re os age of the pueblo viejo epithermal deposit dominican republic re os analyses of pyrite from the pueblo viejo high sulfidation epithermal deposit both monte negro and moore ore zones yield an isochron age of 111 9 3 7 ma and initial 187 os 188 os ratio of 0 22 0 18 mean square of weighted deviates 84 n 21 isochrons grouped by pyrite setting layered versus vein or locations yield ages within uncertainty of the overall isochron and with each other and as such do not yield temporally distinguishable ages sphalerite vein samples as well as shale source rocks show evidence of open system behavior and loss of re and therefore are not included in the above regression these results confirm that the pueblo viejo deposit is early cretaceous in age and coeval with the volcanic los ranchos formation which hosts the deposit recent paleontological age assignments for the hatillo formation which overlies the los ranchos formation show that it is only slightly younger opening the possibility that mineralization in the hatillo formation could also be related to late stages of los ranchos magmatism whether these revised los ranchos hatillo relations provide sufficient cover to account for the paragenetically late formation of pyrophyllite at pueblo viejo remains unclear recognition that pueblo viejo is coeval with the los ranchos formation shows that large scale high sulfidation epithermal mineralization can form from basal island arc tholeiitic magmatism a review of available experimental data confirms that these magmas can generate hydrothermal solutions of the necessary composition favorability of the los ranchos formation might have been enhanced by its bimodal composition these results suggest that exploration for epithermal precious metal deposits should include basal island arc tholeiite terranes

space geodetic and water level gauge constraints on continental uplift and tilting over north america regional convergence of the ice 6g_c vm5a vm6 models

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

a study of strontium diffusion in k feldspar na k feldspar and anorthite using rutherford backscattering spectroscopy abstract sr chemical diffusion has been measured in orthoclase anorthoclase and anorthite under dry 1 atm conditions a strontium oxide aluminosilicate powder mixture was used as the source material with rutherford backscattering spectroscopy rbs used to measure diffusion profiles over the temperature range 725 1075 c the following arrhenius relations were obtained orthoclase normal to 001 d 5 97 10 0 0060 0 0030exp 67900 1600rtcm 2 s 1 measurements of diffusion perpendicular to 010 and 100 indicate little diffusional anisotropy in orthoclase anorthoclase normal to 010 d 4 51 10 1 358 5 6exp 89100 4800rt cm 2 s 1 normal to 001 d 2 25 10 2 1615 31exp 89300 4600rt cm 2 s 1 anorthite normal to 010 d 3 85 10 2 0 380 0 0039 exp 78800 5400rt cm 2 s 1 the correlation of sr uptake with a reduction of k and ca in orthoclase and anorthite respectively indicates that sr is exchanging with these species nuclear reaction analysis nra measurements of al in orthoclase suggests that the coupled exchange sr 2 al 3 k 1 si 4 is taking place as expected sr closure temperatures for feldspars calculated with the above parameters are relatively high compared to those of some other minerals e g biotite muscovite apatite however closure temperatures of feldspars may be significantly depressed if they are exsolved or twinned leading to small effective diffusion lengths feldspar crystals of millimeter size should retain 87 sr 86 sr ratios except when subjected to thermal events of extreme temperature or duration

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

diffusion of osmium in pyrrhotite and pyrite implications for closure of the re os isotopic system abstract in order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite experiments consisted of either 1 isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered os bearing fe sulfide or 2 relaxation of initially high near surface osmium concentrations produced in the latter experiments pyrite only osmium penetration into samples was characterized by depth profiling using rutherford backscattering spectroscopy rbs pyrite or electron microprobe analyses across sectioned run products pyrrhotite results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces with the extent of penetration uncorrelated with run duration images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near surface occurred by solute uptake during step growth and not by volume diffusion prolonged 1000 h relaxation experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for rbs a maximum diffusion coefficient of 2 5 10 23 m2 s at 500 c was calculated experiments involving pyrrhotite over the temperature range of 950 1100 c showed extensive osmium uptake and osmium concentration gradients that conform with fickian diffusion behavior we found that pyrrhotite fe s could be varied by changes in the composition of the starting material and osmium source and over the range of fe s produced in experiments molar fe s 0 83 0 90 we observed no systematic variation in the osmium diffusion coefficient diffusion coefficients measured parallel to the a crystallographic axis were on average 1 4 higher than values measured parallel to c and regression of the c axis data yielded the arrhenius relation d t 1 31 0 16 10 5 m 2 s exp 211 5 14 7 kj mol rt the application of these diffusion data to simple models of diffusive exchange during static or polythermal time temperature histories is used to assess the conditions under which radiogenic osmium will be retained during isothermal annealing calculations indicate that the cores of millimeter sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in 0 5 ma at temperatures exceeding 400 c pyrite undergoing the same process at 500 c requires in excess of 10 ma before crystal cores are affected the relatively short core retention time scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events thus possibly accounting for the scatter that commonly occurs in re os isochrons generated from massive sulfide samples calculated closure temperatures tc for osmium exchange in pyrrhotite yielded values of 300 400 c for grain sizes ranging from 10 to 1000 m these values of tc are similar to those calculated for ar retention in biotite and considerably lower than for sr in apatite and plagioclase for example such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late stage hydrothermal fluids this latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage

plumes in a convecting mantle models and observations for individual hotspots the motion of hotspots and the deformation of their underlying plume conduits as calculated within models of global mantle flow are presented a new list of 44 possible hotspots with associated tracks has been compiled for all of them calculations have been performed under consideration of individual age and anomalous mass flux for three different models of plume buoyancy and mantle flow plume source depth has usually been assumed to be the top of d but an alternative source depth at the 670 km discontinuity has also been considered using models of relative plate motions and boundaries hotspot tracks on plates have been calculated and compared with age data ocean floor topography and distribution of volcanics on continents absolute plate motions have been redetermined under consideration of hotspot motion using a new least squares method for the hawaiian and yellowstone hotspots source locations and hotspot motion have been computed for a total of up to 23 different models the results show plume conduits being tilted with source regions at the d moving in the lowermost mantle flow generally toward large scale upwellings under southern africa and the south central pacific hotspot surface motion often represents the horizontal component of midmantle flow which is frequently opposite to plate motion toward ridges and away from subduction zones in particular almost all models tested predict southward motion of the hawaii and kerguelen hotspots and westward motion of the iceland hotspot for models including hotspot motion the agreement between calculated and observed hotspot tracks is frequently about as good as or better than for the fixed hotspot model but sometimes fixed hotspots give the best fit in some cases where the track ends at a subduction zone e g for the bowie hotspot results can give indications about the otherwise unknown age of the hotspot in other cases especially for the tahiti hotspot results suggest an origin shallower than d and in yet other cases particularly east africa the failure of the hotspot models used supports other evidence indicating the presence of comparatively broad upwellings rather than localized plumes

