deciphering the sardic ordovician and variscan deformations in the eastern pyrenees sw europe detailed geological mapping of the la cerdanya area canigo unit eastern pyrenees provides new data characterizing the different structural styles exhibited by cambrian lower ordovician jujols group and upper ordovician successions their unconformable contact related to the sardic phase ranges from 0 paraconformity to 90 angular discordance the jujols group rocks topped by the unconformity are affected by sardic foliation free open folds the pre sardic succession the sardic unconformity and the lower part of the post sardic succession rabassa conglomerate and cava formations are cut and offset by several late ordovician nne ssw trending synsedimentary extensional faults associated with hydrothermal activity which dramatically affected the thickness of the lower part of the upper ordovician succession we relate 1 the mid ordovician sardic uplift and erosion and 2 a mid to late ordovician upward propagating extensional fault system bounding the outline of half grabens subsequently infilled by alluvial deposits to a thermal doming event about 475 450 ma that led to the uplift and stretching of the ordovician lithosphere thermal doming may be caused by mafic magma underplating and responsible for the coeval calc alkaline magmatic activity broadly developed in the eastern pyrenees we discuss the similarities between the mid ordovician sardic unconformity and other early paleozoic unconformities described in neighbouring areas finally we suggest a geodynamic scenario in which a regional scale thermal event was related to the opening of the rheic ocean that led to the drift of avalonia from the sw european margin of gondwana

a review of the mesosphere inversion layer phenomenon an active topic of current research in aeronomy is the study of the dynamics of the mesosphere and lower thermosphere mlt from 60 to 130 km especially in regard to the influences that govern variability the physical processes of this region are diverse and complex with strong coupling between the mlt and the adjacent atmospheric regions brought about largely by the propagation and dissipation of atmospheric gravity waves gws from sources above and below the measurements of mlt winds and temperatures required for such studies represent daunting technical challenges at low and midlatitudes the mesosphere inversion layer mil phenomenon a 10 km wide region of enhanced temperatures t 15 50k is observed with great regularity in both the upper mesosphere 60 70 km and the mesopause 90 100 km observations are largely based upon rayleigh and na temperature lidar systems but coherent radar observations have shown that the mil phenomenon is linked to layers of turbulence occurring in both the topside and the bottomside regions gw activity is believed to play an important role in the development of a linkage between the mil and the tidal structure through gw coupling that results in an amplification of the tidal thermal structure this linkage is readily evident for the upper mil but is seen only occasionally for the lower mil further study of mil properties should emphasize continual 24 hour temperature observations especially for the lower mil region to confirm the linkage of the development of the mil to the mlt tidal structure

a comparative study of mesospheric solar tides observed at adelaide and kyoto observations of winds in the upper mesosphere and lower thermosphere 80 110 km measured at the geographically conjugate locations of adelaide 35 s 138 e and kyoto 35 n 136 e in the years 1983 1985 are used to study hemispheric differences in the behavior of the solar diurnal and semidiurnal tides comparisons of the tidal amplitude and phase parameters show that there are distinct hemispheric asymmetries the diurnal tide is usually much larger in amplitude at adelaide and it exhibits a height structure which indicates a relatively larger contribution from the propagating 1 1 mode at this location comparisons with recent theoretical work suggest that while some of these differences may be due to hemispheric differences in forcing and or to interactions between the tide and the background winds in the middle atmosphere it is also possible that they indicate weaker turbulent induced damping of the 1 1 mode in the southern hemisphere the characteristics of the semidiurnal tide agree well at the two locations it is found that the zonal wind components are about 6 hours out of phase and the meridional components are in phase in all seasons this behavior taken together with the inferred vertical wavelengths which are greater than 100 km in summer and 45 80 km in winter indicates that there are strong contributions from the antisymmetric 2 3 mode probably forced by wind induced mode coupling from the symmetric 2 2 mode the phases near 90 km exhibit a bimodal or two state behavior with the phases being almost constant in one state near the june solstice and then making a rapid transition of between 4 and 6 hours to another phase stable state near the december solstice the duration of the state near the june solstice 6 8 months is longer than the duration of the state at the december solstice although the agreement between recent models and our observations is relatively good better agreement may be expected when more realistic wind distributions especially for the southern hemisphere are used in the models

u pb shrimp and nd isotopic data from the western bohemian massif bayerischer wald germany implications for upper vendian and lower ordovician magmatism u pb shrimp dating of zircons of metamagmatites from the bayerischer wald germany reveals a complex evolution of this section of the moldanubian zone exposed in the western bohemian massif of the central european variscan belt in the south western part of the bayerischer wald upper vendian magmatism is constrained by pooled 206pb 238u mean ages of 555 12 549 7 and 549 6 ma from metarhyolites and a metabasite inherited zircon cores were not observed zircon overgrowths yielding pooled 206pb 238u ages of 316 10 and 319 5 ma provide evidence for variscan metamorphic zircon growth cathodoluminescence imaging reveals a two stage metamorphic overprint

shrimp u pb zircon geochronology of the strzelin gneiss sw poland evidence for a neoproterozoic thermal event in the fore sudetic block central european variscides zircon ages recorded in gneissic rocks have recently been used as criteria to define and correlate various tectonic units and crustal blocks in the central european variscides a shrimp u pb zircon geochronological study of the strzelin gneiss in the fore sudetic block sw poland indicates the presence of 1 inherited zircon cores of palaeo to mesoproterozoic 206pb 238u ages between ca 2 000 and 1 240 ma and 2 zoned rims of neoproterozoic age with two distinct means of 600 7 and 568 7 ma the proterozoic age range of the cores suggests that different precambrian crustal elements were the source for the protolith of the gneiss a likely scenario is the erosion of various proterozoic granites and gneisses sedimentation after 1 240 ma and partial resistance of the original components to subsequent metamorphic dissolution and or anatectic resorption in neoproterozoic times the zoned zircon rims of both of the younger neoproterozoic ages are indistinguishable in the cathodoluminescence images the data are interpreted in terms of two different thermal events inducing zoned zircon overgrowth at ca 600 and 568 ma in general the new results confirm earlier assumptions of the proterozoic age of the gneiss protoliths and indicate their similarity to orthogneisses in the east sudetes tectonic domain e g the velke vrbno and desna gneisses the neoproterozoic dates are different from the age of 504 3 reported earlier for the go ciecice gneiss from a neighbouring locality in the strzelin massif the new data strongly indicate a moravo silesian bruno vistulian affinity for the strzelin gneiss and support the hypothesis that the strzelin massif lies within the tectonic boundary zone between the west and east sudetes domains which represents the northern continuation of the moldanubian thrust

