a global review of sediment source fingerprinting research incorporating fallout radiocesium 137cs abstract information on the main sources supplying deleterious sediment loads to river systems is needed to improve our understanding of soil erosion processes to better target erosion control measures in particular it is important to quantify the respective contributions of surface and subsurface sources to material degrading waterbodies radiocesium 137cs emitted during thermonuclear bomb testing 1950 1980 and nuclear accidents provides significant discrimination between surface material exposed to atmospheric fallout and subsurface material sheltered from it a systematic worldwide review of research articles n 123 that used 137cs to trace sediment sources showed that the united kingdom n 24 australia n 23 and the united states n 20 had the highest number of publications utilizing 137cs in a sediment tracing framework in contrast few studies were published for catchments in africa n 9 or south america n 2 in the northern hemisphere positive relationships were evident between 137cs activities in surface and subsurface sources and the proportion of thermonuclear bomb fallout however given the low proportions of fallout received in regions between 0 and 20 n and 0 20 s the potential application of 137cs tracing techniques may be limited in this area of the world as well as in agricultural regions with severe soil erosion i e chinese loess plateau and south africa in total 94 of the studies researching surface and subsurface sources that analysed 137cs as a potential tracing property included this parameter in end member mixing models the main challenges for the future of this technique are related to the access to ultra low background gamma spectrometry facilities and the development of surrogate tracers future research should ensure that basic catchment information and details on the sampling design are properly documented to ensure studies are reproducible moreover researchers should provide raw measurement data to help improve our global understanding of 137cs dynamics in soil erosion research

ree composition of an aqueous magmatic fluid a fluid inclusion study from the capitan pluton new mexico u s a abstract the ree content of aqueous magmatic derived fluids trapped in fluid inclusions has been determined by icp ms after crush leach extraction of the fluids in 4 samples the total ree concentration varies between 200 and 1300 ppm and is dominated by the lree especially la ce and nd fluids were released at different times from a melt which changed composition as it underwent fractional crystallisation and this is reflected in the concentration of ree in solution early formed quartz fluorite veins hosted by granophyre contain the highest concentration of ree and appear to be in equilibrium with aplite melt from which the fluid was inferred to have been derived since calculated fluid melt distribution coefficients are in broad agreement with experimentally derived values variation in the ree content of the fluids is independent of salinity which remains constant at 80 wt total salts later veins hosted by aplite contain fluid derived from a porphyritic melt and have lower ree concentrations reflecting the greater incorporation of ree into mineral phases crystallising from the melt titanite and allanite occur in these later veins ree mineral fluid distribution coefficients have been calculated for these minerals and show there is a strong preference for ree to partition into the minerals

palaeomagnetic data suggest link between the archaean proterozoic boundary and inner core nucleation it is generally believed that the earth s magnetic field arises from dynamo action in the convecting outer core1 3 thus the geomagnetic field and especially its strength can provide information about core processes recent determinations of the geomagnetic palaeointensity using archaean and early proterozoic samples from the kaapvaal and superior cratons are consistent with a sharp increase in the magnitude of the geomagnetic field between 2 7 and 2 1 gyr analysis of published late archaean and early proterozoic apparent polar wander paths shows that an abrupt change in the rate and style of continental motion occurred at about 2 5 2 6 gyr ago if this change is also interpreted to be related to the growth of an inner core then an intriguing conjecture arises that the archaean proterozoic transition is related to inner core nucleation

thermal histories of the core and mantle recognition that the cooling of the core is accomplished by conduction of heat into a thermal boundary layer d at the base of the mantle partly decouples calculations of the thermal histories of the core and mantle both are controlled by the temperature dependent rheology of the mantle but in different ways thermal parameters of the earth are more tightly constrained than hitherto by demanding that they satisfy both core and mantle histories we require evolution from an early state in which the temperatures of the top of the core and the base of the mantle were both very close to the mantle solidus to the present state in which a temperature increment estimated to be 800 k has developed across d the thermal history is not very dependent upon the assumption of newtonian or non newtonian mantle rheology the thermal boundary layer at the base of the mantle i e d developed within the first few hundred million years and the temperature increment across it is still increasing slowly in our preferred model the present temperature at the top of the core is 3800 k and the mantle temperature extrapolated to the core boundary without the thermal boundary layer is 3000 k the mantle solidus is 3860 k these temperatures could be varied within quite wide limits without seriously affecting our conclusions core gravitational energy release is found to have been remarkably constant at 3 1011 w nearly 20 of the core heat flux for the past 3 109 y although the total terrestrial heat flux has decreased by a factor of 2 or 3 in that time this gravitational energy can power the chemical dynamo in spite of a core heat flux that is less than that required by conduction down an adiabatic gradient in the outer core part of the gravitational energy is used to redistribute the excess heat back into the core leaving 1 8 1011 w to drive the dynamo at no time was the dynamo thermally driven and the present radioactive heating in the core is negligibly small the dynamo can persist indefinitely into the future available power 1010 y from now is estimated to be 0 3 1011 w if linear mantle rheology is assumed or more if mantle rheology is non linear the assumption that the gravitational constant decreases with time imposes an implausible rate of decrease in dynamo energy with conventional thermodynamics it also requires radiogenic heating of the mantle considerably in excess of the likely content of radioactive elements

potential evidence of fossilised neoproterozoic deep life sem observations on calcite veins from oppaminda creek arkaroola south australia scanning electron microscopy revealed micron sized globular and coccoid objects associated with filaments and mucus like patches in antitaxial fibrous calcite veins from oppaminda creek northern flinders ranges south australia chemically the objects only differ from their calcite caco3 matrix by a higher sulphur content the 585 ma veins formed at about 3 6 km below the surface fluid inclusions indicate a temperature of formation of about 60 80 c and not exceeding 100 c a non biogenic origin of the objects is discussed but considered unlikely instead morphology chemistry and size distribution all indicate that the objects are fossilised microbes that lived in the veins at the time and depth of vein formation

early differentiation of the earth and the problem of mantle siderophile elements a new approach the long standing problem of the excess abundances of siderophile elements in the mantle can be resolved by considering an equilibrium core mantle differentiation in the earth at 3000 to 3500 kelvin this high temperature differentiation results in mantle siderophile element abundances that closely match the observed values some lithophile light elements could enter the core in this process as is necessary to account for its low density the abundances of siderophile elements in the mantle are consistent with the conclusion derived from the recent physical models that the earth was molten during accretion

a novel method for determining residence times of river and lake sediments based on disequilibrium in the thorium decay series sediment fluxes in rivers have proved difficult to measure or model at timescales relevant to land and water resource management decisions determining transport rates and residence times is complicated by the intermittent movement and temporary storage of sediments in natural streams this paper presents a new tool for estimating the residence times of river borne sediments based on the observed disequilibria between the naturally occurring radionuclides 228ra and 232th in the thorium decay series disequilibrium between concentrations of 228ra half life 5 75 years and its long lived parent 232th has been observed in marine environments and in terrestrial freshwaters but has not been previously reported in fluvial sediments or soils here we report 228ra excesses in sandy stream and silty lake sediments from southeastern australia the excess is developed in hillslope soils in the catchment headwaters and begins to decay back to secular equilibrium once the sediment is finally removed from contact with the soil water the short half life of 228ra enables this process to be used to investigate fluvial sediment transfers and alluvial and lacustrine sediment storages over the past 30 years when combined with indicators of sediment source such as 226ra 232th and 230th 232th ratios observation of this excess should provide a useful new tool for examining the residence and transit times of bed load and suspended load sediments in streams and lakes

synthetic fluid inclusions vii re equilibration of fluid inclusions in quartz during laboratory simulated metamorphic burial and uplift p t conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations these observations suggest that inclusions formed during early stages of regional metamorphism continue to re equilibrate during burial and subsequent uplift in response to differential pressure p t conditions accompanying burial and uplift were experimentally simulated by initially forming pure h2o inclusions in quartz at elevated temperatures and pressures and then re equilibrating the inclusions in the presence of a 20 wt nacl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re equilibration in all samples re equilibrated at confining pressures below the internal pressure some inclusions were formed that had compositions of 20 wt nacl and densities in accord with the final p t conditions additionally some inclusions were observed to contain fluids of intermediate salinities between 0 and 20 wt nacl densities of these inclusions were also consistent with formation at the re equilibration p t conditions the remainder of the fluid inclusions observed in these samples contained pure h2o and their homogenization temperatures corresponded to densities intermediate between the initial and final p t conditions in short term experiments 7 days where the initial internal overpressure exceeded 1 kbar no inclusions were found that contained the original density and none were found to have totally re equilibrated instead most h2o inclusions re equilibrated until their internal pressures were between 750 and 1500 bars above the confining pressure regardless of the initial pressure differential in a long term experiment 52 days inclusions re equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar i e total re equilibration and 1 2 kbar above the confining pressure in experiments where the confining pressure during re equilibration exceeded the initial internal pressure densities of pure h2o inclusions increased to values intermediate between the initial and final p t conditions additionally these inclusions were generally surrounded by a three dimensional halo of smaller inclusions also of intermediate density resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure in extreme cases where confining pressures were 4 5 kbar above the initial pressure the parent inclusion almost completely closed leaving only the three dimensional array of small 5 m inclusions the outline of which may be several times the volume of the original inclusion groups of such inclusions closely resemble textures commonly observed in medium to high grade metamorphic rocks inclusions containing 10 and 42 wt nacl solutions trapped at 600 c and 3 kbar were re equilibrated at 600 c and 1 kbar for 5 days in dry argon to evaluate the importance of h2o diffusion as a mechanism of lowering the inclusion bulk density salinities of re equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved density changes similar to those previously described were noted in these experiments in inclusions showing no visible microfractures therefore density variations observed in inclusions in this study re equilibrated under rapid deformation conditions are considered to result from a change in the inclusion volume without significant loss of contents by diffusion or leakage

