variations in magmatic processes along the east greenland volcanic margin summary seismic velocities and the associated thicknesses of rifted and igneous crust provide key constraints on the rifting history the differentiation between non volcanic and volcanic rifted margins the driving force of magmatism at volcanic margins that is active or passive upwelling and the temperature anomaly in the lithosphere this paper presents two new wide angle seismic transects of the east greenland margin and combines the velocity models with a compilation of 30 wide angle seismic velocity models from several publications along the entire east greenland margin compiled maps show the depth to basement depth to moho crustal thickness and thickness of high velocity lower crust hvlc with velocities above 7 0 km s 1 first we present two new wide angle seismic transects which contribute to the compilation at the northeast greenland margin and over the oceanic crust between shannon island and the greenland fracture zone velocity models produced by ray tracing result in total traveltime rms misfits of 100 120 milliseconds and 2 values of 3 7 and 2 3 for the northern and southern profiles with respect to the data quality and structural complexity 2 d gravity modelling is used to verify the structural and lithologic constraints the northernmost profile awi 20030200 reveals a magma starved break up and a rapidly thinning oceanic crust until magnetic anomaly c21 47 1 ma the southern seismic transect awi 20030300 exhibits a positive velocity anomaly associated with the shannon high and a basin of up to 15 km depth beneath flood basalts between shannon island and the continent ocean boundary break up is associated with minor crustal thickening and a rapidly decreasing thickness of oceanic crust out to anomaly c21 the continental region is proposed to be only sparsely penetrated by volcanism and not underplated by magmatic material at all compared to the vast amount of magmatism further south break up is proposed to have occurred at the seaward boundaries of the continent ocean transition zones at between 50 and 54 ma propagating from north to south based on a joint analysis incorporating transects from the kejser franz joseph fjord and godthab gulf secondly the variation of the hvlc along the east greenland margin from 60 to 77 n and from transects of its conjugate margin shows inverted emplacement of prominent landward and seaward hvlc thickness portions from north to south in a distribution chart the differences in the hvlc distribution are attributed to one or more of the following three models in the first model it is inferred that a transfer zone detachment acts as a barrier to northward magma flow in the second model underplating results in thicker and highly intruded lower crust with several small scale feeder dykes that locally increase the lower crustal velocities in the third model a second magmatic event associated with the separation of the jan mayen microcontinent is considered lithospheric scale inhomogeneities might be responsible for the heterogeneous melt generation the inversion of the hvlc distribution in continental and oceanic domains and differences in its velocities

evidence for thin oceanic crust on the extinct aegir ridge norwegian basin ne atlantic derived from satellite gravity inversion 1 satellite gravity inversion incorporating a lithosphere thermal gravity correction has been used to map crustal thickness and lithosphere thinning factor for the ne atlantic predicted oceanic crustal thicknesses in the norwegian basin are between 4 and 7 km on the extinct aegir ridge increasing to 9 14 km at the margins consistent with volcanic margin continental breakup at the end of the paleocene the observation from gravity inversion and seismic refraction studies of thin oceanic crust produced by the aegir ridge in the oligocene may have implications for the temporal evolution of asthenosphere temperature under the ne atlantic during the tertiary thin oligocene oceanic crust may imply cool normal asthenosphere temperatures during the oligocene in contrast to elevated asthenosphere temperatures in the paleocene and miocene recent as indicated by the formation of volcanic margins and iceland respectively

the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

microgranitoid enclave swarms in granitic plutons central sierra nevada california abstract microgranitoid enclaves are common in granitic plutons worldwide occurring individually and in homogeneous or heterogeneous swarms three plutons in the central sierra nevada batholith contain swarms with mostly heterogeneous suites of enclaves in the intermediate composition range and occur in a number of two dimensional shapes specifically as dikes small rafts lenses pipe vortices and large massive shapes swarms are characterized by various features including the nature of their boundary with the host their planar or non planar character internal geometry density of enclave packing presence or absence of schlieren and crystal aggregates and axial ratios and degree of preferred alignment of enclaves we propose that heterogeneous enclave swarms form by one or some combination of the following mechanisms 1 velocity gradient sorting parallel or normal to the flow 2 gravitational sorting or 3 break up of heterogeneous dikes common sites where enclave swarms form include pluton margins or internal viscosity walls within fractures and near the pluton roof

insights into the ecology of epibenthic calcareous foraminifera from a colonization study at 4000 m station m in the ne pacific ocean abstract benthic foraminifera are an abundant and important component of modern and ancient deep sea ecosystems and these single celled organisms generate a fossil record that facilitates the assessment of paleoceanographic changes through time despite recent advances in taxonomic and ecological information about deep sea foraminifera many basic questions remain requiring a better understanding of ecological tolerances morphologic plasticity and distribution of deep sea foraminiferal species this study focuses on the phylogenetics morphology and colonization dynamics of deep sea foraminifera at abyssal station m in the eastern pacific ocean after 368 days at 4000 m on the pacific ocean seafloor 546 foraminifera 80 of which were calcareous species occupied elevated substrate experiments genetic analyses of the most abundant calcareous foraminiferal taxon indicate that this trochospiral species is a morphological variant of cibicidoides wuellerstorfi referred to as c wuellerstorfi var lobatulus although pyrgo and other milioline foraminifera are commonly found within sediments two morphological variants of pyrgo colonized elevated substrates at the station m study site many pyrgo spp and c wuellerstorfi var lobatulus were covered in an organic cyst perhaps as a feeding structure these results suggest that these calcareous foraminifera are able to flourish in deep sea settings where hard substrates are available and may be more widely distributed and diverse in lower bathyal and upper abyssal habitats when elevated substrates are present

pervasive granitoid magma transfer through the lower middle crust during non coaxial compressional deformation granitic magmas migrated through early proterozoic middle lower crust at mt hay central australia via a diverse network of narrow structurally controlled channelways during a period of progressive w sw directed thrusting d1a d1d they utilized existing folds boudins and shear zones or created new channels by magmatic fracture either parallel to layering or rarely in irregular arrays the magmas rose obliquely parallel to the plunging 50 60 regional elongation direction which was defined by coaxial folds boudin necks and a strong mineral elongation lineation megacrystic charnockitic magmas migrated through metre scale conduits during d1a d1b but leucosomes were generally restricted to smaller centimetre scale structures that existed throughout the entire deformation history thus d1a d1b leucosomes were potential feeders of in situ partial melts to the adjacent larger conduits of charnockite magma thereby providing a pervasive interconnected network that allowed efficient migration of all magma types during the early stages of thrusting the upper middle crust of the anmatjira reynolds range area contains abundant megacrystic granitoid sheets that are of similar age and geochemistry to those at mt hay they are considered to have formed as syntectonic intrusions emplaced during w sw directed thrusting as at mt hay suggesting that granitic magmas formed near the base of the continental crust passed through the mid lower crustal level 25 30 km exposed at mt hay and accumulated in batholithic proportions at shallower crustal levels 12 20 km such as the anmatjira reynolds range area the observations imply that granitoid magmas in the deep crust are capable of pervasive migration through the crust during major compressive noncoaxial shear deformation localization of magmas by sequentially developed narrow compressive structures suggests that dilatancy followed successive foliation forming events a situation that can occur during steady state deformation if the effective confining pressures are low which would be a result of high and possibly variable rates of magma influx the inferred rapid melt segregation and migration during deformation suggest that large chambers do not form until magma reaches neutral buoyancy in the middle to upper continental crust

