the role of partial melting in the 15 ma geochemical evolution of gran canaria a blob model for the canary hotspot the subaerial portion of gran canada canary islands was built by three cycles of volcanism a miocene cycle 8 5 15 ma a pliocene cycle 1 8 60 ma and a quaternary cycle 1 8 0 ma only the pliocene cycle is completely exposed on gran canaria the early stages of the miocene cycle are submarine and the quaternary cycle is still in its initial stages during the miocene sio2 saturation of the mafic volcanics decreased systematically from tholeiite to nephelinite for the pliocene cycle sio2 saturation increased and then decreased with decreasing age from nephelinite to tholeiite to nephelinite sio2 saturation increased from nephelinite to basanite and alkali basalt during the quaternary in each of these cycles increasing melt production rates sio2 saturation and concentrations of compatible elements and decreasing concentrations of some incompatible elements are consistent with increasing degrees of partial melting in the sequence melilite nephelinite to tholeiite the mafic volcanics from all three cycles were derived from co2 rich garnet lherzolite sources phlogopite ilmenite sulfide and a phase with high partition coefficients for the light rare earth elements lree u th pb nb and zr possibly zircon were residual during melting to form the miocene nephelinites through tholeiites phlogopite ilmenite and sulfide were residual in the source of the pliocene quaternary nephelinites through alkali basalts highly incompatible element ratios e g nb u pb ce k u nb pb ba rb zr hf la nb ba th rb nb k nb zr nb th nb th la and ba la exhibit extreme variations in many cases larger than those reported for all other ocean island basalts but these ratios correlate well with degree of melting survival of residual phases at higher degrees of melting during the miocene cycle and differences between major and trace element concentrations and melt production rates between the miocene and pliocene tholeiites suggest that the miocene source was more fertile than the pliocene quaternary source s we propose a blob model to explain the multi cycle evolution of canary volcanoes and the temporal variations in chemistry and melt production within cycles each cycle of volcanism represents decompression melting of a discrete blob of plume material small degree nephelinitic and basanitic melts are derived from the cooler margins of the blobs whereas the larger degree tholeiitic and alkali basaltic melts are derived from the hotter centers of the blobs the symmetrical sequence of mafic volcanism for a cycle from highly undersaturated to saturated to highly undersaturated compositions reflects melting of the blob during its ascent beneath an island in the sequence upper margin corelower margin volcanic hiatuses between cycles and within cycles represent periods when residual blob or cooler entrained shallow mantle material fill the melting zone beneath an island

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

the hydrothermally altered ankaramite basalts of punta poyata tenerife canary islands the features of hydrothermal mineral phases hosted in ankaramite basalts from the lower part of the taganana area northside anaga tenerife are studied in this work this area known as arco de taganana constitutes a volcanic rift zone that is overturned to the northwest and now identified by a dense ne sw striking dyke swarm with a distinct se dip the most recent k ar data indicate a mid upper miocene age for the emplacement of the dykes the rocks are intensely altered usually brecciated and are deeply eroded this allows us to look at the roots of a volcanic edifice that has almost disappeared basaltic pyroclastic deposits and lava flows as well as salic breccias associated to the emplacement of salic domes unconformably overly these rocks mineralogical and geochemical characteristics of the mineralization as well as isotopic data are reported in this paper some mineral paragenesis and isotopic data reflect submarine conditions of alteration mineralogy was studied by transmitted and reflected light microscopy xrd sem and electron microprobe in general terms the mineralization consists of major jasper quartz and opal and celadonite in association with minor hematite magnetite fe ca mg carbonates kaersutite calcite and traces of ilmenite which is always associated with magnetite four paragenetic stages were recognized in the studied area two of them exhibit hydrothermal mineralization q 2000 elsevier science b v all rights reserved

controls on the siting and style of volcanogenic massive sulphide deposits abstract volcanogenic massive sulphide vms deposits form in subaqueous environments from circulating hydrothermal fluids heated by volcanic activity these deposits form as sulphide mounds stratiform exhalative and or replacive bodies and commonly have stockwork vein mineralization in their immediate footwall these various styles are essentially facies of mineralization each one being the product of a particular set of conditions that control the ore forming processes and the consequent geometry and architecture style of the deposits these controls include the physical and or chemical nature of the host rocks the temperature and composition of the hydrothermal fluids and the redox state of the depositional environment the style of exhalative deposits is controlled by the salinity of the vented fluids and the redox state at the seafloor hydrothermal fluids with salinities less than twice that of seawater that vented into open oxic oceanic environments typically formed small mound and chimney complexes unless they were rapidly covered by sediments or volcanic rocks the massive sulphides were rapidly oxidized and partly dissolved by seawater in contrast stratiform sheet like deposits are typically formed in anoxic bottom waters anoxic marine conditions were periodically of global extent particularly prior to 2 4 ga or of a regional nature local anoxic conditions can also be self induced by the exhalation of saline and reducing hydrothermal fluids that ponded in bathymetric depressions such as second or third order basins to form a brine pool these exhalative systems may have been initiated as chimney vent complexes and subsequently overlain by stratiform sulphides formed under the self induced anoxic conditions deposits formed in anoxic environments can be significantly larger than those in oxic settings and this is attributed to several factors that include longer lived hydrothermal circulation more efficient sulphide precipitation and reduced or inhibited oxidation thereof replacement of volcanic and sedimentary strata by sulphide typically occurs within the feeder zones beneath the exhalative mineralization however successions with abundant porous permeable and or reactive rocks such as glassy and or pumiceous volcaniclastic rocks and in some cases limestone favoured the development of large replacive deposits that may have had little surficial expression on the sea floor vms deposits at spreading centres within oceanic crust formed almost exclusively as mounds most of them have not been preserved likely due to oxidation of the sulphides in the prevailing oxic environment and or destruction of oceanic crust during subsequent subduction intra continental rifts arc rifts and back arc rifts commonly have more complexity in their structure and facies architecture and environments and can host all styles of vms mineralization in these settings early extension favoured the formation of restricted basins with ideal conditions for the onset of hydrothermal activity and development of anoxic bottom waters whereas in mature rifts the conditions were less conducive for the formation of regionally extensive anoxic environments formation of replacive deposits was permissible in all settings with porous or reactive subsea floor strata replacive mineralization is the most likely to be preserved in the geological record due to the sulphides being physically shielded from oxidative weathering and mechanical erosion at the seafloor the various styles of vms mineralization can rarely be distinguished using a single criterion in most cases multiple criteria are required mound style mineralization is distinguished by a mound or lens shaped morphology b presence of chimney fragments c presence of abundant sedimented sulphide breccias d location on a stratigraphic boundary ore horizon and e association with a thin horizon or thicker stratigraphic interval of fine grained clastic rocks e g shale mudstone that accumulated at slow sedimentation rates stratiform exhalative mineralization is distinguished by a sheet like morphology prior to deformation b presence of fine grained clastic host rocks that accumulated at relatively slow rates e g mudstone c presence of local or extensive planar stratification replacive mineralization is characterized by a irregular geometry and distribution of sulphide bodies b gradation from massive sulphides to semi massive sulphides and disseminated mineralization with relict textures of the host rock and c originally pumiceous glassy or reactive host rocks emplaced at high depositional rates mass flow deposits lavas carbonate altered mass flow deposits or limestone one deposit or district may comprise two or more of these main styles of mineralization in many cases the main styles of vms mineralization present in a particular region can be predicted from examination of the facies architecture and depositional environments of the host succession recognition of the style s of mineralization that occur in a particular basin or mineral belt enables exploration models to be improved and should influence the strategy of exploration for vms deposits

analysis of the spatial coverage of british rainfall fields abstract based on uk radar data the distribution of coverage of an area by rainfall fields is analysed including the influence of spatial and temporal resolution of the data size of the area and topographic and climatic variations the aim is to derive a method allowing the choice of a value of the coverage for example within an atmospheric general circulation model two cases are distinguished that of a coverage which is stationary with respect to the size of the area and that of a varying coverage for areas smaller than a critical size which is generally between 60 km 60 km and 70 km 70 km for the stationary coverage a proposed method consists of the selection based on topography of an average coverage for the given period and the choice of a value of the coverage e from a distribution of mean presenting some dependence on the season and the topography the self similarity of the coverage process for a wide range of area sizes leads to the determination of estimates of the fractal dimension and the examination of the temporal variation of this dimension for the non stationary coverage within the mesoscale and lower mesoscale ranges parabolic curves allow a good approximation to the decrease of coverage with area size

