sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

a technique for determining low concentrations of total carbonate in geologic materials abstract even small quantities of carbonate minerals can impart a significant acid neutralizing capacity to soils impacted by acid waters rain leachate from pyritic mine tailings etc a simple analytical technique is presented for determining the carbonate content of geologic materials containing less than 1 carbonate minerals samples are acidified and the evolved co2 measured accurately using a modified headspace gas chromatographic technique less than 0 001 wt calcite can be accurately detected in geologic samples six replicate analyses of a synthetic sample containing 0 075 wt calcite produced a mean calcite content of 0 079 wt with a standard deviation of 4 7 of the mean a major problem in carbonate determinations where waters high in fe2 are encountered is the loss of carbonates resulting from acid production vis fe2 oxidation during sample collection and handling

experimental grain size sensitive flow of hot pressed brazilian quartz aggregates abstract grain size sensitive flow may be of particular importance in the flow of rocks in natural high strain zones hot pressed aggregates of synthetic ultrafine grained brazilian quartz of nominal grain sizes 0 4 1 3 and 4 5 m were deformed at 300 mpa confining pressure and temperatures of 1273 1473 k fully ductile flow at differential stresses below 200 mpa followed 0 4 exp 220000 r t d 2 where is strain rate s 1 is stress mpa d is grain size microns and r is the gas constant grains remained equant and mostly dislocation free without significant crystallographic fabric water pressure 25 50 mpa was estimated from water adsorbed onto grain boundaries during specimen fabrication flow was inferred to be controlled by silicon volume diffusion and to be sensitive to water fugacity at differential stresses 200 mpa non linear flow involved dislocation motion extrapolation to natural strain rates and temperatures that predict grain size sensitive flow in quartz should only be important at 800 k and very small grain sizes 1 m flow law parameters may change over the extrapolation interval e g through a transition to control by silicon grain boundary diffusion but geological evidence suggests that flow of even very fine grained quartzites commonly occurs by recrystallization accommodated dislocation creep rather than by diffusional accommodation

seasonal cycling and mass loading of dissolved metals and sulfate discharging from an abandoned mine site in northern canada abstract drainage from sulfide rich mine waste can contaminate surface waters directly by surface runoff and indirectly through groundwater discharge the camp lake watershed located in northern manitoba receives both direct and indirect drainage from an abandoned tailings impoundment which has resulted in severely degraded water quality sulfide oxidation has been occurring for over 70 years at an abandoned mine site in this watershed resulting in high concentrations of oxidation products in the surface water and groundwater discharging from the two tailings impoundments both of which flow into the adjacent camp lake a 5 year hydrological and geochemical sampling program was conducted at this small precambrian shield lake prior to the initiation of remedial actions to identify the seasonal distribution and mass loading of dissolved metals and sulfate discharging from camp lake to the downstream kississing lake weekly and biweekly sampling of outflow from the lake clearly showed a seasonal cycle of dissolved metals sulfate and ph during months when the lake was ice covered the discharge water had a neutral ph with low concentrations of dissolved metals and sulfate similar to background concentrations at spring melt the discharge sampled at camp weir revealed abrupt increases in dissolved metal and sulfate concentrations and decreases in ph to values that remained relatively constant until fall freeze up when dissolved metal concentrations and ph returned to winter values the annual and interannual variations in loadings measured at camp weir are different from those measured at the two streams feeding camp lake showing the contribution of groundwater flow through the tailings to so 4 and metal loadings to the lake during dry years and the potential for significant loadings due to flushing of the thick unsaturated zone in the tailings during relatively wet years the abrupt changes in ph metal and sulfate concentrations and the timing of these changes with the appearance and disappearance of ice cover on the lakes suggests a combination of physical and geochemical controls related to shifts in sources of water mixing and changes in solubility despite fairly low average annual metal concentrations measured in camp lake discharge concentrations of zn and cu were elevated above background in bottom sediments of kississing lake in a zone extending 9 5 km 2 from the location of camp lake inflow these results show the importance of the open water period in controlling metal discharge from mine impacted areas and demonstrate that even when average annual concentrations are only slightly elevated long term metal loadings can have a significant impact on the receiving aquatic systems

pore water extraction from the unsaturated and saturated zones a simple inexpensive method for extracting pore water from unsaturated soils which uses a combination of immiscible fluid displacement suction and mechanical compression is described this method uses a squeezing chamber to contain the unsaturated sediments in aluminum core tubing to prevent exposure of the sediments and pore water to atmospheric o2 and subsequent oxidation reactions geochemical artifacts resulting from high compression squeezing are prevented by maintaining the pressure applied during the squeezing at a minimum comparison of squeezed profiles with field measured profiles of ph eh oxidation reduction potential alkalinity and metal speciation indicates good agreement between these parameters using this method depending on the water content of the sediments a range of water volumes several millilitres to excess of 100 ml can be extracted from a single core section 7 6 cm in diameter by 20 cm long pore water was produced immediately from sediments at near saturated condition

adakites from continental collision zones melting of thickened lower crust beneath southern tibet adakites are geochemically distinct intermediate to felsic lavas found exclusively in subduction zones here we report the first example of such magmas from southern tibet in an active continental collision environment the tibetan adakites were emplaced from ca 26 to 10 ma and their overall geochemical characteristics suggest an origin by melting of eclogites and or garnet amphibolites in the lower part 50 km of thickened tibetan crust this lower crustal melting required a significantly elevated geotherm which we attribute to removal of the tectonically thickened lithospheric mantle in late oligocene time the identification of collision type adakites from southern tibet lends new constraints to not only the himalayan tibetan orogenesis how and when the indian lithosphere started underthrusting asia can be depicted but also the growth of the early continental crust on earth that consists dominantly of the tonalite trondhjemite granodiorite suites marked by adakitic geochemical affinities

the early diagenesis of submerged sulphide rich mine tailings in anderson lake manitoba the oxidation of sulphide rich mine tailings stored on land by acidophilic bacteria is frequently associated with severe environmental degradation as metal rich acid drainage from the tailings contaminates groundwater and surface runoff permanent storage of tailings underwater may prove to be more chemically benign if oxidation is inhibited sufficiently to assess this possibility the chemistry of interstitial waters and the associated solid phases in tailings and organic rich 20 30 wt c natural sediments in anderson lake manitoba is examined the lake has been used as a receiving basin for sulphide rich tailings since 1979 and is contaminated with metals as a result of the input of acid mine drainage along the north shore and the discharge of mill process water with the tailings three cores were collected and processed under nitrogen to extract interstitial waters at all sites the occurrence of high concentrations of dissolved iron in shallow pore waters indicates that the deposits are anoxi

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

secondary copper enrichment in tailings at the laver mine northern sweden field and laboratory studies of the sulphide bearing tailings at laver northern sweden show that the present release of metals from the tailings is low especially with regard to cu a large part of the cu released by sulphide oxidation is enriched in a distinct zone just below the oxidation front the enrichment zone occurs almost all over the tailings area except in areas with a shallow groundwater table the cu enrichment is caused by formation of covellite and adsorption onto mineral surfaces the transport of zn co cd ni and s seems to be controlled mainly by adsorption no secondary zone or secondary minerals containing these metals have been found just below the groundwater table metals are released into solution when the enrichment zone reaches the groundwater due to the low ph an increased release of metals especially cu can be expected in the future since the enrichment zone is moving towards the groundwater table

effect of water on the rheology of experimentally deformed quartzite empirical flow laws have been determined for simpson quartzite samples deformed to mechanical steady state in the quartz stability field using griggs blacic solid medium deformation apparatus experiments were conducted on samples both as received dry and with water added via the dehydration of a talc confining medium wet best fits of the power law type yield a stress exponent of 2 72 0 19 an activation enthalpy of 134 32 kj mol 1 and a preexponential constant of 1 16 1 15 0 58 10 7 mpa 2 72 s 1 for the dry quartzite law and are 2 61 0 15 145 17 kj mol 1 and 5 05 5 00 10 6 mpa 2 61 s 1 for the wet quartzite the enhanced hydrolytic weakening of the wet experiments appears to affect the flow laws mostly in the preexponential constants possibly as a defect concentration term that is higher in the wet than in the dry law over the range of experimental conditions 750 900 c 10 7 to 10 4 s 1 and 1 0 1 25 gpa confining pressure dry specimens are 1 5 2 5 times stronger than wet samples deformed at the same conditions the microstructures produced are analogous to those observed in many natural quartz tectonites recrystallization is well developed in the wet but not the dry specimens at flow stresses below 500 mpa microstructures indicative of recovery are well developed a comparison of our creep activation enthalpies with those determined from diffusion experiments are consistent with deformation of wet simpson quartzite that is limited by oxygen self diffusion inconsistencies between the present study and previous studies are probably the result of differences in sample material sample treatment and sample assemblies chemical environment

