the mokrsko west gold deposit bohemian massif czech republic mineralogy deposit setting and classification abstract the mokrsko west deposit is unique among european variscan gold deposits from the points of view of both the structure an approx 200 m thick complex of sheeted several mm thick densely spaced quartz veins and the economic viability gold reserves of about 100 t the deposit is hosted mainly by tonalite of the calc alkaline sazava tonalite suite ca 354 ma of the central bohemian plutonic complex mineralization is characterized by quartz dominated gangue no visible hydrothermal alteration low sulfide content high fineness native gold accompanied by maldonite aurostibite native bismuth and numerous bi te s phases five mineralogical stages are described in great detail arsenopyrite and chlorite thermometers mineral phase stabilities and published isotope and fluid inclusion data are used to reconstruct the temperature and compositional evolution of the system the role of liquid bismuth in the sequestration of gold is also discussed the deposit shares the features of both orogenic gold org and intrusion related gold irg deposits the irg model is advocated by close spatial association between the ore zone and the tonalite host intrusion by the absence scarcity of hydrothermal alteration by the au bi te as elemental association and by marked thermal gradients from the early to late mineralization stages the org model is advocated by an approx 15 10 ma gap between the intrusion of the tonalite host and the ore formation by isotope and geochemical evidence for a key role of metamorphic fluids in the mobilization and transfer of many elements species inclusive s and au the apparently ambiguous classification of the deposit can most probably be attributed to deposit formation at a depth of 9 km and to setting of the deposit at inside a large scale plutonic complex with multiple and prolonged tectonic and intrusive activity

quartz recrystallization regimes c axis texture transitions and fluid inclusion reequilibration in a prograde greenschist to amphibolite facies mylonite zone ribeira shear zone se brazil abstract the crystal plastic behavior of quartz mylonites from the ribeira shear zone se brazil a major strike slip structure that was active during a prograde metamorphic phase related to the neoproterozoic brasiliano pan african orogeny was investigated using a multi method approach geothermobarometry results indicate deformational conditions ranging from 300 to 630 c and 500 700 mpa a strong correlation between mapped metamorphic zones and a dominance of different dynamic recrystallization mechanisms of quartz occurs within the mylonite zone bulging recrystallization blg dominates within the chlorite zone between 300 and 410 c subgrain rotation recrystallization sgr operates within the biotite zone from 410 to 520 c and grain boundary migration recrystallization gbm dominates in the garnet zone above 520 c the development of quartz c axis textures is mainly governed by temperature and dynamic recrystallization mechanisms textures from blg zone mylonites are characterized by maxima around z sgr zone mylonites display single girdles or asymmetric type i crossed girdles and gbm zone mylonites comprise maxima around y and intermediate between x and z the scarcity or absence of water bearing fluid inclusions in quartz mylonites from the sgr and gbm zones which are dominated by carbonic inclusions suggests water deficient conditions whereas blg zone mylonites are dominated by water bearing inclusions this evidence indicates that water was available in the protoliths but has been eliminated with increasing deformation and deformation temperature no effect of the water content variation on the quartz microstructural and recrystallized grain size evolution was detected and little influence on c axis texture development was observed most of the fluid inclusion densities were reequilibrated during the shear zone exhumation history recording a decompression in the range of 300 500 mpa while microstructural reequilibration effects related to the prograde metamorphism are largely preserved fluid inclusion microstructures and densities from two sgr zone samples preserved evidence for a near isothermal compression within the interior of the ribeira shear zone during the prograde metamorphism

a diatom and benthic foraminiferal record from the south tasman rise southeastern indian ocean implications for palaeoceanographic changes for the last 200 000 years abstract the last two glacial interglacial cycles represented in core md88 779 in the southeastern indian ocean over the south tasman rise 47 50 69 s 146 32 75 e 2260 m water depth have been analysed an oceanographic reconstruction for this region is presented based principally on the recovery of benthic foraminiferal and diatom assemblages the most striking feature of the microfossil record from core md88 779 is the lack of diatoms during glacials despite evidence of high oceanic productivity benthic foraminiferal data suggest significant increases in ocean surface productivity during glacial periods and in particular during isotopic stages 2 late 3 and 6 for these periods of elevated surface productivity substantial and at times total dissolution of diatom frustules occurred we propose that increased influx of aeolian dust and especially associated iron during glacial periods may have reduced the intake of silica in diatoms thus resulting in less silicified diatoms additionally winnowing is suggested to have removed remaining frustules from the sedimentary record increased productivity at the sea surface is indicative that both the subtropical front and the subantarctic front may have shifted northward during glacial periods and that the subantarctic front was near the coring site on the south tasman rise for these periods we also postulate based on diatom floral evidence that southward moving eddies generated by the subtropical east australian current may have intermittently reached the coring site even during glacial periods

oceanographic and climatic changes over the past 160 000 years at deep sea drilling project site 594 off southeastern new zealand southwest pacific ocean high resolution textural carbonate microfossil and oxygen 18o and carbon 13c stable isotopic analyses are presented for the late quaternary isotopic stages 1 to 6 interval of a core at deep sea drilling project site 594 situated just south of the present subtropical convergence in northernmost subantarctic surface waters on the southern flank of chatham rise in the southwest pacific downcore alternations of pelagic and hemipelagic oozes correspond to interglacial and glacial episodes respectively interglacial oozes contain a northern subantarctic assemblage of planktonic foraminifera with rare cool subtropical species while glacial oozes are characterized by species typical of southern most subantarctic waters and include radiolaria with affinity for antarctic waters the planktonic 18o record for the site supports a 3 6 c temperature change in near surface waters between interglacial and glacial stages and indicates that during stage 5e the near surface waters were about 1 c warmer than at present a pronounced cooling during stage 5d matches that of the vostok ice core d record and negative excursions at the end of stages 2 and 6 support a southern latitude warming preceding northern hemisphere deglaciation benthic foraminifera typical of cold intermediate to deep waters can increase dramatically in abundance in the hemipelagic ooze intervals when 18o results suggest a temperature drop in glacial stage bottom waters of 2 4 c possibly a result of upward displacement of antarctic intermediate water by circumpolar deep water at the site the foraminiferal 13c records support a reduced influence of north atlantic deep water in the southwest pacific during glacial stages when nutrient enhancement occurred in both bottom and surface waters despite the pronounced changes between interglacial and glacial conditions inferred at site 594 contributed to by a substantial northward shift by at least 5 of latitude in the position of the antarctic convergence south of new zealand during glacial episodes we conclude that the subtropical convergence remained locked to chatham rise approximately 44 s throughout stages 1 to 6 major compression of the intervening belt of subantarctic water during glacial episodes and the associated very steep thermal gradients and intensified atmospheric and oceanic circulation patterns that developed in this part of the southwest pacific account for the harsh frigid environment reported for on land southern new zealand at these times

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

intensified deep pacific inflow and ventilation in pleistocene glacial times the production of cold deep waters in the southern ocean is an important factor in the earth s heat budget1 the supply of deep water to the pacific ocean is presently dominated by a single source the deep western boundary current east of new zealand here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep water properties and speed changes during the pleistocene epoch in physical and isotope proxies we find evidence for intensified deep pacific ocean inflow and ventilation during the glacial periods of the past 1 2 million years the changes in throughflow may be directly related to an increased production of antarctic bottom water during glacial times possible causes for such an increased bottom water production include increasing wind strengths in the southern ocean or an increase in annual sea ice formation leaving dense water after brine rejection and thereby enhancing deep convection we infer also that the global thermohaline circulation was perturbed significantly during the mid pleistocene climate transition between 0 86 and 0 45 million years ago

340 000 year centennial scale marine record of southern hemisphere climatic oscillation in order to investigate rapid climatic changes at mid southern latitudes we have developed centennial scale paleoceanographic records from the southwest pacific that enable detailed comparison with antarctic ice core records these records suggest close coupling of mid southern latitudes with antarctic climate during deglacial and interglacial periods glacial sections display higher variability than is seen in antarctic ice cores which implies climatic decoupling between mid and high southern latitudes due to enhanced circum antarctic circulation structural and temporal similarity with the greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations

the influence of non equilibrium isotope fractionation on the quaternary calcareous nannofossil stable isotope signal in the southwest pacific ocean dsdp site 594 oxygen and carbon isotope values from calcareous nannofossils in the mid late quaternary brunhes interval of core from dsdp site 594 off eastern south island new zealand are compared with the 18o and 13c signal of planktic and benthic foraminifers from the same samples nannofossil 18o values appear strongly affected by non equilibrium fractionation in agreement with previous in vitro studies the nannofossil 18o and 13c signals show a strong down core cross correlation and a significant positive linear correlation this is interpreted as the result of kinetic isotope effects producing non equilibrium fractionation of both18o and13c a previously reported isotope stage carbon shift appears to be related mainly to a pacific wide reduction in the abundance of gephyrocapsids rather than to any significant change in the partitioning of carbon isotopes the strong correlation between nannofossil 18o and 13c can also be interpreted as being influenced by increased productivity during glacial intervals and decreased productivity during interglacials in subantarctic waters

major depositional events under the deep pacific inflow the main inflow of deep water to the pacific is via a deep western boundary current as the current passes along the continental margin off eastern new zealand it receives much terrigenous sediment which together with the biogenic pelagic supply has been reworked into a suite of large drifts ocean drilling program site 1123 on the north chatham drift and site 1124 on the rekohu drift have yielded high resolution and well dated records of carbonate and terrigenous fluxes for the past 3 m y deposition at both drifts was affected by a deep western boundary current background sediment flux and by glacial interglacial cycles in addition drifts received site specific flux pulses caused by 1 sediment remobilization under a vigorous antarctic circumpolar current 2 increased oceanic productivity 3 overspill of sediment from the newly formed hikurangi channel and 4 generally increased discharge from the hikurangi channel under intensified quaternary uplift and paleoclimatic oscillations

perched lobe formation in the gulf of cadiz interactions between gravity processes and contour currents algarve margin southern portugal abstract the gulf of cadiz is swept by the strong saline mediterranean outflow water mow on the algarve margin south portugal this current has constructed fine grained contourite drifts this margin is dissected by the portimao canyon and three short channels that only incise the upper slope and are absent on a terrace located at mid slope depths along the algarve margin high resolution seismic profiles and sediment cores highlight the original architecture of the sedimentary deposits on this terrace coarse grained lenticular chaotic bodies formed during major relative sea level lowstands are intercalated within the drift the lobate shape and sandy nature of the lenticular chaotic bodies and their location at the mouths of the three short channels suggest they are gravity generated deposits that are perched on the middle continental slope in the gulf of cadiz the interaction between contour current and gravity processes is strongly controlled by climatic variations and relative sea level changes during the late quaternary during cold periods when sea level was low erosion intensified on the continental shelf and the deepest part of mow was active sediment was transported downslope through the channels and deposited on sedimentary lobes perched on the mid slope terrace during warm periods when relative sea level was high the supply of sediment from the shelf was shut off and the shallowest part of mow was more active contourite drifts fill the channels and bury the sandy lobes

can the morphology of deep sea benthic foraminifera reveal what caused their extinction during the mid pleistocene climate transition abstract over 100 cosmopolitan species of deep sea benthic foraminifera extinction group ext gp became extinct during the late pliocene middle pleistocene 3 6 0 55 ma most had elongate cylindrical tests and terminal apertures with complex modifications this study provides new hypotheses on the functions of the morphologies that characterised the ext gp and how these features could have been associated with their demise from our functional morphological analysis we infer that i their elongate cylindrical or flabelliform tests combined with fine perforations and a complex terminal apertural face are indicative of infaunal k strategists with a low rate of metabolism and ii their complex apertural faces may also have been an adaptation for gathering or processing their specific phytodetrital food we propose three alternative hypotheses for the cause of these extinctions and where possible test them using our high resolution micropaleontological and geochemical record through the last 1 07 ma in lower bathyal site md 97 2114 in the sw pacific ocean hypothesis 1 is that the ext gp species were unable to adapt to increased variability in the overall quantity or pulsed seasonality of the food supply to the sea floor and were out competed by opportunistic r strategist benthic foraminifera this is supported by the highly variable and increasing abundance of opportunistic foraminifera at our study site during the final phase of the extinction in the mid pleistocene climate transition mpt we doubt however that there was increased variability in phytoplankton productivity throughout the world s oceans sufficient to bring about the global demise of the ext gp hypothesis 2 is that lowered pco2 during increasingly severe mpt glacials which coincided with the final phases of the extinction may have caused the decline and possible loss of the ext gp s phytoplankton food source declining pco2 during neogene cooling was coeval with declining relative abundance of the ext gp and reticulofenestrid nannofossils but the final demise of this latter phytoplankton group occurred slightly later than the mpt in our study site and cannot be implicated with the extinction if this hypothesis has any validity maybe the phytoplankton group left no fossil record our third alternative hypothesis is that maybe our ext gp had much common dna which made them the selective target of pathogens that caused their extinction this does not easily explain their earlier disappearance at abyssal depths than at bathyal depths in our study region which can be accommodated by hypotheses 1 and 2

