bismuth selenides from st andreasberg germany an oxidised five element style of mineralisation and its relation to post variscan vein type deposits of central europe carbonate veinlets at roter bar a former underground mine in the polymetallic st andreasberg vein district of the harz mountains germany host selenide minerals that are characterised as bi ag bearing clausthalite pbse tiemannite hgse guanajuatite bi2se3 and a number of selenides of bi zn cu ag and pd an unnamed bi pb ag selenide species with some hg and cu ideally bi4pb3ag2se10 is reported here specular hematite is disseminated within the clausthalite at the marginal zones of which other selenide minerals are located the occurrence of bohdanowiczite agbise2 and umangite cu3se2 constrains the formation temperature to 120 c and the selenide hematite assemblage plus barite in the carbonate gangue identifies highly oxidised conditions selenide assemblages of pb bi ag with and without co and ni occur in many parts of the variscan basement of central europe harz erzgebirge schwarzwald and bohemian massif and represent a high oxidation variety of five element ag as bi co ni veins

an attempt to detect reflected waves from the lower boundary of a descending slab abstract we attempted to detect reflected waves from deep focus earthquakes at the lower boundary of a descending slab for this purpose we calculated theoretical waveforms in the realistic heterogeneous velocity and q structures beneath the japanese islands and compared them with seismic waveforms observed in the kanto tokai districts of central japan assuming that earthquakes occur within the deeper portion of the slab we investigated the effects of variation in focal mechanisms focal depths velocity contrasts near the lower plate boundary and the q structures on theoretical seismograms on the earth s surface the results show that the amplitudes of the p to p and s to s reflected waves gradually increase toward the subduction zone and take maximum values near the trench axis however travel time difference between the direct wave and the following reflected wave decreases there making it difficult to detect the reflected wave based on these theoretical calculations we investigated digital three component seismograms observed in the kanto tokai districts by the national research institute for earth science and disaster prevention science and technology agency nied the seismograms observed were obtained from deep focus earthquakes from 1990 through 1996 with magnitude of 5 0 and greater after carefully checking seismograms from 15 deep focus events we could not detect the reflected waves from the lower plate boundary systematically at expected arrival times from the theoretical calculation this indicates that the reflected waves are either masked by coda waves followed by the direct p and s waves or below the noise level that is detectable by seismometers there is also a possibility that the seismic velocity contrast between the slab and the underlying upper mantle may not be so sharp however the possibility to detect the s to s reflected waves increases if we check observed waveforms in the horizontal range between 200 to 300 km landward from trench axis for a moderate size deep focus earthquake with down dip compression which occurs near the upper plate boundary at depths of 300 to 400 km

226ra 230th 238u disequilibria of historical kilauea lavas 1790 1982 and the dynamics of mantle melting within the hawaiian plume abstract the geochemical variations of kilauea s historical summit lavas 1790 1982 document a rapid fluctuation in the mantle source and melting history of this volcano these lavas span nearly the entire known range of source composition for kilauea in only 200 yr and record a factor of 2 change in the degree of partial melting in this study we use high precision measurements of the u series isotope abundances of kilauea s historical summit lavas and two ingrowth models dynamic and equilibrium percolation melting to focus on the process of melt generation at this volcano our results show that the 226 ra 230 th 238 u disequilibria of these lavas have remained relatively small and constant with 12 4 excess 226 ra and 2 5 1 6 excess 230 th both are 2 model calculations based mostly on subtle variations in the 230 th 238 u disequilibria suggest that lavas from the 19th to early 20th centuries formed at significantly higher rates of mantle melting and upwelling up to a factor of 10 compared to lavas from 1790 and the late 20th century the shift to higher values for these parameters correlates with a short term decrease in the size of the melting region sampled by the volcano which is consistent with fluid dynamical models that predict an exponential increase in the upwelling rate and thus the melting rate towards the core of the hawaiian plume the pb sr and nd isotope ratios of lavas derived from the smallest source volumes correspond to the kilauea end member of hawaiian volcanoes whereas lavas derived from the largest source volumes overlap isotopically with recent loihi tholeiitic basalts this behavior probably arises from the more effective blending of small scale source heterogeneities as the melting region sampled by kilauea increases in size the source that was preferentially tapped during the early 20th century when the melt fractions were lowest is more chemically and isotopically depleted than the source of the early 19th and late 20th century lavas which formed by the highest melt fractions this inverse relationship between the magnitude of source depletion and melt fraction suggests that source fertility i e lithology controls the degree of partial melting at kilauea thus rapid changes in the size of the melting region sampled by the volcano in the presence of these small scale heterogeneities may regulate most of the source and melting related geochemical variations observed at kilauea over time scales of decades to centuries

paleomagnetism of the cu zn pb bearing kupferschiefer black shale upper permian at sangerhausen germany syngenetic diagenetic and epigenetic models have been proposed for the cu zn pb kupferschiefer mineralization at sangerhausen germany paleomagnetic and rock magnetic measurements have been made on 205 specimens from mine workings on the margin of the sangerhausen syncline the mineralization is richest in the 0 5 m thick upper permian 258 2 ma kupferschiefer black marly shale nine sites and dies out over 0 2 m in the underlying weisliegend sandstones three sites and overlying zechstein carbonates two sites except for one site of fault zone gypsum characteristic remanent magnetization directions were isolated for all 14 sites using alternating field and thermal step demagnetization these directions provide a negative fold test indicating that the remanence postdates jurassic fault block tilting rock magnetic measurements show that the kupferschiefer shale marks a redox front between the oxidized weissliegend sandstones and non oxidized zechstein carbonates the 14 site directions give a late jurassic paleopole at 149 3 ma it is significantly different from the paleopole reported by e c jowett and others for primary or early diagenetic rote faule alteration that gives an age of 254 6 ma on the current apparent polar wander path and is associated with kupferschiefer mineralization we suggest that the late jurassic extensional tectonic event that formed the nearby north german basin also reactivated variscan basement faults and extended them up through the overlying strata thereby allowing hydrothermal basement fluids to ascend and epigenetically mineralize the kupferschiefer shale the possibility of a 53 3 ma mineralization age is also considered

nb in hawaiian magmas constraints on source composition and evolution abstract published th and nb data for basalts from 11 volcanoes from the hawaiian islands and emperor seamount chain yield a nearly uniform concentration ratio of nb th 15 2 1 7 the basalts include tholeiites with nb concentrations ranging down to 4 ppm and alkali basalts with a maximum nb concentration of 127 ppm however nephelinites and melilitites from the honolulu volcanic series have much lower nb th ratios and are excluded from this analysis using the average th u ratio of 3 2 for the five volcanoes of the island of hawaii this corresponds to a nb u 48 6 5 3 which is indistinguishable from the mean value of a worldwide sample of oib and morb nb u 47 10 given by direct nb and u analyses in contrast the earth s primordial mantle had a nb th ratio of 8 6 and a nb u ratio of 30 these data demonstrate that none of the hawaiian volcanoes not even the isotopically most nearly primitive koolau series from oahu has refractory elements derived from an undifferentiated or primordial portion of the mantle an even less likely source is recycled continental crust which has a mean nb u ratio of 10 a consideration of the chromatographic theory of metasomatism and comparison with metasomatic rocks observed in the continental crust show that large scale metasomatism in the mantle which would be needed to account for the very large total volume of hawaiian emperor magmas is expected to produce a strongly zoned mantle yielding chemically highly heterogeneous magmas unless the metasomatic column has reached a steady state the expected heterogeneity is difficult to reconcile with observed chemical homogeneity of the main stage tholeiitic magmas the late stage alkali basalts and the nephelinites must be excluded from this consideration because their isotopic composition shows that they are derived from the depleted lithosphere or asthenosphere the consequence of a steady state metasomatic column would be that the tholeiitic melt itself represents the metasomatic fluid the model of recycled oceanic crust and lithosphere is consistent with the chemical and isotopic data the mantle that originally produced this oceanic crust was already depleted and rehomogenized as a result of prior separation of continental crust uniform source ratios of nb u and ba rb were established during this rehomogenization process the general enrichment of the hawaiian source and the chemical and isotopic heterogeneities found in the present day lavas were produced during the differentiation into oceanic crust and lithosphere secondary pb 1bpb model ages indicate that this crust was probably produced 1 ga ago

numerical model to determine the composition of h2o nacl cacl2 fluid inclusions based on microthermometric and microanalytical data natural fluids approximated by the h2o nacl cacl2 system are common in a wide range of geologic environments including sedimentary basins associated with hydrocarbon occurrences and mvt deposits submarine hydrothermal systems and other metamorphic magmatic and hydrothermal environments we present a comprehensive numerical model and microsoft excel based computer program to determine the compositions of fluid inclusions in the h2o nacl cacl2 system based on microthermometric and microanalytical data the model consists of six polynomial correlation equations that describe liquid salinity as a function of nacl cacl2 ratio and melting temperature on each of the ice hydrohalite halite antarcticite cacl2 4h2o and cacl2 2h2o vapor saturated liquidus surfaces the cotectic and peritectic boundaries are determined from the intersections of the liquidus surfaces the model is implicitly internally consistent and topologically correct the model expands upon the compositional range of applicability and the data types that can be used for compositional determination it reproduces experimental data for all compositions that lie within the h2o nacl cacl2 4h2o compositional triangle in the h2o nacl cacl2 system and yields accurate reproductions of the h2o nacl and h2o cacl2 binaries furthermore in comparison to previously published models the one presented here eliminates systematic errors wavy isotherms and cotectic and peritectic curves with local bumps

case studies on the origin of basalt iii petrogenesis of the mauna ulu eruption kilauea 1969 1971 during the mauna ulu flank eruption on kilauea hawaii the concentrations in the lavas of the minor elements k p na and ti and the incompatible trace elements analyzed by isotope dilution k rb cs ba sr and the ree except yb decreased monotonically and linearly with the time or date of the eruption at the same time the concentrations of the major elements and of yb and the ratios of k rb k cs ba rb 87sr 86sr and 143nd 144nd remained constant most of the scatter in the raw concentration data is removed by a simple correction for olivine plus chromite fractionation previously established by wright et al 1975 these results are explained by simple equilibrium partial melting of a uniform source the degree of melting increased by about 20 of the initial value during the course of the eruption the trace element data are inverted by the method originated by minster and allegre 1978 and simplified by hofmann and feigenson 1983 the source has the following element or isotope ratios k rb 501 7 ba rb 14 0 0 5 rb cs 95 7 rb sr 0 0193 0 0045 0 0090 ce ba cn 1 1 0 1 sr ba cn 1 19 0 30 0 19 87sr 86sr 0 703521 0 000016 and 143nd 144nd 0 512966 0 000008 the ree pattern of the source has a nearly flat or slightly negative slope relative lree enrichment between ce and dy and a strongly positive slope between dy and yb however this relative hree enrichment is poorly constrained by the analytical data is highly model dependent and may not be a true source feature the yb concentration in the source is particularly poorly constrained because it is essentially constant in the melts on the other hand this special feature demonstrates that yb must be buffered by a mineral phase with a high partition coefficient for yb namely garnet the calculated clinopyroxene garnet ratio in the source is roughly equal to one in contrast the source of kohala volcano had previously been found to contain little or no garnet

natural fracking and the genesis of five element veins hydrothermal ag co ni bi as five element vein type ore deposits show very conspicuous textures of the native elements silver bismuth and arsenic indicating formation from a rapid far from equilibrium process such textures include up to dm large tree and wire like aggregates overgrown by co ni fe arsenides and mostly carbonates despite the historical and contemporary importance of five element vein type deposits as sources of silver bismuth and cobalt and despite of spectacular museum specimens their process of formation is not yet understood and has been a matter of debate since centuries we propose based on observations from a number of classical european five element vein deposits and carbon isotope analyses that natural fracking i e liberation of hydrocarbons or hydrocarbon bearing fluids during break up of rocks in the vicinity of an active hydrothermal system and mixing between these hydrocarbons e g methane and or methane bearing fluids and a metal rich hydrothermal fluid is responsible for ore precipitation and the formation of the unusual ore textures and assemblages thermodynamic and isotope mixing calculations show that the textural chemical and isotopic features of the investigated deposits can entirely be explained by this mechanism

seismic velocity structure of the subducting pacific plate in the izu bonin region although numerous studies have been made on the contrast between subducting slabs and surrounding mantle little is known about the internal structure of the oceanic lithosphere after it descends into the mantle at subduction zones the velocity structure within the slab can be expected to be heterogeneous based on thermal and petrological considerations in this study observed travel time residual data from a spatially dense seismic network above deep earthquakes in the izu bonin region are compared with three dimensional ray tracing calculations the data are inconsistent with a homogeneous slab model and consistent with a heterogeneous slab model with regional velocity variations the residual data can be explained by a model that has a velocity gradient within the slab in the subducting pacific plate the velocity near the center of the slab is faster than that near the upper boundary and gradually decreases toward the bottom of the plate a model with a velocity decrease of 3 as predicted by a thermal profile explains the observed data

the source of central american lavas inferences from geochemical inverse modeling the rate earth element chemistry of a large suite of samples from the central american volcanic front has been determined to understand their petrogenesis different segments of the volcanic front are compared on the basis of their calculated source rare earth patterns as deduced from inverse modeling the results yield a range in the extent of light rare earth enrichment of the source as well as in source mineralogy moderateto strong lree enrichment and high modal garnet contents are observed for the sources of both guatemala and central costa rica whereas slight lree depletion and little or no garnet occurs in the nicaraguan source region although distinct source regions beneath each central american segment are permitted by the modeling it is more likely that the mantle wedge is broadly homogeneous but locally heterogeneous small volume relatively enriched garnet bearing veins surrounded by a matrix of isotopically depleted mantle periodotite could exist throughout the mantle wedge apparently distinct sources occur due to the variation in partial melting beneath the different segments controlled by the amount of subduction generated flux per unit wedge volume which in turn is a function of the dip of the subducted lithosphere

petrology and geochronology of basalt breccia from the 1996 earthquake swarm of loihi seamount hawaii magmatic history of its 1996 eruption samples of basalt were collected during the rapid response cruise to loihi seamount from a brec cia that was probably created by the july to august 1996 loihi earthquake swarm the largest swarm ever recorded from a hawaiian volcano 210 po 210 pb dating of two fresh lava blocks from this breccia indicates that they were erupted during the first half of 1996 making this the first documented historical eruption of loihi sonobuoys deployed during the august 1996 cruise re corded popping noises north of the breccia site indicat ing that the eruption may have been continuing during the swarm all of the breccia lava fragments are tho leiitic like the vast majority of loihi s most recent lav as reverse zoning at the rim of clinopyroxene pheno crysts and the presence of two chemically distinct oliv ine phenocryst populations indicate that the magma for the lavas was mixed just prior to eruption the trace element geochemistry of these lavas indicates there has been a reversal in loihi s temporal geochemical trend although the new loihi lavas are similar isotopically and geochemically to recent kilauea lavas and the man tle conduits for these two volcanoes appear to converge at depth distinct trace element ratios for their recent lavas preclude common parental magmas for these two active volcanoes the mineralogy of loihi s recent tho leiitic lavas signify that they crystallized at moderate depths f8 9 km within the volcano which is approx imately 1 km below the hypocenters for earthquakes from the 1996 swarm taken together the petrological and seismic evidence indicates that loihi s current magma chamber is considerably deeper than the shal low magma chamber f3 4 km in the adjoining active shield volcanoes

constraints on partial melting imposed by rare earth element variations in mauna kea basalts thirty one basalts from mauna kea collected through the hawaii scientific drilling project 1994 have been analyzed by inductively coupled plasma icp mass spectrometry for rare earth element ree concentrations the systematic variations in ree abundance provide constraints for theoretical models of mantle partial melting lavas are given a first order correction for the effects of clinopyroxene and olivine fractionation or accumulation so that all lavas can be considered direct mantle melts failure to account for fractionation generates errors in calculated source mineralogies and ree patterns incremental models of melt generation including fractional aggregated fractional and continuous melting are found to reproduce the observed lava compositions only under special conditions a garnet free source a fractionated heavy rare earth element hree source pattern and aggregation of melt fractions these conditions are not consistent with the high pressure phase equilibria for mauna kea lavas equilibrium batch melting provides a significantly better match to the observed lava chemistry and is less sensitive to changes in initial conditions the equations for batch melting can be inverted to compute initial source ree patterns and partitioning behavior and are internally consistent with the calculated forward models successful batch melting models include several with an approximately flat chondrite normalized source ree pattern degrees of melting between about 1 and 18 and a mantle residue containing garnet and clinopyroxene

the role of the kupferschiefer in the formation of hydrothermal base metal mineralization in the spessart ore district germany insight from detailed sulfur isotope studies the spessart district sw germany located at the southwestern margin of the permian kupferschiefer basin in central europe hosts abundant stratabound and structurally controlled base metal mineralization the mineralization styles identified are 1 stratabound cu pb zn ag ores in zechstein sedimentary rocks 2 structurally controlled cu as ag ores in zechstein sedimentary rocks 3 crosscutting co ni bi as and cu fe as veins 4 stratabound metasomatic fe mn carbonate ores in zechstein dolomite 5 barren barite veins and 6 fe mn as veins in permian rhyolites building on previous work that involved mineralogical textural and chemical characterization of the major mineralization types we have performed a comprehensive sulfur isotope study that applied both conventional and novel laser ablation multi collector inductively coupled plasma mass spectrometry techniques the 34s values of sulfide minerals from the different ore types are consistently negative and highly variable in the range between 44 5 and 3 9 whereas the 34s values of barite are all positive in the range between 4 7 and 18 9 remarkably stratabound and structurally controlled mineralization in zechstein sedimentary rocks has the least negative 34s values whereas vein type deposits have consistently more negative 34s values the observed pattern of sulfide 34s values can be best interpreted in terms of fluid mixing at the basement cover interface hydrothermal fluids originating from the crystalline basement migrated upward along subvertical fault zones and were periodically injected into groundwaters that were flowing in the post variscan sedimentary cover these groundwaters had interacted with the zechstein sedimentary rocks resulting in fluids characterized by elevated concentrations of reduced sulfur with negative 34s values and alkaline ph repeated mixing between both chemically contrasting fluids caused rapid and efficient precipitation of sulfide ore minerals in hydrothermal veins with highly variable but distinctly negative 34s values

the primitive lavas of roccamonfina volcano roman region italy new constraints on melting processes and source mineralogy within a large collection of lavas from the roccamonfina volcano are rocks which represent the most mafic samples yet recorded from roccamonfina and which are amongst the least differentiated lavas found in the roman co magmatic region as a whole these rocks extend both high k and low k series to more primitive values however petrographic and geochemical considerations rule out a primary origin and even these mafic samples appear to record the effects of repeated episodes of fractional crystallization and hybridization relatively potassic samples from the low k series are apparently transitional between low k and high k series as previously delineated however these intermediate k samples are not transitional in their sr isotopic composition suggesting that there is no continuum between low k and high k magma source regions rather the compositional range within the low k series appears predominantly to reflect variation in the degree of melting of a common mantle source analysis of the low k series data using an inverse method suggests a source containing amphibole and garnet and indicates that these phases were consumed during the melting processes responsible for the low k series magmas the role of amphibole is further indicated by the association of low k2o with elevated rb concentration and for example higher ce yb such variations are taken to reflect the consumption of high k rb amphibole during the initial phase of partial melting

the sulfur and strontium isotopic compositions of permian evaporites from the zechstein basin northern germany the sulfur isotopic composition of stratigraphically well constrained samples from five evaporitic cycles of the german zechstein upper permian displays no systematic lateral variation and no significant temporal trend with an average 34s value close to 11 results confirm the previously determined sulfur isotope minimum for phanerozoic seawater least radiogenic 87sr 86sr ratios for these sulfates define a clear temporal variation with a minimum value at 0 707008 a conclusive assessment of this temporal trend in comparison with other data sets for upper permian seawater is not possible due to substantial differences in bio stratigraphic assignments

geochemical structure of the hawaiian plume sr nd and os isotopes in the 2 8 km hsdp 2 section of mauna kea volcano 1 sr nd and os isotopic measurements were made on 110 mauna kea lava and hyaloclastite samples from the drillcore retrieved from the second phase of the hawaii scientific drilling project hsdp 2 the samples come from depths of 255 to 3098 meters below sea level span an age range from 200 to about 550 600 kyr and represent an ordered record of the lava output from mauna kea volcano as it drifted a distance of about 40 km over the magma producing region of the hawaiian hot spot the deepest oldest samples represent the time when mauna kea was closest to the center of the melting region of the hawaiian plume the sr and os isotopic ratios in hsdp 2 lavas show only subtle isotopic shifts over the 400 kyr history represented by the core neodymium isotopes nd values increase systematically with decreasing age from an average value of nearly 6 5 to an average value of 7 5 this small change corresponds to subtle shifts in 87sr 86sr and 187os 188os isotope ratios with small shifts of hf a large shift in 208pb 204pb and 208pb 207pb values and with a very large shift in he isotope ratios from r ra values of about 7 8 to values as high as 25 when mauna kea was closest to the plume core the magma source did not have primitive characteristics for nd sr pb hf and os isotopes but did have variable amounts of primitive helium the systematic shifts in nd hf pb and he isotopes are consistent with radial isotopic zoning within the melting region of the plume the melting region constitutes only the innermost highest temperature part of the thermally anomalous plume mantle the different ranges of values observed for each isotopic system and comparison of mauna kea lavas with those of mauna loa suggest that the axial region of the plume which has a radius of 20 km is a mixture of recycled subducted components and primitive lower mantle materials recently combined during the formational stages of the plume at the base of the mantle the proportions of recycled and primitive components are not constant and this requires there be longitudinal vertical heterogeneity within the core of the plume the remainder of the plume outside this plume core zone is less heterogeneous but distinct from upper mantle as represented by mid ocean ridge basalt morb the plume structure may provide a detailed view of mantle isotopic composition near the core mantle boundary

petrology of lavas from the puu oo eruption of kilauea volcano iii the kupaianaha episode 1986 1992 the puu oo eruption has been remarkable in the historical record of kilauea volcano for its duration over 13 years volume 1 km3 and compositional variation 5 7 10 wt mgo during the summer of 1986 the main vent for lava production moved 3 km down the east rift zone and the eruption style changed from episodic geyser like fountaining at puu oo to virtually continuous relatively quiescent effusion at the kupaianaha vent this paper examines this next chapter in the puu oo eruption episodes 48 and 49 and presents new icp ms trace element and pb sr and nd isotope data for the entire eruption 1983 1994 nearly aphyric to weakly olivine phyric lavas were erupted during episodes 48 and 49 the variation in mgo content of kupaianaha lavas erupted before 1990 correlates with changes in tilt at the summit of kilauea both of which probably were controlled by variations in kilauea s magma supply rate these lavas contain euhedral olivines which generally are in equilibrium with whole rock compositions although some of the more mafic lavas which erupted during 1990 a period of frequent pauses in the eruption accumulated 2 4 vol olivine the highest forsterite content of olivines 85 in kupaianaha lavas indicates that the parental magmas for these lavas had mgo contents of 10 wt which equals the highest observed value for lavas during this eruption the composition of the puu oo lavas has progressively changed during the eruption since early 1985 episode 30 when mixing between an evolved rift zone magma and a more mafic summit reservoir derived magma ended the normalized to 10 wt mgo abundances of highly incompatible elements and cao have systematically decreased with time whereas ratios of these trace elements and pb sr and nd isotopes and the abundances of y and yb have remained relatively unchanged these results indicate that the hawaiian plume source for puu oo magmas must be relatively homogeneous on a scale of 10 20 km3 assuming 5 10 partial melting and that localized melting within the plume has apparently progressively depleted its incompatible elements and clinopyroxene component as the eruption continued the rate of variation of highly incompatible elements in puu oo lavas is much greater than that observed for kilauea historical summit lavas e g ba y 0 09 a 1 vs 0 03 a 1 this rapid change indicates that puu oo magmas did not mix thoroughly with magma in the summit reservoir thus except for variable amounts of olivine fractionation the geochemical variation in these lavas is predominantly controlled by mantle processes

melting rates beneath hawaii evidence from uranium series isotopes in recent lavas 238u 232th 230th and 226ra abundances have been measured in six samples of recent hawaiian basalt by high precision mass spectrometry in an attempt to compare the melting process in plumes and at spreading ridges the data reveal a very small range in 230th 238u activity ratio up to a maximum value of 1 02 0 01 and 226ra 230th activity ratios which lie between 1 10 0 015 and 1 19 0 02 uth and rath abundances are linearly correlated demonstrating that the disequilibria predate crystallisation and differentiation using recently published estimates for the bulk partition coefficients of u and th the results are consistent with melting rates 10 3 kg m 3 a 1 at porosities 10 3 for dynamic fractional melting in the garnet stability field

geochemistry of tholeiites from lanai hawaii lanai is the third smallest of the fifteen principal subaerial shield volcanoes of the hawaiian hotspot this volcano apparently became extinct during the shield building stage of volcanism as shown by the absence of both alkalic cap and post erosional lavas major and trace element analyses of 22 new samples collected primarily from 3 stratigraphic sections show that lanai tholeiites span a large range in composition some lanai lavas are unique geochemically among hawaiian tholeiites in having the lowest abundances of incompatible trace elements of any hawaiian lavas and well developed positive eu anomalies the geochemical characteristics of these low abundance lanai tholeiites are not the result of alteration differences in mantle source modal mineralogy the presence of residual accessory mantle phases or fractional crystallization of such phases assimilation of depleted morb wall rock or accumulation resorption of phenocrysts or xenocrysts incompatible trace element ratios e g nb la nb th la th la hf ce pb in lanai tholeiites span considerable ranges and form coherent trends with each other and with absolute abundances of these elements large variations in la sm la yb and absolute ree abundances at constant mgo suggest that lanai tholeiites formed by variable amounts of partial melting however large ranges in incompatible element ratios cannot be explained solely by variations in partial melting of a geochemically homogeneous source but must reflect geochemical heterogeneities in the lanai source partial melting modeling indicates that the mixed lanai source is probably lree enriched i e la yb cn 1 one component in the lanai source exemplified by the low abundance tholeiites has markedly lower ree hfse th hfse alkali hfse and ce pb ratios than other lanai or hawaiian tholeiites and may indicate the presence of recycled residual subduction zone materials in the hawaiian plume source the positive eu anomalies that characterize the low abundance lanai tholeiites are not the result of plagioclase accumulation or assimilation but are a feature of this source component progressive temporal geochemical variations in lanai tholeiites from 2 stratigraphic sections indicate that the source composition of these lavas probably evolved over time this change could have resulted from a progressive decrease in the extent of partial melting of the lanai source the compositional variability of lanai tholeiites suggests that geochemical heterogeneities in their source are larger than the scale of partial melting lanai tholeiites could not have formed by smaller degrees of partial melting of plume material than did the larger volume hawaiian shields therefore volume differences between hawaiian shields must be controlled primarily by differences in the volume of supplied plume material rather than by differences in the degree of partial melting the premature cessation of eruptive activity at lanai may be attributed to relatively large degrees of partial melting of a small plume

