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

shrimp u pb zircon dating of grenville age events in the western part of the musgrave block central australia shrimp u pb zircon dating of structurally constrained felsic orthogneiss samples in the western musgrave block has been used to delineate discrete magmatic and metamorphic events at c 1300 and c 1200 ma the dating of pre d1 and post d1 felsic orthogneiss constrains d1 to have occurred at 1312 16 to 1324 4 ma this is the first geochronological study to identify such a metamorphic and deformation event in the musgrave block d1 was accompanied by a major magmatic event involving the emplacement of voluminous felsic orthogneiss between 1296 and 1324 ma zircon overgrowths on numerous igneous zircon cores give a consistent age of c 1200 ma reflecting zircon growth during a second high grade metamorphic event d2 this c 1200 ma metamorphic event was followed by the intrusion of a c 1190 ma megacrystic granite the c 1300 and c 1200 ma events in the musgrave block can be tentatively correlated with metamorphic events in the albany fraser orogen and the windmill islands and bunger hills in east antarctica a major continuous grenville age orogenic belt joining these areas may have represented a plate boundary between the pre rodinian proto australian continent and proto antarctica during the formation of rodinia in the mesoproterozoic

on the average absolute transport of the deep western boundary currents east of abaco island the bahamas abstract data obtained from a line of absolute current profiler pegasus and ctd stations at 26 5 n east of abaco island in the northern bahamas are used to estimate the average transport and overall level of variability of the deep below 800 m southward flow associated with the so called deep western boundary current dwbc at this latitude from april 1985 to september 1987 a total of 11 sections were made along a line extending from near the island boundary to 85 km offshore as part of the subtropical atlantic climate studies stacs program in all but two cases when pegasus data were obtained over the total depth absolute velocities were determined from 0 to about 3000 db while ctd derived relative velocities were determined over the total depth using the combined datasets it is possible to reference the relative geostrophic velocity with pegasus data thereby obtaining an estimate of the absolute southward transport of the deep flow the average value of transport determined in this man

some isotopic constraints on the evolution of the granulite and upper amphibolite facies terranes in the eastern musgrave block central australia abstract the central to eastern musgrave block central australia consists of the meso to neoproterozoic fregon and mulga park subdomains that are separated by a zone of mylonites and pseudotachylytes known as the woodroffe thrust the subdomains were previously considered to have undergone different geological histories but the differences relate mainly to metamorphic grade the fregon subdomain attained at least transitional granulite facies metamorphic conditions and the mulga park subdomain reached upper amphibolite facies felsic gneisses from both the fregon and mulga park subdomains contain zircons that are structured with euhedral centres overgrown by round elongate rims ion microprobe u pb analyses of the cores yield ages of 1557 24 and 1554 28 ma respectively and are interpreted to represent the time of igneous crystallization these ages place a maximum age constraint on the deposition or emplacement of the gneiss precursor high grade metamorphism grading from upper amphibolite to granulite facies took place between 1200 and 1150 ma and prior to the intrusion of several granitoid suites at around 1150 ma the kulgera adamellite and ayers ranges adamellite granitoid suites of the fregon subdomain yield ion microprobe u pb crystallization ages of 1150 12 and 1152 11 ma respectively a concordant u pb isotope dilution analysis on the ayers ranges adamellite yields a more precise age of 1152 3 ma the porphyritic suite intruding the mulga park subdomain yield an ion microprobe u pb magmatic age of 1159 20 ma these emplacement ages indicate extensive grenvillian felsic magmatism not previously recognized in australia the woodroffe thrust formed during a period of substantial crustal shortening the petermann orogeny 550 ma when the fregon subdomain was thrust onto the mulga park subdomain synkinematic muscovite and biotite record k ar and rb sr ages between 560 and 520 ma this petermann event is not recorded in the fregon subdomain due to confinement of the strain and associated mineral recrystallization to the underlying mulga park subdomain we suggest that the granulites were not exposed prior to the petermann orogeny as the basal quartzites of the amadeus basin occur only on the amphibolite facies mulga park subdomain

determining the strength of the deep western boundary current using the chlorofluoromethane ratio abstract the dilution of a passive tracer during deep water formation and the subsequent advection mixing in a deep boundary current is modeled with application to chlorofluoromethanes cfms in the north atlantic two different types of boundary currents are considered a uniform flow and a simple shear flow in each case the core of the flow mixes with surrounding water which continually accumulates cfms in an extreme case the coupled systems predicts that the cfm ratio in the current is unaltered from the ratio of its source water save for a time lag more realistic cases however suggests that the ratio is not a conserved quantity but is substantially altered in both the overflow basin and boundary current matching the model results to cfm data collected near the grand banks gives a predicted average core speed of 5 10 cm s 1 for the deep western boundary current and provides a constraint on the transport and diffusivity of the flow as well

the flux and mixing rates of antarctic bottom water within the north atlantic calculation was made of the northward flow of antarctic bottom water into the western north atlantic basin through a passageway approximately 300 km wide between the ceara rise and the mid atlantic ridge at about 4 n two moorings carrying four current meters each were placed in the region where currents were expected to be the greatest and were left for 360 days the current was not steady but exhibited large surges with approximately a 60 day time scale whose cause is unknown current meters in the fastest flowing region all exhibited a net northward flow it is estimated that approximately 0 8 106 m3 s 1 of water colder than 1 9 c potential temperature flowed on the average into the north atlantic with this number possibly being too small by 0 3 106 m3 s 1 or too big by 0 1 106 m3 s 1 depending upon estimates of the width of the region which the current meters sample however these numbers differ from geostrophic estimates of 1 98 106 m3 s 1 the disagreement coming almost entirely from the fact that the geostrophic estimates give a sizeable flux of water colder than 1 2 c while the current meters do not based upon the two different flux rates residence times and mixing coefficients are calculated for antarctic bottom water for each 0 1 c potential temperature interval from 1 0 c to 1 9 c finally some comments on the dynamics of the northward flow are made

path of the north atlantic deep water in the brazil basin recent hydrographic sections and high quality historical data sets are used to determine geostrophic currents at subtropical latitudes in the western basin of the south atlantic levels of no motion are determined from water mass information and a mass balance constraint to obtain the transport field of north atlantic deep water nadw in this region the incoming nadw transport of about 20 sv from the north at 19 degrees s appears to be balanced by only one third of this transport leaving in the south and two thirds leaving to the east or northeast at the mid atlantic ridge a simple model is proposed to determine the cause of the nadw branching it is shown that potential vorticity preservation in the presence of topographic changes leads to a similar flow pattern as observed with branching near the vitoria trindade ridge and also an eastward turning of the southward western boundary current at about 28 degrees s the latitude where a balance of planetary vorticity change and stretching can be expected

skarn metallogeny through zircon record an example from the daye cu au fe mo district eastern china abstract the daye district in eastern china hosts more than 50 fe cu au mo porphyry skarn deposits that are associated with intermediate to felsic rocks of early cretaceous ages the origin of these ore related granitoids has been intensively investigated but the petrogenetic factors controlling variable metal associations e g fe cu mo or cu au fe in different skarn deposits remain not well understood here we present hf isotope and trace element data of zircons from ore related intrusions of four representative skarn deposits i e the lingxiang and chengchao fe skarn the tonglushan cu au fe skarn and the tongshankou cu mo porphyry skarn deposits to better understand controls of the source oxidation state and fractionation degree of the magmas on the polymetallic metallogeny in the daye district zircons from the ore related granodiorite at tongshankou quartz diorite at tonglushan and diorite at lingxiang have comparable ehf t values ranging from 11 3 to 1 1 which are similar to values of the early cretaceous mafic rocks ehf t 11 9 to 1 2 in the daye district and adjacent areas this similarity suggests that these ore related intrusions were largely derived from an enriched lithospheric mantle source in comparison zircons from the ore related diorite and quartz monzonite associated with the chengchao fe skarn have much lower ehf t values 11 6 to 25 3 indicating larger degrees of crustal contribution on average zircons from the cu related intrusions at tongshankou and tonglushan have higher ce ce 1100 method of zhong et al 2019 and ce4 ce3 170 method of ballard et al 2002 ratios which are interpreted reflecting higher oxidation state for the magmas in contrast zircons from fe related intrusions at chengchao and lingxiang have much lower average values of ce ce preliminary results presented here further reveal that zircon eu eu ratio can be a useful discrimination for intrusions associated with the various metal associations in the daye district zircon eu eu of 0 45 broadly separates the fe skarns and cu bearing skarns while eu eu of 0 65 can further distinguish the cu au fe skarn from the cu mo variety this study highlights zircon chemistry as a useful indicator for the nature evolution and metallogeny of the ore related intrusions

40ar 39ar thermochronology of the southern gawler craton australia implications for mesoproterozoic and neoproterozoic tectonics of east gondwana and rodinia 40ar 39ar thermochronology of the southern gawler craton australia reveals a protracted history of slow cooling with local crustal heating rapid cooling and fault reactivation between 1700 and 700 ma hornblendes from most of the southern part of the craton including the kalinjala mylonite zone yield ages 1580 1610 ma with younger more discordant samples showing evidence of retrogression these results indicate that the region cooled below 500 c 100 m y after the kimban orogeny and coincident with the gawler range hiltaba suite magmatism to the north perhaps associated with postorogenic extension biotite and k feldspar data indicate that regional cooling after this time was more gradual with a few exceptions locally in the southeastern eyre peninsula rapid cooling at 1425 ma is indicated by nearly concordant hornblende and biotite ages and may record a phase of regional extension other exceptions include areas of lower grade archean rocks that cooled to 350 c by 1700 1640 ma greenschist facies reactivation of shear zones occurred at 1100 ma during the musgravian orogeny on the basis of biotite single grain data and retrogressed amphiboles k feldspar age spectra record cooling at 700 800 ma following regional intrusion of the gairdner dike swarm and or denudation during rifting along the pacific margin of east gondwana and breakup of rodinia tectonothermal events revealed by these results previous geochronological and geological studies and available paleomagnetic data are comparable to other cratons and mobile belts in australia east gondwana and laurentia providing evidence that southeastern australia and north america were adjacent during much of proterozoic time

zircon petrochronology reveals the temporal link between porphyry systems and the magmatic evolution of their hidden plutonic roots the eocene coroccohuayco deposit peru abstract we present zircon geochronologic la icpms and id tims trace element and hf isotopic evidence for a complex evolution of the plutonic roots of the eocene coroccohuayco porphyry system southern peru la icpms u pb dating has initially been carried out to optimize grain selection for subsequent high precision id tims dating and to characterize crustal assimilation xenocrystic cores this combined in situ and whole grain u pb dating of the same grains has been further exploited to derive a robust temporal interpretation of the complex magmatic system associated with the coroccohuayco porphyry skarn deposit our data reveal that a heterogeneous gabbrodioritic complex was emplaced at ca 40 4 ma and was followed by a nearly 5 ma long magmatic lull until the emplacement of dacitic porphyry stocks and dykes associated with the mineralizing event at ca 35 6 ma however at the sample scale zircons from the porphyries provide insight into a 2 ma long lived hidden magmatism probably at 4 9 km paleodepth prior to porphyry intrusion and mineralization for which no other evidence can be found on the surface today these dates together with zircon trace element analysis and hf isotopes argue for the development of a long lived magmatic system dominated by amphibole fractionation with an increasing amount of crustal assimilation and the development of a large and sustained thermal anomaly the system was probably rejuvenated at an increasing rate from 37 5 to 35 6 ma with injection of fresh and oxidized magma from the lower crust which caused cannibalism and remelting of proto plutons the porphyry intrusions at coroccohuayco were emplaced at the peak thermal conditions of this upper crustal magma chamber which subsequently cooled and expelled ore fluids zircon xenocrysts and hf isotopes in the porphyritic rocks suggest that this large upper crustal system evolved at stratigraphic levels corresponding to triassic sediments similar to the mitu group that may be present below the district using the zircon ce anomaly as a proxy for oxidation state of the magma through time we show that the high oxidation state of the porphyries is not the result of upper crustal processes but is rather controlled by magmatic processes occurring at deeper levels a comparison of our data with available high precision geochronologic data at other porphyry systems suggests that such deposits may form when injection rate volume and heat of their long lived upper crustal magmatic system reach their peaks these features might be diagnostic of a productive deposit

hemispheric asymmetry of deep water transport modes in the western atlantic subtropical studies of the atlantic meridional cold water flow show a hemispheric contrast in the dominant southward transport mode below 2000 m in the north atlantic lower deep water ldw 1 8 2 4 c dominates with small transport of middle deep water mdw 2 4 3 2 c while in the south atlantic the opposite is observed we use numerous observations in the western basins of the tropics to show that the transition occurs rapidly near the equator in the western atlantic a meridional section in the central brazil basin suggests zonal flows are responsible for the transition ldw transport from the guiana basin north of the equator flows eastward in the northern brazil basin and is inferred to continue on through the romanche fracture zone into the eastern atlantic an opposing flow of mdw from the eastern tropical atlantic flows toward the western boundary where it bifurcates to supply mdw to the deep western boundary current dwbc of the brazil basin as well as to feed the northward flow of mdw in the guiana basin offshore of the dwbc the magnitude of each of these oppositely directed flows is roughly 7 sv we furthermore speculate that they are connected predominantly by upwelling from ldw to mdw within the low latitude eastern basin the overall deep water transport system below 2000 m in the western basins of the mid and low latitude atlantic is thus found to comprise the following three distinct components 1 a strong dwbc transport of ldw with associated recirculation dominates the guiana basin north of the equator 2 in the northern brazil basin just south of the equator a narrow eastward flow absorbs the ldw and carries it eastward while a somewhat broader westward flow imports mdw into the western basin 3 this mdw flow then bifurcates with the southward branch causing the mdw dominance in the brazil basin where the mdw dominated dwbc and associated recirculations are the third component of the deepwater transport system

eastward flow through the mid atlantic ridge at 11 n and its influence on the abyss of the eastern basin abstract the dilute antarctic bottom water of the north atlantic eastern trough is supplied from the western trough through fractures in the mid atlantic ridge in particular the influence on eastern trough property distributions of flow through the romanche and vema fracture zones near the equator and 11 n respectively has been noted previously here new observations are reported that document the abyssal circulation of the northeastern atlantic basins gambia abyssal plain south canary basin and north canary basin in particular the dominance of vema influence the absence of romanche influence and the existence of a system of deep western boundary currents and estimated transport deep isopycnals slope steeply across the vema s eastern end near 39 w corresponding to a geostrophic transport through the vema of 2 1 to 2 3 106 m3s 1 colder than 2 0 c this is half or more of the estimated bottom water that flows north across the equator into the subtropical western north atlantic this transp

sulfur speciation oxidation state and sulfur concentration in backarc magmas we have determined the fe3 fe2 ratio s content and the so2 4s2 ratio by sk x ray peak shift for a suite of twelve mid ocean ridge and backarc basin glasses these samples range in oxidation state from two orders of magnitude below to 1 5 orders of magnitude above the ni nio oxygen buffer sulfur speciation in the glasses is strongly dependent on magmatic oxidation state we propose that the solubility mechanism for s in basaltic melts changes over the o2 range which characterizes convergent margin magmas in low o2 sulfide saturated basaltic melts such as most morbs s is present largely as s2 and its concentration is controlled by sulfide melt silicate melt equilibrium and varies positively with o2 at higher o2 s where sulfide melt becomes unstable s concentration is controlled by melt vapor equilibrium and decreases with increasing o2 for the range of o2 s in the back arc basin basalts in this study nno 1 to nno 1 5 s is dissolved in the silicate in both oxidized and reduced forms for the lower o2 end of this range s2 dominates and equilibria involving reduced s species control s melt concentration at higher o2 s the proportion of oxidized s increases and melt vapor equilibria involving these species become more important because s partitions strongly into the vapor phase over the o2 range investigated magmatic degassing may be effective at stripping s from the melt the low s concentrations in island arc and backarc lavas do not necessarily reflect a low s source but rather result from higher o2 in the convergent margin environment

deep flow along the western boundary south of the blake bahama outer ridge abstract in june july 1990 hydrographic chlorofluorocarbon cfc and velocity observations were taken along the western boundary of the north atlantic south of the blake bahama outer ridge from 30 to 24 n between the northern bahamas and 71 w the deep flow in the region associated with the deep western boundary current forms a pattern of strong narrow currents and cyclonic gyres close to the continental slope with broad slower southward flow offshore the cfcs reveal that the most recently ventilated water i e having the highest cfc concentrations due to more recent contact with the atmosphere in the northern north atlantic is found along the western boundary in two distinct cores between potential temperatures 4 6 c and 1 9 2 4 c geostrophic transport streamlines were constructed for the deep flow referenced using direct velocity observations at 26 5 n and assuming mass conservation between closed areas bounded by the hydrographic sections the tracers and transports are used together

neoproterozoic stratigraphy of the centralian superbasin australia abstract the basement of central australia includes the arunta block and the 1200 1100 ma musgrave block succeeded by 1075 1000 ma bimodal volcanic rifts and dolerite dykes a regional hiatus at 1000 800 ma interpreted as reflecting a central post volcanic underplated upland was followed at 800 ma by a second swarm of dykes in the musgrave block gawler craton and stuart shelf associated with the crustal sagging that initiated the centralian superbasin the centralian superbasin is defined here to encompass the neoproterozoic fill of the amadeus georgina ngalia officer and savory basins the intra cratonic superbasin was disrupted internally 540 600 ma ago petermann ranges orogeny by a central uplift and associated thrusts and by mid carboniferous 320 ma tectonism alice springs orogeny to form the structural basins listed above the stratigraphy and sedimentology of the relatively well known areas can be used as a basis for predicting those of the poorly known regions new results from acritarch biostratigraphy and isotope chemostratigraphy in conjunction with conventional lithostratigraphy and sequence analysis allow better stratigraphic resolution than previously possible field observations in the recently discovered savory basin in western australia provide a basis for correlations with the adjacent basins

proterozoic granulites from the rauer group east antarctica i decompressional pressure temperature paths deduced from mafic and felsic gneisses

paleomagnetic evidence for 4000 km of crustal shortening across the 1 ga grenville orogen of north america paleomagnetic data from the grenville province of north america suggest that laurentia underwent 4000 1000 km of crustal shortening from ca 1040 1020 ma to 980 ma as a result of the grenville orogeny in which laurentia was in collision with amazonia a corollary is that the size and scale of shortening affect the assembly of continental fragments that include laurentia which before 1 ga may have been significantly larger in area than now by thousands of square kilometers caused by crustal shortening in a broadly northwest southeast direction by the grenville orogeny

hydrography of the romanche and chain fracture zones the romanche and chain fracture zones rfz and cfz are known as pathways for the lower north atlantic deep water lnadw and the antarctic bottom water aabw from the western trough to the eastern trough of the equatorial atlantic ocean across the mid atlantic ridge we report hydrographic observations describing the evolution of the lnadw and aabw properties during their transit through the equatorial fracture zones to the west of the rfz and cfz sills the lnadw and aabw cores are separated by a deep thermocline pycnocline which marks the transition between the two water masses the deep thermocline is eroded eastward and vanishes in the eastern basin this zonal asymmetry is the signature of a zonal baroclinic pressure gradient associated in each fracture zone with eastward flows of lnadw and aabw below 3800 m depth during the eastward transit through the rfz the near bottom aabw becomes less dense saltier 0 07 and warmer 0 7 c richer in oxygen 0 3 ml l 1 but less rich in silicate 30 mol l 1 simultaneously the lnadw core becomes fresher and colder at a given density and the oxygen maximum characterizing the lnadw core weakens by 0 2 ml l 1 we argue that the property changes within the aabw and lnadw are due to intense vertical mixing in addition to vertical mixing with the aabw it seems likely that isopycnal mixing of the lnadw with the eastern basin deep water contributes to the property evolution of the lnadw exiting the rfz in the cfz evidence is also given of mixing occuring within the aabw and the lnadw a sudden change in the aabw properties observed across the cfz main sill suggests the blocking of the eastward progression of the densest aabw by the cfz main sill however this dense water can reach the eastern basin by flowing northeastward through valleys the sills of which are deeper than thoses of the cfz finally a simple hydraulic control model applied to the rfz and cfz flows predicts a transport of 1 4 0 1 106 m3 s 1 of water colder than 1 9 c across the rfz cfz main sill

an experimental study of trace element partitioning between zircon and melt as a function of oxygen fugacity abstract the partitioning of p sc ti sr y nb the rare earth elements ree hf ta th and u between zircon and a synthetic andesitic melt was determined as a function of oxygen fugacity f o 2 over a range of fourteen log units from qfm 8 to qfm 6 where qfm is the quartz fayalite magnetite oxygen buffer at 1300 c and 1 atm using sims and la icp ms the partition coefficients of ce and eu were found to vary systematically with f o 2 relative to those of the other ree producing ce and eu anomalies similar to those that are characteristic of natural igneous zircon these anomalies coexist at terrestrial f o 2 s and were used to quantify eu 3 eu 2 eu 3 and ce 4 ce 3 ce 4 in the melt the partition coefficients of the redox invariant trivalent cations are in excellent agreement with lattice strain theory the values of d ree are related to those determined for natural samples by the expected dependence on temperature the incorporation of ree 3 in zircon was independent of the presence of p d u d th was found to vary systematically with f o 2 indicating the presence of u 4 u 5 and u 6 in the melt at terrestrial conditions d ti was independent of f o 2 despite an expectation of significant ti 3 in the most reduced experiments

the musgrave province stitching north west and south australia abstract the musgrave province in central australia is an east west trending 120 000 km2 region composed of lithologic units that range in age from earliest mesoproterozoic to neoproterozoic it is one of the few terrains in australia that records significant grenvillian aged tectonism and has a distinctly younger geological history than the surrounding fragments of proterozoic australia compared to other proterozoic terranes of australia the evolution of the musgrave province is poorly understood the region contains evidence for the development of earliest mesoproterozoic arc related magmatism with major juvenile crustal additions comprising intercalated felsic and mafic gneisses with protolith ages ranging from ca 1 60 to 1 54 ga this period of arc magmatism was followed by closure of the ocean separating the north australian craton nac from the south australian craton sac at ca 1 54 ga arc magmatism and collision was followed by a period of extension during which protoliths to the metasedimentary rocks of the eastern musgrave province were deposited at ca 1 4 ga the combined juvenile nd isotopic signature and detrital zircon ages from these metasediments suggests provenance from non australian sources with possible sources originating from laurentia granitic magmatic events occurred at ca 1 3 and 1 20 1 14 ga the latter comprising the voluminous a type granites of the pitjantjatjara supersuite the intrusion of these magmatic units provide key temporal constraints on deformational events and are coeval with the voluminous a type suites of laurentia which would invite correlation of australia with laurentia at ca 1 30 1 14 ga these magmatic episodes are accompanied by deformation at granulite facies at ca 1 30 ga unnamed event and 1 23 1 15 ga musgrave orogeny these deformation metamorphic events have completely recrystallised any primary layering within the pre 1 30 ga rocks forcing interpretations on their genesis to be inferred from geochemical and isotopic data the tectonic significance of these events is not clear however they may form part of a larger grenville aged deformational belt extending into the western australian albany fraser province and antarctica emplacement of the voluminous mafic ultramafic giles complex and associated granulite facies metamorphism of the giles event occurred at ca 1 078 ga the layered intrusions of the giles complex are generally fault bound and are considered to represent discrete bodies emplaced in an extensional regime associated with generation of the warakurna large igneous province the ca 1 08 ga alcurra dolerite unnamed ca 1 0 ga olivine dolerites and ca 0 8 ga amata dolerite dissect much of the musgrave province the alcurra dolerite and unnamed olivine dolerite dykes have been proposed as originating from a modified sub continental lithospheric mantle whereas the amata dolerite is proposed to be plume related coinciding with the initiation of rifting creating the centralian superbasin an earliest cambrian intraplate transpressional event is recorded in the ca 550 ma petermann orogeny this resulted in deep crustal exhumation of much of the northern musgrave province from beneath the centralian superbasin with mylonitic deformation recorded at pressures of 12 kbar and temperatures of 700 750 c

relative oxidation states of magmas inferred from ce iv ce iii in zircon application to porphyry copper deposits of northern chile major and trace element compositions of zircons and whole rocks from 14 barren and seven ore bearing calc alkaline intrusions from the chuquicamata el abra porphyry copper belt of northern chile have been measured in situ by excimer laser ablation ela icp ms these data permit the ce iv ce iii ratio within zircon to be calculated using a lattice strain model for mineral melt partitioning of ce iv and ce iii zircon ce iv ce iii and eun eun ratios and by inference magmatic oxidation states generally increase from older mafic to younger felsic units within this sequence porphyry copper mineralization is directly associated only with intrusions with zircon ce iv ce iii 300 and eun eun 0 4 such trends can be understood in terms of interdependent relations between oxygen fugacity sulfur speciation and solubility and chalcophile element partitioning in silicate magmas because zircon occurs in most calc alkaline intrusions and is resistant to subsolidus alteration zircon ce iv ce iii ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic hydrothermal cu au mineralization the approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks

monazite behaviour and age significance in poly metamorphic high grade terrains a case study from the western musgrave block central australia abstract integrated in situ textural chemical and electron microprobe age analysis of monazite grains in a migmatitic metapelitic gneiss from the western musgrave block central australia has identified evidence for multiple events of growth and recrystallisation during poly metamorphism in the mesoproterozoic garnet sillimanite bearing metapelite underwent partial melting and segregation to palaeosome and leucosome during metamorphism between 1330 and 1296 ma with monazite grains in leucosome recording crystallisation at 1300 ma monazite breakdown during melting is inferred to have occurred in the palaeosome during a subsequent granulite facies event at 1200 ma deformation and metamorphism of leucosome and palaeosome resulted in partial disturbance of ages and potential minor growth on 1300 ma monazite in leucosome growth of new high y hree monazite in palaeosome domains occurred during garnet breakdown in the presence of sillimanite to cordierite and spinel as a result of post peak isothermal decompression diffusive enrichment of resorbed garnet rims in y hree suggests garnet breakdown occurred slower than volume diffusion of ree monazite in both palaeosome and leucosome were subsequently partially to penetratively recrystallised during a retrogression event that is suggested to have occurred at 1150 1130 ma the intensity of recrystallisation and disturbance of ages appears linked to proximity to retrogressed garnet porphyroblasts and their occurrence in the relatively reactive or fertile local environments provided by the palaeosome mesosome volumes which caused localised changes in retrogressive fluids towards compositions more aggressive to monazite like reaction textures it is apparent that domainal equilibrium and reaction may control or at least strongly influence monazite ree and u th pb chemistry and hence ages

evolution of neoarchaean and proterozoic basins of australia abstract this study correlates basin initiation sedimentation and major tectonic events on an australia wide scale over the neoarchaean and proterozoic an interpretation of a depth to basement surface and faults based on magnetic and gravity data was calibrated with limited well data magnetic depth models geological maps and depth data from cross sections and literature tectonic events are correlated to basin formation and deposition of basin units event maps show the interpreted active faults a principal stress direction has been assigned to basin forming tectonic events the results of this study can be used as a kinematic stratigraphic and temporal framework to examine the development of individual basins and the regional influence of tectonic events tectonic events are grouped into four major time intervals the neoarchaean and early palaeoproterozoic 2775 2000 ma the mid late palaeoproterozoic to early mesoproterozoic 2000 1400 ma the mid late mesoproterozoic 1400 1000 ma and the neoproterozoic 1000 570 ma during the neoarchaean and early palaeoproterozoic basins formed along the southern pilbara and the northern yilgarn margins mainly in response to differential movements between these and other archaean cratons events in the mid late palaeoproterozoic to early mesoproterozoic were related to the assembly and subsequent intracontinental extension of the australian continent mid late mesoproterozoic events were due to interactions between australia and other continents during assembly of the supercontinent rodinia preservation of sediments from this time period is limited neoproterozoic basin forming events mainly related to the break up of rodinia and led to the formation of the centralian superbasin sedimentation in this basin was terminated at the end of the neoproterozoic due to compression associated with the amalgamation of the gondwana supercontinent

transport of bottom water in the romanche fracture zone and the chain fracture zone abstract two moored arrays deployed in the romanche fracture zone and chain fracture zone in the equatorial atlantic ocean provide two year long time series of current and temperature in the lower north atlantic deep water and the antarctic bottom water total time averaged transport of antarctic bottom water potential temperature 1 9 c across the mid atlantic ridge amounts to 1 22 106 m3 s 1 eastward with a standard deviation of 0 25 106 m3 s 1 a time averaged transport of 0 36 0 23 106 m3 s 1 eastward is found for the lower north atlantic deep water in the 1 9 2 1 c temperature range but this may represent only a fraction of the total flow of this water mass across the ridge contributions of the romanche fracture zone and chain fracture zone to the antarctic bottom water transport are similar while the chain fracture zone has the greater share of lower north atlantic deep water transport semiannual and annual periods are detected in the transport time series and together expl

granulite facies metamorphism palaeo isotherms and disturbance of the u pb systematics of zircon in anorogenic plutonic rocks from the adirondack highlands in the adirondack highlands of new york state the effect of granulite facies metamorphism on the physical and isotopic characteristics of zircon from anorogenic plutonic rocks has a distinct geographical pattern the location of zircon populations which appear to have been altered describes a roughly circular area where metamorphic palaeotemperatures have been determined to be in excess of 750 c zircons from anorogenic plutonic rocks outside this area were undisturbed during metamorphism and yield well constrained ages granitic charnockitic and mangeritic anorogenic plutonic rocks peripheral to the marcy anorthosite massif have large euhedral prismatic zircons that display fine internal magmatic growth zonations and abundant randomly orientated mineral inclusions co genetic zircon fractions yield linear discordant arrays and well constrained upper intercepts of 1125 1157 ma metamorphic zircon is limited to sporadically developed and volumetrically insignificant clear low u overgrowths or protuberances in marked contrast zircons from petrographically and geochemically identical rocks adjacent to or within the marcy anorthosite massif are typically large limpid anhedral to subhedral crystals or crystal fragments lacking internal features except for tubular cavities and co 2 rich inclusions co genetic zircon fractions yield nearly concordant non linear clusters with 207pb 206pb minimum ages of 1073 1095 ma metamorphic overgrowths cannot be readily identified by optical or cathodoluminscence techniques however many grains show complex and unusual external boundaries suggestive of post crystallization modification these data indicate that temperatures as low as 750 c in combination with other factors may have been sufficient to facilitate recrystallization and diffusion of radiogenic pb from the zircon crystal structure during the complex protracted metamorphism of the adirondack highlands

measured and modeled cfc distribution of lower north atlantic deep water in the guiana basin the circulation of the overflow lower north atlantic deep water olnadw in the guiana basin is studied by the measured and modeled distribution of the chlorofluorocarbon component cfc 11 the olnadw is formed in the northern atlantic and transported south to the equatorial region as the densest part of the deep western boundary current dwbc characterized by cfc and oxygen maxima some former studies proposed a northwestward recirculation of the boundary current in the guiana basin because the measured southeastward dwbc transport was larger than the calculated net transport across the entire width of the basin despite the variability of the dwbc reported recently this discrepancy seems to hold an advective diffusive model is presented which includes recirculation in the northern guiana basin as well as horizontal diffusion and the results are compared with a cfc survey in march 1994 because of high cfc concentration in the boundary current one would expect to find a high cfc signal in the recirculated water mass near the mid atlantic ridge as well however this was not observed modeled cfc distributions and observations only agree if the presumed recirculation is located in the center of the northern guiana basin or if no westward recirculation exists at all it was found that the strength of the recirculation is about 3 1 5 sv which is smaller than previously supposed

magnetotelluric constraints on the tectonic setting of grenville aged orogenesis in central australia abstract magnetotelluric mt data were collected over a 480 km long profile in central australia extending from the mesoarchaean palaeoproterozoic gawler craton into the mesoproterozoic neoproterozoic musgrave province the two regions have contrasting geological histories and many reconstruction models of proterozoic australia propose that they were juxtaposed during the mesoproterozoic despite the significant differences in geological background between the gawler craton and the musgrave province the mt data did not image an electrical structure or any change in electrical character between them mt models suggest that southern central australia is electrically separated into two parts the first comprising the northernmost gawler craton and the musgrave province has a 5 km thick layer of moderate resistivity overlying highly resistive crust the second comprising the central northern gawler craton displays moderate resistivity to the base of the crust the lithospheric mantle underlying both electrical regions is uniformly highly resistive our results suggest that the musgrave province and gawler craton are more closely related than is currently recognized we propose that the gawler craton forms basement to the musgrave province and that the grenvillian musgrave orogeny was an intracratonic reworking event that overprinted the older basement

isotopic chronometry of zoned garnets growth kinetics and metamorphic histories basic information on the chronological and pressure temperature evolution of regional metamorphic terrains may in principle be derived from metamorphic garnets because of the similarly low diffusivities of sm nd and major cations in this mineral we report here smnd and rbsr isotopic and major element data on prograde garnets from regionally metamorphosed pelites from newfoundland the garnets preserve a prograde major element zonation as well as a sympathetic variation in sm nd ratio smnd data for separated portions of the garnet from core to rim provide both upper limits on the time for garnet growth and demonstrate synchronous growth of different garnet grains on a hand specimen scale the rbsr data on the same garnet fractions are in general agreement with these results but in some cases cannot be interpreted in terms of growth a minimum heating rate of 3k ma 1 is derived by combining the estimates for garnet growth time with the apparent temperature interval over which the garnet grew deduced from the major element zonation this value is similar to the minimum suggested by theoretical models for the thermal evolution of thickened continental crust the growth rate is within the range of 1 3 19 mm ma 1 set respectively by the isotopic data and the likely upper limit for heating rate during regional metamorphism these growth rates appear too slow to be controlled by surface reaction and suggest that other factors such as transport may be rate limiting in this case the limits set on the effective diffusion coefficient for material transport to the growth site 0 4 6 1 10 17 m2 s 1 suggest that grain boundary diffusion is probably the transport mechanism for supply of material to the growing garnet

saline outflow from the arctic ocean its contribution to the deep waters of the greenland norwegian and iceland seas abstractsince 1985 various investigators have proposed that norwegian sea deep water nsdw is formed by mixing of warm and saline deep water from the arctic ocean with the much colder and fresher deep water formed by convection in the greenland sea gsdw we here report on new observations which suggest significant modification and expansion of this conceptual model we find that saline outflows from the arctic ocean result in several distinct intermediate and deep salinity maxima within the greenland sea the southward transport of the two most saline modes is probably near 2 sv mixing of gsdw and the main outflow core found over the greenland slope derived from about 1700 m in the arctic ocean cannot by itself account for the properties of nsdw instead the formation of nsdw must at least in part involve a source which in the arctic ocean is found below 2000 m the mixing of various saline outflows is diapycnal while significant nsdw production appears to occur in northern fram strait large amounts of saline arctic ocean outflow also traverse the western greenland sea without mixing and enter the iceland sea during the past decade deep convection in the greenland sea has been greatly reduced while deep outflow from the arctic ocean appears to have continued resulting in a markedly warmer slightly more saline and less dense deep regime in the greenland sea american geophysical union 1991

transequatorial flow of antarctic bottom water in the western atlantic ocean abyssal geostrophy at the equator abstract in its general northward flow along the western trough of the atlantic antarctic bottom water aabw must pass over several sills separating the various abyssal basins at the equator the western trough is deformed by major east west offsets of the mid atlantic ridge and the continental margin of brazil forming a newly zonal abyssal channel about 250 km wide centered at the equator and extending approximately 1000 km along its axis in which the aabw is confined thus the general northward flow of aabw is topographically constrained to be westward as it crosses the equator a hydrographic section across this channel at 37 w shows the aabw isopycnals to be bowl shaped within and beneath the level of the channel walls the equatorial geostrophic relation permits us to compute a zonal velocity from the well defined parabolic distribution of dynamic height relative to a reference level at the transition between aarw and the overlying deep water here 4 3 106 m3 s 1 is estimated for the wes

smnd mineral isochron ages of late proterozoic dyke swarms in australia evidence for two distinctive events of mafic magmatism and crustal extension two distinctive events of widespread dyke intrusion have been identified in central southern australia crystallization ages of the dykes were determined using sm nd mineral isochrons obtained by splitting clinopyroxene and plagioclase into different magnetic and density fractions respectively the stuart dyke swarm in the southern arunta inlier and the kulgera dyke swarm in the eastern musgrave inlier define essentially identical crystallization ages of 1076 33 and 1090 32 ma respectively marking the first episode of post orogenic mafic magmatism in the region two samples from the gairdner dyke swarm in the stuart shelf yield sm nd mineral isochron ages of 867 47 and 802 35 ma respectively whilst two samples from the amata suite in the central musgrave inlier 790 40 and 797 49 ma these four ages represent the second episode of mafic magmatism in central southern australia these ages allow new constraints to be placed on the timing of large scale crustal extension and formation of intracratic depositional basins in the region initial nd values of 7 8 to 6 6 for the stuart dykes and 0 7 for the kulgera dykes suggest they were derived from different mantle sources with the stuart dykes being produced from strongly enriched sources in contrast positive and relatively uniform initial nd values of 2 5 to 4 1 for the younger amata suite and gairdner dykes indicate that they were derived from relatively depleted and homogeneous mantle sources the 1076 33 ma sm nd age of the stuart dyke swarm is significantly older than its rb sr mineral isochron age of 897 9 ma previously reported suggesting mobility of rb and or sr and partial resetting of rb sr isotopic systematics this study demonstrates that reliable and relatively precise sm nd ages can be obtained for precambrian dykes despite the limited number of mineral phases available in the dykes

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

the atlantic deep western boundary current water masses and transports near the equator the distributions and transports of deepwater masses at the western boundary in the tropical atlantic off brazil have been studied on three surveys along 35 degrees w and 5 degrees s and one at 10 degrees s transports are obtained from direct measurements of the velocity fields pegasus profiling system and lowered acoustic doppler current profiler and from geostrophic computations using chlorofluoromethane cfm and hydrographic distributions four water masses could be identified forming the north atlantic deep water nadw system two of these have a high cfm content the shallow upper nadw sunadw and the overflow lower nadw olnadw these exhibit the highest velocity signals at 35 degrees w where distinct flow cores seem to exist most of the southeastward flow of the sunadw centered around 1600 m occurs 320 km offshore between 3 degrees 09 s and 1 degrees 50 s 9 7 3 3 sv farther north in that section a highly variable reversing flow is found in a second velocity maximum the transport of olnadw centered around 3800 m of 4 6 2 6 sv is guided by the parnaiba ridge at 1 degrees 45 s 35 degrees w the water masses located between the two cfm maxima the labrador sea water lsw and the lnadw old water mass lnadw old did not show any persistent flow features however a rather constant transport of 11 1 2 6 sv was observed for these two layers the total southeastward flow of the nadw at 35 degrees w showed a transport of 26 8 7 0 sv if one neglects the reversing sunadw north of 1 degrees 50 s at 5 degrees s the flow of all deepwater masses shows vertically aligned cores the main southward transport occurred near the coast 19 5 5 3 sv the boundary current is limited offshore by a flow reversal present in all three surveys but located at different longitudes at 10 degrees s a southward transport of 4 7 sv was observed in november 1992 however the section extended only to 32 degrees 30 w so that probably a significant part of the flow has been missed an important result is the large transport variability between single cruises as well as variability of the spatial distribution of the flow at 35 degrees w which could lead to large uncertainties in the interpretation of single cruise observations despite these uncertainties we suggest a circulation pattern of the various deepwater masses near the equator by combining our mean transport estimates with other observations

crossing of the equator by the deep western boundary current in the western atlantic ocean abstract property distributions and geostrophic shear from a hydrographic section near 37 w in the atlantic ocean show the deep western boundary current dwbc in the north atlantic deep water nadw established against the western boundary of the brazil basin immediately south of the equator between 2 and 5 s the dwbc thus has directly crossed the equator to the south atlantic following the east southeast trend of the continental slope isobaths the estimated dwbc transport of nadw is 35 106 m3 s 1 similar to other estimates from the tropics discussed here these large dwbc transports are opposed by flow of deep water to the north atlantic immediately offshore of the dwbc with as much as two thirds of the dwbc transport being returned as these recirculations one recirculation center is the guiana basin north of the equator but extends at least a few hundred kilometers south of the equator another is visible at 11 s in the brazil basin the degree of connection of these two observed recirculatio

abyssal ocean overturning shaped by seafloor distribution the abyssal ocean is broadly characterized by northward flow of the densest waters and southward flow of less dense waters above them understanding what controls the strength and structure of these interhemispheric flows referred to as the abyssal overturning circulation is key to quantifying the ocean s ability to store carbon and heat on timescales exceeding a century here we show that north of 32 s the depth distribution of the seafloor compels dense southern origin waters to flow northward below a depth of about 4 kilometres and to return southward predominantly at depths greater than 2 5 kilometres unless ventilated from the north the overlying mid depths 1 to 2 5 kilometres deep host comparatively weak mean meridional flow backed by analysis of historical radiocarbon measurements the findings imply that the geometry of the pacific indian and atlantic basins places a major external constraint on the overturning structure

large volumes of anhydrous pseudotachylyte in the woodroffe thrust eastern musgrave ranges australia a mylonitic thrust zone at least 1 5 km thick forms a sharp contact between granulite and amphibolite facies gneisses in the eastern musgrave ranges central australia the thrust dips gently to the south and is interpreted as an extension of the woodroffe thrust which was formed about 550 ma ago mylonites at the base of the thrust grade upwards into ultramylonites which pass abruptly into a pseudotachylyte bearing zone approximately 1 km thick containing approximately 4 of pseudotachylyte veining the orientation of the veins appears to be random pseudotachylytes occur only in the granulite facies rocks and their precursors are felsic pyroxene and or garnet granofelses rotated blocks of ultramylonite are present in some of the pseudotachylytes and some pseudotachylyte veins have been plastically deformed suggesting nearly contemporaneous semiductile and brittle behaviour the matrix of the pseudotachylyte shows spectacular examples of igneous quench microstructures especially skeletal and dendritic crystals of plagioclase and feathery pyroxene dendrites also present are glass devitrification microstructures spherulites evidence of liquid flow and partly melted residual grains with former glassy rims showing different optical properties from those of the surrounding isotropic material these features confirm that the pseudotachylyte formed by melting in anhydrous conditions the matrix of the pseudotachylyte veins is less siliceous than the host rocks owing to non equilibrium melting of pyroxene garnet and plagioclase the igneous assemblages of the melt notably the crystallization of pigeonite are consistent with rapid cooling from very high temperature 1000 c melting and quenching is probably due to very local short lived rises in temperature accompanied by dilation

multi scale integrated structural and aeromagnetic analysis to guide tectonic models an example from the eastern musgrave province central australia abstract in many polydeformed precambrian provinces the understanding of their tectonic history is limited by insufficient exposure which leads to difficulty in developing links between local and regional architecture and results in poorly constrained models of their regional scale architecture high resolution aeromagnetic data allows interpretation and modelling at a scale comparable to structural mapping and by integrating these methods these links can be developed with high confidence as an example we integrate structural mapping aeromagnetic data interpretation and 3d magnetic inversions in a multi scale structural analysis of the polydeformed eastern musgrave province in central australia deformation during the ca 1200 ma musgravian orogeny is characterised by an originally northeast trending structural grain defined by shear zones and tight to isoclinal folds at all scales 3d magnetic inversion models of syn to post musgravian granites indicate that this structural grain is predominantly west dipping this architecture suggests that a northeast oriented fold and thrust belt developed as a result of northwest southeast compression in central australia during the musgravian orogeny the next deformation event is characterised by an array of originally east southeast trending shear zones that truncate and offset the musgravian structural grain with apparent dextral displacements of up to 1 km these shear zones are commonly co located with mafic and granitic dykes suggesting a dilational origin and they are interpreted to have initiated under northeast southwest extension during the ca 1080 ma giles event the architecture of these two mesoproterozoic events was later extensively overprinted by two deformation events during the pan african aged ca 550 ma petermann orogeny the first is characterised by the widespread reactivation of mesoproterozoic structures resulting in a network of shear zones of variable orientation and the second is characterised by the development of crustal scale transpressional shear zones motion on which has caused the rotation of lithospheric blocks and the reorientation of prior structural trends by up to 90 collectively the architecture of these two events suggests broadly north south crustal shortening in central australia as an intraplate response to gondwana assembly this example demonstrates that the integration of structural geology with aeromagnetic interpretation and modelling can be used to develop high confidence links between local and regional structures these links permit the derivation of better constrained models of major tectonic events particularly in regions where outcrop is poor and the structural architecture is complex

two new geobarometers for garnet amphibolites with applications to southeastern vermont two new geobarometers for the assemblage garnet hornblende plagioclase quartz have been calibrated on the basis of the equilibrium 6 anorthite 3 tremolite 2 grossular 1 pyrope 3 tschermakite 6 quartz and its fe end member equivalent data representing 37 natural samples that equilibrated at conditions of 2 5 to 13 kbar and 500 to 800 c were fitted to the general equation rt in keq a bt p i c by using a weighted least squares method multiple correlation coefficients are high 0 98 and 0 97 lines of constant keqhave extremely shallow slopes in p t space 2 to 8 bars per degree suggesting that pressures may be deduced precisely even where temperatures are only poorly constrained typical analytical errors and temperature imprecisions propagate to very small errors in pressure about 500 bars caution is advised in applying the barometers outside the range of calibrant mineral compositions application of the calibrations to samples from southeastern vermont near the strafford chester and athens domes documents relatively high pressure metamorphism 7 to 10 kbar for these structures

sm_nd garnet ages from the uluguru granulite complex of eastern tanzania further evidence for post metamorphic slow cooling in the mozambique belt abstract two samples from the uluguru granulite complex yield garnet sm nd ages of 633 7 and 618 16 ma similar to previously published hornblende 40ar 39ar and k ar ages the similarity of the sm nd to the k ar age suggests that the closure temperature of garnet to nd diffusion is similar to that of hornblende to ar diffusion assuming that published zircon u pb ages of about 700 ma date peak granulite facies metamorphism a mean post metamorphic cooling rate of 2 3 c ma can be calculated for the time interval 700 to 630 ma such slow cooling rates imply thermal relaxation with a thickness length scale greater than the thickness of average continental crust this in turn implies that the thermal perturbation responsible for metamorphism was preceded by regional crustal thickening probably in a collisional orogen

metamorphic events in the eastern arunta inlier part 1 metamorphic petrology abstract in the entia dome of the eastern arunta inlier kyanite facies metamorphism is recorded over a substantial area at least 160 km 2 and thus contrasts with the regionally extensive belts of high temperature low pressure andalusite sillimanite facies metamorphism documented elsewhere in the arunta inlier this amphibolite facies event appears to postdate regional granulite facies metamorphism evidence for which is almost totally obliterated in the entia dome prograde kyanite occurs in meta basites in comparatively rare associations involving hornblende staurolite and anorthite and in other rocks in association with gedrite and hornblende or garnet and biotite these kyanite bearing assemblages equilibrated at intermediate temperatures 570 710 c at peak pressures of 7 kbar and are overprinted by lower pressure assemblages including hornblende gedrite cordierite and sillimanite while this sequence of reactions may be simply interpreted in terms of a single clockwise orogenic cycle textural evidence and the available mineral isotopic data suggest a more complex history involving multiple heating and cooling episodes during the mesoproterozoic and possibly the palaeozoic the occurrence of regional retrogressive kyanite facies assemblages in the eastern arunta inlier provides evidence that the widely held perception that proterozoic crustal evolution in australia involved a distinct ensialic orogenic style characterised by high geothermal gradients etheridge et al 1987 loosveld and etheridge 1990 sandiford and powell 1991 is not universally true rather petrological evidence presented here with isotopic constraints described by foden et al 1995 suggests that the harts range region has experienced substantial crustal reworking at elevated temperatures during both the proterozoic and palaeozoic under thermal regimes more familiar to modern continental collision zones

geometry of a large scale low angle midcrustal thrust woodroffe thrust central australia the musgrave block in central australia exposes numerous large scale mylonitic shear zones developed during the intracontinental petermann orogeny around 560 520 ma the most prominent structure is the crustal scale over 600 km long e w trending woodroffe thrust which is broadly undulate but generally dips shallowly to moderately to the south and shows an approximately top to north sense of movement the estimated metamorphic conditions of mylonitization indicate a regional variation from predominantly midcrustal circa 520 620 c and 0 8 1 1 gpa to lower crustal 650 c and 1 0 1 3 gpa levels in the direction of thrusting which is also reflected in the distribution of preserved deformation microstructures this variation in metamorphic conditions is consistent with a south dipping thrust plane but is only small implying that a 60 km long n s segment of the woodroffe thrust was originally shallowly dipping at an average estimated angle of 6 the reconstructed geometry suggests that basement cored thick skinned midcrustal thrusts can be very shallowly dipping on a scale of many tens of kilometers in the direction of movement such a geometry would require the rocks along the thrust to be weak but field observations e g large volumes of syntectonic pseudotachylyte argue for a strong behavior at least transiently localization on a low angle near planar structure that crosscuts lithological layers requires a weak precursor such as a seismic rupture in the middle to lower crust if this was a single event the intracontinental earthquake must have been large with the rupture extending laterally over hundreds of kilometers

zonal circulation across 52 w in the north atlantic 1 in july august 1997 a hydrographic acoustic doppler current profiler adcp tracer section was occupied along 52 w in the north atlantic as part of the world ocean circulation experiment hydrographic program underway and lowered adcp ladcp data have been used to reference geostrophic velocities calculated from the hydrographic data additional small velocity adjustments provided by an inverse model constraining mass and silicate transports in 17 neutral density layers yield the absolute zonal velocity field for 52 w we find a vigorous circulation throughout the entire section with an unusually strong gulf stream 169 sv and southern deep western boundary current dwbc 64 sv at the time of the cruise at the northern boundary on the west side of the grand banks of newfoundland we find the westward flowing labrador current 8 6 sv whose continuity from the labrador sea east of our section has been disputed directly to the south we identify the slopewater current 12 5 sv eastward and northern dwbc 12 5 sv westward strong departures from strictly zonal flow in the interior which are found in the ladcp data make it difficult to diagnose the circulation there isolated deep property extrema in the southern portion associated with alternating bands of eastward and westward flow are consistent with the idea that the rough topography of the mid atlantic ridge directly east of our section causes enhanced mixing of antarctic bottom water properties into overlying waters with distinctly different properties we calculate heat and freshwater fluxes crossing 52 w that exceed estimates based on air sea exchanges by a factor of 1 7

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

geochemical constraints on cu fe and fe skarn deposits in the edong district middle lower yangtze river metallogenic belt china abstract copper and iron skarn deposits are economically important types of skarn deposits throughout the world especially in china but the differences between cu and fe skarn deposits are poorly constrained the edong ore district in southeastern hubei province middle lower yangtze river metallogenic belt china contains numerous fe and cu fe skarn deposits in this contribution variations in skarn mineralogy mineralization related intrusions and sulfur isotope values between these cu fe and fe skarn deposits are discussed the garnets and pyroxenes of the cu fe and fe skarn deposits in the edong ore district share similar compositions i e dominantly andradite ad 29 100 gr 0 68 and diopside di 54 100 hd 0 38 respectively this feature indicates that the mineral compositions of skarn silicate mineral assemblages were not the critical controlling factors for variations between the cu fe and fe skarn deposits intrusions associated with skarn fe deposits in the edong ore district differ from those cu fe skarn deposits in petrology geochemistry and sr nd isotope intrusions associated with fe deposits have large variations in their la yb n ratios 3 84 24 6 and eu anomalies eu 0 32 1 65 and have relatively low sr y ratios 4 2 44 0 and high yb contents 1 20 11 8 ppm as well as radiogenic sr nd isotopes end t 12 5 to 9 2 and 87 sr 86 sr i 0 7067 to 0 7086 in contrast intrusions associated with cu fe deposits are characterized by relatively high sr y 35 0 81 3 and la yb n 15 0 31 6 ratios low yb contents 1 00 1 62 ppm without obvious eu anomalies eu 0 67 0 97 as well as 87 sr 86 sr i 0 7055 to 0 7068 and end t 7 9 to 3 4 geochemical evidence indicates a greater contribution from the crust in intrusions associated with fe skarn deposits than in intrusions associated with cu fe skarn deposits in the edong ore district the sulfides and sulfates in the cu fe skarn deposits have sulfur isotope signatures that differ from those of fe skarn deposits the cu fe skarn deposits have a narrow range of 34 s values from 6 2 to 8 7 in sulfides and 13 2 to 15 2 in anhydrite while the fe skarn deposits have a wide range of 34 s values from 10 3 to 20 0 in pyrite and 18 9 to 30 8 in anhydrite sulfur isotope data for anhydrite and sedimentary country rocks suggest that the formation of skarns in the edong district involved the interaction between magmatic fluids and variable amounts of evaporites in host rocks

longevity of magmatic hydrothermal systems in the daye cu fe au district eastern china with implications for mineral exploration the daye district represents one of the largest concentrations of cu fe au skarn deposits in china with additional porphyry cu mo deposits these deposits are closely associated with late mesozoic intrusions of intermediate to felsic composition previous studies have yielded important age constraints for several deposits timing and history of metallogenesis for the entire district however remain not well understood in this paper we present twenty five new ages re os 40ar 39ar and u pb to better understand the temporal framework of the district wide polymetallic mineralization these ages when combined with existing data indicate a prolonged history of mineralization lasting 25 million years from late jurassic to early cretaceous 157 132 ma and that most ore deposits of the district are results of multistage hydrothermal activity discrete episodes of ore formation coincide well with emplacement ages of granitoid intrusions within the district as revealed by recent zircon u pb dating this age consistency substantiates a genetic relationship between ore formation and intrusive magmatism prolonged and episodic magmatic and hydrothermal activities must have played significant roles in the formation of polymetallic ore deposits in the district by repeatedly supplying heat fluids and metals previous studies have demonstrated that the daye district was dominated by lithospheric extension during late jurassic to early cretaceous when extensive magmatism and mineralization took place under the extensional setting the area could have experienced significant uplift or extensional exhumation that would have brought early stage intrusions and associated ore deposits to shallower levels with ore bodies formed by subsequent magmatic hydrothermal events tending to be localized at greater depth this in turn indicates potentials to find new ore bodies at depth of known deposits especially for those formed by episodic magmatic hydrothermal processes this view is partly confirmed by the recent success in deep exploration beneath the tieshan fe cu and tonglushan cu au fe deposits

regional high pressure metamorphism during intracratonic deformation the petermann orogeny central australia the petermann orogeny is a late neoproterozoic to cambrian c 560 520 ma intracratonic event that affected the musgrave block and south western amadeus basin in central australia in the mann ranges within the central musgrave block mesoproterozoic granulite facies gneisses granites and mafic dykes have been substantially reworked by deep crustal non coaxial strain of late neoproterozoic to early cambrian age dolerite dykes have recrystallized to garnet granulite facies assemblages associated with the development of a mylonitic fabric at p 12 13 kbar and t 700 750 c migmatization is restricted to discrete shear zones which represent conduits for hydrous fluids during metamorphism peak metamorphism was followed by decompression to c 7 kbar reflecting exhumation of the terrane along the south dipping woodroffe thrust in scattered outcrops north of the mann ranges peak metamorphism occurred at p 9 10 kbar and t c 700 c the woodroffe thrust separates these deep crustal mylonites from granites that were metamorphosed during the petermann orogeny at p c 6 7 kbar and t c 650 c the similarity in peak temperatures at different crustal levels implies an unusual thermal regime during this event the existence of a relatively elevated geotherm corresponding with th and k enriched granites that were in the mid crust during the petermann orogeny suggests that radiogenic heat production may have substantially contributed to the thermal regime during metamorphism this potentially has implications for the mechanisms by which intra plate strain was localized during this event

the age of the ormiston pound granite implications for mesoproterozoic evolution of the arunta inlier central australia the ormiston pound granite southern arunta inlier intruded during the terminal stages late to post d2 of a major n directed overthrust event called the chewings orogeny which deformed supracrustal rocks of the simpsons and chewings assemblages ion probe zircon u pb analysis of the granite indicates an emplacement age of 1603 10 ma more than 500 ma older than the rb sr isochron age timing of emplacement is confirmed by an age of 1575 20 ma for zircon mantles from a gneissic xenolith in the granite zircon cores from the xenolith yield an age of 1678 14 ma which is taken to represent the protolith age of the surrounding gneisses the shrimp age is similar to but more precise than the 1586 69 ma rb sr isochron age for the chewings orogeny determined by marjoribanks and black 1975 penecontemporaneous 1600 ma magmatism is evident as pegmatites and associated fluid flow zones in the anmatjira and reynolds ranges northern arunta inlier 1100 1030 ma rb sr mica ages from the 1600 ma ormiston pound granite coeval pegmatites and 1680 ma host rock gneisses are similar to a sm nd isochron age for the mafic stuart dyke swarm of the southern arunta inlier and the contemporaneous alcarra dyke swarm in the musgrave inlier some 500 km farther south the rb sr mica ages reflect isotopic resetting by a thermal perturbation either associated with regional crustal extension during 1080 ma dyke intrusion or with the 1150 ma magmatic event in the southern arunta cf black and shaw 1992 irrespective the 1050 900 ma ormiston event described by shaw et al 1984 as granite intrusion associated with high grade metamorphism migmatization and folding needs to be re defined or abandoned

indian derived sediments deposited in australia during gondwana assembly abstract sedimentary exchanges across continents during the collisional assembly and lifespan of supercontinents provide a powerful way of testing the assembling process and configuration of supercontinents the ord basin in north western australia contains mid cambrian shallow marine and deltaic sedimentary successions that post date the ca 650 520 ma paterson petermann orogeny ppo but are synchronous with the ca 530 470 ma kurgiakh orogeny in north india we report new u pb ages and hf isotopes of detrital zircons from the mid cambrian ord basin that suggest indian derived sedimentary input to australian cambrian basins compilations of published ediacaran ordovician samples from the centralian superbasin indicate that during the ca 650 520 ma ppo the 1200 1100 ma musgrave province in central australia was exhumed and fed sediments to the syn ppo centralian superbasin soon after the ppo termination the musgrave province likely remained a topographic high and continued to supply detritus to the amadeus and officer basins that were fragmented from the centralian superbasin supplemented by the 630 ma granites of the paterson orogen conversely we conclude that the mid cambrian ord basin did not record similar sedimentary provenance from the musgrave province rather indian derived detritus travelled along the northeastern gondwanan continental margin via longshore currents and in turn incorporated paterson granitic detritus during the assembly of gondwana including the kurgiakh orogeny in north india a broad provenance comparison between potential eastern gondwanan source regions and relevant asian neighbours suggests that south china and south qiangtang are affiliated with northern india but lhasa appears to have had a mixed affiliation between india and australia

architecture and emplacement of the nebo babel gabbronorite hosted magmatic ni cu pge sulphide deposit west musgrave western australia the nebo babel ni cu platinum group element pge sulphide deposit in the west musgrave block western australia is the largest nickel sulphide discovery in the last 10 years the deposit is hosted within a concentrically zoned olivine free tube like chonolithic gabbronorite intrusion associated with the approximately 1 078 ma giles complex layered intrusions in the warakurna large igneous province emplaced into sulphide free amphibolite facies orthogneiss the fault offset nebo babel chonolith extends for 5 km and has a cross section of 1 0 5 km igneous mineralogy fabrics and textures are well preserved the lithostratigraphy includes variably textured leucogabbronorites vlgn that form an outer shell around mineralised gabbronorite mgn with barren gabbronorite bgn and oxide apatite gabbronorite oagn in the middle and lower parts of the chonolith mineral and whole rock geochemistry indicate that the units become progressively evolved in the order vlgn mgn bgn and oagn and that incompatible trace element concentrations increase downwards within the mgn and bgn the mineralisation which is confined to the early more primitive units vlgn and mgn occurs as massive sulphide breccias and stringers and as disseminated gabbronorite hosted sulphides the massive sulphides were emplaced late in the intrusive sequence have different pge chemistry and cu tenor to the disseminated sulphides and have undergone sulphide fractionation the distribution of disseminated sulphides which are primary magmatic in origin is related to chonolith geometry and magma flow regimes rather than to gravitational settling sulfur bearing country rocks are absent in the nebo babel deposit area and thus local crustal s addition was unlikely to have been the major mechanism in achieving sulphide immiscibility the nebo babel intrusion is part of an originally continuous magma chonolith with multiple and related magma pulses the parental magma was medium to low k tholeiite with 8 9 wt mgo the initial magma pulse vlgn the most primitive and sulphide saturated was probably emplaced along a linear weakness in the country rock after crystallisation of vlgn marginally more fractionated sulphide saturated magma was injected through the thermally insulated core of the conduit forming the mgn successive pulse s of more fractionated magma bgn were emplaced in the core of the intrusion after magma flow ceased closed system crystal fractionation produced consistent mineral and chemical fractionation trends within bgn and oagn after crystallisation the intrusion was overturned and then offset by the jameson fault resulting in the apparent reverse chemical and mineral trends in nebo babel

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

zircon u pb chronometry of the pressure and temperature history of granulites in the musgrave ranges central australia ion microprobe u pb measurements of zircon in the musgrave ranges of central australia date the emplacement of a charnockite which is cut by a shear zone containing a garnet clinopyroxene assemblage m2 pt conditions 11 kb and 720 c at 1200 ma veinlets of a post m2 adamellite cut an m4 assemblage pt conditions 6 kb and 670 c contained in a metadolerite inclusion suggesting that the adamellite was emplaced during or after m4 igneous and metamorphic zircons in the adamellite however grew at about 1200 ma indicating that m2 and m4 were synchronous at the level of precision of our data the time interval between the growth of the two assemblages can not have been more than 20 ma we interpret the pressure temperature and time ptt path obtained by combining our thermobarometric data and zircon u pb ages in terms of magmatic heat input in a thickened crustal segment followed by rapid possibly technically driven uplift of the lower part of the thickened crust to a depth of 15 20 km

antarctic bottom water flux in the equatorial western atlantic a moored array at the equator in the western basin of the atlantic provides a 604 day time series of abyssal currents and temperatures spanning the full breadth of the antarctic bottom water aabw flowing from the brazil basin to the guiana basin mean aabw transport is estimated to be 2 0 sv sv 106 m3 s21 comprising organized westward flow of 2 24 sv and return flow of 0 24 sv the low frequency variability is dominated by a quasi annual transport cycle of amplitude 0 9 sv and a 120 day period of amplitude 0 6 sv maximum transports occur in september october while minimum transports occur in february march allowing for this quasiannual cycle and extrapolating the 604 day record to a full two years adds about 7 to the estimated mean aabw transport the array also provides limited sampling in the overlying lower north atlantic deep water lnadw where a southern boundary intensified flow of lnadw gives the strongest recorded mean speed through the array 9 9 cm s21 into the brazil basin the lnadw records also have a quasi annual cycle with strong lnadw flow episodes occurring in april may time series of temperature indicate that the lnadw aabw transition layer rises and falls in synchrony with the quasi annual aabw transport cycle uplifted transition layer during strong aabw transport periods an observed overall warming trend appears to be accompanied by a decline in aabw transport

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

intracratonic strike slip partitioned transpression and the formation and exhumation of eclogite facies rocks an example from the musgrave block central australia mountain belts developed in an intracratonic setting during the neoproterozoic in the center of australia mesoproterozoic granulite and amphibolite facies gneisses of the musgrave block were overprinted during the petermann orogeny 550 ma with zones of high strain concentrated along broadly east west trending shear zones these zones formed under eclogite facies t 650 c and p 12 kbars to greenschist facies conditions and may form part of a strike slip related crustal scale flower type structure granulite facies gneisses preserve ages older than 700 ma suggesting that these rocks did not experience temperatures greater than 350 c at 550 ma for these rocks not to have been thermally equilibrated to temperatures of 350 c at a depth of 12 kbars requires either an extraordinarily low geothermal gradient 9 c km 1 or if the geothermal gradient was more typical 20 c km 1 then transport to that depth and subsequent exhumation occurring in a short time interval 40 myr

mineralization of biogenic materials in the water masses of the south atlantic ocean i assessment and results of an optimum multiparameter analysis abstract this is the first of two manuscripts dealing with the circulation mixing ventilation and organic matter mineralization of the south atlantic ocean sao the present work quantifies the complex mixing of water masses in the sao using a constrained least squares regression optimum multiparameter omp analysis the omp based on temperature salinity silicate and the conservative parameter no was applied on two world ocean circulation woce lines a17 and a14 in the western and eastern sao respectively the constrained omp sensitivity to sources of error in the end member characteristics measured parameters equation weights and oxygen to nitrogen mineralization ratio rn was carefully assessed using perturbation tests perturbation of rn was the only test that changed significantly the mixing proportions although by less than 5 the constrained omp method allowed defining the realm and identifying the core of flow of each water mass to study its circulation the evolution of its chemical composition and eventually to separate the contribution of physical and biogeochemical processes relevant specific outputs of this first manuscript are 1 north of the south equatorial current the silicate maximum is primarily composed of antarctic intermediate water aaiw rather than circumpolar deep water cdw 2 the two degree discontinuity tdd experiences a dramatic meridional change of water masses composition being dominated by north atlantic deep water nadw north of the vema channel and by cdw southwards 3 the 50 proportion horizon of weddell sea deep water wdsw with a of 0 3 c at the entry of the sao defines the upper limit of the wsdw realm more properly than the classical isopycnals of 46 04 or 46 06 4 where the proportion of wsdw is around 75

western boundary current structure and variability east of abaco bahamas at 26 5 n abstract during april 1987 to june 1988 a four mooring transport resolving current meter array was deployed in a section extending 70 km eastward from abaco bahamas at 26 5 n mean currents in the upper layer 800 m showed a clockwise rotation that appears to be associated with a small scale quasi permanent anticyclonic gyre centered just northeast or the bahamas deep mean currents were persistenly southward and indicated a strong deep jet the deep western boundary current dwbc reaching core speeds of 20 cm s 1at 2500 m depth about 25 km seaward of the western boundary vertically integrated meridional volume transport over the section showed a surprisingly large variability ranging from approximately 20 sv northward to 70 sv southward 1 sv 106m3s 1 the mean meridional volume transport was 30 sv to the south with about 3 sv flowing northward above 800 m which could be produced by a weak antilles current and 33 sv flowing southward below 800 m the deep southward transport of 33 sv i

four zircon ages from one rock the history of a 3930 ma old granulite from mount sones enderby land antarctica ion microprobe u th pb analyses of zircons from a granulite grade orthogneiss from mount sones enderby land antarctica record the ages of four principal events in the history of the gneiss three of which already have been recognized through previous isotopic dating of other samples the structure of the zircons indicates at least four different stages of growth the several zircon ages were obtained by grouping the analyses according to the stage they represented in the observed stratigraphic succession of growth and thereby defining separate u pb discordance patterns for each stage the stratigraphically oldest zircon rare discrete cores is indistinguishable in age from the most common euhedrally zoned zircon both crystallized when the tonalitic precursor of the orthogneiss was emplaced into the crust 3927 10 ma ago making the orthogneiss currently the oldest known terrestrial rock the outer parts of most grains and some whole grains recrystallized at 2948 31 17 ma during or immediately after possibly 100 ma of high granulite grade metamorphism the recrystallized zircon was isotopically disturbed by tectonism associated with reactivation of the southern margin of the napier complex at 1000 ma in the intervening time at 2479 23 ma the cores and zoned zircon suffered a major isotopic disturbance involving movement of radiogenic pb which left most of the crystals with radiogenic pb deficiencies but produced local radiogenic pb excesses in others a new generation of zircon characterized by very high th u and low u grew at that time that event deformation and possibly a minor rise in temperature produced widespread perturbations of other isotopic systems throughout the napier complex

an estimate of the upwelling rate in the equatorial atlantic based on the distribution of bomb radiocarbon and quasi geostrophic dynamics estimates of the near surface upwelling in the tropical atlantic ocean 15 s to 15 n made by broecker et al 1978 from a radiocarbon box model and by wunsch 1984 from a quasi geostrophic inversion differ considerably in the former case the range was estimated as about 17 20 sv while the latter obtained an absolute maximum of about 10 sv to understand these two apparently contradictory results 14c constraints were added to the inverse model with realistic estimates of the observational errors in all fields including the radiocarbon it is found that the radiocarbon constraints are consistent with the quasi geostrophic model and with an upwelling estimated as 7 10 sv the near surface circulation in the tropical atlantic is dominated by a northward flux of warm water across the equator necessary to feed the heat losses at high northern latitudes the 14c balance is maintained by the advection of southern hemisphere waters of comparatively low radiocarbon concentration into the tropical zone by upwelling from below of very low radiocarbon water and by its removal to the north also by advection the major uncertainty in the radiocarbon calculations derives from the sparcity of sampling so that very great extrapolations are required to estimate the zonal mean 14c concentrations and the time histories between the prebomb period and 1972

tracer distributions and deep circulation in the western tropical atlantic during cither 1 and etambot cruises 1993 1996 this paper presents cfc and nontransient tracer observations in the western equatorial atlantic ocean on repeated sections along 7 30 n the 35 w meridian and a transect crossing the ceara rise three world ocean circulation experiment cruises have been carried out in this area in february march 1993 cither 1 and september october 1995 and april may 1996 etambot 1 and 2 together with the tracer data the direct current measurements are used to deduce the circulation pathways the data confirm the principal circulation features of the upper north atlantic deep water within the area the deep western boundary current flows southward along the continental slope while adjacent to the dwbc there is a northward flow corresponding to the dwbc recirculation whose origin appears variable the largest variability is observed along the 35 w meridional section where the dwbc bifurcates eastward north of 3 s but the eastward equatorial flow does not appear to be permanent at the middle north atlantic deep water level cfc distributions exhibit the most important contrast between waters of northern and southern origin the circulation at the lower north atlantic deep water level mainly controlled by the topography looks more permanent because the dwbc is regularly observed during the three cruises and there is no evidence for a northwestward recirculation along the mid atlantic ridge the transient behavior of cfc distributions which is superimposed on local circulation effects can be seen clearly through their temporal evolution within the dwbc the variability of the deep circulation observed during the 1993 1996 interval rules out a dominant variability in response to semi annual forcing

deep cross equatorial flow in the atlantic measured with sofar floats neutrally buoyant sofar floats at nominal depths of 800 1800 and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the atlantic near 6 n and at several sites near 11 n as well as along the equator trajectories at 1800 m show a swift 50 cm s narrow 100 km wide southward flowing deep western boundary current dwbc extending from 7 n to the equator the average transport per unit depth in the dwbc was estimated to be 13 8 103 m2 s coupling this value with mean velocities measured in the dwbc by current meters gave a volume transport of 15 106 m3 s between depths of 900 m and 2800 m approximately 6 106 m3 s recirculated northward between the dwbc and the mid atlantic ridge leaving 9 106 m3 s as cross equatorial transport no obvious dwbc nor swift equatorial current was observed by the 3300 m floats a low mean velocity at this depth lay between f 11 and higher velocity cores above and below the 1800 m trajectories also suggest that at times february march 1989 the north atlantic deep water in the dwbc turned eastward and flowed along the equator and at other times august september 1990 the dwbc crossed the equator and continued southward the velocity near the equator calculated by grouping floats in a box along the equator was eastward at 4 1 cm s from february 1989 to february 1990 and westward at 4 6 cm s from march 1990 to november 1990 thus the amount of cross equatorial flow in the dwbc appeared to be linked to low frequency variability of the structure of the equatorial current system floats in antarctic intermediate water at 800 m revealed a northwestward western boundary current although flow patterns were complicated three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm s six 800 m floats drifted eastward along the equator between 5 s and 6 n at a mean velocity of 11 cm s one reached 5 w in the gulf of guinea suggesting that the equatorial currents at this depth extended at least 35 40 along the equator three of these floats reversed direction near the end of the tracking period

tracing lower north atlantic deep water across the equator water whose ultimate source is the overflow at the denmark strait can be traced using maps of salinity dissolved oxygen and silica concentration on deep density surfaces south along the american continent to at least 5 s several property extrema whose resolution is at the limit of accuracy of the measurements occur on these density surfaces which nevertheless may indicate areas of stronger mixing along the crest of the mid atlantic ridge transport estimates for that part of the southward flow within 600 km of the western boundary near 10 n suggest that 10 3 106 m3 s 1 of lower north atlantic deep water moves south there the total southward deep water transport near 10 n is estimated to be closed to 25 106 m3 s 1