environmental controls on biomineralization and fe mound formation in a low temperature hydrothermal system at the jan mayen vent fields abstract diffuse low temperature hydrothermal vents on the seafloor host neutrophilic microaerophilic fe oxidizing bacteria that utilize the fe ii supplied by hydrothermal fluids and produce intricate twisted and branching extracellular stalks the growth behavior of fe oxidizing bacteria in strongly opposing gradients of fe ii and o2 have been thoroughly investigated in laboratory settings to assess whether extracellular stalks and aligned biomineralized fabrics may serve as biosignatures of fe oxidizing bacteria and indications of palaeo redox conditions in the rock record however the processes controlling the growth of biogenic fe oxyhydroxide deposits in natural modern hydrothermal systems are still not well constrained in this study we aimed to establish how variations in the texture of stratified hydrothermal fe oxyhydroxide deposits are linked to the physicochemical conditions of the hydrothermal environment we conducted 16s rrna gene analyses microscopy and geochemical analyses of laminated siliceous fe mounds from the jan mayen vent fields at the arctic mid ocean ridge chemical analyses of low and high temperature hydrothermal fluids were performed to characterize the hydrothermal system in which the fe deposits form our results reveal synchronous inter laminar variations in texture and major and trace element geochemistry the fe deposits are composed of alternating porous laminae of mineralized twisted stalks and branching tubes mn rich horizons with abundant detrital sediment domal internal cavities and thin p and ree enriched lamina characterized by networks of 1 m wide fibers zetaproteobacteria constitute one third of the microbial community in the surface layer of actively forming mounds indicating that microbial fe oxidation is contributing to mound accretion we suggest that mn oxide precipitation and detrital sediment accumulation take place during periodically low hydrothermal fluid discharge conditions the elevated concentrations of p and ree in distinct laminae suggest fe cycling and accumulation of diagenetic species at depth in the deposits during hydrothermal quiescence and co precipitation of these species with fe oxyhydroxides at the mound surface with reinitiated hydrothermal discharge the origin of the low temperature hydrothermal source fluid and the fe deposits are evident by low lree hree ratios and negative eu anomalies which clearly differ from the lree and eu enrichment of nearby high temperature white smoker venting fluids our study demonstrates that hydrothermal fluctuations exert the primary control on the formation of laminae and the activity of fe oxidizing bacteria in marine hydrothermal fe deposits and indicates that ree patterns may be used to distinguish high temperature plume fallout and biomineralized low temperature fe deposits in the rock record

formation of fe si mn oxyhydroxides at the pacmanus hydrothermal field eastern manus basin mineralogical and geochemical evidence samples of fe si mn oxyhydroxides were collected from the pacmanus hydrothermal field which lies in a young back arc setting in the eastern manus basin the purpose of the study was to understand the origin and characteristics of fe si mn oxyhydroxides associated with massive sulfides in a back arc basin the pacmanus fe si mn oxyhydroxides are composed of fe oxyhydroxides and mn oxyhydroxides with opal a and nontronite they have very low concentrations of trace elements except for ba mo v and u and rare earth elements and they show ree distribution patterns with positive eu anomalies and slight enrichments of lrees the fe si mn oxyhydroxides appear to be precipitated mainly from hydrothermal fluid with limited seawater contamination and scavenged trace metals are predominantly from the ambient seawater the differences in the ree distribution patterns between the fe oxyhydroxide fraction and mn oxyhydroxide fraction originate from diagenetic processes there are diverse filamentous microtextures resembling unique microbial populations suggesting microbially mediated mineralization during the precipitation of the fe si mn oxyhydroxides

uptake of elements from seawater by ferromanganese crusts solid phase associations and seawater speciation marine fe mn oxyhydroxide crusts form by precipitation of dissolved components from seawater three hydrogenetic crust samples one phosphatized and two hydrothermal mn oxide samples were subjected to a sequential leaching procedure in order to determine the host phases of 40 elements those host phase associations are discussed with respect to element speciation in seawater the partitioning of elements between the two major phases mn oxide and fe oxyhydroxide can in a first order approximation be explained by a simple sorption model related to the inorganic speciation of the elements in seawater as has been proposed in earlier models free and weakly complexed cations such as alkali and alkaline earth metals mn co ni zn tl i and partly y are sorbed preferentially on the negatively charged surface of the mno2 in hydrogenetic crusts the driving force is a strong coulombic interaction all neutral or negatively charged chloro cd hg tl carbonate cu y pb and u and hydroxide be sc ti fe zr nb in sn sb te hf ta bi th and tl iii complexes and oxyanions v cr as se mo and w bind to the slightly positively charged surface of the amorphous feooh phase while coulombic interaction can explain the sorption of the negatively charged species the binding of neutral species is based on specific chemical interaction organic complexation of elements in deep ocean water seems to be at most of minor importance surface oxidation can explain some strong metal associations e g of co and tl with the mno2 and te with the feooh sorption reactions initially driven by coulombic forces are often followed by the formation of specific bonds between the adsorbate and the atoms of the oxide surface differences in the associations of some metals between the non phosphatized and phosphatized hydrogenetic crusts and between the hydrogenetic and the hydrothermal samples reflect the different physico chemical environments of formation and speciations in oxic seawater vs less oxic fluids especially for the redox sensitive metals such as mo and v these environmental related differences indicate that the methodology of chemical speciation used here in combination with spectroscopic methods may allow for the detection of changes in paleoceanographic conditions recorded during the several tens of millions of years of crust growth

layered hydrothermal barite sulfide mound field east diamante caldera mariana volcanic arc east diamante is a submarine volcano in the southern mariana arc that is host to a complex caldera 5 10 km elongated ene wsw that is breached along its northern and southwestern sectors a large field of barite sulfide mounds was discovered in june 2009 and revisited in july 2010 with the r v natsushima using the rov hyper dolphin the mound field occurs on the northeast flank of a cluster of resurgent dacite domes in the central caldera near an active black smoker vent field a 40ar 39ar age of 20 000 4000 years was obtained from a dacite sample the mound field is aligned along a series of fractures and extends for more than 180 m east west and 120 m north south individual mounds are typically 1 to 3 m tall and 0 5 to 2 m wide with lengths from about 3 to 8 m the mounds are dominated by barite sphalerite layers with the margins of each layer composed of barite with disseminated sulfides rare inactive spires and chimneys sit atop some mounds and also occur as clusters away from the mounds iron and mn oxides are currently forming small 1 m diam 0 5 m tall knolls on the top surface of some of the barite sulfide mounds and may also drape their flanks both diffusely and focused fluids emanate from the small oxide knolls radiometric ages of the layered barite sulfide mounds and chimneys vary from 3 920 to 3 350 years one layer from an outcrop of 10 to 100 cm thick cu rich layers is notably younger with an age of 2 180 years the fe mn oxides were 5 years old at the time of collection in 2009 most mound chimney and layered outcrop samples are dominated by barite silica and sphalerite other sulfides in decreasing order of abundance are galena chalcopyrite and rare pyrite anglesite cerussite and unidentified pb oxychloride and pb phosphate minerals occur as late stage interstitial phases the samples contain high zn up to 23 wt pb to 16 wt ag to 487 ppm and au to 19 ppm contents some layered outcrop samples are dominated by chalcopyrite resulting in 4 78 wt cu in a bulk sample 28 wt for a single lens with a mean of 0 28 wt for other samples other significant metal enrichments are sb to 1 320 ppm cd to 1 150 ppm and hg to 55 ppm the east diamante mound field has a unique set of characteristics compared to other hydrothermal sites in the mariana arc and elsewhere the geochemical differences may predominantly reflect the distribution of fractures and faults and consequently the rock water ratio temperature of the fluid in the upper parts of the circulation system and extensive and prolonged mixing with seawater the location of mineralization is controlled by fractures following resurgent doming within the caldera mineralization resulted from focused flow along small segments of linear fractures rather than from a point source typical of hydrothermal chimney fields based on the mineral assemblage the maximum fluid temperatures were 260 c near the boiling point for the water depths of the mound field 367 406 m lateral fluid flow within the mounds precipitated interstitial sphalerite silica and pb minerals within a network of barite with disseminated sulfides silica was the final phase to precipitate the current low temperature precipitation of fe and mn oxides and silica may represent rejuvenation of the system