phase equilibrium constraints on the viscosity of silicic magmas 1 volcanic plutonic comparison by using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at 104 5 pa s irrespective of their temperature and level of emplacement magmas crystallizing as granitic plutons are not water poor and thus not more viscous than their extrusive equivalents instead comparison between pre eruption magma viscosities of extrusive silicic intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous given the typical strain rates in silicic magma chambers magma rheological behavior is expected to be dominantly newtonian bubbles having a minor rheological influence at depth although exceptions can exist thus whether a silicic intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors but not on the rheology of the magma itself however preemptive viscosities of extrusive magmas rarely exceed 106 pa s which suggests that crystal melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes the narrow range of viscosities displayed by silicic intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas considerations of the relationships between magma crystallinities bulk sio2 and preemptive melt h2o contents show that the higher the melt h2o content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted an empirical correlation is proposed that enables us to estimate preemptive melt h2o contents of erupted magmas by knowing their crystallinity and bulk sio2

crustal structure across the more margin mid norway from wide angle seismic and gravity data the more margin in the ne atlantic represents a dominantly passive margin with an unusual abrupt transition from alpine morphology onshore to a deep sedimentary basin offshore in order to study this transition in detail three ocean bottom seismometer profiles with deep seismic reflection and refraction data were acquired in 2009 two dip profiles which were extended by land stations and one tie profile parallel to the strike of the more trondelag fault complex the modeling of the wide angle seismic data was performed with a combined inversion and forward modeling approach and validated with a 3d density model modeling of the geophysical data indicates the presence of a 12 15 km thick accumulation of sedimentary rocks in the more basin the modeling of the strike profile located closer to land shows a decrease in crustal velocity from north to south near the coast we observe an intra crustal reflector under the trondelag platform but not under the slorebotn sub basin furthermore two lower crustal high velocity bodies are modeled one located near the more marginal high and one beneath the slorebotn sub basin while the outer lower crustal body is modeled with a density allowing an interpretation as magmatic underplating the inner body has a density close to mantle density which might suggest an origin as an eclogized body formed by metamorphosis of lower crustal gabbro during the caledonian orogeny the difference in velocity and extent of the lower crustal bodies seems to be controlled by the jan mayen lineament suggesting that the lineament represents a pre caledonian structural feature in the basement

depositional features and stratigraphic sections in granitic plutons implications for the emplacement and crystallization of granitic magma abstract many granitic plutons contain sheet like masses of dioritic to gabbroic rocks or swarms of mafic to intermediate enclaves which represent the input of higher temperature more mafic magma during crystallization of the granitic plutons small scale structures associated with these bodies e g load cast and compaction features silicic pipes extending from granitic layers into adjacent gabbroic sheets indicate that the sheets and enclave swarms were deposited on a floor of the magma chamber on granitic crystal mush and beneath crystal poor magma while the mafic magma was incompletely crystallized these structures indicate way up typically toward the interior of the intrusions and appear to indicate that packages of mafic sheets and enclave concentrations in these plutons are a record of sequential deposition hence these plutons preserve a stratigraphic history of events involved in the construction filling replenishment and crystallization of the magma chamber the distinctive features of these depositional portions of plutons allow them to be distinguished from sheeted intrusions which usually preserve mutual intrusive contacts and dike sill relations of different magma types the considerable thickness of material that can be interpreted as depositional and the evidence for replenishment suggest that magma chamber volumes at any one time were probably much less than the final size of the pluton thus magma chambers may be constructed much more slowly than presently envisaged the present steep attitudes of these structures in many plutons may have developed gradually as the floor of the chamber along with the underlying solidified granite and country rock sank during continuing episodes of magma chamber replenishment these internal magmatic structures support recent suggestions that the room problem for granites could be largely accommodated by downward movement of country rock beneath the magma chamber

internal structure and emplacement of the papoose flat pluton an integrated structural petrographic and magnetic susceptibility study the papoose flat pluton of eastern california is commonly cited in the geologic literature as a classic example of a forcibly emplaced pluton although the relative importance attributed to magmatic versus tectonic processes in controlling the structural evolution of the pluton has been controversial reexamination of this late cretaceous 83 ma pluton using a combination of new structural petrographic microstructural and anisotropy of magnetic susceptibility ams data on the pluton wall rock system has shown that the pluton is an inclined and internally zoned tabular structure assembled by forcible intrusion of successive pulses of magma at a crustal depth of 12 15 km initial pluton formation involved magma ascent in a vertical west northwest striking feeder dike which was arrested at a stratigraphically controlled mechanical discontinuity in the overlying cambrian metasedimentary rocks leading to formation of a southwest dipping sill subsequent sill inflation accompanied by horizontal infilling from the feeder dike at the base of the sill resulted in deformation and vertical translation of previously emplaced magma pulses and local raising of the sill roof facilitated by thermal weakening as the wall rock temperatures progressively rose during emplacement of successive magma pulses cooling from the roof of the pluton downward resulted in cessation of vertical inflation on the west side of the pluton and promoted lateral expansion toward the northeast and floor depression below the eastern part of the pluton we have been unable to document any regional scale structures e g of equivalence to similar age synplutonic strike slip shear zones in the sierra nevada batholith to the west that may have controlled emplacement of the papoose flat pluton however this fact does not preclude the likelihood that the country rocks were subjected to a regional deviatoric stress field at this time indeed tectonic overpressuring was probably essential for producing sufficiently high magma pressures for laccolith formation at this midcrustal level simple thermal modeling using microstructural and thermobarometric data indicates that the total duration of emplacement of the pluton did not exceed 30 000 yr this rapid emplacement rate may explain why the pluton appears to be anorogenic even though it was emplaced during a period of regional scale deformation

