apatite feldspar u pb thermochronometer a reliable mid range 450 c diffusion controlled system the u pb systematics of apatite are commonly dominated by simple volume diffusion without secondary growth and recrystallization that can affect u pb systematics of sphene monazite and zircon although apatite is a relatively low u mineral both u and pb are lattice bound and thus the u pb systematics are not controlled by micro inclusions as appears to be the case for other low u minerals such as garnet and staurolite closure temperature estimates from both experimental and empirical studies range from 425 c to as high as 500 c for typical diffusion radii 25 m and cooling rates 2 100 c ma respectively this range can be exploited to constrain cooling and exhumation histories of both igneous and metamorphic rocks in addition the closure temperature for pb diffusion in apatite fills a gap between that for pb diffusion in sphene 650 c and diffusion of ar in hornblende 500 c muscovite 350 c and biotite 300 325 c apatite is a common accessory phase in many rock types and u pb apatite dating can be a reliable and powerful thermochronometer as it combines mid range cooling ages with the strength of the u pb system in testing for isotopic closure precisions of u pb apatite dates can range from 1 2 to as low as 0 3 for proterozoic or archean dates the main limitation to accuracy of u pb apatite dates is a moderate to low ratio of u to pb and corresponding dependence of concordia coordinates on the choice of initial pb isotopic composition for proterozoic aged samples with measured 206pb 204pb of 100 the range of geologically reasonable initial pb isotopic compositions can shift the calculated u pb age by 60 ma fortunately even though the diffusion rate of pb in alkali feldspar is less than in apatite it appears that the isotopic composition of pb in coexisting feldspar is a good approximation of the initial isotopic composition in apatite for many geologic settings examples are given from an archean terrane in se wyoming that was unroofed and cooled during proterozoic uplift and from proterozoic terranes in sw us that have contrasting thermal histories

geochemistry of a spring dense karst watershed located in a complex structural setting appalachian great valley west virginia usa the distribution and chemistry of the springs in the tuscarora creek watershed is controlled by both geologic structure and karst dissolution the watershed is located in eastern west virginia in the structurally complex great valley of the appalachian valley and ridge province the upper portion of the stream parallels strike along a mapped fault zone and is bordered by clastic rocks that comprise north mountain the lower reaches of the stream flow cross strike through cambro ordovician carbonates the controlling chemical signature in the spring water is carbonate dissolution little evidence was seen for the recharge from adjacent clastic rocks although differences in the ca mg molar ratio between springs indicated the presence of localized spring basins in headwater reaches na cl and ca generally increased from upstream to downstream in the cross strike reaches comparison of stream and cumulative spring discharge was consistent with significant groundwater base flow contribution directly to the creek particularly in the strike parallel region the largest spring in the watershed 162 l s was sampled during and after a large storm event along with the adjacent creek the creek displayed a typical dilution response with each flood pulse whereas the spring had only a limited or delayed response the overall chemical and thermal stability of the spring relative to the creek indicated the lack of significant direct hydraulic connection between the two the conceptual model for the area includes localized flowpaths in the headwater region where the stream flow is parallel to strike and a thrust fault in addition to the shallow localized flowpaths a deeper more regional flowpath likely exists for a large spring further downstream

preconditioning an ensemble kalman filter for groundwater flow using environmental tracer observations abstract groundwater resources management requires operational regional scale groundwater models accounting for dominant spatial variability of aquifer properties and spatiotemporal variability of groundwater recharge we test the ensemble kalman filter enkf to estimate transient hydraulic heads and groundwater recharge as well as the hydraulic conductivity and specific yield distributions of a virtual phreatic aquifer to speed up computation time we use a coarsened spatial grid in the filter simulations and reconstruct head measurements at observation points by a local model in the vicinity of the piezometer as part of the observation operator we show that the enkf can adequately estimate both the mean and spatial patterns of hydraulic conductivity when assimilating daily values of hydraulic heads from a highly variable initial sample the filter can also estimate temporally variable recharge to a satisfactory level as long as the ensemble size is large enough constraining the parameters on concentrations of groundwater age tracers here tritium and transient hydraulic head observations cannot reasonably be done by the enkf because the concentrations depend on the recharge history over longer times while the head observations have much shorter temporal support we thus use a different method the kalman ensemble generator keg to precondition the initial ensemble of the enkf on the groundwater age tracer data and time averaged hydraulic head values the preconditioned initial ensemble exhibits a smaller spread as well as improved means and spatial patterns the preconditioning improves the enkf particularly for smaller ensemble sizes allowing operational data assimilation with reduced computational effort in a validation scenario of delineating groundwater protection zones the preconditioned filter performs clearly better than the filter using the original initial ensemble

a middle late triassic ladinian rhaetian carbon and oxygen isotope record from the tethyan ocean abstract we obtained bulk sediment 18o and 13c data from biostratigraphically constrained tethyan marine sections at aghia marina greece guri zi albania and brumano and italcementi quarry italy and revised the published chemostratigraphy of the pizzo mondello section italy we migrated these records from the depth to the time domain using available chronostratigraphic tie points generating ladinian rhaetian 13c and 18o records spanning from 242 to 201 ma the 18o record seems to be affected by diagenesis whereas the 13c record appears to preserve a primary signal and shows values increasing by 1 in the ladinian followed by an 0 6 decrease across the ladinian carnian boundary followed by relatively constant but oscillatory carnian values punctuated by a negative excursion at 233 ma in the early carnian a second negative excursion at 229 5 ma across the early late carnian boundary and a positive excursion at 227 ma across the carnian norian boundary the norian record is characterized by a long term decreasing trend and a negative excursion at 216 ma rapid increases and decreases in 13c have been observed in the rhaetian but these may be at least in part due to mixing of different sources of carbonate carbon with different 13c values our triassic 13c record has been compared to data from the literature and a composite 13c record spanning the last 242 myr of earth s history has been generated this composite record shows a sequence of dated 13c trends and events that can be used for stratigraphic correlation as well as for a better understanding of the global carbon cycle in the mesozoic cenozoic

fault assisted vertical pluton growth coastal cordillera north chilean andes abstract extensive tracts of magmatic arc plutonic suites in the mesozoic coastal cordillera of northern chile imply that large volumes of granitic to dioritic magmas were transferred from a lower crustal source to the upper crust space for single intrusions was created by interaction of vertical pluton growth and dip slip reactivation of arc parallel faults during episodic emplacement of subhorizontal compositionally distinct magma pulses cross sectional pluton shapes are broadly tabular in geometry and were controlled by differential subsidence of the pluton floors during fault reactivation and incremental assembly of subhorizontal sheets equal amounts of floor subsidence of the fault footwall and hanging wall during magma accommodation led to symmetrical intrusions whereas differential subsidence caused plutons to grow asymmetrically strongly asymmetrical plutons resulted when only the hanging wall was reactivated to accommodate floor subsidence late post intrusion contractional deformation resulted in open folding of some tabular plutonic units and local inversion of bounding faults which has modified but not obscured the original syn emplacement geometry and fault kinematics

