molybdenum mineralization in an active geothermal system valles caldera new mexico shallow sub ore grade molybdenite mineralization has been discovered in the active high temperature geothermal system penetrated by continental scientific drilling program corehole vc 2a at sulfur springs in the western ring fracture zone of the valles caldera new mexico this mineralization is hosted by fractured quartz sericitized intracaldera ash flow tuffs younger than 1 12 ma the molybdenite is an unusual poorly crystalline variety that occurs in vuggy veinlets and breccia cements also containing quartz sericite illite pyrite and fluorite as well as local sphalerite rhodochrosite and chalcopyrite fluid inclusion data suggest that this assemblage was deposited from very dilute solutions at temperatures near 200 sup 0 c geochemical modeling indicates that under restricted ph and fo sub 2 conditions at 200 sup 0 c the molybdenite and associated phases would be in equilibrium with hydrothermal fluids now circulating in the deep subsurface the shallow molybdenite zone intersected in vc 2a may be the near surface expression of deep climax type stockwork molybdenum mineralization

travertine deposits of soda dam new mexico and their implications for the age and evolution of the valles caldera hydrothermal system uranium thorium disequilibrium dates and stable isotope analyses of travertine deposits at soda dam new mexico have been used to determine the age and to document the evolution of the valles caldera hydrothermal system soda dam discharges from paleozoic and precambrian rocks in san diego canyon southwest of the caldera and the canyon was filled with several hundred metres of upper bandelier tuff during formation of valles caldera 1 12 ma according to the dates the valles hydrothermal system is at least 106 yr old or nearly as old as the caldera the basic hydrology of the system has thus remained virtually unchanged during this time travertine ages indicate pulses in travertine deposition from 1 0 to 0 48 ma from 0 107 to 0 058 ma and from 0 005 ma to present the volume of various travertine deposits suggests that the hot spring system at soda dam was once larger than it is today possibly discharging as much as 5 to 10 times more fluid of na hco3 cl composition stable isotopes of the travertines indicate however that the hot spring system has probably never been more than about 10 c hotter than the present maximum temperature of 48 c stable isotopes also show that the 13c of co2 and 18o of h2o in hot spring waters has remained relatively constant for 106 yr the similar ages between caldera formation and the onset of large scale hydrothermal circulation and travertine deposition on pre bandelier tuff rocks imply that incision rates by the jemez river in bandelier tuff were relatively rapid as much as 400 m of tuff were cut by the ancestral jemez river in 105 yr or less

geochemistry and isotopes of fluids from sulphur springs valles caldera new mexico abstract detailed geochemistry supported by geologic mapping has been used to investigate sulphur springs an acid sulfate hot spring system that issues from the western flank of the resurgent dome inside valles caldera the most intense activity occurs at the intersection of faults offsetting caldera fill deposits and post caldera rhyolites three geothermal wells in the area have encountered pressures 4 8000 mg l these conditions cause argillic alterations throughout a large area non condensible gases consist of roughly 99 co 2 with minor amounts of h 2 s h 2 and ch 4 empirical gas geothermometry suggests a deep reservoir temperature of 215 to 280 c comparison of 13 c and 18 o between caco 3 from well cuttings and co 2 from fumarole steam indicates a fractionation temperature between 200 and 300 c by decarbonation of hydrothermally altered paleozoic limestone and vein calcite in the reservoir rocks tritium concentrations obtained from steam condensed in a mudpot and deep reservoir fluids baca 13 278 c are 2 1 and 1 0 t u respectively suggesting the steam originates from a reservoir whose water is mostly 50 yrs old deuterium contents of fumarole steam deep reservoir fluid and local meteoric water are practically identical even though 18 o contents range through 4 thus precipitation on the resurgent dome of the caldera could recharge the hydrothermal system by slow percolation from analysis of d and 18 o values between fumarol steam and deep reservoir fluid steam reaches the surface either 1 by vaporizing relatively shallow groundwater at 200 c or 2 by means of a two stage boiling process through an intermediate level reservoir at roughly 200 c although many characteristics of known vapor dominated geothermal systems are found at sulphur springs fundamental differences exist in temperature and pressure of our postulated vapor zone we propose that the reservoir beneath sulphur springs is too small or too poorly confined to sustain a true vapor dominated system and that the sulphur springs system may be a dying vapor dominated system that has practically boiled itself dry

open fissure mineralization at 2600 m depth in long valley exploratory well california insight into the history of the hydrothermal system abstract long valley exploratory well drilled into the resurgent dome at long valley caldera california to explore the potential of geothermal power in an active magmatic system achieved temperatures of only ca 100 c at 2500 3000 m depth well below the range expected atop an active magma chamber open fissures encountered at 2600 m depth are coated by mm sized idiomorphic quartz crystals with first and second order growth discontinuities specific growth defects indicating rapid crystallization reflect sudden changes in sio 2 supersaturation fluid inclusions contain low salinity 0 5 wt nacl and low co 2

stratigraphic relations and lithologic variations in the jemez volcanic field new mexico over 100 radiometric dates and recent detailed geologic mapping allow some refinements of the stratigraphic relations of major units and generalization of temporal lithologic variations in the jemez volcanic field volcanism had begun in the area by about 16 5 ma with episodic eruptions of alkaline basalts by 13 ma alkaline volcanism had been replaced with eruptions of more voluminous olivine tholeiite high silica rhyolite derived from melts of lower crust also was erupting by about 13 ma basalt and high silica rhyolite continued to be erupted until about 7 and 6 ma respectively but effusions of dominantly andesitic differentiates of basalt that began as early as about 12 ma volumetrically overshadowed all other eruptive products between 10 and 7 ma from 7 to 3 ma the dominant erupted lithology was dacite which appears to have been generated by mixing of magmas whose compositions are approximated by earlier andesites and high silica rhyolites less than 4 3 ma volcanism was dominated by eruption of rhyolitic tuffs field relations geochemistry and dates specifically indicate the following with regards to stratigraphie relations 1 distinctions among basalt of chamisa mesa paliza canyon formation basalts and lobato basalt for other than geographic reasons are artificial basaltic volcanism was continuous in volcanic field from 13 to 7 ma 2 canovas canyon and bearhead rhyolites form a continuum of high silica rhyolite volcanism from 13 to 6 ma 3 hypabyssal and volcanic rocks of the cochiti mining district probably represent the exhumed interior of a keres group volcano s 4 temporal overlaps exist among the major stratigraphie groups which may imply some genetic relations and 5 the tewa group formation cerro rubio quartz latite may more appropriately be considered part of the tschicoma formation of the polvadera group preliminary analysis of hydrothermal alteration in the context of the volcanic stratigraphy suggests at least three distinct hydrothermal events have occurred in the volcanic field s history

zeolitization of intracaldera sediments and rhyolitic rocks in the 1 25 ma lake of valles caldera new mexico usa abstract quantitative x ray diffraction analysis of about 80 rhyolite and associated lacustrine rocks has characterized previously unrecognized zeolitic alteration throughout the valles caldera resurgent dome the alteration assemblage consists primarily of smectite clinoptilolite mordenite silica which replaces groundmass and fills voids especially in the tuffs and lacustrine rocks original rock textures are routinely preserved mineralization typically extends to depths of only a few tens of meters and resembles shallow caldera type zeolitization as defined by utada et al utada m shimizu m ito t inoue a 1999 alteration of caldera forming rocks related to the sanzugawa volcanotectonic depression northeast honshu japan with special reference to caldera type zeolitization resource geol spec issue no 20 129 140 geology and 40 ar 39 ar dates limit the period of extensive zeolite growth to roughly the first 30 kyr after the current caldera formed ca 1 25 to 1 22 ma zeolitic alteration was promoted by saturation of shallow rocks with alkaline lake water a mixture of meteoric waters and degassed hydrothermal fluids and by high thermal gradients caused by cooling of the underlying magma body and earliest post caldera rhyolite eruptions zeolitic alteration of this type is not found in the later volcanic and lacustrine rocks of the caldera moat 0 8 ma suggesting that later lake waters were cooler and less alkaline the shallow zeolitic alteration does not have characteristics resembling classic alkaline lake zeolite deposits no analcime erionite or chabazite nor does it contain zeolites common in high temperature hydrothermal systems laumontite or wairakite although aerially extensive the early zeolitic alteration does not form laterally continuous beds and are consequently not of economic significance

an interpretation of the alteration assemblages at sulphur springs valles caldera new mexico sulphur springs located near the western edge of the valles caldera north central new mexico is the only vapor dominated surface manifestation of any significance found in the valles the percolating acid sulfate waters and fumarolic gases have leached and oxidized the country rock near the hot springs to a bleached wasteland the near surface mineral assemblages at 90 c are restricted to one and two phases occurring in contact with a variety of solutions and gases the conditions of local equilibrium at 90 g are approximately halotrichite alunogen log fo2 45 log fs2 12 ph 0 3 szomolnokite pyrite log fo2 46 log fs2 16 ph 0 8 alunite log fo2 50 log fs2 10 ph 1 2 kaolinite sulphur log fo2 53 log fs2 10 ph 1 2 log ak 0 0012 m log asio2 0 0033 m and pyrite log fo2 60 log fs2 19 ph 4 3 this study has demonstrated that local equilibrium is closely approached even under the low temperature and pressure conditions found near the surface

fluid inclusion from drill hole dw 5 hohi geothermal area japan evidence of boiling and procedure for estimating co2 content abstract fluid inclusion studies have been used to derive a model for fluid evolution in the hohi geothermal area japan six types of fluid inclusions are found in quartz obtained from the drill core of dw 5 hole they are i primary liquid rich with evidence of boiling ii primary liquid rich without evidence of boiling iii primary vapor rich assumed to have been formed by boiling iv secondary liquid rich with evidence of boiling v secondary liquid rich without evidence of boiling vi secondary vapor rich assumed to have been formed by boiling homogenization temperatures t h range between 196 and 347 c and the final melting point of ice t m between 0 2 and 4 3 c the co 2 content was estimated semiquantitatively to be between 0 and 0 39 wt based on the bubble behavior on crushing nacl equivalent solid solute salinity of fluid inclusions was determined as being between 0 and 6 8 wt after minor correction for co 2 content fluid inclusions in quartz provide a record of geothermal activity of early boiling and later cooling the co 2 contents and homogenization temperatures of fluid inclusions with evidence of boiling generally increase with depth these changes and nacl equivalent solid solute salinity of the fluid can be explained by an adiabatic boiling model for a co 2 bearing low salinity fluid some high salinity inclusions without co 2 are presumed to have formed by a local boiling process due to a temperature increase or a pressure decrease the liquid rich primary and secondary inclusions without evidence of boiling formed during the cooling process the salinity and co 2 content of these inclusions are lower than those in the boiling fluid at the early stage probably as a result of admixture with groundwater

mineralization and hydrothermal history of the tiwi geothermal system philippines tiwi is one of several large geothermal fields in the philippines in 1992 the drilling of matalibong 25 provided nearly 1 650 m of continuous core from the geothermal reservoir a maximum temperature of 275 c at 1 829 m and intense hydrothermal alteration were encountered in this well six stages of alteration and vein mineralization have been documented in the cored portion of the well the earliest stage which reflects the initial development of the system is represented by the deposition of chalcedony and clays stage 1 the transition to a high temperature environment is marked by the appearance of sericite stage 2 deposited by steam heated waters stage 3 reflects episodic cycles of fluid upwelling and boiling followed by the incursion of cooler fluids veins deposited by boiling fluids are filled with quartz adularia epidote pyrite and base metal sulfides whereas heating of the recharging fluids led to the deposition of calcite and or anhydrite maximum temperatures of fluid inclusions trapped in two quartz crystals deposited by the upwelling fluids range from 325 to 332 c temperatures varied widely during the recharge phase of these cycles fluid inclusions trapped in calcite and anhydrite suggest that mineral deposition occurred at temperatures ranging from 333 c to less than 270 c fluid inclusion salinities indicate that seawater dominated below a depth of 1 600 m whereas fresh waters dominated at shallower depths gaseous species trapped in these inclusions were released by crushing or thermal decrepitation and analyzed with a quadrupole mass spectrometer co2 ch4 and n2 ar ratios indicate that the gaseous species trapped in calcite and anhydrite were derived primarily from meteoric and crustal sources in contrast gaseous species in quartz from matalibong 25 and advanced argillic assemblages from other tiwi wells have magmatic and crustal origins stage 4 represents a second major episode of sericite deposition subsequent mineralization consisted of wairakite epidote followed by actinolite and then calcite stage 5 the presence of actinolite implies that temperatures exceeded 300 c at the end of this stage thermochemical modeling indicates that the modern stage 6 fluids are again in equilibrium with sericite 40ar 39ar spectrum dating of stage 3 adularia from three depths has been combined with the mineral parageneses and fluid inclusion homogenization temperatures to constrain the thermal history of the geothermal system taken together these data record the deposition of adularia at 330 c between 314 and 279 ka minor cooling followed by reheating to produce stage 5 actinolite at 200 to 220 ka incursion of marginal waters and cooling to 235 c by 190 ka a long period of quiescence to 50 ka and finally development of the modern thermal regime at 10 to 50 ka in response to a recent subvolcanic intrusion

the precession phase of the boreal summer monsoon as viewed from the eastern mediterranean odp site 968 the astronomical timescale of the eastern mediterranean plio pleistocene builds on tuning of sapropel layers to northern hemisphere summer insolation maxima a 3000 year precession lag has become instrumental in the tuning procedure as radiocarbon dating revealed that the midpoint of the youngest sapropel s1 in the early holocene occurred approximately 3000 years after the insolation maximum the origin of the time lag remains elusive however because sapropels are generally linked to maximum african monsoon intensities and transient climate modeling results indicate an in phase behavior of the african monsoon relative to precession forcing here we present new high resolution records of bulk sediment geochemistry and benthic foraminiferal oxygen isotopes from odp site 968 in the eastern mediterranean we show that the 3000 year precession time lag of the sapropel midpoints is consistent with 1 the global marine isotope chronology 2 maximum monsoonal precipitation conditions in the mediterranean region and china derived from radiometrically dated speleothem records and 3 maximum atmospheric methane concentrations in antarctica ice cores we show that the time lag relates to the occurrence of precession paced north atlantic cold events which systematically delayed the onset of strong boreal summer monsoon intensity our findings may also explain a non stationary behavior of the african monsoon over the past 3 million years due to more frequent and intensive cold events in the late pleistocene

fluid inclusion gas compositions from an active magmatic hydrothermal system a case study of the geysers geothermal field usa abstract hydrothermal alteration and the active vapor dominated geothermal system at the geysers ca are related to a composite hypabyssal granitic pluton emplaced beneath the field 1 1 to 1 2 million years ago deep drill holes provide a complete transect across the thermal system and samples of the modern day steam the hydrothermal system was liquid dominated prior to formation of the modern vapor dominated regime at 0 25 to 0 28 ma maximum temperatures and salinities ranged from 440 c and 44 wt nacl equivalent in the biotite hornfels adjacent to the pluton to 305 c and 5 wt nacl equivalent at distances of 1730 m from the intrusive contact the major minor and noble gas compositions of fluid inclusions in the hydrothermally altered rocks were integrated with microthermometric and mineralogic data to determine their sources and the effects of mixing and boiling major and minor gaseous species were released from the inclusions by crushing or thermal decrepitation noble gases were released by crushing the samples were analyzed by mass spectrometry the analyses document the presence of magmatic crustal and meteoric components in the trapped fluids hydrothermal fluids present during the liquid dominated phase of the system contained gaseous species derived mainly from crustal and magmatic sources at the geysers n 2 ar ratios greater than 525 and 3 he 4 he ratios of 6 10 7 ra are diagnostic of a magmatic component crustal gas has co 2 ch 4 ratios less than 4 n 2 ar ratios between 45 and 525 and low 3 he 4 he ratios 0 5 ra meteoric fluids have co 2 ch 4 ratios greater than 4 and n 2 ar ratios between 38 air saturated water and 84 air however n 2 ar ratios between 15 and 110 can result from boiling ratios less than 15 reflect the incorporation of n 2 into nh 3 bearing clay minerals in the central geysers the incursion of meteoric fluids occurred during the transition from the liquid to vapor dominated regime variations in the relative ch 4 co 2 and h 2 contents of the gas analyses demonstrate that boiling took place under open system conditions the gas data indicate that the inclusions have remained closed to the diffusion of he and h 2 since their formation

gas geochemistry of the valles caldera region new mexico and comparisons with gases at yellowstone long valley and other geothermal systems abstract noncondensible gases from hot springs fumaroles and deep wells within the valles caldera geothermal system 210 300 c consist of roughly 98 5 mol co 2 0 5 mol h 2 s and 1 mol other components 3 he 4 he ratios indicate a deep magmatic source r r a up to 6 whereas 13 c co 2 values 3 to 5 do not discriminate between a mantle magmatic source and a source from subjacent hydrothermally altered paleozoic carbonate rocks regional gases from sites within a 50 km radius beyond valles caldera are relatively enriched in co 2 and he but depleted in h 2 s compared to valles gases regional gases have r r a values 1 2 due to more interaction with the crust and or less contribution from the mantle carbon sources for regional co 2 are varied during 1982 1998 repeat analyses of gases from intracaldera sites at sulphur springs showed relatively constant ch 4 h 2 and h 2 s contents the only exception was gas from footbath spring 1987 1993 which experienced increases in these three components during drilling and testing of scientific wells vc 2a and vc 2b present day valles gases contain substantially less n 2 than fluid inclusion gases trapped in deep early stage post caldera vein minerals this suggests that the long lived valles hydrothermal system ca 1 myr has depleted subsurface paleozoic sedimentary rocks of nitrogen when compared with gases from many other geothermal systems valles caldera gases are relatively enriched in he but depleted in ch 4 n 2 and ar in this respect valles gases resemble end member hydrothermal and magmatic gases discharged at hot spots galapagos kilauea and yellowstone

temporal relations of volcanism and hydrothermal systems in two areas of the jemez volcanic field new mexico two hydrothermal alteration events 8 07 ma one sample 6 51 5 60 ma six samples related to the waning stages of late miocene volcanism ge 13 to le 5 8 ma are recognized at the cochiti district southeast jemez mountains most of the k ar dates 0 83 plus minus 0 11 0 66 plus minus 0 21 ma four samples in the hydrothermally altered caldera fill rocks of core hole vc 2a at sulfur springs valles caldera indicate post valles caldera hydrothermal alteration a sample from acid altered landslide debris of postcaldera tuffs from the upper 13 m of the core hole was too young to be dated by the k ar method and is possibly associated with current hot spring activity and the youngest pulses of volcanism oxygen isotope data from illite smectite clays in the cochiti district are zonally distributed and range from minus 2 15 per thousand to plus 7 97 per thousand smow depending upon temperature extent of rock fluid interaction and composition the samples from vc 2a get lighter with depth minus 0 20 per thousand to plus 1 62 per thousand the k ar and oxygen isotope data provide strong evidence that the epithermal quartz vein hosted gold silver mineralization at cochiti and the sub ore grade molybdenite at vc 2a were deposited in the late miocene 5 99 5 60 ma and mid quaternary approximately 0 66 ma respectively by hydrothermal fluids composed primarily of meteoric water

simulations of ecosystem response during the sapropel s1 deposition event abstract a one dimensional ecosystem numerical model is used to simulate the ecosystem changes that could have occurred in the open ocean areas of the eastern mediterranean sea during the climatic optimum interval 9500 6000 b p mercone et al mercone d thomson j croudace i w siani g paterne m troelstra s 2000 duration of s1 the most recent sapropel in the eastern mediterranean sea as indicated by accelerator mass spectrometry radiocarbon and geochemical evidence paleoceanography 15 336 347 in this period the s1 sapropel was deposited s1 is the most recent sapropel in the succession of organic carbon rich layers intercalated in normal neogene sedimentary sequences different theories have been invoked in order to explain the deposition of this peculiar layer our simulations seem to indicate that the modified thermohaline circulation supplying oxygen only in the first 500 m of the water column is responsible for the sapropel deposition when higher productivity is allowed in the euphotic zone the model shows the importance in this process of bacteria that consume oxygen by decomposing the particulate organic matter pom produced in the upper water column the sinking velocity of pom partially regulates the timescale of the occurrence of anoxia at the bottom and in the whole water column allowing the relatively rapid onset of sapropel deposition

nd isotopic compositions of eastern mediterranean sediments tracers of the nile influence during sapropel s1 formation abstract nd isotopic composition of eastern mediterranean sediments are used to investigate the influence of nile flux variations during the formation of the youngest sapropel s1 four box cores located on an east west transect around 35 n at increasing distance from the nile source were studied nd 0 signatures were measured in the lithogenic alumino silicate residue fraction and the authigenic biogenic carbonates organic matter and fe mn oxyhydroxides fraction of the sediment after 1 m hcl leaching the nd 0 profiles of the residual fraction show more radiogenic values in the sapropel layers than in the adjacent sediments these profiles follow the gaussian shaped ba al profile shape which defines s1 the nd 0 variations can be related to changes in the proportions of two continental sources of particulate material nile particles and saharan aerosols a simple mixing model reveals that the contribution of nile particulates to the sediments increases relative to saharan aerosols during sapropel formation indicating a higher nile discharge and a decrease in eolian input at that time for the cores located closest to the nile fan the nd 0 signatures of the leachable fraction are always higher in the sapropel layer 5 to 4 than in the adjacent sediments 6 the sapropel layer nd 0 values increase with decreasing distance to the nile towards values close to the nile particulates all the results obtained on the leachable fraction point towards a massive input of nile freshwater during s1 deposition

large complex burrow systems from freshwater deposits of the monongahela group virgilian southeast ohio usa abstract a large burrow complex is described from the monongahela group upper pennsylvanian in southeastern ohio the burrow complex consists of a branching network of elliptical to circular horizontal tunnels 1 18 cm in diameter occurring on a single horizontal plane the tunnels branch to form x t and y junctions with branch angles between 60 and 130 branching produces multiple polygonal galleries up to 60 cm wide connected by small horizontal tunnels vertical shafts connecting the galleries to the surface are not preserved tunnel surfaces are irregular with circular to elliptical nodes and depressions elongate ridges and grooves and 1 5 4 0 cm wide nodular patches typically located at branch points the occurrence of these burrow complexes in the monongahela group represents one of the largest examples of a branching burrow complex older than the cretaceous the monongahela burrow complexes are preserved within a succession of floodplain and palustrine sediments suggesting a freshwater habitat for the tracemaking organisms potential tracemakers of the monongahela burrow complexes include a variety of pennsylvanian crustaceans and vertebrates the presence of these and similar paleozoic ichnofossils indicate a long and complex evolutionary history of the trace making behaviors associated with the construction of large open burrow networks

flux forced simulations of the paleocirculation of the mediterranean 1 a series of experiments with an ocean general circulation model of the mediterranean forced by artificial but realistic surface fluxes of heat and freshwater are performed the model has a stable thermohaline circulation under the baseline fluxes small decreases in excess evaporation 8 produce a linear weakening of the thermohaline circulation with less water formation and smaller strait transports levantine intermediate water production is shown to be very sensitive to additional freshwater input the dominant circulation mode in wetter climates is one with adriatic intermediate water formation and dispersal leading to ventilation of intermediate depths of the basin although the deep layers are not ventilated stratification is generally weak as the excess evaporation decreases stratification increases a 60 80 decrease leads to conditions closest to those suggested for sapropel s1 with a west east salinity gradient of half of today

changes in fluid geochemistry and physico chemical conditions of geothermal systems caused by magmatic input the recent abrupt outgassing off the island of panarea aeolian islands italy abstract hydrothermal systems and related vents can exhibit dramatic changes in their physico chemical conditions over time as a response to varying activity in the feeding magmatic systems massive steam condensation and gas scrubbing processes of thermal fluids during their ascent and cooling cause further compositional changes that mask information regarding the conditions evolving at depth in the hydrothermal system here we propose a new stability diagram based on the co2 ch4 co h2 concentrations in vapor which aims at calculating the temperatures and pressures in hydrothermal reservoirs to filter gas scrubbing effects we have also developed a model for selective dissolution of co2 h2s n2 ch4 he ne mixtures in fresh and or air saturated seawater this methodology has been applied to the recent november 2002 crisis that affected the geothermal field off the island of panarea italy where the fluid composition and fluxes have been monitored for the past two decades the chemical and isotopic compositions of the gases suggest that the volatile elements originate from an active magma which feeds a boiling saline solution having temperatures of up to 350 c and containing 12 mol co2 in vapor the thermal fluids undergo cooling and re equilibration processes on account of gas water rock interactions during their ascent along fracture networks furthermore steam condensation and removal of acidic species partial dissolution in cold air saturated seawater and stripping of atmospheric components affect the composition of the geothermal gases at shallow levels the observed geochemical variations are consistent with a new input of magmatic fluids that perturbed the geothermal system and caused the unrest event the present state evolution shows that this dramatic input of fluids is probably over and that the system is now tending towards steady state conditions on a time scale of months

integral view of holocene precipitation and vegetation changes in the nile catchment area as inferred from its delta sediments we compare geochemical and pollen data of several well dated high resolution cores to provide an integral holocene overview of nile outflow sedimentation and vegetation in and around the nile delta we show that the focus point of the nile plume varied considerably as indicated by planktonic foraminifer globigerinoides ruber oxygen isotopes tracing nile discharge differences in an east west delta transect at 13 11 5 cal kyr bp nile discharge was low and runoff was predominantly directed to the western part of the delta sediment arriving in the delta during that period was dominated by ethiopian highland similar to blue nile material shown by high ti al values of the bulk sediment indicating dry conditions in the source area of the blue nile nile discharge increased from similar to 11 5 cal kyr bp and was high across the whole delta from similar to 10 6 5 cal kyr bp during this time the ti al values decreased within most nile delta sediments suggesting that the relative contribution of blue nile sediment decreased this was likely due to an increased vegetation cover causing diminished erosion in the ethiopian highlands nile discharge gradually decreased from similar to 6 5 cal kyr bp to present this decrease was more abrupt in the western province of the delta and became more gradual towards the east as the shrinking nile runoff was directed there the gradual decrease in precipitation in the nile catchment area seems not to be matched by a gradual response in vegetation growing around the river plain in the lower nile catchment our findings suggest a nonlinear response of northeast african vegetation to precipitation from the middle to late holocene c 2015 elsevier ltd all rights reserved

new field evidence bearing on the origin of the el laco magnetite deposit northern chile a reply the el laco magnetite deposit has been interpreted as lava flows and feeder dikes formed from iron oxide magma but more recently as a product of metasomatic replacement open pit exposure created at laco sur during the 1990s reveals that the massive magnetite contains magnetite veined blocks and smaller fragments of altered andesitic volcanic rock clearly supporting the replacement origin open space growth of magnetite and pyroxene along the walls of chimney structures and veins within magnetite indicates precipitation from aqueous fluid rather than from gas alone the native sulfur bearing cristobalite alunite alteration widespread at el laco and broadly contemporaneous with magnetite formation is recognized as part of a steam heated horizon generated in the vadose zone above a paleowater table consequently the magnetite replacement must have taken place beneath the paleowater table but probably 300 m beneath the paleosurface thus magnetite deposition at or immediately beneath the paleosurface is precluded the main outstanding question is how hot hypersaline brine the probable ore forming fluid at el laco attained such shallow crustal levels within a high volcanic edifice without undergoing the extensive groundwater dilution documented from most shallowly preserved hydrothermal systems

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

formation of carbonate chimneys in the mediterranean sea linked to deep water oxygen depletion marine sediments at ocean margins vent substantial amounts of methane1 2 microbial oxidation of the methane released can trigger the precipitation of carbonate within sediments and support a broad diversity of seafloor ecosystems3 4 the factors controlling microbial activity and carbonate precipitation associated with the seepage of submarine fluid over geological time remain poorly constrained here we characterize the petrology and geochemistry of rocks sampled from metre size build ups of methane derived carbonate chimneys located at the amon mud volcano on the nile deep sea fan we find that these carbonates comprise porous structures composed of aggregated spherules of aragonite and closely resemble microbial carbonate reefs forming at present in the anoxic bottom waters of the black sea5 using u series dating we show that the amon carbonate build ups formed between 12 and 7 thousand years ago contemporaneous with the deposition of organic rich sediments in the eastern mediterranean the so called sapropel layer s1 we propose that the onset of deep water suboxic or anoxic conditions associated with sapropel formation resulted in the development of intense anaerobic microbial activity at the sea floor and thus the formation of carbonate chimneys

explosive rhyolitic volcanism in the jemez mountains vent locations caldera development and relation to regional structure the jemez volcanic field straddles the western margin of the rio grande rift where the rift is intersected by the jemez lineament in north central new mexico the field has a record of volcanism extending back to before 13 ma initial basaltic activity was related to active rifting with minor rhyolitic eruptions occurring along n s rift bounding faults between 10 and 7 ma voluminous andesitic volcanism took place in the central jemez mountains area overwhelming contemporaneous basaltic and rhyolitic magmatism an apparent tectonic lull took place from 7 to 4 ma accompanied by lower eruption rates during this interval dacitic magmas were erupted to form the tschicoma volcanic center but mafic and rhyolitic volcanism virtually ceased since 4 ma accompanying resumption of rifting a growing silicic magma system has been present under the central part of the jemez mountains ultimately evolving to the magma body that produced the voluminous rhyolitic bandelier tuffs explosive rhyolitic eruptions from this large magma body have occurred many times since 3 to 4 ma early eruptions 3 6 2 8 ma produced high silica rhyolite ignimbrites restricted to the southwest part of the jemez mountains formation of these units may have been accompanied by caldera collapse these events were followed by the two caldera forming bandelier tuff ignimbrite eruptions 1 45 and 1 12 ma post caldera explosive and effusive rhyolite eruptions have also tapped the magma body from vents generally located along ring fractures after both bandelier events vent and caldera locations for the rhyolitic eruptions during 3 4 ma have been inferred from grain size characteristics dispersal patterns and facies variations in the plinian deposits and ignimbrites lithic breccia zones of the pre bandelier ignimbrites indicate possible caldera sources in the southwest part of the present valles caldera during the eruption of both bandelier tuffs initial plinian falls and early pyroclastic flows emanated from vents centrally located in the jemez mountains in the lower bandelier tuff eruption a transition to ring fracture vents occurred before the emission of later pyroclastic flows but there is no strong evidence to suggest such a transition occurred during the upper bandelier eruption calderas associated with the lower and upper bandelier tuffs toledo and valles respectively are almost identical in location as are the plinian vent sites for these two large eruptions the toledo embayment northeast of the valles caldera contains lava domes from up to 3 6 ma and may be a caldera or crater associated with early explosive dacitic volcanism in the tschicoma volcanic center post 1 4 ma lava domes also fill this depression the main volcanic features of the jemez mountains field including the valles caldera complex eruption vents and the apical graben of the post valles redondo resurgent block appear to be aligned along the ne sw trending jemez fault zone this zone the local expression of a precambrian basement feature the jemez lineament has exerted strong control on the location and style of eruptions from the bandelier rhyolitic magma system

microthermometry of fluid inclusions from the vc 1 core hole in valles caldera new mexico fluid inclusions in vein quartz and calcite from core samples of the vc 1 hole were studied with microscope heating freezing and crushing stages all samples originate from hydrothermally altered paleozoic rocks predating formation of the jemez mountains volcanic field and valles caldera most homogenization temperatures th of the liquid rich inclusions are above the present well temperature but some th of primary inclusions from 515 m and those of secondary inclusions from 723 m fit the present well temperature curve measured 10 months after completion of the well the maximum temperature recorded by the primary inclusions is 275 c from hydrothermal quartz in the sandia formation at 811 m depth the total range of th for samples from several depths 90 c indicates cooling from the maximum temperature the salinity of fluid inclusions in hydrothermal quartz and calcite is generally low 1 wt nacl eq high salinity fluid up to 5 wt nacl eq has been found in several calcite veins from the lower part of the madera limestone the salinity decreases with decrease of th of the secondary inclusions and that with lowest th at the lower part of the madera limestone is similar to those from the other depths these data show that early hot water circulation system involved several types of fluid whereas the later one was a homogeneous fluid the salinity of fluid inclusions in detrital quartz presumably inherited inclusions is higher than that in hydrothermal minerals some of these inclusions show extraordinary low temperatures of final melting point of ice about 40 c suggesting that a cacl2 component is present co2 contents in fluid inclusions were estimated by the bubble behavior on crushing crushing results indicate that co2 content of the early fluid is 0 35 wt and that of the later fluid is 0 2 0 3 wt geothermal fluid trapped in the fluid inclusions representing the present temperature regime is comparable in composition to those from the baca geothermal field inside the caldera and to those from hot springs in san diego canyon

40ar 39ar dating of the bandelier tuff and san diego canyon ignimbrites jemez mountains new mexico temporal constraints on magmatic evolution abstract the jemez mountains volcanic field jmvf located in north central new mexico has been a site of basaltic to rhyolitic volcanism since the mid miocene with major caldera forming eruptions occurring in the pleistocene eruption of the upper bandelier tuff ubt is associated with collapse of the valles caldera whereas eruption of the lower bandelier tuff lbt resulted in formation of the toledo caldera these events were previously dated by k ar at 1 12 0 03 ma and 1 45 0 06 ma respectively pre bandelier explosive eruptions produced the san diego canyon sdc ignimbrites sdc ignimbrite b has been dated at 2 84 0 07 ma whereas sdc ignimbrite a which underlies b has been dated at 3 64 1 64 ma both of these dates are based on single k ar analyses 40ar 39ar dating of single sanidine crystals from these units indicates revision of the previously reported dates isochron analysis of 26 crystals from the ubt gives a common trapped 40ar 36ar component of 304 5 indicating the presence of excess 40ar in this unit and defines an age of 1 14 0 02 ma isochron analysis of 26 crystals from the lbt indicates an atmospheric trapped component and an age of 1 51 0 03 ma an age of 1 78 0 04 ma based on the weighted mean of 5 individual analyses is indicated for sdc ignimbrite b whereas 3 analyses from sdc ignimbrite a give a weighted mean age of 1 78 0 07 ma evidence for xenocrystic contamination in the sdc ignimbrites comes from analyses of a correlative air fall pumice unit in the puye formation alluvial fan giving ages of 1 75 0 08 and 3 50 0 09 ma the presence of xenocrysts in bulk separates used for the original k ar analyses could account for the significantly older ages reported geochemical data indicate that sdc ignimbrites are early eruptions from the magma chamber which evolved to produce the lbt as compositions of sdc ignimbrite b are virtually identical to least evolved lbt samples differentiation during the 270 ka interval between eruption of sdc ignimbrite b and the lbt produced an array of high silica rhyolite compositions which were erupted to form the lbt mixed pumices associated with eruption of the lbt indicated an influx of more mafic magma into the system which produced shifts in some incompatible trace element ratios lavas and tephras of the cerro toledo rhyolite record the geochemical evolution of the bandelier magma system during the 370 ka interval between eruption of the lbt and the ubt the combined geochronologic and geochemical data place the establishment and evolution of the bandelier silicic magma system within a precise temporal framework beginning with eruption of the sdc ignimbrites at 1 78 ma and define a periodicity of 270 370 ka to ash flow eruptions in the jmvf these intervals are comparable to those in other multicyclic caldera complexes and are a measure of the timescales over which substantial fractionation of large silicic magma bodies occur

hydrologic implications of alteration and fluid inclusion studies in the fresnillo district mexico evidence for a brine reservoir and a descending water table during the formation of hydrothermal ag pb zn orebodies ag pb zn mineralization in the fresnillo district formed from a large magma related hydrothermal system between approximately 32 to 28 ma a partial record of this hydrothermal activity is preserved by hydrothermal alteration mineral assemblages and fluid inclusions occurring in barren and mineralized parts of the district these features provide constraints on the hydrologic interpretation of the mineralizing system surficial exposures contain alteration assemblages which reflect two distinct fluid types that are known to occur in the shallow parts of active hydrothermal systems the hydrothermal mineral assemblage comprising quartz calcite illite or interlayered illite montmorillonite plus or minus chlorite pyrite or adularia occurs in scattered exposures around the district and indicates the former widespread presence of near neutral ph chloride waters fluid inclusion data in barren exposures south of the district center indicate that these fluids were dilute containing less than 5 wt percent nacl equiv and had temperatures in the range of 160 degrees to 240 degrees c the assemblage of kaolinite plus or minus alunite and natroalunite occurs locally above blind orebodies in the southern part of the district and in outlying exposures and indicates the former presence of acid sulfate waters geologic and fluid inclusion evidence strongly suggests that these waters originated as steam heated condensates which formed above the water table at plateros which lies north of fresnillo a hotter thermal environment is exposed where fluid inclusion data range from 220 degrees to 300 degrees c in contrast to other surficial exposures in the fresnillo district those that crop out in the center of the district on cerro proano contain significant silver mineralization associated with stockwork quartz veins fluid inclusion data from two quartz crystals indicate part of a complex hydrothermal history in which fluids of 17 10 and 200 degrees c this last feature explains why the tops of late formed orebodies are concealed at 150 to 200 m depth this model implies that dilute hydrothermal fluids devoid of ore metals were the fluids mostly responsible for hydrothermal alteration and vein fillings at the present day surface and that changes to the hydrology significantly altered the position of the ore depositional environment

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

sulfur cycle in the valles caldera volcanic complex new mexico letter 1 sulfate sources in aqueous system and implications for s isotope record in gale crater on mars abstract initial in situ sulfur s isotope measurements of the martian bedrock in gale crater have revealed an unexpectedly wide range of 34 s values 47 to 28 generally it is unclear what processes could have contributed to these large isotope fractionations therefore we studied s sources and aqueous so 4 2 cycling in the valles caldera volcanic complex new mexico to better understand s isotope fractionations related to s degassing hydrothermal activity and low temperature processes in aqueous environment overall our study demonstrates that volcanic systems show large spatial heterogeneity in 34 s magmatic s sources are obvious in steam dominated h2s degassing and precipitation of secondary minerals from hydrothermal fluids with low 34 s values of 0 9 3 locally however hydrothermal processes have resulted in more negative 34 s values in sulfide minerals 18 to 4 and more positive 34 s values in sulfate minerals 1 to 3 major aqueous so 4 2 sources are oxidation of h2s from modern hydrothermal gas emission and oxidation and dissolution of sulfide and sulfate minerals present in the hydrothermally altered bedrock and crater lake sediments the 34 s of aqueous so 4 2 in surface water and groundwater varies widely 8 to 5 and is similar to major s endmembers that undergo oxidation and or dissolution by active hydrological system minor so 4 2 contributions with more positive 34 s values 9 to 14 come from deeply circulating geothermal fluids and negligible amounts from atmospheric deposition 5 to 7 in snow elevated so 4 2 contents are mainly associated with modern and past h2s emissions and oxidations near the surface on regional scale however most of the intracaldera bedrock is s depleted thus the so 4 2 contents are usually low in the surface aquatic system and younger sedimentary lake deposits formed at times of negligible near surface hydrothermal activity in general magmatic hydrothermal processes apparently cause the largest 34 s variation in s bearing minerals on volcanic terrains therefore we infer that the measured wide range of 34 s values in the gale sediments by the curiosity rover on mars can be explained by s isotope composition of magmatic hydrothermal sulfide and sulfate minerals that were present in the initial igneous volcanic rocks prior to crater formation later aqueous processes involved oxidation and dissolution of s minerals initially present in these rocks and led to subsequent formation of diagenetic fluids and alteration products enriched in so 4 2 with relatively large 34 s variation additionally physical erosion transport and deposition of detrital hydrothermal s minerals from igneous volcanic rocks might be in part responsible for the measured wide range of 34 s in gale crater these unique s isotope results measured in situ on another planet for the first time imply the importance of magmatic hydrothermal fluids in s transport on early mars and their subsequent alteration in low temperature aqueous environments

internal geology and evolution of the redondo dome valles caldera new mexico deep geothermal drilling in the resurgent redondo dome of the valles caldera has allowed us to define a consistent intracaldera stratigraphic sequence that differs in a number of respects from the temporally equivalent sequence outside the caldera above the deeply eroded pliocene paliza canyon formation felsic ash flows and sediments in the dome area form a complex sequence of undetermined age that we call the lower tuffs an erosional interval separates these rocks from the overlying otowi member 1 4 m y of the bandelier tuff another period of erosion during which a tuffaceous sandstone was deposited separates the otowi from the overlying tshirege member 1 1 m y of the bandelier both the otowi and tshirege members with maximum thicknesses of 833 and 1155 m respectively are substantially thicker within the caldera than outside indicating simultaneous deposition and cauldron subsidence both are predominantly densely welded with distinctive interior zones of granophyric crystallization resurgent doming was initiated after emplacement of the tshirege member as evidenced by erosion of the upper portions of the cooling unit prior to deposition of overlying units an isopach map of the sandstone deposited during this erosional period shows that streams draining the uplifting dome were localized along the present redondo creek trend subsequent volcanic activity resulted in the formation of at least three additional ash flow tuff cooling units prior to deposition of caldera fill and eruption of the redondo creek member of the valles rhyolite a numerical model applied to formation of the redondo dome suggests that the top of the causative magma body is located at a depth of about 4700 m 1458 m beneath the bottom of the deepest geothermal well in the dome no wells have penetrated intrusives that could be related to this magma we suggest that the locations of faults bounding the apical graben of the dome were influenced by older faults associated with the northeast trending jemez lineament these faults were active early in the uplift history of the dome and account for many of the structural differences between hypothetical dome development and reality

the fluid inclusion and mineralogic record of the transition from liquid to vapor dominated conditions in the geysers geothermal system california the geysers an active vapor dominated geothermal system related to a hypabyssal granitic pluton was liquid dominated from its inception at 1 2 to 0 3 ma when the modern vapor dominated regime formed as the hydrothermal liquids boiled off a vapor dominated heat pipe developed in which the flow of steam was balanced by downward percolation of condensate a record of the transition from liquid to vapor dominated conditions is contained within late stage quartz and calcite crystals that are common in the upper part of the steam reservoir and overlying cap rock samples from three localities were examined in detail quartz from these veins is characterized by corroded crystal faces solid inclusions of contemporaneous calcite that are generally etched coeval high and low salinity fluid inclusions primary low salinity liquid rich inclusions and abundant vapor rich inclusions primary vapor rich inclusions up to 2 mm across were trapped mainly on rhombic and prism faces of skeletal quartz crystals during periods of rapid growth these inclusions nucleate crystals of co2 that disappear by sublimation rather than melting at temperatures ranging from 92 9 to 56 7 c liquid rich fluid inclusions from veins near the top of the modern steam reservoir yield homogenization temperatures ranging from 304 to 188 c these temperatures commonly exceed boiling point to depth relationships based on the paleoground surface suggesting that pressures were initially greater than hydrostatic temperature salinity relationships indicate that the early shallow liquids had salinities of 1 5 to 2 wt percent nacl equiv and that boiling began by 300 c as the fluids boiled off salinities of the residual liquid increased to 3 to 4 wt percent nacl equiv trapping of low salinity fluids 0 0 0 5 wt nacl equiv interpreted as condensate in primary liquid rich inclusions suggest vapor dominated conditions had begun to develop by the time temperatures had dropped to 290 c the primary origin of these inclusion fluids indicates that they were capable of depositing quartz and calcite during the evolution of the vapor dominated system the hydrothermal fluids were at different times but at the same location undersaturated in equilibrium or oversaturated with respect to quartz and calcite the hydrothermal fluids initially deposited quartz and calcite as they boiled off dissolution of these minerals occurred as the condensate which was initially undersaturated with respect to quartz and calcite percolated down subsequent deposition of these minerals occurred as the condensate or mixtures of condensate and boiled liquid that leaked back into the fractures vaporized during periods of intermittent pressure reduction the top of the vapor dominated system migrated downward with time as the overlying fractures were progressively sealed off today pressures within the steam reservoir are vaporstatic and temperatures range from 240 to at least 342 c

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

evolution of the western valles caldera complex new mexico evidence from intracaldera sandstones breccias and surge deposits scientific core drilling in the pleistocene valles caldera complex encompassing the valles 1 13 ma and coaxial toledo 1 50 ma calderas of north central new mexico has provided new insight into the origins of sandstones breccias and pyroclastic surge deposits interbedded with the thick intracaldera ignimbrite sequence these rocks were previously interpreted from geothermal drill cuttings as dominantly fluvial in origin as such representing significant erosional intervals they formed much of the basis for subdividing the intracaldera ignimbrite sequence up to 2000 m in apparent thickness where drilled into four major units the lower tuffs 1 50 ma the otowi 1 50 ma and tshirege 1 13 ma members of the bandelier tuff and a new unit the upper tuffs believed to be post bandelier in age 1 13 ma all but the upper tuffs correspond to mapped outflow facies ignimbrite sheets however continental scientific drilling program core holes vc 2a completed in 1986 and vc 2b completed in 1988 in the sulphur springs area of the valles caldera have provided continuous cores revealing for the first time that some intracaldera rocks previously thought to be exclusively clastic actually have multiple origins some of these rocks are probably pyroclastic surge deposits others could be lithic rich breccias of various origins incorporated nearly instantaneously in ignimbrites during ash flow eruption and concomitant caldera collapse these new findings demonstrate the value of continuous core for subsurface characterization and correlation of complex intracaldera lithologies they also necessitate revision of nielson and hulen s 1984 cuttings based intracaldera stratigraphic framework for example the hematitic s2 sandstone was initially interpreted as marking an erosional interval between the tshirege member of the bandelier tuff and the overlying petrographically similar upper tuffs core from vc 2a and vc 2b however shows that the s2 cuttings could also represent disaggregated permian red bed rich lithic lag breccias or caldera collapse mesobreccias if this is the case then most or all of the upper tuffs are actually uppermost tshirege member ignimbrites in similar fashion and upon review of previously applied correlation criteria the lower tuffs of the western valles caldera complex could represent both genuine pre bandelier ignimbrites and those of the lowermost otowi member the core however shows that in the sulphur springs subsurface the lower tuffs are separated from overlying ignimbrite sheets by prominent erosional and eruptive breaks they appear to be slightly more mafic than the overlying tuffs and host distinctive pumice lapilli at this site the lower tuffs almost certainly predate the otowi member and are probably correlative with the outflow facies san diego canyon ignimbrites 1 78 ma cores from vc 2a and vc 2b support earlier interpretation of the s3 sandstone as a major marker horizon separating the intracaldera otowi and tshirege members of the bandelier tuff but clearly shows that this important unit is not as previously thought entirely a simple intracaldera epiclastic apron in vc 2a the s3 has the superficial appearance of a sandstone but contains abundant blocky shards as well as accretionary and armored lapilli it is also soft sediment deformed and invades overlying nonwelded tuff as small clastic dikes we believe that here the s3 was emplaced by a wet pyroclastic surge in nearby corehole vc 2b the s3 consists of a basal massive sediment gravity flow sandstone overlain by sandstone and dacite breccias with accretionary and armored lapilli bearing tuffaceous matrices these deposits are probably caldera collapse mesobreccias that were formed simultaneously with early tshirege member ash flow eruptions through or into a toledo caldera lake

neodymium isotopic composition of the mediterranean outflow and the eastern north atlantic the neodymium concentration and isotopic composition of the mediterranean outflow in the strait of gibraltar has been directly determined the outflow has a dissolved nd concentration of 23 pmoles kg with nd 0 9 4 these results are in clear disagreement with previous values inferred for the mediterranean this concentration and nd 0 do not sharply contrast with north atlantic deep water nadw values and can produce isotopic anomalies no larger than 1 unit in the north atlantic a new profile in the eastern north atlantic does not exhibit an nd 0 anomaly at the depth of the mediterranean water core in accordance with the above inferences while concentrations and nd 0 at this site indicate that nd is conservative in the deep eastern north atlantic a previously reported nd 0 anomaly in the eastern north atlantic originally associated with the mediterranean outflow has a different source the direct contribution of the mediterranean outflow to the nadw nd budget is small 10 of the high latitude sources however the outflow plus entrained water supply 30 of the total nd associated with northern latitude deep water sources concentrations of dissolved nd in the outflow are enriched compared to the atlantic inflow which has 16 pmoles kg with nd 0 11 8 the principal source of the excess dissolved nd is inferred to be partial dissolution of detrital particles simple mass balance calculations suggest that 0 6 of the nd associated with detrital river transported sediments and or 3 5 of the nd associated with eolian particles delivered to the mediterranean is mobilized during passage into the marine environment if general these mobilization efficiencies imply that the dissolution of detrital particles is a significant source of dissolved nd and other rare earth elements in seawater

mass balance for nd in the mediterranean sea abstract the mass balance for nd in the mediterranean sea has been assessed through the measurement of nd isotope ratios in particulates from rivers entering the mediterranean sea floor clays and ferromanganese crusts and samples of atmospheric dusts nd values for the po and rhone rivers respectively are 10 8 and 9 7 whereas the nile seyhan and tarsus have 3 3 6 2 and 6 3 sea floor clays and ferromanganese crusts range from 2 0 to 10 1 and dust samples vary from 8 2 to 11 0 the relatively radiogenic nd isotope composition of the mediterranean seawater ed 6 to 7 compared to the atlantic nd 12 reflects partial equilibration of the particulate input into the basin rather than merely the dissolved input

fluid inclusion evidence for rapid formation of the vapor dominated zone at sulphur springs valles caldera new mexico usa abstract microthermometric measurements were obtained for 618 fluid inclusions in hydrothermal quartz fluorite and calcite and magmatic quartz phenocrysts in intracaldera tuffs from the vc 2a core hole in order to study evolutionary processes of the sulphur springs hydrothermal system in the valles caldera relatively high t h values in samples from shallow depths indicate erosion of about 200 m of caldera fill since deposition of hydrothermal minerals at shallow depths in the sulphur springs hydrothermal system accompanied by a descent in the water table of the liquid dominated reservoir for samples collected below the current water level of the well the minimum values of homogenization temperature t h fit the present thermal profile whereas minimum t h values of samples from above the water level are several tens of degrees higher than the present thermal profile and fit a paleo thermal profile following the boiling point curve for pure water as adjusted to 92 c at 20 m below the present land surface this is attributed to development of an evolving vapor zone that formed subsequent to a sudden drop in the water table of the liquid dominated reservoir we suggest that these events were caused by the drainage of an intracaldera lake when the southwestern wall of the caldera was breached about 0 5 ma this model indicates that vapor zones above major liquid dominated geothermal reservoirs can be formed due to dramatic changes in geohydrology and not just from simple boiling

divergent mediterranean seawater circulation during holocene sapropel formation reconstructed using nd isotopes in fish debris and foraminifera abstract the recurrent deposition of organic rich sapropel layers in the eastern mediterranean sea ems has been attributed to deep water stagnation and enhanced biological production however the underlying climatic interactions paleoceanographic processes and associated ventilation dynamics are still debated here we present a basin wide reconstruction of circulation systematics during sapropel s1 formation 10 8 6 1 kyr bp using the nd isotope composition e nd as paleo seawater tracer our e nd data from fish debris and foraminifera tests are remarkably radiogenic compared to today and spatially and temporally constant these results predominantly reflect enhanced nile versus atlantic contributions and indicate that ems deep water stagnation prevailed below 800 m water depth during s1 formation additional e nd records obtained from bulk sediment leachates show that such stagnation was preconditioned thousand s of years prior to s1 initiation by intensified nile flooding whereas it terminated with a basin wide deep water renewal in addition decoupling of deep waters between the ems and western mediterranean sea wms is evident for the s1 period using a box model for nd in the ems the observed e nd distribution can be most adequately explained by a 2 fold increase in nile discharge and a 50 decrease in the ems wms exchange that was mostly limited to the surface waters alone the corresponding circulation during s1 was more sluggish and shallow for the ems but largely unaffected for the wms this implies that deep water stagnation is a prerequisite for sapropel formation

climatic forcing of eastern mediterranean deep water formation and benthic ecosystems during the past 22 000 years abstract lateglacial and holocene faunal and stable isotope records from benthic foraminifers in the eastern mediterranean sea ems suggest a high spatiotemporal variability of deep water oxygenation and biogeochemical processes at the sea floor during that time changes in the oxygenation and food availability of the deep sea ecosystems are closely linked to the hydrology of the ems borderlands they reflect orbital and suborbital climate variations of the high northern latitudes and the african monsoon system during the last glacial maximum cool surface waters and high evaporation resulted in maximum convection and oxic deep waters in all sub basins strong wind induced mixing fostered surface water production with seasonal phytodetritus fluxes during the glacial termination and the holocene oxygenation and food availability of deep sea benthic ecosystems were characterized by a pronounced regional differentiation local deep water formation and trophic conditions were particularly variable in the northern aegean sea as a response to changes in riverine runoff and black sea outflow during the interval of sapropel s1 formation in the early holocene average oxygen levels decreased exponentially with increasing water depth suggesting a basin wide shallowing of vertical convection superimposed by local signals in the northernmost aegean sea deep water ventilation persisted during the early period of s1 formation owing to temperature driven local convection and the absence of low salinity black sea outflow at the same time severe temporary anoxia occurred in the eastern levantine basin at water depths as shallow as 900 m this area was likely influenced by enhanced nutrient input of the nile river that resulted in high organic matter fluxes and related high oxygen consumption rates in the water column in the southern aegean and levantine seas we observe a gradual increase in deep water residence times preceding s1 formation by approximately 1 1 5 kyr once oxygen levels fell below a critical threshold the benthic ecosystems collapsed almost synchronously with the onset of s1 deposition the recovery of benthic ecosystems during the terminal phase of s1 formation is controlled by subsequently deeper convection and re ventilation over a period of approximately 1500 years after the re ventilation of the various sub basins had been completed during the middle and late holocene deep water renewal was more or less similar to recent rates during that time deep sea ecosystem variability was driven by short term changes in food quantity and quality as well as in seasonality all of which are linked to millennial scale changes in riverine runoff and associated nutrient input

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels