revisiting the lushan taihua complex new perspectives on the late mesoarchean early neoarchean crustal evolution of the southern north china craton abstract the taihua complex in the lushan area was divided into gneisses series and supracrustal rocks the former is mainly composed of ttg gneisses and amphibolites and records the late mesoarchean early neoarchean crustal evolution of the southern north china craton ncc late mesoarchean amphibolites 2 84 ga are enriched in light rare earth elements lrees and large ion lithophile elements liles with negative nb ta and ti anomalies derived from partial melting of a metasomatic mantle source late mesoarchean ttg gneisses 2 81 ga have high la yb and sr y ratios and low mgo cr and ni contents and are interpreted as resulting from partial melting of a thickened lower crust with residual garnet and amphibole in the source early neoarchean amphibolites 2 80 2 73 ga show flat ree patterns but slightly negative nb ta and ti anomalies due to the fractionation of ti rich minerals and have depleted hf nd isotopes and were derived from large degree partial melting of a depleted mantle source most of the early neoarchean ttg gneisses show pronounced positive eu anomalies and have relatively lower trace element concentrations and more depleted nd hf isotopes than the late mesoarchean ttg gneisses resulted from the partial melting of thickened juvenile lower crust with residual garnet and amphibole in the source and subsequent plagioclase accumulation in addition some of the early neoarchean ttg gneisses have high mgo cr and ni contents which were likely derived from partial melting of delaminated lower crust or a thickened lower crust interacting with mafic melt late mesoarchean amphibolites and ttg gneisses are restricted in the center of lushan area denoting an ancient continental nucleus in contrast early neoarchean amphibolites and ttg gneisses outcrop in peripheral of the ancient nucleus exhibiting as an elongated belt along the dangzehe river which is evidence for the subduction overall the lushan amphibolites and ttg gneisses show slightly negative to positive whole rock end t and ehf t values and zircon ehf t values indicating a dominant crustal accretion with subordinate crustal reworking therefore the continental growth recorded in the lushan taihua complex was caused by the subduction accretion process suggesting a convergent margin in the southern ncc during the late mesoarchean and early neoarchean

low pressure differentiation of tholeiitic lavas as recorded in segregation veins from reykjanes iceland lanzarote canary islands and masaya nicaragua segregation veins are common in lava sheets and result from internal differentiation during lava emplacement and degassing they consist of evolved liquid most likely replaced by gas filter pressing from a 50 crystallised host lava pairs of samples host lavas and associated segregation veins from the reykjanes peninsula iceland lanzarote canary islands and the masaya volcano nicaragua show extreme mineralogical and compositional variations mgo in host lava segregation veins and interstitial glass ranges from 8 10 wt 3 6 wt and to less than 0 01 wt respectively these samples allow the assessment of the internal lava flow differentiation mechanism since both the parental and derived liquid are known in addition to the last magma drops in the form of late interstitial glasses the mineralogical variation mass balance calculated from major and trace element composition and transitional metal partition between crystals and melts are all consistent with fractional crystallisation as the dominant differentiation mechanism the interstitial glasses are highly silicic sio2 70 80 wt and represent a final product of high degree 75 97 fractional crystallisation of olivine tholeiite at a pressure close to one atmosphere the tholeiitic liquid line of decent and the composition of the residual melts are governed by the k2o na2o of the initial basaltic magma the granitic minimum is reached if the initial liquid has a high k2o na2o whereas trondhjemitic composition is the final product of magma with low initial k2o na2o

forty years of ttg research abstract ttgs tonalite trondhjemite granodiorite are one of the archetypical lithologies of archaean cratons since their original description in the 1970s they have been the subject of many studies and discussions relating to archaean geology in this paper we review the ideas concepts and arguments brought forward in these 40 years and try to address some open questions both old and new the late 1960s and the 1970s mark the appearance of grey gneisses ttg in the scientific literature during this period most work was focused on the identification and description of this suite and the recognition that it is a typical archaean lithology ttgs were already recognised as generated by melting of mafic rocks this was corroborated during the next decade when detailed geochemical ttg studies allowed us to constrain their petrogenesis melting of garnet bearing metamafic rocks and to conclude that they must have been generated by archaean geodynamic processes distinct from their modern counterparts however the geodynamic debate raged for the following 30 years as many distinct tectonic scenarios can be imagined all resulting in the melting of mafic rocks in the garnet stability field the 1990s were dominated by experimental petrology work a wealth of independent studies demonstrated that melting of amphibolites as well as of mafic eclogites can give rise to ttg liquids whether amphibolitic or eclogitic conditions are more likely is still an ongoing debate from 1990s onwards one of the key questions became the comparison with modern adakites as originally defined these arc lavas are reasonably close equivalents to archaean ttgs pending issues largely revolve around definitions as the name ttg has now been applied to most archaean plutonic rocks whether sodic or potassic irrespective of their hree contents this leads to a large range of petrogenetic and tectonic scenarios a fair number of which may well have operated concurrently but are applicable only to some of the rocks lumped together in the ever broadening ttg bin

the lefkada barrier and beachrock system nw greece controls on coastal evolution and the significance of extreme wave events abstract the lefkada preveza coastal zone nw greece is characterised by an active barrier system and related extensive beachrock sequences besides the gradual coastal processes of longshore drift and spit evolution the presence of active tectonics and the occurrence of tsunamis have been documented in previous studies and are part of the coastal geomorphological system in this paper we present the results of detailed multi proxy sedimentological and geomorphological investigations carried out along the northern part of the barrier system and in back beach positions our findings suggest that extreme wave events contributed to coastal and environmental changes and involved temporary breakdown of the barrier system sedimentary findings suggest that one generation of event deposits may be related to the 365 ad crete earthquake and associated tsunami according to our results the lefkada coastal system formed by the interaction of both long term gradual and sudden impulsive littoral geomorphodynamics extreme wave events are assumed to have played a significant role in the evolution of the present coastline acting as recurrent impulsive disturbances of the coastal system subsequently the onset of long term gradual coastal processes such as longshore drift re established a state of natural coastal balance by re arranging the coastal sediments

coarse clastic barrier environments evolution and implications for quaternary sea level interpretation abstract this paper reviews recent work particularly from eastern canada on the dynamics and evolution of coarse clastic barriers it is argued that an understanding of quaternary coastal changes on paraglacial glacially influenced coasts can only be achieved with a knowledge of gravel barrier morphodynamics and sedimentation gravel barriers are distinctive coastal forms in which morphological inheritance and sediment sorting provide major behavioral controls spatially adjacent gravel barriers may display different depositional tendencies prograde seawards migrate landward or aggrade vertically such inconsistent spatial behaviour must be considered in terms of an erosional front advancing landward under stationary or rising sea level redistribution of sediment across or along the erosional front supplies sediment for the development of gravel barriers which in turn provides environments for fine grained deposition which is favourable for further barrier migration an example of an erosional front is given from chezzetcook inlet nova scotia three stages are recognized in the development of gravel barriers starting with the initiation of small drift aligned forms at the leading edge of the erosional front as sea level rises this is followed by a period of consolidation and stabilization when drift aligned forms may become swash aligned conditions for this transition are discussed under rising sea levels it is difficult to explain the conditions leading to the formation of multiple parallel swash aligned ridges although three hypotheses are advanced all of which may operate in different locations the third stage is associated with the breakdown of barriers as sediment supply fails and or sea level rises drift aligned forms are inherently unstable and show signs of pre breakdown stress in the form of reworking and remobilization of proximal sediments into cells swash aligned barriers may be breached revert to drift alignment become segmented or be overstepped some gravel is re incoporated in barriers farther landward while other material is passed seaward of the erosional front and becomes abandoned on the shoreface gravel barriers may exert a major influence on estuary and back barrier environments especially where they control the depositional record the implications for the reconstruction and interpretation of quaternary environments are summarized

the solubility of gypsum in calcareous soils abstract three gypsiferous calcareous soils from the al hassa oasis in saudi arabia were examined to determine the conditions under which dissolution of gypsum could be hindered by the formation of coatings of calcite during leaching batch extraction with water of a sandy clay loam a sandy clay and a sandy loam containing 40 26 and 5 gypsum and 14 12 and 13 calcite respectively was followed by chemical analysis of the extracts sem examination and xrd and edx microprobe analysis extraction in closed centrifuge tubes for 1 h or 5 h showed that initially gypsum dissolved to give solutions near to equilibrium but then in the sandy clay loam between one quarter and one third of the gypsum could not dissolve in the sandy clay about one fifth of the gypsum could not dissolve with none remaining in the sandy loam all the extracts were close to equilibrium with calcite sem and edx examination showed that coatings of calcite had formed on the gypsum particles the sandy clay loam was also extracted using an open system in which either air or air 1 co2 was bubbled through the suspensions for 1 h with stirring the gypsum dissolved more rapidly and all of the gypsum dissolved thus where the rate of dissolution of gypsum was rapid calcite did not manage to cover the gypsum surfaces probably because the surface was being continuously removed slower leaching conditions in the field are likely to be conducive to the formation of coatings and less dissolution of gypsum

the motion of large bottom particles cobbles in a wave induced oscillatory flow the purpose of this paper is to present the results of a series of experiments aimed at better understanding the dynamics of the motion of large bottom particles cobbles in a wave induced oscillatory flow this problem is closely related to the motion of cobbles along the bottom in an oscillatory flow such as occurs in coastal waters beyond the region of wave breaking the aims of the study were i to mimic this process in laboratory experiments and ii to develop a physical model to predict cobble movements the oscillatory flow was created in a long tank of rectangular cross section using standing waves of large amplitude objects of different shapes spheres and disks were placed in the flow and their subsequent motion along the tank floor was studied the results of the observations were compared with the predictions of a theoretical model for the range of parameters used in the experiments shape size aspect ratio and density of cobbles amplitude and frequency of the oscillatory flow and bottom friction reasonable agreement between the measured and calculated values of the cobble displacements as a function of time was obtained

the relationship between the rate of mesoscale sea level rise and the rate of retreat of swash aligned gravel dominated barriers abstract in theory a rise in sea level should force swash aligned gravel barriers to retreat landwards evidence from three single crested swash aligned gravel barriers from eastern canada and northwest europe indicates that barrier retreat rate correlates with the rate of sea level rise measured over the lower end of the mesoscale time spectrum subdecadal 10 0 yr 10 1 yr there is also a relationship between a barrier s rate of change in retreat rate and the decadal mesoscale mean rate of sea level rise specified by the duration of the tide gauge record 10 1 yr 10 2 yr specifically the higher the decadal mesoscale sea level rise rate the faster the rate of retreat of the swash aligned gravel barrier however this latter relationship may also be a function of the barrier s inertia as defined by the barrier s cross sectional volume in that barrier retreat rate correlates negatively with barrier inertia

