new evidence of a herd of titanosauriform sauropods from the lower berriasian of the iberian range spain abstract a study of the undescribed part of the las cerradicas tracksite in galve teruel spain has revealed 6 trackways made by small sauropods showing gregarious behaviour parallel trackways las cerradicas is located towards the top of the villar del arzobispo formation early berriasian the wide gauge condition the manus pes distance the kidney shaped morphology of the manus and the subtriangular morphology of the pes with a big digit i that swells medially and a narrow heel oriented posterolaterally suggest that the sauropods in question are more similar to sauropodichnus giganteus than to any other sauropod ichnotaxa some of the features point to the titanosauriforms as the best candidates to be the trackmakers recent work in bone histology the differences with respect to other iberian tracksites of similar age and the differences with respect to other sauropod herds of the track record do not allow us to establish whether the sauropods were juvenile or dwarfs the sauropod skeletal record and other large sauropod footprints in the villar del arzobispo formation could tip the scales in favour of the first hypothesis

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

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

sedimentary recycling in arc magmas geochemical and u pb hf o constraints on the mesoproterozoic suldal arc sw norway the hardangervidda rogaland block within southwest norway is host to 1 52 to 1 48 ga continental building and variable reworking during the 1 1 to 0 9 ga sveconorwegian orogeny due to the lack of geochronological and geochemical data the timing and tectonic setting of early mesoproterozoic magmatism has long been ambiguous this paper presents zircon u pb hf o isotope data combined with whole rock geochemistry to address the age and petrogenesis of basement units within the suldal region located in the centre of the hardangervidda rogaland block the basement comprises variably deformed grey gneisses and granitoids that petrologically and geochemically resemble mature volcanic arc lithologies u pb ages confirm that magmatism occurred from 1 521 to 1 485 ma and conspicuously lack any xenocrystic inheritance of distinctly older crust hafnium isotope data range from ehf initial 1 to 11 suggesting a rather juvenile magmatic source but with possible involvement of late palaeoproterozoic crust oxygen isotope data range from mantle like 18o 5 to elevated 10 suggesting involvement of low temperature altered material e g supracrustal rocks in the magma source the hf o isotope array is compatible with mixing between mantle derived material with young low temperature altered material oceanic crust sediments and older low temperature altered material continent derived sediments this combined with a lack of xenoliths and xenocrysts exposed older crust afc trends and s type geochemistry all point to mixing within a deep crustal magma generation zone a proposed model comprises accretion of altered oceanic crust and the overlying sediments to a pre existing continental margin underthrusting to the magma generation zone and remobilisation during arc magmatism the geodynamic setting for this arc magmatism is comparable with that seen in the phanerozoic e g the sierra nevada and coast range batholiths with compositions in the suldal sector reaching those of average upper continental crust as within these younger examples factors that drive magmatism towards the composition of the average continental crust include the addition of sedimentary material to magma source regions and delamination of cumulate material underthrusting of sedimentary materials and their subsequent involvement in arc magmatism is perhaps a more widespread mechanism involved in continental growth than is currently recognised finally the suldal arc magmatism represents a significant juvenile crustal addition to sw fennoscandia

the identification and significance of pure sediment derived granites the characterization of the geochemical reservoirs of the earth s continental crust including the determination of representative upper and lower crustal compositions underpins our understanding of crustal evolution the classic i and s type granite classification has often been invoked to distinguish between melts derived from igneous protoliths and those derived from the melting of a sedimentary source recent geochemical studies suggest that most granites even those cited as typical examples of s type show evidence for a mixture of mantle and upper crustal sources thereby implying that granite formation is evidence for overall crustal growth we have examined the source of leucogranite bodies in one of the world s youngest collisional orogens using novel zircon techniques that can resolve the presence of even minor mantle contributions 232 zircons from 12 granites from the bhutan himalaya were analysed by in situ techniques for o hf and u pb isotopic signatures in combination with data from the granite host rocks our data show that the himalayan leucogranites were derived solely from metamorphosed crustal sediments and do not record any mantle contribution this finding is consistent with the time lag between crustal thickening and widespread crustal melting and the heat producing capacities of the pelitic source rocks we conclude that himalayan leucogranites provide a more suitable type locality for s type granites than the lachlan area in south east australia where the term was first defined the himalayan leucogranites therefore provide evidence that syn orogenic melting during collisional events does not necessarily result in crustal growth importantly crustal growth models should not always assume that crustal growth is achieved during collisional orogenesis

physical weathering of marbles caused by anisotropic thermal expansion marbles as building stones as well as in their natural environments show complex weathering phenomena the most important damage scenario is based on the highly anisotropic thermal expansion coefficient of calcite i e extreme expansion parallel and contraction normal to the crystallographic c axis therefore the rock fabric and especially the lattice preferred orientation texture of calcite and or dolomite as the predominant mineral phases in marbles have a significant influence on the mechanical weathering the textures of marbles from five different locations vary from a more or less perfect prolate to moderate oblate shape of the 006 pole figure tensor accordingly the texture derived bulk thermal dilatation anisotropy covers a broad range from 0 048 to 0 680 the modelled thermal dilatations correlate with those obtained from experimental measurements the difference in magnitude is basically explained by the microcrack fabrics which was not considered in the computations all samples show a deterioration due to thermal treatment regardless of the strength of texture the directional dependence of a the total magnitude of the thermal dilatation coefficient and b of the residual strain is highest in marbles with a strong texture whereas the carrara marble with a weak texture exhibits a uniform crack formation the progressive loss of cohesion along grain boundaries due to dilatancy may serve as an example for the initial stage of physical weathering

the isotopic and structural age of the aberdeen granite new uranium lead isotope data from monazites yield an emplacement age of 470 1 ma for the 9s9 type aberdeen granite emplacement of this intrusion was late tectonic with respect to the grampian early caledonian orogeny and followed closely on the upper amphibolite facies meta morphic climax in the dalradian country rocks the field relations of the associated vein complexes suggest that this isotopic age also dates the local d3 deformation of the dalradian supergroup previously published isotope data indicate that the granite originated largely by melting of metasediments with a minimum crustal residence time of c 1 2 to 1 8 ga rocks with comparable isotopic characteristics form the migmatitic country rock envelope to the granite and we advocate extensive contemporaneous melting of such rocks at shallow depths below the level of emplacement then 17 20 km

