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

tectonic implications of rapid cooling of lower plate rocks from the buckskin rawhide metamorphic core complex west central arizona lower plate rocks exposed in the buckskin rawhide metamorphic core complex west central arizona underwent a pronounced increase in cooling rate 7 12 m y after the onset of extensional tectonic denudation at ca 27 ma a detailed 40 ar 39 ar study of lower plate rocks exposed near planet peak in the southwest part of the core complex indicates that the highest level mylonitic rocks exposed in the complex cooled below 350 c prior to 20 1 ma at an average rate of 15 c m y thereafter the cooling rate of these rocks increased progressively peaking at 280 80 c m y prior to initial exposure of the core between 15 1 and 13 3 ma published k ar 40 ar 39 ar and fission track ages for the most recently unroofed lower plate rocks exposed at the northeastern end of the core complex are consistent with a similar cooling history although the abrupt increase in cooling rate occurred as many as 5 m y later in this area because the increase in the cooling rate appears to have occurred progressively later toward the northeast it is unlikely to reflect changes in slip rate it appears to have coincided with cooling below 350 300 c and thus is interpreted to reflect steepening of the detachment system above the brittle ductile transition thermochronological data from lower plate rocks in the planet peak area together with constraints on their initial exposure at the surface are consistent with an increase in the dip of the detachment from le 5 at midcrustal depths where it was represented by a shear zone to at temperatures below 200 150 c lower plate rocks at both ends of the core complex probably cooled at rates 130 c m y which can not be reconciled with the average dip le 25 and slip rate 6 12 mm yr for the detachment fault given the likely geothermal gradient 25 c km during the early stages of extension this implies that cooling did not keep pace with denudation at upper crustal levels the very high cooling rates are interpreted to have primarily reflected the development of a pronounced thermal discontinuity across the detachment fault possibly 100 c as hot lower plate rocks were transported to shallow crustal levels rapid cooling of the lower plate at these levels may have been enhanced by interaction with fluids derived from the upper plate consistent with models that link the shallow level

a physically based calving model applied to marine outlet glaciers and implications for the glacier dynamics we present results from numerical ice flow models that include calving criteria based on penetration of surface and basal crevasses which in turn is a function of longitudinal strain rates near the glacier front the position of the calving front is defined as the point where either 1 surface crevasses reach the waterline model cdw or 2 surface and basal crevasses penetrate the full thickness of the glacier model cd for comparison with previous studies results are also presented for a height above buoyancy calving model qualitatively both models cdw and cd produce similar behaviour unlike previous models for calving the new calving criteria are applicable to both grounded termini and floating ice shelves and tongues the numerical ice flow model is applied to an idealized geometry characteristic of marine outlet glaciers results indicate that grounding line dynamics are less sensitive to basal topography than previously suggested stable grounding line positions can be obtained even on a reverse bed slope with or without floating termini the proposed calving criteria also allow calving losses to be linked to surface melt and therefore climate in contrast to previous studies in which calving rate or position of the terminus is linked to local water depth the new calving criterion is able to produce seasonal cycles of retreat and advance as observed for greenland marine outlet glaciers the contrasting dynamical behaviour and stability found for different calving models suggests that a realistic parameterization for the process of calving is crucial for any predictions of marine outlet glacier change

coupled basin detachment systems as paleoaltimetry archives of the western north american cordillera abstract stable isotope paleoaltimetry data from the snake range metamorphic core complex mcc and sacramento pass basin nv usa document that extensional mylonite zones and kinematically linked syntectonic basins reliably record paleotopography in the continental interior of western north america when compared to a sea level reference here we show that this basin mcc pair tracks meteoric fluid flow at different levels of actively extending crust in a high topography region during oligo miocene extension of the basin and range province for paleoaltimetry purposes we compare multi proxy oxygen 18 o and hydrogen d isotope data as well as geochronological information from the snake range mcc to a time equivalent ca 20 ma stable isotopic proxy record from the buckskin mountains mcc az usa which developed next to the pacific coast near miocene sea level we complement this paleoaltimetry study by comparing the buckskin mountains mcc data with older 35 ma lacustrine stable isotope and paleofloral records from the nearby house range ut usa whose paleoelevation has been determined independently through paleobotanical analysis each of the investigated compartments of the paleohydrologic system within the snake range mcc depicts a coherent scenario of low oligo miocene 18 o and d values of meteoric water that reflect precipitation sourced at high elevation a 77 difference in d water between the snake range d water 113 and the buckskin mountains d water 36 is consistent with minimum mean paleoelevation of the snake range of about 3850 650 m above miocene sea level additional support for such elevations comes from a comparison between the buckskin mountains mcc and the eocene house range basin ut usa where differences in 18 o water values are consistent with 2300 500 m minimum paleoelevation of the house range based on the presence of brecciated rock avalanche deposits within the sacramento pass basin we conclude that the snake range was a topographic high and locus of significant relief during regional scale extension within the cordilleran hinterland

formation of hydrothermal deposits at kings triple junction northern lau back arc basin sw pacific the geochemical perspectives an inactive hydrothermal field was discovered near kings triple junction ktj in northern lau back arc basin during 19th cruise of r v akademik mstislav keldysh in 1990 the field consisted of a large elongated basal platform the pedestal with several small chimneys on its periphery and one main mound superposed over it the surrounding region is carpeted with lava pillows having ferromanganese precipitate as infillings the adjoining second field consisted of small chimney like growths termed as christmas tree field the basal pedestal the peripheral chimneys and small christmas tree like growths samples collected by mir submersibles though parts of the same hydrothermal field differ significantly in their mineralogy and elemental composition indicating different history of formation the pedestal slab consisting of chalcopyrite and pyrite as major minerals and rich in cu is likely to have formed at higher temperatures than sphalerite dominated peripheral chimney extremely low concentration of high field strength elements e g zr hf nb and ta and enrichment of light ree in these sulfides indicate prominent influence of aqueous arc magma rich in subduction components the oxide growths in the christmas tree field have two distinct layers fe rich orange red basal part which seems to have formed at very low temperature as precipitates from diffused hydrothermal flows from the seafloor whereas mn rich black surface coating is formed from hydrothermal fluids emanated from the seafloor during another episode of hydrothermal activity perhaps this is for the first time such unique hydrothermal oxide growths are being reported in association with hydrothermal system here we discuss the possible processes responsible for the formation of these different hydrothermal deposits based on their mineralogy and geochemistry

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

shortening in the upper plate of the buckskin rawhide extensional detachment fault southwestern u s and implications for stress conditions during extension commonwealth post graduate research award u s geological survey national cooperative geologic mapping program under statemap g11ac20455

diachronous uplift and cooling history of the menderes core complex western anatolia turkey based on new zircon u th he ages abstract new u th he thermochronology data from the syn extensional granitoids in the central part of the menderes massif in western turkey reveal a minimum slip rate of 12 5 km myr along the alasehir detachment 14 dip angle and denudation rates between 1 75 km myr and 3 25 km myr between 4 ma and 2 ma these values suggest relatively fast exhumation of the central sub massif associated with cooling rates between 53 c myr and 128 c myr which are higher than the estimated footwall cooling rates 60 c myr to 120 c myr from the northern sub massif based on the initial crystallization ages of the syn extensional granitoid intrusions and their exhumation related cooling ages our thermochronological findings suggest that the central sub massif in menderes underwent accelerated uplift and faster exhumation in the latest cenozoic than the northern and southern sub massifs this latest doming and rapid extension of the central sub massif was associated with the asthenospheric upwelling beneath the region and the related na alkaline kula volcanism our results indicate that the menderes massif has had a diachronous uplift and cooling history during its extensional tectonic evolution in the late cenozoic thermal weakening of the young orogenic crust in western anatolia via both lithospheric and asthenospheric melting episodes and magmatism produced higher than normal geothermal gradients and played a significant role in core complex formation

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

glacier crevasses observations models and mass balance implications we review the findings of approximately 60 years of in situ and remote sensing studies of glacier crevasses as well as the three broad classes of numerical models now employed to simulate crevasse fracture the relatively new insight that mixed mode fracture in local stress equilibrium rather than downstream advection alone can introduce nontrivial curvature to crevasse geometry may merit the reinterpretation of some key historical observation studies in the past three decades there have been tremendous advances in the spatial resolution of satellite imagery as well as fully automated algorithms capable of tracking crevasse displacements between repeat images despite considerable advances in developing fully transient three dimensional ice flow models over the past two decades both the zero stress and linear elastic fracture mechanics crevasse models have remained fundamentally unchanged over this time in the past decade however multidimensional and transient formulations of the continuum damage mechanics approach to simulating ice fracture have emerged the combination of employing damage mechanics to represent slow upstream deterioration of ice strength and fracture mechanics to represent rapid failure at downstream termini holds promise for implementation in large scale ice sheet models finally given the broad interest in the sea level rise implications of recent and future cryospheric change we provide a synthesis of 10 mechanisms by which crevasses can influence glacier mass balance

geochemistry of manganese bearing cherts associated with alpine ophiolites and the hawasina formations in oman abstract based on correlation coefficients and analogies with studies on recent mn enrichments the major and trace elements of mn occurrences associated with ophiolites that have been variously affected by regional alpine metamorphism were attributed to different origins mn zn v ce nd and la are hydrothermal al ti k zr rb ga sc and some fe and pb are detrital and si p u y nb and the remainder of the fe are biogenic preliminary studies of mn occurrences in the wahrah formation of oman reveal a very similar geochemistry as the extensive exposure of this formation does not display any evidence of hydrothermal systems only a hydrothermal supply of mn to seawater from a distant source is envisaged for these and other deposits

geochemistry and origin of piemontite bearing and associated manganiferous schists from arrow junction western otago new zealand abstract closely spaced analyses for major minor and trace elements have been made through 3 m of manganiferous quartzose schists and immediately overlying quartzofeldspathic schists at arrow junction otago new zealand chemically the quartzose schists correspond to pelagic siliceous muds or brown clays rather than to typical cherts whole rock oxidation ratios fe 3 100 fe 3 fe 2 increase from 16 to 99 with increasing mn apart from sio2 al2o3 is the most abundant oxide in these rocks al2o3 correlates negatively with sio2 and positively with all other components analysed in the manganiferous quartzose schists including fe2o3 mno tio2 mgo cao na2o k2o ba cr cu ni pb rb v y zn and zr parameters such as al 2 o 3 100 al 2 o 3 mno and fe ti indicate that the quartzose schists have a higher hydrothermal plus hydrogenous component than average pelagic clays but a larger terrigenous component than typical metalliferous sediments from the crest and proximal flanks of the east pacific rise close covariance of al2o3 with tio2 and zr results in ratios ti al 50 10 3 and zr al 2 10 3 conforming closely with average shale and average new zealand alpine schist metasediments but less closely with average andesite the data exclude basalt or rhyolite as the dominant aluminous detrital component al ti and zr are regarded as being of predominantly terrigenous origin normalized for constant al2o3 the following elements are enriched in grey green and in pink piemontite bearing arrow junction quartzose schists relative to average new zealand alpine metase dimentary rocks by average factors indicated mn 32 44 ni 15 15 cu 5 12 si 3 6 2 6 pb 2 4 zn 2 8 2 5 fe 1 8 1 9 y 1 7 1 8 ba 1 2 1 6 and sr 1 0 2 0 the metal enrichment trend can be regarded as being imposed on the products of a silica dilution trend in which al2o3 was reduced to 4 by dilution of end member terrigenous sediment with non terrigenous silica about 97 98 of the mn 93 of the ni 79 91 of the cu 73 61 of the sio2 and 43 48 of the fe is considered to be of a non terrigenous hydrothermal hydrogenous biogenic origin in the quartzose schists covariance of elements other than si with al2o3 within the single bed investigated is attributed firstly to accumulation of femn oxides at a rate essentially constant relative to that of clay minerals and other aluminous phases though diluted by varying amounts of largely biogenic silica and secondarily to the sorptive scavenging properties of the femn oxides and of clay mineral components of the sediment although the base metals may ultimately have been introduced to the ocean from submarine hydrothermal systems these sediments originated at a site relatively remote from a fast spreading ridge or other active submarine hydrothermal source

late quaternary hydrothermal sedimentation adjacent to the central lau spreading center the partition geochemistry of 10 sediment cores collected adjacent to the southward propagating central lau spreading center clsc has been studied the hydrothermal oxide component in these sediments is mainly formed of mn oxides containing other hydrothermally associated elements e g fe zn cu mo and pb the mn oxides represent distal plume fall out derived from hydrothermal vents hydrothermal mn accumulation rates are between 2 6 and 74 4 mg cm 2 ka 1 during the 0 30 ka period and between 2 1 and 12 8 mg cm 2 ka 1 during the 30 120 ka period recent 30 ka hydrothermal input to the sediments adjacent to the clsc has been more variable than in the older sediments from the area this may be attributed to localised hydrothermal activity occurring behind the propagator and possibly to magma chamber development periods of enhanced hydrothermal input from the clsc at ca 30 ka and 175 ka appear to be contemporaneous along the clsc however an enrichment in mn at ca 112 ka probably represents distal hydrothermal plume fall out from increased activity on the valu fa ridge in the southern lau basin hydrothermal mn input derived from the clsc is below that from the vfr

hematite and mn oxide u th he dates from the buckskin rawhide detachment system western arizona gaining insights into hematite u th he systematics

mineralogy paragenesis and genesis of the braunite deposits of the mary valley manganese belt queensland australia the mary valley manganese deposits exhibit mineralogy and textures characteristic of at least four parageneses the deposits consist mainly of isolated occurrences of braunite together with a number of lower and higher valency manganese oxides and manganese silicates in bedded radiolarian cherts and jaspers of permian age the parageneses are a braunite quartz primary b braunite hausmannite spessartine tephroite quartz metamorphic c hydrated manganese silicates barite braunite hausmannite hydrothermal veins d tetravalent manganese oxides pyrolusite cryptomelane manjiroite nsutite supergene the primary mineralisation is interpreted as the result of the geochemical separation of mn from fe in a submarine exhalative system and the precipitation of mn as oxide within bedded radiolarian oozes and submarine lavas during diagenesis this hydrothermal manganese oxide reacted with silica to produce primary braunite the later geological of evolution of this volcanogenicsedimentary deposit involved metamorphism hydrothermal veining by remobilised manganese and supergene enrichment

very high slip rates on continental extensional faults new evidence from u th he thermochronometry of the buckskin mountains arizona abstract new u th he in apatite ages suggest rapid slip rates on the tertiary buckskin rawhide detachment fault which crops out in the buckskin and rawhide mountains of western arizona single crystal u th he in apatite ages were determined for a suite of crystalline rock samples from the footwall to this detachment the samples were collected from a transect parallel to the fault slip direction and proximal to the fault zone they show a linear decrease in age with distance from 14 to 11 ma over 15 km the age versus distance relationship is interpreted to show a slip rate of 4 2 1 2 0 8 mm yr continuing for a period of 3 myr this rate is more or less in agreement with but more precise than previously published slip rates from this and other large offset extensional detachments such slip rates are alarmingly high being roughly 5 10 times faster than rates commonly observed on active structures at the earth s surface these rapid slip rates suggest that significant seismic hazard might be posed by some extensional structures and they raise questions regarding the relationship between such rapidly slipping large offset structures and the slower smaller offset faults that are more commonly observed at the earth s surface

deep methane maxima and 3he anomalies across the pacific entrance to the celebes basin methane and 3he measurements have been performed in deep waters across the sills between the pacific ocean and celebes basin the in situ analyses of dissolved methane have led to the identification of several methane seeps along the flanks of the two south mindanao submarine ridges sangihe and talaud east mindanao 3he excesses in the celebes basin and east of talaud east mindanao ridge at 2000 3000 meter depths are in the range 21 22 a few percent above the philippine sea 3he background the isotopic ratio of the added he is 1 8 times the atmospheric ratio which indicates an input of hydrothermal fluids involving both mantle and crustal sedimentary components methane anomalies are partially associated with these 3he excesses the order of magnitude of the ch43he ratios is comparable to those observed in spreading axis hydrothermal fields at a few tens of kilometers from the top of the sangihe ridge conversely a major methane anomaly 90 times greater than the ch4 background of the philippine sea deep waters was measured at a depth where the waters show no 3he enrichment or anomalous water temperature versus the philippine sea background this result implies that methane could originate largely from shallow sedimentary layers

diffuse flow hydrothermal manganese mineralization along the active mariana and southern izu bonin arc system western pacific 1 abundant ferromanganese oxides were collected along 1200 km of the active izu bonin mariana arc system chemical compositions and mineralogy show that samples were collected from two deposit types fe mn crusts of mixed hydrogenetic hydrothermal origin and hydrothermal mn oxide deposits this paper addresses only the second type mn oxides cement volcaniclastic and biogenic sandstone and breccia layers mn sandstone and form discrete dense stratabound layers along bedding planes and within beds stratabound mn the mn oxide was deposited within coarse grained sediments from diffuse flow systems where precipitation occurred below the seafloor deposits were exposed at the seabed by faulting mass wasting and erosion scanning electron microscopy and microprobe analyses indicate the presence of both amorphous and crystalline 10 a and 7 a manganate minerals the fundamental chemical difference being high water contents in the amorphous mn oxides alternation of amorphous and crystalline laminae occurs in many samples which likely resulted from initial rapid precipitation of amorphous mn oxides from waxing pulses of hydrothermal fluids followed by precipitation of slow forming crystallites during waning stages the chemical composition is characteristic of a hydrothermal origin including strong fractionation between fe mean 0 9 wt and mn mean 48 wt for the stratabound mn generally low trace metal contents and very low rare earth element and platinum group element contents however mo cd zn cu ni and co occur in high concentrations in some samples and may be good indicator elements for proximity to the heat source or to massive sulfide deposits for the mn sandstones fe mean 8 4 and mn 12 4 are not significantly fractionated because of high fe contents in the volcaniclastic material however the proportion of hydrothermal fe nondetrital fe to total fe is remarkably constant 49 58 for all the sample groups regardless of the degree of mn mineralization factor analyses indicate various mixtures of two dominant components hydrothermal mn oxide for the stratabound mn and detrital aluminosilicate for the mn cemented sandstone and two minor components hydrothermal fe oxyhydroxide and biocarbonate biosilica our conceptual model shows that mn mineralization was produced by hydrothermal convection cells within arc volcanoes and sedimentary prisms that occur along the flanks and within calderas the main source of hydrothermal fluid was seawater that penetrated through fractures faults and permeable volcanic edifices the fluids were heated by magma enriched in metals by leaching of basement rocks and sediments and mixed with magmatic fluids and gases dikes and sills may have been another source of heat that drove small scale circulation within sedimentary prisms

geochemistry and u series dating of holocene and fossil marine hydrothermal manganese deposits from the izu ogasawara arc abstract this study investigated holocene and fossil hydrothermal manganese deposits in the izu ogasawara arc mineralogically these deposits comprise 10 a and 7 a manganate minerals and the fossil samples showed higher 10 a stabilities chemical compositions of the holocene samples are typical of other hydrothermal manganese deposits including low fe mn ratios low trace metals and low rare earth elements although the fossil samples generally have similar chemical characteristics they exhibit significant enrichment in ni cu zn cd ba ree tl and pb contents furthermore the chondrite normalized ree patterns showed more light ree enrichment trends these chemical characteristics suggest post depositional uptake of these metals from seawater u th dating of a holocene hydrothermal manganese deposit from the kaikata seamount indicated 8 8 0 94 ka for the uppermost layer and downward growth beneath the seafloor with a growth rate of ca 2 mm kyr this is approximately three orders of magnitude faster than that of hydrogenetic ferromanganese crusts u pb age of a fossil hydrothermal manganese deposit from the nishi jokyo seamount showed 4 4 1 6 ma which was contemporary with basaltic volcanism 5 8 0 3 ma hydrothermal manganese deposits contain high concentrations of high value mn but only small amounts of valuable minor metals their ages constrain the periods of past hydrothermal activity and provide a vector to explore for polymetallic sulfide deposits

geochemical characteristics of the recent sediments from the sea of marmara abstract six box cores one boomerang core and one hundred sixty six surface sediment samples recovered in the sea of marmara were analyzed in an attempt to establish the main controls on distribution and origin of trace metals within the oxic to suboxic basin of this sea surface and downcore data indicate that the abundance and distribution of the total metal concentrations for fe ni zn cr co cu and pb can largely be explained by the variable admixtures of terrigenous components in response to textural variations and biogenic calcareous components poor in metal contents the distribution of cr and ni seems to be controlled in part by a contribution from the weathering of basic ultrabasic sources on the coastal hinterland a small but significant amount of cu zn and pb in sediments from the northeastern sea of marmara probably suggests a pollution effect from the northerly located golden horn estuary that is known as one of the most polluted coastal regions of turkey looking at the data it seems that the mn concentrations are unusually high in the deep water sediments 4498 9127 ppm carbonate free along the east west trending marmara trough but low in sediments from the adjacent shallow waters 307 2059 ppm carbonate free the mn enrichment in deep water relative to shallow water marmara sediments is further indicated by the fe mn ratios being on average 11 23 in deep waters and 34 69 in shallow waters the contents of other metals fe ni zn cr co cu pb in both shallow and deep water sediments fall nearly within the same range as those found in average crustal and sedimentary rocks suggesting no significant enrichment of these metals in the deep marmara basins the downcore changes in the color from reddish brown at the surface top 2 5 cm to greenish gray in the subsurface 5 cm together with the occurrence of high mn concentrations in the surface sediment layers in cores can be attributed at least in part to the diagenetic mn enrichment within the sediment column the usually low organic carbon contents and biogenic components present in sediments reflect that the well known biogenic mechanism for the enrichment of mn seems to be of minor importance in the deep marmara waters the generally low mn concentrations contained in the surface grab and core sediments from the black sea and aegean sea approaching those of the sea of marmara do not provide any conclusion to support significant mn contribution from these two adjacent seas particularly from the so called manganese pump zones in the shallow black sea waters comparison with other deep sea sediments which have been deposited under the influences of hydrothermal activities worldwide suggests mn enrichment in deep water relative to shallow water sediments of the sea of marmara mainly as a result of hydrothermal contributions from this seismically active marine region based on the average fe mn ratios obtained in cores which tend to increase gradually from 11 in the deep central basin to 67 69 in the northeastern and southwestern shelves the central basin of marmara trough can be considered as a possible potential source for hydrothermal solutions leading to the enrichment of mn in the deep marmara waters however this remains to be further investigated

a modified theory of bottom crevasses used as a means for measuring the buttressing effect of ice shelves on inland ice sheets bottom crevasses are fractures that extend upward into floating ice shelves they form when seawater penetrates the base of the ice shelf and ruptures the ice up to the level at which englacial stresses equal the stress of the seawater for a freely floating ice shelf the penetrating level of closely spaced crevasses is estimated at about half the ice thickness h for an isolated crevasse the level is about h 4 however an analysis of the heights and locations of bottom crevasses in the ross ice shelf shows that none of the crevasses approach the predicted limits perhaps because the existing theory does not include the back stress b which is present in bounded ice shelves by reformulating the theory to include a back stress term b can be evaluated experimentally from radar measurements of crevasse height and ice thickness the magnitude of b 2 bars in the grid northwest corner of the ice shelf suggests the ice shelf is playing an important role in buttressing the inland ice sheet

geochemistry of hydrothermal manganese deposits from the pitcairn island hotspot southeastern pacific hydrothermal mn crusts from a submarine volcano in the pitcairn island region have been studied mineralogically radiometrically and by bulk and partition chemical techniques the crusts contain layers that comprise three morphological types a mechanism of formation by downward growth from a mn cemented surface sand hardpan is proposed age dating of the crusts suggests relatively recent and rapid formation mineralogically the crusts exhibit variable amounts of 10a and 7a manganite chemical data however indicate that the crusts do not show element associations characteristic of marine birnessite suggesting that the 7a manganite phase may have transformed from structurally unstable 10a manganite as a result of air drying trace element concentrations in massive finely laminated types 2 and 3 crust layers are significantly lower than those in similar crusts from island arc and back arc settings and in general are comparable with or lower than those of the most trace element poor crusts from mid oceanic ridge environments ree data suggest that these crusts are almost pure hydrothermal deposits with little or no hydrogenous component in the types 2 and 3 crusts only mo shows a significant enrichment that is likely to be hydrothermal in origin although it is enriched to lower levels than in hydrothermal crusts from most other geological settings friable mn cemented sand type 1 crusts contain elevated trace element concentrations in part as a result of incorporation of biogenic and volcaniclastic phases but also as a result of hydrogenous inputs consistent with their greater age and closer proximity to seawater in contrast to types 2 and 3 crusts which show no li enrichment type 1 crusts are enriched in li to levels above those that can be accounted for by hydrogenous input and a hydrothermal source for it is proposed the observed variability in the composition of hydrothermal mn crusts between midplate hotspot mid oceanic ridge island arc and back arc environments may be influenced by variability in basement composition and sea water rock ratio in the hydrothermal systems as both parameters are directly related to tectonic setting this may play an important role in controlling the chemistry of hydrothermal deposits

molybdenum isotopes in hydrothermal manganese crust from the ryukyu arc system implications for the source of molybdenum abstract a high concentration of molybdenum mo is a striking feature of modern marine hydrothermal manganese mn crusts from both low and high temperature hydrothermal systems however the origin of that mo is poorly constrained in this study we analyzed mo isotopic composition 98 95mo in a mn crust collected from the ryukyu arc system and assessed the possible use of 98 95mo to constrain the origin of mo in hydrothermal mn crusts along with mo isotope analysis we also measured the abundance of major and trace elements and the re os isotopic composition the mn crust sample had a high mn content 42 47 and was low in fe 0 2 0 5 among the manganophile elements co ni cu zn and mo only mo showed high concentrations 550 ppm we also found low contents of os 35 ppt with an isotopic composition of 187os 188os 1 00 these results are consistent with previously reported chemical compositions of hydrothermal mn crusts 98 95mo values in the sample ranged from 0 56 to 0 66 which are 2 7 lighter than the present day seawater 98 95mo but similar to those in modern hydrogenous fe mn crusts and mn nodules although current data do not preclude the possible contribution of hydrothermally derived mo the light 98 95mo values can be explained by isotope fractionation associated with a change in coordination number during the adsorption of mo from seawater onto mn oxides we suggest that the 98 95mo data are useful for constraining the source of mo in hydrothermal mn crusts

mineralogy and geochemistry of two metamorphosed sedimentary manganese deposits sierra nevada california usa abstract laminated to massive rhodochrosite hausmannite and mn silicates from the smith prospect and manga chrome mine sierra nevada california were deposited as ocean floor sediments associated with chert and shale the principal lithologies at smith are chert argillite rhodochrosite hausmannite and chlorite rich layers and relatively uncommon layers of jacobsite the manga chrome mine also contains layers rich in manganoan calcite and caryopilite tephroite rhodonite spessartine and accessory alleghanyite and sonolite formed during metamorphism volcaniclastic components are present at manga chrome as metavolcanic clasts and as mn poor red garnet and hematite rich layers there is no evidence such as relict lithologies that mn was introduced into mn poor lithologies such as chert limestone or mudstone replacement of mn poor phases by mn rich phases is observed only in the groundmass of volcanic clasts that appear to have fallen into soft mn rich mud manganiferous samples from the smith prospect and manga chrome mine have high mn fe and low concentrations of ni cu zn co u th and the rare earth elements that are similar to concentrations reported from other ancient mn deposits found in chert greenstone complexes and from manganiferous sediments and crusts that are forming near modern sea floor vents the sierra nevada deposits formed as precipitates of mn rich sediments on the sea floor probably from mixtures of circulating hydrothermal fluids and seawater the composition of a metabasalt from the smith prospect is consistent with those of island arc tholeiites metavolcanic clasts from the manga chrome mine are compositionally distinct from the smith metabasalt and have alkaline to calc alkaline affinities a back arc basin is considered to be the most likely paleoenvironment for the formation of the mn rich lenses at the manga chrome mine and by association the smith prospect layers of rhodochrosite hausmannite and chert preserve the composition and some textures of the sedimentary protoliths at both sierra nevada deposits jacobsite rich layers probably represent a fe rich protolith caryopilite and manganoan calcite represent additional protoliths at the manga chrome mine the metamorphic assemblage prehnite chlorite epidote calcite in a metabasalt from the smith prospect constrains regional metamorphic conditions to a maximum temperature of 325 c and a pressure of 2 kbar slightly higher temperatures are indicated by the presence of actinolite in another metabasalt compositions of mn rich minerals in smith samples are consistent with these metamorphic conditions

implications of middle eocene epizonal plutonism for the unroofing history of the bitterroot metamorphic core complex idaho montana petrologic and geochronologic limits on the progression of east directed extensional unroofing of the bitterroot metamorphic core complex provide a means to compare rates of denudation across the footwall during the earlystages of extensional denudation u pb and 4 0 ar 3 9 ar data from epizonal plutons in the northwestern and southwestern bitterroot metamorphic core complex demonstrate that much of the western footwall was exhumed to shallow levels 1 5 km by ca 49 ma while eastern footwall rocks remained at high temperatures following an episode of isothermal decompression u pb ages of epizonal plutons along the western margins of the footwall suggest that as much as 13 km of unroofing occurred between anatectic melting of belt supergroup metasedimentary rocks in the western footwall no later than 56 ma and emplacement of the adjacent epizonal lolo hot springs batholith at ca 49 ma in the northwestern bitterroot range tectonic denudation during this interval removed roughly the same amount of overburden from eastern footwall rocks suggesting that the initial stages of unroofing may have been accommodated by a planar moderately east dipping 30 50 shear zone 4 0 ar 3 9 ar cooling data show that cooling in the western footwall was synchronous with unroofing in contrast we suggest that a significant delay in cooling of eastern footwall rocks may have resulted from a slight increase in geothermal gradient following this unroofing stage exposure of a west dipping mylonitic shear zone along the western limb of the bitterroot complex may provide a key for interpreting the postmylonitic structural evolution of the core complex if this shear zone can be correlated to the bitterroot mylonite zone to the east then strong evidence for flexural uplift consistent with postmylonitic passage of a rolling hinge emerges

a zero damage model for fission track annealing in zircon a zircon fission track annealing model is calculated on the basis of annealing experiments from the literature with induced tracks in decay event damage free zircon samples empirically derived parallel and fanning equations for this zero damage model yield an excellent fit to the data with the fanning model providing slightly better statistical parameters a comparison between annealing models with fanning iso annealing lines but different decay event damage densities reveals that annealing temperatures and closure temperatures for the estimated partial annealing zone are highest for the zero damage model compilations of existing geologic constraints on the zircon partial annealing zone on one hand and the zircon closure temperature on the other show that these constraints do not or only partly overlap with curves of proposed models for the zircon partial annealing zone and closure temperature this finding is consistent with the fact that the annealing behavior of zircon from long duration temperature evolutions is increasingly influenced by the accumulated decay event damage zircon samples of young age or low u content show a behavior closest to the predictions of the zero damage model and are in the predicted range of published models with low decay event damage density for thermal events of more than 10 myr duration however constraints from field studies show marked differences from proposed partial annealing zone boundaries of the zero or low damage models the applicability of the zero damage model is threefold 1 it predicts correct closure temperatures in the case of very rapid cooling across the partial annealing zone where basically no decay event damage is accumulated 2 it predicts an uppermost boundary for complete annealing of a mixture of zircon components of different age as found in sedimentary samples and in this case may be used as a thermometer 3 it represents an important reference for the establishment of a more comprehensive model of zircon fission track annealing that also includes the influence of decay event damage for such a model two different equations are discussed however additional detailed experimental and field data are needed for a more robust annealing model that includes the influence of decay event damage annealing

hydrothermal metallogenic processes off the islands of nisiros and kos in the hellenic volcanic arc abstract two submarine hydrothermal fields off nisiros and kos islands in the eastern sector of the hellenic volcanic arc have been investigated using analyses of submarine hydrothermal waters and sediments both the waters and the sediments were found to be enriched in fe mn and zn together with as mo and v in the sediments only resulting from seawater rock interaction processes similar to those described from mid ocean ridge systems differences found between the products of these processes in the two hydrothermal fields studied reflect differences between the rock types being leached the physiographic and geological conditions present including the thickness and composition of the sediment column above the volcanic rocks and the rates of mixing of hydrothermal solutions with normal seawater the geochemical features described support possible sub seafloor formation of metal sulphides at both of the hydrothermal fields studied

permian hydrothermal deposits in the mino terrane central japan implications for hydrothermal plumes in an ancient ocean basin abstract geochemical features of metalliferous deposits cherts and basalts from the early permian hashikadani formation in the mino terrane central japan were studied the metalliferous deposits occur as thin fe rich layers about 5 cm thick and mn rich crusts up to 30 cm thick in cherts overlying basalt the fe rich layers contain large amounts of magnetite and are intercalated in the massive chert unit just above the basal basalt the mn rich crusts occur in the bedded chert unit which always overlies massive cherts and their dominant mn mineral is braunite these metalliferous deposits show highly fractionated mno fe 2 o 3 total iron as fe 2 o 3 values and are depleted in such elements as ni co cu and zn these features indicate their hydrothermal origin the values of fe 2 o 3 feo and mno fe 2 o 3 in samples abruptly increase above the lithologic boundary between the massive chert and the bedded chert units this stratigraphic change of lithofacies and chemical characteristics can be attributed to the precipitation of fe oxides prior to mn oxides from a hydrothermal solution that was gradually diluted with seawater and became oxic the formation process of the permian metalliferous deposits from central japan can be inferred by analogy with modern hydrothermal deposits recently discovered along active spreading centres

geochemistry of hydrothermal mn oxide deposits from the s w pacific island arc abstract hydrothermal mn oxide crusts have been removed from the tonga kermadec ridge the first such hydrothermal deposits to be reported in the s w pacific island arc in several respects the deposits are similar to hydrothermal mn crusts from oceanic spreading centre settings they are limited in areal extent comprise well crystalline birnessite and generally display extreme fractionation of mn from fe they are strongly depleted in many elements compared to hydrogenous mn deposits but are comparatively enriched in li zn mo and cd the group ia and group iia metals show strong intercorrelations and the behaviour of mg in the purest samples may indicate the extent to which normal seawater has influenced the composition of the deposits certain aspects of the deposits are not typical of hydrothermal mn deposits in particular at least some of the crusts have developed on a sediment or unconsolidated talus substrate some crusts or specific layers within some crusts display a chemical composition which suggests a significant input from normal seawater

spatial arrangement and size distribution of normal faults buckskin detachment upper plate western arizona abstract fault arrays typically include a wide range of fault sizes and those faults may be randomly located clustered together or regularly or periodically located in a rock volume here we investigate size distribution and spatial arrangement of normal faults using rigorous size scaling methods and normalized correlation count ncc outcrop data from miocene sedimentary rocks in the immediate upper plate of the regional buckskin detachment low angle normal fault have differing patterns of spatial arrangement as a function of displacement offset using lower size thresholds of 1 0 1 0 01 and 0 001 m displacements range over 5 orders of magnitude and have power law frequency distributions spanning four orders of magnitude from less than 0 001 m to more than 100 m with exponents of 0 6 and 0 9 the largest faults with 1 m displacement have a shallower size distribution slope and regular spacing of about 20 m in contrast smaller faults have steep size distribution slopes and irregular spacing with ncc plateau patterns indicating imposed clustering cluster widths are 15 m for the 0 1 m threshold 14 m for 0 01 m and 1 m for 0 001 m displacement threshold faults results demonstrate normalized correlation count effectively characterizes the spatial arrangement patterns of these faults our example from a high strain fault pattern above a detachment is compatible with size and spatial organization that was influenced primarily by boundary conditions such as fault shape mechanical unit thickness and internal stratigraphy on a range of scales rather than purely by interaction among faults during their propagation

active post depositional oxidation of the most recent sapropel s1 in sediments of the eastern mediterranean sea abstract over a wide area of the eastern mediterranean basin two mn rich layers have been observed above the most recent sapropel s1 one immediately above the sapropel top and one a few centimetres closer to the sediment surface different mechanisms have been proposed to explain the occurrence of these two mn peaks either both peaks have a diagenetic origin in which case the upper mn peak is actively forming or the lower peak is actively forming and the upper peak has a different formation mechanism high resolution porewater including a gel sampler used for the first time in marine sediments and solid phase data are now used to demonstrate that the oxidation front is located at the level of the lower mn peak which therefore is presently being formed a barium organic carbon relationship is used to calculate the initial organic carbon profile of the s1 sapropel the palaeoproductivity profiles generated by this method demonstrate that the original sapropel unit was bounded by the upper mn peak this implies that the interval between the two mn peaks where a low organic carbon content is now observed was originally part of the sapropel the initially deposited organic carbon has been oxidised by a progressive downwards moving oxidation front the penetration depth of this oxidation front i e the distance between the two mn peaks is mainly determined by the organic carbon content the sediment accumulation rate and the bioturbation depth the upper mn peak appears to have formed as a result of either mn precipitation upon oxygenation of previously anoxic eastern mediterranean deep water or preservation of a surficial mn peak at the end of the high productivity episode in either case the upper mn peak marks the end of sapropel formation as indicated by the ba profiles this means that formation of the s1 sapropel ceased more recently than is indicated by radiocarbon dating of the visible top of s1

calcareous nannofossil biostratigraphic dating of a ferromanganese crust from schumann seamount abstract calcareous nannofossil biostratigraphy was employed to determine the age and growth rates of the different layers within ferromanganese crusts from schumann seamount 200 miles north of the island of kauai hawaii this work is part of a study to reconstruct the paleoceanographic history of crusts using various geochemical indicators the methods are based on the identification of coccolith imprints not actual coccolith remains age constraints on the time span of a particular horizon are defined either 1 by the presence of a species which was extant for only a limited geological time interval or 2 by the presence of two organisms whose time ranges overlapped age resolution is optimized by short time ranges or narrow overlaps in the crust studied there was considerable inter horizon variability in the preservation of coccolith imprints in imprint abundance and in species diversity some of the crust layers examined were narrowly constrained temporally 1 4 myr while others were less so 10 myr our results indicate that the minimum age for the interval at 27 mm depth is at least eocene this is the maximum age many believe any crust can be the position of this interval however is only about one half of the way through the crust while the data support previous estimates of average crust growth rates 0 5 mm myr the actual apparent growth rate appears to have varied by an order of magnitude 0 1 to 2 mm myr

an experimental investigation of high temperature interactions between seawater and rhyolite andesite basalt and peridotite natural seawater was allowed to react with rhyolite andesite basalt and peridotite at 200 500 c and 1 000 bars at water rock mass ratios of 5 and 50 in order to investigate the effects of rock type water rock ratio and temperature on solution chemistry and alteration mineralogy the results indicate that interactions of seawater with various igneous rocks are similar in the production of a hydrous mg silicate and anhydrite as major alteration products fluids involved in the interactions lose mg to alteration phases while leaching fe mn and si from the rocks the ph of the solutions is primarily controlled by mg oh silicate formation and therefore varies with mg and si concentration of the system other reactions which involve mg such as mg ca exchange or which produce free h cause major differences in fluid chemistry between different seawater rock systems high water rock ratio systems 50 1 are generally more acidic and more efficient in leaching than low ratio systems 5 1 due to relatively more seawater mg available for mgsilicate production the experiments show that large scale seawater rock interaction could exert considerable control on the chemistry of seawater as well as producing large bodies of altered rock with associated ore deposits

anomalous 234 u 238 u ratios in deep sea hydrothermal deposits although hydrothermal ferromanganese deposits often display variable 234u 238u ratios1 5 published values generally do not differ by more than 20 from the seawater value of their hydrogenous counterparts6 here we report very high 234u 238u ratios in hydrothermal manganese crusts recovered from the sanghihe island arc system in the west pacific such ratios about twice that of normal seawater confirm a low temperature hydrothermal supply of uranium which is best explained by leaching of the underlying rocks by the hydrothermal fluids and deposition together with the manganese oxides before mixing with seawater this suggests that the 234u 238u in seafloor deposits may be used as a tracer of low temperature hydrothermal reactions in the ocean crust

the partition of vanadium and molybdenum between manganese oxides and sea water abstract the partition of v and mo between manganese oxides and sea water was investigated in the sea water supply system for aquaria at the marine science museum tokai university where both todorokite and birnessite are precipitated from aerated well sea water the distribution coefficient of v was an order of magnitude higher than that of mo assuming that the distribution coefficients can be applied to marine environments and that manganese oxides are precipitated from sea water the calculated contents of these oxyanionic elements in manganese oxides were comparable to those in marine manganese nodules

mn fe oxyhydroxide crusts from krylov seamount eastern atlantic mineralogy geochemistry and genesis abstract mn fe oxyhydroxide crusts from krylov seamount located in the eastern atlantic on the cape verde plate have been studied mn fe mineralisation on this seamount occurs mostly in the form of 1 10 cm thick crusts on hydrothermally altered subalkali and alkali volcanic breccias and basalts the lower crust layers are composed of fe vernadite mno2 and goethite with admixtures of mixed layered asbolane buserite the upper crust layers consist of fe vernadite and mn feroxyhyte with subordinate amounts of birnessite mixed layered asbolan buserite and goethite the mineral composition and geochemical relationships indicate a general tendency to change from the base to the top of crusts from components characteristic of hydrothermal input to those of hydrogenetic origin crust compositions suggest that diagenetic transformations of mineral phases occurred during the evolution of the crusts

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

development of extension parallel corrugations in the buckskin rawhide metamorphic core complex west central arizona extension parallel detachment fault corrugations are one of the defining features of metamorphic core complexes yet the origin of these corrugations remains disputed structural data from the buckskin rawhide metamorphic core complex in west central arizona demonstrate that prominent ne trending detachment fault corrugations are folds produced by extension perpendicular nw se shortening during the middle to late stages of core complex extension ca 18 10 ma kinematic data indicate that dominant ne directed slip on the buckskin rawhide detachment fault was locally overprinted by nw and se directed slip associated with corrugation folding the last motion recorded along several nw and se dipping flanks of the detachment fault is reverse slip directed toward the corrugation antiform hinges orientation patterns of upper plate bedding across the corrugations are compatible with folding about a ne trending axis extension perpendicular shortening in the lower plate is recorded by synmylonitic constriction and folding constriction and grain scale y axis shortening were most important during the later stages of mylonitization in the synextensional swansea plutonic suite which typically form l s tectonites upright meter and kilometer scale lower plate folds parallel the detachment fault corrugations and are best developed in well layered pre tertiary rocks most lower plate folding occurred by postmylonitic flexural slip that was coeval with detachment faulting the total amount of nw se shortening across the lower plate is 10 but the amount of nw se shortening recorded by the younger detachment fault is only 1 the relatively late stage development of corrugations in the buckskin rawhide metamorphic core complex suggests that the constriction and corrugation folding developed primarily in response to crustal thinning and tectonic denudation

genesis of manganese deposits in southwestern amazonia mineralogy geochemistry and paleoenvironment abstract chemical analysis xrd sem and empa were carried out on five manganese deposits in southwestern amazonia brazil to determine their sources of mn their lithostratigraphic units the environment in which mn accumulated during the proterozoic and the effects of weathering since the late cretaceous on the mineralization process the sedimentary hydrothermal and lateritic environments in this area produced a wide and complex variety of structures textures minerals and geochemical features where coronadite hollandite and romanechite as the main mn minerals changed their chemical compositions during the lateritization process in this context during lateritization more mobile elements mgo cao na 2 o and k 2 o were removed while concentrations of sio 2 al 2 o 3 fe 2 o 3 mno pb and co increased the high concentrations of cu pb and tl and the presence of positive gd anomalies galena and nuggets of ag and zn ni mno 2 in both the protoliths and duricrusts indicate that the ze juliao apui and novo natal deposits record the influences of sulfide and hydrothermal activity the ree zr hf vs tio 2 1000 co ni ratios indicate that felsic and mafic rocks were the sources of mn in these samples

geochemical and iron isotopic insights into hydrothermal iron oxyhydroxide deposit formation at loihi seamount abstract low temperature hydrothermal vents such as those encountered at loihi seamount harbor abundant microbial communities and provide ideal systems to test hypotheses on biotic versus abiotic formation of hydrous ferric oxide feox deposits at the seafloor hydrothermal activity at loihi seamount produces abundant microbial mats associated with rust colored feox deposits and variably encrusted with mn oxyhydroxides here we applied fe isotope systematics together with major and trace element geochemistry to study the formation mechanisms and preservation of such mineralized microbial mats iron isotope composition of warm 2 s depleted hydrothermal fluids yielded 56 fe values near 0 1 indistinguishable from basalt values suspended particles in the vent fluids and feox deposits recovered nearby active vents yielded systematically positive 56 fe values the enrichment in heavy fe isotopes between 1 05 and 1 43 relative to fe ii in vent fluids suggest partial oxidation of fe ii during mixing of the hydrothermal fluid with seawater by comparing the results with experimentally determined fe isotope fractionation factors we determined that less than 20 of fe ii is oxidized within active microbial mats although this number may reach 80 in aged or less active deposits these results are consistent with fe ii oxidation mediated by microbial processes considering the expected slow kinetics of abiotic fe oxidation in low oxygen bottom water at loihi seamount in contrast feox deposits recovered at extinct sites have distinctly negative fe isotope values down to 1 77 together with significant enrichment in mn and occurrence of negative ce anomalies these results are best explained by the near complete oxidation of an isotopically light fe ii source produced during the waning stage of hydrothermal activity under more oxidizing conditions light fe isotope values of feox are therefore generated by subsurface precipitation of isotopically heavy fe oxides rather than by the activity of dissimilatory fe reduction in the subsurface overall fe isotope compositions of microbial mats at loihi seamount display a remarkable range between 1 2 and 1 6 which indicate that fe isotope compositions of hydrothermal fe oxide precipitates are particularly sensitive to local environmental conditions where they form and are less sensitive to abiotic versus biotic origins it follows that feox deposits at loihi seamount provides important modern analogues for ancient seafloor fe rich deposits allowing for testing hypotheses about the biogeochemical cycling of fe isotopes on early earth

submarine hydrothermal activity and mineralization on the kurile and western aleutian island arcs n w pacific the kurile arc consists of at least 100 submarine volcanoes and 5 submarine caldera located mainly in the rear arc the arc is seismically very active particularly in the south and is characterized by extensive volcanism and hydrothermal activity at least one subaerial volcano on the arc medvezhy located on iturup island has an extremely shallow magma chamber and is intensely active three types of submarine hydrothermal deposit were recovered from this area hydrothermal manganese crusts nontronite and hydrothermal manganese crusts overlain by hydrogenous manganese oxides in addition submarine hydrothermal fe oxyhydroxides enriched in p were sampled from the submerged caldera of kraternaya bight in the central part of the arc these deposits appear to be analagous to deposits from santorini caldera on the aegean arc piip submarine volcano located in the western aleutian arc is characterized by two shallow summit craters both intermediate temperature anhydrite gypsum barite amorphous silica pyrite calcite and aragonite and low temperature nontronite fe oxyhydroxides hisingerite and ferromanganese crusts hydrothermal minerals were recovered from this seamount together with bacterial mats and giant clams the maximum measured temperature of the hydrothermal fluids was 133 c although the actual temperature may have reached 250 c both the kurile and aleutian arcs have the potential to host major submarine hydrothermal systems detailed exploration of these poorly studied areas using modern geophysical geochemical and sampling techniques is therefore strongly recommended

precious metals in ferromanganese crusts from the south west pacific little is known about the abundance distribution and origin of the precious metals in marine ferromanganese materials1 4 although it has long been recognized that elements such as silver and gold are frequently enriched in ferromanganese nodules when compared with average crustal abundance5 relative to crustal abundance silver is enriched in nodules5 by a factor of between 50 and 100 and for gold enrichment factors of between 100 and 1 000 have been found3 we know of no similar data in the literature for silver and gold in ferromanganese crusts although halbach et al 4 have described enrichment of platinum in crusts from the central pacific region elsewhere precious metals show significant enrichment possibly to economic grades in massive sulphide deposits associated with active spreading centres such as the east pacific rise and the red sea6 8 we now report an unusual occurrence of silver and gold in ferromanganese crusts from a back arc setting in the south west pacific to our knowledge the first report of material of this kind

the transition from large magnitude extension to distributed dextral faulting in the buckskin rawhide metamorphic core complex west central arizona brittle fault data from the buckskin rawhide metamorphic core complex west central arizona document the miocene transition from large magnitude ne directed extension to distributed e w extension and dextral faulting the buckskin rawhide detachment fault locally records a clockwise rotation of the slip direction from dominant top ne directed slip to ene and e directed slip during the last stages of activity postmylonitic brittle deformation is dominated by normal and dextral slip along moderately to steeply ne dipping faults relative timing relationships indicate that most postmylonitic normal faulting was coeval with middle miocene detachment fault slip whereas dextral and oblique dextral faulting postdates detachment fault slip post 11 ma based on the persistent sw dip of lower plate fabrics and ne dip of abundant normal faults the amount of ne sw brittle extension across the mylonitic lower plate is estimated to be 20 30 in several areas the end of detachment faulting in the buckskin rawhide metamorphic core complex was marked by a transition to dominantly e w extension and associated dextral normal faulting at least 10 ne dipping postdetachment faults record 0 1 1 km dextral or oblique dextral displacement the cumulative amount of dextral shear across the core complex is probably 7 9 km which is the amount needed to restore the topographic trend of lower plate corrugations into alignment with the dominant extension direction postdetachment dextral transtensional faulting across the core complex reflects the increasing influence of the diffuse pacific north america transform plate boundary toward the end of the middle miocene

late stage evolution of the chemehuevi and sacramento detachment faults from apatite u th he thermochronometry evidence for mid miocene accelerated slip the unique low temperature sensitivity of the apatite u th he ahe technique provides valuable new information relating to the late stage thermal evolution of metamorphic core complexes in the southern basin and range province in all the ranges studied the data show greater complexity than previously seen from other thermochronometers in the chemehuevi and northern sacramento mountains a trend of decreasing ages toward the northeast applies only for the structurally shallowest parts of the footwall this is followed by essentially age invariant segments of 15 1 ma reflecting an increase in the rate of detachment fault movement the timing of the change suggested by the data agrees with recently published ahe results from the nearby harcuvar mountains located 125 km to the southeast suggesting that an underlying regional mechanism triggered this change plate reconstructions indicate that the pioneer mendocino fracture zone migrated northward through the area at this time leaving a slab window in its wake we suggest that the additional heat applied to the base of the lithosphere from the slab window resulted in mechanical weakening of the area and that this combined with the extensional strain regime present resulted in an increased rate of slip within the actively extending metamorphic core complexes this agrees well with timing constraints for extension onset in the central basin and range province of southern nevada and suggests that weakening of the southern basin and range province at 15 1 ma was partially responsible for the onset of extension in the central basin and range these findings demonstrate that improved constraints on changes in extension rate within the basin and range province should be possible through the application of the ahe technique to other metamorphic core complex footwalls

submarine hydrothermal metallogenesis associated with the collision of two plates the southern aegean sea region abstract the geochemistry of sediments from the southern aegean sea demonstrates that the active tectonics in the hellenic arc trench system favor hydrothermal mineralization processes involving leaching of oceanic crust the distribution and geochemical behavior of mn fe cu zn p and ba indicate a hydrothermal influence i at plate boundaries such as the pliny and strabon trenches ii in fore arc basins such as maleas iraklion and karpathos iii on the island arc all fore arc basins having greater mn enrichments than the trenches are also characterized by higher heat flow values the greatest mn enrichments occur at maleas basin where a mn dispersion halo is recognized this basin is very tectonically active with the largest group of normal faults along the planes of which magmatic material was injected and the highest heat flow values in the sea of crete it also falls in the eastern mediterranean zone of high seismic activity because the fe mn sediments identified in the above geotectonic units are the end members of the hydrothermal fractionation sequence known from areas where leaching of oceanic crust occurs it is suggested that other members of the sequence such as metal sulfides may be found significant geochemical anomalies of pb and zn found in areas of high heat flow and on lines of normal faulting are considered to be traces of the presence of metal sulfides

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

local variability of manganese nodule facies on small abyssal hills of the central pacific basin abstract local variability of manganese nodule facies and associated sediments were studied around abyssal hills 60 60 km 2 located in the equatorial zone of the central pacific basin small scale variations in nodule occurrence mineralogy chemistry and internal structure are discussed in relation to seismic records and sediment lithology the slow sedimentation rate from the late tertiary to the quaternary appear to have promoted formation of nodules around the abyssal hills although the plio pleistocene hiatus at depths below sediment surface suggests no clear evidence of increased growth of nodules during the period in the area of rapid and continuous sedimentation away from the hill areas nodules are rare probably because of insufficient lifting force for nodules mineralogical and chemical studies reveal that the two principal nodule morphologies smooth and rough surfaces result from preferential deposition of hydrogenous or diagenetic manganese minerals in relation to early diagenesis of surface siliceous sediments regional variability of nodule surface morphology and composition suggests a very local change in sedimentary conditions in space and internal mineral variation suggests changes in sedimentary conditions with time the geological factors controlling the small scale variability of nodule facies seem to be similar to those controlling regional scale variations

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

fish antifreeze proteins and the creep of polycrystalline ice les courbes de fluage obtenues a partir d echantillons de glace polycristalline contenant des concentrations faibles de glycopeptides antigel ne montrent pas l acceleration tertiaire trouvee dans les echantillons de glace pure ces resultats sont compatibles avec des travaux anterieurs montrant que ces proteines interdisent la migration des joints de grains dans la glace vue que le fluage tertiaire est associe avec la nucleation et la croissance de nouveaux grains de glace

chemical environments of deposition of ancient iron and manganese rich sediments and cherts despite detailed classification criteria to distinguish between marine and freshwater environments of deposition in fine grained non clastic sedimentary rocks are scanty data on recent lacustrine and marine chemical precipitates reveal that these two environments can be distinguished in terms of their composition in the cao mgo na2o k2o system provided carbonates and detrital components associated with them are trivial lacustrine ferromanganese precipitates display low na2o and k2o but a high cao cao mgo ratio 0 70 similar to the world average river water in contrast diagenetically mature marine ferromanganese precipitates and nodules show a lower 0 60 cao cao mgo ratio in general and variable na2o and k2o recent pelagic cherts reveal an average cao cao mgo ratio comparable to that of ocean water whereas those affiliated to ocean floor hydrothermal activity span a wide range of composition in cao mgo na2o k2o space and mostly avoid the lacustrine field extension of the observed relations to the ancient archean bifs and cherts from 1 isua supracrustals greenland 2 yilgarn block australia 3 montana usa and proterozoic bifs from 4 hamersley basin australia 5 labrador trough canada 6 biwabik iron formations usa and the late proterozoic 7 upper tindhir group iron formation alaska and many others reveal a marine signature corroborating the inferences based on ree and isotope studies however chemical data on a number of deposits including the late proterozoic bifs mn deposits and cherts from the damara orogen africa bifs from rapitan formation northwest territories canada and several proterozoic mn deposits and cherts from india suggest a freshwater chemical environment of deposition the concurrence in the results obtained from studies on iron and or manganese deposits and coexisting cherts from several archean proterozoic and phanerozoic basins suggests that the chemistry of the more abundant siliceous sedimentary rocks can provide an additional tool for palaeogeographic reconstruction

metamorphic core complexes windows into the mechanics and rheology of the crust metamorphic core complexes are products of normal fault displacements sufficient to exhume rocks from below the brittle ductile transition these faults detachments may initiate within the brittle crust at steep angles but they sole into the ductile middle crust and during displacement rotate to gentler dips due to hanging wall extension the exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping low friction shallow segments of the detachment metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress strain localization and strain rate with decreasing temperature providing a window into physical conditions and deformational processes in the mid crust the metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault in addition to those accompanying exhumation these processes may include diapiric emplacement of gneiss domes or exhumation in a subduction channel and may not be directly related to formation of the core complex factors favouring core complex formation are high gravitational potential energy of the extending crust weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence

hydrothermal sedimentation adjacent to the propagating valu fa ridge lau basin sw pacific abstract the partition geochemistry and hydrothermal metal accumulation rates ar during the late quaternary 3 km from hydrothermally active areas still shows an enrichment of mn ag ba and zn when compared to regional 500 m depth lau basin sea water the elements ni zn cu co and mo are associated with mn oxides in the sediment and are thought to have been scavenged by hydrothermal oxides during the transport of hydrothermal oxides away from the spreading center only a low proportion of fe is bound to the hydrothermal oxide phase in the sediments and this element is mainly associated with silicate phases principal components analysis pca of geochemical data in the detrital free caco 3 free fraction of the sediments supports a geochemical hydrothermal oxide association between mn ni mo cu zn pb p be ba and la with fe associated with the silicate weathered detrital fraction iron manganese ratios in the oxide phase range between 1 2 and 2 8 these values are below those found in sediments at mid ocean ridges peaks in the downcore distribution in mn appear to be contemporaneous in the cores studied and are probably the result of hydrothermal discharges on the vfr hemipelagic sedimentation rates throughout the area average 2 3 cm ka 1 hydrothermal mn ar range between 3 and 82 mg cm 2 ka 1 during the 0 30 ka b p period and between 5 and 65 mg cm 2 ka 1 during the 30 120 ka b p period maximum mn ar adjacent to the vfr are comparable to the highest values previously reported for recent sediments proximal to the east pacific rise epr during the entire period 0 120 ka b p mn ar are highest in core so48 101 located about 90 km behind the propagating tip of the vfr recent hydrothermal input has also occurred about 33 km behind the propagator this is in accord with the suggested location of fully evolved steady state magma chambers occurring some distance tens of kilometers behind propagating rift tips

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

a model for the formation of hydrothermal manganese crusts from the pitcairn island hotspot the distribution of elements in the hydrothermal mn crusts from the pitcairn island hotspot can be explained by considering processes occurring within the hotspot volcano these include the role of boiling of the ascending hydrothermal fluid which leads to sulphide deposition and seawater intrusion into the upper part of the volcano this in turn results in the development of an oxycline above which feooh can precipitate the high mn fe ratios and low contents of ni and zn in the massive crusts are thought to reflect the rapid incorporation of the ore elements into sulphide minerals such that only a small proportion of these elements are available for incorporation in the crusts the small positive eu anomaly in the crusts on a nasc normalized basis reflects the lower temperatures in the hydrothermal fluids at the pitcairn island hotspot 25dgc compared to those at mid ocean ridges c 350 c the oxyanions cro42 vo43 aso43 and po43 the rare earth elements ree and th are scavenged by feooh particles within the upper part of the seamount and can therefore be incorporated into the crusts associated with the fe rich phase molybdenum and uranium are scavenged in only negligible amounts by the feooh molybdenum is therefore most probably scavenged from seawater by manganese oxides during the actual formation of the mn crusts the alkali metals li rb and cs remain in solution in the hydrothermal fluids and are selectively incorporated into the buserite structure of the mn crusts in the absence of strong competition from the divalent transition metal ions the compositional characteristics of the hydrothermal mn crusts can therefore be explained in terms of a simple model of element scavenging and uptake occurring mainly within the seamount a laser ablation icpms profile in one of the hydrothermal crusts ds 63 4 revealed varying ree concentrations and patterns in the different layers of the crust these data indicate that the hydrothermal component was variable during the formation of the crust it was calculated to be almost 100 in the upper 18 0 mm of this crust apart from the samples at 6 0 8 0 mm and about 80 in the lower layers

comparison between datangpo type manganese ores and modern marine ferromanganese oxyhydroxide precipitates based on rare earth elements abstract datangpo type sedimentary manganese deposits which are located in northeastern guizhou province and its adjacent areas are mn carbonate type deposits hosted in black carbonaceous shale that represent a series of medium to large deposits containing a huge tonnage of reserves paas normalized rare earth element distribution patterns of manganese ores record hat shaped rey ree y plots characterized by pronounced middle rare earth element enrichment evident positive ce anomalies weak to strong positive eu anomalies and negligible negative y anomalies these rey geochemical characteristics are different from those of country rocks and record the processes and features of sedimentation and diagenesis manganese was precipitated as mn oxyhydroxide particles in oxidized water columns with the sorption of a certain amount of rare earth elements subsequently transforming from mn oxyhydroxides to rhodochrosite and redistributing rey in reducing alkaline pore water during early diagenesis a number of similarities can be observed through a comparison of datangpo type manganese ores and modern marine ferromanganese oxyhydroxide precipitates based on their rare earth elements the precipitation of datangpo type manganese ores is similar to that of hydrogenetic crusts and nodules based on their positive ce anomalies and relatively higher total rey concentrations however several differences also exist compared to hydrogenetic crusts and nodules datangpo type manganese ores record smaller positive ce anomalies lower total rey concentrations unobvious fractionation between y and ho and weak to strong positive eu anomalies these were caused by quicker sedimentary rates in the oxic water columns of the shallower basin after which pore water became strongly reducing and alkaline due to the degradation of organic matter in the early diagenetic stage in addition compared to typical deposits in the world datangpo type manganese ores are similar to hydrogenetic deposits and different than hydrothermal deposits all of these characteristics of manganese ores indicate that datangpo type manganese ores the principal metallogenic factors of which include oxidation conditions during deposition and reducing conditions during early diagenetic stages represent hydrogenetic deposits

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

accumulation rates chemical partitioning and q mode factor analysis of metalliferous sediments from the north fiji basin abstract in order to assess recent hydrothermal contributions to pelagic sediments from active back arc spreading surface samples collected from the north central north fiji basin and the vanuatu archipelagic apron were chemically and mineralogically analyzed including phase and size partitioning and q mode factor analysis of the chemical data sediment cores were analyzed for accumulation rates by the excess 230 th method using alpha track autoradiography the north central north fiji basin sediments are largely carbonate oozes in which the non carbonate material is dominated by volcanic detritus in the 2 m fraction and by fe montmorillonite amorphous ferromanganese oxides and fine grained volcanic ash in the m fraction phase and size partitioning indicate that metal concentrations in the m fraction approach those for metalliferous sediments from the eastern pacific and that the metalliferous material in the majority of these sediments is concentrated in the oxide portion of the m fraction suggesting potential widespread colloidal dispersion from the source areas iron accumulation rates are similar to those of metalliferous sediments from the east pacific rise the mean mn accumulation rate is about twice the global authigenic rate whereas al is accumulating about ten times faster than in eastern and equatorial pacific pelagic sediments because of volcanic ash contributions from the vanuatu island arc and possible intra basin volcanism q mode factor analysis of the compositional data produced three major factors hydrothermal authigenic and detrital which together account for 90 of the sample variance in both size fractions of the non carbonate material the aerial distribution of the m fraction factor components reveals a major hydrothermal source associated with the south pandora ridge spreading center in general agreement with the mn and as accumulation rate patterns two smaller hydrothermal sources were revealed by the factor analysis which are not associated with any known active tectonic features suggesting that back arc rifting and associated hydrothermal activity in this portion of the north fiji basin may follow both ordered and complex regional modes

a hydrothermal manganese deposit from the eratosthenes seamount eastern mediterranean sea abstract a manganese crust horizon is described from the eratosthenes seamount south of cyprus in the eastern mediterranean sea its morphological and geochemical features coupled with its geotectonic setting suggest that submarine hydrothermal activity is responsible for its formation

hydrothermal manganese oxide deposits from galapagos mounds dsdp leg 70 hole 509b and alvin dives 729 and 721 abstract during dsdp leg 70 a 1 60 m thick manganese oxide layer was sampled in hole 509b this deposit is formed of alternating layers of hard plates of pure todorokite about 2 mm thick and of a more powdery material deeply impregnated with manganese oxide about 3 mm thick a sem study of the plates and the associated powder shows that the powdery material is a transformation of a pre existing sediment while the plates are a direct precipitation from a hydrothermal solution the uranium series disequilibrium method was used to determine the ages of the plates they are found to be in good chronological sequence and in accordance with the sedimentation rate of the area 4 9 cm 103 years which implies that they have been formed at the sediment seawater interface during a pulsed injection of hydrothermal solution the powder presents systematically an older age which is explained by a slowing down of the injection while the normal sediment settles the older age is due to the230th excess of the sediment