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

establishment of a 3 83 ga magmatic age for the akilia tonalite southern west greenland a recurring challenge to ion microprobe u pb zircon geochronology has been to discriminate between preservation of original igneous zircon populations and inherited grains this has proved particularly problematic in studying the polyphase metamorphic rocks that dominate early archean gneissic terranes for example differing interpretations exist for the origin of complex zircon populations investigated by u pb ion microprobe zircon geochronology from a granitoid orthogneiss body previously used to establish a minimum age for a supracrustal enclave on akilia island in southern west greenland we describe a method whereby the geochemistry of the akilia orthogneiss coupled with a u th pb vs age depth profile in a zircon from the same rock permits direct assessment of zircon inheritance results reveal evidence for three phases of concentric zircon growth at 3 83 ga v3 6 ga and 2 7 2 5 ga zircon growth at both v3 6 ga and 2 7 2 5 ga is consistent with precipitation from a metamorphic fluid depth profile u th pb data demonstrate that only the s 3 8 ga zircon core could have crystallized from the host rock we conclude that the magmatic age of this rock is 3 83 7 0 01 ga not v3 65 ga as has been previously proposed the u th pb zircon depth profile technique has wider applications to resolving other geochronological debates in highgrade metamorphic terranes where zircons populations are diverse and individual grains record complex overgrowth and dissolution re precipitation features 2002 elsevier science b v all rights reserved

chloritization of the hydrothermally altered bedrock at the igarape bahia gold deposit carajas brazil the igarape bahia gold deposit has developed from weathering of a near vertical hydrothermal cu au mineralization zone the unweathered bedrock composed of chlorite schists is mainly metamorphosed basalts pyroclastic and clastic sedimentary rocks and iron formation contents and fe fe mg ratios of chlorites increase from distal country rock towards the mineralization zone which can be attributed to different water rock ratios and locations in a hydrothermal system in the hydrothermal system high salinity fluids convected through basin floor rocks stripping metals from the recharge zones with precipitation in discharge zones the chlorite with lower fe fe mg ratios indicates alteration by relatively unreacted mg rich fluids occurring within recharge zones by contrast the chlorite with higher fe fe mg ratios in the mineralization zone formed from solutions rich in fe mn au cu h2s and sio2 within a discharge zone the iron formation could also be formed within the discharge zone or on the basin floor from the fe rich fluids the distal country rock with less chlorite content is a hydrothermal product at low water rock ratios whereas the proximal country rock and the host rock with more chlorite content formed at high water rock ratio conditions the al iv contents of chlorites indicate that the formation temperatures of these rocks range from 204 to 266 c with temperatures slightly increasing from distal country rock towards the mineralization zone

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

tasman front shifts and associated paleoceanographic changes during the last 250 000 years foraminiferal evidence from the lord howe rise abstract the paleoceanography of the tasman sea over the past 250 000 years was studied using benthic 75 m size fraction and planktonic foraminifera 149 m size fraction from three cores collected along 162 e traverse between 25 s and 30 s on the lord howe rise planktonic foraminiferal oxygen isotope stratigraphy dates the cores between ois 1 and 11 r mode cluster and q mode factor analyses were carried out on benthic foraminiferal faunas and q mode factor analysis and the modern analog technique mat were used in analyzing planktonic foraminiferal faunas distinct benthic faunas across latitude from north 25 s to south 30 s and 35 s reflects the difference in primary productivity level in the overlying surface water the mat result is thought to express latitudinal shifts of the tasman front over the last 250 000 years with 1 the tasman front at 35 s during the oxygen isotope stage ois 1 post glacial period 2 migration of the front nearby 25 s during the last glacial period ois 2 ois 4 and slightly northward of its present position during the penultimate glacial period ois 6 and 3 a return of the front to near 35 s during ois 5 and ois 7 based on time series and spatial variations of benthic foraminiferal factor typified by pseudoparrella exigua and uvigerina peregrina and one variety southern winter mixing and convection along the tasman front may have strengthened during the interglacial ois 7 in particular

extended history of a 3 5 ga trondhjemitic gneiss wyoming province usa evidence from upb systematics in zircon abstract the beartooth bighorn magmatic zone bbmz and the montana metasedimentary province mmp are two major subprovinces of the archean wyoming province in the northwestern beartooth mountains these subprovinces are separated by a structurally lithologically and metamorphically complex assemblage of lithotectonic units that include 1 a strongly deformed complex of trondhjemitic gneiss and interlayered amphibolites and 2 an amphibolite facies mafic unit that occurs in a nappe that structurally overlies the gneiss complex zircons from a trondhjemitic blastomylonite in the gneiss complex yield concordant u pb ages of 3 5 ga establishing it as the oldest rock yet documented in the wyoming province two younger events are also recorded by zircons in this rock 1 an apparently protracted period of high grade metamorphism and or intrusion of additional magmas at 3 25 ga and 2 growth of hydrothermal zircon at 2 55 ga apparently associated with ductile deformation that immediately preceded structural emplacement of the gneiss although this latter event appears confined to areas along the bbmz mmp boundary evidence of 3 25 ga igneous activity is found in the overlying amphibolite 3 24 ga and throughout the mmp these data suggest that this boundary first developed as a major intracratonic zone of displacement at or before 3 25 ga the limited occurrences of 2 8 ga magmatic activity in the mmp suggest that it had a controlling influence on late archean magmatism as well

glacial interglacial mis 1 10 migrations of the subtropical front across odp site 1119 canterbury bight southwest pacific ocean abstract ocean drilling program odp site 1119 is located at water depth 395 m near the subtropical front stf here represented by the southland front just downslope from the shelf edge of eastern south island new zealand the upper 86 19 metres composite depth mcd of site 1119 sediment was deposited at an average sedimentation rate of 34 cm kyr during marine isotope stages mis 1 8 0 252 ka and is underlain across a 25 kyr intra mis 8 unconformity by mis 8 5 11 277 367 ka and older sediment deposited at 14 cm kyr a time scale is assigned to site 1119 using radiocarbon dates for the period back to 39 ka and prior to then by matching its climatic record with that of the vostok ice core which it closely resembles four palaeoceanographic proxy measures for surface water masses vary together with the sandy muddy glacial interglacial g i cyclicity at the site interglacial intervals are characterised by heavy 13c high colour reflectance a proxy for carbonate content low ray a proxy for clay content and light 18o conversely glacial intervals exhibit light 13c low reflectance high ray and heavy 18o signatures early interglacial intervals are represented by silty clays with 10 105 cm thick beds of sharp based chondrites burrowed shelly graded fine sand the sands are rich in foraminifera and were deposited distant from the shoreline under the influence of longitudinal flow in relatively deep water glacial intervals comprise mostly micaceous silty clay though with some thin 2 10 cm thick sands present also at peak cold periods and contain the cold water scallop zygochlamys delicatula interglacial sandy intervals are characterised by relatively low sedimentation rates of 5 32 cm kyr cold climate intervals mis 10 6 and 2 have successively higher sedimentation rates of 45 69 and 140 cm kyr counter intuitively and forced by the bathymetric control of a laterally moving shoreline during g i and i g transitions the 1119 core records a southeasterly seaward movement of the stf during early glacial periods accompanied by the incursion of subtropical water stw above the site and northwesterly landward movement during late glacial and interglacial times resulting in a dominant influence then of subantarctic surface water saw the history of passage of these different water masses at the site is clearly delineated by their characteristic 13c values the intervals of thin graded sands muds which occur within mis 2 3 6 7 4 and 10 indicate the onset at times of peak cold of intermittent bottom currents caused by strengthened and expanded frontal flows along the stf which at such times lay near site 1119 in close proximity to seaward encroaching subantarctic waters within the bounty gyre in common with other nearby southern hemisphere records the cold period which represents the last glacial maximum lasted between 23 18 ka at site 1119 during which time the stf and subantarctic front saf probably merged into a single intense frontal zone around the head of the adjacent bounty trough

archaean hydrothermal zircon in the abitibi greenstone belt constraints on the timing of gold mineralisation abstract hydrothermal zircons have been found in archaean mesothermal au veins and altered wallrock selvages at val d or in the abitibi greenstone belt of canada the zircons are paragenetically associated with vein quartz tourmaline mica carbonate scheelite pyrite and gold zirconium mobility and the consequent occurrence of hydrothermal zircon may be associated with the intense tourmalinisation characteristic of archaean gold deposits in this district the shrimp ion microprobe has been used to analyse hydrothermal zircons from four separate mines spatially associated with the bourlamaque batholith and has yielded ages constraining formation of the au bearing vein systems to within 20 ma of emplacement of the pluton the ion microprobe data reveal multiple stages of hydrothermal zircon growth in the vein systems contemporaneous with the regional metamorphic peak and late kinematic activity along regional structures younger including proterozoic ages previously obtained for the veins using other minerals and isotopic schemes must reflect either alteration or renewed mineral growth during much later reactivation of fluids along the same structures up to 400 ma after initial formation of the veins

sedimentary record of the mid pleistocene climate transition in the southeastern south atlantic odp site 1090 abstract one important goal of leg 177 of the ocean drilling program odp was to explore the nature of the mid pleistocene climate transition mpt on the southern hemisphere a suitable mpt record was encountered at site 1090 in the southeastern south atlantic where a 44 m thick sequence of quaternary diatom bearing foraminiferal muds and oozes was recovered on the agulhas ridge environmental responses to the mpt comprised changes in terrestrial climate biological productivity and regional ocean circulation as inferred from compositional sediment data and clay mineralogy a shift towards more arid conditions occurred between 900 and 800 ka in southern africa changes in palaeoceanography already started earlier since 1150 ka northward displacements of the polar front appeared during glacial periods and shifted the area of dominant diatom deposition towards site 1090 likewise glacial interglacial contrasts in regional conveyor circulation strengthened after 1200 ka and became most severe after 650 ka however while changes in regional conveyor circulation likely responded in tune with global ice volume changes and show the onset of 100 kyr cycles after 1200 ka an unusual 130 kyr pattern characterises the pattern of frontal movements between 1200 ka and 650 ka probably in response to imperfect adaptation of regional climate to the global 100 kyr climate cycles

