petedunnite caznsi2o6 stability and phase relations in the system cao zno sio2 the phase relations of petedunnite caznsi2o6 pd were determined experimentally at p t conditions up to 2 5 gpa and 1100 c single phase petedunnite is formed at high pressures p 0 8 gpa reversed experiments show that at lower pressures and temperatures 650 c petedunnite decomposes to willemite zn2sio4 wil hardystonite ca2znsi2o7 har and quartz sio2 qtz according to the reaction 4 pd wil 2 har 3 qtz the boundary curve for this equilibrium reaction is given by p gpa 0 093 0 029 0 0014 0 0003 t c by disregarding the phase transition of quartz the stability field of wil har qtz is restricted toward lower temperatures by zinc feldspar caznsi3o8 zfsp according to the known reaction wil 2 har 7 qtz 4 zfsp these reactions intersect at 650 1 c 0 78 0 01 gpa generating an invariant point i pd additionally petedunnite breakdown reaction is intersected by the low high quartz phase transition curve generating an invariant point i pdqtz at 840 c 1 04 gpa at temperatures 650 c further reactions occur in the system cao zno sio2 including the doubly degenerate reaction zfsp pd qtz and 3 pd har wil zfsp which also intersect the invariant point i pd all reactions involving petedunnite display shallow positive slopes within the p t field indicating that the crystallization of petedunnite is highly pressure sensitive over a wide temperature range this means that an increasing petedunnite component in pyroxene shifts its stability field to higher pressures similar to the effect of a jadeitic component the study of natural clinopyroxene and the correlation of its zinc content with published p t conditions of these mineral assemblages confirmed a significant relationship between extraordinary high zinc concentrations in pyroxene and high metamorphic pressure conditions in addition the petedunnite component is obviously sensitive to the prevailing fluid conditions in terms of the fugacity ratio f s2 f o2 furthermore a distinct temperature dependency of the zinc component was observed in the range of trace element concentration in consequence zn turns out to be a key element with regard to its implementation as a sophisticated petrogenetic indicator of metamorphic conditions therefore routine measurement of zinc in element analyses of clinopyroxenes is strongly recommended

oxygen isotope analyses and pleistocene ice volumes abstract the oxygen isotope record from fossil foraminifera in deep sea sediments is commonly used as a proxy for global ice volume the linkage between 18 o and ice volume however is probably nonlinear we have developed a simple numerical model of the isotopic response of the oceans to ice volume change the major features it simulates are 1 the changing mean isotopic composition of snow as a function of ice volume colder snow temperatures forced by climate change and higher elevation accumulation areas imply more negative mean 18 o 2 the nonequilibrium isotopic composition of ice sheets the past history of an ice sheet is integrated into its mean isotopic composition which introduces a lag of isotopic ice volume i e the measured 18 o record scaled to ice volume units behind true ice volume 3 selective preservation of isotopically more negative colder higher latitude ice this geographic effect can selectively amplify or dampen the isotopic response to the ice volume signal we illustrate the response of our model to simple hypothetical ice volume transitions of ice growth and ice decay sensitivity tests are illustrated for all model parameters the results suggest that oxygen isotope records reproduce the general patterns of ice volume change fairly accurately the foraminiferal isotope record however may misrepresent the true amplitude of the ice volume signal and lag true ice volume by 1000 to 3000 yr

the antarctic viewpoint of the central paratethys cause timing and duration of a deep valley incision in the middle miocene alpine carpathian foredeep of lower austria global glacio eustatic sea level changes massively influenced the depositional history of the central paratethyan region here we correlate middle miocene global 18o shifts with ice volume changes on antarctica and sea level changes with corresponding phases of erosion valley incision and deposition in the lower austrian part of the alpine carpathian foredeep this allows the exact dating of the valley formation two periods of positive 18o shifts resulted in sea level drops of about 60 and 40 m respectively the first drop in the late langhian middle badenian at c 13 9 ma mi3b was fast and caused severe erosion on the emerged foredeep in a second less pronounced step around 13 0 ma mi4 in the middle serravallian late badenian the base level was further deepened after a period of alternating erosion and deposition the combined sea level change 80 120 m fits well with the maximum thickness of sarmatian sediments drilled within incised valley 110 m the global sea level falls affected not only the geological history of the foredeep the intensive erosion valley incision is combined with delta progradation in the adjacent vienna basin due to this massive sea level drop the interruption of marine connections resulted in vast salt deposits and faunal crises within the central paratethys during this time

rapid analytical method for trace zn contents in some mafic minerals using the electron microprobe potential utility as a metallogenetic and petrogenetic indicator abstract an analytical method using an electron probe microanalyser epma has been developed to enable rapid determination of trace zn contents in mafic silicates total matrix correction factors of atomic number absorption and fluorescence zaf correction factors for zn are constant and virtually independent of solid solution composition and mineralogy zn analysis confirmed by inductively coupled plasma optical emission spectrometry icp oes reveals that this epma method is capable of analyzing zn within only 30 s at a detection limit of 50 ppm preliminary studies of zn abundance indicate that 1 clinopyroxenes in skarn deposits tend to vary their zn contents in accordance with the metal type 500 ppm for the w type 2 zn contents of granitic biotites in the ishikawa area northeastern japan increase from 290 to 610 ppm with the advance of crystallization and 3 zn contents of chlorite in weathered granitic rocks are almost equivalent to those of its primary biotite therefore this rapid epma method may have considerable potential for the use of trace zn as a metallogenetic indicator and as a marker for crystallization or alteration processes

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

stability and phase relations of ca znsi3 o8 a new phase with feldspar structure in the system cao zno sio2 zinc feldspar ca znsi 3 o 8 has been synthesized hydrothermally and its phase relations have been investigated in the system cao zno sio 2 up to pressures of 1 0 gpa single phase zn feldspar grew from an oxide mixture at 600 c and 0 7 gpa within 6 days it crystallizes in space group p 1 displaying lattice constants of a 8 121 1 a b 12 927 1 a c 7 206 1 a 93 76 5 116 120 7 84 368 7 v 675 7 a 3 z 2 heuer et al 1998 in zn feldspar zn and si are ordered on the tetrahedral sites and the structure of zn feldspar is more similar to the low albite structure than to that of anorthite due to the tetrahedral ordering scheme zinc feldspar does not melt congruently but decomposes at subsolidus conditions according to the reaction 4 zn feldspar willemite 2 hardystonite 7 quartz 1 reaction 1 was determined by means of reversed experiments and its negative p t slope can be expressed by the equation p gpa 2 797 0 325 0 0031 0 0004 t c introducing the stability relations of the sio 2 system two invariant points i qtz and i trid are generated at 720 c 0 57 gpa and 896 c 0 016 gpa projected on the low high quartz and high quartz tridymite phase transitions respectively the phase assemblage willemite hardystonite quartz is not stable at pressures above 1 2 gpa where petedunnite is formed according to the reaction willemite 2 hardystonite 3 quartz 4 petedunnite 2 rothkopf and fehr 1998 the stability field of zn feldspar is restricted to pressures 3 o 8 component in addition to ca znsi 3 o 8 we recommend inclusion of zn in analysis of feldspars from such paragenesis

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

velocity distribution in snow avalanches in order to investigate the detailed structure of snow avalanches we have made snow flow experiments at the miyanomori ski jump in sapporo and systematic observations in the shiai dani kurobe canyon in the winter of 1995 1996 a new device to measure static pressures was used to estimate velocities in the snow cloud that develops above the flowing layer of avalanches measurements during a large avalanche in the shiai dani which damaged and destroyed some instruments indicate velocities increased rapidly to more than 50 m s soon after the front velocities decreased gradually in the following 10 s velocities of the lower flowing layer were also calculated by differencing measurement of impact pressure both recordings in the snow cloud and in the flowing layer changed with a similar trend and suggest a close interaction between the two layers in addition the velocity showed a periodic change power spectrum analysis of the impact pressure and the static pressure depression showed a strong peak at a frequency between 4 and 6 hz which might imply the existence of either ordered structure or a series of surges in the flow

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

modeling the oxygen isotopic composition of the north american ice sheet and its effect on the isotopic composition of the ocean during the last glacial cycle contribution to the change of seawater d 18 o dw between the last glacial maximum lgm and the holocene and to evaluate the effect of nonequilibrium isotopic composition of the nais on the relationship between ice volume variations and the ocean isotopic enrichment the enrichment due to the nais at the lgm was 0 63 corresponding to 60 of the lgm sea level lowstand and to a mean d 18 o of the nais of approximately 31 the modeled nais volume variations and the induced dw changes over the past 120 000 years indicated no significant time lag the inaccuracy associated with linearly inferring ice volume variations from dw changes was generally less than 10 citation sima a a paul m schulz and j oerlemans 2006 modeling the oxygen isotopic composition of the north american ice sheet and its effect on the isotopic composition of the ocean during the last glacial cycle geophys res lett 33 l15706 doi 10 1029 2006gl026923

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

identifying the causes of sea level change global mean sea level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades a review of the latest work shows that global mean sea level rise is unlikely to exceed one metre over the twenty first century but regional departures from this global mean could reach several decimetres

geology petrography and mineral chemistry of the vazante non sulfide and ambrosia and fagundes sulfide rich carbonate hosted zn pb deposits minas gerais brazil the vazante paracatu region represents the most important zn district known in brazil and includes the vazante hypogene non sulfide zn deposit composed mainly of willemite zn2sio4 and sphalerite rich carbonate hosted zn pb deposits fagundes is a stratabound deposit characterized by strong silicification dolomitization and a fe rich carbonate alteration halo the main ore is represented by rhythmically banded colloform and zoned pyrite sphalerite and galena related to wall rock dissolution and sulfide infilling which probably occurs late during the burial diagenesis later veins and breccia ore types reflect epigenetic mobilization related to brittle ductile structures the ambrosia mineralization is mainly fault controlled and related to brecciated dolomite which is tectonically imbricated with black shales and slates typical features include host rock recrystallization minor silicification baroque dolomite and ankerite formation pyrite marcasite sphalerite and minor galena occur in brecciated comb veins and veinlets which overprint stylolites and tectonic fractures suggesting an epigenetic origin for the ore the vazante deposit differs from all other deposits of the district due to the presence of willemitic ore which is composed of willemite dolomite siderite quartz hematite zn rich chlorite barite franklinite and zincite the willemitic ore occurs tectonically imbricate to small sulfide ore bodies which comprises sphalerite and galena metabasites and hydrothermalized dolomites within the vazante shear zone the relationships between willemite formation and the development of mylonitic structures suggest that willemitic mineralization and deformation are synchronous episodes closely related to the vazante shear zone low zn cd ratios in sphalerite from vazante 64 to 98 and fagundes colloform 96 to 244 and zoned sphalerite 89 to 305 could reflect the regional role of mineralizing fluids with similar low zn cd ratios and low contents of reduced sulfur sred high ge up to 2200 ppm and the low fe cu mn and ag contents in late diagenetic fagundes sphalerite might suggest that this metal bearing fluid could be derived from the underlying basin fill which comprise clastic sediments and organic matter rich pelitic sequences systematic relationships among sphalerite composition and paragenetic evolution of the fagundes and ambrosia deposits suggest that progressive fluid mixing processes were important for the genesis of the sulfide rich deposits in the district these mixing processes possibly involved the hot metal bearing fluid with low contents of reduced sulfur and moderate temperature highly saline fluids which could represent an important sulfur supply the predominance of the highly saline brines in later epigenetic mineralization episodes might be related to episodic migration of hydrothermal fluids mainly derived from reduced shale sequences during the brasiliano compressive events the small variation in chemical and sulfur isotopic composition of the vazante sphalerite could imply that the high temperature metal bearing fluid with low zn cd ratios could represent a minor reservoir of reduced sulfur which permitted only subordinate sphalerite precipitation in the vazante deposit the lack of reduced shale sequences above the vazante deposit could represent a limiting factor for h2s supply additionally overall mixture between this hot sulfur deficient metal bearing fluid and meteoric fluids channeled to the vazante shear zone favor the high fo2 s2 conditions responsible for the stability of the vazante willemitic assemblage

