formal definition and dating of the gssp global stratotype section and point for the base of the holocene using the greenland ngrip ice core and selected auxiliary records the greenland ice core from northgrip ngrip contains a proxy climate record across the pleistocene holocene boundary of unprecedented clarity and resolution analysis of an array of physical and chemical parameters within the ice enables the base of the holocene as reflected in the first signs of climatic warming at the end of the younger dryas greenland stadial 1 cold phase to be located with a high degree of precision this climatic event is most clearly reflected in an abrupt shift in deuterium excess values accompanied by more gradual changes in d 18 o dust concentration a range of chemical species and annual layer thickness a timescale based on multi parameter annual layer counting provides an age of 11 700 calendar yr b2 k before ad 2000 for the base of the holocene with a maximum counting error of 99 yr a proposal that an archived core from this unique sequence should constitute the global stratotype section and point gssp for the base of the holocene series epoch quaternary system period has been ratified by the international union of geological sciences five auxiliary stratotypes for the pleistocene holocene boundary have also been recognised copyright 2008 john wiley sons ltd

zircon xenocrysts from the kambalda volcanics age constraints and direct evidence for older continental crust below the kambalda norseman greenstones abstract the hangingwall basalt at kambalda western australia contains zircons that have been shown by ion microprobe analyses to have very high u and th contents and a wide variety of crystallization ages nearly all of these zircons certainly are xenocrysts a few might relate to intrusive veinlets the age of the youngest xenocrysts 2693 50ma 2 shows that the eruptive age of the basalt cannot exceed 2743 ma this confirms that the apparent sm nd isochron giving 3200 ma 1 2 for kambalda mafic and ultramafic rocks is a mixing line 2 between unrelated components enriched and depleted in light rare earth elements mixing probably occurred at depth by erosion of 3200 3500 ma old felsic crust from the walls of the hwb conduits the zircon xenocryst ages are the first direct evidence for the presence of very old felsic crust in the eastern yilgarn block the latter implies that the kalgoorlie norseman greenstone sequences were formed in a continental rather than an oceanic environment

a new geochemical technique for gold exploration alkali element mobility associated with gold mineralization in the west australian goldfields this study tests the hypothesis that alkali element mobility can be used as a tool to monitor fluid flow associated with gold bearing hydrothermal systems and as a geochemical vector for locating new gold deposits this was achieved by analyzing 114 samples of two mafic rock types from four localities in the archean yilgarn craton of western australia the giant golden mile deposit at kalgoorlie the smaller victory mine at kambalda two drill holes that intersected subeconomic mineralization 8 km south of kalgoorlie and two drill holes well away from gold mineralization the results show that cs rb and ba are enriched in areas that are prospective for gold bearing mineralization and depleted in areas that are not the primitive mantle normalized ratio cs rb th n is used as an alteration index to quantify and discriminate potentially mineralized with cs rb th n 5 from unmineralized areas with cs rb th n n 5 that is 10 to 100 times larger than the visible alteration halo the alkali enrichment halos around the smaller victory deposit and subeconomic mineralization south of kalgoorlie are narrower with lower cs rb th n but are still over 10 times larger than the visible alteration halos adjacent to veins these zones of high cs rb th n around the mineralization show that the hydrothermal fluids penetrated tens of meters and in the case of the golden mile hundreds of meters into the wall rocks within this zone cs rb th n increases toward ore and provides a vector to mineralization

neoarchean orogenic magmatic and hydrothermal events in the kalgoorlie kambalda area western australia constraints on gold mineralization in the boulder lefroy golden mile fault system the boulder lefroy golden mile blf gmf fault system is the most intensely mineralized structure 2150 t au to 2015 in the archean yilgarn craton western australia the fault system links the kalgoorlie and kambalda mining districts in the eastern goldfields province a continental margin orogen subdivided into the western kalgoorlie ensialic rift and the eastern kurnalpi volcanic arc after rifting the 2 73 2 66 ga greenstone greywacke succession in the kalgoorlie kambalda area underwent five phases of orogenic deformation predominantly during ene wsw shortening d1 upright folding at ca 2680 ma d2 sinistral strike slip faulting at 2678 2663 ma d3 folding of late conglomerate turbidite successions at 2665 2655 ma d4 dextral strike slip faulting at 2655 2640 ma and d5 east northeast striking normal faulting regional prehnite pumpellyite to greenschist facies burial metamorphism took place during d1 and d3 crustal thickening and amphibolite facies aureoles formed around granite batholiths during and after d3 at 400 100 mpa pressure the d2 blf offsets d1 folds by 12 km sw side south and contains a porphyry dyke 2676 7 ma boudinaged by transtensional oblique slip along a line pitching 21 southeast the blf is linked by transverse d2 thrusts to other sinistral faults recording strike slip until 2663 7 ma late d2 strike slip movement alternated with early d3 shortening d3 thrusts accommodated strain in fault blocks of rigid mafic ultramafic volcanic rocks consolidated during d1 while the sedimentary rocks in d3 synclines were foliated at high strain biotite sericite alteration and gold pyrite mineralization in the blf gmf system took place at 11 4 km burial depth in faults active during d2 and d3 the golden mile 1708 t au and other deposits are associated with stocks and dykes of high mg monzodiorite tonalite porphyry part of a late orogenic 2665 2645 ma mantle derived suite of adakitic affinity hornblende and apatite compositions indicate that these intrusions are characterized by high water contents 5 6 wt h2o in melt by high oxidation states nno 1 0 to 2 4 log units and by igneous anhydrite some stocks contain pervasive anhydrite pyrite mineralization of low gold grade 0 4 g t biotite sericite pyrite ore bodies such as those at kanowna belle 140 t au also replace faulted metamorphic rocks above batholith domes cored by plutons of the monzodiorite suite the d4 strike slip faults are barren at kambalda but control gold quartz vein ore at kalgoorlie 2651 9 ma and au ag breccia ore at black flag 2648 6 ma

sm nd age of kambalda and kanowna greenstones and heterogeneity in the archaean mantle a precise sm nd age of 2 790 30 myr and an initial ratio corresponding to nd 3 4 0 6 has been determined for the kambalda sequence from the eastern yilgarn block of western australia the high initial 143nd 144nd implies a long lived light rare earth element depleted high sm nd source for the kambalda volcanics and therefore provides definitive evidence for ancient heterogeneities in the archaean mantle

geochemistry of komatiites from kambalda western australia i chalcophile element depletion a consequence of sulfide liquid separation from komatiitic magmas the type examples of archean volcanic peridotite associated ni sulfide deposits occur at or toward the base of the ultramafic lava pile at kambalda western australia spinilex textured komatiites considered to represent silicate liquids derived from the original magma are significantly depleted in chalcophile elements throughout the entire ultramafic sequence relative to unmineralized and poorly mineralized komatiites elsewhere and to a theoretically modeled sulfide undersaturated komatiite system this depletion is not attributed to postformational modification of the komatiites by sea floor alteration or metamorphism although very low sulfur contents in the same rocks probably result from such processes the depletion is best interpreted as the result of scavenging of metals by sulfide liquid in equilibrium with the silicate magma implying that all the silicate magma now represented by the ultramafic sequence equilibrated with sulfide liquids at the magmatic stage these results provide convincing evidence against formation of the sulfide ores by in situ sulfide separation from the thick komatiitic peridotitc host the magnitude of the depletion in the spinilex textured komatiite divisions of the peridotitc hosts is much less than that expected for such an origin but for the entire sequence it is greater than that expected from metal partitioning relations and mass balance calculations for the volume and composition of the ultramafic sequence and the volume of associated sulfides this suggests that a proportion of the sulfide liquid that formed from the ultramafic magma s was lost from the magmatic system prior to extrusion such loss is a natural consequence of models for ascent and eruption of sulfur rich komatiitic magmas that involve prior concentration of sulfides plus olivine in high level magma chambers or separation and segregation of sulfide liquid during ascent from the upper mantle

dating the oldest terrestrial rocks fact and fiction abstract this paper is a review of well documented geochronological and related isotopic evidence for the age and total crustal residence time of the oldest known terrestrial rocks mainly using rb 1bsr sm 1bnd and u 1bpb decay schemes the oldest known stable sialic crust of true continental character predominantly composed of calc alkaline orthogneisses was produced during major mantle differentiation some 3 7 3 5 ga ago and is represented on several continents enclaves of older supracrustal rocks as well as a major remnant of a volcano sedimentary sequence of greenstone belt affinity dated at 3 8 ga are preserved within the surrounding gneisses in southern west greenland recent ionmicroprobe evidence for 4 1 ga old detrital zircon grains in a younger early archaean metasedimentary sequence in western australia is also discussed several cases are reviewed where claims for early archaean 3 4 ga dates are believed to be erroneous and to result from oversimplistic and incorrect interpretation of isotopic data some of the geological and geochemical mechanisms which have given rise to claims for spuriously old sm 1bnd u 1bpb and pb pb dates are critically discussed to supplement published data we present several new sets of whole rock sm 1bnd and pb pb isotopic data from west greenland labrador zimbabwe and eastern india relevant to the overall topic of this review

lodestone natures only permanent magnet what it is and how it gets charged magnetite and titanomagnetite exhibit magnetic properties which are attributable to the micro structures developed during oxidation and exsolution all magnetite iron ores which are lodestones contain maghemite these lodestones have hc between 10 and 30 mt sirm between 8 and 18 am kg and ri between 0 10 and 0 26 magnetite titanomagnetite and metals have rem values ratio of nrm to sirm 0 05 samples called fulgarites obtained from the smithsonian institution have rem values ranging from 0 45 to 0 92 the rem value serves as a witness parameter to the magnetic fields associated with the lightning bolt if a high rem value say 0 1 can be verified as not to be due to contamination by man and does not contain md hematite then the rock has lrm lightning remanent magnetization the magnetic field associated with lightning can be revealed from an isothermal remanent acquisition ra curve

revised sm nd systematics of kambalda greenstones western australia sm nd isotope systematics in mafic ultramafic lavas from the norseman wiluna greenstone belt western australia have been reinvestigated a previous age based on mixing lavas and granites is not confirmed instead a sm nd age of 3 262 44 myr is indicated for the lavas 400 myr older than intruding granites and predating gneisses that have been proposed as basement rocks

the effect of cooling rate on the intensity of thermoremanent magnetization trm acquired by assemblages of pseudo single domain multidomain and interacting single domain grains summary experiments designed to measure the absolute palaeointensity of the geomagnetic field generally do so by comparing the ancient thermoremanent magnetization trm retained by an igneous rock with a new trm imparted in the laboratory one problem with this procedure is that the relative magnitudes of the ancient and laboratory trms may be influenced not only by the external field intensities at the time the two coolings took place but also by the rate at which the coolings themselves occurred here we present new measurements of this cooling rate effect obtained from treatments in the laboratory differing in cooling rate by a factor of 200 synthetic samples containing sized ferrimagnetic grains were used in the experiments theoretical considerations and previous experiments have indicated the cooling rate effect to be dependent on domain state increases in trm magnitude of more than 7percent per order of magnitude decrease in cooling rate have been reported for assemblages of non interacting single domain sd grains here we focus on magnetite grains in the less well studied pseudo single domain psd and multidomain md states using a range of applied field intensities to impart the trms for the first time we also measure the cooling rate effect in grains of titanomagnetite that have been oxyexsolved so that they contain strongly interacting sd lamellae in all cases the cooling rate effect measured was in the same sense as alreadyobservedinidealmagneticallynon interactingsdgrainsbutwasconsiderablyweaker on average the effect did not exceed 3percent increase in trm per order of magnitude decrease in cooling rate and did not show any systematic dependence on appliedfield intensity insomesamples containing coarsergrains thecoolingrateeffectwasnotdistinguishablefrom zero the sense and magnitude of the cooling rate effect remain uncertain in truly md grains as different studies have produced discrepant results for the more practically relevant case of psd and interacting sd grains which commonly dominate the trm in igneous rocks however it appears that we can be more confident in our assertions the cooling rate effect in such materials is in the same sense as in non interacting sd grains but smaller a consequence of long range ordering in lavas and small intrusions containing these it is unlikely to exceed 10percent although a correction should always be attempted the results of palaeointensity studies based upon such samples will generally not be severely biased

magnetic petrology of eastern north america diabases i olivine normative dikes from western south carolina abstract the oxide mineralogy and magnetic properties were examined in a suite of fifteen olivine normative diabase dike samples from western south carolina in an attempt to elucidate their magnetic petrology titanomagnetite 1 2 vol is the dominant fe ti oxide mineral ilmenite and secondary magnetite are generally present in very minor amounts chromite constitutes up to 0 5 vol its abundance and composition correlate with bulk rock cr various types of fine scale microstructure are evident in titanomagnetite crystals the most important are patterned anisotropism and the development of trellis type ilmenite lamellae microprobe analyses indicate 1 titanomagnetite compositions x are mostly between 0 4 and 0 55 and 2 low analytical totals are characteristic of most titanomagnetites curie temperatures of the diabases are 500 540 c which are several hundred degrees higher than predicted from the observed titanomagnetite x s 150 300 c we attribute these higher curie temperatures to oxidation of the titanomagnetites which has produced titanomaghemites having visible microstructure and yielding low analyses because they are cation deficient natural remanence magnetization and rem ratio of natural remanence to saturation remanence vary between 4 and 100 10 4 a m2 kg 1 and 0 0019 and 0 032 respectively these properties inversely correlate with cr content and demonstrably contrast cr rich and cr poor samples initial susceptibility saturation magnetization and coercivity values show a two to three fold range variations in initial susceptibility and coercivities appear to be largely related to the type and extent of oxidation induced microstructure in the titanomagnetites

response of mid latitude north pacific surface temperatures to orbital forcing and linkage to the east asian summer monsoon and tropical ocean atmosphere interactions we present a palaeoceanographic perspective of the north pacific during the last two glacial cycles based on u derived palaeotemperature records of images core md01 2421 off the coast of central japan and cores from the ocean drilling program odp sites 1014 and 1016 off the coast of california the sea surface temperature sst differences between odp sites 1014 and 1016 sstnortheastern pacific nep sstodp1014 sstodp1016 indicate the intensity of the california current comparison of sstnep and the sst from core md01 2421 revealed anti phase variation high sstnep indicating weakening of the california current corresponded to low sst at the japan margin indicating the southward displacement of the north western pacific subarctic boundary and weakening of the kuroshio extension and vice versa this finding suggests that the intensity of the north pacific subtropical gyre circulation has varied in response to precessional forcing and that this response has been linked with changes in tropical ocean atmosphere interactions in the precessional cycle the sst variation derived from core md01 2421 lags ca 2 5 4 ka behind the variations shown by hulu and sanbao stalagmite 18o records and by the pollen temperature index from core md01 2421 suggesting out of phase variations of the north pacific subtropical gyre circulation and the east asian summer monsoon these findings indicate that the behaviour of interactions between tropical ocean atmosphere dynamics and the east asian summer monsoon may have varied in response to the precessional cycle copyright 2009 john wiley sons ltd

emplacement and metamorphism of archaean mafic volcanics at kambalda western australia geochemical and isotopic constraints abstract extensive exploration and mining at kambalda western australia has revealed a conformable mafic ultramafic succession consisting of a sulphide ore bearing ultramafic layer located between metabasalt units geochemical and rb sr u pb isotopic analyses have been carried out on two 70 140 m sections of drill core from the metabasalts and u pb isotopic analyses have been made on sulphide ore samples greenschist metamorphism of the metabasalts is dated at 2610 30 m y and was approximately isochemical except for addition of h 2 o and co 2 and a differential mobilization of k and rb within the units the addition of h 2 o and co 2 is believed to have taken place shortly after extrusion of the metabasalts in a submarine environment resulting in an early greenschist metamorphism the later 2600 m y event is correlated with a high thermal regime also detected at kalgoorlie 50 km to the north a pb pb isochron age of 2720 105 m y may represent the metamorphic event or the time of emplacement of the metabasalts new sm nd data c hauvel et al c laque l ong et al suggest the mafic volcanics are 3200 m y old if true large scale homogenization of pb isotopes is required alternatively the mafic sequence may be only slightly older than 2800 m y and the sm nd data does not have time significance

thermomechanical erosion of ore hosting embayments beneath komatiite lava channels textural evidence from kambalda western australia abstract archean komatiite hosted nickel deposits at kambalda western australia are located in embayments within channelized lava flows the origin of these embayments is controversial the currently favoured model invokes pre existing topographic features filled in by the komatiite and sulfide melt and subsequently modified by thermomechanical erosion new evidence from sulfide deposits on the eastern limb of the kambalda dome includes well preserved magmatic textural relationships of the sulfides with the surrounding rocks suggesting the entire embayment was formed by thermomechanical erosion these textures are particularly well preserved within the moran deposit of the long victor complex which lacks the younger intense structural deformation that other kambalda deposits have undergone the vestiges of an older broad concave embayment are represented by sediment sulfide textures present on the flanks up to 150 m away from the younger steep sided embayment sediment sulfide contacts are marked here by a globular silicate sulfide intergrowth interpreted as emulsion and cumulate like mono sulfide solid solution mss grains surrounded by interstitial silicate melt textures preserved from the formation of a steep sided embayment are frozen into the basalt sulfide contact and include an undulating contact with sulfide filled microfractures and a ferrichromite layer basalt sulfide breccia and interpreted crystallized silicate sulfide liquid emulsions and basalt plumes rising into the sulfides textures from the last step of embayment formation are found in the pinchouts i e where the massive sulfide ore is bounded top and bottom by basalt they include the same textures that were formed during the excavation of the steep sided embayment but they also feature interpreted basalt sulfide emulsions on the upper contact cm scale silicate sulfide ferrichromite layering on the upper contact and a vesicular basalt scum layer floating on the sulfides beneath the solid older basalt all these textures represent frozen examples of different stages during the excavation and formation of the embayment and reflect physical processes responsible for thermomechanical erosion the initial disposition and orientation of ore hosting channels was controlled by paleo topography probably defined by syn volcanic faults but the textures we describe show that within the channel the geometry of the entire embayment was the product of erosion the sulfide melt itself played a major role in the process owing to its high density high heat content and very low viscosity but the hydrated nature of the underlying altered basalt was also critical fluids were released from the basalt due to the high temperature in the 1 2 cm immediately beneath the sulfide melt with instant flash boiling creating a network of microfractures pre existing fracture networks and breccia in the basalt allowed the sulfide melt to locally infiltrate the substrate to a greater depth increasing the hydraulic head at the tip of the fracture thus accelerating the erosion process once a critical sulfide melt thickness is reached partly aided by a growing pile of matrix net textured sulfides the pressure difference on the embayment floor compared to the basalt at the bottom edges of the embayment becomes high enough to allow the liquid sulfides to melt sideways to form a pinchout

late pleistocene stratigraphy and palaeoceanographic implications in northern bering sea slope sediments evidence from the radiolarian speciescycladophora davisiana a high resolution abundance curve of the radiolarian species cycladophora davisiana was obtained from a late pleistocene sediment core pc 23a which was obtained from the northern slope of the bering sea the abundance pattern of this species was high during the glacial period and low during the holocene this general stratigraphic pattern was correlated with a previously reported pattern for the subarctic pacific ocean however planktonic foraminifera based accelerator mass spectrometry 14c dating revealed that a significant peak in the c davisiana curve during the glacial period correlates to 15 5 ka which is younger than that previously estimated as being the last glacial maximum the higher abundance of this species implies that there was well ventilated water with a large amount of organic matter in the intermediate water layer an unusually high propagation of c davisiana during the earliest holocene period bolling allerod b a and dansgaad oescheger interstadial event 12 was most likely related to a significant increase in the amount of organic matter released into the intermediate water depths by a brine pump system via ventilation in addition centennial scale variations in the abundance of c davisiana during the b a period suggest that the intermediate water ventilation was sensitively affected by brine rejection during sea ice formation as well as large scale atmospheric circulations such as the arctic oscillation copyright 2009 john wiley sons ltd

the rock magnetic signal of climate change in the maar lake sequence of lac st front france summary rock magnetic properties of the maar lake sediments of lac st front massif central france reflect environmental changes during the last climatic cycle high magnetic concentrations are measured in the sediments deposited under glacial climatic conditions while lower concentrations correspond with more temperate climatic periods low and high temperature measurements indicate that the remanence is carried by titanium poor magnetite however some maghemite and haematite is present in sediments deposited under temperate conditions normalized intensities and coercivities of the anhysteretic remanent magnetization arm are clearly higher for the sediments deposited during the temperate climatic periods of the eemian st germain i ii and mid glacial than for glacial sediments but other magnetic parameters hardly differ between these groups due to slight differences in magnetic composition and possible effects of grain interactions it is not straightforward to relate this different arm behaviour to magnetic grain size variations for the holocene sediments rock magnetic parameters indicate a larger grain size this trend is also suggested by granulometric experiments with an optical laser granulometer dissolution of smaller grains is the most likely explanation for this larger grain size changes in magnetic composition and grain size are extremely limited for the glacial sediments but magnetic concentration varies considerably magnetic concentration maxima in the glacial sediments of lac st front correlate with those of the nearby lac du bouchet thouveny et al 1994 correlating the susceptibility records of these sequences with the 18o record of the grip ice cores thouveny et al 1994 suggests that magnetic concentration maxima may correspond with short cold climatic episodes associated with heinrich events

origins of nd sr pb isotopic variations in single scheelite grains from archaean gold deposits western australia accessory gangue scheelite cawo4 from the archaean mt charlotte lode au deposit can be divided into two types with different rare earth element ree signatures in some scheelite grains specific ree signatures are reflected by different cathodoluminescence colours which can be used to map their often complex oscillatory intergrowths domains with specific ree contents from two grains were sampled for sm nd rb sr and pb isotopic analyses using a micro drilling technique type i scheelite is strongly enriched in middle ree mree and eu anomalies are either absent or slightly positive four fragments collected from type i regions of two crystals have initial 87sr 86sr and end values ranging from 0 70141 to 0 70163 and 2 5 to 3 5 respectively and pb isotope ratios reflecting the composition of greenstone sequence this may indicate that nd and pb have their source either locally or regionally in the greenstones basic greenstone lithologies have 87sr 86sr 0 7015 and the radiogenic sr signatures indicate that part of the sr originated from felsic lithologies located either within or beneath the host greenstone pile alternatively the sr signature may have evolved from preferential leaching of a rb rich mineral during hydrothermal alteration of the greenstone the ree patterns of type ii scheelite are either flat or mree depleted and have strong positive eu anomalies three fragments collected from type ii regions of the same two crystals have initial 87sr 86sr ratios and end values between 0 70130 and 0 70146 and 1 1 to 2 6 respectively and pb isotope signatures that are once again similar to that of the greenstone this implies that 87sr 86sr ratios in type ii fluids were closer to those of the host dolerite 0 7008 0 7013 due to more extensive fluid interaction with the dolerite a positive correlation between na and ree suggests that ree3 are accommodated by the coupled substitution ree3 na 2 ca2 into both type i and type ii scheelite this is consistent with a fractional crystallisation model to explain the change in ree patterns from type i to type ii but not with a model involving different coupled substitutions and fluids from different origins we propose that the complex ree and isotopic signatures of scheelite at mt charlotte are related to small m to medium km scale processes involving mixing between fresh batches of hydrothermal fluid with fluids that had already been involved in extensive wall rock alteration the very high end values measured in some scheelites have been previously used to link gold mineralisation with komatiites containing unusually high sm nd ratios however tiny 20 m grains of secondary hydroxyl bastnasite were found within micro fractures of one scheelite grain containing an extremely high end signature the hydroxyl bastnasite probably formed during recent ree redistribution within the scheelite as a result of meteoric fluid circulation the scale of this cryptic low temperature alteration is sufficient to explain the anomalously high endi values observed in scheelite from western australia

rb sr study of metavolcanic rocks from the la ronge and flin flon domains northern saskatchewan two whole rock suites of metavolcanic rocks from separate volcanic belts of the churchill province in northern saskatchewan have been dated by rb sr samples from the amisk group of the flin flon snow lake domain provide an isochron date of 1784 44 ma suites from the waddy lake and devil lake areas of the la ronge lynn lake domain yield isochron dates of 1814 26 and 1854 100 ma respectively all are regarded as minima for but close approximations to emplacement ages the maximum crustal age of any suite cannot greatly exceed 1850 ma previous rb sr and u pb isotopic dates together with these new determinations confirm the contemporaneous existence of two volcanic arcs active during the late aphebian 1875 1784 ma in the churchill province low initial 87 sr 86 sr ratios 0 7017 0 7022 are consistent with a petrochemically inferred subduction related origin for the volcanic rocks with no closed system reworking of archean crust and a linear evolution of 87 sr 86 sr ratio in the magmatic arc mantle source region from 4 55 ga to the present

enhanced marine productivity in the kuroshio region off shikoku during the last glacial period inferred from the accumulation and carbon isotopes of sedimentary organic matter we obtained marine primary production records from cores md01 2422 and kh06 3 pc8 in the modern kuroshio flow region in the western north pacific for the last 35 ka the organic carbon content of marine sediments is commonly used as a proxy for export production from the surface ocean most sedimentary organic carbon was derived from marine organisms because carbon isotopes of organic matter d 13 corg in sediments were approximately 21 which is close to the typical marine d 13 corg value the quantities of marine and terrestrial organic matter were reconstructed from the mass balance of d 13 corg in bulk total organic carbon the accumulation of marine organic carbon and presumably marine production was enhanced during the latter half of the last glacial period in the subtropical gyre in the western north pacific terrestrial organic matter varied synchronously with marine organic carbon changes suggesting that both increased in late marine isotope stage mis 2 we conclude that in addition to aeolian dust supplied by the east asia monsoon the lateral transport of nutrients from the east china sea to the subtropical gyre as a result of a sea level rise at the last deglaciation played an essential role in enhancing palaeoproductivity during the last glacial period copyright 2009 john wiley sons ltd

trm arm and isr of two natural magnetites of md and psd grain size summary trm arm and isr stabilities with respect to alternating fields and high and low temperature treatment are compared for a set of artificial rock specimens the specimens contain grain size fractions of a homogeneous natural magnetite and a natural magnetite showing exsolution lamellae the grain size fractions are in the psd md range and vary between 5 and 250 m for large md grains the coercivity spectra of arm are similar to those of isr but differ from those of trm particularly in the lower part of the spectrum for small 5 m grains the coercivity spectrum of arm is similar to that of trm and both spectra are different from the coercivity spectrum of isr the use of arm instead of trm to determine palaeo intensities is discussed in relation to the results obtained during high and low temperature treatment arm behaves similarly to isr but unlike trm for all grain sizes studied the results of this study are discussed in terms of a remanence composed of psd surface moments and md and psd bulk moments

pb isotopic compositions of archean komatiites and sulfides abstract pb isotopic compositions were measured in komatiites and other volcanic rocks from several archean greenstone belts and in magmatic and exhalative sulfides associated with these volcanics thin komatiite flows generally yielded pb pb isochron ages consistent with other geochronological or geological information but thicker basaltic flows gave ages that are too young these results suggest that the thin komatiite flows were hydrothermally altered during eruption and that this event is recorded by the pb pb age thicker basaltic flows resisted alteration during eruption but were affected by later events their pb pb ages probably correspond to the time of metamorphism and not to the time of emplacement magmatic and exhalative sulfides from the abitibi belt in canada fall on the same trend in the 207 pb 204 pb 206 pb 204 pb diagram as komatiites basalts sedimentary rocks and k feldspars from granites the calculated 1 value is 7 8 0 1 a similar suite of rocks and minerals from the kambalda area in australia has distinctly higher 207 pb 204 pb and a higher 1 of 8 3 nd isotopic data demonstrate that some kambalda rocks are highly contaminated with older continental crust the differences in initial pb isotopic compositions are attributed to the presence or absence and the age of underlying granitoid basement kambalda greenstones are underlain and contaminated by old 3 0 ga granitoid crust but significantly older granitoid basement appears absent from the abitibi belt the pb isotopic compositions of kambalda greenstones are dominated by the crustal component and do not represent the composition of the mantle source of these rocks the abitibi greenstones are not highly influenced by crustal contamination and their pb isotopic compositions may reflect those of archean mantle

