mineralogical characterization of low grade nickel laterites from the north oman mountains using mineral liberation analyses scanning electron microscopy based automated quantitative mineralogy abstract afterwards to the late cretaceous obduction of the tethyan semail ophiolite suite intense chemical weathering involved the oman mountains region this weathering produced complex mineral and chemical assemblages that led to the formation of a ni lateritic paleosol in the present study five laterite sections were sampled and studied by using a quantitative mineralogical and petrographic approach mineral liberation analyses mla were carried out for the first time for several selected samples the mla results supported by the electron probe micro analyzer epma and energy dispersive x ray spectroscopy edx analyses revealed that the main ore minerals of the analyzed laterite are chlorite and goethite as the main ni bearing hosts magnetite and chromite are also present as by product minerals the ni bearing chlorite in the saqah 3 and al russayl profiles have coarser grains compared to those in the other saqah localities while the goethite grains are coarse in most of the analyzed samples the presence of approximately 60 to 80 of both the ni bearing minerals chlorite and goethite as liberated phases 95 free is a potential indicator for their future exploration chromite and magnetite grains are present in a wide range of grain sizes seventy percent of the chromite grains in saqah 4 and al russayl profiles and 70 of the magnetite in saqah 2 occur as liberated phases 95 compared to their presence in other profiles where only half of them occur as liberated phases the grain size liberation class relationships showed that ni bearing mineral phases chlorite and goethite are present as liberated phases high grade materials followed by chromite and magnetite which are interlocked with other phases to lower grade materials a better understanding of the mineralogical and geochemical quantitative characterization such as grain size modal analyses mineral association and percentage of interlock between minerals in the deposit can avoid the metallurgical problems thus possibly reducing the operational costs and improving the recovery of metals the above obtained mla parameters can build a good feasibility study during the exploration stage of these low grade ni deposits in the northern oman mountains as well as later during their beneficiation and processing methods if other economic and mining factors are deemed favorable

double flood basalts and plume head separation at the 660 kilometer discontinuity several of the world s flood basalt provinces display two distinct times of major eruptions separated by between 20 million and 90 million years these double flood basalts may occur because a starting mantle plume head can separate from its trailing conduit upon passing the interface between the upper mantle and the lower mantle this detached plume head eventually triggers the first flood basalt event the remaining conduit forms a new plume head which causes the second eruptive event the second plume head is predicted to arrive at the lithosphere at least 10 million years after the first plume head in general agreement with observations regarding double flood basalts

quantitative zn speciation in a contaminated dredged sediment by μ pixe μ sxrf exafs spectroscopy and principal component analysis dredging and disposal of sediments onto agricultural soils is a common practice in industrial and urban areas that can be hazardous to the environment when the sediments contain heavy metals this chemical hazard can be assessed by evaluating the mobility and speciation of metals after sediment deposition in this study the speciation of zn in the coarse 500 to 2000 m and fine 2 m fractions of a contaminated sediment dredged from a ship canal in northern france and deposited on an agricultural soil was determined by physical analytical techniques on raw and chemically treated samples zn partitioning between coexisting mineral phases and its chemical associations were first determined by micro particle induced x ray emission and micro synchrotron based x ray radiation fluorescence zn containing mineral species were then identified by x ray diffraction and powder and polarized extended x ray absorption fine structure spectroscopy exafs the number nature and proportion of zn species were obtained by a coupled principal component analysis pca and least squares fitting lsf procedure applied herein for the first time to qualitatively number and nature of species and quantitatively relative proportion of species speciate a metal in a natural system the coarse fraction consists of slag grains originating from nearby zn smelters in this fraction zn is primarily present as sphalerite zns and to a lesser extent as willemite zn2sio4 zn containing ferric oxyhydr oxides and zincite zno in the fine fraction zns and zn containing fe oxyhydr oxides are the major forms and zn containing phyllosilicate is the minor species weathering of zns zn2sio4 and zno under oxidizing conditions after the sediment disposal accounts for the uptake of zn by fe oxyhydr oxides and phyllosilicates two geochemical processes can explain the retention of zn by secondary minerals uptake on preexisting minerals and precipitation with dissolved fe and si the second process likely occurs because dissolved zn and si are supersaturated with respect to zn phyllosilicate exafs spectroscopy in combination with pca and lsf is shown to be a meaningful approach to quantitatively determining the speciation of trace elements in sediments and soils

three dimensional lithospheric deformation and gravity anomalies associated with oblique continental collision in south island new zealand summary isostatic considerations exhibit differences between the northern central and southern parts of the pacific australian plate collision in south island new zealand in the northern part mean elevations are moderate and the gravity low is small the central part contains the highest elevations and gravity and elevations correspond to each other relatively well and in the southern part the gravity low is strongest whereas the mean elevations are moderate again these differences indicate changes in the character of the isostatic compensation and are explained by increased thickening and widening of the crustal root from north to south and also by the long wavelength gravity response to a mantle density anomaly that increases towards the south a simple 3 d gravity model is derived that includes the detailed crustal structures from the south island geophysical transect sight experiment as well as a high density anomaly in the mantle inferred from teleseismic data the model indicates that cold and therefore dense upper mantle material penetrates the asthenosphere to a greater extent in the south similar to the behaviour of an apparently highly ductile lower crust as plate reconstruction suggests more lithospheric shortening in the north our model corresponds to lithospheric material escaping laterally to the south almost perpendicular to the compression caused by lithospheric shortening of the mantle therefore in addition to the prevailing mantle shear in new zealand there may also be a component of extrusional mantle creep beneath the southern alps orogen which could have caused some of the observed large seismic anisotropy in this region we may have also found evidence for submerged eocene miocene oceanic lithosphere beneath the southeastern part of south island that has been unaccounted for after plate reconstruction

chemical and physical transfers in an ultramafic rock weathering profile part 1 supergene dissolution of pt bearing chromite chemical weathering and supergene dissolution processes of pt bearing chromite have been studied in a lateritic weathering profile developed on ultramafic rocks in new caledonia southwest pacific the chemical distributions of alkaline earth transition metals and precious metals including pt and pd were determined in a weathering profile varying from bedrock at the base upward through coarse and fine saprolites and capped by a mottled zone and a lateritic colluvial nodular horizon chemi cal analyses and mass balance calculations suggest that progressive weathering of the parent rock is characterized by an enrichment of fe co and mn a segregation of ni at the boundary between the bedrock and the coarse sapolite and in the lower part of the fine saprolite and a depletion of mg ca si al and cr the higher concentration of transition metals at the interface between the coarse and fine saprolite is due to vertical transfer and precipitation at the base of the weathering profile in such a lateritic environment the pt bearing chromite grains are progressively dissolved and the pt group minerals pgm are released in the weathering mantle with a preferential depletion of pd with regard to pt

revealing the conditions of ni mineralization in the laterite profiles of new caledonia insights from reactive geochemical transport modelling new caledonia is one of the world s largest nickel laterite deposits that form from intense chemical and mechanical weathering of a peridotite bedrock as a result of such a weathering process a subsequent downward migration of si mg and ni takes place which eventually leads to redistribution of the elements in depth and over time depending on their mobility being released from ultramafic parent rock to groundwater the mobility of nickel is to a great extent controlled by sorption substitution and dissolution precipitation processes therefore the final profile of nickel enrichment is the result of the superposition of these possible fates of nickel the way how ni is redistributed in between them represents and defines its mineralization in laterite knowledge of these processes along with factors controlling them appears to be a key to detailed understanding of laterite formation in this study a numerical model which solves the reaction transport differential equations is used to simulate the formation of laterite profile from ultramafic bedrock with particular emphasis on modelled ni enrichment curve its comparison with in situ observations and detailed understanding of trace elements mobility since nickel deposits in new caledonia is characterized by oxide and hydrous mg silicate ores three different concurrent fates of ni deposition in a profile were taken into account in the modelling i ni in a goethite crystal lattice ii ni sorbed on weak and strong goethite sorption sites and iii ni precipitated with silicates garnierite simulations were performed using phreeqc associated with llnl dat thermodynamic database that has been edited in order to account garnierite minerals used in the calculations the work outline is represented by i long term 10 ma simulation of nickel laterite formation and evolution ii analysis of mobility of the elements and understanding its controlling factors iii comparison of modelled and in situ ni enrichment profile and analysis of nickel distribution in between different retention processes iv modelling and in depth understanding of these retention processes the modelling reveals that the vertical progression of the ph front controls thickening of iron rich zone explains the vertical mobility of the elements and governs the ni enrichment adsorption itself plays an important role in lateritization process retarding ni mobility but i becomes significant in a narrow range of ph slightly alkaline due to competition of mg and ni for sorption sites and ii does not explain such a high nickel content in limonite nowadays suggesting that ni is held in goethite mostly by stronger ties i e substituted for fe in the crystal lattice of iron oxide 1 d modelling appears to be a powerful tool in understanding the general behavior of trace elements upon the formation of laterite and at the same time reveals that locally ni mineralizations should be explained by more complex processes such as lateral transfers convective flows and preferential pathways

ni speciation in a new caledonian lateritic regolith a quantitative x ray absorption spectroscopy investigation abstract changes in ni speciation in a 64 m vertical profile of a new caledonian saprolitic lateritic regolith developed over ultramafic rocks under tropical weathering conditions were investigated by exafs spectroscopy quantitative analysis of the exafs spectra by linear combination least squares fitting lc lsf using a large set of model compound spectra showed that ni hosted in primary silicate minerals olivine and serpentine in the bedrock is incorporated in secondary phyllosilicates serpentine and fe oxides goethite in the saprolite unit and mainly in goethite in the laterite unit a significant concentration of ni up to 30 of total ni is also hosted by mn oxides in the transition laterite i e the lowest part of the laterite unit which contains large amounts of mn oxides however the amount of ni associated with mn oxides does not exceed 20 of the total ni in the overlying laterite unit this sequence of ni species from bedrock to laterite yields information about the behavior of ni during tropical weathering of ultramafic rocks the different ni distributions in phyllosilicates in the bedrock randomly distributed and in the saprolite unit clustered indicate two generations of ni bearing phyllosilicates the first which formed at higher temperature is related to serpentinization of oceanic crust whereas the second one which formed at lower temperature is associated with post obduction weathering of ultramafic rocks in addition the observed decrease in the proportion of ni hosted by mn oxides from the transition laterite to the upper lateritic horizons indicates dissolution of mn oxides during the last stages of differentiation of the lateritic regolith i e lateritization finally the ubiquitous occurrence of ni bearing goethite emphasizes the major role of this phase in ni speciation at the different weathering stages and suggests that goethite represents the major host for ni in the final tropical weathering stages of new caledonian ultramafic rocks

geology mineralogy and chemistry of lateritic nickel cobalt deposits near kalgoorlie western australia in the kalgoorlie area of western australia significant deposits of ni co laterite are developed on large ultramafic complexes at siberia and bulong the ultramafic rocks form part of extensive archean greenstone belts in the granitoid terrain of the southeastern yilgarn block and were lateritized during late cretaceous to early tertiary times the laterite profile developed over serpentinized dunite and peridotite is divided into four zones on the basis of morphology mineralogy and chemical composition in the oxidized bedrock zone ni rich saprolitic serpentine and smectite are developed in joints and fractures in the bedrock the overlying saprolite zone consists predominantly of saprolitic serpentine and may retain bedrock structures and textures it is characterized by a decrease of mg and an increase in ni upward a well defined clay zone is commonly developed over the bulong saprolite zone the clay zone is composed essentially of nontronite and quartz and commonly contains ni values of 1 to 2 percent the limohire zone occurs at the top of the profile and may consist of an upper hematite rich section and a lower goethite rich section the limonite zone is rich in fe al and cr and is formed by residual concentration of stable oxides a concentration of mn oxides commonly containing high co and ni grades occurs at the base of the limonite zone where sufficiently thick co and ni rich mn concentrations have been mined for direct smelter feed to augment co and ni production from kambalda ni sulfides physical and chemical characteristics of the underlying bed rock are important controls on the distribution of ni and co accumulations the mode of occurrence of ni and the presence of co are significant factors in the economics of exploiting these deposits

compression of oceanic lithosphere an analysis of intraplate deformation in the central indian basin intraplate compressional deformation in the central indian basin is expressed as linear e w trending topographic undulations and geoid anomlies with characteristic spacings of approximately 200 km to elucidate the nature of this deformation we develop models of an oceanic lithosphere in a state of horizontal compression the lithosphere is treated as a viscous or plastic layer of uniform strength which overlies a viscous half space in which strength decreases exponentially with depth we compare models in which deformation with a dominant wavelength develops in response to flexural buckling and the hydrodynamic growth of instabilities for the viscous flexural buckling model deformation is constrained to occur in the antisymmetric mode by flexural folding which is characterized by uniform bending of the layer in the hydrodynamic flow model a range of deformational styles are possible in a strong viscous lithosphere deformation of the layer occurs by flexural folding at a wavelength which agrees with that predicted from flexural buckling theory in a lithosphere of intermediate strength the layer deforms by folding characterized by thickening which localizes beneath topographic highs in a relatively weak lithosphere the layer incurs an even greater amount of localized thickening and deforms in the symmetric or pinch and swell mode by inverse boudinage if the layer has a plastic rheology deformation occurs by inverse boudinage independent of the yield stress results from models in which the layer folds either flexurally or with periodic thickening are consistent with the observed depth distribution of seismicity in the central indian basin and with experimental rock rheological data because of the trade off between buoyancy forces and layer strength in determining the dominant wavelength a lithosphere which was overlain by weak sediments when intraplate deformation initiated can be characterized by a compressive layer strength almost a factor of 3 less than a lithosphere which was initially sediment free for a range of plausible models which consider both a sediment covered and sediment free lithosphere the observed wavelength requires deviatoric stresses in the indian plate of several hundreds of mpa

composition and origin of the caldag oxide nickel laterite w turkey the caldag nickel laterite deposit located in the aegean region of w turkey contains a reserve of 33 million tons of ni ore with an average grade of 1 14 ni the deposit is developed on an ophiolitic serpentinite body which was obducted onto triassic dolomites in the late cretaceous the deposit weathering profile is both laterally and vertically variable a limonite zone which is the main ore horizon is located at the base of the profile a hematite horizon is located above the limonite which in the south of the deposit is capped by eocene freshwater limestones and in the north by a siliceous horizon the deposit is unusual in lacking a significant saprolite zone with little development of ni silicates the boundary between the limonite zone and serpentinite below is sharp with a marked decrease in concentrations of mgo from 13 to 1 wt over a distance of 2 mm representing the mg discontinuity ni concentrations within goethite the main ore mineral reach a maximum of 3 wt near the base of the limonite zone silica concentrations are high throughout most of the laterite with up to 80 wt silica in the upper portion of some profiles the combination of a serpentinite protolith and a high water table at caldag in association with an aggressive weathering environment in a tropical climate resulted in the formation of an oxide dominated deposit the precipitation of silica may coincide with a change in climate with silica precipitation linked to an increase in seasonality additional variations within profile morphology are attributed to transportation during and after laterite development as a result of faulting pocket type laterite formation and slumping each of which produces a contrasting set of textural and geochemical features

al substituted goethite an indicator of pedogenic and other weathering environments in south africa abstract over 200 goethite containing samples from widely diverse environments along the eastern seaboard of south africa were examined and described mainly by x ray powder diffraction xrd aluminium substituted goethites ranging from 0 to about 32 mole alooh were identified mainly by xrd line shift and chemical extraction they occur in every soil zone and major soil type in one or other form from sources such as 1 non hydromorphic highly weathered strongly acid soils ferruginous bauxites saprolites and moderately weathered moderately acid soils environments 2 hydromorphic environments mottles concentrations pipe stems crusts ferricretes geodes and 3 crusts in calcareous environments these goethites formed in different climatic and weathering environments were grouped according to their amount of al substitution and crystallinity as determined by xrd line broadening al substitution in goethite formed in hydromorphic moderately acid soils and calcareous environments was generally low 0 15 mole goethite formed in non hydromorphic highly weathered environments was generally high in al substitution 15 32 mole and increased in the following order saprolites and strongly acid freely drained soils this study showed that the degree of al substitution and crystallinity of goethites may reflect the environment in which they have formed and serve as an indicator of soilforming processes

multistage crack seal vein and hydrothermal ni enrichment in serpentinized ultramafic rocks koniambo massif new caledonia sets of fractures and breccia sealed by ni rich silicates and quartz occur within saprock of the new caledonian regolith developed over ultramafic rocks the crystallization sequence in fractures is as follows 1 serpentine stage lizardite polygonal serpentine white lizardite 2 ni stage ni mg kerolite followed by red brown microcrystalline quartz and 3 supergene stages the red brown microcrystalline quartz corresponds to the very last stage of the ni sequence and is inferred to have precipitated within the 50 95 c temperature range it constitutes also the main cement of breccia that has all the typical features of hydraulic fracturing the whole sequence is therefore interpreted as the result of hydrothermal fluid circulation under medium to low temperature and fluctuating fluid pressure although frequently described as the result of a single downward redistribution of ni and mg leached in the upper part of the regolith under ambient temperature the ni silicate veins thus appear as the result of recurrent crack and seal process corresponding to upward medium temperature fluid convection hydraulic fracturing and subsequent fluid mixing and mineral deposition

a multichannel seismic study of lithospheric flexure across the hawaiian emperor seamount chain existing models assume that the thickened crust beneath seamounts is the result of a surface volcanic load flexing an elastic plate new results suggest that flexed oceanic crust beneath the hawaiian emperor seamount chain is underlain by a 4 km thick deep crustal body we intepret the body as a deep crustal sill complex associated with the tholeiitic stage of volcano building along the chain

properties of iron oxides in some new caledonian oxisols abstract oxisols from two toposequences of new caledonia formed from peridotite consist essentially of fe oxides goethite hematite maghemite these fe oxides were characterized by their mineralogy crystal size and morphology al substitution thermal behaviour and dissolution kinetics in 6 m hcl at 25 c in one toposequence the samples were free of hematite goethite only at 1050 m above sea level whereas at lower altitudes hematite was also present al substitution was generally low due to the low al content of the peridotite except in gibbsitic samples on rocks somewhat higher in al the surface areas of goethite and hematite ranged between 50 and 150 m 2 g 1 dithionite extractable ni and cr were between 0 2 and 2 2 ni and 0 3 and 2 3 cr the hematite containing samples tended to be higher in cr and lower in ni whereas the opposite held for samples containing goethite only maghemites had a low unit cell size 8 31 8 32 instead of 8 34 8 35 a which was attributed to al substitution dehydroxylation temperature of goethites was weakly correlated with al substitution dissolution kinetics could be described by a linear form of a modified first order reaction with one straight line for samples containing goethite only and two lines for samples containing goethite plus hematite

geochemistry of laterites stability of al goethite al hematite and fe super 3 kaolinite in bauxites and ferricretes an approach to the mechanism of concretion formation

nickel isotope fractionation during continental weathering abstract recent literature has documented systematic variations in the ni stable isotope compositions of several terrestrial and marine reservoirs of this bioessential trace metal for example dissolved ni in the world s major rivers has been shown to be more enriched in heavy isotopes than the continental rocks from which that ni was derived cameron and vance 2014 geochim cosmochim acta 128 195 211 this observation implies that one or more chemical reactions occurring during weathering of ni rich rock drives stable isotope fractionation that results in retention of lighter isotopes of ni associated with solid phases we present new ni isotope analyses of samples from various horizons of the webster addie laterite near democrat north carolina usa as well as results from two sets of experiments designed to constrain the fundamental mechanism s driving the isotopic variation observed in that weathering profile bedrock samples dunite and talc rich altered dunite have 60 58ni values of 0 06 to 0 20 in excellent agreement with previous research a sample of yellow laterite is enriched in lighter isotopes of ni with 60 58ni 0 21 mixed phase samples containing quartz and traces of serpentine goethite and smectite range from 0 13 to 0 35 experimental leaching of ni from olivine in dilute acid at ambient conditions results in no resolvable fractionation indicating that initial release of ni to solution from bedrock is not responsible for the isotope variation we observe in the natural samples sorption of ni onto montmorillonite a minor secondary weathering product present in laterites is associated with a very small fractionation of 0 11 0 09 with lighter isotopes sorbed on the smectitic clay such adsorption can thus account for some but not all of the isotope systematics observed in the weathering profile given previous evidence that sorption of ni to fe oxyhydroxides does drive a fractionation of appropriate sense and magnitude wasylenki et al 2015 chem geol 400 56 64 we infer that oxidation of fe2 released from bedrock and precipitation result in retention of a light pool of ni in solid weathering products thereby enriching dissolved ni in heavier isotopes because much of the continental crust s ni budget is hosted by mafic and ultramafic rocks which weather very rapidly at earth s surface and for which fe oxyhydroxides are extremely common weathering products this ni fractionation mechanism may be relevant for terrestrial weathering of ni bearing rocks in general even though the overall mineralogy and chemistry of weathering profiles varies with parent lithology and environmental conditions secondary hydrous ni rich mg silicates from veins in the saprolite zone are enriched in heavy isotopes with 60 58ni 0 29 to 0 86 similar ni rich mg silicate samples from several similar profiles around the world display a similar range from 0 36 to 0 90 suggesting that the processes responsible for isotopic fractionation at the north carolina locality are general phenomena characteristic of laterites worldwide we hypothesize that in laterites continual downward percolation of meteoric waters and progressive chromatographic exchange with goethite bound ni progressively shifts the ni contents of solids toward lighter and fluids toward heavier isotopic compositions when fluids reach the mg rich si rich saprolite zone isotopically heavy garnierite minerals precipitate in veins the phenomena we report and discuss here may long have been the dominant controls on the distribution of ni isotopes in earth s near surface terrestrial environment at least since oxygenation of the atmosphere due to lack of abundant oxygen in air and water earlier in earth history the biogeochemical cycle of ni isotopes was almost certainly rather different such that riverine dissolved ni was not necessarily enriched in heavy isotopes relative to continental crust and the oceans may not have been so highly enriched in heavy isotopes of ni as they are presently

folding of oceanic lithosphere folding of the lithosphere just south of the bay of bengal appears as 1 undulations in acoustic basement topography and 2 as linear geoid undulations in the seasat altimeter data from the seasat data we find that the east west trending folds have wavelengths ranging from 130 to 250 km and clustering about 190 km the horizontal gravity disturbances due to the folds range in amplitude from 15 to 50 mgal elastic models of oceanic lithosphere have in the past been used to demonstrate the implausibility of lithosphere buckling or folding in response to compression these elastic models typically predict that compressive stresses of about 5 gpa are required to buckle oceanic lithosphere with an age comparable to that of the northeastern indian ocean 40 70 ma these stresses exceed the strength of lithospheric rock we use an elastic plastic model to show that oceanic lithosphere of this age should have a net compressive strength equal to about 12 of the elastic buckling stress we further demonstrate that loads approaching the net compressive strength cause the lithosphere to fold with a wavelength about 200 km i e the wavelength observed from seasat our results reinforce earlier speculation that this folding may be related to the himalayan orogeny

lateritic nickel deposits of brazil many nickel deposits are known in brazil accounting for about 350 106 tons of ore with an average of 1 5 ni all are of the lateritic type these deposits are scattered throughout the country being rarer in the northeastern region and in the south below 25 s latitude they are mainly associated with mafic ultramafic massifs of large dimensions and ultramafic alkaline complexes and occur in climatic regions of contrasting seasons the weathering profile developed over the fresh rock consists from bottom to top of the following horizons altered rock coarse saprolite argillaceous saprolite ferruginous saprolite and lateritic overburden the thickness of each horizon varies from one deposit to another the whole profile generally exceeding 20 m the saprolitic horizons with inherited minerals serpentine chlorite or neoformed minerals smectites constitute the silicated nickel ore and are thicker were climatic conditions are drier the ferruginous upper horizons made up of iron oxide hydroxides are more developed in more humid regions in brazil the silicated ore generally prevails over the oxidized ore the main ni bearing minerals are serpentine smectite garnierite and goethite the lateritic nickel deposits of brazil may be correlated with two erosion surfaces corresponding to the sul americano lower tertiary and velhas upper tertiary levelling cycles the degree of dismantling of the higher and more ancient surface and the consequent development of the velhas surface control the position of the nickel accumulation in the landscape thus the deposits may be found either in the lowlands or in the highlands where they are always covered by a silcrete layer the alteration profiles in the brazilian lateritic nickel deposits are broadly similar to those described elsewhere in the world however they present two characteristic features the silicated ore prevails over the oxidized ore and a silicified layer covers the profies developed on the highlands

scratching the surface estimating dimensions of large igneous provinces a study of five major basaltic provinces including oceanic plateaus volcanic passive margins and continental flood basalts shows that they are voluminous constructions of extrusive igneous rock underlain by intrusive rock crustal thickness ranges from 20 to 40 km and lower crust is characterized by high 7 0 7 6 km s seismic velocities volumes and emplacement rates derived for two oceanic plateaus the ontong java and kerguelen broken ridge reveal short lived pulses of increased global crustal production and suggest an origin involving the lower mantle the ontong java rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid ocean ridge system despite the importance off large igneous provinces in studies of mantle dynamics and the global environment scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features

evolution of the walvis ridge rio grande rise hot spot system implications for african and south american plate motions over plumes crystallization ages of volcanic rocks dredged or drilled from the walvis ridge ten sites and the rio grande rise one site have been determined by the 40ar 39ar incremental heating technique the fundamentally age progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of tristan da cunha along the walvis ridge and rio grande rise and for the formation of the continental flood basalts located in namibia africa and brazil south america the walvis ridge rio grande rise volcanic system evolved along a section of the south atlantic spreading axis as the african and south american plates migrated apart astride or in close proximity to an upwelling plume reconstructions of the spatial relationship between the spreading axis the tristan hot spot and the evolving walvis ridge rio grande rise volcanic feature show that at about 70 ma the spreading axis began to migrate westward away from the hot spot the resulting transition to intraplate hot spot volcanism along the walvis ridge and associated termination of rio grande rise formation also involved a northward migration of previously formed african seafloor over the hot spot rotation parameters for african motion over fixed hot spots i e absolute motion have been recalculated such that the predicted trail of the tristan hot spot agrees with the distribution of radiometric and fossil basement ages along the walvis ridge african absolute motion has been extended to the south and north american plates by the addition of relative motion reconstruction poles

compensation of swells and plateaus in the north pacific no direct evidence for mantle convection at intermediate and long wavelengths the ratio of geoid height to topography is sensitive to the depth and mode of compensation a low geoid topography ratio 8 m km in conjunction with a poor correlation between geoid height and topography is evidence of mantle convection after subtracting a reference geoid from the observed geoid previous studies have found a regular pattern of geoid highs and lows with a characteristic wavelength of 3000 4000 km since these geoid highs and lows were poorly correlated with topography and resulted in very high geoid topography ratios 10 20 m km they were believed to reflect the planform of mantle convection we show that the regular pattern of geoid highs and lows is an artifact caused by truncating the reference geoid at spherical harmonic degree 10 since the geoid spectrum is red the residual geoid is dominated by degree 11 when the harmonics of the reference geoid are rolled off gradually the regular pattern of geoid highs and lows disappears in the northeast pacific the new residual geoid reflects the lithosphere age offsets across the major fracture zones in the northwest pacific the residual geoid corresponds to isostatically compensated swells and plateaus we have calculated the geoid topography ratio for 10 swells and plateaus and have found a range of compensation depths the highest geoidaopography ratio of 5 5 m km occurs on the flanks of the hawaiian swell intermediate ratios occur in four areas including the midway swell these intermediate ratios reflect a linear combination of the decaying thermal swell and the increasing volume of airy compensated seamounts low geoid topography ratios occur over the remaining five areas e g emperor seamounts reflecting the absence of a thermal swell our findings do not support the hypothesis that the planform of mantle convection is evident in the geoid we see only indirect evidence of thermal plumes reheating the lower lithosphere

goethite aging explains ni depletion in upper units of ultramafic lateritic ores from new caledonia abstract an upward loss of ni is commonly reported in the oxide rich unit of ni laterite deposits developed over ultramafic rocks in tropical regions especially in freely drained and deeply weathered regoliths because goethite is the major mineral constituent of such oxide rich units this ni loss has been linked to compositional changes in goethite in the present study we have investigated possible correlations between ni contents in the bulk laterite and the evolution of goethite in terms of composition and crystallinity in two ni rich and one ni poor lateritic profiles from new caledonia ni k edge extended x ray absorption fine structure exafs spectroscopy indicates that goethite hosts the main fraction of ni in the three profiles investigated asbolane lithiophorite identified as accessory minerals by x ray diffraction xrd have little effect on the vertical variations in bulk ni content in spite of the fact that the ni contents of these mn oxides can be significant at certain depths the gradual decrease in ni content from the bottom to the top of the three ni lateritic profiles correlates with a decrease in the ni content of goethite as determined by electron probe micro analysis in addition xrd data show that these compositional trends are linked to an increase of the mean coherent domain size of goethite these observations support the hypothesis that ni is expelled from goethite as it ages through successive dissolution and recrystallization cycles during the lateritization process comparison of laterites having different degrees of weathering suggests that this aging process could also play a significant role in the regional variability of ni content in ni laterite deposits

contrasting isotopic signatures between anthropogenic and geogenic zn and evidence for post depositional fractionation processes in smelter impacted soils from northern france abstract zinc isotopes have been studied along two smelter impacted soil profiles sampled near one of the largest pb and zn processing plants in europe located in northern france about 50 km south of lille mean 66zn values along these two soil profiles range from 0 22 0 17 2 to 0 34 0 17 2 at the lowest horizons and from 0 38 0 45 2 to 0 76 0 14 2 near the surface the 66zn values in the lowest horizons of the soils are interpreted as being representative of the local geochemical background mean value 0 31 0 38 whereas heavier 66zn values near the surface of the two soils are related to anthropogenic zn this anthropogenic zn occurs in the form of franklinite znfe2o4 bearing slag grains originating from processing wastes at the smelter site and exhibiting 66zn values of 0 81 0 20 2 the presence of franklinite is indicated by exafs analysis of the topsoil samples from both soil profiles as well as by micro xanes analysis of the surface horizon of a third smelter impacted soil from a distant site these results indicate that naturally occurring zn and smelter derived zn exhibit significantly different 66zn values which suggests that zinc isotopes can be used to distinguish between geogenic and anthropogenic sources of zn in smelter impacted soils in addition to a possible influence of additional past sources of light zn likely zn sulfides and zn sulfates directly emitted by the smelter the light 66zn values in the surface horizons compared to smelter derived slag materials are interpreted as resulting mainly from fractionation processes associated with biotic and or abiotic pedological processes zn bearing mineral precipitation zn complexation by organic matter and plant uptake of zn this conclusion emphasizes the need for additional zn isotopic studies before being able to use zn isotopes to trace sources and pathways of this element in surface environments

geochemical balance of lateritization processes and climatic signatures in weathering profiles overlain by ferricretes in central africa a simple geochemical balance of lateritization processes governing the development of several tens of meters of weathering profiles overlain by ferricretes is estimated on the basis of detailed mineralogical and geochemical data the lateritic weathering mantle of the haut mbomou area in central africa is composed of different weathering layers described from the base to the top of vertical profiles as a saprolite a mottled clay layer a soft nodular layer a soft ferricrete and a ferricrete in which kaolinite gibbsite goethite and hematite occur in various quantities incongruent dissolution of kaolinite leads to the formation of gibbsite in the upper saprolite whereas the hematite does not clearly replace the kaolinite according to an epigene process in the upper ferruginous layers of the profiles instead that kaolinite is also transformed into gibbsite according to an incongruent dissolution under hydrated and reducing conditions induced by a relatively humid climatic pattern the respective relations of the silica iron and aluminum balances and the al substitution rate of the hematite on the one hand and of rhg rhg 100 hematite hematite goethite and the kaolinite on the other hand to the consumption or the release of protons h permit differentiation of aggrading ferruginization and degradation processes operating in the different lateritic weathering profiles the al substitution rate of the fe oxyhydroxides varies according to the nature of lateritization processes e g saprolitic weathering and aggrading ferruginization vs degradation the observations and results indicate that the ferruginization process of the weathering materials of parent rocks is not a simple ongoing process as often thought this suggests that the actual lateritic weathering mantle of the haut mbomou area may result from different stages of weathering and erosion during climatic changes

xas evidence for ni sequestration by siderite in a lateritic ni deposit from new caledonia mineralogical and spectroscopic analyses were conducted on a lateritic ni deposit from southern new caledonia results show that ni is incorporated in siderite feco3 found between 37 and 40 m depth in the laterite and saprolite units of the regolith sem edxs analyses of siderite rich samples indicate that a significant amount of nickel can be hosted by this crystalline phase 0 8 wt nio ni and fe k edge extended x ray absorption fine structure exafs spectroscopic analyses of the siderite rich samples from the regolith as well as comparison with synthetic ni bearing and ni free siderites demonstrate isomorphous substitution of ni2 for fe2 in the siderite structure linear combination fitting lcf of the ni k edge exafs data reveals that this ni bearing siderite species accounts for more than 90 of the total ni pool 1 wt nio in the siderite rich horizons of the regolith in addition lcf analysis of the exafs spectra indicates that goethite and serpentine are the major ni hosts in the upper horizons laterite and lower horizons saprolite of the regolith respectively formation of siderite an uncommon mineral species in such oxidized environments is attributed to the development of swampy conditions in organic rich lateritic materials that accumulated at the bottom of dolines these results thus show the importance of siderite as a host for nickel in lateritic ni deposits that have been affected by late hydromorphic and reducing conditions

the mineralogy and geochemistry of the cerro matoso s a ni laterite deposit montelibano colombia the cerro matoso s a ni laterite deposit in northwest colombia is an important producer of ferronickel expanded production of ferronickel is planned to be 55 000 mt by mid 2004 the deposit is developed over a peridotitic protolith that is exposed in the form of an elongated hill the deposit s weathering profile is variable both vertically and laterally and 10 distinct lithostratigraphic units have been characterized two typical sections through the weathering profile were sampled from an area of the mine with high pit 1 and lower pit 2 ni grades bench mapping has shown that pits 1 and 2 have distinctly different weathering profiles from bottom to top the profile in pit 1 is weakly serpentinized peridotitic protolith saprolitized peridotite green saprolite main ore horizon tachylite used by mine geologists to describe an enigmatic fe oxide horizon black saprolite yellow laterite red laterite the sequence is then capped by a magnetic to nonmagnetic ferricrete known locally as canga the succession in pit 2 is from serpentinized peridotite saprolitized peridotite brown saprolite yellow laterite red laterite and lacks the green saprolite ore horizon all the units in pit 2 have currently uneconomic ni grades the thickness of the units is highly variable but most of the major horizons have maximum thicknesses of the order of tens of meters both pits contain abundant fault and joint related silicate veins sometimes in stockworks in the lower part of the sequence these veins contain the distinctive green mineral known as garnierite actually pimelite a form of nickeliferous talc as well as quartz and chalcedony and they can have a ni content of up to 30 to 40 wt percent the bulk geochemistry in most units of both profiles shows a fairly typical ni laterite pattern in which mgo and sio2 are depleted toward the top of the sequence whereas feo increases mineralogic studies confirm that the protolith in both pits is a partly up to 50 serpentinized harzburgite and that in pit 1 the main ni bearing phases in the weathering profile are ni sepiolite ni serpentines and other hydrous silicates the garnierites in cerro matoso have been identified as pimelite in which various amounts of ni have substituted for mg the upper part of the sequence is dominated by amorphous and crystalline fe oxide phases the magnetic canga is composed mainly of maghemite that may have been produced by oxidation of magnetite rich units the mineral content of pit 2 is dominated by poorly structured fe oxides or goethite and by subordinate clay minerals and quartz the geochemistry and mineral content of the deposit suggest that as in many other ni laterite deposits ore genesis is strongly controlled by local climate topography and drainage mass balance calculations indicate that the profiles in pits 1 and 2 had different weathering histories because the degree of profile collapse and residual enrichment in pit 1 is far more extreme than that in pit 2 this difference may be the result of different degrees of serpentinization of the protolith in the two pits and potential dilution of the ore in pit 2 by input from an exotic unit ni in the deposit has also undergone supergene enrichment resulting from the leaching of ni from the upper part of the lateritic profile and its transport to the green saprolite unit where the ni was fixed in silicate minerals

long term tropical morphogenesis of new caledonia southwest pacific importance of positive epeirogeny and climate change extensive mapping of relict lateritic landsurfaces over the 1600 m of relief of mainland new caledonia is used to evaluate long term morphogenesis of the island since its emergence in the oligocene the results support the interpretation of the lateritic levels as abandoned stepped remnant landsurfaces that may be grouped into eight island scale erosion levels recording episodic lowering of base level the separation of the erosion levels results from the combination of positive epeirogenic movements of the new caledonia continental ridge and long term neogene climate variability which is recorded by the contrasted erosion and weathering patterns of the three youngest levels and tentatively correlated with known global and regional paleoclimatic events

discrimination of water inrush source and evolution analysis of hydrochemical environment under mining in renlou coal mine anhui province china with the development of mining the hydrochemical environment has changed in the renlou coal mine anhui province china it will be of great significance to coal mine safety production by exploring the temporal and spatial evolution law of hydrochemistry of main water inrush aquifers in renlou coal mine under the effect of mining groundwater samples from three main water inrush aquifers in different periods were collected to analyze their principal components and establish the discrimination model of water inrush source the first and second principal components with eigenvalues greater than 1 were selected in which the first principal component represents sulfate dissolution and pyrite oxidation and the second principal component represents desulfurization and cation alternating adsorption the evolution law of hydrochemical environment was analyzed by combining the distribution characteristics of principal component scores with the spatial location of misjudged groundwater samples the results show that 1 quaternary aquifer is greatly affected by mining and the hydraulic connections with carboniferous limestone aquifer in the central region leads to two misjudged groundwater samples in the discriminant model 2 permian sandstone aquifer is to a certain extent affected by mining which shows a relatively closed hydrogeological environment in most areas of coal mine and an opened environment in some areas with time there are five misjudged samples in the discriminant model due to hydraulic connections with the quaternary aquifer and carboniferous aquifer in some areas 3 carboniferous limestone aquifer is controlled by typical faults and collapse columns and mining has a slight influence on it in the central area there are hydraulic connections with the quaternary aquifer and the permian sandstone aquifer due to the collapse columns which lead to four misjudged groundwater samples in the discriminant model

seismic imaging of hotspot related crustal underplating beneath the marquesas islands volcanism in active continental rift zones1 2or on rifted continental margins3is frequently associated with unusually high lower crustal seismic velocities indicating the presence of large igneous intrusions at the base of the crust the only comprehensive investigation of crustal underplating at an oceanic hotspot beneath hawaii4 6 has yielded controversial results7 here we report the results of seismic refraction experiments across the marquesas islands hotspot trace which show that the island chain is underlain by crust 15 17 km thick and that a large lower crustal region 275 km wide and 2 8 km thick has seismic velocities 7 3 7 75 km s 1 indicative of crustal underplating wide angle reflections occur near the base of the normal lower crustal velocities and at the base of the underplating complex we interpret these reflectors as the relict pre hotspot moho and the current post hotspot moho respectively the high velocity material may be purely intrusive or may consist of a mixture of intrusive and preexisting rocks the volume of the high velocity body is impressive amounting to nearly twice the volume of volcanics erupted at the surface

analysis of satellite gravity and bathymetry data over ninety east ridge variation in the compensation mechanism and implication for emplacement process 1 we investigate the mode of compensation emplacement history and deep density structure of the ninety east ridge indian ocean using spectral analyses and forward modeling of satellite gravity and bathymetry data we find that the northern 0 10 n and the southern 20 30 s parts of the ridge are flexurally compensated with an effective elastic thickness 15 km whereas the central part 0 20 s is locally compensated furthermore we find that for a part of central block 10 20 s over osborn knoll the compensation depth is unreasonably very high 30 40 km therefore we favor a model with subsurface loading and interpret this to be due to underplating of mafic material at the base of the crust a hypothesis that is supported by seismic results and direct modeling of gravity data along some profiles these results suggest that the northern and southern parts of ninety east ridge were emplaced off to a ridge axis compared to the central one which might have been emplaced on or near a spreading center locally compensated large topography thick underplated crust in the central part near osborn knoll might result from an interaction of a hot spot with the extinct wharton spreading ridge

paired stable isotopes o c and clumped isotope thermometry of magnesite and silica veins in the new caledonia peridotite nappe abstract the stable isotope compositions of veins provide information on the conditions of fluid rock interaction and on the origin of fluids and temperatures in new caledonia magnesite and silica veins occur throughout the peridotite nappe in this work we present stable isotope and clumped isotope data in order to constrain the conditions of fluid circulation and the relationship between fluid circulation and nickel ore forming laterization focusing on the koniambo massif for magnesite veins occurring at the base of the nappe the high 18 o values between 27 8 and 29 5 attest to a low temperature formation clumped isotope analyses on magnesite give temperatures between 26 c and 42 c that are consistent with amorphous silica magnesite oxygen isotope equilibrium the meteoric origin of the fluid is indicated by calculated 18 o water values between 3 4 to 1 5 amorphous silica associated with magnesite or occurring in the coarse saprolite level displays a narrow range of 18 o values between 29 7 and 35 3 for quartz veins occurring at the top of the bedrock and at the saprolite level commonly in association with ni talc like minerals the 18 o values are lower between 21 8 and 29 0 and suggest low temperature hydrothermal conditions 40 95 c thermal equilibration of the fluid along the geothermic gradient before upward flow through the nappe and or influence of exothermic reactions of serpentinization could be the source s of heat needed to form quartz veins under such conditions

an assessment of the accuracy of admittance and coherence estimates using synthetic data previous work has shown that estimates of the admittance between topography and free air gravity anomalies are often biased by spectral leakage even after the application of multiple prolate spheroidal wavefunction data tapers despite this a number of authors who have used the free air admittance method to estimate the weighted average effective elastic thickness of the lithosphere te and to identify topography supported by mantle convection have not tested their methods using synthetic data with a known relationship between topography and gravity in this paper i perform a range of such tests using both synthetic surface data and synthetic line of sight los accelerations of satellites orbiting around an extra terrestrial planet it is found that spectral leakage can cause the estimated admittance and coherence to be significantly in error but only if the box in which they are estimated is too small the definition of small depends on the redness of the gravity spectrum there is minimal error in the whole box weighted average estimate of te if the admittance between surface gravity and topography is estimated within a box at least 3000 km wide when the synthetic uniform te is less than 20 km and the coherence is high the errors in te are mostly 5 km for all box sizes greater than 1000 km on the other hand when the true te is greater than 20 km and the box size is 1000 km the best fitting te is likely to be at least 5 10 km less than the true te however even when the coherence is high it is not possible to use elastic plate admittance models to distinguish between real and spurious small fractions of internal loading when the boxes are smaller than 2000 km in width noise in the gravity introduces error and uncertainty but no additional bias into the estimates of the admittance it does however bias estimates of te calculated using the coherence between bouguer gravity and topography the admittance at wavelengths between 1000 and 4000 km which is of interest when studying mantle convection is only well resolved when the box size is larger than 2000 km or the synthetic te is less than 15 km and the true long wavelength admittance is greater than 30 mgal km 1 when the box size is 1000 km it is not possible to distinguish between real and spurious convective support of long wavelength topography at the altitude of most orbiting satellites 200 400 km gravity is much redder than it is at ground level therefore it is necessary to use much larger boxes when using los accelerations to estimate the admittance than it is when using surface measurements however gradual changes in the altitude of the satellite or even occasional sudden changes make almost no difference to the estimate of the admittance finally three short investigations are undertaken concerning the effect on the admittance of the application of irregular windows to the data of lateral variations in te and of the infilling of flexural moats by low density sediment it is found that the bias due to the application of an irregular window is not significantly greater than the bias due to the application of a regular window of similar size that the best fitting te is strongly biased by the value associated with the highest amplitude topography and that sediment infill raises the admittance at wavelengths corresponding to the width of the moat

goethite and hematite in a climosequence in southern brazil and their application in classification of kaolinitic soils abstract the goethite hematite goethite ratio of 11 profiles of oxisols ultisols and inceptisols along a 600 km e w transect in s brazil varied systematically with climatic and soil factors the ratio increased with decreasing mean annual air temperature increasing excess moisture rainfall minus evapotranspiration increasing soil organic carbon and decreasing ph this is explained in light of the current concept of goethite and hematite formation in soils higher temperatures favor hematite whereas higher excess moisture higher organic carbon and lower ph favor goethite a basis is suggested for using goethite and hematite in the mineralogical classes at the family level of soil taxonomy

parent rock and climatic evolution control on the genesis of ni bearing clays in ni co laterites new inferences from the wingellina deposit western australia abstract oxide type ni laterites seldom contain significant ni phyllosilicates reserves this study is focused on the mineralogy of ni clays mainly occurring in the saprolite zone of the wingellina oxide type ni co laterite deposit despite most of the wingellina reserves occur in the oxide zone the deposit also has a well developed high ni grade saprolite horizon this study presents a mineralogical and chemical characterization of the ni phyllosilicates of the wingellina saprolite ore aimed to understand the role of diverse bedrocks gabbro and serpentinite and the influence of climate on the formation of different clay types the main phyllosilicate in the gabbro derived saprolite consists of dioctahedral al and ni montmorillonite originated from the weathering of pyroxene the genesis of al and ni rich montmorillonite from pyroxene can be explained by an open system alterative process in which al mainly derives from the dissolution of plagioclase in the serpentinite derived saprolite the alteration pathway followed a multistage evolution i lateritic alteration of serpentine i into ni serpentine ii and tri and dioctahedral smectites saponite and nontronite ii late precipitation of interstratified ni clays chlorite smectite and talc smectite as a replacement of former phyllosilicates and as neoformed minerals the latest phenomenon may be related to the late miocene shift from humid and acid tropical climate to saline and alkaline conditions arid to semi arid climate and represents an example of post lateritization processes rarely observed in laterites located on stable cratons the aridity driven precipitation of ni rich interstratified clays in the wingellina laterite can be seen as a new model for explaining the evolution of ni laterites in stable cratonic settings experiencing post lateritization aridity

mineralogy and geochemistry of the berong ni co laterite deposit palawan philippines abstract intense weathering of the serpentinized peridotite resulted in the formation of the berong ni co laterite deposit in palawan philippines the studied laterite profiles are divided from base to top into i serpentinized bedrock ii saprolite horizon and iii limonite horizon olivine in the peridotite contains a significant amount of ni average 0 38 wt nio thus representing the main source of the ore in the laterite horizons six types of ni bearing serpentines up to 6 65 wt nio in the saprock are discriminated based on their textures and raman signatures garnierite a mixture of serpentine kerolite and sepiolite like clays typically occurs as coatings or fracture fillings in the saprock and is characterized by strikingly high nio content up to 34 86 wt goethite and mn oxy hydroxides i e lithiophorite asbolane intermediates are the principal hosts of ni in the limonite up to 2 15 wt nio and 23 89 wt nio respectively with the latter also being the main co carriers up to 12 59 wt coo the whole rock xrf data show typical trends observed in other ni laterite deposits where mg and si are depleted toward the surface and the transition metals i e fe al ni co and mn are retained in the weathered horizons the saprolite horizon is particularly enriched in ni while the lower section of the limonite horizon is enriched in co the mildly acidic environmental condition ph 6 57 in the limonite horizon was found to enhance the mobilization and re distribution of ni from the limonite towards the lower section of the profiles geological observations coupled with mineralogical and geochemical data show that the berong ni co laterite deposit formed in two weathering processes i development of the saprolite and the limonite horizons and ii late precipitation of secondary phyllosilicates i e garnierite mn oxy hydroxides and silica

first palaeomagnetic dating of ferricrete in new caledonia new insight on the morphogenesis and palaeoweathering of grande terre terra nova 24 77 85 2012 abstract comparing palaeolatitudes estimated from remanent magnetization data of ferricrete developed over laterite at two sites goro and tiebaghi against the apparent polar wandering path of australia provides new time constraints for the peridotite weathering in new caledonia the tiebaghi massif of the west coast klippes displays a single episode of ferricrete development during latest oligocene times by contrast the goro site in the southern part of the massif du sud reveals a more complex history with several episodes of ferricrete development from latest oligocene to pliocene quaternary times these data have made it possible to constrain the post obduction geodynamics and associated morphogenesis of new caledonia since related uplift probably prevented regolith development until latest oligocene times moreover the later uplift and deep erosion of the west coast klippes during the early miocene probably prevented further regolith preservation

coal mining impacts on water environs around the barapukuria coal mining area dinajpur bangladesh the present research makes an effort towards awareness of the impact of underground coal mining on water environment around the barapukuria coal mining area dinajpur by direct field investigation questionnaire survey and laboratory analysis for this research the three foremost errands have been mulled over which are the water level data analysis for 10 years from 2001 to 2011 ground water major parametric analysis and the questionnaire survey on the availability of ground water before and after coal mining operation the results of field and laboratory analysis show that the characteristics and concentrations of all the major physical and chemical parameters such as ph ec temperature hco3 no3 so4 2 cl na k mg2 ca2 and fe total are still tolerable for all purposes and also within the standard limit on the other hand the questionnaire survey and water level data analysis confirm almost similar results regarding the depletion of water level the water level has depleted more than 5 m from 2001 to 2011 therefore currently the availability of ground water is normal in the rainy and winter seasons but is slight problematic in the dry season where ground water was available at all times prior to coal mining in the area from these scenarios it is comprehensible that the ground water level moves downwards than earlier because of the excess pumping of water from the mine area besides the natural recharge condition is not enough and somewhere breaks off while some of the mines out areas are subsided consequently the upper part of the water bearing formations aquifer loses its porous and permeable properties resulting water recharging problem which is directly responsible for depleting the ground water level over the area moreover the water levels will also decline relative to the location depth recharge and discharge conditions of the mine both aerially and vertically while there is a typical relationship between the depth of mining and static water level which is water levels will decline more as the mine goes deeper therefore taking into account the current ground water condition and the depth of barapukuria coal mine this research implied that the water level will deplete more in day coming and the water crisis will be more for future thus this research recommends a sustainable guideline for long term planning and also suggests that regular monitoring with time to time more detail qualitative and quantitative assessments of water bodies in the area

characterization of underground tunnel water hydrochemical system and uses through multivariate statistical methods a case study from maddhapara granite mine dinajpur bangladesh a quality study of the drained water from maddhapara granite mine underground tunnel was undertaken to study their hydrochemical variations and suitability for various uses employing chemical analysis basic statistics correlation matrix r cluster analysis principal component factor analyses and anova as the multivariate statistical methods the results of chemical analysis of water show the modest variation in their ionic assemblage among different sampling points of the tunnel where ca hco3 type of hydrochemical facies is principally dominated the correlation matrix shows a very strong to very weak positive even negative correlation relationship suggesting the influence of different processes such as geochemical biochemical processes and multiple anthropogenic sources on controlling the hydrochemical evolution and variations of water in the mine area cluster analysis confirms that cluster 1 contains 68 75 of total samples whereas cluster 2 contains 31 25 on the whole the dominated chemical ions of first cluster groups are ca and hco3 suggesting a natural process similar to dissolution of carbonate minerals the second cluster group consisted of cl and so4 2 ions representing natural and anthropogenic hydrochemical process the results of pca fa analysis illustrate that different processes are involved in controlling the chemical composition of groundwater in the mine area the factor 1 loadings showed that ph ec tds na mg chloride and sulfate which have high loading in this factor are expected to come from carbonate dissolution to oxidation conditions one way anova describes the significance of dependent variables with respect to independent variables anova gives us the idea that ec k fetotal so 4 2 as and pb are the most important factors in controlling spatial differences in water quality in this tunnel but different results have been encountered for different independent variables which might be due to dissimilar sources of water from the qualitative analysis it is clear that water quality is not very favorable for aquatic creatures as well as for drinking purposes the water can be used for irrigation purposes without any doubt as sar and rsc analysis provides good results moreover the results of this research confirmed that the application of multivariate statistical analysis methods is apposite to inferring complex water quality data sets with its possible pollution sources at the end this research recommends 1 as water becomes more and more important water treatment plants should be built before the water being used 2 a detailed water step utilization plan should be set beforehand to guarantee tunnel water being used effectively and 3 after the water being used for agriculture elements in crops should be monitored continuously to ensure that ions and compounds that come from the tunnel water are lower than guideline values for human beings health

compensation of the ontong java plateau by surface and subsurface loading gravity data over ontong java plateau reveal deep crustal structure supporting the plateau s topography at long wavelengths 500 km new shipboard gravity and bathymetry profiles indicate local isostatic compensation at intermediate wavelengths 250 500 km however bouguer anomalies have large amplitudes too high to be explained by models of airy isostasy or volcanic loading on the surface of an elastic lithospheric plate this finding is also evident in admittance functions generated from maps of bathymetry and satellite derived bouguer anomalies which show high values at intermediate wavelengths in addition coherence between two dimensional bouguer gravity and bathymetry spectrums decreases to zero beginning at intermediate wavelengths two possible models can explain the high admittance and low coherence at intermediate wavelengths the first model explains the high admittance by large scale lithospheric folding and explains the low coherence by sedimentation and erosion that is uncorrelated with the igneous crustal structure lithospheric folding might result from tectonic compression imposed on ontong java by the solomon arc and trench system the second model involves a multiple stage accretion history with surface magmatism on a thin elastic plate and magmatic underplating beneath a thick plate the thick plate during underplating is required to explain the high admittance values at intermediate wavelengths while decorrelation between underplating and the surface loaded magmas can explain the low coherence the thick plate also suggests that the lithosphere cooled appreciably since the first magmatic stage and therefore magmatic underplating occurred at a significantly later time than the initial eruption calculations predict that the underplated material could comprise as much as 50 of the total crustal volume suggesting that the later eruptive stage s may have been as or more voluminous than the first

impact origin for the greater ontong java plateau abstract the 120 ma ontong java plateau and neighboring contemporaneous nauru east mariana and probably pigafetta basin flood basalts in the western equatorial pacific ocean comprise the earth s largest flood basalt province geophysical geochemical and geodynamic evidence from the province are difficult to reconcile with mantle plume models absence of an obvious hotspot source or track minor crustal uplift associated with emplacement minor total subsidence compared with normal oceanic crust or other oceanic plateaus and submarine ridges high degrees of melting at shallow upper mantle depths low water contents of basalts enrichment of platinum group elements in basalts and a 300 km deep seismically slow mantle root are more consistent with the consequences of an impacting bolide an object 20 km in diameter impacting relatively young 20 myr pacific lithosphere and penetrating into the uppermost asthenosphere would have initiated massive decompression melting in the upper mantle and may have resulted in emplacement of the greater ontong java plateau

crustal structure and isostatic compensation near the kane fracture zone from topography and gravity measurements i spectral analysis approach summary six gravity and bathymetry profiles perpendicular to the kane fracture zone each more than 300 km long were gathered to study the variation in crustal structure in the vicinity of a major fracture zone and the gravitational edge effect at the contact between lithosphere of two different ages a spectral analysis of the gravity and bathymetric series as a function of wavelength shows that the gravitational edge effect is only significant at the longest wavelengths for remaining wavelengths the admittance the ratio of the amplitude of the gravity anomaly to the amplitude of the bathymetry is best explained by a model of isostasy in which topographic loads are partially supported by the flexural rigidity of an elastic plate about 6 km in thickness after subtracting the gravitational attraction of the bathymetry and its compensation substantial isostatic anomalies remain we interpret these anomalies as being caused by variations in crustal thickness which have little correlation with surface topography except at very long wavelengths the apparent crustal thickness varies by as much as a factor of 2 but there is no evidence indicating systematic thinning of the crust beneath the fracture zone our data do suggest that such density variations within the plate are also compensated by the isostatic response of an elastic plate but with very different effect from those at the surface this indicates that there are two different modes of crustal formation with different gravity and topographic signatures effusive volcanism which loads the surface of the elastic plate producing both topographic relief and coherent gravity anomalies and intrusive volcanism or underplating producing gravity anomalies but little topographic relief

evidence from gravity and topography data for folding of tibet bouguer gravity and topography data from tibet suggest that the surface of the plateau and the subsurface density interfaces are warped into two series of ridges and troughs trending parallel to the collision zone with wavelengths of 150 and 500 km these folds are superimposed on an overall state of isostatic compensation owing to crustal thickening such folding is predicted from models of compressional shortening of a rheologically layered plate the results thus suggest the presence of a weak decoupling zone between the tibetan crust and upper mantle

evidence for diffuse extension of the pacific plate from pukapuka ridges and cross grain gravity lineations satellite altimeter measurements of marine gravity reveal 100 to 200 km wavelength lineations over a wide area of the pacific plate oriented roughly in the direction of absolute plate motion at least three mechanisms have been proposed for their origin small scale convective rolls aligned in the direction of absolute plate motion by shear in the asthenosphere diffuse n s extension of the lithosphere resulting in lineated zones of extension boudins and minihotspots that move slowly with respect to major hotspots and produce intermittent volcanism recently several chains of linear volcanic ridges have been found to be associated with the gravity lineations following ridgelike gravity signatures apparent in high resolution geosat gravity measurements we surveyed a series of volcanic ridges that extend northwest from the east pacific rise flank for 2600 km onto 40 ma seafloor our survey data as well as radiometric dates on samples we collected from the ridges provide tight constraints on their origin 1 individual ridge segments and sets of ridges are highly elongate in the direction of present absolute plate motion 2 the ridges formed along a band 50 to 70 km wide in the trough of one of the more prominent gravity lineations 3 radiometric dates of the largest ridges show no hotspot age progression moreover the directions predicted for minihotspot traces older than 24 ma do not match observed directions of either the gravity lineations or the ridges based on this last observation we reject the minihotspot model the occurrence of the ridges in the trough of the gravity lineation is incompatible with the small scale convection model which would predict increased volcanism above the convective upwelling we favor the diffuse extension model because it is consistent with the occurrence of ridges in the trough above the more highly extended lithosphere however the multibeam data show no evidence for widespread normal faulting of the crust as predicted by the model perhaps the fault scarps are buried under more than 30 m of sediments and or covered by the elongated ridges finally we note that if ridge push force is much smaller than trench pull force then near the ridge axis the direction of maximum tensile stress must be perpendicular to the direction of absolute plate motion

subsidence and growth of pacific cretaceous plateaus abstract the ontong java manihiki and shatsky oceanic plateaus are among the earth s largest igneous provinces and are commonly believed to have erupted rapidly during the surfacing of giant heads of initiating mantle plumes we investigate this hypothesis by using sediment descriptions of deep sea drilling project dsdp and ocean drilling program odp drill cores to constrain plateau subsidence histories which reflect mantle thermal and crustal accretionary processes we find that total plateau subsidence is comparable to that expected of normal seafloor but less than predictions of thermal models of hotspot affected lithosphere if crustal emplacement was rapid then uncertainties in paleo water depths allow for the anomalous subsidence predicted for plumes with only moderate temperature anomalies and volumes comparable to the sources of modern day hotspots such as hawaii and iceland rapid emplacement over a plume head of high temperature and volume however is difficult to reconcile with the subsidence reconstructions an alternative possibility that reconciles low subsidence over a high temperature high volume plume source is a scenario in which plateau subsidence is the superposition of 1 subsidence due to the cooling of the plume source and 2 uplift due to prolonged crustal growth in the form of magmatic underplating this prolonged crustal growth and uplift scenario may explain the low and thus submarine relief during plume initiation the late stage eruptions found on ontong java 90 ma and manihiki 70 ma a large portion of the high seismic velocity lower crust and the widespread normal faults observed throughout and along the margins of the three plateaus such late stage underplating may have occurred continuously or in discrete stages over 30 m y and implies lower magmatic fluxes than previously estimated

lateritic weathering of pyroxenites at niquelandia goias brazil the supergene behavior of nickel two typical lateritic weathering profiles jacuba ahd angiquinho from the niquelandia ni deposits brazil were studied in order to establish the petrological relationship between the supergene ni products and the parental pyroxenes frbm the base to the top of the profiles pyroxenes are replaced by goethite and kaolinite through a series of transitional ni bearing phyllosilicates the mineralogy and the chemical composition especially the ni content of these clay minerals depends on the degree of fracturing and serpentinization of the pyroxenite and the location of the pyroxenite with respect to neighboring dunite within the jacuba profile smectite and pimelite pseudomorphs after pyroxene are especially ni rich and in fact are the most ni enriched clay minerals now known in lateritic weathering profiles

convection beneath young oceanic lithosphere implications for thermal structure and gravity small scale convection under the oceanic lithosphere which begins in the first 5 m y of cooling can produce a gravity signal with the amplitude and wavelength observed for large areas of the central pacific and southern indian oceans using seasat altimeter data the trend of the observed anomalies is parallel to the direction of plate motion as might be expected if they were produced by small scale convection models predict that the wavelengths of gravity anomalies increase more rapidly with age than is observed the persistence of short relatively uniform wavelength anomalies 200 km to crustal ages of 50 ma may indicate that they were produced when the lithosphere was very young and thin and were frozen in as cooling thickened the elastic lithosphere small scale convection which begins under very young lithosphere does not violate other geophysical data such as the rate of seafloor subsidence and variations of geoid height with age after convection has begun the subsidence due to thermal contraction within the lithosphere varies linearly with age in the absence of mantle heat sources although the rate of change of these quantities is affected by convection much of the variation of the geoid height across fracture zones can be fit by a model which includes small scale convection

isotopic evidence for the origin of the manihiki and ontong java oceanic plateaus abstract pb nd and sr isotopic results for lavas of the cretaceous ontong java and manihiki oceanic plateaus fall well within the modern day oceanic island or hotspot field the data provide no evidence of old continental basements but indicate a major involvement of kerguelen type or em i like mantle in the sources of both plateaus which appear to have probably been formed at least in part by hotspots however the presently active hotspots that pacific plate reconstructions suggest might have been possible plateau sources lack kerguelen type isotopic compositions either these hotspots did not participate in the formation of the two plateaus or if they did kerguelen type material must have been volumetrically much more important early in their existence two hypotheses for the origins of these plateaus which involve hotspot sources are consistent with the sparse available geochemical geochronological and geophysical data the first holds that the plateaus formed cataclysmically in association with surfacing plume heads the second posits a relatively steady but robust hotspot at or near a ridge crest and requires a much longer period of formation a near ridge origin appears to be indicated by evidence that most of the pacific plateaus were built largely on relatively young ocean crust however we suggest that a near ridge origin is also compatible with the plume head concept in that plume heads appear very likely to become associated with spreading axes through their influence on rift propagation which should be substantially greater than for ordinary hotspots in either case the lack of hotspot tracks seamount chains attached to the two plateaus would be a consequence of ridge migration or rift propagation in a near ridge setting

evidence for small scale mantle convection from seasat altimeter data evidence for the early development of convective instability in the thermal boundary layer associated with cooling plates has been found from gravity anomalies and residual sea surface heights derived from seasat altimeter data subtle lineated patterns trending in the direction of plate motion in the hot spot reference frame are observed over the younger portions of the fast moving pacific and indo australian plates in particular for the east central pacific ocean the seasat derived data sets reveal lineations with 1 wavelengths in the range 150 500 km perhaps increasing with plate age and 2 peak to trough amplitudes of 5 20 mgal for gravity anomalies the lineated pattern over the pacific plate which first becomes discernable over seafloor 5 to 10 m y old west of the east pacific rise is clearly oblique to the trends of the prominent pacific farallon fracture zones onset of convective instability at such early ages can be understood if young oceanic lithosphere is underlain by a layer having a viscosity of about 1018 pa s 1019 p which is about 3 orders of magnitude less than mantle viscosity inferred from postglacial rebound studies recent numerical studies of convection in fluids with a temperature and pressuredependent viscosity support an early onset time for convective instability and low viscosity zones in the upper mantle beneath young lithosphere such low viscosity zones may correspond to similarly located regions of low shear wave velocities resolved through studies of surface waves

flexural isostasy and loading sequence of the dokdo seamounts on the ulleung basin in the east sea sea of japan abstract the isostatic compensation and loading sequence of the dokdo seamounts on the ulleung basin in the east sea are studied by a flexure model using gravity and bathymetric data the dokdo seamounts comprise dokdo dok island lying as a cluster of emerged small islets surmounting a large submerged volcanic edifice and two voluminous tablemounts simheungtaek and isabu in spite of their similarity in topographic expression a large difference of about 50 mgal between the observed gravity anomaly peaks over dokdo and the isabu tablemount implies different amounts of compensation a comparison between the observed and calculated gravity anomalies of the seamounts shows that the flexural compensation investigated in this study predicts well the observed data the flexure model suggests that the dokdo seamounts might be composed of high density volcanic rocks modeling results show that the flexural rigidity or effective elastic thickness of the lithosphere under dokdo is stronger or thicker than that under the isabu tablemount it implies that the age of lithosphere at the time of loading for isabu was younger than that for dokdo the effective elastic thicknesses associated with the dokdo seamounts approximately follow 200 400 c isotherms in the cooling plate model the results of this study and the former age dating of dokdo suggest that the isabu tablemount was formed first followed by dokdo after the opening of the east sea ceased

geologic constraints on crustal plateau surface histories venus the lava pond and bolide impact hypotheses 1 venusian crustal plateau formation is hotly debated crustal plateaus are large 1500 2500 km quasi circular 0 5 to 4 km high plateaus that host distinctive tectonic fabrics called ribbon tessera debate centers on plateau support and fabric formation detailed geologic mapping of an 360 000 km2 region eastern ovda regio provides critical clues for plateau evolution ribbon tessera fabrics record broadly synchronous layer contraction extension and flooding as an initially strong thin layer 100 m developed across ovda as the layer underwent ductile shortening and brittle extension subsurface lava flooded structural lows with progressive deformation the layer thickened leading to formation of progressively longer wavelength structures early formed shorter wavelength structures and lava filled valleys were carried piggyback on longer wavelength folds this history indicates an extremely large strength contrast that is inconsistent with a conductive geotherm reflecting instead the presence of a near surface molten layer i propose the lava pond hypothesis ribbon tessera fabrics represent progressively solidified scum of a huge lava pond leading to crustal plateau formation i further propose that individual lava ponds formed as a result of large bolide 20 30 km diameter impact with ancient thin lithosphere causing massive partial melting in the upper mantle melt rose buoyantly to form huge 1500 2000 km diameter lava ponds completely resurfacing the local area in the upper mantle depleted residuum would be compositionally more buoyant and stronger than adjacent undepleted mantle isostatic adjustment resulted in pond uplift and plateau formation subsequent secular cooling could freeze a plateau in place or mantle convection could strip away the residuum root leading to plateau collapse

ni cycling in mangrove sediments from new caledonia abstract covering more than 70 of tropical and subtropical coastlines mangrove intertidal forests are well known to accumulate potentially toxic trace metals in their sediments and thus are generally considered to play a protective role in marine and lagoon ecosystems however the chemical forms of these trace metals in mangrove sediments are still not well known even though their molecular level speciation controls their long term behavior here we report the vertical and lateral changes in the chemical forms of nickel which accumulates massively in mangrove sediments downstream from lateritized ultramafic deposits from new caledonia where one of nature s largest accumulations of nickel occurs to accomplish this we used ni k edge extended x ray absorption fine structure exafs spectroscopy data in combination with microscale chemical analyses using scanning electron microscopy coupled with energy dispersive x ray spectroscopy sem edxs after principal component and target transform analyses pca tt the exafs data of the mangrove sediments were reliably least squares fitted by linear combination of 3 components chosen from a large model compound spectral database including synthetic and natural ni bearing sulfides clay minerals oxyhydroxides and organic complexes our results show that in the inland salt flat ni is hosted in minerals inherited from the eroded lateritic materials i e ni poor serpentine 44 58 ni rich talc 20 31 and ni goethite 18 24 in contrast in the hydromorphic sediments beneath the vegetated avicennia and rhizophora stands a large fraction of ni is partly redistributed into a neoformed smectite pool 20 69 of ni montmorillonite and ni speciation significantly changes with depth in the sediment indeed ni rich talc 25 56 and ni goethite 15 23 disappear below 15 cm depth in the sediment and are replaced by ni sorbed pyrite 23 52 in redox active intermediate depth layers and by pyrite 34 55 in the deepest sediment layers ni incorporation in pyrite is especially observed beneath an inland avicennia stand where anoxic conditions are dominant in contrast beneath a rhizophora stand closer to the ocean where the redox cycle is intensified due to the tide cycle partial re oxidation of ni bearing pyrites favors nickel mobility as confirmed by ni mass balance estimates and by higher ni concentration in the pore waters these findings have important environmental implications for better evaluating the protective role of mangroves against trace metal dispersion into marine ecosystems they may also help in predicting the response of mangrove ecosystems to increasing anthropogenic pressure on coastal areas

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

3d modeling of the laterites on top of the koniambo massif new caledonia refinement of the per descensum lateritic model for nickel mineralization resulting from the weathering of the peridotite nappe laterites are abundant in new caledonia and host one of the largest nickel deposits worldwide this work presents a 3d model of the koniambo nickel laterite ore deposit it shows that the laterites are located along the ridges of the massif and organized as hectometric sized patches obliquely cut by the topography and distributed at various elevations three kinds of geometry were observed i a thick laterite cover between 20 and 40 m overlying saprolite and mainly localized on topographic highs ii a thin laterite cover from a few meters to 20 m mainly localized on areas with gentle slopes and iii exposure of saprolite without laterite cover our data show that ni rich and ni poor areas are organized as hectometric sized patches which broadly correlate with the distribution of the laterite thickness the highest ni areas are localized on slopes where laterite cover is thin or absent the areas with lowest ni are located in topographic highs under the thickest laterite cover the vertical ni mass balance for each borehole shows that in areas with thick laterite cover ni is sub equilibrated to slightly depleted whereas in areas with thin laterite cover ni is enriched this suggests the existence of lateral infiltration of water rich in dissolved ni from areas such as topographic highs to downstream slope areas in a process leading to enrichment of saprolite in ni in slope areas mechanical transport and leaching of laterite material on slopes including ni bearing material could also contribute to local enrichment of ni in the saprolite

heat transfer and intraplate deformation in the central indian ocean nineteen new heat flow measurements made across deformed oceanic lithosphere in the central indian ocean and previously published data show that heat flow is significantly higher than predicted by models for cooling oceanic lithosphere over much of the region many of the temperature depth profiles are nonlinear upward convection of water is the most likely explanation for the curvature of the temperature profiles since other possible causes including variations in bottom water temperatures conductivity changes with depth in the sediments and experimental error can be eliminated this interpretation requires water velocities of the order of 7 x 10 sup 8 m s which is unusual because the lithosphere is relatively old 72 82 m y and a thick sedimentary cover 1 2 5 km is present these observations suggest that the processes causing deformation of the plate have increased the heat flux through the sediment water interface we infer that extra heat is being generated at shallow depths perhaps less than 35 km in the plate although the specific mechanism by which deformational energy is converted into heat is difficult to determine

rigidity of the atlantic oceanic lithosphere beneath new england seamounts abstract investigation of the flexural response of the oceanic plate subject to loading of new england seamounts provides an insight into the rigidity of the lithosphere fourier domain analysis of the bathymetry and gravity anomalies over new england seamounts suggests that internal density perturbations exist in the crust and or uppermost mantle the loads due to the topography of the seamounts and density perturbations must have been supported by the lithosphere we group the seamounts into three representative ages and adopt a 3 d thin elastic plate model over an invicid mantle to assess the rigidity of the lithosphere under these loads the rigidity values are about 3 7 10 23 n m for lithospheric ages ranging from 30 to 60 my the base of the elastic part of the lithosphere follows an isotherm in the range of 750 850 c suggesting a strong lithosphere that makes the north atlantic ocean difficult to initiate subduction however the thermal blanketing by the thick sediments at scotian basin reduces the rigidity by one to two orders of magnitude and may facilitate initiation of subduction of the north atlantic oceanic lithosphere at scotian margin

vertical changes of the co and mn speciation along a lateritic regolith developed on peridotites new caledonia because they can host significant amounts of co the mn oxides are commonly considered as the major co bearing mineral species in lateritic environments however little is known about the process leading to the formation and or the weathering of these co rich mn oxides this lack of knowledge is mainly due to the fact that co concentrations are too low in primary silicates for classical speciation analysis in this study we investigated both co and mn speciation in a 64 m thick lateritic regolith developed upon peridotites in new caledonia by combining high energy resolution fluorescence detection x ray absorption near edge structure herfd xanes spectroscopy at the co k edge with classical xanes spectroscopy at the mn k edge bulk chemistry icp and mineralogy xrd the results obtained provide new insights into the evolution of co and mn speciation as a function of the weathering stages co and mn primarily occur as co ii and mn ii iii in olivine and serpentine in the bedrock during the first weathering stage these forms of co and mn are progressively oxidized toward co iii and mn iii iv which occur mainly as co iii bearing mn iii iv oxides in the transition between the saprolite and the laterite in the uppermost lateritic horizons long time weathering resulted in a strong leaching of co and mn and the remaining of these elements occurs as co ii and mn iii substituting for fe iii in goethite this latter scavenging process emphasizes the importance of fe oxides for the long term stabilization of co and mn in such deeply weathered laterites c 2017 elsevier ltd all rights reserved

formation and transformation processes of iron duricrust systems in tropical humid environment abstract formation and transformation processes of iron duricrust developed under tropical humid conditions in the southeastern part of the central african republic have been investigated in terms of geomorphological petrological and geochemical pathways the study of five typical weathering profiles of the most extensive iron duricrust system now known in the world indicates that saprolitization and ferruginization are sequentially involved in such processes as reflected by kaolinite gibbsite and hematite goethite replacements alkali earths rare earths metals and elements belonging to chemically inert minerals segregate during saprolite and iron duricrust formation and degradation mass balance calculations performed on a typical weathering system enable us to quantify net mass element transfers deriving from lateritic weathering processes volumetric change collapse or dilation as well as al and ti clearly discriminate between the saprolitization and ferruginization processes saprolite development preserves the geochemical inheritance of parent rocks whereas ferruginization depletes it and mostly reflects through mineralogical pathways pedoclimatic conditions and global climatic changes the global iron duricrust system of the southern part of central africa derived from previous hematite rich crust and not from ancient bauxites as it is generally believed for iron crusts formed on west african shields

isostatic response of the lithosphere with in plane stress application to central australia the relation between gravity and topography in central australia cannot be described by a conventional isostatic response function whether it assumes local or regional compensation or whether the crust behaves as an elastic or viscoelastic medium in particular the response function exhibits considerable anisotropy hence a theory for isostatic response has been developed for a crust in mechanical equilibrium of surface loads buoyancy and in plane forces and subject to erosion sedimentation and stress relaxation the observed north south response function exhibits extreme isostatic overcompensation at some wavelengths and this can be fully explained by the viscoelastic plate model with in plane compression the observed east west response function is consistent with models of regional or local isostatic compensation the response function implies an effective flexural rigidity of 5 10 1022 n m an effective maxwell relaxation time of 25 50 m y an in plane compression of 125 150 mpa and an erosion time constant of about 200 m y these parameters assume that the model evolved over a period of about 700 m y and are wholly consistent with the evolutionary model developed from geological observations

nickel isotope fractionation during laterite ni ore smelting and refining implications for tracing the sources of ni in smelter affected soils abstract nickel isotope ratios were measured in ores fly ash slags and feni samples from two metallurgical plants located in the goias state brazil barro alto niquel ndia this allowed investigating the mass dependent fractionation of ni isotopes during the ni laterite ore smelting and refining feeding material exhibits a large range of 60 ni values from 0 02 0 10 to 0 20 0 05 n 7 explained by the diversity of ni bearing phases and the average of 60 ni feeding materials was found equal to 0 08 0 08 2sd n 7 both 60 ni values of fly ash 60 ni 0 07 0 07 n 10 and final feni produced 0 05 0 02 n 2 were not significantly different from the feeding materials ones these values are consistent with the very high production yield of the factories however smelting slags present the heaviest 60 ni values of all the smelter samples with 60 ni ranging from 0 11 0 05 to 0 27 0 05 n 8 soils were also collected near and far from the niquel ndia metallurgical plant to evaluate the potential of ni isotopes for tracing the natural vs anthropogenic ni in soils the ni isotopic composition of the non impacted topsoils developed on ultramafic rocks ranges from 0 26 0 09 to 0 04 0 05 n 20 on the contrary the ni isotopic composition of the non ultramafic topsoils collected close to the plant exhibit a large variation of 60 ni ranging from 0 19 0 13 up to 0 10 0 05 n 4 this slight but significant enrichment in heavy isotopes highlights the potential impact of smelting activity in the surrounding area as well as the potential of ni isotopes for discerning anthropogenic samples heavier 60 ni values from natural ones lighter 60 ni values however given the global range of published 60 ni values from 1 03 to 2 5 and more particularly those associated to natural weathering of ultramafic rocks from 0 61 to 0 32 the use of ni isotopes for tracing environmental contamination from smelters will remain challenging

petrological and geochemical differentiation of lateritic iron crust profiles abstract lateritic iron crust profiles developed from metabasic rocks in west africa burkina faso were studied from a petrographical and geochemical point of view at the base of profiles a thick gray purple kaolinitic horizon occurs with frequent macroscopic preservation of original pre existing structures in such an horizon chemical balances clearly show that part of kaolinite crystals could be explained by an absolute accumulation from circulating solutions higher up in the profiles fe accumulation leads to two main facies purplered hematitic spots and nodules and yellow kaolinitic and goethitic spots mottled clay horizon hematite and goethite distribution in that horizon is regulated by water activity in microenvironments hematitic nodules form as kaolinite crystals are completely dissolved in goethitic spots fe accumulation is much less abundant and the first generation of well crystallized kaolinite is replaced by a poorly crystallized and smaller kaolinite crystals showing a greater substitution of al 3 for fe 3 in the upper part of profiles all the kaolinite is gradually dissolved and the maximum of ferruginous concretion formation leads to a hard and nodular iron crust

pin pricking the elephant evidence on the origin of the ontong java plateau from pb sr hf nd isotopic characteristics of odp leg 192 basalts age corrected pb sr and nd isotope ratios early aptian basalt from four widely separated sites on the ontong java plateau that were sampled during ocean drilling program leg 192 cluster within the small range reported for three earlier drill sites for outcrops in the solomon islands and for the nauru and east mariana basins hf isotope ratios also display only a small spread of values a vitric tuff with end t 4 5 that lies immediately above basement at site 1183 represents the only probable example from leg 192 of the singgalo magma type flows of which comprise the upper 46 750 m of sections in the solomon islands and at leg 130 site 807 on the northern flank of the plateau all of the leg 192 lavas including the high mgo 8 10 wt kroenke type basalts found at sites 1185 and 1187 have end t between 5 8 and 6 5 they are isotopically indistinguishable from the abundant kwaimbaita basalt type in the solomon islands and at previous plateau nauru basin and east mariana basin drill sites the little fractionated kroenke type flows thus indicate that the uniform isotopic signature of the more evolved kwaimbaita type basalt with 5 8 wt mgo is not simply a result of homogenization of isotopically variable magmas in extensive magma chambers but instead must reflect the signature of an inherently rather homogeneous relative to the scale of melting mantle source in the context of a plume head model the kwaimbaita type magmas previously have been inferred to represent mantle derived largely from the plume source region our isotopic modelling suggests that such mantle could correspond to originally primitive mantle that experienced a rather minor fractionation event e g a small amount of partial melting approximately 3 ga or earlier and subsequently evolved in nearly closed system fashion until being tapped by plateau magmatism in the early aptian these results are consistent with current models of a compositionally distinct lower mantle and a plume head origin for the plateau however several other key aspects of the plateau are not easily explained by the plume head model the plateau also poses significant challenges for asteroid impact icelandic type and plate separation perisphere models at present no simple model appears to account satisfactorily for all of the observed first order features of the ontong java plateau the geological society of london 2004

discrete alternating hotspot islands formed by interaction of magma transport and lithospheric flexure the large scale geometry and age progression of many hotspot island chains such as the hawaiian emperor chain are well explained by the steady movement of tectonic plates over stationary hotspots but on a smaller scale hotspot tracks are composed of discrete volcanic islands whose spacing correlates with lithospheric thickness1 moreover the volcanic shields themselves are often not positioned along single lines but in more complicated patterns such as the dual line known as the kea and loa trends of the hawaiian islands2 3 here we make use of the hypothesis that island spacing is controlled by lithospheric flexure1 to develop a simple nonlinear model coupling magma flow which feeds volcanic growth to the flexure caused by volcanic loads on the underlying plate for a steady source of melt underneath a moving lithospheric plate magma is found to reach the surface and build a chain of separate volcanic edifices with realistic spacing if a volcano is introduced away from the axis of the chain as might occur following a change in the direction of plate motion the model perpetuates the asymmetry for long distances and times thereby producing an alternating series of edifices similar to that observed in the kea and loa trends of the hawaiian island chain

lithospheric flexure and thermal anomalies plots of effective elastic thickness te of the oceanic lithosphere as a function of age when elastically deformed show a general increase in te with the square root of age although there is much scatter some of the scatter can be eliminated by correcting for the effect of finite yield strength in rocks which makes te for more sharply bent plates underestimate the true depth tm to the rheological boundary at the base of the high strength mechanical lithosphere after converting effective values te to true thicknesses tm it appears that the mechanical lithosphere is always thinner beneath islands and seamounts compared to lithosphere of similar age flexed at subduction zones from several other lines of evidence such as depth anomalies seamount subsidence and heat flow data it has been suggested that the thermal structure in plates subjected to hot spot type volcanism is reset to values appropriate for much younger lithosphere the reduction in mechanical plate thickness beneath hot spot volcanoes is also consistent with this concept of thermal rejuvenation since the strength of rocks decreases exponentially with rising temperature this dependence implies that variations in mechanical plate thickness can be used to map temperature anomalies in the lithosphere since the mechanical plate thickness depends principally upon the temperature at one depth specifically the depth at which the temperature reaches 550 600 c depending on strain rate flexural data are particularly sensitive indicators of the vertical structure of lithospheric reheating compared to quantities dependent on depth integrals of temperature such as swell height and subsidence the thermal rejuvenation hypothesis predicts that the flexural profile should mimic viscoelastic relaxation in the first 10 ma after loading if initially reheating is confined to depths close to and below the 550 c isotherm the flexural data combined with depth anomaly information for hawaii point to extremely rapid reheating localized in the lower lithosphere rejuvenation in the society islands on the other hand is compatible with slower methods of heat injection involving the entire lithospheric column

periodic instabilities during compression or extension of the lithosphere 1 deformation modes from an analytical perturbation method we argue that the plastic rheology of the lithosphere rather than its recoverable elastic properties is responsible for the systematic development of periodic instabilities during compression or extension we use a linear perturbation model with analytical solutions to calculate the instability modes for various rheologies the growth of such periodic instabilities is enhanced by the highly nonlinear stress strain rheologies encountered in the brittle layers of the lithosphere on the contrary ductile layers deforming according to high temperature creep flow laws tend to inhibit these instabilities for oceanic domains we assume that the only brittle layer is the upper part of the lithosphere in compression the only valid instability is a buckling whose wavelength is around 4 times the thickness of the brittle layer calculated wavelengths and growth rates are consistent with observations available for the indian ocean for continental domains a reasonable assumption is the existence of two plastic layers one in the upper crust the other in the upper mantle for moho temperatures between 450 c and 600 c in compression and extension two instabilities develop a long wavelength instability involving the whole lithosphere coupling mode and a short wavelength instability involving the crust and controlled by the upper brittle layer intrinsic crustal mode in compression the coupling mode is a whole lithosphere buckling with a wavelength about 4 times the thickness of the active lithosphere the two plastic layers plus the intermediate ductile layer in extension the coupling mode is a boudinage of opposite phase in the two plastic layers and a folding of the intermediate ductile layer the intrinsic crustal mode is a crustal buckling in compression crustal boudinage in extension neither deflects the moho the intrinsic crustal mode is favored by an increase in thermal gradient and by a decrease in strength of the ductile lower crust

age dependent seismic thickness and mechanical strength of the australian lithosphere 1 we present constraints on the regional variations of the seismic and mechanical thickness of the australian lithosphere we infer the seismic thickness from a waveform tomographic model of s wave speed and as a proxy for the elastic thickness we use the wavelength at which the coherence of surface topography and bouguer gravity drops below half of its long wavelength maximum our results show that on scales 1000 km the relationship between the age of the crust and the thickness of the lithosphere is more complicated than longer wavelength or global averages suggest recent geochemical and geodynamical evidence for small scale secular variations of the composition and stability of continental cratons further illustrates the complexity of the age dependence of seismo mechanical lithospheric properties on regional scales

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

a seismic reflection profile study of lithospheric flexure in the vicinity of the cape verde islands 1 seismic reflection profile data are used to determine the stratigraphic architecture of the flexural moat that flanks the cape verde islands the moat region is characterized by upward of 1 2 km of poorly to well stratified material the two lowermost units thicken from west to east and are attributed to sediment loading and flexure at the nearby west africa continental margin during early cretaceous to early miocene the two uppermost units in contrast thicken concentrically around the islands and are attributed to the infilling of a flexural moat that formed by volcanic loading since the early miocene flexure modeling shows that the thickness of the moat infill cannot be explained only by surface loading and requires that the downward flexure due to surface loads is opposed by an upward acting subsurface load the best fit combined surface and buried loading model is for an elastic thickness te of 29 km a load and infill density of 2700 kg m 3 and a ratio of surface to subsurface loads f of 0 2 these results are in accord with spectral studies of free air gravity anomaly and topography data based on the admittance technique the subsurface loads are spatially limited to the islands and their submarine flanks nevertheless they are associated with a broad regional uplift of up to 400 m the uplift is large enough to explain why the moat infill is generally tilted away from rather than toward the islands the uplift is too small however to account for the height of the swell upon which the cape verde islands are superimposed the origin of the cape verde swell is not known however a normal te and a modest heat flow anomaly suggest that the swell cannot be fully explained by uplift due to thermal reheating of the lithosphere by an underlying hot spot and that other deep seated mantle processes must be involved

intrabasement reflections of the ontong java plateau implications for plateau construction 1 the early cretaceous ontong java plateau ojp in the western equatorial pacific earth s most voluminous large igneous province lip is characterized by intrabasement seismic reflections to investigate the nature of such reflections we have analyzed new and all older multichannel seismic mcs reflection data from the ojp using an instantaneous phase velocity analysis technique and synthetic seismograms intrabasement reflections are most prevalent on the main ojp especially on its crest on mcs data the reflections 1 are semicontinuous and subparallel to the top of igneous basement 2 in places have the opposite phase of seafloor reflections and 3 have an average frequency of 20 hz we calculate synthetic seismograms using impedance contrasts between massive lava and pillow lava flows obtained from downhole logs at ojp scientific drill sites and show that these lithologies can produce intrabasement reflections similar to those observed in the mcs data alternatively to evaluate the possibility of sediment sedimentary rock interbeds causing the intrabasement reflections we use published early cretaceous sedimentation rates determined from ojp drill sites and published estimates for the duration of massive ojp volcanism to calculate a range of possible sedimentary interbed thicknesses the range proves to be below the detection limit of the mcs data therefore we conclude that the intrabasement reflections arise from alternating relatively thin lava flows produced at low effusion rates and relatively thick massive flows generated at high effusion rates both originating from vents and fissures on the ojp probably on its crest

mechanical and thermal isostatic response of the del cano rise and crozet bank southern indian ocean from altimetry data an analysis of the relationship between the bathymetry and the gravity field has been carried out both in the frequency domain admittance technique and in the space domain over the del cano rise and the crozet bank southern indian ocean a bathymetric map contoured from original shipboard data and a geoid anomaly map computed from a merged set of seasat and geos3 data were used the inversion of admittances for water depth crustal thickness crustal density and elastic plate thickness shows that the isostatic response of the lithosphere supporting the del cano rise differs very much from that of the one situated beneath the crozet bank the del cano rise appears to have been formed near the active southwest indian ridge before early eocene and is locally supported by a thickened crust shallow thermal processes contribute to the present topography of the crozet bank emplaced further away from the southeast indian ridge on older crust