middle to late holocene storminess in brittany nw france part i morphological impact and stratigraphical record our study aims to understand the recurring climatic conditions prevailing during the largest storms reaching nw france brittany these storms are responsible for the breaching of coastal barriers and major flooding of lowlands in a first part of our work we examine the morphological impact and stratigraphic record of storm events along western brittany rocky coasts with a special focus on the southern coast of the bay of audierne the most exposed coast of the region in a second paper middle to late holocene storminess in brittany nw france part ii we shall focus on the chronology of storm events and their climate forcing conditions drilling transects and stratigraphic analyses were first undertaken to constrain chronology strength and wind direction during the main holocene storm events new dates observations and a relative sea level rsl curve were then used to inform discussion of the necessary climatic and morphologic conditions leading to destructive storm events most recorded events appear to be linked with cooling episodes of the holocene and a rsl close to present some storms are clearly responsible for breaching and dune building or remobilisation we demonstrate that storm frequency and intensity appear to rise in a stepwise manner during the late holocene maximum efficiency is reached during the little ice age with clustered events probably lasting several days but major storms also occurred immediately prior to the medieval warm period we suggest that recent coastal dune building from c ad 1100 until now despite a sea level close to present and continuously rising may be a direct consequence of the restoration of beaches after periods of recurrent storminess this building activity often occurred during dry negativ

rock coast inheritance an example from galicia northwestern spain a shore platform on the western coast of galicia in northwestern spain has been inherited from interglacial stages when sea level was similar to today the wide gently sloping intertidal platform is backed in places by supratidal rock ledges and in other places by a steeper and narrower supratidal ramp the gradient of the intertidal platform is consistent with the relationship between platform gradient and tidal range but the slope of the ramp is much too high the abandoned and degraded sea cliff is grass covered along most of this coast and the ledges and the ramp which extend up to several metres above the highest tides are covered by lichen and in places by salt tolerant plants radiocarbon dated sediments in the cliff which range up to 36 000 years in age lie on top of an ancient beach deposit the former beach remnants of which are found in situ on the ramp and rock ledges as well as two caves that are filled with the dated sediments are probably last interglacial in age the morphological and sedimentary evidence suggests that the supratidal ramp and ledges were also formed during the last interglacial stage whereas the wider intertidal platform is probably the product of several older interglacials when sea level was generally similar to today a general model is proposed for the inheritance of shore platforms in macro and microtidal environments copyright 1999 john wiley sons ltd

the coastal terrane of the kaoko belt namibia outboard arc terrane and tectonic significance abstract the coastal terrane or westernmost part of the kaoko belt outboard of the three palms mylonite zone has distinct feldspathic arenite sedimentary sequences no basement distinct nd sediment signatures excluding the archaean and suggesting mesoproterozoic neoproterozoic provenance sources and primitive arc like geochemical signatures for i type granitoids it contains evidence for an older metamorphic event at 650 645 ma not present in any other part of the kaoko belt this metamorphism m1 was of high t low p granulite to upper amphibolite facies and includes migmatisation associated with i type granitic magmatism of arc affinity arc growth at 650 640 ma took place outboard within the adamastor ocean while swakop group facies turbidite sedimentation continued inboard along the passive margin overprinting m1 and m2 fabrics and metamorphic assemblages constrain the docking to have occurred between 650 and 580 ma lack of ophiolite fragments and evidence of intermediate to high p metamorphism along the three palms mylonite zone suggest that it is not a suture and more likely to be part of an arc backarc wrench shear system that developed inboard of an e dipping subduction system where the adamastor ocean was subducted beneath the leading edge of the attenuated congo craton oblique collision between 650 and 580 ma due to docking of this outboard coastal terrane with arc affinities caused i crustal scale oblique overriding of the arc terrane over the passive margin of the congo craton ii crustal scale sinistral shear partitioned into two major ductile shear zones iii high t granulite facies metamorphism in an extruded shear zone bounded core and iv outwards or cratonwards verging basement cored fold nappes

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

upb geochronology of the central ribeira belt brazil and implications for the evolution of the brazilian orogeny abstract the ribeira belt in southeastern brazil was generated during the brazilian orogeny the south american equivalent of the pan african orogeny 700 450 ma the central sector of the belt is characterised by a series of northwest vergent crustal scale thrust stacks emplaced under amphibolite grade conditions major shear zones separate four lithotectonic domains andrel ndia to the northwest juiz de fora paraiba and coastal domains analyses of zircon monazite and titanite from a variety of rock types from the four domains lead to the following conclusions all domains record an important tectono thermal event at 590 565 ma represented by partial melting granitoid intrusion and remobilisation of older basement gneisses and corresponding to thrusting and development of dextral shear zones also recorded are older metamorphic ages 611 604 ma of unknown significance only the paraiba and coastal domains in the south record a younger metamorphic event m2 at 535 520 ma most likely associated with another episode of thrusting and shear zone development the absence of m2 metamorphism in the andrel ndia and juiz de fora domains can be explained by post 535 520 ma emplacement of the paraiba domain late to post tectonic activity is represented by 503 492 ma metamorphism precursors of the basement gneisses are 2185 2134 ma old rocks generated during the transamazonian orogeny some of which contain a significant archean component with minimum ages of 2981 2846 ma the ages presented above define specific metamorphic events for the brazilian orogeny for the first time in southeastern brazil in addition together with previously published data they indicate that the basement rocks found in the allochthonous domains of the central ribeira belt represent an extension of the units present in the southern sao francisco craton and indicate that the foreland was more extensive than the presently defined craton

thermochronology of central ribeira fold belt se brazil petrological and geochronological evidence for long term high temperature maintenance during western gondwana amalgamation abstract the studied sector of the central ribeira fold belt se brazil comprises metatexites diatexites charnockites and blastomylonites this study integrates petrological and thermochronological data in order to constrain the thermotectonic and geodynamic evolution of this neoproterozoic ordovician mobile belt during western gondwana amalgamation new data indicate that after an earlier collision stage at 610 ma zircon u pb age peak metamorphism and lower crust partial melting coeval with the main regional high grade d1 thrust deformation occurred at 572 562 ma zircon u pb ages the overall average cooling rate was low 650 c during sub horizontal d2 shearing until 510 470 ma garnet wr sm nd ages 1 2 c ma being then rapidly exhumed cooled 8 30 c ma during post orogenic d3 deformation with late granite emplacement at 490 ma zircon u pb age cooling rates based on garnet biotite fe mg diffusion are broadly consistent with the geochronological cooling rates a metatexites were cooled faster at high temperatures 6 c ma and slowly at low temperatures 0 1 c ma decreasing cooling rates with time b charnockites show low cooling rates 2 c ma near metamorphic peak conditions and high cooling rates 120 c ma at lower temperatures increasing cooling rates during retrogression the charnockite thermal evolution and the extensive production of granitoid melts in the area imply that high geothermal gradients were sustained for a long period of time 50 90 ma this thermal anomaly most likely reflects upwelling of asthenospheric mantle and magma underplating coupled with long term generation of high hpe heat producing elements granitoids these factors must have sustained elevated crustal geotherms for 100 ma promoting widespread charnockite generation at middle to lower crustal levels

a 700 ma sm nd garnet whole rock age from the granulite facies central kaoko zone namibia evidence for a cryptic high grade polymetamorphic history continental collision of the kalahari and the congo craton in africa and the rio de la plata craton in south america resulted in a structurally complex neoproterozoic belt system the kaoko dom feliciano ribeira belt it is uncertain whether these three cratons collided more or less simultaneously during one single orogenic event at 580 550 ma or whether the belt owe its structural and metamorphic features to several so far poorly constrained events the kaoko belt nw nambia representing the belt system between the southern congo craton and the rio de la plata craton is an ideal object to study these complexities within this belt high grade meta igneous and metasedimentary rocks of the sillimanite k feldspar zone contain large garnet porphyroblasts that grew at ca 730 10 c at 6 7 1 2 kbar during peak metamorphic granulite facies conditions a sm nd garnet whole rock errorchron n 7 mswd 6 0 obtained on a siliceous metasediment yielded an unexpected old age of 692 14 ma which is interpreted as an inherited metamorphic age of an older granulite facies event it is evident that the dated garnets survived the younger high grade granulite facies metamorphism that occurred between ca 570 and 520 ma and preserved their old sm nd isotope systematics implying that the closure temperature for sm nd in garnet is higher than ca 730 c in this case these results imply fast cooling rates at different times during the pan african orogeny that prevent isotopic homogenization at sample scale moreover it is suggestive that trace element ree diffusion in garnet is considerably slower than major element diffusion from a regional point of view it is possible that these specific siliceous metasedimentary rocks may be unrelated to the pan african metamorphic evolution of the kaoko belt between 570 and 520 ma and may represent lithological units that belong to so far unrecognized terranes in the kaoko belt 2007 elsevier b v all rights reserved

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

geological comparison of precambrian and early palaeozoic terrains between the southern west coast of africa and the south east coast of south america abstract this paper describes a geological comparison of similar lithostratigraphic sequences of proterozoic and early palaeozoic ages between the southern west coast of africa namibia and south africa and the south east coast of south america brazil and uruguay the oldest terrains present within the compared regions are those comprising the rio de la plata and the richtersveld provinces of 2000 ma both provinces appear to have evolved from earlier archaean terrains i e the guapore craton in south america and the kalahari craton in southern africa during the transamazonic and eburnian orogenic cycles respectively both the namaqua province affected by the kibaran orogenesis at 1200 ma and the sinclair group of 1300 ma seem to have no comparable geological counterparts in southern brazil and uruguay the late precambrian early palaeozoic successions of the gariep and ribeira belts investigated here seem to be remarkably similar and it is suggested that they were parts of the same geological unit i e a mobile belt developed during the pan african brasil iano orogenesis geological comparisons are particularly good between the gariep porongos and lavalleja groups and stratigraphic correlations can be successfully at tempted even between geological formations i e marica piedra de afilar and stink fontein formations the lack of detailed geological maps for south america makes it difficult to separate different geological formations from broad lithostratigraphic successions and consequent ly comparisons can only be drawn between subgroups and several geological formations i e vacacai and minas subgroups with grootderm holgat and oranjemund formations the extensive magmatic activity generated during the brasiliano orogenesis and only present in the south east coast of south america has not affected the southern west coast of africa however two post tectonic complexes i e the kuboos bremen line of intrusives and the sierra de animas complex appear to be geochronologically analogous and petrologically they seem to have certain similarities it is also suggested that the camaqua group in southern brazil and the nama group could perhaps have certain similarities within their lithological successions and their ages may be also com parable the late stages of the geological evolution of the basin represented by molassic sediments are only present in south east brazil finally an interpretation is given of the geological evolution of the proterozoic early palaeozoic terrains compared in this work

