the kraemer island macrodyke east greenland solidification of a flood basalt conduit the kraemer island macrodyke that is exclusively exposed on kraemer island about 7 km west of the skaergaard intrusion belongs to a regional dyke swarm termed the skaergaard like dykes or fg 1 dykes weakly modally layered olivine gabbros dominate the exposed parts of the intrusion that has a width of 650 m to 1000 m plagioclase core an 68 2 and ca rich pyroxene core mg no 79 1 grains are normally zoned whereas olivine grains fo50 65 are homogeneous calculated mineral magma equilibria based on experimentally determined mg fe magma olivine and magma clinopyroxene partition coeffi cients suggest that the observed olivine and clinopyroxene compositions in the gabbros cannot have formed from a common parental magma the unzoned nature of olivine grains and their iron rich com positions relative to clinopyroxene suggest post cumulus mg fe exchange between olivine and interstitial melt a gabbroic pegmatite is developed in the centre of the intrusion along its entire exposed 5 km strike length here mineral zonation is limited and compositions are similar to rims of cumulus minerals in the enveloping olivine gabbros the pegmatite could therefore represent interstitial melt mobilized from gab broic cumulates that later accumulated and crystallized at its present stratigraphic location cumulus olivines in the gabbros are close to equilibrium with ca rich pyroxene in the pegmatite this is interpreted as reflecting interstitial melt mobility during the late stages of solidification of the macrodyke chilled margins are well preserved at the intrusion margins and are rich in fe 14 15 3 feo tot ti 3 3 3 tio2 and light rare earth elements la sm n 1 2 1 3 similar to magmas well represented in the overly ing sequence of contemporaneous high ti series flood basalts it is therefore likely that extensive wall rock melting adjacent to the macrodyke reflects continuous feeding of the overlying flood basalts through the kraemer island macrodyke

postcumulus processes in layered intrusions during the postcumulus stage of solidification in layered intrusions fluid dynamic phenomena play an important role in developing the textural and chemical characteristics of the cumulate rocks one mechanism of adcumulus growth involves crystallization at the top of the cumulate pile where crystals are in direct contact with the magma reservoir convection in the chamber can enable adcumulus growth to occur to form a completely solid contact between cumulate and magma another important process may involve compositional convection in which light differentiated melt released by intercumulus crystallization is continually replaced by denser melt from the overlying magma reservoir this process favours adcumulus growth and can allow adcumulus growth within the pore space of the cumulate pile calculations indicate that this process could reduce residual porosities to a few percent in large layered intrusions but could not form pure monomineralic rocks intercumulus melt may also be replaced by more primitive melt during episodes of magma chamber replenishment dense magma emplaced over a cumulate pile containing lower density differentiated melt may sink several metres into the underlying pile in the form of fingers reactions between melt and matrix may lead to changes in mineral compositions mineral textures and whole rock isotope compositions another important mechanism for forming adcumulate rocks is compaction in which the imbalance of the hydrostatic and lithostatic pressures in the cumulate pile causes the crystalline matrix to deform and intercumulus melt to be expelled for cumulate layers from 10 to 1000 metres in thickness compaction can reduce porosities to very low values 1 and form monomineralic rocks the characteristic time scale for such compaction is theoretically short compared to the time required to solidify a large layered intrusion during compaction changes of mineral compositions and texture may occur as moving melts interact with the surrounding matrix both compaction and compositional convection can be interrupted by solidification in the pore spaces compositional convection will only occur if the rayleigh number is larger than 40 if the residual melt becomes lower in density and the convective velocity exceeds the solidification velocity measured by the rate of crystal accumulation in the chamber orthocumulates are thus more likely to form in rapidly cooled intrusions where residual melt is frozen into the pore spaces before it can be expelled by compaction or replaced by convection

laboratory simulation of volcano seismicity the physical processes generating seismicity within volcanic edifices are highly complex and not fully understood we report results from a laboratory experiment in which basalt from mount etna volcano italy was deformed and fractured the experiment was monitored with an array of transducers around the sample to permit full waveform capture location and analysis of microseismic events rapid post failure decompression of the water filled pore volume and damage zone triggered many low frequency events analogous to volcanic long period seismicity the low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample these events exhibited a weak component of shear double couple slip consistent with fluid driven events occurring beneath active volcanoes

duality of magmatism in the plutonic sequence of the sumail nappe oman abstract detailed field mapping of the crustal sequence in several areas of the sumail ophiolite nappe mainly in the fizh the salahi and the haylayn blocks and comparisons with other well studied areas have shown that the crustal sequence was constructed by two distinct although nearly contemporaneous magmatic series the first a gabbroic series was emplaced during the accretion stage at an oceanic spreading centre which formed the layered gabbro unit the high level isotropic gabbro unit and their by products the sheeted dyke complex and the lower extrusives fine grained homogeneous planar laminated gabbros commonly occur at the top of the layered gabbro sequence in some specific areas wadi haymiliyah and wadi rajmi these are strongly differentiated fe ti rich gabbronorites and norites which coincide with large scale discontinuities within the plutonic sequence interpreted as axial discontinuities of the spreading magma chambers the second series an ultramafic wehrlitic series is locally rooted in the upper mantle i e the impregnated dunitic transition zone this has intruded the whole crustal sequence up to the pillow lavas countless discordant and concordant wehrlitic bodies intruded the plutonic sequence making up 20 40 of it in volume we describe the various settings and forms of these intrusions which were largely underestimated in previous studies we also describe their mineralogy and textures and show with chemical and mineralogical arguments that these bodies evolved as relatively closed systems independently from each other we infer from the study of the contacts that the gabbros were still hot and consolidated just at the moment of the wehrlitic intrusion at the base of the crust however indications of immiscibility between gabbros and wehrlites are common suggesting that both magmatic series were quite contemporaneous the wehrlites are commonly isotropic and may exhibit an internal layering of the dunite wehrlite clinopyroxenite type sometimes appearing at the upper or lower margins of the intrusions in this case the ultramafic layered cumulates show lobate intrusive contacts with the adjacent layered gabbros these plagioclase free ultramafic layered cumulates therefore are not interbedded within the gabbro cumulates but actually belong to the wehrlitic intrusive series picritic dykes radiating from the uppermost intrusions can be traced up to the upper extrusives which are for the main part cogenetic with the wehrlites the time of this second magmatic event coincides with the cessation of the accretion process and with the beginning of the intraoceanic detachment of the ophiolite at the spreading centre we believe that the compressive regime that initiated the detachment acted as an efficient filter press and helped the extraction and ascent of the wehrlitic magmas towards the uppermost levels of the crust

classification and mapping of anthropogenic landforms on cultivated hillslopes using dems and soil thickness data example from the sw parisian basin france this study focuses on linear anthropogenic landforms of decametric width on cultivated hillslopes and their relations to soil thickness variability the 16 ha study area shows a rolling topography supported by cretaceous chalk of the sw parisian basin france two types of landforms were identified lynchets similar to those described as soil terraces occurring on downslope field parts in other contexts and undulations linear convex landforms that cut across fields accurate dem construction and a detailed soil thickness survey were performed all over the study area soil samples were classified considering their location on specific types of anthropogenic landforms the classification tree ct method was applied to assess whether lynchets and undulations can be discriminated through morphometric attributes slope curvature profile curvature and planform curvature and soil thickness ctsoil or through morphometric attributes only cttopo the ct application establishes predictive classification models to map the spatial distribution of lynchets and undulations over the whole study area the validation results of the ctsoil and cttopo applications show model efficiencies of 83 and 67 respectively both models performed well for lynchets errors arise mainly from difficulties in unequivocally discriminating gently convex undulations and undifferentiated surfaces especially when soil thickness is not accounted for mean values of soil thickness are 1 08 0 62 and 0 45 m in lynchets undulations and undifferentiated areas respectively the general shape of the thickened soil is characteristic to each type of anthropogenic landform multi temporal mapping of field border networks shows that undulations are linked to borders that were removed during the latest land consolidation lynchets are associated with current field borders lynchets and undulations which cover 39 of the study area define topographic indicators of human induced soil accumulations the method involves perspectives for efficiently mapping and quantifying the anthropogenically modified spatial variability of soil thickness on agricultural hillsides

transmissivity and morphological features in a chalk aquifer a geostatistical approach of their relationship abstract whether for the management of an aquifer or to locate new wells hydrogeologists have always tried to establish transmissivity maps of regional aquifers with the highest possible accuracy classically the transmissivity is obtained from well tests and or from calibrating a groundwater flow model on the piezometric data in this paper we investigate the possibility of adding new information to improve the estimates of the transmissivity in a shallow chalk aquifer i e the characteristics of certain morphological features here referred to as lynchets which are short lineaments that can be seen on aerial photographs or on topographic maps and represent a sudden breach in slope of the ground surface we implicitly associate the density of these features with the density of vertical fracturing of the chalk which is linked to the transmissivity we selected the chalk aquifer of northern france to test this approach using numerical and geostatistical techniques to construct maps of the density of the lynchets we compared them with transmissivity maps produced either by calibrating a groundwater flow model with piezometric data or by kriging the transmissivity values obtained with well tests we conclude that the lynchet information is clearly correlated with the transmissivity and that this information can best be used by cokriging as a second variable associated with the well test data incidentally to fit our geostatistical models of spatial variability variogram we use a new technique called the integral semi variogram which is ideally suited to cases such as this where the spatial distribution of the data is such that the data points cannot easily be grouped into pairs of increasing lag distance this new technique is described briefly

flow rate dictates permeability enhancement during fluid pressure oscillations in laboratory experiments flow rate dictates permeability enhancement during fluid pressure oscillations in laboratory experiments thibault candela 1 2 emily e brodsky 2 chris marone 1 derek elsworth 1 1 dept geosciences penn state univ university park pa united states 2 dept earth sciences uc santa cruz santa cruz ca united states

the continental margin of central east greenland in relation to north atlantic plate tectonic evolution the east greenland continental margin is inferred to have formed in three stages during the tertiary evolution of the adjacent north atlantic ocean the east greenland basaltic volcanism occurred over a period of 2 3 ma which was just prior to the probable date of onset of seafloor spreading in the early eocene shortly before magnetic anomaly 24b 52 ma the associated coastal flexure is interpreted as marking the edge of a zone of stretched and thinned continental crust beneath the inner denmark strait shelf and jan mayen microcontinent this represents a short lived rifting phase just prior to break up according to the evolutionary model the initial break up produced the margins south of the faeroe transform fault 68 5 n and north of the jan mayen fracture zone 72 n but in the intervening region the microcontinent remained attached to east greenland after break up the outer shelf of denmark strait formed from anomalously thick oceanic crust complementary to the iceland faeroe ridge the blosseville kyst margin 68 5 n to 70 n was initiated after anomaly 20 time 42 ma as the jan mayen microcontinent started to separate from greenland with spreading on both sides the new split occupied the line of the pre existing coastal dyke swarm and flexure the liverpool land margin 70 n to 72 n was also initiated at this time but the main separation of the northern part of the microcontinent only commenced after anomaly 7 time 26 ma when a single spreading axis was relocated west of the microcontinent it is suggested that the blosseville lavas subsided during deposition by loading and slight crustal stretching doming occurred near kangerdlugssuaq at the time of break up otherwise the topography of the lavas remained subdued until the relocation of the spreading axis at 26 ma after which the main regional uplift took place

foreshock characteristics in taiwan potential earthquake warning abstract although foreshocks are often considered as a potential precursor in the short term earthquake prediction how to identify foreshocks before the mainshock occurred is a problem abundant earthquakes in the taiwan area might provide a good opportunity for investigating general foreshock characteristic as well as the potential earthquake warning here 10 earthquake sequences with significantly felt foreshocks ml 4 0 are identified from an examination of 161 earthquakes ml 5 0 in the taiwan area during the period between 1990 and 2004 in addition to addressing larger magnitudes ml 4 0 the criteria for selecting foreshocks have considered that 1 the earthquakes occurred within a distance of 15 km and 5 days to the main shock and 2 focal mechanisms of the main shock and foreshocks were generally consistent the results show felt foreshocks often occurred at the strongly heterogeneous crust particularly along the convergent zone between the eurasian and philippine sea plates besides the absence of clustered earthquakes after some large foreshocks may be considered as a criterion to distinguish felt foreshocks from the main shock for improving our ability of earthquake warnings in the taiwan area

petrology and geochemistry of the loch ba ring dyke mull n w scotland an example of the extreme differentiation of tholeiitic magmas the loch ba ring dyke in the tertiary igneous central complex of mull n w scotland is composed predominantly of a banded rhyolitic welded tuff the rhyolite contains numerous inclusions of dark aphanitic rock the textural relationships between the different rocks indicate rapid violent and intimate mixing during emplacement of the dyke the dark glassy component varies continuously from basaltic andesite to andesite dacite and rhyolite these glasses are enriched in feo and depleted in mgo at a given sio2 content in comparison to other tholeiitic highly differentiated volcanic rocks the rhyolite contains an average of 4 phenocrysts and is associated with the mineral assemblage plagioclase an32 to an21 sanidine or50 60 hedenbergite fayalite magnetite ilmenite apatite zircon mineral aggregates involving either plagioclase hedenbergite ilmenite or plagioclase fayalite magnetite are common but aggregates containing fayalite and hedenbergite together are scarce the dark glassy components are either phenocryst free or contain less than 0 2 phenocrysts the main phenocrysts associated with the dark glasses are plagioclase an65 an30 high calcium clinopyroxene ranging continuously from augite to pure hedenbergite pigeonite magnetite ilmenite and rare apatite zoning in minerals is generally weak or absent the plagioclase feldspar high calcium clinopyroxenes and pigeonites have similar compositional ranges to the minerals observed in the middle and upper zones of the skaergaard intrusion the mineral compositions are systematically related to sio2 content and mg number of the glasses the data demonstrate that mineral compositions and assemblages similar to the skaergaard form from silica rich andesitic to rhyolitic liquids the various mafic glasses are interpreted to have been derived from a zoned magma chamber underlying an upper layer of rhyolitic magma differentiation is attributed to fractional crystallization of the observed mineral assemblages causing sio2 enrichment and feo depletion however glasses with less than 57 sio2 have unusual compositions with very low mgo and p2o5 as well as variable al2o3 and tio2 their peculiarities could be explained by andesitic magmas assimilating cumulate mineral aggregates precipitated from more differentiated dacite and rhyolite magmas the bulk compositions of these cumulates have high feo low sio2 and negligible mgo and p2o5 it is suggested that the high density of the mineral aggregates containing fayalite hedenbergite magnetite and ilmenite caused them to settle through the zoned chamber to be assimilated by high temperature less differentiated magmas

using melt inclusions to determine parent magma compositions of layered intrusions application to the greenhills complex new zealand a platinum group minerals bearing island arc intrusion the permian greenhills complex of southland new zealand is a small ultramafic to mafic layered intrusion that hosts primary magmatic platinum group minerals pgms as inclusions in cumulus chromian spinel grains we have determined the major and trace element chemistry of the parent magmas of the complex using the composition of rehomogenized melt inclusions trapped in cumulus spinel grains from dunite these melt inclusions have compositions similar to those of primitive ankaramite dikes that cut the complex verifying that our data are representative of the parent melt chemistry these magmas have high mgo and cao and are enriched in pb sr and large ion lithophile elements compared to high field strength and rare earth elements we suggest that the parent magmas to the complex were primitive low k island arc tholeiite basalts that formed by high degrees of melting of a spinel peridotite source the platinum group element contents of such magmas are expected to be very high therefore the primary pgms at greenhills are suggested to have precipitated directly from the melt following differentiation and cooling in a shallow magma chamber

paleo pedological record of the rocourt pedosequence at veldwezelt hezerwater belgian pleistocene loess belt part 1 evolution of the parent material as the environment influences soil formation loess paleosols are important archives of former climatic conditions however this record is highly complex and all features need to be evaluated in order to obtain consistent information on soil formation this study revises the pedological record of the rocourt paleosol complex an important pedo stratigraphic marker for the eemian and early weichselian at an exceptionally well preserved in situ sequence veldwezelt hezerwater belgian loess belt contrasting hypotheses exist considering the evolution of the parent material after the deposition of the saalian loess and on the importance of aggrading aeolian deposition in this study soil morphological features and depth functions of x ray diffraction grain size distribution cec base saturation total fe al k na and ca content ph and electrical conductivity were established to reconstruct deposition dynamics weathering and carbonate content of the parent material texture analysis confirms the petrostratigraphic homogeneity of the parent material and suggests that it developed under a regime of fluctuating rates of primary dust deposition intermixed with periods of fluvial reworking of the dust strong weathering was identified in the lower stratigraphic unit supporting the general consensus that it formed during the eemian in saalian loess less information is present to confirm the origin of the upper less developed illuvial units which may have formed by welding or by pedogenesis in locally redistributed or aeolian material the overlying a horizons are clearly less weathered and evidence for early recalcification indicates that deposition of unweathered calcareous sediments gained importance during the formation of these horizons

rhythmic layering formed by deposition of plagioclase phenocrysts from influxes of porphyritic magma in the cuillin centre isle of skye the outer bytownite gabbros of the cuillin centre on the isle of skye include a 175 m rhythmically layered sequence consisting of alternating layers of coarse grained massive gabbro and finer grained laminated gabbro we infer that the massive layers formed from repeated influxes of plagioclase phyric magmas which flowed into an existing magma chamber and deposited their entrained phenocrysts on the chamber floor the phenocrysts accumulated rapidly trapping large amounts of pore liquid in the cumulus pile during the intervals between influxes laminated gabbro layers formed by crystallization of the resident magma these layers accumulated more slowly by crystal settling or in situ growth allowing sufficient time for their pore liquids to be expelled by compaction or adcumulus crystallization the resulting fractions of trapped pore liquid were510 in laminated gabbros and 20 40 in massive gabbros high porosity in the massive layers is attributable to rapid accumulation of a lowdensity cumulus assemblage with trapping of pore liquids facilitated by the confining effects of impermeable laminated cumulates above and below among layers whole rock sr and nd isotope ratios reveal variable degrees of contamination by the archean crust beneath skye in the lower part of the section influxes of plagioclase phyric magma are associated with a shift to more primitive mineral compositions lower sr sr and higher nd nd indicating that the replenishing magmas were initially more primitive and less contaminated than those already residing in the chamber in accordance with this interpretation massive layers have lower sr sr than laminated layers consistent with derivation of the plagioclase phenocrysts from a less contaminated source in the upper part of the section the shift toward more primitive and less contaminated compositions is reversed suggesting that over time the replenishing magmas underwent increasing degrees of fractionation and contamination within the magmatic plumbing system that fed the intrusion these observations and inferences coupled with published evidence for other isotopic reversals support a model for growth of the cuillin centre by frequent replenishment of a small volume magma chamber with pulses of magma that underwent complex histories of fractionation and contamination during their transit through the archean crust periods dominated by assimilation and fractional crystallization within the feeder system alternated with periods of vigorous recharge by relatively primitive and less contaminated magmas these cycles were superimposed on an overall trend toward less contamination through time consistent with increasing dominance of the system by uncontaminated tholeiitic magmas as the hebridean magmatic province matured

a gold and platinum mineralized layer in gabbros of the kap edvard holm complex field petrologic and geochemical relations the lower layered series a cumulates of the kap edvard holm complex contain a stratiform layer 1 to 20 m thick and 6 km long that is mineralized with gold and platinum group elements pges the lower layered series a cumulates 650 m thick are dominated by modally layered gabbro with lesser volumes of granular anorthosite and troctolite that together form 2 to 30 m thick layers that are most abundant above the mineralized layer minor volumes of poikilitic wehrlite form a few 1 to 2 m thick layers throughout the section field and petrographic relations as well as cryptic variations in cumulus mineral compositions indicate that the lower layered series a formed in an open system magma chamber from repeated magma injections within the mineralized layer average concentrations over 3 m thickness are 250 ppb pt 40 ppb pd and 50 ppb au with individual samples containing up to 5 ppm pt and 6 ppm au the concentrations of ir os ru and rh are uniformly low 20 ppb stratigraphic zoning of pt pd and au is consistent along strike with peak au concentrations overlying pt and pd peaks platinum minerals are primary pt fe alloy sperrylite and moncheite with secondary pt sulfide overgrowths gold occurs as alloys with ag and cu these minerals are found in contact with primary and secondary silicates and oxides and with intercumulus base metal sulfides that consist of the assemblage bornite chalcopyrite digenite deposition of the mineralized layer is associated in space and time with injections of plagioclase saturated primitive magma that mixed with more evolved resident magma these events caused efficient partitioning of au and pge into sulfides derived from a large volume of magma deposition of these sulfides to form the mineralized layer and subsequent deposition of the overlying anorthosite layers the wehrlite layers however were formed by postcumulus reactions between gabbro cumulates and hydrous intercumulus melts probably derived from the compacting cumulus pile subsolidus reactions between primary minerals and meteoric hydrothermal solutions caused extensive alteration of the mineralized gabbro oxidation and desulfurization of cu fe sulfides and local recrystallization of pge minerals

from water to tillage erosion dominated landform evolution while water and wind erosion are still considered to be the dominant soil erosion processes on agricultural land there is growing recognition that tillage erosion plays an important role in the redistribution of soil on agricultural land in this study we examined soil redistribution rates and patterns for an agricultural field in the belgian loess belt 137cs derived soil erosion rates have been confronted with historical patterns of soil erosion based on soil profile truncation this allowed an assessment of historical and contemporary landform evolution on agricultural land and its interpretation in relation to the dominant geomorphic process the results clearly show that an important shift in the relative contribution of tillage and water erosion to total soil redistribution on agricultural land has occurred during recent decades historical soil redistribution is dominated by high losses on steep midslope positions and concavities as a result of water erosion leading to landscape incision and steepening of the topography in contrast contemporary soil redistribution is dominated by high losses on convex upperslopes and infilling of slope and valley concavities as a result of tillage resulting in topographic flattening this shift must be attributed to the increased mechanization of agriculture during recent decades this study shows that the typical topographical dependency of soil redistribution processes and their spatial interactions must be accounted for when assessing landform and soil profile evolution

oxygen isotope exchange and mineral alteration in gabbros of the lower layered series kap edvard holm complex east greenland multiple intrusions of gabbros mafic dikes and syenites in the kap edvard holm complex gave rise to prolonged circulation of meteoric hydrothermal solutions and extreme isotope exchange and mineral alteration in the 3600 m thick lower layered series gabbros in the lower layered series 18o of plagioclase varies from 0 3 to 5 8 and it decreases with an increase in the volume of secondary talc chlorite and actinolite in the same gabbros pyroxenes have a more restricted range in 18o from 5 0 to 3 8 and values of 18opyroxeneare independent of the abundance of secondary minerals which ranges from 14 to 30 these relations indicate that large amounts of water continued to flow through the rocks at temperatures of 500 600 c altering the gabbros to assemblages of talc chlorite actinolite epidote albite and causing significant oxygen isotope exchange in plagioclase but not in pyroxene the extensive low temperature secondary mineralization and 18o depletion of plagioclase in the lower layered series are associated with the later emplacement of dikes and gabbros and syenites which created new fracture systems and provided heat sources for hydrothermal fluid circulation this produced subsolidus mineral alteration and isotope exchange in the lower layered series that are distinct from those in the skaergaard and cuillin gabbros of the north atlantic tertiary province but are similar to those observed in some oceanic gabbros

origin of the early permian wajilitag igneous complex and associated fe ti oxide mineralization in the tarim large igneous province nw china abstract the wajilitag igneous complex is part of the early permian tarim large igneous province in nw china and is composed of a layered mafic ultramafic intrusion and associated syenitic plutons in order to better constrain its origin and the conditions of associated fe ti oxide mineralization we carried out an integrated study of mineralogical geochemical and sr nd hf isotopic analyses on selected samples the wajilitag igneous rocks have an oib like compositional affinity similar to the coeval mafic dykes in the bachu region the layered intrusion consists of olivine clinopyroxenite coarse grained clinopyroxenite fine grained clinopyroxenite and gabbro from the base upwards fe ti oxide ores are mainly hosted in fine grained clinopyroxenite forsterite contents in olivines from the olivine clinopyroxenite range from 71 to 76 mol indicating crystallization from an evolved magma reconstructed composition of the parental magma of the layered intrusion is fe ti rich similar to that of the bachu mafic dykes syenite and quartz syenite plutons have end t values ranging from 1 4 to 2 9 identical to that for the layered intrusion they may have formed by differentiation of underplated magmas at depth and subsequent fractional crystallization magnetites enclosed in olivines and clinopyroxenes have cr2o3 contents higher than those interstitial to silicates in the layered intrusion this suggests that the cr rich magnetite is an early crystallized phase whereas interstitial magnetite may have accumulated from evolved fe ti rich melts that percolated through a crystal mush low v content in cr poor magnetite

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

tertiary mineralization and magmatism east greenland lead isotope evidence for remobilization of continental crust abstract well defined lead isotope signatures of sulphides from mineral occurrences associated with tertiary igneous rocks in east greenland fall in two distinct groups 1 sulphide samples from the region south of scoresby sund kangerlussuaq igneous complex have lead characterized by retarded uranogenic evolution and slightly elevated thorogenic isotopic ratios 2 sulphide samples from the region north of scoresby sund werner bjerge kap simpson and kap broer ruys igneous complexes have lead compositions typical of modern average terrestrial lead these distinct signatures in both conventional and 208 pb 204 pb 207 pb 204 pb diagrams lie within linear trends defined by previously published lead isotope data for unmineralized tertiary basalts and intrusive rocks the linear trends are mixing lines between the lead in the tertiary mantle derived magmas and lead remobilized from continental crust tertiary magmas in the region south of scoresby sund remobilized and incorporated lead from low high 208 pb 204 pb crustal sources similar in isotope composition to archaean high grade metamorphic gneisses exposed in the area non to sub parallel distinct lead mixing lines in the 208 pb 204 pb 206 pb 204 pb diagram for the tertiary igneous complexes in this region suggest strong heterogeneity of the remobilized crust more than one half of the lead from sulphide mineral occurrences within the kangerlussuaq alkaline intrusive complex may be derived from local continental crust in the region north of scoresby sund the tertiary magmas remobilized moderately radiogenic lead from local basement and sedimentary basins palaeoproterozoic mesoproterozoic gneisses neoproterozoic ordovician sediments caledonian granites and palaeozoic mesozoic sediments these crustal rocks lack the very low 206 pb 204 pb and 207 pb 204 pb ratios typical of the gneisses from the kangerlussuaq region and mixing trends between mantle derived and crustal lead are therefore much less extensive however because the mantle derived magmas had very low total lead contents even small additions of crustal lead are traceable sulphide mineralized alkaline intrusive complexes are shown to be highly contaminated with crustal lead and it is further shown that the pre tertiary rocks of north east greenland are likely local crustal sources of lead for contaminated tertiary plateau basalts many stratabound sediment hosted hydrothermal base metal occurrences in the palaeozoic mesozoic jameson land basin are thought to be tertiary in age but do not appear to contain tertiary igneous derived lead on the contrary the hydrothermal alteration zones associated with several of the mineralized tertiary igneous complexes attest to extensive fluid rock mass transfer lead and other base metals were leached from the country rocks homogenized and incorporated into sulphide minerals

diffusion in silicate minerals and glasses a data digest and guide to the literature the rates of diffusion of cations oxygen and hydrogen in silicates are of fundamental importance to a wide range of petrological and geochronological problems in order that the earth scientist may readily apply the available experimentally determined diffusion rates to such problems a compilation of data for diffusion in silicate minerals and glasses is presented along with a working guide for its use published data and experimental conditions are listed in tables and these are preceded by an outline of diffusion mechanisms terminology equations and units diffusion regimes factors controlling diffusion rates measurement techniques and diffusional behaviour

fluid motions and compositional gradients produced by crystallization or melting at vertical boundaries the results of a continuing series of laboratory experiments designed to model the fluid motions which accompany crystallization are both described and related in a preliminary way to prototype flows in magma chambers previous experiments have demonstrated the importance of compositional inhomogeneity produced by crystallization and melting in a thermal gradient and coupled with double diffusive effects in driving convective flows which result in thermal and compositional stratification in an originally homogeneous fluid the present experiments examine effects produced in tanks cooled at the side by the upward flow of a less dense boundary layer depleted in the crystallizing component as crystals grow on the side wall these processes are examined in simple two and three component aqueous systems h2o na2co3 h2o na2co3 k2co3 h2o cuso4 na2so4 with one and two crystallizing phases in each of these systems an initially downward flow of a cooled boundary layer against the side wall is reversed as crystallization commences and depletes the boundary layer in the crystallizing component accumulation of this cooler but lighter depleted fluid at the top of the chamber produces thermal and compositional layering by a filling box mechanism partly modified by interchange between the boundary layer and the convecting layers outside when more than one component is present in the solution the crystallization process produces a differentiated fluid column i e one with compositional gradients which are different for each of the components the compositional and thermal distributions within the fluid change with time but finally appear to reach a steady state these distributions are the integrated result of compositional changes produced by crystallization from a thin boundary layer a small proportion of the bulk fluid which evolves in composition and temperature independently of the bulk fluid in a manner controlled by the dynamics of the system the paths of fluid evolution and the resulting sequence and abundance of crystalline products are very different from those predicted on the basis of simple thermally driven crystallization in the static system disequilibrium effects probably involving different kinetics of crystallization of different crystals in part determine crystallization in the experimental system these may or may not be important in real magmatic systems there is still much to learn before even the behaviour in these simple experimental systems is understood fully and the application of the results to the interpretation of the behaviour in real magma chambers in even further away however it is apparent that dynamic effects provide an additional degree of freedom in crystallization processes and allow evolution of small increments of solution to compositions much further along crystallization paths than that allowed in static equilibrium systems petrologists will have to free their thinking from classical constraints of static systems in order to interpret many magmatic phenomena

liquidus temperatures of the skaergaard magma the liquidus temperatures of the skaergaard intrusion can be estimated for the layered series from plagioclase compositions plagioclase saturation in one atmosphere melting experiments on evolved north atlantic basalts is a function of an content mol and can be described by an empirical linear relationship t c 899 3 6 an 1 20 c this relationship predicts a total crystallization interval for the intrusion of 150 c plagioclase crystallized in the hidden zone an 71 at 1155 c at the base of the lower zone an 66 at 1137 c and finally in the sandwich horizon an 30 at 1007 c these temperatures are in good agreement with previous estimates based on melting studies of suitable chilled margin rocks and gabbros from the skaergaard intrusion and liquid line of descent modeling our temperature estimates however are markedly lower by up to 60 c than recent temperature estimates based on an extrapolation of high pressure experimental data for the kiglapait intrusion to skaergaard emplacement conditions proposed variations in magmatic pressure during skaergaard evolution and reasonable estimates of magmatic water contents do not alter these conclusions

episodic volcanism during break up of the north atlantic evidence from the east greenland plateau basalts abstract the lower tertiary upper paleocene lower eocene plateau basalts in the scoresby sund region of east greenland formed during three distinct magmatic episodes the activity of the first episode was centred in the present inland areas to the northwest and produced a voluminous regional basalt sequence lower sequence the activity of the second episode was centred to the southeast offshore the present atlantic coast and this also produced a voluminous regional basalt sequence upper sequence the third episode was centred on the atlantic coast and gave rise to a dense coastal dyke swarm and local lavas which are now only locally preserved by downfaulting the lavas are all tholeiitic basalts after an initial phase the two regional lava sequences of the first and second episodes show a similar vertical compositional zonation pattern a thin lower formation with variable composition is followed by a thick uniform formation which shows systematic compositional change with height from tio2 rich feti basalts to tio2 poor basalts and ending with a reversal to tio2 rich basalts each of these cyclic patterns apparently resulted from a temporary rifting episode and much of the compositional variation found can be explained by magma development in open magma chambers the dykes and lavas of the third episode of activity have chemical affinities to ocean floor basalts and their tio2 p2o5 ratios indicate formation at a spreading ridge centre the pattern of two failed rifting episodes and one event that produced oceanic crust can be correlated with stages in the complicated initiation of seafloor spreading in the region and the volcanism itself is closely related to this process

an ocean ridge type magma chamber at a passive volcanic continental margin the kap edvard holm layered gabbro complex east greenland the gabbros of the tertiary kap edvard holm layered serieshave a stratigraphic thickness of more than 5000 m earlier work has shown that the range in cumulus mineral compositions is restricted plagioclase an 81 an 51 olivine fo 85 fo 66 pyroxenes ca 43 mg 46 fe 11 to ca 43 mg 37 fe 20 field evidence of magma injections is common which together with the restricted range in mineral chemistry suggests that the magma chamber was frequently replenished by a less fractionated magma a detailed study of a 600 m section 900 1500 m in the lower layered series reveals a period of crystallization when the magma chamber behaved as a closed system 900 1300 m the rocks formed during this periodare well laminated olivine gabbros 900 110 m which evolved to well laminated oxide gabbros 1100 1300 m compositional trends in the cumulusminerals are towards more evolved compositions plagioclase an 64 an 58 pyroxene mg from 80 to 76 with stratigraphic height from 1300 m to 1500 m granular olivine gabbros dominate with moreprimitive mineral compositions plagioclase an 67 an 76 pyroxene mg from 78 to 82 the transition olivine gabbro to oxide gabbro at 1100m is a consequence of fractional crystallization and it is shown how changes in activities of feo and fe 2 0 3 in the magma are reflected in the total iron content of plagioclases the transition from oxide gabbro to olivine gabbro at 1300 m results from replenishment by less evolved basaltic magma on the basis of calcic pyroxene chemistry and the mineral crystallization sequence it is concluded that the kap edvard holm layered series crystallized from a tholeiitic magma similar to morb melanogabbroic units occur throughout the intrusion as discordant to subconcordant sill like bodies 0 2 2 0 m thick the melanogabbroic units consist of cr rich augite olivine plagioclase heteradcumulates and contain deformed mica crystals of pre emplacement origin these units crystallized from a wet mgo rich magma which was injected into the layered host gabbros after the formation of the cumulus pile but before the magma was completely solidified the kap edvard holm layered series has several parallels with the plutonic part of ophiolite sequences these include cumulus mineral assemblage compositions of the minerals and the restricted range in compositions with stratigraphic height field evidence of repeated replenishment of basaltic magma dyke swarms overlying the roof zone of the magma chamber and the existence of a late intrusive suite of wet mgo rich magma these parallels suggest that the processes involved in the formation of the kap edvard holm layered series were similar to those involved in the formation of the crustalpart of many ophiolites and beneath present day spreading ridges the kap edvard holm layered series is therefore believed to represent a shallow level magma chamber which acted as a reservoir for basaltic flows at the continental margin during the opening of the north atlantic ocean

lynchets in eastern belgium a geomorphic feature resulting from non mechanised crop farming abstract this paper investigates soil stratigraphy of lynchets in sloping lands in eastern belgium and rates of their development by comparison to tillage translocation by non mechanised agriculture in belgium detailed topographical surveys and augerings were carried out at three sites that were under cropland till 1900 1950 rates and diffusion constants of current non mechanised tillage erosion were monitored in ethiopia using tracers and by precise surveys of tillage steps of known ages the lynchets in belgium consist of colluvium that was removed at the upper border of previously farmed plots repeated tillage with animal drawn implements results in soil translocation fluxes to the lower plot borders in the order of 11 to 91 kg m 1 year 1 for slope gradients between 0 03 and 0 35 m m 1 the studied lynchets in eastern belgium would have required cropping agriculture for a total of 217 585 years on steep and 1037 1867 years on gentle slopes the establishment of lynchets hence took place without any deliberate action of digging but due to repeated tillage even with simple implements and water erosion calculated time spans of tillage indicate that some parts of the study area had already been under cultivation during the gallo roman period others since the middle ages

high pressure fractionation in rift related basaltic magmatism faeroe plateau basalts the lower 3000 m basalt stratigraphy on the faeroe islands shows strong positive correlation between degree of fractionation and zr y ratio this is ascribed to the presence of garnet in the cumulus assemblage during fractionation at the base of the continental crust or in the upper lithospheric mantle at 40 50 km depth later basaltic magmas fractionated at low pressures which is a typical shift in fractionation regime among continental flood basalts seismic velocity v p for the garnet bearing high pressure fractionates is in excess of 7 km s this is comparable to velocities observed in high v p bodies in the basal crust of precambrian shields high pressure fractional crystallization of basaltic magmas may thus be an important process in generating the chemical complexity of continental flood basalts and has implications for crustal underplating

xenoliths of gneisses and the conformable clot like granophyres in the marginal border group skaergaard intrusion east greenland results of this research and the earlier work of wager and his colleagues indicate that contamination influenced the overall character of the marginal border group of the skaergaard intrusion precambrian gneisses were a major source of contamination and are identifiable as xenoliths in the marginal border a variety of other xenoliths occur with a wide compositional range

effects of h2o on phase relations during crystallization of gabbros in the kap edvard holm complex east greenland in the kap edvard holm complex of east greenland layered monly results in the formation of discordant igneous bodies within crystallizing cumulus sequences in some olivine gabbros host numerous small discordant bodies of ultramafic cases partially molten cumulates appear to have reacted rock and magnetite gabbro that formed by late magmatic metasomatic with liquids or fluids that originated within the cumulus replacement of partially solidified gabbroic cumulates similar repile resulting in resorption of cumulus minerals crysplacive rocks are also present as large semi conformable sheet like tallization of intrusive or replacive bodies and rebodies within the layered gabbro sequence replacive bodies of all distribution of mass within the intrusion e g robins sizes are spatially associated with xenoliths of metabasaltic lava 1982 butcher 1985 butcher et al 1985 helz 1987 the small bodies cluster around xenoliths and the large bodies host irvine 1987 boudreau 1988 mcbirney sonnenthal swarms of xenoliths the replacive bodies are inferred to have formed 1990 larsen brooks 1994 scoon mitchell 1994 by reaction of gabbroic cumulates with pore liquids that were mathez 1995 meurer et al 1997 boudreau 1999 in enriched in h2o by degassing or dehydration melting of the other cases partially molten cumulates are inferred to metabasalts as these liquids migrated through the cumulus pile have reacted with externally derived magmas that inthey resorbed plagioclase and produced ultramafic bodies where the truded the cumulus pile resulting in the development liquids came to rest they reacted with gabbroic cumulates to produce of discordant replacive bodies via the reaction of the bodies of magnetite rich gabbro the most evolved pore liquids cumulates with intruding magmas e g morse et al 1987 segregated to form hornblende rich pegmatitic dikes of roughly dacitic bedard et al 1988 tegner wilson 1993 tegner composition suggesting that hydration and possibly oxidation of the robins 1996 because cumulus rocks preserve records magma shifted the liquid line of descent from a tholeiitic trend toward of magmatic fractionation and replenishment in large a calc alkaline trend these inferences imply that contamination of mafic intrusions recognizing and understanding postmagmas by dehydration of hydrothermally altered crustal rocks may cumulus processes such as these can provide insights significantly influence the evolution of mafic magma systems into the evolution of mafic magma chambers and the differentiation of basaltic magmas within the crust near the western margin of the kap edvard holm

intrusive suite documented in the troodos ophiolite plutonic complex cyprus two definable magmatic suites occur within the plutonic complex in the caledonian falls area of the troodos ophiolite cyprus an early suite of generally well layered and structurally concordant gabbros and pyroxenites is intruded by a later suite of poikilitic wehrlites and gabbro norites discordant structural relations can be demonstrated between units belonging to the two magmatic suites xenoliths near the contacts prove relative age relations differences in mineral chemistry between the two suites indicate that the parent magmas of the two suites were of different compositions the petrogenesis of the two cumulate suites may be explained by a second stage melting of a mantle diapir or by compaction of a zone of crystal mush below the moho

parental liquids of the skaergaard intrusion cumulates petrogenetic relationships between compositions advocated as possible liquids parental to the skaergaard layered series cumulates have been investigated using equations for the prediction of liquidus temperature and liquid path followed during fractional crystallization given a suitably defined sequence of primocryst mineral assemblages a variation of the fractionation scheme provides a new method for the calculation of the parent liquid composition

crustal contamination and the granite problem in the british tertiary volcanic province isotopic studies on the british tertiary volcanic province have shown that the granites contain both mantle derived and crustal components while basic rocks display pronounced crustal contamination in order to study contamination mechanisms in greater detail isotopic and chemical variations in skye plateau lavas and cuillins complex intrusive units were examined as a function of time in both cases degrees of crustal contamination generally fall with time which it is argued reflects the progressive melting and sweating out9 of lewisian acid gneissic sheets from the more refractory intermediate basement during repeated intrusion and contamination of sheet like magma reservoirs long lived developing magma chambers do not fit the data well skye granites had basic precursors that suffered similar types of contamination in the lower crust but tended to form longer lived developing magma chambers in the upper crust nevertheless skye granites display similar crustal pb contents to associated basic intrusions and are argued not to be the products of crustal anatexis but the differentiates of preshal mhor basic magmas contaminated by ca 10 with large degree partial melts of lewisian acid gneisses

tertiary plutons monitor climate change in east greenland the d values of amphibole and biotite in tertiary plutons in central eastern greenland decreased by 30 between 55 and 50 ma and then increased by 35 between 50 and 43 ma the d values of amphibole and biotite in in the plutons range from 160 to 123 these low values reflect isotopic exchange between the igneous rocks and hydrothermal fluids that were dominated by meteoric water the changes in mineral d values between 55 and 43 ma are explained most plausibly by shifts in the isotopic composition of meteoric waters that fed hydrothermal recharge areas at 50 ma uplift related to the iceland mantle plume elevated hydrothermal recharge areas by 1 2 km high altitude low d meteoric waters collected by the uplifted recharge areas caused the 30 decrease in mineral d values between 55 and 50 ma the subsequent increase in mineral d values from 50 to 43 ma corresponds to widening of the north atlantic ocean and a change from continental to maritime climate thus tertiary plutons in central eastern greenland represent a network of paleoclimate stations that monitored the d of meteoric water during opening of the north atlantic ocean basin

foreshock and aftershock sequence of the 1998 m 5 0 sendai northeastern japan earthquake and its implications for earthquake nucleation we investigated foreshock and aftershock sequences of a m 5 0 earthquake that occurred on 15 september 1998 near the nagamachi rifu fault an active fault crossing the urban area of sendai city northeastern japan the focal mechanism of this event was a reverse fault type with a nearly horizontal p axis parallel to the plate conversion direction aftershock distribution located by the homogeneousstation method delineates the fault plane of this event dipping to the northwest at an angle of 30 in the depth range of 10 12 km the location of the fault plane and the slip direction thus estimated suggest that this event was a slip at a deep portion of the nagamachi rifu fault three days prior to the mainshock many foreshocks with similar waveforms started to occur very close to the mainshock hypocenter we estimated relative locations of these similar foreshocks based on crossspectrum analyses of waveforms recorded at nearby stations they are located at the deepest portion of the mainshock fault plane and just above the mainshock hypocenter migration of the foreshocks is observed from deeper to shallower depths cumulative coulomb stress changes caused by preceding events show negative values at hypocenters of similar waveform foreshocks our results do not support the cascade model for the process of foreshock generation nucleation phase prior to the high speed rupture of the mainshock is observed in seismograms at nearby stations the initial point of the nucleation phase is located on a deeper extension of the foreshock area the high speed breakout point is located in the area where a large amount of seismic moment release was estimated from waveform inversions these observations probably reflect an underlying aseismic nucleation process preceding the main dynamic rupture of the m 5 0 event

formation of wehrlites through dehydration of metabasalt xenoliths in layered gabbros of the noe nygaard intrusion southeast greenland the noe nygaard intrusion is a 4 2 5 km stock composed of layered gabbros and wehrlites within the precambrian basement of the coastal mountains west of the kialineq plutonic complex transgressive relationships to tertiary mafic dykes and the occurrence of abundant metabasaltic xenoliths signify a tertiary age for the intrusion the intrusion is characterized by alternating zones of gabbro and wehrlite gabbro is both intruded and replaced by wehrlite and the wehrlite zones are characterized by abundant metabasaltic xenoliths based on 87 sr 86 sr ratios mica olivine and oxide gabbros are all cumulates crystallized at different differentiation stages from a common parental magma field relations together with similarities in strontium isotope ratios and in the major and rare earth element ree mineral chemistry between gabbros and wehrlites indicate that the wehrlite bodies were formed by the dissolution of plagioclase from a gabbro cumulate mush by h 2 o derived from dehydration and the partial assimilation of metabasaltic xenoliths in terms of their ree characteristics melts from which the noe nygaard intrusion crystallized are within the compositional range of melts for other early tertiary mafic ultramafic complexes of east greenland however they were generated at a greater mean melting pressure and have less radiogenic strontium isotope ratios than the nearby imilik mafic ultramafic complex supporting existing models for mantle heterogeneity at the time of continental break up the abundance of metabasaltic xenoliths in the noe nygaard intrusion provides further evidence for the lateral extent of the north atlantic flood basalt province which onshore has been mostly removed by glacial erosion south of 68 n in greenland

landform transformation and long term sediment budget for a chernozem dominated lowland agricultural catchment abstract the loess hilly lands of the south west foreland of the west carpathians are characterized by favorable climatic conditions smooth topography fertile soils and a long settlement history for the first time we document changes to human induced landforms in a small zero order dry valley 0 28 km2 with calcic chernozem soils and develop a long term sediment budget the original surface was reconstructed based on interpreting records of erosion and deposition from 185 soil cores and six valley cross sections the topography inherited from the pleistocene was transformed through lowering of hillslope ridges and convexities along with infilling of shallow depressions within the original valley bottom on convex convex landforms had an average net erosion of 0 32 0 01 m while average net accumulation in the valley bottom was estimated at 0 20 0 01 m the correlation between change in soil profile depth with profile curvature 0 51 p

crystallization and compositional convection in a porous medium with application to layered igneous intrusions growing crystals can provide a local source of buoyancy by depleting melt of certain chemical components and vigorous convective motions in the fluid can result we report a quantitative experimental study in which saturated aqueous solutions of cuso4 and na2so4 in porous media of either glass balls or cuso4 5h2o crystals were crystallized by cooling from below the crystals growing in the pore space released light chemically depleted solution which had the potential to convect out of the porous medium and be replaced by additional saturated solution from above we explore the physical and chemical effects of compositional convection during the complete solidification of the interstitial solution by varying the permeability of the porous medium the cooling rate and the initial composition of the solution this type of convection can form adcumulate rocks by enabling continuous circulation of melt from the main magma reservoir through the pores of a cumulus pile adcumulus growth can occur by this mechanism as long as the convective velocity in the porous medium is greater than the velocity of the solidification front we scale the experimental results to magmatic conditions and infer that this process should occur commonly in layered igneous intrusions when our porous media had a small permeability compositional convection enabled the adcumulate growth of a completely solid contact between melt and cumulate trapping of dynamically unstable melt beneath this impermeable layer of crystals also occurred in these experiments and may be important geologically small shallowly emplaced intrusions and the cumulate zones at the base of komatiites are probably cooled too rapidly for significant intercumulus convection to occur

the differentiation of the skaergaard intrusion mcbirney and naslund have missed the two central points that we reiterate for clarity first the composition of the cotectic cumulate extract for the lzc best estimated from the average composition of adcumulate rocks had a substantially lower silica content than any conceivable basaltic liquid so silica enrichment is unavoidable this is true of all the dyke compositions reported by brooks and nielsen even the anomalous rock e with sio2 46 second it is the normal behaviour of tholeiite basaltic magma to produce increasingly iron rich cumulate extracts with little change in silica until feti oxide precipitation occurs when silica enrichment and compositional divergence begins such divergence between equivalent cumulate plutonic and fractionated volcanic rocks hads been widely documented skaergaard magmas do have some uncommon features however similar assemblages exist in volcanic rocks as in the andesitic to rhyolitic glasses of the loch ba ring dyke mull sparks 1988 it is also a basic principle that elements enriched in cumulate rocks often become depleted in the corresponding liquids iron enrichment in the skaergaard cumulates is complementary to iron depletion in liquids

petrology of a leucogabbroic interval within basal layered gabbros at north arm mountain bay of islands ophiolite data from detailed sample traverses in the layered gabbro unit of the north arm mauntain massif bay of islands ophiolite allow meter scale resolution of magmatic processes in spreading ridge magma chambers one suite of 46 samples from a 195 m interval near the base of the layered gabbro unit contains cumulus plagioclase an73 7 87 5 average modal abundance 75 clinopyroxene mg 80 3 86 0 18 and olivine fo76 6 82 1 6 with intergranular orthopyroxene mg 78 0 83 3 1 and accessory cr al spinel cr 32 3 41 4 ilmenite rims spinel in one sample whole rock zr contents range from 6 to 15 ppm plots of stratigraphic height in the traverse versus petrogenetic indicators e g mg s of mafic phases and an in plagioclase reveal both normal and reverse cryptic variation patterns the patterns for all indices are generally correlated the normal portions of the patterns formed during fractional crystallization of basalt batches ranges of mineral compositions in the normal trends suggest that 29 38 crystallization of each batch of basalt occurred before magmatic replenishment the reverse cryptic trends formed by crystallization of hybrid magmas produced during periods of magma mixing other evidence for magma mixing is the systematic association of spinel and reversely zoned plagioclase with the reverse trends experiments and observations of natural assemblages indicate that 55 modal plagioclase crystallizes from basalts at the olivine plagioclase clinopyroxene liquid piercing point the average plagioclase content of this suite of leucogabbros from north arm mountain is too high to have formed from simple crystallization at the piercing point petrologic modeling indicates the leucogabbros may have formed from basalts into which a small amount 10 of plagioclase was resorbed during mixing the initial compositions of these hybrid basalts lie in the plagioclase primary phase volume other suites of layered gabbros from north arm mountain are not so plagioclase rich as the leucogabbros described above crystallization of basalts in the plagioclase primary phase volume and the consequent formation of plagioclaserich gabbros may occur in restricted portions of zoned magma chambers underlying oceanic spreading centers or may occur episodically in the overall lifetimes of the magma chambers

the success of recent land management efforts to reduce soil erosion in northern france abstract soil erosion is an important problem in open field agricultural landscapes with almost no permanent vegetation in small headwater catchments and with few physical obstacles to reduce runoff velocities runoff concentration along linear landscape elements plot boundaries or thalwegs frequently causes ephemeral gullies to form the latter reflecting the poor hydrogeomorphic condition of the land and soilscape to address this problem and to remediate negative on and off site effects land management efforts have multiplied over the past decades in many regions this includes amongst other measures the implementation of vegetation barriers called fascines in the loess dominated aa river basin of northern france where cropland accounts for 67 of the cover we investigated the effect of fascines on ephemeral gully erosion dynamics together with rainfall characteristics and cropland management this was accomplished through a spatially explicit study of 269 sites prone to ephemeral gullying using a diachronic analysis of historical aerial photographs between 1947 and 2012 ephemeral gully densities at the scale of the aa river basin 643 km2 varied between 0 39 and 1 31 m ha 1 long term average of 0 68 m ha 1 with local maxima up to 9 35 m ha 1 densities are however much higher when only considering the most erosion vulnerable municipalities long term average of 2 23 4 30 m ha 1 those values should be used when comparing results from this study to other reports of ephemeral gully erosion fascines were introduced in 2001 and were present in 30 of the gully erosion sites by 2012 although the presence of fascines has an effect on gully length reduction spatial and temporal variations in gully length were mainly driven by cumulative precipitation measurement of sediment deposition at 29 fascines in 2016 showed that only 47 of the fascines functioned as sediment sinks they stored on average 1 7 mg of sediment per winter half year corresponding to 0 009 mg ha 1 the results suggest that fascines positively impact the landscape s resilience and reduce ephemeral gully erosion rates the use of vegetation barriers such as fascines are increasingly implemented for erosion control in western europe but pose problems for the management of open field landscapes

40ar39ar geochronology of tertiary mafic intrusions along the east greenland rifted margin relation to flood basalts and the iceland hotspot track abstract the east greeland tertiary igneous province includes the largest exposed continental flood basalt sequence within the north atlantic borderlands more than ten layered gabbro complexes including the 55 ma skaergaard intrusion and a large dolerite sill complex are the plutonic equivalents of flood basalts both lavas and intrusions have been regarded as synchronous with continental breakup at 57 54 ma we report ten new ages of the mafic intrusions determined by40ar 39ar incremental heating experiments demonstrating that the mafic intrusions formed in two distinct time windows only intrusion ii of the imilik gabbro complex the skaergaard intrusion and the sorgenfri glestcher sill complex formed at 57 55 ma coeval with the eruption of regional flood basalts and continental breakup other layered gabbro intrusions at imilik intrusion iii kruuse fjord igtutarajik nordre aputite q kap edvard holm and lilloise are distinctly younger and formed between 50 and 47 ma plate kinematic models indicate the axis of the ancestral iceland mantle plume was located under central greenland at 60 ma and subsequently crossed the east greenland rifted continental margin we propose that tholeiitic magmatism along the east greenland rifted margin largely occurred in three distinct pulses at 62 59 ma lavas and dykes 57 54 ma lavas dykes sills and some gabbros and 50 47 ma gabbros dykes and rare lavas related to discrete mantle melting episodes triggered by plume impact continental breakup and passage of the plume axis respectively this model implies northwestward continental drift of greenland relative to the plume axis by 3 9 5 0 cm yr between 60 and 49 ma consistent with estimates from seismic studies of submerged flood basalts

processes and rates of rock fragment displacement on cliffs and scree slopes in an amba landscape ethiopia abstract distinct rock fragment displacements occur on the ambas or structurally determined stepped mountains of the northern ethiopian highlands this paper describes the rock fragment detachment from cliffs by rockfall quantifies its annual rate and identifies factors controlling rock fragment movement on the scree slopes it further presents a conceptual model explaining rock fragment cover at the soil surface in these landscapes in the may zegzeg catchment dogu a tembien district tigray rockfall from cliffs and rock fragment movement on debris slopes by runoff and livestock trampling were monitored over a 4 year period 1998 2001 rockfall and rock fragment transport mainly induced by livestock trampling appear to be important geomorphic processes along a 1500 m long section of the amba aradam sandstone cliff at least 80 t of rocks are detached yearly and fall over a mean vertical distance of 24 m resulting in a mean annual cliff retreat rate of 0 37 mm y 1 yearly unit rock fragment transport rates on scree slopes ranged between 23 1 and 37 9 kg m 1 y 1 this process is virtually stopped when exclosures are established corresponding mean rock fragment transport coefficients k are 32 69 kg m 1 y 1 on rangeland but only 3 9 kg m 1 y 1 in densely vegetated exclosures a conceptual model indicates that besides rockfall from cliffs and argillipedoturbation all factors and processes of rock fragment redistribution in the study area are of anthropogenic origin

fluid dynamic and geochemical evolution of cyclic unit 10 rhum eastern layered series lithological major element trace element and sr isotope data from cyclic unit 10 of the rhum eastern layered series are presented the lower 65 metres of the unit are peridotite subdivided on textural and geochemical grounds into a lower homogeneous portion approximately 50 metres thick and an upper heterogeneous portion approximately 15 metres thick the uppermost 16 5 metres of the unit are allivalite there are steep geochemical gradients across the peridotite allivalite boundary in ni content of olivine and whole rock sr isotope composition calculations are presented on the geochemical evolution of a rhum picritic liquid undergoing olivine precipitation both when the olivines remain suspended in the residual liquid as they precipitate and when they are continuously fractionated quenched groundmass and olivine compositions from the rhum dykes and the unit 10 peridotite olivines show good agreement with the suspension model but are inconsistent with the fractionation model the rhum chamber is thought to have been replenished with a picritic liquid from which olivine crystallized while held in suspension however replenishment by a highly olivine phyric basalt is also possible the peridotite probably accumulated rapidly as olivines were dumped out of suspension onto the chamber floor the lower part of the peridotite is a poikilitic adcumulate it is suggested that this formed by convective circulation of melt in the pores of the pile of cumulus olivines in the latter stages of adcumulus growth more fe rich and isotopically contaminated magma entered the top of the cumulus pile causing cumulus olivines to re equilibrate and giving the intercumulus plagioclase a higher sr isotope ratio than lower down the olivines in the allivalite show steep stratigraphic gradients in major element composition but not in their ni content they also show substantial variation in major element composition laterally within the allivalite it is suggested that these features are a consequence of postcumulus re equilibration of olivine with migrating intercumulus magma

flooding of property by runoff from agricultural land in northwestern europe abstract in the last twenty years there has been an increase in the incidence of flooding of property by runoff from agricultural land in many areas of northwestern europe these events take the form of inundations by soil laden water associated with erision and the formation of ephemeral or talweg gullies developed in normally dry valley bottoms costs of such events may be considerable e g almost us 2m at rottingdean southern england in 1987 these costs are largely borne by individual house occupants insurance companies and local councils the distribution of flooding is widespread but areas of high risk can be identified the hilly area of central belgium parts of northern france the south downs in southern england and south limburg the netherlands all these areas have silty more or less loessial soils two types of flooding may be distinguished winter flooding associated with wet soils and the cultivation of winter cereals and summer flooding due to thunderstorm activity and runoff particularly from sugar beet maize and potato crops the distribution of these types of erosion varies in relation to the interaction between physical characteristics soils and topography climatic conditions and land use across the region the reason for the recent increase in flooding events appears to be changes in land use in the area of arable cropping and the continued intensification of farming such as the use of chemical fertilizers the decline in aggregate stability the increase in the size of fields and compaction by farm vehicles in some regions the risk of flooding has also increased because of expansion of urban areas in valley bottom locations communities have responded to the flooding hazard with emergency or protective measures usually involving engineered structures rather than land use change the policy response to the increased risk of flooding has been very limited especially at the national and provincial level the exception being plans developed with farming organisations in south limburg and the pays de caux in southern england initiatives have been few and largely consist of protective measures undertaken by urban municipalities

patterns of rock fragment cover generated by tillage erosion abstract intensively cultivated areas in the upper part of the guadalentin catchment southeast spain show a systematic spatial pattern of surface rock fragment cover rc the objective of this paper is to quantify and to explain this spatial rock fragment cover pattern therefore a map of an intensively cultivated area of 5 km2 was digitised and for each pixel total topographic curvature was calculated next rock fragment cover was determined photographically at 35 sites with a range of total slope curvatures a linear relation between total curvature and rock fragment cover was found except for narrow concavities it was hypothesised that this pattern can be explained by a significant net downslope movement of rock fragments and fine earth by tillage the displacement distances of rock fragments by tillage with a duckfoot chisel were measured by monitoring the displacement of tracers painted rock fragments and aluminium cubes on 5 sites having different slopes the rare of tillage erosion for one tillage pass with a duckfoot chisel expressed by the diffusion constant k equals 282 kg m for up and downslope tillage and only 139 kg m for contour tillage nomograms indicate that mean denudation rates in almond groves due to tillage erosion 3 to 5 tillage passes per year can easily amount to 1 5 2 6 mm year for contour tillage and up to 3 6 5 9 mm year for up and downslope tillage for a field 50 m long and having a slope of 20 these figures are at least one order of magnitude larger than reported denudation rates caused by water erosion in similar environments hence tillage erosion contributes significantly to land degradation the downslope soil flux induced by tillage not only causes considerable denudation on topographic convexities hill tops and spurs and upper field boundaries but also an important sediment accumulation in topographic concavities hollows and valley bottoms and at lower field boundaries kinetic sieving i e the upward migration of rock fragments by the tines of the duckfoot chisel also concentrates the largest rock fragments in the topsoil in such a way that a rock fragment mulch develops in narrow valleys and at the foot of the slopes these results clearly indicate that tillage erosion is the main process responsible for the observed rock fragment cover pattern in the study area since the study area is representative for many parts of southern spain where almond groves have expanded since 1970 the results have a wider application they show to what extent intensive tillage of steep slopes has contributed to the increase in soil degradation to changes in hillslope morphology i e strong denudation of convexities development of lynchets and rapid infilling of narrow valley bottoms and to the development of rock fragment cover patterns which control the spatial variability of the hydrological and water erosion response within such landscapes

animal powered tillage erosion assessment in the southern andes region of ecuador abstract while water erosion has been the focus of past research in the andes former studies show that soil erosion could also be related to the methods used in cultivating the fields the main objective of the present study was to assess i tillage erosion caused by the traditional animal powered yunta or ard plough in the andes and the factors controlling the process and ii the implications for soil conservation erosion rates were experimentally measured on 27 sites having slopes from ca 0 to 60 and soils ranging from andosols to cambisols in the andes region of ecuador gima azuay different tillage methods were assessed i tillage parallel to the contour lines paralelo and ii tillage at an angle with the contour lines statistical analysis points out that erosion caused by animal powered tillage is gravity driven a strong correlation exists between slope and downslope displacement furthermore tillage depth and initial soil condition are important for the paralelo tillage method the tillage transportation coefficient k is below 100 kg m 1 tillage pass 1 for the combined arado cruzado tillage method k may exceed 300 kg m 1 tillage erosion is responsible for the reduction of the slope between the contour strips over a relatively short time period of 20 years resulting in the formation of terraces and therefore the reduction of the water erosion risk however at the same time it may negatively affect soil quality

kiglapait geochemistry vii yttrium and the rare earth elements abstract based on 51 wholerock analyses by xrf and summation over the layered group the kiglapait intrusion contains 4 7 1 6 1 2 ppm y which resides principally in augite and apatite using liquid compositions calculated by summation the partition coefficient daug ly is 0 95 0 12 from 84 to 97 pcs percent solidified and 1 5 0 4 above 97 pcs for feldspar the most likely value for d is 0 028 0 02 n 6 ree analyses for 13 whole rocks were interpreted with the aid of yttrium models to yield trends for wholerocks and liquids vs pcs summations over the rocks of the layered group gave la 2 5 ce 5 8 nd 3 9 sm 1 0 eu 0 8 tb 0 17 yb 0 37 and lu 0 06 ppm with 2 s d errors near 30 all these elements are highly incompatible until the arrival of augite which affects chiefly the hree and apatite which affects all but more strongly the lree the net result is that after apatite arrival at 94 pcs the liquid compositions are nearly constant hence dwr lree 1 0 these results are compatible with the mineralogy of the intrusion and the estimated partition coefficients for feldspar olivine augite apatite and fe ti oxide minerals for pre apatite liquids dfsp lree vary regularly with the normative di content of the liquid and change by an order of magnitude hence the bulk liquid composition must be considered in any attempt to invert the compositions of feldspars to parent liquids the eu anomaly at first decreases in kiglapait liquids due to plagioclase fractionation but then increases due to removal of augite and apatite with negative eu anomalies the features dominantly responsible for eu partitioning are liquid structure and for monoclinic ternary feldspars crystal structure the former is best monitored by the augite or diopside content of the liquid and the latter by the k content of the feldspar the chondrite normalized ree pattern for the intrusion has lan 7 4 lun 1 6 ce yb n 3 6 and eu eu 2 4 indicating its feldspar rich nature the chilled margin of the nearby hettasch intrusion has a similar but more evolved pattern corresponding roughly to the kiglapait liquid at 70 pcs as with other data those for the ree suggest source differences for the two intrusions rather than a relationship due to fractionation

laboratory simulation of fluid driven seismic sequences in shallow crustal conditions 1 we report new laboratory simulations of fluid induced seismicity on pre existing faults in sandstone by introducing pore pressure oscillations faults were activated or reactivated to generate seismic sequences these sequences were analysed using a slip forecast model furthermore field data from the monticello reservoir was used to verify the model our results suggest that short term forecasting is reliant upon the final stages when crack communication begins limiting reservoir induced seismicity ris forecasting strategies to short periods in addition our laboratory data confirms the general accuracy and robustness of short term forecast techniques dealing with natural crack linkage processes whether strain driven or fluid driven ranging from volcanic hazard mitigation to episodic tremors and slips finally oscillating pore pressure can prolong the period of fluid induced seismicity and the aftershock decay rate is slower than that without oscillations

analysis of microearthquake data at cold lake and its applications to reservoir monitoring more than four months of continuously recorded micro earthquake data acquired at cold lake canada was analyzed using advanced algorithms for microearthquake location and subsurface tomography robust determination of the spatial temporal and magnitude distribution of seismicity is the first step toward understanding the relationship between the stress perturbations caused by the cyclic steam stimulation css process and seismicity acquisition geometry was constrained because the receivers were located in a single vertical borehole despite this constraint we were successful in improving event locations by use of the double difference method which highlights several tight event clusters the deep cluster at a depth of 400 m just above the oil reservoir shows very high seismicity during the css processes a second cluster is observed at shallower depths in the successive steam cycle this suggests that repeated steaming causes the deformation to spread to shallower depths the number of events h

the last interglacial palaeosol in the belgian loess belt tl age record abstract in the belgian loess plateau the rocourt soil is a well known luvisol horizon that is regarded as representing the last interglacial the name of the soil comes from the locality of rocourt in the east of the country where it has been observed for the first time later exposures of a similar soil were found in other localities most typically a sequence of three horizons is observed a red brown illuvial bt horizon overlain by a bleached horizon and a compound dark horizon in this paper we present the results of tl age determinations obtained on sediments directly bracketing the soil at the type locality of rocourt and at the locality of momalle more to the west together with some supplementary data for the exposures at kesselt to check a controversial result that was obtained earlier j quaternary sci 13 5 1998 487 the tl analyses involved both the total bleach additive dose and regeneration methods our tl ages confirm the assumed chronostratigraphic position oxygen isotope stage 5 of the soil exposed at the type locality the ages obtained at momalle and kesselt indicate that we are dealing with the same soil here but the palaeodose data are less consistent this is probably due to the fact that the loess has been disturbed by post depositional processes such as solifluction surface run off cryo and bioturbation this seems to be a major problem with the sediments in the eastern part of the belgian loess belt

foreshocks explained by cascades of triggered seismicity 1 the observation of foreshocks preceding large earthquakes and the suggestion that foreshocks have specific properties that may be used to distinguish them from other earthquakes have raised the hope that large earthquakes may be predictable among proposed anomalous properties are the larger proportion than normal of large versus small foreshocks the power law acceleration of seismicity rate as a function of time to the mainshock and the spatial migration of foreshocks toward the mainshock when averaging over many sequences using southern california seismicity we show that these properties and others arise naturally from the simple model that any earthquake may trigger other earthquakes without arbitrary distinction between foreshocks aftershocks and mainshocks we find that foreshock precursory properties are independent of the mainshock size this implies that earthquakes large or small are predictable to the same degree as seismicity rate is predictable from past seismicity by taking into account cascades of triggering the cascades of triggering give rise naturally to long range and long time interactions which can explain the observations of correlations in seismicity over surprisingly large length scales