rhenium osmium systematics of the mount isa copper orebody and the eastern creek volcanics queensland australia implications for ore genesis the syn tectonic breccia hosted mount isa cu deposit in northwest queensland is the largest sediment hosted cu deposit in australia whole rock samples of chalcopyrite rich cu ore form an isochron with a re os age of 1 372 41 ma this age is more than 100 ma younger than the previously accepted age of cu ore formation an ar ar mineral age for biotite separated from the host rocks within the alteration envelope to the cu orebody this discrepancy cannot be unequivocally resolved due to a lack of other absolute geochronological constraints for cu mineralisation or the deformation event associated with cu emplacement the 1 372 41 ma date may reflect a the time of cu deposition b the time of a hydrothermal event that reset the re os signature of the cu ore or c mixing of the re os isotope systematics between the host rocks and cu bearing fluids however a range of published ar ar and rb sr dates for potassic alteration associated with cu mineralisation also records an event between 1 350 and 1 400 ma and these are consistent with the 1 372 ma re os age the 1 8 ga eastern creek volcanics are a series of tholeiitic basalts with a primary magmatic cu enrichment which occur adjacent to the mount isa cu deposit the whole rock os isotopic signature of the eastern creek volcanics ranges from mantle like values for the upper pickwick member to more radiogenic crustal values for the lower cromwell member the re os isotope signature of the cu ores overlaps with those calculated for the two volcanic members at 1 372 ma hence the os isotope data are supportive of the concept that the os in the cu ores was sourced from the eastern creek volcanics by inference it is therefore postulated that the eastern creek volcanics are the source of cu in the mount isa deposit as both os and cu are readily transported by oxidised hydrothermal fluids such as those that are thought to have formed the cu orebody the pickwick member yields a re os isochron age of 1 833 51 ma which is within error of previously reported age constraints the initial 187os 188os isotopic ratio of 0 114 0 067 os 0 7 is slightly subchondritic and together with other trace element geochemical constraints is consistent with a subcontinental lithospheric mantle source the pickwick member records a minimum age of ca 1 95 ga for melt depletion in the subcontinental lithospheric mantle beneath the mount isa inlier prior to the extraction of the magmas which formed the eastern creek volcanics this corresponds with the end of subduction related magmatism along the eastern margin of the northern australian craton which included the mount isa inlier

origin of the inconsistent apparent re os ages of the jinchuan ni cu sulfide ore deposit china post segregation diffusion of os abstract apparent re os ages of some magmatic sulfide ore deposits are older than the zircon and baddeleyite u pb ages which are interpreted as the formation age of the host intrusions the jinchuan ni cu pge deposit of china the world s third largest is such a case we report apparent re os isochron ages of 1117 67 ma 1074 120 ma and 867 75 ma with initial 187os 188os ratios of 0 120 0 012 0 162 0 017 and 0 235 0 027 for disseminated ores sulfides from the disseminated ores and massive ores from jinchuan respectively using these data and re os ages from the literature we find that the oldest apparent re os age and lowest initial os isotope ratio are from disseminated ores which contain small amounts of sulfide minerals the highest initial os isotope ratios and youngest apparent re os ages consistent with the zircon and baddeleyite u pb ages are from massive ores containing 90 100 modal sulfide and net textured ores with about 25 modal sulfides yield apparent re os ages and initial os ratios intermediate between those of the disseminated and massive ores because os diffusion between sulfides is inhibited by the intervening silicates even at high temperatures re equilibration did not occur in the disseminated ore and the samples retained the os ratios of the contaminated magma leading to geologically meaningless ages that are older than the formation age of the rocks while os bearing sulfide minerals and magnetite show low closure temperatures of os diffusion and the sulfide minerals in the massive ore are closely connected with each other facilitating fast diffusion of os re equilibration of os was achieved during cooling of the ore from about 850 c after the segregation to about 400 c thus an age corresponding to the formation time and an elevated initial os ratio were yielded by the massive ore os isotopes in the net textured ore behave in the way intermediate between the disseminated and massive ores pb isotope data support the os results disseminated ores have heterogeneous pb isotope ratios whereas pb in the massive ores is more uniform consistent with pb isotopic equilibration in the massive ores but not in the disseminated ores

re os isotope and pge constraints on the timing and origin of gold mineralisation in the witwatersrand basin abstract analyses of the re os isotope system and pge abundances have been used to investigate the timing and origin of mineralisation in the vaal reefs section of the witwatersrand basin the world s largest gold deposit consistent interelement pge fractionation in both organic and sulphide phases intimately associated with gold mineralisation suggests that the re os isotope system was fractionated during gold mobilisation the re os isotope data on organic separates intimately associated with the gold in this part of the basin indicate open system behaviour until 2 26 0 19 ga 2 of the order of 450 myr younger than the minimum age of sedimentation the overlying ventersdorp volcanics preserve a re os isochron age of 2 43 0 21 ga 250 ma younger than their u pb zircon emplacement age these data indicate substantial post sedimentary noble metal mobility within portions of the witwatersrand basin re os model age calculations on os rich fractions suggest that noble metals were derived from a 3 0 3 1 ga terrain of granite greenstone affinities significantly younger than the barberton greenstone belt these data support a hybrid model involving post depositional mobilisation of ancient probably detrital noble metals for the origin of mineralisation in this part of the witwatersrand basin such a model is applicable to other areas of gold mineralisation in the basin that display similar textural characteristics and geochemistry

glaciation induced perturbations in the earth s rotation a new appraisal we revisit the theory and predictions of glaciation induced perturbations in both the rotation rate of the earth or j 2 and the wander of the rotation pole with respect to the surface geography the two most common theoretical formulations associated with polar wander driven by the surface loading of a viscoelastic earth e g sabadini et al 1982 wu and peltier 1984 appear to disagree by one on the number of rotational normal modes associated with a surface gravitational response having n normal modes we show using a generalized theory that the two formalisms yield essentially equivalent predictions we next consider a benchmark comparison of recent predictions of present day polar wander speed due to glacial isostatic adjustment henceforth gia these comparisons confirm the validity of certain previous analyses e g spada et al 1992a they also reveal that predictions of polar wander speed can be sensitive to an assumption of incompressibility previous studies have noted that predictions of j 2 rotation rate as a function of lower mantle viscosity differ significantly in form from analogous predictions of polar wander speed we investigate these differences by considering the contribution to the predicted anomalies from the individual normal modes of relaxation we find that the normal mode structure of the j 2 rotation rate predictions is fundamentally different from that which characterizes the polar wander response and this difference reflects the distinct physical mechanisms which govern these anomalies finally using a large suite of forward computations as well as the calculation of a set of frechet kernels we investigate the sensitivity of our predictions to variations in the viscoelastic earth model we find for example that a previously noted sensitivity of polar wander speed predictions to variations in lithospheric thickness is only valid for earth models with relatively weak lower mantle viscosities 5 x 10 21 pa s

geodynamic implications of moving indian ocean hotspots abstract the reconstructed positions of many of the indian ocean intraplate volcanic features are inconsistent with the present positions of the hotspots to which they have been ascribed the discrepancy can be explained by the past motion of the hotspots themselves and in the errors introduced in an absolute plate model based on fixed hotspots previous models for the motion of hotspots in the indian ocean e g steinberger and o connell in the history and dynamics of global plate motions 2000 pp 377 398 and geophys j int 132 1998 412 434 antretter et al earth planet sci lett 203 2002 635 650 have had success in matching paleolatitudes of the kerguelen hotspot but not the marion or reunion hotspots we calculate the motion of the indian ocean hotspots using a method described in steinberger and o connell op cit employing a plate motion model revised using identification of mesozoic magnetic anomalies in the enderby basin gaina et al in the evolution and dynamics of the australian plate in press we find a motion of 7 south for the kerguelen plume similar to previous models antretter et al op cit this motion alleviates the discrepancies in the position of the kerguelen plume and its purported involvement in the formation of the ninetyeast ridge rajmahal traps bunbury basalts and assorted volcanics of the western australian margin we find a motion of 5 north and 7 south for the reunion and marion plumes respectively the motion of the reunion hotspot is consistent with paleolatitude estimates the apparent fixity of the marion hotspot torsvik et al earth planet sci lett 164 1998 221 232 is not well constrained but may be due to the combination of hotspot motion and true polar wander acting in opposing directions we present revised absolute finite rotations for the indian plate for the last 65 ma based on the motion of these hotspots which place india farther north in the past than for fixed hotspot models

geodetic vertical velocities affected by recent rapid changes in polar motion summary secular motion of earth s rotation pole results in large scale secular deformation of earth here we investigate the magnitude of the deformation that has resulted from the rapid motion of the rotation pole to the east since 2005 we show that geodetic gnss doris vlbi and slr estimates of vertical velocity since 2005 have been biased by up to 0 38 mm yr 1 relative to the longer term deformation pattern the largest signals occur within regions that include the u s pacific coast europe and south pacific islands where geodetic measurements provide essential measurements of tide gauge vertical movement and important constraints on models of glacial isostatic adjustment consequently geodetic vertical velocities based on recent data should not be interpreted as being identical to centennial or longer term vertical land movement since 2010 the effect is further amplified by the overprediction of the iers polar motion model relative to the ongoing secular change in pole position during this time geodetic vertical velocities based on the iers pole tide model are not just biased relative to the long termratesbutalsofromactualpost 2010earthdeformation forgeophysicalorreference frame studies seeking geodetic vertical velocities that are representative of decadal timescales where interannual variation is considered noise the correction for this non linear effect is straightforward requiring an elastic computation using a reference rate of polar motion that is linear over the timescales of interest

re os isotopic ages of pyrite and chemical composition of magnetite from the cihai magmatic hydrothermal fe deposit nw china the eastern tianshan orogenic belt of the central asian orogenic belt and the beishan terrane of the tarim block nw china host numerous fe deposits the cihai fe deposit 90 mt at 45 6 fe in the beishan terrane is diabase hosted and consists of the cihai cinan and cixi ore clusters ore minerals are dominantly magnetite pyrite and pyrrhotite with minor chalcopyrite galena and sphalerite gangue minerals include pyroxene garnet hornblende and minor plagioclase biotite chlorite epidotite quartz and calcite pyrite from the cihai and cixi ore clusters has similar re os isotope compositions with 14 to 62 ppb re and 10 ppt common os pyrrhotite has 5 to 39 ppb re and 0 6 ppb common os pyrite has a mean re os model age of 262 3 5 6 ma n 13 in agreement with the isochron regression of 187os vs 187re the re os age 262 ma for the cihai fe deposit is within uncertainty in agreement with a previously reported rb sr age 268 25 ma of the hosting diabase indicating a genetic relationship between magmatism and mineralization magnetite from the cihai deposit has mg al ti v cr co ni mn zn ga and sn more elevated than that of typical skarn deposits but both v and ti contents lower than that of magmatic fe ti v deposits magnetite from these two ore clusters at cihai has slightly different trace element concentrations magnetite from the cihai ore cluster has relatively constant trace element compositions some magnetite grains from the cixi ore cluster have higher v ti and cr than those from the cihai ore cluster the compositional variations of magnetite between the ore clusters are possibly due to different formation temperatures combined with regional tectonic evolution of the beishan terrane the re os age of pyrite and the composition of magnetite indicate that the cihai fe deposit may have derived from magmatic hydrothermal fluids related to mafic magmatism probably in an extensional rift environment

an estimate of motion between the spin axis and the hotspots over the past century 1 estimates of the motion of the spin axis over the past century either neglect plate motion or are relative to the mean lithosphere to understand the response of the spin axis to mass changes it is more useful to estimate spin axis motion relative to the hotspots because the hotspots well represent the solid earth the hotspots originate in the lower mantle which comprises 2 3 of the earth s volume relative to the lower mantle the plates and the upper mantle move in opposite directions to a large extent canceling each other out the mean lithosphere moves quickly relative to the hotspots and poorly represents the solid earth the spin axis has moved relative to the hotspots over the past century along the 68 4 w meridian at 4 03 milliarcsecond yr this motion is 11 counterclockwise of 0 5 milliarcsecond yr faster than and 25 different than spin axis motion relative to the mean lithosphere

on the origins of earth rotation anomalies new insights on the basis of both paleogeodetic data and gravity recovery and climate experiment grace data 1 the theory previously developed to predict the impact on earth s rotational state of the late pleistocene glaciation cycle is extended in particular we examine the extent to which a departure of the infinite time asymptote of the viscoelastic tidal love number of degree 2 k2t from the observed fluid love number kf impacts the theory a number of tests of the influence of the difference in these love numbers on theoretical predictions of the model of the glacial isostatic adjustment gia process are explored relative sea level history predictions are shown not to be sensitive to the difference even though they are highly sensitive to the influence of the changing rotational state itself we also explore in detail the accuracy with which the gravity recovery and climate experiment grace satellite system is able to observe the global gia process including the time dependent amplitude of the degree 2 and order 1 spherical harmonic components of the gravitational field the only components that are significantly influenced by rotational effects it is explicitly shown that the grace observation of these properties of the time varying gravitational field is sufficiently accurate to rule out the values predicted by the ice 5g vm2 model of peltier 2004 however we also note that this model is constrained only by data from an epoch during which modern greenhouse gas induced melting of both the great polar ice sheets and small ice sheets and glaciers was not occurring such modern loss of grounded continental ice strongly influences the evolving rotational state of the planet and thus the values of the degree 2 and order 1 stokes coefficients as they are currently being measured by the grace satellite system a series of sensitivity tests are employed to demonstrate this fact we suggest that the accuracy of scenarios for modern land ice melting may be tested by ensuring that such scenarios conform to the grace observations of these crucial time dependent stokes coefficients

late paleozoic sedex deposits in south china formed in a carbonate platform at the northern margin of gondwana abstract sedex sulfide deposits hosted in black shale and carbonate are common in the south china block the dajiangping pyrite deposit is the largest of these deposits and is made up of stratiform orebodies hosted in black shales sandstone interlayered with stratiform orebodies contains detrital zircon grains with the youngest ages of 429 ma pyrite from the orebodies has a re os isochron age of 389 62 ma indicative of formation of the hosting strata and syngenetic pyrite ores in the mid late devonian the hosting strata is a transgression sequence in a passive margin and composed of carbonaceous limestone in the lower part and black shales in the upper part the ore hosting black shales have high toc total organic carbon mo as pb zn and cd indicating an anoxic euxinic deep basin origin the high redox proxies v v ni 0 6 and v cr 1 and the positive correlations of toc with mo and v in black shales are also consistent with an anoxic depositional environment the dajiangping deposit is located close to the ne trending wuchuan sihui fault which was active during the devonian the mid late devonian mineralization age and the anoxic euxinic deep basinal condition of this deposit thus imply that the formation of this deposit was causally linked to hydrothermal fluid exhalation in an anoxic fault bounded basin that developed in a carbonate platform of the south china block the regional distribution of many devonian stratiform carbonaceous sediment hosted sulfide deposits along the ne trending fault bounded basins in south china similar to the dajiangping deposit indicates that these deposits formed at a basin developed in the passive margin setting of the south china block during the devonian this environment was caused by the break up and northward migration of the south china block from gandwana

rhenium osmium isotope systematics of an early mesoproterozoic sedex polymetallic pyrite deposit in the north china craton implications for geological significance and the marine osmium isotopic record abstract the rhenium osmium re os isotopic system preserved in ancient seafloor hydrothermal sulfide deposits can be used to gain insight into the os composition of ancient seawater in particular the age of sedimentary exhalative sedex deposits can be determined by measuring re os isotopes in syn depositional pyrite a common constituent of sedex deposits here we report on the gaobanhe sediment hosted polymetallic pyrite deposit which is hosted within the gaoyuzhuang formation in the central part of the northern margin of the north china craton ncc re os isotopic data from syn depositional pyrite yield an isochron age of 1505 55 ma constraining the timing of primary mineralization as well as the minimum age of the host sediments to the mesoproterozoic analyzed pyrite grains indicate an initial 187os 188os osi value of 0 181 0 066 suggesting that the mineralizing fluids were an admixture of seawater and submarine hydrothermal fluids with the os being primarily derived from seawater the osi value is slightly higher than that of paleoproterozoic seawater 0 13 suggesting that there was a radiogenic riverine flux to the oceans and that atmospheric oxygen must have been sufficiently high at that time to drive this increased continental radiogenic os input to the oceans we propose that the re os isotopic system as recorded by these sedex deposits may provide key insights when examining changes in the os isotopic composition of seawater throughout the precambrian

re os isotope systematics of ni cu sulfide ores sudbury igneous complex ontario evidence for a major crustal component sudbury igneous complex sublayer ores from the levack west falconbridge and strathcona mines were analyzed for their re and os concentrations and os isotopic compositions the re os isotope systematics of three ores from the different mines give isochron ages of1 840 60 ma 1770 60 ma and 1780 110 ma suggesting that the re os system became closed at the time of or soon after the 1850 1 ma crystallization age of the complex the os isotopic compositions of different portions of the complex at the time of crystallization varied considerably with initial187os 186os1850 ranging from 4 64 at levack west to 7 55 at strathcona these heterogeneities require that the os and probably also the other platinum group elements contained in the ores were derived from at least two sources in addition the high initial187os 186os ratios indicate that the os was derived predominantly from ancient crust previous studies have suggested that the complex either crystallized from a mixture of mantle derived basaltic melt and ancient continental crust or was derived exclusively from the fusion of ancient continental crust resulting from a meteorite impact results of modelling suggest that if a contemporaneous mantle derived basaltic melt was involved in the origin of the sic it likely contributed 50 of the os to all three ores the large percentage of ancient crust involved in the production of the ores is most consistent with an interpretation of substantial crustal fusion resulting from meteorite impact

the antarctica component of postglacial rebound model ice 6g_c vm5a based on gps positioning exposure age dating of ice thicknesses and relative sea level histories

pacific plate apparent polar wander hot spot fixity and true polar wander during the formation of the hawaiian island and seamount chain from an analysis of the skewness of magnetic anomaly 20r 44 ma

ice age earth rotation modern predictions of the rotational stability of an ice age earth reflect a convergence of two classic problems in geophysical analysis the modeling of the glacial isostatic adjustment gia process and the rotational stability of terrestrial planets recent theoretical advances in this area have been motivated not by conventional applications such as the inference of earth s deep mantle viscosity but rather by efforts to address vexing problems in global climate change research these advances have demonstrated that traditional calculations of the ongoing motion of the rotation pole relative to the surface geography or true polar wander tpw driven by ice age loading have systematically overestimated this motion by up to a factor of 4 by underestimating by 1 the background flattening of earth s oblate form the physics of this sensitivity is related to concepts that appear in canonical mid twentieth century discussions of earth rotation and avoiding the associated inaccuracy resolves numerous p

re os geochronology of the iimori besshi type massive sulfide deposit in the sanbagawa metamorphic belt japan abstract besshi type cu deposits are strata bound volcanogenic massive sulfide deposits usually associated with mafic volcanic rocks or their metamorphic equivalents although there are numerous besshi type deposits in the sanbagawa metamorphic belt japan their tectonic settings and depositional environments remain controversial because of a lack of depositional age constraints we report re os data for the iimori deposit one of the largest besshi type deposits in western kii peninsula in order to examine the robustness of the re os isotope system for dating sulfide minerals in the high p t metamorphic belt and to elucidate the primary depositional environment of the iimori sulfide ores an 11 point re os isochron plot yields an age of 156 8 3 6 ma as this re os isochron age is significantly older than the timing of the sanbagawa peak metamorphism 110 120 or 90 ma and a well defined isochron was obtained the re os age determined here is most likely the primary depositional age despite high grade metamorphism at up to 520 25 c and 8 9 5 kbar the re os isotope system of the iimori sulfides was not disturbed hence we consider that the whole rock re os closure temperature for the iimori sulfide ores was probably higher than 500 c as the accretion age of the sanbagawa metamorphic belt is considered to be 120 130 or 65 90 ma on the basis of radiolarian and radiometric ages we estimated the time from the iimori sulfide deposition on the paleo seafloor to its accretion at the convergent plate boundary to be greater than 25 myr consequently the depositional environment of the iimori sulfide ores was not in the marginal sea but was truly pelagic

constraining models of postglacial rebound using space geodesy a detailed assessment of model ice 5g vm2 and its relatives summary using global positioning system very long baseline interferometry satellite laser ranging and doppler orbitography and radiopositioning integrated by satellite observations including the canadian base network and fennoscandian bifrost array we constrain in models of postglacial rebound the thickness of the ice sheets as a function of position and time and the viscosity of the mantle as a function of depth we test model ice 5g vm2 t90 rot which well fits many hundred holocene relative sea level histories in north america europe and worldwide ice 5g is the deglaciation history having more ice in western canada than ice 4g vm2 is the mantle viscosity profile having a mean upper mantle viscosity of 0 5 1021 pa s and a mean uppermost lower mantle viscosity of 1 6 1021 pa s t90 is an elastic lithosphere thickness of 90 km and rot designates that the model includes rotational feedback earth s response to the wander of the north pole of earth s spin axis towards canada at a speed of 1 myr 1 the vertical observations in north america show that relative to ice 5g the laurentide ice sheet at last glacial maximum lgm at 26 ka was 1 much thinner in southern manitoba 2 thinner near yellowknife northwest territories 3 thicker in eastern and southern quebec and 4 thicker along the northern british columbia alberta border or that ice was unloaded from these areas later thicker or earlier thinner than in ice 5g the data indicate that the western laurentide ice sheet was intermediate in mass between ice 5g and ice 4g the vertical observations and grace gravity data together suggest that the western laurentide ice sheet was nearly as massive as that in ice 5g but distributed more broadly across northwestern canada vm2 poorly fits the horizontal observations in north america predicting places along the margins of the laurentide ice sheet to be moving laterally away from the ice centre at 2 mm yr 1 in ice 4g and 3 mm yr 1 in ice 5g in disagreement with the observation that the interior of the north american plate is deforming more slowly than 1 mm yr 1 substituting vm5a t60 for vm2 t90 that is introducing into the lithosphere at its base a layer with a high viscosity of 10 1021 pa s greatly improves the fit of the horizontal observations in north america ice 4g vm5a t60 rot predicts most of the north american plate to be moving horizontally more slowly than 1 mm yr 1 in agreement with the data ice 5g vm5a t60 rot well fits both the vertical and horizontal observations in europe the space geodetic data cannot distinguish between models with and without rotational feedback in the vertical because the velocity of earth centre is uncertain and in the horizontal because the areas of the plate interiors having geodetic sites is not large enough to detect the small differences in the predictions of rotational feedback going across the plate interiors

reanalysis of ancient eclipse astronomic and geodetic data a possible route to resolving the enigma of global sea level rise predictions of the earth s response to the ice age appear to simultaneously reconcile a set of astronomical geodetic and ancient eclipse observations related to changes in rotation thus ruling out ice melting as a major contributor to 20th century sea level rise we demonstrate that the reconciliation disappears when an improved theory of rotational stability is applied furthermore our reanalysis of longer satellite records renders previous estimates of the secular change in rotation rate suspect the updated ice age predictions and observations permit an anomalous 20th century ice flux of 1 mm yr equivalent sea level rise thus the full suite of earth rotation observations are consistent with a connection between climatic warming and recent melting of ice reservoirs

data assimilation with a coupled wind wave model a first attempt to assimilate observations into a coupled wind wave model system is presented a special feature of the wind model is that the drag coefficient depends on the wave age reflecting the dependence of the air flow on the wave state usually both wind and wave data are assimilated the assimilation is carried out by means of the adjoint technique this coupled wind wave data assimilation not only corrects successfully both model fields but their dynamical connection is retained furthermore the assimilation of only wave data results in enough information on the atmospheric state at the sea surface that it can correct both wave and wind fields as well moreover there is still some impact of the assimilation during the forecast period this persistence is found to be dependent on the typical relaxation time scale of the wind model and also to be related to the swell decay time scale due to wave breaking the computations reveal the importance of both the coupling and the coupled wind wave data assimilation scheme that has been developed

the pole tide and its effect on grace time variable gravity measurements implications for estimates of surface mass variations gravity recovery and climate experiment grace provides monthly solutions for the earth s gravity field in the form of spherical harmonic coefficients these can be used to infer changes in mass at the earth s surface the pole tide the response of the earth and oceans to polar motion causes gravity signals dominated by harmonics of degree 2 order 1 if the pole tide is not removed from grace data it affects the coefficients of those harmonics c21 s21 and introduces errors when using those coefficients to determine surface mass variations the pole tide is partially removed by grace processing centers before solving for the gravity field but long period pole tide signals are not usually included in the grace pole tide correction and so those signals are still present in the grace coefficients we discuss this issue from the standpoint of somebody who uses the grace gravity fields to infer changes in surface mass we arrive at a recommendation for an optimal grace pole tide correction we describe how to modify the c21 s21 coefficients provided by the processing centers so that they conform with our recommendation we discuss the size of the pole tide contributions to c21 s21 compared to those of the direct load induced contributions as an example we show how an incompletely removed pole tide can impact grace results for the trend in ocean mass we consider the impact of mantle anelasticity on long period pole tide corrections and conclude that it is unlikely to affect those corrections by more than 20

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

mantle viscosity and ice age ice sheet topography ice age paleotopography and mantle viscosity can both be inferred from observations of earth s response to the most recent deglaciation event of the current ice age this procedure requires iterative application of a theoretical model of the global process of glacial isostatic adjustment results demonstrate that the iterative inversion procedure converges to a paleotopography that is extremely close to that from the ice 4g model the accompanying mantle viscosity profile is furthermore shown to reconcile the requirements of aspherical geoid anomalies related to the mantle convection process thus resolving a fundamental issue concerning mantle rheology the combined model also explains postglacial sea level histories for the east coast of the united states

tectonic patterns on reoriented and despun planetary bodies abstract several processes may produce global tectonic patterns on the surface of a planetary body the stresses associated with distortions of biaxial figures due to despinning or reorientation were first calculated by vening meinesz vening meinesz f a 1947 trans am geophys union 28 1 1 23 we adopt a mathematically equivalent but physically more meaningful treatment for distortions associated with rotation the new approach allows us to find analytic solutions for the general case of stresses associated with distortions of biaxial or triaxial planetary figures distortions of biaxial figures may be driven by variations in rotation rate rotation axis orientation or the combination of both distortions of triaxial figures may be driven by the same mechanisms and or variations in tidal axis orientation for tidally deformed satellites while the magnitude of the resulting stresses depends on the adopted elastic and physical parameters the expected tectonic pattern is independent of these parameters for these mechanisms reorientation of the rotation tidal axis alone is expected to produce normal thrust faulting provinces enclosing the initial rotation tidal poles and thrust normal faulting provinces enclosing the final rotation tidal poles reorientation of both the rotation and tidal axis results in a wide variety of tectonic patterns for different reorientation geometries on europa the tidal axis reorientation which generally accompanies rotation axis reorientations may provide an alternative explanation for tectonic features that have been interpreted as evidence for non synchronous rotation the observed tectonic pattern on enceladus is more easily explained by a large reorientation 90 of the rotation axis than by rotation rate variations

ocean mass from grace and glacial isostatic adjustment 1 we examine geoid rates and ocean mass corrections from two published global glacial isostatic adjustment gia models both of which have been used in previous studies to estimate ocean mass trends from gravity recovery and climate experiment grace satellite gravity data these two models are different implementations of the same ice loading history and use similar mantle viscosity profiles the model results are compared with each other and with geoid rates determined from grace during august 2002 to november 2009 when averaged over the global ocean the two models have rates that differ by nearly 1 mm yr 1 of ocean mass with the first model giving a correction closer to 2 mm yr 1 and the second closer to 1 mm yr 1 by comparing the two models we have discovered that 50 of the difference is caused by a global land ocean mean in the first model while it is appropriate to include this mean when subtracting gia effects from measurements of sea level change measured by tide gauges or satellite altimetry the mean should not be included when subtracting gia effects from ocean mass variations derived from satellite gravity data when this mean is removed the ocean mass corrections from the two models still disagree by 0 4 mm yr 1 we trace the residual difference to the fact that the first model also has large trends over the ocean related to large rates in its predicted degree 2 order 1 geoid coefficients such oceanic trends are not observed by grace nor are they predicted by the second model and they are shown to be inconsistent with the polar wander rates predicted by the first model itself if these two problems are corrected we find that the two model predictions agree at the 3 level on the basis of this analysis we conclude that the ocean mass correction for grace is closer to 1 mm yr 1 than 2 mm yr 1 although significant uncertainties remain

an early cretaceous carbonate replacement origin for the xinqiao stratabound massive sulfide deposit middle lower yangtze metallogenic belt china stratabound massive sulfide deposits are widespread along the middle lower yangtze metallogenic belt mlymb and serve as an important copper producer in china two contrasting genetic models have been proposed interpreting the stratabound massive sulfide deposits as a carboniferous sedex protore overprinted by cretaceous magmatic hydrothermal system or an early cretaceous carbonate replacement deposit these two contrasting models have been applied to the xinqiao stratabound cu au sulfide deposit which is dominated by massive sulfide ores hosted in marine carbonates of the carboniferous chuanshan and huanglong formations with minor cu au skarn ores localized in the contact zone between the cretaceous diorite jitou stock and the carboniferous carbonate rocks new sims zircon u pb dating suggests that the jitou stock formed at 138 5 1 1 ma 2 mswd 0 6 pyrite re os dating yields an imprecise date of 142 47 ma 2 mswd 7 8 the geochronological data thus constrain the mineralization of the xinqiao deposit at early cretaceous fluid inclusions in prograde skarn diopside have homogenization temperatures of 450 600 c and calculated salinities of 13 58 wt nacl equiv quartz from the stratabound ores and pyrite quartz vein networks beneath the stratabound ores have homogenization temperatures of 290 360 and 200 300 c with calculated salinities of 5 12 and 2 10 wt nacl equiv respectively quartz from the skarn ores and veins beneath the stratabound ores have 18o values of 12 32 0 55 2 sd n 22 and 15 57 1 92 2 sd n 60 respectively corresponding to calculated 18o values of 6 22 1 59 2 and 6 81 2 76 2 for the equilibrated ore forming fluids the fluid inclusion and oxygen isotope data thus support a magmatic hydrothermal origin rather than a sedex system for the stratabound ores with the hydrothermal fluids most likely being derived from the jitou stock or associated concealed intrusion results from this study have broad implications for the genesis and exploration of other stratabound massive sulfide deposits along the mlymb

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

astrometric and space geodetic observations of polar wander optical astrometric measurements of star positions taken during the past century have been recently re reduced using the final hipparcos star catalog in order to determine variations in the mean location of the earth s rotation pole with respect to the earth s crust this newly available polar motion series which is the longest homogeneous polar motion series currently available allows the drift in the pole path to be newly estimated during the 1900 0 to 1992 0 span of the smoothed hipparcos polar motion series the earth s rotation pole is observed to drift at a mean linear rate of 3 51 0 01 milliarcseconds year mas yr towards 79 2 0 2 w longitude this new estimate for the observed trend in the pole path which can be considered to be the present day expression of true polar wander is nearly the same as that estimated in previous studies using the homogeneous ils polar motion series

re os pyrite and u pb zircon geochronology from the taldybulak levoberezhny gold deposit insight for cambrian metallogeny of the kyrgyz northern tien shan abstract the taldybulak levoberezhny gold deposit located in the eastern part of the kyrgyz northern tien shan is hosted in highly deformed precambrian schist and gneisses that have undergone intense quartz carbonate fuchsite and tourmaline alterations gold mineralization is ultimately subdivided into two stages based on the observation of alteration assemblages orebody geometries and the occurrences of au bearing minerals negative thermal ionization mass spectrometry re os isotopic analyses of five au rich pyrite samples from the early stage yielded an isochron age of 511 18 ma zircon sensitive high resolution ion microprobe u pb dating of a diorite dike sample postdating the late stage mineralization yielded a wide range of ages from 3055 to 291 ma while a weighted mean 206 pb 238 u age of 414 6 6 8 ma is believed to represent the age of dike intrusion and the upper limit on the timing of the late stage quartz tourmaline gold formation the pyrite 187 os 188 os initial ratio of 0 132 0 011 together with os values varying from 0 to 14 indicate a major mantle component for the source of os and by inference ore metals which may be linked to the ophiolite suite of the kopurelisai complex in the taldybulak levoberezhny area considering the geodynamic setting of the kyrgyz northern tien shan during the early paleozoic we suggest that cambrian mineralization of the taldybulak levoberezhny deposit can be attributed to a subduction related setting probably associated with the earliest accretion of the northern tien shan

a benchmark study for glacial isostatic adjustment codes the study of glacial isostatic adjustment gia is gaining an increasingly im portant role within the geophysical community understanding the response of the earth to loading is crucial in various contexts ranging from the the interpretation of modern satellite geodetic measurements e g grace and goce to the projections of future sea level trends in response to climate change modern modeling approaches to gia are based on various techniques that range from purely analytical formulations to fully numerical methods despite various teams independently investigating gia we do not have a suitably large set of explicitly validated numerical results through which they may be validated a community benchmark data set would clearly be valuable following the example of the mantle convection community here we present for the first time the results of a benchmark study of codes designed to model gia the approaches benchmarked are based on significantly different codes and different techniques this effort is performed within the working group 4 wg4 of the esf cost action es0701 improved constraints on models of glacial isostatic adjustment our aims are i testing the codes currently in use by the various teams ii establish a sufficiently large set of agreed results iii correct possible systematic errors embedded in the various physical formulations or computer implementations and iv facilitate the dissemination of numerical tools for surface loading studies to the community and to young scientists the test computations are mainly based on models with spherical symmetry and maxwell rheology and include inputs from various different methods and solution techniques viscoelastic normal modes spectral finite elements and finite elements the tests involve the loading and tidal love numbers and their relaxation spectra the deformation and gravity variations driven by surface loads characterized by simple geometry and time history and the rotational fluctuations in response to glacial unloading in spite of the significant differences in the numerical methods employed the test computations show a satisfactory agreement between the results provided by the participants most of the existing misfits have been addressed during the preparation of the manuscript some others are currently the subject of analysis within the wg4 community

evidence for as contamination and the partitioning of pd into pentlandite and co platinum group elements into pyrite in the fazenda mirabela intrusion brazil the fazenda mirabela intrusion in brazil hosts two zones of mineralization the santa rita ni cu sulfide ore zone occurring predominantly in an orthopyroxenite layer and an underlying basal platinum group element pge anomaly hosted in s poor dunite we show that in the northern and southern marginal zones of the intrusion pt pd ni cu fe bi te 2 minerals are accompanied by as bearing platinum group minerals pgm sperrylite ptas2 and irarsite rhirpt ass these as bearing pgm are extremely rare in the central zone of the intrusion suggesting that as has been introduced into the margins of the intrusion from the country rocks via crustal assimilation or synmagmatic hydrothermal processes other pgm and precious metal minerals pmm including hessite ag2te pd ag tellurides electrum and native au are observed in the santa rita ore zone and do not show any lateral variation in the semimetal and s poor dunite hosting the basal pge anomaly pge are predominantly retained in the base metal sulfides and only minor pge alloys are present in this s poor dunite pt au and semimetals partitioned into a fractionated cu rich liquid which formed during the crystallization of monosulfide solid solution mss and was largely removed by high temperature magmatic fluids palladium was not affected by this process and significant concentrations of pd are identified in pentlandite suggesting that pd preferentially partitioned into mss as it crystallized and subsequently pentlandite as it exsolved pyrite in the santa rita ore zone is co rich and contains higher concentrations of ipge os ir ru and rh than pyrrhotite and pentlandite suggesting that pyrite has not replaced and inherited the pge concentrations of these sulfides the pd poor nature of pyrite also indicates that it has not replaced pd rich pentlandite it is proposed that the ipge and co preferentially partitioned into pyrite as it exsolved from mss

changes in rotation induced by pleistocene ice masses with stratified analytical earth models the rotational response of the earth to pleistocene deglaciation is studied by means of a multilayered viscoelastic earth model based on the preliminary reference earth model prem incompressible viscoelastic deformation is evaluated from a self compressed initial state the novelty of our approach stands on the application of a fully analytical normal mode theory to the response of the earth to surface loads and variations in the centrifugal potential for large numbers of viscoelastic layers as requested by prem assuming that both present day true polar wander tpw and changes in the second degree component of the geopotential are solely due to pleistocene postglacial rebound we obtain for a two layer viscosity model that the upper mantle viscosity must be lowered to about 1 5 1020 pa s with respect to the classical value of 1021 pa s this upper mantle viscosity is accompanied by an increase of the lower mantle viscosity by a factor of 25 in agreement with some recent relative sealevel rsl data analyses and convectively supported long wavelength geoid anomalies when the viscosity contrast is located at 1470 km depth tpw and require a viscosity of 1021 pa s in the upper part of the mantle above 1470 km depth with a moderate viscosity increase in the lowermost portion of the mantle this result indicates that a viscosity of 1021 pa s is appropriate for a wider portion of the mantle than the upper mantle in agreement with haskell s 1935 estimate that was not limited to the seismically inferred 670 km boundary

grace era secular trends in earth rotation parameters a global scale impact of the global warming process 1 recent trends in the two primary anomalies in the rotational state of the planet are analyzed in detail namely those associated with the speed and direction of polar wander and with the non tidal acceleration of the rate of axial rotation via the measurement of the changing oblateness of the earth s shape it is demonstrated that a significant change in the secular trends in both of these independent parameters became evident subsequent to approximately 1992 it is suggested that both parameters might have come to be substantially influenced by mass loss from both the great polar ice sheets and from the very large number of small ice sheets and glaciers that are also being influenced by the global warming phenomenon the modern values for the secular drifts in those parameters that we estimate are appropriate to the period during which measurements have been made by the satellites of the gravity recovery and climate experiment grace thesechangesinsecularratesmightgreatly assist in understanding why the grace inferred values of the time derivatives of the degree two and order one stokes coefficients differ so significantly from those associated with late quaternary ice age influence citation roy k and w r peltier 2011 grace era secular trends in earth rotation parameters a global scale impact of the global warming process geophys res lett 38 l10306 doi 10 1029 2011gl047282

mantle viscosity from the simultaneous inversion of multiple data sets pertaining to postglacial rebound we employ the formalism of bayesian inference to invert three distinct data sets related to the phenomenon of glacial isostatic adjustment these data consist respectively of the wavenumber spectrum of relaxation times for fennoscandian rebound inferred by mcconnell 1968 the characteristic relaxation times for a large collection of distinct 14c dated relative sea level curves from both canada and fennoscandia and two data related to the rotational response of the earth to the glaciation deglaciation cycle of the late pleistocene ice age our analyses show that the spherically symmetric viscosity structure objectively inferred on the basis of these data from the once glaciated regions of the northern hemisphere allows a fully satisfactory reconciliation of both us east coast relative sea level observations as well as providing a close fit to the requirements of aspherical geoid anomalies

preservation of re os isotope signatures in pyrite throughout low t high p eclogite facies metamorphism pyrite in lt hp eclogites from the western tianshan orogenic belt yields a re os age of 378 1 8 9 ma which is 30 70 ma older than ages previously obtained for the same rocks using the rb sr sm nd ar ar u pb and lu hf isotope systems the tianshan lt hp eclogite experienced temperatures of up to 570 c combined with pressures of up to 2 1 gpa during metamorphism these conditions are below the transition of pyrite to pyrrhotite which defines both pyrite stability and possibly its closure temperature for re os pyrite can preserve re os signatures through eclogite facies peak metamorphic conditions and thus allow determination of the formation age of pyrite in the protolith

re os isotopic systematics of the voisey s bay ni cu co magmatic ore system labrador canada abstract re and os concentrations and os isotopic compositions have been obtained for massive matrix and disseminated sulphide ores from three environments within the voisey s bay intrusion the ovoid eastern deeps and discovery hill zone in order to assess the role of crustal contamination in the genesis of this large cu ni co deposit these samples have high re concentrations 148 to 288 ppb in 100 sulphide for their common os concentrations 4 8 to 24 ppb in 100 sulphide yielding high re os ratios 12 to 33 these data confirm that the magma parental to the voisey s bay ore system was broadly basaltic in major element chemistry rather than picritic consistent with the low ni cu ratio of the ores 1 5 re os isotopic data exhibit a limited spread in 187 re 188 os 57 to 157 and define an imprecise 1323 135 ma model 3 isochron likely the result of small r factor variations within the ore system the re os isochron age is within error of 1334 ma u pb ages obtained for baddeleyite from the ore bearing troctolites demonstrating that whole rock re os isotopic systematics have remained closed since crystallisation the initial os isotopic composition of the isochron os 1040 200 implies significant magma interactions with radiogenic os that most likely resides in the nain churchill province crust these data are therefore consistent with the parental magma achieving sulphide saturation as a result of contamination by radiogenic crustal components with further addition of base and precious metals as a function of r factor analyses of sulphide separates from the proterozoic tasiuyak churchill and archaean nain gneisses confirm that both units contained significant os 8 6 ppb and 0 38 ppb respectively that was very radiogenic at 1334 ma os 1908 and 5202 respectively yielding crustal residence tchur model ages of 2200 to 2400 ma however these model ages may have been affected by re and or os mobility during the 1 85 ga torngat and 1 1 ga grenville orogeny re os isotopic modelling suggests that a reasonable fit to the ore data may be obtained via bulk crustal contamination of magmas parental to the nain plutonic suite nps with either tasiuyak 2 contamination or nain 16 contamination gneiss followed by an r factor process 200 to 1000 which improved the tenor of the sulphide liquid during transport in active magma conduits or after deposition in an active replenished voisey s bay intrusion magma chamber however the dominance of plagioclase rich high al2o3 magmas in the mafic members of the nps troctolites and anorthosites may indicate that other deeper forms of lithospheric interaction potentially involving mafic lower crust may be crucial to understanding this style of magmatic sulphide ore system

re os geochronological evidence for multiple paleoproterozoic gold events at the scale of the west african craton the archean proterozoic craton of west africa hosts numerous gold deposits which are spatially and temporally related to the eburnean orogeny that took place between 2250 and 1980 ma and included multiple deformation events the majority of these gold deposits are located along shear zones the structural history is relatively well established for most gold deposits but absolute timing of the mineralization is commonly lacking five deposits hosted in the baoule mossi domain located in the southwestern part of the west african craton were studied to better constrain timing of gold events nassara and kiaka in burkina faso and wassa damang and obuasi in southern ghana gold mineralization was structurally characterized at each deposit and dated by the re os method on pyrite arsenopyrite and pyrrhotite grains that were coeval with the gold deposition combined structural and re os geochronological constraints allow two groups of gold deposits to be distinguished early orogenic gold formed during the eoeburnean orogeny i e between 2190 and 2125 ma as represented by kiaka1 at 2157 24 ma and wassa1 at 2164 14 ma these early gold occurrences are expressed as early disseminated gold enrichment 1 3 g t au at kiaka and gold hosted in folded and boudinaged quartz veins that are transposed along the primary s foliation at wassa these re os ages on the early sulfides at wassa and kiaka are significant because they definitively provide the first direct age constraints on gold only eoeburnean mineralization in the birimian of west africa late orogenic gold hosted by brittle structures and with higher gold grades up to 60g t at kiaka formed during late eburnean deformation d d events between 2120 and 2000 ma as represented by the re os dating of these ores at wassa at 2055 18 ma and obuasi at 2045 40 ma similar style ores dated at nassara at 2131 99 ma and damang at 2080 135 ma but both with large uncertainties and an undated younger event at kiaka are also suggested to be part of this later mineralizing episode the high uncertainties on the nassara and damang ages may be directly linked to the low rhenium and osmium contents of the studied samples these results highlight the polyphase character of the widespread gold mineralization in the west african craton although the late stages of the eburnean orogeny constitute a prolific period for the formation of high grade gold mineralization identification of less well studied early stage gold deposits which can also contain large quantities of gold is critical for mineral exploration in the west african craton

contemporaneous east west extension and north south compression at 43 ma in the himalayan orogen abstract it was previously proposed that the onset of east west extension in the himalayan orogen occurred after ca 19 ma here we present a re os isochron age of ca 43 ma for sulfides from the zhaxikang zn pb sb ag polymetallic deposits which occur within n s striking normal faults that reflect e w extension in the tethyan himalayan orogen this age is consistent with previously reported ages for regional metamorphism ca 48 42 ma granitoids ca 47 40 ma and gabbros ca 45 ma occurring along the indus yarlung suture in addition this type of structure also broadly occurs in the lhasa terrane and plays a critical role in the eocene porphyry skarn copper polymetallic mineralization there by ca 45 43 ma the north south directed horizontal deviatoric stresses had peaked and subducted neo tethyan slab breakoff had occurred at great depth leading to abrupt slowdown of indo asia convergence ca 45 ma e w extension initially developed at shallow depths resulting in formation of the north south trending normal faults in the plateau this type of extension would lead to collapse of the tibetan plateau and decrease in altitude subsequently resulted in central asian and the global climate changes our study places new constraints on the timing and nature of early cenozoic tectonics and metallogenesis in the himalayan orogen and climate changes in central asia

paleolatitude of the hawaiian hot spot since 48 ma evidence for a mid cenozoic true polar stillstand followed by late cenozoic true polar wander coincident with northern hemisphere glaciation

perturbations of the earth s rotation and their implications for the present day mass balance of both polar ice caps summary the present day perturbations of the earth s rotation are sensitive to the glacial isostatic adjustment gia arising from the late pleistocene glacial cycles and also to the recent mass balance of polar ice caps in this study we evaluate the polar wander and the change of degreetwo harmonic of the earth s geopotential j 2 proportional to the rotation rate for four late pleistocene ice models we examine these perturbations as a function of lower and uppermantle viscosities and lithospheric thickness and rheology elastic or viscoelastic in which a compressible earth model with elasticity and density given by the seismological model prem is used by considering the observations and predictions including the gia process arising from the late pleistocene ice and recent mass balance of polar ice caps we discuss the recent mass balance of the antarctic and greenland ice sheets we also examine the effects of internal processes and the melting of mountain glaciers although this work is only preliminary the results shown below seem to be supported even if these effects are included two solutions are obtained for source areas of the recent antarctic melting we denote an equivalent sea level esl rise mm yr 1 from the greenland and antarctic ice sheets as gl and