northland ophiolite new zealand and implications for plate tectonic evolution of the southwest pacific the northland ophiolite and coeval ocean floor sedimentary rock form the northland allochthon obducted from the northeast onto new zealand in the late oligocene the ophiolite was probably emplaced as a single sheet and separated into individual massifs during subse quent movement of the allochthon chemically the bulk of the igneous rocks are normal mid ocean ridge basalts but the ophiolite also includes a younger suite of hornblende modal within plate alkalic rocks believed to represent seamounts two alternative models one involving a subduction flip the other involving continuous westward subduction are proposed to account for the obduction of the upper part of the northland ophiolite the oceanic crust from which the ophiolite originated was formed simultaneously with tasman sea spreading on the western rim of a once much larger south fiji plate assemblage

distribution and mechanism of neogene to present day vertical axis rotations pacific australian plate boundary zone south island new zealand remarkably little knowledge exists about mechanisms of vertical axis rotation in continental crust steeply dipping basement rocks in south island new zealand provide an opportunity to map the distribution of rotations across the pacific australian plate boundary zone and to delineate boundaries of rotated blocks in unusual detail we synthesize new structural data with new and existing paleomagnetic data with geodetic data and with patterns of neogene quaternary faulting in the strike slip marlborough fault system for the past 20 m y vertical axis rotations have been hinged about two crustal scale boundaries near the east coast the ne hinge accommodated 50 of early middle miocene clockwise rotation which caused deformation of the eastern ends of the alpine wairau and clarence strike slip faults the sw hinge has accommodated a further 30 50 of finite clockwise rotation since 4 ma and deflects active fault traces the locus of rotation has shifted southwestward astride a subduction margin that is lengthening in that direction rotating rocks are pinned to the south against a locked collision zone where the continental chatham rise impinges against the margin slip on inland strike slip faults is transformed seaward across a zone of fault termination into rigid body rotation of a large continental block that has been thrust eastward over the downgoing subducted slab of the pacific plate the rotation mechanism is a migrating hinge which resembles a flexed telephone book strike slip faults are translated through a brecciated hinge region that does not coincide with a fixed material line in the rock

global correlation of the radiolarian faunal change across the triassic jurassic boundary precise comparison of the change in radiolarian faunas 3 5 m above a u pb zircon dated 199 6 0 3 ma tuff and approximately coincident with a negative 13 c anomaly in the queen charlotte islands b c canada with inuyama japan sequences indicates that major global changes occurred across the triassic jurassic t j boundary nearly 20 genera and over 130 rhaetian species disappeared at the end of the triassic the index genera betraccium and risella disappear and the final appearance of globolaxtorum tozeri livarella valida and pseudohagiastrum giganteum sp nov are also diagnostic for the end of the triassic the low diversity hettangian survival fauna immediately above the boundary is composed mainly of small primitive spumellarians with spongy or irregularly latticed meshwork and rod like spines and new genera charlottea udalia and parahsuum s l first appear in the lowest hettangian in both localities irrespective of different sedimentation rates and sedimentary environments such as shelf to upper slope queen charlotte islands and deep sea below carbonate compensation depth ccd inuyama radiolarians show a similar turnover pattern at the t j boundary

mesoscale anticyclonic circulations in the lee of the central rocky mountains composite analyses of terrain forced mesoscale anticyclonic circulations over southern wyoming and northern colorado are constructed these suggest two different types of circulations based on upstream flow direction the air within type 1 circulations originates to the west of the continental divide and contains little moisture type 2 circulations form in more moist northerly flow and are sometimes associated with snowbands both types tend to form during the afternoon and dissipate after sunset although type 2 events may follow frontal passages and occur at night case studies of one event of each type suggest that anticyclonic vorticity generation occurs within the lowest kilometer above ground level when that layer is nearly vertically mixed in both potential temperature and velocity an analogy with vorticity generation in mixed layer models is considered and it is shown that the conditions for generating negative vorticity in those models are satisfied in each observed case the mixed layer mechanism is also favored as it naturally explains the diurnal tendency of the circulations and may therefore explain the observed late day snowfall maximum along the front range of colorado

the utility of convection permitting ensembles for the prediction of stationary convective bands abstractthis study examines convection permitting numerical simulations of four cases of terrain locked quasi stationary convective bands over the united kingdom for each case a 2 2 km grid length 12 member ensemble and a 1 5 km grid length deterministic forecast are analyzed each with two different initialization times object based verification is applied to determine whether the simulations capture the structure location timing intensity and duration of the observed precipitation these verification diagnostics reveal that the forecast skill varies greatly between the four cases although the deterministic and ensemble simulations captured some aspects of the precipitation correctly in each case they never simultaneously captured all of them satisfactorily in general the models predicted banded precipitation accumulations at approximately the correct time and location but the precipitating structures were more cellular and less persistent than the coherent quasi stationary bands that were o

observations and modeling of banded orographic convection radar images and numerical simulations of three shallow convective precipitation events over the coastal range in western oregon are presented in one of these events unusually well defined quasi stationary banded formations produced large precipitation enhancements in favored locations while varying degrees of band organization and lighter precipitation accumulations occurred in the other two cases the difference between the more banded and cellular cases appeared to depend on the vertical shear within the orographic cap cloud and the susceptibility of the flow to convection upstream of the mountain numerical simulations showed that the rainbands which appeared to be shear parallel convective roll circulations that formed within the unstable orographic cap cloud developed even over smooth mountains however these banded structures were better organized more stationary and produced greater precipitation enhancement over mountains with small scale topographic obstacles low amplitude random topographic roughness elements were found to be just as effective as more prominent subrange scale peaks at organizing and fixing the location of the orographic rainbands

a suggestion for the origin of mesoscopic fabric in accretionary melange based on features observed in the chrystalls beach complex south island new zealand the chrystalls beach complex a probable accretionary melange of triassic age cropping out in south island new zealand contains a distinctive set of mesoscopic structures all of which contribute to the typically chaotic appearance of the melange these structures are 1 soft sediment bedding pull aparts 2 weakly developed slaty cleavage 3 folds in dismembered bedding with slaty cleavage as the axial surface foliation and 4 quartz fiber lineated shear surfaces analysis of overprinting relations indicates that these structures formed during a single progressive deformation rather than in several discrete events as such they record a change in response to incremental strain from initial ductile behavior toward one dominated by brittle failure it is suggested that this variation resulted from progressive dewatering during shallow level accretion at the base of an inner trench slope

a global climatology of atmospheric fronts 1 atmospheric fronts in the lower troposphere often mark regions of significant weather and serve as an important conceptual tool that is frequently used and well understood by the public this study uses an objective method to identify fronts in the era 40 reanalysis and to compile a quantitative global climatology of their occurrence the climatology confirms the mid latitude storm tracks as the regions of highest front frequency and identifies slow moving frontal boundaries in the subtropics corresponding to major climate features such as the mei yu front the climatology also shows fronts to be common features of the south pacific convergence zone in the northern hemisphere fronts shift poleward in summer in the southern hemisphere this and other aspects of seasonal behavior are rather different

the oroclinal bend in the south island new zealand abstract most of the south island of new zealand lies within an eocene recent continental shear zone related to pacific australia plate motion macroscopic finite strain in this shear zone has in the past been tracked through the deformation of the dun mountain ophiolite belt this paper identifies additional sub vertical basement strain markers including buller takaka terrane boundary darran suite and jurassic volcanic belt within the median batholith taieri wakatipu goulter synform axial trace esk head melange and bedding form surfaces within the buller takaka and torlesse terranes an analysis of the oroclinal bend over the entire zealandia continent shows that it is a composite feature involving pre as well as post eocene bending of basement structures satisfactory paleogeographic reconstructions of zealandia cannot be made without the use of substantial regional scale non rigid intracontinental deformation

cretaceous demise of the moa plate and strike slip motion at the gondwana margin radiolaria and paleomagnetic data from deep sea drilling project sites 595 and 596 indicate that early cretaceous seafloor was formed at moderate to high latitudes in the pacific this inference requires a cretaceous spreading ridge south of the pacific phoenix ridge and substantial dextral strike slip motion at the gondwana margin the previously unrecognized southern oceanic plate called here the moa plate was obliquely subducted beneath the gondwana margin and material accreted from it is now part of the eastern province of new zealand

the spacing of orographic rainbands triggered by small scale topography abstract a combination of idealized numerical simulations and analytical theory is used to investigate the spacing between convective orographic rainbands over the coastal range of western oregon the simulations which are idealized from an observed banded precipitation event over the coastal range indicate that the atmospheric response to conditionally unstable flow over the mountain ridge depends strongly on the subridge scale topographic forcing on the windward side of the ridge when this small scale terrain contains only a single scale of terrain variability the band spacing is identical to but when a spectrum of terrain scales are simultaneously present the band spacing ranges between 5 and 10 km a value that is consistent with observations based on the simulations an inviscid linear model is developed to provide a physical basis for understanding the scale selection of the rainbands this analytical model which captures the transition from lee waves upstream of the orographic cloud t

probabilistic petrophysical properties estimation integrating statistical rock physics with seismic inversion a joint estimation of petrophysical properties is proposed that combines statistical rock physics and bayesian seismic inversion because elastic attributes are correlated with petrophysical variables effective porosity clay content and water saturation and this physical link is associated with uncertainties the petrophysical properties estimation from seismic data can be seen as a bayesian inversion problem the purpose of this work was to develop a strategy for estimating the probability distributions of petrophysical parameters and litho fluid classes from seismics estimation of reservoir properties and the associated uncertainty was performed in three steps linearized seismic inversion to estimate the probabilities of elastic parameters probabilistic upscaling to include the scale changes effect and petrophysical inversion to estimate the probabilities of petrophysical variables andlitho fluid classes rock physics equations provide the linkbetween reservoir properties and velocities and lin