the effect of holocene changes in relative sea level on the morphology of rocky coasts abstract a mathematical wave and weathering model was used to study the effect of holocene changes in relative sea level rsl on rock coast development model runs were made for fast and slow eroding coasts in macro and mesotidal environments using holocene rsl records from sweden northeastern usa southwestern britain central japan western africa and southern australia a further series of otherwise identical runs were made with constant sea level changes in rsl determined the amount of time that marine processes have operated within the modern intertidal zone and rates of wave attenuation and erosion continue to be influenced by subtidal morphology that developed in most areas when rsl was rising to its present level the model suggested that although tidal range is also important holocene rsl changes promoted subhorizontal platform development in australasia and over much of the southern hemisphere and sloping platforms over much of the northern hemisphere shore platforms may have been partly inherited from earlier periods in the holocene when rsl was similar to today s nevertheless most platforms continue to be eroded at all tidal levels where geological and wave conditions are less favourable erosion in the lower intertidal zone has essentially terminated in areas where rsl rose to its present position whereas erosion only occurs today in the lower intertidal zone in places where rsl rose to above its present level in the middle holocene

relative sea level fall since the last interglacial stage are coasts uplifting worldwide the growing interest in quantification of vertical ground motion stems from the need to understand in detail how the earth s crust behaves for both scientific and social reasons however only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies although there are many local studies of quaternary vertical motions of coastlines we know of no comprehensive worldwide synthesis here we provide a compilation of 890 records of paleoshoreline sequences with particular emphasis on the last interglacial stage marine isotopic stage mis 5e 122 ka the quality of dating mis 5e makes it a reliable marker to evaluate vertical ground motion rates during the late quaternary on a global scale the results show that most coastal segments have risen relative to sea level with a mean uplift rate higher than 0 2 mm yr i e more than four times faster than the estimated eustatic drop in sea level the results also reveal that the uplift rate is faster on average for active margins than for passive margins neither dynamic topography nor glacio hydro isostasy may explain sustained uplift of all continental margins as revealed by the wide distribution of uplifted sequences of paleoshorelines instead we suggest that only plate tectonic processes reconcile all observations of quaternary coastal uplift we propose that long term continental accretion has led to compression of continental plates and uplift of their margins therefore this study concludes that plate tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic these results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record

structural evolution and tectonic setting of the porongos belt southern brazil the sw ne striking porongos belt located between juvenile neoproterozoic rocks in the west and the dom feliciano belt characterized by intense reworking of older crust in the east comprises a greenschist to amphibolite facies metavolcano metasedimentary succession porongos sequence of unknown age with some exposures of palaeoproterozoic gneisses encantadas gneisses high temperature ductile deformation of the basement gneisses comprises at least two magmatic events followed by three deformational phases including folding and shearing dt1 dt3 and can be attributed to the palaeoproterozoic trans amazonian orogeny the deformation of the porongos sequence occurred during the neoproterozoic brasiliano orogeny and comprises four ductile deformation phases db1 db4 including two phases of isoclinal folding associated with shearing recorded in mylonitic layers followed by closed nw vergent folding and thrusting leading to formation of a thrust stack uplift of the basement and formation of late tectonic sedimentary basins occurred as a result of semi ductile to brittle block faulting in a sinistral strike slip regime the porongos sequence can be subdivided into a southeastern and a northwestern part trace element analyses as well as sm nd and rb sr geochemical data indicate partial melting and significant contamination by old continental crust for the metavolcanic rocks the metavolcanic rocks show end t 780 ma values of 20 64 and 21 72 northwestern units and 6 87 southeastern sequence the metasedimentary rocks were derived from late palaeoproterozoic to archaean sources and the data indicate different sources for the northwestern and southeastern rock units of the porongos sequence end t 780 ma are 6 25 and 6 85 in the southeastern units with tdm model ages between 1734 and 1954 ma and vary between 14 72 and 17 96 in the northwestern parts which have tdm model ages between 2346 and 2710 ma high 87 sr 86 sr t values between 0 7064 and 0 7286 confirm reworking of older crust isotopic signatures of the porongos sequence do not show indications for a significant contribution from a neoproterozoic juvenile source a passive margin or continental rift environment is suggested for the tectonic setting of the porongos belt which is compatible with both deposition of shallow marine to deep marine sediments and stretching of continental crust leading to volcanism which is characterized by significant contamination by old continental crust

the subtidal morphology of microtidal shore platforms and its implication for wave dynamics on rocky coasts abstract the subtidal portions of shore platforms are important geomorphic features as they can modify deep water wave energy before it impacts the intertidal platform edge in this study an integrated marine and terrestrial aerial lidar dataset is used to analyse the morphology of the subtidal portion of shore platforms semi horizontal intertidal platforms on an 85 km along stretch of microtidal open ocean rocky coast in victoria australia are investigated and described quantitatively three distinct types of subtidal morphology occur i a steep cliff with a mean slope of 8 18 ii a gently sloping ramp with a mean slope of

modeling the development of wave cut shore platforms abstract a mathematical model was used to investigate the development of wave cut shore platforms with constant sea level the model considered the effects of deep water wave height spectra period and wavelength breaker height and depth breaker type the width and bottom roughness of the surf zone the gradient of the submarine slope an erosional threshold related to the strength of the rocks the number of hours each year in which the water level is at each intertidal elevation and the amount and persistence of the debris at the cliff foot intertidal erosion rates were calculated according to the force of the surf reaching the shoreline whereas submarine erosion rates were determined using a depth decay variable each of the two hundred and fifty model runs consisted of 300 000 iterations platform width increased and gradient progressively decreased through model runs and states of static equilibrium were attained by the end of one hundred and nine runs when the wave induced force at each point in the intertidal zone had became too weak to continue eroding the rock runs with mesotidal spring tidal range 3 m generally produced subhorizontal platforms with cliff platform junctions at the mean low water neap tidal level a greater variety of profiles was produced in runs with macrotidal spring tidal ranges 9 m although almost 30 of these runs produced gently sloping platforms with average gradients of only 0 3 about two thirds of the simulated profiles had average gradients ranging from about 1 to 3 simulated platform width increased with tidal range and decreased with the rate of submarine erosion rock resistance the roughness or irregularity of the platform surface the amount and persistence of the cliff foot debris and wave period because higher waves break in deeper water than lower waves there was no consistent relationship between simulated platform width and wave height

evolution of reworked paleoproterozoic basement rocks within the ribeira belt neoproterozoic se brazil based on u pb geochronology implications for paleogeographic reconstructions of the sao francisco congo paleocontinent abstract geological geochemical and geochronological data suggest that the basement exposed in the occidental terrane of the neoproterozoic ordovician ribeira belt represents the continuation of the sao francisco paleocontinent which was amalgamated at the end of the rhyacian transamazonian orogeny the mantiqueira complex represents a cordilleran type active margin of the archean paleocontinent while the juiz de fora complex represents juvenile paleoproterozoic material probably developed within an oceanic setting primitive arc or plateau the latter unit was probably accreted to the active margin of the paleocontinent during the latest stages of the transamazonian orogeny around ca 2 05 ma causing the deformation and metamorphism of the mantiqueira complex at this time to the west and on the cratonic foreland concurrent deformation of the minas passive margin and sedimentation of the sabara basin took place subsequent to the transamazonian orogeny the basement associations were intruded by intraplate alkaline and basic rocks related to rifting events between ca 1 7 and 1 3 ga that resulted in the development of intracratonic basins the paleoproterozoic suture located between the mantiqueira and juiz de fora paleoproterozoic terranes probably controlled the neoproterozoic passive margin tectonics and also the development of a major thrust surface during the neoproterozoic cambrian brasiliano convergence

rhyacian orosirian isotopic records from the basement of the aracuai ribeira orogenic system se brazil links in the congo sao francisco palaeocontinent abstract assembled during the rhyacian orosirian boundary the congo sao francisco palaeocontinent remained linked by a continental bridge from ca 2 ga to the atlantic ocean opening in the cretaceous to the south of that bridge precursor basins and orogenic outcomes encompassed by the neoproterozoic cambrian aracuai ribeira orogenic system aros and its african counterparts developed the aros discloses reworked basement units like the juiz de fora pocrane and quirino complexes which are key units to retrieve the palaeoproterozoic history of the congo sao francisco palaeocontinent this paper presents new u pb ages and the first lu hf in zircon signatures from those complexes all magmatic zircon grains show rhyacian and orosirian ages ranging from c 2250 ma to c 1850 ma the best concordia ages range from 2184 9 ma to 2080 19 ma hf in zircon and whole rock sm nd data disclose mantle related signatures for both the pocrane and juiz de fora complexes suggesting igneous protoliths with no or very few involvement of continental crust similarly to juvenile magmatic arcs conversely hf in zircon data for the quirino complex show an evolved signature compatible with a magmatic arc developed on a continental older crust with archaean components together with a thorough compilation on rhyacian orosirian orogenic systems roos our data allow us to envisage links within the congo sao francisco palaeocontinent comprising orogens characterised by mostly evolved isotopic signatures and zircon inheritance they are grouped into the i w roos including the mantiqueira complex the west segment of the eastern bahia belt intrusions in the south gaviao and porteirinha blocks and parts of the mineiro belt and ii e roos comprising the quirino complex basement rocks of the cabo frio tectonic domain the coastal eastern bahia belt and in africa eburnean and kimezian complexes as well as the western angola shield assembled between the w roos and e roos an orogenic system with prominent juvenile to moderately juvenile isotopic signature ju roos includes the juiz de fora and pocrane complexes and the buerarema complex at the central segment of the eastern bahia belt

titanohematite lattice preferred orientation and magnetic anisotropy in high temperature mylonites magnetic and crystallographic fabric studies were performed in mylonitic granulites from a km wide strike slip shear zone in the ribeira belt southeastern brazil in these mylonites a strong compositional layering underlines the tectonic foliation and the elongation of titanohematite amphibole and orthopyroxene crystals defines a mineral stretching lineation magnetic fabric deduced from anisotropy of magnetic susceptibility ams measurements and tectonic fabric compare favorably rock magnetic studies show that both paramagnetic and ferromagnetic minerals can be carriers of ams the anisotropy of isothermal remanent magnetization which is due to the shape preferred orientation of magnetite grains is coaxial with ams lattice preferred orientation lpo measurements using the electron backscattered diffraction technique show that orthopyroxene amphibole biotite and titanohematite have a strong lpo tightly related to the tectonic fabric among these four minerals titanohematite is the only mineral present in relatively large proportions s 1 5 in all studied samples titanohematite lpo is characterized by a strong concentration of 0001 poles c axes sub perpendicular to the foliation and by a distribution of the poles of the 2110 and 1010 prism planes within the foliation with a maximum close to the lineation this characteristic lpo is interpreted as resulting from dislocation creep during the mylonitization magnetic fabrics and titanohematite lpo fit well the axis of minimum susceptibility is aligned with the c axis maximum and the axis of maximum susceptibility coincides with the maximum concentration of poles of the prism planes titanohematite lpo may provide a valuable constraint for the kinematic interpretation of the magnetic fabrics fl 2002 elsevier science b v all rights reserved

the juiz de fora granulite complex of the central ribeira belt se brazil a paleoproterozoic crustal segment thrust during the pan african orogeny abstract the granulites of the juiz de fora complex occur within thick basement thrust slices associated with the pan african shortening process in the central segment of the ribeira belt five lithological units of the intermediate tectonic domain of the belt can be identified on the basis of detailed geological mapping a orthogranulites b orthogneisses c kinzigite d intrusive garnet charnockite and e amphibolite facies metasediments of probable meso to neoproterozoic age correlated to the cover of the belt petrological data indicate high temperatures and intermediate to low lithostatic pressure conditions for the paleoproterozoic granulite facies metamorphism textures and co 2 rich fluid inclusions are probably related to an ibc path geochemical data do not show relevant compositional change as a result of the granulite metamorphism two calc alkaline suites and tholeiitic to alkaline basic rocks can be related to compressional and extensional settings respectively the overall composition of the granulites the lack of substantial lile depletion as well as the composition of the fluid inclusion points to granulitization process driven by co 2 rich fluids orthogranulites gave rise to banded gneisses as a result of the pan african retrograde metamorphism and intense deformation the u and th depletion detected in few rocks is possibly related with the hydrated conditions of the retrograde reactions

development of shore platforms on kaikoura peninsula south island new zealand ii the role of subaerial weathering the role of subaerial weathering in the development of shore platforms on kaikoura peninsula is investigated evidence for weathering came from a number of distinctive surface morphologies on platforms salt crystal growth water layer weathering and slaking schmidt hammer test data showed that weathering had occurred and that rock strength was reduced through weathering by as much as 50 weathering processes on shore platforms rely on repeated wetting and drying and for this reason the number of wetting and drying cycles was estimated it was found that the number of wetting and drying cycles depend not only on the pattern of tidal water levels but also on algae growth and desiccation the number of cycles ranged from 104 to 379 per year at elevations low in the tide range fewer cycles occurred the greatest number occurring between the peaks of spring and neap tides and where rainfall adds to the number the zone of most cycles was estimated to occur between 0 6 and 0 9 m above mean sea level on the more landward margins of platforms it is at these elevations that the highest rates of erosion occur based on these results it is argued that the development of shore platforms at kaikoura results from subaerial weathering caused by repeated wetting and drying this is contrary to the view that shore platforms result from marine erosion

the use of coal cuttings from underground boreholes to determine gas content of coal with direct desorption method abstract in underground coal mining operations gas content in a coal seam is used to assess the risk of coal and gas outbursts a broadly standard procedure has been adopted to estimate the gas content with coal core in the coal mining industry in soft or friable or geologically complex sections of coal seams it has proven to be extremely troublesome in taking coal cores as cores can be severely fragmented or sometimes it is simply impossible to core with conventional coring methods due to poor borehole stability leaving coal cuttings from boreholes as the only practical alternative for sampling when coal core is replaced with coal cuttings concerns have been raised about the validity and accuracy of the procedure used for gas content determination with coal core in particular with respect to the sampling method of coal cuttings and gas content calculation due to faster initial gas desorption rates of coal cuttings the standard procedure for gas content determination with coal core has been modified to determine gas content of coal with coal cuttings from underground boreholes this paper describes the modified method and presents and discusses the results when it was trialed in a soft coal seam at huainan china

u pb ages of plutonism wollastonite formation and deformation in the central part of the lac saint jean anorthosite suite the lac saint jean anorthosite suite lsjas is the largest ensemble of plutons in the grenville province zircons from a pluton in the central part of the lsjas yield an age of 1140 10 5 ma which accords with existing 1157 1142 ma ages determined from the southern part of the lsjas the du bras granite is a linear pluton emplaced into the dominantly dextral pipmuacan shear zone psz the u pb zircon age of 1148 2 ma for the du bras granite confirms earlier proposals that it is a granophyre formed at greater depths by partial melting of paragneiss by the heat of the crystallizing anorthosite parts of the pluton are strongly deformed by the shear zone and other parts cut the shear zone this suggests that the pluton dates one phase of movement of the psz the canton st onge wollastonite deposit was developed in paragneisses preserved within the psz titanite from this deposit gives an age of 1163 18 ma identical within error to that of the du bras granite indicating that this pluton may have pro

u pb geochronology of the southern brasilia belt se brazil sedimentary provenance neoproterozoic orogeny and assembly of west gondwana abstract the brasilia belt borders the western margin of the sao francisco craton and records the history of ocean opening and closing related to the formation of west gondwana this study reports new u pb data from the southern sector of the belt in order to provide temporal limits for the deposition and ages of provenance of sediments accumulated in passive margin successions around the south and southwestern margins of the sao francisco craton and date the orogenic events leading to the amalgamation of west gondwana ages of detrital zircons by id tims and la mc icpms were obtained from metasedimentary units of the passive margin of the sao francisco craton from the main tectonic domains of the belt the internal allochthons araxa group in the araxa and passos nappes the external allochthons canastra group serra da boa esperanca metasedimentary sequence and andrel ndia group and the autochthonous or cratonic domain andrel ndia group the patterns of provenance ages for these units are uniform and are characterised as follows archean paleoproterozoic ages 3 4 3 3 3 1 2 7 and 2 5 2 4 ga paleoproterozoic ages attributed to the transamazonian event 2 3 1 9 ga with a peak at ca 2 15 ga and to the ca 1 75 ga espinhaco rifting of the sao francisco craton ages between 1 6 and 1 2 ga with a peak at 1 3 ga revealing an unexpected variety of mesoproterozoic sources still undetected in the sao francisco craton and ages between 0 9 and 1 0 ga related to the rifting event that led to the individualisation of the sao francisco paleo continent and formation of its passive margins an amphibolite intercalation in the araxa group yields a rutile age of ca 0 9 ga and documents the occurrence of mafic magmatism coeval with sedimentation in the marginal basin detrital zircons from the autochthonous and parautochthonous andrel ndia group deposited on the southern margin of the sao francisco craton yielded a provenance pattern similar to that of the allochthonous units this result implies that 1 6 1 2 ga source rocks must be present in the sao francisco craton they could be located either in the cratonic area which is mostly covered by the neoproterozoic epicontinental deposits of the bambui group or in the outer paleo continental margin buried under the allochthonous units of the brasilia belt crustal melting and generation of syntectonic crustal granites and migmatisation at ca 630 ma mark the orogenic event that started with westward subduction of the sao francisco plate and ended with continental collision against the parana block and goias terrane continuing collision led to the exhumation and cooling of the araxa and passos metamorphic nappes as indicated by monazite ages of ca 605 ma and mark the final stages of tectonometamorphic activity in the southern brasilia belt whilst continent continent collision was proceeding on the western margin of the sao francisco craton along the southern brasilia belt eastward subduction in the east was generating the 634 599 ma rio negro magmatic arc which collided with the eastern sao francisco margin at 595 560 ma much later than in the brasilia belt thus the tectonic effects of the ribeira belt reached the southernmost sector of the brasilia belt creating a zone of superposition the thermal front of this event affected the proximal andrel ndia group at ca 588 ma as indicated by monazite age the participation of the amazonian craton in the assembly of western gondwana occurred at 545 500 ma in the paraguay belt and ca 500 ma in the araguaia belt this together with the results presented in this work lead to the conclusion that the collision between the parana block and goias terrane with the sao francisco craton along the brasilia belt preceded the accretion of the amazonian craton by 50 100 million years

comment on tectono metamorphic evolution of the central ribeira belt brazil a case of late neoproterozoic intracontinental orogeny and flow of partially molten deep crust during the assembly of west by meira et al

sedimentary provenance in the central ribeira belt based on laser ablation icpms207pb 206pb zircon ages abstract 207 pb 206 pb ages from 420 zircons from 9 upper amphibolite and granulite facies quartzites of the post 1 8 ga metasedimentary cover from the occidental and oriental terranes from the neoproterozoic central ribeira belt in eastern brazil are discussed ages from the occidental terrane show that proterozoic ages predominate with a modal class at 2 1 2 2 ga and that archean ages are less common and lie within the 2 5 3 6 ga range a wider dispersion on proterozoic ages down to 1 1 ga and youngest neoproterozoic ages 550 700 ma were also observed and could be related to the brasiliano panafrican metamorphic events the data show that detrital sediments of the occidental terrane were derived predominantly from erosion of a 1 8 2 2 ga paleoproterozoic terrane with a small proportion of a 2 6 3 6 ga archean crust ages from the oriental terrane are greatly dispersed but show a significant proportion of ages between 1 7 and 2 1 ga although the great majority are between 0 5 and 1 6 ga only 3 out of 144 grains yield archean ages between 2 5 and 2 9 ga based on the greatest errors observed on the data from the oriental terrane 100 300 ma and a continuum of obtained ages between 2072 ma paleoproterozoic and 517 ma cambrian the more plausible interpretation is that the dispersion of ages results from partial resetting of the u pb system by brasiliano metamorphism in proterozoic archean zircons although a mesoproterozoic source could not be discarded

coastal staircase sequences reflecting sea level oscillations and tectonic uplift during the quaternary and neogene many coasts feature sequences of quaternary and neogene shorelines that are shaped by a combination of sea level oscillations and tectonics we compiled a global synthesis of sea level changes for the following highstands mis 1 mis 3 mis 5e and mis 11 also we date the apparent onset of sequences of paleoshorelines either from published data or tentatively extrapolating an age for the uppermost purported oldest shoreline in each sequence including the most documented mis 5e benchmark we identify 926 sequences out of which 185 also feature holocene shorelines six areas are identified where elevations of the mis 3 shorelines are known and 31 feature elevation data for mis 11 shorelines genetic relationships to regional geodynamics are further explored based on the elevations of the mis 5e benchmark mean apparent uplift rates range from 0 01 0 01 mm yr hotspots to 1 47 0 08 mm yr continental collision passive margins appear as ubiquitously uplifting while tectonic segmentation is more important on active margins from the literature and our extrapolations we infer ages for the onset of formation for 180 coastal sequences sea level fingerprinting on coastal sequences started at least during mid miocene and locally as early as eocene whether due to the changes in the bulk volume of seawater or to the temporal variations in the shape of ocean basins estimates of eustasy fail to explain the magnitude of the apparent sea level drop thus vertical ground motion is invoked and we interpret the long lasting development of those paleoshore sequences as the imprint of glacial cycles on globally uplifted margins in response to continental compression the geomorphological expression of the sequences matches the amplitude and frequency of glacial cyclicity from middle pleistocene to present day moderately fast 100 000 yrs oscillating sea levels favor the development of well identified strandlines that are distinct from one another pliocene and lower pleistocene strandlines associated with faster cyclicity 40 000 yrs are more compact and easily merge into rasas whereas older cenozoic low frequency eustatic changes generally led to widespread flat lying coastal plains

