very preliminary reference moon model abstract the deep structure of the moon is a missing piece to understand the formation and evolution of the earth moon system despite the great amount of information brought by the apollo passive seismic experiment alsep the lunar structure below deep moonquakes which occur around 900 km depth remains largely unknown we construct a reference moon model which incorporates physical constraints and fits both geodesic lunar mass and polar moment of inertia and love numbers and seismological body wave arrivals measured by apollo network data in this model the core radius is constrained by the detection of s waves reflected from the core in a first step for each core radius a radial model of the lunar interior including p and s wave velocities and density is inverted from seismic and geodesic data in a second step the core radius is determined from the detection of shear waves reflected on the lunar core by waveform stacking of deep moonquake apollo records this detection has been made possible by careful data selection and processing including a correction of the gain of horizontal sensors based on the principle of energy equipartition inside the coda of lunar seismic records and a precise alignment of sh waveforms by a non linear inversion method the very preliminary reference moon model vpremoon obtained here has a core radius of 380 40 km and an average core mass density of 5200 1000 kg m 3 the large error bars on these estimates are due to the poorly constrained s wave velocity profile at the base of the mantle and to mislocation errors of deep moonquakes the detection of horizontally polarized s waves reflected from the core and the absence of detection of vertically polarized s waves favour a liquid state in the outermost part of the core all these results are consistent within their error bars with previous estimates based on lunar rotation dissipation williams et al 2001 and on lunar induced magnetic moment hood et al 1999

effect of a stably stratified layer near the outer boundary in numerical simulations of a magnetohydrodynamic dynamo in a rotating spherical shell and its implications for earth s core abstract we investigate the effects of stable thermal stratification near the outer boundary in numerical simulations of a magnetohydrodynamic mhd dynamo in a rotating spherical shell the stratified layer acts as an interface for the flow between the convective and stratified regions and filters the magnetic field moreover the stratified boundary also filters the energy generated in the convective region the strongly multipolar magnetic field at high rayleigh numbers without a stratified region could filter a dipolar likemagnetic field when the stratified region is imposed the main findings are described as follows zonal flow would be expected in high latitude region in a stratified layer the penetrative flow in the stratified region is caused by a thermal wind at high latitudes but is not found at mid to low latitudes the horizontal scale of convective flow with and without stratification does not differ greatly the implications for the dynamics in earth s core are as follows 1 a stratified region near the top of the core would be expected at low latitudes but not at high latitudes because thermal winds can penetrate into the stratified region if a dynamo exists 2 for the existence of small scale features in the geomagnetic field laterally heterogeneous heat flux across the core mantle boundary would be necessary or helpful if a stratified region near the top of the earth s core is plausible

combined u pb geochronology and lu hf isotope systematics by lam icpms of zircons from granites and metasedimentary rocks of carrazeda de ansiaes and sabugal areas portugal to constrain granite sources abstract the carrazeda de ansiaes and sabugal areas in the central iberian zone of the iberian variscan belt contain abundant s type granites formed during the post thickening stage of the variscan orogeny syn to post d3 i e the last ductile deformation phase magmatic zircons and inherited zircon cores from two granites g and g5 magmatic zircons from three other granites g1 g4 and g6 and detrital zircons from a chlorite phyllite and a metagraywacke were dated by lam icpms hf isotope data were obtained by the same method to constrain the sources for granites some granites have zircons with negative ehft values g from 8 to 4 g1 from 8 to 1 g4 from 6 to 3 suggesting an origin from heterogeneous crustal anatectic melts or from mantle derived magmas contaminated in the crust magmatic zircons from granites g5 and g6 show a larger variation yielding also some positive ehft values g5 from 8 to 6 g6 from 4 to 4 indicating crystallization from mildly contaminated mantle derived magmas or from a lower crustal source u pb isotope data of inherited zircon cores from granites g and g5 show that neoproterozoic ages dominate but only the inherited zircon cores from granite g have similar initial 176hf 177hf ratios to those from a chlorite phyllite of the formation of ervedosa do douro carrazeda de ansiaes area suggesting that this metasedimentary unit could have been involved in the genesis of the granite g on the other hand the lu hf data suggest that the metagraywacke from sabugal area should not be considered a component involved in the partial melting process that formed the granite g5 the occurrence of mesoproterozoic detrital zircons in both metasediments suggests that these rocks are likely to have evolved from a peri amazonian realm close to west avalonian terranes during the neoproterozoic early palaeozoic however a west african craton provenance could also be considered if a long distance river transportation of mesoproterozoic zircons from the southwest baltica or arabian nubian shield is admitted the u pb isotope data obtained in detrital zircons from both metasedimentary rocks suggest that their maximum depositional ages are ca 578 ma for the chlorite phyllite and ca 577 ma for the metagraywacke

dynamo tests for stratification below the core mantle boundary abstract evidence from seismology mineral physics and core dynamics suggests a layer with an overall stable stratification in the earth s outer core possibly thermal in origin extending below the core mantle boundary cmb for several hundred kilometers yet vigorous deep mantle convection with locally elevated heat flux implies locally unstable thermal stratification below the cmb consistent with interpretations of non dipole geomagnetic field behavior that favor upwelling flows in places below the cmb to resolve this apparent inconsistency we investigate the structure of convection and magnetic fields in the core using numerical dynamos with laterally heterogeneous boundary heat flux strongly heterogeneous boundary heat flux generates localized convection beneath the cmb that coexists with an overall stable stratification there our partially stratified dynamos are distinguished by their time average magnetic field structures without stratification or with stratification confined to a thin layer the octupole component is small and the cmb magnetic field structure includes polar intensity minima with more extensive stratification the octupole component is large and the magnetic field structure includes intense patches or high intensity lobes in the polar regions comparisons with the time averaged geomagnetic field are generally favorable for partial stratification in a thin

multiple crust reworking in the french armorican variscan belt implication for the genesis of uranium fertile leucogranites muscovite peraluminous granites mpgs form by partial melting of the continental crust and can be related to metalliferous deposits such as tin tungsten and uranium u metal enrichment in mpgs commonly results from fractional crystallization but the metal contents of the source play a major role for their fertility between ca 320 and 300 ma late carboniferous the french armorican variscan belt was intruded by numerous u fertile mpgs that contain inherited zircon grains with a wide range of ages from archean to carboniferous u pb and hf isotopic data of zircon grains from brioverian to carboniferous sediments cambrian to early carboniferous granitoids and late carboniferous mpgs indicate that the crust of the armorican massif is made up by detritus mainly derived from the west african craton 3500 1600 ma tdm 3 8 2 3 ga grenvillian belt 1200 900 ma tdm 2 7 1 2 ga and avalonian cadomian belt 800 550 ma tdm 2 5 0 8 ga and that the crust was affected by magmatic events at 510 470 ma tdm 1 6 0 6 ga 410 330 ma tdm 1 6 1 ga and 320 300 ma furthermore they reveal that the late carboniferous mpgs were mainly formed by partial melting of brioverian sediments with cambro ordovician and devonian carboniferous granitoids which are all genetically linked with each other and characterized by th u 4 the new data suggest that the u fertile mpgs result from multiple reworking of u rich brioverian sediments deposited ca 550 ma ago on the northern margin of gondwana and partially molten during several paleozoic events causing a successive increase in u content in the middle upper crust

geochronology of the mid german crystalline rise west of the river rhine the mid german crystalline rise has its westernmost exposures at the western margin of the rhine graben in the southern pfalz and the northern alsace the outcrops are made up of granitoid rocks and minor volcano sedimentary sequences radiometric ages obtained by u pb pb pb sm nd and rb sr analyses of the igneous rocks from this area range from 433 to 325 ma thus covering a time span from the silurian to the end of the lower carboniferous because the investigated rocks are according to their chemical composition largely related to subduction zone environments the following three geodynamical scenarios are postulated always taking subduction of oceanic crust beneath the mid german crystalline rise into account a subduction of the rheic ocean during the silurian from the north b subduction of the rhenohercynian ocean during the late devonian 369 ma from the north c subduction of the saxothuringian ocean during the lower carboniferous 334 ma from the south

formation of the stratified ocean of the core abstract a mechanism of formation of the stably stratified layer of light fluid at the core mantle boundary which we call the stratified ocean of the core is proposed a turbulent diffusion in this stably stratified layer is qualitatively considered the rate of addition of light fluid component to the layer by barodiffusion and light fluid redistribution inside the layer by turbulent diffusion are evaluated the relevant parameters of the formation mechanism are estimated

possibility of a low p wave velocity layer in the outermost core from global smks waveforms abstract a global data set consisting of 1211 smks m 2 waveforms has been analyzed to investigate the radial seismic velocity structure around the core mantle boundary cmb band passed f 0 02 0 1 hz and stacked waveforms coincide with reflectivity synthetic ones for prem very well whereas those for other global models iasp91 ak135 and sp6 yield disagreements a preliminary waveform modeling for the outermost core with prem as initial structure results in a core surface layer with a p wave velocity of 7 95 km s at the core top and thickness of 90 km based on a 3 d global s wave velocity model smks phases collected in this study mainly pierce slightly high velocity regions at the base of the mantle and the predicted differential travel time residuals for s3ks skks are expected to be negative approximately 0 5 s for the averages however positive s3ks skks residuals of which average is 0 3 s are predominant in the stacked waveforms moreover a waveform modeling for the d structure can result in a 30 km thick layer with a 10 s wave velocity reduction at the mantle bottom ulvz in which waveform fitness for the part of mainly s3ks is improved on the other hand the waveform data is not well explained by the lowermost mantle structures with thickness of several hundred kilometers these suggest that the smks data is still affected by the structure of the lowermost several tens kilometers in the mantle that is not sufficiently modeled by a global tomography although the thin low s wave velocity model is not conclusive the possibility of a low p wave velocity layer in the outermost core is remained because the waveform fitness for the part of s4ks is improved by the combination of the ulvz and a 140 km thick layer with a 0 8 p wave velocity reduction at the core top

the palaeozoic variscan oceans revisited abstract geological evidence supported by biogeographical data and in accord with palaeomagnetic constraints indicates that one ocean models for the variscides should be discarded and confirms instead the existence of three gondwana derived microcontinents which were involved in the variscan collision avalonia north armorica franconia and thuringia subdivided by a failed vesser rift and south armorica central iberia armorica bohemia all divided by small oceans in addition parts of south eastern europe including adria and apulia are combined here under the new name of palaeo adria which was also peri gondwanan in the early palaeozoic oceanic separations were formed by the break up of the northern gondwana margin from the late cambrian onwards most of the oceans or seaways remained narrow but much like the alpine cenozoic oceans gave birth to orogenic belts with hp uhp metamorphism and extensive allochthons the saxo thuringian ocean between north and south armorica and the galicia moldanubian ocean between south armorica and palaeo adria only the rheic ocean between avalonia and peri gondwana was wide enough to be unambiguously recorded by biogeography and palaeomagnetism and its north western arm closed before or during the emsian in europe ridge subduction under the northernmost part of armorica in the emsian created the narrow and short lived rheno hercynian ocean it is that ocean and not the rheic whose opening and closure controlled the evolution of the rheno hercynian foldbelt in south west iberia south west england germany and moravia czech republic devonian magmatism and sedimentation set within belts of early variscan deformation and metamorphism are probably strike slip related the first arrival of flysch on the forelands and or the age of deformation of foreland sequences constrains the sequential closure of the variscan seaways galicia moldanubian in the givetian saxo thuringian in the early famennian rheno hercynian in the tournaisian additional mid to late devonian and partly early carboniferous magmatism and extension in the rheno hercynian saxo thuringian and galicia moldanubian basins overlapped with variscan geodynamics as strictly defined the early carboniferous episode was the start of episodic anorogenic heating which lasted until the permian and probably relates to tethys rifting

constraining outermost core velocity with smks waves smks waves m 2 3 4 seismic waves that travel as s waves in the mantle p waves in the core and reflect m 1 times on the underside of the core mantle boundary are well suited for constraining outermost core vp structure this is due to closeness of the mantle paths and also the shallow depth range these waves travel in the outermost core high quality digitized wwssn and canadian network recordings from a deep focus java sea event which sample the outer core beneath the northern pacific the artic and northwestern north america roughly th of the globe are utilized as an example to show the strength of smks waves to resolve outermost core structure s3ks s2ks and s4ks s3ks differential travel times were measured and compared to those from reflectivity synthetics created from core models of past studies constraints and uncertainties in outer core structure using smks are discussed for the event studied the prem core model with possibly a small vp decrease in the outermost 50 km of the core provides a good fit to the data

palaeogeographic significance of mid silurian palaeomagnetic results from southern britain major revision of the apparent polar wander path for eastern avalonia summary wenlock c 430 ma lavas from the east mendips inlier southern briain are characterized by either single component magnetizations type 1 or a more complex system of three magnetization components type 2 during stepwise thermal demagnetization the type of demagnetization behaviour is related to changes in magnetic petrology within the lava pile the lower and intermediate unblocking temperature components of type 2 represent magnetic overprints of tertiary recent and hercynian mid carboniferous origin respectively the primary nature of the high unblocking temperature magnetization component types 1 and 2 dec 095 c inc 24 ag5 8 8 is demonstrated by positive agglomerate tests conversely an overlying upper old red sandstone sequence did not provide primary magnetizations the magnetic signature is governed by syn tectonic hercynian remagnetizations the primary silurian data demonstrate that the east mendips inlier experienced considerable clockwise rotation probably of the order of 80 prior to partial remagnetization during hercynian deformation and folding the silurian palaeopole vgp 13 n 271 e dp dm 5 9 cannot therefore be used for apparent polar wander path construction nevertheless the palaeolatitude estimate 13 f 5s suggests that southern britain eastern avalonia was at comparable mid silurian latitudes to baltica and northern britain 10 20 s both the iapetus ocean and tornquist sea therefore which separated southern britain from laurentia and baltica respectively in ordovician times were closed by wenlock time as ordovician and silurian palaeomagnetic data from baltica and eastern avalonia now record a comparable northwards translation from high southerly to near equatorial latitudes during this time we postulate pre wenlock collision of these blocks to form balonia baltica eastern avalonia a new apparent polar wander path for eastern avalonia constructed on the basis of this palaeogeographic model is presented

lateral variations in cmb heat flux and deep mantle seismic velocity caused by a thermal chemical phase boundary layer in 3d spherical convection article i nfo numerical simulations of thermo chemical multi phase compressible mantle convection in a three dimensional spherical shell are used to investigate the relationship between lateral variations in seismic shear wave velocity vs above the core mantle boundary cmb and lateral variations in heat flux across the cmb qcmb when compositional variations and the post perovskite phase transition are included for simple thermal convection the vs qcmb relationship is reasonably but not perfectly linear the post perovskite transition introduces a non linearity that amplifies fast vs anomalies in cold regions but there is still a unique mapping between vs and qcmb lateral variations in composition such as piles of dense material introduce another non linearity that affects hot upwelling regions and introduces a non uniqueness in vs qcmb if the dense material e g morb is seismically fast compared to the surrounding material in this case dense piles are ringed by sharp low vs anomalies if the cmb is covered by a global dense layer than variations in vs and qcmb are reduced but so is the mean value of qcmb in all cases the peak to peak lateral variation in qcmb is similar to or larger than twice the mean value which might create problems for generating a dynamo according to existing numerical dynamo simulations analytical scalings are developed to explain the observed trends

structural evolution of intermediate crustal rocks in a strike slip and extensional setting variscan odenwald sw germany differential upward transport of metamorphic complexes and changing deformation mechanisms abstract the variscan basement exposed in the odenwald mountains southwest germany is composed of several allochthonous metamorphic complexes showing low pressure metamorphism with varying pt conditions and of syntectonic plutons i and s type during the late devonian early carboniferous times rapid uplift of these rocks caused rapid cooling before and during the thermal peak of metamorphism the metamorphic rocks experienced penetrative strain d 1 d 2 which was probably generated by crustal shortening and stacking the resulting micro structures infer distributed strain activation of c slip in quartz and postkinematic annealing during and after the thermal peak of metamorphism ne sw trending zones of normal oblique sinistral strike shearing d 3 and nne ssw trending zones of normal shearing d 4 developed these episodes of deformation are characterized by strong localization of strain strain softening was caused by reorientation of the lattice of quartz toward an orientation more favorable for easy glide along a and by a change in deformation mechanisms of feldspar from dislocation creep to grain size sensitive creep normal oblique strike shearing and normal shearing caused juxtaposition of mid crustal slivers of dissimilar pt and structural histories and provided mechanisms for their denudation detachment of rocks occurred along domains in which strain softening was operative further transtension and extension facilitated uplift and emplacement of syntectonic plutons which experienced also d 3 and d 4 strain in the plutonic rocks strain was broadly distributed in the initial hot stages and became increasingly localized as the deformation continued through cooling

baltic provenance of top famennian siliciclastic material of the northern rhenish massif rhenohercynian zone of the variscan orogen the provenance of top famennian sedimentary rocks linked to the hangenberg crisis from the northern rhenish massif germany was investigated by the means of detrital zircon u pb geochronology based on the obtained age spectra three main tectonothermal domains are recognized as possible sources paleo and mesoproterozoic 2000 1000 ma units of baltica and early paleozoic caledonian orogen 500 400 ma our interpretation of the detritus having been derived from northern source areas i e baltica and the scandinavian caledonides with a minor input of german polish rugen pomeranian caledonides contradicts the traditional view that during the upper devonian the northern rhenish massif was supplied by detritus from the south complementary mineralogical textural and geochemical analyses point to a derivation of the detritus of drewer and hangenberg sandstones mainly from felsic recycled continental crust the elevated concentrations of pb and zn in the studied sections are a feature attributed to hydrothermal alteration related to the terminal devonian synsedimentary volcanism or post depositional variscan deformation

back to sender tectonic accretion and recycling of baltica derived devonian clastic sediments in the rheno hercynian variscides sedimentary petrography and zircon icp ms laser ablation ages from synorogenic clastic sediments in the rheno hercynian belt of germany rheinisches schiefergebirge harz reveal basal tectonic accretion followed by exhumation and recycling of baltica derived devonian shelf sediments the recycled sediment volume demands a substantial palinspastic addition to the passive northern margin of the rheno hercynian basin detrital zircon ages from the late carboniferous foreland basin and their possible source rocks in the south portuguese zone permit the same interpretation this suggests that synorogenic sedimentation in portugal is related like in germany to the closure of the devonian carboniferous rheno hercynian basin and not to the closure of the ordovician silurian rheic ocean

the stably stratified outermost core revisited the p wave velocity structure of the outermost 200 km of the outer core the e region is analyzed using a suite of differential travel times for sks skks and s waves bottoming below within and above this depth range core penetrating phases with paths beneath alaska exhibit similar sks skks differential travel time patterns to phases sampling the core beneath the central pacific but very different sks s differential travel times these patterns can be explained by a core velocity model in which the outermost 50 to 100 km has 1 2 slower p wave velocities than standard earth models perhaps due to a stably stratified chemical boundary layer combined with 3 lateral variations in s wave velocity in the lowermost mantle

seismic detectability of anomalous structure at the top of the earth s outer core with broadband array analysis of smks phases abstract i have examined precisely the differential travel times and waveforms of smks seismic phases propagating under the southern indian ocean obtained from african broadband seismic arrays the smks phases analyzed in this study travel in the mantle with weak heterogeneity confirmed by a global tomographic study for the distance range of 115 135 the smks differential times were obtained from a vespagram a stack intensity on a time slowness diagram and comparison with the vespagram created from synthetic waveforms with prem gives the travel time residual for each event array pair although the residuals of s3ks s2ks times exhibit apparently a systematic dependence on epicentral distance this is likely due to small scale heterogeneity beneath the oceania where is covered by the smks ray entering points at the cmb waveform modeling was applied to a record section with a small travel time residual that suggests a small effect from the mantle heterogeneity on the data set i found that a low velocity zone in the outermost 50 km in the core rather than prem can explain an additional arrival detected just after the s3ks phase this result is still inconclusive because of the small number of data and non uniqueness of the model and ambiguity due to mantle structure however accumulation of the precise measurement described in this study may help the reduction of uncertainty and trade offs

thermochemical flows couple the earth s inner core growth to mantle heterogeneity the uppermost 100 km of the earth s inner core is subject to an east west divide seismic waves travel more rapidly and are attenuated more severely in the eastern than in the western hemisphere and the west is more anisotropic that is seismic waves travel at different speeds in different directions than the eastern hemisphere the origin of this hemispherical dichotomy has remained enigmatic aubert et al now show that a model incorporating thermochemical convection and dynamo action can account for these effects by producing a large scale long term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle seismic waves sampling the top 100 km of the earth s inner core have revealed that the eastern hemisphere is seismically faster more isotropic and more attenuating than the western hemisphere it is now shown that a single model of thermo chemical convection and dynamo action can account for all these effects by producing a large scale long term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle seismic waves sampling the top 100 km of the earth s inner core reveal that the eastern hemisphere 40 e 180 e is seismically faster1 2 more isotropic2 3 and more attenuating4 than the western hemisphere the origin of this hemispherical dichotomy is a challenging problem for our understanding of the earth as a system of dynamically coupled layers previously laboratory experiments have established that thermal control from the lower mantle can drastically affect fluid flow in the outer core5 which in turn can induce textural heterogeneity on the inner core solidification front6 the resulting texture should be consistent with other expected manifestations of thermal mantle control on the geodynamo specifically magnetic flux concentrations7 8 in the time average palaeomagnetic field9 10 over the past 5 myr and preferred eddy locations11 in flows imaged below the core mantle boundary by the analysis of historical geomagnetic secular variation12 here we show that a single model of thermochemical convection and dynamo action can account for all these effects by producing a large scale long term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle the main feature of this thermochemical wind is a cyclonic circulation below asia which concentrates magnetic field on the core mantle boundary at the observed location and locally agrees with core flow images this wind also causes anomalously high rates of light element release in the eastern hemisphere of the inner core boundary suggesting that lateral seismic anomalies at the top of the inner core result from mantle induced variations in its freezing rate

melting induced stratification above the earth s inner core due to convective translation several observed properties of earth s solid inner core and liquid outer core remain enigmatic including an east west seismic asymmetry and the presence of a roughly 250 kilometre thick layer of reduced seismic velocity at the base of the outer core alboussiere et al now suggest a model that can produce both of these features based on experiment and numerical modelling they propose that simultaneous crystallization and melting at opposite sides of earth s inner core surface can result in a translational mode of thermal convection within the inner core which also introduces an asymmetry between hemispheres these authors show that simultaneous crystallization and melting at the surface of the earth s inner core can result in a translational mode of thermal convection within the inner core producing the observed stratified layer of reduced seismic velocity at the base of the outer core the dynamical model they propose also introduces an asymmetry between hemispheres that may explain the enigmatic east west asymmetry in seismic properties of the inner core in addition to its global north south anisotropy1 there are two other enigmatic seismological observations related to the earth s inner core asymmetry between its eastern and western hemispheres2 3 4 5 6 and the presence of a layer of reduced seismic velocity at the base of the outer core6 7 8 9 10 11 12 this 250 km thick layer has been interpreted as a stably stratified region of reduced composition in light elements13 here we show that this layer can be generated by simultaneous crystallization and melting at the surface of the inner core and that a translational mode of thermal convection in the inner core can produce enough melting and crystallization on each hemisphere respectively for the dense layer to develop the dynamical model we propose introduces a clear asymmetry between a melting and a crystallizing hemisphere which forms a basis for also explaining the east west asymmetry the present translation rate is found to be typically 100 million years for the inner core to be entirely renewed which is one to two orders of magnitude faster than the growth rate of the inner core s radius the resulting strong asymmetry of buoyancy flux caused by light elements is anticipated to have an impact on the dynamics of the outer core and on the geodynamo

effects of fluid flow cooling and deformation as recorded by 40ar 39ar rb sr and zircon fission track ages in very low to low grade metamorphic rocks in avalonian se cape breton island nova scotia canada 40ar 39ar in situ uv laser ablation of white mica rb sr mineral isochrons and zircon fission track dating were applied to determine ages of very low to low grade metamorphic processes at 3 5 0 4 kbar 280 30 c in the avalonian mira terrane of se cape breton island nova scotia the mira terrane comprises neoproterozoic volcanic arc rocks overlain by cambrian sedimentary rocks crystallization of metamorphic white mica was dated in six metavolcanic samples by 40ar 39ar spot age peaks between 396 3 and 363 14 ma rb sr systematics of minerals and mineral aggregates yielded two isochrons at 389 7 ma and 365 8 ma corroborating equilibrium conditions during very low to low grade metamorphism the dated white mica is oriented parallel to foliations produced by sinistral strike slip faulting and or folding related to the middle late devonian transpressive assembly of avalonian terranes during convergence and emplacement of the neighbouring meguma terrane exhumation occurred earlier in the nw mira terrane than in the se transpression was related to the closure of the rheic ocean between gondwana and laurussia by nw directed convergence the 40ar 39ar spot age spectra also display relict age peaks at 477 465 ma 439 ma and 420 428 ma attributed to deformation and fluid access possibly related to the collision of avalonia with composite laurentia or to earlier ordovician silurian rifting fission track ages of zircon from mira terrane samples range between 242 18 and 225 21 ma and reflect late palaeozoic reburial and reheating close to previous peak metamorphic temperatures under fluid absent conditions during rifting prior to opening of the central atlantic ocean

very low grade metamorphism of rheno hercynian allochthons variscides germany facts and tectonic consequences the horre belt in the se part of the rhenish massif has been regarded as autochthonous because of the apparent lack of metamorphic inversion we have performed a k white mica study using powder x ray diffraction derived kubler index ki and k white mica b cell dimension and the spectrally derived wavelength of the 2 200 nm absorption feature 2200wvl of supposedly allochthonous units and the underlying par autochthon ki reveals a slight but significant inversion of metamorphic grade which shows that the horre belt and the hessische schieferserie adjacent to the south were emplaced by thrusting after they had acquired peak metamorphism m 1 in deeper parts of the orogenic wedge only in the westernmost part of the study area the par autochthon and the allochthon show the same grade of anchizonal metamorphism this observation together with k white mica b cell dimensions 9 000 a and 2200wvl 2 204 nm suggests a second low pressure metamorphism m 2 subsequent to the emplacement of the allochthon this is supported by an anomaly of published conodont alteration index data our results expand the original width of the rheno hercynian passive margin to at least 580 more probably to 670 or even 750 km palinspastic restoration also reveals that the givetian to early carboniferous volcanic belt of the lahn dill area is not only younger than the emsian morb type lavas of the rheno hercynian ocean but was also separated from the latter by a largely non volcanic belt of at least c 220 km width apparently the givetian to early carboniferous volcanic episodes were unrelated to the rheno hercynian drift stage

origin of thermohaline staircases hypotheses concerning the origin of thermohaline staircases in salt fingering regions are reviewed and assessed one such hypothesis that staircases arise from thermohaline intrusions is developed into a quantitative theory it is shown that growing intrusions evolve toward staircases when the background density ratio lies below a threshold value and nonlinear computations confirm that staircases are viable intrusion equilibria staircase properties such as step heights lateral density ratios and layer slopes lie closest to observed values when salt fingers are assumed not to contribute to shear stress and when turbulent mixing rates are smaller than usual thermocline values

aspects of the reconstruction of the stress history of a fold and thrust belt rhenish massif federal republic of germany abstract by use of faults and striations parts of the deviatoric stress tensors and thereby essential aspects of the paleostress history of the rhenish massif can be reconstructed the stress history is unexpectedly complex even on the local scale the region under investigation is subdivided into various areas each of which exhibits somewhat different sequences of stress states several mutual aspects are evident in lower devonian rocks in the north which show only very slight deformation a pre folding stress state is preserved with a preferentially n s trending extension attributed to the stage of basin development the stage of folding itself during the carboniferous shows strong regional and temporal heterogeneity under frequently altering stress states after an initial stage of a semi homogeneous stress field this development occurs simultaneously with partial stress uncoupling at larger thrust zones with diverging deformation histories of hangingwalls and footwalls movement patterns in the north evidence subsequent clockwise rotation of the stress field which is only weakly represented in the south on the other hand there is clear evidence of a still younger counterclockwise rotation of the stress field which only affects the southern massif this is probably due to the superpositioning of orthogonal relative movements on the southern rim of the fold belt by a dextral strike slip component during final deformation thus indicating late dextral transpression succeeded by dextral transtension the final extensional stage is related to late paleozoic uplift and crustal stretching perpendicular to the strike of the fold belt followed by a change of direction of extension this state of stress obviously extends into the present although complex the various stress conditions are clearly correlated with other fabric elements in particular with cleavage fold geometry and mineralization

precise seismic wave velocity atop earth s core no evidence for outer core stratification abstract earth s outer core is composed of liquid fe and ni alloyed with a 10 fraction of light elements such as o s or si secular cooling and compositional buoyancy drive vigorous convection that sustains the geodynamo but critical details of light element composition and thermal regime remain uncertain seismic velocities can provide important observational constraints on these parameters but global reference models such as preliminary reference earth model prem iasp91 and ak135 exhibit significant discrepancies in the outermost 200 km of the core here we apply an empirical transfer function method to obtain precise arrival times for smks waves a whispering gallery mode that propagates near the underside of the core mantle boundary models that fit our data are all characterized by seismic velocities and depth gradients in the outermost 200 km of the core that correspond best with prem this similarity to prem which has a smooth velocity profile that satisfies the adiabatic adams and williamson equation argues against the presence of an anomalous layer of light material near the top of the core as suggested in some previous studies a new model ae09 is proposed as a slight modification to prem for use as a reference model of the outermost core

different age response of zircon and monazite during the tectono metamorphic evolution of a high grade paragneiss from the ruhla crystalline complex central germany results of tims sims and sem analyses show that zircon and monazite in a high grade paragneiss of the ruhla crystalline complex central germany were formed and or altered during different stages of a tectono metamorphic history between early devonian and permian times detrital zircon cores of 460 ma place an older limit on the age of anatexis and show that the paragneiss sequence contains rocks at least as young as early cambrian metamorphic zircon growth commenced at 365 ma peaking at 360 355 ma at the same time that granite dykes were emplaced in contrast monazite in the paragneiss preserves little record of the metamorphic peak most monazite grains grew or were recrystallised in the lower carboniferous at 339 ma contemporaneous with the emplacement of voluminous diorite and granite bodies these intrusions and related tectonics caused some of the high u zircon overgrowths to undergo moderate to severe pb loss a second pb loss event between 300 and 280 ma can be related to late carboniferous early permian large scale block faulting

stratification of the top of the core due to chemical interactions with the mantle 1 chemical interactions between the core and the mantle have been proposed as a mechanism to transfer o and si to the core adding light elements to the top of the core creates a stratified layer which grows by chemical diffusion into the underlying convecting region we develop a physical model to describe the evolution of the layer and estimate physical properties to aid in its detection the interface between the stratified layer and the convecting interior is defined by the onset of double diffusive instabilities oscillatory instabilities arise from the interplay of a stable compositional stratification and an unstable thermal stratification due to a superadiabatic heat flow at the core mantle boundary double diffusive convection in the region of neutral stratification establishes the base of the layer and sets the rate of entrainment of excess light element into the interior of the core growth of the layer by diffusion is interrupted by nucleation of the inner core which segregates light elements into the convecting part of the core for calculations using o as the sole light element we find that the base of the stratified layer retreats toward the core mantle boundary as the radius of the inner core increases representative but uncertain model parameters yield a present day layer thickness of 60 to 70 km we also calculate the anomaly in p wave velocity relative to the value for a well mixed core the velocity anomaly decreases almost linearly across the layer with a peak value of 2 at the core mantle boundary this anomaly should be large enough to detect in seismic observations although the sign of the anomaly is opposite to estimates obtained in previous seismic studies we suggest possible explanations for this discrepancy and speculate about the implications for the structure of the earth s interior

array based iterative measurements of smks travel times and their constraints on outermost core structure vigorous convection in earths outer core led to the suggestion that it is chemically homogeneous however there is increasing seismic evidence for structural complexities close to the outer cores upper and lower boundaries both body waves and normal mode data have been used to estimate a p wave velocity vp at the top of the outer core the e layer which is lower than that in the preliminary reference earth model however these low vp models do not agree on the form of this velocity anomaly one reason for this is the difficulty in retrieving and measuring smks arrival times to address this issue we propose a novel approach using data from seismic arrays to iteratively measure smks skks differential travel times this approach extracts individual smks signal from mixed waveforms of the smks series allowing us to reliably measure differential travel times we successfully use this method to measure smks time delays from earthquakes in the fiji tonga and vanuatu subduction zones smks time delays are measured by waveform cross correlation cc between smks and skks and the cc coefficient allows us to access measurement quality we also apply this iterative scheme to synthetic smks seismograms to investigate the 3d mantle structures effects the mantle structure corrections are not negligible for our data and neglecting them could bias the vp estimation of uppermost outer core after mantle structure corrections we can still see substantial time delays of s3ks s4ks and s5ks supporting a low vp at the top of earths outer core

precambrian protoliths and early paleozoic magmatism in the french massif central u pb data and the north gondwana connection in the west european variscan belt abstract u pb geochronological data were collected on zircon by la mc icp ms on orthogneiss and paragneiss from the limousin area in the french massif central fmc in order to investigate the connection between the west european variscan belt and the northern margin of gondwana fifteen samples were collected in the four main tectonostratigraphic units of the fmc namely the para autochthonous unit the lower gneiss unit lgu the upper gneiss unit ugu and the thiviers payzac unit orthogneiss yield intrusion age between 521 7 and 446 6 ma considering all the results from both magmatic and metasedimentary samples two peaks at 531 and 473 ma are recognized rifting processes taking place along the north gondwana margin during the lower paleozoic went on until the end of the ordovician as suggested by the magmatic event recorded around 450 ma several maximum depositional ages were ascertained in the metasedimentary formations of the fmc as determined by the youngest detected detrital zircon crystal ranging from 604 16 ma for metasediments of the para autochthonous unit 573 12 ma for the lgu 564 9 ma for the thiviers payzac unit and 523 4 ma in the ugu minimum depositional ages are given by magmatic emplacement ages obtained in the crosscutting orthogneiss there is some evidence for a decrease of this maximum age upwards in the tectonostratigraphy detrital zircon in metasedimentary formations and inherited zircon in orthogneiss display a wide spectrum of ages with significant peaks at around 590 ma and 560 ma archean paleoproterozoic and neoproterozoic detrital zircons suggest a west african craton source of the sedimentation the large amount of neoproterozoic and lower paleozoic ages obtained in this study suggests that these periods played a significant role in the continental crustal growth history of western europe

isobaric cooling and anti clockwise p t paths in the variscan odenwald crystalline complex germany mineral assemblages in al2o3 rich sio2 and k2o poor metapelitic rocks from the western odenwald crystalline complex variscan mid german crystalline rise southern germany include corundum spinel cordierite sillimanite garnet and staurolite quartz is absent from almost all samples therefore the applicability of conventional geothermobarometry is very limited or even impossible detailed petrographic investigation on selected samples permits inference of the sequence of appearance and disappearance of several mineral assemblages the recognition of such partial re equilibration stages and their associated mineral assemblages together with mineral stabilities predicted from kfmash pseudosections enables the determination of the pressure temperature p t trajectories experienced by these rocks during the variscan metamorphism the rocks were metamorphosed under low p high t conditions and underwent an anti clockwise p t evolution a pressure increase from about 2 kbar to 4 0 5 kbar was accompanied by heating peak metamorphic conditions were reached at pressures of 4 0 5 kbar and temperatures of at least 640 c probably even higher the retrograde evolution is characterised by near isobaric cooling from 640 c to approximately 550 c the rocks underwent the anti clockwise evolution in a subduction related magmatic arc setting the close spatial association of the low p high t rocks with recently discovered metabasic eclogites in the eastern part of the odenwald crystalline complex may indicate a fossil paired metamorphic belt in the central european variscides

evolution of the amphibolite granulite facies transition exposed by the vredefort impact structure kaapvaal craton south africa abstract geological mapping is integrated with high precision u pb zircon and monazite geochronology to document in detail the nature and temporal evolution of the amphibolite granulite facies boundary exposed in the vredefort impact structure of the central kaapvaal craton our study has revealed that the preimpact configuration of the amphibolite granulite facies boundary is best preserved in panels between impact related brittle faults and that past concepts of the boundary must be revised a regional lithologic transition exists between amphibolite facies outer granite gneiss 3 084 3 09 ga and a heterogeneous assemblage of granulite facies gneisses ca 3 1 3 3 ga tabular deformed quartz syenite bodies dated at documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cy

mapping heterogeneity of the uppermost inner core using two pairs of core phases two pairs of core phases pkpcd pkpdf and pkpbc pkpdf are analysed to map the p wave velocity vp of the uppermost inner core waveform analysis of pkpcd pkpdf shows that vp relative to prem vp within 100 km from the inner core boundary icb is laterally heterogeneous by 0 5 to 0 1 with a wavelength of nearly 1000 km differential travel times of pkpbc pkpdf relative to prem tbc df are positive negative for the regions of positive negative vp near the icb this correlation indicates that the lateral vp variation exists predominantly in the inner core side of the icb absolute values of tbc df for both positive and negative vp regions are too large to be explained with models in which lateral vp variation is restricted within the upper 200 km of the inner core the lateral variation appears to extend at least to 300 km below the icb

the deep earth may not be cooling down abstract the earth is a thermal engine generating the fundamental processes of geomagnetic field plate tectonics and volcanism large amounts of heat are permanently lost at the surface yielding the classic view of the deep earth continuously cooling down contrary to this conventional depiction we propose that the temperature profile in the deep earth has remained almost constant for the last 4 3 billion years the core mantle boundary cmb has reached a temperature of 4400 k in probably less than 1 million years after the moon forming impact regardless the initial core temperature this temperature corresponds to an abrupt increase in mantle viscosity atop the cmb when 60 of partial crystallization was achieved accompanied with a major decrease in heat flow at the cmb then the deep earth underwent a very slow cooling until it reached 4100 k today this temperature at or just below the mantle solidus is suggested by seismological evidence of ultra low velocity zones in the d layer such a steady thermal state of the cmb temperature excludes thermal buoyancy from being the predominant mechanism to power the geodynamo over geological time an alternative mechanism to sustain the geodynamo is mechanical forcing by tidal distortion and planetary precession motions in the outer core are generated by the conversion of gravitational and rotational energies of the earth moon sun system mechanical forcing remains efficient to drive the geodynamo even for a sub adiabatic temperature gradient in the outer core our thermal model of the deep earth is compatible with an average cmb heat flow of 3 0 to 4 7 tw furthermore the regime of core instabilities and or secular changes in the astronomical forces could have supplied the lowermost mantle with a heat source of variable intensity through geological time episodic release of large amounts of heat could have remelted the lowermost mantle thereby inducing the dramatic volcanic events that occurred during the earth s history in this scenario because the moon is a necessary ingredient to sustain the magnetic field the habitability on earth appears to require the existence of a large satellite

nature of magmatism and sedimentation at a columbia active margin insights from combined u pb and lu hf isotope data of detrital zircons from nw india abstract detrital zircons from a palaeoproterozoic quartzite deposited between 1 85 and 1 82 ga in the northern aravalli orogen of nw india show a distinctive age peak of ca 1 85 ga and variable but largely subchondritic ehf1 85 ga between 1 3 and 21 0 corresponding to hafnium model ages of 2 5 to 3 6 ga these data indicate an important period of reworking of ancient eo to neoarchaean strongly heterogeneous continental crust at this time prevalence of ca 1 85 ga subduction related granitoids almost identical u pb age spectra and ehft of detrital zircons in ca 1 85 ga metasedimentary rocks in the aravalli orogen and the inner lesser himalaya indicate similar sediment provenances and thus a geological connection between these two terranes during late palaeoproterozoic all together the data constrain a rapid succession of sedimentation metamorphism and subduction related magmatic activity and support the interpretation of an active geodynamic realm along the entire north indian margin at ca 1 85 ga comparison of detrital zircon data in conjunction with published paleomagnetic data from north india and other crustal blocks of the columbia supercontinent additionally suggest a close affinity of north india with madagascar the cathaysia block of south china and south korea during columbia times

comment on baltic provenance of top famennian siliciclastic material of the northern rhenish massif rhenohercynian zone of the variscan orogen by koltonik et al international journal of earth sciences 2018 107 2645 2669 koltonik et al int j earth sci 107 2645 2669 2018 evidence that the late devonian siliciclastic rocks from the rheno hercynian zone in germany derived from baltica and scandinavian caledonides this finding together with what is known about the provenance of the pulo do lobo and south portuguese zones in portugal and spain reinforces the probability that late devonian basins may have been sourced from distinct terranes placed along the variscan suture our comment intends to underline changes in the provenance of the late devonian basins along the active margin of laurussia and also to improve the correlation model for the variscan tectonic units from sw iberia and germany

geodesy constraints on the interior structure and composition of mars abstract knowledge of the interior structure of mars is of fundamental importance to the understanding of its past and present state as well as its future evolution the most prominent interior structure properties are the state of the core solid or liquid its radius and its composition in terms of light elements the thickness of the mantle its composition the presence of a lower mantle and the density of the crust in the absence of seismic sounding only geodesy data allow reliably constraining the deep interior of mars those data are the mass moment of inertia and tides they are related to mars composition to its internal mass distribution and to its deformational response to principally the tidal forcing of the sun here we use the most recent estimates of the moment of inertia and tidal love number k2 in order to infer knowledge about the interior structure of the mars we have built precise models of the interior structure of mars that are parameterized by the crust density and thickness the volume fractions of upper mantle mineral phases the bulk mantle iron concentration and the size and the sulfur concentration of the core from the bulk mantle iron concentration and from the volume fractions of the upper mantle mineral phases the depth dependent mineralogy is deduced by using experimentally determined phase diagrams the thermoelastic properties at each depth inside the mantle are calculated by using equations of state since it is difficult to determine the temperature inside the mantle of mars we here use two end member temperature profiles that have been deduced from studies dedicated to the thermal evolution of mars we calculate the pressure and temperature dependent thermoelastic properties of the core constituents by using equations state and recent data about reference thermoelastic properties of liquid iron liquid iron sulfur and solid iron to determine the size of a possible inner core we use recent data on the melting temperature of iron sulfur within our model assumptions the geodesy data imply that mars has no solid inner core and that the liquid core contains a large fraction of sulfur the absence of a solid inner is in agreement with the absence of a global magnetic field we estimate the radius of the core to be 1794 65 km and its core sulfur concentration to be 16 2 wt we also show that it is possible for mars to have a thin layer of perovskite at the bottom of the mantle if it has a hot mantle temperature moreover a chondritic fe si ratio is shown to be consistent with the geodesy data although significantly different value are also possible our results demonstrate that geodesy data alone even if a mantle temperature is assumed can almost not constrain the mineralogy of the mantle and the crust in order to obtain stronger constraints on the mantle mineralogy bulk properties like a fixed fe si ratio have to be assumed

on the resolution of density within the earth roughly 30 years have passed since the last publication of a linear resolution calculation of density inside the earth since that time the data set of free oscillation degnerate frequencies has been completely re estimated taking into account the biassing effects of splitting and coupling due to 3d structure this paper presents a new resolution analysis based on the new data and focuses on two particular issues 1 the density jump at the inner core boundary which is important in discussions of the maintenance of the geodynamo and 2 a possible density excess in the lowermost mantle which might be indicative of a hot abyssal layer we find that the density jump at the inner core boundary is 0 82 0 18 mg m 3 which is significantly larger than previously thought we also find little support for an excess density in the lowermost mantle though an increase

constraints from material properties on the dynamics and evolution of earth s core the material properties of the earth s core have been better constrained by recent technical and computational advances the properties imply that the core was once hot but is cooling quickly and the inner core is young

orthogneisses in the spessart crystalline complex north west bavaria silurian granitoid magmatism at an active continental margin the spessart crystalline complex north west bavaria contains two orthogneiss units of granitic to granodioritic composition known as the rotgneiss and haibach gneiss respectively which are structurally conformable with associated metasediments the igneous origin of the rotgneiss is apparent from field and textural evidence whereas strong deformation and recrystallization in the haibach gneiss has obscured most primary textures new geochemical data as well as zircon morphology prove the haibach gneiss to be derived from a granitoid precursor which was chemically similar to the rotgneiss protolith thus suggesting a genetic link between those two rock units both gneiss types have chemical compositions typical of anatectic two mica leucogranites they show characteristics of both i and s type granites rb sr whole rock data on the haibach gneiss provide an isochron age of 407 14 ma ir 0 7077 0 0007 mswd 2 2 which is slightly younger than the published date for the rotgneiss 439 15 ma ir 0 7048 0 0026 mswd 4 9 single zircon dating of six idiomorphic grains using the evaporation method yielded a mean 207pb 206pb age of 410 18 ma for the haibach gneiss and 418 18 ma for the rotgneiss both zircon ages are within analytical error of the rb sr isochron dates and are interpreted to reflect the time of protolith emplacement in silurian times three xenocrystic zircon grains from the rotgneiss yielded 207pb 206pb ages of 2278 12 2490 13 and 2734 10 ma respectively suggesting that late archaean to early proterozoic crust was involved in the generation of the granite from which the rotgneiss is derived although it is assumed that the granitic protoliths of the two gneisses were formed through anatexis of older continental crust the relatively low 87sr 86sr initial ratios of both gneisses may also indicate the admixture of a mantle component the rotgneiss and the haibach gneiss thus document granitic magmatism at an active continental margin during late silurian times

emplacement of synkinematic plutons in the variscan odenwald germany controlled by transtensional tectonics in the odenwald area sw germany an intermediate level of variscan magmatic arc is exposed between 360 and 335 ma the neunkirchen intrusive complex intruded into an active ne sw trending zone of ductile divergent strike shear after the thermal peak of metamorphism but before the emplacement of the magmatic rocks shear zones developed in the wall rocks the microfabrics of these zones infer plastic deformation of feldspar hornblende and quartz and an increasing degree of postkinematic annealing towards the intrusive complex during emplacement and solidification the magmatic rocks experienced bulk strain the intrusive complex locally crosscut the shear zones of the wall rocks but show magmatic and also mylonitic foliations which parallel these zones a change from plastic to brittle behavior of feldspar and amphibole and a varying degree of postkinematic annealing of quartz suggest that in the intrusive complex strike shear continued during cooling in wall rocks and plutonic rocks kinematic indicators imply sinistral displacement in the wall rocks adjacent to the intrusive complex strike shear was combined with normal displacement this suggests that a component of horizontal extension which was associated with strike shear transtension facilitated ascend and emplacement of the magma transtension occurred at the same time when the schwarzwald vosges area in the south of the odenwald was subjected to nw se compression transtension was probably initiated by lateral escape of crustal fragments during overall convergent plate movements transtension is also supposed to be associated with significant uplift of metamorphic rocks

magmatic activity at the silurian devonian boundary in the brunovistulia and malopolska terranes s poland possible link with the rheic ocean closure and the onset of the rheno hercynian basin the age of granophyric diorite from the sosnowiec ig 1 borehole brunovistulia terrane was studied by means of u pb single grain zircon analysis performed on a shrimp sensitive high resolution ion microprobe iie device the isotope ages and provenance of zircons from the emsian tuffs cropping out in the southern part of the holy cross mountains malopolska terrane were also investigated using the same method the age of the diorite intrusion 420 2 ma is comparable with the combined ar ar magnetostratigraphic age of the bardo diabase intrusion from the northern part of the malopolska terrane these intrusions were emplaced during the same event of regional tectonic extension associated with the rheic ocean closure and the onset of processes creating the rheno hecynian basin near the silurian devonian boundary a negative nb anomaly characteristic of both intrusions could be linked with the subduction of the rheic oceanic crust under the se margin of the old red continent emsian magmatic activity in the distant rheno hercynian zone provided several tuff layers in the northern part of the malopolska terrane as can be inferred from zircon ages these tuffs were derived from mafic eruptions that cut sedimentary rocks containing detrital zircons transported from baltica this interpretation fits the existing models of development of the rheno hercynian basin in the emsian

core merging and stratification following giant impact the earth s outermost core is thought to be stratified turbulent mixing experiments suggest that merging between the cores of projectile and planet following the moon forming giant impact could have produced the stratification

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

juvenile crust formation in the northeastern kaapvaal craton at 2 97 ga implications for archean terrane accretion and the source of the pietersburg gold abstract combined u pb and lu hf isotope data of detrital and magmatic zircon grains provide evidence that the murchison greenstone belt ne kaapvaal craton south africa hosts an important archean suture zone which primarily formed by a collision 2 97 ga ago between a back arc system to the north and an evolved terrane the proto kaapvaal craton to the south this model is supported by the observations that igneous rocks of the northern terrane comprising mafic rocks and tonalites of the rooiwater complex and felsic volcanics of the rubbervale formation were both emplaced at about 2 97 ga and show highly superchondritic hft of 4 4 to 5 1 in contrast u pb hf isotope data of detrital zircon grains from quartzitic schists of the murchison unit and the la france formation both part of the southern terrane provide evidence for a southern provenance which was affected by granitoid intrusions accompanied by crust re working at 3 53 3 42 ga hft 1 8 to 4 8 3 30 3 20 ga hft 1 8 to 6 3 and 3 13 3 05 ga hft 1 3 to 5 6 pointing to a connection with the barberton greenstone belt and swaziland a spatial separation of the two terranes prior to 2 97 ga is furthermore supported by the facts that the youngest detrital zircon grains of the southern terrane having ages between 2 99 and 2 97 ga show subchondritic hft between 6 5 and 1 5 in contrast to the highly superchondritic hft obtained from the contemporaneous magmatic rocks of the northern terrane the juvenile character of the rooiwater and rubbervale magmatic rocks along with the occurrence of vms deposits makes them a likely candidate for the source of the gold pyrite bearing conglomerates exposed in the adjacent pietersburg greenstone belt

baltica and gondwana derived sediments in the mid german crystalline rise central europe implications for the closure of the rheic ocean abstract combined u pb and lu hf isotope analysis of detrital zircons reveals that the mid german crystalline rise mgcr contains palaeozoic sediments of distinct provenance in close proximity zircons from a metapelite of the brotterode group were derived from a gondwanan source whereas zircons from the rogis quartzite of the ruhla group point to provenance from baltica brotterode zircons mostly yield ages of 500 720 ma and 2 0 2 1 ga and show an age gap between 1 0 and 1 7 ga which is characteristic of gondwana peri gondwanan detrital zircon populations combined u pb and hf isotope data suggest intense crustal recycling at 2 6 2 9 ga 1 8 2 1 ga and 570 720 ma as well as formation of juvenile crust during the latter two periods in contrast zircons of the rogis quartzite mostly yield ages between 0 9 and 1 8 ga which are typical of southwestern baltica minor age populations at 435 466 and 550 660 ma indicate that the quartzite is younger than late ordovician early silurian and that the baltica derived sediment is contaminated by minor peri gondwanan perhaps avalonia derived detritus minor age populations at 2 0 2 56 2 67 and 2 86 ga additionally point to a svecofennian and or karelian source u pb and hf isotope data imply that the baltica derived zircons were produced mainly through melting of juvenile palaeo to mesoproterozoic crust the data presented here indicate that the mgcr hosts the rheic suture between gondwana and balonia and that this suture zone was closed in a complex sequence of stages from the late silurian onwards

palaeogeography and tectonic structure of allochthonous units in the german part of the rheno hercynian belt central european variscides new information on palaeogeography orogenic evolution tectonic structure and boundaries of allochthonous units in the rheno hercynian belt is based on provenance analyses of clastic sediments and field studies 40k 40ar dating of detrital muscovites proved to be a particularly useful method because cadomian caledonian and early variscan provenances of detrital material can be distinguished cadomian muscovite cooling ages are restricted to allochthonous units whereas caledonian ages dominate within par autochthonous and shortly displaced allochthonous units the largest and uppermost preserved nappe the giesen harz nappe is derived from an oceanic flysch basin which was not reached by caledonian detritus the other allochthonous units form a duplex like structure sandwiched between the giesen harz nappe and par autochthonous units at its base the thick and heterogeneous roof and floor thrusts of this structure were previously often misinterpreted as olistostromes the northern margin of allochthonous units is the steeply dipping horre gommern zone it consists of three sub units derived from deep water areas between the shelf at the southern margin of the old red sandstone continent and an oceanic basin to the south the southeastern part of the duplex structure harzgerode zone shows close affinities to armorican terranes

transformation of a magmatic arc and an orogenic root during oblique collision and it s consequences for the evolution of the european variscides mid german crystalline rise the architecture of the european variscides has been subdivided by kossmat 1927 into paleogeographically coherent units which are presently interpreted as former plate fragments the mid german crystalline rise mgcr separates two fragments rhenohercynian and saxothuringian belts at the site of an inferred plate boundary and reequilibrated orogenic root the commonly favoured model interprets the mgcr as the magmatic arc on saxothuringian crust above a south dipping subduction zone in upper devonian and carboniferous times data from the mgcr the kinematic evolution of the mid european variscides and first order volume balancing suggest a reinterpretation of this unit which challenges classical views on the mgcr as well as on the subdivision of variscan architecture the mgcr is composed of two rock groups with different tectonic identity a lower carboniferous low pressure high temperature magmatic arc association on lower paleozoic basement rests tectonically on a stack of medium pressuremedium temperature rocks of inferred rhenohercynian origin the latter were tectonically accreted to the base of the overriding plate by tectonic underplating the entire process was controlled by oblique convergence this led to regional partitioning of the plate kinematic vector into contractional domains lower rhenohercynian plate and back arc area of the upper saxothuringian plate bulk heterogeneous plate margin parallel extensional domains mgcr and plate margin parallel wrench domains mgcr boundaries during this process material was continually transferred from the lower plate to the upper plate uplifted and exhumed by net crustal extension the concomitant removal of parts of the former arc and the entire orogenic root necessitates a reappraisal of variscan architecture and evolution

new detrital zircon age data reveal the location of the rheic suture in the mid german crystalline zone spessart and odenwald crystalline complexes new detrital zircon age data of metasedimentary rocks from the spessart and odenwald basement mid german crystalline zone variscides revealed results which are not compatible with current tectonic models the previously proposed existence of a tectonic window which includes lower plate rhenohercynian rocks within the upper plate saxothuringian zone in the spessart and odenwald basement does not agree with the results of this study this leads to a new course of the rheic suture and therefore a non coherence of the two major fault zones in these complexes the southern spessart crystalline complex accommodates the rheic suture which is most likely explained by a southward displacement of a whole segment of the mid german crystalline zone this displacement might extend over the ruhla crystalline complex a hitherto unknown age spectrum of a unit in the bollsteiner odenwald was found which might indicate a sliver of unidentified material in the variscan collision zone an unknown magmatic age of 350 ma is reported for igneous intrusions in the saxothuringian zone and can be used as an additional indicator to distinguish between laurussia and gondwana related rocks

collision vs subduction related magmatism two contrasting ways of granite formation and implications for crustal growth earth s continental crust is dominantly made of buoyant felsic igneous material granitoids that were ultimately extracted from the mantle as a result of earth s differentiation since felsic melts are not in chemical equilibrium with the mantle they can originate either from melting of older crustal lithologies or from differentiation of a primitive mantle melt only the latter case will contribute to crustal growth to understand the mechanisms of continental crust growth and differentiation through time it is therefore necessary to unravel the respective contribution of these two different mechanisms in the genesis of granitoid suites in modern earth granitoids are chiefly generated in convergent plate boundaries subduction and collision this paper examines the granitic suites in a late collision environment the variscan french massif central fmc and compares them with the suites found in an oceanic arc we therefore describe and compare two end members sites of granite generation in the fmc several main types of granites are described muscovite and cordierite bearing peraluminous granites resp mpg and cpg contain large amounts of inherited zircons and their chemistry demonstrates that their sources were older crustal material resp metasediments and metaigneous on the other hand potassic calc alkaline granites kcg associated to potassic diorites vaugnerites do not contain inherited zircons and ultimately derive from the vaugnerites the vaugnerites in turns form by partial melting of a mantle contaminated by the regional crust therefore although they are isotopically similar to the crust the kcg are net contributors to crustal growth thus we conclude that although late orogenic settings are dominated by crustal melting and recycling they may be sites of net crustal growth even though this is not visible from isotopes only in contrast arc granitoids are purely or almost purely mantle derived however the preservation potential of arcs is much smaller than the preservation of late orogenic domains such that at the scale of a whole orogenic belt late orogenic magmatism is probably as important as arc magmatism finally we speculate that the situation may have been similar in the archaean or even more skewed towards late orogenic sites or similar environments dominated by melting of a altered mafic protocrust owing to the hotter mantle and less stable subductions during that period

geodynamic evolution of the european variscan fold belt palaeomagnetic and geological constraints the variscan fold belt of europe resulted from the collision of africa baltica laurentia and the intervening microplates in early paleozoic times over the past few years many geological palaeobiogeographic and palaeomagnetic studies have led to significant improvements in our understanding of this orogenic belt whereas it is now fairly well established that avalonia drifted from the northern margin of gondwana in early ordovician times and collided with baltica in the late ordovician early silurian the nature of the gondwana derived armorican microplate is more enigmatic geological and new palaeomagnetic data suggest armorica comprises an assemblage of terranes or microblocks palaeobiogeographic data indicate that these terranes had similar drift histories and the rheic ocean separating avalonia from the armorican terrane assemblage closed in late silurian early devonian times an early to mid devonian phase of extensional tectonics along this suture zone resulted in formation of the relatively narrow rhenohercynian basin which closed progressively between the late devonian and early carboniferous in this contribution we review the constraints provided by palaeomagnetic data compare these with geological and palaeobiogeographic evidence and present a sequence of palaeogeographic reconstructions for these circum atlantic plates and microplates from ordovician through to devonian times

array analyses of smks waves and the stratification of earth s outermost core abstract we perform array analyses of smks waves in order to investigate the vp structure of the earth s outermost core for earthquakes recorded by broadband seismometer networks in the world we measure differential travel times between s3ks and s2ks between s4ks and s3ks and between s5ks and s3ks by array techniques the differential times are well fit by a vp model of the earth s outermost core khomc kaneshima and helffrich 2013 differential slownesses of s4ks and s2ks relative to s2ks are also measured for the highest quality data the measured slownesses with unique sensitivity to the outer core 200 400 km below the cmb are matched by khomc these observations consolidate the evidence for the presence at the top of the outer core of a layer that has a distinctively steeper vp gradient than the bulk of the outer core we invert new smks differential time data set by a tau p method and attempt to refine the vp profile of khomc the essential features of khomc are preserved after the model refinement however the newly estimated layer thickness is nearly 450 km which is thicker than that of khomc the vp anomalies relative to prem for the depths 400 800 km below the cmb are less than 0 03 km s consistent with the degree of agreement between different vp models for the depth range

age of intrusion and rapid cooling of the frankenstein gabbro odenwald sw germany evidenced by40ar 39ar and single zircon207pb 206pb measurements the frankenstein gabbro complex in the northern odenwald fr germany is one of the hercynian plutonic bodies of the saxothuringian zone in the variscan belt 87sr 86sr isotopic investigations on pyroxene 40ar 39ar age determinations on hornblendes plagioclases biotites and pyroxenes and207pb 206pb dating on single zircon crystals have been carried out

the timing of metamorphism in the odenwald spessart basement mid german crystalline zone new in situ electron microprobe monazite and white mica 40ar 39ar step heating ages support the proposition that the odenwald spessart basement mid german crystalline zone consists of at least two distinct crustal terranes that experienced different geological histories prior to their juxtaposition the monazite ages constrain tectonothermal events at 430 43 ma 349 14 ma 331 16 ma and 317 12 ma 316 4 ma and the 40ar 39ar analyses provide white mica ages of 322 3 ma and 324 3 ma granulite facies metamorphism occurred in the western odenwald at c 430 and 349 ma and amphibolite facies metamorphism affected the eastern odenwald and the central spessart basements between c 324 and 316 ma we interpret these data to indicate that the otzberg michelbach fault zone which separates the eastern odenwald spessart basement from the western odenwald basement is part of the rheic suture which marks the position of a major variscan plate boundary separating gondwana and avalonia derived crustal terranes the age of the carboniferous granulite facies event in the western odenwald overlaps with the minimum age of eclogite facies metamorphism in the adjacent eastern odenwald the granulite and eclogite facies rocks experienced contrasting pressure temperature paths but occur in close spatial proximity being separated by the rheic suture as high pressure and high temperature metamorphisms are of similar age we interpret the odenwald spessart basement as a paired metamorphic belt and propose that the adjacent high pressure and high temperature rocks were metamorphosed in the same subduction zone system juxtaposition of these rocks occurred during the final stages of the variscan orogeny along the rheic suture

