the tectonothermal evolution of the cadomian belt of northern brittany france a neoproterozoic volcanic arc abstract the neoproterozoic cadomian belt northern brittany france results from the accretion of crustal blocks that record distinctive p t deformation paths in addition abundant gabbro dioritic to granitic intrusions during and after deformation influence the thermal pattern and are used as time markers as a whole the deformation history of the cadomian belt is characterised by a migration in time of the active zones which become younger towards the southeast relics of eocadomian rocks reveal that arc development took place at about 660 640 ma abundant calc alkaline magmatism intruding strongly deformed palaeoproterozoic orthogneisses characterise the northernmost unit of the cadomian belt i e the tregor unit which cooled before 600 ma the lanvollon basin a short lived intra arc rift containing abundant mafic and felsic volcanics followed by greywackes opened at about 600 580 ma the subsequent tectonothermal history of the cadomian belt is divided into two major episodes the first episode is related to the shortening of the intra arc rift and its southwestward thrusting over the guingamp unit this led to crustal thickening inducing partial melting in the guingamp unit exhumation of the latter rocks is accommodated by late extensional shearing along the boundary between the saint brieuc and guingamp units cooling of the saint brieuc unit is dated at about 570 560 ma the second episode is dominated by sinistral wrenching mainly localised in the eastern part of the cadomian belt at the boundary between the domnonean i e the arc domain and mancellian possibly a fore arc basin domains several shear zones developed during this episode some of them being associated with minor granitic intrusions dated around 550 ma the sinistral shear located southeast of the arc domain is reworking or crosscutting earlier high temperature fabrics within the saint brieuc unit in addition the vertical component of this shearing episode contributes significantly to the exhumation of the saint malo migmatites near the proterozoic cambrian boundary cordierite biotite granitoids intruded at shallow depths the fougeres unit their emplacement outlasting deformation of the sedimentary sequences minor stocks of muscovite leucogranites of cambrian age are possible equivalents of the abundant volcanism in an adjacent nw se trending rift this marks a major change in the kinematic framework with predominance of extension finally minor reactivation of the cadomian structures occurred during the carboniferous associated with the variscan orogeny

cadomian terranes wrench faulting and thrusting in the central europe variscides geophysical and geological evidence sixty five per cent of the paleozoic basement of western and central europe is hidden by a sedimen tary cover and or sea this work aims to remove that blanket to detect new structures which could used to build a more comprehensive model of the variscan or ogeny it is based on the interpretation of various forms of data a published gravity maps corrected for the ef fects of the crust mantle boundary topography and light sedimentary basins b aeromagnetic maps c measurements of densities and d induced and rema nent magnetizations on rocks from paleozoic outcrops of the upper rhenish area from the northern b ohem ian massif to the eastern paris basin the saxothurin gian is characterized by a 500 km long belt of gravity highs the most important being the kraichgau high most of the corresponding heavy bodies are buried un der a post early visdan cover they are interpreted as relics of late proterozoic terranes overlain by an early to middle paleozoic sequence equivalent to the bo hemian t errane in the bohemian massif the most probable continuation of these dense bohemian ter ranes toward the west is the southern channel north ern brittany cadomian terrane the gravity lows are correlated with variscan granites and pre and early variscan metagranites gravity and magnetic maps demonstrate large scale displacement in devonian early carboniferous times along the parallel and equidistant nw se striking vistula elbe bavarian bray and south armorican dextral wrench faults in the vosges schwarzwald and central massif the faults continue with the east west striking lalaye lubine ba den baden and marche faults and with south vergent thrusts the bavarian faults shift the kraichgau terrane by 150 km relative to the bohemian terrane whereas the offset of the north ern brittany cadomian relative to the northern vosges kraichgau terranes is estimated at 400km along the bray fault sinistral wrench faults are the ne sw striking sillon houiller rheingraben rodl vitis and diendorf faults the southern vosges schwarzwald devonian dinanti an basin is interpreted as a pull apart basin at the south easterly extremity of the bray fault the bohemian and kraichgau body form allochthonous terranes which were thrust over the saxothuringian crust thrusting to the north west was accompanied by back thrusting and led to the forma tion of pop up structures contemporaneous dextral and sinistral wrench faulting resulted in transpressive strain during collision the zonal structure of the varis cides in the sense of kossmat 1927 is relevant only to the rhenohercynian foreland belt kossmat 1927 al ready spoke of a moldanubian region because it dis plays no real zonal structure the saxothuringian zone was formed by terrane accretion their apparent zonal structure is not a pre collisional feature but only the result of accretion and collision

three dimensional model and late stage warping of the plattengneis shear zone in the eastern alps abstract the plattengneis shear zone is a 250 600 m thick flat lying cretaceous eclogite facies mylonitic shear zone with north over south transport direction that is exposed over almost 1000 km2 in the koralpe region along the eastern margin of the alps although the shear zone is one of the largest in the alps its role in the eoalpine metamorphic evolution and the subsequent exhumation of the region remain enigmatic and its large scale geometry is not well understood the outcrop pattern suggests that the shear zone is made up of a single sheet that is folded into a series of open syn and antiforms with wavelengths of about 10 km eclogite bodies occur above within and below the shear zone and there is no metamorphic grade change across the shear zone in the south the fold axes strike east west and plunge shallowly to the east in the north the fold axes are oriented in north south direction and form a dome shaped structure of the shear zone total shortening during this late stage warping event was of the order of 5 indirect evidence constrains this folding event to have occurred between 80 and 50 ma and the fold geometry implies that the final exhumation in the koralpe occurred somewhat later than further north interestingly the shear zone appears to strike out of the topography in the south and dip into the topography in the north so that north of the shear zone only hanging wall rocks are exposed and south of it only foot wall rocks possibilities for the geometric relationship of the plattengneis shear zone with the surrounding south dipping detachments are discussed

transition from island arc to passive setting on the continental margin of gondwana u pb zircon dating of neoproterozoic metaconglomerates from the se margin of the tepla barrandian unit bohemian massif abstract sedimentological petrological and geochemical data combined with shrimp and la icp ms u pb ages of pebbles of granitic rocks and detrital zircons from neoproterozoic vletice metaconglomerates of the se margin of the tepla barrandian unit were used to characterize the regional geotectonic setting at the proterozoic paleozoic boundary the metaconglomerates form several metres thick intercalations in metasediments of the svrchnice formation roof pendants of central bohemian plutonic complex which is considered to have been deposited in neoproterozoic cambrian times a sedimentological study indicates that the metaconglomerates are products of debris flows deposited in submarine canyons or proximal parts of submarine fans geochemistry of metaconglomerate matrix and petrography of pebbles revealed an obvious difference from the western and central part of the tepla barrandian unit proterozoic where pebbles eroded from uplifted parts of the basin and island arc sources are most common the abundance of quartz quartzite granite and crystalline limestone in pebbles together with the more mature composition of host metagreywackes indicate the presence of relatively evolved continental crust in the source area for the vletice metaconglomerates and shallowing of the neoproterozoic basin to the se in the present geographic co ordinate system the neoproterozoic to lowermost cambrian age of the svrchnice formation suggested by its comparison with similar rocks in the central part of the tepla barrandian unit was confirmed by u pb dating ages of detrital zircons from the metaconglomerate matrix cluster around two values archaean to paleoproterozoic u pb ages between ca 2580 and 1780 ma and neoproterozoic to early cambrian ages between 660 and 520 ma with a significant peaks at 600 and 544 ma suggesting local volcanic activity extending shortly beyond the proterozoic paleozoic boundary zircons separated from two trondhjemite pebbles from the metaconglomerate yielded a mean u pb age of 610 17 ma arguing for active arc magmatism during the latest neoproterozoic the overall age distribution of detrital zircons and the absence of grenvillian zircon ages favour a location of the tepla barrandian unit close to the west african craton at the neoproterozoic paleozoic boundary the rapid onset of a transtensional geotectonic regime and maturing of sediments is evidenced by the overlying cambrian shallow water clastics alternating with predominantly felsic calc alkaline to alkaline volcanics during the cambrian oblique plate convergence the active continental margin was transformed into belts of horsts and narrow pull apart or small rift basins after the ordovician break off of armorican terrane assemblage blocks from gondwana the extensional regime in the tepla barrandian unit continued until the beginning of variscan orogeny in the middle devonian

sm nd isotope characteristics of late cadomian granite magmatism in northern france and the channel islands sm nd isotopic studies of granites within the late precambrian cadomian orogenic belt of the north armorican massif northwestern france and channel islands reveal differences between arc related granite magmatism in outboard terranes and intracrustal granite magmatism in inboard terranes late cadomian c 570 ma arc related granitoids exhibit a range of e nd 2 to 6 and nd model ages t dm 1 0 1 3 ga reflecting variable contamination between late precambrian mantle derived magmas and ancient c 2 0 ga continental crust the contamination did not involve exposed granitic icartian basement to anygreat degree a more likely contaminant being unexposed lower crust of intermediate to acidic granulitic composition or early cadomian plutons which were themselves contaminated by lower crust voluminous granites of the mancellian region c 550 540 ma share common isotopic characteristics e nd 4 to 7 t dm 1 5 1 7 ga with migmatites and anatectic granites produced by partial melting of metasedimentary sequences within the st malo region consistent with a common source

the cadomian orogeny in the north armorican massif a brief review the north armorican massif nam of nw france is the type locality of the late precambrian cadomian orogenic belt the nam largely escaped reworking during the upper palaeozoic variscan cycle with the result that earlier geological relationships are commonly preserved intact a large part of the cadomian belt of the nam comprises variably deformed and metamorphosed supracrustal rocks of the brioverian succession barrois 1895 1896 1908 graindor 1957 cogne 1962 le corre 1977 rabu et al 1982 1983 chantraine et al 1982 the cadomian orogeny which takes its name from cadomus caen in normandy was defined by bertrand 1921 as the late precambrian orogeny which in the nam resulted in the folding and uplift of the brioverian succession prior to the deposition of lower palaeozoic red bed sequences events which have been ascribed to the cadomian orogeny span the period c 700 425 ma during which time the brioverian was heterogeneously deformed and metamorphosed and intruded by calc alkaline igneous complexes the evolution of the belt has been interpreted in terms of the gradual cratonization of calc alkaline arc complexes and syn orogenic sediments in an andean type continental margin brown et al 1990 dupret et al 1990 this contribution reviews briefly the geology of the cadomian belt of the nam fig 1 and outlines some of the more controversial debates concerning the distribution and status of precadomian basement the stratigraphy of the brioverian succession the nature of cadomian magmatism the kinematic significance of major structures and the geotectonic setting of the component parts of the belt

emplacement of lobate sheet flows with hyaloclastites onto soft sediment the erquy neoproterozoic lava pile armorican massif france abstract the neoproterozoic volcano sedimentary succession of the heussaye headland erquy belongs to the cadomian block located in the north east of the armorican massif france the volcanism dated at approximately 608 7 ma zircon u pb data occurred in a back arc basin this site exhibits a noteworthy verticalized pile of moderately metamorphosed greenschist facies basaltic andesite flows of arc back arc tholeiite affinity alternating with metasedimentary layers sandstones and siltstones a large range of volcanic facies characteristic of an underwater soft substrate environment can be continuously studied for over than 200 m parallel to the flow edges they include pillow lavas lava lobes fluidal peperites and sediment matrix hyaloclastites the presence of parallel lava lobes in a sector where one lava flow is capped by a variably thick hyaloclastite carapace together with the occurrence of asymmetric turbiditic folds in interbedded metasedimentary layers suggests the existence of an easterly facing gentle paleoslope the sudden thinning of this hyaloclastite carapace in two spots located approximately 60 m from each other is attributed to the synvolcanic activity of two conjugate normal paleofaults this hypothesis is supported by the observation of a hyaloclastite accumulation in one of the two spots close to a strike slip fault which may have been extensional at the time of the volcanism water entered the lava flow along the faults resulting in an interstitial network of hyaloclastites by quench fragmentation in the upper part of the hanging wall block all these observations are consistent with a model of lava emplacement along a subaqueous slope resulting from synmagmatic extensional faulting in a marginal basin context

brioverian volcanism and cadomian tectonics baie de st brieuc brittany stages in the evolution of a late precambrian ensialic basin

arsenic regeneration from estuarine sediments of the bothnian bay sweden abstract sediments of the bothnian bay between northern sweden and northern finland are contaminated by as giving rise to concentrations in the percent range the enclosure of a sediment and bottom water by benthic chambers resulted in chemical reduction of the water and the oxidized sediment surface layer and a flux of reduced as from the feooh phase of the sediment the release of as could be described by zero or pseudo zero order reaction kinetics the measured flux of as into the water at 20 c was 2 1 mg m 2 day 1 as

tectonothermal chronology of early cadomian arc development in guernsey and sark channel islands the cadomian orogen exposed in nw france and the channel islands comprises a collage of variably displaced terranes which record the late proterozoic evolution of a continental margin within a complex subduction zone on the islands of guernsey and sark calc alkaline quartz diorite stocks were emplaced during early stages of the cadomian orogeny zircons from two stocks of deformed quartz diorite display evidence of inheritance in larger and more magnetic fractions upper intercept ages for these discordant concentrates are c 1300 ma sm nd whole rock model ages t dm suggest older ages of c 2000 ma conversely the smallest and least magnetic zircons exhibit a distinct lead loss pattern suggesting that the 207 pb 206 pb dates of c 700 ma correspond to the time of crystallization of the stocks and provide a lower age constraint for initiation of subduction related magmatism in the cadomian orogen hornblende concentrates from deformed quartz diorite stocks exposed on guernsey and sark display discordant 40 ar 39 ar age spectra five samples record well defined isotope correlation ages ranging between 596 ma and 606 ma a hornblende concentrate from host orthogneiss sark yields a plateau age of 608 ma the hornblende ages are interpreted as dating post metamorphic cooling following late proterozoic deformation and metamorphism within the arc system both magmatic and cooling ages from this early cadomian arc contrast with those of younger initial tectonothermal activity c 570 ma and c 540 ma in other cadomian terrane elements and suggest palinspastic separation until very late stages of the orogeny the polyphase nature of this late proterozoic activity is similar to that of related orogens which probably occupied similar tectonic settings along the margin of gondwana e g sw iberia west africa

short paper cadomian terrane tectonics and magmatism in the armorican massif the north armorican composite terrane nw france is a collage of displaced terranes which result from the amalgamation of cadomian continental arcs and marginal basin complexes by sinistral transpression along a continental margin above a subduction zone early cadomian arc activity occurred at c 700 650 ma but terrane accretion did not occur until c 540 ma and post tectonic magmatism persisted well into the palaeozoic cadomian events thus span a considerably greater period than previously supposed

the cadomian granites of mancellia northeast armorican massif of france relationship to the st malo migmatite belt petrogenesis and tectonic setting abstract the north armorican shear zone nasz divides the cadomian belt of the armorican massif of france into two major terranes the north armorican composite terrane nact and the central armorican terrane cat the nact is a pastiche of displaced blocks and terranes st brieuc terrane st malo terrane and mancellian terrane which results from the amalgamation of cadomian continental arc and basin complexes by sinistral transpression along a continental margin above a southerly dipping subduction zone in the nact the neoproterozoic brioverian succession was deformed and metamorphosed during the cadomian orogeny and intruded by syn to post tectonic plutonic complexes the st malo migmatite belt is a syn tectonic suite of anatectic migmatites derived through partial melting of the brioverian succession using the t test on whole rock geochemical data there is no evidence to suggest that a sample of st malo diatexites comes from a population with a different mean than some samples of the brioverian succession sandstones resulting homogeneous diatexites anatectic granites of the core were emplaced syn kinematically into cadomian strike slip shear zones thus the age of anatexis of 540 ma is also the date of strike slip shearing and provides a minimum age for the sinistral transpression which amalgamated the terranes of the nact the mancellian granites to the southeast of the st malo migmatites were emplaced at 540 ma and are overlain unconformably by cambrian sediments overall geochemistry and a variety of specific geochemical parameters show that the mancellian granites are similar to the diatexites and anatectic granites of the st malo migmatite belt using the t test on whole rock geochemical data there is no evidence to suggest that the sample of mancellian granites comes from a population with a different mean than the sample of st malo diatexites additionally both suites of rocks are peraluminous they have similar distributions of rb sr and ba they have k rb ratios around 225 and they plot largely within the vag field using trace element discrimination diagrams for the interpretation of tectonic setting samples of the brioverian succession sandstones the st malo migmatites and the mancellian granites all exhibit similar primordial mantle normalized element patterns preliminary results of nd and sr isotope studies reveal a similar restricted range of values for nd between 4 0 and 7 3 and sr between 3 and 42 and depleted model ages in the range 1 7 to 1 5 ga tdmur for both mancellian granites and st malo migmatites isotopic features which set these rock types apart from other cadomian granites within the nact the st malo migmatite belt and the mancellian granites are coeval at 540 ma and both developed by anatexis at intermediate crustal depths of the brioverian succession within an inverted but only moderately overthickened behindarc basin in comparison with the st malo migmatites the mancellian granites represent farther travelled products of intracrustal melting but their geochemistry still preserves the characteristic signature of the source

geochemical study of the brioverian late proterozoic volcanic rocks in the northern armorican massif france implications for geodynamic evolution during the cadomian

