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

accelerator mass spectrometer ages for the younger dryas event in atlantic canada abstract in atlantic canada bulk sediment dates for the onset of a late glacial cooling widely regarded as the younger dryas event are highly variable ranging from 14 300 270 to 10 800 100 yr b p we present the first accelerator mass spectrometer ams 14c dates from atlantic canada at or close to the boundaries of this event from six sites in new brunswick and nova scotia the mean of five dates places the onset of this cooling at ca 10 770 yr b p the inclusion of a sixth perhaps anomalously old date changes the mean to 10 880 yr b p the termination averages three dates ca 10 000 yr b p these dates place the timing of the younger dryas event in atlantic canada closer in line with the traditional chronozone boundaries of 11 000 and 10 000 yr b p in northwest europe

genesis of the dongguashan skarn cu au deposit in tongling eastern china evidence from fluid inclusions and h o s pb isotopes abstract the dongguashan copper gold deposit is located in the eastern tongling ore district of the middle lower yangtze river valley metallogenic belt mlyrb eastern china the cu au mineralization is associated with the qingshanjiao quartz monzodiorite and consists of various types including stratiform porphyry vein like and skarn there are three deposit models including 1 stratabound skarn type 2 exhalative sedimentary sedex hydrothermal superimposition type and 3 exhalative sedimentary sedex type the ore forming processes can be divided into the prograde skarn alteration stage i retrograde alteration stage ii and quartz carbonate alteration stage iii four types of fluid inclusions fis are recognized at dongguashan vapor rich two phase aqueous type i liquid rich two phase aqueous type ii daughter mineral bearing three phase homogenized to liquid by the disappearance of vapor phase type iii and daughter mineral bearing three phase homogenized to liquid by the disappearance of daughter minerals type iv all four types of fis are present in stage ii stage i does not contain type iv fis and only type ii fis are found in stage iii for stage i type i ii and iii fis homogenized at 379 548 c 319 522 c and 450 512 c respectively with salinities of 10 1 19 6 5 9 19 4 and 36 7 43 3 wt nacl equivalent for stage ii type i ii iii and iv fis homogenized at 286 378 c 235 372 c 265 349 c and 324 350 c respectively with salinities of 1 4 17 0 4 3 16 1 34 7 40 6 and 34 4 41 0 wt nacl equivalent the type i to iii fis in stage i and ii have similar homogenization temperatures but different salinities which indicates the occurrence of fluid immiscibility hydrogen oxygen isotopes of the quartz d 84 0 to 71 5 18oh2o 4 51 to 8 97 and calcite d 70 7 to 60 95 18oh2o 4 41 to 4 91 suggest that the ore forming fluids were principally magmatic derived 34s values of the stratiform orebodies 4 1 to 5 3 vein like orebodies 4 2 to 5 7 skarn orebodies 4 9 porphyry orebodies 5 1 to 5 7 and the qingshanjiao pluton 2 2 to 5 2 are different from those of the wall rocks 29 5 to 4 6 suggesting that wall rocks were unlikely to be a major sulfur source lead isotopes of the sulfides from the different orebody types are similar to those of the plagioclase from the mesozoic intermediate felsic rocks in the mlyrb suggesting that they have had similar pb source sulfur and lead isotopes suggest that the ore forming materials were derived from a deep seated magmatic source the ore forming fluid immiscibility during stage i and ii may have altered the physicochemical conditions of the hydrothermal fluid system leading to the cu au sulfide precipitation based on the ore geological and alteration mineralization features mineral assemblages ore forming material source and fluid evolution we consider that dongguashan is best classified as a porphyry skarn cu au deposit

breccia hydrothermal alteration and structural geology of the huangtun porphyry au cu deposit in the middle lower yangtze metallogenic belt eastern china abstract luzong basin is an important part of the middle lower yangtze metallogenic belt in eastern china in which the dominant types of deposits are iron oxide apatite and skarn iron deposits however a new porphyry gold copper deposit huangtun deposit has recently been discovered in the north eastern margin of the basin detailed studies of geological characteristics and metallogenic processes of huangtun gold copper deposit are needed to supplement the mineralisation type of the luzong basin based on drill core logging and petrology observations of thin sections and polished sections a north striking sinistrial strike slip major fault and a series of secondary ne striking sinistrial strike slip faults have been identified in the mining area a mineralised breccia pipe at the intersection of the two groups of faults is the main host of the au ore body the alteration types in the mining area from deep to shallow include an albite alteration zone a biotite albite alteration zone a chlorite alteration zone and a sericite pyrite alteration zone a detailed mapping of the breccia pipe has been provided in the mining area seven different breccias facies have been divided according to the internal structure composition morphology matrix content and alteration assemblages genesis of the different breccia facies have been identified based on crosscutting relationships and clast in clast textures which revealed that there are two different faulting and brecciation stages during the first stage matrix supported breccia formed near the fracture zone gold copper mineralisation then occurred along the intersection of the two groups of fracture zones which formed k na silicate to sericite altered magmatic hydrothermal breccia from deep to shallow in addition these different facies of breccia correspond to four stages of fluid evolution the albite stage biotite albite stage chlorite stage and sericite pyrite stage hydrothermal breccia with a high matrix cement ratio then formed when mineralizing fluid permeated the fracture zone during the second stage the ore bodies were faulted to form tectonic breccia containing some massive carbonate quartz pyrite clusters as clasts based on the current study we conclude that the locations of the intersection of fault zones in the northern part of the luzong basin and the northern part of the mining area have potential for further gold mineralisation

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

proterozoic anorthosite granite nain batholith structure and intrusion processes in an active lithosphere scale fault zone northern labrador we present field evidence of the structure and evolution of a typical proterozoic massif type anorthosite the anorthosite forms a batholith composed of numerous plutons and ring complexes intruded episodically in two main sequences each producing anorthositic rocks and monzonite ferrodiorite followed by granite the batholith is located where a lithosphere scale fault zone 50 km wide and extending over 1000 km from greenland to labrador intersected an older continental suture intermittent episodes of mainly sinistral transtension along this gardar voisey s bay fault zone were associated with the generation of a number of pulses of magmatism and controlled the rise of magmas to middle and upper crustal levels between 1363 and 1289 ma both the large and small scale structures and magma intrusion processes are similar to those of many cordilleran batholiths with tabular plutons associated with ring dykes emplaced by cauldron subsidence and basin shaped plutons associated with cone sheets these

magnetite compositions from the baba ali iron deposit in the sanandaj sirjan zone western iran implications for ore genesis abstract the economically significant baba ali iron ore deposit is located in the sanandaj sirjan zone western iran is associated with diorite the mineralization trends in a ene wsw direction with thickness that varies from 30 m up to 50 m and a length of about 250 m the main mineral assemblages are massive magnetite epidote actinolite tourmaline quartz calcite and pyrite using different magnetite compositional discrimination diagrams the low concentrations of ti 0 11 wt al 0 06 wt cr 19 62 ppm and co 20 26 and high ni cr ratios 6 34 are consistent with a hydrothermal origin similar to typical skarn mineralization the different elemental compositions of various magnetite generations might be due to an ore forming fluid that initially a high t magmatic hydrothermal character then evolved to a lower temperture meteoric water dominated system it seems that fe bearing saline fluids infiltrated the carbonate host rocks causing high temperature acid metalliferous fluids to become neutralized during reaction with carbonates causing a decrease in iron solubility and saturating as a magnetite with increasing ph and decreasing the temperature the close spatial and temporal association of the mineralization with the fracture systems suggests that a pressure decrease also had a significant impact on the iron solubility triggering ore precipitation and replacement at relatively low temperatures 300 c under reducing conditions

zircon u pb and phlogopite 40 ar 39 ar age of the chengchao and jinshandian skarn fe deposits southeast hubei province middle lower yangtze river valley metallogenic belt china the chengchao and jinshandian deposits in the southeast hubei province are the two largest skarn fe deposits in the middle lower yangtze river valley metallogenic belt mlyrvmb china they are characterized by nw striking orebodies that are developed along the contacts between the late mesozoic granitoid and triassic carbonate and clastic rocks new sensitive high resolution ion microprobe and laser ablation inductively coupled plasma mass spectrometry zircon u pb dating of the mineralization related quartz diorite and granite at chengchao yield ages of 129 2 and 127 2 ma respectively and those at jinshandian of 127 2 and 133 1 ma respectively these results are interpreted as the crystallization age of these intrusions hydrothermal phlogopite samples from the skarn ores at chengchao and jinshandian have the plateau 40ar 39ar ages of 132 6 1 4 and 131 6 1 2 ma respectively these results confirm that both intrusions and associated skarn fe mineralization were formed contemporaneously in the middle early cretaceous time new zircon u pb and phlogopite 40ar 39ar ages in this study when combined with available precise geochronological data demonstrate that there were two discontinuous igneous events corresponding to two episodes of skarn fe bearing mineralization in the southeast hubei province 1 140 136 ma diorites and quartz diorites and 141 137 ma skarn cu fe or fe cu deposits and 2 133 127 ma quartz diorites and granites and 133 132 ma skarn fe deposits this scenario is similar to that proposed for the entire mlyrvmb the intrusions related to skarn fe deposits show obviously petrological and geochemical differences from those related to skarn cu fe or fe cu deposits the former are quartz diorite and diorite in petrology and have similar adakitic geochemical signatures and in equilibrium with a garnet rich residue whereas the latter are petrologically granite and quartz diorite that are distinguishable from adakitic rocks and in equilibrium with a plagioclase residue these features indicated that two episodes of magmatism and the formation of skarn fe bearing deposits in the southeast hubei province mlyrvmb might be associated lithosphere thinning induced by asthenosphere upwelling during the late mesozoic

the amphi atlantic distribution of the younger dryas paleoclimatic oscillation abstract interest in significant climatic fluctuations affecting large geographic areas but having a time range that is too brief to adduce the milankovitch radiation cycles has focused on the allerod younger dryas event which is a well established phenomenon of western europe manifested by glacial and vegetational reconstructions it is also shown by the foraminiferal evidence for shifts in the polar front in the north atlantic recent pollen and lithostratigraphic investigations in the maritime provinces of eastern canada and in the till plains of west central ohio on opposite sides of the late glacial spruce forest indicate that the event also left a record in eastern north america experiments with an atmospheric general circulation model with the temperature of north atlantic surface waters depressed to full glacial levels lowered summer temperatures in upwind periglacial eastern north america by 2 c just as far inland as they did downwind in western europe where the paleoecological record of cooling is clear a leading hypothesis for the cause for the younger dryas cooling appeals to the influx of tabular icebergs released from arctic ice shelves around the wasting scandinavian and siberian ice sheets during the allerod warming the resulting cooling of the north atlantic waters during the younger dryas could be facilitated or precipitated by the abrupt influx of glacial meltwater derived from almost the entire southern margin of the laurentide ice sheet and emerging from the gulf of st lawrence as brought about by a major shift in drainage direction from the mississippi river to the st lawrence river about 10 8 ka bp a supplemental influx of fresh water may have come from the contemporaneous drainage of the baltic ice lake the diversion of laurentide meltwater to the atlantic was caused by retreat of an ice lobe in northwestern ontario north of minnesota allowing the huge glacial lake agassiz in saskatchewan and manitoba to drain into the great lakes and more than double the inflow of meltwaters in the north atlantic thereby diverting the gulf stream and permitting the influx of icebergs from the north to cool the ocean surface minor readvance of the ice lobe about 10 ka bp temporarily diverted the lake agassiz drainage to the south with the final retreat of the ice the drainage again went to the east but by this time the ice sheets were much diminished and the regional climate had warmed enough so that the effects of the meltwater flux on the gulf stream were muted and the ice sheets bordering the north atlantic had retreated onto the land and no longer delivered enough icebergs to cool the surface waters the younger dryas interval thus was terminated and the warming manifested in the allerod was renewed

climatic and limnological changes associated with the younger dryas in atlantic canada pollen diatom and chironomid fossils from the sediments of a core from brier island bog lake nova scotia were studied in an attempt to relate changes in microfossil composition to a climatic cooling in atlantic canada correlative with the european younger dryas ca 10 to 11 ka our paleolimnological data were then compared to similar types of data from splan pond new brunswick to determine if there were any significant differences between a coastal and a more inland site nonarboreal pollen was dominant throughout the brier island core and the interval 10 0 11 0 ka did not show the typical decline in picea and increases in tundra like vegetation characteristic of many sites in atlantic canada however the limnological indicators did undergo marked changes in taxon composition the chironomid assemblage was initially dominated by shallow water warm adapted chironomid taxa followed by abundant sergentia a cold stenotherm during 10 11 ka sergentia disappeared in the post younger dryas interval and the warm adapted genera resumed dominance chironomid inferred paleotemperature reconstructions revealed that at both brier island bog lake and splan pond summer surface water temperatures dropped abruptly to between 13 and 17 c during the 10 11 ka interval suggesting that a cooler climate was present in atlantic canada correlative with the european younger dryas diatom assemblage changes during the same period corroborate the occurrence of limnological fluctuations

magnetite geochemistry of the longqiao and tieshan fe cu deposits in the middle lower yangtze river belt implications for deposit type and ore genesis abstract magnetite is a common mineral in many ore deposits and their host rocks and contains a wide range of trace elements e g ti v mg cr mn ca al ni ga sn that can be used for deposit type fingerprinting in this study we present new magnetite geochemical data for the longqiao fe deposit luzong ore district and tieshan fe cu deposit edong ore district which are important magmatic hydrothermal deposits in eastern china textural features mineral assemblages and paragenesis of the longqiao and tieshan ore samples have suggested the presence of two main mineralization periods sedimentary and hydrothermal at longqiao among which the hydrothermal period comprises four stages skarn magnetite sulfide and carbonate whilst the tieshan fe cu deposit comprises four mineralization stages skarn magnetite quartz sulfide and carbonate magnetite from the longqiao and tieshan deposits has different geochemistry and can be clearly discriminated by the sn vs ga ni vs cr ga vs al ni vs al v vs ti and al vs mg diagrams such difference may be applied to distinguish other typical skarn tieshan and multi origin hydrothermal longqiao deposits in the mlyrb the fluid rock interactions influence of the co crystallizing minerals and other physicochemical parameters such as temperature and f o 2 may have altogether controlled the magnetite trace element contents of both deposits the tieshan deposit may have had higher degree of f o 2 but lower fluid rock interactions and ore forming temperature than the longqiao deposit the tio 2 al 2 o 3 mgo mno and ca al mn vs ti v magnetite discrimination diagrams show that the longqiao fe deposit has both sedimentary and hydrothermal features whereas the tieshan fe cu deposit is skarn type and was likely formed via hydrothermal metasomatism consistent with the ore characteristics observed

iron rich fragments in the yamansu iron deposit xinjiang nw china constraints on metallogenesis abstract volcanic rock hosted iron deposits are among the important iron ores in china however the nature of primary magma and petrogenesis associated with these iron ores remains controversial here we report iron rich fragments irf from the yamansu iron deposit in eastern tianshan mountains nw china which occurs in association with volcanic breccia submarine volcanic breccia and ignimbrite the irf is composed of five types including oligoclase iron oxide type oio oligoclase albite iron oxide type oaio albite iron oxide type aio albite k feldspar iron oxide type akio and k feldspar iron oxide type kio these fragments display typical volcanic fabric features such as porphyritic texture hyalopilitic texture of the groundmass and vesicles filled by minerals to form amygdales the feldspar phenocrysts of irf are dominantly albite the groundmass of irf consists of magnetite and feldspar the magnetite is distributed in between the feldspar laths and together display hyalopilitic texture which could be observed only in volcanic rocks the vesicles are filled with magnetite feldspar chlorite and calcite from the margin to the interior the irf has high si al fe ca ti na and k contents and low mg content the average total fe is 26 wt the magnetite is mostly titanium vanadium magnetite with the tio2 content ranging up to 4 86 wt and v2o3 content up to 3 20 wt the irf probably came from iron rich melts and represent the products of the fenner magma evolution the basaltic magma evolved into the fe na rich residual melts by crystallization under low oxygen fugacity condition in a closed magma chamber after intruding into the shallow crust the fe na rich residual melts were emplaced in hypabyssal environments or erupted generating the orebodies or providing the material source for the generation of the high grade iron ores which were subsequently enriched by the late stage hydrothermal fluids

geology and geochemistry of the changlongshan skarn iron deposit anhui province china abstract the changlongshan skarn iron deposit is located in the northeastern part of the tongling fanchang fe cu district anhui province people s republic of china it is a specularite fe2o3 dominated iron deposit hosted in middle carboniferous to lower permian limestones with a drill indicated resource of 28 84 million tons of fe grading 35 9 58 6 both skarns and iron orebodies occur as tabular bodies along bedding parallel faults at some distance from the inferred granitic intrusions prograde skarn alteration consists mainly of andradite and hedenbergite whereas retrograde skarn is characterized by the development of actinolite chlorite and calcite the mineralogy of ores is dominated by specularite magnetite calcite and quartz primary fluid inclusions in garnet consist of aqueous liquid a vapour bubble and a halite crystal microthermometric measurements yield a homogenization temperature range for skarn alteration of 423 to 478 c with a salinity of 34 to 49 wt nacl equivalent fluid inclusions in calcite associated with mineralization generally consist of a vapour bubble and a liquid phase with a rare occurrence of three phase inclusions homogenization temperatures for two phase inclusions vary from 239 c to 303 c with a salinity of 13 to 22 wt nacl equivalent homogenization of three phase inclusions was observed between 264 and 287 c coupled with a salinity of 31 to 36 wt nacl equivalent stable isotope data indicate magmatic water was involved in the early stage of skarn formation 18 o h 2 o 3 7 to 7 6 dh2o 71 3 to 51 2 and a mixed magmatic meteoric water was responsible for the subsequent mineralization 18 o h 2 o 2 1 to 3 1 dh2o 40 1 to 28 1 geological and geochemical evidence obtained in this study supports a metasomatic replacement origin for the changlonshan iron deposit a conclusion contrary to previous syngenetic based interpretation

a type granite belts of two chemical subgroups in central eastern china indication of ridge subduction abstract early cretaceous a type granites in the lower yangtze river belt central eastern china with both a 1 and a 2 chemical subgroups formed at 125 2 ma after a cretaceous ridge subduction remarkably a 1 and a 2 group granites are distributed in three zones roughly parallel to each other and to a slightly older adakite belt in general a 1 granites form in intraplate settings whereas a 2 granites near paleo convergent margins the alternate distribution of these two subgroup a type granites is compatible with a proposed cretaceous ridge subduction in the region the subduction of a dry and hot spreading ridge may have only released small amount of fluids so that metasomatism on the overriding lithosphere was undetectable correspondingly resulted in a 1 granites later on in contrast wetter and colder oceanic crust away from the spreading ridge was responsible for mantle metasomatism and consequently the formation of a 2 granites further away from the ridge the subduction angle was much steeper and dehydration of the slab had occurred earlier during the subduction and thus dramatically reduced mantle metasomatism corresponding to a 1 granites again both a 1 and a 2 granites formed within a short period of time due to slab window rollback after the ridge subduction the distribution of the a 1 and a 2 granites together with the adakite belt may be taken as discrimination indice for ancient ridge subduction

radiocarbon dating the devensian lateglacial in britain new evidence from llanilid south wales radiocarbon dates are described from a section through lateglacial and early flandrian sediments at llanilid mid glamorgan south wales comparisons between age determinations on the alkali soluble humic and alkali insoluble humin organic fractions from 12 biostratigraphic horizons reveal the extent of contamination by both older and younger carbon residues the llanilid time scale suggests that for the lateglacial the earliest organic sediments date from around 13 200 yr bp the early interstadial juniperus maximum occurred at ca 12 400 12 500 yr bp with a marked decline some 200 years later the main betula phase lasted only from ca 11 700 to 11 400 yr bp and the end of the interstadial occurred around 11 100 yr bp the beginning of the flandrian dates from ca 10 000 yr bp the juniperus maximum occurred approximately 200 years later the expansion of birch woodland began around 9600 yr bp while the first hazel arrived in the area at ca 9300 yr bp these age determinations are discussed in the context of radiocarbon dates from comparable biostratigraphic horizons in western britain and the dating of lateglacial events in the ocean core records from the north atlantic

petrogenesis and mineralization of the fenghuangshan skarn cu au deposit tongling ore cluster field lower yangtze metallogenic belt article the fenghuangshan copper gold deposit located in the tongling ore cluster field along the lower yangtze metallogenicbelt lyrb ineasternchina mainlyconsistofskarnoreshostedingranodiorite u pb dating of mag matic zircons from fenghuangshan granodiorite yields a weighted mean 206 pb 238 u age of 143 1 1 6 ma five molybdenite samples collected in the fenghuangshan deposit yield a re osisochronage of 141 7 0 8 ma dem onstrating that the ore formation event is coeval with the fenghuangshan granodiorite intrusion the magmatic zircon hf t values vary from 12 0 to 28 3 corresponding two stage hf model ages between 1 6 ga to 2 4 ga geochemical and isotopic signatures suggest that the fenghuangshan granodiorite resembles adakite which was derived from partial melting of the subducted oceanic crust towards lyrb during the early cretaceous the occurrence of inherited zircons shows the intrusive granodiorite was assimilated by old crustal materials dur ing its emplacement the biotite thermobarometry zircon ce iv ce iii ratios and eu anomalies coincidently demonstrate that the magma source of granodiorite was under high to moderate oxidized condition conducive to cu au mineralization the sulfide ores in fenghuangshan deposit are enriched in pd and pt which could also be a consequence of the high oxidized magma source the high re abundance in molybdenite and platinum group element pge contents of sulfide ores suggest that the ore forming materials are characterized by mixed sources from the mantle and crust and were slightly affected by hydrothermal alteration

investigation on the distribution characteristics of ground cracks in the chengchao iron mine china in this study a comprehensive assessment of the distribution characteristics of ground cracks in the chengchao iron mine was conducted by field investigation and monitoring in general ground cracks are initially distributed around collapse pits and subsequently extend outwards centered on the mined out area greater ground deformation leads to more developed ground cracks ground cracks can be divided into cut through crack deep crack and shallow crack based on their downward extension depths furthermore the formation of ground cracks is controlled by both underground mining and geological structures ground cracks can be divided into mining induced crack and tectonic crack based on their main influencing factors moreover many types of ground cracks are caused by different failure modes including tensile failure shear failure and mixed failure ground cracks can be divided into vertical shear crack vertical shear and horizontal tensile crack horizontal tensile crack horizontal shear crack and mixed crack based on their formation mechanisms in particular the movement line and the break line defined as e 2 mm m and 6 mm m respectively can be reasonably regarded as disturbance boundary and crack boundary in a metal mine the disturbance zone caused by underground mining can be divided into collapse zone break zone and movement zone based on the size of ground deformation and the characteristics of ground cracks increases in ground crack width and length exert different degrees of stress release on the rock masses outside and inside the crack thus increasing their deformation difference in addition the extension of ground cracks is related to the ground topography and the strength and integrity of the rock masses and soil cracks on hilltop are more developed than those on flat land and cracks will initially appear in rock mass and soil rather than on a concrete structure due to the lower strain resistance of the rock mass and soil however concrete structures are more sensitive to cracking than rock mass and soil because of the better integrity of concrete structures

the amphi atlantic oscillation a proposed late glacial climatic event a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract numerous palaeoclimatic records from europe greenland and the north atlantic ocean provide evidence for a short term cooling event which preceded the younger dryas stadial of ca 11 10 ka bp the discovery of a similar event in eastern north america the killarney oscillation ko raised the possibility of a single pre younger dryas cooling event that affected the entire north atlantic seaboard this paper reviews evidence for the ko and other pre younger dryas events and discusses the basis for their correlation the informal name amphi atlantic oscillation is proposed as a collective term for the ko and events that correlate with it

formation of the jinshandian fe skarn ore field in the edong district eastern china constraints from u pb and 40ar 39ar geochronology abstract the jinshandian ore field represents one of the largest concentrations of fe skarn deposits in the edong district of eastern china orebodies of these deposits occur in skarn along the contacts between quartz diorite or quartz monzonite and triassic sedimentary country rocks in this paper we present new u pb geochronological data for magmatic zircon and hydrothermal titanite as well as 40 ar 39 ar ages on hydrothermal phlogopite to determine whether multiple magmatic hydrothermal events associated with formation of the fe skarn deposits in the jinshandian ore field the robust u pb zircon ages demonstrate that the quartz monzonite and quartz diorite were emplaced at 130 ma and 127 ma receptively the u pb and 40 ar 39 ar ages of hydrothermal titanite and phlogopite form the skarn indicate that fe mineralization also formed at ca 131 128 ma but with an additional 118 ma hydrothermal event recorded by phlogopite this geochronology confirms a causative linkage between granitic intrusion and skarn mineralization the data also indicate that at least two hydrothermal events took place in the jinshandian ore field one at 131 128 ma and the other at 118 ma integrating these ages from the ore field with previous geochronological data from the broader edong district two regional magmatic hydrothermal events are recognized in the edong district after 135 ma with the older one at 131 127 ma in excellent agreement with the 131 ma formation age of magnetite apatite deposits in the eastern part of middle lower yangtze river region and the younger one at 122 118 ma post dating emplacement of the ca 126 ma a type granite and syenite in the eastern part of middle lower yangtze river region a detailed comparison between the fe skarn deposits and magnetite apatite deposits in the middle lower yangtze river region suggests that these two deposit types not only share similar alteration assemblages and association with the evaporites within the ore forming systems but also may have formed during the same early cretaceous magmatic hydrothermal event

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

deep electrical structure and geological significance of tongling ore district abstract the tongling ore district is one of the most important cu polymetal producers in the lower yangtze river metallogenic belt of china to understand deep crust structure beneath the tongling ore district more comprehensively and objectively and to explore important scientific issues such as characteristics of lithospheric evolution the relationship between the crustal structure and metallogenesis it is necessary to study the variation of crust electrical structure in the study area for this purpose six magnetotelluric mt sounding profiles have been completed by sinoprobe 03 project based on the imaging results of the six profiles electrical conductivity structure of the crust has been analyzed the result shows that the geology beneath the profiles is characterized by layering in vertical direction and block division in horizontal direction the high resistivity features are related to the transparent zones detected at the upper crust in reflection seismic surveys the absence of reflectivity from the depths indicates a homogeneous zone which could often be related to granitic intrusions combining the regional tectonic evolution mt and other geophysical data we suggest that the high resistivity bodies crossing the tongling uplift reveals the center of magma activity and the layering in vertical direction in the lower crust reveals a normal lower crust model and propose a small scale underplating model which is different with both the partial melting of a thickened or delaminated lower continental crust model and the oceanic ridge subduction the underplating might be related to small scale lithospheric or lower crust delamination controlled by deep fault during the early cretaceous the result of this mt survey is important for constraining lithospheric evolution and metallogenesis in the lower yangtze metallogenic belt such as collision of north china craton and yangtze craton underplating models deep structure mechanisms of ne sw trending rift as well as graben basin and probable metallogenesis

the xinqiao cu s fe au deposit in the tongling mineral district china synorogenic remobilization of a stratiform sulfide deposit abstract the cu s fe au deposit at xinqiao is located in the tongling mineral district anhui province people s republic of china it is a large scale polymetallic deposit with drilling indicated reserves of 0 5 million tonnes of cu averaging 0 71 75 5 million tonnes of s averaging 29 3 and 24 9 million tonnes of fe averaging 46 as well as 11 2 tonnes of au averaging at 4 7 g tonne plus 248 4 tonnes of ag averaging at 248 4 g tonne there are two major mineralization types in the xinqiao deposit one is the economically significant stratiform orebody hosted in the lower carboniferous gaolishan siltstone c1g and overlying middle carboniferous huanglong limestone c2h while the other is the less important skarn type mineralization restricted to the contact between the yanshanian diorite 110 168 ma and the lower permian qixia marble p1q the ore in the xinqiao deposit is dominated by massive pyrite with minor amount of chalcopyrite magnetite pyrrhotite galena sphalerite quartz and dolomite four stages of deformation have been recognized to affect the sedimentary rocks in the xinqiao area the first two d1 and d2 produced mainly ne sw and nne ssw trending open folds whereas d3 is characterized by normal faults striking nne ssw and d4 is dominated by post mineralization strike slip faults segmenting the orebody the structural information obtained by this study not only revealed the transgressive nature of the stratiform orebody but also identified a strong structural control on the formation of the deposit it is concluded that the xinqiao polymetallic deposit was formed through remobilization of a carboniferous sulfide source bed by hydrothermal solutions related to late yanshanian plutonism 110 ma during which d3 normal faulting played an important role in localization of the mineralization such a two stage ore forming model is consistent with the most recent genetic interpretations of the deposit

direct dating of the oxygen isotope record of the last deglaciation by 14c accelerator mass spectrometry major trends of quaternary global climate are reflected in the continental ice volume changes which have been reconstructed by oxygen isotope analysis1 2 18o records from deep sea sediments show that the net glacial build up occurs relatively slowly3 but that the end of an ice age occurs quickly in less than 10 000 yr implying a nonlinear response4 5 to simple milankovitch theory6 the latter observation suggests that the cause of the most recent deglaciation was the maximum in summer calorific radiation at the upper latitudes of the northern hemisphere centred around 11 000 yr ago a view supported by early studies7 later work has produced conflicting dates the main source of confusion being problems with obtaining accurate and reliable dates here by using accelerator mass spectrometry we have measured 14c for various species of foraminifera to produce a reliable timescale for the oxygen isotope record our results show that at the end of the last ice age continental ice sheets began to melt more than 4 000 yr before the northern hemisphere maximum of summer calorific radiation

3d lithosphere scale density model of the central european basin system and adjacent areas abstract to analyze the first order structural features characterizing the crust and the lithospheric mantle below the central european basin system and adjacent areas a new lithosphere scale 3d structural density model has been derived that integrates published knowledge with 3d gravity modeling with this study we aim to integrate previous results on sub domains of the study area and regional results of limited resolution in conjunction with 3d gravity analysis to derive the configuration of the lower crust and lithospheric mantle that is consistent with the known density distribution of the sediment fill and with observed deep seismic data as well as with observed gravity the derived 3d density model resolves the internal configuration of the crystalline crust below the central european basin system and adjacent areas at the regional scale and shows that the crystalline crust is characterized by a layered structure the upper to middle crystalline crust is characterized by relatively low seismic p wave velocities and densities it shows strong variations in thickness across the study area that partly correlate spatially with the inherited segmentation in response to crustal amalgamation this upper to middle crystalline crust is underlain by a continuous high density high velocity lower crustal layer locally more than 30 km thick beneath the east european craton and generally decreasing in thickness from the older to the younger tectonic domains though the thickness of this high density lower crust is generally small below the permo cenozoic central european basin system it can reach locally more than 18 km below the northeast german and the norwegian danish basins the derived depth to the lithosphere asthenosphere boundary confirms previously proposed geometries and is up to 230 km deep beneath the precambrian domain but less than 100 km deep beneath the phanerozoic domains implying that the average thermal gradient is higher in the phanerozoic lithosphere than in the precambrian part

late glacial climatic oscillations as recorded in swiss lake sediments regional pollen assemblage zones for the late glacial period of the swiss plateau are introduced and defined they include four major zones artemisia juniperus hippophae betula pinus paz with several subzones pollen and oxygen isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000 9500 yr bp the first oscillation termed the aegelsee fluctuation occurs shortly before 12 000 yr bp and varve counts suggest its duration was ca 100 yr it is characterised by a short decrease in the oxygen isotopes as well as a short increase in nap associated with a depression in birch pollen values the second oscillation which occurs in the 18o record shortly before the deposition of the laacher see tephra ca 11 000 yr bp is termed the gerzensee fluctuation it occurs during a pine dominated phase and its vegetational effects cannot be determined palynologically the most prominent regressive phase is the younger dryas biozone ca 10 700 10 000 yr bp characterised by an increase in heliophilous nap and low 18o values the younger dryas biozone can often be subdivided palynologically into two parts a first part rich in grasses and juniper and a second part with higher filipendula and birch values during the preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios comparison of the swiss oxygen isotope profiles with the greenland dye 3 record suggests that not only the three major shifts in the 18o curves but also the minor ones are closely comparable suggesting some common climatic control

petrogenesis of the middle jurassic yinshan volcanic intrusive complex se china implications for tectonic evolution and cu au mineralization abstract volcanic subvolcanic rocks and associated cu au deposits in yinshan are located in the eastern part of the neoproterozoic jiangnan orogenic belt between the yangtze and cathaysia blocks constituting a large metallogenic district in southeastern china this paper presents new laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating element and sr nd hf isotopic data for yinshan igneous rocks in the dexing region our results show that the yinshan igneous rocks were produced during the middle jurassic ca 176 166 ma geochemically the yinshan igneous rocks are characterized by calc alkaline and show some adakitic affinities with high sr contents up to 903 ppm sr y up to 93 2 and la n yb n ratios 12 4 to 65 1 and low y 2 53 to 15 8 ppm and yb contents 0 22 to 1 39 ppm the absence of a negative eu anomaly extreme depletion in y and yb relatively low mgo contents 0 2 to 2 9 wt and relatively high 207 pb 204 pb ratio 15 555 15 575 indicate that yinshan igneous rocks were likely derived from the partial melting of thickened lower continental crust in addition the yinshan igneous rocks show similar element characteristics to arc derived igneous rocks with bulk earth like e nd t values 1 1 to 1 8 and initial 87 sr 86 sr 0 7036 0 7090 relatively depleted e hf t values 1 5 to 5 8 and hf model ages of 0 8 1 2 ga however there is no arc related evidence in the study area in the middle jurassic which indicates that these arc related elemental and isotopic compositions are possibly inherited from meso to neo proterozoic juvenile continental crust formed by the neoproterozoic oceanic crust subduction along the jiangnan orogen the geodynamic environment responsible for the development of the middle jurassic yinshan igneous rocks is probably a localized intra continental extensional environment along the ne jiangxi deep fault as a tectonic response to far field stress at the margins of south china plate during the early stage of the paleo pacific plate subduction regarding the cu au mineralization we infer that cu au were released from subducted oceanic slab and reserved in the juvenile crust during neoproterozoic subduction along the eastern jiangnan orogen partial melting of cu au rich neoproterozoic juvenile crust during the middle jurassic time in the yinshan area caused the formation of adakitic rocks and large scale cu au deposits our model provides a new insight into genesis of adakitic rocks and related cu au deposits in a non arc setting

limits on the ventilation rate for the deep ocean over the last 12000 years in this paper we present accelerator radiocarbon measurements on hand picked benthic and planktonic foraminifera separated from two deep sea cores raised from the south china sea from the benthic planktonic age differences we are able to place limits on the extent to which the ventilation rate of the deep pacific ocean has changed over the last 12000 years while much work remains to be done before any definitive answers for the global oceans can be given these results on cores with sedimentation rates suitably high to avoid major corrections for bioturbation effects suggest that the ventilation rate of the deep pacific ocean has remained nearly the same throughout holocene time further there is no suggestion that the rate was slower during the period of major glacial retreat these results confirm that the changes in atmospheric14c c ratio over the last 10000 years owe their origin to radiocarbon production rate changes

mesozoic metallogeny in east china and corresponding geodynamic settings an introduction to the special issue abstract the giant east china mesozoic metallogenic province hosts some of the world s largest resources of tungsten tin molybdenum antimony and bismuth ores of gold silver mercury lead zinc copper uranium and iron are also of major importance the province and its constituent metallogenic belts or regions south china middle lower yangtze river valley east qinling dabie interior of north china craton yan liao and north east china are the products of several pulses of igneous activity and mineralisation between 240 and 80 ma each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the mesozoic this geodynamic evolution is linked to a complex series of tectonic events involving far field subduction plate collisions crustal thickening post collision collapse and rifting

short wavelength infrared swir spectroscopy of phyllosilicate minerals from the tonglushan cu au fe deposit eastern china new exploration indicators for concealed skarn orebodies abstract the middle lower yangtze river metallogenic belt mlyrb is one of the most important cu au fe mo skarn porphyry metallogenic belts in eastern china after several decades of mining the shallow level mineral resources have been gradually exhausted which call for new exploration tools for concealed orebodies the tonglushan cu au fe skarn deposit 86 3 mt 1 66 cu 0 94 g t au and 39 4 fe is located in the western mlyrb skarn alteration mineralization are mainly hosted in the contact zone between cretaceous 141 ma quartz monzodiorite and its porphyry and the lower triassic carbonate rocks based on the mineral assemblages and their macro microscopic textural relationships the tonglushan cu au fe mineralization alteration can be divided into five stages pre ore s1 skarn potassic alteration fe ore s2 retrograde alteration and fe oxides cu au ore s3 quartz sulfides carbonate alteration s4 and supergene alteration s5 apart from the major skarn and retrograde alteration and carbonate minerals abundant fine grained phyllosilicate minerals including chlorite white mica illite muscovite and phengite smectite montmorillonite and saponite and kandite kaolinite dickite and halloysite group minerals have been identified at tonglushan by swir spectrometry integrating petrographic observations and swir spectral analysis four alteration zones with distinct phyllosilicate assemblages have been distinguished from the intrusion outward i ore barren quartz monzodiorite and its porphyry montmorillonite illite chlorite ii endoskarn close to the skarn hydrothermal mineralization center montmorillonite illite chlorite kaolinite dickite iii skarn hydrothermal mineralization center saponite chlorite and iv the external contact zone in dolomitic marble montmorillonite chlorite kaolinite dickite for the tonglushan altered rock samples swir spectrometry has identified wavelength shifts in the fe oh al oh and sub al oh absorption features of chlorite white mica montmorillonite and kandite respectively chlorite fe oh absorption occurs at longer wavelengths 2 250 nm white mica montmorillonite al oh absorption occurs at unusually long 2 212 nm and short 2 170 nm in strongly altered skarn proximal samples moreover the presence of kaolinite dickite saponite actinolite phlogopite and or chlorite quartz sulfides veins in these samples can be used as new vectors to explore deep level mineralization centers at tonglushan the distribution of various kinds of phyllosilicate alteration minerals at tonglushan especially the white mica and kandites with higher crystallinity in the deep contact zones indicates that the neutral to acidic hydrothermal fluids may have been generated with the precipitation of fe oxides and sulfides this study also highlights the potential of swir spectroscopy of phyllosilicate minerals for exploring concealed skarn orebodies in the mlyrb

