deglacial valley fill sedimentation pelly river yukon territory canada abstract a thick sequence of deglacial valley fill was studied along the pelly river yukon territory late wisconsinan deglaciation was by regional stagnation of the cordilleran ice sheet resulting in complex sequences of sediments deposited in glacial lakes many above stagnant ice more than 30 sections were described and measured and eight facies were recognized and interpreted the distribution of sediment reflects control by several systems 1 ice depositing basal tills 2 debris flows in glacial lakes depositing diamicton 3 meltwater streams depositing sorted sediment and 4 melting of underlying ice remobilizing and deforming previously deposited sediment a model is constructed that helps to explain sedimentation along pelly river material was deposited into lakes from melting ice valley slopes and adjacent valleys basal tills are relatively rare with most diamictons representing deposition by sediment gravity flows the presence of large thicknesses of highly disturbed sediments indicates that the sediments were deposited onto ice and subsequently failed undisturbed glaciolacustrine sediments were deposited either in more distal parts of the basin or after most of the ice had ablated the adjacent topography and the height of the glacial limits also influenced sedimentation steeper topography provided coarser sediments for deposition while low elevation of glacial limits reduced the availability of sediment even if steep slopes were present this study further contributes to models of supraglacial sedimentation by documenting that sedimentation was in several lake basins that lateral gradations in grain size are present and that fairly significant amounts of diamicton can be present

a simple way to extract baddeleyite zro2 1 baddeleyite is a reliable geochronometer for dating the crystallization of mafic and other silica undersaturated intrusive rocks its high u and negligible initial pb content enable precise age determinations with statistical errors of a few million years or less the widespread use of baddeleyite for dating has however been limited by the low content of baddeleyite in many samples and by difficulties in isolating baddeleyite we have developed a new separation technique that utilizes differences in transport velocity among grains of varying size as they move across the deck of a water shaking table a small sample portion is loaded instantly on the table and only the finest and densest material remaining after similar to120 s is collected repeated recovery of sample portions yields a concentrate strongly enriched in baddeleyite and opaque minerals the latter is easily removed by a hand magnet the water based separation technique will improve yields of baddeleyite from samples processed on a water shaking table and is capable of recovering very fine grains as the entire separation is made in water problems arising from adhesive forces between minerals are minimized as is the risk of cross contamination no heavy liquids are necessary making separation quick uncomplicated and inexpensive

understanding shallow and deep flow for assessing the risk of hydrocarbon development to groundwater quality in recent years concerns have been raised about the potential environmental impacts of oil and gas og 2 potential contaminant release mechanisms related to og and 3 the expected effects that contaminant releases could have on groundwater

geochemistry of groundwater in the saint edouard area quebec canada and its influence on the distribution of methane in shallow aquifers abstract shale gas and tight oil production has undergone a tremendous increase in the last decade in north america which was accompanied by animated scientific debate and local public uproar concerning environmental issues especially the risks of contamination for shallow groundwater resources in quebec eastern canada public concerns led to a de facto moratorium on hydraulic fracturing in 2010 for the st lawrence lowlands where the underlying utica shale is known to contain significant gas resources as only a few exploration gas wells have been drilled this vast area may still be considered virgin in 2012 a 4 year project was initiated by the geological survey of canada which aimed at characterizing aquifer vulnerability to deep industrial activities in the saint edouard region located close to quebec city in the st lawrence lowlands as part of this project a baseline study of hydrocarbons and other geochemical parameters was conducted in shallow aquifers this paper presents groundwater geochemical characteristics in the region and assesses the geological hydrogeological and geochemical controls on methane distribution results show that methane is present in 96 of the 48 sampling points over the 500 km2 study area and that concentrations are highly variable from undetected

thermokarst lake basin sediments tuktoyaktuk coastlands western arctic canada three stages of deposition are distinguished in thermokarst lake basin sequences in ice rich permafrost of the tuktoyaktuk coastlands western arctic canada 1 widespread retrogressive thaw slumping around lake margins that rapidly transports upland sediments into thermokarst lakes forming a distinctive basal unit of impure sand and or diamicton 2 a reduction or cessation of slumping because of the pinching out of adjacent ground ice slump stabilization or climatic cooling that reduces the input of clastic sediment permitting reworking of sediment around lake margins and suspension settling principally in basin centres 3 lakes drain and deposition may continue by gelifluction and accumulation of in situ peat or aeolian sand radiocarbon dating of detrital peat and wood from a progradational sequence basal unit defines a lateral younging trend in the direction of progradation a progradation rate is calculated to be 4 cm yr 1 consistent with rapid deposition during stage 1 above the nonuniform nature of the trend is attributed to episodic influxes of old organic material by slumping and reworking by waves and currents in comparison with thermokarst lake basin sequences previously described in alaska canada and siberia the middle unit of those in the tuktoyaktuk coastlands is similar whereas the basal unit is generally thicker and by contrast often contains diamicton these differences are attributed respectively to larger scale resedimentation of upland sediments by retrogressive thaw slumping and debris flow deposition in thermokarst lakes in the tuktoyaktuk coastlands compared with the sediments within supraglacial lakes in areas of moderate to high relief the middle unit of thermokarst lake basin sequences in the tuktoyaktuk coastlands lacks clastic varves and the basal unit is much thinner and texturally less variable these differences are attributed to higher relief and larger volumes of meltwater and glacigenic sediment in supraglacial lakes which promote more suspension settling and resedimentation of glacigenic sediment than in thermokarst lakes in the tuktoyaktuk coastlands it may be impossible to distinguish glacial and periglacial thermokarst lake basin sediments in permafrost areas of incomplete deglaciation not only is it often difficult to distinguish intrasedimental and buried glacier ice but the depositional processes associated with thaw of both ice types are presumably the same and the host sediments very similar

the role of hydrothermal processes in concentrating high field strength elements in the strange lake peralkaline complex northeastern canada abstract the middle proterozoic peralkaline pluton at strange lake quebec labrador comprises hypersolvus to subsolvus phases which are unusually enriched in zr y rees nb be and f as exotic alkali and alkaline earth silicate minerals the highest concentrations of these elements are in subsolvus granite which underwent intense low temperature 200 c hydrothermal alteration involving hematization and the replacement of alkali high field strength element hfse minerals by calcic equivalents this alteration is interpreted to have been caused by meteoric or formational waters high temperature 350 c alteration attributed to orthomagmatic fluids is evident in other parts of the subsolvus granite by the replacement of arfvedsonite by aegirine comparisons of the chemical compositions of fresh and altered rocks indicate that rocks subjected to high temperature alteration were chemically unaffected except for depletion in zr y and hrees these elements were appreciably enriched in rocks that underwent low temperature alteration other elements affected by low temperature alteration include ca and mg which were added and na which was removed available data on hfse speciation in aqueous fluids and the chemistry of the pluton suggest that the hfses were transported as fluoride complexes if this was the case the low temperature fluid could not have been responsible for hfse transport because the high concentration of ca and low solubility of fluorite would have buffered f activity to levels too low to permit significant complexation we propose that hfse mineralization and accompanying alteration were the result of mixing in the apical parts of the pluton of a f rich essentially ca free orthomagmatic fluid containing significant concentrations of hfses with an externally derived meteoric dominated fluid enriched in ca as a result of interaction with calc silicate gneisses and gabbros according to this interpretation the latter fluid was responsible for the exchange of ca for alkalis mainly na in hfse rich minerals and by sharply reducing f activity in the mixed fluid through fluorite precipitation and or increasing ph destabilised the hfse fluoride complexes causing deposition of hfse bearing minerals an important implication of this study is that major hfse enrichment may be restricted to those rare cases where f rich ca free metal leaching environments and ca rich depositional environments are juxtaposed

tectonic evolution of a composite collision orogen an overview on the qinling tongbai hong an dabie sulu orogenic belt in central china abstract the formation of collisional orogens is a prominent feature in convergent plate margins it is generally a complex process involving multistage tectonism of compression and extension due to continental subduction and collision the paleozoic convergence between the south china block scb and the north china block ncb is associated with a series of tectonic processes such as oceanic subduction terrane accretion and continental collision resulting in the qinling tongbai hong an dabie sulu orogenic belt while the arc continent collision orogeny is significant during the paleozoic in the qinling tongbai hong an orogens of central china the continent continent collision orogeny is prominent during the early mesozoic in the dabie sulu orogens of east central china this article presents an overview of regional geology geochronology and geochemistry for the composite orogenic belt the qinling tongbai hong an orogens exhibit the early paleozoic hp uhp metamorphism the carboniferous hp metamorphism and the paleozoic arc type magmatism but the three tectonothermal events are absent in the dabie sulu orogens the triassic uhp metamorphism is prominent in the dabie sulu orogens but it is absent in the qinling tongbai orogens the hong an orogen records both the hp and uhp metamorphism of triassic age and collided continental margins contain both the juvenile and ancient crustal rocks so do in the qinling and tongbai orogens in contrast only ancient crustal rocks were involved in the uhp metamorphism in the dabie sulu orogenic belt without involvement of the juvenile arc crust on the other hand the deformed and low grade metamorphosed accretionary wedge was developed on the passive continental margin during subduction in the late permian to early triassic along the northern margin of the dabie sulu orogenic belt and it was developed on the passive oceanic margin during subduction in the early paleozoic along the northern margin of the qinling orogen three episodes of arc continent collision are suggested to occur during the paleozoic continental convergence between the scb and ncb the first episode of arc continent collision is caused by northward subduction of the north qinling unit beneath the erlangping unit resulting in uhp metamorphism at ca 480 490 ma and the accretion of the north qinling unit to the ncb the second episode of arc continent collision is caused by northward subduction of the prototethyan oceanic crust beneath an andes type continental arc leading to granulite facies metamorphism at ca 420 430 ma and the accretion of the shangdan arc terrane to the ncb and reworking of the north qinling erlangping and kuanping units the third episode of arc continent collision is caused by northward subduction of the paleotethyan oceanic crust resulting in the hp eclogite facies metamorphism at ca 310 ma in the hong an orogen and low p metamorphism in the qinling tongbai orogens as well as crustal accretion to the ncb the closure of backarc basins is also associated with the arc continent collision processes with the possible cause for granulite facies metamorphism the massive continental subduction of the scb beneath the ncb took place in the triassic with the final continent continent collision and uhp metamorphism at ca 225 240 ma therefore the qinling tongbai hong an dabie sulu orogenic belt records the development of plate tectonics from oceanic subduction and arc type magmatism to arc continent and continent continent collision

coarse grained sediment flow facies in a large supraglacial lake discussion sur l article de eyles n clark b m and clague j j 1987 sedimentology vol 34 93 216

first identification of baddeleyite related linked to contact metamorphism from carbonatites in the world s largest ree deposit bayan obo in north china craton abstract baddeleyite has been recognized as a key mineral to determine the crystallization age of silica undersaturated igneous rocks here we report a new occurrence of baddeleyite identified from ree nb th rich carbonatite in the world s largest ree deposit bayan obo in the north china craton china u th pb dating of three baddeleyite samples yields crystallization ages of 310 270 ma with the best estimated crystallization age of ca 280 ma these ages are significantly younger than the ca 1300 ma bayan obo carbonatites but broadly coeval to nearby permian granitoids intruding into the carbonatites hence the bayan obo baddeleyite did not crystallize from the carbonatitic magma that led to the formation of the bayan obo carbonatites and related ree nb th deposit instead it crystallized from hydrothermal fluids and or a reaction involving zircon and dolomite during contact metamorphism related to the permian granitoid emplacement this is in agreement with the results of electron microprobe analysis that show humite inclusions in baddeleyite since humite is a typical magnesian skarn mineral and occurs in close proximity to the intrusive contacts between carbonatites and granitoids our results show that baddeleyite can be used for dating hydrothermal and contact metamorphic processes

probability of a given magnitude earthquake induced by a fluid injection 1 fluid injections in geothermic and hydrocarbon reservoirs induce small earthquakes 3 m 2 occasionally however earthquakes with larger magnitudes m 4 occur we investigate magnitude distributions and show that for a constant injection pressure the probability to induce an earthquake with a magnitude larger than a given value increases with injection time corresponding to a bi logarithmical law with a proportionality coefficient close to one we find that the process of pressure diffusion in a poroelastic medium with randomly distributed sub critical cracks obeying a gutenberg richter relation well explains our observations the magnitude distribution is mainly inherited from the statistics of pre existing fracture systems the number of earthquakes greater than a given magnitude also increases with the strength of the injection source and the tectonic activity of the injection site our formulation provides a way to estimate expected magnitudes of induced earthquakes it can be used to avoid significant earthquakes by correspondingly planning fluid injections

role of fluid injection on earthquake size in dynamic rupture simulations on rough faults an outstanding question for induced seismicity is whether the volume of injected fluid and or the spatial extent of the resulting pore pressure and stress perturbations limit rupture size we simul

geochemistry of vein and wallrock carbonates from the ediacaran system in south china insights into the origins of depositional and post depositional fluids abstract a combined study of carbon oxygen isotopes and major trace elements was carried out for vein and wallrock carbonates from the lantian formation of the ediacaran system in south china the results provide geochemical constraints on the origins of depositional and post depositional fluids with respect to recognition of the post depositional alteration the lantian formation was subdivided into the upper and lower carbonate units for the upper unit uu petrographic observations indicate that wallrock carbonates only experienced limited post depositional alteration the wallrock exhibits 18 o values of 19 2 to 13 1 and 13 c values of 9 6 to 8 9 both relative to vpdb the vein carbonates are divided into groups a and b based on their 18 o values and ree y patterns group a veins show nearly similar 18 o and 13 c ranges to but different ree y patterns from the wallrock these data indicate that the origin of fluids for group a veins may be similar to that of wallrock which was probably the mixture of continental and marine glacial meltwaters group b veins show both different 18 o values and ree y patterns from but similar 13 c values to the wallrock this indicates that post depositional fluids are different from the depositional fluids and thus of external origin low 18 o values 23 7 to 18 1 for group b veins indicate that the post depositional fluids were derived from continental glacial meltwater there is no correlation between 18 o and 13 c values for these vein and wallrock carbonates suggesting that the wallrock was not extensively altered by the post depositional fluids for the lower unit lu veins exhibit different c o isotope compositions and ree y patterns from wallrock carbonate indicating that post depositional fluids have different geochemical compositions from depositional fluids and thus are of external origin the simultaneous changes in 18 o and 13 c values with different laminations in the wallrock carbonates suggest the preservation of the primary geochemical compositions the 18 o values and ree y patterns for the lu veins indicate that the post depositional fluids were probably the mixtures of continental and marine glacial meltwaters therefore the lantian carbonates record the incorporation of continental glacial meltwater into the marginal sea of ediacaran age nevertheless the geochemical screening can provide constraints on the preservation of primary signatures and thus on the origins of depositional and post depositional fluids in the neoproterozoic marine carbonates

characterization of hydraulic properties of rocks using probability of fluid induced microearthquakes the use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs such injections often induce small magnitude earthquakes the nature of processes leading to triggering of such microseismicity is still not completely understood here we consider induced microseismicity using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight gas sandstone reservoir in all three cases we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks this strongly supports the hypothesis of seismicity triggered by pore pressure moreover this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision

prograde and retrograde fluid flow during contact metamorphism of siliceous carbonate rocks from the ballachulish aureole scotland siliceous dolomites and limestones contain abundant retrograde minerals produced by hydration carbonation reactions as the aureole cooled marbles that contained periclase at the peak of metamorphism bear secondary brucite dolomite and serpentine forsterite dolomite marbles have retrograde tremolite and serpentine wollastonite limestones contain secondary calcite and quartz and wollastonite free limestones have retrograde tremolite secondary tremolite never appears in marbles where brucite has replaced periclase or in wollastonite bearing limestones a model for infiltration of siliceous carbonates by co2 h2o fluid that assumes a vertical upwardly directed flow b fluid flux proportional to cooling rate and c flow and reaction under conditions of local equilibrium between peak temperatures and 400 c reproduces the modes of altered carbonate rocks observed reaction textures and the incompatibility between tremolite and brucite and between tremolite and wollastonite except for samples from a dolomite xenolith retrograde time integrated flux recorded by reaction progress is on the order of 1000 mol fluid cm2 rock local focusing of flow near the contact is indicated by samples from the xenolith that record values an order of magnitude greater formation of periclase forsterite and wollastonite at the peak of metamorphism also required infiltration with prograde time integrated flux approximately 100 1000 mol cm2 the comparatively small values of prograde and retrograde time integrated flux are consistent with lack of stable isotope alteration of the carbonates and with the success of conductive thermal models in reproducing peak metamorphic temperatures recorded by mineral equilibria although isobaric univariant assemblages are ubiquitous in the carbonates most formed during retrograde metamorphism isobaric univariant assemblages observed in metacarbonates from contact aureoles may not record physical conditions at the peak of metamorphism as is commonly assumed

geomechanical analysis of fluid injection and seismic fault slip for the mw4 8 timpson texas earthquake sequence an earthquake sequence that culminated in a mw4 8 strike slip event near timpson east texas the largest reported earthquake to date in that region had previously been attributed to wastewater injection starting 17 months before the onset of recorded seismic activity to test if this earthquake sequence can be attributed to wastewater injection we conducted coupled poroelastic finite element simulations to assess the spatial and temporal evolution of pore pressure and stress field in the vicinity of the injection wells and to calculate the coulomb failure stress on the seismogenic fault as a function of the permeability of the injection layer fault orientation fault permeability and orientation and magnitude of the in situ stress we find that injection induced fault slip is plausible within the range of selected model input parameters with slip favored by low reservoir permeability low fault permeability and a favorable orientation of the fault relative to the in situ stress state other combinations of equally plausible input parameters predict no slip within 96 months of simulated injection under most favorable boundary conditions for fault slip fault slip occurs 7 months after the start of injection our results highlight the importance of detailed geomechanical site characterization for robust fault stability assessment prior to wastewater injection

zircon u pb age trace element and hf isotope composition of kongling terrane in the yangtze craton refining the timing of palaeoproterozoic high grade metamorphism u pb age trace element and hf isotope compositions of zircon were analysed for a metasedimentary rock and two amphibolites from the kongling terrane in the northern part of the yangtze craton the zircon shows distinct morphological and chemical characteristics most zircon in an amphibolite shows oscillatory zoning high th u and 176lu 177hf ratios high formation temperature high trace element contents clear negative eu anomaly as well as hree enriched patterns suggesting that it is igneous the zircon yields a weighted mean 207pb 206pb age of 2857 8 ma representing the age of the magmatic protolith the zircon in the other two samples is metamorphic it has low th u ratios low trace element concentrations variable hree contents 33 8 lun 2213 14 7 lun smn 354 and 176lu 177hf ratios 0 000030 0 001168 the data indicate that the zircon formed in the presence of garnet and under upper amphibolite facies conditions the metamorphic zircon yields a weighted mean 207pb 206pb age of 2010 13 ma these results combined with previously obtained palaeoproterozoic metamorphic ages suggest a c 2 0 ga palaeoproterozoic collisional event in the yangtze craton which may result from the assembly of the supercontinent columbia the zircon in two samples yields weighted mean two stage hf model tdm2 ages of 3217 110 and 2943 50 ma respectively indicating that their protoliths were mainly derived from archean crust

constraints on timing of peak and retrograde metamorphism in the dabie shan ultrahigh pressure metamorphic belt east central china using u th pb dating of zircon and monazite abstract the dabie shan ultrahigh pressure metamorphic uhpm belt occupies the suture between the yangtze and sino korean blocks in east central china the timing of uhpm in the dabie belt is controversial and most recent data come from dating of zircons monazite has recently been recognized as useful for dating of multiple tectonic events due to its preservation of multiple growth zones and monazite growth has been documented to occur during prograde peak and retrograde metamorphism zircons and monazites from uhp mafic rocks from maowu and a uhp jadeite quartzite from shuanghe were imaged in thin sections and in mineral separates and dated using a high resolution ion microprobe maowu mafic rocks are unique in that they contain high light rare earth element concentrations and therefore contain abundant monazite maowu eclogites and garnet pyroxenites contain zircons with mean 206 pb 238 u age of 230 4 ma and monazites from a clinopyroxenite have 208 pb 232 th ages of 209 4 ma multiple lines of evidence suggest that the measured ages represent the timing of new growth and recrystallization and are not cooling ages i e they do not correspond to the cessation of diffusional pb loss as rocks cooled below the closure temperature during exhumation shuanghe jadeite quartzites contain zircons with cores that define a discordia with an upper intercept age 1921 22 ma and lower intercept age of 236 32 ma interpreted to represent the ages of the source rocks and of peak metamorphism respectively zircon rims contain jadeite inclusions that restrict growth to pressures greater than 1 5 gpa their pooled age of 238 3 ma agrees well with the lower intercept defined by cores suggesting that pb loss from cores and growth of new rims occurred during uhpm at 235 240 ma monazite records multiple events during retrograde metamorphism maowu clinopyroxenite and shuanghe jadeite quartzite experienced monazite growth at 209 ma interpreted to reflect regional amphibolite facies overprinting resulting from pervasive retrograde fluid infiltration only the jadeite quartzite records growth at 223 1 ma estimated exhumation rates for maowu are 7 8 km ma

3 d sedimentary architecture of a quaternary gravel delta sw germany implications for hydrostratigraphy abstract this paper investigates a quaternary gilbert type gravel delta that was formed in an ice marginal environment at the end of the last glacial period outcrop sediment core and ground penetrating radar gpr studies reveal the sedimentary facies and depositional architecture of the delta that comprises three major units 1 a 2 5 m thick gravelly topset with an erosional base formed by accretion of bedload sheets in a braided river 2 an up to 40 m thick steeply inclined 13 35 foreset dominated by gravelly lithofacies being the product of cohesionless debris flows and debris falls as well as gravity slides while sandy lithofacies was deposited by traction currents and 3 a 10 20 m thick sandy bottomset comprising low density turbidites syn to postdepositional deformation of parts of the bottomset deposits largely resulted from rapid deposition of overlying gravels and differential loading of the prograding foreset beds the development of the delta was most likely controlled by a high sediment supply and lake level fluctuations the overall coarsening upward succession reflects delta progradation and aggradation into a glaciolacustrine environment outcrop sedimentology served as a direct analogue in order to characterise the three dimensional sedimentary and hydraulic architecture of the nearby gravel delta aquifer applying a multidisciplinary approach sedimentological geophysical and hydrogeological data were integrated within the 3 d modelling package gocad earth decision sciences to develop high resolution 3 d aquifer models

imbibition of hydraulic fracturing fluids into partially saturated shale recent studies suggest that imbibition of hydraulic fracturing fluids into partially saturated shale is an important mechanism that restricts their migration thus reducing the risk of groundwater contamination we present computations of imbibition based on an exact semianalytical solution for spontaneous imbibition these computations lead to quantitative estimates of an imbibition rate parameter a with units of lt 1 2 for shale which is related to porous medium and fluid properties and the initial water saturation our calculations suggest that significant fractions of injected fluid volumes 15 95 can be imbibed in shale gas systems whereas imbibition volumes in shale oil systems is much lower 3 27 we present a nondimensionalization of a which provides insights into the critical factors controlling imbibition and facilitates the estimation of a based on readily measured porous medium and fluid properties for a given set of medium and fluid properties a varies by less than factors of 1 8 gas nonwetting phase and 3 4 oil nonwetting phase over the range of initial water saturations reported for the marcellus shale 0 05 0 6 however for higher initial water saturations a decreases significantly the intrinsic permeability of the shale and the viscosity of the fluids are the most important properties controlling the imbibition rate

baddeleyite zircon relationships in coronitic metagabbro grenville province ontario implications for geochronology in the high grade gneiss terranes of the grenville province in ontario metagabbro with silicate coronas around primary olivine and fe ti oxide contains trace amounts of both baddeleyite and zircon single baddeleyite crystals with radiating columnar coronas of polycrystalline zircon in places with outer rims of garnet are analogous to the coronas around olivine and ilmenite single crystals of zircon and baddeleyite without zircon coronas also occur in the same rocks both zirconium minerals have been isotopically dated at three widely separated localities in each case baddeleyite records an igneous crystallization age of ca 1170 ma 125 ma older than the ca 1045 ma age of the zircons interpreted to be the age of metamorphism these data agree well with u pb ages obtained from other rocks in the same region and refute the alternative interpretation that silicate coronas in these metagabbros formed during cooling following magmatic crystallization the age does not support direct correlation with diabase dykes of either the sudbury or abitibi swarms northwest of the grenville front

zircon u pb age and trace element evidence for paleoproterozoic granulite facies metamorphism and archean crustal rocks in the dabie orogen abstract zircon u pb ages and trace elements were determined for granulites and gneiss at huangtuling which are hosted by ultrahigh pressure metamorphic rocks in the dabie orogen east central china cl images reveal core rim structure for most zircons in the granulites the cores show oscillatory zoning relatively high th u ratios and hree enriched patterns consistent with a magmatic origin they gave a weighted mean 207pb 206pb age of 2766 9 ma interpreted as dating magma emplacement of the protolith the rims are characterized by sector or planar zoning low th u ratios negative eu anomalies and flat hree patterns consistent with their formation under granulite facies metamorphic conditions zircon u pb dating yields a weighted mean 207pb 206pb age of 2029 13 ma which is interpreted to record a metamorphic event possibly during assembly of the supercontinent columbia the gneiss has a protolith age of 1982 14 ma which is younger than the zircon age of the granulite facies metamorphism suggesting a generally delay between ht metamorphism and the intrusion of post collisional granites a few inherited cores with igneous characteristics have 207pb 206pb ages of 2 90 3 28 and 3 53 ga suggesting the presence of mesoarchean to paleoarchean crustal remnants in the yangtze craton a few cretaceous metamorphic ages were also obtained suggesting the influence of post collisional collapse in response to cretaceous extension of the dabie orogen it is inferred that the recently discovered archean basement of the yangtze craton occurs as far north as the dabie orogen

u pb geochronology of hydrothermal zircons from the early cretaceous iron skarn deposits in the handan xingtai district north china craton the handan xingtai district in the north china craton is one of the most important concentrations of iron skarn deposits in china with proven reserves of 900 to 1 000 mt at an average of 40 to 55 wt fe the iron mineralization occurs predominantly along contact zones between early cretaceous intermediate silicic intrusions and middle ordovician marine carbonates intercalated with numerous evaporite beds in this paper we present textural features and laser ablation icp ms u pb dating results of hydrothermal zircon from five major iron skarn deposits to place tight constraints on the timing and duration of the district scale iron mineralization zircon grains from the mineralized skarns are anhedral to subhedral crystals and euhedral tetragonal bipyramids they are closely intergrown or texturally associated with diopside garnet epidote calcite albite and phlogopite other common minerals in the skarn assemblages include f rich hornblende wilkeite f f apatite and fluorite zircon grains typically contain abundant inclusions of skarn minerals and daughter mineral rich mostly magnetite halite and sylvite fluid inclusions compositionally these zircon grains have moderately to extremely high th 518 7 477 ppm and u 109 25 610 ppm contents with highly variable th u ratios ranging from 0 01 to 5 23 the morphological textural and geochemical features of the zircons confirm their hydrothermal origin and indicate that they most likely precipitated from high temperature f rich magmatic derived ore forming fluids the hydrothermal zircon grains yield well defined concordant u pb ages for the five studied iron skarn deposits with weighted mean 206 pb 238 u dates ranging from 133 6 0 9 to 128 5 1 4 ma 2 these ages are remarkably consistent with u pb ages 134 1 1 2 to 128 5 0 9 ma 2 of magmatic zircon grains from the ore related intrusions in each deposit demonstrating that iron skarn mineralization was genetically related to the coeval magmatism our new geochronological data when combined with existing isotopic ages indicate that iron mineralization and associated magmatism in the handan xingtai district took place mainly at the ca 137 133 and 131 128 ma intervals iron skarn deposits of similar ages also occur widely in other parts of the eastern north china craton forming the only known giant mesozoic iron skarn province in a cratonic block on the earth the formation of these iron skarn deposits and associated intrusions coincided in time with lithospheric thinning or destruction of the north china craton strongly suggesting a causal link between the two processes

scaling of seismicity induced by nonlinear fluid rock interaction 1 fluid injections into geothermal systems sometimes can produce significant seismic events with magnitudes of up to 4 however in the case of hydraulic fracturing of hydrocarbon reservoirs such events occur extremely seldom in the last case in contrast to the former one the structure of rocks is being actively destroyed e g opening of tensile fractures and the fluid rock interaction is strongly nonlinear e g a strong increase of permeability what is the role of this nonlinearity we consider nonlinear pore pressure diffusion to explain features of seismicity we formulate seismicity triggering front its propagation is sensitive to a grade of nonlinearity to spatial dimension of diffusion and to the injection rate we show that a probability of an event with a magnitude larger than a given one increases proportionally to the injected mass an increase of this probability with time is insensitive to the nonlinearity we compare different borehole experiments in some cases the injection produces clearly nonlinear impact on rocks in others this impact is approximately linear we find a well agreement with our theory we observe an insensitivity of temporal increments of magnitude probability to the grade of nonlinearity these increments are controlled by injection rate increments in contrast nonlinear fluid rock interactions are characterized by a strong dominance of small earthquakes defects activated by a nonlinear diffusion possibly obey gutenberg richter statistics with anomalous high b values in the case of a linear diffusion magnitude distributions of events are probably inherited from pre existing fracture systems

discrimination between induced triggered and natural earthquakes close to hydrocarbon reservoirs a probabilistic approach based on the modeling of depletion induced stress changes and seismological source parameters earthquakes occurring close to hydrocarbon fields under production are often under critical view of being induced or triggered however clear and testable rules to discriminate the different events have rarely been developed and tested the unresolved scientific problem may lead to lengthy public disputes with unpredictable impact on the local acceptance of the exploitation and field operations we propose a quantitative approach to discriminate induced triggered and natural earthquakes which is based on testable input parameters maxima of occurrence probabilities are compared for the cases under question and a single probability of being triggered or induced is reported the uncertainties of earthquake location and other input parameters are considered in terms of the integration over probability density functions the probability that events have been human triggered induced is derived from the modeling of coulomb stress changes and a rate and state dependent seismicity model in our case a 3 d boundary element method has been adapted for the nuclei of strain approach to estimate the stress changes outside the reservoir which are related to pore pressure changes in the field formation the predicted rate of natural earthquakes is either derived from the background seismicity or in case of rare events from an estimate of the tectonic stress rate instrumentally derived seismological information on the event location source mechanism and the size of the rupture plane is of advantage for the method if the rupture plane has been estimated the discrimination between induced or only triggered events is theoretically possible if probability functions are convolved with a rupture fault filter we apply the approach to three recent main shock events 1 the m w 4 3 ekofisk 2001 north sea earthquake close to the ekofisk oil field 2 the m w 4 4 rotenburg 2004 northern germany earthquake in the vicinity of the sohlingen gas field and 3 the m w 6 1 emilia 2012 northern italy earthquake in the vicinity of a hydrocarbon reservoir the three test cases cover the complete range of possible causes clearly human induced not even human triggered and a third case in between both extremes

groundwater flow patterns in extensive shallow aquifers with gentle relief theory and application to the galena locust grove region of eastern maryland 1 the delmarva peninsula between the chesapeake bay and the atlantic ocean comprises an irregular sequence of almost horizontal sand and silt or clay layers shedlock et al 1999 bohlke and denver 1995 whose connectivity and detailed geometry are not well known a mosaic of groundwater basins with areas generally less than 30 km2 provide the water supply for the region the concentration of dissolved nitrate has increased greatly since 1950 shedlock et al 1999 and a series of test wells drilled in the locust grove area for chemical analyses of the groundwater provide useful data on water table levels at various locations a new depth integrated hydraulic model of the aquifer flow is developed to handle the complex and poorly known structure of the region it requires as inputs 1 historical rainfall data 2 the elevation profiles along potential discharge streambeds and 3 the depth integrated hydraulic conductivity inferred from a few individual well water levels the analysis predicts quantitatively and without arbitrary parameters the distribution of groundwater heights above mean sea level and the patterns of total groundwater flow throughout the study region throughout the test area the predicted and measured groundwater levels generally agree to within 1 meter the groundwater flow patterns show two distinctive types of domain with little intermingling one type originating near the groundwater divide and discharging into the semipermanent streams and the other kind arising between the lower stream sections and discharging directly along the estuary shoreline the measured distribution of water age with depth bohlke and denver 1995 agrees well with a simple formula provided by the theory

control of hazard due to seismicity induced by a hot fractured rock geothermal project in 2003 hydraulic stimulations were carried out in a geothermal field in eastern el salvador central america as part of a project to explore the feasibility of commercial hot fractured rock energy generation a key requisite for this environmentally friendly energy source is that the fracturing of the hot rocks at depths of 1 2 km must not produce levels of ground shaking at the surface that would present a serious disturbance or threat to the local population thresholds of tolerable ground motion were inferred from guidelines and regulations on tolerable levels of vibration and from correlations between instrumental strong motion parameters and intensity considering the vulnerability of the exposed housing stock the thresholds were defined in terms of peak ground velocity pgv and incorporated into a traffic light system that also took account of the frequency of occurrence of the induced earthquakes the system was implemented through a dedicated seismograph array and locally derived predictive equations for pgv the traffic light was used as a decision making tool regarding the duration and intensity of pumping levels during the hydraulic stimulations the system was supplemented by a small number of accelerographs and re calibrated using records obtained during the rock fracturing

three novel isograds in metamorphosed siliceous dolomites from the ballachulish aureole scotland isograds were mapped in siliceous dolomites from the ballachulish aureole on the basis of the formation of geikielite mgti03 baddeleyite zr02 and qandilite mg2ti04 by the following model reactions rutile dolomite geikielite calcite c02 zircon 2 dolomite baddeleyite forsterite 2 calcite 2 c02 and geikielite periclase qandilite the t xco conditions of reaction inferred from 1 mineral equilibria in pelitic rocks 2 calcite dolomite thermometry and 3 the diopside dolomite forsterite calcite tremolite and dolomite periclase calcite equilibria are geikielite isograd 640 655 c 0 76 0 80 baddeleyite isograd 660 710 c 0 76 0 95 qandilite isograd 725 755 c 0 08 these t xco2 conditions for the geikielite and baddeleyite isograds are the same within error of those independently estimated from rutile dolomite geikielite calcite and zircon dolomite baddeleyite forsterite calcite equilibria using berman s thermodynamic data base rutile zircon geikielite and baddeleyite are common in dolomites from at least two other contact aureoles in scotland and montana although the minerals occur in concentrations 0 01 they appear to have been in local equilibrium during metamorphism both with each other and with coexisting carbonates and silicates and are potentially useful but currently unexploited records of the physical conditions of metamorphism

identification of ca 2 65 ga ttgs in the yudongzi complex and its implications for the early evolution of the yangtze block abstract in this contribution we carry out an integrated study of petrology whole rock geochemistry as well as zircon morphology trace element u pb and lu hf isotopes for granitic gneisses and leucogranites from the yudongzi complex a poorly studied archean outcrop in the northwestern yangtze block the granitic gneisses have the ttg affinity characterized by relatively high na2o k2o and sr y ratios and fractionated ree pattern with relatively high lree but low hree concentrations zircon grains in the granitic gneisses show magmatic cores and metamorphic rims u pb dating on zircon core of four granitic gneiss samples yielded their formation ages as 2660 2632 ma with a weighted average of 2650 21 ma mswd 1 6 n 4 their average ehf t values range from 0 6 to 0 5 and two stage model ages from 3 20 to 3 10 ga suggesting that the granitic gneisses were likely generated by remelting of thickened mesoarchean proto mafic crust the metamorphic zircon rims have relatively high th u ratios and identical hf isotope compositions to their corresponding cores indicating that the rims were formed via solid state recrystallization process the metamorphic zircons recorded a metamorphic event at ca 2 5 ga u pb dating and lu hf isotopes on magmatic zircons from a leucogranite sample revealed a magmatic event at 2477 18 ma the recognization of the 2 65 ga ttg magmatism and the 2 48 ga intercrustal remelting event in the yudongzi complex demonstrates the widespread neoarchean magmatism in the yangtze block combined with the age spectra of previous detrital zircons we show that the yangtze block has experienced a major tectonothermal event in the late archean the yudongzi complex has a distinct crustal evolution history compare with the paleoarchean continent nucleus in the eastern part of the yangtze block suggesting that the continent nucleus might have subjected to lateral growth by accretion processes

geochronology and geochemistry of igneous rocks from the kongling terrane implications for mesoarchean to paleoproterozoic crustal evolution of the yangtze block abstract the kongling terrane is a high grade metamorphic complex exposed in the northern part of the yangtze block it mainly consists of ttg gneisses amphibolites migmatites and metasedimentary rocks the amphibolites occur as enclaves or layers in the ttg gneisses and both the amphibolites and the ttg gneisses are intruded by granitic and diabasic dykes u pb ages of zircons from the amphibolite migmatite granite and diabase are determined by la icp ms igneous zircons from an amphibolite have an upper intercept age of 2945 13 ma mswd 1 2 while metamorphic zircons yield an upper intercept age of 2870 13 ma mswd 0 9 igneous zircons from a migmatite and a granite have weighted average 207pb 206pb age and upper intercept age of 1987 5 ma mswd 1 7 and 1985 6 ma mswd 1 3 respectively igneous zircons from a diabase dyke yield an upper intercept age of 1783 23 ma mswd 0 86 the protoliths of the amphibolites are tholeiitic basalts and exhibit slightly depleted to variably enriched lree patterns with moderate enrichment of rb and ba and depletion in nb and zr similar to oceanic island arc volcanics they have high cr co ni mgo and feot content with negative nd t values indicating that the tholeiitic basalts resulted from high degree batch melting of enriched mantle wedge the granites are strongly peraluminous with a cnk 1 1 and they have relatively low hree and y and negative nd t values detailed elemental and isotopic data suggest that they formed by partial melting of recycled products of the ttg gneisses amphibolites and older crustal material in a continental collisional setting the diabases are characterized by relatively high al2o3 feot and tio2 contents and low zr ba ratios their high initial 87sr 86sr ratios and negative nd t values indicate that they were derived from enriched lithospheric mantle in extensional setting therefore the kongling terrane occurred as an oceanic island arc at ca 2 95 ga and experienced earliest metamorphism at ca 2 87 ga which probably contributed to the formation of the high grade metamorphic terrane this terrane experienced a strong collisional event at 2 0 ga which may have led to cratonization over all of the yangtze block and also experienced lithospheric extension during 1 85 1 78 ga the global 2 0 ga paleoproterozoic collisional events were related to the assembly of supercontinent columbia

the application of u pb geochronology to mafic ultramafic and alkaline rocks an evaluation of three mineral standards abstract a key to proving the accuracy of u pb age determinations by the various techniques available is routine analysis of an internal well characterized matrix matched mineral standard of known age in general there are very few well studied natural mineral standards available to the geological community in this study the nature geochemistry and u pb systematics of baddeleyite titanite and perovskite from three potential mineral standards are evaluated a compilation of concordant to near concordant analyses of a single phalaborwa baddeleyite crystal yields a precise u pb age of 2059 60 0 35 ma a large variation in uranium 51 2124 ppm thorium 0 5 73 ppm and lead 19 782 ppm concentrations and the presence of some u bearing mineral inclusions zircon monazite and baddeleyite zircon intergrowths require some caution when using aliquots of this phalaborwa baddeleyite crystal as a mineral standard the khan titanite crystal investigated here overall has a relatively uniform chemical composition e g u 584 95 ppm th 473 73 ppm pb 57 8 ppm th u 0 81 0 05 but parts of the crystal contain abundant mineral inclusions the model 1 upper intercept age of 522 2 2 2 ma for nine khan titanite analyses is considered the current best estimate for its crystallization age some variability in the u pb systematics with 207pb 206pb ages that vary between 508 and 560 ma was observed and could be related to the presence of tiny u bearing mineral inclusions such as rutile or allanite so careful selection of material from this titanite crystal is also required a single perovskite crystal from the ice river alkaline intrusion has a relatively uniform chemical composition uranium 141 25 ppm thorium 1954 270 ppm lead 41 5 ppm and th u 14 5 1 3 the u pb results for eight perovskite fractions yield a weighted average 206pb 238u age of 356 5 1 0 ma although there are always some limitations to using natural mineral crystals as u pb standards such as the presence of mineral inclusions alteration and geochemical heterogeneity the three crystals investigated here are considered suitable to be used as internal u pb standards for any of the currently used u pb dating techniques

high pressure metamorphic rocks from tongbaishan central china u pb and 40ar 39ar age constraints on the provenance of protoliths and timing of metamorphism abstract the tongbaishan area is situated at the junction between the paleozoic north qinling orogen and the mesozoic south qinling dabie sulu orogen the area contains an important geological section for understanding the assembly of the sino korean and yangtze cratons two eclogite zones were recently recognized in this area the peak metamorphic conditions are estimated to be 530 610 c and 17 20 kbar for the northern eclogite zone and 460 560 c and 13 19 kbar for the southern eclogite zone shrimp u pb analyses on zircons of eclogite metagabbro and orthogneiss indicate that their protoliths were formed during the neoproterozoic and experienced high pressure hp recrystallization during the permian triassic period therefore the tongbaishan area belongs to the western extension of the dabieshan hp uhp terrane in addition u pb ages of detrital zircons from quartzite paragneiss and schist show three age populations of 2 49 ga 1 93 ga and 1 85 1 82 ga suggesting that extensive paleoproterozoic orogeny or tectonothermal events took place in the northern margin of the yangtze craton the shrimp dating and complementary 40ar 39ar dating of muscovite from quartzofeldspathic gneiss and quartzite reveal that the crustal rocks were subducted to great depths and underwent hp eclogite facies metamorphism at ca 255 ma slightly earlier than the timing of deep subduction of the uhp slice the hp rocks were later exhumed to mid to upper crustal levels and suffered from retrograde recrystallization at ca 238 ma the dating also discloses a still later phase of deformation and recrystallization at ca 215 ma the available age data throughout the tongbai dabie sulu orogen reflect diachronous exhumation from ca 238 ma for the hp slice to ca 213 ma for the uhp slice such a phenomenon could be explained by successive subduction and exhumation of the broken slices of the subducting yangtze slab

magnitudes of induced earthquakes and geometric scales of fluid stimulated rock volumes sometimes rock stimulations by fluid injections into geothermal boreholes are able to trigger perceptible or even potentially damaging earthquakes this does not seem to be the case for hydraulic fracturing of hydrocarbon reservoirs reasons for such a difference and factors defining magnitudes of induced earthquakes triggered tectonicly as well as induced artificially remain unclear we analyzed microseismic data obtained by fluid stimulations at different geothermal and hydrocarbon sites this analysis indicates that a rupture corresponding to a fluid induced earthquake seems to be only probable along a surface located mainly inside a stimulated rock volume we approximated the stimulated volume by an ellipsoid and compared the statistics of induced events with the statistics of randomly distributed thin flat disks modeling rupture surfaces we found that one of the main factors limiting the probability to induce a large magnitude event is the minimum principal axis of a fluid stimulated rock volume

stable isotope geochemistry of marbles from the coesite uhp terrains of dabieshan and sulu china abstract marbles from dabieshan and sulu china suffered ultra high pressure uhp metamorphism in the coesite eclogite facies at approximately 700 c and 30 kbars during triassic continental collision and subduction the marbles range in isotopic composition from 7 to 25 18 o vsmow and from 0 to 6 13 c vpdb high 13 c values are representative of unmodified protoliths and are similar to those of 13 c enriched sinian carbonate rocks from the yangtze craton high oxygen isotope ratios reflect pristine protoliths but the low values may have been caused by infiltration of low 18 o meteoric water during diagenesis and dolomitization by fracture controlled infiltration of water during subduction by metamorphic mineral reactions or by a combination of these processes no evidence of regional isotopic transport during uhp metamorphism has been found sampling on scales of 1 to 100 m shows marbles to be inhomogeneous in both carbon and oxygen isotopes only samples separated by less than 10 cm have equilibrated oxygen and carbon isotope compositions limited isotopic equilibration between adjacent rocks is consistent with the preservation of unaltered uhp minerals and indicates that the metamorphic fluid rock system was rock dominated during and following peak metamorphism a freely flowing pervasive fluid phase was not present during uhp metamorphism there is no evidence of isotopic exchange between marble and the upper mantle into which it was subducted correlation of geochemical similarities of uhp marbles with sinian limestones implies that the subducted edge of the yangtze craton extends at least as far north as the coesite eclogite facies rocks of dabieshan deposition of protolith carbonates may have taken place in a cold climate either preceding or following but not coincident with neoproterozoic glaciation

in situ u pb sims in sims micro baddeleyite dating of mafic rocks method with examples abstract an in situ u pb sims in sims method to date micro baddeleyite crystals as small as 3 m is presented with results from three samples that span a variety of ages and geologic settings the method complements id tims geochronology by extending the range of dateable crystals to sizes smaller than can be recovered by physical separation x ray mapping and bse imaging are used to locate target grains in thin section followed by sims analysis on a cameca ims 1270 using the field aperture in the transfer column to screen out ions from host phases internal age precisions for the method are anticipated to range from 0 1 for precambrian rocks to 3 7 for phanerozoic rocks results establish a 2689 5 ma age for mafic dikes in the wyoming craton usa a 1540 30 ma age for a subaerial lava flow from the thelon basin of northern canada and a 457 34 ma age for mafic dikes in the platform sequence of southeastern siberia the method is ideal for relatively non destructive dating of small samples such as extraterrestrial rocks and precious terrestrial samples

faults strengthening and seismicity induced by geothermal exploitation on a spreading volcano mt amiata italia abstract seismogenic structures such as faults play a primary role in geothermal system generation recharge and output they are also the most susceptible to release seismic energy over fluid injection extraction operations during anthropic exploitation we describe the microseismic activity recorded in 2000 2001 in the piancastagnaio geothermal field on the se flank of mt amiata volcano southern tuscany italy from our field observations we find that a relatively high percentage i e about 5 of the recorded events are of hydro fracturing origin and have a distinct waveform seismic signature when compared to the recorded events of tectonic shear fracturing origin while hydrofracturing events are mostly concentrated around the geothermal fields the spatial distribution of hypocenters shows a deepening and a density increase of the micro seismic activity from the volcanic axis toward the exploited geothermal reservoir suggesting that volcanic spreading at amiata is still active the study of different data sets from different time periods together with the knowledge from terzaghi s law that production of large quantity of pore fluid with the associated fluid pressure reduction could augment the stress normal to faults surfaces and thus their resistance to slip make us argue that the process of volcanic spreading affecting the edifice of amiata may allow augmented accumulation of stresses on faults eventually leading to the release of higher stress drops once ruptures occur the gutenberg richter magnitude frequency distribution shows that the strongest events on record have a local magnitude in the 5 5 5 m l range for 100 year recurrence time in conclusions we infer that geothermal exploitation at mt amiata should be closely monitored in order to understand how fluid injection production is responsible for the hydrofracturing seismic activity and affects stress accumulation on and rupture of faults within and in the neighborhood of the geothermal fields this understanding may allow a geothermal field management that will hopefully reduce the risk for inducing larger seismic events in the area

diffusion in zircon despite its low abundance in most rocks zircon is extraordinarily useful in interpreting crustal histories the importance of u th pb isotopic dating of zircon is well and long established davis et al this volume parrish et al this volume zircon also tends to incorporate trace elements useful as geochemical tracers such as the ree y and hf a number of characteristics of zircon encourage the preservation of internal isotopic and chemical variations often on extremely fine scale which provide valuable insight into thermal histories and past geochemical environments the relative insolubility of zircon in crustal melts and fluids as well as its general resistance to chemical and physical breakdown often result in the existence of several generations of geochemical information in a single zircon grain the fact that this information is so frequently retained as evidenced through backscattered electron or cathodoluminescence imaging that often reveal fine scale zoning down to the sub micron scale has long suggested that diffusion of most elements is quite sluggish in zircon in this chapter we present an overview of the findings to date from laboratory measurements of diffusion of cations and oxygen in zircon because of its importance as a geochronometer attempts have been made to measure diffusion especially of pb for over 30 years but only in the last decade or so have profiling techniques with adequate depth resolution been employed in these studies resulting in a plethora of new diffusion data these findings have important implications for isotopic dating interpretation of stable isotope ratios closure temperatures and formation and preservation of primary chemical composition and zoning in zircon efforts have been made for some time to quantify and characterize diffusion in zircon most notably of pb in deference to its significance in interpreting pb isotopic signatures and refining understanding of thermal histories as is evident from

calculated silica activities in carbonatite liquids carbonatite magmas precipitate silicates in addition to the abundant carbonates oxides and phosphates calculated silica activities for equilibria involving silicates and a silica component in magmatic liquids predict specific assemblages for silicate and oxide phases in carbonatites these assemblages provide tests of alternative sources carbonatite magma coeval silicate magma or older rock for silicate minerals in carbonatites quartz feldspars and orthopyroxene are unlikely to be primary magmatic phases in carbonatites because the silica activity in carbonatite magmas is too low to stabilize these minerals zircon and titanite should be unstable relative to baddeleyite and perovskite respectively but they do occur in carbonatites liquids dominated by carbonate are strongly nonideal with respect to dissolved silica consequently activity coefficients for a silica component in carbonatite liquids are 1 so that small mole fractions of sio2 translate into silica activities sufficient to stabilize phlogopite clinopyroxene amphibole monticellite and forsterite among other silicates examination of silicate mineral assemblages in carbonatites in the light of silica activity indicates that many carbonatites are contaminated by solid silicate phases from external sources but these xenocrysts can be discriminated from magmatic minerals

capillary tension and imbibition sequester frack fluid in marcellus gas shale in a recent issue of pnas warner et al 1 interpreted local ground water chemistry in the appalachian basin as a signal for cross formational pathways where natural migration of brine from the deep formations may be ongoing today the implication of this paper is that the marcellus is leaking now naturally without any human assistance and that if water based fluid is injected into these cross formational pathways that leakage which is already contaminating the aquifers with salt could be made much worse

genesis of baddeleyite and high δ18o zircon in impure marble from the tongbai orogen central china insights from petrochronology and hf o isotope compositions coexistence of baddeleyite and zircon is rarely documented in metacarbonate rocks and poorly understood in this study metamorphic baddeleyite and zircon were recognized in marbles from the tongbai orogen central china we carried out high spatial resolution analysis of trace element geochemistry and u pb lu hf o isotope systematics for the zircon and baddeleyite sims secondary ion mass spectroscopy u pb analysis yields weighted average 207pb 206pb ages of 1848 0 3 3 ma msdw 1 2 n 12 for baddeleyite and 1840 13 ma mswd 1 7 n 13 for zircon the baddeleyite grains have relatively low ree rare earth element contents ree 1 30 47 3 ppm with flat chondrite normalized patterns and moderate contents of hfse high field strength element which are ascribed to the nature of its host metacarbonate rock and mineral assemblage the zircon grains have low ti contents 1 63 3 56 ppm positive ce anomalies ce ce 1 91 6 96 and mineral inclusions of hematite calcite dolomite lizardite and h2o these characteristics indicate zircon formation in a relatively low temperature setting under oxidizing and water rich conditions the baddeleyite and zircon have similar ranges of ehf t values of 7 7 to 10 5 and 7 8 to 11 6 respectively which suggest their derivation from a relatively uniform hf source the high 18o values of these zircon grains 20 0 21 0 preclude any percolation of external meteoric fluids during their crystallization therefore a detrital zircon dissolution reaction is preferred to provide the zr for the metamorphic zircon and baddeleyite in this study the o isotope disequilibrium between whole rock 18o 16 2 16 3 and metamorphic zircon is most likely caused by metamorphic devolatilization or interaction with an h2o dominant fluid during later metamorphism on the other hand the baddeleyite grains yield 18o values ranging from 4 5 to 8 7 which is in disequilibrium with metamorphic zircon at the temperature of detrital zircon dissolution reaction ca 660 710 c zircon dolomite baddeleyite forsterite calcite co2 the genesis of metamorphic zircon can be interpreted by a baddeleyite to zircon reaction of zro2 sio2 zrsio4 at a retrograde stage consistent with the low ti in zircon temperatures the results highlight the importance of integrating trace element and multiple isotopic compositions in studying the genesis of metamorphic baddeleyite and zircon additionally the u pb geochronology data also indicate that the protoliths of the marble were deposited in the early paleoproterozoic and experienced a metamorphism at 1 85 ga the ca 1 85 ga high grade metamorphic event might have been induced by the coeval magmatism in an extensional setting

u pb hf and o isotope evidence for two episodes of fluid assisted zircon growth in marble hosted eclogites from the dabie orogen abstract a combined study of internal structure u pb age and hf and o isotopes was carried out for metamorphic zircons from ultrahigh pressure eclogite boudins enclosed in marbles from the dabie orogen in china cl imaging identifies two types of zircon that are metamorphically new growth and recrystallized domain respectively the metamorphic zircons have low th and u contents with low th u ratios yielding two groups of 206 pb 238 u age at 245 3 to 240 2 ma and 226 4 to 223 2 ma respectively anomalously high 18 o values were obtained for refractory minerals with 9 9 to 21 4 for garnet and 16 9 for zircon this indicates that eclogite protolith is sedimentary rocks capable of liberating aqueous fluid for zircon growth during continental subduction zone metamorphism most of the zircons are characterized by very low 176 lu 177 hf ratios of 0 000001 0 000028 indicating their growth in association with garnet recrystallization a few of them falling within the older age group have comparatively high 176 lu 177 hf ratios of 0 000192 0 000383 suggesting their growth prior to the formation of garnet in the late stage of subduction the variations in the lu hf ratios for zircons can thus be used to correlate with garnet growth during eclogite facies metamorphism in either case the zircons have variable e hf t values for individual samples suggesting that their protolith is heterogeneous in hf isotope composition with localized fluid availability in the bulk processes of orogenic cycle nevertheless a positive correlation exists between 206 pb 238 u ages and lu hf isotope ratios for the metamorphically recrystallized zircons suggesting that eclogite facies metamorphism in the presence of fluid has the identical effect on zircon lu hf and u th pb isotopic systems we conclude that the zircons of the older group grew in the presence of fluid during the subduction prior to the onset of peak ultrahigh pressure metamorphism whereas the younger zircons grew in the presence of fluid released during the initial exhumation toward high pressure eclogite facies regime

hydraulic fracturing fluid migration in the subsurface a review and expanded modeling results understanding the transport of hydraulic fracturing hf fluid that is injected into the deep subsurface for shale gas extraction is important to ensure that shallow drinking water aquifers are not contaminated topographically driven flow overpressured shale reservoirs permeable pathways such as faults or leaky wellbores the increased formation pressure due to hf fluid injection and the density contrast of the hf fluid to the surrounding brine can encourage upward hf fluid migration in contrast the very low shale permeability and capillary imbibition of water into partially saturated shale may sequester much of the hf fluid and well production will remove hf fluid from the subsurface we review the literature on important aspects of hf fluid migration single phase flow and transport simulations are performed to quantify how much hf fluid is removed via the wellbore with flowback and produced water how much reaches overlying aquifers and how much is permanently sequestered by capillary imbibition which is treated as a sink term based on a semianalytical one dimensional solution for two phase flow these simulations include all of the important aspects of hf fluid migration identified in the literature review and are performed in five stages to faithfully represent the typical operation of a hydraulically fractured well no fracturing fluid reaches the aquifer without a permeable pathway in the presence of a permeable pathway 10 times more fracturing fluid reaches the aquifer if well production and capillary imbibition are not included in the model

deep injection and closely monitored induced seismicity at paradox valley colorado the u s bureau of reclamation s paradox valley unit pvu extracts aquifer brine from nine shallow wells along the dolores river paradox valley in southwestern colorado and after treating high pressure injects the brine 4 3 4 8 km below the surface pvu injects at rates between 800 and 1300 l min since 1991 pvu has emplaced over 4 106 m3 of fluid and induced more than 4000 surface recorded seismic events the events are recorded on the local 15 station paradox valley seismic network the induced seismicity at paradox separates into two distinct source zones a principle zone 95 of the events asymmetrically surrounding the injection well to a maximum radial distance of 3 km and a secondary ellipsoidal zone 2 5 km long and centered 8 km northwest of the injection well the expansion of these zones has stabilized since mid 1999 about three years after the onset of continuous injection within the principal zone hypocenters align in distinct linear patterns showing at depth stratigraphy and the local wray mesa fracture and fault system the primary faults of the wray mesa system are aseismic striking subparallel to the inferred maximum principal stress direction with one or more faults probably acting as fluid conduits to the secondary seismic zone individual seismic events in both zones do not discernibly correlate with short term injection parameters however a 0 5 km2 region immediately northwest of the injection well responds to long term large scale changes in injection rate and the surpassing of a threshold injection pressure focal mechanisms of the induced events are consistent with simple double couple strike slip moments and subhorizontal extension to the northeast in addition the fault planes are consistent with principal stress directions determined from borehole breakouts more than 99 9 of the pvu seismicity is below human detection m 2 5 however approximately 15 events have been felt locally with the largest being a magnitude m 4 3 because of the m 4 3 and two earlier felt m 3 5 events and injection economics pvu changed injection strategies three times since 1996 these changes reduced seismicity from 1100 events year to as low as 60 events year

geochemistry and zircon u pb geochronology of paleoproterozoic arc related granitoid in the northwestern yangtze block and its geological implications abstract the early history of the yangtze block has not been well constrained yet due to the scarce outcrops of archean to paleoproterozoic rocks in this study we report an integrated study of zircon u pb age major and trace element data and sr nd hf isotope compositions for gray gneisses from the houhe complex in the northwestern part of the yangtze block zircon u pb dating yields a weighted mean 207 pb 206 pb age of 2081 9 ma for a gneiss this age is interpreted as the formation age of the houhe complex and thus the houhe complex represents the oldest rocks found in the western part of the yangtze block the gray gneisses from the houhe complex range in sio 2 contents from 58 63 to 68 59 and na 2 o from 3 88 to 5 28 and have relatively high fe 2 o 3 contents of 2 86 6 69 al 2 o 3 of 16 01 18 88 and mgo of 0 97 2 65 these rocks show low sr 149 390 ppm cr 9 07 45 1 ppm and ni 4 97 21 3 ppm contents but high y 12 9 32 7 ppm and yb 0 95 2 25 ppm they are characterized by a relative enrichment in liles and lrees but a depletion in hfses these features are similar to those of calc alkaline granitoids suggesting that their formation might be related to a subduction related process or remelting of preexisted arc rocks compiled age spectra of archean to paleoproterozoic zircon grains reveal that the western and eastern parts of the yangtze block have similar archean and early paleoproterozoic age ranges indicative of the occurrence of an old continental nucleus in both parts on the other hand there are large amounts of ca 2050 2400 ma zircon grains revealed in the western part of the yangtze block implying that there might be a microcontinent with an active type continental margin during the paleoproterozoic times in the western part of the yangtze block because of the poor outcrops of archean to paleoproterozoic rocks in the yangtze block it is no possible to establish the exact nature of such an active margin yet the occurrence of ca 2 0 ga khondalitic and metasedimentary rocks has been documented in the eastern part of the yangtze block implying that there might be a passive type continental margin in the eastern part of the yangtze block at ca 2 0 ga the collision between the western microcontinent and the eastern part may have resulted in the final arc continental collision and the amalgamation of the yangtze block

petrochronology of zircon and baddeleyite in igneous rocks reconstructing magmatic processes at high temporal resolution zircon zrsio4 and baddeleyite zro2 are common accessory minerals in igneous rocks of felsic to mafic composition both minerals host trace elements substituting for zr among them hf th u y rees and many more the excellent chemical and physical resistivity of zircon makes this mineral a perfect archive of chemical and temporal information to trace geological processes in the past utilizing the outstanding power and temporal resolution of the u pb decay schemes baddeleyite is a chemically and physically much more fragile mineral it preserves similar information only where it is shielded from dissolution and physical fragmentation as an inclusion in other minerals or in a fine grained or non reactive rock matrix it offers the potential for dating the solidification of mafic rocks with high precision through its crystallization in small pockets of zr enriched melt after extensive olivine and pyroxene fractionation zircon and baddelelyite u pb dates are for an overwhelming majority of cases and where we can assume a closed system considered to reflect the time of crystallization the development of the u pb dating tool ca id tims chemical abrasion isotope dilution thermal ionization mass spectrometry since 2005 has led to unprecedented precision of better than 0 1 in 206pb 238u dates bowring et al 2005 increased sensitivity of mass spectrometers and low laboratory blanks due to reduction of acid volumes allow routine u pb age determinations of micrograms of material at sufficiently high radiogenic common lead ratios see schoene and baxter 2017 this volume in situ u pb age analysis using laser ablation or primary ion beam sputtering allows analysis of sub microgram quantities of zircon material from polished internal sections or zircon surfaces with spot diameters ranging from 30 m for laser ablation inductively coupled plasma mass spectrometry la icp ms to 10 m for secondary ion mass spectrometry sims lateral resolutions of 2 5 m for nanosims

detailed joint structure in a geothermal reservoir from studies of induced microearthquake clusters microearthquake clusters form distinct planar patterns within five study regions of a geothermal reservoir undergoing hydraulic fracturing at fenton hill new mexico the patterns define individual slipping joint surfaces of dimension 40 120 m containing 80 150 events each sharp straight edges truncate the clusters we interpret these as marking intersections with aseismic joints each edge orientation is consistent with an intersection between the active joint and a plane oriented parallel to one of the other clusters we identify therefore it appears that cluster shapes constrain the geometry of seismic and aseismic joints both could be important components of the fluid flow network the distribution of inferred slip plane orientations is consistent with but fails to provide sufficient constraint to differentiate conclusively between two very different stress field estimates one measured using pressurization and wellbore breakouts the other using focal mechanisms of the largest microearthquakes an impermeable joint model requiring pore pressure in excess of the normal stress on a joint before slip can occur was inconsistent with many of the inferred slip plane orientations the high quality locations were possible because events from the same cluster generated nearly similar waveforms permitting the precise determination of relative arrival times standard deviations of arrival time residuals fall between 0 1 and 1 1 ms for these clusters major axes and aspect ratios of the 90 confidence ellipsoids range from 6 to 28 m and 1 5 to 8 respectively small events dominate the seismic energy release and thoroughly populate the identified active joints allowing the hypocenters to reflect details of the joint structure to further investigate the reservoir structure we applied a source array slant stack technique to waveforms from the well located clusters yielding directions that scattered energy left each cluster by studying paths of scattered waves we expected to pinpoint impedance contrasts that might have indicated concentrations of fluid filled joints however results show that scattered energy in the s wave coda left the source region in the same direction as the direct s wave direct waves may have excited borehole tube waves that became trapped in the vicinity of the geophone tool overwhelming any energy scattered from the reservoir

geochronology of high pressure mafic granulite dykes in sw sweden tracking the p t t path of metamorphism using hf isotopes in zircon and baddeleyite although the u pb zircon chronometer has been widely used for dating metamorphism in moderate to high grade rocks it is generally difficult to link the u pb age of zircon to specific metamorphic reactions in this study the initial hf isotopic composition of secondary zircon is compared with the evolution of hf isotopic composition of the bulk sample back projected from the measured value through time this approach may enhance the interpretation of radiometric ages performed on metamorphic mineral assemblages here u pb sm nd and lu hf geochronology and thermobarometry have been integrated and applied to two metamorphosed diabase dykes in the sveconorwegian orogen sw sweden the dykes are located 5 km east of the nne trending gota alv deformation zone in the idefjorden terrane and trend parallel to this zone the lunden dyke is recrystallized into a coronitic granulite facies assemblage u pb isotopic analyses of baddeleyite in this dyke indicate an emplacement age of 1300 ma thermobarometric techniques applied to garnet and omphacitic clinopyroxene coronas indicate high pressure metamorphism at c 15 kbar and c 740 c growth of polycrystalline zircon at the expense of baddeleyite occurred at 1046 6 ma identical hf isotopic composition of polycrystalline zircon and baddeleyite shows that the baddeleyite to zircon transition took place before hf equilibration among the other metamorphic minerals and hence the c 1046 ma age of polycrystalline zircon sets an upper age limit of metamorphism of this sample the haregarden dyke is recrystallized into a granoblastic transitional upper amphibolite to granulite facies assemblage the estimated p t conditions are c 10 kbar and c 700 c analyses of small 30 m clear and round zircon in this sample yield a concordia u pb age of 1026 4 ma which is indistinguishable from the lu hf and sm nd mineral isochron ages of 1027 9 ma and 1022 34 ma this type of secondary zircon plots at the lower end of the lu hf isochron and indicates simultaneous growth with garnet at c 1026 ma a time when hf isotopic equilibrium among minerals must have been reached

investigation of fault mechanisms during geothermal reservoir stimulation experiments in the cooper basin australia abstract subsequent to an initial reservoir stimulation in 2003 a second long term fluid injection experiment was conducted in the cooper basin australia in 2005 to further enhance and enlarge the existent geothermal reservoir approximately 25 000 m 3 of water were injected into the granitic crust at 4250 m depth thereby inducing about 16 000 seismic events which were recorded by a local eight station network event magnitudes calibrated by recordings of the permanent network of geosciences australia are in the range between m l 1 2 and 2 9 with seismic moments between 10 9 and 10 13 n m hypocenter locations could be determined for 8886 events the spatial hypocenter distribution indicates that the seismicity occurred on the same subhorizontal layer structure identified for the initial reservoir stimulation which is further extended in the course of restimulation early seismicity is located near the outer rim of the previous zone of seismic activity and subsequently migrates both toward and away from the injection well the immediate vicinity of the injection well remains seismically quiet during restimulation these effects can be explained by a simple kaiser effect model where the induced seismicity is controlled by the in situ fluid pressure increase compound fault plane solutions based on p phase polarities indicate a similar fault mechanism for nearly all events the dominating fault mechanism is consistent with the regional stress field acting on a larger scale fracture zone with an orientation as outlined by the hypocenter distribution a small number of events with reverse mechanisms might indicate the existence of conjugated fractures locally intersecting the main fracture zone cumulative slip determined by mapping the slip contribution of individual events onto the fracture zone indicates that most fracture patches in the reservoir slipped repeatedly accumulating up to several centimeters of shear displacement

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

the small effect of poroelastic pressure transients on triggering of production induced earthquakes in the groningen natural gas field over the past decade a steep increase in the number of seismic events has been observed in the groningen gas field the netherlands it is generally accepted that these are induced by compaction of the reservoir rock due to extensive depletion causing a buildup of strain energy in faults that may be released seismically we address the possible triggering of fault slip by the transient pressure field surrounding a well that has undergone a sudden rate change assuming a unilateral decoupling between displacement and pressure numerical experiments are conducted using a sequential finite volume finite element solution strategy that fully incorporates second order terms in the radial flow equation we investigate an idealized groningen like geometry to discover whether the hypothesized possibility of triggering induced seismicity exists explore how some controllable and uncontrollable variables influence its severity and possibly provide clues on how production strategy might be able to avoid its occurrence the results demonstrate that sudden production changes can indeed trigger near well seismic events but that the effect is very small compared to other potential causes changing from sudden to gradual changes in well rates is therefore not expected to lead to a significant reduction in the number or magnitude of production induced earthquakes in the groningen field

u pb zircon and sm nd isotopic study of the huangtuling granulite dabie sulu belt china implication for the paleoproterozoic tectonic history of the yangtze craton sims data demonstrate archean 2 9 to 2 7 ga and paleoproterozoic 1991 43 ma ages for rounded detrital zircon cores and unzoned rims respectively in a graulite sample collected from huangtuling dabie sulu orogenic belt china the granulite rocks in this locality have pelitic compositions and represent an exposure of the northern margin of the yangtze craton the rounded zircon cores show oscillatory zoning and have th u ratios 0 17 0 78 systematically higher than those of the unzoned luminescent rims 0 005 0 03 the age of the detrital zircon cores and whole rock nd isotope model age suggest that the huangtuling granulite was possibly derived from a provenance dominated by archean rocks similar to the kongling complex exposed 200 km in the southwest multiple phases of metamorphism have been identified for the granulites with the dominant granulite facies mineral assemblage defining an early clock wise metamorphic p t path orthopyroxene plagioclase and whole rock material define a linear trend in a 147sm 144nd 143nd 144nd diagram corresponding to an age of 1926 146 ma this result and the u pb data for the zircon rims suggest that a collisional event may have occurred along the northern margin of the yangtze craton at 2 0 ga inviting further study on whether the yangtze craton was involved in the assembly of the recently proposed paleo mesoproterozoic supercontinent columbia

nucleation and arrest of dynamic slip on a pressurized fault 1 elevated pore pressure can lead to reactivation of slip on pre existing fractures and faults when the static coulomb failure is reached locally as the pressurized region spreads diffusively slip can accumulate quasi statically paced by the pore fluid diffusion or dynamically in this work we consider a prestressed fault with a locally peaked diffusively spreading pore pressure field to study 1 conditions leading to the escalation of slip and nucleation of dynamic rupture and 2 rupture run out distance before it is arrested nucleation appears in this model when the fault friction decreases from its peak value with slip while arrest of dynamic propagation is imminent on aseismic faults i e such that prestress b is less than the residual fault strength rat ambient conditions when fluid overpressure is a small to moderate fraction of the ambient value of normal effective stress and prestress is large enough for fault slip to be activated by overpressure dynamic rupture always nucleates and the nucleation length increases with decreasing prestress practically independently of the overpressure value transition from the ultimately unstable b r to the ultimately stable b r fault loading is marked by a strong increase of the nucleation length 1 b r 2 as b approaches r from above for aseismic faults b r no dynamic rupture is nucleated at large fluid overpressures for all but the smallest values of prestress the largest run out distances of dynamic slip on aseismic faults correspond to overpressure prestress just sufficient for slip activation in such cases the dynamically accumulated slip can lead to enhanced dynamic fault weakening resulting in a sustained dynamic rupture and generating a large earthquake this is consistent with field observations when the largest injection induced seismicity occurred after fluid injection ended

balancing reservoir creation and seismic hazard in enhanced geothermal systems summary fractureshear dilatancyisanessentialprocessforenhancingthepermeabilityofdeepgeothermal reservoirs and is usually accompanied by the radiation of seismic waves however the hazard and risk perspective of induced seismicity research typically focuses only on the question of how to reduce the occurrence of induced earthquakes here we present a quantitative analysisofseismichazardasafunctionofthetwokeyfactorsdefininganenhancedgeothermal system the permeability enhancement and the size of the stimulated reservoir our model has two coupled components 1 a pressure diffusion model and 2 a stochastic seismicity model permeability is increased in the source area of each induced earthquake depending on the amount of slip which is determined by the magnitude we show that the few largest earthquakes i e 5 10 events with m 1 5 contribute more than half of the total reservoir stimulation the results further indicate that planning and controlling of reservoir engineering operations may be compromised by the considerable variability of maximum observed magnitude reservoir size the gutenberg richter b value and shapiro s seismogenic index i e a measure of seismic reactivity of a reservoir that arises from the intrinsic stochastic nature of induced seismicity we also find that injection volume has a large impact on both reservoir size and seismic hazard injection rate and injection scheme have a negligible effect the impact of site specific parameters on seismicity and reservoir properties is greater than that of the injected volume in particular conditions that lead to high b values possibly a low differential stress level have a high impact on seismic hazard but also reduce the efficiency of the stimulation in terms of permeability enhancement under such conditions target reservoir permeability can still be achieved without reaching an unacceptable level of seismic hazard if either the initial reservoir permeability is high or if several fractures are stimulated the proposed methodology is a first step towards including induced seismic hazard analysis into the design of reservoir stimulation in a quantitative and robust manner

the 2 65 ga a type granite in the northeastern yangtze craton petrogenesis and geological implications abstract the presence of old residual continental crustal rocks in cratons is crucial for investigation of their early evolution due to the poor exposure of archean rocks the early evolution of the yangtze craton has not been well constrained yet in this study a combined study of zircon u pb and hf o isotopes as well as whole rock major and trace elements and nd isotopes have been conducted for a granite pluton at huji town in the northern part of the yangtze craton u pb dating for magmatic zircons yielded a weighted mean age of 2656 6 ma revealing another archean outcrop in the yangtze craton besides the kongling terrane the granite samples show relatively evaluated k 2 o na 2 o cao tfeo mgo ratios and zr nb ce ga and y contents sharing the same features as the a type granite they have pronounced eu sr and ba negative anomalies on the primitive mantle normalized trace element spidergram implying the residual of plagioclase in the magma sources their high zr contents of 440 529 ppm correspond to initial magma temperatures of 930 962 c the zircons have negative hf t values of 2 7 to 0 1 and hf model ages of ca 3 2 ga respectively the 18 o values of the zircons range between 4 94 and 5 72 and give an average of 5 26 0 14 suggesting no contribution of supracrustal rock into the host magma therefore the hf model ages indicate the generation of the huji granite by reworking of ca 3 2 ga juvenile crustal rocks combined with previous studies the finding of the neoarchean huji granites with ca 3 2 ga hf model ages suggests the widespread of archean basement in the yangtze craton the occurrence of the ca 2 65 ga huji granites likely records the thermally stable lithosphere and thus heralds the craton stabilization of the eastern part of the yangtze block

the origin of high δ18o zircons marbles megacrysts and metamorphism the oxygen isotope ratios 18o of most igneous zircons range from 5 to 8 with 99 of published values from 1345 rocks below 10 metamorphic zircons from quartzite metapelite metabasite and eclogite record 18o values from 5 to 17 with 99 below 15 however zircons with anomalously high 18o up to 23 have been reported in detrital suites source rocks for these unusual zircons have not been identified we report data for zircons from sri lanka and myanmar that constrain a metamorphic petrogenesis for anomalously high 18o in zircon a suite of 28 large detrital zircon megacrysts from mogok myanmar analyzed by laser fluorination yields 18o from 9 4 to 25 5 the u pb standard cz3 a large detrital zircon megacryst from sri lanka yields 18o 15 4 0 1 2 se by ion microprobe a euhedral unzoned zircon in a thin section of sri lanka granulite facies calcite marble yields 18o 19 4 by ion microprobe and confirms a metamorphic petrogenesis of zircon in marble small oxygen isotope fractionations between zircon and most minerals require a high 18o source for the high 18o zircons predicted equilibrium values of 18o calcite zircon 2 3 from 800 to 600 c show that metamorphic zircon crystallizing in a high 18o marble will have high 18o the high 18o zircons 15 from both sri lanka and mogok overlap the values of primary marine carbonates and marbles are known detrital gemstone sources in both localities the high 18o zircons are thus metamorphic the 15 25 zircon values are consistent with a marble origin in a rock dominated system i e low fluid external rock the lower 18o zircon values 9 15 are consistent with an origin in an external fluid dominated system such as skarn derived from marble although many non metasomatized marbles also fall in this range of 18o high 18o 15 and the absence of zoning can thus be used as a tracer to identify a marble source for high 18o detrital zircons this recognition can aid provenance studies in complex metamorphic terranes where age determinations alone may not allow discrimination of coeval source rocks metamorphic zircon megacrysts have not been reported previously and appear to be associated with high grade marble identification of high 18o zircons can also aid geochronology studies that seek to date high grade metamorphic events due to the ability to distinguish metamorphic from detrital zircons in marble

evolution of the se asian continent from u pb and hf isotopes in single grains of zircon and baddeleyite from large rivers to better understand the evolution of the se asian continent 235 single zircon and baddeleyite grains from large rivers were dated by the u pb chronometer and 148 of these grains were simultaneously analyzed for hf isotopes this combination of methods is applied to sand samples from the mekong irrawaddy salween and red rivers which sample the continent on the plate scale u pb dates and hf isotopic signatures of these grains resolve the age spectra of crust and they elucidate source characteristics of magmas involved in continental growth and recycling for sufficient statistical coverage more than 80 of zircons and baddeleyites from each river sample were analyzed representing an erosion area of about 1 6 106 km2 our analyses reveal five different proterozoic crustal growth events occurring at about 2 5 ga 2 3 ga 1 9 ga 1 1 ga and 0 8 ga however none of these basement terrains is exposed in se asia being entirely covered by phanerozoic sediments the data also substantiate granitoid magmatism during the caledonian indosinian and himalayan orogenies initial hf isotope signatures ehfi obtained for grains lying less than 15 discordant in the concordia diagram range between 13 3 and 16 7 plotting in both the domains of strongly lile depleted and enriched reservoirs relative to a chondritic evolution of the mantle approximately half of the grains crystallized in magmas derived from significantly depleted mantle sources and about 18 formed in magmas showing nearly chondritic signatures ehfi 1 37 to 1 59 27 grains the remaining grains yield strongly negative ehfi documenting the incorporation of important amounts of melts generated from crust formed during the paleoproterozoic events at 2 3 and 1 9 ga which seem to have produced the dominant mass of the se asian continent all younger orogenic cycles are characterized by substantial melting of continental material which probably dominate over juvenile crust addition an exception are the irrawaddy terrains where substantial mantle input characterizes post collisional magmatism since 50 ma

zircon growth during progressive recrystallization of gabbro to garnet amphibolite eastern segment sveconorwegian orogen the interpretation of whether a dated metamorphic zircon generation grew during the prograde peak or retrograde stage of a metamorphic cycle is critical to geological interpretation this study documents a case at herrestad in the eastern part of the 1 0 ga sveconorwegian province involving progressive metamorphic recrystallization of gabbro to garnet amphibolite and associated behaviour of zr bearing minerals in this case textures show that baddeleyite is by far the main source of zr for metamorphic zircon growth the amount of metamorphic zircon formed was primarily controlled by the degree of metamorphic recrystallization which in turn was controlled by deformation and the presence of a fluid as a transport medium zircon in the herrestad rocks shows a range of morphologies and internal textures at different degrees of metamorphic recrystallization igneous zircon occurs together with baddeleyite in coarse grained olivine free facies of the gabbro metamorphic polycrystalline zircon rims on baddeleyite and minute 5 m bead like zircon grains at fe ti oxide boundaries characterize the transition to coronitic metagabbro with increasing metamorphic recrystallization polycrystalline zircon rims grow at the expense of baddeleyite and the amount of minute bead like zircon increases forming strings of zircon beads with increasing distance from fe ti oxide grains the progressive breakdown of baddeleyite results in polycrystalline zircon aggregates that become denser and finally form single grains in completely recrystallized garnet amphibolite late magmatic zircon crystallized at 156765 ma whereas metamorphic zircon dates amphibolite facies metamorphic recrystallization at 97067 ma the herrestad case illustrates a general rule that the bulk zr budget in originally baddeleyite bearing rocks will rapidly become locked into metamorphic zircon during the first event of metamorphic recrystallization when silica and zr are released from the igneous minerals incomplete metamorphic recrystallization and partial preservation of baddeleyite however also allows later stages of zircon formation thus in incompletely reacted rocks the final result may be highly complex with microscale zircon of several age generations less

geochemical evidence from coesite bearing jadeite quartzites for large scale flow of metamorphic fluids in a continental subduction channel abstract metamorphic fluids produced by dehydration of subducting crust transport mass and energy at the slab mantle interface in subduction channels it is commonly assumed that fluid flow is significant in oceanic subduction channels but insignificant in continental subduction channels this assumption is challenged by a combined study of whole rock geochemistry mg and o isotopes zircon u pb ages and trace elements in coesite bearing jadeite quartzites from the dabie orogen china although the target samples were collected from different outcrops in an area of 50 km2 zircon u pb dating yields similar discordia lines with not only consistent upper intercept ages of 1 9 2 0 ga but also consistent lower intercept ages of 224 235 ma this indicates the same paleoproterozoic protolith and the same triassic metamorphism for these jadeite quartzites the o isotope analysis of mineral separates and whole rock yields variable 18o values from 6 3 to 9 4 indicating involvement of supracrustal components except for one outlier at 0 43 all the other rocks give variable 26mg values from 0 16 to 0 61 much higher than normal mantle values the whole rock mg isotopes show significant positive correlations not only with mgo contents but also with rb la rb gd and rb nb ratios but a negative correlation with na2o contents these observations indicate that the middle paleoproterozoic protolith of jadeite quartzites was weathered to produce a kind of sedimentary rocks in a passive continental margin and then underwent significant metasomatism by metamorphic fluids with high 26mg values during the continental subduction in the triassic the metamorphic fluids were produced by the breakdown of biotite in the metasedimentary rocks during their subduction to subarc depths for ultrahigh pressure metamorphism they would have acquired their geochemical compositions not only from the biotite breakdown but also through leaching reaction with the ttg provenance in view of the spatial occurrences of the target samples the metamorphic fluids would have flowed inside the continental subduction channel on a large scale this is the first report of the large scale fluid flow in the continental subduction zone and therefore demonstrates that fluid flow can be significant in continental subduction channels

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

stress drop variations of induced earthquakes at the basel geothermal site 1 we determine stress drops from p wave spectra of about 1000 earthquakes induced by hydraulic stimulation in crystalline rock for a deep heat mining project in basel switzerland we observe an increase in stress drop by about a factor of five with radial distance from 10 m to 300 m which suggests that stress drop correlates with pore pressure perturbations due to the injection we test this hypothesis by calculating the injection related pore pressure perturbation based on a simple linear pore pressure diffusion model and find a good correlation of the expected pore pressure perturbation with the estimated stress drops

coesite inclusions in dolomite from eclogite in the southern dabie mountains china the significance of carbonate minerals in uhpm rocks coesite inclusions have been discovered in dolomite from carbonate bearing eclogite in the dabie uhp terrane the eclogite boudins are enclosed in calc silicate rocks that contain quartz aggregatesafter coesite in the matrix the carbonate bearing eclogite is composed of garnet coesite or quartz dolomite magnesite omphacite rutile tminor phengite apatite and zircon and was formed at 760 dc 28 kbar and 0 01 100 km

paleoproterozoic ultrahigh temperature granulite facies metamorphism in the sulu orogen eastern china evidence from zircon and monazite in the pelitic granulite abstract because of their essential information for constraining the timescales of high temperature processes zircon and monazite are the two most important minerals for understanding crustal processes zircon and monazite are common accessory minerals in pelitic granulites sulu orogen eastern china the pelitic granulites have a peak mineral assemblage of garnet sillimanite antiperthite plagioclase quartz rutile biotite zircons from the granulite have low th u ratios

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

evidence for melting mud in earth s mantle from extreme oxygen isotope signatures in zircon evidence for melting mud in earth s mantle from extreme oxygen isotope signatures in zircon

numerical assessment of potential impacts of hydraulically fractured bowland shale on overlying aquifers natural gas extracted from hydraulically fractured shale formations potentially has a big impact on the global energy landscape however there are concerns of potential environmental impacts of hydraulic fracturing of the shale formations particularly those related to water quality to evaluate the potential impact of hydraulically fractured shale on overlying aquifers we conduct realizations of numerical modeling simulations to assess fluid flow and chloride transport from a synthetic bowland shale over a period of 11 000 years the synthetic fractured shale was represented by a three dimensional discrete fracture model that was developed by using the data from a bowland shale gas exploration in lancashire uk chloride mass exchange between fractures and the rock matrix was fully accounted for in the model the assessment was carried out to investigate fluid and chloride mass fluxes before during and after hydraulic fracturing of the bowland shale impacts of the upward fracture height and aperture as well as hydraulic conductivity of the multilayered bedrock system are also included this assessment this modeling revealed that the hydraulically fractured bowland shale is unlikely to pose a risk to its overlying groundwater quality when the induced fracture aperture is 200 m with the fracture aperture 1000 m the upward chloride flux becomes very sensitive to the upward fracture height growth and hydraulic conductivity of the multilayered bedrock system in the extremely unlikely event of the upward fracture growth directly connecting the shale formation to the overlying sherwood sandstone aquifer with the fracture aperture 1000 m the upward chloride mass flux could potentially pose risks to the overlying aquifer in 100 years the model study also revealed that the upward mass flux is significantly intercepted by the horizontal mass flux within a high permeable layer between the bowland shale and its overlying aquifers reducing further upward flux toward the overlying aquifers

statistics of fracture strength and fluid induced microseismicity 1 in this paper we develop an approach for estimating the strength of rocks by analyzing fluid induced microseismicity the strength corresponds to the value of critical pressure in the pore space that must be exceeded in order to activate preexisting fractures i e to trigger earthquakes we assume that during hydraulic injection experiments in boreholes microseismicity is mainly triggered by a diffusive process of pore pressure perturbation an analytical solution can be applied to find time dependent pore pressure perturbations in rocks caused by fluid injections characteristics of the spatiotemporal evolution of microseismic clouds can be then used to estimate minimum and maximum pressures necessary to trigger earthquakes moreover we present a method for reconstruction of the full spectrum of rock strength that is we show how to estimate the probability density function of the critical pressure we verify the approach using numerical data and apply it to real data of injection induced microseismicity from two hot dry rock tests in crystalline rocks and one hydraulic fracturing experiment in a sedimentary rock the results show that such an analysis of microseismicity is able to provide us with a completely new feature of natural fractured rocks in situ namely the statistics of their strength we find that very low critical pressures in the range 0 001 1 mpa characterize the strength of preexisting cracks for all data sets analyzed the range of critical pressures is broadly distributed within 3 to 4 orders of magnitude however the probability density functions of critical pressure change very quickly from the zero level to significant values and from significant values to the zero level at the lower and upper limits of their nonvanishing value ranges respectively the lower bound of critical pressure is possibly defined by the magnitude of tidal induced stresses permanently occurring and relaxing in the earth

in situ u pb dating of micro baddeleyite by secondary ion mass spectrometry abstract we introduce a technique for u pb dating of baddeleyite using secondary ion mass spectrometry sims in situ analysis of ng mass crystals that cannot be efficiently extracted by conventional mineral separation techniques average 207 pb 206 pb ages for precambrian baddeleyite crystals are within 206 pb 238 u ratios are corrected for instrumental fractionation calibrated through linear regression in a pb u relative sensitivity vs uo 2 u calibration plot calibration is performed on separated baddeleyite crystals 100 200 m in maximum dimension mounted in random crystallographic orientation 206 pb 238 u ages for baddeleyite from duluth gabbro fc4b and kovdor are accurate within 1 2 when averaging 15 30 individual spot analyses and relative sensitivities calibrated on phalaborwa baddeleyite the relative difference of 206 pb 238 u between large crystals and micro baddeleyite from fc4b is within 1 comparison between silicate glass and baddeleyite as well as replicate analysis of the same grains in different orientations relative to the incidence direction of the primary beam support previous evidence for bias in pb u sensitivity in baddeleyite due to variable crystal orientations we successfully utilized oxygen flooding and a uo 2 u based calibration to significantly reduce orientation dependent bias

comment on hydraulic fracturing in faulted sedimentary basins numerical simulation of potential contamination of shallow aquifers over long time scales by claire gassiat et al

petrogenesis of the huashanguan a type granite complex and its implications for the early evolution of the yangtze block abstract an integrated study of petrography zircon u pb ages hf o isotope compositions as well as whole rock geochemistry was carried out for a paleoproterozoic granite complex in the northern yangtze block to investigate its petrogenesis and geological significances petrographically the huashanguan complex is a granite complex comprised of monzogranite in the marginal facies and k feldspar granite in the central facies u pb dating of magmatic zircons from the monzogranite and k feldspar granite yielded ages of 1816 50 ma and 1843 9 ma respectively the more precise age of 1843 9 ma is suggested to represent the formation age of the huashanguan complex the granites have uniform negative zircon e hf t values of 20 2 to 15 8 with corresponding t dm2 ages of ca 3 6 3 5 ga the 18 o values average at 6 80 0 09 these indicate that the granites were generated by partly melting of archean rocks implying the widespread of archean basement in the yangtze block the monzogranites display low feo t and mgo contents and evolved trace element features suggesting their formation by more fractional crystallization from similar parent magma of the k feldspar granites the occurrence of the huashanguan granite complex indicates that the yangtze block has experienced a tectonic transition from tectonic convergence to extension at ca 1 85 ga possibly due to the collapse of the ca 2 0 ga orogeny

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

microseismic imaging of a geothermal reservoir stimulation exploitation of geothermal heat energy from rocks at depths of several km has been the goal of vari ous projects since the mid 1970s to exploit the energy in these deep rocks poses technical challenges in drilling well completion creation of the heat exchange reservoir at depth and control of seismicity in spite of the difficulties what are now known as enhanced engineered geothermal systems egs offer almost limitless clean energy so it is not surprising that this technology continues to attract investors however commercial energy production from the greatest potential resource hot rock at depths 5 km or temperatures 200 c remains elusive

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

age of the ballachulish and glencoe igneous complexes scottish highlands and paragenesis of zircon monazite and baddeleyite in the ballachulish aureole u pb zircon ages are presented for the ballachulish igneous complex 207 pb 206 pb age 427 1 ma 206 pb 238 u age 423 0 3 ma and glencoe volcanic complex 207 pb 206 pb age 406 6 ma of the scottish highlands these ages are significantly more precise than pre existing age constraints and discriminate a previously unresolved age difference of c 20 ma between the two complexes this difference in age provides an explanation for the c 10 km difference in crustal level between the two magmatic events and constrains exhumation rates for the argyll region to be on average c 0 4 km ma 1 over the period c 425 405 ma with improved age constraints on the ballachulish igneous complex in place the associated metamorphic aureole is used as a type locality to investigate the metamorphic behaviour of the u bearing accessory minerals baddeleyite zircon and monazite baddeleyite formed in impure dolomites by the reaction of detrital zircon with dolomite and gives the same u pb age as the intrusive complex consistent with its contact metamorphic origin detrital zircon appears to be inert throughout much of the metamorphic aureole with contact metamorphic zircon growth being restricted to migmatite grade rocks a possible exception is the development of enigmatic very narrow overgrowths at temperatures between c 500 and 600 c monazite exhibits a variety of textures in lower grade parts of the aureole

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

evaluating baddeleyite oxygen isotope analysis by secondary ion mass spectrometry sims abstract two baddeleyite megacrysts were evaluated as potential reference materials rms for sims oxygen isotope analysis and utilized to understand and calibrate instrumental mass fractionation imf a baddeleyite crystal s0045 from the phalaborwa carbonatite south africa has a mean 18ovsmow 4 6 0 3 range 0 75 measured using laser fluorination gas source mass spectrometry lf gms and one s0069 from the mogok metamorphic belt myanmar has 18ovsmow 22 2 0 4 range 0 89 sims standardization utilizing these inherently heterogeneous rms is possible by analyzing a number of crystal fragments and utilizing one of them lying at the median of the range metamictization lattice orientation and chemical composition do not appear to be significant sims oxygen isotope analysis of co crystalline zircon and baddeleyite from the 2 2 ga duck lake sill dls in the northwest territories canada yield predominant 18ovsmow modes of 6 0 and 3 2 respectively this difference is consistent with preserving high temperature isotopic equilibrium between zircon and baddeleyite dls baddeleyite 18o data as a whole are negatively skewed to 0 0 and interpreted to reflect low temperature open system behaviour zircon 18o are less affected but also show hints of the same influences of secondary alteration and oxygen isotope exchange

probability of inducing given magnitude earthquakes by perturbing finite volumes of rocks 1 fluid induced seismicity results from an activation of finite rock volumes the finiteness of perturbed volumes influences frequency magnitude statistics previously we observed that induced large magnitude events at geothermal and hydrocarbon reservoirs are frequently underrepresented in comparison with the gutenberg richter law this is an indication that the events are more probable on rupture surfaces contained within the stimulated volume here we theoretically and numerically analyze this effect we consider different possible scenarios of event triggering rupture surfaces located completely within or intersecting only the stimulated volume we approximate the stimulated volume by an ellipsoid or cuboid and derive the statistics of induced events from the statistics of random thin flat discs modeling rupture surfaces we derive lower and upper bounds of the probability to induce a given magnitude event the bounds depend strongly on the minimum principal axis of the stimulated volume we compare the bounds with data on seismicity induced by fluid injections in boreholes fitting the bounds to the frequency magnitude distribution provides estimates of a largest expected induced magnitude and a characteristic stress drop in addition to improved estimates of the gutenberg richter a and b parameters the observed frequency magnitude curves seem to follow mainly the lower bound however in some case studies there are individual large magnitude events clearly deviating from this statistic we propose that such events can be interpreted as triggered ones in contrast to the absolute majority of the induced events following the lower bound

fractal properties of fault systems by scattering of body seismic waves abstract one can obtain the fractal dimension of fault systems from the power frequency dependence of the scattering coefficient of x raying p or s waves this estimation may be based on the use of one of the two alternative models of media a medium with discrete random inclusions or a random continuous medium we have shown that if spectral densities of fluctuations in these models are identical the frequency dependencies of the scattering coefficients of the corresponding body waves are identical too in the weak scattering regime however fractal dimensions of a total surface of inclusions and isosurfaces in a random continuous turbulent medium are different the fractal dimension of the total surface of inclusions estimated by scattering coefficient coincides with the estimations of fractal dimensions of the fault systems in japan and the san andreas fault system we think that the fractal dimension of the total surface of faults in seismic active regions is 2 0 2 5 and in aseismic regions is about 3