unexposed archean components and complex post archean accretion reworking processes beneath the southern yangtze block revealed by zircon xenocrysts from the paleozoic lamproites south china abstract integrated u pb dating and hf isotope analysis of zircon xenocrysts from the baifen lamproites of the zhenyuan area in the southeastern guizhou province offer a unique glimpse into the evolution of the deep continental crust beneath the southern part of the yangtze block south china a total of 148 zircons with 90 110 concordance yield u pb ages varying from 3458 9 ma to 252 2 ma they generally have high th u ratios 0 3 indicating a magmatic origin the two youngest magmatic zircons give a weighted mean 206pb 238u age of 253 0 2 8 ma which is interpreted as the emplacement age of the host baifen lamproites most zircons with pre eruption ages are xenocrysts derived from the deeper crust of the southern yangtze block they define two major paleoproterozoic age populations at 2 17 ga and 1 8 ga with similar hf model ages tcrust of 2 4 2 8 ga peak at 2 64 ga the oldest zircon has a 207pb 206pb age of 3458 9 ma with ehf t 1 47 and tcrust 3 7 ga this demonstrates the presence of archean crustal components or remnants as old as 3 7 ga beneath the southern yangtze block magmatic events involving significant addition of juvenile mantle derived materials mainly occurred at 2 2 2 1 ga and 2 0 1 8 ga but the latter event also involved reworking of the neoarchean crust and might represent the cratonization of the yangtze continent during the middle paleoproterozoic which could be correlated to the assembly of the columbia supercontinent this segment of the yangtze block became tectonically quiescent until 1 2 ga implying that the crustal stabilization lasted for ca 600 million years a few late mesoproterozoic zircon xenocrysts within the age range 1 3 1 0 ga suggest the occurrence of grenville aged events these neoproterozoic zircon xenocrysts 992 547 ma have a wide range of ehf t values 8 47 to 22 07 consistent with the zircon hf isotopic compositions of widespread coeval igneous rocks in the yangtze block the data show that the yangtze block has undergone important crustal growth and reworking during the neoproterozoic in response to the breakup of the rodinia supercontinent the early middle paleozoic zircon xenocrysts 513 357 ma have negative ehf t values 2 97 to 12 69 and tcrust hf model ages of 1 59 2 27 ga indicating reworking of the precambrian crustal basement without juvenile contributions during the caledonian orogeny the positive ehf t values 13 79 to 0 22 of twelve late paleozoic zircons 284 264 ma with a major age peak at ca 275 ma suggest that the precambrian basement beneath the southern yangtze block experienced an episode of strong rejuvenation during the permian we propose a possible linkage between the baifen lamproite magmatism 284 252 ma and the emeishan flood basalt volcanism

an isotopic mixing model for the origin of granitic rocks in southeastern australia a simple mixing process was a significant element in the genesis of many southeastern australian granitic rocks major and trace element abundances are near linearly correlated nd and sr initial isotopic compositions define a simple hyperbolic trend and many initial 87sr 86sr ratios are a regular function of rb sr ratios geological arguments and regression of geochemical variation diagrams place limits on the nature of the end members the high si end member is meta sedimentary derived magma comparable in composition to the cooma granodiorite the one pluton in the region surrounded by and clearly derived from regional metamorphic rocks the low si end member is basaltic material with similarities to rare gabbros also found in the area isotope dilution calculations based upon initial sr and nd isotopic compositions deduced for the end members yield realistic hypothetical sr and nd concentrations for the end members in a demonstration of the internal consistency of the model all of the granitic rocks from hornblende tonalites to cordierite granodiorites are a single broad family products of variable mixing between distinct batches of basaltic material and a uniform partial melt of the regional basement

origin of the late jurassic to early cretaceous peraluminous granitoids in the northeastern hunan province middle yangtze region south china geodynamic implications for the paleo pacific subduction the late mesozoic granitic belt in the northeastern hunan province situated in the south of the middle yangtze region represents the western front of the large magmatic province of se china in order to determine their ages and petrogenesis we carried out zircon u pb dating hf isotope and whole rock geochemical analyses for four granitic plutons namely taohuashan dayunshan mufushan wangxiang and lianyunshan our sims zircon u pb ages together with previously published data reveal that the magmatic activities in this area can be roughly subdivided into three phases at 151 146 ma 132 127 ma and ca 117 ma and the dayunshan mufushan batholith therein is a composite pluton these four plutons are mainly composed of weakly to strongly peraluminous biotite or two mica monzogranites with a minor amount of biotite granodiorites their geochemical features are similar to s type as well as fractionated s type granites with enrichment in lrees and negative ba sr nb p and ti anomalies all samples show negative zircon ehf t values ranging from 12 5 to 3 6 corresponding to crustal hf model tdmc ages of 1 4 2 0 ga it is inferred that these granitoids were derived from partial melting of metasedimentary rocks analogous to the neoproterozoic lengjiaxi group predominantly with psammitic component fractional crystallization probably played an important role in the magma evolution while input of mantle derived magma was insignificant combined with other geological evidence our new data allow us to propose that the cretaceous 132 127 ma and ca 117 ma magmatism might be response to episodic slab rollback of the paleo pacific plate while the early stage 151 146 ma magmatism that overlapped the epilogue of jurassic magmatic flare up and subsequent magmatic quiescence probably foreshadowed the transformation from foundering of a subducted flat slab to slab rollback alternatively slab foundering after a se directed intracontinental subduction in the central scb cannot be ruled out for geodynamic interpretation of the jurassic magmatism in se china

the first record of dinosaur eggshell from the horseshoe canyon formation maastrichtian of alberta canada eggs and eggshell are generally rare in the upper cretaceous rocks of alberta despite being relatively abundant nearby in montana palaeontologists and other people have been prospecting the horse

dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

oxygen isotopic composition and u pb discordance in zircon we have investigated u pb discordance and oxygen isotopic composition of zircon using high spatial resolution 18o measurement by ion microprobe 18o in both concordant and discordant zircon grains provides an indication of the relationship between fluid interaction and discordance our results suggest that three characteristics of zircon are interrelated 1 u pb systematics and concomitant age discordance 2 18o and the water rock interactions implied therein and 3 zircon texture as revealed by cathodoluminescence and bse imaging a key observation is that u pb disturbed zircons are often also variably depleted in 18o but the relationship between discordance and 18o is not systematic 18o values of discordant zircons are generally lighter but irregular in their distribution textural differences between zircon grains can be correlated with both u pb discordance and 18o discordant grains exhibit either a recrystallized fractured or strongly zoned cl texture and are characteristic of 18o depletion we interpret this to be a result of metamictization leading to destruction of the zircon lattice and an increased susceptibility to lead loss conversely grains that are concordant have less expressed zoning and a smoother cl texture and are enriched in 18o from this it is apparent that various stages of water rock interaction as evidenced by systematic variations in 18o leave their imprint on both the texture and u pb systematics of zircon

does neoproterozoic nam co formation in northwest vietnam belong to south china or indochina abstract the nam co belt is located to the northeast of song ma fault in northwestern vietnam the nature of the precambrian basement rocks in this area and its tectonic attribute have still been controversial in this study zircon u pb hf isotopic compositions and whole rock geochemical compositions of meta sedimentary rocks from the nam co formation in this belt have been integrated to reveal the components and tectonic setting of the formation of the basement rocks in the nam co belt zircon u pb dating results show that the nam co formation is of middle late neoproterozoic age the lower nam co formation probably formed between 821 and 726 ma and the upper formation was deposited later than 726 721 ma the sedimentary rocks from the lower and upper nam co formations are characterized by numerous neoproterozoic 900 800 ma detrital materials but the upper part contains more meso to paleoproterozoic sediments than the lower part detrital zircon age distribution and hf isotope compositions of the nam co formation are similar to those of neoproterozoic sedimentary rocks in the southern yangtze block both zircon u pb hf isotopic and whole rock geochemical data suggest that the source materials of the neoproterozoic nam co formation were dominated by felsic rocks with minor mafic materials and the detrital materials were mainly derived from the jiangnan orogenic belt in the southern yangtze block with minor contribution from the panxi belt in the western yangtze block ailaoshan song hong and phan si pan belts the lower nam co formation contains more sediments derived from the panxi belt than the upper part the middle late neoproterozoic nam co formation probably was deposited in a continental extensional basin and the sedimentation environment in later period

neoproterozoic s type granites in the western jiangnan orogenic belt south china implications for petrogenesis and geodynamic significance abstract the neoproterozoic jiangnan orogenic belt in south china was formed by the amalgamation of the yangtze and cathaysia blocks however the timing of its formation is still debated in this study we present whole rock geochemistry u pb zircon ages lu hf and nd isotope systematics on the neoproterozoic yexijiang and baomuping granites occurring in the western segment of the jiangnan orogenic belt these granites mark the initiation of post collision extension environment zircon u pb age data identify 807 805 ma emplacement age for these granites they have low and variable ree concentrations 47 115 ppm and show moderate to highly fractionated ree patterns la sm n 2 83 3 78 with low gd yb n 1 34 2 31 and negative eu anomalies eu 0 34 0 57 geochemical features and presence of peraluminous minerals classify them as s type granites and p t parameters indicate low to moderate temperature 730 791 c and pressure middle crustal level conditions these granites show consistent negative whole rock nd t 5 7 to 6 6 and magmatic zircon hf t values from 0 3 to 3 8 while inherited zircon grains show variable hf t values 2 1 to 13 0 and two stage hf model ages 1 80 to 2 88 ga in particular one neoproterozoic 899 ma inherited zircon grain displays depleted hf hf t 5 4 and tdm2 1 34 ga isotopic characteristic these lines of evidence indicate a sedimentary source for yexijiang and baomuping granites possibly the archean to neoproterozoic crustal rocks and emplacement in a post collision tectonic environment triggered by mafic magma underplating during the amalgamation of the yangtze and cathaysia blocks we infer that convergence in the jiangnan orogenic belt occurred during 830 800 ma therefore unrelated to the global grenvillian orogeny

contrasting mantle crust melting processes within orogenic belts implications from two episodes of mafic magmatism in the western segment of the neoproterozoic jiangnan orogen in south china abstract partial melting of crust and mantle is the dominant mechanism controlling earth s differentiation the two melting processes are commonly associated because mantle derived magmas could simultaneously provide heat and volatiles to promote partial melting of crust to explore how the two melting regimes interact during the evolution of orogenic belts we evaluated the petrogenesis and possible relationships with the rodinia supercontinent of the two episodes of neoproterozoic mafic magmatism in the western segment of the jiangnan orogen in south china the first episode of mafic magmatism took place at ca 830 ma in the baotan area and was associated with widespread peraluminous granitoids in contrast the second formed at ca 770 ma in the longsheng area without significant granitic magmatism the ca 770 ma longsheng mafic ultramafic rocks show radiogenic and coupled nd end t values of 1 3 to 3 1 and hf isotopes ehf t values of 2 6 to 6 7 whereas the ca 830 ma baotan mafic rocks show unradiogenic and decoupled nd hf compositions end t 8 3 to 0 9 ehf t 6 3 to 2 0 crustal contamination cannot result in the enriched isotopic features and the arc like such as strong deletions of nb and ta geochemistry for the baotan rocks because of the absence of correlations of nd isotopes with incompatible elements and sio 2 contents but crust derived components may have been incorporated into the mantle source

u pb and lu hf isotopes of detrital zircon grains from neoproterozoic sedimentary rocks in the central jiangnan orogen south china implications for precambrian crustal evolution abstract the neoproterozoic sedimentary strata in the central jiangnan orogen of south china are separated into the lengjiaxi and banxi groups by a mid neoproterozoic angular unconformity this unconformity previously interpreted as the evidence of continental collision between the yangtze and cathaysia blocks is crucial for understanding the neoproterozoic tectonic regime in the south china craton here we report u pb ages and in situ lu hf isotopes of detrital zircon grains from the sedimentary rocks near this unconformity zircon grains in meta sandstone samples collected from the top part of lengjiaxi group yield maximum depositional ages of 827 ma 828 ma and 836 ma and combined with other available age data we suggest that the upper limit of the sedimentation for lengjiaxi group is at ca 825 ma zircon u pb analysis for two sandstone samples collected from the bottom of banxi group and nanhuan strata yields two youngest ages of 797 ma and 719 ma marking the initial depositional ages for these strata all the samples contain abundant neoproterozoic euhedral zircon grains suggesting their near source provenance the hf isotopic model ages of detrital zircons with positive ehf t values reveal two periods of juvenile crustal growth at 1 5 0 9 ga and 2 8 1 6 ga in the yangtze block several grains display core rim structure with ages of rim part ranging from 864 to 851 ma we correlate these metamorphic ages with the amalgamation of yangtze and cathaysia blocks in the central segments our data in combination with those from other studies suggest that a back arc basin existed in the central jiangnan belt during ca 860 ma to ca 825 ma we propose a four phase crustal evolution model for the central jiangnan belt

