climate logging with a new rapid optical technique at siple dome the dust logger design is based on a decade of experience in the use of light sources to measure optical properties of deep antarctic ice light is emitted at the top of the instrument by side directed leds scattered or absorbed by dust in the ice surrounding the borehole and collected in a downhole pointing photomultiplier tube pmt a meter below with this method the ice is sampled at ambient pressure in a much larger volume than is the case in a core study and the entire length can be logged in one day in ice in which scattering is dominated by bubbles the absorption from dust impurities is perceived as a drop in signal whereas in bubble free ice the scattering from dust increases the light collected we report on results obtained in siple dome hole a in december 2000 the instrument measured increases in dust concentration extending over many meters during glacial maxima as well as narrow spikes due to 1 cm thick ash and dust bands of volcanic origin monte carlo simulation is employed to clarify data analysis and predict the capabilities of future designs

geochronology and geochemistry of late archean adakitic plutons from the taishan granite greenstone terrain implications for tectonic evolution of the eastern north china craton abstract three groups of coeval plutonic rocks with different petrogenetic histories and geochemical features have been recognized in the late archean taishan granite greenstone terrain tsgt in the eastern block of the north china craton zircon u pb dating indicate that they were emplaced contemporaneously at around 2 54 ga geochemically all of the three groups have high al 2 o 3 and sr concentrations low y and yb concentrations and high sr y and la yb ratios they have high sio 2 concentrations ranging from 57 56 to 67 98 wt indicating that they are typical high sio 2 adakites granodiorites from the taishan area and monzodiorites from the zoucheng area have similar geochemistries however the zoucheng monzodiorites have wider ranges in element concentrations than the taishan granodiorites with the latter having higher mg numbers the yishui monzodiorites have higher mgo cr and ni concentrations higher mg numbers and lower sio 2 concentrations but similar ree and spidergram patterns to the zouchang and taishan intruisions these geochemical features indicate that their parental magmas were all derived from the partial melting of a downgoing oceanic slab the zoucheng high sio 2 adakitic rocks were probably produced by this process alone however the taishan and yishui high si adakite groups were formed by interaction between primary adakitic melts and overlying peridotitic mantle in combination with coeval sanukitoid or low sio 2 adakitic magmatism in the study area the rock association indicates partial melting of a peridotitic mantle wedge that was metasomatized by adakitic melts and aqueous fluids derived from the subducting slab the presence of these three high sio 2 adakite groups supports a genetic model involving slab subduction in the late archean 2 54 ga the adakitic intrusions and associated rocks in the region postdate the earlier 2 7 2 6 ga voluminous ttg rocks suggesting that the angle of subduction changed from flat or shallow subduction to steeper subduction likely related to the arrival of an oceanic plateau or thickened lithospheric keel at the subduction zone

contribution of mantle plumes crustal thickening and greenstone blanketing to the 2 75 2 65ga global crisis abstract assuming that the period 2 75 2 65 ga corresponds to a single but global geodynamic event we investigate through numerical experiments the mechanisms that could have led to the profound continental reworking that occurred at that time although the extent of the crisis at the earth s surface pledges in favour of the involvement of mantle plumes our numerical experiments suggest that the thermal impact of mantle plumes is unlikely to explain both the amplitude and timing of the thermal anomaly as observed in the superior province canada and the yilgarn craton australia similarly moderate crustal thickening can not lead to significant reworking of the continental crust within the observed time constraint crustal thickening with a factor 1 5 is also unlikely because it is not consistent with the moderate metamorphic grade observed at the surface of many archaean cratons burial of a radiogenic crust under a 10 km thick greenstone cover also falls short of explaining not so much the amplitude and the extent but the timing of the thermal anomaly in contrast the combination of the thermal anomaly related to the greenstone blanketing effect with the heat transfer from a plume head spreading at the top of the thermal boundary layer can adequately explain the amplitude the timing and the extent of the 2 75 2 65 ga crisis our favoured model involves a global rearrangement of convection cells in the deep mantle and formation of multiple mantle plumes the greenstones emplaced at the surface and the plumes that spread in the thermal boundary layer contributed to heat the crust from both above and below this produced massive crustal partial melting that reached its climax ca 40 myr after the emplacement of the plumes and associated greenstone cover rocks this led to gravitational instabilities in the crust as dense greenstone cover rocks began to sink into the thermally softened crust and granite domes rose in response the extraction of heat producing elements toward the upper part of the crust has contributed to the cooling and stabilisation of the cratons this succession of events which is not incompatible with plate tectonic processes may have profoundly changed the nature of the crust exposed at the surface and could explain the contrasting geochemical signatures of archaean and post archaean shales

late archean sm nd isochron age for mafic ultramafic supracrustal amphibolites from the northeastern sino korean craton china isotopic data published by previous workers document the presence of early archean 3 5 ga metabasaltic enclaves in grey gneisses west of bohai bay eastern hebei province p r c metabasaltic and metakomatiitic amphibolites crop out as lower supracrustal members of the archean section northeast of bohai bay in southern jilin eastern liaoning provinces six analyzed specimens of the latter unit contain more magnesium on analysis averaging approximately 13 vs 7 wt percent mgo but although they exhibit a wider range of ree concentrations they average a similar range of ree abundance patterns la lu 24 7x chondrite as the former 24 9 chondrite new sm nd isotopic and ree analyses combined with available petrologic geologic information indicate that metakomatiitic amphibolites from the sino korean craton northeast of bohai bay are late archean in emplacement age a wholerock sm nd isochron age of 2660 75 2 ma was obtained with nd t 4 4 0 5 as in many parts of the sino korean craton the highly positive nd t value suggests a prior extended history 1 0 ga of depletion of subcontinental mantle sources in some incompatible elements and in lree relative to hree a seventh analyzed sample a mafic inclusion in tonalitic gneiss of unknown age has an unusual chemical composition with strong enrichment in lree sr and zr and severe depletion in ni and cr judging from isotopic data which yield a much younger depleted mantle model age of 1 67 ga it could represent a cognate xenolith in a mid proterozoic tonalitic intrusion shown on present maps as archean in age the protolith might have been an evolved alkali basalt

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

shrimp u pb zircon ages of granitoid rocks in the luliang complex implications for the accretion and evolution of the trans north china orogen abstract the luliang complex is situated in the central segment of the trans north china orogen tnco a continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the basement of the north china craton the complex consists of supracrustal and granitoid rocks of which the latter can be subdivided into pre tectonic ttg gneisses including the yunzhongshan guojiazhuang and chijianling guandishan gneisses syn tectonic gneissic granites represented by the huijiazhuang gneissic granite and post tectonic granites including the luyashan charnockite luchaogou porphyritic granite and tangershang guandishan massive granite the pre tectonic ttg gneisses are mostly calc alkaline and considered to have formed in a magmatic arc environment shrimp u pb analyses reveal that the yunzhongshan gneisses were emplaced at 2499 9 ma representing the earliest arc related magmatic event in the luliang complex this was followed by the intrusion of the guojiazhuang gneisses at 2375 10 ma the most widespread arc related magmatic event in the region was the emplacement of the chijianling guandishan granitoid gneisses of which the tonalitic granodioritic and monzogranitic gneisses were emplaced at 2199 11 ma 2180 7 ma and 2173 7 ma respectively metamorphic zircon overgrowth rims from a tonalitic gneiss yielded a weighted mean 207 pb 206 pb age of 1872 7 ma consistent with the metamorphic age range of 1880 1820 ma defined by metamorphic zircons from various high grade rocks in the tnco thus the evolution of the luliang complex involved emplacement of the yunzhongshan granitoids at 2499 ma the guajiazhuang granitoids at 2375 ma and the chijianling guandishan granitoids at 2199 2173 ma with the final collision between the eastern and western blocks in this area occurring at 1872 7 ma the whole series of magmatic events lasting nearly 650 ma this suggests that the trans north china orogen represents a long lived magmatic arc the new shrimp zircon data combined with structural and petrological studies also reveal the existence of both syn and post collisional granites in the luliang complex the former is represented by the huijiazhuang gneissic granite that was emplaced at 1832 11 ma whereas the latter include the 1815 5 ma luyashan charnockite 1807 10 ma luchaogou porphyritic granite 1798 11 ma guandishan massive granite and 1790 14 ma tangershan massive granite

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

a field investigation of source parameters for the sledgehammer we examined amplitude and frequency changes in shallow seismic reflection data associated with simple source parameter modifications for the sledgehammer seismic data acquired at three sites with different near surface geology show the potential effects of varying the hammer mass the hammer velocity the plate mass and the plate area at these study sites seismic amplitudes depend on plate surface area and on hammer mass but not heavily on hammer velocity or plate mass furthermore although the total bandwidth of the recorded data was independent of source parameter changes the peak frequency at one site was increased approximately 40 hz by increasing the area of the plate the results indicate that the effects of modifying the source parameters for the sledgehammer are site dependent the experiments described are quick cheap and simple and can be duplicated by others at prospective sites to answer site specific questions

nd isotopic constraints on crustal formation in the north china craton abstract recent tectonic analysis suggests that the north china craton consists of two archean continental blocks called the eastern and western blocks separated by the paleoproterozoic trans north china orogen although the published geochronological data are not sufficient to constrain the detailed tectonothermal evolution of the craton the available nd isotopic data show some important differences in nd model ages between the tectonic units the eastern block shows two main nd model age peaks one between 3 6 and 3 2 ga and the other between 3 0 and 2 6 ga limited nd isotopic data from the western block show a large range of model ages between 3 2 and 2 4 ga these differences are consistent with the recently proposed model the nd isotopic data from mantle derived mafic rocks indicate that the mantle beneath the north china craton was depleted in the archean consistent with major crustal growth during this period in the paleoproterozoic however the mantle derived mafic rocks show negative end t values implying crustal contamination this may have resulted from subduction and collision between the eastern and western block implying that the mechanisms of crustal formation and evolution may have been different between the archean and paleoproterozoic the north china craton was re activated by addition of mantle derived magma into the lower crust in the late mesozoic resulting in rejuvenation of the lower crust this indicates that underplating is also an important mechanism for continental addition although in this case it may not equate to crustal growth since it was preceded by removal of lithospheric mantle and possible some lower crust

strain rate enhancement at dye 3 greenland ice at depth in ice sheets can be softer in bed parallel shear than glen s flow law predicts for example at dye 3 greenland enhancement factors of 3 4 are needed in order to explain the rate of borehole tilting previous authors have identified crystal fabric as the dominant contributor but the role of impurities and crystal size is still incompletely resolved here we use two formulations of anisotropic flow laws for ice azuma s and sachs models to account for the effects of anisotropy and show that the measured anisotropy of the ice at dye 3 cannot explain all the detailed variations in the measured strain rates the jump in enhancement across the holocene wisconsin boundary is larger than expected from the measured fabrics alone dust and soluble ion concentration divided by crystal size correlates well with the residual enhancement indicating that most of the excess deformation may be due to impurities or crystal size while the major features of the deformation at dye 3 are explained by anisotropy and temperature results also suggest that further research into the role of impurities and crystal size is warranted

short and long term variations in the reykjanes geothermal reservoir from seismic noise interferometry the reykjanes geothermal system rgs is a high temperature geothermal system located on the reykjanes peninsula a transtensional plate boundary zone located on the southwestern tip of iceland the area is characterized by high seismicity recent volcanism and high temperature geothermal fields we use seismic noise records from april 2014 to august 2015 to study stress changes and potential deformation of the subsurface caused by injection and production operations at rgs through seismic interferometry we retrieve continuous time series of waveform similarity values and seismic velocity changes during this period the s transform of the similarity values allows us to clearly identify three variations in the mechanical properties of the reykjanes peninsula related to rapid changes of rgs production in addition we observe a slow seismic velocity decrease of 0 36 year in the reservoir due to the water deficit and seasonal variations associated with the energy production demand

la icp ms u pb geochronology of detrital zircons from the jining complex north china craton and its tectonic significance abstract la icp ms u pb zircon dating and cathodoluminescene cl image analysis were carried out to determine the protolith and metamorphic ages of high grade al rich gneisses named as khondalites from the jining complex of the north china craton ncc the analytical results of more than 200 detrital zircon grains from the khondalites show three main age populations 2060 ma 1940 ma and 1890 ma these data indicate that the provenance of the jining khondalites is paleoproterozoic in age but not archean as previously suggested and the sediments were derived from a provenance different from the eastern block and the yinshan terrane of the ncc the nearly concordant youngest age of 1842 16 ma 207pb 206pb age for the detrital zircons is interpreted as the maximum depositional age of the khondalites overgrowth rims of detrital zircons yield an age of 1811 23 ma which we interpret as the metamorphic age the new age data are consistent with the recent three fold tectonic subdivision of the ncc and support that the eastern and western blocks collided at 1 8 ga to form the coherent ncc

monitoring stress changes in a concrete bridge with coda wave interferometry coda wave interferometry is a recent analysis method now widely used in seismology it uses the increased sensitivity of multiply scattered elastic waves with long travel times for monitoring weak changes in a medium while its application for structural monitoring has been shown to work under laboratory conditions the usability on a real structure with known material changes had yet to be proven this article presents experiments on a concrete bridge during construction the results show that small velocity perturbations induced by a changing stress state in the structure can be determined even under adverse conditions theoretical estimations based on the stress calculations by the structural engineers are in good agreement with the measured velocity variations

borehole optical stratigraphy and neutron scattering density measurements at summit greenland we have made side by side measurements in several boreholes at summit greenland using borehole optical stratigraphy bos and neutron scattering density logging techniques the bos logs show strong positive correlation at shallow depths with neutron scattering logs taken in the same borehole this supports the hypothesis that bos detects changes in density the positive correlation between returned brightness and density decreases with depth and finally becomes negative we conclude this inversion of correlation is related to changes in densification regime from grain boundary sliding to pressure sintering

a morb arc basalt adakite association in the 2 5 ga wutai greenstone belt late archean magmatism and crustal growth in the north china craton abstract the wutai fuping and hengshan complexes form part of a major 2 5 ga late archean arc system in the northern part of the north china craton the wutai complex is a well preserved greenstone belt dominated by mafic intermediate and felsic volcanic rocks with a mid ocean ridge basalt morb arc back arc basalt adakite association multi element plots for morb type mafic volcanic rocks are characterised by depletion of th nb ta and la nearly flat or lree depleted ree patterns and nb u and nb th ratios greater than primitive mantle values back arc basin basalt babb type rocks have nearly flat trace element patterns with nb ti and y troughs and lree depleted or near flat ree patterns island arc basalt iab type rocks are characterized by negative anomalies of nb ta zr hf ti and y and by lree enrichment the felsic volcanic rocks conform to most compositional criteria for cenozoic adakites including low y and yb high la smn la yb and zr sm ratios and similar trace element and ree patterns trends defined by the association are consistent with magma mixing between morb like melts and subduction slab related melts intra oceanic subduction coupled with contemporary morb type mantle upwelling related to back arc basin extension can account for the interaction between the two components subduction accretion or back arc basin collapse led to accretion of the wutai intra oceanic arc back arc complexes with the magmatic arcs of the fuping and hengshan terranes that are dominated by high grade tonalite trondhjemite granodiorite ttg gneisses this geodynamic interpretation is different from many tectonic models for archean greenstone belts in which magmatism and crustal growth were dominated by mantle plumes or interaction between subduction zones and mantle plumes the final disposition of the arc complexes was controlled by the collision of the eastern and western blocks of the north china craton during the paleoproterozoic resulting in extensive tectonic interleaving within a major orogenic belt that extended throughout the central portion of the north china craton

geochemistry of adakites from neoarchaean active continental margin of shimoga schist belt western dharwar craton india implications for the genesis of ttg abstract adakites are identified for the first time from a neoarchaean active continental margin acm preserved in the eastern part of the shimoga schist belt near ranibennur western dharwar craton india these adakites consists mainly of quartz plagioclase and minor amphiboles and are interlayered with the turbidites they exhibit typical adakitic low y 8 35 14 70 ppm and yb 0 85 1 47 ppm may be classified as high sio2 and low mg ni and cr type adakites other constituents such as na2o k2o nb zr lree and hree and their ratios such as na2o k2o zr sm nb la la yb n gd yb n and th u also closely resemble with the high silica adakites hsa of martin et al martin h smithies r h rapp r moyen j f champion d 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 24 sr y values are moderate generally lower than the high sr low silica cenozoic adakites but within the range of archaean adakites the negative nb ta and ti anomalies characteristic of cenozoic adakites are found in ranibennur adakites also zr zr and hf hf ratios are also similar to hsa these adakites further depict compositional similarities with meso and neoarchaean tonalite trondhjemite granodiorites ttgs such types of adakites have been experimentally generated by the partial melting of hydrous basalts that are similar to adakitic glass veins low mgo cao cr and ni found in peridotite xenoliths of kamchatka arc xiong x l xia b xu j f niu h c xiao w s 2006 na depletion in modern adakites via melt rock reaction within the sub arc mantle chem geol 229 273 292 since archaean had higher geothermal regime subduction of the basaltic slab was most probably shallow and significant mantle wedge was not available to react with adakitic melt hence archaean adakites in general and particularly from ranibennur are relatively depleted in the peridotiitic mantle wedge components their identification from an archaean acm and their compositional similarities with the paleo meso archaean ttgs suggest the possibility of identical origin i e the melting of a shallow hydrous basaltic slab this mechanism during archaean was widespread and rapid resulted in faster continental crustal growth during the early history of the earth identification of archaean adakites in association with island arc turbidites from a greenstone belt sequence supports the rapid subduction mechanism for the crustal growth that coincides with 2 7 ga peak episode of almost all geological processes

time lapse monitoring of rock properties with coda wave interferometry 1 the coda of seismic waves consists of that part of the signal after the directly arriving phases in a finite medium or in one that is strongly heterogeneous the coda is dominated by waves which have repeatedly sampled the medium small changes in a medium which may have no detectable influence on the first arrivals are amplified by this repeated sampling and may thus be detectable in the coda we refer to this use of multiple sampling coda waveforms as coda wave interferometry we have exploited ultrasonic coda waves to monitor time varying rock properties in a laboratory environment we have studied the dependence of velocity on uniaxial stress in berea sandstone the temperature dependence of velocity in granite and in aluminum and the change in velocity due to an increase of water saturation in sandstone there are many other possible applications of coda wave interferometry in geophysics including dam and volcano monitoring time lapse reservoir characterization earthquake relocation and stress monitoring in mining and rock physics

nonlinear elasticity and stress induced anisotropy in rock the elastic nonlinear behavior of rocks as evidenced by deviations from hooke s law in stress strain measurements and attributable to the presence of mechanical defects compliant features such as cracks microfractures grain joints is a well established observation the purpose of this paper is to make the connection between the elastic nonlinearity and stress induced effects on waves in this case uniaxial stress induced transverse isotropy the linear and nonlinear elastic coefficients constitute the most condensed manner in which to characterize the elastic behavior of the rock we present both the second and the third order nonlinear elastic constants obtained from experimental data on rock samples assumed homogeneous and isotropic when unstressed as is normally the case the third order nonlinear constants are found to be much larger than the second order linear elastic constants contrary to results from intact homogeneous solids materials without mechanical defects rocks exhibit weak to strong nonlinearity and always in the same manner i e an increase of the moduli with pressure as a consequence the stress induced p wave anisotropy and s wave birefringence can be large the stress induced p wave anisotropy appears to be much larger than the s wave birefringence the fast direction is parallel to the stress direction and the anisotropy goes as sin2 being the angle between the propagation direction and the stress direction experiments on rocks indicate that at low applied stresses the proportionality of the stress and the induced s birefringence and p anisotropy predicted by theory is well corroborated

holocene tephras highlight complexity of volcanic signals in greenland ice cores 1 acidity peaks in greenland ice cores have been used as critical reference horizons for synchronizing ice core records aiding the construction of a single greenland ice core chronology gicc05 for the holocene guided by gicc05 we examined sub sections of three greenland cores in the search for tephra from specific eruptions that might facilitate the linkage of ice core records the dating of prehistoric tephras and the understanding of the eruptions here we report the identification of 14 horizons with tephra particles including 11 that have not previously been reported from the north atlantic region and that have the potential to be valuable isochrons the positions of tephras whose major element data are consistent with ash from the katmai ad 1912 and oraefajokull ad 1362 eruptions confirm the annually resolved ice core chronology for the last 700 years we provide a more refined date for the so called ad860b tephra a widespread isochron found across nw europe and present new evidence relating to the 17th century bc thera aniakchak debate that shows n american eruptions likely contributed to the acid signals at this time our results emphasize the variable spatial and temporal distributions of volcanic products in greenland ice that call for a more cautious approach in the attribution of acid signals to specific eruptive events

deformation properties of subfreezing glacier ice role of crystal size chemical impurities and rock particles inferred from in situ measurements to improve understanding of the deformation properties of subfreezing polycrystalline glacier ice and in particular the role of crystal size chemical impurities and rock particle impurities we analyze in situ strain rates of the basal layers of meserve glacier antarctica strain rates were monitored on the walls of a subglacial tunnel where down flow shear stress is relatively uniform and ice properties were measured texture fabric and impurity content we propose a simple empirical model describing strain rate variations due to variations in crystal size and impurity content and we use all relevant meserve data to constrain model parameters we conclude that there is a direct dependence of strain rate on crystal size which reflects an important role for a grain size sensitive deformation mechanism such as grain boundary sliding or diffusion chemical impurities are found to enhance the grain size sensitive deformation and are found to be an important control on strain rate variations in the very impure ices of meserve glacier however the per molar sensitivity of strain rate to chemical impurity content is shown to be very low such that in the ice age ices of the greenland ice sheet there is probably an immeasurable contribution of chemical impurities to strain rate enhancement though we cannot exclude chemical enhancements as high as 1 3 there our analyses detect no direct rheologic effect of rock particles in the meserve ices which suggests that rock content is not directly responsible for the low viscosity of dirty basal layers

th u pb monazite geochronology of the luliang and wutai complexes constraints on the tectonothermal evolution of the trans north china orogen abstract recent lithological metamorphic and geochronological studies show that the basement of the north china craton ncc formed by collision of two discrete archean to paleoproterozoic blocks eastern and western blocks along a paleoproterozoic orogen named the trans north china orogen however the timing of the collision is controversial and post collisional exhumation has not been precisely dated this study applies the electron microprobe th u pb monazite dating technique to determine the ages of the peak metamorphic event and subsequent exhumation of the low to medium grade luliang and wutai complexes in the trans north china orogen electron microprobe th u pb monazite data for the luliang complex reveal five tho 2 pbo age ranges 1 1940 1938 ma 2 1880 1847 ma 3 1795 1755 ma 4 1720 1703 ma and 5 1648 ma of these age ranges the first four have also been recorded in the wutai complex which yields tho 2 pbo ages of 1 1930 ma 2 1838 1822 ma 3 1793 ma and 4 1719 ma the oldest age range of 1940 1930 ma is interpreted to record the widespread emplacement of mafic dikes in rocks of the luliang and wutai complexes the age range of 1882 1822 ma is in accord with the shrimp u pb ages of metamorphic zircons and mineral sm nd and 40 ar 39 ar ages obtained for other complexes in the orogen and is interpreted as the age of the major metamorphic event caused by amalgamation between the eastern and the western blocks the age range of 1795 1755 ma is consistent with emplacement of large scale unmetamorphosed mafic swarms at 1800 1765 ma interpreted as the time of post orogenic extension the 1720 1703 ma and 1648 ma ages are considered to date later multiple stages of hydrothermal alteration since monazites with such young ages only occur along fractures in older monazite grains and at the rims these new monazite tho 2 pbo ages support the tectonic model for the evolution of the north china craton that envisages discrete eastern and western blocks colliding along the trans north china orogen at 1 85 ga and then undergoing post collisional extension in the period 1795 1755 ma

coda wave interferometry for estimating nonlinear behavior in seismic velocity in coda wave interferometry one records multiply scattered waves at a limited number of receivers to infer changes in the medium over time with this technique we have determined the nonlinear dependence of the seismic velocity in granite on temperature and the associated acoustic emissions this technique can be used in warning mode to detect the presence of temporal changes in the medium or in diagnostic mode where the temporal change in the medium is quantified

la icp ms u pb zircon ages of the liaohe group in the eastern block of the north china craton constraints on the evolution of the jiao liao ji belt abstract as a major lithostratigraphic unit of the palaeoproterozoic jiao liao ji belt in the eastern block of the north china craton the liaohe group consists of an assemblage that is transitional from a lower arkose and volcanic rich sequence langzishan li eryu and gaojiayu formations through a middle carbonate rich sequence dashiqiao formation to an upper argillaceous sequence gaixian formation tectonically associated with the liaohe group are large volumes of granitoid rocks named the liaoji granite whose emplacement age has been dated at about 2 1 2 2 ga regionally the liaohe group and the associated liaoji granite extend along a nee trending belt that is flanked by 2 45 2 55 ga basement gneisses u pb zircon data and cathodoluminescence cl imaging are used to constrain the maximum depositional and metamorphic ages of the liaohe group which are critical in understanding the tectonic setting and history of the jiao liao ji belt cathodoluminescence images reveal that most detrital zircon grains from the liaohe group are characterized by concentric oscillatory zoning with comparatively low luminescence and high th u ratios suggesting magmatic origin but minor zircon grains have structureless overgrowth or recrystallization rims that are characterized by low th u ratio indicating metamorphic origin results of this study show that the detrital zircon grains of the langzishan formation the lowest sequence of the liaohe group have concordant u pb ages ranging from 2 05 to 2 24 ga suggesting that the liaohe group was deposited at some time after 2 05 ga although most overgrowth or recrystallization rims are too narrow to be analyzed some rims yield concordant or upper intercept ages around 1 93 ga interpreted as the peak metamorphic age of the liaohe group detrital zircon grains from the dashiqiao formation in the middle sequence of the liaohe group have concordant u pb ages ranging from 2 25 to 2 53 ga some of which are similar to those of the basement gneisses in the area this study indicates that the liaohe group was deposited after the emplacement of the liaoji granite and the latter may be a major component of the provenance for the langzishan formation in contrast the protoliths of the middle sequence of the liaohe group were most probably derived from the basement gneisses these new zircon ages for the liaohe group and recent data for the liaoji granite combined with lithological structural and metamorphic considerations support a rifting model for the evolution of the jiao liao ji belt

subduction related origin of the 750 ma xuelongbao adakitic complex sichuan province china implications for the tectonic setting of the giant neoproterozoic magmatic event in south china abstract the xuelongbao plutonic complex in the eastern margin of the tibetan plateau is dated at 748 7 ma using the shrimp zircon u pb method and represents part of the neoproterozoic igneous assemblage of south china rocks in the complex include tonalite and granodiorite and have sio2 ranging from 62 0 to 74 8 wt and al2o3 from 14 3 to 20 9 wt their na2o contents range from 4 2 to 6 7 wt and k2o from 0 47 to 1 96 wt indicating that they belong to the na series these rocks show chondrite normalized ree patterns depleted in hree and variably enriched in lree they have positive sr and negative nb and ti anomalies in the primitive mantle normalized trace elemental spider diagram their sr contents range from 320 to 780 ppm and y contents are lower than 10 ppm resulting in high sr y ratios 52 320 characteristic of typical adakites their end t and initial sr isotopic compositions range from 0 36 to 2 88 and from 0 7033 to 0 7054 respectively the geochemical features of the xuelongbao plutonic complex are consistent with an origin from adakitic magmas that were likely derived from partial melting of a subducted oceanic slab together with arc signatures of other granites and mafic intrusions in the region the 750 ma xuelongbao adakitic complex provides evidence for a major subduction related neoproterozoic magmatic event of south china

shrimp u pb zircon geochronology of the liaoji granitoids constraints on the evolution of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton abstract the paleoproterozoic jiao liao ji belt lies at the eastern margin of the eastern block of the north china craton and is composed mainly of the liaohe group and the liaoji granitoids the liaoji granitoids are divisible into pre tectonic magnetite and hornblende biotite monzogranitic gneisses and post tectonic or anorogenic porphyritic monzogranites and alkaline syenites shrimp u pb zircon geochronology combined with cathodoluminescence cl imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the history of the paleoproterozoic jiao liao ji belt shrimp u pb zircon analyses reveal that the pre tectonic magnetite monzogranitic gneisses were emplaced in the period 2176 2166 ma and metamorphosed at 1914 ma and the pre tectonic hornblende biotite monzogranitic gneisses were emplaced at 2150 2143 ma these data demonstrate that the pre tectonic monzogranitic gneisses of the liaoji granitoids were not younger than the deposition of the liaohe group as previously considered since the latter contains a large amount of 2100 2000 ma detrital zircons in contrast the pre tectonic monzogranitic gneisses of the liaoji granitoids or similar aged granitoids may have been an important component of the provenance for the liaohe group shrimp u pb zircon analyses also reveal that the post tectonic porphyritic monzogranites and granites in the jiao liao ji belt were emplaced at 1875 10 and 1856 31 ma respectively simultaneously with the emplacement of the alkaline syenites that was dated at 1857 20 and 1843 23 ma similar post tecotnic or anorogenic granites are not only limited to the jiao liao ji belt but are also found in the north and south korea suggesting that the 1 85 ga post tectonic or anorogenic granitic magmatic event may have occurred in both the korean peninsula and the eastern block of the north china craton the shrimp zircon ages of this study combined with lithological structural metamorphic and geochemical data is consistent with a rift closure model which suggests that the archean complexes on the northern and southern sides of the jiao liao ji belt were originally situated on a single continental block that underwent paleoproterozoic rifting associated with the formation of the liaohe group and liaoji granitoids and closed upon itself at 1 9 ga

ree geochemistry and isotopic data of archean silicic volcanics and granitoids from the pilbara block western australia implications for the early crustal evolution eighteen silicic volcanic rocks of the warrawoona group and ten associated plutonic rocks from the pilbara block western australia have been chosen for geochemical and isotopic studies silicic volcanics of the unsb upper member of north star basalt are dated at 3 56 3 57 by both the rb sr and the sm nd methods the respective 1 initial isotopic composition values are 0 7005 5 sr and 0 50810 39 nd this age is consistent with the stratigraphic interpretation that the talgatalga subgroup in which the north star basalt occupies the lowermost position is overlain by the duffer formation whose age was earlier established at 3 45 by the zircon u pb method the new rb sr data on six silicic lava samples from the duffer formation yield an isochron of 3 23 0 28 2v though imprecise this age agrees with the zircon age within error limits rb sr ages of 2 3 2 4 obtained for the panorama rocks and the wyman formation do not correspond to their initial eruption ages chemical arguments suggest that these ages represent the time of metasomatism associated with the widespread thermal event in this region about 2 3 2 4 ago geochemically most of these analyzed rocks volcanic and plutonic are of tonalite trondhjemitegranodiorite ttg composition a typical feature found in many other archean terrains they generally show fractionated ree patterns except the panorama formation rocks furthermore the wyman formation rhyolites and the post tectonic adamellites show significant negative eu anomalies suggesting a similar mode of magma generation and a probable genetic link theoretical considerations suggest that most of these ttg rocks could have been generated by partial melting of amphibolitic or basaltic sources followed by fractional crystallization although the archean granitic gneisses often possess mantle like isr values the trace element data indicate that they could not have been derived by direct melting of upper mantle materials the immediate tectonic implication is that in any archean terrain the formation of na rich continental crust of ttg suite must be preceded by the presence of basaltic crust the occurrence of this basaltic crust is a matter of controversy such crust might have been totally destroyed by repeated melting processes or its remnants are now represented by some of the mafic ultramafic enclaves within the tonalite trondhjemite batholiths

tectonothermal history of the basement rocks in the western zone of the north china craton and its tectonic implications the basement of the north china craton can be divided into the eastern central and western zones based on lithological structural metamorphic and geochronological data the western zone comprises two different petrotectonic units archaean tonalitic trondhjemitic granodioritic ttg grey gneisses and metamorphic mafic rocks and palaeoproterozoic khondalite series the former is characterized by isobaric cooling ibc type anticlockwise p t paths in the north northwestern part of the zone and near isothermal decompression itd type clockwise p t paths in the eastern part adjacent to the central zone on the other hand the tectonothermal evolution of palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling defining clockwise p t paths the archaean ttg gneisses and associated mafic rocks with anticlockwise metamorphic p t paths reflects an origin related to underplating and intrusion of mantle derived magmas which may be derived from mantle plumes they represent a late archaean continental block in the western part of the north china craton the palaeoproterozoic khondalite series rocks represent passive continental margin deposits they were metamorphosed and deformed in the late palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the north china craton the itd type clockwise p t t paths of the palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the north china craton at c 1800 ma

physical properties crystalline textures and c axis fabrics of the siple dome antarctica ice core the quality of the ice core from siple dome west antarctica varied widely with significant fracturing below 400 m bubbly ice persisted to the ice rock interface at 1004 m and constituted the brittle zone the core has undergone minimal relaxation and has remained brittle and prone to fracturing more than 5 years after it was drilled this behavior is attributed to unrelieved stresses from kamb and bindschadler ice streams former ice streams c and d flanking the dome melt layers were identified sporadically throughout the core as were inclined layers tilted at angles that occasionally exceeded 10 structurally the ice was characterized by extensive recrystallization including grain size changes from 0 074 cm 2 at 59 m to 50 cm 2 at 992 m and major transitions in c axis fabrics unusual fabrics included vertical c axis clusters superimposed on vertical girdles that may reflect vertical compression acting in conjunction with horizontal tension the sudden appearance of a shear type fabric at 700 800 m appears closely linked to the occurrence of abundant tephra particles embedded in the ice the occurrence of dispersed sediment in the bottom 2 m is attributed to freeze on of basal meltwater

dating the siple dome antarctica ice core by manual and computer interpretation of annual layering the holocene portion of the siple dome antarctica ice core was dated by interpreting the electrical visual and chemical properties of the core the data were interpreted manuallyandwith acomputeralgorithm the algorithm interpretation was adjusted to be consistent with atmospheric methane stratigraphic ties to the gisp2 greenland ice sheet project 2 ice core 10 be stratigraphic ties to the dendrochronology 14 c recordandthedatedvolcanic stratigraphy thealgorithm interpretation ismorecon sistent andbetter quantifiedthanthe tedious and subjective manual interpretation

a late archean foreland fold and thrust belt in the north china craton implications for early collisional tectonics abstract the archean north china craton is divided into the western and eastern blocks along the central orogenic belt a 1600 km long archean foreland basin and thrust belt fringes the eastern side of the central orogenic belt rocks in the orogen form tectonically stacked east vergent fold and thrust sheets including foreland basin sediments 2 50 ga ophiolitic melange and an island arc complex foreland basin sediments overlie a passive margin sequence and include a 2 50 ga deep water turbidite sequence that grades upward and westward into shallow water molasse now disposed in structurally imbricated east verging thrusts and asymmetric folds that gradually migrated craton ward with deformation uplift and erosion of the orogen there is a strong linked relationship of the formation of the foreland basin to collision of the east and west blocks of the north china craton along the central orogenic belt at 2 50 ga the qinglong foreland basin and central orogenic belt of the north china craton represents one of the best preserved archean orogen to craton transitions in the world its classic internal to external zonation and flexural response to loading demonstrate that convergent tectonics in the archean were broadly similar to phanerozoic convergent margin processes

timing of metamorphism in the paleoproterozoic jiao liao ji belt new shrimp u pb zircon dating of granulites gneisses and marbles of the jiaobei massif in the north china craton abstract the paleoproterozoic jiao liao ji belt lies in the eastern block of the north china craton with its southern segment extending across the bohai sea into the jiaobei massif high pressure pelitic and mafic granulites have been recently recognized in the paleoproterozoic jingshan group jiaobei massif new shrimp u th pb geochronology combined with cathodoluminescence cl imaging of zircon has been applied to the determination of the timing of the metamorphism of the high temperature and high pressure granulites and associated gneisses and marbles metamorphic zircons in these high pressure granulites gneisses and marbles occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores metamorphic zircons are all characterized by nebulous zoning or being structureless with high luminescence and relatively low th u values metamorphic zircons from two high pressure mafic granulites yielded 207pb 206pb ages of 1956 41 ma and 1884 24 ma one metamorphic zircon from a garnet sillimanite gneiss also gave an apparent 207pb 206pb age of 1939 15 ma these results are consistent with interval of ages of c 1 93 1 90 ga already obtained by previous studies for the north and south liaohe groups and the laoling group in the northern segment of the jiao liao ji belt metamorphic zircons from a high pressure pelitic granulite and two pelitic gneisses yielded weighted mean 207pb 206pb ages of 1837 8 ma 1821 8 ma and 1836 8 ma respectively two diopside olivine phlogopite marbles yielded weighted mean 207pb 206pb ages of 1817 9 ma and 1790 6 ma these paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of c 1 85 ga produced from the ji an group in the northern segment of the jiao liao ji belt and c 1 86 1 80 ga obtained for the high pressure pelitic granulites from the jingshan group in the southern segment as this metamorphic event was coeval with the emplacement of a type granites in the jiao liao ji belt and its adjacent areas it is interpreted as having resulted from a post orogenic or anorogenic extensional event

single zircon grains record two paleoproterozoic collisional events in the north china craton abstract the western block of the north china craton consists of the yinshan block in the north and the ordos block in the south which were amalgamated along the east west trending khondalite belt at 1 95 ga the western block then collided with the eastern block to form the coherent basement of the north china craton along the north south trending trans north china orogen at 1 85 ga the huaian complex a high grade terrrane located at the conjunction of the khondalite belt and trans north china orogen records metamorphic events associated with both collisions the complex consists of lithologies from both the khondalite belt and trans north china orogen of which the former consist of graphite garnet sillimanite gneiss garnet quartzite felsic paragneiss calc silicate rock and marble together called the khondalite series zircons in the graphite garnet sillimanite gneiss can be divided into three types 1 spherical grains without internal structures 2 grains with a core and rim structure and 3 grains with a dark core surrounded by double rims except for the dark core in type 3 all other types of zircon domains are structureless and highly luminescent with very low th u ratios typical of a metamorphic origin analyses on the cores of type 2 and the inner rims of type 3 from two samples yield upper intercept ages of 1946 26 and 1947 22 ma similar to previously determined metamorphic ages from the khondalite belt and thus interpreted as the time of collision between the yinshan and ordos blocks analyses on type 1 zircons rims of type 2 and the outer rims of type 3 from the same two samples give ages of 1850 15 and 1857 16 ma interpreted as the time of collision between the eastern and western blocks thus zircons in the graphite garnet sillimanite gneiss of the huaian complex record both of the paleoproterozoic collisional events in the north china craton

long wavelength optical logging for high resolution detection of ash layers in glacier ice a new instrument for high resolution optical logging has been built and tested in antarctica its purpose is to obtain records of volcanic products and other scattering features such as bubbles and impurities preserved in polar ice sheets and it achieves this by using long wavelength near infrared light that is absorbed by the ice before many scattering events occur longer wavelengths ensure that the return signal is composed primarily of a single or few backscattering event s that limit its spatial spread the compact optical logger features no components on its body that draw power which minimizes its size and weight a prototype of the logger was built and tested at siple dome a borehole and the results were correlated with prior optical logging profiles and records of volcanic products from collected ice core samples

the relationship between adakitic calc alkaline volcanic rocks and ttgs implications for the tectonic setting of the karelian greenstone belts baltic shield abstract two types of coeval acid intermediate rocks with different petrological geochemical and isotopic features have been discovered among volcanic rocks and surrounding synkinematic tonalite trondhjemite granodiorite ttg plutons of late archaean greenstone belts in the karelian granite greenstone terrane type 1 rocks comprise trondhjemites and sub volcanic occasionally volcanic dacite rhyolite rocks they are characterized by high sr low y and hree contents high sr y ratios and strongly fractionated ree patterns with no significant positive or negative eu anomaly initial nd is positive indicating a generation from juvenile source with little or no contribution of ancient continental crust type 2 is represented by diorite granodiorites and calc alkaline basalt andesite dacite rhyolite badr series as compared to type 1 these rocks differ by their lower sr higher y and hree contents lower sr y ratios and less fractionated hree patterns with negative eu anomalies initial nd varies from negative to positive values thus indicating a variable contribution of sialic crust geochemistry of the two magmatic series suggests their formation in a convergent plate margin setting the type 1 rocks resemble phanerozoic adakites which represent slab derived melts contaminated by overlying mantle wedge the type 2 rocks resemble badr series which were derived from a mantle wedge metasomatized by slab derived fluids and melts with subsequent variable crustal contamination the spatial distribution of these two types of magmatic series defines the asymmetry of the studied granite greenstone structures which presumably reflects the primary lateral zoning of island arc formed under specific thermal conditions in the archaean mantle adakite melts upraised to the surface in the frontal part of the island arc where mantle wedge was thin showing no or little interaction with metasomatized mantle and formed adakite type plutonic and sub volcanic rocks at greater depths adakitic melts and fluids interacted with the overlying mantle wedge and caused its partial melting with generation of calc alkaline badr volcanic rocks and diorite granodiorite plutons in the rear part of the island arc our data suggest that greenstone belt volcano plutonic arcs were initiated on different types of crust which presumably determined the petrogenetic and isotope variations of the studied badr and adakite type island arc complexes

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

u pb and hf isotopic study of zircons of the helanshan complex constrains on the evolution of the khondalite belt in the western block of the north china craton abstract the helanshan complex is located at the westernmost segment of the khondalite belt a continent continent collisional belt along which the yinshan block in the north collided with the ordos block in the south to form the western block of the north china craton the complex consists of s type granites and high grade pelitic granulite gneiss felsic paragneiss quartzite calc silicate rock and marble together called the khondalite series rocks la q icp ms u pb geochronology and la mc icp ms lu hf isotopic data of zircons combined with cathodoluminescence cl imaging enable the resolution of magmatic and metamorphic events that can be directed towards understanding the formation and evolution of the khondalite belt in the western block of the north china craton cl images reveal the coexistence of magmatic type detrital zircons and metamorphic zircons in most of the khondalite series rocks of which the metamorphic zircons occur as either single grains or overgrowth rims surrounding and truncating magmatic type detrital zircon cores la q icp ms u pb analyses on magmatic type detrital zircons reveal two distinct age populations with one in the archaean 2 85 2 53 ga and the other in the palaeoproterozoic 2 2 2 0 ga suggesting that the sedimentary protoliths of the khondalite series rocks in the helanshan complex must have been deposited at some time after 2 0 ga the hf analyses show that the archaean detrital zircons possess negative ehf t values from 7 64 to 0 15 with depleted mantle model ages ranging from 3 34 to 3 10 ga this implies the existence of a paleo mesoarchaean 3 34 3 10 ga crust in the western block which underwent a recycling event in the period 2 85 2 53 ga nearly all palaeoproterozoic 2 2 2 0 ga detrital zircons possess positive ehf t values 0 86 9 38 with depleted mantle model ages of 2 45 2 15 ga suggesting a significant crustal growth event in the western block in the palaeoproterozoic metamorphic zircons yield two groups of age with one at 1 95 ga and the other at 1 87 ga of which the former is considered as the timing of the collision between the yinshan and ordos blocks to form the western block whereas the latter is consistent with the age of 1 86 ga from two s type granites which are considered to have formed by the partial melting of pelitic granulites gneisses at the stage of the exhumation of the helanshan complex

a deep high resolution optical log of dust ash and stratigraphy in south pole glacial ice 1 we describe a new dust logger designed to operate in water filled icecube boreholes in south pole ice and we give examples of its performance we recorded optical effects due to bubbles dust and volcanic ash in situ from 70 to 2100 meters seasonal layering in bubble concentration could also be discerned below 1300 m over the interval 25 ka to 70 ka because of the conversion of all air bubbles to invisible hydrate crystals and the close match between refractive indices of the surrounding ice and the water in the borehole scattering from dust provided fine structure in the depth dependence of concentration with a resolution of 1 cm thin highly absorptive horizons in the data set confirm there is significant fallout at south pole of ash from explosive volcanic events by locating and dating volcanic ash layers in the south pole dust record it may be possible to match them to volcanic layers found across antarctica and in greenland citation bramall n e r c bay k woschnagg r a rohde and p b price 2005 a deep high resolution optical log of dust ash and stratigraphy in south pole glacial ice geophys res lett 32 l21815

use of paleo records in determining variability within the volcanism climate system abstract volcanic eruptions that inject large quantities of sulfur rich gases into the stratosphere have the capability of cooling global climate by 0 2 0 3 c for several years after the eruption equatorial eruptions will impact global climate whereas mid latitude eruptions can cool climate in the hemisphere of origin magnitude of cooling varies by latitude and it is possible for warming to occur in certain regions primarily during the winter although instrumental records have been used to quantify the volcanic impact on climate they are limited in their temporal and spatial coverage and the style and magnitude of eruptions occurring over the two centuries of instrumental records is limited a thorough evaluation of the range of variability in the volcanism climate system requires a multidisciplinary approach that includes the analysis of ice core records geological data atmospheric measurements and visual phenomena tree ring records and other proxy data evaluation of these longer time series indicates that multiple volcanic eruptions have the potential to force climate over decadal to multi decadal time frames especially when these eruptions enhance or extend pre existing cool conditions on the other hand a lack of climatically significant eruptions may result in warmer average temperatures over decadal time frames because the volcanic cooling component within the climate system is absent mega eruptions like the toba eruption of 71 000 73 000 yr ago may impact climate on centennial time frames through positive feedback mechanisms evidence exists which indicates that environmental changes associated with rapid climatic fluctuations such as crustal loading unloading with glaciation deglaciation and variability in glacial meltwater loading on ocean basins may cause an increase in volcanic activity

polar ice stratigraphy from laser light scattering scattering from ice we demonstrate that laser light scattering lls off glacial pre holocene polar ice can be used to measure variations in dust concentration along sections of bubble free ice core we have used this technique with considerable success on the gisp2 ice core that was retrieved from central greenland down to bedrock the technique is fast non destructive and has a very high resolution 1 mm or less

a 12 000 year record of explosive volcanism in the siple dome ice core west antarctica 1 air mass trajectories in the southern hemisphere provide a mechanism for transport to and deposition of volcanic products on the antarctic ice sheet from local volcanoes and from tropical and subtropical volcanic centers this study extends the detailed record of antarctic south american and equatorial volcanism over the last 12 000 years using continuous glaciochemical series developed from the siple dome a sdma ice core west antarctica the largest volcanic sulfate spike 280 g l occurs at 5881 b c e other large signals with unknown sources are observed around 325 b c e 270 g l and 2818 b c e 191 g l ages of several large equatorial or southern hemisphere volcanic eruptions are synchronous with many sulfate peaks detected in the sdma volcanic ice chemistry record the microprobe fingerprinting of glass shards in the sdma core points to the following antarctic volcanic centers as sources of tephra found in the sdma core balenny island pleiades mount berlin mount takahe and mount melbourne as well as mount hudson and possibly mount burney volcanoes of south america identified volcanic sources provide an insight into the poorly resolved transport history of volcanic products from source volcanoes to the west antarctic ice sheet

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

structural monitoring of a highway bridge using passive noise recordings from street traffic structural damage on bridges presents a hazard to public safety and can lead to fatalities this article contributes to the development of an alternative monitoring system for civil structures based on passive measurements of seismic elastic waves cross correlations of traffic noise recorded at geophone receiver pairs were found to be sufficiently stable for comparison and sensitive to velocity changes in the medium as such velocity variations could be caused by damage their detection would be valuable in structural health monitoring systems a method originally introduced for seismological applications and named passive image interferometry was used to quantify small velocity fluctuations in the medium and thereby observe structural changes evaluation of more than 2 months of continuous geophone recordings at a reinforced concrete bridge yielded velocity variations v v in the range of 1 5 to 2 1 the observed fluctuations correlate with associated temperature time series with a striking resem

dubious case for slab melting in the northern volcanic zone of the andes it was first suggested by r w kay that adakites may represent melts of subducted slab since then the term adakite has become synonymous with slab melts based on their unusual geochemical signature this contribution using the northern volcanic zone of the andes as an example aims 1 to expose the weakness in simply associating a geochemical signature with a genetic mechanism and 2 to underline the importance of using several integrated lines of evidence in assessing the viability of slab melting we conclude that although slab melting probably occurs in some arcs regional geochemical trends in the northern volcanic zone and their relationship to the subduction zone architecture are not indicative of slab melting and can be accounted for by normal arc magmatic processes acting on wedge derived basaltic magmas

determination of the flow properties at dye 3 south greenland by bore hole tilting measurements and perturbation modelling les donnees issues d inclinometrie a dye 3 groenland rendent possible le calcul du parametre de la loi de fluage en fonction de la profondeur ce parametre montre une importante variation lors de la transition holocene pleistocene en triplant sa valeur pour la glace formee au cours de la derniere glaciation les parametres d ecoulement et la topographie du lit sont utilises dans un modele de perturbation pour calculer les ondulations de surface et les taux de deformation

annual layers in polar firn detected by borehole optical stratigraphy 1 we have developed a system called borehole optical stratigraphy which can detect annual layers in boreholes in polar firn borehole optical stratigraphy consists of a downhole camera package and post processing routines which allow us to measure the intensity of light emitted from an on board source and returned from the borehole wall we manually identify the annual layers in this optical signal we used this system at siple dome antarctica in the 2001 2002 austral summer season our results agree well with counts of annual layers detected with two different methods in an ice core recovered 50 meters from our borehole

correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods review and evaluation abstract we define tephras and cryptotephras and their components mainly ash sized particles of glass crystals in distal deposits and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental geological and archaeological research we then document and appraise recent advances in analytical methods used to determine the major minor and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures a narrow electron beam diameter 3 5 m can now be used to analyze smaller glass shards than previously attainable reliable analyses of microshards defined here as glass shards in part 2 of the review we describe critically assess and recommend ways in which tephras or cryptotephras can be correlated in conjunction with other information using numerical or statistical analyses of compositional data statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components usually glass or crystals phenocrysts than heuristic alternatives they enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations in common with other scientific hypothesis testing it is easier to infer using such analysis that two or more tephras are different rather than the same adding stratigraphic chronological spatial or palaeoenvironmental data i e multiple criteria is usually necessary and allows for more robust correlations to be made a two stage approach is useful the first focussed on differences in the mean composition of samples or their range which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures similarity coefficients hierarchical cluster analysis informed by distance measures or similarity or cophenetic coefficients and principal components analysis pca some statistical methods cluster analysis discriminant analysis are referred to as machine learning in the computing literature the second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis this stage may involve discriminant function analysis dfa support vector machines svms canonical variates analysis cva and anova or manova or its two sample special case the hotelling two sample t2 test randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices hierarchical cluster analysis and pca such transformations may make the assumption of multivariate normality more appropriate a sequential procedure using mahalanobis distance and the hotelling two sample t2 test is illustrated using glass major element data from trachytic to phonolitic kenyan tephras all these methods require a broad range of high quality compositional data which can be used to compare unknowns with reference training sets that are sufficiently complete to account for all possible correlatives including tephras with heterogeneous glasses that contain multiple compositional groups currently incomplete databases are tending to limit correlation efficacy the development of an open online global database to facilitate progress towards integrated high quality tephrostratigraphic frameworks for different regions is encouraged

a comparison of u pb and hf isotopic compositions of detrital zircons from the north and south liaohe groups constraints on the evolution of the jiao liao ji belt north china craton the jiao liao ji orogenic belt is one of the important paleoproterozoic mobile belts in the north china craton ncc and its central segment consists of the north and south liaohe groups and the liaoji granitoids the north and south liaohe groups consist of sedimentary and volcanic successions metamorphosed from greenschist to lower amphibolite facies and the liaoji granitoids are divisible into 2 2 2 1 ga pre tectonic monzogranitic gneisses and 1 88 1 85 ga post tectonic porphyritic monzogranites and alkaline syenites combined with cathodoluminescence cl imaging we report la icp ms laser ablation inductively coupled plasma mass spectrometry u pb and hf isotopic data for detrital zircons from the north and south liaohe groups zircons grains from both groups have igneous zircon cores that yielded two u pb age populations at 2 0 2 2 ga major and 2 5 ga minor indicating that their provenances were similarly dominated by paleoproterozoic liaoji granitoids and late archean basement rocks some structureless zircon rims in both groups yield concordant or upper intercept ages 1 9 ga interpreted as the peak metamorphic age of the two groups these results suggest that both groups were deposited in the period 2 0 1 9 ga shortly after the emplacement of the liaoji granitoids moreover zircons from both groups have similar hf model age peaks t c dm peaks at 2 66 2 75 ga and 2 80 3 00 ga

deformation history of the hengshan complex implications for the tectonic evolution of the trans north china orogen structural analysis indicates that the hengshan complex underwent five distinct episodes of deformation d1 d5 the d1 episode formed small isoclinal folds f1 penetrative axial planar foliations s1 and mineral stretching lineations l1 d1 fabrics were reworked by following d2 deformation associated with d2 was the development of nw verging asymmetric folds and accompanying thrust faults both d1 and d2 resulted from crustal thickening and coherent with prograde and peak metamorphism d2 deformation was followed by transpressional dextral shearing d3 including top to nw oblique slip shearing and nne ssw dextral strike slip shearing ongoing collision led to development of the zhujiafang ductile shear zone d4 a near e w trending high strain belt across the hengshan complex d5 deformation is characterized by f5 open folds and associated normal faults probably related to exhumation of the complex structural patterns of the hengshan complex can place important insights into a recently proposed tectonic model suggesting that an ocean between the eastern and western blocks underwent eastward directed subduction beneath the western margin of the eastern block and closure of this ocean finally led to collision between the two blocks to form the coherent north china craton

shrimp u pb zircon geochronology of the huai an complex constraints on late archean to paleoproterozoic crustal accretion and collision of the trans north china orogen

polyphase deformation of the fuping complex trans north china orogen structures shrimp u pb zircon ages and tectonic implications abstract the fuping complex is located in the central part of the trans north china orogen tnco a paleoproterozoic collisional belt along which the eastern and western blocks were assembled to form the north china craton three stages of deformation d 1 d 3 have been identified in the fuping complex d 1 formed tight to isoclinal folds f 1 penetrative foliation s 1 and mineral lineation l 1 which resulted from the early nw se orientated thrusting and shearing d 2 progressively overprinted d 1 and was dominated by mostly nw se shortening and top to the se e thrusting under a compressive environment d 1 and d 2 occurred in association with the peak metamorphism m 1 d 3 occurred during the exhumation after the crustal thickening producing regional scale nww see trending open folds f 3 and associated low angle detachment faults and was responsible for the isothermal decompression m 2 metamorphism of the complex following the d 3 deformation the complex was exhumed to shallow crustal levels where the rocks underwent the retrogressive cooling m 3 metamorphism syn tectonic leucocratic dykes are widespread in the fuping complex two leucocratic dykes that did not experience d 1 but underwent d 2 yield shrimp zircon ages of 1843 12 ma and 1844 18 ma which indicate that d 1 must have occurred at some time earlier than 1844 ma whereas d 2 must have occurred at some time later than this age two weakly deformed post d 2 leucocratic dykes yield shrimp zircon ages of 1817 14 ma and 1815 45 ma suggesting that the d 2 deformation occurred in the period 1843 1815 ma the new shrimp data indicate that the collision related deformation of the fuping complex must have occurred in the paleoproterozoic not in the late archean structural and geochronological data presented in this study in association with previous lithological and geochemical data suggest that the fuping complex may have been located in the hinterland of an eastward subduction zone and underwent intensive deformation and metamorphism involved in the final collision between the western and eastern blocks at 1 85 ga

recent advances in understanding ice sheet dynamics abstract glaciers and ice sheets play a dynamic role in earth s climate system influencing regional and global scale climate and responding to climate change on time scales from years to millennia they are also an integral part of earth s landscape in alpine and polar regions where they are an active agent in isostatic tectonic and earth surface processes this review paper summarizes recent progress in understanding and modelling ice sheet dynamics from the microphysical processes of ice deformation in glaciers to continental scale processes that influence ice dynamics based on recent insights and research directions it can be expected that a new generation of ice sheet models will soon replace the current standard improvements that can be foreseen in the near future include i the addition of internally consistent evolutionary equations for ice crystal fabric anisotropic flow laws ii more generalized flow laws that include different deformation mechanisms under different stress regimes iii explicit incorporation of the effects of chemical impurities and grain size dynamic recrystallization on ice deformation iv higher order stress solutions to the momentum balance stokes equation that governs ice sheet flow and v the continued merger of ice sheet models with increasingly complex earth systems models which include fully coupled subglacial hydrological and geological processes examples from the greenland ice sheet and vatnajokull ice cap iceland are used to illustrate several of these new directions and their importance to glacier dynamics