oxygen diffusion in amphiboles the kinetics of oxygen isotope self diffusion in natural samples of hornblende tremolite and richterite have been measured samples were run under hydrothermal conditions using 18o enriched water profiles of 18o 16o 18o vs depth into the crystal were obtained using an ion microprobe the depths of sputtered holes were measured using an optical interferometer at 1000 bars 100 mpa water pressure the activation energies q and pre exponential factors d0 for diffusion parallel to c are d0 cm2 sec q kcal gm atom t c hornblende 1 20 1 10 741 6 650 800 tremolite 2 30 2 10 8 39 5 650 800 richterite 3 5 2 10 4 57 2 650 800 the diffusion coefficient d for hornblende at 800 c and 1000 bars water pressure measured parallel to the c crystallographic direction is at least ten times greater than that parallel to the a or b directions an increase in water pressure from 200 to 2000 bars increases d by a factor of 2 7 for diffusion parallel to c at 800 c the d value for hornblende at 800 c is about 0 01 that for quartz and 0 001 that for anorthite as a result closure temperatures for oxygen exchange in natural primary amphiboles are significantly higher than for quartz or feldspars it is unlikely that amphiboles will exchange oxygen isotopes by diffusion under most crustal conditions

occurrence of old groundwater in a volcanic island on a continental shelf an example from nakano shima island oki dozen japan summary groundwater residence times in nakano shima island oki dozen japan which is situated on the continental shelf are discussed based on groundwater age indices cfcs 3 h and 14 c stable isotopic ratios of hydrogen d oxygen 18 o carbon 13 c and noble gases 3 he 4 he and 4 he 20 ne samples were taken from springs shallow wells up to 5 m deep water supply wells about 10 100 m deep and the hot spring well 866 m deep d and 18 o of all the samples plot along meteoric water lines indicating a meteoric water origin isotope values of the hot spring water were slightly lower than other samples most samples from springs shallow wells and the water supply wells contained higher cfcs and 3 h while samples from two water supply wells w4 and w7 and the hot spring well showed much lower cfcs concentrations this result indicates that mixing ratios of old groundwater that is free of cfcs and 3 h were higher for these samples 14 c concentrations of samples with lower cfcs were measured and corrected for addition of 14 c free dissolved inorganic carbon the corrected 14 c concentration of the hot spring water was lower than that of the water supply well indicating mixing of much older groundwater in the hot spring water because of lower corrected 14 c concentration and lower d and 18 o values groundwater from the hot spring well is considered to be recharged in a colder climate than present day because the island is situated on the continental shelf the seafloor around the island was most likely widely exposed during the last glacial period one possible explanation for the existence of groundwater showing lower d 18 o and 14 c concentrations such as the hot spring water is that fresh groundwater recharged when sea level was lower still remains after transgression without being replaced by salt water

isotopic and geochemical evidence for magma mixing in the petrogenesis of the coire uaigneich granophyre isle of skye n w scotland field relations petrographic features major and selected trace element compositions and sr and pb isotope characteristics indicate that the coire uaigneich granophyre cug was formed by the mixing of two magmas one of these a liquid of high 87sr 86sr ratio ca 0 731 formed by the anatexis of late precambrian torridonian sediments contained relict quartz and zircon the other liquid was an acid differentiate of basaltic magma and was enriched in incompatible elements such as zr and y the two magmas mixed in the proportions of approximately two parts anatectic melt to one part acid differentiate hydrothermal metamorphism had no significant effect on the bulk chemistry of the cug

isotopic evidence for the age and origin of pitchstones and felsites isle of eigg nw scotland an 8 point whole rock and mineral rb sr isochron for the sgurr of eigg yields an age of 52 1 1 0 ma 2 this is the youngest accurate date yet reported for igneous activity in the british tertiary province and indicates that sub acid rocks of the small isles represent one of the latest episodes of hebridean magmatism pb isotope compositions of these rocks yield an apparent age of 2660 75 ma 2 interpreted as a mixing line between lewisian torridonian and mantle derived pb and indicating the presence of lewisian basement under eigg pb sr and nd isotopic evidence points to contamination of basaltic differentiates and granulite facies lewisian melts by torridonian sandstone but precludes significant involvement of amphibolite facies lewisian which may have been largely removed by erosion before deposition of the torridonian sediments in the small isles

dissolution kinetics of plagioclase in the melt of the system diopside albite anorthite and origin of dusty plagioclase in andesites the textures and kinetics of reaction between plagioclase and melts have been investigated experimentally and origin of dusty plagioclase in andesites has been discussed in the experiments plagioclase of different compositions an96 an61 an54 an23 and an22 surrounded by glasses of six different compositions in the system diopside albite anorthite was heated at temperatures ranging from 1 200 to 1 410 c for 30 min to 88 h textures were closely related to temperature and chemical compositions a crystal became smaller and rounded above the plagioclase liquidus temperature of the starting melt glass and remained its original euhedral shape below the liquidus whatever the temperature the crystal melt interface became rough and often more complicated sieve like texture composed of plagioclase melt mixture in the scale of a few m was developed from the surface of the crystal inward formation of mantled plagioclase if the crystal is less calcic than the plagioclase in equilibrium with the surrounding melt and the interface remained smooth if the crystal is more calcic than the equilibrium plagioclase from these results the following two types of dissolution have been recognized 1 a crystal simply dissolves in the melt which is undersaturated with respect to the phase simple dissolution and a crystal is partially dissolved to form mantled plagioclase by reaction between sodic plagioclase and calcic melt partial dissolution the amount of a crystal dissolved and reacted increased proportional to the square root of time this suggests that these processes are controlled by diffusion probably in the crystal mantled plagioclase produced in the experiments were very similar both texturally and chemically to some of the so called resorbed plagioclase in igneous rocks chemical compositions and textures of plagioclase phenocrysts in island arc andesites of magma mixing origin have been examined cores of clear and dusty plagioclase were clacic about an90 and sodic about an50 respectively this result indicates that dusty plagioclases were formed by the partial melting due to reaction between sodic plagioclase already precipitated in a dacitic magma and a melt of intermediate composition in a mixed magma during the magma mixing

salinization processes in paleowaters in coastal sediments of suriname evidence from δ37cl analysis and diffusion modelling in the coastal plain of suriname a stagnant body of fresh 250 mg l cl and moderately brackish 250 1000 mg l cl groundwater of meteoric origin is found in permeable tertiary formations this groundwater body formed during the last wisconsin regression extends offshore into deposits on the continental shelf the authors found that this paleowater is slowly being salinized by downward solute transport from overlying holocene marine clays and upward transport from saline cretaceous sediments the downward transport has been studied at two sites by relating analyses of chloride contents and 37cl 35cl isotope ratios in pore water with computer simulations of diffusive transport optimization of process parameters yielded an effective diffusion coefficient of and a fractionation factor of 1 0027 which agrees well with earlier studies with the computer model the following periods of marine influence were found 6000 4 100 yr bp and 10 000 500 yr bp at the sites located 20 and 3 km from the coastline respectively according to the diffusion model the downward flux of salts has not penetrated deeper than 100 m salts below this depth are thought to originate from the cretaceous sediments however groundwater chloride concentration and chlorine isotope data are scarce below this depth while uncertainty regarding the various regressions and transgressions precludes solute transport modelling clay layers at the base of the tertiary appear to inhibit the upward transport by lateral dispersive mixing at the tertiary cretaceous boundary oil reservoirs are also related to these clay seals the presence of the seal and perhaps the oil below can therefore be predicted by the chloride profile in the upper 250 m

long wavelength s wave velocity structure throughout the mantle summary long wavelength s wave velocity anomalies are obtained for the entire mantle by inverting 6ooo long period 40 100s sh body waves and lo00 long period 100 500 s love waves in the shallow mantle the patterns of fast and slow velocity anomalies correlate well with age and tectonics in the depth range of 400 1000 km we find two antipodal fast velocity anomalies one in the western pacific and the other in south america they form a fairly strong i 2 anomaly moreover the 1 2 anomaly is the largest spherical harmonic component throughout the entire mantle except for in the layer of 1000 1300 km depth a fast velocity anomaly near the caribbean previously reported by several other investigators is found between the depths of 1000 and 1300km with diminishing amplitudes it can be traced to canada and the aleutians and may be related to old subducted slabs in the same depth interval similar size anomalies can be found in the middle of the pacific and in the indian ocean these could be checked by more detailed studies to judge the reliability of this study heterogeneity power has a peak at the surface and a secondary peak at the bottom of the mantle d consistent with the existence of chemical and or thermal boundary layers at the base of the mantle we also find a fast velocity anomaly which surrounds the pacific ocean this feature has been found by other researchers previously but its interpretation is difficult due to the trade off between velocity anomaly and core mantle boundary deformation

isotopic and geochemical investigation of unit 10 from the eastern layered series of the rhum intrusion northwest scotland sr and nd isotopic compositions together with whole rock sr and nd abundances and olivine compositions are presented for cumulates from unit 10 of the eastern layered series of the rhum intrusion northwest scotland the results show an nd sr isotopic correlation consistent with contamination by high 87 sr 86 sr low 143 nd 144 nd crust there is a strong correlation between the degree of contamination sr and nd whole rock abundance and fe enrichment in cumulus olivine the allivalites are the most contaminated while the basal peridotites are uncontaminated this suggests that the cumulates crystallized from a primitive uncontaminated magma and the allivalites from an evolved contaminated magma subsequently movement of contaminated feldspathic intercumulus liquid has perturbed the isotopic trace element and olivine composition of the upper peridotites

isotope domain mapping of 87sr 86sr biosphere variation on the isle of skye scotland abstract the potential of 87 sr 86 sr isotope composition for tracking and determining the origin of material whether it is humans animals water or wine can be fully realized only if high quality reference datasets are available against which to compare the unknowns this is currently not the case despite the rapid increase in 87 sr 86 sr based provenance studies of biosphere materials there are no well documented maps available most researchers resort to generating reference maps from a variety of geological datasets plus the analysis of sparse environmental9 samples a major reason for this lack of reference material is the investment needed to undertake systematic sampling and analysis over large areas a further problem is associated with the choice of proxy material as organisms differ in their habitat and exploitation of resources in this paper various approaches to isotope biosphere sampling are considered some of the problems are assessed the precision required for the study of human populations is discussed and a first attempt is made to condense all of the available information into an isotope package9 map the work is based on a study undertaken on the isle of skye in the inner hebrides and reduces the complexity of geological and isotope data into five main 87 sr 86 sr packages package 1 northern area 0 705 0 7092 package 2 ne coast 0 7082 0 7102 package 3 granitic rocks 0 716 0 720 package 4 metamorphic rocks 0 7092 0 7188 package 5 seawater 0 7092 0 005 2 the approach of trying to constrain the isotope composition of certain areas and or lithologies offers the possibility of extrapolating to other similar areas without having to sample at the original density

origin of differentiated volcanic and plutonic rocks from ascension island south atlantic ocean altered pre existing volcanic basement may have been melted or the first phase of felsic magmatism on ascension island in the assimilated during differentiation of some of the felsic magmas form of trachyte and rhyolite domes coulees lava flows and pyroclastic deposits created the central and eastern parts of the island between about 1 0 and 0 56 my ago the geochemical characteristics of the felsic rocks are largely consistent with an origin by fractional crystallization of high zr nb mafic magmas as

pyrometamorphism and the contamination of basaltic magma at tieveragh co antrim a tertiary dolerite plug at tieveragh co antrim cuts old red sandstone tuffaceous sedimentary rocks glassy buchites have formed by disequilibrium partial melting induced by convective heat transfer from the basaltic magma variation in bulk rock chemistry has produced glasses coexisting with variable proportions of pyroxene cordierite ilmenite hematite magnetite mullite plagioclase and alkali feldspar mixing of the basaltic magma with acid melt illustrates how up to 10 contamination may occur without radically altering the course of crystallization mineral geothermometers indicate maximum temperatures at the contact around 1100 c falling to only 940 at 10 m

degree one components of the earth s interior abstract the earth s geoid is a constraint for models of the composition of the earth s interior the long wavelength non hydrostatic portion of the geoid is assumed to be due to density contrasts associated with the convective forces which drive plate tectonics the longest wavelength component degree one can be set to an arbitrary value by appropriate choice of coordinate systems with negligible effect on other components the degree one component is usually set to zero internal models are unconstrained at degree one and results at degree one are not often analyzed theoretical considerations predict an internal degree one component with an effect at the surface even greater than those of the other nonhydrostatic components of the earth s geoid mantle convection theories relative sea level curves mantle viscosity measurements and geodynamo models may be affected

geographical distribution of 3he 4he ratios in japan implications for arc tectonics and incipient magmatism the 3he 4he and 4he 20ne ratios of 115 natural gas samples including various types of gases from volcanoes hot springs mineral springs water wells petroleum fields and natural gas fields were measured using a mass spectrometer the observed 3he 4he and 4he 20ne ratios range from 7 47 10 8 to 9 65 10 6 and from 0 26 to 1100 respectively the 3he 4he ratios reflect well the geotectonic structure of the japanese islands in northeastern ne japan there is a clear geographical difference in the 3he 4he ratios between the frontal arc forearc and volcanic arc back arc regions lower ratios were found in the trench side region and higher ratios in the back arc side this result suggests that the mantle derived helium in the volcanic arc region is associated with the diapiric uprise of a magma lower 3he 4he ratios in the frontal arc region may be due to radiogenic he produced by radioactive decay of u and th in the crustal and sedimentary rocks in southwestern sw japan there is no clear geographical contrast in the 3he 4he ratios some samples in the frontal arc region show quite high 3he 4he ratios the tendency of the 3he 4he ratios agrees with the distribution of terrestrial heat flow data and reflects geotectonic structures different from ne japan the high 3he 4he ratios observed in the frontal arc region in sw japan may be indicative of renewed or incipient magmatism due to a descending young and warm slab

isotopic composition of lead and strontium in lavas and coarse grained blocks from ascension island south atlantic an addendum abstract new sr and pb isotope data are presented for a selection of lavas and associated coarse grained blocks from ascension island k ar dates for the lavas range up to1 5 0 2ma initial87sr 86sr ratios are consistent with earlier measurements and for most rocks are ca 0 7029 but range up to 0 7135 in the case of the most evolved lavas and blocks pb isotope data are also consistent with earlier measurements but the pb in two gabbroic blocks is less radiogenic than pb in the other rocks it is suggested that these gabbroic blocks crystallized from a magma of tholeiitic composition whose source was similar to that of mid oceanic ridge basalt whereas the lavas and other blocks crystallized from mildly alkaline magmas derived from a source further from the crest of the mid atlantic ridge the high87sr 86sr ratios result from contamination of the most silicic magma by radiogenic sr from pelagic sediments these data and their interpretation are consistent with the petrological and geochemical observations that the granite blocks are the coarse grained equivalents of the volcanic suite 11 and not fragments of relict continental material 2 3

magmatic evolution of the skye igneous centre western scotland modelling of assimilation recharge and fractional crystallization the skye igneous centre forming part of the british tertiary magmatic province developed over a 7 myr period 61 54 ma and is characterized by a complex suite of lavas hypabyssal and intrusive rocks of picritic to granitic composition the intrusion of magma from mantle to crust at 2 10 3 km 3 yr 6 mt yr advected magmatic heat of roughly 0 2 gw averaged over the period of magmatism supporting an excess heat flux of about 130 mw m 2 or about twice the present day average continental heat flow the volume of new crust generated at skye 15 000 km 3 spread over the present day area of skye corresponds to 9 km of new crust the geochemical evolution of the skye magmatic system is constrained using the energy constrained recharge assimilation and fractional crystallization ecrafc model to understand variations in the sr and pb isotopic and sr trace element composition of the exposed magmatic rocks with time the character composition and specific enthalpy of both assimilant and recharge magma appears to change systematically up section suggesting that the magma reservoirs migrated to progressively shallower levels as the system matured the model of the magma transport system that emerges is one in which magma batches are stored initially at lower crustal levels where they undergo rafc evolution residual magma from this stage then migrates to shallower levels where mid crustal wall rock is assimilated the recharge magma at this level is characterized by an increasingly crustal signature for some of the stratigraphically youngest rocks the data suggest that the magma reservoirs ascended into and interacted with upper crustal torridonian metasediments

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

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

mantle dynamics in mars and venus influence of an immobile lithosphere on three dimensional mantle convection numerical calculations of fully three dimensional convection in constant viscosity compressible spherical shells are interpreted in terms of possible convective motions in the mantles of venus and mars the shells are heated both internally and from below to account for radiogenic heating secular cooling and heat flow from the core the lower boundary of each of the shells is isothermal and shear stress free as appropriate to the interface between a mantle and a liquid outer core the upper boundary of each of the shells is rigid and isothermal as appropriate to the base of a thick immobile lithosphere calculations with shear stress free upper boundaries are also carried out to assess the role of the rigid surface condition the ratio of the inner radius of each shell to its outer radius is in accordance with possible core sizes in both venus and mars a calculation is also carried out for a mars model with a small core to simulate mantle convection during early core formation different relative proportions of internal and bottom heating are investigated ranging from nearly complete heating from within to almost all heating from below the rayleigh numbers of all the cases are approximately 100 times the critical rayleigh numbers for the onset of convection cylindrical plumes are the prominent form of upwelling in the models independent of the surface boundary condition so long as sufficient heat derives from the core thus major volcanic centers on mars such as tharsis and elysium and the coronae and some equatorial highlands on venus may be the surface expressions of cylindrical mantle plumes the form of the downwelling sheets is significantly affected by the rigid boundary in that the sheets are more irregular in their horizontal structure than when the top boundary is shear stress free in the mainly heated from within models the downwelling sheets are also shorter and less temporally durable when the top boundary is rigid than when it is stress free thus the free motion of plates on the earth facilitates extensive durable convective currents that drive the plates while the stiffening of the lithospheres on mars and venus promotes a style of convection that is not particularly effective in breaking the lithosphere into plates in the rigid top cases the upper boundary layer surrounding the plumes appears to be interspersed with downwelling currents emanating radially from the plumes axes these currents may establish a stress field at the base of hotspot swells that could lead to radial fractures such as those on tharsis models with rigid upper boundaries have higher interior temperatures than do similar models with shear stress free upper boundaries on this basis venus not only has a higher surface temperature than earth but it would have a hotter mantle as well upwelling plumes are more numerous when the outer boundary is rigid as compared with shear stress free flows dominated by a few stong plumes occur when the proportion of basal heating is large thus if the martian crustal dichotomy were caused by a convective system dominated by spherical harmonic degree l 1 then the convection may have been driven strongly from below by a heating pulse accompanying core formation or from the flow of heat from an early hot core if a convective mechanism is responsible for the crustal dichotomy then the dichotomy is likely a very ancient feature however the small core models we consider consistently produce a convective pattern with a dominant l 2 signature which does not correlate with the martian crustal dichotomy a yet smaller core may be necessary to yield the l 1 pattern the small core convective pattern does correlate with the geoid and topography signatures of tharsis which have strong l 2 components and the model produces dynamic uplift comparable to the total topography of the tharsis rise models with larger cores i e with the probable inner to outer radius ratio of mars present mantle generate 4 km of uncompensated topography similar to estimates of the uncompensated tharsis topography thus the tharsis rise could have achieved its full height early in the evolution of mars by mantle plume dynamic uplift at present the uncompensated portion of the tharsis rise topography can be accounted for by dynamic uplift obviating the need for elastic support the present compensated portion of the tharsis topography could be attributed to volcanic or magmatic crustal thickening or depletion of the underlying mantle large core models appropriate to the present mars produce too many plumes to account for just two major volcanic centers i e tharsis and elysium mantle plume activity could be focussed beneath regions like tharsis if fracturing or thinning of the lithosphere in these regions has facilitated magma and heat transport across the lithosphere a similar mechanism could be responsible for clustering of coronae on venus there are no deep seated active linear upwellings in the venus models that could be associated with linear spreading centers in aphrodite if linear spreading is actually occurring in aphrodite the phenomenon is probably a shallow passive one similar to mid ocean ridges on earth

the 3 d shear wave structure in the mantle by overtone waveform inversion ii inversion of x waves r waves and g waves summary the 3 d upper mantle structure from the surface of the earth to a depth of about 1000 km is obtained by inverting waveforms of fundamental and higher mode surface waves minor and major arc waves of r waves g waves and x waves higher mode wave packets are used as basic data two features of the solution seem fairly robust one is the shallow structure in the upper few hundred kilometres which is strongly correlated with the age of the crust the second feature is the deep fast velocity anomaly near the western pacific indonesia philippines and mariana region and its antipodal region of south america both of which are subduction zones which forms a strong l 2 pattern simple slab models with 100 km thicknesses of 10 per cent faster velocity material do not explain such large scale fast velocity anomalies this may indicate large scale deformation of the 670 km discontinuity piling up of slabs in the upper mantle or thickening lithosphere in the lower mantle or large horizontal motions of subducted material these results are stable whether an earth model 1066a or prem is used as a starting model

pb isotope geochemistry of a massif type anorthositic charnockitic body the hidra massif rogaland s w norway abstract the hidra massif rogaland complex s w norway is a massif type anorthositic charnockitic body it consists of undeformed anorthosites and leuconorites grading into fine grained jotunites at the contact with the granulite facies gneisses of the metamorphic envelope a stockwork of charnockitic dykes cross cuts the massif the pb isotopic compositions of the anorthosites and leuconorites are comparable or slightly less radiogenic than those of the jotunites 206 pb 204 pb from 18 079 to 19 307 207 pb 204 pb from 15 568 to 15 657 and 208 pb 204 pb from 37 617 to 38 493 these values are compatible with an upper mantle origin for the parental magma of jotunitic composition and for the plagioclasic cumulates but show the incorporation of lower crustal material u depleted and thus less radiogenic the charnockitic dykes have significantly less radiogenic pb isotopic compositions 206 pb 204 pb from 17 472 to 19 171 207 pb 204 pb from 15 489 to 15 620and 208 pb 204 pb from 36 991 to 40 922 which can be explained by a larger proportion of lower crustal contamination material the contaminant could be the granulite facies gneisses of the metamorphic envelope this interpretation is compatible with the k rb relationships of these rocks and with the o and sr isotopic geochemistry the proportion of contaminating lead in the charnockitic dykes can be estimated at 55 15 considering the border facies jotunite as the uncontaminated parental magma and the least radiogenic gneiss of the metamorphic envelope as the contaminant

natural partial melting of syenite blocks from ascension island blocks of coarse grained syenite included in a trachyandesite lava flow on ascension island exhibit features attributable to partial melting the liquid so formed has been quenched to a glass and the chemical variation of the glass is considered to depend on the amount of melting the mineralogy and modal proportions of each block especially the presence or absence of quartz and the chemical composition of the minerals subjected to melting partial melting of quartz syenites such as these could have produced magmas of composition similar to that of the comendites and granites found on ascension but differences in major element and minor element chemistry between the glass and the comendites and granites suggest otherwise

flow paths and mixing properties of groundwater using hydrogeochemistry and environmental tracers in the southwestern area of jeju volcanic island summary groundwater from springs test boreholes and domestic wells was investigated to assess the flow system of basaltic aquifers at base flow conditions in the southwestern part of jeju island south korea this study utilized hydrogeochemical parameters and environmental tracers of 18 o 2 h 3 h and chlorofluorocarbons cfcs which showed that well connected flow paths exist between coastal springs regardless of flow rates in contrast test boreholes near the coastal springs exhibited various flow paths nitrate concentrations were much higher than baseline values in mountainous groundwater while those decreased in coastal areas was seemingly contributed from nitrate contamination sources and seawater sources were minimal due to low permeability layers near sea level the water stable isotopes indicated little evaporation and were comparable to the local meteoric water line during the rainy season which was confirmed by deuterium excess values demonstrating that effective infiltration primarily occurs during the rainy season from the effects of altitude on 18 o the mean recharge altitudes for both mountainous and coastal springs were estimated as 300 400 m which implies longer flow paths for the coastal springs the relationship of cfc 12 cfc 113 and that of cfc 12 3 h concordantly indicated that the groundwater consists mainly of binary mixtures composed of 15 25 year old young water and old water with ages greater than 60 years lower nitrate levels in the coastal springs were well represented by the mixing models recharge altitudes for coastal springs increased up to 700 m assuming that old water corresponds to high altitude recharge using the binary mixing model integration of hydrochemical and environmental tracer characteristics revealed that pahoehoe lava flows and hydrovolcanic tuffs play key roles in controlling the groundwater occurrence and quality

dynamics and thermodynamics of magma mixing insights from a simple exploratory model the mixing of magmas of distinct temperature bulk composition mineralogy and physical properties plays a central role in explaining the diversity of magma types on earth and in explaining the growth of continental and oceanic crust magma mixing is also of practical importance for example the mixing of distinct magmas has been cited as an important process in creation of economically important horizons in layered intrusions as well as a triggering mechanism for initiation of volcanic eruptions the motivation for better quantifying the dynamics and thermodynamics of magma mixing and its attendant plutonic and volcanic products is clear the degree of magma mixing which spans a continuum from mingling to complete hybridization depends upon initial and boundary conditions magma properties driving forces and time available for mixing magma mingling produces a heterogeneous mixture of discrete clumps of the end member magmas whereas complete hybridization involves the thermodynamic equilibration of two distinct magmas to form a third qualitatively mixing occurs via reduction in the size of compositional heterogeneities i e clumps through stretching and folding by viscous flow followed by homogenization once shear has reduced the size of compositional anomalies to diffusive length scales quantification of this process relies on two statistical measures the linear scale of segregation defined as the spatial integral of the compositional correlation function related to the size distribution of the segregated clumps within the mixture and the intensity of segregation i a measure that quantifies how much the composition at each location differs from the average the mixing dynamics of a layered system are analyzed in terms of the parameters governing mixing rayleigh lewis and buoyancy numbers and viscosity ratio to estimate how the timescale for magma hybridization h compares to solidification recharge diffusive and assimilation timescales this analysis illustrates that hybridization times can be shorter than or comparable to thermal solidification and replenishment timescales thus formation of hybridized or nearly hybridized magmas is one anticipated outcome of mixing the machinery of thermodynamics can be used to compute the hybrid magma state an exploratory model for the thermochemistry of hybridization is developed based on binary eutectic phase relations and thermodynamics eight thermodynamic parameters define the phase diagram and associated energetics and six parameters initial temperatures compositions mass ratio of mixing magmas and an enthalpy parameter are necessary and sufficient to determine the state of hybrid magma uniquely while relevant combinations of 14 thermodynamic and mixing parameters might suggest that the number of mixing outcomes i e products is too high to systematize monte carlo simulations using the exploratory model document how millions of arbitrary initial states evolve into five possible final mixed states such an analysis implies that a magma mixing taxonomy that defines possible mixed product states can be developed and tied to petrologic indicators of mixing additional insights gained from this exploratory model that are supported by independent results from a multicomponent multiphase thermodynamic model of magma mixing magma chamber simulator include 1 the proclivity of invariant point hybrid states which may explain some instances of compositionally monotonous melts associated with mixed magma eruptions 2 a surprising thermal effect such that the temperature of hybridized magma can be significantly less than the initial temperature of either of the mixing magmas this type of magma mixing may result in crystal resorption thus invalidating an assumption that resorption textures in crystals are typically the result of a magma heating event 3 illustration of the differing effects of stoped block temperature and composition on hybrid magma temperature and phase state and 4 illustration of a cessation of crystallization effect that may pertain to the morb pyroxene paradox differences between adiabatic or r hybridization and diabatic or rfc hybridization are also explored the model can be used to elucidate the thermodynamic principles underlying magma mixing in the hybridization limit these principles are of general applicability and carry over to more compositionally complicated systems

galena mineralization in the orcadian basin scotland geological and isotopic evidence for sources of lead galena and other sulphides are widespread in the old red sandstone devonian orcadian basin syndiagenetic occurrences are associated with organic rich sedimentary rocks especially algal limestones epigenetic galenas are often spatially related to these syndiagenetic occurrences particularly in the vicinity of permo carboniferous igneous intrusions mineralization is concentrated about the granite gneiss basement inlier in southwest orkney

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

groundwater residence time and movement in the maltese islands a geochemical approach the maltese islands are composed of two limestone aquifers the upper and lower coralline limestone separated by an aquitard the blue clay the lower coralline limestone is overlain in part by the poorly permeable globigerina limestone the upper perched aquifers are discontinuous and have very limited saturated thickness and a short water level response time to rainfall frequent detections of coliforms suggest a rapid route to groundwater however the unsaturated zone has a considerable thickness in places and the primary porosity of the upper coralline limestone is high so there is likely to be older recharge by slow matrix flow as well as rapid recharge from fractures measurement of sf6 from a pumping station in a deep part of one of the perched aquifers indicated a mean saturated zone age of about 15 years the main sea level aquifers msl on both malta and gozo have a large unsaturated thickness as water levels are close to sea level on malta parts of the aquifer are capped by the perched aquifers and more extensively by the globigerina limestone the limited detection of coliform bacteria suggests only some rapid recharge from the surface via fractures or karst features transmissivity is low and tritium and cfc sf6 data indicate that saturated zone travel times are in the range 15 40 years on gozo the aquifer is similar but is more extensively capped by impermeable blue clay cfc data show the saturated zone travel time is from 25 years to possibly more than 60 years groundwater age is clearly related to the extent of low permeability cover the 13c signature of groundwater is related to the geochemical processes which occur along the flowpath and is consistent with residence time ages in the sequence perched aquifers malta msl gozo msl the 18o and 2h enriched isotopic signature of post 1983 desalinated water can be seen in more modern groundwater particularly the urbanised areas of the perched and malta msl aquifers in all aquifers movement of solutes from the surface travelling slowly through the matrix provide a long term source of groundwater contaminants such as nitrate

on the role of diapirism in the segregation ascent and final emplacement of granitoid magmas only bodies of magma with a high crystal content and partially molten crustal country rocks can ascend as diapirs once such an envelope is pierced the diapiric ascent of the pluton is arrested by the high viscosity of a solid aureole deformation by shortening of the carapace of these bodies may lead to the expulsion of a magma with a relatively low crystal content which may then continue ascent via fractures and dykes the details of the mechanisms of granitoid magma segregation are still unknown but it appears that many magmas hegin their ascent through the crust as mushes with at least 50 melt and that such magmas are rheologically able to ascend through a thickness of crust this ascent mechanism explains the dearth of structures attributable to the ascent of granitoids in contrast to the abundance of structures that developed during their final emplacement when a magma becomes too crystalline melt 25 to continue its ascent via dykes it is immobilised at approximately this stage a hydrous magma may become saturated with water and release fluids into the aureole making it particularly susceptible to deformation magma that continues to arrive at this level is also immobilised and the pluton grows as a ballooning diapir these characteristically deform themselves and their aureoles by bulk shortening magmas that are able to ascend to shallow depths largely by virtue of lower water contents and higher initial temperatures tend to become finally accommodated by such brittle processes as stoping and cauldron subsidence high level intrusions lend to be tabular are also fed by dykes or conduits and assemble in tabular batholiths

dynamically supported geoid highs over hotspots observation and theory hotspots are associated with long wavelength geoid highs an association that is even stronger when the geoid highs associated with subduction zones are removed we quantify these associations by expanding the hotspot distribution in spherical harmonics and calculating correlation coefficients as a function of harmonic degree the hotspot distribution spectrum is nearly white except for peaks at degrees 2 and 6 it is correlated positively with the slab residual geoid for degrees 2 6 with low seismic velocity in the lower mantle at degree 2 and with low seismic velocity in the upper mantle at degree 6 we test fluid mechanical models for hotspots including lithospheric delamination and hot plumes by calculating their predicted dynamic geoid responses and comparing them to the observations these models include the effects of temperature dependent rheology our preferred hotspot model based on observations of the geoid and seismic tomography has plumes preferentially occurring in regions of large scale background temperature highs in a mantle which has a substantial viscosity increase with depth although other models are possible alternatively strong plumes in the lower mantle may neck down and attenuate in the upper mantle due to changes in plume viscosity the major low density anomalies causing the geoid highs associated with plumes appear to be in the lower mantle we hypothesize that cold lower mantle underlying the complementary geoid lows is due to deeply subducted oceanic lithosphere and that hotspot plumes tend to be excluded from these cold regions of the mantle

hydrogeochemistry and environmental isotopes of ground water in jeju volcanic island korea implications for nitrate contamination ground water from springs and public supply wells was investigated for hydrochemistry and environmental isotopes of 3h 18o and d in jeju volcanic island korea the wells are completed in a basaltic aquifer and the upper part of hydrovolcanic sedimentary formation nitrate contamination is conspicuous in the coastal area where most of the samples have nitrate concentrations well above 1 mg no3n l agricultural land use seems to have a strong influence on the distribution of nitrate in ground water comparison of stable isotopic compositions of precipitation and ground water show that ground water mostly originates from rainy season precipitation without significant secondary modification and that local recharge is dominant 3h concentration of ground water ranged from nearly zero to 5 tu and is poorly correlated with vertical location of well screens the occurrence of the 3h free old ground water is due to the presence of low permeability layers near the boundary of the basaltic aquifer and the hydrovolcanic sedimentary formation which significantly limits ground water flow from the upper basaltic aquifer the old ground water exhibited background level nitrate concentrations despite high nitrate loadings whereas young ground water had considerably higher nitrate concentrations this correlation of 3h and nitrate concentration may be ascribed to the history of fertilizer use that has increased dramatically since the early 1960s in the island this suggests that 3h can be used as a qualitative indicator for aquifer vulnerability to nitrate contamination copyright 2005 john wiley sons ltd

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

isotope signatures and hydrochemistry as tools in assessing groundwater occurrence and dynamics in a coastal arid aquifer groundwater from the la paz arid coastal aquifer in baja california mexico is essentially the only source of drinking water for the local population and tourists as well as irrigation water for agricultural needs the intensive exploitation of the aquifer and water cycling has resulted in groundwater abatement up to 10 m and high salinity up to 5800 mg l 1 a study using hydrochemistry isotopic deuterium oxygen 18 and carbon 14 and gaseous tracers chlorofluorocarbons cfc 11 cfc 12 cfc 113 as well as multivariate statistics was developed to elucidate groundwater composition flow and occurrence groundwater is of meteoric origin and a large proportion is subject to evaporation the primary natural recharge is generated in the el novillo and las cruces ranges and groundwater subsequently flows in a se nw direction toward the coast the initial water type is the result of discordant dissolution of silicate minerals and ion exchange on soils in the lower plain portion the aquifer system is recharged from irrigation return flow and seawater intrusion which significantly affects groundwater chemistry nitrate and chloride concentrations indicate that groundwater is highly affected by an overuse of fertilizers in agricultural activities but there is little effect from urban activities seawater intrusion has progressed rapidly during the past decade and the impact currently extends 13 km inland radiocarbon residence time calculations suggest that groundwater is modern with the exception of chametla and el centerario sites in the central and western lowlands with ages of up to 5000 years these waters indicate an additional recharge source for the upconing of fossil groundwater or regional flow

evidence of magma mixing in the daly gap of alkaline suites a case study from the enclaves of pantelleria italy the island of pantelleria consists of trachytes pantellerites and minor mildly alkaline basalts rocks of intermediate composition falling in the so called daly gap such as mugearites benmoreites and mafic trachytes occur only in the form of enclaves in trachytes and pantellerites inside the main caldera of the island caldera cinque denti which collapsed during the green tuff ignimbrite eruption at 50 ka the enclaves include volcanic subvolcanic and intrusive rock types the enclaves in host trachyte contain traces of glass devitrified glass occurs within enclaves in host pantellerites minerals in the enclaves show regular compositional variations with whole rock silica content glass present in the medium grained samples is interpreted to be the result of incipient melting the major and trace element compositions of the enclaves show regular and linear variations between an evolved mafic magma hawaiite and a felsic end member similar to the green tuff trachyte fractional crystallization modelling of compatible and incompatible trace elements v ni zr la sm lu nb y th does not reproduce the observed trends rocks of intermediate composition within the daly gap can be explained only by magma mixing between an already differentiated mafic magma hawaiite and an anorthoclase rich trachytic melt in the lower and higher parts respectively of a stratified magmatic chamber medium grained enclaves are interpreted as the result of fragmentation of solidified mixing layers in the roof of the magma chamber during the eruption of the green tuff when the collapse of the caldera took place diffusion calculations suggest a residence time of 5 days for the enclaves in their host magmas

inclusions in mount st helens dacite erupted from 1980 through 1983 abstract inclusions of plutonic metavolcanic and volcanic rocks are abundant in dacite pumice and lava from the 1980 1986 eruption sequence at mount st helens point counts of inclusions exposed in talus blocks from the dome from 1980 through 1983 show that inclusions form approximately 3 5 vol of the lava eighty five percent of the inclusions are medium grained gabbros with an average diameter of 6 cm additional rock types include quartz diorite hornfelsic basalt dacite andesite and vein quartz disaggregated inclusions are common and define shear planes within the dome these fragmented inclusions may significantly contaminate analyses of the dacite the gabbroic inclusions are of four distinct types all with mineral assemblages consistent with crystallization pressures of less than 9 kb textures and major element compositions indicate that most of the gabbroic inclusions are cumulates the most abundant inclusion type is laminated gabbronorite which contains up to 9 interstitial glass derived from partial melting the presence of quartz veins and hornblende bearing veins within sheared zones in the laminated gabbronorite indicates that the source of these inclusions was holocrystalline rock that had been penetrated by water rich fluids the gabbronorite contained sufficient water to be susceptible to partial melting when the magma that fed the 1980 1986 eruption sequence was emplaced nearby various types of gabbroic inclusions including the laminated gabbronorite are common in mount st helens lavas of approximately the last 3000 years this coincides with the interval in which mount st helens first erupted basalt and basaltic andesite lavas these observations together with the fact that the gabbroic inclusions are compositionally unlike any of the tertiary intrusive rocks in the mount st helens area strongly suggest that the inclusions are related to the introduction of basalt to the mount st helens magmatic system the source of the gabbros could be a layered mafic pluton formed through crystal accumulation from multiple batches of basaltic magma emplaced at mid to upper crustal depths beneath the volcano the prevalence of explosive eruptions at mount st helens may play a part in bringing the inclusions to the surface the eruptive products of the cataclysmic eruption of may 18 1980 contain notably fewer inclusions than the pyroclastic flows and dome lavas erupted subsequently this suggests that the may 18 eruption shattered conduit wall rock that was subsequently stoped into the magma and carried to the surface later in the eruption series

quantitative pollen based climate reconstruction in central japan application to surface and late quaternary spectra abstract climate reconstruction in japan by the best modern analogues method was tested with 285 surface pollen spectra and then applied to the 47 000 years pollen profile from lake mikata central japan both pollen taxa percentages and plant functional type affinity scores were used in the reconstruction of six climate variables the reconstructed values were compared with the estimated modern climate at each surface pollen site in order to evaluate the accuracy of the pollen based reconstruction the reconstruction of thermal parameters is very reliable correlation coefficient r between 0 86 and 0 89 the reconstruction of annual precipitation is less accurate r 0 7 we also proposed a new technique to calibrate reconstructed values into both probability distribution and or confidence regions of observed values the specialized programs for this calibration polcalib and polhist are available at qsr website http www elsevier nl locate quascirev the reconstruction of the late quaternary climate changes around lake mikata shows that the summer and winter temperatures were 5 c lower than present around 40 uncal kyr bp reached a minimum around 20 uncal kyr bp 10 c lower than present and became similar to present day at 8 uncal kyr bp the estimates for annual precipitation show that it was driest around 20 uncal kyr bp

complex interaction of aluminous metasedimentary xenoliths and siliceous magma an example from mt amiata central italy aluminous silica deficient metasedimentary xenoliths in siliceous lavas of mt amiata have preserved composite zoning patterns indicative for complex processes of magma rock interaction petrographic observations and small scale mineralogical and chemical differences between up to five distinct zones including the core and envelope of lava provide evidence that quartz poor muscovite biotite schists are considered to be the most likely parent rocks and it is believed that release of volatiles from decomposing micas played a significant role in the high temperature metamorphic evolution of the xenoliths and their interaction with the magma the conditions favourable for assimilation were enhanced by injection of mafic magma into the magma chamber although this concurrent operation of magma mixing precludes a quantitative estimate of contamination from the wall rocks which was probably of minor importance the present example indicates that dry acid magma may potentially become more mafic by interaction with partially melted hydrous rocks

geoid pangea and convection abstract we show that the present geoid has a simple low order configuration with an axis of symmetry in the equatorial plane we show further that it is a tennis ball pattern with an equatorial high belt and a polar low one which is clearly controlled by the rotation of the earth finally we show that the outline of pangea between at least 200 ma and 125 ma ago lay along a great circle passing through the paleo poles of rotation thus it also had an axis of symmetry in the equatorial plane this hemispheric super continent configuration ended in middle cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading hotspot outbreaks and high sea level stands we interpret this evidence in terms of separate steady state lower mantle convection responsible for the present geoid weakly coupled to the upper mantle one this weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal the complete cycle from one supercontinent to the next might be of the order of 400 ma

weathering fluxes and sediment provenance on the sw scottish shelf during the last deglaciation the reconstruction of past ice sheet dynamics can shed a light on long term ice stream activity and in turn provide constraints on the response of modern ice sheets to climate change the hebrides ice stream his flowed across part of the western scottish shelf to the shelf break during the last glacial cycle and drained a large portion of the northern sector of the british irish ice sheet to investigate the deglacial dynamics of the his following the last glacial maximum lead pb isotope records were extracted from the femn oxyhydroxide and detrital fractions of recovered laminated glacimarine mud sequences to monitor the changing activity of his during its retreat these provide timing and some source information of glacially weathered inputs to the marine environment the femn oxyhydroxide fraction in the samples is dominated by allochthonous particles pre formed and shows a marked decrease from radiogenic 20 05 206pb 204pb at 21 cal ka bp to less radiogenic pb isotope compositions 19 48 towards the windermere interstadial 15 4 13 ka this decrease represents a reduction in the flux of subglacially derived radiogenic pb to the continental shelf is interpreted as being associated with the break up of the ice stream in western scotland around that time the pb sr and nd isotopic signatures of the detrital fraction indicate a preponderance of moine sourced fine sediments originated from the nw highlands in the core locations from 21 to 15 cal ka bp dimlington stadial windermere interstadial most likely dictated by the orientation of ice flow tidal and oceanic current directions and sediment delivery in contrast ice rafted debris in a 21 cal ka bp old basal diamicton contains volcanic derived material suggesting different provenance for different grain sizes the femn oxyhydroxide 208pb 204pb ratio shows an unusual inversion relative to the other pb isotope ratios and is attributed to the introduction of secondary weathering phases from a source with contrasting 208pb 204pb but similar 206pb 204pb and 207pb 204pb in the detrital fraction the inversions are constrained to periodic spikes which may indicate an increased contribution from a high th u source potentially the neighbouring archaean amphibolitic lewisian basement in the outer hebrides this study demonstrates how geochemical investigation on continental shelves can be used to constrain the timing activity and flow sources of palaeo ice streams

basin structure and tertiary magmatism on skye nw scotland the emplacement of igneous material into upper crustal rocks of sedimentary basins is likely to be strongly controlled by the geometry of the pre existing basin structures these controls are investigated using examples from the tertiary igneous complexes of skye part of the sea of hebrides basin of nw scotland the basin consists of an array of half graben related to se dipping normal faults these pre volcanic mesozoic structures are traced near the igneous complexes using geological relationships preserved unconformably beneath the widespread basaltic lava fields the unconformity represents a period of cretaceous uplift and denudation of the basin and its flanks entirely pre dating the tertiary volcanism of nw scotland this unconformity seals stratigraphically the major basin faults preserving field relationships that permit the tracing of these faults in the country rocks to the tertiary intrusions the major camasunary fault is separated from the raasay fault via a series of minor graben linked by a series of steep nw se trending faults that transfered mesozoic displacements between the principal fault strands a broad range of igneous material of various compositions was intruded into part of the mesozoic sea of hebrides basins and their flanks during palaeocene times different emplacement styles and different structural controls are found the major gabbroic centres do not appear to be controlled by upper crustal structures having been emplaced into the footwalls of major faults however minor synmagmatic displacements on the basin faults may have been sufficient to generate dilatational sites in these footwall positions thereby facilitating emplacement in contrast the granitic melts have been emplaced as sheets and domed into the sediments and overlying lava pile reactivating segments of the basin fault network doming occurred from an array of sills the stratigraphic levels of which can be reconstructed using structural relationships preserved in the roofs and walls of the intrusions the sill levels and their transgressive forms are strongly related to inferred mesozoic basin structures the major fold structures of tertiary age in southern skye are interpreted as accommodating granitic emplacement rather than crustal shortening the nw se mesozoic transfer fault trend appears to have strongly influenced the segmentation of the granite domes these interpretations are illustrated using field relationships mapped in the vicinity of the coire uaigneich granophyre it is concluded that although the higher parts of the basin faults were reactivated to facilitate the doming of granitic intrusions the deeper levels of the mesozoic faults show no evidence of substantial reactivation

a ce nd isotope study of crustal contamination processes affecting palaeocene magmas in skye northwest scotland twelve138ce 136ce isotope determinations 31 nd isotope analyses and 31 ree profiles are presented for tertiary basic to intermediate igneous rocks from the isle of skye nw scotland the aim of this work is to precisely identify the contamination mechanisms of basic magmas emplaced through old crust and to test the effectiveness of ce isotope analysis as a petrogenetic tool

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

geochemistry of a transitional ne trachybasalt q trachyte lava series from patmos dodecanesos greece further evidence for fractionation mixing and assimilation trace element and preliminary sr and o isotopic data are reported for a transitional alkaline sub alkaline lava series mvs from patmos greece the lava types belonging to this series are ne trachybasalt hy trachybasalt hy trachyandesite and q trachyte rb sr and ba contents as well as k rb ratios of the ne trachybasalts differ from those of alkali basalts of oceanic islands and those of k rich alkaline lavas of continental regions and are consistent with the occurrence of these volcanics in a destructive plate margin environment qualitatively the variations shown by many trace elements throughout the mvs are explicable in terms of magma evolution via fractional crystallization involving removal of the observed phenocryst phases cross cutting ree patterns can be explained by removal of small amounts of apatite however certain features of the data cannot be reconciled with the operation of fractional crystallization alone these are a the compatible behavior of ba throughout the mvs b the moderately as opposed to highly incompatible behavior of zr rb and nb relative to th and c the significant decrease of k th rb th zr th zr nb nb th yb th ta th u th and zr ta ratios especially but not exclusively in the mafic part of the series quantitative modeling indicates that the hy trachybasalts are anomalously enriched in both highly incompatible and highly compatible elements and these lavas are shown to be hybrids formed by mixing of ne trachybasalt and hy trachyandesite mixing proportions of the end members calculated from incompatible element abundances 19 ne trachybasalt differ from those calculated from compatible element abundances 62 ne trachybasalt and are inconsistent with proportions calculated from published mineral chemical data in addition mixing cannot account for the observed variations in incompatible element ratios and this is taken as evidence for the simultaneous operation of assimilation isotopic variations 87sr 86sr from 0 7049 to 0 7076 and 18o 16o from 4 7 to 8 6 and the positive correlation of isotope ratios with sio2 and th contents provide conclusive proof that assimilation occurred calculations show that the isotopic characteristics and the concentrations of many trace elements in the q trachytes can be explained by fractional crystallization of ne trachybasalt combined with assimilation of average continental crust 87sr 86sr 0 710 and that large amounts of assimilation are not necessary ma mc 0 55 ree data are not well explained by this model and suggest a crustal end member enriched in lree relative to the average crust zr and hf data are also not well explained and indicate that the assimilant was depleted in hfse relative to average crust or that hfse are held back in relatively insoluble phases such as zircon in the restite during assimilation nevertheless the results of the modeling demonstrate that ba concentrations may decrease during afc processes and that high sr contents 1500 ppm in the mvs ne trachybasalts do not render mafic parental magmas immune to the effects of assimilation in terms of their 87sr 86sr ratios the results of this study confirm conclusions based upon major oxide and mineral chemical data for the mvs lavas but more importantly show that careful analysis of trace element data allows the various processes involved in magma evolution to be identified and quantified even in the absence of major oxide and isotopic data finally it is reiterated that magma mixing and assimilation may be coupled processes in the magma chambers beneath many volcanic centers and recognition of this fact has profound implications for studies of magmas erupted at continental margins and through continental crust

melting and undercooled crystallisation of felsic xenoliths from minor intrusions jebilet massif morocco abstract granitic and gneissic xenoliths within microdiorite dykes from the palaeozoic jebilet massif morocco contain up to 40 of granophyric intergrowths that occur as films along quartz feldspar contacts and form an interconnected grain boundary network the composition of the feldspar megacrysts i e large embayed crystals surrounded by the granophyric intergrowths implies high temperature crystallisation t 900 c and the sievetexture or finger print texture indicates that these crystals underwent incipient melting moreover the microstructural position and bulk composition of the granophyre are similar to that of glass in partly molten felsic xenoliths from lavas or pyroclastics it is argued that the granophyre originated after partial melting of the xenoliths when incorporated into the dioritic magma crystallisation of that melt resulted in most cases in the formation of vermicular and or cuneiform granophyre which testifies to moderate degrees of undercooling a few occurrences of plumose granophyre i e very thin intergrowths that are close to quartz bearing spherulites indicate that some xenoliths crystallised at higher degrees of undercooling together with granophyric xenoliths a number of microgranular inclusions also occur these are characterized by phenocrysts of quartz and feldspar in a microgranular groundmass finger print texture in feldspar suggests that these inclusions like the granophyric xenoliths underwent ultra metamorphism and melting the microgranular groundmass is most probably indicative of crystallisation at lower degrees of undercooling but the relationships between the two types of xenoliths still remain to be explored in detail