wave energy and clast transport in eastern tasman bay new zealand coarse gravel beaches are common features along the eastern margin of tasman bay at the north end of south island new zealand although these features have traditionally been interpreted as spits contemporary incident wave energy appears too small to transport boulders and cobbles persistently along the beaches and platforms by longshore drift an alternative explanation suggests that boulder beaches are essentially derived in situ from resistant bedrock which lies seaward and was buried by gravel during the holocene sea level rise wind wave and clast size data from cable bay and the nelson boulder bank were used to resolve this problem wave and wind data indicate that waves reaching these areas are derived locally in tasman bay and are limited in size and energy hindcasting predicts a 4 7 m wave could propagate from tasman bay however during cyclone yalli the most intense storm in nearly 40 years of wind records the largest wave measured in the nearby area of cable bay was only 2 7 m high maximum orbital velocity on the seabed beneath a 4 7 m is calculated to be 2 9 m s 1 which cannot initiate transport of clasts greater than 0 15 m in diameter clasts on the gravel platforms have average diameters greater than this but some clasts may be as large as 1 0 m in diameter by comparison a swash run up method predicts that a wave 4 7 m high can transport clasts no larger than 0 3 m in diameter these data and approximate calculations strongly suggest that the present wave environment in eastern tasman bay is not capable of consistently transporting clasts on the boulder platforms by longshore drift reduced sea levels in the pre holocene period would further reduce wave energies available in tasman bay copyright 2006 john wiley sons ltd

multiple ways of producing intermediate and silicic rocks within thingmuli and other icelandic volcanoes major and trace element compositions of rocks and coexisting phenocrysts of the thingmuli volcano suggest a revision of the existing models for the formation of intermediate and silicic melts in iceland the new data define two compositional tholeiitic trends with a significant gap between them a high iron trend hfe contains 6 14 wt total feo in silicic rocks with c 1 wt mgo as well as sodic plagioclase and hedenbergite phenocrysts a low iron trend lfe contains 3 5 wt feo at c 1 wt mgo which is typical of iceland but higher than morb compositions the most evolved phenocrysts of the lfe trend do not reach iron rich end members the hfe trend is interpreted as a result of fractional crystallization numerical modelling using the melts algorithm suggests that crystallization took place under redox conditions constrained to one log unit below the fayalite magnetite quartz oxygen buffer fmq 1 the lfe trend is explained by a combination of mixing between rhyolite and ferrobasalt assimilation of hydrated crust and fractional crystallization under higher redox conditions fmq the two trends and the gap are best defined in a plot of mg versus sio2 that is useful to unravel petrogenetic processes for example intermediate and silicic rocks of the holocene volcanic systems of spreading rifts e g krafla propagating rifts e g hekla and off rifts oraefajokull also fall into high and low iron fields and outline a gap similar to thingmuli the identification of two compositional trends in erupted intermediate and silicic volcanic products shows that processes in the deep roots of single volcanic systems are highly diverse and likely controlled by local variations in the thermal gradients and the extend of hydrothermal alteration generalizations about the relationship between the compositions of intermediate and silicic rocks and plate tectonic setting therefore should be avoided

palaeoshorelines of glacial lake kuray chuja south central siberia form sediments and process glacial lake kuray chuja which occupied the kuray and chuja basins during the quaternary period marine isotope stages 2 and 3 left distinct shoreline features around the basin margins at the greatest extent the lake had a surface area of 2951 km2 with wind fetches up to 70 km wind waves constructed erosional erosional accumulative and accumulative strandlines the latter including spits tombolos barrier beaches and offshore bars strandlines range in altitude between c 1600 and 2100 m the range in altitudes demonstrating lake level variations through time the shoreline forms and stratigraphy are detailed particular attention is given to the presence of pocket beaches on rock coasts the alluvial strandlines of which have distinctive alongshore gradients although reasonably ascribed to regional differential tectonic uplift the possibility that the local alongshore gradients are augmented as a process response to alongshore drift of sediment in a sediment starved system of closed coastal cells is explored using a simple numerical model

assessing geomorphological and pedological processes in the genesis of pre desert soils from southern tunisia abstract arid environments are fragile and the associated soils are subject to serious threats like water deficiency erosion salt accumulation and loss of fertility in this context understanding the processes involved in soil genesis may contribute toward protecting land from degradation this study highlights the interconnection between geomorphic and pedogenetic processes in soil formation of the jeffara plain a pre saharan area of southern tunisia to reach this goal one coastal oasis chenini nahel and two inland environments matmata nouvelle and menzel habib were studied after geomorphological and pedological surveys the soils were sampled by genetic horizons and characterized by physical mineralogical and chemical analyses and by microscope observation field observations and laboratory data suggest that soil formation in the jeffara plain was a combination of additions and losses controlled by climate changes at chenini nahel the soils developed by accumulation of wind blown sediments coming from a close area dominated by gypsum bearing rocks at matmata nouvelle the soils mainly formed from sedimentation of repeated mudflows during a rainy period between 9000 and 5000 years before present followed by drought periods finally the soils of menzel habib developed from an early gypsum formation in the presence of a salt rich water table and repeated cycles of sedimentation deflation of wind blown materials the different genesis of these pre desert soils produced characteristic b horizons byy horizons with poorly developed soil structure at chenini nahel bw horizons with a hard rupture resistance at matmata nouvelle and bk horizons at depth due to intense sedimentation with ca bc horizons at the surface due to the accretion of wind blown materials at menzel habib

coastal barriers nomenclature processes and classification issues abstract the designation coastal barrier related terms and their varied interpretations and critical concepts in coastal plain and nearshore geology underwent numerous reincarnations over the years this designation was first applied to shore parallel sand and gravel built ocean front islands and spits that separate open marine environments from paralic inshore environments that they shelter a more recently recognized third category includes mainland strandplain chenier and dunefield barriers either as original components of mainland coasts or subsequently welded to the coastal plain a parallel but closely related terminology developed mostly in australia and brazil identifies several specific process categories recognizable in the three basic barrier groups in the absence of lagoons and tidal wetlands shore ridges that front and are contiguous with the mainland coastal plain have been mistakenly assigned to the barrier island category greatly diminished wave energy and consequently minor littoral drift volumes account for the relative rarity and much smaller dimensions of prograded landforms in estuarine islands and bay shore beaches in paralic inshore basins due to wave and related littoral drift processes however diminished in comparison with open marine shores morphological similarities between aggraded landforms of open marine through estuarine settings are to be expected however the multitude of proposed fetch limited diminished wave energy estuarine islands characterized by diminutive narrow beaches sand spits even occasional small dunes and miniature strandplains lack the essential functional attributes intrinsic to true barrier islands while barrier islands may form even on relatively low wave energy and or sediment deficient marine shores the term is inappropriate for islands located in low energy paralic basins including estuaries or in coastal plains where frontal shore ridges are not backed by lagoons landforms erroneously ascribed in a variety of facies settings as barrier islands or islands frequently are mainland attached beach ridge plains or beach fringed marshlands instead narrow marshland beaches and mainland strandplain barriers are segmented into short islands by intervening narrow tidal creeks fluvial distributary channels or storm cuts that separate them improved fundamental and functional definitions of barrier islands their comparison with the many genetic categories of islands and mainland shore beaches found in estuarine basins and wetlands should lead to a better understanding of paralic island evolution processes on the global scale

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

storm generated dune armouring on a sand gravel barrier system southeastern ireland abstract artificial armouring of beaches and dunes by rockfill is a common response by man following wave induced erosion during severe storms the rarer occurrence that of natural armouring of the seaward edge of a dune system perched as crest decoration on top of a transgressive sand gravel barrier system has been recorded at carnsore point southeastern ireland wave lain stratified coarse sand to fine gravel has been banked against the seaward dune face in the form of ramps at heights of 2 6 m above mean spring high water which effectively armours the dune face from further erosion recent ramps plus deposits of past ramps merge laterally into washover deposits which suggests a common storm origin for both washover deposits and ramps the height of ramp building and dune overtopping above mhws also indicates that severe storms are required to generate sufficient run up to move beach sediment to these elevations ramps are associated with the presence of a supratidal gravel dominated beach terrace ramp building appears to require the conjunction of a severe storm plus surge and high spring tide in order that the swash can reach over the terrace to the dune face the absence of the terrace during severe storms allows swash to erode the dune face while the presence of the terrace acts as a buffer to protect the dune face during storms coincident with a neap tide a model is presented to account for the transformation of erosional storm waves into constructional swash run up by the filtering mechanism of the remnant supratidal terrace

boulders as a signature of storms on rock coasts this paper is the first review of coastal boulder studies it serves as a peer reviewed introduction to a special issue on the topic of boulders as a signature of storms on rock coasts since 2004 and the indian ocean tsunami most coastal boulder research has been focused on using boulders as sedimentary signatures of palaeo tsunami events and the most commonly used transport equations typically suggest that large boulder deposits are products of tsunami rather than storms there is growing empirical evidence demonstrating on inter annual to century timescales that storm waves are capable of transporting and depositing boulders of significant size at elevations well above sea level current process studies of how boulders are eroded transported and deposited have not received wide attention by rock coast geomorphologists or palaeoenvironmental reconstruction scientists this special issue is framed around the goal of highlighting our current understanding of the role of storm waves as a driving mechanism for boulder erosion transport and deposition here we review the current state of knowledge about boulder dynamics boulder responses to storms and boulders as sedimentary signatures of storm events we identify gaps in our conceptual and quantitative understanding lastly we propose means of addressing research gaps improving consistency between researchers and collecting multi purpose data this review and the papers contained within the special issue provide an improved understanding of coastal dynamics particularly the role storms can play in influencing erosion rates and depositional patterns of coarse material i e boulders or larger which has hitherto been under represented in the literature

headlands and offshore islands as dominant controlling factors during late quaternary barrier formation in the forster tuncurry area new south wales australia abstract pleistocene and holocene barrier systems along the coast of southeast australia differ from those of the coastline of the eastern u s a and elsewhere there are no continuous barrier island chains along the coast of new south wales such chains developed only in eastern victoria in new south wales pleistocene and holocene barriers were built within rocky embayments along the coastline the forster tuncurry coastal zone of central new south wales is an excellent example of such embayment it is a mosaic of sedimentary environments that covers about 270 km 2 and includes late pleistocene bay barriers holocene beach ridges tide dominated channels mudflat islands peripheral tidal flats lake sediments and nine beaches of various types headlands and offshore islands played a dominant role in the sedimentary process marine sediment washed into the embayment by refracted waves formed the following type of bay barriers a bay barrier between mid bay headland and an offshore island b between two opposing mid bay headlands and c two barrier types between the outer headlands of the bay mouth and the large centrally located offshore island these barriers are seen as beach ridges in the northern half of the embayment and a lagoon barrier in the southern half the large centrally located cape hawke was an island and the most significant of these features dividing the bay into two compartments through time laterally accreting barriers were generated in the northern compartment and a lagoon barrier was created to the south

the role of relative sea level rise and changing sediment supply on holocene gravel barrier development the example of porlock somerset uk the holocene development of the coastal system at porlock has been driven by variations in the rate of relative sea level rise providing a long term control on longshore sediment supply which in t

postglacial evolution of coastal barriers along the west pomeranian coast ne germany abstract the aim of this study is to present an evolutionary model of the coastal barriers in west pomerania regarding both morphological development and chronostratigraphy the study area is situated on the islands of rugen and usedom in the tideless sw baltic to reconstruct the geological setting 250 cores were collected 20 new radiocarbon dates allow a description of the late pleistocene to holocene evolution of the barriers in all areas investigated the lithofacies sequences are similar which enables the derivation of a general evolutionary model for the sw baltic sea coasts the controlling factors are the relief of the early holocene landscape as well as the sea level history of the baltic sea the base is made up of a pleistocene till the deposition of this till had already determined the configuration of the present day coast late pleistocene to early holocene freshwater deposits follow in the columnar section often overlain by peat during the main phase of the transgression 8000 6000 before present bp the early holocene landscape was drowned and mud accumulated in the depressions beach ridges attached to pleistocene headlands began to develop at 6000 bp simultaneously landward of the beach ridges sediment accumulated in wind flats this depositional environment which can still be recognised along the coast today is controlled by wind driven currents a second peat layer younger than 1000 bp makes up the uppermost part of the sequence in most of the lowland sites the evolution of the coastal barriers in west pomerania follows the scheme developed for tidal paraglacial coasts this study adjusts the scheme to the regional stratigraphy and extends it with regard to tideless conditions and the evolution of wind flats

volgo uralia the first u pb lu hf and sm nd isotopic evidence of preserved paleoarchean crust the crustal segment volgo uralia is the least known part of the east european craton its crystalline crust is hidden beneath a thick neoproterozoic to phanerozoic cover but disclosed by thousands of drill holes in conjunction with the recent tatseis reflection seismic profile we conducted the first isotopic study of the bakaly granitoid block in eastern volgo uralia which represents a subsurface section of the layered upper middle crust the study included whole rock sm nd and ion probe zircon u th pb sims and lu hf la icpms analyses of granitoids from seven drill cores the bakaly block was also targeted because its rocks have never been subjected to granulite facies metamorphism making it possible to date pristine pre metamorphic zircon our study showed that the four principal suites of granitoids in the bakaly block are different in age each corresponding to a particular stage of archean crustal evolution between 3 3 and 2 6 ga the tashliar monzonitic suite belonging to an alkaline series yielded zircon ages of 3 3 and 3 2 ga which are the oldest ages yet found in volgo urafia the epsilon hf t values of the dated zircon and the epsilon nd t values of their host rocks indicate that a paleo to eoarchean protolith with model t dm ages up to 3 8 ga had been involved in the formation of the tashliar melts three neoarchean rock suites one comprising quartz dioritic and tonalitic gneisses the bak 1 another k rich granodiorites granites and migmatites the bak 2 and the third monzonitic granitoids the aktanysh suite were formed sequentially between 2 72 and 2 60 ga the 2 72 ga bak 1 suite is chemically diverse it includes granitoids of the ttg type related to slab subduction melts as well as rocks formed by the re melting of older crust with whole rock nd t dm and hf t dm model ages of 3 4 to 3 2 ga the 2 69 to 2 65 ga bak 2 suite was probably associated with a major collisional event which defined the stacked structure of the archean crust in volgo uralia and its seismic layering our data suggest that the bak 2 melts originated partly from juvenile sources with epsilon hf t zircon values up to 4 8 as well as mixed crustal and juvenile mantle materials some crustal contamination of the melts appears to have occurred as evidenced by incorporated xenocrystic zircon the chemical compositions of bak 2 granitoids from the different plutons their zircon epsilon hf values and the hf and nd t dm ages all mirror a heterogeneous collisional crustal structure during post collisional extension at 2 6 ga the intrusion of aktanysh monzonitic granitoids took place these rocks also bear evidence of a long crustal pre history with nd and hf t dm model ages of 3 3 to 3 5 ga the aktanysh rocks are coeval with the tuymazy gabbro norite anorthosite intrusions which are widely distributed along post collisional shear zones in the bakaly block they could have provided the heat necessary to melt the crust at this stage altogether the isotopic evidence suggests several episodes of crustal growth and recycling possibly reaching back to 3 6 and 3 8 ga metamorphic zircon rims show that the archean crust in the bakaly block were subjected to several tectonothermal overprints in the paleoproterozoic between 2 4 and 1 9 ga ago less

observations of morphological change and sediment transport on a steep gravel beach abstract observations of morphological change and swash sediment loads concurrent with measurements of water level waves and currents were obtained during a spring to spring tidal cycle on a steep macrotidal gravel beach in southwest england the wave conditions experienced during the field experiment were relatively calm and the significant inshore wave height and period averaged 0 4 m and 6 s respectively incident frequency water motions dominated the hydrodynamics and the phasing between water surface elevation and cross shore and alongshore currents was inconsistent with standing edge wave motion morphological change was directly related to maxima in shoreline elevation and four modes of berm adjustment identified regression and rollover in response to falling and rising water levels respectively and removal and reformation during and after storms respectively swash processes transported substantial amounts of sediment at rates comparable to sand beaches and the net transport under modal wave conditions was estimated to be 1 kg per swash onshore per unit metre beach width steep hydrodynamic gradients induced by the abrupt slope breaks of the step and berm are one of the main causes of the large morphological variability characteristic of gravel beaches

coastal barriers fresh look at origins nomenclature and classification issues abstract based on numerous publications and field work on the northern gulf of mexico coast u s and other coastal areas the present objective is to meet the need for an improved system of the definition and classification of barriers and their components this topic includes morphological and functional interrelationships between beach ridges barriers and similar landforms the term beach ridge was applied to a plethora of sub and supratidal ridge types in contrast the presently proposed definition restricts the term to relict berm and foredune ridges composed of sand or gravel and stabilized after isolation from shore zone of active processes barriers sustain paralic hydrology sediment biotic and nutrient condition in the coastal realm in combination with adjacent lagoons and river deltas these landforms represent physical barriers that lessen marine and related influences in brackish paralic coastal environments benefiting from historic evolution of concepts and nomenclature the task also involves the correction of misattributions rooted in early publications island spit and mainland barriers thus maintain lower salinities reduce wave erosion protect nutrient rich paralic deposits and mitigate storm induced inundation fetch limited lagoonal barrier islands are considered valid barriers only in lagoons where they face inlet transmitted full marine conditions mainland barriers of several subcategories often are important sediment archives of past sea levels hydroclimate climate and tectonic isostatic changes they consist mostly of ridgeplains at the start firmly attached or later migrated and welded to the mainland shore in addition to local hydrodynamic and topographic influences formation conditions may reflect overall paleogeographic conditions including fluvial impact in progradational regressive island settings barriers consist mainly of strandplains that laterally may alternate with narrow spit like sectors they include only single marine respectively lagoon side shore ridges with secondary dune fields sandwiched between them field observations and drillcore studies of microfossil and sediment based depositional facies suggest that most barrier islands originated by the often underestimated shoal aggradation mode two additional genetic models are recognizable a fourth remains hypothetical remotely sensed images indicate that post hurricane regeneration of the largest deltaic barrier chain in the gulf of mexico stalled in recent years late pleistocene barriers significantly influenced present coastal landforms in two extensive regions dramatic changes in past decades indicate that sea level rise and stormier future hydroclimate may likely accelerate the degradation of deltaic and non deltaic barrier islands

decadal scale gravel beach evolution on a tectonically uplifting coast wellington new zealand uplift of the shoreline in tectonically active areas can have a profound influence on geomorphology changing the entire process dynamics of the coast as the landforms are removed from the influence of the sea over decadal timescales it is possible for the landforms to return to their pre earthquake condition and this paper examines the re establishment of mixed sand and gravel beaches on the coast of wellington new zealand subsequent to an uplift event in 1855 over 60 topographic profiles were surveyed seven sets of aerial photographs from a 67 year period were mapped and sediment size analyses conducted in order to quantify the nature of beach change following uplift and associated relative sea level fall these data were supported by surveys using ground penetrating radar it is found that uplift raised the gravel beaches out of the swash zone thereby removing them from the littoral zone intertidal rocky reefs which occur between each embayment were also uplifted during the same event and completely interrupted the longshore transport system continued input of gravel material to the littoral zone allowed beaches to re establish sequentially along the coast as each embayment was infilled with sediment this reconnection of the embayments with the longshore drift system is associated with the beach planform being initially drift dominated during infill but then switching to swash alignment once the embayment becomes infilled this has resulted in shoreline accretion of over 100 m in some places at rates of up to 4 m yr covering shore protection works built in the past few decades the ability of the shore to adjust back to its pre uplift condition appears to be a function of the accommodation space created during uplift and the rate of sediment supply copyright 2012 john wiley sons ltd

the importance of extratropical and tropical cyclones on the short term evolution of barrier islands along the northern gulf of mexico usa abstract data are presented indicating the complexity and highly variable response of beaches to cold front passages along the northern gulf of mexico in addition to the impacts of tropical cyclones and winter storms within the past decade an increase in the frequency of tropical storms and hurricanes impacting the northern gulf has dramatically altered the long term equilibrium of a large portion of this coast a time series of net sediment flux for subaerial and nearshore environments has been established for a section of this coast in florida and to a lesser extent mississippi the data incorporate the morphological signature of six tropical storms hurricanes and more than 200 frontal passages data indicate that 1 barrier islands can conserve mass during catastrophic hurricanes e g hurricane opal a strong category 4 hurricane near landfall 2 less severe hurricanes and tropical storms can promote rapid dune aggradation and can contribute sediment to the entire barrier system 3 cold fronts play a critical role in the poststorm adjustment of the barrier by deflating the subaerial portion of the overwash terrace and eroding its marginal lobe along the bayside beach through locally generated high frequency steep waves and 4 barrier systems along the northern gulf do not necessarily enter an immediate poststorm recovery phase although nested in sediment rich nearshore environments while high wave energy conditions associated with cold fronts play an integral role in the evolution and maintenance of barriers along the northern gulf these events are more effective in reworking sediment after the occurrence of extreme events such as hurricanes this relationship is even more apparent during the clustering of tropical cyclones it is anticipated that these findings will have important implications for the longer term evolution of barrier systems in midlatitude microtidal settings where the clustering of storms is apparent and winter storms are significant in intensity and frequency along the coast

examination of mesoscale forcing of a swash aligned gravel barrier from nova scotia abstract the possibility by which the retreat of a swash aligned gravel barrier on nova scotia s atlantic coast may be influenced by varying mesoscale time domains of differential process conditions is examined tide gauge data are used to generate definition of mesoscale process domains regarded as influential in barrier behaviour semi diurnal high water tidal residuals from halifax nova scotia tide gauge 1920 1990 are characterised for both surge magnitude and frequency on an annual basis these two variables are combined to define three event types of annual surge histories first order n th step markov analyses show that significant memory exists in 6 year and 22 year transitions between surge event types the longer transition sequence mirrors a major decadal mesoscale domain change in surge generation which is suggested to be associated with phases of barrier crest reworking that enhance barrier retreat when the domain change occurs the shorter transition sequence may reflect cyclonic activity cycles on the scotian shelf superimposed on the longer term transition

silicic magma petrogenesis in iceland by remelting of hydrothermally altered crust based on oxygen isotope diversity and disequilibria between zircon and magma with implications for morb terra nova 24 227 232 2012 abstract petrogenesis of silicic magmas in iceland has fundamental significance for understanding the relative importance of fractional crystallization of mantle derived basalt and partial melting of hydrothermally altered basaltic crust in formation of the earliest continental crust first results of in situ oxygen isotope investigation of zircons in large volume silicic eruptive products of three volcanoes in iceland askja torfajokull and hekla demonstrate isotope diversity and disequilibria and long u th zircon pre eruptive residence of 103 104 year this suggests that zircons did not grow from their host melts but instead were inherited from older magma batches and leftover cumulates with generally low and variable 18o values this study demonstrates that segregation of cubic kilometres of silicic magma is faster than mineral diffusive or recrystallization time scales estimated at 103 years and it suggests that partial melting of hydrothermally altered and oxidized oceanic crust is the mechanism that best explains silicic rocks in iceland and early earth environments

hawaiian basalt and icelandic rhyolite indicators of differentiation and partial melting in spite of the voluminous basaltic volcanism on the island of hawaii rhyolite is not produced iceland on the other hand exhibits common rhyolitic volcanism amounting to some 10 12 of its surface rocks this contrast is investigated using the fundamental igneous processes exhibited by sheet like hawaiian lava lakes and shonkin sag laccolith in montana highly differentiated residual melts normally reside within inwardly advancing solidification fronts and are generally inaccessible to eruptive processes only when a large initial phenocryst population is present from which a thick basal cumulate can rapidly form is it possible to supply highly differentiated melt into the active i e eruptable portion of the magma chamber although there is protracted control of differentiation at hawaii by settling of olivine further differentiation occurs within the solidification fronts only by repeated transport and holding is it possible to differentiate beyond the critical composition of the leading edge of the solidification front 7 mgo and 51 5 sio2 crystal size distributions csds for hawaii and shonkin sag are used to demonstrate the inferred physical and chemical processes of solidification including the kinetics of crystallization

comment on continental geochemical signatures in dacites from iceland and implications for models of early archaean crust formation by willbold m hegner e stracke a and rocholl a

late holocene sea levels in ireland the course of irish sea levels during the late holocene is not well known yet it is an understanding of this period that will prove crucial in the definition and management of future sea level changes the coastline of ireland embraces wide environmental and glacio isostatic contrasts which serve and to some extent control sea level events at both local and regional scales making definitive resolution of relative sea level changes difficult in the southwest the picture is of inexorable relative sea level rise studies in co kerry show a gradual submergence of terrestrial facies by estuarine and in places marine materials pollen and diatom studies together with 14c dates suggest a decreasing rate of relative sea level rise in the last 2500 years often associated with geomorphological changes sites on the south coast of ireland confirm the evidence from the southwest in cork harbour recent relative sea level rise since 2100 bp was responsible for marginal land submergence while elsewhere rising water levels appear to have caused rapid barrier migrations and coast erosion palaeoenvironmental evidence from this region suggests a distinctive pattern of sea level change associated with sedimentary and or crustal dynamics which is not encountered elsewhere in northwest europe the overall rate of relative sea level change on the south and southwest coasts falls between 0 6 and 1 1 mm year over the last 5000 years in the north there is a clear east to west variation in relative sea level trends following an isostatically controlled peak 3 to 1 m od between 6500 bp east and 3500 bp west falling sea levels from 3500 to 1500 bp have been followed by a general slow rise although there are still local anomalies to this pattern most noticeably at malin head where sea level is currently falling at 2 4mm year relative sea level signatures in ireland differ markedly between the north and south coasts furthermore geomorphological and ecological contexts of this rise vary from east to west providing a complex all ireland framework for future investigations

overwash processes along a gravel beach in south east ireland recent overwashing and to a more limited extent overtopping has occurred on a gravel dominated beach just west of carnsore point in south east ireland at relatively low points swash excursions have breached the duneline and extensive gravel fans have formed on landward facing slopes also at interbreach positions swash ramps have been built up in front of previously eroding dune cliffs allowing overtopping at heights of up to 5 m above mhwost spreading a veneer of sediment over the adjacent dune ridge in both cases events appear to be preceded by erosion and backbeach sand and gravel deposition stratigraphic textural and fabric analyses assist in identifying environmental conditions that prevailed during overwash throat and fan and overtopping ramp sedimentation

artifact preservation and post depositional site formation processes in an urban setting a geoarchaeological study of a 19th century neighborhood in detroit michigan usa a geoarchaeological study was carried out to assess levels of artifact deterioration occurring in a historic period urban soil during the 20th century the study site is a former house lot in a park created in 1919 by demolition of a residential community in detroit michigan usa the results show that despite nearly a century of burial in an urban soil impacted heavily by pollution and other anthropogenic activity many 19th century artifacts are remarkably well preserved the observed weathering stability sequence of glass bone mortar plaster paint is consistent with decreasing solubility product values of the corresponding principal mineral constituent glass apatite portlandite gypsum cerrusite even severely weathered 19th century nails and mortar can often be distinguished using optical petrographic and sem edax methods the excellent state of artifact preservation is attributed to a calcareous soil microenvironment and artificial compaction which limited the weathering effects of water and oxygen artifact preservation was further enhanced by burial beneath a thick biomantle created by the casting activity of an invasive species of earthworm however lumbricus terrestris may now pose the greatest threat to artifact preservation because casting and burrowing activities are decreasing bulk density and promoting the diffusion of air and water into the soil early excavation is recommended to recover artifacts in soils impacted by the combined effects of urban pollution and earthworm burrowing anthropogenic microparticles smaller than those normally classified as microartifacts were found to be useful indicators of human occupation

beach ridges from the varanger peninsula arctic norwegian coast characteristics and significance the most common coastal sedimentary forms on the arctic coast of the varanger peninsula are raised beach ridge plains the majority of the ridges consist of coarse material but there are also sandy beach ridge areas close to the river mouths of some of the major rivers some bays having the same isostatic rebound and dynamic conditions have been studied to test if the number of beach ridges in each locality is significant to prove climatic changes storminess and rates of sediment accumulation or if the number of beach ridges in each bay is only dependent on their intrinsic characteristics and self organization because the number of ridges varies not only from bay to bay but even within the same bay it has to be accounted for by contrasting internal and local evolution sediment supply offshore gradient and coastal evolution these differences between various bays or parts of the same bay invalidate the explanations that global processes planetary orbital forces relative sea level changes or past climatic condition are responsible for beach ridge development

holocene spit development on a regressive shoreline dornoch firth scotland the series of raised and modern spits and beaches which characterise the dornoch firth coastline are described the beaches and spits in the inner firth are relatively small having developed during the mid holocene with little subsequent modification in the central firth large spit complexes developed on the northern and southern shorelines extending westwards during the mid holocene however during the later holocene spit growth was towards the east on the southern shore and towards the southwest on the northern shore in the outer firth spit and beach development mainly occurred during the later holocene the development of spits at the mouth of the firth changed the wave energy environment in the central section and resulted in the marked changes in spit alignment in this area the features also indicate that during the rise and culmination of the main postglacial transgression coarse clastic sediments derived from cliff erosion dominated in contrast during the later holocene when relative sea level fell sand sized material derived from the nearshore and offshore zone predominated

barrier and lagoon coast evolution under differing relative sea level regimes examples from ireland and nova scotia abstract although the coasts of southern ireland and eastern nova scotia possess many basic similarities especially in terms of geology glacial history sediment character resistance to erosion and wave and tide regimes there is a fundamental contrast in holocene sea level history in ireland recent the past 4000 years sea level rise has been limited to less than 1 mm year by contrast the atlantic coast of nova scotia has been experiencing sea level rises up to three to five times greater over the same period under these markedly differing relative sea level rise regimes barrier and lagoon evolution has varied considerably in ireland barrier lagoon form is controlled by local basement expression particularly through the emergence of headlands creating largely closed sediment systems and the requirement to maintain cross shore drainage it is this latter factor that leads to a simple four fold categorization of the irish barriers and lagoons from freshwater seepage to open tidal environments the nova scotian examples are associated with rapidly moving erosional fronts with local basement control relegated to a subordinate role at the expense of rapid changes in sediment supply barriers can both grow and decay under these conditions subject to certain critical but as yet ill defined thresholds simultaneously forcing development and destruction of adjoining lagoons these major differences also find expression in sedimentary sequences

sea level changes in the holocene over the last 30 years the emphasis in studies of the recovery from low last glaciation sea levels has changed significantly the search for a eustatic sea level curve having global relevance has ended studies into the rheology of the earth s crust and recognition that the geoid has not remained stable over time have resulted in the recognition that there must have been regional differences in eustatic response to deglaciation as a part of this re appraisal there has been a growing appreciation that crustal isostatic response to the removal of the weight of ice sheets has been accompanied by a consequential hydro isostatic response particularly in the areas of the shelf seas in the later part of the post war period attention has additionally been focussed on the much greater potential for error over the whole field of palaeoenvironmental reconstruction in the holocene including not only errors in dating but also a large number of possible sources of errors in heighting as a result of this an increasing number of scientists are withholding judgement on the nature of sea level rise and more particularly on the problem of higher than present late holocene eustatic sea levels the problems outstanding in the early 1960s have not yet been resolved but the bases of uncertainty have changed

secular changes in tonalite trondhjemite granodiorite composition as markers of the progressive cooling of earth archean tonalite trondhjemite granodiorite associations ttg are classically thought to generate through partial melting of hydrous metabasalts however the chemical composition of the least differentiated ttg parental magmas evolved from 4 0 to 2 5 ga during this interval the mg as well as the ni and cr contents increased which is interpreted as reflecting increased interactions between felsic melts generated by metabasalt melting and mantle peridotite similarly cao na2o and sr also increased over time thus reflecting an increase in the abundance of plagioclase in the melt residue the presence or absence of residual plagioclase is interpreted in terms of melting depth the demonstrated interaction between ttg parental magmas and the mantle rules out their genesis by fusion of previously underplated metabasalt and favors the melting of subducted slab material at 4 0 ga earth s geothermal gradient was sufficiently high to allow slab melting at shallow depths where plagioclase was stable consequently due to the small thickness of the overlying mantle wedge felsic magmas interacted little with the mantle at 2 5 ga however owing to lower geothermal gradients the melting depth was greater and plagioclase became no longer stable in the thick mantle wedge overlying the subducted slab as a result felsic magmas reacted strongly with the mantle peridotite the changes of ttg composition during archean time can be thus interpreted as reflecting the progressive cooling of earth

coarse clastic barrier beaches a discussion of the distinctive dynamic and morphosedimentary characteristics abstract coarse clastic barriers are common on mid and high latitude coasts they possess a morphosedimentary and dynamic distinctiveness which sets them apart from sandy fineclastic barrier forms the reflective nature of the seaward barrier favors the development of zero mode sub harmonic edge waves particularly during long period swells 10 20 s manifest in the formation of high level cusps in some circumstances the pattern of recent overwashing of the barrier is related to cusps lack of distinct tidal passes due partly to the high seepage potential of coarse barriers means that very little sediment is transported seaward thus the barriers roll steadily onshore and sections show a variety of washover facies related to the volume of overwash surges

morphosedimentary development of drumlin flank barriers with rapidly rising sea level story head nova scotia abstract the morphodynamic and morphosedimentary development of drift aligned and swash aligned coarse clastic barriers plays an important role in the evolution of paraglacial coasts this paper discusses the development of two contrasting barriers attached to a drumlin headland at story head on the atlantic coast of nova scotia southeastern canada a 3 4 mm a 1 sea level rise is forcing rapid barrier changes including landward migration rollover of the swash aligned barrier at 5 8 m a 1 and barrier thinning elongation and breaching morphological development reflects the highly variable longshore distribution of wave power imposed initially by the topography of the drumlin and its position in the incident wave field and later by morphosedimentary feedback resulting from such gradients gradual reduction of an inherently intermittent sediment supply leads to reworking cannibalization of the barrier ultimately finding expression in a series of distinct wave formed sediment cells further diminution of the sediment supply coupled to cell development results in the drift aligned system decaying into a series of high water residuals separated by breach depressions with splayed spit recurves at the margins although the swash aligned barrier is stretched within the predominant overwash regime and may eventually separate from the headland it has remained intact until very recently when an initial breach occurred the evolutionary sequence of the headland barrier system has an important effect on adjacent sedimentary environments

sheet gravel evidence for a late holocene tsunami run up on beach dunes great barrier island new zealand abstract a semi continuous sheet of granule to cobble size clasts forms a distinctive deposit on sand dunes located on a coastal barrier in whangapoua bay great barrier island new zealand the gravel sheet extends from the toe of the foredune to 14 3 m above mean sea level and 200 m landward from the beach clasts are rounded to sub rounded and comprise lithologies consistent with local bedrock terrestrial sources for the gravel are considered highly unlikely due to the isolation of the dunes from hillslopes and streams the only source for the clasts is the nearshore to inner shelf of whangapoua bay where gravel sediments have been previously documented the mechanism for transport of the gravel is unlikely to be storm surge due to the elevation of the deposit maximum recorded storm surge on this coast is 0 8 m above mean high water spring tide aeolian processes are also discounted due to the size of clasts and the elevation at which they occur tsunami is therefore considered the most probable mechanism for gravel transport minimum run up height of the tsunami was 14 3 m based on maximum elevation of gravel deposits optical ages on dune sands beneath and covering the gravel allow age bracketing to 0 4 7 ka within this time frame numerous documented regional seismic and volcanic events could have generated the tsunami notably submarine volcanism along the southern kermadec arc to the east southeast of great barrier island where large magnitude events are documented for the late holocene radiocarbon ages on shell from maori middens that appear to have been reworked by tsunami run up constrain the age of this event to post ca 1400 ad regardless of the precise age of this event the well preserved nature of the whangapoua gravel deposit provides for an improved understanding of the high degree of spatial variability in tsunami run up

could iceland be a modern analogue for the earth s early continental crust for the last two decades iceland and other oceanic plateaux have been considered as potential analogues for the formation of the early earth s continental crust this study examines the compositions of silicic rocks from modern oceanic plateaux revealing their differences to archaean continental rock types trondhjemite tonalite granodiorite or ttg and thereby emphasising the contrasted mechanisms and or sources for their respective origins in most oceanic plateaux felsic magmas are thought to be formed by fractional crystallization of basalts in iceland the interaction between mantle plume and the mid atlantic ridge results in an abnormally high geothermal gradient and melting of the hydrated metabasaltic crust however despite the current archaean like high geothermal gradients melting takes place at a shallow depth and is unable to reproduce the ttg trace element signature consequently oceanic plateaux are not suitable environments for the genesis of the archaean continental crust however their subduction could account for the episodic crustal growth which has occurred throughout the earth s history

mechanisms to account for the longshore spacing of overwash throats on a coarse clastic barrier in southeast ireland abstract the longshore spacing of overwash throats on two contrasting sections of a coarse clastic reflective barrier beach in southeast ireland is examined for evidence of spatial periodicity a fixed barrier section carnsore with an irregular barrier top dune field exhibits random longshore throat positions related to pre existing irregularities in the seaward dune boundary a free barrier section tacumshin without a barrier top dune field shows regular longshore throat positions with a peak throat to throat periodicity of between 30 40 m similar longshore periodicity is found in persistent high level beach cusps above mhws though not always spatially in phase there is no consistent near shore rhythmic morphology that can account for this spacing the storm event which generated the tacumshin overwash appears to have dominant longer incident wave periods than normal in celtic sea storms on weight of circumstantial evidence it is reasoned that this dominant wave period range 9 11 s can be related to a zero mode sub harmonic edge wave whose longshore wavelength matches the peak periodicity of overwash spacing overwash sites on this reflective barrier may be determined by an edge wave controlled extension of run up which generates high level cusps and thereby creates washover routeways the presence or absence of a barrier top dune field is a secondary control on whether washover is successful in reaching the back barrier usually only where surge penetration and pre existing dune irregularities coincide does washover occur

seismic stratigraphy buried beach ridges and contourite drifts the late quaternary history of the closed lago cardiel basin argentina 49 s the results of a seismic stratigraphic analysis of a closed lake basin lago cardiel in southernmost south america are reported very few high resolution continental records spanning the late quaternary have been obtained from this region seismic sequence stratigraphic analysis allows a reconstruction of lake level variations two major hiatuses of unknown age occurred during the early evolution of the basin with the deposition of an alluvial fan in a restricted area in the intervening time period following the development of a relatively shallow lake during the late pleistocene and a short desiccation pulse around 11 220 14c yr bp a transgression of over 135 m occurred at the beginning of the holocene the transgression was associated with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern lago cardiel at four different elevations the preservation of largely unreworked beach ridges indicates a stepwise rise in the lake level there is no seismic evidence of a major lowering of the lake below modern level during the entire holocene deposition since the mid holocene is marked by strong lateral differences in sediment accumulation with a depocentre slightly to the north of the basin midpoint and a pronounced mounded distribution seismic reflection geometries as well as sedimentological characteristics indicate a lacustrine contourite drift covering an area of 80 100 km2 as lago cardiel is under the influence of westerly winds these most likely drove lake circulation the identification of drowned beach ridges and of contourite drifts illustrates that high resolution seismic stratigraphy is not only a powerful tool in reconstructing past lake level elevations for closed lake basins but it can also provide information about the rate of lake level changes and the presence and strength of lake currents

ree geochemistry and isotopic data of archean silicic volcanics and granitoids from the pilbara block western australia implications for the early crustal evolution eighteen silicic volcanic rocks of the warrawoona group and ten associated plutonic rocks from the pilbara block western australia have been chosen for geochemical and isotopic studies silicic volcanics of the unsb upper member of north star basalt are dated at 3 56 3 57 by both the rb sr and the sm nd methods the respective 1 initial isotopic composition values are 0 7005 5 sr and 0 50810 39 nd this age is consistent with the stratigraphic interpretation that the talgatalga subgroup in which the north star basalt occupies the lowermost position is overlain by the duffer formation whose age was earlier established at 3 45 by the zircon u pb method the new rb sr data on six silicic lava samples from the duffer formation yield an isochron of 3 23 0 28 2v though imprecise this age agrees with the zircon age within error limits rb sr ages of 2 3 2 4 obtained for the panorama rocks and the wyman formation do not correspond to their initial eruption ages chemical arguments suggest that these ages represent the time of metasomatism associated with the widespread thermal event in this region about 2 3 2 4 ago geochemically most of these analyzed rocks volcanic and plutonic are of tonalite trondhjemitegranodiorite ttg composition a typical feature found in many other archean terrains they generally show fractionated ree patterns except the panorama formation rocks furthermore the wyman formation rhyolites and the post tectonic adamellites show significant negative eu anomalies suggesting a similar mode of magma generation and a probable genetic link theoretical considerations suggest that most of these ttg rocks could have been generated by partial melting of amphibolitic or basaltic sources followed by fractional crystallization although the archean granitic gneisses often possess mantle like isr values the trace element data indicate that they could not have been derived by direct melting of upper mantle materials the immediate tectonic implication is that in any archean terrain the formation of na rich continental crust of ttg suite must be preceded by the presence of basaltic crust the occurrence of this basaltic crust is a matter of controversy such crust might have been totally destroyed by repeated melting processes or its remnants are now represented by some of the mafic ultramafic enclaves within the tonalite trondhjemite batholiths

chronology chemistry and origin of trachytes from hualalai volcano hawaii 1 hualalai volcano is unique among hawaiian volcanoes in that it possesses a relatively high proportion of evolved trachytic lavas that were erupted at the beginning of the alkalic postshield phase of volcanism these evolved lavas yield insights into magma sources magma supply rates and the evolution of the subvolcanic magmatic plumbing system at this time trachyte lavas are exposed at the puu waawaa pumice dome and puu anahulu flow as blocks in maars on the south flank of the volcano and as flows in water wells drilled on the west flank of hualalai new 40ar 39ar dates show that the puu waawaa and puu anahulu complex is 114 ka a block from the waha pele maar is 103 ka and water well trachytes range from 107 to 92 ka in age indicating a range for trachyte volcanism of 20 ka nd and pb isotopic compositions overlap with younger alkalic basalts from hualalai but are distinct from hualalai tholeiitic basalts and pacific mid ocean ridge basalts linking the trachytes to alkalic parental magmas that underwent extensive crystallization to yield trachytic residual magmas both sr and o isotopic ratios are higher in the trachytes than in hualalai alkalic lavas which is best explained by reaction with or assimilation of altered hualalai shield basalts at shallow depth major trace element and isotopic variations between trachytes are consistent with their evolution by fractional crystallization from a puu anahulu parent the short time gap between the end of tholeiitic volcanism 133 ka and the onset of trachytic alkalic volcanism and the lack of deep origin xenoliths place the magma reservoir within which the trachytes evolved rapidly at shallow 7 km depth whereas mauna kea and kohala volcanoes produced small volumes of highly evolved lavas as magma supply rates dwindled through the postshield stage postshield magma intrusion rates at hualalai were lowest during trachyte formation and increased through a more recent period of alkalic basalt eruptions subtle rare earth element and radiogenic isotopic distinctions between trachytes from the three localities indicate that the roof of the shallow magma reservoir may have been irregular allowing some trachytes to evolve independently from others

earth s earliest evolved crust generated in an iceland like setting the setting in which earth s first continental crust formed is unclear because few rocks survive from that time geochemical analysis of 4 03 billion year old rocks discovered in the acasta gneiss complex canada reveals rocks that are strikingly similar to those formed in iceland today implying earth s first continental crust was generated in an iceland like setting

particle size and shape in pebble beach sedimentation an in depth investigation was made of beach gravel fabrics at two beach sites located on the glamorgan heritage coast wales u k granulometric data from 31 080 pebbles were obtained and analysis confirmed the existence of a basic shape differentiation structure when the b axis was used at gileston beach a low energy location and nash beach a high energy location the use of the b axis in size and shape analysis seems to have led some workers to incorrect rejection of size as a factor in determining the transportational and depositional potential of a particle an inferred energy model can be constructed where the influence of particle size on sorting is predominant when energy conditions are high and particle shape factors predominate when energy conditions are low the c axis standard deviation value was the most effective discriminator of variation in shore parallel sedimentation structures at both beaches for shore normal structural discrimination the c axis mean and standard deviation values were the most effective

recent holocene paleo environmental evolution and coastline changes of kition larnaca cyprus mediterranean sea abstract sedimentological paleontological analysis and 14c dating of 17 cores obtained in the vicinity of the phoenician military harbor viii iv bc of kition bamboula cyprus provide new paleo environmental information for the reconstruction of shoreline changes for kition and larnaca bay over the last 4000 years we propose that a communication existed between the inner harbor of bamboula presently 400 m inland and the northern district of lichines which was a marine embayment our core data led us to revisit the previous hypothesis of a direct east west channel between the harbor and the open sea nicolaou k 1976 the historical topography of kition studies in mediterranean archaeology goteborg vol 153 pp 1 373 gifford j a 1978 paleogeography of archaelogical sites of the larnaca lowlands southeastern cyprus phd thesis university of minnesota pp 1 192 we propose instead that a spit of coarse material isolated the lagoon from the open sea from 2600 to 1600 years bp

planform and mobility in the meaipe maimba embayed beach on the south east coast of brazil the meaipe maimba embayed beach mmeb on the south east coast of brazil has been subject to anthropogenic pressures since the 70 s in this study we discuss the adequacy and contribution of the parabolic planform model to determine the planform and variability of the mmeb taking into consideration variation in wave conditions the role of different controlling conditions on the planform variability is analyzed as well as the morphological and planform mobility mmeb exhibited a new configuration in response to the construction of a harbor which interrupted the longshore sediment transport after four decades three particular morphodynamic sectors have been recognized along the beach the central sector is more exposed to normal wave incidence and cross shore processes predominate the northern and southern sectors are influenced by wave diffraction processes around the headlands and port respectively in the northern sector the presence of secondary headlands and inner islands imposed a geomorphological control on beach morphology and coastal processes the use of the parabolic planform model provided useful insights for the assessment of potential planform mobility since the decadal shoreline evolution combined with beach profiles and sediment characteristics allowed understanding of the beach mobility processes and supported the interpretation of modeling results

temporal evolution of magmatism in the northern volcanic zone of the andes the geology and petrology of cayambe volcanic complex ecuador in the northern volcanic zone of the andes the cayambe volcanic complex consists of 1 a basal mostly effusive volcano the viejo cayambe whose lavas andesites and subordinate dacites and rhyolites are typically calc alkaline and 2 a younger essentially dacitic composite edifice the nevado cayambe characterized by lavas with adakitic signatures and explosive eruptive styles the construction of viejo cayambe began 1 1 myr ago and ended at 1 0 ma the young and still active nevado cayambe grew after a period of quiescence of about 0 6 myr from 0 4 ma to holocene its complex history is divided into at least three large construction phases angureal cone main summit cone and secondary summit cone and comprises large pyroclastic events debris avalanches as well as periods of dome activity geochemical data indicate that fractional crystallization and crustal assimilation processes have a limited role in the genesis of each suite on the contrary field observations and mineralogical and geochemical data show the increasing importance of magma mixing during the evolution of the volcanic complex the adakitic signature of nevado cayambe magmas is related to partial melting of a basaltic source which could be the lower crust or the subducted slab however reliable geophysical and geochemical evidence indicates that the source of adakitic component is the subducted slab thus the viejo cayambe magmas are inferred to come from a mantle wedge source metasomatized by slab derived melts adakites whereas the nevado cayambe magmas indicate a greater involvement of adakitic melts in their petrogenesis this temporal evolution can be related to the presence of the subducted carnegie ridge modifying the geothermal gradient along the wadati benioff zone and favouring slab partial melting

morphology and stratigraphy of small barrier lagoon systems in maine abstract the coast of maine contains over 200 individual barrier lagoon systems most quite small with an aggregate length of nearly 100 km although they represent less than 5 of the tidally influenced coastline of maine they are widely distributed and occur in a variety of dynamic regimes and physiographic regions their morphology and backbarrier stratigraphy are different from better studied coastal plain systems and provide important clues to the holocene evolution of the maine coast in a study of geomorphic form and backbarrier stratigraphy inlet processes and holocene sea level rise have been identified as the principal controls on coarse grained barrier stratigraphy barriers in maine are found in five distinct geomorphic forms identified herein as barrier spits pocket barriers double tombolos cuspate barriers and looped barriers the few long sandy beaches in southwestern maine are mostly barrier spits the remainder of the barrier types is composed primarily of gravel or mixed sand and gravel the barriers protect a variety of backbarrier environments fresh and brackish ponds lagoons and fresh and saltwater marshes the barriers may or may not have inlets normal wave action coarse grain size and a deeply embayed coast result in barriers with steep reflective profiles several meters above mhw occasional storm events completely wash over the barriers building steep lobate gravel fans along their landward margin few if any extensive storm layers are recognized as extending into the distal backbarrier environments however during sea level rise and landward barrier retreat this abrupt storm generated transition zone inters the backbarrier sediments statistical comparisons of barrier morphology location and backbarrier environment type with backbarrier stratigraphy show that holocene backbarrier stratigraphy is best predicted by the modern backbarrier environment type this in turn is influenced most by the absence or presence and long term stability or instability of a tidal inlet geomorphic barrier form and location in coastal geomorphic compartments show little or no correlation with backbarrier stratigraphy in contrast to previous classifications of barrier lagoon systems based primarily on sandy coastal plain examples in maine the shape or origin of the backbarrier system is relatively unimportant the presence or absence of a tidal inlet is of paramount importance in shaping the holocene stratigraphy of the backbarrier region

processes and timescales by which a coastal gravel dominated barrier responds geomorphologically to sea level rise story head barrier nova scotia sea level rise slr is considered to be important for barrier behaviour when barriers are swash aligned and single crested which is typical of only one part of a barrier s lifeterm under such conditions gravel barrier retreat rate correlates with mesoscale sub decadal 102 a slr rate is the critical control on barrier retreat as mesoscale slr variation in combination with surge potential is able to raise water level to the elevation threshold sufficient for barrier overwash and hence drive barrier retreat

crestal overtop and washover sedimentation on a fringing sandy gravel barrier coast carnsore point southeast ireland abstract storm sedimentation on a fringing sandy gravel barrier system in southeast ireland is examined recent wave overtopping and overwashing during severe onshore storms have resulted in a distinctive pattern of crest and backbarrier sedimentation this is not easily matched with available models of washover sedimentation drawn from the barrier islands of the eastern united states beach crest overtopping occurs at heights up to 6 m mhws and is related to the development of upper beach swash ramps that are plastered against storm wave eroded dune scarps located at the barrier crest ramp sediments comprise coarse basal beach gravels overlain by coarsening upward units and finally topped by distinctive seawarddipping fine grit coarse sand couplets in places where ramps reach the dune cre t overtopping swash has deposited a fine marine gravel veneer

silicic ignimbrites within the costa rican volcanic front evidence for the formation of continental crust abstract the origin of silicic magmas greater than 65 silica in areas without old evolved continental crust has long been an enigma in oceanic arcs silicic volcanic deposits are not common which has generally been attributed to subduction related magmas rising without stalling or fractionating through a relatively thin mafic oceanic crust the volcanic arc in costa rica is built on a thick 40 km oceanic plateau and extensive silicic magmatism dominated by silicic ignimbrites has occurred in the region in the absence of old evolved continental crust the silicic deposits display the common large ion lithophile element lile enrichment and high field strength element hfse depletion observed in magmas generated by subduction processes which are not characteristic of melts generated from oceanic plateaus key trace element ratios in the ignimbrites vary with position along the volcanic front and this variation is similar to that of the volcanic front lavas ignimbrites contain unique cumulative frequency distributions of incompatible trace element ratios that demonstrate different magma batches for each unit we propose that the caribbean oceanic plateau in costa rica is being converted to continental crust in large part by the emplacement of silicic magmas in this area the origin of these silicic magmas is due to reprocessing juvenile mantle derived subduction related magmas that have ponded in the crust

origin and early growth rate of continents abstract data suggest that early continents formed over mantle sinks and grew rapidly between 2 7 and 3 0 ga ago nd isotopic results indicate that archean tonalites which are largely responsible for early continental growth are derived chiefly from ancient depleted mantle sources trace element and oxygen isotope data however indicate enriched sources for such tonalites these constraints can be explained if the mantle is fractionated into depleted dmr and enriched emr reservoirs during early degassing of the earth 4 4 ga blocks of emr are recycled back into the mantle and the emr dmr mixtures serve as sources for archean basalts these basalts are enriched in incompatible elements by deep sea alteration metasomatism in sinks or by other mantle processes and then undergo wet partial melting to produce tonalite magmas enrichment must occur not more than 150 ma prior to tonalite production basalt plateaus accumulate at sinks and as cooling continues geotherms at sinks pass into the eclogite stability field dense eclogite roots form on the basalt plateaus which pulls them into the mantle between 2 7 and 3 0 ga ago resulting in rapid tonalite production and thus in rapid continental growth

overwash occurrence consequent on morphodynamic changes following lagoon outlet closure on a coarse clastic barrier the reduction in sediment volume of an ebb tide delta as a consequence of lagoon outlet closure on a coarse clastic barrier in southeast ireland initiated a sequence of beachface and barrier changes downdrift elimination of sediment supply to the ebb delta caused a cessation of downdrift longshore swash bar welding and led to beach volume reductions which in turn allowed a temporal sequence of beach and nearshore morphodynamic domains to develop these domains then controlled the sedimentation regime of the barrier adjacent to the old outlet a temporal sequence of a dissipative barrier b reflective barrier and c inner reflective barrier face outer dissipative subtidal wave regimes match respectively periods of a barrier crest build up by crestal dune development b barrier crest instability barrier width increasing barrier height decreasing due to rhythmic overwash and c a return to barrier crest stability with limited aeolian accretion two barriers at different stages in this sequence are discussed

the meta igneous granulite xenoliths from kerguelen archipelago evidence of a continent nucleation in an oceanic setting xenoliths of meta igneous origin occur as one of the two main types of ultramafic and mafic xenoliths entrained by alkaline lavas of the kerguelen islands these are designated type ii xenoliths and are subdivided into three mineralogical groups subtype iia and iic xenoliths are interpreted as crystallisation products of basaltic melts that were emplaced near the crust mantle boundary during the early tholeiitic transitional magmatic activity of the kerguelen islands younger magmatism became more alkaline and subtype iib xenoliths were formed as high pressure alkaline cumulates related to the last alkaline volcanic stage subsequently the plagioclase bearing type ii rocks have been re equilibrated under granulite facies conditions this addition of mafic material around the crust mantle boundary is consistent with seismic evidence for crustal thickening to 14 20 km calculated compressional seismic velocities vp for the basic granulites are consistent with the range of observed vp in the low velocity region underlying the oceanic crust such growth in the thickness of the oceanic crust may be caused by intrusion of basalts at different levels in the lithosphere and may provide the heat responsible for granulitic metamorphism in the oceanic setting this study suggests that basic granulites can account for the observed seismic characteristics of oceanic plateaux and can be important components of kerguelen oceanic lithosphere where there has been large scale magma production moreover we speculate that the kerguelen islands and perhaps the surrounding plateau represent a continental nucleation process

onshore offshore sediment transport on beaches abstract the onshore offshore transport of sediment on beaches in analyzed by considering the time averaged behaviour of a control volume bounded by the wave breaking zone and by the beach face interactions are determined between the wave radiation stress the wave set up the shear stress on the beach face and the beach permeability simple theoretical relationships are derived which specify beach slope in terms of incident wave attack and beach material properties these relationships indicate that coarser sediment beaches are steeper because of the higher beach permeability it is also shown that any particular beach will decrease its slope as the wave attack increases according to an inverse function of the wave height not only the beach permeability but also the sediment grading curve is shown to be a key factor in determining beach slope the theory is used to discuss and explain some observed behaviour on real beaches and the possible implications for beach failure under storm attack

gravel barrier migration and overstepping abstract despite the widespread occurrence of gravel barriers on mid to high latitude coasts understanding of their stability and relationship to gravel deposits on the inner continental shelf remains rudimentary on sand dominated coasts subject to rising relative sea level barrier overstepping has been postulated as a mechanism for preservation of beach deposits on the shelf but direct observation of overstepping events has been lacking observations at a site on the atlantic coast of canada reveal migration of a gravel barrier at 8 m a 1 landward over back barrier mud following abandonment of part of the barrier volume on the shoreface this provides clear evidence for overstepping and suggests that it may play a role in the formation of inner shelf gravel deposits integrity of the migrating stretching barrier depends on continued sediment supply from the headland source to a connecting ridge which must become progressively longer as the landward displacement of the barrier increases

modelling gravel barrier response to storms and sudden relative sea level change using xbeach g abstract this paper investigates the response of a mixed sand and gravel msg barrier coastline to storms and sudden relative sea level change using the numerical model xbeach g the barrier beaches of southern hawke s bay new zealand provide a natural laboratory for the work owing to spatial variability in instantaneous land deformation that occurred during the 1931 hawke s bay earthquake historic 1931 and contemporary 2017 morphodynamics of one tectonically uplifted 1 5 m and one subsided 0 78 m barrier were modelled under energetic waves hs 1 6 m xbeach g was designed to simulate pure gravel beach morphodynamics but despite this the model demonstrated high quantitative skill when calibrated for the msg coast results reveal the storm impact regimes of each profile and potential linkages to decadal scale barrier development observed in historical beach profile data storm swash processes at the uplifted profile indicate long term barrier stability due to a lack of change at the barrier crest and ridge building observed in model simulations provides a potential formative mechanism for decadal scale beach progradation at the subsided barrier modelled historic crest build up up to 0 3 m and narrowing over 5 m indicate an overtopping mode of response to sudden relative sea level rise simulation results are consistent with historical beach profile observations that also show chronic narrowing of the subsided barrier through time simulations of the modern barrier draw attention to the possibility that it may be on a trajectory toward catastrophic breakdown under extreme conditions but further work is needed to distinguish the relative importance of historical sudden sea level rise versus deficits in sediment supply to this shoreline

major and trace element geochemistry and crustal evolution of archaean granodioritic rocks from eastern finland in the eastern part of central finland vast areas of granodioritic gneisses surround the ca 2 65 ga greenstone belts these granodioritic gneisses can be divided into two chronological and lithological units 1 grey gneisses 2 86 ga old with a typical archaean ttg tonalite trondhjemite granodiorite composition 2 augen gneisses 2 51 ga old with a granodioritic to granitic composition the sr and nd isotopic data preclude derivation of the grey gneisses from very much older continental material the highly fractionated ree distribution patterns la yb n 37 103 with few or no eu anomalies militate against a direct mantle origin the data suggest that the grey gneisses have most likely been derived by partial melting of short lived basaltic crustal material garnet bearing amphibolite it is estimated that the basaltic protoliths were separated from a mantle source no more than 150 ma before the melting such an early basaltic crust might have been completely destroyed or might have left some remnants which are now represented by mafic inclusions in the grey gneisses the augen gneisses have a relatively high isr value 0 705 which suggests an origin by recycling of pre existing crustal material grey gneisses their ree patterns are less fractionated than those of the grey gneisses and sometimes have negative eu anomalies using the sr isotopic and trace element data a model calculation suggests that the augen gneisses could have been derived by partial melting 50 of mixed protoliths with ttg greenstone belt volcanics in a proportion of 70 30 by volume followed by fractional crystallisation

modification of an oceanic plateau aruba dutch caribbean implications for the generation of continental crust the generation of the continental crust may be connected to mantle plume activity however the nature of this link and the processes involved are not well constrained an obstacle to understanding relationships between plume related mafic material and associated silicic rocks is that later tectonic movements are liable to obscure the original relationships particularly in ancient greenstone belts studies of younger analogous regions may help to clarify these relationships on the island of aruba in the southern caribbean a sequence of partly deformed mafic volcanic rocks intruded by a predominantly tonalitic batholith is exposed the mafic lavas show geochemical and isotopic affinities with other basaltic picritic and komatiitic rocks that crop out elsewhere in the caribbean these are well documented as belonging to an 88 91 ma plume related oceanic plateau which is allochthonous with respect to the americas and is thought to have been formed in the pacific region the 85 to 82 ma tonalitic rocks share some geochemical characteristics high sr and ba low nb and y with archaean tonalite trondhjemite granodiorite ttg suites field relationships suggest that deformation of the plateau sequence possibly related to collision with a subduction zone was synchronous with intrusion of the aruba batholith new incremental heating 40ar 39ar dates combined with existing palaeontological evidence show that cooling of the batholith occurred shortly after eruption of the plateau basalt sequence sr nd isotopic data for both rock suites are uniform 87sr 86sri 0 7035 endi 7 whereas pb isotopes are more variable plateau sequence 206pb 204pb 18 6 19 1 207pb 204pb 15 54 15 60 208pb 204pb 38 3 38 75 aruba batholith 206pb 204pb 18 4 18 9 207pb 204pb 15 51 15 56 208pb 204pb 38 0 38 5 this suggests that there has been a minor sedimentary input into the source region of the batholith however the limited time interval between basaltic and tonalitic magmatism makes a normal subduction related origin for the tonalites improbable instead models involving derivation of tonalite from partial melting of the plateau sequence or alternatively genesis in an unusual subduction zone environment are investigated

sediment supply and barrier dynamics as driving mechanisms of holocene coastal change for the southern north sea basin the combined effects of climate change and human impact lead to regional and local coastal responses that pose major challenges for the future resilience of coastal landscapes increasing the vulnerability of communities infrastructure and nature conservation interests using the suffolk coast southeast england as a case study we investigate the importance of sediment supply and barrier dynamics as driving mechanisms of coastal change throughout the holocene litho bio and chronostratigraphic methods are used to decipher the mechanisms of coastal change from the record preserved within coastal stratigraphy results suggest that local coastal configuration and sediment supply were the most influential in determining coastal change during the mid and late holocene against a background control of sea level rise the importance of sedimentological and morphological factors in shaping holocene coastal changes in the southern north sea basin must therefore be considered when using the database of evidence from this region as an analogue for future change under accelerated sea level rise

sedimentology seismic facies and stratigraphy of a holocene spit platform complex interpreted from high resolution shallow seismics lysegrund southern kattegat denmark abstract eighty kilometres of high resolution seismic profile data 8 km km 2 were collected in the lysegrund area southern kattegat denmark to reconstruct the seismic stratigraphy of a holocene spit platform complex comparison of two sets of seismic data shows a significant difference in reflection pattern by using lap style analyses four holocene units were recognised in boomer profiles 0 8 2 0 khz they are closely examined in this paper and their geometry is illustrated in a series of isopach maps drawn to understand the development of the deposit in time and space three vibra cores provide the stratigraphic control and demonstrate the presence of three lithofacies with gradational boundaries in the interval that correlates with the three upper boomer units the three lithofacies are part of a single lithofacies succession in contrast to the boomer profiles the subbottom profiles 3 5 khz demonstrate continuous accretion surfaces within the lithofacies succession comparisons of the boomer and subbottom profile data therefore indicate that the three boomer units are genetically coupled and that there are no significant time gaps between units the three boomer units are interpreted to represent a spit platform complex that developed in three phases during a general rapid rise of relative sea level 10 mm a under conditions of excess sediment supply the source materials were mobilised from glacial fluvial sediments in a headland west of and close to the spit platform during phase 1 spit development occurred in shallow water this acted as a core to the development of a spit platform during phase 2 that consisted of three seismic facies identifiable on 3 5 khz subbottom profiles during phase 3 true foresets and bottomsets developed growth of the platform surface kept pace with sea level rise and the entire spit platform complex formed in less than a thousand years focusing on differences in the seismic data helps avoid pitfalls in choosing methods to interpret data the closely spaced seismic line net forms the basis of a 3d dynamic model of the spit platform that resembles the model of meistrell meistrell f j 1972 the split platform concept laboratory observations of spit development in schwartz m l ed spits and bars dowden hutchinson and ross stroudsberg pp 225 283

