provenance of neoproterozoic and early paleozoic siliciclastic rocks of the tepla barrandian unit bohemian massif evidence from u pb detrital zircon ages abstract new la icp ms u pb detrital zircon ages from ediacaran and paleozoic siliciclastic rocks are used to constrain provenance and paleogeographic affinities of the tepla barrandian unit tbu in the centre of the bohemian massif central europe czech republic the samples taken span the period from 635 ma to 385 ma and permit recognition of provenance changes that reflect changes in geotectonic regime detrital zircon age spectra of two ediacaran one lower cambrian and three upper ordovician samples resemble the ages known from the nw african proportion of gondwana particularly the trans saharan belt while three rocks from higher lower cambrian to lowermost ordovician strata contain detritus that may have been derived exclusively from local sources the age spectrum of the devonian rock is a combination of the nw gondwanan and local features these new findings in combination with a wide range of published data are in agreement with a neoproterozoic subduction related setting at the margin of gondwana followed by a cambrian early ordovician rifting stage and an ordovician passive margin setting furthermore the data are in favour of a position of the tbu at the gondwanan margin throughout pre variscan times

provenance of sediments from mesozoic basins in western shandong implications for the evolution of the eastern north china block abstract this paper reports la icp ms u pb dates and in situ hf isotope analyses of detrital zircons from the mesozoic basins in western shandong china with the aim to constrain the depositional ages and provenances of the mesozoic strata as well as the mesozoic tectonic evolution of the eastern north china block ncb the mesozoic strata in western shandong from bottom to top include the fenghuangshan fangzi santai and wennan formations most of the analyzed zircon grains exhibit oscillatory growth zoning and have relatively high th u ratios generally 0 2 3 4 suggesting a magmatic origin zircons from the fenghuangshan formation in the zhoucun basin yield six main age populations 2489 1854 331 305 282 and 247 ma zircons from the fangzi formation in the zhoucun and mengyin basins yield eight main age populations 2494 1844 927 465 323 273 223 and 159 ma and ten main age populations 2498 1847 932 808 540 431 315 282 227 and 175 ma respectively whereas zircons from the santai formation in the zhoucun and mengyin basins yield nine main age populations 2519 1845 433 325 271 237 192 161 and 146 ma and six main age populations 2464 1845 853 277 191 and 150 ma respectively five main age populations 2558 1330 609 181 and 136 ma are detected for zircons from the wennan formation in the pingyi basin based on the youngest age together with the contact relationships among formations we propose that the fenghuangshan formation formed in the early middle triassic the fangzi formation in the middle late jurassic the santai formation after the late jurassic and the wennan formation after the early cretaceous these results together with previously published data indicate that 1 the sediments of the fenghuangshan formation were sourced from the precambrian basement and from late paleozoic to early mesozoic igneous rocks in the northern part of the ncb 2 the sediments of the fangzi and santai formations were sourced from the precambrian basement late paleozoic to early mesozoic igneous rocks in the northern part of the ncb and the sulu terrane as well as from middle late jurassic igneous rocks in the southeastern part of the ncb and 3 the wennan formation was sourced from the tongshi intrusive complex the sulu terrane and minor precambrian basement and early cretaceous igneous rocks the evolution of detrital provenance indicates that in the early middle triassic the northern part of the ncb was higher than its interior during the late triassic to early jurassic the eastern ncb was uplifted resulting in a period of non deposition and an important transition from a compressional to an extensional tectonic regime occurred during the middle late jurassic the presence of neoproterozoic and triassic detrital zircons in the fangzi formation sourced from the sulu terrane suggests that large scale sinistral strike slip movement along the tan lu fault zone did not occur after the middle jurassic ca 175 ma

uhp metamorphism and exhumation of the dabie orogen china evidence from shrimp dating of zircon and monazite from a uhp granitic gneiss cobble from the hefei basin a shrimp u pb study of zircons separated from an ultrahigh pressure uhp granitic gneiss cobble sample ds12 from the upper jurassic fenghuangtai formation of the hefei basin north of the dabie orogen has identified three different domains 1 cores some of which show straight boundaries and strong oscillatory zoning with th u ratios of 0 12 0 70 and an imprecise upper intercept age of 777 220 ma mswd 2 4 2 mantles variable in shape and cathodoluminescence cl intensity and containing many uhp mineral inclusions including coesite and omphacite and with th u ratios of 0 02 0 26 and a weighted mean 206pb 238u age of 244 5 ma mswd 4 7 and 3 rims which are more homogeneous and luminescent in cl than the mantles and contain fewer uhp mineral inclusions with th u ratios of 0 01 0 05 and a weighted mean 206pb 238u age of 226 2 ma mswd 0 65 monazites from the same sample do not contain coesite and omphacite inclusions but they do show sector zones and are composed of two contrasting domains the light domains in backscattered electron bse images have a th u ratio of 7 3 18 9 and a weighted mean 206pb 238u age of 221 2 ma mswd 0 94 the dark domains in bse have a th u ratio of 2 8 7 2 and have a weighted mean 206pb 238u age of 218 2 ma mswd 0 96 based on these data and a review of the literature it can be concluded that 1 the protolith of gneiss sample ds12 is a granitoid of neoproterozoic age 2 the ages of 244 and 226 ma for the mantle and rim domains of the zircons are time records of two discrete stages in the uhp evolution of dabieshan 3 the ages of 221 and 218 ma for the light and dark gray domains respectively of the monazites record the times of two stages of retrogressive metamorphism during exhumation of the uhp granitic gneiss to a higher crustal level 4 the exhumation rate of the gneiss is estimated to be 6 km ma and 5 the uhp metamorphic blocks of the dabie orogen provided significant detritus to the hefei basin in the jurassic

decay constant errors in u pb concordia intercept ages abstract although almost universally ignored the effect of errors in the uranium decay constants on u pb concordia intercept ages and pb pb ages are significant and not equivalent to those of simple u pb ages equations are derived for concordia intercept age errors that take decay constant errors into account

interpretation of field tracer tests of a single fracture using a transient solute storage model the results and interpretation of five induced gradient tracer tests performed at five different average interborehole fluid velocities in a single fracture in monzonitic gneiss are described the experiments were conducted using radioactive 82br and a fluorescent dye as conservative tracers where the tracers were pulse injected into radial convergent and injection withdrawal flow fields the flow fields were established between straddle packers isolating the fracture in three boreholes over distances of 12 7 29 8 m the tracer breakthrough curves were determined from samples of the withdrawn groundwater and were interpreted using residence time distribution rtd theory and two deterministic simulation models the rtd curves of the tracer experiments were interpreted by fitting to the field data a simple advection dispersion model and an advection dispersion model with transient solute storage in immobile fluid zones both models consider the different flow field geometries associated with injection withdrawal and radial convergent tests comparison of the fits obtained by the simulation models suggest that the initial period of solute transport in single fractures is advection dominated and with increasing tracer residence time or decreasing fluid velocity transport progresses toward more fickian like behavior during the advective dominated period the transient solute storage model is shown to adequately describe the asymmetries and long tails characteristic of the fracture rtds interpretation of the tracer experiments using both simulation models further suggests that induced gradient tracer experiments are likely to underestimate the dispersive characteristics of single fractures under natural flow conditions

detrital zircon u pb geochronology of pennsylvanian permian sandstones from the turnaicum and meliaticum western carpathians slovakia provenance and tectonic implications the blueschist bearing borka nappe regarded as a part of the meliaticum unit s l and the turnaicum unit in its hanging wall were thrusted together to the north on the inner western carpathians basement during the orogenic events of the late jurassic early cretaceous a new u pb sensitive high resolution ion microprobe shrimp magmatic as well as detrital zircon ages were used to constrain provenance and paleogeography the detrital zircon age spectrum of the studied metasediments contains mainly ages of the ediacaran cryogenian 550 720 ma and tonian stenian 0 9 1 1 ga which correspond to the pan african belt and saharan metacraton subordinate archean ages were likely derived from the saharan metacraton of north gondwana 1 7 2 2 and 2 5 2 7 ga the 273 2 ma zircon age of a metarhyolite along with the youngest detrital zircon of 265 4 ma from the associated metasediments specify the maximum depositional age of the bucina fm from the borka nappe to the guadalupian the rhyolite olistoliths from the middle late jurassic meliaticum olistostrome yielded the latest cambrian earliest ordovician 488 6 ma and middle ordovician 465 ma zircon ages this is consistent with the u pb zircon ages from the foot walling southern gemericum basement metavolcanites which are therefore regarded as a potential source the obtained zircon ages confirm the provenance from the southern gemericum basement and its permian envelope for the meliaticum borka nappe and turnaicum sedimentary embayment

sources and petrogenesis of late triassic zhiduo volcanics in the northeast tibet implications for tectonic evolution of the western jinsha paleo tethys ocean abstract the western jinsha suture representing a branch of the paleo tethys makes the junction between the songpan ganzi complex and the north qiangtang block nqb however the triassic tectonic evolution of the western jinsha paleo tethys ocean is poorly constrained this paper shows new la icp ms zircon u pb geochronology major and trace elements and sr nd hf isotopic compositions of the zhiduo dacitic volcanic rocks in the northern margin of the nqb la icp ms zircon u pb dating displays that they erupted between 227 2 and 228 1 ma these rocks exhibit high silica medium k calc alkalic signature and low mgo tio2 p2o5 cr and ni compositions they are enriched in light rare earth elements and large ion lithophile elements with moderate to strong negative eu anomalies eu eu 0 24 0 56 and depleted in heavy rare earth elements and high field strength elements they possess relatively low initial 87sr 86sr ratios 0 7055 0 7084 positive whole rock end t 0 2 to 1 4 and magmatic zircon ehf t values focus on 9 2 2 7 with young nd and hf model ages t2dm nd 885 983 ma t2dm hf 467 1035 ma these features are comparable to those of typical arc volcanic rocks and indicate that they were probably derived from partial melting of a juvenile crust source the eruption of these volcanic rocks could be attributed to southward subduction of the western jinsha paleo tethys ocean in combination with previous studies we propose that the subduction of the western jinsha paleo tethys ocean initiated at the beginning of the late triassic ca 228 ma and closed at the end of the late triassic ca 208 ma in addition there is a universal northeastward younging trend of arc magmas in the northern margin of the nqb which may indicate a model involving the initial shallow subduction and subsequent slab roll back

investigations into the factors influencing long range matrix diffusion rates and pore space accessibility at depth in granite abstract investigations in granite systems have been conducted on 1 diffusion through fissure surfaces 2 the effect of confining pressures on diffusion rates 3 the extent of pore interconnectivity over metre distances and 4 the accessiblity of the pore space to colloidal particles in the size range 0 3 0 09 m diffusion rates through fissure surfaces were found to be greater than or equal to those measured on samples taken well away from such surfaces no evidence for pore blocking by alteration products was found confining pressures of up to 16 mpa reduced diffusion rates at the highest pressures reductions by factors of between 2 and 2 5 compared with diffusion rates measured at ambient pressure were recorded pore connectivity over distances of up to 125 cm on granite cores saturated with 3 m nacl was demonstrated by the measurement of formation factors as a function of core length using a conductivity technique increases in the formation factor for short core lengths 1 cm were ascribed to sample size and pore geometry effects which converted some of the dead end porosity into transport porosity colloidal particles in the size range investigated neither entered the pore structure nor blocked pore apertures to any significant extent

mafic magmatic enclaves and mafic rocks associated with some granitoids of the central sierra nevada batholith california nature origin and relations with the hosts abstract the calc alkaline granitoids of the central sierra nevada batholith are associated with abundant mafic rocks these include both country rock xenoliths and mafic magmatic enclaves mme that commonly have fine grained and less commonly cumulate textures scarce composite enclaves consist of either xenoliths enclosed in mme or of mme enclosed in other mme with different grain size and texture enclaves are often enclosed in mafic aggregates and form meter size polygenic swarms mostly in the margins of normally zoned plutons enclaves may locally divert schlieren layering mafic dikes which also occur in swarms are undisturbed composite or largely hybridized in central sierra nevada with the exception of xenoliths that completely differ from the other rocks host granitoids mafic aggregates mme and some composite dikes exhibit a bulk compositional diversity and at the same time important mineralogical and geochemical including isotopic similarities mme and host granitoids display distinct major and trace element compositions however strong correlations between mme host granitoid pairs indicate interactions and parallel evolution of mme and enclosing granitoid in each pluton identical mafic mineral compositions and isotopic features are the result of these interactions and parallel evolution mafic dikes have broadly the same major and trace element compositions as the mme although variations are large between the different dikes that are at distinctly different stages of hybridization and digestion by the host granitoids the composition of the granitoids and various mafic rocks reflects three distinct stages of hybridization that occurred respectively at depth during ascent and emplacement and after emplacement the occurrence and succession of hybridization processes were tightly controlled by the physical properties of the magmas the sequential thorough or partial mixing and mingling were commonly followed by differentiation and segregation processes unusual mme that contain abundant large crystals of hornblende resulted from disruption of early cumulates at depth whereas those richer in large crystals of biotite were formed by disruption of late mafic aggregates or schlieren layerings at the level of emplacement mme and host granitoids are considered cogenetic because both are hybrid rocks that were produced by the mixing of the same two components in different proportions the felsic component was produced by partial melting of preexisting crustal materials whereas the dominant mafic component was probably derived from the upper mantle however in the lack of a clear mantle signature the origin of the mafic component remains questionable

u pb ages and morphologies of zircon in microgranitoid enclaves and peraluminous host granite evidence for magma mingling granites of the s type wilson s promontory batholith lachlan fold belt australia contain zircons which are euhedral and relatively large their age is 395 ma which can be considered as the best available estimate of the crystallysation age of the granites contrary to their dominance in other s type granites of the lachlan fold belt very few zircon cores give inherited ages varying between 500 and 1700 ma microgranitoid enclaves contained within the granites contain a zircon population that is dominated by relatively small anhedral or elongated crystals these give ages that are indistinguishable from the crystallisation age of the granite some enclaves which are characterised by the presence of megacrysts contain a proportion of larger euhedral zircons these zircons give inherited ages similar to the zircons from the granitic host rocks the data are in agreement with a magma mingling origin for the microgranitoid enclaves the large euhedral zircons are interpreted to have been introduced into the enclave magma during a hybridisation event which also introduced quartz and plagioclase megacrysts into the magma the relatively high proportion of inherited cores within the large zircon population of the enclaves is related to the timing of mixing between enclave and host magma this mixing event took place before the majority of the magmatic zircons crystallised in the granitic magma the small anhedral zircons within the enclaves crystallised during quenching of the globules of enclave magma against the cooler granitic magma

the anatomy of a gondwanan terrane the neoproterozoic ordovician basement of the pre alpine sebes lotru composite terrane south carpathians romania abstract the sebes lotru terrane in the south carpathians mountain range comprises a lower neoproterozoic metamorphic unit lotru and an upper ordovician metamorphic unit cump na that were juxtaposed during the variscan orogeny two orthogneisses from the lotru metamorphic unit yield u pb la icp ms zircon crystallization ages of 549 3 3 8 ma and 587 5 3 ma respectively two orthogneisses from the cump na metamorphic unit yield zircon crystallization ages of 458 9 3 5 ma and 466 0 4 2 ma respectively high u zircons from two other orthogneisses from the cump na metamorphic unit have ages ranging from 400 ma to 320 ma which are interpreted to reflect protracted zircon recrystallization during the regionally significant variscan collisional event detrital zircons from a metasedimentary gneiss in the cump na metamorphic unit have ages ranging from 0 5 ga to 2 8 ga the 0 5 ga age constrains the maximum sediment deposition age to be late cambrian the source most compatible with the range of precambrian detrital ages in the sebes lotru terrane is northeastern gondwana the sebes lotru terrane was part of a continental subduction collision system as a lower plate after about 400 ma and reached peak metamorphic conditions between 350 and 320 ma e g medaris et al 2003 a cross cutting granite vein has a zircon u pb crystallization age of 321 5 3 1 ma which constrains minimum age of ductile deformation during the variscan collision in this region the trace of the rheic suture within the south carpathians is located between the ordovician upper part of the sebes lotru terrane and the dr gsan pre alpine terrane of the danubian domain

the age isotopic signature and significance of the youngest mesozoic granitoids in the jiaodong terrane shandong province north china craton abstract most cretaceous granitoids in the jiaodong terrane of shandong province north china craton were intruded between 130 and 122 ma however four granitoid batholiths are significantly younger with an average zircon u pb shrimp emplacement age of 116 2 ma these are the sanfoshan batholith 118 1 ma the aishan batholith 116 1 ma the yashan pluton 113 2 ma and the laoshan batholith 115 2 ma these granitoids post date proposed delamination that occurred prior to 125 ma in the eastern ncc and their geochemistry thus provides information about the nature of the continental crust at this time the rocks are mostly monzogranites and syenogranites of i type affinity with local alkali feldspar granite of a type affinity in addition a monzogranite sample from the aishan batholith records an age of 125 3 ma indicating a direct association with the slightly older granitoids in the area indeed they all contain inherited zircons with ages of 125 120 ma indicating interaction with these earlier granitoids most samples are metaluminous enriched in light rare earth elements and depleted in high field strength elements paleo to neoarchean t dm2 model ages ranging from 3900 ma to 2491 ma and negative e hf t values imply the involvement of archean basement and older recycled continental crustal material in the magma source region they were likely derived from partial melting of the lower or middle crust due to mafic magma underplating followed by various degrees of interaction between mantle derived mafic magma and felsic crustal magma accompanied by fractional crystallization we propose that lithospheric thinning and extension in the early cretaceous due to roll back of the pacific plate beneath the eastern north china craton led to asthenospheric upwelling and basaltic magmatism this underplating in turn led to crustal melting and evolution of the granitic intrusions described here

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

late cambrian ordovician magmatic arc type volcanism in the southern gemericum basement western carpathians slovakia u pb shrimp data from zircons the low grade crystalline basement of the southern gemeric unit inner western carpathians consists mainly of siliciclastic deep water turbidite sequence associated with a huge mass of redeposited rhyolite dacite volcanics and their volcaniclastics in situ u pb shrimp zircon dating applied to metavolcanic rocks contributed to specification of the southern gemeric crystalline basement stratigraphy the gelnica group zircon populations from ten samples of three lithostratigraphic units of the gelnica group rock complex have been analysed the zircons presented significant magmatic zoning part of the magmatic zircons contained inherited older cores the vlachovo formation gives the 494 1 6 ma zircon average age the bystr potok formation gives 465 8 1 5 ma and the drnava formation 463 9 1 7 ma average age the geochemical data are compatible with an orogenic geodynamic setting dominant rhyolite dacite volcanites belong to the peraluminous calc alkaline high k magmatic series the age data let us presume two phase longlasting magmatic activity starting in the late cambrian and continuing to the middle late ordovician thus the studied late cambrian volcanic sequence of the gelnica group reflects the active continental margin setting the second middle ordovician volcanic phase documents an assumed rifting stage accompanied by a strong volcanic activity with inherited features of the late cambrian magmatic arc the inherited cores of magmatic zircons have proterozoic 600 760 1 000 1 400 2 000 2 700 ma and archean 3 099 3 164 ma ages

multiple sources for the origin of granites geochemical and nd sr isotopic evidence from the gudaoling granite and its mafic enclaves northeast china geochemical and sr and nd isotopic data have been determined for mafic to intermediate microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china the rocks include monzogranite porphyric granodiorite and quartz diorite monzogranites have relatively high 87rb 86sr ratios 0 672 0 853 low initial 87sr 86sr ratios 0 7052 0 7086 and e nd t values 18 5 to 20 9 indicating that they were mainly derived from a newly underplated crustal source with a short crustal residence time quartz diorites have high initial 87sr 86sr ratios 0 7118 0 7120 and negative e nd t values 13 2 to 18 1 coupled with high al2o3 and mgo contents indicating they were derived from enriched lithospheric mantle with contributions of radiogenic sr from plagioclase rich metagreywackes or meta igneous rocks i e ancient lower crust two groups of enclaves with igneous textures and abundant acicular apatites are distinguished dioritic enclaves and biotite monzonitic enclaves dioritic enclaves have low al2o3 13 5 16 4 wt and high mgo mg 72 3 concentrations low initial 87sr 86sr ratios 0 7058 0 7073 and negative e nd t values 7 2 and are enriched in liles and lrees and depleted in hfses suggesting they were derived from an enriched lithospheric mantle source biotite monzonitic enclaves have sr and nd isotopic compositions similar to the monzogranites indicating they were crystal cumulates of the parental magmas of these monzogranites granodiorites have transitional geochemistry and nd and sr isotopic compositions intermediate between the monzogranites quartz diorites and the enclaves geochemical and sr and nd isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mafic mantle derived and juvenile crustal derived magmas coupled with crystal fractionation and assimilation of ancient lower crust is compatible with the data this example shows that at least some calc alkaline granitoids are not produced by pure intracrustal melting but formed through a complex multi stage hybridization process involving mantle and crustal derived magmas and several concomitant magmatic processes crystal fractionation crustal assimilation and crustal anatexis

pyrite rb sr sm nd and fe isotopic constraints on the age and genesis of the qingchengzi pb zn deposits northeastern china abstract sr nd fe isotopes are reported for pyrites and whole rocks of ores and associated rocks for the qingchengzi pb zn deposits in the northeasern china to investigate the age sources and processes of the pb zn mineralization rb sr leaching isotopic dating of pyrites that crystallized coeval with galena and sphalerite from five subsamples of ores yields isochron ages of 143 12 ma to 159 12 ma with a weighted mean age of 151 8 5 2 ma this age can be interpreted to be the timing of pb zn mineralization coeval with the emplacement of late jurassic granites in the region the pyrites have negative end 152 ma values of 17 6 to 22 0 among the neoarchean ttg rocks paleoproterozoic meta sedimetary rocks i e wall rocks and granites and mesozoic mafic dykes and granites however the initial 87sr 86sr ratio of 0 7188 0 0004 is similar to those of late jurassic granites and paleoproterozoic rocks 0 7082 0 7183 distinct from those of mafic dykes 0 7069 0 7110 indicating the ore forming materials i e pb and zn were mainly derived from wall rocks and late jurassic granites combined with the previously published h o isotopes the new age and sr nd isotopic data indicate that the mineralizaing fluids were mainly derived from dehydration of granitic magmas interacted with meteoric water that extracted pb and zn from the wall rocks the 56fe values of pyrites in the pb zn ores and paleoproterozoic meta sedimentary rocks range from 0 23 to 1 09 and 0 49 to 0 17 respectively distinct from those of paleoproterozoic basement rocks and mesozoic rocks 0 03 to 0 28 combined with nd isotopes the large range of 56fe values for pyrites would be the result of rapid precipitation of pyrites in the wall rocks and contemperal deposition of pyrites in the residual fluids during interaction between wall rocks and ore forming fluids collectively our new sr nd fe isotopes of pyrites not only constrain the age and sources of pb and zn mineralization but also reveal the detailed mineralization processes providing a new method to constrain the genesis of hydrothermal pb zn deposits

late carboniferous high end t ehf t granitoids enclaves and dikes in western junggar nw china ridge subduction related magmatism and crustal growth abstract we report results of petrologic geochronological and geochemical investigation of the late carboniferous diorites granodiorites amphibole am bearing granites and associated dioritic and monzonitic enclaves and mafic and granitic dikes in the keramay area of the western junggar region of central asian orogenic belt caob zircon u pb dating suggests that they were generated in the late carboniferous 316 304 ma the diorite and granodiorite compositions extend over a wide range of sio2 53 70 wt sr 240 602 ppm and mg 41 58 values and are characterized by moderately fractionated rare earth element ree patterns nb ta depletion and relatively low y and yb contents the mafic dikes consist of dolerites diorite porphyries and minor granodiorite porphyries and have variable sio2 51 59 wt and high mg cr and ni values with the exception of two samples with relatively high heavy ree hree contents the mafic dikes exhibit trace element characteristics similar to diorites and granodiorites the am bearing granites and a granite porphyry dike sample have high levels of sio2 73 77 wt hrees e g yb 3 46 15 7 ppm and low mg cr and ni contents along with clearly negative eu ba and sr anomalies similar to typical a type granites all granitoids enclaves and dikes in this region have high positive end t 7 13 to 9 74 and zircon ehf t 10 to 16 values and moderate initial 87sr 87sr ratios 0 7004 0 7049 mineral composition data suggest that the parental magmas for mafic dikes are similar to cenozoic sanukitoids in the setouchi arc area japan and were possibly generated under water rich and high oxygen fugacity nno 1 5 to nno 2 7 conditions they most likely originated from partial melting of a mantle source variably modified by subducted oceanic crust derived melts and minor fluids and subsequently underwent fractional crystallization the diorites and granodiorites were possibly generated by magma mixing between enriched lithospheric mantle and juvenile lower crust derived magmas coupled with minor crystal fractionation the am bearing granites and granite porphyry dike were produced by partial melting of juvenile crustal materials at shallow crustal levels taking into account widespread contemporaneous magmatism including morb type basalts and slab derived adakites in western junggar we suggest that the keramay intrusive rocks were generated in a special arc setting related to ridge subduction and resultant slab window which played an important role in the crustal growth of the caob

zircon age constraints on sediment provenance in the caspian region sensitive high resolution ion microprobe shrimp u pb ages for detrital zircons from the caspian region reveal the age ranges of basement terrains that supplied the sediment one sample from the modern volga river has groupings at c 340 370 ma c 900 1300 ma and c 1450 1800 ma with a small number of older zircons this is consistent with derivation from the precambrian basement of the east european craton and palaeozoic arcs in the urals mid and late proterozoic components may be derived from beyond the present volga drainage basin such as the sveconorwegian orogen a bajocian sandstone from the greater caucasus has 73 zircons that post date 350 ma ages cluster at c 165 185 ma c 220 260 ma c 280 360 ma and c 440 460 ma this pattern suggests derivation from palaeozoic basement of the greater caucasus itself and or the scythian platform and igneous rocks generated at a jurassic arc in the lesser caucasus four samples from the lower pliocene productive series of the south caspian basin have common phanerozoic grains and groups between c 900 1300 ma and 1500 2000 ma each sample contains zircons dated to c 2700 ma the overall age patterns in the productive series samples suggest a combination of east european craton and greater caucasus source components

mesozoic crust mantle interaction beneath the north china craton a consequence of the dispersal of gondwanaland and accretion of asia we present evidence from zircons entrained within lower crustal xenoliths in the cenozoic hannuoba basalt of multiple melting events beneath the north china craton in the late mesozoic peak activity was between 180 and 80 ma the upper crustal signature of which was the generation of voluminous granitoids and related volcanic rocks emplacement of dioritic and lamprophyric dikes and widespread gold mineralization the process involved partial loss of mantle lithosphere accompanied by wholesale rising of asthenospheric mantle beneath eastern china we correlate these events with lithospheric thinning resulting from the breakup and dispersal of gondwanaland accompanied by a major mantle overturn fueled by the destruction of oceanic lithosphere and triggered by its sinking into the lower mantle during the subsequent accretion of asia

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

a hybrid origin for the qianshan a type granite northeast china geochemical and sr nd hf isotopic evidence abstract major and trace element whole rock sr and nd isotope and zircon hf isotope data are reported for a suite of a type granites and mafic microgranular enclaves from the early cretaceous 126 2 ma qianshan pluton liaodong peninsula northeast china with the aim of investigating the sources and petrogenesis of a type granites the qianshan pluton includes hornblende alkali feldspar granite graphic biotite granite and mafic microgranular enclaves the hornblende alkali feldspar granites have high sio 2 fe 2 o 3t mgo k 2 o na 2 o rb zr and lree contents and low ba and sr concentrations with strongly negative eu anomalies their high rb sr 87 rb 86 sr 16 76 24 15 and initial 87 sr 86 sr ratios 0 7215 to 0 7283 negative e nd t values 14 1 to 16 5 and zircon e hf t values 18 9 to 11 5 indicate they were mainly derived from a crustal source but with involvement of high e nd t and e hf t materials graphic biotite granites have similar geochemical features and sr nd hf isotopic compositions to enclaves indicating they were the result of crystal fractionation of evolved mafic magmas but with involvement of low e nd t and e hf t materials the mafic enclaves have an igneous texture and contain acicular apatite suggesting quenching of mafic magmas that have co mingled with the host granites they have low initial 87 sr 86 sr ratios 0 7097 0 7148 negative e nd t 14 5 to 11 9 and zircon e hf t 17 1 to 6 9 values and are enriched in liles and lrees and depleted in hfses when coupled with the high mgo mg up to 54 this indicates derivation from an enriched lithospheric mantle source but contaminated by crustal materials geochemical and sr nd and zircon hf isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mantle derived mafic and crustal derived magmas coupled with crystal fractionation is compatible with the data this example shows that at least some a type granites formed through a complex process involving mantle and crustal derived magma mixing crystal fractionation and infracrustal melting

recognition of the latest permian to early triassic cu mo mineralization on the northern margin of the north china block and its geological significance abstract in this paper we present newly obtained molybdenite re os ages for the chehugou copper molybdenum deposit and the yuanbaoshan molybdenum mineral locality from the chifeng area on the northern margin of the north china block combined with u pb zircon ages of the host granites the re os isochron age of six molybdenite samples from the chehugou deposit is 257 5 2 5 ma and one molybdenite sample from the yuanbaoshan locality yields a re os model age of 248 0 2 7 ma these ages clearly indicate the signature latest permian to early triassic cu mo or mo mineralization that has not been previously recognized zircon la icp ms u pb dating shows that the host granites of the chehugou deposit and yuanbaoshan locality formed in the late devonian 376 3 ma and late permian 269 3 ma respectively and is not of jurassic age as previously thought the latest permian to early triassic cu mo mineralization is likely related to extension due to final closure of the paleo asian ocean and amalgamation of the mongolian arc terranes with the northern north china block the establishment of a latest permian to early triassic age for mineralization should encourage renewed exploration aimed at the discovery of new mo or cu mo resources along the northern margin of the north china block

the liaonan wanfu metamorphic core complexes in the liaodong peninsula two stages of exhumation and constraints on the destruction of the north china craton 1 the liaodong peninsula early cretaceous extension province lep located in the eastern part of the north china craton ncc was highly extended in early cretaceous the liaonan and the wanfu metamorphic core complexes mccs are two most important elements in the province both are typical cordilleran type core complexes that are composed of a general three layered structure but show various differences shearing along the jinzhou detachment fault zone in the liaonan mcc generated ductile to brittle tectonites various deformation microstructures and several types of quartz c axis fabrics implying that the mcc has a complicated progressive exhumation history however medium temperature microstructures and fabrics are superimposed by low temperature features along the wanfu detachment fault zone suggesting a relatively short and simple exhumation history of the wanfu mcc magmatic zircon u pb geochronological dating reveals that the early cretaceous extension of the lep began with the initiation of shearing along the jinzhou detachment fault zone and exhumation of the liaonan mcc before ca 134 ma subsequently relatively slow cooling and exhumation of the lower plate accompanied a giant magmatic event from 130 ma to 120 ma exhumation of a new mcc i e the wanfu mcc was triggered by progressive extension after ca 120 ma rapid cooling and exhumation of the metamorphic lower plate of the two mccs are attributed to coeval detachment faulting along both the jinzhou and wanfu faults from 120 ma to 113 ma the extension ended at ca 107 ma these data provide reliable evidence that the two mccs were exhumed progressively and sequentially during two stages of crustal extension of the lep our results indicates that heterogeneous lithosphere extension and upper middle crust upper mantle detachment possibly due to the interaction between the paleo pacific and eurasian plates are among the most important processes during the early cretaceous thinning of the lithosphere tectonic extension may have led to the detachment in east asia which contributed to the thinning of the lithosphere and the destruction of the ncc a phase of uniform and consistent wnw ese extension was responsible for the generation of the extensional structures in the eastern asia continent and the destruction of the ncc

deducing the ancestry of terranes shrimp evidence for south america derived gondwana fragments in central europe we present here an example of how the sensitive high resolution ion microprobe shrimp zircon dating method can provide a terrane specific geochronological fingerprint for a rock and thus help to reveal major tectonic boundaries within orogens this method applied to inherited zircons in a ca 580 ma metagranitoid rock from the eastern bohemian massif has provided for the first time in the central european variscan basement unequivocal evidence for mesoproterozoic and late paleoproterozoic geologic events ca 1 2 ga 1 5 ga and 1 65 1 8 ga the recognition of such zircon ages has important consequences because it implies that parts of the precambrian section of variscan central europe were originally derived from a grenvillian cratonic province as opposed to the common assumption of an african connection a comparison with previously published shrimp data suggests however that these mesoproterozoic and late paleoproterozoic zircon ages may be restricted to the moravo silesian unit in the eastern variscides whereas the saxothuringian and moldanubian zones appear to contain a typical north african i e neoproterozoic plus eburnian inherited zircon age spectrum this finding supports new tectonic concepts according to which variscan europe is composed of a number of completely unrelated terranes with extremely different paleogeographic origins the moravo silesian unit can be best interpreted as a peri gondwana terrane which was situated in the realm of the amazonian cratonic province by the late precambrian comparable to the avalonian terranes of north america and the united kingdom

petrography of modern marine sands from the peru chile trench and adjacent areas sand samples from piston cores taken in the peru chile trench and adjacent areas were examined petrographically in an attempt to characterize sands from the oceanward side of a continent margin volcanic arc framework composition averaged q18f44l38 close to the average reported for this type of setting but showed wide variation in the ratio of feldspar to lithic fragments quartz was uniformly low less than 30 samples rich in lithic grains were from sites that lie off areas of recent volcanism on the adjacent continent samples from off southern central america had compositions more like those found in island arc settings averaging q3f21l76 whereas those from the straits of magellan increased in quartz and decreased in lithic fragments toward the atlantic plagioclase was greatly predominant over k feldspar in all samples and averaged an28 a considerable portion of the plagioclase was close to end member albite suggesting recycling from pre existing sedimentary rocks climate had no obvious effect on the framework proportions or the feldspar composition but the volume of sediment in the trench increases with increasing rainfall on the continent

pb ages of detrital zircons in relation to geodynamic evolution paleozoic of the northern gemericum western carpathians slovakia abstract new u pb sensitive high resolution ion microprobe shrimp detrital zircon ages from early paleozoic to permian siliciclastic metasediments are used to constrain provenance and paleogeographic affinity of the northern gemericum unit ngu in the western carpathians central europe the samples span the time period from 480 ma to 260 ma and permit the recognition of provenance changes that reflect the realm s geodynamic evolution the detrital zircon age spectrum of one early paleozoic sample resembles the neoproterozoic and archean ages of the cadomian belt 550 650 ma and the west african craton provenances 1 8 2 7 ga the origin of the early paleozoic ngu rakovec basin is inferred to be the rifting as followed by back arc spreading which occurred at the cambrian ordovician boundary ca 480 ma as continental pieces started to split off from the gondwanan margin the deformation and closure of the early paleozoic basin is coincident with the 355 ma peak of the post tournaisian detrital zircon age assemblage the detrital zircon age spectra of two post mississippian and two post artinskian samples indicate high exhumation and erosion rates in the variscan collision belt pennsylvanian permian sedimentary troughs formed between 318 and 275 ma record contemporaneous unroofing of the variscan collision belt and magmatic activity during post orogenic transtensional tectonics zircon age spectra reflect these three paleozoic 480 419 ma 340 380 ma 320 275 ma tectono thermal events and permit the recognition of provenances both of which supporting the interpreted changes in geotectonic regime from ordovician rifting to variscan compression and the subsequent extension the zircon age data constrain the provenance linkage of the low grade ngu basement to the cadomian fragments within the west european variscides

gondwana derived microcontinents the constituents of the variscan and alpine collisional orogens abstract the european variscan and alpine mountain chains are collisional orogens and are built up of pre variscan building blocks which in most cases originated at the gondwana margin such pre variscan elements were part of a pre ordovician archipelago like continental ribbon in the former eastern prolongation of avalonia and their present day distribution resulted from juxtaposition through variscan and or alpine tectonic evolution the well known nomenclatures applied to these mountain chains are the mirror of variscan resp alpine organization it is the aim of this paper to present a terminology taking into account their pre variscan evolution at the gondwana margin they may contain relics of volcanic islands with pieces of cadomian crust relics of volcanic arc settings and accretionary wedges which were separated from gondwana by initial stages of rheic ocean opening after a short lived ordovician orogenic event and amalgamation of these elements at the gondwanan margin the still continuing gondwana directed subduction triggered the formation of ordovician al rich granitoids and the latest ordovician opening of palaeo tethys an example from the alps external massifs illustrates the gradual reworking of gondwana derived pre variscan elements during the variscan and alpine tertiary orogenic cycles

early mesozoic alkaline complexes in the northern north china craton implications for cratonic lithospheric destruction abstract early mesozoic alkaline intrusive complexes are widespread in the northern north china craton ncc and constitute an e w trending alkaline magmatic belt that is more than 1500 km long along the northern sino korean craton our new zircon and baddeleyite u pb dating results of the yongfucun yaojiazhuang and sungezhuang alkaline complexes combined with previous geochronological data indicate emplacement of the e w trending alkaline belt in the northern ncc during the middle late triassic at around 235 220 ma geochemical and sr nd hf isotopic data suggest a common source region for the syenites pyroxene syenites and mafic rocks within the complexes they were mainly derived from a metasomatized enriched lithospheric mantle however some materials from depleted asthenospheric mantle have been involved during formation of these alkaline complexes involvement of depleted asthenospheric mantle materials indicates upwelling of the asthenospheric mantle and asthenosphere lithospheric mantle interaction in northern ncc during the early mesozoic initiation of lithospheric thinning and destruction of the northern ncc occurred in the middle late triassic which is much earlier than in other parts of the ncc during the late mesozoic delamination at the root of the subduction induced thick lithospheric mantle is likely main mechanism for the early mesozoic lithospheric thinning and destruction of the northern ncc multiple subduction of oceanic plates beneath the northern southern and eastern parts of the ncc and interactions of the surrounding orogenesis during the late paleozoic to mesozoic may play important roles on the late mesozoic lithospheric destruction of the ncc

evolution of late neoproterozoic to early paleozoic tectonic elements in central and southeast european alpine mountain belts review and synthesis abstract late neoproterozoic to early paleozoic cadomian tectonic elements are widespread in the southeastern alpine mediterranean mountain belts with discontinuous exposure extending from the alps to the menderes massif in turkey the sequences include voluminous plutonic island and continental arc successions some ophiolites of variable late neoproterozoic and cambrian to early ordovician ages high to medium grade metamorphic sequences and subordinate metasediments geological and geochronological data suggest that these cadomian elements partly experienced tectonothermal activity including metamorphism and magmatism between ca 650 and 600 ma followed by further i and s type plutonism in an andean type continental margin setting ca between 570 and 520 ma subsequently a major rift zone developed which resulted in continental stretching and subsequent formation of a back arc basin which is dated as late cambrian rifting is followed by oceanic spreading which commenced ca at the cambrian ordovician boundary possibly in a back arc setting this tectonic scenario suggests that alpine mediterranean cadomian tectonic elements were accreted to gondwana during early cadomian events ca 600 650 ma subsequently they were likely part of a long lasting outer subduction zone of gondwana at the margin of a panthalassa type ocean during late neoproterozoic iii and cambrian due to back arc spreading continental pieces started to split off from gondwana ca at the cambrian ordovician boundary

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

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

primary uranium sources for sedimentary hosted uranium deposits in ne china insight from basement igneous rocks of the erlian basin carboniferous permian triassic and jurassic igneous basement rocks around the erlian basin in northeast china have been investigated through detailed mineralogical whole rock geochemistry geochronological data and sm nd isotope studies carboniferous permian biotite granites and volcanic rocks belong to a calc alkaline association and were emplaced during the late carboniferous early permian 313 1 286 2 ma these rocks are characterised by positive end t 3 3 5 3 and fairly young t dm model ages 485 726 ma suggesting a dominant derivation from partial melting of earlier emplaced juvenile source rocks triassic biotite granites belong to a high k calc alkaline association and were emplaced during the middle triassic 243 3 233 2 ma their negative end t 2 to 0 1 and higher t dm model ages 703 893 ma suggest a contribution from precambrian crust during the magma generation processes leading to a strong enrichment in k and incompatible elements such as th and u highly fractionated magmas crystallised in u rich biotite up to 21 ppm u and two mica granites in biotite granite the major u bearing minerals are uranothorite and allanite they are strongly metamict and the major part of their uranium 90 has been released from the mineral structure and was available for leaching mass balance calculations show that the triassic biotite granites may have at least liberated 14 000 t u km3 and thus correspond to a major primary uranium source for the u deposits hosted in the erlian basin

u pb ages of detrital zircons from paleozoic metasandstones of the gelnica terrane southern gemeric unit western carpathians slovakia evidence for avalonian amazonian provenance u pb shrimp determinations on detrital zircons from the early paleozoic gelnica terrane metasandstones and their permian overlap sediments of the inner western carpathian southern gemeric unit define five age populations based on age probability plots the metasandstones were sampled for detrital zircons from six stratigraphic levels four of them in the late cambrian ordovician gelnica terrane metasandstones and the two in permian envelope sequence the data set includes 84 u pb ages for individual detrital zircons these ages are combined with the previously dated inherited zircons from the associated metavolcanites n 31 the majority of the pre permian detrital and inherited zircons 95 belong to the three main populations population a the paleoproterozoic neoarchean ages ranging from 1 75 to 2 6 ga population b the mesoproterozoic ages with the range of 0 9 to 1 1 ga population c the neoproterozoic ages ranging from 560 to 807 ma the detrital zircon age spectrum from the basal permian sediments reflects the strong recycling from the underlying gelnica terrane with the presence of the dominant precambrian c and b populations 94 of total including the minor populations a the range of the detrital zircon ages from the late permian sandstones is wider with additional population d ranging from 497 to 450 ma and population e with a time span from 369 to 301 ma within the late permian detrital zircon assemblage the proterozoic population a b c form only 25 of total the detrital zircon data suggest that the gelnica terrane belongs to the peri gondwanan terrane with a source area located on the northwestern margin of gondwana close to amazonia this terrane should have travelled a long distance in the phanerozoic times

diffusive transport of water in porous fresh to altered mid ocean ridge basalts abstract studying diffusive transport in porous rocks is of fundamental importance in understanding a variety of geochemical processes including element transfer primary mineral dissolution kinetics and precipitation of secondary phases here we report new findings on the relationship between diffusive transport and textural characteristics of the pore systems on the example of mid oceanic ridge basalts having different degree of alteration but very similar bulk pore volume diffusion processes in porous basalts were studied in situ using h 2 o d 2 o exchange experiments the effective diffusion coefficients of water molecules increase systematically from 5 05 10 11 to 1 19 10 10 m 2 s for fresh and moderately altered basalts and from 2 40 10 11 to 6 72 10 11 m 2 s for completely altered basalt as temperature increases from 5 to 50 c the activation energy of the diffusion process increases from 12 29 0 71 kj mol for fresh and moderately altered basalts to 14 3 1 33 kj mol for completely altered basalt the results indicate that neither the bulk porosity nor the degree of alteration can be used as proxies for the efficiency of element transport during morb water interaction the formation of secondary phases that replace primary minerals and fill the pore space in the rock leads to the formation of tiny pores and phases with large specific surface area these factors might have a dominant control on the transport properties of altered basaltic rocks

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

the effect of dead end porosity on rock matrix diffusion abstract recent theoretical studies on geological disposal of radioactive waste in fractured crystalline rock have indicated the importance of diffusion into the rock matrix in this paper the analysis of results of experiments to find the diffusion coefficients and rock capacity factors for weakly sorbed ions is discussed the simplest analysis using standard diffusion theory often does not account for the results over the whole duration of the experiments improved agreement is obtained by using a new model in which the rock porosity is split into two parts through transport pores and dead end pores this new model is described and its importance in repository calculations considered

diffusion in the matrix of granitic rock field test in the stripa mine three field experiments in granitic rock were performed at 360 m depth in a mine to investigate diffusion in the undisturbed rock matrix the results from all three experiments showed that tracers had migrated through the disturbed zone close to the injection hole and a distance into the undisturbed rock matrix these results show that it is possible for dissolved compounds to migrate into the rock matrix in its natural stress environment diffusivities and hydraulic conductivities obtained in this in situ experiment compare well with those obtained in laboratory experiments

metamorphic core complex dynamics and structural development field evidences from the liaodong peninsula china east asia metamorphic core complexes mcc constitute remarkable features within wide rifts based on analogue and numerical modelling mcc dynamics and structural development are mainly controlled by first geothermal gradient second the compositional layering and after the strain rate and partial melting in the late mesozoic continental extension occurred in east asia leading to the development of mcc magmatism and extensional sedimentary basins based on an integrated study i e structural and finite strain analysis petrofabrics anisotropy of magnetic susceptibility ams and u pb on zircon dating this paper aims at constraining the tectonic evolution and deformation mechanisms in the south liaodong peninsula ne china the gudaoling massif is identified as a migmatitic mcc developed from upper jurassic ca 157 154 ma to early cretaceous ca 128 113 ma intrusion of the yinmawanshan synkinematic pluton early cretaceous to the south of the dome marks out the final stages of shearing along the gudaoling detachment zone and of exhumation of the mcc into the upper crust the gudaoling mcc and the yinmawanshan pluton stay in line with the coeval south liaodong mcc to the south all making a 140x30km wide extensional band formed during a regional e w to nw se crustal stretching the area shows a bi phased development with a slow and a fast stage which correspond to 1 crustal necking and 2 dome amplification exhumation stages according to published thermo mechanical modelling results finally the gudaoling mcc lower unit almost exclusively displays migmatites and anatectic granitoids of late jurassic and early cretaceous respectively occurrence of partial melting during earlier stages of extension seems controlling the initiation of mcc as a soft anomaly within lower crust in east asia a regional scale thermal event during jurassic cretaceous times may have significantly reduced the bulk lithosphere strength and locally induced partial melting emphasizing pervasive deformations and development of a wide rift system

early mesozoic deep crust reworking beneath the central lhasa terrane south tibet evidence from intermediate gneiss xenoliths in granites abstract understanding the rheological behavior of the tibetan plateau and its response to geodynamic processes requires a clear knowledge of the composition evolution and lithological properties of the deep crust here we present u pb hf isotopes of zircons bulk rock geochemistry and mineral compositions for seven intermediate gneiss xenoliths and their host early mesozoic granites 205 6 ma in the central lhasa terrane to probe the deep crust beneath southern tibet the xenoliths contain plagioclase amphibole titanite allanite quartz biotite and muscovite with accessory fe ti oxides apatite and zircon bulk rock and mineral geochemistry suggests that these xenoliths have a magmatic origin and experienced deformation and amphibolite facies metamorphism equilibration at pressures of 0 46 0 83 gpa and temperatures of 650 c before they were captured by the host granite at 205 ma zircons in these xenoliths show complex microstructures including inherited cores magmatic or metamorphic bands and high u th hydrothermal rims inherited zircon cores record u pb ages from 2277 ma to 517 ma igneous zircons show a range of concordant u pb ages suggesting a protracted magmatism from 236 ma to 203 ma metamorphic zircon zones record the timing of amphibolite facies metamorphism from 224 to 192 ma while the high u th hydrothermal rims show a subsequent fluid activity until 150 ma unradiogenic hf isotopic compositions of both xenoliths and host granites xenolith e hf t 11 2 to 0 host granite e hf t 17 3 to 3 3 indicate that the early mesozoic deep crust in the central lhasa terrane originated mainly from ancient i e proterozoic crust with little or no interaction with juvenile magmas this study suggests a possible continental differentiation mechanism during crustal reworking progressive melting may initiate from the lower mafic crust at ca 236 ma and gradually migrate into the sediment rich upper crust until ca 203 ma the reworking results in the transition from small fluxes of intermediate magmas to voluminous peraluminous s type granite in a convergent depth

reactivation of the archean lower crust implications for zircon geochronology elemental and sr nd hf isotopic geochemistry of late mesozoic granitoids from northwestern jiaodong terrane the north china craton the late mesozoic granitoids widely distributed in the northwestern jiaodong terrane are important markers of cratonic destruction and lithospheric thinning of the eastern north china craton ncc here we investigate the late jurassic linglong and luanjiahe granites and report zircon u pb emplacement ages of 157 159 ma these rocks also contain abundant late archean paleoproterozoic neoproterozoic early paleozoic and triassic inherited zircons suggesting the involvement of continental crustal materials from both the ncc and yangtze craton in magma tectonics the rocks investigated in this study show high na2o k2o and low mgo and are peraluminous with enrichment in lrees and liles rb ba u and sr and depletion in hfses nb ta p and ti they also display low ehf t values and high sr y ratios comparable to adakitic rocks suggesting that the linglong and luanjiahe granitoids formed under relatively high pressure conditions and were likely derived from the partial melting of the thickened lower crust of the ncc the guojialing granodiorites were emplaced in the early cretaceous 129 ma and also contain abundant late archean and paleoproterozoic inherited zircons the rocks possess high cao tfe2o3 and mgo and are metaluminous with enrichment in lrees and liles and depletion in hfses they are also characterized by high sr y ratios and have higher end t and ehf t values than the late jurassic granitoids suggesting the involvement of mantle components in the magmatic source we correlate the magma tectonics with the processes accompanying the subduction of the pacific plate beneath the ncc and the associated asthenospheric upwelling

book review enclaves and granite petrology developments in petrology 13 edited by j didier and b barbarin elsevier science publishers amsterdam the netherlands 1991 hardcover xxiv 600 pp price us 143 50 dfl 280 isbn 9 444 89145 5

palaeowind directions and sources of detrital material archived in the roxolany loess section southern ukraine abstract measurements of the anisotropy of whole rock magnetic susceptibility ams and u pb ages of detrital zircons have been combined to define the palaeowind directions and sources of wind blown dust in the loess palaeosol key section at roxolany southern ukraine zircon dating has also been used to determine the age and provenance of the interbedded roxolany tephra the distribution of ams axes in the loess indicates that the prevailing wind during its accumulation blew from the north west the same as the mean present day summer wind direction measured in the nerby city of odessa the u pb isotopic ages of the detrital zircons mostly range between 0 25 and 2 ga with clusters at 0 28 0 32 0 45 0 58 1 0 and 1 5 ga single neoarchean grains ca 2 7 ga were also found these ages indicate that material from carpathian and podolian sources formed the roxolany loess this material initially was transported by the dniester river then was wind blown form the dniester liman and the lower dniester valley located nw of roxolany most of the pyroclastic zircons from the roxolany tephra gave ages of 470 840 ka with a peak between 500 and 750 ka this age range is consistent with their being derived from the ciomadul volcano in romania

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

magma recharge and reactive bulk assimilation in enclave bearing granitoids tonglu south china national nature science foundation of china 41530211 mlr special funds for public welfare projects 201211013 2 state administration of foreign expert affairs of china b07039 most special funds of the state key laboratory of geological processes and mineral resources msfgpmr01

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

formation of wulong mafic dikes via mixing of enriched lithospheric mantle derived and crustal magmas eastern north china craton abstractzircon u pb age and geochemical data are reported for the wulong dike swarms from the liaodong peninsula ne china the studied dikes include diorite lamprophyre and dolerite together with previous dating the diverse rocks have a peak age of ca 120 125 ma they are marked by inversely zoned phenocrysts with mg and cr rich rims and they exhibit mantle like signatures i e high mg cr ni associated with prominent subduction type element enrichments the early diorites have relatively radiogenic sr 0 7143 and less radiogenic nd to 11 0 isotopes coupled with high and variable mgo cr ni contents indicating that they were mainly derived from ancient lower crust with subordinate contributions of enriched lithospheric mantle the transitional lamprophyres are characterized by high rb sr ratios 0 22 0 54 but low initial 87sr 86sr ratios 0 7069 0 7093 moderate negative end t values 14 4 to 12 6 and low promantle elements such as mg cr ni reflecting that juvenile lower crust

nature and evolution of the lower crust in the eastern north china craton a review abstract in this paper published data for granulite terrain rocks exposed at the surface lower crustal xenoliths and mesozoic intermediate felsic igneous rocks from the eastern north china craton ncc are integrated to constrain the nature and evolution of the lower crust in this area u pb zircon dating shows that the protolith ages for most of the granulite terrain rocks are 2500 to 2600 ma and that many of them experienced 1800 1900 ma metamorphism lower crustal xenoliths entrained in volcanic rocks with ages varying from 460 to 10 ma suggest that the lower crust is dominated by neoarchean rocks although there may be minor rocks with ages of meso to paleoarchean 3000 ma 45 ma and possibly 1900 ma locally the mesozoic intrusive rocks although varying from diorite to granite and spanning from triassic to cretaceous contain 2500 ma inherited zircons and have magmatic zircons with hf crust model ages t dm hf c ages of 2500 2700 ma and whole rock sr nd isotopic compositions falling within the field of the granulite terrain rocks pointing to their derivation by the melting of neoarchean lower crust the combined data for the granulite terrain rocks lower crustal xenoliths and mesozoic intermediate felsic igneous rocks indicate that the present lower crust is dominated by rocks with neoarchean ages and is intermediate to mafic in composition i e sio 2 87 sr 86 sr i e nd t and e hf t of the lower crust at 130 ma are considered to be 0 705 to 0 716 10 to 28 and 13 to 28 respectively the e nd t range is very different from that proposed previously 32 to 44 the large range of e hf t for the lower crust implies that significant e hf t variations for magmatic zircons from the mesozoic intermediate felsic igneous rocks do not necessarily reflect mixing of mantle and crustal magmas as commonly thought instead they may reflect heterogeneity in the ancient lower crust given that the voluminous mesozoic intermediate to felsic igneous rocks in the eastern ncc are derived dominantly by partial melting of the archean lower crust it requires that a large amount of archean lower crust be restitic a restite origin can explain some of the hannuoba granulite xenoliths having higher mg than the granulite terrains it may be applicable to other parts of the world

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

evidence for intracontinental thrust related exhumation of the ultra high pressure rocks in china coesite and diamond bearing ultra high pressure metamorphic rocks produced during the triassic continental collision between the sino korean and yangtze plates are offset by about 530 km along the sinistral tanlu fault in eastern china the tanlu fault terminates abruptly south of the ultra high pressure metamorphic terrain in dabie shan and does not extend into the foreland fold belt along the yangtze river this suggests that in this region the mesozoic major sinistral displacement along the tanlu fault was transferred to southward directed thrusting which led to the exhumation of the ultra high pressure metamorphic rocks formed earlier postcollisional himalayan type intracontinental thrusting and concomitant erosion appear to be the main agents in the exhumation of the very high pressure metamorphic rocks in china

effects of drilling and stress release on transport properties and porewater chemistry of crystalline rocks the experimental verification of matrix diffusion in crystalline rocks largely relies on indirect methods performed in the laboratory such methods are prone to perturbations of the rock samples by collection and preparation and therefore the laboratory derived transport properties and fluid composition might not represent in situ conditions we investigated the effects induced by the drilling process and natural rock stress release by mass balance considerations and sensitivity analysis of analytical out diffusion data obtained from originally saturated large sized drillcore material from two locations drilled using traced drilling fluid for in situ stress released drillcores of quartz monzodiorite composition from the aspo hrl sweden tracer mass balance considerations and 1d and 2d diffusion modelling consistently indicated a contamination of 1 of the original pore water this chemically disturbed zone extends to a maximum of 0 1 mm into the drillcore 61 8 mm x 180 1 mm corresponding to about 0 66 of the total pore volume 0 77 vol in contrast the combined effects of stress release and the drilling process which have influenced granodioritic drillcore material from 560 m below surface at forsmark sweden resulted in a maximum contamination of the derived porewater cl concentration of about 8 the mechanically disturbed zone with modified diffusion properties covers the outermost similar to 6 mm of the drillcore 50 mm x 189 mm whereas the chemically disturbed zone extends to a maximum of 0 3 mm based on mass balance considerations and to 0 15 mm to 0 2 mm into the drillcore based on fitting the observed tracer data this corresponds to a maximum of 2 4 of the total pore volume 0 62 vol being affected by the drilling fluid contamination the proportion of rock volume affected initially by drilling fluid or subsequently with experiment water during the laboratory diffusion and re saturation experiments depends on the size of the drillcore material and will become larger the smaller the sample used for the experiment the results are further in support of matrix diffusion taking place in the undisturbed matrix of crystalline rocks at least in the cm range

sr nd isotopic and geochemical constraints on provenance of late paleozoic to early cretaceous sedimentary rocks in the western hills of beijing north china implications for the uplift of the northern north china craton late paleozoic to mesozoic strata which were deposited in the western hills of beijing north china recorded the contemporary tectonic evolution of the northern part of the north china craton ncc fine grained sandstones and siltstones of these strata were analyzed for their major and trace element concentrations and sr nd isotope compositions their la sc th sc la co th co and cr th ratios are similar to those of sediments derived from felsic source rocks indicating that the original source materials were mostly intermediate to acidic rocks their end 0 values show dramatic shifts implying changes in provenances from the late paleozoic to the early cretaceous the end 0 values of the late paleozoic and the late jurassic to early cretaceous formations are very low whereas the end 0 values of the xingshikou and the xiaoyaopo formations are much higher indicating that a juvenile component has been added into their sources based on the sr nd isotope compositions the late paleozoic and the late jurassic to early cretaceous samples fall in the paleozoic to mesozoic magmatic rocks distributed in the northern part of the ncc however the sr nd isotope compositions of the xingshikou and the xiayaopo formations vary between the xing meng orogenic belt xmob and the north part of the ncc components these changes can be interpreted by the complex uplift and exhumation history of the northern ncc from the late paleozoic to the early cretaceous during the late carboniferous the uplift of the inner mongolia paleo uplift impu which probably commenced at the late carboniferous might supply detrital materials to the late paleozoic strata in the late triassic the uplift of the xmob and impu was responsible for the mixing source of the xingshikou formation after that the northern xmob became the main source of the xiayaopo formation resulting from the uplift of the xmob due to the collision of siberia and north china mongolia plates during the middle to late jurassic finally the uplift of the yftb which occurred from the late jurassic to early cretaceous provided the source materials and blocked the input of the xmob components

early palaeozoic tectonothermal events in basement complexes of the eastern greywacke zone eastern alps evidence from u pb zircon data field observations and u pb zircon data yield evidence that the kaintaleck complex represents a distinct crystalline basement unit of the eastern greywacke zone and contrasts partly with other pre alpine basement complexes of the eastern alps the age data indicate possible late archean rock formation several magmatic and metamorphic events in the early palaeozoic ca 520 490 and ca 400 360 ma and low grade metamorphic overprint in the cretaceous zircons from a garnet gneiss layer in a plagioclase gneiss and amphibolite sequence yield an upper intercept age of ca 2 55 ga which is interpreted as a possible protolith age the lower intercept age at 514 ma represents either 1 a magmatic event or 2 a metamorphic overprint within amphibolite facies conditions magmatic zircons derived from granitic orthogneiss boulders of the kalwang conglomerate which covers the crystalline basement crystallised at ca 500 ma the lower discordia intercepts of the orthogneiss boulders mark the cretaceous low grade metamorphic overprint the lower intercept age of paragneiss zircons from another slice of the kaintaleck complex suggests a likely devonian metamorphic event at ca 390 400 ma the new data demonstrate that the kaintaleck complex experienced several stages of tectonothermal evolutions which are in contrast to the evolution of the main mass of the austroalpine basement the data constrain linkages of this part of the austroalpine basement to the cordillere ligerienne and cadomian block within west european variscides

high precision pb sr nd hf isotopic characterization of usgs bhvo 1 and bhvo 2 reference materials the recent development of multiple collector inductively coupled plasma mass spectrometry mc icp ms and increasing use of the technique have created the need for well characterized rock standards especially for isotopic systems where no internal fractionation correction can be applied this paper presents a careful leaching experiment on the u s geological survey usgs reference materials bhvo 1 and bhvo 2 hawaiian basalts and documents the evidence for contamination of the rock powders during processing this contamination accounts for the difference in pb isotopic ratios of bhvo 1 and bhvo 2 as well as for their lack of homogeneity both in pb isotopic compositions and in some trace element contents copyright 2005 by the american geophysical union

tracing magma mixing in granite genesis in situ u pb dating and hf isotope analysis of zircons in situ zircon u pb and hf isotopic data have been determined for mafic microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china in order to constrain the sources and petrogenesis of granites the zircon u pb age of the enclaves 120 1 ma is identical to that of the host monzogranite 120 1 ma establishing that the mafic and felsic magmas were coeval the hf isotopic composition of the enclaves ehf t 4 5 to 6 2 is distinct from the host monzogranite ehf t 15 1 to 25 4 indicating that both depleted mantle and crustal sources contributed to their origin the depleted mantle component was not previously revealed by geochemical and nd and sr isotopic studies showing that zircon hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information some wall rock contamination is indicated by inherited zircons with considerably older u pb ages and low initial hf isotopic compositions hafnium isotopic variations in early cretaceous zircons rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data

formation of the baiyun gold deposit liaodong gold province ne china constraints from zircon u pb age fluid inclusion and c h o pb he isotopes abstract the baiyun gold deposit is located in the liaodong peninsula in ne china the gold orebodies are hosted in the paleoproterozoic liaohe group metamorphic rocks the alteration mineralization can be divided into three stages i quartz pyrite k feldspar veins ii quartz polymetallic sulfide veins iii quartz carbonate veins new la icp ms zircon u pb dating suggests all the ore related porphyries including monzonite porphyry 224 2 1 3 ma quartz porphyry 221 4 1 2 ma and diorite porphyry 221 8 1 2 ma were emplaced in the late triassic four types of fluid inclusions fis are identified in the ore related quartz i e liquid rich two phase vapor rich two phase co2 bearing and pure co2 fis the ore forming fluids were likely characterized by medium temperature low salinity low density co2 rich and belong to the h2o nacl co2 n2 c4h6 system we propose that fluid phase separation likely caused rapid precipitation of the ore minerals the c h o pb isotope data indicate that the ore forming fluids may have had multiple sources including magmatic metamorphic and meteoric fluids the ore forming materials may have mainly derived from metamorphic rocks of the proterozoic gaixian formation and minor from the triassic intermediate felsic rocks the he ar isotope data indicate that the ore forming fluids were mainly crust derived we conclude that the baiyun gold deposit is an orogenic type system formed during the late triassic north china yangtze continent continent collision

geochronology and geochemistry of igneous rocks in the southeastern lesser xing an range northeastern china petrogenesis and implications for the early mesozoic tectonic evolution we present systematic u pb age data collected by laser ablation multi collector inductively coupled plasma mass spectrometry precise geochemical data and nd isotope data for igneous rocks from th

pre variscan geological events in the austrian part of the bohemian massif deduced from u pb zircon ages in an attempt to elucidate the pre variscan evolution history of the various geological units in the austrian part of the bohemian massif we have analysed zircons from 12 rocks mainly orthogneisses by means of shrimp conventional multi grain and single grain u pb isotope dilution mass spectrometry two of the orthogneisses studied represent cadomian metagranitoids that formed at ca 610 ma spitz gneiss and ca 580 ma bittesch gneiss a metagranite from the thaya batholith also gave a cadomian zircon age 567 5 ma traces of neoproterozoic zircon growth were also identified in several other samples underlining the great importance of the cadomian orogeny for the evolution of crust in the southern bohemian massif however important magmatic events also occurred in the early palaeozoic a sample of the gfohl gneiss was recognised as a 488 6 ma old granite a tonalite gneiss from the realm of the south bohemian batholith was dated at 456 3 ma and zircon cores in a moldanubian metagranitic granulite gave similar ages of 440 450 ma this ordovician phase of magmatism in the moldanubian unit is tentatively interpreted as related to the rifting and drift of south armorica from the african gondwana margin the oldest inherited zircons in a migmatite from the south bohemian batholith yielded an age of ca 2 6 ga and many zircon cores in both moravian and moldanubian meta granitoid rocks gave ages around 2 0 ga however rocks from the moldanubian unit show a striking lack of zircon ages between 1 8 and 1 0 ga reflecting an ancestry from armorica and the north african part of gondwana respectively whereas the moravian bittesch gneiss contains many inherited zircons with mesoproterozoic and early palaeoproterozoic ages of ca 1 2 1 5 and 1 65 1 8 ga indicating a derivation from the south american part of gondwana

neodymium and strontium isotope content of microdiorite enclaves points to mantle input to granitoid production microdiorite enclaves are arguably the most poorly understood of the more prominent features of granitoids surprisingly they have been invoked as support for completely different models for the origin of chemical zonation in granitoids depending on whether they are interpreted as restites syn plutonic blobs of magma remobilized cumulate or basified country rock xenoliths here we present the first detailed neodymium and strontium isotope study of suites of such enclaves from two plutons in both cases we find relatively high nd values most readily explained if enclaves represent syn plutonic injections of mafic magma into the host granitoid magma as such they are the tangible remains of a very important process of mantle derived heat and mass transfer operating in the generation of granitic magmas

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

crustal thickening versus lateral expulsion in the indian asian continental collision since the beginning of the continental collision between india and asia there has been about 2500 km of convergence and the northward movement of india has been accommodated by major internal deformation of the asian lithosphere the crustal thickening in and around the tibetan plateau is clearly a direct consequence of this collision but there is considerable debate as to whether a large fraction of the indentation has been accommodated by eastward motion of the lithospheric blocks of southeastern asia and southern china numerical experiments described here test this hypothesis for a range of indentation geometries and rheological models of the lithosphere we employ a thin viscous sheet model of the lithosphere with a depth averaged nonlinear viscous rheology described by a stress strain rate exponent n and including gravitational buoyancy forces scaled by the dimensionless argand number ar the eastern boundary for the collision region is described as a lithostatic boundary the precollision normal stress is determined by static balance and that constant stress is applied throughout the collision the experiments show that during collision the eastern boundary is smoothly displaced to the east at a rate about 1 4 of the indentation rate with only minor variation due to geometry or rheology crustal thickening rates in the region of the plateau are reduced by between 10 and 25 of the corresponding rates determined for similar experiments with a rigid eastern boundary to generalize from the results of these experiments the total north south shortening strain produced by the collision is partitioned between crustal thickening and eastward displacement in the ratio of at least 3 1 and more probably 4 1

geochronology and petrogenesis of the granites in malanyu anticline in eastern north china block abstract widespread mesozoic magmatism and intracontinental deformation is recorded in the north china block ncb but few studies have considered the link between the emplacement of the granite and deformation the malanyu anticline is a large scale east trending fold exposed in the eastern part of ncb and is intruded by many plutons whole rock geochemistry la icp ms zircon u pb ages sr nd isotopic composition as well as zircon hf isotopic data for eight granitic bodies in the anticline have been studied in detail and are reported in this contribution fourteen zircon la icp ms u pb ages have been obtained ranging from ca 218 to 126 ma spanning the triassic to cretaceous with a major population at ca 220 160 ma this age range is different from rest of the mesozoic igneous rocks in ncb indicating the emplacement of the granites in the anticline was structurally controlled although the regional tectonic setting during the mesozoic played an important role in magmatism in the region all of the granites in the malanyu anticline are enriched in light rare earth elements relative to heavy rare earth elements and have similar trace elements patterns with depletions in ba nb sr p and ti and enrichments in rb th u k la ce sm and tb the triassic to jurassic granites two stage depleted mantle nd model t2dm ages are both paleoproterozoic with similar end t values and two stage depleted mantle nd model ages their in situ zircon two stage depleted mantle hf model ages tdm2 range from ca 2861 to 1406 ma integrated with the sr nd hf data from previous studies the triassic dushan granite in the study area has high sr and low y assays derived from the partial melting of archean ttgs in the lower crust with a minor contribution from a depleted mantle source the emplacement was during a post collisional setting following the closure of the paleo asian ocean along the suolun suture in the north the emplacement of most of the jurassic granites involved the superimposition of the initial subduction of the paleo pacific ocean plate beneath ncb while the emplacement of the minor jurassic and cretaceous granites are probably related to the partial melting of the precambrian crust due to widespread extensional tectonics at the northern margin of the ncb

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

geochronology and geochemistry of early mesozoic magmatism in the northeastern north china craton implications for tectonic evolution abstract this paper reports geochronological geochemical zircon u pb and hf o isotopic data of the late triassic and early jurassic intrusive rocks in the northeastern north china craton ncc with the aim of reconstructing the tectonic evolution and constraining the spatial temporal extent of multiple tectonic regimes during the early mesozoic zircon u pb ages indicate that the early mesozoic magmatism in the northeastern ncc can be subdivided into two stages late triassic 221 219 ma and early jurassic 180 177 ma late triassic magmatism produced mainly granodiorite and monzogranite which occur as a ne sw trending belt parallel to the sulu jingji belt geochemically they are classified as high k calc alkaline and metaluminous to weakly peraluminous granitoids and are enriched in large ion lithophile elements liles and light rare earth elements lrees and depleted in high field strength elements hfses e g nb ta ti and p and heavy rare earth elements hrees indicating an affinity to adakite combined with their ehf t values 17 9 to 3 2 and two stage model ages 2387 1459 ma we conclude that the late triassic granitoid magma in the northeastern ncc was derived from partial melting of the thickened lower crust of the ncc and was related to deep subduction and collision between the ncc and the yangtze craton yc the early jurassic magmatism is composed mainly of monzogranites which are classified as metaluminous high k calc alkaline and i type granite their ehf t values and two stage model ages are 16 7 to 4 2 and 2282 1491 ma respectively compared with the late triassic granitoids the early jurassic granitoids have relatively high hree contents similar to calc alkaline igneous rocks in an active continental margin setting these early jurassic granitoids together with the coeval calc alkaline volcanic rocks and gabbro diorite granodiorite association in the northeastern ne asian continental margin comprise a nne ssw trending belt parallel to the ne asian continental margin indicative of the onset of paleo pacific plate subduction beneath eurasia

the birth of the rheic ocean early palaeozoic subsidence patterns and subsequent tectonic plate scenarios abstract new plate tectonic reconstructions of the gondwana margin suggest that the location of gondwana derived terranes should not only be guided by the models but should also consider the possible detrital input from some asian blocks hunia supposed to have been located along the cambrian gondwana margin and accreted in the silurian to the north chinese block consequently the gondwana margin has to be subdivided into a more western domain where the future avalonian blocks will be separated from gondwana by the opening rheic ocean whereas in its eastern continuation hosting the future basement areas of central europe different periods of crustal extension should be distinguished instead of applying a rather cylindrical model it is supposed that crustal extension follows a much more complex pattern where local back arcs or intra continental rifts are involved guided by the age data of magmatic rocks and the pattern of subsidence curves the following extensional events can be distinguished during the early to middle cambrian a back arc setting guided the evolution at the gondwana margin contemporaneous intra continental rift basins developed at other places related to a general post pan african extensional phase affecting africa upper cambrian formation of oceanic crust is manifested in the chamrousse area and may have lateral cryptic relics preserved in other places this is regarded as the oceanisation of some marginal basins in a context of back arc rifting these basins were closed in a mid ordovician tectonic phase related to the subduction of buoyant material mid ocean ridge since the early ordovician a new phase of extension is observed accompanied by a large scale volcanic activity erosion of the rift shoulders generated detritus armorican quartzite and the rift basins collected detrital zircons from a wide hinterland this phase heralded the opening of palaeotethys but it failed due to the silurian collision eo variscan phase of an intra oceanic arc with the gondwana margin during this time period at the eastern wing of the gondwana margin begins the drift of the future hunia microcontinents through the opening of an eastern prolongation of the already existing rheic ocean the passive margin of the remaining gondwana was composed of the galatian superterranes constituents of the future variscan basement areas remaining under the influence of crustal extension they will start their drift to laurussia since the earliest devonian during the opening of the palaeotethys ocean

geochronology geochemistry and hf isotope of late triassic magmatic rocks of qingchengzi district in liaodong peninsula northeast china abstract the initiation timing and mechanism of lithospheric thinning of the north china craton ncc was still controversial late triassic igneous rocks especially mantle derived mafic rocks would provide constrains on early mesozoic lithospheric mantle geodynamics and initiation of lithospheric thinning this paper reports late triassic magmatic rocks including lamprophyre diorite dykes and biotite monzogranite cropped out in qingchengzi district of liaodong peninsula northeastern ncc la icpms zircon u pb dating yield ages of 210 227 ma and 224 ma for lamprophyres and biotite monzogranite respectively lamprophyre is ultrapotassic strongly enriched in ree and liles depleted in hfses and negative hf isotopes which are discriminating signatures of crustal source but distinguishingly high compatible element contents indicate the primary magma originated from mantle source a fertile one lamprophyre derived from partial melting of an enriched lithospheric mantle which was modified by slab derived hydrous fluids melts associated with deep subduction between the yangtze craton and the ncc the diorite displays distinct features with relatively enriched nb ta hree and depleted th u which suggest it derived from a relatively depleted source the depletion was caused by break off of the yangtze slab during deep subduction introducing asthenospheric mantle into the source the biotite monzogranite shows adakitic affinity and originated from partial melting of the thickened lower crust with addition of small proportion of mantle material the recognition of late triassic magmatism implies extensional tectonic settings in liaodong peninsula and suggests initiation of lithospheric thinning of north china craton in eastern segment might begin early in late triassic

petrogenesis of late triassic intrusive rocks in the northern liaodong peninsula related to decratonization of the north china craton zircon u pb age and hf o isotope evidence abstract major and trace element whole rock sr nd and hf isotopes and zircon u pb age and hf o isotope data have been determined for mafic to felsic intrusive rocks from the late triassic mayihe myh longtou chaxinzi xiaoweishahe lcx and nankouqian xidadingzi nx intrusions in the northern liaodong peninsula ne china in order to investigate their sources and petrogenesis related to decrationization of the north china craton the rocks include clinopyroxene diorite monzodiorite quartz diorite granodiorite monzogranite and mafic microgranular enclaves laser ablation inductively coupled plasma mass spectrometry la icpms and secondary ion mass spectrometer sims u pb analyses of zircon from myh lxc to nx intrusions yield late triassic ages of 224 218 ma establishing that the mafic and felsic magmas were coeval the clinopyroxene diorites from the myh pluton have high mgo concentrations at low silica contents with positive whole rock e nd t up to 3 8 and e hf t up to 6 2 and zircon e hf t values and some mantle like 18 o values they are enriched in large ion lithophile liles and light rare earth elements lrees and depleted in high field strength elements hfses which can be explained as melts derived from a depleted mantle with some subsequent crustal contamination however the diorites from the lxc and nx intrusions are high k rocks and have high mgo concentrations and mantle like 18 o values but with negative whole rock e nd t 12 9 to 7 6 and e hf t 14 0 to 5 6 and zircon e hf t values distinct from those of myh pyroxene diorites indicating that their parental magmas were derived from partial melting of an ancient lithospheric mantle the granitoids from three plutons have high sio 2 contents and low mgo concentrations suggesting they were mainly derived from crustal sources however the myh monzogranite and granodiorite have positive whole rock e nd t and e hf t up to 3 0 and zircon e hf t values indicating a juvenile crustal source whereas the lxc and nx granitoids have strong negative and variable whole rock e nd t and e hf t and zircon e hf t values indicating that they were derived from partial melting of ancient lower crustal materials with involvement of mantle components field observations geochronology geochemistry sr nd hf isotopic and zircon hf o isotopic compositions point to a complex petrogenesis where mantle and crust derived magma mixing was coupled with crystal fractionation thus explaining the genetic link between mafic and felsic rocks identification of four components i e depleted and enriched mantle and juvenile and ancient crust in the late triassic magmatism in the northern liaodong peninsula suggests a strong mantle crust interaction process related to decratonization of the north china craton

matrix diffusion in northern negev fractured chalk and its correlation to porosity abstract in this paper we report on vertical variations in the values of the effective diffusion coefficient determined on 19 chalk samples collected throughout most of the eocene section 285 m in the northern negev desert israel the dependence of the measured values on sample depth porosity permeability and mineralogy was also evaluated finally a correlation between the measured effective diffusion coefficient and porosity is suggested for these samples the calculated values of the diffusion coefficient ranged from 1 22 to 2 55 10 6 cm 2 s these values are significantly higher than those measured on consolidated rock samples and similar to values reported for british cretaceous chalk our results demonstrate that the effective diffusion coefficient values for the eocene chalk in the northern negev desert israel are exclusively dependent on the porosity of the chalk matrix by d e d 0 e 2 m 2 in archie s law and not on its mineralogy or permeability the fitted exponent m falls between the two extreme values of 1 5 and 2 5 that were mentioned by diffusion in natural porous media 1998 for porous media however a linear relationship between the effective diffusion coefficient and porosity fits better the data within the range of the measured of porosities these correlations provide an easier and less costly method of estimating the diffusion coefficient in chalk samples from the eocene group in the northern negev desert israel

early cretaceous na rich granitoids and their enclaves in the tengchong block sw china magmatism in relation to subduction of the bangong nujiang tethys ocean abstract the na rich intermediate to felsic granitic rocks provide insights into the generation of magmas in subduction zones this paper presents zircon la icp ms u pb ages as well as whole rock geochemical mineral chemical and in situ zircon hf isotopic data on na rich granitic rocks from the tengchong block sw china the granodiorites and associated mafic magmatic enclaves mmes from the menglian batholith yield zircon u pb ages of 116 1 0 8 to 117 8 0 6 ma and 117 7 0 7 ma respectively both host granodiorites and enclaves show calc alkaline and sodium rich nature enrichment in large ion lithophile elements liles and variable depletion in zircon hf isotopic compositions euhedral amphiboles in both granodiorites and associated enclaves are magnesian hornblende with high mg and ca and contain euhedral plagioclase inclusions of labradorite to andesine an36 57 composition the granodiorite was most likely derived through the mixing of partial melts derived from juvenile basaltic lower crust and a minor evolved component of ancient crustal sources the quartz monzodiorite granodiorites and associated mmes from the xiaotang mangdong batholith yield zircon u pb ages of 120 3 1 3 to 122 6 0 8 ma and 120 7 1 5 ma these rocks are also sodium rich and show calc alkaline trend with negative zircon hf isotopic compositions 5 55 to 0 58 the mmes in the host intrusions are monzogabbro with variable and depleted zircon hf isotopic compositions the amphiboles in the both host intrusions and the enclaves show al rich ferro tschermakite composition we infer that the quartz monzodiorite granodiorites were derived from magmas generated by the melting of ancient basaltic rocks in the lower arc crust induced by the underplating of mantle derived mafic magmas the formation of the different types of na rich granitic rocks is correlated to the subduction of bangong nujiang tethyan ocean a comparison with magmatism in the northern magmatic belt suggests that mantle derived magmas played an important role in the genesis of early cretaceous intrusions from tengchong to lhasa blocks although crustal melting is the dominant contributor

detrital zircons reveal no jurassic plateau in the eastern north china craton abstract u pb hf isotopic analyses have been carried out on detrital zircons from late permian jurassic strata in the western shandong bohai bay wsbb basins with aims of constraining the paleogeography and evolution of the eastern north china craton ncc four major groups of u pb ages namely 3 0 2 3 ga 2 2 1 4 ga 1250 430 ma and 410 150 ma are recognized for zircons from the fine grained sandstones the post paleoproterozoic zircons of the late permian sample show an age cluster of 344 255 ma with e hf t values of 18 to 8 being similar to those extracted from late paleozoic igneous rocks from the yinshan yanshan orogenic belt yyob on the northern margin of the ncc however the devonian jurassic zircons 390 150 ma from the jurassic sediments have e hf t values from 45 to 14 very similar to the mixture of phanerozoic zircons from the xing meng orogenic belt xmob and the yyob but significantly different from those of the liaodong peninsula jiaodong peninsula and the western shandong uplift in addition cambrian silurian zircons 535 430 ma of the jurassic samples have e hf t values from 27 to 7 resembling the early paleozoic zircons extracted from the northern qinling orogen nqo the u pb age spectra and hf isotope of devonian jurassic zircons as well as bulk nd isotopes suggest that the central eastern ncc received some juvenile materials from the xmob the yyob and the nqo during the jurassic this indicates widespread prototype basins and a low elevation during the jurassic arguing against the presence of a paleo plateau in the eastern ncc at that time the lack of evidence predicted by lithospheric delamination e g large scale elevation or doming after late triassic makes the delamination unlikely to be a viable mechanism of lithospheric thinning of the ncc the subsidence rather than elevation of the eastern ncc after late triassic might be related to thermo chemical erosion of the lithosphere by underlying convective mantle in a back arc setting

a review of the geodynamic setting of large scale late mesozoic gold mineralization in the north china craton an association with lithospheric thinning abstract abundant gold deposits are distributed along the margins of the north china craton ncc occurring throughout the precambrian basement and located in or proximal to mesozoic granitoids these deposits show a consistent spatial temporal association with late jurassic early cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock their ages are mainly early cretaceous 130 110 ma and constrain a very short period of metallogenesis sr nd pb isotopic tracers of ores minerals and associated rocks indicate that gold and associated metals mainly were derived from multi sources i e the wall rocks precambrian basement and mesozoic granites and associated mafic rocks previous studies including high surface heat flow uplift and later basin development slow seismic wave speeds in the upper mantle and a change in the character of mantle xenoliths sampled by paleozoic to cenozoic magmas have been used to suggest that ancient cratonic mantle lithosphere was removed from the base of the ncc some time after the ordovician and replaced by younger less refractory lithospheric mantle the geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization 130 110 ma indicate that they were derived from an ancient enriched lithospheric mantle source whereas the mafic dikes and volcanic rocks younger than 110 ma were derived from a relatively depleted mantle source i e asthenospheric mantle according to their age and sources relation to magmatism and geodynamic framework the gold deposits were formed during lithospheric thinning the removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature the fluids derived from the lower crust were mixed with magmatic and meteoric waters and resulted in the deposition of gold and associated metals

the palaeozoic evolution in the alps from gondwana to pangea more than 50 of the alps expose fragments of palaeozoic basement which were assembled during the alpine orogeny although the tectonic and metamorphic history of the basement units can be compared to that of the variscan crust in the alpine foreland most of the basement pieces of the alps do not represent the direct southern continuation of variscan structural elements evident in the massif central the vosges black forest or the bohemian massif the basement units of the alps all originated at the gondwana margin they were derived from a precambrian volcanic arc suture fringing the northern margin of gondwana from which they were rifted during the cambrian ordovician and silurian a short lived ordovician orogenic event interrupted the general rifting tendency at the gondwana active margin after the ordovician the different blocks drifted from the gondwana margin to their pangea position colliding either parallel to armorica with laurussia or with originally peri gondwanan blocks assembled presently in armorica from the devonian onwards many basement subunits underwent the complex evolution of apparently oblique collision and nappe stacking docking started in the external massifs the penninic and lower and middle austroalpine units in approximately devonian early carboniferous times followed by the upper austroalpine and the south alpine domains in the visean and the namurian times respectively wrenching is probably the best mechanism to explain all syn and post collisional phenomena since the visean followed by post orogenic collapse and extension it explains the occurrence of strike slip faults at different crustal levels the formation of sedimentary troughs as well as the extrusion and intrusion of crustal and mantle derived magmas and allows for contemporaneous rapid uplift of lower crustal levels and their erosion from the stephanian onwards all regions were deeply eroded by large river systems

petrogenesis and tectonic implications of the mesozoic granitoid intrusions in the eastern liaoning peninsula ne china abstract mesozoic magmatic rocks are widely distributed in the eastern region of the north china craton ncc providing important information for understanding the mesozoic tectonic regimes in this area this paper reports newly obtained geological geochemical and zircon u pb lu hf isotope data for the xiaoheishan daheishan intrusion xdi and the yanghezhen dayingzhen intrusion ydi newly identified from precambrian metamorphic basement range in the eastern liaoning peninsula and provides a case study demonstrating that the petrogenesis of granitoid rocks was closely related to the tectonic regimes the middle late jurassic xdi granitoids commonly have the adakite like geochemical characteristics and their primary magma was derived from the partial melting of mafic rocks and neoarchean tonalites in the thickened lower crust the early cretaceous ydi granitoid rocks generally show diversified geochemical characteristics and their primary magma was generated by the partial melting of paleoproterozoic metagreywackes and neoarchean tonalites in the lower crust with minor addition of mantle derived magma these differences indicate that the granitoid magmatism in the eastern liaoning peninsula has occurred a significant variation during the jurassic to cretaceous the variation of late mesozoic granitoid magmatism may be responses to the regional tectonic transition from compression to extension in the eastern liaoning peninsula which is induced by the geodynamic regime of the paleo pacific plate from low angle subduction to slab rollback

measurement of important parameters determining aqueous phase diffusion rates through crystalline rock matrices one of the options being considered for the disposal of radioactive waste is deep burial in crystalline rocks such as granite recent theoretical studies on the migration of radionuclides in the groundwater circulating through the fissure networks which are likely to be present to some extent in crystalline rocks have indicated the importance of diffusion into the rock matrix as a retardation mechanism matrix diffusion will retard all radionuclides but is of particular relevance to those exhibiting little or no sorption and which would otherwise migrate at or near the groundwater velocity diffusion measurements have been made on granites obtained from four different regions of the united kingdom in most of the experiments the weakly sorbed iodide ion was used as tracer although the diffusion of tc 99 as the pertechnetate ion has also been measured details of the experimental technique and method of analysis are set out and results given for the most important diffusion parameters namely di the intrinsic diffusion coefficient the rock capacity factor and a pore geometry parameter which is a characteristic of the rock type in question in the pre steady state region a discrepancy between experiment and theory was observed the cause of this has been interpreted as being due to the presence of two types of porosity through transport porosity which carries the diffusion flux across the sample and dead end porosity which comprises of cross linking pores and pores closed at one end a series of equations were set up and solved using this concept from the analysis of experimental data in the pre steady state region estimates of the through transport porosity and mean length of dead end pores l were calculated in addition some initial results are given for diffusion through weathered fracture surfaces significant increases in both di and were measured the implications of these results are discussed

3800 to 2500 ma crustal evolution in the anshan area of liaoning province northeastern china shrimp u pb zircon geochronology has revealed several generations of granitoids and gneisses from the anshan area of northeastern china two samples of the baijiafen granite sensu lato 3804 5 and 3812 4 ma chentaigou granite 3306 13 ma lishan granite 3142 7 ma east and west anshan granites 3001 4 and 2994 8 ma tiejiashan granite 2962 4 and 2964 6 ma and qidashan granite 2475 ma the 3800 ma baijiafen granite consists of banded migmatitic trondhjemitic gneisses and forms only a small part of the area nonetheless they are the oldest known rocks in asia and are one of very few locations in the world where rocks of this antiquity have been found the younger suites are predominantly granite sensu stricto in composition and although foliated they have not been transformed into banded gneisses nd isotopic data suggest that the 3800 ma granites were produced at least in part by remelting of very ancient lree enriched sources perhaps like the exposed remnants of the 3800 ma rocks the chentaigou supracrustals contain layered mafic and ultramafic rocks banded iron formation bif and siliceous layered rocks of probable volcanogenic origin a sample of the latter has yielded a concordant u pb zircon age of 3362 5 ma interpreted as the age of deposition a trondhjemitic sheet cutting these rocks has yielded a u pb zircon age of 3342 6 ma the chentaigou supracrustals are the oldest recognised in the area younger supracrustal sequences collectively known as the anshan group contains the main economic bif units in the area bif is intruded by the 2475 ma qidashan granite indicating that the anshan group is archaean or earliest proterozoic in age

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

implications of pore space characteristics on diffusive transport in basalts and granites a detailed characterization of the pore space is crucial for understanding of transport and element transfer in rocks here the effect of differences in texture and content of secondary minerals on transport in pore systems was determined for two rocks of widespread occurrence mid ocean ridge basalts morb and granites pore space characteristics were analyzed by hg porosimetry intrusion of a molten alloy and synchrotron based x ray tomographic microscopy for evaluating the role of pore space characteristics for the prediction of diffusive transport data on porosity and the effective diffusion coefficient deff were compared extended connective pore systems due to cracks and mineral dissolution are present in samples of both rocks indicating high internal specific surface area uneven pore size distributions in altered morb samples can be assigned to secondary minerals pore spaces determined by x ray tomography used to determine main direction of pores in the 3 d orthogonal system suggest a slight anisotropy in log log plots both rocks show roughly a linear dependence of deff for h2o and compounds with comparable diffusivities d2o monovalent cations and anions on porosity but at same porosity deff is clearly higher in granitic than in basaltic samples this difference is increasing with decreasing porosity indicating that at low porosities the efficiency of element transport in basaltic samples is diminished mainly inherited by the presence of small pores slowing down diffusion the fact that diffusive transport in basaltic rocks is stronger dependent on porosity than in granitic rocks shows that also other rock characteristics such as pore size distribution and tortuosity of the pore network highly affected by the alteration degree can markedly affect transport and reactivity of pore solution