persistent scatterer interferometric synthetic aperture radar for crustal deformation analysis with application to volcan alcedo galapagos 1 while conventional interferometric synthetic aperture radar insar is a very effective technique for measuring crustal deformation almost any interferogram includes large areas where the signals decorrelate and no measurement is possible persistent scatterer ps insar overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms existing ps methods have been very successful in analysis of urban areas where stable angular structures produce efficient reflectors that dominate background scattering however man made structures are absent from most of the earth s surface furthermore existing methods identify ps pixels based on the similarity of their phase history to an assumed model for how deformation varies with time whereas characterizing the temporal pattern of deformation is commonly one of the aims of any deformation study we describe here a method for ps analysis stamps that uses spatial correlation of interferogram phase to find pixels with low phase variance in all terrains with or without buildings prior knowledge of temporal variations in the deformation rate is not required for their identification we apply stamps to volcan alcedo where conventional insar fails because of dense vegetation on the upper volcano flanks that causes most pixels to decorrelate with time we detect two sources of deformation the first we model as a contracting pipe like body which we interpret to be a crystallizing magma chamber the second is downward and lateral motion on the inner slopes of the caldera which we interpret as landsliding

deformation and hydrothermal metamorphism of gabbroic rocks within the godzilla megamullion parece vela basin philippine sea abstract microstructural and petrologic analyses of 7 gabbroic rocks sampled from the medial area of the godzilla megamullion site kh07 02 d18 located along the parece vela basin spreading ridge parece vela rift philippine sea reveal the development of a high temperature ductile shear zone associated with hydrothermal metamorphism in the lower crust the deformed gabbroic rocks are petrographically classified into mylonites and an ultramylonite and are characterized by porphyroclastic textures consisting mainly of coarse plagioclase and clinopyroxene amphibole porphyroclasts in a fine grained matrix plagioclase crystallographic preferred orientations vary from 010 100 and 001 100 patterns in the mylonites to a weak 001 100 pattern in the some mylonites and ultramylonite suggesting a change in the deformation mechanism from dislocation creep to grain size sensitive creep with increasing intensity of deformation the chemical composition of matrix plagioclase is generally more sodic than that of porphyroclasts secondary amphibole is ubiquitous consisting mainly of pargasite and magnesiohornblende brown hornblende and actinolite green hornblende the mineral assemblage is consistent with the hydrothermal metamorphic reaction clinopyroxene calcic plagioclase fluid amphibole sodic plagioclase compared with deformed gabbroic rocks from the breakaway and termination areas of the godzilla megamullion the samples record ductile shearing under high temperature conditions possibly related to the development of the godzilla megamullion although hydrothermal activity in the medial area appears to have been less intense than in both the breakaway and termination areas

the challenging retrieval of the displacement field from insar data for andesitic stratovolcanoes case study of popocatepetl and colima volcano mexico abstract despite the ability of synthetic aperture radar sar interferometry to measure ground motion with high resolution application of this remote sensing technique to monitor andesitic stratovolcanoes remains limited specific acquisition conditions characterizing andesitic stratovolcanoes mainly vegetated areas with large elevation ranges induce low signal coherence as well as strong tropospheric artefacts that result in small signal to noise ratio we propose here a way to mitigate these difficulties and improve the sar measurements we derive ground motions for two of the most active mexican stratovolcanoes popocatepetl and colima volcano from the time series of sar data acquired from december 2002 to august 2006 the sar data are processed using a method that combines both persistent scatterers and small baseline approaches stratified tropospheric delays are estimated for each interferogram using inputs from the global atmospheric model narr up to a maximum of 10 rad km these delays are validated using spectrometer data as well as the correlation between the wrapped phase and the elevation the tropospheric effect is removed from the wrapped phase in order to improve the unwrapping process on popocatepetl we observe no significant deformation the colima summit area exhibits a constant subsidence rate of more than 1 cm year centered on the summit but enhanced reaching more than 2 cm year around the 1998 lava flow we model this subsidence considering both a deflating magma source at depth and the effect of the eruptive deposits load

magma supply dynamics at westdahl volcano alaska modeled from satellite radar interferometry 1 a group of satellite radar interferograms that span the time period from 1991 to 2000 shows that westdahl volcano alaska deflated during its 1991 1992 eruption and is reinflating at a rate that could produce another eruption within the next several years the rates of inflation and deflation are approximated by exponential decay functions having time constants of about 6 years and a few days respectively this behavior is consistent with a deep constant pressure magma source connected to a shallow reservoir by a magma filled conduit an elastic deformation model indicates that the reservoir is located about 6 km below sea level and beneath westdahl peak we propose that the magma flow rate through the conduit is governed by the pressure gradient between the deep source and the reservoir the pressure gradient and hence the flow rate are greatest immediately after eruptions pressurization of the reservoir decreases both the pressure gradient and the flow rate but eventually the reservoir ruptures and an eruption or intrusion ensues the eruption rate is controlled partly by the pressure gradient between the reservoir and surface and therefore it too decreases with time when the supply of eruptible magma is exhausted the eruption stops the reservoir begins to repressurize at a high rate and the cycle repeats this model might also be appropriate for other frequently active volcanoes with stable magma sources and relatively simple magma storage systems

seismic quantification of the explosions that destroyed the dome of volcan de colima mexico in july august 2003 in july august 2003 the andesitic lava dome at volcan de colima mexico was destroyed by a sequence of explosions that replaced the 2 106 m3 dome with a crater 200 m across and 30 m deep the two strongest explosions occurred on july 17 and august 28 the initial low frequency impulses that they produced which were recorded on broadband seismic records allowed an estimation of the counter forces of the initiating process as being equal to 0 3 1011 n and 1 1011 n for the july and august events respectively the seismic characteristics follow the nishimura hamaguchi scaling law for volcanic explosions reflecting self similarity in the processes initiating explosive events the results also show that counter forces can discriminate between the sizes of explosive eruptions that are assigned the same magnitude by conventional methods of classification such as the volcanic explosivity index the increasing use of broadband seismometers may therefore provide the basis for using counter forces to determine the magnitude of explosive eruptions

geotectonic significance of gneissic amphibolites from the vema fracture zone equatorial mid atlantic ridge a large collection of gneissic amphibolites was recovered by two close dredge hauls from the deepest part of the north facing slope of the transverse ridge forming the south wall of the vema fracture zone serpentinites and various types of gabbroic rocks ranging from undeformed slightly uralitized gabbros and norites to flaser and mylonitic gabbros were associated with the gneissic amphibolites in the shallowest of the dredge hauls petrological studies indicate that the amphibolites were derived from similar gabbroic rocks that reequilibrated under stress in the conditions of the amphibolite facies on the other hand the associated meta gabbros display sequences of secondary minerals indicating complex cooling and cataclastic histories without reaching metamorphic equilibrium we tentatively suggest that the gneissic amphibolites and associated metagabbros formed in a vertical shear zone generated in oceanic layer 3 by tectonism associated with the vema fracture zone hydrothermal circulation of seawater along the highly permeable shear zone was activated by magmatic intrusions k ar dating suggests within relatively large analytical uncertainties that the amphibolite metamorphism took place 10 m y ago i e at a time when the dredging sites were located in the vicinity of the spreading center

satellite radar interferometry 1993 1999 suggests deep accumulation of magma near the crust mantle boundary at the krafla volcanic system iceland 1 deep magma accumulation near the crust mantle boundary 21 km depth at the krafla volcanic system is suggested from insar observations a best fit model derived from four interferograms covering 1993 1999 comprises an opening dike representing plate spreading and post rifting deformation and two mogi sources a mogi source deflating at a rate of 0 3 106 m3 yr coincides with the shallow krafla magma chamber while a deeper inflating mogi source further north at 21 km depth inflates at a rate of 26 106 m3 yr the inflating source is at or near the crust mantle boundary as identified by seismic studies and is interpreted as accumulating magma

monitoring the 2004 andesitic block lava extrusion at volcan de colima mexico from seismic activity and so2 emission the 2004 andesitic block lava extrusion at volcan de colima mexico was accompanied and followed by numerous seismic signals associated with rockfalls pyroclastic flows and explosive events we analyze temporal variations in the number of rockfalls and explosions the seismic signal duration of rockfalls and the energy of the explosion and compare this with both the rate of magma discharge and so2 emission characteristics of seismic signals and so2 emission are compared with those observed during the 1998 1999 volcan de colima block lava extrusion for both eruptions the explosive activity was low during the lava extrusion and increased after its termination the variation in the daily number and the total duration of rockfall seismic signals gives a good reflection of the development of the lava emission process an increase in magmatic degassing so2 flux was observed some days before the onset of lava extrusion the degassing strongly decreased some days before the peak in the rate of the 1998 1999 lava emission but reached its peak together with the peak in the rate of the 2004 lava emission these features of seismic activity and so2 emission demonstrate that they are good tools for monitoring the extrusion process

a revised subduction inception model to explain the late cretaceous double vergent orogen in the precollisional western tethys evidence from the northern apennines the meso cenozoic alpine belts of the mediterranean area are characterized by complex architectures result of a complex subduction and collision evolution that preserve also a legacy of the rifting related configuration of the continental margins the northern apennines is a segment of these belts originated during closure of the ligure piemontese ocean and collision between the europe and adria plates the different configuration of the adria and europe margins inherited from asymmetric rifting is recorded in the ligurian units that preserve incorporation into the subduction factory of fragments of the oceanic domain internal ligurian units and portions of the ocean continent transition zone octz toward adria external ligurian units we provide here unpublished data on the stratigraphy and sedimentology of these units together with a review of what is already established in literature both datasets combined testify that at 80 m a an accretionary prism was growing between the deposition basins of the two groups of units and fed both basins with clasts from the ocean realm the continental crust and the subcontinental mantle we propose that closure of the ligure piemontese ocean occurred through subduction that nucleated at the transition from the oceanic plate and the thinned adria margin and developed a double vergent prism by accreting oceanic material and continental extensional allochthons from the octz we believe the revised site of subduction initiation and the pre collisional architecture inherited from the rifting and spreading phases allow reconciling most of the discrepancies between the various interpretation proposed in literature for the pre collisional evolution of the apennines

submarine metamorphism of gabbros from the mid cayman rise petrographic and mineralogic constraints on hydrothermal processes at slow spreading ridges the coarse grained submersible collected rocks from the mid cayman rise in our study span a vertical section of about 700 m and range from amphibolite to gabbro petrographic and mineralogic studies showed that 1 some deformation is present in all rocks 2 the distribution of deformation is not uniform within a specimen and 3 alteration has taken place preferentially in the deformed zones the abundance of amphibole decreases with sample depth and argues that seawater flux into the oceanic crust decreased with depth the compositional changes in rocks indicate that partially exchanged seawater was the metamorphic fluid that supplied na k and h2o to and removed ca from the rock in all about 15 of the original rock has been transformed to amphibolite in the 700 m vertical section our study indicates that deformation of oceanic crust is necessary for providing pathways for seawater penetration which in turn is necessary for the submarine metamorphism to occur if deformation continues to take place during the spreading of seafloor alteration may also continue to occur along newly formed fractures and cracks

drilling constraints on lithospheric accretion and evolution at atlantis massif mid atlantic ridge 30 n expeditions 304 and 305 of the integrated ocean drilling program cored and logged a 1 4 km section of the domal core of atlantis massif postdrilling research results summarized here constrain the structure and lithology of the central dome of this oceanic core complex the dominantly gabbroic sequence recovered contrasts with predrilling predictions application of the ground truth in subsequent geophysical processing has produced self consistent models for the central dome the presence of many thin interfingered petrologic units indicates that the intrusions forming the domal core were emplaced over a minimum of 100 220 kyr and not as a single magma pulse isotopic and mineralogical alteration is intense in the upper 100 m but decreases in intensity with depth below 800 m alteration is restricted to narrow zones surrounding faults veins igneous contacts and to an interval of locally intense serpentinization in olivine rich troctolite hydration of the lithosphere occurred over the complete range of temperature conditions from granulite to zeolite facies but was predominantly in the amphibolite and greenschist range deformation of the sequence was remarkably localized despite paleomagnetic indications that the dome has undergone at least 45 degrees rotation presumably during unroofing via detachment faulting both the deformation pattern and the lithology contrast with what is known from seafloor studies on the adjacent southern ridge of the massif there the detachment capping the domal core deformed a 100 m thick zone and serpentinized peridotite comprises similar to 70 of recovered samples we develop a working model of the evolution of atlantis massif over the past 2 myr outlining several stages that could explain the observed similarities and differences between the central dome and the southern ridge

deformation of popocatepetl volcano using gps regional geodynamic context and constraints on its magma chamber we have operated a gps network on popocatepetl volcano since 1994 consisting of a total of 7 continuous gps stations on its northern and southwestern flanks and one additional station in the vicinity of the volcano the overall characteristic behavior of popocatepetl volcano during this period can be described as a minimally deforming system in sharp contrast with its essentially continuous visible eruptive activity a north component motion analysis assuming a fixed north american plate shows a close correspondence of the popocatepetl sites to those of other regional gps sites most of the large deformation transients observed on the popocatepetl sites are therefore not of magmatic origin but instead reflect aseismic transients that have been recognized recently as part of the mid american trench subduction process the surface deformation record of popocatepetl volcano therefore suggests a magmatic system that lacks a well defined shallow magma chamber where most of the magma storage transport and ascent is carried out via a network of deep rooted conduits that eventually extend to the summit crater in most cases popocatepetl seems to operate as a semi open system thereby preventing any significant pressure build up

the deformation field of the august 2003 eruption at piton de la fournaise reunion island mapped by asar interferometry 1 three independent asar interferograms spanning the august 2003 piton de la fournaise eruption reveal a 3 by 3 km asymmetric pattern of range changes centred on the dolomieu crater northern flank it corresponds to 30 cm of displacement towards the satellite east of the eruptive fissures and 7 cm away from the satellite west of the fissures displacements are caused by dyke emplacement below fissures we model the deformation using a 3d mixed boundary element method for elastic media this consists of a dyke defined by six geometric parameters and an overpressure gradient a neighbourhood algorithm was applied to explore this 7 dimensional parameter space the best fit model is a 57 eastward dipping dyke with a base lying around 1520 m a s l the model provides new evidence of the dyke intrusion related seaward displacements of the volcano eastern flank

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

time dependent land uplift and subsidence in the santa clara valley california from a large interferometric synthetic aperture radar data set 1 we invert 115 differential interferograms derived from 47 synthetic aperture radar sar scenes for a time dependent deformation signal in the santa clara valley california the time dependent deformation is calculated by performing a linear inversion that solves for the incremental range change between sar scene acquisitions a nonlinear range change signal is extracted from the ers insar data without imposing a model of the expected deformation in the santa clara valley cumulative land uplift is observed during the period from 1992 to 2000 with a maximum uplift of 41 18 mm centered north of sunnyvale uplift is also observed east of san jose seasonal uplift and subsidence dominate west of the silver creek fault near san jose with a maximum peak to trough amplitude of 35 mm the pattern of seasonal versus long term uplift provides constraints on the spatial and temporal characteristics of water bearing units within the aquifer the silver creek fault partitions the uplift behavior of the basin suggesting that it acts as a hydrologic barrier to groundwater flow while no tectonic creep is observed along the fault the development of a low permeability barrier that bisects the alluvium suggests that the fault has been active since the deposition of quaternary units

conditions for detection of ground deformation induced by conduit flow and evolution 1 at mature andesitic volcanoes magma can reach the surface through the same path for several eruptions thus forming a volcanic conduit because of degassing cooling and crystallization magma viscosity increase in the upper part of the conduit may induce the formation of a viscous plug we conducted numerical simulations to quantify the deformation field caused by this plug emplacement and evolution stress continuity between newtonian magma flow and elastic crust is considered plug emplacement causes a ground inflation correlated to a decrease of the magma discharge rate a parametric study shows that surface displacements depend on three dimensionless numbers the conduit aspect ratio radius length the length ratio between the plug and the conduit and the viscosity contrast between the plug and the magma column larger displacements are obtained for high viscosity plugs emplaced in large aspect ratio conduits we find that only tiltmeters or gps located close to the vent a few hundred meters might record the plug emplacement at immediate proximity of the vent plug emplacement might even dominate the deformation signal over dome growth or magma reservoir pressurization effects for given plug thicknesses and viscosity profiles our model explains well the amplitude of tilt variations from 1 to 25 rad measured at montserrat and mt st helens we also demonstrate that at montserrat even if most of the tilt signal is due to shear stress induced by magma flow pressurization beneath the plug accounts for 20 of the signal

deflation of mount etna monitored by spaceborne radar interferometry ground based measurements of volcano deformation can be used to assess eruptive hazard but require the costly and often hazardous installation and maintenance of an instrument network here we show that spaceborne radar interferometry which has already shown its utility in mapping earthquake related deformation1 can be used to monitor long term volcano deformation two families of synthetic aperture radar images acquired from ascending and descending orbits by the satellite ers 1 and looking at mount etna from opposite sides cover the time period from 17 may 1992 to 24 october 1993 and include the second half of etna s most recent eruption despite artefacts of the interferometric technique we can observe a volcano wide deflation which is an expected consequence of the eruption but which had not previously been appreciated we quantify it using a simple model based on the change of pressure in a sphere located in an elastic half space the modelled deformation increases linearly with time until the end of the eruption our results show that it will be possible to use this technique to detect the inflation of volcanic edifices that usually precedes eruptions

fossil oceanic core complexes recognized in the blueschist metaophiolites of western alps and corsica tethyan ophiolites show an apparent poorly organized association of ultramafic andmafic rocks by contrast tothe complete mantle crustal sections of semail type ophiolite sheets tethyan ophiolites are characterized by asmaller amount of mafic rocks gabbros and basalts by the absence of any sheeted dyke complex and by thefrequent occurrence of oceanic sediments stratigraphically overlying mantle derived peridotites and associatedgabbroic intrusions therefore they are considered as typical remnants of oceanic lithosphere formed in slowspreadingenvironment or in ocean continent transition at distal passive margins in the very first models offormation of the tethyan ophiolites in the years 1980 the geodynamical processes leading to mantle unroofingwere poorly understood due to the paucity of data and concepts available at that time from the present dayoceans in particular at that time little work had focused on the distribution origin and significance ofmafic rocks with respect to the dominant surrounding ultramafics here we reconsider the geology of sometypical metaophiolites from the western alps and corsica and we show how results from the past decadeobtained in the current oceans ask for reassessing the significance of the tethyan ophiolites in general revisitedexamples include a set of representative metaophiolites from the blueschists units of the western alps queyrasregion and from alpine corsica golo valley field relationships between the ophiolitic basement andthe metasedimentary metavolcanic oceanic cover are described outlining a typical character of the tethyanophiolite lithological associations jurassic marbles and polymictic ophiolite metabreccias are unconformablyoverlying the mantle gabbo basement in a way strictly similar to what is observed in the non metamorphicappennine ophiolites or chenaillet massif this confirms that very early tectonic juxtaposition of ultramafic andmafic rocks occurred in the oceanic domain before subduction this juxtaposition resulted from tectonic activitythat is now assigned to the development of detachment faults and to the formation of oceanic core complexes occs at the axis of slow spreading ridges this fundamental plate tectonics process is responsible for the exhumationand for the axial denudation of mantle rocks and gabbros at diverging plate boundaries in addition fieldrelationships between the discontinuous basaltic formations and the ultramafic mafic basement indicate that thistectonic stage is followed or not by a volcanic stage we discuss this issue in the light of available field constraints

reactive flow as dominant evolution process in the lowermost oceanic crust evidence from olivine of the pineto ophiolite corsica the jurassic pineto ophiolite from corsica exposes a 1 km thick troctolite olivine gabbro sequence interpreted to represent a lowermost sector of the gabbroic oceanic crust from a ultra slow spreading system to constrain the petrogenesis of the olivine gabbros minor and trace element analyses of olivine forsterite 84 82 mol were carried out olivine from the olivine gabbros is depleted in incompatible trace elements sc v ti y zr and heavy rare earth elements with respect to olivines from associated troctolites depleted incompatible element compositions are also shown by olivine forsterite 86 mol from a clinopyroxene rich troctolite the incompatible element compositions of olivine argue against a petrogenetic process entirely driven by fractional crystallization we propose that melts migrating through an olivine plagioclase crystal mush chemically evolved by reaction with the existing minerals changing in composition as it flowed upward the melt residual from these interactions led to partial dissolution of preexisting olivine and to crystallization of clinopyroxene generating olivine gabbro bodies within a troctolite matrix reactive flow was the major evolution process active in the 1 km crustal transect exposed at the pineto ophiolite producing lithological variations classically attributed to fractional crystallization processes

persistent summit subsidence at volcan de colima mexico 1982 1999 strong evidence against mogi deflation this paper re examines recent ground deformation measurements at volcan de colima mexico to test the hypothesis that the observed movements are in response to pressure changes within a sub volcanic magma chamber as suggested for other volcanoes by mogi 1958 earthq res inst 36 99 134 measurements of vertical ground deformation across the summit dome complex of volcan de colima from a precise levelling network between 1982 and 1999 together with vertical and horizontal displacements derived from dual frequency gps measurements in 1994 and 1997 show continuous subsidence the deformation pattern derived from the levelling shows that subsidence increases towards the summit the closest stations to the summit 1 1 km distant show a mean subsidence rate of 5 mm per year compared to the reference station at 2 3 km distance which may be subsiding itself vertical displacements of individual stations since 1982 show that the subsidence has been fairly continuous the gps stations which are distributed more widely and include some close to the edge of the active dome confirm summit subsidence the largest measured value a decrease of 280 mm or 93 mm subsidence per year was obtained at the edge of the dome horizontal displacements measured during 1994 1997 also show the largest values at the summit but these are much smaller than the vertical displacements with the maximum rate of 23 mm per year recorded close to the dome it is conclusively shown that these measured movements cannot be due to deflation of a buried mogi source as vertical and horizontal displacements for some stations are in contrary directions to those predicted by the model and there is no consistent pattern to the horizontal movements we attribute the measured deformation to downslope creep settling and compaction of the edifice gravitational spreading or a combination of these processes

precursory seismicity of the 1994 eruption of popocatepetl volcano central mexico popocatepetl volcano is located in the central mexican volcanic belt within a densely populated region inhabited by over 20 million people the eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions including plinian events after nearly 70 years of quiescence popocatepetl reawakened in december 21 1994 the eruptive activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth and destruction episodes similar to events that have apparently been typical for popocatepetl since the fourteenth century in this regime the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence in this paper we analyze five years of volcano tectonic seismicity preceding the initial eruption of the current episode the evolution of the v t seismicity shows four distinct stages which we interpret in terms of the internal processes which precede an eruption after a long period of quiescence the thermal effects of a magma intrusion at depth the fracturing related to the slow development of magma related fluid pathways the concentration of stress causing a protracted acceleration of this process and a final relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of v t seismic energy release a hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically forecast the time of the eruption the total seismic energy release needed to produce an eruption after a long period of quiescence is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes limit that was reached by popocatepetl before the eruption

accuracy of topographic maps derived from ers 1 interferometric radar an interferometric radar technique for topographic mapping of surfaces promises a high resolution approach to the generation of digital elevation models the authors present analyses of data collected by the synthetic aperture radar instrument on board the ers 1 satellite on successive orbits use of a single satellite in a nearly repeating orbit is attractive for reducing cost and spaceborne hardware complexity also it permits inference of changes in the surface from the correlation properties of the radar echoes the data have been reduced to correlation maps and digital elevation models the correlation maps show that temporal correlation decreases significantly with time but not necessarily at a constant well defined rate likely depending on environmental factors when correlation among passes remains high however it is possible to form digital elevation models analyses of noise expected in ers 1 interferometric data collected over alaska and the southwestern united states indicate that maps with relative errors less than 5 m rms are possible in some regions however orbit uncertainties imply that tie points are required in order to reduce absolute height errors to a similar magnitude the authors find that about 6 tie points per 40 spl times 40 km scene with 5 m rms or better height accuracy are needed to keep systematic map height errors below 5 m rms the performance of the ers 1 radar system for topographic applications though useful for a variety of regional and local discipline studies may be improved with respect to temporal decorrelation errors and absolute height acuity by modifying the orbit repeat period and incorporating precise orbit determination techniques the resulting implementation will meet many but not all objectives of a global mapping mission

the magmatic hydrothermal transition in the lower oceanic crust clues from the ligurian ophiolites italy abstract the gabbroic bodies from the jurassic ligurian ophiolites are structurally and compositionally similar to the gabbroic sequences from the oceanic core complexes of the mid atlantic ridge initial cooling of the ligurian gabbros is associated with local development of hornblende bearing felsic dykes and hornblende vein networks the hornblende veining is correlated with the widespread development of hornblende as coronas pseudomorphs after the clinopyroxene in the host gabbros in addition the studied gabbroic body includes a mantle sliver locally containing hornblende gabbros and hornblendite veins the hornblendes from the felsic dykes and the hornblende rich rocks within the mantle sliver show a similar geochemical signature characterized by low mg cao and al2o3 negligible cl and high tio2 k2o ree y zr and nb concentrations the whole rock sm nd isotopic compositions of the felsic dykes and the hornblende rich rocks define a sm nd isochron corresponding to an age of 154 20 ma and an initial end of 9 2 0 5 the 18o of the hornblendes and coexisting zircons from these rocks about 4 5 and 5 8 respectively do not indicate the presence of a seawater component in these melts the formation of the felsic dykes and of the hornblende rich rocks within the mantle sliver involved sio2 rich silicate melts with negligible seawater component which presumably were derived from high degree fractional crystallization of mor type basalts the vein and the coronitic pseudomorphic hornblendes show high mg and cao significant cl 0 02 0 17 wt and low tio2 and k2o concentrations the coronitic pseudomorphic hornblendes have trace element compositions similar to those of the clinopyroxenes from the gabbros and 18o values 1 0 to 0 7 close to seawater suggesting an origin by reaction between migrating seawater derived fluids and the host gabbros the vein hornblendes commonly show slight lree enrichment relatively high concentrations of nb up to 2 5 ppm and 18o ranging from 3 7 to 0 8 the crystallization of these hornblendes most likely involved both seawater and magmatic components

dating the growth of oceanic crust at a slow spreading ridge nineteen uranium lead zircon ages of lower crustal gabbros from atlantis bank southwest indian ridge constrain the growth and construction of oceanic crust at this slow spreading midocean ridge approximately 75 of the gabbros accreted within error of the predicted seafloor magnetic age whereas 25 are significantly older these anomalously old samples suggest either spatially varying stochastic intrusion at the ridge axis or more likely crystallization of older gabbros at depths of 5 to 18 kilometers below the base of crust in the cold axial lithosphere which were uplifted and intruded by shallow level magmas during the creation of atlantis bank

two scales of inflation at lastarria cordon del azufre volcanic complex central andes revealed from asar envisat interferometric data abstract asar envisat interferometric synthetic aperture radar insar data collected over the lastarria cordon del azufre complex chile argentina between march 2003 and may 2005 show the persistence of the large wavelength ground inflation revealed by pritchard and simons in 2002 from the analysis of ers insar data nature 418 2002 167 170 after reducing the tropospheric contribution in the interferograms using a combination of data network adjustment and analysis of modis images we produced an accurate interferometric time series showing a 2 yr long temporal evolution of the ground displacements patterns two distinct inflating signals are detected the main signal covers an elliptical area with a 45 km nne ssw major axis and a 37 km minor axis it is correlated with a regional topographic dome we estimated its maximum inflation rate to 2 5 cm yr 1 we inverted the insar data for a range of source geometries spherical prolate ellipsoids penny shaped cracks the inferred source parameters for 2003 2005 period are consistent with an over pressured reservoir at shallow to intermediate crustal depths 7 15 km with an average volumetric rate of inflation of about 14 106 m3 yr 1 in addition to this main signal a new feature highlighted by the asar data is short wavelength inflation 6 km wide at the location of lastarria volcano on the northern margin of the large wavelength signal we explain this short wavelength signal by a spherical over pressured source lying 1000 m below the summit of lastarria volcano we estimate the average volumetric rate of inflation during the observation period to be 35 103 m3 yr 1 it is remarkable that both volumetric variations for the large and small inflations exhibit the same evolution during the 2003 2005 period suggesting that both processes could be related on the basis of the inversion results and of arguments provided by field evidences and a morpho structural analysis of the digital elevation model of the area we propose that the deep source have a magmatic origin while the shallow source is most likely related to hydrothermal fluids in our interpretation the on going deformation processes observed at lastarria cordon del azufre volcanic complex could represent an evolving pre caldera silicic system further field geological and geophysical investigations will be required to confirm these hypotheses and refine the proposed model mostly based on satellite observations

constraints on magma flux from displacements data at merapi volcano java indonesia the displacement field has been monitored in the vicinity of the crater rim at mount merapi indonesia from 1993 to 1997 during this period the volcanic activity has been quasicontinuous with dome growth explosions and pyroclastic flows we measured a nine point network every year with the global positioning system static method interpretation of results is conducted with a three dimensional elastostatic boundary elements code that takes into account topography fractures and complex magma source geometry the inversion technique yields an estimate of the variation with time of the boundary conditions at the magma duct interface together with the probability associated with the best model the young s modulus of the equivalent continuum is found to be very low of the order of 1 gpa a feature which suggests that a viscoelastic behavior may be more appropriate for this rock mass given the observed seismic velocities for the domain of interest a striking compatibility is outlined between observed deformations and the rate of occurrence of multiphase seismic events once the main fractures of the structure have been taken into consideration this suggests that the summit elastic or viscoelastic deformation field is controlled by the magma flux within the duct rather than by magma pressure variations in addition a nonelastic displacement has been identified at the westernmost point of the network this was considered critical for the stability of the summit structure a concern whose validity has been verified a posteriori by the july 1998 explosion

an insar based survey of volcanic deformation in the central andes we extend an earlier interferometric synthetic aperture radar insar survey covering about 900 remote volcanos of the central andes 14 27 s between the years 1992 and 2002 our survey reveals broad 10s of km roughly axisymmetric deformation at 4 volcanic centers two stratovolcanoes are inflating uturuncu bolivia and hualca hualca peru another source of inflation on the border between chile and argentina is not obviously associated with a volcanic edifice here called lazufre and a caldera cerro blanco also called robledo in northwest argentina is subsiding we explore the range of source depths and volumes allowed by our observations using spherical ellipsoidal and crack like source geometries we further examine the effects of local topography upon the deformation field and invert for a spherical point source in both elastic half space and layered space crustal models we use a global search algorithm with gradient search methods used to further constrain best fitting models inferred source depths are model dependent with differences in the assumed source geometry generating a larger range of accepted depths than variations in elastic structure source depths relative to sea level are 8 18 km at hualca hualca 12 25 km for uturuncu 5 13 km for lazufre and 5 10 km at cerro blanco deformation at all four volcanoes seems to be time dependent and only uturuncu and cerro blanco were deforming during the entire time period of observation inflation at hualca hualca stopped in 1997 perhaps related to a large eruption of nearby sabancaya volcano in may 1997 although there is no obvious relation between the rate of deformation and the eruptions of sabancaya we do not observe any deformation associated with eruptions of lascar chile at 16 other volcanoes that had recent small eruptions or fumarolic activity or associated with a short lived thermal anomaly at chiliques volcano we posit a hydrothermal system at cerro blanco to explain the rate of subsidence there for the last decade we calculate the ratio of the volume of magma intruded to extruded is between 1 10 and that the combined rate of intrusion and extrusion is within an order of magnitude of the inferred geologic rate

cooling rates and the depth of detachment faulting at oceanic core complexes evidence from zircon pb u and u th he ages oceanic detachment faulting represents a distinct mode of seafloor spreading at slow spreading mid ocean ridges but many questions persist about the thermal evolution and depth of faulting we present new pb u and u th he zircon ages and combine them with magnetic anomaly ages to define the cooling histories of gabbroic crust exposed by oceanic detachment faults at three sites along the mid atlantic ridge ocean drilling program odp holes 1270d and 1275d near the 15 20 n transform and atlantis massif at 30 n closure temperatures for the pb u 800 c 850 c and u th he 210 c isotopic systems in zircon bracket acquisition of magnetic remanence collectively providing a temperature time history during faulting results indicate cooling to 200 c in 0 3 0 5 myr after zircon crystallization recording time averaged cooling rates of 1000 c 2000 c myr assuming the footwalls were denuded along single continuous faults differences in pb u and u th he zircon ages together with independently determined slip rates allow the distance between the 850 c and 200 c isotherms along the fault plane to be estimated calculated distances are 8 4 4 2 km and 5 0 2 1 km from holes 1275d and 1270d and 8 4 1 4 km at atlantis massif estimating an initial subsurface fault dip of 50 and a depth of 1 5 km to the 200 c isotherm leads to the prediction that the 850 c isotherm lies 5 7 km below seafloor at the time of faulting these depth estimates for active fault systems are consistent with depths of microseismicity observed beneath the hypothesized detachment fault at the tag hydrothermal field and high temperature fault rocks recovered from many oceanic detachment faults

protracted construction of gabbroic crust at a slow spreading ridge constraints from 206pb 238u zircon ages from atlantis massif and iodp hole u1309d 30 n mar sensitive high resolution ion microprobe shrimp u pb zircon ages of 24 samples from oceanic crust recovered in integrated ocean drilling program iodp hole u1309d and from the surface of atlantis massif mid atlantic ridge mar 30 n document a protracted history of accretion in the footwall to an oceanic detachment fault ages for 18 samples of evolved fe ti oxide gabbro and felsic dikes collected 40 1415 m below seafloor in u1309d yield a weighted mean of 1 20 0 03 ma mean square of weighted deviates 7 1 however the ages range from 1 08 0 07 ma and 1 28 0 05 ma indicating crustal construction occurred over a minimum of 100 200 ka the zircon ages along with petrologic observations indicate at least 2 major periods of intrusive activity with age peaks separated by 70 ka the oldest ages are observed below 600 mbsf an observation inconsistent with models requiring constant depth melt intrusion beneath a detachment fault the data are most consistent with a multiple sill model whereby sills intrude at random depths below the ridge axis over a length scale greater than 1 4 km zircon ages from broadly spaced samples collected along the southern ridge of atlantis massif yield a detachment fault slip rate of 28 7 6 7 mm a and imply significant asymmetric plate spreading up to 100 on the north american plate for at least 200 ka during core complex formation

diversity of melt conduits in the izu bonin mariana forearc mantle implications for the earliest stage of arc magmatism abstract magmatic processes during the earliest stage of subduction initiation are still not well understood we examined peridotites recovered from an exhumed crust mantle section exposed along the landward slopes of the northern izu bonin trench using the japan agency for marine earth science and technology9s remotely operated vehicle kaiko7000ii based on the cr cr cr al atomic ratio of spinel two distinctive groups 1 high cr 0 8 dunite and 2 medium cr 0 4 0 6 dunite occur close to each other and are associated with refractory harzburgite two distinctive melts were in equilibrium with these dunites a boninitic melt for the high cr dunite and a mid oceanic ridge basalt morb like melt for the medium cr dunite the tio 2 content of the latter melt is lower than typical morb compositions we suggest that the medium cr dunite was a melt conduit for a basalt recently reported from the mariana forearc that was erupted at the inception of subduction the wide range of variation in the cr s of spinels in dunites from the izu bonin mariana forearc probably reflects changing melt compositions from morb like melts to boninitic melts in the forearc setting due to an increase of slab derived hydrous fluids and or melts during subduction initiation

tropospheric corrections of sar interferograms with strong topography application to etna the accuracy of spaceborne geodetic techniques including sar interferometry is limited by the time and spatial variation and altitude dependance of the propagation delay of electomagnetic waves in the lower troposphere particularly in mountainous areas in this paper we use a 1d model developed for tropospheric corrections of gps and doris measurements to correct sar data the differential tropospheric delay is computed at each pixel of the interferogram from ground temperature humidity and pressure using two empirical parameters calibrated from several radio soundings acquired in various latitude and climate conditions it is shown that with such a model given the 3300 meters topography of etna tropospheric variations can generate up to 4 phase rotations between the top and the bottom of the volcano in 16 out of the 20 interferograms processed with images acquired between august 1992 and october 1993 correction of the tropospheric effect reduces the number of fringes associated with the 1991 93 eruption from previous estimates the remaining deformation is consistant with a deforming source located at a depth of 14 1 km during the second half of the eruption the subsidence rate at the top of the volcano is roughly stable at 13 3 mm month these values are in good agreement with tiltmeter data collected on etna during the same period and with the estimated volume of erupted material no significant deformation can be observed during the last month of eruption inflation of the volcano seems to resume immediately after the end of the eruption at a rate of 3 mm month

cooling rates in the lower crust of the oman ophiolite ca in olivine revisited debate over the mechanism of accretion of the lower oceanic crust has centered around the gabbro glacier and the sheeted sills models the thermal profile of the crust specifically the roles of hydrothermal circulation and cooling rate is a key component in distinguishing between these two models results of this study show no systematic variation of cooling rate with depth in the lower crust of the khafifah section in the wadi tayin massif of the oman ophiolite additionally very high rates recorded near the base of the crust suggest that hydrothermal circulation plays an important role in the removal of heat throughout the crust while the conclusions presented here do not rule out the possibility of accretion by gabbro glacier they do contradict the initial tenet of the gabbro glacier model convective heat loss by hydrothermal circulation can penetrate to moho depths and crystallization is not by necessity constrained to the upper crust on the basis of these results it can be concluded that the sheeted sills model is a thermally viable mechanism for accretion of oceanic lower crust

shear stress along the conduit wall as a plausible source of tilt at soufriere hills volcano montserrat 1 surface deformations recorded in close proximity to the active lava dome at soufriere hills volcano montserrat can be used to infer stresses within the uppermost 1000 m of the conduit system most deformation source models consider only isotropic pressurisation of the conduit we show that tilt recorded during rapid magma extrusion in 1997 could have also been generated by shear stresses sustained along the conduit wall these stresses are a consequence of pressure gradients that develop along the conduit numerical modelling incorporating realistic topography can reproduce both the morphology and half the amplitude of the measured deformation field using a realistic shear stress amplitude equivalent to a pressure gradient of 3 5 104 pa m 1 along a 1000 m long conduit with a 15 m radius this shear stress model has advantages over the isotropic pressure models because it does not require either physically unattainable overpressures or source radii larger than 200 m to explain the same deformation

petrology and sr nd and pb isotope geochemistry of mid ocean ridge basalt glasses from the 11 45 n to 15 00 n segment of the east pacific rise 1 basaltic glasses from the geophysically well studied section of the east pacific rise epr between 11 45 n to 15 00 n range from normal mid ocean ridge basalts morb to transitional morb and their major element variations correlate with isotopic and trace element indices of enrichment to first order basalts enriched in na8 0 incompatible elements 87sr 86sr and 206pb 204pb but low in fe8 0 and 143nd 144nd are more prevalent along the shallow portions of the ridge axis in detail the samples can be divided into two chemical and geographical groups the southern bathymetric dome extending from the 11 45 n overlapping spreading center to 14 10 n and the northern group extending from 14 10 n to the orozco transform the boundary between these two groups is apparent in a change in isotopic composition results indicate that there are three mantle source components that produce the compositional variability observed among samples from the 11 45 n to 15 00 n segment of the epr a depleted mantle component a seamount type enriched mantle component and an indian morb like mantle component south of 14 10 n the geochemical variability is dominated by binary mixing between a depleted mantle component and an enriched component similar to near ridge seamounts north of 14 10 n the low 206pb 204pb high 207pb 204pb indian morb like component exerts a major influence on the geochemical variability of the axial lavas regional averages of major element composition e g na8 0 and fe8 0 show relatively limited variability consistent with the restricted range in depth for this region and plot within the pacific field of the previously defined global trends major element variations among individual samples however parallel the global array and their correlation with indices of mantle enrichment supports the idea that the pacific type local trend results from small scale heterogeneities in the mantle beneath the epr our results also indicate that tectonic segmentation and magmatic boundaries are probably not causally related in this study area and that the sizes of the present magma chambers are not a dominant factor in determining the compositional variability of erupted lavas

insight into ground deformations at lascar volcano chile from sar interferometry photogrammetry and gps data implications on volcano dynamics and future space monitoring abstract we present a detailed study of lascar volcano chile based on the combination of satellite aerial and ground based data in order i to better characterize the deformation style of andean explosive volcanoes and ii to provide new insights on the potential of space techniques to monitor active volcanic deformations on such edifices lascar is one of the most active volcanoes in central andes characterized by a recent cyclic activity additionally it is located in favourable conditions for radar imaging lascar thus offers very good conditions for studying large to small scale ground deformations associated with volcano dynamics the analysis of insar synthetic aperture radar interferometry time series data from the european and japanese satellites ers jers acquired between 1993 and 2000 encompassing three eruptive events confirmed the absence of broad far field deformation signal thus during the recent activity of lascar we discard significant magmatic input at depth the following approaches were used to improve the insar signal noise ratio in order to detect possible local deformation we carried out a quantitative evaluation of the potential tropospheric contribution in insar interferograms for the salar de atacama lascar area using radar asar envisat and spectrometer modis data we also used an accurate aerial photogrammetric and gps constrained dem in our insar data reprocessing we find a co eruptive ground deformation confined into the summit crater for the 1995 eruption this deformation has spatial dimension of 500 by 400 m and relates to a subsidence of crater floor up to 17 mm we interpret it as pressure or volume decrease at subsurface levels below the active crater our study made it possible to image a new near field volcanic deformation confined within the summit crater of the lascar volcano it also demonstrates that the combination of precise photogrammetry dem and insar data can significantly improve our ability to remotely sense subtle surface deformation on these explosive volcanoes this methodology might contribute to better understand volcano dynamics and to complement their monitoring in remote areas

effects of wall rock elasticity on magma flow in dykes during explosive eruptions abstract magma flow during explosive volcanic eruptions has been described assuming rigid conduits with simple cylindrical or planar geometries here we study the dynamics of explosive volcanic flows to take account of the role of elastic deformation of the conduit influenced by local magmatic pressure three cases are investigated a dyke with elliptical cross section a cylindrical conduit and a deep dyke connected to a shallow cylinder the model cpiuc macedonio et al 2005 was used for simulations and generalized to account for elastic deformations of the conduit cross section area due to magmatic overpressure fragmentation level is typically deeper in a dyke than in a cylinder for flows in wide dykes pressure at the fragmentation depth can be lower than the surrounding lithostatic pressure by several tens of mpa indicating that the wall rocks of the dyke will be unstable constraining the dyke width and eventually blocking the eruption on the other hand when the fragmentation level is shallow the corresponding lithostatic pressure is not large enough to close the dyke and eruptions from wide dykes are possible the behaviour changes drastically when we assume the conduit is a dyke at depth that evolves to a cylinder near the surface in this case even very wide dykes can be stable because the fragmentation level moves into the cylindrical region where deformation is negligible

the crustal structure of the continental margin east of the falkland islands abstract the 1500 km long falkland plateau is the most prominent morphological structure in the southern south atlantic ocean which crustal composition and development is mainly unknown at the westernmost boundary of the plateau the falkland islands precambrian geology provides the only insight into basement structure and age the question of whether continental basement of a similar age and origin underlies the falkland plateau further east is strongly disputed we present new high quality constraints on the crustal fabric of the plateau east of the falkland islands based on wide angle seismic and potential field data acquired in 2013 the p wave velocity model supported by amplitude and density modelling shows that the falkland plateau basin is filled with 8 km of sediments continental crust of 34 km thickness underlies the falkland islands the eastern continental margin of the falkland islands can be classified as a volcanic rifted margin the falkland plateau basin is floored by up to 20 km thick oceanic crust the exceptionally thick igneous crust and its high lower crustal velocities up to 7 4 km s indicate the influence of a regional thermal mantle anomaly during its formation which provided extra melt material the wide angle model revises published crustal models which predicted thin oceanic or thick extended continental crust below the falkland plateau basin our results provide a sound basis for future tectonic interpretations of the area

stacked gabbro units and intervening mantle a detailed look at a section of iodp leg 305 hole u1309d hole u1309d integrated ocean drilling program iodp legs 304 305 penetrated 1415 m into the seafloor of the atlantis massif an oceanic core complex at 30 n mid atlantic ridge more than 96 of all recovered rocks are gabbroic on the basis of a mineral chemical overview we suggest that between 800 and 1100 m below sea floor mbsf a magmatic unit occurs ranging from olivine gabbro and troctolite in the lower part to gabbronorite and oxide gabbro in the upper part below 1235 mbsf massive gabbronorites oxide gabbros were drilled and they may represent the roof of an underlying magmatic unit the focus here is on the zone where both units interact and screens totaling 50 m of a microstructurally distinct olivine rich troctolite occur we argue that the olivine rich troctolite is a former mantle rock which was converted to a crust mantle transition zone dunite at the base of the upper magmatic unit later as melts derived from the lower magmatic unit percolated through it it was equilibrated to a more evolved chemistry and transformed to a fine grained olivine rich troctolite our main arguments against a possible cumulate nature of the olivine rich troctolite are the lack of a systematic downhole trend in compatible elements within the olivine rich troctolite its distinctly fine grained microstructure the high cr content of cpx and its ni rich olivine composition the high nio for a given mg mg fe in the olivine rich troctolite can be modeled by simple equilibration of relict mantle olivine with a mildly evolved melt evidence for the percolation of evolved melts through the olivine rich troctolites are ti rich interstitial pyroxenes and as inclusions in cr spinel highly evolved amphiboles and orthopyroxenes plus the occurrence of millimeter scale noritic veins the percolation by evolved melts would also be the major difference to otherwise conceptually similar rocks from the ophiolitic crust mantle transition zone

effects of topography on the interpretation of the deformation field of prominent volcanoes application to etna we have investigated the effects of topography on the surface deformation field of volcanoes our study provides limits to the use of classical half space models considering axisymmetrical volcanoes we show that interpreting ground surface displacements with half space models can lead to erroneous estimations of the shape of the deformation source when the average slope of the flanks of a volcano exceeds 20 tilting in the summit area is reversed to that expected for a flat surface thus neglecting topography may lead to misinterpreting an inflation of the source as a deflation comparisons of mogi s model with a three dimensional model shows that ignoring topography may lead to an overestimate of the source volume change by as much as 50 for a slope of 30 this comparison also shows that the depths calculated by using mogi s solution for prominent volcanoes should be considered as depths from the summit of the edifices finally we illustrate these topographic effects by analyzing the deformation field measured by radar interferometry at mount etna during its 1991 1993 eruption a three dimensional modeling calculation shows that the flattening of the deflation field near the volcano s summit is probably a topographic effect

building of the deepest crust at a fossil slow spreading centre pineto gabbroic sequence alpine jurassic ophiolites this work presents new field and petrological data on a poorly known lower crustal section from the alpine jurassic ophiolites the pineto gabbroic sequence from corsica france the pineto gabbroic sequence is estimated to be 1 5 km thick and mainly consists of clinopyroxene rich gabbros to gabbronorites near its stratigraphic top and of troctolites and minor olivine gab bros in its deeper sector the sequence also encloses olivine rich troctolite and mantle peridotite bodies at dif ferent stratigraphic heights the composition and the lith ological variability of the pineto gabbroic sequence recall those of the lower crustal sections at slow and ultra slow spreading ridges the gabbroic sequence considered in this study is distinct in the high proportion of troctolites and olivine gabbros which approximately constitute 2 3 of the section in particular the lower sector of the pineto gab broic sequence shows the existence of large scale frag ments of the deepest oceanic crust displaying a highly primitive bulk composition the mineral chemical varia tions document that the origin and the evolution of the pineto gabbroic rocks were mostly constrained by a process of fractional crystallisation the clinopyroxenes from the olivine gabbros and the olivine rich troctolites also record the infiltration of olivine dissolving cr2o3 rich melts that presumably formed within the mantle into replacive dunite bodies cooling rates of the troctolites and the olivine gabbros were evaluated using the ca in olivine geospee dometer we obtained high and nearly constant values of 2 2 to 1 7 c year log units which were correlated with the building of the pineto gabbroic sequence through multiple gabbroic intrusions intruded into a cold litho spheric mantle

movement and emplacement of lava flows at volcan de colima mexico november 1998 february 1999 abstract the first lava eruption of volcan de colima since 1991 was anticipated beginning in mid 1997 when seismic activity began to exceed background levels on 20 november 1998 growth of a new andesitic lava dome began inside a crater produced by an explosion through the summit dome in july 1994 the 1998 block lava dome grew rapidly at a rate of 4 4 m 3 s attaining a volume of 3 8 10 5 m 3 in 24 h about mid day on 21 november the lava dome began to collapse generating a series of block and ash flows that descended the ssw flank at speeds of 80 90 km h at intervals of 3 5 min these pyroclastic flows were mostly deposited in the three branches of barranca el cordoban reaching a maximum distance of 4 8 km from the summit at an altitude of 2040 m the largest pyroclastic flows were emplaced on 25 26 november and their deposits had an estimated volume of 7 3 10 5 m 3 an andesitic block lava flow 59 wt sio 2 then followed down the three branches of barranca el cordoban reaching a maximum distance of 3 8 km in the central branch the lava fronts of the western and central branches almost touched at 2300 m elevation the eastern lava flow reached 2 8 km at 2560 m elevation the total volume of the three lava flows is estimated as 39 10 6 m 3 assuming an average thickness of 20 m the advance rate of the lava fronts in the early hours reached 36 m h on steep slopes up to 40 these diminished to 0 2 1 0 m h on flatter slopes 14 in early february as the activity waned the viscosity of the block lava flows estimated from field observations was extremely high 10 9 10 10 pa s 6 orders of magnitude greater than viscosities estimated for fluid basaltic magmas the lava flows ceased movement in early february 1999 and the style of eruptive activity entered a more explosive phase with a series of dome explosions that have continued into february 2001