response of nannoplankton to major changes in sea surface temperature and movements of hydrological fronts over site dsdp 594 south chatham rise southeastern new zealand during the last 130 kyr abstract a high resolution history of paleoceanographic changes in the subpolar waters of the southern margin of the subtropical convergence zone during the last 130 kyr is present in foraminiferal assemblages of dsdp site 594 the foraminifera indicate that sea surface temperatures during the last interglacial climax were warmer than today and that between substage 5d through to the end of isotope stage 2 temperatures were mostly cooler than holocene temperatures the paleotemperatures suggest that 1 the subtropical convergence was located over the site during substage 5e later moving further north then moving southwards to near the site during the holocene and 2 the polar front was positioned over the site during glacial stages 6 4 2 and possibly parts of stage 3 several major events are indicated by the nannofloral assemblages during these large changes in sea surface temperature and associated reorganization of ocean circulation first the time progressive trends between e huxleyi and medium to large gephyrocapsa are unique to this site with e huxleyi dominating over medium gephyrocapsa during stages 5c a middle part of stage 4 and after the middle point of stage 3 this unusual trend may at least partly be caused by the shift of the polar front across the site second upwelling flora e huxleyi and small placoliths increase in abundance during stages 1 3 and 5 suggesting that upwelling or disturbance of water stratification took place during the interglacials thirdly there are no significant differences between the distribution patterns of the various morphotypes of medium to large gephyrocapsa and the combined value of all medium gephyrocapsa increases in abundance during glacials stages 2 and 4 and the end of stage 6 similar to the abundance trends in benthic foraminifera finally subordinate nannofossil taxa also show distinctive climatic trends during the last glacial cycle 1 syracosphaera spp are present in increased abundance during warmer extremes in climate substages 5e 5a and stage 1 2 coccolithus pelagicus and calcidiscus leptoporus dominate the subordinate nannofossil taxa and their relative proportions seem to provide a useful paleoceanographic index with c pelagicus dominating when the polar front zone is over the site stages 6 4 and 2 whilst c leptoporus is relatively more abundant when the stc is positioned over the site stages 1 and 5e increased abundance of c pelagicus also can indicate intensified coastal upwelling

last glacial jetting of cold waters through the subtropical convergence zone in the southwest pacific off eastern new zealand and some geological implications recent evidence suggests that the subtropical convergence stc zone east of new zealand shifted little from its modern position along chatham rise during the last glaciation and that offshore surface waters north of the stc zone cooled only slightly however at nearshore core site p69 2195 m depth 115 km off the east coast of north island and ca 300 km north of the modern stc zone planktonic foraminiferal species transfer function data and stable oxygen and carbon isotope records suggest that surface waters were colder by up to 6 c during the late last glacial period compared to the holocene and included a strong upwelling signature presently site p69 is bathed by south flowing subtropical waters in the east cape current the nearshore western end of chatham rise supports a major bathymetric depression the mernoo saddle through which some exchange between northern subtropical and southern subantarctic water presently occurs it is proposed that as a result of much intensified current flows south of the rise during the last glaciation a consequence of more compressed subantarctic water masses lowered sea level and an expanded and stronger westerly wind system there was accelerated leakage northwards of both australasian subantarctic water and upwelled antarctic intermediate water over mernoo saddle in a modified and intensified southland current the expanded cold water masses displaced the south flowing warm east cape current off southeastern north island and offshore divergence was accompanied by wind assisted upwelling of nutrient rich waters in the vicinity of p69 a comparable kind of inshore cold water jetting possibly characterised most glacial periods since the latest miocene and may account for the occasional occurrence of subantarctic marine fossils in onland late cenozoic deposits north of the stc zone rather than invoking wholesale major oscillations of the oceanic stc itself

a fluid inclusion study of the hetai goldfield in the qinzhou bay hangzhou bay metallogenic belt south china abstract the hetai goldfield is located in the southern section of the qinzhou bay hangzhou bay metallogenic belt qhmb south china gold mineralization is controlled by ne trending ductile shear zones gold grade is higher at the shear zone centers and decreases sharply away from the shear zones regardless of the host rock type fluid inclusions fis preserved in the auriferous quartz veins have been analyzed to constrain their genesis three types of gold mineralization related fis including moderate salinity aqueous a type low salinity h 2 o co 2 b type and co 2 dominated c type have been newly identified the measured homogenization temperatures t h range from 130 c to 310 c with two peaks of about 245 c and 170 c the calculated pressures of fis range from 50 mpa to 170 mpa immiscibility and co 2 effervescence of fluids may have played an important role in gold precipitation during the ascent of the ore forming fluids the hetai goldfield is a typical example of orogenic gold deposits originating from auriferous metamorphic fluids

eastern asia and the western pacific timing and spatial distribution of rifting in china abstract a compilation of recognized rifts in china indicates that five distinct episodes of rifting have occurred these episodes occurred at approximately 2 3 ga 1 85 1 7 ga 1 0 0 7 ga 550 190 ma and 175 ma to present the timing and location of rifting has largely been a function of tectonic activity along the margins of the various chinese paleocontinents some of the oldest rocks in china are found in the sino korean and tarim cratons and most of the identified precambrian rifts are found within or on the margins of these cratons these cratons are viewed as the continental nucleus of china and fold belts and microcontinents have been accreted to this nucleus through time much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin especially in the paleozoic beginning in the middle mesozoic rifting commenced along the entire eastern margin of china extension occurred concomitantly with subduction in a backarc setting this is the dominant cenozoic extensional regime in china and is still active today to date few cenozoic rifts have been found in western china where most tectonism is probably a consequence of the collision between india and china but it seems likely that more rifts will be discovered in this area as it becomes better studied

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

crustal scale shear zones and their significance to archaean gold mineralization in western australia many large archaean epigenetic gold deposits show a broad spatial relationship to regional lineaments in greenstone belts although in detail they are sited in subsidiary brittle ductile fault structures fluids originating from a deep source follow a complex path and re equilibrate with different lithologies and with metamorphic fluid during migration to higher crustal levels temperature and pressure conditions at or below the amphibolite greenschist metamorphic boundary where most gold deposits are located favour the establishment of brittle ductile and brittle subsidiary structures the preferred structural setting of gold deposits physical gradients between the regional ductile structures and more brittle subsidiary structures ensure transient strongly localized fluid flow into the latter where lower temperatures and suitable host rocks with high fe fe mg ratios favour gold deposition the multi source origin and continuous re equilibration of the fluid with crustal rock which includes granitoid and greenstone belt lithologies of different ages is reflected in the diverse isotopic and geochemical signature of the gold deposits

millennial scale changes in north atlantic deep water circulation during marine isotope stages 11 and 12 linkage to antarctic climate the time interval represented by marine isotope stages mis 11 and 12 ca 360 470 ka may contain the most extreme glacial and interglacial climate conditions of the late pleistocene sediments from the bermuda rise western north atlantic provide clues to the nature of climate variability during this period our geochemical records indicate that millennial scale climate instability and associated changes in north atlantic deep water nadw production occurred during both interglacial mis 11 and glacial mis 12 stage 12 is punctuated by a series of interstadial events that occurred at a 5 6 k y periodicity and the occurrence of ice rafted debris at various times during stage 12 indicates that icebergs were present at least as far south as 34 n during this glacial period within the limits of our correlation the atmospheric temperature changes recently reported for the vostok ice core for the stage 11 time period appear to be represented by coeval changes in nadw flow specifically warming in antarctica is associated with increased production of nadw

ne sw trending hepu hetai dextral shear zone in southern china penetration of the yunkai promontory of south china into indochina abstract the ne sw trending hepu hetai shear zone extends for about 480 km along the boundary between guangdong and guangxi provinces in the southern part of south china field mapping and kinematic analyses indicate that the zone is characterized by dextral ductile strike slip deformation with an estimated displacement along the fault zone in excess of 500 km studies of synkinematic phengite and gas liquid inclusions in quartz within mylonite suggest that the ductile shear deformation occurred under medium temperature pressure conditions of the greenschist facies and 40ar 39ar analyses of muscovite yield ages of 213 195 ma based on these data and late paleozoic mesozoic paleogeographic data for southern china we propose that the hepu hetai shear zone originated via the penetration of the yunkai promontory of south china into indochina during the triassic

factors influencing the distribution patterns of recent deep sea benthic foraminifera east of new zealand southwest pacific ocean abstract this study investigates which combination of environmental factors most strongly influences the distribution patterns of benthic foraminferal tests 0 63 m in a region bisected by the subtropical front east of new zealand seafloor sample sites extend from outer shelf 90 m to abyssal 4700 m depths across substrates ranging from biogenic terrigenous gravelly sand to hemipelagic mud and occur under the influence of antarctic intermediate water aaiw and circumpolar deep waters as well as receiving detritus from both subtropical and subantarctic surface water masses elevated values of the planktic foraminiferal fragmentation index and reworked small paleogene planktic foraminifera at outer shelf and bathyal depths coincide with areas of strong bottom currents q mode cluster analysis on the census counts of 398 benthic species clusters the 66 samples into three large groups shallow bathyal abyssal and at a lower level 10 mappable associations are recognised a combination of canonical correspondence analysis and a correlation coefficient matrix was used to relate the faunal data to a set of measured environmental proxies these analyses show that factors that have a relationship with depth are the most significant in determining foraminiferal distribution the principal environmental factors which appear to most strongly influence this benthic foraminiferal distribution are dissolved oxygen content in bottom waters sustainability of organic carbon flux rates seasonality of food supply lateral advection of water masses bottom water carbonate corrosiveness energetic state at the benthic boundary layer grain size composition of substrate salinity and temperature of the bottom waters shallow water associations 90 1250 m dominated by cassidulina carinata and trifarina angulosa occur within coarse substrates under well oxygenated high energy regimes and sustained food input the occurrence of the bathyal associations 230 2840 m dominated by c carinata alabaminella weddellensis and abditodentrix pseudothalmanni closely mirrors the distribution of aaiw within a region of variable food supply the sustainability of food supply combined with bottom water type and associated ventilation and dissolution strongly influence the composition of abyssal associations 1200 4700 m mostly dominated by epistominella exigua and a weddellensis

orbital insolation ice volume and greenhouse gases abstract the specmap models of orbital scale climate change imbrie et al paleoceanography 7 1992 701 paleoceanography 8 1993 699 are the most comprehensive to date all major climatic observations were analyzed within the framework of the three orbital signals subsequently tuning of signals in vostok ice to insolation forcing has fixed the timing of greenhouse gas changes closely enough to permit an assessment of their orbital scale climatic role in addition evidence from several sources has suggested changes in the specmap 18 o time scale this new information indicates that the timing of co 2 changes at the periods of precession and obliquity does not fit the 1992 specmap model of a train of responses initiated in the north propagated to the south and later returning north to force the ice sheets in addition analysis of the effects of rectification on 100 000 year climatic signals reveals that all have a phase on or near that of eccentricity this close clustering of phases rules out the long time constants for 100 000 year ice sheets required by the 1993 specmap model a new hypotheses presented here revives elements of an earlier climap view hays et al science 194 1976a 1121 but adds a new assessment of the role of greenhouse gases as proposed by milankovitch summer mid july insolation forces northern hemisphere ice sheets at the obliquity and precession periods with an ice time constant derived here of 10 000 years changes in ice volume at 41 000 years drive ice proximal signals sst nadw dust that produce a strong positive co 2 feedback and further amplify ice volume changes at the precession period july insolation forces ice sheets but it also drives fast and early responses in ch 4 through changes in tropical monsoons and boreal wetlands and variations in co 2 through southern hemisphere processes these ch 4 and co 2 responses enhance insolation forcing of ice volume climatic responses at 100 000 years result from eccentricity pacing of forced processes embedded in obliquity and precession cycles increased modulation of precession by eccentricity every 100 000 years produces 23 000 year co 2 and ch 4 maxima that enhance ablation caused by summer insolation and drive climate deeper into an interglacial state when eccentricity modulation decreases at the 100 000 year cycle ice sheets grow larger in response to obliquity forcing and activate a 41 000 year co 2 feedback that drives climate deeper into a glacial state alternation of these forced processes because of eccentricity pacing produces the 100 000 year cycle the 100 000 year cycle began 0 9 myr ago because gradual global cooling allowed ice sheets to survive during weak precession insolation maxima and grow large enough during 41 000 year ice volume maxima to generate strong positive co 2 feedback the natural orbital scale timing of these processes indicates that ice sheets should have appeared 6000 3500 years ago and that co 2 and ch 4 concentrations should have fallen steadily from 11 000 years ago until now but new ice did not appear and co 2 and ch 4 began anomalous increases at 8000 and 5000 years ago respectively human generation of co 2 and ch 4 is implicated in these anomalous trends and in the failure of ice sheets to appear in canada