evolution of the rheic ocean the rheic ocean which separated laurussia from gondwana following the closure of iapetus is arguably the most important ocean of the palaeozoic its suture extends from mexico to turkey and its closure produced the climactic variscan alleghanian ouachita orogeny that assembled the supercontinent pangaea following protracted cambrian rifting that represented a continuum from neoproterozoic orogenic processes the rheic ocean opened in the early ordovician with the separation of several neoproterozoic arc terranes from the continental margin of northern gondwana separation occurred along the line of a former neoproterozoic suture following the onset of subduction in the outboard iapetus ocean the timing of rift drift transition and drive for subsequent spreading was likely governed by slab pull accounting for the rapid rate 8 10 cm yr at which the rheic ocean widened during the ordovician the ocean broadened at the expense of iapetus and attained its greatest width 4000 km in the silurian by which time baltica had sutured to laurentia and the neoproterozoic arc terranes had accreted to laurussia closing iapetus in the process closure of the rheic ocean began in the devonian and was facilitated by northward subduction beneath southern baltica and southward subduction beneath northwest gondwana closure was largely complete by the mississippian as gondwana and laurussia sutured to build pangaea north africa colliding with southern europe to create the variscan orogen in the devonian carboniferous and west africa and south america suturing to north america to form the alleghanian and ouachita orogens respectively during the carboniferous permian the rheic ocean consequently plays a dominant role in the basement geology of southern europe in the appalachian ouachita orogeny of north america and in the palaeozoic sedimentary structural and tectonothermal record from middle america to the middle east with its closure the ocean brought about the assembly of pangaea and brought the palaeozoic era to an end

lidar observations of the middle atmospheric thermal tides and comparison with the high resolution doppler imager and global scale wave model 1 methodology and winter observations at table mountain 34 4 n the tidal signature in the middle atmospheric thermal structure was investigated using more than 140 hours of nighttime lidar measurements at table mountain 34 4 n during january 1997 and february 1998 the lidar profiles 30 85 km revealed the presence of persistent mesospheric temperature inversions around 65 to 70 km altitude with a clear local solar time lst dependence daytime temperature profiles 65 105 km obtained by the high resolution doppler imager hrdi on board the upper atmosphere research satellite uars in january and february from 1994 to 1997 and zonally averaged at the latitude of the table mountain facility tmf were considered together with the lidar results the daytime hrdi and nighttime lidar temperature differences from their respective daytime and nighttime averages were compared to the equivalent differences predicted by the global scale wave model gswm a remarkable consistency was observed between the lidar and the hrdi upper mesospheric thermal structure with a continuous downward propagation of warm temperatures from 100 km at 1000 lst to 75 km at 2000 lst and 65 70 km at 0300 0500 lst surrounded above and below by colder temperatures this structure was predicted by gswm but with a 2 to 4 hour delay and a weaker amplitude on the lower side of this structure i e 65 70 km a thin layer characterized by early night cold temperatures and late night warm temperatures was identified as the result of the downward propagation of the temperature inversions using a new analysis technique which we have named constrained wave adjustment for convenience in future reference and assuming that the observed temperature variability was entirely driven by tides some estimations of the diurnal and semidiurnal phases and amplitudes were made from the lidar measurements between 40 and 85 km altitude although it does not allow a complete and accurate extraction of the tidal components this new method appeared to work well for the present tmf study the estimated diurnal amplitude exhibited a minimum at 63 km with a fast phase transition characteristic of the transition between the upper stratospheric trapped modes phase at 1800 lst and the upward propagating modes this transition layer was predicted by gswm to be at 5 km lower altitude this altitude shift was present throughout the middle mesosphere immediately above the transition layer the very fast growing diurnal amplitude between 65 and 72 km was followed by a substantial decrease and by the emergence of the semidiurnal component resulting in the formation of the mesospheric temperature inversion layers however the amplitude of the inversions remained large compared to the theoretical tidal predictions and a different formation mechanism should possibly be considered recent modeling studies have shown that gravity wave breaking can be significantly affected by the tidal background winds and some preferential wave breaking times could emerge that are dependent on the phase of the diurnal tide and the characteristics of the dissipating waves this lst filtering could result in lst dependent temperature inversion layers similar to those observed by lidar the new analysis technique presented in this paper was also applied to study the temperature tidal oscillations at mauna loa observatory 19 5 n the results are presented in a companion paper leblanc et al this issue

geochronology and geochemistry of the pola de allande granitoids northern spain their bearing on the cadomian avalonian evolution of northwest iberia the pola de allande pre variscan tonalite granodiorite plutons are located in the narcea antiform at the boundary zone between the cantabrian and west asturian leonese zones of the iberian variscan belt these granitoids were intruded into a neoproterozoic siliciclastic sedimentary sequence with subordinate volcanic intercalations and were subsequently overprinted by variscan thrust related shear deformation u pb laser ablation inductively coupled plasma mass spectrometry icp ms dating of zircons from two plutons yielded concordant ages of intrusion of 605 10 and 580 15 ma to the authors knowledge this is the first reported u pb cadomian avalonian age for igneous rocks in this section of the iberian variscan belt these intrusions are coeval with the main episode of dominantly calc alkaline magmatic activity related to cadomian avalonian subduction major and trace element composition of the granitoids is characteristic of i type high k calc alkaline granitoids generated in continental arc se

u pb age and lead isotopic characterization of au bearing skarn related to the andorra granite central pyrenees spain auriferous skarns are associated with post and late kinematic hercynian granites that intruded into cambro ordovician to devonian sediments of the central pyrenees we determined the age of the andorra granite and the associated skarn at 305 3 ma by u pb dating titanite from the endo skarn the sulfur isotopic composition from sulfides in the skarn cardellach et al 1992 shows a significant variation with isotopically light sulfur 34s 3 in the barren skarns and heavy sulfur 34s 11 in the gold bearing skarns outwards it increasingly resembles sulfur from arsenopyrite disseminations in the cambro ordovician sediments the lead isotopic composition from sulfides of the skarns is very homogeneous 206pb 204pb 18 410 207pb 204pb 15 699 208pb 204pb 38 574 in contrast to the one in gold bearing arsenopyrite veins and in arsenopyrite disseminations in the sediments e g 206pb 204pb varies from 18 54 to 30 36 combined sulfur and lead isotope data indicate that the lead in the skarn is dominantly derived from the granite whereas the sulfur is derived at variable portions from both the granite and the sediments

the late neoproterozoic magmatism in the ediacaran series of the eastern pyrenees new ages and isotope geochemistry geochronological u pb la icp ms geochemical and isotopic data from metavolcanic felsic rocks of the canigo and cap de creus massifs in the eastern pyrenees provide evidence of an ediacaran magmatic event lasting 30 ma in ne iberia these data also constrain the age of the late neoproterozoic succession in the cap de creus massif where depositional ages range from 577 to 558 ma and in the canigo massif where the data 575 568 ma represent minimum ages the geochemistry of the felsic rocks indicates that they were formed in a back arc environment and they record a fragment of a long lived subduction related magmatic arc 620 520 ma in the active northern gondwana margin the homogeneity shown by all these crustal fragments along this margin suggests that the individualization of the pyrenean basement from the iberian massif started later probably during its transition from an active to a passive margin in cambro ordovician times