regional distribution of volcanism within the north atlantic igneous province an overview of the distribution of volcanic facies units was compiled over the north atlantic region the new maps establish the pattern of volcanism associated with breakup and the initiation of seafloor spreading over the main part of the north atlantic igneous province naip the maps include new analysis of the faroe shetlands region that allows for a consistent volcanic facies map to be constructed over the entire eastern margin of the north atlantic for the first time a key result is that the various conjugate margin segments show a number of asymmetric patterns that are interpreted to result in part from pre existing crustal and lithospheric structures the compilation further shows that while the lateral extent of volcanism extends equally far to the south of the iceland hot spot as it does to the north the volume of material emplaced to the south is nearly double of that to the north this suggests that a possible southward deflection of the iceland mantle plume is a long lived phenomenon originating during or shortly after impact of the plume

break up and seafloor spreading domains in the ne atlantic an updated magnetic anomaly grid of the ne atlantic and an improved database of magnetic anomaly and fracture zone identifications allow the kinematic history of this region to be revisited at break up time continental rupture occurred parallel to the mesozoic rift axes in the south but obliquely to the previous rifting trend in the north probably due to the proximity of the iceland plume at 57 54 ma the new oceanic lithosphere age grid is based on 30 isochrons c from c24n old 53 93 ma to c1n old 0 78 ma and documents ridge reorganizations in the se lofoten basin the jan mayen fracture zone region in iceland and offshore faroe islands updated continent ocean boundaries including the jan mayen microcontinent and detailed kinematics of the eocene present greenland eurasia relative motions are included in this model variations in the subduction regime in the ne pacific could have caused the sudden northwards motion of greenland and subsequent eurekan deformation these events caused seafloor spreading changes in the neighbouring labrador sea and a decrease in spreading rates in the ne atlantic boundaries between major oceanic crustal domains were formed when the european plate changed its absolute motion direction probably caused by successive adjustments along its southern boundary supplementary material figures showing the long wavelength of the nag tec magnetic anomaly grid detailed magnetic anomalies and isochrons and a table documenting aeromagnetic surveys for nag tec magnetic compilation are available at https doi org 10 6084 m9 figshare c 3661925

an upper mantle s wave velocity model for northern europe from love and rayleigh group velocities summary a model of upper mantle s wave velocity and transverse anisotropy beneath northwestern europe is presented based on regional surface wave observations group velocities for both love and rayleigh surface waves are measured on waveform data from international and regional data archives including temporary deployments and then inverted for group velocity maps using a method accounting for fresnel zone sensitivity the group velocity variations are larger than in global reference maps and we are able to resolve unprecedented details we then apply a linear inversion scheme to invert for local 1 d shear wave velocity profiles which are consequently assembled to a 3 d model by choosing conservative regularization parameters in the 2 d inversion we ensure the smoothness of the group velocity maps and hence of the resulting 3 d shear wave speed model to account for the different tectonic regimes in the study region and investigate the sensitivity of the 1 d inversions to inaccuracies in crustal parameters we analyse inversions with different reference models of increasing complexity pure 1 d 3 d crust 1 d mantle and pure 3 d we find that all inverted models are very consistent at depths below 70 km at shallower depths the constraints put by the reference models primarily moho depth which we do not invert for remain the main cause for uncertainty in our inversion the final 3 d model shows large variations in s wave velocity of up to 12 per cent we image an intriguing low velocity anomaly in the depth range 70 150 km that extends from the iceland plume beneath the north atlantic and in a more than 400 km wide channel under southern scandinavia beneath southern norway the negative perturbations are around 10 per cent with respect to ak135 and a shallowing of the anomaly is indicated which could be related to the sustained uplift of southern scandinavia in neogene times furthermore our upper mantle model reveals good alignment to ancient plate boundaries and first order crustal fronts around the triple junction of the baltica avalonia laurentia collision in the north sea

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

effect of thermal contrasts on gravity modeling at passive margins results from the western barents sea the western barents sea passive margin is a key locality to demonstrate the effect of the thermal structure of the lithosphere on forward gravity modeling this margin developed by shear motion between the eurasian and greenland plates during the early tertiary and it is a significant border zone between young hot oceanic lithosphere and cooler continental lithosphere we construct two dimensional gravity models of 125 km thick lithosphere based on expansion of mantle rocks determined from thermal modeling the approach has a substantial impact over traditional shallow gravity models here demonstrated on a previously published model on the basis of a 140 mgal free air anomaly the old model proposes an anomalous high density oceanic crust emplaced in a leaky transform adjacent to the continent during early margin development however the lithospheric models predict a homogeneous oceanic crust while preserving regional isostasy at base lithosphere from continent to ocean two further tests agree with this conclusion a map of bouguer corrected ers 1 satellite data reveals no residual anomalies originating from the oceanic crust at the margin admittance analysis shows a strong oceanic lithosphere and the high coherence between bathymetry and free air gravity discounts a significant subsurface load the high gravity anomalies at the margin are thus an edge effect enhanced by sedimentation onto the strong oceanic lithosphere and shaped by the effect of the lithospheric thermal field other results of this work include a new continent ocean boundary map and two crustal transects across the margin

structure of the jan mayen microcontinent and implications for its evolution an extensive seismic survey using ocean bottom seismographs obs was performed in the area across the jan mayen basin north atlantic from the jan mayen ridge to the iceland plateau the jan mayen ridge and surrounding area are considered to be a fragment of a continent which was separated from greenland just prior to magnetic anomaly 6 this study presents the crustal structure of the jan mayen microcontinent and the ocean continent transition to the west of the jan mayen ridge the crustal structures from the centre of the jan mayen ridge to the jan mayen basin are characterized by a deep sedimentary basin a thin basaltic layer within the sedimentary section and extreme thinning of the continental crust towards the iceland plateau the obs data indicate that a continental upper crust v p 5 8 6 1 km s 1 and lower crust v p 6 7 6 8 km s 1 underlie the deep sedimentary basin the thickness of the continental lower crust varies significantly from 12 km beneath the jan mayen ridge to almost zero thickness beneath the northwestern part of the jan mayen basin an ocean continent transition zone is found at the western edge of the jan mayen basin within the 10 km wide transition zone crustal velocities increase towards the iceland plateau and approach the velocities of the oceanic crust obtained at the iceland plateau that is 3 8 5 1 km s 1 oceanic layer 2a 5 9 6 5 km s 1 oceanic layer 2b and 6 8 7 3 km s 1 oceanic layer 3 the crustal model indicates very thin oceanic crust 5 km immediately oceanwards of the ocean continent transition zone beneath the iceland plateau the oceanic crust is thicker 9 km than the typical thickness of normal oceanic crust this might imply that the oceanic crust at the iceland plateau has been generated by asthenospheric material slightly hotter than normal from the crustal structure obtained by the present study it is proposed that the western part of the jan mayen ridge may be referred to as a non volcanic continental margin generated by a long duration of rifting even if the asthenospheric material upwelling along the margin were hotter than normal only small amounts of magmatic intrusions and extrusions would have been generated because of significant conductive cooling under the long duration of rifting

