zircon u pb geochronological and hf isotopic constraints on petrogenesis of late mesozoic intrusions in the southeast hubei province middle lower yangtze river belt mlyrb east china abstract during the late mesozoic extensive magmatism and associated ore deposits were developed in the southeast hubei province middle lower yangtze river metallogenic belt mlyrb east china to understand the petrogenesis of the intrusions in the area we performed in situ zircon u pb and hf isotopic analyses on 14 samples from the fengshangdong stock and from the echeng tieshan wangbaoshan jinshandian and yangxin batholiths three major suites of intrusive rocks are recognized in the southeast hubei province 1 141 146 ma granodiorite and granite porphyries associated with 143 144 ma porphyry skarn cu mo deposits have enriched radiogenic hf isotopic compositions ehf t 9 5 to 1 6 comparable to those of cretaceous pyroxene diorites trachyandesites and basalts ehf t 8 9 to 1 3 in the mlyrb which were derived from an enriched lithospheric mantle 2 voluminous 136 143 ma gabbros diorites and quartz diorites associated with 137 144 ma skarn cu fe fe cu and au cu deposits have variable hf isotopic compositions ehf t 19 1 to 5 4 indicating an origin via the hybridization of enriched mantle derived mafic magma and variable amounts of ancient lower crustal components 3 127 133 ma diorites quartz diorites and granites associated with 132 133 ma skarn fe deposits characterized by a wide range of ehf t values 28 2 to 6 4 suggest the assimilation of various ancient lower crustal materials by enriched mantle derived basaltic magma the intrusions of suites 1 and 2 are characterized by high sr contents 329 2087 ppm and high sr yb 36 1710 and la yb n ratios 17 6 172 but low yb contents 0 45 1 82 ppm and do not show negative eu anomalies eu 0 74 1 4 the intrusions have radiogenic sr nd isotopic compositions end t 10 0 to 3 4 and 87 sr 86 sr i 0 7054 0 7084 compared with the intrusions of suites 1 and 2 rocks of suite 3 have relatively low sr contents 60 5 327 ppm and low sr yb 33 0 315 and la yb n ratios 2 28 30 0 but relatively high yb contents 1 04 5 17 ppm and significant negative eu anomalies eu 0 22 0 73 the rocks of suite 3 are characterized by a wide range of radiogenic sr nd isotopes with end t values of 12 5 to 4 9 and 87 sr 86 sr i 0 7057 0 7085 the proposed magma sources combined with the geochemical and sr nd isotopic differences between these three suites of intrusive rocks indicate that late mesozoic magmatic activity in the southeast hubei province mlyrb was associated with lithospheric thinning induced by asthenospheric upwelling at that time

late mesozoic bimodal volcanic rocks in the jinniu basin middle lower yangtze river belt yrb east china age petrogenesis and tectonic implications abstract late mesozoic intrusive and volcanic rocks are widespread in the southeast hubei province middle lower yangtze river belt yrb east china detailed in situ zircon u pb and hf isotope elemental and sr nd pb isotopic data are presented in this paper for late mesozoic volcanic rocks from the jinniu basin yrb aiming to constrain their age petrogenesis and tectonic implications the jinniu volcanic rocks show a bimodal distribution in composition with dominant rhyolite and dacite and subordinate basalt and basaltic andesite new shrimp and la icpms zircon u pb ages indicate that the volcanic rocks of three formations in the jinniu basin were erupted at quite a short age range of about 5 ma during the early cretaceous 130 125 ma the mafic rocks are moderately enriched in large ion lithophile elements lile e g ba th u and pb and light rare earth elements lree and are characterized by negative nb ta and ti anomalies and relatively high tio2 0 72 2 06 and nb 9 20 26 5 ppm contents these analyses indicate that the geochemical characteristics of the mafic rocks in the jinniu basin are similar to worldwide phanerozoic nb enriched basalt and andesites neba new in situ zircon u pb ages and field geological relationships demonstrate that neba in the southeast hubei province are not spatially or temporally associated with high silica adakitic rocks but were most likely derived from an enriched lithospheric mantle with assimilation of minor crustal materials and then fractional crystallization during the evolution of the magma overall the felsic rocks in the jinniu basin have geochemical characteristics and sr nd pb signatures and in situ zircon hf isotopic compositions similar to those of the mafic rocks compared with the mafic rocks the felsic rocks are characterized by enriched and variable concentrations of lile and ree e g ba 33 3 1372 ppm y 11 4 33 6 ppm ybc 5 07 18 7 and negative eu anomalies eu 0 22 0 98 as well as a wide range of radiogenic nd pb isotopic values with end t 10 2 to 2 4 206pb 204pb i 17 659 18 705 207pb 204pb i 15 478 15 663 and 208pb 204pb i 37 654 38 935 and in situ zircon hf compositions of ehf t 12 7 to 1 8 these features indicate that the genesis of felsic magma in the jinniu basin is consistent with extensive fractional crystallization and large amounts of crustal contamination from an evolved mafic magma sio2 55 the bimodal volcanic rocks in this study provide convincing evidence that early cretaceous volcanic rocks in the yrb developed in a back arc extensional tectonic regime

cretaceous ridge subduction along the lower yangtze river belt eastern china the lower yangtze river belt is one of the most important metallogenic belts in china the mechanisms responsible for ore genesis and the formation of related cretaceous igneous rocks such as adakite a type granitoid and nb enriched basalt remain controversial mesozoic granitoids in the lower yangtze river belt were mostly formed in the early cretaceous 140 125 ma and three granitoid belts the inner the south and the north have been defined according to petrological and geochemical characteristics previously based mainly on negative end and high initial sr isotope values the adakitic rocks were generally attributed to partial melting of thickened or delaminated lower crust both of which require crustal thickening mesozoic crustal thickening however is not supported by the development of extensional basins in the region from the late jurassic to cretaceous eastern china was closely associated with subduction of the pacific plate in the south and the izanagi plate in the north the midocean ridge mor between these two plates was drifting toward and likely subducting under the lower yangtze river belt a ridge subduction model can therefore explain the distribution of different magmatic rocks and ore deposits in the belt partial melting of subducting young hot oceanic slabs close to the ridge formed adakitic rocks the negative end values of adakitic rocks can be plausibly interpreted by mixing between adakitic magmas and enriched components in the lithospheric mantle and or crustal materials through afc process a slab window opened during ridge subduction as indicated by a type granitoids in the center of the inner belt nb enriched basalt found in the belt was likely formed by partial melting of a mantle wedge metasomatized by fluids released from the subducting slab at shallow depths

plutonic rocks of intermediate composition on gran canaria the missing link of the bimodal volcanic rock suite analysis of abundant plutonic fragments in the voluminous miocene rhyolitic basaltic composite ignimbrite p1 the initial felsic cooling unit overlying the basaltic shield on gran canaria helps to solve the problem of bimodal volcanism syenogabbros dominate the plutonic suite and provide evidence that magmas of intermediate composition formed abundantly at depth but did not erupt the entire suite of plutonic fragments comprises 1 pyroxenitic to gabbroic cumulates that directly influenced the liquid line of descent of p1 magmas 2 gabbro syenogabbro syenodiorite and quartz syenite fragments showing moderate degrees of hydrothermal alteration chloritization partial melting and 3 diverse xenoliths differing significantly in bulk rock composition and texture from the erupted p1 magmas the compositions of plutonic series 2 overlap with both bulk rock and mineral compositions of the erupted magmas whereas series 1 rocks show lower alkali and silica contents compositional variations among the plutonic rocks are compatible with fractional crystallization as the major petrogenetic process locally modified by magma mixing and selective element contamination variations in trace element concentrations of the plutonic rocks however are inferred to be the result of evolved interstitial melts penetrating into or draining out of crystalline mushes during slow intratelluric solidification the presence of f rich amphibole suggests that crystalline mushes were invaded by f bearing fluids overall compositional similarity and the fact that selective contamination effects are similar support the interpretation that the series 2 plutonic fragments represent solidified portions of the magmatic system that ultimately produced the erupted p1 magmas this system extended from the zone of underplating at the mantle crust boundary through the lower and into the upper crust of gran canaria and was roughly vertically zoned in composition as shown by geobarometric calculations

mantle lithosphere delamination driving plateau uplift and synconvergent extension in eastern anatolia eastern anatolia is the site of lithospheric thinning plateau uplift heating and synconvergent extension using numerical geodynamic experiments we test the hypothesis that these tectonic anomalies are all related and the consequence of delamination of the mantle lithosphere our findings indicate that delamination during plate convergence results in 2 km high plateau uplift the removal of mantle lithosphere induces distinct regions of contraction and thickening as well as extension and thinning of the crust the latter occurs even within a regime of plate shortening although it is muted with increasing plate convergence detachment of the delaminating slab results in minor surface topographic perturbation but only above the delamination hinge the plateau uplift and pattern of surface contraction and or extension are consistent with a topographic profile at 42 e and geologically interpreted zone of synconvergent extension at eastern anatolia

introduction to the pomme special section thermocline ventilation and biogeochemical tracer distribution in the northeast atlantic ocean and impact of mesoscale dynamics conducted in the northeast atlantic ocean 15 20 21 20 w 38 n 45 n the programme ocean multidisciplinaire meso echelle pomme is a research project aimed at a better understanding of the biological production and the carbon budget of the region in relation to the formation mechanisms of the 11 12 c mode water of the northeast atlantic with the help of two research vessels several tens of floats and drifters and nine moorings the field experiment was carried out between autumn 2000 and autumn 2001 with a more intensive phase in the winter and early spring of 2001 the field experiment resolved small several kilometers to regional several hundred kilometers scales and daily to seasonal variability a first analysis of the rich data set focused on the large scale and the mesoscale variability it shows that the distribution of water mass characteristics and biological activity is strongly influenced by the mesoscales in this supposedly quiet transition zone between the subtropical and subpolar gyres the seasonal variability however presents an imprint of the large scale structures with a clear north south gradient in properties and budgets this region is found on an annual average to be a sink of atmospheric co2 smaller scales associated with fronts and filaments were clearly observed in many fields temperature but also chlorophyll oxygen biogenic particles etc with modeling studies suggesting that they play a significant role in subduction ventilation and transport of biogeochemical tracers in the pomme region

origin of nb enriched basalts and adakites in baja california mexico revisited reply maury et al 2009 present new and detailed field observations and petrologic analyses to argue that the new model that i propose as an alternative explanation for postsubduction magmatism in baja california mexico castillo 2008 1 is incorrect specifically they claim that their new

a mantle derived bimodal suite in the hercynian belt nd isotope and trace element evidence for a subduction related rift origin of the late devonian brevenne metavolcanics massif central france in the brevenne series ne massif central a low grade bimodal association of metabasalts and metarhyolites is exposed together with intrusive trondhjemite bodies zircon u pb dating constrains their magmatic emplacement at 366 5 ma and 358 1 ma respectively the metabasalts are characterized by a distinct enrichment in incompatible elements e g th and lree and positive ndi from 5 to 8 combined isotope and trace element systematics rule out crustal contamination of mafic melts as a suitable cause of the lile large ion lithophile element enrichment rather a mixing process between a component similar to mid ocean ridge basalts and an enriched end member with ndi 5 is suggested an enriched mantle source of ocean island basalt affinity is precluded by the relative depletion of high field strength elements especially nb which shows negative anomalies in chondrite normalized patterns on the contrary a subduction related origin for the lile enrichment would be more consistent it may be inferred that arc like melts enriched in th and lree light rare earth elements and depleted in nb with ndi 5 were produced through partial melting of a depleted mantle source to which a small amount of crustally derived component had been added the metarhyolites are enriched in lile and have a close genetic relationship with the metabasalts as evidenced by their high ndi from 4 7 to 6 8 although the chemical evidence remains ambiguous it is suggested that fractional crystallization accompanied by subordinate assimilation is the petrogenetic process most consistent with the data the trondhjemites are isotopically distinct from the metarhyolites their ndi values from 1 0 to 2 2 reflect an important contribution of continental crust to their genesis and disprove their inferred cogenetism with the felsic volcanics a review of modern environments in which such bimodal suites are exposed shows that settings involving incipient rifting of a volcanic arc fringing a continental margin or built upon young thin continental crust might provide suitable analogues geodynamic reconstructions are complicated by subsequent tectonic events which disrupted the initial patterns and by mesozoic cenozoic sedimentary cover however this subduction related magmatism enlarges the growing body of evidence for southward subduction processes until the late devonian during the evolution of the northern flank of the european variscides as a general implication it is suggested that the combined use of the sm nd system with incompatible elements relatively resistant during alteration and low grade metamorphism ree th zr nb may provide diagnostic criteria for recognizing the tectonic setting of bimodal metaigneous suites in ancient orogenic belts

magmatic relationships and ages between adakites magnesian andesites and nb enriched basalt andesites from hispaniola record of a major change in the caribbean island arc magma sources abstract located in the cordillera central of the dominican republic the late cretaceous tireo fm tf records a major change of the magma sources in the caribbean island arc it comprises a 3 km thick sequence of arc related volcanic and volcano sedimentary rocks with variable geochemical characteristics combined detailed mapping stratigraphy geochemistry and u pb ar ar geochronology show that the volcanic rocks of the tireo fm include two main volcanic sequences the lower volcanic sequence is dominated by monotonous submarine vitric lithic tuffs and volcanic breccias of andesite to basaltic andesite with minor interbedded flows of basalts and andesites fossil and u pb and 40ar 39ar geochronological data show that arc magmatism in the lower sequence began to accumulate before 90 ma from the aptian to turonian these rocks constitute an island arc tholeiitic suite derived from melting by fluxing of a mantle wedge with subduction related hydrous fluids the upper volcanic sequence is characterized by a spatial and temporal association of adakites high mg andesites and nb enriched basalts which collectivelly define a shift in the composition of the subduction related erupted lavas a dacitic to rhyolitic explosive volcanism with subaerial and episodic aerial eruptions and sub volcanic emplacements of domes characterize mainly this stratigraphic interval the onset of this volcanism took place at turonian coniacian boundary and continued in the santonian to lower campanian with minor events in the late campanian adakites represent melts of the subducting slab magnesian andesites the product of hybridization of adakite liquids with mantle peridotite and nb enriched basalts melts of the residue from hybridization we propose a model of oblique ridge subduction at 90 ma and possibly subsequent slab window formation as principal cause of magmatic variations recorded in the caribbean island arc above a southwestern dipping subduction zone

petrogenesis of cretaceous adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china implications for geodynamics and cu au mineralization both adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china are associated with cretaceous cu au mineralization the shaxi quartz diorite porphyrites exhibit adakite like geochemical features such as light rare earth element lree enrichment heavy ree hree depletion high al2o3 mgo sr sr y and la yb values and low y and yb contents they have low end t values 3 46 to 6 28 and high 87sr 86sr i ratios 0 7051 0 7057 sensitive high resolution ion microprobe shrimp zircon analyses indicate a crystallization age of 136 3 ma for the adakitic rocks most volcanic rocks and the majority of monzonites and syenites in the luzong area are k rich or shoshonitic and were also produced during the cretaceous 140 125 ma they are enriched in lree and large ion lithophile elements and depleted in ti and nb and ba and exhibit relatively lower end t values ranging from 4 65 to 7 03 and relatively higher 87sr 86sr i ratios varying between 0 7057 and 0 7062 the shoshonitic and adakitic rocks in the luzong area have similar pb isotopic compositions 206pb 204pb 17 90 18 83 207pb 204pb 15 45 15 62 and 208pb 204pb 38 07 38 80 geological data from the luzong area suggest that the cretaceous igneous rocks are distributed along ne fault zones e g tanlu and yangtze river fault zones in eastern china and were likely formed in an extensional setting within the yangtze block the shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of 50 km i e 1 5 gpa possibly leaving rutile bearing eclogitic residue the shoshonitic magmas in contrast originated mainly from an enriched mantle metasomatized by subducted oceanic sediments they underwent early high pressure 1 5 gpa fractional crystallization at the boundary between thickened 50 km lower crust and lithospheric mantle and late low pressure 1 5 gpa fractional crystallization in the shallow 50 km crust the adakitic and shoshonitic rocks appear to be linked to an intra continental extensional setting where partial melting of enriched mantle and delaminated lower crust was probably controlled by lithospheric thinning and upwelling of hot asthenosphere along ne fault zones e g tanlu and yangtze river fault zones in eastern china both the shoshonitic and adakitic magmas were fertile with respect to cu au mineralization

geochemical constraints on the origin of bimodal magmatism at the okinawa trough an incipient back arc basin abstract the magmatism at the axial zone of the middle okinawa trough a young continental back arc basin comprises a bimodal basaltic rhyolitic suite accompanied by minor intermediate rocks we report major and trace element and sr nd isotopie data for the intermediate to silicic suites to provide constraints on their petrogenesis the rhyolites recovered as lava and pumice fall into three geochemical groups type 1 2 and 3 rhyolites type 1 rhyolites have 87sr 86sr 0 7040 0 7042 and 143nd 144nd 0 5128 0 5129 identical to those of associated basalts and are characterized by highly fractionated ree patterns petrogenesis of type 1 rhyolites is explicable in terms of fractional crystallization of the associated basalt in contrast type 2 rhyolites and andesite have slightly higher 87sr 86sr 0 7044 0 7047 but similar 143nd 144nd 0 5128 compared to those of the basalts the compositions of type 2 rhyolite and andesite can be explained by assimilation and fractional crystallization afc processes of the basalt magma quantitative analysis suggests assimilation fractional crystallization ma mc ratios of 0 05 hybrid andesite generated by mixing of evolved basalt and type 1 rhyolite is also present we emphasize that mechanical extension in this part of the okinawa trough involves gabbro ic lower crust that resulted from fractionation of mantle derived basaltic magmas type 3 rhyolite occurs only as pumice which makes its derivation questionable this rhyolite has major and trace element compositions and sr nd isotopie ratios which suggests that it may be derived from volcanic activity on the southern ryukyu volcanic front and arrived in the okinawa trough by drifting on the kuroshio current

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

bimodal cyclical archean basalts and rhyolites from the michipicoten wawa greenstone belt ontario geochemical evidence for magma contributions from the asthenospheric mantle and ancient continental lithosphere near the southern margin of the superior province abstract the petrographic and geochemical variations in the middle to late archean volcanic rocks of the michipicoten wawa greenstone belt mgb ontario record bimodal basalt rhyolite magmatic activity at approximately 2 9 2 75 and 2 7 ga along what has previously been interpreted to be a southward dipping convergent plate margin which is underlain by continental crust cycle 1 komatiitic basalts have elevated mg number 0 51 0 83 compared to cycle 2 and 3 tholeiites mg number 0 44 0 56 and dominantly flat ree patterns with negative ta nb anomalies la ta 4 35 cycles 2 and 3 are more evolved than cycle 1 but all three cycles have broadly similar ratios of the incompatible trace elements compared to modern oceanic basalts the basaltic members of cycles 1 3 have a moderate ta nb anomaly la ta 4 46 and low la yb n 1 18 1 56 low la ta is a feature of oceanic lavas whereas high la ta is a feature of magmas which contain contributions from a crustal reservoir the mafic volcanic rocks are believed to be derived from asthenospheric mantle with assimilation of older continental crust the felsic volcanic rocks have elevated th nb 0 7 1 6 and ce yb n 10 2 16 4 and are enriched in light rare earth elements lree and large ion lithophile elements lile relative to rhyolites from other superior province greenstone belts we suggest that the rhyolites record the geochemical traits of their sources and these could be interpreted to be moderate to high degree melts of tonalitic upper crust rather than fractionated magmas or partial melts derived from the underlying mafic volcanics this contrasts with models for many other rhyolites in superior province greenstone belts such as the southern volcanic zone of the abitibi greenstone belt where variations require a more mafic crustal source to generate the fractionated low la sm gd yb and high zr th rhyolites believed to be locally associated with volcanogenic massive sulphide deposits the absence of significant volumes of compositionally intermediate volcanic rocks and the evidence for crustal contributions to mgb cyclical magmatism raises the possibility that these are archean analogues of the phanerozoic flood basalts which straddle the margins of continental shield areas such as the java ontong sequence and are not relics of either archean oceanic crust or subduction related volcanics

east asia seismotectonics magmatism and mantle dynamics abstract in this article we review the significant recent results of geophysical studies and discuss their implications on seismotectonics magmatism and mantle dynamics in east asia high resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes which may reflect magma and fluids that affected the rupture nucleation of large earthquakes in subduction zone regions the crustal fluids originate from the dehydration of the subducting slab magmatism in arc and back arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab the intraplate magmatism has different origins the continental volcanoes in northeast asia such as changbai and wudalianchi seem to be caused by the corner flow in the big mantle wedge bmw above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well the tengchong volcano in southwest china is possibly caused by a similar process in bmw above the subducting burma microplate or indian plate the hainan volcano in southernmost china seems to be a hotspot fed by a lower mantle plume associated with the pacific and philippine sea slabs deep subduction in the east and the indian slab s deep subduction in the west down to the lower mantle the occurrence of deep earthquakes under the japan sea and the east asia margin may be related to a metastable olivine wedge in the subducting pacific slab the stagnant slab finally collapses down to the bottom of the mantle which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and cause the slab plume interactions some of these issues such as the origin of intraplate magmatism are still controversial and so further detailed studies are needed from now

early ordovician continental break up in variscan europe ndsr isotope and trace element evidence from bimodal igneous associations of the southern massif central france abstract the high grade marvejols group and the low grade albigeois cevennes sedimentary sequence contain bimodal igneous rocks of early ordovician age which are representative of a widespread thermal event in the european variscides comparison of their nd sr isotope and trace element characteristics provides additional evidence for their origin in an ensialic extensional setting as an alternative to the back arc model proposed by previous authors we propose that these associations record a continental break up episode unrelated to contemporaneous subduction in this model the widespread early paleozoic bimodal magmatism marks the birth of a mid european oceanic arm we propose that the break up was controlled by both transtensional processes and mantle plume activity high grade associations such as the marvejols group and low grade bimodal associations such as the albigeois cevennes might be regarded as representing opposite rifted passive margins the northern marvejols type margin was involved in a late ordovician silurian subduction like process with hp ht metamorphism in contrast the southern albigeois cevennes margin remained largely unaffected possibly as part of the overriding plate of the subduction zone pseudo calc alkaline signatures unrelated to subduction processes may occur in magmatic rocks associated with continental break up episodes in this case negative nb anomalies are produced by the addition of crustal components enriched in th and lree relative to nb this inferred alternative origin of nb anomalies has important bearing on the paleogeodynamic settings based on geochemical data

aircraft measurements of very short lived halocarbons over the tropical atlantic ocean 1 atmospheric mixing ratios of c2h5i ch2cli ch2br2 and chbr3 were quantified from whole air samples collected aboard the faam bae 146 301 atmospheric research aircraft during flights over the tropical atlantic ocean 30 n to 10 s as part of the trade wind ozone photochemistry experiment trompex in september 2009 mixing ratios of c2h5i and ch2cli increased with decreasing latitude and concentrations of all measured halocarbons were elevated with increasing proximity to the oceanic upwelling along the coast of mauritania vertical profiles highlighted the rapid photolytic degradation of these compounds within the tropical troposphere with ch2cli concentrations reduced by 50 at the top of the boundary layer the spatial distributions of ch2cli indicated an open ocean source

metallogeny of copper and iron deposits in the eastern yangtse craton east central china abstract the eastern yangtse craton of central to eastern china is an important fe cu metallogenic province based on studies of the regional geology and tectonic evolution this metallogenic belt is controlled by faults and aulacogens in the continental plate in the early yanshan epoch jurassic the dominant west northwest and east west lithospheric faults controlled the distribution of cu mo and au mineralization whereas in the late yanshan epoch cretaceous the north northeast and northeast lithospheric faults controlled cu fe mineralization in a mineral district the distribution of ore fields is under the dual control of basement fault s and near surface fault s based on the relation of ring and lineament faults to intrusions a three level model of vertical zonation is proposed systematic petrochemical studies of mesozoic igneous rocks and mineralization identify three subseries 1 a calc alkaline intermediate to silicic subseries rich in potassium 2 a calc alkaline intermediate to felsic subseries rich in sodium and 3 a calc alkaline intermediate to mafic subseries rich in sodium genetic types of ore deposits are diverse including fe and cu skarns cu porphyries fe ore magma injections ningwu luzong fe deposits from late orthomagmatic to pegmatitic pneumato hydrothermal and to mesothermal epithermal associated with subvolcanic rocks and remobilized sedimentary fe and or cu deposits the genetic types of ore deposits form two metallogenic series 1 a sedimentary metallogenic series active mainly in the paleozoic and 2 a magmatic hydrothermal metallogenic series consisting of three subseries active predominantly in the jurassic and cretaceous with the latter being more important in this region the superposition and compounding of these two metallogenic series contribute to many styles of mineralization in this mineral province

a tectono genetic model for porphyry skarn stratabound cu au mo fe and magnetite apatite deposits along the middle lower yangtze river valley eastern china abstract the middle lower yangtze river valley metallogenic belt yrb situated along the northern margin of the yangtze craton is characterized by porphyry skarn stratabound cu au mo fe deposits in the areas of uplift and magnetite apatite deposits in cretaceous fault basins following detailed field investigations and a review of published data we recognize two episodes of magmatism and mineralization in the yrb 1 156 137 ma high k calc alkaline granitoids associated with 148 135 ma porphyry skarn stratabound cu au mo fe deposits and 2 135 123 ma shoshonitic series associated with 134 9 122 9 ma magnetite apatite deposits a type granitoids and associated alkaline volcanic have a small age range from 126 5 to 124 8 ma and are temporally spatially and genetically associated with the second episode the geodynamic history of the yrb did not experience the paleozoic to mesozoic lithospheric thickening that took place in the north china craton this process is inferred to be linked to partial melting of the delaminated lower crust at high pressures resulting in the development of c type adakitic rocks the petrochemical and sr nd isotopic data show that both the shoshonitic series and a type granitoids are quite different from adakites with only some of the k calc alkaline granitoids having adakitic signatures previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono thermal evolution from 150 to 100 ma all data obtained for the middle lower yangtze river region consistently show that the tan lu regional strike slip fault zone initiated at 233 6 to 225 6 ma from the collision between the north china and yangtze cratons and was reactivated at ca 160 ma the tan lu fault was caused by the oblique subduction of the izanagi plate which along the yrb the low angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks the high k calc alkaline granitoids magmas were derived from melting of the subducted slab with some input of crustal material these magmas were emplaced at the intersections between ne and ew trending faults and formed porphyry skarn stratabound cu au mo fe deposits between 156 and 137 ma after 135 ma the subducted plate changed its direction of motion to northeast now running parallel to the eurasian continental margin and leading to large scale continental extension the shoshonitic series and subsequent a type granitoids magmatism and the development of magnetite apatite ores in the yrb took place in both fault basins and ne trending rifts between 135 and 124 ma

magnesian andesites nb enriched basalt andesites and adakites from late archean 2 7 ga wawa greenstone belts superior province canada implications for late archean subduction zone petrogenetic processes magnesian andesites ma occur with normal tholeiitic to calc alkaline basalt andesite suites in four greenstone belts of the 2 7 ga wawa subprovince canada collectively the magnesian andesites span ranges of sio2 56 64 wt mg number 0 64 0 50 with cr and ni contents of 531 106 and 230 21 ppm respectively relative to normal andesites the magnesian andesites form distinct trends on variation diagrams with relatively high th and lree contents uniform yb over a range of mgo more fractionated hree and lower nb thpm and nb lapm ratios niobium enriched basalts and andesites neba nb 7 16 ppm and an al enriched rhyolite adakite suite are associated in space and time with the magnesian andesites nb enriched basalts and andesites are characterized by high tio2 p2o5 th and zr contents variably high zr hf 36 44 ratios and more fractionated hree gd ybcn 1 3 4 1 compared to the normal tholeiitic to calc alkaline basalt andesite suites the adakite suite has the high al al2o3 16 18 wt high la ybcn 21 43 and low yb 0 4 1 2 ppm of archean tonalite trondhjemite granodiorite ttg suites and cenozoic adakites indicative of liquids derived mainly from slab melting the basalt andesite suites are not characterized by normal tholeiitic or calc alkaline fractionation trends of major or trace elements rather compositional trends can be accounted for by some combination of fractional crystallization and variable degrees of metasomatism of the source of basalt and or andesites by adakitic liquids the occurrence of magnesian andesites nb enriched basalts andesites and adakites has been described from certain phanerozoic arcs featuring shallow subduction of young and or hot oceanic lithosphere adakites likely represent slab melts magnesian andesites the product of hybridization of adakite liquids with mantle peridotite and nb enriched basalts andesites melts of the residue from hybridization geological similarities between the late archean wawa greenstone belts and certain cenozoic transpressional orogens with the ma neba adakite association suggest that subduction of young hot oceanic lithosphere may have played an important role in the production of this arc related association in the late archean

geochemistry and nd sr isotopic studies of late mesozoic granitoids in the southeastern hubei province middle lower yangtze river belt eastern china petrogenesis and tectonic setting abstract a geochemical and isotopic study was carried out for the mesozoic yangxin tieshan and echeng granitoid batholiths in the southeastern hubei province eastern china in order to constrain their petrogenesis and tectonic setting these granitoids dominantly consist of quartz diorite monzonite and granite they are characterized by sio 2 and na 2 o compositions of between 54 6 and 76 6 wt and 2 9 to 5 6 wt respectively enrichment in light rare earth elements lree and large ion lithophile elements lile and relative depletion in y concentrations ranging from 5 17 to 29 3 ppm and yb 0 34 2 83 ppm with the majority of the granitoids being geochemically similar to high sio 2 adakites hsa their initial nd e nd 12 5 to 6 1 and sr 87 sr 86 sr i 0 7054 0 7085 isotopic compositions however distinguish them from adakites produced by partial melting of subducted slab and those produced by partial melting of the lower crust of the yangtze craton in the late mesozoic the granitoid batholiths in the southeastern hubei province exhibit very low mgo ranging from 0 09 to 2 19 wt with an average of 0 96 wt and large variations in negative to positive eu anomalies eu eu 0 22 1 4 especially the tieshan granites and yangxin granite porphyry eu eu 0 22 0 73 geochemical and nd sr isotopic data demonstrate that these granitoids originated as partial melts of an enriched mantle source that experienced significant contamination of lower crust materials and fractional crystallization during magma ascent late mesozoic granitoids in the southeastern hubei province of the middle lower yangtze river belt were dominantly emplaced in an extensional tectonic regime in response to basaltic underplating which was followed by lithospheric thinning during the early cretaceous

laser ablation icp ms titanite u th pb dating of hydrothermal ore deposits a case study of the tonglushan cu fe au skarn deposit se hubei province china abstract titanite from the tonglushan cu fe au skarn deposit daye district eastern china has been successfully dated by laser ablation inductively coupled plasma mass spectrometry la icp ms hydrothermal titanite from both skarn ores and calcite veins cutting the ore bodies are characterized by having much lower ree and th u and lu hf ratios compared to their magmatic equivalents from the ore related yangxin quartz diorite intrusion and a late stage albitite dike titanite from the yangxin quartz diorite and an albitite dike which intrudes both the quartz diorite intrusion and ore bodies yield weighted mean 206pb 238u ages of 136 0 1 5 ma and 120 6 2 3 ma 2 respectively in agreement within analytical uncertainty to their 208pb 232th ages in situ analysis of epidote enclosed hydrothermal titanite in thin sections of a skarn ore sample yields a mean 206pb 238u age of 135 9 1 3 ma and 208pb 232th age of 138 2 4 5 ma whereas titanite in calcite from a calcite dominated vein cross cutting the skarn ore body has consistent 206pb 238u and 208pb 232th ages of ca 121 ma the data thus reveal two independent hydrothermal events the earlier event was responsible for the known cu fe au skarn mineralization at tonglushan and throughout the daye district and was caused by coeval magmatism that has resulted in the emplacement of the yangxin quartz diorite the later event previously unrecognized was associated with a second magmatic pulse as represented by the albitite dikes and provides potential for discovering new mineral deposits at tonglushan and possibly over the daye district this study represents the first direct dating of skarn deposits using titanite u th pb geochronometer and signifies the utilization of titanite for precise dating of hydrothermal ore formation

timing of skarn deposit formation of the tonglushan ore district southeastern hubei province middle lower yangtze river valley metallogenic belt and its implications abstract the tonglushan ore district in the middle lower yangtze river valley metallogenic belt includes the tonglushan cu fe the jiguanzui au cu and the taohuazui au cu skarn deposits they are characterized by ne striking ore bodies and hosted at the contact of triassic carbonate rocks and late mesozoic granitoid deposits new sensitive high resolution ion microprobe shrimp and laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb molybdenite re os and phlogopite 40 ar 39 ar ages indicate that these skarn deposits formed between 140 3 1 1 and 137 3 2 4 ma these dates are identical to the zircon u pb ages for host quartz diorites ranging from 140 2 to 139 1 ma these results confirm that both skarn mineralization and related intrusions were initiated during the early cretaceous the high rhenium contents 261 4 1152 g g of molybdenites indicate that a metasomatic mantle fluid was involved in the ore forming process of these skarn ore systems this conclusion is consistent with previously published constraints from sulfur deuterium and oxygen isotope compositions and the geochemical signatures and sr nd isotopic data of the mineralization hosting intrusions geological and geochronological evidence demonstrates that there were two igneous events in the tonglushan ore district the first resulted in the emplacement of quartz diorite during the early cretaceous 140 2 to 139 1 ma and the second is characterized by the eruption of volcanic rocks during the mid early cretaceous 130 2 to 124 2 ma the former is spatially temporally and genetically associated with skarn gold bearing mineralization 140 3 1 1 to 137 3 2 4 ma the recognition of these two igneous events invalidates previous models that proposed continuous magmatism and associated mineral deposits in the middle lower yangtze river valley metallogenic belt

temporal relationship between granite cooling and hydrothermal uranium mineralization at dalongshan in china a combined radiometric and oxygen isotopic study abstract a combined study using multi radiometric dating and oxygen isotopic geothermometry was carried out for mesozoic quartz syenite alkali feldspar granite and associated hydrothermal uranium mineralization at dalongshan in the middle lower yangtze valley of east central china radiometric dating of the quartz syenite yields a whole rock rb sr isochron age of 135 6 4 3 ma a zircon u pb isochron age of 132 9 2 2 ma and k ar ages of 126 2 118 3 and 94 4 ma for hornblende biotite and orthoclase respectively the alkali feldspar granite yields a whole rock rb sr isochron age of 117 3 3 3 ma a zircon u pb isochron age of 114 7 2 1 ma and k ar ages of 112 2 109 3 and 88 4 ma for hornblende biotite and orthoclase respectively oxygen isotope thermometry for both granites gives temperatures of 685 to 720 555 to 580 435 to 460 and 320 to 330 c for hornblende magnetite biotite and orthoclase respectively when paired with quartz the systematic differences among the ages by the different techniques on the different minerals are used to reconstruct the cooling history of the granite the results yield rapid cooling rates of 27 4 to 58 6 c ma from 800 to 300 c in the early stage but slow cooling rates of 6 3 to 7 2 c ma from 300 to 150 c in the late stage the regular sequence of oxygen isotope temperatures for the different quartz mineral pairs demonstrates that diffusion is a dominant factor controlling the closure of both radiometric and o isotopic systems during granite cooling pitchblende u pb isochron dating yields an uranium mineralization age of 106 4 2 9 ma which is younger than the age of the granite emplacement and thus considerably postdates the time of magma crystallization but is close to the closure time of the k ar system in the biotite this points to a close relationship between granite cooling and ore forming process it appears that hydrothermal mineralization took place in the stage of slow cooling of the granite whereas the rapid cooling of the granite was concurrent with the migration of hydrothermal fluids along fault structures therefore the activity of the ore forming hydrothermal system is temporally dictated by the cooling rates of the granite and may lag about 25 to 30 ma behind the crystallization timing of associated granite

lithospheric thickness thinning subduction and interaction with the asthenosphere beneath china from the joint inversion of seismic s wave train fits and rayleigh wave dispersion curves abstract a joint inversion method of simultaneously inverting regional multimode surface waveforms and fundamental mode surface wave dispersion curves is used to better constrain a 3 d s wave velocity model for the upper mantle beneath china thousands of broadband vertical component seismograms were processed and 16 500 rayleigh wave group velocity measurements were retrieved at a period of 20 s with fewer measurements at shorter and longer periods in addition 4947 regional rayleigh waveforms were obtained for paths passing mainly through the chinese mainland the joint inversion of this dataset provides new s wave velocity structures at upper mantle depths down to 400 km in particular the new model is resolved to greater depths than the approximately 200 km depth obtainable in most fundamental mode surface wave tomographic studies and is better resolved at shallow lithospheric depths than that possible in teleseismic body wave tomographic studies because the upper mantle s wave velocity is controlled mainly by temperature rather than by composition thermal structures estimated from the tomographic s wave velocity model are used to estimate the thickness of the lithosphere beneath china the results indicate that in eastern china the north china craton and the yangtze craton are characterized by pronounced variations in lithospheric thickness with the lithosphere thinning from west to east the underlying low velocity layer and deeper level high velocities provide important evidence in support of the idea that lithospheric thinning beneath eastern china is related to the westward subduction of oceanic lithosphere to the east and related thermal and dehydration processes beneath western china thickened lithosphere is imaged beneath the qinghai tibetan plateau except for beneath qiangtang in the northern part of the plateau which is underlain by low velocities the present model generally supports the interpretation of low velocities beneath qiangtang as mantle material squeezed out by convergence between the indian and asian lithospheres moreover two separate segments of the subducting indian lithosphere are imaged indicating that the deeper portion of the subducting slab may have started to break off from the shallower portion as early as 20 ma

geochemistry and geochronology of the bimodal volcanic rocks of the suguti area in the southern part of the musoma mara greenstone belt northern tanzania abstract the suguti volcanic rocks of the southern musoma mara greenstone belt in northern tanzania comprise mainly of a bimodal suite of tholeiitic basalts basaltic andesites and calc alkaline rhyolites with a subordinate amount of intermediate rocks zircon u pb and whole rock sm nd geochronology suggests that the two suites are cogenetic and were emplaced at 2755 1 ma with a common initial nd value of 2 1 the tholeiitic basalts are characterised by relatively flat chondrite normalised ree patterns with la ybcn ratios of 0 8 1 6 mean 1 0 the basalts also exhibit negative ti and nb anomalies in primitive mantle normalised multi element diagrams the flat ree patterns the presence of prominent negative nb anomalies and the positive initial nd value of 2 1 suggest that the basalts were formed by low pressure melting of a mantle wedge in an active continental margin setting compared to the tholeiitic basalts the calc alkaline rhyolites are characterised by low abundances of the transition elements cr

composition gaps critical crystallinity and fractional crystallization in orogenic calc alkaline magmatic systems the recognition of a three way correlation between magmatic sio2 content critical crystallinity and the size magnitude of crystal fractionation generated composition gaps in calc alkaline magmatic systems suggests an important control of magmatic critical crystallinity on the formation of such composition gaps to explain this correlation it is proposed that fractionation generated composition gaps are caused by 1 simultaneous interior i e non substrate crystallization and vigorous chamberwide convection which leads to progessive crystal suspension 2 cessation of convection when the percentage of suspended crystals reaches the critical crystallinity of the magma and 3 eventual buoyancy driven crystal liquid segregation producing a discrete body of fractionated magma which is separated from the initial magma by a composition gap this mechanism implies that many if not most magma bodies are characterized by interior crystallization and vigorous convection conditions which are not universally agreed upon at present given that such conditions characterize natural magma bodies fractional crystallization through crystal settling in low velocity boundary layers should be an important mechanism of fractional crystallization in a crystallizing and convecting body of magma composition gap formation should represent one endmember of a complete spectrum of possible evolutionary paths governed by the relative rates of crystal settling and crystal retention as a given volcanic plumbing system matures with time average settling retention ratios within individual magma bodies should increase due to higher average wall rock temperatures it follows that within a given volcanic center early stage volcanism should be more likely to display fractionation generated composition gaps than later stage volcanism such a temporal evolution has been documented at at least two aleutian calc alkaline volcanic centers

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