paleointensity determination using anhysteretic remanence and saturation isothermal remanence 1 determining the strength of ancient planetary magnetic field is pivotal to understanding the evolution of planets and asteroids in the solar system while the thellier type double heating technique provides the most faithful field strength information for rocks carrying a thermoremanent magnetization trm many extraterrestrial rock samples respond unfavorably to heat treatment the present study systematically examined the two well known normalization techniques that avoid any heating by comparing the ratios of trm anhysteretic remanent magnetization arm and trm saturation isothermal remanent magnetization sirm both the ratios of trm arm and trm sirm are dependent on the grain size as well as the volume concentration of magnetite the remanence ratios also were found to increase as the alternating field increased during demagnetization for fine grained magnetite a new calibration relation of 2 60 1 32 for the trm arm and of 3 62 1 28 10 2 for the trm sirm was defined for an external field of 50 t the trm sirm is superior to trm arm because the former showed less dispersion in the grain size dependence the volume concentration dependence and the stability against af demagnetization in addition the standard error of the mean for the trm sirm ratio was smaller than that for the trm arm ratio thus whenever heating is inapplicable the sirm method seems to be a better choice than the arm method however it should be emphasized that the uncertainty of trm arm and trm sirm is still nearly an order of magnitude larger than that of the high fidelity thellier estimation and thus must be limited in use only when samples are irreversibly altered during heating in practice the best approach is to carry out both arm and sirm methods and check whether the two estimations agree within the uncertainties

landsat mss imagery applied to geological investigation of the norseman area granitoid greenstone terrain southeast yilgarn block western australia interactively processed landsat mss imagery has been used as an aid to studying the regional geology of approximately 10 800 km 2 of terrain at the southeast margin of the archaean yilgarn block in western australia the technique proved successful in extending positions of known lithological contacts and lineaments into poorly exposed inaccessible areas and in revealing new geological features especially faults previously unrecognized at ground level during this investigation the distribution of granitoids and greenstones was more precisely defined internal greenstone structures highlighted and three main fault trends were identified 1 nw nnw and 2 ene both within archaean shield and 3 ne nne within the transition to adjacent proterozoic mobile belt in order for the most information to be extracted from landsat mss images it is recommended that whenever possible image processing should follow ground based studies as well as precede them and that field geologist and landsat specialist should work at the image processing system together

lead lead age of komatiitic lavas and limitations on the structure and evolution of the precambrian mantle abstract using lead isotopes we have studied komatiites and associated sulfides from three complexes at barberton the lead lead isochron gives an age of 3 46 0 07gy in good agreement with the sm nd age at munro township three distinct komatiitic flows yield significantly different ages pyke hill is 2 72 0 02gy theo s flow is 2 47 0 13gy and fred s flow is 2 58 0 02gy old 2 72 gy is the emplacement age while the alignment obtained on theo s flow and fred s flow clearly points out the effect of a metamorphism posterior to 2 7 gy at cape smith the age obtained by the lead lead method is 1 6 0 13gy this age is younger than that obtained by other methods in contrast the isochron obtained on sulfide gives an age of 1 88 0 17gy in agreement with sm nd methods these results together with others from the literature are used to describe the evolution of pb in the mantle the important result inferred is that the mantle 2 70 gy ago was very different from the primitive mantle according to both th u and u pb values indeed the latter are lower than the planetary values this evolution is the result of the formation of the continental crust

a comparative study of the arm and isr of some natural magnetites of md and psd grain size summary arm and isr stability with respect to alternating field and low temperature treatment were measured for a set of artificial rock specimens each of the specimens contained a known amount of a natural magnetic mineral of a known grain size the following minerals were used a homogeneous natural magnetite a natural titanomagnetite with submicroscopic fe rich inclusions and a natural titanomagnetite and a natural titano maghemite that both show exsolution phenomena the grain size of the fractions varied from 5 to 250 m it is found that the stability of arm and irs of multi domain grains with respect to alternating fields and low temperature treatment is similar whereas for the smallest grains studied 5 m arm is more stable than isr multi domain arm data from this study are in agreement with current multi domain arm theory low temperature behaviour of arm and isr can be explained either in terms of a model in which stable moments in the bulk of the grains are screened by the surrounding matrix or in terms of a model in which regeneration of the bulk remanence plays a role and in which stable moments are situated on the surfaces of the grains

an experimental investigation of high temperature interactions between seawater and rhyolite andesite basalt and peridotite natural seawater was allowed to react with rhyolite andesite basalt and peridotite at 200 500 c and 1 000 bars at water rock mass ratios of 5 and 50 in order to investigate the effects of rock type water rock ratio and temperature on solution chemistry and alteration mineralogy the results indicate that interactions of seawater with various igneous rocks are similar in the production of a hydrous mg silicate and anhydrite as major alteration products fluids involved in the interactions lose mg to alteration phases while leaching fe mn and si from the rocks the ph of the solutions is primarily controlled by mg oh silicate formation and therefore varies with mg and si concentration of the system other reactions which involve mg such as mg ca exchange or which produce free h cause major differences in fluid chemistry between different seawater rock systems high water rock ratio systems 50 1 are generally more acidic and more efficient in leaching than low ratio systems 5 1 due to relatively more seawater mg available for mgsilicate production the experiments show that large scale seawater rock interaction could exert considerable control on the chemistry of seawater as well as producing large bodies of altered rock with associated ore deposits

dynamothermal transition zone between archaean greenstone and granitoid gneiss at lake dundas western australia abstract a 500 m wide shear zone occurs between the base of an archaean greenstone sequence and adjacent granitoid gneiss complex on the shores of lake dundas western australia the dynamothermal margin remains distinguishable due to the preservation of upper amphibolite facies assemblages related granitoid anatectites and mylonitic schistose and gneissose fabrics developed parallel to the contact which itself lies subparallel to the greenstone bedding surface the margin contrasts with less deformed greenschist to low amphibolite facies assemblages which characterize lithologies within the greenstone belt many of which retain igneous textures and relict primary phases structural petrological and textural evidence indicates that the dynamothermal contact originally evolved as a subhorizontal ductile shear zone during juxtaposition of the greenstone pile with granitoid gneiss and that its formation preceded regional folding greenschist facies overprinting and granitoid intrusion which occurred at about 2700 ma the amount of heat generated within the transition zone during thrusting was limited to maximum temperatures of c 650 c due to the buffering effect of granitoid anatexis

early pleistocene evolution of the japan sea intermediate water the early pleistocene fossil record of the japan sea reveals that the planktonic foraminifer globorotalia inflata succeeded in expanding its range from the east china sea to the japan sea during interglacial stages of the early pleistocene however the species is only found in surface sediment samples from the southwestern most part of the sea based on the ecology of g inflata and the water mass structure of the japan sea it appears that its geographical distribution is mainly controlled by the low temperature of the intermediate water which is caused by the cool water mass of japan sea proper water the temporal and spatial patterns of g inflata occurrence indicate that the intermediate water at 200 m depth during interglacial stages between 1 46 and 1 3 ma was warmest during the quaternary this warm intermediate water probably resulted from the influence of the low salinity nature of the tsushima current due to the large inflow of east china sea coastal water after 1 3 ma the intermediate water at 200 m depth became cooler in a step wise manner this cooling can be explained by an intensification of thermohaline circulation in the japan sea associated with strengthening of the east asian winter monsoon and an increase in salinity due to enlargement of the southern strait copyright 2009 john wiley sons ltd

nd isotopic evolution of the precambrian mantle abstract the most convincing examples of proterozoic oceanic crust assemblages occur in the circum superior fold belt of quebec nd isotope analyses of the chukotat and hellancourt basalts from this belt constrain the e nd of the early proterozoic depleted mantle reservoir at 4 to 6 along with data for phanerozoic ophiolites and modern morb the proterozoic basalts infer a constant rate of evolution of the depleted mantle at a rate of 2 2 e nd units per ga recalculation of sm nd isotopic data for archaean greenstone belts to their most reasonable pb pb or u pb ages suggests significantly greater isotopic heterogeneity in the archaean presumed uncontaminated tholeiites and al undepleted komatiites fall within the extrapolated growth limits for the proterozoic phanerozoic depleted mantle while al depleted komatiites adk in early archaean greenstone belts have significantly higher e nd the latter require derivation from a source whose isotopic composition evolved at 2 4 times the rate of the al undepleted komatiite and tholeiite source the isotopic heterogeneities noted for the archaean indicate a compositionally layered mantle by the late archaean the adk source was either isolated by declining geothermal gradients or had become remixed with the overlying mantle giving rise to the present depleted mantle reservoir

orbital and millennial scale fluctuations in late quaternary marine pollen records from the japan sea quaternary surface water conditions within the japan sea change with eustatic sea level changes and fluctuations in the east asian summer monsoon easm influencing regional climate and vegetation through the delivery of heat and moisture our marine pollen data suggest overall cooling from the last interglacial ca 125 ka to the last glacial maximum lgm a cold climate during marine isotope stage mis 2 gradual warming from 12 ka and rapid warming after 10 ka these stages are concordant with published palaeoceanographic changes in the japan sea during mid mis 5 to mis 3 marine sediments in the japan sea are characterised by fine alternations of dark and light coloured layers that formed under the influence of fluctuations in the easm possibly correlated with dansgaard oeschger cycles during the deposition of dark layers high levels of precipitation are inferred from the abundance of cryptomeria in contrast a cool and dry climate is interpreted for the light layers based on an abundance of subarctic conifer pollen the palaeoclimate of the japan sea region appears to have been influenced by orbital scale changes in global climate and millennial scale fluctuations in the easm copyright 2009 john wiley sons ltd

development of a low temperature insert for the measurement of remanent magnetization direction using superconducting quantum interference device rock magnetometers data on the directional changes of a full magnetization vector during cycling to cryogenic temperatures can provide important insights into the low temperature magnetic properties of natural and synthetic materials these data also provide an empirical basis for the application of low temperature treatments in paleomagnetism for example the removal of viscous magnetization in magnetite bearing rocks however existing instruments only allow continuous measurement of magnetization along a single axis hampering experimental and theoretical advances in rock magnetism and the implementation of low temperature techniques into regular paleomagnetic practices here we describe development of a novel low temperature insert designed in collaboration with william s goree inc which allows measurement of directional behavior of a full magnetization vector during zero field low temperature cycling pilot experiments on well controlled polycrystalline samples of pseudo single domain psd and multidomain magnetite as well as on a natural sample containing psd magnetite indicate that the orientation of a saturation isothermal remanent magnetization sirm imparted at room temperature remains constant during low temperature cycling to 20 k this observation lends additional support to low temperature cycling as a cleaning technique in paleomagnetism the sirm imparted in an individual crystal of magnetite showed systematic albeit small changes upon both cooling and warming through the verwey temperature which may reflect switching between the easy magnetization directions however the switching effect may be significantly attenuated by crystallographic twinning in magnetite below the transition overall our results demonstrate the potential of the directional low temperature magnetometry for the advancement of our understanding of the properties of natural and synthetic materials

aspects of the validation of magnetic remanence in meteorites meteorite magnetic records constitute physical evidence of processes acting during early solar system evolution consequently the validation of these records is important in meteorite research the first step in the validation process should be the rem value the rem value is the ratio of natural remanence nrm to saturation remanent magnetization imparted by a 1 t magnetic field sirm the rem values range over 3 to 4 orders of magnitude for stony meteorites and for chondrules from allende c3v s1 bjurbole l4 s1 and chainpur ll3 s1 meteorites the rem values computed from published nrm and sirm data identify many orders of magnitude range in the rem values including rem values 100 10 3 these data suggest a dependence for the nrm intensity on the curatorial location from which the sample was obtained any earth rock acquiring thermoremanent magnetization trm in the geomagnetic field has a restricted range in rem mostly between 5 and 50 10 3 the exception being the mineral hematite in the multidomain size range the only terrestrial samples with rem much greater than 100 10 3 are those struck by lightning the rem value provides a physical basis for recognition between valid records and those that might be contaminated the isothermal remanence acquisition ra curve is presented as a contamination curve that allows an indication of the level of magnetic field contamination required to give the computed rem rm sirm value in the case of the bjurbole and chainpur chondrules with rem values 100 10 3 the ra curve indicates that unrealistically large contamination magnetic fields would be required to give rem values greater than 100 10 3 this would suggest contamination other than by a hand magnet that is normally available to an experimenter this would require an explanation that would involve large magnetic fields during chondrule formation or some extraordinary remanence acquisition mechanism that remains to be described magnetic contamination experiments using 80 and 40 mt magnets demonstrate that the rem values and extent of modification of the magnetic vector record are mineralogy dependent and this is mostly related to the amount and characteristics of the mineral tetrataenite the complexity of the meteorite records suggest validation of the record as a first step the rem value is the first physical statement that can be made in this validation

relationship between median destructive field and remanent coercive forces for dispersed natural magnetite titanomagnetite and hematite summary remanent acquisition curves remanent hysteresis curves and alternating field demagnetization curves were determined for a number of artificial rock specimens containing well defined grain size fractions between 5 and 250 m of natural magnetite titanomagnetite and hematite from these curves the remanent acquisition coercive force h cr the remanent coercive force hcr and the median destructive field of irm h i were determined theoretically these parameters should be the same for an assembly of non interacting homogeneously distributed randomly oriented single domain grains for a given hematite specimen h cr hcr and h i have about the same value in spite of the strong grain size dependence of these parameters for each specimen of magnetite and titanomagnetite the value of h cr is larger than hcr which again is larger than h i however the ratios h cr hcr and h i hcr appear to have a different constant value an interesting relationship which appears to hold for dispersed magnetite titanomagnetite or hematite grains between 5 and 250 m independently of grain size quantity and packing density of the magnetic material is

the sm nd age of kambalda volcanics is 500 ma too old although sm nd isotopic analyses of volcanics from kambalda western australia form a 3 2 ga linear array pb pb analyses of the same suite give an isochron age of 2 73 0 03 ga and a 2 7 ga model age for the associated sulphides we suggest that the 3 2 ga age is incorrect and that the sm nd array results from mixing between depleted mantle and either older continental crust or enriched mantle

the age of the kambalda greenstones resolved by ion microprobe implications for archaean dating methods abstract a chert horizon within the archaean basalt pile at kambalda western australia contains zircons from air fall tuffs erupted as the sediment was laid down ion microprobe analyses of these magmatic zircons constrain the long sought age of the kambalda lavas to 2692 4ma 2 and show that regional metamorphism and deformation of the greenstone pile occurred within 30 ma of deposition rare zircon xenocrysts are evidence of pre greenstone crust as old as 3450 ma exposed remnants of which are yet to be identified subsets of both the magmatic and xenocryst zircons show evidence of hitherto unsuspected low temperature u and or pb mobility in the proterozoic long after stabilisation of the craton the ion microprobe data unravel complexities of isotopic inheritance and alteration illustrating the hazards of using bulk or whole rock samples in archaean isotopic investigations identification of interflow cherts as a precisely dateable rock type opens the way to direct ion probe dating of mafic ultramafic piles and close numerical age control of the complex but ill exposed stratigraphic and structural relations in this richly mineralised greenstone belt

assessment of the u th pb system in two archean metabasalts deciphering the complex histories of sulphides and silicates using acid leaching methods abstract a u th pb study of archean metabasalts from two greenstone belts in the eastern wawa subprovince of the canadian shield indicated variable disturbances had occurred in both whole rock systems changes in the pb content appear to predominate over loss of parent elements and meaningful pb isochron ages could not be obtained from either of the metabasalts detailed leaching experiments on the rocks and analysis of associated disseminated sulphides indicate that the pb isotopic compositions of the whole rocks are dominated by updated but for the most part cogenetic sulphides model ages for pb released by sulphides and metabasalt acid leaches suggest that the sulphide pb has been updated or remobilized during discrete thermal episodes the validity of the inferred events is supported by ages indicated by other isotopic systems for nearby rocks the silicate residues of the acid leached volcanics give well defined pb isochron ages the gamitagama belt metabasalt has a pb isochron age of 2694 54 ma zircons from this rock unit have been dated by u pb at 2691 ma demonstrating that the acid leaching technique on whole rocks can isolate residues which give meaningful ages sulphides in this metabasalt appear to be affected by an event at 2 55 ga a similar rock from the michipicoten belt has undergone a multistage history and yields a pb isochron age of 2761 36 ma consistent with a zircon u pb date for overlying felsic metavolcanic rocks later events affecting this basalt occurred at approximately 2 4 2 2 and 1 6 ga the results show that through acid leaching the primary ages of metabasalts and their later overprinting histories can be approximated initial pb ratios for these metabasalts have been estimated it appears that both depleted and enriched mantle reservoirs contributed to volcanism in this area acid leaching combined with measurement of u and th contents appears to be a useful tool for better understanding the pb isotope systematics of archean metabasalts

nonheating methods for absolute paleointensity determination comparison and calibration using synthetic and natural magnetite bearing samples nonheating paleointensity methods utilize an anhysteretic remanent magnetization arm or a saturation isothermal remanent magnetization to model the natural thermal remanent magnetization trm to avoid heating induced alteration we report the results of paleointensity experiments using the arm pseudo thellier and ratio of equivalent magnetization rem methods conducted to investigate their relative efficiency in recovering the true paleofield strength and to provide additional estimates of their calibration factors the experiments on synthetic magnetite bearing samples representing single domain sd and pseudo single domain psd magnetic states indicated that the correction factors for the arm based methods depend on the magnetic grain size domain state changing from 6 3 for sd grains to 4 1 for 1 5 m psd grains the pseudo thellier method yielded correct absolute paleointensity values when normalization by the trm arm demagnetization slope was used when applied to samples of lava flows and dikes from the 32 kyr lemptegy volcano france both the arm and pseudo thellier methods produced similar paleointensity estimates 28 0 5 1 t and 26 9 4 7 t respectively consistent with the available thellier data for the 31 33 kyr time interval the correction factors estimated from our synthetic samples for the rem 3000 and for remc 1500 and rem 1500 variants are consistent with the previously published estimates however all rem variants yielded unrealistically high estimates 110 t of the paleofield strength from our natural samples our experimental results support arm as a better proxy of trm and suggest that the arm based methods currently represent the best alternative to heating based absolute paleointensity method

grain size dependence of initial susceptibility and saturation magnetization related parameters of four natural magnetites in the psd md range summary initial susceptibility coercive force and several types of remanent coercive forces were measured on a set of artificial rock specimens containing grain size fractions of a natural magnetite and titanomagnetite both of which are optically homogeneous and a natural titanomagnetite and titanomaghemite both of which show exsolution phenomena it was found subsequently that the optically homogeneous titanomagnetite contains some submicroscopic fe rich inclusions these inclusions are magnetically screened in coarse grains only for the lower grain sizes studied they have an appreciable influence on the data the size of the fractions varied from 5 to 250 m the parameters and several parameter ratios are plotted as a function of grain size several of these parameters can be used as mineralogical and grain size indicators the varying degree of exsolution of the minerals is reflected in the gradients of the plots from plots of initial susceptibility versus grain size it is concluded that the shape of the grains does not play a dominant role in determining the change of this parameter with grain size variation of the various parameters with grain size is explained in terms of a gradual transition from large psd grains to md grains without there being any sharp transition for titanomagnetite x 0 55 the transition takes place at grain sizes that are about 15 m larger than for magnetite

genesis of basalt hosted massive sulphide deposits from the trondheim and sulitjelma districts norway ore lead isotopic considerations lead isotopic ratios of bulk sulphides from eleven stratigraphically equivalent deposits from the koli nappe sequence in the trondheim district and eleven from the koli sequence at sulitjelma norway have been determined when plotted on 207pb 204pb 206pb 204pb diagrams the data define a linear trend extending from the mantle to the upper crustal model growth curves of doe and zartman 1979 moreover the data from both districts lie on the same trend this isotopic trend is interpreted as resulting from the mixing of lead from a mantle source probably the host basalts with that of an upper crustal end member either sialic basement or the terrigenous sediments surrounding the host basalts it is also concluded that the deposits in both camps formed more or less contemporaneously the isotopic mixing line is comparable with that obtained from besshi ore pyrites in japan for which an aulacogenic depositional environment similar to that found today in the gulf of california has been proposed fox 1984 it is concluded that a similar depositional environment was responsible for the trondheim and sulitjelma ores although an ensialic back arc basin or other possible environments cannot be entirely ruled out

the geology of the kambalda nickel field western australia the kambalda nickel field contains the major concentration of volcanic peridotitc associated nickel ores in the archean of australia it occupies an area of 400 km 2 underlain by two sequences of ultramafic mafic and felsic volcanics and sedimentary rocks which can be broadly correlated with previously erected regional stratigraphic sections most ores occur in the lower kambalda sequence at the base of the kambalda ultramafic rocks the ultramafic rocks of the upper bluebush sequence contain only minor mineralization four phases of deformation occurred over an interval of more than 300 m y resulting in a dominant north northwest structural trend faulting was active during original volcanism and continued intermittently until after mafic felsic dike intrusion the ultramafic rocks have been serpentinized and all rocks have exerienced low strain upper greenschist to lower amphibolite facies metamorphism and variable carbonation and potash metasomatism the kambalda ultramafic rocks are of variable thickness and in places exceed 1 000 m the lower member of the ultramafic rocks occupying approximately one third of the sequence comprises thicker high magnesium flows i e generally 36 volatile free mgo commonly separated by sulfidic quartz albite sediments thinner lower magnesium flow units characterize much of the upper member the ores occur in 24 shoot complexes each containing multiple ore surfaces caused by structural dislocation of a few grouped ribbonlike original orebodies eighty percent is contact ore occurring at the base of the lowermost ultramafic flow and generally occupying elongate troughs in the footwall basalt ultramafic contact these troughs are thought to be original volcanic depressions which focused later deformation the remainder is hanging wall ore usually occurring directly above contact ore at the base of the second or third ultramafic flow hanging wall orebodies occasionally grade into stratigraphically equivalent interflow sediments the ores contain varying proportions of massive matrix and disseminated sulfides the hypogene mineral assemblage is pyrrhotite pentlandite pyrite chalcopyrite but millerite is locally significant the massive ores in particular are commonly severely deformed and some have been remobilized tens of meters from their original contact position metamorphism has caused recrystallization of the ores and some redistribution of elements there is commonly marked variation of mineralogy and s ni ratios between contact and overlying hanging wall ores and within and between original ore surfaces within shoots but the relative contributions of primary composition and metamorphism to this variation are uncertain in ore environments the footwall basalt ultramafic contact is more deformed than in non ore environments the basal ultramafic flows are thicker and richer in magnesium the trend toward lower magnesium flows upward through the ultramafic formation is less well developed and there is better textural development and compositional differentiation within flows non ore environments usually contain interflow sediments whereas there is generally a sediment free prism of ultramafic rocks above ore environments most ores are interpreted to have originated by either simultaneous or sequential extrusion of sulfide melts and ultramafic lavas rich in olivine phenocrysts along active linear fissures in a basaltic ocean floor volcanic exhalations probably contributed to minor ore in sulfidic sediments

archaean au ag mineralisation at racetrack near kalgoorlie western australia a high crustal level expression of the archaean composite lode gold system the racetrack au ag deposit in the archaean yilgarn block western australia is hosted by a porphyritic basalt in a low greenschist facies setting and is associated with a brittle strike slip fault system three distinct and successive stages of hydrothermal activity and late quartz carbonate veining resulted in multiple veining and or brecciation stages i and ii are au bearing whereas stage iii and late veins are barren the ore shows features of both classic epithermal and mesothermal deposits alteration assemblages typified by sericitization carbonization silicification and chloritization are similar to those of mesothermal gold deposits wheras the quartz vein textures including comb rosette plumose and banded ore mineralogyof arsenopyrite pyrite chalcopyrite sphalerite galena freibergite tetrahedrite tennantite fahlore electrum and gold and metal associations cu as ag sn sb w au and pb are more characteristics of epithermal deposits fluid inclusions related to stage ii are two phase and aqueous with 1 8 average 4 wt nacl equiv and co2 content of 0 85 molal pressure corrected homogenisation temperatures range from 190 c to 260 c mineral assemblages indicate that ore fluid ph ranged between 4 2 and 5 3 fo 2 between 10 38 8 and 10 39 6 bars and m s between 10 3 2 and 10 3 6 calculated chemical and stable isotope compositions require a component of surface water in the ore fluid depositing the mineralisation but evidence for deep crustal pb indicates that deeply sourced fluids were also involved the deposit is interpreted to have formed in a shallow environment via mixing of deeply sourced fluids from at least as deep as the base of the greenstone belt with surface waters it therefore represents the upper crustal end member of the crustal depth spectrum of archaean lode gold mineralisation

thermoremanent behavior in synthetic samples containing natural oxyexsolved titanomagnetite understanding earth s geodynamo provides us a window into the evolution of the earth s core which requires accurate data about how its strength varies with time classic thellier style paleointensity experiments assume that studied specimens contain only noninteracting single domain sd magnetic particles interacting grains commonly occur in volcanic rocks but are generally assumed to behave like equivalently sized sd grains multidomain md grains can cause erroneous pi estimates or cause thellier style experiments to fail entirely synthetic specimens containing naturally formed magnetite with md grains and oxyexsolved titanomagnetite closely packed sd grains were subjected to various partial thermoremanent magnetization ptrm experiments which tested nonideal behavior as a function of ptrm acquisition and loss inequality thermal history and repeated heating steps for all grain sizes and domain states ptrmc heating and cooling in a nonzero field gives larger values compared to ptrmb heating in a zero field and cooling in a nonzero field by 5 5 oxyexsolved grains appear prone to the same concave up nonideal arai plots commonly observed in md specimens which also has potential implications for the multiple specimen domain state corrected protocol repeated heatings cause additive deviations from ideality with relatively small impacts on arai plot curvature for both grain types experiments with higher initial demagnetization temperatures had lower curvatures with the most sd like behavior occurring in the uppermost 20 urn x wiley 15252027 media ggge21571 ggge21571 math 0001c of the un blocking temperature range samples containing mixtures of magnetic domain sizes are likely to behave less ideally at lower temperatures but become more ideal with increasing temperature as the nonideal grains unblock

age and origin of granitic rocks in the kalgoorlie norseman region of western australia implications for the origin of archaean crust three granites from the norseman area at stennet rocks buldania rocks and east of lake johnston have u pb zircon ages of 2691 8 95 c l 2689 22 and 2661 8 ma respectively one stennet rocks contains 3100 3200 ma cores providing support for oversby s 1975 argument that all three plutons were derived by anatexis of much older basement common leads within the zircons show evidence of having been derived from within the rock and represent mixtures of initial rock leads and radiogenic leads the unusually 208pb rich compositions of the common leads suggest the breakdown of a th rich phase perhaps uranothorite as a major contributor to the radiogenic component available zircon geochemical and isotopic data are used to develop a two stage model for archaean crustal development in this region with formation of primitive crust of broadly andesitic composition from depleted mantle or basalt beginning at 3400 ma followed by extensive thermal reworking and possibly continued growth over the period 3000 3300 ma in the second stage at 2700 ma anatexis resulted in large scale intra crustal differentiation giving a thick upper granitic layer and a lower crust residual from anatexis it is this second major thermal event that is recorded by most geochronometers implicit in the andesitic crustal growth model is that because the sm nd and rb sr ratios of newly formed archaean crust are close to mantle values this process is transparent to the sm nd and rb sr isotope systems until recycling of incompatible element rich sediment becomes important following the late archaean production of a wide spread differentiated upper crust

postcrystallization disturbance in the neodymium and lead isotope systems of metabasalts from the ramagiri schist belt southern india archean metabasaltic rocks from three separate blocks that constitute the north south trending ramagiri schist belt of the eastern dharwar craton have large variations in nd2750 even samples of the same rock type from one outcrop that are less than 50 cm apart from each other show a range of up to 5 5 nd2750 units the trends of the fields defined by the three suites in smnd vs nd2750 space intersect at smnd 0 1 to 0 2 and nd2750 8 to 12 suggesting that these rocks have lost lrees and have interacted with and exchanged at least nd with a common extraneous phase the isotopic composition of this phase suggest derivation of its neodymium from sources which had a long term history of lree enrichment this phase may have derived its isotopic composition from older continental crust one of the unaltered dikes cutting the three blocks in the belt and the surrounding gneisses gives a 147sm144nd 143nd144nd age of 2454 100 ma a minimum for the time of block assembly and alteration of rees including nd while a set of samples from the central block lie along an isochron with a pb pb age of 2746 64 ma the samples from the eastern and western blocks show large uncorrelated variations in 207pb204pb with 206pb204pb residues after acid leaching of sample powders have lead isotope ratios that are distinct for samples from each of the block and are compatible with their derivation from archean mantle the lead isotope composition of the acid leaches suggest disturbance of the metabasalts by an isotopically extraneous phase that had variable and high 207pb204pb and 208pb204pb ratios for a given 206ph204pb relative to expected archean mantle values both lead and neodymium isotope disturbances are best explained as a result of alteration of these rocks by an extraneous phase which had derived its isotopic composition from ca 3 5 ga continental crust

the source of lead in archaean lode gold deposits of the menzies kalgoorlie kambalda region yilgarn block western australia the archaean greenstone terrane between menzies and kambalda exhibits a coherent although deformed stratigraphic sequence intruded by granitoids and bounded by major nnw trending shear and or fault zones the greenstone terrane hosts a large number of lode gold prospects and deposits including the giant kalgoorlie deposits the initial pb isotope compositions of lode gold deposits as determined from ore related galena and pyrite vary systematically in a linear trend on a207pb 204pb versus206pb 204pb diagram which reflects crustal heterogeneity at the time of mineralisation deposits hosted within a 90 km section of the menzies boorara shear zone have a uniform radiogenic initial pb isotope composition irrespective of temperature of mineralisation and proximity to granitoid gneiss in plan view the pb in these deposits is considered to be derived largely from older felsic crust underlying the greenstone belt and was accessed via this major shear zone system deposits in a transect unrelated to a major shear zone show a systematic correlation between initial pb isotope compositions and proximity to granitoid gneiss and or to mineralisation temperature these compositions are less radiogenic than those within the menzies boorara shear zone but trend on a207pb 204pb versus606pb 204pb diagram between this isotope signature and the uniform pb isotope signature which characterises the 100 km greenstone transect from the mt pleasant area through kalgoorlie to kambalda these data are interpreted to reflect pb derivation from discrete crustal segments within and below the greenstones and require that mineralisation was related to crustal scale hydrothermal systems that accessed both sialic mid to lower crust and the greenstone succession

low temperature behavior of single domain through multidomain magnetite abstract we have investigated the low temperature behavior of a suite of grown synthetic and natural magnetites that span single domain sd and multidomain md behavior synthetic samples had been grown in the laboratory either in an aqueous medium or in glass natural samples included sd magnetites occurring in plagioclase and truly md magnetites in the form of large octahedra in all experiments a sample was first given a saturation remanence at room temperature next moment was measured continuously during cooling and warming between 230 k and 60 k similar to results reported earlier by other workers magnetic memory is large in sd samples whereas truly md samples are almost completely demagnetized by cycling between room temperature and 60 k pseudo single domain samples exhibit behavior that is intermediate with respect to that of the sd and truly md states when data from this study are combined with data obtained by hartstra 10 from sized natural magnetites it is found that the percentage of total remanence that survives cycling between room temperature and 60 k decreases linearly with the logarithm of grain size and thus with increasing number of domains this relation suggests that memory can provide a reasonable estimate of grain size in those magnetite bearing rocks for which these samples provide good analogues remarkably some of the large natural octahedra provide a magnified view of md response to low temperatures and thus reveal two surprising and intriguing types of behavior first below approximately 180 k these octahedra demagnetize through a series of large barkhausen jumps second near 117 k these same octahedra exhibit a wild zone where magnetic moment executes large random excursions we interpret these two phenomena as direct evidence for the unpinning and irreversible displacement of domain walls in response to the drop in coercivity and possibly the broadening of domain walls as temperatures drop toward the isotropic point one implication of this behavior is that cooling to progressively lower temperatures could provide an effective method for stepwise removal of paleomagnetic components carried by md grains even without passage through the isotropic point of magnetite

magnetic hysteresis of 0 6 110 μm magnetites across the verwey transition we report saturation magnetization ms saturation remanence mrs coercive force hc and remanence coercivity hcr as a function of grain size d and temperature t for 0 6 135 m magnetites

how accurately can nrm sirm determine the ancient planetary magnetic field intensity abstract the present study tested grain size dependence of thermoremanent magnetization trm saturation isothermal remanent magnetization sirm as well as its stability against demagnetization the trm sirm ratio is dependent on the grain size of magnetite suggesting that a strong constraint on grain size characterization is necessary to be used as a paleointensity proxy in planetary magnetism in addition the trm sirm ratio increases as the alternating field increases for fine grained magnetite accuracy of trm sirm was investigated using historic showa lava erupted in 1946 it was observed that the natural remanent magnetization nrm sirm ratio of 0 032 is comparable to the field intensity of 46 80 t however the uncertainty of nrm sirm was an order of magnitude larger than that of the companion thellier estimation therefore the nrm sirm ratio can only provide crude estimations on the absolute planetary magnetic field intensity in practice anisotropy correction is advisable to reduce the scatter of nrm sirm

metastability of domain state in multidomain magnetite consequences for remanence acquisition experimental studies on isothermal remanent magnetization irm acquisition of synthetic specimens containing crushed natural magnetite in seven grain sizes from 5 10 m to 100 150 m show that the initial demagnetization state before irm acquisition strongly affects the samples ability to acquire irm it is easier to acquire irm from an initially thermally demagnetized state than from an alternating field af demagnetized state and low temperature demagnetization of the thermally demagnetized state increases resistance to irm acquisition these data are interpreted as confirmation of the existence of a number of possible domain states metastable states which have variable capacity for remanence acquisition our results also demonstrate that activation of domain structure is much more effective by af than by direct dc fields we suggest that the continually changing external field experienced during af demagnetization allows the magnetic structure to reorganize incrementally towards the demagnetized state requiring a considerably lower peak field about 3 times lower to achieve the same demagnetization effect thermoremanent magnetization trm in larger grain sizes is partially self reversed a difference in grain size dependence is observed for a number of magnetic parameters all parameters vary with grain size below about 50 m above 50 m parameters associated with coercivity af demagnetization or low temperature treatment hcr saturation irm sirm memory trm memory median acquisition field maf of irm after af median destructive fields mdf of sirm are independent of grain size parameters associated with trm or thermal demagnetization mdf oftrm maf of irm after thermal demagnetization maf of irm after thermal demagnetization followed by low temperature demagnetization self reversal as percentage of trm show grain size dependency throughout the grain size range our interpretation of the data invokes the existence of subtle material inhomogeneities in both natural and synthetic magnetites giving rise to a limited range of curie temperatures below 580 c perhaps down to 560 c we suggest that their control over the local energy minima states available to the grain is more significant in the trm or thermally demagnetized state while shielding by soft domain walls is dominant in the af demagnetized state where walls are in the simplest domain configuration leading to differing grain size dependencies of these different states

high temperature characteristics of a natural titanomagnetite summary continuous recordings were made of thermal demagnetizations of isr arm and trm induced in artificial rock specimens the artificial rock specimens contained well defined grain size fractions of a natural titanomagnetite which under an optical microscope was homogeneous using a transmission electron microscope it was shown that submicroscopic inclusions exist within the titanomagnetite screening of the remanence of these inclusions by the surrounding titanomagnetite is thought to be responsible for the occurrence of peaks in the continuous thermal decay curves of isr and arm higher peaks observed in the case of trm are thought to be caused by the combined effects of screening and an anti parallel remanence in the titanomagnetite further submicroscopic exsolution processes which occur in the titanomagnetite as a result of repeated heating can be deduced from the development of new peaks from changes in the temperature at which the peak s occur their shape and their relative height the use of stepwise demagnetization techniques on the titanomagnetite yielded erroneous directional results due to the screening in the titanomagnetite the biasing effects due to screening could be avoided by using continuous thermal demagnetization techniques

low temperature cycling of isothermal and anhysteretic remanence microcoercivity and magnetic memory abstract this paper reports low temperature cycling ltc through the verwey transition of anhysteretic remanence arm partial arms and partially demagnetised saturation isothermal remanence sirm induced at room temperature in pseudo single domain and multidomain md magnetite the remanences were cooled in zero field to 50 k and then heated back to room temperature by inducing partial arms over different field ranges and by partially alternating field demagnetising sirms it was possible to isolate both low coercive force and high coercive force fractions of remanence on cooling through the verwey transition a sharp increase in the remanence was observed the relative size of the jump increased as the high coercive force fraction was increasingly isolated this behaviour is interpreted as being due to both an increase in the single domain multidomain threshold size on cooling through the verwey transition and to the reduction or elimination of closure domains in the low temperature phase in addition the memory ratio i e the fraction of remanence remaining after ltc divided by the initial remanence was found to be higher for the high coercive force fraction than the low coercive force fraction in our interpretation the high coercivity fraction behaviour is associated with reversible domain re organisation effects whilst the low coercive force fraction s behaviour is associated with irreversible domain re organisation and de nucleation processes due to the decrease in magnetocrystalline anisotropy on cooling to the verwey transition the high coercive force fraction is likely to be magnetoelastically controlled thus a rock displaying high coercive force behaviour is likely to carry a palaeomagnetically meaningful remanence with high unblocking temperatures in addition ltc analysis can be used to identify the domain state dominating the natural remanence in magnetite bearing rocks

the relationship between archaean gold mineralization and spatially associated minor intrusions at the kambalda and norseman gold camps western australia lead isotope evidence many archaean mesothermal gold deposits are spatially associated with felsic to lamprophyric minor intrusions and it has been suggested that magmatic processes related to such intrusions may be important in the genesis of these deposits a comparison of the pb isotopic signature of gold related galenas from kambalda and norseman with that of spatially associated minor intrusions at the time of mineralization indicates that the ore fluid pb cannot have been derived solely from the intrusions or their source regions for both study areas the galena pb isotopic compositions are bracketed by those of local volcanic mafic and intrusive largely felsic rock types this is consistent with the ore fluid having derived metallic components from the crust or crustally derived granitic rocks and the mantle or mantle derived rocks of the greenstone succession via metamorphic dewatering or mantle crustal degassing interaction of granite derived magmatic fluids with greenstone lithologies could plausibly produce a similar array of pb isotopic signatures the norseman data as a whole are more radiogenic than the kambalda data for broadly synchronous mineralization reflecting the greater abundance of older granitic rocks with respect to mafic ultramafic rocks in the norseman district the provinciality exhibited by the pb isotopic composition of the ore fluid indicates that the gold mineralizing process formed galena whose pb isotopic composition was very sensitive to local variations in crustal pb isotopic composition either within the source region of the fluid or along fluid conduits

ground melting and ocellar komatiites a lead isotopic study at kambalda western australia stratigraphically and geographically restricted ocellar komatiite flows at kambalda western australia appear to represent the products of ground melting of sulphidic sediments by komatiites in lava channels that localized the fe ni cu sulphide ores an immiscible sulphide liquid formed and gravitationally separated from the melted sediment xenomelt the resultant buoyant silicate liquid being partly or wholly assimilated by the turbulently convecting komatiite magma rarely the xenomelt gravitationally migrated to the top of flows and overflowed into the less turbulent lava levees where it collected to form a separate layer overlying a komatiitic layer within a single flow there was selective preservation of the hybrid felsic layer as an upper ocellar unit within an ocellar komatiite flow in lava levees flanking lava channels the ocellar unit is enriched in elements previously concentrated in the sediments and shows u th pb isotopic systematics akin to the underlying sediments moreover the partitioning relationships of u and pb between the immiscible xenomelt and sulphide liquid enhances the range of u pb ratios for components of the ocellar unit thus allowing sufficient spread of modern uranogenic pb isotopic ratios to form isochrons albeit imprecise ones the range and similarity of model th u data from these flows 2 8 3 9 and adjacent sulphidic sediments 2 3 4 4 mostly 2 8 3 9 contrasts with the generally invariable th u within kambalda ultrabasic basic flows 3 6 3 9 and further supports the ground melting hypothesis

magnetic properties of natural goethite iii magnetic behaviour and properties of minerals originating from goethite dehydration during thermal demagnetization summary the magnetic behaviour during stepwise demagnetization of a set of artificial samples containing well defined natural goethite from five localities chemical composition crystallite size and grain size are known is reported differential scanning calorimetry measurements indicated that the goethites converted to haematite between 260 and 360 c in this temperature range a small decrease in initial susceptibility and an additional remanence decay leading toward an extra bending point in the thermal decay curve are observed because titanomagnetite or pyrrhotite are absent in the samples this extra bending point is tentatively interpreted as being due to recrystallization of the minor haematite already present in the original goethite concentrates facilitated by water made available through the goethite haematite conversion at much higher temperatures at some 600 c a self reversal of the remanence is observed in most specimens the haematite derived from the goethites between 260 and 360 c appeared to be prone to further alteration at successive higher demagnetization temperatures chemical alterations in the magnetic mineral suite starting at temperatures from 380 c upward depending on the grain size of the original goethite were inferred from an increase in initial susceptibility the susceptibility behaviour showed an appreciable variation due to the creation of varying trace amounts of magnetite which appeared to be already present after the 400 c step after the final 685 c demagnetization step the magnetic mineralogy was usually dominated by magnetite the observed variation is thought to be the result of local within specimen differences in availability of the amount and possibly also the composition of the vapour phase the vapour phase is due to chemical reactions between the matrix constituents waterglass and calcite leading to a c02 h20 vapour phase reducing capacity necessary for the magnetite formation is envisaged to be created by decomposition of trace amounts of organic matter at relatively low temperatures up to some 400 c at higher temperatures over 550 c decomposition of traces of ferrous iron bearing clayminerals presumably donates the ferrous iron differences in the magnetite haematite ratio as well as in the properties of both minerals were assessed in some detail with more or less routine rockmagnetic methods acquisition of the isothermal remanent magnetization at room temperature in fields up to 11 2mam or 14t af demagnetization and low temperature cycling of the saturation remanence this was done after the 400 c step to study the magnetic properties of the newly formed haematite and after the 685 c step to evaluate the properties of the magnetite and more evolved haematite after the 400 c step the haematite appeared to be very fine crystalline and magnetically extremely hard its saturation remanence is considerably lower than that of well crystalline haematite after the 685 c step its hardness has decreased and its saturation remanence slightly increased chemical differences between the

lead ages reset rubidium strontium ages and implications for the archaean crustal evolution of the diemals area central yilgarn block western australia abstract the pb pb whole rock geochronology of archaean granitic and gneissic rocks from the diemals area in the central yilgarn granite greenstone terrain provides important constraints on crustal evolution the regionally extensive banded gneisses previously considered as candidates for basement to the greenstones give a pb pb whole rock age of 2700 97 ma 2 errors this is within error of previously published rb sr and sm nd gneiss ages and also within error of the sm nd ages on the greenstones in the eastern goldfields province two synkinematic plutons give pb pb whole rock ages 2737 62 ma and 2700 100 ma and pb isotopic compositions consistent with the hypothesis based on field and geochemical relations that these plutons were derived by partial melting of the precursors to the banded gneisses assuming this the combined data date the melting event at 2723 25 ma with a model source value of 8 18 0 02 this source value is close to the range postulated for mantle values and restricts the crustal history of the precursors to less than 200 ma a post kinematic pluton with a whole rock pb pb age of 2685 26 ma and value of 8 26 0 02 puts a younger limit on this relatively short lived crustal accretion differentiation event comparison of pb pb and rb sr whole rock dates for the plutons suggests that the latter became closed systems up to 200 ma after the pb pb ages and that the plutons gained or lost rb or sr at this time

criteria for determining initial lead isotopic compositions of pyrite in archaean lode gold deposits a case study at victory kambalda western australia abstract the initial pb isotopic compositions of ore associated sulphides are important in isotopic tracer studies studies of archaean lode gold deposits from western australia indicate that the pb isotopic data distribution for ore associated galenas and pyrites is commonly linear and determination of the initial pb ratio relies on selecting the least radiogenic composition this detailed pb isotopic study of sulphides from the 32 ore zone which transects a variety of rocks in the victory mine mineralisation dated at 2627 ma has resolved the origin of the pb isotopic heterogeneities which yield linear arrays it has led to the development of criteria for sample selection which more efficiently and effectively target pyrite samples which best preserve the initial pb ratio of the sulphide and hence the ore fluid the most important controls on the displacement of the measured pb ratio of pyrite from the initial pb ratio are in order of importance 1 pb content of pyrite 2 pyrite abundance 3 proximity of pyrite to ore fluid channelway i e vein and 4 host rock the host rock is important because the th u and pb contents and presence of minor u th bearing phases influence the amount and nature of any post formation pb represented in the pyrite data the first three parameters control the magnitude of that influence a high pb content high pyrite abundance and setting in a vein or at a vein margin produce a pb isotopic composition which is more likely to be dominated or buffered by fluid pb i e more accurately reflects the initial pb isotopic ratio conversely pyrite with a low pb content low abundance and siting distal from veining is likely to be more susceptible to post formation modification by contributions from the host rock resulting in a more radiogenic pb isotopic composition

the last 100 000 years palaeoenvironmental changes inferred from the diatom assemblages of core md012404 from the okinawa trough east china sea the diatom assemblage records preserved in a sedimentary core md012404 retrieved from the okinawa trough in the east china sea ecs imply palaeoenvironmental changes of the last 100 ka our statistical analyses of diatom species abundance data indicate that the assemblages dominate open ocean and warm water coastal water and freshwater masses in the ecs these proxy species were used to infer the long term variation in surface hydrological conditions and palaeoclimate cycles of ca 23 ka observed in the relative abundance of the tychopelagic species paralia sulcata indicate that the increases in precipitation driven by solar insolation might have controlled the diatom assemblages in the ecs the diatom records also indicate relatively low abundances of tropical tychopelagic and freshwater species during millennial scale cold events such as the younger dryas and heinrich events which have been well expressed in the high latitude northern hemisphere climate the floral patterns are interpreted as synchronous cooling and more saline sea surface conditions in the ecs caused by the enhanced asian winter monsoon during the northern hemisphere cold events the higher abundances of tropical species during deglaciation and the holocene might have been linked to gradual increases in the inflow of the kuroshio into the okinawa trough the records also suggest a temporary reduction in tropical species from 5 to 3 ka corresponding to the pulleniatina minimum event during which the warm water planktic foraminifer pulleniatina obliquiloculata was rare copyright 2009 john wiley sons ltd

orbital scale anti phase variation of sea surface temperature in mid latitude north pacific margins during the last 145 000 years 1 the late quaternary records of alkenone sea surface temperature sst in the japan and california margins showed orbital scale anti phase sst variations between the two margins this east west seesaw like change agreed well with the long term el nino southern oscillation enso behavior predicted by the zebiak cane enso model clement et al 1999 as regards both the timing and frequency during 0 60 ka and 120 145 ka and is attributed to the precession controlled change in tropical enso behavior this anti phase sst change was not clearly demonstrated during 60 120 ka this finding suggests that the influence of tropical climatic dynamics on the mid latitude north pacific varied in response to glacial interglacial cycles