genesis of the world s largest gold deposits controversy has surrounded the formation of the largest gold deposits on earth in witwatersrand south africa as frimmel explains in his perspective the report by kirket al should lay the controversy to rest by providing age data for the gold the results indicate that the gold was brought into its host rocks by mechanical erosion of gold bearing hinterland and fluvial transport into a sedimentary basin

multiscale organisation of organic matter associated with gold and uranium minerals in the witwatersrand basin south africa abstract organic matter from the northern part of the early proterozoic witwatersrand basin carbon leader reef was investigated using optical om and transmission electron tem microscopes completed by xrd analysis the multiscale organization texture microtexture structure of the organic matter was observed in order to gain information about the processes which affected organic material after its deposition in sediments in the micrometre scale optical microscope the shape and size of the reflectance indicating surface ris of the organic matter were determined the organic matter reveals a prevailing biaxial symmetry the size of ris is generally dependent on uranium and increases with increasing uranium concentration furthermore it appears that more than one ris is present within the scale of a single sample each with a different symmetry and size the presence of domains differing in organisation of the aromatic framework was confirmed by tem observation in the df mode the aromatic skeleton of organic matter is composed of short often crumpled mostly isolated non stacked polyaromatic layers whose fringe length corresponds to 3 16 aromatic rings the data indicate reorganization of the polyaromatic organic matter structure under stress in high pressure and relatively low temperature conditions the organic matter was in a solid state within the rocks before the pressure event

tertiary sedimentary history and structure of the valencia trough western mediterranean abstract we present here main results of the common depth point cdp data acquired during the valsis 2 cruise in 1988 in the valencia trough the profiles are tied in with industrial well data and this correlation allows the sedimentary and structural history of the region to be deduced the valsis cruise seismic profiles have been supplemented by a very dense grid of industrial seismic lines and these data permit us to establish an accurate depth to basement map the formation of the initial grabens coeval with those of the gulf of lions is related to the early miocene opening of the northwestern mediterranean basin and the barcelona graben is filled by the same sedimentary layers including evaporites as that of the provencal region nevertheless the valencia catalan grabens have been reactivated by young extensional tectonics which could be a consequence of the convergence of africa relative to europe the valencia trough is segmented by transfer faults which trend nw se these faults which have a more accentuated structural expression than the valencia and catalonia grabens may act as transform faults separating the individual balearic islands the transfer faults are in strike with volcanic ridges which have been sampled during the dsdp leg 13 the dense seismic grid allows us to delineate several widespread volcanic features in the valencia trough which have been active from the early miocene to the pleistocene however we note that the volcanic features are mainly miocene in age whereas the recent volcanism is restricted to a narrow zone columbretes islands the compressional tectonics which deformed the balearic islands does not appear to extend far towards the north we delineate the compressional front north of ibiza but we failed to determine any thrust or fold north of mallorca whereas an extensional tectonics is evident

cenozoic magmatism of the valencia trough western mediterranean relationship between structural evolution and volcanism abstract the cenozoic magmatism of the valencia trough is characterized by the existence of two volcanic cycles the first cycle early miocene middle miocene comprises calc alkaline rocks which have been recognized in the central to eastern offshore areas and in mallorca the second cycle middle miocene to recent is represented mainly by poorly differentiated alkaline rocks which are predominantly distributed along the iberian margin of the valencia trough in accordance with the inferred structural evolution of the valencia trough petrological and geochemical data as well as volcanological evidence we suggest that two different geodynamic environments existed during these magmatic cycles the early to middle miocene calc alkaline volcanism developed under compressive tectonic conditions and seems to be associated with the northwestern dipping subduction of the african plate in contrast the middle miocene to recent alkaline volcanism is associated with extensional tectonics and can be explained within the framework of a low volcanicity rift model three zones catalan valencian and columbretes each located at different parts of the rift structure can be distinguished in the middle miocene to recent volcanism this intraplate volcanism results from partial melting due to extension driven decompression with the largest degrees of melting in the centre of the valencia trough columbretes volcanic zone in the catalan volcanic zone a progressive increase in the extension rate from the first to the last volcanic episode has occurred favouring the interaction of two mantle sources

the surface circulation of the balearic sea until recently the surface circulation of the balearic sea has been viewed as largely cyclonic with a fairly quiescent central dome however recent studies involving ship data tracked drifters current meter moorings and satellite imagery indicate that this sea has strong mesoscale variability and a more complex general circulation these studies together with an examination of registered satellite imagery collected during the western mediterranean circulation experiment wmce indicate that the surface circulation is strong year round and characterized by two permanent density fronts located on the continental shelf slope the catalan front and the balearic islands shelf slope the balearic front the catalan front is the more active of the two fronts in the northern area a plume of cold water is frequently observed moving southward along the continental slope region shedding dipole eddies along the leading edge of the plume in addition the catalan front continuously spawns energetic filaments that appear to be associated with the plume of cool water the likely mechanism of formation of these filaments is the deflection of the cold water by the regional submarine canyons

complex interaction between strombolian and phreatomagmatic eruptions in the quaternary monogenetic volcanism of the catalan volcanic zone ne of spain the catalan volcanic zone cvz at the ne of the iberian peninsula is one of the quaternary alkaline volcanic provinces of the european rifts system the cvz has been active during the last 12 ma despite the fact that this volcanism is significant in extension and volume and that eruptions have also occurred in holocene times it is mostly unknown compared to the contemporaneous alkaline volcanism in other parts of western and central europe volcanism younger than 0 5 ma is mostly concentrated in an area of about 100 km2 located between the main cities of olot and girona this basaltic volcanic field comprises more than 50 monogenetic cones including scoria cones lava flows tuff rings and maars magmatic eruptions range from hawaiian to violent strombolian phreatomagmatism is also common and has contributed to the construction of more than a half of these volcanic edifices frequently associated with the strombolian activity but also independently giving rise to a large variety of eruptive sequences we describe the main characteristics of this volcanism and analyse in particular the successions of deposits that form some of these volcanoes and discuss the potential causes of such a wide diversity of eruptive sequences we find that the main cause of such complex eruptive behaviour resides in the stratigraphic structural and hydrogeological characteristics of the substrate above which the volcanoes were emplaced rather than on the compositional characteristics of the erupting magma as they do not show significant variations among the different volcanoes studied

migration based microseismic event location in the schlema alberoda mining area abstract mining operations in the schlema alberoda uranium mine located in south west saxony germany stopped in 1990 and the mine was then allowed to flood the region is seismically active and has been monitored for a long time we have located some of the microseismic events which occurred between 2005 and 2012 in the mining area to investigate the nature of the seismicity as well as the long term role of mining induced and triggered seismicity in this study we used pseudo synthetic data obtained from the vertical component records of a local seismic network to accurately locate the hypocenters the location procedure is based on a kirchhoff prestack depth migration approach in order to assess the accuracy of the migration results a homogeneous and a 3 d velocity model are tested in the migration algorithm both of these velocity models were previously used to migrate data acquired by a 3 d reflection seismic survey in this area the resulting images were comparable with minor differences to the reflectors in our area of interest in contrast we found that the errors in the velocity model can strongly affect the migration based earthquake localization the located hypocenters are compared to the 3 d reflection seismic image of the area to determine possible correlations between the seismicity and reflectivity this comparison shows that some of reflectors can be directly correlated with the induced and triggered seismicity of the area the results also indicate that the main causes of the post mining seismicity are changes in the mine flooding level and the consequent changes in the pore pressure of the subsurface structures finally we confirm that the hypocenters are often bound to preexisting subsurface structures like faults and fractures in the area in particular the spatial pattern of the hypocenters proves the existence of a previously unmapped extension of the ruhmvoll fault this pattern also suggests a connection between this structure and the roter kamm fault a major component of the larger gera jachymov fault zone

hydrothermal alteration in the witwatersrand goldfields abstract alteration is recorded throughout much of the 3 km thick upper witwatersrand succession in south africa and extends for 300 km around the basin and 50 km into the basin the evidence for this alteration comes from petrography mineralogy geochemistry rock fabrics and stratigraphy the alteration conceived as a giant halo enveloping each major goldfield requires a major hydrothermal event focused on the auriferous upper wits central rand group the scale and nature of the alteration and its relationship to gold distribution on various scales strongly support a hydrothermal model for gold deposition such a model can account for the 50 000 t of gold mined from the witwatersrand goldfields the model works within the context of the major advances in understanding of the geological framework of the witwatersrand basin including the recognition of the importance of post burial processes it is highly significant that the age of witwatersrand sedimentation is much older than 2700 my and thus the host rocks for gold were deposited at least 100 my before the major global archean greenstone gold event the shale units from 40 major mines covering the seven goldfields are examined to establish the nature and distribution of the alteration and to make the connection between the fluid infiltration that caused the alteration and the introduction of gold into the witwatersrand basin in the hydrothermal model described here an auriferous low salinity fluid is produced at about 500 c during the metamorphism of mafic material that was below and adjacent to the witwatersrand basin large shear zones in the footwall of goldfields are the inferred fluid pathways into the upper wits succession and then unconformities smaller shear zones veins and the reef packages guide local fluid flow in this model gold precipitation occurs in response to the reaction of the fluid with carbon and iron bearing rocks that are abundant in the reef packages immediately overlying unconformity surfaces gold precipitation occurred at about 350 c and 10 km depth with the implication of a high geothermal gradient approaching 35 c per km the alteration of the shales but lack of abundant gold in them is predicted from the paucity of appropriate rocks or minerals in the shale units to precipitate gold but fluid infiltration still changed their composition fundamentally the source of the witwatersrand gold its present distribution and the alteration are explained within this hydrothermal model with similarities to the models invoked for other major gold provinces it is worth noting that quartz pebble conglomerate is a poor term for this gold type and has almost certainly limited exploration opportunities globally

a detrital model for the origin of gold and sulfides in the witwatersrand basin based on re os isotopes abstract the re os systematics of gold and sulfides from the witwatersrand basin were utilized to determine whether the gold is detrital or was introduced by hydrothermal solutions from outside the basin gold from a gravity concentrate from the western areas gold plant and gold from the vaal reef have very high os concentrations of approximately 73 to 10000 ppb and 3 to 32 ppb re resulting in 187re 188os ratios of 0 010 to 0 185 the gold has subchondritic 187os 188os ratios between 0 1056 to 0 1099 and an average value of 0 1067 rhenium depletion ages trd range from 3 5 ga to 2 9 ga with a median age of 3 3 ga pyrite from the vaal reef have os concentrations ranging from 0 26 to 0 68 ppb re concentrations of 1 7 to 2 8 ppb and187re 188os ratios of approximately 14 to 87 the pyrite samples have measured 187os 188os ratios of 0 84 to 4 7 and define an isochron with an age of 2 99 0 11 ga mswd 0 77 the os isotopic data from the direct measurement of gold preclude introduction of gold to the witwatersrand basin from crustally derived metamorphic or hydrothermal fluids between 2 7 to 2 0 ga the unradiogenic 187os 188os ratios old trd ages of the western areas and vaal reef gold samples as well as the contemporaneously old age of the vaal reef pyrite are consistent with detrital deposition of gold during the formation of the witswatersrand basin the os data will allow for minor hydrothermal remobilization and or overprinting of hydrothermal gold on preexisting detrital gold grains but does not support the introduction of gold solely by hydrothermal fluids

structure and present day compression in the offshore area between alicante and ibiza island eastern iberian margin abstract this study deals with the structure and recent deformation of the eastern iberian margin extending from basement to seafloor and including the south western margin of the valencia basin the alicante shelf the ibiza channel and its southern margin descending into the algerian basin this area underwent a complex tectonic evolution linked to the back arc opening of the north western mediterranean and the concomitant contraction of the betic belt due to the collision with blocks located between africa and europe this oligo miocene structural heritage gave rise to a complex and continuous deformation through times including late miocene post orogenic extension and pliocene to quaternary compression in the western balearic area and coeval extension in the valencia basin this study presents maps of the depth to basement and base of the pliocene as well as bathymetry data and seismic lines which provide a precise integrated 3d study of the offshore domain it reveals a major reactivation of the area represented by the n80 to n60 trending structures small discontinuous folds and thrusts in the ibiza channel and a large flexure on the alicante shelf the structures are picked out by erosion surfaces or deposits linked to the messinian salinity crisis msc these markers are ubiquitous in the seismic sedimentary sequences and record the lateral and vertical deformation active from the messinian salinity crisis to the present the contraction in the western iberian margin and concomitant extension in the southern valencia basin are consistent with the regional stress field as determined from the focal mechanisms of offshore earthquakes or recent gps measurements the tectonic compression of the studied area casts doubt on the eventual propagation of the present day compressive stress from the algerian margin to the western balearic promontory

gold and sulphide minerals in tertiary quartz pebble conglomerate gold placers southland new zealand abstract auriferous quartz pebble conglomerates qpc formed during tertiary sedimentary recycling in the waimumu district southland new zealand these sediments contain fine grained gold of detrital origin with abundant surface textures and gold forms associated with authigenic gold remobilisation most authigenic gold contains no detectable silver and occurs as overgrowths on detrital au ag and au ag hg alloys that contain up to 13 wt ag and 9 wt hg fine grained au ag and au ag hg alloys are compositionally heterogeneous exhibiting both well defined silver depleted and silver enriched rims rare coarse au ag alloy is intergrown with quartz and is homogenous discrete grains of authigenic porous sheet like gold occur in carbonaceous mudstone within a qpc sequence some qpc contain abundant sulphide minerals some of these sulphides pyrite and arsenopyrite are of long distance detrital origin presumably from the otago schist whereas the bulk of the sulphide suite is marcasite of variably transported diagenetic origin derived from the erosion of qpc and underlying tertiary sediments there has also been authigenic deposition of sulphide minerals in the qpc themselves these diagenetic sulphides include framboidal and anhedral marcasite and framboidal and euhedral pyrite sulphur isotope data for the sulphide minerals range from 45 to 18 relative to vcdt sulphur isotope data for euhedral detrital pyrite and arsenopyrite range from 9 to 1 and are most likely derived from the otago schist to the north both framboidal and anhedral marcasite have lower values both the gold and diagenetic sulphides from the belle brook qpc are compositionally similar to gold and sulphides from archaean qpc porous sheet like authigenic gold is morphologically similar to gold associated with carbonaceous material in the witwatersrand in addition southland marcasite textures resemble the rounded and banded pyrite in witwatersrand qpc placers there is abundant evidence from these tertiary qpc in southern new zealand for sedimentary transport of sulphide minerals and post depositional sulphide mineralisation in the surficial environment despite an oxygen rich atmosphere these young deposits thus provide an example of authigenic gold and sulphide textures formed during diagenesis in unmetamorphosed placers many of these textures are similar to those commonly ascribed to metamorphic processes in archaean auriferous qpc

analysis of the geological evolution and vertical movements in the valencia trough area western mediterranean abstract the valencia trough located between the iberian peninsula and the balearic islands corresponds to the south west prolongation of the provencal basin the analysis of recently released seismic lines shows that the present day tectonics of the valencia trough are the result of the coeval development of 1 a system of horsts and grabens in the north west part of the basin during the late oligocene early miocene catalan valencian domain and 2 a thrust and fold system which lasted up to the middle miocene and which was followed by extensional tectonics during the late miocene betic balearic domain in an attempt to characterize the evolution of the valencia trough subsidence curves have been calculated for 18 wells and three regional cross sections distributed across the basin backstripping of these data shows two major stages of tectonic subsidence history 1 a first stage coeval with basin formation 30 15 my characterized by a rapid and strong tectonic subsidence which attains its maximum values in the central basin areas and close to the balearic islands and 2 a second stage 15 0 my in which the tectonic subsidence decreases gradually the amount of crustal thinning estimated from a comparison of the observed and modelled tectonic subsidence ranges between 1 5 iberian margin areas and 4 5 central and south western basin areas these values agree with the crustal thicknesses inferred from seismic refraction data and gravimetric modelling nevertheless such a degree of thinning cannot be explained by the neogene extensional structure the presence of thick mesozoic deposits suggests that the present crustal thinning is partly due to previous mesozoic extension

the neogene structure of the eastern iberian margin structural constraints on the crustal evolution of the valencia trough western mediterranean abstract the presence of a thinned crust beneath the valencia trough has been recognized for a long time however to date no attempt to link this thinning inferred from geophysical data with the superficial structures has been made a quantification of the neogene extensional processes in the crustal evolution of the valencia trough is presented as a consequence of the complexity of the betic balearic domain the analysis has been done for the catalan valencian domain northwestern areas of the trough crustal and superficial data in this area show that neogene extension was accommodated by a listric normal fault system detached in a deep upper crustal level 13 15 km in the marginal zone of the domain quantitative analysis of the neogene structure shows the incoherence between the upper crustal thinning inferred from the geometric analysis of the superficial structures factor 1 4 1 5 and from geophysical data 1 8 although the latter value agrees with that deduced from the analysis of neogene subsidence this incoherence suggests that the present thinned crust would be partially inherited from the mesozoic extension in this way mesozoic subsidence analysts and the recognized mesozoic structure show that the mesozoic extension was almost as important as the neogene one

sea level change along the french mediterranean coast for the past 30 000 years abstract observational evidence for sea level change along the french mediterranean coast has been examined and compared with glacio hydro isostatic models to predict the spatial and temporal patterns of change for about the past 30 000 14c years these predictions are pertinent to discussions of changing ocean volumes during this interval the tectonic stability or otherwise of the coastal areas mantle rheology and the timing of possible human occupation of the now submerged coastal plain and caves such as cosquer cave near marseille the principal results from the analysis are i sea levels along this section of the coast have risen continually since the time of the last glacial maximum lgm and at no time during the holocene has the mean sea level been higher than that of today ii the coast has been tectonically stable between marseille and nice as well as further to the west in roussillon western corsica may have experienced a slow tectonic uplift of between 0 15 0 3 mm year for the past 3000 years but northernmost corsica appears to have been stable during this same interval iii during the lgm sea levels along the coast and immediate off shore areas stood at between 105 115 m below present level the range reflecting the importance of the isostatic contributions during oxygen isotope stage 3 sea levels do not appear to have risen locally above about 60 m iv the rebound parameters describing the mantle rheology and ice sheets required to match the limited observational evidence are consistent with the results of similar analyses carried out for other parts of europe because of its distance from the former northern ice sheets the isostatic factors are particularly sensitive to the value of the lower mantle viscosity v the model predictions for sea level change at the cosquer cave site and for its immediate environments indicate that the cave was last readily accessible before about 10 700 500 14c years about 12 500 500 cal years bp and that the cave entrance was completely flooded by 9000 200 radiocarbon years bp between about 9800 and 10 300 calibrated years bp the cave was above sea level throughout the oxygen isotope stage 3

re os isotope and pge constraints on the timing and origin of gold mineralisation in the witwatersrand basin abstract analyses of the re os isotope system and pge abundances have been used to investigate the timing and origin of mineralisation in the vaal reefs section of the witwatersrand basin the world s largest gold deposit consistent interelement pge fractionation in both organic and sulphide phases intimately associated with gold mineralisation suggests that the re os isotope system was fractionated during gold mobilisation the re os isotope data on organic separates intimately associated with the gold in this part of the basin indicate open system behaviour until 2 26 0 19 ga 2 of the order of 450 myr younger than the minimum age of sedimentation the overlying ventersdorp volcanics preserve a re os isochron age of 2 43 0 21 ga 250 ma younger than their u pb zircon emplacement age these data indicate substantial post sedimentary noble metal mobility within portions of the witwatersrand basin re os model age calculations on os rich fractions suggest that noble metals were derived from a 3 0 3 1 ga terrain of granite greenstone affinities significantly younger than the barberton greenstone belt these data support a hybrid model involving post depositional mobilisation of ancient probably detrital noble metals for the origin of mineralisation in this part of the witwatersrand basin such a model is applicable to other areas of gold mineralisation in the basin that display similar textural characteristics and geochemistry

three dimensional focused seismic imaging for geothermal exploration in crystalline rock near schneeberg germany we present the results of a 3d seismic survey acquired near the city of schneeberg in the western erzgebirge germany the main objective of this survey was to use reflection seismic exploration methods to image a major fault zone in crystalline rock which could serve as a geothermal reservoir at a target depth of about 5 km 6 kmwith expected temperatures between 160 c 180 c for this purpose a high resolution 3d vibroseis survey was performed in late 2012 covering an area of about 10 km 12 km the 3d survey was complemented by a wide angle seismic survey for obtaining velocity information from greater depths using explosives along ten profile lines radially centred at the target area the region itself is dominated by the northwestsoutheast striking gera j achymov fault system and the southwest northeast striking l ossnitz zw onitz syncline the main geological features in the survey area are well known from intensive mining activities down to a depth of about 2 km the seismic investigations aimed at imaging the partly steeply dipping fault branches at greater depths in particular a dominant steeply northeast dipping fault roter kamm in the central part of the survey area in addition to this main structure the gera j achymov fault zone consists of a series of steeply southwest dipping conjugate faults for imaging these structures we used a focusing pre stack depth migration technique where the wavefield coherency at neighbouring receivers is used for weighting the amplitudes during migration this method delivers a clear focused image of the 3d structures within the target area a 3d velocity model for depth imaging was obtained by first arrival tomography of the wide angle survey data with this approach we were able to image several pronounced structures interpreted as faults within the crystalline rock units which partly reach the target depth where the temperatures for a geothermal usage would be sufficient in general the results show a complex three dimensional image of the geological structures with different reflection characteristics which can serve as a basis for a detailed characterization of the potential deep geothermal reservoir

sedimentary signatures of cyclic growth and destruction of stratovolcanoes a case study from mt taranaki new zealand abstract the long term behaviour of andesite stratovolcanoes is characterised by a repetition of edifice growth phases followed by collapse this cyclic pattern represents a natural frequency at varying timescales in the growth dynamics of stratovolcanoes worldwide around the 130 ka mt taranaki egmont volcano new zealand coastal cliff successions at 20 40 km distance comprise repeating packages of lithologically and sedimentologically distinctive mass flow deposits varying depositional mechanisms and source properties of these units record growth and collapse cycles of the central edifice these are used to construct a model for cyclic volcaniclastic sedimentation in the surrounds of stratovolcanoes during edifice construction phases thick packages of tabular predominantly monolithologic hyperconcentrated flow and debris flow deposits accumulate with intercalated tephra beds the mass flow units commonly contain large proportions of fresh pumice or juvenile lithic andesite intervals of quiescence separating eruptive periods are characterised by landscape re adjustment accompanied by deposition of fluvial and aeolian sediments along with steady accretion of medial ash in contrast brief episodes of destruction are marked by wide spread distinctively clay rich polylithologic debris avalanche deposits and related marginal debris flow units the growth stages can be terminated by an eruption triggered sector collapse or by external forces once the edifice exceeds a critical stable height or profile dependent on eruptive style and local geo tectonic conditions once the edifice becomes metastable regional tectonic earthquakes or shallow level intrusion events are likely triggers for collapse although the resulting debris avalanches represent the greatest individual hazard from such andesite stratovolcanoes their frequency is relatively low compared with other types of mass flows generated during edifice growth phases accurate forecasts of future hazard from mass flow events are therefore dependent on recognition of both the frequency of a stratovolcano s growth cycle and its current position in that cycle

the valencia trough and the origin of the western mediterranean basins abstract evolutionary models for the valencia trough must be necessarily related to the neogene present geodynamics of the western mediterranean basins all these basins occupy new space created in the wake of the westward translation of the alboran block and the counter clockwise rotation of the corso sardinian block this escape tectonics microplate dispersal model can account for the co existence and progressive migration of compressional and extensional strain fields within the africa europe broad zone of convergence in this escape tectonics model the valencia trough has resulted in a complex evolution which includes 1 latest oligocene early miocene rifting along the catalan valencian margin due to the opening of the gulf of lions 2 almost simultaneous early miocene transpressive thrusting in the balearic margin related to the initiation of displacement of the alboran block and 3 late miocene generalized extension as a consequence of the opening of the south balearic basin

the late oligocene miocene opening of the north balearic sea valencia basin western mediterranean a working hypothesis involving mantle upwelling and extensional detachment tectonics abstract the north balearic sea valencia basin is one of the western mediterranean basins that opened during the late oligocene miocene however in contrast with neighbouring basins the valencia basin is floored by highly attenuated continental crust the geological and geophysical characteristics of this realm indicate that extensional tectonics and mantle instability played a major role in the opening of the basin and consequent se directed drifting of its eastern flank balearic rise a model for the generation of this basin is proposed involving the intrusion of asthenospheric mantle and subsequent extensional detachment tectonics during late oligocene miocene times this model accounts for the asymmetrical rifting of the north balearic sea and the clockwise drifting rotation of the balearic rise

morphogenesis of the sw balearic continental slope and adjacent abyssal plain western mediterranean sea we present the seafloor morphology and shallow seismic structure of the continental slope south east of the balearic promontory and of the adjacent algero balearic abyssal plain from multibeam and chirp sonar data the main purpose of this research was to identify the sediment pathways from the balearic promontory to the algero balearic deep basin from the early pliocene to the present the morphology of the southern balearic margin is controlled by a sw ne structural trend whose main expressions are the emile baudot escarpment transform fault and a newly discovered wsw ene trend that affects the sw end of the escarpment and the abyssal plain we relate the two structural trends to right lateral simple shear as a consequence of the miocene westward migration of the gibraltar arc newly discovered steep and narrow volcanic ridges were probably enabled to grow by local transtension along the transform margin abyssal plain knolls and seahills relate to the subsurface deformation of early stage halokinetic structures such as salt rollers salt anticlines and salt pillows the limited thickness of the overburden and the limited amount of deformation in the deep basin prevent the formation of more mature halokinetic structures such as diapirs salt walls bulbs and salt extrusions the uppermost sediment cover is affected by a dense pattern of sub vertical small throw normal faults resulting from extensional stress induced in the overburden by subsurface salt deformation structures shallow gas seismic character and the possible presence of an active polygonal fault system suggest upward fluid migration and fluid and sediment expulsion at the seafloor through a probable mud volcano and other piercement structures one large debris flow deposit named formentera debris flow has been identified on the lower slope and rise of the south formentera margin based on current observations we hypothesize that the landslide originating the formentera debris flow occurred in the holocene perhaps in historical times

seismicity and stress field in the vicinity of the ktb location a local broadband seismic network of four observatory quality stations ktb net was operated during the drilling of the ktb hole within the framework of the interdisciplinary german continental deep drilling program ktb the aim was to investigate the seismic activity with regard to the tectonic stress field and to compare it with data from in situ measurements in the 9 1 km deep borehole sections bottom temperature of 260 c and heat flow of 82 85 mw m2 from october 1990 to november 1995 over 80 local microearthquakes with magnitudes from 0 2 to 2 8 ml were recorded eight small events by the ktb net only and four earthquake swarms with 73 events by the ktb net and stations of the vogtland western bohemia networks six of the small events are located within or close to the ktb net the swarm events occurred at the southwestern extension of the ohre rift in an area 20 km north of the drill site which is revealed to be part of the vogtland western bohemia seismotectonic unit characterized by swarm activity the hypocenters are limited to the upper 13 km of the crust with a distinct concentration between 10 and 12 km all types of fault plane solutions are found but at depths greater than 8 km reversed faulting mechanisms predominate p axes are very uniformly oriented in a nnw sse direction corresponding to the well known regional stress orientation in central europe and in agreement with the special in situ stress measurements of the ktb program the focal mechanism of a ml 1 2 event induced by a fluid injection experiment fits into the results obtained from the natural events possible indications for the brittle ductile transition are discussed in view of the observed earthquake depth and focal mechanism distributions

evidence for the multi stage formation of the south western valencia trough a basin evolution model for the south western valencia trough is established using thermal and palaeo thermal data bottomhole temperature and drillstem test data from oil wells have been used to determine the geothermal gradient in the study area a combination of well log data and x ray diffractometry analyses carried out on rock samples from the ibiza marino well has allowed an estimation of the bulk thermal conductivity and heat flow density integrating these data with previous seafloor heat flow measurements yields a regional surface heat flow density of about 90 100 mw m 2 vitrinite reflectance data available from the ibiza marino well have been used as a palaeo thermal constraint for the proposed tectonic models two different modelling approaches are tested a single rift phase model and a multi phase formation model the single rifting phase which considers different eroded thicknesses is ruled out as it does not match the observed data a multi stage evolution coherent with the geological and geophysical data is proposed and consists of three mesozoic rifting events palaeogene compression to which erosion of about 5 km of late jurassic and cretaceous sediments is related and a neogene rifting event that gave rise to the present day valencia trough surface heat flow vitrinite data and eroded thickness are successfully integrated in the proposed model

geodynamics of the emile baudot escarpment and the balearic promontory western mediterranean abstract the 348 km long 105 155 km wide and 1000 2000 m high northeast trending balearic promontory separates the valencia trough to the northwest from the south balearic algerian basin to the southeast it consists of three blocks ibiza at the southwest end mallorca in the center and menorca at the northeast end of the promontory the ibiza and mallorca blocks were thrust faulted and folded in the miocene the menorca block appears to be undisturbed but strata within the transform separating the mallorca and menorca blocks are folded and faulted miocene and younger volcanic pinnacles also are extensive along the transform separating the ibiza and mallorca blocks we infer that the tectonic features on the balearic promontory are the creations of the late oligocene miocene southeast migration of the blocks making up the promontory way from the spanish margin leading to the opening of the valencia trough behind them the westward displacement of the alboran microplate along the emile baudot escarpment on the southeast side of the promontory and the opening of the south baleric algeria basin behind it and the clockwise rotation of the ibiza and mallorca blocks produced by the passing alboran microplate

numerical modelling of mud volcanoes and their flows using constraints from the gulf of cadiz it is estimated that the total number of submarine mud volcanoes is between 1000 and 100 000 because many are associated with greenhouse gases such as methane it is argued that the global flux of these gases to the atmosphere from the world s terrestrial and submarine mud volcanoes is highly significant clues to the processes forming submarine mud volcanoes can be found in variations to their height shape surface morphology physical properties and internal structure a model of isostatic compensation between the mud column and the sediment overlying the mud source is used to predict a depth to the mud reservoir beneath mud volcanoes once erupted the general behaviour of an individual mud flow can be described and predicted using a viscous gravity current model the model shows that conical shaped mud volcanoes comprise multiple superimposed radial flows in which the thickness eruption rate and speed of individual mud flows strongly depends on the viscosity density and over pressure of the erupted mud using these parameters the model predicts the lowermost flows will be the oldest thickest and have the greatest length of run out while the uppermost flows will be the youngest thinnest and shortest this model is in contrast to more traditional models of stratiform mud volcano construction in which younger flows progressively bury older ones and travel furthest from the summit applying the model to the two mud volcanoes studied in the gulf of cadiz quantitative estimates are derived for the depths to mud sources exit and flow velocities eruption duration and volume fluxes flow thickness and conduit radii for example with an average kinematic viscosity of 1 5 m2 s 1 for the erupted mud a density of 1 8 103 kg m 3 and a thickness for the youngest flows of about 0 5 m the model predicts a lowermost flow thickness of 3 6 m an average eruption duration of 7 h and a conduit radius of about 9 m to construct a conical shaped mud volcano of 260 m height similar to those studied in the gulf of cadiz is estimated to require a mud source at 4 6 km depth and a total of at least 100 individually erupted flows

the big 95 submarine landslide generated tsunami a numerical simulation abstractthis article presents a reasonable present day sea level highstand numerical simulation and scenario for a potential tsunami generated by a landslide with the characteristics of the big 95 debris flow which occurred on the ebro margin in the western mediterranean sea in prehistoric times 11 500 cal yr bp the submarine landslide deposit covers an area of 2200 km2 of the slope and base of slope 200 1800 m water depth involving a volume of 26 km3 a leapfrog finite difference model comcot cornell multigrid coupled tsunami model is used to simulate the propagation of the debris flow generated tsunami and its associated impact on the nearby balearic islands and iberian coastlines as a requisite of the model reconstruction of the bathymetry before the landslide occurrence and seafloor variation during landsliding have been developed based on the conceptual and numerical model of lastras et al 2005 we have also taken into account all available multibeam bathymetry of the area and high r

sea floor morphology of the ebro shelf in the region of the columbretes islands western mediterranean abstract widespread volcanism off eastern spain in the western mediterranean is associated with cenozoic crustal attenuation and sinistral motion along the trans moroccan western mediterranean european mega shear extending from northern morocco to the north sea via the alboran basin eastern iberia the valencian and lyons basins france and germany the quaternary columbretes islands volcanic field is the most prominent example of this volcanism associated with this mega shear the islands are located in the ebro continental shelf on top of a structural horst probably made of paleozoic metamorphic rocks surrounding the emerged islands are volcanic structures and associated flows partially mantled by a sediment drift whose morphology is controlled by the southwestward flowing catalan current this association is rather unique and appears to have never been described from a continental shelf in the mediterranean sea or outside the sea the morphology of both kinds of structures obtained by means of swath bathymetry data and very high resolution seismic profiles is presented in this study they provide striking images of this previously unstudied part of the western mediterranean seafloor these images suggest that the volcanic structures are intruded into the surficial holocene sediments indicating that volcanism in the columbretes has extended into holocene

magnitude of the sediment transport event due to the late pleistocene sector collapse of asama volcano central japan abstract a rapid large scale sediment transport event due to a catastrophic landslide plays an important role in changing drainage basin topography however volumetric evaluation of such events that occurred before the holocene has been limited this study quantitatively examines the volume of sediments derived from the late pleistocene 24 ka sector collapse of asama volcano central japan a sequence of sediments supplied from the sector collapse was identified based on geological and geomorphological field surveys and literature search the total volume of the sediments was estimated from borehole columns to be 4 9 5 4 km3 reconstruction of the morphology of the volcanic edifice before and after the collapse provided an estimated volume of the lost sector of 4 0 km3 the greater estimated volume of the sediments released by the collapse is attributed to the entrainment of fluvial material during the flow of volcanic debris and to dilation of the original volcanic material

compositional variations and morphological evolution in platinum beach placers southern new zealand morphologies of placer platinum group minerals pgm are more variable and resistant to modification during transport than placer gold grains this study documents morphological evolution of pgm placer grains during up to 120 km of transport in beach placers after river transport from inferred sources up to 200 km inland pgm morphological changes are calibrated with changes in morphology of associated placer gold most of the pgm are pt fe alloy and have been fed into the beach placer system from a large river at the western end of the beaches on the south coast of new zealand the incoming fluvial pgm suite includes os ir and ru alloys which may have been derived from distal ophiolitic sources more proximal sources have ural alaskan affinities and these contributed cooperite and braggite or sperrylite locally as well as pt fe alloy grains some pgm may have been recycled through cretaceous quaternary fluvial sediments before entering the modern placer system recycled placer pgm grains have also been derived from elevated quaternary beaches near the coastline pgm grains entering beach placers have rough surfaces with remnants of crystal faces and these evolve to smooth flakes with progressive long shore transport pgm flakes have slightly thickened rims caused by impacts by saltating sand on windy beaches and the most distal beach placers contain flakes with incipient toroidal shapes these pgm incipient toroids are poorly developed compared to accompanying well formed toroidal gold that has developed in nearly all beach placers including those on elevated quaternary beaches typical pgm and gold placer grain size decreases with increasing distance of transport from fluvial grain size of 400 1 000 to 200 microns on the most distal beaches accompanied by eastward loss of equant pgm grains and associated increase in proportion of flakes although net transport distance is 120 km in the beach placer complex frequent aeolian transport of grains from beach to dunes and subsequent recycling by storm surges substantially increased total transport distance in a dynamic windy tectonic environment

textural and geochemical discrimination between xenotime of different origin in the archaean witwatersrand basin south africa abstract xenotime ypo4 of detrital diagenetic and hydrothermal origin within siliciclastic rocks of the archaean witwatersrand basin south africa has been identified on the basis of petrography and in situ ion microprobe shrimp age data the chemical composition of xenotime determined by in situ electron microprobe analysis can be correlated with its origin this allows the origin of any xenotime grain to be assessed by a non destructive microanalytical method prior to ion microprobe geochronology the main chemical discriminators are mree hree abundance normalised hree slope and eu anomaly and in some cases u and th contents igneous detrital xenotime 2800 ma is distinguished from diagenetic 2780 ma and hydrothermal

placer formation in gravel bedded rivers a review the literature on placer formation processes within fluvial systems is widespread and ranges between detailed laboratory studies of the hydrodynamic segregation processes through to the intuitive interpretation of the distribution of minerals within geological sections however there are few if any comprehensive reviews of the literature surprisingly given the economic importance of placers the theoretical framework relating to the hydrodynamics of physical grain sorting is not well developed and there are relatively few detailed laboratory hydraulic investigations to inform theory in this wide ranging review the history of the development of principles of placer formation is explored as far as possible in a non technical fashion a consideration is given to the hydrodynamics of physical grain sorting above lower stage and upper stage bedforms and the typical internal sedimentary structures associated with placer concentrations are detailed finally examples of the depositional environment of diamond tin and gold placers are considered

structural controls on witwatersrand gold mineralisation abstract structural controls on the distribution of gold in the witwatersrand basin can be seen at scales ranging from that of thin sections up to regional seismic data sets at the thin section scale gold occurs largely in fractures with hydrocarbons these fractures are associated with pulses of thrusting deformation that occurred in the latter stages of the basin s development the distribution of thrust fracture networks and therefore gold is controlled by the mechanical attributes of the host stratigraphy thrust displacements are generally very low with structures exploiting depositional contacts and mesoscale sedimentary bedforms many of the small faults are isolated from each other with bimodal vergence between larger scale thrusts of the same age early formed faults and fractures become folded and faulted by subsequent propagation of larger scale thrusts these characteristics are consistent with formation of the mineralised thrust fracture networks in the frontal low displacement parts of a thrust system in the carletonville goldfield the prospectivity of the ventersdorp contact reef vcr has been evaluated by using underground observations to pinpoint the structural habitat of gold and therefore characterise the size of prospective zones around structures intersecting the vcr mapped within 3d seismic data in the welkom goldfield the controls on gold distribution at the tshepong mine have been characterised from 3d seismic data drilling and underground observations and used to develop an ore body model that aids reserve estimation and production planning

irrefutable detrital origin of witwatersrand gold and evidence of eolian signatures toroidal shaped gold particles extracted from a sample of the basal reef orebody in the welkom gold field that contained crossbedded gold have been recognized in thin section demonstrating that the form in question is not an artifact of extraction but is a genuine detrital form similar forms have been recovered in great abundance from an eolian paleosurface in yakutia and from a recent storm beach placer in new zealand indicating the likelihood that eolian processes produced these forms this has been confirmed by means of wind tunnel experiments toroids in various states of preservation have been extracted from a number of other witwatersrand paleoplacers where there is an association with ventifacts indicating that wind deflation might have played a role in concentrating gold from placer sand deposits

real time earthquake location using kirchhoff reconstruction real time location of earthquakes can be achieved by using direct imaging of the recorded wave field based on a kirchhoff reconstruction method similar to that used in the migration of seismic reflection data the standard method of event location requires the wave arrival at each sensor to be picked and associated with an event by using direct imaging the event is identified once in the imaged wave field the computation is independent of the level of seismic activity and can be carried out on a typical desktop computer the procedure has been successfully demonstrated in two and three dimensions using data from the southern california seismic network trinet at higher resolutions the reconstruction method can identify finite source effects further work considers extending the method by implementing full elastic theory and solving for moment tensors at all locations in the mesh

the morpho tectonic setting of the southeast margin of iberia and the adjacent oceanic algero balearic basin abstract multi beam bathymetry and high resolution low penetration seismic reflection profiles of the offshore extensions of the betic internal zone off sierra de cartagena la union margin along its south side and the mar menor margin along its east side the mazarron escarpment forming its southern boundary and the adjacent oceanic algero balearic basin have provided images of the neo tectonic structures of the region equal to those provided by subaerial photography for the first time we mapped with unprecedented detail the mazarron escarpment and the southeast margin of iberia the first order structures of the region are due to the consequence of the collision of the african and eurasian plates during the alpine orogeny in late oligocene middle miocene the westward migration of the alboran plate in the middle miocene and the desiccation of the mediterranean in the messinian late miocene that led to the deposition of evaporites in the algero balearic basin and erosion of the mazarron escarpment the sierra de cartagena la union shelf the mar menor margin and the adjacent coast our data images second order tectonic features neo tectonic features superimposed on the larger structures these include the deformation of the strata in the algero balearic basin by the gliding of the plio quaternary sediments on messinian halite on the margins of the basin and sediment loading in its center the late miocene quaternary deformation of the area north of the mazarron escarpment resulting from the continuous oblique convergence of the african and eurasian plates in a nnw sse direction the miocene to pleistocene volcanic edifices and pinnacles dikes the pockmarks formed by the extrusion of gas water via faults and the massive gravitational failure of the mazarron escarpment triggered by this plate convergence the data also show in detail features formed on the mazarron escarpment during the messinian pliocene and pleistocene regressions and those on the shelf formed during the pleistocene glacially induced regressions transgression and sediment drifts generated by modern currents