the significance of the theropod collections of the royal tyrrell museum of palaeontology to our understanding of late cretaceous theropod diversity1 significant specimens of theropod dinosaurs were part of the collections that were transferred to the royal tyrrell museum of palaeontology when it split off from the provincial museum of alberta in 1981 collecting activity of the institution increased dramatically in the period leading up to the opening of the building and displays in 1985 and resulted in the recovery and preparation of many fine theropod skeletons new specimens have been added to the collection every year since the museum opened several mostly small taxa are only represented by isolated bones partial skeletons and or teeth theropod specimens also include footprints coprolites eggs and feathers in amber although theropods are relatively rare in comparison with herbivorous dinosaurs the tyrrell has managed to build one of the finest research collections of late cretaceous forms thirty seven species of theropods in the tyrrell are currently accepted as being valid of which 30 are from the upper cretaceous deposits of alberta

from arc accretion to continental collision in the eastern jiangnan orogen evidence from two phases of s type granites abstract the ne jiangxi ophiolitic melange separates the huaiyu and jiuling terranes in the eastern jiangnan orogen of the south china block two phases of s type granites which are geochemically and mineralogically similar to the himalayan leucogranites are newly recognized in mantle peridotites of the ne jiangxi ophiolite the first phase a tourmaline bearing granite porphyry has a sims zircon u pb age of 904 4 4 8 ma and is strongly enriched in k2o 4 00 4 26 wt and strongly peraluminous a cnk 2 94 3 24 it further shows high rb sr ratios and highly fractionated ree patterns indicating an origin due to fluid absent melting of metapelites at relatively high temperatures the granite porphyry exhibits highly evolved zircon hf 6 0 to 1 0 and whole rock nd 4 2 to 5 1 isotopes which is in contrast to juvenile derived magmatic rocks in the huaiyu terrane we thus propose that the granite porphyry was formed by melting of the metapelites sourced from the yangtze block subsequent to the accretion of the huaiyu arc to the jiuling terrane the continental margin of the yangtze block the second phase a muscovite bearing quartz porphyry is strongly peraluminous a cnk 1 29 1 34 with low cao na2o ratios 0 11 0 14 and low feot mgo tio2 contents 2 39 2 75 wt similar to melts derived from fluid fluxed melting of metapelites zircon grains from the quartz porphyry yielded u pb ages of ca 803 801 ma with mainly positive ehf t values 1 9 to 8 7 which are younger than the depositional ages of the basement sequences and nearly identical to the accumulation of the overlying unmetamorphosed cover in the jiangnan orogen therefore it is suggested that the quartz porphyry was formed in a post collisional extensional setting subsequent to the final assembly of the yangtze and cathaysia blocks in conjunction with published data we conclude that multiple subduction accretion events may have been involved in the formation of the south china block during neoproterozoic times

constraints from zircon u pb ages o and hf isotopic compositions on the origin of neoproterozoic peraluminous granitoids from the jiangnan fold belt south china zircon textures and micro chemical compositions precisely record the origin and petrogenesis of granitoids which are crucial for evaluating crustal growth and reworking thermal and geodynamic evolution zircons in peraluminous granitoids from the three largest 820 ma complexes guibei yueyang and jiuling in the jiangnan fold belt in south china are used to constrain their sources and petrogenetic processes zircons in the guibei granitoids have complex internal structures nearly all magmatic and inherited zircons have similar ehf 6 8 to 5 6 and 18o values 8 8 11 6 and dominantly lie between ehf evolution vectors for a crust created between 1 7 and 2 1 ga suggesting that the guibei granitoids were produced by partial melting of recycled heterogeneous supracrustal material however the yueyang granitoids contain zircons with high ehf 0 5 to 9 7 and relatively low 18o values 5 9 8 4 and two stage model ages of 1 1 1 8 ga and thus may have been formed by melting of mafic rocks from the lower crust the jiuling granitoids and their enclaves contain more complex zircons with more variable ehf 7 2 to 9 7 and 18o values 7 0 10 6 and lie along the mixing trend between the above proposed infracrustal and supracrustal granitoids therefore the neoproterozoic peraluminous granitoids in the jiangnan fold belt were produced by melting and mixing of continental crust compared with extremely low 4 and negative 18o values of neoproterozoic igneous zircons formed in its northern active continental margin the high 18o peraluminous granitoids in the southeastern yangtze block are considered to have been formed by melting of hydrothermally unaltered continental crust triggered by asthenosphere upwelling in the nanhua back arc basin

contrasting zircon hf and o isotopes in the two episodes of neoproterozoic granitoids in south china implications for growth and reworking of continental crust abstract the genetic links among rift magmatism crustal growth and water rock interaction are an important issue about mass and heat transfer between mantle and crust during supercontinent breakup a combined study of hf and o isotopes in zircons from neoproterozoic granitoids in south china provides evidence for growth and reworking of juvenile and ancient crusts with different styles of water rock interactions along rift tectonic zones two generations of the granitoids show contrasting features in both zircon hf and o isotope compositions indicating their distinct petrogenesis the 825 ma granitoids exhibit negative ehf t values of 3 4 0 8 to 1 6 0 8 with old model hf ages of 1 81 0 07 to 1 92 0 10 ga and high 18o values of 8 7 to 10 4 these indicate that the source material of granitoid magmas was derived from melting of paleoproterozoic basement that has the hf isotope signature similar to the enriched mantle but experienced chemical weathering process before anatexis reworking of ancient crust is demonstrated to occur at 825 ma in the orogenic collapse zone with overprinting of subsolidus hydrothermal alteration during magma emplacement in contrast the 760 750 ma bimodal intrusives are characterized by positive ehf t values of 3 5 0 8 to 9 9 0 8 with young model hf ages of 0 94 0 06 to 1 18 0 06 ga and both low and high 18o values of 4 2 to 6 2 relative to 5 3 0 3 for the normal mantle zircon prompt reworking of juvenile crust is suggested to occur at 750 ma in the rifted tectonic zone with occurrence of supersolidus hydrothermal alteration and local low 18o magmatism during supercontinent breakup contributions of the depleted mantle to their magma sources are contrasting in the two episodes of magmatism in association with breakup of the supercontinent rodinia while the change in melt source from the crust to the mantle keeps pace with the advance from continental rifting to supercontinent breakup significant transport of both heat and material from the depleted mantle to the continental crust only occurred along the active rifting zone in either case the growth and reworking of continental crust are episodically associated with rift magmatism

petrogenesis and tectonic significance of the baoxing granitic and mafic intrusions southwestern china evidence from zircon u pb dating and lu hf isotopes and whole rock geochemistry abstract voluminous neoproterozoic gabbros gabbro diorites and granites are exposed in the baoxing area along the western margin of the yangtze block we present here zircon u pb and lu hf isotope data as well as whole rock geochemical data for these rocks which help constrain the tectonic characteristics and evolution of the western margin of the yangtze block zircons from these rocks have high th and u contents and th u ratios 0 2 and show striped absorption patterns growth striations or zoning indicating a typical magmatic origin zircon u pb dating and lu hf isotope results show that the gabbros formed at ca 850 ma with e hf 5 44 to 11 94 and a single stage model age t hf of 1 04 ga suggesting a depleted mantle derived source the gabbro diorites formed at ca 800 ma with major e hf 3 99 to 14 62 and t hf 0 97 ga and minor e hf 0 68 to 5 66 and t hf 1 27 ga again suggesting a depleted mantle derived source the granites were emplaced at ca 770 ma with e hf 2 53 to 10 58 and t hf 1 07 ga indicating that they were derived from the partial melting of juvenile crust the geochemical data show that the gabbros and gabbro diorites are characterized by low sio 2 contents high mg values and cr co and ni contents significant enrichment in light rare earth elements and large ion lithophile elements depletion in high field strength elements e g nb ta zr and hf and relatively high nb u ta u and ce pb ratios these data suggest that the rocks were derived from the partial melting of depleted lithospheric mantle that had been metasomatized by subduction derived fluids or melts and which underwent very minimal crustal contamination during magma evolution and ascent the granites have high sio 2 and k 2 o and low mgo contents exhibit enrichment in rb ba th and pb and depletion in nb ta and ti and have low sr y and la yb n ratios and high y and yb contents which together with their hf isotopic compositions imply a juvenile crust source taking into account regional pre 750 ma arc related magmatism and the subsequent extensional setting it is proposed that a long lived active continental margin setting may have evolved along the western margin of the yangtze block during the neoproterozoic and that the coeval granitic and mafic rocks in the baoxing area were formed by the subduction of the western yangtze block

low δ18o zircons u pb dating and the age of the qinglongshan oxygen and hydrogen isotope anomaly near donghai in jiangsu province china zircons from metamorphosed granites exposed near qinglongshan have 18ovsmow values of 7 to 0 in both grain rims and cores the concordant 238u 206pb ages of zircon cores are 684 to 754 ma with rims at 221 ma discordant 238u 206pb ages range from 242 to 632 ma results demonstrate a neoproterozoic age for the origin of the qinglongshan oxygen and hydrogen isotope anomaly the low 18o values were imprinted on the rocks by a hydrothermal system charged with meteoric water from a cold climate groundwater circulation was driven by heat from cooling granitic magma the geologic age of the hydrothermal system correlates with that of the nantuo tillite in the sinian strata of the south china block suggesting that qinglongshan s cold climate may be a manifestation of neoproterozoic snowball earth

igneous and metamorphic enclaves in the s type deddick granodiorite lachlan fold belt se australia petrographic geochemical and nd sr isotopic evidence for crustal melting and magma mixing the deddick granodiorite a mafic s type pluton in the lachlan introduction fold belt contains abundant enclaves most are derived from enclaves in granites and volcanic rocks can provide high grade metasediments of pelitic psammitic composition and petrogenetic information not readily available from their migmatites are common among these discrete fragments of host rocks didier 1973 didier barbarin 1991 for melanosomes rich in cordierite and garnet are restites from partial example metasedimentary enclaves can place constraints melting however compositional and nd sr isotopic data indicate on the age composition and deformational history of they are not restite in equilibrium with the melt component of the magma source regions within continental crust fleming host magma but may have formed part of a spectrum of diverse 1991 steele et al 1991 enclaves formed by acmagma source lithologies alternatively they may be accidental cumulation of early phenocrysts autoliths document xenoliths regardless of their origin data for these enclaves suggest the early evolution of the host magma whereas others their precursors could represent deeply buried age equivalents of the may represent commingled magmas and illustrate the ubiquitous ordovician turbidites of the lachlan fold belt three possible role of hybridization didier 1987 types of microgranular enclaves with igneous textures are disenclave suites in the relatively mafic s type granitoids tinguished the most common type are small and rounded mafic of se australia are often diverse including abundant enclaves of tonalitic composition they carry xenocrysts derived from enclaves of metasedimentary origin and microgranular the host magma and some contain high mg pyroxene derived from enclaves phillips et al 1981 price 1983 chen et al a mafic magma isotopic data form an array with end from 6 to 1989 wyborn et al 1991 the metasedimentary en 12 and sr sr from 0 7130 to 0 7167 host rock 10 and claves are lithologically diverse including gneissic 0 715 respectively these enclaves formed as globules of hybrid migmatitic types and biotite rich surmicaceous types mafic magma commingled with and contaminated by the more apart from their potential as indicators of crustal structure felsic host magma other enclave types were derived from disrupted and composition they are of interest as possible fragments syn plutonic dykes having a distinct isotopic composition and from of source material and or refractory residue from which a cogenetic marginal facies of the host peraluminous melts were generated and extracted by

diagenesis in prehistoric caves the use of minerals that form in situ to assess the completeness of the archaeological record an interpretation of the archaeological record in particular that of a prehistoric cave site is complicated by the diversity of depositional and post depositional processes that affect the material deposited here we propose to use the authigenic minerals that form in situ within the cave sediments to reconstruct the ancient chemical environments in the sediments this can be done by experimentally determining the conditions under which each of the authigenic minerals are stable although this information is not available to date for minerals formed in a prehistoric cave we present calculated stability field data for the relevant minerals the results clearly demonstrate the feasibility of this approach this information particularly if based on measurements of real authigenic cave minerals will facilitate an assessment of the completeness of the cave archaeological record this is particularly important for determining whether or not the distributions of archaeologically important materials such as bones teeth plant phytoliths charcoal and ash reflect their original burial distributions or were altered as a result of secondary diagenetic processes

do s type granites commonly sample infracrustal sources new results from an integrated o u pb and hf isotope study of zircon in contrast to i type granites which commonly comprise infracrustal and supracrustal sources s type granites typically incorporate predominantly supracrustal sources the initial aim of this study was to identify the sources of three scottish caledonian 460 ma s type granites kemnay cove and nigg bay by conducting oxygen u pb and hf isotope analyses in zircon in order to characterise one potential end member magma involved in the genesis of the voluminous late caledonian 430 400 ma i type granites field whole rock geochemical and isotopic data are consistent with the generation of the s type granites by melting their dalradian supergroup country rocks while hf isotope compositions of magmatic zircon u pb data of inherited zircons and high mean zircon 18o values of 9 0 2 7 2sd and 9 8 2 0 for the kemnay and cove granites support this model the nigg bay granite contains zircons with much lower 18o values 6 8 2 1 similar to those found in scottish i type granites this suggests that the nigg bay granite contains low 18o material representing either altered supracrustal material or more likely an infracrustal source component with mantle like 18o mixing trends in plots of 18o vs ehf for s type granite zircons indicate involvement of at least two sources in all three granites this pilot study of scottish caledonian s type granites demonstrates that while field and whole rock geochemical data are consistent with local melting of only supracrustal sources the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources

s type granitic magmas petrogenetic issues models and evidence abstract despite a perception that it represents a perverse divergence it is perfectly possible to believe in the existence of s and i type granites and the implications for the nature of their protoliths and to disbelieve in the applicability of the restite unmixing model for chemical variation in granitic magmas white and chappell erected the s i classification with impeccable validity the isotopic evidence demands contrasting source reservoirs for s and i type granitic magmas however the major advance was not the classification but the recognition that highly contrasting parental materials must be involved in the genesis of granitic magmas the restite unmixing model is commonly seen as a companion to the s i classification but it is really a separate issue this model implies that the compositions of granites image those of their source rocks in a simple way however there are other equally valid models that can explain the data and none of them represents a unique solution the most cogent explanation for the high grade metasedimentary enclaves in most s type granites is that they represent mid crustal xenoliths restitic enclaves are either rare or absent inherited zircons in s type rocks are certainly restitic however the occurrence of a substantial restitic zircon population does not imply an equally substantial restitic component in the rest of the rock zircon and zirconium behaviours are controlled by disequilibrium and kinetics and zr contents of granitic rocks can rarely be used to infer magma temperatures since the dominant ages among inherited zircons in lachlan fold belt lfb s type granites are ordovician and proterozoic it seems likely that crust of this age but geochemically different from the exposed rocks not only underlies much of the lfb but also forms a component in the granite magma sources the evidence is overwhelming that the dark microgranular enclaves that occur in both s and i type granites are igneous in origin they represent globules of quenched more mafic magma mingled and modified by exchange with the host granitic magma however magma mixing does not appear to be a significant process affecting the chemical evolution of the host magmas likewise the multicomponent mixing models erected for some granitic rock suites are mathematically nonunique and in some cases violate constraints from isotopic studies s and i type magmas commonly retain their distinct identities this suggests limited source mixing limited magma mixing and limited wall rock assimilation though intermediate types certainly exist they are probably relatively minor in volume crystal fractionation probably plays the major role in the differentiation of very many granitic magmas including most s types especially those emplaced at high crustal levels or in the volcanic environment minor mechanisms include magma mixing wall rock assimilation and restite unmixing isotopic variations within plutons and in granite suites could be caused by source heterogeneities magma mixing assimilation and even by isotopic disequilibrium however source heterogeneity coupled with the inefficiency of magma mixing is probably the major cause of observed heterogeneity normal geothermal gradients are seldom sufficient to provide the necessary heat for partial melting of the crust and crustal thickening likewise fails to provide sufficient heat generally the mantle must be the major heat source this might be provided through mantle upwelling and crustal thinning and possibly through the intra and underplating of mafic magmas upper crustal extension seems to have been common in regions undergoing granitic magmatism migmatites probably provide poor analogues of granite source regions because they are mostly formed by fluid present reactions granitic magmas are mostly formed by fluid absent processes where we do see rare evidence for arrested fluid absent partial melting the melt fraction is invariably concentrated into small shear zones veinlets and small dykes thus it seems likely that dyking is important in transporting granitic magma on a variety of scales and at many crustal levels however one major missing link in the chain is the mechanism by which melt fractions in small scale segregations occurring over a wide area can be gathered and focused to efficiently feed much wider spaced major magma conduits answers may lie in the geometry of the melting zones and in the tendency of younger propagating fractures to curve toward and merge with older ones self organization almost certainly plays a role

deciphering the source and contamination history of peraluminous magmas using δ 18 o of accessory minerals examples from garnet bearing plutons of the sierra nevada batholith peraluminous granitoids provide critical insight as to the amount and kinds of supracrustal material recycled in the central sierra nevada batholith california major element concentrations indicate sierran peraluminous granitoids are high sio2 68 9 76 9 and slightly peraluminous average molar al2o3 cao na2o k2o 1 06 both major and trace element trends mimic those of other high silica sierran plutons garnet grt in the peraluminous plutons is almandine spessartine rich and of magmatic origin low grossular contents are consistent with shallow 4 kbar depths of garnet crystallization metasediments of the kings sequence commonly occur as wallrocks associated with the plutons including biotite schists that are highly peraluminous a cnk 2 25 and have high whole rock wr 18o values 9 6 21 8 average 14 5 2 9 n 26 ultramafic wallrocks of the kings kaweah ophiolite have lower average 18o 7 1 1 3 n 9 the 18o wr of the kings sequence is variable from west to east higher 18o values occur in the west where quartz in schists is derived from marine chert values decrease eastward as the proportion of quartz from igneous and metamorphic sources increases peraluminous plutons have high 18o wr values 9 5 13 consistent with supracrustal enrichment of their sources however relatively low initial 87sr 86sr values 0 705 0 708 indicate that the supracrustal component in the source of peraluminous magmas was dominantly altered ocean crust and or greywacke also plutons lack or have very low abundances 1 of grains of inherited zircon zrc cores average 18o zrc is 7 9 in peraluminous plutons a higher value than in coeval metaluminous plutons 6 7 diorites associated with peraluminous plutons also have high 18o zrc 7 4 8 3 which is consistent with the diorites being derived from a similar source magmatic garnet has variable 18o 6 6 10 5 avg 7 9 due to complex contamination and crystallization histories evidenced by multiple garnet populations in some rocks comparison of 18o zrc and 18o grt commonly reveals disequilibrium which documents evolving magma composition minor 5 7 contamination by high 18o wallrocks occurred in the middle and upper crust in some cases although low 18o wallrock may have been a contaminant in one case overall oxygen isotope analysis of minerals having slow oxygen diffusion and different times of crystallization e g zircon and garnet together with detailed textural analysis can be used to monitor assimilation in peraluminous magmas moreover oxygen isotope studies are a valuable way to identify magmatic versus xenocrystic minerals in igneous rocks

phase relations of peraluminous granitic rocks and their petrogenetic implications peraluminous granitic rocks are magmatic rocks that contain quartz po tassic feldspar and or sodic plagioclase and one or more aluminum rich minerals thus these rocks contain more aluminum than could be accom modated by feldspar in a cipw normative calculation and show normative corundum peraluminous granites are defined by their chemical nature but their recognition is often based on petrography this discrepancy thus may lead to inconsistency although peraluminous granitic rocks are com monly true granite streckeisen 1973 they range from tonalite to granite of special interest are strongly peraluminous as defi ned below granite granodiorite or in rare instances trondhjemite these rocks contain alumi nous minerals almandinic garnet cordierite tourmaline muscovite that are thought to be stable in silicate magmas only if these magmas are themselves peraluminous the origin of peraluminous granite and related intrusive rocks is of much current interest many of these form shallow level intrusions and they can reach enormous sizes examples are the batholiths in the lachlan fold belt in southeastern australia white chappell 1983 the cornub ian batholith in england exley stone 1966 the south mountain batholith in nova scotia mckenzie clarke 1975 the manaslu batho lith in the himalayas lefort 1981 much of the idaho batholith

the behavior of the hf isotope system in radiation damaged zircon during experimental hydrothermal alteration the application of the hf isotope composition of zircon as a geochemical tracer requires the preservation of lu hf systematics within individual grains we performed hydrothermal experiments on a self irradiation damaged zircon to test whether hydrothermal alteration would affect its hf isotopic composition severely radiation damaged zircon from sri lanka was reacted in either teflon reactors or gold capsules at 200 c 1080 h autogeneous pressure 400 c 120 h 1 kbar and 600 c 72 h 1 kbar in a 1 m hcl 0 2 m hf solution that was spiked with 300 ppm non natural hf 98 2 180 hf and 970 ppm yb laser ablation inductively coupled plasma mass spectrometry measurements of the hf and u pb isotope compositions of the altered domains revealed that the u pb system of such domains was severely disturbed resulting in a discordia pointing toward the origin of the concordia diagram but that the hf isotope composition was unaffected in addition yb enrichment was observed in the reacted zircon domains predominantly near the zircon solution interface the yb has apparently diffused into the altered domains the new data are fully consistent with a diffusion controlled aqueous alteration process occurring within radiation damaged zircon

shrimp zircon u pb geochronological and whole rock geochemical evidence for an early neoproterozoic sibaoan magmatic arc along the southeastern margin of the yangtze block abstract it has been generally accepted that the south china block was formed through amalgamation of the yangtze and cathaysia blocks during the proterozoic sibaoan orogenesis but the timing and kinematics of the sibao orogeny are still not well constrained we report here shrimp u pb zircon geochronological and geochemical data for the taohong and xiqiu tonalite granodiorite stocks from northeastern zhejiang southeastern margin of the yangtze block our data demonstrate that these rocks dated at 913 15 ma and 905 14 ma are typical amphibole rich calc alkaline granitoids formed in an active continental margin combined with previously reported isotopic dates for the 1 0 ga ophiolites and 0 97 ga adakitic rocks from northeastern jiangxi the timing of the sibao orogenesis is thus believed to be between 1 0 and 0 9 ga in its eastern segment it is noted that the sibao orogeny in south china is in general contemporaneous with some other early neoproterozoic 1 0 0 9 ga orogenic belts such as the eastern ghats belt of india and the rayner province in east antarctica indicating that the assembly of rodinia was not finally completed until 0 9 ga

recrystallization rims in zircon valle d arbedo switzerland an integrated cathodoluminescence la icp ms shrimp and tem study recrystallization rims are a common feature of zircon crystals that underwent metamorphism we present a microstructural and microchemical study of partially recrystallized zircon grains collected in polymetamorphic migmatites valle d arbedo ticino switzerland the rims are bright in cathodoluminescence cl with sharp and convex contacts characterized by inward penetrating embayments transgressing igneous zircon cores laser ablation inductively coupled plasma mass spectrometry la icp ms data and transmission electron microscopy tem imaging indicate that the rims are chemically and microstructurally different from the cores the rims are strongly depleted in ree with concentrations up to two orders of magnitude lower than in the cores indicating a significant loss of ree during zircon recrystallization enrichment in non formula elements such as ca has not been observed in the rims the microstructure of zircon cores shows a dappled intensity at and below the 100 nm scale possibly due to radiation damage other defects such as pores and dislocations are absent in the core except at healed cracks zircon rims are mostly dapple free but contain nanoscale pores and strain centers interpreted as fluid inclusions and chemical residues respectively sensitive high resolution ion microprobe shrimp u pb ages show that the recrystallization of the rims took place 200 ma ago when the parent igneous zircon was not metamict the chemical composition and the low ti content of the rims indicate that they form at sub solidus temperatures 550 650 c recrystallization rims in valle d arbedo zircon are interpreted as the result of the migration of chemical reaction fronts in which fluid triggered in situ and contemporaneous interface coupled dissolution reprecipitation mechanisms this study indicates that strong lattice strain resulting from the incorporation of a large amount of impurities and structural defects is not a necessary condition for zircon to recrystallize our observations suggest that the early formation of recrystallization rims played a major role in preserving zircon from the more recent alpine metamorphic overprint

