a geophysically constrained litho structural analysis of the eburnean greenstone belts and associated granitoid domains burkina faso west africa abstract interpretation of airborne geophysical data integrated with field structural and lithological observation was successfully employed in the creation of the litho structural framework in a poorly exposed paleoproterozoic granite greenstone terrain of the west african craton the geophysical data portray with sufficient detail all of the lithological units and structural features present the results suggest that the granitoid domains are formed by numerous small to medium sized plutons the existence of several generations of magmatic episodes has a significant impact on the development of a regional tectonic model the magnetic data provided a better definition of the actual pluton shapes and several highly magnetic late orogenic plutons were reliably identified relic f1 fold hinges were recognized in the hounde and boromo greenstone belts the d1 penetrative structures are generally affected by the d2 transcurrent shear zones which often form as well the granite greenstone belt boundaries previously unreported s2 shear zones including the bossie shear zone transecting the sideradougou granitoid domain and abundant small scale shear zones affecting all of the lithologies represent prospective areas for gold exploration airborne gamma ray spectrometry data aided in the mapping process in areas with less regolith cover including erosional ridges and parts of the banfora greenstone belt the magnetic data revealed at least three generations of doleritic dykes crosscutting the western burkina faso

sea level change along the italian coast during the holocene and projections for the future published and new sea level data are used to provide projections of sea level change in italy for the year 2100 by adding new isostatic and tectonic component to the ipcc and rahmstorf projections comparison of the observations from more than 130 sites with different geomorphological and archaeological sea level markers with the predicted sea level curves provides estimates of the vertical tectonic contribution to the relative sea level change the results are based on the most recent anu model for the ice sheets of both hemispheres including an alpine deglaciation model on the basis of the eustatic tectonic and isostatic components to the sea level change projections are provided for marine inundation scenarios for the italian coastal plains for the year 2100 that today are at elevations close to current sea level

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

upper holocene sea level changes in the west saronic gulf greece abstract along the peloponnesian coast of the saronic gulf and on the coast of aegina and poros islands submerged coastal geomorphological features related directly with submerged ancient coastal constructions indicate three distinct sea levels submerged tidal notches incised on the carbonate basement beachrocks formed in the intertidal zone and archaeological indicators such as the ancient harbour installations in kenchreai and epidaurus and on aegina island the extended coastal buildings and constructions in agios vlasis psifta and palaiokastro methana and vagionia on poros island are used to determine the age and magnitude of submersion and the extent of the upper holocene marine transgression by the correlation of geomorphological historical and archaeological indications three distinct sea levels were identified at 3 30 0 15 m 0 90 0 15 m and 0 55 0 05 m initial change in sea level occurred definitely after ad 400 100 the intermediate change is dated between ad 1586 and 1839 and the most recent change after 1839 sea transgression followed a long period of sea level stability which lasted at least 2200 years from the middle bronze age to the late roman period

kinematics of large syn orogenic intrusions example of the lower proterozoic saraya batholith eastern senegal the large saraya batholith intruded the lower proterozoic sequences of eastern senegal structural analysis indicates that this large granitic batholith corresponds to a composite body consisting of several coalescent plutons and interfering diapirs interpretation of the structural fabric patterns in these plutons and in the host rocks constitutes the basis of a hypothetical model of initiation ascent and emplacement as follows 1 development of a deep n s granitic ridge controled by a major crustal fracture generated by an earlier extensional phase re activated by a strike slip fault which probably would facilitate segregation collection and ascent of magmas 2 intrusion and splitting up of the ridge into several diapirs which ascended simultaneously and separately in a setting of a n s sinistral transcurrent deformation inducing a transverse nw se shortening and forceful emplacement of plutons and 3 final emplacement characterized by interference between regional deformation and pluton ballooning the latter leading to the coalescence of intrusions and to the formation of a larger apparently homogeneous body

control of granite emplacement by regional deformation abstract a combination of structural measurements and gravity data is used to investigate the mode of granite emplacement in various tectonic settings the deepest zones revealed by gravity data provided those zones also show vertical lineations in outcrop are interpreted as magma feeder channels these structures or root zones reflect the flow pattern of the upwelling magma while being emplaced they can be interpreted within the regional stress field active during that time granites intruded during transcurrent shearing have only a few feeder channels these roots are not connected to the main shear zone all of them lie within locally extensional areas of the regional stress field this situation is also observed in granites emplaced during a compressional phase of deformation when emplaced during a regionally extensional phase the granitic plutons are very thin with many small deeper zones in which variously evolved granite types may be intrusive these regions vertically differentiated are also interpreted as feeder channels the different morphology at depth as well as the difference in the number of root zones suggest that deformation controls the emplacement of granitic plutons the root zones are oriented at a high angle to the direction of maximum compression when magma is emplaced in a plastic crust if the pluton is emplaced higher in a brittle crust then the roots are aligned with the maximum compression according to the andersonian theory of fracture the orientation of the root zone along the direction of extension in a plastic crust may be explained by shearing which acts as a valve mechanism for segregating magma in all the examples the geometry of the root zone relative to the major fault plane implies that the shear zone does not induce magma generation and that it does not serve as a guide for magma emplacement

nucleation and growth of myrmekite during ductile shear deformation in metagranites myrmekite is extensively developed along strain gradients of continuous lower amphibolite facies shear zones in metagranites of the gran paradiso unit western alps to evaluate the role of stress strain energy and fluid phase in the formation of myrmekite we studied a sample suite consisting of weakly deformed porphyric granites wdgs foliated granites fgs representative of intermediate strains and mylonitic granites mgs in the protolith most k feldspar is microcline with different sets of perthite lamellae and fractures in the wdgs abundant quartz oligoclase myrmekite developed inside k feldspar only along preexisting perthite lamellae and fractures oriented at a high angle to the incremental shortening direction in the wdgs stress played a direct role in the nucleation of myrmekites along interfaces already characterized by high stored elastic strain because of lattice mismatch between k feldspar and albite in the fgs and mgs k feldspar was progressively dismembered along the growing network of microshear zones exploiting the fine grained recrystallized myrmekite and perthite aggregates this was accompanied by a more pervasive fluid influx into the reaction surfaces and myrmekite occurs more or less pervasively along all the differently oriented internal perthites and fractures independently of the kinematic framework of the shear zone in the mgs myrmekite forms complete rims along the outer boundary of the small k feldspar porphyroclasts which are almost completely free of internal reaction interfaces therefore we infer that the role of fluid in the nucleation of myrmekite became increasingly important as deformation progressed and outweighed that of stress mass balance calculations indicate that in al si conservative conditions myrmekite growth was associated with a volume loss of 8 5 this resulted in microporosity within myrmekite that enhanced the diffusion of chemical components to the reaction sites and hence the further development of myrmekite

chemical and boron isotope composition of tourmaline from the kiaka orogenic gold deposit burkina faso west african craton as a proxy for ore forming processes the kiaka orogenic gold deposit burkina faso located in the paleoproterozoic domain of the west african craton is characterized by a two stage gold mineralization hosted in volcano sedimentary metamorphic rocks that was formed during the eoeburnean 2 20 2 13 ga and eburnean 2 13 2 05 ga orogenic cycles these two stages include an early disseminated low grade gold mineralization and a late vein hosted high grade gold mineralization paragenetic studies indicate that the first gold stage was coeval with the deposition of hydrothermal tourmaline the aim of this paper is twofold i to determine the processes responsible for deposition of the economic disseminated gold mineralization and ii to identify the source of the mineralizing fluids for this purpose we performed an in situ study on tourmaline by combining electron probe microanalysis and secondary ion mass spectrometry measurements of boron isotopes hydrothermal tourmaline hosted in metamafic volcanic rocks and metagreywackes has a dravite composition but shows different 11b values falling within the two intervals of 25 1 to 22 0 and 19 6 to 15 1 respectively our results suggest that tourmaline formed from a distal high temperature ca 400 c reduced and low salinity hydrothermal fluid that interacted with the local host rocks based on the modeling of tourmaline fluid boron isotope fractionation we propose a metamorphic fluid origin derived from devolatilization of deeply buried muscovite schists during the regional prograde to peak metamorphism prior ca 2 13 ga this metamorphic fluid rock interaction model may possibly extend to other orogenic gold deposits in the west african craton

modern style plate subduction preserved in the palaeoproterozoic west african craton the timing of onset of modern style plate tectonics on earth is debated analysis of rocks in the west african metamorphic province which is more than 2 gyr old reveals that some minerals formed under conditions similar to those in modern day subduction zones suggesting that subduction occurred on the palaeoproterozoic earth

new insights on the relative sea level change during holocene along the coasts of tunisia and western libya from archaeological and geomorphological markers new data of sea level changes for the mediterranean region along the coasts of northern africa are presented data are inferred from archaeological sites of punic roman age located along the coast of tunisia between tunis and jerba island and along the western coast of libya between sabratha and leptis magna data are based on precise measures of presently submerged archaeological markers that are good indicators of past sea level elevation nineteen selected archaeological sites were studied in tunisia and four in libya all aged between 2 0 and 1 5 ka bp the functional elevations of significant archaeological markers were measured with respect to the sea level at the time of measurements applying corrections for tide and atmospheric pressure values the functional elevations of specific architectural parts of the sites were interpreted related to sea level at the time of their construction providing data on the relative changes between land and sea observations were compared against sea level change predictions derived from the glacio hydro isostatic model associated with the last glacial cycle the results indicate that local relative sea level change along the coast of tunisia and libya has increased 0 2 0 5 m since the last 2 ka besides minor vertical tectonic movements of the land the observed changes are produced by eustatic and glacio hydro isostatic variations acting in the mediterranean basin since the end of the last glacial maximum

petrology major and trace element geochemistry geochronology and isotopic composition of granitic intrusions from the vicinity of the bosumtwi impact crater ghana abstract the bosumtwi crater is 10 5 km in diameter 1 07 ma old well preserved impact structure located in ghana centered at 06 30 n 01 25 w it was excavated in rocks of the early proterozoic birimian supergroup part of the west african craton here we present a full and detailed characterization of the three granitoid complexes and one mafic dike in the vicinity of the bosumtwi crater in terms of petrology major and trace element geochemistry geochronology and isotopic composition this allows us to characterize magmatic evolution of the west african craton in this area and better understand the geological framework and target rocks of the impact this study shows that the similar composition strongly peraluminous muscovite granites and granodiorites and age between 2092 6 ma and 2098 6 ma of all granitic intrusions in the proximity of the bosumtwi crater suggest that they are co genetic granitoids were probably formed as a result of anatexis of ttgs or rocks derived from them at relatively low pressure and temperature we propose that the intrusions from the bosumtwi area are genetically related to the banso granite occurring to the east of the crater and can be classified as basin type late stage granitoids also a mafic dike located to the ne of the bosumtwi crater seems to be genetically related to those felsic intrusions based on those findings a revised version of the geological map of the bosumtwi crater area is proposed

zircon hf and o isotope constraints on the evolution of the paleoproterozoic baoule mossi domain of the southern west african craton abstract the use of zircon isotopic systems such as lu hf and o has proven to be an invaluable tool for unraveling the evolution of the early earth in order to achieve a comprehensive understanding of the evolution of the southern west african craton and in particular the paleoproterozoic baoule mossi domain zircon grains from 75 felsic intrusions were analyzed for hf isotopes 22 of those samples were analyzed for o isotopes covering an area that covers more than 1000 km2 from southwest burkina faso across southern mali and into eastern guinea the results of the study reveal that the baoule mossi domain comprises two magmatic regions that display broadly juvenile isotopic character but with significant localized evidence of crustal contamination the hf model age data show that the crustal contaminant is potentially as old as ca 2800 ma and indicate that the two domains may have evolved slightly differently in fact the westernmost region presents a slightly older or less radiogenic hf isotope signature when compared to the easternmost region furthermore the o isotopic data support the notion that the felsic magmas were subject to supra crustal contamination as 18o values range between 6 and 12 the data presented in this study provide robust evidence that the baoule mossi domain of the southern west african craton evolved by accretionary processes between ca 2250 2050 ma

petrogenesis of juvenile type birimian paleoproterozoic granitoids in central cote d ivoire west africa geochemistry and geochronology abstract the birimian paleoproterozoic granitoids of central cote d ivoire are associated either with greenstone belts or with basin sedimentary rocks field data indicate two stages of granitoid emplacement which according to singlezircon and monazite 207 pb 206 pb age determinations occurred within a short period of time the first generation of granitoids 2123 2108 ma intruded and metamorphosed the greenstone belts whereas the second generation 2108 2097 ma intruded and metamorphosed the sedimentary pile and subordinate andesitic volcanic rocks of the bandama basin unconformably overlying the greenstone belts geochemical and isotopic data show that the various granitoids belong to four magmatic groups 1 sodic calc alkaline nacg 2 potassic calc alkaline kcg 3 peraluminous alg and 4 alkaline alkg all the granitoids show juvenile features with mantle like low initial sr isotopic compositions 0 700 0 702 and positive epsilon nd values 1 5 2 7 these data indicate that a the nacg may have formed by partial melting of a garnet amphibolite crust b the kcg and alkg derived from partial melting of crustal mafic to intermediate metaigneous rocks and c the alg epsilon nd 1 5 represent infracrustal melting of young sialic igneous materials during a regional crustal shortening in a transcurrent tectonic context sm nd model ages 2 25 2 4 ga preclude the existence of an archean crust reworked in the birimian magmas an underplating model is discussed

successive granitic magma batches during pluton emplacement the case of cabeza de araya spain we present a dynamic scenario of granite emplacement in the upper introduction crust for the pluton of cabeza de araya extramadura spain various mechanisms have been suggested to account for based on interpretations of gravity data internal structures and the emplacement of granitic bodies they range from geochemical variations the three dimensional shape of the pluton forceful intrusion via diapirism cruden 1988 or dyking is derived from the inversion of gravity data and the magma flow clemens mawer 1992 to permitted intrusion assisted structures are obtained by mapping the rock anisotropy of magnetic by deformation hutton 1982 castro 1985 guinesusceptibility the deepest zones of the pluton which also correspond berteau et al 1987 hutton et al 1990 between these to vertical lineations are interpreted as feeder zones from which modes ballooning brun et al 1990 nested diapirs magma upwelled these feeders form small distinct areas connected bouchez diot 1990 paterson vernon 1995 to the pluton s floor 6 km below the present surface level we propose stoping paterson fowler 1993 and also recognition that the two main feeders of the pluton represent tension gashes that of the ubiquity of syntectonic magmatism hutton 1997 formed at the base of the brittle crust and served as conduits for call for a competition depending on the crustal level the magma that was ready to be tapped in the southern half of of observation between mechanisms driven by magma the pluton granite type a is cross cut by type b in the magmatic pressure and those involving tectonic accommodation state these magmas show a continuum in their chemistries attributed evidence for the original segregation and ascent of to progressive differentiation a fine grained leucocratic granite more felsic magmas now frozen as plutons is difficult to evolved chemically cross cuts the surrounding facies and crops out observe in the field as a consequence these processes above the southern feeder zone it is interpreted as a late magma have to be inferred from petrological and rheological batch coming from a different source that intruded into the models of both the magma and country rock e g cruden incompletely crystallized surrounding facies the normal petrographic 1988 weinberg podladchikov 1994 stages of magma zoning of the massif of cabeza de araya is therefore viewed as a generation and transport have however little influence succession of continuous and discontinuous infillings sequentially on the mode of the final ponding of the magma which permissive and forceful of increasingly evolved magma batches into in turn is not directly observable in the field in addition a reservoir that opened at varying rates within the brittle crust to considerations from regional geology information from

