geodynamic evolution of the sw europe variscides 1 the early evolution of sw europe variscides started by opening of the rheic ocean at 500 ma splitting avalonia from armorica iberia subduction on the se side of rheic generated the paleotethys back arc basin 430 390 ma splitting armorica from iberia with development of porto tomar ferreira do alentejo ptfa dextral transform defining the boundary between continental armorica and finisterra microplate to the w obduction of paleotethys was followed by armorica iberia collision and emplacement of nw iberian allochthonous units at 390 370 ma whereas toward the west of ptfa there was antithetic ophiolite obduction beja acebuches and rheic ophiolites plus finisterra continental slices on top of ossa morena zone with simultaneous development of eclogites and orogenic magmatism under a flake double wedge tectonic regime continued convergence 370 ma proceeded by intracontinental deformation with progressive tightening of the ibero armorican arc through dextral transpression on the cantabrian indentor from iberia to armorica the proposed model is discussed at the light of the driving mechanism of soft plate tectonics

age of amphibolitic metamorphism in the ophiolitic unit of the morais allochthon portugal implications for early hercynian orogenesis in the iberian massif structurally lower portions of the allochthonous morais complex are comprised of an ophiolitic unit exposed in two contrasting structural units separated by a ductile thrust fault the lower unit is dominated by variably foliated amphibolite whereas the upper unit is largely comprised of metaperidotite and metagabbro most of the ophiolitic unit has recrystallized synkinematically under amphibolite facies metamorphic conditions c 500 c and 5 kbar amphiboles formed during this metamorphism are typically magnesio hornblende an amphibole concentrate from the lower structural unit records a 39 ar 40 ar plateau age of 397 3 4 ma an amphibole concentrate from the upper structural unit displays an internally discordant 39 ar 40 ar age spectrum corresponding to a total gas age of 431 1 27 3 ma gas fractions evolved from each amphibole concentrate at intermediate and high experimental temperatures are characterized by similar apparent k ca ratios and yield well defined 36 ar 40 ar v 39 ar 40 ar isotope correlations which result in similar ages of 384 2 5 2 and 392 4 7 3 ma these are considered to be more reliable than the plateau ages and are interpreted as dating the last cooling through those temperatures required for intracrystalline retention of argon within constituent amphibole grains the associated tectonothermal event represented a first stage of hercynian orogenesis in the iberian massif it was probably related to oceanic closure and associated obduction of granulitic eclogitic massifs which at present structurally overlie the ophiolitic unit

from magmatic to hydrothermal sn li nb ta w mineralization the argemela area central portugal abstract the argemela mineralized area ama central portugal exhibits a nearly continuous magmatic to hydrothermal ore forming sequence typical of variscan granite related rare metal deposits disseminated and vein type mineralization are distributed in two systems the argemela mine am and the cabeco da argemela ca disseminated mineralization includes montebrasite cassiterite and columbite tantalite dispersed in rare metal granites vein type mineralization occurs both in granites and country rocks the ca system exposes three generations of intragranitic veins with montebrasite in the two earliest and montebrasite wolframite cassiterite and columbite tantalite in the latest country rock veins include a swarm of cassiterite and montebrasite veins am and rare isolated wolframite veins ca disseminated cassiterites are enriched in ta2o5 and nb2o5 compared to vein cassiterites disseminated columbite tantalites evolve toward mn and ta rich chemistries that contrast with the more fe and nb rich compositions in intragranitic veins in the ca system both intragranitic and country rock veins crystallize early mn rich wolframites followed by late more fe rich compositions associated with nb ta poor cassiterite the later replaced by stannite field relations structural mineralogical and geochemical data suggest that the disseminated and vein type mineralization are expressions of a continuous metallogenic evolution initiated at the magmatic stage pursued during the magmatic hydrothermal transition and ended with hydrothermal circulations in country rock the two mineralized systems share similarities but they also show major differences structural analysis demonstrates that the intragranitic veins in the ca and the country rock veins in the am were emplaced under the same tectonic regime therefore the two systems are variants of the same local metallogenic evolution sn and w show markedly contrasted behaviors both have a magmatic source but only sn reaches concentrations leading to saturation of the melt with cassiterite w is deposited later and preferentially to sn in intragranitic veins at the hydrothermal stage cassiterite and wolframite deposition are disconnected and overall wolframite occurs only in minor amounts the metallogenic model proposed for the ama emphasizes magmatic rare metal concentration processes exsolution of magmatic fluids and selective deposition of metals during the magmatic hydrothermal and later hydrothermal stages the sn li nb ta dominated and w poor signature of the ama makes it similar to lct pegmatites of the central iberian zone but is distinctive from the world class w sn cu panasqueira deposit nearby

constriction in a transpressive regime an example in the iberian branch of the ibero armorican arc abstract detailed strain analyses in the armorican quartzites have been performed in various places within the centro iberian zone of western europe the observed strain pattern shows that in the inner ibero armorican arc as well as near the hinge zone sinistral transpression produces constrictive ellipsoids in the outer arc away from the hinge zone the deformation regime produces plane strain to oblate strain ellipsoids some of these data clearly contradict existent kinematical models which associate constriction with transtension and consider transpression zones to generate oblate strain ellipsoids however newly developed models show that it is possible to obtain a wide range of finite strain ellipsoids in transpression zones if one takes account of lateral escape axial depression and volume change the geodynamic implications of the strain analyses suggest generation of constriction in a transpressive regime caused by lateral expulsion in front of the cantabrian indenter that produced the ibero armorican arc this mechanism was responsible for the variscan wrench component in western europe which was mainly sinistral in iberia and dextral in britanny in iberia the displacement by lateral escape was easily accommodated by subduction of the south portuguese terrane under the ossa morena zone of the iberian terrane

nitrogen isotopic composition of a gas rich ordinary chondrite alha 77216 abstract nitrogen abundance and isotopic composition in a gas rich chondrite alha 77216 l3 or h3 was measured in order to obtain an independent estimate of the average nitrogen isotopic composition of the solar system nitrogen ne and ar were extracted by a stepped combustion method and measured using a static mass spectrometer the cosmic ray exposure age based on the 21 ne abundance is about 35 3 1 1 million yr isotopically heavy nitrogen is observed at 700 1100 c the abundance in a bulk sample is 1 38 ppm with 0 61 ppb excess 15 n of which 0 17 ppb could be due to cosmogenic nitrogen heavy nitrogen is enriched in the metal phases compared with silicates a 15 n value as large as 174 was observed for a the 800 c step of a magnetic separate the abundance ratio of nitrogen to solar type rare gases in this meteorite is higher than those in lunar samples we suggest that the isotopically heavy nitrogen is of solar origin but other possibilities presolar and indigenous nitrogen cannot be completely ruled out

irradiation of olivine by 4 kev he simulation of space weathering by the solar wind 1 we have studied the effects of 4 kev he ion irradiation on olivine while measuring in situ changes in the near infrared nir reflectance and in the chemical composition of the surface the observed changes in reflectance are reddening and the attenuation of the fe 3d absorption bands in the nir spectral reddening of irradiated olivine powder 45 m correlates with the amount of metallic iron formed by ion impact consistent with the idea that space weathering effects in the reflectance of olivine bearing s type asteroids are due to the formation of metallic iron the metallization rate of the powder is about half that of a sectioned rock of olivine which we propose is a consequence of redeposition of sputtered material the nir spectral changes observed in ion irradiation experiments are similar to those observed in our previous experiments on vapor redeposition indicating that different space weathering mechanisms can lead to similar final effects on reflectance finally we estimate that at 1 au the spectral reddening caused by the solar wind saturates approximately 2 orders of magnitude faster than comparable reddening caused by micrometeorite impacts

occlusion of noble gases he ne ar kr xe into synthetic magnetite at 500 1300 c abstract the trapping mechanism of noble gases during growth of magnetite is investigated by oxidizing fe with water vapor at temperatures ranging from 500 to 1300 c an apparent negative correlation between the concentration of argon and synthetic temperatures suggests that gases are trapped by adsorption the fixation of adsorbed gas atoms is probably due to crystal growth the elemental fractionation pattern of noble gases resembles so called planetary type patterns with enrichments in heavier noble gases at high trapping temperatures however at lower temperatures significant fractionation is not observed reflecting a smaller absolute value of the negative heat of adsorption for lighter noble gases the amount of argon in chondritic magnetite orgueil ci can be explained by adsorptive trapping of ambient noble gases at the suggested condensation temperature of magnetite in the solar nebular 400 k solar type helium neon and argon elemental ratios observed for the orgueil magnetite are also qualitatively consistent with the results of the present experiments comparison experiments which synthesize magnetite with aqueous water are necessary for further discussion on the origin of the chondritic magnetite and its noble gases

plate and intraplate processes of hercynian europe during the late paleozoic abstract it is speculated that until late carboniferous time the region of hercynian europe was occupied by an elongated island arc system underlain by a segment of continental crust in the upper carboniferous two subduction zones are assumed to have extended from the north and south beneath hercynian europe an extensive zone of hot partially molten upper mantle lay above and between these and diapiric uprise of portions of this material led to separation of mafic magmas widespread partial melting in the lower and middle crust high temperature low pressure metamorphism in crustal rocks and regional uplift and extension of the crust as indicated by intermontane troughs and their associated volcanic rocks in visean to westphalian time hercynian europe collided with both the large neighbouring plates north america europe and africa during these diachronous collisions and owing to reduced rigidity of the relatively hot island arc crust the irregular continental margins of the larger and thicker continental plates induced oroclinal bending of hercynian europe after the collision processes had been terminated processes of upper mantle activity continued causing further crustal uplift and even enhanced crustal extension for several tens of million years into the lower permian decline of the upper mantle activity beneath hercynian europe is indicated by crustal subsidence and formation of a peneplain in permian time followed by the upper permian transgression of both the zechstein sea and the tethys sea which mark the end of the hercynian geodynamic cycle

metallogenesis at the carris w mo sn deposit geres portugal constraints from fluid inclusions mineral geochemistry re os and he ar isotopes abstract the carris orebody consists of two partially exploited w mo sn quartz veins formed during successive shear stages and multipulse fluid fillings they cut the variscan post d3 geres i type granite the most important ore minerals are wolframite scheelite molybdenite and cassiterite there are two generations of wolframite the earlier generation of wolframite is rare and has the highest wo4mn content 91 mol and the most common wolframite contains 26 57 mol wo4mn re os dating of molybdenite from the ore quartz veins and surrounding granite yields ages of 279 1 2 ma and 280 3 1 2 ma respectively which are in very good agreement with the previous id tims u pb zircon age for the carris granite 280 5 ma 3he 4he ratio of pyrite ranging between 0 73 and 2 71 ra 1 ra 1 39 10 6 and high 3he 36ar 0 8 5 10 3 indicate a mixture of a crustal radiogenic helium fluid with a mantle derived fluid the fluid inclusion studies on quartz intergrown with wolframite and scheelite beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit the first was a low to medium salinity aqueous carbonic fluid co2 between 4 and 14 mol with less than 1 95 mol n2 which was only found in quartz associated with wolframite the other was a low salinity aqueous fluid found in all the four minerals the homogenization temperatures indicate minimum entrapment temperatures of 226 310 c average 280 c for the h2o co2 n2 nacl fluid and average temperatures of 266 c for scheelite and 242 c 190 c and 160 c for the last generations of beryl fluorite and quartz respectively it was estimated that wolframite was deposited 7 km depth assuming a lithostatic pressure probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event precipitation of scheelite and sulphides took place later at the same depth but under a hydrostatic or suprahydrostatic pressure regime and probably caused by mixing between the magmatic hydrothermal fluid and meteoric waters that deeply penetrated the basement during post variscan decompression

kinematic and geochronological constraints on shear deformation in the ferriere mollieres shear zone argentera mercantour massif western alps implications for the evolution of the southern european variscan belt in the western alps a steeply dipping km scale shear zone the ferriere mollieres shear zone cross cuts variscan migmatites in the argentera mercantour external crystalline massif structural analysis joined with kinematic vorticity and finite strain analyses allowed to recognize a high temperature deformation associated with dextral transpression characterized by a variation in the percentage of pure shear and simple shear along a deformation gradient u th pb dating of syn kinematic monazites was performed on mylonites the oldest 340 ma ages were obtained in protomylonites whereas ages of 320 ma were found in mylonites from the core of the shear zone these ages indicate that the ferriere mollieres shear zone is a still preserved variscan shear zone ages of 320 ma obtained in this work are in agreement with ages of the dextral transpressional shear zones occurring in the maures tanneron massif and corsica sardinia however transpression in the argentera mercantour massif started earlier than in other sectors of the southern variscan belt this is possibly caused by the curvature of the belt triggering the progressive migration of shear deformation our data allow a correlation between the argentera mercantour massif and other segments of the southern european variscan belt in particular with maures tanneron massif and corsica sardinia and contribute to fill a gap in the age of activity and in the kinematics of the flow of the system of dextral shear zones of the southern portion of the evsz

strike slip orogens an explanation for the hercynides the nature of oblique plate interactions is not yet well understood the oblique interaction of pacific and n american plates has resulted in large scale migration rotation and accretion of microplates intervening basins are ephemeral individually filled and deformed oblique motion results in zones of both compression and extension the latter may be sufficient to generate new oceanic crust and the former to obduct it both subduction and collision are restricted in time and space the resulting orogen is extraordinarily complex in detail the far more complicated hercynides are the result of dextral interaction between continental plates europe and africa the lateral variability of the orogen the major and long lived strike slip faults the bimodal volcanism and related ore deposits of the european trough the lizard ophiolite and its melanges the nw spanish ophiolites and the iberian pyrite belt are all explained using an oblique collision model in particular the generation deformation and obduction of ophiolites in oblique slip mobile zones is discussed

upper palaeozoic ophiolite generation and obduction in south cornwall the gramscatho flysch sequence of south cornwall including the melanges of the meneage formation and the lizard ophiolite are described in relation to the development of the gramscatho basin the timing and geotectonic evolution of this feature are considered in its regional context within the rhenohercynian zone of northwest europe this zone is interpreted as an intracontinental dextral transform system that developed during the devonian closure of the so called massif central ocean a basin and rise topography is attributed to extension and compression at offsets on major faults e w extension of the gramscatho pull apart basin in middle and upper devonian times is believed to have caused rifting and the development of ocean crust from which the lizard ophiolite was assembled in an oceanic setting at a ridge transform junction the meneage formation was generated as a result of intrabasinal uplift on transcurrent faults a major change of plate motions took place when the massif central ocean finally closed at the end of the devonian and the weak rhenohercynian zone became a site of crustal convergence from which thrust nappes were transported northwards foreland basins were sequentially developed and deformed by thin skinned tectonics as the system advanced northwards during the carboniferous

paleomagnetism and the orocline hypothesis eldredge s bachtadse v and van der voo r 1985 paleomagnetism and the orocline hypothesis in n l carter and s uyeda editors collision tectonics deformation of continental lithosphere tectonophysics 119 153 179 oroclines were originally defined by carey as curved mountain belts which initially were straight or at feast straighter than they are today in the last few years the definition has been broadened to include any curved mountain belt regardless of its original shape since the occurrence of oroclinal bending is best recorded in the change of declination as a function of tectonic setting paleomagnetic and structural data from six potential oroclines have been compiled and analyzed to determine the amount of rotation displayed by the change of paleomagnetic declination relative to the change in strike of the fold belt the arcuate belts investigated are the sicilian calabr n arc and the umbrian arc of italy the swiss portion of the jura mountains the central portion of the appalachian mountains from pennsylvania to virginia u s a the wyoming idaho overthrust belt of western north america and the hercynides of western and central europe the jura mountains and the pennsylvania virginia portion of the appalachians fail to show significant oroclinal bending the wyoming idaho belt shows a combination of rotated possibly oroclinai and unrotated thrust sheets in the sicilian calabrian arc significant oroclinat bending caused by the impingement of the calabria peloritani nappes in the late tertiary can be demonstrated while the umbrian arc of similar age in the northern apennines also shows oroclinal bending on a smaller scale hercynian europe the only belt included in which deformation of basement rocks can be demonstrated shows oroclinal bending at least so as well as a marked original curvature 70 in its western part common to all the orociines studied in this paper is the probable impingement of a rigid block or continental margin during the orogeny causing subsequent deformation and bending of the fold belt

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

correlation between the palaeozoic structures from west iberian and grand banks margins using inversion of magnetic anomalies abstract the ibero armorican arc iaa is a huge geological structure of pre cambrian origin tightened during hercynian times and deeply affected by the opening of the atlantic ocean and the bay of biscay its remnants now lie in iberia north western france and the canadian grand banks margins the qualitative correlation between these three blocks has been attempted by several authors e g lefort j p 1980 un fit structural de l atlantique nord arguments geologiques pour correler les marqueurs geophysiques reconnus sur les deux marges mar geol 37 355 369 lefort j p 1983 a new geophysical criterion to correlate the acadian and hercynian orogenies of western europe and eastern america mem geol soc am 158 3 18 galdeano a miranda j m matte p mouge p rossignol c 1990 aeromagnetic data a tool for studying the variscan arc of western europe and its correlation with transatlantic structures tectonophysics 177 293 305 using magnetic anomalies mainly because they seem to preserve the hercynian zonation in spite of the strong thermal and mechanical processes that took place during rifting and ocean spreading in this paper we present a new contribution to the study of the iaa structure based on the processing of a compilation of magnetic data from iberia and grand banks margins to interpret the magnetic signature a fourier domain based inversion technique was applied considering a layer with a constant thickness of 10 km and taking into account only the induced field the digital terrain model was derived from etopo5 etopo5 1986 relief map of the earth s surface eos 67 121 and terrainbase terrainbase 1995 in row iii l w hastings d a dunbar p k eds worldwide digital terrain data documentation manual cd rom release 1 0 geodas ngdc key to geophysical records documentation n 30 april databases the pseudo susceptibility distribution obtained was repositioned for the 156 5 ma epoch using the srivastava and verhoef srivastava s p verhoef j 1992 evolution of mesozoic sedimentary basins around the north central atlantic a preliminary plate kinematic solution in parnell j ed basins on the atlantic seaboard petroleum geology sedimentology and basin evolution geological society special publication no 62 pp 397 420 pole using this coherent magnetic framework we can verify that the continuity between adjacent blocks is quite good in terms of the amplitude wavenumber and magnetic susceptibility pattern if we accept that the magnetic properties can be taken as a marker of the hercynian zonation as was verified in previous studies miranda j m galdeano a rossignol j c mendes victor l a 1989 aeromagnetic anomalies in mainland portugal and their tectonic implications earth planet sci lett 95 161 177 galdeano a miranda j m matte p mouge p rossignol c 1990 aeromagnetic data a tool for studying the variscan arc of western europe and its correlation with transatlantic structures tectonophysics 177 293 305 socias i 1994 estudios de los elementos del campo magnetico en la espana peninsular a partir de datos aeromagmaneticos ph d thesis university of madrid we can conclude that 1 the characteristic magnetic signature of ossa morena zone is absent on the iberian margin and west of it 2 no eastward continuation of the collector anomaly is found in iberia 3 only the inner zones of the variscan belt can be followed towards nw france 4 there is a major left lateral strike slip fault along the northern portuguese shoreline that cuts the iaa and significantly displaces the once contiguous variscan units

constraints on the flux of meteoritic and cometary water on the moon from volatile element n ar analyses of single lunar soil grains luna 24 core abstract we report new nitrogen and argon isotope and abundance results for single breccia clasts and agglutinates from four different sections of the luna 24 drill core in order to re evaluate the provenance of n trapped in lunar regolith and to place limits on the flux of planetary material to the moon s surface single luna 24 grains with 40ar 36ar ratios 10 1126 science 188 4184 162 is no longer apparent when the luna and apollo data are combined instead the n isotope signatures corrected for cosmogenic 15n are consistent with binary mixing between isotopically light solar wind sw n and a planetary n component with a 15n value of 100 to 160 the lower 15n values of luna 24 grains compared to apollo samples reflect a higher relative proportion of solar n resulting from the higher sw fluence in the region of mare crisium compared to the central near side of the moon carbonaceous chondrite like micro impactors match well the required isotope characteristics of the non solar n component trapped in low antiquity lunar regolith in contrast a possible cometary contribution to the non solar n flux is constrained to be 3 13 based on the mixing ratio of sw to planetary n obtained for recently exposed lunar soils we estimate the flux of micro impactors to be 2 2 5 7 103 tons yr 1 at the surface of the moon our estimate for luna 24 agrees well with that for young apollo regolith indicating that the supply of planetary material does not depend on lunar location thus the continuous influx of water bearing cosmic dust may have represented an important source of water for the lunar surface over the past 1 ga provided that water removal rates i e by meteorite impacts photodissociation and sputtering do not exceed accumulation rates

estimation of the crustal bulk properties beneath mainland portugal from p wave teleseismic receiver functions in this work we present results from teleseismic p wave receiver functions prfs obtained in portugal western iberia a dense seismic station deployment conducted between 2010 and 2012 in the scope of the wilas project and covering the entire country allowed the most spatially extensive probing on the bulk crustal seismic properties of portugal up to date the application of the h stacking algorithm to the prfs enabled us to estimate the crustal thickness h and the average crustal ratio of the p and s waves velocities v p v s for the region observations of moho conversions indicate that this interface is relatively smooth with the crustal thickness ranging between 24 and 34 km with an average of 30 km the highest v p v s values are found on the mesozoic cenozoic crust beneath the western and southern coastal domain of portugal whereas the lowest values correspond to palaeozoic crust underlying the remaining part of the subject area an average v p v s is found to be 1 72 ranging 1 63 1 86 across the study area indicating a predominantly felsic composition overall we systematically observe a decrease of v p v s with increasing crustal thickness taken as a whole our results indicate a clear distinction between the geological zones of the variscan iberian massif in portugal the overall shape of the anomalies conditioned by the shape of the ibero armorican arc and associated late paleozoic suture zones and the meso cenozoic basin associated with atlantic rifting stages thickened crust 30 34 km across the studied region may be inherited from continental collision during the paleozoic variscan orogeny an anomalous crustal thinning to around 28 km is observed beneath the central part of the central iberian zone and the eastern part of south portuguese zone

u pb ages from sw poland evidence for a caledonian suture zone between baltica and gondwana faunal and palaeomagnetic evidence suggests the existence of a c 3000 km wide tornquist sea between gondwana and baltica in early ordovician times which narrowed to 50 2 ma an unmetamorphosed ophiolite gives a 420 20 2 ma age whilst in two other terranes amphibolite facies island arc lavas have fossiliferous lower ludlow 424 415 ma sequences all are unconformably overlain by unmetamorphosed upper devonian conglomerates a sinistral transpressive regime is observed in regionally extensive mylonite zones titanite and zircon ages 338 2 3 and 339 4 ma record variscan magmatism the data suggest considerable narrowing of the tornquist sea during the ordovician continuing ocean floor and island arc activity in the silurian and final sinistral transpressive closure by the mid devonian

correlating deformation in variscan nw iberia using porphyroblasts implications for the ibero armorican arc abstract 3 d microstructural analysis of 30 porphyroblastic samples from the variscan orogen in nw iberia has revealed four sets of inclusion trails with distinctive geographic trends and relative timing the chronological and orientational consistency of these microstructures provides a reference frame for the correlation of macroscopic structural successions the two younger inclusion trail sets correlate with the main map scale structures of middle to upper carboniferous age whereas the two older sets correspond to mesoscopic structures preserved locally in low strain pods and dating back as far as 365 ma upper devonian inclusion trail orientations appear uninfluenced by a major orocline in the study area ibero armorican arc outlined by late stage folds and thrusts with variable trends it is proposed that the orocline developed by wnw ese trending transpression superposed on originally n s to ne sw trending structures during a late stage of the orogeny upper carboniferous domains of low or zero strain e g porphyroblasts are inferred to have maintained relatively constant orientations in the zone of transpression presumably due to deformation partitioning effects consequently they preserve a succession of pre orocline structural trends the collected microstructural data also indicate moderate preferred vertical and horizontal orientations of inclusion trails in the analysed samples as reported earlier in other variscan regions this probably witnesses a dynamic equilibrium between tectonic forces and gravity during four periods of differently oriented crustal shortening that generated the four recognised sets of inclusion trails

seismic signature and tectonic cross section of the variscan crust in western france deep seismic reflection profiling ecors program vertical and wide angle survey coupled with field and subsurface geology are used to propose a complete nne ssw section of the variscan belt in western france from belgium to southern brittany on this 800 km long profile which probably crosses two paleozoic sutures the variscan belt appears as a broad fanlike orogen characterized by large 100 km northward and southward overthrusts with polyphase deformation and metamorphism the central part of the belt central armorican zone suffered a simpler dextral shearing parallel to the strike of the belt with only green schist metamorphism deep reflection profiling shows that all the large thrusts visible at the surface root deeply in the lower crust or even crosscut the moho in the same way all the large strike slip faults parallel to the belt appear at depth as narrow discontinuities which crosscut the whole crust and in some cases the moho the seismically well layered crust develops essentially at depth in the most deformed and metamorphic internal parts of the belt in contrast with the relatively transparent brabant foreland basement which escaped the variscan deformation the moho appears as a relatively flat boundary at an average depth of 35 km with different characters it is sharp and strongly reflective both by wide angle and vertical seismics below the internal thrust zones much less distinct in the central armorican zone and only defined by low frequency signals at wide angle below the brabant foreland all these characteristics led us to consider the layering of the lower crust and the moho itself as initially tectonometamorphic features essentially produced by shearing and crust mantle decollement during the variscan stacking of the crust by intracontinental lithospheric subduction

helium ion implantation into minerals abstract we implanted rock forming minerals olivine magnetite ilmenite and rutile with a 3 6 kev helium ion beam which simulates solar wind particles and analyzed implanted helium a total fusion experiment shows that nearly 100 of impinging helium ions is trapped in a target at smaller doses while the concentration of trapped helium tends to be saturated above a helium ion dose of 10 16 ions cm 2 there is no appreciable difference in the concentration of trapped helium among minerals a stepwise heating experiment shows that implanted helium is retained more firmly in magnetite and rutile than in olivine on the basis of the experimental results a high degree of loss of implanted helium out of idps is suggested this may be attributed to decomposition of helium bearing minerals in idps during their entry into the earth s atmosphere

crustal thickening and deformation sequence in the footwall to the suture of the variscan belt of northwest spain abstract the sequence of formation and propagation of structures as well as the evolution of crustal thickening in the variscan belt of northwest spain are proposed in this paper the foreland of this mountain belt shows thin skinned tectonics a polyphase deformation with associated regional metamorphism is recognized in the hinterland zones two important culminations the narcea and lugo antiforms are present in an e w cross section through the footwall to the suture of this orogen such culminations are derived from the stacking of several thrust systems generated during two successive periods the sequence of thrust emplacement helps to clarify the formation of different types of structures at the same time in different places in the orogen

episodic exhumation of hp rocks inferred from structural data and p t paths from the southwestern massif central variscan belt france abstract in the southwestern massif central france hp rocks are found in lower allochthonous units i e hp units sandwiched between upper allochthonous units i e lp units and the parautochthonous unit both devoid of hp rocks hp rocks were formed at minimum conditions of 1 7 gpa 700 c in response to the northward subduction of gondwana beneath armorica during the silurian 430 390 ma their exhumation results from an 80 ma long sequence of tectonic processes effective at various scales and active specifically at each main stage of the evolution of the gondwana lithosphere hp rocks were first exhumed by upward southwestward extrusion during the early devonian 390 380 ma in relation to late stage of subduction in the northern area exhumation is achieved by rifting during the upper devonian 365 ma the most obvious event corresponds to the northwestward thrusting of lp units above hp units during early stages of continental collision 355 ma hp rocks were exhumed for a second time during orogen parallel transpression in response to late stage of continental collision 350 345 ma exhumation in internal zones is achieved by crustal scale normal faulting and erosion during the middle carboniferous 335 315 ma synorogenic extension while compression was still active in the southern external zones exhumation of the whole region is completed by regional uplift and erosional denudation during the upper carboniferous 310 290 ma postorogenic extension subduction and collision have played a key role for driving hp rocks to the surface but their efficiency and the resulting strain pattern depend on the angle of convergence upper devonian rifting and the subsequent early carboniferous crustal thickening prevents to consider exhumation of variscan hp rocks as a single and continuous process and open new questions on the related paleozoic lithosphere history

the ibero armorican arc a collision effect against an irregular continent the ibero armorican arc is the main variscan macrostructure in western europe although it was recognized in the 1920s its genesis is still debatable and the proposed models for its generation questionable however even if some doubts persist it seems that most agree on the general geodynamic evolution of this virgation in both branches in the middle to late devonian iberia was deformed by a sinistral transpressive regime while in the northern branch thrusting events were predominant in the carboniferous a dextral transpression begins to predominate in the armorican branch while the southern branch was deformed by southward thrusting in an attempt to correlate these events we propose that during the late devonian a cantabrian indentor moved northward producing the oblique closure of the southern part of the rheic ocean and an almost orthogonal closure in central europe in the carboniferous the collision with the irregular margin of laurasia induced a rotation of the indentor the intracontinental deformation was then achieved by dextral transpression in the northern branch and thrusting in the southern one

the esmolfe matanca granite penalva do castelo central portugal a keystone to understand the ascent and emplacement of magmas under low tectonic stress abstract the esmolfe matanca ilmenite type granite is analyzed using petrography microstructures anisotropy of magnetic susceptibility and microfracturing the granite occurs in two separated bodies outcropping in distinct villages esmolfe and matanca which are located in the termination of the juzbado penalva do castelo jpcsz and durico beirao dbsz shear zones the petrography shows a progressive textural overprint from magmatic through high medium and low t solid state deformation microstructures the presence of dominantly magmatic microstructures and the absence of deformation patterns at macroscopic scale may indicate an emplacement under low tectonic stress the directional magnetic data indicates a magma ascending and emplacement conditioned by the jpcsz and dbsz the magma passive intruded upwards along the confluence zone between the jpcsz and dbsz and it spread laterally forming an asymmetric laccolithic body the dbsz worked as physical barrier in esmolfe avoiding the spreading of the magma to the north leading to the rotation of the magnetic lineations and foliations drawing onion type trajectories in matanca the magnetic lineations and foliations are dominantly nw se oriented in the western side and ene wsw oriented in the eastern side parallel to the jpcsz regional trend the fluid inclusions planes demonstrated three distinct brittle deformational events linked to the rotation of 1

geodynamic evolution of the sw variscides orogenic collapse shown by new tectonometamorphic and isotopic data from western ossa morena zone sw iberia 1 the pre mesozoic geodynamic evolution of sw iberia has been investigated on the basis of detailed structural analysis isotope dating and petrologic study of high pressure hp rocks revealing the superposition of several tectonometamorphic events 1 an hp event older than circa 358 ma is recorded in basic rocks preserved inside marbles which suggests subduction of a continental margin the deformation associated with this stage is recorded by a refractory graphite fabric and noncoaxial mesoscopic structures found within the host metasediments the sense of shear is top to south revealing thrusting synthetic with subduction underthrusting to the north 2 recrystallization before circa 358 ma is due to a regional scale thermal episode and magmatism 3 noncoaxial deformation with top to north sense of shear in northward dipping large scale shear zones is associated with pervasive hydration and metamorphic retrogression under mostly greenschist facies this indicates exhumation by normal faulting in a detachment zone confined to the top to north and north dipping shear zones during postorogenic collapse soon after 358 ma ago inversion of earlier top to south thrusts 4 static recrystallization at circa 318 ma is due to regional scale granitic intrusions

delimiting geochemical anomalies in the exploration of covered deposits with multifractal methods and using stream sediment data from the iberian pyrite belt southwest iberia abstract the iberian pyrite belt ipb is a world class province of upper paleozoic age for volcanic and shale hosted massive sulfides that includes 5 of the 10 supergiant 150 mt deposits of their kind in the world the volcano sedimentary sequences hosting the ores are locally exposed commonly covered by flysch type successions of variable thickness the baixo alentejo flysch group bafg as a result of primary sedimentary features and superimposed effects due to variscan folding and tectonic stacking in addition and when affected by late developed geomorphic depressions the exhumed paleozoic basement is also capped by meso cenozoic sediments the total thickness of cover sequences on top of the litho stratigraphic sequence of interest can reach 100 s of meters creating problems for mineral exploration a large stream sediment multi element geochemical database for the ipb was done in the 90 s during a wide ranging regional survey this database was reassessed by means of multifractal methods in view of their faculty to enhance the detection of faint geochemical anomalies and provide geochemical indicators to deep buried ore systems several anomalies were detected namely for cu zn and co along nw se to wnw ese trends the main anomalous geochemical trends identified include zones that i extend along the mira formation of bafg opening for the first time two non traditional areas for further exploration studies ii run along the boundary between the mira and mertola formations of bafg probably related to different geochemical signatures and late developed fault controlled epigenetic ore systems and iii overlap windows of volcanic sedimentary sequences within the cenozoic detrital cover and the site below which the deep buried deposit of lagoa salgada is located

a review of the arcuate structures in the iberian variscides constraints and genetic models abstract in the iberian variscides several first order arcuate structures have been considered in spite of being highly studied their characterization formation mechanisms and even existence is still debatable the main ibero armorican arc iaa is essentially defined by a predominant nw se trend in the iberian branch and an e w trend in the brittany one however in northern spain it presents a 180 rotation sometimes known as the cantabrian arc ca the relation between both arcs is controversial being considered either as a single arc due to one tectonic event or as the result of a polyphasic process according to the last assumption there is a later arcuate structure ca overlapping a previous major one iaa whatever the models they must be able to explain the presence of a variscan sinistral transpression in iberia and a dextral one in armorica and a deformation spanning from the devonian to the upper carboniferous another arcuate structure in continuity with the ca the central iberian arc cia was recently proposed mainly based upon on magnetic anomalies geometry of major folds and ordovician paleocurrents the critical review of the structural stratigraphic and geophysical data supports both the iaa and the ca but as independent structures however the presence of a cia is highly questionable and could not be supported the complex strain pattern of the iaa and the ca could be explained by a devonian carboniferous polyphasic indentation of a gondwana promontory in this model the ca is essentially a thin skinned arc while the iaa has a more complex and longer evolution that has led to a thick skinned first order structure nevertheless both arcs are essentially the result of a lithospheric bending process during the iberian variscides

transpression and the build up of the cordillera the example of the bucaramanga fault eastern cordillera colombia widespread wrench tectonics have been described along the northern andes the bucaramanga fault described as sinistral strike slip bounds the high santander massif we combine structural and thermochronological data from the central southern portion of the fault to investigate the vertical displacement the structural survey data show old phases of activity preserved in the host rocks along the fault trace with the superimposition of different generations of slickenlines and both strike slip and dip slip kinematics indicators new and previous thermochronological data show that differential exhumation of the fault walls has been ongoing for the last 50 ma the hanging wall the santander massif records in the central portion decreasing exhumation rates from the early miocene to the mid to late miocene and in the southern portion constant rates from the late oligocene to the pliocene combining such observations the thermochronological offset resulting from the relative motion of the two fault walls is comparable with the observed drop in elevation across the fault suggesting that the present topography of the santander massif is related to vertical movement along the bucaramanga fault we infer that the fault has a significant neogene reverse component consistent with the present day horizontal global positioning system vector data long term exhumation rates and the structural assemblage supplementary material the supplementary materials contain methodological information on the thermochronological procedures a compilation of the previously published data used in this study and the structural geology dataset https doi org 10 6084 m9 figshare c 4620140

tectonics of the beja acebuches ophiolite a major suture in the iberian variscan foldbelt the beja acebuches ophiolitic complex baoc south portugal spain corresponds to a high grade metamorphic belt along the boundary between ossa morena and the south portuguese zones and comprises a lithostratigraphic sequence including from top to bottom metabasalts metamorphosed multiple dyke intrusions in gabbro flasergabbros and metaserpentinites it is affected by three deformation phases d1 affects the ophiolite lower stratigraphic units and is represented by a mylonitic cleavage with a stretching lineation where shear criteria indicates the sense of shear to be towards the north north east this deformation event can be related to the ophiolite emplacement above the crystalline footwall of the serpa antiform affecting precambrian basement and cambrian cover rocks the obduction polarity ist north eastwards similar to the subduction polarity that generates the beja gabbroic complex bgc implying a flake geometry the second deformation phase d2 is represented by an intense wnw ese sinistral shear event which is responsible for the shattered appearance of the suture d2 is reactivated later by a more brittle d3 event involving thrusting to the south west again with a sinistral component 40ar 39ar isotopic ages were obtained for metamorphosed multiple dyke intrusions in the baoc s gabbro 342 6 1 4 ma for metagabbroic cumulates 340 7 1 9 ma and for the undeformed unmetamorphosed bgc 341 1 1 3 ma occurring to the north of the ophiolitic suture these ages reflect a last regional cooling event in the area which post dates the ophiolite emplacement and the intrusion of the bgc through this oceanic sequence

seismic imaging of the western iberian crust using ambient noise boundaries and internal structure of the iberian massif abstract we present new rayleigh wave dispersion maps of the western iberian peninsula for periods between 8 and 30 s obtained from correlations of seismic ambient noise following the recent increase in seismic broadband network density in portugal and spain group velocities have been computed for each station pair using the empirical green s functions generated by cross correlating one day length seismic ambient noise records the resulting high path density allows us to obtain lateral variations of the group velocities as a function of period in cells of 0 5 0 5 with an unprecedented resolution as a result we were able to address some of the unknowns regarding the lithospheric structure beneath sw iberia the dispersion maps allow the imaging of the major structural units namely the iberian massif and the lusitanian and algarve meso cenozoic basins the cadiz gulf gibraltar strait area corresponds to a strong low velocity anomaly which can be followed to the largest period inverted although slightly shifted to the east at longer periods within the iberian massif second order perturbations in the group velocities are consistent with the transitions between tectonic units composing the massif

palaeomagnetism of the ibero armorican arc and the hercynian orogeny in western europe van der voo1 has pointed out that further advances in the understanding of the hercynian orogeny require palaeomagnetic data from well studied orogenic areas we report here palaeomagnetic results of palaeozoic rocks taken in brittany portugal and spain in the ibero armorican arc iaa a large geological feature considered to be a key area for the hercynian orogeny in western europe they show evidence that the iaa formed in two stages extending results obtained in spain by ries et al 2 giving precise constraints for the former shape of the arc we can use pre hercynian palaeomagnetic directions found in spain and portugal to follow its evolution during palaeozoic times this megastructure linking brittany to iberia squeezed between gondwana and the northern continents during the carboniferous did break away from the former block during ordovician times

images of lithospheric heterogeneities in the armorican segment of the hercynian range in france the armorican massif is located in western france it is a part of the hercynian range formed in several phases of se nw compression from devonian to carboniferous time ca 400 300 ma the main tectonic features are the north and south armorican shear zones with wnw ese strike in the framework of the geofrance3d program we have installed 35 seismological stations along two ns lines crossing the main hercynian wnw ese fault systems the data set collected during the experiment allows us to compute a 3d p velocity model and to map s wave seismic anisotropy at depth using teleseismic shear waves splitting measurements the south armorican shear zone sasz is characterized by a strong 4 5 velocity contrast and a fast shear wave azimuth parallel to its strike the north armorican shear zone nasz does not show any significant lithospheric signature the tomographic image and anisotropy results suggest that the armorican lithosphere consists of the juxtaposition of distinct lithospheric blocks assembled in a subduction type process predating the hercynian orogeny d 2002 elsevier science b v all rights reserved

analyses of nitrogen and argon in single lunar grains towards a quantification of the asteroidal contribution to planetary surfaces abstract we performed nitrogen and argon isotopic analyses in single 200 m sized ilmenite grains of lunar regolith samples 71501 79035 and 79135 cosmogenic and trapped components were discriminated using stepwise heating with a power controlled co 2 laser cosmogenic 15 n and 38 ar correlate among different ilmenite grains yielding a mean 15 n c 38 ar c production ratio of 14 4 1 0 atoms atom this yields a 15 n production rate in bulk lunar samples of 3 8 5 6 pg g rock 1 ma 1 which agrees well with previous estimates the trapped 15 n values show large variations up to 300 among different grains of a given soil reflecting complex histories of mixing between different end members the 36 ar 14 n ratio which is expected to increase with increasing contribution of solar ions varies from 0 007 to 0 44 times the solar abundance ratio the trapped 15 n values correlate roughly with the 36 ar 14 n ratios from a non solar end member characterized by a 36 ar 14 n ratio close to 0 and variable but generally positive 15 n values to lower 15 n values accompanied by increasing 36 ar 14 n ratios supporting the claim of hashizume et al 2000 that solar nitrogen is largely depleted in 15 n relative to meteoritic or terrestrial nitrogen nevertheless the 36 ar 14 n ratio of the 15 n depleted solar end member is lower than the solar abundance ratio by a factor of 2 5 5 we explain this by a reprocessing of implanted solar wind atoms during which part of the chemically inert rare gases were lost we estimate that the flux of non solar n necessary to account for the observed 15 n values is comparable to the flux of micrometeorites and interplanetary dust particles estimated for the earth hence we propose that the variations in 15 n values observed in lunar regolith can be simply explained by mixing between solar wind contributions and micrometeoritic ones infalling on the moon temporal variations of 15 n values among samples of different antiquities could be due to changes in the micrometeoritic flux through time in which case such flux has increased by up to an order of magnitude during the last 0 5 ga

kinematic constraints on buckling a lithospheric scale orocline along the northern margin of gondwana a geologic synthesis abstract the paleozoic variscan orogeny was a large scale collisional event involving amalgamation of multiple continents and micro continents existing data suggests oroclinal buckling of an originally near linear convergent margin during the last stages of variscan deformation in the late paleozoic closure of the rheic ocean resulted in e w shortening present day coordinates in the carboniferous producing a near linear n s trending east verging belt subsequent n s shortening near the carb permian boundary resulted in oroclinal buckling this late stage orogenic event remains an enigmatic part of final pangea amalgamation the present day arc curvature of the variscan has inspired many tectonic models with little agreement between them while there is general consensus that two separate phases of deformation occurred various models consider that curvature was caused by dextral transpression around a gondwana indentor strike slip wrench tectonics or a change in tectonic transport direction due to changing stress fields more recent models explain the curvature as an orocline with potentially two opposite facing bends caused by secondary rotations deciphering the kinematic history of curved orogens is difficult and requires establishment of two deformation phases an initial compressive phase that forms a relatively linear belt and a second phase that causes vertical axis rotation of the orogenic limbs historically the most robust technique to accurately quantify vertical axis rotation in curved orogens is paleomagnetic analysis but recently other types of data including fracture geochemical petrologic paleo current and calcite twin data have been used to corroborate secondary buckling a review of existing and new variscan data from iberia is presented that argues for secondary buckling of an originally linear orogenic system together these data constrain oroclinal buckling of the cantabrian orocline to have occurred in about 10 ma during the latest carboniferous which agrees well with recent geodynamical models and structural data that relate oroclinal buckling with lithospheric delamination in the variscan

paleozoic evolution of the armorica plate on the basis of paleomagnetic data new paleomagnetic data support the contention that armorica and gondwana formed a coherent block until ordovician time however by early devonian time armorica collided with the north american northern european assembly to form the old red continent and the collision itself was responsible for the acadian orogeny not for the earlier taconic orogeny as postulated previously the carboniferous collision of gondwana with the old red continent subsequently formed pangaea and produced the appalachian hercynian orogeny

late variscan emplacement and genesis of the vieira do minho composite pluton central iberian zone constraints from u pb zircon geochronology ams data and sr nd o isotope geochemistry abstract in the central iberian zone synorogenic syn and late d3 the last deformation phase composite batholiths of biotite rich granitods with peraluminous character are well represented we report here u pb zircon and monazite ages geochemical sr nd o isotopic data and anisotropy of magnetic susceptibility ams studies for the late d3 vieira do minho pluton in northern portugal ams reveals the paramagnetic behaviour of these granites and the magnetic fabric enhances the major role of nw se regional anisotropies on controlling the ascent and emplacement of the magmas magnetic anisotropy and medium temperature microstructures also point out the evolution of regional tectonics during crystallization of the magma u pb zircon and monazite analyses yield consistent ages of 310 2 ma and 312 2 ma interpreted as emplacement age the vieira do minho pluton consists of two peraluminous monzogranites the vmg and the mrg both have similar end values vmg 5 2 to 5 7 mrg 4 98 to 5 96 but the vmg is slightly enriched in 87sr 86i 0 7087 0 7098 as well as in 18o in the range of 10 6 to 11 0 than the mrg with 87sr 86i 0 7064 0 7075 and 18o 9 9 10 5 these granites are associated with coeval scarce grabroic intrusions and or mafic microgranular enclaves which are not considered as mafic precursors of the associated granitic magmatism instead a lower metaigneous crustal source at different levels is proposed based on the available data set

brine pool deposition for the zn pb cu massive sulphide deposits of the bathurst mining camp new brunswick canada i comparisons with the iberian pyrite belt abstract the ordovician zn pb cu massive sulphide ore deposits of the bathurst mining camp share many features with those of the devonian carboniferous iberian pyrite belt particularly the tendency to large size tonnage and metal content shape as far as can be determined after allowing for deformation metal content particularly fe cu pb zn and sn mineral assemblages pyrite arsenopyrite pyrrhotite and lack or rarity of sulphates sulphide textures particularly framboidal pyrite lack of chimney structures and rubble mounds irregular metal or mineral zoning and the low degree of zone refining compared to hokuroku ores the major differences between the provinces are the lack of vent complexes and the presence of sn cu ores in the iberian pyrite belt there are also similarities in the geological setting of the two camps both lie within continental terranes undergoing arc continent and continent continent collision and in each case massive sulphide mineralisation followed ophiolite obduction the ore deposits are associated with bimodal volcanic rocks derived from morb and continental crust and marine shales and mineralisation was locally accompanied or followed by deposition of iron formations fluid inclusion data from veins in stockworks from at least six of the iberian massive sulphide deposits point to sulphide deposition having taken place in basins containing mostly spent saline ore forming fluids brine pools and it is suggested that most of the major features of the bathurst deposits can be explained by similar processes the proposed model is largely independent of ocean sulphate and o 2 content whereas low values of each are requisites for the current spreading plume model of sulphide deposition in the bathurst camp

change of nappe transport direction during the variscan collisional evolution of central southern sardinia italy abstract the collisional variscan early carboniferous evolution of the greenschist facies metamorphic basement of sardinia is characterized by three deformation phases and two 90 reorientations of shortening direction during the first phase of deformation n s shortening occurred with south facing isoclinal folding south directed nappe emplacement and mylonitization in central and southeastern sardinia and large scale e w striking upright folds in southwestern sardinia emplacement of the barbagia meana sardo gerrei and riu gruppa units took place during this event this deformation phase was followed by e w shortening with w directed emplacement of the sarrabus and arburese units along the villasalto thrust and upright to e dipping large scale n s striking upright folds in southwestern sardinia during the third deformation event the shortening direction again rotated 90 and n s shortening produced kilometer scale antiforms and synforms the most prominent features in the metamorphic basement of sardinia the limbs of the kilometer scale antiforms and synforms are vertically shortened during gravitational collapse with contemporaneous faulting and conjugate shear zone development presence of large scale e w oriented antiforms was therefore critical for the formation of late variscan extensional features such as e w striking low angle normal faulting

new kinematic constraints on the cantabrian orocline a paleomagnetic study from the penalba and truchas synclines nw spain abstract the cantabrian orocline is a large structure that bends the variscan orogen of western europe in nw iberia the extensively studied kinematics of its core the foreland of the orogen indicates that the structure is secondary i e acquired after the formation of the orogenic edifice however the extent of the cantabrian orocline away from its core is under debate in this paper we study the kinematics of the cantabrian orocline beyond the foreland we collected and analyzed samples from the northern and central parts of the truchas syncline which provides new data within the hinterland of the orogen in nw iberia the analysis of 320 samples shows a late carboniferous remagnetization with an e to ne declination and shallow downward inclinations these results suggest a counter clockwise rotation of 60 and peri equatorial but still southern hemisphere latitude for iberia during the uppermost carboniferous early permian this rotation fits with the expected kinematic evolution of the truchas syncline if it indeed was part of the cantabrian orocline

a new model for the hercynian orogen of gondwanan france and iberia abstract the hercynian orogen of gondwanan france and iberia is a collage of disparate terranes separated by faults plate reconstructions indicate that the orogen developed during a massive dextral transpression as laurentia slid along the boundary of gondwana and as laurentia baltica and east avalonia rotated clockwise to form pangea it is proposed therefore that the collage is the result of this transpression and that it is an amalgamation of displaced tectonostratigraphic terranes which represent the dismembering of the gondwanan shelf with its stable platform ordovician devonian sedimentary sequence and the neighbouring rheic ocean specifically it is proposed that 1 the slice of the gondwanan shelf that now forms north brittany was displaced dextrally from nw africa around iberia by more than 2000 km 2 the ophiolites oceanic material and volcanic arcs of south armorica and the massif central represent slices of the rheic ocean displaced dextrally along the gondwana margin and shuffled in amongst slices of gondwanan shelf 3 the convergent component of the transpression is represented by thrusts throughout the region the leon terrane of france and ophiolite bearing klippe in nw iberia the ibero armorican arc was formed by wrapping the mobile dextral shear belts about a rigid iberian basement block the dextral porto tomar shear zone represents the more important shearing in iberia and the iberian sinistral shears are interpreted as bookshelf type structures subsidiary to the dextral shearing

kinematics and vorticity of flow associated with post collisional oblique transpression in the variscan inner zone of northern sardinia italy abstract quartz c axis fabrics vorticity of flow and deformation temperatures were analyzed in samples collected in the central sector of the variscan inner zone in sardinia italy in order to constrain the kinematics of exhumation of medium and high grade metamorphic rocks during d2 post collisional deformation we investigated two shear belts with opposing shear senses these shear belts are developed parallel to the trend of the inner zone which marks the boundary between two metamorphic complexes our data suggest that the sinistral shear belt initiated during the early stage of d2 deformation in a simple shear dominated regime whereas the dextral shear belt initiated later in a pure shear dominated regime we document a general non coaxial flow regime with contemporaneous pure and simple shear components geometrical relationships reveal the operation of oblique extrusion during a compressive regime where the coaxial component acted sub horizontal and orthogonal to the trend of the axial zone changes in the kinematics vorticity of flow and strain geometry that occurred during d2 deformation may be related to post collisional orogen parallel displacement caught up in the variscan orogeny

emplacement mechanism of caria vila da ponte pluton northern portugal building and internal magmatic record abstract the late to post tectonic biotite granites from caria vila da ponte area were studied for their mineralogical microstructural and petrophysical standpoint using anisotropy of magnetic susceptibility coupled to petrography and scanning electron microscopy one main direction n339 345 e of stretching magnetic lineations was found indicating that the emplacement of these granites was tectonically controlled although the caria ca on the w and vila da ponte vp on the e granites outcrops in distinct bodies the results pointed out similar petrographic and petrophysical characteristics for both thus it is suggested that both granites belong to only one asymmetric laccolith with a deep root feeder zone located in vp massif a five stage model is proposed i passive magma ascent along nnw sse deep faults and in situ doming emplacement recorded in the magnetic magmatic fabric ii after total crystallization of the pluton a late alteration most evident in the vp granite promoted a normal zoning of the magnetic susceptibility iii nnw sse to nne ssw regional faults promoted the uplift of the ca relatively to vp iv laying of quartz veins implied the development of an intense sericitization most evident in the ca v circulation of later hot fluids implied alteration and concentration of metallic phases

transcurrent continental tectonics model for the ossa morena zone neoproterozoic paleozoic evolution sw iberian massif portugal the ossa morena zone sw iberian massif was affected by continuous orogen parallel transcurrent continental tectonics from the neoproterozoic to the carboniferous times involving transtension tt and transpression tp processes that co existed together occurred separately in neighbouring regions by the means of strain partitioning or even worked diachronically a first stage of transpression tp1 took place during the late neoproterozoic lower cambrian as a result of cadomian arc continent collisional processes structures generated by transtension tt1 from cambrian to lower devonian were related to strong lithosphere stretching responsible for the development of basins controlled by major detachments tilting rifting and important tectono thermal diachronic processes denudation phenomena and inhibition of sedimentation related with thermal uplift asthenosphere upwelling and consequent subsidence caused by isostatic equilibrium involving generalized transgressions were processes responsible for major unconformities the variscan tp2 tt2 episodes that followed diachronically tp1 tt1 by maintaining the orogen parallel transport direction were concomitant with syntectonic deposition of continental basins in the omz and foreland basins in the spz tt2 local transtension and tectonic exhumation of deep crustal rocks along major shear zones favoured the opening of tectonic troughs filled up by sediments and volcanism tp2 shortening have generated fold axes parallel to the orogen strike and composite dissymmetric flower structures

a non cylindrical model for the northwest iberian allochthonous terranes and their equivalents in the hercynian belt of western europe abstract a case is made for a non cylindrical development of the european hercynian belt far travelled allochthonous terranes in the belt consist of a mixture of units including catazonal units ophiolites and units derived from the continental margin of gondwana they often depict a metamorphic history of intermediate to high pressure type and caledonian to eo hercynian age and are thought to have been put together in the early stages of the orogeny through a process partly obductive directed onto the continental margin of gondwana considerations upon the disposition of the terranes their relationships with the paleogeography of the gondwana realm and the structures in them suggest that their emplacement took place in an oblique fashion at a small angle to the margin of the continent the proposed allochthon could be related to the development of an island arc or a wedge like subplate in the southern part of the baltica plate later convergence between gondwana and laurussia involving transcurrent mostly dextral movements combined with tectonic escape phenomena would account for the present complexity of the belt and for the narrow strip the allochthonous terranes delineate in westernmost europe

experiments on thermal release of implanted noble gases from minerals and their implications for noble gases in lunar soil grains abstract experiments on ion implantation were performed in order to study the release mechanisms of solar particles from lunar soil grains helium neon and argon ions were implanted into olivine and ilmenite the release temperatures of noble gases were investigated by heating samples stepwise the results show that they depend on irradiation energy and dose we conclude that the release temperature is related to the size of bubbles in which noble gases are trapped noble gases in small and large bubbles are released at 400 600 c and 800 1200 c respectively in ne and ar implantation experiments into olivine a component was released during recrystallization of amorphized surfaces based on these experimental results we suggest that components released from lunar ilmenite grains at different temperatures would correspond to solar particles of different energies we also suggest that he and ne of solar wind energy about 1 kev amu should be retained in lunar ilmenite grains while they should be lost from olivine grains

rheologically induced structural anomalies in transpressive regimes abstract local structural anomalies are sometimes found in transpressive regimes they can be related to strain partitioning processes but in some cases other types of heterogeneities could affect the deformation style this paper shows that rheological heterogeneities can radically influence the geometry of faults in transpression zones and cause them to be markedly non planar in the marao region of northern portugal a zone in which variscan structures are sw facing is found within the regional ne facing geometry this anomaly is adjacent to a complex shear zone mina ribeira das cestas where the fault plane is curved however the surrounding material does not show any signs of a related folding event detailed field studies mainly concerning the rheological contrasts between the deformed lithostratigraphic units show a close relationship between the structural anomaly and the movement along rheological anisotropies these observations complemented by experimental deformation of multilayers composed of analogue materials allow the construction of a generic model strain partitioning during the initial stage of the sinistral transpressive variscan deformation produced the juxtaposition of lithostratigraphic units with strongly different rheological contrasts subsequent flattening deformation induced heterogeneous indentation phenomena producing the non planar geometry of the complex shear zone the structural heterogeneities caused could have an important role in the evolution of a transpressive domain

relative timing of transcurrent displacements in northern gondwana u pb laser ablation icp ms zircon and monazite geochronology of gneisses and sheared granites from the western iberian massif portugal abstract the variscan belt of western and central europe was formed by the oblique subduction of the rheic ocean and the collision of laurussia with gondwana during the late palaeozoic we present field relationships and new u pb la icp ms zircon and monazite ages for variscan gneisses and granites from a key section of the western iberian massif the martinchel section records the interplay of two kilometre scale variscan transcurrent shear zones active in the gondwana basement of pangaea the porto tomar fault zone ptfz and the coimbra cordoba shear zone ccsz different kinematic models have been invoked to explain the formation and evolution of these major variscan structures mainly based on assumptions made in the absence of reliable radiometric ages we show that 1 ductile deformation and metamorphism were active in the ccsz during the visean serpukhovian c 335 318 ma and created conditions for amphibolite facies metamorphism and coeval emplacement of granites and 2 later ductile brittle deformation related to dextral movements along the ptfz overprinted the earlier foliation and folds derived from the ccsz deformation and deformed the previously intruded granites u pb dating of zircon and monazites yield c 335 ma ages for the ductile deformation developed under amphibolite facies metamorphic conditions in the martinchel gneisses of the ccsz the gneisses were intruded by granites at c 335 318 ma and both were later deformed under ductile brittle conditions by dextral motion on the ptfz the geometry of the martinchel gneisses typical of the ccsz changed from one of thrusting to one of normal faulting by refolding of the early foliation stretching lineation and asymmetric structures related to the later ptfz dextral shear episode this pattern of interference is not fully considered in previous models and may lead to incorrect tectonic interpretations according to our data and recently published ages we suggest that the ptfz was active after the serpukhovian kasimovian since the c 318 308 ma granites are deformed by north south 170 dextral shear planes these data are critical to the interpretation of large scale carboniferous transcurrent displacements in northern gondwana iberian massif and bear upon global models of crustal deformation that emphasize the importance of long lived dextral movements during the collision between northern gondwana and laurussia following the closure of the rheic ocean

paleomagnetic results in support of a model for the origin of the asturian arc abstract paleomagnetic directions have been determined at 17 cambrian and 28 carboniferous limestone sites distributed along the asturian arc of the hercynian fold belt in northwestern spain the stable vectors are carried by hematite in all cases and also by magnetite in some grey carboniferous limestones a secondary component of magnetization is usually removed well below 400 c and the higher temperature component is taken to be the characteristic direction the structure at each site was carefully evaluated in order to make optimum local tectonic corrections in addition the data must be corrected for rotations about a vertical axis to allow for a phase of radial folding superimposed on earlier structures the corrected paleomagnetic declinations are found to vary systematically along the arc of the fold belt consequently paleomagnetic data from the asturian arc should not be included in compilations used for the construction of a paleozoic apparent polar wander path the paleomagnetic data allow us to distinguish between different tectonic models for the evolution of the asturian arc a two stage model for the development of the present curvature is favored part of the curvature appears to be primary preceding the hercynian deformation the first stage of the model involved rotations of thrust sheets during their emplacement producing a more tightly curved arc than the original form in a second stage the development of radial folds further tightened the curvature of the arc both stages result in clockwise rotations in the north and anticlockwise rotations in the south

structural evolution of the southernmost segment of the west european variscides the south portuguese zone sw iberia abstract the south portuguese zone spz represents the southernmost unit of the iberian massif it is mainly composed of three structural domains from north to south the beja acebuches ophiolitic complex baoc the pulo do lobo antiform pla and the iberian pyrite belt ipb this study proposes a structural analysis of the spanish part of the spz that allows us to point out two main kinds of deformation one accommodated by early top to the south and following sinistral strike slip tectonics in the northern part of the spz and the other by top to the south thrusting in a wide southern branch this transition underlining the strain partitioning is analysed by lattice preferred orientation of quartz using the texture goniometry method it shows that the deformation is accommodated in the pla at low to middle temperature by basal and prismatic a slip quartz textures suggest increasing thermal conditions of deformation from thrust to strike slip tectonics our work within the ipb allows us to present a sequence of deformation showing a primary south verging ductile thrusting and coeval crustal thickening in response to the thin skinned tectonics the progressive deformation generated backthrusts while it turns shallower southward these features are summarised in an interpretative cross section of the spz that underlines the main structural style of deformation the fore mentioned southward propagating thin skinned thrusts

fry and rf ϕ strain methods constraints and fold transection mechanisms in the nw iberian variscides abstract apulia is a small portuguese sector in nw of central iberian zone that have been deformed in a non coaxial sinistral transpressive regime during the first and main variscan tectonic event d1 this deformation give rise to a major nw se anticline where the s1 n s cleavage transect the inverted short ne limb two and three dimensional strains analysis have been done in the low metamorphic grade ordovician quartzites of this limb using fry and rf methods the data show that most deformation was due to intergranular deformation mechanisms the intragranular deformation leading to the distortion of strain markers and to cleavage was very incipient and a latter event in the d1 phase the apparent plane strain ellipsoids if no volume change is assumed related to the intragranular mechanisms contrast with the more prolate strain ellipsoids related to the bulk deformation of apulia quartzites this constrictional bulk strain fabrics are characteristic of the sinistral transpressive regimes dominant in the northern sectors of the central iberian zone

a new model for the hercynian orogen of gondwanan france and iberia discussion the study by shelley and bossieare 2000 is an important contribution to the discussion concerning the ibero armorican arc iaa generation model this model comes as one of a sequence of previous ideas already published in several papers bard 1971 matte and ribeiro 1975 lefort and ribeiro 1980 ribeiro et al 1980 burg et al 1981 brun and burg 1982 julivert 1987 ribeiro et al 1990 dias and ribeiro 1995 ribeiro et al 1995 silva 1997 a common feature of the interpretations in these papers is the great importance attributed to two major transcurrent faults the dextral porto tomar shear zone ptsz and the sinistral tomar badajoz cordoba shear zone bcsz to explain the extension of the iberian structures into the armorican massif in the form of trace the arcuate shape of the iaa the large scale migration rotation and accretion of microplates controlled by oblique interactions have been a matter of controversy since researchers applied different kinematic models to reconstruct such global tectonic movements for example badham 1982 interpreted the hercynides as the result of dextral interaction between europe and africa and considered the arcuate geometry of the iaa as a secondary structure in contrast matte 1986 compared the present example of the himalayas with the structures of the iaa in terms of an indentation of crustal fragments and proposed the progressive development of the symmetrical outward lateral escape of blocks in france and iberia in this model the indentor migration caused opposing strike slip movements on either side represented by the major transcurrent faults of the armorican massif and the iberian massif this geometry and kinematics were considered to be syngenetic with the formation of the arcuate structure of the iaa however the main geologic lines linking these western european hercynian massifs through major shear zones are still questionable e g lefort 1989 in this comment we believe that the regional approach regarding the transcurrent faults of hercynian iberia bcsz and ptsz cannot be considered to be well established in the following text we will comment on signi cant omissions concerning available work of the last decade and also focus our discussion on eld data and the structural interpretation of hercynian iberia portugal and spain

zn pb cu massive sulfide deposits brine pool types occur in collisional orogens black smoker types occur in backarc and or arc basins volcanic hosted massive sulfide deposits of zn pb cu type were derived either from seawater dominated buoyant fluids that built mounds on the seafloor e g the ores of the hokuroku basin japan or from saline fluids that reversed buoyancy on mixing with seawater and filled basins on the seafloor e g several ores of the iberian pyrite belt and the mount read province in tasmania the hokuroku ores formed above subduction zones during protracted periods of regional extension but both the iberian pyrite belt and the mount read province formed under extensional stress during continent continent iberia or arc continent mount read collision and orogenesis in the iberian pyrite belt oblique convergence resulted in transcurrent faulting and this may also be the case for the mount read province transcurrent faulting may have allowed easy vertical access for the ore related magmas some of which were sourced in the asthenosphere as well as the blueschist and eclogitic facies emplaced in adjacent terrains and possibly also saline fluids exsolved from the magmas

magmatic structures and kinematics emplacement of the variscan granites from central portugal serra da estrela and castro daire areas abstract the late d3 variscan granites which represent the most important volume of granites of central portugal are studied here for their magmatic and solid state fabrics by means of the anisotropy of magnetic susceptibility ams technique in a 5000 km 2 area located between guarda and castro daire including the serra da estrela region two main directions n150e and n20e of stretching lineations are found indicating that the emplacement of these late kinematic granitoids was tectonically controlled a three stage model is proposed in which a openings along n150 striking dextral strike slip faults allow the first granitic magmas to be emplaced in the upper crust of palaeozoic metasediments and syn d3 granitoids b openings along n20 striking possibly sinistral strike slip faults conjugates to the prior strike slip faults and allow the enlargement of the granitic plutons and c the final emplacement of this huge volume of granitic rocks was mainly controlled by the magma pressure which explains the rarity of structures related to this stage of granites emplacement in the country rocks this structural study of granitic rocks yields new constraints on the tectonic evolution of this part of the variscan orogenic belt at c 300 ma

fluid inclusion and s c o pb isotope study of pb zn cu ag hydrothermal veins from central and northern portugal metallogenic implications abstract the pb zn cu ag hydrothermal veins from central and northern portugal occur in two distinct districts aveiro moinho da pena carvalhal palhal and telhadela and braganca ferronho vale da madre estevais and olgas the ore veins are composed by sulfides galena sphalerite chalcopyrite pyrite several quartz generations in both districts and dolomite as a gangue mineral in the aveiro district palhal and telhadela a mineralogical fluid inclusion and s c o pb isotopic study was carried out on ore mineralization with the aim to explain its genesis and metallogenic evolution aqueous fluids of h2o cacl2 or h2o nacl cacl2 in composition were identified in both districts the th tmi evolution starts with fluids of medium temperature 250 oc and low to moderate salinity 1 eq wt nacl in the aveiro district and 0 5 eq wt in the braganca district evolving to lower temperatures 250 to 100 oc and higher salinity for the aveiro district 20 eq wt nacl and lower salinity 4 eq wt nacl for the braganca district fluids of high salinity 20 eq wt nacl were trapped during the final stage at temperatures below to 100 c a mixing magmatic and meteoric fluid explained the wide negative values range of 34s measured for the samples from the aveiro district high positive 34s values measured on samples collected from the braganca district confirm a seawater source the c and o stable isotope measured on dolomite and calcite show a 13c depleted source for both carbonates pointing to a carbon source s related to the organic matter oxidation the pb isotope data confirm an uranogenic and a thoriogenic source the pb zn ore deposits from the aveiro and braganca districts are related to episodes of fluid circulation in the upper crust during late to post variscan period the lack of spatial and temporal relationship with magmatic episodes and the presence of basinal and superficial origin fluids support this idea

combined thrusting and wrenching in the ibero armorican arc a corner effect during continental collision this paper is an attempt to reconcile strain pattern and deformation history in an overall arcuate structure with continental collision processes geological data are first presented for the early history 400 ma of the variscan orogenic belt in france principal stretch trajectories are on a large scale more or less parallel with the trend of the belt they became strongly oblique to this trend near the basal surfaces of the nappes a kinematic model combining two orthogonal shear components is proposed to explain such a strain pattern it is concluded that the observed strain trajectories result from a combination of a southward thrusting and a sinistral wrenching this conclusion is in good agreement with previous conclusions gained by several local microtectonic studies the geodynamic significance of combined thrusting and wrenching at the scale of the ibero armorican arc is discussed and a progressive deformation model is proposed

polyphase variscan emplacement of exotic terranes morais and braganca massifs onto iberian successions evidence from 40ar 39ar mineral ages abstract the braganca and morais nappe complexes comprise internally imbricated continental tectonic units including schists deformed metagranite granulite and local eclogite and a structurally underlying ophiolite nappe high pressure assemblages in some of the continental sequences were variably retrogressed during an amphibolite facies metamorphic overprint by contrast rocks within the ophiolite nappe display prograde amphibolite facies assemblages hornblende concentrates from both tectonic units exposed in the braganca nappe complex record 40 ar 39 ar plateau and isotope correlation ages of c 385 390 ma a similar date is recorded by hornblende within mylonitic amphibolite ophiolite protolith along a ductile thrust which separates the two major nappe units muscovite within blastomylonitic metagranite lagoa augen gneiss in upper structural levels of the morais massif records 370 375 ma 40 ar 39 ar plateau ages muscovite within phyllinite developed along a ductile thrust separating the gneiss from the structurally underlying ophiolite nappe records a 375 ma age together the 40 ar 39 ar data suggest that a regionally significant early variscan amphibolite facies metamorphism occurred prior to c 385 390 ma early devonian this was associated with ductile imbrication of continental and ophiolite structural units with resultant formation of a composite nappe complex the composite nappe complex must have been maintained at relatively high structural levels throughout the remaining variscan evolution because there is no evidence for post 370 ma rejuvenation of intracrystalline argon systems in any of crystalline structural units examined this is in marked contrast to a significant late devonian c 330 ma locally high pressure metamorphism which is recorded in structurally underlying elements of the lower allochthon part of a foreland thrust complex composed of metasedimentary units with iberian protolith affinities together available chronologic constraints indicate emplacement of the previously assembled composite nappe complex into its present relative structural position at c 330 ma with resultant deformation and metamorphism of structurally underlying components of the iberian thrust complex

superposition of shear zones during orogenic development an example from the nw variscan belt viana do castelo nw portugal abstract the viana do castelo region of nw portugal is the only domain in the west variscan where the transition from the d 1 strike slip structures to the d 1 east vergent flat lying structures formed during devonian carboniferous continental collision has been recognized although intrusion of voluminous granite bodies has resulted in extensive recrystallization of host rocks kinematic analysis of these rocks using mesoscopic criteria and quartz cpos crystallographic preferred orientation reveals shear senses coherent with the field evidence and suggests that d 1 deformation was partitioned into transpressional and compressional components we also interpret the strain patterns to the effects of non cylindrical superposed shear zones the above aspects can be useful to understand the complex tectonic evolution of the most internal zone of the variscan belt and of other internal zones of collisional orogenic belts with similar characteristics

discussion on a new model for the hercynian orogen of gondwana france and iberia by d shelley g bossiere journal of structural geology 2000 22 757 776

dating of lithospheric buckling 40ar 39ar ages of syn orocline strike slip shear zones in northwestern iberia abstract orogenic curvature is a ubiquitous feature of mountain belts and the plate tectonic and geodynamic setting responsible for the development of curved orogens is a subject of debate in order to distinguish between different models of orocline formation it is necessary to tightly constrain the absolute timing of oroclinal development however determining the absolute isotopic timing of oroclinal bending is challenging the most direct method available to constrain the time interval during which an orocline formed is to obtain absolute age constraints on fabrics generated within syn orocline strike slip shear zones that accommodated rotations around a vertical axis during the development of crustal or lithospheric scale orogenic curvature here we present a data set of 40ar 39ar ages obtained from five shear zones some of which display curved traces parallel to the cantabrian orocline structural grain in nw iberia and are interpreted to have been generated coevally to it the 40ar 39ar ages were obtained by laser rastering induced step heating on single muscovite crystals that grew synkinematically during shearing all five samples yielded ages that cluster tightly at 308 3 ma providing direct evidence for the age of oroclinal bending this age is consistent with the age constraints obtained from paleomagnetic and structural data that place the onset of oroclinal bending in moscovian times our 40ar 39ar age determinations therefore provide a reliable absolute constraint on the age of buckling of the variscan orogen around a vertical axis and provide further evidence that oroclinal bending is unrelated to variscan convergence collision or the subsequent extensional collapse of the mountain belt

late devonian early carboniferous contraction dominated deformation in central armorica monts d arree brittany france and its relationship with the closure of the rheic ocean abstract in the monts d arree western brittany france a high strain slate belt is well exposed the slate belt is located in the central armorica terrane a low grade middle to upper crustal domain in the armorican massif composed of a cadomian basement and its neoproterozoic and palaeozoic metasedimentary cover sequence the slate belt consists of highly deformed siliciclastic rocks of the pridolian to lochkovian plougastel formation a structural analysis has demonstrated that the slate belt primarily reflects a coaxial contraction dominated deformation history resulting from a top to the nw shearing on top of a weakly dipping decollement it resulted in nw verging folding and a pervasive cleavage development giving rise to a pronounced subvertical mechanical anisotropy only during the later stages of deformation history incipient strain partitioning on this anisotropy lead to the development of punctuated strain heterogeneities consistently reflecting dextral belt parallel strike slip strain the deformation largely occurred prior to the emplacement of the early carboniferous granitoid intrusions in central armorica and can therefore be correlated with the late devonian early carboniferous bretonian tectonometamorphic event the kinematics inferred in the monts d arree moreover are consistent with the top to the nw thrusting and nappe stacking inferred in the leon terrane situated to the northwest of the central armorican terrane these new insights allow linkage of the early variscan contraction dominated deformation in central armorica to the closure of the rheic ocean and the continental collision of the leon microcontinental block with armorica our study also reveals the importance of the bretonian tectonometamorphic event in the entire north western parts of central armorica the main cleavage forming deformation was diachronous and followed by subordinate wrench related deformation

deciphering fluid flow at the magmatic hydrothermal transition a case study from the world class panasqueira w sn cu ore deposit portugal abstract deciphering the behavior of fluid flow at the magmatic hydrothermal transition is crucial to understanding the physical processes leading to the formation of intrusion related ore deposits and hence to predicting the locations of mineralized bodies however the hydrodynamics direction and velocity of the hydrothermal fluid flows related to this transitional stage remains poorly constrained here we present a coupled textural and chemical study performed on tourmaline growth bands to constrain fluid flow during the initiation of the hydrothermal system of the panasqueira w sn cu deposit this exceptional deposit consists of a dense network of flat wolframite and cassiterite bearing quartz veins intensely developed above a well known but hidden greisen cupola the w sn mineralization is preceded by a tourmalinization stage occurring as metasomatic halos around veins and as selvages developed along the vein wall rocks contacts results emphasize the key role of the greisen cupola in fluid focusing and the role of fluid overpressure during vein opening velocity values highlight an efficient transport of metals in veins largely dominated by advective processes 10 4 to 10 3 m s 1 whereas fluid flow in the altered wall rocks is slow and pervasive 10 6 to 10 5 m s 1 suggesting that element transport through the metasedimentary host rock was low and limited to the alteration haloes la icp ms analyses of tourmaline growth bands reveal that fluids coming from the cupola are enriched in na k li sr and sn emphasizing the contribution of magmatic fluids during vein formation and the metasomatic alteration of the wall rocks more generally this study demonstrates that the apical portions of granite bodies act as emanative centers of mineralizing fluids and highlights the usefulness of mineral growth band analysis in the search for intrusion related mineralization

distinct sources for syntectonic variscan granitoids insights from the aguiar da beira region central portugal abstract the variscan syntectonic granitoid plutons from the aguiar da beira region central portugal were emplaced into metasediments of late proterozoic early cambrian age during the last variscan ductile tectonic event d 3 which is related to dextral and sinistral shearing the older intrusion with a u pb id tims zircon age of 321 8 2 0 ma consists of porphyritic biotite granodiorite granite with transitional i s type geochemical signature relatively low 87 sr 86 sr 322 ratios 0 7070 0 7074 end 322 values of 3 9 to 4 6 and whole rock and zircon 18 o values of 10 6 and 8 0 respectively by contrast the younger intrusion is an s type muscovite biotite leucogranite emplaced at 317 0 1 1 ma showing more radiogenic 87 sr 86 sr 317 0 7104 0 7146 lower end 317 values of 7 7 to 8 7 and higher 18 o wr 11 3 and 18 o zr 9 5 the combined isotopic and geochemical evidence supports a lower crustal origin for the biotite granodiorite granite involving the anatexis of lower crustal metaigneous protoliths and possible hybridization with mantle derived magmas a shallower origin at mid crustal levels from pure crustal derivation through moderate degrees of partial melting of proterozoic cambrian metasediments is proposed instead for the muscovite biotite leucogranite

the structure of sw cornwall and its bearing on the emplacement of the lizard complex six phases of deformation can be recognized in the devonian metasediments to the n of the lizard complex the first two phases d 1 d 2 show a variety of orientations and styles but with a general n or nw vergence these phases while respresenting regional deformation events are considerably modified by the emplacement of the lizard complex there is a general increase in intensity of both d 1 and d 2 structures towards the lizard boundary this is accompanied by variation in the orientation of both early phases of deformation leading to a variety of interference patterns domains of oblique f 1 folds with axes trending n s are developed in the rocks immediately to the ne and nw of the lizard and are considered to have formed by differential nnw directed thrusting of slabs of the complex during the early regional deformation d 2 produced discrete shear zones ahead and below the lizard rocks and may have resulted from the gravitational collapse of the d 1 nappes the d 3 deformation post dates the lizard emplacement being related to the cornubian batholith subsequent phases represent essentially post batholith and hence post lizard emplacement deformation