magma host interactions during differentiation and emplacement of a shallow level zoned granitic pluton tarcouate pluton morocco implications for magma emplacement the tarcouate pluton anti atlas morocco is an inversely zoned laccolith emplaced 583 ma ago into low grade metasediments with the following succession leucocratic granites biotite granodiorites monzodiorites hornblende granodiorites monzodiorites and monzodiorites syn plutonic dykes these rocks form two distinct chemically coherent units 1 a main unit consists of layered 57 sio2 59 wt and homogeneous 63 sio2 67 hornblende granodiorites biotite granodiorites 67 sio2 72 and aplites 70 sio2 76 all these rocks are metaluminous to peraluminous and display fractionated hree depleted patterns la ybn 14 61 ybn 0 7 6 8 initial 87sr 86sr ratios 0 7072 to 0 7080 increase whereas end t values 1 7 to 2 8 decrease from the hornblende to the biotite granodiorites monzodiorites occur as mafic microgranular enclaves or syn plutonic dykes 2 a subordinate unit consists of leucocratic distinctly peraluminous muscovite bearing granites 72 sio2 75 occurring at the northern edge of the pluton and as dykes in the surrounding schists towards the top of the pluton these rocks are free of monzodioritic enclaves they display less fractionated patterns with higher hree contents la ybn 2 19 ybn 11 18 a distinct end t value 11 8 and a 87sr 86sr initial ratio 0 7480 within those of the surrounding schists 0 7393 0 7819 magma host interactions are closely related to differentiation and occurred at different levels but mainly before emplacement field relationships and petrogenetic modelling show that the bt granodiorites formed at levels deeper than the level of emplacement by fractional crystallisation 0 65 f 0 85 with limited amounts of contamination by crustal material 5 wt the hbl granodiorites differentiated at the level of emplacement by fractional crystallisation leading to residual melts f 0 55 slightly contaminated by the country rocks 2 wt and represented by aplite dykes the leucocratic granites are likely to derive by partial melting of lithologies similar in composition to the country metasediments these data preclude any significant material transfer process for the emplacement of the tarcouate pluton but rather suggest assembly of successive pulses of variably differentiated crystal poor magmas these shallow level granitic plutons can be considered as an end member of magma emplacement with minimum interactions with the country rocks

a review of the ne atlantic conjugate margins based on seismic refraction data the ne atlantic region evolved through several rift episodes leading to break up in the eocene that was associated with voluminous magmatism along the conjugate margins of east greenland and nw europe existing seismic refraction data provide good constraints on the overall tectonic development of the margins despite data gaps at the ne greenland shear margin and the southern jan mayen microcontinent the maximum thickness of the initial oceanic crust is 40 km at the greenland iceland faroe ridge but decreases with increasing distance to the iceland plume high velocity lower crust interpreted as magmatic underplating or sill intrusions is observed along most margins but disappears north of the east greenland ridge and the lofoten margin with the exception of the vestbakken volcanic province at the sw barents sea margin south of the narrow lofoten margin the european side is characterized by wide margins the opposite trend is seen in greenland with a wide margin in the ne and narrow margins elsewhere the thin crust beneath the basins is generally underlain by rocks with velocities of 7 km s 1 interpreted as serpentinized mantle in the porcupine and southern rockall basins while off norway alternative interpretations such as eclogite bodies and underplating are also discussed

benthic foraminiferal turnover across the cretaceous paleogene boundary at agost southeastern spain paleoenvironmental inferences abstract we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where 5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them

development of igneous layering during growth of pluton the tarcouate laccolith morocco abstract we discuss the significance of igneous layering with respect to pluton growth processes the case study is the tarcouate laccolith morocco whose core consists of modally layered hornblende granodiorites with high amount of monzodioritic enclaves contrasting with peripheral non layered biotite granodiorites with low amount of enclaves rhythmic layering with modal grading cross stratification and trough layering is associated with monzodioritic layers and wraps around mafic enclaves its steep dips 45 result from tilting that occurred above solidus conditions as indicated by sub vertical and synmagmatic granite aplite and monzodiorite dykes cutting across the layering the systematic association of igneous layering with mafic enclaves in calc alkaline plutons suggests that layering originates from recurrent injection of mafic magma viscosity calculations suggest that the physicochemical properties of magma alone cannot account for the presence of layering in the central hornblende granodiorite and its coeval absence in the peripheral biotite granodiorite of the tarcouate laccolith intermittent pulses of hot mafic magma into crystallizing granodiorite likely produced thermal perturbations able to trigger local convection formation of mafic enclaves and development of igneous layering through protracted crystallization

lithospheric control on asthenospheric flow from the iceland plume 3 d density modeling of the jan mayen east greenland region ne atlantic

interface scattering versus body scattering in subbasalt imaging and application of prestack wave equation datuming the presence of high velocity highly heterogeneous layers such as basalt have a detrimental effect on imaging below those structures internal characteristics of the basalt itself can also degrade the subbasalt image quality in many cases the boundary surfaces of a basalt sequence are not smooth but contain some roughness at a scale similar to the seismic wavelength interface scattering resulting from interface roughness can be a serious problem in this paper body and interface scattering problems are addressed through acoustic finite difference modeling interface scattering seems to have the most detrimental effect on imaging at depth a wave equation prestack datuming procedure is applied to synthetic acoustic data to remove the effects of rough interfaces this computational process transforms seismic data to a new datum plane in the subsurface eliminating propagation effects between the surface and the new datum plane the technique leads to a much improved image of below the basalt with the g

middle late miocene benthic foraminifera in a western equatorial indian ocean depth transect paleoceanographic implications abstract middle through upper miocene 17 5 ma benthic foraminiferal faunas 63 m from a depth transect in the western equatorial indian ocean dsdp site 237 odp sites 707 709 and 710 water depth 1500 3800 m underwent significant faunal changes at 14 13 ma and 11 8 ma these faunal changes are not easily interpreted because of the complex factors controlling benthic foraminiferal distribution and abundance at 14 13 ma the relative abundance of high productivity taxa bolivina bulimina melonis and uvigerina species although highly variable generally increased at the two shallower sites 237 and 707 as did the percentage of epistominella exigua indicative of seasonal productivity and nuttallides umbonifera indicative of corrosive bottom waters at the two deeper sites 709 and 710 the latter species had a peak in abundance at the deepest site 710 between 11 and 9 ma benthic foraminiferal accumulation rates bfars increased strongly at the shallower sites starting at 11 ma peaking between 9 and 8 ma and increased weakly at the deeper two sites starting at 11 ma elongate cylindrical taxa decreased in abundance between 12 and 11 ma at all sites the abundance of planktic foraminiferal fragments was as expected overall higher at the deeper sites with some high values after 12 13 ma at the shallower sites the faunal changes suggest that overall the food supply to the sea floor increased but also became more pulsed or seasonal peaking at 9 8 ma while deep and intermediate waters may have become more ventilated the first phase of faunal change 14 13 ma was coeval with the global increase in benthic foraminiferal oxygen isotope values worldwide turnover in benthic foraminiferal faunas and possibly increased production of antarctic bottom water aabw and northern component water ncw the overall faunal turnover may reflect the composite faunal response to increased food input resulting from heightened productivity and increased bottom water ventilation associated with a combination of monsoonal intensification global cooling and changes in ocean circulation but there is no unequivocal evidence for the presence of tethyan outflow water tow over the studied time and depth range in contrast to earlier publications

multistage emplacement of the mount givens pluton central sierra nevada batholith california the ca 90 ma mount givens pluton is one of the largest granodioritic to granitic intrusions in the sierra nevada batholith of california emplacement of the pluton occurred during a critical time in the tectonic evolution of the central sierra nevada magmatic arc marked by a transition from regional contraction to dextral transcurrent shear a model for the emplacement of the intrusion is developed based on detailed mapping of the pluton and its wall rocks and characterization of its internal structure by measurements of the anisotropy of magnetic susceptibility ams at 351 stations one of the key results of the study is documentation of a strong correlation between petrologic and structural fabrics in the pluton and determination that these fabrics reflect internal magma chamber dynamics more than regional tectonic strain the 80 km long 15 30 km wide pluton crystallized from a multiphase three segment magma chamber marked by a bulbous northern lobe and linear central and southern segments the pluton is interpreted to be tabular in shape with a thickness of 5 km most of the space for the pluton was created by piecemeal block downdrop of the magma chamber floor along three principal fracture sets the most important of which were steeply dipping northwest trending fractures formed parallel to the structural grain of the arc and vertical north trending extension fractures formed in response to a component of arc parallel dextral shear some of these fractures acted as magma conduits episodically filling the pluton as source rocks became depleted in melt an initial voluminous intrusive event stage 1 quickly filled the southern chamber with granodiorite magma but only partially filled the northern and central chambers stage 2 magmatism involved underplating of megacrystic granite in the northern chamber and lateral flow of a large batch of this magma from the northern to the central chamber the latter delineated by a 20 km long belt of megacrystic granite containing subhorizontal magnetic lineations that connects the pluton segments floor downdrop eventually ceased to be an effective space making process in the northern lobe and renewed magmatism stage 3 led to expansion and doming of the chamber as the northern lobe cooled a ring fault ruptured within the viscoelastic stage 1 2 carapace allowing ring dike intrusion stage 4 and sinking of a central flap of consolidated material the temporal and spatial variations in emplacement mechanisms demonstrated for the mount givens pluton i e fracture generation floor downdrop underplating inflation ring diking suggest that end member models e g fracture vs diapir are oversimplifications of the pluton assembly process

moho and basement depth in the ne atlantic ocean based on seismic refraction data and receiver functions seismic refraction data and results from receiver functions were used to compile the depth to the basement and moho in the ne atlantic ocean for interpolation between the unevenly spaced data points the kriging technique was used free air gravity data were used as constraints in the kriging process for the basement that way structures with little or no seismic coverage are still presented on the basement map in particular the basins off east greenland the rift basins off nw europe are mapped as a continuous zone with basement depths of between 5 and 15 km maximum basement depths off ne greenland are 8 km but these are probably underestimated plate reconstructions for chron c24 c 54 ma suggest that the poorly known ammassalik basin off se greenland may correlate with the northern termination of the hatton basin at the conjugate margin the most prominent feature on the moho map is the greenland iceland faroe ridge with moho depths 28 km crustal thickness is compiled from the moho and basement depths the oceanic crust displays an increased thickness close to the volcanic margins affected by the iceland plume

benthic foraminifera and environmental turnover across the cretaceous paleogene boundary at blake nose odp hole 1049c northwestern atlantic sediments recovered at lower bathyal odp site 1049 on blake nose northwestern atlantic offer an opportunity to study environmental changes at the cretaceous paleogene k p boundary relatively close to the chicxulub impact structure on the yucatan peninsula mexico in hole 1049c the boundary is located at the base of a 9 cm thick layer with abundant spherules considered to be impact ejecta uppermost maastrichtian oozes below and lowermost danian pelagic oozes above the spherulebed contain well preserved bathyal benthic foraminifera the spherule bed itself in contrast contains a mixture of shallow neritic and deeper bathyal species and specimens vary strongly in preservation this assemblage was probably formed by reworking and down slope transport triggered by the k p impact across the spherule bed i e the k p boundary only f7 of benthic foraminiferal species became extinct similar to the low extinction rates of benthic foraminifera worldwide quantitative analysis of benthic foraminiferal assemblages and morphogroups in the 63 am size fraction indicates a relatively eutrophic stable environment during the latest maastrichtian interrupted by a sudden decrease in the food supply to the benthos at the k p boundary and a decrease in diversity of the faunas followed by a stepped recovery during the earliest danian the recovery was probably linked to the gradual recovery of surface dwelling primary producers d 2004 elsevier b v all rights reserved

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

origin of sierra nevadan granite evidence from small scale composite dikes composite dikes at hell hole meadow in the central sierra nevada contain hybrids created by small scale mixing of andesitic and rhyolitic magmas early rhyolitic injections had partially solidified when subsequent andesitic magmas arrived and mixed with small increments of remnant rhyolitic magma in major element chemistry the hybrid rocks define linear mgo variation diagrams that closely resemble those for the half dome mt givens and eagle peak granodiorites the patterns suggest that mixing of mafic and felsic magmas has been important in the evolution of these plutons

emplacement kinematics of a granite diapir the chindamora batholith zimbabwe the geometric features of a large 50 40 km granitic batholith and its surrounding greenstone belt envelope are described the batholith is made up of several intrusive components and an intrusion sequence based on contact relations and xenoliths has been established the igneous rocks show a local foliation s fabric and preferred orientation of minerals the intensity of this fabric accords with the finite strain determined from xenolith shape analysis when the strain variations are analysed in detail it appears that the batholith was built up by a succession of magmatic pulses each of which led to a stretching of the previously consolidated igneous material so called balloon tectonics evidence is presented that xenolith deformation commences only when the surrounding igneous material has crystallized and a method is suggested whereby the position of the surface separating crystal supported phase plastic behaviour from melt supported phase liquid behaviour at different stages in the plutonic history can be determined ductile shear zones are present and their geometry accords well with the shape changes necessary to allow the outer parts of the pluton to stretch