open system processes in the genesis of silica oversaturated alkaline rocks of the rallier du baty peninsula kerguelen archipelago indian ocean abstract the rallier du baty peninsula forms the southwestern part of the kerguelen archipelago indian ocean whose magmatic activity is related to the long lived 115 ma kerguelen plume the peninsula is mostly made of alkaline rocks constituting two well defined ring complexes this paper focuses on the northern ring complex which is not yet known recent field studies have revealed seven discrete syenitic ring dykes ranging in age from 6 2 to 4 9 ma and two later volcanic systems 40ar 39ar dating of a trachytic ignimbrite linked to the dome carva volcano complex yields an age of 26 3 ka this represents the last major eruptive event on the kerguelen archipelago the volcanism is bimodal with trachybasalts and trachyandesites constituting the mafic lavas and trachytes and rhyolites constituting the felsic lavas the volume of erupted felsic magma is by far the larger and is represented by abundant pyroclastic deposits and lava flows boulders of plutonic rocks are found to the northwest of dome carva and represent intermediate rocks i e monzogabbros and monzonites that are not present at the surface basic rocks are mostly trachybasalts and trachyandesites while true basalts are scarce their mineralogy consists chiefly of plagioclase olivine diopside and oxides sieve textured plagioclase is common as well as corroded olivine and diopside phenocrysts peralkaline commenditic trachytes are the most abundant type of acid volcanic rocks they consist of abundant sanidine augite and magnetite phenocrysts and interstitial quartz aegerinic pyroxenes and na amphiboles ring dykes of quartz poor alkali feldspar syenites display the same mineralogy except hornblende is common and replaces diopside hornblende is particularly abundant in intermediate monzogabbros major and trace element variations of volcanic rocks emphasise the predominant role of fractional crystallisation with a general decrease of mgo cao p2o5 tio2 feo ba sr and ni from basic to felsic rocks however the scattering of the data from the basic rocks indicates that other processes have operated the overall evolution from trachyte to rhyolite is in agreement with the fractionation of sanidine as the major control an increase of incompatible elements from trachyte to rhyolite is observed the felsic lavas display an increase of 87sr 86sr i without any significant variations in the nd isotopic composition the genesis of the basic rocks is complex and reflects concomitant processes of fractional crystallisation mixing between different basic magmas and probable assimilation of ba rich oceanic crust major and trace element modelling confirms the possibility of producing the trachytes through continuous differentiation from a basaltic alkaline parent discrepancies observed for some trace elements can be explained by the crystallisation of amphibole at an intermediate stage of magma evolution the overall evolution from trachyte to rhyolite is thought to be controlled by crystal fractionation high 87sr 86sr i of the trachytes is interpreted to reflect interaction with an ocean derived component probably during assimilation of hydrothermally altered oceanic crust boulders of amphibole bearing monzonites and monzogabbros found to the northwest of dome carva are thought to represent intermediate magma composition that formed at depths but did not erupt

characteristics of diamondiferous plio pleistocene littoral deposits within the palaeo orange river mouth namibia abstract the orange river the principal conduit transporting diamonds from hinterland sources to the namibian coast in post cretaceous times is characterised by an extreme wave dominated delta that has given rise to a progression of coarse rudaceous littoral deposits preserved onshore for 150 km north of the mouth under the long lived prevailing vigorous wave wind and northward longshore drift regimes the orange river outfall has been reworked into amongst others a series of economically viable diamondiferous plio pleistocene onshore gravel beach deposits these placers comprise spits and barrier beaches in the proximal reach within the palaeo orange river mouth that after ca 5 km northwards merge into extensive but narrow linear beaches that in turn after ca 70 km give way to pocket beaches gravel and diamond size decreases northwards away from the ancestral orange river mouth the linear and pocket beach types have considerably higher diamond content but lower average diamond stone size than the two proximal units that are characterised by low diamond grade but comparatively large average diamond size given the risk of delineating low grade alluvial diamond deposits accurately we present here sedimentological reconstructions of the subtidal intertidal and supra tidal facies that constitute the spit and barrier beach sequences based largely on face mapping of exploration trenches and open cast mine cuts as well as the results of large tonnage sampling campaigns diamond distribution is also linked convincingly to basic littoral processes that were operational within the palaeo orange river mouth during the complex transgression that gave rise to the 30 m package in plio pleistocene times in both the spit and barrier beach settings the intertidal deposits prove to be the most promising targets whereas the subtidal sediments are the least economic the constant raking associated with coarse cobble boulder sized gravel foreshore deposits in an energetic micro tidal wave regime increased the average diamond stone size in the intertidal deposits to 1 to 2 carats per stone cts stn but the lack of fixed trapsites no competent footwall within the palaeo orange river mouth at that level prohibited the accumulation of substantially enriched diamondiferous gravels consequently grades of only 1 5 to 6 carats per 100 tons cpht are realised the highest grades 2 to 6 cpht are found in the landward facing intertidal beach deposits on the spits where gentle reworking in that sheltered environment had somewhat enriched and preserved the diamond content significantly the low average stone size of ca 0 5 cts stn in this lower energy setting probably reflects that of the general diamond population available at that time in contrast the sand rich subtidal deposits in the spit sequence return the lowest grades 0 1 to 0 5 cpht similar to those in the slightly younger subtidal transgressive boulder lags of the barrier beaches however the stone size in the spit subtidal sediments is also low 0 1 to 0 5 cts stn due to the highly mobile fine grained character of those deposits whereas that in the subtidal transgressive lag is large 2 to 3 cts stn as a result of the local semi permanent turbulence associated with the boulder sized clasts in these gravel sheets diamond distribution is therefore also influenced by littoral facies and associated beach types in addition to the spatial and temporal parameters that have already been documented for the onshore marine placers of the southern namibian coast

a late pleistocene coarse grained spit platform sequence in northern jylland denmark several well preserved late pleistocene spit systems occur uplifted in northern jylland denmark their present day morphological expression allows detailed study of spit growth patterns while the internal sedimentological organisation can be examined in a series of pits distributed along the length of the spits two characteristic vertical sequences are recognized in the systems the first sequence i consists of a giant scale cross bedded foreset unit overlain by topset and beach units while the second sequence ii consists of the foreset unit overlain by bar trough and beach units the two sequence types pass laterally into each other with a short overlap zone they can be interpreted in terms of meistrell s 1966 1972 model for spit platform growth based on scaled wave tank experiments the giant scale cross bedded unit corresponds to prograding of a coarse grained subaqueous spit platform while the topset bar trough and beach units reflect the growth of the subaerial spit the alternation between sequence i and ii reflects the inversely related growth of the spit and platform structures when the rate of subaqueous platform progradation declines the subaerial spit grows uniformly and when the platform progrades uniformly spit growth declines the model is probably only valid for relatively coarse grained systems because only these deposits would have a relatively steep front the water depth in which the spit system progrades and thus bottom topography determines the thickness of the giant scale cross bedded foreset unit because the water depth over the top of the platform is relatively constant if the water is less than a few metres deep the spit platform is not developed as seen where the late pleistocene spit systems prograded over elevations of the sea bottom conversely the correct recognition of spit platform sequences allows precise determination of sea level and water depth at the time of formation finally the model adds one further mode of formation of giant scale cross bedding to those already known from fluvial transverse lateral and point bars subtidal sand waves and gilbert deltas

development of spit lagoon complexes in response to little ice age rapid sea level changes in the central guilan coast south caspian sea iran the central guilan coast along the iranian caspian coastline is characterized by sandy beaches and the development of spit lagoon complexes which are prone to preserve past sea level fluctuations the morphology of three spit lagoon complexes along the central guilan coast was studied using ground penetrating radar gpr and sediment sequences to understand the effects of past sea level changes on spit lagoon development the results showed the prominent role of coastal setting in conditioning the development of spit lagoon formation in response to sea level change when the caspian sea experienced a highstand in the little ice age the coast of central guilan recorded fluctuations in sedimentation which are reflected for example by river avulsion and beach ridge formation depending on physical setting in the western half of the central guilan eastward longshore currents and strong wave action on a w e coastline coupled with sea level changes shaped the anzali spit lagoon complex while in the eastern part of the studied area river avulsion and changing the coastline orientation are responsible for development of the amirkola and kiashahr spit lagoon complexes under the same sea level fluctuations although sea level change has a major role in spit lagoon development an increase in the frequency of storms changes in sediment supply due to more precipitation and river avulsion are other players in spit lagoon development in the central guilan during the little ice age and more recent times

petrogenesis of archaean trondhjemites tonalites and granodiorites from eastern finland major and trace element geochemistry

leucocratic and gabbroic xenoliths from hualalai volcano hawai i a diverse range of crustal xenoliths is hosted in young alkali basalt lavas and scoria deposits erupted 3 5 ka at the summit of hual alai leucocratic xenoliths including monzodiorites diorites and syenogabbros are distinctive among hawaiian plutonic rocks in having alkali feldspar apatite zircon and biotite and evolved mineral compositions e g albitic feldspar clinopyroxene mgnumber 67 78 fine grained diorites and monzodiorites are plutonic equivalents of mugearite lavas which are unknown at hual alai these xenoliths appear to represent melt compositions falling along a liquid line of descent leading to trachyte a magma type which erupted from hual alai as a prodigious lava flow and scoria cone at 114 ka inferred fractionating assemblages melts modeling pyroxene geobarometry and whole rock norms all point to formation of the parent rocks of the leucocratic xenoliths at 3 7 kbar pressure this depth constraint on xenolith formation coupled with a demonstrated affinity to hypersthenenormative basalt and petrologic links between the xenoliths and the trachyte suggests that the shift from shield to post shield magmatism at hual alai was accompanied by significant deepening of the active magma reservoir and a gradual transition from tholeiitic to alkalic magmas subsequent differentiation of transitional basalts by fractional crystallization was apparently both extreme culminating in 5 5 km of trachyte and rapid at 2 75 10 m magma crystallized year