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

beach etching and shore platforms etch forms are widely recognised in continental landscapes but little attention has been given to the etch factor in the coastal context evidence mainly from south australia and the iberian peninsula is cited of weathering fronts fortuitously located within the tidal zone and exposed by the stripping of a regolith by waves in addition the possible effects of beach etching or weathering by waters retained by beach sediments are discussed such weathering is difficult to prove in detail but circumstantial evidence from south australian sites suggests it contributes to the development of shore platforms as well as to cliff foot depressions and an assemblage of minor forms such as basins rock doughnuts and fonts the zonation of basins and gutters noted on some coasts may also and in part reflect beach etching

shore platform abrasion in a para periglacial environment galicia northwestern spain abstract the schmidt rock test hammer was used to study the effect of abrasion on shore platforms in galicia northwestern spain on platforms where tidally induced weathering salt wetting and drying etc is dominant rock strength is significantly lower than in areas where abrasion is or has been active in the recent past this suggests that abrasion removes weathered surface material exposing the stronger less weathered rock below abrasion downwearing measured with a transverse micro erosion meter ranged between 0 13 and 1 8 mm yr 1 over the last year most active abrasion occurs in the upper part of the intertidal zone but weathering is slowly destroying formerly abraded surfaces at lower elevations these abandoned surfaces were abraded by materials supplied by erosion of fluvio nival and periglacial slope deposits that covered or partially covered parts of the galician coast during the middle and late weichselian during the holocene rising sea level and erosion of the slope deposits caused the abrasion zone to gradually migrate up to its present position near the high tidal level the spatial and temporal role of abrasion on this coast is therefore closely associated with the exhumation and inheritance of ancient platform surfaces from beneath weichselian deposits

comportement du systeme u pb dans la monazite et chronologie de la deformation et du metamorphisme des metasediments du domaine de kisseynew orogene trans hudsonien manitoba canada the kisseynew domain is the central unit of the reindeer zone of the paleoproterozoic trans hudson orogen in manitoba and saskatchewan the southern flank of the domain is a transition zone betwee

a structural transect across the coastal mobile belt in the brazilian highlands latitude 20 s the roots of a precambrian transpressional orogen abstract we present results of a detailed structural analysis from a 250 km long east west trending transect crossing the coastal mobile belt a part of the precambrian orogen which lies between the eastern edge of the sao francisco craton and the atlantic coast the region exposes amphibolite granulite grade metamorphic rocks and migmatites which formed at mid lower crustal depths during the brasiliano orogeny 0 63 0 52 ga this event marked the closure of the northernmost adamastor ocean and collision between the sao francisco and congo cratons during west gondwana assembly brasiliano deformation resulted in w vergent structures including thrust faults which accommodated kilometer scale transport of crystalline basement overturned kilometer scale folds sheath folds and penetratively developed gneissosity and schistosity isolated relics of an older folded fabric occur locally and may represent transamazonian 2 2 2 0 ga deformation the orogen is kinematically partitioned with the eastern 175 km dominated by moderately to steeply dipping north trending dextral strike slip and oblique slip faults and associated flower structures whereas the western 75 km is dominated by w vergent shallowly to moderately east dipping thrust faults the boundary between these two provinces may mark a brasiliano suture throughout the transect quartzite and metasedimentary belts form strongly deformed zones between massive crystalline basement thrust sheets the granulite cored serra do caparau massif the highest mountains in south america outside of the andes and guyana shield occupies a restraining bend between two brasiliano dextral shear zones the w vergent coastal mobile belt formed contiguously with the e vergent pan african west congo orogen now exposed along the conjugate margin of africa thus an important late precambrian boundary between structurally linked but kinematically opposed structural provinces must lie hidden in the extended offshore continental margins of either continent cretaceous opening of the south atlantic and separation of the west congo belt from the coastal mobile belt may have been structurally influenced by this boundary

temperature constraints on microfabric patterns in quartzofeldsphatic mylonites ribeira belt se brazil abstract based on samples from the major high temperature tres rios alem paraiba padua transpressive shear zone in the ribeira orogenic belt brazil we discuss the applicability of titaniq geothermometry to constrain peak temperature conditions during high temperature mylonitization of quartzofeldspatic rocks and explore the microfabrics formed at these conditions we discuss various aspects of the titaniq method and conclude that deformation occurred at temperatures ranging from 612 to 740 20 c in the studied segment of the shear zone this high temperature deformation resulted in relatively large grain size quartz ribbons and abundant intracrystalline deformation however the cpo fabrics are weak and microstructures suggest that quartz deformation was accommodated by dynamic recrystallization involving grain boundary migration with subsequent grain growth and later some subgrain rotation during exhumation we relate the weak fabrics to diffusion processes during or immediately after dynamic recrystallization and dislocation creep and to the effect of competing slip systems during deformation in terms of rheology evidence for dauphine twinning in our samples suggest strain softening during mylonitization and we suggest that such twinning may add to the rheologically weak nature of quartzo feldspatic portions of hot middle to lower crust

quaternary evolution of a large alluvial fan in a periglacial setting crau plain se france constrained by terrestrial cosmogenic nuclide 10be abstract located in the foreland of the western alps the crau plain was the outlet of the durance river in the pleistocene in order to constrain its geodynamic evolution in terms of chronology and denudation rates the two main quaternary deposits of this plain have been studied based on cosmogenic nuclide 10 be concentration measurements along depth profiles the abandonment of the miramas and luquier alluvial surfaces occurred at the beginning of glacial periods wurm isotopic stage 4 and riss isotopic stage 6 respectively discrepancy in denudation rates under similar geomorphological and lithological conditions suggests different denudation processes during glacial and interglacial periods the denudation rate has been estimated at about 25 mm ka 1 for the interglacial period and about 60 mm ka 1 for the glacial period the abandonment of the crau plain as the outlet of the durance river occurred sometime between 75 and 35 ka

two phase rate transient analysis of a hydraulically fractured coal seam gas well a case study from the ordos basin china abstract apart from implications related to coal seam gas csg reservoir engineering such as stress and desorption dependent permeability 2 phase flow of gas and water adds further complications to rate transient analysis rta techniques in csg reservoirs this paper introduces the concept of area of influence ai to calculate water saturation in transient formation linear flow for 2 phase rta in hydraulically fractured csg wells the relevant equations are derived and discussed and the application of the ai is demonstrated using reservoir simulation the area of influence allows a superior estimation of water saturation compared to the dynamic drainage area dda in under saturated csg reservoirs and hence improves the estimation of fracture half length a practical workflow is also developed and presented to estimate reservoir and hydraulic fracture properties using 2 phase rta for hydraulically fractured vertical wells the presented workflow works in a reverse order by first analysing boundary dominated flow regime and then proceeds to other existing flow regimes developed at earlier production history of the well although analysis of each flow regime provides a standalone method to calculate some of reservoir properties the full development of all flow regimes allows crosschecking and brings more confidence into calculation in this workflow the reservoir properties derived from later flow regimes feeds earlier flow regimes to extract other reservoir variables such as fracture half length a hydraulically fractured csg well from the ordos basin china is analysed using ai and the proposed workflow to demonstrate the field application of this study

u pb age of detrital zircon from the embu sequence ribeira belt se brazil abstract the embu complex crops out in the southeastern part of sao paulo state in brazil and consists mainly of neoproterozoic metasedimentary rocks belonging to the interference zone between the brasilia and ribeira fold belts we present u pb ages la ipcms supported by cathodoluminescence images for detrital zircon from these rocks in order to constrain the formation and evolution of the source area of this complex in this paper we choose to individualize within the embu complex a paleoproterozoic basement a metasedimentary sequence the embu sequence and neoproterozoic intrusive bodies now largely orthogneisses six distinct rock types were recognized in the embu sequence biotite gneiss biotite schist quartzite amphibolite calc silicate rock and talc schist the sequence is strongly deformed by several deformation phases and metamorphosed into amphibolite facies an important shear zone the buquira shear zone separates the embu complex from the socorro guaxupe nappe to the north considered to be part of the upper plate of the southern brasilia belt collision however our mapping showed that the shear zone cuts obliquely into the embu complex diminishing considerably its regional importance three samples were separated for dating a schist north of the shear zone and two quartzites south of the shear zone the results show that the ages of detrital zircon of these samples are mainly paleoproterozoic with a minor archean component the youngest igneous zircon grain from the schist produced an age of about 1000 ma indicating the maximum sedimentation age for the sequence no significant difference appears between the samples north and south of the shear zone reforcing the interpretation that this zone is only of local importance important metamorphic overgrowth of zircon in the age range 670 640 is present in all three samples it is interpreted as related to the installment of a continental magmatic arc in the socorro guaxupe nappe and in the embu complex a second metamorphic pulse between 621 and 599 ma is only apparent in one sample according to the literature this was the period of continental collision between the paranapanema and sao francisco paleocontinents leading to the formation of the southern brasilia belt possibly the fact that the analyzed samples are localized some 30 km away from the suture in the upper plate explains that the increase in temperature during the collision in this area was insufficient to grow significant new zircon a third metamorphic pulse with ages of 576 574 ma possibly related to collision in the ribeira belt is only detected in three analyses of metamorphic rims in the schist sample earlier reported ages of about 790 ma both for igneous crystallization and metamorphism in a more westerly part of the embu complex are only recognized in one analysis of metamorphic overgrowth 794 24 ma from the schist sample and two probably hybrid analyses of 830 19 ma and 767 14 ma from the northern quartzite sample it is concluded that the results show that the detritic zircon is probably derived from the paranapanema paleocontinent

evolution of the south atlantic passive continental margin in southern brazil derived from zircon and apatite u th sm he and fission track data abstract the area between sao paulo and porto alegre in southeastern brazil plays a key area to understand and quantify the evolution of the south atlantic passive continental margin sapcm in brazil in this contribution we present new thermochronological data attained by fission track and u th sm he analysis on apatites and zircons from metamorphic sedimentary and intrusive rocks the zircon fission track ages range between 108 4 15 0 and 539 9 68 4 ma the zircon u th sm he ages between 72 9 5 8 and 525 1 2 4 ma whereas the apatite fission track ages range between 40 0 5 3 and 134 7 8 0 ma and the apatite u th sm he ages between 32 1 1 5 and 93 0 2 5 ma the spatial distribution of these ages shows three distinct blocks with a different evolution cut by old fracture zones while the central block exhibits an old stable block the northern and especially the southern block underwent complex post rift exhumation the sample of the northern block shows two distinct cooling phases in the upper cretaceous and the paleogene to neogene after sedimentation of the permian sandstones the samples of the central block were never heated up over 100 c with a following moderate to fast cooling phase in cretaceous to eocene time and a fast cooling between oligocene to miocene the five thermal models obtained in the southern block indicate a complex evolution with three cooling phases the exhumation events of the three blocks correspond with the parana etendekka event the alkaline intrusions due to the trinidad hotspot and the evolution of the continental rift basins in se brazil and are therefore most likely to be the major force for the post rift evolution of the passive continental margin in se brazil which therefore corresponds to the three main phases of the andean orogeny

slow rates of rock surface erosion and sediment production across the namib desert and escarpment southern africa slow erosion has characterized the namib desert the namibian escarpment and the adjacent namibian highlands over the pleistocene paired analyses n 66 of in situ produced 10be and 26al in quartz bearing samples of bedrock primarily from inselbergs of sediment from dry river and stream channels and of clasts from desert surfaces reveal large inventories of these cosmogenic nuclides indicating significant landscape stability over at least the past million years bedrock samples n 47 collected in three transects from the coast across the escarpment and into the highlands show no spatial pattern in elevation normalized nuclide abundance despite a difference in mean annual precipitation map between sample sites at the coast map 400 mm yr 1 average model erosion rates inland of the escarpment 3 2 1 5 n 9 are indistinguishable from average rates seaward of the escarpment 3 6 1 9 n 38 indicating that rock on the pedimented coastal plain is eroding at the same rate as rock in the highlands sediment samples n 3 from small streams suggest that the landscape as a whole is eroding more rapidly than the bedrock outcrops and that a basin in the steep escarpment zone is eroding several times faster 16 m my 1 than either a basin in the highlands 5 m my 1 or a basin in the coastal plain 8 m my 1 data from large rivers n 4 constrain erosion rates averaged over 105 yrs and 104 to 105 km2 between 3 and 9 m my 1 small quartz clasts n 12 collected from four desert surfaces record extraordinarily long variable and in some cases complex exposure histories simple 10be model ages are as high as 1 8 my some minimum total histories considering both 10be and 26al and including both burial and exposure exceed 2 7 my as a group the namibian cosmogenic data do not support the model of significant and on going escarpment retreat the similarity of erosion rates calculated from 10be analysis of fluvial sediments and longer term 107 yr average mass removal rates estimated by others using fission track analysis of rock suggests that namibian erosion rates have reached a steady state and are changing little over time at outcrop scales the concordance of 10be and 26al in most bedrock samples suggests that the model of steady uniform bedrock erosion is valid there is no indication of intermittent burial shedding of thick rock slabs or stripping of previous cover at an intermediate scale a transect of bedrock samples north of gobabeb demonstrates that the northern boundary of the massive namib sand sea has been steady and unshifting similarly low cosmogenically estimated erosion rates across west and central namibia suggest that the landscape is in geomorphic steady state its overall appearance changing only slowly through time

quaternary geomorphological evolution of a granitic shore platform constrained by in situ 10 be concentrations penmarc h sw brittany france abstract the penmarc h granitic coastal domain sw brittany western france offers the opportunity to address the little investigated issue of erosional processes in a granitic coastal context from land to sea the granitic coast is composed of 1 an aerial marine terrace 10 be analyses supplies new constraints on the weathering and denudation processes recorded by the penmarc h platform in quaternary times the role of at least two denudation events is emphasized i a 1 8 m thick level of granitic material is assumed to have been removed by erosion during the mis5 sea level highstand both in the offshore domain and in the low part of the marine terrace ii an additional 0 6 m thick level of the granitic substratum was later removed during the last holocene transgression mainly in the marine domain the lack of any morphological step between the subaerial marine terrace and the shore platform is here attributed to the combined effect of multiple factors including i a quaternary tectonic quiescence ii a major eustatic transgression mis5 shaping both the shore platform and the low part of the marine terrace iii the mechanically strong behaviour of the granitic basement with regard to erosion and iv the moderate influence of the holocene sea level stillstand since 6 ka on the shore platform thanks to 10 be content analysis a range of vertical erosion rates of ca 3 6 m ma 1 is obtained for the onshore domain showing no discernable difference between the intertidal and aerial erosion rates from that result it is thus determined that the long term development of the penmarc h granitic shore platform was mainly driven by marine erosive processes during the mis5 and holocene marine transgressions whereas subaerial erosive processes prevailed after the mis5 event

erosion of rocky shore platforms by block detachment from layered stratigraphy the majority of shore platforms form in rocks that are characterised by layered stratigraphy and pervasive jointing plucking of weathered joint and bed bounded blocks is an important erosion process that existing models of platform development do not represent globally measuring platform erosion rates have focused on microscale 1 mm surface lowering rather than mesoscale 0 1 1 m block detachment yet the latter appears to dominate the morphological development of discontinuity rich platforms given the sporadic nature of block detachment on platforms observations of erosion from storm event to multi decadal timescales and beyond are required to quantify shore platform erosion rates to this end we collected aerial photography using an unmanned aerial vehicle to produce structure from motion derived digital elevation models and orthophotos these were combined with historical aerial photographs to characterise and quantify the erosion of two actively eroding stratigraphic layers on a shore platform in glamorgan south wales uk over 78 years we find that volumetric erosion rates vary over two orders of magnitude 0 1 10 m3 yr 1 and do not scale with the length of the record average rates over the full 78 year record are 2 5 m3 yr 1 these rates are equivalent to 1 2 5 3 mm yr 1 surface lowering rates an order of magnitude faster than previously published both at our site and around the world in similar rock types we show that meso scale platform erosion via block detachment processes is a dominant erosion process on shore platforms across seasonal to multi decadal timescales that have been hitherto under investigated

architecture of late orogenic plutons in the aracuai ribeira fold belt southeast brazil abstract post collisional to late orogenic magmatism 580 to 480 ma in the aracuai ribeira fold belt se brazil is characterized by the predominance of high k metaluminous allanite titanite bearing granitoids small lenses of coronitic gabbro anorthosite pyroxenite and phlogopite peridotite are also common in deeper exposed areas of this fold belt in the region of southern espirito santo state the deep erosional level associated with a steep topography reveals the internal architecture of the intrusions a tendency to funnel shaped bodies with sub vertical hemi ellipsoidal conical roots changing upwards to shallow dipping tops associated stocks sills and dykes of basic and acid rocks generally intrude the enclosing gneisses along the foliation planes local ductile shear zones and parallel to fold hinges the contact between intrusions and the enclosing rocks is sharp in deeply eroded plutons e g santa angelica venda nova mimoso do sul and varzea alegre but at shallow levels e g castelo pedra azul and conceicao de muqui agmatic stoping zones occur along the borders a magmatic foliation within the granitoids is usually well marked but the schistosity in the surrounding gneisses wraps around the plutons the intrusions have a bimodal chemical distribution and generally are reversely zoned with mafic cores gabbro diorite to tonalite surrounded by a mingled marble cake zone where basic and acid rocks are interfingered and an external zone of syenomonzonite and granite widespread evidence of mingling and mixing between contrasting magmas of gabbroic and granitic and or syenomonzonitic compositions is characteristic for all intrusive complexes we suggest that replacement of lithospheric mantle by hot asthenospheric mantle induced partial melting of the crust the mantle exchange was due to lithospheric mantle delamination and slab breakoff following collisional orogenesis the bimodal plutons result from interaction among the contrasting magmas ascent and emplacement followed older regional structures such as regional fold hinges and ductile shear zones

u pb ages for magmatism and deformation in the new quebec orogen the new quebec orogen is a paleoproterozoic fold and thrust belt active from 2 17 to 1 77 ga bordering the eastern margin of the archean superior province the orogen developed on a long lived passive continental margin and comprises two volcanic sedimentary sequences the ages presented in this study help to bracket the magmatic and deformational history of the orogen a glomeroporphyritic gabbro from the hellancourt formation was dated at 1874 3 ma and a rhyodacite from the upper murdoch formation yielded an identical age of 1870 4 ma these data allow the correlation of the two units and indicate that they are 10 14 ma younger than the estimated age for the sokoman formation these ages together with already published work indicate that magmatism related to the younger magmatic event occurred at 1884 1870 ma albitized pelites from the murdoch formation contain euhedral detrital zircons 2707 2690 ma old indicating that the source rocks were archean an undeformed monzonitic intrusion occurr

erosion of a granite inselberg gross spitzkoppe namib desert abstract namibia with its passive margin setting long term tectonic stability and long lasting arid climate is a typical granitic landscape characterized by numerous dominating inselbergs the namib has been the focus of quantitative studies on the overall rates of bedrock exhumation escarpment retreat and sediment generation transport and deposition results from these studies indicate steady bedrock erosion rates ranging between 1 and 5 mm kyr 1 over the last 105 106 yr this rate was determined from samples collected mostly from small inselbergs with low relief how fast the large and classic inselbergs which dominate the namib desert landscape erode generate sediment and contribute to the overall sediment supply has yet to be systematically examined we document erosion rates of the gross spitzkoppe gs one of the largest inselbergs in the namib desert namibia based on measured concentrations of 10be in samples collected from bedrock boulders and surface grus the results suggest a slow lowering rate 1 2 mm kyr 1 while the overall slope processes deliver sediment to the base of the cliff with 5 6 105 atoms g 1 quartz this concentration is equivalent to an average erosion rate of 8 mm kyr 1 2 3 times faster than the bedrock lowering rate thus the inselberg has been eroding by cliff retreat the concentration of cosmogenic isotopes in slope sediment is controlled by exposure time on the slope weathering of exposed bedrock and weathering of subsurface bedrock sediment continues to accumulate cosmogenic isotopes while being transported on the flat pediments surrounding the inselberg within 1 2 km from the base of the gs the concentration doubles to 10 105 atoms g 1 quartz the increase is achieved by dosing due to exposure and mixing with highly dosed sediment eroded from near subsurface bedrock from this area grus is transported through a network of low gradient channels to the atlantic ocean 100 km away cosmogenic isotope concentration in sediment increases to 30 105 atoms of 10be g 1 quartz which is 3 4 times higher than that measured in the grus close to the gs and is controlled by the erosion rate of stable bedrock throughout the entire drainage basin dosing due to exposure during transport obviously contributes to the overall measured concentration in the sediment as it approaches the ocean