geochemical characterization evolution and source of a mesozoic accretionary wedge the torlesse terrane new zealand whole rock major and trace element compositions of quartzofeldspathic permian cretaceous sandstones of the torlesse terrane new zealand display progressive changes which compare well with published petrographic data chemical indices in three permian early late triassic rakaia subterrane petrofacies show small contrasts as do the modes reflecting original source compositions a late triassic rakaia petrofacies displays sharp increases in sio 2 al 2 o 3 k 2 o na 2 o th sc la sc ce sc la n y n and decreases in ti zr and v la consistent with partial cannibalistic recycling and a small influx of lithic volcanic detritus in the post collisional late jurassic early cretaceous pahau subterrane sio 2 al 2 o 3 remains high but other indices decrease to levels seen in the permian due to recycling of the earlier rakaia petrofacies and influx of 10 30 mafic intermediate volcaniclastic detritus derived from inboard volcanogenic terranes the results are confirmed by additional suites including mudstones which cover a larger area but also show that some spatial variation occurs within the terrane as a whole whole rock data and chemical index of alteration indices indicate that the torlesse was derived from a relatively unweathered source with granodioritic bulk composition comparisons with data from a proposed rakaia source in the new england and hodgkinson orogens of eastern australia suggest that the observed chemical and modal compositions cannot be simply derived from that area as presently exposed

travel time of accreted igneous assemblages in western pacific orogenic belts and their associated sedimentary rocks abstract accreted igneous assemblages in orogenic belts maybe divided into three types depending on whether they derive from seamounts ocean ridges or subduction related ophiolites seamount type basalts are associated with shallow water sediments mostly reefoidal limestones ocean ridge type basalts are generally overlain by pelagic cherts subduction related ophiolitic eruptives often underlain by gabbroic and ultramafic rocks are associated with hemipelagic mudstones the age of such diverse eruptive lithologic assemblages reflects the time taken for them to have traveled from their locus of generation to their place of accretion at a continental margin this relationship has been established for each type of accretionary complex examples being taken mostly from japan and the western pacific rim in order to represent evolutionary processes at a typical active plate margin in general the seamount types are older ridge types are of intermediate age and the ophiolitic types are by far the youngest usually close to zero age seamount type basalts are accreted by shallower scraping of the seamount s sediment apron together with fragments of seamount basalt ridge type by peeling due to permeability contrast and the ophiolitic types by deeper scraping as a consequence of an inflected temperature gradient accordingly it is concluded that the ophiolitic rocks are generated close to the trench and may be accreted as a result of ridge subduction

origin of the torlesse terrane and coeval rocks south island new zealand the carboniferous to lower cretaceous torlesse terrane and haast schist derivatives constitute the major part of the complexly deformed facies of the eastern province of new zealand strata consist mainly of quartzofeldspathic graywacke and mudstone intercalated with minor but widely distributed conglomerate and volcanics with associated chert and limestone clastic rocks were deposited largely by sediment gravity flow mechanisms in a deep marine environment also present are a few highly fossiliferous shallow marine and terrestrial deposits of limited areal extent which rest unconformably on or in fault contact with torlesse flysch several periods of deformation are recognized and melange is present on both local and regional scales metamorphism ranges from zeolite to greenschist facies the bulk of the rocks fall into five areally extensive and mutually exclusive fossil zones of the following ages permian atomodesma middle triassic early late triassic torlessia late triassic monotis and late jurassic early cretaceous contacts between major fossil zones are mainly tectonic petrographic analysis permits subdivision of torlesse sandstones into five major petrofacies that correspond in age to the five major fossil zones the sandstone petrofacies mainly arkosic together with the composition of conglomerate clasts mainly indurated torlesse rocks indicate that the source terrane was a continental volcano plutonic arc probably part of gondwanaland coupled with autocannibalistic reworking of older uplifted torlesse rocks in contrast to the quartzofeldspathic nature of the torlesse coeval sedimentary rocks of the eastern province are volcanogenic they are thought to represent related forearc basin maitai murihiku terranes and trench complex caples terrane deposits derived from a volcanic island arc brook street terrane three petrofacies are established for maitai murihiku and caples sandstones the petrofacies indicate a common evolving immature to submature volcanic island arc source for these terranes a reconstruction of new zealand s eastern and western provinces is proposed in permian and triassic times the torlesse was deposited in trench slope or borderland basins along a trench transform margin fronting a continental volcano plutonic arc source western province gondwanaland deposition was spasmodic but voluminous and was accompanied by concurrent deformation and accretion resulting in parallel belts of torlesse rock younging outward from the gondwanaland margin at the same time the brook street terrane volcanic arc and associated terranes were forming to the west of the torlesse site separated from gondwanaland by a marginal sea in latest triassic or early jurassic times the torlesse was rafted into the volcanic arc system via transform faulting approximately parallel to the gondwana margin the collision event resulted in tectonic thickening of torlesse and caples rocks at the plate interface and metamorphism to haast schist the source was then dominated by older partly metamorphosed torlesse terrane newly uplifted along the collision front closing of the marginal sea behind the brook street terrane in late jurassic early cretaceous times resulted in juxtapositioning with the western province gondwanaland along the median tectonic line

rotation and offset of the gondwana convergent margin in the new zealand region following cretaceous jamming of hikurangi plateau large igneous province subduction jamming of the hikurangi plateau large igneous province subduction within the chatham rise convergent margin of gondwana at circa 105 ma led to offset and rotation of the convergent margin before subduction ceased in the new zealand region at circa 100 ma the southern limit of the plateau following leading slab break off is highlighted by a lineament of prominent horst blocks in the southern bounty trough subduction jamming of the gondwana margin and accompanying compression of the onshore margin and or extension of the offshore margin has led to two 60 km left lateral sse offsets of the chatham rise convergent margin at the coast and in inland canterbury recognition of the onshore chatham rise using the gravity data also highlights the correlation of the inland chatham rise and central south island seismicity in a similar manner to the rotation of cretaceous spreading ridge and transform fault fabric adjacent to the osbourn trough spreading ridge the convergence direction at the gondwana margin was rotated anticlockwise to n s between 105 and 100 ma most of this rotation has been accommodated by offshore extension and margin offset the divergence between the anticlockwise rotation of offshore crustal structure and the jammed onshore margin led to the development of the great south basin at 105 100 ma further offshore in the bounty trough extensional zones formed between crustal blocks rotated to adjust to a changed cretaceous direction of subduction are evident in gravity and seismic profiles

tectonic rotation about the termination of a major strike slip fault marlborough fault system new zealand the marlborough fault system comprises a series of major right lateral strike slip faults that link the alpine fault to the hikurangi subduction zone in the pacific australia plate boundary zone in new zealand all of the major active faults of the marlborough fault system have continuous traces except for the clarence fault which terminates abruptly near the ward syncline paleomagnetic data from upper miocene and lower pliocene sedimentary rocks between the marlborough faults indicate a consistent post early pliocene regional clockwise rotation of about 20 an additional rotation of about 10 is evident at many localities near the termination of the clarence fault it is proposed that the additional rotation relative to the rest of the region is caused by a velocity gradient that likely exists between the active awatere fault and the termination of the clarence fault the existence of such a velocity gradient is consistent with inferences from geodetic strain data which suggest that one third of the displacement in the marlborough fault system occurs between the awatere and clarence faults the kinematics of rotation can be modelled by treating the area as a rigid block that pivots about the termination of the clarence fault the block rotation model satisfies field constraints on the styles of deformation observed at the boundaries of the block and is consistent with available paleomagnetic and geodetic data

the role of moist processes in the formation and evolution of mesoscale snowbands within the comma head of northeast u s cyclones abstract the role of moist processes in regulating mesoscale snowband life cycle within the comma head portion of three northeast u s cyclones is investigated using piecewise potential vorticity pv inversion modeling experiments and potential temperature tendency budgets snowband formation in each case occurred along a mesoscale trough that extended poleward of a 700 hpa low this 700 hpa trough was associated with intense frontogenetical forcing for ascent a variety of pv evolutions among the cases contributed to midlevel trough formation and associated frontogenesis however in each case the induced flow from diabatic pv anomalies accounted for a majority of the midlevel frontogenesis during the band s life cycle highlighting the important role that latent heat release plays in band evolution simulations with varying degrees of latent heating show that diabatic processes associated with the band itself were critical to the development and maintenance of the band however changes in the meso

mapping lithofacies and pore fluid probabilities in a north sea reservoir seismic inversions and statistical rock physics reliably predicting lithologic and saturation heterogeneities is one of the key problems in reservoir characterization in this study we show how statistical rock physics techniques combined with seismic information can be used to classify reservoir lithologies and pore fluids one of the innovations was to use a seismic impedance attribute related to the vp vs ratio that incorporates far offset data but at the same time can be practically obtained using normal incidence inversion algorithms the methods were applied to a north sea turbidite system we incorporated well log measurements with calibration from core data to estimate the near offset and far offset reflectivity and impedance attributes multivariate probability distributions were estimated from the data to identify the attribute clusters and their separability for different facies and fluid saturations a training data was set up using monte carlo simulations based on the well log derived probability distributions fluid substitution by ga

mesozoic radiolarian faunas from the antarctic peninsula age tectonic and palaeoceanographic significance new assemblages of radiolaria including some of the few occurrences of high southern latitude jurassic and cretaceous radiolarian faunas show that several localities in the lemay group of alexander island range in age from latest jurassic earliest cretaceous to at least albian by demonstrating that sedimentation and deformation in the lemay group was diachronous younging oceanwards to the northwest these new age assessments support the model of the lemay group as an accretionary complex the polarity of subduction beneath alexander island was not affected by arc collisions from at least the lower jurassic to the oligocene and such a long period of continuous accretion appears to be unusual deposition of the lemay group spans the kimmeridgian to albian sedimentation in the fossil bluff group fore arc basin thus making the earlier concept of the lemay group as pre jurassic basement untenable allochthonous latest jurassic earliest cretaceous radiolarian assemblages with some supposed tethyan affinities are present in the lemay group in contrast an in situ latest jurassic assemblage from the nordenskjold formation of the back arc basin and a further jurassic assemblage from a probable trench slope basin have characteristics believed diagnostic of high latitudes the biogeographic affinities of radiolarians from cherts in the lemay group accretionary complex suggest that both these cherts and associated basalts are far travelled slices of the phoenix plate rocks from the probable trench slope basin formerly assigned to the younger fossil bluff group fore arc basin sequence now appear to be part of a new previously unrecognized formation

tectonic and paleobiogeographic significance of radiolarian microfaunas in the permian to mesozoic basement rocks of the north island new zealand abstract from the terranes sutured to the new zealand gondwana margin in mid cretaceous time the murihiku waipapa torlesse and mata river terranes have yielded tectonically and paleographically significant radiolarian faunas a late jurassic fauna from the murihiku forearc terrane is more cosmopolitan than coeval faunas from the waipapa faunas from the terranes east of the murihiku which all show evidence of accretion tectonics can be subdivided into ocean floor assemblages and assemblages of terrigenous clastic deposits waipapa ocean floor assemblages are typically tethyan while the terrigenous clastic assemblages are non tethyan possibly of southern hemisphere high latitude origin ocean floor assemblages show the same eastward younging trends opposed to the westward sedimentological younging due to imbrication as do the assemblages of the terrigenous clastics but are always a few tens of million years older radiolarians from ophiolites tangihua volcanics and matakaoa volcanics indicate that significant portions of the ocean floor obducted onto new zealand in late oligocene to earliest miocene time were of late cretaceous to early tertiary age

paleomagnetic results from the waipapa terrane northland peninsula north island new zealand tectonic implications from widespread remagnetizations paleomagnetic samples were collected from a wide variety of rock types of the waipapa terrane which is exposed along the eastern coast of the northland peninsula twelve sites yield stable magnetic directions which fail both a fold and regional attitude test at the 99 confidence level and indicate that widespread remagnetization has occurred over a large 200 km area rock magnetic experiments suggest that the mechanism for remagnetization was through the formation of fine grained magnetite and hematite and was probably controlled by local variation in fluid migration the mean in situ direction for the 12 sites is i 70 2 d 14 4 95 7 1 kappa 38 6 which is significantly different from the predicted axial dipole field directions at the 95 confidence level the age of the remagnetization is unclear in an effort to date the remagnetization a synthetic apparent polar wander apw path was constructed for new zealand using australian data and the apparent south pole from the remagnetized waipapa sites latitude 69 7 s longitude 150 7 e 95 11 2 was compared to this apw path using this method the age of the remagnetization is constrained to be between 12 and 58 ma a major change in the tectonic regime occurred at 25 ma which is evidenced by obduction of the northland allochthon and initiation of arc volcanism and subduction fluid migration and or elevated temperatures driven by the initiation of subduction and arc volcanism along with the obduction of the northland allochthon seem likely mechanisms for the remagnetization

mesozoic tectonic evolution of the proto south china sea a perspective from radiolarian paleobiogeography abstract the proto south china sea pscs represents the lithosphere that formerly occupied the region southeast of south china where the present day south china sea is located the subduction and demise of the pscs have attracted wide attention whereas the pre subduction history particular the mesozoic of the region remains relatively neglected in this paper the radiolarian paleobiogeography of the region is analyzed to identify the paleobiogeographic affinity and paleo connectivity of the pscs with the pacific and tethys oceans during the mesozoic then the continent ocean configuration and tectonic evolution of the pscs and adjacent areas are discussed through the integration of paleobiogeographical results and associated paleomagnetic stratigraphic and petrologic data the main conclusions are as follows 1 during the triassic the pscs was situated in the transition zone between the pacific and tethys oceans and its paleobiogeography was influenced by both oceans the pscs was characterized by complex tectonic overprinting by the pacific and tethyan tectonic regimes 2 in the early middle jurassic the pscs was well connected to the pacific ocean but poorly connected to the tethys ocean consistent with the paleobiogeography of the pscs being mainly constrained by the pacific ocean the pscs was part of the paleo pacific slab 3 during the late jurassic cretaceous the pscs was in a semi closed environment the late jurassic early late cretaceous pscs was part of a west facing andean type subduction zone and the late late cretaceous pscs was situated in an extensional tectonic setting

trench sedimentation versus accreted submarine fan an approach to regional scale facies analysis in a mesozoic accretionary complex torlesse terrane northeastern north island new zealand abstract the waioeka subterrane of the north island new zealand considered as the youngest part of the torlesse terrane is interpreted as a late mesozoic accretionary complex at the gondwana margin these basement rocks are characterized by sedimentological and petrological monotony scarcity of bio and lithostratigraphic markers and tectonic complexity due to accretion in an oblique subduction regime and possible post accretionary strike slip overprint a modified approach to facies analysis is presented which allows the recognition of distinct characteristics of a turbidite system and which reduces the number of possible interpretation schemes despite the lack of lateral correlation of sedimentary sequences in addition criteria such as complexity of the pattern of facies distribution position of slumping of oligomict material and proximal to distal distribution of bouma sequences and conglomerate fabrics are suggested to distinguish between two end members of possible pre accretionary depositional environments a a trench depositional environment and b a submarine fan on a broad basin plain the waioeka subterrane is characterized by mud sand to sand rich sediments consisting dominantly of very thick sandstones facies b and alternating sandstone mudstone sequences facies c2 and only minor conglomerates facies a and silty muddy deposits facies d overall sedimentological features suggest a depositional setting beyond a significant lower slope break base of slope at the lower reaches of a turbidite system with sediment supplied by a small number of large point sourced channels five defined facies associations are interpreted as major and minor midfan type channel deposits lobe and lobe fan fringe facies and or trench axial channel facies and levee overbank facies proposed criteria favour a trench depositional environment rather than an earlier postulated submarine fan setting on a basin plain subsequently accreted at a convergent margin

synoptic versus orographic control on stationary convective banding quasi stationary convective bands can cause large localised rainfall accumulations and are often anchored by topographic features here the predictability of and mechanisms causing one such band are determined using ensembles of the met office unified model at convection permitting resolution 1 5 km grid length the band was stationary over the uk for 3 h and produced rainfall accumulations of up to 34 mm the amount and location of the predicted rainfall was highly variable despite only small differences between the large scale conditions of the ensemble members only three of 21 members of the control ensemble produced a stationary rain band these three had the weakest upstream winds and hence lowest froude number band formation was due to the superposition of two processes lee side convergence resulting from flow around an upstream obstacle and thermally forced convergence resulting from elevated heating over the upstream terrain both mechanisms were enhanced when the froude number was lower by increasing the terrain height thus reducing the froude number the band became more predictable an ensemble approach is required to successfully predict the possible occurrence of such quasi stationary convective events because the rainfall variability is largely modulated by small variations of the large scale flow however high resolution models are required to accurately resolve the small scale interactions of the flow with the topography upon which the band formation depends thus although topography provides some predictability the quasi stationary convective bands anchored by it are likely to remain a forecasting challenge for many years to come

radiolarian diversity patterns in the latest jurassic earliest cretaceous abstract the global diversity patterns of latest jurassic earliest cretaceous tithonian berriasian radiolarian faunas were analyzed based on samples from the european alps oman philippines and antarctica and an extensive literature survey several measures of diversity were applied to faunas from tropical oman mexico pacific subtropical alps california philippines japan and subpolar antarctic peninsula new zealand northern russia localities original diversity patterns are obscured by taxonomic sedimentological and preservational biases qualitative and quantitative corrections of these biases indicated a significant diversity gradient from tropical subtropical to subpolar latitudes but no significant difference between tropical and subtropical assemblages the latitudinal diversity gradient was apparently asymmetrical being steeper in the northern hemisphere than in the southern hemisphere in the southern hemisphere the diversity gradient was similar to the one observed in modern radiolarian sedimentary assemblages considering the more equable climate of the tithonian berriasian it appears unlikely that temperature was the only control of the observed diversity patterns the results substantiate the notion of latitudinal diversity gradients as a time invariant feature of the earth possibly driven by gradients in biome size

evidence from u pb zircon and 40ar 39ar muscovite detrital mineral ages in metasandstones for movement of the torlesse suspect terrane around the eastern margin of gondwanaland new u pb detrital zircon ages from triassic metasandstones of the torlesse terrane in new zealand are compared with 40ar 39ar muscovite data and together reveal four main source components i major triassic permian 210 270 myr old and ii minor permian carboniferous 280 350 myr old granitoids recorded in zircon and muscovite data iii minor early middle palaeozoic metamorphic rocks recorded mainly by muscovite 420 460 myr old and iv minor late precambrian cambrian igneous and metamorphic complexes 480 570 myr old recorded by zircon only there are also proterozoic zircon ages with no clear grouping 580 1270 myr the relative absence of late palaeozoic 350 420 myr old components excludes granitoid terranes in the southern lachlan fold belt australia and its continuation into north victoria land east antarctica and marie byrd land west antarctica as a potential source for the torlesse the age data are compatible with derivation from granitoid terranes of the northern new england orogen and hinterland in ne australia this confirms that the torlesse terrane of new zealand is a suspect terrane that probably originated at the ne australian permian triassic gondwanaland margin and then 200 120 ma moved 2500 km southwards to its present new zealand position by the late cretaceous 90 ma this sense of movement is analogous to that suggested for palaeozoic mesozoic terranes at the north american pacific margin

atmospheric factors governing banded orographic convection abstract the three dimensional structure of shallow orographic convection is investigated through simulations performed with a cloud resolving numerical model in moist flows that overcome a given topographic barrier to form statically unstable cap clouds the organization of the convection depends on both the atmospheric structure and the mechanism by which the convection is initiated convection initiated by background thermal fluctuations embedded in the flow over a smooth mountain without any small scale topographic features tends to be cellular and disorganized except that shear parallel bands may form in flows with strong unidirectional vertical shear the development of well organized bands is favored when there is weak static instability inside the cloud and when the dry air surrounding the cloud is strongly stable these bands move with the flow and distribute their cumulative precipitation evenly over the mountain upslope similar shear parallel bands also develop in flows where convection is

snowbands over the english channel and irish sea during cold air outbreaks persistent northerly to easterly cold air outbreaks affected the uk during the winters of 2009 10 and 2010 11 with the resulting convection frequently organizing into snowbands over the english channel and irish sea sounding data and composite radar reflectivity images from the met office nimrod precipitation radar network reveal that these bands formed along the major axis of each body of water or sea when the boundary layer flow was roughly parallel to each of those axes along channel for both seas a band was present the majority of times that the 850 hpa flow was along channel of these times of along channel flow the 850 hpa wind speed and surface to 850 hpa temperature difference were significantly greater when bands were present than when they were not for the english channel only the land sea temperature difference was also significantly greater when bands were present than when they were not in a real data weather research and forecasting model wrf control simulation of a typical band over the english channel a trough develops over the water and offshore air streams from either side converge along it in the absence of surface fluxes the trough convergence and organized precipitation fail to develop altogether orography and roughness length variations are less important in band development affecting only the location and morphology

mean radar echo characteristics during project gale abstract the mean radar echo characteristics during the genesis of atlantic lows experiment gale are presented for the southeastern united states during the 15 january 15 march 1986 field phase of the program the echo characteristics were derived from the operational national weather service nws wsr 57 10 cm network radars radar echo frequency and intensity were subjectively tabulated on a 0 5 latitude longitude grid from objectively contoured three hourly nws maps routinely transmitted over facsimile the objectively contoured maps were derived from manually digitized radar observations at each nws radar location the principal findings include 1 a greater occurrence of vip intensity level 1 and greater echoes in the coastal waters from georgia to north carolina 2 a concentrated region of vip intensity level 1 3 and 5 radar echoes 100 km cast of cape hatteras north carolina along the edge of the gulf stream 3 a considerably greater likelihood of offshore versus onshore radar echoes along t

a newly proposed radiolarian zonation for the jurassic of japan abstract eight radiolarian zones are established on the basis of biostratigraphic investigations on the japanese jurassic these are theparahsuum sp c archicapsa pachyderma laxtorum jurassicum tricolocapsa plicarum tricolocapsa conexa stylocapsa spiralis cinguloturris carpatica andpseudodictyomitra primitiva zones in ascending order biohorizons reflecting evolutionary lineages are utilized where possible in defining the zonal boundaries in the case of absence of adequate lineages biohorizons of the first or last appearance of characteristic species are applied the zones are compared with the zones previously proposed by several workers in japan

provenance of the sedimentary rakaia sub terrane torlesse terrane south island new zealand the use of igneous clast compositions to define the source abstract the permian to late triassic rakaia sub terrane part of the torlesse superterrane of the new zealand eastern province is an accretionary complex that comprises an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages the field of provenance analysis has undergone a revolution with the development of single crystal isotope dating techniques using mainly silt to sand sized single mineral grains fine sand and mud may be transported over thousands of kilometres with potential problems for provenance studies reinforcing the need for caution when interpreting provenance evidence from single heavy mineral grains this study focuses on coarser grained rocks notably conglomerates which involve much shorter transport distances and therefore may be used to trace proximal sources a detailed rock sampling programme and geochronological geochemical and sr nd isotope analysis of igneous clasts from four conglomerates boundary creek te moana mckenzie pass and lake hill have broadly characterised the igneous source for the rakaia sub terrane shrimp u pb zircon ages of rakaia sub terrane igneous clasts define three distinct periods of magmatic crystallisation the first period ranges in age from 292 to 243 ma permian to middle triassic with two clusters recognisable a minor early permian one ranging in age from 292 to 277 ma and a major late permian to middle triassic one from 258 to 243 ma all these clasts are confined to the kazanian permian te moana the dorashamian permian mckenzie pass and the carnian late triassic lake hill conglomerates the clasts which are subduction related calc alkaline to high k calc alkaline and metaluminous to peraluminous range in lithology from andesite to rhyolite and their plutonic equivalents many clasts at lake hill have chemical compositions characteristic of partial melts of a source of basaltic composition in equilibrium with amphibole pyroxene garnet adakites indicative of a thick crust in the clast source area the second period comprises carboniferous calc alkaline metaluminous to weakly peraluminous clasts of the permian boundary creek conglomerate ranging in age from 356 to 325 ma the third group consists of two cambrian clasts a monzogranite from te moana c 497 8 ma and a dacite from lake hill c 517 ma geochronology geochemistry and sr nd isotopes of rakaia igneous clasts correlate broadly with those of permian to triassic plutons and volcanics from the amundsen and ross provinces of marie byrd land thus the antarctic sector of the panthalassan margin of gondwana is the probable source for the rakaia sub terranes as opposed to the other postulated sources in eastern australia

tracking crustal processes by ft thermochronology in a forearc high hikurangi margin new zealand involving cretaceous subduction termination and mid cenozoic subduction initiation abstract raukumara peninsula is a forearc high on the pacific margin of new zealand its basement comprises two sedimentary terranes that formed in subduction prisms during the late jurassic mid cretaceous marking the end of subduction along the pacific margin of eastern gondwanaland the cover includes allochthonous late cretaceous oligocene passive margin slope to basin facies emplaced into the forearc during the early miocene initiation of the current subduction regime as well as autochthonous neogene sediments apatite and zircon fission track ft data are reported and interpreted for the basement and cover sediments the detrital zircon ft ages constrain the maximum depositional ages of the low grade zeolite and pumpellyite facies basement pahau terrane is no older than 152 13 ma this zircon ft mode and older ones 198 8 ma 232 58 ma recording cooling denudation in the source areas probably including rakaia terrane waioeka terrane located oceanward of pahau terrane is no older than 125 2 ma being the age of volcanic derived zircons and supports early cretaceous dinoflagellate ages reported previously omaio petrofacies comprises the youngest part of the waioeka terrane and has a zircon ft age of 108 6 3 ma this indicates that basement sequences accumulated in the northeast contemporaneously with cover sequences koranga fm in the southwestern part of the peninsula these zircon ft ages together with the results of thermal history modelling of certain waioeka terrane samples are consistent with migration of a thrust system in a subduction prism environment during the late jurassic cretaceous until about 85 ma as proposed earlier when mesozoic subduction terminated apatite ft data indicate for all basement samples a phase of neogene heating and cooling associated with basin formation sediment accumulation and subsequent uplift and erosion resulting in almost complete removal of the neogene stratigraphic record over western parts of the peninsula forward modelling of the data imply rapid earliest miocene downwarping of the crust in bay of plenty coinciding with initiation of subduction of pacific plate followed by emplacement of a 1 5 2 0 km thick wedge of east coast allochthon from the northeast early miocene sediments accumulated in a foredeep along the front sw margin of the allochthon probably sourced from a block of pahau basement west of whakatane fault which was exhumed and denuded by 4 km contemporaneously during the late early to middle miocene the basin depocentre migrated further to the southwest while areas previously downwarped northeast were uplifted and eroded the depocentre migration and subsequent inversion is a pattern that affected most of north island and is related to mechanical or dynamical interaction of the two plates as the slab of pacific oceanic lithosphere was emplaced beneath north island this may be a general feature of young subduction zones

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones xi comparisons between observational and theoretical aspects of rainbands abstract comparisons are made between the characteristics of several types of rainbands observed in an extratropical cyclone and dynamical mechanisms relevant on the mesoscale the warm sector flow ahead of the cold front and above the cold frontal zone aloft was unstable to conditional symmetric instability and theoretical predictions for this mechanism am consistent with several aspects of the warm sector and wide cold frontal rainbands in the case of the warm sector rainbands other mechanisms e g wave cisk and mixed dynamic convective instabilities may have also played a role the core structure of the narrow cold frontal rainbands appeared to be affected by an instability that derived its energy from the horizontal shear across the surface front also many aspects of the narrow cold frontal rainband were similar to a density current shear induced gravity waves appeared to be responsible for the wavelike rainbands observed in the vicinity of the cold frontal zone aloft the orientation of the

statistical analysis of facies clustering in submarine fan turbidite successions abstract the hurst statistic converted easily into a fractal dimension quantifies the degree of clustering of high and low values in spatial or temporal series of data in an effort to better understand the stratigraphic organization of submarine fan deposits the hurst statistic was calculated for nineteen turbidite sections that span a wide range of geological time tectonic settings facies characteristics and depositional environments three bed by bed variables were considered coarse division thickness i e net thickness in a single bed of conglomerate sandstone siltstone grain size and coarse division thickness percentage relative to thickness of overlying mudstone caps sixteen of the 19 turbidite sections analyzed 84 2 show the hurst phenomenon i e irregular long term clustering of high and low values of the three bed by bed variables this clustering is related to stratigraphic changes of sedimentary facies caused by lateral shifting of sub environments on a submarine fan surface there is no evidence that the clustering is controlled by sea level fluctuations the strength of the clustering inferred from hurst k values holds promise as an index to distinguish submarine fan sub environments preliminary results suggest that channel levee deposits tend to have strong clustering lobe interlobe deposits tend to display moderate clustering and basin floor sheet sand systems tend to have weak clustering combining facies characteristics with these statistical results provides more reliable criteria for the identification of submarine fan sub environments than are available from recently discredited models based on asymmetric cycles of bed thickness or grain size

early hettangian ammonites and radiolarians from the queen charlotte islands british columbia and their bearing on the definition of the triassic jurassic boundary abstract the triassic jurassic boundary t j boundary interval is one of the most important but poorly understood intervals in the phanerozoic here we fully document the ammonite and radiolarian successions at several sites in the queen charlotte islands qci british columbia eleven ammonite taxa are described and eighteen radiolarian taxa are discussed with the radiolarian genus tipperella described as new type species t kennecottensis n sp there are two continuous t j boundary sections in the qci one is located at kennecott point on graham island section i the other on the southeastern shore of kunga island section iii a second section at kennecott point contains fossils of early hettangian age only section ii radiolarian faunas include taxa from the upper rhaetian globolaxtorum tozeri zone in the two continuous sections and the lower hettangian canoptum merum zone in all three sections in each section the lowest hettangian fossils are radiolarians and a few collections contain rare rhaetian holdovers these mixed faunas may equate with the lowest hettangian ammonite zone the spelae zone of the north american succession the upper portion of section i contains a sparse ammonite fauna which indicates an early hettangian age this section has also provided carbon isotope data with a negative excursion spanning the t j boundary section ii contains a more diverse early hettangian ammonite assemblage that permits correlation of the upper portion of this section with the lower hettangian minutus zone section iii has been previously proposed as a potential basal hettangian global stratotype section and point gssp in addition to an outstanding radiolarian fauna the section contains moderately diverse early hettangian ammonites that permit correlation of the lower portion of the section with the minutus and pacificum zones and the upper portion with the lower hettangian polymorphum zone this section has previously provided a u pb date of 199 6 0 3 ma from 3 6 m below the t j boundary currently there are four candidates and no ideal gssp for the basal hettangian a section in new york canyon nevada has also been proposed as a potential gssp this section is easily accessible and provides a virtually complete ammonoid succession but lacks geochronology and microfossils the section on kunga island in the qci provides geochronologic data and excellent radiolarian constraints in essence the sections at kunga island in the qci and new york canyon in nevada are complementary close correlations between the two sections are possible using ammonite faunas we suggest the section from nevada be designated as holostratotype for the basal hettangian and the qci section be designated as a parastratotype to improve recognition of this interval

diagenesis and very low grade metamorphism of volcaniclastic sandstones from contrasting geodynamic environments north island new zealand the murihiku and waipapa terranes the mesozoic murihiku and waipapa terranes are two accretionary wedges of linked forearc and trench sediments respectively that were juxtaposed in the early cretaceous late triassic to late jurassic murihiku terrane volcaniclastic sediments are folded into a regional syncline and have been diagenetically altered there is a general relationship between zeolite occurrence clay mineralogy vitrinite reflectance and stratigraphic position youngest jurassic sediments contain heulandite analcime and stilbite whereas late triassic to mid jurassic sediments have laumontite and heulandite in detail the zeolite distribution is complicated tuffaceous horizons on the eastern limb of the syncline are calcitized rather than zeolitized post diagenetic fractures associated with uplift are laumontite filled the inferred geothermal gradient is c 15 c km 1 the waipapa terrane is an accretionary complex dominated by imbricated terrigenous sediments of triassic and jurassic age with enclosed permian to jurassic pelagic sediments and basalts late jurassic sediments are massive volaniclastic sandstones the sediments are non foliated and metamorphic minerals in the massive sandstones have crystallized in specific domains the observed metamorphic succession of prehnite pumpellyite and pumpellyite actinolite facies assemblages was overprinted in the imbricated rocks during a thermal event that was late in the deformation sequence and broadly coincident with hydraulic fracturing and veining the metamorphic successions in the two terranes and their relationships to structural features are in excellent accord with accretionary complex models

the mid cretaceous transition from basement to cover within sedimentary rocks in eastern new zealand evidence from detrital zircon age patterns detrital zircon u pb ages for 30 late jurassic and cretaceous sandstones from the eastern province of eastern new zealand combined with previously published geochronological and palaeontological data constrain the time of deposition in the pahau and waioeka terranes of the cretaceous accretionary margin of zealandia and their adjacent cover strata the zircon age patterns also constrain possible sediment source areas and mid cretaceous geodynamic models of the transition from basement accretionary wedge to passive margin cover successions pahau terrane deposition was mainly barremian to aptian but continued locally through to late albian time with major source areas in the adjacent kaweka and waipapa terranes and minor inputs from the inboard median batholith waioeka terrane deposition was mainly albian with distinctive and exclusive sediment sources principally from the median batholith but with minor inputs from the western province alternative tectonic models to deliver such exclusive median batholith and western province derived sediment to the mid cretaceous zealandia continental margin are 1 the creation of a rift depression across zealandia or 2 sinistral displacement of south zealandia with respect to north zealandia to expose western province rocks directly at the zealandia margin detrital zircon age patterns of cretaceous cover successions of the eastern province of eastern new zealand demonstrate purely local sources in the adjacent kaweka and waipapa terranes cretaceous zircon components show a decline in successions of late early cretaceous age and disappear by late late cretaceous time suggesting the abandonment or loss of access to both the median batholith and western province as sediment sources

evolution of mesoscale precipitation band environments within the comma head of northeast u s cyclones abstract this paper explores the mesoscale forcing and stability evolution of intense precipitation bands in the comma head sector of extratropical cyclones using the 32 km north american regional reanalysis hourly 20 km rapid update cycle analyses and 2 km composite radar reflectivity data a statistical and composite analysis of 36 banded events occurring during the 2002 08 cool seasons reveals a common cyclone evolution and associated band life cycle a majority 61 of banded events develop along the northern portion of a hook shaped upper level potential vorticity pv anomaly during the 6 h leading up to band formation lower tropospheric frontogenesis nearly doubles and the conditional stability above the frontal zone is reduced the frontogenesis increase is primarily due to changes in the kinematic flow associated with the development of a mesoscale geopotential height trough this trough extends poleward of the 700 hpa low and is the vertical extension of the surface warm front and surface

a satellite based climatology of central and southeastern u s mesoscale convective systems abstracta satellite based climatology is presented of 9607 mesoscale convective systems mcss that occurred over the central and southeastern united states from 1996 2017 this climatology is cons

reactivation of tectonics crustal underplating and uplift after 60 myr of passive subsidence raukumara basin hikurangi kermadec fore arc new zealand implications for global growth and recycling of continents we use seismic reflection and refraction data to determine crustal structure to map a fore arc basin containing 12 km of sediment and to image the subduction thrust at 35 km depth seismic reflection megasequences within the basin are correlated with onshore geology megasequence x late cretaceous and paleogene marine passive margin sediments megasequence y a similar to 10 000 km 3 submarine landslide emplaced during subduction initiation at 22 ma and megasequence z a neogene subduction margin megasequence the moho lies at 17 km beneath the basin center and at 35 km at the southern margin beneath the western basin margin we interpret reflective units as deformed gondwana fore arc sediment that was thrust in cretaceous time over oceanic crust 7 km thick raukumara basin has normal faults at its western margin and is uplifted along its eastern and southern margins raukumara basin represents a rigid fore arc block 150 km long which contrasts with widespread faulting and large neogene vertical axis rotations farther south taper of the western edge of allochthonous unit y and westward thickening and downlap of immediately overlying strata suggest westward or northwestward paleoslope and emplacement direction rather than southwestward as proposed for the correlative onshore allochthon spatial correlation between rock uplift of the eastern and southern basin margins with the intersection between moho and subduction thrust leads us to suggest that crustal underplating is modulated by fore arc crustal thickness the trench slope has many small extensional faults and lacks coherent internal reflections suggesting collapse of indurated rock rather than accretion of 1 km of sediment from the downgoing plate the lack of volcanic intrusion east of the active arc and stratigraphic evidence for the broadening of east cape ridge with time suggests net fore arc accretion since 22 ma we propose a cyclical fore arc kinematic rock moves down a subduction channel to near the base of the crust where underplating drives rock uplift oversteepens the trench slope and causes collapse toward the trench and subduction channel cyclical rock particle paths led to persistent trench slope subsidence during net accretion existing global estimates of fore arc loss are systematically too high because they assume vertical particle paths citation sutherland r et al 2009 reactivation of tectonics crustal underplating and uplift after 60 myr of passive subsidence raukumara basin hikurangi kermadec fore arc new zealand implications for global growth and recycling of continents tectonics 28 tc5017 doi 10 1029 2008tc002356

artificial neural network assisted prediction of dissolution spatial distribution in the volcanic weathered crust a case study from chepaizi bulge of junggar basin northwestern china abstract the reservoir rocks in the volcanic weathered crust are characterized by plentiful dissolution pores caverns and fractures however as an essential control factor of the reservoir distribution volcanic dissolution is often ignored in quantitative studies in this paper we propose a complete artificial intelligence workflow to model and predict the volcanic dissolution distribution by integrating the image logging semi quantitative analysis with seismic prediction a synthetic reservoir property named dcv dissolution comprehensive values is generated as logging curves from xrmi resistivity pseudo pictures to indicate the intensity of dissolution these curves are then used as the target for the seismic based prediction in an artificial intelligence framework a multi layer artificial neural network ann model is constructed in order to map the seismic attributes into the dcv the methodology is demonstrated on a real case study from the junggar basin in northwestern china the maps and profiles from the prediction represent the dissolution values in the volcanic weathered crust the predictions are consistent with the geological volcanic dissolution model provided by geological knowledge it is concluded that the spatial dissolution distribution in volcanic weathered crust can be reliably predicted by this integrated method

evolution properties and spatial variability of mjo convection near and off the equator during dynamo abstractthis study investigates the evolution structure and spatial variability of madden julian oscillation mjo convection observed during the 2011 12 dynamics of the mjo dynamo field campaign generally the c band radars located in the near equatorial indian ocean shared mobile atmospheric research and teaching radar smart r on addu atoll gan and nasa toga on the r v roger revelle revelle observed similar trends in echo top heights stratiform rain fraction and precipitation feature size across the mjo life cycle these trends are closely related to changes in mid to upper tropospheric moisture sea surface temperature sst zonal wind and diagnosed vertical air motions however the evolution of convection moisture and vertical air motion at the r v mirai mirai located in the intertropical convergence zone itcz at 8 s exhibited a pattern nearly opposite to gan and revelle when the mjo was active over the equator convection was suppressed around mirai owing to induced subsiden

origin of the oceanic basalt basement of the solomon islands arc and its relationship to the ontong java plateau insights from cenozoic plate motion models abstract cenozoic global plate motion models based on a hotspot reference frame may provide a useful framework for analyzing the tectonic evolution of the solomon islands convergent margin a postulated late miocene collision of the ontong java plateau ojp with a ne facing arc is consistent with the predicted path of the ojp across the pacific basin and its miocene arrival at the trench late stage igneous activity 65 30 ma predicted for the ojp as it rode over the samoan hotspot occurred in correlative stratigraphic sections on malaita the supposed accreted flake of ojp in the solomon islands arc convergence similar to the present velocities between australia and the pacific plates was characteristic of the last 43 million years prior to 43 ma pacific australia plate motions were divergent seemingly at odds with geologic evidence for early tertiary convergence particularly in papua new guinea a postulated south pacific plate may have existed between australia and the pacific plate and would have allowed implied northward subduction along the northeastern australia plate boundary that lasted into the early eocene subsequent reorganization of plate motions in the middle eocene correlates with middle eocene marginal basin formation along ridges oblique to the main plate boundary cessation of spreading on the pacific south pacific ridge and its subsequent subduction beneath asia followed the change in pacific plate motion at 43 ma a trapped remnant of the extinct nw trending ridge may still lie beneath the western philippine sea the terminal deformation metamorphism and ophiolite obduction in the eocene orogen of the southwest pacific also correlates with the major change in pacific plate motion at 43 ma and the subsequent compression of the dying eocene arc against outlying continental and oceanic crustal blocks of the australian plate the solomon islands oceanic basement may represent juxtaposition of oceanic plateaus of the australian plate beneath overthrust dismembered ophiolite derived from adjacent marginal basin crust

critical wedge theory and the mesozoic accretionary wedge of new zealand abstract we apply principles of critical wedge theory to explain the jurassic and early cretaceous tectonic development of the mesozoic accretionary wedge of new zealand one of the best exposed subduction complexes on earth by summarizing factors that can lead to drastic changes in wedge balance the wedge has a carboniferous to cretaceous 330 110 ma stratigraphic record with an early cretaceous 145 130 ma hiatus in clastic deposition across the esk head melange near the front of the wedge in the rear of the wedge the age of moderately high pressure metamorphism of the otago schist which represents the forearc high of the wedge occurred near the end of this stratigraphic hiatus the otago schist has a subhorizontal foliation indicative of underplating as the mode of accretion the outer frontal part of the wedge has a subvertical foliation indicative of frontal accretion we propose that in the jurassic and earliest cretaceous the wedge grew by frontal accretion by 135 ma the wedge became too long and was subcritical this resulted in tectonic erosion of the front of the wedge the tectonically eroded material was underthrust underplated beneath the rear of the wedge to form the subhorizontally foliated otago schist colliding seamounts and or oceanic plateaux preserved in the esk head melange may have aided wedge instability the proposed wedge instability and increased horizontal shortening was largely coeval with major changes in the chemistry of subduction related arc magmatism and a phase of shortening and high pressure metamorphism in the arc our model provides a holistic and coherent interpretation explaining the major tectonic features of the long lived new zealand part of the east gondwana subduction zone

topographically forced convergence in western washington state abstract several times a year when the low level winds from off the pacific ocean are within a narrow range of speed and direction air passes both north and south of the olympic mountains of washington state and is forced to converge in puget sound by the north south oriented cascade range this phenomenon termed the puget sound convergence zone often results in a band of cloudiness and precipitation in northern and central puget sound with clear subsiding air to the north and south this paper presents the results of a series of case studies in which the structure of the zone its meteorological manifestations and the environmental conditions necessary for its formation are explored it is shown that the convergence zone is skillfully forecast by surface coastal winds and undergoes a strong annual and diurnal cycle being most frequent during the late spring and early summer months and during the afternoon and early evening it is also found that the zone is structurally similar to a shallow cold fr

thermochronology of the torlesse accretionary complex wellington region new zealand the torlesse complex comprises several mesozoic accretionary prism complexes together forming continental basement over large parts of new zealand this study focuses on the thermal history of relatively low grade graywacke rocks exposed in a transect in southern north island that crosses the structural grain of the torlesse complex including its older and younger parts zircon fission track ft ages for the late triassic rakaia terrane which is the most inboard of the accretionary complexes are partially annealed some possibly reset and may indicate early cretaceous 134 10 ma cooling from maximum temperatures tmax probably related to imbrication of younger complexes of the pahau terrane numerical modeling of the zircon ft ages and published 40ara 39ar muscovite and biotite ages for the rakaia terrane suggest tmax values of 265 310 c and exhumation from depths of 10 12 km the rocks underlying the aorangi range and involving the youngest accretionary complex have experienced much lower tmax values of 210 and 110 c bracketed by reset apatite ft ages and detrital zircon ft ages the occurrence of a circa 100 ma component of zircon ft ages in both the weakly and highly indurated rocks beneath the aorangi range as well as in remnants of an overlying albian accretionary slope basin whatarangi formation imply multistorey accretion and incorporation of sediment into the youngest prism this circa 100 ma zircon ft age component also places a maximum age on the termination of mesozoic subduction beneath the new zealand region the occurrence of reset apatite ft ages across the whole of the wellington transect indicates that at least 4 km of exhumation occurred during the late miocene

stability and charging characteristics of the comma head region of continental winter cyclones abstractthis paper presents analyses of the finescale structure of convection in the comma head of two continental winter cyclones and a 16 storm climatology analyzing the distribution of lightning within the comma head a case study of a deep cyclone is presented illustrating how upper tropospheric dry air associated with the dry slot can intrude over moist gulf air creating two zones of precipitation within the comma head a northern zone characterized by deep stratiform clouds topped by generating cells and a southern zone marked by elevated convection lightning when it occurred originated from the elevated convection a second case study of a cutoff low is presented to examine the relationship between lightning flashes and wintertime convection updrafts within convective cells in both storms approached 6 8 m s 1 and convective available potential energy in the cell environment reached approximately 50 250 j kg 1 radar measurements obtained in convective updraft regions showed enhanced spectral

behavior of the decollement at the toe of the middle america trench seismic reflection data from three areas of the middle america trench provide insights into the behavior of the decollement that separates subducted and offscraped sediment the range of responses observed along this single subduction system provides clues as to how the decollement forms and is influenced by local conditions the location of the decollement and whether or not the subducting basement topography influences the decollement are apparently controlled by the type and thickness of sediment in the trench where subducting basement topography and oceanic plate hemipelagic sediments are buried by sandy terrigenous turbidites such as in the trench axis off mexico the decollement is localized near the base of the turbidite section subducting normal fault blocks in the oceanic crust control thrust ramps and hanging wall anticlines form above the ramps

new biostratigraphic elements for dating upper norian strata from the sandilands formation queen charlotte islands british columbia canada abstract upper norian radiolarians have been recovered from the basal sandilands formation on northwest graham island kennecott point kunga island and louise island queen charlotte islands rare conodonts and ammonoids are associated with the radiolarians at several levels at kennecott point over 90 m of the lower sandilands formation is coarser and less tuffaceous than is typical of the formation elsewhere and appears to represent continuous sedimentation diverse well preserved radiolarians have been found in limestone concretions in the lower 75 m of section which has also yielded conodonts from the epigondolella bidentata zone approximates cordilleranus to basal crickmayi ammonoid zones and ammonoids from the crickmayi zone at kunga island in the southern queen charlotte islands excellent radiolarian faunas have also been recovered from a 30 m interval beginning 80 m above the final occurrence of monotis cordilleranus zone and from a second 90 m interval lying structurally above the former that contains the upper norian conodont epigondolella bidentata at the base three preliminary radiolarian assemblages are recognized for upper norian strata lying above the monotis beds assemblage 1 the lower one is tentatively correlated with the upper part of the cordilleranus zone assemblage 2 approximates the amoenum zone and assemblage 3 is correlated with the crickmayi zone the age of the sandilands formation is now confirmed to be late norian and hettangian as well as sinemurian considering the record of apparently uninterrupted sedimentation the section thickness and the excellent fossil recovery the sandilands formation has been shown to contain an unusually thick upper norian sequence and probably the triassic jurassic boundary

influence of terrain resolution on banded convection in the lee of the rocky mountains abstracton 16 17 february 2007 snowbands formed in the lee of the rocky mountains in wyoming colorado and nebraska on the anticyclonic shear side of a midlevel jet streak two types of bands were prevalent a longer wider band associated with frontogenesis along an equatorward moving cold front major band and multiple shorter narrower bands farther poleward minor bands to understand how the upstream terrain affected the occurrence and intensity of the bands multiple mesoscale model simulations were performed in which the terrain was incrementally smoothed the evolutions of the synoptic patterns were similar in all simulations that included topography but the synoptic pattern differed and no bands developed in a simulation with a flat land surface these results allowed a focus on the changes to the banded precipitation due to the terrain resolution remarkably although the exact location of the bands differed from run to run the bands in all simulations with topography were in roughly the s

numerical simulation of orographic rainbands 1 this study based on a statistical analysis of simulated warm rain event and radar data aims at highlighting the main physical mechanisms that lead to organize shallow convection on the relief the region of investigation the cevennes vivarais is located in the southeast part of france radar images from the cevennes experiment fall 1986 1988 reveal a characteristic and repetitive structure of the rain distribution organized in narrow bands or plumes oriented south north in the case of stationary southerly mediterranean flow the event of 14 november 1986 has been selected and constitutes the data set of this numerical study this work is closely associated with the previous work by miniscloux et al 2001 which presents in detail the results of a geostatistical analysis of the radar data set extracted from the cevennes experiment data base the main results highlight the physical characteristics and the dynamics of the rain patterns following the recent work of cosma et al 2002 high resolution i km simulations have been continued with the nonhydrostatic three dimensional 3d atmospheric model mesonh in order to reproduce the observed rainbands over the ceveunes region the numerical model correctly reproduces the structure and the dynamics of the rainbands the geostatistical analysis has been applied for the simulated rain fields the model slightly overestimates the northward advection velocity of the rain cells within the bands 75 km h 1 against 60 km h 1 for the observation and the simulated rainbands are narrower and more organized around the n 180 direction than the observed rain field the comparison allows the qualification and validation of the choice of the numerical methodology and realism of the physical parameterizations the analysis of the 3d simulated fields confirms the physical mechanisms responsible for the rain organization demonstrated by cosma et al 2002 through idealized simulations the statistical analysis highlights the presence of mean topographic features under low level convergence zones composed of a succession of ridges and penetrating valleys orientated east west the rainbands are generated upstream of these topographic features and enhanced on the leeside due to the convergence created by the flow deflection around the obstacle and its penetration into the valleys the simulated triggering takes place further to the south than the observed one and the triggering is active as soon as the relief is suitably described in the model

continental subduction and three dimensional crustal structure the northern south island new zealand the three dimensional vp and vp vs structure of a region where subduction transitions to oblique transform faulting has been determined using arrival times from 579 local earthquakes recorded during a temporary deployment and 3146 earthquakes have been relocated between 40 km and 100 km depth the subducted plate is imaged as a relatively low velocity feature in the uppermost mantle reflecting the continental nature of the subducted crust in this region an increase in amplitude of this low velocity feature from northeast to southwest can be related to an increase in the thickness of the crust of the subducted plate in this direction velocity variations within the subducted and overlying plates show some spatial correlation this suggests an interaction between the plates which extends well beyond the plate interface and is consistent with other geophysical and geological evidence that the plate interface beneath marlborough is currently not accommodating much active subduction in the overlying plate the awatere fault is a major structural feature associated with a low velocity zone extending to 23 km depth there is a marked change in structure near this fault with seismic velocities being lower to the southeast a relatively high level of seismicity occurs in this region of lower seismic velocities suggesting a relationship between the two a possible explanation for this is elevated pore pressures caused by fluids derived from dehydration of the continental subducted crust the low velocity region in the overlying plate coincides with the region of most intense active deformation suggesting it is relatively weak

juxtaposition of tethyan and non tethyan mesozoic radiolarian faunas in melanges waipapa terrane north island new zealand red cherts from kawakawa bay near auckland have yielded late triassic and early jurassic radiolarians the cherts occur as blocks in melanges that have a green argillite matrix containing middle and late jurassic callovian oxfordian radiolarians the melanges mark fault zones along which the waipapa terrane has been imbricated callovian oxfordian green argillites are also found in stratigraphic contact with overlying kimmeridgian tithonian green argillites and gray terrigenous clastics the late triassic and early jurassic radiolaria are tethyan but the middle and late jurassic faunas are dominantly non tethyan because the two sets of faunas are of low latitude and of high latitude origin respectively or because they originated in areas of differing ocean productivity occurrence of both late triassic and early jurassic radiolarians in one red chert horizon indicates sedimentary reworking

seven million years of strike slip and related off fault deformation northeastern marlborough fault system south island new zealand the marlborough fault system mfs south island new zealand is remarkable for the oblique slip nature of its active faulting and can be placed in a framework of pacific australian pac aus plate motions and geodetic strain new zealand illustrates changing degrees of upper plate slip partitioning in an obliquely convergent margin that varies along strike in crustal type and subduction geometry in this paper we focus on the ne part of this transcurrent fault system especially the awatere fault which is the only marlborough fault to offset a major neogene basin strike slip on an ancestral eastern strand of this fault began after 7 4 6 4 ma later vertical axis rotation may have caused it to be abandoned in favor of the currently active strand since 7 ma at least 34 10 km of dextral slip has accrued on the awatere fault 6 km of slip has accrued on two nearby strands and 4 km has accrued on the currently active coastal strand comparison of miocene with late quaternary offsets suggests that rates of strike slip on the fault have been nearly constant or have possibly decelerated we interpret spatial and temporal patterns of strike slip in the mfs to reflect southward migration of transform motion resulting from increased pac aus plate convergence late neogene to present day shortening directions in ne south island are indicative of a partially slip partitioned margin slip partitioning diminishes southward as the underlying subduction interface becomes strongly coupled suggesting a simple mechanical relationship between these processes

radiolarian stratigraphy and origin of the mesozoic terranes of the continental framework of the northwestern pacific russia abstract tectonostratigraphic investigation shows that the mesozoic triassic neocomian allochthonous terranes of the anadyr koryak accretionary region from the northwestern continental framing of the pacific ocean form isolated tectonic nappes and slices dispersed all over the region rather than fragments undeformed paleostructures nappes and slices of different stratigraphic horizons derived from various geodynamic and paleolatitudinal environments have been tectonically amalgamated into the anadyr koryak region furthermore these tectonostratigraphic units are accompanied by slabs of paleozoic sequences which were also accumulated in various different paleoenvironments correlations of the tectonically separated mesozoic formations are based on the radiolarians and geochemical and lithologic methods the tectonostratigraphic units range from middle triassic to hauterivian and are tectonically arranged in various spatial patterns formations of several different geodynamic environments are recognized oceanic abyssal plain and mor island arcs and marginal basins the radiolarian assemblages suggest that the early mesozoic formations were deposited at different paleolatitudes tethyan anisian sinemurian north tethyan and boreal pliensbachian early bajocian and in a vast zone from the equator to south boreal late bajocian hauterivian early to late mesozoic tectonic paleoenvironments spanned a width greater than 3000 km this zone was later shortened to a width of 300 km the development of nappes and slices of the anadyr koryak region and the koryak west kamchatka orogenic belt on the whole was due to several collisions near the asian continental margin the main collision event occurred in the interval 125 105 ma

isotopic microanalysis of seawater strontium in biogenic calcite to assess subsequent rehomogenisation during metamorphism abstract precise lam mc icpms in situ microanalyses of 87 sr 86 sr ratios in biogenic calcite of the bivalve atomodesma are reported for 14 horizons in low grade metasediments of late early permian to late late permian age in south island new zealand atomodesma shells and associated skeletal echinoderm calcite in zeolite and possibly to lower prehnite pumpellyite mineral facies material yield isotopic data that are interpreted as primary seawater 87 sr 86 sr values data for higher metamorphic grade probable upper prehnite pumpellyite to lawsonite albite facies samples consistently show evidence of sr isotopic homogenisation between atomodesma calcite and host matrix and thus seawater 87 sr 86 sr values are not retained in shell debris under any circumstances

quantitative log interpretation and uncertainty propagation of petrophysical properties and facies classification from rock physics modeling and formation evaluation analysis abstractformation evaluation analysis rock physics models and log facies classification are powerful tools to link the physical properties measured at wells with petrophysical elastic and seismic properties however this link can be affected by several sources of uncertainty we proposed a complete statistical workflow for obtaining petrophysical properties at the well location and the corresponding log facies classification this methodology is based on traditional formation evaluation models and cluster analysis techniques but it introduces a full monte carlo approach to account for uncertainty evaluation the workflow includes rock physics models in log facies classification to preserve the link between petrophysical properties elastic properties and facies the use of rock physics model predictions guarantees obtaining a consistent set of well log data that can be used both to calibrate the usual physical models used in seismic reservoir characterization and to condition reservoir models the

limestone and chert in tectonic blocks from the esk head subterrane south island new zealand the esk head subterrane is a continuous belt generally 10 20 km wide of tectonic melange and broken formation on the south island of new zealand this subterrane separates older and younger parts of the torlesse terrane which is an extensive accretionary prism composed mostly of quartzo feldspathic submarine fan deposits ranging from permian to early cretaceous in age the torlesse is the most pacific ward of several permian and mesozoic accreted terranes in new zealand that record tectonic amalgamation and ultimate accretion against the pacific facing gondwana margin the esk head subterrane of the torlesse is especially informative because it includes within it conspicuous tectonic blocks of submarine basalt and a variety of basalt associated seamount and sea floor limestones and cherty rocks thought to be representative of the subducted plate limestones in tectonic blocks are of late triassic and probably jurassic ages and include 1 submarine cemented pelagic bivalve geopetal packstone grainstone 2 brachiopod bryozoan encrinite and 3 radiolarian pelagic lime mudstone most of the triassic blocks have been dated using conodonts which have remarkably low color alteration index cai values paleogeographic inferences drawn from megafossils bioclasts and radiolarians as well as from carbonate cements indicate deposition of the oceanic sedimentary rocks at paleolatitudes somewhat lower than that of the new zealand part of the gondwana margin but higher than paleoequatorial latitudes these oceanic sediments and their basaltic substrates were evidently emplaced in the torlesse accretionary prism following off scraping from an extensive subducting oceanic plate probably the phoenix plate which was obliquely convergent with the northwest trending gondwana margin during late jurassic and or early cretaceous time

provenance analysis using conglomerate clast lithologies a case study from the pahau terrane of new zealand abstract the field of provenance analysis has undergone a revolution with the development of single crystal isotope dating techniques using mainly silt to sand sized single minerals this study focuses on coarser grained rocks notably conglomerates which involve much shorter transport distances and therefore may be used to trace proximal sources the torlesse terranes part of the new zealand eastern province are accretionary complexes that comprise an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages two terranes are recognised in the south island the permian to late triassic rakaia terrane and the late jurassic to early cretaceous pahau terrane geochronology geochemistry and sr nd isotopes of igneous clasts from pahau terrane conglomerates identify the median tectonic zone s l as a major contributor of detritus to the pahau depositional basin shrimp u pb zircon ages of igneous clasts range from 128 to 123 ma and from 147 to 135 ma calc alkaline clasts of the latter range are indistinguishable in age chemical composition and petrogenesis from the calc alkaline granitoids of the darran suite whereas alkaline clasts correlate with the electric granite both parts of the median tectonic zone an early jurassic calc alkaline rhyolite clast from kekerengu 188 3 ma correlates with the bounty island granite campbell plateau the petrography and geochemistry of pahau terrane sandstone clasts indicate the recycling of permian to early late triassic older rakaia terrane rocks this is further supported by the detrital zircon age data igneous conglomerate clasts are capable of placing exceptionally tight constraints on pahau provenance and on its mesozoic tectonic setting within the southwest pacific margin of gondwana they provide the best evidence yet that the pahau terrane is locally derived

convective snowbands downstream of the rocky mountains in an environment with conditional dry symmetric and inertial instabilities abstract convective snowbands moved slowly over wyoming and northern colorado on 16 17 february 2007 and produced up to 71 mm 2 8 in of snow that was unpredicted by operational numerical weather prediction models and human forecasters the northwest southeast oriented bands lasted for over 6 h comprising both a single major band more than 30 km wide and multiple minor bands about 10 km wide the convective bands initiated within the ascending branch of a secondary circulation associated with both near surface and elevated frontogenesis but the bands remained nearly stationary while the near surface frontogenesis moved quickly equatorward the bands occurred downstream of complex terrain on the anticyclonic shear side of a midlevel jet streak where conditional dry symmetric negative potential vorticity and inertial negative absolute vorticity instabilities were present to determine the mechanisms responsible for the development and organization of these bands simulations using a convectio

statistical facies classification from multiple seismic attributes comparison between bayesian classification and expectation maximization method and application in petrophysical inversion we present here a comparison between two statistical methods for facies classifications bayesian classification and expectation maximization method the classification can be performed using multiple seismic attributes and can be extended from well logs to three dimensional volumes in this work we propose for both methods a sensitivity study to investigate the impact of the choice of seismic attributes used to condition the classification in the second part we integrate the facies classification in a bayesian inversion setting for the estimation of continuous rock properties such as porosity and lithological fractions from the same set of seismic attributes the advantage of the expectation maximization method is that this algorithm does not require a training dataset which is instead required in a traditional bayesian classifier and still provides similar results we show the application comparison and analysis of these methods in a real case study in the north sea where eight sedimentological facies have been defined the facies classification is computed at the well location and compared with the sedimentological profile and then extended to the 3d reservoir model using up to 14 seismic attributes

triassic radiolarian biostratigraphy this paper summarizes 30 years of research on the biostratigraphy of triassic radio larians and presents a correlation of currently used radiolarian zonations established in north america europe japan and far east russia an up to date stratigraphic distribution of all hitherto described and still valid triassic genera is provided this new range chart consists of 282 genera and allows an accurate dating to substage level it also clearly manifests general trends in radiolar ian evolution through the triassic the end permian extinction the most severe extinction in the history of radiolarians was followed by a long recovery until the early anisian the middle and late anisian were then characterized by a rapid explosion of new morphologies maximum generic diversity was attained during the early carnian but the first severe extinctions also occurred in the carnian a progressive decline of diversity took place through the norian and rhaetian and ended in a mass extinction around the triassic jurassic boundary since the revolution that signified the use of the hydrofluoric acid method in extracting radiolarians from hard siliceous rocks radiolarians have proven to be of great importance in reconstructing the stratigraphy of the mesozoic particularly the triassic system this methodology discovered independently by dumitrica 1970 and pessagno newport 1972 together with the building of a new taxonomic system for mesozoic radiolarians

the eastern palmer land shear zone a new terrane accretion model for the mesozoic development of the antarctic peninsula a major ductile fault zone the eastern palmer land shear zone has been identified east of the spine of the southern antarctic peninsula this shear zone separates newly identified geological domains and indicates that during late jurassic terrane accretion and collision two and possibly three separate terranes collided resulting in the palmer land orogeny the orogeny is best developed in eastern palmer land and eastern ellsworth land there shallow marine sedimentary rocks of the latady formation and a metamorphic and igneous basement complex of possible lower palaeozoic to pre early jurassic age are thrust and folded this forms an arcuate east directed foreland fold and thrust belt up to 100 km wide and 750 km long parallel to the axis of the antarctic peninsula the newly identified antarctic peninsula domains include 1 a parautochthonous eastern domain that represents part of the margin of the gondwana continent comparable to the western province of new zealand the ross province superterrane of marie byrd land the eastern series of south central chile the pampa de agnia and tepuel rocks of north patagonia and the cordillera darwin rocks of tierra del fuego 2 a suspect central domain that represents an allochthonous microcontinental magmatic arc terrane comparable to the median tectonic zone of new zealand the amundsen province superterrane of marie byrd land and coastal cordillera of north chile and 3 a suspect western domain with strong similarities to the eastern province of new zealand western series of south central chile and chonos metamorphic complex of north patagonia that represents either a subduction accretion complex to the central domain or another separate crustal fragment although an allochthonous terrane hypothesis for the antarctic peninsula remains to be fully tested this has much in common with models for the new zealand and south american parts of the pacific margin of gondwana the identification of a potential allochthonous terrane continent collision zone allows us to define the edge of the gondwana continent in the antarctic peninsula sector of the supercontinent margin which has implications for mesozoic reconstructions of gondwana

crustal deformation of the marlborough fault zone in the south island of new zealand geodetic constraints over the interval 1982 1994 crustal deformation across the marlborough fault zone in the south island of new zealand has been investigated by resurveying with the global positioning system gps a triangulation and trilateration network across part of the zone the principal strain rates which mostly have errors between 5 and 10 vary systematically across the region the principal axis of horizontal contraction gradually swings from se nw southeast of the hope fault to almost east west in the west the component of velocity parallel to the strike of the faults can account for 95 of the relative motion between the australian and pacific plates this component exhibits little variation west of the alpine wairau fault and shows an almost linear variation from the wairau fault to the east coast the horizontal strain rate northwest of the wairau fault is a small east west uniaxial contraction 0 1 ppm yr 1 if it is assumed that the crustal blocks bounded by the major faults are primarily driven by basal shear tractions with stresses on the faults being relatively insignificant then the slip rates expected on the faults may be derived from the observed velocity variations across the fault zone these predicted slip rates are in good agreement with geologically observed slip rates the larger slip rates on the hope fault are related to the observation that the strain field extends southeast of the fault over a distance large compared with the spacing between the faults the agreement between predicted and geological slip rates lends support to the idea that the observed pattern of deformation reflects that in the lower lithosphere

aeromagnetic imaging of the dun mountain ophiolite belt in northern new zealand insight into the fine structure of a major sw pacific terrane suture a new aeromagnetic survey of the junction magnetic anomaly in northern new zealand reveals that it is associated with up to 10 subparallel lineaments the junction magnetic anomaly delineates the dun mountain ophiolite belt a remarkably linear though sigmoidally bent major boundary zone traceable through most of new zealand which separates terranes sutured onto the new zealand gondwana margin in late mesozoic time modelling of the lineaments in conjunction with a new review of structures along the dun mountain ophiolite belt throughout new zealand indicates that the dun mountain ophiolite belt in auckland consists of a number of imbricate slices most of which are likely to dip steeply to the east i e overturned away from the former trench and extend to considerable depth in the crust the source bodies for the central high amplitude magnetic lineaments are interpreted to be serpentinite shear or melange zones cutting a large lensoid body of ultramafic rocks similar to those occurring elsewhere along the length of the dun mountain ophiolite belt our data have revealed that a formerly postulated offset of the dun mountain ophiolite belt in the region instead resembles a duplex or thrust imbricate like bundling of shear zones these shear zones were probably initiated as accretion thrusts but complexities in their pattern indicate subsequent shearing including backfolding to an overturned attitude and possibly strike slip to produce the linear nature of the dun mountain ophiolite belt the outer lineaments mostly mark accretion thrusts in the adjacent terranes this study demonstrates that detailed aeromagnetic surveys can delineate the fine structure in ophiolite complexes and thereby give valuable insights into the effects of micro continental collision on an accretionary margin

precipitation banding in idealized baroclinic waves abstractmoist idealized baroclinic wave simulations show the development of precipitation bands from a zonally uniform initial midlatitude jet for a frictionless lower boundary and with no latent heat release or surface heat and moisture fluxes warm advection is strong and a bent back warm front forms although a narrow vertical velocity maximum forms within the area of synoptic scale ascent near the triple point only a wide warm frontal band forms as surface roughness length increases between simulations to that of an ocean then a land surface warm advection is reduced and the cold front becomes stronger relative to the warm front a separate narrow rainband forms along the cold front which is more intense and farther removed from the wide warm frontal band when roughness length is greater in the simulation with roughness length appropriate to the ocean after the narrow band decays the precipitation becomes oriented along the warm conveyor belt in the warm sector when latent heat release is in

climatology of banded precipitation over the contiguous united states abstracta climatology of banded precipitation features over the contiguous united states from 2003 to 2014 is constructed a band is defined as a precipitation feature with a major axis of 100 km or greater and a ratio of major axis length to minor axis length hereafter aspect ratio of 3 1 or greater by applying an automated feature based detection algorithm to composite radar imagery a database of 48 916 844 precipitation features is created of which 7 213 505 14 8 are bands this algorithm produces the first climatology of precipitation bands over the contiguous united states banded precipitation occurrence is broadly similar to total precipitation occurrence with a maximum of 175 h of banded precipitation annually over the ohio river valley in the warm season there is a strong diurnal signature associated with convective storm development for both the precipitation feature area and total area covered by precipitation but little diurnal signature in aspect ratio strong west east gradients

the mississippi valley convection minimum on summer afternoons observations and numerical simulations abstractanalysis of 15 years of composite radar images over the continental united states reveals a distinct minimum of deep convection occurrence over the interior lower mississippi valley on summer afternoons relative to surrounding areas to understand the mechanisms behind this convection signature quasi idealized numerical simulations with the weather research and forecasting wrf model are performed the simulations which broadly reproduce the valley convection minimum suggest that convective inhibition is maximized and low level ascent minimized over the flat valley terrain by contrast weaker inhibition and stronger mechanically forced ascent over the hills flanking the valley combine to initiate convection more readily although the orography of the region is unremarkable it has a stronger influence on the regional convection pattern than do variations in land use

banded convection caused by frontogenesis in a conditionally symmetrically and inertially unstable environment abstract several east west oriented bands of clouds and light rain formed on 20 july 2005 over eastern montana and the dakotas the cloud bands were spaced about 150 km apart and the most intense band was about 20 km wide and 300 km long featuring areas of maximum radar reflectivity factor of about 50 dbz the cloud bands formed poleward of an area of lower tropospheric frontogenesis where air of modest convective available potential energy was being lifted during initiation and maintenance of the bands mesoscale regions of dry symmetric and inertial instability were present in the region of the bands suggesting a possible mechanism for the banding interpretation of the extant instabilities in the region of the bands was sensitive to the methodology to assess the instability the release of these instabilities produced circulations with enough vertical motion to lift parcels to their lifting condensation level resulting in the observed cloud bands a high resolution numerical weather prediction m

delineation of a large ultramafic massif embedded within a major sw pacific suture using gravity methods abstract gravity studies have delineated the largest ultramafic massif in new zealand embedded within a buried major sw pacific crustal suture zone this suture records terrane collision onto the gondwana margin during the mesozoic and separates a forearc terrane from an outboard accretionary prism terrane it can be traced throughout the length of new zealand as the junction magnetic anomaly and contains the permian dun mountain ophiolite belt which in the south island of new zealand is characterized by a string of isolated ultramafic massifs in a sheared matrix of serpentinite and sediment our analysis reveals a steep gravity gradient at the suture boundary which is attributed to a newly recognised density contrast 0 1 mg m 3 between terranes of the forearc and the accretionary prism the massif itself is marked by the occurrence of a strong elongate residual gravity anomaly 120 g u extending 50 km along the suture and coincident with the junction magnetic anomaly it is modelled at its southern end as a dense 15 km wide source body extending to at least 6 km in depth in conjunction with detailed aeromagnetic data this modeling indicates the presence of a spindle shaped ultramafic massif analogous to but larger than similar bodies found within the dun mountain ophiolite belt elsewhere this fabric of sheared serpentinites enclosing ultramafic massifs therefore extends at least the length of new zealand and probably beyond in part it may result from accretion of asperities in the subducting plate but it is also due to disruption of larger ultramafic bodies during subsequent strike slip motion which caused the remarkable linearity of the dun mountain belt given the common occurrence of the plate tectonic processes involved it is likely that such structures can be found in other regions around the world using similar geophysical potential field methods

the role of small scale orographic features in the spatial distribution of precipitation radar images from the cevennes experiment which took place during the autumns of 1986 88 on the southeastern flank of the massif central in france reveal a characteristic and repetitive structure of the precipitation distribution in southerly mediterranean flows which are frequent there in autumn precipitation is often organized into narrow bands or plumes oriented south north the period 14 and 15 november 1986 has been selected as an example on which to perform numerical simulations and analyse the mechanism yielding this specific precipitation organization the numerical model correctly reproduces the bands especially at high horizontal resolution 1 km these rainfall bands are focused on the small scale topography oriented east west composed of a succession of ridges and penetrating valleys the bands are generated upstream of these ridges and enhanced on the lee side by convergence created by deflection around the obstacle and penetration of the flow into the valleys idealized simulations and sensitivity experiments have been carried out to verify these hypotheses these simulations suggest that small scale orography plays a decisive role in forcing the precipitation into bands while upstream moisture conditions mainly affect the precipitation intensity and its south north extent copyright 2002 royal meteorological society