petrogenesis p t t path and tectonic significance of high pressure mafic granulites from the jiaobei terrane north china craton abstract high pressure hp mafic granulites in the jiaobei terrane are composed predominantly of garnet mafic granulites garnet hypersthene granulites and garnet amphibolites and they are found as irregular lenses or deformed dike swarms within tonalitic trondhjemitic granodioritic gneisses and granitic gneisses the hp mafic granulites contain four distinct metamorphic assemblages of which the early prograde assemblage m 1 is represented by the cores of garnets together with mineral inclusions of clinopyxene plagioclase quartz and it formed at 740 770 c and 0 90 1 00 gpa in contrast the peak assemblage m 2 consists of high ca cores in garnet high al cores in clinopyroxene and high na cores in plagioclase in the matrix which formed under p t conditions of 850 880 c and 1 45 1 65 gpa the peak metamorphism was followed by near isothermal decompression m 3 which resulted in the development of orthopyroxene clinopyxene plagioclase quartz amphibole magnetitie symplectites or coronas surrounding some garnet grains with p t conditions of 780 830 c and 0 65 0 85 gpa surrounding some garnet grains are symplectites of amphibole plagioclase quartz magnetitie which formed during a cooling retrograde stage m 4 with p t conditions of 590 650 c and 0 62 0 82 gpa an integrated study involving laser raman analysis of mineral inclusions cathodoluminescence imaging and in situ u pb dating of zircons shows that the protolith ages of the hp mafic granulites are mainly 2550 2500 ma and that the timing of the peak metamorphism of the hp mafic granulites ranges from 1900 to 1860 ma as recorded by the cores of metamorphic zircons on the other hand the medium to low pressure granulite amphibolite facies retrogression occurred mainly at 1860 1820 ma as recorded by the rims of some single zircon grains and the zircon grains that contain inclusions of garnet orthopyroxene plagioclase sphene the combination of petrography mineral compositions metamorphic reaction history thermobarometry and geochronology defines a near isothermal decompressional clockwise p t t path for the jiaobei hp mafic granulites suggesting that the jiaobei terrane underwent initial crustal thickening during 1950 1860 ma followed by relatively rapid exhumation cooling and retrogression in the period 1860 1820 ma this tectonothermal path was probably generated by subduction and collision related tectonic processes

earliest paleoproterozoic supracrustal rocks in the north china craton recognized from the daqingshan area of the khondalite belt constraints on craton evolution abstract the upper wulashan subgroup at daqingshan in the khondalite belt of the western block of the north china craton contains an early paleoproterozoic 2 5 2 45 ga supracrustal sequence incorporating banded iron formations which we refer to as the daqingshan supracrustal rocks they contain rounded to elliptical zircon grains that commonly show core rim or core mantle rim structures and precise shrimp u pb dating of these domains allows the discrimination of a series of tectono thermal events that straddle the archean proterozoic boundary detrital zircon cores with oscillatory zoning have formation ages ranging from 2 55 to 2 50 ga indicating derivation from late neoarchean magmatic rocks as a result of exhumation and erosion these became incorporated in earliest paleoproterozoic sediments that were deposited between 2 50 and 2 45 ga and then underwent high grade metamorphism at 2 45 2 40 ga this event variously recrystallized the cores into two main domains a dark inner domain and a gray outer domain as imaged in cathodoluminescence the gray domains commonly show sector zoning and have th u ratios of 0 1 0 5 a feature commonly noted in zircons recrystallized under high grade metamorphic conditions metamorphic mantles are generally more homogeneous in structure and have lower th u ratios commonly

the growth reworking and metamorphism of early precambrian crust in the jiaobei terrane the north china craton constraints from u th pb and lu hf isotopic systematics and ree concentrations of zircon from archean granitoid gneisses abstract archean granitoid tonalite trondhjemite granodiorite ttg gneisses are widely distributed in the early precambrian metamorphic basement of the jiaobei terrane the north china craton ncc and record the formation and evolution of the continental crust in the early precambrian in this study zircon cathodoluminescence cl images have assisted in obtaining u th pb and lu hf isotopic systematics and rare earth element ree concentrations from distinct zircon domains of complex zircons and the results have been integrated in order to unravel the growth reworking and metamorphism of the early precambrian crust in the jiaobei terrane zircons from seven representative archean granitoid samples collected from the jiaobei terrane record three groups of magmatic ages of 2 9 2 7 and 2 5 ga and two groups of metamorphic ages of 2 5 and 1 86 ga the 2 5 ga metamorphic event is thought to be linked to underplating of large amounts of mantle derived magma and the 1 86 ga metamorphic event to arc or continent continent collision magmatic zircons have positive hf t values 0 7 to 12 58 average 5 5 and two stage hf model ages cluster at 2 7 2 8 and 2 9 3 0 ga this indicates that the archean granitoid rocks were derived from partial melting of juvenile crust that was formed mainly during 2 7 2 8 and 2 9 3 0 ga which represent two periods of growth of juvenile crust the most significant period of crustal growth is 2 7 2 8 ga whereas 2 5 ga represents a period of reworking of the 2 7 2 8 ga juvenile crust in the jiaobei terrane as well as other areas in the ncc

the palaeoproterozoic boron deposits in eastern liaoning china a metamorphosed evaporite abstract we have carried out a field study of the palaeoproterozoic borate deposits of eastern liaoning province china the borates are hosted within mg silicate and mg carbonate rocks and have previously been interpreted as either skarns or metamorphosed volcanogenic exhalative deposits the deposits contain textures that are compatible with a sedimentary origin of the borates and there is a lack of the associated mineralization that is characteristic of magnesian skarns in addition preliminary boron isotope data indicate that the boron within the borates was not derived from the footwall rocks that have been proposed as the source of the skarn fluids a purely exhalative model can be dismissed on the basis of geochemical arguments and comparison with modern environments which show that borates are too soluble to precipitate directly from hydrothermal fluids the geology and field relationships show a number of similarities with recent non marine evaporite settings and young continental rifts in arid environments we conclude therefore that the liaoning deposits are metamorphosed evaporites in which the boron was originally present as primary evaporite borate minerals this model places the liaoning borates in the same category as the majority of other economic borate deposits in the world

