hatton bank northwest u k continental margin structure summary the continent ocean transition near hatton bank was studied using a dense grid of single ship and two ship multichannel seismic mcs profiles extensive oceanward dipping reflectors in a sequence of igneous rocks are developed in the upper crust across the entire margin at the landward shallowest end the dipping reflectors overlie continental crust while at the seaward end they are formed above oceanic crust beneath the central and lower part of the margin is a mid crustal layer approximately 5 km thick that could be either stretched and thinned continental crust or maybe newly formed igneous crust generated at the same time as the dipping reflector sequence beneath this mid crustal layer and above a well defined seismic moho which rises from 27 km continental end to 15 km oceanic end across the margin the present lower crust comprises a 10 15 km thick lens of material with a seismic velocity of 7 3 to 7 4 kds we interpret the present lower crustal lens as underplated igneous rocks left after extraction of the extruded basaltic lavas a considerable quantity of new material has been added to the crust under the rifted margin the present moho is a new boundary formed during creation of the margin and cannot therefore be used to determine the amount of thinning

crustal velocity structure of the british isles a comparison of receiver functions and wide angle seismic data summary magmatic underplating at the base of the continental crust is thought to be an important consequence of mantle plume activity geochemical evidence supports the hypothesis of underplating beneath the british tertiary igneous province during palaeocene times a process that has been invoked to explain at least part of the observed pattern of cenozoic denudation and consequent offshore deposition this study uses receiver functions to independently test the results of modelling of four wide angle seismic lines across the british isles several of which indicate the presence of a lens of high velocity material at the base of the crust this lens has been interpreted as evidence of palaeogene magmatic underplating receiver functions were calculated for three permanent and two temporary three component broad band seismometers in order to detect p to s conversions from intracrustal velocity discontinuities high frequencies were preserved in the calculation of the receiver functions receiver functions were modelled using the delay times of the p to s converted arrivals only with constraints on the vp and vp vs structure imposed from controlled source data this pragmatic method of interpreting receiver function data agrees well with the results of applying an established inversion technique resulting crustal velocity models are broadly consistent with the velocity models from the wide angle lines showing evidence for a four layer crust with laterally varying moho depths of between 33 2 5 km beneath southwest ireland 32 2 5 km beneath northern and eastern ireland 31 2 km beneath the isle of man and 35 3 km beneath northern england while these velocity models are consistent with the presence of a lower crustal layer receiver functions are insensitive to the p wave velocity structure and so unfortunately they cannot be used to independently constrain the p wave velocity of the lower crust which is an important diagnostic of the presence of magmatic underplating

influence of sediment source on the shapes and surface textures of glacial quartz sand grains a study of the shapes and surface textures of glacial quartz sand grains that were largely derived from sediment sources of different rock types was conducted in order to evaluate the influence of the sediment source on these textures the results show that the roundness and surface textures of glacial quartz sand grains are largely dictated by their sources and that surface textures may not always be reliable indicators of ancient glacial deposits

age and petrology of alkalic postshield and rejuvenated stage lava from kauai hawaii at the top of the waimea canyon basalt on the island of kauai rare flows of alkalic postshield stage hawaiite and mugearite overlie tholeiitic flows of the shield stage these postshield stage flows are 3 92 ma and provide a younger limit for the age of the tholeiitic shield stage the younger koloa volcanics consist of widespread alkalic rejuvenated stage flows and vents of alkalic basalt basanite nephelinite and nepheline melilitite that erupted between 3 65 and 0 52 ma all the flows older than 1 7 ma occur in the west northwestern half of the island and all the flows younger than 1 5 ma occur in the east southeastern half the lithologies have no spatial or chronological pattern the flows of the koloa volcanics are near primary magmas generated by variable small degrees of partial melting of a compositionally heterogeneous garnet bearing source that has about two thirds the concentration of p2o5 rare earth elements and sr of the source of the honolulu volcanics on the island of oahu the same lithology in the koloa and honolulu volcanics is generated by similar degrees of partial melting of distinct source compositions the lavas of the koloa volcanics can be generated by as little as 3 percent to as much as 17 percent partial melting for nepheline melilitite through alkalic basalt respectively phases that remain in the residue of the honolulu volcanics such as rutile and phlogopite are exhausted during formation of the koloa volcanics at all but the smallest degrees of partial melting the mantle source for kauai lava becomes systematically more depleted in 87sr 86sr as the volcano evolves from the tholeiitic shield stage to the alkalic postshield stage to the alkalic rejuvenated stage at the same time the lavas become systematically more enriched in incompatible trace elements on a shorter timescale the lavas of the koloa volcanics display the same compositional trends but at a lower rate of change the source characteristics of the koloa volcanics considered along with those of the honolulu volcanics support a mixing model in which the source of rejuvenated stage lava represents large percent melts of a plume source mixed with small amounts of small percent melts of a heterogeneous mid ocean ridge source

trans atlantic correlation of the palaeogene volcanic successions in the faeroe islands and east greenland before continental break up in the ne atlantic the faeroe islands and central east greenland were within a distance of 100 120 km chemical and lithological data for complete sections through the 5 km thick piles of contemporaneous palaeogene flood basalts in the faeroe islands and in the nansen fjord area in east greenland show very similar basalt compositions and evolution patterns with time the faeroes lower basalt formation and the equivalent nansen fjord formation in east greenland form a pre break up succession overlain by a sediment horizon a syn break up succession consists of the faeroes middle and upper basalt formations and the equivalent milne land formation in east greenland in which five intervals can be correlated with a compositional evolution from ti rich magnesian basalts and picrites at the base to a dominance of morb like low ti basalts at the top the successions were generated in the same mantle melting column beneath a thinning continent with a rift zone that eventually ruptured the continent the evolution pattern is very similar to that seen on the se greenland margin but spreading according to the palmason model of 1973 was not yet established the pre and syn break up successions formed volcanic megasystems stretching across the rift zone with areal extents of 70 000 and 220 000 km 2 and volumes of 120 000 and 250 000 km 3 rocks from the pre and syn break up successions can be discriminated based on a simple major element plot the overlying succession was 3 3 5 km thick in e greenland but was thin or absent in the faeroes the energy source for the melting appears to have been concentrated on the greenland side

crustal structure of iceland and greenland from receiver function studies 1 we used data from both permanent and temporary seismic networks on iceland and greenland to investigate the crustal thickness by partly reinterpreting earlier data p receiver functions and adding s receiver functions to better constrain the results we obtained good conversions from the moho and also crustal multiples in both iceland and greenland the central ice covered part of greenland has an average crustal thickness of 40 km typical for a craton at the edges of greenland the crustal thickness decreases to 30 40 km on the east coast of greenland where the track of the iceland plume is thought to have affected the lithosphere the crustal thickness is only 24 26 km in contrast to previous studies we find that the crustal thickness in the east and the northwest coastal regions of iceland is more than 40 km similar to beneath the active volcanic region in the southwest region of iceland and along the mid ocean ridge the crustal thickness is only 25 km or less also in contrast to earlier receiver function interpretations which deduced a broad crust mantle transition zone for iceland we find indications for a normal sharper moho beneath a number of sites

a crustal study off lofoten n norway by use of 3 component ocean bottom seismographs abstract twenty four 3 component ocean bottom seismographs obs were used in august 1988 in a combined seismic refraction and reflection study off lofoten n norway the purpose of the experiment was to map the crustal structure from the continental shelf to the oceanic crust off lofoten the very high data quality is demonstrated by the strong p wave and shear wave reflections as well as converted waves from the moho observed on the continental shelf these arrivals are observed continuously from near vertical to wide angle incidence very high seismic sea floor velocities in this area 3 1 km s to 5 1 km s indicates absence or very thin sequences of mesozoic sediments the 5 1 km s refractor coincides with the base cretaceous reflection interpreted from the multichannel reflection data the crystalline continental crust is here divided in layers with velocities of 6 0 km s 6 4 km s and 6 8 km s respectively on the seaward side of the escarpment tertiary sediments varying in thickness from 1 0 1 5 km are situated on top of a 1 5 2 0 km thick layer of flood basalt containing seaward dipping reflectors a layer with velocity of 6 7 km s is observed above the lower crust which in this area is found to have a velocity as high as 7 3 km s these high velocities indicate that the crust in this area is of oceanic origin or alternatively the high velocity layer in the lower crust might represent a magmatic body underplating highly thinned and intruded continental crust seven obss were deployed in the area that was covered by landward flowing basalt deposited during the early eocene breakup between norway and greenland the survey was partly performed to investigate whether this method can be used to map structures below the basalt which is impenetrable with conventional seismic reflection techniques the obs data contain considerable information about structures below the flood basalt pre opening sediments up to 4 0 km thick are indicated below the 1 0 2 5 km thick landward flowing basalt the velocities of the crystalline portion of the crust are found to be similar to those observed under the continental shelf 6 0 6 8 km s which implies that the crust east of the escarpment is of continental origin the crystalline crust is strongly thinned in this area showing a minimum thickness of about 6 km the depth to the moho increases from about 15 km in the western part of the area to about 26 km on the continental shelf the success of the obs survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and potentially in other areas where highly reflective surfaces make the reflection technique inefficient

crustal structure beneath the faroe islands from teleseismic receiver functions we use teleseismic receiver function analysis to constrain the crustal structure beneath the faroe islands on the northwest european volcanic continental margin a cluster of 45 broad band seismometers on the glyvursnes peninsula streymoy island recorded 10 teleseismic events ranging in magnitude from 6 1 to 8 0 during july december 2003 receiver functions show a clear ps peak for the first time in this region the depth of the converting boundary is estimated as 29 32 km using forward and inverse modelling and thickness versus vp vs ratio stacking techniques modelling experiments suggest that this estimate may represent the conversion from a region of high velocity lower crust rather than the crust mantle transition at the moho the best fit modelling results were achieved with a gradational high velocity region at least 6 km thick in the lower crust this is interpreted as due to the emplacement of sills into pre existing continental crust rather than the simple underplating of a block of high velocity igneous material at its base

imaging and regional distribution of basalt flows in the faeroe shetland basin we demonstrate that the use of long offset seismic data allows wide angle reflections and diving waves to be recorded and that these can be used in conjunction with prestack depth migrations to constrain and to image the base of the basalt flows and the underlying structure in the faeroe shetland basin crustal velocity models are built first by inverting the traveltimes of the recorded reflections and diving waves using ray tracing methods finer details of the velocity structure can then be refined by analysis of the amplitudes and waveforms of the arrivals we show that prestack depth migration of selected wide angle arrivals of known origin such as the base basalt reflection using the crustal velocity model allows us to build a composite image of the structure down to the pre rift basement this has the advantage that the wide angle first arriving energy must be primary and not from one of the many multiples or mode converted phases that plague near offset seismic data this allows us to tag these primary arrivals with confidence and then to identify the same arrivals on higher resolution prestack migrations that include data from all offsets examples are drawn from the faeroe shetland basin with a series of regional maps of the entire area showing the basalt depths and the thickness of the basalt flows and underlying sediment down to the top of the pre rift basement the maps show how the basalts thin to the southeast away from their presumed source west of the present faeroe islands and also show the extent to which the structure of the pre rift basement controls the considerable variations in sediment thickness between the basement and the cap formed by the overlying basalt flows

hydrochemical characterisation of water quality in the sarcheshmeh copper complex se iran hydrochemical investigations were conducted to identify variations in surface water chemistry in different parts of the sarcheshmeh copper complex twenty three water samples from mine drainage stream water processing water of the concentrator plant and tailings dam water were collected to understand processes that control the elements mobility changes in trace metal concentrations and variation of major ions show two distinct water types a neutral mine drainage nmd associated with the sarcheshmeh mine waters containing lower trace metal so42 concentrations and neutral ph values and b acid mine drainage amd with waters from tailings impoundments and waste rock dumps corresponding to higher trace metals fe cu zn mo and major anions so42 and cl than the first type with typically acidic ph contents as a result of cu mo sulphides flotation process under alkaline conditions high ph values high mo concentration and low contamination loads of al mn fe cu and cd were observed in reject waters from the concentrator plant sulphide oxidation especially pyrite dissolution precipitation of the secondary minerals and discharge of the reject waters from concentrator plant were some of the most important factors that influence water quality at the tailings impoundments the results of phreeqc speciation and solubility modelling indicated supersaturation of the waters in the tailings impoundments with respect to hydronium jarosite schwertmannite and gypsum

a spheroidal weathering model coupling porewater chemistry to soil thicknesses during steady state denudation abstract spheroidal weathering a common mechanism that initiates the transformation of bedrock to saprolite creates concentric fractures demarcating relatively unaltered corestones and progressively more altered rindlets in the spheroidally weathering rio blanco quartz diorite puerto rico diffusion of oxygen into corestones initiates oxidation of ferrous minerals and precipitation of ferric oxides a positive v of reaction results in the build up of elastic strain energy in the rock formation of each fracture is postulated to occur when the strain energy in a layer equals the fracture surface energy the rate of spheroidal weathering is thus a function of the concentration of reactants the reaction rate the rate of transport and the mechanical properties of the rock substitution of reasonable values for the parameters involved in the model produces results consistent with the observed thickness of rindlets in the rio icacos bedrock 2 3 cm and a time interval between fractures 200 300 a based on an assumption of steady state denudation at the measured rate of 0 01 cm a averaged over times longer than this interval the rate of advance of the bedrock saprolite interface during spheroidal weathering the weathering advance rate is constant with time assuming that the oxygen concentration at the bedrock saprolite interface varies with the thickness of soil saprolite yields predictive equations for how weathering advance rate and steady state saprolite soil thickness depend upon atmospheric oxygen levels and upon denudation rate the denudation and weathering advance rates at steady state are therefore related through a condition on the concentration of porewater oxygen at the base of the saprolite in our model for spheroidal weathering of the rio blanco quartz diorite fractures occur every 250 yr ferric oxide is fully depleted over a four rindlet set in 1000 yr and saprolitization is completed in 5000 yr in the zone containing 20 rindlets spheroidal weathering thus allows weathering to keep up with the high rate of denudation by enhancing access of bedrock to reactants by fracturing coupling of denudation and weathering advance rates can also occur for the case that weathering occurs without spheroidal fractures but for the same kinetics and transport parameters the maximum rate of saprolitization achieved would be far smaller than the rate of denudation for the rio blanco system the spheroidal weathering model provides a quantitative picture of how physical and chemical processes can be coupled explicitly during bedrock alteration to soil to explain weathering advance rates that are constant in time

finite duration extension and decompression melting abstract decompression melting of the upwelling mantle during extension of continental lithosphere provides a viable mechanism for the magmatism observed in many rifted sedimentary basins and passive volcanic margins a model has been developed in which in addition to the adiabatic temperature decrease syntectonic conductive cooling melt transport and emplacement at crustal levels are accounted for the heat equation including latent heat is solved numerically and the incremental melt fraction is traced to simulate dynamic melting the emplaced magma is considered an integral part of the continental crust we find that relative to an instantaneous rifting model with only adiabatic cooling there is a more than 10 decrease in the melt thickness even when the duration of rifting is as short as 1 m y whether extension takes place with constant horizontal velocity or strain rate has important implications for the amount of melt produced consequently pressure release melting does not only depend on the amount of stretching and duration of the rift episode but also on how extension develops through time

controls on the location of compressional deformation on the nw european margin the distribution of cenozoic compressional structures along the nw european margin has been compared with maps of the thickness of the crystalline crust derived from a compilation of seismic refraction interpretations and gravity modelling and with the distribution of high velocity lower crust and or partially serpentinized upper mantle detected by seismic experiments only a subset of the mapped compressional structures coincide with areas susceptible to lithospheric weakening as a result of crustal hyperextension and partial serpentinization of the upper mantle notably partially serpentinized upper mantle is well documented beneath the central part of the southern rockall basin but compressional features are sparse in that area where compressional structures have formed but the upper mantle is not serpentinized simple rheological modelling suggests an alternative weakening mechanism involving ductile lower crust and lithospheric decoupling the presence of pre existing weak zones associated with the properties of the gouge and overpressure in fault zones and local stress magnitude and orientation are important contributing factors

deep structure of the u s atlantic continental margin offshore south carolina from coincident ocean bottom and multichannel seismic data we present the results of a combined multichannel seismic reflection mcs and wide angle ocean bottom seismic profile collected in 1988 across the carolina trough on the u s atlantic continental margin inversion of vertical incidence and wide angle travel time data has produced a velocity model of the entire crust across the continent ocean transition the margin consists of three structural elements 1 rifted continental crust comprising 1 4 km of post rift sedimentary rocks overlying a 30 34 km thick subsedimentary crust 2 transitional crust a 70 to 80 km wide zone comprising up to 12 km of postrift sedimentary rocks overlying a 10 to 24 km thick subsedimentary crust and 3 oceanic crust comprising 8 km of sedimentary rocks overlying an 8 km thick crystalline crust the boundary between rifted continental and transitional crust marked by the brunswick magnetic anomaly represents an abrupt change in physical properties with strong lateral increases in seismic velocity density and magnetic susceptibility the transitional crust contains mid crustal seaward dipping reflections observed on the mcs section and has seismic velocities of 6 5 6 9 km s in the midcrust and 7 2 7 5 km s in the lower crust modeling of potential field data shows that transitional crust also produces the prominent margin parallel gravity anomaly and the brunswick and east coast magnetic anomalies these observations support the interpretation that the transitional crust was formed by magmatism during continental breakup the prodigious thickness up to 24 km of igneous material rivals that interpreted on continental margins of the north atlantic e g hatton bank and voring plateau which formed in the vicinity of the iceland hotspot these observations when combined with other transects across the margin confirm previous suggestions that the u s atlantic margin is strongly volcanic and further imply that the magmatism was not the result of a long lived mantle plume

lower crustal intrusion on the north atlantic continental margin near the faroe islands in the north atlantic the majority of basalt is intruded into the continent ocean transition rather than extruded onto the surface this melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 melt as has often been assumed when continents break apart the rifting is sometimes accompanied by the production of large volumes of molten rock1 2 3 the total melt volume however is uncertain because only part of it has erupted at the surface furthermore the cause of the magmatism is still disputed specifically whether or not it is due to increased mantle temperatures we recorded deep penetration normal incidence and wide angle seismic profiles across the faroe and hatton bank volcanic margins in the northeast atlantic here we show that near the faroe islands for every 1 km along strike 360 400 km3 of basalt is extruded while 540 600 km3 is intruded into the continent ocean transition we find that lower crustal intrusions are focused mainly into a narrow zone 50 km wide on the transition although extruded basalts flow more than 100 km from the rift seismic profiles show that the melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 per cent melt as has often been assumed evidence from the measured seismic velocities and from igneous thicknesses are consistent with the dominant control on melt production being increased mantle temperatures with no requirement for either significant active small scale mantle convection under the rift or the presence of fertile mantle at the time of continental break up as has previously been suggested for the north atlantic ocean4 5 6

large igneous province on the us atlantic margin and implications for magmatism during continental breakup rifted continental margins commonly include sections of igneous rock more than twice as thick as normal oceanic crust explanations for this voluminous magmatic accretion during rifting include plume models1 3 which require a deep seated thermal or chemical anomaly in upwelling mantle and non plume models4 7 which call on broad shallow thermal anomalies and or rapid upwelling of mantle through the melting zone new seismic models from two transects across the continent ocean transition on the us atlantic margin8 10 confirm the presence of a 20 25 km thick igneous section here we argue that the similarity of the crustal structure on these and two previous transects spanning 1 000 km of the margin and the association of thick igneous crust with the east coast magnetic anomaly11 imply that the thick igneous section extends along the entire margin and may have a volume of as much as 3 2 106 km3 the distribution of volcanic and plutonic rocks details of the seismic structure and lack of independent evidence for a hotspot are difficult to reconcile with plume models and suggest that non plume processes created the thick igneous crust

resolution of the scripps noaa marine gravity field from satellite altimetry the july 1995 declassification of the entire geosat gm satellite altimeter data set enabled a joint scripps noaa effort to compute a new version 7 2 marine gravity field on a 2 minute grid this gravity field covers the world oceans between 72 n and 72 s and is derived from a combination of ers 1 and geosat gm and erm data an earlier noaa geosat only gravity field solution was confined to the southern latitudes because the 1992 declassification was limited to gm data south of 30 s a simple coherence analysis between accurately navigated ship gravity profiles and comparable gravity profiles obtained from the gravity grids reveals that the scripps noaa gravity field is coherent with ship gravity down to 23 30 km this slight increase in resolution over the previous noaa geosat only gravity field short wavelength resolution of 26 30 km implies that the increased spatial coverage provided by the ers i altimeter when combined with geosat improves the solution coherence analyses between satellite gravity and ship topography and ship gravity and ship topography show that even shorter wavelength gravity anomalies 13 km are present in sea surface measurements made by ship even so the scripps noaa marine gravity field does an excellent job of resolving most of the short wavelength gravity anomalies covering the world oceans

structure of the se greenland margin from seismic reflection and refraction data implications for nascent spreading center subsidence and asymmetric crustal accretion during north atlantic opening 1 seismic reflection and refraction data from the se greenland margin provide a detailed view of a volcanic rifted margin from archean continental crust to near to average oceanic crust over a spatial scale of 400 km the sigma iii transect located 600 km south of the greenland iceland ridge and the presumed track of the iceland hot spot shows that the continent ocean transition is abrupt and only a small amount of crustal thinning occurred prior to final breakup initially 18 3 km thick crust accreted to the margin and the productivity decreased through time until a steady state ridge system was established that produced 8 10 km thick crust changes in the morphology of the basaltic extrusives provide evidence for vertical motions of the ridge system which was close to sea level for at least 1 m y of subaerial spreading despite a reduction in productivity from 17 to 13 5 km thick crust over this time interval this could be explained if a small component of active upwelling associated with thermal buoyancy from a modest thermal anomaly provided dynamic support to the rift system the thermal anomaly must be exhaustible consistent with recent suggestions that plume material was emplaced into a preexisting lithospheric thin spot as a thin sheet exhaustion of the thin sheet led to rapid subsidence of the spreading system and a change from subaerial to shallow marine and finally to deep marine extrusion in 2 m y is shown by the morphological changes in addition comparison to the conjugate hatton bank shows a clear asymmetry in the early accretion history of north atlantic oceanic crust nearly double the volume of material was emplaced on the greenland margin compared to hatton bank and may indicate east directed ridge migration during initial opening

a north south seismic profile across the caledonian suture zone in ireland abstract coole i caledonian onshore offshore lithospheric experiment line i is a 284 km seismic refraction profile extending from bundoran n to ardmore s in ireland fifty nine recording stations were deployed along this profile and it was served by a total of six shotpoints the profile crosses the predominant ne sw caledonian strike at a steep angle using both one dimensional and two dimensional seismic inversion techniques a travel time and relative amplitude study of the observed p wave data was undertaken gravity data along the profile was modelled to test the plausability of the derived velocity depth section the upper crustal structure along the profile is highly variable but some features stand out a large low velocity body towards the south of the traverse correlates well with a bouguer anomaly low and is interpreted as the southwest extension of the buried leinster batholith the mid crust is approximately 10 km thick and is bound at its top and bottom by two laterally continuous reflecting horizons both reflectors shallow northwards by about 5 km over a horizontal distance of some 60 km this northwards shallowing is a feature also displayed by a number of isolines in the upper crust and it marks a broad region of crustal change along the traverse in the zone of proposed caledonian suturing crustal thickness beneath coole i is approximately 30 km and the moho is a transition zone about 2 km thick which shallows slightly towards the coasts

hydrochemistry mineralogy and chemical fractionation of mine and processing wastes associated with porphyry copper mines a case study from the sarcheshmeh mine se iran abstract the sarcheshmeh is one of the largest oligo miocene porphyry cu deposits in the world comparative hydrochemical mineralogical and chemical fractionation associated with mining efflorescence salts and processing wastes of this mine are discussed hydrochemical results showed that rock waste dumps reject wastes and old impoundments of tailings are the main sources of acid mine drainage waters amd that contain potentially toxic metals such as cd co cu mn ni and zn as well as al episodic fluxes of highly contaminated acidic waters were produced in a tailings dam over a short period of time secondary soluble minerals provide important controls on the quality of amd produced especially in old dry tailings impoundments secondary sulfate minerals such as gypsum magnesiocopiapite hydronium jarosite kornelite and coquimbite were found in rock waste drainages and in old weathered reject wastes highly soluble secondary minerals such as gypsum eriochalcite and bonattite are also observed in an evaporative layer on old tailings impoundments chemical fractionation patterns of potentially toxic elements showed that the geochemical behavior of metals is primarily controlled by the mineralogical composition of waste samples elements such as co cr cu mn ni and zn are readily released into the water soluble fraction from efflorescence salts associated with rock waste drainages as well as from the evaporative layer of old tailings potentially toxic elements such as as mo and pb are principally adsorbed or co precipitated with amorphous and crystalline fe oxides but they may also be associated with oxidizing primary sulfides and residual fractions following the development of the dammed tailings pond the secondary minerals were dissolved producing acidic waters contaminated by al 154 mg l 1 cu 150 mg l 1 cd 0 31 m gl 1 co 2 13 mg l 1 mn 73 7 mg l 1 ni 1 74 mg l 1 zn 20 3 mg l 1 and cl 1690 mg l 1 therefore the potential use of recycled water from the sarcheshmenh dammed tailings pond is diminished by the presence of corrosive ions like cl in highly acidic fluids that promote corrosion of pipes and pumps in the water recycling system

provenance of multicycle quartz arenites of pliocene age at arcos southwestern spain abstract a typical deposit of multicycle quartz arenites of considerable economic significance located in arcos sw spain has been studied to establish the provenance of the grains and their stages of sedimentary evolution the quartz grains were studied by sem and the composition of the sand determined by modal analysis of the heavy and light minerals the sources of the silica sands were the numidic sandstones known as aljibe in the betic cordilleras and the late miocene calcarenites of the guadalquivir basin four phases in the evolution of the arcos quartzose sands are a the initial surface features upturned plates b mechanical features an association of conchoidal fractures and arcuate steps formed in littoral environments inherited from the late miocene calcarenites c fluviatile features such as mechanical v s and grooves and d a final stage of chemical features oriented etch pits solution pits and hollows and silica globules developed in a hot humid climate the most important process producing the enrichment of the quartzose sands takes place during erosion depositional cycles

crustal structure of edoras bank continental margin and mantle thermal anomalies beneath the north atlantic we discuss the structure of the continent ocean transition of the edoras bank area of the ne atlantic margin and the influence of the iceland mantle plume during continental breakup edoras bank lies close to the present day limit of influence of the iceland plume sequences of seaward dipping reflectors imaged on multichannel seismic profiles are well developed over much of the margin they form aerially extensive dipping sheets with individual reflectors imaged on margin parallel profiles as laterally continuous and subhorizontal features we interpret them as basalt flows extruded from linear fissure vents close to sea level at the time of continental breakup a crustal velocity model for the margin was developed by travel time modeling of wide angle refractions and reflections recorded on digital ocean bottom hydrophones and the structure confirmed by gravity modeling oceanic crust formed immediately after breakup is 10 km thick and exhibits classic layer 2 and layer 3 seismic velocities the crustal thickness increases to the se reaching 17 km beneath the continental fragment of edoras bank the continent ocean transition is dominated in the lower crust by a lens up to 8 km thick of high velocity material 7 2 7 5 km s 1 which exhibits a very low velocity gradient it extends over a 60 km wide region beneath the seaward dipping reflectors the high velocities and densities of the lower crust are probably caused by igneous rock with a high mgo content that underplated the margin or heavily intruded pre existing crustal material during continental breakup both the addition of large quantities of melt to the margin and the subsidence curves inferred from postrift sediments sampled by deep sea drilling project dsdp boreholes on the margin indicate the presence of abnormally hot mantle beneath the area at the time of continental breakup comparison of the structure and subsidence history of the edoras bank margin with other areas of the nw european margin allows us to deduce the spatial extent and temporal variation of the thermal anomalies caused by the iceland mantle plume during and following continental breakup we find that at the time of breakup a thin layer of anomalously hot asthenospheric mantle 150 c hotter than normal lay beneath the 2000 km long rift extending from the lofoten margin off norway in the north to the edoras bank margin in the south over a period of 5 10 m y following the onset of rifting the mantle thermal anomaly decayed rapidly to only 50 c or so above normal as the thin layer of abnormally hot mantle decompressed beneath the rift and produced a large pulse of magmatism

a review of the ne atlantic conjugate margins based on seismic refraction data the ne atlantic region evolved through several rift episodes leading to break up in the eocene that was associated with voluminous magmatism along the conjugate margins of east greenland and nw europe existing seismic refraction data provide good constraints on the overall tectonic development of the margins despite data gaps at the ne greenland shear margin and the southern jan mayen microcontinent the maximum thickness of the initial oceanic crust is 40 km at the greenland iceland faroe ridge but decreases with increasing distance to the iceland plume high velocity lower crust interpreted as magmatic underplating or sill intrusions is observed along most margins but disappears north of the east greenland ridge and the lofoten margin with the exception of the vestbakken volcanic province at the sw barents sea margin south of the narrow lofoten margin the european side is characterized by wide margins the opposite trend is seen in greenland with a wide margin in the ne and narrow margins elsewhere the thin crust beneath the basins is generally underlain by rocks with velocities of 7 km s 1 interpreted as serpentinized mantle in the porcupine and southern rockall basins while off norway alternative interpretations such as eclogite bodies and underplating are also discussed

stream water geochemistry from mine wastes in pena de hierro riotinto area sw spain a case of extreme acid mine drainage in this work we have studied the geochemistry of stream waters arising from waste dumps at the pena de hierro mine iberian pyrite belt sw spain and we have correlated them with the mineralogical and geochemical characteristics of the wastes to asses the source and factors affecting the release of trace elements the mineralogical composition and geochemistry of 58 borehole samples of waste dumps were studied in the 2 mm fraction twenty eight water samples collected in winter and summer from streams emerging from the waste dumps were analysed for ph eh conductivity temperature sulphates and major and trace elements the leachates from pyrite rich volcanic tuffs produced very acidic waters usually with phs below 2 and reaching values as low as 0 7 the partial dissolution of gossan which is mainly composed of fe oxy hydroxides and is rich in trace elements released high concentrations of fetot up to 33 g l as up to 72 mo up to 11 mg l on the other hand cd zn and pb reached up to 0 85 142 and 0 42 mg l respectively in the stream arising from roasted pyrite ashes and other pyritic wastes several elements such as al fe as co cu and mo were strongly correlated with the ph but cd and zn were not correlated under such acidic conditions the precipitation of jarosite seems to be an important factor in the retention of pb the mobility sequence of trace elements shows that co zn and cd were among the most mobile elements cu as and mo had intermediate mobility and pb was the most immobile this work shows that uncontrolled waste dumping increases the pollution potential and a selective management could reduce the release of trace elements into stream waters and mitigate the contamination

