks are bimodal and in the eastern heilongjiang jilin provinces where the volcanics are a type rhyolites implying that they formed in an extensional environment after the final closure of the paleo asian ocean the early middle jurassic 190 173 ma volcanic rocks both in the erguna massif and the eastern heilongjiang jilin provinces belong chemically to the calc alkaline series implying an active continental margin setting the volcanics in the erguna massif are related to the subduction of the mongol okhotsk oceanic plate beneath the massif and those in the eastern jilin heilongjiang provinces are related to the subduction of the paleo pacific plate beneath the eurasian continent the coeval bimodal volcanic rocks in the lesser xing an zhangguangcai ranges were probably formed under an extensional environment similar to a backarc setting of double direction subduction volcanic rocks of middle late jurassic 155 166 ma and early early cretaceous 145 138 ma age only occur in the great xing an range and the northern hebei and western liaoning provinces limited to the west of the songliao basin and they belong chemically to high k calc alkaline series and a type rhyolites respectively combined with the regional unconformity and thrust structures in the northern hebei and western liaoning provinces we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the mongol okhotsk suture belt the late early cretaceous volcanic rocks widely distributed in ne china belong chemically to a low to medium k calc alkaline series in the eastern heilongjiang jilin provinces i e the eurasian continental margin and to a bimodal volcanic rock association within both the songliao basin and the great xing an range the volcanics in the eastern heilongjiang jilin provinces formed in an active continental margin setting related to the subduction of the paleo pacific plate beneath the eurasian continent and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust or both late cretaceous volcanics limited to the eastern heilongjiang jilin provinces and the eastern north china craton ncc consist of calc alkaline rocks in the eastern heilongjiang jilin provinces and alkaline basalts in the eastern ncc suggesting that the former originated during subduction of the paleo pacific plate beneath the eurasian continent whereas the latter formed in an extensional environment similar to a backarc setting taking all this into account we conclude that 1 the transformation from the paleo asian ocean regime to the circum pacific tectonic regime happened during the late triassic to early jurassic 2 the effect of the mongol okhotsk suture belt on ne china was mainly in the early jurassic middle late jurassic and early early cretaceous and 3 the late early cretaceous and late cretaceous volcanics can be attributed to the subduction of the paleo pacific plate beneath the eurasian continent

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

hydrographic observations along the code central line off northern california 1981 abstract repeated ctd observations were made along a single section spanning the continental shelf off northern california at 38 40 n during 1981 the section consisted of nine standard stations between 1 and 46 km from the shore in water depths between 40 and 1700 m the shelf break was at a depth of 150 m about 25 km from shore the section was occupied 17 times between 13 april and 3 august and twice in december and a similar section had been occupied in february during the april august period winds were strong and persistently favorable for upwelling isotherms isohalines and isopycnals in the upper 200 in sloped persistently upward toward the coast and coldest saltiest and densest surface waters almost always occurred at the most inshore nation variations in wind strength caused changes in the surface layer over the entire shelf stronger winds were associated with lower temperatures and higher salinities subsurface temperatures increased gradually between april and august we were unable to

evolution of the late cretaceous dadaepo basin se korea in response to oblique subduction of the proto pacific izanagi kula or pacific plate abstract the dadaepo basin is a small late cretaceous sedimentary basin in se korea located on the eastern margin of asia the basin is an isolated extensional basin situated between the nne striking yangsan and dongnae faults the basin fill sediments named the dadaepo formation consist of channelized conglomerates and sandstones intercalated with dominantly purple mudstones in the lower part the upper part is dominated by fine to coarse grained tuffaceous sandstones and olive to dark gray mudstones with abundant volcanic interbeds the formation unconformably overlies dacitic rocks dated at ca 94 ma and is overlain by basaltic andesite dated at ca 69 ma ar ar ages the overall configuration of the strata of the dadaepo formation indicates syndepositional tilting of the basin floor to the north northeast a number of outcrop scale faults are observed in the basin fill sediments of which the majority are nw striking normal faults including syndepositional growth faults the orientations of mafic magmatic and clastic dikes interpreted as being approximately contemporaneous with the deposition of the dadaepo formation are also nearly parallel to the strikes of outcrop scale normal faults all these extensional structures consistently indicate ne sw extension of the basin and obliquely intersect the basin bounding yangsan and dongnae faults at angles of 40 60 it is thus concluded that the dadaepo formation was deposited in a pull apart basin that subsided as a result of nne striking sinistral strike slip faulting in the southeastern part of the korean peninsula during the campanian late cretaceous this strike slip faulting was related to north northwestward oblique subduction of the proto pacific izanagi kula or pacific plate under the eastern margin of the eurasian plate

shrimp u pb dating and geochemistry of the cretaceous plutonic rocks in the korean peninsula a new tectonic model of the cretaceous korean peninsula abstract the cretaceous tectonomagmatism of the korean peninsula was examined based on geochemical and geochronological data of the cretaceous plutonic rocks along with distribution of volcano sedimentary nonmarine n to ne trending fault bounded sedimentary basins we conducted sensitive high resolution ion microprobe shrimp zircon u pb ages and whole rock geochemical compositions of 21 cretaceous plutonic rocks together with previously published data from the central to southern korean peninsula four age groups of plutonic rocks were identified group i ca 119 106 ma in the northern to central area group ii ca 99 87 ma in the central southern area group iii ca 85 82 ma in the central to southern area and group iv ca 76 67 ma in the southernmost area these results indicate a sporadic trenchward younging trend of the cretaceous magmatism in the korean peninsula the group i ii and iii rocks are dominated by high k calc alkaline i type rocks with rift related a type granitoids in contrast the group iv rocks are high k calc alkaline i type plutonic rocks with no a type rocks the geochemical signatures of the entire groups indicated lrees light rare earth elements enrichments and negative nb ta and ti anomalies indicating normal arc magmatism a new tectonic model of the cretaceous korean peninsula was proposed based on temporal and spatial distribution of the cretaceous plutons represented by four age groups 1 magmatic quiescence throughout the korean peninsula from ca 160 to 120 ma 2 intrusions of the i and a type granitoids in the northern and central korean peninsula group i plutonic rocks from ca 120 to 100 ma resulted from the partial melting of the lower continental crust due to the rollback of the izanagi plate expressed as the conversion from flat lying subduction to normal subduction the gyeongsang nonmarine sedimentary rift basin in the korean peninsula and adakite magmatism preserved in the present day japanese islands supported the slab rollback followed by steepening of the izanagi plate with an injection of upwelling of the hot asthenosphere into the mantle wedge 3 alternating shallow from 100 to 85 ma to steep from 85 to 65 ma subduction resulted in the migration of the normal arc magmatism in the southern korean peninsula expressed as the intruded i and a type group iii and i type granitoids group iv respectively the tectonomagmatism of the korean peninsula showed the unique style of evolution different from those of south china and japanese islands

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

adakites without slab melting high pressure differentiation of island arc magma mindanao the philippines abstract new geochemical data for pleistocene magmatic rocks from the surigao peninsula eastern mindanao the philippines demonstrate typical adakitic traits including elevation of sr y and depletion of the heavy rare earth elements 87sr 86sr and 143nd 144nd ratios of the adakites do not support melting of the subducted philippine sea plate but resemble pliocene arc lavas generated in the same subduction zone excepting the heavy rare earth elements the adakites and arc lavas also possess similar ratios of incompatible elements suggesting that the adakites were ultimately derived from melting of the mantle wedge the wide range of sio2 in the adakites and its strong correlation with trace element concentrations and ratios indicate two possible mechanisms for generating the adakitic signature 1 adakitic melt was produced from basaltic arc magma by fractional crystallisation of a garnet bearing assemblage 2 solidified basaltic rock containing garnet melted to yield adakitic magma in either case the basaltic precursor was generated from fluid modified mantle then differentiated within the garnet stability field in surigao this requires differentiation within mantle the surigao example suggests that any subduction zone has the potential to produce adakitic magma if basalt crystallises at sufficient depth this has important implications for the geodynamics of modern and ancient subduction zones that have generated similar rocks

mesoscale patterns in the cape sao vicente iberian peninsula upwelling region 1 the coastal upwelling region near cape sao vicente the southwestern tip of the iberian peninsula where the southern zonal coast meets the meridional western coast was studied using over 1200 advanced very high resolution radiometer avhrr satellite images of sea surface temperature and time series of sea level height wind velocities and nearshore sea surface temperature recorded at coastal sites within 200 km of the cape summer upwelling is more intense and persistent off the western coast than off the southern coast where a recurrent warm coastal countercurrent flows westward and at times turns northward along the western coast after reaching the cape in this region the equatorward current jet of cold water upwelled off the western coast is no longer bounded by a coast three preferred directions for the spreading of this water are identified the most persistent is eastward along the southern shelf break and slope possibly merging with waters previously upwelled locally which becomes separated from shore by the coastal progression of the warmer counterflow the second preferred direction results in the southward development of a cold filament feature fed by cold waters upwelled farther north and represents the southernmost extent of the intense coastal upwelling jet which overshoots the cape the least frequent feature to develop is a cold filament that grows westward at the latitude of the cape appearing to result from the meandering of the equatorward jet the coastal countercurrent is seen to interact with the equatorward jet at times of relaxation not only by separating the cold upwelled water from the coast but when it is energetic enough breaking westward offshore through the equatorward cold flow and separating the eastward and southward cold features from the upcoast cold waters empirical evidence shows the presence of an alongshore pressure gradient stronger in summer driving the coastal progression of the warm counterflow wind forcing plays an important role in the circulation by augmenting or diminishing the effect of the preexisting alongshore pressure gradients the extent of the progression of the warm coastal countercurrent along the southern and western coast is dictated by the the strength of the upwelling favorable wind stress which is able to balance and reverse the alongshore flow at least in the upper layers

plate bending at subduction zones consequences for the direction of plate motions abstract bending of lithospheric plates at subduction zones is thought to be an important source of dissipation for convection in the earth s mantle however the influence of bending on plate motion is uncertain here we use a variational description of mantle convection to show that bending strongly affects the direction of plate motion subduction of slabs and subsidence of oceanic lithosphere with age provide the primary driving forces dissipation is partitioned between plate bending and various sources of friction at plate boundaries and in the interior of the mantle due to viscous flow we determine the poles of rotation for the pacific and nazca plates by requiring the net work to be stationary with respect to small changes in the direction of motion the best fit to the observed rotation poles is obtained with an effective lithospheric viscosity of 6 1022 pa s bending of the pacific plate dissipates roughly 40 of the energy released by subduction through the upper mantle

mesoscale surveys over the shelf and slope in the upwelling region near point arena california repeated mesoscale surveys of a 40 km wide 100 km long coastal region near point arena california were conducted during the upwelling season april august in 1981 and 1982 each survey included conventional conductivity temperature depth casts at standard locations over the continental shelf and slope between 38 n and 39 10 n and continuous operation of a doppler acoustic log to obtain velocity profiles in the 20 to 150 m depth range synoptic surveys covered the entire grid in 2 3 days winds were strongly favorable for upwelling during the three 1981 surveys and were weak or variable during the three 1982 surveys surface temperature and salinity fields reflect the influence of both the seasonal winds and day to day variations in the wind persistently low surface salinities offshore reflect the general southward advection of subarctic waters and sporadic low salinities over the inner shelf reflect north ward advection of local runoff through an intermittent narrow countercurrent along the coast circulation patterns during all but one of the surveys were very complex and included meandering equatorward flow cyclonic and anticyclonic eddies and inshore countercurrents the simple two dimensional equatorward baroclinic coastal jet usually associated with coastal upwelling was observed during only one of our surveys overall average fields are relatively simple they show broad equatorward surface flow a very weak inshore countercurrent and a definite poleward undercurrent at the shelf break average temperature salinity and density fields are generally congruent with the average flow pattern average isotherms and isohalines are not strictly parallel to the coastline south of the coastline bend at point arena they diverge gradually from the coast comparison of average sections calculated from 10 matched pairs of central and arena lines separated by 50 km shows there are systematic differences between them warmer fresher waters lie nearer shore and in shallower water off point arena than on the central line this suggests that the surface waters flowing past point arena have sufficient southward momentum to cross isobaths comparison of average velocity sections on these two lines shows some differences in structure since the variability is large these may not be significant comparison of the measured and geostrophic average shears suggests there is a significant ageostrophic component in the upper layers above 40 m it may be the signature of an average wind driven ekman spiral

geochronology and geochemistry of late cretaceous paleocene granitoids in the sikhote alin orogenic belt petrogenesis and implications for the oblique subduction of the paleo pacific plate we present zircon u pb ages major and trace element analyses and zircon hf isotope data on the late cretaceous paleocene granitoids at the southern end of the sikhote alin orogenic belt of the russian far east these data are used to discuss the petrogenesis of the granitoids in the context of the paleo pacific subduction beneath the eastern eurasia zircons from four granitoid samples give emplacement ages of 56 83 91 and 92 ma these granitoids with high sio2 73 43 76 76 wt are metaluminous to weakly peraluminous a cnk 0 97 1 03 and belong to the high k calc alkaline series k2o 3 75 4 95 wt they are all enriched in light rare earth elements lrees and large ion lithophile elements liles and relatively depleted in high field strength elements hfses with striking depletion also in ba sr p and eu they are petrographically and geochemically consistent with being of i type granitoids the zircons have ehf t values 0 8 to 7 6 higher than whole rock ehf t values predicted from whole rock end t 4 1 to 0 5 in the literature all these observations suggest that primary magmas parental to these granitoids were likely to have derived from partial melting of a juvenile lower crust accompanied by assimilation with ancient mature crust during magma ascent and evolution a recent study illustrates that the collision of an exotic terrane carried by the paleo pacific plate with the continental china at 100 ma accreted the basement of the chinese continental shelf beneath east and south china seas and resulted in a new plate boundary of transform nature between the nnw moving paleo pacific plate and the eastern margin of the shelf our new data and analysis of existing data support this hypothesis but we hypothesize that this transform becomes transpressional in its northern segment with oblique subduction of the paleo pacific plate beneath northeastern asia as manifested by the late cretaceous paleocene granitoids in the russian far east ne china 97 56 ma and south korea sw japan 96 71 ma these tectonic and magmatic events took place prior to the opening of the huanghai bohai and japan seas which are of rift origin from continental china much later our study emphasizes the necessity and significance of plate tectonics reconstruction in the greater northwestern pacific region since the cretaceous