the compositional variation of synthetic sodic amphiboles at high and ultra high pressures sodic amphiboles in high pressure and ultra high pressure uhp metamorphic rocks are complex solid solutions in the system na2o mgo al2o3 sio2 h2o nmash whose compositions vary with pressure and temperature we conducted piston cylinder experi ments at 20 30 kbar and 700 800 c to investigate the stability and compositional variations of sodic amphi boles based on the reaction glaucophanea 2jade ite talc by using the starting assemblage of natural glaucophane talc and quartz with synthetic jadeite a close approach to equilibrium was achieved by performing compositional reversals by evaluating compositional changes with time and by suppressing the formation of na phyllosilicates stem observations show that the abundance of wide chain structures in the synthetic amphiboles is low an important feature of sodic amphibole in the nmash system is that the assemblage jadeite talc a quartz does not fix its com position at glaucophane this is because other amphi bole species such as cummingtonite cm nyboite nyb al na cummingtonite al na cm and sodium anthophyllite na anth are also buaered via the model reactions 3cummingtonite 4quartz 4h2oa 7talc nyboite 3quartza 3jadeite talc 3al na cumming tonite 11quartz 2h2oa 6jadeite 5talc and 3 sodium anthophyllite 13quartz 4h2oa 3 jade itea 7talc we observed that at all pressures and tem peratures investigated the compositions of newly grown amphiboles deviate significantly from stoichiometric glaucophane due to varying substitutions of al iv for si mg on the m 4 site and na on the a site the deviation can be described chiefly by two compositional vectors na a al iv h a si edenite toward nyboite and na m4 al vi mg m4 mg vi toward cummington ite the extent of nyboite and cummingtonite substitu tion increases with temperature and decreases with pressure in the experiments similar compositional vari ations occur in sodic amphiboles from uhp rocks the experimentally calibrated compositional changes therefore may prove useful for thermobarometric applications

matrix deformation mechanisms in hp lt tectonic melanges microstructural record of jadeite blueschist from the franciscan complex california abstract exhumed high pressure low temperature metamorphic melanges of tectonic origin are believed to reflect high strain accumulated in large scale interplate shear zones during subduction rigid blocks of widely varying size are embedded in a weak matrix which takes up the deformation and controls the rheology of the composite the microfabrics of a highly deformed jadeite blueschist from the franciscan complex california are investigated to help understand deformation mechanisms at depth the specimen shows a transposed foliation with dismembered fold hinges and boudinage structures several generations of open fractures have been sealed to become veins at high pressure metamorphic conditions the shape of these veins frequently restricted to specific layers indicates distributed host rock deformation during and after sealing small cracks in jadeite and lawsonite are healed with tiny quartz inclusions aligned along the former fracture surface large jadeite porphyroblasts show strain caps and strain shadows open fractures are sealed by quartz and new jadeite epitactically grown on the broken host monophase glaucophane aggregates consist of undeformed needles with a diameter between 0 1 and 2 m grown after formation of isoclinal folds only quartz microfabrics indicate some stage of crystal plastic deformation followed by annealing and grain growth aragonite in the latest vein generation shows retrogression to calcite along its rims the entire deformation happened under hp lt metamorphic conditions in the stability field of jadeite and quartz at temperatures between 300 and 450 c and pressures exceeding 1 1 4 gpa the microfabrics indicate that dissolution precipitation creep was the predominant deformation mechanism accompanied by brittle failure and vein formation at quasi lithostatic pore fluid pressure this indicates low flow strength and combined with high strain rates expected for localized deformation between the plates a very low viscosity of material in the interplate shear zone at a depth 30 45 km

the carbonate hosted willemite prospects of the zambezi metamorphic belt zambia zambian willemite zn2sio4 deposits occur in the metasedimentary carbonate rocks of the proterozoic katangan supergroup the most important orebodies are located around kabwe and contain both sulphides and willemite in dolomites of low metamorphic grade the star zinc and excelsior prospects lusaka area discovered in the early 1920s occur in the metamorphic lithotypes of the late proterozoic zambezi supracrustal sequence which were deposited in a transtensional basin formed during the oblique collision of the kalahari and congo cratons the deposits are hosted by the limestone and dolomitic marbles of the cheta and lusaka formations structural analysis indicates that several fracture sets host the deposits which may be genetically related to the pan african mwembeshi dislocation zone a major geotectonic boundary between the lufilian arc and the zambezi belt in both prospects willemite replaces the marbles and is found along joints and fissures with open space filling textures and locally may develop colloform and vuggy fabrics as well silver as well as traces of germanium and cadmium have been detected within the willemite ore and lead or zinc sulphides are scarce or absent calcite locally replaces willemite willemite is associated with specular hematite and franklinite and post dates the zn spinel gahnite in the paragenesis genthelvite zn4be3 sio4 3s occurs as a minor phase in irregular aggregates the willemites from the lusaka area though mn poor show green cathodoluminescence colours and bright green fluorescence in short wave uv as the high temperature willemites in usa thermometric analyses of primary fluid inclusions in willemite yield homogenization temperatures that range from 160 c to 240 c and salinities of 8 16 wt equiv nacl the homogenization temperatures suggest a hypogene hydrothermal origin for the willemite concentrations the geochemistry of fluid inclusion leachates suggests that the hydrothermal fluids were brines derived from highly evaporated seawater precise age constraints are currently lacking for the lusaka area deposits though the deposits are not deformed indicating that they post date the lufilian orogeny 520 ma the possibility of precursor ores exists the gahnite franklinite willemite deposits could have been derived from a metamorphosed primary sulphide or even nonsulphide concentration that has subsequently been completely destroyed however there is no real evidence of such a primary source for the willemite mineral association the lusaka zinc ores may have been produced by an extensive hydrothermal system with fluids discharging along basinal fracture zones controlled by the pre pan african rifting stage a paragenesis similar to that of the lusaka prospects has been proposed to be a vector towards massive sulphide ores in several parts of the world therefore it is possible that these small willemite showings in zambia may be part of a much bigger and still unexplored zinc province

metamorphic rocks in the antarctic peninsula region the distribution of metamorphic rocks in the antarctic peninsula region new quantitative peak pressure temperature data along the antarctic peninsula and a literature review on the current knowledge of metamorphic conditions in the antarctic peninsula region have been compiled into a single metamorphic map the pressure temperature data for the antarctic peninsula indicate 1 burial of supracrustal rocks to low to mid crustal depth along the eastern and western side of the antarctic peninsula and on some islands adjacent to the western side of the peninsula 2 uplift of lower to mid crustal metamorphic rocks along major shear and fault zones and 3 a reversed succession of metamorphic grades for the western domain of the antarctic peninsula region compared to the eastern domain along the eastern palmer land shear zone eplsz of the antarctic peninsula the metamorphic data are consistent with oblique convergence between alexander island the western domain palmer land central domain and the gondwana margin the eastern domain supporting a model of 1 exhumation and shearing of the higher pressure rocks from central western up to 9 4 kbar and from northeast 7 kbar to 9 kbar palmer land 2 the exhumation and shearing of low to medium pressure rocks in western palmer land and along the eastern palmer land shear zone and 3 shallow burial and subsequent exhumation of sediments of the gondwana margin along the eastern palmer land shear zone based on the high amphibolite grade rocks exposed in central western palmer land our data also support earlier suggestions that the eastern palmer land shear zone is the surface expression of a northwest to west dipping deep level high temperature crustal shear zone extending below the western part of the central domain of the antarctic peninsula

the 100 kyr ice age cycle internal oscillation or inclinational forcing the ice age hypothesis of muller and macdonald 1995 1997a 1997b has two parts a the 100 kyr cycle does not owe its existence to milankovitch forcing and b variations in inclination of earth s orbit i e the orbit s angle with the solar system invariable plane provide the mechanism sought in support of the first proposition muller and macdonald point to the paradox that the spectrum of oxygen isotope series from deep sea sediments contains no power for two prominent eccentricity cycles 125 and 400 kyr in support of the second proposition they offer a match between the specmap record imbrie et al 1984 and a plot of the amplitude of orbital inclination shifted by 33 kyr the hypothesis of muller and macdonald is rejected in both parts although an influence of inclination forcing is not precluded entirely the paradox of the missing eccentricity cycles 125 and 400 kyr is explained by suppression of the two longer cycles and enhancement of the one near 96 kyr as a result of internal oscillation a muller macdonald machine for making the 100 kyr ice age cycles however conceived would have to have a memory near 30 kyr to provide for phase shift between input and output precisely this amount of memory is sufficient to produce the needed oscillation in milankovitch machine here applied thus there is no advantage from the point of view of either necessity or simplicity in replacing milankovitch forcing with its precise phasing despite the fuzzy physics with inclination forcing and with its severe problems in phasing and thus far no physics at all

late quaternary bottom current activity in the south aegean sea reflecting climate driven dense water production abstract the eastern mediterranean transient emt represents a recent early 1990s to today water circulation phenomenon during which more arid climatic conditions in the mediterranean lead to the production of very dense surface water masses in the north aegean sea the produced north aegean dense water nadw sinks to seafloor flows to the south aegean sea and then spills into the eastern mediterranean sea through the cretan straits contributing to the rejuvenation of the bottom water a large dataset of vintage high resolution seismic reflection profiles indicates that the floors of the basins in the southwest aegean sea are characterised by late quaternary erosional gullies abraded surfaces and channel related sediment drifts such structures provide evidence for the presence of strong bottom currents which originate from the southward propagation of nadw masses the basins have depths of 300 m to 1000 m and are connected to each other by narrow a few km straits and sills the dominance of abraded surfaces and erosional gullies on the northern flank of the basins and in the narrow straits sills between them provides evidence that the southward propagation of the nadw occurs by the filling and flooding of each basin by dense water which then spills and cascades into the next basin southward seismic stratigraphy suggests that the formation of the drifts started at marine isotope stage mis 11 420 ka bp the coincidence of at least three erosional surfaces within the sediment drifts with interglacial mis 11 5 and 1 respectively suggests that bottom currents were mostly active during high sea level stands and sluggish during glacial low sea level stands a 90 100 m drop of the sea level below the current level would have resulted in the emergence of the eastern cyclades plateau and thus in the disconnection of the southwest aegean sea from the north aegean sea several 0 05 0 5 m thick beds of gravelly sand with algal and mollusc debris laminated to mottled sand and mottled mud are observed in the sediment cores analysed in this paper these beds can be confidently correlated from core to core and are interpreted as bottom current deposits the separation of these beds by hemipelagic sediments indicates that bottom current activity in the southwest aegean is not permanently established but episodic six episodes of intense bottom current activity are recorded in the mis 2 4 10 80 ka sediments and they appear to correlate well with the cold and dry younger dryas and heinrich 3 4 5 6 and 7 events in contrast at least three episodes of intense bottom current activity are recorded in the cores during the holocene the higher frequency of strong bottom current episodes in the southwest aegean sea during the holocene is attributed to the higher sea level stand that makes the circulation of water masses in the aegean sea more sensitive to climatic changes

pyroxene composition as an indicator in the classification of skarn deposits the chemical compositions of pyroxenes from 46 skarn deposits in japan were statistically examined after compiling published and newly analyzed compositional data in order to put constraints on skarn metallogeny the mn fe ratio and zn content of pyroxene in each deposit are relatively constant and tend to vary regionally in accordance with metal type most pyroxenes of cu fe deposits are characterized by a low mn fe ratio 0 2 and a high zn content 200 ppm pyroxenes of w deposits have an intermediate mn fe ratio around 0 15 and a very high zn content especially those of w sn f deposits 500 ppm the systematic relation between the pyroxene composition and the metal type extends to the mn fe ratio and cd content of skarn sphalerites these compositional features of pyroxenes and sphalerites seem to indicate that the proportion of fe mn zn and cd contents in hydrothermal fluids did not change significantly from the time of pyroxene formation to the period of the later sulfide deposition on the scale of the deposit the mn fe ratio and zn content of skarn pyroxene can serve as an additional aid in the classification and defining of the environment of skarn formation

mixing properties and stability of jadeite acmite pyroxene in the presence of albite and quartz the stability of synthetic jadeite acmite pyroxene coexisting with albite and quartz has been determined at 600 700 and 900 c the end member reaction albite jadeite quartz has been determined to lie between 1 67 and 1 70 gpa at 600 c 1 88 and 1 90 gpa at 700 c and 2 44 and 2 48 gpa at 900 c jd78acm22 quartz is stable above 1 58 1 78 and 2 33 gpa at 600 700 and 900 c respectively jd61acm39 quartz is stable above 1 47 1 67 and 2 18 gpa at 600 700 and 900 c respectively addition of as much as 40 of acmite component in jadeite extends pyroxene stability by less than 300 mpa at 900 c unit cell parameters measured for synthetic jadeite acmite pyroxenes indicate linear volume composition relations the data are consistent with ideal mixing in jadeite acmite solutions

the deglaciation of the northern hemisphere a global perspective orbitally induced increase in northern summer insolation after growth of a large ice sheet triggered deglaciation and associated global warming ice albedo sealevel and greenhouse gas feedbacks together with tropical warming from weakening winds in response to polar amplification of warming caused regionalto global near synchronization of deglaciation effects were larger at orbital rather than millennial frequencies because ice sheets and carbon dioxide vary slowly ice sheet linked changes in freshwater delivery to the north atlantic and possibly free oscillations in the climate system forced millennial climate oscillations associated with changes in north atlantic deep water nadw flow the north atlantic typically operates in one of three modes modern glacial and heinrich deglaciation occurred from a glacial mode ocean that in comparison to modern had shallower depth of penetration of nadw formed further south causing strong northern cooling and the widespread cold dry and windy conditions associated with the glacial maximum and the cold phases of the millennial dansgaard oeschger oscillations the glacial mode was punctuated by meltwater forced heinrich conditions that caused only small additional cooling at high northern latitudes but greatly reduced the formation of nadw and triggered an oceanic seesaw that warmed some high latitude southern regions centered in the south atlantic

danube loess stratigraphy towards a pan european loess stratigraphic model abstract the danube river drainage basin is the second largest river catchment in europe and contains a significant and extensive region of thick loess deposits that preserve a record of a wide variety of recent and past environments indeed the danube river and tributaries may themselves be responsible for the transportation of large volumes of silt that ultimately drive loess formation in the middle and lower reaches of this large catchment however this vast loess province lacks a unified stratigraphic scheme european loess research started in the late 17th century in the danube basin with the work of count luigi ferdinand marsigli since that time numerous investigations provided the basis for the pioneering stratigraphic framework proposed initially by kukla 1970 1977 in his correlations of loess with deep sea sediments loess palaeosol sequences in the middle and lower reaches of the danube river basin were a key part of this framework and contain some of the longest and most complete continental climate records in europe covering more than the last million years however the very size of the danube loess belt and the large number of countries it covers presents a major limiting factor in developing a unified approach that enables continental scale analysis of the deposits local loess palaeosol stratigraphic schemes have been defined separately in different countries and the difficulties in correlating such schemes which often change significantly with advances in age dating have limited the number of basin wide studies a unified basin wide stratigraphic model would greatly alleviate these difficulties and facilitate research into the wider significance of these loess records therefore we review the existing stratigraphic schemes and define a new danube basin wide loess stratigraphy based around a synthetic type section of the mosorin and stari slankamen sites in serbia we present a detailed comparison with the sedimentological and palaeoclimatic records preserved in sediments of the chinese loess plateau with the oxygen isotope records from deep sea sediments and with classic european pleistocene stratigraphic subdivisions the hierarchy of danubian stratigraphic units is determined by climatically controlled environmental shifts in a similar way to the chinese loess stratigraphic scheme a new unified danube loess stratigraphic model has a number of advantages including preventing confusion resulting from the use of multiple national schemes a more transparent basis and the potential to set pleistocene palaeoenvironmental changes recorded in the danube catchment area into a global context the use of a very simple labelling system based on the well established chinese loess scheme facilitates interpretation of palaeoenvironmental information reported from the danube basin loess sites in a wider more accessible context that can be readily correlated world wide this stratigraphic approach also provides for the first time an appropriate framework for the development of an integrated pan european and potentially pan eurasian loess stratigraphic scheme

origin of a carbonate hosted fe mn ba as pb sb w deposit of langban type in central sweden the sjogruvan deposit is one of the langban type fe mn oxide deposits hosted by marble interbeds within svecofennian metavolcanic rocks in the bergslagen region central sweden mineralogical and geochemical studies have been carried out to clarify the premetamorphic origin of this type of deposit which is set apart from most other mn mineralizations by a significant enrichment in ba as sb pb w and be contained by various oxyminerals the principal ore types at sjogruvan are 1 hematite quartz magnetite 2 hausmannite calcite tephroite and 3 braunite celsian phlogopite the mn ores are compositionally akin to modern mn deposits formed by submarine hydrothermal processes with a high mn fe ratio and low contents of co ni th u and ree and likely owe their existence to similar mechanisms of formation pb isotope data indicate that the metal source and timing of deposition is similar to the major stratabound base metal and iron deposits in bergslagen all the key elements have been leached from the local felsic volcanic units and were deposited on the sea floor the excellent mn fe separation occurred in an eh ph gradient that essentially corresponded to the mixing zone of hydrothermal solutions and seawater the braunite ore is chemically distinct from the hausmannite ore with a high concentration of refractory elements al ti zr and a positive ce anomaly which indicate a detrital hydrogenetic contribution to its protolith carbon isotope 13c values around 0 relative pdb suggest that carbonates in the deposit formed directly from seawater

control of paleoshorelines by trench forebulge uplift loyalty islands abstract unlike most tropical pacific islands which lie along island arcs or hotspot chains the loyalty islands between new caledonia and vanuatu owe their existence and morphology to the uplift of pre existing atolls on the flexural forebulge of the new hebrides trench the configuration and topography of each island is a function of distance from the crest of the uplifted forebulge both mare and lifou are fully emergent paleoatolls upon which ancient barrier reefs form highstanding annular ridges that enclose interior plateaus representing paleolagoon floors whereas the partially emergent ouvea paleoatoll rim flanks a drowned remnant lagoon emergent paleoshoreline features exposed by island uplift include paleoreef flats constructed as ancient fringing reefs built to past low tide levels and emergent tidal notches incised at past high tide levels present paleoshoreline elevations record uplift rates of the islands since last interglacial and mid holocene highstands in global and regional sea levels respectively and paleoreef stratigraphy reflects net quaternary island emergence the empirical uplift rates vary in harmony with theoretical uplift rates inferred from the different positions of the islands in transit across the trench forebulge at the trench subduction rate the loyalty islands provide a case study of island environments controlled primarily by neotectonics

controls on the distribution and growth of isolated carbonate build ups in the timor sea nw australia during the quaternary abstract isolated carbonate build ups icbs represent attractive hydrocarbon exploration targets they are often seen as long term transgressive features but their distribution within basins and growth history can be difficult to predict as they respond to the interplay between various tectonic eustatic and oceanographic parameters here we use a 3d seismic megasurvey 18 000 km2 combined with well data to understand the timing and mechanisms of formation of tropical quaternary icbs in nw australia at present the icbs are typically 1 30 km wide and form clusters of 150 build ups developing 2 85 km from the edge of a 650 km wide continental shelf our results demonstrate that the structural evolution of the margin had a major impact on the distribution of the icbs main period of fault activity commenced during the latest miocene early pliocene corresponding to the initial collision of the australian plate with banda arc fault activity increased from late pliocene and peaked during the early pleistocene it was associated with flexural reactivation of structural highs uplift and lows subsidence along the shelf margin seismic evidence of moat channel and drift deposits suggest that contour current activity intensified during the late early pleistocene ca 1 ma bp despite potentially good conditions for carbonate production basement highs and warm water ocean currents icbs did not form until the mid pleistocene ca 0 582 0 8 ma bp this age corresponds to the onset of major sea level fluctuations associated with repeated high amplitude 120 m rapid deglacial rises and slow falls thus we infer that the nw australia icbs formed due to 1 structural shaping of the margin 2 oceanographic changes and most importantly 3 onset of repeated high amplitude transgressions reactivating the carbonate production along isolated highs following 4th 5th order lowstand exposures and allowing catching up carbonate morphologies to develop

isotopic evidence for channeled fluid flow in low grade metamorphosed jurassic accretionary complex in the northern chichibu belt western shikoku japan the low grade metamorphosed jurassic accretionary complex of the northern chichibu belt hijikawa area western shikoku is divided into two units the hijikawa and kanogawa units that are separated by an out of sequence thrust oost the ozu kawabegawa fault the kanogawa unit south of the ozu kawabegawa fault consists mainly of sandstone shale broken formation of alternating sandstone and shale greenstone chert and pelitic melange while the hijikawa unit is characterized by a stack of subunits separated by small scale thrusts the subunits are mainly made up of basic pelitic and psammitic semischists schistose pelitic melange and chert petrological and mineralogical constraints suggest peak metamorphic conditions of 204 247 c at 1 3 kbar in the kanogawa unit and 228 289 c at 3 5 6 kbar in the hijikawa unit quartz and quartz calcite veins are widely developed in the study area especially in the hijikawa unit regional variations in stable isotopic data show that the 18oquartz and 18ocalcite values in veins tend to increase towards the ozu kawabegawa fault the 18owhole rock values are remarkably high in some subunits close to oosts within the hijikawa unit oxygen isotopic compositions from vein quartz indicate that a higher 18o fluid migrated upward from depth along the ozu kawabegawa fault within the accretionary prism during prehnite pumpellyite facies metamorphism the fluid source is inferred to be pelitic rocks at higher temperatures and greater depths within the accretionary prism

petedunnite caznsi 2 o 6 a new zinc clinopyroxene from franklin new jersey and phase equilibria for zincian pyroxenes

sea level in the late quaternary patterns of variation and implications studies of oxygen isotopes in foraminifers from deepsea sediments yield information about rates of change of sea level for hundreds of thousands of years with a resolution of roughly 1 000 years the statistics regarding fluctuations for the late quaternary the last 900 000 years suggest that a rise of 10 m per 1 000 years 1 m per century is not unusual even when the system resides within a warm stage as now values near 2 m per century while rare are well within the range of a warm system beyond the 5 percentile of the overall range once sea level is near 10 m further rise becomes highly unlikely within the conditions of the late quaternary suggesting the presence of some kind of natural barrier that is lack of vulnerable ice the present volume of ice generally considered vulnerable greenland and west antarctic ice sheet adds up roughly to the observed limit

stratigraphic architecture and spatio temporal variability of high frequency milankovitch depositional cycles on modern continental margins an overview abstract this study is a review of quaternary milankovitch cycles as recorded on modern continental shelves worldwide on the background of the many existing examples we focus on selected case studies from mediterranean adriatic and tyrrhenian seas and atlantic gulfs of mexico and cadiz margins that represent general and peculiar characters of middle upper pleistocene sequences forming under the control of composite 100 and 20 ka milankovitch cycles the most pervasive stratigraphic pattern displayed by shelf deposits is referred to the 100 ka sea level cycle and consists of fairly uniform depositional sequences mostly composed by regressive deposits forming during the falling limb of the sea level curve these are generally classified as falling stage systems tract fsst and display a regressive facies architecture reflecting the dominant control of sea level on many margins fsst units may show slight though significant differences with respect to highstand systems tract hst and lowstand systems tract lst regressive units more closely reflecting environmental changes and the local variability of depositional systems in contrast with the theoretical and overall scale independent model developed to predict composite stratigraphic cycles and sequences the middle upper pleistocene stratigraphic record from numerous shelf settings shows a subdued signature of the higher frequency 20 ka milankovitch cyclicity however when detectable the 20 ka architectural pattern is characterized by a relatively greater spatial and temporal variability compared to 100 ka sequences this fact likely reflects the increasing importance of factors controlling the depositional environment e g seafloor morphology oceanographic regime sediment input and dispersal etc with respect to sea level change during the shorter intervals encompassed by 20 ka cycles on this basis two end member cases have been distinguished depending on the generation or not of high frequency sequence boundaries a prerequisite to qualify the higher frequency motifs as depositional sequences these two end members are comprehensive of the highly variable patterns displayed by middle upper pleistocene shelf sequences which in turn reflect the interplay between the geological setting the dominant sea level control and the effective response of sedimentary systems the variable stratigraphic patterns of milankovitch cycles represent conceptual and practical constraints as to the classification of high frequency quaternary sequences under the general schemes of the standard sequence stratigraphy model

experimentally determined compositions of diopside jadeite pyroxene in equilibrium with albite and quartz at 1200 1350 c and 15 34 kbar abstract equilibrium compositions of diopside jadeite pyroxene coexisting with albite and quartz were experimentally determined at 25 different p t conditions using an electron microprobe for analysis the new data and the 600 c data of holland 1983 provided the following mixing properties of the diopside di jadeite jd solid solution j k g xs x jd x di 12600 9 45 t 12600 7 6 t x jd x di 21400 16 2 t x jd x di 2 the di jd solution is close to ideal above 1000 c but immiscible below 565 c the di jd solvus is slightly asymmetric with the crest at composition di 42 4 jd 57 6 excess enthalpy is positive but smaller than indicated by the enthalpy of solution measurements of wood et al 1980 disorder in the di jd solution is significantly smaller than complete disorder implied by the ionic two site model

a study of the size of snow particles in powder snow avalanches in this work we study the size of the particles involved in a powder snow avalanche phenomenon to determine these sizes we study all the phenomena the particles have to face before arriving in the body of the avalanche we study the boundary layer which is at the bottom of the avalanche we determine with the help of experimental data the range of size of the particles that can be entrained by the avalanche we then examine the possibility for these particles to reach the top of the boundary layer and so to take part in the avalanche our final result is that the more frequent particles suspended in a powder snow avalanche have a size lower than 200 micrometers

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

stable isotope and petrologic evidence for the origin of regional marble hosted magnetite deposits and the zinc deposits at franklin and sterling hill new jersey highlands united states mesoproterozoic marble in the new jersey highlands hosts small magnetite deposits that occur in discrete groups along linear trends and are concentrated mainly in the western part of the region magnetite also forms a layer structurally beneath the zn fe mn orebody at the franklin mine marble host rocks are interlayered at fe and zn fe mn deposits with bimodal metavolcanic rocks amphibolite and rhyolitic gneiss that were deposited synchronously in a back arc basin developed on the eastern margin of laurentia between 1 3 and 1 25 ga magnetite in the deposits ranges from massive to disseminated and is characterized by low ti variable mn and locally high s concentrations of as v sb and zn are enriched in magnetite compared to marble host rocks and associated metavolcanic rocks carbon and oxygen isotope ratios of the marbles are consistent with water rock interaction between the marble protolith and a mixture of igneous fluids and seawater regional geology petrology and isotope data indicate that fe was introduced into the carbonate protolith as low temperature fe oxides and hydroxides via hydrothermal fluids discharged along basinal fracture zones on the sea floor related marble hosted zn fe mn deposits at franklin and sterling hill contain the assemblage willemite zincite franklinite stable isotope compositions of the zn deposits are consistent with alteration of host rocks by water rich fluids preserving protolith carbon isotope ratios stable isotope modeling suggests that zn silicate oxides or hydroxides represent an appropriate protolith for the high grade zn ores alteration of metavolcanic rocks at the fe deposits combined with the isotope data and other petrologic and geochemical evidence document the presence of an extensive hydrothermal system of grenville age centered in the western highlands metals precipitating from this hydrothermal system were responsible for fe in the marble hosted magnetite deposits and zn in the deposits at franklin and sterling hill from the same or a related hydrothermal system underplating of the back arc by mafic magma provided the heat to melt the lower crust and drive the hydrothermal system resulting in carbonate hosted fe and zn ore deposits and associated bimodal volcanism

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

quaternary oceans and climate change lessons for the future there is much interest in ice age studies in recent decades in the context of global warming the relevant findings are these large regular changes in climate occurred within the last million years especially in the northern north atlantic extreme conditions were similar suggesting strong negative feedback at the edges of the range of variation the nature of the periods of climate variation suggests orbital forcing by modulation of internal oscillations involving lagged negative feedback on ice buildup transitions from cold to warm were rapid and they were not readily reversed indicating that ice dynamics underlies abrupt climate change accelerated rates of ice decay upon warming correspond to a sea level rise of one to two m century millennial scale abrupt disturbances known as dansgaard oeschger and heinrich events occur when large ice masses are present in the northern hemisphere they may be considered experiments on the ocean s response to massive meltwater input when using results from ice age studies to project future developments one must be aware that the future will be largely outside of experience with regard to the recent geologic past also there are as yet no generally accepted explanations for striking changes in the past such as the rapid rise of carbon dioxide during deglaciation demonstrating a profound lack of understanding of climate dynamics this is so far the lesson from ice age studies they say much about the deficiencies in our level of understanding and not so much about what is ahead

reconstruction of atmospheric co2 from ice core data and the deep sea record of ontong java plateau the milankovitch chron we provide a reconstruction of atmospheric co2 from deep sea sediments for the past 625000 years milankovitch chron our database consists of a milankovitch template of sea level variation in combination with a unique data set for the deep sea record for ontong java plateau in the western equatorial pacific we redate the vostok ice core data of barnola et al 1987 to make the reconstructions we employ multiple regression between deep sea data on one hand and ice core co2 data in antarctica on the other the patterns of correlation suggest that the main factors controlling atmospheric co2 can be described as a combination of sea level state and sea level change for best results squared values of state and change are used the square of sea level rule agrees with the concept that shelf processes are important modulators of atmospheric co2 e g budgets of shelf organic carbon and shelf carbonate nitrate reduction the square of change rule implies that on short timescales any major disturbance of the system results in a temporary rise in atmospheric co2

rapid quench hydrothermal experiments at mantle pressures and temperatures new experimental methods for the encapsulation extraction and analysis of large volumes of aqueous fluids enable studies of mineral solubilities and dissolution kinetics with the piston cylinder apparatus quench rates and volumes of experimental fluids with these methods are comparable with those used in modern hydrothermal experiments employing cold seal vessels analyses of fluid compositions are reproducible and consistent with independent results the techniques permit experimental investigations that will better characterize fluid rock interaction in such environments as subducting slabs the mantle wedge barrovian metamorphic belts and middle to lower crustal granulites