development of shore platforms on kaikoura peninsula south island new zealand abstract the role of waves in shore platform development has been investigated on kaikoura peninsula by direct measurement of waves in deep water and on platforms at high tide this showed that the deepwater wave environment off the kaikoura peninsula is very energetic but the amount of energy delivered to platforms is very low in deep water wave power ranged from 5900 to 106 700 n m s 1 per m of crest when calculated from mean significant wave height and when calculated from maximum wave height it ranged from 31 400 to 5 370 000 n m s 1 per m of crest a comparison of deep water wave energy flux with wave energy flux at the high tide cliff of platforms showed that there was a reduction by as much as five orders of magnitude during storm conditions an analysis of the role of breaking waves revealed that these are ineffective as an erosional agent because the depth of water offshore causes breaking before waves arrive on platform surfaces depth of water controlling wave breaking causes larger storm waves to break further from shore preventing direct attack at the cliff base shear stresses and dynamic forces under waves were calculated from waves measured on shore platforms this showed that these forces never exceeded the compressive strength of the platform rocks at kaikoura it is concluded that wave forces are not directly capable of causing erosion on shore platforms at kaikoura

550 490ma pre to post collisional shoshonitic rocks in the ribeira belt se brazil and their tectonic significance abstract this work presents a detailed study in a new occurrence of shoshonite rocks in the central ribeira belt se brazil it is the tingui unit a hornblende biotite orthogneiss with shoshonitic affinity and undeformed dykes of similar composition they crop out along the contact between costeiro part of oriental terrane ribeira belt and cabo frio tectonic domains the tingui unit is represented by mesocratic orthogneiss ranging from quartz diorite to granodiorite in composition plagioclase biotite quartz hornblende microcline titanite apatite allanite zircon and opaque minerals are the main minerals tonalitic to granodioritic dykes with similar composition cross cut the tingui orthogneiss besides mineralogical similarities analyzed samples from both the orthogneiss and the dykes have shoshonitic signature with crustal and mantle nd sr isotope nature they are basic to intermediate rocks with low fe contents and high alkalis ba rb sr zr and lree values high k2o na2o up to 2 06 and lree hree ratios along with others geochemical parameters reinforce the shoshonitic signature sm nd data point to end values of 13 2 to 4 38 and 1 7 to 1 2g a tdm nd model ages although the 143nd 144nd ratios indicate a predominance of lower continental crust heritage the 87sr 86sr ratios ranging from ca 0 705 to 0 707 suggest an enriched mantle contribution nevertheless geochronological data from tingui orthogneiss and tonalitic dykes reveal a difference of ca 50 m y in their crystallization ages concordia ages of 551 3 ma for the orthogneiss 495 4 ma and 488 4 ma for the mesocratic and leucocratic tonalitic dykes respectively comparing our new data and the tectonomagmatic events recorded in the oriental terrane we propose a tectonic model emphasizing the role of this shoshonitic magma interpreted as pre and post collisional intrusions regarding to the buzios orogeny and possibly derived from the similar source this magmatic activity is attributed to a long term maintenance of high temperatures and low cooling rates in the ribeira belt considered as a hot orogen the 50 m y crystallization age gap between the studied rocks could be assigned to two periods of melting of a similar or even same source at different tectonic stages of the orogen pre and post collisional

rock coasts with particular emphasis on shore platforms rock coasts are one of the most common elements of the world s littoral zone and they are often important sources of sediment for estuaries and beaches economic development growing populations and the potential effects of rising sea level provide a practical need to understand the dynamics of these coasts although there have been significant advances in our understanding of rocky coastal systems further progress has been hindered by a lack of researchers and by the often imperceptible changes that generally occur within human time scales this paper reviews rock coast processes and landforms in a variety of morphogenic environments one of our most fundamental challenges is to determine the degree to which rock coasts are contemporary rather than inherited features from the quaternary when changes in sea level and climate were responsible for marked variations in the nature intensity and elevational distribution of the marine and subaerial processes that sculpture rock coasts

large scale relief development related to quaternary tectonic uplift of a proterozoic paleozoic basement the armorican massif nw france the topography of basements located in intraplate domains has often been interpreted in terms of planation theory by examining the remnants of paleosurfaces in this paper we address the significance of the present day drainage networks that erode such topographies by looking at the relief development on the armorican massif basement northwestern france using digital elevation model dem analysis the topography of this massif is characterized by large scale 250 km relief variations that define high elevation domains heds these domains control the pattern of drainage networks by setting the location of the main drainage divides and the polarity of the regional slopes large scale relief is strongly associated with the existence of scarps along inherited fault zones suggesting that relief development is mainly controlled by tectonics through fault reactivation a surface evolution study shows that drainage networks developed during the quaternary which corresponds to the timing of the tectonic activity which also led to relief development the study of quaternary fluvial erosion through a new method for measuring incision shows that the drainage basins of the heds record greater amounts of base level fall during quaternary times this implies that differential uplift is responsible for the large scale relief development of the armorican massif during the quaternary our study suggests that as seen in active settings the topography of basements corresponds to a dynamic signal between tectonics and erosional processes which can be used for example in the study of intraplate deformation

erosion rates on subalpine paleosurfaces in the western mediterranean by in situ 10be concentrations in granites implications for surface processes and long term landscape evolution in corsica france a study of erosion rates by in situ 10be concentrations in granites of miocene high elevation paleosurfaces in corsica indicates maximum erosion rates between 8 and 24 mm kyear the regional distribution of measured erosion rates indicates that the local climatic conditions namely precipitation the petrographic composition of granites and the degree of brittle deformation govern erosion rates chemical erosion dominates even at elevations around 2 000 m in presently subalpine climate conditions field evidence indicates that erosion operates by continuous dissolution and or disintegration to grains grusification the erosion rates are relatively high with respect to the preservation of inferred early miocene landscapes we infer temporal burial in the middle miocene and significantly lower erosion rates in the neogene until 3 ma to explain the preservation of paleosurfaces in line with fission track data valley incision rates that are a magnitude higher than erosion rates on summit surfaces result in relief enhancement and long term isostatic surface uplift on the other hand widening and deepening of valleys by cyclic glaciation progressively destroys the summit surface relics

refining the eustatic sea level curve since the last glacial maximum using far and intermediate field sites the eustatic component of relative sea level change provides a measure of the amount of ice transferred between the continents and oceans during glacial cycles this has been quantified for the period since the last glacial maximum by correcting observed sea level change for the glacio hydro isostatic contributions using realistic ice distribution and earth models during the last glacial maximum lgm the eustatic sea level was 125 5 m lower than the present day equivalent to a land based ice volume of 4 6 4 9 107 km3 evidence for a non uniform rise in eustatic sea level from the lgm to the end of the deglaciation is examined the initial rate of rise from ca 21 to 17 ka was relatively slow with an average rate of ca 6 m ka 1 followed by an average rate of ca 10 m ka 1 for the next 10 ka significant departures from these average rates may have occurred at the time of the younger dryas and possibly also around 14 ka most of the decay of the large ice sheets was completed by 7 ka but 3 5 m of water has been added to the oceans since that time

u pb geochronology of the granite magmatism in the embu terrane implications for the evolution of the central ribeira belt se brazil abstract the embu domain represents the central part of the ribeira fold belt in sao paulo brazil it hosts several granitic occurrences of varied composition ranging from small granitic bodies that outcrop in a domain bounded by the intersection of two major sutures taxaquara and guararema faults and batholitic masses outcropping to the east understanding the evolution of such granites is of vital importance to better constrain evolutionary models for the ribeira belt in the present study a set of samples from eleven main granite occurrences from the east of sao paulo state was selected for geochronological investigation using laser ablation multicollector inductively coupled plasma spectrometry la mc icp ms and thermal ionization mass spectrometry tims u pb dating of zircon and monazite crystals respectively the results indicate a remarkable cluster of ages around 590 ma with older events of granite magmatism between 660 and 600 ma registered for four plutons indicating a long history of crustal reworking and magma generation the ages of reworked sources were evaluated from inherited zircon cores although highly discordant these point to the predominance of paleoproterozoic 2 4 2 1 ga sources with minor contributions from mesoproterozoic 1 1 0 9 ga and archean sources 3 1 ga the new data bring important insights into the role played by the embu domain on the paleogeography and evolution of the ribeira belt