millstone coastal quarries of the mediterranean a new class of sea level indicator abstract the coasts of italy still preserve several remnants of coastal quarries built in antiquity that now provide insights into the intervening sea level changes occurred during the last millennia in this paper we show and discuss a new class of sea level indicator consisting of millstones carved along the rocky coast of southern italy since 2500 bp that are currently submerged they were extracted from beachrocks sandstones or similar sedimentary rocks easier for carving by ancient carving tools our study focuses on 10 coastal sites located at capo d orlando avola and letojanni in sicily soverato tropea and capo dell armi in calabria castellabate palinuro and scario in campania and polignano san vito in apulia unfortunately only limited archaeological information is available for these anthropic structures scario one of these millstone quarries discussed here has been dated through independent archaeological remains allowing us to restrict the exploitation age to the end of xvii century present day elevations of these coastal sites were obtained through geo archaeological surveys calibrated using the nearest tidal stations together with geomorphological and tectonic interpretations data were compared against the latest sea level predictions based on glacio hydro isostatic models our results allow proposal of the age range of these millstone quarries and to estimate the intervening relative sea level changes since the time when they were carved

questions about myrmekite in deformed rocks abstract several questions about the development of myrmekite in deformed felsic and metapelitic rocks remain unanswered although a general relationship between deformation and myrmekite appears to be well established the fact that myrmekite grows into relatively non deformed k feldspar while being simultaneously deformed and recrystallized at the rear of the growing lobes suggests that strain energy may not be a major contributor to the advance of the growth interface of the myrmekite colony furthermore because myrmekite typically nucleates on existing plagioclase rather than in k feldspar strain energy may not contribute directly to nucleation of myrmekite either at least in many instances however strain energy probably contributes indirectly by facilitating access of fluids to growth sites thereby altering the local chemical environment and so promoting development of myrmekite because myrmekite recrystallizes readily in deformed felsic rocks it is one of the main contributors to the development of folia

magnetic susceptibility magnetic mineralogy and magnetic fabrics in a late archean granitoid gneiss belt abstract the opatica belt is a late archean granitoid gneiss terrane situated within the northern abitibi subprovince along the northern margin of the abitibi greenstone belt quebec this belt is composed of several suites of tonalite granodiorite granite composition variably deformed under epidote amphibolite to upper amphibolite grade conditions specimens from 87 sampling sites within the opatica belt show a wide range in variation of magnetic susceptibility k the large variations are due essentially to varying proportions of ferromagnetic trace minerals detailed study of the opaque mineralogy by reflected light petrography electron microprobe analysis and sem observations as well as alternating field and thermal demagnetization experiments confirm that multi domain very pure magnetite is the dominant ferromagnetic phase which along with ferrosilicates contribute to the magnetic susceptibility in some cases hematite may also make a significant contribution to k in rocks with low k the susceptibility may be dominated by the ferrosilicates hornblende and biotite intensity of anisotropy of magnetic susceptibility ams is also highly variable and appears to be controlled by the mineralogy of the rock rather than by strain intensity or deformation state the shapes of ams ellipsoids are also controlled by mineralogy detailed comparisons are made of ams fabrics with field measurements of magmatic and metamorphic foliations and mineral and stretching lineations and with mineral lineations determined by image analysis of polished slabs there is very good agreement between the average orientations of poles to structural foliations and the average orientation of the k3 principal axes of the susceptibility ellipsoids in all outcrops in most cases there is also good agreement between average structural lineations and the average k1 axis in quartz monzodiorites disagreement between the average lineation and average k1 may be due to complex textural occurrences of magnetite and the presence of abundant hematite in gneisses broad scatter of the orientations of k1 for individual samples from an outcrop quantified by statistical confidence regions about the principal axes locally occurs within the foliation plane and may be attributed to the partial overprinting of earlier fabrics by subsequent deformation

geology and archaeology submerged landscapes of the continental shelf an introduction sea level change has influenced human populations globally since prehistoric times even in early phases of cultural development human populations were faced with marine regression and transgression associated with the glacial interglacial climatic cycle amplified by glacio isostatic adjustments in some regions global marine regression during the last glaciation changed the palaeogeography of the continental shelf converting former marine environments to attractive terrestrial habitats for prehistoric human occupation and adding an extensive new increment of land in the case of europe amounting to an additional 40 of the existing land area and on a global scale to some 20 million km of additional territory that is now submerged these areas of the shelf were used as hunting and gathering areas and as pathways of dispersal between regions and between continents until they were resubmerged by the post glacial marine transgression they also most probably witnessed the earliest developments in seafaring marine exploitation and permanent settlements based on modern marine research technologies and the integration of large databases proxy data are now becoming available for the reconstruction of these submerged quaternary landscapes concerted efforts are also now being devoted to the search for prehistoric archaeological sites and artefacts on the seabed often in collaboration with marine scientists this search has been stimulated by the increasing amount of material that has demonstrably survived inundation often with excellent preservation of organic remains by closer collaboration with offshore industry and by the growing realization of the importance of these submerged data for understanding human prehistoric developments during periods of rapidly changing climate and environment moreover these new research trends are not simply being driven by an archaeological need for scientific and technological input from other disciplines but by collaborations involving genuine mutual benefit in which all partners have something to gain archaeological problems often pose new questions about geological change stimulating new techniques of observation new technologies and new investigations which in their turn can offer new data often at higher resolution and with better dates in relation to geological and environmental issues such as sea level change and palaeoclimatic variability on the continental shelf the expansion of early human populations to occupy new territory and new continents is one of the great narratives of human evolution it is currently a theme of wide interest and topicality and has received significant impetus and publicity from the new science of palaeogenetics together with ongoing discoveries of new fossil and archaeological material and new studies of palaeoclimate and palaeoenvironment the field itself is rapidly expanding leading to new discoveries and new controversies grine et al 2009 gamble 2013 smith ahern 2013 all the current indications are that the human species originated in africa with at least two major episodes of dispersal the earliest some time after about 2 myr ago led to the expansion of homo ergaster erectus populations across southern europe and asia extending from britain in the west to china and indonesia in the east and south the second involved our own species homo sapiens anatomically modern humans or amh and took place some time after about 200 ka this resulted in the replacement of earlier hominin populations in europe and asia and expansion further afield into new guinea and australia certainly involving sea crossings over distances of at least 50 km by about 50 ka to the higher latitudes of northern eurasia with entry into the americas by at least 15 ka and into new territory exposed by the melting of the northern hemisphere ice sheets less than 10 kyr ago anthropological and archaeological investigations of these processes are directly connected

archean granite greenstone tectonics at kolar south india interplay of diapirism and bulk inhomogeneous contraction during juvenile magmatic accretion 1 the structural study of the kolar greenstone belt and surrounding granite gneiss terrains combined with u pb dating reveals that the middle and lower crustal tectonoplutonic pattern of the eastern dharwar craton developed during a major magmatic accretion event between 2550 and 2530 ma the granite greenstone pattern resulted from the interference of gravity driven sagging of the greenstones i e diapirism e w bulk inhomogeneous shortening combined with horizontal n s stretching and syntectonic juvenile pluton emplacement bulk inhomogeneous contraction is accommodated by the synchronous development of a pervasive n s trending vertical foliation shallow stretching lineation and conjugate strike slip shear zone pattern within and outside the greenstone belt resulting in regional horizontal pure shear deformation the plutons around the greenstone belt record regional contraction by developing one set of strike slip c s fabrics of the shear zone pattern the development of the granite greenstone pattern was coeval and compatible with deformation during juvenile magmatic accretion melting and granulite metamorphism in the lower crust the kolar example points to a specific crustal rheology that allowed sagduction of the greenstones and regional distributed bulk inhomogeneous strain due to mechanical homogeneity and low viscosity provided by large scale melting during the accretion event this example further suggests specific boundary conditions to the craton that allowed e w inhomogeneous shortening to be accommodated by n s stretching and spreading of the crust without significant tectonic thickening such tectonoplutonic pattern is specific to the archean and may develop as a consequence of mantle plume activity in intracontinental settings

comparison between coastal and inland karst limestone lowering rates in the northeastern adriatic region italy and croatia a comparison among lowering rates collected in the limestones of the northeastern adriatic region italy and croatia gives a picture of the erosion patterns in the inland and coastal classical karst and istrian karst erosion rates were measured using either a micro erosion meter or a traversing micro erosion meter beginning from a large dataset spread over a maximum of 26 years significant differences in limestone lowering rates have been recognized in the surveyed area the mean lowering rate for the inland classical karst area is 0 018 mm yr whereas in the inland istrian karst it is 0 009 mm yr in the coastal sectors the mean erosion rate varies between 0 14 mm yr in the gulf of trieste and 0 04 mm yr in the sites located along the istrian shoreline these differences are probably due to the climatic setting of the classical karst area mediterranean continental to sub alpine climate and istrian peninsula mediterranean climate moreover along the coasts of the gulf of trieste there are many submarine springs which are absent along the istrian coast it is hypothesized that these underwater springs stress the effect of rainfall along the coast which is both direct rain on the measurement site and mainly indirect freshwater outflow from submarine springs higher lowering rates were surveyed during autumn rainfall therefore also freshwater outflow from submarine springs is particularly high at the end of the summer and in autumn

structure and emplacement of granite plutons in the paleoproterozoic crust of eastern burkina faso rheological implications the fada n gourma area in burkina faso is underlain by paleoproterozoic rocks that make the northeastern west african craton this region is composed of ne trending volcano sedimentary belts and foliated tonalites affected by several shear zones a generation of younger 2100 ma old non foliated biotite bearing granites intrudes the former rock units we have investigated the younger granite pluton of kouare that was previously considered as forming a single body with the pluton of satenga to the west a pluton which likely belongs to the 20 ma more recent tenkodogo yamba batholith magnetic fabric measurements have been combined with microstructural observations and the analysis of field and aeromagnetic data the granite encloses angular enclaves of the host tonalites magmatic microstructures are preserved inside the pluton and solid state high temperature deformation features are ubiquitous at its periphery the presence of steeply plunging lineations in the pluton of kouare and its adjacent host rocks suggests that large volumes of granitic magmas became crystallized while they were ascending through the crust that was softened and steepened close to the contact around kouare the foliation in the host tonalites conforms with a map scale z shaped fold in between nne trending shear zones implying a bulk clockwise rotation of the material contained in between the shear zones including the emplacing pluton regionally the fada n gourma area is concluded to result from nw shortening associated with transcurrent shearing and vertical transfer of granitic magmas this study concludes that the 2200 myears old juvenile crust of burkina faso was brittle before the intrusion of the biotite granites became softened close to them and that gravity driven and regional scale wrench tectonics were active together

conflicting shear sense indicators in shear zones the problem of non ideal sections abstract deflection of pre existing planar structures such as foliations or veins by ductile shear zones is geometrically very similar to the curvature of newly developed shear zone restricted foliations in zones that cut a rock with a random fabric sense of curvature of shear zone restricted foliations can be used to determine shear sense but the deflection of pre existing planar structures is less reliable two examples are presented of shear zones in australia where both types of structures seem to represent conflicting shear sense this conflict can be attributed to a geometrical effect which causes deflection of older structures in an opposite direction to shear sense on outcrop surfaces oblique to the displacement vector if the orientation of the displacement vector cannot be accurately determined in shear zones e g because of limited outcrop or unclear lineations most shear sense indicators can still be used to determine shear sense but pre existing planar structures are notoriously unreliable

emplacement petrological and magnetic susceptibility characteristics of diverse magmatic epidote bearing granitoid rocks in brazil argentina and chile abstract magmatic epidote mep bearing granitoids from five neoproterozoic tectonostratigraphic terranes in northeastern ne brazil early palaeozoic calc alkalic granitoids in northwestern nw argentina and from three batholiths in chile have been studied the elongated shape of some of these plutons suggests that magmas filled fractures and that dyking was probably the major mechanism of emplacement textures reveal that in many cases epidote underwent partial dissolution by host magma and in these cases may have survived dissolution by relatively rapid upward transport by the host magma in plutons where such a mechanism is not evident unevenly distributed epidote at outcrop scale is armoured by biotite or near solidus k feldspar aggregates which probably grew much faster than epidote dissolution preventing complete resorption of epidote by the melt al in hornblende barometry indicates that in most cases amphibole crystallized at p 5 kbar kyanite bearing thermal aureoles surrounding plutons that intruded low grade metamorphic rocks in ne brazil support pluton emplacement at intermediate to high pressure mep show overall chemical variation from 20 to 30 mol mole percent pistacite ps and can be grouped into two compositional ranges ps20 24 and ps27 30 the highest ps contents are in epidotes of plutons in which hornblende solidified under p 3 0 10 3 si typical of magnetite series granitoids crystallized under higher oxygen fugacity in ne brazil argentina and chile it seems that mep is more common in precambrian to palaeozoic ilmenite series granitoids while its occurrence in magnetite series granitoids is more restricted to mesozoic to tertiary granitoids