clay mineral fluctuations and surface textural analysis of quartz grains in pliocene quaternary marine sediments from wilkes land continental rise east antarctica paleoenvironmental significance abstract pliocene quaternary marine sediments from wilkes land continental rise were investigated using clay mineral analysis and quartz grain surface texture observations the studied piston cores were collected during a geophysical and geological survey in the framework of the italian and australian wega project the cores were collected along two transects crossing the channel mound system that characterizes the wilkes land continental rise massive and laminated facies were recognized in these sedimentary sequences the clay mineral assemblages are dominated by illite smectite and chlorite occur in intermediate amounts whereas kaolinite is scarce illite derives from the hinterland of the mertz and ninnis glaciers smectite and kaolinite derive from the ross sea area and they are transported by westward marine bottom currents chlorite is derived both from the adjacent continent and from the victoria land different concentrations of individual clay minerals in the massive and laminated facies are controlled by the interplay between different source areas and the main sedimentary processes glacial and eolian quartz grains prevail in the massive units indicating short transportation and rapid deposition from melting ices with no further significant transport action by marine currents in the laminated facies the high amount of quartz grains affected by high energy subaqueous transport features are related both to turbiditic processes and to bottom current transport

far reaching effects of the hawaiian islands on the pacific ocean atmosphere system using satellite data we detected a wind wake trailing westward behind the hawaiian islands for 3000 kilometers a length many times greater than observed anywhere else on earth this wind wake drives an eastward ocean current that draws warm water from the asian coast 8000 kilometers away leaving marked changes in surface and subsurface ocean temperature standing in the path of the steady trade winds hawaii triggers an air sea interaction that provides the feedback to sustain the influence of these small islands over a long stretch of the pacific ocean

continent ocean transition and voluminous magmatic underplating derived from p wave velocity modelling of the east greenland continental margin summary deep seismic refraction data were gathered across the entire east greenland rifted margin north of the jan mayen fracture zone between 72 n and 75 n in 2003 investigations of the deep crustal structure of this continental margin provide constraints on the formation of the margin and its structural evolution during and after late cretaceous early tertiary rifting and continental break up we present here the results along two profiles located in the prolongation of the godthab gulf and the kejser franz joseph fjord regional p wave velocity models were derived from forward traveltime modelling of land stations and ocean bottom hydrophone obh recordings for the first time long deep seismic sounding transects off east greenland provide a full insight into the crustal architecture of the transition from continental to oceanic crust a mean result is the identification of voluminous magmatic underplating which is wider and thicker than previously thought p wave velocities of the underplated material range between 7 1 and 7 4 km s 1 and the horizontal extents on the profiles are 225 and 190 km the maximum thickness of the underplated material is 15 16 km furthermore the p wave velocity models reveal a 120 130 km wide continent ocean transition zone cot based on an interpretation of the extent of cretaceous syn rift sediments mixed with basaltic intrusions and the lateral increase of velocities in the crustal layers excess magmatism must have been present during a long term rifting process accompanying the extension of the continental crust and giving rise to the voluminous magmatic underplating a consequence of our interpretation of the seismic refraction data is a likely rift propagation in the greenland sea from north to south additionally a comparison of p wave velocity models of the east greenland margin and voring margin reveals significantly asymmetric crustal architectures the voluminous magmatic underplating and asymmetrical conjugate margins formations are considered as a mirror of complex pre and syn rift processes

the structure of the rockall trough from seismic refraction and wide angle reflection measurements there are few detailed descriptions of the deep crustal structure of failed cratonic rifts and passive margins despite their import ance in constraining the variety of structural models invoked to account for their common structural symmetry or gross half graben form1 3 such deep crustal structure profiles also have considerable value in defining the continent ocean boundary con straining plate reconstructions and determining the overall setting of sedimentary basin development the rockall trough in the north atlantic ocean is a sinuous elongate bathymetric depression 200 km wide and more than 2 000 m deep lying between rockall plateau and the british isles and the structure nature and age of its underlying crust are disputed in the absence of deep crustal structure profiles the presence of oceanic crust has been assumed because the trough has to be accommodated in reconstructions of the north atlantic although stretched continental crust is equally plausible the nature of the crust is important for the precise reconstruction of the late jurassic early cretaceous plate history and setting of sedimentary basins of the north atlantic4 8 the nature of the crust beneath the trough as well as the structure thickness and composition of the sedimentary cover is also relevant to oil exploration here we report the first observations of deep crustal structure across the rockall trough and its margins from seismic refraction and wide angle reflection profiles our results show that the northern rockall trough is underlain by highly stretched continental crust and not by oceanic crust as previously postulated

factors influencing magmatism during continental breakup new insights from a wide angle seismic experiment across the conjugate seychelles indian margins we present a model of the northern seychelles continental margin derived from controlled source wide angle seismic traveltime inversion and teleseismic receiver functions this margin has been widely cited as a classic example of rifting in association with a continental flood basalt province the deccan traps however we do not find the typical set of geophysical characteristics reported at other margins linked to continental flood basalts such as those of the north atlantic the oceanic crust formed immediately after breakup and throughout the first 3 ma of seafloor spreading is just 5 2 km thick less than half that typically seen at other volcanic margins the continent ocean transition zone is narrow and while two packages of seaward dipping reflectors are imaged within this transition they are weakly developed beneath the thinned continental crust there is an approximately 4 km thick layer of high velocity material 7 5 7 8 km s that we interpret as mafic material intruded and underplating the lower crust however we believe that this underplating most likely happened prior to the breakup overall the observations show that the rifting of india from the seychelles was characterized by modest magmatism the spatial extent of the deccan flood basalt province is therefore smaller than previously thought we speculate that either the lateral flow of deccan related hot material beneath the breakup region was hampered perhaps as the rifted margins did not intersect the center of the deccan source or there was incomplete melt extraction from the wide melting region that formed between the rapidly diverging plates if the latter explanation is correct then the rate of plate separation as indicated by the initial seafloor spreading rate is more important in controlling the volume of magmatism generated during continental rifting than has been previously recognized

moho and basement depth in the ne atlantic ocean based on seismic refraction data and receiver functions seismic refraction data and results from receiver functions were used to compile the depth to the basement and moho in the ne atlantic ocean for interpolation between the unevenly spaced data points the kriging technique was used free air gravity data were used as constraints in the kriging process for the basement that way structures with little or no seismic coverage are still presented on the basement map in particular the basins off east greenland the rift basins off nw europe are mapped as a continuous zone with basement depths of between 5 and 15 km maximum basement depths off ne greenland are 8 km but these are probably underestimated plate reconstructions for chron c24 c 54 ma suggest that the poorly known ammassalik basin off se greenland may correlate with the northern termination of the hatton basin at the conjugate margin the most prominent feature on the moho map is the greenland iceland faroe ridge with moho depths 28 km crustal thickness is compiled from the moho and basement depths the oceanic crust displays an increased thickness close to the volcanic margins affected by the iceland plume

crustal structure of the ne rockall trough from wide angle seismic data modeling two wide angle seismic lines located in the northern rockall trough were acquired in may 2000 one line line e crosses the trough from the continental shelf off lewis to normal oceanic crust west of lousy bank in nw se direction the other line line d intersects with line e crosses the wyville thomson ridge in a sw ne direction and ends in the faeroe shetland basin sonobuoy data and expanding spread profiles acquired in the same area have been remodeled analysis of the seismic data using travel times and amplitudes reveals an up to 5 km thick sedimentary basin including an up to 1 5 km thick basaltic layer which is present in most of the trough further conclusions of this study are that the rockall trough is underlain by highly stretched continental crust of 13 km thickness the crust thickens to 24 km beneath lousy bank which is interpreted to be of continental nature beneath the hebrides continental shelf a three layer continental crust of 26 km is modeled an up to 12 km thick high velocity layer is observed underneath the ocean continent boundary and is interpreted as magmatic underplating resulting from excess volcanism during rifting no evidence for an underplate layer could be distinguished beneath the trough area modeling of the structure of the wyville thomson ridge revealed no existing igneous core of the ridge confirming existing theories that it is a compressional structure

effect of acid mine drainage on a karst basin a case study on the high as coal mining area in guizhou province china acid mine drainage amd is a common pollution in mining areas due to the oxidation of pyrite and associated sulfide minerals at mines tailings and mine dumps elevated metals fe mn al and metalloids as hg in amd would deteriorate the local aquatic environment and influence the water supply a carbonate basin with deposits of high arsenic coal in xingren county southwestern china was chosen to study the behavior of as and other chemical constituents along a river receiving amd heavy metals fe mn and major ions such as ca2 mg2 cl so42 in surface water and as in sediment and surface water were analyzed it was found that high concentrations of so42 1 324 7 560 mg l and fe 369 1 472 mg l in surface water were mainly controlled by the interactions between water and rocks such as the oxidation of pyrite in the local coal seams precipitation and adsorption of iron minerals although ubiquitous carbonate minerals in the bedrock and the riverbeds low ph 3 water was maintained until 2 km downstream from the amd source due to the fe hydro oxide minerals coating on the surface of carbonate minerals to restrain the neutralization of acidic water moreover the formation of fe hydro oxide precipitations absorbed as was dominated the attenuation of as from water to sediment whereas the dilution also played an important role in decrease of as in river water

assessing mine drainage ph from the color and spectral reflectance of chemical precipitates the ph of mine impacted waters was estimated from the spectral reflectance of resident sediments composed mostly of chemical precipitates mine drainage sediments were collected from sites in the anthracite region of eastern pennsylvania representing acid to near neutral ph sediments occurring in acidic waters contained primarily schwertmannite and goethite while near neutral waters produced ferrihydrite the minerals comprising the sediments occurring at each ph mode were spectrally separable spectral angle difference mapping was used to correlate sediment color with stream water ph r 2 0 76 band center and band depth analysis of spectral absorption features were also used to discriminate ferrihydrite and goethite and or schwertmannite by analyzing the 4 t1 6 a1 crystal field transition 900 1000 nm the presence of these minerals accurately predicted stream water ph r 2 0 87 and provided a qualitative estimate of dissolved so4 concentrations spectral analysis results were used to analyze airborne digital multispectral video dmsv imagery for several sites in the region the high spatial resolution of the dmsv sensor allowed for precise mapping of the mine drainage sediments the results from this study indicate that airborne and space borne imaging spectrometers may be used to accurately classify streams impacted by acid vs neutral to alkaline mine drainage after appropriate spectral libraries are developed published by elsevier science ltd

surface textural analysis of quartz sand grains from odp site 918 off the southeast coast of greenland suggests glaciation of southern greenland at 11 ma shipboard analysis of the 1 183 m sedimentary section recovered at site 918 in the irminger basin during ocean drilling program leg 152 revealed material of glacial origin diamictons ice rafted debris ird and dropstones as deep as 543 m below sea floor bsf the sediment containing the deepest dropstone was biostratigraphically dated shipboard as approximately 7 ma pushing back the date for the onset of glaciation on southern greenland by 5 ma thin layers of fine sand were found as much as 60 m deeper in the core raising the possibility of an even earlier date for glaciation to determine the sedimentary history of these deeper sand layers the surface textures on quartz grains from eleven cores bracketing the interval of interest were analyzed by scanning electron microscope the results suggest that the grains in the 60 m interval below the deepest dropstone have a glacial history at that level an 11 ma sr isotope date was obtained from planktonic foraminifers this late miocene timing is supported biostratigraphically by both nanofossil and foraminifer assemblages indicating a new minimum age for the onset of glaciation on southern greenland and in the north atlantic

early paleozoic transform margin structure beneath the mississippi coastal plain southeast united states a geophysical transect across the central gulf of mexico coastal plain shows that the early paleozoic continental margin of southern laurentia is preserved in a nearly pristine state beneath younger strata that were emplaced during the late paleozoic ouachita orogeny and formation of the modern gulf of mexico coastal plain the thickness of the crystalline crust decreases abruptly across the margin over a distance of 50 km from 35 km beneath the black warrior foreland basin to 10 km beneath the ouachita fold and thrust belt this abrupt decrease in crustal thickness is similar to modern transform margins but very different from most rifted margins which display much more gradual transitions in crustal thickness the geophysical data indicate an absence of synrift intrusive and volcanic rocks underplated mafic rocks at the base of the crust and abnormally thick oceanic crust adjacent to the margin the lack of these features is also characteristic of modern transform margins combined with transects across the margin farther west the data confirm previous suggestions that the central gulf of mexico coastal plain overlies an 800 km long transform segment of the late proterozoic early paleozoic southern laurentian continental margin that extends continuously from western arkansas to southeast alabama

the edoras bank margin continental break up in the presence of a mantle plume abstract edoras bank lies on the eastern continental margin of the north atlantic about 900 km south of the present day iceland plume we studied the continent ocean transition of the rifted margin using normal incidence and wide angle seismic reflection data seaward dipping reflectors are well developed over much of the margin and are underlain by a high velocity 7 3 7 5 km s 1 lower crust this is interpreted as either igneous underplating or as existing crust heavily intruded at the time of break up by melts with high mgo contents and suggests that the thermal anomaly associated with the iceland plume was well developed in this area at the time of break up

a crustal model for a northeast southwest profile through ireland abstract the irish caledonian suture seismic project icssp consisting of a 250 km seismic refraction line was carried out in conjunction with and as an extension of the caledonian suture seismic project cssp of the university of durham 51 seismic recording sites at 5 km intervals were deployed on the northwest flank of the suture zone in ireland recordings were made from three shot points at the southwest of the line and from 31 shot points of the durham programme in the north irish sea a crustal model is presented which is based exclusively on a travel time interpretation the p g velocities recorded in eastern ireland rise quite rapidly with depth to 6 3 6 5 km s but in the western part of the profile lower velocities between 6 0 and 6 3 km s were recorded prominent energy in later arrivals can be correlated by two reflected phases from a mid crustal boundary and the moho a low velocity zone is present at the northeastern end of the line and a mid crustal layer with an average velocity of about 6 4 km s is separated from the lower crust mean velocity 6 8 km s by a well established mid crustal boundary zone of 1 2 km thickness at about 20 km depth the moho around 32 km at its deepest shallows towards the sea at both ends of the line it is a sharp discontinuity under western ireland but a transition zone of 3 4 km thickness in the east an interpretation is given which takes into account 1 a the geologic and tectonic history of ireland and 2 b data derived from the gravity and magnetic fields

north atlantic volcanic margins dimensions and production rates early tertiary lithospheric breakup between eurasia and greenland was accompanied by a transient 3 m y igneous event emplacing both the onshore flood basalts of the north atlantic volcanic province navp and huge extrusive complexes along the continent ocean transition on the rifted continental margins seismic data show that volcanic margins extend 2600 km along the early eocene plate boundary in places underlain by high velocity 7 2 7 7 km s lower crustal bodies quantitative calculations of navp dimensions considered minimum estimates reveal an areal extent of 1 3 106 km2 and a volume of flood basalts of 1 8 106 km3 yielding a mean eruption rate of 0 6 km3 yr or 2 4 km3 yr if two thirds of the basalts were emplaced within 0 5 m y the total crustal volume is 6 6 106 km3 resulting in a mean crustal accretion rate of 2 2 km3 yr thus navp ranks among the world s larger igneous provinces if the volcanic margins are considered the velocity structure of the expanded crust seaward of the continent ocean boundary differs from standard oceanic and continental crustal models based on seismic velocities this volcanic margin crust can be divided into three units of which the upper unit corresponds to basaltic extrusives the regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust including the high velocity lower crust which extends some distance landward of the continent ocean boundary was emplaced during and subsequent to breakup the volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling probably reflecting the interaction of a mantle plume and a lithosphere already extending

hydrochemistry of reservoirs of damodar river basin india weathering processes and water quality assessment water samples collected from the six reservoirs of damodar river basin in pre and post monsoon have been analysed to study the major ion chemistry and the weathering and geochemical processes controlling the water composition ca na and hco3 dominate the chemical composition of the reservoir water the seasonal data shows a minimum concentration of most of the ions in post monsoon and a maximum concentration in pre monsoon seasons reflecting the concentrating effects due to elevated temperature and increased evaporation during the low water level period of the pre monsoon season water chemistry of the reservoirs strongly reflects the dominance of continental weathering aided by atmospheric and anthropogenic activities in the catchment area higher concentration of so4 and tds in panchet durgapur and tenughat reservoirs indicate mining and anthropogenic impact on water quality the high contribution of ca mg to the total cations high concentration of dissolved silica relatively high na k tz ratio 0 3 and low equivalent ratio of ca mg na k suggests combined influence of carbonate and silicate weathering kaolinite is the possible mineral that is in equilibrium with the water implying that the chemistry of reservoir water favours kaolinite formation the calculated values of sar rsc and sodium percentage indicate the excellent to good quality of water for irrigation uses

the development of irish offshore sedimentary basins a variety of ensialic mesozoic and cenozoic sedimentary basins surround ireland three main periods of basin development occurred the first in the permo triassic produced a series of small rift basins which nucleated along reactivated generally caledonian structures the second in the mid and late jurassic represents a period of crustal extension and rifting the third phase reflects thermal subsidence of cretaceous and tertiary age and coincides with seafloor spreading in the north atlantic the basins developed in response to general east west extension simple extensional structures accompanied by crustal thinning dominated in the north south trending porcupine basin the ne sw oriented basins in the celtic sea slyne erris donegal and rockall areas developed in a transtensional setting until early cretaceous times the goban spur basins at the confluence of regional structural trends and adjacent to the continent ocean boundary are dominated by transtensional structures the effects of early tertiary alpine compression are seen especially in the celtic sea basins the basins whilst having some broad geological similarities which reflect eustatic sea level variations differ in their detailed evolution each basin experienced unique facets of local structural control tectonic history and facies distribution

observations of the trade wind wakes of kauai and oahu 1 the hawaiian islands of kauai and oahu stand in the path of the east northeasterly trade winds creating wakes in the lee for the first time the structure of the wakes and their diurnal cycle were observed on a cruise during 18 20 december 2006 the dynamic wakes characterized by reduced trades extend about 1 km in height with strong wind shear at the top thermal forcing of these small islands also affects the wake circulations sea breezes develop in the afternoon turning the winds into westerly near the shore in the wakes at night land breezes advect cool air from the islands creating a shallow cool layer between the sea surface and a capping inversion the warming in the wake in the afternoon extends much deeper 1 4 km than the cool layer 0 5 km at night the effect of diurnal changes on cloud formation in the wakes is discussed and the sharp variations in wind velocity lee of the islands may affect ocean currents waves and mixing

microtextures on quartz grains in tills from antarctica quartz grains of the sand 63 2000 m fractions from tills of oligocene to quaternary age in antarctica were analyzed by scanning electron microscope sem to test the hypothesis that relative ice thickness and distance of transport influence the type and range of microtextures observed on individual grains in this study replicated subsamples were analyzed from tills emplaced by thick glaciers with both short and long transport distances till samples with grains transported over long distances up to several hundred km under thick ice 1000 m were compared with quartz grains from relatively thinner e g 500 m thick outlet glaciers with shorter transport distances 100 km a range of microtextures including subparallel linear fractures conchoidal fractures arc shaped steps grain relief edge sharpness grain angularity and roundness straight and curved grooves crescentic gouges dissolution features precipitation features and presence of adhering particles was used to determine the environmental history of these grains microtextures on sand size clasts including microfractures abrasion etching and coatings can provide important information on paleoenvironmental history including glacier activity and severity of weathering inferred from etching and dissolution features

the velocity structure of the sediments in the southern rockall basin results from new wide angle seismic modelling abstract travel time modelling of first and second arrivals have been used to produce p wave velocity models of the sedimentary structure on three new wide angle reflection refraction profiles from the irish sector of the rockall basin the models indicate a sedimentary succession that is typically 4 5 km thick and reaches a maximum thickness of 7 km the sediments are typically horizontal within the basin centre but display significant structural complexities towards the margins where sediment depocentres and large fault blocks are interpreted up to seven layers with velocities ranging from 1 8 to 5 2 km s 1 have been resolved within which three distinct seismic packages have been identified an upper package interpreted as oligocene and neogene in age is approximately 1 5 km thick and confined within the rockall basin pinching out onto the basin margins this overlies a structurally complex middle package ca 1 5 km thick confined predominantly within the basinal areas which is interpreted as being of cretaceous to early tertiary age a regionally extensive lower package up to 4 km thick is interpreted as being of probable late palaeozoic to jurassic age the new data provide a much clearer picture than was hitherto available of the entire sedimentary succession in the basins that underlie the rockall trough they show a significant variability in thickness of the various sedimentary layers and in particular illustrate a marked topographic irregularity at the base of the sedimentary succession