time frame of 753 680 ma juvenile accretion during the sao gabriel orogeny southern brazilian shield abstract the time frame of the three main geological events in the neoproterozoic cambai complex juvenile sao gabriel belt in the southern brazilian shield is established by integrating field mapping back scattered electron imaging and sensitive high resolution ion microprobe shrimp ii u pb dating of 96 zircon crystals from nine granitic and metasedimentary rock samples the three events are 1 voluminous flat lying paragneisses cambaizinho complex and orthogneisses vila nova gneisses between 735 and 718 ma 2 tonalite trondhjemite association lagoa da meia lua suite between 710 and 690 ma and 3 late granodiorite intrusions sanga do jobim suite at 680 ma an additional older volcanic event campestre formation was dated at 753 ma these results are most significant for the reconstruction of west gondwana

on cooling of the earth s core abstract we have constructed a self consistent model for cooling of the earth s core in which the thermal history of the core is computed as a function of the time evolution of the heat flux delivered to the mantle across the core mantle boundary the temperature profile in the convecting core is first assumed to be adiabatic and its evolution in time is calculated with the only constraint that energy be globally conserved when the temperature at the centre drops below the freezing point of the core alloy the inner core starts growing and cools by conduction it is found that it cannot have reached its present size in more than 1 7 billion years if the heat flux delivered to the mantle becomes less than that conducted down the adiabat the temperature profile becomes subadiabatic in a shell at the top of the core through which heat is evacuated by conduction although it is stable against thermal convection this shell is not necessarily stagnant and may be the seat of motions owing to compositional convection

protolith ages and timing of deformation in the eastern marginal part of the sveconorwegian orogen southwestern sweden abstract u pb zircon and titanite ages from variably metamorphosed igneous rocks in the eastern marginal part of the sveconorwegian orogen eastern segment north of lake vanern sweden suggest that these rocks belong to the younger c 1 71 1 65 ga igneous suite of the c 1 85 1 65 ga transscandinavian igneous belt tib two porphyritic meta granites and one isotropic monzonite yield u pb zircon ages of 1661 27 1674 7 and 1674 7 ma respectively these ages support earlier interpretations that the eastern segment north of lake vanern contains tectonically reworked tib rocks and that there is no major lithological discontinuity either across the sveconorwegian frontal deformation zone or within the eastern segment igneous brown coloured titanites from five samples yield similar u pb ages as the zircons in contrast colourless and oblate shaped titanites from the western penetratively deformed parts of the eastern segment give concordant ages of 976 4 and 956 6 ma further to the east similar titanite from both a penetratively deformed meta granite and a ductile shear zone within a porphyritic quartz monzonite are strongly discordant close to late sveconorwegian lower intercept ages this type of titanite is interpreted to be syntectonic and formed during the upper greenschist east to amphibolite west facies fabric forming event in the eastern segment since the brown igneous titanites and the zircons share a common igneous origin and the single type of metamorphic titanites are either concordant or strongly discordant towards late sveconorwegian intercept ages it is inferred that no major tectonothermal event occurred between the time of tib emplacement and the late sveconorwegian tectonothermal reworking pre sveconorwegian palaeo to mesoproterozoic deformational and metamorphic events gothian which have been inferred west of and further south within the eastern segment appear to be absent in the northern part of this crustal unit

early carboniferous extension in east avalonia 350 my record of lithospheric memory abstract despite reactivations during variscan and alpine orogenies and the opening of the northern atlantic avalonia is one of the few regions where the initial mid paleozoic basin structure is still recognisable largely intact and well studied its kinematics and dynamics remain however largely unknown in particular in view of the successive late paleozoic to recent evolution of the basin consequently the importance of the mid palaeozoic tectonic evolution and structural controls are often overlooked and poorly understood in basin studies in this paper we reassess the importance of mid palaeozoic tectonics on subsequent sedimentary basin evolution of north western europe to this end we analyse the dynamics of early variscan extension in avalonia based on the integration and re evaluation of available geophysical and geological data from lithosphere to basin scales based on a revised crustal map of the thor suture zone we present a new paleo tectonic reconstruction and tectonic scenario for the devonian carboniferous rifting these findings are key for a better understanding of long lived tectonic segmentation and post rifting deformation phases our findings indicate that the structural grain of many crustal fault dominated sedimentary basin structures such as the north sea central graben were created in the early carboniferous consequently the main basement structuration of northwest europe was completed before the variscan orogeny and successive post variscan extension and inversion phases reactivated the existing basement structures without creating major new fault groups incorporation of the paleozoic structural grain allows for a consistent tectonic framework for the mesozoic contributing to fundamental understanding of basin evolution from our tectonic framework analysis avalonia therefore stands out as a fine example of long lived lithosphere memory spanning over 350 my of structural control in geodynamic evolution

causes and consequences of outer core stratification abstract the earth s outer core appears to be compositionally layered exotic mechanisms such as an original chemically layered core preserved from the earth s accretionary period or compositionally different core material delivered by a moon creating impactor are conceivable but require a core whose outermost part has been stratified throughout core history relying on unknowable processes to achieve barodiffusion and core mantle reaction lead to layers significantly thinner than observed we show that a balance of mass transferred from the inner core to the top of the outer core is possible and that the stratification could arise as a byproduct of light element accumulation however if a subadiabatic thermal gradient at the top of the outer core exists that quells radial flow it could serve as a witness of light element accumulation by preventing mixing with the convecting part of the core the temperature difference through a subadiabatic layer could be 80 300 k and carry heat fluxes through the core mantle boundary of 0 5 23 tw given uncertainty in core properties

subduction related magmatism of late ordovician age in eastern england deep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the caledonian basement in eastern england the isotopic compositions of these rocks reveal that many of them are of late ordovician age 440 460 ma and their geochemical compositions suggest calc alkaline affinities the intermediate diorite tonalite plutonic rocks are associated with a prominent northwest southeast trending belt of aeromagnetic anomalies extending from derby to st ives hunts which is interpreted to work the plutonic core of a calc alkaline magmatic arc it is inferred that this arc was generated by the subduction of oceanic lithosphere possibly from the tornquist sea in a south or southwest direction beneath the midlands microcraton in late ordovician times the age and geochemical composition of concealed ordovician volcanic rocks in eastern england and hypabyssal intrusions of the midlands minor intrusive suite in central england is compatible with such a hypothesis

improving seismic resolution of outermost core structure by multichannel analysis and deconvolution of broadband smks phases the presence of a thin 12km layer atop the outermost core has important implications for the geodynamic and geomagnetic nature of the earth but detecting such a layer is difficult smks seismic phases which traverse the mantle as an s wave and reflect m 1timesfromtheundersideofthecore mantleboundary cmb offerameanstotestproposedmodelssincetheyareextremely sensitive to the velocity structure of the outermost core to improve seismic resolution in this region we have developed and validated a modified vespagram slant stack technique that makes use of phase independent amplitude envelope traces confidence limits on arrival time and slowness estimates are obtained by bootstrap resampling in order to mitigate the effects of waveform complexity and facilitate comparison between observed and modeled waveforms we have used a simple deconvolution method similar to techniques used in exploration seismology we have applied these methods to high quality broadband recordings of three deep focus earthquakes recorded by seismic arrays in canada some of our measurements have turning depths 190km in the outer core a region of sparse coverage in previous global compilations of smks measurements based on the analysis of travel times our data show that the p wave velocity of the outermost core is prem like until the outer 150km or less where it becomes much slower than prem and most standard earth models additionally amplitudes of s3ks s4ks phases relative to skksac are significantlylargerthanthosepredictedbystandardmodels usingreflectivitysyntheticseismogramsweshowthatnopreviousearth

provenance of upper devonian clastic meta sediments of the bollstein odenwald mid german crystalline zone variscides detrital zircons separated from paragneisses of the northern bollstein odenwald mid german crystalline zone variscides yielded cambrian to upper devonian u pb ages the age of the youngest detrital zircon population 371 3 ma and the lower carboniferous metamorphic overprint indicate an upper devonian depositional age of the paragneiss protolith the age spectra of detrital zircons suggest the latter to be derived from 1 ordovician igneous rocks of the saxothuringian zone 2 a late cadomian magmatic arc tepla barrandian unit and 3 a silurian devonian magmatic arc cadomian igneous activity is also documented by cambrian zircon cores in lower to middle devonian detrital zircons meso and paleoproterozoic detrital zircons which are typical for the old red continent and the rhenohercynian zone are entirely lacking the restricted palaeozoic detrital zircon age spectrum is attributed to a silurian devonian intra arc or trench setting both the lack of mesoproterozoic detrital zircons and the striking similarity of the u pb ages of the detrital zircon obtained from the bollstein odenwald with u pb ages from crystalline rocks of the saxothuringian basement rules out that the bollstein odenwald is forming a tectonic window rhenohercynian lower plate inside the mid german crystalline zone saxothuringian upper plate