mechanisms of pluton emplacement and structural evolution of a 2 1 ga juvenile continental crust the birimian of southwestern niger abstract the 2 1 ga birimian terranes of southwestern niger consist of a granite greenstone association the structures of the greenstone belts result from the interference between pluton emplacement and regional transcurrent deformation sinistral n s strike slip faults ne sw trending schistosity the regional cleavage trend is observed to change in the vicinity of elliptical plutons cleavage trajectories bend around their contacts resulting in triple junctions at the pluton extremities and narrow aureoles of intense penetrative schistosity and high grade amphibolitefacies metamorphism are developed around them structural features of plutons suggest syntectonic emplacement and age data indicate that all plutons were emplaced between 2 16 and 2 10 ga the plutons are assembled in two distinct types of batholith elongated either parallel or perpendicular to the inferred regional shortening direction a batholith parallel to the inferred regional shortening direction dolbel batholith consists of km sized subcircular alkali granite plutons except for the southernmost one which is of a larger size and exhibits an elliptical shape with a nw se short axis parallel to the shortening direction crosscutting relationships indicate a progressively northward emplacement trend for those plutons internal fabrics generally correspond to layering and magmatic flow fabrics and accessorily to schistosity and shear zones which represent late stage plastic deformation restricted to the pluton margin batholiths which are perpendicular to the inferred regional shortening direction are composed of large elliptical plutons 500 to 5000 km 2 in area consisting mainly of granodiorite and covering 70 of the region the plutons never show crosscutting relationships but are moulded against each other their internal fabric corresponds to a solid state foliation it either dips towards the centre of the pluton funnel or teardrop shaped intrusions or is subhorizontal in the centre and vertical at the margin dome shaped intrusions the foliation and the geometry of the largest pluton tera pluton were acquired during pluton ascent and inflation whereas the geometry of later shear zones indicates that deformation in the pluton was then passively acquired at the final emplacement level due to regional deformation the contrast in both the orientation and structural features of the batholiths reflects distinct emplacement mechanisms the small alkali granite plutons resulted from magma injection within nw se fractures parallel to the inferred regional shortening direction whereas the granodiorite plutons are assumed to be emplaced as diapirs forceful intrusions with long axes perpendicular to the shortening direction these two intrusion mechanisms for plutons emplaced during the same deformation event and at the same crustal level are considered to reflect a local change in the rheological behaviour of the crustal segment studied in connection with the thermal effect induced by the large granodioritic plutons this vertical tectonic regime appears to be typical of palaeoproterozoic juvenile continental crust areas and related to an interplay between emplacement of tremendous volumes of granodioritic magma and a regional transcurrent deformation

sea level change and vertical land movements since the last two millennia along the coasts of southwestern turkey and israel abstract this paper provides new relative sea level data inferred from coastal archaeological sites located along the turkish coasts of the gulf of fethye 8 sites and israel between akziv and caesarea 5 sites the structures selected are those that for effective functioning can be accurately related to sea level at the time of their construction thus their positions with respect to present sea level provide a measure of the relative sea level change since their time of construction useful information was obtained from the investigated sites spanning an age range of 2 3 1 6 ka bp the inferred changes in relative sea level for the two areas are distinctly different from a rise of 2 41 to 4 50 m in turkey and from 0 to 0 18 m in israel sea level change is the combination of several processes including vertical tectonics glacio hydro isostatic signals associated with the last glacial cycle and changes in ocean volume for the israel section the present elevations of the mis 5 5 tyrrhenian terraces occur at a few meters above present sea level and vertical tectonic displacements are small data from gps and tide gauge measurements also indicate that any recent vertical movements are small the mis 5 5 shorelines are absent from the investigated section of the turkish coast consistent with crustal subsidence associated with the hellenic arc the isostatic signals for the israel section of the coast are also small ranging from 0 11 mm yr to 0 14 mm yr depending on site and earth model and the observed eustatic average sea level change corrected for this contribution is a rise of 13 5 2 6 cm during the past 2 ka this is attributed to the time integrated contribution to sea level from a combination of thermal expansion and other increases in ocean volume the observed sea levels from the turkish sites in contrast indicate a much greater rise of up to 2 2 mm yr since 2 3 ka bp occurring in a wide area between knidos and kekova the isostatic signal here is also one of a rising sea level of up to 1 mm yr and site and earth model dependent and the corrected tectonic rate of land subsidence is 1 48 mm yr this is the primary cause of dramatic relative sea level rise for this part of the coast

lithostratigraphy and composition of 2 1 ga greenstone belts of the west african craton and their bearing on crustal evolution and the archean proterozoic boundary we have determined the lithostratigraphy of three early proterozoic 2 1 ga birimian greenstone belts in the west african craton and measured the concentrations of major and trace elements in samples of volcanic rocks from those belts the nangodi belt largely consists of tholeiitic basalt flows with mg numbers of 37 to 69 and flat to slightly lree depleted chondrite normalized ree patterns overlain by sodic na 2 o k 2 o 3 7 29 calc alkaline dacitic tuffs and lavas that are hree depleted la yb 4 5 8 9 times chondrites yb 3 9 8 7 times chondrites the volcanic sequence is capped by calc alkaline andesitic crystal tuffs with high mg numbers 66 75 and a high la yb ratio 10 5 times chondrites similar to archean and modern sanukitoids the dixcove belt largely consists of tholeiitic hyaloclastites and pillow lavas mg numbers 52 61 that grade upward into high mg mg numbers 59 calc alkaline andesitic tuffs and flows the winneba belt largely consists of massive tholeiitic h

magnetic fabric vs magnetite and biotite shape fabrics of the magnetite bearing granite pluton of gameleiras northeast brazil abstract a well defined orientation pattern has been evidenced by the magnetic fabric lineation and foliation of the granite pluton of gameleiras northeast brazil this magnetic fabric is roughly parallel to the magmatic fabric defined by the elongate mafic enclaves and by the planar arrangement of tabular k feldspar phenocrysts low field anisotropy of magnetic susceptibility properties as well as magnetic mineralogy studies and optical microscopy observations indicate that multidomian iron rich magnetite is the main carrier of the magnetic susceptibility and its anisotropy to examine in more detail the relationships between the magnetic and magmatic fabrics measurements of two dimensional shape fabrics of grain populations of biotite and magnetite have been carried out on a total of 500 grains using an automatic shape fabric analysis procedure on carefully selected and oriented thin sections angular departure has been calculated between the maximum elongation of the mineral shape fabric of the given grain population and the maximum susceptibility axis of the corresponding macroscopic specimen we found that the fabric of biotite correlates strongly with the magnetic fabric 7 8 the fabric of magnetite although not as well defined mainly because of its weak shape anisotropy still correlates with the magnetic fabric 12 18 origin of low field magnetic fabric in the pluton of gameleiras is concluded to be controlled principally by the statistical alignment of the long axes of inequant magnetite grains magnetic interactions between the grains of magnetite where they form clusters may account for the observed scattering or abnormal magnitudes of the magnetic anisotropy concerning the orientation of the magnetic fabric as the long dimensions of the magnetites preferentially align with the boundaries of the other minerals particularly biotite and titanite the magnetic fabric as defined by the grains of magnetite is concluded to approximate closely the magmatic fabric defined by the shape fabric of biotite however as no correlation exists between shapes or clustering of magnetites and strain undergone by the deforming magma the strength of the magnetic fabric in ferromagnetic granites cannot be used in a simple way as a measure of strain intensity

early proterozoic ore deposits and tectonics of the birimian orogenic belt west africa abstract the early proterozoic of the west african craton comprises a series of volcanic troughs and sedimentary basins the birimian with granitic terranes accreted on archean nuclei in the man and reguibat shields studies of the birimian of the man shield indicate a model of polycyclic evolution with a major collision event d 1 2 1 ga thrusting part of the proterozoic terrane over the archean before individualization of numerous volcanic troughs and clastic infill basins the proposed evolution for the birimian orogenic belt comprises 1 deposition of the sedimentary lower birimian b1 with minor tholeiitic volcano sedimentary intercalations containing chert and or mn formations and with most of the detritus being derived from early proterozoic sources apart from contamination near the proterozoic archean contact 2 pre b2 crustal thickening related to d 1 thrusting 3 formation over about 40 ma of the upper birimian b2 with numerous volcanic troughs of different composition tholeiitic and rare komatiitic bimodal tholeiitic to calc alkaline volcano plutonic and tarkwaian clastic infill basins and 4 major transcurrent tectonics with sinistral d 2 and dextral d 3 strike slip faults such a tectonic evolution from a collision d 1 phase to a transcurrent d 2 d 3 phase is typical of collision belts and in the present case the evolution of the birimian orogenic belt can be extended into guyana the metallogenic history of the birimian shows a three phase evolution coinciding with the orogenic evolution and extends over almost 150 ma from the perkoa massive zn ag sulfides 2 12 ga with a clear mantle affinity to the latemesothermal au quartz veins 2 ga with according to lead isotopes a high crustal participation the economic mineralization of belt thus consists of 1 1 pre orogenic pre d 1 deposits related to early extension zones this was diverse with stratiform au tourmalinite type 1 au loulo in mali dorlin in guyana stratiform fe cu faleme in senegal and mn nsuta in ghana tambao in burkina faso and a single massive zn ag sulfide deposit perkoa in burkina faso associated with regional volcanosedimentary variably tholeiitic stratigraphic marker beds 2 2 syn orogenic post d 1 to syn d 2 d 3 deposits with disseminated au sulfides type 2 au yaoure in the ivory coast in extensional zones of the b2 followed by auriferous paleoplacers type 3 au in b2 extensional zones tarkwaian banket conglomerate or syn d 2 transtensional zones debris flow of orapu in guyana 3 3 late orogenic post peak d 2 d 3 deposits with mesothermal au mineralization evolving from a disseminated gold bearing arsenopyrite and au quartz lode type type 4 au ashanti in ghana to a quartz vein type with free gold and cu pb zn ag bi paragenesis most of the gold in west africa comes from this phase finally the metallogeny of the birimian appears as rich in au and mn formations and poor in volcanogenic mineralization and bif it differs from the archean metallogeny of west africa and other regions through the presence of certain deposit types such as au stratiform tourmalinite gold bearing conglomerate with au and fe ti oxides but no uranium or sulfides and au arsenopyrite rich shear zone deposits that are very common in but not exclusive to the proterozoic and paleozoic

archaeological remains as sea level change markers a review abstract the mediterranean sea constitutes a unique basin from an historical and archaeological point of view as it has been a privileged way of communication for thousands of years for the people that dwelled on its shores their passage has left many traces on the seabeds in the areas where the ancient commercial routes passed and remains of structures where moorings havens or dwellings existed some of these structures nowadays submerged offer interesting indications aiding the reconstruction of the ancient coastlines this contribution aims to examine recent work in coastal geo archaeology targeting both 1 gathering and discussion of the data particularly those pertaining to the italian coasts and 2 commentary on the methodological debate and verification of the possibility of a protocol that may contain unequivocal referring elements to investigate the archaeological evidence currently underwater because of the relative sea level variations harbour infrastructures fishponds villae maritimae caves nymphaei private or public buildings or town quarters pre and protohistorical villages quarries caves etc a clear and more coherent methodological assumption may be needed the archaeological interpretation must initially establish the maritime and or harbour nature and vocation of the site determine its typology and specific usage analyze the elements of its building techniques that reveal themselves as meaningful markers of height or depth at the time of building and its functional elements the measure of the emerged part with respect to the average sea level and point out the time of construction its chronological range of usage frequentation the dynamics of its abandonment destruction obliteration the evaluation of both the height and functional depth to the mean sea level depends on the typology of the archaeological evidence its use and the local tide amplitudes the surface of a pier surely has a functional elevation different from that of a haulage area or a platea or a pavement

sea level in roman time in the central mediterranean and implications for recent change instrumental records indicate that ocean volumes during the 20th century have increased so as to raise eustatic sea level by f1 2 mm year and the few available records suggest that this is higher than for the previous century geological data indicate that ocean volumes have increased since the main phase of deglaciation about 7000 years ago but whether this continued into the recent past remains unclear yet this is important for establishing whether the recent rise is associated with global warming or is part of a longer duration non anthropogenic signal here we present results for sea level change in the central mediterranean basin for the roman period using new archaeological evidence these data provide a precise measure of local sea level of 1 35f0 07 m at 2000 years ago part of this change is the result of ongoing glacio hydro isostatic adjustment of the crust subsequent to the last deglaciation when corrected for this using geologically constrained model predictions the change in eustatic sea level since the roman period is 0 13f0 09 m a comparison with tide gauge records from nearby locations and with geologically constrained model predictions of the glacio isostatic contributions establishes that the onset of modern sea level rise occurred in recent time at f100f53 years before present d 2004 elsevier b v all rights reserved

new data on the pleistocene of mallorca abstract stratigraphic geomorphologic and isoleucine epimerization studies at 15 sites in mallorca define four aminozones a c e and f g of increasing age that are related to transgressive regressive marine cycles from the holocene to the mid pleistocene calibration of aminozone e glycymeris aile ile mean from all sites 0 41 0 03 n 38 is provided by a 129 7 ka u series coral age on cladocora caespitosa from son grauet of the younger aminozones a relates to the holocene transgression and aminozone c to a mid to late isotopic stage 5 event 90 15 ka revealed only by supralittoral eolianites assigning an age to the older poorly resolved aminozones f and g called f g in this case is uncertain without supporting radiometric data but an age of 180 ka can be assigned to these aminozone s f g based on a kinetic model and other examples in the mediterranean several deposits previously dated u series molluscs between 75 and 300 ka appear to belong to the last interglacial complex stage 5 and aminozone e a proposed revision of the positive sea level history of mallorca shows multiple minor oscillations during the major last interglacial cycle stage 5 and two mid pleistocene sea levels one lower than present and the other at about 14 m a s l

modification of the regional stress field by magma intrusion and formation of tabular granitic plutons granitic intrusions typically have large aspect ratios with an horizontal major axis about 4 8 times the vertical one combined structural and geophysical gravity data allows distinction between two main types of plutons flat floored plutons the most represented are rather thin 3 4 km and extend in every horizontal direction with a gently dipping floor toward several root zones these contrast with the thick 10 km wedge shaped plutons more elongated in one direction with a few root zones we interpret the shape of flat floored plutons as the result of a switch in the stress pattern caused by the emplacement of magma magma is preferentially emplaced into the plane 1 2 perpendicular to the least principal stress component 3 this plane is initially vertical except for compressional conditions this dilation causes a local re organization of the stress field by increasing the minor and intermediate principal stress components when they overcome the lithostatic load a drastic change in the orientation of the opening plane results switching from vertical to horizontal this constitutes a change from vertically oriented dike shaped intrusions to sub horizontal laccoliths crustal anisotropies vertical faults or horizontal zones of different rheology also contribute to modify the shape of the intrusions the continual exchange of the intermediate stress components also explains the rounded shape of intrusions in strongly extended regions our analysis suggests that the concept of magmas rising to a level of neutral buoyancy is not applicable to many settings rather we suggest that the feedback between displacements resulting from magma intrusion and the local stress pattern controls the geometry of magma emplacement

partial melt topology in statically and dynamically recrystallized granite microstructures of the murray granite pluton central ontario canada show evidence of both static and dynamic crystallization subsequent to partial melting backscattered electron analyses reveal interstitial k feldspar and plagioclase at triple junctions of strain free isometric quartz grains the geometry of the quartz feldspar boundaries mimics the original topology of the quartz melt contacts during crystallization this conclusion is suggested by the occurrence of both rounded and planar faces of quartz grains and by low 27 dihedral angles of quartz quartz feldspar boundaries similar to dihedral angles in experimentally crystallized quartz quartz silicic melt systems in contrast feldspar seams in deformed granites have high axial ratios are usually elongated perpendicular to the foliation plane and are located preferentially along individual grain boundaries quartz grains are dynamically recrystallized and occasionally transected by feldspar seams indicating that fracturing occurred in the presence of melt during crystal plastic deformation of quartz the subparallel orientation in quartz grains of intragranular feldspar bearing fractures and interstitial feldspar seams suggests that these features originated as intragranular and intergranular fractures respectively partial melt topology was therefore controlled by intergranular and occasionally by intragranular fracturing

a paleoproterozoic ultramafic mafic assemblage and associated volcanic rocks of the boromo greenstone belt fractionates originating from island arc volcanic activity in the west african craton abstract the loraboue birimian ultramafic mafic assemblage located in the boromo greenstone belt burkina faso is interpreted as the remains of a magma chamber that crystallized at the base of an island arc the ultramafic rocks exhibit an heteradcumulate texture being generally made up of wehrlites and more rarely dunites the crystallization sequence inferred from the cumulates is olivine chromite followed by clinopyroxene amphibole orthopyroxene biotite the gabbroic rocks are mainly layered and grade into more differentiated facies with sub pegmatitic texture containing up to 70 modal plagioclase including zircon and more commonly apatite crystals textural relationships and mineral phase chemistry are indicative of crystallization at elevated pressures 8 kbar the parental magma being generated by a moderate to high degree of partial melting of a mantle source affected by previous metasomatic events above a subducted oceanic slab the loraboue volcanic formations exhibit a range of geochemical features they consist dominantly of calc alkaline basalts pyroclastites and rhyolite and more rarely of basalt dolerite and gabbro of tholeiitic affinity these different types of basalt as well as the dolerite and the isolated massive gabbro show the classic features of arc magmatic suites namely lile and pb enrichment depleted hfse patterns and high ce nb and th nb ratios thus the calc alkaline plutonic and volcanic assemblages of loraboue could represent the roots of an island arc and the associated coeval volcanic rocks the paleoproterozoic crust of the west african craton was heterogeneous and was not the consequence of a single process of genesis as some modern igneous province the birimian crust was generated by both volcanic arc accretion and oceanic plateau accretion

millstones as indicators of relative sea level changes in northern sicily and southern calabria coastlines italy abstract new data are presented for late holocene relative sea level changes in two coastal sites of sicily and calabria southern italy reconstructions are based on precise measurements of submerged archaeological remains that are valuable indicators of past sea level position the archaeological remains are millstone quarries carved on sandstone coastal rocks and nowadays partially submerged which to the authors knowledge are used for the first time as sea level markers millstones of similar typology are located on the coast of capo d orlando northern sicily and capo dell armi southern calabria when the archeologically based sea level position is compared with the shoreline elevation provided by geological markers holocene beachrock late pleistocene marine terraces a refined understanding of relative sea level changes and rates of vertical tectonic movements for these coastline locations is gained

uranium series ages of fossil corals from mallorca spain the neotyrrhenian high stand of the mediterranean sea revisited abstract the emergent marine deposits of the mediterranean basin have been recognized as an important record of quaternary sea level history for more than a century previous workers identified what have been interpreted to be two separate high stands of sea in the late quaternary namely the eutyrrhenian thought to be 120 ka and the neotyrrhenian thought to be either 100 ka or 80 ka on mallorca spain both of these named deposits lie close to present sea level implying paleo sea levels slightly above present during both marine isotope stages mis 5 5 5e and either 5 3 5c or 5 1 5a if these interpretations are correct they conflict at least in part with sea level records from far field localities we analyzed corals from the neotyrrhenian beds on mallorca which gave u series ages from 126 ka to 118 ka these ages are consistent with previously published amino acid data that show that the neotyrrhenian and eutyrrhenian deposits are not significantly different in age a fossil molluscan fauna from the neotyrrhenian deposits on mallorca has a warm water paleozoogeographic aspect with nine southward ranging species and four extralimital southern species when compared with sea surface temperatures obtained from planktonic foraminifera and alkenones from odp core 977 in the nearby alboran sea the only time period that shows comparable warmth is mis 5 5 5e consistent with the u series ages of corals from the neotyrrhenian deposits we propose that the neotyrrhenian deposits are a beachrock facies of the same age as the eutyrrhenian deposits this interpretation is consistent with the differences in physical sedimentology of the two deposits explains the u series and amino acid data indicating the same age is consistent with the very slight elevation difference of the neotyrrhenian and eutyrrhenian beds and explains the similar though not identical paleozoogeographic aspects of their fossil faunas

millstone quarries along the mediterranean coast chronology morphological variability and relationships with past sea levels abstract the coast of the mediterranean provide several remnants of ancient coastal quarries which are now useful to study sea level change occurring during the last millennia millstones quarries were exploited with same quarrying techniques from rocks like beachrocks sandstones or similar lithologies were shaped to be suitable to grind olives seeds and wheat to produce oil and flour or to break apart soft rocks in this study we integrated historical sources aerial photography field surveys and palaeo sea level modelling to investigate a number of millstones quarries with the aim to asses the intervening sea level change that occurred since the quarries were abandoned we investigated on their chronology spatial distribution and spatial relationship to the sea level our results indicate that most of these were carved close to sea level between 1 45 ka and 0 25 ka cal bp but mainly around 0 45 cal ka bp despite the uncertainties associated with the chronology in we found good agreement between their lowest elevation between 0 33 m and 0 06 m and the paleo sea levels as predicted by the gia models

a new metamorphic constraint for the eburnean orogeny from paleoproterozoic formations of the man shield aribinda and tampelga countries burkina faso abstract progressive metamorphic zones developed in pelites around the aribinda granite burkina faso indicate contact metamorphism at 5 6 kbar biotite chloritoid staurolite kyanite zones are distributed concentrically around the aribinda pluton on its northern margin but are displaced by later thrust faults in the south of the aribinda area and in the nearly tampelga area these metamorphic and structural characteristics provide new constraints for the geodynamical evolution of the eburnean orogeny in the north part of the baoule mossi domain they show the leading part of the granitoid emplacement in the thermic structuration of the greenstone belts and the post metamorphic character of the tangential tectonic in burkina faso the eburnean orogeny underwent 1 initial greenschist facies metamorphism 2 emplacement of granitoids at mid deep crustal levels leading to unusual medium pressure metamorphism 3 later thrusting

k feldspar quartz and k feldspar plagioclase phase boundary interactions in garnet orthopyroxene gneiss s from the val strona di omegna ivrea verbano zone northern italy a detailed study based on textural observations combined with microanalysis back scattered electron imaging bse and electron microprobe analysis empa and microstructural data transmission electron microscopy tem has been made of k feldspar micro veins along quartz plagioclase phase and plagioclase plagioclase grain boundaries in granulite facies orthopyroxene garnet bearing gneiss s 700 825 c 6 8 kbar from the val strona di omegna ivrea verbano zone northern italy the k feldspar micro veins are commonly associated with quartz and plagioclase and are not found in quartz absent regions of the thin section this association appears to represent a localised reaction texture resulting from a common high grade dehydration reaction namely amphibole quartz orthopyroxene clinopyroxene plagioclase k feldspar h2o which occurred during the granulite facies metamorphism of these rocks there are a number of lines of evidence for this these include abundant ti rich biotite which was apparently stable during granulite facies metamorphism and total lack of amphibole which apparently was not disorder between al and si in the k feldspar indicates crystallisation at temperatures 500 c myrmekite and albitic rim intergrowths in the k feldspar along the k feldspar plagioclase interface could only have formed at temperatures 500 600 c symplectic intergrowths of albite and ca rich plagioclase between these albitic rim intergrowths and plagioclase suggest a high temperature grain boundary reaction which most likely occurred at the start of decompression in conjunction with a fluid phase relatively high dislocation densities 2 109 to 3 109 cm2 in the k feldspar suggest plastic deformation at temperatures 500 c we propose that this plastic deformation is linked with the extensional tectonic environment present during the mafic underplating event responsible for the granulite facies metamorphism in these rocks lastly apparently active garnet grain rims associated with side inclusions of k feldspar and quartz and an exterior k feldspar micro vein indicate equilibrium temperatures within 20 30 c of the peak metamorphic temperatures estimated for the sample 770 c contact between these k feldspar micro veins and fe mg silicate minerals such as garnet orthopyroxene clinopyroxene or biotite along the interface is observed to be very clean with no signs of melt textures or alteration to sheet silicates this lends support to the idea that these micro veins did not originate from a melt and if fluid induced that the water activity of these fluids must have been relatively low all of these lines of evidence point to a high grade origin for the k feldspar micro veins and support the hypothesis that they formed during the granulite facies metamorphism of the metabasite layers in an extensional tectonic environment as the consequence of localised dehydration reactions involving the breakdown of amphibole in the presence of quartz to orthopyroxene clinopyroxene plagioclase k feldspar and h2o it is proposed that the dehydration of the metabasite layers to an orthopyroxene garnet bearing gneiss over a 4 km traverse in the upper val strona during granulite facies metamorphism was a metasomatic event initiated by the presence of a high grade low h2o activity fluid most likely a nacl kcl supercritical brine related to the magmatic underplating event responsible for the mafic formation and that this dehydration event did not involve partial melting

plane confined magnetic lineations in mingled mafic and felsic magmas the sazava pluton bohemian massif abstract multiple magnetic lineations were revealed using the anisotropy of magnetic susceptibility ams and anisotropy of magnetic remanence amr methods in a domain of mafic felsic magma mingling at the northwestern margin of the sazava pluton central bohemian plutonic complex bohemian massif gabbrodioritic enclave swarms and sheets are steeply oriented and exhibit magnetic lineations plunging at steep to moderate angles mostly 40 70 whereas in their tonalitic host lineations plunge from vertical to horizontal angles but mostly less than 40 the magnetic lineations in both rock types spread along a nne ssw steep plane that could be simplified as representing an average margin parallel magmatic foliation in the pluton concordant with an average regional cleavage in the wall rock the plane confined lineations are interpreted as having recorded the heterogeneous superposition of two processes 1 vertical stretching during emplacement and magma mingling which left behind the steep lineations and 2 regional tectonic stretching which progressively rotated the mineral grains in rheologically weaker domains chiefly in the host tonalite to form the sub horizontal lineation the average foliation bearing the multiple lineations is interpreted as a composite foliation that recorded both margin perpendicular shortening during emplacement overprinted by coaxial regional tectonic shortening this example reaffirms that 1 magmatic fabrics in crystallizing magmas can record accumulated strain resulting from both emplacement and regional tectonic deformation and that 2 separating magmatic and also magnetic fabrics related exclusively to the internal chamber processes from fabrics caused by regional tectonic deformation is problematic or even impossible in cases where composite fabrics are recognized

beach deposits of mis 5e high sea stand as indicators for tectonic stability of the carmel coastal plain israel abstract ten beach deposits mainly beachrock on the carmel coastal plain northern israel are discussed six are reported for the first time the deposits are situated within or close to the following seasonal stream locally termed nahal channels nahal ahuza amiram ovadia galim megadim bir ibdawiya me arot and kebara the morphology and lithology of most of the deposits are similar their uppermost altitude varies from 0 to 9 m above the present sea level most of the deposits are composed mainly of fine quartz sand and marine mollusk shells carbonate cemented the dominant mollusk families are glycymerididae cardiidae and donacidae most of the beach deposits are situated between cemented aeolian sandstones locally termed kurkar layers on the carmel coast ridge in the nahal ahuza deposit a marine gastropod lentigo latus an index fossil for the mis 5e high sea stand in the mediterranean area was discovered according to lithology and chronostratigraphy the presence of lentigo latus th u aar and rtl dating and flint artifacts the beach deposits were related to the last interglacial maximum about 125 ka bp i e the mis 5e high sea stand these beach deposits are used to identify the palaeo sea levels and coastlines and to study the tectonics along the carmel coastal plain by comparing the elevations and characteristics of the beach deposits to known mis 5e deposits elsewhere and by analyzing archaeological data it is concluded that during the last 125 ka the maximum possible vertical displacement was less than 48 mm ka and the carmel coastal plain was relatively tectonically stable

influence of preexisting backstop structure on oblique tectonic accretion the fiordland margin southwestern new zealand the thinned continental crust of the australian plate is being obliquely subducted beneath the south island on the pacific plate along the fiordland margin of new zealand morphostructural analysis reveals that the continental slope of fiordland is cut by faults that appear to splay southwestward from the onland transpressive dextral alpine fault system active strike slip movement occurs close to the shoreline where upper canyon courses are dextrally offset relative to the fiords the canyons however postdate strike slip movement on the fault splays on the slope indicating that the splays are no longer active these now inactive strike slip faults have imparted a saw tooth backstop geometry to the margin that controls the locus of sediment accretion in the trench accretion occurs as two discrete lobes each at a left step in the backstop the morphology and internal structure of the accretionary lobes indicate that there is partial strain partitioning between the alpine fault and the base of the continental slope oblique convergence in association with a stepped backstop produces strongly curved fold axes and thrusts that abut almost orthogonally against the toe of the margin thus fiordland provides a tectonic model for oblique convergence at a previously structured margin

dike transport of granitoid magmas thermal and fluid dynamical analyses suggest that for viscosities and density contrasts spanning the range considered typical for many calc alkalic granitoids dike ascent is a viable mechanism for the transport of large volumes of granitoid melt through the continental crust we present calculations showing that a granitoid melt with calculated viscosity of the order of 10 6 pa s and a density contrast between magma and crust of 200 kg m 3 can be transported 30 km through the crust in 1 month corresponding to a mean ascent velocity of 1 cm s using analysis modified from numerical studies of the flow of basaltic magmas in dikes we also present an expression that allows the calculation of the critical minimum dike or fault width required for granitic magma to ascend without freezing for all reasonable estimates of cordilleran granitoid viscosity and density contrast the critical dike width is determined to be between 2 and 7 m calculated peak batholith filling rates are orders of magnitude greater than mean cavity opening rates based on estimated fault slippage which is consistent with chemical evidence for intermittent supply of magma pulses

shear zone related folds folds in ductile shear zones are common structures that have a variety of origins these can be pre existing folds that become modified or folds developed during the shearing event among the syn shearing folds a second subdivision is based on the relative age of the folded surface which can be pre existing or newly formed during the shearing event in each of the three categories final fold geometry and orientation show complex relationships with the kinematic frame the final fold geometry depends on the vorticity within the shear zone the rheology and the initial orientation of the folded surface relative to the kinematic framework it follows that folds are complex structures difficult to use as kinematic indicators however in shear zones where undeformed wall rocks with pre shear structures are accessible and where kinematics can be well established folds can provide a valuable natural means to understand the initiation and evolution of structures under non coaxial regimes we point to the need of discriminating among different plausible categories based on the nature of the folded surface and on the inherent structural features of each category q 2004 elsevier ltd all rights reserved