crust generated above the iceland mantle plume from continental rift to oceanic spreading center since the north atlantic continental breakup in the early tertiary the process of rifting above a mantle plume has produced large thicknesses of igneous crust we report results of an integrated offshore onshore seismic study of the crust and upper mantle along a transect of the aseismic faroe iceland ridge between the continental fragment beneath the faroe islands and the present day spreading center in northeast iceland normal incidence seismic data provide an image of the uppermost crust which is complemented by a velocity model from streamer refraction analyses these data together image four sedimentary basins up to 400 m deep along the crest of the ridge the streamer refraction velocity model in turn forms the uppermost section of a full crustal velocity model derived from travel time modeling of air gun and explosive data the compressional to shear wave velocity ratio in the crust of the faroe iceland ridge is 1 77 0 02 similar to that of eastern iceland the moho beneath the faroe iceland ridge lies at a depth of 25 30 km crust of 25 30 km thickness requires an upper mantle potential temperature elevated 200 250 c above normal if formed by passive adiabatic decompression melting of the mantle or a somewhat less elevated temperature if as is likely there is a component of active convection in the underlying mantle plume core

morphologies and emplacement mechanisms of the lava flows of the faroe islands basalt group faroe islands ne atlantic ocean the palaeogene faroe islands basalt group fibg comprises three eruptive sequences or formations all emplaced into a subaerial environment during the development of the extensive continental flood basalt province that stretches from east greenland through the faroe islands and into the faroe shetland basin the beinisvor formation having a tabular classic facies architecture is composed of a sequence of simple flows each comprising a single sheet lobe the beinisvor formation is overlain by the distinctly contrasting malinstindur formation that has a compound braided facies architecture the enni formation occurs at the top of the sequence and consists of a mixture of simple and compound flows with tabular classic and compound braided facies architectures respectively surface and internal characteristics of the sheet lobes of the beinisvor and enni formations indicate emplacement through inflation which is more obvious for the tube fed compound flows of the malinstindur and enni formations the difference between the simple and compound flow sequences of the fibg is most likely linked to the manner in which the lava was supplied during the eruption and the eruptive style of the volcanic system the sheet lobes were erupted over laterally extensive areas from fissure systems which had a continuous supply of lava which contrasts with the tube fed compound flows which were erupted in a gradual piecemeal manner from point sourced low shield volcanoes with limited areal extents

the structure and subsidence of rockall trough from two ship seismic experiments coincident multichannel seismic reflection and refraction profiles acquired northwest of britain during a two ship seismic experiment in the southern rockall trough provide evidence for a thin 6 km syn rift crust below rockall trough the variation of seismic velocity with depth is consistent with either oceanic crust similar to that found in other parts of the north atlantic or with thinned continental crust heavily intruded by syn rift igneous rocks the syn rift crust beneath rockall trough is now buried by nearly 5 km of sediments that are intruded by tertiary volcanics varying in extent from isolated sills to a large sill complex extending 100 km laterally the basement imaged on seismic profiles exhibits a band of subhorizontal reflectors that extend laterally over distances of up to 40 km which they interpret as sediments intercalated with submarine lava flow generated during the opening of the trough estimates of stretching from crustal thinning and from subsidence indicate that rockall trough has undergone extensive rifting beta 6 upwelling asthenosphere beneath the thinned lithosphere generated at least 1 3 km thickness of melt as it decompressed the molten rock rose upward from the mantle until it was in part extruded as lava flows and in partmore intruded into the crust less

structural and petrologic evolution of the lihue basin and eastern kauai hawaii the topography of the eastern part of the hawaiian island of kauai is dominated by the lihue basin a large 110 km 2 semicircular depression bounded by steep cliffs and partly filled by late rejuvenated stage or posterosional stage volcanic material as with other large semicircular basins on ocean island volcanoes the subsurface geology and origin e g structural collapse vs fluvial erosion of the lihue basin are poorly understood new analyses of samples collected from eastern kauai and drill holes within the basin document several important features of the late stage geologic evolution of kauai first thick 300 m sequences of rejuvenated stage koloa volcanics in the lihue basin show systematic basin wide geochemical trends of increasingly incompatible elements with time indicating a gradual decrease in the extent of partial melting of mantle sources with time second beneath the rejuvenated stage volcanics in the basin a thin layer of postshield alkalic stage lavas e g hawaiites and mugearites overlies older shield stage tholeiitic lavas of the napali member indicating that the lihue basin formed by structural collapse not fluvial erosion third a large 2 5 km 3 matrix supported breccia interpreted as deposits of one or more debris flows is within the rejuvenated stage volcanics throughout the basin and correlates with surficial exposures of the palikea breccia west of the basin isotopic compositions of the bulk breccia are similar to those of tholeiites from the east side of kauai and distinct from those of west kauai tholeiites clasts within the breccia are dominantly hawaiite and alkali gabbro the source region of the breccia in the steep cliffs and highlands of the central massif to the west of the basin must contain magmatic products of an extensive postshield alkalic stage including hawaiite flows and one or more large intrusive bodies or ponded sequences of alkali gabbro

crustal structure beneath the faroe islands and the faroe iceland ridge abstract we have mapped the transition from the continental faroe block the faroe islands and surrounding shelf to the thickened oceanic crust of the faroe iceland ridge in the north atlantic using the results of a detailed sea to land seismic profile with wide angle to normal incidence recordings of explosive and airgun shots fired at sea along the faroe iceland ridge interpretation of all available seismic and gravity data indicates that this aseismic ridge is composed of 30 3 km thick oceanic crust with a gradual transition to ancient continental crust from 100 to 40 km northwest of the faroe islands close to the shelf edge this confirms that the crust beneath the faroe islands which may be up to 46 km thick comprises continental material in agreement with previous seismic and geochemical results results suggest that the upper 5 2 0 7 km of the faroe crust consists of tertiary basalts generated during continental breakup overlying the continental crust beneath the lower crust where seismic constraint is poor may exhibit high seismic velocities 7 1 7 6 km s 1 which we attribute to underplating or intrusion by mafic melts during continental breakup in the early tertiary

late palaeozoic mesozoic tectonostratigraphic development of the eastern faroe shetland basin new insights from high resolution 3d seismic and well data abstract the faroe shetland basin fsb belongs to the sedimentary basins that encompass outer parts of the ne atlantic continental margin the fsb contains several kilometres thick cenozoic and cretaceous strata which overlie poorly understood pre cretaceous strata regional high resolution 3d seismic reflection data used in this study covers the eastern half of the basin generally devoid of thick basaltic successions the pre cretaceous successions are preserved as erosional remnants of originally more extensive deposits throughout the fsb devono carboniferous and permo triassic rifting probably took place in the fsb but the magnitude and regional extent of each phase is less constrained than in the neighbouring inner hebrides shetland rift basins major rifting took place in jurassic times and generated a fault controlled marine basin during the apto albian and cenomanian distributed extension occurred throughout the fsb suggesting wide rift mode of extension the subsequent campanian maastrichtian extensional phase on the contrary was localized in the flett sub basin controlled by the westray and corona faults along its western margin and oppositely dipping faults along the eastern basin margin the fault controlled cretaceous deposition in the fsb is a distinct feature that is documented in the basins along the mid norwegian margin but rarely recorded in other large cretaceous basins along the ne atlantic margin in the fsb late cretaceous faults frequently reactivated earlier structures suggesting that a structural inheritance played an important role in basin development the existence of permo triassic evaporites is postulated to explain geometries of jurassic and lower cretaceous strata and fault patterns in the foula sub basin a partial mantle serpentinization during early cretaceous times proposed for other outer basins along the ne atlantic margin is unlikely to have occurred in the fsb

the lithosphere below the rockall trough wide angle seismic evidence for extensive serpentinisation abstract the longer range data from wide angle seismic reflection experiments along an axial and transverse profile determined the seismic properties of the shallow mantle lithosphere beneath the rockall trough in the north atlantic two subcrustal p and s wave reflections are observed the first defines a layer 3 10 km thick below the moho where p wave velocities vary from 7 5 to 7 8 km s v p v s ratios increase within this layer from 1 80 in the north to 1 83 in the south of the basin along the axial profile the second reflection from approximately 34 km depth identifies a layer 15 20 km thick with a vp velocity of approximately 8 1 km s and a v p v s ratio of 1 73 these values are typical for normal mantle peridotites both p and s wave velocities and v p v s ratios constrain the possible composition of the first layer which is interpreted as a zone of partially serpentinised peridotites below the moho about 15 volume alteration of the parent mantle peridotite is required to produce the observed seismic properties this degree of alteration accounts for a systematic deficit in total tectonic subsidence when compared with that predicted from the variation in bulk crustal stretching along the axis of the basin syntectonic cooling occurred during differential lithospheric stretching as the upper to mid crust became more extended over a narrower region than the mantle lithosphere this served to rheologically couple the lower crust to the mantle near the final stage of deformation as the primary brittle ductile transition zone in the crust migrated downwards into the mantle lithosphere the resultant fracturing generated the permeability necessary to facilitate the seawater circulation which hydrated the cold mantle

the transition between the erris and the rockall basins new evidence from wide angle seismic data abstract the rockall trough is a deep water basin west of britain and ireland the origin of the basin and the nature of the crust beneath it is controversial a series of seismic wide angle experiments carried out during 1988 and 1990 help to clarify the crustal and upper mantle structure in the region results for the crustal structure from a profile which straddles the shelf break between the basin and the irish shelf are discussed here these data together with the available geological information indicate that the basin probably formed in the late palaeozoic to early mesozoic as part of a regionally linked basin assemblage which includes the hatton basin and the shallow sea basins surrounding ireland and britain good data quality has allowed the transition between the relatively unstretched crust of the irish and british mainland defined by previous onshore seismic refraction experiments to be well resolved the erris trough one of the small late palaeozoic to early mesozoic basins which fringe the mainland shelf region north of the porcupine basin is a half graben its major bounding fault is located on its western margin and the basin is divided from the rockall trough by a narrow horst the erris ridge the shelf trajectory along the western flank of the horst deepens smoothly towards the trough centre where the crust thins to 5 km near the trough margin below a sedimentary and water column 8 km thick surprisingly the crustal thickness is slightly greater over a 150 km broad zone at the trough centre i e ca 6 km this change in crustal thickness may be due to lateral strain migration to the warmer basin margins as its centre cooled during the deformation the crustal structure beneath the sediment pile at the trough centre is two layered as opposed to the three layered seismic refraction structure found onshore however the basic character of the lower crust present in onshore ireland in particular the presence of a gradient zone defining the crust mantle transition is still preserved in the trough this similarity in structure precludes the presence of magmatic underplating the crustal structure observed in the rockall trough can be formed by differential stretching of the lithosphere in this model the lower ductile crust and mantle lithosphere are stretched over a wide region by 2 2 3 strain focusing into a much narrower region of brittle upper crust generates severe amounts of crustal thinning 1 8 10 and is responsible for the fusing of the upper and mid crustal seismic refraction layers found beneath onshore ireland and britain mediating detachment surfaces sited at the brittle ductile transition at any time served to relay the strain from the lower lithosphere into the upper crust syntectonic heat loss plays an important role in controlling the deformation pattern

seismic studies in the north celtic sea basin implications for basin development modelling of seismic refraction data from the north celtic sea basin offshore ireland demonstrates the presence of a nnw trending basement flexure mesozoic sediments are 4 km thick on the west and 6 km thick on the east of the feature which is interpreted as a transfer fault zone lying along a major reactivated basement fracture bulk extension is greater in the lower lithosphere than in the upper crust with the interface being a rheologically regulated mid crustal detachment surface the basin developed in response to the interplay between periodic disengagement along the detachment and selective strain transfer into the upper crust

evidence for kilometre scale neogene exhumation driven by compressional deformation in the irish sea basin system simon p holford paul f green jonathan p turner gareth a williams richard r hillis david r tappin ian r duddy

microtextures of quartz grains from modern terrestrial and subaqueous environments north slope of alaska abstract scanning electron microscopic sem analysis of surface features on detrital monocrystalline quartz sand grains is used in conjunction with existing information on hydrology climate and depositional environment in an attempt to unravel the history of surface deposits on the alaskan north slope and shelf samples from along the colville and sagavanirktok rivers ranging from the high relief headwaters to the subaerial deltas were analyzed together with a suite of continental shelf samples that form a transect from shallow submerged deltas across barrier islands shoals and out to the shelf break twenty to thirty grains from each sample were analyzed and assigned to one of eight grain types the classification was devised by the authors to represent increasing aquatic and eolian a rasion and resultant destruction of the original grain form and evolution towards a rounded and chemically altered form our study leads to the following conclusions 1 increasing abrasion occurs with increasing river transport distance but this pattern does not extend across the shelf where modern erosion of underlying shelf deposits is believed to mask the riverine influence 2 a considerable number of freshly fractured grains occur in samples from delta nearshore and shelf environments but are completely absent in the fluvial environment suggesting that the process of refracturing grains is associated with modern littoral or marine processes 3 the large number of refractured grains in the shoal environment suggests that intense impacting of grains through ice related sediment ry processes may provide a mechanism for fracturing the grains 4 samples from the barrier islands stamukhi shoal and the general shelf surface are so similar that the question of whether such shoals represent drowned barrier islands or modern constructional features cannot be answered 5 the similarity between all shelf samples with a preponderance of eolian grain types suggest that sands with similar abrasional histories cover the shelf and this blanket may have developed from deposits strongly influenced by eolian processes during times when the shelf was subaerially exposed 6 the extensive chemical features on the surface of many of the grains from the shelf environment suggest a relict or erosional source for the grains

analysis of the crustal velocity structure of the british isles using teleseismic receiver functions summary the onshore crustal and upper mantle velocity structure of the british isles has been investigated by teleseismic receiver function analysis the results of the study augment the dense offshore and sparse onshore models of the velocity structure beneath the area in total almost 1500 receiver functions have been analysed which have been calculated using teleseismic data from 34 broadband and short period three component seismic recording instruments the crustal structure has primarily been investigated using 1 d grid search and forward modelling techniques returning crustal thicknesses bulk crustal vp vs ratio and velocity depth models h stacking reveals crustal thicknesses between 25 and 36 km and vp vs ratios between 1 6 and 1 9 the crustal thicknesses correlate with the results of previous seismic reflection and refraction profiles to within 2 km the significant exceptions are the stations close to the iapetus suture where the receiver function crustal thicknesses are up to 5 km less than the seismic refraction moho this mismatch could be linked to the presence of underplated magmatic material at the base of the crust 1 d forward modelling has revealed subcrustal structures in northern scotland these correlate with results from other uk receiver function studies and correspond with the flannan and w reflectors the structures are truncated or pinch out before they reach the midland valley of scotland the isolated subcrustal structure at station gim on the isle of man may be related to the closure of the iapetus ocean

first cycle grain weathering processes compositions and textures of sea glass from port allen kauai hawaii abstract chemical and mechanical weathering textures on siliciclastic grains have provided important information concerning depositional processes and environments yet understanding is limited by the multicycle origin of most sedimentary deposits sea glass grains sampled from a beach in port allen kauai hawaii were analyzed for mechanical and chemical weathering features using scanning electron microscopy sem energy dispersive x ray edx analysis and x ray photoelectron spectroscopy xps as a result of a proximal dumping ground source the sea glass offers a unique opportunity to study first cycle grain weathering processes in a moderate to high energy shoreline environment grain size analysis indicates that the largest grains are located behind natural barriers such as outcrops and boulders the best sorted samples are from the lower to middle foreshore environment whereas moderately sorted deposits are located closer to the backshore where storm waves predominate although there is no preferred distribution of different colored sea glass grains on the beach nonfrosted grains predominate over frosted varieties suggesting constant input of fresh material grain surface textures can be divided into mechanically dominated and chemically dominated weathering groups evidence of mechanical weathering is provided by conchoidal fractures crescentic gouges and straight grooves whereas chemical weathering is indicated by c shaped cracks halite salt and silica precipitation and solution pits combinations of these features demonstrate that both weathering processes work together to degrade the grains xps depth profiling of individual grains indicates that chemical weathering occurs at different grain depths with leaching of sodium from the glass surfaces this study provides a rare opportunity to relate grain compositions and textures with depositional and weathering processes due to the first cycle origin of the sea glass the results show that using xps and sem techniques is a broadly applicable approach toward unraveling chemical and mechanical breakdown of sediment in beach environments

the southern margin of the rockall plateau stratigraphy tertiary volcanism and plate tectonic evolution the geological evolution of the southwest rockall plateau in the area of edoras bank has been clarified using seismic reflection gravity and magnetic data four principal reflectors are observed within the tertiary sedimentary sequence i late miocene ii latest early miocene iii late eocene iv earliest eocene a period of pronounced sediment drift accumulation marks the interval i ii reflector iii the top of a sediment wedge prograding southward from edoras bank marks a change from terrigenous to pelagic sedimentation that is probably related to subsidence of the rockall plateau following the separation of greenland from eurasia in the earliest eocene reflector iv marks the top of a wedge shaped seismically transparent layer that also thins southward away from edoras bank on the basis of its seismic attributes and magnetic signature this layer is interpreted as a volcanic sheet formed as part of the north atlantic tertiary volcanic province during rifting of greenland from eurasia the recognition of voluminous volcanic rocks south of edoras bank extends the known area of the tertiary volcanic province several hundred kilometres to the south gravity anomaly modelling and continental reconstructions suggest that the region south of edoras bank is underlain by thinned continental crust a four stage geological evolution for this region is indicated i initial rifting associated with the separation of labrador from greenland in the late cretaceous is characterized by enhanced crustal thinning and subsidence in the region of a rift triple junction ii passive subsidence and accumulation of late cretaceous and earliest tertiary sediments followed the initiation of seafloor spreading in the labrador sea iii blanketing of the area by palaeocene volcanic rocks masked pre existing magnetic lineations providing an explanation for some of the problems in earlier interpretations based mainly on magnetic data iv post volcanic sedimentation continuing to the present day

geochemical distribution and removal of as fe mn and al in a surface water system affected by acid mine drainage at a coalfield in southwestern china the chemical characteristics formation and natural attenuation of pollutants in the coal acid mine drainage amd at xingren coalfield southwest china are discussed in this paper based on the results of a geochemical investigation as well as geological and hydrogeological background information the chemical composition of the amd is controlled by the dissolution of sulfide minerals in the coal seam the initial composition of the groundwater and the water rock interaction the amd is characterized by high sulfate concentrations high levels of dissolved metals fe al mn etc and low ph values ca2 and so42 are the dominant cation and anion in the amd respectively while ca2 and hco3 are present at significant levels in background water and surface water after the drainage leaves the mine site the ph and alkalinity increase asymptotically with the distance along the flow path while concentrations of sulfate ferrous iron aluminum and manganese are typically controlled by the deposition of secondary minerals low concentrations of as and other pollutants in the surface waters of the xingren coalfield could be due to relatively low quantities being released from coal seams to adsorption and coprecipitation on secondary minerals in stream sediments and to dilution by unpolluted surface recharge although as is not the most serious water quality problem in the xingren region at present it is still a potential environmental problem

the crustal structure of the rockall trough differential stretching without underplating the crustal structure along the axis of the rockall trough in the north atlantic has been studied along a 600 km refraction wide angle reflection transect containing three lines each 200 to 250 km long using explosives and ocean bottom seismometers one dimensional inversions of each section were made using the p method and forward modeling of the observed travel times in the next stage travel times and amplitudes were modeled using ray tracing techniques through two dimensional heterogeneous structures the results indicate that there are three sedimentary layers with velocities ranging from 2 km s to 4 5 km s the whole sedimentary section is up to 6 km thick and interpreted as late paleozoic to tertiary in age a two layer continental crust 5 to 7 km thick occurs along the length of the profile the upper crust 6 0 6 3 km s is circa 2 km thick and the lower crust 6 6 6 9 km s is circa 3 km thick a moho transition zone approximately 1 km thick lies at the base of the crust velocities in this transition zone increase from 6 9 km s up to 7 8 km s along the profile the underlying upper mantle has a laterally variable velocity between 7 6 and 7 8 km s unstretched crust onshore in ireland comprises a three layered crust with each layer approximately 10 km thick and a moho transition zone which is about 3 km thick the two upper layers in the onshore region are interpreted as corresponding to the upper crust in the rockall trough and indicate a stretching factor of 8 10 the velocity pattern in the lower crust in the rockall trough and under ireland are similar suggesting significantly less stretching 2 3 the differential stretching model is supported by the presence of the moho transition zone which is stretched by a similar factor to the lower crust the bulk stretching factor for the crust as a whole is in the range of 4 6 if this represents the lithospheric stretching factor significant underplating would be expected however if the stretching factor for the lower crust in the differential stretching model is more representative of overall lithospheric stretching little or no underplating is predicted the velocity patterns observed in the rockall trough indicate the absence of any significant underplating at the base of the crust such as that observed at the continental margin west of the hatton basin

a refraction seismic transect from the faroe islands to the hatton rockall basin 1 the crustal structure of the faroe rockall plateau was studied by a 790 km long refraction seismic transect consisting of two intersecting lines the air gun shot spacing was 200 m and the signals were recorded by 77 ocean bottom seismometers a p wave velocity model was developed from forward and inverse modeling of the wide angle seismic data and incorporation of coincident multichannel reflection seismic data continental crust with velocities ranging from 5 6 to 6 8 km s can be traced from the faroe islands across the banks to the sw of the faroes and into the hatton rockall basin the thickness of the subvolcanic crust is up to 25 km on the banks but is as little as 8 km in the channels between the banks the thinning in the channels may be related to nw trending shear zones extending from major lineaments in ne rockall trough basalt layers are found along the entire transect with a total thickness of up to 4 km two layers with velocities of 4 9 5 2 and 5 3 5 6 km s are thought to represent paleogene flood basalts that can be correlated from the faroe islands to george bligh bank close to george bligh bank an 80 km wide and up to 9 km thick body with velocities of 6 5 km s is interpreted as intrusion a 5 km thick high velocity lower crustal layer 7 3 km s extends from the area of the intrusion into the northern hatton rockall basin at the northern flank of lousy bank the transition zone to oceanic crust was encountered

the hatton bank continental margin ii deep structure from two ship expanding spread seismic profiles summary the continent ocean transition adjacent to hatton bank was studied using a dense grid of single ship and two ship multichannel seismic profiles the interpretation of the explosive expanding spread profiles esps which were shot as part of this survey are discussed here in detail extensive seaward dipping reflectors are developed in the upper crust across the entire margin these seaward dipping reflectors continue northwards on the faeroes and voring margins where they have been shown to be caused by basaltic lavas as well as on the conjugate margin of east greenland the dipping reflectors are an important feature of the rifting history of the margin and show that extensive volcanism was associated with the extension the esps show clear seismic arrivals out to ranges of 100 km wide angle moho reflections can be seen on all the lines as well as good mid and lower crustal arrivals the determination of seismic velocity structure was constrained by ray tracing and by amplitude modelling using reflectivity synthetic seismograms the results from the esps show that there is a thick region of lower crustal material beneath the margin with an unusually high crustal velocity of 7 3 7 4 km s this lower crustal material reaches a maximum thickness of 14 km beneath the central part of the margin and is terminated at depth by the moho the lower crustal lens of high velocity material is interpreted as underplated or intruded igneous rocks associated with the large volumes of extrusive basaltic lavas now seen as dipping reflectors on the margin

characterisation of the sarcheshmeh copper mine tailings kerman province southeast of iran mineral processing operation at the sarcheshmeh porphyry copper mine has produced huge quantities of tailings materials containing sulphide minerals in particular pyrite these tailings materials were geochemically and mineralogically characterised to assess pyrite and chalcopyrite oxidation acid mine drainage generation and trace element mobility to lead development of a proper remediation plan five vertical trenches up to 4 2 m deep were excavated from the tailings surface and 70 solid samples were taken in 0 3 m intervals the samples were first mineralogically analysed pyrite was the main sulphide mineral found in the tailings the gangue minerals include quartz muscovite illite chlorite albite orthoclase halite the samples were geochemically analysed for total concentrations of 62 elements paste ph so4 2 co3 2 and hco3 the maximum concentrations of so4 2 1 300 1 170 1 852 1 960 and 837 mg l were observed at a depth of 0 9 m in profiles a b c d and e respectively the tailings have a high acid producing potential and low acid neutralising potential pyrite 4 6 wt calcite 1 wt fe2 so4 3 cuso4 mgso4 and mnso4 were the dominant secondary sulphate minerals in the tailings the lowest ph values 2 9 3 and 3 were measured at a depth of 0 3 m in the profiles a b and c 3 9 at a depth of 0 6 m in the profile d and 3 at a depth of 0 9 m in the profile e the upper portions of the profiles c 1 8 m and d 2 1 m were moderately oxidised while oxidation in the profiles a b and e did not extend more than 1 2 1 2 and 1 5 m beneath the tailings surface zn pb rb u hf nd zr and ga show almost a constant trend with depth cd sr th la and ce increased with increasing depth of the tailings materials while co v ti cr cu as mn ag mo and ni exhibit initially a decreasing trend from tailings surface to the depths that vary between 0 9 and 1 2 they then remained constant with the depth the results show pyrite and chalcopyrite oxidation at surface layers of the tailings and subsequent leaching of the oxidation products and trace elements by infiltrated atmospheric precipitation

the hatton basin and continental margin crustal structure from wide angle seismic and gravity data results from a wide angle seismic and gravity study between the rockall bank and the iceland basin in the north atlantic are presented crustal and sedimentary structures are resolved in the hatton basin and across the hatton continental margin hcm east of magnetic anomaly 24 the structure of the oceanic crust west of the anomaly is also determined gravity data support the seismic model in areas of good seismic coverage and are used to control the model where the wide angle seismic data are poor a two layer sedimentary sequence is present both in the hatton basin and across the continental margin the lower layer with p wave velocity of about 4 km s is interpreted as pre eocene synrift sediments and is up to 3 5 km thick a younger and thinner 1 2 5 km postrift sequence with a velocity of about 2 km s defines a strong velocity contrast which suggests an erosional unconformity surface the sedimentary structure is distinctly different from that in the rockall trough where a third intermediate layer vp 3 km s occurs the three layer crust characterized by two intracrustal reflections pip1 and pip2 varies from 30 km thick under the rockall bank to about 15 km below the hatton basin where it is stretched by a factor of 2 relative to onshore ireland the crust is thinnest below the hatton bank where the presence of a single intracrustal reflection indicates that the lower crustal layer thins to below the seismic resolution limit below the hcm a region of thick lower crust with anomalously high velocity vp 7 2 km s is resolved by the seismic and gravity data it is connected west of anomaly 24 to a region of oceanic crust which is thicker than in the iceland basin these relationships between the thick lower crust below the hcm and the oceanic crust in the iceland basin are interpreted as evidence for magmatic underplating consistent with previous models for the hcm the inferred unconformity surface between the synrift and postrift layers may be due to regional uplift driven by upwelling of hot asthenosphere before anomaly 24 early eocene time

the hatton bank continental margin iii structure from wide angle obs and multichannel seismic refraction profiles summary in two recent papers normal incidence and expanding spread profiles esps shot across the hatton bank passive continental margin showed seaward dipping reflectors in the upper crust and elevated velocities in the lower crust the reflectors were interpreted as subaerial basalt flows and the high velocities as underplated or intruded igneous material in the lower crust a recent gravity model shows high densities in the lower crust supporting the velocity model in this study we present the forward modelling of two wide angle seismic refraction datasets shot perpendicular to strike and through the esp midpoints the final velocity model across the margin is consistent with all the seismic datasets but differs in some important respects from the esp based model a high velocity volcanic pile is outlined mid way up the continental slope and the inferred velocities in the lower cnst are slightly lower the differences between the two models can be explained by the three dimensional nature of the margin the esps were modelled assuming that the sub sediment structure was invariant along strike the final velocity model is used to obtain an estimate of the total thickness of melt accreted across the margin which is calculated to thicken from zero at hatton bank to about 12 km mid way down the continental slope at the bottom of the continental slope the adjacent igneous section forming the oceanic crust is about 18 km thick and thins rapidly northwestwards to 11 km as the oceanic crust thins its seismic velocity decreases this suggests that it is less mafic and that there is a post rift decrease in the percentage of mantle melting this decrease may be explained by a decrease in asthenospheric temperature and or by a reduction in volatile content

wavelet and multitaper coherence methods for assessing the elastic thickness of the irish atlantic margin summary there have been some inconsistencies in estimates of the effective elastic thickness of the continental lithosphere te based upon admittance or coherence relationships between gravity and topography this paper compares multitaper and wavelet methods to analyse the coherence between bouguer gravity and bathymetric data over the irish atlantic margin the analyses show that similar lateral te variations can be recovered from the data but demonstrate that the size of the data window can give rise to a significant downward bias in te estimates a seismically constrained 3 d gravity inversion over the rockall basin shows the presence of surface and subsurface loads whose ratio is loosely correlated with load ratio variations generated from the wavelet coherence method the te and load ratio f variations can be plausibly related to major geological structures on the margin if the load ratio variations can be interpreted geologically it implies that spectral based methods to estimate effective elastic thickness must incorporate subsurface loads within the underlying theoretical model on the irish atlantic margin te is generally low 6 18 km and is associated with a ne sw caledonian trend the weakest lithosphere is in the southern rockall basin porcupine bank and porcupine basin and the strongest lithosphere is along the rockall hatton region the low te values are consistent with results from other passive margins the reasons for such low te values on the irish atlantic margin remain unclear but may be the consequence of te being frozen into the lithosphere when loads were emplaced during continental breakup and temperature gradients were high the process of sedimentation and the presence of fluids may be contributory factors there is an indication of a geological and rheological divide between the rockall hatton region and the rockall basin possibly associated with the caledonian orogenic front

the crustal structure of the continental margin east of the falkland islands abstract the 1500 km long falkland plateau is the most prominent morphological structure in the southern south atlantic ocean which crustal composition and development is mainly unknown at the westernmost boundary of the plateau the falkland islands precambrian geology provides the only insight into basement structure and age the question of whether continental basement of a similar age and origin underlies the falkland plateau further east is strongly disputed we present new high quality constraints on the crustal fabric of the plateau east of the falkland islands based on wide angle seismic and potential field data acquired in 2013 the p wave velocity model supported by amplitude and density modelling shows that the falkland plateau basin is filled with 8 km of sediments continental crust of 34 km thickness underlies the falkland islands the eastern continental margin of the falkland islands can be classified as a volcanic rifted margin the falkland plateau basin is floored by up to 20 km thick oceanic crust the exceptionally thick igneous crust and its high lower crustal velocities up to 7 4 km s indicate the influence of a regional thermal mantle anomaly during its formation which provided extra melt material the wide angle model revises published crustal models which predicted thin oceanic or thick extended continental crust below the falkland plateau basin our results provide a sound basis for future tectonic interpretations of the area

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved