petrogenesis of late paleozoic volcanics from the zhaheba depression east junggar insights into collisional event in an accretionary orogen of central asia abstract the carboniferous to permian period marks an important transition from accretion to collision in the east junggar terrane nw china field and well fuqian 1 well core data from the zhaheba depression provide a better window for understanding the magmatic process during this period and its implications for the continental growth of central asia field investigations reveal structural features characterized by ne sw compression with lithology composed of basic and intermediate felsic volcanic rocks and pyroclastic rocks the core samples from well fuqian 1 show dominantly basalt basaltic andesite dacite and minor pyroclastic rocks we report zircon shrimp u pb ages of 276 0 279 8 ma from rhyolites and zircon la icp ms u pb ages of 315 4 317 4 ma from dacite and basaltic andesite our data suggest that the volcanic rocks from surface exposures and the well cores of well fuqian 1 formed in the early permian and the late carboniferous respectively the late carboniferous mafic rocks have geochemical characteristics similar to the intercalated early permian felsic rocks the mafic rocks show low initial 87 sr 86 sr 0 703162 0 703783 and high e nd t 5 5 7 5 enrichment in lree and some liles such as rb and th as well as hfses such as zr y and depletion in nb ta and ti furthermore they also display lower sm th 1 6 8 4 and higher th y 0 03 0 12 ratios than those of morb and variable th zr 0 004 0 016 ba th 61 839 ba la 6 13 48 77 and ba nb 10 101 ratios the geochemical data suggest that these rocks were derived dominantly from a 5 10 partial melting of a mainly garnet rich with minor spinel bearing iherzolite mantle source metasomatized by slab derived fluids the felsic rocks are rich in silica sio 2 57 43 78 07 and alkalis k 2 o na 2 o 5 33 9 28 and possess high tfe 2 o 3 0 70 6 95 contents and ga al ratios and low cao 0 18 5 11 and mgo 0 13 2 02 contents they represent typical high medium k calc alkaline a type rhyolite with enrichment of lree and hfse zr hf and depletion of ba sr eu nb and ta these rocks display high e nd t 6 9 7 3 and e hf t 10 3 14 6 values and young crustal model ages 348 557 ma integrating regional geological data from the east junggar terrane and the available data from the proximal ophiolite belt we propose that an arc arc or arc continent post collisional setting in the zhaheba area commenced at ca 317 ma the late carboniferous early permian felsic and mafic magmas were derived from the partial melting of the juvenile mafic lower crust and subcontinental lithospheric mantle metasomatized by pre carboniferous subduction related fluids through asthenospheric upwelling this post collisional event suggests that vertical accretion played an important role not only in the late carboniferous early permian continental growth of the east junggar but also in the final evolutionary phase of the accretionary orogen

geochemical and mineralogical control of different genetic types of deep sea nodules from the pacific ocean deep sea nodules from the northeast pacific nodule belt and the southeast pacific sonne basin being formed in areas bordering the equatorial zone of high biological productivity accumulate by two basically different growth processes a early diagenetic growth by supply from pore water and b hydrogenetic growth by supply from near bottom sea water these growth processes lead to different genetic types of nodules early diagenetic type a hydrogenetic type b and mixed type ab a further type ac very rich in mn is being formed by increasing influence of early diagenesis these types can clearly be distinguished by their shapes surface textures mineral constituents of oxide fraction internal microstructures and geochemistry a genetical classification is being proposed on the basis of statistically computed interelement relationships todorokite very poor in fe is the main mn phase in the early diagenetic substance mno2 intimately intergrown with feooh xh2o is the main phase in the hydrogenetic substance consequently an important difference can be pointed out the metal supply for the growth of the early diagenetic nodules is based on an ionic solution of me2 e g mn2 ni2 cu2 zn2 whereas the supply for the hydrogenetic nodules is caused by transport of colloidal particles mobilization of mn2 and fractionation from fe is controlled by the amount of decomposing organic matter in the peneliquid layer of the sediments the main factor controlling the intensity of early diagenesis is the biological productivity in surface waters the crucial point of reversal at a mn fe ratio of about 5 obtained by hyperbolical regression of the analyses of nodules from the southeast pacific represents best concentrations in ni and cu mn fe quotients greater than 5 cause a decrease of ni and cu content nodules from the northeast pacific nodule belt generally contain higher concentrations in cu than nodules from the southeast pacific this can be explained by an additional supply of cu transported below ccd by siliceous plankton

neoproterozoic adakitic plutons in the northern margin of the yangtze block china partial melting of a thickened lower crust and implications for secular crustal evolution abstract numerous neoproterozoic felsic and mafic ultramafic intrusions occur in the hannan region at the northern margin of the yangtze block among these the wudumen and erliba plutons consist of granodiorites and have shrimp zircon u pb ages of 735 ma the rocks have high k 2 o 0 8 3 6 wt and na 2 o 4 4 6 4 wt and low mgo 0 4 1 7 wt they also have high sr y 32 209 and la yb n ratios 4 4 38 6 their e nd values range from 0 41 to 0 92 and zircon initial 176 hf 177 hf ratios from 0 282353 to 0 282581 these geochemical features are similar to those of adakitic rocks produced by partial melting of a thickened lower crust our new analytical results combined with the occurrence of voluminous arc related mafic ultramafic intrusions emplaced before 740 ma lead us to propose that the crustal evolution in the northern margin of the yangtze block during neoproterozoic involved 1 rapid crustal growth and thickening by underplating of mafic magmas from the mantle which was modified by materials coming from the subducting oceanic slab from 1 0 to 0 74 ga and 2 partial melting of the thickened lower crust due to a thermal anomaly induced by upwelling of asthenosphere through an oceanic slab window producing the 735 ma adakitic wudumen and erliba plutons our model suggests that the crustal thickness was more than 50 km at the northern margin of the yangtze block at 735 ma and rule out the possibility of a mantle plume impact causing the 735 ma magmatism in the region

magmatic record of neoarchean arc polarity reversal from the dengfeng segment of the central orogenic belt north china craton abstract the dengfeng segment of the archean central orogenic belt in the north china craton ncc includes circa 2 66 2 5 ga metavolcanics metasedimentary and plutonic rocks all units are intruded by 2 5 2 4 ga mafic dykes and a suite of coeval circa 2 5 2 45 ga potassic granites and leucogranitic veins mafic dykes are characterized by mixed alkaline and calc alkaline affinities enriched lree and negative nb and zr anomalies indicating a lithospheric mantle source region potassic granitic dykes exhibit highly fractionated lree patterns and negative hfse anomalies and positive zircon ehf t values which are similar to those of ttg gneisses in the area leucogranitic veins cutting across the diorites are characterized by high contents of sio2 and k2o lree enriched patterns positive eu and sr anomalies negative nb and ti anomalies we suggest that the granitic dykes and leucogranitic veins were derived from partial melting of thickened older crusts combined with other reported 2 5 ga mafic dykes and potassic granites from the ncc we propose that they demonstrate an ancient example of arc polarity reversal and provide a record of the formation of a new plate boundary in the archean the underplating of the mafic dyke source beneath the newly accreted eastern block may have generated the widespread 2 5 2 47 ht lp metamorphism with anticlockwise p t paths in the eastern block

estimating growth rates of ferromanganese nodules from chemical compositions implications for nodule formation processes abstract using available information on the accretion rates and the bulk chemical compositions of oceanic ferromanganese nodules it can be shown that the accumulation rate of manganese is proportional to the square of the accumulation rate of iron this relationship has been used to derive an equation that predicts nodule growth rates from their chemical compositions the equation accurately predicts growth rates up to about 50 mm 10 6 yr but yields incorrect rates for faster growing concretions from this relationship nodules underneath water of high primary productivity grow most rapidly and accumulate transition metals most rapidly however nodules from regions of highest primary productivity do not have the highest concentrations of nickel and copper reduction of manganese within the sediment column and remobilization of a fraction to the surface sediments adds manganese to nodules without substantially augmenting the supply of other transition elements the addition of remobilized manganese to the nodule dilutes the concentrations of nickel copper and iron even though their rates of accumulation are also high

criteria for stratigraphic correlation using aerial photographs examples from the south central pyrenees photostratigraphy a new method of aerial photo interpretation establishes local photostratigraphic correlation frameworks with relative chronostratigraphic significance this method is based on the analysis of strata geometry their relationships and the photographic aspect of the rocks for identification and hierarchic organization of photostratigraphic units the definition of these units does not presuppose any a priori genetic implications the units represent volumes of rocks bounded by surfaces with chronostratigraphic significance photostratigraphic units contain time transgressive photofacies and photofacies units which record lithologic and depositional characteristics of the strata the procedure for establishing photostratigraphic correlation frameworks is illustrated through examples from the south central pyrenees direct integration with field data allows the comparison of photostratigraphic frameworks with frameworks based on other stratigraphic criteria photostratigraphy is proposed as an independent and relatively rapid preliminary approach to the study of a basin

metasomatic mantle source and crustal contamination for the formation of the neoproterozoic mafic dike swarm in the northern yangtze block south china abstract in the huangling region of the northern yangtze block south china the 820 ma huangling felsic pluton was intruded by 800 ma mafic dikes these dikes are composed of fine to medium grained diabase porphyritic diabase and olivine gabbro quartz xenocrysts occur locally in the olivine gabbro the rocks are alkaline to sub alkaline in composition and have sio2 ranging from 43 3 to 57 2 wt mgo from 3 7 to 9 2 wt and total alkali from 3 0 to 7 3 wt they exhibit lree enrichment la yb n 3 3 28 5 with slightly negative eu anomalies eu eu 0 6 1 0 their primitive mantle normalized trace element patterns are characterized by enrichment of large ion lithophile elements rb ba th and u depletion of high field strength elements nb ta zr and hf and positive pb and negative ti anomalies they have relatively high initial 87sr 86sr ratios ranging from 0 7052 to 0 7080 and variably negative end t values from 4 2 to 10 9 the rocks have a large range of whole rock ehf values 0 35 to 11 34 and a relatively narrow range of pb isotope ratios 206pb 204pb 16 96 to 17 97 207pb 204pb 15 41 to 15 58 and 208pb 204pb 38 08 to 39 66 initial 87sr 86sr ratios correlate negatively with 206pb 204pb ratios whereas 143nd 144nd and 208pb 204pb ratios and ehf values correlate positively with 206pb 204pb ratios these features are indicative of an em2 source region suggesting a lithospheric mantle source modified by subducted components during the neoproterozoic the quartz xenocrysts and linear isotopic variations indicate strong crustal contamination during magma emplacement the energy constrained assimilation and fractional crystallization ec afc modeling calculations reveal that the parental magmas were contaminated by continental crust including archaean amphibolites granitic gneisses metasedimentary rocks and granitic rocks the mafic dikes are 20 myrs younger than the huangling felsic pluton which was produced by partial melting of a thickened continental crust suggesting that the mafic dikes were a consequence of post orogenic extension the huangling region may have originally been located at the centre of the yangtze block the possible heat source for the generation of the huangling felsic pluton and mafic dikes was asthenospheric wedging resulting from oceanic slab subduction beneath the northern margin of the yangtze block this conclusion rules out the possibility that the yangtze block was located in the central part of the rodinia supercontinent the block was more likely situated along the margin of rodinia

ordovician appinites in the wugongshan domain of the cathaysia block south china geochronological and geochemical evidence for intrusion into a local extensional zone within an intracontinental regime abstract palaeozoic mafic igneous rocks are potentially significant in constraining the tectonic nature and evolution of the kwangsian orogeny in the eastern south china block yet they have received little attention because of their limited outcrop geochemistry and geochronology was carried out on newly identified ordovician ultramafic mafic appinites in the wugongshan domain of the cathaysia block seven appinite samples yielded 206pb 238u crystallisation ages ranging from 452 4 ma to 473 3 ma abundant 480 500 ma zircon xenocrysts and or inherited zircons were found in the appinites possibly indicating an earlier magmatism episode in the early palaeozoic period the wugongshan appinites are ultramafic to mafic in composition and the ultramafic rocks display features of cumulates high concentrations of mgo fe2o3t cr ni and low concentrations of total alkali and total rare earth elements ree the appinite geochemistry displays relatively flat chondrite normalised ree patterns with slight enrichment in light ree and weak negative eu anomalies enrichment in large ion lithophile elements such as rb k and weak depletion in nb ta in primitive mantle normalised trace element patterns we suggest that the wugongshan appinites likely originated from an ancient metasomatised mantle and that crustal assimilation fractional crystallisation afc magma mingling and hydration were involved in the petrogenetic process based on the combination of geochemistry crust like bulk sr nd and zircon hf isotopic compositions end t 8 2 to 3 2 initial 87sr 86sr ratios of 0 7067 0 7144 zircon ehf t values peaking at 9 to 3 and regional geological data further considering the alignment and chronology of the appinites we suggest that the appinitic magmas probably were emplaced along the jiangshan shaoxing fault in a local extensional zone in an intracontinental regime in the early palaeozoic

evolution and tectonic setting of the malani nagarparkar igneous suite a neoproterozoic silicic dominated large igneous province in nw india se pakistan abstract the neoproterozoic malani igneous suite mis in nw india along with analogous magmatic rocks from the adjoining nagarparkar region in se pakistan can be collectively classified as a silicic dominated large igneous province slip this magmatic event includes bimodal predominantly felsic volcanism granite emplacement and felsic and mafic dyke intrusions felsic rocks have typical a type affinity as indicated by high abundance of silica alkali high field strength and large ion lithophile element concentrations and low cao and mgo contents their nb negative anomalies and zr saturation parameters indicate significant crustal input and high temperature melting mafic volcanics and dykes show geochemical homogeneity and derivation from a depleted continental mantle source without any significant crustal contamination low u and th contents and no visible nb anomaly the region extending from the mount abu batholith in the east to jaswantpura in the west 2700 km2 representing a transition from the metamorphic sirohi terrane to the undeformed mis was evaluated through an integrated structural including satellite image analysis geochemical and geochronological study during the initial stage prior to 760 ma the granitic basement erinpura granites and overlying sirohi metasediments behaved in a brittle manner that led to development of linear fractures and nne trending rift structures and bimodal volcanic activity emplacement of voluminous granitic bodies in response to progressive extension of the crust is inferred during the more evolved second stage younger than 760 ma mirpur granite a representative of this younger granitic suite jalor type pink granite has yielded 753 9 ma zircon u pb crystallization age granitic plutons mark regions of crustal extension as seen in parallel alignment of plutonic bodies jaswantpura granitic belt and parallel mafic dyke swarms 340 transecting the granites structural analysis further identified an episode of crustal convergence which is documented in folding and faulting of the sindreth basin sequence and in tectonic overprint of early stage mafic rocks rifting and bimodal magmatic activity in mis is coeval with similar rock types in nagarparkar in se pakistan further traceable into the seychelles microplate and central madagascar considering the neoproterozoic paleogeography and our observations an extensional setting and an active continental margin position for mis is inferred

orientated plant fragments revealing tidal palaeocurrents in the fumanya mudflat maastrichtian southern pyrenees insights in palaeogeographic reconstructions abstract leafy axis fragments of frenelopsis sp leaves of sabalites longirhachis unger kvacek et herman and logs are common in the maastrichtian of the basal tremp formation in the vallcebre syncline southern pyrenees the largest plant remains i e leaves of s longirhachis and logs appear scattered and randomly orientated whereas the smallest plant remains i e frenelopsis sp are aligned in a clear east west trend this orientation based on 117 measurements is consistent with the basin palaeogeography which was an e w elongated foreland trough that confined tidal palaeoflow and deposits such as tidal bores in the absence of usual sedimentary indicators e g tractive structures and base marks the accurate study of fossil plant orientations can largely assist palaeoflow determinations in palaeogeographic reconstruction

distribution of rare earth elements ree in size fractions of recent sediments of the indian ocean abstract a sample of each of five sediment types from the indian ocean all presenting a flat shale normalized ree pattern has been divided into eight size fractions 35 20 35 5 20 2 5 1 2 0 5 1 0 2 0 5 and m each fraction was examined for mineralogy and ree content ree patterns of coarser fractions exhibit a negative cerium anomaly related to biogenic components while fine fractions composed almost exclusively of smectite show a positive ce anomaly thus flat whole sample ree patterns which are usually interpreted as indicating a ferrigenous origin can also be due to a mixture of cedepleted and enriched phases the ree distribution was studied in fifteen other sediments thirteen fine size fractions m exhibit a positive ce anomaly and two are ce depleted while the ree patterns of whole samples are flat slightly ce depleted or enriched the ce enrichment of most fine fractions could occur during submarine alteration of volcanic material forming smectite but may also be produced or accentuated during reworking or subsequent to the deposition of sediments

morphological and interlayer geochemical studies on manganese nodules from the southwestern carlsberg ridge abstract mixed facies of manganese nodules from the southwestern carlsberg ridge have been analysed for mn fe ni cu co and zn we present 71 analyses including the averages for outer layer inner layer and near core material morphological studies show seven types of nodules of which medium size spheroidal ellipsoidal and intergrown nodules are most abundant only spheroidal and ellipsoidal nodules with rough surfaces show higher concentrations of mn fe cu ni co and zn towards the outer layer whereas the smooth surface nodules other than the spheroidal type show higher concentrations of these elements towards the core region the other nodule types show a decreasing content of these elements in all the layers analysed copper and ni are present in low concentrations and are associated with zn and mn the mineralogy indicates diagenetic processes involving metal remobilisation and the chemistry suggests the precipitation of metals mostly from seawater variations in the source of supply of the elements are responsible for the observed variations in the chemical composition of the nodules

geochronology geochemistry and petrogenesis of late triassic dolerites associated with the nibao gold deposit youjiang basin southwestern china implications for post collisional magmatism and its relationships with carlin like gold mineralization abstract the relationship between gold mineralization and magmatism within the youjiang basin of sw china remains poorly constrained as a result of the lack of outcropping igneous units in this region this study presents new geological geochronological and geochemical data for recently discovered dolerite dykes associated with the nibao gold deposit which is located within the nw youjiang basin of sw china zircon laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of these dykes yielded an age of 213 6 2 5 ma indicating that these dykes were emplaced during the late triassic and providing new evidence for late triassic magmatism within the study area these dykes also represent an opportunity to investigate the petrogenesis of mafic rocks and the tectonic setting of the late triassic magmatism in the youjiang basin these nibao dolerite dykes contain relatively low concentrations of sio 2 46 03 47 66 wt have moderate total alkali contents k 2 o na 2 o 2 71 3 15 wt and high total fe as fe 2 o 3 tfe 2 o 3 contents 13 49 14 96 wt their trace element compositions are indicative of an oib like geochemical affinity barring depletion in the high field strength elements hfse such as nb ta and th the nibao dolerites have homogeneous lu hf and sr nd isotopic compositions with 87 sr 86 sr i and 143 nd 144 nd i value of 0 70562 0 70677 and 0 51233 0 51239 respectively these dykes have associated e nd t and e hf t values that exhibit a narrow range from 0 70 to 0 51 and from 0 04 to 3 24 respectively these geochemical data indicate that the dolerites associated with the nibao gold deposit were derived from an enriched region of the asthenopheric mantle 90 km depth and the magmas that formed these dykes were generated by 5 10 partial melting of 75 garnet peridotite and 25 spinel peridotite material the ascending magmas underwent both crustal contamination and the fractional crystallization of olivine clinopyroxene and fe oxides e g magnetite or ilmenite prior to emplacement the nibao dolerites are geochemically distinct from mafic rocks related to the emeishan large igneous province suggesting that they are not linked to this mantle plume event instead they formed in an extensional setting generated by the subduction of the song ma oceanic plate beneath south china block and the subsequent collision between the indochina block and south china block the breakoff of the song ma oceanic slab was the process that caused the partial melting of the mantle source region for the nibao dolerite dykes these relationships suggest that the post collision extensional environment associated with this breakoff contributed to the deeply sourced mantle derived late triassic magmatism in this area and perhaps as well the gold mineralization in the youjiang basin most importantly the new geochronological data presented in this study the timing of extension in this region and the results of previous research together suggest that the carlin like gold deposits in the youjiang basin formed at around 213 ma i e the late triassic

manganese nodules and other ferromanganese oxide deposits from the indian ocean ferromanganese oxide concretions from the indian ocean exhibit considerable mineralogical and chemical variation often differentiated on a regional basis nodules richest in mn ni cu and zn are found in sub equatorial basin areas but enrichments of some of these metals also occur in nodules elsewhere particularly where there is evidence of major biogenic contributions to their underlying sediments fe co and pb are most enriched in concretions from sea mounts and the mid ocean ridge system but also attain high values in some basin areas local variations in concretion composition have been found off southern africa and are due to both biological and continental influences there are several major controls on the compositions of the concretions source variations influence composition in that mn ni and cu show evidence of diagenetic enrichment in deposits after being cycled through the biogenic component of sediments whereas fe co and pb appear to be supplied mainly by normal seawater environmental influences including bottom water characteristics affect the degree of dissolution of biogenic remains and this affects the sediment type and the supply of metals to the deposits and also their mineralogy which in turn affects trace metal uptake in the central indian basin source and environmental influences combine to produce ore grade nodules

1 01 0 98 ga mafic intra plate magmatism and related cu au mineralization in the eastern jiangnan orogen evidence from liujia and tieshajie basalts abstract the grenvillian aged mafic magmatism is critical for understanding the regional tectonic settings and testing different tectonic models of south china however the geochronology petrogenesis and geodynamic setting of grenvillian aged mafic rocks in the jiangnan orogen remain unclear an integrated study on la icp ms zircon u pb geochronology elemental and zircon hf isotopic geochemistry has been conducted on the liujia and tieshajie basalts in the eastern jiangnan orogen two samples yielded zircon u pb ages of ca 1012 980 ma the liujia and tieshajie basalts show typical oib like trace element patterns and have high ti concentrations and positive hf t values implying a fertile asthenospheric mantle as their magma source the liujia and tieshajie basalts have relative low mg values 36 58 indicating that their parental magma experienced moderately to strong fractional crystallization of olivine and clinopyroxene most samples of the basalts have high nb la 1 05 1 39 and nb th 19 04 19 53 values indicating an insignificant crustal contamination the 1 01 0 98 ga intra plate mafic magmatism argued against the existence of grenvillian orogeny in the jiangnan orogen the geochemical signatures of mafic rocks along the jiangnan orogen display systematic changes from 1 01 0 98 ga oib like mafic rocks to 0 97 0 83 ga island arc and arc like basalts to 0 80 0 76 ga oib and arc like mafic rocks the systematic geochemical variations of mafic rocks demonstrate that tectonic switch occurred from an intra plate regime to an oceanic subduction related setting to a post orogenic environment with respect to cu au mineralization this study suggests that the tieshajie deposit is one of the oldest regional mineralization events and the formation of coeval metal rich juvenile crust is a critical step for the generation of later regional large scale cu au mineralization

late maastrichtian continental vertebrates from southwestern france correlation with marine fauna abstract the cassagnau locality marignac laspeyres haute garonne department has yielded the richest vertebrate assemblage of late maastrichtian age in western europe numerous bones can be referred to various fishes amphibians chelonians squamates crocodiles dinosaurs and birds some of which constitute the first late maastrichtian occurrences in europe a large varanoid lizard a longirostrine crocodile an enantiornithine bird or in southern france a titanosaurid dinosaur the latter discovery shows that at least five dinosaur families were represented in the late maastrichtian of western europe as for other localities of the french petites pyrenees the age of the cassagnau locality can be directly constrained by biostratigraphical and biochronological evidence based on associated marine and continental microfauna and microflora therefore the assemblages from these localities can be considered as reference assemblages for the continental late maastrichtian localities of southern europe the age of which has been much disputed

neoproterozoic high k granites produced by melting of newly formed mafic crust in the huangling region south china abstract the huangling igneous complex in the central yangtze block south china consists of the 850 ma tonalite and trondhjemite which were intruded by the 826 13 ma high k granite the granites are composed of plagioclase 30 60 alkali feldspar 10 30 quartz 20 30 biotite 2 63 1 73 3 wt k 2 o 2 58 4 79 wt and na 2 o 3 90 5 89 wt and low mgo 0 49 1 78 wt and are magnesian alkali calcic in composition their chondrite normalized ree patterns are characterized by enrichment of lree la yb n 14 5 32 8 and mostly negative eu anomalies eu eu 0 5 1 1 they have moderately high sr 202 698 ppm and low y 6 13 18 7 ppm with sr y ratios of 14 64 these large elemental variations probably resulted from fractional crystallization they also have negative whole rock nd 9 75 to 11 73 and zircon hf values 7 1 to 15 8 which are similar to those of the neoproterozoic mafic rocks in the same region suggesting that the granites may have been produced by melting of newly emplaced mafic rocks tonalites and trondhjemites of the huangling complex previously were considered as products by differentiation of water rich basaltic magmas and melting of the thickened archean continental crust in an arc setting respectively therefore the crustal growth and reworking of the yangtze block were probably wholly controlled by the subduction system which resulted in formation of the stable continent during the neoproterozoic

paleoproterozoic subduction related magmatism and crustal evolution of the dunhuang block nw china abstract the precambrian basement rocks of the tarim craton nw china occur mostly along the margins of the craton these rocks have been metamorphosed under amphibolite facies or granulite facies particularly in the dunhuang and kuluketage blocks whose crustal evolution and paleographic relationship are still unclear this study presents in situ zircon u pb ages and lu hf isotopes and whole rock elemental compositions for the paleoproterozoic meta felsic and mafic rocks in the ne altyn tagh area in order to constrain the paleoproterozoic tectono thermal events of the dunhuang block and to further investigate its relation to the kuluketage block the meta felsic rocks have a crystallization age of 1 96 ga their zircon ehf t values vary from 0 5 to 7 2 with tdm1 model ages from 2 4 to 2 1 ga suggesting that their parental magmas were mainly derived from juvenile sources with a relatively small contribution from pre existing ancient materials the meta felsic rocks have geochemical affinities with typical high al ttg generated by slab melting except for the extremely low cr ni ratios the steeply negative slope of their ree patterns indicates that garnet and or hornblende extraction was involved in the magma generation process the 2 06 meta mafic rocks have slightly variable positive ehf t values 0 to 3 4 corresponding to fairly uniform tdm1 model ages of 2 4 2 3 ga these results indicate that their parental magma was sourced mainly from juvenile components with minor old materials the meta mafic rocks have nearly flat ree patterns that bear a remarkably close resemblance to e morb but the depletion in nb ta zr hf and th is typical of arc rocks the wide range of zircon ehf t values from the meta felsic and mafic rocks indicates that the dunhuang block experienced both crustal growth and crustal reworking during the paleoproterozoic in both the dunhuang and kuluketage blocks plenty of early precambrian basement rocks experienced comparable magmatism and metamorphism however the dunhuang block has a crust formation age peaked at 2 83 ga and it experienced intensive tectono thermal events in paleoproterozoic these events are nearly absent in the kuluketage block the discrepancy implies that the dunhuang and kuluketage blocks were probably unrelated terranes before paleoproterozoic

asthenospheric and lower lithospheric mantle contributions to continental extensional magmatism an example from the british tertiary province abstract the compositions of palaeocene basic magmas in skye and mull british tertiary igneous province btip shed light on the general problem of the relative importance of lithospheric and asthenospheric mantle as sources of continental magmatism during extension after the effects of crustal contamination in some magmas have been detected and the samples showing it eliminated from consideration the remainder show a significant diversity of trace element compositions basic lavas from skye and mull which lack crustal contamination have contents of compatible and moderately compatible elements e g ni cr y yb and also of moderately incompatible elements e g ti p zr hf sr mree which are within the range shown by the tholeiitic and mildly alkalic ocean island basalts oib as from iceland in contrast their contents of strongly and very strongly incompatible elements e g k rb ba u th nb ta lree are within the range shown by normal mid ocean ridge basalts these btip magmas are interpreted as second stage melts from mantle which had already lost a very small melt fraction the latter is thought to be represented by the strongly alkalic permo carboniferous dyke swarms associated with rifting at that time in nw scotland residual uppermost asthenosphere from the late palaeozoic magma genesis event is postulated to have become attached to the thickening lithosphere beneath nw scotland and thus to have remained coupled to it throughout the mesozoic until reactivated by palaeocene stretching occasional hawaiites in the top third of the skye lava pile remnant and also basalt dykes of the swarm cutting the granites of the central complex the last significant magmatic event at this centre have the elemental characteristics of typical north atlantic oib notably la ta 10 12 these compositions are thought to demonstrate input from asthenospheric source basic magmas throughout the lithospheric source dominated skye and mull magmatism it is suggested that all the basic magmas in this province are ultimately derived from asthenospheric sources but that the larger magma batches became contaminated during uprise by melting and assimilating the most fusible parts of overlying lithospheric mantle followed by lower crust in many cases smaller magma batches traverse the overlying lithosphere with little or no contamination perhaps the difference between the two lies in their flow behaviour laminar or turbulent during uprise

mineralogy of polymetallic nodules and associated sediments from the central indian ocean basin abstract todorokite is the dominant mineral phase in the nodules of the northern central indian ocean basin these nodules are characterised by a rough surface texture are relatively rich in mn cu and ni and are associated with radiolarian sediments rich in montmorillonite chlorite and illite mno 2 is the dominant mineral phase in the nodules of the southern central indian ocean basin these nodules have a smooth surface texture are relatively rich in fe and co and are associated with pelagic clay sized sediments comprising keels of foraminifera zeolite and the clay minerals chlorite and illite the formation of these mineral phases and their composition in the nodules may have been controlled by the properties of associated sediments and the nucleus of the nodule does not influence the oxide layer mineralogy

mantle source magma differentiation and sulfide saturation of the 637ma zhouan mafic ultramafic intrusion in the northern margin of the yangtze block central china abstract the sill like zhouan mafic ultramafic intrusion in the northern margin of the yangtze block formed at 637 4 ma and consists of a lherzolite unit and an olivine gabbronorite unit with a marginal zone between the lower margin of the olivine gabbronorite unit and the underlying country rocks composed of marble and schist of the meso to neoproterozoic zhujiashan formation rocks from the lherzolite unit have 41 4 44 0 wt sio2 and 29 0 38 4 wt mgo and contain olivine with fo values ranging from 80 to 85 mole indicating crystallization from a moderately evolved magma they commonly have we propose that moderately evolved magmas may have reached sulfide saturation due to fractionation of olivine in a deep seated staging magma chamber forming an olivine laden crystal mush with minor sulfide droplets in the lower part and more evolved pge depleted magmas in the upper part of the chamber the evolved pge depleted magmas were forced out of the staging chamber and entered the shallow magma chamber to form the olivine gabbronorite unit the lherzolite unit formed from the emplacement of the olivine laden crystal mush into the same chamber because of paucity of extensive crustal contamination only minor amounts of sulfide segregation occurred in the olivine gabbronorite unit and the marginal zone the zhouan intrusion thus may not be a good target for economic ni cu sulfide deposit

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

paleoproterozoic mafic dike swarms of northeast laurentia products of plumes or ambient mantle abstract the occurrence of mafic dike swarms in archean and paleoproterozoic terranes is often cited as evidence for mantle plume activity associated with abnormally high mantle potential temperatures t p quantitative modeling of rare earth element ree abundances for the 2 04 ga kang miut dike swarm in west greenland and comparisons among other paleoproterozoic dike swarms in northeast laurentia indicates that the conditions for mantle melt generation were similar beneath much of laurentia and only ca 120 c hotter than present day ambient mantle t p ca 1300 c these thermal conditions correspond closely to estimates of ambient mantle potential temperatures during the paleoproterozoic era based on secular cooling models and continental freeboard constraints thus the geochemistry of most paleoproterozoic dikes of northeast laurentia can be accounted for by partial melting of upwelling mantle accompanying passive rifting and do not necessitate plume activity ambient mantle conditions during the paleoproterozoic t p ca 1420 c are similar to those inferred for the paleogene volcanic rift margins of the north atlantic igneous province where the rate of crustal production associated with early oceanic spreading was two to three times higher than at the modern ridge likewise rifting under ambient mantle conditions in the precambrian could have resulted in similar rates of crustal productivity and thus contributed significantly to continental growth

a type granite and adakitic magmatism association in songpan garze fold belt eastern tibetan plateau implication for lithospheric delamination abstract the songpan garze fold belt covers a huge triangular area 200 000 km2 confined by the south china yangtze north china and tibetan plateau continental blocks in the songpan garze fold belt triassic adakitic granitoids have been identified however whether there are triassic a type granites is unclear here we report our first finding of an a type granite nianbaoyeche which occurs in the central part of the songpan garze fold belt the nianbaoyeche granite 820 km2 is characterized by arfvedsonite in its mineral assemblage using both la icpms and tims u pb zircon dating methods we obtain a magma crystallization age of 211 1 ma which is slightly younger than triassic adakitic granitoids 216 221 ma in the songpan garze fold belt the nianbaoyeche granite is enriched in si k na rb ree hfse nb ta zr hf with elevated feotot feotot mgo and ga al ratios but is depleted in al mg ca ba and sr the ree compositions show moderately fractionated patterns with la yb n 2 67 7 54 and eu eu 0 09 0 34 these geochemical characteristics indicate that the nianbaoyeche granite has an a type affinity geochemical data and u pb zircon age combined with regional studies show that the nianbaoyeche granite formed in a post collisional tectonic setting sr nd isotopic data for the granite exhibit isr 0 7090 0 7123 and end t 2 72 to 4 26 with tdm 1 15 1 51 ga suggesting that the magma has a dominantly crustal source though a minor contribution from the mantle cannot be ruled out melting to produce an a type granite may have resulted from triassic lithospheric delamination after triassic crustal thickening of the songpan garze fold belt due to convergence between the yangtze north china and north tibet continental blocks the lithospheric delamination model also helps to explain the triassic adakitic magma generation in the songpan garze belt we conclude that association of a type granite and adakitic granitoids in post collisional environment could be a useful indicator of lithospheric delamination

origin of late triassic mafic ultramafic intrusions in the hongqiling ni cu sulfide deposit northeast china evidence from trace element and sr nd isotope geochemistry there are many late triassic mafic ultramafic intrusions in the hongqiling magmatic ni cu sulfide deposit northeast china research on magma evolution leading to formation of these mafic ultramafi

neoproterozoic tonalite and trondhjemite in the huangling complex south china crustal growth and reworking in a continental arc environment the huangling igneous complex in the central yangtze block of south china is composed of 850 ma tonalite and trondhjemite intruded by 820 ma granite tonalites mainly consist of plagioclase and quartz with abundant hornblende and biotite and contain fine to coarse grained hornblende rich igneous enclaves they have variably low sio2 56 4 67 5 wt and sr 230 517 ppm and high mgo 1 47 4 02 wt and high y 8 87 15 7 ppm with low sr y 17 43 unlike archean tonalites their whole rock end values range from 8 3 to 10 3 and zircon ehf values from 3 9 to 12 6 similar to those of spatially associated neoproterozoic mafic rocks the tonalites are thus proposed to have been produced by three stages involving partial melting of subduction modified lithospheric mantle 5 to 20 percent crustal contamination of hydrous basaltic magmas in the middle to lower crust and fractional crystallization of amphibole plagioclase biotite magnetite trondhjemites are composed of plagioclase quartz and alkali feldspar with minor biotite and hornblende they have high sio2 67 3 75 6 wt and sr 340 840 ppm and low mgo 0 09 0 78 wt and y 4 8 11 2 ppm with high sr y 32 162 similar to archean trondhjemites and high pressure partial melts of mafic rocks these rocks have extremely negative end 18 7 to 19 9 and zircon ehf values 18 9 to 49 2 with two stage hf isotope model ages of 2 46 to 3 90 ga indicating their formation in the lower crust by melting of archean amphibolites and granulites which were probably widely distributed beneath the yangtze block their highly variable chemical compositions also resulted from fractional crystallization of plagioclase hornblende biotite thus the association of the tonalite and trondhjemite is different from the archean ttg series this difference may reflect different geothermal gradients however modeling using tonalitic and trondhjemitic samples of the huangling complex suggests that mixing of the two magmas can generate a typical ttg affinity series suggesting that the origin of some ttg series may have involved both crustally derived and mantle derived melts the generation of the huangling igneous complex was linked to slab subduction beneath the northern margin of the yangtze block during the neoproterozoic similar to the cenozoic arc magmatism in the andes therefore melting of metasomatized hydrous mantle in arc settings can generate mafic magmas that not only under plated and contributed to continental crustal growth but also caused melting of thickened ancient crust and newly formed lower mafic crust

zircon u pb ages hf o isotopes and whole rock sr nd pb isotopic geochemistry of granitoids in the jinshajiang suture zone sw china constraints on petrogenesis and tectonic evolution of the paleo tethys ocean the jinshajiang suture zone located in the eastern part of the tethyan tectonic domain is noticeable for a large scale distribution of late jurassic to triassic granitoids these granitoids were genetically related to the evolution of the paleo tethys ocean beiwu linong and lunong granitoids occur in the middle zone of the jinshajiang suture zone and possess similar geochemical features indicating that they share a common magma source sims zircon u pb dating reveals that the beiwu linong and lunong granitic intrusions were emplaced at 233 9 1 4 ma 2 233 1 1 4 ma 2 and 231 0 1 6 ma 2 respectively all of these granitoids are enriched in abundances of si sio2t 65 2 73 5 wt and large ion lithophile elements liles but depleted in high field strength elements contents hfses e g nb ta and ti in addition they have low p2o5 contents 0 06 0 11 wt a cnk values molecular al2o3 cao na2o k2o mostly 1 1 and 10 000 ga al ratios 1 7 2 2 consistent with the characteristics of i type granites in terms of isotopic compositions these granitoids have high initial 87sr 86sr ratios 0 7078 0 7148 pb isotopic compositions 206pb 204pb t 18 213 18 598 207pb 204pb t 15 637 15 730 and 208pb 204pb t 38 323 38 791 zircon 18o values 7 3 9 3 and negative end t values 5 1 to 6 7 suggesting they were predominantly derived from the continental crust their nb ta ratios average value 8 6 are consistent with those of the lower continental crust lcc however variable ehf t values 8 6 to 2 8 and the occurrences of mafic microgranular enclaves mmes suggest that mantle derived melts and lower crustal magmas were involved in the generation of these granitoids moreover the high pb isotopic ratios and elevated zircon 18o values of these rocks indicate a significant contribution of the upper crustal composition we propose a model in which the beiwu linong and lunong granitoids were generated under a late collisional or post collisional setting it is possible that this collision was completed before late triassic decompression induced mantle derived magmas to be underplated and provided the heat for the anatexis of the crust hybrid melts including mantle derived and the lower crustal magmas were then generated the hybrid melts thereafter ascended to a shallow depth and resulted in some degree of sedimentary rock assimilation such three component mixing magma source and subsequent fractional crystallization could be responsible for the formation of the beiwu linong and lunong granitoids

the diversity of sauropod dinosaurs and their first taxonomic succession from the latest cretaceous of southwestern europe clues to demise and extinction article i nfo southwestern europe is a key setting to evaluate the diversity of non avian dinosaurs before the end of the cretaceous below the k pg boundary the ancient ibero armorican island encompassing the current regions of north east iberia and south france provides a substantial record of sauropod fossils the study of multiple sauropod femora from localities where upper campanian to uppermost maastrichtian successions are both exposed together with the integration of the information gathered from previously known localities has allowed the biodiversity of sauropods to be reassessed within a precise and clear chronostratigraphic framework from the studied sample several titanosaur forms have been distin guished including a gracile and small sized titanosaur lirainosaurus astibiae a robust medium sized titanosaur ampelosaurus atacis a gracile medium sized titanosaur atsinganosaurus velauciensis and five other indeterminate but distinct titanosaurs which span the late campanian through the entire maastrichtian the youngest of these occurs in the uppermost part of palaeomagnetic chron c30n in the latest maastrichtian 0 4 1m a before the k pg boundary representing the youngest sauropod yet doc umented in eurasia the pattern of diversity on the ibero armorican island rules out a decline in sauropod diversity at the very end of the cretaceous as with other regions during the late cretaceous the abundance and quality of the sauropod fossil record is probably influenced by multiple biases sampling ecological and environmental

neoproterozoic quartz monzodiorite granodiorite association from the luding kangding area implications for the interpretation of an active continental margin along the yangtze block south china block abstract neoproterozoic magmatism along the western margin of the yangtze block can provide important information about the evolution of the supercontinent rodinia for this reason this study is focused on neoproterozoic high mg quartz monzodiorite and granodiorite from the luding kangding area detailed zircon la icp ms u pb dating indicates that the high mg quartz monzodiorite and the granodiorite have identical ages of 754 10 ma mswd 0 51 2 and 748 11 ma mswd 0 33 2 respectively the high mg quartz monzodiorite are characterized by low sio2 contents 60 76 63 78 and high tio2 contents 0 41 0 56 and they are sodic and meta aluminous they are enriched in lree with la yb n values of 4 14 8 51 and without significant negative eu anomalies eu eu 0 79 0 92 the high mg quartz monzodiorite have relative low initial 87sr 86sr i ratios of 0 703513 0 704519 and positive nd t values of 2 4 to 4 8 and are depleted in hfses nb and ta thus it can be inferred that these high mg quartz monzodiorite were formed by high degree 40 partial melting of newly formed mafic lower crust and that their high mg values were the result of assimilation of some residual mafic minerals in their source region the granodiorite are characterized by higher sio2 contents 65 32 67 59 and they are also sodic and meta aluminous they have more evolved sr nd isotopic compositions and higher sr 425 537 ppm and ba 705 1074 ppm contents than the quartz monzodiorite suggesting that they were derived from a plagioclase rich source region based on their field occurrence and geochemical features we propose that both the neoproterozoic high mg quartz monzodiorite and the granodiorite were formed in an active continental arc setting but they derived from two distinct source regions

sequential leaching of marine ferromanganese precipitates genetic implications abstract sequential leaching experiments were carried out on twenty one hydrogenetic crust samples from different locations in the central pacific and the results are compared with four crust and nodule samples of different genetic origin fe vernadite mno2 is the most important minor and trace metal bearing mineral phase and shows high concentrations of co ni cd ti ba zn and cu which are present in seawater mainly as hydrated and labile complexed cations elements forming carbonate and hydroxide complexes and oxyanions in seawater like pb mo v and minor proportions of cu and zn are bound in the fe00h fraction the ca carbonate phase and the residual fraction which consists of aluminosilicates and crystalline oxides show only minor heavy metal associations e g cu and zn only a small part of the high ti concentrations in hydrogenetic crusts is of detrital origin ti mainly forms a hydrogenetic phase probably consisting of ti02 2h20 intergrown with the amorphous fe00h phase analyses of different sample types and crust layers show that aging and diagenetic effects can change the phase associations of some elements the most notable change was observed for pb which during phosphatization of crusts is transferred from the mn fe oxide fraction to the apatite fraction a colloid chemical model for the hydrogenetic precipitation of ferromanganese crusts on seamounts is proposed in the first stage mn2 rich water from the oxygen minimum zone is mixed with oxygen rich deep water and oxidized mn iv and other metals like fe ti al and si form oxide and hydroxide colloids these form mixed colloidal phases and scavenge trace metals by sorptive processes which are dominated by coulombic and chemical interactions between colloid surfaces and dissolved metal species in stage two the colloidal phases precipitate on the substrate rocks of the seamounts as ferromanganese oxide encrustations incorporating the sorbed heavy metals into the mineral phases

neoproterozoic arc related mafic intrusions along the northern margin of south china implications for the accretion of rodinia abstract south china has been considered as part of the rodinian supercontinent during neoproterozoic time although its paleogeographic position within this supercontinent is still a matter of debate the wangjiangshan and bijigou complexes along the northern margin of south china are among the largest mafic intrusions in china new shrimp zircon u pb results indicate that these two intrusions have crystallization ages of 820 ma and 780 ma respectively enrichment of large ion lithophile and light rare earth elements and depletion of high field strength elements in these intrusions suggest derivation from an active arc along a continental margin this interpretation of these intrusions as part of a continental arc assemblage is in contrast with the previous view that they were products of a neoproterozoic mantle plume that initiated the breakup of rodinia the presence of a neoproterozoic magmatic arc suggests that rodinian oceanic lithosphere was subducted beneath the present northern margin of south

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

geochemistry of neoarchean mafic volcanic rocks and late mafic dikes in the zanhuang complex central orogenic belt north china craton implications for geodynamic setting abstract an archean melange belt has been recognized in the zanhuang complex central orogenic belt cob north china craton ncc all units of the melange belt are intruded by a ca 2 5 ga granite pluton and cross cut by undeformed 2 5 ga pegmatites which constrains the archean formation age of the melange some exotic mafic ultramafic blocks are tectonically dispersed in the metasedimentary matrix to the melange and mainly consist of metabasaltic rocks deformed pillow lavas with epidosite cores gabbros and ultramafic rocks both metabasalts and epidosites are characterized by enrichment in light rare earth elements lree and pronounced negative nb and zr anomalies on chondrite and primitive mantle normalized diagrams these geochemical characteristics are consistent with supra subduction zone geochemical signatures based on the pillow structures and seafloor hydrothermal alteration combined with the geochemical characteristics an intra oceanic arc forearc setting is proposed for the formation of these exotic blocks furthermore a west dipping intra oceanic subduction zone is proposed to have formed in an ocean between the eastern block and an arc terrane prior to 2 5 ga the collision between the arc and the eastern block of the ncc happened at ca 2 5 ga resulting in the formation of the archean melange belt in the zanhuang complex all of the units of the melange belt were intruded by late mafic dikes which are present as boudinaged or lenticular shapes in the melange and surrounding gneisses and are intruded by younger ca 2 5 ga pegmatites geochemical characteristics of the late mafic dikes are consistent with an arc related mantle source region rather than an oib like source accordingly pending determination of their precise age an arc polarity reversal event is proposed to have occurred following the arc continent collision resulting in east dipping subduction beneath the newly accreted arc and eastern block forming the swarm of arc affinity mafic dikes the new subduction zone further resulted in ponded magma below the accreted arc block which induced the partial melting of thickened crust and the intrusion of ca 2 5 ga granitic and pegmatitic melts into the melange and the mafic dikes the mafic dikes were then deformed and metamorphosed when the remaining open part of the ocean between the arc collision modified margin of the eastern block collided with the western block of the ncc

depositional setting and early diagenesis of the dinosaur eggshell bearing aren fm at bastus late campanian south central pyrenees the late cretaceous aren fm exposed north of bastus in the tremp basin south central pyrenees preserves an excellent record of dinosaur eggs laid in a marine littoral setting different from other cases reported in literature at the bastus site the preferential nesting ground was original beach sand the coastal deposits of aren fm can be grouped into four facies assemblages representing respectively shoreface beachface beach ridge plain and backbarrier lagoon environments shoreface deposits include fine to coarsegrained hybrid arenites and subordinate quartz dominated conglomerates with ripple structures of wave and wave current origin beachface deposits are mainly storm beach conglomerates but parallel laminated foreshore arenites locally occur backbarrier lagoon deposits comprise of washover sandy conglomerates that grade laterally into sandy lime mudstones biomicrites and marls beach ridge sediment wherein the bulk of dinosaur eggs and eggshell debris occurs predominantly is a reddish hybrid arenite that has undergone a complex early diagenetic evolution including marine and meteoric cementation followed by soil development the reddish arenites overlie wave dominated shoreface deposits and in places pass laterally into lagoonal deposits they originally formed shore ridges that became stabilized during progradational episodes by pedogenesis beach ridge sensu otvos e g 2000 beach ridges definitions and significance geomorphology 32 83 108 which also affected the dinosaur eggs the eggshell bearing beach ridge arenites are typically preserved at the top of parasequences forming the systems tracts of a third order sequence thick packages of this facies resulted from aggradation of barrier beach ridge deposits whose preservation below surfaces of transgressive erosion was favoured by incipient lithification

trace element and isotope characteristics of cenozoic basalts around the tanlu fault with implications for the eastern plate boundary between north and south china a reply abstract cenozoic intraplate basalts in eastern china show variations of pb sr and nd isotope ratios that essentially correspond to major lithospheric domains with distinct tectonic histories whereas an enriched mantle em1 type isotope signature is commonly observed in basalts from the north china block an em2 type isotope signature appears to dominate in those from the south china block this study reports new trace element data for cenozoic basalts occurring around the tanlu fault zone a sinistral translithospheric fault related to the triassic continental collision between the north and south china blocks combining published isotope data basalts from the subei basin in the east of the tanlu fault exhibit the em1 type geochemical and isotopic features implying that their lithospheric mantle source region is structurally affiliated with the north china block this is consistent with the crustal detachment collision model that suggests a subsurface suture between the north and south china blocks

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

slab breakoff a model for caledonian late granite syn collisional magmatism in the orthotectonic metamorphic zone of scotland and donegal ireland abstract none of the existing models for calc alkaline late granite siluro devonian genesis in the metamorphic caledonian orogenic belt of ireland and scotland fully explains their spatial age or chemical character a consistent model must involve the closure of iapetus ocean where slab breakoff is a natural consequence of attempted subduction of continental crust expected outcome is a long linear belt of high k calc alkaline magmas some with characteristic trace element signatures specifically high ba sr and zr other features include the critical magmatic association of coeval appinite and granite rapid uplift erosion and the low grade regional metamorphism in the southern uplands the linear heat pulse on breakoff is spatially intensity and time limited producing small volume melts emplaced as separated plutons over a short time span magmatism in the caledonian metamorphic belt is accurately accounted for by slab breakoff on collision of baltica with the scoto greenland margin during the scandian orogeny following iapetus ocean closure the two chemically isotopically and areally distinctive suites in the metamorphic belt in scotland viz the argyll and cairngorm suites can be modelled by reference to the donegal granites where sequential partial melting of new lamprophyric underplated crust then shallower old crust as heat conduction moved up through the crust on slab breakoff produced magmas characteristic of the two suites

geochemistry of polymetallic nodules from the central indian ocean basin abstract polymetallic nodules dredged at fourteen stations between 12 15 s and 76 80 e in the central indian ocean basin ciob display wide variations in shape size texture mineral phases and chemical composition among the thirteen different types of nodules present only spherical and ellipsoidal nodules ranging in size from in the ciob the nodules of a particular size range have common morphological mineralogical and chemical properties compared to the larger nodules the smaller nodules are enriched in mn cu and ni have higher growth rates and higher cu ni ce la and ce fe ratios and todorokite as the major mineral phase the smaller nodules also show enrichment in heavy rees and exhibit a negative ce anomaly comparison of the average cu ni co content in the different sized nodules indicates that only smaller nodules have grades 2 61 3 04 for nodules different sized nodules from the ciob suggest formation at different places and indicate movement due to bottom currents from the place of formation to the deeper water regions three models are suggested to explain the observed morphological mineralogical and geochemical variations with respect to nodule size 1 in the ccd model the smaller nodules 4 cm which have high fe and moisture and low todorokite contents are formed mainly by hydrogenesis 3 the mixing model indicated shifting of the smaller nodules formed close to the ccd to deep sea regions and mixing with larger nodules formed from hydrogenous precipitation

geochemistry and geochronology of carboniferous volcanic rocks in the eastern junggar terrane nw china implication for a tectonic transition the carboniferous tectonic setting of the junggar terrane northern xinjiang nw china has long been a matter of debate voluminous carboniferous volcanic rocks are widely distributed in the karamaili area the southern part of the eastern junggar terrane early carboniferous rocks comprise basalts and basaltic andesites with enrichment of lree and lile and depletion of hfse and uniformly high end t 3 7 to 4 0 late carboniferous rocks consist of basalts basaltic andesites rhyolites and minor dacites and can be subdivided into basic and felsic groups the basic rocks are depleted in hfse and show variable high end t 4 8 to 6 9 they have higher cr and ni and lower na2o u and th contents than early carboniferous basic rocks the felsic rocks show a type affinity with typical enrichment of alkalis lree and hfse and strong depletion in ba sr eu and ti they have high values of end t and zircon ehf t 11 6 to 17 9 new la icpms zircon u pb analyses constrain their emplacement to late carboniferous time 306 5 314 3 ma the carboniferous basic rocks show negative zr hf anomalies and low th ce 0 07 and th la 0 06 0 16 excluding significant crustal contamination during magma evolution they have low la ba 0 03 0 12 ce y 3 and tb yb n 2 and variable ba th 28 318 and ba la 3 1 34 suggesting that they were derived from a main spinel with minor garnet lherzolite mantle source metasomatized by slab derived fluids the late carboniferous felsic rocks were produced when upwelling asthenosphere triggered partial melting of juvenile lower crust the early carboniferous volcanism occurred in an island arc setting related to the southward subduction of the paleo junggar ocean plate whereas the late carboniferous rocks erupted in a post collisional extensional setting thus a rapid tectonic transition from arc to post collisional extension may have occurred between early and late carboniferous and probably resulted from slab break off or lithospheric delamination

the flaw in the crustal zircon archive mixed hf isotope signatures record progressive contamination of late stage liquid in mafic ultramafic layered intrusions

distribution des terres rares dans les fractions de sediments et nodules de fe et mn associes en l ocean indien abstract the ree distribution in size fractions of sediments and associated ferromanganese nodules from the indian ocean was studied bulk sample patterns of sediments result from the combination of coarsest fractions depleted in ce and fine fractions enriched in ce ce depletion of the coarsest fractions is related to biogenic silica on the contrary ree distribution patterns of fine fractions are closely similar to those of associated ferromanganese nodules the ce excess in fine fractions is probably of continental origin but it could also be derived from submarine weathering of volcanic glass or related to ce oxydation in the marine environment in fine fractions ce is probably in its tetravalent state hence it can easily be scavenged by fine clays and oxyhydroxydes trivalent ree can be incorporated in nodules partly by occlusion of fine clays or oxyhydroxydes and partly by surface to surface transfer as was proposed by ehrlich 1968 comparison between ree patterns of fine sized fractions nodules and seawater also supported adsorption as a possible mechanism governing the incorporation of ree of sediments and nodules from seawater light ree are probably incorporated as oxyhydroxyde complexes whereas heavy ree are markedly fractionated with increasing atomic number this fractionation reflects the complexed form of the heavy ree in seawater

the longmenshan tectonic complex and adjacent tectonic units in the eastern margin of the tibetan plateau a review abstract the longmenshan tectonic complex lstc along the eastern margin of the tibetan plateau the site of devastating earthquakes such as the magnitude 8 0 wenchuan earthquake on 12 may 2008 preserves an exceptionally complete history of the tectonic evolution of the yangtze block and its relations to adjacent tectonic units due to sequential tectonic superposition and tectonic reactivation the tectonic nature of the lstc and in particularly the older history has been profoundly debated and many different tectonic models have been proposed herein we summarize the current understandings of the major tectonic events that have shaped this important tectonic complex highlighting problems left to be solved by future work including 1 the nature and constraints for at least 6 regional tectonic events i e building of the metamorphic basement art the columbia nuna supercontinent pt1t the rodinia supercontinent pt3t the paleozoic passive continental margin pzt the paleotethys orogeny mzt and the neotethys orogeny kzt 2 metamorphic basement exposures and their tectonic implications including rock types and geochronological constraints for the archean paleoproterozoic and neoproterozoic basements 3 nature of the present lstc and its affinity with adjacent tectonic units 4 consideration of the ne striking longmenshan thrust belt and arcuate shape yanyuan muli thrust belt as parts of a single tectonic feature 5 mountain basin coupled systems recording past tectonic eposides we draw the following conclusions and tectonic models based on published research combined with our own recent studies 1 the well preserved archean yudongzi gneiss group in the lstc has a genetic affinity with the kongling group and thus belongs to the yangtze block 2 the paleoproterozoic hejiayan group juxtaposed adjacent to the archean yudongzi group may represent a 2000 1800 ma orogenic belt which corresponds to the supercontinent nuna columbia amalgamation event 3 a neoproterozoic trench arc basin system which is reconstructed based on identification of a neoproterozoic ophiolite complex arc type magmatic rock assemblages and volcaniclastic basinal deposits along the western margin of the yangtze block and the lstc may represent the record of eastward subduction of the neoproterozoic mozambique oceanic lithosphere beneath the yangtze block during the assembly of the rodinia supercontinent 4 a complete bidirectional wilson cycle was reconstructed by the formation of the late permian to the middle late triassic back arc ganze litang rift and ocean following the early paleozoic mianlue continental rift and ocean and subsequent closure of the ocean basin by simultaneous bidirectional northward and southwestward subduction and later collision this relatively uncommon bidirectional wilson cycle might be attributed to the formation of the three armed rift system in the eastern paleotethys associated with the late permian eemeishan large igneous province in the lstc 5 a three stage tectonic sequence of in sequence imbricate thrust in the lstc during india eurasian collisional orogeny at 55 15 ma extrusion from 15 to 5 ma and the plateau uplift since 5 ma resulting from lower crustal channel flow is proposed for the formation of the present lstc

the yanbian terrane southern sichuan province sw china a neoproterozoic arc assemblage in the western margin of the yangtze block abstract the magmatic and tectonic history of the yangtze block and its possible affinity with other neoproterozoic arc terranes are important elements in the reconstruction of neoproterozoic plate tectonics the yanbian terrane in the western margin of the yangtze block is a typical arc assemblage composed of a flysch type sedimentary sequence intruded by gabbroic and granodioritic plutons the sedimentary sequence consists chiefly of tuffaceous material with interlayered chert sandstone and pillow basalts laser ablation icp ms u pb dating of detrital zircons from the sandstones yield ages as young as 840 ma the gaojiacun and lengshuiqing mafic intrusions are dated at 812 3 ma and 806 4 ma respectively using the shrimp zircon u pb technique geochemical data show that both the gaojiacun and lengshuiqing intrusions have arc signatures with nd t values of 1 5 to 6 0 initial 87 sr 86 sr ratios of 0 705 0 706 and pronounced negative nb ta and zr hf anomalies their geochemical variations are best explained by fractional crystallization without major crustal contamination the yanbian terrane represents a typical arc assemblage formed on the western edge of the yangtze block during neoproterozoic time the sedimentary sequence was deposited in an oceanic setting probably in a back arc basin environment the depleted subduction modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized this scenario suggests subduction of oceanic lithosphere eastward present day orientation underneath the yangtze block

local variability of manganese nodule facies on small abyssal hills of the central pacific basin abstract local variability of manganese nodule facies and associated sediments were studied around abyssal hills 60 60 km 2 located in the equatorial zone of the central pacific basin small scale variations in nodule occurrence mineralogy chemistry and internal structure are discussed in relation to seismic records and sediment lithology the slow sedimentation rate from the late tertiary to the quaternary appear to have promoted formation of nodules around the abyssal hills although the plio pleistocene hiatus at depths below sediment surface suggests no clear evidence of increased growth of nodules during the period in the area of rapid and continuous sedimentation away from the hill areas nodules are rare probably because of insufficient lifting force for nodules mineralogical and chemical studies reveal that the two principal nodule morphologies smooth and rough surfaces result from preferential deposition of hydrogenous or diagenetic manganese minerals in relation to early diagenesis of surface siliceous sediments regional variability of nodule surface morphology and composition suggests a very local change in sedimentary conditions in space and internal mineral variation suggests changes in sedimentary conditions with time the geological factors controlling the small scale variability of nodule facies seem to be similar to those controlling regional scale variations

early neoproterozoic assembly of the yangtze block decoded from metasedimentary rocks of the miaowan complex abstract the present yangtze block was proposed to be formed as a unified block in the mesoproterozoic neoproterozoic transition but the detailed timing and process are poorly constrained here we report integrated in situ u pb and hf o isotopic analyses of detrital zircons from the xiaoxikou metamorphosed sedimentary rocks of the miaowan complex in the yangtze block as well as u th pb and nd o isotopic analyses of magmatic monazites from an undeformed and unmetamorphosed leucocratic vein intruding these metasedimentary rocks u pb dating results for detrital zircons from the metasedimentary rocks display two main age peaks at ca 970 and 900 ma the 970 ma zircons are dominantly characterized by mantle like 18ozir values 4 5 5 8 and highly depleted ehf t values 5 to 14 the 900 ma zircons mostly have o and hf isotopic features similar to the 970 ma zircons except relative small proportion of grains with high 18o values 6 0 9 2 and variable ehf t values 33 to 7 monazites from the vein are dated at ca 850 ma and have uniform 18o values 5 4 6 6 but significantly enriched end t values 14 5 to 12 6 based on the new isotopic results and immature lithology the xiaoxikou metasedimentary rocks are interpreted to be deposited between 900 ma and 850 ma in a fore arc basin and clastic materials derived from 970 900 ma arc rocks were related to the northward subduction present day coordinates of the miaowan oceanic plate the 850 ma leucocratic vein shows geological and isotopic characteristics consistent with local 860 840 ma post tectonic granitic plutons and may represent a fractionated product of local coeval granitic magmas we propose that the closure of the miaowan oceanic basin and formation of the current unified yangtze block occurred between 900 ma and 860 ma i e later than the deposition of the fore arc metasedimentary rocks while earlier than the emplacement of the post tectonic plutons

variability of mn fe ni cu and co in manganese nodules from the central indian ocean basin abstract the trace element variations in manganese nodules from the central indian ocean basin have been related to the underlying sediment type percentages of mn cu and ni are high in nodules occurring in siliceous sediments compared with nodules from the red clays which contain higher fe and co clustering of analyses shows that ni and cu are geochemically associated with mn and co with fe in both sediment types however the degree of correlation between all the elements is higher in the nodules from red clay sediments compared to the siliceous ooze area nodules similarly there is an increase in the ni and cu values and a decrease in co content with increasing mn fe ratio but the scatter plot of the elements from the red clay sediments show more linearity than the siliceous sediments where the plots are more scattered the variations in the mn fe ratio reflect variability in the composition of bottom water which in turn influences the type of underlying sediments and supply of metal to the deposits the higher concentrations of mn ni and cu in the nodules from siliceous sediments reflect the influence of early diagenesis of the biogenic components whereas the higher fe and co contents in the nodules occurring in red clay areas are a result of their precipitation as authigenic oxyhydroxides

contrasting geochemical and sm nd isotopic compositions of archean metasediments from the kongling high grade terrain of the yangtze craton evidence for cratonic evolution and redistribution of ree during crustal anatexis abstract twenty three clastic metasediments from the kongling high grade terrain of the yangtze craton south china were analyzed for major trace and rare earth elements and sm nd isotopic ratios associated dioritic tonalitic trondhjemitic dtt and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance the results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical geochemical and sm nd isotopic compositions group a is characterized by having no to slight negative eu anomalies eu eu 0 82 1 07 being high in cr 191 396 ppm and ni 68 137 ppm and low in th 3 3 7 8 ppm and ree ree 99 156 ppm these characteristics are similar to those of metasediments from archean greenstone belts in addition the group a metasediments have the value of the chemical index of alteration ciw close to felsic gneisses their sm nd isotopic ree and trace element compositions can be interpreted by mixtures of the dtt gneisses and amphibolites dating of detrital zircons from 2 group a samples by shrimp reveals a major concordant age group of 2 87 3 0 ga which is identical to the age of the trondhjemitic gneiss these results strongly suggest that group a was principally the first cycle erosion product of the local kongling dtt gneiss and amphibolite moreover the higher than amphibolite cr content and slight eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3 0 3 3 ga in age also played a role group b is characterized by the presence of graphite and shows a more evolved composition similar to post archean shales with a prominent negative eu anomaly eu eu 0 48 0 77 and high ciw on paired cr th vs la co and co th plots group b samples conform to a two end member mixing line of the kongling granitic gneiss and amphibolite however data on nd model age and ciw suggest that the granite component should be younger than the sampled granitic gneiss and derived from a distal source both groups a and b exhibit a clear positive correlation between ciw and tdm and a negative one between ciw and eu eu these correlations point to the crustal evolution of the yangtze craton towards coupled increasing ciw and eu depletion with decreasing age this in turn reflects the change of granitoid magmatism from local na rich dioritic tonalitic trondhjemitic rocks to widespread k feldspar granite the change led to the intracrustal differentiation stabilization and growth of the craton group c is restite and contains abundant sillimanite and garnet and unusually high ilmenite 7 11vol which can be seen to be dehydration melting products of biotite under the microscope this group shows extremely varied ree distributions from lree enriched to depleted and from negative to strong positive eu eu 1 63 eu anomalies compared to groups a and b group c is severely depleted in na2o k2o lree rb and ba whereas tio2 co v sc and hree and y are considerably enriched this is accompanied by anomalous high sm nd 0 21 0 28 147sm 144nd 0 1361 0 1738 and 143nd 144nd 0 511589 0 511958 ratios tdm correlates clearly with sm nd ratio and 2 out of 3 samples give significantly older to unrealistic tdm 3 9 4 9 ga the results document redistribution of ree and an open behavior of the sm nd isotope system during the biotite dehydration melting of metasediments

petrogenesis of early cretaceous alkaline dolerite dykes in the dabie orogen china constraints on the timing of lithospheric thinning abstract the dabie orogen in central china has long been proposed to transform from triassic compression related to northward deep subduction to late jurassic to early cretaceous extension involving marked crustal thinning and doming processes zircon u pb ages mineral chemistry and whole rock geochemistry of alkaline dykes intruding early cretaceous intermediate mafic ultramafic complexes are presented herein to provide evidence for the timing of lithospheric thinning and extension these dykes of dominantly dolerites with minor monzodiorites have zircon u pb ages of 128 3 129 7 ma and are characterized by sr nd isotopic ratios around the enriched mantle i the dolerites can be divided into two groups with the first group having lower incompatible elements but more enriched sr nd isotopes than the second group equilibrium partial melting and isotopic mixing modeling show that the dolerites were first generated from partial melting of a heterogeneous enriched mantle at different degrees and then experienced fractional crystallization and crustal assimilation systematic normative minerals trace elements and isotopic contrasts of early cretaceous gabbros 125 130 ma dolerite dykes of this study and early cretaceous mafic dykes 111 115 ma indicate that the source regions for the dolerites are deeper than those for the host gabbros therefore the lithospheric mantle thickening probably continued until the formation of the dolerites and the lithospheric mantle thinning occurred significantly later than previously proposed the thickness of the lithosphere was more than the depth range for the source region of alkaline basalts at 125 130 ma but changed to less than that for the source region of tholeiitic basalts before 115 ma suggesting a minimum decrease of 20 km within 10 m y this rate of thinning can be explained only by delamination of voluminous crustal root with the underlying lithospheric mantle between 125 and 115 ma

magnetostratigraphy and biostratigraphy of cretaceous tertiary continental deposits ager basin province of lerida spain abstract at fontllonga northeast spain province of lerida a nearly continuous outcrop covers the stratigraphic interval from the maastrichtian to the thanetian in continental deposits magnetostratigraphy of the section was determined from 72 samples the magnetic polarity sequence was satisfactorily correlated with chrons 32r to 26r top of lower maastrichtian to lower thanetian chron 29r in which the k t boundary occurs is unambiguously recognizable considering the biostratigraphic data charophyte ostracod palynomorph the k t boundary occurs in the uppermost part of the microchara cristata subzone which includes late cretaceous and early palaeocene species this subzone is interpreted as an interval of crisis following the late maastrichtian extinctions and preceeding the palaeocene radiation no ir rich horizon has been yet found in this section the stratigraphic position of the last dinosaur remains found in the chron 31n interval leaves open the question of a causal link between the extinction of cretaceous reptiles and the k t event

the bear river dykes 1265 1269 ma westward continuation of the mackenzie dyke swarm into yukon canada abstract the 1 27 ga mackenzie dyke swarm the largest on earth radiates from a point in the western canadian arctic and extends across much of the canadian shield possible western extensions of the swarm are largely obscured by younger sedimentary cover paleoproterozoic inliers in northern yukon host the bear river dykes brd herein dated by u pb baddeleyite and zircon methods at 1268 5 1 5 ma and 1264 6 1 2 ma the brd share similar geochemical and nd isotopic characteristics with the mackenzie dykes and the coeval coppermine river basalts and are regarded as products of the same plume hydrothermal activity at 1270 ma in breccia of the nor mineral occurrence northwest of the brd was probably generated by brd at depth the brd generally strike northwest approximately 90 to the orientation predicted by the radiating dyke model this difference may be explained by an anomalous local stress field at the time of brd emplacement or reorientation of brd during subsequent events of cordilleran deformation using the nor mineral occurrence as the westernmost locale of mackenzie dyking and assuming a model of uniform dyke radiation the arc of the mackenzie swarm is at least 50 greater than previously recognized bringing the total arc of dyke radiation to 150

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

two episodes of paleoproterozoic mafic intrusions from liaoning province north china craton petrogenesis and tectonic implications abstract mafic dyke swarms constitute a common occurrence within the cratonic provinces in the world since the archean proterozoic boundary and their geneses harbor critical information for facilitating regional tectonic and supercontinental reconstruction this zircon u pb dating and geochemical study documents two episodes of paleoproterozoic mafic intrusions from liaoning province north china craton ncc the haicheng suite hcs with an emplacement age of ca 2125 ma from the liaodong peninsula and the guohua suite ghs with an age of ca 1816 ma from the western liaoning terrane the hcs meta gabbros are tholeiitic in composition with an sio 2 range from 46 to 52 modest enrichment in light rare earth elements lree and depletion in high field strength elements hfse and possess radiogenic whole rock nd nd t 1 91 to 4 21 and zircon hf hf t 4 02 to 8 48 isotopic compositions these features endow the hcs with a juvenile subduction fluid metasomatized lithospheric mantle source by contrast the ghs exhibits a meta gabbroic to dioritic composition and a transitional character from tholeiitic to calc alkali with variably enriched lrees and more evolved isotopic signatures nd t 0 20 to 5 82 zircon hf t 0 09 to 4 91 than the hcs while the relatively intact high fe gabbroic samples are supposed to represent partial melts from a fertile cratonic sub continental lithospheric mantle source in the garnet spinel stability field the low fe dioritic ones tend to bear the imprints of subsequent assimilation and fractional crystallization process apart from making an important contribution to the present archive of the paleoproterozoic mafic dyke swarms in the ncc the present two mafic magmatic suites witnessed a shift in tectonic setting from a subduction related continental arc environment to a post orogenic extensional regime synthesizing two suites with coeval felsic igneous episodes as well as concomitant episodic metamorphic events in the jiao liao ji belt leads to the characterization of a possible divergent double subduction system in the eastern ncc during the time span of ca 2 2 1 80 ga synchronized beating of episodic magmatic and metamorphic pulses in the constituent mobile belts of the ncc carries further implication of attesting to the ubiquity and importance of divergent double subduction system in the cratonic amalgamation and its incorporation within the supercontinent columbia

palaeomagnetism of the upper cretaceous sânpetru formation haţeg basin south carpathians abstract this paper reports on the palaeomagnetism of 10 localities from upper cretaceous sediments of the s npetru formation exposed in the ha eg basin south carpathians romania the s npetru formation is one of the best exposed latest cretaceous continental successions of eastern europe being famous for its unique assemblage of dinosaurs mammals and other vertebrates a total of 169 samples were collected from 66 strata through an 860 m thick section for most of the samples the remanences were soft and or noisy forcing us to reject 63 of the collection in the rest of the collection both polarities are observed and inclination only analysis indicates that pre tilting remanence is preserved for many samples these data along with published palaeomagnetic results from the ha eg basin pass a regional fold test the palaeomagnetic study has provided an acceptable magnetostratigraphy which shows that the studied part of the s npetru formation was deposited between the beginning of the chron 32n 1n and the end of chron 31n these first palaeomagnetic results obtained from the upper cretaceous sedimentary rocks from the south carpathians confirm the previous palaeomagnetic results obtained from magmatic rocks the subtropical palaeolatitude during late cretaceous and the large clockwise rotation during the tertiary

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

timing of diagenetic haematite growth in red pelagic limestones from gubbio italy abstract magnetite haematite and to a minor extent maghaemite are recognised in the cretaceous and paleocene red pelagic limestones at gubbio the magnetite is detrital or biological whereas the haematite grew during diagenesis from a goethitic precursor thermal and af demagnetization of samples collected from close to reversal boundaries indicate that the various magnetization components do not record the polarity reversal at exactly the same stratigraphic level in the few tens of centimetersbelow a recorded geomagnetic reversal defined by the magnetite magnetization some of the haematite grains are magnetized in the post reversal field the blocking temperature spectra of this haematite fraction with post reversal magnetization are found to shift toward higher temperatures as the reversal boundary is approached the blocking temperature spectra reflect the grain size spectra of the haematite which we interpret as arising by the continual nucleation of grains down to a certain burial depth where the conditions are no longer conducive to further haematite growth the depth below reversal boundaries to which haematite with post reversal magnetization can occur is estimated to be about 60 cm after compaction and is equivalent to a time of about 105 years for these particular sediments a detailed study of the magnetization components at reversal boundaries indicates that the first diagenetic growth of haematite through the single domain critical volume occurs prior to the mechanical fixation of the detrital or biological magnetite subsequently the diagenetic haematite grains do not rotate in response to the ambient geomagnetic field polarity as easily as the magnetite because of their occurrence as pigmentary coatings on larger non magnetic grains

a balanced model of the southern central andes to explain the actual crustal thickness of the southern central andes a balanced cross section at 21 s latitude was modeled a forward modeling procedure was used on a crustal scale to explain the gross crustal structure obtained by seismic refraction investigations in the model 320 km of shortening since late cretaceous based on balanced geological cross sections are assumed for the whole andes from the trench to the foreland and the initial crustal thickness varies between 30 and 40 km it results that about 20 of the actual crustal volume must be explained by other sources than crustal shortening structures of high velocity material in the upper crust of the eastern cordillera can be explained by detached and overthrust material from the crustal base thus producing a crustal doubling in the back arc underplating of continental material that was removed by subduction erosion and magmatic addition of derivates of the subducted nazca plate may contribute to the lower crust of the forearc and arc regions crustal thickening of the eastern cordillera and parts of the altiplano was undoubtedly produced by tectonic thickening whereas the sources of thickening in the western cordillera and forearc region are uncertain

rare earth element zonation in pacific ferromanganese nodules abstract the lower surfaces of ferromanganese nodules from the north equatorial pacific ocean which are enriched in mn cu and ni and the upper surfaces which are enriched in fe p and co have been analyzed for la ce nd sm eu gd dy er and yb the ree contents are lower and the ce anomaly is smaller in the lower surfaces than in the upper surfaces the magnitude of the ce anomaly increases with decreasing mn fe ratio indicative of a seawater origin the zonal distribution of the other ree supports the conclusion derived previously from inter nodule and nodule sediment relationships that diagenetic fixation of rare earths in sediments affects their enrichment by nodular iron oxyhydroxides

geochronology and geochemistry of the paleoproterozoic meta basalts from the jiao liao ji belt north china craton implications for petrogenesis and tectonic setting abstract geochronology geochemical and isotopic studies were carried out on the paleoproterozoic meta basalts and related rocks from the jiao liao ji belt north china craton to understand the mantle source characteristics and the geodynamic setting u pb isotopic dating using the la icpms method on zircons from the metamorphosed volcanic rocks reveals that they formed at ca 2204 2158 ma and were metamorphosed at ca 1895 1919 ma respectively the meta basalts are of calc alkali affinity and have arc like geochemical compositions they are enriched in lrees la yb n 3 5 5 1 and liles sr ba rb depleted in hfses nb ta zr hf ti and show variable high nd t values 2 4 to 4 5 the basaltic rocks experienced significant fractional crystallization and minor crustal contamination during magma evolution modeling suggests that the parent magma of the meta basalts was derived from 20 partial melting of spinel garnet lherzolites that were previously metasomatized by subduction zone fluids melts in the late archean petrological geochronological and geochemical data suggest that the paleoproterozoic volcanic rocks formed in an active continental margin setting and were subsequently deformed and metamorphosed to amphibolite facies due to the arc continental collision at ca 1 9 ga rather than in a continental rifting setting as previously thought by most workers

geochronology mantle source composition and geodynamic constraints on the origin of neoarchean mafic dikes in the zanhuang complex central orogenic belt north china craton abstract mafic granulitic and amphibolitic boudins dispersed in archean felsic gneisses are widely distributed in the central orogenic belt cob and the eastern block of the north china craton ncc and are considered to constitute deformed mafic dike swarms previous studies have demonstrated that the mafic dikes in the zanhuang complex of the ncc intruded the fabrics of an archean melange belt and were boudinaged during younger deformation igneous zircons from an undeformed mafic dike yield a 207 pb 206 pb age of 2535 30 ma which is interpreted as the crystallization age in addition pegmatites cutting across the mafic dikes in the field also yield an igneous zircon 207 pb 206 pb age of 2504 16 ma providing strong evidence that the mafic dikes in the ncc intruded during the neoarchean metamorphic zircons from one deformed mafic dike sample yield a metamorphic 207 pb 206 pb age of 2090 83 ma and another four samples from deformed mafic dikes have a consistent metamorphic zircon age of ca 1850 ma indicating that the mafic dikes underwent at least two generations of paleoproterozoic metamorphism of ca 2 1 ga and ca 1 85 ga previously reported trace element systematics of the mafic dikes are consistent with an arc related lithospheric mantle source region rather than an ocean island basalt oib like source region the new whole rock nd isotopic composition nd t 0 71 to 3 70 is relatively more evolved compared to that of the depleted mantle at 2 5 ga indicating an enriched lithospheric mantle source accordingly the mafic dikes are proposed to have been formed in a subduction related environment and their enriched mantle source was metasomatized by the melts and fluids derived from the subducted slab based on previous studies of the ncc and new geochronological and isotopic data in this contribution a new comprehensive tectonic model is proposed for the evolution of the ncc between 2 7 ga and 1 85 ga 1 from 2 7 to 2 5 ga an oceanic arc terrane belt developed in what is now the cob of the ncc while a passive margin sequence was deposited on the western edge of the eastern block on the margin of the intervening ocean 2 the oceanic arc terrane collided with the passive margin sequence at 2 5 ga above a west dipping subduction zone 3 the subduction polarity was reversed at ca 2 5 ga and a new east dipping subduction zone gave rise to the intrusion of the 2 5 ga mafic dikes of the ncc 4 the final collision between the western block and the eastern block occurred at ca 2 1 ga 5 the whole ncc then collided with the columbia supercontinent along the north margin of the craton at 1 9 1 8 ga

dinosaur eggshell isotope geochemistry as tools of palaeoenvironmental reconstruction for the upper cretaceous from the tremp formation southern pyrenees abstract the isotopic compositions 13 c and 18 o of dinosaur eggshells have been widely used in palaeoenvironmental studies although the geochemical signatures of eggshells are not usually contrasted with other proxies in this work the isotopic signatures of eggshells from a large maastrichtian succession from the tremp formation southern pyrenees spain are compared to those of carbonate pedogenic nodules occurring in the same levels the isotopic signatures of eggshells vary according to the stratigraphic unit and geographical location a group of samples from several localities corresponding to eggshells without significant diagenetic imprints has isotopic values differing from the associated nodules the late cretaceous isotopic composition record from the tremp fm is consistent that is the eggshells have distinct primary signatures preserved however the eggshells from another locality which exhibit neomorphed textures display isotopic signatures similar to the associated pedogenic carbonate which suggests a diagenetic isotopic signature and confirms alteration in the eggshells both microscopic and geochemical data suggest that an early meteoric diagenesis pedogenesis is responsible for the secondary signatures the 13 c values in the carbonate pedogenic nodules indicate a carbon isotopic composition typical of c3 plants although the slight difference in 13 c between the palaeosol carbonate of coeval successions may be due to slightly different palaeoenvironmental conditions the small discrepancy in the 13 c calculated for c3 plants from carbonate nodules and from eggshells may be because the palaeosol carbonate gives the isotopic composition of the vegetation grown at a local site whereas the 13 c from eggshells is a proxy for the ingested food in the area in which the dinosaurs lived the oxygen isotopic compositions from palaeosol carbonate nodules have been used for calculation of the air temperature and we may conclude that the mean air temperature in the studied area during the late cretaceous was approximately 21 c the use of this temperature gives rational results in the calculation of the oxygen isotopic composition of palaeosol carbonate by means of the isotopic composition of the eggshell carbonate additionally a relatively continuous isotopic record of nodules shows an overall vertical trend towards negative 13 c values and a high relative and steady 18 o content throughout the maastrichtian the k pg boundary was recorded by a negative excursion in 13 c in the carbonate nodules

neoproterozoic adakitic plutons and arc magmatism along the western margin of the yangtze block south china abstract neoproterozoic adakitic plutons that crop out along the western margin of the yangtze block south china from kangding on the north to panxi on the south provide constraints on the origin of the giant jinningian magmatic event of south china representative plutons include the xuelongbao 750 ma datian 760 ma and dajianshan intrusions the latter two bodies consist mainly of granodiorite with relatively high sio2 51 0 73 4 wt and mg s 0 36 0 55 they have fractionated rare earth element patterns with la yb n ratios ranging from 2 6 to 101 8 and are characterized by high sr 344 1018 ppm and low y 4 3 17 9 ppm yielding sr y ratios ranging from 27 to 111 on primitive mantle normalized trace element diagrams these rocks show enrichment of large ion lithophile elements and depletion of high field strength elements nb ta with positive zr hf and negative ti anomalies consistent with an arc related setting they have relatively constant initial whole rock 87sr 86sr ratios 0 70

ferromanganese oxide deposits from the central pacific ocean ii nodules and associated sediments bulk chemical mineralogical and selective leach analyses have been made on a suite of abyssal ferromanganese nodules and associated sediments from the s w equatorial pacific ocean compositional relations between nodules sediment oxyhydroxides and nearby ferromanganese encrustations are drawn assuming that the crusts represent purely hydrogenetic ferromanganese material crusts mno2 rich nodules and sediment oxyhydroxides are compositionally similar and distinct from diagenetic todorokitebearing nodules compared to fe mn crusts sediment oxyhydroxides are however slightly enriched relative to mn and ni in fe cu zn ti and al and depleted in co and pb reflecting processes of non hydrogenous element supply and diagenesis mno2 nodules exhibit compositions intermediate between fe mn crusts and sediment oxyhydroxides and thus are considered to accrete oxides from both the water column and associated sediments deep ocean vertical element fluxes associated with large organic aggregates biogenic calcite silica and soft parts have been calculated for the study area fluxes associated with organic aggregates are one to three orders of magnitude greater than those associated with the other phases considered are in good agreement with element accumulation rates in sediments and are up to four orders of magnitude greater than element accumulation rates in nodules metal release from labile biogenic material in surface sediments can qualitatively explain the differences between the composition of fe mn crusts and sediment oxyhydroxides todorokite rich diagenetic nodules are confined to an eastwards widening equatorial wedge it is proposed that todorokite precipitates directly from interstitial waters since the transition metal chemistry of interstitial waters is controlled dominantly by reactions involving the breakdown of organic carbon the supply and degradation rate of organic material is a critical factor in the formation of diagenetic nodules the wide range of trace metal mn ratios observed in marine todorokite reflects a balance between the release of trace metals from labile biogenic phases and the reductive remobilisation of mn oxide both of which are related to the breakdown of organic carbon

paleomagnetic constraints of the lower triassic strata in south qinling belt evidence for a discrete terrane between the north and south china blocks

subduction related metasomatic mantle source in the eastern central asian orogenic belt evidence from amphibolites in the xilingol complex inner mongolia china abstract the central asian orogenic belt caob formed mainly in the paleozoic due to the closure of the paleo asian oceanic basins and accompanying prolonged accretion of pelagic sediments oceanic crust magmatic arcs and precambrian terranes the timing of subduction accretion processes and closure of the paleo asian ocean has long been controversial and is addressed in a geochemical and isotopic investigation of mafic rocks which can yield important insight into the geodynamics of subduction zone environments the xilingol complex located on the northern subduction accretion zone of the caob mainly comprises strongly deformed quartzo feldspathic gneisses with intercalated lenticular or quasi lamellar amphibolite bodies an integrated study of the petrology geochemistry and geochronology of a suite of amphibolites from the complex constrains the nature of the mantle source and the tectono metamorphic events in the belt the protoliths of these amphibolites are gabbros and gabbroic diorites that intruded at ca 340 321 ma with positive ehf t values ranging from 2 89 to 12 98 their t dm1 model ages range from 455 to 855 ma and peak at 617 ma suggesting that these mafic rocks are derived from a depleted continental lithospheric mantle the primitive magma was generated by variable degrees of partial melting of spinel bearing peridotites fractionation of olivine clinopyroxene and hornblende has played a dominant role during magma differentiation with little or no crustal contamination the mafic rocks are derived from a late neoproterozoic depleted mantle source that was subsequently enriched by melts affected by slab derived fluids and sediments or melts with a sedimentary source rock the carboniferous mafic rocks in the northern accretionary zone of the caob record a regional extensional event after the early paleozoic subduction of the paleo asian ocean both addition of mantle derived magmas and recycling of oceanic crust played key roles in significant late carboniferous ca 340 309 ma vertical crustal growth in the caob amphibolite facies metamorphism p 0 34 0 52 gpa t 675 708 c affected these mafic rocks in the xilingol complex at ca 306 296 ma which may be related to the crustal thickening by northward subduction of a forearc oceanic crust beneath the southern margin of the south mongolian microcontinent the final formation of the solonker zone may have lasted until ca 228 ma

the chronostratigraphic framework of the south pyrenean maastrichtian succession reappraised implications for basin development and end cretaceous dinosaur faunal turnover abstract the evolution of the end cretaceous terrestrial ecosystems and faunas outside of north america is largely restricted to the european archipelago the information scattered in this last area can only be integrated in a chronostratigraphic framework on the basis of robust age constraints and stratigraphy therefore we have revisited the puzzling age calibration of the sedimentary infilling from the isona sector in the tremp syncline south central pyrenees an area renowned for its rich maastrichtian dinosaur fossil record aiming to shed light to existing controversial age determinations we carried out a new magnetostratigraphic study along the 420 m long orcau and nerets sections of that area our results reveal that most of the succession correlates to the early maastrichtian mostly chron c31r in accordance to ages proposed by recent planktonic foraminifera biostratigraphy the resulting chronostratigraphic framework of the entire maastrichtian basin recorded in the tremp syncline shows that a significant sedimentary hiatus of about 3 my characterizes most of the late maastrichtian in the study area this hiatus related to an abrupt migration of the basin depocenter is temporally close to similar hiatuses decreases in sedimentary rates and facies shifts recorded in other southwestern european areas the present chronologic framework sets the basis for a thorough assessment of end cretaceous terrestrial faunal turnover and extinction patterns and the establishment of a more rigorous pyrenean basin evolution analysis

complex precambrian crustal evolution beneath the northeastern yangtze craton reflected by zircons from mesozoic volcanic rocks of the fanchang basin anhui province abstract our knowledge of the precambrian accretion and reworking history of deep crust beneath the northeastern yangtze craton is still sparse zircons from volcanic rocks can not only give accurate crystallization ages for zircons within the host magmas but also provide unique information on the history of deep crustal rocks sampled during magma ascent in situ u pb ages and hf isotopes were analyzed on zircons from two trachyandesites from the late mesozoic zhongfencun and kedoushan formations in the fanchang basin anhui province the zircons exhibit relatively complex internal structures four zircons in the zhongfencun trachyandesite yield a lower intercept 206 pb 238 u age of 133 0 3 2 ma with hf model ages of 2 8 2 4 ga t crust and significantly negative hf t 25 15 to 18 72 demonstrating that this lava formed in early cretaceous time zircons in the kedoushan biotite trachyandesite yield a 206 pb 238 u age of 126 1 ma as well as negative but relatively high hf t values up to 4 34 revealing it formed roughly coeval with the cretaceous a type granites and bimodal magmatism in this region more significantly u pb ages and hf isotopes for proterozoic zircon xenocrysts in the fanchang volcanic rocks reveal that the northeastern yangtze deep crust probably contains unexposed archean e g 3 4 2 9 ga and 2 8 2 5 ga components rarely identified from the outcrops in this area and has undergone complex evolutional history including the addition of juvenile mantle derived materials at 3 4 2 9 ga ca 2 65 ga and ca 0 8 ga and reworking of the precambrian crust at ca 2 0 1 8 ga ca 0 8 ga and 133 126 ma the history of the continental crust s accretion and reworking of the northeastern yangtze craton may not fully coincide with the major episodes of crustal evolution in the wider yangtze craton especially during the archean to paleoproterozoic periods

cerium anomaly variations in ferromanganese nodules and crusts from the indian ocean fifty analyses of rare earth elements as well as mineralogical studies have been carried out on a suite of manganese nodules and crusts from the central indian basin and the western indian ocean the aim was to identify the processes controlling the ree patterns of the phases hosting the ree in the manganese nodules with an emphasis on an understanding of the ce anomaly this has involved separating the encrusting layers and nuclei physically as well as fe mn oxides from the aluminosilicate phase chemically using a 2 m hcl leach prior to analysis the presence of nodule nuclei seems to have little influence mostly 5 to a maximum of 30 on the overall magnitude of the ce anomalies in these nodules the ratios of concentrations of elements in the acid leachates and the corresponding bulk values yield flat ree patterns indicating that the aluminosilicate phase contributes very little to the ce anomalies interelement relations indicate that the ce anomalies are largely controlled by the amorphous mineral phase feooh xh2o the relationship of fe ce anomaly and mno2 further suggests that ce is chemisorbed onto iron oxyhydroxides which are epitaxially intergrown with mno2 the regional distribution of the ce anomaly values appears to depend on many of the factors responsible for the uptake of other minor metals in nodules and crusts

geochemistry and petrogenesis of early carboniferous volcanic rocks in east junggar north xinjiang implications for post collisional magmatism and geodynamic process abstract early carboniferous volcanic rocks in the batamayineishan formation overlie unconformably the molasse deposits and the ophiolitic melanges and are restricted in narrow zones along both sides of the kalamaili orogenic belt in north xinjiang southern central asian orogenic belt these rocks demonstrate the post collisional setting in east junggar commenced in tournaisian and also mark an important transitional period from the final amalgamation to late paleozoic voluminous juvenile granitoids in east junggar the volcanic rocks are composed of basalt basaltic andesite andesite trachyte and rhyolite both mafic and felsic rocks are characterized by enrichments in large ion lithophile elements light rare earth elements and depletion in nb and ta low initial 87sr 86sr and high positive nd t three groups of mafic rocks have been identified shoshonitic group 1 has the highest mgo cao ni and cr and the lowest na2o al2o3 la ba la yb and ba th with primary magma features group 2 calc alkaline and high k calc alkaline mafic rocks have the lowest k2o p2o5 th and th nb and the highest tio2 and group 3 shoshonitic to potassic alkaline has the highest k2o p2o5 la ba la yb and th nb and the lowest tio2 the a type like felsic rocks were derived from the differentiation of the mafic magma geological and geochemical evidences indicate that the batamayineishan formation was generated from the process of slab breakoff detachment group 1 samples are produced by decompressional melting of the upwelling asthenosphere mainly composed of spinel and garnet 50 50 lherzolite which has been enriched by overlying metasomatized lithosphere during ascent group 2 is derived from 5 10 partial melting of shallower spinel bearing lithospheric mantle induced by the hot rising asthenosphere where the contribution of slab derived fluid is predominant low partial melting 3 5 of the mantle wedge and or thickened lithospheric mantle enriched by slab derived components generates group 3 slab breakoff as an important geodynamic process accounts for the post collisional magmatism between 343 5 ma 330 ma providing a model for post collisional crust mantle interaction in the caob