new gravity data in the arctic ocean comparison of airborne and ers gravity new gravity fields from airborne gravimetry and from ers 1 and 2 satellite altimetry cover extensive portions of the arctic ocean these two data sets may constitute as much as 60 of the data contributions to the arctic gravity project compilation here we evaluate the accuracy and resolution of these data and quantify their impact on the compilation both gravity determinations compare favorably with geological survey of canada surface measurements in the beaufort sea airborne 1 86 2 09 mgal rms ers 2 64 3 11 mgal rms comparisons between the airborne and ers data over the chukchi borderlands reveal a 4 38 mgal rms difference over the smoother region of the field and 7 36 mgal rms over the rugose field generated by the shallow ridges and deep troughs coherency between the two data sets in the chukchi region implies a resolution of 19 km comparison with science ice expedition submarine measurements over chukchi plateau suggests that the ers field resolves even shorter wavelength signal than the airborne data whereas in the beaufort sea the airborne data showed better coherence to ground truth data long wavelength differences exist between the two data sets expressed as a 2 3 mgal offset over the chukchi region this study highlights the respective strengths of the two data sets the ers gravity field has the advantage of ubiquitous coverage of the ocean south of 81 5 degreesn a denser sampling of the gravity field and a recovery of signal down to similar to 15 km the airborne data cover a significant portion of the polar hole in the satellite coverage have lower measurement noise and recover somewhat higher anomaly amplitudes in the 25 100 km wavelength range

gravity modeling of the ocean continent transition along the south atlantic margins 1 gravity magnetic and seismic data have been used to examine changes in crustal structure of conjugate portions of the south atlantic volcanic margins south of the walvis ridge rio grande rise hot spot tracks we have constructed 18 seismically constrained crustal scale gravity models of the ocean continent transition 12 across the african margin and 6 across the south american margin we attribute changes in character of the gravity anomalies to variations in crustal thickness sedimentation and magmatic underplating to investigate variations in the lower crust and upper mantle we have removed the relatively well constrained contributions to the gravity field from shallow sources the resulting residual anomalies delineate distinct crustal domains associated with crustal thinning and regions of underplating that correspond well with those independently identified from limited seismic refraction data near the hot spot tracks we find underplated crust to be symmetrically distributed with a horizontal extent of 240 km for each margin further south however the underplated region is asymmetric with significantly more beneath the african than the corresponding south american margin residual gravity anomalies indicate that the width of underplated crust decreases from 240 km to 150 km at 33 s on the african side and to 100 km at 38 s on the south american side the wider underplated region on the african side suggests an asymmetric rifting mechanism in which greater melts accumulate beneath an upper plate margin our results are consistent with recently proposed asymmetric rifting models that involve strain softening of a coupled cold frictional upper lithosphere at low rifting velocities such models also predict greater symmetry for areas with more heat such as those associated with the hot spot

sequential nesting of magmas in marble southwestern grenville province quebec from fracture propagation to diapirism abstract in the southwestern grenville province quebec 1090 1070 my old k rich alkaline equidimensional plutons such as the kensington pluton occur in marble rich country rock but coeval dykes bearing lower crustal xenoliths are found only in a quartzofeldspathic gneiss complex the sequential nesting of magmas the various episodes of skarn formation and the progressively more mafic character of the intruding magmas of the kensington pluton are interpreted in terms of magma ascent through a series of propagating fractures cessation of upward fracturing and pooling of magma in marble rich ductile crust diapirism radial shortening of wall rock and in situ pluton expansion this suite provides evidence that at deep crustal levels the country rock rheology influences the mode of magma ascent and emplacement and that diapirism is a possible mechanism of magma transport through rocks behaving rheologically by a power law model

crustal structure and evolution of the outer more margin ne atlantic abstract five regional ocean bottom seismic profiles from the northwestern part of the more margin ne atlantic have been modeled with regard to crustal structure and the interpretations have been supported by the use of multi channel seismic and potential field data the chi squared values uncertainty for the studied profiles are generally in the range 1 3 and the uncertainty in the moho depth is estimated to 1 km the continent ocean transition is found to be relatively sharp 10 40 km wide expressing a change in physical properties corresponding to felsic continental crust along the landward part of the marginal high vp 6 2 6 5 km s and thick mafic oceanic crust further northwestwards the early eocene breakup was associated with excessive magmatism and the models document direct continuity between this magmatism and a lower crustal high velocity layer in the more basin vp 7 1 7 3 km s suggesting a genetic link the jan mayen lineament is observed across the entire study area as northeastward termination of the lower crustal body as well as structuring in the top of the crystalline basement and the moho we present a speculative model involving lower crustal bodies of eclogites vp 8 km s inferred in the easternmost part of the more basin linking the jan mayen lineament to the post caledonian nordfjord sogn detachment

integrated geophysical modelling of a lateral transition zone in the lithospheric mantle under norway and sweden summary the scandinavian mountain chain the scandes exhibits characteristics that are unusual for an old palaeozoic mountain belt these include renewed neogene uplift in a passive margin setting and the lack of a pronounced crustal root we investigate the influence of present day thermal compositional and geometric structures in the crust and mantle on the topography of the southern scandes and the resulting implications for the tectonic history of fennoscandia a self consistent 3 d subsurface model of southern norway and sweden is constructed from recent geophysical data sets that constrain the crustal architecture lithosphere geometry density distributions and thermal properties recent seismological studies show evidence for a relatively abrupt transition from seismically slower lithospheric mantle underneath southern norway to seismically faster lithospheric mantle underneath southern sweden we find that a transition from thin subcontinental lithospheric mantle sclm underneath southern norway to a significantly thicker sclm beneath southern sweden can explain this velocitytrend adifferenceincompositionbetweenthetwosclmdomains owingtodifferent depletion refertilization is required to satisfy the gravity field and isostatically compensated topography but contributes only slightly to the observed velocity contrast such a lateral transition zone constituting a major change in the lithospheric structure in southwestern fennoscandia can be related to several major proterozoic and phanerozoic tectonic events such as the sveconorwegian orogeny the permian oslo rift and perhaps even the opening of the atlantic

crustal structure and origin of the eggvin bank west of jan mayen ne atlantic the eggvin bank located between the jan mayen island and greenland is an unusually shallow area containing several submarine volcanic peaks confined by two transforms on the northern kolbeinsey ridge nkr we represent p and s wave velocity models for the eggvin bank based on an ocean bottom seismometer profile collected in 2011 showing igneous crustal thickness variations from 8 km to 13 km a 2 5 km increase is associated with two separate 20 30 km wide segments under the main seamounts the oceanic crust has three layers upper crust l2a 2 8 4 8 km s middle crust l2b 5 5 6 5 km s and lower crust l3 6 7 7 35 km s both the thick layer 2 a b and the high ratio of layer 2 a b thickness to total crustal thickness indicate that secondary intraplate magmatism built the seamounts of the eggvin bank the seamount in the north where the crust is thickest has a flat top indicating subaerial exposure but is deeper than those with rounded tops in the south and is therefore probably older comparing lower crustal seismic velocity with crustal thickness also indicates that the degree of mantle melting may be higher in the north than in the south an enriched mantle source presently feeds the nkr magmatism and probably influenced the eggvin bank development also at earlier times to what extent the eggvin bank has been influenced by the iceland plume is uncertain both an enriched mantle component and elevated mantle temperature may have played a role at different times and locations

crustal structure beneath the faroe islands and the faroe iceland ridge abstract we have mapped the transition from the continental faroe block the faroe islands and surrounding shelf to the thickened oceanic crust of the faroe iceland ridge in the north atlantic using the results of a detailed sea to land seismic profile with wide angle to normal incidence recordings of explosive and airgun shots fired at sea along the faroe iceland ridge interpretation of all available seismic and gravity data indicates that this aseismic ridge is composed of 30 3 km thick oceanic crust with a gradual transition to ancient continental crust from 100 to 40 km northwest of the faroe islands close to the shelf edge this confirms that the crust beneath the faroe islands which may be up to 46 km thick comprises continental material in agreement with previous seismic and geochemical results results suggest that the upper 5 2 0 7 km of the faroe crust consists of tertiary basalts generated during continental breakup overlying the continental crust beneath the lower crust where seismic constraint is poor may exhibit high seismic velocities 7 1 7 6 km s 1 which we attribute to underplating or intrusion by mafic melts during continental breakup in the early tertiary

laboratory observations of rates and patterns of movement of continental margin benthic foraminifera living calcareous and agglutinated benthic foraminifera were collected from a water depth of 220 m on the charleston bump east of charleston south carolina and maintained in aquaria at ambient bottom water temperatures of 12 c and 1 atm in the laboratory the rates and patterns of movement of two species cibicidoides pachyderma rzehak 1886 a calcareous foraminifer and ammodiscus anguillae hoglund 1947 an agglutinated foraminifer are described and compared with published rates of movement for shallow and deep water taxa cibicidoides pachyderma and a anguillae move laterally on a thin veneer of sediment in meandering patterns and both vertically and horizontally in thicker sediments with predominantly straighter patterns in the vertical plane the recorded rates of movement at the substrate surface of c pachyderma and a anguillae vary from 1 0 to 23 and 1 0 to 20 mm day respectively within the sediment 0 5 cm a anguillae moved with a rate varying between 1 0 and 10 mm day these rates are similar to rates for deep sea foraminifera and to the slowest rates of shallow water foraminifera in the laboratory and in the absence of bioturbating organisms both species moved in and out of sediments suggesting that in nature they may be epifaunal and or shallow infaunal taxa

palaeocene recent plate boundaries in the ne atlantic and the formation of the jan mayen microcontinent abstract breakup and sea floor spreading between greenland and eurasia established a series of new plate boundaries in the north atlantic region since the late palaeocene a conventional kinematic model from pre breakup to the present day assumes that eurasia and greenland moved apart as a two plate system however new regional geophysical datasets and quantitative kinematic parameters indicate that this system underwent several adjustments since its inception and suggest that additional short lived plate boundaries existed in the ne atlantic among the consequences of numerous plate boundary relocations is the formation of a highly extended or even fragmented jan mayen microcontinent and subsequent deformation of its margins and surrounding regions the major oligocene plate boundary reorganization and microcontinent formation might have been precluded by various ridge propagations and or short lived triple junctions ne and possibly sw of the jan mayen microcontinent from the inception of sea floor spreading 54 ma to c18 40 ma our model implies a series of failed ridges offshore the faeroe islands a northern propagation of the aegir ridge ne of the jan mayen microcontinent and a series of triple junctions and or propagators in the southern greenland basin

a 3d regional crustal model of the ne atlantic based on seismic and gravity data abstract we present a 3d regional crustal model for the north atlantic which is based on the integration of seismic constraints and gravity data the model addresses the crustal thickness geometry and includes information on sedimentary thickness the presence of high velocity zones in the lower crust and information on the crustal density distribution in the continental and oceanic domains using an iterative forward and inverse modelling approach we adhere to the seismic constraints within their uncertainty but manage to enhance the crustal geometry in areas where seismic data are sparse or absent a number of basins are resolved with more detail recently released seismic reflection data beneath the ne greenland shelf allowed for a major improvement of the crustal thickness estimates estimated moho depths beneath the basins there vary between 15 and 25 km which is compatible with the conjugate norwegian margin a major lower crustal seismic velocity anomaly in the vicinity of the greenland iceland faroe ridge complex is supported by density modelling we discuss the validity and uncertainties of our model assumptions and discuss the correlation with the main structural elements of the north atlantic

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

combined satellite gravity field model goco01s derived from goce and grace 1 the satellite only gravity field model goco01s is a combination solution based on 61 days of goce gravity gradient data and 7 years of grace gps and k band range rate data resolved up to degree order 224 of a harmonic series expansion the combination was performed consistently by addition of full normal equations and stochastic modeling of goce and grace observations the model has been validated against external global gravity models and regional gps leveling observations while low to medium degrees are mainly determined by grace significant contributions by the new measurement type of goce gradients can already be observed at degree 100 beyond degree 150 goce becomes the dominant contributor correspondingly with goco01s a global gravity field model with high performance for the complete spectral range up to degree order 224 is now available this new gravity model will be beneficial for many applications in geophysics oceanography and geodesy

mafic injections in situ hybridization and crystal accumulation in the pyramid peak granite california located in the northern sierra nevada the middle jurassic pyramid peak granite and associated dioritic rocks display superbly exposed interlayered sheets of mafic felsic and hybrid rocks the mafic hybrid layers show a consistent asymmetry sharply chilled on one side and gradational through hybrids to granite on the other and dip to the southwest load casts and silicic pipes along the chilled mafic northeastern margins of the sheets indicate that depositional way up is to the southwest and that the adjacent mount tallac roof pendant was the original floor of the intrusion orientations of the pipes indicate that the layers were tilted after deposition and solidification we interpret the sheets to be intramagmatic flows that formed by injections of mafic magma into a silicic magma chamber followed by flow across the crystal rich base of that chamber the granitic and hybrid rocks interlayered with the mafic sheets represent material that accumulated on the chamber floor between episodes of mafic replenishment most contamination of the mafic sheets probably occurred because of flow front instabilities generated as the mafic magma entered and spread across the chamber floor the upward gradation from diorite to granite with decreasing abundance and size of mafic enclaves can best be explained by convective stirring at the upper boundaries of the dioritic replenishments the pyramid peak granite was probably initiated as a thin concordant sheet intruding into gently dipping jurassic supracrustal rocks the pluton was constructed incrementally with many replenishments of felsic and mafic magma and dominantly solidified by accumulation of crystals on the floor of the chamber the present steep dips of the layers suggest that downward warping of the chamber floor may have been a factor in accommodating the incrementally constructed pluton

