recovering shear wave anisotropy of the lower crust the influence of systematic errors on travel time inversion studies of seismic anisotropy in situ can help to discriminate between different rock types for the lower crust in this context we investigate the sensitivity of an iterative linearized 3 d travel time inversion scheme for transversely isotropic media with respect to two types of systematic errors wrong velocities and interface topography of the hanging wall of the lower crust the computations simulate realistic field conditions such as found for the variscan crust at the urach geothermal anomaly the study focusses on the possible information content of split s m s arrivals observed along two orthogonal expanding spread profiles it ensues that an imperfect knowledge of the layer geometry is of minor importance compared to errors in the velocities of the hanging wall in particular upper crust anisotropy has to be considered carefully generally the anisotropy of transversely polarized shear waves sh waves was recovered with higher accuracy than the anisotropy of vertically polarized shear waves sv waves

shear wave anisotropy of laminated lower crust beneath urach sw germany a comparison with xenoliths and with exposed lower crustal sections in order to investigate the laminated lower crust beneath urach sw germany we analysed 1 the anisotropy and reflectivity of seismic shear waves and 2 the composition of xenoliths samples we conclude that the directional dependence of shear waves of the lower crust is effectively transversely isotropic with a maximum velocity difference of 3 to 6 both seismic signature and petrological information are compared with reference profiles deduced from the exposed lower crustal sections of ivrea and calabria italy the comparison based on synthetic seismograms shows that the observed combination of shear wave anisotropy and reflectivity pattern corresponds to alternating layers containing a high amount of metapelites such as found in the calabria profile and in the val strona subsection of ivrea the main portion of the whole rock anisotropy is caused by the lattice preferred orientation of anisotropic minerals so called intrinsic anisotropy the effect of alternating rock layering so called layering anisotropy contributes only a minor portion to the whole rock anisotropy layered mafic intrusions such as found in the val sesia subsection of ivrea are nearly isotropic both seismic anisotropy and xenoliths indicate that mafic layers do not play a major role for the laminated lower crust at urach they may be restricted to a thin layer at the crust mantle boundary

two magma series and associated ore deposit types in the permian emeishan large igneous province sw china the late middle permian 260 ma emeishan large igneous province in sw china contains two magmatic series one comprising high ti basalts and fe rich gabbroic and syenitic intrusions the other low ti basalts and mafic ultramafic intrusions the fe rich gabbros are spatially and temporally associated with syenites each series is associated with a distinctive type of mineralization the first with giant fe ti v oxide ore deposits such as panzhihua and baima the second with ni cu pge sulfide deposits such as jinbaoshan limahe and zhubu new shrimp zircon u pb isotopic data yielded 263 3 ma for the limahe intrusion 261 2 ma for the zhubu intrusion and 262 2 ma for a syenitic intrusion these new age dates together with previously reported shrimp zircon u pb ages suggest that all these intrusions are contemporaneous with the emeishan flood basalts and formed during a major igneous event at ca 260 ma the oxide bearing intrusions have higher al2o3 feo as total iron and total alkalis na2o k2o but lower mgo than the sulfide bearing intrusions all intrusions are variably enriched in lree relative to hree the oxide bearing intrusions display positive nb and ti anomalies and in certain cases negative zr hf anomalies whereas the sulfide bearing intrusions have obvious negative nb and ti anomalies a feature of crustal contamination individual intrusions have relatively small ranges of nd t values all the intrusions however have nd t values ranging from 3 9 to 4 6 and initial 87sr 86sr ratios from 0 7039 to 0 7105 the syenites have very low mgo 2 wt but highly variable fe2o3 2 5 to 13 wt with initial 87sr 86sr ratios ranging from 0 7039 to 0 7089 magmas from both series could have derived by melting of a heterogeneous mantle plume the high ti series from a fe rich more fertile source and the low ti series from a fe poor more refractory source in addition the low ti series underwent significant crustal contamination the two magma series evolved along different paths that led to distinct mineralization styles

the effect of crustal anisotropy on reflector depth and velocity determination from wide angle seismic data a synthetic example based on south island new zealand when deriving velocity models by forward modelling or inverting travel time arrivals from seismic refraction data a heterogeneous but isotropic earth is usually assumed in regions where the earth is not isotropic at the scale at which it is being sampled the assumption of isotropy can lead to significant errors in the velocities determined for the crust and the depths calculated to reflecting boundaries laboratory velocity measurements on rocks collected from the haast schist terrane of south island new zealand show significant up to 20 compressional p wave velocity anisotropy field data collected parallel and perpendicular to the foliation of the haast schist exhibit as much as 11 p wave velocity anisotropy we demonstrate using finite difference full wavefield modelling the types of errors and problems that might be encountered if isotropic methods are used to create velocity models from data collected in anisotropic regions these reflector depth errors could be as much as 10 15 for a 10 km thick layer with significant 20 p wave velocity anisotropy the implications for south island new zealand where the problem is compounded by extreme orientations of highly anisotropic rocks foliation which varies from horizontal to near vertical are considered finally we discuss how the presence of a significant subsurface anisotropic body might manifest itself in wide angle reflection refraction and passive seismic datasets and suggest ways in which such datasets may be used to determine the presence and extent of such anisotropic bodies d 2002 elsevier science b v all rights reserved

inversion technique for recovering the elastic constants of transversely isotropic materials a least squares iterative inversion technique has been developed for the determination of the elastic parameter of any transversely isotropic modeling material in the laboratory for most applications in petroleum geophysics the elastic parameter is very important and is the crucial anisotropic parameter for near vertical p wave propagation despite the potential importance of in seismic exploration and for resolution in an anisotropic medium the conventional procedures adopted in estimating its value unfortunately are faced with many ambiguities and the reliability of its measurement is doubtful prior to the development of this technique the anisotropic inverse modeling technique finds the best fitting solution to optimize the accuracy of the results presented in this paper analytical rather than numerical differentiations were implemented and the modeling procedures allow for controlled iterative adjustments in resolving the parameter inversion of the first arrival traveltimes obtained

comments on liquid immiscibility and the evolution of basaltic magma journal of petrology 48 2187 2210 veksler et al 2007 have conducted a series of experiments that have led them to conclude that the evolving skaergaard magma reached a two liquid field near middle zone much earlier than all previous studies have indicated this conclusion is based on an incorrect extrapolation of questionable experimental results and is clearly inconsistent with evidence found in the field relations the nature of late differentiates of the iron rich skaergaard magma has been a subject of considerable interest since they were first described by wager and his co workers wager deer 1939 pp 209 213 wager brown 1968 pp 137 143 three principal types of granophyre were recognized as follows

magma chamber processes in the tellnes ilmenite deposit rogaland anorthosite province sw norway and the formation of fe ti ores in massif type anorthosites the origin of igneous fe ti oxide ores associated with massif type anorthosites is investigated through a detailed study of the world class tellnes ilmenite deposit part of the late proterozoic 930 920 ma amc series of the rogaland anorthosite province sw norway more than 100 samples from drill cores reveal significant petrographical and compositional variations within the ore body four zones are defined based on variations in modal proportions and cumulus mineral assemblages the lower and upper central zones and the lower and upper marginal zones plagioclase and whole rock compositions discriminate the zones and display patterns interpreted as a result of mixing of either plagioclase ilmenite or plagioclase ilmenite orthopyroxene olivine cumulates with a melt of ferrodioritic jotunitic composition with a content decreasing from 80 to 20 from the margins to the central part of the ore body phase diagrams for a jotunitic parental magma reproduce the crystallization sequence at 5 kb the orthopyroxene olivine liquidus boundary is a peritectic in the bjerkreim sokndal layered intrusion and a cotectic in tellnes and this explains the differences in the sequence of crystallization of the two intrusions the high concentration of ilmenite well above cotectic proportions resulted from gravity sorting in the tellnes ore body which represents the lower part of a larger magma chamber uniform sr isotope ratios do not support magma mixing the cryptic layering of the ore body precludes injection as a crystal mush but favours in situ crystallization from an evolving magma in a sill like magma chamber the present trough shape and mineral orientations result from deformation during gravity induced subsidence and by up doming of the anorthosite fractional crystallization of a tio2 rich magma with ilmenite as an early liquidus mineral and plagioclase buoyancy are the principal mechanisms responsible for the formation of fe ti deposits in proterozoic massif type anorthosites

shear wave anisotropy of laminated lower crust at the urach geothermal anomaly abstract deep seismic reflection studies have shown that lamellae are a widespread reflectivity pattern of the lower crust of the central european variscan belt this pattern has been interpreted inter alia as alternating subhorizontal layering of mafic and felsic rocks implying a tectonic process of structural and textural ordering consequently laminated lower crust should be elastically anisotropic the specific type of anisotropy should provide some insight into the mineral composition and the preferred orientation of minerals in the lower crust we have investigated this problem in the area of the urach geothermal anomaly south germany where a classical example of lower crust lamellae is found a restricted range of subsurface points was probed in a controlled source expanding spread seismic experiment with two orthogonal azimuths of observation up to 90 km source geophone offset both p and s waves were recorded with 3 component geophones at 80 140 m geophone spacing based on polarization analysis and traveltime interpretation the following results were obtained 1 s wave splitting is observed only for sms arrivals not for shallower reflections implying that the lower crust is anisotropic 2 the type of anisotropy is quasihexagonal transversely isotropic implying that there is no preferred mineral orientation within the horizontal plane 3 the coefficient of s wave anisotropy v max v min v min is estimated at 6 13 for sv type waves the sh wave velocity shows only small variation with offset 4 the observed relation between direction and velocity of s wave propagation can be explained by mafic rocks containing a high amount of orthopyroxene minerals horizontally aligned in the pure shear stress regime

precise age determination of mafic and felsic intrusive rocks from the permian emeishan large igneous province sw china abstract radiogenic isotopic dating using different mainly micro beam analyses techniques of rocks from the emeishan large igneous province elip has yielded a range of ages from the capitanian to the early triassic in contrast estimates based on paleontological and paleomagnetic data suggest the elip was emplaced rapidly 2 ma and that volcanism ended by 257 ma new zircon ca tims u pb ages that have superior precision compared to ages from micro beam analyses were obtained from strategic intrusive rocks of the panxi region inner zone of the elip the huangcao 258 9 0 7 ma daheishan 259 1 0 5 ma woshui 259 6 0 5 ma and cida 258 4 0 6 ma syenitic and granitic plutons and three mafic dykes 259 2 0 4 ma 259 5 0 8 ma 257 6 0 5 ma yielded a narrow range of ages between 257 ma and 260 ma the new results are consistent with the estimates from magneto biostratigraphic data and a rapid emplacement model the new wuchiapinqian ages of the huangcao and daheishan plutons suggests that magmatism may have lasted significantly less than 10 ma as previously suggested and the precise ages of the mafic dykes refute the hypothesis that emeishan high ti basalts represent the waning stages of the elip magmatism the short duration of magmatism also implies that degassing of the host sediments mostly carbonates and thus releasing of greenhouse gasses occurred within a substantially shorter interval than previously thought which significantly changes the loading of atmosphere per time unit the latter corollary potentially has severe environmental effects that may have contributed to causing the end guadalupian mass extinction

platinum group element geochemistry of the hongge fe v ti deposit in the pan xi area southwestern china mafic and ultramafic intrusions in the pan xi area along the western margin of the yangtze block southwestern china are spatially associated with the late permian emeishan flood basalts of the emeishan large igneous province the hongge layered intrusion is one of the plutonic bodies of this province and hosts a giant fe v ti deposit this intrusion has three zones a lower olivine clinopyroxenite zone a middle clinopyroxenite zone and an upper gabbro zone each of these zones consists of one or two compositional cycles which have distinct mg values tio2 concentrations and total ree contents the middle clinopyroxenite zone and upper gabbro zone contain thick 14 84 m magnetite mineralized layers samples from the lower olivine clinopyroxenite zone and middle clinopyroxenite zone of the hongge intrusion are enriched in platinum and palladium relative to iridium and ruthenium rocks of the lower olivine clinopyroxenite zone have pd ir ratios 1 8 22 3 lower than those of the middle clinopyroxenite zone 6 2 to 83 in its lower part and 3 6 to 49 in its upper part the pd ir ratios increase progressively upwards in each cyclic unit chromite is the major phase controlling concentrations of iridium and ruthenium the cu pd ratios at the bottom of each cyclic unit are close to that of the mantle and increase upwards this variation suggests that each cyclic unit represents a new batch of magma and sulfide mineral segregation removes pge platinum group elements ni and cu each cyclic unit in the hongge layered intrusion might have resulted from crystal fractionation and mixing between a primary and evolved magma the high cu pd ti pd ni pd and cu ir ratios of the intrusion suggest that the sulfide mineral segregation may have played an important role in pge differentiation if this interpretation is correct then there is a potential to find economic pge rich horizon in the hongge type intrusions in the region

abundant fe ti oxide inclusions in olivine from the panzhihua and hongge layered intrusions sw china evidence for early saturation of fe ti oxides in ferrobasaltic magma abundant fe ti oxide inclusions in cumulus olivine fo77 81 from the panzhihua and hongge intrusions emeishan large igneous province sw china document the first evidence for early crystallization of fe ti oxides in ferrobasaltic systems in nature the intrusions also contain significant stratiform fe ti v oxide ores the oxide inclusions are sub rounded or irregular range from 5 to 50 m in diameter and are dominated by either titanomagnetite or ilmenite the fact that the inclusions are either titanomagnetite or ilmenite dominant suggests that they are trapped crystals instead of immiscible oxide melt formed during growth of the host olivine the absence of other silicate phases in the inclusion bearing olivine is difficult to reconcile with a possible xenocrystic origin of the oxide inclusions these oxide inclusions are thus interpreted to be cumulus minerals crystallized together and trapped in olivine from the same parental magma in addition to fe ti oxides some inclusions contain amphibole biotite fluorapatite that might have formed by reaction of trapped hydrous liquid with the host olivine numerical modeling of high ti emeishan basalts using the melts program successfully simulates early crystallization of olivine fo81 and fe ti spinel in the presence of a moderate amount of h2o 1 5 wt under pressure and fo2 conditions generally pertinent to the panzhihua and hongge intrusions the modal mineralogy of the oxide inclusions is in good agreement with the bulk compositions of the ore as inferred from whole rock data in a given intrusion this is consistent with the interpretation that the stratiform oxide ores in the intrusions formed by accumulation of fe ti oxide crystals that appeared on the liquidus with olivine and clinopyroxene

seismic velocities and anisotropy of the lower continental crust a review seismic anisotropy is often neglected in seismic studies of the earth s crust since anisotropy is a common property of many typically deep crustal rocks its potential contribution to solving questions of the deep crust is evaluated the anisotropic seismic velocities obtained from laboratory measurements can be verified by computations based on the elastic constants and on numerical data pertaining to the texture of rock forming minerals for typical lower crustal rocks the influence of layering is significantly less important than the influence of rock texture surprisingly most natural lower crustal rocks show a hexagonal type of anisotropy maximum anisotropy is observed for rocks with a high content of aligned mica it seems possible to distinguish between layered intrusives and metasediments on the basis of in situ measurements of anisotropy which can thus be used to validate different scenarios of crustal evolution

mineral compositional constraints on petrogenesis and oxide ore genesis of the late permian panzhihua layered gabbroic intrusion sw china a systematic study of mineral compositions has been carried out on stratigraphic sections through the panzhihua intrusion a layered gabbroic sill of late permian age that hosts significant magmatic fe ti v oxide deposits in the emeishan large igneous province sw china the intrusion which is 19 km long and 2 km thick is divided into a marginal zone mgz lower zone lz middle zone sub zones mza and mzb and upper zone uz from the base upwards compositions of the most primitive cumulus olivine fo81 and plagioclase an73 found in the intrusion suggest that the parental magma was similar to the mg rich end member of the coeval high ti basalts in the region two reversals in terms of mineral compositions are found in the intrusion one in the lower mza and the other at the transition between the mzb and the uz the first reversal is marked by a gradual increase in the an content of plagioclase an60 to an70 over a 100 m vertical interval the other is characterized by abrupt changes in the compositions of olivine fo28 to fo70 clinopyroxene mg 51 to 75 and plagioclase an24 to an51 over a 20 m vertical interval these suggest that the panzhihua intrusion opened at least twice for recharge of more primitive magmas strong depletion of incompatible trace elements such as zr in the cumulate sequence without corresponding enrichment in any border series is suggested to be evidence for significant loss of residual liquid at a late stage during solidification of the intrusion compared to other well studied layered intrusions the panzhihua intrusion contains fe ti oxides crystallized at a high temperature consistent with evidence obtained in earlier studies early appearance of liquidus fe ti oxides in the panzhihua magma is most likely a combined effect of a rather high degree of initial oxidation and elevated volatile fugacity

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

an interpretation of wide angle compressional and shear wave data in southwest germany poisson s ratio and petrological implications shear wave velocity especially when used with compressional wave velocity is an important constraint on estimates of the composition and physical state of the continental lithosphere we present shear velocity s models derived from high quality s wave data along three profiles in southwest germany which combine with existing p wave velocity p models to give poisson s ratio in the crust and uppermost mantle we then construct a laterally varying petrological model of the crust by comparing our p and s models with published laboratory measured rock velocities in general poisson s ratio is 0 25 in the uppermost crust 0 22 0 23 in the mid crust but reaching a low of 0 15 in the black forest low p zone and varies laterally from 0 24 to 0 30 in the lower crust the average poisson s ratio of the whole crust is everywhere about 0 25 the laminated signature of the lower crust prominent on reflection and p wave refraction data is absent on the s wave refraction data implying a strong high low alternation of poisson s ratio in the lower crust this suggests that the lower crustal laminae represent mafic silicic compositional layering for example basic sills in an originally more quartz rich lower crust rather than alternating zones of high and low pore pressure there is no evidence for a shear wave low velocity zone lvz in the black forest mid crust despite the presence of a strong p wave lvz this suggests high quartz content and the presence of pore fluids at low not high pore pressure a clear p to s converted moho reflection pm s is visible on several shots indicating that the moho is at least locally a first order discontinuity no shear wave refractions from the upper mantle are present even where strong p wave refractions are observed possibly indicating an increase of poisson s ratio with depth in the upper mantle the petrological modeling indicates that the upper and middle crust are probably of granitic composition that the mid crustal low p zones have high quartz content and that the lower crust probably consists of granulites of laterally varying bulk composition from granodioritic to gabbroic the lower crust is more mafic in areas of high reflection density on seismic reflection profiles suggesting that the laminations are caused by mafic intrusions into the lower crust either prior to the variscan orogeny or during tertiary volcanic activity

plagioclase content of cyclic units in the bushveld complex south africa the upper critical zone of the bushveld complex south africa has been divided into so called cyclic units ideally they should consist of from the base upward layers of chromitite pyroxenite norite and anorthosite some hypotheses for their origin suggest that they result from the addition and mixing of a magnesian magma having orthopyroxene or olivine as liquidus mineral these models predict that the bulk cumulate composition in a cyclic unit formed from such magma ought to contain excess orthopyroxene to plagioclase relative to their cotectic proportions an hypothesis tested here all rocks investigated here from the upper critical zone at impala platinum mine are mixtures of cumulus plagioclase and orthopyroxene except for the chromitites with very minor intercumulus minerals mainly clinopyroxene hence the proportion of plagioclase can be determined by measurement of the density of a sample the density of every piece of continuous bore core from the upper group 2 ug2 and merensky cyclic units has been determined and the proportion of plagioclase calculated for the bastard cyclic unit estimates of the proportion of plagioclase have been made based on published modal and chemical analyses vertical summation of the proportion of plagioclase indicates that these three cyclic units ug2 merensky and bastard respectively contain 64 74 and over 80 plagioclase by weight for the merensky and bastard cyclic units such proportions exceed that of the plagioclase orthopyroxene cotectic and could not have been produced by processes involving magnesian magma

vertical seismic profile synthetics by dynamic ray tracing in laterally varying layered anisotropic structures dynamic ray tracing drt is important in evaluating high frequency seismic wave fields in complicated structures two formulations of the drt equations for inhomogeneous anisotropic media are presented one of them is represented by the classical drt system suggested by cerven 15 years ago both systems are specified in cartesian coordinates the drt equations are supplemented with formulae for the transformation of drt across a smoothly curved interface between two inhomogeneous anisotropic media cerven s formulation of the drt is applied to the computation of vertical seismic profile vsp synthetics the results of drt are used for the evaluation of the geometrical spreading and of the coefficients of the paraxial ray approximation for travel times and ray amplitudes in addition the drt is also used in the interval ray tracing procedure a procedure searching for rays starling from the source and terminating in a specified interval on a profile results of numerical modeling of vsp measurements in a three dimensional laterally varying structure consisting of isotropic and anisotropic layers separated by curved interfaces are presented ray diagrams of selected elementary waves time distance curves and multisource three component vsp synthetics generated for two different source locations calculated for the anisotropic model are compared with the results determined for a reference isotropic model the latter is obtained by averaging phase velocities of the anisotropic model this comparison clearly shows the effects of anisotropy and the lateral variation of the model on seismic wave fields the reliability of the ray synthetics is briefly discussed

seismic refraction investigation of the black forest abstract within the framework of site surveys of the deep continental drilling program ktb deep seismic sounding experiments were carried out in the black forest southwest germany in august 1984 these site surveys comprised seismic refraction as well as seismic reflection measurements this paper will concentrate on the interpretation of the refraction data which were observed along a 240 km long line approximately following the morphological axis of the black forest in a n s direction and extending in the south into the swiss molasse basin from the available seismic refraction data a detailed velocity depth model of the crust and uppermost mantle was derived a clear phase refracted in the basement with a velocity of 5 9 km s is observed for all shots this phase is followed by a reflection from the upper boundary of a low velocity zone this zone is very accentuated under the northern and central black forest and is characterized by a velocity decrease from 6 2 to 5 4 km s between depths of about 8 and 14 km towards the south the velocity inversion gradually loses its intensity under the center of the southern black forest velocities of about 6 km s prevail throughout the upper crust the lower crust which starts at the lower boundary of the low velocity zone shows a very complicated response in the record sections due to long reverberations between travel times of 1 5 3 5 s reduced by 6 0 km s at an epicentral distance of approximately 30 70 km a classical phase correlation is not possible based on a combined interpretation of near angle and wide angle reflection data the lower crust is characterized by a stack of thin layers with alternating high and low velocities the average velocity of the laminated zone is 6 7 km s the reflection from the moho at a depth of 25 26 km is the most prominent phase at epicentral distances greater than 60 km

a three dimensional crustal model of southwest germany derived from seismic refraction data abstract from densely covered seismic refraction data obtained in 1978 urach experiment and 1984 schwarzer zollern wald experiment and from seismic reflection data and results from previous refraction investigations a three dimensional crustal model of southwest germany was derived travel time and amplitude information of seismic refraction data were interpreted with two dimensional forward modeling ray tracing to calculate two crustal cross sections in southwest germany these results fill a gap in the existing data and enabled the construction of a detailed three dimensional crustal model while seismically the upper crust is laterally homogeneous 5 9 6 0 km s throughout the area the middle and lower crust show pronounced lateral variations in thickness velocity and reflectivity the moho is a flat surface at a relatively shallow depth 25 26 km we classify the middle and lower crust of southwest germany into two characteristic crustal types type i consists of a mid crustal low velocity zone 5 4 5 8 km s overlying a thick 10 km high velocity 6 6 6 8 km s lower crust type ii has no prominent mid crustal low velocity zone and a thin

importance of iron rich tholeiitic magmas at divergent plate margins a reappraisal when a tholeiitic liquid differentiates it may give rise to either iron poor silica rich rhyolitic differentiates or to iron rich silica poor differentiates as found in the skaergaard intrusion iron rich differentiated liquids are rare among erupted rocks but are found in small quantities from several localities at divergent plate margins among the tertiary basalts and intrusions in east greenland normal erupted basalts may be mixtures of primitive liquid and differentiated iron rich liquid which exists at depth but normally does not reach the surface because of its high density the evolved liquids of the skaergaard intrusion were of this kind data from mid oceanic ridges confirm this view we believe that iron rich differentiated liquids despite their scarcity on the surface are much more voluminous at depth as picrites at the other side of the density minimum attained during liquid evolution are thought to be the trend toward iron enrichment develops when the tholeiitic magma differentiates in a closed system at a relatively low oxidation state whereas the trend toward silica enrichment and iron depletion occurs when the magma has interacted with the oxidized and hydrated surroundings in the crust

mesospheric planetary waves over antarctica during 2002 1 wind measurements from a series of atmospheric radars located around antarctica have been used to characterize the mesospheric planetary wave field during the winter of 2002 combining winds from the medium frequency mf radar at rothera 68 s 68 w and the superdarn high frequency meteor wind radars at halley 76 s 27 w sanae 72 s 3 w and syowa 69 s 40 e stations we have been able to measure the period wavenumber and propagation direction of the most prominent planetary waves the results show that the planetary wave field before the unusual stratospheric warming in 2002 was dominated by a very long period 43 days westward and upward propagating zonal planetary wavenumber 1 however after the stratospheric warming events began in late winter the character of the wave field changed and a shorter period 14 days westward zonal wavenumber 1 became established it would appear that the previously reported oscillations of the mesospheric hydroxyl airglow temperatures at rothera and halley which were strongly anti correlated to the meridional wind were the result of these planetary waves

permian bimodal dyke of tarim basin nw china geochemical characteristics and tectonic implications abstract this study reports for the first time the occurrence of bimodal dyke in the shuigongtuan area of bachu county tarim basin nw china here quartz syenite porphyry and diabase dykes occur in direct contact showing bimodal feature the quartz syenitic porphyry is metaluminous enriched in k2o na2o 10 11 wt and total rare earth elements ree with low mg mg fe ratios high lree hree and negative eu anomalies the chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with a type granites the diabase dyke shows 45 52 wt sio2 and mg mg fe ratio in the range of with high total ree high lree hree ratios and lack of eu anomalies broadly corresponding to tholeiitic composition based on low y nb as low as 0 4 and less than 1 2 enrichment in lile and hfse and uniform nb enrichment patterns in spider diagram for the quartz syenitic porphyry together with the geochemical patterns of the diabases this biomodal association is interpreted to be derived from a mantle source and formed under typical within plate environment the quartz syenitic porphyry and diabase have daly gap of 46 wt 67 wt in sio2 which is explained through formation under bimodal rifting the quartz syenitic dyke probably formed during early permian 277 ma and has geochemical affinity with the xiaohaizi syenitic body we propose that magmas sourced from the mantle intruded into middle upper crust and were emplaced as dykes which indicate large scale extension during the permian in tarim basin the bimodal dyke has genetic affinity with the huge volume of permian basalts and igneous rocks 248 292 ma that occur in the tarim basin the magmatism manifests the culmination of the major thermal event in the tarim basin

mineral characteristics and metallogenesis of the wajilitag layered mafic ultramafic intrusion and associated fe ti v oxide deposit in the tarim large igneous province northwest china abstract the wajilitag layered mafic ultramafic intrusion as an important lithological unit of the permian tarim large igneous province has genetic link with a large scale v bearing ilmenite titanomagnetite series mineralization it consists mainly of olivine pyroxenite pyroxenite and gabbro with layered structures olivine from the mafic ultramafic rocks has low fo values molar 100 mg mg fe of 67 76 mol probably indicating that the wajilitag magmas have experienced fractional crystallization with an early removal of olivine magmas in equilibrium with olivine have high feo mgo ratios ranging of 1 1 1 6 ilmenite exsolution lamellae are present in clinopyroxene the wajilitag magmas therefore are considered to be enriched in iron and titanium which may account for the large amounts of fe ti oxides hosted therein high sm yb ratios indicate that the fe ti rich wajilitag magmas may be produced by low degree of partial melting from the mantle source layered structures and variable mineral compositions of olivine and clinopyroxene of the intrusion suggest that the magmas become more fe ti rich under extensively fractional crystallization from the evolved magma a few fe ti oxide crystals enclosed in the olivine of the olivine pyroxenite with slightly higher cr2o3 contents than other oxides indicate that minor oxides crystallized in the early stage of the magmatic process whereas most oxides interstitial to the silicate minerals denote that they were accumulated in the late stage of the magmatic process we propose that the fe ti oxides of the wajilitag intrusion were formed by fractionation processes with two stages the presence of ilmenite exsolution lamellae in magnetite suggests that the wajilitag layered mafic ultramafic intrusion and the massive fe ti ore deposits hosted therein formed in a slowly cooling magmatic crystallization process from a deep magma chamber

seismic anisotropy of the crystalline crust what does it tell us the study of the directional dependence of seismic velocities seismic anisotropy promises more refined insight into mineral composition and physical properties of the crystalline crust than conventional deep seismic refraction or reflection profiles providing average values of p and s wave velocities the alignment of specific minerals by ductile rock deformation for instance causes specific types of seismic anisotropy which can be identified by appropriate field measurements vice versa the determination of anisotropy can help to discriminate between different rock candidates in the deep crust seismic field measurements at the continental deep drilling site ktb s germany are shown as an example that anisotropy has to be considered in crustal studies at the ktb the dependence of seismic velocity on the direction of wave propagation in situ was found to be compatible with the texture composition and fracture density of drilled crustal rocks

nature of crustal reflectivity along the dekorp profiles in germany in comparison with reflection patterns from different tectonic units worldwide a review reflectivity of the continental crust displays many different patterns the dekorp lines are used as a basis for comparing and reviewing reflectivity in different tectonic units the brittle upper crust generally exhibits only two types of reflectivity it is either rather transparent preferably in some extensional provinces or and it shows traces of thrust and shear zones of former or present ruptures as these zones have a low impedance interior with few exceptions their first reflection onsets have a negative polarity and evince strong but short signals which sometimes can be correlated over several kilometers the generally ductile lower crust displays a completely different reflectivity in warm extensional and thin crusts the lower part is full of reflecting lamellae it is suggested that this type of reflectivity has a thermo rheological origin the creation of lamellae must take place in a ductile material with contrasting impedance under extensional stresses it can be associated with mineral alignment and corresponding seismic anisotropy destruction of lamellae may take place by a cooling process transforming parts of the lower crust into a brittle regime small stresses might deform or break the lamellae and leave a certain dispersed reflectivity like that in some old and cold shields there are no observations of reflecting lamellae in the upper crust or in the upper mantle in all areas the moho is the last reflecting band reflection moho which most often is identical with the classical refraction moho there are isolated mostly dipping reflections in the uppermost mantle in zones where the last tectonic event a delamination or subduction was not succeeded by a heating process the uppermost mantle is brittle again in most areas and may keep the memory of a cold collision over billions of years

temporal evolution of the permian large igneous province in tarim basin in northwestern china abstract the temporal relations of different types of rocks in the tarim large igneous province tlip are studied using stratigraphic correlation lithologically spatial distribution and isotopic ages the tlip covers an area 250 000 km2 in the western and central part of the tarim basin the lithological units of the tlip include basalt diabase layered intrusive rock breccia pipe mica olivine pyroxenite olivine pyroxenite gabbro ultramafic dyke quartz syenite quartz syenite porphyry and bimodal dyke this is the first report for the spatial distribution of the tlip from the spatial section lines which shows the stratigraphic correlation among basaltic lava tuff interlayered mudstone siltstone and sandstone and the thicknesses of the basaltic lavas from different field sections and drill holes and the basalts from the kupukuziman and kaipaizileike formations were subdivided in the drill hole sections this indicates that the basaltic lavas were widely distributed in the tarim basin combined with previous study of geochemical and sr nd pb isotopic characterization from the basalts and their genetic link with mantle plume activity and large diabase swarms developments the permian igneous units constitute a tarim large igneous province zircon shrimp u pb dating firstly yields 284 3 2 8 ma for the quartz syenite porphyry recent shrimp and la icp ms zircon u pb and 40ar 39ar ages are used to discuss temporal relations of different rock units in the tlip formed between 290 and 274 ma and these data are more reliable than the k ar ages of 220 310 ma reported previously the sequence of magmatism of the tlip in the central and western parts of the tarim basin are basaltic lava in the kupukuziman and kaipaizileike formations 285 290 ma layered mafic ultramafic rock mica olivine pyroxenite breccia pipe diabase and ultramafic dyke quartz syenite quartz syenite porphyry and bimodal dyke 274 284 ma

origin of the giant allard lake ilmenite ore deposit canada by fractional crystallization multiple magma pulses and mixing abstract the late proterozoic allard lake ilmenite deposit is located in the havre saint pierre anorthosite complex part of the allochtonous polycyclic belt of the grenville province presently the world s largest fe ti oxide deposit it had a pre mining amount in excess of 200 mt at grades over 60 wt hemo ilmenite the main ore body is a funnel shaped intrusion measuring 1 03 1 10 km and 100 300 m thick two smaller bodies are separated by faults and anorthosite the ore is an ilmenite rich norite or ilmenitite made up of hemo ilmenite hem22 6 29 4 66 2 wt on average andesine plagioclase an45 50 aluminous spinel and locally orthopyroxene whole rock chemical compositions are controlled by the proportions of ilmenite and plagioclase orthopyroxene which supports the cumulate origin of the deposit ore forming processes are further constrained by normal and reverse fractionation trends of cr concentration in cumulus ilmenite that reveal multiple magma emplacements and alternating periods of fractional crystallization and magma mixing mixing of magmas produced hybrids located in the stability field of ilmenite resulted in periodic crystallization of ilmenite alone the unsystematic differentiation trends in the allard lake deposit arising from a succession of magma pulses hybridisation and the fractionation of hemo ilmenite alone or together with plagioclase suggest that the deposit formed within a magma conduit this dynamic emplacement mechanism associated with continuous gravity driven accumulation of fe ti oxides and possibly plagioclase buoyancy in a fractionating ferrobasalt explains the huge concentration of hemo ilmenite the occurrence of sapphirine associated with aluminous spinel and high alumina orthopyroxene 7 6 9 1 wt al2o3 lacking exsolved plagioclase supports the involvement of a metamorphic overprint during the synchronous ottawan orogeny which is also responsible for strong textural equilibration and external granule of exsolved aluminous spinel due to slow cooling