late weichselian vegetation climate and floral migration at liastemmen north rogaland south western norway palynological results from liastemmen indicate a tripartite division of the late weichselian in the pleniglacial period from deglaciation ca 14000 bp to ca 13000 bp artemisia dominated pioneer vegetation on disturbed mineral soil was strongly influenced by cold winters and katabatic winds the late weichselian interstadial ca 13000 bp ca 11000 bp comprises a salix shrub consolidation phase and from ca 12700 bp a tree birch phase in the last 500 years of this period july and january means are estimated to about 16 c and between 2 c and 6 c respectively in the younger dryas stadial ca 11000 bp ca 10200 bp artemisia dominated vegetation returns three brief climatic deteriorations ca 12 250 bp 11 700 bp and 11 300 bp unfavourable to woody vegetation on humus soils are demonstrated within the interstadial critical climatic factors include cool winters and strong winds exposing vegetation and soil to frost drought and erosion the oldest and strongest oscillation probably involving local deforestation is correlated with the older dryas deterioration boreal circumpolar eurasiatic and arctic alpine plants dominated the late glacial flora for the majority of the late glacial taxa a northward migration is demonstrated this may also apply for papaver radicatum pinguicula alpina and primula scandinavica all with bicentric distributions in norway today

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

dissolution reprecipitation process of magnetite from the chengchao iron deposit insights into ore genesis and implication for in situ chemical analysis of magnetite abstract magnetite formed in different environments commonly has distinct assemblages and concentrations of trace elements that can potentially be used as a genetic indicator of this mineral and associated ore deposits in this paper we present textural and compositional data of magnetite from the chengchao iron deposit daye district china to provide a better understanding in the formation mechanism and genesis of the deposit and shed light on analytical protocols for in situ chemical analysis of hydrothermal magnetite magnetite grains from the ore related granitoid pluton mineralized endoskarn magnetite dominated exoskarn and vein type iron ores hosted in marine carbonate intruded by the pluton were examined using scanning electron microscopy and analyzed for major and trace elements using electron microprobe back scattered electron images reveal that primary magnetite from the mineralized skarns and vein type ores were all partly reequilibrated with late stage hydrothermal fluids forming secondary magnetite domains that are featured by abundant porosity and have sharp contact with the primary magnetite these textures are interpreted as resulting from a dissolution reprecipitation process of magnetite which however are mostly obscure under optically primary magnetite grains from the mineralized endoskarn and vein type ores contain high sio 2 0 92 3 21 wt al 2 o 3 0 51 2 83 wt and low mgo 0 15 0 67 wt whereas varieties from the exoskarn ores have high mgo 2 76 3 07 wt and low sio 2 0 03 0 23 wt and al 2 o 3 0 54 1 05 wt this compositional contrast indicates that trace element geochemical composition of magnetite is largely controlled by the compositions of magmatic fluids and host rocks of the ores that have reacted with the fluids compared to its precursor mineral secondary magnetite is significantly depleted in most trace elements with sio 2 deceasing from 1 87 to 0 47 wt on average and al 2 o 3 from 0 89 to 0 08 wt in mineralized endoskarn and vein type ores and mgo from 2 87 to 0 60 wt in exoskarn ores on the contrary average content of iron is notably increased from 69 2 wt to 71 9 wt in the secondary magnetite grains the results suggest that the dissolution reprecipitation process has been important in significantly removing trace elements from early stage magnetite to form high grade high quality iron ores in hydrothermal environments the textural and compositional data confirm that the chengchao iron deposit is of hydrothermal origin rather than being crystallized from immiscible iron oxide melts as previously suggested this study also highlights the importance of textural characterization using various imaging techniques before in situ chemical analysis of magnetite as is the case for texturally complicated u th bearing accessory minerals that have been widely used for u pb geochronology study

cold climatic episode of younger dryas age in tierra del fuego pronounced climatic change during the last glacial maximum is recognized as global in extent and has been attributed to orbital forcing1 not readily explained in a global context because of the equivocal nature of the evidence are the late glacial climatic events of short 100 1 000 yr duration the cold climate of the younger dryas chron 11 000 10 000 yr bp for example is known to have been particularly pronounced over the north atlantic and parts of europe and north america2 3 whereas in the southern hemisphere cold conditions for that time are not well established here we present evidence for late glacial climatic cooling in southernmost south america from studies of radiocarbon dated glacial and pollen stratigraphy at sites along the beagle channel in tierra del fuego where a forest tundra tension zone in the region is especially sensitive to shifting climate we conclude that the cold episode corresponds with the time of the younger dryas in europe when a drop in temperature ascribed most recently to colder sea surface temperatures and production rate of deep water in the north atlantic4 5 apparently occurred worldwide

geological geochronological and mineralogical constraints on the genesis of the chengchao skarn fe deposit edong ore district middle lower yangtze river valley metallogenic belt eastern china abstract the edong ore district is located within the westernmost middle lower yangtze river valley metallogenic belt mlyrb and hosts the largest concentration of skarn fe deposits in china although the origin of these deposits remains controversial the chengchao deposit is the largest skarn fe deposit so far discovered within the mlyrb and provides a good opportunity to address the debate surrounding the origin of these skarn fe deposits here we present geological geochronological and mineralogical data from the chengchao skarn deposit and associated intrusions and discuss the relationships between granitoids and mineralization in the chengchao deposit the nw se striking orebodies in the study area have porphyritic quartz monzonite and or granite footwalls and triassic marble or diorite hangingwalls indicating a spatial relationship between these intrusions and fe mineralization zircon u pb data from the granite porphyritic quartz monzonite diorite and porphyritic diabase dike within the deposit show ages of 129 1 128 1 140 1 and 126 1 ma respectively these ages and the previously reported ages on the timing of mineralization suggest that the porphyritic quartz monzonite and granite are coeval with the formation of the skarn fe deposit our data confirm that the granitic rocks are temporally associated with fe mineralization the prograde substage of skarn development is characterized by two stages of andradite adr98 38grs61 2prp2 0sps1 0alm1 0 and diopside di95 61hd37 5jo3 0 including an early stage of garnet and pyroxene formation that is genetically associated with the mineralization the early stage garnets are more andradite rich adr98 50grs49 2prp1 0sps1 0alm0 than the late veinlet garnets characterized by intermediate grandite compositions adr67 37grs61 31prp2 0sps1 0alm1 0 the early stage pyroxenes di95 74hd26 5jo1 0 are compositionally distinct from the late stage pyroxenes di84 61hd37 16jo3 0 compositional variations of early stage garnets in the zoned skarns indicate that skarn formation and fe mineralization are genetically associated with the porphyritic quartz monzonite and granite intrusions the geological geochronological and mineralogical evidence indicates that the porphyritic quartz monzonite and granite intrusions in the chengchao fe deposit are spatially temporally and genetically associated with fe mineralization

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

ore fluid geochemistry of the hehuashan pb zn deposit in the tongling ore district anhui province china evidence from ree and c h o isotopes of calcite abstract calcite is the main gangue mineral of the hehuashan lead zinc deposit which is located in the tongling ore district anhui province east china the ore bodies of the hehuashan deposit are hosted by dissolution breccia of the lower triassic carbonate sediments we report petrography rare earth elements ree and c h o isotope data of four generations of calcite recognized in the hehuashan deposit namely the pre ore stage calcite cal 1 early ore forming stage calcite cal 2 late ore forming stage calcite cal 3 and post ore stage calcite cal 4 in addition we also report c h o isotopes data of dolostone from the lower triassic carbonate sediments all four calcite generations show a low ree content 13 50 ppm on average indicating that the related ore forming fluids may not have been derived a magmatic fluid but rather be derived from the carbonate sediments or basinal brines low lree hree ratio 1 1 6 1 on average of all four calcite generations implies that no significant ree fractionation happened during the mineralizing processes the wide distribution of y ho ratios 17 70 of calcite indicates a result of fluids mixing the 13c values of calcite 1 4 to 4 2 are comparable to marine carbonates but the 18o values are lower indicating possibly a result of carbonates dissolution calculated 18o of the fluid in equilibrium with calcite vary from 3 1 to 0 1 combining the dv smow 100 to 81 implying a fluid mixing of a brine fluid and meteoric water or diagenetic pore water for the mineralization of the hehuashan deposit

distinctive features of late palaeozoic massive sulphide deposits in south china abstract more than 20 sediment hosted massive sulphide deposits occur in late palaeozoic basins in south china these deposits are accompanied by a certain amount of volcanic rocks in the host sequence and are economically important for their cu pb zn au and ag reserves the deposits and their host strata were commonly intruded by mesozoic granitoids remobilisation of sedimentary ores and magmatic hydrothermal overprinting processes resulted in the coexistence of massive sulphides with vein skarn and porphyry type orebodies in the same region or within a single deposit the ore containing basins occur in different tectonic settings the lower yangtze basin occurs on a passive continental margin where the deposits are high in cu and au with minor pb and zn and recoverable ag co and mo the ores have a lower concentration of radiogenic lead and 34s values close to zero fluid inclusions are highly saline and na rich fluids and metals of the lower yangtze region are interpreted to have been derived essentially from deep sources including the precambrian basement by contrast basins of the nanling region formed in an intracontinental setting developed on a folded caledonian basement these deposits are higher in pb zn sn and w as well as cu with recoverable ag sb hg u bi tl and mo the ores are characterised by a higher concentration of radiogenic lead and a wide variation of 34s composition fluid inclusions have lower salinities and higher k na ratios fluids are considered to have been sourced substantially from seawater by convection metals for the nanling deposits were essentially derived from the caledonian basement by leaching the contrast in ore composition between these two regions appears to have been controlled by differences in basement composition of the ore forming basins

genesis of the kaladawan fe mo ore field in altyn xinjiang china constraints from mineralogy and geochemistry abstract the kaladawan fe mo ore field in altyn xinjiang province nw china contains six fe mo deposits with total proven reserves of 60 mt fe and 10 000 t mo tabular lensoidal and stratiform orebodies occur in the cambrian foliated marble phyllite carbonaceous slate chlorite sericite schist and quartz sericite schist along the exocontact zone of the kaladawan granite skarns are extensively developed and dominated by garnet pyroxene epidote tremolite and actinolite with minor chlorite zoisite quartz and calcite ore minerals are mainly magnetite and molybdenite five alteration and mineralization stages i v were identified the prograde i and retrograde ii skarns are characterized by assemblages of garnet pyroxene and epidote tremolite actinolite respectively intruded and replaced by mineral assemblages of magnetite epidote zoisite iii quartz sulfides iv and calcite chlorite v in younging order the kaladawan garnet contains more andradite 61 2 94 4 mol than grossularite 37 5 5 0 mol pyroxene is mg rich and fe poor with an endmember range of 55 4 94 7 mol diopside and 42 5 4 7 mol hedenbergite amphibole comprises mainly tremolite and actinolite the kaladawan skarn mineral contents resemble typical skarn fe and mo deposits in situ la icp ms magnetite trace element analysis had identified unusually high mg mo and cr concentrations the high mo and the absence of molybdenite inclusions in magnetite suggest that the hydrothermal fluids may have been mo rich the magnetite also contains similar ti v and al mn values with typical skarn fe deposits therefore the kaladawan fe mo mineralization is best attributed to be skarn type and related to the kaladawan granite intrusion

microfabrics in situ trace element and sulfur isotope compositions of pyrite from the jinjiwo copper deposit in chengmenshan orefield northern yangtze block syngenetic stratabound mineralization and hydrothermal remobilization abstract the jinjiwo copper deposit is located in the jiurui ore district of the middle lower yangtze metallogenic belt the deposit has stratiform orebodies hosted by late carboniferous carbonate units pyrite is the dominant metallic mineral in the ores here we report on an integrated study on the microfabrics raman spectroscopy in situ la mc icp ms trace element and sulfur isotope of pyrite with a view to understand the geochemical variation genesis of copper mineralization and ore forming process textural observations suggested four types of pyrite corresponding to three metallogenic episodes syngenetic sedimentation pyi metamorphism or deformation pyii and skarn hydrothermal mineralization including the late skarn stage pyiii and hydrothermal stage pyiv raman spectra of pyrite reveal subtle differences in band position and widths fwhm and display the increasing formation temperature of from pyi through pyiv and pyiii to pyii colloform and laminated pyrite pyi share similarities in behavior of pairs of elements and have low co ni ratios and the former contains the highest concentrations of bi cu pb zn ag au mn that suggest rapid precipitation from highly saturated fluids pyii shows high co ni and as concentrations and co ni ratios of 0 03 to 6 19 pyiii and pyiv have greatly varying co ni ratios of 1 07 to 29 and typically low au concentrations suggesting a hydrothermal source pyiii is rich in co and se but is depleted in as cu pb zn ag and au in comparison with pyiv there are two kinds of sulfur one is that 34s values are near zero suggesting that the pyrite sulfur in the ores was derived from a mixed source in deep crust and the other is that 34s values are less than 39 1 indicating the sedimentary pyrite sulfur was originated from bacterial sulfate reduction the combined textural and compositional data of pyrite suggest that the formation of the jinjiwo copper deposit might have recorded the submarine exhalation sedimentation and the mesozoic tectonic transition deformation and hydrothermal overprint

rates of change and chronological problems during the late glacial period results of high resolution ams 14c dating of terrestrial plant macrofossils from late glacial and early holocene lake deposits in switzerland show three periods with constant radiocarbon ages these plateaux of constant age occur at 12700 10000 and 9500 y bp a comparison of this radiocarbon chronology with a varve chronology documents discrepancies between the sidereal and the radiocarbon time scale for the late glacial period the age plateaux and the time scale discrepancies have a significant impact on the estimation of rates of change during this period estimates of rates of change can be very misleading if calculated on the basis of radiocarbon ages this is illustrated by an example of estimated rates of late glacial and early holocene palynological change in switzerland

geodynamic constraints on orebody localization in the anqing orefield china computational modeling and facilitating predictive exploration of deep deposits abstract the anqing fe cu skarn deposit with an age of 134 to 142 ma and resources of 62 4 mt at 0 906 cu and 32 2 fe is one of the most important deposits in the yangtze river metallogenic belt east china to better understand the localization of orebodies and thus facilitate predictive exploration of deep orebodies computational modeling is used to simulate the coupled geodynamic processes during the syn tectonic cooling of the ore related intrusion based on geological and geophysical investigations in the anqing orefield the occurrences of the ore veins and veinlets in diorite and skarn as well as the sharp zigzag boundary of the orebody indicate that the cu ores were deposited after the solidification of the diorite and skarn formation and were located in some tensional structural spaces that are unevenly distributed along the contact zone between the felsic intrusion and sedimentary carbonates the locations of orebodies are closely associated with the contact zone shape the computational results of two models with two typical contact shapes show that pore fluid flow was focused into the dilation zones from different sources all the significant dilation zones in which the existing orebodies were located are distributed in some specific places of the south contact zone of the intrusion in addition these dilation zones are closely related to the contact zone shape of the intrusion and can control the location of orebodies through the coupled mechano thermo hydrological processes during cooling of the intrusion in the extension setting the skarns are not critical for controlling the localization of orebodies this means that exploration for deep ore should target deep dilation zones close to the contact boundary of the intrusion such recognition may provide a useful guide in selecting exploration targets in the anqing orefield as a direct result of computational modeling an orebody has been discovered in the deep dilation zone in this orefield it demonstrates that computational modeling is a promising tool for understanding the metallogenic processes and for facilitating the deep exploration of hidden orebodies that are related to intrusions

allerod younger dryas lake temperatures from midge fossils in atlantic canada remains of freshwater midges are abundant in lake sediments and their species distributions are closely related to the surface water temperature of lakes their distributions thus provide a powerful tool for paleoclimatology the distribution of species in a core from splan pond in atlantic canada indicates that there were abrupt transitions in late glacial temperatures between warm and cold states the transitions are correlative with the well known warm allerod and cold younger dryas events in europe these data thus confirm the inference from palynological data that these events affected regions on both sides of the atlantic

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

geologic setting of selected copper deposits of china seven selected major copper deposits of china are described baiyin of gansu province dexing of jiangxi province yulong of xizang tibet autonomous region zhongtiaoshan of shanxi province daye of hubei province tongling of anhui province and dongchuan of yunnan province these copper deposits can be classified into four types according to their geologic settings 1 volcanogenic deposits baiyin 2 porphyry copper deposits dexing yulong and zongtiaoshan 3 skarn deposits daye and tongling and 4 strata bound deposits dongchuan the dexing mines have by far the largest proven reserves 1 5 billion tons of copper ores

gushan magnetite apatite deposit in the ningwu basin lower yangtze river valley se china hydrothermal or kiruna type abstract the gushan deposit is one of the typical magnetite apatite deposits associated with dioritic porphyries in the lower yangtze river valley belt of the eastern yangtze craton the origin of this deposit is still uncertain and remains a controversial issue divergent opinions are centered on whether the iron deposits are magmatic or hydrothermal in origin however our field observations and mineralogical studies combined with previous published petrological and geochemical features strongly suggest that the main ore bodies in the gushan magnetite apatite deposit are magmatic specific evidence includes the existence of gas bubbles tubes and miarolitic and amygdaloidal structures melt flow banding structure and the presence of ore breccia new electron microprobe analyses of the pyroxene phenocrysts of the dioritic porphyry genetically associated with the gushan magnetite apatite deposit show that the fe contents in the evolving magma dramatically decrease and then gradually increase because there is no evidence of mafic magma recharge this scenario decreasing fe could be plausibly interpreted by fe rich melts separated from fe poor silicate melts i e liquid immiscibility was triggered by minor addition of phosphorus by crustal contamination the occurrence of massive iron ore bodies can be satisfactorily explained by the immiscible fe rich melt with enormous volatile contents was driven to the top of the magma chamber due to the low density the hot and volatile rich iron ore magma was injected along fractures and spaces between the dioritic intrusions and wall rocks and led to an explosion near the surface resulting in the immediate fragmentation of the roof of the intrusion and wall rocks forming brecciated ores moreover other types of ores can be considered as a result of post magmatic hydrothermal activities our proposed metallogenic model involving the kiruna type mineralization is consistent with the observed phenomenon in the gushan deposit

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

zircon u pb geochronology and hf isotopic compositions of the mesozoic granites in southern anhui province china abstract mesozoic magmatism is extensively developed in eastern china along the eastern asian continental margin but the geochronological framework is not well understood for each area in this study seventy eight samples were collected from the mesozoic igneous rocks in south anhui province east central china in order to precisely constrain their formation ages and contributions to crustal growth zircon u pb age determination using ion probe and laser ablation techniques indicate that magmatism in the area can be divided into two separate stages at 150 136 and 136 120 ma respectively the first stage of granitic rocks not documented in other areas of eastern china is mostly composed of hornblende bearing i type granodiorite and monzogranite and is considered to be formed by slab tearing during pacific subduction the second stage of magmatism coeval to that in other areas of eastern china is characterized by the occurrence of a type granite and syenite and their volcanic counterparts although i type granitic rocks are also developed locally these rocks are mostly distributed around and within the fault controlled volcanic basins and some are closely related to detachment shearing indicating their formation in an extensional setting zircon hf isotopic analyses indicate that archean material might be present in the area but that the main episode of crustal growth took place during the mesoproterozoic with very little juvenile material in the mesozoic

pge geochemistry of the fengshan porphyry skarn cu mo deposit hubei province eastern china abstract the fengshan cu mo deposit is located in the western part of the jiurui cu au mo district in the late mesozoic middle lower yangtze river metallogenic belt yrmb eastern china the mineralization is spatially associated with the fengshan granodiorite porphyry stock 149 138 ma where two types of ore bodies porphyry skarn occur the fengshan deposit is located on the yangtze craton i e in an intracontinental extensional environment a geological setting not considered by previous studies of pge abundance and distribution in porphyry systems for the present investigation the pge geochemistry of fourteen samples of the granodiorite ore and flotation concentrates were determined by icp ms after preconcentration by the lead fire assay technique from large 30 g samples a maximum of 32 ppb pd and 81 2 ppb pt is reported for the molybdenum flotation concentrate cu au pt pd contents from flotation concentrate samples are almost 1 to 2 orders of magnitude higher than those reported for ore samples this is especially true for the pt content covariant diagrams of cu and mo with noble metals au ag pt and pd reveal weak correlation between cu vs au ag and mo vs pt also au shows a slightly positive relationship with pt and pd it is apparent that pd and pt contents of flotation concentrate from the fengshan deposit are considerably lower than those reported for porphyry deposits in an island arc setting however au and ag appear to be elevated in the fengshan deposit the intrusion derived from an enriched mantle source high oxygen fugacity fo2 and liberation of mantle sulfates during partial melting are the first steps for pge enrichment in porphyry cu deposits however the fengshan granodiorite was most likely generated by partial melting of enriched mantle that was previously metasomatized by slab melts related to an ancient subduction system au pt and pd in potassic alteration zones and or endocontact zones are transported as an aqueous chloride complex in high temperature hypersaline fluid in contrast au pt and pd would be transported by bisulfide complex in low temperature intermediate salinity fluid in phyllic alteration zones and or exocontact marble that is distinctly different from the porphyry cu deposits in an island arc environment where intrusion derived directly from slab melting and pd and pt are transported only as chloride complexes

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

a genetic link between iron oxide apatite and iron skarn mineralization in the jinniu volcanic basin daye district eastern china evidence from magnetite geochemistry and multi mineral u pb geochronology various styles of ore deposits may form from a single magmatic hydrothermal system identification of a possible genetic link between different ore types in a region is not only of critical importance for a better understanding of the magmatic hydrothermal processes but can also help in successful mineral exploration both iron oxide apatite ioa and iron skarn deposits are closely associated with intrusive rocks of intermediate to felsic in composition but whether these two ore types can form from the same magmatic intrusion remains poorly understood in this study we present a comparative study between a newly identified subsurface ioa ore body located at the apex of a diorite porphyry and the iron skarn ore bodies located immediately above it in the jinniu volcanic basin of the daye district middle lower yangtze river metal logenetic belt mlyrmb eastern china in order to highlight a genetic link between these two styles of mineralization the ioa ores are dominated by ti rich magnetite with variable amounts of fluorapatite diopside and actinolite this mineralogical assemblage is distinctly different from the iron skarn ores which consist mainly of ti depleted magnetite and subordinate pre ore garnet and diopside and post ore quartz chlorite calcite and pyrite in addition magnetite from the ioa ores is characterized by well developed ilmenite lamellae and has high concentrations of ni v co and ga consistent with high temperature crystallization whereas magnetite grains from the iron skarn ores usually exhibit oscillatory growth zones and contain much lower ni v co and ga indicating their formation under relatively low temperatures titanite and fluorapatite from the ioa ores have u pb ages of 132 5 2 4 ma to 128 4 3 0 ma which match a titanite u pb age for the associated iron skarn ores 1323 2 0 ma and are consistent with zircon u pb ages for the ore hosting diorite porphyry 130 4 0 7 ma to 130 3 0 5 ma this age consistency supports a possible genetic link among the diorite porphyry ioa ores and iron skarn ores we propose that the ioa and skarn ores are the products of two consecutive mineralization stages of the same magmatic hydrothermal system involving a high temperature hypersaline fluid coexisting with the diorite porphyry magma during emplacement and a subsequent low temperature diluted hydrothermal fluid other ioa and iron skarn deposits of similar ages 130 ma are found in a series of volcanic basins in the mlyrmb which forms one of the world s largest ioa metallogenic belts the close association of the two ore styles identified at daye provides a useful exploration guide for ioa and iron skarn deposits both on a local and regional scale

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

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

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

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

thermodynamic study of the association and separation of copper and gold in the shizishan ore field tongling anhui province china abstract the shizishan ore field is the largest gold copper ore field in the tongling ore district of anhui province china copper and gold deposits in the district are present as one commodity deposits or as deposits with both commodities copper and gold mineralization are either cogenetic or are temporally and spatially distinct we present the results of systematic geochemical analysis of fluid inclusions from typical au cu deposits in the shizishan ore field these data are used to determine the solubility of cu and au in the ore forming fluids and to ascertain the mechanisms and factors that controlled variations in the association and separation of copper and gold mineralization our results indicate that copper in the ore forming fluids was transported as cucl2 and cucl0 complexes and that the solubility of copper was controlled by variations in cl concentration in addition the precipitation of copper was controlled by changes in temperature ph fo2 and fo2 in comparison gold in the ore forming fluids was transported as au hs 2 and au2s hs 22 complexes and the solubility of gold was controlled by variations in total sulfur concentration the precipitation of gold was controlled by temperature ph fo2 and fo2 these differences between the two elements meant that copper and gold in the ore forming fluids responded in different ways to changes in physicochemical conditions copper precipitated under relatively acidic conditions at high temperatures while gold precipitated under weakly alkaline conditions at relatively low temperatures this dissociation resulted in the temporal and spatial separation and zonation of copper and gold mineralization in the shizishan ore field

iron isotope fractionation during skarn type metallogeny a case study of xinqiao cu s fe au deposit in the middle lower yangtze valley abstract fe isotope compositions of mineral separates and bulk samples from xinqiao cu s fe au skarn type deposit were investigated an overall variation in 57 fe values from 1 22 to 0 73 has been observed which shows some regularity the 57 fe values of endoskarn and the earliest formed fe mineral phase magnetite are ca 1 2 and ca 0 3 lower respectively relative to the quartz monzodiorite stock indicating that fluid exsolved from the stock is enriched in light fe isotopes moreover spatial and temporal variations in 57 fe values are observed which suggest iron isotope fractionation during fluid evolution precipitation of fe bearing minerals results in the fe isotope composition of residual fluids evolving with time precipitation of fe iii minerals incorporating heavy iron isotopes preferentially leaves the remaining fluid enriched in light isotopes while precipitation of fe ii minerals preferentially taking up light iron isotopes and makes the fe isotopic composition of the fluid progressively heavier the regularity of fe isotope variations occurred during fluid exsolution and evolution indicates that the dominant fe source of xinqiao deposit is magmatic overall this study demonstrates that fe isotope composition has great potential in unraveling ore forming processes as well as constraining the metal sources of ore deposits

global nature of the younger dryas cooling event inferred from oxygen isotope data from sulu sea cores the younger dryas an approximately 1 000 year long return to near glacial conditions interrupted the glacial holocene climate transition during which most of the northern hemisphere ice sheets melted evidence for the younger dryas event has been found mainly in sediments from the north atlantic ocean and northwest europe and this has led to the idea that the event was caused by an injection of meltwater into the north atlantic ocean1 3 this model however has been recently questioned in the light of coral reef data on the rate of sea level changes during this transition4 here we present high resolution oxygen isotope records from benthic and planktonic foraminifera from two radiocarbon dated cores in the sulu sea showing that the younger dry as occurred synchronously in the surface and deep waters of the sulu sea and the northern atlantic ocean by combining our results with other palaeoclimate data we suggest that the younger dry as event was a global phenomenon and we believe it to have been caused by low atmospheric co2concentrations

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

chlorite chemistry of tongshankou porphyry related cu mo w skarn deposit eastern china implications for hydrothermal fluid evolution and exploration vectoring to concealed orebodies abstract recent years the depletion of shallow mineral resources has drawn increasing attention to the exploration of hidden ore bodies in deep of skarn type deposits chemical composition of chlorite is an effective tool for tracing the hydrothermal fluid evolution and has been increasingly used for deep level exploration of porphyry cu au deposits pcds however the technique was rarely applied onto porphyry related skarn deposits the tongshankou cu mo w deposit 0 55 mt cu 0 86 0 01 mt mo 0 10 and 0 12 mt wo3 0 19 is one of the largest skarn porphyry deposits in the middle lower yangtze river metallogenic belt mlyrb in eastern china in this study new petrographic and trace element data of the hydrothermal chlorites from tongshankou were presented to constrain the ore fluid evolution and to explore the vectoring potential of the concealed orebodies at tongshankou four types of chlorite have been identified i e g type chlorite that replaced the original magmatic biotite or hornblende v type chlorite in chlorite quartz sulfides veins in the granodiorite porphyry alteration zones i and ii s type chlorite that replaced garnet in the intensive skarn alteration zone iii and m type chlorite quartz calcite sulfides veins that cut the dolomitic marble in the distal alteration zones iv and v all the four types of chlorites are typically trioctahedral chlorite the fe mg tschermark and di trioctahedral substitution mechanisms likely control the geochemical variations of the tongshankou chlorites empirical thermometer indicates that the tongshankou chlorites were crystallized at 169 322 compared with typical metamorphic chlorites the higher zn and sr contents but lower al content in the tongshankou chlorites can potentially distinguish the skarn type hydrothermal chlorites from typical metamorphic ones compared with the chlorites in the typical pcds the tongshankou g type chlorite has higher fe zn as and sn contents but lower al mg co and cu contents which likely reflect its protolithic and or fluid geochemical inheritance the tongshankou v m and s type chlorites have high contents of mobile elements such as sr ca sn and b and metals such as fe cu as zn and pb indicating that they were directly precipitated from the hydrothermal fluids from the granodiorite porphyry to the marble wallrocks the spatial chlorite geochemical variations at tongshankou indicate that the increasing zn mn ga ge and pb contents and decreasing v sc and ti contents are potential vectors toward concealed mineralized porphyries at tongshankou our study highlights that the chlorite geochemistry is a potential tool for ore fluid tracer and vectoring tool toward concealed skarn porphyry orebodies in the mlyrb

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

multiple mesozoic mineralization events in south china an introduction to the thematic issue mesozoic mineral deposits in south china include world class deposits of w sn and sb and those that provide the major sources of ta cu hg as tl pb zn au and ag for the entire country these deposits can be classified into polymetallic hydrothermal systems closely related to felsic intrusive rocks sn w mo granites cu porphyries polymetallic and fe skarns and polymetallic vein deposits and low temperature hydrothermal systems with no direct connection to igneous activities mvt deposits epithermal au and sb deposits recent studies have shown that they formed in the triassic indosinian jurassic cretaceous early yanshanian and cretaceous late yanshanian stages indosinian deposits include major mvt pb zn ag deposits and granite related w sn deposits early yanshanian deposits are low temperature sb au and high temperature w sn and cu porphyry types many late yanshanian deposits are low temperature au as sb hg and u deposits and also include high temperature w sn polymetallic deposits the formation of these deposits is linked with a specific tectonothermal evolution and igneous activities this special issue brings together some of the latest information in eight papers that deal with the origins and tectonic environments of mineral deposits formed in these stages we anticipate that this issue will stimulate more interests in these ore deposits in south china

geochronology petrogenesis and metallogenic implications of mineralization related intrusive rocks in the xuancheng ore district eastern china abstract the xuancheng ore district is a newly discovered ore district within the middle and lower yangtze river metallogenic belt mlyrmb of eastern china this district contains numerous skarn porphyry deposits and this study focuses on four intrusions associated with known skarn mineralization within this district namely the shizishan pyroxene diorite spd the changshan biotite pyroxene diorite cbpd the maweishan quartz diorite mqd and the magushan porphyritic granodiorite mpg new u pb zircon age data indicate that all of these intrusions formed between 136 and 132 ma they are all calc alkaline enriched in the large ion lithophile elements lile and the light rare earth elements lree are depleted in the high field strength elements hfse and the heavy ree hree and have slightly negative eu anomalies the spd and cbpd have similar 87sr 86sr i 0 7060 0 7068 and 0 7065 0 7068 end t 10 6 to 9 5 and 10 1 to 9 9 and zircon ehf t 16 5 to 10 3 and 13 2 to 9 9 values whereas the mqd intrusion has similar 87sr 86sr i 0 7062 0 7076 values but higher end t 8 7 to 8 2 and zircon ehf t values 11 9 to 6 2 than the spd and the cbpd this indicates that the magmas were predominantly derived from the enriched lithospheric mantle but the mqd magmas incorporated less crust derived material than the spd and cbpd magmas the mpg intrusion has different 87sr 86sr i 0 7079 0 7086 end t 6 0 to 5 7 and zircon ehf t values 5 1 to 2 1 than the other intrusions indicating this intrusion formed from magmas derived from the lithospheric mantle that assimilated upper crustal material prior to and or during emplacement the compositions of plagioclase within the mqd and mpg intrusions provide no evidence of magma mixing these new data indicate that the 136 132 ma magmatism within the xuancheng region formed from magmas generated by the partial melting of an enriched region of the lithospheric mantle that was previously metasomatized by fluids derived from a subducted oceanic lithospheric slab the magmas then underwent fractional crystallization e g the mqd intrusion and or the assimilation of crustal material e g the mpg intrusion these processes generated parental magmas that were enriched in h2o s and metals e g cu increasing their mineralizing potential and potentially leading to the formation of the skarn deposits within the xuancheng ore district identifying intrusions with similar characteristics may be a useful exploration tool for skarn type mineralization within this region and the wider mlyrmb

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

molybdenite re os dating zircon u pb age and geochemistry of granitoids in the yangchuling porphyry w mo deposit jiangnan tungsten ore belt china implications for petrogenesis mineralization and geodynamic setting abstract the yangchuling w mo deposit located in the jiangnan porphyry skarn jnb tungsten ore belt is the first recognized typical porphyry w mo deposit in china in the 1980 s stockworks and disseminated w mo mineralization occur in the roof pendant of a 0 3 km 2 monzogranitic porphyry stock that intruded into a granodiorite stock hosted by neoproterozoic phyllite and slate la icpms zircon u pb analyses suggest that of the monzogranitic porphyry and granodiorite were formed at 143 8 0 5 ma and 149 8 0 6 ma respectively six molybdenite samples yielded a re os weighted mean age of 146 4 1 0 ma geochemical data show that both granodiorite and monzogranitic porphyry are characterized by enrichment of large ion lithophile elements lile relative to high field strength elements hfse indicating a peraluminous nature a cnk 1 01 1 08 two granitoids are characterized by a negative slope with significant light ree heavy ree fractionation la yb n 8 38 23 20 and negative eu anomalies eu eu 0 69 0 76 the p 2 o 5 contents of the yangchuling granitoids range from 0 12 to 0 17 and exhibit a negative correlation with sio 2 reflecting that they are highly fractionated i type they have high initial 87 sr 86 sr ratios 0 7104 0 7116 low negative e nd t 5 05 to 5 67 and homogeneous e hf t between 1 39 and 2 17 indicating similar sources additionally two stage nd model ages t dm2 of 1 3 1 4 ga and two stage hf model ages t dm2 of 1 2 1 3 ga are consistent indicating that neoproterozoic crustal rocks of the shuangqiaoshan group could have contributed to form the yangchuling magmas considering the two groups of parallel late mesozoic ore belts namely the jiangnan porphyry skarn tungsten belt jnb in the south and the middle lower yangtze river porphyry skarn cu au mo fe ore belt yrb in the north the nanling granite related w sn ore belt nlb in the south the neighboring qin hang porphyry skarn cu mo hydrothermal pb zn ag ore belt qhb in the north as well as the southeastern coast porphyry skarn cu mo au ore belt scb recognized in south china in this paper we propose that the latest jurassic to earliest cretaceous granitoids and associated ores were formed during a tearing of the subducting izanagi slab this tearing of the subduction slab caused the upwelling of asthenosphere and the resulting mantle crust interaction the granitoid related w ore systems in jnb resulted from the remelting of the proterozoic crust the mafic ultramafic volcanic rocks of the shuangqiaoshan group intercalated with phyllite and slate ophiolitic melange and magmatic arc rocks mainly comprising i type granite basalt andesite rhyolite pyroclastics together with subduction related metasomatized lithospheric mantle would have provided additional mantle material in this case the partial melting of rocks of the shuangqiaoshan group can produce s i and transitional type granitoids after strong differentiation it formed tungsten bearing granitoids characterized by enrichment of high alkali silicon and volatile components in the yangchuling mine area the small monzogranitic porphyry stock has stronger fractionation volatile content and ore forming components than the older granodiorite resulting in the development of the porphyry w mo ore system