low temperature shallow water hydrothermal vent mineralization following the recent submarine eruption of tagoro volcano el hierro canary islands abstract hydrothermal iron fe rich sediments were recovered from the tagoro underwater volcano central atlantic that formed during the 2011 2012 volcanic event cruises in 2012 and 2014 enabled the monitoring and sampling of the early stage establishment of a hydrothermal system degassing vents produced acoustic flares imaged on echo sounders in june 2012 four months after the eruption a novel hydrothermal vent system was discovered and sampled in 2014 during a rov dive the system is characterized by hornito like structures and chimneys showing active co2 degassing and anomalous temperatures at 120 89 m water depth and along the se flank at 215 185 m water depth associated with secondary cones iron and silica rich gelatinous deposits pooled over and between basanite in the hornitos brecciated lavas and lapilli the low temperature shallow water hydrothermal system was discovered by the venting of fe rich fluids that produced a seafloor draped by extensive fe flocculate deposits precipitated from the neutrally buoyant plumes located along the oxic photic zone at 50 70 m water depths the basanite is capped by mm to cm thick hydrothermally derived fe oxyhydroxide sediment and contains micro cracks and degasification vesicles filled by sulfides mostly pyrite mineralogically the fe oxyhydroxide sediment consists of proto ferrihydrite and ferrihydrite with scarce pyrite at their base the fe rich endmember contains low concentrations of most trace elements in comparison with hydrogenetic ferromanganese deposits and the sediments show some dilution of the fe oxyhydroxide by volcanic ash the fe oxyhydroxide phase with a mean particle size of 3 4 nm low average la fe ratios of the mineralized deposits from the various sampling sites and the positive eu anomalies indicate rapid deposition of the fe oxyhydroxide near the hydrothermal vents electron microprobe studies show the presence of various organomineral structures mainly twisted stalks and sheaths covered by iron silica deposits within the mineralized samples reflecting microbial iron oxidation from the hydrothermal fluids sequencing of 16 s rrna genes also reveals the presence of other microorganisms involved in sulfur and methane cycles samples collected from hornito chimneys contain silicified microorganisms coated by fe rich precipitates the rapid silicification may have been indirectly promoted by microorganisms acting as nucleation sites we suggest that this type of hydrothermal deposit might be more frequent than presently reported to occur in submarine volcanoes on a geological scale these volcanic eruptions and low temperature hydrothermal vents might contribute to increased dissolved metals in seawater and generate considerable fe oxyhydroxide deposits as identified in older hot spot seamounts

geology water geochemistry and geothermal potential of the jemez springs area canon de san diego new mexico abstract studies of the geology geochemistry of thermal waters and of one exploratory geothermal well show that two related hot spring systems discharge in canon de san diego at soda dam 48 c and jemez springs 72 c the hot springs discharge from separate strands of the jemez fault zone which trends northeastward towards the center of valles caldera exploration drilling to precambrian basement beneath jemez springs encountered a hot aquifer 68 c at the top of paleozoic limestone of appropriate temperature and composition to be the local source of the fluids in the surface hot springs at jemez springs comparisons of the soluble elements na li cl and b arguments based on isotopic evidence and chemical geothermometry indicate that the hot spring fluids are derivatives of the deep geothermal fluid within valles caldera no hot aquifer was discovered in or on top of precambrian basement it appears that low to moderate temperature geothermal reservoirs

multi event oceanic island landslides new onshore offshore insights from el hierro island canary archipelago abstract this paper presents a combined onshore offshore morpho structural characterization of the el golfo giant landslide island of el hierro canary archipelago spain offshore data from multibeam echosounders chirp sub bottom profiles and multichannel seismic reflection data and onshore data coming from water wells and galleries have been analyzed the geomorphology and the internal architecture of this giant flank collapse are defined in order to determine its multi event nature the subaerial headscarp shows a non continuous arcuate profile formed by two nested semi circular amphitheaters that extend offshore along a smooth chute suggesting the occurrence of at least two large retrogressive events channels gullies and escarpments developed along the submarine sector of the scar also indicate smaller scale events and predominance of sediment bypass in the lower slope two subunits of submarine mass transport deposits mtds debris avalanche are identified on multichannel seismic reflection profiles with a total estimated volume of 318 km3 84 km3 and 234 km3 for the younger and older mtds respectively data from wells and galleries show abrasion platforms with beach deposits at sea level 0 masl formed after the landslide scar and buried by the post collapse el golfo lavas infill suggesting an age at least older than 23 5 82 5 ka for the landslide

mercury and silver rich ferromanganese oxides southern california borderland deposit model and environmental implications mercury and silver enriched ferromanganese oxide crusts were recovered at water depths of 1 750 to1 300 m from la victoria knoll located about 72 km off the coast of northern baja california no other ferromanganese precipitate found so far in the modern ocean basins is similarly enriched in hg and ag the precipitates consist of submetallic gray brecciated mn oxide layers overlain by brown earthy laminated fe mn oxide crusts both oxide types are rich in hg to 10 ppm and ag to 5 5 ppm the mn rich layers are composed of mno 2 with lesser amounts of 10a and 7a manganates whereas the mn phase in the fe mn crusts is solely mno 2 the fe phase in both layers is x ray amorphous established criteria for distinguishing hydrothermal versus hydrogenetic crusts indicate that the mn rich layers are predominantly of low temperature hydrothermal origin whereas the fe mn crusts are hydrogenetic although there is some overlap in the source of chemical components in both types la victoria knoll is uplifted continental basement rock with basalt andesite and schist cropping out at the surface the knoll may have an intrusive core the hg and ag were derived from leaching by hydrothermal fluids of organic matter rich sediments in basins adjacent to la victoria knoll and to a lesser extent from continental basement rocks underlying the knoll and adjacent basins both rock types are notably enriched in ag and hg faults were the main fluid transport pathway and hydrothermal circulation was driven by high heat flow associated with thinned crust other elements derived from the hydrothermal fluids include tl cd cr and li the main host for hg and ag is feooh although mno 2 likely hosts some of the ag minor sulfide and barite also may contain small amounts of these metals possible analogs in the geologic record for this deposit type are found in the basin and range province of the western united states and mexico the discovery highlights the fact that fluids circulating along faults in the offshore california borderland are transporting potentially toxic metals hg ag tl as cd cr pb and ni and depositing them on and just below the ocean floor

strategic and rare elements in cretaceous cenozoic cobalt rich ferromanganese crusts from seamounts in the canary island seamount province northeastern tropical atlantic abstract thick ferromanganese fe mn crusts from four cretaceous seamounts the paps tropic echo and drago at the southern canary island seamount province cisp in the northeastern tropical atlantic were recovered along the flanks and summits from 1700 to 3000 m water depths cisp is composed of 100 seamounts and submarine hills is likely the oldest hotspot track in the atlantic ocean and is the most long lived of known hotspots globally the fe mn crusts grow on basalt sedimentary rock substrates below the northeastern tropical atlantic core of the oxygen minimum zone omz with a maximum thickness of 250 mm at a water depth of 2400 m the mineralogical and chemical composition of these fe mn crusts indicate a hydrogenetic origin the main mn minerals are vernadite with minor interlayered todorokite and asbolane buserite fe oxides are essentially ferroxyhyte and goethite the fe mn crusts show high average contents in fe 23 5 wt mn 16 1 wt and trace elements like co 4700 g g ni 2800 g g v 2400 g g and pb 1600 g g rare earth elements plus yttrium rey averages 2800 g g with high proportions of ce 1600 g g total platinum group elements pges average 230 ng g with average pt of 182 ng g two main types of growth layers form the crusts 1 a dense laminae of oxides with high contents in mn co and ni associated with vernadite and cu ni and zn associated with todorokite 2 botryoidal layers with high contents in fe ti v and rey associated with goethite the fe mn crusts from the cisp region show higher contents in fe v pb and rey but lower mn co ni and pges contents than pacific or indian ocean seamount crusts the oldest maximum age of initiation of crust growth was at 76 ma campanian late cretaceous using a combination of high resolution co chronometer and geochemical data along an electron probe micro analysis epma transect four stages in morphology chemical contents and growth rates can be differentiated in the the cenozoic crusts since 28 ma which we interpret as due to changes in the ventilation of the north atlantic omz and to the increase of saharian dust inputs an earliest growth period characterized by similar contents of fe and mn in the interval 27 8 24 45 ma late oligocene early miocene reflects slow precipitation related to a thick omz an intermediate laminated zone with higher contents of fe si and p high growth rates reaching 4 5 mm ma and precipitation of fe mn oxides during the interval 24 5 16 ma is related to periods of ventilation of the omz by intrusion of deep upwelling currents significant increase in fe contents at ca 16 ma correlates with the onset of incursions of northern component waters into the north atlantic finally since 12 ma the very low growth rates

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

the 2011 2012 submarine eruption off el hierro canary islands new lessons in oceanic island growth and volcanic crisis management forty years after the eruption of the teneguia volcano on la palma 1971 the last volcanic event in the canary islands a submarine eruption took place in 2011 off shore el hierro the smallest an

discriminating between different genetic types of marine ferro manganese crusts and nodules based on rare earth elements and yttrium marine ferro manganese fe mn crusts and nodules are metal rich chemical sediments that are archives of paleoceanographic proxies and potential metal resources and targets of deep sea mining traditionally crusts and nodules are subdivided into hydrogenetic diagenetic and hydrothermal types because these are characterized by different compositions and hence economic resource potential a useable genetic classification is not only a tool for geochemical studies but may also help to characterize potential exploration targets we propose two easy to use yet robust discrimination diagrams based on geochemical relationships controlling the rare earths and yttrium rey inventory of marine fe mn oxyhydr oxide deposits the rey are a set of trace elements that show coherent behavior are routinely determined in geochemical studies and for which the analytical quality can easily be evaluated graphs of ce anomaly vs nd concentration and ce anomaly vs y anomaly effectively discriminate between the different types of precipitates regardless of their diverse mineralogical composition both hydrogenetic crusts and nodules show positive ce anomalies negative y anomalies and high nd concentrations of 100 mg kg 1 although nodules tend to have slightly lower nd concentrations than crusts in marked contrast hydrothermal deposits generally yield negative ce anomalies positive y anomalies and low nd concentrations of 10 mg kg 1 in spite of their large geochemical mineralogical and sedimentological diversity diagenetic nodules show negative ce anomalies negative y anomalies and intermediate nd concentrations between 10 and 100 mg kg 1 we discuss the geochemical background of these diagrams the respective sources of rey in the different precipitates and address the processes that control their rey inventory besides the three end members we also use rey systematics to define mixed type diagenetic hydrogenetic nodules and classify well studied international reference standards

candidate sites for future hot dry rock development in the united states generalized geologic and other data are tabulated for 24 potential hot dry rock hdr sites in the contiguous united states the data show that hdr resources occur in many geologic and tectonic settings potential reservoir rocks at each prospect are described and each system is cateogrized accoridng to inferred heat sources the fenton hill area in new mexico is discussed in detail because this region may be considered ideal for hdr development three other prospectively valuable localities are described the geysers clear lake region in california the roosevelt hot springs area in utah and the white mountains region in new hampshire these areas are singled out to illustrate the roles of significantly different geology and geophysics reservoir rocks and reservoir heat contents in possible hdr developments

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

rock water interactions in hot dry rock geothermal systems field investigations of in situ geochemical behavior abstract two hot dry rock hdr geothermal energy reservoirs have been created by hydraulic fracturing of precambrian granitic rock between two wells on the west flank of the valles caldera in the jemez mountains of northern new mexico heat is extracted by injecting water into one well flowing it through the fractured region and recovering the heated water from the second well the produced fluid is cooled on the surface and reinjected into the system the first reservoir was formed by fracturing the injection well at a depth of 2 75 km where the initial rock temperature was 185 c a heat extraction experiment conducted in this reservoir was run from january 27 to april 13 1978 a second larger reservoir was created after cementing the fracture to wellbore connections at 2 75 km in the injection well and refracturing 180 m deeper this second reservoir was tested from october 23 to november 16 1979 during each of these experiments samples of the geothermal fluids and gases were collected at regular intervals from the injection wellhead the production wellhead and at the make up pump which provided the water from storage ponds to replace the water lost downhole by permeation into the reservoir walls changes in the composition of the produced fluid provide a means for studying the reservoir behaviour under normal recirculating operating conditions certain of the dissolved species appear to be derived by displacement of an indigenous pore fluid while others appear to be derived by dissolving minerals known to be present in the reservoir rock in this paper we describe the results of the chemical analysis of the geothermal fluids and relate the fluid and gas chemistry to geochemical processes that result from the heat extraction experiments in particular the implications of the silica and na k ca geothermometers and the pore fluid displacement theory are examined for insight about the long term effects of fluid geochemistry on heat extraction from hdr reservoirs

1300 m high rising bubbles from mud volcanoes at 2080m in the black sea hydroacoustic characteristics and temporal variability a mud volcano area in the deep waters 2000 m of the black sea was studied by hydroacoustic measurements during several cruises between january 2002 and june 2004 gas bubbles in the water column give strong backscatter signals and thus can be detected even in great water depths by echosounders as the 38 khz ek500 scientific split beam system that was used during the surveys because of their shape in echograms and to differentiate against geochemical plumes and real upwelling bubble water plumes we call these hydroacoustic manifestations of bubbles in the water column flares digital recording and processing of the data allows a 3d visualization and data comparison over the entire observation period without artefacts caused by changing system settings during our surveys we discovered bubble release from three separate mud volcanoes dvurechenskiy dmv vodianitskiy vmv and the nameless seep site nss in about 2080 m water depth simultaneously bubble release was observed between 9 june 2003 and 5 june 2004 the most frequently surveyed dmv was found to be inactive during very intensive studies in january 2002 the first activity was observed on 27 june 2002 which finally ceased between 5 and 15 june 2004 after a period of continuously decreasing activity this observed 2 yr bubble release period at a mud volcano may give an indication for the duration of active periods the absence of short term variations within days or hours may indicate that the bubble release from the observed mud volcanoes does not undergo rapid changes the recorded echograms show that bubbles rise about 1300 m high through the water column to a final water depth of about 770 m which is 75 m below the phase boundary of pure methane hydrate in the black sea with a release depth from 2068 m and a detected rise height of 1300 m the flare at vmv is among the deepest and highest reported so far and gives evidence of highly extended bubble life times up to 108 min in deep marine environments to better understand how a methane bubble gas analyses of the pore water and gas hydrate gave 99 4 methane can rise so high without dissolving we applied a recently developed bubble dissolution model that takes into account a decreased mass transfer due to an immediately formed gas hydrate rim using the hydroacoustically determined bubble rising speeds 19 22 cm s at the bottom 12 14 cm s at the flare top and the relation between the rising speed of dirty gas hydrate rimmed bubbles and the bubble size we could validate that a gas hydrate rimmed bubble with a diameter of 9 mm could survive the 1300 m rise through the water column before it is finally dissolved a diameter of about 9 mm is reasonable for bubbles released at seep sites and the coincidence between the observed bubble rising speed and the model approach of a 9 mm bubble supports the assumption of gas hydrate rimmed bubbles

hydrothermal iron rich deposits from the teahitia mehitia and macdonald hot spot areas southwest pacific abstract during cruise so 47 of r v sonne iron oxyhydroxide crusts of restricted extent were recovered from teahitia and moua pihaa seamounts in the teahitia mehetia hot spot area and from macdonald seamount in the macdonald hot spot area the crusts show complex layering and incorporate volcanic ash layers they consist of goethite feldspar and pyroxene and display low contents of transition elements apart from fe it is believed that the crusts were deposited from relatively low temperature hydrothermal fluids these low temperatures preclude the formation of sulphide deposits the type of hydrothermal mineral recovered may be a function of the thermal regime of the system and the elevation which controls the pressure of the venting fluids the shallower depths of these seamounts compared to the axes of mid ocean ridges may therefore be responsible for the style of mineralization initially magmatic vapours migrating upwards through the hot spot volcano are thought to be absorbed into seawater at comparatively shallow levels to deposit sulphide minerals within the volcanic pile the fe oxyhydroxide deposits are the residual low temperature deposits formed when the spent hydrothermal fluid reached the crest of the seamount these deposits therefore differ fundamentally from those found at the crest of mid ocean ridges where sulphide mounds are deposited directly upon interaction of the boiling hydrothermal fluid with seawater the discovery of hydrothermal iron oxyhydroxide crusts in these two hot spot areas is only the second such finding after loihi seamount southeast of hawaii

composition and origin of hydrothermal ironstones from central pacific seamounts abstract ironstones recovered from five late cretaceous seamounts in the central pacific region probably formed during late stage edifice building volcanism ironstones are dense and compact with the appearance of brown chert the ironstones are characterized by a goethite mineralogy with feooh contents up to 88 extreme fractionation of fe and mn low trace element and rare earth element abundances low co zn ratios and isotopic equilibration temperatures of about 20 45 c these characteristics indicate that the ironstones formed from hydrothermal fluids ironstones probably formed below the seawater seafloor interface as indicated by their occurrence as a proximal hydrothermal deposit presence of primary goethite cement pervasive replacement of rocks by goethite and absence of interbedded pyro clastic beds