geochemistry and mineralogy of seafloor hydrothermal and hydrogenetic mn oxide deposits from the manus basin and bismarck archipelago region of the southwest pacific ocean abstract petrographic chemical and mineralogical data are presented for ferromanganese deposits from the manus basin bismarck archipelago region of the southwest pacific the samples were dredged from water depths of between 800 and 2700 m range up to 3 cm in thickness and occur on a variety of substrates including basalt and partially lithified sediments the physical appearance bulk composition and mineralogy of the majority of these samples suggest a hydrogenetic origin however one sample from northwest of manus island and two from inside the active spreading ridge of the manus basin show extreme fractionation of fe and mn depletion of minor trace metals and radiometric isotope compositions indicative of a hydrothermal origin the first report of such material from this region the co content in the deposits is low compared to crusts from other parts of the pacific basin and thus it would appear that the resource potential for co in the manus basin bismarck archipelago region may be limited the presence of mn rich crusts of hydrothermal origin does however suggest that further sampling in selected areas for potentially economic reserves of polymetallic sulphides may be warranted

mylonitization in the lower plate of the buckskin rawhide detachment fault west central arizona implications for the geometric evolution of metamorphic core complexes abstract in metamorphic core complexes it is commonly unclear whether lower plate mylonites formed as the down dip continuation of a detachment fault or whether they represent a subhorizontal shear zone that was captured by a more steeply dipping detachment fault detailed microstructural fabric and strain data from mylonites in the buckskin rawhide metamorphic core complex west central arizona constrain the structural development of the lower plate shear zone widespread exposures of 22 21 ma granitoids of the swansea plutonic suite enable us to separate miocene strain coeval with core complex extension from older deformation mylonites across the lower plate consistently record top to the ne directed shear miocene quartz and feldspar deformation recrystallization mechanisms indicate 450 500 c mylonitization temperatures that were relatively uniform across a distance of 35 km in the extension direction quartz dynamically recrystallized grain sizes do not systematically vary in the extension direction strain recorded in the swansea plutonic suite is also relatively uniform in the extension direction which is incompatible with models in which lower plate mylonites form as the ductile root of a major detachment fault altogether these data suggest the mylonitic shear zone initiated with a 4 dip and was unroofed by a more steeply dipping detachment fault system lower plate mylonites in the buckskin rawhide metamorphic core complex thus represent a captured subhorizontal shear zone rather than the down dip continuation of a detachment fault

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

possible origin and significance of extension parallel drainages in arizona s metamorphic core complexes the corrugated form of the harcuvar south mountains and catalina metamorphic core complexes in arizona reflects the shape of the middle tertiary extensional detachment fault that projects over each complex corrugation axes are approximately parallel to the fault displacement direction and to the footwall mylonitic lineation the core complexes are locally incised by enigmatic linear drainages that parallel corrugation axes and the inferred extension direction and are especially conspicuous on the crests of antiformal corrugations these drainages have been attributed to erosional incision on a freshly denuded planar inclined fault ramp followed by folding that elevated and preserved some drainages on the crests of rising antiforms according to this hypothesis corrugations were produced by folding after subaerial exposure of detachment fault footwalls an alternative hypothesis proposed here is as follows in a setting where preexisting drainages cross an active normal fault each fault slip event will cut each drainage into two segments separated by a freshly denuded fault ramp the upper and lower drainage segments will remain hydraulically linked after each fault slip event if the drainage in the hanging wall block is incised even if the stream is on the flank of an antiformal corrugation and there is a large component of strike slip fault movement maintenance of hydraulic linkage during sequential fault slip events will guide the lengthening stream down the fault ramp as the ramp is uncovered and stream incision will form a progressively lengthening extension parallel linear drainage segment this mechanism for linear drainage genesis is compatible with corrugations as original irregularities of the detachment fault and does not require folding after early to middle miocene footwall exhumation this is desirable because many drainages are incised into nonmylonitic crystalline footwall rocks that were probably not folded under low temperature surface conditions an alternative hypothesis that drainages were localized by small fault grooves as footwalls were uncovered is not supported by analysis of a down plunge fault projection for the southern rincon mountains that shows a linear drainage aligned with the crest of a small antiformal groove on the detachment fault but this process could have been effective elsewhere lineation parallel drainages now plunge gently southwestward on the southwest ends of antiformal corrugations in the south and buckskin mountains but these drainages must have originally plunged northeastward if they formed by either of the two alternative processes proposed here footwall exhumation and incision by northeast flowing streams was apparently followed by core complex arching and drainage reversal

timing rate and magnitude of slip on the buckskin rawhide detachment fault west central arizona we present thermochronologic and geochronologic data that constrain the slip history of the buckskin rawhide detachment fault in west central arizona one of the largest extensional fault systems in the north american cordillera u th he zircon and apatite thermochronology integrated with 40ar 39ar geochronology of postdetachment volcanic rocks indicate that large magnitude extension associated with the detachment fault initiated at 21 20 ma and continued until 12 11 ma in the southwestern portion of the buckskin rawhide metamorphic core complex u th he footwall cooling ages from the breakaway zone in the western bouse hills to upper greenschist facies mylonites in the southern buckskin mountains indicate that the slip rate on the detachment fault was 3 1 5 1 km myr during the early miocene space time patterns of hanging wall tilting suggest that at 17 16 ma a secondary detachment fault breakaway developed 12 km northeast of the primary detachment fault breakaway proximal conglomerates deposited in a supradetachment basin adjacent to the secondary breakaway scarp were displaced 6 11 km northeast in the middle miocene by the buckskin rawhide detachment fault at a slip rate of 1 2 2 7 km myr the total displacement across the detachment fault in the southwestern portion of the core complex is 24 10 km well short of the previous estimate of 66 8 km across the entire core complex based on these data and new observations we propose that total displacement on the buckskin rawhide detachment fault system increases in the slip direction to 40 50 km at the northeastern end of the exposed footwall corresponding to time averaged slip rates that ranged from 2 km myr to 6 km myr across the entire core complex

hydrothermal manganese deposits in island arcs and related to subduction processes a possible model for genesis abstract submarine hydrothermal manganese deposits have recently been recovered from a number of island arc settings such as the tonga kermadec ridge ogasawa arc trench bonin arc mariana arc and bismarck archipelago it has also been shown that large volumes of fluid are released during dewatering of subducting sediments the amount of water subducted globally 1 5 10 15 g yr 1 is about two orders of magnitude less than that advected at ocean spreading centres hydrothermal manganese deposits may be precipitated from these waters the distribution of terrestrial manganese deposits around the circum pacific belt and elsewhere suggests that some of these deposits may be of hydrothermal origin related to subduction processes at present most of these terrestrial deposits are inadequately described to permit the establishment of the precise tectonic setting at the time of deposition of the manganese deposits and therefore an unambiguous assessment of this hypothesis

metalliferous manganese oxide mineralization associated with the boleo cu co zn district mexico apart from its large reserves of cu co zn mineralization contained within stratiform ore beds or mantos the boleo district of central baja mexico also contains significant concentrations of mn oxides typically 2 3 wt mn interspersed with hydrothermal sulfides and both hydrothermal and weathering related metal oxide minerals within the mantos mn oxides occur as concentric nodules disk shaped concretions laminae granules or aggregates veins dendrites and various replacements the oxides are composed of varying amounts of hollandite cryptomelane todorkite romanechite pyrolusite and x ray amorphous mn oxide chemically the manto oxides are unique owing to their extraordinarily high abundances of co cu pb and zn typically 2 5 wt but up to 23 wt existing mineralogical and geochemical classifications are ambiguous regarding the genetic classification of mn oxides within the mantos a new mno 2 fe 2 o 3 t mgo diagram is proposed in order to discriminate among highly metalliferous mn oxides based on the new classification scheme manto mn oxides record a complex interaction between hydrothermal and diagenetic processes to better understand the mechanism of oxide deposition radiogenic isotopes sr and pb and ree geochemistry were used to delineate fluid and metal sources isotopic and ree constraints indicate that the boleo mn oxides are largely hydrothermal in origin however they show varying degrees of modification resulting from diagenetic processes hydrothermal mn oxides are syngenetic synsedimentary to syndiagenetic in origin and were precipitated in association with sulfides reflecting localized variations in redox conditions within the manto sequence due to the downward infiltration of metal bearing brines apart from morphological and stratigraphic evidence e g occurrence of nodular crusts along the upper contact of the manto a syngenetic origin is supported by a single k ar date of 7 0 0 2 ma which is within the estimated age range for deposition of boleo formation clastic sediments interaction between brine and seawater or brine and pore fluid as it infiltrates the sedimentary pile produced hydrothermal precipitates with certain hydrogenetic attributes i e positive ce anomaly lree enrichment on the other hand oxides with hydrogenetic and with mixed hydrothermal hydrogenetic affinities represent diagenetic alteration and remobilization of earlier formed hydrothermal oxides by meteoric fluids by far the greatest degree of remobilization occurred in response to compactional dewatering of the manto where the dewatering pore waters enriched the uppermost manto strata in mn fe zn co and to lesser degrees cu later diagenetic modifications coincided with the development of a supergene overprint which typifies boleo formation strata at elevations above the present day water table

a hydrothermal deposit from explorer ridge in the northeast pacific ocean abstract crusts composed of nontronite and ferromanganese oxides were recovered from explorer ridge a spreading ridge segment in the northeastern pacific ocean located off the west coast of canada the chemical and mineralogical composition of the crusts closely resembles that of the mound like hydrothermal deposits recently discovered at the famous site on the mid atlantic ridge and on the galapagos spreading centre compositional anomalies suggest that the crusts are precipitates of hydrothermal vent solutions which were ejected discontinuously and subsequently mixed with seawater