archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part i geologic relations and formation of the vein system the sigma deposit consists of an archean gold bearing vein system in metavolcanic rocks intruded by an irregular body of porphyritic diorite both affected by regional deformation and in turn cut by younger undeformed feldspar porphyry dikes the veins cut all rock types and are composed chiefly of quartz and tourmaline with minor amounts of carbonates pyrite chlorite scheelite and free gold they were emplaced during or after a greenschist facies metamorphism postdating the intrusion of feldspar porphyry dikes the veins were not significantly affected by any subsequent metamorphism or tectonism two principal types of veins occur in the mine subvertical veins and subhorizontal veins they are contemporaneous and cogenetic subvertical veins occur within steeply dipping east west trending ductile shear zones along which reverse subvertical displacements have taken place the veins occupy openings created by overriding of undulations and irregularities of foliation and slip planes during progressive shearing movements within the shears subhorizontal veins occupy extensional fractures which developed between ductile shear zones preferentially in the more competent host rocks these veins were formed by one or several episodes of open space filling geologic relations indicate that the mineralized veins were emplaced progressively in a dynamic tectonic environment during and shortly after the formation of ductile shear zones a structural analysis has shown that the ductile shear zones and the two vein types can be related to a single strain ellipsoid of the following orientation the z axis trending north south and horizontal the y axis plunging 10 degrees west and the x axis plunging 80 degrees east the deformation responsible for the generation of ductile shear zones and emplacement of the veins is ascribed to a late north south trending compression postdating regional deformation

geology of the bousquet 2 mine an example of a deformed gold bearing polymetallic sulfide deposit the bousquet 2 mine is a deformed pyritic polymetallic archean gold deposit located within a zone of intense ductile brittle deformation composed of highly sheared and altered metamorphic tectonites of contrasting rheological properties the ore occurs in a metamorphosed zone of aluminous alteration and is composed of foliation parallel massive and semimassive pyritic lenses overprinted by late en echelon extensional veinlets containing au ag cu mineralization structural and textural analyses show that the gold bearing sulfide bodies and enclosing host rocks contain discrete tectono metamorphic features resulting from two principal episodes of metamorphism m 1 and m 2 the earlier prograde event m 1 and coeval regional deformation d 1 were accompanied by overall ductile deformation of sulfides and by recrystallization and remobilization of the mineralization parallel to foliation m 1 caused development of a pervasive east west trending metamorphic layering of the pyritic mineralization transposition and elongation of the pyritic bodies parallel to mineral stretching l 1 lineations meter scale folding of sulfides sulfide brecciation coarsening and annealing recrystallization of pyrite and ductile remobilization of incompetent sulfides and gold into interstices and triple point junctions of juxtaposed pyrite grains extensive differential remobilization of ductile sulfides mainly sphalerite pyrrhotite galena chalcopyrite chalcocite and bornite and gold took place during m 1 and gave rise to planar zones enriched in au ag cu mineralization along the interfaces of pyritic lenses and their adjacent silicate rocks m 2 metamorphism is chronologically related to a late brittle incremental stage of the progressive deformation and is characterized by high fluid influx pervasive retrogression of peak metamorphic minerals and remobilization of sulfides and gold into transgressive structures the retrograde mineralization displays a wide range of small scale structures resulting from fluid assisted remobilization of ductile sulfides including piercement and injection structures as well as foliation oblique extensional veinlets metamorphic remobilization of ore constituents took place mainly at ore wall rock interfaces fe pb zn and au ag cu bearing extensional veinlets generally occur in foliation parallel protores of similar mineralogical composition and are interpreted as having resulted from in situ metamorphic remobilization gold and copper show a corelationship throughout the deposit the highest gold and copper values occur within extensional veins overprinting previously au cu enriched planar zones mineralogical zoning in the sulfide masses is structurally controlled and can be related directly to abundant au cu bearing veinlets that represent mineralized segments of a systematic joint system structural and textural evidence suggests that gold mineralization with its present textural relations formed during m 1 and m 2 but that a large proportion of the structurally controlled vein mineralization resulted from in situ remobilization rather than from additions from an external source

introduction to special section magnetotectonics the application of methods frompalaeomagnetism and rock magnetism totectonic problems already has a longhistory of success however in recentyears there has been a growing awarenessof the remarkable potential of trulyintegrated studies performed in closecooperation by geophysicists and structuralgeologists the scale of tectonic problemsencountered goes from planetary to metric and now to microscopic most early studiesof deformed rocks used the classicalunfolding method of graham 1949 in whichall rotations are assumed to be rigid bodyand around horizontal axes subsequently more complicated cases of rigid rotationshave been envisioned e g macdonald 1980 and now problems involving multiplephases of folding and internal deformationare being tackled the recognition of theimportance of remagnetizations hasperformed an important role in this evolution with the advent of more sensitivemagnetometers and of more sophisticated means ofanalyzing demagnetization diagrams suchstudies are made even more powerful whencombined with age determinations chemicaland petrographical analyses

geology and wall rock alteration at the hercynian draa sfar zn pb cu massive sulphide deposit morocco abstract draa sfar is a siliciclastic felsic volcanogenic massive sulphide vms zn pb cu deposit located 15 km north of marrakesh within the jebilet massif of the western moroccan meseta the draa sfar deposit occurs within the sarhlef series a volcano sedimentary succession that hosts other massive sulphide deposits e g hajar kettara within the dominantly siliciclastic sedimentary succession of the lower central jebilet at draa sfar the footwall lithofacies are dominated by grey to black argillite carbonaceous argillite and intercalated siltstone with localized rhyodacitic flows and domes associated in situ and transported autoclastic deposits and lesser dykes of aphanitic basalt and gabbro thin to thick bedded black carbonaceous argillite minor intercalated siltstone and a large gabbro sill dominate the hanging wall lithofacies the main lithologies strike nne ssw parallel to a pronounced s1 foliation and have a low grade chlorite muscovite quartz albite oligoclase metamorphic assemblage the draa sfar deposit consists of two stratabound sulphide orebodies tazakourt to the south and sidi m barek to the north both orebodies are hosted by argillite in the upper part of the lower volcano sedimentary unit the tazakourt and sidi m barek orebodies are highly deformed sheet like bodies of massive pyrrhotite up to 95 pyrrhotite with lesser sphalerite galena chalcopyrite and pyrite the draa sfar deposit formed within a restricted sediment starved fault controlled anoxic volcano sedimentary rift basin the deposit formed at and below the seafloor within anoxic pelagic muds the argillaceous sedimentary rocks that surround the draa sfar orebodies are characterized by a pronounced zonation of alteration assemblages and geochemical patterns in the more proximal volcanic area to the south the abundance of medium to dark green chlorite progressively increases within the argillite toward the base of the tazakourt orebody chlorite alteration is manifested by the replacement of feldspar and a decrease in muscovite abundance related to a net addition of fe and mg and a loss of k and na in the volcanically distal and northern sidi m barek orebody alteration within the footwall argillite is characterized by a modal increase of sericite relative to chlorite a calcite quartz muscovite assemblage and a pronounced decrease in chlorite characterize argillite within the immediate hanging wall to the entire draa sfar deposit the sympathetic lateral change from predominantly sericite to chlorite alteration within the footwall argillite with increasing volcanic proximity suggests that the higher temperature part of the hydrothermal system is coincident with a volcanic vent defined by localized rhyodacitic flow domes within the footwall succession

apercu sur les amas sulfures massifs des hercynides marocaines les amas sulfures massifs contenus dans les ilots hercyniens du maroc nord occidental presentent quatre particularites essentielles il s agit d amas massifs de pyrrhotite a morphologie concordante avec la stratification des roches encaissantes ils sont recherches pour leur soufre et surtout pour les metaux de base qui l accompagnent le volcanisme auquel ces amas sont associes est souvent discret encore que partout il soit present notamment sous la forme de roches d epanchement acides rhyolitiques et surtout quartz keratophyriques d emission sous marine en revanche le plutonisme de l encaissant est basique et generalement posterieur aux epanchements acides les stockworks sous jacents aux amas stratiformes sont frequents mais non systematiques presents ils s inscrivent dans les roches silto argileuses plus ou moins carbonatees au mur des mineralisations sulfurees et apparaissent comme des impregnations fissurales transformees par recristallisation epimetamorphique et par l acquisition d une schistosite generalement concordante avec s0 les alterites et exhalites associees sont de trois types sericitite ou roche riche en biotite chloritite et ou roche tres siliceuse

age and depositional environment of the draa sfar massive sulfide deposit morocco the draa sfar mineralization consists of two main stratabound orebodies sidi m barek and tazacourt located north and south of the tensift river oued tessift respectively each orebody is comprised by at least two massive sulfide lenses the hosting rocks are predominantly black shales although minor rhyolitic rocks are also present in the footwall to the southern orebody shales rhyolitic volcanic rocks and massive sulfides are all included into the sarhlef series which is recognized as one of the main stratigraphic units of the moroccan variscan meseta hydrothermal activity related with an anomalous thermal gradient together with a high sedimentation rate in a tectonically driven pull apart marine basin favored the accumulation of organic rich mud in the deepest parts of the basin and the sedimentary environment suitable for massive sulfide deposition and preservation this took place by replacement of the hosting unlithified wet mud below the sediment water interface geochemical data suggest a sedimentary environment characterized by oxic water column and anoxic sediment pile with the redox boundary below the sediment water interface the low oxygen availability within the sediment pile inhibited oxidation and pyritization of pyrrhotite biostratigraphic analysis based on the palynological content of the hosting black shales restricts the age of the sulfides to the asbian substage mid mississippian this age is consistent with earlier geochronological constraints

structural evolution of sulphide tectonites and their host rocks stratmat mine new brunswick the sulphide orebodies at the stratmat mine in new brunswick are treated as tectonites because their primary characteristics have been so modified by deformation recrystallization and vein injection that most of their original features have been obscured pb zn cu sulphide orebodies at the stratmat mine consist of sulphide and sulphide silicate tectonites gneisses schists phyllites and slates produced by the mixing of two sulphide precursors and silicate host rocks by polyphase deformation much of which relates to progressive non coaxial deformation quartz vein injection during and after this period of deformation and the intermixing of nonsulphide lithotypes led to dilution of the initial ore composition both the deformation of the orebodies and fluid migration manifested by vein injection reflect processes that were operative in a major shear zone no indisputable primary characteristics of the orebodies are preserved although a number of tectonic and or tectonically modified features m

wave dominated shallow marine sediments in the lower carboniferous of morocco abstract the jebilet paleozoic inlier near marrakech morocco contains a series of lower carboniferous outcrops that were previously grouped together as a single flysch formation two of these areas display a succession of at least 1100 m of exclusively shallow marine sediments comprising conglomerates sandstones and mudrocks with abundant shell fragments and plant debris the conglomerates contain exclusively intraformational clasts and some occur as couplets with sandstone caps interpreted as storm deposits in the sandstones flat lamination and low angle cross stratification predominate and there are abundant wave rippled surfaces these sandstones are interpreted as shoreface and inner shelf deposits mudrocks are less common but in places form thick units with delicately preserved fo sils a tranquil probably outer shelf environment is envisaged for these thicker mudrocks the major sediment input was probably via a wave dominated delta but there is no evidence for active distributaries in the area described although some paleocurrent indicators such as wave ripples show a consistent orientation there is insufficient evidence at present to fix the shoreline orientation however important thicknesses of wave dominated shallow marine sediments can now be clearly demonstrated in an area that also has thick turbidite successions of equivalent age the larger scale paleogeographic implications must await further data

textural evidence for remobilization in metamorphic environments remobilization of stratabound massive sulphide deposits involves both dislocation flow mechanical remobilization and fluid state processes chemical remobilization textural support for such remobilization is presented at micro meso and macroscales microscale evidence establishes the degree the amount of a deposit affected of remobilization likewise mesoscale textures establish the degree and may provide mesoscale models of macroscale remobilization processes but still do not establish the extent the distance over which translocation may have occurred of remobilization where macrotexture indicates a departure from an original conformable relationship gross remobilization is suggested and may be the consequence of mechanical and or chemical processes the case for gross mechanical and or chemical remobilization is often difficult to sustain because alternative hypotheses e g hydrothermal replacement may be compatible with the observed relationships remobilization of a conformable ore layer may involve internal redistribution during which sulphides have been modified by dislocation flow and or fluid state processes within the layer constraints or external where the layer constraints have been substantially transgressed during dislocation flow and or fluid phase remobilization if mesoscale textures indicate remobilization of the external type then macroscale gross remobilization remains a possibility subject to substantiation

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

remagnetizations as a tool to analyze the tectonic history of inverted sedimentary basins a case study from the basque cantabrian basin north spain 1 in this work we use syntectonic remagnetization data to determine the synrift geometry of inverted basins this methodology analyzes remagnetization directions in order to obtain the tilting of beds at the moment of the acquisition of the overprint filtering the subsequent compressional deformation we collected samples from jurassic and lower cretaceous limestones and red beds cabuerniga and pas groups in the cabuerniga basin one of the most important mesozoic basins developed near the iberia europe mesozoic plate boundary in northern spain that later inverted during the uplift of the pyrenees these deposits represent the synrift sequence linked to a widespread extensional stage in the iberian basins during the mesozoic all sampled rocks show a normal polarity remagnetization fold and conglomerate tests indicate that remagnetization postdates the main extensional stage of basin formation late jurassic barremian and was acquired before the subsequent compressional deformation the analysis of these overprinted directions allows the basin geometry of the studied area to be restored at the moment of acquisition of the remagnetization this approach represents a powerful tool to study basinal evolution and uplift of sedimentary basins to be tested in other inverted basins with syn extensional related secondary overprints

crustal xenoliths in triassic lamprophyre dykes in western morocco tectonic implications for the rheic ocean suture dykes of calc alkaline lamprophyre cutting granite of the hercynian jebilet massif of the moroccan meseta western morocco contain crustal xenoliths the xenoliths range in composition from mafic cognate cumulates and upper crustal granitic rocks through gneisses to middle crustal felsic granulites shrimp u th pb zircon analyses of these rocks indicate that the dykes were likely intruded during middle triassic times similar 235 ma whereas the xenoliths contain zircons with concordant carboniferous early permian neoproterozoic and palaeoproterozoic ages 280 328 ma c 540 615 ma 700 ma and similar 2000 ma the 280 328 ma ages appear to record synchronous intrusive and high grade up to granulite facies variscan metamorphic events suggesting that high grade metamorphism may have facilitated the s type granitic magmatism on the other hand the similar 540 615 ma 700 ma and 2000 ma ages correspond with pan african and eburnian orogenic events recorded in the west african craton in a triassic reconstruction morocco is juxtaposed against nova scotia canada and some have proposed that the basement of the easternmost terrane meguma terrane is a piece of the west african craton however lower crustal xenoliths from devonian dykes similar 370 ma cutting the meguma terrane have yielded late devonian neo and mesoproterozoic ages 378 ma 575 629 ma similar 880 1050 ma and similar 1530 ma the presence of similar 1 ga ages suggests that the basement of the meguma terrane is avalonian rather than west african implying that in a pangean reconstruction the rheic ocean suture between nw africa and maritime canada coincides with the atlantic ocean

early carboniferous basins of the atlas meseta domain morocco sedimentary model and geodynamic evolution in the atlas meseta basins of morocco early carboniferous clastics comprise wave dominated shelf sediments turbidites and mass flow deposits crustal extension controlled the formation of troughs continental uplift and general marine subsidence sedimentation passed from turbidites into storm deposits the moroccan meseta formed a complex marine basin composed of deep troughs shallow shelves and islands the late visean marine transgression advanced from the north and reached as far south in the high atlas domain as the tizi n test fault zone the variscan compressive phase ended the early carboniferous sedimentation

lead isotope systematics of the giant massive sulphide deposits in the iberian pyrite belt lead isotope analyses were performed on 26 polymetallic massive sulphide deposits of the iberian pyrite belt as well as on overlying gossans and associated volcanic rocks all the massive sulphide deposits except for neves corvo and nearly all the volcanic rocks show very similar isotopic compositions grouped around 18 183 206pb 204pb 15 622 207pb 204pb and 38 191 208pb 204pb indicating that most of the ore deposit lead was derived from the same continental crust environment as the associated volcanic rocks the isotopic compositions are representative of the average south iberian crust during the devonian to early carboniferous dinantian and their constancy implies a homogenization of the mineralizing fluids before the deposition of the massive sulphides from hydrothermal fluids circulating through interconnected regional fracture systems this isotopic constancy is incompatible with multiple small independent hydrothermal cells of the east pacific rise type and fits much better with a model of hydrothermal convections driven by magmatic floor heating neves corvo is the only south iberian massive sulphide deposit to have a heterogeneous isotopic composition with in particular a highly radiogenic stanniferous ore 206pb 204pb of the cassiterite is 18 40 a model of lead mixing with three components is proposed to explain these variations 1 one derived from the devonian to early carboniferous dinantian continental crust that generated all the other massive ores 2 an eohercynian stanniferous mineralization partly remobilized during the formation of the massive sulphides but independent of them and 3 a precambrian continental crust component the juxtaposition of three different sources places neves corvo in a specific paleogeographic situation that could also explain its mineralogical specificity the geodynamic context that best explains all the obtained isotopic results is one of an accretionary prism the fact that lead isotope signatures of the gossans are almost identical to those of the underlying massive sulphides means that this technique could be a useful exploration tool for the iberian pyrite belt

determining steady state accumulation area ratios of outlet glaciers for application of outlets in climate reconstructions abstract a steady state glacier equilibrium line altitude ela can be determined by the accumulation area ratio aar method aar varies with climate balance ratio and glacier type glacier geometry the method involves calculating steady state accumulation area ratios aar0 from mass balance characteristics of glaciers by statistical methods in order to confirm the application of linear regression to calculate aar0 in the case of outlet glaciers a method to reveal the mathematical relationship between annual net balance bn and aar was developed analyses carried out on bn aar data sets for 14 outlet glaciers showed that the best approximation for the bn aar relationship is linear with an average squared correlation coefficient of 0 786 but relatively strong non linearity was detected for several glaciers a possible explanation lies in the hypsometry of the observed glaciers results confirm the application of linear regression to calculation of aar0s for outlet glaciers an average aar0 of 0 58 was estimated as the type specific aar0 for outlet glaciers

transition from basin plain to shelf deposits in the carboniferous flysch of southern morocco abstract in the jebilet palaeozoic inlier 20 km north of marrakech there are extensive exposures of carboniferous flysch deposits although there are some structural complications due to over riding nappes with associated chaotic breccias one clearly unbroken succession from basin plain turbidites to shallow marine deposits can be examined the succession is more than 2 km thick and is dated as upper viscan in the uppermost part the lowermost unit of b and c based turbidites shows no sequential organisation and is interpreted as a typical basin plain association above this are similar turbidites arranged in thickening upward sequences that may represent outer fan or base of slope deposits succeeding these are thin bedded turbidites with interbedded units formed by mass movement that represent a slope deposit the overlying lenticular bedded facies resembles previously described overflow deposits of submarine fan channels but is here interpreted as comprising storm generated deposits on the outer shelf upper slope these deposits are genetically linked with the overlying parallel laminated sandstones with irregular rippled tops for which a storm surge origin is suggested the upper part of the succession shows cross bedded oolitic bioclastic sandy limestones with bipolar current structures sandwiched between low energy siltstones containing thin graded silt sand beds these are collectively interpreted as shelf deposits that formed under different depths due to transgressive regressive events the sequence differs from many described in the literature in that there is an absence of most submarine fan facies locally a nne ssw basin strike is proposed with a basin margin to the ese but there is at present little control on regional palaeogeography

structural characteristics of granitic plutons emplaced during weak regional deformation examples from late carboniferous plutons morocco abstract strain patterns have been investigated around shallow crustal granitic plutons emplaced during weak regional deformation in the western moroccan hercynian belt the plutons are distributed along reactivated deep faults and display elliptical shapes which are consistently oriented with respect to the regional strain field pluton age orientation and ellipticity can be correlated with strain history ductile deformation and contact metamorphism are mainly located in the thermally softened aureoles finite strain gradients towards plutons are accompanied by the development of superimposed microstructures finite strain trajectories and variations of strain ellipsoid shapes exhibit perturbations of the regional strain field around plutons structures internal to the plutons are continuous with regional structures foliation development in granitoids records a decrease in temperature during syntectonic pluton cooling geometry and kinematics of deformation reflect the influence of both regional deformation and pluton intrusion

understanding the mesozoic kinematic evolution in the cameros basin iberian range ne spain from magnetic subfabrics and mesostructures abstract analysis of anisotropy of magnetic susceptibility ams and brittle mesostructures hydroplastic synsedimentary faults and tension gashes is applied in this study in order to characterize the mesozoic tectonic events in the cameros basin nw iberian range formed between tithonian and albian times low field ams at room and low temperature lf ams at rt and lf ams at lt respectively together with high field ams hf ams measurements allow separating ferro and paramagnetic fabrics the combination of lf ams at lt and hf ams torque measurements confirms the reliability of both procedures in terms of isolating the paramagnetic contribution to the ams magnetic fabric results combined with the analyses of synsedimentary faults indicate a nw se extension direction during aptian and probably barremian times this extension direction is perpendicular to the main extension direction ne sw prevailing during early and late stages of basin evolution it is also consistent with extension direction deduced from large scale bending folds and tension gashes developed after partial lithification cleavage development during albian enhanced the orientation of the magnetic fabric in lithologies where the previous extensional magnetic lineation is coaxial with the expected one for compression

the south western branch of the variscan belt evidence from morocco abstract this work is based on the compilation and re evaluation of the most significant data either personal or from the literature concerning the moroccan variscides the latter constitute the only moderately disturbed or even undisturbed part of the south western branch of the variscan belt facing directly nw gondwana they include two orogenic segments namely the northern mauritanides and the meseta domain exposed in the saharan and atlas meseta regions respectively and a foreland belt cropping out essentially in the anti atlas the eastward thrust units of saharan morocco oulad dlim mostly originate from the west african craton wac border in an area of thin palaeozoic sedimentation thin skinned fold thrust foreland arcs develop progressively northward zemmour at the expense of the increasingly thick palaeozoic series whereas thick skinned deformation characterizes the inverted proximal paleomargin in the anti atlas domain as suggested by the meseta and anti atlas stratigraphic similarities the meseta domain corresponds to a collage of moderately displaced thinned crustal blocks from the distal gondwana paleomargin variscan deformation is dominated by nw verging thrusts and metamorphism developed in the thickened tectonic prism in relation with crustal anatexis at depth the meseta anti atlas boundary is a major ene trending transpressional dextral fault referred to as the south meseta fault smf discussing the correlations between the variscan segments of morocco and sw iberia allows us to suggest that a latitudinal transform zone similar to the smf separated these segments during the late palaeozoic subduction of the rheic ocean crust would have been directed se ward along both the iberian and moroccan meseta and nw ward south of the smf i e along the wac

geochemical and sr nd isotopic constraints on the petrogenesis and geodynamic significance of the jebilet magmatism variscan belt morocco in the variscan fold belt of morocco the jebilet massif is characterized by palaeozoic metasedimentary rocks intruded by syntectonic magmatism that includes an ultramafic granitoid bimodal association and peraluminous granodiorites emplaced c 330 ma intruded by younger leucogranites c 300 ma the mafic ultramafic rocks belong to a tholeiitic series and display chemical and isotopic signatures consistent with mixing between mantle derived and crust derived magmas or assimilation and fractional crystallization the granites within the bimodal association are mainly metaluminous to weakly peraluminous microgranites that show characteristics of a2 type granites the peraluminous calc alkaline series consists mainly of cordierite bearing granodiorites enclosing magmatic microgranular enclaves and pelitic xenoliths detailed element and isotope data suggest that the alkaline and the peraluminous granitoids were formed in the shallow crust 30 km by partial melting of tonalitic sources at high temperatures up to 900 c and by partial melting of metasedimentary protoliths at relatively low temperatures c 750 c respectively mixing between the coeval mantle derived and crust derived magmas contributed to the large variation of initial end values and initial sr isotopic ratios observed in the granitoids further contamination occurred by wall rock assimilation during ascent of the granodioritic plutons to the upper crust the ultramafic granitoid association has been intruded by leucogranites that have high initial sr isotopic ratios and low initial end values indicating a purely crustal origin the heating events that caused emplacement of the jebilet magmatism are related to cessation of continental subduction and convective erosion thinning of the lithospheric mantle during plate convergence

les bassins d avant pays de la chaine hercynienne au carbonifere inferieur the evolution of marine sedimentary basins deformed by the hercynian orogeny was studied in germany france iberia northwest africa and north america in the lower carboniferous these basins opened along strike slip faults and were filled with turbidites and shelf deposits until the main compressive phase at the end of visean and the namurian the infilling was interrupted with frequent volcanic episodes and gravity induced movements according to sedimentary vergence these basins were set into two festoons on both sides of an elongated and emergent swell structured during the devonian and corresponding to the internal zones of the orogen these basins were filled during a general tectonic compression phase they correspond to the foreland basins of the hercynian belt

multidisciplinary approach to an extensional syncline model for the mesozoic cameros basin n spain abstract in this paper we explore the possibility of reconstructing the initial geometry of inverted basins using combined geophysical and geological methods seismic reflection profiles paleomagnetism analogue modelling and 3d geometrical analysis these techniques allow for some unknowns in the geometry and evolution of extensional sedimentary basins mainly the normal drag reverse drag geometrical problem to be solved the example chosen for checking these techniques is the cameros basin northern iberian chain formed during the late jurassic early cretaceous and inverted during the tertiary compressional stage according to the reconstruction proposed the cameros basin can be characterised as a lens shaped syncline basin with maximum thickness of deposits of about 8000 m in its depocenter gradually diminishing toward the north and south the extensional geometry of the cameros basin is defined by 1 a large scale growth syncline over the major basement fault with southward dipping beds in the northern basin margin forming a southward opening sedimentary wedge with upward decreasing dip values large scale normal drag geometry 2 roll over anticlines at the contact between the pre rift series against the normal fault limiting the basin smaller scale reverse drag geometry the combined syncline anticline syn extensional structures were characterised by means of paleomagnetic analysis of a remagnetization acquired at the time of extension analogue models indicate that the development of syncline basin geometries in extensional settings as the one interpreted for the cameros basin is closely related to the presence of a detachment level in the pre rift sequence above the main basement faults

evidence of a cretaceous remagnetization in the cameros basin north spain implications for basin geometry abstract the paleomagnetic results obtained in 23 sites from red beds of the northern border of the inverted cameros basin northern iberian peninsula prove a cretaceous widespread remagnetization paleomagnetic and rock magnetic analyses indicate that the natural remanent magnetization nrm is dominated by a stable and always normal polarity component carried by haematite two conglomerate test and five fold test indicate that this component is a syn tectonic overprint dated between albian and santonian times most probably albian contemporary with a low grade metamorphism remagnetization was acquired before compressional deformation and post dates the main extensional stage of basin formation berriasian albian incremental fold tests provide best clustering solutions showing dispersed results and far from the expected direction an alternative procedure to obtain fold test solution was applied considering asymmetric limb rotation mean directions obtained from these asymmetric solutions are consistent with the expected direction and yield a statistical value for significant grouping at the 95 confidence level in all fold tests performed this reconstruction allows to determine the tilting of beds at the moment of acquisition of magnetization these original dips were used to reconstruct the original geometry of the northern basin border later modified during the tertiary inversion stage this extensional geometry can be characterised as a large scale syn sedimentary normal fault drag with a minor roll over anticline the procedure developed in this paper should be tested in other inverted basins that also have undergone burial remagnetizations

timing of diagenesis and very low grade metamorphism in the eastern sector of the sierra de cameros iberian range spain a u pb shrimp study on monazite the sierra de cameros is an intracontinental orogen and represents the north western part of the iberian range in northern spain it comprises a thick sequence of syn rift continental sediments mainly sandstones and carbonates deposited during lower cretaceous times a unique characteristic of the sierra de cameros in relation to the rest of the iberian range is the presence of low grade metamorphism in certain parts of the basin an event that predates basin inversion this paper describes the presence textural relationships and geochemical aspects of authigenic and or metamorphic monazite within different lithologies from the deepest parts of the basin sensitive high resolution ion microprobe shrimp u pb dating of monazite records the presence of two age populations the first with 206 pb 238 u ages ranging from 122 to 116 ma which is considered as diagenetic in origin whilst the second is dated at 99 2 ma and postdates the metamorphic climax

testing iberian kinematics at jurassic cretaceous times 1 paleogeographic reconstructions of iberia at the mesozoic are still a matter of debate the incompatibility between kinematic models and paleomagnetic data older than 120 ma is a major problem for which no cause has yet been determined here we use a new method to investigate the origin of this misfit we solve the inverse problem of finding the euler poles that fit paleomagnetic poles with the global apparent polar wander path gapwp and then test their implications on iberian reconstructions we show that iberian poles from the early cretaceous mean poles for 123 and 130 ma are incompatible with the gapwp bringing into question their validity contrarily late jurassic data mean pole at 151 ma are compatible with the gapwp and thus can be considered reliable based on these results we propose a new magnetic reconstruction of iberia and surrounding plates at 150 ma m22 anomaly this work provides new constraints for the kinematic evolution of iberia during jurassic cretaceous however the development of a detailed and consensual model for the kinematic evolution of iberia is dependent on the acquisition of new high quality paleomagnetic data and a reevaluation of seafloor magnetic anomalies