characteristics of semidiurnal tides observed by the kyoto meteor radar and saskatoon medium frequency radar we have compared seasonal variations of semidiurnal tides in the upper middle atmosphere observed by the kyoto meteor radar and the saskatoon medium frequency partial reflection radar in 1983 1985 amplitudes of semidiurnal tides are generally larger at saskatoon than at kyoto seasonal variations of phases at 90 km agree fairly well for both zonal and meridional components between kyoto and saskatoon the seasonal variation is mainly composed of two fundamental states appearing in summer centered april may september october and winter centered months november february march which are characterized by long and relatively short vertical wavelengths respectively clear transitions between the two states occur in equinoxes february april and october november using determinations at kyoto and saskatoon with 4 to 5 day observation intervals we have studied the behavior of semidiurnal tides during the transitions in october november in 1983 1985 and february april in 1985 precise comparisons have shown that the transitions are slightly delayed at saskatoon in both vernal and autumnal equinoxes abrupt changes in phases of semidiurnal tides coincide with reduction and pulsating fluctuations of their amplitudes suggesting the existence of interference between fundamental and higher modes which are dominant in summerlike and winterlike months respectively

rayleigh lidar observations of mesosphere temperature structure ground based observations of atmospheric density profiles to 92 km were obtained for four successive seasons between summer 1989 and spring 1990 these results were obtained with a powerful rayleigh lidar facility located at wright patterson air force base dayton ohio this instrument combined a 14 w xef laser transmitter with a 2 54 m receiver mirror to observe returns from altitudes between 40 and 95 km analysis of the scale height dependence of the density profiles produced temperatures with a measurement error of about 5 k 2 5 at 90 km when the lidar data was averaged for 20 min and smoothed in height over 2 7 km examination of these profiles for the total of 18 nights showed that there often existed in the mesophere a layer of enhanced temperatures when compared with the u s standard profile the layer centroid height was about 85 km for summer and 70 to 75 km for winter data obtained for the equinoctial periods showed the amplitude of these layers to be weak the winter temperature profiles showed evidence forlong period waves passing through the region of the thermal anomaly while the equinox profiles revealed more sporadic wave activity with shorter vertical wavelengths both the winter and summer temperature data displayed regions where the observed lapse rate approached the adiabatic lapse rate in the summer the wave activity near the inversion layer was weak

the cadomian orogeny in saxo thuringia germany geochemical and nd sr pb isotopic characterization of marginal basins with constraints to geotectonic setting and provenance abstract the cadomian basement and the cambro ordovician overstep sequence in saxo thuringia is characterized by clastic sedimentation from the late neoproterozoic to the ordovician magmatism in the avalonian cadomian arc preserved in saxo thuringia occurred between ca 570 and 540 ma peri gondwanan basin remnants with cadomian to early palaeozoic rocks are exposed as very low grade metamorphosed rocks in six areas schwarzburg anticline berga anticline doberlug syncline north saxon anticline lausitz anticline and elbe zone a hiatus in sedimentation between 540 and 530 ma cadomian unconformity is related to the cadomian orogeny a second gap in sedimentation occurred during the upper cambrian 500 to 490 ma and is documented by a disconformity between lower to middle cambrian rocks and overlying tremadocian sediments major and trace element signatures of the cadomian sediments reflect an active margin continental arc those of the ordovician sediments a passive margin the cambrian sediments have inherited the arc signature through the input of relatively unaltered cadomian detritus initial nd and pb isotope data from the six saxo thuringian areas demonstrate that there is no change in source area with time for each location but that there are minor contrasts among the locations 1 cadomian sediments from the lausitz anticline the doberlug syncline and the elbe zone have lower 207pb 204pb than all other areas 2 the core of the schwarzburg anticline which is overprinted by greenschist facies conditions and detached is isotopically heterogeneous one part of its metasedimentary units has less radiogenic nd than sediments from other low grade units of similar age in the same area 3 cadomian sediments from the schwarzburg anticline show an input of younger felsic crust 4 the rothstein group shows distinct input of young volcanic material also 5 cadomian sediments from the lausitz anticline the elbe zone and parts of the north saxon anticline are characterized by input from an old mafic crust nd isotope data of the remaining areas yield average crustal residence ages of the sediment source of 1 5 1 9 ga which suggests derivation from an old craton as found for other parts of the iberian armorican terrane collage similarly the pb isotope data of all areas indicate sediment provenance from an old craton the rapid change of lithologies from greywacke to quartzite from the late neoproterozoic cadomian basement to the ordovician does not reflect changes in sediment provenance but is essentially due to increased reworking of older sediments and old weathering crusts that formed during various hiatus of sedimentation this change in sediment maturity takes its chemical expression in lower overall trace element contents in the quartzite dilution effect by quartz and relative enrichment of some trace elements zr mree hree due to detrital zircon and garnet the rb sr systematics of the quartzites and one ordovician tuffite was disturbed most likely during the variscan orogeny which suggests a lithology controlled mobility of alkali and calc alkali elements by comparison with available data it seems unlikely that only nd tdm model ages are useful to distinguish between west african and amazonian provenance nd tdm model ages of 1 5 to 1 9 ga in combination with paleobiogeographic aspects age data from detrital zircon and palaeogeographic constraints especially through tillites of the saharan glaciation in the hirnantian strongly indicate a provenance of saxo thuringia from the west african craton

detrital zircons from the ordovician rocks of the pyrenees geochronological constraints and provenance abstract the first la icp ms u pb detrital zircon ages from quartzites located below three samples and above one sample the upper ordovician unconformity in the central pyrenees the rabassa dome andorra were investigated the maximum depositional age for the jujols group below the unconformity based on the youngest detrital zircon population is around 475 ma early ordovician whereas for the bar quartzite fm above the unconformity the presence of only two zircons of 442 and 443 ma precludes obtaining a precise maximum sedimentation age a time gap of 20 million years for the upper ordovician unconformity in the pyrenees can be proposed similar to that of the sardic unconformity in sardinia the similar age patterns obtained on both sides of the upper ordovician unconformity suggest that there was no change in the source area of these series while the absence of a middle ordovician age population may be due to a lack of sedimentation at that time the four study samples present very similar u pb age patterns the main age populations correspond to neoproterozoic ediacarian cryogenian ca 550 750 ma grenvillian tonian stenian ca 850 1100 ma paleoproterozoic orosirian ca 1900 2100 ma and neoarchean ca 2500 2650 ma the similarity with the sardinian age distribution suggests that these two terranes could share the same source area and that they were paleogeographically close in ordovician times in front of the arabian nubian shield

ordovician deformations in the pyrenees new insights into the significance of pre variscan sardic tectonics two deformational events which developed prior to the variscan structures can be characterized in the palaeozoic rocks of the pyrenees a middle ordovician folding event and a late ordovician fracture episode the middle ordovician folding event gives rise to nw se to n s oriented metric to hectometric sized folds without cleavage formation or related metamorphism these folds can account for the deformation and uplift of the pre upper ordovician cambro ordovician sequence and for the formation of the upper ordovician unconformity ordovician folds control the orientation of the variscan main folding phase minor structures fold axes and intersection lineation in the cambro ordovician sediments the late ordovician fracture episode gave rise to normal faults affecting the lower part of the upper ordovician series the basal unconformity and the underlying cambro ordovician metasediments displacement of some of these faults diminishes progressively upwards of the series and tapers off in the upper part of the upper ordovician rocks indicating that the faults became inactive during late ordovician times before deposition of the ashgillian metasediments normal faults can be linked to the upper ordovician volcanic activity which has been extensively described in the pyrenees the aforementioned deformation episodes took place after the early ordovician magmatic event which gave rise to a large volume of plutonic rocks in the pyrenees as in other segments of the european variscides this middle ordovician contractional event separated two extensional events in the pyrenees from early ordovician to silurian times this event prevents us from assuming the existence of a continuous extensional regime through ordovician and silurian times and suggests a more complex evolution of this segment of the northern gondwana margin during the ordovician

the augen gneisses of the peloritani mountains ne sicily granitoid magma production during rapid evolution of the northern gondwana margin at the end of the precambrian abstract the medium to high grade polymetamorphic basement rocks of the peloritani mountains northern sicily include large volumes of augen gneiss of controversial age and origin by means of a geochemical and shrimp zircon study of representative samples the emplacement age of the original granitoid protoliths of the augen gneisses and the most likely processes and sources involved in that granitoid magmatism have been determined u pb dating of three samples from widely spaced localities in the peloritani mountains yielded igneous protolith ages of 565 5 545 4 and 545 4 ma respectively these late ediacaran early cambrian ages are much older than was previously assumed on geological grounds and are typical of the peri gondwanan terranes involved in the geodynamic evolution of the northern gondwana margin at the end of the avalonian cadomian orogeny major and trace element compositions and sr nd isotopic data in combination with zircon inheritance age patterns suggest that the granitoid protoliths of the sicilian and coeval calabrian augen gneisses were generated by different degrees of mixing between sediment and mantle derived magmas the magmas forming the ca 545 ma inheritance rich granitoids appear to have had a significant contribution from partial melting of paragneiss that is the dominant rock type in the medium to high grade peloritanian basement the closeness of the inferred deposition age of the greywacke protoliths of the paragneisses with the intrusion age of the granitoids indicates rapid latest precambrian crustal recycling involving erosion burial metamorphism to partial melting conditions and extensive granitoid magmatism in less than ca 10 ma

superposed hercynian and cadomian orogenic cycles in the ossa morena zone and related areas of the iberian massif polyphase ductile deformation and metamorphism in the ossa morena zone of the iberian massif are related to a complex evolution including two major tectonothermal episodes of cadomian late proterozoic to early cambrian and hercynian age middle to late paleozoic petrological structural and geochronological data attest to a number of tectonic episodes in the 620 480 ma interval the model presented for this orogeny comprises stages of volcanic arc generation backarc extension tectonic inversion crustal thickening and cratonization in an andean type continental margin the hercynian cycle began in the early paleozoic with episodes of continental rifting orogenic events occurred in the 390 300 ma interval and affected both the cadomian basement which was heterogeneously reworked and overprinted and the paleozoic cover hercynian regional metamorphism was generally of low grade high pressure assemblages and thermal domes developed locally and were related to subduction and late extensional events the geodynamic model proposed for the cadomian and hercynian orogenies and the correlation with comparable areas from pre mesozoic massifs elsewhere in western europe account for the geodynamic scenarios that drove the fate of cadomian terranes

long lasting cadomian magmatic activity along an active northern gondwana margin u pb zircon and sr nd isotopic evidence from the brunovistulian domain eastern bohemian massif manuscript published version available in international journal of earth sciences 2016 doi 10 1007 s00531 016 1416 y

semidiurnal and diurnal tidal effects in the middle atmosphere as seen by rayleigh lidar the rayleigh lidar at the centre d essais des landes has been adjusted to provide continuous day and nighttime measurements when clear weather permits with high resolution in both time and space these measurements are processed to show tidal effects in the 30 to 80 km height range the observed temperature variations in two 11 day series of data from november 1988 and january 1989 are treated by spectral analysis and by least squares fitting sinusoids for 12 and 24 hour periods the observed tidal amplitudes correspond with experimental results from rocket studies and are generally consistent though somewhat larger than predicted in theoretical models observed lidar phases are roughly corroborated by radar observations and also follow the same general trends as model predicitions

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

arc related ediacaran magmatism along the northern margin of gondwana geochronology and isotopic geochemistry from northern iberia abstract field petrographic geochemical and geochronological studies carried out in northwest iberia constrain the nature and origin of the ediacaran magmatic rocks cropping out in the narcea antiform the results indicate the presence of a long lived subduction related magmatic arc between ca 580 and ca 560 ma in two tectonic units magmatic rocks in the allande group are major intrusive calc alkaline bodies and limited volcanic rocks in the eastern navelgas group there are no intrusive bodies and volcanic rocks are widespread and represent large edifices exposed over tens of square km sm nd and rb sr geochemical isotopic data indicate derivation of the magmatic rocks of both units from a ca 1 1 ga lithospheric mantle as well as varying degrees of crustal contamination geocronological u pb la icp ms and id tims data constrain the magmatic activity to 575 565 ma in the allande group and to ca 560 ma in the navelgas group further constraints on the evolution of the magmatic arc have been obtained from the study of pebbles in early cambrian conglomerates that were derived from the magmatic rocks of these ediacaran units we interpret these ediacaran units to have been formed in a back arc environment in the narcea antiform and to record a multi stage evolution along this segment of the northern gondwana magmatic arc as revealed by their isotopic and geochronological differences

neoproterozoic cambrian synsedimentary magmatism in the central iberian zone spain geology petrology and geodynamic significance petrographic geochemical and field studies in low grade metamorphic areas ciudad rodrigo hurdes sierra de gata domain crhsg central western spain show that neoproterozoic lowermost cambrian series in the central iberian zone ciz record two kinds of provenance sources including 1 detrital material derived from recycled orogens and 2 a cadomian coeval juvenile contribution that governs their isotopic signature evidence of magmatism contemporaneous with neoproterozoic cambrian sedimentation is provided by the presence of coherent massive volcanic rocks metabasalts metaandesites and metarhyolites volcaniclastic shales sandstones conglomerates and breccias the appearance of volcanogenic lithic fragments and crystals mixed in different proportions with siliciclastic constituents and also present within calcareous components in the sedimentary succession reinforces this evidence although most of the selected volcanic and volcaniclastic samples appear to show tholeiitic affinity some of them display calc alkaline affinity different trace element ratios such as sm nd nb yb and ta yb suggest a magmatic evolution in the same tectonic setting the geochemical results reported here support the existence of an active geodynamic setting as a direct contributor to the synsedimentary and magmatic content of the neoproterozoic lowermost cambrian successions in the ciz in particular the relatively high end t values and the high range of f sm nd ratios are consistent with an active margin during the neoproterozoic early cambrian the existence of tectonic activity is also confirmed by the presence of synsedimentary deformation and volcanic rocks all of these traits favour a geodynamic model in which the iberian cadomian segment represented in the ciz would have been part of an active northern margin of gondwana with an associated magmatic arc and related basins during neoproterozoic lower cambrian times a proposed link between the ossa morena and the central iberian zones might account for late cadomian pull apart basins developed on both sides of the magmatic arc sharing the same scenario and involving similar magmatic activity during the neoproterozoic cambrian transition

composition and textures of chromite and platinum group minerals in chromitites of the western ophiolitic belt from pampean ranges of cordoba argentina abstract chromitite bodies hosted in the neoproterozoic western ophiolitic belt of pampean ranges of cordoba argentina were studied at los congos and los guanacos ultramafic bodies with regard to the composition and textures of the chromite and platinum group minerals primary chromite composition is only preserved in some massive chromitites from the los guanacos ultramafic body and is similar to al rich ophiolitic chromitites suggesting that they crystallized from melts with back arc basin basalts babb affinity in the suprasubduction mantle subsequently these chromitites underwent a prograde metamorphism chromites from chromitites and associated metamorphosed ultramafic rocks show complex replacement and exsolution textures mineral chemistry and texture indicate that the chromite composition records two main metamorphic trends a first trend defined by chromite from massive chromitite in which there is an enrichment in fe3 and fe2 cr remain relatively constant and slightly depleted in al mg a second trend is defined by chromite from disseminated chromitite and metamorphosed dunite and harzburgite in which a fe rich phase is replacing the al rich chromite this alteration trend is characterized by enrichment in the total iron content fe3 fe2 and a strong depletion in al and mg the chemical composition of all analyzed spinels from los guanacos and los congos as plotted on the ternary fe3 cr al diagram correlates well with the cr spinels from the upper amphibolite to granulite facies metamorphism platinum group minerals pgm identified include native osmium laurite erlichmanite irarsite platinum and a number of inadequately identified phases such as an oxide or hydroxide of ru pt and ir ru pt telluride ir ru as se and ir ru ti compounds native osmium was the only pgm which remained unaltered other pgm underwent mineralogical reworking during metamorphism although it is difficult to establish the extent of platinum group element mobilization based on mineralogical observation our results suggest that the ru os ir pgm in the los guanacos and los congos chromitites were modified in situ producing re distribution of these pge on a small scale the presence of rare pt and pge as se minerals was possibly related to remobilization of pt as and se by fluids during the alteration processes

evolution of late neoproterozoic to early paleozoic tectonic elements in central and southeast european alpine mountain belts review and synthesis abstract late neoproterozoic to early paleozoic cadomian tectonic elements are widespread in the southeastern alpine mediterranean mountain belts with discontinuous exposure extending from the alps to the menderes massif in turkey the sequences include voluminous plutonic island and continental arc successions some ophiolites of variable late neoproterozoic and cambrian to early ordovician ages high to medium grade metamorphic sequences and subordinate metasediments geological and geochronological data suggest that these cadomian elements partly experienced tectonothermal activity including metamorphism and magmatism between ca 650 and 600 ma followed by further i and s type plutonism in an andean type continental margin setting ca between 570 and 520 ma subsequently a major rift zone developed which resulted in continental stretching and subsequent formation of a back arc basin which is dated as late cambrian rifting is followed by oceanic spreading which commenced ca at the cambrian ordovician boundary possibly in a back arc setting this tectonic scenario suggests that alpine mediterranean cadomian tectonic elements were accreted to gondwana during early cadomian events ca 600 650 ma subsequently they were likely part of a long lasting outer subduction zone of gondwana at the margin of a panthalassa type ocean during late neoproterozoic iii and cambrian due to back arc spreading continental pieces started to split off from gondwana ca at the cambrian ordovician boundary

trace element fingerprints of chromite magnetite and sulfides from the 3 1 ga ultramafic mafic rocks of the nuggihalli greenstone belt western dharwar craton india the 3 1 ga nuggihalli greenstone belt in the western dharwar craton is comprised of chromitite bearing sill like ultramafic mafic rocks that are surrounded by metavolcanic schists compositionally komatiitic to komatiitic basalts and a suite of tonalite trondhjemite granodiorite gneissic rocks the sill like plutonic unit consists of a succession of serpentinite after dunite peridotite pyroxenite and gabbro with bands of titaniferous magnetite ore the chromitite ore bodies length 30 500 m width 2 15 m are hosted by the serpentinite peridotite unit unaltered chromites from massive chromitites 80 modal chromite of the byrapur and bhaktarhalli chromite mines in the greenstone belt are characterized by high cr 100cr cr al of 78 86 and moderate mg 100 mg mg fe2 of 45 55 in situ trace element analysis la icpms of unaltered chromites indicates that the parental magma of the chromitite ore bodies was a komatiite lacking nickel sulfide mineralization in the ga fe3 versus ti fe3 diagram the byrapur chromites plot in the field of suprasubduction zone ssz chromites while those from bhaktarhalli lie in the mor field the above results corroborate our previous results based on major element characteristics of the chromites where the calculated parental melt of the byrapur chromites was komatiitic to komatiitic basalt and the bhaktarhalli chromite was derived from archean high mg basalt the major element chromite data hinted at the possibility of a ssz environment existing in the archean altered and compositionally zoned chromite grains in our study show a decrease in ga v co zn mn and enrichments of ni and ti in the ferritchromit rims trace element heterogeneity in the altered chromites is attributed to serpentinization the trace element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic fe ti v rich magnetite bands in layered intrusions and magnetites from andesitic melts suggesting that magnetite crystallized from an evolved gabbroic melt enrichments of ni co te as and bi in disseminated millerite and niccolite occurring within chromitites and in disseminated bravoite within magnetites reflect element mobility during serpentinization monosulfide solid solution inclusions within pyroxenes altered to actinolite in pyroxenite and interstitial pyrites and chalcopyrites in magnetite retain primary characteristics except for fe enrichment in chalcopyrite probably due to sub solidus re equilibration with magnetite disseminated sulfides are depleted in platinum group elements pge due to late sulfide saturation and the pge depleted nature of the mantle source of the sill like ultramafic mafic plutonic rocks in the nuggihalli greenstone belt

geochemical characterization and isotopic age of caradocian magmatism in the northeastern iberian peninsula insights into the late ordovician evolution of the northern gondwana margin this paper presents new geochronological geochemical and isotopic data for late ordovician magmatism 455 2 ma from the variscan massifs in the northeastern iberian peninsula this magmatism is mainly composed of aluminous and metaluminous plutonic rocks and a sequence of calc alkaline ignimbrites and epiclastic volcanic rocks which were deformed and metamorphosed during the variscan orogeny the metaplutonic rocks are located in the lower part of a neoproterozoic early cambrian metasedimentary sequence in the canigo massif eastern pyrenees aluminous orthogneisses have isotopic signatures that indicate a crustal origin whereas metaluminous orthogneisses originate from a mixture of juvenile and crustal melts the metavolcanic rocks define a calc alkaline ignimbritic sequence of crustal origin located in the lower part of the late ordovician sequence in the les gavarres massif catalan coastal ranges tdm ages for all the studied late ordovician rocks range from mesoproterozoic to paleoproterozoic 1 3 ga 1 5 ga 1 7 ga and 2 2 ga suggesting a neoproterozoic crust with paleoproterozoic components and an arc signature as the most probable source for the crustal melts the isotopic similarities between the studied samples and other early ordovician magmatic rocks of the central and western iberian massif suggest repeated melt extractions from a common basement as the source for the early and late ordovician magmatism in the iberian realm however the studied massifs are more closely linked to other massifs from the mediterranean realm the most probable tectonic setting for the emplacement of the late ordovician volcanic and plutonic bodies is that of an extensional regime which postdates a previous ordovician contractional event and the opening of the rheic ocean

ruthenium in komatiitic chromite abstract the distinction between ru in solid solution and ru bearing inclusions is essential for the predictive modeling of platinum group element pge geochemistry in applications such as the lithogeochemical exploration for magmatic sulfide deposits in komatiites this study investigates the role of chromite in the fractionation of ru in ultramafic melts by analyzing chromite grains from sulfide undersaturated komatiites and a komatiitic basalt from the yilgarn craton in western australia in situ analysis using laser ablation icp ms yields uniform ru concentrations in chromites both within grain and on a sample scale with concentrations between 220 and 540 ppb all other platinum group elements are below the detection limit of the laser ablation icp ms analysis carius tube digestion isotope dilution icp ms analysis of chromite concentrates confirms the accuracy of the in situ method time resolved laser ablation icp ms analyses have identified the presence of sub micron ir bearing inclusions in some chromite grains from the komatiitic basalt however ru bearing inclusions have not been recognized in the analyzed chromites and this combined with the in situ data suggests that ru exists in solid solution in the crystal lattice of chromite these results show that chromite can control the fractionation and concentration of ru in ultramafic systems

rayleigh lidar observations of a mesospheric inversion layer during night and day a narrow field of view rayleigh lidar has been constructed at millstone hill mit haystack observatory 42 6 n 71 5 w for observations of middle atmospheric temperatures throughout the diurnal cycle during a 31 5 h measurement on 19 21 march 2001 a mesospheric thermal inversion layer was observed in both the night and day it developed near 60 km in altitude progressed downward at 0 40 0 06 km h and had an overlying adiabatic lapse rate the inversion amplitude correlated with the evolution of stratospheric gravity wave activity although the mesospheric perturbations were too large to be due to conservative gravity wave growth alone the 24 h mean temperature profile shows no evidence of a residual inversion layer

mesosphere inversion layers and stratosphere temperature enhancements 1 it has been known for at least 30 years that vertically narrow thermal layers form within the middle atmosphere two types of temperature enhancements the low latitude to midlatitude mesosphere inversion layer mil and the high latitude winter stratosphere temperature enhancement ste have both received much attention within the atmospheric science community because of their unexplained formation mechanisms and potential impacts on the middle atmosphere global circulation numerous experimental numerical and theoretical studies have attempted to explain certain aspects of these respective thermal layers but no one theory consistently and satisfactorily describes all the features observed we present a review of the literature and explicitly propose a classification scheme based on the different formation mechanisms suspected to cause these events for the mil we demonstrate that there are two subtypes the first one is tidally driven and tends to occur above 85 km this mil originates from large amplitude tidal waves propagating into the mesosphere and their subsequent nonlinear interactions with gravity waves which can often create the appearance of a double mil separated by approximately one vertical tidal wavelength 25 km the other subtype of mil is formed by a climatological planetary wave dissipation mechanism that occurs at a zero wind line the dissipation of the planetary wave tends to generate a mesoscale 1000 km inversion layer in the range of 65 80 km these two formation mechanisms explain a host of observed characteristics including the reason behind the downward progression of some mils and not others the different climatological nature of the two forms of mil events and the relative scarcity of mil observations at high latitudes the ste is believed to be generated by an altogether different process namely the nonlinear interaction between the polar vortex and planetary waves aleutian high the induced temperatures typically peak around 40 km and often exceed 300 k generating what appears to be a low hot stratopause when vertical temperature profiles are combined with synoptic analyses one observes that the ste is the consequence of high latitude vortex interactions creating a baroclinic atmosphere i e a downward adiabatic compression induced by an ageostropic flow we summarize the details of the relationship between this feature and sudden stratospheric warmings as well as the potential for in situ gravity wave generation we close with a review of currently unexplained mil ste features and offer new directions for future middle atmosphere thermal layer research

polyphase magmatic pulses along the northern gondwana margin u pb zircon geochronology from gneiss domes of the pyrenees abstract alkaline granitic dikes intruding the metasedimentary mantle and orthogneiss cores of the aston and hospitalet domes of the axial zone of the pyrenees are subjects of a laser ablation icp ms u pb zircon geochronology study the age spectra recorded by detrital magmatic xenocrystic and inherited zircons reveal a more complex nearly continuous paleozoic magmatic history of the variscan basement of the pyrenees than previously known inherited and detrital zircons of mesoarchean paleoproterozoic to ediacaran ages attest to the peri gondwana location of the cambrian sediments that later form the metamorphic core of the variscan pyrenees the youngest magmatic zircon ages fall into the late carboniferous and earliest permian ranging from ca 306 297 ma and represent the emplacement ages of the dikes and small granite intrusions the age spectra of magmatic xenocrystic zircons contain several maxima middle 475 465 ma and late ordovician 455 445 ma early 415 402 ma and late devonian 385 383 ma early 356 351 ma and middle carboniferous ca 328 ma middle ordovician and middle carboniferous ages are obtained from xenocrystic zircons that were assimilated from the rocks the dikes intruded the aston and hospitalet orthogneisses and the soulcem granite the presence of early mid carboniferous magmatic zircons in several samples lends further support to a wide spread early variscan magmatic activity in the central pyrenees the other age peaks do not have equivalent igneous or metaigneous rocks in the central axial zone but are thought to be present in the pyrenean crust not exposed and yet to be identified the diversity of ordovician devonian and carboniferous up to permian magmatic ages indicates polyphase emplacement of intrusive bodies during pre variscan and variscan orogenies the source of the heat for the devonian to early mid carboniferous magmatic activity remains elusive and may involve intracontinental subduction zone lithospheric scale shearing or a mantle plume tuzo

unraveling the sequence of serpentinization reactions petrography mineral chemistry and petrophysics of serpentinites from mar 15 n odp leg 209 site 1274 1 the results of detailed textural mineral chemical and petrophysical studies shed new light on the poorly constrained fluid rock reaction pathways during retrograde serpentinization at mid ocean ridges uniformly depleted harzburgites and dunites from the mid atlantic ridge at 15 n show variable extents of static serpentinization they reveal a simple sequence of reactions serpentinization of olivine and development of a typical mesh texture with serpentine brucite mesh rims followed by replacement of olivine mesh centers by serpentine and brucite the serpentine mesh rims on relic olivine are devoid of magnetite conversely domains in the rock that are completely serpentinized show abundant magnetite we propose that low fluid flux serpentinization of olivine to serpentine and ferroan brucite is followed by later stages of serpentinization under more open system conditions and formation of magnetite by the breakdown of ferroan brucite modeling of this sequence of reactions can account for covariations in magnetic susceptibility and grain density of the rocks citation bach w h paulick c j garrido b ildefonse w p meurer and s e humphris 2006 unraveling the sequence of serpentinization reactions petrography mineral chemistry and petrophysics of serpentinites from mar 15 n odp leg 209 site 1274 geophys res lett 33 l13306

tectonic and sediment provenance evolution of the south eastern pyrenean foreland basins during rift margin inversion and orogenic uplift abstract the cretaceous to oligocene detrital record in the southern eastern pyrenees is utilized to address the degree to which precursor basin architecture and hyper extensional rift structures impacted subsequent sedimentary provenance and dispersal systems and foreland basin evolution this study presents new isotopic provenance analysis of detrital zircon u pb and u th he double dating and detrital rutile u pb and trace element geochemistry to track sediment provenance evolution late cretaceous paleocene sediments show zircon with dominantly variscan u pb and jurassic early cretaceous zhe cooling ages that are derived from southeastern catalan coastal ranges and eastern corsica sardinia regions and localized structural inversion along inherited mesozoic extensional faults and erosional recycling of syn rift sediments eocene deposits have multimodal u pb ages that stratigraphically upsection change to unimodal variscan ages with the appearance and upsection increase in pyrenean zhe ages and increase in variscan aged detrital rutile that record a significant shift in sediment source area to northern sources recording exhumation and unroofing of the axial zone paleozoic basement sources and development of new ramp flat style structures in the southern pyrenean zone fold thrust belt during the oligocene incipient foreland basin deposits were cannibalized and recycled into the foreland basin as thrusting advanced toward the foreland the eastern pyrenean foreland basin records a different provenance history from central pyrenean tremp basin suggesting the basins were segmented throughout the late cretaceous to oligocene while the ripoll and ager basins appear to have shared similar source areas the sediment provenance evolution coupled with pyrenean fault activity and shortening rates hinterland exhumation foreland basin subsidence and climate proxies presents a detailed dataset to understand these relationships within the eastern pyrenean orogenic system and highlight the dominant control precursor basins and structural inheritance has on the subsequent fold thrust belts and foreland basin evolution

new late middle to early late ordovician u pb zircon ages of extension related felsic volcanic rocks in the eastern pyrenees ne iberia tectonic implications pre variscan basement rocks from the pyrenees provide evidence of several magmatic episodes with complex geodynamic histories from late neoproterozoic to palaeozoic times one of the most significant episodes consisting of several granitic and granodioritic bodies and volcanic rocks mostly pyroclastic in nature dates from the late ordovician period in the eastern pyrenees this magmatism is well represented in the ribes de freser and nuria areas here the nuria orthogneiss and the ribes granophyre both dated at c 457 460 ma seem to form a calc alkaline plutonic suite emplaced at different crustal levels the presence of numerous pyroclastic deposits and lavas interbedded with upper ordovician sandbian lower katian formerly caradoc sediments intruded by the ribes granophyre suggests that this magmatic episode also generated significant volcanism moreover the area hosts an important volume of rhyolitic ignimbrites and andesitic lavas affected by alpine deformation these volcanic rocks were previously attributed to late variscan volcanism extensively represented in other areas of the pyrenees here we present the first five laser ablation u pb zircon dates for this ignimbritic succession and two new ages for the ribes granophyre the ages of the ignimbrites overlapping within error are all 460 ma suggesting a genetic relationship between the plutonic and volcanic rocks and indicating that the sandbian katian magmatism is much more voluminous than reported in previous studies and possibly includes mega eruptions linked to the formation of collapse calderas

satellite observations of thermospheric tides results from the wind imaging interferometer on uars thermospheric winds measured by the wind imaging interferometer windii on the upper atmosphere research satellite are analyzed for migrating solar tides the data cover a 2 year period commencing february 1992 and are obtained from the atomic oxygen o 1s 557 7 nm emission which provides observations of the 90 to 200 km altitude range during daytime and the 90 to 110 km range at night the subtropical lower thermosphere is dominated by the diurnal propagating tide which exhibits a vertical wavelength of approximately 22 km grows in amplitude up to 95 km and decays rapidly above where molecular diffusion greatly reduces the vertical shears although the phase remains fairly uniform throughout the year a pronounced semiannual oscillation is observed in the diurnal tide amplitude at both 20 n and 20 s the meridional and zonal wind components attain their maximum values at equinox of approximately 70 and 40 m s respectively while the solstitial minima are nearly a factor of 2 smaller at 35 n the diurnal tide semiannual amplitude oscillation is still present in the lower thermosphere but above 100 km it is replaced by an annual cycle with a maximum in july and august this contrasts with 35 s where the july august peak is absent and the semiannual oscillation extends to 110 km at midlatitudes the zonal and meridional winds are of similar magnitude and no significant hemispheric asymmetries in amplitudes are observed in the lower thermosphere the semidiurnal tide amplitude exhibits an annual oscillation with maximum values of 30 to 40 m s occurring in june july near 100 km at 35 n 35 s and the equator a bimodal structure in the seasonal variation of the semidiurnal phase is observed this feature is characterized by rapid equinoctial transitions and is particularly well defined at the equator examination of the equatorial middle thermosphere indicates that the semidiurnal tide attains its maximum amplitude at 140 km and exhibits a vertical wavelength of approximately 60 km these findings indicate the predominance of the antisymmetric 2 3 hough mode in the tropics

diurnal tide in the equatorial middle atmosphere as seen in lims temperatures abstract the distribution of day night temperature differences in the middle atmosphere determined by the nimbus 7 lims experiment is described day night differences maximize at and are approximately symmetric about the equator successive centers of opposite sign increase in amplitude with altitude the pattern having a vertical wavelength of 25 km profiles of rocket meridional wind at kwajalein 8 7 n and ascension island 8 0 s taken near local noon and averaged over the lims data period exhibit maxima which support the tidal interpretation of the equatorial temperature pattern these characteristics are in general agreement with previous observational and theoretical results for the solar driven diurnal tide substantial time variations in amplitude and in location of the temperature maxima are observed the diurnal tide near the equatorial stratopause appears to be influenced by the phase of the semiannual oscillation

compositional effects on the solubility of minor and trace elements in oxide spinel minerals insights from crystal crystal partition coefficients in chromite exsolution chromite from los congos and los guanacos in the eastern pampean ranges of cordoba argentinian central andes shows homogenous and exsolution textures the composition of the exsolved phases in chromite approaches the end members of spinel mgal 2 o 4 spl and magnetite fe 2 fe 2 3 o 4 mag that define the corners of the spinel prism at relatively constant cr 3 r 3 ratio where r 3 is cr al fe 3 the exsolution of these phases from the original chromite is estimated to have accounted at 600 c on the basis of the major element compositions of chromite with homogenous and exsolution textures that are in equilibrium with forsterite rich olivine fo 95 the relatively large size of the exsolved phases in chromite up to ca 200 m provided for the first time the ability to conduct in situ analysis with laser ablation inductively coupled plasma mass spectrometry for a suite of minor and trace elements to constrain their crystal crystal partition coefficient between the spinel rich and magnetite rich phases d i spl mag minor and trace elements listed in increasing order of compatibility with the spinel rich phase are ti sc ni v ge mn cu sn co ga and zn d i spl mag values span more than an order of magnitude from d ti spl mag 0 30 0 06 to d zn spl mag 5 48 0 63 our results are in remarkable agreement with data available for exsolutions of spinel rich and magnetite rich phases in other chromite from nature despite their different cr 3 r 3 ratio the estimated crystal crystal partitioning coefficients reflect the effect that crystal chemistry of the exsolved phases from chromite imposes on all investigated elements excepting cu and sc and only slightly for mn the observed preferential partitioning of ti and sc into the magnetite rich phase is consistent with high temperature chromite melt experiments and suggests a significant dependence on fe 3 substitution in the spinel structure a compositional effect of major elements on ga co and zn is observed in the exsolved phases from chromite but not in the experiments this might be due to crystal chemistry differences along the mgfe 1 al 2 fe 2 3 exchange vector which is poorly covered experimentally this inference is supported by the strong covariance of ga co and zn observed only in chromite from layered intrusions where this exchange vector is important a systematic increase of zn and co coupled with a net decrease in ga during hydrous metamorphism of chromitite bodies cannot be explained exclusively by compositional changes of major elements in the chromite which are enriched in the magnetite component the most likely explanation is that the contents of minor and trace elements in chromite from metamorphosed chromitites are controlled by interactions with metamorphic fluids involved in the formation of chlorite

climatology and trends of the middle atmospheric temperature 33 87 km as seen by rayleigh lidar over the south of france the technique of the rayleigh lidar provides temperature profiles with a good temporal and vertical resolution in the middle atmosphere data obtained by 2 rayleigh lidars set up at the observatory of haute provence 44 n 6 e and at biscarrosse 44 n 1 w from 1978 to 1989 led to a unique set of data of 1200 night mean temperature profiles from 37 to 87 km a climatology of the temperature over the south of france has been established from this data base and new results concerning both the short term and long term variability of the middle atmosphere are presented in this paper the observed temperature around 44 n 0 w is in general colder than the mean temperature given in the cospar international reference atmosphere 1986 near 75 km and warmer above 80 km a clear semiannual variation is observed near 65 km with maxima occurring just after the equinoxes the study of the short term variability indicates clearly two frequency domains long periods below 65 km with a maximum in december january which relate to planetary waves and shorter periods above 65 km induced by the breaking of gravity waves a correlation with the 11 year solar cycle negative in the stratosphere and positive in the mesosphere is found to be well above the 95 confidence level with an amplitude larger in winter than in summer however with only 11 years of data it is obviously difficult to conclude that this atmospheric perturbation is induced by the solar forcing a cooling of the mesosphere of about 4 k decade at 60 70 km is found but is at the limit of the 95 confidence level whereas we do not observe any significant trend in the stratosphere

ordovician magmatism in the eastern pyrenees implications for the geodynamic evolution of northern gondwana new data on the geochemistry and geochronology of different felsic gneisses and metabasites from the variscan massifs of eastern pyrenees have allowed us to shed some light on the ordovician magmat

multiple archaean to early palaeozoic events of the northern gondwana margin witnessed by detrital zircons from the radzimowice slates kaczawa complex central european variscides sims dating of detrital zircons from the stratigraphically enigmatic radzimowice slates of the kaczawa mountains sudetes sw poland near the eastern termination of the european variscides has yielded age populations of 1 493 512 ma corresponding to late cambrian to early ordovician magmatism and constraining a maximum depositional age 2 between 550 and 650 ma reflecting input from diverse cadomian sources and 3 older inherited components ranging to c 3 3 ga with age spectra similar to those from gondwanan north africa the new data show that the radzimowice slates cannot form a proterozoic base to the kaczawa mountains succession as suggested by earlier models but was deposited at the earliest as an extensional basin fill during a relatively late stage of the break up of this part of northern gondwana

evolution of the middle crust of the pyrenees during the paleozoic new data on the plutonic rocks from the north pyrenean agly massif the variscan middle crust of the eastern pyrenees is represented by the belesta and caramany gneissic units of the north pyrenean agly massif in this study we date and reinterpret the orthogneisses and granites composing these units we characterize a recurrent plutonic activity spanning all the paleozoic in this part of the pyrenean crust the belesta unit amphibolite facies is mainly composed of sills of latest ediacaran earliest cambrian 542 4 and 540 4 ma orthogneisses 70 of the series almost unknown in the pyrenees until now and latest carboniferous earliest permian 307 3 298 3 ma time span granites 15 of the series these plutonic rocks were emplaced in probably ediacaran aluminous pelites later transformed into paragneisses 15 of the series the caramany unit granulite facies is mainly composed of precambrian aluminous paragneisses migmatized during the latest carboniferous earliest permian 299 4 ma sills of earliest cambrian 529 5 ma orthogneisses and sills about 30 of the series of late carboniferous 308 3 299 3 ma opxbearing and opx free granodiorites grt bearing leucogranites and norites among these last rocks the ansignan charnockite forming a 800 m thick laccolith near the base of the caramany unit and previously dated at 314 6 7 ma respaut lancelot neues jahrbuch miner abh 147 1 21 34 1983 is refined at 307 3 ma our results confirm the importance of the late carboniferous plutonism in deep levels of the pyrenean crust which largely resulted from recycling of older para and orthoderived rocks of this crust the emplacement of hundreds of metres in thickness of granites and other plutonic rocks in the variscan pyrenees occurred in a rather short time both as sills in these deep levels and as large plutons in shallower levels a fact which necessarily had consequences on the ht lp carboniferous metamorphism

temperature tides and waves near the mesopause from lidar observations at two latitudes 1 daytime and nighttime temperature measurements covering several days enable the detection of tidal and wave perturbations in the mesopause region this study presents two potassium lidar observations from 28 n and 54 n which cover more than 100 hours each the temperature variations during this time show significant wave features and numerical analyses allow to separate those of tidal and nontidal origin the tidal activity under winter conditions is found to be dominated by upward propagating semidiurnal tides with amplitudes of about 10 k whereas a diurnal tide was also seen at 54 n it was not detectable at 28 n the data are discussed with respect to various available data sets and models comparisons with current numerical models show that especially the semidiurnal tide is clearly underestimated at both latitudes the tidal activity exhibits a strong variability this indicates nonlinear interactions with planetary waves which have also been observed

strata bound as au mineralization in pre caradocian rocks from the vall de ribes eastern pyrenees spain in the lower part of a pre caradocian series associated with volcanics there are disseminations and lenses of arsenopyrite and pyrite with gold and bi ag cu pb zn w minerals these ores are accompanied by veins and epigenetic masses of the same mineralogical composition the disseminations are found in psammopelitic rhythmites and dolomites which also contain cmthick lenses the epigenetic bodies also enclosed in the rhythmites and dolomites are interpreted as reconcentrations of preexisting disseminations and lenses caused by subsequent phases of deformation