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

burrows and trails produced by quinqueloculina impressa reuss a benthic foraminifer in fine grained sediment the benthic foraminifer quinqueloculina impressa reuss was buried in various types of sediment in order to assess its capability for producing sediment disturbances and thus ichnofossils silts and silty clays showed distinct burrows fine sands did not two types of burrows were produced fairly straight vertical burrows from 4 cm below the water sediment interface to within 1 cm of the sediment surface and a horizontal and vertical maze like burrow system in the top centimetre of the sediment individuals moving on the sediment surface also produced visible trails when the sediments were dried the burrows were always destroyed in some cases the surface trails were preserved we propose that the vertical burrows are escape structures and that the horizontal and vertical maze like structures are living burrows ichnofossils similar to the escape structures and surface structures have been described presence of these ichnofossils indicates a low energy sedimentary environment and a lack of macrofaunal bioturbation the presence of escape structures may indicate a pulsatory pattern of sedimentation

insights from the jan mayen system in the norwegian greenland sea i mapping of a microcontinent summary in this contribution we present a model of microcontinent architecture within a system that involves a complex rifted margin setting and different phases of deformation and continental breakup our case study is the jan mayen microcontinent jmmc located in the central part of the norwegian greenland sea we have revised its basement and sedimentary geometries using modern and vintage seismic reflection profiles and updated potential field data the northern part of the jmmc consists of a 10 15 km thick continental crust body flanked by two major sedimentary basins we propose that the microcontinent is divided into six distinct segments characterized by different basement and sedimentary architectures the shallow stratigraphy is well imaged and has been detailed three distinct sedimentary units have been defined together with pronounced reflectors ja red jo and f related to erosional magmatic thermal or uplift events the continent ocean boundary has been revised together with the mapping of the distinct volcanic events that characterize the evolution of the microcontinent a companion paper aims to further detail the interpretation of the jmmc structure presented here by constraining the conjugated mid norwegian and mid east greenland structures

growth rates of dike fed plutons are they compatible with observations in the middle and upper crust diapirism and dike fed expansion are two popular models for the ascent and emplacement of large batches of granitoid magma into the middle and upper crust many structural and petrologic relationships in and around plutons can be cited as permissive evidence for either model and so it has been difficult to differentiate between them on these grounds here we consider wall rock strain rates resulting from dike fed expansion at a constant volume pluton filling rate considering end member pluton shapes and dike flow rates and dikes 1 km in plan length the dike fed expansion model predicts wall rock strain rates over the entire pluton growth period that are up to six orders of magnitude faster than the fastest accepted regional tectonic strain rates 10 213 s 21 strain rates in the very early stages of growth can reach values several orders of magnitude faster our results suggest that evidence for or against very fast strain rates in deformation aureoles around plutons may form a key criterion for identifying dike fed expansion on the other hand our ability to extract strain rate information from pluton aureoles is currently extremely limited

structure of the scandes lithosphere from surface to depth abstract in this review we give an overview of geophysical data and models available for the scandinavian mountains and adjacent areas as they are of relevance to the debate about the existence and cause of neogene uplift emphasis is given to potential field and petrophysical data of which the earth science communities of norway and sweden have a long tradition of acquisition and interpretation this is reflected in the wealth and dense coverage of data available the topography of the scandes mountain chain correlates to a large degree with a bouguer gravity low which suggests isostatic compensation but comparison with magnetic and petrophysical data shows that the gravity low is partly influenced by the trans scandinavian igneous belt signals due to the effects of surface geology can be further eliminated by considering the near surface density distribution as provided by petrophysical sampling to illuminate the entire lithospheric structure active and passive seismic and magnetotelluric data can be used recent and ongoing experiments are aimed at improving the existing models of the lithosphere integration of these different geophysical data sets allows the structure of the lithosphere of the scandes and its surroundings to be addressed seismic models show no pronounced crustal root below the scandes which could provide isostatic compensation but instead an increase of crustal thickness towards the central fennoscandian shield from the integrated model isostatic compensation is inferred to be largely controlled by the density distribution of the crust and that a high density lower crust to the east of the scandes is necessary to achieve isostatic equilibrium on a regional scale we demonstrate the typical crustal structure with profiles crossing from the scandes into the shield and a combined onshore offshore basement map

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved

lower crustal bodies in the more volcanic rifted margin geophysical determination and geological implications abstract understanding nature structure and age of lower crustal bodies lcbs and their relation to the crustal structure of the more margin mid norwegian margin and in a more general way of magma rich rifted margins is a key issue to decipher the tectono magmatic processes found in volcanic rifted margins in light of 2d potential field modelling combined with reflection and refraction seismic data we reinvestigated the crustal nature of the more margin and adjacent jan mayen corridor in the proximal domain our study shows that the lcbs most likely represent inherited crustal bodies and not necessarily rift related serpentinised mantle as previously proposed to fit all geophysical observations both lower and middle crustal layers need to be preserved over a large part of the more basin for the distal margin the interpretation of the lcbs is more difficult our preferred interpretation is that they are mainly made of boudins of hyper extended pre rift lower continental crustal rocks more or less intruded by early tertiary magmatic material our seismic magnetic and gravity data does not easily support large scale exhumation of serpentinised mantle in the inner and is unlikely in the outer parts of the more basin the deep structures of the mid norwegian magma rich rifted margin result from the poly phase stretching and thinning of complex inherited crustal structures locally intruded by early tertiary magmatic material

the ne atlantic region a reappraisal of crustal structure tectonostratigraphy and magmatic evolution an introduction to the nag tec project the ne atlantic region and its continental margins fig 1 hold unique information for understanding many aspects of earth science from global geodynamics to palaeoceanography and global environmental change it also holds some of the world s most important hydrocarbon reserves from the north sea along the atlantic margins of ireland britain and norway and into the arctic in the barents sea historically studies in the ne atlantic were important for establishing many of the key ideas during the early part of the plate tectonic revolution