ash bones and guano a study of the minerals and phytoliths in the sediments of grotte xvi dordogne france abstract very few prehistoric cave deposits in western europe contain visible hearth remains even though there is abundant evidence of fire use by cave inhabitants grotte xvi dordogne france is exceptional in this respect in that it contains a most conspicuous layer couche c characterized by a series of brightly coloured bedded sediments the formation of couche c has previously been ascribed to the ash and charcoal produced by the cave s mousterian occupants burning mainly lichens the mousterian sedimentary layers below couche c and the upper palaeolithic sediments unconformably overlying couche c are quite different in texture and colour and show no visible evidence of ash deposits analyses of the minerals microstructures and phytoliths in couche c are consistent with the notion that these sediments were derived mainly from ash produced by burning wood and to a lesser extent grass the original calcite component of the ash has been diagenetically altered to carbonated apatite around the cave periphery and to even more insoluble phosphate minerals in the centre one such mineral newberyite most likely formed by the reaction between guano degradation products and the ash under these circumstances bone preservation is also affected the overlying upper palaeolithic sediments contain calcite one of these layers abb contains much more calcite than all the other layers as well as abundant phytoliths derived from wood and grass this layer also contained many artifacts and bones it is thus concluded that ash is a major component of layer abb even though it is not visible to the maked eye in the form of hearths

oxygen isotope ratios of zircon magma genesis of low δ18o granites from the british tertiary igneous province western scotland igneous zircons from granites of the british tertiary igneous province btip in western scotland preserve magmatic oxygen isotope ratios in spite of hydrothermal alteration and thus provide new evidence for the genesis of granites co2 laser and mass spectrometer based bulk 1 3 mg oxygen isotope analyses from individual plutons show remarkable homogeneity in zircon 18o regardless of zircon size and magnetism average reproducibility of 18o zrc in a single pluton is 0 2 in addition ion microprobe analysis shows that individual zircons all have the same 18o and thus bulk samples are homogeneous fourteen granite bodies from the isle of skye show extreme variability in zircon 18o values from pluton to pluton 18o zrc 0 6 5 3 vsmow all the granites record zircon 18o values less than would be in high temperature equilibrium with normal mantle 18o zrc 5 except for the beinn an dubhaich granite zircons from one intrusion in the mafic cuillins center also have low 18o 2 5 similar variability is observed in 18o amongst three intrusions on the isle of mull 18o zrc 3 4 5 9 both mull and skye are characterized by intense shallow paleohydrothermal systems and the low and variable 18o values of the magmas likely result from melting or interaction with hydrothermally altered country rock analysis of granites on the isle of arran where the percentage of low 18o country rocks is much less yields higher 18o zrc of 6 8 and 5 4 published trace element and radiogenic isotope data for btip mafic and felsic rocks have supported the hypothesis that the granites are formed primarily by differentiation from the mantle with magmas experiencing minimal crustal input dickin et al phil trans r soc london a 310 1984 755 780 however conservative estimates based on oxygen isotope compositions suggest that some of the btip granites can only be formed from normal magmas 18o wr 6 if they assimilated significant amounts of hydrothermally altered crustal material some granites require up to 40 bulk crustal input and are better explained as the result of wall rock melting by an adjacent mafic pluton whereas pb and sr suggest a general trend towards increasing input of shallow crust for the younger granites dickin et al phil trans r soc london a 310 1984 755 780 the correlation between age and 18o is less apparent suggesting that pb and sr isotopic compositions are decoupled from oxygen isotopes this would be expected of melted country rock that was hydrothermally altered in oxygen isotope ratios but not in pb and sr isotope ratios

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

zircon u pb dating of water rock interaction during neoproterozoic rift magmatism in south china abstract a combined study of zircon u pb dating and mineral o isotope analysis was carried out for neoproterozoic granite gabbro and gabbrodiorite from the beihuaiyang zone that marks a rifted margin between the south china block and the supercontinent rodinia the results provide precise constraints on timing of water rock interaction resulting in unusual 18 o depletion in igneous minerals cl imaging reveals that zircons mostly show clear oscillatory and or sector zoning with or without thin alteration rims no metamorphic zircon occurs in the igneous intrusives although they suffered greenschist facies metamorphism during triassic continental collision la icpms zircon u pb dating yields consistent ages of 739 8 to 754 5 ma which are interpreted as timing of magma crystallization mineral separates have highly variable 18 o values of 0 6 to 6 8 for zircon 1 2 to 12 5 for quartz and 0 3 to 8 4 for plagioclase oxygen isotope heterogeneities exist within single intrusions and between different intrusions magmatic zircons with low 18 o values and a weighted mean u pb age of 748 6 ma crystallized from low 18 o magmas that were derived from melting of hydrothermally altered low 18 o rocks both low and normal 18 o intrusives in the beihuaiyang zone are shown to form at the same time contemporaneous with the rodinia breakup thus tectonic evolution from supercontinental rift to breakup is proposed to create conditions for alternating processes of high t hydrothermal alteration and low 18 o magmatism such processes are a characteristic feature of high t water rock interaction in volcanic rift margins associated with localized water saturated melting while the occurrence of low 18 o magmas demonstrates penetration of meteoric water into the rift tectonic zone of crustal melting the existence of normal 18 o magmas indicates that their emplacement may serve as a thermal engine to drive the second stage of meteoric water rock interaction resulting in the unusual 18 o depletion in adjacent rocks the concurrent occurrence of both low and normal 18 o magmas appears to indicate highly heterogeneous high t water rock interaction during rift magmatism

tectonic transition from subduction to retreat of the palaeo pacific plate new geochemical constraints from the late mesozoic volcanic sequence in eastern fujian province se china

mineral assemblages in theopetra greece a framework for understanding diagenesis in a prehistoric cave abstract prehistoric cave sediments are often subjected to severe mechanical and chemical alteration making it difficult to interpret aspects of their archaeology theopetra cave offers unique opportunities to resolve aspects of this problem particularly in relation to chemical changes because it has a relatively well defined stratigraphy and its older deposits have been subjected to unusually severe diagenesis a study of the mineralogy and micromorphology of the sediments and in particular the phosphatic minerals that formed in the sediments after deposition shows that each stratigraphic unit has its own pattern of authigenic mineral distribution in some units these patterns vary sequentially in both lateral and vertical directions these variations reflect changing degrees of diagenesis and the observed patterns imply that every unit obtained its diagenetic fingerprint fairly soon after burial the prominent ash layers in the older sediments were subjected to unusually severe diagenetic alteration such that most of the relatively stable siliceous components of ash decomposed into amorphous silica an intimate association between ash minerals and the k fe phosphate mineral leucophosphite was also observed the sequential changes in authigenic mineral assemblages in theopetra are basically similar to those observed in several caves in israel raising the possibility that common processes are involved and that information obtained from these detailed studies can be applied to other caves in diverse geographic regions

dehydration melting and water saturated melting of basaltic and andesitic greenstones and amphibolites at 1 3 and 6 9 kb

cooling and exhumation of the oldest sanqiliu uranium ore system in motianling district south china block the sanqiliu uranium deposit belongs to a uranium ore system in motianling district it is the oldest uranium deposit in south china primary uranium mineralization occurred almost simultaneously with the emplacement of the host granites and subsequent dykes and it has a relatively high grade of uranium 0 421 we clarify the age of mineralization and investigate the cooling history through new pitchblende u pb and apatite fission track thermochronology the pitchblende u pb results indicate that uranium mineralization occurred at 801 759 ma fractionation of uranium and lead at 374 295 ma is interpreted as remobilization and resetting of the original uranium the motianling area has apatite fission track ages of 57 to 18 ma by combining our results with previous work we conclude that the deposit cooled slowly and was exposed at the surface during the cenozoic the timing and depth of exhumation helped to preserve and avoid erosion of the uranium deposit and highlight the potential for regional uranium exploration

the source of uranium within hydrothermal uranium deposits of the motianling mining district guangxi south china abstract uranium deposits are diverse as a result of their formation in a wide variety of geological environments however the source of the uranium within these deposits is difficult to identify and as a result it is usually poorly understood this study focuses on the hydrothermal sanqiliu and sanqisi uranium deposits both of which formed within ne sw striking shear zones that cross cut the sanfang batholith and low grade metasedimentary rocks of the motianling district southern china the deposits contain vein hosted pitchblende quartz pyrite chlorite mica orebodies fluid inclusions within quartz in the orebodies in the district homogenize at temperatures between 205 c and 222 c indicating the deposit formed as a result of low to intermediate temperature hydrothermal activity pitchblende associated hydrothermal pyrite within the sanqiliu and sanqisi deposits has 34s values from 24 7 to 19 7 and from 6 0 to 13 6 respectively quartz separates from the sanqiliu deposit yield 18o values of 1 4 11 5 mean of 5 8 for syn ore hydrothermal fluids these stable isotope data indicate that the fluids that formed these deposits were derived from the sanfang granites sediments of the sibao group and meteoric sources in addition uraninite from the host sanfang granite yields u pb ages of ca 732 773 ma combining these data with the geology of the ore deposits in this region suggests that these deposits were generated from deeply circulating meteoric water and the uraninite within the highly fractionated sanfang granite is the source of the uranium within the sanqiliu and sanqisi uranium deposits

cave sediments upper pleistocene stratigraphy and mousterian facies in cantabrian spain abstract archaeological sediments are analysed from karst cave columns in cantabrian spain cueva morin el pendo the castillo cave complex including la flecha las chimeneas la pasiega las monedas hornos de la pena and cobalejos external sediment influx including loess is calibrated by an index of cave and slope run off energy while other features slope and roof rubble chemical precipitates cryoturbations fine soil derivatives and cultural components are discussed the key sequences morin el pendo castillo are each interpreted in local terms and then combined into a regional climatostratigraphy that includes 40 environmental phases within deep sea isotope stages 2 5 trends in run off energy reflecting slope stability temperature and summer moisture are rarely in phase indicating complex environmental change mid pleistocene and older deposits exist but have largely been destroyed explaining the apparent absence of acheulian settlement mousterian occupation is verified by isotope stage 5b and two or three mousterian facies that span 25 50 000 years are coeval in several caves regardless of the direction of climatic oscillations this suggests the flexible lithic technology of a single population maintaining an adaptive steady state despite repeated environmental changes by contrast the distinct upper palaeolithic industries each span only a few millennia but in part overlap temporally within the region between 35 000 and 9500 bp

nature of parent rocks mineralization styles and ore genesis of regolith hosted ree deposits in south china an integrated genetic model abstract regolith hosted rare earth element ree deposits also called ion adsorption or weathered crust elution deposited ree deposits are distributed over jiangxi guangdong fujian hunan guangxi and yunnan provinces in south china in general these deposits can be categorized into the hree dominated type for example the famous zudong deposit in southern jiangxi province and the lree dominated type such as the heling and dingnan deposits in southern jiangxi province most of these deposits form from weathering of biotite and muscovite granites syenites monzogranites granodiorites granite porphyries and rhyolitic tuffs the parent rocks are generally peraluminous siliceous alkaline and contain a variety of ree bearing minerals mostly ree patterns of regolith are inherited from the parent rocks and therefore characteristics of the parent rocks impose a significant control on the ore formation data compilation shows that autometasomatism during the latest stage of granite crystallization is likely essential in forming the hree enriched granites whereas lree enriched granites could form through magmatic differentiation these deposits are normally two to three fold but could be up to ten fold enrichment in ree compared to the parent granites where the maximum enrichment usually occurs from the lower b to the upper c horizon ce shows different behavior with the other rees strongly positive ce anomalies commonly occur at the upper part of weathering profiles likely due to oxidation of ce 3 to ce 4 and removal of ce from soil solutions through precipitation of cerianite vertical ph and redox gradients in weathering crusts facilitate dissolution of ree bearing minerals at shallow level and fixation of ree at depth through either adsorption on clay minerals or precipitation of secondary minerals at the same time mass removal of major elements plays an important role in concentrating ree in regolith combination of mass removal and eluviation illuviation dynamics is the main mechanism for ree accumulation in weathering crusts favorable exogenetic factors facilitate the accumulation of ree in regolith and preservation of the ore bodies these include quasi equilibrium between denudation and exhumation at regional scales local geomorphology dominated by low lying gentle slopes adequate rainfall and favorable groundwater conditions continuous operation of such a dynamic weathering system is essential in the formation of regolith hosted ree deposits

petrogenesis of the jiaoziding granitoids and associated basaltic porphyries implications for extensive early neoproterozoic arc magmatism in western yangtze block abstract middle neoproterozoic ca 860 750 ma granitoids are widely distributed in the western margin of the yangtze block china yet their magma sources and tectonic settings are unclear the geochronology and geochemistry of the granitoids and associated basaltic porphyries which intruded the 970 ma tongmuliang arc volcanic rocks in the jiaoziding area east of pingwu county were investigated in this study la icp ms zircon u pb dating indicates that the jiaoziding granitoids and basaltic porphyries were formed at 795 6 ma and 790 20 ma respectively the granitoids have high sio 2 69 2 76 9 wt k 2 o 2 3 5 6 wt and na 2 o 3 2 5 1 wt contents and a low al 2 o 3 12 4 14 5 wt content the basaltic porphyries contain high concentrations of tio 2 3 wt and high field strength elements have steep rare earth element patterns and are depleted in nd and hf isotopes batch partial melting modelling indicates that the jiaoziding granitoids could have been derived by 5 and 50 70 partial melting of tongmuliang mafic rocks and quartz keratophyres respectively formation of the basaltic porphyries by melting of upwelling asthenospheric mantle would have been facilitated by extensive lithospheric delamination during the neoproterozoic this study established a link between mid neoproterozoic granitic magmatism and 970 ma juvenile arc crust indicating that extensive early neoproterozoic juvenile arc crust and partial melting of this crust in an extensional setting favoured the formation of middle neoproterozoic granitic rocks along the w nw margin of the yangtze block

petrogenesis and geodynamic significance of the 850 ma dongling a type granites in south china abstract the ongoing controversy on the timing of amalgamation of the yangtze and cathaysia blocks either prior to 890 ma or later than 830 ma impedes a proper understanding of geological evolution of the south china block and its role in the breakup of rodinia supercontinent in this study we report 850 ma la icp ms zircon u pb ages and whole rock geochemistry of the dongling granites from the southeastern yangtze block that did not receive much geoscientific attention as compared to the better studied 830 760 ma sedimentary and igneous rocks in the south china block the studied dongling granites have high k2o na2o 7 44 9 09 wt and low mgo 0 07 0 54 wt and cao 0 16 1 21 wt contents their high feot feot mgo 0 82 0 94 and ga al 2 6 values and hfse abundance zr nb ce y 443 965 ppm allow their grouping as a type granite in the chondrite normalized diagrams these granites display right inclined ree patterns and strong to moderate negative eu anomalies eu eu 0 32 0 70 the dongling granites have variable and negative whole rock end t 14 6 to 8 6 and zircon ehf t 12 8 to 4 4 with paleoproterozoic two stage nd 2 20 2 69 ga and hf model ages 2 01 2 41 ga zircon saturation parameters tzr suggest 850 c temperature and other geochemical characteristics reveal low melting pressure 350 to

fingerprinting feldspar phenocrysts using crystal isotopic composition stratigraphy implications for crystal transfer and magma mingling in s type granites microsampling of cm scale feldspar crystals within an s type granite from the lachlan fold belt of southeastern australia has revealed complex internal sr and nd isotopic variations the observed isotopic zonations are in part interpreted as recording feldspar crystallisation in a dynamically mixing magma system the isotopic composition of which was varying in response to the influx of more mafic and isotopically more mantle like magmas the latter stages of which are now represented in modified form by microgranular enclaves similar core to rim isotopic variations in feldspar megacrysts from a microgranular enclave and the adjacent host granite strongly suggest megacrysts in the enclave were transferred from the granitic magma during crystallisation feldspar rims have higher 87sr 86sri and lower nd i than adjacent whole rock analyses but match those of mineral separates from the surrounding enclave matrix this suggests that the final stages of megacryst growth occurred in the presence of a component that had previously interacted with a high 87sr 86sr low nd i component such as metasedimentary wall rocks isotopic heterogeneities are also presererved within different mineral phases in the enclave matrix suggesting that differing phases grew at differing stages of equilibration between the enclave magma and its host granitic magma our results reveal major isotopic heterogeneities on a single crystal and also inter mineral scale in a pluton which shows well constrained evidence for magma mingling these results indicate the suitability of feldspars as recorders of isotopic change in magmatic systems even those which have cooled slowly in the plutonic environment and suggest that much heterogeneity in plutonic systems may be overlooked on a whole rock scale

magmatic evolution and crustal recycling for neoproterozoic strongly peraluminous granitoids from southern china hf and o isotopes in zircon zircons can retain a grain scale record of granitoid compositional evolution that is accessible through microanalysis in situ u pb hf and o isotope data yield new insights into the petrogenesis and evolution of the neoproterozoic strongly peraluminous granitoids of the jiangnan orogen jo southern china a negative correlation of th u versus d 18 o is found for most analyses some zircons from eastern jo granitoids show d 18 o variations of 3 6 from core to rim indicating a dramatic shift toward higher oxygen isotope values by voluminous partial melting of supracrustal rocks and signaling a transition from i type like to s type like magmas during the later stage of magmatic evolution this mechanism provides a reasonable explanation why some granitoids have intermediate geochemical features between s type and i type granites hf isotope trends indicate that a larger proportion of mature continental crust was incorporated into the magma sources of the western jo granitoids whereas more juvenile arc crust was incorporated into the eastern jo magmas no significant depleted mantle derived mafic magma was injected into the jo granitoid magmas instead radiogenic hf and nd signatures in jo granitoids reflect incorporated juvenile arc crust and document crustal growth in southern china during the early neoproterozoic ca 900 ma thus our zircon data suggest that strongly peraluminous granitoids which are widely regarded as the products of orogenesis that primarily recycle evolved crust can also record important information about early crustal growth

residence resorption and recycling of zircons in devils kitchen rhyolite coso volcanic field california zircons from the devils kitchen rhyolite in the pleistocene coso volcanic field california have been analyzed by in situ pb u ion microprobe shrimp rg and by detailed cathodoluminescence imaging the zircons yield common pb corrected and disequilibrium corrected pb u ages that predate a previously reported k ar sanidine age by up to 200 kyr and the range of ages exhibited by the zircons is also approximately 200 kyr cathodoluminescence imaging indicates that zircons formed in contrasting environments most zircons are euhedral and a majority of the zircons are weakly zoned but many also have anhedral embayed cores with euhedral overgrowths and multiple internal surfaces that are truncated by later crystal zones concentrations of u and th vary by two orders of magnitude within the zircon population and by 10 20 times between zones within some zircon crystals indicating that zircons were transferred between contrasting chemical environments a zircon saturation temperature of 750 c overlaps within error a previously reported phenocryst equilibration temperature of 740 25 c textures in zircons indicative of repeated dissolution and subsequent regrowth are probably caused by punctuated heating by mafic magma input into rhyolite the overall span of ages and large variation in u and th concentrations combined with calculated zircon saturation temperatures and resorption times are most compatible with crystallization in magma bodies that were emplaced piecemeal in the crust at coso over 200 kyr prior to eruption and that were periodically rejuvenated or melted by subsequent basaltic injections

systematics of internal zircon morphology in major variscan granitoid types the internal morphologies of zircon crystals from different types of granitoids alkaline calcalkaline and anatectic are revealed by cathodoluminescence imaging and are described in terms of growth rates of the crystal faces relative to each other zircons in the alkaline granitoids are characterized by high and constant growth rates of 010 relative to the pyramidal forms and by symmetric grwoth of 011 zircons in the calcalkaline and anatectic granitoids are characterized by fluctuating or gradually decreasing relative growth rates of 010 by asymmetric and highly variable growth of 011 and by a tendency of 110 to become grwoth inhibited corrosion events are interspersed during zircon growth in the calcalkaline magmas in the calcalkaline and anatectic magmas a discontinuity breaks the morphological evolution at late stages of crystallization the discontinuity coincides with a sharp drop in cathodoluminescence the growth behaviour of each crystal form is analysed and compared with predictions made by the periodic bond chain pbc theory it is argued that the relative growth rate of 010 depends on supersaturation that the growth rates of 011 faces are changed in response to different ratios of adsorbing cations na k al and that 110 faces become growth inhibited by the adsorption of h2o or trace elements enriched in the residual liquid morphological and chemical discontinuities at late stages of crystallization are reasonably explained by the formation of larger growth units from smaller ionic entities in the residual liquid important factors controlling the zircon morphology in different types of granitoids are high cooling rates alkaline magmas magma mixing calcalkaline magmas enrichment of h2o and trace elements in residual liquids calcalkaline and anatectic magmas and the major element chemistry of the magma possibly the ratio of na and k to al agpaicity

neoproterozoic post collisional extension of the central jiangnan orogen geochemical geochronological and lu hf isotopic constraints from the ca 820 800 ma magmatic rocks abstract neoproterozoic magmatic rocks in south china contain important information on evaluating crustal reworking during the yangtze cathaysia collision and post collisional extension we present here geochemical geochronological and lu hf isotopic data of a suite of granitoids and diorites from the jiuling and meixian plutons of the central jiangnan orogen the granitoids display intermediate geochemical features between s type and i type granites they exhibit arc like patterns of ree and trace element partition reflecting inheritance of juvenile arc derived crust igneous zircons from the jiuling and meixian granitoids yield u pb ages of 822 819 ma and 816 815 ma respectively inherited zircons from the granitoids commonly yield a major age population of 980 860 ma consistent with the time of the shuangxiwu volcanic arc the igneous and inherited zircons have highly variable ehf t values ranging from 9 to 12 2 we interpret the granitoids to have been generated by remelting and binary mixing of 1 juvenile arc derived crustal material and 2 supracrustal material of the shuangqiaoshan meta sedimentary rocks the previous crustal thickening achieved by the yangtze cathaysia collision is a prerequisite for their generation the two granitoids together with regional 825 815 ma s type granites indicate incipient post collisional collapse of thickened crust heralding tectonic switch from compression to extension the meixian diorites display arc like geochemical characteristics and yield zircon u pb ages of 805 804 ma and neutral to positive zircon ehf t values 0 1 7 5 the diorites were generated by decompression melting of arc derived lower crust associated with asthenospheric mantle upwelling during continental rifting such rifting may be part of global neoproterozoic rifting events that finally led to breakup of the rodinia supercontinent

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

do hf isotopes in magmatic zircons represent those of their host rocks abstract lu hf isotopic system in zircon is a powerful and widely used geochemical tracer in studying petrogenesis of magmatic rocks and crustal evolution assuming that zircon hf isotopes can represent initial hf isotopes of their parental whole rock however this assumption may not always be valid disequilibrium partial melting of continental crust would preferentially melt out non zircon minerals with high time integrated lu hf ratios and generate partial melts with hf isotope compositions that are more radiogenic than those of its magma source dissolution experiments with hotplate bomb and sintering procedures of zircon bearing samples demonstrate this disequilibrium effect where partial dissolution yielded variable and more radiogenic hf isotope compositions than fully dissolved samples a case study from the neoproterozoic jiuling batholith in southern china shows that about half of the investigated samples show decoupled hf isotopes between zircons and the bulk rocks this decoupling could reflect complex and prolonged magmatic processes such as crustal assimilation magma mixing and disequilibrium melting which are consistent with the wide temperature spectrum from 630 c to 900 c by ti in zircon thermometer we suggest that magmatic zircons may only record the hf isotopic composition of their surrounding melt during crystallization and it is uncertain whether their hf isotopic compositions can represent the primary hf isotopic compositions of the bulk magmas in this regard using zircon hf isotopic compositions to trace crustal evolution may be biased since most of these could be originally from disequilibrium partial melts

multiple emplacement and exhumation history of the late mesozoic dayunshan mufushan batholith in southeast china and its tectonic significance 1 structural analysis and geochronological constraints the south china block scb experienced a polyphase reworking by the phanerozoic tectono thermal events to better understand its late mesozoic tectonics an integrated multidisciplinary investigation has been conducted on the dayunshan mufushan composite batholith in the north central scb this batholith consists of two major intrusions that recorded distinct emplacement features according to our structural analysis two deformation events in relation to batholith emplacement and subsequent exhumation are identified the early one d1 was observed mostly at the southern border of the batholith characterized by a top to the sw ductile shearing in the early stage intrusion and along its contact zone this deformation chiefly associated with the pluton emplacement at ca 150 ma was probably assisted by far field compression from the yangtze foreland belt the second but main event d2 involved two phases 1 ductile shearing d2a prominently expressed along the dayunshan detachment fault at the western border of the batholith where the syntectonic late stage intrusion and minor metasedimentary basement in the footwall suffered mylonitization with top to the nw kinematics 2 subsequent brittle faulting d2b further exhumed the entire batholith that behaved as rift shoulder with half graben basins developed on its both sides geochronological constraints show that the crustal ductile extension occurred during 132 95 ma such a cretaceous nw se extensional tectonic regime as indicated by the d2 event has been recognized in a vast area of east asia this tectonism was responsible not only for the destruction of the north china craton but also for the formation of the so called southeast china basin and range tectonics

latest cretaceous eggshell assemblage from the willow creek formation upper maastrichtian lower paleocene of alberta canada reveals higher dinosaur diversity than represented by skeletal remains the willow creek formation upper maastrichtian lower paleocene of southwestern alberta is a poorly fossiliferous formation that preserves a low end cretaceous dinosaur diversity compared with most correlative terrestrial deposits in the north american western interior although only three dinosaur taxa are known from skeletal remains tyrannosaurus rex hadrosauridae indet and leptoceratopsidae indet study of hundreds of dinosaur eggshells recovered from several sites in the formation reveals the presence of a more diverse dinosaur assemblage morphological and histological analyses of the eggshells indicate the presence of at least seven dinosaur ootaxa continuoolithus montanoolithus porituberoolithus prismatoolithus spp spheroolithus spp these ootaxa are referable to at least two ornithopod and five small theropod species likely including dromaeosaurids oviraptorosaurs and troodontids when considering the taxonomic affinity of eggshells and skeletal remains the present study tripl

internal structures of zircons from archaean granites from the darling range batholith implications for zircon stability and the interpretation of zircon u pb ages internal structures in zircons from granitoids from the late archaean darling range batholith show secondary features revealed by hf etching which record reconstitution of the zircons and modification of the distribution of trace elements during post crystallisation cooling of the granitoid zircons from the granites commonly contain unzoned to weakly zoned cores surrounded by rims showing oscillatory zoning which has been modified by recrystallisation the most striking feature is the development of high trace element concentration areas found in zircons from a number of granites these structures range from enhanced trace element concentrations in primary zones to a single accumulation of most trace elements in one band about half way between the outer edge and the centre of the zircon in any zircon the extent of the concentration of trace elements towards the formation of a single trace element band appears to be inversely related to the fading and broadening of primary oscillatory zones in the outer rim this suggests that the trace element bands formed by migration of trace elements from the outer primary zones to new concentration sites on an inner set of primary zones this explanation is supported by the formation of multiple curved trace element bands that transgress primary zoning and the determination of younger shrimp ages on depleted zircon outer rims compared to remnant primary oscillatory zoned areas of the zircon and unzoned centres also observed in some granite zircons is a finely convoluted zoning which overprints oscillatory zoning in parts of a zoned zircon and in rare cases occurs throughout the zircon this structure is explained in terms of secondary migration and reconcentration of trace elements in curved bands all structures can be transgressed by generally rounded lobes and patches of low u weakly nebulously zoned zircon this is interpreted as a late stage interaction between the zircon and fluids formed during cooling and crystallisation of the granitoid resulting in recrystallisation of affected parts of the zircon with accompanying loss of trace elements from the zircon

zircon u pb age and o isotope evidence for neoproterozoic low 18o magmatism during supercontinental rifting in south china implications for the snowball earth event identification of neoproterozoic low 18 o igneous rocks is a key to demonstrate that high t water rock interaction and low 18 o magmatism in rift tectonic zones can serve as an efficient interface to transport heat and material from the earth s interior to exterior at the onset of the snowball earth event low 18 o values of 10 9 to 4 4 permil characteristic of meteoric origin were observed on an areal extent over 30 000 km2 for mid neoproterozoic metaigneous zircons from the ultrahigh pressure eclogite facies metamorphic belt of triassic ages along the dabie sulu orogenic belt china although the zircon o isotope system could be reset to acquire its low 18 o values by exchange with matrix minerals during wet eclogite facies metamorphism the abnormal 18 o depletion is confirmed by occurrence of neoproterozoic low 18 o zircons in low grade metaigneous rocks in the same belt cathodoluminscence imaging of zircons from low grade metagranitoid and metavolcanic rocks shows preservation of the internal structures of oscillatory zoning typical of magmatic origin hornblende from two granites of low 18 o zircons gave ar ar plateau ages of 747 6 and 776 12 ma ruling out that phanerozoic metamorphism effected mineral o isotope values two groups of u pb ages were measured at 756 5 ma and 782 5 ma respectively for the low 18 o zircons this indicates that low 18 o zircons crystallized during two episodes of low 18 o magmatism in response to tectonic evolution from supercontinental rifting at 780 ma to breakup at 750 ma the second episode of low 18 o magmatism is contemporaneous with the continental kaigas iceage a plate rift model is advanced to account for the tectonic connection between the low 18 o magmatism the continental glaciation and the supercontinental rifting during the cryogenian period high t meteoric water rock interaction occurred prior to low 18 o magmatism in rift tectonic zones and caldera collapse was responsible for melting of hydrothermally altered low 18 o rocks during rifting of the south china block from the rodinia supercontinent

the source magmatic contamination and alteration of the idaho batholith zircons from cretaceous and tertiary granitic rocks of the idaho batholith preserve the best record of magmatic oxygen isotope ratios the coupling of oxygen isotope data from refractory minerals such as zircon and garnet with that from less refractory minerals such as quartz reveals the complex evolution and alteration history of the idaho batholith values of 18o zircon throughout the batholith are relatively homogeneous at 6 9 0 9 1 sd n 21 rocks despite variations in age and chemistry samples from the bitterroot lobe have an average 18o zircon of 7 1 0 3 n 7 rocks and samples from the atlanta lobe have an average 18o zircon of 7 0 1 0 n 9 rocks four epizonal tertiary plutons have an average 18o zircon of 7 2 0 2 n 4 rocks these data indicate a similar magmatic source for all granitic rocks of the idaho batholith except the tertiary epizonal casto pluton which has a 18o zircon of 4 0 0 1 n 1 rock the zircon data show that the range of normal magmatic 18o is considerably more restricted than was previously inferred despite some samples containing two micas and or garnet or having a mildly peraluminous character quartz is more variable than zircon in 18o average 18o quartz for the entire batholith is 10 4 1 1 1 sd n 65 rocks with a range of 7 7 to 12 4 excluding the casto pluton the spread of quartz values is 2 7 larger and typically higher than that calculated relative to zircon quartz data from the bitterroot lobe and epizonal tertiary plutons suggest the alteration of primary 18o during metamorphic events quartz data from the atlanta lobe suggest closed system diffusional exchange during cooling igneous garnet 18o values are higher than and out of equilibrium with those of coexisting zircon by 0 1 0 9 assuming an average 18o for unaltered wall rock metasediments the incorporation of 10 metasediment into a magma after crystallization of zircon raises the 18o magma by 0 9 the largest measured garnet zircon these quartz and garnet 18o from the atlanta and bitterroot lobes suggest magmatic contamination with a high 18o rock after the crystallization of zircon and before that of garnet and quartz

neoproterozoic high mg basalts formed by melting of ambient mantle in south china abstract the southeastern yangtze block south china contains voluminous late neoproterozoic felsic plutonic rocks and minor mafic ultramafic volcanic rocks some ca 830 ma lavas hosted in the neoproterozoic strata have pillow structures and micro spinifex textures and thus previously were considered as komatiitic basalts derived from a mantle plume these rocks have high mgo 10 1 16 3 wt variable cao 6 57 11 2 wt restricted al2o3 11 2 13 4 wt and low tio2 0 50 0 61 wt p2o5 0 03 0 04 wt and incompatible trace elements they also have negative nd 5 4 to 2 9 and high 207pb 204pb 15 71 15 76 and initial 187os 188os ratios 0 1100 0 1931 indicating crustal contamination the most primitive samples show arc like trace elemental features which are characterized by enrichment of lree and lile relative to hfse in the primitive mantle normalized trace element diagrams suggesting derivation from enriched mantle sources primelt2 modeling shows that their primary magmas were produced by about 30 partial melting of a fertile peridotite source having a mantle potential temperature of 1440 1500 c such a potential temperature is in agreement with the estimates for ambient mantle during the neoproterozoic these evidence suggest that the high mg basalts are similar to boninites and probably be part of an ophiolite assemblage they were generated by melting of a hot ambient mantle source in relation to slab subduction during the amalgamation of the yangtze and cathaysia blocks

petrogenesis of the early cretaceous intermediate and felsic intrusions at the southern margin of the north china craton implications for crust mantle interaction abstract new major and trace element whole rock sr and nd isotopes and zircon u pb ages and hf isotope data are presented for rocks from the early cretaceous tianqiaogou dioritic and taishanmiao granitic plutons at the southern margin of the north china craton ncc in order to investigate their petrogenesis and geological evolution la icp ms u pb analyses for zircons from these two plutons yield similar 206 pb 238 u ages of 122 ma and 115 125 ma respectively monzodiorites from the tianqiaogou pluton have whole rock e nd t values ranging from 6 2 to 1 3 and zircon e hf t values from 2 9 to 6 2 they are variably enriched in ra ba and sr and depleted in nb ta zr hf and ti indicating that they were derived from a depleted mantle and underwent subsequent magma differentiation and crustal contamination the taishanmiao pluton is composed of metaluminous to peraluminous highly fractionated i type granites that have high sio 2 na 2 o k 2 o rb th and u and low p ba sr ti and eu contents the granites have strong negative whole rock e nd t values 16 1 to 7 5 and zircon e hf t values 20 9 to 6 1 their nd t dm ages 1 19 to 2 01 ga and zircon hf t c dm ages 1565 to 2490 ma are much younger than the basement rocks beneath the southern margin of the ncc suggesting derivation from an ancient crustal source with minor involvement of mantle derived components therefore rocks from the tianqiaogou dioritic pluton were partial melts of the mantle source underplating of the mafic magmas initiated partial melting of the ancient continental crust resulting in the formation of the taishanmiao granitic pluton their complex petrogenesis reflects a strong crust mantle interaction process related to lithospheric thinning beneath the southern margin of the ncc in early cretaceous

cenozoic exhumation of the neoproterozoic sanfang batholith in south china the 1500 km long jiangnan tectonic belt in china is well known for large outcrops of proterozoic basement rocks although the exhumation history of the exposed basement is poorly constrained the thermochronology of the sanfang batholith in the southernmost section of this belt was used to constrain the timing and mechanism of exhumation using apatite fission track analysis of granite samples collected along three transects the results show that the ages of single apatite grains are much younger than the neoproterozoic crystallization age of the sanfang batholith the apparent age v elevation diagram shows two stage cooling during the paleogene and miocene the cooling stages are coincident with unconformities between the paleogene and underlying strata and between the neogene and the paleogene with movement on high angle normal faults a compilation of apatite fission track data from this and previous studies suggests that the batholith was exhumed in the cenozoic and the timing of rapid cooling is progressively younger to the east as a result of slab rollback leading to cenozoic back arc extension the exhumation of the sanfang batholith therefore indicates that cenozoic erosion and extensional tectonics played a key part in exhuming the basement rocks and forming the present architecture of the jiangnan tectonic belt

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

introduction to the special issue commemorating the 30th anniversary of the royal tyrrell museum of palaeontology with a summary of the museum s early history and its research contributions located just west of drumheller in southern alberta canada the royal tyrrell museum of palaeontology rtmp is nestled among outcrops of the upper cretaceous horseshoe canyon formation exposed along the red deer river valley fig 1 since it officially opened on 25 september 19851 the museum has become one of alberta s must see tourist attractions a significant contributor to the local economy and earned an international reputation for the quality of its palaeontological collections and the research conducted by its scientists the rtmp is unique within canada in being the only government supported museum dedicated to palaeontology and it is one of the few such institutions in the world fig 1 the royal tyrrell museum of palaeontology a front of museum and main entrance circa 2010 looking westwards and with horizontal beds of the upper cretaceous horseshoe canyon formation exposed in the walls of the red deer river valley in the distance b aerial photograph oblique angle and looking to the north northeast the museum sits on top of the number 7 coal seam sensu gibson 1977 and at the base of the horsethief member of the horseshoe canyon formation d a eberth pers comm 2015 that stratigraphic position correlates with an age of about 71 5 ma i e late campanian and lies within the upper part of the edmontosaurus regalis pachyrhinosaurus canadensis dinosaur assemblage zone see eberth et al 2013 fig 6 c the iconic running theropod logo that until recently graced the exterior of the museum below a life sized tyrannosaurid sculpture by brian cooley one of many such sculptures by cooley that have been featured at the museum since its opening in 1985 and with the education wing opened in 2003 as the atco tyrrell learning centre in the background d the cretaceous alberta life sized diorama opened in 2007 an example of a rtmp exhibit that relies heavily on discoveries and interpretations by museum researchers in this case work done in the albertosaurus bonebed and at other localities throughout the horseshoe canyon formation all photographs courtesy of the royal tyrrell museum of palaeontology this special issue of the canadian journal of earth sciences presents a collection of papers commemorating the rtmp s 30th or pearl anniversary our rationale for doing a 30th anniversary volume was two fold first it is an opportunity to showcase the breadth of research conducted by current and former museum scientists as well as by some colleagues having a history of collaboration with the rtmp the 13 invited papers included in this volume are a mix of review and original research papers all thematically focused on the geology and palaeontology of alberta to varying degrees each contribution is the result of work supported by the rtmp and relies on specimens housed in the museum s collections second the 30th anniversary is an opportunity to reflect on the rtmp s history and its research program as is typical for most institutions the rtmp has done little to formally document its own history this year likely will be the last major milestone for which the original generation of museum staff are still working and available to share their recollections about the museum fieldwork and research already deaths and departures have winnowed away part of the original

giant dinosaur eggs from the tiantai basin zhejiang province china giant dinosaur eggs occur within the mid cretaceous liangtoutang formation of the tiantai basin in zhejiang province of southeastern china the 43 cm 14 5 cm eggs represent the first discovery of macroelongatoolithus xixiaensis specimens from the region the eggshell exhibits variation in surface ornamentation and eggshell thickness with smoother and thicker eggshell characteristic of the poles the tiantai eggs differ from the stratigraphically younger type specimen of macroelongatoolithus xixiaensis from henan province in their mammillary to continuous layer ratio three new features potentially useful for phylogenetic analysis and previously unreported in macroelongatoolithus and other eggs in the oofamily elongatoolithidae include prismatic columns tabular structure within the prisms and splaying of the crystals in the upper mammillae that extend into the overlying continuous layer microstructural features of the two nearly complete eggs suggest that the specimens are referable to a potentiall

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

application of the restite model to the deddick granodiorite and its enclaves a reinterpretation of the observations and data of maas et al 1997 mafic s type granites of the lachlan fold belt always contain a introduction distinctive suite of enclaves dominated by schists and gneisses of high maas et al 1997 have proposed complex models of metamorphic grade generally with lesser numbers of microgranular crustal melting and magma mixing to account for the enclaves maas et al 1997 journal of petrology 38 chemical and isotopic features of several kinds of enclaves 815 841 recently described enclaves from the s type deddick in the s type deddick granodiorite of the lachlan fold granodiorite they concluded that the metasedimentary enclaves belt lfb exposed at mckillops bridge that grancould be either source lithologies or accidental xenoliths and that odiorite is a member of the bullenbalong suite area the most common microgranular enclaves formed as globules of 3100 km white chappell 1988 itself part of the hybrid magma that mingled with the host magma all features of very extensive and slightly more diverse bullenbalong the metasedimentary enclaves are consistent with an origin as lithic supersuite total area 8750 km plus 4000 km of restite fragments from the source and their ubiquity in the mafic svolcanic rocks it occurs near the southern extremity of type granites and their rarity in both felsic varieties and in i type those granites these are the rocks that have been used granites conform with such an origin the argument that these as primary examples of restite and of the restite model enclaves are not in chemical equilibrium with the host granite in s type granites hine et al 1976 white chappell because they do not complement its composition is not valid as they 1977 chappell et al 1987 chappell 1996b and the represent less fertile parts of the source that did not melt to the point enclosed enclaves have been regarded by us as lithic of disaggregation unaltered cores of microgranular enclaves in the restite white chappell 1988 chen et al 1989 s type granites have compositions that do not match those of any chappell white 1991 white et al 1991 wyborn known igneous rock and an origin by metamorphism of a calcareous et al 1991 sediment is probable partial melting during that metamorphism maas et al 1997 mostly reject the presence of restite accounts for the pseudo igneous textures seen in these enclaves enclaves in the deddick granodiorite however the

petrogenesis of the mesozoic shuikoushan peraluminous i type granodioritic intrusion in hunan province south china middle lower crustal reworking in an extensional tectonic setting abstract the mesozoic shuikoushan granitoid intrusion in the jiangnan orogen between the yangtze and the cathaysia blocks in southern hunan province south china provides an opportunity to probe deep crustal composition and structure and to investigate the geodynamic evolution of south china the intrusion is composed of granodiorite with i type geochemical affinities and contains zircon with an u pb concordant age of 158 3 1 2 ma rocks from the intrusion have variable sio2 from 58 4 wt to 65 2 wt al2o3 from 15 0 wt to 17 2 wt tio2 from 0 57 wt to 0 76 wt and p2o5 from 0 27 wt to 0 52 wt they have a cnk from 0 97 to 1 23 1 04 on average and are dominantly peraluminous they are characterized by enrichment in lree la sm n 3 47 5 19 and lil e g k rb and depletion in hfse e g u th in primitive mantle normalized trace element diagrams these geochemical features indicate that the rocks are i type granodiorites and have undergone extensive fractional crystallization of hornblende biotite titanite and apatite all samples show negative ehf t 10 6 to 8 1 and end t 5 92 to 6 13 values with relatively high initial 87sr 86sr isr 0 7101 0 7102 and 18o ratios 8 4 9 7 these values significantly differ from mantle values suggesting that they are generated by the amphibole dehydration melting of a mafic source in the middle to lower crust beneath the jiangnan orogen the emplacement of the shuikoushan granitoid intrusion is contemporaneous with the late jurassic to early cretaceous extension within the shi hang rift zone indicating that it may have been formed under an extensional regime in response to both the pacific superplume activity and westward subduction of the pacific plate the extensional processes along with asthenosphere upwelling and basaltic underplating may have triggered the widespread late jurassic granitoid intrusion in southern hunan province and possibly in south china

an egg clutch of prismatoolithus levis oosp nov from the oldman formation upper cretaceous devil s coulee southern alberta a clutch of 12 eggs and numerous eggshell fragments recovered from the oldman formation at devil s coulee southern alberta are described as prismatoolithus levis oosp nov the eggs are elongate with a smooth outer surface and an eggshell structure that is referable to the angustiprismatic morphotype of the dinosauroid prismatic basic type the parataxonomy of prismatoolithus zhao and li 1993 is discussed and a new replacement name preprismatoolithus is proposed for the junior homonym prismatoolithus hirsch 1994

dinosaur eggshells from the lower maastrichtian st mary river formation of southern alberta canada north america is known for its rich uppermost cretaceous record of dinosaur egg remains although a notable fossil gap exists during the lower maastrichtian here we describe a diverse dinosaur eggshell assemblage from the st mary river formation of southern alberta that in conjunction with recently described eggs from the same formation in montana helps fill this gap and sheds light on the dinosaur diversity in this poorly fossiliferous formation three theropod eggshell types continuoolithus cf c canadensis montanoolithus cf m strongorum and prismatoolithus cf p levis and one ornithopod spheroolithus cf s albertensis are reported from albertan exposures of the st mary river formation increasing the ootaxonomic diversity of the formation from two to five ootaxa the taxonomic composition of the eggshell assemblage is consistent with the dinosaurian fauna known from the st mary river formation based on skeletal remains spheroolithus eggshells constitute the majority of identifiable e

neoproterozoic peraluminous granitoids in the jiangnan fold belt implications for lithospheric differentiation and crustal growth abstract neoproterozoic magmatism in the jiangnan fold belt of south china is characterized by voluminous ca 820 ma peraluminous granitoids which show a large range of chemical compositions the meixian dioritic and the lantian granitic intrusions from the central jiangnan fold belt were emplaced at 821 6 ma and 823 7 ma respectively the meixian diorites are mainly composed of amphibole 10 40 biotite 5 30 plagioclase 30 60 and quartz 5 10 they have low sio 2 59 42 63 15 wt moderate mgo 2 96 3 56 wt and na 2 o 3 51 4 39 wt and relatively high v 102 137 ppm and cr 47 1 58 7 ppm they show nearly zero end 0 6 to 0 1 and high ehf values 2 3 to 10 6 these mineralogical and geochemical features suggest that mantle derived melts were involved in their petrogenesis modeling calculations reveal that the meixian diorites were formed by fractional crystallization of mantle derived melts associated with 10 30 contamination by the country rocks however the lantian granites are fractionated i type granites that are composed of plagioclase 10 25 quartz 30 40 k feldspar 15 20 biotite 5 15 and amphibole 5 they have high sio 2 72 3 80 2 wt moderate k 2 o 1 58 4 11 wt and na 2 o 2 78 3 94 wt and low mgo 0 50 0 80 wt and cao 0 16 0 50 wt their negative end 2 3 to 1 4 and positive ehf values 0 4 to 9 9 are similar to those of the neoproterozoic arc affinity mafic rocks in the region suggesting that the lantian granites were derived from the mafic juvenile crust the neoproterozoic igneous rocks in the jiangnan fold belt are mainly composed of peraluminous granites with minor diorites the large volume of peraluminous granitoids are generally partial melts of the continental crust whereas the limited diorites are differentiation products of the basaltic magmas the petrogenesis of the granitoids in the jiangnan fold belt suggests that basaltic magma underplating triggered crustal anatexis during or after collision between the yangtze and cathaysia blocks

supracrustal input to magmas in the deep crust of sierra nevada batholith evidence from high δ 18 o zircon oxygen isotope ratios of zircon zc from intrusives exposed in the tehachapi mountains southern california reveal large inputs of high 18 o supracrustal contaminant into gabbroic and tonalitic magmas deep 30 km in the cretaceous sierra nevada batholith high 18 o zc values 7 8 0 7 predominate in the deep parts of the batholith but lower values 6 1 0 9 occur in shallower parts this indicates a larger gradient in 18 o with depth in the batholith than occurs from west to east across it oxygen sr and nd isotope data show that the supracrustal contaminant was likely young paleozoic or mesozoic hydrothermally altered upper oceanic crust or volcanic arc sediments such rocks were subducted or underthrust beneath the sierran arc during accretion of oceanic terranes onto north america this component yielded high 18 o magmas that were added to the base of the batholith on average gabbros in the southern sierra contain at least 18 of the subducted supracrustal component some tonalite and granodiorite magmas were additionally contaminated by kings sequence metasedimentary rocks as evidenced by 18 o zc and initial 87 sr 86 sr that trend toward values measured for the kings sequence besides high 18 o values in the southern sierra xenoliths in the central sierra also have elevated 18 o which confirms the widespread abundance of supracrustal material in the sub arc lithospheric mantle in contrast to 18 o zc whole rock 18 o values of many samples have undergone post magmatic alteration that obscures the magmatic contamination history of those rocks such alteration previously prevented confident determination of the mass of young hydrothermally altered mantle rocks that contributed to sierran granitoids

a cryptic record of magma mixing in diorites revealed by high precision sims oxygen isotope analysis of zircons high precision in situ ion microprobe sims oxygen isotope analysis of zircons from two diorite intrusions associated with the late caledonian lochnagar pluton in scotland has revealed large differences in the degree of heterogeneity in zircon 18o between the diorites zircon crystals from the cul nan gad diorite cng show a unimodal distribution of oxygen isotope values 18o 6 0 0 6 2 and no or only minor grain scale variation those from the allt darrarie diorite ad1 show a large range in 18o and an apparent bimodal distribution with modes of 6 6 0 4 and 7 3 0 4 variations of up to 1 2 occur between and within grains both an increase and decrease in 18o with zircon growth has been observed the 18o composition of growing zircon can only change if open system processes affect the magma composition i e if material of contrasting 18o composition is added to the magma the variability in ad1 is interpreted to represent a cryptic record of magma mixing a deep crustal hot zone is a likely site for generation of the dioritic magmas which developed by mixing of residual melts and crustal partial melts or by melting of mafic lower crustal rocks the overall small number of zircons with mantle like 18o values 5 3 0 6 2 in the lochnagar diorites is largely the product of crustal differentiation rather than crustal growth the 18o of quartz from the cng and ad1 diorites shows only minor variation cng 10 9 0 5 2 ad1 11 7 0 6 2 within single populations with no evidence of mixing quartz zircon isotopic disequilibrium is consistent with later crystallisation of quartz from late magmatic fluids and in case of the ad1 diorite after the inferred magma mixing from a homogenised higher 18o melt high precision sims oxygen isotope analysis of zircon provides a new approach to identifying and resolving previously undetected early stage magma mixing and constraining the compositions and origins of the component magmas a combination of zircon quartz and whole rock data has proven to be a powerful tool in reconstructing the petrogenetic evolution of diorite from early crystallisation to late alteration

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

petrogenesis of early cretaceous granites and associated microgranular enclaves in the xiabie co area central tibet crust derived magma mixing and melt extraction abstract multiple petrogenesis models have been proposed for granitic rocks and the mafic microgranular enclaves mmes hosted in them the mantle and crust derived magma mixing mingling process was widely suggested for the formation of mmes or the host granitoids however whether the mixing between magmas derived from different crustal sources may also form microgranular enclaves mes not restricted to mafic or the host granites remain unclear here we report petrological geochemical and zircon in situ hf o isotopic data for mes and their host granites in the northern nyima area southern qiangtang terrane sqt central tibet the host granitic rocks consist of amphibole bearing biotite granites and syenogranite minor granodiorite and aplite veins and mes comprising diorite and granodiorite host rocks and mes are contemporaneous and were generated in the early cretaceous 120 ma host granitoid samples are high k calc alkaline rocks and have high sio2 66 78 wt and low mgo 5 wt high zr 500 ppm with zr hf ratios 45 and high ba 400 ppm implying biotite and zircon concentrations combining this information with embayed feldspars curved biotites and closely spaced feldspar grains we suggest that liquid loss resulted from crystal compaction or filter pressing both the fine grained syenogranites and aplite veins exhibit high sio2 and rb sr ratios in addition to low zr hf ratios and zr and ba concentrations with remarkably negative eu anomalies indicating that they are highly differentiated melts extracted from felsic crystal mush such a crystal mush is possibly represented by the biotite granites gradual contact relationships between variable granitic phases indicate that melt extraction and crystal concentration were coeval residual melt extraction from the crystal mush was facilitated by mush remobilization resulting from magma replenishment we suggest that for the host rocks the biotite granites were mainly derived by partial melting of ancient crust and the granodiorites most likely resulted from the magma mixing mingling that might be accompanied with the loss of melts the fine grained syenogranites and aplites represent highly evolved residual melts mes are geochemically characterized by intermediate to felsic compositions sio2 56 3 67 8 wt with low mgo

petrogenesis of the early cretaceous funiushan granites on the southern margin of the north china craton implications for the mesozoic geological evolution abstract late mesozoic granitoids are ubiquitous in the southern margin of the north china craton and are keys to the understanding of the mesozoic geological evolution the early cretaceous funiushan granitic pluton in the southern margin of the north china craton is composed of porphyritic biotite monzogranites rocks from the funiushan pluton have high sio2 64 45 73 98 wt na2o 3 19 4 67 wt and k2o 3 76 7 95 wt and low mgo 0 11 1 34 wt they are enriched in rb ba th u and lree la yb n 9 63 45 0 and depleted in nb ta ti and p and have negative eu anomalies eu eu 0 29 0 72 this geochemical feature is similar to those of typical i type granites zircons from the granites were dated using la icp ms and sims and yielded 206pb 238u ages of 115 131 ma they have ehf t values mainly vary from 17 7 to 0 9 and t dm c ages mainly from 2301 to 1118 ma whole rock end t values range from 20 3 to 9 6 and tdm ages from 1 49 to 2 29 ga indicating that the magma was produced by partial melting of the neoarchean to paleoproterozoic crustal rocks as represented by the taihua group basement rocks with minor involvement of mantle derived melts the funiushan pluton is considered to have been formed through a strong crust mantle interaction process under a low pressure condition in an extensional setting due to the lithospheric thinning caused by westward subduction of the paleo pacific oceanic crust

neoproterozoic tourmaline bearing peraluminous granitoids in the western jiangnan orogen south china geochemistry petrogenesis and tectonic implications abstract neoproterozoic granitoids are widespread in the jiangnan orogen in south china that was formed by assemblage between the yangtze and cathaysia blocks the peraluminous s type granitoids from the guibei region in the western jiangnan orogen are composed of quartz alkali feldspar and plagioclase with subordinate biotite and muscovite they show large variable feo mgo 1 9 12 8 and k2o na2o cao 2 84 ratios indicating the rocks experienced fractional crystallization their end values 9 31 to 5 45 and two stage nd model ages 1 83 2 34 ga suggest that the guibei granitoids were derived from a mature source that was mainly composed of recycled supracrustal materials the tourmalines occurring as disseminated and nodular grains show high na k 0 56 0 77 apfu low ca 0 01 0 08 apfu and x site vacancy 0 18 0 51 apfu and belong to the alkali group their high fe 1 64 2 28 apfu low mg 0 14 0 80 apfu and mg mg fe 0 016 0 325 suggest that the minerals are dominated by schorl end member in the schorl dravite solid solution series the tourmalines have constant and strong negative 11b values 13 4 to 9 5 and the nodular tourmalines are isotopically lighter 11b 10 0 to 13 4 than the disseminated tourmalines 11b 9 5 to 12 5 the disseminated tourmalines are suggested to have been crystallized in melts at the early magmatic stage whereas the nodular tourmalines formed in fluid rich immiscible melts at the late magmatic stage the boron isotopic variations within or among the tourmaline generations are mainly controlled by rayleigh fractionation in combined with the regional geology the peraluminous granitoids in this study are considered to be partial melts of the supracrustal rocks in the post orogenic setting

genesis of the two main types of peraluminous granitoids two mica monzogranites to leucogranites and biotite rich cordierite bearing tonalites to monzogranites form two distinct groups of peraluminous granitoids they can be distinguished by mineral and rock associations and by the variation of their peraluminosity during differentiation except for the rare muscovite bearing granitoids produced by extreme fractionation or local contamination of metaluminous magmas the majority of peraluminous granitoids are produced by partial melting of crustal rocks production of either muscovite bearing granites or biotite rich cordierite bearing granitoids does not depend only on the nature of the sources but is also controlled by the physical parameters of partial melting and consequently by the way anatexis of a thickened crust is enhanced biotite rich cordierite bearing granitoids are generated where mantle derived magmas are injected into or have underplated crustal rocks two mica granites are generated where thickened crust is affected by major crustal shears or thrusts correlations between differentiation and peraluminosity indicate the dominant role of either restite unmixing or fractional crystallization in the production and evolution of the various types of peraluminous granitoids

low δ18o magma isle of skye scotland evidence from zircons abstract zircons in tertiary granitic rocks from the isle of skye scotland were resistant to measurable oxygen isotope exchange during intense hydrothermal activity in the subvolcanic environment five granite bodies from the western red hills complex were investigated four have 18o zrc 4 1 0 2 o vsmow while the fifth which intruded before major cauldron subsidence is 2 lower zircons from lewisian gneiss are visually and isotopically distinct indicating that zircons in the granite are not xenocrysts from the lewisian basement analysis of different magnetic and size fractions of zircon shows no significant correlation to 18o supporting the conclusion that these values represent the true magmatic compositions and that the western red hills granites intruded as low 18o magmas with a whole rock 18o 6 0 quartz separates from four granites are close to the calculated magmatic values in 18o but in the fifth values are 5 lower indicating variable exchange of quartz with low 18o heated meteoric waters these results might be explained by magmatic interaction with hydrothermally altered crust early in the evolution of the granites before crystallization of zircon followed by interaction with later hydrothermal fluids alternatively independent evidence for low 18o mafic magmatism in nw scotland suggests the presence of large quantities of low 18o subducted ocean crust in the subcontinental lithosphere that could contaminate or be the source of low 18o mantle derived melts

u pb zircon ages of granites from the southern margin of the yangtze block timing of neoproterozoic jinning orogeny in se china and implications for rodinia assembly abstract neoproterozoic jinningian bendong granodiorite and sanfang and yuanbaoshan granites occurred in northern guangxi southern margin of the yangtze block se china and were generally considered to be of orogenic origin that is the collision between the yangtze and huanan blocks during the jinning orogeny these granites were intruded into the mesoproterozoic sibao metamorphic basement and covered unconformably by the neoproterozoic danzhou metasediments they are dominantly peraluminous asi 1 18 1 29 and have low initial end values of 4 8 to 7 6 indicating derivation from a supracrustal source with strong enrichment in rb k and th and relatively low zr hf and higher rare earth elements they are similar to post collision granites zircon u pb ages of 819 9 826 10 and 824 4 ma were obtained for the bendong granodiorite and the sanfang and yuanbaoshan granites respectively by both shrimp and conventional dating methods the age result precludes the existence of any late mesoproterozoic grenville age granitic magmatism in the southern margin of yangtze block together with previous age determinations of ophiolites along the southern margin of the yangtze block the jinning orogeny is referred to the neoproterozoic orogeny which took place between 1 0 and 0 80 ga and likely ended at 0 82 ga the granite formation age of 0 82 ga also supports the basal boundary age of 0 80 ga for the post orogenic sinian system which is probably stratigraphically correlated with the adeladean system in south australia as the link between australia east antarctica and laurentia in the configuration of the supercontinent rodinia the collision between the yangtze and huanan blocks during the neoproterozoic jinning orogeny probably marks the termination of the rodinia assembly

genetic types mineralization styles and geodynamic settings of mesozoic tungsten deposits in south china abstract south china hosts the most abundant and largest tungsten w deposits in the world being a famous w metallogenic region located at the eastern part of the south china block which was formed by amalgamation of the yangtze and cathaysia blocks during the neoproterozoic these w deposits were mainly formed during the mesozoic the w mineralization is dominanted by greisen quartz vein skarn and porphyry types all of which are genetically related to the evolution of highly fractionated granitoids four episodes of w mineralization are recognized 1 late triassic 230 210 ma in the central and western parts of south china 2 middle jurassic ca 170 ma to early cretaceous ca 140 ma in the interior of south china with the mineralization being concentrated in southern jiangxi province between 165 and 150 ma 3 early cretaceous 136 120 ma with deposits across south china and 4 late cretaceous 100 80 ma mainly in the southwestern parts of south china these four periods of mineralization are closely related to the closure of paleo tethys and subduction of the paleo pacific plate in the late triassic these two events caused local extensional environments facilitating emplacement of the peraluminous granitoids and formation of the w deposits in the middle jurassic break off of the subducting oceanic plate resulted in emplacement of highly fractionated granites in the nanling region later anticlockwise rotation of the paleo pacific plate created widespread s type granitoids and associated middle jurassic to early cretaceous w mineralization in the interior of south china since 136 ma rollback of the subducting pacific plate resulted in weak w mineralization across south china finally a change of direction in the retreating plate from se to ese resulted in intensive mineralization of the southwestern part of south china

ca 830 ma back arc type volcanic rocks in the eastern part of the jiangnan orogen implications for the neoproterozoic tectonic evolution of south china block abstract the volcanic rocks in the eastern part of jiangnan orogen provide an important suite to investigate magma petrogenesis and tectonic evolution of south china block we carried out a combined study of geochronology and geochemistry for the bimodal association of basalts and rhyolitic tuffs from the shuangqiaoshan group in south anhui province zircons from a basalt and two rhyolitic tuff samples yield crystallization ages of 829 12 ma 832 9 ma and 832 10 ma respectively the basalts are characterized by left sloping ree distribution patterns enriched large iron lithosphere elements liles e g rb ba k and depleted high field strength elements hfses e g nb ta relative to those in n morb resembling those of modern central lau back arc basin basalts babb in addition they have positive nd t values 4 6 to 5 7 with initial 87sr 86sr ratios in the range of 0 70706 0 70719 these geochemical and isotopic signatures indicate that the basalts were derived from an n morb like source modified by slab derived fluids the rhyolitic tuffs have high sio2 72 9 78 3 wt contents and high 10 000 ga al ratios mostly 2 6 taking into account their aluminous nature a cnk 1 1 they are affinitive to aluminous a type granites they invariably show a relative enrichment in light ree and strong negative eu anomalies eu eu 0 16 0 31 and negative anomalies in hfse sr and p compared with the neighboring elements in their trace element spidergrams their nd t values range from 2 1 to 0 1 detailed elemental and isotopic data suggest that the rhyolitic tuffs formed by partial melting of mafic lower crust triggered by asthenosphere upwelling the occurrence of bimodal volcanic rocks with the basalts showing geochemical affinity to intra oceanic babb appears to support the development of a neoproterozoic back arc basin in the eastern part of jiangnan orogen at ca 830 ma combined with the published data from central and western part of jiangnan orogen it is inferred that the back arc basin developed in the entire jiangnan orogen during 850 810 ma considering the age of the strata overlying the folded basement sequence we suggest that the final collision of the yangtze and cathaysia blocks happened during 820 810 ma along the jiangnan orogen

hydrothermal alteration of oxygen isotope ratios in quartz phenocrysts kidd creek mine ontario magmatic values are preserved in zircon zircons from rhyolites hosting the kidd creek volcanogenic massive sulfide deposit preserve magmatic oxygen isotope ratios 18 o 5 4 0 3 n 11 that are indistinguishable from average values of other plutonic and volcanic rocks of the superior province oxygen isotope ratios of petrographically pristine primary quartz phenocrysts however are greatly elevated in 18 o and heterogeneous 18 o 14 2 to 16 1 such phenocrysts are not a good monitor of magmatic processes the presence of healed microcracks in quartz phenocrysts as seen in cathodoluminescence images and the variability of quartz oxygen isotope ratios suggest that recrystallization is the process of 18 o elevation in contrast to the variability of quartz the 18 o zircon values do not vary regardless of the degree of magnetic susceptibility the 18 o values of zircon are interpreted to reflect the primitive magmatic oxygen consistent with the rhyolite geochemistry for magmas derived by partial melting of a tholeiitic source our data show that the 18 o values of quartz and whole rock at kidd creek are a good monitor of hydrothermal exchange and are 5 higher than the magmatic value that is preserved in zircon due to its refractory nature