concentration mechanisms of rare earth element nb zr be mineralization in the baerzhe deposit northeast china insights from textural and chemical features of amphibole and rare metal minerals

surface waves generated by underwater explosions offshore scotland summary underwater explosions in the kirkcaldy bay region of the firth of forth scotland recorded by the british geological survey s lownet array crampin et al generate seismograms which are characterized by a long dispersed wavetrain on the assumption that these waves are caused by the shape of the dispersion curves phase and group velocities are analysed to determine the structural parameters of a model of the kirkcaldy bay region to which they are most sensitive the shear wave velocity and thickness of the sea bottom sediments are found to be most influential in determining the shape of these dispersion curves simple synthetic seismograms constructed for a solid model of the kirkcaldy bay region formed by excluding the water and sediment layers confirm that the extended wavetrain cannot be caused by the source the source effects increase the duration of the seismogram by only a few seconds compared to over 30 s for the effects of dispersion and are thus not significant it is demonstrated that for surface wave studies intended to probe the deeper solid basement using underwater explosions care must be exercised in selecting a shot location free from significant sediment thickness because these sediments effectively screen structure to between 10 and 100 times their own depth on the other hand the kirkcaldy bay surface wave seismograms also illustrate the detail with which sediment structure may be determined for acoustic and geological studies for example a 40 m thick sea bed sedimentary layer with shear wave velocity of about 0 2 km s 1 is resolved overlying a 1 4 km s 1 solid layer of 260 m thickness

the role of hydrothermal processes in concentrating high field strength elements in the strange lake peralkaline complex northeastern canada abstract the middle proterozoic peralkaline pluton at strange lake quebec labrador comprises hypersolvus to subsolvus phases which are unusually enriched in zr y rees nb be and f as exotic alkali and alkaline earth silicate minerals the highest concentrations of these elements are in subsolvus granite which underwent intense low temperature 200 c hydrothermal alteration involving hematization and the replacement of alkali high field strength element hfse minerals by calcic equivalents this alteration is interpreted to have been caused by meteoric or formational waters high temperature 350 c alteration attributed to orthomagmatic fluids is evident in other parts of the subsolvus granite by the replacement of arfvedsonite by aegirine comparisons of the chemical compositions of fresh and altered rocks indicate that rocks subjected to high temperature alteration were chemically unaffected except for depletion in zr y and hrees these elements were appreciably enriched in rocks that underwent low temperature alteration other elements affected by low temperature alteration include ca and mg which were added and na which was removed available data on hfse speciation in aqueous fluids and the chemistry of the pluton suggest that the hfses were transported as fluoride complexes if this was the case the low temperature fluid could not have been responsible for hfse transport because the high concentration of ca and low solubility of fluorite would have buffered f activity to levels too low to permit significant complexation we propose that hfse mineralization and accompanying alteration were the result of mixing in the apical parts of the pluton of a f rich essentially ca free orthomagmatic fluid containing significant concentrations of hfses with an externally derived meteoric dominated fluid enriched in ca as a result of interaction with calc silicate gneisses and gabbros according to this interpretation the latter fluid was responsible for the exchange of ca for alkalis mainly na in hfse rich minerals and by sharply reducing f activity in the mixed fluid through fluorite precipitation and or increasing ph destabilised the hfse fluoride complexes causing deposition of hfse bearing minerals an important implication of this study is that major hfse enrichment may be restricted to those rare cases where f rich ca free metal leaching environments and ca rich depositional environments are juxtaposed

crustal structure measurements near fram ii in the pole abyssal plain abstract an extensive refraction profiling program was carried out during the fram ii experiment march may 1980 in the eastern arctic ocean two structural areas were covered north of the ice camp 86 n 24 w into the basin of the pole abyssal plain and south onto the flanks of the morris jesup rise digital multichannel data on an 800 by 800 m 24 channel hydrophone array and a single 2 component ocean bottom seismometer obs were recorded for offsets from 2 5 to 100 km arrival times amplitudes and phase velocities of the seismic signals recieved on the hydrophone array were determined using high resolution array processing from these measurements and the obs data preliminary velocity structural models of the crust have been derived for the purposes of this paper 2 refraction lines have been analyzed a 40 km line on a flat region of the pole abyssal plain and an 86 km line on a slightly dipping region taken as the drifting ice camp shoaled on the morris jesup rise these preliminary analyses yield a sedimentary layer with a gradually increasing velocity 1 5 2 km thick this cover overlays a crust with a thin layer 2 and yields a total ocean bottom to mantle thickness of 4 7 km

magma chamber scale liquid immiscibility in the siberian traps represented by melt pools in native iron magma unmixing i e separation of a homogeneous silicate melt into two or more liquids is responsible for sudden changes in the evolution of common melts element fractionation and potential formation of orthomagmatic ore deposits although immiscible phases are a common phenomenon in the mesostasis of many tholeiitic basalts evidence of unmixing in intrusive rocks is more difficult to record because of the transient nature of immiscibility during decompression cooling and crystallization in this paper we document a clear case of liquid immiscibility in an intrusive body of tholeiitic gabbro in the siberian large igneous province using textures and compositions of millimeter sized silicate melt pools in native iron the native iron crystallized from a metallic iron liquid which originated as disseminated globules during reduction of the basaltic magma upon interaction with coal bearing sedimentary rocks in the siberian craton the silicate melts entrapped and armored by the native iron are composed of two types of globules that represent the aluminosilicate 60 77 wt sio2 and silica poor fe ti ca p rich in wt sio2 15 46 feo 15 22 tio2 2 7 cao 11 27 p2o5 5 30 conjugate liquids different proportions and the correlated compositions of these globules in individual melt pools suggest a continuously evolving environment of magmatic immiscibility during magma cooling these natural immiscible melts correspond extremely well to the conjugate liquids experimentally produced in common basaltic compositions at 1025 c our results show that immiscibility can occur at large scale in magma chambers and can be instrumental in generating felsic magmas and fe ti ca p rich melts in the continental igneous provinces

the role of hydrothermal processes in the granite hosted zr y ree deposit at strange lake quebec labrador evidence from fluid inclusions abstract the strange lake zr y ree nb and be deposit is hosted by a small high level late proterozoic peralkaline granite stock that intruded into high grade metamorphic gneisses on the quebec labrador border the stock is extensively altered early alteration is manifested by the replacement of arfvedsonite with aegirine later alteration involved ca na exchange zr ti y rees nb and be are concentrated in ca bearing minerals that together with quartz commonly pseudomorph na bearing minerals fluid inclusions in pseudomorphs comprise several distinct types high salinity 13 to 24 wt nacl eq ca rich aqueous inclusions that homogenize to liquid between 135 and 195 c mixed aqueousmethane inclusions methane inclusions and solid bearing inclusions aqueous methane inclusions represent heterogeneous entrapment of immiscible high salinity aqueous liquid and methane bastnasite tentatively identified by sem analysis occurs as a daughter mineral other daughter or trapped minerals include a y hree bearing mineral possibly gagarinite and hematite galena sphalerite fluorite pyrochlore kutnahorite and griceite the first three inclusion types also occur in quartz in pegmatites and veins together with lower temperature lower salinity na dominated aqueous inclusions the entrapment temperature inferred for the aqueous inclusions from microthermometry and the na k ca geothermometer range from 155 to 195 c for the higher salinity inclusions and 100 to 165 c for the low salinity inclusions a model is proposed in which the intrusion of a peralkaline granite to high crustal levels initiated a ground formational water dominated hydrothermal system in adjacent gabbroic calc silicate and graphitic gneisses reaction of the high salinity ca rich liquid with the graphitic gneisses led to the production of an immiscible methane gas subsequent interaction of this liquid with the granite led to extensive replacement of sodic minerals by calcium analogues at temperatures of less than 200 c some time after the onset of ca metasomatism the high salinity liquid mixed with a ca poor low salinity low temperature liquid that had leached f and rare metals from the granite yttrium and ree mineral deposition occurred as a result of the decreased ligand concentration that accompanied fluorite deposition during mixing of the ca rich and ca poor aqueous liquids

evidence for aqueous liquid liquid immiscibility in highly evolved tin bearing granites mount pleasant new brunswick canada abstract three distinct types of fluid inclusions i e liquid vapor lv liquid vapor solid lvs and v only co exist within a single primary fluid inclusion assemblage in fluorite crystals that formed prior to and in close association with cassiterite mineralization in an assemblage comprising fluorite arsenopyrite topaz cassiterite in the sn w mo deposit of the north zone mount pleasant new brunswick the mineral assemblage occurs in vugs with late quartz and chlorite filling the remainder of the open space solid bearing inclusions contain up to eight optically different solids which are estimated to occupy up to approximately 70 vol of the fluid inclusions in a given fluid inclusion assemblage each type of fluid inclusion shows consistent l v or l v s phase ratios the results of microthermometric analyses show that lv inclusions have low salinities that vary from 0 to 10 wt nacl eq and homogenization temperatures that vary from 91 to 250 c within a given assemblage the ranges of salinity and homogenization temperatures of lv inclusions are even less in contrast co existing lvs inclusions are highly saline with salinities ranging from 36 to 40 wt nacl eq and have much higher homogenization temperatures that vary from 425 c to 600 c the upper limit of the microthermometric stage the salinity and homogenization temperature ranges of lvs inclusions show a limited range for a given assemblage the solids in lvs inclusions are interpreted as daughter phases due to consistent phase ratios in lvs fluid inclusions and because during heating experiments all solid phases melted prior to liquid vapor homogenization the consistency of phase ratios and the results of microthermometric analysis among lv or among lvs inclusions show that these inclusions were not formed through necking down of larger inclusions in addition the absence of sweat halos and re entrants rules out water loss as a possible mechanism for producing these coexisting fluid inclusions fluid inclusions of highly contrasting salinities and homogenization temperatures are therefore interpreted to be the result of trapping from two immiscible aqueous liquids it is unknown whether the two liquids exsolved from one single aqueous fluid or have different origins but consideration of the nature of inclusion assemblages in samples from other parts of the system suggest the latter topaz and cassiterite within the same mineral assemblage as well as late quartz contain lv fluid inclusion assemblages with microthermometric behaviors that are similar to the lv type inclusions in coexisting fluorite hosted lv and lvs inclusions suggesting that cassiterite deposited from the low salinity and temperature fluid

strength asperities along oceanic transform faults a model for the origin of extensional earthquakes on the eltanin transform system abstract we use finite element simulations of the state of stress in the vicinity of the eltanin transform system to investigate the possible origin of earthquakes occurring on or in the immediate vicinity of transform segments and featuring normal faulting mechanisms with tension axes oriented approximately 45 away from the azimuth of plate motion in principle unexpected along transform faults in addition to solutions previously described in the literature we report on seven new such mechanisms including a large event with magnitude 6 in 2001 we model the transform segments as either weak i e featuring the same elastic properties as the ridge or strong i e featuring the same properties as the surrounding cooled oceanic lithosphere in addition we allow irregularities in the geometry of the transform contact in the form of either bends in the plate boundary jogs or asperities i e strong elements in an otherwise weak transform system we also consider the effect of oblique ridge push on the pacific plate we conclude that the seismic properties of the eltanin transform system are best described by the model of a weak transform in which a few strong asperities are embedded we speculate that their origin may be linked to the complex and recent history of readjustments in rates and directions of spreading notably to the south of the eltanin system

equatorial pacific seismic reflectors as indicators of global oceanographic events the origin of a series of regionally correlatable seismic horizons in the neogene sediments of the central equatorial pacific is examined through seismic modeling and the detailed analyses of stratigraphic and physical property relationships in deep sea drilling project cores these regionally traceable reflectors are synchronous the younger reflectors are the direct result of carbonate dissolution events the older ones of stratigraphically selective diagenetic processes the changes in ocean chemistry associated with these events appear to be linked to global reorganizations of surface and bottom water circulation patterns the most dramatic of which are associated with reorganizations of north atlantic bottom waters these deepwater seismic horizons appear to correlate with the major events on the relative sea level curve of vail et al for the neogene

source characteristics of large deep earthquakes constraint on the faulting mechanism at great depths 1 source parameters for eight large deep earthquakes are inferred from broadband data of the global seismograph network we completed an unprecedented data set composed of 14 largest deep earthquakes mw ranging from 7 0 to 8 3 from six different subduction zones studied with identical source parameter inversion methods the study confirms earlier findings that deep earthquake source properties vary with the temperature of the subducting plate events in cold slabs show high aftershock activity high rupture velocity and high seismic efficiency in contrast earthquakes in warm slabs generally have low aftershock productivity low rupture velocity and low seismic efficiency however the 23 june 1991 argentina event has source properties that are rather characteristic for earthquakes in cold slabs and that differ from those of other large south american events we suggest that two types of deep earthquakes occur in south america and we interpret these results in the context of the shear instability model for the mechanism of deep earthquakes in this model shear failure occurs through a thermal runaway mechanism within a shear zone at great depth and low seismic efficiency might indicate significant energy dissipation due to heating and possible melt production the 1991 argentina event located in a pocket of deep seismicity within the slab core may represent a shear instability with little melting as would be the case for large deep earthquakes in cold subduction zones whereas the other known south american large deep events such as 1963 peru 1970 colombia and 1994 bolivia are located in relatively aseismic regions and may involve significant melting within warmer regions of the slab

liquidus equilibria in the system k2o na2o al2o3 sio2 f2o 1 h2o to 100 mpa ii differentiation paths of fluorosilicic magmas in hydrous systems we investigated phase equilibria in the six component system na2o k2o al2o3 sio2 f2o 1 h2o at 100mpa to characterize differentiation paths of natural fluorine bearing granitic and rhyolitic magmas topaz and cryolite are stable saturating solid phases in calcium poor systems at 100mpa the maximum solidus depression and fluorine solubility in evolving silicic melts are controlled by the eutectics haplogranite cryolite h2o at 6408c and 4 wt f and haplogranite topaz h2o at 6408c and 2 wt f topaz and cryolite form a binary peralkaline eutectic at 6608c 100mpa and fluid saturation the low temperature nature of this invariant point causes displacement of multiphase eutectics with quartz and alkali feldspar towards the topaz cryolite join and enables the silicate liquidus and cotectic surfaces to extend to very high fluorine concentrations more than 30 wt f for weakly peraluminous and subaluminous compositions the differentiation of fluorine bearing magmas follows two distinct paths of fluorine behavior depending on whether additional minerals buffer the alkali alumina ratio in the melt in systems with micas or aluminosilicates that buffer the activity of alumina magmatic crystallization will reach either topaz or cryolite saturation and the system solidifies at low fluorine concentration in leucogranitic suites precipitating quartz and feldspar only the liquid line of descent will reach topaz or cryolite but fluorine will continue to increase until the quaternary eutectic with two fluorine bearing solid phases is reached at 5408c 100mpa and aqueous fluid saturation the maximum water solubility in the haplogranitic melts increases with the fluorine content and reaches 12 5 0 5 wt h2oat the quartz cryolite topaz eutectic composition a continuous transition between hydrous fluorosilicate melts and solute rich aqueous fluids is not documented by this study our experimental results are applicable to leucocratic fluorosilicic magmas in multicomponent systems however the presence of calcium may severely limit enrichment of fluorine by crystallization of fluorite

liquid immiscibility in the caf2 granite system and trace element partitioning between the immiscible liquids abstract the recent discoveries of ca fluoride melt in magmatic systems especially in peralkaline granites with rare earth element enrichment has raised questions about the presence and nature of liquid immiscibility in caf2 granite systems as well as the partitioning behavior of trace elements between such immiscible liquids we have experimentally explored the immiscibility in this system using natural granite fluorite starting materials at fast and slow cooling rates temperatures from 500 c to 1200 c and 1 atmosphere pressure our experiments confirm the presence of a miscibility gap in the caf2 granite system over a wide range of temperatures the two immiscible liquids are a mafic fluorosilicate melt fm with high cao and f and a felsic oxysilicate melt sm with high sio2 and alkalis immiscibility is encountered when the bulk f content exceeds approximately 4 4 wt at 1200 c and then rapidly decreases to only 0 75 wt at low temperature below 900 c this indicates that calcic magmas are able to evolve to the liquid immiscibility domain by the residual enrichment of fluorine resulting from fractional crystallization and that liquid immiscibility should be common the peritectic reaction fm sm fluorite removes the fluorosilicate liquid around 600 c and could explain the absence of fluorosilicate observations in natural granites the compositions of the liquids in fast cooling experiments show a significantly larger miscibility gap which is characterized by compared to slow cooling runs similar sm compositions but higher ca and f content in fm this difference is caused by suppression of fluorite nucleation and is interpreted as a metastable extension of the high temperature liquid immiscibility immiscibility results in strong fractionation of trace elements which is primarily governed by melt structure and the ionic potential z r of the elements the behavior of trace elements can be categorized into three groups 1 network formers si al ga pb b partition into the oxysilicate melt 2 the partitioning of the alkalis and alkali earths is strongly dependent on the ionic potential with the partitioning coefficients d fm sm in the order dcs

liquid immiscibility and its role at the magmatic hydrothermal transition a summary of experimental studies several types of fluid immiscibility may affect the evolution of volatile rich magmatic systems at the magmatic hydrothermal transition the topology of silicate salt h2o systems implies that three fluid immiscibility silicate melt hydrosaline melt vapour should be stable in a broad range of compositions and p t conditions the most important factor controlling the immiscibility appears to be the coulombic properties electric charges z and ionic radii r of the main network modifying cations and the capacity for immiscibility appears to decrease in the following sequence mg ca sr ba li na k liquid immiscibility is enhanced in peralkaline compositions and in the presence of nonsilicate anions such as f cl co32 and bo33 in volatile rich magmatic systems the h2o is likely to react with the chloride fluoride borate and carbonate species and the chemical effects of high temperature hydrolysis may be greatly enhanced by phase separation in systems with multiple immiscible fluid phases natural granitic magmas can thus exsolve a range of chemically and physically diverse hydrosaline liquids and the role of these fluid phases is likely to be especially significant in pegmatites and li f rare metal granites

coherent noise in marine seismic data three mechanisms that might produce noise patterns on stacked sections are examined direct and trapped waves that propagate outward from the seismic source cable motion caused by the tugging action of the boat and tail buoy and scattered energy from irregularities in the water bottom and sub bottom different noise patterns can be observed on shot profiles and common midpoint cmp gathers these patterns can be diagnostic of the dominant mechanism in a set of data field data suggest that the dominant noise is from waves scattered within the shallow sub bottom this type of noise is enhanced by cmp stacking moreover it can be as strong as surface wave noise on stacked land seismic data as well moveout filtering is best for suppressing the noise while preserving signal since the scattered noise does not exhibit a linear moveout pattern on cmp sorted gathers moveout filtering must be applied either to traces within shot records and common receiver gathers or to stacked traces our data example demonstrates that although it is more costly moveout filtering of the unstacked data is particularly effective because it conditions the data for the critical data dependent processing steps of predictive deconvolution and velocity analysis modified journal abstract

alkali pyroxenes and amphiboles a window on rare earth elements and other high field strength elements behavior through the magmatic hydrothermal transition of peralkaline granitic systems peralkaline granites and pegmatites are a prime repository of ree and hfse critical raw materials although it is accepted that magmatic processes are fundamental in concentrating these metals the role of hydrothermal fluids in concentrating and fractionating these elements remains unclear this paper investigates the global reproducibility of the magmatic hydrothermal evolution of alkaline silica saturated systems using alkali pyroxene and amphiboles from six alkaline complexes these minerals contain significant amounts of ree and other hfse and pyroxene is stable throughout the magmatic and hydrothermal stages amphibole consists of mostly unzoned arfvedsonite leakeite and katophorite while pyroxene is always aegirine two types of aegirine were defined in all complexes type i aegirine is zoned its core is enriched in ca ree zr hf sc and sn and the rims in na fe3 and contains secondary rare metal bearing minerals and fluid inclusions type ii aegirine replaces amphibole and is oscillatory zoned we interpret the amphiboles and ree rich cores of type i aegirine to have grown during the magmatic stage whereas the rims of ree poorer type i and ii aegirine are formed during the hydrothermal stage during magmatic crystallization ree intake into amphiboles and pyroxene as well as lree hree fractionation were favored by their crystallographic properties and by competition among them and other minerals during subsequent hydrothermal stages ree and other hfse were remobilized locally reconcentrated and fractionated in mineral pseudomorphs and secondary pyroxene these observations point out the importance of studying rock forming minerals such as pyroxenes and amphiboles to unravel geological events controlled by common processes globally

immiscibility and continuous felsic melt fluid evolution within the rio blanco porphyry system chile evidence from inclusions in magmatic quartz the 5 2 to 3 9 ma late porphyries at rio blanco are spatially associated with hydrothermal tourmaline cemented breccias and a significant cu mo deposit magmatic inclusions in quartz from these rocks are used to better understand late stage magmatic processes particularly those involving melt melt and melt fluid immiscibility inclusions are represented by glass of common rhyolitic composition hereafter type 1 crystallized volatile rich felsic melt type 2 h2o and salt rich fluids and microphenocrysts coexistence of types 1 and 2 material within the same growth plane and within a single inclusion suggests that crystallizing rhyolitic magma separated into two silicate melts volatile poor and volatile rich the volatile rich silicate melt had a prolonged evolution extending below the solidus of volatile poor silicate melt with a progressive reduction of the silicate volatile ratio and ultimately to highly saline fluids the latter may have been the source of hydrothermal fluids that had the potential to transport metals the occurrence of immiscibility in the rio blanco rhyolites may be in some ways comparable to that in volatile rich pegmatites and strongly suggests that this process may be common in other se normal felsic magmas and important in the origin of mineralized porphyries

revisiting complete miscibility between silicate melts and hydrous fluids and the extreme enrichment of some elements in the supercritical state consequences for the formation of pegmatites and ore deposits abstract using water and major and trace element data obtained from melt inclusions primarily in pegmatite quartz we have shown in this and previous papers that melt melt fluid immiscibility is widespread and an important process during the generation of granitic pegmatites furthermore we have shown that the formation of pegmatites actually begins in the supercritical melt fluid stage in this study we extend previous work and in particular explore the behavior of 10 different elements be f p s cl as rb sn cs and ta in the supercritical range from preliminary studies we suggest that other elements such as b na k zn nb and sb will behave similarly near the solvus crest of a generalized pseudo binary melt water system this provides important evidence that pegmatite forming processes have already begun at high temperatures in the range of 850 750 c and that may require a re think on the partitioning behavior of metals in late stage residual melts exsolved from granitic magmas the existence of this parental supercritical silicate melt fluid although derived from granitic magmas imposes significant constraints of its own so drawing conclusions about pegmatite forming processes from data gained from slightly modified granite compositions becomes highly problematic we propose that the extremely high concentration of some elements over a small but well defined water concentration range symmetrically distributed around the critical point of the pseudo binary solvus must be derived from the unusual properties of the near critical or supercritical phases these unusual properties include extremely low density viscosity and surface tension and high diffusivity reactivity and mobility these are exactly the qualities that make such supercritical fluids an excellent medium for the formations of pegmatites by reactions with the existing matrix melt crystal mush and for the extreme enrichment of some ore forming elements highly soluble in alkali and water rich supercritical fluids a very important point in mineral crystallization is the non uniform local enrichment of rare and economically significant elements at specific locations in pegmatites granites and other rocks given the properties of the supercritical phase identified from melt inclusions the process of ostwald ripening can operate very effectively the driving force for ostwald ripening arises because the concentration of solute in the vicinity of small crystals or clusters is greater than and in the vicinity of larger crystals or clusters less than the average supersaturation the solute in the supercritical fluid therefore flows from the small crystals to the larger crystals and permits the growth of very large crystals at the expense of smaller ones this is favored by the extraordinary properties of supercritical fluids given the low surface tension the supercritical fluid can move also through grain boundaries and small channels or dislocation pipes aiding incompatible element transport additionally their consequences for the formation of some important granite related ore deposits are briefly outlined

solubility of fluorite in haplogranitic melt of variable alkalis and alumina content at 800 1000 c and 100 mpa 1 to study the behavior of fluorite in sio2 al2o3 na2o k2o h2o melts we conducted both crystallization and dissolution experiments in the first case fluorite crystallized from melts enriched in ca relative to f in the second case ground fluorite 10 m was partially dissolved into melts of initially f free or f doped glass experiments were conducted at 800 1000 c and 100 mpa for 7 to 240 hours using a series of finely ground subaluminous and peralkaline haplogranitic glasses electron microprobe emp analysis of the run products glass crystals documented increasing fluorite solubility with melt alkalinity these molar relationships can be described by cf 2 1 3 asi 2 3 at 900 c and cf 2 cca 2 1 asi 3 8 at 1000 c where asi is the aluminum saturation index measured in experimental glasses as al na k 2ca cf 2 is one half the molar concentration of f and cca is the mol of ca in the glass fluorite solubility may be defined as either cf 2 cca or both solubilities at 800 900 and 1000 c for the melts with asi between 0 58 and 0 59 approach log linear with 104 t k slope 0 45 the joint effect of f and temperature on fluorite solubility is significant solubility rises from 0 28 mol at 800 c 4 96 mol doped f to 0 99 mol at 900 c 2 17 mol doped f solubilities at 800 850 and 900 c for the melts with the same initial f contents 4 96 mol approach log linear with 104 t k slope 0 33

fluorite 87sr 86sr and ree constraints on fluid melt relations crystallization time span and bulk dsr of evolved high silica granites tabuleiro granites santa catarina brazil abstract the evolved high silica tabuleiro granites within the early paleozoic santa catarina composite massif pelotas batholith southern brazil are characterized by the presence of euhedral to subeuhedral accessory fluorite and geochemical features typical of topaz rhyolites and related a type granites sr isotopes and ree data of the tabuleiro granites and their accessory fluorite are used to constrain fluid melt relations crystallization time span and bulk crystal melt sr partition coefficient d sr correlations involving ree eu eu rb sr sr and 87 sr 86 sr in fluorite and fluorite host granites show that fluorite records the differentiation trend of the host tabuleiro granites ree normalized patterns and eu eu relations in fluorite bearing granites indicate that fluorite forms after the crystallization of the quartzo feldspathic framework in residual melts the tabuleiro accessory fluorites yield high and variable 87 sr 86 sr ratios between 0 72334 and 0 8192 these ratios are neither the result of fluorite precipitation from a fluid nor sr isotopic resetting they result from 87 rb decay in fluorine rich high rb sr melts evolved by fractional crystallization in a magmatic system with a long crystallization time span melt residence times of 300 to 700 ka and d sr of 4 7 to 6 0 are necessary to yield the high fluorite 87 sr 86 sr ratios these results are compatible with those deduced elsewhere from high silica rhyolitic volcanic equivalents

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

compositional and kinetic controls on liquid immiscibility in ferrobasalt rhyolite volcanic and plutonic series we present major element compositions of basalts and their differentiation products for some major tholeiitic series the dry low pressure liquid lines of descent are shown to approach or intersect the experimentally defined compositional space of silicate liquid immiscibility ferrobasalt rhyolite unmixing along tholeiitic trends in both volcanic and plutonic environments is supported by worldwide occurrence of immiscible globules in the mesostasis of erupted basalts unmixed melt inclusions in cumulus phases of major layered intrusions such as skaergaard and sept iles and oxide rich ferrogabbros closely associated with plagiogranites in the lower oceanic crust liquid immiscibility is promoted by low pressure anhydrous fractional crystallization that drives the low al2o3 high feo liquids into the two liquid field kinetic controls can be important in the development of two liquid separation the undercooling that occurs at the slow cooling rates of plutonic environments promotes early development of liquid immiscibility at higher temperature in contrast rapid cooling in erupted lavas leads to large undercoolings and liquid immiscibility develops at significantly lower temperatures unmixing leads to the development of a compositional gap characterized by the absence of intermediate compositions a feature of many tholeiitic provinces the compositions of experimental unmixed silica rich melts coincide with those of natural rhyolites and plagiogranites with high feotot and low al2o3 suggesting the potential role of large scale separation of immiscible si rich liquid in the petrogenesis of late stage residual melts no trace of the paired ferrobasaltic melt is found in volcanic environments because of its uneruptable characteristics instead fe ti p rich gabbros are the cumulate products of immiscible fe rich melts in plutonic settings the immiscibility process may be difficult to identify because both melts crystallize the same phases with the same compositions the two liquids might form incompletely segregated emulsions so that both liquids continue to exchange as they crystallize and remain in equilibrium even if segregated both melts evolve on the binodal surface and exsolve continuously with decreasing temperature the two liquids do not differentiate independently and keep crystallizing the same phases with differentiation further evolution by fractional crystallization potentially drives the bulk liquid out of the twoliquid field so that very late stage liquids could evolve into the single melt phase stability field

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

geology and genesis of the toongi rare metal zr hf nb ta y and ree deposit nsw australia and implications for rare metal mineralization in peralkaline igneous rocks the toongi deposit located in central nsw australia hosts significant resources of zr hf nb ta y and ree within a small ca 0 3 km2 rapidly cooled trachyte laccolith toongi is part of regional late triassic to jurassic alkaline magmatic field but is distinguished from the other igneous bodies by its peralkaline composition and economically significant rare metal content that is homogenously distributed throughout the trachyte body the primary ore minerals are evenly dispersed throughout the rock and include lueshite natroniobite and complex na fe zr nb y ree silicate minerals dominated by a eudialyte group mineral egm the egm occurs in a unique textural setting in the rock commonly forming spheroidal or irregular shaped globules herein called snowballs within the rock matrix the snowballs are often protruded by aegirine and feldspar phenocrysts and contain swarms of fine aegirine and feldspar grains that often form spiral or swirling patterns within the snowball secondary ore minerals include ree carbonates y milarite catapleiite and gaidonnayite that fill fractures and vesicles in the rock based on bulk rock geochemical and nd isotope data and thermodynamic modelling of magma fractionation the alkaline rocks of the region are interpreted to represent extrusive to hyperbyssal products of mantle derived magma that ponded at mid crustal levels ca 0 3 gpa and underwent extensive fractionation under low oxygen fugacity conditions the high na2o peralkaline nature of the toongi deposit trachyte developed via extensive fractionation of an alkali olivine basalt parental magma initially in the mid crust and subsequently at shallow levels ca 0 1 gpa this extended fractionation under low fo2 and relatively low h2o activity conditions limited volatile release and allowed build up of rare metal contents to ore grades we speculate that the ore minerals may have originally formed from rare metal rich sodic silicate melt that formed immiscible globules subsequently crystallized to egm in the magma shortly before emplacement and rapid cooling subsequent hydrothermal alteration caused relatively limited and localized remobilization of some ore metals into fractures and vesicles in the rock

the paleoproterozoic montviel carbonatite hosted ree nb deposit abitibi canada geology mineralogy geochemistry and genesis abstract the montviel 250 mt carbonatite hosted ree nb deposit is hosted in a paleoproterozoic alkaline suite located in the sub province of abitibi in the archean province of the superior the alkaline intrusion consists of biotite clinopyroxenites melano to leucosyenites a melteigite ijolite urtite series riebeckite granite a series of carbonatites and a carbonatite polygenic breccia the carbonatite series includes silicocarbonatites calciocarbonatites rare magnesiocarbonatites ferrocarbonatites and mixed carbonatites and are cut by a late high energy carbonatite polygenic breccia diamond drill hole assays and microscope observations indicate that nb is hosted in pyrochlore from silicocarbonatite whereas the ree mineralization is mainly hosted in ferrocarbonatite late mixed carbonatites and polygenic breccia in ree bearing carbonates and fluorocarbonate minerals diamond drill hole underground mapping and systematic assays have shed light on zones enriched in nd and lree with preferential ba and sr hydrothermal precipitation and zones enriched in dy y and hree displaying preferential f and p bearing hydrothermal precipitation petrographic observations electron microprobe analyses la icpms and x ray diffraction were used to study the mineralization processes and to identify and quantify the ree bearing burbankite ce carbocernaite ce ewaldite y huanghoite nd cordylite ce cordylite nd kukharenkoite ce and synchysite ce most minerals are enriched in total lree with values around 19 3 wt have total mree values around 2 2 wt and extremely variable total hree values with very high contents of dy and y averaging around 0 3 wt and 1 0 wt respectively and with total hree reaching up to 10 0 wt a paragenetic sequence is proposed that consists of 1 a silicocarbonatite nb stage and 2 a calciocarbonatite stage dominated by magmatism but accompanied by hydrothermal fluids 3 a main ferrocarbonatite stage dominated by episodes of ba and sr hydrothermalism and lree mineralization f and p hydrothermalism and hree mineralization and evolved ferrocarbonatitic magmatism 4 a renewed mixed carbonatite magmatic stage with minor but increasing hydrothermalism and 5 a terminal stage of fluid pressure buildup and explosion leading to the creation of a hree enriched polygenic breccia globular melt inclusions of ba cl f si o may indicate the presence and contribution of barium bearing chlorofluoride melts during hydrothermal activity and mineralization of the carbonatite

centroid moment tensor solutions for april june 1999 abstract centroid moment tensor solutions are presented for 218 earthquakes that occurred during the second quarter of 1999 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging plenum 19 785 797 a model of anelastic attenuation of durek j j ekstrom g 1996 a radial model of anelasticity consistent with long period surface wave attenuation bull seismol soc am 86 144 158 is used to predict the decay of the waveforms

experimental constraints on the effect of phosphorous and boron on nb and ta ore formation abstract evolved granites and pegmatites are important sources for critical metals including niobium nb and tantalum ta the ore deposits that are commonly associated with these granitic rocks are commonly enriched in phosphorous p and boron b yet there are few experimental constraints on the influence of these fluxing compounds on ore forming processes here the effects of phosphorous p boron b temperature and melt alkalinity on the solubility of manganocolumbite mnnb 2 o 6 and manganotantalite mnta 2 o 6 in evolved fluid saturated granitic melts were studied solubility experiments were performed at 100 mpa and 800 to 1000 c using three haplogranitic melt compositions with alumina saturation indices asi of 0 8 peralkaline 1 0 subaluminous and 1 2 peraluminous the possible effect of p and the influence of b in p rich granitic systems were investigated by adding 4 wt p 2 o 5 and 4 wt p 2 o 5 4 wt b 2 o 3 respectively to the starting compositions the addition of p decreased the solubility of manganocolumbite and manganotantalite in peralkaline granitic melts in agreement with previous studies we suggest that p was present as network forming alkali phosphate complexes such as m x po y in the peralkaline melt structure m k na etc resulting in the observed effect of p at asi 0 8 the presence of p had a positive effect on the solubility of manganocolumbite and manganotantalite in subaluminous granitic melts which became less significant in peraluminous systems this may reflect the formation of complexes such as al x po y and ta nb x po y in the melt empirical relationships describing the effect of p on manganocolumbite and manganotantalite solubility in the aforementioned haplogranitc melts at 100 mpa and 800 c were determined the addition of b to p rich peralkaline melts had a minor effect on manganocolumbite solubility but resulted in an increase of manganocolumbite and manganotantalite solubility in subaluminous systems for peraluminous melts a minor increase of the solubility of manganocolumbite and manganotantalite with the addition of b was typically observed we propose that the addition of b to the p enriched melts resulted in the formation of network forming boro phosphate complexes until the b p molar ratio in the melts reached unity once the b p molar ratio was greater than one polymerizing mbo 2 complexes were probably formed in peralkaline melts while b acted presumably as a network modifier in subaluminous and peraluminous systems with b p 1 in combination with literature data we determined similar dissolution enthalpies for manganocolumbite and manganotantalite for given a asi and pressure where the dissolution enthalpy increased with asi from 60 kj mol at asi 0 6 to 150 kj mol at asi 1 2 cooling is thus likely to be of greater importance for magmatic mineralization in peraluminous compared to peralkaline systems the primary influence of b and p in peraluminous systems is to act as fluxes lowering the crystallization temperature of melts which allows for the crystallization of primary magmatic tantalite

the amphiboles of the ree rich a type peralkaline strange lake pluton fingerprints of magma evolution abstract major and trace element compositions of amphibole in igneous environments commonly reflect evolving magma compositions in this study we use the amphibole group minerals from the strange lake ree enriched peralkaline granitic pluton to gain insights into the evolution of the magma this 1240 ma old pluton consists of two main intrusive facies an early hypersolvus granite which occurs as separate northern and southern intrusions and a more evolved transsolvus granite in the hypersolvus granite the amphibole is a late interstitial phase whereas in the transsolvus granite it is present as phenocrysts the amphibole compositions vary from calcic sodic ferro ferri katophorite in the southern hypersolvus granite to sodic arfvedsonite ferro ferri leakeite in the other more evolved granitic units high na si li and low al and ca concentrations in the amphibole phenocrysts of the transsolvus granite indicate formation from a more evolved magma compared to the hypersolvus granite despite the fact that these crystals formed early we interpret the increasing fe 3 fe 2 ratios in the amphibole of the hypersolvus granite to reflect crystal chemical effects na ca ratio and increasingly oxidizing conditions in the magma whereas in the phenocrysts of the transsolvus granite the increasing ratio was the product of increasing proportions of f and oh in the melt the amphiboles of all the granite units have elevated nb zr hf and ree concentrations compared to the bulk rock suggesting that these elements are compatible in amphibole by contrast the much lower ti concentration was due to saturation of the magma in sodium titanosilicates the amphibole ree concentrations vary greatly among the granite units amphibole of the southern and northern hypersolvus granite contains 0 16 and 0 07 wt ree y on average respectively and in the transsolvus granite the average ree content is only 0 01 wt despite the more evolved nature of its host transsolvus granite we intrepret this compositional difference to be due to the fact that the latter represents phenocrysts which crystallized early whereas the hypersolvus arfvedsonite is a late interstitial phase chondrite normalized ree profiles emphasise the wide range in lree and the narrow range in hree concentrations of the amphiboles the variations in the lree profiles reflect the variable crystallization of primary lree bearing phases including monazite ce pyrochlore group minerals and gagarinite ce prior to or contemporaneous with the amphibole as well as the exsolution of a lree rich fluoride melt the lree are incompatible in the amphibole structure apparent d d 1 owing to their small ionic radius and their compatibility with the amphibole structure hree concentrations were more controlled by partitioning crystal chemical effects than by the concentrations in the corresponding magma large proportions of the bulk hree content up to 70 reside in the amphibole and their later release through hydrothermal replacement helps to explain the extreme and unusual hree enrichment of the strange lake pluton

formation by silicate fluoride phosphate melt immiscibility of ree rich globular segregations within aplite dikes aplite dikes intruding the proterozoic 1 42 3 ga longs peak st vrain silver plume type peraluminous granite near jamestown colorado contain f p and rare earth element ree rich globular segregations with 40 46 ree 3 7 4 8 wt p2o5 and 5 8 wt f a combination of textural features and geochemical data suggest that the aplite and ree rich globular segregations co existed as two co genetic liquids prior to their crystallization and we propose that they are formed by silicate fluoride phosphate s co2 melt immiscibility following ascent cooling and decompression of what was initially a single homogeneous magma that intruded the granite the ree distribution coefficients between the silica rich aplites and ree rich segregations are in good agreement with experimentally determined distribution coefficients for immiscible silicate fluoride phosphate melts although monazite ce and uraninite u th pb microprobe ages for the segregations yield 1 420 25 and 1 442 8 ga respectively thus suggesting a co genetic relationship with their host granite end1 42ga values for the granites and related granitic pegmatites range from 3 3 to 4 7 average 3 9 and differ from the values for both the aplites and ree rich segregations which range from 1 0 to 2 2 average 1 6 furthermore the granites and pegmatites have la yb n 100 and absence of an eu anomaly in both the aplites and segregations these data are consistent with the aplite dikes and the ree rich segregations they contain being co genetic but derived from a source different from that of the granite the higher end1 42ga values for the aplites and ree rich segregations suggest that the magma from which they separated had a more mafic and deeper dryer and hotter source in the lower crust or upper mantle compared to the quartzo feldspathic upper crustal source proposed for the longs peak st vrain granite

fluid evolution in the strange lake granitic pluton canada implications for hfse mobilisation abstract strange lake is a mid proterozoic peralkaline granite pluton quebec labrador canada that underwent extreme enrichment in high field strength elements hfse including the rare earth elements ree the hfse mineralisation is confined to highly altered pegmatites and the most altered parts of the granites implying a genetic association between hydrothermal fluids and hfse enrichment this study uses analyses of fluid inclusions to investigate the hydrothermal evolution of the strange lake pluton and the role of hydrothermal processes in concentrating the hfse to potentially exploitable levels five groups of inclusions were distinguished from earliest to latest these groups are primary aqueous inclusions 25 wt nacl eq associated with melt inclusions group 1 primary aqueous inclusions 13 23 wt nacl eq associated with ch 4 inclusions groups 2a and b primary aqueous inclusions 9 wt nacl eq associated with co 2 inclusions group 3 primary aqueous inclusions 9 wt nacl eq which contain no carbonic component group 4 and finally secondary aqueous inclusions 19 wt nacl eq including inclusions that outline mineral pseudomorphs also with no detectable carbonic component group 5 most of the inclusions except those in group 5 have conspicuous implosion haloes evident as numerous tiny voids this indicates that the inclusions re equilibrated most likely during isobaric cooling fluid evolution commenced with the exsolution of a saline aqueous liquid 25 wt nacl eq and an immiscible ch 4 h 2 gas from the pegmatitic melt at temperatures of 450 500 c and a pressure of 1100 bars during isobaric cooling the gas component of the fluid was gradually oxidised evolving from being ch 4 dominant to a ch 4 fluid with a significant proportion of higher order hydrocarbons due to oxidative coupling of methane induced by the consumption of o 2 through the alteration of arfvedsonite to aegirine 325 360 c and finally to a co 2 dominated fluid at 300 c the apparent salinity of the aqueous fluid decreased from 25 to 4 5 wt nacl eq due to fluid rock interaction the latter also caused precipitation of nahcolite as a result of the reaction of newly formed co 2 with sodium from decomposing minerals formation of pseudomorphs after primary na zirconosilicates and na titanosilicates and replacement of primary ree silicates by bastnasite ce owing to this interaction the carbonic component of the fluid was consumed which together with the consumption of h 2 o to form al k and fe phyllosilicates contributed to an increase in the fluid salinity up to 19 wt nacl eq light rare earth elements lree were remobilised over 10s to 100 s of metres by the high temperature high salinity fluid preserved as group 1 and 2a inclusions whereas heavy rare earth elements hree were remobilised on a much smaller scale by a late low temperature high salinity fluid trapped as inclusion group 5 fluid preserved as inclusion group 3 may have been responsible for remobilisation of zr and ti

alkali zirconosilicates in peralkaline rocks based on the crystal chemistry of alkali zirconosilicates azs it is argued that zr in silicate melts is a network modifier rather than a complex former with the aid of silicate melt theory the late crystallization of azs in peralkaline melts can be explained the high ks ns and high q calculated in some norms of peralkaline rocks but not expected from the modes is the result of calculating zrsio4 rather than k na 2zrsio5 xsio2

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

partial melting fractional crystallisation liquid immiscibility and hydrothermal mobilisation a recipe for the formation of economic a type granite hosted hfse deposits abstract a number of a type granites host resources of the high field strength elements hfse including the rare earth elements ree that have been considered for economic exploitation the best known of them is the strange lake pluton canada with a resource of 20 mt grading 1 44 wt ree2o3 of which 50 are heavy rare earth oxides in this paper we examine the various processes that are likely to be responsible for the hyper enrichment of the hfse starting with the generation of a parental magma through a very low degree of partial melting of a mantle plume or a metasomatically enriched mantle in both cases below a continental crust continental rift we trace the evolution of this magma olivine nephelinite through fractional crystallisation of olivine and clinopyroxene followed by plagioclase k rich alkali feldspar and arfvedsonite to the final residues of hyper enriched hfse granitic pegmatites in so doing we show that at least two additional steps are essential to the process of hfse enrichment the first of these is the abrupt termination of plagioclase crystallisation prior to the final consumption of ca or assimilation of a ca source and the resulting exsolution of an immiscible ca fluoride melt that sequesters the lree and y the second of these steps is prolonged crystallisation of arfvedsonite which delays saturation of the magma with an aqueous phase and ensures the development of an agpaitic assemblage of na bearing hfse minerals e g na zirconosilicates and na titanosilicates finally we show that saturation of the magma with an aqueous carbonic fluid which evolves to a very acidic composition is an essential ingredient in the recipe for the formation of an economic a type granite hosted hfse deposit

from mantle to motzfeldt a genetic model for syenite hosted ta nb mineralisation abstract a genetic model for the motzfeldt tantalum niobium rich syenite in south west greenland considered to be one of the world s largest ta prospects is presented the motzfeldt primary magma formed early in regional gardar 1273 6 ma rifting isotope signatures indicate that the hf had multiple sources involving juvenile gardar hf mixed with older palaeoproterozoic or archaean hf we infer that other high field strength elements hfse similarly had multiple sources the magma differentiated in the crust and ascended before emplacement at the regional unconformity between ketilidian basement and eriksfjord supracrustals the hfse rich magmas crystallised ta rich pyrochlore which formed pyrochlore rich crystal mushes and it is these pyrochlore rich horizons rich in ta and nb that are the focus of exploration the roof zone chilled and repeated sheeting at the roof provided a complex suite of cross cutting syenite variants including pyrochlore microsyenite in a hot sheeted roof model the area was subject to hydrothermal alteration which recrystallized alkali feldspar to coarse perthite and modified the mafic minerals to hematite creating the friable and striking pink nature of the motzfeldt so centre carbon and oxygen isotope investigation of carbonate constrains fluid evolution and shows that carbonate is primarily mantle derived but late stage hydrothermal alteration moved the oxygen isotopes towards more positive values up to 21 the hydrothermal fluid was exceptionally fluorine rich and mobilised many elements including u and pb but did not transport hfse such as ta hf and nb although the u and pb content of the pyrochlore was enhanced by the fluid the hfse contents remained unchanged and therefore hf isotopes were unaffected by fluid interaction while the effect on hydrothermal alteration on the visual appearance of the rock is striking magmatic processes concentrated hfse including ta and the hydrothermal phase has not altered the grade exploration for hfse mineralisation commonly relies on airborne radiometric surveying which is particularly sensitive to the presence of u th a crucial lesson from motzfeldt is that the best target is unaltered pyrochlore which was identified less easily by radiometric survey careful petrological mineral studies are necessary before airborne survey data can be fully interpreted

rare metal indicator minerals in bedrock and till at the strange lake peralkaline complex quebec and labrador canada a study of rare metal indicator minerals and glacial dispersal was carried out at the strange lake zr y heavy rare earth element deposit in northern quebec and labrador canada the heavy miner

the memory of the accreting plate boundary and the continuity of fracture zones a detailed aeromagnetic anomaly map of the mesozoic seafloor spreading lineations southwest of bermuda reveals the dominant magnetic grain of the oceanic crust and the character of the accreting boundary at the time of crustal formation the magnetic anomaly pattern is that of a series of elongate lobes perpendicular to the fracture zone flowline trends the linear sets of magnetic anomaly peaks and troughs have narrow regions of reduced amplitude anomalies associated with the fracture zones during the period of mesozoic geomagnetic polarity reversals when 1200 km of central north atlantic seafloor formed the atlantic accreting boundary consisted of stationary elongate spreading center cells that maintained their independence even though sometimes only minor spatial offsets existed between cells normal oceanic crustal structure was formed in the spreading center cells but structural anomalies and discontinuities characteristic of fracture zones were formed at their boundaries which parallel flowlines of mesozoic relative plate motion in the central north atlantic we suggest that the memory for a stationary pattern of independent spreading center cells resides in the young brittle lithosphere at the accreting boundary where the lithosphere is weakest here each spreading center cell independently goes through its cylce of stress buildup stress release and crustal accretion after which its memory is refreshed the temporal offset between the peaks of the accretionary activity that takes place within each cell may provide the mechanism for maintaining the independence of adjacent spreading center cells through times when no spatial offset between the cells exists

fluorite stability in silicic magmas recent experimental evidence is used to assess the conditions under which fluorite forms an early crystallising phase in silicic magmas fluorite solubility primarily depends on the na k al balance in the coexisting silicic melt reaching a minimum in metaluminous melts it can display reaction relationships with topaz and titanite depending on changes in melt composition during crystallisation an empirical model of fluorite stability in ca poor peralkaline rhyolite melts is derived and applied to selected rocks text f text melt left text wt right left left text na text k text al right left 2 1110 3 text t left circ c right 1 5778 right right 2 789

the structure of young oceanic crust near a very fast spreading ridge we have modeled the structure of the young oceanic crust near the fastest spreading ridge ever to be profiled using seismic refraction techniques the data were originally collected during the capricorn expedition of the scripps institute of oceanography in 1953 one of the split leg profiles from that expedition c22 was conducted near the east pacific rise at 15 s where the half spreading rate is over 80 mm yr by digitizing the data and modeling the two splits of c22 using synthetic seismograms we have found that the crust is normal in thickness 5 to 7 km and in velocity structure an upper crustal transition zone is present on both legs and would appear to be a regular feature of young oceanic crust it is probably too deep 1 5 to 2 km beneath the seafloor to be correlated with the boundary between pillow basalts and sheeted dikes instead we attribute this transition zone to changes in crustal porosity and or hydrous minerals in the oceanic crust from the appearance of wide angle moho reflections near the rise axis we suggest that the very large crustal magma chamber that might be expected under this fast spreading ridge is not present this presumably results from the cooling of the crust by pervasive hydrothermal circulation

fluoride silicate melt immiscibility and its role in ree ore formation evidence from the strange lake rare metal deposit quebec labrador canada pegmatites and adjacent subsolvus granites two alkali feldspars of the mid proterozoic strange lake pluton quebec labrador canada host potentially economic concentrations of high field strength elements hfse including the rare earth elements ree zirconium and niobium previous studies have proposed that these concentrations were the result of a com bination of extreme fractionation of a peralkaline granitic magma and later hydrothermal remobilization however the recent discovery of melt inclusions which after heating to 900 or 950 c quench to immiscible fluoride and silicate glasses suggests an additional mechanism of hfse concentration crystallized melt inclusions are common in quartz phenocrysts of the early hypersolvus and transsolvus granite after heating four types of inclusions were discerned type 1 inclusions quench to a single silicate glass containing a high concen tration of zr nb and ti quenching of type 2 inclusions produces a zr nb ti rich silicate glass containing a globule of calcium rich fluoride glass with a high concentration of the ree the third inclusion type is similar to type 2 except that the calcium rich fluoride glass contains a globule of ree fluoride glass up to 50 wt total ree type 4 inclusions contain calcium fluoride glass with multiple silicate globules we propose that during or soon after emplacement the early granitic magma exsolved a calcium fluoride melt into which rare earth elements ree partitioned preferentially the conjugate silicate melt was consequently depleted in ca and the ree and enriched in zr nb and ti crystallization of the fluoride melt occurred late in the crystallization history of the silicate magma allowing it to accumulate in the volatile rich residual magma that formed the pegmatites this played a major role in the extreme enrichment of the pegmatites in ca f and ree crystallization of the pegmatites proceeded inwards from an outer zone in which feldspars quartz arfvedsonite and zirconosilicate minerals dominate to a core where the immiscible fluoride liquid collected and crystallized fluorite and ree minerals fluid exsolved from the silicate melt reacted with the products of both the silicate and fluoride melts remobilizing most of the hfse including the ree this study reports a rare example of silicate fluoride melt immiscibility and the first in which such immiscibility played a role in concentrating the ree to potentially economic levels 2014 elsevier ltd all rights reserved

centroid moment tensor solutions for july september 1999 abstract centroid moment tensor cmt solutions are presented for 231 earthquakes that occurred during the third quarter of 1999 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging plenum new york vol 19 pp 785 797 a model of anelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of anelasticity consistent with long period surface wave attenuation bull seismol soc am 86 144 158 is used to predict the decay of the waveforms

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

magmatic evolution and controls on rare metal enrichment of the strange lake a type peralkaline granitic pluton quebec labrador abstract although it is well known that a type granites are enriched in the rare earth elements ree and other high field strength elements hfse the magmatic processes that concentrate these elements are still poorly understood the 1 24 ga strange lake pluton in northern quebec labrador provides an extraordinary example of hyper enrichment in the ree zr and nb in a peralkaline a type granite the pluton consists of two hypersolvus granite units southern and northern and a transsolvus granite all of which contain perthitic alkali feldspar as the earliest major mineral the transsolvus granite also contains separate albite and microcline crystals arfvedsonite a sodic amphibole occurs exclusively as phenocrysts in the transsolvus granite whereas in the hypersolvus granite it is present as a late interstitial phase the primary hfse minerals are zircon monazite ce gagarinite ce and the pyrochlore group minerals magma evolution was monitored by the alumina content in the bulk rock which decreases from the southern to the northern hypersolvus granite and is lowest in the transsolvus granite alkalinity indices and bulk si fe rb ree zr nb concentrations show the opposite trend alkali feldspar compositions mirror the trend shown by the bulk rock i e decreasing al contents are accompanied by increasing si fe3 ree zr and nb contents the major driving forces for the evolution of the hypersolvus magma prior to emplacement were the early separation of a fluoride melt from the silicate melt and the crystallization of alkali feldspar and hfse rich phases zircon monazite ce pyrochlore group an alkali feldspar rich crystal mush containing lree fluoride melt droplets was emplaced as the least evolved southern hypersolvus granite massive fractionation of alkali feldspar led to a sharp increase in h2o and f activity in the magma chamber that triggered the crystallization of arfvedsonite and was followed by emplacement of the northern hypersolvus granite which contained a higher proportion of lree fluoride melt droplets further evolution in the magma chamber led to a transition from a miaskitic to an agpaitic composition the transsolvus granite was intruded in the form of a low viscosity crystal mush of alkali feldspar quartz arfvedsonite after appreciable crystallization of arfvedsonite and lree fluoride melt droplets upon emplacement arfvedsonite and gagarinite ce crystals segregated as cumulates in response to a combination of flow differentiation and gravity settling the immiscible fluoride melt accumulated in a volatile rich residual silicate magma which migrated to the top of the pluton where it formed the f ree rich cores of highly mineralized pegmatites

geochronology geochemistry mineralogy and metallogenic implications of the zhaojinggou nb ta deposit in the northern margin of the north china craton china abstract the large zhaojinggou nb ta deposit is located in the northern margin of the north china craton ncc inner mongolia china the deposit is mainly hosted in the mineralized dikes around the hutoushan pluton and the residual pegmatite shell at the top of the pluton samples from the pluton and the mineralized dikes are characterized by high contents of sio2 73 3 84 3 total alkalis 5 24 9 60 and al2o3 7 94 13 8 and moderate a cnk values with an average of 1 04 indicating a weakly peraluminous affinity the trace element patterns are characterized by rb nb ta zr and hf enrichment and markedly negative ba sr p eu and ti anomalies zircon u pb dating suggests that the emplacement of the pluton and the nb ta mineralization occurred coevally in the early cretaceous 126 1 ma and 127 2 ma respectively variations in both bulk rock geochemistry k rb zr hf nb ta and mineral composition mica and columbite consistently unveil a magmatic evolutionary trend from the hutoushan alkali feldspar granite through the hutoushan pegmatite shell to the mineralized dikes typical a type characteristics of the granite and ancient hf isotopic features ehf t ranging from 6 80 to 12 95 and crust model ages from 1 61 to 2 00 ga indicate that the parental magma was derived from the partial melting of palaeoproterozoic crust with insignificant mantle material involved considering the significantly higher bulk contents of nb ta and f in the pegmatite shell and the mineralized dikes than that in the alkali feldspar granite as well as the similar composition in the biotite from the pegmatite shell and the alkali feldspar granite we propose that a residual nb ta enriched brine melt phase segregated from the crystal mush at the late stage of crystallization the progressive concentration of f in the melt was conducive to the solubility of nb and ta in granitic melts and decreased the viscosity by depolymerizing the melt and thus contributed to the high magma differentiation and nb ta concentration the post magmatic fluid triggered the fluid rock interaction resulting in the extensive albitization m type tetrad effect extremely low nb ta ratio

phase relations of a f enriched peraluminous granite an experimental study of the kymi topaz granite stock southern finland phase relations of f rich kymi equigranular topaz granite have been investigated experimentally at 100 500 mpa as a function of water activity and f content fluorite and topaz can crystallize as liquidus phases in f rich peraluminous systems but the f content of the melt should exceed 2 5 3 0 wt for the crystallization of topaz in peraluminous f bearing melts containing more than 1 wt f topaz and muscovite are expected to be the first f bearing phases to crystallize at high pressure whereas fluorite and topaz should crystallize first at low pressure following reaction models the saturation of fluorite and topaz caal2si2o8 plagioclase 2 alf3 melt caf2 fluorite 2al2sio4f2 topaz the obtained partition coefficient for f between biotite and glass d f bt glass ranges from 1 89 to 0 80 average value 1 29 and can be used as an empirical fluormeter to determine the f content of coexisting melts combined petrological and experimental studies of the kymi equigranular topaz granite indicate that plagioclase was the liquidus phase at nearly water saturated fluid saturated conditions and that the f content of the melt was at least 2 wt the mean f content of natural biotite 3 92 wt suggests that the late stage crystallization of biotite occurred in melts containing about 3 wt f the early crystallization of biotite and the presence of muscovite in our experiments at 200 mpa contrasts with the late stage crystallization of biotite and the absence of muscovite in the natural assemblage indicating that crystallization pressure may have been lower than 200 mpa for the granite

shallow crustal structure of the continental margin off nova scotia the nature of the upper sediments of the shelf and slope on a passive margin was investigated by using high quality refraction profiles recorded by ocean bottom seismometers off nova scotia in agreement with previously published reflection profiles well data and lithospheric models for the evolution of passive margins we found little thickening of the post early cretaceous section implying an even sedimentation rate over the outer shelf for this time period the velocity model determined from slant stacks agreed reasonably well with well log data but had velocities slightly lower than those found from a nearby refraction line using first arrival travel time methods starting at the sea floor the compressional velocity depth model consists of a gradient of roughly 0 4 s 1 to a depth of about 1 25 km followed by another gradient of roughly 1 s 1 to a depth of about 3 5 km beneath this depth the velocity gradient approaches zero and can be modelled as a constant velocity layer stoneley waves were us