3d geological modeling of the kasserine aquifer system central tunisia new insights into aquifer geometry and interconnections for a better assessment of groundwater resources summary the challenge of this study was to create a 3d geological and structural model of the kasserine aquifer system kas in central tunisia and its natural extension into north east algeria this was achieved using an implicit 3d method which honors prior geological data for both formation boundaries and faults a current model is presented which provides defendable predictions for the spatial distribution of geology and water resources in aquifers throughout the model domain this work has allowed validation of regional scale geology and fault networks in the kas and has facilitated the first ever estimations of groundwater resources in this region by a 3d method the model enables a preliminary assessment of the hydraulic significance of the major faults by evaluating their influence and role on groundwater flow within and between four compartments of the multi layered kas hydrogeological system thus a representative hydrogeological model of the study area is constructed the possible dual nature of faults in the kas is discussed in the context that some faults appear to be acting both as barriers to horizontal groundwater flow and simultaneously as conduits for vertical flow also discussed is the possibility that two flow directions occur within the kas at a small syncline area of near feriana in summary this work evaluates the influence of aquifer connectivity and the role of faults and geology in groundwater flow within the kas aquifer system the current kas geological model can now be used to guide groundwater managers on the best placement for drilling to test and further refine the understanding of the groundwater system including the faults connectivity as more geological data become available the current model can be easily edited and re computed to provide an updated model ready for the next stage of investigation by numerical flow modeling

evidence for multiple high t metamorphism and regional migmatization within the cadomian belt of northern brittany france the cadomian orogeny is characterized by two major tec tonometamorphic events one that pre dates 570 ma and another at c 540 ma until recently the majority of migmatites occurring within the cadomian belt of northern brittany were interpreted as having been formed during the second event the discovery of the jouguet migmatites which have been hornfelsed by the st brieuc diorite emplaced at 533 l2 ma suggests that a migmatitic event occurred before 540 ma these data demand a reinterpretation of the structural sketch of the cadomian orogeny

geochemistry and geotectonic interpretation of the penthievre crystalline massif northern brittany france abstract in the armorican massif of brittany and normandy northern france and the channel islands u k an episode of crust formation spanning the period from 700 ma to the early palaeozoic can be recognized and is attributed to the cadomian orogenic cycle during the early part of this orogenic cycle the components of the penthievre crystalline massif were emplaced to produce the basement upon which local brioverian volcanism and sedimentation took place three separate episodes of crustal accretion have been recognised in the penthievre crystalline massif the first is represented by the yffiniac group which is dominantly of basic to intermediate composition with a minor acidic component this suite which was metamorphosed at amphibolite facies shows geochemical characteristics of island arc tholeiitic to continental calc alkaline igneous activity ree profiles are flat to lree enriched cen ybn in the range 1 18 4 89 incompatible element spidergrams show relative enrichment of for example th u lree and lil elements and depletion of ta nb and ti ta la and nb la ratios are low the second suite is represented by the port morvan group a linear belt of leucocratic orthogneisses containing net veined rafts of deformed yffiniac group rocks the port morvan group gneisses are trondhjemitic to quartz dioritic in composition with na2o k2o up to 32 9 the third assemblage comprises the jospinet group and the fort de la latte complex these are part of a compositionally expanded mantle derived plutonic suite ranging from ultrabasic to aplitic in composition flat chondritic ree profiles characterise gabbros whereas lree enriched profiles characterise calc alkaline and alkali calcic granitoid plutons there is evidence in penthievre for protracted destructive plate margin activity and associated plutonism of andean type the penthievre crystalline massif probably represents the roots of juxtaposed island arc and continental margin terranes produced in three crust forming episodes during the cadomian orogenic cycle brioverian sedimentation and volcanism took place in ensialic basins on rifted crust the closure of these brioverian basins was accompanied by the emplacement of calc alkaline plutons into the crystalline basement

precadomian relicts in the armorican massif their age and role in the evolution of the western and central european cadomian hercynian belt abstract well dated precambrian is mostly developed in the north of the armorican massif in which area voluminous cadomian magmatism is dated at between 650 and 550 ma much older relicts occur at cap de la hague in guernsey and in the tregor and are also found in the northern continental margin of the iberian peninsula in all these occurrences whole rock systems have been opened so that the true ages cannot be determined by the rb sr whole rock isochron method four u pb zircon ages are between 1 8 and 2 ga in guernsey icart orthogneisses in tregor port beni trebeurden morguignen orthogneisses there is no evidence from strontium isotopes that these isolated and scattered relicts have a wide extension or that such ancient continental crust played an important role in magma genesis from 650 ma to 270 ma ago on the contrary the evolution of initial 87sr 86sr ratios with time shows that the observed mid and west european continental crust is probably not older than 700 ma the increase of the initial 87sr 86sr ratios of the magmas with time suggests that after its formation in cadomian times this segment of continental crust evolved virtually as a closed system and hercynian magmatism arose principally from re melting of relatively young sialic components

behaviour of rb sr whole rock and u pb zircon systems during partial melting as shown in migmatitic gneisses from the st malo massif ne brittany france the age of regional metamorphism and partial melting in the late proterozoic succession of the st malo area has been established at around 540 ma whole rock homogenization of the sr isotope systems has been achieved only in the anatectic granites whereas the associated metatexitic and diatexitic gneisses remain highly heterogeneous at lower grade than the sillimanite isograd metasedimentary gneisses contain detrital zircons which record the regional metamorphic event as a u pb lower intercept age 536 14 ma in the sillimanite zone u pb zircon lower intercept ages are around 500 10 ma and suggest a recent loss of radiogenic pb from the observed overgrowths zircons from the anatectic granites do not yield u pb intercept ages due to the presence of inherited radiogenic pb but the finer fractions define a discordant array whose upper intercept on concordia yields 555 13 ma an age significantly older than the partial melting event indicated by the lower grade zircon ages the lower intercept defined by the fine grained anatectic zircons yields a date in the future negative ordinate value in their regional context the st malo migmatites can be considered as resulting from late stage crustal melting in the cadomian orogenic belt following genesis of calc alkaline magma at an active margin around 600 ma ago an age of 540 ma for partial melting in the st malo migmatites places the end of the cadomian orogeny near the precambrian cambrian boundary

synoptic conditions associated with propagating and nonpropagating cloud rainfall episodes during the warm season over the east asian continent abstractusing european centre for medium range weather forecasts ecmwf analyses this study identifies common synoptic flow patterns associated with propagating long lived and nonpropagating short lived precipitation cloud episodes in the warm season over east asia 25 40 n 95 125 e among 123 initial cases during may july 1997 2003 86 were classified into three categories propagating cases with strong and weak forcing and nonpropagating ones with strong inhibition consisting of 10 types based on their 500 hpa flow patterns for each type composites at various levels when episodes moved across 100 105 110 115 and 120 e were made and discussed to elucidate the influence of synoptic conditions for propagating episodes with strong 500 hpa forcing 46 cases four types were identified in their composites favorable positive vorticity advection forcing from an approaching trough short wave exists aloft and concurrent development of southwest vortex and front wind shift line at low lev

incipient strain partitioning in a slate belt evidence from the early variscan monts d arree slate belt brittany france abstract partitioning of strain is a fundamental process during mountain building it commonly causes a compartmentalisation of a bulk regional strain into deformational domains with contrasting strain characteristics and largely oriented parallel to the orogenic grain the monts d arree slate belt brittany france offers an opportunity to study strain partitioning in a slate belt deformed in an overall transpressional regime the slate belt consists of highly deformed low grade siliciclastic metasediments of upper silurian to lower devonian age the deformation occurred during an early variscan nappe stacking event bretonian phase an extensive structural analysis has demonstrated that the slate belt reflects the initial stages of strain partitioning the slate belt primarily reflects coaxial contraction dominated deformation it resulted in nw verging folding and a pervasive cleavage development giving rise to a pronounced mechanical anisotropy during the later stages of deformation incipient strain partitioning lead to the development of punctuated strain heterogeneities consistently reflecting dextral belt parallel strike slip strain these structures are not organised in networks or domains incipient strain partitioning in the monts d arree slate belt did not reach the stage of compartmentalisation by the formation of an interlinked discontinuity network or wrench dominated deformational domains

the structural evolution of the english channel area the structural evolution of the english channel area is controlled by structure and particularly by the pre existing cadomian and variscan crustal discontinuities which have been reactivated repeatedly in post variscan times they controlled the crustal subsidence that produced basin development in the mesozoic prior to the sea floor spreading in the north atlantic region they were then reactivated during the cenozoic compression and basin inversion the english channel development is ascribed to mid tertiary differential uplift oligocene to miocene during late tertiary to quaternary times the channel displays characteristics of a tectonically controlled fluvial basin periodically invaded by the sea at the lithospheric scale the channel can be considered as an active intraplate area influenced by the nw se alpine push the nw se atlantic ridge push and glacial rebound stresses copyright 2003 john wiley sons ltd

u pb geochronological constraints on the tectonothermal evolution of the paleoproterozoic basement of cadomia la hague nw france abstract the la hague region of nw france provides some of the best exposures of paleoproterozoic basement in the northernmost segment of the cadomian orogen one of several neoproterozoic arc fragments in the circum atlantic region the basement rocks which include orthogneiss metasediments and metabsites contain a comparable series of structures with a common metamorphic history thus the basement units are regarded to have undergone the same broad tectonothermal evolution the metasedimentary succession includes migmatites that preserve relict kyanite overprinted by sillimanite associated with the development of garnet bearing leucosome biotite dehydration at a metamorphic peak of 700 800 c and 8 9 kbar is considered responsible for the anatexis evident in both the metasediments and orthogneiss units a u pb zircon crystallization age of 2061 2 7 ma for the culeron orthogneiss a member of the metamorphic suite confirms the paleoproterozoic protolith age idioblastic rims to 2 06 ga zircons from the culeron orthogneiss yield shrimp u pb dates of c 618 ma providing the first geochronological constraints on the likely age of high grade metamorphism and anatexis of the paleoproterozoic basement in cadomia foliated c 615 610 ma intrusions that intrude the metamorphic units record magmatic to solid state fabrics that parallel metamorphic fabrics within the basement consistent with deformation and metamorphism being late neoproterozoic in age

late precambrian thrust and wrench zones in northern brittany france abstract brioverian units of northern brittany armorican massif france were deformed and metamorphosed during a late precambrian tectonic episode the cadomian orogeny kinematic study strain and displacement in the st cast st brieuc area shows that this tectonic episode was characterized by the obduction of a back arc basin over a continental margin around 580 590 ma ago strain pattern analysis reveals a constant interaction between ssw directed imbricated thrust zones and ductile sinistral wrench zones trending n 50 e the arcuate pattern of cadomian structures in this area results from such an interaction thickening as a result of the thrusts induced migmatization and the development of a high temperature belt around 540 ma in the st malo guingamp area

gravity modellings of the cadomian active margin of northern brittany abstract the geometrical relationships existing between the saint brieuc saint malo and guingamp units which form the cadomian active margin of northern brittany have been determined by gravity analyses and 2 5d modelling correlated with other geophysical magnetic seismic etc and geological observations automatic structural analyses were performed before modelling to identify lateral gravity discontinuities averaged density measurements were used for 2 5d gravity modelling along six profiles across the arcuate geological and gravity shape of the cadomian basement this study allowed the third dimension to be obtained through correlating each profile with its neighbours we propose that orthogneiss formations equivalent to the port morvan orthogneiss constitute the saint brieuc upper crustal unit below the lanvollon formation 2 5d gravity modelling outlines downward geological differences in the western and eastern parts of the ploufragan complex as previously indicated by surface mapping these results stress the necessity for distinguishing between the guingamp and saint malo units

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

early diagenesis of arsenic in sediments of the kalix river estuary northern sweden solid phase as fe mn s and al and pore water total as fe mn and s have been determined for two cores from the kalix river estuary at the same station the depositional flux of arsenic was measured sediment traps fe iii oxides persist in the anoxic zone of the sediment and act as a carrier for arsenic down to depths of 10 15 cm the release of arsenic into the pore water is controlled by the reduction dissolution of these oxides as a result internal cycling of arsenic i e upward diffusion in pore water re adsorption onto fe iii oxides in the oxidized surface layer and reburial occurs in the uppermost 10 15 cm at the base of the arsenic cycling zone solid phase arsenic maxima 160 170 g g 1 of probable diagenetic origin occur the quantity of arsenic diffusing back towards the oxidized surface layer 2 2 g cm 2 yr 1 as is close to 75 of the quantity of arsenic being deposited due to sedimentation 2 9 g cm 2 yr 1 as however a mass balance for the surface layer indicates that re adsorption of arsenic onto fe iii oxides may effectively prevent diffusion of dissolved arsenic back into the overlying water column it is concluded that the interpretation of sedimentary arsenic profiles may be severely complicated due to post depositional migration of arsenic

geochemistry and origin of ferromanganese concretions in the gulf of bothnia abstract ferromanganese concretions cover large areas of the gulf of bothnia they are flat to well rounded the rounded ones being richer in oxyhydroxides of iron and manganese rounded and ellipsoidal nodules particularly those in the northern gulf of bothnia are richest in mn ni ba and cu which probably coexist in a mn oxyhydroxide phase flat nodules are enriched in fe p rare earths and as probably associated with an fe oxy hydroxide component aluminum v cr and ti occur in still another phase the sediments of the gulf generally consist of a 10 50 mm thick layer of oxidized surface sediment enriched in mn ba p and ni lying on top of reduced sediments which are diagenetically depleted in these elements the remobilized elements have redeposited in the nodules but this process cannot explain the origin of all the nodular material some released mn ba and ni furthermore enter into suspended phases which eventually leave the baltic sea the economic value of the nodules in the gulf of bothnia is probably limited at present

why nocturnal long duration rainfall presents an eastward delayed diurnal phase of rainfall down the yangtze river valley hourly observational records and 6 hourly reanalysis data were used to investigate the influences of large scale forcings on the diurnal variation of summer rainfall along the yangtze river yr the results show that longduration more than six hours rainfall events dominate the summer rainfall along the yr these events tend to start during the night and to peak after several hours of development the eastward delayed initiation of the nocturnal long duration rainfall events is thought to be due to the diurnal clockwise rotation of the lowtropospheric circulation especially the accelerated nocturnal southwesterlies in the early evening the anomalous easterly flow toward the tibetan plateau tp causes low level convergence over the plateau s eastern slope that induces the formation of rainfall in the upper yr valley the anomalous wind sequentially rotates clockwise to a southerly flow at midnight and accelerates the meridional wind in the middle valley resulting in the initiation of rainfall between 2300 and 0300 lst in the early morning the accelerated southwesterlies in southern china when combined with decelerated winds in the north of the yr causes a strong convergence along the yr and contributes to the early morning rainfall in the lower valley furthermore the development of the convection systems is suppressed in the afternoon by the mid and low level warm advection downstream from the tp this helps explain why long duration events do not typically start in the afternoon in the upper yr valley

analytical solutions for analysing pumping tests in a sub vertical and anisotropic fault zone draining shallow aquifers summary we present new analytical solutions for examining the influence during a pumping test in a well of an infinite linear and anisotropic strip aquifer that drains shallow aquifers of different diffusivity and thickness the whole system is confined and the aquifer geometry can be represented by a t an aquifer geometry resembling a sub vertical fault or a sub vertical vein cross cutting shallower aquifers the proposed solutions are based upon an unconventional application of well image theory without limitation of the diffusivity contrast between the three domains solutions for drawdown were developed for the three domains i e the strip aquifer and the two shallow compartments and flow signatures are discussed in detail and compared to numerical modelling the proposed solutions are not shown to be exact solutions to the appropriate partial differential equation but very good and useful approximations the solutions were applied to a 63 day pumping test in a steep fault zone in crystalline aquifer rock of brittany france after that the flow contributions of the fault zone and of the shallow aquifers deduced from groundwater dating were compared to analytical solutions the solutions and theoretical type curve examples can help in understanding flow processes from tests conducted in settings that are similar to such a conceptual model

3d cartographic modeling of the alpine arc we built a 3d cartography of the alpine arc a highly non cylindrical mountain belt using the 3d geomodeller of the brgm french geological survey the model allows to handle the large scale 3d structure of seventeen major crustal units of the belt from the lower crust to the sedimentary cover nappes and two main discontinuities the insubric line and the crustal penninic front it provides a unique document to better understand their structural relationships and to produce new sections the study area comprises the western alpine arc from the jura to the northwest up to the bergell granite intrusion and the lepontine dome to the east and is limited to the south by the ligurian basin the model is limited vertically 10 km above sea level at the top and the moho interface at the bottom we discarded the structural relationships between the alps sensus stricto and the surrounding geodynamic systems such as the rhine graben or the connection with the apennines the 3d model is based on the global integration of various data such as the dem of the alps the moho isobaths the simplified geological and tectonic maps of the belt the crustal cross sections ecors crop and nfp 20 and complementary cross sections specifically built to precise local complexities the database has first been integrated in a gis project to prepare their implementation in the geomodeller by homogenizing the different spatial referencing systems the global model is finally interpolated from all these data using the potential field method the final document is a new tri dimensional cartography that would be used as input for further alpine studies

neoproterozoic shear zone tectonics within the icartian basement of guernsey and sark channel islands the channel islands of guernsey and sark are amongst the few localities within the neoproterozoic cadomian orogenic belt where palaeoproterozoic basement is exposed basement units collectively referred to as icartian comprise orthogneisses e g the c 2000 ma icart granite gneiss metasediments and amphibolites on guernsey the protolith to the icart granite gneiss was intruded into metasediments already deformed during a d 1 deformation event both were variably deformed during a d 2 event within an approximately north south trending steeply dipping oblique dextral shear zone on sark metasediments and amphibolites carry a d 1 fabric not necessarily correlatable with that on guernsey which was deformed during d 2 to form recumbent gently inclined folds and tectonic fabrics which locally carry top to the south kinematic indicators early cadomian quartz diorites which intruded the icartian basement carry variably developed magmatic and moderate temperature 400 550 c ls solid state fabrics which are similarly oriented to d 2 basement structures this indicates that the quartz diorites were emplaced and deformed during a protracted d 2 event published 40 ar 39 ar amphibole cooling ages of c 600 ma from guernsey and sark quartz diorites and a host icartian amphibolite are consistent with reworking of basement units during the cadomian orogeny the contrasting kinematic pattern during cadomian deformation implies that a flat lying shear zone on sark may have accommodated oblique dextral strike slip movement on guernsey with an overall southerly direction of tectonic transport deformation most likely occurred in the hanging wall of a major south dipping neoproterozoic subduction zone

chronology of cadomian tectonothermal activity in the baie de saint brieuc north brittany france evidence from 40ar 39ar mineral ages the late precambrian cadomian orogen exposed in the north armorican massif northwest france is a collage of displaced terranes that in part developed during amalgamation of continental arc and marginal basin complexes 40ar 39ar mineral ages reported here place new constraints on the timing of cadomian tectonothermal activity in the southern part of the st brieuc terrane in the baie de saint brieuc area brioverian supracrustal units were deformed metamorphosed and intruded by calc alkaline plutonic complexes metamorphic hornblende from a metabasic amphibolite sheet within brioverian rocks records an isotope correlation age of 568 4 2 6 ma interpreted to date postmetamorphic cooling through appropriate argon closure temperatures similar isotope correlation cooling ages are recorded by metamorphic hornblende within both an amphibolite sheet intrusive into the penthievre complex 567 5 1 2 ma and the la croix gibat amphibolite 574 8 2 1 ma igneous hornblende from the late tectonic to pos

provenance of quartz rich metamorphic tectonite pebbles from the black flysch w pyrenees n spain an ebsd and detrital zircon la icp ms study abstract metasandstone and quartz tectonite conglomerate pebbles from the albian black flysch encapsulate evidence of pre mesozoic igneous and metamorphic events quartz deformation microstructures and crystallographic fabrics characterize plastic flow under sub greenschists 250 300 c to high grade metamorphic conditions above 550 600 c detrital zircon grains from the pebbles provide concordant 206pb 238u radiometric ages ranging from 473 26 ma to 2261 59 ma with four major populations clustered in the intervals 1 96 1 80 ga paleoproterozoic 1 11 0 93 ga stenian tonian 765 571 ma neoproterozoic and 500 475 ma cambro ordovician the youngest zircons and the probability distribution of the studied population permit us to establish an early ordovician maximum depositional age for tectonite pebble protoliths and relate them with the armorican quartzite detrital zircon signature we identify the currently submerged landes massif of the armorican platform as the most likely candidate to being the source of black flysch metamorphic conglomerate pebbles

role of eastward propagating convection systems in the diurnal cycle and seasonal mean of summertime rainfall over the u s great plains by diagnosing the 3 hourly north american regional reanalysis rainfall dataset for the 1979 2003 period it is illustrated that the eastward propagation of convection systems from the rockies to the great plains plays an essential role for the warm season climate over the central u s this eastward propagating mode could be the deciding factor for the observed nocturnal rainfall peak over the great plains the results also suggest that nearly half of the total summer mean rainfall over this region is associated with these propagating convection systems for instance the extreme wet condition of the 1993 summer may be attributed to the frequent occurrence of propagating convection events and enhanced diurnal rainfall amplitude over the great plains thus proper representation of this important propagating component in gcms is essential for simulating the diurnal and seasonal mean characteristics of summertime rainfall over the central us

towards incorporating uncertainty of structural data in 3d geological inversion abstract all geological models are subject to several kinds of uncertainty these can be classified into three different types data imprecision and quality inherent randomness and incomplete knowledge with our approach we address uncertainties introduced by input data quality in complex three dimensional 3d models of subsurface structures geological models as input data we consider parameters of geological structures i e formation and fault boundary points and orientation measurements our method consists of five steps construction of an initial geological model with an implicit potential field method assignment of probability distributions to data positions and orientation measurements simulation of several input data sets construction of several model realisations based on these simulated data sets and finally the visualisation and analysis of the uncertainties we test our approach in two generic models a simple graben setting and a complex dome structure the first model shows that our approach can evaluate uncertainties from different structures and their interaction furthermore it indicates that the final uncertainty of the model is not simply the sum of all input data uncertainties but complex interactions exist the second example demonstrates that our approach can handle full three dimensional settings with overturned surfaces results of the uncertainty simulation can be visualised and analysed in several ways ranging from borehole histograms to uncertainty maps for complex 3d visualisation and analysis we use indicator functions when we apply these we can treat the visualisation of uncertainties in complex settings in a self consistent manner with our simulation method it is possible to analyse and visualise the uncertainties directly introduced by imprecision in the input data our approach is intuitive and straight forward and suitable in both simple and complex geological settings it enables detailed insights into the model quality even for the non expert in cases where a geological model is the basis for geophysical simulation it opens up the way to geological data driven ensemble modelling and inversion

mineralogical and δ18o δd isotopic study of kaolinized micaschists at penestin armorican massif france new constraint in the kaolinization process abstract many kaolinite occurrences developed from paleozoic rocks forming the basement of the armorican massif in western france their origin hydrothermal alteration and or weathering is still discussed in order to provide new constraints to this debate we studied the kaolinite occurrence at penestin in the southern part of the armorican massif using several approaches including field and petrological observations mineralogical analyses xrd and stable oxygen hydrogen isotope analyses an alteration profile was developed from faulted micaschists showing from the bottom to the top of the profile a reddish saprolite zone with pure white kaolinite fissures cutting across the schistosity and a white kaolinite zone 5 10 m thick the detailed study by xrd of the layer silicates enabled us to characterize a mineralogical sequence with increasing alteration intensity which is coherent with a weathering evolution mica chlorite illite vermiculite chlorite mixed layer mineral vermiculite vermiculite kaolinite mixed layer mineral kaolinite moreover an intense iron leaching process occurs within the kaolinite zone which is characterized by a bleaching of this zone combined with iron oxyhydroxide precipitation along within fractures and cracks the isotopic analyses of kaolinite from the zone and fissures gave 18o values ranging from 19 64 to 21 21 and d values ranging from 69 4 to 65 8 this confirms that kaolinite was formed by low temperature water rock interactions in contact with meteoric fluids during weathering processes isotopic and stratigraphic data suggest that this weathering occurred before the messinian 7 ma and probably dates back to the eocene during which the climate was sub tropical at this location

geodynamic evolution of a cadomian arc region the northern ossa morena zone iberian massif abstract ductile deformation and polyphase metamorphism in the ossa morena zone of the iberian massif are related to two major tectonothermal episodes of cadomian late neoproterozoic to early cambrian and variscan age middle to late paleozoic the available petrological structural and geochronological data suggest that a number of tectono metamorphic and magmatic episodes occurred during the 620 480 ma interval that would comprise a complete cadomian wilson cycle the geodynamic scenario was that of an andean type continental margin an evolutionary model is presented for this orogeny comprising stages of volcanic arc generation crustal thickening back arc extension tectonic inversion and cratonization a correlation with comparable areas from pre mesozoic massifs elsewhere in europe is proposed in particular with the armorican massif of northern france

convective instability associated with the eastward propagating rainfall episodes over eastern china during the warm season abstractanalysis of the latest satellite rainfall and reanalysis datasets from 1998 to 2012 demonstrates that eastward propagating rainfall episodes which typically occur in late night and morning are determinant factors for the rainfall diurnal cycle and climate anomalies over eastern china the episode growth and propagation are facilitated by an elevated layer of conditionally unstable air in a mesoscale zone at their eastern leading edge the convective available potential energy cape despite convection consumption and nocturnal cooling decreases only from a high value to a moderate one during episode duration an estimate of the cape generation budget suggests that low level horizontal advection and vertical lifting of the warm moist air can produce sufficient cape to balance other stabilization effects sustaining the mesoscale maximum of convective instability ahead of rainfall episodes these instability geneses are pronounced at the convection growth stage and linked closely to a mesoscale

arsenic retention and remobilization in muddy sediments with high iron and sulfur contents from a heavily contaminated estuary in china the wuli estuary and its offshore area the bay of jinzhou have received large amount of wastewater and smelting slag from a non ferrous smelter for decades we collected three sediment cores from the wuli estuary the middle and the mouth of the bay of jinzhou respectively chemical sequential extraction and x ray absorption near edge structure spectrometry xanes for arsenic as accompanying with fe mn tom s and ca analyses were conducted to investigate as retention and remobilization in this estuary bay system the concentrations of as in the sediment up to 3400 g g and porewater up to 1100 g l have been significantly elevated in the wuli estuary and serious as contamination has been spreading to the bay of jinzhou sequential extraction displayed that adsorbed as was the dominant form of as in sediments from the wuli estuary but in the bay of jinzhou xanes data showed that a portion of as 10 was precipitated as as sulfides correlation analysis showed that total as ast hcl extractable as ashcl in sediment correlated well with total fe fet and hcl extractable fe fehcl in the estuary with fehcl total s st and acid volatile sulfur avs in the middle of the bay and with avs in the mouth of the bay the results indicated that as retention in the wuli estuary is very likely fe controlled region while the impact of s becomes more pronounced in the bay of jinzhou pseudo partition coefficients pseudo kd for ast the ratio of dissolved ast in porewater to ast in sediment decreased systematically from the wuli estuary to the mouth of the bay of jinzhou indicating that mobility of as decreased during the migration and digenetic processes the dominant form of dissolved as in porewater was present in the form of asiii 87 100 in the wuli estuary the reduction of arsenate asv to arsenite asiii 23 91 mediated by microbial activities was the most important cause for as release from solid to aqueous phase whereas the role of reductive dissolution of fe in remobilization of as was likely very limited

preferred mineral orientation of a chloritoid bearing slate in relation to its magnetic fabric 2014 elsevier ltd a regional analysis of the anisotropy of the magnetic susceptibility on low grade metamorphic chloritoid bearing slates of the paleozoic in central armorica brittany france revealed very high values for the degree of anisotropy up to 1 43 nonetheless high field torque magnetometry indicates that the magnetic fabric is dominantly paramagnetic chloritoid s intrinsic degree of anisotropy of 1 47 0 06 suggests that chloritoid bearing slates can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic ferromagnetic s l minerals to validate this assumption we performed a texture analysis on a representative sample of the chloritoid bearing slates using hard x ray synchrotron diffraction the preferred orientation patterns of both muscovite and chloritoid are extremely strong 38 6m r d for muscovite 20 9m r d for chloritoid and display roughly axial symmetry about the minimum magnetic susceptibility axis indeed suggesting that chloritoid may have a profound impact on the magnetic fabric of chloritoid bearing rocks however modeling the anisotropy of magnetic susceptibility by averaging single crystal properties indicates that the cpo of chloritoid only partially explains the slate s anisotropy

3d computational shape and cooling process modeling of magmatic intrusion and its implication for genesis and exploration of intrusion related ore deposits an example from the yueshan intrusion in anqing china abstract computational modeling is a promising method for investigating the spatial topographic characteristics and geodynamic processes of complex geological systems involving irregularly shaped geological bodies the ore deposits in the anqing orefield are of skarn type and show close association with the cooling process of the irregularly shaped intrusion yueshan intrusion in this paper we apply the methods of 3d geometric shape and geodynamic process modeling to investigate the yueshan intrusion related mineralization systems in the anqing orefield china we have developed a c program to transform a 3d geometric solid model to the 3d geodynamic discrete model for simulating the geodynamic process of irregular geological bodies the 3d geometric shape modeling is used to simulate the spatial and topographic features of the yueshan intrusion and its association with the cu orebodies while the geodynamic modeling is used to reconstruct the cooling process of the intrusion and to investigate the controlling mechanism of intrusion on orebodies the modeling results demonstrate that the orebodies are located in some specific places where the intrusion boundary is concave and in contact with its carbonate rocks these mineralized zones are also the high dilation zones where the fluids from different sources are focused as a result of the coupled mechano thermo hydrological mth processes during the syn extensional cooling of the intrusion the modeling results provide a useful guide for selecting further exploration targets which has led to the discovery of a new mineralization zone in dilation zones close to the intrusion contact

3d volumetric modelling of cadomian terranes northern brittany france an automatic method using voronoi diagrams abstract an automatic method based on the use of voronoi diagrams is proposed for the 3d volumetric reconstruction of geological objects it enables volumes to be constructed starting from the combined use of geological maps and cross sections defined in multiple directions and can also take into account incomplete information on geological interfaces and faults the method is suitable for global modelling of a set of geological objects it gives a consistent 3d volumic partition of space according to geological information contained in the maps and the cross sections the method is described and applied to modelling the main domains of the cadomian collisional orogenic belt of panafrican age in northern brittany france thanks to the contrasting densities of the main units involved in the collisional process the gravimetric effect of the volumic model can be calculated its comparison with the observed anomaly allows us to discuss the validity of the geological model although some improvements appear to be necessary it is concluded that the method can make geological modelling more efficient through providing the possibility of rapidly testing many hypotheses

helium trapping in apatite damage insights from u th sm he dating of different granitoid lithologies apatite u th sm he ahe thermochronometry is widely used to constrain thermal histories and rates of tectonic exhumation and erosion processes however data interpretation is often challenging especially when the thermal history includes extended residence time in the he partial retention zone heprz with highly dispersed dates revealing the complexity of diffusion processes in natural systems this study investigates chemical and physical factors that may have impacted he diffusion in apatite over long timescales in a context of protracted residence in the heprz nine samples from the ploumanac h pluton and north tregor armorican massif france were collected in granitoids differing in petrography and chemisty this area was chosen because these samples underwent a similar thermal history since 300 ma we report new u th sm he dates along with apatite fission track aft data as well as lithological and chemical characterization the results show dispersed u th sm he dates ranging from 87 7 to 291 23 ma whereas central aft dates vary from 142 6 to 199 9 ma current predictive models for he diffusion and fission track annealing in apatite could not reproduce the two datasets together however this apparent discrepancy gives insight into the parameters influencing he diffusion at geological timescales the data confirm that radiation damage enhances he trapping as the ahe dates are positively correlated to effective uranium eu concentration the he age dispersion for constant eu content cannot be explained just by variations in grain size or chemical composition to explore the potential influence of recoil damage trapping behavior and annealing kinetics on ahe dates we tested a new diffusion model from gerin et al 2017 given the expected model of the thermal history provided by aft inversion we investigated the influence of the trapping energy on ahe dates the ahe date variations can be explained only if the trapping energy evolves from one crystal to another increasing with the amount of damage for a given trapping energy minor variations in the recoil damage annealing rate can consistently explain most of the remaining dispersion of the ahe dates

geochronological constraints on late precambrian intrusion metamorphism and tectonism in the anti atlas mountains the bou azzer inlier anti atlas morocco is a critical element for understanding gondwanan geology because it exposes rocks formed during the paleosuturing of the gondwanan margin with peri gondwanan arc terranes numerous intrusions within the inlier allow specific tectonic events associated with the tectonic evolution of the gondwanan margin to be bracketed detailed examination of plutons within the inlier reveal down temperature magmatic to solid state fabrics and contact relationships indicative of emplacement during oblique collision between the margin and one or more arc terranes u pb geochronological data for the ao t abdulla diorite ma and 653 8 1 6 bou offroh granodiorite ma provide a limit to the onset of collision and regional metamorphism a 653 0 1 3 precise age of ma for the ousdrat quartz diorite provides an indication of the lower limit of the collision 640 8 1 4 in the region tectonothermal activity in the anti atlas at ca 650 ma correlates with similar periods of tectonism in the peri gondwanan terranes of avalonia and cadomia and points to the emergence of continent wide tectonism in western gondwana as early as 650 ma

inherited arc signature in ediacaran and early cambrian basins of the ossa morena zone iberian massif portugal paleogeographic link with european and north african cadomian correlatives abstract geochemical data from clastic rocks of the ossa morena zone iberian massif show that the main source for the ediacaran and the early cambrian sediments was a recycled cadomian magmatic arc along the northern gondwana margin the geodynamic scenario for this segment of the avalonian cadomian active margin is considered in terms of three main stages 1 the 570 540 ma evolution of an active continental margin evolving oblique collision with accretion of oceanic crust a continental magmatic arc and the development of related marginal basins 2 the ediacaran early cambrian transition 540 520 ma coeval with important orogenic magmatism and the formation of transtensional basins with detritus derived from remnants of the magmatic arc and 3 gondwana fragmentation with the formation of early cambrian 520 510 ma shallow water platforms in transtensional grabens accompanied by rift related magmatism these processes are comparable to similar cadomian successions in other regions of gondwanan europe and northwest africa ediacaran and early cambrian basins preserved in the ossa morena zone portugal and spain the north armorican cadomian belt france the saxo thuringian zone germany the western meseta and the western high atlas morocco share a similar geotectonic evolution probably situated in the same paleogeographic west african peri gondwanan region of the avalonian cadomian active margin

planation surfaces of the armorican massif western france denudation chronology of a mesozoic land surface twice exhumed in response to relative crustal movements between iberia and eurasia the armorican massif an extensive outcrop of variscan basement in western france is shaped by several planation surfaces of debated origin and age we propose an evolution model for these landforms and their deformation based on detailed mapping of the planation surfaces their relative chronology and their relationships with dated outcrops of sediments and weathering products the armorican landscape consists of six stepped planation surfaces labelled ps1 to ps6 later incised by two successive river networks these landforms are pediments and pediplains or polygenic landforms armorican planation surface ps5 resulting from two periods of etchplanation these planation surfaces are mostly pre late cretaceous in age based on the age of the sediments overlapping these pediments the three older ones ps1 to ps3 are pre pliensbachian 191 183 ma ps4 is pre bajocian 170 168 ma ps5 here called the armorican planation surface is polygenic and ranges from the base of the early cretaceous to the base of the bartonian 140 40 ma and the youngest ps6 which is poorly constrained is older than 40 ma base of the bartonian or 15 ma base of the middle miocene most of these old landforms are exhumed i e they were buried by sediments and later re exposed by denudation at least two phases of burial and exhumation have been identified 1 burial in jurassic time followed by denudation during the early cretaceous and 2 burial in late cretaceous time followed by denudation during the latest cretaceous to early eocene the depth of burial is unknown but is probably low due to the small amount of coeval siliciclastic sediments in the surrounding basins the two periods of exhumation correspond to critical periods in the plate movements between africa iberia and eurasia the first is probably related to the initiation and breakup of the rift between iberia and eurasia and the second to the convergence between these two plates

constraints of deep crustal structures on large deposits in the cloncurry district australia evidence from spatial analysis abstract deep structures are commonly recognized as critical factors for controlling the formation of large hydrothermal deposits it is of great importance for the metallogenic studies to quantitatively describe the spatial associations of deep structures with mineral deposits in the cloncurry district of the mt isa province australia many large deposits have been discovered and district scale deep structures have also been recognized from the magnetic gravity seismic and magnetotelluric data in this paper we delineate the 3d configuration of the deep structures by 3d geometric modeling and gaussian curvature analysis and quantify spatial associations of the deep structures with the large deposits by the weights of evidence method the results demonstrate that the configuration of deep structures has a positive spatial constraint on the distribution of deposits many deposits are located close to the high curvature portion of the deep structures according to this rule there are some potential target areas where curvature of the deep structural surfaces is high but no deposits have been discovered such results can be used to identify targets with potential for finding undiscovered deposits

cadomian tectonics in northern brittany a contribution of 3 d crustal scale modelling abstract both available and newly acquired geological and geophysical data processed in the framework of the armor project have been used to construct a 3 d geometric and geological model of the cadomian domain of northern brittany the major results of the data processing are presented and discussed relative to a composite profile transecting the studied domain and constructed from the surface geology reflection seismics magnetotelluric soundings and gravimetric data they are then extrapolated at regional scale through a series of cross sections compiled from the surface geology and gravimetric data and calibrated onto the composite profile the 3 d crustal scale models were computed according to two procedures the first using a strim matra datavision modeler defines various interfaces through correlation between adjacent cross sections and is well adapted to the 3 d representation of geological structures the second based on voronoi diagrams leads to a volumetric model of the geological units and is a powerful tool for calculating 3 d geophysical responses of the model when the physical properties of the rock units are known the tectonic implications of the computed 3 d crustal scale geometry of the cadomian domain are then discussed in terms of volcanic arc thrusting with special emphasis being placed on the obliquity of the shortening direction by reference to the thrust fault trend finally the data are used to demonstrate the reactivation of some cadomian faults during the deposition of ordovician sandstones and following the emplacement of the paleozoic dolerite dyke swarm of northern brittany

comparison of 40ar 39ar conventional and laser dating of biotites from the north tregor batholith bulk samples and single grains of biotites from the north tregor batholite armorican massif france were analysed by the 40ar39ar method apparently pure single biotite grains analysed by the step heating procedure with the laser probe displayed plateau ages or slightly disturbed age spectra one strongly chloritized single biotite grain gave a very disturbed age spectrum with younger ages the bulk samples of biotites of the same rocks displayed disturbed age spectra characterized by younger low temperature ages and a hump at intermediate temperature steps these disturbances are explained by 39ar recoil from the biotite into the chlorite which is clearly evidenced by hrtem observations and not by excess 40ar the more concordant results obtained on single biotites are probably due to a more careful selection of the minerals in most cases we obtain good concordance of the ages 600 610 ma measured on the apparently pure single biotite grains and the high temperature ages of both the bulk samples of amphiboles and biotites from the same rocks

timing of cadomian deformation and magmatism within la hague nw france the la hague peninsula normandy nw france contains the most northerly components of the late neoproterozoic cadomian orogeny u pb dates for single grain and small multiple grain zircon separates from carefully selected plutons provide geochronological constraints on the timing of deformation and magmatism within the region the syntectonic jardeheu quartz diorite and omonville granodiorite were emplaced and contemporaneously deformed during the development of a greenschist facies fabric pervasive across the peninsula u pb zircon dates of 610 1 ma for the jardeheu quartz diorite and 608 2 ma for the omonville granodiorite are similar to a previously reported sensitive high resolution ion microprobe u pb date for metamorphism of the basement and indicate that a regionally significant period of metamorphism and magmatism occurred between 620 and 608 ma an emplacement age of 573 9 1 3 0 9 ma for the syntectonic thiebot granodiorite places limits on the timing of deformation along the thiebot shear zone zircons from the undeformed st martin monzonite give a precise u pb age of 581 3 1 1 ma the new dates point to reactivation of magmatism and localized greenschist facies deformation between 582 and 573 ma

the impact of different gridding methods on catchment geomorphology and soil erosion over long timescales using a landscape evolution model many digital elevation models are gridded from irregularly spaced data this study examines differences in catchment geomorphology and hydrology as a result of kriging and delaunay triangulation gridding methods both methods have been widely used as tools for placing irregularly spaced data onto a regular grid in the past numerical modelling has been performed with little assessment of model input variability and the variability produced by different gridding methods has not been fully assessed given the importance of the impact of digital elevation model error and potential impact on model output little work has been done to understand the impact of this type of potential error examination of the different catchment realizations demonstrates that when using kriging point or block or delaunay triangulation there are subtle differences in catchment area and elevation as well as networking properties subtle differences also exist in hillslope profile nevertheless when comparing catchment descriptors such as the hypsometric curve area slope relationship and cumulative area distribution there is little hydrological and geomorphological difference between these catchments further when these digital elevation models are used as landscape input in a long term landscape evolution model i e siberia there is little geomorphological difference or hydrological difference between the two digital elevation models after a 50 000 year modelled period consequently either method is appropriate for the study catchment these findings provide confidence in the conversion of irregularly spaced data onto a regular grid using kriging or delaunay triangulation and that either method can be used copyright 2006 john wiley sons ltd

diurnal variations of precipitation deep convection and lightning over and east of the eastern tibetan plateau abstract diurnal cycles of total rainfall precipitation features mesoscale convective systems mcss deep convection precipitation vertical structure and lightning over the eastern tibetan plateau tp and eastward through china are investigated using 11 yr of tropical rainfall measuring mission trmm measurements diurnal cycles of rainfall and precipitation features present apparent phase propagation eastward from the eastern tp for about 1000 km the phase propagation is most evident during the pre mei yu and mei yu seasons however it weakens with the northward progress of the east asian monsoon and ceases in midsummer during the pre mei yu season diurnal cycles of storm population total rainfall deep convection and lightning over the central and eastern tp foothills are in phase peaking during the early morning another striking feature of the pre mei yu season is that nocturnal rainfall and mcss prevail over the southeastern tp foothills following the deep convection and lightning maxim

mechanisms supporting long lived episodes of propagating nocturnal convection within a 7 day wrf model simulation abstract a large domain explicit convection simulation is used to investigate the life cycle of nocturnal convection for a one week period of successive zonally propagating heavy precipitation episodes occurring over the central united states similar to climatological studies of phase coherent warm season convection the longest lived precipitation episodes initiate during the late afternoon over the western great plains 105 100 w reach their greatest intensity at night over the central great plains 100 95 w and typically weaken around or slightly after sunrise over the midwest 95 85 w the longest lived episodes exhibit average zonal phase speeds of 20 m s 1 consistent with radar observations during the period composite analysis of the life cycle of five long lived nocturnal precipitation episodes indicates that convection both develops and then propagates eastward along an east west oriented lower tropospheric frontal zone an elevated 2 km deep layer of high e air helps sustain convect

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

a climatology of warm season cloud patterns over east asia based on gms infrared brightness temperature observations abstract in the present study hourly infrared ir brightness temperatures observed by the geostationary meteorological satellite gms over the region 20 40 n 95 145 e in may august 1998 2001 are used to compile a climatology of warm season cloud precipitation episodes over east asia with a goal to better understand the characteristics of warm season convection and the behavior of these episodes results are compared with those obtained in north america using radar derived data the convection in east asia similar to that in north america is shown to also exhibit coherent patterns and characteristics of propagating events in the longitude time hovmoller space with a preferred phase speed of 10 25 m s 1 considerably faster than warm season synoptic scale waves near the eastern edge of the tibetan plateau convection was most active with a strong diurnal signal peaking in late afternoon or early evening then propagating eastward the zonal span and duration of episodes could reach 3000 km and

the quasi stationary feature of nocturnal precipitation in the sichuan basin and the role of the tibetan plateau the nocturnal precipitation in the sichuan basin in summer has been studied in many previous works this paper expands the study on the diurnal cycle of precipitation in the sichuan basin to the whole year results show that the nocturnal precipitation has a specific quasi stationary feature in the basin it occurs not only in summer but also in other three seasons even more remarkable in spring and autumn than in summer there is a prominent eastward timing delay in the nocturnal precipitation that is the diurnal peak of precipitation occurs at early night in the western basin whereas at late night in the center and east of the basin the tibetan plateau plays an essential role in the formation of this quasi stationary nocturnal precipitation the early night peak of precipitation in the western basin is largely due to strong ascending over the plateau and its eastern lee side in the central and eastern basin three coexisting factors contribute to the late night peak of precipitation one is the lower tropospheric southwesterly flow around the southeastern edge of the tibetan plateau which creates a strong cyclonic rotation and ascendance in the basin at late night as well as brings abundant water vapor the second is the descending motion downslope along the eastern lee side of the plateau together with an air mass accumulation caused by the warmer air mass transport from the southeast of the yunnan guizhou plateau creating a diabatic warming at low level of the troposphere in the central basin the third is a cold advection from the plateau to the basin at late night which leads to a cooling in the middle troposphere over the central basin all these factors are responsible for precipitation to occur at late night in the central to eastern basin

the cadomian active margin north armorican massif france a segment of the north atlantic panafrican belt abstract within the european variscan belt the armorican massif northwestern france contains an isolated fragment of the north atlantic panafrican belt the cadomian block mostly unaffected by variscan deformation this block is composed of neoproterozoic rocks ranging in age from 620 to 540 ma brioverian locally overlying a composite basement of icartian 2000 ma or pentevrian 750 ma age the cadomian tectonics the last magmatic manifestations of which are dated at around 540 ma were sealed by a cover of early cambrian rocks in normandy and early ordovician rocks in brittany five units are distinguished in this cadomian block tregor saint brieuc guingamp saint malo and fougeres although the units are bound by major faults the overall coherence of their different protolithic characteristics suggests that they can be fitted into a simple geodynamic model the tregor unit represented by the north tregor batholith of crustal affinity and its icartian host rock probably reflects an early cadomian evolution the saint brieuc unit essentially made up of magmatic rocks of juvenile affinity includes two assemblages juxtaposed by the cadomian tectonics 1 a volcanosedimentary succession formed in a typical island arc setting reflecting subduction around 610 ma and 2 a volcanic plutonic complex emplaced around 590 ma in an extensional active continental margin of pentevrian age the guingamp unit predominantly migmatitic includes a tectonic slice of deep origin the extrusion of which accompanied the exhumation of the migmatites it may represent the trace of a possible suture the saint malo unit is composed of brioverian detrital rocks the significance of which is uncertain passive continental margin or accretionary prism it is structured around a late migmatitic dome 540 ma the fougeres unit corresponds to the outer domain of the cadomian orogeny it was only weakly deformed by cadomian tectonics and is intruded by the large mancellian batholith of crustal origin dated at 540 ma together the structural units are interpreted in the framework of an evolving active margin juxtaposing continental margin marginal basin and volcanic arc before being shortened during the cadomian convergent tectonics

iron and manganese layering in recent sediments in the gulf of bothnia abstract the oxidized surface layer of recent soft sediments in the gulf of bothnia northern part of the baltic sea has been investigated distinct stratification of fe and mn is observed with up to five different horizons in well developed profiles these layered top sediments although not previously noticed occur extensively in the gulf of bothnia there is a close association of mn and ni ba zn and cu whereas p ca and sr are associated with fe high dissolved fe and mn contents coupled with a strong redox gradient are recorded in the interstitial waters formation of these layers is linked to varying redox conditions fe and mn tend to be dissolved under reducing conditions to migrate upwards and to reprecipitate as oxyhydroxides along favourable redox horizons reaching oxidizing conditions fe precipitates prior to mn and is always found below the mnrich strata the character of the oxidized zone is quite different in the two sub basins of the gulf of bothnia mn rich horizons together with spherical mn rich nodules are frequently found in the bothnian bay while in the bothnian sea mostly fe rich layers are present together with abundant fe rich flat concretions this difference is interpreted as being due to a lower redox level in the bothnian sea

late proterozoic zircon ages from a basic ultrabasic complex a possible cadomian orogenic complex in the hercynian belt of western europe the basic ultrabasic complex of belle isie en terre northwestern part of the armorican massif france has been dated at 602 4 1 m y by the u pb zircon method the calc alkaline trend of the metabasic rocks and the geologic context suggest that this ophiolite like complex is related to a back arc orogenic setting similar to the geodynamic environment that has been proposed for pan african calc alkaline ophiolite like complexes of late proterozoic age around the west african craton our results are compatible with the closing in late proterozoic time of a channel ocean north of the basement and formed during the cadomian orogeny rather than with possible caledonian or hercynian subduction