microstructures in feldspars from a major crustal thrust zone the grenville front ontario canada abstract samples collected across the nw grenville front in ontario canada have been used to document the change in feldspar microstructures produced during shearing under metamorphic conditions that range from upper amphibolite to lower greenschist grade the differential displacement across this 5 km thick section of the grenville front tectonic zone is at least 10 km at upper to mid amphibolite conditions both plagioclase and potassium feldspars behave plastically grainsize reduction occurs through grain boundary migration and or subgrain rotation and produces a core and mantle structure at middle to lower amphibolite grade grain size reduction is accomplished through grain boundary migration at lower amphibolite to upper greenschist grade grain size reduction occurs by the nucleation and growth of new grains with a different composition the abundance of intracrystalline deformation at this grade is inversely proportional to the amount of fine grained matrix in ultramylonite with a high matrix to porphyroclast ratio few intracrystalline strain features occur other than ubiquitous undulatory extinction myrmekite is well developed on the high stress boundaries in k feldspar at upper to mid greenshist conditions feldspars deform mainly by slip on synthetic shear fractures deformation twins undulatory extinction deformation bands and kink bands occur in plagioclase and perthite flames and myrmekite occur principally on high stress boundaries in k feldspar grain size reduction in feldspar is accomplished through cataclasis at middle to lower greenschist facies deformation in feldspars is dominated by antithetic fractures the transition from the dominance of synthetic to antithetic fractures is gradational below lower greenschist grade rocks deform by pervasive cataclasis of all minerals

benthic foraminiferal proxy evidence for the neogene palaeoceanographic history of the southwest pacific east of new zealand abstract canonical correspondence analysis indicates that the distribution of neogene benthic foraminiferal faunas 63 m in seven dsdp and odp sites 500 4500 m water depth east of new zealand 38 51 s 170 e 170 w is most strongly influenced by depth water mass stratification and secondly by age palaeoceanographic changes influencing faunal composition and biotic evolution stratigraphic faunal changes are interpretted in terms of the pulsed sequential development of southern and later northern polar glaciation and consequent cooling of bottom waters increased vertical and lateral stratification of ocean water masses and increased overall and seasonal surface water productivity oligocene initiation of the antarctic circumpolar current and deep western boundary current dwbc flowing northwards past new zealand resulted in extensive hiatuses throughout the southwest pacific some extending through into the miocene planktic foraminiferal fragmentation index values indicate that carbonate dissolution was significant at abyssal depths throughout most of the neogene peaking at upper abyssal depths in the late miocene 11 7 ma with the lysocline progressively deepened thereafter miocene abyssal faunas are dominated by globocassidulina subglobosa and oridorsalis umbonatus with increasing epistominella exigua after 16 ma at upper abyssal depths peak abundances of epistominella umbonifera indicate increased input of cold southern component water to the dwbc at 7 6 ma faunal association changes imply establishment of the modern oxygen minimum zone upper circumpolar deep water in the latest miocene significant latitudinal differences between the benthic foraminiferal faunas at lower bathyal depths indicate the existence of an oceanic front along the chatham rise location of present subtropical front since the early late miocene at least with more pulsed productivity higher e exigua along the south side modern antarctic intermediate water faunal associations were established north of the chatham rise at 10 9 ma and south of it at 3 1 5 ma middle upper bathyal faunas on the campbell plateau are dominated by reticulate bolivinids during the early and middle miocene indicative of sustained productivity above relatively sluggish suboxic bottom waters faunal changes and hiatuses indicate increased current vigour over the campbell plateau from the latest miocene on surface water productivity food supply appears to have increased in three steps at times of enhanced global cooling marked by substantially increased relative abundance of 1 abditodentrix pseudothalmanni alabaminella weddellensis cassidulina norvangi 16 15 ma increased pulsed productivity 2 bulimina marginata f aculeata nonionella auris trifarina angulosa uvigerina peregrina 3 1 5 ma increased overall productivity and 3 cassidulina carinata 1 0 5 ma increased overall productivity three intervals of deep sea benthic foraminiferal taxonomic turnover are recognised 16 15 11 5 10 2 0 5 ma corresponding to intervals of enhanced global cooling and possible productivity changes the late pliocene middle pleistocene extinction associated with increasing northern hemisphere glaciation culminating in the middle pleistocene climatic transition was more significant in the study area than the earlier neogene turnovers

the mid pleistocene climate transition as documented in the deep south atlantic ocean initiation interim state and terminal event abstract the mid pleistocene transition mpt of the global climate system initiated by a shift towards much larger northern hemisphere ice shields at around 920 ka and ending with predominance of 100 kyr ice age cyclicity since about 640 ka is one of the fundamental enigmas in quaternary climate evolution climate proxy records not exclusively linked to global ice volume are necessary to advance understanding of the mpt here we present a high resolution pleistocene magnetic susceptibility time series of 12 sediment cores from the subtropical south atlantic essentially reflecting dissolution driven variations in carbonate accumulation controlled by changes in deep water circulation in addition to characteristics known from 18o records the data sets reveal three remarkable features intimately related to the mpt 1 an all pleistocene minimum of carbonate accumulation in the south atlantic at 920 ka 2 a mpt interim state of reduced carbonate deposition indicating that the mpt period may have been a discrete state of the pleistocene deep water circulation and climate system and 3 a terminal mpt event at around 540 530 ka documented in several peculiarities such as thick laminated layers of the giant diatom ethmodiscus rex

a synoptic survey of young mesoscale eddies in the eastern gulf of alaska eddies in the gulf of alaska are important sources of coastal water and associated nutrients iron and biota to the high nutrient low chlorophyll central gulf of alaska three primary eddy formation regions along the eastern boundary of the gulf have been identified from south to north haida sitka and yakutat in the spring of 2005 three eddies one of each type were sampled soon after their formation the subsurface eddy core water in all three eddies was defined by high iron concentrations and low dissolved oxygen compared with surrounding basin water the sitka and yakutat core waters also exhibited a subsurface temperature maximum mesothermal water coincident in depth with the iron maximum suggesting that eddies may play a role in the formation of temperature inversions observed throughout the gulf of alaska the data suggest different formation regions with the yakutat eddy forming in shallow shelf water with riverine input while the sitka and haida eddies appear to form in deeper water

relative timing of deformation and two stage gold mineralization at the hutti mine dharwar craton india gold mineralization at hutti is confined to a series of nine parallel n s to nnw sse trending steeply dipping shear zones the host rocks are amphibolites and meta rhyolites metamorphosed at peak conditions of 660 40 c and 4 1 kbar they are weakly foliated s1 and contain barren quartz extension veins the auriferous shear zones reefs are typically characterized by four alteration assemblages and laminated quartz veins which in places occupy the entire reef width of 2 10 m and contain the bulk of gold mineralization a 1 5 m wide distal chlorite sericite biotite calcite plagioclase alteration zone can be distinguished from a 3 5 m wide proximal biotite plagioclase quartz muscovite calcite alteration zone gold is both spatially and temporally associated with disseminated arsenopyrite and pyrite mineralization an inner chlorite k feldspar quartz calcite scheelite tourmaline sphene epidote sericite alteration halo which rims the laminated quartz veins is characterized by a pyrrhotite chalcopyrite sphalerite ilmenite rutile and gold paragenesis the distal chlorite sericite and proximal biotite plagioclase alteration assemblages are developed in microlithons of the s2 s3 crenulation cleavage and are replaced along s3 by the inner chlorite k feldspar alteration indicating a two stage evolution for gold mineralization ductile d2 shearing alteration and gold mineralization formed the reefs during retrograde evolution and fluid infiltration under upper greenschist to lower amphibolite facies conditions 560 60 c 2 1 kbar the reefs were reactivated in the d3 dextral strike slip to oblique slip environment by fault valve behavior at lower greenschist facies conditions ca 300 350 c which formed the auriferous laminated quartz veins later d4 crosscutting veins and d5 faults overprint the gold mineralization the alteration mineralogy and the structural control of the deposit clearly points to an orogenic style of gold mineralization which took place either during isobaric cooling or at different levels of the archean crust from overlaps in the tectono metamorphic history it is concluded that gold mineralization occurred during two tectonic events affecting the eastern dharwar craton in south india between ca 2550 2530 ma 1 the assemblage of various terranes of the eastern block and 2 a tectono magmatic event which caused late to posttectonic plutonism and a thermal perturbation it differs however from the pre peak metamorphic gold mineralization at kolar and the single stage mineralization at ramagiri notably greenschist facies gold mineralization occurred at hutti 35 90 million years later than in the western dharwar craton

continental shelf progradation by sediment drift accretion multi channel seismic profiles from the canterbury basin on the eastern margin of the south island of new zealand reveal the importance of current activity in shaping a neogene shelf sediment prism the shelf prism prograded across a broad near horizontal platform in water depths of 1 000 to 1 750 m the platform was formed above a condensed section of late eocene to late oligocene limestones which overlie cretaceous to paleogene rift fill and transgressive sediments the neogene sediment prism contains sediment drifts which are as much as 25 km long and 15 km wide and extend up to 1 600 m uncompacted vertically individual drifts migrated westward and can be traced between dip profiles revealing that the long axes of most are subparallel to the present coastline and shelf edge channel like features at the landward edges of the drifts correspond to residual space left between the landward prograding off shelf sediment drift and the adjacent shelf foreslope erosion or slow deposition characterized the foreslope progradation of the shelf was by the accretion of successive sediment drifts before ca 11 5 ma pink horizon the shelf edge parallel drifts were distributed across the central part of the basin whereas subsequently they were concentrated to the northeast the seismic architecture of the neogene sediment prism results from the interplay of an abundant western sediment source and an offshore boundary current system present day ocean circulation involves northward flow along the east coast of the south island the basin may have been subjected to a middle miocene to late pliocene phase of intensified flow caused by local topographic enhancement and or global paleoceanographic events current activity has played a crucial role in the sedimentary evolution of the canterbury basin neogene shelf prism

the archaean mount gibson gold deposits yilgarn craton western australia products of combined synvolcanic and syntectonic alteration and mineralisation abstract the mount gibson gold deposits are sited at the southern tip of the archaean yalgoo singleton greenstone belt in the southern portion of the murchison province yilgarn craton western australia primary gold mineralisation is hosted within an eastward facing dominantly tholeiitic metabasalt sequence which has been metamorphosed to amphibolite facies conditions alteration and mineralisation occurs within the north to north northeast striking steeply east dipping mount gibson shear zone paralleling primary layering within the tholeiitic mine sequence two main styles of wallrock alteration and associated sulphide mineralisation are present the first of these is represented by garnet spessartine almandine gahnite and cordierite muscovite bearing schists these lithologies are unusual for lode gold mineralisation and despite their apparently pelitic nature have mafic precursors and reflect pre metamorphic alteration of tholeiitic basalts the garnet bearing schists form a coherent stratiform horizon which overlies the main ore zone at the orion two deposit and are associated with recrystallised metamorphosed polymetallic sphalerite galena pyrite pyrrhotite chalcopyrite tetrahedrite mineralisation a more typical for archaean lode gold pervasive syn peak metamorphic syn shearing quartz biotite sulphide alteration envelope is associated with pyrrhotite pyrite chalcopyrite mineralisation at mount gibson although free gold is rare there is a strong empirical relationship between enhanced gold grades and the pyrrhotite pyrite chalcopyrite assemblage suggesting that gold was introduced as part of this event mass balance calculations at orion two show enrichment of au ag k rb ba and w and depletion of na ca and sr over mineralised zones which is typical of lode gold mineralisation however the deposit also exhibits strong base metal enrichment particularly within the garnet bearing schists and zonation from the au cu enrichment of the main ore zone to the overlying stratiform pb zn ag mn enrichment which is dominant in the garnet bearing schist horizon these features are typical of vhms mineralisation hornet exhibits similar overall elemental enrichment and depletion to orion two lead isotope data for sulphides from orion two and hornet provide evidence of two discrete mineralising events at mount gibson separated by approximately 300 m y a two stage model best explains the features of the mount gibson gold deposits metamorphism of the aluminous alteration and weak mineralisation associated with an early synvolcanic event resulted in the formation of cordierite muscovite and garnet spessartine almandine gahnite bearing assemblages respectively which were less competent than the surrounding tholeiitic metabasalts and consequently tended to localise shearing shear hosted lode gold mineralisation was synchronous with peak metamorphism and shearing like the shearing hydrothermal alteration was mostly concentrated in and around the less competent rocks which were produced by metamorphism of synvolcanically altered precursors resulting in a fundamental stratigraphic control on gold mineralisation at mount gibson

indosinian high strain deformation for the yunkaidashan tectonic belt south china kinematics and 40ar 39ar geochronological constraints 1 structural and 40ar 39ar data from the yunkaidashan belt document kinematic and tectonothermal characteristics of early mesozoic indosinian orogenesis in the southern part of the south china block the yunkaidashan belt is tectonically divided from east to west into the wuchuang sihui shear zone xinyi gaozhou block and the fengshan qinxi shear zone indosinian structural elements ascribed to the indosinian orogeny include d2 and d3 deformation the early d2 phase is characterized by folding and thrusting with associated foliation and lineation development related to nw se transpression under amphibolite to greenschist facies conditions this event is heterogeneously overprinted by d3 deformation characterized by a gentle dipping s3 foliation subhorizontally to shallowly plunging l3 lineation some reactived d2 folds and low angle normal faults the d3 fabrics suggest a sinistral transtensional regime under greenschist facies metamorphism the timing of the d2 and d3 events have been constrained to the early to middle triassic 248 220 ma and late triassic 220 200 ma respectively on the basis of 40ar 39ar geochronology and regional geological relations the change from oblique thrusting d2 to sinistral transtension d3 may reflect oblique convergence and crustal thickening followed by relaxation of the overthickened crust in combination with the regional relations from xuefengshan to yunkaidashan and on to wuyishan the early phase of the indosinian orogeny constituted a large scale positive flower structure and is related to the intracontinental convergence during the assembly of pangea in which the less competent south china orogen was squeezed between the more competent north china and indosinian blocks

pacific caco3 preservation and δ18o since 4 ma paleoceanic and paleoclimatic implications the pliocene pleistocene history of caco3 preservation in the central equatorial pacific is reconstructed from a suite of deep sea cores and is compared to fluctuations in global ice volume inferred from 18o records the results are highlighted by 1 a strong covariation between caco3 preservation and ice volume over 104 to 106 year time scales 2 a long term increase in ice volume and caco3 preservation since 3 9 ma demonstrated by a deepening of the lysocline and the carbonate critical depth 3 a dramatic shift to greater caco3 preservation at 2 9 ma 4 distinctive ice volume growth and caco3 preservation events at 2 4 ma which are associated with the significant intensification of northern hemisphere glaciation 5 a mid pleistocene transition to 100 kyr cyclicity in both caco3 preservation and ice volume and 6 a 600 kyr brunhes dissolution cycle superimposed on the late pleistocene glacial interglacial 100 kyr cycles caco3 preservation primarily reflects the carbonate chemistry of abyssal waters and is controlled by long term 106 year and short term 104 to 105 year biogeochemical cycling and by distinct paleoclimatic events we attribute the long term increase in caco3 preservation primarily to a fractionation of caco3 deposition from continental shelf to ocean basin and secondarily to a gradual rise in the riverine and glaciofluvial flux of ca on shorter time scales the fluctuations in caco3 preservation slightly lag ice volume fluctuations and are attributed to climatically induced changes in the circulation and chemistry of pacific deep water

late quaternary palaeoceanography near tasmania southern australia abstract this study of the palaeoceanographic record south of australia is based on two cores taken from lower circumpolar deep water depths core e27 30 located south of tasmania in water depth of 3552 m to the north of the present location of the subtropical convergence and core e55 6 from the continental margin off victoria at 2346 m depth in a region of very low surface productivity a preliminary examination of planktonic foraminiferal faunas in core e27 30 located south of tasmania provides a record of movement of the subtropical convergence through the late quaternary that is consistent with records elsewhere in the southeast indian ocean the convergence has been located equatorward of its present position through much of the late quaternary with poleward excursions in the holocene and at oxygen isotope stage 5e benthic foraminiferal faunas contrast strongly in the two cores despite their location at similar depths within the same water mass core e55 6 is largely dominated by deep infaunal taxa while core e27 30 has a high proportion throughout of epifaunal taxa the benthic foraminiferal fauna in core e27 30 is dominated by epistominella exigua known to feed directly on phytoplankton detritus in the modern deep sea abundances of that species coincide with the presence of the subtropical convergence at or near the site indicating that surface phytoplankton production has had a major influence on benthic productivity dissolution records in the two cores also differ markedly core e55 6 records a strong dissolution event in oxygen isotope stage 4 the cause of the event is not clear although it appears to be associated with increased productivity levels this pronounced dissolution event is not evident in core e27 30 suggesting either the event is localised or that the record in core e27 30 has been overprinted by the convergence the extent to which the records in the two cores vary emphasises the influence of frontal structures on core records in this region and the need to take this into account when investigating southern ocean history

late quaternary paleoclimatic and paleoceanographic change over northern chatham rise new zealand four cores from the lower northwestern flank 3010 3726 m water depth of the chatham rise east of new zealand penetrated a post glacial to last glacial sequence of mainly hemipelagic muds an accurate time frame for this study is provided by well dated tephra layers and additional 14c dates a hiatus is detected at the core tops of all cores studied with the last 900 to 1000 years missing sedimentological and micropaleontological analyses reveal that 1 1 isotope stage 2 ended ca 15 000 yr b p after a transitional period with a fluctuating composition of planktonic foraminifera assemblages and fluctuating isotopic values more stable post glacial conditions were established at ca 10 000 yr b p 2 2 from the end of isotope stage 2 to isotope stage 1 accumulation rates of diatoms aeolian quartz and calcareous microfossils decreased stepwise by a factor of 10 4 and ca 1 5 respectively in response to decreasing wind intensities and upwelling 3 3 in spite of significant climatic and oceanographic changes from the last glacial to the present the chatham rise has remained the northern distributional boundary for endemic subantarctic diatoms this implies that east of new zealand the subtropical convergence has remained bound or close to the chatham rise during both glacial and post glacial times 4 4 sediments are slight influences of contour currents or turbidity currents are recognised only in sediments younger than 16 000 years

tracing the ore formation history of the shear zone controlled huogeqi cu pb zn deposit in inner mongolia northern china using h o s and fe isotopes abstract the original ore fluid of the huogeqi cu pb zn deposit in inner mongolia northern china was enriched in heavy oxygen isotopes with 18o values ranging from 9 9 to 11 4 per mil which is characteristic of the metamorphic devolatilization of pelitic rocks the d values determined by direct measurement of syn ore hydrothermal tremolite range from 116 to 82 per mil lying between the domains of typical metamorphic fluid and meteoric water which is in equilibrium with organic matter oxygen and hydrogen isotope ratios indicate that the ore fluid was derived from deep sourced metamorphic fluid and interacted with organic rich shale during fluid migration which is consistent with the fluid evolution history revealed by a previous fluid inclusion study sulfides in the deposit are characteristically enriched in heavy s isotopes with an average 34s value of 13 4 6 2 per mil 1 n 103 the s isotope ratios are identical to stratabound sulfides generated through the non bacterial reduction of neoproterozoic marine sulfate with 34s values of 17 per mil previous studies on lead isotopes of sulfides revealed that the ore forming metals cu pb and zn at the huogeqi deposit were also remobilized from a stratabound source this source was syngenetically elevated in its cu pb and zn sulfide content as a result of submarine hydrothermal activities forming sulfide rich layers within a rift tectonic setting the fe isotope ratios for sulfides are consistent with those of an intercalated iron formation within the ore hosting rocks suggesting that the fe in the sulfides was derived from local host rocks during sulfide precipitation and the fe rich rocks are favorable lithological units for high grade mineralization the heterogeneous sources of ore fluid s ore forming metals and fe are explained by a multistage genetic model which is supported by the geological characteristic of the deposit the enriched sulfides were subsequently remobilized and enriched by metamorphic devolatilization during the permian and triassic periods the metamorphic ore fluid ascended along a shear zone and interacted with organic rich shale sulfides eventually precipitated within the shear zone at a shallower crustal level especially where the shear zone intersected fe rich host rocks this multistage genetic model has implications for mineral exploration greenschist to amphibolite facies terranes containing thick neoproterozoic rift sequences are ideal regions for potential cu pb zn mineralization in particular intercalated volcanic rocks within the rift sequences are indicative of high heat flow and are ideal for the development of submarine hydrothermal systems the primary structures hosting mineralization and ore shoots in the huogeqi area are jogs in the shear zones in addition fe rich lithological units such as iron formations are ideal hosts for high grade ore

mid pleistocene revolution and the eccentricity myth the mid pleistocene revolution mpr is the term used to describe the transition between 41 ka and 100 ka glacial interglacial cycles which occurred about one million years ago despite eccentricity having by far the weakest influence on insolation received at the earth s surface of any of the orbital parameters it is often assumed to be the primary driver of the post mpr 100 ka climate cycles the traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity this eccentricity myth is a simplified view of the relationship between global climate and orbital forcing and is in part due to an artefact of spectral analysis our aim here is to clarify the often confused role of eccentricity and review current theories of the mpr we suggest that the post mpr 100 ka glacial interglacial cycles are more closely linked to precession with the saw toothed climate cycles being defined by every four or five precessional cycle because control over the number of precessional cycles involved is determined by eccentricity eccentricity at most paces rather than drives the system if true then one must also question whether the mpr itself defined by an abrupt change in spectral characteristics is not also somewhat misconceived

global deep sea extinctions during the pleistocene ice ages the dark near freezing environment of the deep oceans is regarded as one of the most stable habitats on earth and this stability is generally reflected in the slow turnover rates extinctions and appearances of the organisms that live there by far the best fossil record of deep sea organisms is provided by the shells of benthic foraminifera protista a little known global extinction of deep sea benthic foraminifera occurred during the pleistocene ice ages in the southwest pacific it caused the disappearance of at least two families 15 genera and 48 species 15 25 of the fauna of dominantly uniserial elongate foraminifera with distinctive apertural modifications these forms progressively died back and became extinct during glacial periods in the late pliocene to middle pleistocene ca 2 5 0 6 ma most extinctions occurred between 1 0 and 0 6 ma at the time of the middle pleistocene climatic revolution this first high resolution study of this extinction event indicates that it was far more significant for deep sea diversity loss than previously reported 10 species the middle pleistocene extinction was the most dramatic last phase of a worldwide decline in the abundance of these elongate forms a phase that began during cooling near the eocene oligocene boundary and continued during the middle miocene clearly these taxa declined when the world cooled but the reason is yet to be resolved

new evidence for changes in plio pleistocene deep water circulation from southern ocean odp leg 177 site 1090 abstract changes in atlantic deep water circulation were reconstructed by comparing the benthic foraminiferal 13c record at odp site 1090 in the south atlantic with similar records from the north atlantic sites 982 607 925 929 and deep pacific site 849 oceans important deep water circulation changes occurred in the early pleistocene at 1 55 myr and during the mid pleistocene transition at 0 9 myr at 1 55 myr glacial 13c values in the southern ocean became significantly lower than those in the deep pacific establishing a pattern that persisted throughout the late pleistocene we propose that the lowering of 13c values of southern component water scw at this time resulted from expansion of sea ice and reduced ventilation of deep water during glacial periods after marine isotope stage 52 accompanying this change in southern ocean deep water circulation was enhanced interhemispheric coupling between the north and south atlantic after 1 55 myr at 0 9 myr the magnitude of glacial to interglacial variability in 13c increased and shifted to a longer frequency 100 kyr along with oceanic 18o ice volume calculation of percent northern component water ncw using site 1090 as the scw end member yielded 20 30 less reduction of ncw during glacial periods of the late pleistocene also a trend toward reduced glacial suppression of ncw during the past 400 kyr is not evident the apparent decoupling of ice volume and deep water circulation reported previously may be an artifact of using a pacific rather than a southern ocean carbon isotopic record to calculate past mixing ratios of ncw and scw

recent benthic foraminiferal associations and ecology of the scotia sea and argentine basin abstract we investigated 88 surface sediment samples taken with a multiple corer from the southwestern south atlantic ocean for their live rose bengal stained and dead benthic foraminiferal content using q mode principal component analysis six live and six dead associations are differentiated live and dead association distributions correspond fairly well differences are mainly caused by downslope transport and selective test destruction in addition four potential fossil associations are calculated from the dead data set after removal of non fossilizable species these potential fossil associations are expected to be useful for paleoceanographic reconstructions environments are described in detail for the live and potential fossil associations and for selected species along the upper argentine continental slope strong bottom currents control the occurrence of live dead and potential fossil angulogerina angulosa associations here particles of a high organic carbon flux rate remain suspended below this high energy environment live dead and potential fossil uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates the live a angulosa and u peregrina associations correlate with high standing crops furthermore live and dead epistominella exigua nuttallides umbonifer associations were separated dominance of a nuttallides umbonifer potential fossil association relates to coverage by antarctic bottom water aabw and lower circumpolar deep water lcdw above the calcite compensation depth ccd three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by aabw or cdw a reophax difflugiformis association was found in mud rich and diatomaceous sediments below the ccd a psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a cribrostomoides subglobosus ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30 one single eggerella bradyi martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the ccd if only preservable species are considered for calculation

foraminiferal responses to major pleistocene paleoceanographic changes in the southern south china sea a detailed age model for core 17957 2 of the southern south china sea was developed based on delta 18 o coarse fraction magnetostratigraphy and biostratigraphy for the last 1500 kyr the delta 18 o record has clear similar to 100 kyr cycles after the mid pleistocene revolution mpr at the entrance of marine isotopic stage mis 22 planktonic foraminifera responded to the mpr immediately showing the increased sea surface temperature sst and dissolution after the mpr benthic foraminifera did not respond to it until the brunhes matuyama boundary since the mpr the depth of thermocline gradually became shallower until miss 6 5 this major change within miss 6 5 was also reflected in the decreased ssts and increased productivity and deep water mass thus two major pleistocene paleoceanographic changes were found one was around the mpr the other occurred within miss 6 5 which speculatively might be ascribed to the reorganization of surface and deep circulation possibly induced by tectonic forces

development of sediment drifts approaching an active plate margin under the sw pacific deep western boundary current the abyssal pacific ocean is fed by a 1000 km wide deep western boundary current dwbc that flows northward along the continental margin east of new zealand between the passive margin of chatham rise and the subduction zone of kermadec trench a distance of 1200 km the dwbc has formed a suite of sediment drifts over a depth range of 2200 5700 m airgun and 3 5 khz profiles record a variety of drift types that reflect regional variations in bathymetry sediment supply and the tectonic volcanic framework on chatham rise the dwbc has deposited a sinuous linear body along the south flank 3000 m an extensive apronlike drift on the north flank 2200 4500 m and a ridgelike drift about the rise base 4500 5200 m the flow has also deposited a body of sediment over 400 km long within a moat at the base of the nearby louisville seamount chain further downcurrent the 250 km long rekohu drift 3600 4190 m has developed northward to 39 s south of this latitude drifts comprise mainly reworked pelagic hemipelagic material and sediment transported from distant southerly sources in contrast drifts north of 39 s have received a major injection of terrigenous sediment from hikurangi channel which runs 1400 km from new zealand eastward across the hikurangi plateau to disgorge on to the abyssal floor at the plateau edge en route turbidity current overspill from the channel has moved north under the influence of the shallow dwbc to contribute to a series of small ridge and patch drifts among the numerous seamounts on the plateau at 3500 4200 m off hikurangi channel mouth a large fan has accumulated the dwbc has extended the fan into a drift running over 250 km along the base of hikurangi plateau 5150 5770 m toward kermadec trench here drift sediment becomes increasingly disrupted by mass wasting associated with the active subduction in this area the seismic stratigraphy reveals the drifts to rest mainly on a widespread erosional surface that is interpreted to mark the inception of the dwbc in the region with the late oligocene opening of the australian antarctic seaway drift construction commenced during the miocene but was punctuated in the late miocene by another period of erosion that coincided with increased bottom water production in antarctica deposition resumed in plio pleistocene times when large quantities of sediment from the rapidly rising landmass of new zealand were injected into the boundary current the modern flow continues to affect drift deposition as manifest by an active boundary channel along the foot of hikurangi plateau and widespread scour zones and sediment wave fields

response of surface water masses and circulation to late quaternary climate change east of new zealand a series of cores from east of new zealand have been examined to determine the paleoceanographic history of the late quaternary in the sw pacific using planktonic foraminiferal data distinct shifts of species can be seen between glacial and interglacial times especially south of chatham rise east of south island foraminiferal fragmentation ratios and benthic planktonic foraminiferal ratios both show increased dissolution during glacials especially isotope stage 2 to the south of chatham rise the present day subtropical convergence appears to be tied to the chatham rise at 44 s but during glacial times this rise separated cold water to the south from much warmer water to the north with an associated strong thermal gradient across the rise we estimate that this gradient could have presented as much as an 8 c temperature change across 4 of latitude during the maximum of the last ice age there is only weak evidence of the younger dryas cool event but there is a clear climatic optimum between 8 and 6 4 ka with temperatures 1 2 c higher than the present day the marine changes compare well with vegetational changes on both south and north island

brittle origins for disseminated gold mineralization in mylonite gaocun gold deposit hetai goldfield guangdong proince south china gold mineralization in the hetai goldfield in south china is almost entirely confined to a series of steeply dipping ductile shear zones generated during hercynian indosinian orogenesis of sinian host rocks approximately half of the mineralization is in the form of disseminations in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in einlets and as sulfide cement to brecciated mesoscopic quartz eins heaily influenced by the presence of disseminated mineralization all publications on hetai determine a major role for ductile deformation in the introduction of gold into the deposit the brittle deformation is typically regarded as redistributing within the host structures the gold initially introduced as a result of ductile deformation mechanisms howeer textures of the sulfides associated with the gold indicate an entirely postductile deformation timing as they display none of the features attributed to ductile deformation during the eident brittle deformation phase competence contrasts at the microscopic scale allowed fracturing to focus on the quartz sericite domain boundaries of the mylonite foliation thus permitting the introduction of auriferous fluid into the mylonite to create disseminated mineralization the control exerted by preexisting structures is further reflected in the restriction of disseminated mineralization to the quartz domains presumably because the sericite domains accommodated the deformation in a more distributed fashion seeral other lines of eidence support an origin of the hetai deposit in an upper crustal regime a similar style of disseminated mineralization to that seen in the mylonite surrounds microeinlet terminations in the brecciated quartz eins as well as oerprinting pseudotachylite which is associated with cataclasite there are also large olumes of unmineralized mylonite indicating no connection between the intensity of strain and gold grade we conclude that in structurally controlled deposits the textural category of disseminated gold mineralization can be generated either under entirely ductile or entirely brittle conditions and that microtextural eidence has to be carefully analyzed to determine the mode of formation of a deposit

cenozoic deep sea benthic foraminifers tracers for changes in oceanic productivity from late middle eocene through earliest oligocene high latitude regions cooled and by the end of the period continental ice sheets existed in antarctica diversity of planktonic microorganisms declined and modern groups of terrestrial vertebrates originated coeval faunal changes in deep sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation cooling however occurred globally whereas species richness declined at high latitudes and not in the tropics the late eocene and younger lower diversity high latitude faunas typically contain common epistominella exigua and alabaminella weddellensis opportunistic phytodetritus exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor we speculate that the species richness gradient and increase in abundance of phytodetritus exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply especially at high latitudes

geochronological and mineralogical constraints on mineralization of the hetai goldfield in guangdong province south china abstract the hetai goldfield located in the southern segment of the qinzhou bay hangzhou bay juncture orogenic belt qhjb is the largest concentration of gold deposits in guangdong province south china the gold mineralization is hosted within the late neoproterozoic to early paleozoic yunkai group and strictly confined to mylonite ductile shear zones the nature of the structural control of mineralization in particular the role of ductile versus brittle deformation and their ages which remain unclear despite numerous previous studies are examined in this paper through an integrated study of geochronology and mineralogy lamellar and filament structures shown by pyrite and pyrrhotite in the ores suggest that sulfidation took place during ductile deformation and syntectonic metamorphism but the majority of the ores are associated with brittle deformation features in combination with macroscopic and microscopy observations on shear fabrics la icp ms u pb dating on zircons of hydrothermal origin from mylonites suggests that the hetai goldfield was subjected to two shearing events an early sinistral ductile shearing at ca 240 ma and a late dextral ductile brittle shearing at ca 204 ma indosinian these ages are ca 90 30 ma older than the previously published gold mineralizing ages of ca 175 152 ma yanshanian suggesting that the main gold mineralization and related brittle deformation significantly postdate the ductile deformation this inference is supported by the mineralization temperatures estimated from geothermometers of arsenopyrite ca 350 290 c chlorite ca 260 230 c and sphalerite ca 230 170 c intergrown with native gold which are considerably lower than that for the ductile deformation 500 300 c or higher based on these data we propose that the gold mineralization in the hetai goldfield predominantly occurred during the yanshanian event and only minor gold mineralization and associated sulfidation took place during the earlier indosinian ductile deformation

the mid pleistocene climate transition a deep sea carbon isotopic perspective five 13c records from the deep ocean extending back to 1 3 ma were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41 to 100 ka climate transition these data show that significant perturbations in mean ocean carbon chemistry were associated with the mid pleistocene climate transition notable features of the last 1 3 myr are 1 a pronounced 0 3 decrease in mean ocean 13c between 0 9 and 1 0 myr followed by a return to pre 1 0 ma values by 400 ka b p which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean possibly associated with an increase in global aridity and decrease in the size of the biosphere across the 41 to 100 ka transition 2 no change in the atlantic pacific a p 13c gradient over the last 1 3 myr suggesting no change in mean ocean nutrient content accompanied the addition of light carbon and 3 stronger vertical nutrient fractionation in the north atlantic in the middle pleistocene between sites 607 and 552 suggesting weaker north atlantic deep water formation at this time relative to the early and late pleistocene we also find evidence for a more pronounced deep recirculation gyre in the western north atlantic basin in the early brunhes as evidenced by aging of deep northern basin water site 607 relative to deep water in the equatorial atlantic site 664

benthic foraminifera and the late quaternary last 150 ka paleoceanographic and sedimentary history of the bounty trough east of new zealand abstract the bounty trough east of new zealand lies along the southeastern edge of the present day subtropical front stf and is a major conduit via the bounty channel for terrigenous sediment supply from the uplifted southern alps to the abyssal bounty fan census data on 65 benthic foraminiferal faunas 63 m from upper bathyal odp 1119 lower bathyal dsdp 594 and abyssal odp 1122 sequences test and refine existing models for the paleoceanographic and sedimentary history of the trough through the last 150 ka marine isotope stages mis 6 1 cluster analysis allows recognition of six species groups whose distribution patterns coincide with bathymetry the climate cycles and displaced turbidite beds detrended canonical correspondence analysis and comparisons with modern faunal patterns suggest that the groups are most strongly influenced by food supply organic carbon flux and to a lesser extent by bottom water oxygen and factors relating to sediment type major faunal changes at upper bathyal depths 1119 probably resulted from cycles of counter intuitive seaward landward migrations of the southland front sf north south sector of the stf benthic foraminiferal changes suggest that lower nutrient cool subantarctic surface water saw was overhead in warm intervals and higher nutrient bearing warm neritic subtropical surface water stw was overhead in cold intervals at lower bathyal depths 594 foraminiferal changes indicate increased glacial productivity and lowered bottom oxygen attributed to increased upwelling and inflow of cold nutrient rich antarctic intermediate water aaiw and shallowing of the oxygen minimum zone upper circum polar deep water cpdw the observed cyclical benthic foraminiferal changes are not a result of associations migrating up and down the slope as glacial faunas dominated by globocassidulina canalisuturata and eilohedra levicula at upper and lower bathyal depths respectively are markedly different from those currently living in the bounty trough on the abyssal bounty fan 1122 faunal changes correlate most strongly with grain size and are attributed to varying amounts of mixing of displaced and in situ faunas most of the displaced foraminifera in turbiditic sand beds are sourced from mid outer shelf depths at the head of the bounty channel turbidity currents were more prevalent during but not restricted to glacial intervals

glacial interglacial variations in quaternary production of marine organic matter at dsdp site 594 chatham rise southeastern new zealand margin abstract caco3 and total organic carbon concentrations organic matter c n and carbon isotope ratios and sediment accumulation rates in late quaternary sediments from dsdp site 594 provide information about glacial interglacial variations in the delivery of organic matter to the chatham rise offshore of southeastern new zealand low c n ratios and nearly constant organic 13c values of 23 indicate that marine production dominates organic matter supply in both glacial and interglacial times during oxygen isotope stages 1 through 6 0 140 ka and 17 through 19 660 790 ka increased organic carbon mass accumulation rates in isotope stages 2 4 6 and 18 record enhanced marine productivity during glacial maxima excursions of organic 13c values to ca 29 in portions of isotope stage 2 suggest that the local concentration of dissolved co2 was occasionally elevated during the last glacial maximum probably as a result of short periods of lowered sea surface temperature dilution of carbonates by clastic continental sediment generally increases at this location during glacial maxima but enhanced delivery of land derived organic matter does not accompany the increased accumulation of clastic sediments

grain scale variations in trace element composition of fluid altered zircon acasta gneiss complex northwestern canada sem back scattered electron images of zircon separates from a 2 9 ga granitic dyke from the acasta gneiss complex slave province reveal primary igneous oscillatory zoning which is transgressively overprinted by irregular alteration domains electron microprobe analyses show that altered zircon domains are depleted in zr and si relative to unaltered zircon while retaining a constant zr si ratio sims trace element analyses indicate that lree are preferentially enriched in the altered domains altered zircon contains elevated concentrations of ba up to 580 ppm ca up to 2 weight of the element and common pb 50 ppb the presence of lree ca ba and common pb in the zircons is interpreted to be the result of secondary alteration by an aqueous fluid and not by primary incorporation during crystallization we propose that the alteration related elements are located in amorphous zircon domains

auriferous mineralization in some shear zones a three stage model of metallogenesis studies of numerous shear zones hosting auriferous quartz veins suggest a three stage model of formation for such veins these stages are indicative of the progressive increase of the gold concentration with the evolution of the shear zone and comprise an early stage with invisible gold an intermediate stage with finegrained gold and a late stage with gold nuggets the early stage consisting of two consecutive episodes comprises the development of the shear zone sensu stricto which results in the formation of a structure characterized by mylonite this structure subsequently acts as a drain for hydrothermal fluids under the combined action of deformation and hydrothermal circulation the rocks in this structure undergo mineralogical transformations that depend on the initial composition of the rock these phenomena occur with increasing intensity towards the cores of the structures the sites of substantial silicification and sulfidation gold is first fixed in the crystal lattice of pyrrhotite up to 30 ppm of gold disseminated throughout the structure as a whole in the core it is destabilized to pyrite marcasite during the second episode of this early stage and the gold thus freed is trapped in the lattice of locally abundant ferriferous sulfides pyrite arsenopyrite up to 1 6 wt gold and berthierite at the intermediate stage again consisting of two consecutive episodes the shear zone can generate openings allowing the emplacement of lenses and veins of milky white quartz when these various veins are in turn crushed by continuing tectonic activity microsaccharoidal quartz forms by cataclasis and acts as a receptacle for the gold mineralization therefore textbook auriferous quartz veins are only one particular aspect of this stage characterized by the appearance of visible native gold caused by destabilization of the auriferous sulfides of the early stage this gold is generally very fine grained several micrometres and relatively silverfree the late stage i e the fifth episode in a brittle domain can occur within a structure of the early or intermediate stage it corresponds to a stage of opening during which stockworks of quartz or of quartz and carbonate form causing in situ remobilization of the auriferous mineralization from the earlier stages this phenomenon is accompanied by the appearance of gold nuggets several millimetres in size very often rich in silver electrum

setting new constrains on the age of crustal scale extensional shear zone vivero fault implications for the evolution of variscan orogeny in the iberian massif the vivero fault is crustal scale extensional shear zone parallel to the variscan orogen in the iberian massif belt with an associated dip slip movement toward the hinterland to constrain the timing of the extension accommodated by this structure we performed zircon u pb la icp ms geochronology in several deformed plutons some of them emplaced syntectonically the different crystallization ages obtained indicate that the fault was active at least between 303 2 and 287 3 ma implying a minimum tectonic activity of 16 5 ma along the fault the onset of the faulting is established to have occurred later than 314 2 ma the geochronological data confirm that the vivero fault postdates the main variscan deformation events in the nw of the iberian massif and that the extension direction of the late carboniferous early permian crustal scale extensional shear zones along the ibero armorican arc was consistently perpendicular to the general arcuate trend of the belt in sw europe

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

pliocene paleoceanography circulation and oceanographic changes associated with the 2 4 ma glacial event high resolution 18o records from the equatorial pacific site 503b equatorial atlantic site 665a and north atlantic site 606a based on the benthic foraminifera cibicidoides wuellerstorfi show the 2 4 ma onset of major northern hemispheric glaciation to be a package of three events occurring at 2 39 2 35 and 2 31 ma in which a periodicity of about 40 kyr is evident the amplitude of the signals at the three sites indicates that these events were 1 2 to 2 3 the size of the latest quaternary glaciation and also indicates cooling of northern source bottom water by 2 7 4 1 c relative to southern source water during glaciations carbon isotopes indicate that southern source waters were less oxygenated than in the quaternary and that there was reduced production of northern source water during glacial intervals the dominant presence of southern source water in the eastern basin of the equatorial atlantic regardless of climatic cycles throughout the late pliocene indicates a greater influence of these waters relative to northern source waters in the late pliocene ocean

a benthic foraminiferal proxy of pulsed organic matter paleofluxes in the temperate open ocean of the modern northeast atlantic the spring bloom of phytoplankton leads to a seasonal pulse of detrital organic material phytodetritus to the ocean floor opportunistic benthic foraminifera rapidly colonise this food resource producing large numbers of individuals whose tests are ultimately added to the sediment one of these taxa epistominella exigua shows periodic peaks in abundance in the fossil record at many open ocean sites previously such peaks have been commonly interpreted to result from changes in physicochemical properties of bottom water mass and thus deep sea circulation the main purpose of this paper is to propose thate exigua may be used as a proxy of pulsed organic matter inputs to the deep ocean and therefore as an indicator of relative changes in productivity

past hydrographic and climatic changes in the subantarctic zone of the south atlantic the pleistocene record from odp site 1090 abstract pleistocene summer sea surface temperatures ssst have been reconstructed on a composite core section recovered in the subantarctic zone of the southern ocean from planktonic foraminifers applying the modern analog technique the composite consists of core ps2489 2 and the sections recovered at odp site 1090 and documents the last 1 83 ma three distinct climatic periods can be identified that mirror the pleistocene development of the southern ocean hydrography cold climatic conditions prevailed at 43 s during glacial as well as during interglacial periods during the early pleistocene 1 83 0 87 ma indicating a northward shift of isotherms that characterize the present day polar front zone by about 7 of latitude evidence shows a strong linkage between southern ocean and low latitude climate during that interval time between the mid pleistocene revolution ca 0 9 ma and the mid brunhes event ca 0 4 ma we observe higher amplitude fluctuations in the ssst between glacial and interglacial periods corresponding to the temperature range between the present polar front and subantarctic front these climatic variations have been related to changes in the northern hemisphere ice sheets the past 0 4 ma are characterized by strong ssst variations of up to 8 c between glacials and interglacials only during the climatic optima stages 11 3 9 3 7 5 7 1 5 5 and the early holocene ssst exceeded present ssst at the core locality 10 2 c although the carbonate dissolution record exhibits high variability during the pleistocene it can be shown that ssst estimates were not significantly biased the mid brunhes dissolution cycle as well as the mid pleistocene enhanced carbonate preservation appear to belong to a global long term variability in carbonate preservation

the sedimentary regime beneath the deep western boundary current inflow to the southwest pacific ocean abstract a review of hydrographic sections single channel seismic profiles bottom photographs and nephelometer profiles collected by the u s n s eltanin plus new seismic and sedimentary data from the r v rapuhia provide an insight into the sedimentary regime beneath the pacific deep western boundary current dwbc where it enters the sw pacific off southernmost new zealand at macquarie ridge and campbell plateau there the dwbc is reinforced by the antarctic circumpolar current acc largely through the generation of deep reaching eddies formed by interaction of the acc with the pronounced bathymetry it is therefore a region of high eddy kinetic energy which induces widespread abyssal erosion it is also where the dwbc receives its first major injection of terrigenous se iment which is transferred from southern new zealand along the 450 km long solander channel from macquarie ridge the acc dwbc travels northeast onto the subantarctic slope of campbell plateau this high steep western boundary intensifies the flow causing erosion along the slope base east of the scour the 800 km long campbell drift has been deposited this drift extends to 51 s where the acc swings east to continue its circum antarctic journey while the dwbc continues northeast to bounty trough where the combination of abundant sediment supplied by bounty channel a subdued western boundary and a less energetic dwbc have allowed the bounty fan to form directly across the current path apart from localized winnowing near zones of high relief evidence for widespread dwbc in luence on the fan is inconclusive however current effects become more apparent north of bounty fan where the steep western boundary resumes in the form of chatham rise eroded fan sediments have contributed to a series of small drifts at 4400 5000 m depth whereas at 2400 3400 m depth on the flank of chatham rise the dwbc has molded a sinuous terrace like drift viewed regionally sedimentation beneath the boundary current south of chatham rise contrasts strongly with the regime to the north the southern current is energetic and terrigenous supply is intermittent being restricted to glacial lowstands consequently erosion is common and drifts are few and are themselves subject to erosion by comparison the current north of the rise is generally slower and has a more consistent terrigenous supply particularly near hikurangi channel which has been active irrespective of sea level thus widespread drift deposition is favored

glacial to interglacial changes in non carbonate and carbonate accumulation in the sw pacific ocean new zealand abstract fluxes of carbonate and non carbonate terrigenous biogenic siliceous sediment back to a maximum of marine isotope stage mis 6 were determined for 54 cores from off eastern new zealand mass accumulation rates mars were derived using dry bulk densities measured directly from fresh cores or in the case of dry archived samples on estimates from a density carbonate relationship mars exhibit wide spatial and temporal variability in response to i the location of cores relative to the terrigenous source of new zealand current pathways and local oceanographic features and ii palaeoclimatic change for mis 1 2 non carbonate accumulated at a high rate between 27 and 18 ka calendar years due to an influx of waterborne and aeolian terrigenous detritus together with localised production of biogenic silica under a northward intrusion of subantarctic waters and an increase in wind induced upwelling by 18 12 ka non carbonate mars reduced as winds ameliorated and sea level rose to confine some of the terrigenous load to the continental shelf the holocene transgression was accompanied by warmer sea surface temperatures the formation of coastal and lacustrine sediment traps and more widespread terrestrial vegetation these conditions further reduced the deep oceanic non carbonate flux to levels about half those of glacial periods in contrast carbonate mars were lower in cold periods reflecting lower productivity increased dissolution and in the case of the generally productive waters of chatham rise to redistribution by bottom currents however off central new zealand carbonate production was higher on the continental margin possibly because of enhanced upwelling under the strong wind regime of mis 2 such localised effects produced glacial carbonate mars higher than interglacial mis 1 values for the rest of the region carbonate fluxes increased to an early to middle mis 1 maximum before generally declining in recent times

zircon u pb and muscovite 40ar 39ar geochronology of the gold bearing tianger mylonitized granite xinjiang northwest china implications for radiometric dating of mylonitized magmatic rocks abstract this study focuses on zircon u pb and muscovite 40ar 39ar geochronology of gold bearing mylonitized granite in the north tianshan of china all zircon samples have euhedral hydrothermal rims which have replaced their igneous mantles igneous zircon mantles with narrow hydrothermal rims in sample ts06 give a weighted average u pb age of 403 7 5 6 ma 1 standard error mswd 1 5 n 18 zircons in ts277 show a complex texture with core detrital origin 1276 2215 ma indicating igneous mantle and a hydrothermal rim the igneous mantles give a weighted average u pb age of 443 4 3 3 ma mswd 3 1 n 10 two younger ages 394 and 400 ma have been obtained on hydrothermal rims the mantles plus rims of all zircons have positive ehf t values with an average of 3 99 0 86 mswd 2 8 n 23 the positive ehf t values suggest that the granite magma is derived from melting of juvenile crustal rocks the shearing deformation post dated granite intrusion and introduced fluid which replaced igneous zircons via dissolution and reprecipitation however the age data for zircon hydrothermal rims do not represent the time of the dissolution re precipitation the zircons crystallized in granite in the early silurian 443 ma have been replaced on their rims during middle triassic deformation 248 238 ma which was followed by brittle deformation accompanied by gold deposition at 220 ma based on 40ar 39ar dating of muscovite

the rožna uranium deposit bohemian massif czech republic shear zone hosted late variscan and post variscan hydrothermal mineralization three major mineralization events are recorded at the ro na uranium deposit total mine production of 23 000 t u average grade of 0 24 u 1 pre uranium quartz sulfide and carbonate sulfide mineralization 2 uranium and 3 post uranium quartz carbonate sulfide mineralization 1 k ar ages for white mica from wall rock alteration of the pre uranium mineralization style range from 304 5 5 8 to 307 6 6 0 ma coinciding with the post orogenic exhumation of the moldanubian orogenic root and retrograde metamorphic equilibration of the high grade metamorphic host rocks the fluid inclusion record consists of low salinity aqueous inclusions together with h2o co2 ch4 co2 ch4 and pure ch4 inclusions the fluid inclusion paragenetic and isotope data suggest that the pre uranium mineralization formed from a reduced low salinity aqueous fluid at temperatures close to 300 c 2 the uraniferous hydrothermal event is subdivided into the pre ore ore and post ore substages k ar ages of pre ore authigenic k feldspar range from 296 3 7 5 to 281 0 5 4 ma and coincide with the transcurrent reorganization of crustal blocks of the bohemian massif and with late stephanian to early permian rifting massive hematitization albitization and desilicification of the pre ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the moldanubian domain the wide range of salinities of fluid inclusions is interpreted as a result of the large scale mixing of basinal brines with meteoric water the cationic composition of these fluids indicates extensive interaction with crystalline rocks chlorite thermometry yielded temperatures of 260 c to 310 c during this substage uranium was probably leached from the moldanubian crystalline rocks the hydrothermal alteration of the ore substage followed or partly overlapped in time the pre ore substage alteration k ar ages of illite from ore substage alteration range from 277 2 5 5 to 264 0 4 3 ma and roughly correspond with the results of chemical u pb dating of authigenic monazite 268 50 ma the uranium ore deposition was accompanied by large scale decomposition of biotite and pre ore chlorite to fe rich illite and iron hydrooxides therefore it is proposed that the deposition of uranium ore was mostly in response to the reduction of the ore bearing fluid by interaction with ferrous iron bearing silicates biotite and pre ore chlorite the th data on primary mostly aqueous inclusions trapped in carbonates of the ore substage range between 152 c and 174 c and total salinity ranges over a relatively wide interval of 3 1 to 23 1 wt nacl eq gradual reduction of the fluid system during the post ore substage is manifested by the appearance of a new generation of authigenic chlorite and pyrite chlorite thermometry yielded temperatures of 150 c to 170 c solid bitumens that post date uranium mineralization indicate radiolytic polymerization of gaseous and liquid hydrocarbons and their derivatives the origin of the organic compounds can be related to the diagenetic and catagenetic transformation of organic matter in upper stephanian and permian sediments 3 k ar ages on illite from post uranium quartz carbonate sulfide mineralization range from 233 7 4 7 to 227 5 4 6 ma and are consistent with the early tethys central atlantic rifting and tectonic reactivation of the variscan structures of the bohemian massif a minor part of the late variscan uranium mineralization was remobilized during this hydrothermal event

sphalerite geobarometry in the cu fe zn s system phase relations have been determined among sphalerite pyrite pyrrhotite and intermediate solid solution iss from 439 degrees to 725 degrees c at 1 bar and 353 degrees to 760 degrees c at 5 kb the extents of solid solution in the four phase assemblage are described as functions of temperature in kelvins by the following equations log mole zns in iss 1 bar 2 795 1 632 t super 1 log mole zns in iss 5 kb 2 659 1 608 t super 1 log mole cus in pyrrhotite 1 bar 2 546 1 866 t super 1 log mole cus in sphalerite 1 bar 4 202 3 755 t super 1 and log mole cus in sphalerite 5 kb 4 084 3 791 t super 1 the pressure dependence in kb of the composition of sphalerite in equilibrium with pyrite and pyrrhotite with or without iss can be expressed for the temperature independent portion of the sphalerite geobarometer as p 42 30 32 10 log mole fes because of the low solubility of copper in sphalerite in the four phase assemblage below 650 degrees c the presence of chalcopyrite in natural ores should be of no consequence to sphalerite geobarometry over its temperature independent portion nevertheless sphalerites which are inhomogeneous in fes and which contain abundant blebs of chalcopyrite in excess of the amount that can be reasonably accounted for by an equilibrium process of solubility and subsequent exsolution are a common feature of many sulfide ores such sphalerite grains should be avoided in applying the geobarometer the chalcopyrite blebs may be a product of a premetamorphic sphalerite chalcopyrite intergrowth or represent true exsolution from sphalerite in any one of 1 a former sphalerite pyrrhotite iss equilibrium 2 a stable four phase assemblage at temperatures above the temperature independent portion of the geobarometer or 3 a metastable four phase assemblage in which pyrite was inert use of the sphalerite geobarometer requires a thorough understanding of the textural relationships and discrimination of equilibrium from disequilibrium or low temperature reequilibrated assemblages

near synchroneity of new zealand alpine glaciations and northern hemisphere continental glaciations during the past 750 kyr the brunhes magnetochron 0 730 kyr at deep sea drilling project site 594 off eastern south island new zealand comprises up to 100 m of alternating units of pelagic and hemipelagic ooze formed during interglacial and glacial periods respectively the youngest hemipelagic interval corresponds to glacial isotope stage 2 and can be correlated with extensive glacial and glacio fluvial deposits of the late last glaciation 27 13 kyr bp on south island inferring the same genetic link for the other hemipelagic sediment units down core we show here that as many as 12 major episodes of expanded alpine glaciation have occurred on south island in the past 730 kyr each of these glacial episodes coincided with a period of significant 18o enrichment 2 in the core resulting from changes in ocean isotope composition associated with major growth phases of the northern hemisphere ice sheets the inferred history of alpine glaciations on this remote south pacific island appears to be closely phase locked 3 kyr to world wide climate changes

u pb dating of hydrothermal zircon from the dongping gold deposit in north china constraints on the mineralization processes abstract the dongping gold deposit is a large deposit with total gold reserves of 100 tons it is located at the northern margin of the north china craton northwestern hebei province china the ore bodies are hosted by the devonian shuiquangou syenite complex and consist mainly of auriferous quartz veins and disseminated ore in the altered and silicified syenite u pb dating of zircon from hornblende syenite on the western margin of the complex yields a crystallization age of 400 3 5 ma mswd 0 018 morphology cathodoluminescence imaging and geochemical classifications of zircon from the first stage of disseminated ore and gray auriferous quartz veins and from later stage low grade quartz veins point to their newly crystallized hydrothermal origin the hydrothermal zircon from the disseminated ore and auriferous gray quartz vein are dated at 389 1 0 ma and 385 5 7 ma respectively which are detectably younger than but close to the crystallization age of the syenite complex and might have been formed by post magmatic hydrothermal processes both types of ore are dominant in the ore deposit and we propose that the pervasive post magmatic hydrothermal alteration is the main ore forming stage hydrothermal zircon from a low grade auriferous quartz vein yields a u pb age of 140 ma interpreted as forming during a younger period of superimposed yanshanian hydrothermal mineralization thus the ore of the dongping gold mine represents a post magmatic devonian hydrothermal ore deposit with jurassic cretaceous hydrothermal overprinting

ages of ultrahigh pressure metamorphism and protolith orthogneisses from the eastern dabie shan u pb zircon geochronology the dabie shan contains two rare geologic features one the occurrence of ultra high pressure metamorphic rocks peak p 2 7 gpa uhp in the east central part of this belt and two some of these uhp rocks are characterized by anomalously 18o depleted oxygen isotopic compositions geochronological data are presented that constrain the age of the uhp metamorphism the ages of protoliths and potentially the age of hydrothermal alteration believed to be responsible for the anomalous oxygen isotopic compositions the age of uhp metamorphism in the eastern dabie shan is dated at 218 5 1 7 ma using u pb in zircon separated from host gneisses this age is identical within uncertainty with a less precise age using u pb in zircon separated from uhp eclogite 225 5 3 6 ma and with previously published ages from uhp eclogites of the dabie shan map relationships strongly support an in situ as opposed to exotic orgin of the uhp eclogites in this region the identical ages of uhp metamorphism in the gneisses and eclogites provides additional support for this interpretation the age of the protolith gneisses is dated as 772 5 9 5 ma based on the upper intercept of the zircons which accords well with other dates of granitic gneisses in the qinling belt the association of mafic and felsic magmatism is interpreted to reflect rifting along the northern margin of the yangtze block at this time these upper intercept ages may date the hydrothermal circulation of 18o depleted meteoric water which gave rise to the anomalously 18o depleted uhp protoliths of the dabie shan and sulu region the coincidence of these protolith ages with the early sinian glaciation of south china is consonant with the suggestion that the highly anomalous oxygen isotopic compositions in this region date from this time the upper intercept age of the eclogite is imprecisely determined at 447 82 79 ma but is younger than the host gneisses and is not characterized by anomalous oxygen isotopic compositions

planktic foraminiferal and sea surface temperature record during the last 1 myr across the subtropical front southwest pacific planktic foraminiferal faunas and modern analogue technique estimates of sea surface temperature sst for the last 1 million years myr are compared between core sites to the north odp 1125 178 faunas and south dsdp 594 374 faunas of the present location of the subtropical front stf east of new zealand faunas beneath cool subtropical water stw north of the stf are dominated by dextral neogloboquadrina pachyderma globorotalia inflata and globigerina bulloides whereas faunas to the south are strongly dominated by sinistral n pachyderma 80 95 in glacials with increased g bulloides 20 50 and dextral n pachyderma 15 50 in interglacials beneath subantarctic water or saw canonical correspondence analysis indicates that at both sites sst and related factors were the most important environmental influences on faunal composition greater climate related faunal fluctuations occur in the south significant faunal changes occur through time at both sites particularly towards the end of the mid pleistocene climate transition mis18 15 e g decline of globorotalia crassula in stw disappearance of globorotalia puncticulata in saw and during mis8 5 interglacial sst estimates in the north are similar to the present day throughout the last 1 myr to the south interglacial ssts are more variable with peaks 4 7 c cooler than present through much of the early and middle pleistocene but in mis11 mis5 5 and early mis1 peaks are estimated to have been 2 4 c warmer than present these high temperatures are attributed to southward spread of the stf across the submarine chatham rise along which the stf appears to have been dynamically positioned throughout most of the last 1 myr for much of the last 1 myr glacial sst estimates in the north were only 1 2 c cooler than the present interglacial except in mis16 mis8 mis6 and mis4 2 when estimates are 4 7 c cooler these cooler temperatures are attributed to jetting of saw through the mernoo saddle across the chatham rise and or waning of the stw current to the south glacial sst estimates were consistently 10 11 c cooler than present similar to temperatures and faunas currently found in the vicinity of the polar front one interpretation is that these cold temperatures reflect thermocline changes and increased circumpolar surface water spinning off the subantarctic front as an enhanced bounty gyre along the south side of the chatham rise for most of the last 1 myr the temperature gradient across the stf has been considerably greater than the present 4 c during glacial episodes the stf in this region did not migrate northwards but instead there was an intensification of the temperature gradient across it interglacials 4 11 c glacials 8 14 c

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression