origin and metamorphic history of an early cretaceous polybaric granulite terrain fiordland southwest new zealand regionally extensive two pyroxene granulites in fiordland southwest new zealand are products of metamorphism of a suite of anhydrous magmas which crystallized two pyroxenes the granulite protolith igneous charnockitic rock synkinematically intruded metasediment and other orthogneiss in an early cretaceous subduction related magmatic arc and during cooling experienced deformation induced recrystallization to form granoblastic gneiss the granulites occur side by side with coeval rocks of amphibolite facies mineral zoning and textural relationships in both granulites and amphibolite facies rocks provide evidence of two distinct periods of crystallization 1 an early high temperature comparatively low pressure event accompanying magmatic intrusion andalusite sillimanite facies series recorded locally in the country rock followed by 2 high pressure metamorphism under conditions of 650 700 c at 12 13 kbar garnet granulite locally overprinted earlier formed two pyroxene granulite during the latter event the pressure increase 6 kbar between the two events is attributed to crustal thickening by overthrusting and is equivalent to unloading of a 20 km thick slab over rocks already buried at mid crustal depths both events occurred over a 20 m y interval between the time of magmatic emplacement of the granulite protolith and uplift controlled final cooling of the terrain the phanerozoic granulites in fiordland share some petrologic similarities with precambrian granulite terrains suggesting that at least some aspects of the former may serve as a useful model for development of the latter

linear trends of zonally averaged thermosteric halosteric and total steric sea level for individual ocean basins and the world ocean 1955 1959 1994 1998 1 we present estimates of the linear trends of zonally averaged fields of thermosteric halosteric and steric sea level by pentads 1955 1959 1994 1998 for individual ocean basins and the world ocean the atlantic is characterized by density compensating linear trends in the thermosteric and halosteric components of steric sea level change northward of approximately 45 n the halosteric trend acts to increase steric sea level and the thermosteric trend acts to decrease sea level southward of 45 n these two terms are reversed in sign similar to the atlantic the indian ocean is characterized by density compensating trends at most latitudes a major exception being 28 s 38 s the pacific is different from the atlantic and indian oceans the two components act in concert to change sea level in the same way with the exception of the 34 n 45 n and 22 s 38 s regions

metamorphism and deformation of mafic and felsic rocks in a magma transfer zone stewart island new zealand in the mingled mafic felsic halfmoon pluton at the neck stewart island part of the median batholith of new zealand some hornblende gabbros and diorites retain magmatic structures whereas others show evidence of major changes in grain and inclusion shapes and still others are amphibolite facies granofelses with few or no igneous relicts these mafic to intermediate magmas crystallized in felsic magma relatively quickly with the result that most deformation occurred at subsolidus conditions it is suggested that mafic intermediate rocks with predominantly igneous microstructures spent less time in the magmatic system the metamorphism of the mafic rocks appears to be autometamorphic in the sense that elevated temperatures were maintained by magmatic heat during subsolidus cooling elevated temperatures were maintained because of repeated sheet injection and subconcordant dyke injection of hot basaltic and composite mafic felsic magmas into a dominantly transtensional km scale outboard migrating magmatic shear zone that operated semi continuously for between c 140 and c 130 ma complete cooling occurred only when the system evolved to transpressional and the locus of magmatism migrated inboard southward between c 130 and c 120 ma associated with solid state mylonitic deformation intermingled granitic rocks escaped metamorphism because they remained magmatic to lower temperatures and experienced shorter and lower temperature subsolidus cooling intervals however the felsic rocks underwent relatively high temperature solid state deformation as indicated by myrmekite replacing k feldspar and chess board subgrain patterns in quartz locally they developed felsic mylonites the felsic rocks were deformed in the solid state because of their high proportion of relatively weak minerals quartz and biotite whereas the mafic rocks mostly escaped subsolidus deformation except in local high strain zones of hornblende plagioclase schist because of their high proportion of relatively strong minerals hornblende and plagioclase we suggest that such contrasting microstructural features are diagnostic of long lived syntectonic magma transfer zones and contrast with the more typical complex batholith scale magma chambers of magmatic arcs

quantifying crustal thickness variations in evolving orogens correlation between arc basalt composition and moho depth a compilation of geochemical data from 50 active volcanoes where seismically defined moho depth measurements are available representing most volcanic arcs around the world indicates a relation exists between crustal thickness moho depth and the trace element composition of basalts the best correlation exists for maximum light heavy rare earth element ree ratios and we use maximum ce y r2 0 90 to show the exponential function with increasing depth to 50 km application to new zealand part of the eastern gondwanan margin through much of the phanerozoic shows that higher ce y ratios in arc basalts correspond to two periods of recognized crustal thickening plus an additional event at ca 240 ma which links new zealand to the gondwanide orogeny conversely low ce y ratios in basalts correlate with periods of recognized extension in eastern gondwana very high ce y ratios in ca 120 ma rocks imply an unusually thickened 50 km arc crust consistent with independent geological estimates of crustal thickness at that time the correlation shows that crustal thickness variations during orogenesis can be conservatively estimated to within 3 km

igneous garnet and amphibole fractionation in the roots of island arcs experimental constraints on andesitic liquids to evaluate the role of garnet and amphibole fractionation at conditions relevant for the crystallization of magmas in the roots of island arcs a series of experiments were performed on a synthetic andesite at conditions ranging from 0 8 to 1 2 gpa 800 1 000 c and variable h2o contents at water undersaturated conditions and fo2 established around qfm garnet has a wide stability field at 1 2 gpa garnet amphibole are the high temperature liquidus phases followed by plagioclase at lower temperature clinopyroxene reaches its maximal stability at h2o contents 9 wt at 950 c and is replaced by amphibole at lower temperature the slopes of the plagioclase in boundaries are moderately negative in text t text x text h 2 text o space at 0 8 gpa garnet is stable at magmatic h2o contents exceeding 8 wt and is replaced by spinel at decreasing dissolved h2o the liquids formed by crystallization evolve through continuous silica increase from andesite to dacite and rhyolite for the 1 2 gpa series but show substantial enrichment in feo mgo for the 0 8 gpa series related to the contrasting roles of garnet and amphibole in fractionating fe mg in derivative liquids our experiments indicate that the stability of igneous garnet increases with increasing dissolved h2o in silicate liquids and is thus likely to affect trace element compositions of h2o rich derivative arc volcanic rocks by fractionation garnet controlled trace element ratios cannot be used as a proxy for slab melting or dehydration melting in the deep arc garnet fractionation either in the deep crust via formation of garnet gabbros or in the upper mantle via formation of garnet pyroxenites remains an important alternative despite the rare occurrence of magmatic garnet in volcanic rocks

a decadal spiciness mode in the tropics analysis of a complex climate model suggests the existence of a mode of coupled ocean atmosphere variability in the tropical pacific with the following dynamics anomalous strong pacific trade winds accelerate the north equatorial current and countercurrent at 10 to 15 n in the central pacific thermocline this causes anomalous advection across mean gradients of temperature and salinity on isopycnal surfaces and generates cool fresh spiciness anomalies of the order of 0 3 k these are advected by the mean circulation via the western boundary region to the equatorial pacific in approximately five years at the equatorial outcrops of the isopycnals the cool fresh anomalies affect the surface heat budget and are hypothesized to initiate a relaxation of the trade winds that is reinforced by positive feedbacks with the slope of the thermocline and with air sea fluxes of heat and freshwater at 5 to 10 s the decrease of the trades generates by anomalous advection cool fresh spiciness anomalies that migrate to the equator in one to two years and provide a positive feedback at 10 to 15 n the decrease of the trades decelerates north equatorial current and countercurrent and causes warm salty anomalies on isopycnals that arrive at the equator five years later and close the cycle

thermal limitations on incorporation of wall rock into magma incorporation of solid wall rocks is an oft cited process in the evolution of magmas but this process is severely limited by the energy required to dissolve xenoliths disaggregation without melting has been proposed as an alternative process for incorporating xenoliths into magma because disaggregation avoids expending the energy required for melting analysis of these processes using enthalpy composition diagrams shows that both processes rapidly lead to high crystal contents in the hybrid magma for example incorporation of 25 granite at 400 c into basalt magma at 1125 c produces a hybrid magma at 1050 c with 50 crystals if the granite disaggregates without melting the crystal content is 65 70 once the crystal content reaches 50 the viscosity of the magma is too high to allow further magma movement or xenolith incorporation thus both processes are self limiting and probably restricted in natural systems to at most a few tens of percent incorporation of xenoliths

a simulation of thermohaline effects of a great salinity anomaly abstract model simulations of an idealistic great salinity anomaly gsa demonstrate that variability in the sea ice export from the arctic when concentrated to short pulses can have a large influence on the meridional heat transport and can lead to an altered overturning state one single freshwater disturbance resulting from excess ice export as in 1968 can disrupt the deep mixing process the critical condition for a large oceanic response is defined by the intensity duration and timing of the ice pulse in particular as it exits through the denmark strait a recovery from this event takes several years for advection and diffusion to remove the salinity anomaly concurrently the influence of the gsa propagates to the subtropics via the boundary currents and baroclinic adjustment as a result of this adjustment there are large up to 20 changes in the strength of the overturning cell and in the meridional heat transport in the subtropics and subpolar areas simulations show a temperature sali

magmatic crystallization isobaric cooling and decompression of the garnet bearing assemblages of the jijal sequence kohistan terrane western himalayas the jijal ultramafic mafic sequence is the lowermost exposed part of the kohistan terrane petrography and geothermobarometry show that garnet bearing assemblages of the jijal sequence consist of a mosaic of magmatic and metamorphic equilibria garnet bearing magmatic assemblages started their crystallization at a depth 50 km either at the base of a thickened arc type crust or within rising magmatic batches in the upper mantle quasi isobaric cooling of magmatic assemblages occurred in the high p high t granulite field without reaching the eclogite field subsequently these assemblages were partly retrograded under amphibolite to greenschist facies conditions this succession of equilibria attests to a switch from a high p quasi isobaric cooling regime to a major decompression followed by final cooling at the upper crustal level this p t evolution is best explained by a yet unrecognized tectonic event that consists of partial exhumation of the base of the kohistan terrane during its accretion to the asian plate final cooling and unloading in turn could be related to extension following the obduction of the kohistan terrane onto the indian plate

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

experimentally derived high pressure cumulates from hydrous arc magmas and consequences for the seismic velocity structure of lower arc crust 1 this contribution explores the consequences of experimentally derived ultramafic plutonic rocks for estimates of continental crust composition the formation of high pressure cumulates from primitive to evolved hydrous arc magmas was investigated in the range 0 8 1 5 gpa and 1350 800 c to provide constraints on solid assemblages that form the roots of island arc crust at pressures exceeding 0 8 gpa 25km 40 60 of ultramafic cumulates are produced to obtain andesite to dacite compositions that are typical for evolved island arc volcanic and plutonic rocks calculated cumulate densities are comparable or higher than upper mantle values while seismic velocities vp vary continuously between 7 3 and 8 km s resulting in a broad crust mantle transition the moho represents a plagioclase saturation boundary our results are consistent with seismic imaging from continental margins and island arcs revealing that beneath an active volcanic front a sharp geophysical moho signature is sometimes absent

granulite formation during continental extension in fiordland new zealand the formation of the high pressure high temperature rocks known as granulites has traditionally been attributed to metamorphism in the deeper parts of continental collision zones and magmatic arcs1 3 more recently greater consideration has been given to the possibility of granulite formation during continental rifting4 6 and in particular4 to whether granulites are forming today beneath the north american basin and range province here we report thermobarometric data and single zircon u pb ages for an analogous but much more deeply exhumed extensional terrain in fiord land new zealand7 8 where early cretaceous granulites underwent renewed granulite facies metamorphism at significantly shallower crustal levels following the extensional collapse of magmatically thickened continental crust our data show that granulite facies metamorphism can take place during continental extension and demonstrate that in western new zealand it was accompanied at higher structural levels by the emplacement of one or more metamorphic core complexes7 9 in keeping with the model postulated4 for the basin and range province

synconvergent ductile flow in variable strength continental crust numerical models with application to the western grenville orogen 1 we present results from numerical models for a convergent orogen with laterally variable lower crustal strength representing a simplified orogenic system in which a strong craton flanked by progressively weaker terranes collides with another continent with progressive convergence crustal thickening and thermal relaxation lower crust becomes decoupled from upper and middle crust forming a ductile orogenic infrastructure beneath a stronger superstructure collision with strong external crust results in uplift and expulsion of ductile nappes from the orogenic core creating allochthonous terranes overlying a lower crustal indentor the extent of transport and exhumation of lower crustal nappes over the indentor reflects the amount of convergence and the erosion rate the western grenville orogen displays across strike variations in age tectonic history and protolith association suggesting a systematic variation in precollision crustal strength the laurentian craton margin and accreted terranes were variably reworked at synorogenic depths of 25 35 km during the ottawan orogeny deformation propagated from younger monocyclic rocks in the southeast into older polycyclic rocks flanking the craton on the northwest a comparison between numerical model results and crustal scale cross sections from the georgian bay and montreal val d or transects shows close correspondence between crustal structure and model geometry this indicates that the models produce geologically realistic results and provides a context for interpreting the tectonic evolution of the western grenville orogen contrasts between the results of homogeneous channel flow models and the present ductile nappe models suggest that the effects of different styles of ductile flow can be distinguished in the geologic record

silicate liquid immiscibility within the crystal mush late stage magmatic microstructures in the skaergaard intrusion east greenland late stage microstructures developed during the last stages of solidification of the skaergaard intrusion comprise a wide array of reactive and non reactive intergrowths reactive microstructures ascribed to open system behaviour include serrated grain boundaries between pyroxene and plagioclase primocrysts fish hook pyroxenes and mafic symplectites they form by the addition of fe and ca and removal of alkalis and silica other microstructures include those formed by internally generated redox reactions between olivine fe ti oxides and pyroxene non reactive microstructures include closely spatially associated granophyric intergrowths and previously undescribed ilmenite rich intergrowths that are interpreted as a consequence of crystallization of separated conjugate immiscible liquids the open system reactive microstructures occur predominantly in the cumulates on the chamber floor appearing in lzb and disappearing to be replaced by a granophyre ilmenite rich intergrowth association in the upper zone they are not common in the marginal border series their distribution mirrors that of efficient expulsion of trapped liquid and can be attributed to the gravitationally driven loss of a si rich immiscible component from the interstitial liquid the loss of the si rich component causes the remaining fe rich liquid to react with the primocrysts bulk rock major element data are consistent with little or no preferential loss of the si rich liquid from the mush but the resolution of the available data is not sufficient to assess the effect of this relative movement on the liquid line of descent of the bulk magma the first appearance of the paired conjugate non reactive intergrowths in mz marginal border series points to the early onset of immiscibility in the bulk liquid

local and remote impacts of a tropical atlantic salinity anomaly the climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical atlantic are investigated in a coupled ocean atmosphere general circulation model locally the salinity increase leads to a rapid deepening and cooling of the surface mixed layer this induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current a remote atmospheric response to the tropical atlantic perturbation is detected in the north atlantic sector after ten years it has the form of a robust wave like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the amazonian basin meanwhile the salt anomaly is carried northward by the mean oceanic circulation it is traced up to the convection sites and then on its return path at depth towards lower latitudes consistent with the density increase deep convection is enhanced after the arrival of the salt anomaly and the atlantic meridional overturning circulation amoc intensifies about 20 years after the beginning of the perturbation the adjustment of the tropical atlantic to the amoc intensification then modifies its initial response to the freshwater forcing leading to a weaker cooling in the northern tropical atlantic than in the southern tropical atlantic a slight northward shift of the tropical atlantic precipitation pattern and an intensification of the north brazil current on the other hand no significant anomalous precipitations are found in the pacific the initial remote atmospheric response is also modulated by an nao like response to the amoc intensification

propagation of north pacific interdecadal subsurface temperature anomalies in an ocean gcm propagation of subsurface north pacic inter decadal variations is investigated with an ocean general cir culation model forced by observed sea surface temperature anomalies subsurface temperature anomalies subducted in the central subtropical north pacic take a more westward pathway than a passive temperature tracer and reach the western boundary to the north of the bifurcation latitude this prevents them from extending into the equator on the boundary between the subtropical and the subarctic gyres on the other hand the upper 500 m heat content anomaly is found to propagate eastward as high vertical modes of rossby waves advectedbythemean eastward cur rent this notion is supported by a sign reversal in temper ature anomaly underneath

generation mechanism of spiciness anomalies an ogcm analysis in the north atlantic subtropical gyre oceanic teleconnections between the low and midlatitudes are a key mechanism to understanding the climate variability spiciness anomalies density compensated anomalies have been shown to transport temperature and salinity signals when propagating along current streamlines in the subtropical gyres of the atlantic and pacific oceans the generation mechanism of spiciness anomalies in the north atlantic subtropical gyre is investigated using an analytical model based on the late winter subduction of salinity and temperatureanomalies along isopycnal surfaces the keystone ofthis approachisthe change ofthe coordinates frame from isobaric to isopycnic surfaces suited for subduction problems the isopycnal nature of spiciness anomalies and the use of a linear density equation allows for the analytical model to depend only upon surface temperature and salinity anomalies the mean thermocline currents and the surface density ratio this model clarifies and above all quantifies the mechanism by which surface temperature and salinity anomalies are modulated by density ratios to produce fully different isopycnal temperature and salinity anomalies

formation of salinity maximum water and its contribution to the overturning circulation in the north atlantic as revealed by a global general circulation model 1 the formation of salinity maximum water in the north atlantic is investigated using a simulated passive tracer and its adjoint the results reveal that most salinity maximum water in the north atlantic comes from the northwestern part of the subtropical gyre and direct contribution from the evaporation precipitation maximum region via the surface ekman current is minor water originating from the evaporation precipitation maximum region has to recirculate in the subtropical gyre before entering the sea surface salinity maximum region from the northwest once subducted some portion 10 of the salinity maximum water enters the equatorial region in the shallow subtropical cell but most 70 of it appears to turn northward to join the north atlantic deep water the latter pathway involves a three dimensional circulation when the warm fresh surface water flows northward along the western boundary it turns eastward in the northern subtropical gyre as a result of the large excess of evaporation over precipitation this water gradually gains its salinity on the route until it reaches the sea surface salinity maximum region in the central subtropical gyre from there the salinity maximum water is subducted and flows back to the western boundary in the depth range of the thermocline with its high salinity nature a major portion of this water penetrates into the subpolar region and directly contributes to the deep thermohaline circulation

reconstructing the subsurface ocean decadal variability using surface nudging in a perfect model framework initialising the ocean internal variability for decadal predictability studies is a new area of research and a variety of ad hoc methods are currently proposed in this study we explore how nudging with sea surface temperature sst and salinity sss can reconstruct the three dimensional variability of the ocean in a perfect model framework this approach builds on the hypothesis that oceanic processes themselves will transport the surface information into the ocean interior as seen in ocean only simulations five nudged simulations are designed to reconstruct a 150 years target simulation defined as a portion of a long control simulation the nudged simulations differ by the variables restored to sst or sst sss and by the area where the nudging is applied the strength of the heat flux feedback is diagnosed from observations and the restoring coefficients for sss use the same time scale we observed that this choice prevents spurious convection at high latitudes and near sea ice border when nudging both sst and sss in the tropics nudging the sst is enough to reconstruct the tropical atmosphere circulation and the associated dynamical and thermodynamical impacts on the underlying ocean in the tropical pacific ocean the profiles for temperature show a significant correlation from the surface down to 2 000 m due to dynamical adjustment of the isopycnals at mid to high latitudes sss nudging is required to reconstruct both the temperature and the salinity below the seasonal thermocline this is particularly true in the north atlantic where adding sss nudging enables to reconstruct the deep convection regions of the target by initiating a previously documented 20 year cycle of the model the sst sss nudging is also able to reproduce most of the amoc variations a key source of decadal predictability reconstruction at depth does not significantly improve with amount of time spent nudging and the efficiency of the surface nudging rather depends on the period events considered the joint sst sss nudging applied everywhere is the most efficient approach it ensures that the right water masses are formed at the right surface density the subsequent circulation subduction and deep convection further transporting them at depth the results of this study underline the potential key role of sss for decadal predictability and further make the case for sustained large scale observations of this field

a lagrangian numerical investigation of the origins and fates of the salinity maximum water in the atlantic the origins and fates of the atlantic salinity maximum water smw formed through excess evaporation in the tropics and subtropics of both hemispheres are studied using monthly mean outputs of a numerical simulation of the world ocean climatological circulation after defining formation domains from the surface salinity field and the vertical stratification a lagrangian technique is used to estimate the formation rates and main pathways in each hemisphere and the role of this water in the framework of the warm water return flow of the meridional overturning cell formation rates around 9 and 11 sv are found in the southern and northern hemispheres respectively while the export of the southern smw from its formation area is realized by the western boundary currents that of the northern smw mainly results from interior subduction equatorward of the formation regions a fraction of each smw variety is entrained in the subtropical cells that connect the subtropics to the equatorial region poleward of them both varieties are seen to feed the regions of subtropical mode water stmw formation around 35 of latitude in both hemispheres the bulk of the transport associated with each variety eventually turns northward this amounts to 6 sv of southern smw gathered in the north brazil undercurrent nbuc and 10 sv of northern smw found in the gulf stream at 35 n of which 8 sv have gone through the caribbean sea of the 13 4 sv northward transport of the meridional overturning cell estimated by the model at 47 n more than 50 6 9 sv is found to have transited through at least one of the smw regions this gives an indication of the likely important role of smw formation in the observed northward salinity increase of the upper atlantic ocean

foundering of lower island arc crust as an explanation for the origin of the continental moho a long standing theory for the genesis of continental crust is that it is formed in subduction zones however the observed seismic properties of lower crust and upper mantle in oceanic island arcs differ significantly from those in the continental crust accordingly significant modifications of lower arc crust must occur if continental crust is indeed formed from island arcs here we investigate how the seismic characteristics of arc crust are transformed into those of the continental crust by calculating the density and seismic structure of two exposed sections of island arc kohistan and talkeetna the kohistan crustal section is negatively buoyant with respect to the underlying depleted upper mantle at depths exceeding 40 kilometres and is characterized by a steady increase in seismic velocity similar to that observed in active arcs in contrast the lower talkeetna crust is density sorted preserving only relicts about ten to a hundred metres thick of rock with density exceeding that of the underlying mantle specifically the foundering of the lower talkeetna crust resulted in the replacement of dense mafic and ultramafic cumulates by residual upper mantle producing a sharp seismic discontinuity at depths of around 38 to 42 kilometres characteristic of the continental mohorovicic discontinuity the moho dynamic calculations indicate that foundering is an episodic process that occurs in most arcs with a periodicity of half a million to five million years moreover because foundering will continue after arc magmatism ceases this process ultimately results in the formation of the continental moho

tectonic inheritance and continental rift architecture numerical and analogue models of the east african rift system 1 the western branch of the east african rift is composed of an arcuate succession of elongate asymmetric basins which differ in terms of interaction geometry fault architecture and kinematics and patterns of uplift subsidence and erosion sedimentation the basins are located within proterozoic mobile belts at the edge of the strong tanzanian craton surface geology suggests that the geometry of these weak zones is an important parameter in controlling rift development and architecture although other processes have been proposed in this study we use lithosphere scale numerical models and crustal scale analogue experiments to shed light on the relations between preexisting structures and rift architecture results illustrate that on a regional scale rift localization within the mobile belts at the curved craton s western border results in an arcuate rift system which implies that under a constant extensional stress field part of the western branch experienced orthogonal extension and part oblique extension largest depocenters are predicted to form mostly orthogonal to the extension direction and smaller depocenters will form along the oblique parts of the rift the varying extension direction along the rift zone furthermore results in lengthwise varying rift asymmetry segmentation characteristics and border fault architecture trend length and kinematics analogue models predict that discrete upper crustal fabrics may influence the location of accommodation zones and control the architecture of extension related faults at a local scale models support that fabric reactivation is responsible for the oblique slip kinematics on faults and for the development of z shaped or arcuate normal faults typically documented in nature

north atlantic subtropical underwater and its year to year variability in annual subduction rate during the argo period abstractsubtropical underwater stuw and its year to year variability in annual subduction rate are investigated using recently available argo data in the north atlantic for the period of observation 2002 14 the mean annual subduction rate of the stuw is 7 3 1 2 sv 1 sv 106 m3 s 1 within the density range between 25 0 and 26 0 kg m 3 once subducted the stuw spreads in the subtropical gyre as a vertical salinity maximum in the mean the spatial changes in temperature and salinity of the stuw tend to compensate each other and the density of the water mass remains rather stable near 25 5 kg m 3 in the southwestern part of the subtropical gyre the annual subduction rate of the stuw varies from year to year and most of this variability is due to lateral induction which in turn is directly linked to the variability of the winter mixed layer depth through modulation of surface buoyancy wind anomalies associated with the north atlantic oscillation are primarily responsible for this variability

structural criteria for identifying granitic cumulates abstractcumulates are igneous rocks that reflect relative concentration of crystals and or loss of melt and that therefore did not crystallize entirely from a magma of their current whole rock composition however this definition does not help to identify cumulates and so the problem is to determine whether the current whole rock composition reflects cumulate processes which is where structural criteria can be useful identification of cumulates in granitoids can be difficult especially in the absence of major whole rock compositional differences between cumulate and host structural and structural mineralogical criteria diagnostic of or at least consistent with granitic cumulates include 1 locally high concentrations of particular minerals relative to concentrations in the bulk of the intrusion 2 abundant euhedral crystals in contact at least with regard to cores that touched before any overgrowths and consequent molding of minerals about each other occurred 3 abundant antecrysts or mantle

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

observational evidence of winter spice injection abstract temperature and salinity t s profiles from the global array of argo floats support the existence of spice formation regions in the subtropics of each ocean basin where large destabilizing vertical salinity gradients coincide with weak stratification in winter in these characteristic regions convective boundary layer mixing generates a strongly density compensated sdc layer at the base of the well mixed layer the degree of density compensation of the t s gradients of an upper ocean water column is quantified using a bulk vertical turner angle tub between the surface and upper pycnocline the winter generation of the sdc layer in spice formation zones is clearly seen in argo data as a large amplitude seasonal cycle of tub in regions of the subtropical oceans characterized by high mean tub in formation regions argo floats provide ample evidence of large abrupt spice injection t s increase on subducted isopycnals due to vertical mixing associated with the winter increase in tub a simp

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

observation of spiciness interannual variability in the pacific pycnocline monthly gridded fields predominantly based on global argo in situ temperature and salinity data are used to analyze the density compensated anomaly of salinity spiciness anomaly in the pycnocline of the subtropical and tropical pacific ocean between 2004 and 2011 interannual variability in the formation propagation and fate of spiciness anomalies are investigated the spiciness anomalies propagate on the isopycnal surface sq 25 5 along the subtropical tropical pycnocline advected by the mean currents they reach the pacific western tropics in about 5 6 years in the southern hemisphere and about 7 8 years in the northern hemisphere their amplitude strongly diminishes along the way and only very weak spiciness anomalies seem to reach the equator in the western tropics a complex eof analysis of interannual salinity anomalies on sq 25 5 highlights two dominant modes of variability at interannual scale i the former shows a variability of 5 7 years predominant in the northern hemisphere and ii the latter displays an interannual variability of 2 to 3 years more marked in the southern hemisphere the significant correlation of this second mode with enso index suggests that spiciness formation in the southeastern pacific sep is affected by enso tropical interannual variability a diagnosis of the mechanisms governing the interannual generation of spiciness in the sep region leads the authors to suggest that the spiciness interannual variability in the sub surface is linked to the equatorward migration of the isopycnal outcrop line sq 25 5 into the area of maximum salinity quantitative analysis based on turner angle reveals the dominance of the spiciness injection mechanism occurring through convective mixing at the base of mixed layer

earthquakes in the garhwal himalaya of the central seismic gap a study of historical and present seismicity and their implications to the seismotectonics the historical and the present seismicity catalogues of the garhwal himalaya have been studied for their spatio temporal variations and their implications on the seismotectonics of the region the micro seismicity fractal dimensions dc and frequency magnitude distribution b value coupled with the available literature on geology geomorphology and geophysics have been used to derive the seismotectonics and stress level changes in the region the seismic cross sections for the relocated micro seismicity focal mechanisms and the swath profiles for the presence of physiographic transition 2 pt2 at the foothill of the higher himalaya indicate the constant presence of the mid crustal ramp mcr in the detachment plane and its active seismogenic nature the comparison of this scenario suggests the constant presence of seismogenically active mcr structure throughout the central seismic gap the seismic cross sections further reveal that the sensu stricto main central thrust munsiari thrust is also a site of generation of the micro seismicity in few segments due to its reactivation by thrusting along the mcr the high fractal dimension value dc 1 47 suggests the heterogeneous nature of the region owing to the presence of local faults and transverse tectonics the high stress accumulation in the garhwal himalaya with low b value b 0 70 suggests the high probability of occurrence of a larger or greater earthquake in the near future further the study also reveals that the 2011 chamoli earthquake of m 5 0 preceded by a quiescence period of nearly a year shows different stress levels before and after its occurrence which is well constrained with the increased moderate earthquake activity around the chamoli region this increased seismic activity and stress conditions in the chamoli region suggest the high possibility of the occurrence of major earthquakes hence the study recommend for a detailed seismic hazard evaluation of the region

crustal thickness variations in the central andes we estimated the crustal thickness along an east west transect across the andes at lat 20 s and along a north south transect along the eastern edge of the altiplano from data recorded on two arrays of portable broadband seismic stations banjo and seda waveforms of deep regional events in the downgoing nazca slab and teleseismic earthquakes were processed to isolate the p to s converted phases from the moho in order to compute the crustal thickness we found crustal thickness variations of nearly 40 km across the andes maximum crustal thicknesses of 70 74 km under the western cordillera and the eastern cordillera thin to 32 38 km 200 km east of the andes in the chaco plain the central altiplano at 20 s has crustal thicknesses of 60 to 65 km the crust also appears to thicken from north 16 s 55 60 km to south 20 s 70 74 km along the eastern cordillera the subandean zone crust has intermediate thicknesses of 43 to 47 km crustal thickness predictions for the andes based on airy type isostatic behavior show remarkable overall correlation with observed crustal thickness in the regions of high elevation in contrast at the boundary between the eastern cordillera and the subandean zone and in the chaco plain the crust is thinner than predicted suggesting that the crust in these regions is supported in part by the flexural rigidity of a strong lithosphere with additional constraints we conclude that the observation of airy type isostasy is consistent with thickening associated with compressional shortening of a weak lithosphere squeezed between the stronger lithosphere of the subducting nazca plate and the cratonic lithosphere of the brazilian craton

kinematics of the pacific equatorial undercurrent an eulerian and lagrangian approach from gcm results abstract three dimensional monthly velocity fields from an ocean general circulation model are used to study the annual mean mass balance of the pacific equatorial undercurrent euc eulerian diagnostics are used to evaluate the various meridional vertical and zonal mass fluxes related to the euc there are several distinct regimes along the equator showing clear asymmetries between the western and eastern parts of the basin and between the northern and southern edges of the euc meridional fluxes are decomposed into pure ekman divergence and geostrophic convergence and it is shown that the asymmetries are mainly related to the spatial structure of the ekman divergence and thus to that of the trade winds lagrangian calculations are used to evaluate accurately the mass transfers between various sections of the euc and between the euc domain and the tropics the authors show that geostrophic convergence only ventilates the upper layers of the euc and that the euc really is a tongue of water flowing

granulite facies thermal aureoles and metastable amphibolite facies assemblages adjacent to the western fiordland orthogneiss in southwest fiordland new zealand in southwest new zealand a suite of felsic diorite intrusions known as the western fiordland orthogneiss wfo were emplaced into the mid to deep crust and partially recrystallized to high p 12 kbar granulite facies assemblages this study focuses on the southern most pluton within the wfo suite malaspina pluton between doubtful and dusky sounds new mapping shows intrusive contacts between the malaspina pluton and adjacent palaeozoic metasedimentary country rocks with a thermal aureole 200 1000 m wide adjacent to the malaspina pluton in the surrounding rocks thermobarometry on assemblages in the aureole indicates that the malaspina pluton intruded the adjacent amphibolite facies rocks while they were at depths of 10 14 kbar similar p t conditions are recorded in high p granulite facies assemblages developed locally throughout the malaspina pluton palaeozoic rocks more than 200 1000 m from the malaspina pluton retain medium p mid amphibolite facies assemblages despite having been subjected to pressures of 10 14 kbar for 5 myr these observations contradict previous interpretations of the wfo malaspina pluton as the lower plate of a metamorphic core complex everywhere separated from the metasedimentary rocks by a regional scale extensional shear zone doubtful sound shear zone slow reaction kinetics lack of available h2o lack of widespread penetrative deformation and cooling of the malaspina pluton thermal anomaly within c 3 4 myr likely prevented recrystallization of mid amphibolite facies assemblages outside the thermal aureole if not for the evidence within the thermal aureole there would be little to suggest that gneissic rocks which underlie several 100 km2 of southwest new zealand had experienced metamorphic pressures of 10 14 kbar similar high p metamorphic events may therefore be more common than presently recognized

sm nd and rb sr isotopic and geochemical systematics in phanerozoic granulites from fiordland southwest new zealand sm nd and rb sr isotopic analyses are reported for granulite facies orthogneisses from fiordland southwest new zealand whole rock samples define a rb sr isochron age of 120 15 ma and an initial 87sr 86sr ratio of 0 70391 4 nd values at 120 ma show a relatively wide range of from 0 4 to 2 7 indicating decoupling of sr nd isotope systems associated ultramafic rocks have initial 87sr 86sr ratios of from 0 70380 to 0 70430 and nd values of from 0 1 to 3 0 the different initial ratios suggest that the various intrusions although contemporaneous were not derived through fractionation of a single parent magma a metasedimentary enclave incorporated during emplacement of the granulitic rocks preserves a proterozoic isotopic signature with a measured nd 0 value of 10 2 87sr 86sr ratio of 0 73679 and a tnd provenance age of 1490 ma the rb sr whole rock age of the granulites is the same as obtained from recent u pb zircon dating mattinson et al 1986 and is interpreted as the time of magmatic emplacement and essentially contemporaneous granulite facies metamorphism rb sr and sm nd analyses of mineral systems indicate that the terrain had cooled below 300 c by 100 ma providing further evidence that high grade metamorphism was of exceptionally short duration

exsolution of rutile or apatite precipitates surrounding ruptured inclusions in garnet from uht and uhp rocks this study describes halos of rutile apatite needles and or plates centred on quartz inferred former coesite inclusions or multiphase inclusions in garnet both types of central inclusions are surrounded by cracks the multiphase inclusions contain mica or carbonate minerals and are interpreted to represent decrepitated fluid inclusions examples from two localities are examined i ultrahigh temperature uht metapelitic gneisses from the southern end of the central maine terrane in northeastern connecticut usa rutile only and ii ultrahigh pressure uhp diamondiferous saidenbachite from the saxonian erzgebirge rutile and apatite the needles of apatite or rutile are typically oriented in three directions within garnet chemical zonation in garnet shows clear ti or p depletion halos corresponding spatially with the rutile or apatite inclusion halos the radii of the inclusion halos when measured from the centre of the central inclusions are about two to several times the radii of the central inclusions we propose that the inclusion halos of rutile apatite formed by exsolution out of ti bearing and or p bearing garnet during retrogression because of its strength garnet can internally maintain higher pressures than the surrounding matrix nonetheless if the inclusion pressure is significantly greater than the confining lithostatic pressure then deformation of the host garnet can occur during exhumation high internal pressures relative to the matrix can result from retention of fluid entrapment pressure or a phase change with a large positive volume increase e g coesite quartz the differential stress imposed on the garnet adjacent to the central inclusion preceding and during mechanical failure would create dislocations and other crystalline defects which are ideal sites for exsolved precipitates to nucleate and grow the strain induced exsolution hypothesis is consistent with observations i the radii of the halos are roughly consistent with the pressure vessel model or the multi anvil model for an inclusion which predict that differential stress will drop off sharply away from the boundary of the central inclusion into the host garnet ii the rutile or apatite inclusions formed in ti or p bearing garnet adjacent to ruptured central inclusions rutile or apatite are rare or absent elsewhere in garnet even in areas of high ti or high p concentration in addition rutile is absent in areas surrounding the central inclusion that were depleted in ti prior to rupturing e g garnet rims that lost ti during retrogression thus both elevated ti p concentrations and proximity to inclusions which deformed the host garnet were necessary for halo formation iii reintegrated garnet ti or p contents in and adjacent to the halos obtained using wide beam electron probe microanalysis are consistent with local derivation of the ti or p necessary to form rutile and apatite from garnet elevated ti p concentrations in aluminous garnet are mostly found in uht hp uhp granulite and mantle environments consequently the phenomena described will most likely occur in such settings

systematics of zircon crystallisation in the cretaceous separation point suite new zealand using u pb isotopes ree and ti geothermometry plutonic zircons from the cretaceous separation point suite sps were analysed by la icpms for u pb isotope ratios and trace element concentrations pooled 206pb 238u ages range from 112 to 124 ma cathodoluminescence imaging reveals minor inheritence and textural evidence of repeated dissolution and re precipitation of zircon core and rim spot analyses however document zircon growth during extended periods of time 2 myr protracted crystallisation histories for simple plutonic systems are inconsistent with generalised thermal constraints which predict cooling below the solidus within 1 myr consequently we conclude that the sps granitoids sampled in this study were not emplaced rapidly but incrementally over extended time periods zircon th u and zr hf ratios are positively correlated with crystallisation temperatures consistent with crystallisation from evolving melts however highly variable trace element concentrations along with temperature reversals are indicative of complex crystallisation histories involving continuous fractional crystallisation repeatedly punctuated by hotter more mafic magma recharge normalised abundances of the redox sensitive elements eu and ce in zircon vary systematically with degrees of whole rock differentiation pointing to evolutionary trends in magmatic oxidation states coupled with feldspar crystallisation

isotopic ages from the nelson region of south island new zealand crustal structure and definition of the median tectonic zone abstract plutonic rocks in the rotoroa complex and drumduan terrane of south island new zealand yield zircon u pb dates of 156 and 142 ma respectively that are interpreted as crystallization ages hornblende and biotite 40 ar 39 ar dates of 140 130 ma from the rotoroa represent either emplacement ages cooling ages or a metamorphic resetting event these two units crop out between the brook street terrane and the separation point batholith and lack any clear affinity with tectonostratigraphic terranes of the new zealand western or eastern provinces the rotoroa complex and drumduan terrane are interpreted as part of a series of dismembered mesozoic volcanic plutonic arc complexes that are sandwiched between terranes of the western and eastern provinces occupying a structural position here referred to as the median tectonic zone mtz correlative units in fiordland on the opposite side of the alpine fault include the mackay intrusives darran complex largs terrane lochburn formation and the halfway peak gabbro farther south on stewart island the anglern complex and paterson group are part of the same structural belt the mtz is an extension of the original concept of the median tectonic line put forth by landis and coombs 1967 dismemberment and juxtaposition of arc magmatic assemblages in the mtz with western and eastern province terranes is related to large scale transcurrent faulting in the early cretaceous its essential features as a regional tectonostratigraphic terrane were established by 117 ma as indicated by stitching of the rotoroa complex to the takaka terrane western province by the separation point batholith 117 114 ma the echinus granite yields a 310 ma u pb zircon crystallization age that suggests the granite and associated gneisses are part of the western province which may constrain the position of the western margin of the mtz near nelson city

spiciness anomalies in the upper south indian ocean abstractthis study investigates an isopycnal temperature salinity t s or spiciness anomaly in the upper south indian ocean for the period from 2004 to 2015 using observations and reanalyses spic

poleward propagation of spiciness anomalies in the north atlantic ocean 1 recent modelling results suggest that subsurface salinity anomalies propagating from the tropics can reach and precondition the deep water formation regions thus modulating the thc variability the forcing and propagative aspects of this mechanism are presented in the north atlantic ocean over 1948 2002 using an ogcm density compensated salinity anomalies of 0 1 up to 0 35 psu along s 26 kg m 3 are generated in the salinity maximum region at interannual to decadal frequency the relation between subsurface conditions and late winter sea surface salinity variability supports the subduction mechanism they circulate over isopycnals ranging from 25 6s to 26 2s at current speed between 150 m and 250 m depth toward cape hatteras via the gulf of mexico on a typical 6 year transit although mixing along the pathway reduces the amplitude of salinity anomalies by about 66 they largely determine the subsurface spiciness of the gulf stream up to 30 n upstream of the outcrop region citation laurian a a lazar g reverdin k rodgers and p terray 2006 poleward propagation of spiciness anomalies in the north atlantic ocean geophys res lett 33 l13603

late winter generation of spiciness on subducted isopycnals the origins of density compensating anomalies of temperature and salinity spice are investigated using a model forced with the most realistic surface products available over the 40 years 1958 97 in this hindcast the largest interannual spiciness anomalies are found in the pacific ocean near the isopycnal s 0 5 25 5 where deviations as great as 1 28c and 0 6 psu are generated equatorward of winter outcropping in the eastern subtropics in both hemispheres these source regions are characterized by very unstable salinity gradients and low mean density stratification in winter two related signatures of winter mixing in the southeast pacific sep are density that is well mixed deeper than either temperature or salinity and subsurface density ratios that approach 1 all ocean basins in the model are shown to have regions with these characteristics and signatures however the resultant spiciness signals are focused on different isopycnals ranging from s 0 5 25 0 in the northeast pacific to s 0 5 26 5 in the south indian ocean a detailed examination of the sep finds that large positive anomalies are generated by diapycnal mixing across subducted isopycnals e g s 0 5 25 5 whereas negative anomalies are the result of a steady isopycnal advection moderated by vertical advection and heave there is considerable interannual variability in the strength of anomalies and in the density on which they occur historical observations are consistent with the model results but are insufficient to verify all aspects of the hindcast including the processes of anomaly generation in the sep it was not possible to relate isopycnal anomaly genesis to local surface forcing of any kind a complex scenario involving basinwide circulation of both the ocean and atmosphere especially of surface water through the subtropical evaporation zones is put forward to explain the decadal time scale evident in sep salinity anomalies on s 0 5 25 5 pacific anomalies generated on s 0 5 25 5 can be traced along mean geostrophic streamlines to the western boundary where decadal salinity variations at 78s are about 2 times as large order 60 1 psu as at 128n although there may be more variance on shallower isopycnals in the north at least portions of the s 0 5 25 5 signals appear to continue along the boundary to a convergence at the equator suggesting that the most robust sources of pacific spiciness variance coincide with equatorial exchange pathways

generation of low frequency spiciness variability in the thermocline abstract the generation of variance by anomalous advection of a passive tracer in the thermocline is investigated using the example of density compensated temperature and salinity anomalies or spiciness a coupled markov model is developed in which wind stress curl forces the large scale baroclinic ocean pressure that in turn controls the anomalous geostrophic advection of spiciness the double integration of white noise atmospheric forcing by this markov model results in a frequency spectrum of large scale spiciness proportional to 4 so that spiciness variability is concentrated at low frequencies an eddy permitting regional model hindcast of the northeast pacific 1950 2007 confirms that time series of large scale spiciness variability are exceptionally smooth with frequency spectra 4 for frequencies greater than 0 2 cpy at shorter spatial scales wavelengths less than 500 km the spiciness frequency spectrum is whitened by mesoscale eddies but this eddy forced variability can be fi

dubious case for slab melting in the northern volcanic zone of the andes it was first suggested by r w kay that adakites may represent melts of subducted slab since then the term adakite has become synonymous with slab melts based on their unusual geochemical signature this contribution using the northern volcanic zone of the andes as an example aims 1 to expose the weakness in simply associating a geochemical signature with a genetic mechanism and 2 to underline the importance of using several integrated lines of evidence in assessing the viability of slab melting we conclude that although slab melting probably occurs in some arcs regional geochemical trends in the northern volcanic zone and their relationship to the subduction zone architecture are not indicative of slab melting and can be accounted for by normal arc magmatic processes acting on wedge derived basaltic magmas

linear trends in salinity for the world ocean 1955 1998 1 quality controlled oceanographic profile salinity measurements from the world ocean database 2001 wod01 were used to calculate linear trends of zonally averaged salinity anomalies for running five year periods from 1955 1959 through 1994 1998 for the world ocean and the atlantic pacific and indian ocean basins from the surface to 3000 meters depth each basin exhibits large scale coherent trends most of the pacific is freshening with the exception of the subtropical south pacific the atlantic exhibits a deep freshening in the subpolar gyre and a shallower more intense increase in salinity in the tropics and subtropics the indian ocean is becoming more saline at all latitudes in the upper 150 meter layer with a subsurface freshening between 40 s and the equator in the 250 1000 meter layer there is freshening in both the weddell and ross seas