upper mantle structure of the northern cascadia subduction zone previous knowledge of the structure of the cascadia subduction zone north of the canada united states border has been derived from a variety of geophysical studies that accurately delineated the downgoing juan de fuca plate from the offshore deformation front to depths of 50 60 km beneath south central vancouver island and the georgia strait little is known however of the structure of the cascadia subduction zone farther westward and to greater depths in the upper mantle we have assembled a set of some 1100 teleseismic traveltimes from events recorded on the western canadian telemetered network to augment a previously existing data set recorded on the washington regional seismograph network the composite data set is inverted for upper mantle structure below washington oregon and southwestern british columbia we analyze the new northern portion of the model between 48 5 50 n and 118 127 w which provides the first images of the deep slab structure in this region the model is parameterized using s

the dead sea sinkhole hazard geophysical assessment of salt dissolution and collapse abstract a geophysical approach is presented for analyzing processes of subsurface salt dissolution and associated sinkhole hazard along the dead sea the implemented methods include seismic refraction srfr transient electromagnetic method tem electric resistivity tomography ert and ground penetration radar gpr the combination of these methods allows the delineation of the salt layer boundaries estimating its porosity distribution finding cavities within the salt layer and identifying deformations in the overlying sediments this approach is shown to be useful for anticipating the occurrence of specific sinkholes as demonstrated on both shores of the dead sea these sinkholes are observed mainly along the edge of a salt layer deposited during the latest pleistocene when lake lisan receded to later become the dead sea this salt layer is dissolved by aggressive water flowing from adjacent and underlying aquifers which drain to the dead sea sinkhole formation is accelerating today due to the rapid fall of the dead sea levels during the last 30 years caused by anthropogenic use of its water

sharpness of upper mantle discontinuities determined from high frequency reflections an understanding of the nature of seismic discontinuities in the earth s upper mantle is important for understanding mantle processes in particular the amplitude and sharpness of these discontinuities are critical for assessing models of upper mantle phase changes and chemical layering so far seismic studies aimed at determining the thickness and lateral variability of upper mantle discontinuities have yielded equivocal results particularly for the discontinuity at 410km depth1 2 here we present short period 0 8 2 0 s recordings of upper mantle precursors to the seismic phase p p pkppkp from two south american earthquakes recorded by the 700 station short period array in california our results show that the 410 and 660 km discontinuities beneath the indian ocean are locally simple and sharp corresponding to transi tion zones of 4 km or less these observations pose problems for mineral physics models3 5 which predict a transitional thickness greater than 6 km for the peridotite to spinel phase transition in contrast to the results of long period studies6 7 we observe no short period arrivals from near 520 km depth

geomorphology and natural hazards in karst areas a review 1 introductionsince human beings started to colonise the world slowly migrat ing in multiple directions from the african rift and ultimatelyreaching the southernmost territories of the americas they haveinteracted with the natural environment using its resources and suf fering from its hazardous processes survival of mankind was possiblethanks to its ability to adapt to an ever changing environment and itscapability to learn and communicate the new ndings from the ear liest times geomorphic features and processes were an essential partof social survival crozier et al 2011 in karst terrains caves wereused as shelters as well as burial and sacred places playing an instru mental role in the day to day struggle for survival especially duringthe ice ages fig 1 spectacular karst landmarks such as big cave en trances blue karst springs deep collapse sinkholes cenotes or rockarches just to name a few have often become part of the naturaland supernatural heritage of our ancestors in prehistoric times the human impact on the karst environmentwas very limited like the probability of properties and people beingdamaged by karst processes e g subsidence ooding both impactsandhazardsinkarstterrainshaveincreaseddramaticallyover thelasttwo centuries along with the exponential increase in population andour capability to modify the natural environment largely related tothe economic and technological development of the societies an in creasing number of scientists consider that humans are nowadaysthe most effective geomorphic agent and a prime factor in landscapeevolution zalasiewicz et al 2010 price et al 2011 in fact the for mal de nition of the anthropocene as a new epoch of the geologicaltime scale characterised by a signi cant and global human impact onthe earth s ecosystems is being debated at the present time around25 of the earth s population lives on or nearby karst areas ford andwilliams 2007 and the increasing exploitation of karst resources such as water and building material is leading to severe environmen tal impacts and unsustainable situations drew and hotzl 1999 gunn 2004 unfortunately the number of karst areas affected bywater pollution landscape degradation and other impacts is growingveryrapidly additionally thedamagecausedbyhazardouskarstpro cesses especially subsidence sinkholes beck 2003 waltham et al 2005 gutierrez et al 2008a will most likely keep on increasing exposed human elements augment and anthropogenic changes inthe karst systems frequently result in hazard enhancement karstgeomorphologists and hydrologists can play a decisive role in pre venting natural disasters in karst areas particularly those inducedby human activities dams with leakage and sinkhole problems milanovic 2000 cooper and gutierrez 2011 mines and tunnelsaffected by ooding and subsidence li and zhou 1999 autin 2002 casagrandeet al 2005 luchaetal 2008 high speedrailwaysbuilt in sinkhole prone areas guerrero et al 2008 or developmentof sinkholes at huge rates induced by lake level yechieli et al 2006 or water table sprynskyy et al 2009 declines the importance of properly managing karst areas and mitigatingthe detrimental effects caused by human activities on these inherentlysensitive environments has been boosted by a series of conferencesand projects since the early 1990s ford 1993 williams 1993 pariseet al 2008 2009 raising public awareness on the need to protectour endangered natural resources especially in developed countries has promoted the production of karst speci c environmental impactassessments veni 1999 recently severalapproacheshavebeenpro posedtoassessthedegreeofhuman induceddisturbanceinkarstareas van beynen and townsend 2005 calo and parise 2006 de waele 2009 north et al 2009 although these studies are essential for apropermanagementofthekarstresources theymaybefutileifnotfol lowed by adequate administrative decisions and regulations 2 karst geomorphology2 1 karst processeskarst is characterised by the predominance of rock dissolution overmechanical erosion and is typical of present temperate cold andwarm and tropical environments ford and williams 2007 in karstterrains surface and subsurface geomorphology and hydrology arelargely governed by dissolution of carbonate and or evaporite rocks in the most classical common situation surface waters acidi ed byco

mantle discontinuity structure beneath china mantle reflectivity profiles obtained from long period recordings of multiple scs reverberations from intermediate and deep focus earthquakes surrounding china reveal remarkably sharp images of china deep structure the tibetan plateau and fold belts to the north are underlain by a midlithospheric low velocity zone lvz evidenced by coincident g lid lvz boundary and l base of the lvz reflectors and a thickened lithosphere consistent with uniform thickening as the dominant mode of north south deformation the mantle beneath northeastern china mongolia and southeastern russia has a typically cratonic reflectivity signature with h hales and deep l lehmann discontinuities the sino korean paraplatform of eastern china is a region of active extensional tectonics as expressed by an oceanic reflectivity pattern at shallow depths a g discontinuity at 80 km but a more continental structure below the southern sea of japan korean peninsula yellow sea and bordering regions of the china mainland are underlain by a 5 4 impedance decrease near 330 km depth that we interpret as the upper limit of dense silicate melt atop the 410 km discontinuity produced at the subduction zones to the east regional inversion of the reflection coefficient of the 410 km discontinuity r 410 reveals a pronounced high beneath mongolia and north to northwestern china which is best explained by increased upper mantle olivine content signifying extensive basalt depletion in a tectosphere that extends below the 410 km discontinuity a low value of r 660 associated with topographic depression of the 660 km discontinuity beneath eastern asia is consistent with a horizontally inclined slab atop the phase transition marking the seismic discontinuity reflection defocusing is an alternative but requires 38 km of intermediate scale topography within the depressed region exceeding the amplitude of the depression by a factor of 1 5 2 either mechanism requires strong heterogeneity far west of seismically active slabs two lower mantle reflectors one beneath southern honshu kyushu and the sea of japan the other below shantung province china and the yellow sea correlate with horizontally elongated velocity anomalies in western pacific seismic tomography models we speculate that they may represent slabs stagnating below the 660 km discontinuity

sinkhole swarms from initiation to stabilisation based on in situ high resolution 3 d observations abstract we study in this paper the evolution of sinkhole fields along the dead sea coastal plains from initiation to stabilisation the prevailing hypothesis attributes their formation to the dissolution of a buried halite layer by groundwater but fails to explain their evolution in some places and their stability in others based on thirteen years of high resolution laser scanning and field surveys we trace a complete evolutionary cycle of sinkholes and show that the prevailing theory explains only the first out of a four stage cycle we show that following the formation stage an acceleration phase begins when the sinkholes interact with the drainage system a deepening and spatial localisation phase ensues then some parts of the field cease to expand leading to a fourth stage of stabilisation we further show that during their embryonic stage sinkhole development is limited due to a lack of connectivity between the surface and subsurface hydrological processes but as this connectivity evolves the development rate increases up to three orders of magnitude moreover observations show a high correlation with hydrological seasonality the most active field demonstrated a development rate of 13 540 m 3 month during the wet season in contrast to a rate of 1010 m 3 month during the dry season these measurements and observations allow us to propose a new theoretical model for sinkhole swarm development from initiation to stabilisation with linkage to seasonality and hydrology

quantitative assessment of in situ salt karstification using shear wave velocity dead sea abstract the dead sea ds coastal areas have been dramatically affected by sinkhole formation since around 1990 such sinkholes along both israeli and jordanian shores are linked to karst cavities that form through slow salt dissolution a quantitative estimate of such in situ salt karstification would be an important indicator of sinkhole hazard one of the indications of salt karstification is its increased hydraulic conductivity caused by the development of dissolution cavities forming conducting channels within the salt layer we measured the hydraulic conductivity k versus shear wave velocity vs of ds salt in situ for estimating the actual salt karstification in areas of sinkhole development these parameters were measured with the magnetic resonance sounding mrs and multichannel analysis of surface waves masw methods respectively understanding of the field relationships was augmented by similar inter relations obtained in the laboratory on samples of ds salt in situ salt velocities vs vary from 750 m s to over 1650 m s while hydraulic conductivity k in the same zones varies between about 10 4 m s to slightly over 10 8 m s both field and laboratory k and vs values fit the exponential function ln k 0 0045 vs 5 416 with a determination coefficient r2 of 0 88 a classification based on vs and k was generated for salt conditions and the corresponding degrees of sinkhole hazard which was verified in the mineral beach sinkhole development area the mapping of sinkhole sites shows that they form within highly conductive zones with k 5 5 10 5 it is suggested that this methodology with some modification can be used for evaluating the conductive properties of karstified rock and associated sinkhole hazards

fault dissolution front relations and the dead sea sinkhole problem abstract there are two conflicting models of sinkhole development along the dead sea ds the first one considers structural control on sinkholes constraining them to tectonic lineaments this hypothesis is based on seismic reflection studies suggesting that sinkholes are the surface manifestations of active neotectonic faults that may serve as conduits for under saturated groundwater enabling its access across aquiclude layers another hypothesis based on results of multidisciplinary geophysical studies considers the salt edge dissolution front as the major site of sinkhole formation this hypothesis associates sinkholes with karstification of the salt edge by deep and shallow undersaturated groundwater our recent seismic reflection and surface wave studies suggest that salt formed along the active neotectonic faults sinkholes form in a narrow strip 60 100 m wide along a paleo shoreline constrained by faults and alluvial fans which determined the edge of the salt layer this scenario reconciles the two major competing frameworks for sinkhole formation

geology fluid inclusion and stable isotope study of the yueyang ag au cu deposit zijinshan orefield fujian province china abstract the large yueyang ag au cu deposit is commonly regarded as a low sulfidation epithermal deposit in the zijinshan orefield fujian province southeastern china the ag ag cu orebodies hosted in the zijinshan granitic batholith are mainly stratoid and lens in shape and controlled by a series of nw trending listric faults with shallow dip angles four mineralization stages are recognized on the basis of mineral assemblage ore fabrics and crosscutting relationships of the ore veins namely pre ore pyrite sericite quartz chlorite main cu chalcopyrite pyrite sericite quartz bornite main ag au ag and au minerals pyrite quartz adularia calcite apatite chalcopyrite galena sphalerite and post ore quartz chalcedony calcite stages fluid inclusions fis in the deposit include aqueous liquid rich wl aqueous vapor rich wv and minor carbonic c and daughter mineral bearing s type ones wl subtype is the main inclusion type in the yueyang deposit accounting for more than 90 in proportion in each stage minor wv subtype inclusions occur in both the main cu and ag stages while the c type and s type ones are only observed in the main cu stage fluid inclusion and h o isotope study indicated that the ore forming fluid of the main cu stage is primarily magmatic vapor which further underwent fluid boiling and mixing with meteoric water while the ore forming fluid of the main ag stage is meteoric water dominated and the precipitation of silver and gold was mainly resulted from fluid boiling and the precipitation of other sulfides on the basis of the aforementioned geological fluid inclusion and stable isotope studies we proposed a two stage model for the yueyang deposit including a magmatic vapor related porphyry type cu mineralization and meteoric water related low sulfidation epithermal ag au cu mineralization although the porphyry cu mineralization is very limited in scale the mineralization and exhumation depths of the yueyang deposit are estimated to be 448 527 m and 18 97 m respectively by comparison with the exhumation depths of other deposits in the zijinshan orefield it is suggested that more epithermal deposits could be found in the southwest of the orefield due to less uplift and exhumation therein

s p conversion from the transition zone beneath tonga and the nature of the 670 km discontinuity summary using more than 300 recordings of deep tonga earthquakes from the warramunga seismic array central australia we have searched for short period s p conversions from the 670 km discontinuity arriving in the p wave codas the array seismograms were stacked and plotted in sections to optimize observation of s670p yielding the following results for the northern part of tonga 17 3 18 4 s s670p phases are observed with apparent conversion depths between about 660 and 680 km for the central part 20 2 22 3 s s670p is not clearly observed for the southern part 23 1 25 7 s s670p is observed for conversion depths between about 660 and 700 km intermittent occurrence of s p conversion may result from different characteristic source radiation patterns among the three sections overall uncertainties in conversion depths resulting from unmodelled lateral velocity variations and hypocentral location errors are perhaps a few tens of kilometres the s p rays must travel either within or very close to the subducted slab because of the source receiver slab dip geometry so we conclude that large 50 km deformations of the 670 km discontinuity do not occur beneath tonga our observations appear to be inconsistent with a chemical discontinuity at 670 km but are easily explained if the 670 km discontinuity is a strongly pressure dependent and perhaps moderately endothermic phase change in both the slab and surrounding mantle

mineralogy and composition of the upper mantle seismic velocities are calculated for two petrological models of the upper mantle an olivine rich assemblage pyrolite and a garnet clinopyroxene rich olivine bearing assemblage piclogite these are compared with recent seismic profiles for various tectonic provinces the shield data is most consistent with a cold olivine and orthopyroxene rich lid the seismic lithosphere extending to 150 km followed by a high temperature gradient and or a change in mineralogy that serves to decrease the velocity from 200 to 400 km the velocities follow a 1400 c adiabat the rise tectonic mantle is much slower presumably hotter and is likely to be above the solidus to depths of at least 300 km the high v p v s ratio of the lower oceanic lithosphere in the western pacific is most consistent with eclogite

magmatic vapor expansion and the formation of high sulfidation gold deposits chemical controls on alteration and mineralization abstract large bulk tonnage high sulfidation gold deposits such as yanacocha peru are the surface expression of structurally controlled lode gold deposits such as el indio chile both formed in active andesite dacite volcanic terranes fluid inclusion stable isotope and geologic data show that lode deposits formed within 1500 m of the paleo surface as a consequence of the expansion of low salinity low density magmatic vapor with very limited if any groundwater mixing they are characterized by an initial sulfate stage of advanced argillic wallrock alteration alunite commonly with intense silicification followed by a sulfide stage a succession of discrete sulfide sulfosalt veins that may be ore grade in gold and silver fluid inclusions in quartz formed during wallrock alteration have homogenization temperatures between 100 and over 500 c and preserve a record of a vapor rich environment recent data for el indio and similar deposits show that at the commencement of the sulfide stage condensation of cu as s sulfosalt melts with trace concentrations of sb te bi ag and au occurred at 600 c following pyrite deposition euhedral quartz crystals were simultaneously deposited from the vapor phase during crystallization of the vapor saturated melt occurs to fe tennantite with progressive non equilibrium fractionation of heavy metals between melt vapor and solid vugs containing a range of sulfides sulfosalts and gold record the changing composition of the vapor published fluid inclusion and mineralogical data are reviewed in the context of geological relationships to establish boundary conditions through which to trace the expansion of magmatic vapor from source to surface and consequent alteration and mineralization initially heat loss from the vapor is high resulting in the formation of acid condensate permeating through the wallrock this sulfate stage alteration effectively isolates the expansion of magmatic vapor in subsurface fracture arrays from any external contemporary hydrothermal activity subsequent fracturing is localized by the embrittled wallrock to provide high permeability fracture arrays that constrain vapor expansion with minimization of heat loss the sulfide stage vein sequence is then a consequence of destabilization of metal vapor species in response to depressurization and decrease in vapor density the geology mineralogy fluid inclusion and stable isotope data and geothermometry for high sulfidation bulk tonnage and lode deposits are quite different from those for epithermal gold silver deposits such as mclaughlin california that formed near surface in groundwater dominated hydrothermal systems where magmatic fluid has been diluted to less than about 30 high sulfidation gold deposits are better termed solfataric gold deposits to emphasize this distinction the magmatic vapor expansion hypothesis also applies to the phenomenology of acidic geothermal systems in active volcanic systems and equivalent magmatic vapor discharges on the flanks of submarine volcanoes

human induced geological hazards along the dead sea coast the dead sea is a terminal lake whose level is currently dropping at a rate of about 1 m per year due to the over exploitation of all its tributaries the lowering started about four decades ago but geological hazards appeared more and more frequently from the end of the 1980s the water level lowering is matched by a parallel groundwater level drop which results in an increasing intensity of underground and surface water flow the diagonal interface between the dead sea brine and the fresh groundwater is pushed downwards and seawards nowadays sinkholes subsidence landslides and reactivated salt karsts affect wide coastal segments until now mainly infrastructures were damaged and few people animals were injured but the ongoing development of tourism in this very attractive situation will increase the risk if precautionary measures are not included in the development plans this paper discusses the main observations made all around the dead sea and shed a light on the differences between the geological hazards of the western shore israel palestinian authority and the eastern shore jordan it is the first attempt to bring together an overview of the human induced geological hazards encountered along the dead sea coast

salt dissolution and sinkhole formation along the dead sea shore 1 the formation of sinkholes at the dead sea area reflects subsurface cavities formed by salt dissolution this dissolution is related to the recession of the dead sea the groundwater level and the fresh saline water interface along the shore decline at a similar rate to the rate of the dead sea recession and brines that used to occupy layers below this interface are flushed out by freshwater our finite element modeling shows that dissolution of this salt layer is a plausible mechanism to explain the rapid creation of subsurface holes that collapse and form sinkholes the positive feedback between the rate of flow the rate of chemical reaction and the change in permeability accelerates the dissolution processes and might result in reactive infiltration instability which is manifested in fingers of cavities into which fluid is channeled and salt is dissolved the spacing between the sinkholes and the rate of their creation is controlled by several factors including properties of lineaments faults incoming groundwater flux the salinity of the incoming groundwater the rate of dissolution the effective specific surface area the permeability of the salt and clay layers the permeability porosity relation the dispersivity and the thickness of the layers we show that the creation of sinkholes occurs only under specific conditions these conditions must cause an unstable dissolution front which then causes formation of cavities and eventually sinkholes the simulations which utilized the best estimated parameters of the studied area yield results that are similar to those exhibited in the field

mantle layering from scs reverberations 2 the transition zone this is the second paper in a four part sequence that examines the nature of mantle layering using the scsn phases and internal reflections observed within the reverberative interval of sh polarized seismograms mantle reflectivity profiles for 18 seismic corridors sampling portions of indonesia australia and the western and central pacific are constructed from low frequency 25 mhz scs reverberations i e scsn type phases reflected once from internal mantle discontinuities modeling the reflectivity profiles using synthetic seismograms yields precise path specific estimates of the travel times to the 410 km and 660 km discontinuities and their reflection coefficients the data are consistent with an olivine dominated model of the transition zone marked by two major phase transitions having average apparent depths of 414 2 km and 660 2 km and impedance contrasts of 0 046 0 010 and 0 072 0 010 respectively the interpath variations observed in the reverberation travel times imply that the topography on the two discontinuities is of the order of 20 km peak to peak and is negatively correlated consistent with an endothermic transition at 660 km whose clapeyron slope magnitude is comparable to that of the 410 km exothermic transition in the case of the 660 km discontinuity we have been able to supplement these long wavelength 1500 5000 km observations with an estimate of intrapath topography inferred from the frequency dependence of the 660 km reflection coefficient which gives peak to peak variations less than 40 km on scale lengths of 500 1500 km for the 660 km discontinuity the observed topography is significantly less than the dynamic topography expected for a simple compositional interface in regions of subduction however we do observed an intriguing negative correlation between the apparent depth and the reflection coefficient of the 660 km discontinuity which may involve small compositional variations plausible explanations for this correlation include heating of an initially cool chemical boundary layer gravitationally trapped above an endothermic phase transition loss of reflected energy due to local curvature or roughness of the reflector and or extreme topography occurring on a small compositional component to the discontinuity 40 of the total impedance contrast by stripping the 410 km and 660 km peaks from the composite path reflectivity profile we identify three minor reflectors at mean depths of 520 710 and 900 km the shallowest may mark the phase spinel phase transition the 710 km discontinuity can be attributed to the ilmenite gamet perovskite phase transition although changes in perovskite symmetry can potentially provide explanations for both the 710 km and 900 km features

velocity resistivity versus porosity permeability inter relations in dead sea salt samples abstract this study is intended to investigate dead sea ds salt porosity permeability hydraulic conductivity inter relations as well as their relationship to geophysical parameters such as compression and shear wave velocities vp vs respectively and specific resistivity x in laboratory and field conditions to estimate representative properties affected by porosity changes during sinkhole development some 41 salt samples were subjected to porosity measurements and 25 samples were tested to reveal hydraulic conductivity the salt of the coastal dead sea area composed of halite is revealed in 10 200 10 800 year old layers the halite commonly appears as rock salt the 7 30 m thick salt unit is located below the groundwater table at depths of 20 50 m from the surface salt layers are very conductive hydraulically and water saturated with the ds brine is of very high salinity with total dissolved solids tds of 340 380 g l two types of salt have been studied crystalline transparent salt cts distributed along the entire ds s western shore and white massive salt wms found locally along the southern ds and along the dike salt porosity measured in samples varies in the range of 5 21 whereas hydraulic conductivity varies between 10 5 to 10 9 m s density is changed in the range of 1681 2116 kg m 3 in wet samples and between 1638 and 2106 kg m 3 in dry samples during the laboratory testing of ds salt samples we have measured the following geophysical parameters vp 3700 4460 m s vs 1900 2620 m s and x 2 100 m on the other hand our previous field studies based on s wave seismic refraction surface wave prospecting swp and transient electromagnetic tem methods have shown that in in situ salt velocities vp range between 2900 and 4240 m s vs varies between limits of 750 m s to more than 1650 m s and x is of 0 8 to 2 5 m these values are considerably less than the analogous parameters measured in the salt samples the same conclusion has been made from the comparison of salt sample properties and borehole logging both studied by ultrasonic method geophysical data testify that in situ porosity calculated using relationships obtained during this study exceeds those in the laboratory samples especially in zones of heightened voidness where it is 25 hydraulic conductivities in the same zones exceed a value of 10 6 m s and even 10 5 m s we expect that in larger salt volumes these parameters can yet increase

evolution of fluids in the dasuji porphyry mo deposit on the northern margin of the north china craton constraints from microthermometric and la icp ms analyses of fluid inclusions abstract the newly discovered dasuji mo deposit is located on the northern margin of the north china craton and the mo mineralization is related to triassic granite porphyry and quartz porphyry alteration associated with the deposit includes silicification sericitization chloritization k feldspathization kaolinitization carbonatization and fluoritization the silicification and sericitization phyllic alteration are closely related to the mo mineralization based on mineral assemblages and cross cutting relationships the hydrothermal ore forming process can be divided into four stages stage 1 is characterized by k feldspathization with minor molybdenum mineralization stage 2 is the main stage of molybdenum mineralization stage 3 is involved in lead zinc mineralization and stage 4 is characterized by no mineralization four types of fluid inclusions are recognized liquid rich gas rich co2 h2o and daughter mineral bearing microthermometric data show a decrease in homogenization temperatures and salinities from the early to late stages so that stages 1 4 show homogenization temperatures of 468 375 435 271 318 206 and 222 142 c respectively and the fluids of stages 1 3 and 4 had salinities of 2 57 16 50 along with a few high salinity inclusions 32 04 48 05 0 88 11 19 and 0 88 7 45 wt nacl equiv respectively the salinities of stage 2 fluid inclusions have a bimodal distribution 1 40 17 48 and 29 20 53 25 wt nacl equiv laser ablation inductive coupled plasma mass spectrometer la icp ms analyses show that the fluid compositions are dominated by na k fe and mn in stage 2 fluid inclusions the mo concentrations vary over a range of more than one order of magnitude more than for any other element as a result of fluid rock interactions and molybdenite precipitation cu concentrations remain always relatively high in the fluids during their evolution 26 7092 ppm because there was little chalcopyrite precipitation the stage 3 fluid inclusions are rich in mn pb and zn while ag concentrations increased in stage 3 and 4 fluid due to the addition of meteoric water from the surrounding rock reactions between the wallrock and hydrothermal fluids affected the composition of the hydrothermal fluids sericitic alteration in particular had a great effect on fluid compositions manifesting the variety of the content of sr ba ca pb the ore forming fluids were mainly magmatic hydrothermal fluids that were mixed with meteoric water during stages 3 and 4 fluid immiscibility a rapid decrease in pressure fluid rock reactions and fluid cooling were collectively responsible for the sulfide precipitation in the dasuji deposit

sinkhole swarms along the dead sea coast reflection of disturbance of lake and adjacent groundwater systems more than a thousand sinkholes have developed along the western coast of the dead sea since the early 1980s more than 75 of them since 1997 all occurring within a narrow strip 60 km long and 1 km wide this highly dynamic sinkhole development has accelerated in recent years to a rate of 150 200 sinkholes per year the sinkholes cluster mostly over specific sites up to 1000 m long and 200 m wide which spread parallel to the general direction of the fault system associated with the dead sea transform research employing borehole and geophysical tools reveals that the sinkhole formation results from the dissolution of an 10 000 yr old salt layer buried at a depth of 20 70 m below the surface the salt dissolution by groundwater is evidenced by direct observations in test boreholes these observations include large cavities within the salt layer and groundwater within the confined subaquifer beneath the salt layer that is undersaturated with respect to halite moreover the groundwater brine within the salt layer exhibits geochemical evidence for actual salt dissolution na cl 0 5 0 6 compared to na cl 0 25 in the dead sea brine the groundwater heads below the salt layer have the potential for upward cross layer flow and the water is actually invading the salt layer apparently along cracks and active faults the abrupt appearance of the sinkholes and their accelerated expansion thereafter reflects a change in the groundwater regime around the shrinking lake and the extreme solubility of halite in water the eastward retreat of the shoreline and the declining sea level cause an eastward migration of the fresh saline water interface as a result the salt layer which originally was saturated with dead sea water over its entire spread is gradually being invaded by fresh groundwater at its western boundary which mixes and displaces the original dead sea brine accordingly the location of the western boundary of the salt layer which dates back to the shrinkage of the former lake lisan and its transition to the current dead sea constrains the sinkhole distribution to a narrow strip along the dead sea coast the entire phenomenon can be described as a hydrological chain reaction it starts by intensive extraction of fresh water upstream of the dead sea continues with the eastward retreat of the lake shoreline which in turn modifies the groundwater regime finally triggering the formation of sinkholes

locating water filled karst caverns and estimating their volume using magnetic resonance soundings magnetic resonance sounding mrs is a geophysical technique developed for groundwater exploration this technique can be used for investigating karst aquifers generally the study ofakarstrequiresa3dfieldsetupandcorrespondingmultichannel data acquisition instruments now only single channel mrs equipment is available i e the time needed for a 3d mrs field survey is multiplied by a factor of four or five where karst caverns are natural hazards as in the dead sea coastal area at nahal hever israel even an approximate localization of potentially dangerous zones and a corresponding estimation of the hazard dimensions are useful we studied numerically the accuracy of mrs estimations of the volume of different 3d targets around nahalhever shiftinga3dtargetinsidethemrsloopandcalculating the volume estimation errors for each target position the calculations covered targets of different sizes the size and position of a target being unknown factors in a field survey the numerical data were considered as random values to be analyzed statistically using a 1d approximation of the mrs solution and assuming a 100 100 m 2 mrs loop the volume of a 3d target under nahal hever conditions is estimated within a 75 error when the target is smaller than the mrs loop and within a 50 error when the target size is about the same as the mrs loop the lower threshold of karst cavity detection with mrs is about 6500 m3 for such estimation only one sounding is

detection of subsurface brines freshwater bodies and the interface configuration in between by the time domain electromagnetic method in the dead sea rift israel high radon fluxes in the seismically active dead sea rift seem to be affected by the hydrological system and the different salinities of groundwater bodies involved the time domain electromagnetic tdem method was employed to delineate those different bodies and the configuration of the interfaces between them the present hydrological system and the related brines and interfaces are controlled by the dead sea base level presently at 408 m below msl tdem measurements detect low resistivity 1 ohm m units representing brines and the interface between them as well as the overlying fresher water bodies in addition high resistivity freshwater units are also detected underlying the brines related herein to a multiple hydrological system low resistivity brines detected above the present base level are interpreted herein as yet unflushed ones which correspond to a former higher base level higher sequences below historical sixteenth century base levels are already devoid of brines which gives an indication as to the rate of flushing

ps conversions from the upper mantle transition zone beneath the canadian landmass broadband teleseismic p waveforms recorded on the canadian national seismograph network have been processed to isolate near receiver ps conversions originating from upper mantle discontinuities at approximately 410 and 660 km depth a simultaneous deconvolution procedure which removes source effects and exploits the move out characteristics of the weak ps phases is used to raise signal above the noise levels in the p coda large amplitude arrivals exhibiting times and slownesses consistent with an interpretation as ps converted phases from the 410 and 660 km discontinuities are observed at 18 and 20 of the 24 stations examined respectively the arrival times corrected for crustal heterogeneity show strong correlation with upper mantle structure above 410 km depth as determined in previous studies stations in the cordillera above low velocity mantle are characterized by residuals up to 3 3 s slow relative to the iasp91 model whereas sites overlying the high velocity root below the canadian shield are advanced by as much as 1 9 s the difference between the p660s and p410s times provides information on the structure of the transition zone beneath canadian stations the trend of the data indicates that topography on the discontinuities is at or below resolvable levels 5 km over most of the region in general accord with a previous study of the transition zone beneath continental stations but in contrast with results for the pacific basin

sulfosalt melts evidence of high temperature vapor transport of metals in the formation of high sulfidation lode gold deposits in enargite gold high sulfidation vein deposits magmatic fluid is considered responsible for the transport of metals and sulfur into the depositional regime new data from field emission sem analyses of sulfosalt mineral assemblages primarily enargite and tennantite from el indio chile and summitville colorado provide direct evidence of high temperature deposition including the following 1 the preservation of delicate euhedral quartz assemblages in sulfosalts 2 a range of discrete sb rich sulfosalt quartz feldspar and flourapatite vug filling minerals and 3 symplectic sulfosalt chalcopyrite textures that are arguably quenched melts together these features indicate formation from the vapor phase at high temperatures furthermore euhedral quartz crystals from el indio contain high temperature vapor rich fluid inclusions combined these observations are interpreted as suggestive of deposition in response to vapor phase decompression within fracture arrays that may be considered the analogues of the feeder fractures beneath large low grade silver gold deposits such as yanacocha peru

pre existing caverns in salt formations could be the major cause of sinkhole hazards along the coast of the dead sea since 1990 hundreds of sinkholes have appeared along the coast of the dead sea in the literature the rapid development of sinkholes is explained as a result of a drop in the level of the dead sea this model assumes very fast dissolution of large volumes of salt and the creation of new caverns that cause sinkholes in 10 to 20 years however the results of our geophysical study do not confirm the fast dissolution assumption to explain the available field observations we propose the following model 1 slow dissolution of salt much longer than 20 years with the creation of caverns without development of sinkholes 2 sinkhole development is triggered by the lowering of the groundwater level because the rocks overlying the salt formation become unsaturated 3 the time of sinkhole appearance is controlled by the mechanical properties of the rocks that overlie pre existing caverns

late holocene lake levels of the dead sea this work presents a high resolution lake level record of the late holocene dead sea a hypersaline terminal lake whose drainage basin encompasses both mediterranean and hyperarid climatic zones the lake level curve reflects the regional hydrologic variations in the drainage basin which in turn represent the levant paleoclimates the curve is based on 46 radiocarbon ages of organic remains from well exposed sedimentary sequences along the dead sea shores these sequences record fluvial and lacustrine depositional environments the paleolakeshores are marked by shore ridges coarse sand units and aragonite crusts in the modern dead sea such features indicate the exact elevation of the shore the late holocene dead sea level fluctuated within the range of 390 to 415 m below sea level mbsl for most of the time the lake was below the topographic sill 402 mbsl separating the northern and southern basins of the dead sea and was confined to the deep northern basin nevertheless short term rises in the late holocene dead sea level caused the flooding of the shallow and flat southern basin highstands occurred in the second and first centuries b c and the fourth century a d during the roman and early byzan tine periods respectively in the eleventh and twelfth centuries a d during the crusader period and at the end of the nineteenth century a d the rises mark a significant change in the annual rainfall in the region which likely exceeded the instrumentally measured modern average the curve also indicates drastic drops that exposed the sedimentary sequences to erosion the oldest and probably deepest drop in the lake level culminated during the fifteenth and fourteenth centuries b c after a retreat from a higher lake stand the longest lowstand occurred after the byzantine period and continued at least until the ninth century a d this arid period coincided with the invasion of moslem arab tribes into the area during the seventh century a d the dramatic fall of the dead sea level during the twentieth century is primarily artificial and has been caused by the diversion of runoff water for the drainage basin but the magnitude is not considered exceptional for the late holocene although the past drops in the lake never exceeded the modern artificial drop rates they do represent extreme arid conditions that occurred frequently over the past several thousand years

geophysical prediction and following development sinkholes in two dead sea areas israel and jordan geophysical methods seismic refraction srfr electrical resistivity tomography ert and microgravity were applied to the dead sea ds sinkhole problem in the ein gedi area at the earlier stage of the sinkhole development 1998 2002 they allowed determining the sinkhole formation mechanism and localizing the sinkhole hazardous zones the srfr method permitted to delineate the underground edge of a salt layer at the depth of 50 m the salt edge was shaped like the sinkhole line on the surface it was concluded that the sinkhole development is linked to the salt edge geoelectrical quasi 3d mapping based on the ert technique detected large resistivity anomalies with 250 300 m2 diameter and 25 35 m deep the ein gedi area has been also mapped by the use of microgravity method the residual bouguer gravity anomaly map shows negative anomalies arranged along the edge of the salt layer those gravity anomalies overall are very similar in plan to the resistivity distribution in this area the results of forward modeling indicate that both high resistivity and residual gravity anomalies are associated with a subsurface decompaction of the soil mass and deep cavity at the sinkhole site following monitoring of the sinkhole development carried out by the geological survey of israel confirmed our suggestions the drilling of numerous boreholes verified the location of the salt edge geographical information system gis database testifies that during 2003 2009 new sinkholes are continuing to develop along the salt edge within a narrow 50 100 m wide strip oriented approximately in north south direction slightly parallel to the shoreline no promotion in west east direction perpendicularly to the ds shoreline was observed in israel collapse of sinkholes and their clustering have been occurred within the area of high resistivity anomaly and negative residual gravity anomaly similar studies carried out at the ghor al haditha area jordan have shown that sinkholes there are also arranged along the winding line conforming to the salt edge in this area sinkholes are slowly moved to the dead sea direction results of geophysical studies in numerous ds sites indicate similar sinkhole development it allowed generating of the sinkhole formation model based on ancient 10 000 11 000 year old salt belt girding the dead sea along its shores

stromatolites in caves of the dead sea fault escarpment implications to latest pleistocene lake levels and tectonic subsidence abstract a varied assemblage of algal stromatolites was encountered in caves along the northern section of the dead sea fault escarpment the caves are situated at the lower part of the escarpment at altitudes 310 to 188 m relative to mean sea level m s l i e ca 110 230 m above the present dead sea level the cave stromatolites are mainly composed of aragonite yielding u th ages of 75 17 ka the altitude mineralogy and ages as well as comparison with previously documented stromatolite outcrops in the area ascribe the cave stromatolites to the aragonite precipitating hypersaline lake lisan the late pleistocene predecessor of the dead sea the stromatolites are used as a lake level gauge based on the algae being reliant upon the light of the upper water layer preservation of the original structure and aragonite mineralogy of the stromatolites suggests a closed system regarding the radioactive elements enabling reliable u th dating a curve of lake lisan levels is constructed based on the stromatolite ages and cave elevations the following points are noted 1 lake levels of 247 m relative to m s l are recorded at 75 72 5 ka 2 relatively high lake levels above 220 m relative to m s l are achieved at 41 5 ka and are still recorded at 17 ka 3 the peak level is 188 m relative to m s l at 35 5 29 5 ka these results indicate lake stands up to 80 m higher than previously accepted for large parts of the lake lisan time span this difference is explained by tectonic subsidence of up to 2 2 m ka within the dead sea depression since the latest pleistocene this subsidence rate is in the same order of magnitude with previously calculated subsidence rates for the dead sea depression begin z b zilberman e 1997 main stages and rate of the relief development in israel geological survey of israel report jerusalem unlike previous lake lisan level estimations the new curve is measured at the relatively stable shoulders of the dead sea depression

the chemistry of fumarolic vapor and thermal spring discharges from the nevado del ruiz volcanic magmatic hydrothermal system colombia on the basis of three sets of gas samples taken during the three months preceding the november 13 1985 eruption of nevado del ruiz from fumaroles on the crater floor the composition of the vapors discharged following minor eruptive activity in september corresponded to that of an essentially magmatic gas during the subsequent quiet period in october the proportion of a hydrothermal component in the vapor discharge increased steadily up until the major eruption the gases were found to be exceptionally high in total sulfur and are super saturated with respect to elemental sulfur their thermodynamic equilibration temperatures range from 200 to 600 c gases and waters from fumaroles and thermal springs on the flanks of the volcano are likely to be derived from a two phase vapor brine envelope surrounding the magmatic system the chemistry of the fumarole discharges is compatible with the assumption of an eruptive mechanism involving the build up of pressure in an extensive vapor zone by gas released from an essentially stagnant already extensively degassed body of magmatic material at depth production of such a residual gas over extended periods may account for the large amount of so2 discharged from the volcano in relation to the small amount of ejected solids

introduction to the special section on the transition zone summary in the 40 years since birch s paper we have made great progress toward a more complete understanding of the transition zone in the last few years digital seis mometers improvements in high pressure experimental techniques and more powerful computers have opened up the possibility of reexamining some of the longstand ing questions related to the transition zone and the dy namics of the mantle however these advances alone are probably not sufficient to advance our understand ing of the transition zone as far as we would like this can be illustrated by looking at the focus areas in this special section while it is clear that phase changes can have a major influence on large scale flows in constant viscosity fluids with simple equations of state cf solhelm and peltlet this issue tackley et al this issue a better under standing of the rheology of the mantle in particular the lateral variations in viscosity and around a sub ducting slab are necessary to make definitive statements

salt dissolution and sinkhole formation results of laboratory experiments the accepted mechanism for the formation of thousands of sinkholes along the coast of the dead sea suggests that their primary cause is dissolution of a salt layer by groundwater undersaturated with respect to halite this is related to the drop in the dead sea level which caused a corresponding drop of the freshwater saltwater interface resulting in fresher groundwater replacing the brines that were in contact with the salt layer in this study we used physical laboratory experiments to examine the validity of this mechanism by reproducing the full dynamic natural process and to examine the impact of different hydrogeological characteristics on this process the experimental results show surface subsidence and sinkhole formation the stratigraphic configurations of the aquifer together with the mechanical properties of the salt layer determine the dynamic patterns of the sinkhole formation instantaneous versus gradual formation laboratory experiments were also used to study the potential impact of future stratification in the dead sea if and when the red sea dead sea canal project is carried out and the dead sea level remains stable the results show that the dissolution rates are slower by 1 order of magnitude in comparison with a nonstratified saltwater body and therefore the processes of salt dissolution and sinkhole formation will be relatively restrained under these conditions

quantitative interpretation of magnetic anomalies from bodies approximated by thick bed models in complex environments magnetic prospecting is a rapid and inexpensive geophysical tool and one of the most widely used methods for geophysical prospection throughout the world however the noise factors such as inclined magnetization complex geological structure of investigated areas and uneven terrain relief strongly obscure the interpretation of observed magnetic anomalies the developed methodology of magnetic anomalies interpretation from models of thin beds and horizontal circular cylinders spheres in complex environments oblique magnetization rugged relief and unknown levels of the normal magnetic field using improved versions of characteristic points and tangents was presented in detail in the author s previous publications however many geological targets have a geometrical form of thick beds and thin horizontal plates and intermediate forms that crop up between these two models in this paper a methodology for interpreting magnetic anomalies produced by thick bed models in complex environments is explicitly described it shows that quantitative analysis of magnetic anomalies due to intermediate targets could be successfully carried out using the methodology developed for the thick bed model in the case of a thin horizontal plate with a large horizontal size two distinct anomalies from the left and right ends may be interpreted as anomalies from thin beds the interpretation methodology was successfully tested both on typical models and on real geological targets it was concluded that these methods could be effectively applied for quantitative analysis of magnetic surveys for geological geophysical mapping archeological target delineation ore body searching revealing oil and gas traps and solving other geological and environmental problems

kinematic inversion of first arrivals of refracted waves a combined approach the inversion of first arrival times of refracted waves in media with laterally varying parameters can be performed using the refraction tomography technique tomographic inversion implemented as a linearized constrained least squares iterative scheme requires some a priori information on either refractor depth or velocity above the refractor however such information may be unavailable on the other hand in many cases a reasonable estimate of the average velocity distribution above the refractor can be obtained by a nontomographic technique such as the generalized reciprocal method grm i propose a combined approach to the inversion problem that uses the advantages of both the refraction tomography and grm techniques and which does not require additional information not contained in first arrival times the approach is based upon two assumptions which prove to be true in most situations the first is that a reasonable local estimate of refractor velocity can be obtained by tomographic inversion independently of other model parameters and the second is that the derivative of the velocity analysis function as defined by the grm gives a good local approximation of the refractor slowness the proposed combined inversion scheme can be described as a three step procedure in the first step the laterally varying refractor velocity is estimated by tomographic inversion in the second step local estimation of laterally varying average velocity above the refractor is performed by the grm on the basis of the previously estimated refractor velocity in the third step the estimated values of the average velocity are used as the corresponding constrained initial parameters for tomographic inversion

a comparison of the receiver structure beneath stations of the canadian national seismograph network three component broadband data from the recently deployed canadian national seismograph network provide a new opportunity to examine the structure of the crust and upper mantle beneath the canadian landmass receiver function analysis is an ideal method to use with this data set as it can provide constraints on the s velocity structure beneath each station of this seismograph network this analysis method is particularly useful in that it provides site specific information i e within 5 15 km of the station low velocity layers can be identified and it is possible to examine structure to upper mantle depths in this study receiver functions were computed for each of the 19 stations that made up the seismograph network in june 1994 five stations sampling a variety of tectonic environments including the appalachian orogen the canadian shield the western canadian sedimentary basin and the cascadia subduction zone were chosen for detailed modelling the results presented here are the first estimates of the s velocity structure beneath these five stations for those stations where comparisons can be made with seismic reflection and refraction results there is excellent agreement in eastern canada simple receiver functions and clear moho ps conversions at most stations indicate a relatively transparent crust and a moho depth of 40 45 km in northwestern canada moho ps phases indicate a crustal thickness of 33 38 km beneath inuvik northwest territories the moho is interpreted as two velocity steps separated in depth by 5 km and an upper mantle low velocity zone is near 47 km depth in western canada the data indicate a mid crustal low velocity zone beneath edmonton the moho of the subducting juan de fuca plate is interpreted at 52 krn depth beneath southern vancouver island several stations exhibiting complex receiver functions warrant further study they include stations at scheffewille quebec in the canadian shield deer lake newfoundland on the boundary of the grenville province and the appalachian orogen and yellowknife northwest territories at the intersection of the churchill and slave provinces and the western plains

cave detection near the dead sea a micromagnetic feasibility study sinkholes are a serious hazard in the dead sea area they started appearing in the area in the last two decades due to the dramatic drop in the dead sea s water level and soon became a major problem for commercial and industrial development sites with large open sinkholes and collapse features have been identified throughout a wide region white squares in figure 1 the most alarming cases are sinkholes that have occurred recently in resort areas on and around highway 90 and at israeli and jordanian potash plants several geophysical methods have been employed to investigate and predict the occurrences these include seismic geoelectric em microgravity and now micromagnetics

spatial sampling considerations and their applications to characterizing fractured rock and karst systems assessing the existence location and mapping of geologic anomalies such as fractures and cavities within soil and rock are common to both engineering and hydrologic project needs there are numerous measurement techniques available to detect map and characterize fractures and cavities a summary of the common methods available for fracture and cavity detection and mapping are presented along with their spatial sampling capabilities the remote sensing and geophysical methods are but a small part of this list but provide a wide range of tools to attack the problem they include some of the most effective methods for locating and mapping fractures and cavities and cover the complete range of spatial sampling from regional to no more than the surface of a borehole wall an understanding of all of the tools available and their spatial sampling limitations is a necessary part of planning and carrying out an effective fracture cavity investigation

constraints on upper mantle discontinuities from observations of long period reflected and converted phases stacked images combining over 5 years of long period global digital seismograph network data reveal many phases associated with reflections and conversions from upper mantle discontinuities these images show travel time and amplitude relative to a reference phase which is aligned and normalized on all seismograms prior to stacking results obtained for p s ss and pp reference arrivals resolve numerous phases from discontinuities near 410 and 660 km while some of the stacks also show evidence for a weaker discontinuity near 520 km phases of particular interest include p and sh multiples resulting from topside reflections precursors to ss from underside reflections and p to sv converted phases these phases can be clearly seen both in the waveform stacks and in cross correlation analysis of individual seismograms travel times for these arrivals are converted to discontinuity depths relative to velocities in the preliminary reference earth model and empirical corrections are applied for the effects of lateral velocity variations in the upper mantle average apparent depths to the discontinuities for the different phases agree to within 3 km for the 410 km discontinuity to within 4 km for the 520 km discontinuity and to within 8 km for the 660 km discontinuity the best global averages are obtained from the ss precursor data which indicate discontinuities at 415 519 and 659 km discontinuity depths obtained from the p to sv converted phases at over 35 individual seismic stations exhibit variations of less than 20 km apparent depths to the 660 km discontinuity consistently show greater variability than depths to the 410 km discontinuity supporting recent laboratory results which indicate that the clapeyron slope for the 660 km discontinuity is significantly larger in magnitude than the slope for the 410 km discontinuity precursors to ss seen between 110 and 180 are particularly useful for mapping possible lateral variations in discontinuity depths since each arrival can be associated with a single underside reflection point apparent discontinuity depths computed from ss precursors for different tectonic regions agree to within about 5 km the ss precursors have especially good coverage near the subducting slabs in the northwest pacific analysis of apparent discontinuity depths in this area suggests the presence of a broad 1000 to 1500 km wide region near the slab in which the 660 km discontinuity is depressed by about 20 km measuring absolute amplitudes for these phases is difficult due to the large corrections required to compensate for the effects of incoherent stacking relative amplitude analysis suggests that the p and s wave impedance changes at 410 km are about 0 8 1 1 times the size of the changes at 660 km and that the contrasts at 520 km are between 0 3 and 0 6 of the changes at 410 km

identification prediction and mitigation of sinkhole hazards in evaporite karst areas sinkholes usually have a higher probability of occurrence and a greater genetic diversity in evaporite terrains than in carbonate karst areas this is because evaporites have a higher solubility and commonly a lower mechanical strength subsidence damage resulting from evaporite dissolution generates substantial losses throughout the world but the causes are only well understood in a few areas to deal with these hazards a phased approach is needed for sinkhole identification investigation prediction and mitigation identification techniques include field surveys and geomorphological mapping combined with accounts from local people and historical sources detailed sinkhole maps can be constructed from sequential historical maps recent topographical maps and digital elevation models dems complemented with building damage surveying remote sensing and high resolution geodetic surveys on a more detailed level information from exposed paleosubsidence features paleokarst speleological explorations geophysical investigations trenching dating techniques and boreholes may help in investigating dissolution and subsidence features information on the hydrogeological pathways including caves springs and swallow holes are particularly important especially when corroborated by tracer tests these diverse data sources make a valuable database the karst inventory from this dataset sinkhole susceptibility zonations relative probability may be produced based on the spatial distribution of the features and good knowledge of the local geology sinkhole distribution can be investigated by spatial distribution analysis techniques including studies of preferential elongation alignment and nearest neighbor analysis more objective susceptibility models may be obtained by analyzing the statistical relationships between the known sinkholes and the conditioning factors chronological information on sinkhole formation is required to estimate the probability of occurrence of sinkholes number of sinkholes km2 year such spatial and temporal predictions frequently derived from limited records and based on the assumption that past sinkhole activity may be extrapolated to the future are non corroborated hypotheses validation methods allow us to assess the predictive capability of the susceptibility maps and to transform them into probability maps avoiding the most hazardous areas by preventive planning is the safest strategy for development in sinkhole prone areas corrective measures could be applied to reduce the dissolution activity and subsidence processes a more practical solution for safe development is to reduce the vulnerability of the structures by using subsidence proof designs

fluid inclusion and stable isotope constraints on ore genesis of the zajkan epithermal base metal deposit tarom hashtjin metallogenic belt nw iran in the zajkan pb zn cu au ag deposit of the tarom hashtjin metallogenic belt thmb northwest iran mineralization occurs as quartz base metal sulfide veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation four stages of ore formation are identified at zajkan 1 quartz chalcopyrite pyrite veins 2 quartz galena sphalerite chalcopyrite pyrite veins and breccias 3 quartz hematite veins and breccias and 4 barren quartz carbonate veinlets the primary metallic minerals are pyrite chalcopyrite sphalerite galena and trace amounts of hematite gangue minerals are mainly quartz sericite chlorite and calcite the main wall rock alteration is silicification and intermediate argillic and propylitic alteration the coexistence of different types of fluid inclusions lv vl and v in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping excluding the heterogeneously entrapped fluid inclusions the microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 degrees c from fluids with salinities between 1 7 and 6 4 wt nacl equiv the oxygen isotopic compositions delta o 18 water vsmow of 3 7 to 1 1 parts per thousand indicate that the ore forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore stages sulfur isotopic values of sulfide minerals vary over a narrow range from 5 0 to 0 9 parts per thousand vcdt averaging 2 2 parts per thousand vcdt suggesting that sulfur was derived from a homogeneous magmatic source the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at zajkan our data suggest that the zajkan deposit is an intermediate sulficiation style epithermal mineralization the estimated ore formation depth of zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the thmb

in situ measurements of shear wave velocity in sediments with higher mode rayleigh waves a seismic survey was carried out on a tidal flat in the sw netherlands in order to determine shear wave velocities in sediments by means of higher mode rayleigh waves the dispersion properties of these rayleigh waves were measured in the 2 d amplitude spectrum or f k spectrum and resulted in phase velocities for six different modes as a function of frequency 5 30 hz these observed phase velocities were inverted for a nine layer model for the shear wave velocity to a depth of 50 m

the thickness of upper mantle discontinuities as inferred from short period j array data the thickness of upper mantle discontinuities at depths around 410 km and 660 km provides a critical clue to our understanding of deep earth since the amplitude of reflected or s p converted waves is controlled by the thickness of discontinuities short period studies of such waves may give a fine constraint on the thickness of upper mantle discontinuities in this study we analysed short period and vertical waveform data from 14 deep events in the fiji tonga region the data were obtained from j array a short period and large aperture seismic array in japan with slant stack analyses of these data we detected short period reflections or s to p conversions from 410 km and 660 km discontinuities near sources which implies that both discontinuities are quite sharp to directly measure the frequency content of these waves linear slant stacks were made with various frequency pass bands 0 2 0 5 0 5 1 0 and 1 0 2 0 hz synthetic traces were generated for the models with various thicknesses of the 410 km and the 660 km discontinuities comparison of slant stacks with synthetic traces indicates that the thickness of both discontinuities is at most 5 km

variations in sks splitting across western canada measurements of sks splitting parameters have been made at stations of the canadian national seismograph network for events over the period 1993 mid1994 here we report on results obtained from western stations in the northern cordillera the alignment of polarization directions with major transcurrent fault systems suggests that the crust and upper mantle are being deformed coherently splitting parameters in the southern cordillera however are oriented approximately perpendicular to the strike of major tectonic features notably the cascadia subduction zone this contrast in the character of fast polarization directions between the southern and northern cordillera is thought to reflect the change in the tectonic style of the adjacent plate margin from convergent along the southern b c coast to transform north of the triple junction one plausible explanation is that upper mantle anisotropy in the southern region is due primarily to mantle flow perpendicular to the margin involving upwelling at the juan de fuca ridge subduction along the coast and associated back arc asthenospheric flow beneath the b c interior

heterogeneities in the mantle transition zone from observations of p to sv converted waves abstract the method of detection of p to sv converted waves from distant earthquakes vinnik 1977 was applied to sets of long period records from a few seismograph stations in europe and the west of north america the results obtained suggest that the converted phases related to the major boundaries in the mantle can be reliably detected and the depths of conversion evaluated with an accuracy of a few kilometres the depth of the olivine spinel transition is close to 400 km and no difference between the estimates for the north of europe and the west of north america is found the depth of the boundary separating the upper and lower mantle is close to 640 km which is 30 km less than in the recent earth reference models fine s velocity stratification of this transition changes laterally from a high gradient layer 50 km thick terminated at the bottom by a sharp discontinuity to a gradient layer 100 km or more thick without the discontinuity a striking anomaly of the mantle transition zone is found in the rio grande rift area where a well pronounced boundary is found at 510 km depth

sharpness of the mantle discontinuities seismic estimates of sharpness of the mantle discontinuities are important for constraining models of composition and temperature in the deep earth but these data are difficult to obtain we explore a possibility to determine sharpness of the major mantle discontinuities those at depths around 400 and 650 km from the broad band records of phases converted from p to s underneath the receiver our estimates are obtained from a comparative analysis of waveforms of the converted phases and those of the p waves in the teleseismic records of brv kazakhstan grf germany nre0 norway and ykw canada the data indicate that the shape of the pulse converted at the 400 km discontinuity is close to that of the p wave whereas the pulse of the 650 km conversion is substantially broader we infer from this comparison that the 400 km discontinuity is sharp width of the transition zone is less than 5 7 km the 650 km transition is modelled by a linear gradient zone 20 30 km thick

factors controlling the spatial distribution of soil piping erosion on loess derived soils a case study from central belgium abstract collapsible loess derived soils are prone to soil piping erosion where enlargement of macropores may lead to a subsurface pipe network and eventually to soil collapse and gully development this study aims at understanding the main factors controlling spatial patterns of piping in loess derived soils under a temperate climate to map the spatial distribution of piping and identify the environmental controls on its distribution a regional survey was carried out in a 236 km2 study area in the flemish ardennes belgium orthophotos taken at optimal field conditions winter were analyzed to detect piping in open landscapes and ground thruthing was systematically done through field surveys in total 137 parcels having 560 collapsed pipes were mapped dimensions of the sinkholes and local slope gradient were measured in the field and topographical variables were derived from lidar data land use plays an important role as 97 of the sites with piping are found under pasture the probability of piping increases rapidly on hillslopes with gradients exceeding 8 and with a concave profile and plan curvature enhancing subsurface flow concentration the zones with soil profiles on shallow loess over a relatively thin layer of homogeneous blue massive clays aalbeke member are most prone to piping soil characteristics are of less importance to explain piping occurrence furthermore the topographical threshold line indicating the critical slope gradient for a given contributing drainage area was determined this threshold line negative power relation is similar to the threshold line for shallow gully initiation

geology geochemistry and genesis of axi a paleozoic low sulfidation type epithermal gold deposit in xinjiang china abstract axi is a low sulfidation type epithermal gold deposit hosted in paleozoic subaerial volcanic rocks in the western tianshan orogenic belt xinjiang china the resource is more than 50 t gold at an average grade of 4 4 ppm the deposit occurs in the tulasu volcanic fault basin in the paleozoic active continental margin on the northern side of the yili central tianshan plate the host rocks are andesitic volcaniclastic rocks of the paleozoic dahalajunshan formation and the orebodies occur as veins in annular faults of a paleocaldera mineralization at axi can be subdivided into five stages quartz and or chalcedony vein quartz vein quartz carbonate vein sulfide vein and carbonate vein there are two types of ore host quartz vein and altered rocks ore minerals are native gold electrum pyrite marcasite arsenopyrite hematite limonite and trace amounts of pyrargyrite polybasite naumannite cerargyrite sphalerite chalcopyrite tetrahedrite galena pyrrhotite and clausthalite gangue minerals are mainly quartz chalcedony illite calcite siderite dolomite adularia and laumontite the main wall rock alteration is silicification and phyllic alteration carbonatization and propylitization the deposit is characterized by an enrichment relative to crustal abundance of au ag as sb bi hg se te and mo depletion in base metals cu pb and zn and a low ag au ratio 0 5 3 7 three types of fluid inclusions were recognized in quartz from the major mineralization stages liquid aqueous inclusions liquid rich two phase inclusions and small amounts of vapor rich two phase inclusions microthermometric measurements indicate that the final ice melting temperatures are 0 3 to 4 4 c corresponding to salinities of 0 5 6 9 wt nacl equiv 2 2 wt nacl equiv in average the peak temperatures of ice melting varies from 0 4 to 1 9 c corresponding to salinities of 0 7 3 1 wt nacl equiv homogenization temperatures range mainly between 120 and 240 c with an average of 190 c and a maximum of 335 c the fluid density is 0 73 to 0 95 g cm 3 and thus the estimated maximum mineralization depth is about 700 m hydrogen and oxygen isotopic compositions of the ore fluids lie within a narrow range d h2o is 98 to 116 and 18 o h2o 1 8 to 0 4 3 he 4 he ranges from 0 0218 to 0 138 ra with an average of 0 044 ra indicating that he derived predominantly from crust with negligible mantle he in the ore fluids by contrast the 40 ar 36 ar ranges from 317 7 to 866 0 suggesting that crust derived radioactive 40 ar accounts for 7 0 to 66 and atmospheric 40 ar about 43 to 93 in the ore fluids hydrogen oxygen carbon sulfur and noble gas isotopes indicate that the ore forming fluids of the axi gold deposit consisted predominantly of circulating meteoric water ore forming metals may have derived mainly from the host volcaniclastic rocks of the dahalajunshan formation and basement rocks the occurrence of adularia platy calcite and quartz or sulfide aggregates as pseudomorphs after bladed calcite in ore veins and occurrence of aqueous liquid and liquid rich and vapor rich two phase inclusions indicates that boiling of the ore forming fluid have occurred leading to supersaturation of the hydrothermal solution and deposition of ore metals this is the main mineralization mechanism for quartz vein type ores in axi the ore forming fluid was buffered to a near neutral ph in a reduced environment during mineralization the preservation of this paleozoic axi deposit and its discovery required a rapid accumulation of sediments in the basin after formation of the deposit and minimal amount of erosion after late cenozoic uplift

upper mantle seismic discontinuities and the thermal structure of subduction zones the precise depths at which seismic velocities change abruptly in the upper mantle are revealed by the analysis of data from hundreds of seismometers across the western united states the boundary near 410km depth is locally elevated that near 660 km depressed the depths of these boundaries which mark phase transitions provide an in situ thermometer in subduction zones the observed temperature contrasts require at least moderate thickening of the subducting slab near 660 km depth in addition a reflector near 210 km depth may mark the bottom of the aesthenosphere

intermediate sulfidation type base metal mineralization at aliabad khanchy tarom hashtjin metallogenic belt nw iran abstract the aliabad khanchy epithermal base metal deposit is located in the tarom hashtjin metallogenic belt thmb of northwest iran the mineralization occurs as cu bearing brecciated quartz veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation ore formation can be divided into five stages with most ore minerals such as pyrite and chalcopyrite being formed in the early stages the main wall rock alteration is silicification and chlorite argillic and propylitic alteration microthermometric measurements of fluid inclusion assemblages show that the ore forming fluids have eutectic temperatures between 30 and 52 c trapping temperatures of 150 290 c and salinities of 6 6 12 4 wt nacl equiv these data demonstrate that the ore forming fluids were medium to high temperature medium to low salinity and low density h2o nacl cacl2 fluids calculated 18o values indicate that ore forming hydrothermal fluids had 18owater ranging from 3 6 to 0 8 confirming that the ore fluid system evolved from dominantly magmatic to dominantly meteoric the calculated 34sh2s values range from 8 1 to 5 0 consistent with derivation of the sulfur from either magma or possibly from local volcanic wall rock combined the fluid inclusion and stable isotope data indicate that the aliabad khanchy deposit formed from magmatic hydrothermal fluids after rising to a depth of between 790 and 500 m the fluid boiled and subsequent hydraulic fracturing may have led to inflow and or mixing of early magmatic fluids with circulating groundwater causing deposition of base metals due to dilution and or cooling the aliabad khanchy deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the mineralization at aliabad khanchy and other epithermal deposits of the thmb formed by hydrothermal activity related to shallow late eocene magmatism the altered eocene volcanic and volcaniclastic rocks especially at the intersection of subvolcanic stocks with faults were the most favorable sites for epithermal ore bodies in the thmb

fluid inclusion studies of the chinkuashih high sulfidation gold copper deposits in taiwan epithermal high sulfidation au cu deposits at chinkuashih in northeastern taiwan are found both within pleistocene calc alkaline volcanic rocks and the miocene sedimentary rocks the deposits consist of gold copper veins of the penshan group and breccia pipes of the tushihshan changjen group primary two phase inclusions in hydrothermal quartz and secondary two phase inclusions in hydrothermal quartz as well as igneous quartz phenocrysts probably represent fluids related to mineralization these inclusions have homogenization temperatures generally between 1908c and 2808c and salinities mostly from 0 5 5 0 wt nacl eq in the penshan group microthermometric data indicate that variable amounts of boiling mixing and cooling occurred in the hydrothermal system based on the th of inclusions trapped from boiling fluids and the co contents of the inclusions the hydrostatic pressure is estimated at 6 9 7 9 mpa in the tushihshan 2 changjen group the microthermometry of sulfur gas bearing secondary two phase fluid inclusions from hydrothermal quartz shows bimodal contents for a certain th value perhaps due to the intermittent incursion of brine at depth by phreatic or phreato magmatic explosions the presence of poly phase liquid q vaporq halite sylvite opaques fluid inclusions with high th 3078c 4848c and high salinities 30 51 wt nacl eq in one sample suggests a dense brine of probable magmatic derivation circulated in the chinkuashih system halite bearing inclusions which were homogenized by vapor disappearance coexisting with low salinity vapor rich inclusions in this sample may have been trapped in an immiscibility field at vapor pressures from 7 5 to 21 5 mpa halite bearing inclusions which were homogenized by halite dissolution after the vapor disappearance may have been trapped under even greater pressures fluid inclusion gas in samples were analyzed with a qms the results of bulk analyses indicate that these inclusions contain 99 45 99 67 mol h o 0 27 0 52 mol 2 co 0 015 0 066 mol n 0 0015 0 015 mol ch and small amounts of so in three samples these data suggest that 22 4 2 the inclusion fluids are dominantly meteoric waters that interacted with host rocks and accumulated upward fluxing magmatic volatiles the fluid inclusion data indicate that the hydrothermal fluids related to the ore deposition of the high sulfidation au cu deposits at chinkuashih are characterized by the interaction of magmatic fluids with meteoric water under epithermal conditions q 1999 elsevier science b v all rights reserved

geology mineralogy and fluid inclusion data of the furtei high sulfidation gold deposit sardinia italy the epithermal high sulfidation gold deposit at furtei sardinia italy contains at least 2 15 million metric tons mt at 2 82 g t au 725 000 t oxidized ore 1 375 000 t sulfide ore and 50 000 t mixed ore potential by products are silver and copper the geology of the area features an oligocene miocene volcano sedimentary sequence including andesite porphyry domes and associated block and ash flows pyroclastic flows fall and surge deposits and interlayered epiclastic and sedimentary sequences a phreatic and or phreatomagmatic diatreme breccia also crops out in the mineralized area the volcanic rocks belong to the calc alkaline sardinian magmatism their k ar ages in the area are 23 6 to 25 5 ma hydrothermal circulation affected most of the volcano sedimentary sequence over an area of about 5 km 2 during or immediately after volcanic activity early hydrothermal activity was responsible for the acid alteration typical of high sulfidation deposits with formation of four hypogene alteration types of decreasing intensity silicification advanced argillic alteration argillic alteration and propylitization these alteration styles show a rough spatial zonation silicification consists of massive and vuggy silica veins and bodies these are controlled by preferential structural directions n 140 degrees n 40 degrees and n s and by the contacts between the andesite porphyry domes and the diatreme breccias or between domes and epiclastic pyroclastic sequences the advanced argillic alteration borders vuggy and massive silica alteration zones and is characterized by the widespread presence of kaolinite dickite minerals this alteration pervasively affects the diatreme breccia and epiclastic pyroclastic units advanced argillic alteration grades outward into argillic alteration marked by the presence of montmorillonite which passes to a districtwide propylitic alteration halo the ore stage clearly postdates hydrothermal alteration as indicated by the occurrence of ore minerals in vuggy cavities and fractures in silica bodies the furtei mineralization comprises a surficial oxidized zone of supergene nature and a deeper primary sulfide zone and is largely hosted by the diatreme breccia the sulfide zone up to 300 m of vertical extension is characterized by a vertical zoning of the mineral assemblage at higher levels pyrite enargite luzonite gold are present whereas in the deep zone the above minerals are accompanied by tennantite and tellurides native gold with 0 7 7 8 wt ag occurs as blebs in enargite and luzonite fluid inclusions indicate that the fluid present at the time of alteration and epithermal mineralization had temperatures generally between 190 degrees and 280 degrees c and relatively low salinity max 5 5 wt nacl equiv the local coexistence of liquid and vapor rich inclusions suggests boiling conditions the inclusions were trapped at depths of between 60 and 680 m below the water table the occurrence of high salinity 31 5 44 8 wt nacl equiv high temperature 390 degrees 500 degrees c inclusions in cataclastic hydrothermal quartz suggests that a dense brine of probable magmatic derivation circulated in the furtei system this is consistent with geophysical data suggesting the presence of an intrusion at approximately a 1 to 1 5 km depth a few relatively high salinity around 22 wt nacl equiv low temperature 255 degrees 275 degrees c inclusions may be the result of episodic mixing of deep saline brines with low salinity meteoric fluids late stage barite contains low salinity

refinement of the evaluation of the role of co 2 in modifying estimates of the pressure of epithermal mineralization pressure is the most important of the intensive parameters for relating epithermal mineralization to the geologic setting this paper describes the limitations on pressure and therefore depth of mineralization that may reasonably be derived from simple observations of the behavior of fluid inclusions i e the existence of ice or co 2 clathrate on the liquidus the amount of expansion or contraction of the bubble as the host inclusion is crushed in oil on the microscope stage and the freezing and homogenization temperatures for the inclusion it is based on the reasonable model that mineralization occurs from a hydrostatically pressured nacl co 2 h 2 o fluid consistent with the probability that h 2 o and co 2 are the only gases contributing significantly to the total pressure the pressure of co 2 is of course a function of co 2 content but from 100 degrees to 300 degrees c it is a surprisingly minor function of either temperature or salinity the presence of the clathrate in freezing studies of fluid inclusions indicates pressures of co 2 that add at least 1 km to the probable depth of inclusion trapping compared to that estimated from co 2 free water thus undetected i e no clathrates on cooling co 2 in fluid inclusions can nonetheless contribute very significantly to the possible depth of epithermal mineralization on the other hand the observation that fluid inclusions crushed in oil have bubbles that do not expand i e 2 at 25 degrees c demonstrates co 2 contents that could add at most a few tens of meters to the depth of mineralization

lake levels and sequence stratigraphy of lake lisan the late pleistocene precursor of the dead sea lake lisan the late pleistocene precursor of the dead sea existed from 70 000 to 15 000 yr b p it evolved through frequent water level fluctuations which reflected the regional hydrological and climatic conditions we determined the water level of the lake for the time interval 55 000 15 000 cal yr b p by mapping offshore nearshore and fan delta sediments by application of sequence stratigraphy methods and by dating with radiocarbon and u series methods during the studied time interval the lake level fluctuated between 340 and 160 m below mean sea level msl between 55 000 and 30 000 cal yr b p the lake evolved through short term fluctuations around 280 290 m below msl punctuated at 48 000 43 000 cal yr b p by a drop event to at least 340 m below msl at 27 000 cal yr b p the lake began to rise sharply reaching its maximum elevation of about 164 m below msl between 26 000 and 23 000 cal yr b p then it began dropping and reached 300 m below msl at 15 000 cal yr b p during the holocene the lake corresponding to the present dead sea stabilized at ca 400 m below msl with minor fluctuations the hypsometric curve of the basin indicates that large changes in lake area are expected at above 403 and 385 m below msl at these elevations the lake level is buffered lake lisan was always higher than 380 m below msl indicating a significantly large water contribution to the basin the long and repetitious periods of stabilization at 280 290 m below msl during lake lisan time indicate hydrological control combined with the existence of a physical sill at this elevation crossing this sill could not have been achieved without a dramatic increase in the total water input to the lake as occurred during the fast and intense lake rise from 280 to 160 m below msl at 27 000 cal yr b p

a global study of s to p and p to s conversions from the upper mantle transition zone summary long period data of the global digital seismograph network gdsn recorded over the three year period from 1984 to 1986 were studied for the occurrence of s p and p s conversions from the upper mantle transition zone that appear as precursors to teleseismic s arrivals conversions of this type were identified on a large number of single station records simple stacking of many records enhanced the appearance of converted phases and demonstrated that no major lateral variations in the nature of the transition zone exist between various tectonic regions s p and p s conversions from the 400 km discontinuity were best observed at distances between 70 and 85 while conversions from the 670 km discontinuity showed up best at distances beyond 87 the analysis of published source mechanisms and comparison with synthetic seismograms suggests that the appearance of converted phases is primarily governed by the earthquake radiation pattern phases that have undergone s p conversions beneath the receiver are best observed from dip slip events that radiate strong sv and weak p waves towards the station p s conversions beneath the source area on the other hand are frequently observed from events that radiate strong p and little sv energy towards the station and also from some strike slip events comparison of observed with synthetic seismograms suggests that the prem model of dziewonski anderson 1981 explains most of the observations observed s p and p s conversions from the 670 km discontinuity however often have larger amplitudes than in the synthetics constructive interference of converted waves with the p wave coda source radiation effects and a velocity contrast across the 670 km discontinuity which is higher than in prem may all contribute to the discrepancy

microthermometry of enargite hosted fluid inclusions from the lepanto philippines high sulfidation cuau deposit abstract the spatial relation between porphyry and high sulfidation epithermal deposits is particularly well revealed in the mankayan mineral district of northern luzon philippines where the lepanto high sulfidation cu au deposit lies over and adjacent to the far southeast fse porphyry cu au deposit consequently a study was undertaken to characterize the fluids responsible for epithermal mineralization in this environment the ore stage at lepanto consists of enargite luzonite cu 3 ass 4 pyrite tennantite tetrahedrite and chalcopyrite infrared petrography of the enargite reveals variable transparency with growth banding and twinning visible in euhedral specimens two phase liquid vapor fluid inclusions occur as primary and secondary types ranging from t h of fluid inclusions in enargite were measured from within the lateral 3 0 km and vertical 0 5 km extent of the enargite mineralization these values show a cooling trend toward the northwest away from the area over the porphyry deposit with average t h ranging from 285 c proximal to 166 c distal ice melting temperatures t m were measured using a cycling technique as ice was usually not visible in frozen inclusions apparent salinities range from 4 5 to 0 2 eq wt nacl with samples from the margins of the deposit showing a general decrease in apparent salinity with lower t h secondary fluid inclusions in quartz phenocrysts tend to have a higher average t h and lower apparent salinities compared to enargite hosted inclusion fluids from the same locations several samples of pyrite are also transparent to ir radiation and show internal features such as growth banding and in one instance a two phase liquid vapor fluid inclusion this inclusion yielded a salinity of 1 2 eq wt nacl there is a large discrepancy in t h and apparent salinities between the enargite mineralization and the subjacent porphyry deposit despite contemporaneous formation suggesting that the hot 500 c hypersaline magmatic brines associated with porphyry mineralization did not directly ascend to the elevation of the enargite deposit however absorbtion of magmatic vapors into overlying meteoric water may have created the mineralizing fluid of the lepanto deposit as this liquid moved to the northwest along the lepanto fault it was cooled and diluted by mixing with groundwater resulting in enargite deposition

origin and evolution of hydrothermal fluids in the marshoun epithermal pb zn cu ag deposit tarom hashtjin metallogenic belt nw iran abstract the marshoun epithermal pb zn cu ag deposit is located in the tarom hashtjin metallogenic belt thmb northwest iran the epithermal base metal veins are mainly hosted in eocene volcanic and volcaniclastic rocks of the karaj formation and late eocene pyroxene quartz monzodiorite the mineralization process can be divided into five stages 1 quartz chalcopyrite pyrite veins and breccias 2 quartz calcite sphalerite galena chalcopyrite pyrite veins and breccias 3 barren post ore quartz veinlets 4 barren post ore calcite veinlets and 5 supergene mineral assemblages the primary metallic minerals are pyrite chalcopyrite sphalerite and galena gangue minerals are mainly quartz calcite sericite and chlorite the main wall rock alteration is silicification intermediate argillic carbonate and propylitic alteration microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 c from fluids with salinities between 3 4 and 6 3 wt nacl equiv coexisting lv vl and v inclusions in quartz and sphalerite provide evidence for boiling in ore stage breccia and veins additionally the occurrence of bladed calcite as well as plumose and colloform crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling obtained oxygen and sulfur isotope compositions 18owater 9 2 to 1 5 34sh2s 10 0 to 5 7 indicate there was a major contribution from a magmatic component to metallogenesis the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at marshoun the marshoun deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the epithermal mineralization in the thmb are related to late eocene ca 36 37 ma shallow magmatic hydrothermal activity the altered eocene volcanic subvolcanic rocks particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at thmb

direct evolution of brine from a crystallizing silicic melt at the questa new mexico molybdenum deposit molybdenum mineralization in the southwest orebody at the questa deposit is associated with crystallization of aplite porphyry explosive brecciation and exsolution of magmatic hydrothermal fluids quartz k feldspar fluorophlogopite and molybdenite precipitated from exsolving aqueous fluids and cemented aplite porphyry and andesite wall rock clasts forming a magmatic hydrothermal breccia ore fluid inclusions in quartz in the breccia matrix trapped aqueous fluids that transported and precipitated molybdenum two fluid inclusion populations associated with molybdenite mineralization were identified the largest population commonly contains liquid vapor halite sylvite and one or more opaque daughter crystals these inclusions homogenize between 200 degrees and 500 degrees c and have a prominent mode at 360 degrees to 400 degrees c salinities vary from 31 to 57 wt percent nacl equiv low first ice melting temperatures suggest that additional fluid components possibly calcium or magnesium chlorides may be present approximately 80 percent of these inclusions homogenize by halite dissolution phase equilibria constraints require that these inclusions trapped fluids in the vapor absent field the remaining saline inclusions homogenize to liquid at temperatures above halite dissolution temperatures significantly the saline fluid did not coexist with a low density aqueous fluid a second population of inclusions contains fluids with salinities of 2 7 to 25 0 wt percent nacl equiv and homogenizes by vapor bubble disappearance vapor bubble expansion or critical behavior textural relationships and phase behavior during microthermometry indicate that these inclusions constitute a single population which formed as pressure and temperature fluctuated at near critical conditions pressure changes related to brecciation followed by crystallization and system resealing produced the observed fluids saline fluids were trapped as the system sealed following a major brecciation event these high salinity fluids were produced as the melt under pressure that increased from hydrostatic to lithostatic partitioned increasing amounts of chlorine into the exsolving aqueous fluid renewed fracturing and abrupt pressure decrease to hydrostatic conditions reduced the mass of chlorine partitioning to the exsolving fluid lower salinity fluids exsolved at near critical conditions and were trapped by inclusions that homogenize to liquid to vapor or by critical behavior the lack of cogenetic liquid and vapor rich fluid inclusions and phase equilibria constraints indicate that high salinity fluids or 57 wt nacl equiv were generated directly by the crystallizing magma and were not a product of aqueous fluid immiscibility

origin of the duvertepe kaolin alunite deposits in simav graben turkey timing and styles of hydrothermal mineralization abstract the duvertepe district located on the western end of the simav graben is the largest known fossil hydrothermal kaolin deposit in turkey active hot springs occur to the north of simav city eynal citgol nasa and geothermal fields occur to the west of the graben hisaralan kaolin in the duvertepe district formed at the expense of miocene rhyolites rhyodacites and tuffs emplaced in a tectonically active system undergoing n s extension upward fan shaped deposits of silicification and kaolin are found along fault zones and define areas of enhanced kaolinization silica sinters located above the kaolin zones suggest that hydrothermal fluids followed the fracture systems and mark outflow of geothermal waters fractured volcanic rocks rich in glass shards bear sufficient porosity and permeability for hydrothermal circulation two mineral facies kaolinite and alunite dominate the deposits which respectively include 1 kaolinite alunite quartz and 2 alunite opal ct quartz halloysite kaolinite crystals are well formed hexagonal vermiform habits and alunite crystals are idiomorphic rhombohedral forms needle and tubular shaped halloysites are common in the alunite facies the 34 s values for alunite range from 1 55 to 6 18 kaolinites have d ranging from 49 0 to 94 3 and the 18 o values range from 5 8 to 14 8 calculated formation temperatures of kaolin mineralization using 18 o values suggest that hydrothermal alteration occurred in the range of 38 to 129 c independent k ar and 40 ar 39 ar ages of alunite are concordant and indicate that alteration occurred from 20 1 to 20 6 ma in the southern part of the graben and 17 3 to 19 2 ma in the northern part these results suggest that metasomatism by steam heated hydrothermal fluids sourced by rhyolitic magma is responsible for the duvertepe kaolin and alunite deposit origins

natural versus human control on subsurface salt dissolution and development of thousands of sinkholes along the dead sea coast one of the most hazardous results of the human induced dead sea ds shrinkage is the formation of more than 6000 sinkholes over the last 25 years the ds shrinkage caused eastward retreat of underground brine replaced by fresh groundwater which in turn dissolved a subsurface salt layer to generate cavities and collapse sinkholes the areal growth rate of sinkhole clusters is considered the most pertinent proxy for sinkholes development analysis of light detection and ranging lidar digital elevation models dems and interferometric synthetic aperture radar insar allows translation of the areal growth rate to a salt dissolution rate of the salt layer revealing two peaks in the history of the salt dissolution rate these peaks cannot be attributed to the decline of the ds level instead we show that they are related to long term variations of precipitation in the groundwater source region the judea mountains and the delayed response of the aquifer system between the mountains and the ds rift this response is documented by groundwater levels and salinity variations we thus conclude that while the ds level decline is the major trigger for sinkholes formation the rainfall variations more than 30 km to the west dominate their evolution rate the influence of increasing rainfall in the judea mountains reaches the ds at a typical time lag of four years and the resulting increase in the salt dissolution rate lags by a total time of 5 6 years

identification of sinkhole development mechanism based on a combined geophysical study in nahal hever south area dead sea coast of israel seismic refraction magnetic resonance sounding mrs and the transient electromagnetic tem method were applied to investigate the geological and hydrogeological conditions in the nahal hever south sinkhole development area at the dead sea ds coast of israel microgravity and mrs results reliably reveal large karst cavity in the central part of investigated area the map of the seismic velocity shows that sinkholes in nahal hever can be divided into two major groups sinkholes close to the salt edge and sinkholes over compact salt formations between a few tens to a hundred meters from the major cavern the present study shows that the formation of sinkholes of the first group is caused by soil collapsing into the cavern in the area occupied by sinkholes of the second group karst was not detected either by mrs or by seismic diffraction methods tem results reveal shallow clay layer saturated with ds brine underlain sinkholes of this group it allows suggestion that the water drainage and intensive water circulation during rain events wash out fine rock particles from the unsaturated zone into the pre existing cavern initiating the formation of sinkholes of the second group karst development takes place at a very low bulk resistivity 1 m of the ds aquifer attesting to the fact that pores are filled with a highly saline solution refilling of the karstic cavities with collapsing and flushed soil slows down sinkhole development in the area the sinkhole formation cycle at the site is estimated at 10 years sinkhole development throughout the studied area is triggered by a drop in the level of the ds which reduces the head of the confined aquifer and the strength of the overlain sediments

holocene climate variability and cultural evolution in the near east from the dead sea sedimentary record abstract a comprehensive record of lake level changes in the dead sea has been reconstructed using multiple well dated sediment cores recovered from the dead sea shore interpreting the lake level changes as monitors of precipitation in the dead sea drainage area and the regional eastern mediterranean palaeoclimate we document the presence of two major wet phases 10 8 6 and 5 6 3 5 cal kyr bp and multiple abrupt arid events during the holocene the arid events in the holocene dead sea appear to coincide with major breaks in the near east cultural evolution at 8 6 8 2 4 2 3 5 cal kyr bp wetter periods are marked by the enlargement of smaller settlements and growth of farming communities in desert regions suggesting a parallelism between climate and near east cultural development

variability of p660s phases as a consequence of topography of the 660 km discontinuity abstract records from the broad band nars nl array deployed in the netherlands western germany and belgium have been analyzed for p to s converted phases from the 660 km discontinuity p660s no individual seismogram from this array shows a clear p660s phase stacks of up to 113 crosscorrelograms show p660s energy that is weak in comparison with similar stacks elsewhere very high amplitude observations of p660s in single seismograms from the same region have been made in a previous study paulssen 1985 geophys res lett 12 709 712 paulssen 1988 j geophys res 93 10489 10500 such variations may be due to relief on the 660 km discontinuity in this paper we quantify the effects of different topographies on the time delays amplitudes and waveforms of the direct p wave as well as on the p660s converted wave synthetic p and p660s waveforms are calculated by applying a kirchhoff helmholtz integration over the wave fields at the 660 km discontinuity interface for topography on scales of a few hundreds of kilometers the effects on the p wave are very small compared with those on the p660s phases time delays focused and defocused amplitudes and waveform distortion of p660s phases influenced by such topography diminish the coherence of p660s in synthetic stacks our results show that topography of the 660 km discontinuity with dominant scale lengths of a few hundreds of kilometers and variations in depth of 15 km to 25 km is consistent with the pattern of p660s observations in single seismograms and stacks

dead sea sinkholes an ever developing hazard sinkhole development along the western shore of the dead sea became a major concern in 1990 with the appearance of a series of holes 2 15 m diameter and up to 7 m deep in the newe zohar area one of these sinkholes below the asphalt surface of the main road along the western shore of the dead sea was opened by a passing bus repeated infilling and collapse of these holes indicated the extent of this ongoing process and the significance of this developing hazard since then sinkholes have developed in other areas including qalia ein samar ein gedi and mineral beach

sinkhole hazards along the eastern dead sea shoreline area jordan a geological and geotechnical consideration for the last four decades the level of the dead sea has been subjected to continual variation which among other important factors has led to the occurrence of much subsidence and many sinkholes in the southern dead sea area sinkhole activities occurred repetitively and were observed in open farms across roads near dwellings and near an existing factory thus causing a serious threat to the locals and farmers of the area and their properties this paper presents the main results from detailed geological and geotechnical studies of this area aerial photo interpretation and borehole drilling aided these studies parallel geophysical investigations vertical electrical sounding and seismic refraction and hydrological and hydrogeological studies were made by others in the same area to also investigate this phenomenon it was found that sinkholes are aligned to and follow old water channels and are concentrated parallel to the recent shoreline of the dead sea the development of subsurface cavities is associated mainly with the variation in the level of the dead sea over the four past decades the presence of regional salt intrusion under the surface of salt beds the fluctuation of the water table and continuous dissolution and the active tectonism of the area moreover this work showed that the area is still under active sinkhole hazards and other parts of the area will be inevitably affected by sinkholes in the future no practical engineering solution to this problem is feasible

the upper mantle discontinuities correlated or anticorrelated the discontinuities in the earth s upper mantle at 410km and 660km are frequently considered as phase changes which are exothermic and endothermic respectively from this follows that at laterally changing temperatures both discontinuities move in opposing vertical directions that means they are negatively correlated we attempt to test this hypothesis using travel times of seismic waves converted at both discontinuities underneath seismic stations the broadband stations used are located in areas of high e g western us and low heat flow e g central asia sclater et al 1980 we observe a clear positive correlation of the conversion times of both discontinuities which can however be explained with known lateral velocity changes above 410km from the scatter of our data we conclude that the limit of a possibly existing and negatively correlated topography of the two discontinuities is about 28km this is in contrast to recently claimed observations of about 35 km anticorrelated topography in the western pacific revenaugh jordan 1991 stammler kind 1992

silicate replacive high sulfidation massive sulfide orebodies in a porphyry cu au system bor serbia the cu au deposit of bor serbia represents a continuum of mineralization styles from porphyry style ore occurring in quartz magnetite chalcopyrite veins and chalcopyrite disseminations to high sulfidation epithermal cu au ores in pyrite chalcopyrite and anhydrite sulfide veins decisive for the great economic importance of bor is the presence of exceptionally rich high sulfidation massive sulfide orebodies composed of pyrite covellite chalcocite digenite and minor anhydrite and enargite they form irregular bodies measuring 0 5 10 million tons of ore grading up to 7 cu hosted by andesites and surrounded by intense argillic alteration this study focuses on a small but rich underground orebody mined out recently where limited drillcore is preserved for quantitative geochemical study this paper documents the vein relationships within the deep porphyry style orebody of borska reka the transitional porphyry epithermal veins and the overlying and laterally surrounding epithermal massive sulfides of the bor deposit geological observations indicate that the formation of massive sulfide orebodies concludes the ore formation mass balance calculations recast into geologically realistic bulk fluid rock reactions confirm textural evidence that near isovolumetric replacement of andesite host rocks is the dominant formation mechanism of massive sulfide orebodies at bor whereby all lithophile elements including si are dissolved and only ti stays relatively immobile while net volume changes for individual mineralization styles within the massive sulfide orebody vary from 16 volume loss to 127 volume gain overall volume change for the whole massive sulfide orebody was probably slightly negative brecciation is important only as means of creating channelways for reactive fluid that turns the andesite protolith into massive sulfide whereas net breccia infill occurred only locally

identification of sinkhole origin using surface geophysical methods dead sea israel abstract the western and eastern dead sea ds shores are hit by intensive sinkhole collapse during the last 30 years the first researchers have considered a piping model of sinkhole formation based on washing out fines by underground flows then it was proved by numerous boreholes and seismic refraction surveys that sinkholes along western shore are caused by dissolution of buried salt layers and collapse of the surface into dissolution caverns however signs of piping and subsurface flows were observed in some sinkhole sites in this paper we show that robust identification of sinkhole origin can be achieved when proper geophysical methodologies and their application are used we consider newe zohar site located in the southern part of the dead sea in order to analyse different signs of sinkhole formation models using various geophysical methods the seismic refraction method srfr enables us to discover the salt layer based on longitudinal wave velocity vp the multichannel analysis of surface waves masw method allows to determine the salt layer properties rigidity based on shear wave velocity vs finally the time electromagnetic tem method allows us to evaluate the degree of aggressiveness of groundwater with respect to salt based on bulk resistivity values here we analyse competitive models of sinkhole formation and suggest geophysical methods to determine the subsurface geomorphology we show that various geophysical methods should be applied in concert to explore the subsurface for the occurrence of salt as well as understanding sinkhole formation processes the underlying voids along the dead sea are shown to form primarily by salt dissolution with some cases of additional piping applying the right geophysical parameters for groundwater and salt sediments classification proves to be crucial for understanding the subsurface geomorphology

geology geochemistry and origin of high sulfidation cu au mineralization in the nansatsu district japan the nansatsu district of southern kyushu has been the site of calc alkaline volcanism for the last 10 m y shifting eastward with time associated hydrothermal activity followed deposition of the volcanic host rocks by about 0 5 m y and was characterized by interaction of magmatic fluids with meteoric water under epithermal conditions resulting in the formation of high sulfidation cu au deposits at kasuga iwato and akeshi the orebodies consist of 95 wt percent sio 2 and result from leaching of the original andesite lava and pyroclastic flows by acid chloride sulfate waters these are inferred to have formed when magmatic vapors containing hcl and so 2 condensed into meteoric water the residual silica now quartz orebodies are best developed where the host was initially permeable the margins of the quartz bodies are abrupt with narrow 1 2 m halos representing the reaction front of acid waters isochemically dissolving the host rock the halo comprises alunite strongly zoned in na and k with p rich cores dickite and or kaolinite or pyrophyllite grading out into illite and interlayered illite smectite clays and finally propylitic alteration this pattern is characteristic of deposits of this type throughout the world for example at summitville colorado and lepanto philippines mineralization occurred after initial leaching by the vapor condensates with metals transported by a dense magmatic fluid mixing with meteoric water and the subsequent temperature decrease caused the general decrease in grade toward the margin of the quartz bodies ore grades are restricted to the quartz bodies gold is most closely associated with enargite and pyrite later minerals include covellite and then sulfur the last stage of activity was steam heated with descending waters oxidizing sulfides to goethite and locally remobilizing au into fractures this varies in degree between deposits erosion exposed the orebodies to supergene weathering continuing the sulfide oxidation and au remobilization stable isotope results indicate that hypogene alunite formed from a mixture of magmatic fluid delta 18 o 7 or 2 per thousand delta d 25 or 5 per thousand similar to nearby active volcanic discharges with local meteoric water in contrast the clays in the marginal halo have isotopic compositions indicating a delta 18 o shift of 6 to 8 per mil from local meteoric water values probably due to water rock interaction and the delta 18 o values of residual silica quartz may also be due to meteoric water domination fluid inclusion study of postmineralization quartz crystals indicates that the fluids had a salinity of about 1 wt percent nacl equiv during late quartz growth though there is evidence in one sample for higher salinity fluid having been present up to 30 wt percent nacl equiv some inclusions contain daughter minerals of halite and sulfur the t h values of over 1 000 measurements on late quartz from the ore zones indicate that the mean temperature during that stage ranged from 200 degrees c at akeshi to about 200 degrees c at iwato and 230 degrees c at kasuga the presence of vapor rich inclusions some with t hv similar to t hl indicate the presence at times of a two phase fluid in the center of the ore zones with depths of about 150 to 300 m below the paleowater table the mineralizing fluid was relatively oxidized sulfide sulfate ratio about 3 1 close to pyrite alunite coexistence under these redox conditions a ph of 3 and over a temperature range of 200 degrees to 300 degrees c aucl 2 super complexing may dominate over hau sh 2 at salinities above about 2 wt percent nacl several conditions are conducive for high sulfidation mineralization to occur 1 a crystallizing magma exsolves a fluid with lower pressure conditions favoring metal fractionation from melt to fluid 2 the exsolved fluid separates into vapor and saline liquid phases due to immiscibility with the latter being metal rich 3 the gas rich hcl and so 2 h 2 s vapor ascends to the surface with at least a portion condensed into meteoric water forming an acid fluid which leaches the host rock to create permeable zones for later mixing and 4 the dense metal bearing fluid also ascends into this leached zoned and precipitates cu sulfosalts sulfides and au upon mixing with meteoric water if the saline liquid is not released from its source adjacent to the magma due to lack of fracturing or if there is a strong hydraulic gradient caused by high relief only the vapor related stage may occur this will leave leached barren rock which is characteristic of many eroded volcanic terranes

cave detection and 4 d monitoring a microgravity case history near the dead sea sinkholes large open holes that result from the earth simply collapsing are a serious environmental problem and hazard around the dead sea figure 1 the largest is about 30 m in diameter and 15 m deep figure 2 the most alarming case is a recent collapse on both sides of the main highway at e n gedi a popular destination for recreation and tourism sinkholes initially opened at a campsite east of the road figure 3 subsequently several sinkholes opened west of the road in a palm grove warning of a possible collapse of the highway

sinkholes subsidence and subrosion on the eastern shore of the dead sea as revealed by a close range photogrammetric survey abstract ground subsidence and sinkhole collapse are phenomena affecting regions of karst geology worldwide the rapid development of such phenomena around the dead sea in the last four decades poses a major geological hazard to the local population agriculture and industry nonetheless many aspects of this hazard are still incompletely described and understood especially on the eastern dead sea shore in this work we present a first low altitude our analysis reveals a kilometer scale sinuous depression bound partly by flexure and partly by non tectonic faults the estimated minimum volume loss of this subsided zone is 1 83 106 m3 with an average subsidence rate of 0 21 m yr 1 over the last 25 years sinkholes in the surveyed area are localized mainly within this depression the sinkholes are commonly elliptically shaped mean eccentricity 1 31 and clustered nearest neighbor ratio 0 69 their morphologies and orientations depend on the type of sediment they form in in mud sinkholes have a low depth to diameter ratio 0 14 and a long axis azimuth of nne ne in alluvium sinkholes have a higher ratio 0 4 and are orientated nnw n from field work we identify actively evolving artesian springs and channelized sediment laden groundwater flows that appear locally in the main depression consequently subrosion i e subsurface mechanical erosion is identified as a key physical process in addition to dissolution behind the subsidence and sinkhole hazard furthermore satellite image analysis links the development of the sinuous depression and sinkhole formation at ghor al haditha to preferential groundwater flow paths along ancient and current wadi riverbeds