fe ti v p ore deposits associated with proterozoic massif type anorthosites and related rocks abstract magmatic rocks containing economic concentrations of iron titanium vanadium and phosphorous are commonly associated with massif type anorthosites and related rocks this rock association is part of the anorthosite mangerite charnockite rapakivi granite suites that are restricted to the proterozoic understanding the geochemistry and emplacement mechanisms of ilmenite magnetite and apatite ore deposits is crucial for exploration efficient mining operations and ore processing this review discusses the controlling factors on the grade of an ore its mineralogy and its major and trace element distribution we present petrogenetic models of currently mined deposits lac tio tellnes damiao and discuss the characteristics of minor ore bodies from anorthosite provinces worldwide grenville north china craton east european craton rogaland laramie models of formation of anorthosite and related rocks are presented as well as the nature of the possible parental magmas of the suite a mineralogical classification of fe ti ores is proposed 1 gabbro noritic ilmenite ore apatite magnetite 2 ti magnetite dominated ore 3 nelsonite fe ti oxides apatite and 4 rutile ilmenite ore the stability of ilmenite and magnetite is then critically reviewed and the influence of various factors particularly oxygen fugacity and crystallization pressure is examined we discuss liquidus compositions of fe ti oxides and the behavior of important trace elements such as cr and v both of which are sensitive to fo2 variations post cumulus evolution of both oxides can occur due to re equilibration with trapped liquid re equilibration with ferromagnesian silicates exsolution oxidation reaction between ilmenite and magnetite and metamorphic overprinting these various processes are described and their effects on the oxide geochemistry are emphasized several potential ore forming processes have been invoked and can explain the formation of huge concentration of ilmenite magnetite apatite fractional crystallization can be combined with crystal sorting and plagioclase buoyancy to produce relative enrichment of dense ore minerals silicate liquid immiscibility can segregate conjugate si rich and fe rich melts the latter being enriched in fe ti p magma mixing can produce hybrid magmas located in a single phase field of the phase diagram and precipitate a pure ilmenite cumulate alternative processes are also described such as ejection of fe ti enriched residual melts by filter pressing and compaction solid state remobilization of ilmenite in veins and hydrothermal transport of fe and ti from the host anorthosite followed by concentration in veins and lenticular ore bodies the magnetic properties of fe ti ore deposits present contrasting signatures depending on whether the natural remanent magnetization is dominated by hemo ilmenite or multi domain magnetite micro and macro scale deformation features of ore rocks are intimately correlated with magma emplacement and with ballooning of the anorthosite diapir associated with gravitational sagging of dense ore bodies exploration perspectives show that oxide apatite gabbronorites are interesting targets because ilmenite in these rocks is poorer in cr and mg and because the ti resource may be combined with apatite and vanadiferous magnetite

subaerial weathering versus wave processes in shore platform development reappraising the old hat island evidence one of the longest standing debates in rocky coast geomorphology is whether subaerial weathering or wave processes dominate shore platform evolution the origins of this debate date to the mid nineteenth century when the first descriptions of old hat islands were provided from northern new zealand old hat islands are surrounded by a broad near horizontal shore platform their formation was inferred to relate to subaerial weathering of bedrock to a level of permanent saturation with wave processes acting only to remove the weathered debris to date no detailed topographic surveys have been conducted on the old hat islands in new zealand that initiated this debate in this study we provide the first quantitative data on the original field sites topographical surveying and schmidt hammer hardness testing were conducted on 25 profiles of varying wave exposure in contrast to the classic descriptions platform elevation varies from just above mean high water spring mhws at the most exposed sites to mean high water neap mhwn at the most protected sites or mean sea level msl where beaches occur on the platform surface there is no significant difference between the hardness of the cliffs and the platforms fronting them and no clear relationship between wave exposure and platform width rather than being exclusively dominated by subaerial process the formation of microtidal sheltered old hat island platforms is considered to be a function of i the rate of weathering ii exposure to wave energy iii nearshore water depth and iv rock resistance shore platform elevation in the study area is thought to be a function of the level at which waves erode cliff rock and the action of weathering which lowers platform surfaces the width of platforms is strongly influenced by the ability of waves to dissect the platform edge along vertical joint lines copyright 2010 john wiley sons ltd

shore platform erosion and evolution implications for cosmogenic nuclide analysis abstract determining rates and modes of shore platform development and the age of associated elements are among the greatest challenges facing rock coast researchers today these coasts generally lack dateable deposits but cosmogenic nuclide analysis cna can be applied directly to bare rock surfaces to estimate erosion rates or the time that a surface has been exposed over millennial timescales therefore this technique has the potential to revolutionize current theories on rock coast evolution and modes of development because environmental and geomorphological factors affect rates of nuclide accumulation and retention however the results of cna analysis are dependent on the validity of the theoretical models that have to be employed according to the particular application among the important assumptions that may be made are those concerned with shading tidal immersion beach sediment covers and other factors that influence rates of nuclide accumulation and with possible spatial and temporal patterns in shore platform erosion primarily by wave generated backwearing and weathering induced downwearing that reduce nuclide concentrations our lack of understanding of the factors that control these variables and in particular shore platform erosion which is the subject of this review has important implications for modelling rock coast evolution assessing the possible contribution of inheritance and dating especially by cna the occurrence of important formative events

early to late ediacaran conglomeratic wedges from a complete foreland basin cycle in the southwest sao francisco craton bambui group brazil abstract stratigraphic isotopic and geochronological data from two late neoproterozoic aged conglomerate wedges in the southwest sao francisco craton support the interpretation that the ediacaran bambui group in east central brazil was deposited in a foreland basin the sambura formation forms the base of the bambui group in the southwestern part of the bambui basin and was deposited synchronously with the brasilia orogeny it is interpreted to be a sedimentary product of a retrogradational coastal alluvial fan system deposited in an underfilled flexural foredeep during the early stages of foreland basin development sometime between 630 and 560 ma the basal sete lagoas formation carbonates were deposited towards the cratonic margin on the forebulge which provided an ideal environment for carbonate production the lateral relationship between the sambura and sete lagoas formations further implies that an unconformity was generated by foreland flexure and that this unconformity separates an early ediacaran phase of the foreland basin from a late ediacaran phase the lagoa formosa formation was deposited in the latter phase after peak orogenesis with a provenance that includes post orogenic granites and zircons as young as 560 ma it records a prograding turbidite fan system in the lagoa formosa formation that was deposited during orogenic unroofing and basin wide shallowing in a filled stage of the foreland basin a shift from highly enriched 13 c values towards global like carbon isotopes values in carbonates within the lagoa formation in conjunction with the occurrence of banded iron formation may suggest deposition in a basin with anoxic and ferruginous deep waters in the bambui basin in the latest ediacaran

uncertainty of gas saturation estimates in a subbituminous coal seam abstract to assess the commercial viability of a coalbed methane prospect two of the key geological parameters measured are gas content desorbed gas and gas holding capacity adsorption capacity these two measures together with reservoir pressure give an estimate of the gas saturation of the reservoir typically gas saturation has been assessed by collecting one adsorption isotherm sample and assuming it is representative of the whole seam reservoir conditions this study addresses that assumption to understand the level of variation and thus the inherent uncertainty in saturation one core jasper 1 from the huntly coalfield in new zealand was analysed in detail ten samples representing the whole coal seam were placed into gas desorption canisters and desorbed for ten days and then analysed for adsorption capacity desorption analyses for total measured gas content average in situ basis ranged from 2 32 to 2 89 m 3 t standard deviation sd 0 18 and gas adsorptive capacity at 4 mpa average in situ basis from 2 11 to 3 51 m 3 t sd 0 38 resulting in saturations ranging from 66 to 120 sd 15 determination of how many samples are required to make a realistic assessment of average reservoir properties requires a consideration of i the level of accuracy desired ii the limit of accuracy possible which is governed by the magnitude of experimental error and iii the innate variability of the seam it was found that a minimum of five samples each for adsorption and desorption were required in order to significantly decrease the uncertainty in gas saturation estimates for a subbituminous coal

u pb evidence of late archean tectono thermal activity in the southern sao francisco shield brazil the sao francisco craton in eastern brazil is one of the major shield areas in south america in the quadrilatero ferrifero area southern sector of the craton the archean rio das velhas greenstone belt is surrounded by granite gneiss terrane and is overlain by proterozoic sedimentary successions the bonfim metamorphic complex is the only area of the granite gneiss terrane adjacent to the greenstone belt that has been mapped it comprises two gneissic units tonalites and late granitic dykes which crosscut the regional north south shear fabric samples of gneiss two tonalites and a granitic dyke were dated by u pb a zircon core from the alberto flores gneiss yielded a minimum age of 2920 ma whereas the overgrowth is concordant at 2772 6 ma two tonalites from the vicinity of serra da moeda are old and a late dyke yielded an age of these data together with previously published u pb ages show that i greenstone belt volcanism was coeval with granitoid intrusion and with metamorphism of older

migrating cretaceous eocene magmatismin the serra do mar alkaline province se brazil melts from the deflected trindade mantle plume department of geological sciences university of durham south road durham dh1 3le uk department of earth sciences university of cambridge downing street cambridge cb2 3eq uk department of physics the university newcastle upon tyne ne1 7ru uk department of geology mcmaster university 1280 main street west hamilton ont canada l8s 4m1 departmento de geoquimica e recursos minerais instituto de geociencias universidade de brasilia

granitic coastal geomorphology applying integrated terrestrial and bathymetric lidar with multibeam sonar to examine coastal landscape evolution coasts composed of resistant lithologies such as granite are generally highly resistant to erosion they tend to evolve over multiple sea level cycles with highstands acting to remove subaerially weathered material this often results in a landscape dominated by plunging cliffs with shore platforms rarely occurring the long term evolution of these landforms means that throughout the quaternary these coasts have been variably exposed to different sea level elevations which means erosion may have been concentrated at different elevations from today investigations of the submarine landscape of granitic coasts have however been hindered by an inability to accurately image the nearshore morphology only with the advent of multibeam sonar and aerial laser surveying can topographic data now be seamlessly collected from above and below sea level this study tests the utility of these techniques and finds that very accurate measurements can be made of the nearshore thereby allowing researchers to study the submarine profile with the same accuracy as the subaerial profile from a combination of terrestrial and marine lidar data with multibeam sonar data it is found that the morphology of granite domes is virtually unaffected by erosion at sea level it appears that evolution of these landscapes on the coast is a very slow process with modern sea level acting only to remove subaerially weathered debris the size and orientation of the joints determines the erosional potential of the granite where joints are densely spaced 2 m apart or the bedrock is highly weathered can semi horizontal surfaces form copyright 2014 john wiley sons ltd

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

tectonic implications of precambrian sm nd dates from the southern sao francisco craton and adjacent aracuai and ribeira belts brazil abstract the archean and paleoproterozoic sao francisco craton of eastern brazil is surrounded on all sides by brasiliano pan african orogens the n ne trending orogen that separates the eastern edge of the southern sao francisco craton from the atlantic coast can be divided into the largely greenschist and amphibolite facies aracuai belt on the west and the largely granulite facies ribeira belt on the east a pronounced linear gravity and magnetic anomaly the abre campo discontinuity defines the boundary between these two belts we obtained sm nd mineral ages and whole rock sm nd model ages for garnet bearing metamorphic rocks along an e w transect across the southern sao francisco craton the southern aracuai belt and the ribeira belt at about latitude 20 s a recrystallization age of 2 1 ga from metasediments recrystallized during the development of the classic dome and keel province of the southern sao francisco craton the quadrilatero ferrifero indicates that dome emplacement occurred during the waning stages extensional collapse of the transamazonian collisional orogeny seven mineral ages from the southern aracuai and ribeira belts date the thermal peak of metamorphism at between 538 and 589 ma confirming that these belts were pervasively remobilized during the brasiliano event samples from the aracuai belt yield either archean 2 6 ga or transamazonian 2 1 2 3 ga tdm model ages indicating that the protoliths were either fragments of the sao francisco craton crust or were sediments derived from that craton which presumably had been stretched to form a thinned continental margin during meso and neo proterozoic rifting events notably a mixed meta pelite and metabasite sequence in the southern aracuai belt the dom silverio group has transamazonian ancestry and thus may represent oceanic sediments deposited on or east of this stretched margin and then thrust back onto the continent to mark a collisional suture between the sao francisco block and an archean crustal sliver to the east the rocks of the ribeira belt i e the region east of the abre campo discontinuity have younger model ages tdm 1 6 2 0 ga indicating that this belt was not originally part of the sao francisco craton it may represent an accreted transamazonian terrane therefore the abre campo discontinuity marks an important crustal boundary possibly a suture brasiliano shear zones appear to steepen and root into the abre campo discontinuity suggesting that it formed in brasiliano time

modelling the quaternary evolution of shore platforms and erosional continental shelves a mathematical model was used to investigate the effect of glacially induced fluctuations in sea level on the evolution of wave cut shore platforms and erosional continental shelves during the quaternary the model used two deep water wave sets which were used to calculate breaker height and depth and the force of the waves at the waterline according to the width and bottom roughness of the surf zone and the gradient of the submarine slope the model also incorporated an erosional threshold related to the strength of the rocks the number of hours each year in which the water level is at each intertidal elevation and the amount and persistence of the debris at the cliff foot most runs were made using a sea level model that consisted of 26 glacial cycles from 2 million to 0 9 million years ago and nine of approximately twice the amplitude and wavelength in the last 0 9 million years the model emphasized the dynamic association between the contemporary intertidal platform and the continental shelf both surfaces trend towards a state of static equilibrium under oscillating sea level conditions when attenuated waves are unable to continue eroding the rock if there has not been enough time to reduce the gradient of the shallower portions of the continental shelf however intertidal shore platforms can be in a temporary though possibly long lasting state of dynamic equilibrium the model suggests that most platforms are at least in part inherited from one or in many cases more interglacial stages when sea level was similar to today s copyright 2001 john wiley sons ltd

u pb geochronology of archean magmatism and proterozoic metamorphism in the quadrilatero ferrifero southern sao francisco craton brazil the quadrilatero ferrifero is a metallogenic district au fe mn located in the southernmost sao francisco craton in eastern brazil it is composed of archean granitoids gneisses and a greenstone belt sequence rio das velhas supergroup overlain by a proterozoic clastic chemical sedimentary sequence hosting a thick lake superior type banded iron formation minas supergroup a u pb study of the main units leads to the following conclusions granitoid emplacement was dated at 2776 7 6 ma and 2721 3 ma two felsic volcanic rocks from the rio das velhas supergroup yielded ages of 2776 23 10 ma and 2772 6 ma these data indicate that greenstone belt volcanism was coeval with granitoid emplacement a common feature of greenstone belt terrains but so far undocumented in the southern sao francisco shield the younger granitoid intrusion marks the stabilization of the shield in late archean time zircon cores older than 2776 ma together with other data indicate the presence of continental crust 2 88 3 1 ga old in the quadrilatero ferrifero a detrital zircon from the uppermost formation in the minas supergroup sabara formation is concordant at 2125 4 ma and provides the first age constraint on the deposition of the supergroup monazite from two pegmatites and titanite from an amphibolite enclave in gneisses from the bacao complex in central quadrilatero ferrifero yielded ages between 2060 ma and 2030 ma these data may constrain the minimum age for the deposition of the minas supergroup in addition they indicate that the early proterozoic transamazomian orogeny is represented by amphibolite facies metamorphism and partial melting of archean crust

age and isotopic composition of late archean leucogranites implications for continental collision in the western superior province u pb and sm nd isotopic data are presented for leucogranites and pegmatites from the boundary zones of the english river winnipeg river and wabigoon subprovinces in the late archean superior prov

simultaneous resetting of the muscovite k ar and monazite u pb geochronometers a story of fluids terra nova 23 390 398 2011 abstract although water is ubiquitous in the continental crust its effect on geochronometers through mineral reequilibration is rarely taken into account herein we present 40ar 39ar analyses on muscovite and u pb isotopic data on zircon and monazite from a variscan syn tectonic granite from western france both the k ar in the muscovite and u pb in the monazite isotopic systems were hydrothermally reset whereas the u pb radiogenic system in most of the zircons was unaffected and dates the granite emplacement age titanium chemical maps obtained on muscovites from various dated samples display a spectacular overprinting of their magmatic zoning resulting from increasing fluid rock interaction these results reiterate the need to combine geochronological data with petrological mineralogical and geochemical studies to accurately interpret ages obtained in this type of geodynamical settings

neoproterozoic high pressure metamorphism and tectonic constraint from the nappe system south of the sao francisco craton southeast brazil abstract the neoproterozoic giant nappe system exposed south of the sao francisco craton underwent a minimum of 150 km of near horizontal northeastward displacement this nappe system comprises an uppermost unit derived from a plutonic magmatic arc terrane with high pressure high temperature intermediate to mafic granulites at its base socorro guaxupe nappe underlain in sequence by a high pressure kyanite granulite nappe an amphibolite facies metapelite nappe and finally by a quartzite nappe which forms the lowest part of the pile and rests on a parautochthonous unit related to the passive margin of the craton the kyanite granulites crystallized ca 13 kbar 750 c and have only at their top sillimanite related to t increase overprinting t 890 c a consequence of downward heat advection from the overlying socorro guaxupe granulites equilibrated at 900 c pressures of 13 14 kbar are documented in the underlying metapelite nappe with temperatures of 640 670 c in which lenses of eclogite indicate p max of ca 17 5 kbar phyllites of the parautochthonous unit are directly overlain by hp granulites in the north and record p 7 kbar and t 500 c the distribution of metamorphic facies is reminiscent of inverted metamorphism with eclogites from subduction related metamorphism and kyanite granulites from early extrusion of subducted continental crust the metamorphic conditions of the parautochthon may represent a stage achieved during late metamorphic thinning of the nappe pile the overall picture suggests that high pressure units recrystallized in a subduction zone located to the wsw the frontal thrusts of the nappe system show a late north northeastward transported thin skinned pattern

cosmogenic exposure and erosion history of australian bedrock landforms exceptionally high activities of in situ produced 1 0 be and 2 6 al indicate that australian bedrock surfaces are some of the most stable in the world these cosmogenic nuclides demonstrate that australian granite exposed and sampled at 10 sites along a transect from the eyre peninsula 33 s to the kakadu area in the northern territory 14 s has in some places eroded only decimeters over the past million years however nuclide activities are not saturated in any of the 61 exposed samples we analyzed mandating that the surfaces we sampled are losing mass albeit slowly over time such mass loss indicates that inselbergs are dynamic landforms confounding the assignment of discreet ages to inselberg surfaces nevertheless the differential between slow rates of erosion measured on the very stable uppermost parts of these landforms and the more rapid rates measured below their flanks and below the adjacent grus covered planes suggests that the forms of many large inselbergs which stand meters to tens of meters high must be at least tertiary in age and possibly much older activities of 1 0 be and 2 6 al in 61 exposed australian samples range from 5 1 0 1 10 6 to 5 3 0 6 x 10 5 atoms g 1 and 2 1 0 1 x 10 7 to 3 4 0 5 x 10 6 atoms g 1 respectively normalized to sea level at latitudes of 60 using only neutron scaling activities of 1 0 be and 2 6 al in seven shielded samples 3 5 13 m below the surface are much lower ranging from 3 4 0 2 x 10 4 to 7 0 0 1 x 10 4 atoms g 1 and 1 6 0 1 x 10 5 to 2 8 0 2 x 10 5 atoms g 1 respectively 2 6 al 1 0 be ratios of exposed samples range from 3 89 0 19 to 6 29 0 82 if 2 uncertainty ranges and a nominal sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 are considered ratio data for all but one surface sample are consistent with continuous surface or near surface exposure and or erosion rock surfaces farther north in australia where the climate is more humid have lower nuclide activities thus we infer that surface stability is inversely related to mean annual precipitation from 61 exposed samples we calculated maximum limiting single nuclide model erosion rates of 0 3 0 1 to 5 7 1 0 m m y and minimum limiting single nuclide model exposure ages of 105 16 to 1310 190 ka by assuming a sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 seven shielded samples in which the nuclide inventory is muon generated also have nuclide activities consistent with similarly low rates of erosion but over even longer time scales it appears that the eyre peninsula inselbergs have been and are eroding so slowly that they may well be direct descendents of cenozoic and perhaps even mesozoic forms

origin of the giant allard lake ilmenite ore deposit canada by fractional crystallization multiple magma pulses and mixing abstract the late proterozoic allard lake ilmenite deposit is located in the havre saint pierre anorthosite complex part of the allochtonous polycyclic belt of the grenville province presently the world s largest fe ti oxide deposit it had a pre mining amount in excess of 200 mt at grades over 60 wt hemo ilmenite the main ore body is a funnel shaped intrusion measuring 1 03 1 10 km and 100 300 m thick two smaller bodies are separated by faults and anorthosite the ore is an ilmenite rich norite or ilmenitite made up of hemo ilmenite hem22 6 29 4 66 2 wt on average andesine plagioclase an45 50 aluminous spinel and locally orthopyroxene whole rock chemical compositions are controlled by the proportions of ilmenite and plagioclase orthopyroxene which supports the cumulate origin of the deposit ore forming processes are further constrained by normal and reverse fractionation trends of cr concentration in cumulus ilmenite that reveal multiple magma emplacements and alternating periods of fractional crystallization and magma mixing mixing of magmas produced hybrids located in the stability field of ilmenite resulted in periodic crystallization of ilmenite alone the unsystematic differentiation trends in the allard lake deposit arising from a succession of magma pulses hybridisation and the fractionation of hemo ilmenite alone or together with plagioclase suggest that the deposit formed within a magma conduit this dynamic emplacement mechanism associated with continuous gravity driven accumulation of fe ti oxides and possibly plagioclase buoyancy in a fractionating ferrobasalt explains the huge concentration of hemo ilmenite the occurrence of sapphirine associated with aluminous spinel and high alumina orthopyroxene 7 6 9 1 wt al2o3 lacking exsolved plagioclase supports the involvement of a metamorphic overprint during the synchronous ottawan orogeny which is also responsible for strong textural equilibration and external granule of exsolved aluminous spinel due to slow cooling