mid cretaceous primitive alkaline magmatism in the northern calcareous alps significance for austroalpine geodynamics basanitic dykes local name ehrwaldite occur over a distance of at least fifty kilometres in a narrow east west trending zone within the lechtal nappe of the northern calcareous alps the dykes crosscut mesozoic sedimentary strata up to the lower cretaceous the sedimentary rocks show contact metamorphism in the immediate vicinity of the dykes the ehrwaldites vary in mineral content from olivine fo 91 87 titanian augite basanites to basanites containing also kaersutite titanian biotite and zeolites minor phases are titanian magnetite picotite llmenite carbonate and sulfides mantle derived xenoliths and xenocrysts form up to five percent of the rock bulk chemical analyses show the typical characteristics of nepheline basanites ne 11 17 wt mg number 74 78 and demonstrate that the ehrwaldites are primitive mantle derived melts trace element contents of the dykes are in excellent agreement with those for basanites and olivine nephelinites from tertiary and quaternary european provinces the same is true for the isotope characteristics of the dykes with average initial esr and end values of 8 2 and 4 7 respectively these data demonstrate similarities in the mantle source rocks and in the melting characteristics with european alkaline rocks and thus similarities in the european subcontinental mantle at different localities for the last 100 ma these data are in clear contrast with the value for the penninic suboceanic mantle geochemical constraints and piston cylinder experiments indicate a depth of origin of 80 kilometres at temperatures of at least 1250 c for the ehrwaldites potassium argon bulk rock data of petrographically different samples of the dykes from different localities yield consistent ages around 100 ma upper albian after emplacement the ehrwaldites underwent conditions of the zone of diagenesis with temperatures around 120 c which the late magmatic zeolites survived

magma mixing origin of intermediate rocks and enclaves from volcanism to plutonism abstract intermediate magmatic rocks are rarely homogeneous a common example is the presence of magmatic enclaves volcanic examples show that they are indications of magma mixing processes mixing events in the trachyandesitic suites from the sancy volcano france the volcanic activity from sancy consists of several brief trachyandesitic cycles each of them begins with the eruption of highly heterogeneous benmoreites followed by more homogeneous mugearites light porphyritic trachyandesites enclose numerous inclusions of varied darker lavas the crenulated geometry of the contacts the presence of chilled margins the vesiculation of the core of the basic parts suggest that these different rock types were magmatic at the same time although under marked thermal disequilibrium xenocrysts are common partly resorbed sanidine rimmed with plagioclase in a basic matrix reactional olivines in tridymite bearing trachytes this shows that the mixing occurred between partially crystallized and fractionated magmas chemical compositions are continuously variable from basalts to trachytes within the same eruptive cycle all these facts might be interpreted as the result of a mechanical intermingling more or less achieved between two end members of contrasting composition in the reservoir in the sancy volcano this phenomenon occurred at least 4 or 5 times during a 600 000 y span mixing evidence in hercynian granodiorites from france similar observations may be described in granodioritic rocks the more widespread enclaves exhibit the same characteristics as their volcanic equivalents although most of them are small more important volumes of basic rocks may be associated in the same massif in the neighbourhood of such large bodies swarms of smaller enclaves recall the generation of basic pillows the nature of the contact between small microgranular enclaves and their host rocks the occurrence of xenocrysts with reaction rims rapakivi feldspars and quartz ocelli in a basic surrounding amphibole pyroxene clots in a granitic matrix and geochemical variations again suggest thermal and mineralogical disequilibrium such observations indicate the comagmatic character of enclaves with regard to their host rocks they cannot be interpreted as restites and are best described as co igneous inclusions resulting from non achieved mixing between coexisting magmas photonic rocks are less suitable to demonstrate such petrogenetic processes because they result from slow cooling and crystallization during a longer residence time in a magmatic chamber the successive mixing episodes giving rise to different generations of co igneous inclusions are also difficult to recognize on the other hand in volcanism this process is quenched and periodically sampled by eruptions in conclusion the heterogeneity and the variability of many intermediate rocks cannot be explained only in terms of simple partial fusion and fractional crystallization processes in a closed system volcanic examples point to a complex evolution of magmatic reservoirs that were continuously fractionated periodically tapped periodically refilled and mixed

mixing and chemical interdiffusion of trachytic and latitic magma in a subvolcanic complex of the tertiary westerwald germany abstract a special kind of magma mixing is extraordinarily well exposed in the bittersberg subvolcanic complex in the tertiary volcanic field of the german westerwald a trachytic melt has been penetrated by a latitic dyke which has been dispersed within the host magma as small spherical enclaves globules whole rock analyses of the globules show a change in composition that cannot be explained by a simple mechanical mixing between the endmembers the most evolved globules have a phonolitic composition microprobe measurements in the microlithic matrix of the host rock and the guest indicate a diffusive motion of the alkalis from the host into the globules on the other hand an opposite trend can be observed for ca mg fe and ti which are impoverished in the globules the trace elements and the middle rare earth elements mree has also been involved in the diffusive exchange the ree pattern of the most evolved phonolitic globules shows a characteristic trough in the area of the mree which is almost identical to the ree pattern of many phonolites the phonolites and the alkali rich trachytes of the westerwald show similar globular textures as the bittersberg volcanics therefore generation of these rocks involving diffusive element exchange during mixing processes in a magma reservoir situated on a deeper crustal level may be possible

magma mixing in alkaline series an example from sancy volcano mont dore massif central france three magmatic units grande cascade pyroclastic deposits grande cascade lava flow durbise nuee ardente deposits from the quaternary volcano sancy mont dore area auvergne france show textural evidences of magma mixing between a silica undersaturated basic magma alkali basalt and hawaiite and an acid magma quartz bearing trachyte three kinds of mixed rock types are described basic inclusions within an acid host emulsified rocks showing infracentimetric basic globules disseminated within an acid groundmass and banded rocks in which elongated acid and basic zones alternate the chemical compositions of mixed rocks plot systematically onto linear trends in petrographic diagrams microprobe analyses of the groundmass show similar linear variations between basic and acid end members the mineralogical associations of these mixed rocks are highly complex and present many disequilibrium features olivine is stable in the basic component and becomes rimmed by orthopyroxene in the acid one zoning patterns of feldspars are complex clinopyroxene kaersutite and phlogopite phenocrysts have increasing component mg contents from core to rim both in the basic and the acid titanomagnetite and hemoilmenite phenocrysts were equilibrated at 900 800 c under high oxygen fugacities mixing results primarily from a mechanical disintegration of partly liquid basic inclusions within their acid host and also from a mechanical transfer of phenocrysts from one component to the other in which they often remain surrounded by a coating of their original groundmass chemical data on the groundmass indicates that some true hybridization between coexisting acid and basic liquids may also have occurred the extent of mixing is controlled by the type of emplacement for pyroclastic deposits a chemical gap exists between basic inclusions and their acid hosts in contrast mechanical mixing was enhanced during the emplacement of the viscous grande cascade lava flow and complete transitions occur between basic and acid components the two end members are genetically associated the latter deriving from the former by crystal fractionation mixing appears as a late stage phenomenon in the petrogenetic history of the mont dore series in the case of the grande cascade lava flow its extent is primarily dependent on emplacement modalities

sulfur bearing magmatic accessory minerals almost all magmas contain sulfide or sulfate bearing phases in most natural samples the sulfur bearing phase is a sulfide which typically is pyrrhotite fe1 x s or pyrite fes2 although chalcopyrite cufes2 pentlandite fe ni 9s8 sphalerite zns or molybdenite mos2 may be present as well sulfate minerals are rare at magmatic conditions and anhydrite caso4 is the most common other magmatic so4 bearing minerals include the sodalite group minerals hauyne simplified formula na ca 4 8 al6si6 o s 24 so4 cl 1 2 scapolite minerals silvialite ca na 4al6si6o24 so4 co3 and s bearing apatite ca5 po4 3 f cl oh barite baso4 has been mentioned in rare cases marchev 1991 sulfur bearing minerals usually constitute a negligible fraction of the mineral assemblage in magmatic rocks and thus can be classified as accessory minerals the crystallization of sulfide sulfate and s bearing minerals strongly depends on melt composition temperature and pressure and the s speciation in melt which in turn is strongly dependent on the prevailing oxygen fugacity baker and moretti 2011 this volume wilke et al 2011 this volume irrespectively of the low abundance of s bearing minerals the evolution of sulfur in magmas may be evaluated from the occurrence of sulfides and sulfates these minerals are critical for estimating the activity of various sulfur bearing species in magmas and can be used to constrain the oxygen fugacity and the s concentration in the melt e g pre eruptive sulfur concentration in melts the presence of either sulfide or sulfate in silicate melt indicates that the predominant dissolved sulfur species in the melt are s2 or s6 respectively typically one of these species is dominant but there are conditions where s2

a rhaetian 40 ar 39 ar age for the rochechouart impact structure france and implications for the latest triassic sedimentary record ar 39 ar dating of potassium feldspar primary spherulitic blocky and secondary idiomorphic k feldspar separated from impact metamorphosed gneiss found near videix in the western central part of the rochechouart impact structure nw massif central france yielded a rhaetian combined age of 201 2 ma 2r indistinguishable within uncertainty from the age of the triassic jurassic boundary ballen quartz intergrown with the primary k feldspar indicates post shock temperatures exceeding approximately 1000 c that affected the precursor gneiss geochemically both feldspar types represent essentially pure potassium end members apart from the approximately 15 km diameter impact deposit area the youngest crystallization age known for basement rocks in this part of the massif central is approximately 300 ma no endogenic magmatic thermal events are known to have occurred later in this region the k feldspar recrystallized from local feldspar melts and superimposed post shock hydrothermal crystallization probably within some thousands of years after the impact it is therefore suggested that the 40 ar 39 ar age for the videix gneiss as a potassic impact metasomatite dates the rochechouart impact in consistence with evidence for k metasomatism in the rochechouart impactites the new age value is distinctly younger than the previously obtained karnian norian age for rochechouart and thus contradicts the late triassic multiple impact theory postulated some years ago in agreement with the paleogeographic conditions in the western tethys domain around the triassic jurassic boundary the near coastal to shallow marine rochechouart impact is compatible with the formation of seismites and tsunami deposits in the latest triassic of the british isles and possible related deposits in other parts of europe

40 ar 39 ar and unspiked 40 k 40 ar dating of upper pleistocene volcanic activity in the bas vivarais ardeche france abstract fifteen basanitic and tephritic flows from bas vivarais the youngest volcanic field in the french massif central together with the chaine des puys were dated by 40ar 39ar and 40k 40ar on separated groundmass and studied for paleomagnetism an almost systematic discrepancy between the two types of ages is observed the 40k 40ar method providing ages up to 8 5 times the 40ar 39ar ones microscopic observations and geochemical analyses lead us to conclude that most of the k ar ages measured on bas vivarais samples are in error due to extraneous argon originating from contamination by xenocrysts from disintegrated crustal and mantle xenoliths however 40ar 39ar experiments do not evidence any excess argon suggesting two possibilities 1 the extraneous argon contribution was eliminated during the pre degassing of the samples at 600 c prior to the step heating experiments 2 k ar ages may be older because larger quantities of xenocrysts potential carriers of extraneous argon were involved in the k ar experiments than in the 40ar 39ar ones 40ar 39ar ages are thus little or not affected by contamination and provide reliable ages for the studied volcanoes combined 40ar 39ar datings and magnetic directions for each flow point out to three successive stages in the volcanic evolution of bas vivarais stage 1 limited to the northern part of the field has a mean age of 187 3 19 0 ka in its southern part stages 2 and 3 emplaced magmas at 31 1 3 9 ka and 23 9 8 1 ka respectively these two last stages are consistent with available 14c dates but not with previous thermoluminescence data

crystal fractionation and the evolution of intra plate hy normative igneous suites insights from their feldspars feldspars and normative feldspar constituents of bulk magma show complexes and anorogenic granites is associated with hotspot and continental rift environments a major chartrends supportive of fractional crystallization in the three main types of hy normative intraplate suites that contain qz oversaturated acteristic of this magmatism is the production of suites of compositionally diverse rocks that are temporally and rocks ocean island and continental alkalic suites ocean island tholeiitic suites and continental tholeiitic suites these suites are spatially associated much is still unknown about the processes that have led to the diversity of magmas within characterized by the presence of a single feldspar in each suite member a shift of this feldspar from plagioclase to alkali feldspar such suites or to the global diversity of intra plate suite types and k enrichment of alkali feldspar with decreasing temperature in the trachytic members the modal feldspars provide evidence for a many ocean island and continental hotspot and continental rift related suites are characterized by rocks with reaction relationship between feldspars and indicate a build up of magmatic volatile content towards saturation with progressive high alkali silica ratios that fall into the alkalic field of irvine baragar 1971 fig 1 regardless of their state fractionation of a parental magma having low initial volatile content the feldspar and normative feldspar evolutionary paths are unique of silica saturation such alkalic suites range from those that are strongly silica undersaturated containing rocks for each of the three suite types but similar for different suites within the same type this characteristic extends to the felsic members such as nephelinites or leucitites in the more potassic making it easy to distinguish between rhyolitic or granitic rocks suites to mildly silica undersaturated suites the kenfrom the different suite types the feldspars in natural volcanic nedy series of miyashiro 1978 containing alkali basalts suites commonly show evidence for a polybaric history particularly silica undersaturated trachytes and phonolites and in the least evolved suite members late stage feldspars of the finally to hy normative suites the coombs trend of intermediate members and feldspars of the most evolved members miyashiro 1978 that include olivine basalts trachytes show paths indicative of significantly lower temperature and pressure and rhyolites hy normative alkalic suites that contain regimes silica oversaturated rocks on ocean islands are widespread and include those from ascension island e g harris 1983 the samoan islands macdonald 1968 terceira azores e g white et al 1979 and clarion island mexico

tertiary and quaternary volcanism in the massif central france summary continental alkaline volcanics of the french massif central range in age from 65 ma to 3450 years bp and can be divided by geography and age into 20 separate areas there is no correlation between the age of an area and the geographic locality two magma series are present a silica undersaturated basanite tephrite phonolite series and an alkali basalt trachyandesite trachyte rhyolite series the evolved members of which are silica saturated rare nephelinites are also found primitive magmas of both main series may be derived from 2 20 partial melting of a mantle enriched with light rare earth elements with variable amounts of garnet in the residue nephelinites were formed from a source which was isotopically and chemically distinct fractional crystallization of observed phases accounts for the diversity of intermediate and evolved products amphibole fractionation in basalts at depth causes the trend towards silica saturation while alkali feldspar fractionation dominates the final stages of crystallization removal of small quantities of sphene and zircon explains trace element depletions in trachytes phonolites and rhyolites up to 30 crustal contamination has occurred in the evolved magmas but contamination is generally absent from their basaltic parents sr nd and pb isotope data indicate that the most probable contaminant is undepleted meta sedimentary granulite facies lower crust variations in sr and nd isotope ratios also constrain petrogenetic hypotheses such as amphibole fractionation and magma mixing mineralogical disequilibrium compositional banding and emulsification textures indicate extensive magma mixing some flows are homogeneous hybrid lavas in which only the unusual composition and rare mineral disequilibria indicate the mode of formation

magma mixing at la nugere volcano chaine des puys massif central france role in the trachyandesites genesis a succession of heterogeneous pyroclastites with contrasted composition hawaiite trachyte and homogeneous intermediate lava flows benmoreite is present at puy de la nugere chaine des puys massif central france mineralogical disequilibrium assemblages are present in both the explosive en effusive products textural mineralogical and geochemical data on these formations are compatible with a magma mixing model the origin of the trachyandesitic rocks in the alkaline suite of chaine des puys would be controlled by fractional crystallization and magma mixing

an attempt to define a neotectonic period for central and northern europe the neotectonic period is the youngest period of tectonic evolution and extends up to the present the beginning of the neotectonic period during the cenozoic may be regarded as having begun when characteristic changes in the tectonic evolution of a region of interest have occurred for the last time changes in the different tectonic facets which characterize the evolution of a region need not be simultaneous and hence the times of the last change may differ between facets this leads to the definition of a transitional time interval wherein elements of both the palaeotectonic and neotectonic period are present the length of this transitional time interval depends on the regional geological evolution where a broad transitional time interval exists the beginning of the neotectonic period may be defined by the earliest time marker by when most of the characteristic changes of the tectonic evolution of the region had occurred

1d geothermal inversion of the lunar deep interior temperature and heat production in the equatorial area abstract we present a study on lunar interior temperature and heat production by 1d geothermal inversion with the layered structure and thermal state of the lunar interior reported by lunar seismic and magnetic sounding research a forward modeling of deep temperature is given based on the theory of thermal conduction then the particle swarm optimization pso method is applied to implement the inversion of lunar interior heat production a six layer model is solved using a global heat flux of 12 mw m2 and a near surface temperature of 250 k the inversion results show that the crust has an average heat production of approximately 210 nw m3 the mantle has a depleted heat production varying from 3 7 to 8 1 nw m3 and the heat production in the lunar core varies from 30 to 36 nw m3 the distribution of heat production indicates that the present radioisotopes are mainly concentrated in the lunar crust different from previous estimates the heat release in the lunar core may be considerable similar to the average heat production in the moon implying that the residual heat from lunar accretion or radioactive decay is probably substantial in contrast perhaps the core was involved to a limit in the material exchange with the mantle in addition the obtained heat flux at the core mantle boundary meets the value required for the core adiabatic process indicating that the core convection may have stopped

crustal origin of early proterozoic syenites in the congo craton ntem complex south cameroon two petrographically different syenite suites can be distinguished in the mostly archean ntem complex of cameroon a suite of two pyroxene syenites and a suite of clinopyroxene syenites the syenites occur as discrete intrusions surrounded by archean gneisses based on structural relationships the syenites are of late to post orogenic origin the pb pb zircon evaporation ages indicate that the syenites intruded at ca 2 3 ga and thus postdate significantly the archean episode of crust formation and differentiation that generated the surrounding gneiss terrane the isotope signatures and the trace elements provide unambiguous evidence that the two syenite suites are of crustal origin the syenite suites do not show simple chemical trends have highly variable trace element contents and display only a small variation in their major element contents particularly in their sio2 contents the isotope characteristics including 143nd 144nd 87sr 86sr and common pb point to a heterogeneous source or multiple sources for the syenites the sr isotope compositions calculated for the time of intrusion vary over a wide range from an unrealistically low 87sr 86sr ratio of 0 690 to high values of 0 713 in contrast the initial 143nd 144nd ratios are more homogenous with end 2320 from 5 8 to 7 5 the pb isotopes from leached k feldspars indicate that the sources of the syenites had a history of u depletion and th u enrichment the syenites show the same isotope characteristics as the surrounding gneiss terrane thus the deep continental crust of the ntem complex itself is the most likely source for the syenite melts this conclusion is also supported by the heterogeneity of the trace elements in the syenites that exclude a homogenous source in addition inherited zircons from the syenites yield pb pb evaporation ages that are consistent with ages obtained for zircons extracted from the surrounding gneisses in contrast to many other syenites worldwide the syenites in the ntem complex do not contain juvenile mantle material but are the sole products of crustal reworking thus the syenites did not contribute to the crustal growth in the ntem complex however this conclusion may not preclude the possibility that the syenites were generated in the deep crust during a time of addition of mantle material to the continental crust the cause for the generation of these large syenite bodies in the ntem complex is most likely an episode of deep seated thermal activity that was so far not known from this part of the congo craton

ndsr isotope and ree geochemistry of alkali basalts from the massif central france abstract nd and sr isotopic compositions as well as trace element concentrations have been determined on a suite of alkali basalts from the massif central in france samples show a typical enrichment in incompatible elements in particular the ree patterns exhibit a strong fractionation characterized by a la yb n ratio of about 20 the ybn content is about 10 times chondrite the 143 nd 144 nd ratios exhibit a range from 0 512775 to 0 512989 values quite comparable to those from oceanic island basalts the 87 sr 86 sr ratios vary between 0 70338 and 0 70458 and are anti correlated with the nd isotopic ratio the isotopic and the trace element in particular ree data have been used in order to quantitatively model the genesis of the alkali basalts among the several types of models tested here the most likely one appears to be the model of mantle metasomatism a semi quantitative approach shows that the source of alkali basalts from the massif central was metasomatized prior to melting in such a model the basalts could be produced by rather high degrees of partial melting such as 10 or 15 of the metasomatically enriched mantle

petrology and geochemistry of the shuiquangou syenitic complex northern margin of the north china craton the palaeozoic shuiquangou complex is a major syenitic intrusion along the northern margin of the north china craton that hosts a number of gold deposits despite the heterogeneity of the complex in terms of texture and modal mineralogy mineral compositions whole rock chemistry as well as radiogenic isotope compositions show a well constrained magmatic evolutionary trend the whole rock major element and ree trends are broadly consistent with fractional crystallization dominated by clinopyroxene amphibole and accessory minerals initial nd sr isotopic compositions suggest that the parent magmas to the complex were ultimately derived from an enriched mantle with relatively high initial 87 sr 86 sr ratios and negative nd values the enrichment of the mantle source was probably inherited from an older lithospheric mantle beneath the north china craton sr isotopic data indicate that the rb sr system was disturbed by later alteration processes whereas nd isotopes are essentially unaffected and exhibit a broad trend consistent with simultaneous fractional crystallization and country rock assimilation afc quantitative modelling indicates that a very high bulk distribution coefficient for nd and low ratios of assimilation to crystallization are needed to produce the observed nd isotope evolutionary trend

imaging a mantle plume beneath the french massif central abstract teleseismic tomography is now widely recognised as a very powerful tool for studying the velocity structure of the lithosphere asthenosphere system on both local and regional scales a prime objective is to identify velocity perturbations and to constrain their location and intensity here we use the arrival times of p waves from teleseismic events recorded by a dense network of mobile and permanent stations within the french massif central to derive a 3d p velocity model for an area of 425 km 300 km combined with knowledge of the basement geology of the area and the timing and geochemical characteristics of tertiary quaternary volcanic activity we consider that the velocity model provides unequivocal evidence for the ascent of a thermally and chemically anomalous mantle plume beneath the massif central during tertiary times our model is consistent with regional bouger gravity anomalies documented patterns of neogene recent uplift and deformation fabrics within lithosphere derived mantle xenoliths exhumed by the volcanics

isotopic evidence of lead sources in loire river sediment sediments along the loire river central france were investigated by means of pb isotopes determined on the labile sediment fraction or acid extractable matter aem the combination of trace elements and pb isotopes allows deciphering the origin of the elements i e natural or anthropogenic and their history in the sediment from two small watersheds one draining basalt the other one granite gneiss both in present day suspended matter in loire river water and in sediment from the loire estuary crustal weathering as confirmed by the pb isotope ratios for most sample points is the main source of pb in the upstream part of the loire river as well as that transported in the middle part of the basin and in the estuary among anthropogenic sources the use of pb isotopic compositions shows an influence of agriculturally derived pb inputs and a major input of pb derived from gasoline particularly in the estuary due to harbor activities

chronological and geochemical study of lavas from the chaine des puys massif central france evidence for crustal contamination datations of ancient lavas from the chaine des puys through the 230th 238u radioactive disequilibrium method confirm the eruption of several basaltic or slightly differentiated lavas around 40 000 years ago the study of 230th 232th 0 initial ratios of these lava flows clearly demonstrates the influence of a crustal contamination of magmas superimposed to crystal fractionation this contamination probably affects many trace elements in particular u th and sr a model based on the 230th 232th 0 initial ratio variations of non contaminated lavas permits to consider that the first eruptions in the chaine des puys could have occurred about 100 000 years ago

soil slips on weathering limited slopes underlain by coarse grained granite or fine grained gneiss near seoul republic of korea abstract the chemical mineral physical and mechanical properties of two soil layers on soil slip scars in slopes underlain by coarse grained granite and fine grained granitic gneiss near seoul republic of korea were examined our aim is to study the effect of the mineral grain size of the bedrock on the soil layer structure and the return period of shallow soil slips because of the coarser slope materials in granite resulting from weathering the permeability is larger and the weathering front has a copious water supply also because of the smaller specific surface area of the minerals restricted leaching produces grus from the bedrock so that the rate of formation of soil and in particular the slip plane due to chemical weathering is faster since on granite slopes the leaching proceeds toward the surface the sliding plane is deeper with coarser soft grus resulting in the existence of a minimum c value in the soil layer on gneiss slopes by contrast leaching cannot proceed with decreasing soil depth and the sliding plane is deeper with finer soft grus just above hard grus and has similar c and values as the upper soft grus because the grain size of both soils is the same in the granite soil layers the sliding plane corresponds to the minimum shearing resistance whereas in the gneiss soil layers the shearing resistance increases gradually with soil depth and the sliding plane is formed when the weathering front is located deeper because of the faster soil formation rate and the shallower slip depth in granite slopes the return period of occurrence of soil slips should be shorter in granite slopes than in gneiss slopes

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

petrogenesis of syenites at a rifted continental margin origin contamination and interaction of alkaline mafic and felsic magmas in the astrophyllite bay complex east greenland the astrophyllite bay complex in east greenland part of the palaeogene north atlantic igneous province consists of an alkaline diorite plug with detached trachyandesitic pillows surrounded by co magmatic syenite that was emplaced into archaean basement the diorite intrusion has yielded a 47 11 0 68 ma rb sr isochron age saw cut profiles through pillow syenite gneiss sections have been taken to resolve close spatial elemental and isotopic sr nd hf pb o variations the diorite and syenite formed from alkaline basaltic mantle derived melts with complex histories of prolonged assimilation and fractional crystallisation each evolved to different extents in separate magma chambers during the establishment of new plumbing systems in the kangerlussuaq area the diorite is dominated by lower crustal granulite facies contamination whereas the syenite shows evidence for greater degrees of upper crustal amphibolite facies contamination indicating stalling and fractionation of magmas at different levels within the crust the syenite and diorite magmas were subsequently emplaced as separate pulses into the basement gneisses at astrophyllite bay giving rise to superimposed local contamination trends between pillow syenite and syenite gneiss respectively