genesis of adakitic granitoids by partial melting of thickened lower crust and its implications for early crustal growth a case study from the huichizi pluton qinling orogen central china abstract adakitic rocks are often considered as a key to deciphering the genesis of archean ttgs and the early crustal growth granites from the huichizi pluton in the north qinling nq unit have high sr y and la yb n ratios similar to adakites their relatively high sio 2 k 2 o and na 2 o and very low mgo cr and ni contents are in the range of high sio 2 adakites and early archean ttgs and are compositionally similar to experimental melts derived from metabasalt sources new sims zircon u pb dating constrains the emplacement age of the huichizi pluton at 422 5 ma rock samples from the huichizi pluton have e nd t and zircon e hf t values similar to the neoproterozoic metabasalts in the nq unit in combination with their normal mantle like 18 o zir values these adakites are best explained by partial melting of the neoproterozoic mafic crustal root due to subduction of the shangdan ocean regional geological data suggest that the crust was probably thickened by a ca 490 ma arc collision process prior to the emplacement of the huichizi pluton our results confirm that underplating of mafic magma and its subsequent fusion triggered by slab subduction under high pressure conditions could be an important mechanism for the formation of early continental crust

the ordovician evolution of the south mayo trough western ireland the south mayo trough a broad synclinorium containing a 10 km sequence of early ordovician turbidites passing up into shallow water sandstones is interpreted as a forearc basin with an ophiolitic basement that formed a backstop to an accretionary prism on the northern edge of a north facing arc the arc collided with the laurentian margin in early llanvirn times to deform the dalradian supergroup rifted margin clastic sequence prior to the late llandovery sinistral transcurrent faulting transposed the connemara dalradian terrane to its present position on the outboard ocean ward side of the south mayo trough the south mayo trough was fed principally by arc and ophiolite derived elastics during the arenig with an increasing metamorphic component during the llanvirn the late ordovician transpressional docking of connemara provided the southerly source for high grade metamorphic clasts in the deny veeny formation

a nd isotope investigation of sediments related to crustal development in the british isles the times of original fractionation of the sm and nd component of clastic sediments from a mantle source crustal residence age have been estimated from sm nd model ages calculated relative to a depleted mantle evolution in this way the provenance and evolution of selected precambrian and phanerozoic sediments and metasediments from the british isles have been examined whereas some archaean and early proterozoic sediments have sm nd model ages that are close to their stratigraphic age the phanerozoic sediments analysed have model ages as much as 2 0 ga in excess of their stratigraphic age a more detailed study of lower palaeozoic sediments deposited on the northern margin of the iapetus ocean provides evidence for a marked change of provenance in the ordovician after the deposition of the dalradian supergroup a component with comparatively high143nd 144nd and sm nd ratio presumably basaltic is present in the sediments throughout the accretionary prism crustal residence age estimates average about 1 5 ga for both these lower palaeozoic sediments and modern pelagic clays and collectively fail to provide any evidence for significant continental growth during the phanerozoic

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

dinosaur footprints with skin impressions from the cretaceous of alberta and colorado cretaceous dinosaur footprints discovered in the j sandstone of the south platte formation dakota group in colorado and the st mary river formation of southwestern alberta exhibit the first repo

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

middle triassic archosaur population structure interpretation based on isochirotherium delicatum fossil footprints southern alps italy abstract well preserved archosaur footprints have recently been found on a single bedding plane in the italian alps the tracks are referable to isochirotherium delicatum courel and demathieu 1976 a form that was identified for the first time at the anisian ladinian boundary in the area of argentiere ardeche france the isochirotherium delicatum footprints and trackways from gampenpass represent a possible social group or herd estimating the age of the trackmakers from the examination of the footprints is difficult and complicated by the fact that the sample can be divided into two groups of tracks distinguishable by the l w cross axis and interdigital angle the diversity of the tracks is here interpreted as an indication of sexual dimorphism

sr o and pb isotope evidence for origin and evolution of etive igneous complex scotland a multi isotope approach has been applied to the origin of one of the largest and latest newer granite complexes of the scottish caledonides contributions from both mantle and unexposed late proterozoic lower continental crust are recognized indicating that granite magmatism is a mechanism for both primary crustal growth and reworking of older crustal rocks

recycled metaigneous crustal sources for s and i type variscan granitoids from the spanish central system batholith constraints from hf isotope zircon composition abstract the spanish central system scs is one of the largest granite batholiths in the european variscan belt zircons from five granitic intrusions from the eastern scs have been separated and analysed for hf isotopes by laser ablation mc icpms in order to evaluate the nature of granitic magma source two samples are cordierite bearing s type granites the rest are amphibole bearing i type monzogranites hf isotope composition of zircons from these granites defines a narrow range of negative hf values 1 1 to 5 8 typical of crustal protoliths the within sample variation of zircon hf isotope composition is slightly above the analytical uncertainty 1 5 units suggesting the mixing of different magma batches during pluton assembly the s and i type granites display the same range of initial hf values that is in agreement with previous data showing that both scs granite types have similar sr nd o pb isotope signatures these isotopic data suggest that they derived from similar sources while the variation in peraluminosity could be related to different partial melting conditions the presence of a lower ordovician inherited zircon population 478 462 ma at least in i type granites suggests the involvement of cambro ordovician orthogneisses as components in the source of some scs granites inherited zircon population of similar age has also been identified in the scs lower crustal granulites the hf isotope composition of the analysed granite zircons is within that of zircons from the above granulites moreover some evidence of a juvenile input at 560 595 ma is recorded by hf isotope data in zircons from both the scs granites and granulite xenoliths hf isotope signature in conjunction with other chemical isotopic sr nd o pb and geochronological evidences suggests that scs granites were probably derived from metaigneous lower crustal sources the variscan magmatism in central spain is dominantly a crustal reworking event

insolation weathering and hygric dilatation two competitive factors in stone degradation in the natural environment temperature and moisture are very important parameters in stone degradation therefore on 28 samples from different lithologies magmatic metamorphic and sedimentary rocks thermal and hygric expansion measurements were performed in order to constrain their behaviour related to environmental changes it was shown that marbles even those that are dolomitic are sensitive to temperature impacts for rocks with clay minerals the effect of temperature may be responsible for shrinking finally the amount of residual strain i e the formation of microcracks due to temperature action controls the rate of stone degradation for most sedimentary rocks no residual strain after heating was observed in contrast to most magmatic and metamorphic low porosity rocks sedimentary rocks contain swelling minerals like smectite and even phyllosilicates which are very sensitive to hygric attacks the cycles of wetting and drying i e the natural environmental effects may significantly control the deterioration velocity caused by hygric expansion

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

probable palaeogeographic influences of the lower cretaceous iberian rifting phase in the eastern cameros basin spain on dinosaur trackway orientations abstract the cameros basin sedimentary infill comprises a large essentially continental megasequence ranging from the tithonian upper jurassic to the albian lower cretaceous it occupies an area of some 5500 km2 and is home to around 300 dinosaur tracksites most of these tracksites are found in either the huerteles formation which is part of the oncala group berriasian or the enciso group lower aptian both of which represent early cretaceous lacustrine episodes dinosaur trackways n 1170 from both episodes were analysed in order to establish the preferred direction of dinosaur movement and to determine whether these movements were influenced by the palaeogeographic and palaeoenvironmental conditions of the area the huerteles formation is interpreted as a complex record of alluvial plain systems distally connected with a playa lake its dinosaur tracksites are distributed throughout its alluvial plain facies and trackways show two preferential unidirectional orientations 1 nw more or less parallel to the distribution of the facies belt and 2 nne the enciso group is represented by a wide and shallow lacustrine system connected with marine environments towards the se iberian basin realm and in close proximity to marine settings to the nw basque cantabrian basin realm rendering the cameros basin as the only continental connection between the ebro and iberian massifs the fluctuating but always shallow water level of the system with frequent desiccations probably allowed dinosaurs to pass through the lake basin as a consequence of these paleogeographic restrictions the dinosaur trackways generally show a bidirectional ne sw orientation despite the temporal and geographical differences between the huerteles formation and enciso group the ichnocenoses of both are dominated by theropod dinosaur trackways 85 as a mean value this is probably explained by these dinosaurs being more active than others a consequence of their searching hunting behaviour

geochronology geochemistry and isotope compositions of piaochi s type granitic intrusion in the qinling orogen central china petrogenesis and tectonic significance abstract s type peraluminous granite can crop out in various tectonic settings the paleozoic piaochi granitic intrusion is a large s type peraluminous intrusion located in the north qinling orogen and has important implication for its tectonic evolution though intensively studied the age and tectonic setting of this intrusion are still controversial in this study we carried out an integrated study of zircon u pb age major and trace elements and sr nd hf o isotope compositions for the piaochi intrusion with aims to constrain its petrogenesis and tectonic significance sims and la icpms u pb zircon data obtained from magmatic zircons indicate that the piaochi intrusion was emplaced at 473 4 ma and contained ca 490 ma inherited zircons the granite samples from the piaochi intrusion show typical s type characteristics such as the relatively moderate aluminum saturation index 1 00 1 08 low zirconium saturation temperatures occurrences of muscovite and high zircon 18 o values 8 70 to 9 54 the relatively low sm nd 0 13 0 20 and feo t mgo ratios 2 21 3 9 suggest that the granites are unfractionated the geochemical compositions reveal that they were derived from partial melting of a clay poor but plagioclase and biotite rich psammitic source similar to metasedimentary rocks outcropping in the north qinling unit moreover the piaochi granites are moderately depleted in eu and heavy rare earth elements and have relatively high la yb n values 22 8 56 8 implying a high pressure plagioclase poor and garnet rich residual assemblage the piaochi granites have high and variable initial 87 sr 86 sr ratios 0 72167 0 72511 and low e nd t from 10 23 to 8 71 values with two stage nd model ages t dm2 of 1 91 2 03 ga which are comparable with those of supracrustal materials in the north qinling unit in addition our results show that the ca 470 ma magmatic zircons display a narrow e hf t array within those of the inherited cores these imply that the piaochi granites inherited their isotopic characteristics wholly from their sources and the hf isotopes might have been differently homogenized during the partial melting our new zircon u pb ages indicate that the piaochi granites were emplaced after the climax of the uhp metamorphism coeval with later retrograde metamorphism during exhumation therefore we suggest that the formation of the early paleozoic piaochi intrusion was triggered by the exhumation of the uhp rocks

fast tectonometamorphism and exhumation in the type area of the barrovian and buchan zones the beginning of the grampian episode of tectonometamorphism in scotland is dated by collision and obduction of the ballantrae ophiolite complex at 478 8 ma for the first time we have used zircon and garnet to radiometrically date the peak of the caledonian buchan and barrovian tectonometamorphism in their type areas as contemporaneous at 467 2 5 ma detrital garnet from the neighboring southern uplands flysch terrane has the same radiometric age and occurs in 465 2 5 ma molasse in the midland valley we show that the entire grampian episode lasted 15 2 5 m y and that it took fewer than 7 6 m y to expose high grade rocks following the peak of metamorphism those who study precambrian orogeny should note the brevity of this scottish tectonometamorphic episode and the speed of exhumation

peraluminous granites frequently with mantle like isotope compositions the continental type murzinka and dzhabyk batholiths of the eastern urals murzinka and dzhabyk are continental type batholiths of the middle and southern east uralian domain they comprise mainly undeformed peraluminous k rich granites whose elemental composition is similar to some late variscan granites of western europe but with much more primitive sr and nd isotope ratios murzinka 254 5 ma is composed of silica rich granites forming two different rock series with a 87sr 86srinit of 0 709 and 0 704 respectively both series have enormous variations in end255 11 9 to 0 1 and 8 9 to 4 1 that reveal derivation from heterogeneous sources dzhabyk 291 4 ma also comprises two coeval magmas which yielded voluminous granites and quartz monzonites respectively with smaller differences in 87sr 86srinit and end290 0 7043 0 8 to 1 6 and 0 7049 0 0 to 0 8 despite their isotope compositions both batholiths lack evidence of genetic involvement of a mantle derived parental magma moreover we suggest that dzhabyk granitoids were generated by polybaric partial melting of paleozoic island arc material whereas murzinka granitoids derived from an extremely heterogeneous source consisting mainly of paleozoic and proterozoic metagreywackes this implies a relative fast reworking of juvenile arc crust and burial of the protoliths during the orogenic evolution of the urals since there is neither evidence of significant extension nor a direct link with subduction we suggest that the main cause for late orogenic anatexis was elevated heat production and fertility in the protolith perhaps combined with some additional heat from unexposed mafic intrusions

timing and heat sources for the barrovian metamorphism scotland abstract new shrimp u pb zircon ages of 472 2 5 8 ma and 471 2 5 9 ma are presented for the age of peak metamorphism of barrovian migmatites 40 ar 39 ar ages for white mica from the barrovian metamorphic series are presented and are recalculated using recently proposed revisions to the 40 k decay constants to allow more precise and accurate comparison with u pb ages the 40 ar 39 ar ages are found to vary systematically with increasing metamorphic grade between c 465 ma for the biotite zone and c 461 ma for the sillimanite zone there is no evidence for any significant metamorphic heating during the first 15 myr of the grampian orogeny before c 473 ma or the final 4 myr after c 465 ma the barrovian metamorphism occurred over a period of 8 myr within the 27 myr grampian orogeny the barrovian metamorphism records punctuated heating was temporally and spatially associated with large scale bimodal magmatism and developed within crust that was not overthickened the temporally distinct nature of the barrovian metamorphic episode within the grampian orogeny and its heating pattern and tectonic context are not consistent with significant heat contribution from thermal equilibration of overthickened crust rather the barrovian metamorphism records a transient phase of crustal thermal disequilibrium during the grampian orogeny temporal and spatial association with grampian bimodal magmatism is consistent with production of the barrovian metamorphic series within the middle crust as the result of advection of heat from the lower crust and or mantle the barrovian metamorphic series the classic example of orogenic regional metamorphism did not form in response to crustal thickening and thermal relaxation but appears to record large scale contact metamorphism

new sims u pb zircon ages from the langavat belt south harris nw scotland implications for the lewisian terrane model secondary ionization mass spectrometry sims u pb dating of zircon has been applied to rocks of the lewisian complex of south harris outer hebrides nw scotland yielding insights into the complex geological evolution of this region and enhancing our understanding of terranes in the lewisian gneiss complex results show that tonalite trondhjemite granodiorite magmatism occurred in the tarbert terrane between c 2850 and 2830 ma equivalent to similar rocks in other parts of the outer hebrides magmatism was accompanied or closely followed by high grade metamorphism at c 2830 ma the first reported occurrence of such an event at this time these rocks were affected by a subsequent high grade metamorphic event at c 2730 ma which has correlatives both in the outer hebrides and in the mainland lewisian gruinard terrane these data suggest that the terranes forming the outer hebrides and parts of the mainland lewisian were once contiguous and were fragmented by post 2730 ma events the c 1700 1660 ma ages from felsic sheets and pegmatites within the langavat shear zone may record the reassembly of these crustal fragments

oxygen isotope compositions and magmatic epidote from two contrasting metaluminous granitoids ne brazil oxygen isotope compositions of mineral separates were determined from two metaluminous granitoids emas and sao rafael plutons from northeastern brazil the i type emas pluton has high 18o wr values 11 5 11 8 whereas the sao rafael pluton has low 18o wr values 7 5 8 1 but sr and nd are characteristics of s type granitoids measured mineral mineral fractionations suggest continuous sub solidus inter mineral isotope exchange among all minerals except zircon there is a large and consistent quartz epidote fractionation that gives apparent temperatures that are much lower than anticipated closure temperatures for epidote oxygen isotope fractionation between natural zircon and magmatic epidote is opposite to that predicted from theoretical determinations as 18o epidote 18o zircon an empirical calibration based on these results would suggests a closure t for oxygen in epidote of 500 c and qtz epi 5 19 at 500 c

generation of early archaean felsic greenstone volcanic rocks through crustal melting in the kaapvaal craton southern africa abstract high potassium felsic volcanic rocks interlayered with basalt and komatiite in early archaean greenstone sequences in the barberton greenstone belt of south africa and swaziland previously considered to be derived from melting of mafic precursors are shown to be the result of melting of significantly older felsic crust this is documented by a combination of shrimp zircon dating with hf in zircon and whole rock lu hf and sm nd isotopic data zircons from felsic rocks of the oldest barberton unit the 3 53 ga theespruit formation yielded predominantly negative e hf t values whereas whole rock e hf t and e nd t data are slightly negative to slightly positive similar results were obtained for ca 3 45 ga felsic rocks in the hoeggenoog and noisy formations higher up in the greenstone stratigraphy these data rule out derivation of the felsic units from melting of basaltic precursors and favor a crustal source most likely of ttg composition the isotopic data are not compatible with an entirely oceanic origin of the barberton greenstone sequences and favor a pre greenstone basement beneath the volcanic rocks crustal melting of eo to paleoarchaean lower crust probably generated the felsic volcanic rocks and is likely to have been responsible for gradual stabilization of the kaapvaal craton

linking lithospheric thinning and magmatic evolution of late jurassic to early cretaceous granitoids in the jiaobei terrane southeastern north china craton abstract late mesozoic granitoids are widely distributed in the jiaobei terrane southeastern north china craton ncc and crucial to understanding the processes and mechanisms of the lithospheric thinning here we present petro geochemical zircon u pb lu hf and o isotopic constrains on three stages of granitoids building an integrated model of lithospheric thinning from beginning through peak to waning stages the early stage linglong granite 166 158 ma is geochemically comparable to adakitic rocks with negative nd t 21 3 to 19 2 zircon hf t 26 8 to 18 7 and high zircon 18o 6 7 8 3 it was originated from the subduction thickened lower crust of the eastern ncc with minor contribution from the subducted yangtze block in an extensional setting representing the beginning of lithospheric thinning the middle stage guojialing granodiorite 130 128 ma characterized by higher sr y ba 898 5075 ppm sr 657 2256 ppm nd t 19 1 to 11 5 zircon hf t 19 0 to 11 6 and 18o 7 5 8 7 than the linglong granite addressing a fluid metasomatized lithospheric mantle and extensive crust mantle interaction in the paleoproterozoic crustal source is coeval with peak lithospheric thinning due to roll back of the subducted pacific plate the late stage aishan complex 118 115 ma which is composed of granodiorite syenogranite porphyritic quartz syenogranite alkali granite and monzodiorite exhibits slightly lower nd t 17 9 to 16 2 zircon hf t 21 4 to 15 3 and 18o 6 6 7 9 than the guojialing granodiorite it was derived from the melting of neoarchean paleoproterozoic crust with limited crust mantle interaction and experienced crustal assimilation and fractional crystallization indicating an extended process associated with the waning stage of lithospheric thinning we document the magmatic responses to the lithospheric thinning at different stages which account for the genesis and evolution of the continental adakitic rocks and decratonization of the ncc

nd o hf isotopic decoupling in s type granites implications for ridge subduction abstract the generation of s type granites in the continental crust generally requires partial melting of metasedimentary rocks at relatively high temperatures and is typically associated with syn or post collisional tectonics these melts are generally expected to inherit the geochemical characteristics of their metasedimentary protoliths and their nd hf and o isotopic compositions have been widely used to trace the origin of the magmas here we show that these isotopic systems are decoupled in s type granites from the chinese altai displaying a wide range of zircon hf t values 0 7 to 6 2 and a limited range of whole rock nd t values 6 1 to 2 2 and zircon 18o values 8 49 to 12 91 zircon xenocrysts are common in these plutons and show markedly negative hf t values from 30 7 to 18 and highly positive 18o values from 9 61 to 13 03 in addition these granites exhibit high lu hf 0 15 to 1 38 ratios and substantial depletions in zr and hf we develop a new model to explain the observed relationship between residual zircon content and nd hf o isotope decoupling we propose that these s type granites formed from partial melting of metasedimentary crustal rocks associated with a ridge subduction related heat source limited crustal heating due to mantle upwelling through the slab window on a small scale may have resulted in significant disequilibrium melting of the metasedimentary crust our findings provide new insights into melting processes in the deep continental crust

metamorphism and cooling of the ne dalradian the buchan area of dalradian rocks represents a distinct tectonothermal domain within the scottish highlands and the portsoy duchray hill lineament on the western margin of this block is one of the best examples of a long lived domain boundary rb sr mica cooling ages from metamorphic rocks from across the trace of this lineament document a prolonged ordovician cooling history delayed but then relatively rapid cooling to the west of the portsoy duchray hill lineament is recognized whereas to the east the age data point to a high heat flow regime lasting more than 50 ma the isotopic ages suggest that c 460 ma was a time of active tectonism resulting in final cooling of the low grade rocks and differential uplift and rapid cooling of deeper structural levels to the west the radiometric ages do not support previous tectonic models for the region that have invoked thrust thickening along the line of the portsoy duchray hill lineament and a new model for the metamorphism is proposed the overprinting of andalusite bearing assemblages by kyanite to the west of the portsoy duchray hill lineament is linked to pressure increases associated with the intrusion of the newer gabbros and represents a magmatic loading related to the same tectonothermal event that generated the low pressure metamorphism rather than a separate tectonic episode

crustal homogenization revealed by u pb zircon ages and hf isotope evidence from the late cretaceous granitoids of the agacoren intrusive suite central anatolia turkey geochemical and isotopic evidence from the agacoren igneous association in central anatolia turkey indicates that this suite of calc alkaline granitic rocks have undergone crustal homogenization during regional metamorphic and related magmatic events whole rock chemical and sr nd isotopic data of the granitoids reveal crustal affinity with an earlier subduction component zircons show inherited cores and subsequent magmatic overgrowths the laser ablation icp ms 206pb 238u zircon ages are determined as 84 1 1 0 ma for the biotite muscovite granite 82 3 0 8 1 1 ma for the hornblende biotite granite 79 1 2 1 1 5 ma for the granite porphyry dyke 75 0 1 0 1 0 ma for the alkali feldspar dyke and 73 6 0 4 ma for the monzonite this is interpreted as continuous magma generation possibly from heterogeneous sources from ca 84 to 74 ma during the closure of the northern branch of the neotethyan ocean the oldest granitoids 84 82 ma were probably formed due to crustal thickening after obduction of the morb type oceanic crust onto the tauride anatolide microplate the younger granitoids are interpreted to be related to the subsequent post collisional extension after lithospheric delamination combination of the laser ablation icp ms zircon lu hf isotope data with the u pb ages of inherited cores suggests that cretaceous granitoids formed by melting of heterogeneous crustal protoliths which results in significant variation in ehf t data from 12 9 to 2 2 these protoliths were probably composed of reworked early proterozoic crust minor juvenile late proterozoic magmatic components and paleozoic to pre late cretaceous recycled crustal material moreover the late cretaceous zircon domains of the different granitoids are characterized by a crustal signature with a relatively restricted zircon ehf t data ranging from 4 1 to 8 8 this variation is only about twice the reproducibility ca 1 ehf of the data but much smaller than the isotope variability of inherited zircons our preferred interpretation is effective isotopic homogenization of the heterogeneous central anatolian crust during the late cretaceous high grade metamorphic and magmatic events a process that we propose to be relevant for other active continental margins

depositional history of lower cretaceous strata in northeastern new mexico implications for regional tectonics and depositional sequences lower cretaceous strata in northeastern new mexico reflect deposition during marine transgression and regression associated with the kiowa skull creek cycle development of regionally significant unconformities can be directly related to shoreline shifts during this cycle topography related to early cretaceous tectonic activity on crystalline basement structures including the dalhart basin tucumcari basin and the intervening bravo dome also had a direct effect on early cretaceous deposition and is reflected by thickness trends in marine strata the kiowa skull creek transgression was preceded by infilling of paleovalleys represented by the long canyon and campana sandstone beds of the glencairn formation and tucumcari shale respectively the long canyon and campana sandstone beds are equivalent to the plainview formation of central colorado and together they represent an extensive drainage network developed over a correlative unconformity that is preserved throughout most of the southern western interior glencairn and tucumcari marine shales represent clastic deposition during kiowa skull creek transgression and early regression base level drop associated with kiowa skull creek regression resulted in dramatic shoreline regression and deposition of fluvial channel sandstone in the dalhart basin which maintained a low offshore gradient this produced an erosional unconformity at the base of mesa rica channel sandstone that correlates with the well documented erosional surface at the base of the muddy sandstone in central colorado the tucumcari basin which maintained a steeper offshore gradient accumulated marine deltaic mesa rica sandstone at this time marine strata in both the tucumcari and dalhart basins thin toward the bravo dome mesa rica and upper tucumcari strata represent the only extensive marginal marine lowstand deposits found on the high plains to date associated with the southern arm of the kiowa skull creek sea major mesa rica deposition was followed by transgression that infilled only those mesa rica fluvial channels that were active at that time and also that deposited marine influenced strata of the basal pajarito formation this event most likely represents onset of the greenhorn cycle in northeastern new mexico other crystalline basement structures in the northern part of the united states western interior basin were active during early cretaceous time tectonism in these areas may be related to structures in northeastern new mexico and thus may be expressions of broad scale crustal strain in the early cretaceous western interior that is undocumented by present tectonic models

ultrasonic tomography non destructive evaluation of the weathering state on a marble obelisk considering the effects of structural properties the use of ultrasonic methods for a non destructive investigation of immovable high ranking cultural heritage landmark buildings and sculptures made of natural stone has developed into the state of the art testing throughout the last 20 years this routinely applied transmission method gives information about the rock as a whole but no detailed information concerning the internal structures onsite measurements have been executed in a tomographic approach for a marble obelisk in the neuer garten potsdam germany to obtain an assessment on its internal weathering conditions detailed mapping of macroscopically visible structures and weathering phenomena has been performed on a scale of 1 1 to prove the validity of this data the rock properties for the same marble variety were examined under laboratory conditions to gain data on their directional dependence influencing factors like water content and artificial weathering behaviour these results were used to cross check the ultrasonic measurements onsite and the tests under laboratory conditions to obtain a reliable interpretation the ultrasonic velocity distributions measured under defined conditions revealed a possible anisotropy between 9 and 30 which is a basic input parameter for the calculated tomograms the synthetic tomograms clearly show the great impact of anisotropy considering the velocity distribution modelled for the measured planes based on the laboratory data an amount of 20 anisotropy was applied to the tomograms which improved the ability to distinguish the velocity variation due to deterioration from that caused by rock fabric the results demonstrate that the rock fabric and its anisotropy need to be considered for interpreting the tomographic investigation before an adequate assertion can be made the above influences must be considered as a basis for conservation purposes

episodic growth of the gondwana supercontinent from hafnium and oxygen isotopes in zircon it is thought that continental crust existed as early as 150 million years after planetary accretion but assessing the rates and processes of subsequent crustal growth requires linking the apparently contradictory information from the igneous and sedimentary rock records for example the striking global peaks in juvenile igneous activity 2 7 1 9 and 1 2 gyr ago imply rapid crustal generation in response to the emplacement of mantle super plumes rather than by the continuous process of subduction yet uncertainties persist over whether these age peaks are artefacts of selective preservation and over how to reconcile episodic crust formation with the smooth crustal evolution curves inferred from neodymium isotope variations of sedimentary rocks detrital zircons encapsulate a more representative record of igneous events than the exposed geology and their hafnium isotope ratios reflect the time since the source of the parental magmas separated from the mantle these model ages are only meaningful if the host magma lacked a mixed or sedimentary source component but the latter can be diagnosed by oxygen isotopes which are strongly fractionated by rock hydrosphere interactions here we report the first study that integrates hafnium and oxygen isotopes all measured in situ on the same precisely dated detrital zircon grains the data reveal that crust generation in part of gondwana was limited to major pulses at 1 9 and 3 3 gyr ago and that the zircons crystallized during repeated reworking of crust formed at these times the implication is that the mechanisms of crust formation differed from those of crustal differentiation in ancient orogenic belts

three age groups of ornithopods inferred from footprints in the mid cretaceous dakota group eastern colorado north america abstract ornithopod population structure is inferred from a large sample of footprints from the mid cretaceous dakota group of colorado new mexico and oklahoma allometric analyses and size frequency distributions suggest size age classes or recruitments for tracks identified as caririchnium leonardii ornithopoda from sequence 3 of the mid cretaceous dakota group of the rocky mountain front range high plains region five hundred ninety eight footprints from 284 trackways were used in the statistical analysis tests were conducted that revealed no significant difference between analyses of right and left footprints or between casts and molds allometric analysis suggests a growth curve that can be subdivided into three segments corresponding to foot lengths of 16 5 21 7 21 7 29 3 and 29 3 55 0 cm respectively these are interpreted as juvenile possibly yearlings subadults and adults the former two categories may correspond to animal recruitments n n 1 whereas the latter category may represent several recruitments n 2 n 3 n 4 etc once ornithopod growth curves of the type proposed for maiasaura are established there is considerable potential for estimating dinosaur age from footprints in the meantime however large track samples can be analyzed for the size class information they contain

age and origin of post collision baltoro granites south karakoram north pakistan insights from in situ u pb hf and oxygen isotopic record of zircons abstract origin of post collision plutonism is critical to understand the tectonothermal evolution of the over thickened continental crust in collision zones this has proven difficult to reconcile with the conventional whole rock geochemical and field based studies alone we report in situ study of zircon u pb hf and o isotopes from five samples of the baltoro plutonic unit bpu in south karakoram the plutonic unit is the western part of the southern asian margin of the india asia convergent zone baltoro granites and a biotite rich enclave yielded similar and overlapping u pb ages ranging from 26 to 15 ma hafnium isotopic composition ehf 0 is very heterogeneous ranging from 17 1 to 4 4 while the oxygen isotopic composition of the granites is homogeneous with mean 18 o ranging from 7 2 to 9 4 based on u pb geochronology and hf o isotopic composition the involvement of two main sources is suggested 1 cretaceous calc alkaline karakoram crust and 2 karakoram gneisses moreover possible involvement of metasomatized asian lithospheric mantle is supported by elevated oxygen composition of granites and identical hf composition of biotite rich enclave to the mantle derived baltoro lamprophyre however direct contribution from juvenile pristine mantle is unlikely as no juvenile mantle type hf and oxygen values were obtained this also precludes the involvement of southward juvenile arc related component of kohistan ladakh batholith our new u pb and hf data are comparable to the mesozoic karakoram batholith miocene two mica leucogranites in the pangong range and magmatism from the lhasa terrane in south tibet suggesting a genetic link between the karakoram and the rocks to the east this magmatic event is best explained by lower crust partial melting promoted by both thermal equilibration following crustal thickening and heat advection by ultrapotassic magmas associated with the breakoff of the indian continental margin

uncoupled o and hf isotopic systems in zircon from the contrasting granite suites of the new england orogen eastern australia implications for studies of phanerozoic magma genesis abstract the permo triassic granites of the new england orogen eastern australia were emplaced into a volcanic arc complex accreted to the eastern gondwana margin in the late devonian or early carboniferous zircon u pb dating shows that the s type hillgrove 297 ma and bundarra 287 ma supersuites predated intrusion of the i type moonbi supersuite 250 ma by up to 50 ma the high 18ozrn of the s type granites 10 0 11 5 and range of u pb ages 370 300 ma and 18ozrn 5 10 of their inherited zircon cores show that their source rocks were predominantly weathered carboniferous volcaniclastics the youngest deposited

jewish cemetery in hamburg altona germany state of marble deterioration and provenance several highly ornamented marble tombstones from the jewish cemetery in hamburg altona were investigated concerning their state of preservation and their provenance ultrasonic measurements were performed on site and on drill cores in the laboratory for the determination of the rock decay the investigations show that the predominantly strong decay of the marbles can only be determined exactly in the laboratory since on site the influence of water leads to an increase of ultrasonic velocities the water content has to be taken into account when dealing with ultrasonic analysis in addition to the rock fabric investigations geochemical analysis of the stable isotopes of carbon and oxygen as well as the major and trace elements were used to identify the provenance all the information gathered in this study points to the quarries of carrara as the rock source

coupled sm nd and u pb systematics in late caledonian granites and the basement under northern britain the british late caledonian granites display a close correspondence between inherited u pb systematics in zircons and initial end indicating that both were controlled by the age of a major component of continental crust the data confirm and refine previous models of a basement comprising young crust in the south which includes arc and oceanic crust scrapings and progressively older continental crust northwestwards across scotland

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

origin and evolution of silicic magmatism at yellowstone based on ion microprobe analysis of isotopically zoned zircons the origin of large volume yellowstone ignimbrites and smallervolume intra caldera lavas requires shallow remelting of enormous volumes of variably o depleted volcanic and sub volcanic rocks altered by hydrothermal activity zircons provide probes of these processes as they preserve older ages and inherited do values this study presents a high resolution oxygen isotope examination of volcanism at yellowstone using ion microprobe analysis with an average precision of 0 2o and a 10 mm spot size we report 357 analyses of cores and rims of zircons and isotope profiles of 142 single zircons in 11 units that represent majoryellowstone ignimbrites and post caldera lavas many zircons from these samples were previously dated in the same spots by sensitive high resolution ion microprobe shrimp and all zircons were analyzed for oxygen isotope ratios in bulk as a function of grain size by laser fluorination we additionally report oxygen isotope analyses of quartz crystals in three units the results of this work provide the following new observations 1 most zircons from post caldera low do lavas are zoned with higher do values and highly variable u pb ages in the cores that suggest inheritance from pre caldera rocks exposed on the surface 2 many of the higher do zircon cores in these lavas have u pb zircon crystallization ages that postdate caldera formation but pre date the eruption age by 10 20 kyr and represent inheritance of unexposed post caldera sub volcanic units that have do similar to the lava creek tuff 3 young and voluminous 0 25 0 1ma intra caldera lavas which represent the latest volcanic activity atyellowstone contain zircons with both high do and lowdo cores surrounded by an intermediate do rim this implies inheritance of a variety of rocks from high do pre caldera and low do post caldera units followed by residence in a common intermediate do melt prior to eruption 4 major ignimbrites of huckleberry ridge and to a lesser extent the lava creek and mesa falls tuffs contain zoned zircons with lower do zircon cores suggesting that melting and zircon inheritance from the lowdo hydrothermally altered carapace was an important process during formation of these large magma bodies prior to caldera collapse 5 the do zoning in the majority of zircon core rim interfaces is step like rather than smoothly inflected suggesting that processes of solution reprecipitation were more important than intracrystalline oxygen diffusion concave downward zircon crystal size distributions support dissolution of the smaller crystals and growth of rims on larger crystals this study suggests that silicic magmatism atyellowstone proceeded via rapid shallow level remelting of earlier erupted and hydrothermally alteredyellowstone source rocks and that pulses of basaltic magma provided the heat for melting each postcaldera yellowstone lava represents an independent homogenized magma batch that was generated rapidly by remelting of source rocks of various ages and do values the commonly held model of a single large volume super solidus mushy state magma chamber that is periodically reactivated and produces rhyolitic offspring is not supported by our data rather the source rocks for theyellowstone volcanism were cooled below the solidus hydrothermally altered by heated meteoric waters that caused low do values and then remelted in distinct pockets by intrusion of basic magmas each packet of new melt inherited zircons that retained older age and do values this interpretation may have significance for interpreting seismic data for crustal low velocity zones in which magma mush and solidified areas experiencing hydrothermal circulation occur side by side new basalt intrusions into this solidifying batholith are required to form the youngest volcanic rocks that erupted as independent rhyolitic magmas we also suggest that the lava creek tuff

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

first report of sauropod tracks from the upper jurassic tianchihe formation of guxian county shanxi province china abstract this paper presents the first report of sauropod tracks from the upper jurassic of shanxi province china dinosaur tracks appear concentrated in five trackways in different stratigraphic levels of the late jurassic tianchihe formation tracks are dominantly small and medium size sauropod tracks and are tentatively assigned to brontopodus based on preserved track morphology trackway pattern and statistical analysis the tianchihe formation in which the tracks appear shows a gradual change from meandering fluvial to sandy braided fluvial depositional systems developed in a seasonally arid environment comparisons of the evaluated speed of bipedal to quadruped trackways indicate that the slower walk more easily produces pes dominated overprints trackways in the guxian tracksite appear following different orientations suggesting that these trackways were produced by different sauropods at different times an unusual trackway following a curved pattern has been identified in the site and could represent a special locomotion character or a social behavior the presence of eolian deposits in central shanxi province could have acted as a paleogeographic and paleoenvironmental barrier for the dispersion of the yanliao biota that survived in northern hebei western liaoning and northestern shanxi province to the ordos basin during the late jurassic

evidence for melting mud in earth s mantle from extreme oxygen isotope signatures in zircon evidence for melting mud in earth s mantle from extreme oxygen isotope signatures in zircon

record of multiple stage channelized fluid and melt activities in deeply subducted slab from zircon u pb age and hf o isotope compositions abstract geochemical features of island arc rocks require two slab derived components of a melt and a fluid added to their sources these two liquids may unite to an intermediate aqueous melt at the base of volcanic arc direct evidence of this process has been scarce yet here we present an integrated study of in situ u pb age trace element and o hf isotope for zircons from a suite of a quartz vein a felsic vein their host eclogite and surrounding gneiss at the xitieshan uhp terrane of the north qaidam metamorphic belt nqmb oscillatory zoned zircons from the quartz vein are enriched in u li nb and ree with a formation age of 442 6 ma consistent with the timing of the peak uhp metamorphism this demonstrates there is no temporal gap between the uhp metamorphism and fluid flow in the xitieshan terrane in particular the oscillatory zoned zircons of the quartz vein have similar hf isotope compositions to zircons from the surrounding gneiss but variable o isotope compositions between the host eclogite and surrounding gneiss the fluid from surrounded gneiss was thus an aqueous melt with high transport ability for lu and hf and o while the fluid from the host eclogite was an aqueous fluid only with the ability to transport o according to the similar behaviors of granitic rock and sediment it is inferred that a channelized hydrous melt can be formed in the downgoing sediment layer where an aqueous fluid can be formed from underlying basalt and or peridotite layers at the sub arc depth the two types of fluid are fed to the overlying mantle wedge from subducting slab to form island arc rock by contrast the zircons in the felsic vein yield a weighted mean 206pb 238u age of 420 4 ma which can be regard as the timing of partial melting during the exhumed stage for the xitieshan uhp rocks the zircon o and hf isotopic features of the felsic vein are between the country gneiss and host eclogite compatible with their emanating from hydrous melt of both the eclogite and gneiss during the exhumation stage of the uhp rocks this indicates that hydrous melt would be released from both the sediment and basalt or peridotite layers of the subducting slabs at relatively shallow depth

yeosu dinosaur track sites of korea the youngest dinosaur track records in asia abstract eighty two dinosaur trackways were newly discovered in upper cretaceous lacustrine deposits on islands in the vicinity of yeosu korea most dinosaur tracks occur in marginal lake deposits with polygonal desiccation cracks the dinosaur tracks at the yeosu site include 65 ornithopod trackways 16 theropod trackways and one sauropod trackway the prevalence of ornithopod tracks and the limited occurrence of sauropod tracks at the yeosu site evidently reflect decreased sauropod diversity in the upper cretaceous all ornithopod trackways represent bipeds and most of the ornithopod tracks are similar to caririchnium from other sites of the korean peninsula all fossil wood specimens collected in the study area represent conifers three species of cupressaceous and two species of taxodiaceous conifers and a new species except for one which is a discotyledon it is thus inferred that the southwestern part of the korean peninsula was primarily covered with mesic forests with taxodiaceous trees during the late cretaceous the k ar age of the yeosu tracksite is determined as 81 65 ma camapnian to maastrichtian it indicates that the yeosu track site contains the last records of dinosaurs living in asia consequently semi arid palaeoclimatic conditions together with a large lake as a persistent water source and rich vegetation of gymnosperm trees as food resulted in the preservation of abundant dinosaur tracks in the upper cretaceous on the korean peninsula

petrogenesis of ore forming granites with implications for w mineralization in the super large shimensi tungsten dominated polymetallic deposit in northern jiangxi province south china abstract the shimensi deposit is a newly discovered super large tungsten w polymetallic deposit in northwestern jiangxi province south china in this paper we reported new zircon u pb ages for the ore bearing porphyritic biotite granite 151 3 2 8 ma and fine grained granite 150 1 1 2 ma and 150 7 2 4 ma which represent the oldest mesozoic granitic magmatism reported at shimensi our ore bearing granite porphyry ages 142 7 2 3 ma and 143 3 1 5 ma have better constrained the timing of the jurassic early cretaceous ore forming magmatism geochemically the shimensi granitoids are strongly peraluminous with high contents of sio2 70 7 78 7 wt and k2o 4 0 wt p2o5 rb ta and u and low contents of ti sr ba and hrees the rocks also show positive p2o5 vs sio2 correlation suggesting a highly fractionated s type affinity different from most w bearing granites in the jiangxi region the calculated zircon ehf t 10 0 to 2 4 two stage model ages 1350 1824 ma and 18ozircon values 6 40 to 8 87 of the shimensi granites suggest that the latter were mainly derived from the partial melting of heterogeneous source rocks probably with combined contributions from the neoproterozoic shuangqiaoshan group metamorphic rocks and jiuling granodiorite the calculated zircon eu eu 0 05 0 58 mean 0 20 and ce4 ce3 3 83 96 49 mean 20 99 ratios of the granites indicate very low oxygen fugacity fo2 for the ore forming magmas a highly favorable factor for w mineralization potentially w and cu rich source rocks and highly fractionated and reducing granitic magmas were important factors that triggered super large w mineralization at shimensi

permo triassic anatexis continental rifting and the disassembly of western pangaea crustal anatectites are frequently observed along ocean continent active margins although their origins are disputed with interpretations varying between rift related and collisional we report geochemical isotopic and geochronological data that define an 1500 km long belt of s type meta granites along the andes of colombia and ecuador which formed during 275 223 ma these are accompanied by amphibolitized tholeiitic basaltic dykes that yield concordant zircon u pb dates ranging between 240 and 223 ma a model is presented which places these rocks within a compressive permian arc setting that existed during the amalgamation of westernmost pangaea anatexis and mafic intrusion during 240 223 ma are interpreted to have occurred during continental rifting which culminated in the formation of oceanic crust and initiated the break up of western pangaea compression during 275 240 ma generated small volumes of crustal melting rifting during 240 225 ma was characterized by basaltic underplating the intrusion of tholeiitic basalts and a peak in crustal melting tholeiitic intrusions during 225 216 ma isotopically resemble depleted mantle and yield no evidence for contamination by continental crust and we assign this period to the onset of continental drift dissected ophiolitic sequences in northern colombia yield zircon u pb dates of 216 ma the permo triassic margin of ecuador and colombia exhibits close temporal faunal and geochemical similarities with various crustal blocks that form the basement to parts of mexico and thus these may represent the relict conjugate margin to nw gondwana the magmatic record of the early disassembly of pangaea spans 20 ma 240 216 ma and the duration of rifting and rift drift transition is similar to that documented in cretaceous tertiary rift settings such as the west iberia newfoundland conjugate margins and the taupo lau havre system where rifting and continental disassembly also occurred over periods lasting 20 ma

magma mixing in granite petrogenesis insights from biotite inclusions in quartz and feldspar of mesozoic granites from south china abstract magma mixing is a common process in granite petrogenesis the major element composition of biotites in granites is primarily controlled by the composition of magmas from which they crystallized biotite grains enclosed in quartz and feldspars of granites are naturally protected by their host minerals so that their compositions are likely original and can potentially be used to track the magma mixing this is illustrated by a combined study of matrix and inclusion biotites from mesozoic granites in the nanling range south china three granite samples have been used in this study one two mica granite and two biotite granites the biotites of different occurrences in the two mica granite have no compositional distinctions biotites in the two mica granite have higher al2o3 and lower mgo than those in the biotite granites the former is consistent with biotites from typical s type granites of metasedimentary origin in contrast biotites from the biotite granites can be categorized into different groups based on their paragenetic minerals and geochemical compositions they have relatively low aluminous saturation indices but higher mg numbers falling in the transitional field between typical s and i type granites in addition there are two contrasting zircon populations with nearly identical u pb ages in the biotite granites one shows clearly oscillatory zonings in cl images whereas the other is totally dark and often overgrew on the former one the zircons with oscillatory zonings have higher 18o values than the dark ones indicating their growth from two compositionally different magmas respectively with different sources an integrated interpretation of all these data indicates that mixing of two different magmas was responsible for the petrogenesis of biotite granites therefore the study of biotite inclusions provides insights into the magma mixing in granite petrogenesis

the role of crustal melting in the formation of rhyolites constraints from sims oxygen isotope data chon aike province patagonia argentina