a submarine hydrothermal manganese deposit from the south west pacific island arc hydrothermal deposits of a wide variety of types are being found with increasing frequency on or near actively spreading mid ocean ridges1 4 however they also have a potential to occur in other submarine volcanic settings including island arcs5 to follow up indications of mineralization associated with submarine hydrothermal activity in the south west pacific island arc6 a joint new zealand oceanographic institute imperial college research cruise was mounted in may 1981 aboard the rv tangaroa during this cruise over 130 sampling stations were occupied at one of which were dredged manganese deposits with strong hydrothermal affinities this is the first report of such deposits from an island arc setting

ferromanganese oxide deposits from the central pacific ocean i encrustations from the line islands archipelago abstract chemical and mineralogical analyses of a well controlled suite of ferromanganese encrustations from the line islands archipelago central pacific suggest that they represent purely hydrogenous deposits i e they have formed through the slow accumulation of trace metal enriched oxides directly from the water column mineralogically they consist predominantly of mno2 and amorphous feoohxh2o compositionally they are similar to mno2 nodules from adjoining basinal areas but are enriched in both mn mean 20 4 max 29 3 and co mean 0 55 max 1 57 mno2 is the most important trace metal bearing phase strong associations are noted between it and co mo ni zn and cd whilst only be is associated specifically with feooh v sr and pb are partitioned between the authigenic oxide phases whilst ti most probably occurs as tio2xh2o cu is contained in both aluminosilicate contaminant phases and fe oxide phases these relations are considered to reflect the differing scavenging behaviour of mn and fe oxides in the water column crusts from 1 2 km are enriched in mn and the mn related elements and exhibit higher mn fe ratios than deeper crusts which are compositionally constant the higher mn fe ratios may result from a supply of mn from continental borderland sediments at these depths which is transported horizontally by advective diffusive processes since manganophile elements are enriched relative to mn in the 1 2 km crusts it is considered that the supply of mn is scavenged by existing oxides is oxidised and effectively occludes them a higher proportion of oxide particles thus exhibit mn oxide scavenging properties in the 1 2 km depth zone the increased vertical flux of mn resulting from the supply at 1 2 km is not reflected by higher mn fe ratios in deeper crusts so that the vertical flux of oxides is not simply related to the standing crop the mn fe ratios of the crusts thus reflect the composition of suspended oxides at similar depths

release of ni from birnessite during transformation of birnessite to todorokite implications for ni cycling in marine sediments abstract the phyllomanganate birnessite is the main mn bearing phase in oxic marine sediments where it exerts a primary control on the concentration of micronutrient trace metals in seawater however during sediment diagenesis and under mild hydrothermal conditions birnessite transforms into the tectomanganate todorokite we have recently shown that the transformation of birnessite to todorokite proceeds via a four stage nucleation and growth mechanism beginning with todorokite nucleation then crystal growth from solution to form todorokite primary particles followed by their self assembly and oriented growth via oriented attachment to form crystalline todorokite laths culminating in traditional crystal ripening atkins et al 2014 here we determine the fate and mobility of ni sorbed by birnessite during this transformation process specifically in our recent work we predict that the presence of ni within the phyllomanganate matrix will disrupt the formation of todorokite primary particles as such contrary to current understanding we suggest that ni sorbed by birnessite will slow the transformation of birnessite to todorokite and or be released to marine porewaters during sediment diagenesis here we transform a synthetic poorly crystalline ni sorbed 1 wt ni hexagonal birnessite analogous to marine birnessite into todorokite under a mild reflux procedure developed to mimic marine diagenesis and mild hydrothermal conditions we characterise our birnessite and reflux products as a time series including x ray diffraction xrd high resolution transmission electron microscopy hr tem and extended x ray absorption fine structure exafs spectroscopy in addition we determine ni speciation and mineral phase associations in a suite of natural marine ferromanganese precipitates containing intermixed phyllomanganate and todorokite our work shows for the first time that ni significantly slows the transformation of birnessite to todorokite and reduces the crystallinity of the neo formed todorokite phase but does not alter the mechanism and pathway of todorokite formation compared to a ni free system furthermore in systems tending towards todorokite as the final diagenetic product we see that up to 50 of the ni originally sequestered by birnessite is released to solution during the transformation our work indicates that the transformation of birnessite to todorokite in oxic marine sediments likely provides a significant source of ni to marine sedimentary porewaters and potentially a hitherto unrecognized benthic flux of ni to seawater

three dimensional deformation and strain induced by municipal pumping part 1 analysis of field data a 62 day controlled aquifer test was performed at the site of a new municipal well that penetrates a thick sequence of compressible basin fill deposits in mesquite nevada observation data were acquired from a high precision global positioning system gps network to accompany the water level data from the pumped well and a nearby observation well the purpose of the investigation was to quantify and characterize three dimensional surface deformation and strain associated with cyclic pumping and to evaluate aquifer properties on the basis of these data results indicate that both horizontal 8 mm total displacement with 0 2 mm precision and vertical deformation 12 mm total displacement with 2 mm precision were measuredwithinthefirst22daysofpumpingwithaslowlymigratingoutwardwaveofcompressionalstraininspiteofthefactthat an 83 m brittle unsaturated zone resided over the dynamically active aquifer the hydraulic head and strain data indicate that steady state pumping conditions were likely reached after 35 40 days results also indicate that vertical mechanical rebound occurs after about 35 days even though the rate of pumping remains unchanged strain analyses indicate that this result is due to the changing shape in the pore structure of the pumped aquifer as an elongation occurs in the horizontal direction to more than accommodateasmallcompressionalstrainintheverticaldirection uniaxialspecificstoragewasestimatedfromtime subsidence

twelve years of vertical birefringence in nine component vsp data since 1986 when industry scientists first publicly showed data supporting the presence of azimuthal anisotropy in sedimentary rock we have studied vertical shear wave s wave birefringence in 23 different wells in western north america the data were from nine component vertical seismic profiles vsps supplemented in recent years with data from wireline crossed dipole logs this paper summarizes our results including birefringence results in tabular form for 54 depth intervals in 19 of those 23 wells in the appendix we present our conclusions about how to record vsp data optimally for study of vertical birefringence we arrived at four principal conclusions about vertical s wave birefringence first birefringence was common but not universal second birefringence ranged from 0 21 but values larger than 4 occurred only in shallow formations 1200 m within 40 km of california s san andreas fault third at large scales birefringence tended to be blocky that is both the birefringence magnitude

the distribution of rare earth and minor elements in manganese nodules and sediments from the equatorial and s w pacific abstract 62 manganese nodules and 17 associated sediments from the equatorial and s w pacific have been analyzed for a number of elements including the rare earth elements ree by instrumental neutron activation sc co as hf th and ree occur in higher concentrations in s w pacific than in equatorial pacific nodules reflecting the higher iron content of the s w pacific nodules these elements are probably incorporated nondiscriminantly into the iron oxyhydroxide structure by direct sorption from seawater because they are too large to be incorporated into the manganese oxide structure the highest ce la ratios are also found in the s w pacific nodules this may result from the fact that these nodules lie beneath the path of the fast flowing well oxygenated antarctic bottom water aabw which facilitates oxidation of ce to the tetravalent state if so this supports the idea that the ce la ratio of manganese nodules is an important redox indicator negative cerium anomalies were noted for nodules from areas f and g can be interpreted on the same model the ree contents in equatorial pacific siliceous oozes and s w pacific red clays are similar on a carbonate free basis the ce la ratio of the s w pacific red clays is however much higher than that of the equatorial pacific sediments possibly reflecting the preferential oxidation of ce to the tetravalent state beneath the aabw there appears to be no systematic relationship between the ree abundance in the nodules and their associated sediments although absolute ree abundances are higher in nodules than in their associated sediments nodules with the highest ce la ratios are however found on sediments with the highest ce la ratios the principal difference in the ree distribution pattern of the nodules and sediments lies in the well known cerium anomaly which is positive to slightly negative for nodules and always negative for sediments

phosphorites co rich mn nodules and fe mn crusts from galicia bank ne atlantic reflections of cenozoic tectonics and paleoceanography a wide variety of marine mineral deposits were recovered from 750 to 1400 m water depths on galicia bank iberian margin mineral deposits include 1 carbonate fluorapatite phosphorite slabs and nodules that replaced limestone and preserved original protolith fabric 2 ferromanganese vernadite crusts with high mn and fe mn fe 1 contents and thick stratabound layers consisting mainly of mn up to 27 mno and fe 15 fe2o3 which impregnated and replaced the phosphorite 3 co rich mn nodules are composed of romanechite and todorokite laminae mn rich layers up to 58 mno contain up to 1 8 co 4 goethite nodules with fe up to 67 fe2o3 have low mn and trace metals we interpret this mineralization paragenesis to be related to major changes in oceanographic and tectonic regimes three phosphatization generations formed hardgrounds dated by 87sr 86sr isotopes as late oligocene early miocene and latest early miocene during the latest early miocene the hardground was fractured and breached due to regional intraplate tectonism which was coeval with a widespread regional erosional unconformity the stratabound layers and co rich manganese nodules were derived from low temperature geothermally driven hydrothermal fluids with fluid conduits along reactivated faults during middle and late miocene the introduction of vigorous deep water flow from the arctic generated growth of hydrogenetic ferromanganese crusts finally growth of diagenetic fe rich nodules late pliocene was promoted by the introduction of hypersaline mediterranean outflow water into the atlantic ocean

critical metal enrichment mechanism of deep sea hydrogenetic nodules insights from mineralogy and element mobility abstract the micro nano textural features major and trace element compositions of ferromanganese nodule from the marcus wake seamount group of the western pacific ocean were documented in this study the ferromanganese nodules genetically comprise a core and three types of layers the core is made up of porous quartz and locally fe mn oxides layer close to the core layer i mantle ii and rim iii are featured by a massive dense layer with stromatolite like structure laminated and detrital and dendritic rim respectively these layers contain mainly birnessite goethite and quartz the mn fe ratios 1 0 4 1 mean 1 9 demonstrate a hydrogenetic genesis for these nodules the nodules have moderate enrichments 1000 10 000 ppm of na mg al p k ti co ni and cu with minor enrichments 100 1000 ppm of v zn as sr y zr nb mo ba and pb whereas other elements li sc cr ge se rb sn cs hf w bi th and u have concentrations of several tens of ppm based on the growth rate calculated by co concentration layer i has the lowest mean growth rate 1 8 mm myr followed by layer ii 2 3 mm myr and then layer iii 2 7 mm myr integrating the previous marine nodule studies in the south china sea we suggest that the massive dense layers were possibly resulted from a slow growth rate the conduits of various scales may have promoted the post depositional processes as they enlarged the surface area for fluid dissolution and reprecipitation nickel enrichment is associated with birnessite and promoted by the post depositional processes as evidenced by the higher ni content in the early formed layer i and its decreasing trend from core to rim cobalt may have associated with mn3 and has less effect by post depositional accumulation the fe content which may have related to goethite fe3 o oh shows good correlations with the rey ree y contents this correlation demonstrates the scavenging of reys by hydrothermal fe oxyhydr oxides reys are likely released during the post deposition as the rey contents are decreasing from the core to rim and negatively correlated with the accumulation time the similarity of rey distribution pattern between hydrothermal nodule and goethite bearing and mn oxides free banded iron formation bif may suggest hydrothermal fe may have linked to rey enrichments in deep sea sediments these micro nano sized conduits are well developed in either type i ii or iii layer which likely served as fluid circulating conduits and facilitate post depositional processes

fully coupled three dimensional nonlinear numerical simulation of pumping induced land movement excessive groundwater extraction can cause aquifer systems to move three dimensionally based on the equilibrium of soil skeleton and continuity of groundwater flow a fully coupled nonlinear three dimensional mathematical model has been constructed which incorporates the prevalent nonlinear mechanical and hydraulic properties of aquifer systems the horizontal and vertical displacements with regard to nonlinear mechanical properties are obviously less than those results with linear stress strain relationship and the discrepancy between them increases with the elapsed time compared with the results with regard to the constant hydraulic properties the horizontal and vertical displacement and the drawdown with nonlinear hydraulic conductivity increase the discrepancy between the results with and without nonlinear hydraulic properties also increases with the elapsed time for the ideal aquifer systems addressed in this study horizontal displacement is predominant when groundwater is pumped from aquifer units the horizontal strain is compressive within the zone contiguous to the pumping well and it is tensile beyond that however the horizontal strain especially the tensile strain is negligible such small tensile strain cannot result in tensile stress because there is original compressive stress in soils the nonlinear mechanical and hydraulic properties of aquifer systems have clear impacts on the numerical simulation of the displacement and the pore water pressure in hydrostratigraphic units and their impacts increase with pumping time they should be considered in land movement simulation due to long term groundwater withdrawal

nucleation and growth of todorokite from birnessite implications for trace metal cycling in marine sediments the phyllomanganate birnessite is the main mn bearing phase in oxic marine sediments and through coupled sorption and redox exerts a strong control on the oceanic concentration of micronutrient trace metals however under diagenesis and mild hydrothermal conditions birnessite undergoes transformation to the tectomanganate todorokite the mechanistic details of this transformation are important for the speciation and mobility of metals sequestered by birnessite and are necessary in order to quantify the role of marine sediments in global trace element cycles here we transform a synthetic poorly crystalline hexagonal birnessite analogous to marine birnessite into todorokite under a mild reflux procedure developed to mimic marine diagenesis and mild hydrothermal conditions we characterize our birnessite and reflux products as a time series employing x ray diffraction xrd fourier transform infrared spectroscopy ftir bet surface area analysis scanning electron microscopy sem high resolution transmission electron microscopy hr tem and extended x ray absorption fine structure spectroscopy exafs we provide new insight into the crystallization pathway and mechanism of todorokite formation from birnessite under conditions analogous to those found in marine diagenetic and hydrothermal settings specifically we propose a new four stage process for the transformation of birnessite to todorokite beginning with todorokite nucleation then crystal growth from solution to form todorokite primary particles followed by their self assembly and oriented growth via oriented attachment to form crystalline todorokite laths culminating in traditional crystal ripening we suggest that contrary to current understanding trace metals like ni might retard the transformation of birnessite to todorokite and be released to marine sedimentary pore waters during this diagenetic process thus potentially providing a benthic flux of these micronutrients to seawater

rare earth element geochemistry of ferromanganese crusts from the hawaiian archipelago central pacific abstract the rare earth element ree composition of ferromanganese deposits from the hawaiian archipelago was determined as part of a geochemical investigation into the origin and environment of deposition of crusts most samples exhibit shale normalized ree patterns which are typical of hydrogenous ferromanganese deposits patterns of two todorokite and manjiroite rich crusts are significantly different from those of the other samples the range of concentrations in typical hawaiian crusts sum of ree 0 15 0 25 wt is in the uppermost portion of that reported for deep sea fe mn nodules shallow water 2000 m as well as slightly greater ree fractionation large positive ce anomalies attributed to the oxidative scavenging at the mno 2 surface are observed on all samples except one the slight light ree lree depletion in shallow water crusts relative to deeper samples is discussed in terms of variations in the ree concentrations in the water column and the relative complexing behavior of the ree no significant trend in ce concentration with depth is observed partition coefficient calculations suggest that concentrations of trivalent ree in crusts are affected by their availability in seawater to a greater extent than by the composition of the scavenging ferromanganese oxide flocs

manganese microchimneys buried in the central pacific pelagic sediments evidence of intraplate water circulation abstract manganese oxide deposits of an irregular tube like shape with unique composition and structure were found within pliocene siliceous sediments from an abyssal hill in the central pacific manganese nodule province effective separation of mn from fe and probably a rapid rate of mn deposition are suggested from the chemical composition a very high mn fe ratio up to 400 and low concentrations of transition metals the ree pattern is similar to other marine low temperature hydrothermal and sub oxic diagenetic mn deposits low total ree abundance and strong negative ce anomaly the deposit consists of major todorokite with minor buserites showing a hydrothermal signature blade like crystals of the minerals typically grow within open tubes several mm thick and lack detrital minerals all data indicate a low temperature hydrothermal or cold seep origin or less likely a sub oxic diagenetic origin this unusual manganese deposit from a pelagic environment is thought to have formed on the sea floor from mn bearing waters that passed through sediments or basement rocks we speculate that intraplate water circulation took place during the late pliocene to pleistocene due to the uplift and or block faulting after the deposition of pelagic pliocene sediments

recent mn ag deposits in coastal hydrothermal springs in the baja california peninsula mexico hot springs with associated mn ag mineralization were identified in the intertidal zone of the bahia concepcion bay of the central eastern baja california peninsula hot spring activity is related to a system of nw se faults that are associated with the opening of the gulf of california the hot springs are hosted by miocene volcanic and volcaniclastic units of the comondu group the maximum discharge temperature recorded is 72 c with the ph ranging from 6 2 to 6 5 and salinity values reaching up to 27 g kg veins stockworks breccias crusts and organosedimentary stromatolites of silica carbonate and mn oxides are associated with the hot springs the mn oxide and silica deposits show an association with ag as ba ca cu mg pb sb sr tl v w and zn acanthite and native silver occur along with pyrite in a mineral assemblage rich in opal a todorokite romanechite aragonite high mg calcite and barite three distinct mineral associations characterized by sulfides sulfates and oxides are recognized the silver minerals formed late in the paragenesis textural evidence suggests a microbial mediation for the mn mineral deposition pourbaix diagrams for mn and ag species were constructed for the physicochemical conditions of the coastal hot springs these diagrams show that both mn and ag minerals are stable at low temperature 65 c and near neutral ph under slightly reducing or oxidizing conditions the characteristics of the subaerial to shallow submarine hot springs and the results of the geochemical modeling suggest that the hydrothermal system in the bahia conception bay is formed through convection of meteoric waters intermixed with some saline fluids or seawater

fossil manganese deposits buried within dsdp odp cores legs 1 126 abstract probable in situ manganese deposits larger than 1 cm in diameter buried in odp dsdp cores were selected for study after examining previous descriptions of the manganese deposits in site reports and the odp data base most of the selected samples from 11 cores occur at or just above sedimentary hiatuses or in slowly deposited sediments and are overlain by rapidly deposited sediments of biogenic terrigenous or volcanogenic origin the changes in sedimentation recorded in the lithostratigraphic sections around these deposits are closely related to changes in tectonic evolution deep water circulation or biological productivity at the sites the similarity in composition and structure of the buried deposits to those of the modern manganese nodules and crusts with no evidence of post depositional change suggest that buried manganese deposits may be used as indicators of past sedimentary conditions during which they formed their major components are hydrogenetic and early diagenetic manganese minerals as well as detrital minerals the characteristics of these manganese deposits suggests that similar processes of deposition have taken place since the paleogene or older

importance of poroelastic coupling in dynamically active aquifers of the po river basin italy uncoupling between the flow field and the stress field in pumped aquifers is the basis of the classical groundwater hydrology recently some authors have disputed the assumption of uncoupling with regard to both fluid dynamics and porous medium deformation the issue is very important as it could undermine the traditional approach to simulate subsurface flow analyze pumping tests and predict land subsidence caused by fluid withdrawal the present paper addresses the problem of coupling versus uncoupling in the po river plain a normally consolidated and normally pressurized basin which has experienced in the last 50 years a pronounced pore pressure drawdown because of water and gas removal and where a large hydromechanical database is available from the ground surface down to 4000 m depth a numerical study is performed which shows that the matrix which relates flow to stress is very similar to the capacity matrix of the uncoupled flow equation a comparison of results obtained with the finite element integration of the coupled and uncoupled models indicates that pore pressure is rather insensitive to coupling anywhere within the pumped formation while in the adjacent aquitard aquifer units coupling induces a slight overpressure which quickly dissipates in time with a small initial influence on medium deformation and specifically on land subsidence as a major consequence the uncoupled solutions to the fluid dynamic and the structural problems appear to be fully warranted on any timescale of practical interest in a typical normally consolidated and pressurized basin

land subsidence and earth fissures due to groundwater withdrawal in the southern yangtse delta china excessive extraction of groundwater has caused severe land subsidence and earth fissures in the southern yangtse delta china based on field data the temporal and spatial distribution of land subsidence is investigated and the causes for earth fissures are analyzed the areal distribution of the land subsidence is closely related to the cones of depression in the main exploited aquifers the compaction of a hydrostratigraphic unit depends on its mechanical behavior thickness compressibility and the piezometric level changing the primary subsidence layers in shanghai have been the first aquitard before 1990 and the third confined aquifer since then but the second aquitard unit was the primary subsidence layer in changzhou earth fissures trending in several directions occurred in the husu tectonic zone they were mainly caused by differential subsidence and horizontal displacement that resulted from tensile stress and shear stress in units the majority of fissures in the study area are tensile

distribution and mineral assemblages of bedded manganese deposits in shikoku southwest japan implications for accretion tectonics abstract numerous bedded manganese and manganese iron ore deposits occur in shikoku southwest japan the mineralogy wall rock characteristics and fossil age data of the deposits are synthesized in this paper their mineral assemblages correlate well with the progressive metamorphic grade of the accretionary complexes in shikoku based on the plate tectonic framework of subduction accretion process the deposits are considered to have formed by metamorphism of mn fe nodule bearing siliceous sediments on the ocean floor

crystal chemistry of ni in marine ferromanganese crusts and nodules marine ferromanganese crusts and nodules are highly enriched in transition metals such as ni and co yet the crystal chemistry and mode of incorporation of these metals is poorly known we characterized the crystal chemistry of ni in two hydrogenetic pacific ocean ferromanganese crust samples and a hydrogenetic nodule from the madeira abyssal plain energy dispersive spectrometry shows that ni is associated with the manganese oxide phases in agreement with previous work x ray diffraction patterns show that the dominant mn3 4 oxide is a phyllomanganate similar to hexagonal birnessite or mno2 extended x ray absorption fine structure spectroscopy shows that the coordination environment of ni results from structural incorporation into the phyllomanganate phase by replacement of mn3 4 in contrast ni initially sorbs to freshly prepared synthetic birnessite by surface complexation over vacancy sites in the mno2 layer we propose that the transformation of ni sorption from surface complexation to structural incorporation provides a potentially irreversible sink for ni in seawater

processes controlling the heavy metal distribution in pacific ferromanganese nodules and crusts the ferromanganese precipitates existing in deep sea waters of the pacific consist of two types of deposits 1 nodules mainly are distributed in pelagic basins beneath the ccd calcite compensation depth where the rate of sedimentation is low 2 polymetallic encrustations are formed on exposed seamount rocks where currents prevent normal sediment accumulation nodules being formed in areas bordering the equatorial zone of high biological productivity grow by two different processes a early diagenetic growth by supply of metals and metal compounds from pore water and b hydrogenetic growth by supply of colloidal particles from near bottom seawater these processes lead to different kinds of oxide and different metal contents

statistical and hydro mechanical coupling analyses on groundwater drawdown and soil deformation caused by dewatering in a multi aquifer aquitard system abstract groundwater withdrawn in a multi aquifer aquitard system maas may cause vertical cross flow supplement and result in groundwater drawdown and soil deformation in both aquifers and aquitards this study investigates the responses of groundwater and deep soils to dewatering in the maas through statistical and numerical analyses field data of ten pumping tests conducted in the maas in shanghai urban area are collected and a statistical analysis for groundwater drawdown and ground settlement is performed field measurements indicate that the drawdowns are distributed linearly along radial distance in logarithmic coordinates however the ground settlements are disproportional to the drawdowns and show a trilinear distribution along the radial direction to examine the inconsistent distributions of the groundwater drawdown and the ground settlement representative dewatering models are developed numerically and solved explicitly by the coupled biot s three dimensional consolidation theory numerical results of dewatering in maas are compared to those obtained by a non coupling formula moreover effect of a micro confined aquifer on drawdown and soil deformation is discussed it is found that soil compression in each stratum is closely related to the decline of the pore pressure whilst small expansions are observed in early dewatering stages due to the hydro mechanical coupling effect the ground surface settlement near the pumping well obtained by the coupled numerical method is significantly smaller than that by the non coupling formula owing to horizontal and vertical cross flow supplement an additional aquifer embedded in aquitard above the pumping aquifer can relief both the groundwater drawdown and ground surface settlement significantly

towards balancing the oceanic ni budget abstract nickel isotopes are a novel and promising tracer of the chemistry of past ocean environments but realisation of this tracer s potential requires a comprehensive understanding of the controls on ni burial in the marine sedimentary archive an outstanding puzzle in the marine budget of ni first recognised in the 1970s is a major imbalance in the known inputs and outputs to and from the ocean the sedimentary outputs of ni are much larger than the inputs rivers dust much more recently it has also been recognised that the outputs are also considerably isotopically heavier than the inputs in this study we find light ni isotope compositions 60 ninist srm986 0 2 to 0 8 for mn rich sediments from the eastern pacific compared to fe mn crusts at about 1 6 these data suggest that diagenetic remobilisation of isotopically heavy ni leads to a significant benthic ni flux estimated at 0 6 2 3 10 8 mol yr similar in magnitude to the riverine flux to the ocean diagenetic remobilisation of ni may occur either via cycles of mn oxide dissolution and precipitation with associated ni sorption and release or during mineralogical transformation of birnessite to todorokite a minor role for retention of isotopically light ni by fe oxides or fe rich authigenic clays is also proposed overall a benthic flux of isotopically heavy ni at about 3 can balance the marine ni budget pinpointing diagenesis as a key missing piece of the ni puzzle

mineralogical control on transition metal distributions in marine manganese nodules abstract electron microprobe and x ray diffraction data for north pacific manganese nodules reveal that the transition metal distributions are controlled by the mineralogy microlayers rich in 10a manganates generally have high mn fe ratios and positive correlations between ni cu and mn and between co and fe microlayers rich in vernadite on the other hand show low mn fe ratios and co ni and cu all show positive correlations with mn the 10a manganates form mainly in porewaters with high mn fe ratios the ni2 and cu2 ions are post depositionally incorporated into the interlayers of the manganates whereas co3 is substituted for fe3 in ferric oxyhydroxides in seawater with a low mn fe ratio on the other hand the adsorption of positively charged ferric oxyhydroxides on negatively charged mno6 octahedral layers suppresses the growth of 10a manganates enhancing the formation of vernadite positively charged hydroxides of co3 ni2 and cu2 are also adsorbed on the mno6 layers these mechanisms of mineral formation and metal uptake are corroborated by data for other oceanic non hydrothermal manganese nodules and crusts

the formation of todorokite and birnessite in sea water pumped from under ground abstract manganese oxides precipitated from aerated well sea water at the marine science museum tokai university have been analyzed chemically and mineralogically the o mn ratios are lower in todorokite than in birnessite but these minerals have similar contents of minor transition metals which can be taken up additionally from sea water after the precipitation of mn oxides on the basis of these results the genesis of mn minerals is discussed in relation to marine mn nodules

ree redistribution during hydrothermal alteration of ores of the kalahari manganese deposit abstract the kalahari manganese deposit kmd is the largest land based manganese deposit hosting approximately 80 of the world s known mineable manganese resources the deposit located near kuruman in the northern cape province of south africa is one of five erosional relics of the paleoproterozoic ca 2 2 ga hotazel formation with sedimentary manganese ores occurring as up to 50 m thick beds interbedded with banded iron formation bif and hematite lutite the study focuses on the manganese ores of the nchwaning gloria mining area of the northern kmd in this area pronounced mineralogical and major element alteration was imparted on the sedimentary manganese ores by a structurally controlled hydrothermal fluid flow event most notable effects of hydrothermal alteration are the decomposition and leaching of ca and mg carbonate and marked residual enrichment of manganese on the basis of mineral assemblage grade texture and geochemical characteristics three ore types were distinguished in the studied sample set classified into least altered la partially altered pa and advanced altered aa types advanced altered ores may be further classified into five different types based on mineral assemblages that contain hausmannite and or braunite as significant minerals the rare earth element ree geochemistry of these fundamental ore types was studied in detail to document ree mobility during hydrothermal alteration total ree concentrations in la ores were found to be very low 14 22 ppm and remarkably uniform within the range typically observed for bif hydrothermal alteration results in residual enrichment and a much larger scatter in ree contents a small ce anomaly observed in the protolith remains similar in magnitude when observed in paas normalised ree plots the data define however a power trend in the ce ce vs pr pr diagram such behaviour is interpreted in terms of a conservative system that was predominantly protolith buffered local remobilisation of ree during hydrothermal alteration is attributed to the dissolution of diagenetic apatite and redistribution of hydrothermal trace minerals including neoformed apatite monazite and cerianite

two modes of back arc spreading back arc spreading is initiated with rifting along the volcanic zone of an island arc under extensional tectonics the width of the volcanic zone of the arc which is closely related to the dip angle of the subducting slab should cause a variation in the style of initial rifting and subsequent back arc spreading two modes of back arc spreading single rift type and multirift type are introduced from the comparative study of the bonin arc and the japan sea divergent tectonics in an island arc above a steeply dipping slab will cause a single rift system in a narrow volcanic zone but will cause a multirift system in a broad volcanic zone which is related to a shallow dipping angle of subduction

petrogenesis of ferromanganese nodules from east of the chagos archipelago central indian basin indian ocean abstract deep sea ferromanganese nodules occur over a large area and on many different sediment types of the central indian basin indian ocean selected samples were studied to determine their chemical and mineralogical compositions and microstructural features repeated laminations of variable thickness alternately dominated by todorokite and vernadite are characteristic of these nodules these laminae show on electron microprobe line scans corresponding interlaminar partitioning of mn cu ni and fe co the bulk chemical compositions of these nodules plot in both the hydrogenetic and early diagenetic fields on the fe mn ni cu co 10 ternary diagram the binary diagram depicting the covariation of mn ni cu against fe co shows two distinct parallel regression lines one delineated by nodules from terrigenous siliceous ooze and siliceous ooze terrigenous sediments and the other by nodules from red clay siliceous ooze red clay and calcareous ooze red clay an increasing diagenetic influence in the nodules with the nature of the host sediment types was observed in the sequence terrigenous siliceous ooze and red clay siliceous calcareous ooze red clay a negative correlation between mn fe ratio and co and a positive correlation between mn fe ratio and ni cu was established the nodules show dendritic laminated and globular microstructures formed by primary growth of fe mn oxide laminae depositional hiatuses in the primary microstructures indicate that the growth of these nodules was episodic the oxide laminations show extremely complex growth patterns scattered biogenic remains and mineral grains acted as accessory seeds for growth of oxide layers in addition to the main nuclei none of the primary microstructures can be uniquely linked to a particular growth process or growth rate radial cracks cutting across primary microstructures are often filled by todorokite of a later generation post depositional modifications of the nodules were largely controlled by accreted biogenic remains as indicated by their progressive dissolution with increasing depth from nodule surfaces their pseudomorphic replacement by todorokite and the later growth of phillipsite and todorokite in the microfossil molds the growth patterns of the in filled oxides are often controlled entirely by the cavity walls and are discordant with the primary growth fabric primary todorokite was recrystallized to coarser grains of different chemical composition later generation veins of todorokite cut across and chaotically disrupted primary laminae

sorption of ni by birnessite equilibrium controls on ni in seawater abstract synthetic hexagonal birnessite hx birnessite is a close analogue to natural poorly crystalline phyllomanganate phases found in soils and marine ferromanganese deposits these phases are often highly enriched in trace metals such as ni and co we measured the sorption of ni ii onto synthetic hexagonal birnessite hx birnessite from ph 1 to 7 exafs spectra show that at ph 3 7 ni is adsorbed to the hx birnessite surface above vacancy sites on 001 as a tridentate corner sharing complex we developed a surface complexation model for ni adsorption based on the equilibria 3 mn 2 o 2 3 ni 2 mn 2 o 3 ni 0 3 mn 2 o 2 3 ni 2 h 2 o mn 2 o 3 ni oh h using this surface complexation model we predict the concentration of ni in seawater in equilibrium with ni bearing birnessite found in hydrogenetic femn crusts and nodules our predicted results are in good agreement with observed ni concentrations in seawater and suggest that the concentration of dissolved ni in seawater is buffered by sorption to birnessite or a related mno 2 phase however in addition to the surface complex ni also sorbs by structural incorporation into the vacancy site in our synthetic samples at ph 7 exafs shows 10 of ni is structurally incorporated into hx birnessite in natural birnessites found in marine ferromanganese crusts and nodules exafs shows that all of the sorbed ni is structurally incorporated structural incorporation suggests that ni sorption may be irreversible

structural stability of marine 10 a manganates from the ogasawara bonin arc implication for low temperature hydrothermal activity abstract hydrothermal 10 a manganate deposits with distinct differences in structural stability when exposed to air were found on the kaikata seamount of the ogasawara arc western pacific the most stable 10 a manganates are concentrated near the center of the hydrothermal field while the unstable ones occur towards the field margins all manganates are characterized by very high mn fe ratios and extremely low contents of transition elements such as cu co and ni the variation in 10 a stability of the hydrothermal manganates is not regulated by mineral chemistry or aging but appears to be determined by other factors e g the hydrothermal fluid temperature at mineral deposition we propose a structural model for marine manganates showing two continuous series of increasingly stabilized 10 a manganates one series is of hydrothermal origin structurally similar to todorokite with a tunnel structure fixed at deposition and the other is a buserite like series of diagenetic origin comprising phyllomanganates all the marine 10 a manganates can be progressively stabilized in two different manners the todorokite like series by the establishment of smaller tunnels and the buserite like series by post depositional uptake of 10 a stabilizing interlayer cations both series are linked together with a common end member the most unstable 10 a manganate which appears to be formed at low temperature and easily transforms to a 7 a manganate in air

mineralogical crystal morphological and isotopic characteristics of smooth slope travertine deposits at reshuitang tengchong china abstract reshuitang is an important active hydrothermal area in the tengchong geothermal field and is characterized by many hot springs and their associated deposits detailed mineralogical crystal morphological and stable isotopic investigations of the smooth slope fossil travertines at reshuitang and hydrochemical studies of two active springs around the fossil travertines were conducted to study their genesis the results show that 1 the modern springs discharge waters with high temperature 70 c near neutral ph 6 3 8 34 and high saturation indices of calcite and aragonite 2 the fossil travertines contain calcite and small amounts of mn fe oxides halite thenardite and non carbonate debris 3 the calcite include ray crystals dendrite crystals platy crystals and spike crystals and 4 13c and 18o of the fossil travertines at reshuitang range from 1 59 to 0 87 and 6 48 to 7 80 respectively according to comparison between the travertines at reshuitang and other travertines in tengchong all these travertines are thermogene travertines with a large contribution of mantle degassing to their parent co2 but are formed at different temperatures the fossil travertines at reshuitang similar to those at shuzhishi are formed at high temperatures near 100 c which results in weak microbial activities during the formation of the fossil travertines most of the calcite crystals at reshuitang were non equilibrium products precipitated directly from the spring waters during the deposition process while the spike crystals originated from diagenetic dissolution of large calcite crystals comparison between the fossil travertines at reshuitang and other smooth slope travertines from other areas shows these smooth slope travertines have different lithofacies and fabrics in smooth slope environments temperature may control the distribution and development of microbes and the intensity of co2 degassing and consequently cause the precipitation of contrasting fabrics and lithofacies

hrtem investigation of trilling todorokite and nano phase mn oxides in manganese dendrites we characterized manganese dendrites on three different substrate rocks rhyolite clayey siltstone and limestone using high resolution transmission electron microscopy manganese dendrites are mainly composed of nanometer scale mn hydr oxides fe oxy hydroxide sulfate and clay minerals including hollandite todorokite birnessite goethite amorphous fe hydroxide smectite illite and gypsum each sample has a different main manganese phase two dendrite samples have more than one manganese phase todorokite crystals on a limestone sample from altmuhl valley germany showed trilling intergrowths chain width disorder and chain termination occur in todorokite the sum of the numbers of octahedral wall layers and octahedral chains were equal at both sides beyond the termination the chain termination rule was explained by the geometry of octahedral chains and the octahedral wall layer the trilling intergrowths of todorokite might be formed by transforming the structure from birnessite to todorokite or by multiple epitaxial todorokite nucleations on octahedral wall layer of todorokite or birnessite based on chain width disorder in the todorokite we suggest that the todorokite might have been transformed from birnessite

geochemical constraints on the genesis of the montana de manganeso vein type mn deposit mexican plateau abstract manganese mineralization at montana de manganeso san luis potosi state consists of oxide ores that form sharp contacts with volcanic host rocks the orebodies are generally in the form of veins and irregular masses and locally as mineralized breccias petrographic analyses indicate that the mineralization is multi episodic with colloform and crustiform textures predominating the x ray diffraction and electron microscopy show that manganese oxides todorokite birnessite pyrolusite romanechite and cryptomelane are the main ore minerals while iron oxides goethite and hematite are accessory the most common gangue minerals are calcite and quartz with subordinate amounts of barite according to fluid inclusion microthermometry the mineralization is associated with aqueous solutions of intermediate salinity 8 to 16 wt nacl equivalent and temperatures between 101 and 140 c stable isotope analysis of calcite 13cpdb 7 76 to 6 32 18opdb 8 01 to 4 71 and barite 34s 7 9 to 13 6 shows a contribution of magmatic volatiles to hydrothermal fluids dominated by meteoric water calculated 18ofluid 6 58 to 13 14 relative to smow argillic alteration is the most widespread hydrothermal alteration at montana de manganeso and indicates fluid temperature below 150 c and near neutral ph much more local advanced argillic alteration revealed by the occurrence of kaolinite is interpreted as a steam heated overprint which in turn suggests a boiling process that must have happened at greater depths the mn ores formed through a process of mixing of a boiled off hydrothermal fluids with b cold diluted meteoric water our results support a hot spring deposit model according to which montana de manganeso corresponds to the shallowest portion of an epithermal system formed in a continental volcanic arc setting

geochemical and mineralogical studies of ca 12 ma hydrothermal manganese rich rocks in the hokuroku district in japan abstract geological and geochemical studies were performed on ca 12 ma mn rich rocks in the hokuroku district in japan to constrain the origin of mn rich hydrothermal fluids and precipitation pathways of mn oxides mn rich rocks occur in hyaloclastites of rhyolite lavas in the studied areas colloform textures of mn oxides were common in those mn rich rocks carbonaceous layers uniquely alternate with mn oxides in the colloform textures the mn oxides layers in the colloform textures were composed of aggregates of nano scale todorokite birnessite and pyrolusite the carbonaceous layers also host apatite nano crystals these findings imply that the carbonaceous layers most likely represent fossilized microbial mats of mn oxidizing bacteria the close association of nano scale mn oxides with organic matter clay and silica minerals suggests that mn oxides initially precipitated near venting areas of low temperature hydrothermal fluids the early mn oxides were trapped in the hyaloclastites and experienced diagenetic modifications combined with hydrothermal alteration seawater penetration and microbial activities in the hyaloclastites such secondary processes further enriched mn in the hyaloclastites forming various mn silicates e g pennantite and shirozulite and veins made of mn ii and iii silicate and oxide silicate e g rhodonite and braunite later hydrothermal fluids also brecciated the massive mn rich rocks rhodochrosite and rhodonite occurred in such brecciated mn rich rocks or sheared hyaloclastites preferentially the carbon isotope compositions of rhodochrosite ranged from 26 7 to 20 8 vpdb the mudstone and early colloform textures in the hyaloclastites contained appreciable amounts of organic matter such organic matter was degraded by microbial processes under the influence of the later hydrothermal activities followed by the formation of rhodochrosite these findings contribute not only to understanding the formation mechanisms of hydrothermal mn rich rocks but also to future exploration of mn deposits

active hydrothermal mounds in the okinawa trough backarc basin japan abstract dive studies by the shinkai 2000 were made in september 1984 and july 1986 in the central axial rift of the middle okinawa trough a possible active backarc basin in a nascent stage hydrothermally active mounds were discovered on a small knoll 27 34 4 n 127 08 6 e directly south of the area where a high heat flow higher than 1 w m2 had been observed previously the largest mound 5 6 m high and 15 25 m wide has several peaks and ridges along which yellow materials are exposed shimmering water was noted at several places on the yellow materials the rest of the mound is thinly covered by brown materials the temperature of the ejecting water was higher than that of the ambient seawater by 2 3 c and a 40 cm long thermometer inserted into the mound recorded a temperature of 20 50 c analysis of the ejected water showed a methane content of about 200 nl kg it is possible that further dive studies will reveal larger scale hydrothermal activity in the area

an integrated method for the quantitative evaluation of mineral resources of cobalt rich crusts on seamounts abstract cobalt rich crusts on seamounts potentially have the economic value of multiple metals in the field of exploration it is important to perform quantitative evaluations of mineral resources and delineate promising areas in survey regions for future mining accordingly this study based on prior knowledge develops an integrated method to quantitatively evaluate mineral resources of cobalt rich crusts on seamounts and gives an application example to demonstrate this method the method includes four steps first defining units with certain areas and shapes on the target seamount a 20 km2 square block in the application example and estimating characteristic values of the cobalt rich crust for each unit with known geological survey data using a space interpolation method such as kriging second presenting several model algorithms i e regional coverage of crusts suitable slope percentage for mining and fitting area on slopes to extract the corresponding regional metallogenic factors for each unit by inputting regional surveying data such as bathymetry data into these models third considering both the features and regional metallogenic factors of cobalt rich crusts in each unit to estimate their distribution of mineral resources on the entire seamount and last according to the distribution of the mineral resources and international social and economic requirements such as the regulations of the international seabed authority delineating a promising area for future mining

shear wave amplitude anomalies in south central wyoming amoco recently acquired four surface seismic shear wave lines four multicomponent vsp s and three crossed dipole sonic logs in south central wyoming a feature of this region is that areas of increased gas production correlate with areas of increased fracturing after seismic processing of the shear wave lines it was observed that reductions in the relative amplitude of the slow shear wave s2 seismic section with respect to the fast shear wave s1 section correlate with areas of greater gas production

fe mn oxyhydr oxides as an indicator of rey enrichment in deep sea sediments from the central north pacific abstract nowadays pelagic sediments are globally explored as a potential resource of rare earth elements and yttrium termed as rey and have received unprecedented attention however the formation mechanism of rey rich deep sea mud remains controversial the fe mn oxyhydr oxides are ubiquitous in oxic marine sediments and potentially beneficial for the rey enrichment the research of them is important for understanding the ore formation of rey rich mud and thus can help to evaluate the role of marine sediments in global rey cycles in this contribution using advanced in situ analytical techniques we provide new results on the nanoscale mineralogy and geochemistry of fe mn oxyhydr oxides that are recovered from rey rich deep sea sediments in central north pacific ocean in situ x ray diffraction analyzer and scanning electron microscope reveal that the fe mn minerals e g vernadite birnessite and todorokite occur as overgrowths on the surface of nuclei to form fe mn micronodules transmission electron microscope tem imaging reveals that these fe mn minerals are composed of nanocrystals with high intercrystalline porosity indicating a potential strong adsorption capacity the tem observations also imply a mineral phase transformation from birnessite vernadite to todorokite during the oxic diagenesis accompanied by corresponding changes in geochemical compositions laser ablation inductively coupled plasma mass spectrometry demonstrates that fe mn oxyhydr oxides contain high rey concentrations varying from 439 to 1 654 ppm with an average of 790 ppm and can be regarded as an important host of rey furthermore the paas normalized and seawater normalized rey patterns both infer that the rey contents of fe mn oxyhydr oxides are ultimately derived from seawater and characterized by preferential scavenging of ce overall fe mn oxyhydr oxides not only contribute a moderate proportion of rey but also provide specific information for understanding geochemical processes related to rey enrichment in deep sea sediments

exceptional preservation of mn oxidizing microbes in cave stromatolites el soplao spain abstract many ferromanganese stromatolites of el soplao cave n spain are characterized for the exceptional preservation and high diversity of microbial fossils probably representing the best example of microbial preservation described in ferromanganese deposits so far the el soplao stromatolites are mainly formed by polymetallic mn rich oxides with subordinate and variable amounts of detrital material and consist of both dendritic and laminar microfacies in both microfacies microbial forms are abundant in the relatively pure mn oxide rich material whereas they are scarce in areas with significant detrital material microbial forms are observed either in cross section completely embedded in the mn oxide rich matrix or in three dimensions lining the walls of pores based on their morphology we have separated the most abundant microbial forms into six main morphotypes and six additional submorphotypes most of which can be assigned to bacteria most morphotypes consist of coccoid coccobacilus or filamentous forms therefore they are not diagnostic of any particular bacterial group however the ovoid cells of morphotype b show cylindrical polar protuberances typical of prosthecate alpha proteobacteria on the basis of characteristic morphological features three submorphotypes of morphotype b can be assigned to three alpha proteobacteria genera hyphomicrobium pedomicrobium and caulobacter this ascription is supported by the well known mn oxidizing behavior of both pedomicrobium and caulobacter and by the common presence of hyphomicrobium in ferromanganese deposits elsewhere the excellent microbial preservation is partly related to the origin of the ferromanganese oxides i e extracellular precipitation induced by microbial metabolism other factors contributing to the good microbial preservation are the relatively low degree of diagenetic alteration and the relatively high accretion rates of stromatolites compared to other ferromanganese deposits the generally low degree of diagenesis is likely because the stromatolites have remained relatively stable and at a rather low temperature since they were formed at least 1 ma ago still some stromatolites have suffered diagenetic alteration partial dissolution and replacement by calcium carbonates and fe rich oxides obscuring or even obliterating their bioforms the el soplao case represents an example of how easily biogenic mn oxides can be altered and their bioforms blurred in a relatively short geological time span in spite of being in a relatively stable alkaline and low temperature setting a geological implication is that the absence of bioforms in other ferromanganese deposits including rock varnish and precambrian iron formations does not disprove their possible biogenic origin since the high chemical reactivity of biogenic manganese oxides makes them highly vulnerable to diagenesis

stabilization of 10a manganates by interlayer cations and hydrothermal treatment implications for the mineralogy of marine manganese concretions abstract experimental substitutions of transition and alkaline earth cations into synthetic 10a na manganate show that cation uptake and the stability of the cation substituted mineral increase with stability of the hydroxide of the cation hydrothermal treatment of synthetic 10a manganates with different metal contents as well as marine diagenetic and hydrothermal 10a manganates shows that the stabilities of their structures are enhanced with increasing temperature the stabilization is due to reinforcement of the tunnel walls supporting the mn4 o2 6 octaheral layers the diagenetic 10a manganates have initially unstable buserite like structures with each interlayer wall composed of two mn2 o2 3 x oh 3 x octahedra 0 x 3 with either a na o2 2x oh n 2x unit n 6 and or 8 or less frequently a mn2 o2 2x oh 2 2x octahedron in between some of these cations in the walls are post depositionally substituted by highly hydrated divalent metal cations particularly cu2 and ni2 while some of the mn2 ions are slowly oxidized to mn4 these interlayer changes result in higher crystal field stabilization energy and shifts from interlayer van der waal s forces and weak coordination links to strong coordination links which stabilize the mineral structures low temperature hydrothermal 10a manganates have todorokite like structures with tunnel walls constructed predominantly of mn2 o2 3 x oh 3 x and mn2 o2 2x oh 6 2x octahedra high temperature hydrothermal 10a manganates have stable todorokite structures with the walls constructed of mn4 o2 6 octahedra the positive correlation between the formation or post depositional alteration temperatures and the mineral stability is due to the increase in oxidation rate of interlayer mn2 ions with increasing temperature of the hydrothermal fluids marine 10a manganates can be used as genetic indicators for manganese concretions and the sediments in which they occur and as a geothermometer in the search of ancient and modern hydrothermal vents where massive sulphide deposits are often found

submarine hydrothermal manganese deposits from the ogasawara bonin arc off the japan islands abstract numerous submarine hydrothermal sulfide and oxide deposits have been found in the mid ocean ridge systems but until now no activity has been found in an island arc system the geological survey of japan gsj has started a geological geophysical and geochemical investigation program in the bonin mariana arc since 1984 aiming at evaluation of submarine hydrothermal metal deposits and understanding of their geological background during the reconnaissance survey by r v hakurei maru in june 1984 thick hydrothermal manganese crusts were recovered from three seamounts of the bonin arc at a depth of ca 1000 m the chemical and mineralogical features and characteristic structure and occurrence of associated calcareous fossils and nontronite claystones suggest the quaternary low temperature hydrothermal activity forming well crystallized todorokite pyrolusite goethite and nontronite deposits thin hydrogenous ferromanganese encrustations on the hydrothermal crusts from a guyot of the northern arc indicate that the recent very active hydrothermal activities around this area may be declining or already finished whereas the fresh hydrothermal manganese crusts from the kaikata seamount suggest recent hydrothermal activity

ni cu co rich hydrothermal manganese mineralization in the wallis and futuna back arc environment sw pacific abstract the wallis and futuna back arc system is a complex area composed of at least two active oceanic spreading centers the futuna and alofi spreading centers and young volcanic zones characterized by diffuse magmatism locally affected by the samoan hotspot this geological setting is favorable to the establishment of hydrothermal systems in the form of either high temperature ht hydrothermal venting or low temperature lt diffuse flow during the 2010 futuna cruise aboard the r v l atalante three remarkable inactive lt fe si mn deposits were discovered utu uli anakele and utu sega some of the mn rich precipitates discovered exhibit the highest base metals concentrations so far recorded in ferromanganese rocks including in the well documented hydrogenetic crusts and polymetallic nodules the deposits lie on top of volcanoes and formed in close association with the volcanic facies the manganese mineralization occurs in the form of massive layered crusts and mn rich cements within strongly altered basaltic pyroclastic rocks brecciated lavas and more rarely in sediments field observations and mineralogical and chemical studies support a hydrothermal origin for the mineralization and show that nickel cobalt and copper enrichments are controlled by the precipitation of 7 a and 10 a manganates the conventional geochemical classifications e g bonatti et al 1972 used to decipher the origin of mn mineralization cannot be used for this new type of deposit and new robust discrimination diagrams need to be established we suggest that the unusual enrichment of metals recorded in our samples is due to i a lack of precipitation of high temperature massive sulfides at depths that would have retained metals e g cu ni co ii isolation of the hydrothermal system thereby avoiding ni co and cu losses in the water column and iii the ability of birnessite and buserite todorokite to scavenge co ni and cu from aqueous fluids the utu uli and anakele deposits share certain characteristics with the active hydrothermal system at loihi seamount e g the depth of mineralization relationships with pyroclastic volcanoes and the influence of a mantle plume source and thus might represent late stage products of this specific type of hydrothermal activity elsewhere the co rich mineralization of the calatrava volcanic field cvf in spain may be a potential analog of the utu sega deposit the mn co deposits of the cvf formed in close proximity to pliocene volcanic rocks metals were transported by epithermal hydrothermal solutions with high fo 2 and cobalt was scavenged by mn oxides together with the well documented stratabound mn deposits gonzalez et al 2016 hein et al 2008 hein et al 1996 the mn deposits discovered in the wallis and futuna back arc provide crucial insights into lt hydrothermal activity in the deep ocean the metal rich character of this lt hydrothermal activity may be of major importance for future research on the net flux of hydrothermally derived metals e g ni co cu to the open ocean

paleomagnetism of the mn wad deposit at niimi hot springs hokkaido japan the niimi hot springs is located at the foot of mt shyakunage in the active niseko volcanic area hokkaido japan the manganese mn wad deposit was precipitated from the hot spring water by biom

mineralogy and crystal chemistry of mn fe co ni and cu in a deep sea pacific polymetallic nodule minor element concentrations in marine ferromanganese nodules are primarily controlled by the mineralogy which itself depends on redox conditions at the sediment water interface results are presented for the first in depth x ray microstructural and microspectroscopic investigation of a mixed hydrogenetic diagenetic nodule which is representative of ferromanganese deposits on abyssal plains the measurements were conducted by micro x ray diffraction and x ray absorption spectroscopy both xanes and exafs on hydrogeneous and diagenetic regions of the nodule the hydrogenetic diagenetic interface was imaged by x ray microfluorescence after which regions of interest were chosen to represent mineralogical and chemical transformations that occurred at the early stage of suboxic diagenesis in the hydrogenetic nodule oxic environment mn is speciated as fe vernadite a nanocomposite material composed of intergrown feroxyhite feooh and monodispersed phyllomanganate layers having no interlayer mn vernadite in the diagenetic nodule suboxic environment mn is speciated dominantly as mg rich 10 a vernadite which consists of a random intergrowth of vernadite and its transformation product todorokite the authigenic 10 a vernadite precipitated from the components of vernadite in fe vernadite that were dissolved in suboxic microenvironments of the sediment direct evidence supporting a redox driven dissolution reaction is provided by the valence composition of mn as measured by micro xanes which is 0 69mn4 0 24mn3 0 07mn2 average 3 62 0 04 v u for fe vernadite and 0 61mn4 0 23mn3 0 16mn2 average 3 28 0 04 v u for 10 a vernadite ni and cu derived mainly from dissolved vernadite and oxidized organic matter replace structural mn3 4 in both the mno2 layer and todorokite domains of 10 a vernadite pure todorokite in highly diagenetic regions of the nodule has an average formula of mg2 0 167 mn4 0 783 mn3 0 099co3 0 002ni2 0 076cu2 0 040 o2 n h2o with an atomic ratio of cu ni co mn 0 13 which is slightly lower than 0 167 1 6 the maximum metal uptake capacity reported for marine nodules by analogy with synthetic todorokites we infer that mg2 which has a hydrated diameter close to that of the 3 3 tunnel size of todorokite and mn3 and cu2 which prefer jahn teller distorted octahedra play a crucial role in templating the topotactic transformation of 10 a vernadite to todorokite and stabilizing todorokite in suboxic marine sediments

origin of negative ce anomalies in mixed hydrothermal hydrogenetic fe mn crusts from the central indian ridge abstract layered fe mn crusts from the off axis region of the first segment of the central indian ridge north of the rodrigues triple junction were studied geochemically and mineralogically vernadite mno2 is the main mineral oxide phase 230thxs and co concentrations suggest high growth rates of up to 29 mm myr and a maximum age of the basal crust layer of 1 ma whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation co pb ni and ti concentrations are strikingly lower concentrations and distribution of the strictly trivalent rare earths and yttrium rey are typical of hydrogenetic ferromanganese oxide precipitates but in marked contrast the crusts are characterized by negative cesn shale normalized anomalies and ce pr sn ratios less than unity profiles through the crusts reveal only minor variations of the rey distribution and ce pr sn ratios range from 0 45 to 0 68 compared to ratios of up to 2 for typical hydrogenetic crusts from the central indian basin the apparent bulk partition coefficients between the crusts and seawater suggest that for the strictly trivalent rey the adsorption desorption equilibrium has been reached positive ce anomalies in the partition coefficient patterns reveal preferential uptake of ce but to a lesser extent than in normal hydrogenetic crusts a new parameter excess ce cexs to quantify the degree of decoupling of ce from rey iii is established on the basis of partition coefficients cexs cebulk ratios suggest that the cir crusts formed by precipitation of fe mn oxides from a hydrothermal plume and that in hydrothermal plumes and normal seawater the enrichment of ce results from the same oxidative sorption process the growth rates calculated with 230thxs data as well as with the co formula are inversely related to cexs

geomechanical simulation to predict open subsurface fractures geomechanical simulation of the evolution of a geological structure can play an important role in predicting open fracture development for all stages in that structure s development in this work three such geomechanical simulations are used to predict the evolving stress and strain fields including dilational and compactional changes in the rock fabric in developing fault and fold systems their consequences for open fracture development and flow are addressed these simulated stress and strain fields show considerable spatial and temporal heterogeneity that is consistent with deformation patterns observed in both natural examples and in laboratory deformed analogues but the stress and strain states that develop are neither co axial nor do they bear a simple relationship to one another the dilational and compactional strains manifest as open fracturing or sealing represent some significantly increased or significantly decreased flow rates however open fracture predictions based on such geomechanical simulations are extremely difficult to validate with any degree of confidence as there is little direct evidence of sub surface fracture distributions in this context we also discuss possible integration of seismic anisotropy measurements as an independent measure of open fracture alignment to support the geomechanically derived fracture predictions the focus of this work is on volumetric strains in fault zone evolution though folding is also addressed

iron mineral structure reactivity and isotopic composition in a south pacific gyre ferromanganese nodule over 4ma abstract deep sea ferromanganese nodules accumulate trace elements from seawater and underlying sediment porewaters during the growth of concentric mineral layers over millions of years these trace elements have the potential to record past ocean geochemical conditions the goal of this study was to determine whether fe mineral alteration occurs and how the speciation of trace elements responds to alteration over 3 7 ma of marine ferromanganese nodule mfn formation a timeline constrained by estimates from 9be 10be concentrations in the nodule material we determined fe bearing phases and fe isotope composition in a south pacific gyre spg nodule specifically the distribution patterns and speciation of trace element uptake by these fe phases were investigated the time interval covered by the growth of our sample of the nodule was derived from 9be 10be accelerator mass spectrometry ams the composition and distribution of major and trace elements were mapped at various spatial scales using micro x ray fluorescence xrf electron microprobe analysis empa and inductively coupled plasma mass spectrometry icp ms fe phases were characterized by micro extended x ray absorption fine structure exafs spectroscopy and micro x ray diffraction xrd speciation of ti and v associated with fe was measured using micro x ray absorption near edge structure xanes spectroscopy iron isotope composition 56 54fe in subsamples of 1 3 mm increments along the radius of the nodule was determined with multiple collector icp ms mc icp ms the spg nodule formed through primarily hydrogeneous inputs at a rate of 4 0 0 4 mm ma the nodule exhibited a high diversity of fe mineral phases feroxyhite feooh goethite feooh lepidocrocite feooh and poorly ordered ferrihydrite like phases these findings provide evidence that fe oxyhydroxides within the nodule undergo alteration to more stable phases over millions of years trace ti and v were spatially correlated with fe and found to be adsorbed to fe bearing minerals ti fe and v fe ratios and ti and v speciation did not vary along the nodule radius the 56 54fe values when averaged over sample increments representing 0 25 0 75 ma were homogeneous within uncertainty along the nodule radius at 0 12 0 07 2sd n 10 our results indicate that the fe isotope composition of the nodule remained constant during nodule growth and that mineral alteration did not affect the primary fe isotope composition of the nodule furthermore the average 56 54fe value of 0 12 we find is consistent with fe sourced from continental eolian particles dust despite mineral alteration the trace element partitioning of ti and v and fe isotope composition do not appear to change within the sensitivity of our measurements these findings suggest that fe oxyhydroxides within hydrogenetic ferromanganese nodules are out of geochemical contact with seawater once they are covered by subsequent concentric mineral layers even though fe bearing minerals are altered trace element ratios speciation and fe isotope composition are preserved within the nodule

high resolution la icp ms mapping of deep sea polymetallic micronodules and its implications on element mobility abstract enrichments of rey rare earth yttrium and other trace metals co and ni in deep sea ferromanganese fe mn micronodules have received increasing attention in both deep sea research and mineral exploration due to the presence of multiple easily crushed and poorly crystallized phases in micronodules the genesis of micronodules and their adsorption of various trace elements are poorly understood to address this gap we examined the spatial distributions of elements in cross sections of micronodules from the western tropical north pacific ocean using high resolution hr la icp ms raster mapping coupled with laser raman and x ray photoelectron spectroscopy xps the ferromanganese micronodules we studied are dominated by fe and mn oxides with minor carbonate minerals such as siderite rhodochrosite and calcite la icp ms maps show that these micronodules consist of a mn rich core and a fe rich rim the fe enriched rim is enriched in as and surrounds a mg mn cu co and ni concreted core laser raman maps show that the micronodule core contains more birnessite an important scavenger of trace metals in deep sea sediments than the rim the birnessite filled core of these micronodules does not have elevated rey indeed birnessite line channels may feed metal rich fluid containing rey to adjacent minerals including well crystallized bio apatite and zeolite as high ce and y levels are spatially correlated with these minerals the observed element profiles and xps observations showing the coexistence of multiple oxidation states of mn 2 3 and 4 fe 2 and 3 and ce 3 4 demonstrate that the fe mn phases of these micronodules are of a diagenetic origin and that they are sites of redox driven metal enrichment in deep sea sediment

the relationship between manganese minerals and metallic elements in deep sea manganese nodules abstract the relationship between manganese minerals and the concentration of fe cu ni zn and al in mn rich crystalline areas in deep sea manganese nodules were investigated using microdiffraction and electron microprobe analysis thirty three microsamples were obtained from eight polished sections of five pacific ocean manganese nodules birnessite and todorokite are the principal manganese minerals in the x ray diffraction powder patterns on polished sections kept in a vacuum only birnessite was identified in sixteen microsamples only todorokite was identified in one microsample another sixteen microsamples were mixtures of birnessite and todorokite microsamples in which only birnessite was identified contain cu ni and zn in the same concentrations as the microsamples in which both birnessite and todorokite were identified it appears that birnessite as well as todorokite can incorporate cu ni and zn with the exception that no todorokite was observed in microsamples with very small amounts of fe cu and ni there is no systematic correlation between the manganese mineralogy and the concentration of fe cu ni and zn in the microsamples the microsamples examined in this study contain varying amounts of al 0 01 2 57 wt 0 92 wt on average todorokite appeared in the microsamples which contained more than 0 7 wt al mineralogical considerations suggest that at least part of the al detected may be incorporated in todorokite

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

ferruginous vernadite in an indian ocean ferromanganese nodule select area electron diffraction and microanalysis of the optically dark component of a ferromanganese nodule from the south east indian ocean manganese field indicate that this is composed of a random stratification of crystallites of vernadite mno 2 r 2 o ro r 2 o 3 x y h 2 o where r represents elements such as k ba na ca mg and a disordered hydrated iron oxide possibly ferrihydrite 5fe 2 o 3 9h 2 o or feroxyhyte feooh whether the dark component is an irregular mixed layer hybrid mineral or a layered accumulation resulting from epitaxy of the above phases is uncertain

three dimensional deformation and strain induced by municipal pumping part 2 numerical analysis summary field measurements consisting of water levels from a municipal well and three dimensional surface deformations and strains from high precision gps measurements at various radial distances from the well were collected as part of a 62 day controlled aquifer test at mesquite nv these measurements were used as observations in several numerical models and a parameter estimation code to characterize and constrain hydraulic and mechanical properties of a 400 m thick basin fill aquifer a parsimonious approach was used in conceptualizing the aquifer system nonetheless results from the calibrated deformation and flow models accurately reproduced the observed head and deformations during the first 20 days of pumping the time at which a new equilibrium was achieved surface deformations were shown to reflect hydraulic anisotropy and direction of principal conductivity in addition the radius of influence and cone of depression from pumping was approximated in spite of the fact that no monitoring well data existed at the site sensitivity analysis indicates that cyclical head values are most sensitive to changes in horizontal hydraulic conductivity while time dependent vertical deformations are most sensitive to changes in skeletal specific storage this investigation shows that gps monitoring can be used in place of costly monitoring wells to characterize aquifers for water management purposes where skeletal deformation tends to be elastic

fine scale study of major and trace elements in the fe mn nodules from the south china sea and their metallogenic constraints abstract many marine fe mn polymetallic nodules may contain high concentrations of mn cu ni zn co and rare earth elements plus yttrium rey to determine the occurrence and enrichment processes of these metals in the fe mn nodules we conducted high resolution mineralogical and geochemical studies on the fe mn nodules collected from the south china sea in situ epma and la icp ms analyses and elemental imaging were performed on individual microlayers of the nodules to reveal the major and trace element distributions the whole rock mineralogical and chemical compositions of the fe mn nodules indicate a hydrogenetic origin the mn mineral phases are mainly composed of nanocrystalline vernadite with interlayered 10 a and 7 a phyllomanganates such as todorokite birnessite and buserite fe ti oxides hydroxides are intergrown and essentially x ray amorphous feroxyhyte and goethite we recognize two main types of microlayers type a layer suboxic diagenetic precipitates containing a high mn fe ratio and high concentrations of cu ni zn ba li and mg and type b layer oxic hydrogenetic accretions with low fractionation of mn and fe and high contents of co rey ti sr and pb furthermore elemental mapping indicates that the enrichments of co and rey are mainly associated with fe mineral phases rather than mn ones which are enriched in mg cu ni zn li and ba two mineralization processes and metal distributions in the individual microlayers are identified in the fe or mn mineral phases the occurrence of 10 a and 7 a phyllomanganates in type a layers are commonly enriched in trace metals such as ni cu zn li ba and mg whereas the metals for the type b layers include co ti pb sr rey which may be carried by the intergrowing fe ti oxyhydroxides and vernadite thus hydrogenesis and diagenesis facilitate the enrichment of fe co ti sr pb rey and mn ni zn cu li ba mg respectively during the mineralization of the south china sea nodules

submersible observations of hydrothermal manganese deposits on the kaikata seamount izu ogasawara bonin arc abstract during dive 408 of shinkai 2000 on the flank of the kaikata seamount located on the volcanic front of the izu ogasawara bonin arc possibly recent hydrothermal manganese deposits were observed on sandy volcanic sediments at water depths of between 800 and 1200 m the deposits cover almost the entire surface sediment across the manganese belt on the northwestern flank on the seamount on a scale of kilometers the occurrence of the deposits seafloor morphology and temperature of the sediments together with previous shipboard results lead to a possible model for the formation of the manganese deposits a low temperature hydrothermal solution ascends through fractures or faults in the volcanic substrate into permeable volcanic sands and precipitates manganate minerals which cement several centimeters of surface sand as hardpan more intense and probably intermittent discharge of hydrothermal solution follows and forms many typical ridge like vents and mounds on the seafloor subsequently pure dense manganate layers developed beneath the semi consolidated volcanic sandstone and act as a cap to the ascending fluids the proposed mechanism may be the dominant type of low temperature hydrothermal mineralization in submarine island arc volcanoes and rifts similar hydrothermal manganese deopsits most probably occur in other active areas of the modern seafloors and in inactive island arcs

mathematical model for regional land subsidence due to pumping 2 integrated aquifer subsidence equations for vertical and horizontal displacements a mathematical model for regional subsidence due to pumping from an aquifer is developed on the basis of biot s work on coupled three dimensional consolidation following biot s work on threedimensional consolidation with coupling between mass conservation and equilibrium equations a mathematical model for regional subsidence due to pumping from an aquifer is developed by averaging the three dimensional model over the thickness of the aquifer and assuming conditions of plane stress both vertical land subsidence and horizontal displacements as functions of plane coordinates and time can be estimated by solving the model equations for a given confined or leaky confined aquifer an analytical solution is presented for the special case of a single well pumping from an infinite homogeneous isotropic aquifer the solution provides estimates of changes in averaged over the vertical values of piezometric head vertical subsidence and horizontal displacement the results indicate that under the conditions of the studied case of radial flow the solution for piezometric head is identical to the one obtained by noncoupled models furthermore half the volume strain is produced by vertical subsidence while the other half by the horizontal displacement hence the vertical subsidence is only approximately half the value obtained in noncoupled models which neglect horizontal displacement a numerical example demonstrates these conclusions

oxidative scavenging of thallium by birnessite explanation for thallium enrichment and stable isotope fractionation in marine ferromanganese precipitates tl stable isotopes recorded in marine ferromanganese crusts show great promise as a tracer of past marine and climatic conditions key to interpreting recent tl stable isotope time series data is a detailed molecular level understanding of tl scavenging by ferromanganese crust minerals and tl stable isotope fractionation occurring during uptake to this end we determine the mechanism of tl sorption to the primary ferromanganese minerals in crusts namely hexagonal birnessite todorokite and ferrihydrite using xas we compliment our data with micro focus xas of a tl enriched hydrogenetic ferromanganese crust we show that tl i is oxidised to tl iii during sorption to hexagonal birnessite but not during sorption to todorokite triclinic birnessite and ferrihydrite tl iii forms an inner sphere complex at the hexagonal birnessite surface located at vacant octahedral sites in the phyllomanganate sheets we show that oxidation of tl i to tl iii during reductive dissolution of birnessite is thermodynamically unfavourable and propose that oxidation of tl i is driven by the formation of the tl iii surface complex recent theoretical calculations predict a large equilibrium stable isotope fractionation between tl i and tl iii leading to tl iii species that are enriched in the heavy 205tl isotope in light of this work we propose a molecular sorption oxidation fractionation mechanism that provides a unifying explanation for the recently observed geochemical behaviour of tl in marine ferromanganese rich sediments in this mechanism the proportion of hexagonal birnessite dictates the extent of tl oxidation which controls the extent of tl enrichment and isotope fractionation this work is among the first to provide a molecular explanation for reported trends in trace element enrichments and stable isotope compositions in geologic deposits our molecular sorption oxidation fractionation mechanism will ultimately help interpret tl signals in marine sedimentary archives to provide new constraints on past oceanic and climatic change in addition our mechanism should also help explain compositional relationships of other redox sensitive elements in ferromanganese rich marine sediments that might also be used as paleoceanographic and paleoclimate proxies

three dimensional numerical simulation of fully coupled groundwater flow and land deformation due to groundwater pumping in an unsaturated fluvial aquifer system a series of three dimensional numerical simulations using a hydrogeomechanical numerical model is performed to analyze and predict fully coupled groundwater flow and land deformation due to groundwater pumping in an unsaturated fluvial aquifer system which has irregular lateral boundaries the aquifer system is composed of a loam layer underlain by a sand layer on bedrock a steady state numerical simulation is performed first to obtain initial spatial distributions of pressure head hydraulic head and groundwater flow velocity before groundwater pumping and its results are illustrated and validated reasonably with respect to field measurements of hydraulic head a transient state numerical simulation is then performed to obtain spatial and temporal distributions of pressure head hydraulic head groundwater flow velocity and land displacement vector during groundwater pumping and its results are also illustrated and validated reasonably with respect to field measurements of both hydraulic head and vertical displacement these numerical simulation results show that hydrogeomechanical numerical modeling can be a useful tool for analyzing and predicting long term groundwater level fluctuation and land deformation due to groundwater pumping in actual three dimensional aquifer systems

mechanical modeling of aquifer sands under long term groundwater withdrawal abstract long term excessive groundwater withdrawal causes severe land subsidence and considerable economic loss during the period of land subsidence aquifer sands present complex deformation characteristics field data in the southern yangtse delta china have shown that the deformation characteristics of aquifer sands are closely related to the changing patterns of groundwater level the aquifer units have experienced when the groundwater level fluctuates yearly within a certain range the aquifer unit behaves primarily as an elastic material when the groundwater level rises and falls alternatively with the average decreasing but higher than the previous lowest value the unit has experienced the aquifer unit behaves primarily as a visco elastic and elasto plastic material however when the average level decreases and is lower than the previous lowest value the unit has experienced the aquifer unit behaves primarily as a visco elastic elasto plastic and visco plastic material the plastic and creep deformation of aquifer sands is also proved through laboratory tests with the increasing cycle number of loading the creep and plastic deformation decreases and the expansion under unloading is closer to the compression under loading in a single cycle on the basis of field and laboratory data a new mechanical model is constructed which can describe various kinds of deformation characteristics under different changing patterns of groundwater level including elastic visco elastic plastic and visco plastic deformation the model includes two yielding stresses and six parameters when the appropriate field data are available the six parameters of the model can be determined through graphic methods then the deformation of aquifer units can be calculated if the changing groundwater level is known

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago

volcanic and hydrothermal history of ridge segments near the rodrigues triple junction central indian ocean deduced from sediment geochemistry abstract sediments from the central indian ridge cir and southeast indian ridge seir near the rodrigues triple junction rtj were investigated in order to relate the accumulation rates of sediment components to the volcanic and hydrothermal history of the respective ridge segments the sediments contain 50 90 biogenic carbonates and have been deposited over at least the last 2 5 myr without large hiatuses since there is no early diagenetic element mobilization the main primary geochemical signals are preserved in the sediments a three step multivariate analysis of carbonate free geochemical data showed that the sediments consist of two main endmembers with respect to si ti al fe mg k mn cu ni and zn which are mixed in different ratios in the samples the first endmember comprises volcanic detrital components mainly basalt fragments basaltic glass and their weathering products smectites the second endmember is made up of hydrothermal fe mn oxides the volcanic detritus is distributed via bottom currents the fe mn oxides are formed as particle fallout from hydrothermal plumes the first component dominates in the rift valley the second on the ridge flanks along the seir varying accumulation rates were found to reflect the cyclic magmatic volcanic activity of the intermediate spreading rift axis in cores from the cir the accumulation of both endmembers reflects the evolution of a non transform fault separating the first and second cir segments rather than the spreading axis history