basin related uranium mineral systems in australia a review of critical features abstract this paper reviews critical features of basin related uranium mineral systems in australia these mineral systems include proterozoic unconformity related uranium systems formed predominantly from diagenetic fluids expelled from sandstones overlying the unconformity sandstone hosted uranium systems formed from the influx of oxidised groundwaters through sandstone aquifers and calcrete uranium systems formed from oxidised groundwaters flowing through palaeochannel aquifers sand and calcrete the review uses the so called source pathway trap paradigm to summarise critical features of fertile mineral systems however the scheme is expanded to include information on the geological setting age and relative timing of mineralisation and preservation of mineral systems the critical features are also summarised in three separate tables these features can provide the basis to conduct mineral potential and prospectivity analysis in an area such analysis requires identification of mappable signatures of above mentioned critical features in geological geophysical and geochemical datasets the review of fertile basin related systems shows that these systems require the presence of at least four ingredients a source of leachable uranium and vanadium and potassium for calcrete uranium deposits suitable hydrological architecture enabling connection between the source and the sink site of accumulation physical and chemical sinks or traps and a post mineralisation setting favourable for preservation the review also discusses factors that may control the efficiency of mineral systems assuming that world class deposits result from more efficient mineral systems the review presents a brief discussion of factors which may have controlled the formation of large deposits in the lake frome region in south australia the chu sarysu and syrdarya basins in kazakhstan and calcrete uranium deposits in the yilgarn region western australia

petrology and u pb geochronology of mafic high pressure metamorphic coronites from the tshenukutish domain eastern grenville province abstract a suite of mafic and ultramafic rocks from the tshenukutish domain eastern grenville province have been the subject of a detailed petrographic and geochemical study combined with u pb geochronology the tshenukutish domain is the highest tectonic level in the recently discovered eclogite bearing manicouagan imbricate zone the mafic and ultramafic rocks are characteristic of two of the lithotectonic segments in the domain the lac espadon segment and the baie du nord segment in the lac espadon segment cumulate textures and geochemical characteristics suggest that the units represent a layered mafic and ultramafic complex and an unrelated apatite rich fe ti mafic pegmatite nelsonite body in contrast the samples from the baie du nord segment represent fairly homogeneous fe ti gabbros and anorthosites the samples studied show abundant petrographic evidence for high pressure metamorphism for instance the widespread development of garnet clinopyroxene and kyanite bearing metamorphic assemblages estimates of the conditions of high pressure metamorphism in previous studies and melting textures in deformed and hydrated gabbro margins are in the range 750 900 c and 1600 1800 mpa the gabbroic end members from both segments suggest within plate tholeiite petrotectonic signatures ree patterns of gabbros and cumulates in both segments suggest fractionation from a tholeiitic source cumulate textures fractionation and inherited zircons suggest high crustal level emplacement of the magmatic protoliths in the tshenukutish domain in the lac espadon segment u pb ages of igneous zircon and baddeleyite give an age range of 1643 1629 ma for the emplacement of the layered complex the nelsonite in the les gives a poorly constrained igneous zircon age of 1596 126 99 ma in the baie du nord segment baddeleyite gives an age of 1170 5 ma for emplacement of the fe ti gabbros this is the youngest intrusion in the td and thus gives a maximum limit for the onset of grenvillian metamorphism ages of high p metamorphism are further constrained by zircon formed during partial melting of deformed and hydrated fe ti gabbro margins 1046 3 ma overgrowth of igneous zircon 1042 22 28 ma in the nelsonite saccharoidal zircon replacing baddeleyite 1030 10 7 ma and 1030 12 ma and new growth of equant zircon 1012 12 ma from the undeformed interior of the gabbros these ages indicate that the high p metamorphism of the tshenukutish domain was late grenvillian ottawan retrogression to amphibolite facies is constrained by the ages of titanite 1006 997 ma in deformed gabbro margins rutile ages range between 960 and 929 ma and are interpreted as cooling ages the difference between the ages of titanite and rutile suggest slow cooling of the tshenukutish domain after initial high pressure and temperature metamorphism and exhumation

multiphase carbonate salt immiscibility in carbonatite melts data on melt inclusions from the krestovskiy massif minerals polar siberia minerals of olivine melilite and olivine monticellite rocks from the krestovskiy massif contain primary silicate salt carbonate salt and salt melt inclusions silicate salt inclusions are present in perovskite i and melilite thermometric experiments conducted on these inclusions at 1 230 1 250 c showed silicate carbonate liquid immiscibility globules of composite carbonate salt melt rich in alkalies p s and cl separated in silicate melt carbonate salt globules in some inclusions from perovskite ii at 1 190 1 200 c separated into immiscible liquid phases of simpler composition carbonate salt and salt inclusions occur in monticellite melilite and garnet and homogenize at close temperatures 980 780 c they contain alkalies ca p so3 cl and co2 according to the ratio of these components and predominance of one of them melt inclusions are divided into 6 types i hyperalkaline cao na2o k2o 1 carbonate melts ii moderately alkaline cao na2o k2o 1 carbonate melts iii sulfate alkaline melts iv phosphate alkaline melts v alkali chloridic melts and vi calc carbonate melts joint occurrence of all the above types and their syngenetic character were established some inclusions demonstrated carbonate salt immiscibility phenomena at 840 800 c a conclusion in made that the origin of carbonate melts during the formation of intrusion rocks is related to silicate carbonate immiscibility in parental alkali ultrabasic magma the separated carbonate melt had a complex alkaline composition under unstable conditions the melt began to decompose into simpler immiscible fractions different types of carbonate salt and salt inclusions seem to reflect the composition of these spatially isolated immiscible fractions liquid carbonate salt immiscibility took place in a wide temperature range from 1 200 1 190 c to 800 c the occurrence of this kind of processes under macroconditions might most likely cause the appearance of different types of immiscible carbonate salt melts and lead to the formation of different types of carbonatites alkali phosphatic alkali sulfatic alkali chloridic and most widespread calcitic ones

magmatic immiscibility and fluid phase evolution in the mount genis granite southeastern sardinia italy the mount genis granite is one of the post tectonic intrusives emplaced late in the magmatic history of the hercynian batholith in sardinia devitrified silicate melt inclusions are present in some magmatic rock forming and miarolitic quartz these magmatic remnants show initial melting at 680 720 c high temperature observations 700 800 c revealed the presence in some of the inclusions of mixed hydrosaline melt l1 and silicate melt l2 with extremely variable l1l2 ratios electron microprobe analyses indicate l1 to be k na dominated chlorides inclusions of mixed silicate and hydrosaline melts are interpreted to have been formed by heterogeneous trapping of two immiscible fluid phases silicate hydrosaline after second boiling most likely during the final crystallization stage magma derived brines 63 eq wt nacl circulated at subsolidus conditions from 600 c and were retained in the miarolitic cavities down to about 400 c fluid unmixing occurred locally in the miarolitic cavities from 550 to 412 c at temperatures of 400 to 100 c the microgranite was invaded by diluted waters 4 5 eq wt nacl a possible model for fluid evolution begins with a hydrosaline melt exsolving from the magma at the late magmatic stage the absence of boiling within the volatile hydrosaline system shows that brines can occur by direct magmatic immiscibility the comprehensive hydrothermal evolution suggests a nearly isobaric cooling path with local boiling episodes in the miaroles probably in coincidence with invasion of external waters

francoisite ce a new mineral species from la creusaz uranium deposit valais switzerland and from radium ridge flinders ranges south australia description and genesis the new mineral francoisite ce ce nd ca uo 2 3 o oh po 4 2 6h 2 o is the ce analog of francoisite nd it has been discovered simultaneously at the la creusaz uranium deposit near les marecottes in valais switzerland and at the number 2 uranium workings radium ridge near mt painter arkaroola area northern flinders ranges in south australia francoisite ce is a uranyl bearing supergene mineral that results from the alteration under oxidative conditions of ree and u 4 bearing hypogene minerals allanite ce monazite ce uraninite at les marecottes monazite ce ishikawaite samarskite and an unknown primary u mineral at radium ridge the ree composition of francoisite ce results from a short aqueous transport of ree leached out of primary minerals most likely monazite ce at radium ridge and allanite ce at la creusaz with fractionation among ree resulting mainly from aqueous transport with only limited ce loss due to oxidation to ce 4 during transport

discordant iron rich ultramafic pegmatites in the bushveld complex and their relationship to iron rich intercumulus and residual liquids the iron rich ultramafic pegmatites comprise a suite of coarse grained rocks that form discordant bodies within the layered sequence of the bushveld complex these pegmatites which are considerably more abundant than is generally realized provide evidence for the differentiation of iron rich residual melts the pegmatites are composed largely of iron rich olivine and clinopyroxene together with ti magnetite and ilmenite feldspar is characteristically absent but paradoxically the pegmatites preferentially replace anorthositic cumulates two subgroups are recognized olivine clinopyroxene pegmatite and fe ti oxide pegmatite with increased stratigraphic height the pegmatites become richer in fe ti oxides thus olivine clinopyroxene pegmatite is prevalent in the upper critical and lower main zones whereas fe ti oxide pegmatite is restricted to the upper main and upper zones zoned pegmatite with a core of fe ti oxide pegmatite is transitional between the two subgroups new whole rock and electron microprobe analyses of olivine clinopyroxene pegmatite from the upper critical and lower main zones provide convincing evidence that their composition is directly related to height cryptic compositional variations are analogous to those displayed by the layered cumulates but for a given height the pegmatites are always more evolved compositions of clinopyroxene in the pegmatites reflect a near linear relationship with height whereas cumulus pyroxenes display upward iron enrichment trends complicated by replenishment and reaction with trapped intercumulus liquid the olivine clinopyroxene pegmatite formed by magmatic replacement of earlier formed cumulates in response to infiltration of iron rich melts suitably differentiated melts comprised intercumulus and residual liquids derived from thick anorthosite layers the absence of feldspar although not fully understood is attributed to an immiscible relationship between dense iron rich melts and light silica alkali rich liquids the latter infiltrated upward to be reincorporated into the resident magma the iron rich melts however drained down into the crystallizing cumulate pile channelling along early formed fractures and joints was significant locally resulting in huge pipe like bodies of pegmatite the iron rich melts became increasingly differentiated with height partly in response to the fractional crystallization of more evolved cumulates the olivine clinopyroxene pegmatites are related to infiltration of fe ti oxide rich silicate melt whereas fe ti oxide pegmatite is ascribed to fe ti oxide liquid as originally argued by bateman 1951 the bushveld complex followed the fenner trend of almost uninterrupted iron enrichment evidence of pronounced iron enrichment is however manifested in the discordant iron rich ultramafic pegmatites several thousands of metres below the height at which iron rich cumulates are observed

