geology and tectonics of the betic zone se spain abstract the southern margin of the iberian continent comprises a complex geological history which can be traced back into the proterozoic when a gneissic basement was formed a cover of nevado filabride rocks was deposited onto this proterozoic basement during the palaeozoic the permian intrusion of the bedar granite suggests that the palaeozoic sedimentary rocks now exposed in the betic cordilleras have been affected by the hercynian orogeny similar to that of palaeozoic rocks in the adjoining ossa morena zone the hercynian basement was probably covered by alpujarride carbonates in the mesozoic when rifting opened tethys and intruded 140 ma old basic dyke swarms the palaeozoic basement of the betic cordilleras comprises a suture of late cretaceous subduction 80 85 ma b p this can be inferred from hp lt metamorphic facies obducted in coeval thrust slices of nevado filabride rocks the nevado filabride nappes include mesozoic carbonates transformed into marbles macael the suture was probably annnealed after the closure of tethys the mesozoic boundary between africa and europe and the rifting in tethys ceased during the palaeogene when the atlas mountains were formed 36 ma b p subsequently relative movements between africa and europe in the neogene were accommodated by strike slip faults these define the iberian microplate moving eastward by atlantic spreading and possibly subducting under italy neogene deformation of iberia is most intensive in southeastern spain due to emplacement of a mantle diapir under the alboran area this occurred early in the neogene aquitanian and caused nappe spreading involving alpujarride and malaguide rocks the subsequent neogene history has now been studied in great detail and is reviewed here it involves clear examples of calc alkaline volcanism most probably not related to subduction seismic motion along strike slip faults within the iberian microplate and syntectonic deposition in intermontane neogene basins

sulfate minerals control dissolved rare earth element flux and nd isotope signature of buoyant hydrothermal plume emso azores 37 n mid atlantic ridge abstract while hydrothermal vents are now thought to be a major source of dissolved iron to the oceans they have always been considered to be a sink for the dissolved rare earth elements drees however true dissolved ree observations in hydrothermal plumes are still lacking here we report for the first time the dree concentrations and neodymium isotopic compositions dend of buoyant hydrothermal fluids at lucky strike mid atlantic ridge we find that 27 to 62 of total hydrothermal drees are rapidly scavenged by anhydrite precipitation at the onset of buoyant plume formation after this initial loss all drees behave quasi conservatively within the buoyant plume dissolved phase end dend in the evolving plume are identical to black smoker dend of 9 0 and contrast radically with dend of the local deep water mass at 12 0 plume dend as low as 6 6 may be reconciled by dissolution of newly formed barite in the local environment and carrying seawater dend signature we find based on the first plume dree observations that hydrothermal plumes are in fact a source of dree to the north atlantic deep water precipitation dissolution processes of hydrothermally derived minerals i e sulfates in the buoyant plume and fe oxy hydroxide in the non buoyant plume will likely affect the fate of other trace metals and their isotopic composition

rare earth element geochemistry of massive sulfides sulfates and gossans on the southern explorer ridge massive sulfide sulfate deposits on the southern explorer ridge were analyzed for 14 rare earth elements ree by a modified inductively coupled plasma mass spectrometric technique that included a correction for high ba content bulk samples of finely intermixed sulfides sulfate and amorphous silica contain ree concentrations of 6 ppm ree patterns range from 1 strongly enriched in light ree with positive eu anomalies to 2 relatively flat with positive eu anomalies and slightly negative ce anomalies to 3 slightly enriched in light ree with moderately negative ce anomalies pattern 1 is similar to that of 300 350 c solutions discharging at vents on the east pacific rise and the mid atlantic ridge whereas pattern 3 resembles ree distributions in normal oceanic bottom waters the sulfide sulfate patterns are interpreted to result from variable mixtures of hydrothermal and normal seawater barite in gossans capping the mounds has an ree pattern almost identical to patterns of high temperature vent solutions hydrothermal barite has lower ree contents and a different ree pattern relative to hydrogenous barite formed slowly on the sea floor

geochemical behavior during mineralization and alteration events in the baiyinchang volcanic hosted massive sulfide deposits gansu province china abstract the zheyaoshan deposit is the largest within the baiyinchang byc volcanic hosted massive sulfide vhms district located in the northern qilian orogenic belt of north china the deposit is hosted by quartz keratophyre tuffs with wall rock alteration mainly comprising chlorite sericite quartz pyrite and epidote mineral assemblages within the altered host rocks can be divided into a sericite quartz dominant assemblage sericite silicified zone a chlorite dominant assemblage chlorite dominant zone and a pyrite dominant assemblage mineralized zone based on geochemical analysis and alteration characteristics we have conducted detailed processing and critical analysis of the geochemical data of both the altered and least altered host rocks in order to investigate the problem of closure in the geochemical dataset to eliminate the influence that each component has on the other in terms of mass change and have applied the standardized method of the mass change calculation to analyze this data the results show that 1 the sericite silicified zone formed along fissures due to the ingress of hydrothermal fluids with mno 2 na 2 o and cao being mobilized into the hydrothermal fluids leached and mgo fe 2 o 3 sio 2 k 2 o bao deposited additionally ag cu and chalcophile elements ag as and bi were enriched while pb zn and large ion lithophile elements liles cs sr eu be were mobilized into hydrothermal fluids 2 the physiochemical conditions and ph levels of the hydrothermal fluids changed during sericitization with mgo fe 2 o 3 bao being further enriched and mno na 2 o cao further depleted leading to formation of chlorite and the initial precipitation of metallogenic the cu zn pb and chalcophile elements ag as bi 3 the negative eu anomaly was mainly due to its strong activity when eu is mobilized into the hydrothermal fluids during since plagioclase break down during the sericite silicification process 4 ai and ccpi values gradually increase towards the orebody the chlorite dominant assemblage and sericite quartz dominant assemblage on the periphery of the chlorite dominant zone can all be used as vectors towards the volcanic massive sulfide orebody and for regional scale mineral exploration either leached elements or enriched elements can be considered as significant indicator elements and as prospective indicators for geochemical exploration within the byc district the eu anomaly may be especially useful as an indicator for distinguishing the least altered rocks which has great significance for exploration on the regional scale

influence of the atlantic inflow and mediterranean outflow currents on late quaternary sedimentary facies of the gulf of cadiz continental margin abstract the late quaternary pattern of sedimentary facies on the spanish gulf of cadiz continental shelf results from an interaction between a number of controlling factors that are dominated by the atlantic inflow currents flowing southeastward across the cadiz shelf toward the strait of gibraltar an inner shelf shoreface sand facies formed by shoaling waves is modified by the inflow currents to form a belt of sand dunes at 10 20 m that extends deeper and obliquely down paleo valleys as a result of southward down valley flow a mid shelf holocene mud facies progrades offshore from river mouth sources but atlantic inflow currents cause extensive progradation along shelf toward the southeast increased inflow current speeds near the strait of gibraltar and the strong mediterranean outflow currents there result in lack of mud deposition and development of a reworked transgressive sand dune facies across the entire southernmost shelf at the outer shelf edge and underlying the mid shelf mud and inner shelf sand facies is a late pleistocene to holocene transgressive sand sheet formed by the eustatic shoreline advance the late quaternary pattern of contourite deposits on the spanish gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are oblique to slope contours and the mediterranean outflow current flowing northwestward parallel to the slope contours and down valleys between the ridges coincident with the northwestward decrease in outflow current speeds from the strait there is the following northwestward gradation of contourite sediment facies 1 upper slope sand to silt bed facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins by comparison the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean outflow current the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies radiocarbon ages verify that the inner shelf shoreface sand facies sedimentation rate 7 1 cm kyr mid shelf mud facies maximum rate 234 cm kyr and surface sandy contourite layer of 0 2 1 2 m thickness on the cadiz slope 1 12 cm kyr have deposited during holocene time when high sea level results in maximum water depth over the gibraltar sill and full development of the atlantic inflow and mediterranean outflow currents the transgressive sand sheet of the shelf and the mud layer underlying the surface contourite sand sheet of the slope correlate respectively with the late pleistocene sea level lowstand and apparent weak mediterranean outflow current

microbial methane turnover at mud volcanoes of the gulf of cadiz the gulf of cadiz is a tectonically active area of the european continental margin and characterised by a high abundance of mud volcanoes diapirs pockmarks and carbonate chimneys during the r v sonne expedition gap gibraltar arc processes so 175 in december 2003 several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes captain arutyunov bonjardim ginsburg gemini and a newly discovered mud volcano like structure called no name show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed the presence of a distinct sulphate methane transition zone smt overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor anaerobic oxidation of methane aom and sulphate reduction sr rates show maxima at the smt which was found between 20 and 200 cm below seafloor at the different mud volcanoes in comparison to other methane seeps aom activity 383 mmol m 2 year 1 and diffusive methane fluxes 321 mmol m 2 year 1 in mud volcano sediments of the gulf of cadiz are low to mid range corresponding lipid biomarker and 16s rdna clone library analysis give evidence that aom is mediated by a mixed community of anaerobic methanotrophic archaea and associated sulphate reducing bacteria srb in the studied mud volcanoes little is known about the variability of methane fluxes in this environment carbonate crusts littering the seafloor of mud volcanoes in the northern part of the gulf of cadiz had strongly 13c depleted lipid signatures indicative of higher seepage activities in the past however actual seafloor video observations showed only scarce traces of methane seepage and associated biological processes at the seafloor no active fluid or free gas escape to the hydrosphere was observed visually at any of the surveyed mud volcanoes and biogeochemical measurements indicate a complete methane consumption in the seafloor our observations suggest that the emission of methane to the hydrosphere from the mud volcano structures studied here may be insignificant at present

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

factors affecting the rare earth element compositions in massive sulfides from deep sea hydrothermal systems to reconstruct the evolution of ore forming fluids and determine the physicochemical conditions of deposition associated with seafloor massive sulfides we must better understand the sources of rare earth elements rees the factors that affect the ree abundance in the sulfides and the ree flux from hydrothermal fluids to the sulfides here we examine the ree profiles of 46 massive sulfide samples collected from seven seafloor hydrothermal systems these profiles feature variable total ree concentrations 37 2 4092 ppb and ree distribution patterns la cn lu cn ratios 2 00 73 8 eu eu cn ratios 0 34 7 60 the majority of the ree distribution patterns in the sulfides are similar to those of vent fluids with the sulfides also exhibiting light ree enrichment we demonstrate that the variable ree concentrations eu anomalies and fractionation between light rees and heavy rees in the sulfides exhibit a relationship with the ree properties of the sulfide forming fluids and the massive sulfide chemistry based on the sulfide ree data we estimate that modern seafloor sulfide deposits contain approximately 280 t of rees according to the flux of hydrothermal fluids at mid ocean ridges mors and an average ree concentration of 3 ng g in these fluids hydrothermal vents at mors alone transport more rees 360 t to the oceans over the course of just 2 years than the total quantity of rees in seafloor sulfides the excess rees i e the quantity not captured by massive sulfides may be transported away from the systems and become bound in sulfate deposits and metalliferous sediments

emplacement of a passive margin evaporitic allochthon in the betic cordillera of spain the triassic section of the external domain of the betic cordillera is rootless and thus allochthonous the frontal accretionary wedge of the guadalquivir allochthon consists dominantly of triassic evaporites and red beds forming a melange with upper cretaceous paleogene deep water sedimentary rocks throughout the unit jurassic rocks are absent it is here proposed that the widespread triassic evaporites of the guadalquivir allochthon were originally emplaced as gravitational allochthonous masses in a passive margin setting much like the widespread allochthonous salt of the texas louisiana gulf of mexico thus on the betic passive margin allochthonous evaporites were first emplaced during the late cretaceous paleogene later during neogene time these evaporites were overthrusted as an accretionary wedge to form the guadalquivir allochthon a schematic reconstructed position of the guadalquivir allochthon places the original passive margin allochthon in its continental slope setting

the glacier creek cu zn vms deposit southeast alaska an addition to the alexander triassic metallogenic belt the glacier creek volcanogenic massive sulfide vms deposit alaska is hosted within late triassic oceanic back arc or intraarc rift related bimodal volcanic rocks of the allochthonous alexander terrane known as the alexander triassic metallogenic belt the alexander triassic metallogenic belt is host to the world class greens creek zn pb ag vms deposit near juneau in the south and the giant windy craggy cu co vms deposit in british columbia about 250 km to the north the glacier creek deposit located 80 km southeast of windy craggy consists of four tabular massive sulfide lenses within a bimodal mafic volcaniclastic and rhyolitic sequence the mineralization hosting stratigraphy is folded by a deposit scale anticline and offset by a thrust fault near the axial surface of the fold a resource of 8 13 mt has been inferred from drilling with grades of 1 41 cu 5 25 zn 0 15 pb 0 32 g t au and 31 7 g t ag six main mineralization types are recognized dominated by massive barite sphalerite pyrite which is replaced at the base and center of the main lenses by massive and semimassive chalcopyrite pyrite quartz the flanks and tops of the lenses are carbonate rich and consist of interbedded calcite dolomite barite and sulfide resedimented massive barite sulfide and mineralized massive carbonate rocks tuffaceous hydrothermal sediment with a distinct positive eu anomaly overlies the massive sulfide pyrrhotite and chalcopyrite in stringers constitute the main feeder zone stringer style sphalerite pyrite mineralization occurs above and below the lenses fe poor sphalerite is dominant throughout the lenses whereas fe rich sphalerite occurs at the stratigraphic top and bottom of the lenses in pyrrhotite rich zones galena tennantite tetrahedrite and arsenopyrite are the most important trace minerals within massive barite sphalerite pyrite mineralization which is generally enriched in sb hg and tl mineralization related gangue minerals include barite quartz barian muscovite calcite dolomite albite chlorite hyalophane and celsian four types of alteration are recognized in the dominantly basaltic host rocks pervasive muscovite rich alteration quartz pyrite alteration associated with sulfide stringers stratabound carbonate bearing alteration and background epidote bearing alteration mass balance calculations indicate gains of s fe si and k with coincident losses of ca na and mg in all of the alteration types trace elements tl sb hg ba zn cu and as were added to the rocks whereas sr was lost short wavelength infrared swir spectroscopy shows an increase in the wavelength of the aloh absorption feature toward mineralization at a scale of 30 to 50 m coincident with a general decrease in the na k and al and increase in the fe mg and ba content of muscovite the glacier creek deposit is transitional in character between greens creek which is more zn pb and precious metal rich and the windy craggy deposit which is more cu and co rich reflecting differences in the basement rocks and depositional settings within the alexander triassic metallogenic belt mineral chemical studies and sulfur isotope data suggest that the glacier creek deposit formed under initially oxidized and sulfate rich conditions that evolved to more reduced conditions in the latest stages of mineralization the abundant argillite and presence of hyalophane rather than barite in the immediate hanging wall of the deposit may be an indication of a deepening basin and development of local anoxia similar to greens creek

the use of sem eds pixe and edxrf for obsidian provenance studies in the near east a case study from neolithic catalhoyuk central anatolia in this paper we evaluate the relative analytical capabilities of sem eds pixe and edxrf for characterizing archaeologically significant anatolian obsidians on the basis of their elemental compositions the study involves 54 geological samples from various sources together with an archaeological case study involving 100 artifacts from neolithic catalhoyuk central anatolia with each technique the artifacts formed two compositional groups that correlated with the east gollu dag and nenezi dag sources the non destructive capabilities of these methods are emphasized albeit with certain analytical limitations in the case of sem eds suggesting important new techniques for near eastern obsidian provenance studies

potential geologic hazards on the eastern gulf of cadiz slope sw spain abstract geologic hazards resulting from sedimentary oceanographic and tectonic processes affect more than one third of the offshore gulf of cadiz and are identified by interpreting high resolution seismic profiles and sonographs hazards of sedimentary origin include the occurrence of slope instability processes in the form of single or multiple slumps occupying up to 147 km 2 mainly concentrated in the steeper upper slope area besides the presence of steep slopes the triggering of submarine landslides is probably due to seismic activity and favoured by the presence of biogenic gas within the sediment gassy sediments and associated seafloor pockmarks cover more than 240 km 2 in the upper slope hazards from oceanographic processes result from the complex system of bottom currents created by the interaction of the strong mediterranean undercurrent and the rough seafloor physiography the local intensification of bottom currents is responsible for erosive processes along more than 1900 km 2 in the upper slope and in the canyons eroded in the central area of the slope undermining slopes and causing instability the strong bottom currents also create a mobile seafloor containing bedforms in an area of the gulf that extends more than 2500 km 2 mostly in the continental slope terraces hazards of tectonic origin are important because the gulf of cadiz straddles two major tectonic regions the azores gibraltar fracture zone and the betic range which results in diapir uplift over an area of more than 1000 km 2 and in active seismicity with earthquakes of moderate magnitude also tsunamis produced by strong earthquakes occur in the gulf of cadiz and are related to the tectonic activity along the azores gibraltar fracture zone

benthic foraminifera based reconstruction of the first mediterranean atlantic exchange in the early pliocene gulf of cadiz abstract upper miocene to lower pliocene sediment cores from integrated ocean drilling program iodp hole u1387c iodp expedition 339 have been studied the main goal of this study is to reconstruct initial mediterranean atlantic water exchange after the opening of the gibraltar strait in the early pliocene benthic foraminiferal assemblages are the focus of the palaeoceanographic analyses of this work a distinct faunal turnover indicates a considerable change of the depositional environment at the miocene pliocene boundary foraminiferal composition suggests high rates of organic carbon flux and poorly oxygenated sea floor environment for the basal late messinian interval in contrast earliest pliocene assemblages point to periodic advection of warm better ventilated and likely mediterranean sourced waters to the studied site parallel periodic changes in siphonina tubulosa globocassidulina subglobosa and planulina ariminensis and previously established sedimentological and geochemical records zr al 18o suggest a rather sluggish mediterranean outflow between 5 3 and 5 2 ma benthic foraminifera along with sedimentological and geochemical data thus provide the earliest indications of mediterranean atlantic water exchange following the opening of the gibraltar strait sandy layers become frequent towards the top of the interval these sediments are rich in shelf foraminifera reflecting episodes of turbidite deposition possibly caused by tectonic adjustments related to the opening of the gibraltar strait the allochthonous assemblages frequently contain cibicides lobatulus and c refulgens species that have been considered indicators of mediterranean outflow water mow in previous studies our results warrant for caution when applying these species as mow proxy in the fossil record if there is evidence for downslope transport

perched lobe formation in the gulf of cadiz interactions between gravity processes and contour currents algarve margin southern portugal abstract the gulf of cadiz is swept by the strong saline mediterranean outflow water mow on the algarve margin south portugal this current has constructed fine grained contourite drifts this margin is dissected by the portimao canyon and three short channels that only incise the upper slope and are absent on a terrace located at mid slope depths along the algarve margin high resolution seismic profiles and sediment cores highlight the original architecture of the sedimentary deposits on this terrace coarse grained lenticular chaotic bodies formed during major relative sea level lowstands are intercalated within the drift the lobate shape and sandy nature of the lenticular chaotic bodies and their location at the mouths of the three short channels suggest they are gravity generated deposits that are perched on the middle continental slope in the gulf of cadiz the interaction between contour current and gravity processes is strongly controlled by climatic variations and relative sea level changes during the late quaternary during cold periods when sea level was low erosion intensified on the continental shelf and the deepest part of mow was active sediment was transported downslope through the channels and deposited on sedimentary lobes perched on the mid slope terrace during warm periods when relative sea level was high the supply of sediment from the shelf was shut off and the shallowest part of mow was more active contourite drifts fill the channels and bury the sandy lobes

iberian plate kinematics a jumping plate boundary between eurasia and africa the rotation of iberia and its relation to the formation of the pyrenees has been difficult to decipher because of the lack of detailed sea floor spreading data although several models have been proposed1 7 here we use detailed aeromagnetic measurements from the sea floor offshore of the grand banks of newfoundland to show that iberia moved as part of the african plate from late cretaceous to mid eocene time with a plate boundary extending westward from the bay of biscay when motion along this boundary ceased a boundary linking extension in the king s trough to compression along the pyrenees came into existence finally since the late oligocene iberia has been part of the eurasian plate with the boundary between eurasia and africa situated along the azores gibraltar fracture zone

seafloor massive sulfides from mid ocean ridges exploring the causes of their geochemical variability with multivariate analysis abstract the neovolcanic zones of mid ocean ridges are host to seawater derived hydrothermal systems forming seafloor massive sulfide sms deposits these deposits have high concentrations of base metals and potentially economic enrichment of a wide range of trace elements the factors controlling this enrichment are currently poorly understood we have investigated the main factors controlling sms compositional variability through robust principal component analysis and robust factor analysis of published and newly obtained bulk geochemical data for samples collected from sms deposits worldwide we found that a large part of the observed variability is produced by a combination of three independent factors which are interpreted to reflect in order of importance 1 the temperature of deposition 2 the ridge spreading rate and 3 zone refining the first and the third factors are mostly related to processes operating near the seafloor such as conductive cooling mixing of the hydrothermal fluids with seawater and metal remobilization and determine the relative proportions of the main minerals and thus of cu and zn co se sb pb the ridge spreading rate influences the structure of the oceanic lithosphere which exerts a major control on the length and depth of the hydrothermal convection cell and on the rock to water ratios in the reaction zone which in turn control the behavior of the precious metals au and ag and elements including ni mo se despite the obvious role of substrate rocks as metal sources their composition specifically mafic vs ultramafic does not emerge as a statistically significant independent factor

geochemistry of femn formations of the archaean sandur schist belt india mixing of clastic and chemical processes at a shallow shelf abstract the late archaean greenstone belts of karnataka are unique in having manganese formations with mineable ores an excellent example of these mn bearing greenstone belts is the sandur schist belt where fe mn formations are confined to the basin shelf clearly separated from the deeper water manganese free bif that accumulated at the basin margin and flanking the marine basin sedimentary textures and structures including stromatolites show that fe mn formations have been deposited on a shallow shelf within the photic zone and above wave base along with quartz fe mn minerals found in arenites argillites and carbonates include ripidolite mg chlorite sericite mn siderite kutnahorite dolomite ferroan dolomite psilomelane pyrolusite cryptomelane haematite and magnetite the manganese and iron contents of these rocks range up to 25 and 46 respectively al 2 o 3 tio 2 mgo cao mno 2 fe 2 o 3 t abundances and ratios show a wide variation ni cr co zr v sc rb sr u th ree lree hree la ce and eu anomalies and their binary relationships indicate that wherever the terrigenous component has increased the concentration of elements of felsic parentage such as zr and hf has gone up elevated concentrations of ni cr co and sc are contributed by chlorite and other components characteristic of basic volcanic debris the carbonates where clastic input is minimal are extremely depleted in ree and other trace elements it is proposed that feo mno and sio 2 probably were added to archaean ocean water at oceanic ridge vents the compositional data suggest that the fe mn formations of the sandur schist belt were generated by chemical and clastic sedimentary processes on a shallow shelf that led into a deeper basin open on one side in this environment chemical and clastic sediments and organic matter were mixed and buried during transgression chemical precipitation took place at the sediment water interface whereas at the time of regression these chemical sediments were buried by clastic sediments redox potential differences between the watermasses on the shallower and deeper shelf respectively fractionated fe and mn the fe mn formations were deposited within the photic zone and above wave base and in a setting where the water column was oxygenated but organic material accumulated by contrast bif was deposited below both wave base and photic zone in a relatively oxygen deficient setting where formation of stable mn oxides was not possible fe mn formation and bif provide an important constraint on greenstone tectonics a shorter distance between archaean oceanic ridge and shelf environments namely the smaller plates model appears to explain several features of fe mn formations bifs and greenstone belts

late quaternary seismic facies of the gulf of cadiz spanish margin depositional processes influenced by sea level change and tectonic controls abstract seismic facies and quaternary depositional systems of the gulf of cadiz have been characterized by means of high resolution seismic profiles airguns geopulse and ore 3 5 khz a total of 11 pleistocene and two holocene sequences separated by type 1 or type 2 discontinuities were identified the age of the depositional sequences was determined based on foraminifera ages from boreholes and by correlation with seismic profiles of the slope areas with uniform deposition and without significant discontinuities these seismic units have been mapped throughout the margin allowing to establish the correlation with eustatic sea level curves and global climatic trends the distribution and geometry of the units reveals that most of the sedimentary record was developed during episodes of forced regression ten regressive periods corresponding to 5th order cycles arranged into 4th order were distinguished absolute water depths for the development of coastal deposits in each unit were calculated using depth from present day sea level corrected for tectonic subsidence in the area the model for the evolution of the depositional system of the gulf of cadiz continental margin highlights the strong influence of tectonism in the development of depositional bodies controlling the distribution of deposits generally produced during episodes of sea level fall

obsidian source characterization in the cordillera real and eastern piedmont of the north ecuadorian andes abstract recent research in the quijos and cosanga valleys of the eastern piedmont of ecuador s cordillera real has revealed and substantiated previous knowledge of obsidian sources that are unrelated to obsidian flow systems in the sierra de guamani ecuador neutron activation analysis naa and x ray fluorescence xrf were carried out on 47 obsidian source samples collected from several contexts in and adjacent to the study area from samples within the study area three distinct obsidians were characterized cosanga a cosanga b and bermejo these obsidians originate from a number of obsidian bearing rhyolitic domes recently identified in the hills west of the rio cosanga extensive survey of these dome localities has identified obsidian cobbles large enough for formal and informal tool manufacture beyond the study area samples were collected and analyzed from the el tablon source in the sierra de guamani providing much needed data on this poorly understood source in addition a sample from the newly identified conda dome source near the cotopaxi volcano was characterized with xrf all samples were then compared to 57 pre existing samples from the mullumica callejones yanaurco quiscatola and carboncillo sources in the ecuadoran cordillera real as well as to artifacts from the sumaco area in the ecuadorian amazon results of the elemental characterization indicate that the cosanga valley el tablon and conda dome obsidians are chemically distinct further visual characteristics of cosanga valley obsidian types are useful in source attribution for the large artifact samples from the region finally obsidian collected from the el tablon flow suggests that this source may have produced obsidian suitable for tool manufacture

neogene extensional collapse in the western mediterranean betic rif alpine orogenic belt implications for the genesis of the gilbraltar arc and magmatic activity the betic rif orogenic belt crops out in the western mediterranean and constitutes the westernmost part of the alpine edifice the building up of this belt by compressional nappe tectonics occured during a series of alpine deformational episodes subsequent neogene extension resulted from the collapse of the previous compressional edifice through major extensional detachment systems this episode was accompanied by cafe alkaline to shoshonitic and lamproitic volcanism tectonic denudation of metamorphic core complexes and emplacement of peridotite bodies as a final consequence of the evolution of detachment systems furthermore we relate the generation of the gibraltar arc and the opening of the alboran sea to this major extensional event finally two main stages of tectonic denudation of these detachment systems are defined 1 nevado filabride stage with ex humation of metamorphic core complexes and 2 ronda beni boussera stage with a more advanced degree of denudation leading to the exhumation of upper mantle peridotites which may be tentatively termed mantle core complexes

structure and palaeogeography of the external betic cordillera southern spain abstract a structural interpretation of the external betic cordillera in the granada jaen area of southern spain is proposed based on the interpretation of seismic reflection profiles subsurface well control and a balanced cross section restoration of this balanced cross section results in a new palaeogeographical interpretation for the area and a total estimated shortening of approximately 200 km traditionally the betic fold thrust belt has been described as a series of north vergent imbricate thrust sheets each having relatively little displacement 10 15 km restoration of this structural model to an undeformed state results in a mesozoic palaeogeographical scenario of three carbonate platforms separated by two deep basins an alternative interpretation is presented in this paper that the structural style of the granada jaen area is characterized by large displacement thrust faults restoration of the proposed cross section leads to the palaeogeographical interpretation of a single mesozoic basin along the transect of the cross section this palaeo basin is bounded to the north and south by platformal margins the major implication of this study is that the palaeogeographical interpretation of a fold thrust belt can be highly dependent on the structural interpretation

stress and palaeostress in the betic rif cordilleras miocene to the present palaeostress orientation in the betic rif cordilleras can be determined for the miocene to the quaternary by analysis of brittle microstructures faults joints striated pebbles and stylolites in the central and northern south iberian domain 1 was subhorizontal and trended nw se from the early miocene to the present in the northern alboran domain from the burdigalian to the serravallian palaeostress ellipsoids were oblate with 3 subhorizontal and trending ene wsw in the southern part of the south iberian domain and in the northern part of the alboran domain betic cordillera from the tortonian to the quaternary palaeostress ellipsoids were variable in the granada region they were prolate with 1 subvertical but in the almeria region they were triaxial with 2 subvertical and 3 subhorizontal and trending ne sw to e w in the rif the alboran and african maghrebian domains were affected by palaeostresses with 1 subhorizontal varying from ne sw in tortonian times to n s in the plio quaternary a study of earthquake focal mechanisms by the right dihedra method indicates that the present day general stress field around the betic rif cordilleras is compressional with 1 subhorizontal and trending nw se in the betic rif cordilleras this general stress field is modified and the present day orientations of 1 2 and 3 are nearly the same as those of the palaeostresses in the pliocene and quaternary the distribution and evolution of stresses in the betic rif cordilleras from the miocene to the present can be correlated with the main neogene deformations extensional structures in the central and northern alboran domain and the southern part of the south iberian domain and compressional structures in the south iberian and african maghrebian domains and in the southern part of the alboran domain

mobilization of ree during crustal aging in the troodos ophiolite cyprus ree data for secondary minerals from low and high temperature alteration environments in the troodos ophiolite have been determined using a combined mass spectrometry neutron activation technique smectite and analcime ree mimic fresh rock profiles and have concentrations ranging from 1 5 times chondritic values celadonite is depleted in lree and total ree relative to the rocks groundmass replacing chlorite and epidote are similar to or enriched in ree relative to fresh rocks in contrast fault related chlorite and void filling epidote are lree enriched with large positive eu anomalies and yield comparable ree profiles to those of hydrothermal fluids venting at mid ocean ridges the zeolites clinoptilolite and laumontite are also lree enriched with ree contents significantly lower than rock values carbonate is enriched in hree relative to lree and concentrations vary from 0 2 to 18 times chondritic values ree data for these minerals indicate that seawater ree contents are modified by seawater rock interaction in volcanic sequences and sheeted dykes in oceanic crust during axial hydrothermal alternation and subsequent crustal aging the absolute and relative abundances of ree in seawater derived solutions evolve in response to the precipitation of secondary minerals and the prevailing water rock ratios rocks altered at low temperatures will show no change or a decrease in ree content the lree hree ratio will reflect the proportion of smectite celadonite and carbonate in the groundmass assemblage in contrast rocks altered at high temperatures will show no change or an increase in ree the lree hree ratio will reflect the proportion of void filling and groundmass replacing chlorite and epidote in the rock

hydrate occurrence in europe a review of available evidence abstract large national programs in the united states and several asian countries have defined and characterised their marine methane hydrate occurrences in some detail but european hydrate occurrence has received less attention the european union funded project marine gas hydrate an indigenous resource of natural gas for europe migrate aimed to determine the european potential inventory of exploitable gas hydrate to assess current technologies for their production and to evaluate the associated risks we present a synthesis of results from a migrate working group that focused on the definition and assessment of hydrate in europe our review includes the western and eastern margins of greenland the barents sea and onshore and offshore svalbard the atlantic margin of europe extending south to the northwestern margin of morocco the mediterranean sea the sea of marmara and the western and southern margins of the black sea we have not attempted to cover the high arctic the russian ukrainian and georgian sectors of the black sea or overseas territories of european nations following a formalised process we defined a range of indicators of hydrate presence based on geophysical geochemical and geological data our study was framed by the constraint of the hydrate stability field in european seas direct hydrate indicators included sampling of hydrate the presence of bottom simulating reflectors in seismic reflection profiles gas seepage into the ocean and chlorinity anomalies in sediment cores indirect indicators included geophysical survey evidence for seismic velocity and or resistivity anomalies seismic reflectivity anomalies or subsurface gas escape structures various seabed features associated with gas escape and the presence of an underlying conventional petroleum system we used these indicators to develop a database of hydrate occurrence across europe we identified a series of regions where there is substantial evidence for hydrate occurrence some areas offshore greenland offshore west svalbard the barents sea the mid norwegian margin the gulf of cadiz parts of the eastern mediterranean the sea of marmara and the black sea and regions where the evidence is more tenuous other areas offshore greenland and of the eastern mediterranean onshore svalbard offshore ireland and offshore northwest iberia we provide an overview of the evidence for hydrate occurrence in each of these regions we conclude that around europe areas with strong evidence for the presence of hydrate commonly coincide with conventional thermogenic hydrocarbon provinces

a dual origin for the hydrothermal component in a metalliferous sediment core from the mid atlantic ridge a highly metalliferous sediment core collected from tag 26 n mid atlantic ridge has been analyzed for uranium series isotopes rare earth elements ree and radiogenic isotopes two types of deposition of hydrothermal material have been identified and characterized the first is sulfide material which has been rapidly deposited and is sometimes clearly turbiditic this material exhibits high u fe and eu sm ratios and low 230th fe and ree fe ratios it is proposed that u is incorporated into the sulfides by diffusion through the oxidized coating with reductive fixation near the sulfide oxide boundary the second hydrothermal component is particulate fallout from the neutrally buoyant plume which is diluted by the background pelagic sedimentation this component exhibits u fe ratios around 2 10 5 an order of magnitude greater than reported plume particulate levels but the 230th fe ree fe and eu sm ratios are similar to plume values nd and pb isotopes have been used to differentiate the hydrothermal and pelagic end members within this sediment core

tectonics and mud volcano development in the gulf of cadiz many structures associated with fluid escape including mud volcanoes mud carbonate mounds pockmarks and slides have been identified and characterized in the gulf of cadiz most of the mud volcanoes following ne sw and nw se main trends are found at 350 2000 m depth in the eastern domain of the gulf of cadiz which corresponds to the betic rifean margin scattered mud volcanoes have also been recognized on the lower slope at 2300 3900 m depth the major tectonic structures are thrust faults extensional faults strikeslip faults and diapirs all these tectonic structures have provided escape pathways for overpressured material and fluids or have favoured upward fluid movement along the sedimentary column and eventually the build up of mud volcanoes in this work we present images of the mud volcano plumbing systems and the relationship between regional tectonics and mud volcano development seismic profiles acquired during the tasyo 2000 and mvseis ttr 15 cruises are used to image and interpret the link between the mud volcano edifices and the subsurface tectonic structures

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

present day kinematics of the plate boundary zone between africa and europe from the azores to the aegean anticlockwise rotation of africa relative to europe around an euler pole in the eastern atlantic causes plate convergence in the central mediterranean towards n20 w at rate considered a priori to be 5 10 mm yr 1 however previous summaries of the present day deformation sense in the central mediterranean are inconsistent with observations in southern italy recent investigations of italy and adjacent parts of north africa enable local deformation sense observed to be reconciled with sense predicted from relative plate motions suggested angular velocity of the african plate relative to europe is 0 07 myr 1 around a pole near 21 n 21 w this predicts 2 6 mm yr 1 maximum extension rate towards n64 e near the azores consistent with the minimum local accretion of new oceanic crust in the past few millions of years and 4 3 mm yr 1 plate convergence towards n20 w in the central mediterranean at 13 e further east the northern margin of the african plate can be regarded as the gargano seismic zone in the central adriatic sea the northern adriatic sea is a microplate rotating anticlockwise relative to europe at 0 3 myr 1 around a pole in northwestern italy causing northeastward shortening in yugoslavia and up to 4 mm yr 1 extension in central and northern italy the african plate is deforming internally in tunisia and northern libya extending obliquely in direction e10 s at rate up to 5 5 mm yr 1 the resultant velocity relative to europe in the ionian and southern adriatic seas 5 mm yr 1 towards n50 e explains the observed relative velocity across southern italy kinematic consistency requires present day shortening rate east of calabria associated with subduction on the tyrrhenian sea benioff zone and tyrrhenian sea extension rate to be both zero or equal to within 1 mm yr 1

mediterranean undercurrent sandy contourites gulf of cadiz spain abstract the pliocene quaternary pattern of contourite deposits on the eastern gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are perpendicular to slope contours and the mediterranean undercurrent that has flowed northwestward parallel to the slope contours and down valleys between the ridges since the late miocene opening of the strait of gibraltar coincident with the northwestward decrease in undercurrent speeds from the strait there is the following northwestward gradation of sediment facies associations 1 upper slope facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins compared to this the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand further northwestward sediment drift grades to biogenous silt near the faro drift at the portuguese border because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean undercurrent the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies the bottom current deposits of valleys and the contourites of the cadiz slope intervalley areas are distinct from turbidite systems the valley sequences are not aggradational like turbidite channel levee complexes but typically exhibit bedrock walls against ridges extensive scour and fill into adjacent contourites transverse bedform fields and bioclastic lag deposits both valley and contourite deposits exhibit reverse graded bedding and sharp upper bed contacts in coarse grained layers low deposition rates and a regional pattern of bedform zones textural variation and compositional gradation the surface sandy contourite layer of 0 2 1 2 m thickness that covers the gulf of cadiz slope has formed during the present holocene high sea level because high sea level results in maximum water depth over the gibraltar sill and full development of the mediterranean undercurrent the late pleistocene age of the mud underlying the surface sand sheet correlates with the age of the last sea level lowstand and apparent weak mediterranean undercurrent development thus the cyclic deposition of sand or mud layers and contourite or drape sequences appear to be related to late pliocene and quaternary sea level changes and mediterranean water circulation patterns since its pliocene origin the contourite sequence has had low deposition rates of

archean seawater composition and depositional environment geochemical and isotopic signatures from the stromatolitic carbonates of dharwar craton india abstract the well preserved stromatolitic carbonates from neoarchean sandur chitradurga and shimoga greenstone belts of dharwar craton were studied to constrain the depositional conditions geochemical isotopic characteristics and the archean seawater temperatures these rocks display limited diversity in their morphological features such as columnar occasionally branched pseudo columnar domal crinkly laminated and oval elliptical shapes the stromatolites are associated with fe mn formations along with arenites argillites limestones and carbonaceous shales these stromatolites are cherty dolomites having variable sio2 mgo and cao contents the stromatolitic carbonates of the three greenstone belts possess low total rare earth elements plus ytterium rey along with positive la eu gd y anomalies and y ho ratios reflecting their deposition in marine conditions with variable hydrothermal and terrigenous inputs these stromatolites display predominantly negative 13c values ranging from 1 61 to 0 01 vpdb of sandur 2 53 to 1 35 vpdb of chitradurga and positive 13c of shimoga varying from 0 30 to 1 29 vpdb combined with the negative 18o values 20 95 to 7 72 vpdb our studies indicate fluctuating oxic to anoxic acidic to alkaline environment responsible for the deposition of these stromatolites with locally varying archean ocean temperatures from 25 to 75 c these conditions favoured the deposition of cherty dolomitic stromatolites in a shallow marine environment ranging from supra to subtidal zones with the minor influence of hydrothermal activity which is evident for the existence of archean smaller plate tectonics

evolution of a volcanogenic hydrothermal system recorded by the behavior of lree and eu case study of the key tuffite at bracemac mcleod deposits matagami canada abstract the distribution of rare earth elements ree in the alteration zones surrounding modern and ancient volcanogenic massive sulfide vms deposits is often characterized by a wide range of variations comprising both gains and losses of light ree lree la to sm and europium the evolution of the hydrothermal system is recorded by mineral assemblages and their chemical composition to address the behavior of the ree in such a context the bracemac mcleod archean vms deposits of the matagami district are used there mineralization was formed mainly by subsea floor replacement along a tuffaceous marker unit key tuffite of homogenous andesitic composition hence providing a single protolith to account for mineral and chemical variations in relation to ore position we combine whole rock and mineral ree data in both distal sericite and proximal chlorite alteration surrounding the mineralization a model integrating observed textural relationships geochemical data and current understanding of mineral stabilities is proposed to explain the redistribution of the ree during the evolution of the vms hydrothermal system the distal sericite zone represents the early low temperature alteration it is characterized by the destruction of volcanic glass and plagioclase leading to a negative eu anomaly in the whole rock analyses and the depletion of lree the proximal chlorite zone was formed during the thermal evolution of a fertile vms hydrothermal system it is generally characterized by gains of lree and eu although some chloritized samples are depleted in lree petrographic observations suggest that the coprecipitation of allanite with chlorite explains the increase of lree whereas a mass balance calculation indicates that the precipitation of apatite carbonates essentially controls the eu local silicification occurring as pulses during the hydrothermal system life is also of interest because it could preserve an intermediate alteration state and thus provide additional information on the evolution of the hydrothermal system the mobility of ree is indicative of specific hydrothermal conditions which may reflect the efficiency of a mineralizing hydrothermal system at matagami the mobility of lree and eu could be used for vectoring in exploration especially eu which has an anomalous behavior that extends far beyond the limit of the sulfide zone into the distal sericitic low temperature alteration up to 400 m from the ore zones

oxidative dissolution of hydrothermal mixed sulphide ore an assessment of current knowledge in relation to seafloor massive sulphide mining highlights seafloor massive sulphides vary in mineralogy and oxidise at different rates galvanic cells play a role in increasing dissolution rates sms deposits that have been inactive for some time may have lost economic value the geochemistry of oxidation products has potential to be an exploration tool potential for anthropogenic release of heavy metals during seafloor mining any risk needs addressing by the isa prior to the formation of mining regulations the weathering process of seafloor massive sulphide sms deposits can be considered analogous to weathering of terrestrial volcanogenic massive sulphides vms deposits however in the context of sms deposits the process occurs in chemically buffered waters of near neutral ph resulting in the formation of insoluble fe oxy hydroxide minerals including goethite and hematite as well as sulphates such as jarosite as a result of this precipitation it is commonly assumed that any sms deposit is unlikely to exhibit a significant loss of metals dissolution and release of heavy metals into the water column however galvanic interactions have never been considered in this seafloor context whilst they have already been shown to have the ability to increase dissolution significantly in terrestrial deposits if heavy metal release is not temporally balanced by precipitation of oxide phases there is the potential that these metal occurrences lose economic value this is specifically significant if there is an industrial focus on exploiting deposits associated with hydrothermal vents that have been inactive for some time not only this but the geochemistry of weathering products gossans that are formed have the potential to be used as tools for exploration furthermore it is unknown what impact galvanic coupling may have with regards to anthropogenic release of heavy metals during seafloor mining of deposits associated with either active or inactive vents disturbance of sediment plume generation and dewatering process this environmental impact needs to be addressed prior to the formulation of regulations for deep sea mining by the international seabed authority the present review examines our current understanding of oxidation and dissolution of a mixed sulphide ore bringing together lines of evidence from a range of literature sources based on this review different seafloor sulphide ore deposits will dissolve by oxidation and release a variety of different metals economic and or toxic all at different rates with galvanic cells playing a role by increasing dissolution rates while precipitation of oxide and oxy hydroxide phases will occur it is unknown in both a natural weathering and anthropogenic mining context whether heavy metal release including economic and toxic metals is temporally balanced by this precipitation and any subsequent adsorption based on our current understanding certain sites will be more predisposed to oxidation as a result of their mineralogy those containing significant pyrrhotite marcasite galena and secondary copper sulphides and or environment higher temperatures and oxygen concentrations lower ph s furthermore certain sites pose more of an environmental risk in terms of toxicity than others with arc related sms deposits associated with higher concentrations of as pb sb cd and hg and ultra mafic hosted sms deposits associated with high concentrations of co and ni the review highlights the need for subsequent studies that investigate the natural weathering process of seafloor sulphide ore deposits including how this process impacts their economic value and consequent geochemical signature of oxides that are produced over time moreover this review underlines the necessity for experiments to elucidate the oxidative dissolution of ore throughout any mining process

increasing data inaa on ecuadorian obsidian artifacts preliminary provenance and a clue for pre columbian eastward trade in this work we carried out inaa major na k ca and fe and trace ppm elements plus mn by faas analysis of 15 obsidian samples waste flakes coming from an unknown archaeological site 14c ams age of 1425 ad located on the south eastern flank of the back arc sumaco volcano to the east of the cordillera real and from two already known pre columbian archaeological localities la florida quito and milan cayambe literature compositional data of the ecuadorian obsidian outcrops provide some constraints on the provenance of the analyzed waste flakes even though different methods of analyses make comparisons a difficult task concerning the obsidian artifacts of la florida and milan they come from the well known sierra de guamani obsidian sources cordillera real by contrast the obsidian fragments of the sumaco settlement show some compositional characters compatible with obsidian erratic pebbles recently discovered in some river banks of the amazonian foothills draining the easternmost flanks of the antisana volcano in the cordillera real as well in this way the obsidian artifacts found at the sumaco site reinforce the opinion that ecuadorian source inventory is not yet exhaustive although the antisana volcano seems to be the best candidate to find out additional primary outcrops of obsidian sources it cannot be also excluded that sub andean and amazonian people directly took advantage from obsidian secondary sources e g river banks rather than procurements from primary outcrops in the cordillera real the new archaeological findings at the sumaco volcano are really of paramount importance in tracing the ancient routes of a possible obsidian eastward trade toward the amazonian region

discovery of the west 45 volcanic hosted massive sulfide deposit using oxygen isotopes and ree geochemistry a number of innovative geochemical techniques were tested around the thalanga volcanic hosted massive sulfide vhms deposit in north queensland with the objective of being able to recognize a near miss in the exploration drilling in and around the mine whole rock oxygen isotope analyses were used to determine temperature gradients in the footwall rocks just beneath the ore horizon by assuming a water 6180 value of 0 per mil consistent with a seawater dominated hydrothermal system an alteration temperature was calculated for each sample a quantitative determination of the mineralogy was used to work out a weighted fractionation factor for each sample so that the variance attributable to differences in mineralogy could be taken into account comparison of the temperatures to a sodium depletion index indicates that the 6180 halo is comparable in size to an alteration mineralogy halo but the distribution of na is somewhat unpredictable in the distal parts of the hydrothermal system this study identified a hot spot i km west of the limit of the mine workings the mount windsor volcanics which host the thalanga deposit contain a large number of stratiform quartz hematite lenses red jaspers rather than drill test all of these occurrences a geochemical index was determined to assist in ranking them elevated ba s and pb along with positive chondrite normalized europium anomalies were found to be characteristics of proximal jaspers as compared to barren jaspers a red jasper outcrop west of thalanga coincident with the 6180 hot spot was the most anomalous sample in this study subsequent drill testing of this target led to the discovery of the west 45 vhms deposit

structural analysis and miocene to present tectonic evolution of a lithospheric scale transcurrent lineament the sciacca fault sicilian channel central mediterranean sea abstract seismo stratigraphic and structural analysis of a large number of multichannel seismic reflection profiles acquired in the northern part of the sicilian channel allowed a 3 d reconstruction of a regional ns trending transfer zone which displays a transcurrent tectonic regime and that is of broad relevance for its seismotectonic and geodynamic implications it is constituted of two major transcurrent faults delimiting a 30 km wide mostly undeformed basin the western fault capo granitola does not show clear evidence of present day tectonic activity and toward the south it is connected with the volcanic area of the graham bank the eastern fault sciacca is structurally more complex showing active deformation at the sea floor particularly evident along the nerita bank the sciacca fault is constituted of a master and splay faults compatible with a right lateral kinematics sciacca fault is superimposed on an inherited weakness zone a mesozoic carbonate ramp which borders to the east a 2 5 km thick plio quaternary basin and that was reactivated during the pliocene a set of scaled claybox analogue models was carried out in order to better understand the tectonic processes that led to the structural setting displayed by seismic data tectonic structures and uplift subsidence patterns generated by the models are compatible with the 3 d model obtained from seismic reflection profiles the best fit between the tectonic setting deriving from the interpretation of seismic profiles and the analogue models was obtained considering a right lateral movement for the sciacca fault nevertheless the stress field in the study area derived from gps measurements does not support the present day modelled right lateral kinematics along the sciacca fault moreover seismic events along this fault show focal mechanisms with a left lateral component we ascribe the slip change along the sciacca fault from a right lateral transcurrent regime to the present day left lateral kinematics to a change of principal horizontal stress direction starting from late pliocene

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

linked halokinesis and mud volcanism at the mercator mud volcano gulf of cadiz mud volcanoes are seafloor expressions of focused fluid flow that are common in compressional tectonic settings new high resolution 3 d seismic data from the mercator mud volcano mmv and an adjacent buried mud volcano bmv image the internal structure of the top 800 m of sediment at both mud volcanoes revealing that both are linked and have been active episodically the total volumes of extruded mud range between 0 15 and 0 35 km3 and 0 02 0 05 km3 for the mmv and the bmv respectively the pore water composition of surface sediment samples suggests that halokinesis has played an important role in the evolution of the mud volcanoes we propose that erosion of the top of the vernadsky ridge that underlies the mud volcanoes activated salt movement triggering deep migration of fluids dissolution of salt and sediment liquefaction and mobilization since the end of the pliocene since beginning of mud volcanism in this area the mud volcanoes erupted four times while there was only one reactivation of salt tectonics this implies that there are other mechanisms that trigger mud eruptions the stratigraphic relationship of mudflows from the mmv and bmv indicates that the bmv was triggered by the mmv eruptions this may either be caused by loading induced hydrofracturing within the bmv or due to a common feeder system for both mud volcanoes this study shows that the mud volcanoes in the el arraiche mud volcano field are long lived features that erupt with intervals of several tens of thousands of years

rare earth element geochemistry of hydrothermal deposits from the active tag mound 26 n mid atlantic ridge the rare earth element ree geochemistry of various phases from the active tag hydrothermal mound has been examined and related to their mineralogy and fluid chemistry the mound deposits range from black and white smoker chimneys massive anhydrite sulphide mixtures oxides and ochres all phases except black smoker chimney anhydrite demonstrate a positive eu anomaly when normalised to chondrite ree values ree substitution into sulphide and sulphate phases appears to be strongly influenced by crystallographic control for all ree other than eu precipitation of anhydrite within the tag mound is the major mechanism for removal of ree during mound circulation and 0 15 0 35 g anhydrite is inferred to precipitate from every kg of fluid venting from the white smoker chimneys oxides from the mound fall into three different categories with distinct ree patterns oxide rims on sulphides atacamite bearing oxides and silica rich fe oxides and ochres the oxide rim phases contain sulphide and seawater derived rees whereas the atacamite bearing oxides and the ochreous material exhibit no seawater signature which suggests precipitation from or alteration by a modified hydrothermal fluid

mineralogy bulk and rare earth element geochemistry of massive sulphide associated hydrothermal sediments of the brunswick horizon bathurst mining camp new brunswick massive sulphides are spatially and temporally associated with iron formation if and other hydrothermal sedimentary rocks in the vicinity of the brunswick no 12 brunswick no 6 and austin brook deposits bathurst mining camp sulphide carbonate oxide and silicate predominant if is present carbonate predominant if is best developed in and around the brunswick no 12 deposit whereas hematite bearing if is absent here but prominent in the austin brook brunswick no 6 area the if is composed dominantly of si co2 fe mn and ca minor constituents include mg p ti al and s statistically significant interelement correlations between eu fe mn pb zn cd au ca sr ba p co2 and s indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor positive interelement correlations between si ti al mg k zr rare earth elements ree s except eu se v y yb co ni and cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and

imaging active faulting in a region of distributed deformation from the joint clustering of focal mechanisms and hypocentres application to the azores western mediterranean region abstract the matching between linear trends of hypocentres and fault planes indicated by focal mechanisms fms is frequently used to infer the location and geometry of active faults this practice works well in regions of fast lithospheric deformation where earthquake patterns are clear and major structures accommodate the bulk of deformation but typically fails in regions of slow and distributed deformation we present a new joint fm and hypocentre cluster algorithm that is able to detect systematically the consistency between hypocentre lineations and fms even in regions of distributed deformation we apply the method to the azores western mediterranean region with particular emphasis on western iberia the analysis relies on a compilation of hypocentres and fms taken from regional and global earthquake catalogues academic theses and technical reports complemented by new fms for western iberia the joint clustering algorithm images both well known and new seismo tectonic features the azores triple junction is characterised by fms with vertical pressure p axes in good agreement with the divergent setting and the iberian domain is characterised by nw se oriented p axes indicating a response of the lithosphere to the ongoing oblique convergence between nubia and eurasia several earthquakes remain unclustered in the western mediterranean domain which may indicate a response to local stresses the major regions of consistent faulting that we identify are the mid atlantic ridge the terceira rift the trans alboran shear zone and the north coast of algeria in addition other smaller earthquake clusters present a good match between epicentre lineations and fm fault planes these clusters may signal single active faults or wide zones of distributed but consistent faulting mainland portugal is dominated by strike slip earthquakes with fault planes coincident with the predominant nne ssw and wnw ese oriented earthquake lineations clusters offshore sw iberia are predominantly strike slip or reverse confirming previous suggestions of slip partitioning

seismicity and focal mechanisms in south spain abstract recent improvements in regional seismological networks allow a better definition of the seismicity and the determination of focal mechanisms in south spain this region is part of the lithospheric plate boundary between africa and eurasia and shows a continuous seismic activity of moderate magnitude m h h 650 km earthquakes also occurring in the region eight fault plane solutions have been determined that can be related to the tectonics of the area the solutions for the shallow shocks are compatible with regional stresses with horizontal compressions in nw se direction and tensions in e w direction that produce normal faulting along the n30 to 60 w and n10 to 30 e systems of faults the mechanisms of the intermediate depth shocks can be explained in terms of a subduction zone from africa in a nw direction that is under compression

formation of massive sulfide deposits on oceanic ridge crests incremental reaction models for mixing between hydrothermal solutions and seawater equilibrium path calculations have been used to model mixing between hot 350 c hydrothermal solutions and ambient seawater in an attempt to simulate mineral precipitation at seafloor vents these calculations predict temperatures of precipitation paragenetic sequence of minerals and chemical composition of chimney deposits associated with vents on the seafloor at 21 n epr assuming sulfate sulfide disequilibrium during mixing the paragenetic sequence revealed is chalcopyrite anhydrite pyrrhotite pyrite sphalerite graphite and barite when sulfate sulfide equilibria is permitted during mixing however reduction of small amounts of sulfate results in early precipitation of pyrite and a sequence of cu rich sulfide minerals chalcopyrite bornite chalcocite covellite this sequence is analogous to that observed in thin chimney walls the calculations indicate that sulfide mineral precipitation occurs in response to both cooling and change in composition of the hydrothermal solutions as a result of mixing varying the amount of mixing with respect to temperature simulating conductive heating of seawater prior to mixing results in only minor variations in the sequence and abundance of precipitated phases anhydrite precipitation during mixing occurs early which is consistent with formation of an anhydrite leading edge of chimney structures similarly extrapolation of warm spring data from galapagos to zero so4 concentration suggests anhydrite formation due to mixing with seawater beneath the seafloor most likely below the level of reactive calcareous sediments subsequent interaction of the mixed hydrothermal solution with those sediments results in elevated and variable ca concentrations estimated for end member solutions from the galapagos precipitation of mg hydroxide sulfate hydrate in the walls of the vent chimneys at 21 n epr occurs as a result of conductive heating of ambient seawater with only very minor amounts of mixing in contrast precipitation of amorphous silica in the vents must be due to conductive cooling of the hydrothermal solutions thus incremental reaction calculations demonstrate that reactions occurring in and associated with venting ridge crest hydrothermal solutions can be effectively modeled using the thermodynamic data and reaction modeling codes available today departures from equilibrium required to accurately model the mixing process are easily accommodated and consistent with data from the vents and vent forming materials

seismic reflection applied to sedimentology and gas discovery in the gulf of cadiz in the gulf of cadiz a tertiary basin became filled by clastic series during miocene and pliocene times this terrigenous influx derived from the iberic meseta in the north is characterized by a sandy episode during the tortonian and messinian the sand deposits were probably connected with uplift and major erosion of the meseta during the sliding of the olistostrome which occupied the south of the basin from late helvetian to middle tortonian high resolution seismic techniques produced a good picture of the stratigraphy and of the depositional environment of the sands a further study using the amplitude of the reflections inversion of seismic traces into acoustic impedance traces and modeling provides a remarkable example of the possibilities of seismic stratigraphy for depicting the lateral evolution of facies and localizing hydrocarbon occurrences out of seven exploratory wells based upon seismic information six encountered gas bearing sands with economic potential

genesis of mud volcano fluids in the gulf of cadiz using a novel basin scale model approach abstract mud volcanism and fluid seepage are widespread phenomena in the gulf of cadiz sw iberian margin in this seismically active region located at the boundary between the african and eurasian plates fluid flow is typically focused on deeply rooted active strike slip faults the geochemical signature of emanating fluids from various mud volcanoes mvs has been interpreted as being largely affected by clay mineral dehydration and recrystallization of upper jurassic carbonates here we present the results of a novel fully coupled 1d basin scale reactive transport model capable of simulating major fluid forming processes and related geochemical signatures by considering the growth of the sediment column over time compaction of sediments diffusion and advection of fluids as well as convective and conductive heat flow the outcome of the model is a realistic approximation to the development of the sediment pore water system over geological time scales in the gulf of cadiz combined with a geochemical reaction transport model for clay mineral dehydration and calcium carbonate recrystallization we were able to reproduce measured concentrations of cl strontium and 87sr 86sr of emanating mud volcano fluids these results support previously made qualitative interpretations and add further constraints on fluid forming processes reaction rates and source depths the geochemical signature at porto mv posed a specific problem because of insufficient constraints on non radiogenic 87sr 86sr sources at this location we favour a scenario of basement derived fluid injection into basal upper jurassic carbonate deposits hensen et al 2015 although the mechanism behind such basement derived flow e g along permeable faults remains speculative at this stage it provides an additional source of low 87sr 86sr fluids and offers an idea on how formation water from the deepest sedimentary strata above the basement can be mobilized and eventually initiate the advection of fluids feeding mvs at the seafloor the dynamic reactive transport model presented in this study provides a new tool addressing the combined simulation of complex physical geochemical processes in sedimentary systems the model can easily be extended and applied to similar geological settings and thus help us to provide a fundamental understanding of fluid dynamics and element recycling in sedimentary basins

metalliferous sediments associated with presently forming volcanogenic massive sulfides the susu knolls hydrothermal field eastern manus basin papua new guinea short sediment cores were examined from the active susu knolls hydrothermal field in the eastern manus back arc basin papua new guinea in order to explain the origin of the currently accumulating metalliferous sediments the mineralogy and geochemistry of the sediments were studied by x ray diffraction scanning electron microscopy energy dispersive x ray fluorescence and instrumental neutron activation analysis sediments of the suzette site originated from the deposition of volcaniclastic material with the addition of a hydrothermal component from the mass wasting of old oxidized chimneys a strong mass wasting event was recognized at the base of the studied sedimentary succession from the occurrence of chalcopyrite pyrite and barite aggregates similar to those found in chimneys as well as the presence of atacamite the metalliferous component is characterized by high concentrations of cu up to 2 3 and au up to 3 5 ppm elevated concentrations of as ba zn and fe as well as a positive eu anomaly the material derived from eroded chimneys was deposited together with abundant glass fragments eroded from the volcanic edifice the mass wasting was succeeded by deposition of volcaniclastic sediment containing dacite fragments ca plagioclase pyroxene glass shards cristobalite si rich amorphous material alunite pyrite barite and magnetite the volcaniclastic sediment may have originated from hydrothermal eruptions at north su and south su the present day plume at suzette is a likely source of rare barite aggregates amorphous cu containing aggregates and cu fe sulfides creating geochemical anomalies of ba and cu in the uppermost sediments at suzette interbedded volcaniclastic and hemipelagic sediments were retrieved east and west of susu knolls the enrichment of mn in these sediments is considered to be a result of settling of mn oxides from a hydrothermal plume

paleomagnetic rotations and the kinematics of the gibraltar arc paleomagnetic investigations of a mesozoic limestone sequence around the gibraltar arc show that there have been large systematic rotations about a vertical axis and imply that there must have been a significant component of westward motion within the betic rif orogenic belt rotations of the late jurassic and late cretaceous limestones in the betic cordillera of southern spain are clockwise with the exception of the unrotated sierra gorda whereas the jurassic sites in the rif mountains of morocco are rotated counterclockwise except in the area around tetuan these data are generally consistent with formation of the arc either by a westward moving alboran microplate or by extensional collapse of a collisional mountain chain the former model however fails to recognize the nonrigid nonplate like character of the alboran domain and lacks a definable driving mechanism a model of a collapsing east west elongated ridge that takes into account the obliquity of the convergence along the active margin may provide mechanisms both for the observed rotations and for the large westward component of motion and therefore can explain the geometry of the gibraltar are

the rif chain northern morocco in the late tortonian early messinian tectonics of the western mediterranean orogenic belt evidence from the tanger al manzla wedge top basin

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

controls of fluid chemistry and complexation on rare earth element contents of anhydrite from the pacmanus subseafloor hydrothermal system manus basin papua new guinea ocean drilling program odp leg 193 successfully drilled four deep holes 126 to 386 m into basement underlying the active dacite hosted pacmanus hydrothermal field in the eastern manus basin anhydrite is abundant in the drill core material filling veins and vesicles cementing breccias and occasionally replacing igneous material we report rare earth element ree contents of anhydrite from a site of diffuse venting site 1188 which show extreme variability in terms of both absolute concentrations e g 0 08 28 3 ppm nd and pattern shape lan smn 0 08 3 78 smn ybn 0 48 23 1 eu eu 0 59 6 1 the range of ree patterns in anhydrite includes enrichments in the middle and heavy rees and variable eu anomalies the patterns differ markedly from those of anhydrite recovered during odp leg 158 from the tag hydrothermal system at the mid atlantic ridge which display uniform lree enriched patterns with positive eu anomalies very similar to tag vent fluid patterns as the system is active the host rock composition is uniform and the anhydrite veins appear to relate to the same hydrothermal stage we can rule out predominant host rock and transport control instead we propose that the variation in ree content reflects waxing and waning input of magmatic volatiles hf so2 and variable complexation of rees in the fluids ree speciation calculations suggest that increased fluoride and possibly sulfate concentrations at pacmanus may affect ree complexation in fluids whereas at tag only chloride and hydroxide complexes play a significant role the majority of the anhydrites do not show positive eu anomalies suggesting that the fluids were more oxidizing than in typical mid ocean ridge hydrothermal systems we use other hydrothermal fluids from the manus basin vienna woods and desmos which bracket the pacmanus fluids in terms of acidity and ligand concentrations to examine the dependence of ree complexation on fluid composition geochemical modeling reveals that under the prevailing conditions at pacmanus ph 3 5 t 250 300 c eu oxidation state and the relative importance of fluoride versus chloride complexing are very sensitive to small variations in oxygen fugacity temperature and ph patterns with extreme mid ree enrichment may reflect speciation effects free ion abundance coupled with crystal chemical control we conclude that the great variability in ree concentrations and pattern shape is likely due to variable fluid composition and ree complexation in the fluids

thousands of cold water coral mounds along the moroccan atlantic continental margin distribution and morphometry abstract coral mounds formed by framework forming cold water corals pierce the seabed along most continental margins of the atlantic ocean and new sites are continuously being discovered here we describe an extremely high accumulation of coral mounds at the nw moroccan atlantic margin between 35 n and 35 5 n within an area of only 1440 km2 3400 mounds were found exposed at the seabed the coral mounds are nowadays characterized by an almost complete lack of living cold water corals in addition numerous buried mounds were identified in hydroacoustic sub bottom profiles and are estimated to be 3 7 times more frequent than the exposed mounds consequently a total of 16 000 buried and exposed mounds is estimated for the entire study area the exposed mounds are rather small with a mean height of 18 m and show a conspicuous arrangement in two slope parallel belts that centre in water depths between 720 and 870 m and 890 980 m respectively putting them among the deepest mound occurrences discovered so far in the atlantic the mostly elongated mounds largely stretch downslope pointing to a significant influence of internal waves in the mound formation process moreover based on their average dimensions the entire coral mound volume can be estimated as 1 3 km3 which means the mounds store a considerable amount of coral carbonate highlighting their potentially important role as regional carbonate factories in combination with further occurrences of coral mounds along the moroccan margin both in the mediterranean and in the atlantic ocean these new findings underline morocco s role as a hotspot for the occurrence of cold water coral mounds

paleo environmental variation and its control on organic matter enrichment of black shales from shallow shelf to slope regions on the upper yangtze platform during cambrian stage 3 abstract to understand the evolution of oceanic redox conditions and organic matter om accumulation in the shelf and slope regions of the upper yangtze platform during cambrian stage 3 high resolution geochemical data were obtained from two wells respectively representing shelf and slope environments based on redox proxies widespread anoxic euxinic waters with intermittent sulfidic water columns were formed from shallow shelf to deep water slope and basinal regions during stage 2 and early stage 3 then widespread anoxic waters were reduced and oxic waters expanded during the middle stage 3 after which fluctuating suboxic and oxic occasionally anoxic environments became predominant during late stage 3 the presence of hyalophane and positive eu anomalies suggest strong ba rich hydrothermal activities in the shelf and deep basin regions during early and middle stage 3 the ba rich hydrothermal fluids and upwelling events enhanced the primary productivity in surface waters and subsequently promoted organic matter enrichment during stage 2 and early stage 3 the high primary productivity driven by coastal upwelling and hydrothermal activity were the main factors controlling om enrichment during middle stage 3 the local anoxic water condition became responsible for om enrichment when oxic waters began to gradually expand during late stage 3 both primary productivity and redox conditions became the main control factors for om enrichment according to the analysis of primary productivity redox conditions hydrothermal activity and upwelling events an evolution model is proposed to account for the paleo environmental variation and the om enrichment from shallow shelf to slope regions during cambrian stage 3

early middle miocene stratigraphic turning points in the alicante region se spain reflections of western mediterranean plate tectonic reorganizations abstract the paper concerns the miocene deposits of the alicante region se spain which forms part of the prebetic and intermediate units representing the former southern passive margin of the iberian continent from the late jurassic up to the miocene the alicante region was the scene of a facies distribution with more continental lagoonal or shallow marine conditions in the north and northwest and more open or deeper marine in the south and southeast the early middle miocene deposits can be divided in three sedimentary cycles each one controlled by a different tectonic regime cycle i aquitanian is deposits after a block faulting phase at about 25 ma related to the formation of the ligurian and balearic troughs cycle ii burdigalian early langhian is separated from first cycle sediments by a complete reorientation of palaeogeography at 19 5 ma due to the collision of iberia with africa the southern part of the region is folded and uplifted and separated from a northern emerged area by a trough cycle iii late langhian serravallian is controlled by strike slip movements caused by the continuing convergence between africa and europe and resulting in the development of a new set of basins at 15 5 ma at the middle late miocene boundary the alicante region emerges thus younger important tectonics could not be dated our results are in conflict with several recent plate tectonic models for the miocene history of the western mediterranean where the internal betic zone is placed juxtaposed to the alicante region prior to the burdigalian

transport and deposition of ree in h2s rich fluids evidence from accessory mineral assemblages abstract it is shown in four examples from geologically different environments that accessory or minor minerals rich in rare earth elements ree are often texturally associated with base metal sulfides the examples demonstrate that ree can migrate in hydrothermal fluids containing large amounts of reduced sulfur s ii species i e h 2 s hs and s 2 in certain fluids complexes of ree with s ii species may be important for the ree transport but most probably only in the absence of other strong ligands such as fluoride carbonate or possibly phosphate textural relationships and geochemical data suggest that the formation of ree bearing minerals in s ii rich environments is genetically related to the precipitation of basemetal sulfides

rare earth element geochemistry of standard sediments a study using inductively coupled plasma spectrometry the rare earth elements ree and y have been determined in 15 international standard sediments from france german democratic republic canada and the u s a samples were prepared using conventional rock dissolution techniques and the ree and y were separated from other constituents using cation exchange chromatography the ree la ce pr nd sm eu gd dy ho er yb lu and y were analysed simultaneously by inductively coupled plasma atomic emission spectrometry results indicate that u s g s standard shale sco 1 cody shale is a good reference material to use for the normalisation of the ree distributions of sediments data normalised to sco 1 are more readily interpreted than those normalised to existing estimates of average shale the ree patterns of standard sediments vary considerably in shape span an order of magnitude in absolute concentration and provide valuable reference values for the ree analysis of other sedimentary materials

europium redox equilibria in aqueous solution thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous eu2 and eu3 over a wide range of temperatures and pressures at low temperatures near earth surface conditions the aqueous geochemistry of europium should be dominated by the trivalent state except possibly in the most reducing alkaline pore waters of anoxic marine sediments however at temperatures greater than about 250 c and elevated pressures divalent europium should predominate even with significant amounts of complexing trivalent europium is not stable at elevated temperatures and pressures consequently under most hydrothermal and metamorphic conditions europium in aqueous solution should be divalent at intermediate temperatures around 100 c significant activities of both eu2 and eu3 and related complexes can occur in aqueous solutions depending on the oxidation state and the ph of the solutions and the activities of potential ligands such as sulfate carbonate and chloride the predicted stability of divalent europium in aqueous solution at elevated temperatures is consistent with the large positive europium anomalies in rare earth element patterns of high temperature barites of hydrothermal and metamorphic origin reported by guichard et al 5 and with the observed depletion of europium as a result of high temperature sericitization of feldspar bearing assemblages discovered by alderton et al 1 it is suggested that significant fractionation of europium relative to the other rare earth elements may take place during high temperature hydrothermal alteration processes such as in the mid oceanic ridge systems because of the expected stability of divalent europium during these processes

geological setting mineralogy geochemistry and genesis of the middle archaean kalyadi copper deposit western dharwar craton southern india the kalyadi polymetallic copper deposit occurs within the middle archaean 3 0 ga medium grade kalyadi schist belt which consists predominantly of ultramafic mafic schists interbedded with chemogenic chert detrital high al mg schists and siliceous schists this sedimentary exhalative type sedex type ore body is the only copper deposit hosted in cherts in the western dharwar craton the kalyadi supracrustal rocks are intruded by tonalite trondhjemitic gneisses ca 3 0 ga and granite ca 2 6 ga the kalyadi copper deposit is polygenetic in nature the primary ores represented by disseminations of pyrite linneite and chalcopyrite magnetite essentially along the bedding lamination of the metachert are referred to as the metamorphosed chert sulphide rhythmites of a primary stratiform type the ore is of low grade and records imprints of at least two events of deformation pyrite is characterised by high co values 262 4524 ppm and high co ni ratios 3 0 19 7 rare earth element patterns of the primary ores and the host metacherts are identical characterised by la enrichment absence of eu anomalies and flat to depleted hree patterns with 34 s 0 8 the secondary remobilised ores are structurally controlled occurring as veins and stringers discordant to the bedding lamination or schistosity the constituent ores are chalcopyrite pyrite pyrrhotite with minor pentlandite these sulphides with low co ni ratios 0 87 1 80 have either a strong positive or negative eu anomaly and show slight hree enrichment the 34 s value ranges from 2 64 to 4 29 it is interpreted that the primary stratiform ores and the cherts were derived from volcanogenic hydrothermal fluids as syngenetic chemical deposits in a deep sea environment the secondary epigenetic mineralisation is related to subsequent migmatisation deformational events and granitic activity

magmatic evolution of the alboran region the role of subduction in forming the western mediterranean and causing the messinian salinity crisis the magmatic evolution of the alboran region westernmost mediterranean contains important clues for improving our understanding of the origin of mediterranean style back arc basins and the desiccation of the mediterranean sea in the messinian we use new laser 40ar 39ar age and geochemical major and trace element and o sr nd pb isotope data from igneous rocks from southern spain the alboran sea and northern morocco to reconstruct the magmatic evolution of the westernmost mediterranean since the eocene lower oligocene dikes near malaga 33 6 0 6 ma and middle to upper miocene volcanic rocks from the alboran sea area 6 57 0 04 to 11 8 0 4 ma can be subdivided into two groups 1 lree depleted relative to n morb primarily tholeiitic series and 2 lree enriched primarily calc alkaline series volcanic rocks both groups are generally enriched in fluid mobile elements e g rb th u k and pb relative to fluid immobile elements e g nb ta lree the lree depleted group has 143nd 144nd 0 5128 0 5130 isotope ratios similar to atlantic morb but higher 87sr 86sr 0 7046 0 7100 in contrast the lree enriched group has less radiogenic nd 0 5121 0 5126 and tend to more radiogenic sr 0 7066 0 7205 isotopic composition pb isotope ratios are surprisingly uniform and have compositions similar to marine sediments analyses of mineral separates show that mafic melts with relatively low 18o 5 6 7 2 had high 87sr 86sr 0 7048 0 7088 7 4 10 6 14 1 and 8 4 40 0 49 3 modeling of the trace elements and sr nd pb o isotopic compositions provides compelling evidence for the contamination of the mantle source with hydrous fluids melts which can be explained through subduction of oceanic lithosphere beneath the alboran basin but not through detachment delamination of lithospheric mantle we present a geodynamic model that reconstructs the late eocene to quaternary evolution of the western mediterranean through westward roll back of subducted tethys oceanic lithosphere slab roll back resulted in a large scale reorganization of the western mediterranean paleogeography causing the closure of marine gateways linking the atlantic ocean to the mediterranean sea isolation of the mediterranean sea led to its desiccation causing the messinian salinity crisis

seismicity source mechanisms and tectonics of the azores gibraltar plate boundary abstract a study and partial revision of the seismicity and source mechanisms of earthquakes are presented for the oceanic plate boundary of eurasia and africa from the azores islands to the strait of gibraltar focal mechanisms of 36 earthquakes wave form modelling of 4 and seismic moments and dimensions of 28 have been calculated these results indicate that the boundary is divided into three sections with different characteristics the azores the central section and the east section the azores section has high seismicity of moderate magnitude and a low slip rate 0 76 cm yr the predominant mechanism is normal or transform faulting with horizontal tensions on average in a n25 e direction in the central section large earthquakes occur with strike slip right lateral motion along faults in an e w direction there is a high slip rate 3 39 cm yr the east section is of more complex nature large earthquakes also occur but the predominant mechanism is reverse faulting with a horizontal pressure axis in the n30 w direction resulting in underthrusting of africa from the slip vectors the pole of rotation for the african plate is located at 28 2 n 21 1 w nearer to the boundary than previous locations close to the continent there is a continuation in the ocean crust of some structural features of the iberian peninsula

geologic evolution of the betic cordilleras in the western mediterranean miocene to the present abstract the betic cordilleras were formed during the eo meso and neo alpine evolution of the western mediterranean area during the neo alpine stage the northward subduction of the african plate took place and the algerian provencal basin opened with the creation of oceanic floor associated space problems produced the expulsion and extensive stretching of the internal zones to the west which in turn disrupted and deformed the external zones of the betic and rif cordilleras these occurrences essentially took place in the burdigalian and continued with diminished intensity into the middle miocene following the suturing of the transcurrent contact between the internal and external zones important n60 90 e and nw se faults occurred the betic cordilleras are characterized as having been deformed by regional horizontal shortening compression oriented wnw ese or nw se which gradually rotated to the nnw sse in the late miocene when its most important intramontane neogene basins were formed the alboran basin with a thinned continental crust was formed as a western prolongation of the opening of the algerian provencal basin with its basic features already apparent in the burdigalian the volcanism present in the southeast of the betic cordilleras and in northeast morocco crossing the alboran basin is mainly late miocene in age it is linked to fracturing and exhibits chemistry related to the different thickness of the crust

high element mobility in 1 9 1 86 ga hydrothermal alteration zones bergslagen central sweden relationships with exhalative fe ore mineralizations abstract the 1 9 1 86 ga ensialic belt of western bergslagen sweden comprizes a 12 km thick felsic volcano sedimentary sequence intruded by syn volcanic granitic plutons and mafic dykes and sheets developed in a rifted continental setting regional low temperature alteration of the supracrustal sequence produced greenschist to low amphibolite facies mineral assemblages localized cross cutting zones of intense alteration are developed in felsic volcanics which have been affected by the regional alteration producing drastic changes in both mineralogy and chemistry these zones are found close to the hjulsjo granite granophyre intrusive complex most probably the heat source for the hydrothermal system and related to the exhalative sirsjoberg osjoberg fe oxide deposits the hjulsjo zones are subdivided into inner and outer zones based on differences in mineralogy and chemistry resulting from the variable intensity of alteration while the degree to which most elements are leached increases from the outer into the inner zones mg increases with alteration intensity and si and al stay unchanged although they were mobilized during alteration initially k rb fe and mn increase in the outer zones but are depleted in the inner zones rare earth elements ree are depleted with the light ree being more depleted than the heavy ree a pronounced negative eu anomaly is generally present the hydrothermal fluid was enriched in ore forming metals during alteration and leaching ree patterns of exhalative minerals indicate that the fe oxide deposits were derived from these hydrothermal fluids

ferruginous and manganiferous haloes around massive sulphide deposits of the urals proximal brecciform ferruginous and manganiferous rocks related to vms deposits of the urals are subdivided into jasperites gossanites and umbers in addition to thin bedded jaspers and cherts the coherence of host rock composition and mn fe fertility of the sediments have been established fe poor pink hematitic and gray sulphidic chert are typical of the felsic class of vms deposits in contrast the contents of fe vary from high to moderate in ferruginous rocks enclosed in basaltic units associate with vms deposits fe and mn rich ferruginous rocks and umbers occur in association with limestones and calcareous sedimentary rocks in both types of volcanic sequences a common feature of jasperites and umbers is the abundance of replacement textures of hyaloclastites and carbonates by hematite and silica in addition replacement of clastic sulphides by hematite and magnetite is a characteristic genetic feature of gossanites all of these sedimentary rocks are accompanied by pseudomorphs of hematite and quartz formed after bacterial filaments the abundance of replacement textures are supportive of the halmyrolysis model in addition to hydrothermal sedimentary and sub seafloor hydrothermal replacement theories study of chemical zonation of altered hyaloclasts shows depletion of their rims not only in mobile na k mg but also in immobile al ti and ree whereas si and fe are concentrated in situ the halmyrolysis model presented here involving organic rich calcareous hyaloclastic sediments resolves the problem of subtraction of al ti ree and other elements which are commonly immobile under hydrothermal conditions the evolution of the halmyrolysis process from acidic reducing to alkaline oxidized conditions infers a possible range in transformation from fe ii mg smectites to fe silicates and fe si oxides as precursors of brecciform jasperite and thin bedded jasper the higher acidic initial stage of gossanite formation seems to be required for oxidation of organic matter and or pyrite the acidic condition facilitates the temporal preservation of immobile elements al ti ree in immature chlorite hematite gossanites another peculiarity of the gossanite forming processes is the likely sorption of p u and v by iron hydroxides displacing sulphides the general evolution of all ferruginous sediments results in complete fe 2 oxidation and silicification accompanied by subtraction of other elements the vertical diagenetic differentiation leads to concentration of mn carbonates silicates and oxyhydroxides into the tops of jasperite and gossanite layers mn oxyhydroxides scavenge positively charged hydrated cations like co and ni near vent bacterial communities may activate the processes of volcanic glass and sulphide degradation the proposed processes of halmyrolysis followed by silicification in situ may resolve the enigma of silica rich sediment formation in a silica undersaturated ocean the discrimination between gossanite and jasperite is useful for elaboration of new criteria for local exploration of vms and mn deposits halo dispersion of gossanites covering an area about two to three times that of the massive sulphide deposit is a good vector for ore body discovery proximal gossanites can be differentiated from jasperites by presence of relic sulphide clasts or elevated contents of chalcophile elements cu fe zn pb bi te as sb ba noble metals au ag and distinct ree patterns with la and eu positive anomalies the development of halmyrolysis and biomineralization models merit further elaboration and testing in on going research in order to add or revise theories of iron and manganese deposit formation 2012 elsevier b v

multiple origins of bondi cave and ortvale klde nw georgia obsidians and human mobility in transcaucasia during the middle and upper palaeolithic abstract using pixe four types of elemental compositions were found among obsidian artefacts from the bondi cave and ortvale klde middle to upper palaeolithic sites in nw georgia one of those types corresponds to obsidians from the chikiani source whose compositions were determined with a very good agreement by pixe and icp aes ms the composition of chikiani obsidians is remarkably constant despite k ar and 39ar 40ar extrusion ages from ca 2 4 and 2 8 ma the compositions of two other groups of obsidian artefacts are similar to source materials from eastern anatolia and armenia in particular ikisdere sarikamis gutansar and hatis obsidian is only a minority component in the lithic assemblages at the bondi cave and ortvale klde both neanderthal and modern human populations used obsidian in particular from chikiani considering that the shortest walking distance to this nearest source is at minimum of about 180 km and to other potential sources of more than 350 km it is suggested that this material reached these two sites mostly if not exclusively by a series of down the line exchanges

the ree content of some hydrothermal fluids ree concentrations were determined in solutions from submarine hydrothermal vents on the east pacific rise and for the first time from continental geothermal fields in tibet and bulgaria they indicate that in hydrothermal systems ree are immobile at temperatures below 350 c and for water rock ratios of 105 nd values of submarine solutions and anhydrites 4 7 to 6 2 suggests recharge on the sedimentcovered flanks of the ridge carbonate anions as measured by alkalinity appear to increase the solubility of heavy ree somewhat but not to the extent that substantial amounts of ree could be driven out from rocks by hydrothermal activity

eastern segment of the azores gibraltar line central eastern atlantic an oceanic plate boundary with diffuse compressional deformation new seismic reflection images across the eastern segment of the azores gibraltar line west of the collisional area between the african and iberian plates have revealed a complex pattern of compressional deformation involving the mesozoic oceanic lithosphere the compressional deformation developed in a region of slow plate convergence and is diffused at different lithospheric levels across an area spanning 200 km from the gorringe ridge to the seine plain the convergence between the african and iberian plates has been active since tertiary time and our results indicate that no subduction zone exists across this part of the plate boundary

paleogeographic evolution of a segmented oblique passive margin the case of the sw iberian margin the sw iberian margin is an oblique passive margin developed during the mesozoic as part of the opening of the westernmost ligurian tethys the algarve basin developed on the sw iberian margin and its sedimentary record was strongly controlled by tectonics the algarve basin was dominated during the mesozoic by wsw ene trending extensional faults and their associated depocenters segmented by oblique nw se transfer zones two major nw se trending transfer zones connected the algarve basin to the gorringe bank in the west and to the betic basin in the east the sw iberian margin was later inverted during late cretaceous to cenozoic times due to convergence between africa and iberia inversion of the algarve basin and the sw iberian margin was controlled by both the wsw ene and nw se trending structures formed during the passive margin phase the evolution of the algarve basin during the mesozoic and up to the paleogene is documented in this paper through paleogeographic reconstructions based on field geology and reinterpretation of offshore seismic and well data

interaction of tectonic and depositional processes that control the evolution of the iberian gulf of cadiz margin abstract this study provides an integrated view of the growth patterns and factors that controlled the evolution of the gulf of cadiz continental margin based on studies of the tectonic sedimentologic and oceanographic history of the area seven sedimentary regimes are identified but there are more extensive descriptions of the late cenozoic regimes because of the larger data base the regimes of the mesozoic passive margin include carbonate platforms which become mixed calcareous terrigenous deposits during the late cretaceous early tertiary the oligocene and early miocene terrigenous regimes developed in contrast over the active and transcurrent margins near the african iberian plate boundary the top of the gulf of cadiz olistostrome emplaced in the late miocene is used as a key horizon to define the post orogenic depositional regimes the late miocene progradational margin regime is characterized by a large terrigenous sediment supply to the margin and coincides with the closing of the miocene atlantic mediterranean gateways the terrigenous drift depositional regime of the early pliocene resulted from the occurrence of high eustatic sea level and the characteristics of the mediterranean outflow currents that developed after the opening of the strait of gibraltar the late pliocene and quaternary regimes are dominated by sequences of deposits related to cycles of high and low sea levels deposition of shelf margin deltas and slope wedges correlate with regressive and low sea level regimes caused by eustasy and subsidence during the highstand regimes of the holocene inner shelf prograding deltas and deep water sediment drifts were developed under the influence of the atlantic inflow and mediterranean outflow currents respectively a modern human cultural regime began 2000 years ago with the roman occupation of iberia human cultural effects on sedimentary regimes may have equalled natural factors such as climate change interplay of tectonic and oceanographic controls dominated the evolution of the cadiz margin during the cenozoic depositional sequences formed where the tectonic setting provided the accommodation space and the shape of the deposits has been greatly influenced by the strong unidirectional atlantic inflow currents on the shelf and mediterranean outflow currents on the slope the entire cycle of the inflow and outflow deposition along the margin has been controlled first by the tectonic evolution of the betic and rif gateways which become closed during the late miocene and after the messinian by the opening of the strait of gibraltar strong current development during eustatic sea level highstands of the pliocene and quaternary has controlled deposition because of maximum sill depths at gibraltar for water circulation lowstand sea levels slowed circulation and resulted in mud drapes over the slope and regressive stratigraphic sequences over the shelf more recently the human industrial revolution has caused heavy metal contamination of sediment and water over the cadiz margin human activity also has affected sedimentation rates because of deforestation that caused increased depositional rates near undammed rivers and decreased rates where rivers have been dammed future research efforts will need to focus on 1 the effect of increased mediterranean outflow caused by river damming plus global warming and the increased outflow as a potential trigger for new ice ages 2 assessments of geologic hazards for planning man made shoreline structures developing offshore petroleum resources and maintaining undersea communications cables and 3 confirmation of the general geologic history of the cadiz margin

the betic orogen and the iberian african boundary in the gulf of cadiz geological evolution central north atlantic abstract the study of the gulf of cadiz on the basis of multichannel seismic profiles and wells illustrates the stratigraphy and tectonics the evolution of the southern iberian margins was more complex than in most north atlantic margins since it entailed several phases of rifting convergence and strike slip motions three main tectonic provinces surround the internal zones of the gibraltar arc orogenic belt these include in the iberian margin of the gulf of cadiz the flysch units of the campo de gibraltar complex the betic external zones and the neogene basins of the guadalquivir valley fault bounded blocks of flysch and subbetic units crops out over large areas of the southeastern iberian shelf the basement of the northwestern area in contrast is represented by the paleozoic rocks of the hercynian massif of iberia half graben structures determined the main structural trends of the margin during the mesozoic which were affected by inversion structures during the neogene compressional stages the mesozoic and lower cenozoic units are best observed in wells and seismic profiles from the northern area these units are either obscure below a thick olistostrome deposit or are absent in most of the rest of the gulf of cadiz seven lithoseismic units from triassic to upper oligocene and another seven neogene and quaternary units are identified based on the relationship to the depositional sequence and the emplacement of the olistostrome the first tectonic phase was characterized by a passive margin which was controlled by the development of half graben extensional structures and carbonate platforms this evolution comprises the mesozoic and early cenozoic ocean spreading in the north atlantic induced extensional tectonics which deformed the cretaceous syn tectonic post aptian deposits increased amounts of terrigenous materials were supplied to the margin from aptian to albian times controlling depositional patterns while terrigenous siliciclastic facies replaced the jurassic carbonate platforms from middle eocene to early miocene the margin was influenced by the relative motions of iberia and africa and the development of the alpine orogeny the iberian african boundary in the gulf of cadiz experienced transpression and the mesozoic basins probably underwent subduction the emplacement of an olistostrome took place in the gulf of cadiz towards the central atlantic basin plains during the tortonian the end of the olistostrome emplacement during the late miocene coincides with accelerated tectonic subsidence while thick progradational and aggradational depositional sequences were developed the occurrence of closely juxtaposed regions of compression and extension during the miocene may reflect the westwards progression of the gibraltar arc mountain front over a subducting thinned tethys crust when the motion between iberian and africa was n s to nnw sse oriented the migration of the arcuate mountain front into the eastern gulf of cadiz is attributed to a mechanism of collision induced delamination of the mantle lithosphere in contrast to the betic rif belts however there is no geophysical evidence to postulate that continental collision took place in the gulf of cadiz during the cenozoic

obsidian provenance studies in colombia and ecuador obsidian sources revisited the field occurrences elemental compositions and formation ages of colombian and ecuadorian obsidians are revisited it is shown that the regional sources of this raw material are linked to two major volcanic structures the chacana and the paletara calderas localised on the eastern cordillera of ecuador and on the central andean cordillera of south colombia respectively seventy two samples were analysed by inductively coupled plasma atomic emission spectroscopy icp aes inductively coupled plasma mass spectrometry icp ms and or particle induced x ray emission pixe the same 10 types of elemental compositions were identified independently from icp and pixe four of these types were previously unknown the formation ages of these obsidians previously determined by fission tracks dating are in the range 0 17 1 58 ma at chacana and 3 46 4 27 ma at paletara most colombian and ecuadorian pre hispanic artefacts present elemental compositions compatible with a chacana or paletara derived origin of the raw material however some of them present fission track ages discordant with the present day known obsidian occurrences which implies that the regional source inventory is not yet exhaustive

tracing organic compounds in aerobically altered methane derived carbonate pipes gulf of cadiz sw iberia abstract the primary geochemical process at methane seeps is anaerobic oxidation of methane aom performed by methanotrophic archaea and sulfate reducing bacteria srb the molecular fingerprints biomarkers of these chemosynthetic microorganisms can be preserved in carbonates formed through aom however thermal maturity and aerobic degradation can change the original preserved compounds making it difficult to establish the relation between aom and carbonate precipitation here we report a study of amino acid and lipid abundances in carbonate matrices of aerobically altered pipes recovered from the seafloor of the gulf of cadiz sw iberian peninsula this area is characterized by a complex tectonic regime that supports numerous cold seeps studies so far have not determined whether the precipitation of carbonate pipes in the gulf of cadiz is a purely chemical process or whether microbial communities are involved samples from this site show signs of exposure to oxygenated waters and of aerobic alteration such as oxidation of authigenic iron sulfides in addition the degradation index calculated from the relative abundance of preserved amino acids indicates aerobic degradation of organic matter although crocetane was the only lipid identified from methanotrophic archaea the organic compounds detected n alkanes regular isoprenoids and alcohols are compatible with an origin from aom coupled with bacterial sulfate reduction bsr and subsequent aerobic degradation we establish a relation among aom bsr and pipe formation in the gulf of cadiz through three types of analysis 1 stable carbon and oxygen isotopic composition of carbonate minerals 2 carbonate microfabrics and 3 mineralogical composition our results suggest that carbonate pipes may form through a process similar to the precipitation of vast amounts of carbonate pavements often found at cold seeps our approach suggests that some organic compound patterns in combination with additional evidence of aom and bsr may help indicate the source of altered methane derived carbonates commonly occurring in ancient and modern deposits