gis based variability of building materials towards the ile de france cuesta paris basin france inventory distribution uses and relationship with the environment the pays re mois in the eastern paris basin is an administrative area of 1394 km2 in the surroundings of reims france two main geological substrata are separated by the i le de france cuesta the tertiary substratum in the western part is composed of various types of geomaterials clay sandstone limestone burrstone whereas the substratum in the eastern part is composed only of cretaceous chalk a field survey in each commune of the pays re moisidentified 26 building materials documented in a geographic information system database gis database that includes information about them lithology petrographical and petrophysical data weathering and the corresponding buildings e g town georeferenced data building type position on the fac ade the spatial analysis of the building materials distribution standard deviational ellipse with gis identifies their uses and the criteria established for the selection of the materials availability efficiency workability and durability some lithologies were preferred for particular buildings or selected for their efficiency in specific positions the study also defines the relation between the stones origin local and non local stones and their application this database is useful to establish stone replacement strategies in the pays re mois

age and petrology of alkalic postshield and rejuvenated stage lava from kauai hawaii at the top of the waimea canyon basalt on the island of kauai rare flows of alkalic postshield stage hawaiite and mugearite overlie tholeiitic flows of the shield stage these postshield stage flows are 3 92 ma and provide a younger limit for the age of the tholeiitic shield stage the younger koloa volcanics consist of widespread alkalic rejuvenated stage flows and vents of alkalic basalt basanite nephelinite and nepheline melilitite that erupted between 3 65 and 0 52 ma all the flows older than 1 7 ma occur in the west northwestern half of the island and all the flows younger than 1 5 ma occur in the east southeastern half the lithologies have no spatial or chronological pattern the flows of the koloa volcanics are near primary magmas generated by variable small degrees of partial melting of a compositionally heterogeneous garnet bearing source that has about two thirds the concentration of p2o5 rare earth elements and sr of the source of the honolulu volcanics on the island of oahu the same lithology in the koloa and honolulu volcanics is generated by similar degrees of partial melting of distinct source compositions the lavas of the koloa volcanics can be generated by as little as 3 percent to as much as 17 percent partial melting for nepheline melilitite through alkalic basalt respectively phases that remain in the residue of the honolulu volcanics such as rutile and phlogopite are exhausted during formation of the koloa volcanics at all but the smallest degrees of partial melting the mantle source for kauai lava becomes systematically more depleted in 87sr 86sr as the volcano evolves from the tholeiitic shield stage to the alkalic postshield stage to the alkalic rejuvenated stage at the same time the lavas become systematically more enriched in incompatible trace elements on a shorter timescale the lavas of the koloa volcanics display the same compositional trends but at a lower rate of change the source characteristics of the koloa volcanics considered along with those of the honolulu volcanics support a mixing model in which the source of rejuvenated stage lava represents large percent melts of a plume source mixed with small amounts of small percent melts of a heterogeneous mid ocean ridge source

relations among subduction parameters clues to the dynamics of the subduction process are found in the many measurable parameters of modern subduction zones based on a critical appraisal of the geophysical and geological literature 26 parameters are estimated for each of 39 modern subduction zones to isolate causal relationships among these parameters multivariate analysis is applied to this data set this analysis yields empirical quantitative relations that predict strain regime and strike slip faulting in the overriding plate maximum earthquake magnitude benioff zone length slab dip arc trench gap and maximum trench depth excellent correlation is found between length of the benioff zone and the product of convergence rate and age of the downgoing slab this relationship is consistent with the conductive heating model of molnar et al 1979 if the model is modified in one respect the rate of heating of the slab is not constant it is substantially slower during passage of the slab beneath the accretionary prism and overriding plate the structural style in the overriding plate is determined by its stress state though the stress state of overriding plates cannot be quantified one can classify each individual subduction zone into one of seven semiquantitative strain classes that form a continuum from strongly extensional class 1 back arc spreading to strongly compressional class 7 active folding and thrusting this analysis indicates that strain class is probably determined by a linear combination of convergence rate slab age and shallow slab dip interplate coupling controlled by convergence rate and slab age is an important control on strain regime and the primary control on earthquake magnitude arc parallel strike slip faulting is a common feature of convergent margins forming a forearc sliver between the strike slip fault and trench optimum conditions for the development of forearc slivers are oblique convergence a compressional environment and a continental overriding plate the primary factor controlling presence of strike slip faulting is coupling strongly oblique convergence is not required the rate of strike slip faulting is affected by both convergence obliquity and convergence rate maximum trench depth is a response to flexure of the underthrusting plate the amount of flexural deflection at the trench depends on the vertical component of slab pull force which is very sensitive to slab age and shallow slab dip shallow slab dip conforms to the cross sectional shape of the overriding plate which is controlled by width of the accretionary prism and duration of subduction deep slab dip is affected by the mantle trajectory established at shallow depth but may be modified by mantle flow much of the structural complexity of convergent margins is probably attributable to terrane juxtaposition associated with temporal changes in both forearc strike slip faulting and strain regime empirical equations relating subduction parameters can provide both a focus for future theoretical studies and a conceptual and kinematic link between plate tectonics and the geology of subduction zones

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

isotopic evolution of lavas from haleakala crater hawaii pb and sr isotopic ratios have been determined for tholeiitic shield building alkalic cap and post erosional stage lavas from haleakala crater pb isotopic compositions of the tholeiites overlap those of the alkalic cap lavas although87sr 86sr ratios of these two suites are distinct alkalic cap and post erosional lavas appear to be indistinguishable on the basis of sr and pb isotopic composition sr and pb isotopic ratios of haleakala post shield building lavas are positively correlated such a trend is previously undocumented for any suite of hawaiian lavas and contrasts with the general negative correlation observed for data from hawaiian tholeiites these relations are consistent with a three component petrogenetic mixing model specifically it is proposed that magma batches at individual hawaiian volcanoes formed by 1 mixing of melts generated from mantle plumes containing two isotopically distinct mantle components primitive vs enriched and 2 subsequent variable degrees of interaction between these plume melts and a third morb signature mantle reservoir prior to their emplacement in a crustal magma chamber these observations and inferences provide new constraints on physical models of hawaiian magmatism based on observed temporal isotopic variations of haleakala lavas it is suggested that the ratio of enriched primitive mantle components in the hawaiian plume source decreases during the waning stages of alkalic volcanism over the same time interval both decreasing melt production and protracted residence of ascending melts within the upper mantle contribute to a systematic increase in the ratio of depleted vs plume component

physical properties and localization investigations associated with the 2003 mars exploration rovers 1 a number of physical properties experiments will be conducted during the nasa 2003 mars exploration rover mission as the two vehicles explore meridiani planum and the floor of gusev crater the investigations will include quantifying dust accumulation and dispersal dynamics by periodically monitoring the rover decks with the athena pancam and mini tes instruments properties of soil like materials will be inferred from analyses of wheel track patterns depths and wheel slippage dynamics during traverses the rovers will be modeled as dynamic mechanical systems to extract along track terrain topography and physical properties from times series of rover tilt vectors wheel encoder counts azimuths motor currents and rocker and bogie angles trenches will be excavated using rover wheels to characterize mechanical properties of soil like materials with depth and to expose subsurface materials for remote and in situ observations using the athena payload the rock abrasion tools will be used to expose rock subsurfaces for detailed analyses motor currents and penetration magnitudes will be compared to a database of rocks excavated by an engineering model of the rock abrasion tool to understand martian rock mechanical properties image based localization analyses will be pursued to better understand rover traverse directions and magnitudes and thus rover locations as a function of time the physical properties and localization investigations when combined with analyses of the full ensemble of athena observations will greatly improve our understanding of martian surface properties and provide significant technology lessons for future landed missions

comment on consequences of progressive eclogitization on crustal exhumation a mechanical study by h raimbourg l jolivet and y leroy summary two simple end member models of a subduction channel have been proposed in the literature i the pressure imposed model for which the pressure within the channel is assumed to be lithostatic the channel walls have negligible strength with respect to lateral pressure gradients and the channel geometry therefore varies with time and ii the geometry imposed model of constant channel geometry rigid walls and resultant lateral variation in pressure neither of these models is realistic but they provide lower and upper bounds to potential pressure distributions in natural subduction zones the critical parameter is the relative strength of the confining plates reflected in the effective viscosity ratio between the channel fill and the walls the assertion that the geometry imposed model is internally inconsistent is incorrect it merely represents one bound to possible behaviour and a bound that may be approached for realistic values of the effective viscosity for weak channel fill e g unconsolidated ocean floor sediments and relatively cold and strong subducting and overriding lithospheric plates

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

role of olivine cumulates in destabilizing the flanks of hawaiian volcanoes the south flank of kilauea volcano is unstable and has the structure of a huge landslide it is one of at least 17 enormous catastrophic landslides shed from the hawaiian islands mechanisms previously proposed for movement of the south flank invoke slip of the volcanic pile over seafloor sediments slip on a low friction decollement alone cannot explain why the thickest and widest sector of the flank moves more rapidly than the rest or why this section contains a 300 km3 aseismic volume above the seismically defined decollement it is proposed that this aseismic volume adjacent to the caldera in the direction of flank slip consists of olivine cumulates that creep outward pushing the south flank seawards average primary kilauea tholeiitic magma contains about 16 5 wt mgo compared with an average 10 wt mgo for erupted subaerial and submarine basalts this difference requires fractionation of 17 wt 14 vol olivine phenocrysts that accumulate near the base of the magma reservoir where they form cumulates submarine erupted kilauea lavas contain abundant deformed olivine xenocrysts derived from these cumulates deformed dunite formed during the tholeiitic shield stage is also erupted as xenoliths in subsequent alkalic lavas the deformation structures in olivine xenocrysts suggest that the cumulus olivine was densely packed probably with as little as 5 10 vol intercumulus liquid before entrainment of the xenocrysts the olivine cumulates were at magmatic temperatures 1100 c when the xenocrysts were entrained olivine at 1100 c has a rheology similar to ice and the olivine cumulates should flow down and away from the summit of the volcano flow of the olivine cumulates places constant pressure on the unbuttressed seaward flank leading to an extensional region that localizes deep intrusions behind the flank these intrusions add to the seaward push this mechanism ties the source of gravitational instability to the caldera complex and deep rift systems and therefore limits catastrophic sector failure of hawaiian volcanoes to their active growth phase when the core of olivine cumulates is still hot enough to flow

volcano spacing and plate rigidity in plane stresses which accompany the flexural deformation of the lithosphere under the load adjacent volcanoes may govern the spacing of volcanoes in hotspot provinces specifically compressive stresses in the vicinity of a volcano prevent new upwelling in this area forcing a new volcano to develop at a minimum distance that is equal to the distance in which the radial stresses change from compressional to tensile the inflection point if a volcano is modeled as a point load on a thin elastic plate then the distance to the inflection point is proportional to the thickness of the plate to the power of 3 4 compilation of volcano spacing in seven volcanic groups in east africa and seven volcanic groups of oceanic hotspots shows significant correlation with the elastic thickness of the plate and matches the calculated distance to the inflection point in contrast volcano spacing in island arcs and over subduction zones is fairly uniform and is much larger than predicted by the distance to the inflection point reflecting differences in the geometry of the source and the upwelling areas

the origin of large or great thrust type earthquakes along subducting plate boundaries abstract seismicity deformation state of stress and abundance of fluids along subducting plate boundaries are reviewed and the origin of large or great thrust type earthquakes is discussed based on the recent experimental results on the slip behavior of halite and serpentine gouges shallow subducting plate boundaries above 20 25 km in depth are characterized by low seismicity low tectonic stress inter plate decoupling ductile deformation associated with the formation of metamorphic schistosity except at very shallow depths metamorphism suggesting solution processes on massive scale and presence of abundant h 2 o it is argued that these unique features are due to pressure solution processes to high fluid pressure to low strength and stable behavior of clayey sediments under wet environments and or to the deformation of soft unconsolidated sediments at very shallow depths the low seismicity in this zone is in marked contrast with major strike slip faults along which large earthquakes occur at depths shallower than 15 20 km it is emphasized that these unique features are expected only for restricted regions where there is constant supply of h 2 o due to progressive metamorphism or where fluids in the rocks are trapped and cannot escape to the surface large or great thrust type earthquakes in subduction zones initiate at depths of 30 50 km below the shallow decoupled zone in this focal depth range the supply of h 2 o during progressive metamorphism perhaps diminishes downwards the overriding and subducting plates are coupled and stick to each other during much of the inter seismic period and the resistance to slip or shear stress is presumably high it is suggested that these earthquakes begin to occur at a depth where the plate boundary zone becomes fairly dry deformation at these depths appears to be predominantly ductile so that the earthquakes cannot be regarded simply as a brittle phenomenon 1 creep instability i e instability associated with plastic deformation and 2 dehydration induced instability are the most likely mechanisms for initiating the earthquakes and both have some experimental support stick slip of halite gouge while undergoing ductile deformation primarily by intracrystalline gliding is described and discussed as a supporting evidence for 1 shear resistance of halite gouge increases with increasing confining pressure in stick slip regimes hence the observed stick slip may be a semi brittle phenomenon with respect to the pressure dependence of the shear resistance although the deformation texture cannot be distinguished from that formed by pressure insensitive flow serpentine gouge exhibits violent stick slip upon its decomposition under dry not wet environments supporting the mechanism 2 above exact mechanisms which lead to the unstable fault motion are poorly understood as yet but stick slip of both halite and serpentine gouges is recognized only when the slip rate dependence of friction is negative i e lower friction at faster slip rate consistent with the theoretical prediction of rice and ruina 1983 there is a possibility that the thrust type earthquakes can be explained essentially within the framework of fault constitutive laws developed by dieterich 1979 and ruina 1983

re os isotopic systematics of primitive lavas from the lassen region of the cascade arc california abstract rhenium osmium isotopic systematics of primitive calc alkaline lavas from the lassen region appear to be controlled by mantle wedge processes lavas with a large proportion of slab component have relatively low re and os abundances and have radiogenic os and mid ocean ridge basalt like sr and pb isotopic compositions lavas with a small proportion of slab component have higher re and os elemental abundances and display mantle like os sr nd and pb isotopic compositions assimilation with fractional crystallization can only generate the re os systematics of the lassen lavas from a common parent if the distribution coefficient for re in sulfide is 40 1100 times higher than most published estimates and if most incompatible element abundances decrease during differentiation high re os ratios in mid ocean ridge basalts makes subducted oceanic crust a potential source of radiogenic os in volcanic arcs the slab beneath the southernmost cascades is estimated to have 187os 188os ratios as high as 1 4 mixing between a slab component and mantle wedge peridotite can generate the os isotopic systematics of the lassen lavas provided the slab component has a sr os ratio of 7 5 105 and os abundances that are 100 600 times higher than mid ocean ridge basalts for this model to be correct os must be readily mobilized and concentrated in the slab component perhaps as a result of high water and hcl fugacities in this subduction environment another possible mechanism to account for the correlation between the magnitude of the subduction geochemical signature and os isotopic composition involves increasing the stability of an os bearing phase in mantle wedge peridotites as a result of fluxing with the slab component melting of such a source could yield low os magmas that are more susceptible to crustal contamination and hence have more radiogenic os isotopic compositions than magmas derived from sources with a smaller contribution from the slab thus the addition of the slab component to the mantle wedge appears to result in either the direct or indirect addition of radiogenic os to arc magmas

east molokai and other kea trend volcanoes magmatic processes and sources as they migrate away from the hawaiian hot spot 1 there are geochemical differences between shield lavas from the two parallel trends kea and loa defined by young hawaiian volcanoes the shield of east molokai volcano at greater than 1 5 ma is the oldest volcano on the kea trend sequences of older tholeiitic to younger alkalic basalt that erupted as this volcano evolved from the shield to postshield stage of volcanism are well exposed much younger 0 34 0 57 ma alkalic basalt and basanite erupted during rejuvenated stage volcanism like rejuvenated stage lavas erupted at other hawaiian volcanoes rejuvenated stage east molokai lavas have relatively low 87sr 86sr and high 143nd 144nd such ratios reflect a source component with a long term depletion in abundance of incompatible elements on the basis of positive correlations of 87sr 86sr versus 206pb 204pb and negative correlations of these isotopic ratios with nb zr a smaller proportion of this depleted component also contributed to the late shield postshield lavas erupted at east molokai and the other kea trend volcanoes haleakala and mauna kea at each of these kea trend volcanoes as the volcano moved away from the hot spot the extent of melting and magma supply from the mantle decreased the depth of melt segregation increased and there was an increasing role for a component with long term relative depletion in incompatible elements this depleted component has kea trend pb isotopic characteristics and relatively low 208pb 204pb at a given 206pb 204pb and it is probably not related to oceanic lithosphere or the source of mid ocean ridge basalt the overlap in sr nd and pb isotope ratios of recent kilauea shield lavas and 550 ka mauna kea shield lavas has been used to argue that kea trend shield volcanism samples a vertically continuous geochemically distinct stripe which persisted in the hot spot source for 550 kyr eisele et al 2003 abouchami et al 2005 as kea trend volcanoes migrate away from the hot spot and evolve from the shield to postshield stage there are systematic changes in sr nd and pb isotope ratios however the overlap of sr nd and pb isotope ratios in late shield postshield lavas from mauna kea 350 ka and east molokai 1 5 ma show that the periphery of the hot spot sampled by kea trend postshield lavas also had long term geochemical homogeneity

solitary waves in mantle plumes numerical calculations in two dimensions show that solitary wave disturbances can propagate along thermal plumes in a homogeneous viscous fluid with a thermally activated rheology similar to the mantle comparison of the numerical results with analytic results from an idealized two fluid model indicates that the two fluid model can be applied to solitary waves in the thermally activated plume a two fluid model of solitary waves on cylindrical conduits is accordingly applied to mantle plumes to estimate the propagation speeds time durations and pulse lengths of solitary waves in mantle plumes as a function of background mantle viscosity plume flux plume density deficit plume viscosity and the volume of material transported by the solitary wave it is inferred that mantle plumes may be episodic via solitary waves and that these disturbances might account for observed 0 10 m y variations in the durations and spacings of episodes of enhanced hotspot volcanic activity solitary waves in mantle plumes could be generated by interactions among plumes and between plumes and the large scale time dependent mantle circulation

natural stones for monuments their availability for restoration and evaluation this paper represents the introduction to the volume focused on the various aspects of natural stone research from the topic issues studied recently four major aspects are covered 1 availability of certain stone types for monuments 2 strategies aiming to strengthen our knowledge of past resources through the establishment of natural stone databases and inventories 3 evaluation of natural stone properties and assessment of the compatibility of repair stones and 4 decay studies of natural stone on monuments and on natural exposures this paper also aims to highlight the importance of the use of local stone resources a practice that has seriously declined during the 20th century in most of the industrialized countries the availability of natural stone from monuments is also discussed in terms of sandstones and travertine in the czech republic and hungary as a typical example natural stone has become the expression to describe the versatile durable and aesthetically plausible building materials currier 1960 from the very beginning of civilization important structures and monuments were built from or were principally based on natural stone the use of local stone resources was mostly in balance with the local environment although highly durable when properly applied no stone type can be considered immortal schaffer 1932 and most of the stone varieties are affected by a polluted atmosphere winkler 1997 deteriorated stone on monuments should be preferably replaced by stone varieties of the same composition from the same quarries however this is often not possible and so stone having similar properties and appearance must be sourced p ikryl 2007 the main aim of this research is to find compatible stones in terms of appearance and geochemical physical properties this task requires a thorough understanding of both the rock properties and its response to external conditions and weathering agents availability of natural stone

rejuvenated stage volcanism after 0 6 m y quiescence at west maui volcano hawaii new evidence from k ar ages and chemistry of lahaina volcanics abstract west maui s rejuvenated stage lahaina volcanics were erupted from four discrete sites new k ar ages indicate two pulses of volcanism the older about 0 6 ma and the younger about 0 4 ma compositionally the lava flows are entirely basanitic but each pulse is diverse the underlying postshield stage honolua volcanics were emplaced by about 1 2 ma on the basis of previously published ages therefore the duration of volcanic quiescence prior to rejuvenation is about 0 6 m y at west maui much longer than estimated previously

evidence for two shield volcanoes exposed on the island of kauai hawaii the island of kauai has always been interpreted as a single shield volcano but lavas of previously correlated reversed to normal magnetic polarity transitions on opposite sides of the island differ significantly in isotopic composition samples from west kauai have 87sr 86sr 18 25 samples from east kauai have 87sr 86sr 0 7037 nd 6 14 and 206pb 204pb 18 25 available data suggest that a younger eastern shield grew on the collapsed flank of an older western one

stretching and mixing of viscous blobs in earth s mantle the stretching and mixing of blobs more viscous than the surrounding mantle is an important issue the subducted lithospheric material at depth might be more viscous than the surrounding mantle and its ability to mix affects its properties as a geochemical reservoir in order to study the effect of the viscosity ratio viscosity of the blob to the viscosity of the surrounding mantle on the deformation we perform three types of two dimensional numerical simulations a pure shear simulation a simulation of steady state convection and a simulation of time dependent convection in a pure shear flow the inverse of the rate of deformation of a viscous blob is to a first approximation a linear function of the ratio ar where ar is the aspect ratio of the blob for a viscous blob in a steady convection cell a periodic deformation is superimposed on the long term deformation the period corresponds to an overturn time along the streamline followed by the blob the strains of this periodic deformation obey the laws found for pure shear in a time dependent flow more representative of the mantle flow we find that the average distance a between two tracers situated within a viscous blob obeys the relationship ln a a0 at 1 2 and that it is independent of the aspect ratio of the blob these two results are well explained by a simple model of successive strains in arbitrary directions the viscosity contrast controls the mixing efficiency and it has an effect much larger than predicted by earlier studies blobs of matter more viscous than the average mantle can therefore persist unmixed in the mantle over earth s history

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

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

structural and petrologic evolution of the lihue basin and eastern kauai hawaii the topography of the eastern part of the hawaiian island of kauai is dominated by the lihue basin a large 110 km 2 semicircular depression bounded by steep cliffs and partly filled by late rejuvenated stage or posterosional stage volcanic material as with other large semicircular basins on ocean island volcanoes the subsurface geology and origin e g structural collapse vs fluvial erosion of the lihue basin are poorly understood new analyses of samples collected from eastern kauai and drill holes within the basin document several important features of the late stage geologic evolution of kauai first thick 300 m sequences of rejuvenated stage koloa volcanics in the lihue basin show systematic basin wide geochemical trends of increasingly incompatible elements with time indicating a gradual decrease in the extent of partial melting of mantle sources with time second beneath the rejuvenated stage volcanics in the basin a thin layer of postshield alkalic stage lavas e g hawaiites and mugearites overlies older shield stage tholeiitic lavas of the napali member indicating that the lihue basin formed by structural collapse not fluvial erosion third a large 2 5 km 3 matrix supported breccia interpreted as deposits of one or more debris flows is within the rejuvenated stage volcanics throughout the basin and correlates with surficial exposures of the palikea breccia west of the basin isotopic compositions of the bulk breccia are similar to those of tholeiites from the east side of kauai and distinct from those of west kauai tholeiites clasts within the breccia are dominantly hawaiite and alkali gabbro the source region of the breccia in the steep cliffs and highlands of the central massif to the west of the basin must contain magmatic products of an extensive postshield alkalic stage including hawaiite flows and one or more large intrusive bodies or ponded sequences of alkali gabbro

geochemistry of diverse basalt types from loihi seamount hawaii petrogenetic implications the wide variety of basalt types tholeiitic to basanite dredged from loihi seamount have minor and trace element abundances that are characteristic of subaerial hawaiian basalts thereby confirming that loihi seamount is a manifestation of the hawaiian hot spot within the loihi sample suite there are well defined positive correlations among abundances of highly incompatible elements p k rb ba nb light ree and ta and moderately incompatible elements sr ti zr and hf and between mgo ni and cr however within the loihi suite abundance ratios of geochemically similar elements zr hf nb ta and la ce vary by factors of 1 2 1 5 and abundance ratios of highly incompatible elements such as p ce p th k rb ba th and la nb vary by factors of 1 2 2 5 these abundance ratios are not readily changed by different degrees of fractionation and melting therefore we conclude that these samples are not genetically related by different degrees of melting of a compositionally homogeneous source on the basis of k p k ti p ce zr nb th p and la sm abundance ratios the twelve samples studied in detail can be divided into six geochemical groups samples within each group are similar in 87sr 86sr 1 and intra group compositional variations may reflect low pressure fractionation and different degrees of melting in addition crossing chondrite normalized ree patterns within the alkalic basalt groups reflect equilibration of the magmas with garnet in ratio ratio plots involving abundance ratios of highly incompatible elements e g la p nb p k p rb p ba p and th p the geochemical groups define linear arrays suggestive of mixing however these data combined with the isotopic data are not consistent with two component mixing

glacial isostatic adjustment of scandinavia and northwestern europe and the radial viscosity structure of the earth s mantle summary during the last glacial maximum lgm large ice sheets covered scandinavia the barents sea and the northern british isles subsequent to the lgm the ice sheets disappeared and the solid earth readjusted towards a new isostatic equilibrium the glacial isostatic adjustment process is documented in numerous observations for example palaeoshorelines covering the last deglaciation phase and ongoing crustal deformations monitored by gps stations for example the bifrost project in this study we use palaeoshoreline data from scandinavia the barents sea and northwestern europe nw as well as radial crustal velocities from the bifrost campaign to infer the radial viscosity structure of the earth s mantle underneath scandinavia and nw europe a global inverse procedure based on the neighbourhood algorithm allows us to explore the hypothesis of a low viscosity zone in the upper mantle which has been proposed in the literature our results indicate a low viscosity zone underneath the barents sea with viscosities between 1019 and 1020 pa s in a depth interval of 160 200 km no such low viscosity zone is found underneath scandinavia and no clear indication for such a zone underneath nw europe the thickness of the rheological lithosphere increases from 60 to 70 km underneath nw europe and the barents sea towards values exceeding 120 km underneath scandinavia

a submarine perspective of the honolulu volcanics oahu lavas and volcaniclastic deposits were observed and collected from 4 submarine cones that are part of the honolulu volcanics on oahu hawaii the locations of these and a few additional but unsampled vents demonstrate that nearly all the vents are located on or very close to the shoreline of oahu with the most distal vent just 12 km offshore the clastic samples and outcrops range from coarse breccias to cross bedded ash deposits and show that explosive volcanism at depths between about 350 and 590 m depth played a part in forming these volcanic cones the eruptive styles appear to be dominantly effusive to strombolian at greater depths but apparently include violent phreatomagmatic explosive activity at the shallower sites along the submarine southwest extension of the koko rift the compositions of the recovered samples are broadly similar to the strongly alkalic subaerial honolulu volcanics lavas but the submarine lavas erupted further from the koolau caldera have slightly more radiogenic sr isotopic ratios and trace element patterns that are distinct from either the subaerial honolulu volcanics or the submarine north arch lavas these patterns are characterized by moderate to strong positive sr and p anomalies and moderate to strong negative cs rb u th zr and hf anomalies most samples have strong negative k and moderate negative ti anomalies as do all subaerial honolulu volcanics and north arch samples but one group of samples from the koko rift lack this chemical signature the data are consistent with more garnet in the source region for the off shore samples than for either the on shore honolulu volcanics lavas new ar ar ages show that eruptions at the submarine vents and diamond head occurred between about 0 5 ma and 0 1 ma with the youngest ages from the koko rift these ages are in general agreement with most published ages for the formation and suggest that some much younger ages reported previously from the koko rift are probably erroneously young d 2005 elsevier b v all rights reserved

ages rare earth element enrichment and petrogenesis of tholeiitic and alkalic basalts from kahoolawe island hawaii kahoolawe island hawaii 18 11 km is a basaltic shield volcano with caldera filling lavas seven identified postshield vents and at least two occurrences of apparent rejuvenated stage eruptive we examined 42 samples that represent all stages of kahoolawe volcano stratigraphy for their petrography whole rock major and trace element contents mineral compositions and k ar ages the two oldest shield samples have an average age of 1 34 0 08 ma and four postshield samples 3 are alkalic average 1 15 0 03 ma ages of 1 08 and 0 99 ma for two additional tholeiitic samples probably are minimum ages whole rock major and trace element and mineral compositions of kahoolawe shield and caldera fill laves are generally similar to the lavas forming kilauea and mauna loa tholeiitic shields but in detail kahoolawe shield lavas have distinctive compositions an unusual aspect of many postshield ka hoolawe lavas is anomalously high ree and y abundances up to 200 ppm la and 175 ppm y and negative ce anomalies these enrichments reflect surficial processes where weathering and soil development promoted ree y transport at the weathering front major element abundances mgo 10 6 wt for shield and caldera fill basalts are consistent with fractionation of ol px pl in frequently replenished magma reservoirs in general tholeiitic basalts erupted from late vents are higher in sio2 than the shield lavas and temporal differences in parental magma compositions are the likely explanation alkalic basalts that erupted from vents are comparable in composition to those at other hawaiian volcanoes trace element abundance ratios indicate that alkalic basalts represent either relatively lower degrees of melting of the shield source or a distinct source apparent rejuvenated stage basalts i e emplaced after substantial kahoolawe erosion are tholeiitic unlike the rejuvenated stages at other hawaiian volcanoes alkalic kahoolawe like several other hawaiian volcanoes has intercalated tholeiitic and alkalic basalts in the postshield stage but it is the only volcano that appears to have produced tholeiitic rejuvenated stage lavas

high resolution 40ar 39ar geochronology of the louisville seamounts iodp expedition 330 drill sites implications for the duration of hot spot related volcanism and age progressions

consequences of progressive eclogitization on crustal exhumation a mechanical study summary the very low water content of the granulitic unit of holsnoy in the bergen arcs norway caused its partial metastable preservation throughout caledonian burial end exhumation leading to the observed mixture of completely eclogitized and uneclogitized rocks the eclogitization of the granulite facies protolith led to a density increase 10 but also to a large rheological weakening that resulted in the localization of all deep ductile deformation in the eclogite fraction we address the consequences on subduction dynamics of the concomitant evolution of large scale density and rheology during progressive eclogitization of crust by comparing the behaviour of buried crust with various properties in the channel flow model large scale buoyancy and density are integrated in a single adimensional parameter the exhumation number which describes the capacity of the crust to exhume for a crust whose eclogitization causes a very large viscosity decrease burial resistant end member goes through a maximum in the partially eclogitized zone that is there is a given proportion of eclogite for which the crust is strongly weakened but still significantly lighter than surrounding mantle for this partially eclogitized crust with max the maximum possible downward flow is very low this zone acts as a bottleneck and all incoming crust in excess is forced backwards and starts exhuming this return flow zone is bounded downwards in the partially eclogitized zone by max while its upper limit propagates upwards at a constant rate the curve eclogite fraction controls the maximum proportion of eclogite of the crust that can be exhumed we also demonstrate that large exhumation rates reached by certain uhp units are incompatible with any stationary flow regime whatever the nature of subducted crust the additional presence of a weak layer on top of the channel favours burial for narrow channels and exhumation for large ones but does not qualitatively change the dynamics of the subduction channel this study shows that deep crustal circulation in subduction zones and exhumation from large depths are controlled by the evolution of large scale crustal properties with progressive eclogitization

trace element abundances of high mgo glasses from kilauea mauna loa and haleakala volcanoes hawaii we performed an ion microprobe study of eleven high mgo 6 7 14 8 wt tholeiite glasses from the hawaiian volcanoes kilauea mauna loa and haleakala we determined the rare earth re high field strength and other selected trace element abundances of these glasses and used the data to establish their relationship to typical hawaiian shield tholeiite and to infer characteristics of their source the glasses have trace element abundance characteristics generally similar to those of typical shield tholeiites e g l light ree h heavy reec1 1 the kilauea and mauna loa glasses however display trace and major element characteristics that cross geochemical discriminants observed between kilauea and mauna loa shield lavas the glasses contain a blend of these discriminating chemical characteristics and are not exactly like the typical shield lavas from either volcano the production of these hybrid magmas likely requires a complexly zoned source rather than two unique sources when corrected for olivine fractionation the glass data show correlations between cao concentration and incompatible trace element abundances indicating that cao may behave incompatibly during melting of the tholeiite source furthermore the tholeiite source must contain residual garnet and clinopyroxene to account for the variation in trace element abundances of the kilauea glasses inversion modeling indicates that the kilauea source is flat relative to c1 chondrites and has a higher bulk distribution coefficient for the hree than the lree

population density and zoning of olivine phenocrysts in tholeiites from kauai hawaii the population density of olivine phenocrysts of the tholeiites display an exponential variation which is typical of igneous as well as contact metamorphic rocks the exponential variation is explained by a new growth probability model which is consistent with experimental work the forsterite content of the olivine phenocrysts decreases with decreasing size various phenocryst features suggest that the tholeiites first crystallized slowly in a magma chamber after which they underwent crystallization for a short period of time in a feeder dyke before eruption took place

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

nonlithostatic pressure during sediment subduction and the development and exhumation of high pressure metamorphic rocks a subduction shear zone can be modeled as a long narrow channel with the flow of subducted metasedimentary rocks in the channel driven by two sets of forces the downward shearing force exerted by the subducting slab and the gradient in the hydraulic potential which combines the effect of both pressure and buoyancy if the channel walls are effectively rigid very slight narrowing or broadening of the channel convergence angles 2 gpa in the channel at only 40 km depth the model is consistent with a horizontal balance of forces across the plates and with a reasonable value for the thickness of subducted sediment 650 m the practical limit for overpressures attainable in subduction zones is determined by the strength and permeability of the channel walls at 40 km depth the channel is effectively confined on both sides by cold lithospheric mantle which should be strong enough to support a significant tectonic overpressure episodic failure of the upper plate to produce great earthquakes at 30 40 km focal depth could vent overpressured fluid from the channel allowing a cyclical buildup and release of both rock and fluid pressure topography on the subducting plate e g seamounts and thinned continental crust may lead to an anvil like jamming of the channel and local high overpressures tectonic erosion by topography on the lower plate of slivers from overlying continental crust and the compression of these slivers between the topography and the narrowing channel walls could produce high overpressures in continental rocks a decrease in the convergence rate or cessation of subduction with a consequent general warming within the channel and associated viscosity decrease promotes exhumation by buoyant reverse flow the most rapid reverse flow occurs in the region of previously greatest overpressure since the exhumation distance is shorter than for a simple lithostatic pressure distribution and any increase in temperature is coupled with a strong increase in the rate of exhumation preservation of high pressure assemblages at the surface in fossil subduction zones is promoted for such a model

formation of submarine flat topped volcanic cones in hawai i high resolution bathymetric mapping has shown that submarine flat topped volcanic cones morphologically similar to ones on the deep sea floor and near mid ocean ridges are common on or near submarine rift zones of kilauea kohala or mauna kea mahukona and haleakala volcanoes four flat topped cones on kohala were explored and sampled with the pisces v submersible in october 1998 samples show that flat topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage similarly shaped flat topped cones on the northwest submarine flank of ni ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage submarine postshield stage eruptions on hilo ridge mahukona hana ridge and offshore ni ihau form pointed cones of alkalic basalt and hawaiite the shield stage flat topped cones have steep 25 sides remarkably flat horizontal tops basal diameters of 1 3 km and heights 300 m the flat tops commonly have either a low mound or a deep crater in the center the rejuvenated stage flat topped cones have the same shape with steep sides and flat horizontal tops but are much larger with basal diameters up to 5 5 km and heights commonly greater than 200 m the flat tops have a central low mound shallow crater or levees that surrounded lava ponds as large as 1 km across most of the rejuvenated stage flat topped cones formed on slopes 10 and formed adjacent semicircular steps down the flank of ni ihau rather than circular structures all the flat topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades these and other submarine volcanic cones of similar size and shape apparently form as continuously overflowing submarine lava ponds a lava pond surrounded by a levee forms above a sea floor vent as lava continues to flow into the pond the lava flow surface rises and overflows the lowest point on the levee forming elongate pillow lava flows that simultaneously build the rim outward and upward but also dam and fill in the low point on the rim the process repeats at the new lowest point forming a circular structure with a flat horizontal top and steep pillowed margins there is a delicate balance between lava heat supply to the pond and cooling and thickening of the floating crust factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents moderate to high confining pressure at moderate to great ocean depth long lived steady eruption years to decades moderate effusion rates probably ca 0 1 km3 year and low but not necessarily flat slopes with higher effusion rates sheet flows flood the slope with lower effusion rates pillow mounds form hawaiian shield stage eruptions begin as fissure eruptions if the eruption is too brief it will not consolidate activity at a point and fissure fed flows will form a pond with irregular levees the pond will solidify between eruptive pulses if the eruption is not steady lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones as occurs during the post shield stage the steady effusion of lava on land constructs lava shields which are probably the subaerial analogs to submarine flat topped cones but formed under different cooling conditions

glacial rebound of the british isles iii constraints on mantle viscosity summary observations of sea level change since the time of the last glacial maximum provide important constraints on the response of the earth to changes in surface loading on time scales of 103 104 years this response is conveniently described by an effective elastic lithospheric thickness and effective viscosities for one or more mantle layers considerable trade off between the parameters describing these layers can occur and different combinations can give rise to comparable predictions of sea level change in particular the trade off between lithospheric thickness and upper mantle viscosity can be important and for any reasonable value for the lithospheric thickness a corresponding mantle viscosity structure can be found that gives a plausible comparison of sealevel predictions with observations in particular thin lithosphere models will lead to low estimates for the upper mantle viscosity while thick lithosphere models lead to high viscosity values however either solution may represent only a local minimum in the model parameter space and may not correspond to the optimum solution it becomes important therefore that in the inversion of observational data a comprehensive search is conducted throughout the entire model parameter space to ensure that the solution identified does indeed correspond to the optimum solution the sea level data for the british isles lend themselves well to such an inversion because of the relatively high quality of the data the good geographic distribution of the data relative to the former ice sheet and reasonable observational constraints on the dimensions of the former ice sheet and on its retreat furthermore because of the contribution to the sea level signal from the distant ice sheets as well as from the melt water load the observational data base for the region also has some resolving power for the viscosity of the deeper mantle the parameter space explored is defined by up to five mantle layers the lithosphere of effective elastic thickness d and a series of upper mantle layers i 2 4 extending down to depths of 200 400 and 670 km respectively each of viscosity qi and a lower mantle layer of viscosity qlm extending down to the coremantle boundary the range of parameters explored is 30 d i 120 km 3 x loi9 iqi

high magnesium primary magmas from haleakala volcano east maui hawaii petrography nickel and major element constraints abstract for any given volcanic field the compositions of primary melts provide important constraints on models of magmatic processes and volcanic eruptions in this paper based on petrography olivine and bulk rock compositions two tholeiitic picrites samples c122 and c123 from haleakala volcano east maui are evaluated as possible primary melts sample c122 bulk rock mgo 16 6 has a high apparent mg fe exchange coefficient kd between olivine phenocrysts and bulk rock 0 6 however major elements and ni mass balance calculations show that the olivines in c122 are in equilibrium with the residual melt matrix after closed system equilibrium fractionation of 25 wt olivine therefore the mg fe ratio ca content and ni content of c122 are consistent with the hypothesis that the bulk composition of c122 is close to a primary melt formed by partial melting of a mantle containing olivine with composition around fo89 to fo91 the uniform composition and small size mostly 0 2 0 3 mm of the olivine and the glass patches in the matrix suggest fast ascent and rapid cooling at shallow depth for c122 on the contrary sample c123 which has an apparent kd between the most mafic olivine megacrysts and the bulk rock close to the equilibrium value 0 27 the multiple planar subgrain boundaries in most of the olivine crystals indicate that it may not be a primary melt unless the deformed olivines are generated at magmatic condition as phenocrysts if the deformed subgrain boundary texture in olivine could indeed be generated at magmatic condition then the wide compositional range of olivine crystals in c123 fo74 to fo91 suggests multi stage crystallization over a wide range of cooling temperatures the compositions of the two picrites and a differentiated basalt which does not contain xenocrysts suggest that the haleakala tholeiites are derived from primary melts with at least 16 17 wt mgo lavas with such high mgo content are rare in haleakala and other hawaiian volcanoes therefore most hawaiian tholeiites must have undergone extensive fractionation histories

hawaiian xenolith populations magma supply rates and development of magma chambers hawaiian volcanoes pass through a sequence of four eruptive stages characterized by distinct lava types magma supply rates and xenolith populations magma supply rates are low in the earliest and two latest alkalic stages and high in the tholeiitic second stage magma storage reservoirs develop at shallow and intermediate depths as the magma supply rate increases during the earliest stage magma in these reservoirs solidifies as the supply rate declines during the alkalic third stage these magma storage reservoirs function as hydraulic filters and remove dense xenoliths that the ascending magma has entrained during the earliest and latest stages no magma storage zone exists and mantle xenoliths of lherzolite are carried to the surface in primitive alkalic lava during the tholeiitic second stage magma storage reservoirs develop and persist both at the base of the ocean crust and 3 7 km below the caldera only xenoliths of shallow origin are carried to the surface by differentiated lava during the alkalic third stage magma in the shallow subcaldera reservoir solidifies and crustal xenoliths including oceanic crustal rocks are carried to the surface in lava that fractionates in an intermediate depth reservoir worldwide xenolith populations in tholeiitic and alkalic lava may reflect the presence or absence of subvolcanic magma storage reservoirs

south arch volcanic field newly identified young lava flows on the sea floor south of the hawaiian ridge several young lava fields were imaged by gloria sidescan sonar along the hawaiian arch south of hawaii the largest 35 by 50 km across includes a central area characterized by high sonar backscatter and composed of several flow lobes radiating from a vent area reflection profiling and sea floor photography indicate that the central lobes are flat sheet flowsbounded by pillowed margins thin surface sediment and thin palagonite rinds on lava surfaces suggest ages of 1 10 ka vents are localized along the arch crest near bases of cretaceous seamounts two dredged flows are basanite and alkalic basalt broadly similar to rejuvenated stage and some pre shield alkalic lavas on the hawaiian ridge arch volcanism representsperipheral leakage of melt from the hawaiian hot spot over much larger areas than previously recognized

an o isotope profile through the hp lt corsican ophiolite france and its implications for fluid flow during subduction abstract subduction zones are important sites for fluid generation as the downgoing slab undergoes progressive high pressure metamorphism these fluids are thought to play an important role in the generation of arc magmas but their affect on the subducted slab itself is less clear in this study the stable isotope geochemistry of the corsican ophiolite which is variably affected by subduction related metamorphism was investigated to assess the impact of subduction zone fluid flow on the downgoing slab a total of 170 stable isotope analyses oxygen and carbon showed the following features 1 overall the ophiolite preserves the same oxygen isotope profile with depth as unmetamorphosed ophiolites 2 the variation in oxygen isotope values for different areas does not correlate with metamorphic grade 3 oxygen and carbon isotope values for calcite in the ophiolite are not in equilibrium with the ophiolite but are similar to those of the overlying calc schists schistes lustres and 4 hydrogen isotopes indicate that serpentinitisation of ultramafics occurred during sub seafloor hydrothermal alteration and probably also during tectonic emplacement of the ophiolite these features indicate that large scale fluid flow did not affect the corsican ophiolite during subduction zone metamorphism calcite in the ophiolite was probably precipitated from co2 bearing fluids derived from decompression dehydration reactions affecting the overlying schistes lustres during exhumation of the ophiolite bearing schistes lustres nappes given that ocean crust must undergo at least some dehydration during prograde subduction zone metamorphism the evolved fluids must be either highly channelled or exit the slab relatively quickly so as to not interact with it the results of this study indicate that the important fluid pathways on corsica have yet to be identified but are probably the shear zones and fault systems that bound different slices of the high pressure nappe stack

paleosecular variation of brunhes age lava flows from british columbia canada 1 brunhes age lava flows have been sampled for paleosecular variation studies from several volcanic fields of southern british columbia silverthrone garibaldi lake mt meager clearwater wells gray park and kelowna area a total of 52 lava flows were sampled and 7 to 10 samples were drilled at each site previous radiometric studies indicate that the ages of these lava flows range from 2 3 to 760 ka stepwise thermal demagnetization 14 to 21 steps was carried out for all the samples in each site and af demagnetization was performed on one sample per site forty five sites were selected based on rigorous criteria 95 5 to calculate a mean direction d 356 9 i 70 2 95 2 8 that is statistically indistinguishable from the direction of the dipole field at the area i 68 3 virtual geomagnetic poles vgps do not show the far sided effect and the angular standard deviation is 17 5 a value in agreement with the paleomagnetic field dispersion for that latitude these high quality results are expected to improve the time averaged field taf and secular variation models

evolution of alkalic lavas at haleakala volcano east maui hawaii the postshield and posterosional stages of haleakala volcano contain intercalated alkalic basalt and evolved alkalic lavas isotopic and incompatible element abundance ratios in the haleakala postshield basalts changed systematically with time providing evidence for significant temporal changes in the mantle components contributing to the magmatic sources specifically a depleted i e low87sr 86sr and high143nd 144nd mantle component is more abundant in younger lavas however as magma production rates decreased during the postshield and posterosional stages basaltic melts in magma reservoirs cooled and fractionated leading to evolved residual melts such as hawaiite because primary basalt compositions changed with time the evolved haleakala lavas formed from a range of parental compositions however basalts and evolved lavas of similar age and isotopic ratios sr and nd have major and trace element contents that are consistent with a crystal fractionation model although alkalic basalt and hawaiite are the dominant lavas of the postshield stages of both haleakala and mauna kea volcanoes there are important differences between their lavas for example compositional differences between the hawaiite suites at haleakala and mauna kea indicate that on average the evolved lavas at haleakala formed at lower pressures also at haleakala basalts are intercalated with hawaiites whereas at mauna kea basalts and hawaiites are separated by a sharp boundary these differences probably reflect a higher magma supply rate to the haleakala volcano

new k ar ages and the geologic evidence against rejuvenated stage volcanism at haleakalā east maui a postshield stage volcano of the hawaiian island chain the postshield and previously inferred rejuvenated stage history of haleakal volcano is reevaluated on the basis of 52 new k ar ages 42 from the postshield kula volcanics and 10 from the overlying h na volcanics postshield extrusion was robust from 0 93 to 0 76 ma a period of low extrusion rate or volcanic quiescence occurred between 0 76 and 0 65 ma well within kula time a chemical change to increasingly alkalic lava occurred at this time as the volcano changed from broadly hawaiitic to basanitic in its eruptive products and robust extrusion resumed a slightly longer period of low extrusion rate or quiescence occurred after ca 0 4 ma but only trifling change in geochemical character is observed geochemically the h na volcanics unit chiefly basanitic overlaps greatly with the upper part of the kula volcanics there is a weak tendency to slightly more alkaline character among the h na volcanics the age of the kula h na boundary is ca 0 15 0 12 ma thus volcanic quiescence of only 0 03 m y separates the two formations much shorter than the previously known limit of 0 25 0 30 m y the brevity of this hiatus coupled with coincident vent loci and broadly similar geochemical characteristics for the h na and the upper part of the kula volcanics indicates that the h na volcanics unit comprises deposits of postshield stage volcanism that has waned substantially since ca 0 4 0 3 ma haleakal has not yet begun a classically defined rejuvenated stage our findings support recent numerical modeling of plume lithosphere interactions that predict that haleakal is near the end of its postshield growth

geochemistry of kauai volcanics and a mixing model for the origin of hawaiian alkali basalts a comprehensive model is developed to explain the major trace element and strontium and neodymium isotopic characteristics of alkali basalts from hawaii the model is similar to that of chen and frey 1983 in that it requires mixing of a small melt fraction of morb source material with another component to generate the alkalic suite of a particular hawaiian volcano it differs from the chen and frey model in that the other end member must be different from primitive mantle if it is to be consistent with both trace element and isotopic data alkali basalts and tholeiites from kauai analyzed in this study show a nearly complete transition in sr and nd isotopes there is a relatively well constrained array on a nd sr isotope correlation plot that can be explained by two component mixing of kauai tholeiite magma and a small amount of melt of east pacific rise source rock after corrections are made for fractional crystallization involving primarily clinopyroxene and olivine the sr and ba concentrations of kauai lavas plot along mixing curves defined by the above sources providing positive tests of the mixing hypothesis implications of this model are 1 the main source of hawaiian shield building tholeiites is a mixture of subducted crust primitive mantle and depleted asthenosphere that has been homogenized prior to melting 2 early alkalic volcanism as at loihi seamount will be characterized by greater isotopic heterogeneity than will late stage alkali basalt production and 3 there are two fundamentally distinct types of alkalic lavas erupted towards the end of magmatism at a given hawaiian volcano one represents smaller degrees of melting of the same source that generated shield building tholeiites kohala type the other derives from the mixed source discussed in this paper haleakala kauai type