paleoproterozoic tectonic transition from collision to extension in the eastern cathaysia block south china evidence from geochemistry zircon u pb geochronology and nd hf isotopes of a granite charnockite suite in southwestern zhejiang abstract the badu complex and associated paleoproterozoic granitoids are among the oldest known rocks in the cathaysia block in south china the paleoproterozoic units of the badu complex are dominantly composed of metapelitic rocks and meta greywackes here we report la ss icp ms laser ablation split stream inductively coupled plasma mass spectrometry zircon u pb data from a newly discovered garnet bearing granite which show an emplacement age of 1929 15 ma and metamorphism at 1872 34 ma we also report u pb ages of 1886 16 ma 1858 7 ma 1848 11 ma from a gneissic granodiorite and two charnockites respectively the garnet bearing granite is peraluminous with a cnk range from 1 1 to 1 3 the rock shows relatively high sio2 k2o and rb contents and low total ree sr cao and ferromagnesian components typical of leucogranites the whole rock nd two stage model age tdm2 nd of this rock is ca 2 7 ga zircon hf crustal model ages tdmc hf peak at about 2 7 ga and abundant inherited zircons occur with u pb ages in the range of 2044 to 2803 ma evidences from zircon u pb age and hf isotope compositions whole rock nd isotopes and whole rock major and trace elements suggest a metasedimentary protolith and that the garnet bearing granite leucogranite was derived by partial melting in a thickened crust at about 1 93 ga the gneissic granodiorite and charnockites show indistinguishable major and trace element features as well as zircon hf and whole rock nd isotope compositions indicating that they were generated from the same source rocks the gneissic granodiorite and charnockites are ferroan calc alkalic and metaluminous with a cnk range from 0 80 to 0 98 they display relatively low sio2 contents and ga al ratios suggesting their a type affinity their zircon tdmc hf age peak is 2 9 ga and whole rock tdm2 nd ages range from 2 8 to 2 9 ga these high temperature rocks were generated possibly through the partial melting of ancient amphibolites 2 9 ga with heat input from asthenosphere upwelling and magmatic underplating in an extensional setting at about 1 85 1 88 ga combined with data from previous studies we suggest three episodes of major crustal growth in this region at 1 8 1 9 ga 2 7 ga and 2 9 ga during the 1 8 1 9 ga event extensive reworking also took place from the 1 93 ga syn collision leucogranite garnet bearing granite the 1 88 1 85 ga post collision a type granites and charnockites the granite charnockite suite and the1 85 1 77 ga intraplate basaltic rocks li 1997 and xiang et al 2008 in the region a paleoproterozoic orogenic cycle can be deciphered in the cathaysia block the rapid transition of tectonic regime from collision to post collisional extension can be correlated to the assembly of the supercontinent columbia

850 790 ma bimodal volcanic and intrusive rocks in northern zhejiang south china a major episode of continental rift magmatism during the breakup of rodinia abstract shrimp u pb zircon ages and geochemical and nd isotopic data are reported for mid neoproterozoic igneous rocks in northern zhejiang province south china the shenwu dolerite dykes the daolinshan granite diabase complex and the shangshu bimodal basalt rhyolite volcanic rocks were dated at 849 7 ma 794 9 ma and 792 5 ma respectively all the studied mafic rocks are tholeiitic in compositions and exhibit overall moderate enrichments in most incompatible trace elements resembling intraplate basaltic rocks in continental rifts the 850 ma shenwu dolerites are the earliest anorogenic basaltic rocks identified so far after the ca 1 1 0 9 ga sibao orogeny but seem to predate the neoproterozoic rifting our results are clearly at variance with the alternative tectonic model that an active continental margin existed along the southern margin of the yangtze block until ca 800 ma the intensive 790 ma bimodal volcanic and plutonic rocks part of a major phase of mid neoproterozoic rifting are concurrent with the widespread mid neoproterozoic intraplate magmatism throughout south china they are most likely related to the proposed mantle superplume that led to the breakup of the supercontinent rodinia