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

timing of collision of the sino korean and yangtse cratons u pb zircon dating of coesite bearing eclogites the suture zone between the sino korean and yangtse cratons in central china is marked by a series of fault bounded belts composed of crustal protoliths in the dabie mountains some of these blocks contain coesite and diamond indicating subduction to minimum depths of 120 km as a result of continental collision the blocks range from the structurally lowest ultrahigh pressure metamorphic belt and decrease in metamorphic grade upsection to the structurally highest low greenschist facies belt furthermore the faults mark large contrasts in metamorphic grade these features form a structure that is similar to metamorphic core complexes indicating extension as part of the exhumation process timing of the continental collision has previously been inferred as late triassic from regional geologic relations or caledonian from 40 ar 39 ar dating of the adjacent and possibly related qinling metamorphic belt u pb dating of zircon from ultra high pressure eclogites yields a metamorphic age of 209 2 ma this age coincides with later stages of collision and is therefore a minimum estimate of the time of collision

archean crustal evolution in china the taishan complex and evidence for juvenile crustal addition from long term depleted mantle abstract the main framework for crustal evolution of the late archean taishan complex in the shandong province of china is constructed using data from field investigation petrographic examination geochemical analysis and isotopic age determination the history of the complex began with emplacement of basic and tonalitic magmas about 2 7 2 75 ga ago which were metamorphosed designated as metamorphism i to amphibolites and grey gneisses shortly after their emplacement these rocks constitute a metamorphic basement termed the wangfushan gneisses the basement gneisses were later intruded by a plutonic association including 1 alkali and light rare earth element lree enriched dioritic rocks and their differentiates 2 6 ga ago 2 granites and trondhjemites collectively termed the hushan granites also 2 6 ga ago and 3 the aolaishan type granites sensu stricto 2 4 2 5 ga ago the plutonic association in conjunction with the older basement gneisses was later subjected to a second period of deformation and metamorphism metamorphism ii 2 ga ago as inferred from published k ar biotite dates the chronological order of all the above events has been determined by a multichronometric approach and the age results in ma with 2 uncertainties are summarized as follows the relatively low i sr initial 87 sr 86 sr ratio and high positive nd t values for the wangfushan gneisses and the diorite group provides strong evidence for continental growth by addition of juvenile material ultimately separated from long term depleted mantle sources by contrast the sr and nd isotopic data for the aolaishan type granites coherently suggest that they are likely to be derived by anatexis of the basement gneisses at shallow depths crustal evolution of the taishan complex offers an additional example supporting the concept of a continental accretion differentiation superevent that during such a worldwide tectonothermal episode particularly in the archean important differentiation of the upper mantle has contributed to the growth of the continental crust by addition of juvenile material

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

reactive transport modelling of the hydro geochemical behaviour of partially oxidized acid generating mine tailings with a monolayer cover abstract the efficiency of a monolayer cover to prevent acid mine drainage amd generation from two pre oxidized tailings impoundments was assessed using the min3p code a finite volume model for coupled groundwater flow oxygen diffusion and multi component reactive transport numerical simulations were validated using large column tests set up in the laboratory and monitored during 19 wetting and drying cycles over approximately two years results indicate that a monolayer cover made of either non acid generating tailings or a till was not able to prevent sulfide oxidation in the underlying reactive tailings both for the conditions applied in the laboratory and under conditions more representative of field observations the efficiency of the simulated monolayer cover was highly dependent on the position of the water table despite improved water quality the reactive tailings nonetheless continued to oxidize and generate amd even when the water table was close to the surface of the tailings 1 m depth the results from this study indicate that the efficiency criteria for cover systems on fresh unoxidized tailings may not be directly applicable for pre oxidized tailings the paper also presents a few modifications to the min3p code that were successfully applied to simulate the hydrogeological and geochemical response of pre oxidized already acidic and highly contaminated tailings

interpreting magmatic fabric patterns in plutons abstract most plutons have widespread magmatic fabrics the interpretation of which remains controversial we propose a method to constrain likely causes of fabric patterns the application of which indicates the following 1 preserved fabric patterns often form after chamber construction and only rarely provide information about ascent or emplacement 2 fabrics are poor recorders of total strain and are easily reset preserving only the last increment of strain during crystallization 3 in magmatic systems mechanically decoupled from host rocks patterns may result from strain during internally driven flow filter pressing or porous flow in relatively static chambers or by final increments of strain during emplacement 4 with greater emplacement depths fabric patterns increasingly reflect strain caused by regional deformation and 5 given that magmatic fabrics are easily reset and reflect only the last increment of strain of comparatively weak materials they may provide a relatively direct record of paleostress in orogenic belts

the stability of sulfate and hydrated sulfate minerals near ambient conditions and their significance in environmental and planetary sciences abstract sulfate and hydrated sulfate minerals are abundant and ubiquitous on the surface of the earth and also on other planets and their satellites the humidity buffer technique has been applied to study the stability of some of these minerals at 0 1 mpa in terms of temperature relative humidity space on the basis of hydration dehydration reversal experiments updated phase relations in the binary system mgso 4 h 2 o are presented as an example to show how reliable thermodynamic data for these minerals could be obtained based on these experimental results and thermodynamic principles this approach has been applied to sulfate and hydrated sulfate minerals of other metals including fe both ferrous and ferric zn ni co cd and cu metal sulfate salts play important roles in the cycling of metals and sulfate in terrestrial systems and the number of phases extends well beyond the simple sulfate salts that have thus far been investigated experimentally the oxidation of sulfide minerals particularly pyrite is a common process that initiates the formation of efflorescent metal sulfate minerals also the overall abundance of iron bearing sulfate salts in nature reflects the fact that the weathering of pyrite or pyrrhotite is the ultimate source for many of these phases many aspects of their environmental significance are reviewed particularly in acute effects to aquatic ecosystems related to the dissolution of sulfate salts during rain storms or snow melt events hydrous mg ca and fe sulfates were identified on mars with wide distribution and very large quantities at many locations on the basis of spectroscopic observations from orbital remote sensing and surface explorations by rovers however many of these findings do not reveal the detailed information on the degree of hydration that is essential for rigorous interpretation of the hydrologic history of mars laboratory experiments on stability fields reactions pathways and reaction rates of hydrous sulfates likely to be found on mars enhance our understanding of the degrees of hydration of various sulfates that should currently exist on mars at various seasons and locations and during various atmospheric pressure and obliquity periods two sets of systematic experiments were described one on hydrous mg sulfates and the other on hydrous fe 3 sulfates also their implications to mars sulfates mineralogy were discussed

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

syntectonic emplacement of the triassic biotite syenogranite intrusions in the taili area western liaoning ne china insights from petrogenesis rheology and geochronology abstract the north china craton ncc is one of the oldest cratons in the world and it recently becomes a hot study area because of large volumes of mesozoic intrusions associated with lithospheric thinning contributing to cratonic destruction in late mesozoic times however the timing of initial thinning and destruction is still controversial the taili area western liaoning province in the northeastern part of the ncc well exposes the archean basement rocks and the mesozoic magmatic rocks with variable plastic deformation this study focuses on the syntectonic emplacement of the triassic biotite syenogranite intrusions in order to understand their petrogenesis timing as well as the geological significance zircon la icp ms u pb ages reveal that the biotite syenogranites formed between 246 and 191 ma and contain many ancient 2564 2317 ma zircon xenocrysts geochemical data suggests that the biotite syenogranites display an adakitic affinity with high sr y 135 167 and la yb n 48 69 as well as negligible eu anomalies eu 0 87 0 94 high negative zircon ehf t values 15 5 to 21 5 and ancient tdm2 ages 2246 2598 ma this data suggests that the parent magmas were generated from partial melting of thickened archean lower crustal rocks probably due to the bidirectional amalgamation of the ncc with the ne china micro blocks and the yangtze craton in its north and south respectively in the middle part of the taili area magmatic fabrics are well preserved in the biotite syenogranite intrusion characterized by the strong preferred orientation of biotite and hornblende crystals which parallel to the intrusion margin and are slightly oblique to the gneissosity of the sheared host neoarchean granitic gneisses the quartz grain size piezometer suggests that the paleo differential stresses weaken toward to the central part of the intrusion ranging from 21 40 22 22 mpa to 16 74 19 34 mpa during quartz crystallization in the emplacement stage this allow deduce much higher strain rates in the center 1 26 10 11 2 24 10 9 s 1 than at the margin 9 07 10 12 1 31 10 9 s 1 of the pluton these observations are interpreted by the rheological behavior of magma during the magmatic pipe flow the adakitic source melts ascended through the conduits along weak ne trending sinistral shear zones and emplaced at the shallower depth of 16 km before early jurassic 190 ma the biotite syenogranites were still in a semisolid state when garnet bearing granitic aplites injected at 220 ma this stage records elongate constrictional strain under the sinistral shear stresses particularly in quartz grains occurring in the margin of intrusions in combination with previous studies an exhumation rate of the ncc s archean basement from 25 km to 11 km in depth is calculated as initial low exhumation rate of 4 0 mm kyr from neoarchean to late triassic and subsequent a rapid exhumation process of 63 mm kyr between late triassic to early cretaceous all the results presented here allow us to consider the geodynamic evolution of the eastern ncc and constrain the onset of lithospheric thinning and cratonic destruction of the ncc as early as middle triassic 240 ma triggered by the amalgamation of adjacent blocks it developed prosperously since late triassic due to the oblique subduction of the paleo pacific plate

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

mine tailings dams characteristics failure environmental impacts and remediation on a global scale demand for the products of the extractive industries is ever increasing extraction of the targeted resource results in the concurrent production of a significant volume of waste material including tailings which are mixtures of crushed rock and processing fluids from mills washeries or concentrators that remain after the extraction of economic metals minerals mineral fuels or coal the volume of tailings is normally far in excess of the liberated resource and the tailings often contain potentially hazardous contaminants a priority for a reasonable and responsible mining organization must be to proactively isolate the tailings so as to forestall them from entering groundwaters rivers lakes and the wind there is ample evidence that should such tailings enter these environments they may contaminate food chains and drinking water furthermore the tailings undergo physical and chemical change after they have been deposited the chemical changes are most often a function of exposure to atmospheric oxidation and tends to make previously perhaps safely held contaminants mobile and available if the tailings are stored under water contact with the atmosphere is substantially reduced thereby forestalling oxygen mediated chemical change it is therefore accepted practice for tailings to be stored in isolated impoundments under water and behind dams however these dams frequently fail releasing enormous quantities of tailings into river catchments these accidents pose a serious threat to animal and human health and are of concern for extractive industries and the wider community it is therefore of importance to understand the nature of the material held within these dams what best safety practice is for these structures and should the worst happen what adverse effects such accidents might have on the wider environment and how these might be mitigated this paper reviews these factors covering the characteristics types and magnitudes environmental impacts and remediation of mine tailings dam failures

experimental data for a proposed empirical igneous geobarometer aluminum in hornblende at 10 kbar pressure knowledge of the depth of solidification of talc alkalic plutons is critical to understanding and unraveling the complex spatial temporal and chemical evolution of orogenic belts an empirical geobarometer has recently been proposed based on the total al content alt of near solidus calcic hornblendes in tonalite and granodiorite intrusive rocks in the pressure range 1 to 8 kbar pressures were estimated from mineral assemblages in associated metamorphic country rocks we report experimental data on newly crystallized near solidus amphiboles in partly melted vapor absent garnet tonalite at 10 kbar that provide some experimental support for the proposed geobarometer consistent with the extrapolated empirical result and confirm its limited applicability to specific multimineral assemblages

carbon and nitrogen isotopic composition of red deer cervus elaphus collagen as a tool for tracking palaeoenvironmental change during the late glacial and early holocene in the northern jura france abstract red deer bone collagen from rochedane in the jura france was analysed for carbon and nitrogen isotopic composition the specimens range in 14c age from about 13 000 to 8000 yr bp uncalibrated and cover the late glacial and early holocene a time period during which climatic conditions shifted from periglacial to temperate the carbon isotopic compositions of red deer collagen suggest changes in the vegetation cover around the site that are consistent with other palaeoenvironmental indicators such as the palynological record in the jura the nitrogen isotopic compositions exhibit a large range of around 6 interpreted as reflecting changes in the intensity of n cycling coeval to vegetation changes red deer bone collagen appears thus as a valuable proxy for reconstructing palaeoenvironmental changes in continental western europe during the late glacial and holocene

mine drainage from the weathering of sulfide minerals and magnetite pyrite and pyrrhotite are the principal minerals that generate acid drainage in mine wastes low ph conditions derived from fe sulfide oxidation result in the mobilization of contaminant metals such as zn cd ni and cr and metalloids such as as which are of environmental concern this paper uses data from detailed mineralogical and geochemical studies conducted at two canadian tailings impoundments to examine the mineralogical changes that pyrite pyrrhotite sphalerite and magnetite undergo during and after sulfide oxidation and the subsequent release and attenuation of associated trace elements the stability of sphalerite in tailings impoundments generally is greater than that of pyrrhotite but less than pyrite dissolved ni and co derived from fe sulfides and to a lesser extent dissolved zn and cd from sphalerite are commonly attenuated by early formed fe oxyhydroxides as oxidation progresses a recycling occurs due to continued leaching from low ph pore waters and because the crystallinity of fe oxyhydroxides gradually increases which decreases their sorptive capacity unlike many other elements such as cu pb and cr which form secondary minerals or remain incorporated into mature fe oxyhydroxides zn and ni become mobile magnetite which is a potential source of cr is relatively stable except under extremely low ph conditions a conceptual model for the sequence of events that typically occurs in an oxidizing tailings impoundment is developed outlining the progressive oxidation of a unit of mine waste containing a mixed assemblage of pyrrhotite and pyrite

release transport and attenuation of metals from an old tailings impoundment abstract the oxidation of sulfide minerals from mine wastes results in the release of oxidation products to groundwater and surface water the abandoned high sulfide camp tailings impoundment at sherridon manitoba wherein the tailings have undergone oxidation for more than 70 a was investigated by hydrogeological geochemical and mineralogical techniques mineralogical analysis indicates that the unoxidized tailings contain nearly equal proportions of pyrite and pyrrhotite which make up to 60 wt of the total tailings and which are accompanied by minor amounts of chalcopyrite and sphalerite and minute amounts of galena and arsenopyrite extensive oxidation in the upper 50 cm of the tailings has resulted in extremely high concentrations of dissolved so4 and metals and as in the tailings pore water ph 1 m thick geochemical modeling and mineralogical analysis indicate that the hardpan layer consists of secondary melanterite rozenite gypsum jarosite and goethite the minerals indicated mainly control the dissolved concentrations of so4 fe ca and k the highest concentrations of dissolved metals are observed directly above and within the massive hardpan layer near the water table at a depth of 4 m most metals and so4 sharply decline in concentration although dissolved concentrations of metals and so4 decrease below the water table these concentrations remain elevated throughout the tailings with up to 60 600 mg l 1 fe and 91 600 mg l 1 so4 observed in the deeper groundwater during precipitation events surface seeps develop along the flanks of the impoundment and discharge pore water with a geochemical composition that is similar to the composition of water directly above the hardpan these results suggest that shallow lateral flow of water from a transient perched water table is resulting in higher contaminant loadings than would be predicted if it were assumed that discharge is derived solely from the deeper primary water table the abundance of residual sulfide minerals the depletion of aluminosilicate minerals in the upper meter of the tailings and the presence of a significant mass of residual sulfide minerals in this zone after 70 a of oxidation suggest that sulfide oxidation will continue to release acid metals and so4 to the environment for decades to centuries

pattern and kinematic polarity of late mesozoic extension in continental ne asia perspectives from metamorphic core complexes 1 late mesozoic extension in ne asia resulted in the development of a large extensional province metamorphic core complexes mccs are the major features in this province and have 40ar 39ar ages of 130 110 ma for the mylonites and u pb zircon ages of 150 110 ma for the integral granitic intrusions based on this and previous studies this paper summarizes major characteristics of these mccs and recognizes a regional kinematic shear sense most mccs in the transbaikalia region sino mongolia border tract and the northwest central portion of the north china craton ncc show a top to the southeast se shear whereas those in the eastern and southern ncc locally underwent top to the northwest nw shear the three largest basins songliao huabei and ordos in north china are located in the transitional zone between domains of opposing shear sense we interpret the extension in the transbaikalia sino mongolia tract and northwestern part of the ncc to reflect late orogenic collapse of thickened crust following middle late jurassic collision along the okhotsk suture the southeastward extension is probably controlled by crustal scale top to the se tangential shear the transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage ecc i e c in sub horizontal ductile shear zones late in orogenic crustal thickening the combined effect of gravitational loading and thermal uplifting is considered to be the origin of the late or post orogenic collapse the top to the nw extension in the ne of the ncc might reflect antithetic sub extensional zones or mesozoic back arc extension as a far field effect of cretaceous pacific plate subduction

spatial variations in water composition at a northern canadian lake impacted by mine drainage abstract release of acid drainage from mine waste disposal areas is a problem of international scale contaminated surface water derived from mine wastes orginates both as direct surface runoff and indirectly as subsurface groundwater flow at camp lake a small canadian shield lake that is in northern manitoba and is ice covered 6 months of the year direct and indirect release of drainage from an adjacent sulfide rich tailings impoundment has severely affected the quality of the lake water concentrations of the products from sulfide oxidation are extremely high in the pore waters of the tailings impoundment groundwater and surface water derived from the impoundment discharge into a semi isolated shallow bay in camp lake the incorporation of this aqueous effluent has altered the composition of the lake water which in turn has modified the physical limnology of the lake geochemical profiles of the water column indicate that despite its shallow depth 6 m the bay is stratified throughout the year the greatest accumulation of dissolved metals and so 4 is in the lower portion of the water column with concentrations up to 8500 mg l 1 fe 20 000 mg l 1 so 4 30 mg l 1 zn 100 mg l 1 al and elevated concentrations of cu cd pb and ni meromictic conditions and very high solute concentrations are limited to the bay outside the bay solute concentrations are lower and some stratification of the water column exists identification of locations and composition of groundwater discharge relative to lake bathymetry is a fundamental aspect of understanding chemical evolution and physical stability of mine impacted lakes

granite magma generation ascent and emplacement within a transpressional orogen crustal thickening during transpressive orogenesis may produce anatectic granites which may then localize deformation leading to transcurrent movement granites may be transported from sites of generation through the mid crust in dyke like channelways within relatively narrow strike slip shear zones which link to major fault zones in the upper crust extensional jogs within fault systems provide developing sites for the assembly of plutons from magma arriving from below the model is based upon observations from the cadomian belt of nw france which exposes sections through middle and upper levels of the late precambrian crust within different elements of the orogen the mechanism provides a favourable alternative to diapirism and explains the common collocation of granites and shear zone fault systems within orogenic belts

geochemical and mineralogical aspects of sulfide mine tailings abstract tailings generated during processing of sulfide ores represent a substantial risk to water resources the oxidation of sulfide minerals within tailings deposits can generate low quality water containing elevated concentrations of so 4 fe and associated metal loid s acid generated during the oxidation of pyrite fes 2 pyrrhotite fe 1 x s and other sulfide minerals is neutralized to varying degrees by the dissolution of carbonate oxy hydroxide and silicate minerals the extent of acid neutralization and therefore pore water ph is a principal control on the mobility of sulfide oxidation products within tailings deposits metals including fe iii cu zn and ni often occur at high concentrations and exhibit greater mobility at low ph characteristic of acid mine drainage amd in contrast hydr oxyanion forming elements including as sb se and mo commonly exhibit greater mobility at circumneutral ph associated with neutral mine drainage nmd these differences in mobility largely result from the ph dependence of mineral precipitation dissolution and sorption desorption reactions cemented layers of secondary oxy hydroxide and hydroxy sulfate minerals referred to as hardpans may promote attenuation of sulfide mineral oxidation products within and below the oxidation zone hardpans may also limit oxygen ingress and pore water migration within sulfide tailings deposits reduction oxidation redox processes are another important control on metal loid mobility within sulfide tailings deposits reductive dissolution or transformation of secondary oxy hydroxide phases can enhance fe mn and as mobility within sulfide tailings production of h 2 s via microbial sulfate reduction may promote attenuation of sulfide oxidation products including fe zn ni and tl via metal sulfide precipitation understanding the dynamics of these interrelated geochemical and mineralogical processes is critical for anticipating and managing water quality associated with sulfide mine tailings

pluton accommodation at high strain rates in the upper continental crust the example of the central extremadura batholith spain abstract emplacement in the tensional bridge of a stepped dextral shear zone system is proposed for the central extremadura batholith spain the country rocks show a pervasive anisotropy that conditioned the style of the structures developed as a consequence of the transference of displacement from the stepped shear zones to the releasing area the kinematic evolution of the resulting megakink fold provided the volume increase necessary for the granite emplacement thermal and kinematic models suggest that the growth of individual plutons took place in periods of no more than several hundred to a few thousand years fast strain rates 10 10 10 11 s 1 must concentrate in local structures e g initiation of kink folds even in zones deforming as a whole under typical strain rates 10 14 1 s 1 granite plutons might be used as strain rate gauges for syn plutonic structures

fractal analysis of experimentally dynamically recrystallized quartz grains and its possible application as a strain rate meter abstract fractal analysis of experimentally recrystallized quartz grain shapes has been employed to study the relationship between the microstructures of dynamically recrystallized quartz grains and the deformation conditions such as temperature and strain rate samples used are quartz aggregates deformed under high temperature 800 c 900 c and 1000 c and high confining pressure 400 mpa the fractal dimension is useful to quantify the shapes of the recrystallized quartz grain boundaries at each set of conditions the fractal dimension is determined as the slope of a log log plot of the length of the grain boundaries perimeters against the grain size calculated as diameters of circles having the same areas as the actual grains the results show that the shapes of grains are self similar and the fractal dimensions d change systematically being dependent on both temperature and strain rate the skew of the grain boundary defined as d 1 and showing the degree of the serration may be proportional to the logarithm of the zener hollomon parameter that includes a component of the arrhenius term this relation indicates that strain rate can be calculated from the fractal dimension and the temperature it may therefore provide a new paleo strain rate meter for plastically deformed natural rocks

palaeogeothermal response and record of late mesozoic lithospheric thinning in the eastern north china craton the palaeotemperature recorded by vitrinite reflectance ro in the pre cenozoic uplifted stratigraphic strata and in palaeozoic mesozoic remnant basins outside the cenozoic depocentres has not been overprinted by later thermal events in the eastern north china craton ncc based on downhole ro data from the palaeozoic and the mesozoic subsections we reconstruct the temperature gradients when the subsections reached their maximum palaeotem peratures in the middle triassic and the cretaceous and calculate the corresponding heat flow his tories since the early mesozoic the temperature gradient and heat flow were much higher in the cretaceous 35 43 8 ck m 21 and 73 83 mw m 22 respectively than in the middle triassic and at the present the high palaeo heatflow during the late mesozoicimplies that the thickness of the thermal lithosphere at that time was c 65 km about half the thickness of c 135 km estimated for the early mesozoic the change from a stable thermal regime to an active thermal regime took place during the late jurassic early cretaceous c 110 ma this tectonothermal event was accompanied by extensive surface erosion and is also evidenced in the areas adjacent to the ncc such as the south yellow sea and east china sea basins our study provides not only geothermal evidence for the late mesozoic lithospheric thinning but also additional constraints on the thinning mechanism which is currently being debated

long term mineralogical and geochemical evolution of sulfide mine tailings under a shallow water cover abstract the long term influence of a shallow water cover limiting sulfide mineral oxidation was examined in tailings deposited near the end of operation in 1951 of the former sherritt gordon zn cu mine sherridon manitoba canada surface water pore water and core samples were collected in 2001 and 2009 from above and within tailings deposited into a natural lake mineralogical and geochemical characterization focused on two contrasting areas of this deposit i sub aerial tailings with the water table positioned at a depth of approximately 50 cm and ii sub aqueous tailings stored under a 100 cm water cover mineralogical analyses of the sub aerial tailings showed a zone of extensive sulfide mineral alteration extending 40 cm below the tailings surface moderate alteration was observed at depths ranging from 40 to 60 cm and was limited to depths 60 cm in contrast sulfide mineral alteration within the submerged tailings was confined to a

oxygen penetration and subsequent reactions in flooded sulphidic mine tailings a study at stekenjokk northern sweden abstract a study of o2 penetration and pore water geochemistry of the flooded tailings at stekenjokk has been performed the results show that there is a diffusion of elements from the tailings pore water to the overlying water the presence of elements such as ca mg s si ba and sr are likely the result of diffusion of older process water trapped in the tailings oxygen concentrations in the tailings measured with microelectrodes show that there is o2 available down to 16 to 17 mm depth in the tailings pore water analyses show that there are subsurface maxima for the elements cu zn ni co and cd at depths of 0 25 to 2 75 cm the highest concentrations of almost all elements were found where previously oxidised material was deposited before the flooding lower ph is measured in the uppermost part of the tailings compared with the pond water and the tailings pore water at depth oxidation of sulphides in the uppermost part of the tailings is probably occurring a decrease in oxidation rate can be expected in the future due to deposition of organic material at the tailings surface flooding seems to be an efficient remediation method at stekenjokk

rotation behaviour of rigid inclusions in multiple association insights from experimental and theoretical models many rocks are representative of inclusion matrix systems where rigid inclusions float on a ductile matrix the geological analogues of such inclusion matrix systems are theoretically modelled with the help of jeffery s 1922 theory in recent years there have been a number of reinvestigations on the rotational motion of rigid inclusions to account for some geological observations that are not yet predicted in models based on jeffery s theory adding to this effort this paper investigates the effects of 1 inclusion concentration and 2 the degree of coherence at the inclusion matrix interface on the rotation behaviour of rigid inclusions in a multiple inclusion system during simple shear deformation shear box experiments were run on models containing multiple identical elliptic cylinders of wax mimicking rigid inclusion embedded within putty representing ductile matrix two sets of experiments were performed with and without lubrication at the inclusion matrix interfaces each model had an isolated inclusion to reveal the variation of rotations of single and multiple inclusions increase in inclusion concentration results in contrasting rotation behaviour of isolated and multiple inclusions initially oriented parallel to the shear direction when the interfaces were not lubricated inclusions in multiple association rotated antithetically whereas the isolated one almost remained stationary in models wherein the inclusion matrix interfaces were lubricated with liquid soap both isolated and multiple inclusions rotated antithetically but the isolated inclusion rotated at a lower rate with increasing inclusion concentration the difference in the rates of antithetic rotation between isolated and multiple inclusions tended to be larger in both lubricated and non lubricated conditions the sense of rotation of isolated as well as multiple inclusions initially oriented perpendicular to the shear direction was always synthetic irrespective of the nature of the interface lubricated or non lubricated however the instantaneous rotation rates of inclusions in multiple association were higher than that of the isolated inclusions disposed in the same orientation rotation of inclusion in an inclusion matrix system is basically induced by the traction exerted by the flowing matrix on the surface of the inclusion during deformation employing a hydrodynamic model it is shown that mutual mechanical interaction among inclusions which is a function of inclusion concentration modifies the stresses at the inclusion matrix interface to a large extent moment calculations reveal that inclusions oriented parallel to the shear direction experience an antithetic moment in response to the normal stress components the magnitude of which increases with increasing inclusion concentration this implies that rotation of shear parallel inclusions in antithetic sense is favoured by higher inclusion concentration on the other hand inclusions oriented perpendicular to shear direction experience a moment that induces synthetic rotation the magnitude of the synthetic moment is larger for larger inclusion concentration leading to increase in the rate of synthetic rotation using the theoretical model the moments are calculated as a function of the aspect ratio of inclusions and the inferences based on this moment calculation are complemented with experimental findings

syntectonic granite emplacement at different structural levels the closepet granite south india abstract the closepet granite in south india is a large 400 km long but only 30 km wide elongate late archaean granitic body structural levels from deep crust to upper levels crop out as evidenced by a shallowing of paleo depths from north to south all along the closepet granite this allows the study of the emplacement of the same granitic body at various crustal levels four zones have been identified a root zone where magmas are collected in active shear zones a transfer zone featuring large scale magma ascent and crystal liquid partitioning in the granitic mush a gap where the mush was filtered allowing only the liquids to rise shallow intrusions filled with this liquid the closepet granite was emplaced syntectonically field work and anisotropy of magnetic susceptibility allowed documentation of steep foliations with subhorizontal lineations both in the root and transfer zones and in the shallow intrusions remote sensing evidenced a network of shear zones bounding the closepet granite in the porphyritic root and transfer zones magmas cooled slowly thus developing strong fabrics during large scale dextral shearing ascent of residual liquids amidst the crystallizing solid framework was not recorded in the fabrics however these liquids were channelised through the gap and infilled the homogeneous shallow intrusions where rapid cooling only permitted the development of feint although wholly consistent fabrics

origin of potassic c type adakite magmas experimental and field constraints the postcollisional mesozoic c type or high k adakitic intrusions k adakites of china lack either temporal or spatial association with subduction and have k2o na2o around unity otherwise their geochemistry is very similar to ordinary adakites new experimental data geological observations and theoretical considerations lead us to suggest that these k adakites were high t 1050 and probably 1075 c rather hydrous magmas 6 wt h2o produced by fluid absent partial melting of metatonalites meta andesites or possibly potassic metabasalts at pressures exceeding 2 gpa their peculiar chemistry is a consequence of both the elevated k2o na2o in the protolith and the very high pressure of partial melting the most likely tectonic setting is one of extreme crustal thickening followed by delamination of the eclogitic keel and partial melting of this continental crustal material at mantle depths with high mantle heat flow during orogenic collapse

the pore water geochemistry and the mineralogy of the vadose zone of sulfide tailings waite amulet quebec canada low ph waters requiring treatment because of high concentrations of dissolved metals are being discharged from a decommissioned tailings impoundment at the former waite amulet zncu mine in northeastern quebec canada a detailed study of the vadose zone of the tailings comparing mineralogical and geochemical analyses of the tailings solids with geochemical analysis of the tailings pore water and pore gas indicates the presence of three zones within the tailings these zones include an upper sulfide depleted zone in which the sulfides have been extensively removed and oxidation is largely complete an intermediate zone where sulfide oxidation and acid neutralization reactions are occurring and an unoxidized zone below the depth of oxygen penetration where sulfides are unoxidized high aqueous concentrations of dissolved solids are being displaced downward from the sulfide depleted zone through the unoxidized zone toward the water table sulfide oxidation and acid neutralization reactions have generated concentrations of dissolved solids high enough to lead to the precipitation of a series of secondary solid phases precipitation dissolution reactions involving these solid phases control the concentrations of the major ions in the tailings pore water concentrations of dissolved metals are controlled by precipitation dissolution crystal structural replacement and adsorption coprecipitation reactions predictions based on the observed data and numerical simulations suggest that in the absence of an effective remedial program sulfide oxidation and h production will continue for several centuries

microbial populations associated with the generation and treatment of acid mine drainage bacterial populations and water chemistry were profiled throughout the groundwater flow system associated with the nickel rim mine tailings impoundment ontario canada groundwater containing high concentrations of sulfate 2000 12 000 mg l and iron 500 4000 mg l flows from the tailings into an adjacent aquifer a portion of the plume then discharges to the surface where ferrous iron is oxidized creating low ph ph 3 conditions the remaining groundwater passes through a permeable reactive barrier which induces sulfate reduction and metal sulfide precipitation elevated populations of iron oxidizing bacteria iob and sulfur oxidizing bacteria sob are restricted to hydrologically defined zones of recharge and discharge sulfur oxidizers are highest in the tailings 1 27 103 most probable number mpn g where sulfide minerals are exposed to oxygen and oxygen rich recharge water iob were highest 9 56 105 mpn g where tailings derived effluent rich in fe ii discharges to the aerobic surface water environment populations of both iron and sob bacteria in the zone of active oxidation are low compared to those found at other less mature tailing sites active oxidation in the nickel rim tailings is occurring immediately above the water table where the water content is high the high water content limits oxygen ingress and sulfide oxidation and the associated populations of oxidizing bacteria are low populations of sulfate reducing bacteria srb are elevated in the tailings and in portions of the down gradient aquifer where organic carbon concentrations are high the highest population 3 73 107 mpn g of srb were found where sulfate bearing water migrates through the organic carbon rich permeable reactive barrier at locations with high populations of srb elevated populations of sob were also found suggesting sob in these zones are metabolizing the reduced sulfur species produced by the srb in adjacent but disparate redox microenvironments

formation of secondary pyrite and carbonate minerals in the lower williams lake tailings basin elliot lake ontario canada the lower williams lake tailings which resulted from u milling operations during the late 1950s and early 1960s cover an area of 2 ha in a small bog under partial water cover the tailings are underlain by a sand unit containing decaying organic material above the natural base consisting of sand till and gravel the tailings are composed predominantly of quartz muscovite k feldspar plagioclase and clinochlore residual pyrite grains displaying angular to subangular particles measuring less than 1 to 250 m occur in concentrations ranging from trace to approximately 6 wt framboidal pyrite has formed within the tailings basin in association with organic rich material the appearance of framboidal pyrite in the tailings indicates a reversal of the oxidation process and reprecipitation of fe sulfides in addition the tailings include calcite calcian siderite fe oxyhydroxides and fe si oxyhydroxides as secondary precipitates and replacement products groundwaters in the tailings and the underlying units are saturated with respect to gypsum and siderite these and the other saturation indices calculated for calcite goethite and barite are consistent with the secondary mineralogy of the tailings conditions promoting the formation of pyrite can be described as neutral to weakly alkaline and reducing assisted by microbial activity this study provides the first account of secondary carbonates and framboidal pyrite in the elliot lake tailings the existing environmental conditions at the site are favorable for the desired site rehabilitation

reactive transport modelling of mine tailings columns with capillarity induced high water saturation for preventing sulfide oxidation abstract a series of laboratory column tests on reactive mine tailings was numerically simulated to study the effect of high water saturation on preventing sulfide mineral oxidation and acid mine drainage amd the approach also known as an elevated water table ewt is a promising alternative to full water covers for the management and closure of sulfidic tailings impoundments and for the long term control of acid mine drainage the instrumented columns contained reactive tailings from the louvicourt mine quebec and were overlain by a protective sand cover over a 13 19 month period the columns were exposed to atmospheric o 2 and flushed approximately every month with demineralized water a free draining control column with no sand cover was also used during each cycle water table elevations were controlled by fixing the pressure at the column base and drainage water was collected and analyzed for ph and eh major ions and dissolved metals fe zn cu pb and mg the columns were simulated using the multi component reactive transport model min3p which solves the coupled nonlinear equations for transient water flow o 2 diffusion advective dispersive transport and kinetic geochemical reactions physical properties and mineralogical compositions for the material layers were obtained from independent laboratory data the simulated and observed data showed that as the water table elevation increased the effluent ph became more neutral and so 4 and dissolved metal concentrations decreased by factors on the order of 10 2 10 3 it is concluded that water table depths less than or equal to one half of the air entry value aev can keep mine tailings sufficiently saturated over the long term thus reducing sulfide oxidation and amd production

cooling paths of the ne china crust during the mesozoic extensional tectonics example from the south liaodong peninsula metamorphic core complex abstract the south liaodong peninsula massif is the easternmost mesozoic metamorphic core complex recognized in eastern china it provides a good example of the combination of ductile shearing syn kinematic plutonism and polyphase exhumation the jurassic granodioritic plutons located at the footwall of the detachment normal fault and dated here at ca 160 ma recorded two different phases of cooling a slow cooling regime of about 3 10 c my prevailing before 122 ma was followed by a significant increase in cooling rate of about 40 55 c my after that time by contrast a single fast cooling path was recorded by the cretaceous monzogranite situated in the footwall of the detachment normal fault this result indicates that the jurassic and cretaceous plutons recorded different exhumation processes a jurassic slow or negligible exhumation and a cretaceous fast one assisted by normal faulting these two cooling stages correspond to distinct geodynamic processes during the jurassic and cretaceous extensional tectonics seems not significant before early cretaceous the second stage dominated by an extensional regime which develops after ca 120 ma is tentatively correlated to the lithosphere removal of the north china craton

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

microscale measurements of oxygen diffusion and consumption in subaqueous sulfide tailings the disposal of sulfide mine tailings in an environmentally sound yet cost effective manner is an issue facing most metal mines subaqueous tailing disposal is considered an attractive option for disposal that limits oxygen o2 availability within sulfide mine tailings and controlling sulfide oxidation and the resultant acid mine drainage amd assuming that o2 profiles represent steady state conditions we aim to evaluate the depth dependent and temperature dependent rates of o2 consumption in saturated mine tailings measurements include microscale o2 gradients and diffusivity profiles within columns representing undisturbed mine tailing profiles from an impoundment near nanisivik mine in northern canada measurements were made across the diffusive boundary layer dbl above the tailing water interface as well as in the tailings below laboratory measurements of o2 profiles are compared to in situ profiles from the laboratory results it is possible to evaluate the o2 flux across the dbl and the depth integrated o2 uptake the results are compared with the average sulfate production rate over 3 months o2 uptake in saturated tailings is discussed in relation to o2 uptake measured in columns after free drainage the methods applied provide consistent o2 consumption rates as well as reliable predictions for controlling amd by keeping tailings under water

genesis of the hengling magmatic belt in the north china craton implications for paleoproterozoic tectonics abstract the 2200 1880 ma igneous rocks in the central and eastern parts of the north china craton ncc constitute a new hengling magmatic belt hmb which includes the 2147 ma hengling mafic sill dyke swarm the 2060 ma yixingzhai mafic dyke swarm and the 1973 ma xiwangshan mafic dyke swarm the three swarms are contiguous and have experienced variable degrees of metamorphism from greenschist to low amphibolite facies hengling medium granulite facies yixingzhai and medium high pressure granulite facies xiwangshan they are all tholeiitic in composition typically with 47 52 wt sio 2 and 4 10 wt mgo and all show light rare earth element enrichments and nb and ta depletion their nd t dm ages are in the range of 2 5 3 0 ga specifically the hengling and yixingzhai dykes sills are depleted in th u zr hf and ti whereas the xiwangshan dykes are enriched in u and weakly depleted in other elements variable sr anomalies indicate significant feldspar accumulation positive anomalies or fractionation the end t values of the three swarms are 3 2 3 0 hengling 1 7 1 8 yixingzhai and 1 4 1 0 xiwangshan these mafic representatives of the hmb originated from the 2 5 ga sub continental lithospheric mantle of the ncc and with a type granites and other igneous associations in this belt they likely evolved in an intra continental rift the progressive changing compositions of the three swarms are interpreted in terms of their source regions at different depths i e shallower and shallower through time and the decrease in scale and size of the intrusions and their magma volumes indicate the progressive weakening of magmatism in this rift the rocks in this belt are different chronologically petrologically and chemically from those in the xuwujia magmatic belt xmb we propose that the two magmatic belts represent two different magmatic systems in different blocks of the ncc i e an eastern block with the hmb and a western block with the xmb terminal collision was possibly a result of ridge subduction between the two blocks which led to exhumation of the igneous rocks in the two belts from different crustal levels distinguishable by their different grades of metamorphism

zircon geochronology and metamorphic evolution of mafic dykes in the hengshan complex of northern china evidence for late palaeoproterozoic extension and subsequent high pressure metamorphism in the north china craton abstract magmatic and metamorphic zircons have been dated from ductilely deformed gabbroic dykes defining a dyke swarm and signifying crustal extension in the northern part of the hengshan complex of the north china craton these dykes now occur as boudins and deformed sheets within migmatitic tonalitic trondhjemitic granodioritic and granitic gneisses and are conspicuous due to relics of high pressure granulite or even former eclogite facies garnet pyroxene bearing assemblages shrimp ages for magmatic zircons from two dykes reflect the time of dyke emplacement at 1915 ma whereas metamorphic zircons dated by both shrimp and evaporation techniques are consistently in the range 1848 1888 ma the youngest granitoid gneiss yet dated in the hengshan has an emplacement age of 1872 17 ma these results complement recent geochronological studies from the neighbouring wutai and fuping complexes to the se of the hengshan showing that a crustal extension event occurred in the late palaeoproterozoic this preceded a major high pressure collision type metamorphic event in the central part of the north china craton that occurred in the palaeoproterozoic and not in the late archaean as previously thought our data support recent suggestions that the north china craton experienced a major craton wide orogenic event in the late palaeoproterozoic after which it became cratonized and acted as a stable block

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

the recrystallized grain size piezometer for quartz d 1 0 3 56 0 27 s 1 26 0 13 with no change in slope at the regime 2 3 transition and no effect of temperature or a b stability field another experimental piezometer relation for regime 1 of hirth and tullis 1992 differs in slope suggesting that different recrystallization mechanisms require different piezometer calibrations index terms 3902 mineral physics creep and deformation 5120 physical properties of rocks plasticity diffusion and creep 8030 structural geology microstructures 8159 tectonophysics rheology crust and lithosphere 8164 tectonophysics stresses crust and lithosphere citation stipp m and j tullis the recrystallized grain size piezometer for quartz geophys res lett 30 21 2088 doi 10 1029 2003gl018444 2003

petrogenesis of late triassic granitoids and their enclaves with implications for post collisional lithospheric thinning of the liaodong peninsula north china craton abstract major and trace element sr nd and hf isotope zircon u pb and hf isotope data are reported for mafic microgranular enclaves and host granitoids from the xiuyan pluton in the liaodong peninsula of the eastern north china craton in order to investigate their sources petrogenesis and tectonic implications the zircon u pb age of the enclaves 211 1 ma is identical to that of the host granite 210 1 ma establishing that the mafic and felsic magmas were coeval the enclaves have high mgo concentrations at low silica contents and positive ehf t values they are enriched in large ion lithophile and light rare earth elements and depleted in high field strength elements which can be explained as melts derived from a depleted asthenospheric mantle with some crustal contamination the host granitoids have high sio2 contents variable initial 87sr 86sr ratios and highly negative end t and ehf t values suggesting they were mainly derived from an ancient crustal source heated by the input of asthenospheric mantle derived magmas field observations geochronology geochemistry sr and nd isotopic and zircon hf isotopic compositions point to a complex petrogenesis where asthenospheric mantle and crust derived magma mixing was coupled with crystal fractionation thus explaining the genetic link between enclaves and host rocks identification of an asthenospheric mantle component in the xiuyan granitoids suggests asthenospheric mantle upwelling and decompressional melting of the mantle indicating that post collisional lithospheric thinning in the liaodong peninsula was initiated in the late triassic

structural characteristics and la icp ms u pb zircon geochronology of the deformed granitic rocks from the mesozoic xingcheng taili ductile shear zone in the north china craton abstract we describe the recently detected ene trending xingcheng taili ductile strike slip shear zone which is an important mesozoic low to middle grade tectonic element formed during the reactivation of the north china craton ncc at the eastern termination of the yanshanian orogenic belt within the xingcheng taili ductile shear zone the degree of deformation weakens gradually from nw to se three main types of banded granitic gneisses represent low to middle grade metamorphic tectonites new u pb zircon dating gives a wide range of protolith ages neoarchean granitic rocks with an emplacement age of 2498 4 6 3 ma have obvious e w trending banded structures upper triassic granitic rocks with u pb zircon ages of 219 7 1 1 ma 218 74 0 61 ma 212 1 1 6 ma and 212 3 1 9 ma are considered to relate to the collision of the ncc and yangtze craton in early mesozoic times the emplacement of biotite adamellite bodies with ages of 159 0 0 8 ma and 152 4 1 9 ma is related to the thinning of the ncc s continental crust an ene trending sinistral ductile shear zone developed within these granites the strongly deformed biotite adamellite bodies bear a gneissosity with s c fabrics ene trending sinistral shear zones and show the deformation characteristics of a shallow crustal level reflecting decratonization of the ncc crystal lattice preferred orientations lpo of quartz determined by electron back scatter diffraction suggest sinistral strike slip shear and a deformation temperature at about 400 to 500 c quartz mainly shows low temperature fabrics with a dominant 0001 slip system similar to the temperature estimated by the micro structural characteristics of quartz and feldspar this deformation event might have occurred in early cretaceous times and is related to the lithospheric thinning and extension of the north china craton triggered by an ongoing roll back of the pacific plate beneath the eastern north china craton

geophysical and geological tests of tectonic models of the north china craton abstract the geometry and timing of amalgamation of the north china craton have been controversial with three main models offering significantly different interpretations of regional structure geochronology and geological relationships one model suggests that the eastern and western blocks of the ncc formed separately in the archean and an active margin was developed on the eastern block between 2 5 and 1 85 ga when the two blocks collided above an east dipping subduction zone a second presumes the eastern block rifted from an unknown larger continent at circa 2 7 ga and experienced a collision with an arc perhaps attached to the western block above a west dipping subduction zone at 2 5 ga and the 1 85 ga metamorphism is related to a collision along the northern margin of the craton when the ncc joined the columbia supercontinent a third model suggests two collisions in the central orogenic belt at 2 1 and 1 88 ga but recognizes an early undated deformation event recent seismic results reveal details of the deep crustal and lithospheric structure that support both the second and third models showing that subduction beneath the central orogenic belt was west directed and that there is a second west dipping paleosubduction zone located to the east of the cob dipping beneath the western block ordos craton the boundaries identified through geophysics do not correlate with the boundaries of the trans north china orogen suggested in the first model and the subduction polarity is opposite that predicted by that model high pressure granulite facies metamorphism at 1 85 ga is not restricted to the tnco as suggested by the first model but is documented across the ncc as predicted by the second model suggesting a major continent continent collision along the north margin of the craton at 1 85 ga further it has recently been shown that in the southern tnco there is no record of metamorphism at circa 1 85 ga but only at 2 7 2 5 ga showing that the tnco as defined as a circa 1 85 ga orogen does not exist this is further confirmed by recent re os isotopic studies which show that the subcontinental lithospheric mantle beneath the southern cob is late archean in age and that a province in the northern ncc is circa 1 8 ga correlating with the proposed collision belt of the ncc with the columbia supercontinent across the entire ncc the cob is an archean convergent belt re worked in the paleoproterozoic and the paleoproterozoic tectonism is widespread across the ncc as predicted by the model whereby the previously amalgamated eastern and western blocks experienced a continental collision with columbia at circa 1 85 ga but uplift exhumation rates are slow necessitating a re evaluation of the tectonic models of the ncc

accommodation of transpressional strain in the arabia eurasia collision zone new constraints from u th he thermochronology in the alborz mountains north iran the alborz range of n iran provides key information on the spatiotemporal evolution and characteristics of the arabia eurasia continental collision zone the southwestern alborz range constitutes a transpressional duplex which accommodates oblique shortening between central iran and the south caspian basin the duplex comprises nw striking frontal ramps that are kinematically linked to inherited e w striking right stepping lateral to obliquely oriented ramps new zircon and apatite u th he data provide a high resolution framework to unravel the evolution of collisional tectonics in this region our data record two pulses of fast cooling associated with sw directed thrusting across the frontal ramps at 18 14 and 9 5 7 5 ma resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half u shaped geometry uniform cooling ages of 7 6 ma along the southernmost e w striking oblique ramp and across its associated nw striking frontal ramps suggests that the ramp was reactivated as a master throughgoing n dipping thrust we interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from ne to n nne the reduction in the obliquity of thrusting may indicate the termination of strike slip faulting and possibly thrusting across the iranian plateau which could have been triggered by an increase in elevation furthermore we suggest that 7 6 m y old s directed thrusting predated inception of the westward motion of the south caspian basin

structures kinematic analysis rheological parameters and temperature pressure estimate of the mesozoic xingcheng taili ductile shear zone in the north china craton abstract the ne to ene trending mesozoic xingcheng taili ductile shear zone of the northeastern north china craton was shaped by three phases of deformation deformation phase d 1 is characterized by a steep generally e w striking gneissosity it was then overprinted by deformation phase d 2 with ne sinistral shear with k feldspar porphyroclasts forming a subhorizontal low angle stretching lineation on a steep foliation during deformation phase d 3 lateral motion accommodated by ene sinistral strike slip shear zones dominated associated fabrics developed at upper greenschist metamorphic facies conditions and show the deformation characteristics of middle to shallow crustal levels in some parts the older structures have been in turn overprinted by late stage sinistral d 3 shearing finite strain and kinematic vorticity in all deformed granitic rocks indicate a prolate ellipsoid l s tectonites near plane strain simple shear dominated general shear during d 3 deformation is probably of general significance the quartz c axis textures indicate prism gliding with a dominant rhomb slip and basal slip system formed mainly at low middle temperatures mineral deformation behavior quartz c axis textures quartz grain size and the kruhl thermometer demonstrate that the ductile shear zone developed under greenschist facies metamorphic conditions at deformation temperatures ranging from 400 to 500 c dislocation creep is the main deformation mechanism at a shallow crustal level fractal analysis showed that the boundaries of recrystallized quartz grains had statistically self similarities differential stresses deduced from dynamically recrystallized quartz grain size are at around 20 39 mpa and strain rates in the order of 10 12 to 10 14 s 1 this indicates deformation of granitic rocks in the xingcheng taili ductile shear zone at low strain rates which is consistent with most other ductile shear zones hornblende plagioclase thermometer and white mica barometer indicate metamorphic conditions of medium pressures at around ca 3 5 kbar and temperatures of 400 500 c within greenschist facies conditions the main d 3 deformation of the ene trending sinistral strike slip ductile shearing is related to the roll back of the subducting pacific plate beneath the north china craton

late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block constraints on the composition and evolution of the lithospheric mantle abstract the late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block ncb are used to constrain the isotopic composition and evolution of mantle reservoirs during different tectonic stages prior to the initiation of lithosphere destruction in the late mesozoic zircon u pb ages show that emplacement of the mafic ultramafic complexes occurred in at least three stages middle devonian ca 395 ma late carboniferous early permian 308 276 ma and triassic 250 220 ma most of the middle devonian complexes display low initial 87sr 86sr ratios of 0 70467 0 70492 weak to moderate negative end t values from 6 3 to 1 5 and weakly negative to weakly positive zircon ehf t values from 11 5 to 5 5 indicating that the parent magma was derived from slightly enriched lithospheric mantle the late carboniferous early permian complexes are characterized by low initial 87sr 86sr ratios of 0 70521 0 70604 significant negative end t values from 14 1 to 9 3 and zircon ehf t values from 17 0 to 10 5 and were probably derived from metasomatized lithospheric mantle the early triassic complexes exhibit initial 87sr 86sr ratios of 0 70656 0 70825 and significant negative end t values from 17 1 to 8 2 indicating their derivation from enriched lithospheric mantle however the late triassic mafic ultramafic complexes display weakly negative to weakly positive end t values of 4 4 to 0 5 and zircon ehf t values from 2 9 to 1 7 indicating that magma sources likely resulted from mixing of depleted asthenospheric mantle and enriched lithospheric mantle zircon ages geochemistry and sr nd hf isotopic studies suggest that the lithospheric mantle beneath the northern ncb had a slightly enriched signature during the middle devonian but it became significantly enriched during the late carboniferous to early permian due to metasomatism of lithospheric mantle during the southward subduction of the paleo asian oceanic plate after final closure of the paleo asian ocean and amalgamation of the mongolian arc terranes with the northern ncb in the latest permian to earliest triassic enriched lithospheric mantle still existed beneath the northern ncb during the early triassic however in the late triassic involvement of asthenospheric mantle became significant owing to strong upwelling of asthenospheric mantle and post collisional lithospheric delamination in the early late triassic these results suggest that the cratonic lithospheric mantle beneath the northern ncb underwent multiple stages of modification prior to its destruction and thinning initiation of lithospheric destruction and thinning in the northern ncb likely occurred during the early late triassic which is much earlier than in other parts of the ncb where it occurred in the late mesozoic it appears likely that lithospheric destruction and thinning of the ncb initially started at the northern and eastern margins of the craton as a result of post collisional lithospheric delamination and then spread to the interior of the craton

early diagenesis of copper and molybdenum in mine tailings and natural sediments in rupert and holberg inlets british columbia the distribution and behaviour of cu and mo in interstitial waters collected from cu and mo rich mine tailings and natural sediments in rupert and holberg inlets vancouver island british columbia are discussed dissolved fe mn and h2s distributions and solid phase cu mo mn and organic carbon data are used to constrain the interpretation of cu and mo diagenesis in both tailings and natural sediment facies cu is released to solution at or near the sediment water interface in both facies either by decomposing labile organic material or as a probable result of oxidation of sulphide minerals within the tailings mo is significantly enriched up to 0 6 mol l 1 in tailings pore water probably as a result of dissolution of soluble mo oxides produced initially by oxidation of mos2 during milling of the ore in natural sediments both cu and mo are removed from solution at depth probably by precipitation as their sulphides or in solid solution with an iron sulphide phase similar reactions appear t

granitoid evolution in the late archean wutai complex north china craton abstract two temporally discrete episodes of granite magmatism have been identified in the wutai complex of the north china craton based on shrimp u pb zircon dating of all major granitoid bodies in the area the older period is latest archean and ranges in age from 2560 to 2515 ma whereas the younger episode is paleoproterozoic with magmatism at 2170 and 2120 ma archean magmatism can be further separated into two pulses based on geochemistry and the association of the younger plutons with extensive coeval volcanic activity in the wutai complex the early phase of archean activity is represented by the lanzhishan ekou and portions of the chechang betai granites with ages ranging from 2560 to 2540 ma the lanzhishan granite is the only one at wutaishan that contains inherited zircon with a number of cores and individual grains giving ages in excess of 2700 ma these are relatively evolved granitoids interpreted to be derived from older basement of the eastern block of the north china craton the shifo guangmingshi the main grey phase of the wangjiahui granite and the major components of the chechang betai granite have ages of 2540 2515 ma and are coeval with felsic volcanism in the wutai complex which is a consequence of subduction and related arc magmatism the dawaliang granite and pink phase of the wangjiahui granite are considerably younger with paleoproterozoic ages of 2170 and 2120 ma respectively these are also evolved granitoids most likely derived by partial melting of the older basement although we have found no evidence of inheritance the petrogenesis of the granitoids reflects the precambrian amalgamation history of the north china craton indicating derivation along the western edge of the eastern block during development and amalgamation of the wutai arc and prior to collision with the western block of the craton 1 8 ga ago

mineralogical and geochemical characterization of the old tailings dam australia evaluating the effectiveness of a water cover for long term amd control abstract establishing a shallow water cover over tailings deposited in a designated storage facility is one option to limit oxygen diffusion and retard oxidation of sulfides which have the potential to form acid mine drainage amd the old tailings dam otd located at the savage river mine western tasmania contains 38 million tonnes of pyritic tailings deposited from 1967 to 1982 and is actively generating amd the otd was constructed on a natural gradient resulting in sub aerial exposure of the southern area with the northern area under a natural water cover this physical contrast allowed for the examination of tailings mineralogy and geochemistry as a function of water cover depth across the otd tailings samples n 144 depth 1 5 m were collected and subjected to a range of geochemical and mineralogical evaluations tailings from the southern and northern extents of the otd showed similar amd potential based on geochemical nag ph range 2 1 to 4 2 and bulk mineralogical parameters particularly at depth however sulfide alteration index sai assessments highlighted the microscale contrast in oxidation in the sub aerial zone pyrite grains are moderately oxidized to a depth of 0 3 m maximum sai of 6 10 under both gravel fill and oxidized covers with secondary minerals e g ferrihydrite and goethite developed along rims and fractures beneath this mildly oxidized pyrite is seen in fresh tailings sai 2 9 10 to 5 8 10 in the sub aqueous zone the degree of pyrite oxidation demonstrates a direct relationship with cover depth with unoxidized potentially reactive tailings identified from 2 5 m directly beneath an organic rich sediment layer sai 0 to 1 10 these findings are broadly similar to other tailings storage facilities e g fox lake sherritt gordon zn cu mine canada and stekenjokk mine sweden where water covers up to 2 m have successfully reduced amd whilst geotechnical properties of the otd restrict the extension of the water cover pyrite is enriched in cobalt up to 2 6 wt indicating reprocessing of tailings as an alternative management option through adoption of an integrated mineralogical and geochemical characterization approach for tailings assessment robust management strategies after mine closure can be developed

dynamic recrystallization of quartz correlation between natural and experimental conditions quartz veins in the eastern tonale mylonite zone italian alps were deformed in strike slip shear due to the synkinematic emplacement of the adamello pluton a temperature gradient between 280 c and 700 c was effected across this fault zone the resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization subgrain rotation recrystallization and grain boundary migration recrystallization the transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships deformation temperatures are obtained from metamorphic reactions in the deformed host rock flow stresses and deformation temperatures are used to determine the strain rate of the tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10 14s 1 to 10 12s 1 the deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of hirth tullis linking the microstructures of the naturally and experimentally deformed quartz rocks a recrystallization mechanism map is presented this map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known

sulfur cycling in an acid mining lake and its vicinity in lusatia germany the sulfur cycle plays a key role in the hydrochemical development of lignite and coal mining districts which are often characterized by acid mine drainage identification of sulfur sources and transformations is essential if we are to understand the current status of acid lakes and propose successful remediation strategies we utilized stable isotope 34ssulfate 18osulfate 34sdissolved sulfide 18owater and hydrochemical data of lake and groundwater samples as well as the concentrations and isotope ratios of various sedimentary sulfur compounds acid soluble sulfate ass acid volatile sulfur avs chromium reducible sulfur crs in aquifer and lake sediments for assessing the biogeochemical sulfur cycle in a lusatian acidic mining lake ml111 and the surrounding area pyrite oxidation is the dominant source of sulfate and iron in the two aquifers west and east of mining lake ml111 concentration and isotope data for dissolved sulfate suggest that bacterial dissimilatory sulfate reduction became an increasingly important process in the flow direction of the western aquifer thereby improving water quality in contrast bacterial sulfate reduction was only of local importance in the dump aquifer on the eastern side of the lake oxygen isotope ratios of the lake water sulfate and mass and isotope balances demonstrate that 80 of the sulfate in mining lake ml111 is derived via groundwater influx from the dump aquifer with the remainder contributed by the western aquifer in lake pyrite oxidation or bacterial sulfate reduction in the water column are insignificant the latter process is restricted to the monimolimnion which represents less than 1 of the lake volume hence the potential for natural generation of alkalinity by bacterial dissimilatory sulfate reduction is presently low for successful remediation of ml111 it is essential to reduce significantly the continuous input of sulfate and acidity from inflowing dump groundwater

controls on lineation development in low to medium grade shear zones a study from the cap de creus peninsula ne spain lineations composed of similarly oriented elongate mineral aggregates or grains are a common feature in deformed rocks but it is unclear which factors control the development of such lineations field observations and microstructural analysis of samples which were taken from discrete greenschist to lower amphibolite facies shear zones of the easternmost variscan pyrenees show that strain is only one of several factors that control the strength and type of a lineation dynamic recrystallization metamorphic reactions and rigid body rotation are also important controlling factors for the development of lineations the most important of these is dynamic recrystallization the way in which dynamic recrystallization influences lineation development is largely a function of the initial fabric in a specific rock type different lithologies with different initial fabrics produce distinctly different types and strengths of lineations even if deformed to the same finite strain in the same shear zone an initial fine grain size and a monomineralic composition of the parent rock type commonly hinder the development of lineations in contrast in initially coarse grained polymineralic rocks well developed lineations commonly develop therefore the ratio of initial to dynamically recrystallized grain size determines to a large extend the development of such lineations

a new mechanism of granite emplacement intrusion in active extensional shear zones one of the principal ways in which continental crust grows is by the incorporation from deeper within the earth of large volumes of granitic magma a space problem exists1 as to how these magmas are accommodated in the crust traditionally two main emplacement mechanisms have been emphasized forceful intrusion whereby buoyancy driven magmas physically push the crust aside creating granitic diapirs and balloons and passive emplacement characterized by replacive mechanisms such as cauldron subsidence and stoping although more recent work2 3 has demonstrated that space for granites may be created within bends and offsets of large transcurrent faults the simple view of either forceful or passive still fails to account for the intrusive mechanisms of many granites here we report the discovery of a new igneous intrusion mechanism in the superbly exposed proterozoic continental crust of south greenland we have observed that rapakivi granite was intruded as large scale sheets along ductile extensional shear zones that were active during emplacement in such a process the space problem seems to be simply resolved

grain size distribution and rheology of the upper mantle abstract the physical processes that govern the grain size of rocks in the upper mantle are examined the analysis is based on the experimental data on creep recrystallization and grain growth in dunites and on a theoretical model for the thermomechanical structure of the cooling moving lithosphere the grain size of rocks is shown to be determined by the in situ stress only at the deeper part where the temperature is high enough to allow significant strain rate above this depth the microstructures record the thermomechanical history of rocks rather than the in situ stress in the case of the oceanic lithosphere where the thermomechanical history is best known the following features of grain size distribution are found at the uppermost mantle where the amount of grain growth is limited the grain size is determined by the initial value and the growth rate and where the effect of grain growth dominates it increases with depth when the amount of grain growth becomes large and the grain size reaches the steady state size corresponding to the ambient stress while the rock is hot enough to deform the grain size is then determined by the applied stress this grain size is however frozen when the rock gets cool and the strain rate becomes too small to induce any further dynamic recrystallization thus at the intermediate depth region the grain size records the fossil frozen stress at which the microstructures of rock have been frozen since the frozen stress increases with age the grain size in this depth interval decreases with depth finally the grain size below this level reflects the in situ stress and increases with depth its extent being dependent on the nature of return flow in the deep mantle thus the grain size versus depth relation may show a sigmoid curve the qualitative features of this curve may be similar also in the case of the continental lithosphere if a similar thermal event i e the intrusion of hot material and subsequent cooling occurs the results are quite consistent with the observed depth variation of olivine grain size in peridotite nodules ave lallemant et al 1980 the present model suggests that the depth of minimum grain size 65 and 150 km at the continental rift zone and the shield region respectively corresponds to that where the mechanical properties of the upper mantle change from elastic to ductile at tectonic stress levels 1 mpa and in the geological time scale this result leads to a new definition of the thickness of lithosphere in terms of its rheological properties this thickness is about twice as large as that inferred from the flexure of lithosphere but approximately equal to seismic thickness the model suggests the importance of grain growth as well as dynamic recrystallization and plastic flow in determining the texture of upper mantle rocks and therefore seismic anisotropy

a statistical approach to determination of a mineral lineation abstract a statistical model of the bipolar von mises type was applied to the analysis of mineral lineation defined by the preferred dimensional orientation of inequant grains on a foliation surface orientation data of 203 258 grains from each of four rock specimens fit the model well suggesting a useful analytical technique with three advantages 1 confidence in whether a metamorphic tectonite has a mineral lineation can be determined using a 2 test 2 the orientation of the mineral lineation can be represented by the mean direction with a specified confidence interval and 3 the degree of preferred dimensional orientation of grains can be quantified by the concentration parameter