vertical ocean loading amplitudes from vlbi measurements vertical ocean loading amplitudes are determined by analysis of iris geodetic vlbi data the 4 nearly diurnal k1 p1 o1 q1 and 4 nearly semidiurnal k2 s2 m2 and n2 component amplitudes can be inferred from the data with accuracies of 1 2 mm uncertainties of total displacements can approach 1 cm empirically determined total displacements are considerably larger than the values calculated from two geophysical models the scherneck model is found to give a better representation of vlbi delay data than the model of pagiatakis by about 3 mm in residuals at 6 sites empirical estimation of the ocean loading amplitudes reduces 2 by 3067 for the 96 additional degrees of freedom in a fit to 273 000 iris vlbi observations and reduces the rms residuals by 3 mm relative to a fit using the fixed scherneck model vertical ocean loading amplitudes can thus be inferred from vlbi data at a level which improves the overall model but detailed assessment of individual tidal components is presently obscured by incomplete modeling at the tidal frequencies

a synthetic fluid inclusion study of the solubility of monazite la and xenotime y in h2o na k cl f co2 fluids at 800 c and 0 5 gpa abstract alkali rich f cl co2 bearing aqueous fluids are thought to be common ore forming fluids of carbonatite associated rare earth element ree deposits solubilities of synthetic monazite la and xenotime y end members in such fluids were determined at 800 c and 0 5 gpa in a series of piston cylinder experiments at run conditions solutions of nacl kcl 1 9 mol kg co2 5 mole nacl kcl 1 7 mol kg naf kf 0 2 mol kg were trapped as synthetic fluid inclusions in quartz and subsequently analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms the resultant concentrations in these fluids are extremely low ranging from 2 92 10 6 to 3 05 10 5 mol la kg h2o and 3 97 10 6 to 2 74 10 5 mol y kg h2o such low solubilities indicate that fluids expelled from carbonatite melts contain insufficient phosphate and ree simultaneously to form ree deposits mixing ree bearing fluids with phosphate bearing aqueous fluids or interacting with apatite in the wall rock may be a key control on the deposition of ree phosphate minerals in addition our results show that at nearly equal total ligand molality solubilities of la and y are both higher in f or co2 bearing solutions than in cl only solutions and the highest solubilities obtained overall were in nacl naf solutions which significantly increase by a factor of 9 4 for la and 6 1 for y relative to nacl only solutions moreover the solubility differences between xenotime and monazite in f co2 bearing solutions shown as y la molality ratio are higher in k bearing solutions than in na bearing solutions y la in the nacl f co2 solutions are close to 1 whereas in the kcl f co2 solutions y la increase to 2 9 and 2 0 respectively these results indicate that during the evolution of carbonatitic fluids enrichment of na and f can significantly increase solubilities of all ree whilst enrichment of k may promote the fractionation of hree from lree in the presence of f or co2

influence of oxygen fugacity on mineral compositions in peralkaline melts the katzenbuckel volcano southwest germany the igneous rocks of the katzenbuckel southwest germany represent a unique and unusual alkaline to peralkaline association within the european volcanic province the magmatic activity can be subdivided into two main phases phase i comprises the main rock bodies of phonolite and nepheline syenite which were later intruded by different peralkaline dyke rocks tinguaites and alkali feldspar syenite dykes of phase ii the dyke assemblage was accompanied by magnetite and apatite veins and was followed by a late stage pneumatolytic activity causing autometasomatic alterations as is typical for alkaline to peralkaline igneous rocks early mafic minerals of phase i rocks comprise olivine augite and fe ti oxides which are substituted in the course of fractionation by na amphibole and na pyroxene for the early magmatic stage calculated temperatures range between 880 and 780 8c with low silica activities 0 4 to 0 6 but high relative oxygen fugacities between 0 5 and 1 9 log units above the fmq buffer even higher oxygen fugacities above the hm buffer are indicated for the autometasomatic alteration which occurred at temperatures between 585 and 780 8c and resulted in the formation of pseudobrookite and hematite the unusually high oxygen fugacities even during the early magmatic stage are recorded by the major element compositions of the mafic minerals forsterite content in olivine between 68 and 78 mol up to 6 2 wt zro2 and 8 5 wt tio2 in clinopyroxene the unusual mineral assemblages pseudobrookite freudenbergite and by the enrichment of fe 3 in the felsic

rare earth element mobility in the roffna gneiss switzerland the roffna gneiss a deformed hercynian granite porphyry within the penninic nappes of eastern switzerland underwent extreme cataclasis with the progressive development of phengite towards the margins of the nappe under conditions of the glaucophane schist to greenschist facies this resulted in the selective mobilization of major and trace elements over distances of 10 s to 100 s of meters and the resetting of the rb sr whole rock isotopic systems some 100 my ago the component ratios and compositionvolume relationships of progressively deformed gneiss samples studied here suggest that this process was essentially isovolumetric the mineralogy of the deformation sequence appears to have been controlled by a reaction involving the breakdown of microcline albite and biotite and the formation of phengite and quartz the fluids introduced mg and h2o promoting the development of phengite and removed the na being released by the breakdown of albite the fluids were most probably derived from the surrounding triassic carbonates and quartzites these relatively high fo2 and carbonate rich fluids also introduced rare earth elements ree into the gneiss the gneiss was progressively enriched in eu up to 60 y up to 40 and yb up to 100 these enrichments are associated with the development of epitaxial xenotime around zircon in the most phengite rich sample while the ree were mobile uranium and thorium were essentially immobile the formation of xenotime was suggested to explain the observed heavy ree enrichment when large differences in the ree contents were found for replicate analyses using hf and then lithium metaborate for dissolution these differences arose because xenotime like monazite can be difficult if not impossible to dissolve in hydrofluoric acid due to the possibility of incomplete sample dissolution we now recommend fusion with lithium metaborate for all ree lu hf or sm nd studies

fluid rock interaction during progressive migration of carbonatitic fluids derived from small scale trace element and sr pb isotope distribution in hydrothermal fluorite associated with the cretaceous okorusu carbonatite complex namibia is a hydrothermal fluorite mineralization hosted in pan african country rock marbles which resulted from fluid rock reaction between the marbles and orthomagmatic carbonatitic fluids expelled from the carbonatite yellow fluorite i was deposited in veins up to 5 cm away from the wallrock contact followed by purple and colorless fluorite ii smoky quartz and barite a mn rich crust on early calcite and pure calcite this clear cut sequence of mineral growth allows an investigation into fluid rock interaction processes between the marble and the migrating carbonatitic fluid and element fractionation patterns between the fluid and subsequent hydrothermal precipitates fluorite i shows a progressive change in color from dark yellow to colorless with purple laminations over time of deposition subsequent fluorite i precipitates show an increase in ca and a continuous decrease in f sr ree y th u and pb contents the ratios eu eu cn th pb and u pb increase whereas y ho th u and la yb cn decrease the sr isotopic composition remains constant at 87sr 86sr 0 70456 0 70459 but with varying highly radiogenic pb 206pb 204pb 32 190 238u 204pb 7 63 fluorite ii has 87sr 86sr 0 70454 0 70459 206pb 204pb 18 349 and 207pb 204pb 15 600 and a chemical composition similar to youngest fluorite i the mn rich crust on early calcite accumulated ree ba pb zr cs th and u developing into pure calcite with a prominent negative ce anomaly and successively more radiogenic sr the calculated degrees of fluid rock interaction f weight fraction of fluid fluid marble decrease from fluorite i and most fluorite ii f 0 5 to calcite f 0 2 0 3 and hydrothermal quartz f 0 1 a crush leach experiment for fluid inclusions in the hydrothermal quartz yielded a rb sr isochron age of 103 12 ma crush leach analysis for the carbonatitic fluid trapped in the wallrock yielded a trend from the fluid leachate to the host quartz 206pb 204pb 18 224 and 18 602 207pb 204pb 15 616 and 15 636 respectively extending from carbonatite towards crustal rocks calculated trace element distribution coefficients fluorite fluid are below unity throughout and increase from la to yb elements largely excluded from fluorite ba pb lree relative to hree were incorporated later into the mn rich crust on calcite the trace element patterns of the hydrothermal minerals are related to changing aco2 and af in the fluid during continued fluid marble reaction a predominance of carbonate over fluoride complexing in the fluid as reactions proceeded controlled the y ho th u and ree patterns in the fluid and the crystallizing phases deviations from these trends indicate discontinuous processes of fluid rock reaction

the chemistry of fenitization examples from fen norway abstract at fen two main types of fenites occur predominantly potassic fenites associated with ijolite intrusions and predominantly sodic fenites associated with the intrusions of pyroxene sovites the fenitization is described quantitatively by mass transfer equations referring to the average wall rock composition awr a chemical index of fenitization f i is defined as the sum of mass gains during the process and is suggested as a complementary measure of fenitization f i shows close correlation with the grade of fenitization as is established by petrography preliminary computations of volatile phase compositions in equilibrium with possible sources further illustrate the process according to their setting the fenites are subdivided into contact fenites aureole fenites and vein fenites this classification which seems to be applicable on a general basis accounts for the occurrence of different types of fenites being produced by the same type of source rock

origin of the high temperature olserum djupedal ree phosphate mineralisation se sweden a unique contact metamorphic hydrothermal system abstract the swedish part of the fennoscandian shield hosts a variety of rare earth element ree deposits including magmatic to magmatic hydrothermal types this paper focuses on the origin of the olserum djupedal ree phosphate mineralisation located in the sparsely studied vastervik region se sweden here mineralisation occurs in three main areas olserum djupedal and bersummen primary hydrothermal ree mineralisation formed at high temperatures about 600 c leading to precipitation of monazite ce xenotime y fluorapatite and minor y ree u fe nb ta oxides in veins and vein zones dominated by biotite amphibole magnetite and quartz the veins are hosted primarily by metasedimentary rocks present close to or within the contact aureole of a local 1 8 ga ferroan alkali feldspar granite pluton but also occur within in the chemically most primitive granite in the outermost part of that pluton in the djupedal area ree mineralised metasedimentary bodies are extensively migmatised with migmatisation post dating the main stage of mineralisation in the olserum and bersummen areas the ree bearing veins are cross cut by abundant pegmatitic to granitic dykes the field relationships demonstrate a protracted magmatic evolution of the granitic pluton and a clear spatial and temporal relationship of the ree mineralisation to the granite the major and trace element chemistry of ore associated biotite and magnetite support genetic links between all mineralised areas biotite mineral chemistry data further demonstrate a distinct chemical trend from metasediment hosted ore associated biotite distal to the major contact of the granite to the biotite in the granite hosted veins this trend is characterised by a systematic decrease in mg and na and a coupled increase in fe and ti with proximity to the granite hosted veins the halogen compositions of ore associated biotite indicate elevated contents of hcl and hf in the primary ree mineralising fluid calculated log fhf fhcl values in the olserum area suggest a constant ratio of about 1 at temperatures of 650 550 c during the evolution of the primary hydrothermal system in the djupedal and bersummen areas the fluid locally equilibrated at lower log fhf fhcl values down to 2 high na contents in ore associated biotite and amphibole and the abundance of primary ore associated biotite indicate a k and na rich character of the primary ree mineralising fluid and suggest initial high temperature k na metasomatism with subsequent cooling of the system the fluid evolved locally to more ca rich compositions as indicated by the presence of the ca rich minerals allanite ce and uvitic tourmaline and by the significant calcic alteration of monazite ce the later ca rich stages were probably coeval with low to medium high temperature 200 500 c na ca metasomatism variably affecting the granite and the wall rocks producing distinct white quartz plagioclase rocks all observations and data lead us to discard the prevailing model that the ree mineralisation in the olserum djupedal district represents assimilated and remobilised former heavy mineral rich beds instead we propose that the primary ree mineralisation formed by granite derived fluids enriched in ree and p that were expelled early during the evolution of a local granitic pluton the ree mineralisation developed primarily in the contact aureole of this granite and represents the product of a high temperature contact metamorphic hydrothermal mineralising system the ree mineralisation probably formed synchronously with k na and subsequent na ca metasomatism affecting the granite and the wall rocks the later na ca metasomatic stage is probably related to a regional na ca metasomatic and associated u ree mineralising system operating concurrently with granitic magmatism at c 1 8 ga in the vastervik region this highlights the potential for discovering hitherto unknown ree deposits and for the reappraisal of already known deposits in this part of the fennoscandian shield

displacements of the earth s surface due to atmospheric loading effects on gravity and baseline measurements atmospheric mass loads and deforms the earth s crust by performing a convolution sum between daily global barometric pressure data and mass loading green s functions we estimate the time dependent effects of atmospheric loading including those associated with short term synoptic storms on surface point positioning measurements and surface gravity observations we calculate the response for both an oceanless earth and an earth with an inverted barometer ocean load responses for near coastal stations are significantly affected by the inclusion of an inverted barometer ocean peak to peak vertical displacements are frequently 15 20 mm with accompanying gravity perturbations of 3 6 gal baseline changes can be as large as 20 mm or more the perturbations are largest at higher latitudes and during winter months these amplitudes are consistent with the results of rabbel and zschau 1985 who modeled synoptic pressure disturbances as gaussian functions of radius around a central point deformation can be adequately computed using real pressure data from points within about 1000 km of the station knowledge of local pressure alone is not sufficient rabbel and zschau s hypothesized corrections for these displacements which use local pressure and the regionally averaged pressure prove accurate at points well inland but are in general inadequate within a few hundred kilometers of the coast

geodetic radio interferometric surveying applications and results very long baseline interferometry vlbi observations collected primarily under projects polaris polar motion analysis by radio interferometric surveying and iris international radio interferometric surveying since 1980 have been used to derive polar motion and ut1 time series the typical 24 hour observing sessions using the multistation north america europe network yield estimates of the x and y components of the pole with uncertainties of 1 2 milliseconds of arc mas and ut1 with uncertainties of 0 05 0 1 ms of time preliminary experimental results indicate that ut1 can be tracked by a single vlbi interferometer to the 0 1 ms level in observing periods of about 1 hour the same observations have been used to estimate the relative rates of motion of the north american and european tectonic plates and investigate possible regional deformations of the north american plate with uncertainties of a few millimeters per year check the accuracy of the adopted nutation series to the millisecond of arc level estimate earth tide love numbers for each observatory site with uncertainties of about 1 in h and 25 in l and determine the coordinates of 20 radio sources to a few milliseconds of arc temporal variations in the apparent positions of the radio sources caused by relativistic deflections of the radio signals in the solar gravitational field have been used to estimate the relativistic deflection parameter yielding a value of 1 000 0 003

crustal velocities from geodetic very long baseline interferometry we have used very long baseline interferometry observations from the international radio interferometric surveying and crustal dynamics project programs taken over a time span of 5 8 years through august 1990 to derive relative velocities of 16 sites on the north american eurasian pacific and african plates the data reduction scheme simultaneously estimates earth orientation parameters and nutation for each session local atmosphere and clock correction terms source positions and initial site positions as well as the site velocities no a priori geophysical crustal model whatsoever is imposed to obtain the velocities instead we introduce a minimal set of geometric constraints to obtain the solution two alternative constraint formulations are considered they are shown to be equivalent in that they yield equivalent velocity sets with allowance for translation and rotation these are 1 setting the secular motion of the pole and mean length of day to fixed values and 2 fixing the net rotation of the sites the resulting velocities have formal standard errors typically 0 2 cm yr and most velocities are significantly different from zero they agree closely to within 0 5 cm yr with velocities predicted by the minster jordan and nuvel 1 plate motion models after allowing for the arbitrary rotation and translation between the systems the velocity of kashima japan is much more consistent with the north american plate than the eurasian plate where current plate model boundaries place it we suggest another possibility kashima does lie on the eurasia plate but its motion is so modified by interaction with the nearby pacific plate as to result in the observed velocity sites near the active plate boundary in california also show motions intermediate between those of the adjoining plates

major and trace element compositional variation of phlogopite from kimberlites and carbonatites as a petrogenetic indicator abstract ferromagnesian trioctahedral micas are a common macrocryst phenocryst phase in kimberlites and carbonatites we explored the possibility of using the chemistry of ferromagnesian micas to discriminate between these rocks in order to assess their economic potential we determined the extent of major and trace element variations of micas from 14 selected kimberlite and carbonatite localities worldwide representing several different kimberlite fields and alkaline carbonatite provinces phlogopite macrocrysts from kimberlites follow two principal evolutionary trends primary macrocrystic involving an increase in ba al ti cr zr nb and sr contents at decreasing mg towards the rim and transitional macrocryst groundmass trend involving an increase in kinoshitalite component at decreasing fe ti and cr contents micas from dolomite calcite carbonatites cover a much greater compositional range than those from kimberlites defining evolutionary trends towards annite tetra ferriphlogopite and kinoshitalite our data confirm that macrocrystic micas from kimberlites cannot be reliably distinguished from carbonatitic phlogopite on the basis of their major element compositions exceptions are fe al rich fe fe mg 0 2 and na rich 0 3 wt na 2 o micas that seem to be virtually restricted to carbonatites the generally higher levels of na in carbonatitic micas relative to those from kimberlites can be explained by the lower na abundances in the latter relative to carbonatites our data indicate that the trace element composition of mica determined by la icp ms can be used as a reliable petrogenetic indicator kimberlitic phlogopite is characteristically enriched in cr up to 12030 ppm ni up to 1600 ppm and co 40 70 ppm and depleted in mn 280 ppm nb 28 ppm sr 55 ppm sc 8 ppm zr 12 ppm and to some extent cs 7 ppm and ta 3 ppm with respect to carbonatitic micas 315 ppm cr 470 ppm ni 34 ppm co up to 17200 ppm mn 1080 ppm nb 830 ppm sr 80 ppm sc 105 ppm zr 27 ppm cs and 19 ppm ta with the exception of zr the observed differences in trace element composition of mica probably reflect the contrasting trace element geochemistry of kimberlitic and carbonatitic magmas the depletion of kimberlitic phlogopite in zr and possibly nb ta can be explained by sequestration of these elements in the earlier crystallized ilmenite variations in ba rb and v contents are similar in mica from both rock types and cannot be used as a petrogenetic indicator

determination of relative site motions in the western united states using mark iii very long baseline interferometry four years of very long baseline interferometry vlbi measurements involving fixed and mobile stations in the western united states are analyzed using weighted least squares baseline solution time series are used to estimate rates of change of the vector baselines between pairs of vlbi stations horizontal vector motions are determined for 18 sites with respect to a site in the mojave desert six sites west of and two sites just to the east of the san andreas fault show northwestward motion closely parallel to the san andreas fault their motions range from 18 to 43 mm yr and are significant at confidence levels greater than 99 motions in california relative to interior north american plate sites are used to estimate an integrated contribution from basin and range spreading to the total relative pacific plate motion as 9 10 mm yr a maximum relative velocity of 50 51 mm yr is found between the interior north american sites and the western california sites in close agreement with the nuvel i plate motion model

geodesy by radio interferometry evidence for contemporary plate motion analysis of 211 very long baseline interferometry observing sessions carried out between november 1979 and august 1984 has yielded estimates of the distances between various radio telescopes located in north america and europe the average rate of change of the distances between four radio telescopes in north america haystack observatory massachusetts westford radio telescope massachusetts george r agassiz station texas and owens valley radio observatory california and one in europe onsala space observatory sweden obtained from the analysis of these data is 19 10 mm yr where the 68 confidence interval standard deviation is for the estimate of the rate of change of the haystack onsala baseline length the one determined most accurately from these data this estimate of the standard deviation is dominated by the effects of correlated systematic errors due mostly to errors in the model used for the atmospheric delay which we infer introduces errors in each baseline length estimate of 40 mm standard deviation and 60 days correlation time by contrast the statistical standard deviation is only 2 mm yr the estimated geologic rates of change of these baseline lengths averaged over 106 years are 15 to 17 3 mm yr for the various north american sites to onsala improvements in our model of the atmosphere and continued monitoring of the distances between north american and european telescopes will allow the uncertainty of the rate estimates to be reduced over the next few years to a value small compared to our estimated rate of change of these baseline lengths the use of multiple radio telescopes in europe will allow us also to separate possible local site motions from plate motions

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

alteration of plagioclase to nepheline in the khariar alkaline complex se india constraints on metasomatic replacement reaction mechanisms abstract at the khariar alkaline complex in southeastern india some tholeiitic amphibolites inter layered with syenite and nepheline syenite show microtextural evidence of fenitization typical metasomatic textures include the replacement of plagioclase by vein nepheline and albitic plagioclase or by symplectitic nepheline albite na al rich clinopyroxene whole rock mass balance calculations indicate that the fenitized variants gained alkalis na k some large ion lithophile elements sr rb and ba and high field strength elements like zr and hf during the metasomatic exchange the plagioclase replacement textures can be explained by a fluid mediated coupled dissolution reprecipitation process whereby the infiltration of alkali bearing fluid along grain boundaries and deformation induced intragranular fractures led to the dissolution of the host plagioclase along an inward moving reaction interface na ions were introduced and ca 2 ions removed by the fluid phase the al and si released from the breakdown of the anorthite component of the plagioclase combined with na from the fluid to precipitate nepheline albitic plagioclase or na al rich clinopyroxene reaction enhanced cracking during metasomatism due to local volume changes in the alteration zone produced a hierarchical system of fractures mass balance calculations using the volume proportion of phases in the plagioclase replacement zones show that sio 2 and al 2 o 3 were broadly conserved during the replacement there was significant loss of cao ca 73 and huge gains of na 2 o and k 2 o these results indicate that alkali and alkaline elements na k and ca were exchanged freely between the fluid phase and the reaction zone whereas si and al released during plagioclase dissolution were consumed in the replacement zone itself to form nepheline and albite rich plagioclase or na al rich clinopyroxene the trace element and sr nd isotope signature of the rocks indicate that the fenitizing fluids were derived from the nepheline syenites

volume characteristics and element transfer of fenite aureoles a case study from the iivaara alkaline complex finland abstract fenitization in granodioritic rocks has been investigated taking the iivaara alkaline complex finland as a case study five main fenitization reactions responsible for the transition from a granodioritic precursor mineral assemblage to a syenitic or even cancrinite syenitic mineral assemblage of the fenites are set up an assessment of element transfer and volume change associated with each of these reactions indicates a general volume loss of about 20 due to fenitization high activities of na ca mg and fe as well as a low h2o co2 ratio in the fenitizing fluid phase are indicated si which is the main component released from the precursor rock was redistributed within the aureole and formed pyroxene dominated mineral assemblages in a reaction with the fenitizing fluid these vein type pyroxenites can be found cross cutting all fenite types compositional data of aegirine augite in the fenites reveal disequilibria and feldspar compositions point to minimum temperatures for the production of fenites with syenitic compositions of 660 c and also indicate fast cooling a sr isotope characterization of the fenites allows assessment of minimum fluid rock weight ratios in the fenite aureole of 0 023 2 3 the element transfer scheme developed in this study is applicable to other localities since many aureoles formed in granitic to granodioritic host rocks have petrographic characteristics similar to the iivaara fenites

fenitization at the alno carbonatite complex sweden distribution mineralogy and genesis re mapping of the alno complex has radically reduced the area identified as fenite in comparison with the classic work of eckermann 1948 a marginal fenite zone generally 500 600 m wide is present around the complex and the petrography and mineralogy of six selected key areas have been investigated in detail fenitization of the country rock migmatitic gneiss led to replacement of quartz feldspars biotite and chlorite by alkali pyroxene and amphibole new generations of feldspars calcite titanite fluorite and apatite in some areas however a distinctive narrow band of fenitization referred to as contact fenite adjacent to large sovite dykes contains mineral assemblages that include phlogopite nepheline melanite and wollastonite amphiboles in the fenites are richterite katophorite arfvedsonite and eckermannite there is a very wide variation in the composition of pyroxenes which vary between diopside aergirine augite and aergirine although trends from aergirine to aegirine augite and aegirine augite to diopside have been defined which are similar to those of other fenite localities distinctive trends for the eastern part of the aureole have been identified that converge on aegirine and approximate trends in some series of alkaline igneous rocks analyses of mica garnet wollastonite and feldspar are also presented and discussed the mineralogical data are used to estimate the conditions of temperature oxidation state and activity of co2 h2o and silica pertaining during the fenitization process the fluids with which the fenites equilibrated were apparently different in composition in different parts of the aureole and varied with time implying more than one magmatic source the various evolutionary trends identified in the pyroxenes and amphiboles in particular are explained in terms of two main fluid types which emanated from ijolitic and carbonatitic magma sources

magmatic fluids in the fen carbonatite complex s e norway three different types of carbonatite magma may be recognized in the cambrian fen complex s e norway 1 peralkaline calcite carbonatite magma derived from ijolitic magma 2 alkaline magnesian calcite carbonatite magma which yielded biotite amphibole sovite and dolomite carbonatite and 3 ferrocarbonatite liquids related to 2 and or to alkaline lamprophyre magma damjernite apatite formed during the pre emplacement evolution of 2 contains inclusions of calcite and dolomite devitrified mafic silicate glass and aqueous fluid all of these inclusions have a magmatic origin and were trapped during a mid crustal fractionation event p 4 kbars t 625 c where apatite and carbonates precipitated from a carbonatite magma which coexisted with a mafic silicate melt the fluid inclusions contain water dissolved ionic species mainly nacl with minor polyvalent metal salts and in some cases co2 two main groups of fluid inclusions are recognized type a co2 bearing inclusions of approximate molar composition h2o 88 90 co 27 5 nacl 5 d 0 85 0 87 g cm3 type b co2 free aqueous inclusions with salinities from 1 to 24 wt nacleq and densities betwen 0 7 and 1 0 g cm3 more strongly saline type b inclusions salinity ca 35wt d 1 0 to 1 1 g cm3 contain solid halite at room temperature and occur in overgrowths on apatite type a inclusions probably contain the most primitive fluid from which type b fluids have evolved during fractionation of the magmatic system type b inclusions define a continuous trend from low towards higher salinities and densities and formed as a result of cooling and partitioning of alkali chloride components in the carbonatite system into the fluid phase available petrological data on the carbonatites show that the fluid evolution in the fen complex leads from a regime dominated by juvenile co2 h2o fluids during the magmatic stage to groundwater derived aqueous fluids during post magmatic reequilibration

mass transfer and ree mobility during fenitization at alno sweden the precambrian migmatitic gneisses at alno have been altered to fenite by fluids emanating from alkaline and carbonatitic magmas intruded during early to middle cambrian times fenitization related to carbonatitic sources was promoted by peralkaline carbonate rich fluids in which the main chemical components and ree were mobile composition volume relationships of progressively fenitized protolith suggest mainly isovolumetric equilibration but a modest decrease of volume 6 did occur in the highest grade of the process the fenitizing fluids introduced essentially cao co2 na2o and k2o while removing sio2 and al2o3 different trends of fenitization defined as sodic potassic and intermediate show differing ree distribution and abundance patterns the sodic carbonate rich fluid introduced all the ree but the la lu ratio was high the extreme ree enrichments of high grade fenites are associated with the widespread formation of calcite apatite and possibly titanite the potassic carbonaterich fluid introduced essentially light ree but produced also the redistribution of heavy ree in the high grade fenites ree distribution patterns of intermediate fenites suggest the re equilibration of fenite with a highly oxidizing alkaline fluorine rich fluid possibly in a later post magmatic episode

compositional variations major and trace elements of clinopyroxene and ti andradite from pyroxenite ijolite and nepheline syenite alno island sweden compositional variations major and trace elements of clinopyroxene and ti andradite from pyroxenite ijolite and nepheline syenite alno island sweden

ijolite versus carbonatite as sources of fenitization ijolite carbonatite complexes are ubiquitously surrounded of an aureole of metasomatically altered rocks the process of alteration is termed fenitization and is generally caused by peralkaline fluids emanating from cooling alkaline i e ijolite and carbonatite magmas ijolites and carbonatites normally occur together and attempts to determine the source of the fenitizing fluids may therefore lead to controversial if not erroneous conclusions mineralogical and chemical data of fenites from oldoinyo lengai tanzania fen norway and alno sweden are reviewed in the present paper in order to reveal the main factors controlling the fenitization around ijolite and carbonatite despite the overall alkaline nature of the process variables such as xco2 of the fluid activity gradients of sio2 al2o3 and cao feo mgo ratio fo2 and temperature gradients may differ producing distinctive patterns of fenitization around the two magmatic sources the ijolitic type fluid has low xco2 high activities of alkalies sio2 and al2o3 and low activity of cao the fo2 evolves along the hm mt buffer conditions and the temperature falls gradually with distance from the magmatic source the carbonatitic type fluid has high xco2 high activities of alkalies and cao and low activities of sio2 and al2o3 temperatures and fo2 are initially high but decrease sharply with distance from the source moreover the co2 rich fluid may complex and transport the ree

petrography and petrogenesis of nephelinized metagabbros from finnmark northern norway plagioclase in olivine metagabbros metasomatized by nepheline syenite magmas was replaced by intergrowths of nepheline and vesuvianite or salite together with smaller amounts of calcic amphibole olivine was simultaneously replaced by diopside the survival of the gross features of protolith textures and clustering of line intersections in composition volume diagrams suggest that nephelinization took place at approximately constant volume and oxygen content nephelinization involved the introduction of na k and fe3 in an infiltrating peralkaline fluid and depletion of fe2 and fetot and was promoted by the primary mineral parageneses of the protoliths concurrent fenitization of quartzo feldspathic gneiss without the generation of feld spathoids shows that the processes of nephelinization and fenitization may result from the same fluid

measurement of thermal conductivity of omphacite jadeite and diopside up to 14 gpa and 1000 k implication for the role of eclogite in subduction slab thermal conductivity and diffusivity for three pyroxenes omphacite jadeite and diopside were determined up to 14 gpa and 1000 k in the kawai type multianvil apparatus via the pulse heating method measurements for omphacite are characterized by much lower thermal conductivity and thermal diffusivity than those of its two end members of jadeite and diopside presumably because of the complex substitution of four cations na 1 ca 2 al 3 and mg 2 in omphacite therefore simple arithmetic averaging is unsuitable for estimating thermal conductivity and diffusivity of the jadeite diopside solid solution system the thermal property of eclogite was estimated from those of garnet and omphacite the thermal conductivity of eclogite is much smaller than that of harzburgite which is assumed to compose of 80 olivine and 20 enstatite implying that subducted oceanic crust impedes thermal conduction from the hotter wedge mantle to the subducting slab thermal structure simulation results show that temperature of the subduction zone is about 50 c decreased when the effect of oceanic crust is included

fluid rock interaction in autoliths of agpaitic nepheline syenites in the ilimaussaq intrusion south greenland abstract within the 1 16 ga old ilimaussaq intrusion up to 700 m large autoliths occur in one stratigraphic unit of the layered floor series of agpaitic nepheline syenites kakortokites these autoliths consist of two different rock types augite syenite and naujaite agpaitic nepheline syenite all three rock types show a number of alteration features related to the entrapment of the autoliths in the kakortokite magma caused by the interaction with a fluid phase in the kakortokites the oxidation of primary arfvedsonite to aegirine and fluorite is restricted to the close proximity to the autoliths close to the surrounding kakortokite the primary mafic phases of the augite syenites augite fayalite fe ti oxides are completely replaced by arfvedsonite aenigmatite biotite aegirine and fluorite the decomposition of primary hastingsite to spectacular aegirine augite nepheline aenigmatite symplectites can be observed up to several meters inside the autoliths additionally fluorite formed at grain boundaries of primary nepheline in the naujaite autoliths primary arfvedsonite is replaced by aegirine biotite intergrowths and abundant aenigmatite is occasionally replaced by ti rich aegirine and fe ti oxides the mineral reactions in the autoliths are used to decipher details of the late to post magmatic processes in a peralkaline syenitic intrusion mineral equilibria record an evolution governed by falling temperature 620 to ca 500 c and increasing relative oxygen fugacity from fmq 1 to above fmq 4 quantification of the observed mineral reactions reveals the infiltration of the autoliths with an oxidizing fluid phase rich in na and f and minor addition of k volatiles h and f and in some cases also fe ti and ca mg released from primary autolith phases were mainly just relocated within the autoliths

na and k distribution in agpaitic pegmatites abstract composition and zoning of amphibole in agpaitic pegmatites of the 1 16 ga ilimaussaq complex south greenland record the chemical evolution of the final stages of an already extremely fractionated melt our results show that the general differentiation trends found in the earlier rocks of the complex are continued in the pegmatites albeit with some significant modifications the dominating exchange mechanism of na si ca al in the amphiboles of the magmatic stage changes to k si ca al and k na in some pegmatitic samples na k ratios in amphiboles which generally increase in the course of the ilimaussaq fractionation partly display a reversal during the crystallization of the most differentiated amphiboles the alkali trends are probably related to the buffering of na and k activity by the co crystallization of albite and microcline this buffering favors na in cooling fluids this mechanism is lost when analcime replaces feldspar as a stable phase in the late stages of crystallization e g due to locally elevated h2o activity analcime does not incorporate significant amounts of k and accordingly amphibole incorporates more k in analcime bearing assemblages the na k variation in amphiboles in the ilimaussaq pegmatites allow a detailed view into the late stage evolutionary trends of a textbook agpaitic complex the transition from silicate melt to aqueous fluid is recorded by the change of the dominant alkali ion in the pegmatitic amphiboles from na to k only in the very latest stage virtually k free mineral assemblages in analcime aegirine veins support the existence of a na dominated aqueous fluid

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism