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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

petroleum system modeling in the eastern cordillera of colombia using geochemistry and timing of thrusting and deformation in the present study stratigraphic data from cores and outcrop sections are integrated with data on thermal maturity organic facies and thermochronometric information to reconstruct the tectonic and associated petroleum system evolution of the eastern foothills thrust belt along the colombian eastern cordillera one of the most prolific hydrocarbon provinces in northern south america sedimentary and tectonic burial of the foreland autochthon caused maturation of the coniacian to santonian shallow marine chipaque formation resulting in successive and diachronous episodes of hydrocarbon migration and trapping one dimensional and two dimensional maturation modeling indicates that oil generation from the chipaque formation began at the paleocene eocene boundary 55 ma in the southern parts of what is now the eastern cordillera and progressed to the north by the late oligocene tectonic inversion of the eastern cordillera exhumed most of these kitchens terminating the oil generation from the chipaque formation kitchens migrated northward and eastward during the oligocene and early miocene because of the absence or subsequent erosion of traps it is likely that the southernmost source rocks expelled most of their oil without any appreciable accumulation our modeling indicates that there were two important kitchens during the cenozoic the larger of the two was located in the present day eastern cordillera and it was most productive in the late eocene early oligocene the second kitchen which generated oil throughout the neogene was located in the foredeep of the llanos basin adjacent to the mountain front considerable amounts of oil from this recent pulse have accumulated in both deep and shallow reservoirs along the eastern foothills the modeled reservoir charge history also explains the substantial biodegradation of oils in reservoirs that are today much too deep to support the process biodegradation must have occurred when the reservoirs were shallower and at cooler temperatures and they remained active until the reservoirs were buried to depths where temperatures were high enough to prevent further bacterial activity

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

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

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

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

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

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

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

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

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

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

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

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

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

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

paleoclimate and the global distribution of paleosols a theoretical model is developed for the relationship between paleoclimate and paleosols for the time interval following the widespread appearance of vascular land plants the model defines four paleoclimatic zones 1 a wet equatorial zone primarily characterized by oxisols and secondarily by argillisols and histosols 2 a subtropical dry zone containing calcisols and less commonly gypsisols and vertisols 3 a moist mid latitude zone with argillisols spodosols gleysols and histosols and 4 a polar zone featuring protosols and gleysols the model is general in nature and its application to the geologic past will be affected by variability through time in paleogeography and paleoclimatic parameters

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

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