simultaneous determination of the three dimensional crustal structure and hypocenters beneath the kanto tokai district japan abstract a new method is proposed for determining the two dimensional depth distributions to the conrad and the moho together with station corrections and source parameters from first arrival time data in the present study the velocity structure is modelled by a hyperbolic function tanh and the configuration of each interface is expressed in a series of chebyshev functions with coefficients which are unknown parameters a non linear inversion method by tarantola and valette is applied for inversion an approximate ray tracing method with sufficient accuracy for a complex region is adopted for computation of seismic ray paths and travel times the method is applied to p wave first arrival time data from local earthquakes and explosions gathered in the seismological network by the national research center for disaster prevention to reveal the crustal structure beneath the kanto tokai district japan the results obtained in this study are very interesting and show the usefulness of the present method for the study of the crustal structure the distribution of station corrections is reasonable where there is information on the shallow structure low velocity zones appear around tokyo bay and the cape of omae and high velocity zones appear in the mountainous regions the depth to the conrad is about 12 16 km and its lateral change is gentle while the lateral change in the depth to the moho is comparatively large and there is a narrow region where the depth to the moho exceeds 40 km except for this region the central mountainous region the agreement of the crustal structure obtained in the present study with those by the previous refraction studies is fairly good in comparing our results to fractional velocity perturbation in layer 1 0 32 km derived with aki and lee s method by ishida and hasemi our work provides good information on the features causing the crustal velocity anomalies which have been unable to be constrained in ishida and hasemi s work

chemical and isotopic variations in mauna loa tholeiites abstract a suite of basaltic lavas of known eruption age from mauna loa hawaii has provided the basis for a detailed investigation of the evolution of the melting process beneath hawaii high precision 238 u 230 th 226 ra measurements by mass spectrometry reveal that 230 th 238 u ratios are close to 1 02 in all samples younger than 7 ka and that age corrected 226 ra 230 th ratios for three samples less than 2 ka are 1 15 1 20 these results are indistinguishable from the disequilibria reported previously for young kilauea lavas and are consistent with dynamic mantle melting within the garnet stability field at high melting rates 0 001 kg m 3 a 1 and low porosities 230 th 238 u ratios of up to 1 16 are found in some older mauna loa lavas but these are likely to have resulted from post eruptive loss of u by weathering as 230 th 238 u ratios correlate positively with th u ratios and inversely with k and rb abundances sr and nd isotopes define an excellent inverse correlation even though the total range in 143 nd 144 nd is only 1 nd however changes in the sr and nd isotopic compositions over the last 30 ka have not been progressive but have occurred rapidly and with an apparent cyclicity of 4 5 ka moreover these isotopic changes are mirrored by cyclical changes in certain trace element abundance ratios if the melts were produced within a single melting column then all elements must have travelled at similar velocities because the isotopic and abundance ratios of elements of widely differing compatibilities 143 nd 144 nd 87 sr 86 sr ba th la yb vary coherently in the lavas in this scenario chromatographic exchange between melt and matrix must have been minimal however it is more likely that the lava compositions record the mixing of melts from two or more source regions of different compositions 226 ra 230 th ratios in excess of unity in the lavas indicate that the transport of melt was rapid after leaving the melt column and suggest that melt movement through the lithosphere took place in cracks or fractures

predicted equilibrium constants for solid and aqueous selenium species to 300 c applications to selenium rich mineral deposits abstract in this study an attempt has been made to assess aqueous speciation of selenium and solubility product constants of common selenides at elevated temperatures up to 300 c by using various extrapolation methods this study predicts that reduced selenium species are dominant species in many geological processes even under relatively oxidized conditions such as those dictated by the magnetite hematite buffer on the basis of extrapolated equilibrium constants and solubility product constants for common se bearing mineral phases critical se s ratios molal ratios in mineralizing fluids are proposed for independent selenium mineralization the minimum se s ratios in mineralizing fluids for independent selenium mineralization should be at least 10 6 10 5 and 10 4 at 100 200 and 300 c respectively for giant independent selenium deposits such as the la erma and qiongmo au se deposits in the western qingling mountains and yutangba se deposits in hubei province china the mineralizing fluids have reached much higher se s ratios ranging from 10 1 to 10 3 at 200 c this study also suggests that the equilibrium assemblage of pyrite ferroselite among the common ore minerals requires the highest se s ratios in mineralizing fluids followed in decreasing order by the assemblages of stibnite antimonselite galena clausthalite cinnabar tiemannite and acanthite argentite naumannite the assemblage of pyrite ferroselite can also be formed under relatively oxidizing conditions where h 2 se h 2 s ratios can be high enough for the formation of independent ferroselite

constraints on the origin of mafic alkaline volcanics and included xenoliths from oberon new south wales australia basanites and alkali basalts from oberon nsw australia contain variable abundances of small cr diopside lherzolite xenoliths despite a limited range in metamorphic textures and modal mineralogy there is significant variation in mineral chemistry mineral thermometric data applied to the geotherm of o reilly and griffin 1985 suggests equilibration over a narrow pressure interval corresponding to depths of 30 45 km these data show that significant compositional variations exist over a small depth interval in the subcontinental mantle

facies variation and mineralization in central europe from the late paleozoic through the cenozoic after the variscan orogeny from the upper carboniferous to the quaternary syn dia genetic and epigenetic mineralization occurred in the mid european basin uranium base metal sr f ba fe mn and au sn placer deposits are strata bound within clastic volcaniclastic and calcareous rocks some vein type and veinlike mineralization of post variscan age is found in the uplifted basement blocks and is spatially related to late variscan and late alpine unconformities post variscan mineralization may be subdivided into seven types with respect to the deposited environment of their host rocks 1 saprolite peneplain cu pb zn f ba fe mn 2 alluvial fan fe sn au u pb zn f ba 3 braided streams bed load fluvial systems pb zn u f ba 4 meandering to anastomosing streams mixed load fluvial systems u pb cu 5 high energy shore zone of lake margins or coastal regions fe pb cu u 6 low energy lake centers or near shore marine deposits lagoons fe pb zn cu u and 7 mixed terrigenous calcareous shelf deposits f sr zn pb there were various sources of metals for the strata bound mineralization during the late paleozoic and lower triassic the metals were supplied from volcanites and volcaniclastic rocks of calc alkaline affiliation volcanic arc the cu pb zn mining districts in the kupferschiefer are located above or close to a suture zone that delineates a former active plate margin with endogenous cu mo deposits following down the stratigraphic column in the footwall of the kupferschiefer the elements increase in reverse order of deposition from the lower triassic to the upper jurassic metamorphic and granitic rocks in variscan basement highs became exposed to chemical weathering and acted as the metal source denudation of the variscan basement is mirrored by the element spectrum of triassic strata bound deposits commencing with pb zn gneisses and leading to u deposits granites from the lower cretaceous onward some of the metals in the mineralization were derived from the basement most of the mineralization however originated from intrabasinal intra mesozoic redeposition e g ironstones five metallogenic sequences may be delineated four of which start with mineralization in a fluvial environment and terminate with precipitation of sr and f in a mixed clastic carbonate shelf environment sabkha metallogenic sequences reflect marine transgression and regression which may be correlated with different rifting and spreading stages in the atlantic ocean two major unconformities one caused by the variscan uplift the other by subhercynian and laramide movements may be traced across the basin supergene e g u mn fe and hypogene e g pb zn mineralizations are directly related to these first order geohydraulic planes minor unconformities and erosional surfaces also influenced the development of host environments of strata bound ore deposits and the termination of metallogenic sequences low relief erosional surfaces favored restricted water circulation and resulted in the formation oftransgressive black shales e g kupferschiefer the development ofa sabkha and its related mineral deposits also requires the presence of a low topography as well as an arid climate and resultant strong evapotranspiration karstification essential to mid european mississippi valley type deposits commenced more or less contemporaneously with the evolution of tidal fiats on these erosional surfaces in a supratidal zone and persisted until the hydrology was changed by a new transgression vein type mineralization related to these unconformities was at least in part supplied by sulfur and strontium from sabkha derived evaporites as suggested by sr and s isotope analyses it is difficult to define the time of formation ofpost variscan ore mineralization except for syngenetic fe mn u ores tertiary and fe cretaceous and sn placers quaternary the bulk of strata bound ore mineralization in the mid european basin formed by diagenetic and epigenetic processes the few age data and some evidence from basin subsidence suggest that there were two intervals of diagenetic and or epigenetic ore mineralization the period from lower triassic to upper dogger correlates with early rifting in the central parts of the atlantic ocean another set of data which derived from u f deposits in the upper cretaceous and mississippi valley type deposits attests to a thermal and fluid influx from deepseated rifts rhine graben ohre rift during the late tertiary

a sr isotope study on fluorite and siderite from post orogenic mineral veins in the eastern harz mountains germany rb sr isotope data for siderite and fluorite from sediment hosted epithermal mineral veins in the eastern harz mountains germany are presented several fluorite and siderite bearing paragenetic stages have been proposed for these veins with the most important mineralization being related to a quartz sulfide and a subsequent calcite fluorite quartz stage which occurred at 226 1 and 209 2 ma respectively our rb sr data do not permit the identification of distinct generations of siderite and fluorite but rather reveal straight internal mixing relations reflecting mixing of fluids or differential fluid rock interaction processes this indicates merely two significant phases of mineral deposition related to the quartz sulfide and calcite fluorite quartz stages it is shown that the paleozoic sedimentary host rocks of the veins are the most likely source for the siderite sr whereas fluorite displays a two component mixture between sedimentary sr and radiogenic sr derived from locally occurring permian metavolcanic rocks

evolution of mauna kea volcano inferences from lava compositions recovered in the hawaii scientific drilling project the lower 776 m of core recovered during the initial phase of the hawaii scientific drilling project hsdp contains lavas erupted from mauna kea volcano tholeiitic and alkalic basalts including an fe ti rich flow are intercalated in the upper 58 m of mauna kea lavas similar basaltic sections are subaerially exposed on the lower east flank of mauna kea the fe ti rich lavas reflect large amounts of clinopyroxene plagioclase and olivine fractionation within the crust and upper mantle but the range from tholeiitic to alkalic compositions reflects variable extents of melting of a garnet bearing source based on abundances of incompatible elements the extent of melting for a basanitoid was a factor of 2 less than that for nearly coeval tholeiitic lavas all flow units in the lower 718 m of the hsdp core are tholeiitic lavas their variability in major element compositions reflect variable accumulation of olivine incompatible element abundance ratios in these lavas reflect a complex temporal variation in extent of melting within the tholeiitic part of the core lavas from 800 m to 950 m formed by the largest extent of melting whereas tholeiitic lavas from the bottom of the core and from just below the tholeiitic to alkalic transition formed by lower degrees of melting inferred melt compositions at 16 mgo show that the 200 to 400 ka mauna kea lavas from the hsdp core and the 250 ka subaerial exposures define an inverse correlation between sio2 and feo contents based on experimental studies this correlation is caused by differing pressures of melt segregation furthermore abundances of nb and sio2 are also inversely correlated in these calculated melts in general the younger lavas are relatively enriched in feo and incompatible elements but are depleted in sio2 these trends are interpreted to reflect an overall trend of increasing pressure of melt segregation and decreasing extent of melting with decreasing eruption age there are however geochemical variations which indicate short term reversals in this long term trend previously the geochemical trends accompanying the transition from tholeiitic to alkalic volcanism at hawaiian volcanoes have been interpreted as reflecting the effects of increasing distance from the plume axis the long term geochemical trends of tholeiitic lavas in the hsdp core also reflect migration of mauna kea away from the hawaiian plume

metal accumulation during and after deposition of the kupferschiefer from the sangerhausen basin germany abstract a densely sampled profile 58 cm in thickness composed of 13 samples of the kupferschiefer and overlying zechstein carbonates from the sangerhausen basin germany has been analysed by various geochemical and microscopic methods in order to clarify the mechanism of base metal accumulation in this location the kupferschiefer is only slightly influenced by the hematite bearing oxidized fluids called rote faule the determination of facies dependent parameters along the profile indicates that kupferschiefer from the sangerhausen basin was largely deposited in a marine environment only at the beginning of kupferschiefer sedimentation did euxinic conditions prevail the bottom part of the profile is significantly enriched in trace elements such as cu ph zn as co ag and u the cu concentration amounts to 19 88 wt post depositional oxidation of the organic matter is observed only in the transition zone between the kupferschiefer and the zechstein conglomerate indicating the influence of ascending oxidizing brines microscopic analyses show that only fe sulfides form framboidal textures cu minerals are present along the total profile preferentially in fractures and as patchy structures composed of chalcocite chalcopyrite and bornite in the highly mineralized bottom section cu sulfides are associated with pyrobitumen sparry calcite and arsenopyrite results from maturation studies of organic matter suggest that the maximum temperature affecting the kupferschiefer was approximately 130 c a 3 step process of metal accumulation is proposed during deposition of the sediment framboidal pyrite and pyrite precursors were precipitated by bacterial so 4 2 reduction bsr during diagenesis the pyrite and pyrite precursors were largely replaced by mixed cu fe minerals and by chalcocite pr in the section with very high cu contents 8 reduced sulfur from fe sulfides was not sufficient for precipitation of cu and other trace metals from ascending solutions in this part of the profile thermochemical so 4 2 reduction tsr occurred after pyrite replacement as indicated by the presence of pyrobitumen and sparry calcite

upper mantle velocity structure estimated from ps converted wave beneath the north eastern japan arc summary the upper boundary of the descending oceanic plate is located by using ps waves converted from p to s at the boundary in the tohoku district the north eastern part of honshu japan the observed ps p time data are well explained by a two layered oceanic plate model composed of a thin low velocity upper layer whose thickness is less than 10 km and a thick high velocity lower layer the upper and lower layers respectively have 6 per cent lower and 6 per cent higher velocity than the overriding mantle the estimated location of the upper boundary is just above the upper seismic plane of the double planed deep seismic zone this result indicates that events in the upper seismic plane at least in the depth range from 60 to 150 km occur within the thin low velocity layer on the surface of the oceanic plate

estimation of the degree of partial melting by na2o k2o and al2o3sio2 of basic magmas abstract equations for estimating the degree of partial melting f of basic magmas in terms of na2o k2o and al 2 o 3 sio 2 and based on previously published batch equilibrium melting and experimental and petrochemical data are proposed as follows for f 0 10 0 50 f a 1 0 957 na 2 o k 2 o s na 2 o k 2 o m 0 0149 for f f b 1 0 694 na 2 o k 2 o s na 2 o k 2 o m 0 0516 for f 0 15 0 35 f c 0 9348 al 2 o 3 sio 2 s al 2 o sio 2 m 0 1532 0 108 al 2 o 3 sio 2 s al 2 o sio 2 m 0 597 for f f d 1 2437 al 2 o 3 sio 2 s al 2 o sio 2 m 0 2470 3 308 al 2 o 3 sio 2 s al 2 o sio 2 m 0 237 the subscripts s and m denote source and supposedly primary magma or melt respectively a correct estimate or choice of source composition and composition of primary magma for the calculation is important if both compositions can be reasonably assigned or estimated then the degree of partial melting can be calculated from one of these equations with errors generally

oxygen osmium isotope systematics of west maui lavas a record of shallow level magmatic processes new 18 o and 187 os 188 os data from late shield building stage lavas from west maui volcano hawai i indicate that a range of distinct shallow level processes can affect compositions of plume generated ocean island magmas the relative ages of the samples studied were determined either on the basis of field relationships or from collection depth in a water well the stratigraphically lower lavas have os 61 399 ppt initial 187 os 188 os 0 1311 0 1324 and 18 o olivine 4 53 4 88 the stratigraphically higher lavas have os 20 273 ppt initial 187 os 188 os 0 1323 0 1390 with the exception of one low os sample with 187 os 188 os 0 1517 and 18 o olivine 4 73 5 21 these compositions are generally similar to those of kea type hawaiian lavas from mauna kea and kilauea volcanoes but in detail there are some significant differences between the west maui lavas and other kea type lavas the stratigraphically lower lavas have 187 os 188 os similar to those previously observed for mauna kea and kilauea lavas and define a nearly flat 87 sr 86 sr vs 187 os 188 os trend that is consistent with assimilation by these magmas of small degree melts of pacific oceanic crustal gabbros the stratigraphically higher west maui lavas extend to 187 os 188 os higher than observed at mauna kea or kilauea this probably results from interaction of these magmas with the hydrothermally altered volcanic edifice during the waning phases of the shield building stage this process is likely to affect the isotope systematics of os and o but will have little effect on those of hf nd pb or sr

the tholeiite to alkalic basalt transition at haleakala volcano maui hawaii previous studies of alkalic lavas erupted during the waning growth stages 0 9 ma to present of haleakala volcano identified systematic temporal changes in isotopic and incompatible element abundance ratios these geochemical trends reflect a mantle mixing process with a systematic change in the proportions of mixing components we studied lavas from a 250 m thick stratigraphic sequence in honomanu gulch that includes the oldest 1 1 ma subaerial basalts exposed at haleakaka the lower 200 m of section is intercalated tholeiitic and alkalic basalt with similar isotopic sr nd pb and incompatible element abundance ratios e g nb la la ce la sr hf sm ti eu these lava compositions are consistent with derivation of alkalic and tholeiitic basalt by partial melting of a compositionally homogeneous clinopyroxene rich garnet lherzolite source the intercalated tholeiitic and alkalic honomanu lavas may reflect a process which tapped melts generated in different portions of a rising plume and we infer that the tholeiitic lavas reflect a melting range of 10 to 15 while the intercalated alkalic lavas reflect a range of 6 5 to 8 melting however within the uppermost 50 m of section 87sr 86sr decreases from 0 70371 to 0 70328 as eruption age decreased from 0 97 ma to 0 78 ma we infer that as lava compositions changed from intercalated tholeiitic and alkalic lavas to only alkalic lavas at 0 93 ma the mixing proportions of source components changed with a morb related mantle component becoming increasingly important as eruption age decreased

melting in the hawaiian plume at 1 2 ma as recorded at maui nui the role of eclogite peridotite and source mixing 1 the volcanoes of maui nui west moloka i east moloka i lana i west maui haleakala and kaho olawe record hawaiian magmatism at 1 2 ma lavas from these volcanoes nearly span the compositional range erupted from all the hawaiian volcanoes over the past 5 myr and represent both the kea and ko olau compositional end members of hawaiian lavas many aspects of major and trace element and isotope compositions of hawaiian shield stage lavas are consistent with ancient recycled oceanic lithosphere in the plume sources of kea and ko olau type magmas lassiter and hauri 1998 blichert toft et al 1999 hypotheses that describe the compositional range of hawaiian lavas as originating from ancient oceanic lithosphere in the hawaiian plume implicitly or explicitly infer lithologic heterogeneity in the plume we present trace element models for the origin of these end members that explicitly address the petrologic complexities of melting eclogite derived from ancient oceanic lithosphere in the plume trace element la nb sm yb sm hf and sm nb major element and isotope compositions of lana i which erupts dominantly ko olau type lavas are consistent with the origin of these lavas in large degree 60 70 melts of ancient upper oceanic crust basalt sediment that mix with plume derived haleakala type melts trace element sm yb hf zr and hf nb and isotope compositions of west maui and east moloka i which erupt dominantly kea type magmas are consistent with an origin in ancient depleted oceanic lithosphere that has been refertilized with moderate degree melts 10 30 of associated crustal gabbro the physical mechanisms melt melt versus melt solid mixing through which the oceanic crustal components melt and mix within the plume lead to the generation of isotopically homogeneous kea type lavas and isotopically heterogeneous ko olau type lavas the volcanoes of maui nui record the exhaustion of the ko olau component and the initiation of the kea component as dominant compositional end members in the hawaiian plume

beryllium systematics in young volcanic rocks implications for 10 be beryllium is an incompatible trace element that closely parallels neodymium in its geochemical behavior be analyses conducted on well characterized oceanic and arc volcanic rock suites as well as on marine sediments suggest a bulk solid liquid distribution coefficient of 0 03 0 06 for melting of the mantle and crystallization of basalts the be nd ratio for many volcanic rocks from diverse tectonic environments is approximately 05 similar to the ratio in chondrites be data for samples from volcanic arcs show that there are significant variations in 10be 9be among different arcs and that variations in 10be are not due to variations in be concentration alone for at least one volcano bogoslof the 10be 9be ratio is constant for samples that vary by a factor of three in both their be and 10be concentrations suggesting that 10be is an inherited magmatic signature and not simply a result of contamination near the surface in addition the be nd and pb isotope systems for this volcano are all consistent with a model in which small amounts of sediment were incorporated into the bogoslof source region provided the mantle wedge has the isotopic characteristics of depleted morb since 10be exists only in the uppermost tens of meters of oceanic sediments the data suggest an efficient return flux of sediment to the mantle at subduction zones

isotopic age determinations of crystalline rocks of the upper harz mountains germany dating of crystalline rocks occurring in the upper harz mountains was carried out by means of u pb isotope investigations on zircons and sphene as well as by rb sr isotope measurements on whole rock samples and biotites

provenance of cretaceous clastics in the subhercynian basin constraints to exhumation of the harz mountains and timing of inversion tectonics in central europe the harz mountains and the adjacent subhercynian cretaceous basin figure as the most prominent surface representative for late cretaceous inversion structures in central europe facies depositional architecture and provenance of the basin fill reflect mechanisms and timing of the exhumation of the harz from hauterivian to early santonian there is no evidence for detrital input from the nearby harz area sediments are mature quartzarenites derived from paleozoic basement rocks and or recycled permian to mesozoic sedimentary rocks this situation changed drastically in middle to late santonian when freshly exhumed and eroded mesozoic sedimentary cover rocks of the harz were delivered into the basin feldspar and lithoclasts reflect erosion of triassic and in places jurassic to turonian strata apatite and garnet in heavy mineral spectra are derived from largely unweathered lower triassic buntsandstein as indicated by apatite and garnet chemistry in early campanian paleozoic lithoclasts indicate erosion cutting down into the basement of the harz simultaneous strong decrease of feldspar garnet and apatite suggest an almost complete removal of the 2 3 km thick mesozoic cover of the harz within only 2 4 myr this translates into an exhumation rate of approximately 1 mm a consistent with apatite fission track data from granitoid rocks of the harz mountains

seismological evidence on velocity structure inside the subducting pacific plate abstract a three dimensional seismic tracing scheme was applied to resolve the complex inside structure of the subducting plate and it was found that a model with a rapid increase in p wave velocity in the upper few tens of kilometres thickness and a gradual decrease within the rest of the plate explains the observation better than models with velocity maxima at different locations

trace element mobility during spheroidal weathering of basalts and andesites in hawaii and guatemala abstract trace element mobility has been studied in spheroidally weathered corestone shell complexes developed on late tertiary and quaternary volcanic rocks the parent materials are basalts and andesites related to 1 a subduction zone tecuamburro and moyuta volcanoes guatemala and 2 a hot spot hawaiian islands of oahu maui and hawai i the initial major element compositions are largely preserved in the corestones each corestone sample shows major element abundances characteristic of the different magmatic processes through which the lavas were generated however the changes in trace element compositions due to weathering show similar patterns in the corestone shell complexes independent of the tectonic setting and age element mobility within the different corestone shell complex was determined using an isovolumetric reference frame in this method bulk density is chosen as an independent measure of the extent of weathering based on volumetric concentrations the notion of element immobility cannot be applied to all the corestone shell complexes elements commonly assumed to be immobile e g zr ti and al vary in volumetric concentration for some corestone shell complex despite petrographic evidence of only minor weathering two corestones oahu and tecuamburro have become enriched in ree 3 relative to other lava flows from the same volcanoes and display negative ce anomalies the exfoliated shells from these complexes tend to have lower concentrations of ree 3 and have positive ce anomalies the fractionation of ce from the other rare earth elements ree is inferred to be a manifestation of changes in the valence state of ce from trivalent to tetravalent under oxidizing conditions in settings where the development of corestone shell complex is advanced an acidic solution can mobilize trivalent ree leach them out of more extensively weathered materials and transport them to less acidic portions of the regolith undergoing incipient weathering the precipitation of the ree 3 in the rinds and centers of the corestones are likely due to increases of the ph of the weathering solution systematic weathering induced ree behavior enrichment of most ree with lesser ce enrichment resulting in a negative ce anomaly can be discerned even in corestone samples that exhibit major element abundances and petrographic features otherwise similar to unweathered basalts and andesites

authigenic heavy minerals a clue to unravel supergene and hypogene alteration of marine and continental sediments of triassic to cretaceous age se germany abstract siliciclastic continental marine sediments of triassic through jurassic age resting unconformably on the crystalline rocks of the central european variscides and marine deltaic sediments of cretaceous age deposited in a narrow embankment are well exposed in the wackersdorf area se germany these sediments were investigated for their variegated spectrum of authigenic heavy minerals hm and heavy mineral hm aggregates the majority of which belongs to the semi opaque group of minerals using petrographic and ore microscopy supplemented by sem edx and by empa these hms originated from supergene weathering diagenesis and hypogene alteration hydrothermal processes related to faults and unconformities the physical and chemical conditions during which these authigenic minerals developed are discussed by means of eh ph diagrams under different temperature conditions ilmenite pseudorutile anatase series may be used as a measure for the intensity of supergene alteration under rising oxygen fugacity pseudorutile and anatase also formed during hypogene alteration and developed different crystal morphologies compared with their supergene counterparts found in the above series the authigenic hm fluorite barite niccolite acanthite silver bravoite ni marcasite pyrite sphalerite galena chalcopyrite chalcocite and rhabdophane ce were produced by hypogene hydrothermal processes the hypogene mineralization in the mesozoic foreland sediments belongs to two types 1 epi mesothermal ree f mineralization controlled by the structural reactivation along a deep seated lineamentary fault zone and 2 epithermal ni cu zn as s mineralization related to the geohydraulic plane of the late variscan unconformity permo triassic peneplain

clausthalite pbse and tiemannite hgse from the type locality new observations and implications for metallogenesis in the harz mountains germany abstract clausthalite and tiemannite from the type locality clausthal in the harz mountains germany have virtually gone undocumented since their discovery in the nineteenth century the minerals and their selenide assemblages are here documented in historical samples from the konigin charlotte mine in the former clausthal pb zn ag mining district clausthalite and tiemannite are the main selenide components naumannite is generally subordinate whereas klockmannite and eskebornite are accessory minerals the absence of inversion lamellae in naumannite constrains the formation temperature to 87 sr 86 sr values of 0 70914 and 0 71133 for two samples of tiemannite aggregates containing celestine anhydrite inclusions the clausthal selenide assemblages postdated the main sulfide bearing polymetallic vein style mineralisation of the harz mountains

deep magma transport at kilauea volcano hawaii the shallow part of kilauea s magma system is conceptually well understood long period and short period brittle failure earthquake swarms outline a near vertical magma transport path beneath kilauea s summit to 20 km depth a gravity high centered above the magma transport path demonstrates that kilauea s shallow magma system established early in the volcano s history has remained fixed in place low seismicity at 4 7 km outlines a storage region from which magma is supplied for eruptions and intrusions brittle failure earthquake swarms shallower than 5 km beneath the rift zones accompany dike emplacement sparse earthquakes extend to a decollement at 10 12 km along which the south flank of kilauea is sliding seaward this zone below 5 km can sustain aseismic magma transport consistent with recent tomographic studies long period earthquake clusters deeper than 40 km occur parallel to and offshore of kilauea s south coast defining the deepest seismic response to magma transport from the hawaiian hot spot a path connecting the shallow and deep long period earthquakes is defined by mainshock aftershock locations of brittle failure earthquakes unique to kilauea whose hypocenters are deeper than 25 km with magnitudes from 4 4 to 5 2 separation of deep and shallow long period clusters occurs as the shallow plumbing moves with the volcanic edifice while the deep plumbing is centered over the hotspot recent gps data agrees with the volcano propagation vector from kauai to maui suggesting that pacific plate motion azimuth 293 58 and rate of 7 4 cm yr has been constant over kilauea s lifetime however volcano propagation on the island of hawaii azimuth 3258 rate 13 cm yr requires southwesterly migration of the locus of melting within the broad hotspot deep long period earthquakes lie west of the extrapolated position of kilauea backward in time along a plate motion vector requiring southwesterly migration of kilauea s magma source assumed ages of 0 4 my for kilauea and 0 8 my for mauna loa are consistent with this model younger ages would apply if kilauea began its growth south of the locus of maximum melting as is true for loihi seamount we conclude that kilauea is fed from below the eastern end of the zone of deep long period earthquakes magma transport is vertical below 30 km then sub horizontal following the oceanic mantle boundary separating plagioclase and spinel peridotite then near vertical beneath kilauea s summit the migration of the melting region within the hotspot and kilauea s sampling of different sources within the melting region can explain 1 the long term geochemical separation of

geochemical and isotopic monitoring of mt etna 1989 1993 eruptive activity bearing on the shallow feeding system two flank eruptions took place at mt etna during 1989 1993 the former september october 1989 produced lavas among the most primitive of this century while the latter december 1991 march 1993 was unusually long lasting and the largest of the last three centuries alkali basalts of 1989 displayed initial enrichments of rb and k accompanied by an higher value of radiogenic sr and isotopic disequilibrium between host rock and clinopyroxene 0 70364 and 0 70356 respectively subsequently within one week k rb and 87sr86sr ratio decreased to constant values 87sr86sr 0 70355 nd isotopic ratio did not show significant variations these features can be explained by a selective contamination process involving essentially rb k and radiogenic sr the bulk from the 1991 1993 eruption hawaiites were erupted between january and may 1992 in this period lavas here called jml were characterised by uniform geochemical and isotopic compositions and sr isotopic equilibrium between whole rock and pyroxene 0 70355 in other periods december 1991 and june 1992 we observed lower and variable sr isotopic compositions coupled with disequilibria between lavas and their clinopyroxenes 0 70351 in the w r and 0 70345 in the cpx of the sample of 15 december 1991 starting from june 1992 the products seem to reveal fractionation effects as suggested by the continuous rise in concentrations of incompatible elements when the observed variability cannot be ascribed to fractionation effects we are not able to discriminate mixing from selective contamination however lavas erupted during december 1991 evolved towards the isotope composition of jml that was never exceeded moreover the regular behaviour of rb k and radiogenic sr of 1989 lavas was not observed during the 1991 1993 eruption thus we prefer to interpret these variations as mainly due to mixing processes between an end member of jml composition and another one having the same or lower isotopic composition of the clinopyroxene found in the sample of december 1991 several petrogenetic processes are contemporaneously active at mt etna they encompass magma mixing selective contamination and fractional crystallization their relative importance varies according to the original volume of each magma batch and to the status of the shallow feeding system the complexity of these processes acting in the short time span of a few months claims caution about the geochemical representativity of a single lava sample for each eruption

intershield geochemical differences among hawaiian volcanoes implications for source compositions melting process and magma ascent paths as hawaiian volcanoes develop their lavas systematically change in composition and isotopic ratios of sr nd and pb these trends provide important constraints for understanding plume related volcanism as a volcano migrates away from the hotspot there are also geochemical differences between hawaiian shields in particular lavas from adjacent shields such as kilauea and mauna loa on hawaii and koolau and waianae on oahu have significant differences in abundances of some major and incompatible elements and isotopic ratios of sr nd and pb some incompatible element abundance ratios such as zr nb and sr nb are correlated with intershield differences in sr and nd isotope ratios but these isotopic ratios are not correlated with intershield differences in major element composition or even parent daughter abundance ratios such as rb sr and sm nd moreover at kilauea and mauna loa the intershield differences have apparently persisted for a relatively long time perhaps 100 ka these intershield geochemical differences provide important constraints on plume volcanism specifically i each volcano must have distinct magma ascent paths from the region of melt segregation ii the 25 50 km distance between adjacent but geochemically distinct shields requires that the sources vary on a similar scale and that the melt production region is similarly restricted the absence of correlations between lava compositions and radiogenic isotope ratios provides evidence for significant differences in melting process such as each shield forming by a different mean extent of melting with melt segregation at different mean pressures two types of models are consistent with the intershield geochemical differences i a relatively large radius ca 40 km plume conduit with a systematic spatial distribution of geochemical heterogeneities or ii a small radius less than 20 km plume conduit composed of geochemically distinct diapirs because relatively small radius diapirs of limited vertical extent are too small to create the large hawaiian shields a possible alternative is a continuous conduit containing solitary waves which transport geochemically distinct packets of material

the behavior of the uranium decay chain nuclides and thorium during the flank eruptions of kilauea hawaii between 1983 and 1985 abstract the concentrations of members of the 238u decay chain and 232th have been determined for the lavas that erupted on the east rift zone of kilauea volcano hawaii puu oo between january 1983 and january 1985 there was a decrease during the first 180 days in the abundances of all nuclides following the behavior of the incompatible elements 230th 238u varies with 232th 238u yielding a batch process age for the source magma of 127 800 28 500 2 y similar to east pacific rise basalts no 226ra 230th disequilibrium was evident at puu oo although haleakala and loihi show significant excesses of 226ra over 230th the initial 210pb excess relative to 226ra implies strong incompatibility of 210pb probably with the help of chloride complexing and the deficiency in later episodes indicates volatilization from the melt mediated by the formation of volatile chloride compounds

tomography the geoid and plate motions the dynamics of the earth s mantle and its relationship to mantle structure as revealed by seismic tomography the geoid and plate motions are discussed in a critical review of u s research from the period 1987 1990 sections are devoted to plates and mantle convection seismic anomalies flow and the geoid subducted slabs and the 670 km discontinuity the physical properties of the mantle plumes and computational and experimental modeling efforts also included is a comprehensive bibliography for the period 248 refs

petrogenesis of dunite xenoliths from koolau volcano oahu hawaii implications for hawaiian volcanism ultramafic xenoliths from koolau volcano on the island of oahu hawaii are divided into spinel lherzolite pyroxenite and dunite suites on the basis of a study of the petrography and mineral compositions of 43 spinel lherzolites 12 pyroxenites and 20 dunites the following characteristics of the dunites in relation to the other nodule types and to hawaiian lavas emerge 1 the forsterite content of olivines in the koolau dunites fo82 6 fo89 7 overlap those of hawaiian tholeiitic and alkalic lavas and are generally lower than those in abyssal lherzolites and dunites and in koolau spinel lherzolites 2 most of the dunites contain no orthopyroxene all except two contain chrome spinel and a few contain interstitial plagioclase and clinopyroxene 3 chrome spinels from the koolau dunites are distinctly higher in cr cr al lower in mg mg fe2 and higher in tio2 than those from abyssal basalts and peridotites chrome spinels in the dunites correspond closely in composition to chrome spinels in hawaiian tholeiitic and alkalic lavas 4 the abundance of dunite relative to other nodule types decreases outward from the central part of the volcano the dunites are interpreted not as residues of partial fusion of the mantle but as crystal accumulations stored at shallow depths beneath the central part of koolau volcano and derived from picritic magmas parental to the shield building tholeiitic lavas

magma solidification processes beneath kilauea volcano hawaii a quantitative textural and geochemical study of the 1969 1974 mauna ulu lavas sents a late magma component formed in the summit magma storage region our results are consistent with the hypothesis that the components of the mu magmas followed two different routes the deformed olivine bearing magma moved along the deep basal

geochemical variations in lavas from kahoolawe volcano hawaii evidence for open system evolution of plume derived magmas the kahoolawe shield volcano produced precaldera and caldera filling tholeiites and mildly alkalic post caldera lavas that petrographically and compositionally resemble such lavas from other hawaiian shield volcanoes however kahoolawe tholeiites display wide ranges in incompatible trace element ratios e g nb th 9 24 th ta 0 6 1 3 87sr 86sr 0 70379 0 70440 143nd 144nd 0 51273 0 51298 and 206pb 204pb 17 92 18 37 the isotopic variation exceeds that at any other hawaiian shield volcano and spans about half the range for all hawaiian tholeiites quasi cyclic temporal evolution of kahoolawe tholeiites is consistent with combined fractional crystallization and periodic recharge by primitive magmas ratios of highly incompatible trace elements and sr nd and pb isotopic ratios from coherent sub trends that reflect recurrent interactions between variably evolved magmas and two other mantle components whose compositions are constrained by intersections between these trends the most mgo rich kahoolawe tholeiites are partial melts of a high nb th 23 5 ascending plume possibly comprising ancient subducted oceanic lithosphere slightly evolved tholeiites experienced combined crystal fractionation and assimilation afc of material derived from a distinct reservoir nb th 9 of asthenospheric derivation the most evolved tholeiites display compositional shifts toward a third component having mid ocean ridge basalt like isotopic ratios but enriched oib like trace element ratios representing part of the lithospheric mantle or melts thereof periodic recurrence of all three magma variants suggests that eruptions may have tapped coeval reservoirs distributed over a large depth range kahoolawe provides new evidence concerning the nature of the hawaiian plume the distribution of compositional heterogeneities in the suboeanic mantle and the processes by which hawaiian tholeiites form and evolve

1998 eruption at volcan cerro azul galapagos islands i syn eruptive petrogenesis the 1998 eruption of volcn cerro azul in the galpagos islands produced two intra caldera vents and a flank vent that erupted more than 1 0 10 8 m 3 of lava lava compositions changed notably during the 5 week eruption and contemporaneous eruptions in the caldera and on the flank produced different compositions lavas erupted from the flank vent range from 6 3 to 14 1 mgo nearly the entire range of mgo contents previously reported from the volcano on site monitoring of eruptive activity is linked with petrogenetic processes such that geochemical variations are evaluated in a temporal con text lavas from the 1998 eruption record two petroge netic stages characterized by progressively more mafic lavas as the eruption proceeded crystal compositions whole rock major and trace element compositions and isotope ratios indicate that early lavas are the product of mixing between 1998 magma and remnant magma of the 1979 eruption intra caldera lavas and later lavas have no 1979 signature but were produced by the 1998 mag ma incorporating olivine and clinopyroxene xenocrysts thus early magma petrogenesis is characterized by mix ing with the 1979 magma followed by the magma pro gressively entraining wehrlite cumulate mush

origin of archean ferropicrites geochemical constraints from the boston creek flow abitibi greenstone belt ontario canada abstract new major element trace element and nd isotope data for non cumulate samples from the fe enriched boston creek flow bcf have permitted the development of a petrogenetic model for the origin of this geochemically unusual flow the data reveal high contents of nb ta lree ti ni co and ir as well as in fe and low contents of al al 2 o 3 tio 2 6 hree y v sc pd and pt compared to komatiitic rocks and typical tholeiitic rocks of similar magnesian content primitive mantlenormalized incompatible trace element profiles for the bcf peak in the ta nb la region la sm n 2 0 la yb n 5 4 th ta n 0 7 and bottom in the al sc region la sc n 11 0 la al n 9 7 and reveal slight depletions in zr and hf relative to mree sm zr n 1 3 and ti nd t 2720 ma values for the flow are 2 5 indicating derivation of the parental melt from a long term depleted mantle source these geochemical characteristics are somewhat similar to those of modern oceanic within plate basalts these unusual geochemical characteristics and comparisons to proterozoic ferropicrite flows at pechenga russia indicate that the bcf is ferropicritic rather than komatiitic in affinity alteration assimilation and magma mixing and crystal fractionation processes cannot explain the bcf therefore the distinctive geochemistry of the bcf is concluded to have been a feature of its mantle source and is attributed to mantle processes models involving melting of core material in the mantle source may explain the enrichment of fe and high ni in the bcf but they are contradicted by the relatively low pt and pd models involving olivine equilibration in the mantle are consistent with the high ni and co similar composition of assumed bcf parental melt equilibrium olivine at 25 kbar and that of modern fe rich lherzolite olivine fo85 and comparison of the mgo and feo content of the melt with those of experimentally derived melts that are saturated in olivine at high pressure models involving garnet equilibration in the mantle could explain the low al hree y v and sc but are contradicted by the very low al2o3 content of the assumed parental melt compared with those of experimentally derived melts of similar feo and mgo content that are saturated in garnet at high pressure alternatively the unusual geochemistry of the bcf can be explained by a two source component mixing model somewhat like those commonly accepted for oceanic within plate basalts petrogenesis the first source component is peridotite depleted by extraction of melt s prior to generation of the bcf parental melt which explains the relatively high compatible element contents and low al hree sc pd and pt contents the second source component is highly enriched small degree melt fractions formed at mantle depths sufficient to stabilize garnet majorite which explains the relative enrichments in fe ti and the highly incompatible elements mixing of the two source components must have occurred immediately prior to melting to maintain the depleted nd isotope composition and may have been facilitated by metasomatic amphibole stabilization at relatively shallow 100 km depths in the mantle

a petrologic perspective of kīlauea volcano s summit magma reservoir two hundred years of magmatic history are documented by the lavas and tephra sampled from k olauea s historical summit eruptions this paper presents detailed petrographic and geochemical data for a comprehensive suite of samples erupted within or near k olauea s summit caldera since the 17th century our results elucidate the range of magmatic processes that operate within the volcano s summit magma reservoir and document two compositional trends that span nearly the entire known range for the volcano prior to the 1924 summit crater collapse a trend of increasing incompatible element and cao and decreasing sio2 abundances at a constant mgo prevailed thereafter the trend reversed direction and has persisted for the rest of the 20th century including during the current puau a oa o eruption the rapid and systematic nature of these temporal geochemical variations indicates that the summit reservoir is a single relatively small body rather than a plexus of dikes and sills olivine fractionation is the dominant petrologic process within this reservoir petrographic observations and olivine and whole rock geochemical data suggest that the summit reservoir has a crown of aphyric more evolved low density magma differentiation within this crown involving clinopyroxene and plagioclase is more extensive than previously recognized in k olauea summit lavas the effects of crystal fractionation are superimposed upon an evolving hybrid magma composition produced by mixing new mantle derived magmas with more fractionated reservoir magma frequent eruptions of these hybrid reservoir magmas document the rapid variation in parental magma composition these compositional variations correlate with magma supply rate both are thought to be influenced by the degree of melting of small scale source heterogeneities within the hawaiian plume however k olauea s source compositions and partial melting processes have varied only within a narrow range over the past 350 kyr

decoupled evolution of nd and sr isotopes in the continental crust and the mantle nd and sr isotopes evolve independently in clastic sedimentary rocks and the continental crust as a whole because sr is recycled preferentially from the continents to the mantle as a result the differentiation age of the mantle inferred from sr isotopes and the mean rb sr age of the continental crust are younger than their true ages

the petrology of some picrites from mauna loa and kilauea volcanoes hawaii the mineralogy and chemistry of picrites from mauna loa and kilauea have been investigated to evaluate for hawaiian tholeiitic picrites the contrasting genetic models which have been proposed for these mg rich volcanics namely products of direct crystallization of high mg melts 20 25 mgo or the result of accumulation of olivine phenocrysts into less mg rich melts genetic interpretations rely heavily on mg fe partitioning relations between olivines and their picrite hosts although the 100 mg mg fe2 ratios m of picrites are wide ranging m 73 6 82 9 for fe2o3 feo 0 15 with mgo as high as 27 8 the average 100 mg mg fe ratios mg of the cores of olivine phenocrysts megacrysts show only restricted compositional variation mg 87 2 89 0 successive olivine generations are progressively more fe rich olivine liquid mg fe partitioning data and the mn and ni abundances in olivine phenocrysts collectively indicate that they were precipitated by mg rich basaltic melts with 12 14 mgo spinel compositions range from liquidus magnesiochromites occurring mainly as inclusions in olivine phenocrysts to groundmass titanomagnetites which crystallized at nearsolidus temperatures the cr2o3 contents and m values of liquidus magnesiochromites suggest that their parent melts were neither mg rich picritic mgo 20 nor relatively mg poor basaltic types