a magmatic hydrothermal transition in arkaroola northern flinders ranges south australia from diopside titanite pegmatites to hematite quartz growth a set of palaeozoic diopside titanite veins are present in mesoproterozoic metagranites and metasediments that constitute the basement mt painter inlier of the adelaide fold belt south aus tralia these massive veins up to 1 m of pegmatitic nature contain large crystals of diopside lree y enriched titanite up to 40 cm in length and minor amounts of quartz they can be used to trace the sys tem s development from a high temperature magmatic stage through to a massive hydrothermal event the pegmatitic origin of these veins is evident from a complex fluid melt inclusion assemblage consisting of a highly saline inhomogeneous fluid and relicts of melt immiscibility of melt and heterogeneous highly saline fluids exceeding 61 eq mass nacl is preserved in primary inclusions in diopside and secondary inclusions in titanite indicating relatively shallow conditions of formation 510 20 c and 130 10 mpa graphic intergrowth of diopside and albite occurs at the contact with granitic pegmatites the system evolved into hydrothermal conditions which can be deduced from a later population of only fluid inclusions homogeneous and less saline 40 eq mass nacl trapped around 350 20 c and 80 10 mpa during quartz crystallization the conditions moved across the halite liquidus resulting in a heterogeneous mixture of brine and halite crystals which were trapped at 200 20 c and 50 10 mpa brecciation and a palaeo geother mal system overprinted the pegmatitic veins with an epithermal hematite quartz assemblage and lesser amounts of bladed calcite and fluorite in an intermit tently boiling hydrothermal system of fairly pure h2o at 100 140 c and 1 5 mpa remobilization of lrees and y from titanite and or the granitic host rock is evidenced by precipitation of apatite allanite and wakefieldite in an intermediate stage occasional incorporation of radioactive elements or minerals presumably u rich in the fluorite is responsible for radiolysis of h2 ot o h 2

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

magmatic hydrothermal evolution of highly fractionated granites evidence from the kuiqi miarolite in fujian province se china abstract the kuiqi miarolite a highly evolved alkaline granite pluton is situated in fujian province southeastern china quartz crystals from the kuiqi miarolite contain abundant inclusions which have preserved a complete record of the magmatic hydrothermal evolution five inclusion type were identified i e the melt m type melt fluid ml type daughter mineral bearing s type vapor rich v type and aqueous l type inclusions integrated petrographic microthermometric and laser raman spectroscopy studies demonstrate that the whole magmatic hydrothermal evolution at kuiqi comprises three stages i e the magmatic magmatic hydrothermal and hydrothermal stages the m type inclusions minimal trapping temperatures ca 710 800 c represent the melts entrapped at the magmatic stage of crystallization while the occurrence of euhedral prismatic arfvedsonites in these melt inclusions indicates that the granitic magma was probably volatile rich at the magmatic hydrothermal stage both the ml type inclusions t h ca 500 710 c and coexisting m and v type inclusions reflect the presence of late magmatic fluid circulation and melt volatile immiscibility exhibiting a transition toward the hydrothermal stage at the hydrothermal stage the pressure and temperature 700 485 c drop may have led to oversaturation of the primary saline fluids resulting in the phase separation a highly saline and a volatile rich fluid occurred accompanied by the widespread vapor brine immiscibility the l type inclusions in the miarolitic quartz display bimodal salinity distribution the t h and salinity of the inclusions at the bottom l 1 miarolitic quartz are ca 303 427 c and ca 6 6 17 9 wt nacl equiv respectively while that of the inclusions at the top l 2 are ca 165 232 c and ca 0 2 5 7 wt nacl equiv respectively this indicates a drop of fluid temperature and salinity during the miarolitic cavity formation moreover the low homogenization temperatures and salinities of the l type inclusions suggest an influx of meteoric water during the late hydrothermal evolution stage

cooling the core and mantle by plume and plate flows summary coupled thermal histories of the mantle and core are computed under various assumptions about the way the core is cooled using empirical constraints on the present amounts of heat being transported by various modes of mantle flow the mantle is cooled mainly by the large scale flow associated with plates assumed here to have operated throughout earth history the core is cooled by removal of heat from the thermal boundary at the base of the mantle plumes both tails and heads will accomplish much of this removal if they originate at the core mantle boundary while there may also be a significant effect from the plate scale flow removal by non plume upwelling from the lower boundary layer cannot be ruled out the thermal history of the core and the relative importance of plumes depend strongly on whether the heat removal is controlled by the viscosity at the core mantle boundary as would be the case with plumes or by the viscosity within the bulk of the mantle as would be the case for plate scale flow or non plume flow if plumes are the dominant means of core cooling the core will not have cooled by more than about 300 c during earth history plumes would have been established early and their heat flux would have been fairly constant on the other hand if non plume upwelling or the plate scale flow are significant at present they and plumes could have been much more important in the past and the core could have cooled by up to 1000 c

cooling history of earth s core with high thermal conductivity abstract thermal evolution models of earth s core constrain the power available to the geodynamo process that generates the geomagnetic field the evolution of the solid inner core and the thermal history of the overlying mantle recent upward revision of the thermal conductivity of liquid iron mixtures by a factor of 2 3 has drastically reduced the estimated power available to generate the present day geomagnetic field moreover this high conductivity increases the amount of heat that is conducted out of the core down the adiabatic gradient bringing it into line with the highest estimates of present day core mantle boundary heat flow these issues raise problems with the standard scenario of core cooling in which the core has remained completely well mixed and relatively cool for the past 3 5 ga this paper presents cooling histories for earth s core spanning the last 3 5 ga to constrain the thermodynamic conditions corresponding to marginal dynamo evolution i e where the ohmic dissipation remains just positive over time the radial variation of core properties is represented by polynomials which gives good agreement with radial profiles derived from seismological and mineralogical data and allows the governing energy and entropy equations to be solved analytically time dependent evolution of liquid and solid light element concentrations the melting curve and gravitational energy are calculated for an fe o s si model of core chemistry a suite of cooling histories are presented by varying the inner core boundary density jump thermal conductivity and amount of radiogenic heat production in the core all models where the core remains superadiabatic predict an inner core age of 600 myr about two times younger than estimates based on old lower thermal conductivity estimates and core temperatures that exceed present estimates of the lower mantle solidus prior to the last 0 5 1 5 ga allowing the top of the core to become strongly subadiabatic in recent times pushes the onset of inner core nucleation back to 1 5 gyr but the ancient core temperature still implies a partially molten mantle prior to 2 ga based on these results the scenario of a long lived basal magma ocean and subadiabatic present day core seems hard to avoid

magnetodynamo lifetimes for rocky earth mass exoplanets with contrasting mantle convection regimes 1 we used a thermal model of an iron core to calculate magnetodynamo evolution in earth mass rocky planets to determine the sensitivity of dynamo lifetime and intensity to planets with different mantle tectonic regimes surface temperatures and core properties the heat flow at the core mantle boundary cmb is derived from numerical models of mantle convection with a viscous pseudoplastic rheology that captures the phenomenology of plate like tectonics our thermal evolution models predict a long lived 8 gyr field for earth and similar dynamo evolution for earth mass exoplanets with plate tectonics both elevated surface temperature and pressure dependent mantle viscosity reduce the cmb heat flow but produce only slightly longer lived dynamos 8 9 5 gyr single plate stagnant lid planets with relatively low cmb heat flow produce long lived 10 5 gyr dynamos these weaker dynamos can cease for several billions of years and subsequently reactivate due to the additional entropy production associated with inner core growth a possible explanation for the absence of a magnetic field on present day venus we also show that dynamo operation is sensitive to the initial temperature size and solidus of a planet s core these dependencies would severely challenge any attempt to distinguish exoplanets with plate tectonics and stagnant lids based on the presence or absence of a magnetic field

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

highly differentiated fluorine rich alkaline granitic magma linked to rare metal mineralization a case study from the boziguo er rare metal granitic pluton in south tianshan terrane xinjiang nw china abstract rare metal bearing alkaline granites have attracted extensive interests because of their economic significance the early permian 290 ma boziguo er alkaline granitic pluton exposed in the middle segment of the south tianshan terrane xinjiang nw china contain nb ta zr th u and ree bearing accessory minerals and host a large scale rare metal deposit the unalterated alkaline granites are mainly composed of alkali feldspars 40 vol orthoclase microcline and 30 vol albite quartz 20 vol arfvedsonite 5 vol and biotite 5 vol with accessory minerals at least including zircon monazite pyrochlore fe ti oxides xenotime bastnasite and astrophyllite the existence of two types of alkaline feldspars which respectively show nearly pure ab and or end member compositions suggest that the boziguo er pluton can be classified as subsolvus granites rare metal elements in the pluton are mainly contained by pyrochlore nb ta zircon zr hf th u and hree and monazite lrees grains mineral chemistry suggests that the pyrochlore and monazite are of primary igneous mineral based on morphology internal texture and mineral chemistry four types of zircons have been identified type i zircon may have crystallized from volatile undersaturated early stage magmas while type iia zircon crystallized from volatile fluorine saturated magmas the type iib and type iii zircons could have grown in an lree depleted silicate melt after the crystallization of the lree rich minerals e g monazite or an early aqueous fluid during the transition from a magmatic to hydrothermal system the type iv zircons can be regarded as low temperature hydrothermal ones a semiquantitative calculation based on mineral compositions of biotites yields 0 51 2 14 wt for f contents in granitic melts the high contents of fluorine in the hydrous minerals suggest a fluorine enriched characteristic for melt which would not only prolong the duration of the magmatic differentiation but can also enhance the solubility of ore forming elements in magma the magmatic differentiation was mainly dominated by fractional crystallization of alkali feldspar and amphibole extensive rare metal mineralization in the pluton likely occurred within a limited temperature interval and was related to the crystallization of a highly evolved intergranular melt at the latest magmatic stage

the role of magmatic and hydrothermal processes in the evolution of be bearing pegmatites evidence from beryl and its breakdown products beryl and euclase crystals from the mina do santino and the jacu pegmatites in the borborema pegmatite province in northeastern brazil contain several generations of melt and fluid inclusions which allow interpretation of p t x conditions responsible for beryl crystallization and for alteration of a primary pegmatitic mineral assemblage to a mixture of hydrothermal minerals euclase bertrandite kaolinite and quartz primary melt and fluid inclusions hosted by beryl were trapped simultaneously however their homogenization temperatures are significantly higher 870 900 c than the values previously reported for pegmatitic systems 712 c and should be treated with caution an isobaric drop of temperature resulted in the exsolution of a fluid a low salinity co2 enriched phase and a saline water rich phase were trapped in pseudosecondary inclusions in beryl at a pressure of 2 1 2 7 kbar and temperature of 390 480 c cooling of the country rocks below 400 c caused a ductile to brittle transition and allowed infiltration of cold groundwater which further decreased the temperature in the system to 190 240 c at the same time the pressure dropped from a lithostatic 2 1 2 7 kbar to a hydrostatic value 0 57 0 73 kbar consequently minerals deposited under magmatic conditions feldspars and beryl became unstable and a newly formed hydrothermal mineral paragenesis euclase bertrandite kaolinite and quartz overprinted the earlier one the hydrothermal fluids responsible for the alteration differ from the earlier exsolved fluids in having a lower salinity lower homogenization temperature the absence of co2 and the presence of ch4

geochemistry of th u ree mineralizing magmatic fluids capitan mountains new mexico the capitan mountains in south central new mexico are formed by an east west trending tertiary 28 3 ma alkali feldspar granitic pluton which intruded permian sedimentary rocks of the yeso and san andres formations several widely distributed th u ree veins which occur along the western end and flanks of the pluton are characterized by smoky and clear quartz fluorite adularia hematite calcite thorite titanite allanite chlorite and clay minerals four main types of fluid inclusions representing a large range in temperature and salinity occur in the quartz and fluorite type 1 inclusions are the dominant type and represent high temperature high salinity fluids with th up to 600 degrees c and bulk salinities up to 84 wt percent nacl kcl equiv inclusion types 2 3 and 4 have decreasing t h and salinities type 1 and 2 inclusions define a halite trend when plotted in the nacl kcl h 2 o system the observed t h salinity trends suggest a fluid evolution from the original parent fluid by cooling and crystallization of halite the chemical composition of the inclusion fluid was determined by a crush and leach extraction and analysis by icp ms icp aes and ion chromatography the cations are dominated by na k ca mn and fe other cations analyzed include mg al ba li sr rb cs pb zn and ree cu was below detection the dominant anions are cl and so 4 levels of i and br were usually low the main controls on fluid compositional variations are thought to be partitioning during vapor exsolution from the magma and mineral precipitation in the veins the delta 18 o from quartz and delta d from inclusion fluids in quartz values of the fluids are 7 1 to 8 0 and 54 to 80 per mil respectively based on field relations fluid inclusion microthermometry stable isotope data petrographic data and inclusion fluid chemistry the fluids responsible for the th u ree mineralized zones in the western half of the capitan mountains are most likely of magmatic origin as a result of cooling induced fracturing of the outer carapace of the capitan pluton the exsolved magmatic fluids were introduced into brecciated zones halogen ratios and sulfate concentrations are suggestive of evaporite assimilations into the magma before fluid exsolution

the significance of various sediment magnetic mineral fractions for tracing sediment sources in killimicat creek abstract the mineral magnetic properties of sediment are increasingly being used to determine the sources of sediment and associated nutrients and contaminants in drainage basins this study was undertaken to measure the relative contributions of the magnetic mineral components in sediment i e components associated with surface bound fe the heavy mineral fraction and as inclusions in particles to determine the extent to which they represent the bulk of the sediment deposited channel sediment samples from the tributaries and downstream reach at the first major confluence in the headwaters of killimicat creek new south wales were sieved to separate 6 particle size fractions and the mineral magnetic properties measured to determine the relative contribution of sediment from the smaller tributary basin the finest sand component 63 125 m was then separated into light and heavy mineral fractions and magnetic measurements made on each fraction magnetic parameter data from the 63 125 m fraction measured before density separation show a dominance of sediment 70 12 derived from the smaller tributary basin measurements of the light sediment fraction give a similar result 73 13 the proportion of the heavy mineral fraction delivered from the smaller tributary is 78 38 the light mineral fraction of all of the samples were treated with hcl to remove surface bound fe and subsequent magnetic measurements show that 41 94 of the mass specific magnetic susceptibility is attributable to magnetic minerals associated with surface bound fe the heavy mineral component while 60 is associated with sediment particles rather than the discrete heavy mineral component

volatiles associated with alkaline igneous rift activity fluid inclusions in the ilimaussaq intrusion and the gardar granitic complexes south greenland abstract fluid inclusions in minerals from si oversaturated and si undersaturated alkalic igneous complexes belonging to the precambrian gardar rift province in south greenland contain distinctly different carbon bearing gases granites and quartz syenites are characterized by co2 and only minor ch4 whereas agpaitic nepheline syenites are dominated by hydrocarbons essentially ch4 and contain only insignificant amounts of co2 and or co in the alkaline ilimaussaq intrusion the hydrocarbon rich gases may well reflect equilibration with graphite at magmatic temperatures and at oxygen fugacities approaching those defined by the synthetic mw buffer reaction in general formation of hydrocarbon gases in agpaitic nepheline syenites is considered to reflect the fulfillment of three basic conditions 1 low oxygen fugacities 2 a wide temperature range of crystallization and a low temperature solidus and 3 retention of volatiles during crystallization the characteristic carbon bearing vapour associated with continental alkaline igneous activity is however considered to be co2

determining the origins and history of sedimentation in an underground river system using natural and fallout radionuclides abstract natural and anthropogenic radionuclides were used to characterize the source of sediment reaching the underground river in the karst system at jenolan new south wales australia it was found that the relationship between 226 ra and 232 th concentrations in both spatially averaged soil samples and transported sediments distinguished between two of the most likely source subcatchments sedimentary sequences collected from within the underground system showed that contemporary deposition was made up of an equal mixture of sediment from these two sources however at least three earlier deposition periods were also identifiable each with different relative contributions from the source catchments the first appearance of 137 cs in the sedimentary sequence and correlations with historical information provided a chronology for these changes and it is concluded that the contemporary phase was initiated in the early 1950s most probably by forestry activities this work demonstrates that natural radioactivity can be used as a tracer of the origins of sediment providing an important new approach to problems in sediment supply transport and deposition

the distribution and main geologic features of discordant bodies of iron rich ultramafic pegmatite in the bushveld complex transgressive bodies of iron rich ultramafic pegmatite composed predominantly of varying proportions of hortonolite clinopyroxene ilmenite and ti magnetite are abundantly distributed throughout the layered mafic sequence of the bushveld complex new information from field and underground studies together with interpretations of detailed magnetic surveys is presented along with an overview of the available literature some whole rock and mineralogical chemical data are also included within the bushveld complex a number of distinct but possibly genetically related groups of postcumulus ultramafic rock are recognized these include besides the main group of iron rich ultramafic pegmatite bodies of magnesian dunite and the well known platiniferous ultramafic or dunitic pipes transgressive often pipelike bodies composed almost entirely of fe ti oxides occur in the main and upper zones of the complex which although part of the iron rich ultramafic pegmatite suite are described separately composite bodies in which massive fe ti oxides occur as a core within a peripheral shell of silicate rich pegmatite are also recognized the major occurrences of iron rich ultramafic pegmatite are documented and depicted in a series of maps their distribution is subject to two major stratigraphic controls iron rich ultramafic pegmatite occurs largely above the ultramafic cumulates in the lower and lower critical zones it is abundant in the upper critical and main zones where plagioclase is a major cumulus phase but is rarely observed above the highest cumulus ti magnetite layer in the upper zone it is also evident that these rocks become increasingly iron rich toward the top of the layered sequence so that in the upper zone fe ti oxide pegmatite is the dominant variety many bodies particularly the large ones are structurally controlled and occur in disturbed areas characterized by faulting and post bushveld dikes stratigraphic magnetic anomalies in the complex may be related to anorthositic layers containing small specks of iron rich ferromagnesian silicates and fe ti oxides this iron rich material is considered to represent the accumulated and trapped late stage residual and intercumulus fluid resulting from fractional crystallization within a cyclic unit lateral migration and channeling of these pegmatitic fluids into areas of structural weakness resulted in the formation of large pipelike bodies of iron rich ultramafic pegmatite these bodies may have resulted from metasomatic replacement of preexisting cumulates or they may have crystallized directly from the pegmatitic fluids the authors believe that the pegmatitic fluids have been derived from within the crystallizing cumulate pile and it is concluded that the formation of iron rich ultramafic pegmatite is an integral feature of the layered sequence

multi year tracking of sediment sources in a small agricultural watershed using rare earth elements rare earth elements rees have been successfully used as a sediment tracer but the ree technique has never been used for studying sediment sources for a multi year period a nearly four year field experiment was conducted on a small agricultural watershed near coshocton oh usa to assess the applicability of the ree technique for a multi year period and to evaluate the relative contributions of sediment sources in the watershed tracer depletion and tracer enrichment ratio ratio of the tracer concentrations in sediment to the concentrations in the soil in the areas of application were evaluated to examine the applicability and accuracy of the technique a minimum of 91 per cent of the mass of the applied elements was still available on any individual morphological element at the end of the experimental period the tracer enrichment ratio varied from 0 4 to 2 3 and it was not significantly related to time the relative contributions of six morphological elements within the watershed were evaluated as proportions to total sediment yield the relative contribution of the lower channel was significantly increased as a function of the amount of sediment yield while that of the lower backslope was significantly decreased the relative contribution of the lower channel significantly decreased as a function of cumulative sediment yield while the contributions of the shoulder and the upper backslope significantly increased our results showed that the ree technique can be used to track sediment sources for a relatively long period with two limitations or potential sources of error associated with a selective depletion of tracers and a contamination of downslope areas with tagged sediments from upslope areas copyright 2006 john wiley sons ltd

ree bearing minerals in a ti rich vein from the adamello contact aureole italy zirconolite aeschynite ce titanite and apatite have been found as minor or accessory minerals in a ti rich tio2 2 1 4 5 wt hydrothermal vein occurring in dolomite marbles at the contact with a tonalite intrusion of the tertiary adamello batholith northern italy the vein consists of four distinct mineral zones comprising from margin to center 1 forsterite calcite 2 pargasite calcite titanite sulfides 3 phlogopite calcite titanite sulfides and 4 titanian clinohumite spinel calcite sulfides zirconolite occurs in two vein zones only in the phlogopite zone it is invariably anhedral often corroded and exhibits complex chemical zonation patterns in the titanian clinohumite zone zirconolite is idiomorphic and characterized by a pronounced discontinous chemical zoning but shows no evidence of corrosion the considerable compositional variation observed for zirconolite in wt ree2o3 0 74 16 8 uo2 0 59 24 0 tho2 0 67 17 1 is due to the zoning and may be attributed to four major substitutions described by the exchange vectors 1 th u mg fe2 ca 1 ti 1 2 ree al ca 1 ti 1 3 ree fe2 nb ta ca 1 ti 1 4 hf zr 1

mobile sediment in an urbanizing karst aquifer implications for contaminant transport here we investigate geochemical characteristics of sediment in different compartments of a karst aquifer and demonstrate that mobile sediments in a karst aquifer can exhibit a wide range of properties affecting their contaminant transport potential sediment samples were collected from surface streams sinkholes caves wells and springs of a karst aquifer the barton springs portion of the edwards balcones fault zone aquifer central texas and their mineralogy grain size distribution organic carbon content and specific surface area analyzed statistical analysis of the sediments separated the sampling sites into three distinct groups 1 streambeds sinkholes and small springs 2 wells and 3 caves sediments from the primary discharge spring were a mix of these three groups high organic carbon content and high specific surface area gives some sediments an increased potential to transport contaminants the volume of these sediments is likely to increase with continued urbanization of the watershed

palaeozoic granites of the umberatana region south australia the role of volatiles in the crystallization of some alkaline peralkaline granites palaeozoic alkaline to peralkaline sodic granites of the umberatana area of south australia have high mno p5o5 nb ta be f and b abundances as is typical of a type or anorogenic granites abundant f and b in the magma permitted primary muscovite to crystallize at pressures that may have been as low as 1 kbar because of the lowered solidus temperatures these volatile rich magmas precipitated both albite and two generations of k rich alkali feldspar the hydrothermal fluids released during crystallization of these magmas resulted in considerable element redistribution and recrystallization both in the plutons and the adjacent country rocks

boron isotopic constraints on the nb and ta mineralization of the syenitic dikes in the 260 ma emeishan large igneous province sw china abstract both nb ta mineralized and nb ta poor syenitic dikes in the panxi region sw china are spatially and temporally associated with syenitic plutons which are part of the 260 ma emeishan large igneous province these syenitic dikes are nw striking and have width varying from 1 to 5 m and length from 50 to 300 m the dikes are mainly composed of k feldspar albite aegirine and arfvedsonite however mineral modes are different in the nb ta mineralized and nb ta poor syenitic dikes the major nb ta bearing mineral in the dikes is pyrochlore which is closely associated with albite and occurs in places with intensive albitization rocks of the nb ta mineralized syenitic dikes contain more albite and less k feldspar than the nb ta poor dikes and have compositions more evolved than the nb ta poor dikes indicating that the nb ta mineralized syenitic dikes formed from a highly evolved magma we analyzed the b concentrations and b isotopic compositions of the samples of both nb ta mineralized and nb ta poor syenitic dikes and associated syenitic pluton using a single column purification method and icp aes and mc icp ms techniques the samples of the nb ta mineralized syenitic dikes have whole rock b concentrations ranging from 11 4 to 23 9 ppm and 11b values from 17 95 to 14 54 whereas the samples of the nb ta poor dikes and syenitic plutons have b concentrations varying from 3 32 to 16 5 ppm and 11b values from 13 45 to 10 02 the high b concentration of the nb ta mineralized dikes relative to the nb ta poor dikes is consistent with that b is incompatible and tends to be rich in more evolved magma the relatively low 11b values of the nb ta mineralized dikes indicate that the b isotopes may have fractionated between fluids and rocks in a transitional magmatic hydrothermal stage we propose that the highly evolved magmas in a transitional magmatic hydrothermal stage may have nb and ta fluorine complexes dissolved in the hydrothermal fluids in the presence of na albite crystallization due to intensive albitization in this stage resulted in the decrease of na in the fluids decomposing the nb and ta fluorine complexes the released nb and ta from the complexes were then dissolved in the fluids and finally entered the lattice of pyrochlore crystals in the stage of albitization

testing the izzi protocol of geomagnetic field intensity determination 1 a new paleointensity determination protocol the izzi method was recently proposed the izzi technique combines the aitken in field zero field iz and coe zero field in field zi methods the izzi protocol of paleointensity method was experimentally tested showing a strong angular dependence resulting from the undemagnetized portions of partial thermoremanent magnetization ptrm tails the izzi method is better than the conventional techniques aitken coe and thellier in three respects 1 it can easily detect the angular dependence 2 it provides a quantitative estimate for the consistency of the outcome between iz and zi step and 3 it is quicker because the extra ptrm tail check step is unnecessary

bicarbonate rich fluid inclusions and hydrogen diffusion in quartz from the libcice orogenic gold deposit bohemian massif abstract unusual paleofluid composition is reported for the libcice orogenic type gold deposit located in the central bohemian plutonic complex cbpc czech republic unexpected bicarbonate rich fluids and their complex chemistry variations characterize primary fluid inclusions from the main gold bearing quartz vein a detailed microthermometry laser raman micro spectroscopy lrms and sem cathodoluminescence study was used to understand the complex chemistry and p t x history the results indicate the presence of h 2 o and h 2 o co 2 ch 4 n 2 h 2 s fluids the latter displaying variations of the co 2 ch 4 ratio in the gaseous phase from 6 8 to 0 06 variation of the ch 4 content across single grains and between different levels of the mine was recorded the presence of nahcolite h 2 up to 6 mol and ethane 0 0 2 mol in the fluids were also discovered by lrms potential models for the formation of different types of fluids present in the deposit are discussed including the genesis of hco 3 rich fluids as well as h 2 and c 2 h 6 presence in the primary fluid inclusions the potential influence of organic matter bearing sediments as well as the impact of the intrusion of cbpc re equilibration and or re speciation of fluid inclusions during the post entrapment history is considered to have the main impact on the complex paleofluid chemistry based on the thermodynamic modeling h 2 diffusion into the fluid inclusions was shown to be the main reason for the ch 4 variation on the scale of a single grain as well as across the whole vein although the exact processes of production formation of hco 3 and h 2 at the libcice deposit remain open to discussion reactions in the c o h system are considered to be a possible formation mechanism this work also contributes to our understanding of the importance of post entrapment modifications and reactions in the c o h system on interpretation deciphering the processes in orogenic type deposits

kelvin and the age of the earth kelvin s estimate of about 10 8 years for the age of the earth based on the time required for an initially uniform and hot thermal structure to decay to the presently observed surface temperature gradient is briefly reviewed the later realization that the earth was at least several billion years old 4 5 times 10 9 years posed a dilemma how to reconcile thermal evolution with this great age radiogenic heat production alone is demonstrably insufficient to effect the reconciliation and in the end it is mantle convection with its ability to exploit the entire internal heat of the earth that provides the way out the present usefulness of thermal structure as a measure of age age now taken to mean local as opposed to global age is reviewed for oceanic and continental regions as for kelvin he was quite right in arguing that the earth s age was not only finite but measurable measurable however by methods he did not anticipate

late alteration in titanite catisio5 redistribution and remobilization of rare earth elements and implications for u pb and th pb geochronology and nuclear waste disposal abstract translucent dark coloured titanites from a wide variety of geological environments are commonly partly replaced by very fine grained aggregates of ree rich minerals including allanite monazite and bastnasite rutile quartz calcite apatite and chlorite along grain fractures and boundaries the aggregates of ree rich minerals are bordered by an irregular zone of altered titanite which by secondary ion mass spectrometry sims is considerably lower in rees u and th than the adjacent unaltered matrix light rees and th are differentially depleted in the altered zone and correspondingly enriched in secondary minerals additionally hrees and u have been lost to the external system the loss of hrees being in proportion to the increase in atomic number natural radiation damage was not an important factor in promoting the late alteration of titanite titanite which has been subjected to late hydrothermal activity would not remain a closed system in respect to either u or th decay series and therefore cannot be used for u pb and th pb geochronology the observed leaching and partial dissolution of titanite under hydrothermal conditions are generally consistent with laboratory experimentation indicating that proper isolation from any communication with hydrothermal fluids is essential in the application of titanite based ceramics for the immobilization of radioactive waste

large scale silicate liquid immiscibility a possible example from northeastern brazil abstract ultrapotassic peralkalic silica saturated plutons 580 ma are widespread in the cachoeirinha salgueiro foldbelt northeastern brazil they consist of alkali feldspar syenites with pyroxenite as co magmatic inclusions and syn plutonic or late stage dikes pyroxenite and syenite have the same mineral phases aegirine augite microcline sphene apatite blue amphibole magnetite but only in different proportions rare inclusions of a mixed rock about 60 syenite 40 pyroxenite in an emulsion like texture are also present pyroxenes in the three units are all only slightly zoned silica saturated and extremely low in al2o3 0 2 1 4 amphiboles are mostly k rich richterite characterized by high sio2 low al2o3 and tio2 contents and low mg the three rock types have similar ree chondrite normalized patterns with negative slopes and lack of eu anomaly with the total ree in the pyroxenite greater than that of the syenite trace element patterns for the mixed rock are intermediate between those for the pyroxenite and syenite major element partitioning between pyroxenite and syenite has the same sense as that one observed between immiscible liquids in volcanic lavas and trace element partitioning is similar to the experimentally determined partition of immiscible liquid pairs the rocks have similar high 18o values avg w r 8 smow corrected from pyroxene high initial 87 sr 86 sr ratios about 0 710 and low 143 nd 144 nd avg 0 51104 field and geochemical characteristics indicate chemical equilibrium among the three rock types and suggest liquid immiscibility between syenite and pyroxenite the mixed rock representing the original magma composition

origins of calcite in a boiling geothermal system the formation of hydrothermal calcite relates to the movement of carbon dioxide in a geothermal system as governed by boiling dilution and condensation in this paper we show how these processes control the occurrence distribution and stable isotope composition of calcite based on a study at broadlands ohaaki the two principal calcite occurrences in the broadlands ohaaki geothermal system are 1 as replacement of rock forming minerals and volcanic glass and 2 as platy crystals infilling voids both are stable over a broad temperature range from 160 degrees c to 300 degrees c replacement calcite is widespread and forms through hydrolysis reactions involving calcium alumino silicates and sub boiling liquids that contain 0 3 to 0 75 m co 2 platy calcite in contrast forms over a restricted vertical interval of a few hundred meters within the upflow zone it precipitates from boiling fluids through exsolution of carbon dioxide as indicated by coeval liquid rich and vapor rich fluid inclusions and its formation in the two phase zone fluid inclusion data help to define the boiling paths of fluids from which platy calcite formed homogenization temperatures range from 160 degrees c to 310 degrees c and are consistent within the present geothermal regime ice melting temperatures range from 0 0 to 1 0 degrees c and indicate the presence of up to 0 5 m dissolved carbon dioxide model boiling curves calculated to match these data show how the concentration of dissolved carbon dioxide in the preboiled fluid dictates the depth of first boiling most fluid inclusion data lie along a model boiling path characteristic of the centre of the upflow zone in which the rising fluid initially containing 0 75 m co 2 begins to boil at approximately 320 degrees c and approximately 2000 m depth data from well br 18 instead matches a curve in which the rising fluid initially containing 0 53 m co 2 begins boiling at approximately 245 degrees c and approximately 900 m depth the shallowing of the depth of first boiling likely results from dilution of dissolved carbon dioxide in the parent chloride water as it rises and mixes with marginal waters calcite precipitates from both shallow formed steam headed groundwater and deeply derived chloride water and these waters are isotopically distinct at broadlands ohaaki the delta 18 0 values of calcite at 200 degrees c range from 0 5 to 7 5 per mil whereas delta 18 0 values of calcite at 200 degrees c range from 4 to 10 per mil taking appropriate temperature dependent fractionation factors into account these data indicate equilibration with chloride water delta 18 0 h2o 4 5 per mil and steam heated groundwater delta 18 o h2o 7 0 per mil respectively oxygen isotopes of hydrothermal calcites in the nearby wairakei and waiotapu geothermal systems show similar patterns consistent with the occurrence of both chloride and steam heated waters there calcite formation is explained by a model that describes the distribution of two phase conditions and aqueous carbon dioxide concentrations in a column of hydrothermal fluid rising through a rock matrix of isotropic permeability in this ideal situation platy calcite forms along the inner margin of the two phase zone having the shape of an inverted cone whereas replacement calcite mostly forms in the surrounding one phase liquid only zone the sparse occurrence of calcite at less than or equal to 800 m depth in the central upflow of the ohaaki sector at broadlands ohaaki is compatible with this model and appears related to the exsolution of dissolved carbon dioxide through boiling deeper in the system

the age of the inner core abstract the energy conservation law when applied to the earth s core and integrated between the onset of the crystallization of the inner core and the present time gives an equation for the age of the inner core in this equation all the terms can be expressed theoretically and given values and uncertainties of all relevant physical parameters the age of the inner core can be obtained as a function of the heat flux at the core mantle boundary and the concentrations in radioactive elements it is found that in absence of radioactive elements in the core the age of the inner core cannot exceed 2 5 ga and is most likely around 1 ga in addition to have an inner core as old as the earth concentrations in radioactive elements needed in the core are too high to be acceptable on geochemical grounds

anomalous alkaline rocks of soustov kola evidence of mantle derived metasomatic fluids affecting crustal materials the intrusive complexes of gremiakha vyrmes and soustov represent the two extremes of the early proterozoic alkaline plutons of kola predominantly composed of feldespathoidal syenites gremiakha vyrmes rocks zircon age 1 884 6 ma have trace element and isotope signatures 87sr 86srt 0 704 endt 3 1 3 compatible with an ultimate mantle origin soustov syenites zircon age 1 872 8 ma are totally different and show an acute crustal imprint they have sodaline and analcite instead of nepheline contain a plethora of ree hfse rich accessories and are characterised by elevated contents of f cl ree y th u zr hf nb ta sn be li rb tl pb and cs negative eu anomalies k rb 190 160 nd th 3 and nb ta 12 with extremely high 87sr 86srt 0 720 and at the same time relatively high endt 1 6 1 7 in this paper we explore the idea that the anomalous features of soustov syenites can be explained if we assume they are derived from a metasomatic agent initially an h2o co2 supercritical fluid released by alkaline mafic magmas that was profoundly contaminated during percolation through crustal materials as percolation advanced the bulk composition of the fluid solute changed from alkali halides and carbonates to a silica undersaturated alkaline melt when the fluid cooled to a temperature of 550 600 c it reached the point at which vapor and melt were no longer miscible and split into two components a vapour phase and a cl and f rich silica undersaturated silicate melt that crystallised to produce soustov syenites to study this process we have developed a numerical method for modelling the solute composition of the fluid during the infiltration metasomatism our results using the lree abundances and the sr and nd isotope composition of a gremiakha vyrmes pegmatite as the starting solute composition of the fluid and the mode and mineral trace element and isotope composition of a common kola gneiss as representative of percolated materials indicate that the fluid would have acquired a signature closely matching soustov s even in the case of nd isotopes if the gneiss age is 2 9 ga near its real age this model is still a mere working hypothesis that needs further refinements but may represent a reasonable explanation of the genesis of anomalous alkaline rocks with high 87sr 86srt and endt 0 either saturated or undersaturated which are difficult to understand in terms of magmatic fractionation contamination

the dynamical and thermal structure of deep mantle plumes abstract if the interpretation of the d layer at the base of the mantle as a thermal boundary layer with a temperature increment in the order of 800 k is correct then the formation of deep mantle plumes to vent material from it appears inevitable we demonstrate quantitatively that the strong temperature dependence of viscosity guides the upward flow into long lived chimneys that are 20 km in diameter near the base of the mantle and decrease in width with progressive upward softening and partial melting of plume material the speed of flow up the axis of the plume is correspondingly fast 1 6 m y 1 at the base and 4 8 m y 1 at 670 km depth thermal diffusive spreading of a heated plume is compensated by a slow horizontal convergence of mantle material toward the chimney in response to the lower pressure there this convergence which contributes only a small increment to the flux of material up the plume also serves to throttle the flow in the chimney the global plume mass flux necessary to transport 1 6 10 12 w of core heat upward through the mantle is 1 8 10 6 kg s 1 at its base plume material is probably still significantly below its solidus or eutectic temperature but substantial partial melting is very likely as it rises we speculate that a small fraction of this fluid component eventually emerges at the surface in hot spots with the fate of the remainder being unknown the behaviour and properties of d and of plumes are closely coupled not only are plumes a necessary consequence of a thermal boundary layer but their existence is impossible without that layer

fundamentals of laminar free convection in internally heated fluids at values of the rayleigh roberts number up to motions in the solid mantle of silicate planets are predominantly driven by internal heat sources and occur in laminar regimes that have not been systematically investigated using high resolution numerical simulations conducted in three dimensions for a large range of rayleigh roberts numbers we have determined the characteristics of flow in internally heated fluid layers with both rigid and free slip boundaries superficial planforms evolve with increasing from a steady state tessellation of hexagonal cells with axial downwellings to time dependent clusters of thin linear downwellings within large areas of nearly isothermal fluid the transition between the two types of planforms occurs as a remarkable flow polarity reversal over a small range such that downwellings go from isolated cylindrical structures encircled by upwellings to thin interconnected linear segments outlining polygonal cells in time dependent regimes at large values of linear downwellings dominate the flow field at shallow depth but split and merge at intermediate depths into nearly cylindrical plume like structures that go through the whole layer with increasing the number of plumes per unit area and their velocities increase whilst the amplitude of thermal anomalies decreases scaling laws for the main flow characteristics are derived for values in a range for given plumes are significantly colder narrower and wider apart beneath free boundaries than beneath rigid ones from the perspective of planetary studies these results alert to the dramatic changes of convective planform that can occur along secular cooling

on the formation of peridotite derived os rich pge alloys osmium rich pt group element pge alloys occur worldwide in association with chromite in ultramafic peridotite complexes it has been suggested that these os rich alloys formed under extreme p t conditions in the lowermost mantle before the metallic core of the earth formed or later in the outer core and have been transported to the upper mantle as xenoliths in deep rooted mantle plumes

the application of fallout radionuclides to determine the dominant erosion process in water supply catchments of subtropical south east queensland australia previous studies using fallout radionuclides 137cs and 210pbex to determine the relative contributions of surface soil and channel erosion including gullies and channel banks to stream sediments have used a relatively small number of composite samples 25 to characterize the source end members and concentrations in each of the source end members have through the use of means and standard errors been assumed to be normally distributed here we examine 137cs activity concentrations to determine the erosion processes supplying sediment in seven water supply catchments in south east queensland first we test some of the underlying assumptions in the method using concentrations of 137cs and 210pbex in composite samples collected from 109 surface soil sites and 39 channel bank sites paired composite samples each consisting of 20 subsamples from five sites are used to demonstrate that this sampling approach was sufficient to average out any local variations in surface soil 210pbex and 137cs concentrations across the 300 m2 sampled we derive probability distributions for 137cs and 210pbex concentrations in the group of samples from each of the end members and show that only the distribution of 210pbex in samples from surface soils is normally distributed we use the probability distributions for 137cs which provides the greatest discrimination between sources to show that the 137cs concentrations on the river sediment samples are consistent with channel erosion being the dominant source conservation works aimed at reducing the supply of sediments in these catchments should therefore focus on rehabilitation of the channel network and decreasing the runoff to the channel network these findings are consistent with other similar studies on tropical australian rivers copyright 2012 john wiley sons ltd

assemblages with titanite catiosio4 ca mg fe olivine and pyroxenes fe mg ti oxides and quartz part ii application in the system cao mgo feo fe2o3 tio2 sio2 equilibria among titanite pyroxene s olivine spinel phase ilmenite and quartz constrain f o2 t a sio2 a tio2 a fe and the compositional variables tife2 fe 23 c a mg fe 1 and consequently mg fe 1 among the silicate and oxide phases these equilibria can provide the framework for a better understanding of relevant titanite bearing natural assemblages in addition such equilibria can constrain the variables that operate during crystallization of igneous and metamorphic rocks titanite bearing assemblages with pyroxene s fe mg ti ilmenite and spinel olivine and quartz are rare in metamorphic rocks but are common in igneous rocks where they are more commonly reported in plutonic than in volcanic rocks probably because at high temperatures titanite cannot coexist with the relative common in volcanic rocks sub assemblage augite orthopyroxene olivine spinel phase ilmenite moreover decreasing pressure and temperature conditions appear to favor titanite thus it is not surprising that titanite is commonly observed in slowly cooled rocks albeit most typically in association with amphibole we argue that the titanite amphibole association is favored by high a h2o and because a h2o typically increases during crystallization of a pluton titanite amphibole and consequently titanite is more common in plutonic than in volcanic rocks we have used a modified version of the program quilf that includes our thermodynamic data for titanite and appropriate titanite bearing assemblages to estimate the equilibrium crystallization conditions of samples from 1 a tonalite from the myoken zan granitic complex in japan 2 the sandwich horizon in the skaergaard intrusion in greenland 3 rhyodacites dacites and andesites from the sajama porquesa and parinacota volcanoes in the andes 4 the fish canyon tuff in colorado and 5 a quartz rich calc silicate gneiss adjacent to the horse creek anorthosite complex in wyoming the calculations suggest that 1 these titanite bearing assemblages crystallized at values of f o2 that ranged from slightly below fmq to more than 3 log f o2 units above fmq at 500 800 c and 2 the stability of titanite is controlled by t f o2 a sio2 and the compositions of the coexisting oxides and silicates

moderate pressure metamorphism and anatexis due to anorthosite intrusion western adirondack highlands new york garnet sillimanite biotite gneiss near port leyden in the western adirondack highlands new york contains mineral assemblages and textures that formed during high temperature metamorphism and anatexis at mid crustal pressures evidence for melting includes thin plagioclase rich veins sieve textures in biotite and the presence of small euhedral garnet neoblasts hercynite silicate equilibria in combination with the solidus for biotite dehydration melting indicate metamorphic pressure was between 4 and 6 4 kbar at the temperature of melting ca 735 c the gneiss is intruded by a small discordant fe ti oxide apatite nelsonite dike reported field occurrences of nelsonite demonstrate its common association with anorthosite plutons although no anorthosite bodies are exposed in the port leyden region the presence of nelsonite is evidence of anorthositic magmatism in the western adirondacks post intrusion metamorphism has caused partial apatite recrystallization and produced a weak foliated texture in the dike u pb ages from zircon and monazite from both the gneiss and the nelsonite dike indicate that these rocks experienced a complex polymetamorphic history that we interpret to reflect two thermal episodes an older event is recorded by discordant zircons in the gneiss which indicate a minimum age of 1129 6 ma a linear best fit to the data yields an upper intercept at 1166 53 ma this range of ages coincides with anorthosite suite magmatism in the adirondacks a minimum zircon age of 1104 3 ma was obtained from the nelsonite dike lead loss or late zircon crystallization at about 1020 ma affected the u pb systematics of zircon in the dike monazite ages from both rocks also indicate high temperature metamorphism 700 c between 1040 and 960 ma the older zircon ages and textural relations in the metapelite are viewed as evidence for anatexis at ca 1150 ma and the presence of nelsonite suggests that the intrusion of anorthosite was coincident with partial melting in the gneiss p t estimates of metamorphism therefore imply that anorthosite was emplaced to about 15 km depth in the western adirondack highlands

the fluid inclusion and mineralogic record of the transition from liquid to vapor dominated conditions in the geysers geothermal system california the geysers an active vapor dominated geothermal system related to a hypabyssal granitic pluton was liquid dominated from its inception at 1 2 to 0 3 ma when the modern vapor dominated regime formed as the hydrothermal liquids boiled off a vapor dominated heat pipe developed in which the flow of steam was balanced by downward percolation of condensate a record of the transition from liquid to vapor dominated conditions is contained within late stage quartz and calcite crystals that are common in the upper part of the steam reservoir and overlying cap rock samples from three localities were examined in detail quartz from these veins is characterized by corroded crystal faces solid inclusions of contemporaneous calcite that are generally etched coeval high and low salinity fluid inclusions primary low salinity liquid rich inclusions and abundant vapor rich inclusions primary vapor rich inclusions up to 2 mm across were trapped mainly on rhombic and prism faces of skeletal quartz crystals during periods of rapid growth these inclusions nucleate crystals of co2 that disappear by sublimation rather than melting at temperatures ranging from 92 9 to 56 7 c liquid rich fluid inclusions from veins near the top of the modern steam reservoir yield homogenization temperatures ranging from 304 to 188 c these temperatures commonly exceed boiling point to depth relationships based on the paleoground surface suggesting that pressures were initially greater than hydrostatic temperature salinity relationships indicate that the early shallow liquids had salinities of 1 5 to 2 wt percent nacl equiv and that boiling began by 300 c as the fluids boiled off salinities of the residual liquid increased to 3 to 4 wt percent nacl equiv trapping of low salinity fluids 0 0 0 5 wt nacl equiv interpreted as condensate in primary liquid rich inclusions suggest vapor dominated conditions had begun to develop by the time temperatures had dropped to 290 c the primary origin of these inclusion fluids indicates that they were capable of depositing quartz and calcite during the evolution of the vapor dominated system the hydrothermal fluids were at different times but at the same location undersaturated in equilibrium or oversaturated with respect to quartz and calcite the hydrothermal fluids initially deposited quartz and calcite as they boiled off dissolution of these minerals occurred as the condensate which was initially undersaturated with respect to quartz and calcite percolated down subsequent deposition of these minerals occurred as the condensate or mixtures of condensate and boiled liquid that leaked back into the fractures vaporized during periods of intermittent pressure reduction the top of the vapor dominated system migrated downward with time as the overlying fractures were progressively sealed off today pressures within the steam reservoir are vaporstatic and temperatures range from 240 to at least 342 c

core evolution driven by mantle global circulation abstract reconstructions of the phanerozoic history of mantle global circulation that include past plate motions are used to constrain the thermochemical evolution of the core according to our mantle global circulation models the present day global average heat flux at the core mantle boundary lies in the range 80 90 mw m 2 with peak to peak long wavelength lateral variations up to 100 mw m 2 associated with compositional and thermal heterogeneity in the d layer for core thermal conductivity in the range k 100 130 w m 1 k 1 we infer that the present day outer core is thermally unstable beneath the high seismic velocity regions in the lower mantle but thermally stable beneath the large low seismic velocity provinces a numerical dynamo shows how this boundary heat flux heterogeneity generates departures from axial symmetry in the time average geomagnetic field and the pattern of flow in the outer core standard thermochemical evolution models of the core driven by mantle global circulation heat flow predict inner core nucleation between 400 and 1100 ma with thermal conductivity k 100 w m 1 k 1 the core heat flow derived from our mantle global circulation models is adequate for maintaining the geodynamo since inner core nucleation supercritical for dynamo action by thermal convection just prior to inner core nucleation and marginal for inner core convection

pyroxene in enclaves and syenites of the red hill complex new hampshire an ion and electron microprobe study the red hill complex new hampshire contains both silica undersaturated and silica saturated to oversaturated syenites ion microprobe analyses of pyroxene from the nepheline sodalite syenite nss and its enclaves reveal that the ree abundances increase in a systematic manner from low values in the enclave pyroxenes to higher values in the nss host rock pyroxenes this variation is interpreted to have resulted from differentiation and coupled with previously published mineral and bulk rock compositions suggests that the enclaves represent samples of nss parental liquids that intruded into residual syenitic liquids in a zoned magma chamber pyroxene analyses of the garland peak syenite gps and its enclaves indicate that the enclaves are of several populations some may be related to the gps others are not the gps itself is heterogeneous and pyroxene trace element zoning is difficult to explain by fractionation processes the silica oversaturated outer coarse syenite ocs contains pyroxenes with trace element characteristics that are distinct from the nss the low v concentrations suggest that the ocs exprienced magnetite fractionation prior to pyroxene growth it is proposed that high f o2in the ocs magma caused fe ti oxide crystallization which in turn influenced magmatic silica activity the chondrite normalized ree patterns of ocs pyroxenes are also suggestive of titanite crystallization another indication of high f o2 in contrast to the influence of magnetite crystallization the high and rimwardly increasing y and yb concentrations in both the nss and the ocs pyroxenes suggest that amphibole fractionation was not the major influence on silica activity therefore it is unlikely that the ocs was derived by amphibole fractionation from a nss precursor magma

geochemistry and origin of proterozoic skarns at the mount elliott cu au co ni deposit cloncurry district nw queensland australia diopside rich skarn hosted copper gold ore derived primarily from carbonaceous metapelites at mount elliott forms a distinctive member of the spectrum of cu au fe oxide deposit styles in the cloncurry district of the paleoproterozoic to mesoproterozoic mount isa block the mine sequence is a package of carbonaceous metapelites and metagreywackes containing amphibolites derived from tholeiitic basic rocks a 40ar 39ar age spectrum with an extensive plateau like segment at 1 510 3 ma from an actinolite associated with sulfides is taken to represent the age of mineralization and is identical within error to the ages of most of the nearby batholithic granitoids the mine sequence is locally intruded by 1 to 10 m thick late to post tectonic trachyandesite dykes which were emplaced during the hydrothermal activity that created the orebodies and have affinities with the regional high potassium eureka supersuite granitoids stable isotope data are consistent with dominantly magmatic fluids during mineralization and the regionally distinctive skarn ca mg and cu au ni co te se low pb zn ag sb chalcophile element associations may reflect a primitive magmatic fluid source and or leaching of these elements from country rocks mount elliott is an unusual skarn deposit characterized by pronounced early albitization k fe mg depletion of the host rocks succeeded by predominantly open space deposition of sodic diopside actinolite scapolite andradite magnetite sulfides apatite allanite tourmaline calcite the ca fe mg na rich manganese poor chemistry was imposed from the fluid phase in the absence of carbonate rich protoliths immobile trace element ti zr nb geochemistry shows that mount elliott skarns formed in both metasedimentary and mafic metavolcanic host rocks but the former are the main hosts of ore in upper and lower ore zones that represent most of the resource banded skarns derived from a distinct calc silicate marble package at the nearby swan prospect have higher nb tio2 and zr tio2 ratios than the mount elliott metasediment derived skarns consistent with different provenance of the detrital components in the two sequences medium to coarse grained massive skarn and skarn breccia in the mount elliott lower ore zone formed in pelites and the trachyandesite dykes are the only intrusive rocks that could be genetically related to the mineralization in the immediate vicinity of the orebodies

on cooling of the earth s core abstract we have constructed a self consistent model for cooling of the earth s core in which the thermal history of the core is computed as a function of the time evolution of the heat flux delivered to the mantle across the core mantle boundary the temperature profile in the convecting core is first assumed to be adiabatic and its evolution in time is calculated with the only constraint that energy be globally conserved when the temperature at the centre drops below the freezing point of the core alloy the inner core starts growing and cools by conduction it is found that it cannot have reached its present size in more than 1 7 billion years if the heat flux delivered to the mantle becomes less than that conducted down the adiabat the temperature profile becomes subadiabatic in a shell at the top of the core through which heat is evacuated by conduction although it is stable against thermal convection this shell is not necessarily stagnant and may be the seat of motions owing to compositional convection

boiling and fluid mixing in the chlorite zone of the larderello geothermal system abstract the geochemical features of the geothermal fluids produced within the boiling zone in the relatively shallow parts of the larderello geothermal system italy have been documented as a result of deep drilling which provided samples from 1480 to 2500 m depth four wells monteverdi 1 monteverdi 2a sasso 22 and capannoli 2b have been sampled in the intermediate parts of the larderello aquifer located in a metamorphic basement underlying the tertiary nappe complex which constitutes the shallow aquifer at larderello fluid inclusions from recrystallized quartz lenses and quartz veins in samples displaying a predominant quartz chlorite epidote adularia paragenesis have been studied by microthermometry and raman spectroscopy the inclusions are primary and pseudo secondary in origin when formed in authigenic quartz or of secondary origin when located in fluid inclusion planes related to microfracturing of metamorphic quartz lenses several generations of fluids are present and include h 2 o co 2 dominated vapours and liquids and a series of aqueous liquids for the most part of relatively low salinity the t m ice of both early and late inclusions are mostly between 0 0 and 4 5 c indicating that the salinities of the hydrothermal fluid were very low to moderate however rare fluid inclusions with lower t m ice from 4 9 to 25 0 c were also observed these inclusions may record the occasional input of saline fluids which may be derived from the interaction of the hydrothermal waters with the evaporites present in the shallow part of the larderello field at capannoli 2b earliest h 2 o co 2 liquids were trapped under minimal pressures of 610 645 bars which bracket the estimated present day lithostatic pressure 640 bars in all other samples the main stage of quartz chlorite crystallization occurs under boiling conditions attested by the presence of liquid and vapour rich inclusions that in some instances can be texturally interpreted to be coeval their trapping conditions 350 375 c 160 215 bars are higher than the present day temperatures at the same depth later fluid inclusions attest to a significant cooling of the fluids down to temperatures similar to the present day temperatures during this time pressures were close to hydrostatic conditions most fluid inclusions were trapped within the liquid field this indicating that a significant pressure drop has since affected the main aquifers or fractured zones which are at present under vaporstatic conditions

long lived crustal scale fluid flow the hydrothermal mega breccia of hidden valley mt painter inlier south australia the palaeozoic hidden valley breccia in the northern flinders ranges of south australia is exceptional for 1 its size of about 10 km2 2 the large continuous range in clast sizes from tens of microns to hundreds of metres and 3 thorough mixing of lithologies of different provenance some originally kilometres apart stratigraphically the size distribution follows a single fractal dimension of about unity over at least 6 orders of magnitude implying that a single process was responsible for diminution from the 100 m scale down to 12 km exhumation which lasted about 200 myrs starting during the 500 ma delamerian orogeny and continuing during the alice springs orogeny fluids released during exhumation were structurally focussed towards hidden valley where an estimated 20 5 30 km3 total fluid volume caused the extensive brecciation brecciation initiated in neoproterozoic cover metasedimentary rocks at a level that is now fully exhumed as hydrothermal fluid ascent continued with ongoing exhumation the level of brecciation shifted down into the underlying mesoproterozoic basement rocks taking with it clasts of cover rocks in this model rocks pass through the zone of brecciation which can thus incorporate a variety of lithologies that were originally kilometres apart

the dynamical structures of d and deep plumes in a non newtonian mantle the dynamical structures of the d layer and deep mantle plumes have been determined for a mantle with a power law creep rheology generalising recent newtonian analyses the lateral scales of d and plumes are determined by a balance between thermal diffusive thickening and lateral inflow the non newtonian effect of concentrating shear in regions of high stress acts to thicken the region of rapid flow in both d and plumes this effect is nearly counterbalanced by the increased lateral inflow in the non newtonian case resulting in a modest broadening of the lateral scales of the regions of rapid flow these changes are structurally unimportant and the essential physics of core cooling via convective flow in a thin d layer and narrow plumes is remarkably independent of mantle rheology

tectonics alteration and the fractal distribution of hydrothermal veins in the lower ocean crust abstract gabbros from hole 735b preserve the igneous structural and metamorphic history beneath the southwest indian ridge down to middle amphibolite facies conditions the gabbro was isolated from the zone of lithospheric necking by detachment faulting unroofing and block uplift at the inside corner high of the atlantis ii transform lower crustal accretion as preserved in the core is a complex integration of igneous hydrothermal and tectonic processes alteration began at anhydrous granulite conditions as surface faulting penetrated the brittle ductile transition to form brittle ductile shear zones in the amphibolite facies hydrous alteration around these zones was extensive while undeformed sections remained virtually unaltered amphibole veins formed during the brittle ductile deformation have a high fractal dimension reflecting an unclustered distribution consistent with high strain and cracking rates in the zone of lithospheric necking beneath the ridge however the fractal dimensions of the two major gneissic amphibolite zones in hole 735b are different and suggest that they represent discrete fault zones formed at different times below middle amphibolite facies a dramatic drop in the extent of alteration reflects cooling cracking and alteration under static conditions similar to layered intrusions initially fracture and vein formation exploited undeformed sections where elastic strain accumulated during cooling from high temperatures was unrelieved by recrystallization plagioclase diopside veins formed at this time have the same orientation as higher temperature veins but a mineralogy reflecting much lower rock permeabilities and a low fractal dimension reflecting a tight clustering of veins as would be anticipated for crack formation at low strain rates late zeolite and carbonate veins and irregular smectite lined near vertical cracks also have a very low fractal dimension reflecting clustering appropriate to low strain near static conditions these however show no preference for undeformed sections of the core and are oriented with subvertical and subhorizontal maxima this indicates crack formation under the present day stress field thus elastic strain due to cooling from high temperatures and extension during lithospheric necking dissipated after plagioclase diopside vein formation

agpaitic magmatism in the northeastern baltic shield a study of the niva intrusion kola peninsula russia abstract the recently discovered niva agpaitic syenite intrusion is located 50 km southwest of the khibina complex central kola peninsula it forms a lense like body 1 5 2 km in size that outcrops over an area of 300 200 m on the southern bank of the imandra lake rb sr 379 21 ma and sm nd 383 58 ma isochron ages of the intrusion coincide with the age of the khibina and lovozero complexes a characteristic feature of the niva rocks is their extremely high agpaicity and enrichment in sr ba y zr nb rb lree and volatiles the mineral association in the agpaitic syenite is k feldspar aegirine diopside biotite lamprophyllite aenigmatite and shcherbakovite isotopic compositions indicate the absence of contamination by continental crust during formation of the niva alkaline magmas a depleted asthenospheric mantle reservoir mixed with a slightly enriched mantle component is suggested to be the main source of the niva magma a metasomatically altered garnet granulite xenolith from the western contact of the niva intrusion contains a primary paragenesis of diopside garnet and plagioclase with chemical characteristics similar to those in the granulite suite of the adjacent lapland zone and lower crustal granulite xenoliths from devonian pipes in the kandalaksha area additionally the granulite contains vinogradovite neptunite pectolite and natrolite which partially replace both primary minerals of the granulite assemblage and secondary minerals which were formed during a later regional metamorphism pt estimates support the lower crustal origin of the xenolith the u pb zircon age of the niva garnet granulite is 2711 7 ma