multiphase u pb geochronology of sintered breccias from the steen river impact structure canada mixed target considerations for a jurassic cretaceous boundary event abstract in situ u pb geochronology has been conducted using laser ablation inductively coupled mass spectrometry la icp ms on shocked and thermally metamorphosed apatite titanite and zircon grains from the steen river impact structure canada the dated relict mineral phases occur within impact melt bearing breccias that underwent post deposition sintering at 450 c t

geochemical signals of the late jurassic marine mjolnir impact of the only seven submarine impact craters that have been found globally the mjolnir crater is one of the best preserved and retains crater and ejecta geochemical studies organic pyrolysis using the rock eval technique and xrf analysis for major minor and trace elements of the institute for petroleum research iku core 7430 10 u 01 that was taken from a drillhole located 30 km north northeast of the crater rim show gradual establishment of anoxic sea floor conditions through the late jurassic these poorly ventilated water conditions were overturned due to the mjolnir impact event waves and currents transported impact glass which is now partly weathered to smectite into the depositional area where the drillhole is located the succeeding crater collapse transported impact material e g shocked quartz and ir from the crater rim and deeper levels to the core site normal marine depositional conditions were established a short time after the crater collapsed

the effect of crystal melt partitioning on the budgets of cu au and ag we have performed five separate sets of experiments to elucidate the effects of magnetite ulvospinel magnetite solid solution and pyrrhotite crystallization on the budgets of au cu and ag at magmatic conditions the experiments were done in both hydrous and anhydrous assemblages at temperatures between 800 and 1050 c pressures from ambient to 140 mpa log f o2 from nno 0 25 to nno and log f s2 from 1 5 to 3 0 nernst type partition coefficients 1 at 800 c in a water saturated assemblage are d agmt melt 2 10 4 2 10 9 d cumt melt 0 82 0 69 d cuusp melt 26 17 d auusp melt 50 31 d cupo melt 174 25 nernst type partition coefficients 1 at 1050 c in an anhydrous assemblage are d cupo melt 200 d agpo melt 58 8 d aupo melt 120 50 the calculated values for d auusp melt and d cuusp melt indicate that the addition of ti to magnetite increases significantly the au and cu scavenging potential of ulvospinel relative to end member magnetite partition coefficients for cu and au between pyrrhotite and melt indicate that a temperature change from 1050 to 800 c in an anhydrous and hydrous assemblage respectively results in no observable change in cu partitioning the calculated partition coefficients are used to model the effect of crystal fractionation on the concentrations of ag cu and au model results suggest that the co crystallization of magnetite and pyrrhotite sequester no more than 2 ag 7 cu and 37 au from the melt over the first 25 solidification if the melt reaches volatile saturation after 25 crystallization the presence of end member magnetite and pyrrhotite do not appear to inhibit the cu au and ag ore potential of the magma ulvospinel magnetite however may reduce the au concentration in the melt by approximately one third relative to its initial value that decreases the overall au available to partition into the volatile phase

tsunami generation and propagation from the mjolnir asteroid impact in the late jurassic period about 142 million years ago an asteroid hit the shallow paleo barents sea north of present day norway the geological structure resulting from the impact is today known as the mjlnir crater the present work attempts to model the generation and the propagation of the tsunami from the mjolnir impact a multi material hydrocode sova is used to model the impact and the early stages of tsunami generation while models based on shallow water theories are used to study the subsequent wave propagation in the paleo barents sea we apply several wave models of varying computational complexity this includes both three dimensional and radially symmetric weakly dispersive and nonlinear boussinesq equations as well as equations based on nonlinear ray theory these tsunami models require a reconstruction of the bathymetry of the paleo barents sea the mjolnir tsunami is characteristic of large bolides impacting in shallow sea in this case the asteroid was about 1 6 km in diameter and the water depth was around 400 m contrary to earthquake and slide generated tsunamis this tsunami featured crucial dispersive and nonlinear effects a few minutes after the impact the ocean surface was formed into an undular bore which developed further into a train of solitary waves our simulations indicate wave amplitudes above 200 m and during shoaling the waves break far from the coastlines in rather deep water the tsunami induced strong bottom currents in the range of 30 90 km h which presumably caused a strong reworking of bottom sediments with dramatic consequences for the marine environment

gold speciation and transport in geological fluids insights from experiments and physical chemical modelling this contribution provides an overview of available experimental thermodynamic and molecular data on au aqueous speciation solubility and partitioning in major types of geological fluids in the earth s crust from low temperature aqueous solution to supercritical hydrothermal magmatic fluids vapours and silicate melts critical revisions of these data allow generation of a set of thermodynamic properties of the auoh aucl 2 auhs and au hs 2 complexes dominant in aqueous hydrothermal solutions however other complexes involving different sulphur forms chloride and alkali metals may operate in high temperature sulphur rich fluids vapours and melts the large affinity of au for reduced sulphur is responsible for au enrichment in s rich vapours and sulphide melts which are important gold sources for hydrothermal deposits thermo dynamic speciation and partitioning data and their comparison with au and s contents in natural fluid inclusions from magmatic hydrothermal gold deposits provide new constraints on the major physical chemical parameters temperature pressure salinity acidity redox and ubiquitous fluid components sulphur carbon dioxide arsenic affecting au concentration transport precipitation and fractionation from other metals in the crust the availability and speciation of sulphur and their changes with the fluid and melt evolution are the key factors controlling gold behaviour in most geological situations

ore metal redistribution by hydrocarbon brine and hydrocarbon halide melt phases north range footwall of the sudbury igneous complex ontario canada we report methane dominant hydrocarbon fluid inclusions ch4 c2h6 c2h2 c3h8 coexisting with primary brine inclusions and secondary halide melt solid nacl inclusions in au pt rich quartz sulfide epidote alteration veins associated with the footwall style cu pge platinum group element au deposits at the fraser mine north range of the sudbury igneous complex evidence for coentrapment of immiscible hydrocarbon brine and hydrocarbon halide melt mixtures is demonstrated a primary ch4 brine assemblage was trapped during quartz growth at relatively low t min ttrapping 145 315 c and p max ptrapping 500 bar prior to the crystallization of sulfide minerals in the veins secondary inclusions contain solid halite and a mixture of ch4 c2h6 c2h2 and c3h8 and were trapped at a minimum t of 710 c the halite inclusions may represent halide melt that exsolved from crystallizing sulfide ores that texturally postdate by replacement early alteration quartz hosting the primary lower t brine ch4 assemblage laser ablation icp ms analyses show that the brine hydrocarbon and halide melt inclusions contain significant concentrations of cu 0 1 1 wt range au bi ag and pt all 0 1 10 ppm range cu pt and cu au ratios in the inclusions are significantly up to 4 log units lower than in the host alteration veins and adjacent massive sulfide ore veins suggesting either 1 early cu loss from the volatiles by chalcopyrite precipitation or 2 enhanced au and pt solubilities relative to cu at the temperatures of entrapment concentration ratios between coexisting brine and ch4 inclusions c rm elem rm brine c rm elem rm ch 4 are lower for cu au bi and ag than for other elements na ca fe mn zn pb indicating that during interaction with the brine the hydrocarbon phase was enriched in ore metals the high concentrations of ore metals in hydrocarbon brine and halide melt phases confirm that both aqueous and non aqueous volatiles were carriers of precious metals in the sudbury environment over a wide range of temperatures volatile evolution and magmatic sulfide differentiation were clearly part of a single continuous process in the sudbury footwall the exsolution of h2o poor volatiles from fractionated sulfide liquid may have been a principal mechanism controlling the final distribution of pge and au in the footwall ore systems the study reports the first measurements of precious metal concentrations in fluid inclusions from a magmatic ni cu pge environment the sudbury district

geochemical facies analysis of fine grained siliciclastics using th u zr rb and zr rb sr ratios abstract abundance of the trace elements zr rb sr th and u may provide insight into the sedimentological origin of fine grained siliciclastic sediments provided that the units are derived from similar source areas as demonstrated here with suites of the fine grained jurassic and cretaceous rocks from the barents sea and svalbard zr rb ratios can be interpreted to indicate grain size variations while zr rb sr values reflect variations in the siliciclastic versus carbonate contents the th u ratio can be applied as an indicator of the redox conditions in 3d plots such as presented here the interplay between these geochemical factors can be interpreted in terms of the sedimentological evolution of the depositional basin the geochemical facies analyses show that similar depositional conditions existed on the jurassic shelf in the two studied localities the succeeding prodeltaic cretaceous beds were generally coarser grained and deposited in ventilated depositional conditions

sedimentary signatures and processes during marine bolide impacts a review abstract studies of submarine impact craters resulting from impacts of comets or asteroids demonstrate that the presence of water and the physical properties of target rocks have a major influence on sedimentary processes associated with meteorite impacts this results in difference in sedimentary signature of bolide impacts in marine environments compared to subaerial impact craters in subaerial impacts the targets are commonly hard rocks frequently of igneous and or metamorphic origin whereas in submarine impacts the targets are mostly unconsolidated or poorly lithified sediments or sedimentary rocks with high volumes of pore water such differences result in variability in crater morphology and in sedimentary processes inside and outside the impact area impacts in shallow water marine neritic environments produced craters with low or absent rims and wide and shallow brims as characterize by both the montagnais on the scotian shelf the mjolnir in the barents sea 45 and 40 km in diameter respectively and the chesapeake bay 90 km in diameter lack of elevated rims is thought to be the result of current reworking and resurge of the water back into the excavated cavity as the water in the crater is vaporized during this process resurge gullies can be cut across the rim while mass and debris flows turbidites and other gravity deposits are produced as results of tsunami and crater wall and central high collapse during and after the crater excavation stage such deposits are found both within and outside the crater structure the only difference between gravity deposits triggered by an impact or other rare events such as earthquakes is the admixture of various melt particles and possible enrichments in iridium in the former impacts near the shelf edge may cause partial collapse of the continental margin as shown by the montagnais and chicxulub impacts some of the gravity and debris flows generated by margin collapse may be channelized with final deposits up to several hundred meters thick extending for hundreds of kilometers from the impact site other impact features such as shatter cones tektites spherules and ni spinels shocked quartz isotropication and partial melts are common to both submarine and subaerial impacts theoretical calculations of the destructive forces of mega tsunami waves triggered by meteorite impact in the ocean greatly exceed those based on geologic evidence a dearth of gigantic tsunami evidence for the chicxulub impact outside of the gulf of mexico where from theoretical modelling the maximum near bottom orbital velocity of water flow crossing the deep north atlantic basin should have been 1 m s could be the result of the mitigating effect of the bathymetry of surrounding area causing wave diffraction and interference calculated maximum horizontal orbital velocity near the seafloor at the shelf for the montagnais impact is 22 m s for a 200 m high wave 5 5 m s for a 50 m high wave at 500 km decreasing to 0 5 m s at 1000 km strong enough to scour the deep ocean bottom and produce distinct erosion surfaces and disconformities in marine sedimentary record however lack of cores across impact horizon prevents confirmation of occurrence of such bottom water flows

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

the partitioning behavior of silver in a vapor brine rhyolite melt assemblage abstract the partitioning of silver in a sulfur free rhyolite melt vapor brine assemblage has been quantified at 800 c pressures of 100 and 140 mpa and f o 2 nno nickel nickel oxide silver solubility 2 in rhyolite increases 5 fold from 105 21 to 675 98 g g as pressure increases from 100 to 140 mpa nernst type partition coefficients d ag i j 2 describing the mass transfer of silver at 100 mpa between vapor and melt brine and melt and vapor and brine are 32 30 1151 238 and 0 026 0 004 respectively at 140 mpa values for d ag i j 2 for vapor and melt brine and melt and vapor and brine are 32 10 413 172 and 0 06 0 03 respectively apparent equilibrium constant values 2 describing the exchange of silver and sodium between vapor and melt k ag na v m at 100 and 140 mpa are 105 68 and 14 6 the average values 2 for silver and sodium exchange between brine and melt k ag na b m at 100 and 140 mpa are 313 288 and 65 12 these data indicate that the mass transfer of silver from rhyolite melt to an exsolved volatile phase s is enhanced at 100 mpa relative to 140 mpa suggesting that decompression increases the silver ore generative potential of an evolving silicate magma model calculations using the new data suggest that the evolution of low density aqueous fluid i e vapor may be responsible for the the silver tonnage of many porphyry type and perhaps epithermal type ore deposits for example halter et al halter w e pettke t and heinrich c a 2002 the origin of cu au ratios in porphyry type ore deposits science 296 1842 1844 used detailed silicate and sulfide melt inclusion and vapor and brine fluid inclusions analyses to estimate a melt volume on the order of 15 km3 to satisfy the copper budget at the bajo de la alumbrera copper gold silver ore deposit using their melt volume estimate with the data presented here model calculations for a 15 km3 felsic melt saturated with pyrrhotite and magnetite suggest that a low salinity magmatic vapor may scavenge on the order of 7 1012 g of silver from the melt this quantity of silver exceeds the discovered 2 109 g of ag at alumbrera calculated tonnages for numerous other deposits yield similar results the excess silver in the vapor remaining after porphyry formation is then available to precipitate at lower ptconditions in the stratigraphically higher epithermal environment these data suggest that silver and perhaps other ore metals in the porphyry epithermal continuum may be derived solely from the time integrated flux of dominantly low salinity vapor exsolved from a series of sequential magma batches

the mjolnir marine impact crater porosity anomaly abstract we have developed a quantitative model for the porosity change induced by the mjolnir impact using density and seismic traveltime distributions and postimpact sediment deformation compared with the surrounding undisturbed platform sediments the porosity increased immediately after impact up to 6 3 in the collapsed and brecciated crater periphery whereas porosity decreased by 1 in the dense central uplift following impact the crater was progressively buried by a 2 2 5 km thick overburden which caused radially varying differential compaction among the disrupted sedimentary rocks this compaction has significantly affected the postimpact crater evolution and decreased the porosity anomaly to values of 2 5 in the periphery and 2 2 in the center high resolution seismic profiles reveal possible gas related seismic amplitude anomalies spatially related to the 13 33 km3 excess pore space in impact deformed strata along the crater periphery potential plays may include lower to middle jurassic sands structurally trapped by impact generated tilted fault blocks and the synimpact extensively fractured allochthonous breccia however the crater is a very high risk hydrocarbon prospect because reservoir properties may have been destroyed by the deep mesozoic burial followed by large scale cenozoic uplift and erosion nonetheless the mjolnir porosity anomaly provides new data about the postimpact crater deformation similar data are almost entirely absent from the terrestrial impact record

synthetic fluid inclusions viii vapor saturated halite solubility in part of the system nacl cacl2 h2o with application to fluid inclusions from oceanic hydrothermal systems abstract halite solubility along part of the vapor saturated liquidus in the system nacl cacl 2 h 2 o has been determined using the synthetic fluid inclusion technique data allow the construction of liquidus isotherms for temperatures up to 500 c and bulk compositions containing 60 wt total salt and as much as 25 wt cacl 2 combined with previous data for the binary system nacl h 2 o and for the ternary system nacl cacl 2 h 2 o in the low salinity low temperature region a preliminary ternary phase diagram can be constructed that remains incomplete only in the cacl 2 rich region results are applied to the interpretation of saline fluid inclusions from quartz veins in oceanic metagabbros and can be applied to many other natural inclusions containing aqueous solutions with nacl and cacl 2 the dominant solutes microthermometric measurements at equilibrium of the melting temperature of ice tm ice and of the dissolution temperature of halite tm halite are sufficient to determine the bulk composition of the nacl cacl 2 h 2 o fluid

copper deposition during quartz dissolution by cooling magmatic hydrothermal fluids the bingham porphyry abstract scanning electron microscope cathodoluminescence imaging is used to map successive generations of fluid inclusions in texturally complex quartz veinlets representing the main stage of ore metal introduction into the porphyry cu au mo deposit at bingham utah following conventional fluid inclusion microthermometry laser ablation inductively coupled plasma mass spectrometry la icpms is applied to quantify copper and other major and trace element concentrations in the evolving fluid with the aim of identifying the ore forming processes textures visible in cathodoluminescence consistently show that the bulk of vein quartz q1 characterized by bright luminescence crystallized early in the vein history cu fe sulfides are precipitated later in these veins in a microfracture network finally filled with a second generation of dull luminescing q2 quartz mapping of brine and vapor inclusion assemblages in these successive quartz generations in combination with la icpms microanalysis shows that the fluids trapped before and after cu fe sulfide precipitation are very similar with respect to their major and minor element composition except for copper copper concentrations in inclusions associated with ore formation drop by two orders of magnitude in a tight pressure temperature interval between 21 and 14 mpa and 425 350 c several hundred degrees below the temperature of fluid exsolution from the magma copper deposition occurs within a limited p t region in which sulfide solubility shows strong normal temperature dependence while quartz solubility is retrograde this permits copper sulfide deposition while secondary vein permeability is generated by quartz dissolution the brittle to ductile transition of the quartz feldspar rich host rocks occurs in the same temperature range which further enhances vein reactivation and promotes cooling and expansion of fluids ascending across the transition from lithostatic to hydrostatic conditions

extraterrestrial impact events the record in the rocks and the stratigraphic column abstract the known terrestrial impact record is a biased sample of a much larger population of impact events the biases are due to the modifying effects of terrestrial geologic processes coupled with incomplete searches for impact structures and impact related materials terrestrial impact structures have the same basic forms as impact craters on the other planets of the inner solar system but because of post impact modification by terrestrial geologic process are recognised by the occurrence of shock metamorphic effects in some cases siderophile anomalies have been identified in impact lithologies and have been used to estimate the composition of the impacting body similar shock metamorphic effects and a siderophile anomaly in k t boundary materials are indicative of a major impact event which has been correlated with the formation of the chicxulub structure mexico evidence of a small number of other impacts occur in the stratigraphic record most commonly as tektite or microtektite horizons in some cases they are known to be accompanied by geochemical anomalies in other cases a number of ir anomalies have been reported in the stratigraphic record but there is no confirmatory evidence that they are due to impact the majority of known impact events in the stratigraphic record are from relatively recent geologic time logic dictates however that many more impacts must be recorded in terrestrial sediments and model calculations indicate that relatively small impacts d 20 km have the potential to cause atmospheric blow out and thus global dispersion of some of the impact products geochemical detection however of such events may not be easy in some cases because of relatively small absolute signals against the background of the daily infall of cosmic material in addition non chondritic bodies may result in no appreciable geochemical anomaly in view of this any claim to a geochemical signature of impact in the stratigraphic record should be accompanied by a physical search for impact materials although in the case of impacts into oceanic crust this too will be difficult given the k t experience however and the fact that large scale impact on earth is a natural consequence of the character of the solar system the potential of impacts to provide local and global marker horizons can not be ignored similarly the fact that impacts may have the potential to result in short term biologic or climatic excursions can not be dismissed arbitrarily when considering the causes of such phenomena as stable isotope anomalies in the stratigraphic record

the effect of fluid chemistry on quartz microcrack lifetimes abstract metamorphic porosity consists of a branching hierarchy of primary features grain boundaries secondary features 3 and 4 grain junction tubules tertiary features microcracks and higher order features fractures while some of these features are rarely open to bulk fluid flow e g boundaries higher order features are open to fluid flow for timescales which vary significantly as a function of temperature pressure and fluid and rock chemistry the kinetics of microcrack healing in quartz between 300 600 c at 200 mpa increases as a function of fluid chemistry in the following order co 2 h 2 o 2 o m nacl 2 m cacl 2 6 m nacl changes in fluid chemistry which increase quartz solubility correlate with increased rates of healing these observations suggest that local redistribution of quartz occurs by solution precipitation driven by gradients in curvature along the crack surface and is possibly rate limited by pore fluid diffusion however the effect of crack geometry is larger than the effect of fluid chemistry at elevated temperatures and pressures aqueous fluids with elevated nacl concentrations can penetrate pervasively into polycrystalline quartz along a branching hierarchy consisting of episodically open fractures connected to 3 and 4 grain junction tubule networks while pure water or h 2 o co 2 fluid can only infiltrate pervasively along episodically open fractures 1 at lower temperatures and pressures 3 and 4 grain tubule networks in polycrystalline rocks may be closed to all fluids limiting fluid infiltration to microfacture networks lifetimes of quartz microcracks in all these fluids p fluid p confining is geologically short even at temperatures as low as 200 c

a possible tsunami deposit around the jurassic cretaceous boundary in the boulonnais area northern france abstract an unusual succession of facies locally deposited around the jurassic cretaceous boundary in the boulonnais northern france is attributed to a tsunami event by comparison with recent tsunami deposits this sedimentary succession includes basal erosion with reworked lithified blocks soft sediment deformations an erosional conglomerate overlain by wood fragments and clays containing continental and marine fossils in one setting and conglomerate with mixed fauna in an other setting the tsunami probably affected the coast of the boulonnais area of the london brabant massif the origin of the event is unknown it was most probably triggered by an earthquake but other origins such as volcanic eruptions a giant landslide or even the impact of an extraterrestrial bolide into the ocean may also be considered

synthetic fluid inclusions in natural quartz i compositional types synthesized and applications to experimental geochemistry synthetic fluid inclusions having a wide range of geologically applicable compositions in the c o h s na k ca cl cu fe system have been formed by healing fractures in inclusion free natural quartz and by precipitating new quartz overgrowths on an original seed crystal inclusion types synthesized include 1 1 liquid rich pure h2o inclusions of primary and secondary origin 2 2 pure h2o inclusions with the critical density 3 3 liquid rich inclusions containing undersaturated aqueous solutions of nacl or kcl or cacl2 or mixtures of the three salts 4 4 h2o nacl inclusions containing halite daughter minerals 5 5 h2o nacl kcl inclusions containing halite and sylvite daughter minerals 6 6 h2o co2 inclusions of various compositions containing liquid h2o and either co2 vapor or co2 liquid or both at 25 c 7 7 h2o co2 nacl inclusions containing an aqueous phase liquid and vapor co2 and halite at 25 c 8 8 c o h inclusions containing liquid h2o a co2 ch4 liquid phase and graphite daughter minerals at 25 c 9 9 h2o nacl inclusions that contain a chalcopyrite daughter mineral and 10 10 inclusions representing trapping of the coexisting immiscible fluids in the h2o nacl h2o co2 nacl and na c o h systems the inclusions exhibit uniform phase ratios at room temperature and the temperatures of various phase changes within individual inclusions agree with those predicted from experimental and theoretical data indicating that the inclusion fluid has the same composition and density as the parent solution these miniature autoclaves thus may be used to study various problems related to fluid inclusion research to calibrate analytical equipment used to study natural inclusions and to study phase equilibria solubility and pvt relations of a variety of chemical systems

post impact structural crater modification due to sediment loading an overlooked process post impact crater morphology and structure modifications due to sediment loading are analyzed in detail and exemplified in five well preserved impact craters mjolnir chesapeake bay chicxulub montagnais and bosumtwi the analysis demonstrates that the geometry and the structural and stratigraphic relations of post impact strata provide information about the amplitude the spatial distribution and the mode of post impact deformation reconstruction of the original morphology and structure for the mjolnir chicxulub and bosumtwi craters demonstrates the long term subsidence and differential compaction that takes place between the crater and the outside platform region and laterally within the crater structure at mjolnir the central high developed as a prominent feature during post impact burial the height of the peak ring was enhanced and the cumulative throw on the rim faults was increased the original chicxulub crater exhibited considerably less prominent peakring and inner ring crater rim features than the present crater the original relief of the peak ring was on the order of 420 570 m currently 535 575 m the relief on the inner ring crater rim was 300 450 m currently 700 m the original bosumtwi crater exhibited a central uplift high whose structural relief increased during burial current height 101 110 m in contrast to the original height of 85 110 m whereas the surrounding western part of the annular trough was subdued more that the eastern part exhibiting original depths of 43 68 m currently 46 m and 49 55 m currently 50 m respectively furthermore a quantitative model for the porosity change caused by the chesapeake bay impact was developed utilizing the modeled density distribution the model shows that compared with the surrounding platform the porosity increased immediately after impact up to 8 5 in the collapsed and brecciated crater center currently 6 due to post impact compaction in contrast porosity decreased by 2 3 currently 3 to 4 5 due to post impact compaction in the peak ring region the lateral variations in porosity at chesapeake bay crater are compatible with similar porosity variations at mjolnir crater and are considered to be responsible for the moderate chesapeake bay gravity signature annular low of 8 mgal instead of 15 mgal the analysis shows that the reconstructions and the long term alterations due to post impact burial are closely related to the impact disturbed target rock volume and a brecciated region of laterally varying thickness and depth varying physical properties the study further shows that several crater morphological and structural parameters are prone to post impact burial modification and are either exaggerated or subdued during post impact burial preliminary correction factors are established based on the integrated reconstruction and post impact deformation analysis the crater morphological and structural parameters corrected from post impact loading and modification effects can be used to better constrain cratering scaling law estimates and impact related consequences

downsizing the mjolnir impact structure barents sea norway abstract stratigraphic relationships indicate that the submarine mjolnir impact structure in the sw barents sea is of cretaceous age 142 ma and the impact palaeolatitude is estimated at 56 n though the crater has been intensively studied its dimensions at depth are uncertain density and magnetic susceptibility measurements of core samples are presented and used to interpret a newly available aeromagnetic survey and gravity data and to model the potential field anomaly data of the area jointly so as to constrain better the signature of the crater forward modelling suggests that the crater diameter is about 20 km and thus needs downscaling to about half of the earlier proposed size

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

the distribution and geochemistry of platinum group elements as event markers in the phanerozoic abstract the discovery of the platinum group element pge enrichment in the cretaceous tertiary k t boundary impact layer popularized the use of pges as geochemical event markers and prompted an explosion of interest in these elements whose geochemical behavior is poorly understood instead of concentrating on the more easily analyzed pges e g iridium many studies now include the entire group analytical methods have been improved to the point where small samples 5 g can be analyzed confidently at the sub ppb level allowing the determination of the distribution of pges in the oceans atmosphere and biosphere the presence or absence of a pge anomaly is often used as a criterion for determining whether an event horizon is impact related however to date only the k t boundary yields a distinct pge anomaly with positive interelement correlations and solar interelement ratios terrestrial sources such as volcanic emissions are also being investigated as potential contributors to pge anomalies at other phanerozoic event horizons primary signatures e g interelement ratios characteristic of the pge source may be altered during various high and or low temperature processes for example fractionation during impact melting vaporization condensation remobilization redistribution and diagenesis can obscure original signatures and make determination of the pge source difficult future research might be directed towards establishing the behavior of the pges during such processes

when a cosmic impact strikes the sea bed most bolides that collide with the earth hit the sea limited knowledge about marine target impacts hampers predictions about their perilousness this study presents geological features that are particular to craters formed at sea the features are most likely a result of the influence of the target on the cratering process marine target craters form only if the target sea is shallow enough to admit sufficient kinetic energy into the sea bed when the crater diameter is large compared to the water depth the crater resembles its counterparts that are formed on land craters formed in deeper water are concentric and often lack melt sheets and rim walls but have deposits and radial gullies formed by the resurge of the sea impacts on the deep shelf are probably much more energetic than is suggested by the dimensions of the preserved crater

mjolnir structure an impact crater in the barents sea a systematic search for impact indicators was conducted on a core of late jurassic early cretaceous sedimentary strata from the vicinity of the proposed mjolnir impact structure barents sea a 0 8 m thick section of the core was found to contain unequivocal indicators of meteoritic impact shocked quartz grains and a strong enrichment in iridium the ejecta bearing strata were discovered only 30 km north northeast of the structure within a stratigraphic interval corresponding to the seismically defined deformation event at mjolnir further study of this unusually well presented impact crater ejecta layer pair may help constrain poorly understood aspects of large magnitude meteorite impacts into the oceans 14 refs 4 figs

a study of candidate marine target impact craters in arabia terra mars previous workers have proposed that a northern ocean existed early during martian geologic history and the shorelines of that ocean would coincide roughly with the crustal dichotomy that divides the smooth northern lowlands with the cratered southern highlands arabia terra is a region on mars that straddles the crustal dichotomy and several proposed shorelines are located in the area shallow marine impact craters on mars likely would exhibit features like those on earth including characteristic morphological features that are distinctly different from that of craters formed on land common attributes of terrestrial marine impact craters include features of wet mass movement such as gravity slumps and debris flows radial gullies leading into the crater depression resurge deposits and blocks of dislocated materials crater rim collapse or breaching of the crater wall a central peak terrace or peak ring terrace and subdued topography an indicator of both age and possible flood inundation immediately following impact in this article these features have been used to evaluate craters on mars as to a possible marine origin this study used a simple quantification system to approximately judge and rank shallow marine impact crater candidates based on features observed in terrestrial analogs based on the quantification system 77 potential shallow marine impact craters were found within an area bounded by 20 n and 40 n as well as 20 w and 20 e nine exemplary candidates were ranked with total scores of 70 or more in a second smaller study area impact craters of approximately similar size and age were evaluated as a comparison and average total scores are 35 indicating that there is some morphological difference between craters inside and outside the proposed shorelines results of this type of study are useful in helping to develop a general means of classification and characterization of potential marine craters

formation of resurge gullies at impacts at sea the lockne crater sweden the lockne crater in sweden is a marine target crater formed in a shelf sea approximately 460 ma ago the crater structure consists of an inner crater surrounded by an outer inclined surface that extends to almost 12 km from the center marine craters differ in several respects from craters formed on land one special feature is the formation of resurge gullies excavated by the erosional force of the resurging sea water after the impact the formation of these gullies strongly depends on the ratio crater rim height to water depth as well as on the size of the impact structure such gullies are known from very few marine target craters at the lockne impact site four gullies are identified each of which cuts radially through the rim of the outer crater the rapid collapse of that part of the crater cavity which formed in the seawater resulted in forceful flooding of the crater the resurging seawater not only contained fallback ejecta on its way towards the cavity on the sea bottom it incorporated fractured lithologies from the sea bottom as well this entrained material disintegrated during transport and constitutes today the dominantly monomict lower part of the resurge sequence the resurge flood was highly turbulent highly erosive and developed to a probable hyperconcentrated flow or a possible water flood the erosion in the gullies proceeded as headward erosion down to the transition zone between the brecciated and the less disintegrated crystalline basement

lignin biomarker and isotopic records of paleovegetation and climate changes from lake erhai southwest china since 18 5kabp abstract a sound knowledge of paleovegetation is fundamental to better understanding of past climate variability and provides necessary background for improving predictions of future climate changes in the present study stable isotopes 13c and 15n and lignin biomarker of sedimentary organic matter som from lake erhai 25 50 n 100 10 e southwest china were determined to reconstruct paleovegetation and to find vegetation climate relationships the stable carbon isotope signatures suggested that the organic matter mostly derived from c3 plants throughout the depositional periods since 18 5 ka bp the variability of isotopic values of carbon 13c 28 8 to 23 9 and nitrogen 15n 1 2 4 1 might be related to changes in terrestrial runoff i e precipitation compositions of the alkaline cuo oxidation products of lignin showed a significant change in terrestrial vegetation from gymnosperm rich to angiosperm rich plants at lake catchments in the early holocene the lignin phenol vegetation index lpvi also indicated changes in terrestrial vegetation with few more subtle changes during the last 18 5 ka as a single proxy of entire characteristic of terrestrial vegetation in comparison to past asian monsoon records 18o record in stalagmite of dongge cave lpvi suggested a direct linkage between vegetation changes and asian monsoon variability that might be influenced by global climate changes

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

reconciling fluid inclusion types fluid processes and fluid sources in skarns an example from the bismark deposit mexico the bismark deposit 8 5 mt at 8 zn 0 5 pb 0 2 cu and 50 g t ag located in northern mexico is an example of a stock contact skarn end member of a continuum of deposit types collectively called high temperature carbonate replacement deposits the deposit is hosted by massive sulfide within altered limestone adjacent to the bismark quartz monzonite stock 42 ma and the bismark fault alteration concurrently developed in both the intrusion and limestone the former contains early potassic alteration comprising k feldspar and biotite which was overprinted by kaolinite rich veins and alteration and later quartz sericite and pyrite with minor sphalerite and chalcopyrite prograde exoskarn alteration in the limestone consists of green andradite and diopside and transitional skarn comprising red brown andradite green hedenbergite and minor vesuvinite calcite fluorite and quartz the main ore stage post dates calc silicate minerals and comprises sphalerite and galena with gangue pyrite pyrrhotite calcite fluorite and quartz the entire hydrothermal system developed synchronously with faulting fluid inclusion studies reveal several distinct temporal compositional and thermal populations in pre syn and post ore quartz fluorite and calcite the earliest primary fluid inclusions are coexisting vapor rich type 2a and halite bearing type 3a type 3b contain sylvite brine inclusions 32 to 60 total wt salts that occur in pre ore fluorite trapping temperatures are estimated to have been in excess of 400 c under lithostatic pressures of 450 bar 1 5 km depth primary fluid inclusions trapped in syn ore quartz display critical to near critical behavior type 1c have moderate salinity 8 4 to 10 9 wt nacl equiv and homogenization temperatures th ranging from 351 to 438 c liquid rich type 1a and 1b calcite bearing inclusions occur as primary to secondary inclusions predominantly in fluorite and show a range in th 104 336 c and salinity 2 7 11 8 wt nacl equiv which at the higher th and salinity ranges overlap with type 1c inclusions oxygen isotope analysis was carried out on garnet quartz and calcite plus carbon isotopes in pre syn post ore and peripheral veins pre ore skarn related garnets have a 18omineral range between 3 9 and 8 4 quartz from the main ore stage range between 13 6 and 16 0 calcite from the main ore stage has 13c values of 2 9 to 5 1 and 18o values of 12 3 to 14 1 which are clearly distinct from post ore veins and peripheral prospects that have much higher 18o 16 6 27 3 and 13c 1 3 3 1 values despite the numerous fluid inclusion types only two fluid sources can be inferred namely a magmatic fluid and an external fluid that equilibrated with limestone furthermore isotopic data does not indicate any significant mixing between the two fluids although fluid inclusion data may be interpreted otherwise thus the various fluid types were likely to have formed from varying pressure temperature conditions through faulting during exsolution of magmatic fluids late stage hydrothermal fluid activity was dominated by the non magmatic fluids and was post ore

experimental determination of au solubility in rhyolite melt and magnetite constraints on magmatic au budgets the solubility of au metal in rhyolite melt and coexisting magnetite has been determined at 800 c 140 mpa and f 0 2 nno in a au metal saturated sulfur free vapor brine silicate melt system whole crystals of magnetite suspended within quenched rhyolite glass were analyzed by la icp ms these data yield a solubility of au in magnetite on the order of 2 g g the solubility of au metal in rhyolite melt hosting the magnetite crystals is on the order of 500 ng g these data indicate a partition coefficient for au between magnetite and melt d m t m e l l au 4 using reasonable estimates of the mass fraction of magnetite that crystallizes in crustal magmatic systems we modeled the proportion of au sequestered by magnetite during fractional crystallization we considered fractionation in two steps the idealized derivation of a rhyolite by fractionation of basalt at depth and the closed system crystallization of the rhyolite in a magma chamber below the site of ore deposition magnetite sequesters 14 54 au from basaltic parent melt that produces a rhyolite melt via crystal fractionation at modal abundances of 1 5 less then 4 au is sequestered from a crystallizing rhyolite melt because of low modal abundances of magnetite 2 our experimental and model results suggest that early crystallization of magnetite can play a mitigating role in the ability of a calc alkaline magmatic system to yield a au rich ore fluid

solubility of excess alumina in hydrous granitic melts in equilibrium with peraluminous minerals at 700 800 c and 200 mpa and applications of the aluminum saturation index we have studied the controls on the alumi num saturation index asi molec al2o3 cao na2o k2o and the concentration of normative corundum of granitic liquids saturated in alumina by equilibrating peraluminous minerals with initially meta luminous haplogranitic minimum composition liquids at 700 800 c and 200 mpa at and below h2o saturation the asi and normative corundum increase with increasing h2o concentration in the melt 0 04 to 0 10 moles excess al2o3 per mole of h2o temperature and with addition of the non haplogranitic components fe mg and b the asi parameter and concentration of normative corundum cannot be used to monitor aal2o3 between different mineral assemblages and melt because other components that affect the solubility of alumina including h2o fe mg and b do not appear in their formulations asi and normative corundum however provide petrogenetic information about magmas gener ated by partial melting of strongly peraluminous proto liths by virtue of their regular and predictable variation with melt composition e g h2o concentration and temperature for the application of these data to natural rocks it is necessary to choose as an analogue system the asi solubility or normative corundum solubility relations of the most chemically complex peraluminous mineral present in the rock comparison of asi values of anatectic leucosomes and allochthonous leucogranites with experimentally predicted values suggests low h2o concentrations in melt during crustal partial melting rapid melt segregation before equilibration with restitic peraluminous phases is also suggested in some cases

synthetic fluid inclusions as recorders of microfracture healing and overgrowth formation rates aqueous fluid inclusions have been synthesized within fluorite microfractures t 200 c p p sat t 30 days quartz microfractures and quartz overgrowths t 400 to 300 c p 400 bars t 20 days the experiments were designed to determine the time necessary to form the inclusions within a minute in a fluorite host and within a day in a quartz host the results permit estimation of the time needed to heal microfractures or create overgrowths which is accomplished by measuring the melting temperature t m of the inclusions in fluorite and the homogenization temperature t h of the inclusions in quartz for the fluorite experiments the results show that fluorite nh4cl solution equilibrium took 82 hours moreover the healing process appears to be an irregular process along the microfracture fluorite experiments mimic boiling processes occurring in natural hydrothermal or epithermal systems and show how a boiling fluid may be progressively salted during vaporization and trapped as fluid inclusions for the experiments involving quartz the quartz h2o nacl solution equilibrium was reached on the first day for synthetic quartz and on the sixth day for natural quartz this difference is linked to the hydration state of the two types of quartz the decrease in t h of synthetic fluid inclusions from the core overgrowth boundary to the external part of the quartz overgrowth shows that the growth of quartz is a progressive and protracted process which involves a silica oversaturated solution

the anatomy of a buried complex impact structure the mjolnir structure barents sea analysis of the prominent seismic disturbance at the 40 km diameter mjolnir impact structure based on an extensive seismic reflection database shows that the observed broad brimmed bowl shaped disturbance was formed as a result of the impact of an asteroid or comet during volgian berriasian time 149 141 m seismic mapping exhibits and visualizes a 850 1400 km3 disturbed volume and analysis of several structural features within the disturbance provides insight into major cratering processes such as brecciation and excavation melting gravitational collapse of the transient crater and structural uplift a transient crater of 16 km in diameter and 4 5 km in depth is determined from transient and final crater dimensions we obtain an estimate of the degree of gravitational collapse of the order of 2 5 considerably larger than the average expected values for typical terrestrial craters the extensive collapse took place by low angle decollement surfaces at the periphery and by chaotic debris mass flows toward the center furthermore we estimate the mjolnir projectile to have been 0 9 3 km in diameter and that the physical impact released energy in the range of 2 4 53 1020 j corresponding to an earthquake of magnitude 8 3 the mjolnir impact is not associated with a significant mass extinction however dissipation of the energy released during the mjolnir impact was sufficient to have caused several short term near field perturbations such as large amplitude tsunami waves affecting the barents sea region and possibly adjacent areas in the arctic

mapping chicxulub crater structure with gravity and seismic reflection data the chicxulub crater buried under the yucat n platform of mjxico affords one of the most favourable opportunities on earth for structural studies of a large complex impact crater due to its preservation and accessibility the crater was buried soon after rim erosion in an environment with only minor subsequent tectonic disturbance it is also of interest as the chicxulub impact apparently ended the cretaceous period and the crater s ejecta blanket is known globally at hundreds of localities the buried crater is half overlain by a coastal plain and half by a shallow sea allowing exploration by both marineand land based techniques as well as hybrid combinations the radial symmetry of the crater allows application of data acquired in either terrain to the entire structure using the common data sets of magneticand gravity field anomalies gravity data sets covering the yucat n platform e g 1 2 reveal an 180 km diameter low with internal concentric structure e g 3 4 that is the expression of the chicxulub crater impact lithologies and crater fill the gravity signature is complicated by regional anomalies and early modifications to the crater rim and the northern half of the crater is not well imaged due to the scarcity and imprecision of marine data also an 20 km wide gap in survey coverage due to shallow water occurs between the land data and the nearest seismic profile of camargo and suarez 5 fig 1 which roughly corresponds to the beginning of offshore coverage during september and october 1996 a marine gravity survey was successively conducted on 32 and 10 5 m vessels to survey this gap and offshore seismic lines of the imperial college birps u of texas seismic project offshore coverage was 2 400 line km followed by 1 500 line km inshore with 1 3 and 1 9 mgal unadjusted crossovers respectively data precision was strongly influenced by sea conditions preliminary results from the marine surveys confirm the provisional ties of gravity gradient features to the seismic line the perimeter fault crater fill margin slump faults and collapsed transient cavity margin may all be linked to gradient features unfortunately the clearest crater expression in the gravity field is on the east side where the seismic lines lose resolution at the basin margin to the west the strong peripheral gradient splits with one component corresponding to the perimeter slump fault and a larger feature corresponding to the basin margin this splitting is interpreted as resulting from prompt backwash of crater ejecta into the northwestern part of the crater regional gradients also obscure the crater signature to a greater extent to the west asymmetry of the central high is indicated although a weak feature may extend to the ne the surrounding sharp low continues until it abuts the regional high to the nw additional land surveys support the correlation of the cenote ring to gravity gradient features and suggest that a weak high may correlate to the rim uplift in some places

an evaluation of synthetic fluid inclusions for the purpose of trapping equilibrated coexisting immiscible fluid phases at magmatic conditions we report data that allow us to evaluate the method of trapping immiscible saline aqueous fluids i e vapor and brine in the nacl kcl hcl fecl2 auhcl2 h2o system as synthetic fluid inclusions in pre fractured quartz cores in order to quantify the concentrations of au fe k and na among coexisting three phase immiscible fluids i e haplogranite melt brine and vapor at magmatic conditions coexisting vapor and brine were trapped experimentally at 800 c and 100 110 mpa as synthetic fluid inclusions in both quartz microfractures and quenched silicate melt i e glass and also sampled indirectly using the recovered quenched aqueous fluid quartz hosted and glass hosted brine inclusions were analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms and instrumental neutron activation analysis inaa respectively quenched aqueous fluid from each experiment containing a quartz core was recovered and analyzed by atomic absorption spectrophotometry aas the composition of aqueous fluids trapped as quartz hosted inclusions glass hosted inclusions and those recovered after quench yield consistent and precise data at the 2 uncertainty level for the elements of interest the overlapping au fe k and na concentrations in aqueous fluids trapped and analyzed via three entirely different instrumental techniques i e la icpms inaa and aas suggest strongly that quartz microfractures heal on a slow enough time scale to permit entrapment of fully equilibrated aqueous fluids at our experimental ptx conditions the data evince clearly that the chemical composition of fluids in quartz microfractures at the time of self healing represents equilibrium conditions hence synthetic fluid inclusions in experiments with low thermal gradients across the charge provide a reasonable estimate of fluid composition at least at the experimental conditions examined in this study

gravity modelling of lockne a marine impact structure in jamtland central sweden abstract the lockne impact structure in jamtland 63 00 20 n 14 49 30 e formed in the middle ordovician at approximately 455 ma the structure is interpreted as a concentric crater with a total diameter of 13 5 km the impact took place in a marine environment with a water depth exceeding 200 m the gravity survey of the structure and its surroundings comprises 467 measurements the residual gravity map reveals a negative anomaly reaching a maximum of 22 g u the gravity modelling of the structure revealed its morphology with a central uplift surrounded by a moat the fracture zone grades out and diminishes at an approximate depth of 2 km the model also shows a slight northwestward tilt 1 2 of the structure the anomaly of 22 g u is relatively small compared to the ones occurring in other craters of similar size a good preservation state and a crystalline target normally favour larger negative anomalies than occur in eroded structures of the same size in sedimentary strata the lockne structure occurs in crystalline target rock and is well preserved therefore a small density contrast of rocks in the lockne structure is the main reason for the small anomaly in lockne the impact breccia has only 1 10 of the density contrast compared to the average supra aquatic impact structure furthermore the fractured target rock shows 1 4 of the density contrast that one finds in average supra aquatic impact structures the interpretation is that the cavity and fractures were filled mainly by calcite precipitated by the hydrothermal system acting after the impact the abundant water and the residual heat from the impact gave the opportunity for the hydrothermal system to develop

formation of anhydrous and hydrous skarn in cu au ore deposits by magmatic fluids most skarn ore deposits are characterized by two distinctly different alteration styles an early prograde stage with anhydrous minerals such as garnet and pyroxene forms from relatively high temperature hypersaline liquid a later retrograde stage with hydrous minerals such as epidote amphibole and chlorite plus sulfide ore minerals forms from lower temperature lower salinity fluids these two alteration stages commonly have been thought to reflect a dominance of magmatic and meteoric water respectively with relevance to the source of ore metals we report data from two different skarn systems one being part of the world s largest cu au resource stable isotope compositions of anhydrous and hydrous alteration minerals from both deposits indicate a magmatic source for both the prograde and retrograde stages 18o averages 5 0 per mil for garnet range 3 4 7 2 6 5 per mil for pyroxene 4 3 8 2 and 7 1 per mil for amphibole 4 3 8 7 the d values of late amphibole are more complex with magmatic values 77 to 78 for one deposit and both magmatic and lighter values for another deposit that could be explained either by magmatic degassing or by limited mixing with meteoric water we conclude that the differences in fluid composition prograde versus retrograde stages resulted from a magmatic fluid that intersected its solvus during the early stage creating vapor and hypersaline liquid whereas in the later stage this magmatic fluid did not intersect its solvus because it followed a different cooling path this late low salinity liquid only boiled once its vapor pressure curve was reached causing sulfide ore to precipitate during the retrograde stage

the greenland norwegian seaway a key area for understanding late jurassic to early cretaceous paleoenvironments the paleoclimatology and paleoceanology of the late jurassic and early cretaceous are of special interest because this was a time when large amounts of marine organic matter were deposited in sediments that have subsequently become petroleum source rocks however because of the lack of outcrops most studies have concentrated on low latitudes in particular the tethys and the boreal realm where information has been based largely on material from northwest germany the north sea and england these areas were all south of 40 n latitude during the late jurassic and early cretaceous we have studied sediment samples of kimmeridgian 154 ma to barremian 121 ma age from cores taken at sites offshore mid norway and in the barents sea that lay in a narrow seaway connecting the tethys with the northern polar ocean during the late jurassic early cretaceous these sites had paleolatitudes of 42 67 n the late jurassic early cretaceous sequences at these sites reflect the global sea level rise during the volgian hauterivian and a climatic shift from warm humid conditions in volgian times to arid cold climates in the early hauterivian the sediments indicate orbital control of climate reflected in fluctuations in the clastic influx and variations in carbonate and organic matter production trace element concentrations in the volgian berriasian sediments suggest that the central part of the greenland norwegian seaway might have had suboxic bottom water beneath an oxic water column both marine and terrigenous organic matter are present in the seaway sediments the volgian berriasian strata have unusually high contents of organic carbon and are the source rocks for petroleum and gas fields in the region the accumulation of organic carbon is attributed to restricted conditions in the seaway during this time of low sea level it might be that the greenland norwegian segment was the deepest part of the transcontinental seaway bounded at both ends by relatively shallow swells the decline in organic matter content of the sediments in the valanginian hauterivian indicates greater ventilation and more active flow through the seaway as the sea level rose the same benthic foraminifera assemblages are encountered throughout the seaway endemic assemblages of arenaceous foraminifera in the volgian berriasian give way to more diverse and cosmopolitan valanginian hauterivian benthic communities that include calcareous species the foraminiferal assemblages also suggest low oxygen content bottom waters during the earlier cretaceous changing to more fully oxygenated conditions later the calcareous nannoplankton particularly crucibiscutum salebrosum which is rare at low latitudes and abundant in high latitudes reflect the meridional thermal gradient they indicate that the greenland norwegian segment of the seaway was north of a subtropical frontal zone that acted as a barrier between the tethyan and boreal realms this implies the existence of stable climatic belts during the early valanginian and hauterivian significant meridional temperature gradients and moderate ice house conditions

relationships between sem cathodoluminescence response and trace element composition of hydrothermal vein quartz laser ablation icp ms data of hydrothermal vein quartz with zonation in scanning electron microscope cathodoluminescence reveal two groups of trace elements one that co varies in concentration with luminosity and another that remains uniform throughout bright luminosity correlates with a high total abundance of trace elements in early quartz including al up to 410 g g ti up to 240 g g k up to 330 g g li up to 8 g g na up to 36 g g and fe up to 20 g g up to 20 times lower concentrations of these elements are associated with dark luminosity in late quartz concentrations of p 21 g g ga 0 3 g g ge 1 3 g g sn 1 5 g g cu 0 3 g g and ag 0 1 g g demonstrate no relationship with luminosity charge balance cannot be achieved for bright luminescent quartz unless the presence of up to 6 g g h not analyzed by la icpms or interstitial al3 is invoked interestingly the inferred 6 g g h remains constant for quartz containing more than 10 mol total trace elements and might represent the solubility of h in hydrothermal quartz at temperatures between 450 and 700 c la icpms results indicate that the fluid chemistry determines the quartz trace element pattern which may serve as a monitor for the chemical environment from which quartz crystallized ratios of na al and ti al are uniform whereas k al evolves toward lower values with decreasing luminosity combined evidence including quartz vein textures silica solubility data and estimates of the temperature of quartz growth suggest that early quartz crystallized fast but late quartz grew more slowly at 350 to 425 c it is speculated that the higher the quartz growth rate is the more trace elements are incorporated into quartz besides the temperature dependence known from the literature clearly growth rate temperature and fluid chemistry are important parameters affecting luminosity however their relative importance may vary from case to case

a method to synthesize large fluid inclusions in quartz at controlled times and under unfavorable growth conditions a new synthesis technique allows large fluid inclusions to be produced at conditions under which one normally would obtain only small inclusions with the additional advantage that the timing of fluid entrapment can be controlled in the first step primary fluid inclusions are grown at p t conditions under which it is relatively easy to produce large inclusions in the second step which can be performed either during the same experiment or during a separate experiment after a desired time of pre equilibration some of the primary inclusions produced during the first step are re opened by in situ fracturing causing partial replacement of the inclusion content the sample is then left at high pressure and temperature until the cracks leading to the re opened inclusions are healed to test the method and quantify the efficiency of fluid replacement in the re opened inclusions we produced primary inclusions at 700 c 200 mpa and re opened them during a second experiment in the presence of a compositionally different fluid at 500 c 70 mpa laser ablation icp ms la icp ms analyses of eight primary and 11 refilled inclusions demonstrate that in the latter more than 97 of the original fluid was replaced by new fluid thus the refilled inclusions are representative of the surrounding fluid at the time of in situ fracturing

continental scientific drilling project of cretaceous songliao basin scientific objectives and drilling technology abstract the continental scientific drilling project at the cretaceous age songliao basin is a drilling initiative under the framework of the international continental scientific drilling program to recover a nearly complete cretaceous terrestrial sedimentary record in the songliao basin northeastern china the recovered cores will provide unique opportunities for the geosciences community to advance the understanding of climate change in the cretaceous greenhouse world and provide a documentation of geological events relevant to the carbon cycle during this time period this drilling project will address significant geological questions such as the identification of important stratigraphic boundaries and the marine terrestrial correlations of stratigraphy the reasons for the biotic response to the terrestrial environmental changes the terrestrial response to the cretaceous oceanic anoxic events the formation of terrestrial petroleum source rocks and the mechanisms for the cretaceous magnetic normal superchron cns in the first stage of this drilling project the ski drilling rock cores of 2485 89 m in total length were recovered and the recovery ratio reached 96 46 a series of drilling and coring technologies including regular confined directional and sealed coring were utilized to ensure a higher recovery ratio for the core and will be described at the end of this paper well loggings were conducted right after coring core handling and storage were arranged in such a way that the scientific research was conducted on half of each core whereas the other half of each core was preserved for long term storage the upcoming second stage the skii drilling will combine with data from the existing ski to provide complete high resolution climate records of the terrestrial environment for the whole cretaceous time period

computer modelling of the water resurge at a marine impact the lockne crater sweden abstract when a cosmic impact occurs at sea the resulting crater can form completely in the water mass or extend into the seafloor at intermediate to great water depths the collapse of the water cavity generates a forceful resurge of water along the seafloor towards the central part of the crater the erosive effects as well as certain conspicuous deposits from resurge flows are known from several craters this study uses numerical modelling to estimate the magnitude of the resurge in the case of the 455 myr old marine target lockne impact crater sweden the water depth at the lockne target site was at least 200 m possibly even as great as 1 km field evidence show that the resurge was strong enough to erode gullies hundreds of metres wide tens of metres deep and kilometres long with computer modelling we studied the behaviour of the flow to get a notion of its magnitude the calculations required simplification of the reality we used a fixed seafloor topography and pure water a rim in the water mass is expected but was neglected in the calculations the simplification likely led to underestimation of the magnitude of the resurge the effect of different target water depths was studied at 200 m target water depth about 1 2 10 11 m 3 of water were needed to fill the lockne crater including the water cavity this took about 2200 s it has been suggested that the main gully formation occurs when the resurge passes the inner rim of the crater that phase lasts for about 700 s with a 500 m target water depth these processes are 3 4 times faster the erosive force of the flow i e unit stream power is 1 9 10 5 wm 2 in the 200 m water depth model this is of the same magnitude as the lake missoula flood the greatest catastrophic flooding known on earth at 500 m target water the unit stream power is a magnitude greater

numerical simulations of the mjolnir marine impact crater 1 the 40 km diameter mjolnir crater in the barents sea was created by a meteoroid impact into a 400 m shallow sea about 142 ma we have used a multimaterial hydrocode with depth depending target strength to model numerically the cratering and early modification stages of the mjolnir impact our models are constrained by the observed crater morphology and structure the best results were obtained for a composite target strength structure very low strength for the upper 3 km of sedimentary rocks and gradual increase from 3 to 6 5 km depth before using strength values typical for granitic rocks at greater depths the low strength of the target sediments at shallow depths led to exceptionally intensive slumping and gravitational collapse of the order of 2 0 2 5 considerably larger than the average expected values for typical terrestrial craters as a result we obtain a crater collapse in between simple and complex where slumping and gravitational collapse counteract the crater floor uplift and lead to suppression and burial of the central high the mjolnir impact in a shallow sea was responsible for a major disturbance of the water column following the impact induced outward water surge large amplitude tsunamis were formed and the rapid resurge of seawater into the excavated crater transported large amounts of ejecta and crater wall material back into the crater accounting for the redestribution of ejecta material and extensive infilling

kardla hiiumaa island estonia the buried and well preserved ordovician marine impact structure abstract the kardla marine impact structure estonia 58 58 n 22 46 e was formed at 455 ma upper ordovician in a shallow epicontinental sea some tens of kilometres from the land and erosion area the iron rich projectile about 200 m in diameter approached from the west at an angle of 30 45 the impactor penetrated about 50 m thick water layer and the sedimentary cover and exploded in the uppermost part of the crystalline basement a complex crater 4 km wide and about 500 m deep with a central uplift rising 130 m from the crater floor was formed the highest point of the rimwall is 110 m above the target level the rimwall is cut by at least two resurge excavated gullies the variable height of the rimwall obviously results from the obliqueness of the impact outside the crater an elliptical area was revealed 12 15 km in diameter with deformed sedimentary rocks below the target level the elliptical shape of this area may also be due to the oblique impact because the crater and its surroundings were buried directly after the impact the whole complex of impact related sediments is preserved there they are recovered by 160 wells six of which penetrate the entire complex of impact breccias inside the crater

the corossol structure a possible impact crater on the seafloor of the northwestern gulf of st lawrence eastern canada we report on a 4 1 0 2 km diameter and 185 m deep circular submarine structure exposed on the seabed in 40 m water depths in the northwestern gulf of st lawrence eastern canada from the analysis of high resolution multibeam bathymetric and seismic data the presence of a circular form characterized by a central uplift and concentric rings resembles the morphology and geometry of complex meteorite impact structures also other origins such as kimberlites intrusions karsts or diapirs can be eliminated on geological criteria a single 4 cm long breccia fragment recovered from the central uplift has numerous glassy droplets of fluorapatite composition assumed to be impact melts and a single quartz grain with planar intersection features thought to be shock induced planar deformation features pdfs the absolute age of this possible impact structure is unknown but its geological setting indicates that it was formed long after the mid ordovician and before regional pre quaternary sea level lowstands present results outline the need for further examination to confirm an impact origin and to precisely date the formation of the structure

synthetic fluid inclusions in natural quartz ii application to pvt studies synthetic fluid inclusions have been used to determine volumetric properties of h2o and a 20 wt kcl solution from 300 700 c and 1 3 kb comparison of results obtained for h2o with previously published data indicates that the synthetic fluid inclusion technique provides pvt data that are within a few percent of those obtained from conventional pvt studies this technique thus provides a fast relatively simple means of determining pvt properties of many fluids of geologic interest

platinum solubility and partitioning in a felsic melt vapor brine assemblage abstract the solubility and partitioning of pt in a s free vapor brine rhyolite melt pt metal assemblage has been quantified at 800 c f o 2 nno and pressures of 100 and 140 mpa vapor and brine were sampled at run conditions by trapping these phases as glass hosted fluid inclusions as the melt cooled through the glass transition temperature the vapor and brine were in equilibrium with the melt at the time of trapping and thus represent fluids which were sampled at the termination of each experimental run the microthermometrically determined salinities of vapor and brine are 2 and 63 wt nacl eq and 9 and 43 wt nacl eq at 100 and 140 mpa respectively platinum solubilities in vapor brine and glass i e quenched melt were quantified by using laser ablation inductively coupled plasma mass spectrometry la icp ms equilibrium is discussed with reference to the major and trace element concentrations of glass hosted fluid inclusions as well as the silicate melt over run times that varied from 110 to 377 h at 140 mpa and 159 to 564 h at 100 mpa platinum solubility values 1 in h2o saturated felsic melt are 0 28 0 13 g g and 0 38 0 06 g g at 140 and 100 mpa respectively platinum solubility values 1 x at 140 and 100 mpa respectively in aqueous vapor are 0 91 0 29 g g and 0 37 0 17 g g and in are brine 16 10 g g and 3 3 1 0 g g the measured solubility data were used to calculate nernst type partition coefficients for pt between vapor melt brine melt and vapor brine the partition coefficient values 1 x for vapor melt brine melt and vapor brine at 140 mpa are 2 9 1 0 67 27 and 0 13 0 05 and at 100 mpa are 1 0 0 2 6 8 2 4 and 0 15 0 05 the partitioning data were used to model the pt scavenging capacity of vapor and brine during the crystallization driven degassing i e second boiling of a felsic silicate melt over a depth range i e 3 6 km consistent with the evolution of magmatic hydrothermal ore deposits model calculations suggest that aqueous vapor and brine can scavenge sufficient quantities of pt and by analogy other platinum group elements pge to produce economically important pge rich magmatic hydrothermal ore deposits in earth s upper continental crust

the importance of being cratered the new role of meteorite impact as a normal geological process this paper is a personal and in many ways incomplete view of the past development of impact geology and of the newly recognized importance of impact events in terrestrial geological history it also identifies some exciting scientific challenges for future investigators to determine the full range of impact effects preserved on the earth to apply the knowledge obtained from impact phenomena to more general geological problems and to continue the merger of the once exotic field of impact geology with mainstream geosciences since the recognition of an impact event at the cretaceous tertiary k t boundary much current activity in impact geology has been promoted by traditionally trained geoscientists who have unexpectedly encountered impact effects in the course of their work their studies have involved 1 the recognition of additional major impact effects in the geological record the chesapeake bay crater the alamo breccia and multiple layers of impact spherules in precambrian rocks and 2 the use of impact structures as laboratories to study general geological processes e g igneous petrogenesis at sudbury canada and archean crustal evolution at vredefort south africa other research areas in which impact studies could contribute to major geoscience problems in the future include 1 comparative studies between low level 7 gpa shock deformation of quartz and the production of quartz cleavage in both impact and tectonic environments and 2 the nature origin and significance of bulk organic carbon kerogen and other carbon species in some impact structures gardnos norway and sudbury canada

extreme chemical heterogeneity of granite derived hydrothermal fluids an example from inclusions in a single crystal of miarolitic quartz magma derived fluids are important in geologic processes e g metal sequestration and ore deposition but are intrinsically transient samples of magmatic fluids represented by fluid inclusions in a single zoned quartz crystal from a miarolitic cavity within a porphyritic leucogranite hosting the industrialnoe tin deposit northeastern russia were studied by using modern in situ analytical methods laser raman spectroscopy proton induced x ray emission the fluid inclusions are either dominated by vapor or by complex multiphase brines the inclusions within a given trapping plane have similar phase relationships however there are significant variations between inclusions in different healed fractures phase and chemical compositions of individual brine inclusions demonstrate significant compositional heterogeneity in terms of absolute element concentrations and ratios of high temperature magmatic fluids accumulated in the miarolitic cavity this finding suggests that fluids leaving a crystallizing magma may have variable initial compositions that are subsequently modified by reactions with the rocks while the fluid is in transit to a miarolitic cavity as well as by processes in the cavity such as mixing crystallization and boiling the inferred chemical diversity and fractionation of granite derived fluids at near magmatic conditions imply that fluids entering a cooler hydrothermal system are extremely complex and their metallogenic signature may differ from that of related ore deposits

trace metal signatures of jurassic cretaceous black shales from the norwegian shelf and the barents sea abstract black shale samples of jurassic to cretaceous age recovered during the norwegian shelf drilling program between 1987 and 1991 from sites 7430 10 u 01 barents sea 6814 04 u 02 norwegian shelf near the lofoten and 6307 07 u 02 norwegian shelf near trondheim were analyzed for major and trace elements these laminated black shales are characterized by high total organic carbon toc and total sulfur ts contents as well as by significant enrichments in several redox sensitive and or sulfide forming trace metals ag bi cd co cr cu mo ni re sb tl u v and zn enrichment factors relative to average shale are comparable to those found in cenomanian turonian boundary event ctbe black shales and mediterranean sapropels the re content is high in the studied black shales with maximum values up to 1221 ng g re mo ratios averaging 2 3 10 3 are close to the seawater value high trace metal enrichments and re mo ratios close to the seawater value point to a dominantly anoxic and sulfidic water column during black shale formation interbeds with higher re mo ratios especially in high resolution sampled core sections point to brief periods of suboxic conditions additionally enhanced zn concentrations in the black shales from the barents sea support the assumption that hydrothermal activity was also high during black shale deposition trace metal signatures of black shales at different drill sites on a transect along the norwegian shelf are not only influenced by water depth but also by their location in the boreal realm metal enrichments are higher in the northern compared to the southern sites volgian tithonian 151 144 ma bp black shales exhibit elevated trace metal contents in comparison to their berriasian 144 137 ma bp counterparts this probably reflects a change in the circulation pattern during periods of black shale formation therefore different paleoceanographic conditions probably controlled by climatic change linked to the transgression of the paleo sealevel and the north atlantic opening may have developed from the volgian to the berriasian

rapid quench hydrothermal experiments at mantle pressures and temperatures new experimental methods for the encapsulation extraction and analysis of large volumes of aqueous fluids enable studies of mineral solubilities and dissolution kinetics with the piston cylinder apparatus quench rates and volumes of experimental fluids with these methods are comparable with those used in modern hydrothermal experiments employing cold seal vessels analyses of fluid compositions are reproducible and consistent with independent results the techniques permit experimental investigations that will better characterize fluid rock interaction in such environments as subducting slabs the mantle wedge barrovian metamorphic belts and middle to lower crustal granulites