low temperature hydrothermal alteration of intra caldera tuffs miocene tejeda caldera gran canaria canary islands abstract the miocene tejeda caldera on gran canaria erupted 20 rhyolite trachyte ignimbrites mogan group 14 13 3 ma followed by 20 phonolitic lava flows and ignimbrites fataga group 13 8 5 ma upper mogan tuffs have been severely altered immediately within the caldera margin whereas extra caldera mogan ignimbrites and overlying fataga units are apparently unaltered the altered intra caldera samples contain minerals characteristic of secondary fluid rock interaction clays zeolites adularia and relics of the primary mineral assemblage identified in unaltered ignimbrites k feldspar plagioclase pyroxene amphibole and groundmass quartz major and trace element data indicate that si na k pb sr and rb were strongly mobilized during fluid rock interaction whereas ti zr and nb behaved in a more refractory manner experiencing only minor mobilization the 18o values of the altered intra caldera tuffs are significantly higher than in unaltered extra caldera ignimbrites consistent with an overall low temperature alteration environment unaltered extra caldera ignimbrites have d values between 110 and 173 which may reflect rayleigh type magma degassing and or post depositional vapour release the d values of the altered intra caldera tuffs range from 52 to 131 with ambient meteoric water at the alteration site estimated at ca 15 interaction and equilibration of the intra caldera tuffs with ambient meteoric water at low temperature can only account for whole rock d values of around 45 given that dclay water is ca 30 at 100 c and decreases in magnitude at higher temperatures all altered tuff samples have d values that are substantially lower than 45 indicating interaction with a meteoric water source with a d value more negative than 15 which may have been produced in low temperature steam fumaroles supported by numerical modeling our gran canaria data reflect the near surface epithermal part of a larger fault controlled hydrothermal system associated with the emplacement of the high level fataga magma chamber system in this near surface environment fluid temperatures probably did not exceed 200 250 c

gravity and thermal models for the twin peaks silicic volcanic center southwestern utah gravity heat flow and surface geology observations have been used as constraints for a thermal model of a late tertiary silicic volcanic center at twin peaks utah silicic volcanism began in the area with the extrusion of the coyote hills rhyolite 2 74 0 1 m y ago followed by the cudahy mine obsidian felsite and volcanoclastics and finally by a complex sequence of domes and flows that lasted until 2 3 0 1 m y ago basalt sequence span the time 2 5 to 0 9 m y terrain corrected bouguer gravity anomalies at twin peaks are shaped by three features of varying characteristic dimensions 1 a major north northeast trending 30 mgal gravity trough roughly 40 km wide caused by a thick sequence of cenozoic sediments in the black rock desert valley 2 a local roughly circular 7 mgal gravity low 26 km across probably related to an intrusive body in the basement and 3 a series of narrow positive anomalies up to 10 mgal produced by the major twin peaks volcanic domes the intrusive bodies have been modeled as three dimensional vertical cylinders the total volume of intrusive material is estimated to be about 500 km sup 3 simple models assuming conductive heat transfer and using geometricalmore constraints from the gravity results predict that a negligible thermal anomaly should exist 1 m y after emplacement of the intrusion this prediction is consistent with an average heat flow of 96 mw m sup 2 for the area not significantly different from eastern basin and range values elsewhere magmatic longevity of this system 2 7 to 2 3 m y for silicic volcanism of 2 5 to 0 9 m y for basaltic volcanism does not seem to prolong the cooling of the system substantially beyond that predicted by conductive cooling less

subsurface processes at the lucky strike hydrothermal field mid atlantic ridge evidence from sulfur selenium and iron isotopes at lucky strike near the azores triple junction the seafloor setting of the hydrothermal field in a caldera system with abundant low permeability layers of cemented breccia provides a unique opportunity to study the influence of subsurface geological conditions on the hydrothermal fluid evolution coupled analyses of s isotopes performed in conjunction with se and fe isotopes have been applied for the first time to the study of seafloor hydrothermal systems these data provide a tool for resolving the different abiotic and potential biotic near surface hydrothermal reactions the 34s between 1 5 and 4 6 and se values between 213 and 1640 ppm of chalcopyrite suggest a high temperature end member hydrothermal fluid with a dual source of sulfur sulfur that was leached from basaltic rocks and sulfur derived from the reduction of seawater sulfate in contrast pyrite and marcasite generally have lower 34s within the range of magmatic values 0 1 and are characterized by low concentrations of se 50 ppm for 82se 76se ratios the 82se values range from basaltic values of near 1 5 to 7 the large range and highly negative values of hydrothermal deposits observed cannot be explained by simple mixing between se leached from igneous rock and se derived from seawater we interpret the se isotope signature to be a result of leaching and mixing of a fractionated se source located beneath hydrothermal chimneys in the hydrothermal fluid at lucky strike we consider two sources for s and se 1 the end member hydrothermal fluid with basaltic se isotopic values 1 5 and typical s isotope hydrothermal values of 1 5 2 a fractionated source hosted in subsurface environment with negative 34s values probably from bacterial reduction of seawater sulfate and negative 82se values possibly derived from inorganic reduction of se oxyanions fluid trapped in the subsurface environment is conductively cooled and has restricted mixing and provide favorable conditions for subsurface microbial activity which is potentially recorded by s isotopes fe isotope systematic reveals that se rich high temperature samples have 57fe values close to basaltic values 0 whereas se depleted samples precipitated at medium to low temperature are systematically lighter 57fe values between 1 to 3 an important implication of our finding is that light fe isotope composition down to 3 2 may be explained entirely by abiotic fractionation in which a reservoir effect during sulfide precipitation was able to produce highly fractionated compositions

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

earlier history of the 70 ma old canary hotspot based on the temporal and geochemical evolution of the selvagen archipelago and neighboring seamounts in the eastern north atlantic major element trace element and sr nd pb isotope data combined with 40ar 39ar age determinations of volcanic rocks from the selvagen islands and neighboring seamounts in the eastern north atlantic reveal the earlier history of the 70 ma old canary hotspot a basanitic to phonolitic late shield stage intrusive complex 29 ma is exposed on selvagem pequena the evolution of selvagem grande can be divided into three magmatic phases a tephritic to phonolitic late shield stage intrusive complex 24 26 ma and two rejuvenated or post erosional stages 8 12 and 3 4 ma consisting of alkali basalt basanite and rare phonolite during the early to mid miocene volcanic hiatus 12 24 ma the top of the volcano was beneath sea level as evidenced by marine carbonate sediments 13 24 ma dated through correlation of 87sr 86sr with the seawater sr isotope curve the geochemistry of the shield stage lavas indicates that they derive from plume sources whereas the post erosional lavas are derived from metasomatized lithospheric sources five sampled seamounts to the east and northeast of the islands range in composition from alkali basalt and basanite to phonolite samples from dacia conception bank and lars were dated at 9 17 and 68 ma respectively geochemical data suggest that the dredged samples come from the post erosional stage of volcanism and therefore the dates represent minimum ages for the seamount volcanoes the elevation of erosional platforms formed at wave base decrease from selvagen grande 100 m above sea level to lars seamount 900 m below sea level suggesting a southwest to northwest age progression and that all of these seamounts are older than the selvagen islands trace element and sr nd pb isotopic composition of the selvagen islands and neighboring seamounts are consistent with their origin from the canary plume interaction of the weak canary mantle plume with a slow moving plate appears to be responsible for generating a 450 km wide irregular hotspot track extending 800 km from the youngest canary island of hierro in the southwest to lars seamount in the northeast

thermal waters along the konocti bay fault zone lake county california a re evaluation abstract the konocti bay fault zone kbfz initially regarded by some as a promising target for liquid dominated geothermal systems has been a disappointment at least five exploratory wells were drilled in the vicinity of the kbfz but none were successful although the na k ca and na li geothermometers indicate that the thermal waters discharging in the vicinity of howard and seigler springs may have equilibrated at temperatures greater than 200 c the spring temperatures and fluid discharges are low most thermal waters along the kbfz contain 100 mg l mg high concentrations of dissolved magnesium are usually indicative of relatively cool hydrothermal systems dissolution of serpentine at shallow depths may contribute dissolved silica and magnesium to rising thermal waters most thermal waters are saturated with respect to amorphous silica at the measured spring temperature silica geothermometers and mixing models are useless because the dissolved silica concentration is not controlled by the solubility of either quartz or chalcedony cation geothermometry indicates the possibility of a high temperature fluid 200 c only in the vicinity of howard and seigler springs however even if the fluid temperature is as high as that indicated by the geothermometers the permeability may be low deuterium and oxygen 18 values of the thermal waters indicate that they recharged locally and became enriched in oxygen 18 by exchange with rock diluting meteoric water and the thermal water appear to have the same deuterium value lack of tritium in the diluted spring waters suggest that the diluting water is old

resources of the sea floor in his perspective rona reviews recent advances in knowledge of sea floor resources knowledge is expanding from those minerals eroded from land metals gemstones sand and gravel to those minerals concentrated by plate tectonic processes in ocean basins exploration of the oceans is at an early stage and development of marine mining is subject to economic and environmental considerations

hydrothermal manganese oxide deposits from baby bare seamount in the northeast pacific ocean abstract manganese oxide crusts were recovered from baby bare seamount in order to investigate the history of off axis hydrothermal venting baby bare is a small basement high protruding from a regional sediment cover on the eastern flank of the juan de fuca ridge that acts as a focus for discharging crustal fluids stratabound mn oxide crusts were collected where warm venting has been observed near the seamount summit mn oxide crusts are composed primarily of 10 a manganate pyrolusite with minor nontronite saponite and or barite these assemblage and chemical characteristics such as high mn fe ratios and low trace metal and ree concentrations are indicative of a hydrothermal origin minimum ages for these deposits calculated using growth rates 324 to 1800 mm ma and estimated thicknesses of manganese outcrops show that baby bare has been hydrothermally active for at least 0 5 myr and possibly since its formation 1 7 2 7 ma hydrothermal manganese oxide crusts such as these from baby bare record interactions between the hydrothermal fluids and seawater and are important tools for estimating the longevity of off axis hydrothermal activity

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

mn ba hg mineralization at shallow submarine hydrothermal vents in bahia concepcion baja california sur mexico coastal submarine hydrothermal venting occurs on the west shore of the fault bounded bay of bahia concepcion along a stretch of about 700 m of rocky shoreline diffuse hydrothermal seepage of water and continuous gas bubbling mainly co2 and n2 take place through the sediment covered seafloor at shallow depth 5 to 15 m in addition at about 500 m se a cluster of hot springs occurs within the intertidal zone the temperature and ph of the hydrothermal fluids varies from 72 to 87 c and 5 95 to 6 02 in the submarine diffuse venting area and reaches 62 c and ph of 6 68 in the intertidal hot springs mn ba hg mineralization is presently forming as a result of the hydrothermal venting at the intertidal hot springs moss like crusts of manganese oxides and structureless detrital aggregates cemented by opal a barite and calcite occur around the main discharge conduits these aggregates are overlaid by silica carbonate fine layered stromatolitic aggregates that extend some meters from the hot springs forming crusts and coalescing rims over volcanic pebbles and boulders manganese crusts are made up of barium rich x ray amorphous todorokite like and romanechite phases and represent a rare example of a manganese deposit formed in a shallow submarine hydrothermal environment in the submarine diffuse venting area the hydrothermal precipitates are less conspicuous and consist in millimeter thick iron oxyhydroxide coatings on volcanic cobbles and boulders these coatings are composed of poorly crystallized six line ferrihydrite accompanied by minor cinnabar and fine grained colloform pyrite textures and fabrics of the mineral assemblages suggest microbial mediation for mineral deposition the vent precipitates display a significant enrichment of hg as and sb arsenic is probably adsorbed onto mn and fe oxide substrates the nasc north american shale composite normalized ree patterns of the vent precipitates show a pronounced positive eu anomaly that is probably inherited from the hydrothermal fluid

evolution of submarine eruptive activity during the 2011 2012 el hierro event as documented by hydroacoustic images and remotely operated vehicle observations submarine volcanic eruptions are frequent and important events yet they are rarely observed here we relate bathymetric and hydroacoustic images from the 2011 to 2012 el hierro eruption with surface observations and deposits imaged and sampled by rov as a result of the shallow submarine eruption a new volcano named tagoro grew from 375 to 89 m depth the eruption consisted of two main phases of edifice construction intercalated with collapse events hydroacoustic images show that the eruptions ranged from explosive to effusive with variable plume types and resulting deposits even over short time intervals at the base of the edifice rov observations show large accumulations of lava balloons changing in size and type downslope coinciding with the area where floating lava balloon fallout was observed peaks in eruption intensity during explosive phases generated vigorous bubbling at the surface extensive ash vesicular lapilli and formed high density currents which together with periods of edifice gravitational collapse produced extensive deep volcaniclastic aprons secondary cones developed in the last stages and show evidence for effusive activity with lava ponds and lava flows that cover deposits of stacked lava balloons chaotic masses of heterometric boulders around the summit of the principal cone are related to progressive sealing of the vent with decreasing or variable magma supply hornitos represent the final eruptive activity with hydrothermal alteration and bacterial mats at the summit our study documents the distinct evolution of a submarine volcano and highlights the range of deposit types that may form and be rapidly destroyed in such eruptions

evidence of a modern deep water magmatic hydrothermal system in the canary basin eastern central atlantic ocean new seismic profiles bathymetric data and sediment rock sampling document for the first time the discovery of hydrothermal vent complexes and volcanic cones at 4800 5200 m depth related to recent volcanic and intrusive activity in an unexplored area of the canary basin eastern atlantic ocean 500 km west of the canary islands a complex of sill intrusions is imaged on seismic profiles showing saucer shaped parallel or inclined geometries three main types of structures are related to these intrusions type i consists of cone shaped depressions developed above inclined sills interpreted as hydrothermal vents type ii is the most abundant and is represented by isolated or clustered hydrothermal domes bounded by faults rooted at the tips of saucer shaped sills domes are interpreted as seabed expressions of reservoirs of ch4 and co2 rich fluids formed by degassing and contact metamorphism of organic rich sediments around sill intrusions type iii are hydrothermal volcanic complexes originated above stratified or branched inclined sills connected by a chimney to the seabed volcanic edifice parallel sills sourced from the magmatic chimney formed also domes surrounding the volcanic cones core and dredges revealed that these volcanoes which must be among the deepest in the world are constituted by oib type basanites with an outer ring of blue green hydrothermal al rich smectite muds magmatic activity is dated based on lava samples at 0 78 0 05 and 1 61 0 09 ma k ar methods and on tephra layers within cores at 25 237 ky the subvent hydrothermal volcanic complex constitutes the first modern system reported in deep water oceanic basins related to intraplate hotspot activity

geochemistry of diverse basalt types from loihi seamount hawaii petrogenetic implications the wide variety of basalt types tholeiitic to basanite dredged from loihi seamount have minor and trace element abundances that are characteristic of subaerial hawaiian basalts thereby confirming that loihi seamount is a manifestation of the hawaiian hot spot within the loihi sample suite there are well defined positive correlations among abundances of highly incompatible elements p k rb ba nb light ree and ta and moderately incompatible elements sr ti zr and hf and between mgo ni and cr however within the loihi suite abundance ratios of geochemically similar elements zr hf nb ta and la ce vary by factors of 1 2 1 5 and abundance ratios of highly incompatible elements such as p ce p th k rb ba th and la nb vary by factors of 1 2 2 5 these abundance ratios are not readily changed by different degrees of fractionation and melting therefore we conclude that these samples are not genetically related by different degrees of melting of a compositionally homogeneous source on the basis of k p k ti p ce zr nb th p and la sm abundance ratios the twelve samples studied in detail can be divided into six geochemical groups samples within each group are similar in 87sr 86sr 1 and intra group compositional variations may reflect low pressure fractionation and different degrees of melting in addition crossing chondrite normalized ree patterns within the alkalic basalt groups reflect equilibration of the magmas with garnet in ratio ratio plots involving abundance ratios of highly incompatible elements e g la p nb p k p rb p ba p and th p the geochemical groups define linear arrays suggestive of mixing however these data combined with the isotopic data are not consistent with two component mixing

volcanic and geochemical evolution of the teno massif tenerife canary islands some repercussions of giant landslides on ocean island magmatism large scale catastrophic mass wasting is a major process contributing to the dismantling of oceanic intraplate volcanoes recent studies however have highlighted a possible feedback relationship between flank collapse or incipient instability and subsequent episodes of structural rearrangement and or renewed volcano growth the teno massif located in northwestern tenerife canary islands is a deeply eroded miocene shield volcano that was built in four major eruptive phases punctuated by two lateral collapses each removing 20 25 km3 of the volcano s north flank in this paper we use detailed field observations and petrological and geochemical data to evaluate possible links between large scale landslides and subsequent volcanism magmatism during teno s evolution inspection of key stratigraphic sequences reveals that steep angular unconformities relics of paleolandslide scars are marked by polymict breccias near their base these deposits typically include abundant juvenile pyroclastic material otherwise scarce in the region while some of teno s most evolved low density magmas were produced just before flank collapses early postlandslide lava sequences are characterized by anomalously high proportions of dense ankaramite flows extremely rich in clinopyroxene and olivine crystals a detailed sampling profile shows transitions from low mg lavas relatively rich in sio2 to lavas with low silica content and comparatively high mg after both landslides long term variations in zr nb normative nepheline and la lu are coupled but do not show a systematic correlation with stratigraphic boundaries we propose that whereas loading of the growing precollapse volcano promoted magma stagnation and differentiation the successive giant landslides modified the shallow volcano tectonic stress field at teno resulting in widespread pyroclastic eruptions and shallow magma reservoir drainage this rapid unloading of several tens of km3 of near surface rocks appears to have upset magma differentiation processes while facilitating the remobilization and tapping of denser ankaramite magmas that were stored in the uppermost mantle degrees of mantle melting coincidently reached a maximum in the short time interval between the two landslides and declined shortly after probably reflecting intrinsic plume processes rather than a collapse induced influence on mantle melting our study of teno volcano bears implications for other oceanic volcanoes where short term compositional variations may also directly relate to major flank collapse events

monitoring the volcanic unrest of el hierro canary islands before the onset of the 2011 2012 submarine eruption 1 on 10 october 2011 a submarine volcanic eruption started 2 km south from el hierro island spain since july 2011 a dense multiparametric monitoring network was deployed all over the island by instituto geografico nacional ign by the time the eruption started almost 10000 earthquakes had been located and the deformation analyses showed a maximum deformation of more than 5 cm earthquake migration from the north to the south of the island and acceleration of seismicity are in good correlation with changes in the deformation pattern as well as with some anomalies in geochemical and geomagnetic parameters an earthquake of local magnitude 4 3 at 12 km depth 8 october 2011 and shallower seismicity a day after preceded the onset of the eruption this is the first time that a volcanic eruption is fully monitored in the canary islands data recorded during this unrest episode at el hierro will contribute to understand reawakening of volcanic activity in this region and others of similar characteristics

k ar ages and magnetic stratigraphy of a hotspot induced fast grown oceanic island el hierro canary islands abstract the combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands this method has been successfully applied on the island of el hierro the westernmost island of the canaries archipelago for the emerged part of this island built in the last 1 2 ma magnetic stratigraphy and mapping show the presence of four consecutive subchrons k ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy the ages show that the magnetic polarity zones correlate to the upper part of the matuyama and to the brunhes chrons the jaramillo normal polarity subchron of the upper part of the matuyama reverse polarity chron is recorded in one of the lava sequences the lower limit of this event is constrained by two ages of 1 04 0 02 ma and one of 1 05 0 02 ma close to the value deduced from the astronomically tuned magnetic polarity time scale apts the volcanic history can be summarised by two consecutive main basaltic volcanic edifices the el tinor active during the upper part of the matuyama chron and the el golfo edifice constructed during the brunhes chron

the history of intrusive activity on the island of la palma canary islands abstract the island of la palma located in the northwest of the canary archipelago consists of two main geological units 1 the subaerial extrusive coberta series covers most of the island and consists of alkali basaltic lavas phonolitic plugs and pyroclastic rocks erupted between 1 61 ma and the recent 2 the basement complex is exposed in the barranco de las angustias and the caldera de taburiente and consists of the submarine intrusive and extrusive seamount series and a basal plutonic complex alkali basaltic dikes of different ages and orientations intruded in both units three groups of dikes and sills can be distinguished based on their field relationships petrography geochemistry and ages the oldest group i represent the feeder dikes to the seamount series intruded between 2 9 and 4 0 ma b p they were originally steep with a n05 w strike and perpendicular to the originally nearly flat bedding of the layered seamount series subsequent to emplacement group i dikes and the extrusives of the seamount series were rotated into their present orientation group ii sills intruded parallel to the bedding of the seamount series 45 230 are coeval with or younger than group i but older than the erosional unconformity separating the coberta and the basement complex i e 1 6 ma 50 vol of the volcanic edifice of the la palma seamount and highlight the importance of intrusive processes for island growth intrusions into central oceanic volcanoes like la palma may result in an uplift and rotation of more than 30 km 3 by up to 45

extreme spatial and temporal variability of hydrothermal microbial mat communities along the mariana island arc and southern mariana back arc system 1 twenty five microbial communities were sampled from 18 different hydrothermal systems located at seven different sites along the mariana island arc and at a single site from the southern mariana spreading center over a 3 year period terminal restriction fragment length polymorphism t rflp analysis of the small subunit rrna gene revealed that the microbial community diversity is much greater along the mariana arc back arc than at either hot spot volcanoes or mid ocean ridges along the same spatial scale cluster analysis of t rflp fingerprints reveals the microbial communities formed three distinct clusters designated mariana clusters i ii and iii microbial communities in mariana cluster i are all associated with iron rich microbial mats and are dominated by members of the proteobacteria and by unique phylotypes clustering deeply in the proteobacteria and within the nitrospira division mariana cluster ii communities are all from shallow hydrothermal systems and mostly from colder sediments or microbial mats that are dominated by putative heterotrophic phylotypes usually associated with seawater and sediments not generally associated with hydrothermal fluid inputs mariana cluster iii is generally from much hotter vent sites and is dominated by sulfur oxidizing proteobacteria quantitative polymerase chain reaction q pcr of archaeal abundance reveal that all of the microbial communities are dominated by members of the bacterial domain sampling of microbial mats from iceberg vent at nw rota 1 in 2004 and again in 2006 reveal the community has shown a transition from caminibacter group proteobacteria phylotypes to a mixed population of caminibacter sulfurovum and sulfurimonas group proteobacteria

growth structure instability and collapse of canarian volcanoes and comparisons with hawaiian volcanoes recent onshore and offshore investigations in the canarian archipelago especially in the western islands of la palma and el hierro have greatly improved the understanding of the genesis and evolution of these islands and allow interesting comparisons with other hotspot induced oceanic island volcanoes especially the hawaiian archipelago genesis induced by hotspot activity and consequently shield and post erosional stages of growth allow the definition of similar main stratigraphic units the canarian and hawaiian volcanoes show common constructional and structural features such as rift zones progressive volcano instability and multiple gravitational collapses however the canaries present some important geological differences from the prototypical hotspot volcanoes of the hawaiian islands particularly the absence of significant subsidence the canarian volcanoes remain emergent until completely mass wasted by gravitational collapses and erosion volcanic formations over 20 million years are observable in outcrop in the canaries including the seamount stages of growth in several of the islands

hot dry rock geothermal reservoir testing 1978 to 1980 abstract the phase i hot dry rock geothermal energy reservoirs at the fenton hill field site grew continuously during run segments 2 through 5 january 1978 to december 1980 reservoir growth was caused not only by pressurization and hydraulic fracturing but also by heat extraction and thermal contraction effects reservoir heat transfer area grew from 8000 to 50 000 m2 and reservoir fracture volume grew from 11 to 266 m3 despite this reservoir growth the water loss rate increased only 30 under similar pressure environments for comparable temperature and pressure conditions the flow impedance a measure of the resistance to circulation of water through the reservoir remained essentially unchanged and if reproduced in the phase ii reservoir under development could result in self pumping geochemical and seismic hazards have been nonexistent in the phase i reservoirs the produced water is relatively low in total dissolved solids and shows little tendency for corrosion or scaling the largest microearthquake associated with heat extraction measures less than minus one on the extrapolated richter scale

a new scenario for the mass transport deposits west canary volcanic province abstract a new temporal history of mass wasting processes for the west of the canary volcanic province is presented its onset has been estimated in the middle upper miocene 13 5 1 2 ma matching with a critical period of construction for this volcanic province seismic profiles show an emplacement longevity from the miocene to quaternary in multiple events defined by stacked lobes of debrites linked to the flank collapses and volcanic avalanches of the volcanic edifices islands and seamounts an evolution of pathways and source areas has been detected from east miocene to west quaternary as well as a migration of the activity to the northwest west of the canary islands e g el hierro and la palma six connected branches i vi three of them described for the first time here of quaternary seismic units of mass transport deposits mtds have been characterized the pleistocene makes up a huge buried mtds system until now unknown pointing a new mass transport sedimentological scenario finally the two southernmost branches v vi up to now unknown are a mainly buried system of stacked and terraced lobes of debrites sourced mainly from the flank collapses of the volcanic seamounts of the canary island seamount province apparently inactive from upper cretaceous

comparison of iron isotope variations in modern and ordovician siliceous fe oxyhydroxide deposits abstract formation pathways of ancient siliceous iron formations and related fe isotopic fractionation are still not completely understood investigating these processes however is difficult as good modern analogues to ancient iron formations are scarce modern siliceous fe oxyhydroxide deposits are found at marine hydrothermal vent sites where they precipitate from diffuse low temperature fluids along faults and fissures on the seafloor these deposits exhibit textural and chemical features that are similar to some phanerozoic iron formations raising the question as to whether the latter could have precipitated from diffuse hydrothermal fluids rather than from hydrothermal plumes in this study we present the first data on modern fe oxyhydroxide deposits from the jan mayen hydrothermal vent fields norwegian greenland sea the samples we investigated exhibited very low 56fe values between 2 09 and 0 66 due to various degrees of partial oxidation the fe oxyhydroxides are with one exception either indistinguishable from low temperature hydrothermal fluids from which they precipitated 1 84 and 1 53 in 56fe or are enriched in the heavy fe isotopes in addition we investigated fe isotope variations in ordovician jasper beds from the lokken ophiolite complex norway which have been interpreted to represent diagenetic products of siliceous ferrihydrite precursors that precipitated in a hydrothermal plume in order to compare different formation pathways of fe oxyhydroxide deposits iron isotopes in the jasper samples have higher 56fe values 0 38 to 0 89 relative to modern high temperature hydrothermal vent fluids ca 0 40 on average supporting the fallout model however formation of the ordovician jaspers by diffuse venting cannot be excluded due to lithological differences of the subsurface of the two investigated vent systems our study shows that reliable interpretation of fe isotope variations in modern and ancient marine fe oxyhydroxide deposits depends on comprehensive knowledge of the geological context furthermore we demonstrate that very negative 56fe values in such samples might not be the result of microbial dissimilatory iron reduction but could be caused instead by inorganic reactions

loihi seamount hawaii a mid plate volcano with a distinctive hydrothermal system the initial discovery of deep sea hydrothermal vents at the galapagos rift1 2 has resulted in a decade of exploration and experimentation subsequent discoveries in the pacific3 8 and atlantic9 ocean basins have established the importance of these features as sources of mantle derived gases and solutes10 2 and as loci for heat dissipation13 14 polymetallic sulphide mineral deposition15 16 and geochemical exchange17 19 the presence of dense communities of bacteria and specialized macrofauna20 22 has called into question the absolute role of sunlight as the principal energy source for marine organisms until recently these deep sea vents were known only at or near plate boundaries but recent dredging23 24 near bottom water sampling25 27 and sea floor camera survey28 programmes have indicated that hydrothermal vents are present at the summit of loihi seamount a mid plate hotspot submarine volcano at the southern end of the hawaiian island chain29 here we report results obtained from sampling two active vent fields the fluid chemistry especially high co2 and fe presence of alkalic lavas and iron depositing bacteria and absence of macrofauna suggest that mid plate vents may differ from the hydrothermal vents found at mid ocean ridges

geochemistry of hydrothermal deposits from loihi submarine volcano hawaii abstract dredging across the northeast rim of the summit crater of loihi seamount recovered several morphologically similar but chemically and mineralogically distinct hydrothermal deposits encrusting the surface of fresh pillow lava talus the multicolored deposits suggest a precipitation sequence that may be controlled by an oxidation reduction gradient in which smectite ranging in composition from fe montmorillonite to nontronite has precipitated along with iron oxide under slightly reducing conditions this deposition was apparently followed by amorphous iron oxide and silica precipitation possibly under more oxic conditions oxygen isotope geothermometry indicates formation temperatures in the range of 31 57 c for the loihi smectites trace element enrichments appear to be positively correlated with the isotopic formation temperature of the smectite suggesting either increased trace element solubility within the higher temperature vent fluids or increased smectite and iron oxide scavenging with increased precipitation rates the trace element abundances further suggest the presence of polymetallic sulfides that either are directly associated with the smectites as amorphous phases or occur beneath these deposits in the volcanic pile of the seamount

experimental study of iron and silica immobilization by bacteria in mixed fe si systems implications for microbial silicification in hot springs the immobilization of silica and iron by the bacteria bacillus subtilis was monitored in controlled microcosms to elucidate the role iron may play in aiding bacterial silicification in hot springs silica and iron immobilization was monitored as a function of bacterial concentration iron concentration and silica concentration both undersaturated and oversaturated with respect to amorphous silica results demonstrate that bacterial cells do immobilize more fe than bacteria free systems in solutions with iron concentrations 50 ppm fe however as iron concentrations increase the difference between fe immobilization in bacterial and bacteria free systems decreases as non bacterially mediated precipitation processes dominate additionally bacterial systems that had immobilized more fe compared with bacteria free systems did not immobilize more silica than bacteria free systems by comparing molar ratios of silica in solution bacterially bound fe it is evident that insufficient iron is bound to the bacterial surface to act as an effective salt bridge for silica sorption this appears to be because much of the iron is immobilized by non bacterially mediated precipitation of phases such as fe oh 3 and poorly ordered hydrous iron silicates it follows that in silica enriched hot springs silica and iron immobilization processes are significantly dominated by non bacterially mediated precipitation any bacterially mediated processes are exceedingly small and outside the resolution of these experiments

hydrothermal oxide and nontronite deposits on seamounts in the eastern pacific deposits of fe oxide mud nontronite and fe mn crusts were sampled from the summits of two seamounts in the eastern pacific where low temperature 0 15 c hydrothermal fluids are issuing the deposits consist of x ray amorphous fe oxyhydroxide and are rich in fe 43 wt contain minor si and p 4 and 3 5 respectively and have very low mn 0 01 and other trace element contents other deposits where no current hydrothermal activity was observed consist of mud and crusts composed of amorphous material and poorly crystalline hematite goethite and smectite these deposits have slightly higher mn up to 2 and other trace element contents the mineralogical and chemical differences between the active and inactive deposits and crusts are interpreted to be due to recrystallization and contamination with detrital biogenic hydrogenous and possibly hydrothermal sulfide material nontronite deposits capped by fe mn oxides were sampled from one of the seamounts these deposits have compositions similar to other seafloor nontronite deposits and formed at low temperatures 30 c during mixing of low temperature hydrothermal fluids with seawater the oxide deposits consist almost entirely of long delicate filaments remarkably similar in morphology to genera of fe oxidizing bacteria such bacteria were probably important in catalyzing the oxidation and precipitation of iron from hydrothermal fluids on the seamounts the occurrence of nearly identical filament rich oxide deposits on two widely separated seamounts suggests that this type of deposit may be common on seamounts but previously unrecognized

a regional strategy for geothermal exploration with emphasis on gravity and magnetotellurics abstract as part of the resource evaluation and exploration program conducted by los alamos scientific laboratory for the national hot dry rock hdr geothermal program a regional magnetotelluric mt survey of new mexico and arizona is being performed the mt lines are being located in areas where the results of analysis of residual gravity anomaly maps of arizona and new mexico integrated with other geologic and geophysical studies indicate the greatest potential for hdr resources the residual gravity anomalies are derived by applying the concept of predicting gravity anomalies from topography this can be accomplished by employing reductions similar to those used in some isostatic investigations in which a regional topographic surface is used as the bouguer reduction datum the datum is derived by comparison of various harmonics of bouguer anomalies and elevations of stations topography can be used to predict bouguer anomalies because of isostatic compensation the resultant anomalies can be considered high frequency residual anomalies or isostatic anomalies corrected for regional compensation such maps have been produced for arizona new mexico west texas and chihuahua mexico the main objective of the mt project is to produce a regional geoelectric contour map of the pervasive deep electrical conductor within the crust and or upper mantle beneath the colorado plateau and the adjacent basin and range province and rio grande rift the mt survey consists of 200 sites along several long profiles with site spacing of 15 20 km pre existing available mt data are being integrated with the new data after the data are processed a one dimensional inversion is applied to the sounding curve and used as a starting point for 2 d modeling such a project and ultimate map will be of major value in studying the regional geophysics and tectonics of the southwest united states as they now apply to hdr resources in particular and geothermal resources in general electrical conductivity anomalies of large areal extent are of particular interest in geothermal exploration correlation analysis of large conductive anomalies with other geophysical geological and geotectonic data is being performed preliminary analysis of the data has suggested several major regions of anomalously shallow high electrical conductivity among these is the aquarius area of northwest arizona which is the site of a longwavelength residual anomaly low which when modeled and correlated with other geophysical data can be shown to be possibly related to low density and high temperature in the crust at depths of 20 km or less preliminary analysis of mt data indicates the possible existence of a mid crustal high electrical conductivity anomaly in this same region