observations and models of inertial waves in the deep ocean the structure of the inertial peak in deep ocean kinetic energy spectra is studied here records were obtained from polymode arrays deployed in the western north atlantic ocean 40 w to 70 w 15 n to 42 n the results are interpreted both in terms of local sources and of turning point effects on internal waves generated at lower latitudes in most of the data there is a prominent inertial peak slightly above f however the peak height above the background continuum varies with depth and geographical environment three classes of environment and their corresponding spectra emerge from peak height variations class 1 is the 1500 m level near the mid atlantic ridge with the greatest peak height of 18 db class 2 includes a the upper ocean depth less than 2000 m b the deep ocean depth greater than 2000 m over rough topography and c the deep ocean underneath the gulf stream with intermediate peak height of 11 5 db class 3 is the deep ocean over smooth topography with the lowest peak height of 7 5 db near f the horizontal coherence scale is 0 60 km at depths from 200 m to 600 m and the vertical coherence scale is 0 200 m in the lower part of the main thermocline and 0 1000 m in the deep water the phase difference suggests a downward energy propagation in the lower thermocline and standing waves in the deep water a one turning point model is developed to describe inertial waves at mid latitudes based on the assumption that inertial waves are randomly generated at lower latitudes global generation where their frequency wave number spectrum is given by the model of garrett and munk 1972 1975 using the globally valid wave functions obtained by munk and phillips 1968 various frequency spectra near f are calculated numerically the model yields a prominent inertial peak of 7 db in the horizontal velocity spectrum but no peaks in the temperature spectrum the model is latitudinally dependent the frequency shift and bandwidth of the inertial peak decrease with latitude energy level near f is minimum at about 30 and higher at low and high latitudes the observations of class 3 can be well described by the model a low zonal wave number cutoff is required to produce the observed frequency shift of the inertial peak the differences between the global generation model and the observations of class 1 and class 2 are interpreted as the effects of local sources a locally forced model is developed based on the latitudinal modal decomposition of a localized source function asymptotic eigensolutions of laplace s tidal equation are therefore derived and used as a set of expansion functions the forcing is through a vertical velocity field specified at the top or bottom boundaries of the ocean for white noise forcing the horizontal velocity spectrum of the response has an inertial peak which diminishes in the far field with the forcing located at either the surface or the bottom several properties of the class 2 observations can be described qualitatively by a combination of the global and local models the reflection of inertial waves from a turbulent benthic boundary layer is studied by a slab model of given depth frictional effects are confined to the boundary layer and modeled by a quadratic drag law for given incident waves reflection coefficients are found to be greater than 0 9 for the long waves which contain most of the energy this result suggests that energy containing inertial waves can propagate over great distance as is required by the validity of the model of global generation

annual cycle and depth penetration of wind generated near inertial internal waves at ocean station papa in the northeast pacific abstractthe downward propagation of near inertial internal waves following winter storms is examined in the context of a 2 yr record of velocity in the upper 800 m at ocean station papa the long time series allow accurate estimation of wave frequency whereas the continuous data in depth allow separation into upward and downward propagating components near inertial kinetic energy kein dominates the record at all measured depths energy in downgoing motions exceeds that of upward propagating motions by factors of 3 7 whereas kein is elevated by a factor of 3 5 in winter relative to summer the two successive winters are qualitatively similar but show important differences in timing and depth penetration energy is seen radiating downward in a finite number of wave groups which are tagged and catalogued to determine the vertical group velocity cgz which has a mean of about 1 5 10 4 m s 1 13 m day 1 case studies of three of these are presented in detail downward energy flux is estimated as cgz

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

geochronology and geochemistry of a suite of mafic rocks in chencai area south china implications for petrogenesis and tectonic setting abstract paleozoic crust mantle interaction and geodynamic setting of the south china block have remained largely elusive due to the scarcity of mafic rock suites here we report data from a suite of mafic rocks including norite mafic granulite garnet bearing amphibolite biotite bearing amphibolite and amphibolite from the chencai region in the northeastern cathaysia block of south china that mostly record amphibolite to granulite facies metamorphism u pb dating of zircons from the mafic granulite and biotite bearing amphibolite show broadly coeval magmatism and amphibolite to granulite facies metamorphism during 435 438 ma the garnet bearing amphibolite also records metamorphism at 436 ma and the magmatic age of its protolith is constrained to be between 436 ma and 496 ma the norite has an emplacement age of 422 ma geochemically the amphibolite and granulite have high al2o3 contents and belong to the high alumina group the garnet bearing amphibolite belongs to the intermediate alumina group whereas the norite and biotite bearing amphibolite belong to the low alumina group a cumulate origin is proposed for the norite with orthopyroxene as the main cumulus phase based on their similar trace element and lu hf isotopic signatures it is inferred that the protoliths of amphibolite and granulite belonging to high alumina group were likely generated from the same source furthermore their lree enrichment relative to hree positive eu anomaly and negative nb ta and zr anomalies suggest derivation from the same enriched mantle source perhaps in a continental arc environment zircons from the garnet bearing amphibolite belonging to intermediate alumina group have high positive hf t values with a peak of 14 and trace element signatures similar to n morb suggesting a depleted asthenospheric mantle source the rock suite from chencai suggests formation in an active continental margin with the garnet bearing amphibolite representing relics of the paleozoic oceanic crust in northeastern south china and the high and low alumina mafic rocks representing layered cumulates that developed in the arc root the amphibolite to granulite facies metamorphism recorded by these mafic and supracrustal rocks of chencai complex is consistent with high heat flow in an arc root

mesozoic overthrust tectonics in south china whether south china was a platform or a para platform after the mid paleozoic deformation or whether the mountains of huanan south china form a mesozoic collision type orogen depends upon whether the ophiolite melange in the yangtze region is precambrian basement or was overthrust onto a foreland thrust belt during the mesozoic this paper presents evidence of tectonic windows under the melange and basement klippes above the melange in the yangtze region

improved global maps and 54 year history of wind work on ocean inertial motions 1 the global distribution and 54 year time dependence of the energy flux from the wind to near inertial motions is computed by driving a slab mixed layer model with ncep ncar reanalysis winds improving upon previous estimates alford 2001 watanabe and hibiya 2002 the slab model is solved spectrally with frequency dependent damping the resulting solutions are more physically sensible than the previous and more skillful at high latitudes where the inertial frequency approaches the 4 daily sampling of the reanalysis winds this enables alford s calculation whose domain was limited to 50 to be extended to the poles the high latitude reliability is demonstrated by direct comparison with a high resolution regional model remo in the ne atlantic the total power input 0 47 tw has increased by 25 since 1948 paralleling observed increases in extratropical cyclone frequency and intensity if believable the trend may have important consequences for modulation of the meridional overturning circulation

processes influencing the non linear interaction between inertial oscillations near inertial internal waves and internal tides 1 a numerical model of the hebrides shelf edge represented by a cross section is used to examine the non linear interactions producing energy at the fm2 frequency calculations show that in the near coastal ocean this is primarily due to coupling between wind induced inertial oscillations although near inertial internal waves are present and the m2 internal tide the major non linear interaction and hence largest fm2 currents occurs in the region of the thermocline and is associated with shear in the inertial oscillation and the vertical velocity due to the internal tide this non linear process represents an important contribution to the energy cascade from the wind and tide into higher frequency waves and eventually mixing the fm2 current is shown to be a maximum in the shelf edge region and hence measurements in this area will be particularly valuable in determining the extent to which models can represent non linear processes

jiangnan orogen in south china developing from divergent double subduction abstract the jiangnan orogen is considered as a continent continent collisional belt resulting from the closure of a meso neoproterozoic ocean separating the southeastern margin of the yangtze block from the northwestern margin of the cathaysia block recent data indicate the existence of early neoproterozoic 1000 825 ma volcanic arc assemblages on both sides of the orogen suggesting that the ocean lithosphere between the yangtze and cathaysia blocks must have undergone divergent double sided subduction during the period of 1000 825 ma the divergent double subduction eventually resulted in the closure of the ocean basin at 825 ma leading to the soft collision of the yangtze and cathaysia blocks to form the jiangnan orogen without involvement of continental deep subduction high grade metamorphism of continental crust and uplift exhumation of high grade metamorphic rocks shortly after the collision the initial detachment of the ocean lithosphere from the overlying crust and sedimentary sections induced underplating of mantle magmas triggering partial melting of accretionary wedge strata to form some peraluminous s type granites in the period 825 815 ma finally the sinking of the oceanic slab pulled down the overlying strata to form some basins in which the banxi group and its equivalent strata including bimodal volcanic rocks were formed in the period 815 750 ma

examination of the deep levels of an island arc evidence from the tonsina ultramafic mafic assemblage tonsina alaska the tonsina ultramafic and mafic assemblage located in the northern chugach mountains along the trans alaska crustal transect tact is interpreted to be the remains of a magma chamber that crystallized at the base of a mature interoceanic island arc it is one of a number of isolated masses of peridotite and gabbro that comprise the basal part of the peninsular terrane along the northern fringe of the chugach mountains in southern alaska these masses the roots of a mid jurassic island arc have been uplifted along the north dipping border ranges fault system and crop out sporadically for 700 km from kodiak island to eastern alaska the tonsina ultramafic mafic assemblage is a layered sequence whose basal rocks are dunite and harzburgite 1 km thick overlain by a narrow zone of websterite and clinopyroxenite above these ultramafic rocks is a 5 to 6 km thick layered gabbro that is garnet bearing at its base textural relationships and chemical trends throughout the series of dunite pyroxenite garnet bearing gabbro and spinel gabbronorite point to an origin by igneous accumulation from a hydrous tholeiitic parent magma at deep levels i e at the base of a mature island arc before being emplaced along the border ranges fault the rocks were crystallized from a melt at pressures between 9 5 and 11 kbar 28 to 33 km depth and equilibrated at temperatures of 800 to 90o c based on phase relationships in the cumulus assemblages pyroxene thermobarometry and olivine spinel thermometry transitional sequences from ultramafic to mafic rocks are characterized by increasingly al rich pyroxenes and spinels or garnet and the absence of olivine plagioclase assemblages deep level fractionation of al poor phases such as olivine and pyroxene at moderately high pressures and temperatures resulted in concentration of al in the evolving magma as crystallization continued the phases recorded this alumina concentration and the resultant gabbros are al rich this observed trend supports the theory of high alumina basalt generation by fractional crystallization of olivine and pyroxene comparison of the tonsina rocks with aleutian lower crustal xenoliths as well as other exposures of arc related lower crustal magma chambers in japan pakistan and western north america indicates that this process is a common mechanism for island arc magma evolution at depth

zircon u th pb hf isotopes of the basement rocks in northeastern cathaysia block south china implications for phanerozoic multiple metamorphic reworking of a paleoproterozoic terrane abstract the cathaysia block records a complex tectonic history the understanding of which is central to the debate on the evolution of the south china block and its position in various supercontinent assemblies here we investigate two key formations from this block the mayuan group in the northern fujian province northeastern cathaysia block and its equivalent the badu group in southwestern zhejiang province previous studies traced the paleoproterozoic records from the badu group whereas a neoproterozoic age was proposed for the mayuan group the rocks sampled in this study from both groups show similar mineral assemblages of garnet sillimanite biotite plagioclase quartz k feldspar muscovite graphite as well as high contents of sio 2 and al 2 o 3 typical of amphibolite to granulite facies metapelitic rocks zircon u pb data yield two discordia intercept ages of 1990 ma and 2450 ma from one sample and discordia intercept ages of 3 5 ga 2 5 ga 1 86 ga and 233 ma from another in the badu group zircons in two samples from the mayuan group yield intercept ages of 1859 ma and 249 ma in one sample and 2 6 ga 1 87 ga 257 ma and a weighted mean 206 pb 238 u age of 248 ma in the other the ca 1 86 1 87 ga and 230 250 ma ages are interpreted to represent the time of metamorphic reworking because zircon grains of these ages tend to have low th u ratios flat hree patterns and unzoned internal texture as revealed by cathodoluminescene cl images these results confirm that the badu group is a paleoproterozoic lithostratigraphic unit and also suggest that at least part if not all of the mayuan group is paleoproterozoic evidence for paleozoic metamorphic reworking that is considered to have affected the whole of cathaysia block is not revealed in this study in contrast our data clearly show obvious mesozoic metamorphic reworking at ca 230 250 ma zircon hf t values range from 19 to 11 with a peak at 5 5 and show t dm c hf ranging from 1 9 to 4 1 ga with a peak at ca 2 7 3 0 ga suggesting that a major crustal growth took place during this time this interpretation is consistent with the previously suggested crustal growth peaks of 2 7 ga and 2 9ga a synthesis of the reliable geochronological data gathered so far on phanerozoic metamorphic reworking of the northeastern cathaysia block reveals that the imprints of these tectonothermal events is differently distributed in the different zones rocks metamorphosed during the paleozoic tectonothermal event dominantly occur in the western zone whereas those reworked by high grade metamorphism during the mesozoic tectonothermal event mainly outcrop in the eastern zone our study alerts the previous notion of a uniform distribution of the reworked rocks by high grade metamorphism all across the northeastern cathaysia block and provides new insights on the evolution of the south china block

barotropic and baroclinic tidal currents in the eastern basins of the north atlantic data from a large scale moored array in the iberian and canary basins are used to determine the energies of barotropic and baroclinic m2 and s2 tides an analysis of time varying dynamical modes is performed the results for barotropic modes confirm the global surface tide model results of schwiderski 1980 for this region the barotropic modes dominate in the deep basins but increased baroclinic contributions are usually found over rough topography at three locations near the continental slope in the southern canary basin the baroclinic modes dominate the barotropic mode results from an array of three moorings at the northern part of the cape verde rise show an inverse behavior of barotropic and baroclinic energies such that the baroclinic energy is steadily enhanced while the barotropic energy is reduced towards the continental margin the increase in baroclinic energy is consistent with a generation of internal tides close to the shelf by surface tidal forcing over topography further evidence for this process is provided by the 2 week periodicity of the first order baroclinic mode at the slope corresponding to the spring neap cycle of the barotropic tide

kinematics and geochronology of the proterozoic dongxiang shexian ductile shear zone with hp metamorphism and ophiolitic melange jiangnan region south china abstract a kinematic and geochronological analysis of the 10 20 km wide northeast trending dongxiang shexian ductile shear zone that trends along a length of 250 km in the eastern part of the jiangnan belt indicates a sinistral strike slip ductile shear that was formed during the neo proterozoic the zone experienced polyphase deformation related to tectonic collision between the huaiyu and the jiuling terranes geochronological data and kinematic analysis of macroscopic structures microscopic shear indicators and quartz c axes fabrics shows that a ductile southeastward thrusting occurred at about 950 900 ma followed by a sinistral strike slip shearing along a northeast trend at about 770 ma coarse clastic sedimentary rocks of sinian age were deposited unconformably on the entire jiangnan belt including the huaiyu and the jiuling terranes this paper emphasizes that the jiangnan belt in the se margin of yangzi plate is a neo proterozoic orogenic belt with hp metamorphism and ophiolitic melange not a late paleozoic mesozoic collisional orogen

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

inertial oscillations on the continental shelf of the gulf of lions observations and theory abstract observations in the gulf of lions northwestern mediterranean sea in summer have shown that gusts of wind lasting a few days generate transient upwellings and inertial motions oscillations at the inertial frequency were observed in current meter data near the shore and at a frequency 10 greater in the temperature data vertical coherences in current meter data show a strong baroclinic mode at frequencies greater than inertial frequency a simple one dimensional two layer transient model suggests that these motions are associated with two different physical processes the first process describes the local response of the ocean to meteorological forcing the second is associated with the propagation of long internal waves generated in the transient phase of the geostrophic adjustment process as suggested by the model the direction of propagation of the internal waves is computed from current and temperature data measured at one point and it is found that the shore is the source zone

mixing estimates from a large scale hydrographic survey in the north atlantic 1 a large scale hydrographic survey from 2003 rv meteor cruise m59 2 is used to map turbulent mixing by means of eddy diffusivities from finescale shear and strain in the subpolar north atlantic covering various hydrographic and bathymetric conditions results from the analysis indicate small o 10 5 m2s 1 diffusivities below the labrador sea water layer at mid depth in the open ocean higher values exceeding 10 4 m2s 1 are found in the abyss close to rough topography and over the flanks of the mid atlantic ridge the strongest mixing with diffusivities of 10 3 m2s 1 occurs in the deep western boundary current off flemish cap the results of this study convey the need to map mixing globally from existing sets of ctd ladcp data as well as its feasibility the similarities and differences in mixing patterns as compared to other studies indicate that large scale patterns of small scale processes are still not well known and understood

the impact of zircon garnet ree distribution data on the interpretation of zircon u pb ages in complex high grade terrains an example from the rauer islands east antarctica abstract the responsiveness of zircon to granulite metamorphism and post peak fluid infiltration in polymetamorphic terranes has been investigated utilising a case study from the rauer islands of east antarctica imaging bse cl textural analysis in situ ion microprobe trace element analysis of zircon garnet orthopyroxene plagioclase and apatite and ion microprobe oxygen isotope analysis of zircon have been integrated to establish the event significance of c 510 ma zircon age domains that occur within and on c 2840 ma protolith magmatic zircons initial magmatic zircon is characterised by moderate th u 0 4 0 6 and elevated steep hree yb n gd n 20 c 510 ma zircon domains feature lobate cuspate and planar bse and cl zones that have lower th u to 0 05 and either decreased mree or decreased mree and hree metamorphic garnet initially characterised by flat hree shows extensive replacement by orthopyroxene and plagioclase accompanied by near rim increases in hree to values that are consistent with equilibrium between garnet rims and product orthopyroxene zircon garnet mree hree distribution coefficients d ree calculated using compositions of modified zircon domains coupled with both initial metamorphic garnet cores and rims are far removed from presently accepted equilibrium values with the zircon mree being strongly depleted relative to garnet these d ree indicate that the observed modification of zircon did not occur in response to the major high grade metamorphic events recorded in the studied rock mineralogy but instead occurred after the high grade metamorphism the zircon was blind to these metamorphic events but instead was responsive to a later post peak fluid infiltration episode that shifted zircon 18 o values downwards by some 3 the likelihood of blind or unresponsive behaviour of zircon to high grade metamorphism must be considered when reconstructing crustal histories and terrane scenarios based on u pb age data and tested for using an integrated approach that includes in situ ree and other trace element analysis of zircon and its potentially coexisting minerals

spatial variability of deep ocean motions above an abyssal plain 1 near bottom current observations are discussed from an array of moorings separated by 8 40 km horizontally in the madeira abyssal plain north atlantic ocean the area is topographically smooth but observed currents varied strongly over short distances across horizontal scales o 10 km incoherent internal wave properties were retrieved such as conservation of relative frequency bandwidth and internal wave polarization at inertial tidal and higher harmonics frequencies in the vertical between 10 110 110 650 m above the bottom mab at 5000 m the current differences shear were predominantly at the local inertial frequency f near f the largest variance was found at 110 mab with peaks in power at 0 99f and 1 03f as stratification was weak n 2f the subinertial frequency peak was well within the combined internal inertio gravity wave band at 650 mab n 4f and smaller peaks at 1 00f and 1 03f were observed toward the bottom subinertial currents increased in magnitude the horizontal scale of variation of subinertial and inertial motions was small 30 km the magnitude of horizontal current differences in these frequency bands was equal to that in the tidal band although the energetically dominant highly deterministic tidal currents were predominantly barotropic confirming a previous study their horizontal scale of variation was 300 km due to small bottom relief results are discussed relevant for matching records from nearby moorings to generate extra long time series

longitudinal and topographic variations in north atlantic tidal and inertial energy around latitudes 30 10 n 1 open ocean kinetic energy is investigated at dominant inertial and semidiurnal tidal frequencies using historic current observations from the north atlantic ocean around midlatitudes focus is on possible energy variations due to major topography changes between the eastern canary and western hatteras sohm basins thereby crossing the mid atlantic ridge mar while in open basins on both sides of mar semidiurnal kinetic energy drops in magnitude by some 50 between latitudes 20 n 28 n in agreement with tpxo elevation data an even larger longitudinal dependence is observed west of mar semidiurnal energy is up to 30 times less than east of it inertial kinetic energy is either decreasing by a factor of 2 4 westward or more or less independent of longitude this contrasts strongly with westward intensified near surface inertial energy fluxes previously found the latter fluxes also did not show an increase by a factor of 5 10 for 25 n 30 n as observed here for inertial energy in both basins west of mar the internal wave background level for frequencies up to sixth diurnal is much less by a factor of 3 10 at tidal inertial interaction frequencies than east of mar no significant atmospheric or large scale vorticity influence or seasonal variations therein is found on inertial energy content across the basin as no individual peaks are observed at frequencies k1 o1 and m1 s1 direct diurnal tidal forcing and subharmonic resonance must be accompanied by nonlinear interactions in possibly enhancing inertial energy at the critical diurnal latitude

a numerical study of sea breeze driven ocean poincare wave propagation and mixing near the critical latitude abstract near the vicinity of 30 latitude the coincidence of the period of sea breeze and the inertial period of the ocean leads to a maximum near inertial ocean response to sea breeze this produces a propagating inertial internal poincare wave response that transfers energy laterally away from the coast and provides significant vertical mixing in this paper the latitudinal dependence of this wave propagation and its associated vertical mixing are investigated primarily using a nonlinear numerical ocean model three dimensional idealized simulations show that the coastal oceanic response to sea breeze is trapped poleward of 30 latitude however it can propagate offshore as poincare waves equatorward of 30 latitude near 30 latitude the maximum oceanic response to sea breeze moves offshore slowly because of the near zero group speed of poincare waves at this latitude the lateral energy flux convergence plus the energy input from the wind is maximum near the critical latitude leading to increa

subtropical catastrophe significant loss of low mode tidal energy at 28 9 1 an idealized numerical study of a northward propagating internal tide reveals a dramatic loss of energy to small scale subharmonic instabilities near 28 9 n inspired by observations of the internal tide radiating northward from the hawaiian ridge a three dimensional numerical model is initialized with a northward baroclinic tidal flux of approximately 1 7 kw m after an initial spinup period energy is quickly transferred from the baroclinic tide to subharmonic motions with half the horizontal tidal wavenumber and small vertical scales through nonlinear advection of horizontal tidal velocity gradients potential oceanic implications are twofold first once a steady state has been reached the instability acts as a partial filter of northward tidal flux between 27 5 and 29 5 n in rough agreement with some altimetric tidal observations second elevated shear of the subharmonic motions suggests the potential for elevated near surface dissipation rates near the critical latitude that may be important for upper ocean mixing

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

the cumulate paradigm reconsidered the cumulate terminology outlined by wager and coworkers provided a logical system for describing the textures of the rocks of layered intrusions but recent work shows that this model fails to accommodate all the processes responsible for the petrographic features of coarse grained rocks textures of adcumulates and orthocumulates in the skaergaard intrusion cannot be correlated with concentrations of incompatible elements representing trapped liquid compaction and open system percolative processes have altered their textures modes and even bulk compositions although a rock may be a cumulate in the absence of other evidence it can be misleading to refer to it in terms of the cumulate nomenclature

near resonant ocean response to sea breeze on a stratified continental shelf abstract the spatial structure and temporal characteristics of sea breeze and the associated coastal ocean response in the northwest gulf of mexico are investigated using moored instruments hydrographic stations and wind measurements near the study area of 30 n motions in the diurnal inertial band dib may be significantly enhanced by a near resonant condition between local inertial and diurnal forcing frequencies wavelet analysis is used to quantify the results results indicate that diurnal sea breeze variability peaks in summer and extends at least 300 km offshore with continuous seaward phase propagation the maximum dib oceanic response occurs in june when there is a shallow mixed layer strong stratification and an approximately 10 day period of continuous sea breeze forcing dib current variance decreases in july and august as the consequence of the deepening of the mixed layer and a more variable phase relationship between the wind and current river discharge varies interannually and can s

u pb geochronology and hf nd isotopic geochemistry of the badu complex southeastern china implications for the precambrian crustal evolution and paleogeography of the cathaysia block abstract the oldest rocks of the cathaysia block south china comprise the badu complex and paleoproterozoic granites in the wuyishan area southern zhejiang and northwestern fujian provinces new zircon u pb ages hf isotopes and trace elements for metamorphic rocks from the badu complex and bulk nd isotope compositions of these rocks and granites in the wuyishan area provide important constraints on the precambrian crustal evolution of the cathaysia block inherited cores of zircon grains from the metamorphic rocks are of magmatic origin predominantly formed at ca 2 5 ga while overgrowth rims reflect two episodes of granulite facies metamorphism related to collisional orogeny at 1 89 1 88 ga and 252 234 ma the unimodal age distribution 2 5 ga of detrital zircons and the positive hf t of most neoarchean zircons suggest that the detritus of these sedimentary protoliths of the badu complex came from a proximal volcanic arc and that they were deposited in an arc basin synchronously with 2 5 ga volcanism zircon u pb ages and hf isotopes with whole rock nd isotopes suggest that the juvenile crust of the eastern cathaysia block was generated mainly at 2 5 ga and 2 8 ga and minor at 3 5 3 3 ga with some evidence for the generation at 3 7 3 6 ga and 4 0 ga a strong 1 9 ga orogeny and the 3 3 3 0 ga thermal event only involved the reworking of older crust material paleoproterozoic 1 89 1 86 ga granitic magmatic activity and high grade metamorphism in the eastern cathaysia block were synchronous with the assembly of the columbia supercontinent using integrated geochronological hf nd isotopic and petrologic data as a barcode we compare the cathaysia block with other paleoproterozoic orogens worldwide and argue that its closest affinity is with the south korean peninsula and the lesser himalaya of nw india consequently the eastern cathaysia block and the south korean massif as the united cathay south korea terrane was close to the lesser himalaya terrane in the paleoproterozoic configuration of the columbia supercontinent the spatial linkage was maintained for ca 1 ga until the fragmentation of the rodinia supercontinent during neoproterozoic time

anatomy of zircon growth in high pressure granulites sims u pb geochronology and lu hf isotopes from the jiaobei terrane eastern north china craton abstract granulite facies rocks that witnessed high pressure and high temperature metamorphism preserve important records of the growth and recrystallizaton of zircons during the multiple stages of tectonic evolution of orogenic belts developed in complex subduction collision settings here we investigate zircons in the paleoproterozoic high pressure hp granulites from jiaobei terrane in the eastern north china craton that experienced a multi stage metamorphic evolution we present sims zircon u pb ages for zircons from garnet amphibolites mafic granulites and pelitic granulites our data show four age peaks at 2 5 ga 1 92 ga 1 87 1 85 ga and 1 83 ga zircons belonging to the latter three age groups show similar characteristics of low th and u contents low th u ratios 176 lu 177 hf ratios and low 176 hf 177 hf ratios of zircons from the protoliths the youngest u pb age of ca 1899 ma is interpreted as the maximum estimate of the time of peak metamorphism zircons formed through intergranular melt growth during low to medium pressure retrogression display homogeneous lu hf isotope compositions low 176 lu 177 hf and high 176 hf 177 hf ratios the u pb age of 1870 1850 ma yielded by zircons crystallized from intergranular melt is interpreted to represent the time of low to medium pressure granulite facies retrogression some zircon grains with prismatic morphology and low 176 lu 177 hf and 176 hf 177 hf ratios display heterogeneous lu hf isotopic compositions possibly related to coupled dissolution reprecipitation the u pb ages of these zircons are identical to those formed from intergranular melt and these two groups of zircons formed during the same metamorphic stage zircons formed through subsolidus growth show large variations in lu hf isotopic compositions and their ca 1833 ma age represents the timing of amphibolite facies retrogression the hp granulite facies metamorphism in jiaobei is thus constrained between 1870 and 1899 ma with low to medium pressure granulite facies retrogression at ca 1850 1870 ma followed by amphibolite facies retrogression at ca 1833 ma our data show that several zircon cores and recrystallized grains were entrained from basement rocks during the emplacement of the mafic magmatic protoliths in the case of mafic granulites for the pelitic granulites the older zircons are detrital grains of magmatic origin the hf crustal model ages of these zircons that show peaks at ca 2 7 ga and 2 9 ga are consistent with the timing of mafic magmatism in the region as identified in previous studies the lu hf isotopes of newly grown metamorphic zircons which have equilibrated chemical compositions trace the nature of the protolith the zircon hf crustal model age of ca 2 5 2 7 ga from the pelitic granulites is consistent with that of the basement rocks in the jiaobei terrane and the zircon hf model ages t dm of ca 2 0 ga and 2 2 2 3 ga from the mafic granulites might represent the time of magma generation from the mantle with crustal contamination the geochronology of the basement rocks as revealed by the old zircon cores and the metamorphic evolution of the jiaobei terrane are comparable with the tectonic history of the central and western north china craton and provide insights into the complex tectonothermal events associated with the neoarchean paleoproterozoic crustal evolution history of the craton also the pervasive 2 5 ga zircons in a variety of rocks seem to suggest that the jiaobei terrane was already part of a coherent tectonic unit at such time

challenges in high pressure granulite metamorphism in the era of pseudosections reaction textures compositional zoning and tectonic interpretation with examples from the bohemian massif high pressure granulites are an important record of geodynamic processes in overthickened or subducted continental crust orthopyroxene free assemblages in granitic ternary feldspar s quartz garnet kyanite rutile intermediate ternary feldspar s quartz garnet clinopyroxene kyanite rutile titanite and basic garnet clinopyroxene plagioclase quartz rutile compositions indicate formation conditions at mantle depths clinopyroxene compositions in variscan high pressure granulites are unusual in that they include omphacite in plagioclase bearing rocks thus not eclogite and al rich diopside i e indicating high ca tschermak content with both yielding temperatures above 900 c problems such as compositional zoning multiple generations of key phases in reaction domains and unmixing of high temperature solid solution phases during cooling ternary feldspars omphacite clearly indicate disequilibrium and require very careful interpretation as to which phases and compositions possibly represent a former equilibrium association pressure temperature p t determination by the pseudosection method although allowing prediction of mineral assemblages compositions and molar proportions for a fixed bulk composition for modelled p t conditions still requires reliable activity composition information for the key phases feldspar and clinopyroxene as well as an interpretation of former equilibrium compositions in the investigated samples i e the same restrictions applying to conventional thermobarometry the interpretations of some recently determined pseudosections for the composition of variscan clinopyroxene bearing high pressure granulites contradict numerous published p t paths however quantitative information from thermobarometry or pseudosections must be integrated with key petrographic observations in the case of the variscan example it is argued that petrographic observations and published p t paths are consistent with mineral assemblages predicted in pseudosections and support existing tectonometamorphic models

high pressure granulites formation recovery of peak conditions and implications for tectonics high pressure granulites are characterised by the key associations garnet clinopyroxene plagioclase quartz in basic rocks and kyanite k feldspar metapelites and felsic rocks and are typically orthopyroxene free in both basic and felsic bulk compositions in regional metamorphic areas two essential varieties exist a high to ultrahigh temperature group and a group representing overprinted eclogites the high to ultrahigh temperature type formerly contained high temperature ternary feldspar now mesoperthite coexisting with kyanite is associated with garnet peridotites and formed at conditions above 900 c and 1 5 gpa clinopyroxene in subordinate basic rocks is al rich and textural evidence points to a high pressure high temperature melting history the second variety contains symplectite like or poikilitic clinopyroxene plagioclase intergrowths indicating former plagioclase free i e eclogite facies assemblages this type of rock formed at conditions straddling the high pressure amphibolite high pressure granulite field at around 700 850 c 1 0 1 4 gpa importantly in the majority of high pressure granulites orthopyroxene is secondary and is a product of reactions at pressures lower than the peak recorded pressure in contrast to low and medium pressure granulites which form at conditions attainable in the mid to lower levels of normal continental crust high pressure granulites of nonxenolith origin mostly represent rocks formed as a result of short lived tectonic events that led to crustal thickening or subduction of the crust into the mantle short times at high temperature conditions are reflected in the preservation of prograde zoning in garnet and pyroxene high pressure granulites of both regional types although rare are known from both old and young metamorphic terranes e g c 45 ma namche barwa e himalaya 400 340 ma european variscides 1 8 ga hengshan china 1 9 ga snowbird saskatchewan and 2 5 ga jianping china this spread of ages supports proposals suggesting that thermal and tectonic processes in the lithosphere have not changed significantly since at least the end of the archean

u pb zircon ages of granites from the southern margin of the yangtze block timing of neoproterozoic jinning orogeny in se china and implications for rodinia assembly abstract neoproterozoic jinningian bendong granodiorite and sanfang and yuanbaoshan granites occurred in northern guangxi southern margin of the yangtze block se china and were generally considered to be of orogenic origin that is the collision between the yangtze and huanan blocks during the jinning orogeny these granites were intruded into the mesoproterozoic sibao metamorphic basement and covered unconformably by the neoproterozoic danzhou metasediments they are dominantly peraluminous asi 1 18 1 29 and have low initial end values of 4 8 to 7 6 indicating derivation from a supracrustal source with strong enrichment in rb k and th and relatively low zr hf and higher rare earth elements they are similar to post collision granites zircon u pb ages of 819 9 826 10 and 824 4 ma were obtained for the bendong granodiorite and the sanfang and yuanbaoshan granites respectively by both shrimp and conventional dating methods the age result precludes the existence of any late mesoproterozoic grenville age granitic magmatism in the southern margin of yangtze block together with previous age determinations of ophiolites along the southern margin of the yangtze block the jinning orogeny is referred to the neoproterozoic orogeny which took place between 1 0 and 0 80 ga and likely ended at 0 82 ga the granite formation age of 0 82 ga also supports the basal boundary age of 0 80 ga for the post orogenic sinian system which is probably stratigraphically correlated with the adeladean system in south australia as the link between australia east antarctica and laurentia in the configuration of the supercontinent rodinia the collision between the yangtze and huanan blocks during the neoproterozoic jinning orogeny probably marks the termination of the rodinia assembly

on the origin of high alumina arc basalt and the mechanics of melt extraction most models of high alumina arc basalt petrogenesis rely heavily on the supposition that the abundances of certain trace elements in particular the relatively unfractionated rare earth element ree patterns and the unusually high concentrations of k rb sr and ba are incompatible with a garnet bearing subducted oceanic crustal quartz eclogite source rock we have carefully examined this apparently unequivocal evidence in light of recent progress on the physics of melt extraction and the heat transfer and mechanics of magma ascent the weakest element of all trace element models involving a quartz eclogite source is the assumption that the element concentrations are fixed at the source and only later modified in the near surface environment we expand on such models by monitoring the concentrations of r ee and major and trace elements during initial melting ascent and extraction of magma this is done by combining calculated cooling curves for ascending magmatic bodies with high pressure phase equilibria the amount that each phase contributes to the melt is monitored along with the composition of the melt and residual solids with quartz eclogite initial melting initiates gravitational instability of the entire source material melt plus solids before melt extraction can occur during ascent of this mush melting increases until the solids can be repacked to free the melt this extraction takes place some 15 20 km above the slab after about 50 per cent melting at which point the melt has a pattern of ree and other trace element concentrations almost identical to those observed in high alumina arc basalts assuming an initial composition equivalent to altered oceanic crust plus 5 per cent pelagic sediment sr abundances are the only ones which are not well matched by this process the major element concentrations of the extracted melt also closely match those of high alumina arc basalt a similar but less detailed evaluation of both fertile and depleted peridotite source rocks yields good agreement for the ree and other trace element concentrations assuming a lree enriched source rock strongly enriched in k rb sr and ba ni cr and co abundances are satisfied only through substantial low pressure fractionation of mafic phases in particular olivine though not rigorously tested such a process may be compatible with the observed major element concentrations of high alumina basalt however the experimentally verified fact that high alumina basalts could never have been in equilibrium with either an olivine beari ng magma or source rock eliminates this possibility altogether thus the simultaneous consideration of the mechanics of ascent and melt extraction along with phase equilibria clearly shows that partial melting of quartz eclogite best satisfies the chemical constraints of major trace and ree characteristics of high alumina arc basalts

chemical models of solute acquisition in glacial melt waters chemical models for the evolution of bulk melt waters can be constructed by assuming that rock mineral weathering and solute acquisition are controlled by carbonate equilibria different open and closed system models are defined by variations in the rates of weathering relative to the rate of hydrogen ion supply by the dissolution and dissociation of co2 and can be recognized by characteristic ph and relationships the observed and inferred compositions of englacial and subglacial melt suggest that mixing is unlikely to be conservative and that closed system conditions result where post mixing weathering reactions occur the final composition of bulk melt waters is determined by the mixing ratio between englacial and subglacial melt the extent of post mixing evolution and opportunity for mixing with ground waters or re equilibration with the atmosphere