the triassic isotope record a variety of stable isotope measurements have been found useful in studying processes of environmental change measurements of d 13 c d 18 o d 34 s and 87 sr 86 sr all can provide infor mation about the conditions of the water column in which sediment deposition occurred but the most widely applied of these is d 13 c the carbon isotope record for the triassic system is a complex one a pronounced negative excursion begins below the base of the triassic system and continues into the basal triassic the succeeding 4 to 6 ma lower triassic interval is marked by isotopic instability with positive and negative excursions continuing through the basal middle triassic in contrast to the lower triassic most of the middle and upper triassic display relative isotopic stability with rising values of d 13 c likely reflecting environmental recov ery and increasing storage of organic carbon in terrestrial environments the uppermost triassic is marked by a pronounced negative excursion near the system boundary that has been linked to significant biotic turnover the causes of the various excursions remain under investigation particularly those at the system boundaries with outgassing during volcanic activity changes in productivity ocean anoxia and seafloor methane releases all suggested as mechanisms both for perturbing the global carbon cycle and for forcing biotic extinction

direct ion microprobe u pb dating of fossil tooth of a permian shark abstract we report here direct ion microprobe dating of fossil tooth dentine of a permian fresh water shark orthacanthus senckenbergianus using the shrimp instrument recently installed at hiroshima university fifteen spots on the small sample approximately 2 mm 1 mm indicate a 238 u 206 pb isochron age of 266 18 ma and a tera wasserburg concordia intercept age of 266 24 ma in a three dimensional 238 u 206 pb 207 pb 206 pb 204 pb 206 pb diagram these permian ages are consistent with a 235 u 207 pb age of 453 170 ma and a 232 th 208 pb age of 235 310 ma suggesting indistinguishable depositional and early diagenetic ages of the fossil in its sedimentary sequences the success of the method depends on the chemical fractionation of uranium from lead in a specimen a few hundred microns in size and the consequent variations in lead isotopic compositions due to radioactive decay

the origin and timing of multiphase cementation in carbonates impact of regional scale geodynamic events on the middle jurassic limestones diagenesis paris basin france the middle jurassic carbonates of the eastern part of the paris basin display surprisingly low values of porosity and permeability 15 and k 0 5 md the main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs a fate that did not befall their equivalents in deeper central parts of the paris basin using petrographic and geochemical analyses stable o and c isotopes sr isotopes major elements we identify six calcitic spar stages two dolomite stages and several episodes of fracturing and stylolitization ordered in paragenetic sequence cement quantification shows the predominance of two blocky calcite cement stages 75 of total cementation o and sr isotopes from these calcite cements suggest that the parent fluids resulted either from a mixing of trapped jurassic seawater and meteoric water or from buffered meteoric waters in the geological history of the paris basin major meteoric water inputs were possible during the early cretaceous when the middle jurassic carbonates cropped out at its northern and eastern borders lateral meteoric recharge may have occurred as a result of two separate uplift events late cimmerian unconformity and late aptian unconformity and the related exposures of carbonates to the north of the study area this palaeohydrological circulation brought about a significant reduction of porosity from 40 to 10 through calcite cement precipitation the early cretaceous events are of great importance in the diagenetic evolution of the sedimentary basins bordering the london brabant massif across all of northwestern europe a subsequent dolomite and calcite cementation stage accounts for about 5 of the total cement volumes this late cementation may have been caused by hydrothermal fluids ascending along permeable fractures during the late oligocene extension episode

assessing the utility of fe al and fe speciation to record water column redox conditions in carbonate rich sediments abstract geochemical proxies based on fe abundance fe al and fe speciation have been widely applied to marine sediments in order to unravel paleo depositional redox conditions though geological time to date however these fe proxies have only been calibrated in relation to modern and ancient fine grained siliciclastic marine sediments this clearly limits their use particularly in relation to carbonate rich sediments and rocks to address this we here explore the applicability of fe based redox proxies in carbonates through three approaches first we have compiled fe al data for modern marine sediments to investigate variability in fe enrichments as a function of carbonate content and depositional setting second we have expanded this approach with a compilation of new and existing fe speciation data for modern and ancient marine sediments deposited under oxic and euxinic anoxic sulfidic water column conditions finally we show new data from paired limestone and dolomite sample sets to demonstrate the potential significance of deep burial dolomitization on the fe speciation redox proxy modern marine sediments deposited under oxic conditions show no relationship between fe al and carbonate content these sediments have an average fe al ratio of 0 55 0 11 with some higher values potentially being attributable to steady state early diagenetic remobilization of fe towards the sediment water interface in contrast significant fe al enrichments occur as a consequence of water column fe mineral formation and deposition either under anoxic conditions or due to input of anoxic hydrothermal fluids into oxic seawater iron speciation data also show no direct correlation with carbonate content and instead three groups can be distinguished based on total fe fe t and organic c contents sediments deposited under oxic water column conditions with fe t 0 5 wt generally plot below the lower fe hr fe t siliciclastic reference threshold 0 38 for distinguishing anoxic environments regardless of carbonate content also consistent with siliciclastic calibrations carbonate rich sediments deposited under anoxic water column conditions tend to have fe hr fe t ratios 0 38 in contrast oxic carbonate rich sediments with low fe t hr fe t ratios suggesting that the use of fe speciation for such samples is not appropriate for evaluating water column redox conditions taken together our data suggest that an fe t content of 0 5 wt rather than carbonate content represents the most suitable basis for identifying whether carbonate rich sediments are appropriate for fe based redox proxy analyses analysis of burial dolostones suggests that the fe speciation proxy may also be compromised by deep burial dolomitization where there has been a source of mobile fe to enrich rocks during recrystallization however pre screening can identify such samples this new assessment expands the utility of fe based redox proxies to also incorporate appropriate carbonate rich rocks provided that care is taken to assess the possible impact of deep burial dolomitization

maximum link distance between strike slip faults observations and constraints the maximum fault link distance lateral separation between two interacting strike slip faults is studied in relation to fault length combined length of the two interacting faults data collected for laboratory generated strike slip faults indicate that fault linkage takes place when the lateral separation between two strike slip faults is less than one tenth of the combined length of the two faults strike slip faults developed in clay models require a smaller link distance than those developed in gouge materials about 98 of the data collected for natural strike slip faults and 93 of earthquake rupture data derived from knuepfer 1989 follow the rule these observations support a simple scaling relationship for strike slip faults i e w 0 1 l where wis lateral link distance and l the combined fault length an and sammis 1996a two possible explanations are discussed assuming a fault continues to be dominantly strike slip after various fault coalescences the fault link distance for both compressional coalescence leading to restraining bend and extensional coalescence leading to releasing bend can be constrained within 0 134 l assuming fault coalescence is caused by interaction between breakdown zones at fault tips then the scaling relationship b 0 1 l between the size of a breakdown zone b and the individual fault length l scholz et al 1993 leads to the scaling relationship w max 0 1 l where w max is the maximum link distance the above observed relationship between w max and l may not hold if faults coalesce through preexisting faults if a fault has a mixed mode other than strike slip or if a fault bend is caused by cross faulting rather than fault coalescence limited exposure of natural fault traces may also lead to errors in link distance measurements

inter comparison exercises on dissolved gases for groundwater dating 1 goals of the exercise and site choice validation of the sampling strategy abstract two international inter comparison exercises devoted to dissolved gases and isotope analyses in groundwater used as tools for groundwater dating were organized in 2012 in france ides universite paris sud cnrs and osur universite rennes 1 cnrs the goal was to compare sampling and analytical protocols through results obtained by the community of groundwater dating laboratories the two exercises were gdat1 on three supply boreholes in a homogeneous sand aquifer of fontainebleau paris basin france and gdat2 on two supply boreholes shallow and deep in a fractured rock aquifer in french brittany this two step exercise is the first exercise which included a large number of gases and isotopes usually used in groundwater as dating tools and also permit to discuss the uncertainties related to sampling protocols issuing from each laboratory methods the two tests allowed 31 laboratories from 14 countries to compare their protocols for both sampling and analyses this paper presents the participants and parameters measured and focuses on the validation of the sampling strategy two laboratories analyzed cfc and sf6 samples collected at regular intervals during the sampling operations in order to verify water homogeneity the results obtained by the two reference laboratories along with monitoring of field parameters showed no clear trend of gas concentration or physic chemical properties it can be concluded that the pumped groundwater composition remained constant during sampling this study also shows the potential for relatively constant pumped groundwater composition from a specific well despite the complexity and or mixing processes that may occur at a larger scale in the aquifer

integrated ediacaran chronostratigraphy wernecke mountains northwestern canada abstract terminal neoproterozoic ediacaran ca 600 543 ma strata of the upper part of the windermere supergroup are well exposed in the mackenzie mountains and the wernecke mountains of northwestern canada windermere strata in the mackenzie mountains contain an exceptional ediacaran biostratigraphic and isotopic c and sr record while the sequence stratigraphic record is subtle throughout this predominantly deep water succession coeval strata in the wernecke mountains can be correlated with the succession in the mackenzie mountains on a formational level in contrast to the deep water setting of the mackenzies succession the werneckes succession preserves a predominantly shallow water succession amenable to detailed sequence stratigraphy integrated lithostratigraphy chemostratigraphy biostratigraphy and sedimentology partitions the wernecke mountains succession into five depositional sequences and constrains correlation with strata in the mackenzie mountains the siliciclastic and carbonate sediments deposited along the margin of the proto pacific ocean record accumulation in continental slope neritic and terrestrial paleoenvironments distinctive temporal chemostratigraphic and biostratigraphic attributes allow these strata to be correlated with other ediacaran successions worldwide integrating sequence stratigraphy with these attributes is a robust yet under utilized correlation tool and is a step toward erecting a more detailed working neoproterozoic chronostratigraphy

natural cf4 and sf6 on earth the occurrence of cf4 and sf6 in natural fluorites caf2 is reported contents are found to be typically 200 2000 ppt mass for cf4 and 50 100 ppt mass for sf6 cf4 and sf6 were also detected in granites where fluorite is an accessory mineral cf4 and sf6 thus possess a large reservoir in the continental crust that by degassing can sustain natural atmospheric background levels of 40 ppt mole and up to 0 01 ppt mole respectively the article also discusses how natural sf6 may cause interference in hydrological tracer studies

granite magma migration and emplacement along thrusts this paper investigates the influence exerted by brittle tectonic structures in the emplacement of granite plutons in contractional settings we address both cases where contractional tectonics and magma intrusion are 1 coeval to study how active contractional tectonics controls the transport of magma and 2 diachronous to study the role of pre existing structures on the transport of magma in light of new experimental models we show that magma can rise along thrusts ramps and flats this phenomenon occurs for both low viscosity magma basalts to andesite and high viscosity magma dry granite the experimental results also allow the evaluation of the role played by magma viscosity in determining pluton geometries in addition a review of literature demonstrates a spatial and causal relationship between granites and thrusts and highlights the geometric control of magma pathways in the pluton final shape the abundance of subhorizontal and tabular granitic intrusions indicates that the location of inflating granitic sills along thrust flats can be common we argue that active and pre existing flats and ramps thrusts provide a preferential continuous planar anisotropy susceptible to become a granitic magma migration pathway

global warming and the end permian extinction event proxy and modeling perspectives abstract the mass extinction event that occurred at the close of the permian period 252 million years ago represents the most severe biodiversity loss in the ocean of the phanerozoic the links between the global carbon cycle climate change and mass extinction are complex and involve a whole range of often inter related geochemical biological ecologic and climatic factors it has become widely accepted that the end permian mass extinction was associated with a global warming event because the age of the siberian trap eruption a potentially massive source of carbon dioxide coincides within error with the extinction event however geologic data that are in support of this global warming event are relatively sparse the chain of events and the causal relationship between the eruption of siberian traps and mass extinction is not well established global warming in particular has only been reported from limited proxy data and climate models for which the pco2 in the atmosphere just before and during the end permian extinction event is poorly known this study critically assesses both the proxy climate data and the existing paleoclimate simulations with the goals of assessing our current understanding of the link between mass extinction and climate change and providing some guidance for future studies proxies indicate that prior to the end permian extinction event tropical sea surface temperatures ranged from 22 to 25 c and possible pco2 values ranged from 500 to 4000 ppm before the extinction event during the peak extinction tropical temperatures rose up to 30 c while pco2 perhaps increased up to 8000 ppm climate models that use different pre event pco2 values show similar amount of co2 doubling to replicate the observed carbon isotope excursions we find that the temperature anomaly during the end permian extinction is consistent with 1 5 doublings of atmospheric pco2 and that the implied climate sensitivity is 5 6 c within the upper range of values produced by climate models

ion microprobe sr isotope analysis of carbonates with about 5μm spatial resolution an example from an ayu otolith abstract a high lateral resolution secondary ion mass spectrometer nanosims ns50 ion microprobe has been used to measure 87sr 86sr ratios in natural caco3 samples a 2 na o primary beam was used to sputter a 5 7 m diameter crater on the sample surface and secondary positive ions were extracted for mass analysis using an accelerating voltage of 8 kv and a mattauch herzog geometry the multi collector system was adjusted to detect 43ca by a detector em 2 80 ca 2 em 3 86sr em 4 and 87sr em 4b ions at the same time then the magnetic field was scanned for the em 4 to detect 85rb 86sr and 87sr while the em 4b can measure 86sr 87sr and 88sr respectively a mass resolution of 3600 at 10 peak height was attained with a flat peak top while the sensitivity of sr was about 10 cps na ppm an aragonite sample coral skeleton standard jcp 1 was used as a reference for sr isotope ratio calibration repeated analyses of the jcp 1 show that the 87sr 86sr ratio agrees well with the seawater signature within a precision of 0 3 at 2 after the series of corrections such as the ca dimer 87rb and a mass bias estimated by the 88sr 86sr ratio the method was applied to an otolith ear stone from ayu plecoglossus altivelis altivelis collected from the yodo river japan although experimental errors are relatively large up to 3 at 2 the ratios of the core region are higher than the seawater signature while more distal values agree well with seawater the very outermost part again shows the relatively higher 87sr 86sr ratios the spatial variation of 87sr 86sr ratios was consistent with amphidromous migration of the fish namely born in the lake and grown in the coastal sea and finally collected in a river

compilation and time series analysis of a marine carbonate δ18o δ13c 87sr 86sr and δ34s database through earth history abstract the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results 1 oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval 2 all oxygen isotope habitat records show a strong coherent 30 45 ma 38 ma cyclicity throughout the cretaceous and the cenozoic 3 up to 70 of the multi million year variability in the 18o record of the last 115 ma can be simulated by the following equation 18 o 0 64 sin 2 t 120 ma 0 9 x sin 2 t 38 3 ma 1 1 with x ranging from 0 4 0 6 for the low high latitude and deep sea habitats to 0 8 for the mid latitude realm 1 a 120 20 ma cycle occurs in the paleozoic and neoproterozoic 18o record consistent with paleoclimate variability as interpreted from sedimentological and faunal records 2 the offset of 13c values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous 3 sr and s isotope records exhibit a 60 70 ma cyclicity throughout the phanerozoic

composition and timing of carbonate vein precipitation within the igneous basement of the early cretaceous shatsky rise nw pacific numerous calcium carbonate veins were recovered from the igneous basement of the early cretaceous shatsky rise during integrated ocean drilling program iodp expedition 324 the chemical sr ca mg ca and isotopic 87sr 86sr 143nd 144nd 18o 13c compositions of these veins were determined to constrain the timing of vein formation a dominant control by seawater chemistry on calcite composition is evident for most vein samples with variable contributions fromthe basaltic basement slightly elevated precipitation temperatures as inferred from oxygen isotope ratios indicative of hydrothermal vein formation are only observed at site u1350 in the central part of shatsky rise the highest 87sr 86sr ratios least basement influence of vein samples at each drill site range from 0 70726 to 0 70755 and are believed to reflect the contemporaneous seawater composition during the time of calcite precipitation in principle age information can be deduced by correlating these ratios with the global seawater sr isotope evolution since the sr isotopic composition of seawater has fluctuated three times between the early and mid cretaceous no unambiguous precipitation ages can be constrained by this method and vein precipitation could have occurred at any time between 80 and 140 ma however based on combined chemical and isotopic data and correlations of vein compositionwith formation depth and inferred temperature we argue for a rather early precipitation of the veins shortly after basement formation at each respective drill site

dissolved gases in groundwater and groundwater dating methods how useful for hydrogeological modeling foreword to the special issue one of the major challenges in hydrogeology is the basic spatial lack of continuous data as this is restricted to available boreholes basic information is provided by the measurements of physical parameters e g porosity and permeability at the well scale information related to a larger part of the aquifer are provided for example by continuous measurement of piezometric levels or spring flow temporal information is extremely powerful in order to characterize aquifer functioning globally groundwater dating has thus been developed in order to provide time constraints in aquifer studies

50 myr recovery from the largest negative δ13c excursion in the ediacaran ocean sedimentary rocks deposited during the ediacaran period 630 542 ma contain carbonates whose carbon isotopic ratios show a marked negative excursion consisting of a precipitous drop from 5 to 12 followed by a sub linear recovery to positive 13c values isotopic ages u pb and thermal subsidence modelling are combined to constrain the excursion in time and indicate an onset at 600 ma and duration of recovery of approximately 50 myr the excursion is widely recognized in oman and has potential correlatives in ediacaran strata elsewhere and may thus represent a characteristic feature of the ediacaran period the amplitude of this carbon isotope excursion far exceeds those of other neoproterozoic anomalies the isotopic trend of negative excursion and long term recovery spanned at least one short lived glacial episode at 580 ma but appears unrelated to glaciation which indicates that negative anomalies in the neoproterozoic marine carbon isotope record are not directly or uniquely linked to ice ages

nanosims u pb dating of fossil associated apatite crystals from ediacaran 570 ma doushantuo formation abstract sedimentary rocks record a wealth of information on the evolution of lithosphere hydrosphere atmosphere and biosphere however uncertainty about the age of many precambrian sequences makes it very difficult to establish the accurate temporal framework which can dramatically improve our understanding of the scale and duration of geological and biological events the neoproterozoic doushantuo formation south china preserve unique assemblages of early multicellular fossils and records valuable paleoenvironmental information the age of these formations is thus critical for understanding the important biological and climatic events that occurred towards the end of the proterozoic eon in this study we used nanosims to date samples from the doushantuo formations by apatite u pb geochronology fossil associated precipitated apatite grains were identified using optical microscope and raman spectrometer the resultant age is 305 26 ma high common pb and low u concentration in those apatite specimens limit the precision of age determination while the yielded age suggests that the doushantuo formation may have experience a post depositional hydrothermal event

dating groundwater with trifluoromethyl sulfurpentafluoride sf5cf3 sulfur hexafluoride sf6 cf3cl cfc 13 and cf2cl2 cfc 12 1 a new groundwater dating procedure using the transient atmospheric signal of the environmental tracers sf5cf3 cfc 13 sf6 and cfc 12 was developed the analytical procedure determines concentrations of the four tracers in air and water samples sf5cf3 and cfc 13 can be used to date groundwaters in some environments where the cfcs and sf6 have previously failed because these new tracers have increasing atmospheric input functions no known terrigenic source and are believed to be stable under reducing conditions sf5cf3 has a dating range from 1970 to modern the mixing ratio mole fraction in north american air has increased from the detection limit of 0 005 parts per trillion ppt to the 2006 mole fraction of about 0 16 ppt no evidence was found for degradation of sf5cf3 in laboratory anaerobic systems the solubility of sf5cf3 was measured in water from 1 to 35 c groundwater samples that contained large amounts of terrigenic sf6 did not contain terrigenic sf5cf3 cfc 13 is a trace atmospheric gas with a dating range in groundwater of about 1965 to modern cfc 13 has been used primarily in very low temperature refrigeration thus groundwater environments are less likely to be contaminated with nonatmospheric sources as compared to other widely used cfcs because of the low solubility of sf5cf3 and cfc 13 in water an excess air correction must be applied to the apparent ages the new dating procedure was tested in water samples from wells and springs from maryland virginia and west virginia

isotope wallrock alteration associated with hypogene karst of the crimean piedmont ukraine although it is commonly perceived that isotopic alteration of carbonate rock is suppressed at low temperatures below ca 80 100 c this study demonstrates that alteration halos do develop in permeable limestones of relatively low textural maturity the study of paleogene carbonate bedrock constituting the walls of hypogene karst conduits of the crimean piedmont ukraine revealed several events of water rock interaction each resulting in isotopic alteration of the bedrock early development of hypogene karst conduits shifted 18o and 13c toward lower values by 1 2 and 1 3 respectively the width of the alteration zone locally exceeds several meters the case hardening associated with cavernous weathering shifted 18o and 13c of the bedrock toward slightly more positive values by up to 3 and 1 respectively the thickness of isotopic halos ranges from a few centimeters to tens of centimeters during late stage hypogene karstification the 18o values of the bedrock was shifted toward lower values by 5 6 forming a thin 5 15 mm alteration halo in most cases 13c was also shifted toward lower values by 6 9 but in one case a shift toward higher values by ca 2 was observed water involved in early hypogene karst and in the origin of cavernous weathering structures was enriched in 18 such waters are known in crimea in association with mud volcanoes on the kerch peninsula we suggest that similar deep seated water affected the crimean piedmont during the middle miocene water involved in late hypogene karstification had d values of 75 to 68 and 18o values of 10 to 9 fluid inclusion data similar to present day spring and well water in crimea isotopic calculations and fluid inclusion data indicate that the late hypogene karst processes occurred at low temperatures ca 50 c these processes ceased before 130 ka when the crimean piedmont was uplifted dissected by erosion and acquired its modern morphology

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

modern soil system constraints on reconstructing deep time atmospheric co2 abstract paleosol carbonate based estimates of paleo atmospheric co 2 play a prominent role in constraining radiative forcing and climate sensitivity in the deep time large uncertainty in paleo co 2 estimates made using the paleosol carbonate co 2 barometer however arises primarily from their sensitivity to soil respired co 2 s z this parameter is poorly constrained due to a paucity of soil co 2 measurements during carbonate formation in modern soils and a lack of widely applicable proxies of paleo soil co 2 here the 13 c values of carbonate and soil organic matter som pairs from 130 holocene soils are applied to a two component co 2 mixing equation to define soil order specific ranges of soil co 2 applicable for constraining s z in their corresponding paleosol analogs equilibrium carbonate som pairs characterized by 13 c carb som values of 12 2 15 8 define a mean effective fractionation of 14 1 and overall inferred total soil co 2 contents during calcite formation of s z during calcite formation is 1500 2000 ppmv range of 500 2500 ppmv overall higher values 2000 5000 ppmv are indicated by the subset of these soils characterized by higher moisture content and productivity near atmospheric levels 400 200 ppmv of estimated s z are indicated by immature soils recording their low soil productivity vertisols define the largest range in total soil co 2 25 000 ppmv reflecting their seasonally driven dynamic hydrochemistry a s z range of 1000 10 000 ppmv is suggested for paleo vertisols for which calcite precipitation can be constrained to have occurred in an open system with two component co 2 mixing with a best estimate of 2000 ppmv 1000 ppmv appropriate for paleo vertisols for which evidence of protracted water saturation is lacking mollisol pairs define a best estimate of s z of 2500 ppmv range of 600 4000 ppmv for late cretaceous and cenozoic analogs non equilibrium pairs with 13 c values 16 make up 51 of the dataset lending support to the hypothesis that pedogenic carbonate precipitation occurs during periods of low productivity in a soil atmosphere with a large component of atmospheric co 2 predictable scaling between estimated soil co 2 and the difference in 13 c between measured pedogenic carbonate and that predicted to have formed from soil respired co 2 inferred from measured som can be used to further constrain appropriate ranges of s z for reconstruction of paleo atmospheric p co 2 soil co 2 estimates are poorly correlated to mean annual precipitation likely reflecting that for carbonate bearing soils where moisture limits co 2 production total soil co 2 is most strongly influenced by actual evapotranspiration

ion microprobe u pb dating of zircon with a 15 micrometer spatial resolution using nanosims abstract we developed a 238u 206pb and 207pb 206pb zircon dating method using a cameca nanosims ns50 ion microprobe a 7 to 9 na o primary beam was used to sputter a 15 m crater and secondary positive ions were extracted for mass analysis using the mattauch herzog geometry the multicollector system was modified to detect 90zr 204pb 206pb 238u16o and 238u16o2 ions simultaneously a mass resolution of about 4000 at 10 peak height and with a flat peak top was attained and the sensitivity of pb was about 4 cps na 1 ppm 1 a multicrystal zircon standard qgng from south australia with a u pb age of 1842 ma was used as a reference for pb uo uo2 uo calibration and on the basis of the positive correlation between these ratios we determined the sample 206pb 238u ratios 207pb 206pb ratios were measured by magnetic scanning in single collector mode the standard zircons 91500 from canada and sl13 from sri lanka were analyzed against qgng observed 238u 206pb and 207pb 206pb ages agreed well with published ages within experimental error then 16 zircon grains in a metamorphic rock from nagasaki japan were analyzed observed ages were compatible with shrimp ages suggesting that the nanosims with a 15 m probe diameter is suitable for ion microprobe u pb zircon dating

influence of crystallised igneous intrusions on fault nucleation and reactivation during continental extension abstract continental rifting is commonly accommodated by the nucleation of normal faults slip on pre existing fault surfaces and or magmatic intrusion because crystallised igneous intrusions are pervasive in many rift basins and are commonly more competent i e higher shear strengths and young s moduli than the host rock it is theoretically plausible that they locally intersect and modify the mechanical properties of pre existing normal faults we illustrate the influence that crystallised igneous intrusions may have on fault reactivation using a conceptual model and observations from field and subsurface datasets our results show that igneous rocks may initially resist failure and promote the preferential reactivation of favourably oriented pre existing faults that are not spatially associated with solidified intrusions fault segments situated along strike from laterally restricted fault intrusion intersections may similarly be reactivated this spatial and temporal control on strain distribution may generate 1 supra intrusion folds in the hanging wall 2 new dip slip faults adjacent to the igneous body or 3 sub vertical oblique slip faults oriented parallel to the extension direction importantly stress accumulation within igneous intrusions may eventually initiate failure and further localise strain the results of our study have important implications for the structural of sedimentary basins and the subsurface migration of hydrocarbons and mineral bearing fluids

rapid cross density ocean mixing at mid depths in the drake passage measured by tracer release diapycnal mixing across density surfaces is an important process in the global ocean overturning circulation1 2 3 mixing in the interior of most of the ocean however is thought to have a magnitude just one tenth of that required to close the global circulation by the downward mixing of less dense waters4 some of this deficit is made up by intense near bottom mixing occurring in restricted hot spots associated with rough ocean floor topography5 6 but it is not clear whether the waters at mid depth 1 000 to 3 000 metres are returned to the surface by cross density mixing or by along density flows7 here we show that diapycnal mixing of mid depth 1 500 metres waters undergoes a sustained 20 fold increase as the antarctic circumpolar current flows through the drake passage between the southern tip of south america and antarctica our results are based on an open ocean tracer release of trifluoromethyl sulphur pentafluoride we ascribe the increased mixing to turbulence generated by the deep reaching antarctic circumpolar current as it flows over rough bottom topography in the drake passage scaled to the entire circumpolar current the mixing we observe is compatible with there being a southern component to the global overturning in which about 20 sverdrups 1 sv 106 m3 s 1 upwell in the southern ocean with cross density mixing contributing a significant fraction 20 to 30 per cent of this total and the remainder upwelling along constant density surfaces the great majority of the diapycnal flux is the result of interaction with restricted regions of rough ocean floor topography

in situ ion microprobe u pb dating and ree abundances of a carboniferous conodont we report here in situ ion microprobe u pb dating of a conodont micro fossil using an ion microprobe method thirteen spots on the single fragment of the carboniferous conodont size approximately 800 m 100 m yield a 238u 206pb isochron age of 323 36 ma and a tera wasserburg concordia intercept age of 332 44 ma in a three dimensional 238u 206pb 207pb 206 pb 204pb 206pb diagram these ages are consistent with the depositional and early diagenetic ages of the fossil in its host mississippian sedimentary sequence within experimental error the success of the method depends on the chemical fractionation of u from pb within a hundred m length scale and the consequent variations in pb isotopic compositions due to radioactive decay shale normalized rare earth element ree abundances of two spots on the same sample show flat patterns from light ree to middle ree and decreases from middle ree to heavy ree with negative anomalies of both ce and eu the ree characteristics are significantly different from those of devonian conodonts reported by other workers suggesting discrepant redox states and or formation environments

springwater provenance and flowpath evaluation in blue lake bonneville basin utah abstract water in utah and nevada is important for agriculture municipal use solute transport and ecosystem preservation large spring wetland systems occur on the playa margin of the bonneville basin including blue lake 15 km south of the bonneville salt flats on the utah nevada state border large spring systems have historically been studied as water budgets don t apparently balance from direct mountain front recharge nelson and mayo 2014 gardner and heilweil 2014 and others blue lake is no exception prior studies here have suggested discharge rates 0 04 0 05 km3 yr louderback and rhode 2009 greater than expected for modelled recharge in the surrounding mountain range 0 03 km3 yr three hypothesized recharge mechanisms for blue lake are tested mountain front recharge interbasinal groundwater flow and infiltration from historic lake bonneville remote sensing suggests that a conservative estimate of blue lake discharge constitutes 50 64 of modelled mountain front recharge flint et al 2011 major ions 18o 2h dissolved gases 14c 3he 4he ne ar kr xe and trace elements sr and 87sr 86sr isotopes comprehensively constrain recharge conditions water rock interactions flowpaths and groundwater provenance of this large spring system 14c signatures suggest that blue lake discharge has a transit time between 5 600 and 12 200 years older than that of fish springs noble gas concentrations in blue lake water suggest an elevated recharge temperature greater than 19 c and low salinity indicating a deep water table and high geothermal gradient in the recharge area 87sr 86sr ratios of playa margin springs are elevated from that of mid playa groundwaters springwaters from the adjacent mountain range and alluvial fill groundwater from the valley directly south of blue lake playa margin spring sr isotope values 0 713 0 714 are most similar to direct runoff from the deep creek range granodiorite outcrop 0 713 interbasinal groundwater flow in combination with mountain front recharge is best supported by chemical data rather than mountain front recharge alone or the slow discharge of regional aquifers recharged by lacustrine infiltration from lake bonneville

integrated ediacaran sinian chronostratigraphy of south china abstract the ediacaran period was a critical time in the history of life and earth understanding the complex interactions between geological and biological events during this interval requires high resolution chronostratigraphy thanks to its uniquely favorable palaeogeographic setting south china is an ideal region for constructing a framework for global chronostratigraphic correlation of ediacaran strata here continuous ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles as part of the present study 62 reference sections distributed throughout the yangtze platform were investigated analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies three major sequence boundaries occur respectively in the middle and upper parts of the doushantuo formation and in the middle part of the dengying formation subdivision and correlation of the ediacaran successions of the yangtze platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections 1075 samples the sequence boundary sb2 in the middle part of the doushantuo formation is suggested here as the lower xiadongian upper yangtzean series boundary of the ediacaran which coincides with several globally recognizable events namely 1 the end of the neoproterozoic glaciations 2 the first appearance of animals 3 the sudden increase in the diversity of acanthomorphic acritarchs and 4 a negative 13 c excursion the ediacaran system of south china may be subdivided into five stages furthermore the criteria for defining these stages may be applicable throughout the world also the composite carbon isotope profile of the ediacaran of south china can be used as a global reference for chronostratigraphic subdivision and correlation in addition to the globally recognizable negative 13 c excursion in the cap carbonate at the base of the ediacaran the negative 13 c excursion in the uppermost doushantuo wonoka shuram interval represents another globally correlatable major excursion the positive 13 c excursion immediately following the uppermost doushantuo excursion and ending at 548 ma is also useful for global correlation current ediacaran chronostratigraphy and global correlations indicate that the upper doushantuo wonoka shuram negative 13 c excursion ranges from ca 560 ma to 551 ma and therefore coincides with the evolutionary renovation of life feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative 13 c excursion in earth history our chronostratigraphic correlations also imply that the earliest known metazoan biotas namely the weng an and characteristic ediacaran biotas do not constitute two temporally separate evolutionary lineages as proposed previously but represent two parallel evolutionary pathways preceding the cambrian explosion of animal life

conditions during syntectonic vein formation in the footwall of the absaroka thrust fault idaho wyoming utah fold and thrust belt abstract the twin creek limestone in the footwall of the absaroka thrust sheet contains three sets of bed normal syntectonic calcite veins vein formation occurred during cretaceous motion along the absaroka thrust fault as indicated by 1 crosscutting relationships among these vein sets 2 a previously dated solution cleavage and 3 calcite twin analysis fluid inclusions in the veins and overburden estimates constrain inclusion entrapment temperatures to be between 175 c and 328 c results from stable oxygen isotopes indicate that the host and vein fluid compositions were in near isotopic equilibrium applying both reasonable geothermal gradients and constraints on overburden temperature yields fluid pressures during vein precipitation that are near hydrostatic all data taken together suggest both that vein formation within the twin creek formation occurred in a relatively closed system and that the veins filled near hydrostatic fluid pressure because the veins fill precursory cracks vein filling might not reflect the maximum fluid pressure that existed during the complete vein forming process

variscan granitoids related to shear zones and faults examples from the central sudetes bohemian massif and the middle odra fault zone the granitoid intrusions of the central sudetes cs and of the middle odra fault zone mofz ne part of the bohemian massif are both spatially and temporally related to large scale shear zones and faults including possible terrane boundaries that provided effective channels for melt migration summarizing common features of the cs and mofz granitoids we have delineated a set of characteristics of the fault related and shear zone related granitoids 1 they are mainly generated by partial melting of crustal sources with variable contribution or no contribution of mantle materials 2 the sheet like steeply inclined narrow and rather small granitoid intrusions are emplaced within shear zones at mid crustal level c 20 km depth whereas the larger flat lying plutons intrude into the upper crust outside or above these shear zones 3 the magmatic foliation and lineation in granitoids of the deeper sheet like intrusions are concordant with those in the surrounding metamorphic rocks suggesting that the solidification of granitoids was coeval with the deformation in the shear zones instead the magmatic foliation in the shallower and larger dome like plutons reflects magma flow 4 ductile transcurrent movements along the shear zones postdate medium pressure regional metamorphism and are accompanied by an increase in the local thermal gradient as documented by the crystallization of cordierite andalusite and sillimanite 5 the increase in the thermal gradient precedes the emplacement of granitoids and their concomitant thermal influence on the country rocks the granitoids related to the final stages of tectonothermal activity of the shear zones are good time markers of their evolutionary path

evidence from the oman ophiolite for sudden stress changes during melt injection at oceanic spreading centres the system of dikes in the uppermost mantle below oceanic spreading centres bears witness to the processes involved in the supply of melt to the ridge such systems cannot be studied on currently active ridges but can be seen in ophiolites in particular the oman ophiolite allows us to examine segments of a fast spreading ridge1 here we present a statistical analysis of the orientation of intrusions in the uppermost mantle section of the oman ophiolite spreading centres which points to the existence of two systems dikes whose azimuth is parallel to the sheeted dikes which we thus consider as related to the extensional lithospheric stress field and sills roughly parallel to the moho2 branching contemporaneous dikes and sills are frequently observed we suggest that these relations can be explained by repeated sudden changes of the dominant stress field from lithospheric to asthenospheric such changes could result from the episodic relaxation of lithospheric stress in response to tension fracturing of the lithospheric lid related to sudden melt surges this episodic behaviour is recorded in the sheeted dike complex with each dike each about one metre wide representing one of these fractures

in defense of magmatic diapirs abstract diapirism as a crustal magma ascent mechanism has been recently criticized we contend that this reflects an overly simplistic view that diapirs must resemble modeled hot stokes diapirs and the perception that magma ascent in dikes is a more problem free mechanism for the construction of plutons we describe four cordilleran plutons that have characteristics much more compatible with diapirs than dike fed chambers these plutons were emplaced at depths ranging from 10 to 30 km and record different parts of diapiric ascent paths most ascended during complex visco elastic flow of host rock during regional deformation have narrow structural aureoles indicating power law behavior of host rock and were constructed of multiple batches of magma attributes enabling them to ascend greater distances than single hot stokes diapirs some features of these plutons are not typically attributed to diapirs and thus we introduce the term visco elastic diapir for bodies consisting of one or more batches of magma rising together with length to width ratios

natural fluorinated organics in fluorite and rocks results of measurements of fluorinated compounds in gasses extracted from igneous and metamorphic rocks are reported a new extraction method analogous to a pepper mill for geological samples is described it permits extraction at low temperatures and ensures a rapid transfer of extracted gases from active surfaces to cryogenic pre concentration loop values for cf4 cf3cl cf2cl2 cfcl3 chf3 sf6 and nf3 in fluorites granites basalts and other igneous and metamorphic rocks are reported it is proposed that trifluoroacetic acid tfa that was recently discovered in various environmental archives could also origin from similar geogenic sources

magma emplacement during arc perpendicular shortening an example from the cascades crystalline core washington it is increasingly inferred by others that active arcs at all crustal levels are undergoing arc perpendicular extension and that magma utilizes this extension or extension along arc parallel strike slip faults during emplacement however a review of stress fields in modern arcs and deformation which occurred during magmatism in ancient arcs and our own emplacement studies of individual plutons indicate that magma emplacement typically occurred during arc perpendicular shortening without the aid of strike slip faulting this conclusion raises the question of how host rock is displaced during magma emplacement in shortening and thickening orogens evaluation of host rock material transfer processes that operated during emplacement of the 93 ma 10 to 14 km deep mount stuart batholith washington provides one example and includes the following 1 ductile downward flow in a narrow 0 2 body radii structural aureole 2 stoping and of lesser importance 3 regional folding thrusting and subhorizontal arc parallel extension we see no evidence that arc perpendicular extension or local extension along strike slip faults made space for this pluton nor for most other plutons in contractional arcs instead we argue that both localized and rapid around plutons and regional and slower downward flow during growth of crustal roots is a common process in such arcs

ion microprobe u pb dating and sr isotope measurement of a protoconodont abstract this report describes in situ ion microprobe u pb dating of a protoconodont an early cambrian phosphate microfossil using laterally high resolution secondary ion mass spectrometry nanosims on a single fragment of a fossil approximately 850 m 250 m derived from a sedimentary layer in the meishucunian yuhucun formation yunnan province southern china 23 spots provide a 238u 206pb isochron age of 547 43 ma 2 mswd 1 9 which is consistent with the depositional age 536 5 2 5 ma estimated using zircon u pb dating of interbedded tuffs however five spots on a small region approximately 250 m 100 m in the same protoconodont yield an isochron age of 417 74 ma 2 mswd 0 31 apparently younger than the formation age the younger age might be attributable to a later hydrothermal event perhaps associated with caledonian orogenic activity recorded in younger zircon with an age of 420 440 ma we also measured 87sr 86sr ratios of the protoconodont by nanosims in the older domain 19 spots give the 87sr 86sr ratio of 0 71032 0 00023 2 although seven spots on the younger region provide the ratio of 0 70862 0 00045 this is significantly less radiogenic than the older domain this is the first report of u pb age and sr isotope heterogeneity within a single fragment of micro fossil 215

linking mineral deposit models to quantitative risk analysis and decision making in exploration this paper describes a methodology of translating mineral deposit models into flexible probabilistic structures based on 1 extraction of ore components fluids metals and ligands from crustal or mantle sources or both 2 fluid or melt assisted transport of ore components from source to trap zones 3 formation of trap zones i e effective melt or fluid channels that can focus melt or fluid migration and accommodate large amounts of metal and 4 operation of the physicochemical processes that promote and sustain the deposition of metal from fluids or melts passing through a particular trap site our approach integrates these critical mineralization processes and conditions with concepts of probability theory decision analysis and financial modeling the principal objective is to make mineral deposit models amenable to financial risk and value analysis and suitable for communication of value creating geologic concepts to financial stakeholders in economic terms a case study based on an actual porphyry copper project illustrates how the resulting probabilistic mineral systems model can generate a measure of the probability of ore occurrence as an input for exploration decision trees and simulations to calculate the expected value of an exploration project and the probability distribution of all possible surrounding net present values npvs within a minimum and maximum range formulation of the probabilistic model closely follows and combines principles of the well established petroleum and mineral systems approaches and makes use of excel based model templates with decision tree and simulation add in software packages

deformation across the western united states a local estimate of pacific north america transform deformation we obtain a locally based estimate of pacific north america relative motion and an uncertainty in this estimate by integrating deformation rate along three different paths leading west across southwestern north america from east of the rio grande rift to near the continental escarpment data are primarily quaternary geologic slip rate estimates and resulting deformation determinations therefore are instantaneous in a geologic sense but long term with respect to earthquake cycles we deduce a rate of motion of the pacific plate relative to north america that is 48 2 mm yr a rate indistinguishable from that predicted by the global kinematic models rm2 and nuvel 1 however we obtain an orientation that is 5 9 counterclockwise of these models a more westerly motion of the pacific plate with respect to north america is calculated from all three paths the relatively westerly motion of the pacific plate is accommodated by deformation in the north american continent that includes slip on relatively counterclockwise oriented strike slip faults including the san andreas fault which is especially relevant in and south of the transverse ranges and a margin normal component of net extension across the continent which is especially relevant north of the transverse ranges deformation of the sw united states occurs in regionally coherent domains within which the style of deformation is approximately uniform in the vicinity of the transverse ranges two important shear systems splay from the san andreas fault the eastern california shear zone trending nnw from the eastern transverse ranges and the trans peninsular faults trending sse from the western and central transverse ranges within the transverse ranges the right lateral san andreas fault steps left seemingly requiring large amounts of convergence there however most of this convergence is avoided through a funneling flow of the crust toward the western transverse ranges and into the relatively narrow central california coast ranges and the northern motion of the mojave the former process involves an alternation of rotation direction from counterclockwise in and south of the central transverse ranges to clockwise in the western transverse ranges

eocene shoshonitic mafic dykes intruding the monashee complex british columbia a petrogenetic relationship with the kamloops group volcanic sequence the newly named three valley suite tvs kersantite lamprophyre to shoshonitic mafic dykes of the monashee complex are inferred to be hypabyssal feeder dykes to an alkaline to calc alkaline volcanic suite related to the kamloops group these dykes were emplaced in a subvertical north trending orientation coincident with inferred eocene crustal extension 50 0 ma based on the flat 40ar 39ar step heating plateau of contact metamorphic muscovite on the margin of a tvs dyke these weakly altered mafic dykes are fine grained with phenocrysts 0 5 2 0 mm of phlogopite augite amphibole and olivine pseudomorphed by clays rare labradorite and both primary and secondary carbonates set in a fine grained groundmass of similar mineralogy consistent with their classification as plagioclase bearing potassic diorite to kersantite lamprophyre the dykes are weakly silica undersaturated and alkalic 2 8 wt k2o 7 7 wt mgo with high large ion lithophile element contents 300 times primitive mantle and ele

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

uranium and thorium distributions in fossil bones from olduvai gorge tanzania and kanam kenya abstract the micro distributions of uranium and thorium have been studied in fossil bone cortices in samples from olduvai gorge tanzania and kanam kenya and compared with modern bones collected from the surface at olduvai gorge concentrations in excess of 800 ppm u and 200 ppm th are recorded in sections of some fossil bones whereas concentrations do not exceed 20 ppm u or 1 ppm th in the modern bones in fossil bones th has a larger intra bone variation than u the distribution profiles of the two elements across the fossil bone cortices are quite distinct and reflect differences in their geochemical behaviour in the supergene environment in particular the two possible oxidation states of u compared with one for th allow u to be more mobile than th but also more susceptible to variations in the redox potential of the depositional environment in some fossil bone samples secondary leaching of u has occurred whereas th is retained in the bone cortex u is incorporated into fossil bone earlier than th

rates of processes in magmatic arcs implications for the timing and nature of pluton emplacement and wall rock deformation abstract the construction of arcs and in many cases the emplacement of plutons occur in tectonically active regions it is critical therefore to evaluate the rates of structural and magmatic processes when trying to understand the evolution of arcs and the associated pluton wall rock systems our best estimates of average rates or durations of processes in shallow to moderate level arc environments are the following 1 crystal growth rates in magma of 10 4 cm year 1 2 growth rates of metamorphic porphyroblasts between 10 5 and 10 2 cm year 1 3 long term magma supply rates of 10 1 km 3 year 1 and short term rates of up to 350 km 3 year 1 4 diapiric ascent rates for mafic plutons of 1 3 m year 1 5 cooling of plutons to ambient wall rock temperatures in 10 5 10 6 years 6 final crystallization of plutons in a small fraction of the time needed for complete cooling 7 fault displacements of 3 cm year 1 8 development of cleavages in fault zones in less than 10 6 years at strain rates of 10 13 s 1 or higher and 9 the development of regional cleavages in 10 6 years at strain rates of 10 14 s 1 these rates indicate that processes operating in magmatic arcs are relatively rapid pluton emplacement cleavage development etc occur over time spans of tens of thousands to no more than a few million years however the rate of ascent and crystallization of plutons at shallow levels is generally shorter than that needed to get large displacements on faults or widespread cleavages developed at deeper levels or in zones undergoing faster strain rates the time spans of the various processes approach one another thus plutons with otherwise similar characteristics emplaced in regions undergoing fast strain rates or at deeper crustal levels may appear quite different structurally from those emplaced at shallow levels or in regions undergoing slower strain rates comparison of these data also suggests that the rate at which wall rock deforms is the limiting factor controlling the rates of other structural processes during emplacement of plutons unless fast strain rates or multiple deformation mechanisms are considered thus emplacement mechanisms that rely on the transport of magma over 10 5 to 10 6 years are favored and need further consideration finally we argue that the structural and other characteristics of pluton wall rock systems will depend on rates of various processes involved and that these rates at the very least influence and sometimes invalidate the timing criteria previously published by us and others

compilation and time series analysis of a marine carbonate delta o 18 delta c 13 sr 87 sr 86 and delta s 34 database through earth history the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval all oxygen isotope habitat records show a strong coherent 30 45 ma similar to 38 ma cyclicity throughout the cretaceous and the cenozoicup to 70 of the multi million year variability in the 6180 record of the last 115 ma can be simulated by the following equation delta o 18 parts per thousand 0 64 sin 27 pi t 120 ma 0 9 xsin 2 pi t 38 3 ma 1 1 with x ranging from 0 4 0 6 parts per thousand for the low high latitude and deep sea habitats to 0 8 parts per thousand for the mid latitude realm a similar to 120 20 ma cycle occurs in the paleozoic and neoproterozoic delta o 18 record consistent with paleoclimate variability as interpreted from sedimentological and faunal records the offset of delta c 13 values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous sr and s isotope records exhibit a similar to 60 70 ma cyclicity throughout the phanerozoic c 2008 elsevier b v all rights reserved

the role of magma overpressure in suppressing earthquakes and topography worldwide examples in an extending terrane basaltic magma supplied at a pressure greater than the least principal stress overpressure may be capable of suppressing normal faulting and the earthquakes and topographic relief that commonly accompany normal faulting as vertical dikes intrude they press against their walls in the direction opposite the least principal stress and increase its magnitude the emplacement of tabular intrusions causes the internal magma pressure to act selectively in opposition to tectonic stresses this process tends to equalize the stresses and thus diminishes the deviatoric stress difference between maximum and minimum stresses that creates faults and causes earthquakes observations of the pattern of seismicity and magmatism worldwide indicate that magmatism commonly supplants large earthquakes as the primary mechanism for accommodating tectonic extension recognizing the extent of magmatic stress accommodation is important in assessing seismic and volcanic risks

the origins of the mengye potash deposit in the lanping simao basin yunnan province western china abstract the lanping simao basin lsb is a mesozoic cenozoic continental margin rift basin in western china it formed during the opening and closing of the tethys ocean this basin is also known as a metal belt as it hosts several metal deposits besides the mengye potash deposit however the exact dates of the formation either in the paleocene or the cretaceous and thus the origins of the marine continental or mixed origins of the mengye deposits remain disputed based on the basin s evolution materials of marine origin and or remnant seawater should be present but instead the salt layers of the mengye potash deposit present typically continental lithological features this study examines and reviews evaporative minerals br cl and i cl molar ratios and isotopes of s b and sr i and i cl data for this area has not been previously reported the basin s evaporative minerals are dominated by halite and sylvite the amounts of anhydrite chlorocalcite langbeinite glaserite tachyhydrite and glauberite are small all of these form in both marine and continental environments the values of i and the i cl molar ratios of halite and sylvite are from 0 07 to 0 27 ppm and from 0 03 to 0 11 10 6 respectively dependent on organic substances br and molar br cl values are from 89 08 to 555 45 ppm and from 0 06 10 3 to 0 38 10 3 respectively all of the br cl molar ratios are lower than those of seawater and most of them are 34 s 11 b and 87 sr 86 sr values for evaporative minerals indicate a continental origin for the mengye potash deposit however materials of hydrothermal origin are widely distributed in the basin and may have played an active role for the formation of the potash deposit thus the mengye potash deposit could be of continental origin with a remnant seawater trace