zircon u pb geochronology and hf isotopes of major lithologies from the jiaodong terrane implications for the crustal evolution of the eastern block of the north china craton abstract as an important component of the western shandong complex in the eastern block of the north china craton the yishui terrane consists of neoarchean high grade supracrustal rocks granitoid gneisses and charnockites la icp ms zircon u pb dating and hf isotopic analyses on these lithologies have been carried out and the results provide new insights into the neoarchean crustal evolution of the eastern block of the north china craton new zircon dating results reveal that the magmatic precursors of the supracrustal metapelites and granitoid gneisses were generated at 2 54 2 53 ga and 2 57 2 55 ga respectively and the charnockites were emplaced contemporaneously around 2 56 2 53 ga single metamorphic zircon grains and overgrowth rims from these rocks document consistent metamorphic ages at 2 50 ga suggesting that the yishui terrane experienced a high grade metamorphic event at the end of the neoarchean detrital zircons from pelitic gneisses yield 207pb 206pb ages of 2 89 2 65 ga with a major age peak at 2 53 ga and a subordinate age peak at 2 70 ga implying that the sedimentary protoliths of the pelitic gneisses may have been sourced from 2 53 ga rocks in the yishui terrane and 2 70 ga rocks in the adjacent luxi granite greenstone terrane hf isotopic compositions show that the neoarchean magmatic zircons have positive ehf t values ranging from 1 4 to 7 8 and depleted mantle model ages of 2 92 2 60 ga with a prominent peak at 2 8 2 7 ga suggesting that the neoarchean crust was derived mainly from juvenile sources and partly from the recycling of old continental crust in the yishui area combined with previous data from the adjacent luxi granite greenstone terrane and other complexes in the eastern block it is concluded that the neoarchean was an important period of crust accretion in the eastern block of the north china craton

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

remapping the thickness distribution in sea ice models in sea ice models with multiple thickness categories the ice thickness distribution evolves in time the evolution of the thickness distribution as ice grows and melts is analogous to one dimensional fluid transport and can be treated by similar numerical methods one such method remapping is applied here thickness categories are represented as lagrangian grid cells whose boundaries are projected forward in time the thickness distribution is approximated as a linear or quadratic polynomial in each displaced category and ice area and volume are transferred between categories so as to restore the original boundaries in simple test problems and in a single column model with forcing typical of the central arctic remapping performs significantly better than methods previously used in sea ice models it is less diffusive than a scheme that fixes the ice thickness in each category and behaves better numerically than a scheme that represents the thickness distribution as a set of delta functions also remapping converges faster i e with fewer thickness categories than the alternative schemes with five to seven categories the errors due to finite resolution of the thickness distribution are much smaller than the errors due to other sources linear remapping performs as well as the more complex quadratic version and is recommended for climate modeling its computational cost is minimal compared to other sea ice model components

sedimentary rocks and crustal evolution tectonic setting and secular trends a significant change in the composition of turbidites deposited at active tectonic settings is seen at the archean post archean transition in comparison to post archean active margin turbidites archean greenstone turbidites exhibit more uniform th sc ratios but with a similar average greater hree depletion gd n yb n 2 less eu depletion eu eu mostly 0 85 and an absence of low th u ratios th u 3 these data indicate that differing mantle sources and or conditions of mantle melting existed during the archean and that intracrustally differentiated rocks older cratons or young differentiated arcs were relatively unimportant as provenance components for archean turbidites in contrast some sedimentary rocks preserved in archean platformal sequences of high grade terranes display significant negative eu anomalies similar to the majority of post archean shales indicating that the general process of cratonization including intracrustal differentiation has taken place since at least 3

degassing of mantle derived co2 and he from springs in the southern colorado plateau region neotectonic connections and implications for groundwater systems groundwaters of the southern colorado plateau arizona transition zone region are a heterogeneous mixture of chemically diverse waters including meteoric epigenic fluids karst aquifer waters and deeply sourced endogenic fluids we investigate the composition of travertine depositing co 2 rich springs to determine the origin transport and mixing of these various components the san francisco mountain recharge area has little surface flow instead waters discharge through major springs hundreds of kilometers away about 70 9340 l s of the total recharge 13 500 l s discharges 100 km to the north in the incised aquifer system at grand canyon most of this water 85 8070 l s emerges through two travertine depositing karst spring systems blue springs 6230 l s and havasu springs 1840 l s about 30 of recharge 4150 l s flows to the south and discharges along nw striking faults in the arizona transition zone forming the base flow for the verde river geochemical data define regional mixing trends between meteoric recharge and different endogenic end members that range from bicarbonate waters to sulfate waters water quality in the region is dictated by the percentage and character of the endogenic inputs that cause a measurable degradation of groundwater quality for water supply sources for the high co 2 include dissolution of limestone and dolostone c carb and external carbon c external c external is computed as the bicarbonate alkalinity dissolved inorganic carbon dic minus the c carb c external dic c carb c external is deconvolved using carbon isotopes into biogenically derived sedimentary carbon c organic and deep co 2 inputs c endogenic measured 13 c values are 17 to 3 versus pee dee belemnite pdb assuming 13 c carb 2 13 c organic 28 and 13 c endogenic 5 water chemistry mixing models indicate that an average of 42 of the total dic comes from dissolution of carbonate rocks 25 from organic carbon including soil respired co 2 and 33 from deep endogenic sources helium isotope values 3 he 4 he in gases dissolved in spring waters in the southern colorado plateau region range from 0 10 to 1 16 r a relative to air indicating that a significant component of the deeply derived fluid is from the mantle mean of 5 asthenospheric or 10 subcontinental lithospheric mantle source measured co 2 3 he ratios of 2 10 9 to 1 4 10 13 are adjusted by removing the proportion of co 2 from c carb and c organic to give values 10 for all but four samples various mixing models using co 2 3 he suggest that the mantle derived components of the co 2 load are highly variable from spring to spring and may make up an average of 10 of the total co 2 load of the regional springs fluid rock interactions involving endogenic fluids are suggested by 87 sr 86 sr 18 o and other tracers the endogenic co 2 component multiplied by discharge for each spring yields an integrated annual flux of deeply derived co 2 to the groundwater system of 1 4 10 9 mol yr this co 2 emission from the colorado plateau region reflects a complex tectonic evolution involving laramide hydration of the lithosphere above the farallon slab addition of fluids from mid tertiary mantle tectonism during slab removal and ongoing fluid movement induced by neotectonic small scale asthenospheric convection

carbon dioxide earth degassing and seismogenesis in central and southern italy 1 we present the first regional map of co2 earth degassing from a large area most of central and south italy derived from the carbon of deep provenance dissolved in the main springs of the region the investigation shows that a globally significant amount of deeply derived co2 10 of the estimated global co2 emitted from subaerial volcanoes is released by two large areas located in western italy the anomalous flux of co2 suddenly disappears in the apennine in correspondence to a narrow band where most of seismicity concentrates here at depth the gas accumulates in crustal traps generating co2 overpressurized reservoirs which induce seismicity

the isotopic composition of radiogenic helium and its use to study groundwater movement in confined aquifers abstract the 3 he 4 he ratio for radiogenic he is shown to be primarily determined by the abundance of li and neutron absorbing elements in the host formations and is almost independent of the radioelement abundance the 3 he 4 he ratios have been computed for various li contents in rock matrices with average abundances of other elements the 3 he 4 he ratio is specific for each formation and may therefore be used to study crustal diffusion of he it is shown however that both the 3he and 4he contents of continental basements are likely to exceed those of the mantle so that diffusion of mantle he through continental crust is not likely to occur changes in the 3 he 4 he ratio for dissolved he have potential for studying groundwater movement and mixing processes atmospheric he which was dissolved at recharge is progressively diluted by radiogenic he with an isotopic ratio characteristic of the aquifer as the groundwater migrates down dip mixing proportions for formation he and atmospheric he in aquifers for which there is admixture of fracture borne water and interstitially stored water can also be estimated from isotopic measurements these processes are discussed in relation to two aquifers in eastern england

the fate of mantle derived carbon in a continental sedimentary basin integration of c he relationships and stable isotope signatures abstract the isotopic composition and abundances of the rare gases he ne and ar and active gases co2 ch4 have been determined in a series of commercial gas reservoirs in the pannonian and vienna basins of hungary and austria respectively in these zones of continental extension significant components of mantle derived 4he up to 39 8 and 21ne up to 58 are identified the results of this study indicate a major component of mantle derived carbon in these systems as well ranging in composition from close to 100 co2 to ch4 dominated reservoirs with trace concentrations ppm of co2 these gas reservoirs provide a unique opportunity to examine the relationship of the conservative rare gases to the active gas components and to examine the sources and sinks for mantle and crustal derived carbon phases with the exception of kismarja gas field which shows evidence of addition of 3he depleted crustal co2 all gas fields exhibit a trend whereby the most co2 rich samples approach co 2 3 he mntl values similar to morb 2 109 to 7 109 while co2 depleted samples extend to co 2 3 he mntl values as low as 105 the lack of any correlation of co 2 3 he mntl ratios with r ra values indicates the observed trends are not a function of mixing between crustal and mantle derived endmembers but instead reflect progressive loss of the mantle derived co2 carrier phase during volatile transport and emplacement in the continental crust based on stable isotopic signatures from the kismarja field a crustal co2 endmember with an isotopic composition of 6 8 and a mantle co2 endmember with an isotopic composition no more depleted in 13c than 5 0 can be identified one of the few instances where the isotopic signatures of mantle and crustal derived co2 can be reliably distinguished in a continental setting covariation in 13cco2 and 13cch4 values in the gas fields is used to place constraints on two alternative models whereby the trends in percent co2 and co 2 3 he mntl ratios can be accounted for by 1 loss of the mantle derived co2 carrier phase 2 addition of crustal derived co2 3 addition of crustal derived thermogenic ch4 and potentially 4 conversion of the co2mntl carrier phase to mantle derived ch4 based on an estimated total mantle 4he flux for the pannonian basin of 4 2 108 atoms m 2 s 1 mantle carbon flux estimates for this basin alone range from 3 108 g c yr to 1 109 g c yr which over the lifetime of the basin is only 4 5 orders of magnitude less than flux estimates based on the total area of the spreading ridges clearly the addition of mantle derived carbon to the crust in areas of continental extension is significant and may have been previously underestimated we demonstrate here that integration of 13c data with rare gas isotopic tracers provides an important tool in constraining models of mantle carbon sources and sinks in continental settings

where is the north china south china block boundary in eastern china the qinling dabieshan belt results from the collision of the north china and south china blocks the eastern extension of the belt the sulu area consists of several stacked units from top to bottom these are 1 a weakly metamorphosed slate sandstone unit of neoproterozoic paleozoic age 2 a gneiss quartzite unit metamorphosed under high pressure p conditions 3 a marble amphibolite unit 4 an ultrahigh p unit that was very deeply subducted and then exhumed and 5 a migmatitic dome resulting from the melting of ultrahigh p rocks all these units underwent the same deformation which was characterized by a top to the northwest extensional ductile shearing during their exhumation granulite facies restites in the migmatite are not significantly different from granulitized eclogites derived from the ultrahigh p rocks the migmatite exhibits the same structural and petrologic evolution as that determined for the other units the resemblance of petrologic and structural features and the lack of ocean basin rock shows that the boundary between the north china block and south china block must be placed north of the sulu area

the application of zircon cathodoluminescence imaging th u pb chemistry and u pb ages in interpreting discrete magmatic and high grade metamorphic events in the north china craton at the archean proterozoic boundary abstract two distinct late neoarchean to early paleoproterozoic magmatic events are recognized at the northern margin of the eastern block of the north china craton based on interpretation of zircon structure cathodoluminescence signature th u pb chemistry and age the first event is represented by emplacement of the chaihe trondhjemite and xianjinchang tonalite with magmatic zircon core ages ranging from 2559 2553 7 ma respectively these rocks experienced a subsequent high grade metamorphic event constrained by partial recrystallization of primary magmatic zircon and growth of new zircon rims between 2517 and 2490 ma a second magmatic episode generated by partial melting of crustal rocks during this metamorphic event is represented by the hongshilazi syenogranite with an age of 2502 11 ma the short time interval between initial magmatism and high grade regional metamorphism signifies they were related to the same major tectonothermal event when considered along with evidence of a similar sequence of events at this time 800 km to the south in eastern hebei and the previously established 2500 ma age of granulite facies metamorphism in mafic rocks across the craton it is proposed that a large mantle plume developed beneath the north china craton at the close of the archean

introduction to tectonics of china abstract the continental crust of china is a mosaic of cratonic blocks and orogenic belts containing small cratons and terranes with various tectonic settings they have diverse origins and complex histories of amalgamation and often suffered repeated reworking after multiple episodes of amalgamation in the last three decades extensive geological geochemical and geophysical investigations have been carried out on these cratonic blocks and intervening orogenic belts producing an abundant amount of new data and competing interpretations this provides important insights into understanding the formation and evolution of the chinese continents the papers assembled in this volume present a timely and comprehensive overview on major advancements and controversial issues related to the formation and evolution of continental crust in china complex tectonic histories were experienced not only by the large scale cratonic blocks and orogenic belts but also by small scale terranes and orogens between and inside these blocks nevertheless our understanding of lithotectonic units and geological processes has been greatly advanced by recent studies of zirconology and geochemistry for various rock types from major petrotectonic units in china it has been further advanced from integrated interpretations of geochemical and petrological data for petrogenesis of magmatic rocks an overview of these observations and interpretations provides new insights into understanding the continental plate tectonics and the chemical geodynamics of subduction zones

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

complex subduction and small scale convection revealed by body wave tomography of the western united states upper mantle abstract new high resolution p and s wave tomography of the united states upper mantle from the pacific coast to the great plains reveals strong multi scale heterogeneity closely correlated with tectonic and magmatic activity we invert teleseismic travel time residuals from the earthscope transportable array and more than 1700 additional temporary and permanent stations for 3 d velocity perturbations to a depth of 1000 km the inversion uses recent advances in western u s crust models to better isolate the mantle component of travel time residuals and frequency dependent 3 d sensitivity kernels to map travel time residuals measured in multiple frequency bands into velocity structure in addition to separate v p and v s models we jointly invert the two datasets for v p v s perturbations by imposing a smoothness constraint on the ln v s ln v p field the joint inversion helps us identify regions where partial melt is probable the amplitude of v p v s and v p v s variations is greatest in the upper 200 km of the mantle and the form of velocity anomalies suggests a provincially heterogeneous lithosphere and the occurrence of widespread small scale convection partially molten mantle is inferred beneath yellowstone and the eastern snake river plain srp the salton trough and the clear lake volcanic field the inferred depth extent of partial melt is consistent with a generally hydrated upper mantle and elevated temperatures beneath the eastern srp and yellowstone despite continuous subduction since the cretaceous the distribution of sub lithospheric high velocity anomalies is dissected similar to other recent studies based on our new tomography models western u s geologic history and plate tectonic reconstructions we infer patchy and incomplete removal of the flat subducting laramide slab and slab tearing associated with eocene accretion in the northwestern u s

dissected hydrologic system at the grand canyon interaction between deeply derived fluids and plateau aquifer waters in modern springs and travertine geochemical study of water and gas discharging from the deeply incised aquifer system at the grand canyon arizona provides a paradigm for understanding complex groundwater mixing phenomena and quaternary travertines deposited from cool springs provide a paleohydrologic record of this mixing geochemical data show that springs have marked compositional variability those associated with active travertine accumulations deeply derived endogenic waters are more saline richer in co2 and elevated in 87sr 86sr relative to springs derived dominantly from surface recharge of plateau aquifers epigenic waters endogenic waters and associated travertine are preferentially located along basement penetrating faults we propose a model whereby deeply derived fluids are conveyed upward via both magmatism and seismicity our model is supported by 1 gas analyses from spring waters with high he ar and he n2 and 3he 4he ratios indicating the presence of mantle derived he 2 large volumes of travertine and co2 rich gases in springs recording high co2 fluxes and 3 87sr 86sr in these springs that indicate circulation of waters through precambrian basement geochemical trends are explained by mixing of epigenic waters of the colorado plateau aquifers with different endogenic end member waters in different tectonic subprovinces endogenic waters are volumetrically minor but have significant effects on water chemistry they are an important and largely unrecognized component of the hydrogeochemistry and neotectonics of the southwestern united states

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

diversity of rock varnish bacterial communities from black canyon new mexico 1 scientists vigorously debate the degree to which rock varnish is formed through the actions of microorganisms to investigate this enigma we utilized a three pronged approach that combined 1 culture independent molecular methods to characterize bacterial communities associated with varnish that coats the rhyolitic volcanic rocks of black canyon new mexico and rocks with no visible varnish 2 culturing of varnish in media supplemented with reduced forms of manganese and or iron and no or low amounts of carbon to isolate bacteria capable of precipitating iron and or manganese oxides and 3 scanning electron microscopy sem of varnish and nearby rock that lacks macroscopically visible varnish our culture independent studies revealed significant differences between varnish and nonvarnish communities chloroflexi and ktedobacteria dominated one varnish site while the other varnish site was dominated by cyanobacteria the nonvarnish sites were dominated by actinobacteria and to a lesser extent cyanobacteria and were the only samples to contain deinococcus thermus sequences approximately 65 of varnish cultures produced visible manganese precipitates most culture isolates were not closely related to known manganese oxidizers with the exception of bacillus spp sem revealed microbial morphologies and two types of varnish morphologies 1 relatively smooth layers and 2 patches of botryoidal pinnacles which were often associated with increased manganese concentrations bare rock showed evidence of incipient varnish these results have important implications for the detection of life on extraterrestrial planets such as mars where putative varnish coatings have been observed and represent some of the first culture independent characterizations of varnish communities

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

shrimp u pb zircon geochronology of palaeoproterozoic metasedimentary rocks in the north china craton evidence for a major late palaeoproterozoic tectonothermal event abstract although metasedimentary successions are widely distributed across the north china craton those of palaeoproterozoic age are restricted to three orogenic belts namely the trans north china orogen the khondalite belt and the jiao liao ji belt prior to this work some of those successions were considered to be archaean in age the palaeoproterozoic metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 0 to 2 1 ga with the majority recording an age between 2 3 and 2 0 ga this latter group define a series of magmatic events that occurred between formation of the archaean basement and deposition of the metasedimentary rock protoliths the metasedimentary rocks occur as two associations older volcano sedimentary units that formed between 2 37 and 2 0 ma and younger sedimentary units that formed mainly between 2 0 and 1 88 ga all these rock associations were then subjected to metamorphism during the late palaeoproterozoic 1 88 and 1 85 ga tectonothermal event named the luliang movement in early chinese literature which was a continent continent collision that led to the amalgamation of the north china craton

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

flow of mantle fluids through the ductile lower crust helium isotope trends heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust minimum 3he 4he ratios in surface fluids from the northern basin and range province western north america increase systematically from low crustal values in the east to high mantle values in the west a regional trend that correlates with the rates of active crustal deformation the highest ratios occur where the extension and shear strain rates are greatest the correspondence of helium isotope ratios and active transtensional deformation indicates a deformation enhanced permeability and that mantle fluids can penetrate the ductile lithosphere even in regions where there is no substantial magmatism superimposed on the regional trend are local high 3he 4he anomalies indicating hidden magmatic activity and or deep fluid production with locally enhanced permeability identifying zones with high resource potential particularly for geothermal energy development

distributed deformation across the rio grande rift great plains and colorado plateau we use continuous measurements of gps sites from across the rio grande rift great plains and colorado plateau to estimate present day surface velocities and strain rates velocity gradients from five east west profiles suggest an average of 1 2 nanostrains yr east west extensional strain rate across these three physiographic provinces the extensional deformation is not concentrated in a narrow zone centered on the rio grande rift but rather is distributed broadly from the western edge of the colorado plateau well into the western great plains this unexpected pattern of broadly distributed deformation at the surface has important implications for our understanding of how low strain rate deformation within continental interiors is accommodated

growth of a pleistocene giant carbonate vein and nearby thermogene travertine deposits at semproniano southern tuscany italy estimate of co2 leakage abstract a giant carbonate vein 50 m thick fissure ridge travertines and nearby travertine plateaus in the semproniano area mt amiata geothermal field southern tuscany italy are investigated through a multidisciplinary approach including field and laboratory geochemical analyses u th geochronology c nd o and sr isotope systematics ree abundances and fluid inclusion microthermometry the main aim of this work is to understand 1 modes and rates for the growth of the giant vein and nearby travertine deposits within a quaternary volcano tectonic domain 2 implications in terms of the co 2 leakage and 3 possible relationships with quaternary paleoclimate and hydrological oscillations results show that the giant vein was the inner portion of a large fissure ridge travertine and grew asymmetrically and ataxially through repeated shallow fluid injections between 650 and 85 ka with growth rates in the 10 2 10 3 mm a order the giant vein developed mainly during warm humid interglacial periods partially overlapping with the growth of nearby travertine plateaus estimated values of co 2 leakage connected with the vein precipitation are between about 5 10 6 and 3 10 7 mol a 1 km 2 approximately representing one millionth of the present global co 2 leakage from volcanic areas temperature estimates obtained from o isotopes and fluid inclusion microthermometry indicate epithermal conditions 90 50 c for the circulating fluid during the giant vein growth with only slight evidence of cooling with time geochemical and isotope data document that the travertine deposits formed mainly during pleistocene warm humid periods within a tectonically controlled convective fluid circuit fed by meteoric infiltration and maintained by the regional geothermal anomaly hosted by the carbonate reservoir of the mt amiata field

geology and timing of mineralization at the cangshang gold deposit north western jiaodong peninsula china the cangshang gold deposit of the north western jiaodong peninsula contains reserves of greater than 50 tonnes t and is developed by the largest open pit gold mine in china this deposit is a jiaojia style i e disseminated and veinlet deposit it is controlled by the san cang fault zone which trends 040 and dips 40 75 se at the mine site the main no 1 orebody lies between a hanging wall of precambrian metamorphic rocks mainly amphibolite of the fenzishan group and a footwall composed of the mesozoic linglong granitoid the ore zone is mainly composed of pyritized sericitized and silicified granitoid which has undergone variable degrees of cataclasis shrimp u pb dating of zircon indicates that the protolith of the hanging wall amphibolite was formed at 2530 17 ma and underwent metamorphism at 1852 37 ma the footwall granodiorite has been dated at 166 4 ma whereas zircons from the ore zone yield a younger age of 154 5 ma cathodoluminescence images of zircons from the granodiorite and ore zone show oscillatory zonation indicative of an igneous origin for both and the ages of these zircons therefore are all interpreted to be representative of magmatic crystallization dating of sericite by 40ar 39ar has been used to directly determine the timing of formation of the cangshang deposit providing the first time absolute age on formation of the jiaojia style gold deposits the well defined age of 121 3 0 2 ma provides the precise timing of gold mineralization at the cangshang deposit this age is consistent with those of linglong style vein type gold mineralization also from the north western jiaodong peninsula at between 126 and 120 ma therefore our work indicates that both styles of gold deposits in the jiaodong peninsula were formed during the same mineralization event

continental smokers couple mantle degassing and distinctive microbiology within continents abstract the discovery of oceanic black and white smokers revolutionized our understanding of mid ocean ridges and led to the recognition of new organisms and ecosystems continental smokers defined here to include a broad range of carbonic springs hot springs and fumaroles that vent mantle derived fluids in continental settings exhibit many of the same processes of heat and mass transfer and ecosystem niche differentiation helium isotope 3he 4he analyses indicate that widespread mantle degassing is taking place in the western u s a and that variations in mantle helium values correlate best with low seismic velocity domains in the mantle and lateral contrasts in mantle velocity rather than crustal parameters such as gps proximity to volcanoes crustal velocity or composition microbial community analyses indicate that these springs can host novel microorganisms a targeted analysis of four springs in new mexico yield the first published occurrence of chemolithoautotrophic zetaproteobacteria in a continental setting these observations lead to two linked hypotheses that mantle derived volatiles transit through conduits in extending continental lithosphere preferentially above and at the edges of mantle low velocity domains high co2 and other constituents ultimately derived from mantle volatiles drive water rock interactions and heterogeneous fluid mixing that help structure diverse and distinctive microbial communities

a synthesis of geochemistry and sm nd isotopes of archean granitoid gneisses in the jiaodong terrane constraints on petrogenesis and tectonic evolution of the eastern block north china craton abstract the jiaodong terrane is situated in the northeastern part of the shandong province in eastern china experiencing multi stage magmatism during the mesoarchean 2 9 ga and neoarchean 2 7 ga and 2 5 ga it consists dominantly of granitoid gneisses with minor amphibolite enclaves or lenses this study presents new whole rock geochemical and sm nd isotopic data for the archean granitoid gneisses from the jiaodong terrane in order to constrain their petrogenesis and tectonic setting geochemical studies and petrological features suggest that the protoliths of most granitoid gneisses are typical archean tonalitic trondhjemitic granodioritic ttg suites which are high in sio2 60 9 76 8 wt al2o3 12 6 16 8 wt na2o 3 3 5 3 wt sr 135 604 ppm and sr y ratios 13 9 84 but low in mgo 0 4 4 5 wt k2o 0 7 3 4 wt tio2 0 2 0 9 wt cr

lithospheric dismemberment and magmatic processes of the great basin colorado plateau transition utah implied from magnetotellurics 1 to illuminate rifting processes across the transition zone between the extensional great basin and stable colorado plateau interior we collected an east west profile of 117 wideband and 30 long period magnetotelluric mt soundings along latitude 38 5 n from southeastern nevada across utah to the colorado border regularized two dimensional inversion shows a strong lower crustal conductor below the great basin and its transition zone in the 15 35 km depth range interpreted as reflecting modern basaltic underplating hybridization and hydrothermal fluid release this structure explains most of the geomagnetic variation anomaly in the region first measured in the late 1960s hence the transition zone while historically included with the colorado plateau physiographically possesses a deep thermal regime and tectonic activity like that of the great basin the deep crustal conductor is consistent with a rheological profile of a brittle upper crust over a weak lower crust in turn on a stronger upper mantle jelly sandwich model under the incipiently faulted transition zone the conductor implies a vertically nonuniform mode of extension resembling early stages of continental margin formation colorado plateau lithosphere begins sharply below the western boundary of capitol reef national park as a resistive keel in the deep crust and upper mantle with only a thin and weak moho level crustal conductor near 45 km depth several narrow steep conductors connect conductive lower crust with major surface faulting some including modern geothermal systems and in the context of other great basin mt surveying suggest connections between deep magma sourced fluids and the upper crustal meteoric regime the mt data also suggest anisotropically interconnected melt over a broad zone in the upper mantle of the eastern great basin which has supplied magma to the lower crust consistent with extensional mantle melting models and local shear wave splitting observations we support a hypothesis that the transition zone location and geometry ultimately reflect the middle proterozoic suturing between the stronger yavapai lithosphere to the east and the somewhat weaker mojave terrane to the west we conclude that strength heterogeneity is the primary control on locus of deformation across the transition zone with modulating force components

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

zircon u pb and lu hf isotope study of the neoproterozoic haizhou group in the sulu orogen provenance and tectonic implications abstract the neoproterozoic haizhou group crops out sporadically in the sulu orogen in east central china it is divided into the jinping and yuntai formations and consists of quartzite quartz schist marble and graphite and apatite bearing sequences major and trace element data for quartz schist from the two formations indicate that these rocks have a greywacke protolith and have been deposited during strong tectonic activity la icpms u pb dating of detrital zircon yields ages of 635 to 1074 ma for three samples from the jinping formation and 611 to 943 ma for two samples from the yuntai formation more than 78 of the detrital zircons from the two formations have u pb ages grouped between 700 and 890 ma with two clusters peaking at 758 ma and 828 ma respectively this indicates that their provenance is magmatic rocks of neoproterozoic age that have a tectonic affinity to the south china block scb a few older zircon populations with peak u pb ages at 943 and 1074 ma are also present a younger population shows peaks at 661 and 611 ma this suggests that deposition of the haizhou group was later than 611 ma rather than during the mesoproterozoic as previously thought zircon lu hf isotope data collected from the same u pb sites show negative ehf t values of 22 8 to 7 4 and hf model ages of 2341 to 3100 ma this indicates that the neoproterozoic magmatic rocks were derived from reworking of ancient paleoproterozoic to archean crust the results support the contention that the haizhou group is similar to the wulian group at the northwestern edge of the sulu orogen both having a scb affinity but that the penglai group does not belong to the scb because of the absence of neoproterozoic ages this lends support to the conclusion that the triassic suture between the north china and south china blocks is located along the baichihe yantai fault which lies north of the wulian complex and south of the jiaobei terrane thus the wulian yantai fault is not the suture zone as is traditionally proposed

mantle derived volatiles in continental crust the massif central of france co2 rich gases and groundwaters from springs and boreholes originating within the basement of the massif central have variable3he 4he ratios with correspondingr ra values ranging from 0 8 to 5 5 and 0 3 to 2 8 respectively indicating the presence of a significant component of mantle helium molar concentrations of rare gases in the co2 rich gases are approximately 5 orders of magnitude greater than in the waters and suggest that a near surface henry s law fractionation has occurred between exsolving co2 and water 13c values of the co2 rich gases are in the range 4 2 to 6 1 i e in that range normally attributed to mantle carbon but which could also represent an average crustal composition and therefore do not discriminate between mantle and crustal sources c 3he ratios show 4 orders of magnitude variation from 1 4 1012 to 5 108 and compared to a mantlec 3he ratio of 109 indicate that either a complex fractionation has occurred between mantle helium and mantle co2 or more likely that mantle rare gases have been diluted by large quantities of co2 with an average crustal carbon isotope composition the regional distribution of3he and c does not show any obvious relationship to age or proximity of volcanic centres or major faults suggesting that mantle derived c and he components decoupled from their silicate melt sources at some depth the results from this area of active fluid circulation suggest that c isotope data derived from metamorphic terrains should be interpreted with great caution but that input of some mantle derived carbon is expected to accompany crustal extension

rejuvenation vs recycling of archean crust in the gawler craton south australia evidence from u pb and hf isotopes in detrital zircon abstract zircon grains from modern and ancient drainages of the gawler craton south australia have been analysed to define the relative contributions of juvenile sources and recycled crust to magmatic activity as a function of time and to constrain the role of mantle inputs during the proterozoic rejuvenation of the archean gawler craton the integration of hf isotope data with u pb age spectra shows that the crustal evolution was dominated by long periods of crustal reworking and that crust generated in the paleoarchean 3 2 3 5 ga was largely reworked during proterozoic time four periods of juvenile mantle input can be recognised at ca 2540 ma 1853 ma 1595 ma and 1169 ma the 1169 ma event is not previously recognised in the gawler craton but the absence of other important age peaks argues against the transport of these zircons from the musgrave block only minor proportions of the magmatic zircons with paleoproterozoic to mesoproterozoic ages have strongly juvenile signatures e hf 4 indicating that crustal reworking was the dominant process with relatively minor mantle input comparison of the crustal evolution with that of nearby australian terranes suggests that although the gawler craton shows some similarities with the mount isa block and the georgetown inlier in neoarchean paleoproterozoic time it evolved independently between ca 1800 and 1550 ma

mantle 3he and co2 degassing in carbonic and geothermal springs of colorado and implications for neotectonics of the rocky mountains helium isotope 3 he 4 he data from geothermal springs in the colorado rocky mountains western united states provide unequivocal evidence for a remarkable mantle to groundwater connection with contributions of up to 27 mantle derived helium hydrochemical modeling of springs shows the mantle helium is associated with high p co 2 with 76 20 of the co 2 also derived from endogenic deep geologic sources these springs occur preferentially along faults have highest 3 he 4 he values above domains of low mantle velocity and demonstrate unexpectedly widespread neotectonic mantle degassing total co 2 flux through these springs is 3 10 8 mol yr a small but persistent contribution to the co 2 budget and an important baseline for carbon sequestration leakage studies

mantle helium in sacramento basin natural gas wells abstract helium isotope ratios in sacramento basin natural gas wells show a strong mantle signal the3he 4he ratios range from 0 11 times the atmospheric ratio 0 11 ra in the rio vista field to 2 75 ra in the moon bend field indicating that 1 to 34 of the helium is mantle derived 3he 4he versus ch4 4he ratios provide evidence of two component mixing between crustal and magmatic end members extrapolation of the linear regression line to ch4 4he 0 gives a hypothetical magmatic end member 3he 4he ratio of 3 84 ra half the typical mantle ratio this indicates that the magmatic end member may actually represent a mixture of mantle and crustal helium gases which deviate from the simple two component mixture can be explained by addition of pure methane radiogenic 4he or a high n2 he component with 3he 4he 0 6 ra to 1 0 ra the ch4 3he ratio of the magmatic end member remains poorly constrained 0 to 3 109 and one cannot rule out the possibility that a significant proportion of the methane in some fields may be of deep earth origin however fields with the highest 3he 4he ratios are associated with buried plio pleistocene intrusives which have up arched sediments to form hydrocarbon traps the methane in these fields may have been produced by rapid thermal alteration of the intruded sediment elsewhere the methane appears either to have migrated from deeply buried sediments in the western basin or to have been produced by local microbial activity

evaluating the geogenic co2 flux from geothermal areas by analysing quaternary travertine masses new data from western central italy and review of previous co2 flux data abstract quantification of carbon fluxes between solid earth and its atmosphere is necessary to understand the global geological carbon cycle some of the main co2 contributors are metamorphism and magmatic mantle degassing co2 is discharged from active and quiescent volcanoes fault zones geothermal systems and co2 rich groundwater here a new method for the estimation of the geogenic flux of co2 from tectonically active regions based on the volume composition and age of travertine deposits is proposed the method is applied to the travertine deposits of western central italy where travertine deposition is driven by degassing of co2 charged groundwater results show that the study areas are characterized since middle pleistocene by diffuse co2 degassing processes with time averaged co2 fluxes ranging between 1 24 0 12 106 mol y 1 km 2 and 1 38 0 42 106 mol y 1 km 2 these values are of the same order of magnitude of carbon dioxide fluxes measured by different methods in western central italy and are higher than the global baseline co2 flux from high heat flow regions the review of the available 234u 230th and 14c data shows that the co2 degassing processes that affects western central italy nowadays were already active at least 350 ka ago proving that this region is a globally relevant case for the study of earth degassing considering the widespread occurrence of travertine deposits in tectonically active areas worldwide the proposed approach can be used as a reliable tool to estimate the co2 flux in different geodynamic settings within system earth

hydrothermal circulation through mid ocean ridge flanks fluxes of heat and magnesium thermally driven convection of seawater occurs through oceanic crust of all ages at the seafloor spreading axis on mid ocean ridge flanks and in the ocean basins at the ridge axis and on the flanks circulating seawater produces a major chemical exchange between the oceans and the crust based on heat budget constraints and the composition of hot springs between 10 and 40 of the river flux of mg can be taken up during high temperature alteration of the basaltic crust along the ridge axis most of the hydrothermal heat loss however occurs on the mid ocean ridge flanks where the temperatures are lower and the seawater flux correspondingly larger the estimated heat loss on the flanks is so large that upwelling must occur over a large fraction 5 30 of the seafloor less than 65 ma in age if temperatures are 20 c and seepage velocities are on the order of 10 to 100 cm y the circulating seawater needs to lose on average less than 1 2 of its mg content in order to solve the mg mass balance for the oceans chemical fluxes through mid ocean ridge flanks are poorly known because of the wide range of crustal conditions that prevail there and the paucity of study to date the most critical parameter for characterizing crustal conditions is temperature in basement which is a function of crustal age basement topography and sediment thickness and permeability basement temperature which can usually be inferred from heat flow and seismic reflection surveys largely determines the change in the composition of seawater circulating through basement this change can be inferred in turn from profiles of sediment porewater chemistry all sites studied to date with temperatures at the sediment basement interface 25 c have a large component of advective heat loss and show only a small 80 mg loss both types of sites may be important for chemical fluxes whether the cooler sites are important depends on how much the seawater changes in composition as it circulates through the crust only small changes are needed whether the warmer sites are important depends on how much heat is lost by advection in this type of setting the warmer sites could produce significant chemical fluxes even if they are scarce they could account for the entire river input of mg to the oceans even if they represent only 8 20 of the total advective heat loss on ridge flanks

the noble gas geochemistry of natural co2 gas reservoirs from the colorado plateau and rocky mountain provinces usa identification of the source of co2 in natural reservoirs and development of physical models to account for the migration and interaction of this co2 with the groundwater is essential for developing a quantitative understanding of the long term storage potential of co2 in the subsurface we present the results of 57 noble gas determinations in co2 rich fields 82 from three natural reservoirs to the east of the colorado plateau uplift province usa bravo dome nm sheep mountain co and mccallum dome co and from two reservoirs from within the uplift area st john s dome az and mcelmo dome co we demonstrate that all fields have co2 3he ratios consistent with a dominantly magmatic source the most recent volcanics in the province date from 8 to 10 ka and are associated with the bravo dome field the oldest magmatic activity dates from 42 to 70 ma and is associated with the mcelmo dome field located in the tectonically stable centre of the colorado plateau co2 can be stored within the subsurface on a millennia timescale the manner and extent of contact of the co2 phase with the groundwater system is a critical parameter in using these systems as natural analogues for geological storage of anthropogenic co2 we show that coherent fractionation of groundwater 20ne 36ar with crustal radiogenic noble gases 4he 21ne 40ar is explained by a two stage re dissolution model stage 1 magmatic co2 injection into the groundwater system strips dissolved air derived noble gases asw and accumulated crustal radiogenic noble gas by co2 water phase partitioning the co2 containing the groundwater stripped gases provides the first reservoir fluid charge subsequent charges of co2 provide no more asw or crustal noble gases and serve only to dilute the original asw and crustal noble gas rich co2 reservoir scale preservation of concentration gradients in asw derived noble gases thus provide co2 filling direction this is seen in the bravo dome and st john s dome fields stage 2 the noble gases re dissolve into any available gas stripped groundwater this is modeled as a rayleigh distillation process and enables us to quantify for each sample 1 the volume of groundwater originally stripped on reservoir filling and 2 the volume of groundwater involved in subsequent interaction the original water volume that is gas stripped varies from as low as 0 0005 cm3 groundwater cm3 gas stp in one bravo dome sample to 2 56 cm3 groundwater cm3 gas stp in a st john s dome sample subsequent gas groundwater equilibration varies within all fields each showing a similar range from zero to 100 cm3 water cm3 gas at reservoir pressure and temperature

hydrogeochemistry of the middle rio grande aquifer system fluid mixing and salinization of the rio grande due to fault inputs abstract deeply derived fluids influence river and groundwater hydrochemistry at the socorro constriction in the central new mexico rio grande rift new hydrochemical transects in the rio grande rift provide three dimensional perspectives on sources contributing to surface and groundwaters in addition to abrupt salinity increases in the rio grande major and trace ion chemistry 18o d 13c 87sr 86sr 3h and 3he 4he variations in springs and wells across the rift are best explained by mixing of deeply derived endogenic fluids containing both mantle and crustal inputs with shallow groundwater endogenic fluids ascend along rift bounding and intra rift faults and can cause increased salinity accompanied by an increase in metals and overall degradation of water quality our data reinforce models that attribute a downstream increase in salinity to geological not agricultural influences hydrochemical mixing of endogenic waters along faults in shallow aquifers has a major influence on groundwater and surface water quality and variability in arid tectonically active regions with important ramifications for water management

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

a serpentinite hosted ecosystem the lost city hydrothermal field the serpentinite hosted lost city hydrothermal field is a remarkable submarine ecosystem in which geological chemical and biological processes are intimately interlinked reactions between seawater and upper mantle peridotite produce methane and hydrogen rich fluids with temperatures ranging from 40 to 90 c at ph 9 to 11 and carbonate chimneys 30 to 60 meters tall a low diversity of microorganisms related to methane cycling archaea thrive in the warm porous interiors of the edifices macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the mid atlantic ridge but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems

withdrawn detrital zircon u pb ages and hf isotopes of the metasedimentary rocks from the jiaodong group jiaobei terrane provenance and implications for the crustal evolution in the 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

exhumation tectonics of the ultrahigh pressure metamorphic rocks in the qinling orogen in east china new petrological structural radiometric insights from the shandong peninsula 1 in eastern china the sulu area is recognized as the eastern extension of the qinling dabie belt which is famous for its ultrahigh pressure uhp metamorphism although numerous petrologic and geochemical works are available structural data are still rare this paper provides the first extensive study of bulk geometry and kinematic analysis of the shandong peninsula the study area is divided into three tectonic areas by cretaceous faults namely a southern uhp belt or sulu area a northern migmatite area and an eastern eclogite and migmatite area or weihai area conversely to the deeply entrenched idea that the later area belongs to the north china belt and the two others to the south china block scb we argue that all three areas are parts of the scb structural petrologic 40ar 39ar and u pb data comply with this new interpretation in the north shandong area mafic granulites enclosed as blocks within gneissic migmatites do not significantly differ from the sulu and weihai eclogites which also experienced a granulite facies overprint before migmatization the circa 210 200 ma age of the main ductile deformation is related to an extensional event during the triassic or indosinian orogeny this date corresponds to the temperature climax but the time of the pressure peak i e the real age of the uhp metamorphism is discussed

carbonic springs as distal manifestations of geothermal systems highlighting the importance of fault pathways and hydrochemical mixing example from the jemez mountains new mexico abstract we examine a series of carbonic warm and hot springs in northern new mexico usa 1 tierra amarilla springs 2 penasco springs and 3 soda dam jemez and indian hot springs spring geochemistry is compared to waters from the valles caldera geothermal system and to groundwater in nearby sedimentary aquifers multiple hydrochemical tracers are applied to quantitatively evaluate flow paths and mixing at varying distances from the caldera we test three hypotheses for source and transport of waters to tierra amarilla and penasco springs san juan basin origin meteoric flow from the nacimiento mountains and or influence from the valles caldera geothermal system geochemically carbonic spring groups are distinct from meteoric and sedimentary aquifer waters based on isotopes of he and sr and concentrations of cl so4 li and b we interpret these carbonic springs to be distal manifestations of fluid circulation along faults with a mixture of valles caldera geothermal waters local meteoric and paleozoic aquifer waters with the potential for small contributions from the san juan basin aquifers semi confined fault conduits the jemez fault and nacimiento fault systems provide connectivity and help explain geochemical similarities and mixing trends within carbonic spring systems and between these systems and the distal valles caldera in addition penasco springs are interpreted to reflect a component of outflow from the geothermal system that crosses the nacimiento mountain basement block along ne trending faults input of deeply sourced waters can degrade water quality by contributing significant salinity and trace metals to groundwater at distances of 50 km from geothermal systems with faults acting as conduits for subsurface fluid flow