quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

holocene climate variability and change a data based review the holocene thermal maximum with peak temperatures prior to 7 ka bp is mostly accentuated in the northern hemisphere still visible in the southern hemisphere and possibly did not exist in the tropics between this period and the modern warming a remarkable negative temperature trend occurred in the northern hemisphere which was probably the effect of a decreasing orbital induced insolation during the boreal summer on average the northern hemisphere humidity precipitation records do not show any significant trend a mechanistic explanation for the multi decadal to century scale holocene cold relapses which mainly occurred in the atlantic european regions exists for only the early holocene cooling events which are probably the result of a collapse of the meridional overturning circulation owing to freshwater outbursts from the laurentide ice sheet possibly the late holocene cold events after c 4 ka bp are influenced by the covarying influence of major tropical volcanic eruptions and grand solar minima

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

conventional and in situ geochronology of the tepla crystalline unit bohemian massif implications for the processes involving monazite formation the tepla crystalline unit tcu western bohemian massif proves highly suitable for studying the effects of differential metamorphic reworking on the u th pb systematics in monazite as the overprint of variscan regional metamorphism onto high grade cadomian paragneisses intensifies progressively towards the northwest although variably hampered by scarcity small size and low uranium contents of monazite isotope dilution thermal ionisation mass spectrometry of monazite from paragneisses from the garnet staurolite and kyanite zones of the tcu gives a narrow 206pb 238u age range from 387 to 382 ma for variscan peak metamorphism these data are supported by 382 373 ma monazite ages derived from electron microprobe analyses inheritance of older components in grains from the central tcu imply major resetting of pre variscan monazite around 380 ma possibly due to widespread garnet growth during variscan metamorphism which led to the consumption of pre variscan high y monazite and subsequent growth of new low y monazite concordant 498 494 ma monazite ages in a migmatitic paragneiss close to the adjacent marianske lazn complex mlc grew in response to metagabbro emplacement in the mlc from 503 to 496 ma and not during either cadomian or variscan regional metamorphism backscatter imaging and electron microprobe analyses reveal that discordant monazite of the migmatite comprises a mix of various age domains that range from ca 540 to 380 ma combined evidence presented here suggests that instead of pb loss by volume diffusion the apparent resetting of the u th pb systematics in monazite rather involves new crystal growth or regrowth by recrystallisation and dissolution reprecipitation

two generations of variscan garnet implications from a petrochronological study of a high grade avalonia derived paragneiss from the drosendorf unit bohemian massif abstract garnets in metapelitic paragneisses from the southern drosendorf unit in the austrian part of the bohemian massif exhibit two episodes of growth during the variscan orogeny which can be distinguished on textural and chemical grounds the first garnet grt1 records evidence of high grade metamorphism in the late devonian frasnian famennian while the second garnet grt2 formed by a second high grade event in the early carboniferous visean both garnet generations contain abundant inclusions of which monazite rutile and crystallised melt droplets are particularly useful for reconstructing p t t conditions the late devonian age 373 9 ma for the first episode of garnet growth was obtained from chemical dating of monazite inclusions in grt1 metamorphic conditions during the first episode of garnet growth are estimated to have been between 0 7 and 0 8 gpa at 680 700 c and 0 95 1 10 gpa at 745 785 c there followed a phase of cooling and exhumation after which the second garnet grt2 were formed beginning under amphibolite facies conditions and continuing prograde to peak conditions of 0 95 1 10 gpa and 745 785 c which are similar to those of the first garnet forming event subsequently the rocks experienced near isothermal decompression to 0 5 0 8 gpa chemical dating of both monazite inclusions in grt2 and the matrix provide a visean age 343 3 ma a study of detrital zircons in these paragneisses revealed zircon forming events at around 1 2 1 5 and 1 8 ga suggesting an avalonian provenance the lack of zircons younger than 1 ga and the presence of cadomian metamorphic monazite relics 652 15 ma indicates an early neoproterozoic deposition age for the sedimentary protolith likely our documentation of a late devonian high grade metamorphic event in rocks derived from avalonian corroborates tectonic models which assume that frontal parts of the armorican terrane had already docked with avalonia by this time

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

shrimp and electron microprobe chronology of uht metamorphism in the napier complex east antarctica implications for zircon growth at 1 000 c zircons in ultra high temperature uht metamorphosed paragneisses from mt riiser larsen in the napier complex east antarctica were dated by using ion microprobe shrimp and electron microprobe emp both shrimp and emp analyses yield consistent 2520 2460 ma age populations for garnet orthopyroxene bearing paragneiss and leucosomes enclosed within the peak uht event was dated at 2480 ma by shrimp analyses on metamorphic zircons from the garnet orthopyroxene paragneiss and those on magmatic zircons from the leucosomes which are interpreted to be formed at syn uht as obtained by shrimp the uht metamorphic event was terminated no later than 2460 ma minor 2520 ma shrimp age suggests either the onset of prograde metamorphism or another high grade metamorphic event unrelated to the uht emp analyses on metamorphic zircons from sapphirine quartz and osumilite bearing magnesian paragneisses give c 2500 2450 ma ages inherited igneous zircon cores of the magnesian paragneisses yield relatively scattered emp ages ranging over c 3000 2650 ma suggesting that igneous materials of these ages sourced the protoliths of the paragneisses and that they were deposited during the interval c 2650 2520 ma

formation of monazite and rhabdophane at the expense of allanite during alpine low temperature retrogression of metapelitic basement rocks from crete greece microprobe data and geochronological implications abstract accessory lree bearing minerals have been investigated in a sequence of palaeozoic amphibolite facies metapelites in eastern crete greece which were overprinted by alpine low t metamorphism 300 c the series is dominated by al ca rich metapelite layers which contain palaeozoic allanite secondary alpine monazite with low y contents only in some quartz rich layers of metapelites which are allanite free is primary palaeozoic monazite to be found in such special variants alpine monazite or rhabdophane appear to be absent and the lrees remained trapped in the palaeozoic monazite not even the outermost rims of the old monazites experienced alteration during the alpine retrograde metamorphism and preserve undisturbed palaeozoic th u pb ages this observations made in this study confirm other recent work according to which in many cases monazite and not allanite is the stable lree phase under low grade metamorphic conditions rocks with primary allanite contents can be considered particularly fertile for the production of monazite at low metamorphic grades in contrast rocks without allanite but with primary monazite are unfertile for the growth of a secondary monazite generation a composite lithologically variable basement with a low temperature overprint will therefore often include both remnant and new monazite although the two monazite generations will commonly occur in different lithologies and rarely together in the same samples therefore if a cunning sampling strategy is applied monazite geochronology is capable of yielding the ages of both primary and secondary events in such settings

constraints on the timing of late eburnean metamorphism gold mineralisation and regional exhumation at damang mine ghana the damang gold deposit in southwest ghana is unique among known deposits in ghana comprising gold mineralisation in two distinct styles early gold hosted in a stratigraphically controlled auriferous quartz pebble conglomerate horizon is overprinted by later gold mineralisation contained in a sub horizontal fault fracture quartz vein array a multi system geochronological study is used to constrain the timing of igneous activity regional metamorphism gold mineralisation and the thermal history at damang u pb analysis of zircons from birimian volcaniclastic and intrusive rocks constrain volcanism and associated intrusive activity at 2178 0 9 3 ma and 2164 6 8 0 ma respectively which is consistent with previous studies the age of formation of staurolite grade amphibolite facies peak metamorphic mineral assemblages at 2005 26 ma is provided by u th total pb epma analysis of metamorphic monazite grains in the tarkwa phyllite measured 40ar 39ar biotite ages range between 1980 9 ma and 1898 11 ma argon diffusion modelling with the programme diffarg suggests that this age range could be achieved by a period of rapid cooling at a rate of approximately 17 c ma followed by a prolonged period of much slower cooling at a rate of 0 15 c ma the period of rapid cooling is interpreted to represent localised exhumation of the damang host rocks during the latest stage of the eburnean orogeny at the time of hydrothermal gold mineralisation given these age constraints hydrothermal gold mineralisation is inferred to have occurred between approximately 2030 ma and 1980 ma these ages constrain metamorphism fluid flow and gold mineralisation at damang and are the youngest currently recognised in the birimian of sw ghana

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

multiple tectonothermal events in the granulite blocks of southern india revealed from epma dating implications on the history of supercontinents abstract we report age data on zircon monazite uraninite and huttonite from a suite of 29 samples covering four major granulite blocks in southern india using an electron microprobe technique the rocks analysed in this study cover all of the major lithounits in these terrains and include garnet bearing and garnet free charnockites garnet biotite gneisses khondalites calc silicate rocks and a suite of orthogneisses biotite gneiss biotite hornblende gneiss two pink metagranites representing the magmatic phase were also analysed zircons from the madras block yield well defined isochrons at 2 5 2 6 ga core to rim analyses of single zircon grains show age zoning with 2 6 2 9 ga igneous cores mantled by 2 4 2 5 ga rims detrital zircons show age up to ca 3 2 ga monazites in this block have cores and rims with 2 5 2 3 ga a suite of 19 samples from the madurai block brings out the multiple tectonothermal events in this terrain zircons from an orthogneiss yield well defined isochrons at 1 7 0 1 ga 0 82 0 05 ga and 0 58 0 04 ga from core inner rim and rim portions respectively zircon grains in other rocks preserve either core or secondary growth ages at 0 8 1 0 ga zircons in a pink metagranite from this block show sharply defined isochrons of 0 68 0 03 ga for the core and 0 57 0 01 ga for the secondary portion a late pan african overprint is observed throughout this block with zircon rims monazite uraninite and huttonite yielding age values in the range of 0 45 0 60 ga zircons from both the trivandrum and nagercoil blocks show a major tectonothermal event at 0 55 ga with faint indications of previous tectonothermal events during 0 8 1 0 and 1 7 2 0 ga monazite data from both the trivandrum and nagercoil blocks are essentially similar to those from the madurai block except for presence of relic monazite in the former our study confirms the notion that the palghat cauvery shear zone marks the major terrain boundary between an archean craton in the north and proterozoic terrains in the south it also strengthens the view of paleoproterozoic accretion and pan african reworking of blocks south of this shear zone the ages of production accretion and reworking in the terrains of southern india yield important information for the histories of columbia 1 8 1 5 ga rodinia 1 1 1 0 ga and gondwana 0 6 0 5 ga supercontinents the southern indian terrains formed part of a worldwide network of orogenic belts that is centered around 1 8 ga and outlines the configuration of columbia accretion of terrains in the madurai block to archean rocks north of the palghat cauvery shear zone at this time is consistent with the ages suggested to be the oldest metamorphic event in the eastern ghats orogen of eastern india and the rayner belt of coastal east antarctica our data confirm earlier evidence that all of southernmost india underwent resetting of isotopic systems during the final accretion of gondwana at the time of the pan african orogeny 0 5 ga the possibility that the trivandrum and nagercoil terrains accreted to the madurai block after 0 7 ga suggests that this pan african zone may also have involved accretion and closure of ocean basins if that happened then this zone may be the long sought suture between east and west gondwana

satellite monazites in polymetamorphic basement rocks of the alps their origin and petrological significance allanite fluorapatite reaction coronas around monazite are abundant in metamorphic rocks we report here special cases where a new generation of satellite monazite grains formed within these coronas using examples from different p t regions in the eastern alps we examine the origin and the petrological significance of this complex mineralogical association by means of the electron microprobe utilizing th u pb monazite dating and high resolution bse imaging satellite monazite grains form when a monazite bearing rock is metamorphosed in the allanite stability field partial breakdown of first generation monazite to fluorapatite plus allanite and is then heated to temperatures that permit a back reaction of fluorapatite plus allanite to secondary satellite monazite grains surrounding the remaining original first generation monazite depending on the whole rock geochemistry satellite monazites can form under upper greenschist as well as amphibolite facies conditions in each of the three examples focused on here the inherited core monazite was resistant to recrystallization and isotopic resetting even though in one of the samples the metamorphic temperatures reached 720 c this shows that in greenschist and amphibolite facies polymetamorphic rocks individual grains of inherited and newly formed monazite can and often will occur side by side the original inherited monazite will preferentially be preserved in low ca high al lithologies where its breakdown to allanite plus fluorapatite is suppressed conversely a medium or high ca monazite bearing rock will become particularly fertile for secondary monazite regrowth after passing through a phase of strong retrogression in the allanite stability field based on this knowledge specific sampling strategies for monazite dating campaigns in polymetamorphic basement can be developed

fluid mediated partial alteration in monazite the role of coupled dissolution reprecipitation in element redistribution and mass transfer monazite ce lree th u ca p si o4 with complex zoning in th and other elements is commonly observed in metamorphic and igneous rocks the hypothesis that this alteration is a product of fluid mediated element mass transfer has been tested in the piston cylinder press caf2 assembly cylindrical graphite oven at 1 000 mpa and 900 c and in cold seal autoclaves on a hydrothermal line at 500 mpa and 600 c experiments included a relatively homogeneous monazite ce 7 8 wt tho2 from a heavy mineral sand plus a series of alkali bearing fluids including 2n naoh 2n koh and na2si2o5 h2o experiments were conducted using bse imaging emp analysis and both tem and hrtem a subset of monazite grains from each experiment show evidence of partial alteration in the form of areas enriched in th si with sharp curvilinear compositional boundaries extending from the grain rim into the monazite interior these thsio4 enriched textures are similar to those commonly seen in natural examples of metasomatised monazite in both magmatic and metamorphic rocks in the na2si2o5 h2o experiments scarce inclusions of britholite formed in the altered monazite the altered monazite is also characterised by strong depletion in pb ca and y thorium and si mobility coupled with the formation of britholite inclusions during partial alteration in the monazite grain is considered to be the product of fluid aided coupled dissolution reprecipitation as opposed to solid state diffusion since other fluids including nacl and kcl brines do not result in the formation of these textures the experimental replication of thsio4 enriched areas in the monazite strongly suggests that similar textures in monazite observed in nature are fluid induced specifically by alkali bearing fluids if true complex metasomatically induced textures in monazite could yield information concerning the nature of the fluid responsible for their formation as well as allow for the dating of the metasomatic event presuming that all the original radiogenic pb has been removed

complexity in the behavior and recrystallization of monazite during high t metamorphism and fluid infiltration abstract a detailed study of monazite grains in silica undersaturated and quartz bearing mg al metapelite from the oygarden group of islands east antarctica reveals a complex history of growth and recrystallization during two separate events in the neoproterozoic and earliest cambrian monazite grains from garnet poor and garnet rich metapelite preserve core domains that have ages corresponding to growth and or recrystallization at granulite facies p 9 1 0 gpa t 850 900 c conditions during the rayner structural episode between 930 and 890 ma high th rims 22 wt tho 2 that are in textural equilibrium with sapphirine orthopyroxene symplectites formed after garnet during late rayner decompression occur on monazite grains in garnet rich assemblages and give electron microprobe ages 883 18 ma within error of core domains 903 14 ma these high th rim domains are interpreted to have formed through recrystallization of liberated inclusions via a process dominated by coupled dissolution reprecipitation reactions facilitated by transient fluid films on the large surface areas in the symplectite and not by new growth in garnet poor metapelite monazite grains that have grain boundaries in textural equilibrium with the granulite facies assemblage also show alteration to higher th compositions on rims and along vein like fractures this compositional shift is accompanied by partial to complete resetting of ages to 500 ma along with minor modification of core domain ages textures and patterns of chemical age resetting are interpreted to also be the result of a coupled dissolution reprecipitation reaction process but in contrast to garnet bearing assemblages this alteration occurred during a fluid influx at lower temperatures during regional pan african tectonism this study highlights the susceptibility of monazite to resetting with fluid present conditions dramatically increasing the potential for recrystallization

geochronology of shear zones a review abstract shear zones play a major role in the deformation of the crust at a variety of scales as expressions of strain localization during orogeny and rifting and also as reactivated structures they influence the geometry and evolution of orogenic belts and rifts crustal rheology magma ascent and emplacement and fluid flow consequently assessing the timing of shear zone activity is crucial to reconstruct the tectonometamorphic evolution of the lithosphere the interpretation of thermochronologic data from shear zones is however not straightforward in the first place closure temperatures depend on a number of factors grain size cooling rate mineral composition and pressure among others on the other hand deformation related processes such as dynamic recrystallization neocrystallization and fluid circulation seem to be crucial for isotopic systems and thus the obtained ages cannot be solely interpreted as a function of temperature in sheared rocks for this reason geochronologic data from shear zones might not only record cooling below closure temperature conditions but may also be affected by neo or recrystallization fluid assisted deformation and inheritance of the protolith age s in order to robustly reconstruct p t e t paths of long term crustal scale shear zones structural microstructural and petrologic data from mylonites need to be integrated with ages from different thermochronometric systems in addition geochronologic data from associated intrusions and adjacent blocks can provide further irreplaceable constraints on the timing of deformation and its regional implications one of the most challenging aspects that future lines of investigation should analyze is the quantitative evaluation of so far poorly explored aspects of isotopic diffusion particularly the coupling with deformation processes based on natural theoretical and experimental data future works should also investigate the role of strain partitioning and localization processes in order to constrain the timing of deformation in different parts of a shear zone or in different branches of anastomosing shear zone networks

provenance of turbidite sands from iodp exp 1301 in the northwestern cascadia basin western north america abstract the northwestern cascadia basin of western north america accumulated high sedimentation rate sequences during the pleistocene sea level low stands the continental shelf was largely exposed at that time and rivers and estuaries delivered large sediment fluxes directly to the deep ocean the iodp exp1301 core which was taken from the middle portion of the cascadia basin is well preserved and exhibits the deeper and more distal sedimentary facies the lithology in this location is composed of two units 1 hemipelagic mud with a thin sand layer and 2 thick coarsening upward silt sand turbidites with a small proportion of granules at the top we will focus on the detailed sand grain proportions in order to understand the origin of these sediments we determined the modal proportions of the heavy minerals and the chemical composition of olivine and orthopyroxene in fourteen samples these are characterized by an abundance of amphibole pyroxenes and epidote and the presence of minerals derived from peridotite there is no drastic change in the modal and mineral compositions of the sands and silts between the turbidite and hemipelagic sequences there were two probable drainage systems on the continent the frazer and columbia rivers which shed turbidites into the cascadia basin after 1 6 ma especially at 0 46 0 76 ma based on a comparison of the modal and mineral compositions the northern cascadia basin has been supplied with sediments mainly from the frazer river through the straits of juan de fuca by pleistocene to holocene turbidites

permian triassic red stained albitized profiles in the granitic basement of ne spain evidence for deep alteration related to the triassic palaeosurface extensive areas of the variscan granitic basement in ne spain display profiles of red stained albitized facies characterized by albitization of ca plagioclase chloritization of biotite and microclinization of orthoclase along with the alteration of igneous quartz to secondary cl dark quartz these profiles have a geopetal structure beneath the triassic unconformity with a very intense and pervasive alteration in the upper part that progressively decreases with depth to 150 200 m where the alteration is restricted to the walls of fractures the red albitized facies contains secondary maghemite and hematite that indicate oxidizing conditions dating of microclinized orthoclase and secondary monazite that have formed in the red stained albitized facies yielded k ar and u th pbtotal ages of 240 and 250 ma respectively suggesting that the alteration developed during the permian triassic period the geopetal disposition of the red albitized profile with respect to the triassic unconformity its large regional extent and the fracture controlled alteration in the lower part of the profile indicate groundwater interaction the 18o values of albitized plagioclase 11 microclinized orthoclase 13 and secondary cl dark quartz 12 suggest that the alteration temperature was about 55 c this low temperature suggests that the alteration occurred during interaction of the granitic rocks with na rich fluids below a surficial weathering mantle on the permian triassic palaeosurface the latter is possibly related to triassic evaporitic environments in long lasting stable landscapes in which na rich solutions infiltrated deep regional groundwaters

provenance of jurassic accretionary complex mino terrane inner zone of south west japan implications for palaeogeography of eastern asia provenance and tectonic history of the jurassic accretionary complex mino terrane located in the inner zone of south west japan were studied using sandstone framework composition and mudrock geochemistry modal analysis of sandstones shows that the tectonic setting of the source area for the studied mino terrane clastic rocks was uplifted basement largely dominated by high grade metamorphic terrain composed of quartz and feldspar especially plagioclase the textural and mineralogical immaturity extent of alkali and alkaline earth element leaching low chemical index of alteration values and depleted rare earth element ree contents suggest rapid uplift and erosion within the source terrain and a relatively weak weathering intensity factor analysis revealed that grain size effects governed compositional heterogeneity in the studied sediments provenance of the sediments is interpreted as being plagioclase enriched felsic basement rock such as granodiorite within a continental margin and evolved arc tectonic setting rather than active volcanic arc lack of a contribution from active volcanic arcs may have resulted from the cessation of volcanism during the reorganization of the subducting plate system and or erosion of arc volcanics and exposure of basement considering the previous studies on palaeogeography and palaeocurrent reconstruction the north eastern part of the yeongnam massif in the korean peninsula is interpreted as the most probable source area for the studied turbidites the results of mixing calculation for mino terrane sediments suggest that precambrian leucocratic granite and the basement rock of the cretaceous gyeongsang basin shed large amounts of sediments to the mino trench whilst precambrian granitic gneiss and the triassic pluton supplied lesser amounts the results of this study reveal that although active subduction accretion processes were occurring the mino trench was bordered by continental basement rocks this knowledge contributes to enhanced understanding of the jurassic palaeogeography of the east asia continental margin

mid holocene el nino southern oscillation enso attenuation revealed by individual foraminifera in eastern tropical pacific sediments holocene reconstructions of the el nino southern oscillation enso provide valuable perspective on its recent evolution and can be important for assessing its future optimal assessment of past enso variability requires observations from its center of action in the eastern equatorial pacific but these are limited due to paucity of high resolution paleoceanographic archives e g corals here we use a new approach to quantify past enso variance based on the oxygen isotopic composition 18 o of individual foraminifera globigerinoides ruber from deep sea sediments in the enso source region individual g ruber foraminifera behave as monthly recorders of sea surface conditions including enso extremes circumventing the lack of annual resolution in the sediments intrapopulation 18 o distributions derived with this method from a core near the galapagos islands reveal mid holocene reductions in variance of 50 requiring drastic attenuation of the enso amplitude furthermore mg ca thermometry indicates that mid holocene background conditions were accompanied by a stronger zonal temperature gradient that coincided with a northward displaced intertropical convergence zone itcz the results suggest that the position of the itcz is an important factor in the low frequency modulation of enso and could influence its future evolution

zr bearing minerals as indicators for the polymetamorphic evolution of the eastern lower austroalpine nappes stubenberg granite contact aureole styria eastern alps austria abstract contact metamorphism during emplacement of the permian stubenberg granite has led to the formation of the assemblage forsterite calcite titanian clinohumite phlogopite chlorite in the adjacent marbles during intrusion of the granite veins rich in ti zr ree and actinides u th formed these veins show a distinct mineralogical zoning sequence with four zones going from the center of the vein to the margin these zones include the assemblages 1 geikielite baddeleyite zirconolite apatite calcite chlorite magnetite pyrrhotite assemblage 2 calcite chlorite 3 forsterite titanian clinohumite chlorite calcite phlogopite and 4 calcite forsterite baddeleyite is always replaced by zirconolite possibly via the model reaction baddeleyite 2 geikielite 3 calcite co 2 zirconolite 2 dolomite zirconolite zirc i shows a strong internal oscillatory zoning and distinct overgrowths zirc ii which have a different chemical composition the chemical variation between the cores zirc i and the rims zirc ii can be explained by using the substitutions me 5 me 2 ti 4 me 3 and ree 3 me 5 me 2 ca 2 2ti 4 in contrast to zirconolite from metacarbonates associated with contact aureoles these analyses show elevated nb contents of up to 4 5 wt nb 2 o 5 and unusually high w contents of 1 2 wt wo 3 a strong eo alpine metamorphic overprint led locally to the formation of the assemblage chlorite dolomite calcite ilmenite zirconolite ii geikielite fe sulfides late zircon grew locally presumably as the last zr bearing mineral in the carbonates which formed during permian contact metamorphism the zr mineral sequence baddeleyite zirconolite zircon implies an increasing a sio 2 and f co 2 during the growth of these minerals electron microprobe dating of zirconolite zirc i yields a weighted average age of 263 16 ma and indicates that the hfse and ree rich assemblages formed during the permian emplacement of the stubenberg granite as a result of the subsequent high p eo alpine metamorphic overprint 111 15 ma hfse and ree were locally re mobilized leading to dissolution of zirc i and reprecipitation of the ree and nb rich overgrowths of zirc ii

feasibility of chemical u th total pb baddeleyite dating by electron microprobe abstract we evaluate the potential for applying the electron microprobe em chemical dating technique to the mineral baddeleyite zro 2 an accessory phase commonly used to determine crystallization ages of mafic rocks in conventional isotopic u pb studies baddeleyite is well suited for em chemical dating because it has relatively high concentrations of u negligible common pb and is highly resistant to pb loss em chemical and isotope dilution u pb ages are presented for five baddeleyite reference samples including the 780 ma faber lake gabbro sheet great bear magmatic zone canada the 1109 ma moore lakes gabbro churchill province canada the 1269 ma muskox intrusion slave craton canada the 2060 ma phalaborwa carbonatite s africa and the 2410 ma binneringie gabbro dyke yilgarn craton australia overall the em chemical ages show good correlation with the conventional u pb ages three of the reference samples yielded em ages within 30 60 ma of the conventional ages well within analytical uncertainty for reasons that are not known two of the samples yielded em chemical ages that are systematically old by 140 ma we conclude from these data that the em chemical dating technique provides reasonable first order age information for typical precambrian baddeleyite the systematic variation of u and pb at the micron scale in baddeleyite coupled with the excellent spatial resolution of the em 1 m allows for determination of chemical u th total pb isochrons from individual baddeleyite crystals in polished thin section em chemical dating offers a non destructive time efficient a matter of hours for each sample and cost effective way to obtain contextural age information from baddeleyite in mafic rocks with a grain size too small for isolation and conventional u pb dating

reconstruction of holocene relative sea level change and residual uplift in the lake inba area japan abstract we collected and analyzed fossil diatoms and volcanic ash and determined 14 c ages in core samples from the lowlands around lake inba in the eastern kanto plain central japan an area where late quaternary sea level change fluvial erosion and tectonic uplift have affected a region of archeological interest we inferred holocene paleoenvironmental changes and relative sea levels on the basis of indicators such as high tide levels derived from fossil diatom assemblages as well as the stratigraphic positions of 14 c dated samples and the k ah tephra our results lead to estimates of the upper half tidal range during 6800 7000 cal yr bp of 1 7 m the holocene highstand took place at approximately 6400 6500 cal yr bp and mean sea level reached an elevation of 1 9 m however the timing of this sea level rise is earlier in the lake inba area than documented in previous studies and it is suggested that the timing of the holocene highstand may appear at least 1000 years earlier as a result of holocene residual uplift after this sea level fell abruptly around 4000 cal yr bp we also recognized a sea level fall corresponding to the yayoi regression at about 2600 cal yr bp during which the mean relative sea level may have been as low as 2 5 m after compensating for uplift subsidence or geomorphologic effects in this area

provenance implications of th u pb electron microprobe ages from detrital monazite in the carboniferous upper silesia coal basin poland abstract this paper reports the results of chime chemical th u pb isochron method dating of detrital monazites from carboniferous sandstones in the upper silesia coal basin uscb a total of 4739 spots on 863 monazite grains were analyzed from samples of sandstone derived from six stratigraphic units in the sedimentary sequence age distributions were identified in detrital monazites from the uscb sequence and correlated with specific dated domains in potential source areas most monazites in all samples yielded ca 300 320 ma variscan ages however eo variscan caledonian and cadomian ages were also obtained the predominant ages are comparable to reported ages of certain tectonostratigraphic domains in the polyorogenic bohemian massif bm which suggests that various crystalline lithologies in the bm were the dominant sources of uscb sediments

environmental change and its impacts on human settlement in the yangtze delta p r china abstract archaeological excavations and environment archaeology studies over many years in the yangtze delta region have provided exceptional information about climatic variations growth and demise of human civilization and human environment interactions the archaeological excavations show that the cultural layers of the neolithic sites are interrupted by barren layers without any cultural relics so called cultural interruptions which may be the result of harsh environmental conditions arid flooding extreme cold or warmth temporal and spatial analyses of 14c dates for buried trees peat shell ridges and neolithic sites show that environmental changes are responsible for the rise and fall of human civilization the progress of human civilization was interrupted at least 5 times in the yangtze delta matching 5 periods of high sea level peat accumulation and burial of trees the collapse of the liangzhu culture about 4000 bp was followed by the less developed maqiao culture and resulted from extreme environmental and hydrological conditions such as floods

chemical non isotopic and isotopic dating of phanerozoic zircon a case study of durbachite from the třebic pluton bohemian massif abstract although chemical non isotopic u th pb dating of monazite by electron microprobe is well established dating of zircon by this method is still controversial relatively u rich zircon up to 2500 ppm of u from the t ebic pluton provides a test case for the technique zircon grains are commonly partially or completely metamict and therefore susceptible to pb loss and common pb contamination using ca and k contents as indicators of damaged or contaminated zircon a chime chemical u th total pb method age of 347 8 18 ma was obtained from data with 0 0062 wt of pbo this age was confirmed by isotopic u pb shrimp dating 341 6 2 8 ma these results are in agreement with previous estimates for the timing of durbachitic intrusions into the root of the variscan orogen and from the variscan basement incorporated into western alps between 343 and 332 ma

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

a three dimensional method for calculating independent chemical u pb and th pb ages of accessory minerals abstract previous theoretical considerations on the chemical u th total pb dating method failed to distinguish between thorogenic and uranogenic lead however it can be shown that the data points are located on a plane in the three dimensional tho2 pbo uo2 space the calculation of the best fit plane yields a slope in the tho2 pbo and uo2 pbo coordinate projections and an initial pbo value from the two slopes th pb and u pb ages can be calculated independently the method described in this paper is applied to monazites from the hercynian g4 granite of the fichtelgebirge germany th pb and u pb ages were calculated at 323 20 ma and 304 15 ma respectively the intercept value close to zero indicates that no significant amounts of common lead are present in the monazites studied

th u pb monazite ages from al mg rich metapelites rauer group east antarctica the age of high temperature granulite facies metamorphism 800 850 c in the rauer group prydz bay east antarctica is relevant for establishing the metamorphic and temporal architecture of the prydz bay mobile belt monazites within al mg rich granulite facies metapelites give an overall tanh estimated pan african age of 511 4 ma 2r using in situ electron microprobe based th u pb chronology consistent with existing u pb zircon geochronology from the rauer group and prydz bay monazite occurs primarily within cordierite bearing coronae and symplectic min eral reaction textures and also within biotite pan african granulite facies metamorphism is preferred as responsible for the development of the cordierite bearing microstructures and probably peak coarse grained assemblages constrained using an integrated geologic geochronologic and metamorphic framework thus pan african granulite facies metamorphism affected the rauer group within the prydz bay mobile belt moreover integrated monazite geochronology may be used to decipher the temporal metamorphic histories of potentially complex high temperature terrains

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

electron microprobe observations of pb diffusion in metamorphosed detrital monazites electron microprobe analyses have been made on monazite grains from paragneiss samples in the andalusite sillimanite transition 620 15 c and sillimanite orthoclase 680 15 c zones of the cretaceous ryoke metamorphic belt southwest japan monazites from pelitic gneisses are of metamorphic origin euhedral to subhedral and chronologically homogeneous giving chemical th u total pb isochron chime ages of 98 8 3 3 98 0 3 2 ma two psammitic gneisses of individual metamorphic grade contain both metamorphic monazite grains and detrital ones as old as ca 1700 ma most detrital monazite grains are heterogeneous in the tho2 and uo2 concentrations and have multiple or single rims as young as ca 100 ma several detrital monazite grains are well rounded in form exhibit homogeneous th and u distributions and show a pb diffusion profile in the margin the width of the diffusion zones is approximately constant throughout grains from each psammitic gneiss 18 22 m for 620 c and 48 58 m for 680 c assuming the isothermal diffusion of pb from homogeneous monazite spheres during a 5 ma duration of peak metamorphism we obtain diffusion coefficients of 1 9 0 3 10 21 and 1 5 0 3 10 20 cm2 s at 620 c and 680 c respectively these data derive an activation energy of 2 44 2 85 1 26 105 j mol and a frequency factor of 3 4 10 7 8 5 10 12 2 2 107 cm2 s taking account of uncertainties of 15 c in the temperatures and of 20 in the diffusion coefficients the diffusion parameters obtained from natural samples in this study provide a reliable insight into the closure temperature for pb in monazite that has been poorly understood so far

petrochronology based on ree minerals monazite allanite xenotime apatite ree minerals monazite xenotime and allanite are ree1 minerals sensu stricto because lanthanides la lu and yttrium are critical constituents in them apatite does not require ree but because it contains substantial ree in many rocks it is included in this review all four minerals also host unusually high radionuclide concentrations notably th and u forming the basis of their utility as geochronometers this quartet of accessory minerals is playing an increasingly important role in petrochronology because they provide ways to link robust spot ages to petrogenetic p t conditions so can lend petrogenetic context to chronology based on other minerals part i of this review assembles the basic requisites prior to integrative petrochronologic analysis individual characteristics of the four ree minerals are addressed first i e their crystal chemistry and stability relations thermobarometers and trace element geochemistry used for tracing petrogenesis are discussed next and finally their chronology is summarized part ii presents case studies to highlight the specific strengths of ree minerals used to resolve the dynamics of a broad range of processes from diagenetic to magmatic conditions finally a brief section at the end outlines a few of the current challenges and promising perspectives for future work to introduce the four ree minerals in style let us recall the origins of their names the three phosphates have well respected greek grandparents and allanite has solid scottish roots yet of all four of them show idiosyncracies in etymology or type material apatite had long puzzled naturalists as it shows great chemical and physical variability and can resemble other minerals once properly identified abraham gottlieb werner named it apatite his reasoning referred to the greek root and giving the precise latin translation decipio taken literally both mean i deceive or i mislead which sounds like an apt confession from this mineral for having fooled

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

age constraints on late paleozoic evolution of continental crust from electron microprobe dating of monazite in the peloritani mountains southern italy another example of resetting of monazite ages in high grade rocks in situ monazite microprobe dating has been performed for the first time on trondhjemite and amphibolite facies metasediments from the peloritani mountains in order to obtain information about the age of metamorphism and intrusive magmatism within this still poorly known sector of the hercynian belt all samples show single stage monazite growth of hercynian age one migmatite and one biotitic paragneiss yielded monazite ages of 311 4 and 298 6 ma respectively these ages fit with previous age determinations in similar rocks from southern calabria indicating a thermal metamorphic peak at about 300 ma at the same time as widespread granitoid magmatism the older of the two ages might represent a slightly earlier event possibly associated with the emplacement of an adjacent trondhjemite pluton previously dated by shrimp at 314 ma no evidence for pre hercynian events and only a little indication for some monazite crystallization starting from ca 360 ma were obtained from monazite dating of the metasediments suggesting either a single stage metamorphic evolution or a significant resetting of the monazite isotope system during the main hercynian event ca 300 ma rare monazite from a trondhjemite sample yields evidence for a late hercynian age of about 275 ma this age is interpreted as representing a post magmatic stage of metasomatic monazite crystallization which significantly postdates the emplacement of the original magmatic body

middle precambrian detrital monazite and zircon from the hida gneiss on oki dogo island japan their origin and implications for the correlation of basement gneiss of southwest japan and korea abstract monazite and zircon from seven paragneiss samples of the upper amphibolite facies grade from oki dogo island in the hida terrane western japan were analyzed for th u and pb on an electron microprobe most monazite grains are chronologically unzoned and give unequivocal chime chemical th u total pb isochron ages of 250 ma but some grains show a distinct core overgrowth relationship the cores retain evidence of pre 250 ma ages and are interpreted to be of detrital origin suggesting that monazite can be more immune to diagenetic and low grade metamorphic decompositions than had been thought previously zircon grains rounded to nearly euhedral give chime ages ranging from 3000 to 350 ma of particular interest are several rounded 3000 ma recycled zircons which perhaps originated from an archean terrain in the sino korean craton the youngest age of detrital zircons constrains that the gneiss protolith deposited after the 350 ma event the chime monazite and zircon ages for the paragneisses from oki dogo island and from the main part of the hida terrane reveal that the gneisses formed from permo carboniferous clastic sediments during a single metamorphism at ca 250 ma the results are in marked contrast to the current view that 1 the hida gneiss is a polymetamorphosed precambrian complex 2 the central part hida gneiss region and the eastern marginal part unazuki schist region of the hida terrane are correlative with the precambrian kyonggi massif and the paleozoic okchon zone in the korean peninsula respectively instead we consider that the okchon zone alone can be correlatable with the paleozoic hida terrane

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

precise electron microprobe age determination in altered uraninite consequences on the intrusion age and the metallogenic significance of the kirchberg granite erzgebirge germany an integral method of data evaluation for chemical dating of accessory uraninite by electron microprobe analysis and electron microscopy is proposed the internal structure of uraninite grains the contents of si ca and fe and tests for loss or gain of pb and u are suitable criteria to decide whether or not a given crystal area was affected by secondary alteration the method was applied to uraninite from the kirchberg granite erzgebirge germany and an age of 330 5 ma 2 was constrained this result supports earlier assumptions that there were at least two events of hercynian granite magmatism separated by a time gap of about 40 ma and that the magmatic evolution of the kirchberg granite is not related to the formation of the w mineralisation developed in the endocontact of this granite secondary alteration of uraninite is probably closely related to the formation of u deposits in the vicinity of the kirchberg massif which was extensively mined in the past

geochronology and tectonic evolution of karimnagar and bhopalpatnam granulite belts central india abstract the karimnagar granulite belt kgb and the bhopalpatnam granulite belt bgb occur along both flanks of the pranhita godavari pg rift basin we present a state of the art overview on the geochronological and tectonic aspects of these belts and surrounding geologic domains and report new age data on zircon monazite and uraninite recovered from granulite facies assemblages from kgb and bgb based on electron microprobe analyses epma zircons from kgb charnockites show core ages of up to 3 1 ga mantled by rims of 2 6 ga zircons from bgb have 1 9 ga cores mantled by 1 7 ga rims zircons with core ages of 1 6 to 1 7 ga in bgb rocks suggest new growth at this time monazites and uranitite from kgb show clear peaks with well defined ages in the narrow range between 2 42 0 08 ga and 2 47 0 03 ga rims of monazite show mean age of 2 21 0 08 ga monazites from bgb define sharp linear trend in pbo vs tho2 diagram delineating a clear isochron with age of 1 59 0 03 ga age data from kgb and bgb presented in this report negate current models linking these terrains to godavari granulite belt and considering them as single and contemporaneous entity the mid archaean to early palaeoproterozoic signature recognized from kgb is totally missing in bgb on the other hand kgb rocks do not record any evidence for major mesoproterozoic thermal regime the two granulite belts shouldering the pg rift basin have therefore evolved in different times under distinct p t conditions and thermal regimes our results have important implications in evaluating models of supercontinent assemblies particularly the older assemblies of ur columbia and rodinia while tectonothermal events in kgb broadly match with those of east dharwar we propose that bgb represents a 1 6 ga collisional mobile belt between the bastar and the dharwar cratons the 1 6 ga collisional mobile belt at the southern margin of the bastar craton was superposed by rift activity along the pg basin at 1 5 ga this sequence of events goes against the existence of a 3 0 ga old contiguous assembly of ur but closely matches with the history of accretion and break up of the columbia further parts of the pg basin located away from the influence of the eastern ghats mobile belt neither recorded any grenville ages 1 0 ga corresponding to the rodinia accretion nor late pan african ages ca 550 ma relating to the gondwana amalgamation indicating that the region did not witness any of these younger tectonic events

sedimentary system response to the global sea level change in the east china seas since the last glacial maximum abstract the east china seas ecs is one of the world s largest continental shelf seas based on the combination of global sea level change and sequence stratigraphy we systematically investigated the evolution of sedimentary system in the ecs since the last glacial maximum lgm we have defined the transgressive boundary layer and constructed several sedimentary models of the ecs on the sequence stratigraphy and evolution of tidal sand ridges since the lgm and sediment source to sink during the high sea level the result shows that the ecs represent a typical case for large scale continental shelf response to the global sea level change three sedimentary system tracts had been formed in the ecs since the lgm first is the lowstand system tract corresponding to the late of last glaciation and lgm 23 15 4 cal kyr b p the progressive wedge occurred along the okinawa trough slope and the paleo coastal zone pcz along the continental shelf edge second is the transgressive system tract corresponding to the last deglaciation 15 4 7 cal kyr b p a large scale transgressive boundary layer and tidal sand ridges were formed in this stage third is the highstand system tract corresponding to the high sea level since 7 cal kyr b p the eddy mud coastal current mud present tidal sand ridge delta tidal flat and beach have been accumulating since then the global sea level change after lgm can be divided into seven phases of which four rapidly rising phases rrp i ii iii iv and three slowly rising phases srp i ii iii are distinguished the tidal sand ridges were formed in the srp and transgressive boundary layer in the rrp the tidal sand ridges can be divided into three types including radicalized channel and emanative the modern circulation current system of the ecs had been built in the end of the last deglaciation the effect of sediment source to sink in the ecs is closely correlative to the current system driven by the interaction of the east asian monsoon and kuroshio the major sediment source is from the river discharge of the huanghe and changjiang river and coastal resuspension the muddy sediment in the eddy and coastal current which cover the tidal sand ridges and transgressive boundary layer is a major sediment sink in the modern ecs

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire

superimposed neoarchaean and paleoproterozoic tectonics in the terre adelie craton east antarctica evidence from th u pb ages on monazite and 40ar 39ar ages in order to understand the tectonic behaviour of a stabilized neoarchaean continental crust during subsequent tectonic activity we investigated the compositemetamorphic basement along the terre adelie and george vth land coastline also known as the terre adelie craton east antarctica two domains are recognized 1 a neoarchaean basement composed of granulite rocks to the east and overlain to thewest by amphibolites and 2 two paleoproterozoic detrital basins overly theneoarchaean crust and extend further west newgeochronological data fromthe terre adelie craton define a tectonic evolution with threemajor peaks activity th u pb electron probe analyses of monazite from the neoarchaean granulites constrain the main structuration event at ca 2 45 ga in agreement with zircon ages from throughout the neoarchaean domain local resetting together with low temperature recrystallization of monazites occurred at ca 1 7ga along hydrated anastomozing metre scale shear zones new 40ar 39ar ages obtained by stepwise heating techniques on amphibole biotite and muscovite from both the neoarchaean basement and the paleoproterozoic basins illustrate the differential evolutions of basement and its sedimentary cover during the major 1 7ga transpressive event a final event at ca 1 55 1 50 ga is only recognized close to the mertz shear zone 145 e bounding the terre adelie craton to the east the new data allow us to propose detailed geological pictures of the terre adelie craton geodynamic evolution from the neoarchaean to the mesoproterozoic

chemical th u total pb dating by electron microprobe analysis of monazite xenotime and zircon from the archean napier complex east antarctica evidence for ultra high temperature metamorphism at 2400 ma abstract the chemical th u total pb isochron method chime of dating was carried out on monazite xenotime zircon and polycrase in six samples of ultra high temperature uht granulites and one of pegmatite from five localities in the napier complex enderby land east antarctica despite the chronological heterogeneity in many grains the chime ages overall show strong evidence for a major event near 2420 ma analyzed monazite and xenotime grains except monazite from mt riiser larsen have a narrow range of chime ages 2412 42 ma from beaver island and 2429 36 2421 18 and 2431 22 ma from reference peak these ages are indistinguishable from chime ages on zircon 2436 17 and 2420 20 ma and on central older domains of monazite 2404 54 ma from mt riiser larsen and on a zircon rim 2430 15 ma from mt cronus we conclude that the ca 2420 ma ages relate to the uht metamorphism but we do not exclude the possibility that lead loss has lowered the ages by some 50 ma this interpretation is consistent with a preponderance of ages obtained by other methods on the napier complex particularly the ca 2475 25 ma age for a generation of pegmatites coeval with the uht event and containing the uht mineral assemblage beryllian sapphirine khmaralite quartz events prior to 2500 ma and after 2420 ma have also left their imprint on the chime ages for example a 3646 ma chime age suggests that a zircon core is inherited whereas ca 2200 and 2000 ma chime ages in zoned monazite could be due to further lead loss during post uht activity the much younger chime age of 1094 67 ma for monazite from a pegmatite at zircon point casey bay confirms 1000 1100 ma lead loss ages reported for this region and could result from fluid activity in an outlier of rayner activity near the boundary between the rayner and napier complexes approximately 2500 ma ages have been reported from granulite facies but not uht rocks in the madras and nilgiri blocks in south india these blocks and the napier complex could have constituted a single structural unit by late archean time

abrupt weakening of the summer monsoon in northwest india 4100 yr ago climate change has been suggested as a possible cause for the decline of urban centers of the indus civilization 4000 yr ago but extant paleoclimatic evidence has been derived from locations well outside the distribution of indus settlements here we report an oxygen iso tope record of gastropod aragonite 18 o a from holocene sediments of paleolake kotla dahar haryana india which is adjacent to indus settlements and documents indian summer mon soon ism variability for the past 6 5 k y a 4 increase in 18 o a occurred at ca 4 1 ka mark ing a peak in the evaporation precipitation ratio in the lake catchment related to weakening of the ism although dating uncertainty exists in both climate and archaeological records the drought event 4 1 ka on the northwestern indian plains is within the radiocarbon age range for the beginning of indus de urbanization suggesting that climate may have played a role in the indus cultural transformation

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

new isotopic constraints on the age of the halls reward metamorphics north queensland australia delamerian metamorphic ages and grenville detrital zircons abstract the halls reward metamorphics in north queensland australia consist mainly of mica schist and have previously been regarded as a part of the proterozoic craton and separated from the paleozoic orogenic zone on its eastern margin by the tasman tectonic line however our rb sr dating by whole rock muscovite isochron from the halls reward metamorphics shows ca 500 ma k ar dating of muscovite in the quartz mica schist also shows the same age furthermore u th pb chemical dating chime gives ca 510 ma crystallization age for monazite these results suggest that the halls reward metamorphics is not the part of the proterozoic craton but belongs to the early paleozoic delamerian orogenic belt extending the length of the eastern gondwana margin the location of the tasman tectonic line should therefore be west of the halls reward metamorphics u th pb chemical dating of detrital zircon from quartz mica schists also shows an age distribution of peak at ca 1000 ma with some older components the presence of 1000 ma grenvillian detrital zircon from both geological units is consistent with the close proximity of grenville age source suggested by the ausmex continental reconstruction

electron microprobe dating of monazites from western carpathian basement granitoids plutonic evidence for an important permian rifting event subsequent to variscan crustal anatexis accessory monazites from 35 granitoid samples from the western carpathian basement have been analysed with the electron microprobe in an attempt to broadly constrain their formation ages on the basis of their th u and pb contents the sample set includes representative granite types from the tatric veporic and gemeric tectonic units in most cases lower carboniferous variscan ages have been obtained however a much younger mid permian age has been recorded for the specialised s type granites of the gemeric unit and several small a and s type granite bodies in the veporic unit and the southern tatric unit this distinct permian plutonic activity in the southern part of the western carpathians is an important although previously little considered geological feature it appears to be not related to the variscan orogeny and is interpreted here to reflect the onset of the alpine orogenic cycle with magma generation in response to continental rifting the voluminous carboniferous granitoid bodies in the tatric and veporic units comprise s and i type variants which document crustal anatexis accompanying the collapse of a compressional variscan orogen sector the variscan magmas were most likely produced through the remelting of a subducted precambrian volcanic arc type crust which included both igneous and sedimentary reworked volcanic arc material although the 2 errors of the applied dating method are quite large and typically 10 20 ma for single samples it would appear from the data that the variscan s type granitoids 333 367 ma are systematically older than the variscan i type granitoids 308 345 ma this feature is interpreted in terms of a prograde temperature evolution in the deeper parts of the post collisional variscan crust in accordance with recently published zircon ages this study shows that the western carpathian basement must be viewed as a distinct eastern tectonomagmatic province in the variscan collision zone where the post collisional crustal melting processes occurred 20 ma earlier than in the central sector south bohemian batholith hohe tauern batholith

isotope geochronology geochemistry and mineral chemistry of the u bearing and barren granites from the zhuguangshan complex south china implications for petrogenesis and uranium mineralization abstract the zhuguangshan complex carries some of the most important granite hosted uranium deposits in south china here we investigate the changjiang and jiufeng granites which represent typical u bearing and barren granites in the complex using zircon u pb ages whole rock geochemistry sr nd isotopic and zircon hf isotopic data and mineral chemistry to constrain the petrogenesis and uranium mineralization la icp ms zircon u pb dating shows that both the changjiang and jiufeng granites were emplaced ca 160 ma these rocks show high silica weakly to strongly peraluminous compositions enrichment in rb th and u and depletion in ba nb sr p and ti these features coupled with the high initial 87 sr 86 sr ratios negative end t values and ehf t values and the paleoproterozoic two stage model ages of these two granites suggest that the two granites belong to s type granites and the parental magmas of the two granites were derived from the paleoproterozoic metasedimentary rocks however the granitoids show different mineralogical characteristics the biotite in the changjiang granite belongs to siderophyllite marking higher degree of chloritization whereas the biotite in the jiufeng granite is ferribiotite characterized by only slight chloritization compared with the jiufeng granite the biotite in the changjiang granite has lower crystallization temperature and oxygen fugacity but higher f content and the uraninite has higher uo 2 content but lower tho 2 content and stronger corrosion the chemical ages of uraninites from both granites are within error consistent with the zircon u pb ages and are considered to represent the emplacement ages of granites chemical ages of pitchblende in the changjiang granite yield 118 8 ma 87 4 ma and 68 6 ma representing multiple episodes of hydrothermal events that are responsible for the precipitation of u ores in the changjiang uranium ore field our study suggests that the degree of magma differentiation and physicochemical conditions of the magmatic hydrothermal system are the key factors that control the different u contents of these two granites the mineralogical characteristics of uraninite and biotite can be used to distinguish between u bearing and barren granites and serve as a potential tool for prospecting granite hosted uranium deposits

three metamorphic monazite generations in a high pressure rock from the bohemian massif and the potentially important role of apatite in stimulating polyphase monazite growth along a pt loop abstract based on microstructural and compositional criteria three generations of monazite can be identified in a peraluminous garnet rich high pressure metamorphic rock from the bohemian massif the first monazite generation m1 formed probably on the prograde part of the clockwise pt loop a second m2 during the high pressure stage 26 3 kbar and 830 30 c and a third generation m3 during subsequent near isothermal decompression of the rock to 8 2 kbar the high pressure m2 monazites are volumetrically dominant and form 100 300 m grains they are characterised by an unusual sr brabantite component sro up to 2 wt and grew together with accessory sr rich fluorapatites sro up to 33 wt the sr contents of both minerals are indicative of high pressure conditions and result from the breakdown of plagioclase and the release of sr that occurred during this process m3 monazites occur exclusively as small grains 10 100 m within and at the rims of apatite microstructures show that they grew at the expense of the apatite extracting lrees from the latter under retrograde conditions these parasite monazites in apatite are characterised by very low th contents which is consistent with having been derived primarily from an apatite source m1 monazites are represented by resorbed irregular shaped cores which are occasionally preserved within the sr brabantite rich high pressure monazites m2 these m1 cores are generally sr poor indicating that they should have formed prior to the high pressure stage in the presence of plagioclase the dissolution of m1 monazite and the reprecipitation of a th u enriched m2 monazite during the high pressure stage implies that lrees were taken up by the high pressure sr rich fluorapatite to some extent and not completely processed for the formation of the m2 monazite this would also explain the widespread retrograde growth of m3 monazite within the apatite the ability of apatite to act as an interim host for lrees at peak pt conditions could be one of the reasons why monazite growth during regional metamorphism is often periodic

late holocene vegetation and climate change in jeju island korea and its implications for enso influences abstract several recent studies suggest the hypothesis that the el nino southern oscillation enso is an important factor controlling the holocene east asian monsoon eam however the mechanism underlying this influence remains unclear due to the lack of high resolution paleoclimate records from the coast of east asia here we provide a new record of late holocene climate change in coastal east asia based on multi proxy evidence pollen organic content magnetic susceptibility grain size obtained from a sediment core from jeju island south korea as jeju island is strongly influenced by the kuroshio flow our sediment proxy records contain enso signals from the tropical pacific the study area was affected by dry cool conditions in the western tropical pacific wtp between 4350 and 1920 cal yr bp when el ninos were frequent and by rapid warming wetting and forestation since 1920 cal yr bp when la ninas were more common jeju island was relatively dry cool between 2100 and 1600 1300 1200 1100 1000 800 650 and 300 50 cal yr bp as opposed to the galapagos islands which were relatively wet warm reflecting the enso related negative correlation between eastern and western margins of pacific wet conditions may have prevailed during the early little ice age lia 620 280 cal yr bp despite consistent cooling this period of high precipitation may have been associated with the increased landfall of typhoons and with warmer kuroshio currents under la nina like conditions according to our results eam on the east asian coastal margin was predominantly driven by enso activity rather than by the precession effect paleoclimatic data from jeju island with its insular position and closeness to warm kuroshio currents provide clear evidence of these enso influences

mid to late holocene cooling events in the korean peninsula and their possible impact on ancient societies we present a multiproxy record using pollen magnetic susceptibility carbon isotopic composition carbon nitrogen ratio and particle size of mid to late holocene environmental changes based on a sediment core from the pomaeho lagoon on the east coast of korea the records indicate that climate deteriorations around 6400 cal yr bp and 4000 cal yr bp caused rapid vegetation changes in the study area which were presumably attributable to low sunspot activity and strong el nino like conditions respectively these two cooling events were likely modulated by different climate mechanisms as el nino southern oscillation activity began to strengthen around 5000 cal yr bp these events may have had a substantial impact on ancient societies in the study area combining our results with archaeological findings indicated that climate deterioration led to drastic declines in local populations around 6400 cal yr bp 4400 cal yr bp and 4000 cal yr bp because of its high population coastal east asia e g eastern china japan and korea is particularly vulnerable to potential cooling events in the future therefore there is a strong need for detailed paleoclimate information in this region

geochemistry and sedimentary petrology of archean clastic sedimentary rocks at mt goldsworthy pilbara craton western australia evidence for the early evolution of continental crust and hydrothermal alteration abstract geochemical and petrological analyses of archean clastic metasedimentary rocks at mt goldsworthy in the pilbara craton western australia reveal the early evolution of continental crust and the earth s surface environment the succession correlative to the ca 3 4 ga strelley pool chert is composed dominantly of silicified medium grained to very coarse grained sandstone siltstone and shale with minor chert and precipitative beds of nahcolite and barite the sandstone is generally rich in detrital quartz with the coarse grained sandstone containing abundant very well rounded mono crystalline quartz that is assumed to be derived from older sedimentary rocks the recycled detritus is mixed with first cycle detrital material such as feldspar and barite that is sourced from reworked precipitative beds the sandstone also contains zircon fe ti oxides sulfides and lithic fragments of various origins including mafic ultramafic volcanic rocks sedimentary and possibly metamorphic rocks al ti zr systematics indicates that the source area for the mt goldsworthy clastic metasedimentary rocks was locally subjected to hydrothermal alteration reaction with the acid solution resulted in al dissolution and the formation of zr and ti enriched residual detrital material the enrichment in heavy rare earth elements and low al 2 o 3 tio 2 values of mt goldsworthy samples reflects the inflow of the residual zircon and ti oxides enriched detritus th sc la sc and eu eu ratios that are unaffected by contamination by the residual detritus indicate a mixed provenance with a significant contribution from granitoid rocks the presence of detrital zircon older than 3 5 ga was also demonstrated in this study

on the application of in situ monazite chemical geochronology to constraining p t t histories in high temperature 850 c polymetamorphic granulites from prydz bay east antarctica we present electron microprobe based in situ th u pb monazite chemical age data from granulite facies metapelites in prydz bay east antarctica the monazite age data define two distinct age populations late neoproterozoic to early palaeozoic c 570 520 ma and neoproterozoic c 950 820 ma that confirm the polytectonic nature of prydz bay our data suggest that similarity in lineation orientation along the prydz bay coast is not sufficient to necessarily indicate time equivalance the minimum duration of early palaeozoic tectonism spanning at least 60 ma is constrained from an mg al rich metapelite monazite hosted by coarse grained orthopyroxene defines the oldest early palaeozoic population whereas cordierite orthopyroxene symplectites define the youngest early palaeozoic population the spatial distribution of monazites and their ages is correlatable with the inferred mineral assemblage evolution we are able to characterize the evolution of early palaeozoic tectonism in quantitative p t t mineral assemblage space demonstrating that ultrahigh temperature tectono metamorphism in prydz bay is of early palaeozoic age the survival of neoproterozoic inheritance in fe al rich metapelites has implications for high pb retentivity in monazite when chemical and kinetic conditions are favourable the approach and logic applied herein are entirely and directly transferable to the interrogation of any other metamorphic terrane

freshwater outbursts to the oceans from glacial lake agassiz and their role in climate change during the last deglaciation abstract lake agassiz was the largest lake in north america during the last deglaciation as the laurentide ice sheet lis retreated large volumes of water stored in this proglacial lake were episodically released into the oceans these waters were variably routed to the gulf of mexico arctic ocean north atlantic ocean and hudson bay during this period the three largest cooling events in the northern hemisphere closely followed 4 of the 5 largest outbursts from lake agassiz 1 the younger dryas which was preceded by a release of 9500 km 3 2 the preboreal oscillation preceded by releases of 9300 km 3 and 5900 km 3 and 3 the 8 2 ka cold event preceded by a 163 000 km 3 outburst these are respectively fluxes of 0 30 sv 0 29 sv 0 19 sv and 5 2 sv if released in 1 year because the influx of freshwater reaching the north atlantic ocean can inhibit thermohaline circulation partly depending on whether the ocean was in a glacial interglacial or transitional mode of circulation we believe that at least these large outbursts from lake agassiz may have provided the triggers for changes in ocean circulation and in turn for widespread climate change

discovery of a c 370 ma granitic gneiss clast from the hwanggangri pebble bearing phyllite in the okcheon metamorphic belt korea abstract the chemical th u total pb isochron method chime of dating was carried out on accessory minerals in samples from the okcheon metamorphic belt in korea dated minerals include xenotime and monazite with overgrown mantles in a granitic gneiss clast from the hwanggangri formation metamorphic allanite in garnet bearing muscovite chlorite schist of the munjuri formation and polycrase and monazite in post tectonic granite from the hwanggangri area overgrowth of mantles took place at 369 10 ma on c 1750 ma cores of xenotime and monazite in the granitic gneiss allanite occurring in textural equilibrium with peak metamorphic minerals yields a chime age of 246 15 ma that is discriminably older than the polycrase 170 6 ma and monazite 170 3 ma ages of the post tectonic granite these chronological data suggest that some of the metasedimentary rocks in the belt formed through a single stage of metamorphism at c 250 ma from post 370 ma sediments late permian age signatures have also been reported from the precambrian gyeonggi and yeongnam massifs that border the okcheon metamorphic belt and indicate that parts of the basement massifs and the metamorphic belt were affected by the same regional metamorphic event

cretaceous high temperature rapid loading and unloading in the abukuma metamorphic terrane japan the cretaceous abukuma metamorphic terrane consists of the oceanic gosaisyo series overthrust onto the terrigenous takanuki series although the dominant mineralogy defines one of the classic areas of andalusite sillimanite type progressive metamorphism there are several lines of evidence suggesting an earlier higher pressure up to c 12 kbar history of the takanuki series and the nearby gosaisyo series these are 1 the occurrence of rare although widespread relic kyanite in sillimanite k feldspar zone grade pelitic rocks 2 the high grossular content of garnet interiors up to c 30 mol overgrown by ca poor rims c 2 mol grossular in pelitic rocks containing al2sio5 minerals sillimanite relic kyanite retrograde andalusite plagioclase and quartz 3 the occurrence of rutile as inclusions in garnet in pelitic rocks and 4 the occurrence of relic corundum almandine association in silica poor and al fe rich rocks garnet in the takanuki series pelitic rocks commonly shows textural sector zoning and preserves growth zoning despite the high metamorphic grade suggesting rapid changes in p t conditions and a relatively short duration of high temperature conditions combined with radiometric dating these observations suggest that the abukuma sillimanite k feldspar zone grade rocks underwent a clockwise p t path with very fast 4 mm y 1 average burial and exhumation rates

contrasting ages between isotopic chronometers in granulites monazite dating and metamorphism in the higo complex japan abstract the higo complex of west central kyushu western japan is a 25 km long body of metasedimentary and metabasic lithologies that increase in metamorphic grade from schist in the north to migmatitic granulite in the south where granitoids are emplaced along the southern margin the timing of granulite metamorphism has been extensively investigated and debated previously published sm nd mineral isochrons for garnet bearing metapelite yielded ca 220 280 ma ages suggesting high grade equilibration older than the lower grade schist to the north which yielded ca 180 ma k ar muscovite ages ion and electron microprobe analyses on zircon have yielded detrital grains with rim ages of ca 250 ma and ca 110 ma electron microprobe ages from monazite and xenotime are consistently 110 130 ma two models have been proposed 1 high grade metamorphism and tectonism at ca 115 ma with older ages attributed to inheritance and 2 high grade metamorphism at ca 250 ma with resetting of isotopic systems by contact metamorphism at ca 105 ma during the intrusion of granodiorite these models are evaluated through petrographic investigation and electron microprobe th u total pb dating of monazite in metapelitic migmatites and associated lithologies in situ investigation of monazite reveals growth and dissolution features associated with prograde and retrograde stages of progressive metamorphism and deformation monazite th u pb isochrons from metapelite diatexite and late deformational felsic dykes consistently yield ca 110 120 ma ages earlier and later stages of monazite growth cannot be temporally resolved the preservation of petrogenetic relationships coupled with the low diffusion rate of pb at

provenance diversification within an arc trench system induced by batholith development the cretaceous japan case by comparing detrital zircon u pb age spectra of coeval fore arc and back intra arc basin sandstones we identified the overall distributary pattern of terrigenous clastic material within the cretaceous arc system of sw japan abundant proterozoic c 1500 2500 ma detrital grains from the interior of east asia are present in the cretaceous intra arc basin however after a barrier mountain range formed during batholith emplacement proterozoic clastics were rarely transported into the fore arc domain episodic batholith formation in pacific type orogens likely played a major role in controlling terrigenous supply routes between coeval back arc and fore arc domains the cretaceous orogen in japan thus provides a good template for analysing the tectono sedimentary development of other arc related basins

genesis and transformations of monazite florencite and rhabdophane during medium grade metamorphism examples from the sopron hills eastern alps electron microprobe studies on the age mineral chemistry and alteration on accessory lree phosphate minerals have been carried out in medium grade metamorphic rocks of the sopron hills belonging to the lower austroalpine tectonic unit monazite and xenotime is relatively common whereas rhabdophane and florencite are restricted to certain rock types a first generation of monazite was formed in mica schists during the pre alpine hercynian metamorphism at 575 700 jc and 1 8 3 8 kbar as evidenced by p t data from the literature their mineral paragenetic and textural characteristics and supported by th u total pb ages of ca 300 ma in orthogneisses monazite is rare and of igneous origin kyanite quartzites and leucophyllites that were formed by mg metasomatism contain inherited monazite from the precursor rocks a new generation of monazite was also formed during the alpine metamorphism at v550 jc 13 kbar according to the literature data giving ages around 75 ma pronounced negative eu anomalies were found in the igneous monazites eu eu 0 4 small differences have been observed in yand hree contents whereas the lree sections of the rare earth element ree patterns nearly coincide th and ca enter the monazite structure at the expense of ree nearly according to the brabantitic replacement 2ree 3 xth 4 ca 2 in some mica schists monazite is altered to rhabdophane rhabdophane distinguished from monazite by quantitative electron microprobe analysis by low oxide total is found in many mica schists and orthogneisses it forms fine grained aggregates often attached to apatite or monazite it usually has higher yand ca contents and a less pronounced negative eu anomaly than that of coexisting monazite it may have been formed either by crystallization from ree containing hydrous solutions or from monazite reacting with y ca containing solutions florencite appears only in some leuchtenbergite bearing leucophyllites kyanite quartzites and ree rich clasts it is often idioblastic and may be grown on apatite or monazite it is chemically close to its ideal composition but ca sr and th may replace ree in minor amounts in some grains tho2 may reach 10 wt the data indicate that the charge balance is maintained by different mechanisms in low and high thorian florencite no yor hree above gd could be measured in florencite no fractionation was observed between coexisting monazite and florencite however monazite inclusions in florencite are depleted in la ce and enriched in hree d 2002 elsevier science b v all rights reserved

mass transport and fractionation during monazite alteration by anisotropic replacement abstract the present experimental study investigates the causes of anisotropic replacement and its impact on the element mass transfer during monazite alteration by combining in situ characterization of solid and fluid products starting material of standard manangotry monazite was placed at 200 mpa with 18 o doped fluids at temperature t between 300 and 600 c for durations between 14 and 114 days in some cases with hematite magnetite buffer and in presence of pre fractured quartz crystals for all experiments with naoh at t 400 c monazite products show a replacement rim altered domain but with complex microstructures that are best explained by nanoscale observations at 400 c and 500 c replacement propagates anisotropically through the unaltered domain due to preferentially oriented dissolution and or fracturing at the reaction interface the altered domain corresponds to nanochannels of secondary monazite mnz2 intruding primary monazite mnz1 with nanopores filled by amorphous si rich inclusions at the reaction front interface at 600 c the altered domain increases in volume and becomes homogeneous and non porous due to textural and chemical reequilibration however nanoscale observations reveal an anisotropic propagation associated with dislocations and preservation of mnz1 relics within the apparently homogeneous altered domain textural equilibration leads to transient pores inclusions which preferentially move toward the reaction front in all experimental products the abundant porosity attests to significant mass transfer during monazite replacement nanomixture within altered domains hampers accurate determination of mnz2 composition and is assumed to be responsible for the pb measured in the rim due to mnz1 contribution however composition measurements indicate that mnz2 contains higher light rare earth elements lree higher th u ratio but lower y th u pb and ca contents compared to mnz1 elements released in the fluid by monazite replacement are mobilized from the reaction front toward the grain boundary and then redistributed between secondary th silicates and phosphates si rich gel like material and aqueous fluids at t 500 c analyses of inclusions trapped in replaced quartz confirm an efficient ree solubility in the alkaline solutions the si rich gel like inclusions contain high amounts of ree e g 950 4600 ppm ce th 4480 6170 ppm and u 30 110 ppm while aqueous fluid inclusions have high concentrations of ree and th around 100 s of ppm compared to common natural brines there is a fractionation of th and u during mnz1 replacement th u 70 with low th u ratios in the aqueous fluid 7 23 compared to the secondary solid products up to 150 independently of the initial presence of hematite magnetite buffer this accounts for a fractionation within the isotopic th pb and u pb ages within the altered domain in natural samples observed microscopically the complex anisotropic geometry of the replacement can lead to a nanomixture within apparently homogeneous altered domains with partial resetting of the u th pb geochronometer and to misleading interpretations of secondary inclusions within apparently unaltered domain

redox change in sedimentary environments of triassic bedded cherts central japan possible reflection of sea level change middle triassic radiolarian bedded cherts in the mino belt central japan include a sequence showing an abrupt facies change from the lower to the upper where grey black bedded cherts enriched in carbonaceous matter and framboidal pyrite are overlain by brick red hematitic bed ded cherts brownish yellow chert enriched in goethite and purple red chert occur at the boundary between the grey black bedded cherts and the brick red bedded cherts this facies change is in accor dance with stratigraphic variations of geochemical characteristics the lower section grey black bedded cherts compared with the upper section brick red bedded cherts are enriched in ctot and stot and are characterized by lower mno tio 2 higher feo fe 2 o 3 total iron as fe 2 o 3 and more variable fe2o3 tio2 values some of the lower section samples in addition are characterized by an enrich ment in some transition metals ni cu and zn the covariation of mineralogical and geochemical characteristics indicates that sedimentary environments and diagenetic processes were different between the lower and the upper section bedded cherts during the deposition of the lower section bedded cherts the sedimentary environment was anoxic and bacterial sulphate reduction occurred during the early diagenetic stage in contrast the upper section bedded cherts were subjected to less reducing diagenetic processes active sulphate reduction did not occur the change of sedimentary environment and diagenetic process at the site of deposition is likely to be attributed to the fluctuated concentration of dissolved oxygen in the water mass of a semi closed marginal ocean basin which was potentially caused by sea level change that occurred during middle triassic time

geochronology of polygenetic monazites constrained by in situ electron microprobe th u total lead determination implications for lead behaviour in monazite abstract monazite grains are generally concordant and with an electron microprobe give th u total pb isochron ages in agreement with conventional u pb data monazites from four samples of post archean migmatite from the ivory coast record two main ages an archean age at 2 80 ga partly overprinted by a late migmatization event at 2 03 ga the in situ electron microprobe determination has also shown a third event that systematically appears at 2 72 ga for all the monazites from two of the four studied rocks the three events at 2 80 2 72 and 2 03 ga recorded by the th u total pb system in monazite were each obtained on independent homogeneous parts of a single grain with no sign of pb diffusion thus the oldest monazite remained closed during a high grade resetting migmatization at a temperature estimated at around 700 c and also remained closed during the growth of secondary monazite conventional u pb data isotope dilution on monazite from the same rocks did not allow precise age determinations because the representative points were highly up to 83 discordant and did not fit well along a chord in the concordia diagram the u pb isotope dilution method gave a lower intercept age of 2029 25 ma in agreement with the electron microprobe age although with an unusually high uncertainty due to a poor fit of the data the pb evaporation method gave an old archean age at 2830 7 ma and proterozoic ages ranging from 2417 10 to 2074 7 ma thus although the oldest archean age obtained with the pb evaporation and electron microprobe methods is similar within the analytical error the proterozoic ages obtained by the pb evaporation method are significantly older than the th u total pb proterozoic age obtained with the electron microprobe this discrepancy is presumed to be due to the influence in the pb evaporation method of radiogenic lead contained within archean zones of the monazite grains in other words it means that migmatization took place later than 2074 7 ma and probably around 2030 ma the second archean event at 2 72 ga revealed by high spatial resolution of the electron microprobe could not be determined by other methods the th u total pb method appears to be an inexpensive alternative method for dating simple monazites with a precision close to 20 ma even if the u pb isotopic dilution technique remains the reference method moreover owing to the very high spatial resolution 1 m of the electron microprobe it appears to have no competitor for dating complex polygenetic monazites especially when more than two events are recorded homogeneous zones of different ages coexist in a single grain with no major indication of lead diffusion a procedure for age and error calculations is defined

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

holocene relative sea level change and rate of sea level rise from coastal deposits in the toyooka basin western japan this study presents relative sea level rsl change from 11 200 to 500 cal bp in the toyooka basin western japan diatom assemblage and sedimentary sulfur analyses were performed for 32 sediment

geochemistry and zircon u pb hf isotopes of the mante aobao granite porphyry at east ujimqin banner inner mongolia implications for petrogenesis and tectonic setting we present detailed petrography geochemistry and zircon u pb hf isotopes of the mante aobao granite porphyry in east ujimqin banner inner mongolia with the aim of determining its age and petrogenesis important for understanding the early palaeozoic tectonic evolution of the xing an mongolian orogenic belt the mante aobao granite porphyry consists of plagioclase quartz and minor biotite but without amphibole zircon u pb analyses yield ages of 450 1 ma and 445 2 ma for the granite porphyry indicating that it formed during late ordovician time the granite porphyry is metaluminous to slightly peraluminous aluminous saturation index a cnk 0 98 1 11 with high sio 2 k 2 o and na 2 o concentrations and differentiation index di 85 90 chondrite normalized rare earth element ree patterns display enrichment of light rees lrees with high ratios of la yb n and negative eu anomalies in the mantle normalized multi element variation diagrams all samples are characterized by depletions of high field strength elements hfses nb ta and ti and enrichments of large ion lithophiles liles rb th u and k these geochemical features indicate that the granite porphyry is a highly fractionated i type granite and formed in a subduction related setting zircon grains have positive e hf t values of 9 2 to 11 2 and t dm2 hf ages of 691 821 ma suggesting that the granite porphyry was generated by partial melting of neoproterozoic juvenile crust with involvement of fractional crystallization during magmatic evolution it is likely that underplating of mantle derived magmas during late ordovician time provided the necessary heat to partially melt this juvenile crust combined with the regional geological data we infer that the mante aobao granite porphyry was emplaced in an active continental margin setting that was probably related to the northwards subduction of the paleo asian plate beneath the south mongolian terrane along the sonid zuoqi xilinhot axis

late paleoproterozoic magmatism in delhi fold belt nw india and its implication evidence from epma chemical ages of zircons abstract zircons from six granitoid plutons occurring in the northern part of the delhi fold belt nw india have been chemically dated using an electron microprobe most of the zircons occurring in the granites are chronologically unzoned and gave ages around 1 78 1 71 ga but younger ages of 1 1 0 9 ga have also been obtained from the rim of some grains monazite and zircons from the metasediments of delhi supergroup adjacent to the granitoids were also analyzed the older age of 1 9 1 7 ga obtained for monazites could possibly indicate their provenance age detrital zircon grains mostly rounded in the delhi metasediments which gave older ages of 1 9 ga could possibly have been derived from the archaean basement rocks exposed in this aravalli delhi fold belt the geochemical signatures of these granitoids are consistent with an extensional tectonic regime it is quite likely that contrary to the prevailing assumption of the granitoids being intrusive our geochronologic data suggests them to be the basement for sedimentation the new geochronologic information on these granitoids in the northern part of the delhi fold belt and their comparison with other correlative events establishes a widespread thermal event during late paleoproterozoic

contrasting p t t paths from the basement of the tisia unit slavonian mts ne croatia application of quantitative phase diagrams and monazite age dating abstract medium grade mica schists and intercalated paragneisses and amphibolites from the basement of the tisia unit slavonian mountains northeastern croatia contain complexly zoned garnets at the kutjevo locality mica schists are characterised by garnets with mn rich cores and ca rich rims mn decreases steadily from core to rim and ca increases abruptly this is in contrast to the paragneisses and amphibolites which contain garnets with smoothly decreasing ca from core to rim quantitative phase diagrams and garnet composition isopleths calculated from bulk rock analyses reveal that the ca poor garnet cores in the mica schists formed during an earlier event at 584 592 c and 6 4 7 8 kbar ca rich rims formed at conditions of 600 660 c and 11 12 kbar calculated using garnet isopleths and mineral thermobarometry the paragneiss and amphibolite provide similar p t information for the later peak event ca 650 c 10 12 kbar but do not preserve a record of the earlier lower p t event and modelling shows that garnet was not stable at these conditions contrary to previous studies on this outcrop and rock type no staurolite was observed and quantitative phase diagrams contoured for h 2 o mode isopleths indicate that the rock did not cross staurolite bearing fields during the retrograde p t path mica schists from the krndija locality contain zoned polyphase garnets phase diagram calculations reveal that ca rich garnet cores formed between 520 and 630 c and 7 8 kbar rims have a lower ca content and formed at considerably reduced pressures together with andalusite and staurolite at ca 530 570 c and 3 4 kbar since both localities were traditionally considered to be part of the same tectono metamorphic unit evidence presented here clearly shows that this cannot be the case emp monazite ages are variscan 350 ma in the krndija mica schists and around pre or early variscan 440 ma in the kutjevo mica schists we therefore propose a more complex internal structure and metamorphic history for this area than previously recognised suggesting a metamorphic evolution of the slavonian mountains that includes a pre variscan and a variscan cycle

detrital and newly formed metamorphic monazite in amphibolite facies metapelites from the motajica massif bosnia abstract the motajica massif in bosnia situated in the sava zone between the tisza unit and the dinarides hosts a late cretaceous flysch series which is partly preserved in an anchimetamorphic state partly affected by amphibolite facies overprint samples from both parts contain abundant accessory monazite which was investigated by means of the electron microprobe with reference to age and composition in the amphibolite facies samples new metamorphic monazite has formed chemical th u pb monazite ages indicate that the regional metamorphic event happened in the late cretaceous or the early palaeogene in addition inherited detrital monazite of permian age has been identified based on various observations it is argued that the detrital monazite was not the direct precursor to the metamorphic monazite the latter may rather have grown from other more reactive ree carrier minerals either detrital ones e g detrital allanite or such that formed during diagenesis and low grade metamorphism a later greenschist facies event that occurred in connection with a ca 27 ma old granodiorite intrusion led in some samples to the formation of late fluorapatite allanite coronas around both detrital and newly formed monazites the anchimetamorphic samples contain exclusively detrital monazite these are partly of permian as well as jurassic to early cretaceous age based on their compositional and textural features the jurassic to early cretaceous monazite relics are considered to be mainly derived from metamorphic rocks the permian monazite displays high yttrium content up to ca 3 5 wt y 2 o 3 indicating a high formation temperature 650 c and therefore probably a magmatic origin apart from almost ubiquitous permian high y monazite the motajica flysch also contains large permian xenotime with magmatic zoning patterns fluorapatite with parasitic monazite inclusions formerly ree rich fluorapatite and zircon with a type granite morphology this accessory mineral spectrum implies that among others rift related ree rich permian a type granites or rhyolites should be considered as a source for the sava zone flysch

pb isotopic composition colour and microstructure of monazites from a polymetamorphic rock in antarctica a moderate to high grade regionally metamorphosed paragneiss from antarctica contains monazites of several different colours brown yellow and grey each colour type has a distinctive u pb isotopic composition which appears to result from different proportions of radiogenic pb loss isotopic differences are neither related to la nd ce p ca ti and or ba nor to u or th content all colour types have similar structures at the submicron scale as determined by both conventional and high resolution transmission electron microscopy tem these show that the grains are essenttially non metamict but are composed of 100 a crystalline domains misoriented from each other by no more than 2 10 3 radians and separated by narrow confused boundary regions where misorientation is probably accommodated by imperfect atomic arrangements these regions of mismatch form potential zones of high permeability diffusivity which are believed to be fundamental to the isotopic and colour differences between grains colour type is apparently related to the capacity of different minerals to shield included monazite grains from fluids circulating in the rock system

late paleozoic mesozoic tectonic evolution of sw japan a review reappraisal of the accretionary orogeny and revalidation of the collisional model abstract this paper makes a review of the interpretations of the tectonic evolution of sw japan during the last three decades in the late 1970s the dominant model was the so called pacific type orogeny emphasizing the purported absence of nappes and the contrast with the alpine chains and interpreting the evolution as due to a steady oceanic subduction since the paleozoic time in the 80s the discovery of the actual structure made of a pile of large thrust sheets led authors to propose collisional models involving the intermittent underthrusting of buoyant blocks like micro continents at the same time the use of high resolution biostratigraphy allowed several authors to recognize ancient accretionary wedges with a reconstructed ocean plate stratigraphy of individual accreted units especially in the tanba and shimanto zones also precise radiometric dating permitted the distinction of metamorphosed units especially in sanbagawa and shimanto belts as a result of these new data since the 1990s the plate tectonic interpretation of the history of the japanese islands was revised by japanese scientists and presented again in terms of accretionary processes linked to a steadily oceanic subduction with an episodic ridge subduction the so called miyashiro type orogeny the review of different data leads to the following conclusions the structure of sw japan is made of a pile of sub horizontal nappes polydeformed with a geometry similar to the one encountered in collisional orogens the geodynamic mechanisms advocated for the tectonic building within the accretionary orogeny concept miyashiro type orogeny are inappropriate a permanent oceanic subduction with the intermittent collision actually subduction of an active ridge or seamount chain is unable to build such structures as this process induces in fact an acceleration of the tectonic erosion and collapse of the upper plate the underthrusting of a micro continent or mature arc is likely needed the exhumation story of sanbagawa hp schists suggests the setting of a continental subduction the petrological and new geochemical data from the literature strongly support the existence beneath the nappes of accretionary complexes of continental bodies showing affinities with south china from which they were once separated the episodic collision underthrusting of such blocks was responsible for the tectonic piling tectonic erosion plaid likely a major role in removing material during the intervening subduction stages a revised geodynamic model implying the collision of the honshu south kitakami kurosegawa and shimanto blocks is proposed for explaining the three orogenic crises which took place respectively at around 240 130 and 80 60 ma ago in sw japan the paleogeographic position and affinity of the hida block with surrounding units in the hinterland are still unclear more work is needed to solve this question

zirconolite and baddeleyite in an ultramafic suite from southern india early ordovician carbonatite type melts associated with extensional collapse of the gondwana crust abstract we report here the occurrence of rare zirconium bearing minerals zirconolite cazrti2o7 and baddeleyite zro2 from an unusual ultramafic suite within the achankovil shear zone acsz in southern india zirconolite occurs as inclusions within spinel in phlogopite graphite spinellite and shows characteristic development of radial cracks baddeleyite is commonly observed as an included phase within phlogopite from phlogopite dunite and graphite spinel glimmerite the mineral also occurs less commonly within spinel and graphite from graphite spinel glimmerite the composition of zirconolite is characterized by an enrichment of u and th over rare earth elements baddeleyite shows abundance of zr with minor hf ti and u the mode of occurrence along with the chemical composition of these minerals implies their formation as early stage crystallization products from a silica undersaturated melt that was enriched in carbonatite phile elements such as ca zr ti and volatiles co2 and h2o we report

improving u th pb electron microprobe dating using monazite age references abstract this article proposes an improved approach to monazite dating by electron microprobe that includes a monazite age reference correction marc during analysis a set of differing monazite standard reference materials with established isotopic ages are measured at the start of the session these measurements are used to test the analytical set up and if necessary to calculate marc factors that can be applied to monazite samples the marc is not intended as a way to correct systematic errors due to problems in set up but rather as a fine scale adjustment for factors that cannot be readily assessed during single sessions long term multi session calculation of marc factors allows for precise monitoring of anomalous behavior among monazite age reference materials during individual sessions the method can also assist in the identification of chemical inhomogeneity in monazite such as that commonly produced by interaction with metasomatic fluids a representative set of electron microprobe monazite age reference materials are presented including two reference monazites that are good examples of monazite with age disturbance induced by metasomatism additional modifications to analytic protocols are proposed including a corrections for count rate increases during long beam dwell times and b improved estimation of background values at line positions by accounting for the effect of mean atomic number

electron microprobe dating of monazite the story abstract this paper is a testimony of how electron microprobe dating of monazite was developed in the early days of this technique in the 90 s five contributions have been collected from nagoya clermont ferrand orleans salzburg and amherst the technique was designed in nagoya by professor suzuki using an old jxa 5a jeol electron microprobe the first results were published in 1991 with great difficulty professor suzuki also created the isochron like pb th diagram to present the data progressive improvement of the method finally allowed the nagoya team to date cenozoic monazite the technique was re discovered in clermont ferrand using a cameca camebax microprobe this team demonstrated the accuracy of the method and proposed statistical tools to improve the precision and to handle multimodal populations the first results were published in 1993 in orleans the french geological survey brgm developed the method with a cameca sx50 to support mapping projects they developed a new method for calculating the age and showed that this technique was very efficient for dating monazite in migmatites in salzburg the first results were obtained in 1996 using a jeol jx 8600 it proved to be very efficient in the alps to distinguish cadomian ordovician variscan and alpine events it allowed this team to directly date a monazite allanite reaction they described for the first time finally the amherst team investigated in detail the technical issues of electron microprobe monazite dating they showed that the best analytical procedures must include at least detailed chemical mapping several interference corrections and special care for background measurements with the help of cameca they designed a specific microprobe for dating named ultrachron with this machine high precision ages can be obtained on well characterized individual grains in thin section giving birth to a new era in geochronology of complex metamorphic rocks

differential response of u pb systems in coexisting accessory minerals winnipeg river subprovince canadian shield implications for archean crustal growth and stabilization the u pb isotopic systems of zircon monazite titanite and some apatite and the pb isotopic composition of k feldspar have been investigated in three areas of the winnipeg river subprovince wrs of the superior province canada in order to define the timing of magmatic and metamorphic processes in this archean gneissic granitoid terrain

changes in garnet chemistry show a progressive denudation of the source areas for permian jurassic sandstones southern kitakami terrane japan abstract garnet is a widespread detrital mineral in permian jurassic sandstones of the southern kitakami terrane electron probe microanalyses of these garnets show a gradual change of chemistry with the age of the sandstones the dominant garnet suites in permian triassic sandstones are grandite with some spessartine almandine in upper triassic sandstones however in lower jurassic sandstones pyrope almandine and spessartine almandine garnets are common whereas grandite garnets are absent garnet suites in middle to upper jurassic sandstones are dominated by pyrope almandine garnet the grandite dominant suites are associated with hornblende epidote and titanite whereas the pyrope almandine dominant suites are associated with biotite these grandite garnets are rich in andradite and have very low spessartine almandine and pyrope contents some of the grandite garnets are anisotropic with oscillatory zoning and sector twinning typical of calcic skarn deposits spessartine almandine garnets are common in low grade metamorphic rocks the diverse suites of pyrope almandine garnets up to 42 mol pyrope from the jurassic sandstones are typical of epidote amphibolite to granulite facies metamorphic rocks the chemistry and optical properties of garnets and the heavy mineral data show that low grade or contact metamorphic rocks such as skarns and hornfelses were widely exposed in the source areas of the permian triassic sandstones high grade metamorphic rocks including granulites and intrusive rocks appeared in early jurassic time and were widespread during the middle jurassic the critical change in the source areas for the southern kitakami terrane occurred during late triassic to early jurassic time and may correspond to the indosinian movements associated with the collision between the north china and south china blocks

middle precambrian provenance of jurassic sandstone in the mino terrane central japan th u total pb evidence from an electron microprobe monazite study precise electron microprobe analyses have been made on detrital monazites in jurassic sandstones of the mino terrane central japan and their th u pb relations are examined in terms of pbo and tho2 tho2 tho2 plus the equivalent of uo2 the pbo tho2 ratios of most detrital monazites 403 of 581 grains cluster in the range from 0 0763 to 0 0618 other grains show the ratio of about 0 0541 46 grains 0 0364 29 grains 0 0170 24 grains and 0 0116 79 grains the pbo tho2 ratio of 0 0763 0 0618 is nearly identical with that of monazites in a middle precambrian 1740 ma gneiss clast from the kamiaso conglomerate of the mino terrane this strongly suggests that the detrital monazites were derived from gneisses and or granitoids of middle precambrian age the ratio of 0 0116 is nearly the same as that of monazites in a permian 274 ma paragneiss of the hida terrane north to the mino terrane the pbo tho2 monazite data coupled with palaeocurrent analyses and petrological characteristics of sandstones show that middle precambrian high grade metamorphic rocks and granitoids were widespread both in the northern and southern source regions of the e w trending jurassic basin of the mino terrane the pbo tho2 ratio of detrial monazites is a useful new measure for the provenance analysis of clastic rocks

chime dating of monazite xenotime zircon and polycrase protocol pitfalls and chemical criterion of possibly discordant age data abstract this paper outlines the chime chemical th u total pb isochron method dating method which is based on precise electron microprobe analyses of th u and pb in th and u bearing accessory minerals such as monazite xenotime zircon and polycrase the age mapping technique that is applicable to young monazite and zircon is also described chime dating consists of analyzing multiple spots within homogeneous age domains that show sufficient compositional variation and then these data are used to construct a pseudo isochron from which an age can be obtained via regression this method when coupled with discrimination of possibly concordant age data by chemical criteria such as the ca si th u pb s ratio for monazite and ca and s contents for zircon has the potential advantage of significant precision and the ability to work with minerals that have a significant initial common pb component this technique can identify two or more homogeneous domains that are separated by age gaps smaller than the error on individual spot age analysis many features that are insignificant in major element analysis can have major impact in the acquisition of trace element data critical factors include the roles of collimator slit detector gas background estimation accelerating voltage probe current x ray interferences and count rate in affecting the accuracy and a way to apply the th and u interference correction without pure th and u oxides or synthesized pure thsio4 the age mapping procedure for young monazite and zircon includes acquiring pbm or pbm intensity of individual pixels with multiple spectrometers correcting background with background maps computed from a measured background intensity by the intensity relationships determined in advance of the measurement calibrating of intensity with standards and calculating of ages from the th u and pb concentrations this technique provides age maps that show differences in age domains on the order of 20 ma with in monazite as young as 100 ma the effect of sample damage by irradiation of intense and prolonged probe measurement is also described

the cleaverville group in the west pilbara coastal granitoid greenstone terrain of western australia an example of a mid archaean immature oceanic island arc succession abstract the 4400 m thick volcanosedimentary succession that forms the 3200 3000 yr old cleaverville group is well preserved along the western coastline of the pilbara in northwestern western australia two lithological assemblages namely the volcanic rock assemblage and the chemical volcanosedimentary rock assemblage are identified in the cleaverville group the volcanic rock assemblage is approximately 3300 m thick and consists mainly of pillow basalt and rhyolitic flow rocks the chemical volcanosedimentary rock assemblage which is at least 1100 m thick comprises chemogenic sedimentary rocks chert and banded iron formation and volcanosedimentary rocks coarse and fine grained tuffs three volcanosedimentary cycles have been recognized from stratigraphic patterns displayed by the cleaverville group each cycle involved an initial episode of basaltic volcanism that was followed by rhyolitic volcanism and then by chemogenic sedimentation boundaries between each cyclic package of basalt rhyolite and chemogenic sedimentary rocks are conformable surfaces the thickness of volcanic rocks relative to chemogenic sedimentary rocks within each package decreases upwards within the succession the upward decrease in the proportion of volcanic rocks in each package suggests that bimodal volcanic activity at the depositional site decreased in intensity through time basalts are primarily non vesicular whereas chemogenic sedimentary rocks are very finely laminated and lack evidence of continental derivation these features imply that the cleaverville group was deposited in an offshore probably deep sea environment the lizard hills formation lies above an angular unconformity on the cleaverville group the formation records the first appearance in the west pilbara coastal granitoid greenstone terrain of sedimentary rocks that are of a continental origin the cyclic record of bimodal volcanism and accompanying volcanogenic sedimentation within an oceanic setting suggests that the cleaverville group originated in a tectonic environment similar to a modern immature oceanic island arc furthermore it is possible that continentally derived sedimentary rocks of the lizard hills formation record an arc continent collision event

mid holocene sea level highstand along the southeast coast of china various sea level curves have been proposed for the coast of china in the past two decades these sea level curves indicate a complex history of holocene sea level and so the debate on whether or not a higher mid holocene sea level highstand exists in the coast of china has continued this paper aims to re examine the holocene sea level history for the low latitude part of the china coast between 18 n and 32 n by re assessing all the sea level data available from the east to south coasts and separating them according to geological settings in order to examine the influences of global and local factors the reconstructed sea level histories from different coastal sectors of the china coast reveal a certain degree of variability in the timing and height of mid holocene sea level highstand within large river deltas the mid holocene sea level highstand occurred earlier by almost 1000 years than that from other coastal sites the highstand from large river deltas appears also lower in altitude a few metres below the present day sea level due probably to the local factors of subsidence and sediment consolidation in geologically stable coastal sites the highstand is recorded at the same altitude as the present day sea level a 1 2 m higher highstand is found from sites where tectonic uplift is observed