a common feeding system of the ne and s rifts as revealed by the bilateral 2002 2003 eruptive event at mt etna sicily italy mount etna volcano is often characterized by bilateral eruptive events involving both the south s and the north east ne rifts the last event occurred in 2002 2003 from october 27 to january 28 a detailed stratigraphically time controlled sampling of lavas and tephra of the southern eruptive fissure was performed in order to 1 track the petrological features of products during the eruption and 2 integrate the results with those previously obtained on the ne rift whole rock composition and textural observations were implemented by major and minor element analyses of plagioclases in lavas and tephra from both sides of the volcano fractionation models constrained by mass balance major and trace elements and rayleigh calculations suggest that magmas are linked by the same liquid line of descent by fractionating 9 11 of a mineral assemblage of cpx 52 69 plg 21 41 and ol 7 46 these new data allowed us to identify at least two feeding episodes through the southern fissure and infer that high k2o porphyritic magmas emitted on both the s and ne rifts derives by fractionation from the same parent magma however lavas and tephra from the southern flank were slightly more primitive textural and petrological study of plagioclase moreover indicates that chemical physical conditions in the deep feeding system were similar for magmas erupting from both rifts as suggested by the presence of dissolved rounded cores in both lavas magmas evolved differently on the s and the ne rifts only at shallow levels comparison with published seismotectonic data supports the idea that the main magma feeding the eruption on october 27 ascended along the same pathway at depth and was intercepted by the fracture system of the s and ne rifts at shallow depth between 6 and 3 km b s l

southern california permanent gps geodetic array continuous measurements of regional crustal deformation between the 1992 landers and 1994 northridge earthquakes the southern california permanent gps geodetic array pgga was established in 1990 across the pacific north america plate boundary to continuously monitor crustal deformation we describe the development of the array and the time series of daily positions estimated for its first 10 sites in the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes we compare displacement rates at four site locations with those reported by feigl et al 1993 which were derived from an independent set of global positioning system gps and very long baseline interferometry vlbi measurements collected over nearly a decade prior to the landers earthquake the velocity differences for three sites 65 100 km from the earthquake s epicenter are of order of 3 5 mm yr and are systematically coupled with the corresponding directions of coseismic displacement the fourth site 300 km from the epicenter shows no significant velocity difference these observations suggest large scale postseismic deformation with a relaxation time of at least 800 days the statistical significance of our observations is complicated by our incomplete knowledge of the noise properties of the two data sets two possible noise models fit the pgga data equally well as described in the companion paper by zhang et al this issue the pre landers data are too sparse and heterogeneous to derive a reliable noise model under a fractal white noise model for the pgga data we find that the velocity differences for all three sites are statistically different at the 99 significance level a white noise plus flicker noise model results in significance levels of only 94 43 and 88 additional investigations of the pre landers data and analysis of longer spans of pgga data could have an important effect on the significance of these results and will be addressed in future work

trace element evidence for plagioclase recycling in calc alkaline magmas abstract trace element zoning in plutonic plagioclase feldspars from the val fredda complex southern adamello massif italy has been measured using secondary ion mass spectrometry sims the studied samples range from hornblende gabbro through diorite to granitoid with an overall range in plagioclase composition from an96 to an15 individual plagioclases display extensive zonation in anorthite through a considerable variety of zoning textures there is equally extensive zoning in trace elements notably sr and ba broadly similar trace element zoning patterns and concentrations are displayed by all plagioclases irrespective of host rock composition using a relationship betweenxan and the distribution coefficientsdsr anddba trace element concentrations in plagioclase are converted to those of the melt which precipitated each crystal zone the calculated variations in ba and sr are greater than can be attributed to changes in pressure or temperature alone indicating that compositional variation in the coexisting melt was the principal cause of zoning the ba sr melt trend for each crystal describes a two stage crystallisation history the calcic cores of all crystals show melt trends of increasing sr and ba which are attributed to mixing and fractionation in parental hydrous picrobasalt magmas in contrast the melt trends recorded by the rims vary from sample to sample but essentially show decreasing sr and ba consistent with fractionation of sodic plagioclase alkali feldspar and or biotite the plagioclase cores are thought to have crystallised in a common magma chamber at 6 10 kbar pressure while the rims crystallised at the emplacement level 1 5 kbar from interstitial melt whose composition is determined by that of the host magma the data suggest that early formed calcic plagioclase was recycled by the magma during fractionation vigorous convection is invoked to both retain relatively dense calcic plagioclase within the evolving magma and to periodically re entrain cumulus crystals into more evolved magmas the occurrence of calcic plagioclase cores in felsic derivative magmas indicates that fractionation from picrobasalt to tonalite occurred on a relatively short time scale

geodesy using the swedish permanent gps network effects of snow accumulation on estimates of site positions we have observed variations at the several centimeter level in estimates of the vertical coordinate of site position the estimates are obtained from our analysis of data acquired from the swedish permanent global positioning system gps network the observed variations are strongly correlated with changes in the indirectly inferred accumulation of snow which we assume collects on the radomes and pillars the gps sites could not be observed directly due to their remoteness numerical simulations which assume a simple geometry for the snow cover are used to study the effects of snow accumulation on gps phase observables and hence on estimates of the vertical coordinate of site position obtained from these observables our results indicate that the variations in the vertical coordinate of site position can be fully explained by reasonable accumulations of snow which retard the gps signals and enhance signal scattering effects

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

displacement of surface monuments vertical motion several measurements of vertical ground motion at pinon flat observatory california indicate the overall weakness and instability of the earth s weathered surface with respect to the underlying rock cumulative long period motions of order 0 5 mm per year dominate these records though smaller elastic deformations caused by precipitation loading atmospheric loading and tidal strains are evident at higher frequencies all of these help to characterize the near surface material the long period records suggest that near surface weathering is the dominant influence on monument motion at least at this site on crystalline rock in a semi arid environment rainfall loading gives an average vertical modulus of 2 6 gpa for the material in the uppermost 26 m of the ground compared with 88 gpa for granite under moderate confining stress atmospheric loading gives similar results but indicates the ground is permeable to airflow at periods longer than a few hours earth tide records show poisson s ratio to be 0 09 in contrast to the normative range of 0 2 0 25 establishing that horizontal strains couple only weakly into vertical ones so that vertical strains near the surface are a poor measure of areal strain the form of the ground surface displacement power spectrum indicates that analyses of geodetic surveys would be improved with the inclusion of a monument positioning error budget that increases with time because of ground instability and the generally small rate of crustal tectonic motions deeply emplaced monuments will be needed for observational programs designed to detect short term changes in crustal deformation over baselengths of order 10 km and less

observations of plagioclase zoning using interference imaging abstract interference imaging techniques laser interference microscopy in transmitted light and nomarski differential interference contrast in reflected light have been used to study different types of zoning in magmatic plagioclase crystals samples studied come from a wide range of rock types and geological environments analysis of zoning profiles for individual unit zones shows that a saw tooth pattern in which an initially high an decreases as growth proceeds is the most common type of zoning configuration we recognize 2 major types of zoning type 1 small zones usually less than 10 microns thick with compositional amplitudes up to 10 an and type 2 zones up to50 microns thick with large compositional amplitudes of up to 35 an detailed analysis of zoning patterns shows that oscillatory zoning is not actually oscillatory in the sense of a sine wave it is discontinuous unit zones are characteristically bounded by discontinuities this common pattern is consistent with alternating periods of growth and periods of dissolution reaction and lack of growth or possibly very slow growth our observations firmly establish that dissolution and magmatic reaction involving both growth and dissolution are common during growth of the magmatic plagioclase which we have studied type 1 zonation appears consistent with perturbations of local conditions in a diffusion controlled boundary layer around the growing crystal type 2 zoning is probably due to large scale conditions faceted planar growth surfaces appear to be the rule in magmatic crystallization although in some instances rounded or irregular convolute zonation can occur the repetitive nature of many of the features we have observed is consistent with and suggestive of some form of self organization

magma mixing at nisyros volcano as inferred from incompatible trace element systematics abstract rocks of the calc alkaline volcanic complex of nisyros at the eastern end of the quaternary south aegean volcanic arc range in composition from basaltic andesite to rhyodacite major and compatible trace element systematics are dominated by crystal fractionation involving olivine clinopyroxene plagioclase and magnetite in the mafic to intermediate compositional range and plagioclase clinopyroxene hypersthene fe ti oxides and apatite in the intermediate to silicic range although there is a marked paucity of lavas with 60 66 wt sio 2 the occurrence of andesitic inclusions in pre and post caldera dacites as well as reversely zoned and or partly resorbed phenocrysts exotic mineralogy e g forsteritic olivine compositionally bimodal plagioclase phenocryst populations and the observation of two distinct glass phases in melt inclusions and pumices all indicate that magma mixing processes have played a role in the petrogenesis of nisyros incompatible trace element systematics are consistent with mixing between mafic and silicic end members major element binary mixing calculations between end members successfully reproduce the dacite composition the eruptive sequence at nisyros suggests the existence of a compositionally zoned magma chamber in which mixing between underlying more mafic magma and overlying rhyodacitic melt result in the formation of dacitic magmas inherent mineral assemblages in basaltic andesites indicate that mixing between mafic liquids and between mafic and more silicic liquids played also a role in their petrogenesis

monument motion and measurements of crustal velocities it is usually assumed in geodetic studies that measurement errors are independent from one measurement to the next and that the rate of deformation velocity is constant over the duration of the experiment any temporal correlation between measurements can substantially affect the uncertainty in this velocity estimate when it is determined from the time series of measurements one source of possible long term correlation is motion of the geodetic monument with respect to the deep crust available measurements suggest that this motion introduces errors that have the form of a random walk process we show how such errors affect the uncertainty of velocity estimates for a geodetic experiment of set duration we calculate the velocity uncertainty as a function of the number of observations and of the relative amount of correlated and uncorrelated noise we find that 1 neglecting long term temporal correlations makes the uncertainty in the estimated velocities much too small and that 2 when the correlated and independent noise sources are of similar magnitude the expected improvement in uncertainty from having more measurement is not realized there is almost no improvement in some cases we have also examined the effect of outliers blunders on the velocity uncertainty for a frequency of outliers typical of geodetic field campaigns the previous two conclusions remain unchanged these results suggest that long term correlations have a large effect on estimating deformation rates unless these correlations are small frequent observations give little advantage if frequent observations are planned the amount of correlated noise due to monument instability must be kept small if the full capabilities of the measurement technique are to be realized

the optical anchor a geophysical strainmeter an instrument has been developed to monitor the horizontal displacement of near surface monuments so as to reduce the noise of observatory based strain measurements the device measures the shear strain in the upper 24 m of the earth s crust using an equal path length michelson interferometer the magnitude of the observations 50 m indicates that such measurements are needed to interpret the records produced by precision strainmeters

interseismic deformation and moment deficit along the manila subduction zone and the philippine fault system we examine interseismic coupling of the manila subduction zone and fault activity in the luzon area using a block model constrained by gps data collected from 1998 to 2015 estimated long term slip rates along the manila subduction zone show a gradual southward decrease from 90 100 mm yr at the northwest tip of luzon to 65 80 mm yr at the southern portion of the manila trench we provide two block models models a and b to illustrate possible realizations of coupling along the manila trench which may be used to infer future earthquake rupture scenarios model a shows a low coupling ratio of 0 34 offshore western luzon and continuous creeping on the plate interface at latitudes 18 19 n model b includes the north luzon trough fault and shows prevalent coupling on the plate interface with a coupling ratio of 0 48 both models fit gps velocities well though they have significantly different tectonic implications the accumulated strain along the manila subduction zone at latitudes 15 19 n could be balanced by earthquakes with composite magnitudes of mw 8 8 9 2 assuming recurrence intervals of 500 1000 years gps observations are consistent with full locking of the majority of active faults in luzon to a depth of 20 km inferred moments of large inland earthquakes in luzon fall in the range of mw 6 9 7 6 assuming a recurrence interval of 100 years

a new velocity field for africa from combined gps and doris space geodetic solutions contribution to the definition of the african reference frame afref 1 we analyzed 16 years of gps and 17 years of doppler orbitography and radiopositioning integrated by satellite doris data at continuously operating geodetic sites in africa and surroundings to describe the present day kinematics of the nubian and somalian plates and constrain relative motions across the east african rift the resulting velocity field describes horizontal and vertical motion at 133 gps sites and 9 doris sites horizontal velocities at sites located on stable nubia fit a single plate model with a weighted root mean square residual of 0 6 mm yr maximum residual 1 mm yr an upper bound for plate wide motions and for regional scale deformation in the seismically active southern africa and cameroon volcanic line we confirm significant southward motion 1 5 mm yr in morocco with respect to nubia consistent with earlier findings we propose an updated angular velocity for the divergence between nubia and somalia which provides the kinematic boundary conditions to rifting in east africa we update a plate motion model for the east african rift and revise the counterclockwise rotation of the victoria plate and clockwise rotation of the rovuma plate with respect to nubia vertical velocities range from 2 to 2 mm yr close to their uncertainties with no clear geographic pattern this study provides the first continent wide position velocity solution for africa expressed in international terrestrial reference frame itrf2008 a contribution to the upcoming african reference frame afref except for a few regions the african continent remains largely under sampled by continuous space geodetic data efforts are needed to augment the geodetic infrastructure and openly share existing data sets so that the objectives of afref can be fully reached

magma mixing in the subvolcanic environment petrology of the gerena interaction zone near seville spain the mechanisms by which felsic and mafic magmas interact and approach a uniform hybrid composition through the processes of mingling and mixing have been studied in a high level subvolcanic setting in the spanish hercynian at gerena near seville the compositions involved are calc alkaline and the situation is one of tonalite quartz diorite synplutonic dykes injected into a granitic magma chamber the resulting hybrids include dykes pillows and globules of tonalite with chilled margins which are variously disrupted and homogenised with the host granite the present investigation is based on field and petrographic observations of hybridization textures the identification of different stages in the crystallisation history of the tonalite through mineral textures and the characterization of mineral compositions at these various stages proportions of the end member magmas involved were obtained by major oxide mixing models and tested satisfactorily with trace elements a mechanistic model is presented to account for these observations which involves the early quenching of the tonalite when it was emplaced into the granite magma chamber after high temperature crystallization had occurred the two magmas attained thermal equilibrium and disruption of the tonalite in the high energy regime of this subvolcanic complex resulted in dispersion of fragments and crystals through the granite giving rise to hybrid granodiorite compositions it is argued that such high energy flow conditions are a necessary requirement for effective hybridization in this environment in contrast to most large scale magma chamber settings where mixing is driven by thermal and buoyancy contrasts

the origin and implications of undercooled andesitic inclusions in rhyolites clear lake volcanics california at clear lake california undercooled andesitic inclusions are common in rhyolitic to dacitic lava flows and pyroclastic deposits one group of rhyolite lava flows contains about 1 vol undercooled andesitic inclusions 2 cm in size the inclusions are evenly distributed in several flows and do not vary significantly in size or abundance they consist of plagioclase orthopyroxene ilmenite apatite needles and vesicular rhyolitic glass olivine clinopyroxene microphenocryst size in these small inclusions correlates positively with inclusion size suggesting that inclusions have not undergone extensive disaggregation since formation texturally similar inclusions up to 50 cm in size occur in associated pyroclastic deposits none of the inclusions represent the mafic end member of the system rather they represent intermediate magmas formed by liquid crystal fractionation and hybridization of distinct andesitic magmas at or near the base of a silicic magma chamber the large inclusions are transitional in composition and mineralogy between clear lake basaltic andesites and smaller inclusions which show more evidence of hybridization these differences suggest similar but distinct sources and mechanisms of formation for the large and small inclusions the small inclusions probably formed by episodic mingling across an interface or hybrid zone separating rhyolitic and andesitic magmas we speculate that earthquakes generated along the san andreas fault system may have triggered mingling events this occurrence demonstrates that dispersion of undercooled intermediate to mafic inclusions in silicic magma chambers is the dominant mode of mafic felsic magma interaction in some systems

unusual magma storage conditions at mt etna southern italy as evidenced by plagioclase megacryst bearing lavas implications for the plumbing system geometry and summit caldera collapse at mt etna volcano the emission of plagioclase megacryst bearing lavas known locally as cicirara has occurred rarely and generally in association with unusual volcanological phenomena in this work we interpret the magma chamber processes and the structural features of the plumbing system that led to the production of these peculiar volcanic rocks based on a detailed study of plagioclase megacrysts including their oscillatory zoning sieve textures and fluid inclusions patchy zoning suggests limited ascent in the deep levels of the plumbing system based on the plagioclase nucleation threshold and the volatile saturation depth at intermediate water undersaturated levels of the plumbing system ascent is faster as indicated by crystals with coarse sieve textures storage at shallow water saturated levels less than 6 km deep is associated with oscillatory zoning with very small changes in an slightly larger an variations coupled with different wavelengths provide evidence of convection of crystals across distinct zones of the chamber stripes of melt inclusions formed at steps of magma ascent and volatile loss whereas layers of fluid inclusions may be related to episodes of volatile flushing into the magma chamber in contrast strongly sieve textured envelopes with an increase and constant feo may be related to mixing with more volatile rich magmas of similar composition we interpret the repeated occurrence of cicirara lavas as evidence that the shallow portion of the plumbing system underwent a progressive coalescence of a complex network of dykes and sills in response to increasing rates of magma supply from depth major magma withdrawals from this larger reservoir may be linked to episodes of summit instability associated with major caldera collapses

displacement of surface monuments horizontal motion measurements of tectonic deformation depend on both accurate instrumentation and adequate coupling of the apparatus to the earth s crust existing techniques capable of resolving the signals of interest strain rates of 10 n yr are mainly observatory based the limitation in the baselength of these instruments 1 km results in a requirement that the reference monuments be exceptionally stable 10 tzm yr however records from pition flat observatory california show that the actual horizontal displacements for massive near surface monuments eraplaced in competent weathered granite are of the order of 50 tzm yr the low noise level of the strain measurements at this site indicates that this magnitude of monument displacement is abnormally small until high accuracy geodetic techniques are developed sophisticated monuments or monument monitoring devices will be necessary to record faithfully continuous crustal deformation

gas burst vs gas rich magma recharge a multidisciplinary study to reveal factors controlling triggering of the recent paroxysmal eruptions at mt etna abstract since january 2011 mt etna volcano has been affected by more than forty paroxysmal eruptions at the summit new south east crater nsec on the basis of their very variable duration seven eruptions have been selected among the twenty five of 2011 2012 in order to decipher potential differences in their triggering mechanism paroxysms have been investigated through a multidisciplinary approach that integrates data from volcanic tremor and petrology textures and micro analysis on plagioclase crystals our results lead to the conclusion that close relationships exist between the duration of the eruptions and the temporal evolution of the volcanic tremor amplitude especially during the strombolian phase preceding the paroxysmal activity in this regard we distinguished 1 paroxysms preceded by long lasting initial strombolian phases characterized by low rate of volcanic tremor amplitude increase and 2 eruptions preceded by short initial strombolian phases showing high rate of volcanic tremor amplitude increase based on the pattern of volcanic tremor amplitude increase the former mainly showed a ramp shaped morphology while the latter a bell shaped trend location of the volcanic tremor centroid during the quiescent intervals between the paroxysmal eruptions has highlighted the presence of a magmatic volume at 1 2 km a s l beneath the north east crater nec during the syn eruptive strombolian and lava fountaining phases the centroid of volcanic tremor migrates below the nsec this leads to the consideration that the magma batch residing beneath nec played an important role in the volcanic activity at nsec during the considered period also the textures and compositional zoning anorthite and iron variations in selected plagioclase crystals of the analyzed lavas suggest relations between duration of the paroxysms and dynamics of pre eruptive magmatic processes at depth particularly two mechanisms have been accounted for triggering of eruptions at the nsec on the basis of the concordant or discordant behavior of anorthite and iron in plagioclase coupled with disequilibrium textures at the rim concordant anorthite and iron increases in plagioclase crystals with sieve textured rims indicate recharge by more mafic gas rich magma this textural compositional behavior has been related to long lasting eruptions whose volcanic tremor amplitude evolution produced ramp shaped increase of the volcanic tremor amplitude before the paroxysmal phase on the contrary crystals with sieve textures at the rim characterized by increasing iron at rather constant or decreasing anorthite suggest the prominent role of gas injections into the residing system in this instance the compositional behavior has been linked with short lasting eruptions whose volcanic tremor amplitude evolution led to a sudden increase of the seismic amplitude before the climax of the eruption thus our work put forward the idea that the evolution and duration of the strombolian phase preceding the paroxysmal eruptions of 2011 2012 at mt etna are strongly controlled by the eruption triggering mechanism which can be either gas burst or gas rich magma recharge

magmatic crystal stratigraphy and constraints on magma chamber dynamics laser interference results on individual phenocrysts this work reports progress in current studies of zoning of magmatic crystals from basalts and andesites a simple law of normal growth is tested using zoning profiles of olivine and plagioclase crystals and is shown to be compatible with the zoning profiles of some olivines and parts of complexly zoned plagioclases using a convenient linearizing technique in which the ratio of compositional end members is plotted against volume we can identify those parts of the zoning profile which fit a simple normal growth law this technique permits easy identification of those parts of a complexly zoned crystal which require a more complex law of growth calculations used in this modeling are similar to those previously used for olivine pearce 1984c 1987 and are now extended to plagioclase it is concluded that it is both theoretically possible and practically feasible to make inferences about the liquid in the local system from which a crystal grew by examining the detailed zoning pattern of the crystal

geodesy using the global positioning system the effects of signal scattering on estimates of site position analysis of global positioning system gps data from two sites separated by a horizontal distance of only 2 2 m yielded phase residuals exhibiting a systematic elevation angle dependence one of the two gps antennas was mounted on an 1 m high concrete pillar and the other was mounted on a standard wooden tripod we performed elevation angle cutoff tests with these data and established that the estimate of the vertical coordinate of site position was sensitive to the minimum elevation angle elevation cutoff of the data analyzed for example the estimate of the vertical coordinate of site position changed by 9 7 0 8 mm when the minimum elevation angle was increased from 10 to 25 we performed simulations based on a simple ray tracing multipath model with a single horizontal reflector which demonstrated that the results from the elevation angle cutoff tests and the pattern of the residuals versus elevation angle could be qualitatively reproduced if the reflector were located 0 1 0 2 m beneath the antenna phase center we therefore hypothesized that the elevation angle dependent error was caused by scattering from the horizontal surface of the pillar located a distance of 0 2 m beneath the antenna phase center we tested this hypothesis by placing microwave absorbing material between the antenna and the pillar in a number of configurations and by analyzing the changes in apparent position of the antenna the results indicate that 1 the horizontal surface of the pillar is indeed the main scatterer 2 both the concrete and the metal plate embedded in the pillar are significant sources of scattering and 3 the scattering can be reduced greatly by the use of microwave absorbing materials these results have significant implications for the accuracy of global gps geodetic tracking networks which use pillar antenna configurations identical or similar to the one used for this study at the westford wfrd gps site

plagioclase xenocrysts and mafic magmatic enclaves in some granitoids of the sierra nevada batholith california plagioclase phenocrysts from mafic magmatic enclaves and plagioclase crystals from host granitoids of some plutons of the central part of the sierra nevada batholith are complexly zoned and commonly divided into three neatly distinct parts an oscillatory locally patchy zoned andesine or more calcic core a ring with dusty calcic plagioclase and a normally zoned rim of sodic plagioclase although aspect of the calcic rings and width and zoning of the rims may slightly vary from the enclaves to the hosts cores of both phenocrysts and large plagioclase crystals show similar zoning and composition the andesine or more calcic cores are interpreted to have crystallized in the felsic or the mafic magma respectively and been incorporated into the coeval magma when the two magmas mixed introduction of the xenocrystic cores into a magma where they were not in equilibrium resulted in partial dissolution development of abundant patchy zoning and coating with dusty calcic plagioclase in both granitoids and mafic magmatic enclaves composition and zoning contrast between cores and rims of the plagioclase crystals reflect drastic changes in conditions of crystallization before and after the mechanical mixing event mixing of two magmas with contrasted compositions is suggested to be the major mechanism for generating complexly zoned plagioclase xenocrysts in granitoids and mafic magmatic enclaves this hypothesis is consistent with many recent models in which mixing of two contrasting components is proposed to play a fundamental part in the generation of calc alkaline granitoids and mafic magmatic enclaves of the sierra nevada batholith plagioclase xenocrysts may also provide information on the timing of the different mixing processes and on the magmatic evolution of the plutons

structure and petrology of newly discovered volcanic centers in the northern kermadec southern tofua arc south pacific ocean 1 the nzaplume iii expedition of september october 2004 to the northern kermadec southern tofua nkst arc between 28 52 s and 25 07 s resulted in the discovery of at least seven new submarine volcanic centers and a substantial caldera complex adjacent to the previously known monowai seamount the volcanic centers form a sublinear chain that coincides with the kermadec ridge crest in the south hinetapeka and diverges 45 km westward of the ridge crest in the north v just to the south of where the louisville ridge intersects with the arc all of the centers contain calderas or caldera like structures as well as multiple cones domes fissure ridges and vent fields all show signs of recent eruptive and current hydrothermal activity there are strong structural controls on edifice location with cones and fissure ridges typically associated with faulting parallel to the regional 12 strike of the arc front several of the calderas are ellipsoidal orientated northwest southeast in the general direction of least compressive stress sampled volcanic rocks representing the most recently erupted lavas are all low k tholeiites two of the centers gamble and rakahore yielded only high silica dacite to rhyolite 69 74 wt silica whereas two others monowai and v yielded only basalt to andesite 48 63 wt silica mineral assemblages are plagioclase pyroxene dominated with accessory fe ti oxides apatite olivine and quartz tridymite cristobalite typical of dry volcanic arc systems hornblende occurs only in a felsitic rhyolite from hinepuia volcanic center and zircon is absent glass contents range to 57 in basalts andesites mean 20 and 97 in andesites rhyolites mean 59 and other quench textures including swallow tailed plumose or dendritic crystal forms and crystallites are common most lavas are highly vesicular 63 mean 28 and have low volatile contents mostly 2 wt which together with the occurrence of tridymite or cristobalite indicates explosive eruption and rapid cooling exceptions are rocks from u volcanic center which have low vesicularity and low glass contents across a wide compositional range indicating effusive eruption disequilibrium mineral textures the frequent occurrence of xenoliths and xenocrysts and macroscopic evidence for magma mingling indicate that many of the lavas are hybrids having resided only a short time in upper crustal reservoirs prior to eruption silicic magmas are major components of nkst arc volcanism and caldera formation is the dominant eruptive style the scale of silicic magmatism is in marked contrast to the dominant basaltic andesitic magmatism in the southern kermadec arc with evidence from other arcs silicic magmatism is now recognized as a major feature of intraoceanic arcs globally

correlated errors in geodetic time series implications for time dependent deformation analysis of frequent trilateration observations from the two color electronic distance measuring networks in california demonstrate that the noise power spectra are dominated by white noise at higher frequencies and power law behavior at lower frequencies in contrast earth scientists typically have assumed that only white noise is present in a geodetic time series since a combination of infrequent measurements and low precision usually preclude identifying the time correlated signature in such data after removing a linear trend from the two color data it becomes evident that there are primarily two recognizable types of time correlated noise present in the residuals the first type is a seasonal variation in displacement which is probably a result of measuring to shallow surface monuments installed in clayey soil which responds to seasonally occurring rainfall this noise is significant only for a small fraction of the sites analyzed the second type of correlated noise becomes evident only after spectral analysis of line length changes and shows a functional relation at long periods between power and frequency of 1 where is frequency and 2 with 2 this type of correlated noise is termed random walk noise and its source is mainly thought to be small random motions of geodetic monuments with respect to the earth s crust though other sources are possible because the line length changes in the two color networks are measured at irregular intervals power spectral techniques cannot reliably estimate the level of 1 noise rather we also use here a maximum likelihood estimation technique which assumes that there are only two sources of noise in the residual time series white noise and random walk noise and estimates the amount of each from this analysis we find that the random walk noise level averages about 1 3 mm yr and that our estimates of the white noise component confirm theoretical limitations of the measurement technique in addition the seasonal noise can be as large as 3 mm in amplitude but typically is less than 0 5 mm because of the presence of random walk noise in these time series modeling and interpretation of the geodetic data must account for this source of error by way of example we show that estimating the time varying strain tensor a form of spatial averaging from geodetic data having both random walk and white noise error components results in seemingly significant variations in the rate of strain accumulation spatial averaging does reduce the size of both noise components but not their relative influence on the resulting strain accumulation model

accretion of the southern banda arc to the australian plate margin determined by global positioning system measurements global positioning system geodetic measurements at thirteen locations in indonesia and four in australia reveal that the australian continent has accreted the banda island arc to its margin small relative velocities of five sites on west java south kalimantan bali and south sulawesi define a rigid sunda shelf that moves relative to northern australia in a manner consistent with pole locations from nuvel 1 australia eurasia but at a rate that is about 7 slower block like northward motion of the southern banda arc toward the sunda shelf at nearly the same rate as australia suggests that the timor trough is now inactive as a thrust little of the convergence of australia with eurasia is accommodated by strain within the banda arc structure most of the convergence appears to occur as northward translation of the rigid arc with shortening on the flores and wetar thrusts and possibly on faults within the back arc basin

a transient subduction zone slip episode in southwest japan observed by the nationwide gps array 1 we investigate the spatiotemporal variation of fault slip on the subduction interface in southwest japan following the two 1996 hyuganada earthquakes m 6 7 using continuous gps observations a silent thrust slip event has been reported by hirose et al 1999 following these earthquakes approximately 100 km to the north beneath the bungo channel we employ the network inversion filter to rigorously invert for the fault slip distribution in space and time the gps time series is modeled as a sum of 1 secular deformation 2 coseismic station displacements 3 transient fault slip 4 random benchmark motion 5 reference frame shifts and 6 observational errors nonnegativity constraints effectively prohibit normal faulting on the subduction interface spatial and temporal smoothing parameters are estimated by the extended kalman filter the estimated fault slip rate images postseismic slip following the two hyuganada earthquakes slip associated with the silent thrust event began roughly 1 month after the second earthquake but initiated 100 km to the northeast of the hyuganada earthquakes the slow event propagated southwest and downdip beneath the bungo channel lasting approximately 1 year with maximum slip rates of 0 6 m yr the equivalent seismic moment was mw 7 2 we can rule out the possibility that slip propagated from the source region of the hyuganada earthquakes to the location of the silent earthquake however the timing of the events suggests a causal connection perhaps due to static stress transfer this kind of transient event or silent earthquake may reflect different fault zone characteristics and may be responsible for accommodating strain that would otherwise be released in large earthquakes

plagioclase zoning as an indicator of magma processes at bezymianny volcano kamchatka back scattered electron bse derived zoning patterns of plagioclase phenocrysts are used to identify magma processes at bezymianny volcano kamchatka based on the 2000 2007 sequence of eruptive products the erupted magmas are two pyroxene andesites which last equilibrated at 915 c temperature 77 87 mpa pressure and a water content of 1 4 wt textural and compositional zoning of individual plagioclase phenocrysts typically includes a repeated core to rim sequence of oscillatory zoning an50 60 truncated by a dissolution surface followed by an abrupt increase in an content up to an85 which then gradually decreases rimward this zoning pattern is interpreted to be the result of frequent replenishments of the magma chamber which cause both thermal and chemical interaction between resident and recharge magmas the outermost 70 to 150 m wide zoning patterns of plagioclase phenocrysts are composed of dissolution surface with a subsequent increase in an and fe contents zoning patterns of the rims exhibit correlation among plagioclase phenocrysts within one eruption rims are interpreted as a result of crystallization of a batch of magma in the conduit after recharge event

the record of magma chamber processes in plagioclase phenocrysts at thera volcano aegean volcanic arc greece lavas and pyroclastic rocks throughout the volcanic stratigraphy of the tertiary quaternary volcanic complex of thera in the aegean island arc display inhomogenous plagioclase populations and phenocryst resorption textures interpreted as indicative of magma mixing plagioclase zoning characteristics studied by nomarski and laser interferometry techniques establish three main categories of plagioclase i inherited plagioclase nucleated in endmember prior to initial mixing event ii in situ plagioclase nucleated in mixed or hybrid magma and iii xenocrystic plagioclase nomarski contrast images and linearized compositional zoning profiles reveal striking differences between calcic and sodic plagioclases depending on the composition of the lava in which they are hosted these differences reflect the contrasting effects of changes in physical chemical parameters in basic vis a vis more acidic melts during magma mixing and or influx of new magma into the subvolcanic magma chamber as well as the influence of magma chamber dynamics on plagioclase equilibration variations in bulk major and trace element abundances of thera volcanic products reflect the dominant overprint of crystal fractionation but decoupling between major and trace element fractionation models and variations in incompatible trace element distributions are all indicative of magma mixing processes consistent with compositional and textural zoning in plagioclases

estimation of intraplate strain accumulation in the new madrid seismic zone from repeat gps surveys the new madrid seismic zone nmsz a region within the eastern portion of the north american plate where great earthquakes occurred in 1811 1812 provides a type example of large earthquakes within a relatively stable continental interior assessing the scale and causes of deformation in such regions as well estimation of the recurrence interval for the large earthquakes within them has long been recognized as an important but challenging issue for which the advent of space based geodesy provides an important new tool here we report initial results from two global positioning system gps surveys of a geodetic network spanning the new madrid seismic zone because the expected strain signal is small the data were analyzed in three different ways first site velocities were estimated and analyzed for spatial gradients parallel and perpendicular to the trend of the major strike slip faults inferred from seismicity this analysis suggests but does not require a few millimeters per year of right lateral shear across the southern portion of the seismic zone consistent with the earthquake focal mechanisms second we divided the network into near field subnetworks and found possibly significant shear associated with approximately e w shortening within the southern nmsz and possible n s shortening across the left step connecting the presumed strike slip faults third we compared the strain observed along individual baselines to that predicted from the results of earlier near field surveys which combined gps and triangulation data in the southern part of the seismic zone we found general agreement with the earlier study although our data suggest lower strain rates hence after only 2 years of measurements the gps data suggest but do not yet require detectable strain accumulation however given that great earthquakes occur in the area and that our results are reasonably consistent with the results of other geodetic studies using different data and with earthquake mechanisms it seems likely that we are seeing strain accumulation in the southern nmsz a simple interpretation of the data as showing about 3 to 5 mm yr 1 of right lateral fault parallel motion implies a 1000 to 3300 year recurrence for great earthquakes with 5 to 10 m slip assuming all the accumulating strain is released seismically this recurrence interval may be an underestimate if the observed strains are largely postseismic effects of the 1811 1812 earthquakes a possibility suggested by the observation that plate wide data show less motion across the nmsz future surveys should resolve this issue as the longer measurement spans yield more precise velocity estimates

continuous gps observations across the hayward fault california 1991 1994 in september 1991 the u s geological survey began continuous operation of two permanent global positioning system gps sites near the hayward fault we use two and one half years of data from an 8 km baseline to investigate gps processing strategies errors in the time and frequency domains and the uncertainties of rates of change calculated from such data experiments with session lengths show that at least 6 hours of data should be used to obtain a precision of 2 to 4 mm experiments with broadcast and improved orbits show that the broadcast orbit is sufficient for this short baseline single frequency solutions have larger rms scatter for scenarios made mostly in daylight ionospheric delay systematically shortens the baseline length by 2 4 parts per million for l1 and 4 0 parts per million for l2 for the dual frequency results the rms scatter about the best fitting straight line is 2 1 mm for baseline length 2 2 mm for north 2 9 mm for east and 11 2 mm for vertical for winton relative to chabot the rates of change are 0 6 0 1 mm yr in length 2 8 0 1 mm yr in north 8 1 0 2 mm yr in east and 8 1 0 6 mm yr in vertical the baseline rate of change is consistent with right lateral shear across the hayward fault but is not consistent with the 3 5 mm yr predicted by the model of lienkaemper et al 1991 the large westward and downward motion of winton relative to chabot may be due to monument instability power spectra appear white at high frequencies the estimated standard deviations for periods shorter than 5 days are 1 2 mm for length and north 1 9 mm for east and 5 5 mm for vertical power spectral density increases only slightly as frequency decreases from 0 2 to 0 03 cycle per day and there is no distinct corner in particular no characteristic 1 2 signature of random walk monument noise emerges from the white noise estimated autocorrelations for length north east and vertical fall to about 0 1 for lag times shorter than 10 days and fluctuate about zero for lag times longer than about 25 days because the time series is short it is possible that random walk monument noise exists but is undetectable in the estimated power spectral density and autocorrelation functions we use the estimated full covariance matrix to calculate the standard deviations of the baseline rate of change for various sampling schemes the theoretical standard deviation of dl dt determined from 1 year of daily observations is 0 28 times that determined from 1 year of annual observations we can obtain a similar uncertainty from 2 years of measurements made every 30 days and better results from 5 years of annual measurements however daily measurements allow the detection and correction of offsets that sometimes occur with equipment or firmware changes

magma storage ascent and recharge history prior to the 1991 eruption at avachinsky volcano kamchatka russia inferences on the plumbing system geometry article i nfo textural and compositional features of plagioclase phenocrysts of the 1991 eruption lavas at avachinsky volcano kamchatka russia were used to investigate the feeding system processes volcanics are porphyritic basaltic andesites and andesites with low k affinity a fractionation modeling for both major and trace elements was per formed to justify the development of these evolved compositions the occurrence of other magma chamber pro cesses was verified through high contrast bse images and core to rim compositional profiles an and feo wt on plagioclase crystals textural types include small and large scale oscillation patterns disequilibrium textures at the crystal core patchy zoning coarse sieve textures dissolved cores disequilibrium textures at the crystal rim sieve textures melt inclusion alignments at the rim disequilibrium textures at the cores may testify episodes of destabilization at various decompression rates under water undersaturated conditions which suggests different pathways of magma ascent at depth at shallower water saturated conditions plagioclase crystallization continues in a system not affected by important chemical physical perturbations oscillatory zoning develops strongly sieve textured rims along with an increase at rather constant feo are evidence of mixing before the 1991 eruption between a residing magma and a hotter and volatile richer one the textural evidence implies that crystals underwent common histories at shallow levels supporting the existence of a large magma reservoir whose top is at 5 5 km of depth distinct textures at the outer rims in a hand size sample are evidence that crys

the extent of u series disequilibria produced during partial melting of the lower crust with implications for the formation of the mount st helens dacites the extent to which u series disequilibria can be produced during partial melting of mafic lower crust is quantified using a simple batch melting model and both experimental and theoretical partition coefficients for u th and ra we show that partial melting of mafic lower crust can only produce small disequilibria between 238u 230th and 226ra crystallisation of basalt and mixing between young basalt and crustal derived melts will have a similar or smaller effect consequently u series disequilibrium in arc andesites and dacites can generally only be an inherited feature derived from a mantle parent unless the timescales of silicic magma production within the crust are short compared to the half life of 226ra our results have profound implications for several recent models of silicic magma production by thermal incubation and partial melting of the lower crust we show that the 226ra excess observed in most arc andesites and dacites requires extremely rapid differentiation and or the involvement of mantle derived basalts less than a few thousand years old application to mount st helens suggests that crystallisation of young mantle derived magma is likely to be the dominant process in the formation of these dacites

textural and chemical variation in plagioclase phenocrysts from the 1980 eruptions of mount st helens usa this study presents major and trace element chemistry of plagioclase phenocrysts from the 1980 eruptions of mount st helens volcano despite the considerable variation in textures and composition of plagioclase phenocrysts distinct segments have been cross correlated between crystals the variation of sr and ba concentration in the melt as calculated from the concentration in the phenocrysts using partition coefficients suggests the cores and rims crystallised from compositionally different melts offset by the plagioclase crystallisation vector in both of these melts sr and ba are correlated despite the abundance of plagioclase in the 1980 dacites we propose that rapid crystallisation of plagioclase upon magma ascent caused a shift in melt composition towards lower sr and higher ba as documented in the rims of the phenocrysts although the cores of the phenocrysts crystallised at relatively shallow depths they preserve the sr and ba of the deep seated melts as they ascended from a deeper region further magma ascent resulted in microlite nucleation which is responsible for a similar shift to even lower sr concentration as observed in the groundmass of post 18 may 1980 samples

global positioning system network analysis with phase ambiguity resolution applied to crustal deformation studies in california a 5 year campaign is in progress in central and southern california to monitor tectonic motions using observations of the global positioning system gps satellites evidence from geological and space geodetic data indicates that significant horizontal deformations of order 10 mm yr are occurring west of the san andreas fault along the california margin we demonstrate using data from initial epoch measurements in january 1987 that the goal of measuring horizontal deformations with an accuracy of 5 mm yr over the duration of the campaign should be readily achievable the gps network was designed to span a wide range of baseline lengths within california and across north america to aid in phase ambiguity resolution an important factor in achieving highest accuracy baseline determinations we present an efficient algorithm for multisession network analysis of gps data with simultaneous orbit determination and ambiguity resolution using this algorithm with the california data we demonstrate the improvement obtained in station position and satellite orbit estimation when the phase ambiguities are resolved we demonstrate several millimeters 1 part in 108 short term repeatability over five single session daily analyses for horizontal baseline components and length and several tens of millimeters for the vertical comparison with the independently determined very long baseline interferometry baseline between mojave and owens valley suggests that the accuracy is at the same level as the repeatability we show that simultaneous multisession analyses with ambiguity resolution improve the baseline and satellite orbit estimates compared to the single session analyses with the single session analyses we were able to resolve all phase ambiguities on baselines within california with the multisession analyses we were able to resolve the phase ambiguities for most of the network over regional and continental scales

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

improved stability of a deeply anchored geodetic monument for deformation monitoring a test of two different monument designs used in geodetic networks shows that monuments installed to depths of 5 to 10 meters and laterally braced exhibit less environmentally caused displacement than those installed to 2 meters depth at parkfield california we have been monitoring the lengths of 17 baselines over the past decade with a 2 to 3 day interval between measurements using a two color geodimeter with a nominal precision of 0 5 mm over 5 km long baselines significant variations are observed on many of these baselines which appear to be related to the seasonally occurring rainfall with the larger variations approaching 10 mm over the past decade to test whether we could improve upon the measurements on some of the more susceptible lines at two sites we installed new monuments within about 30 meters of the original monuments after 1 5 years of measurements it is evident that the new monuments significantly attenuate the seasonal displacements to less than 1 mm the use of deeply anchored monuments should improve the ability of fault scale geodetic monitoring arrays to detect small tectonic displacements

mid pleistocene basalt from the seguam volcanic center central aleutian arc alaska local lithospheric structures and source variability in the aleutian arc recent geophysical and tectonic studies make it possible to examine the relation between local structural and tectonic evolution of the modern aleutian arc and the sources and processes that produce the broad spectrum of aleutian basaltic lavas mid pleistocene basalt from the seguam island volcanic center in the central aleutian arc erupted through strongly extended arc crust contains 4 8 mgo is low in k2o 18 and is distinguished from aleutian basalt erupted through less extended crust by a low abundance of incompatible and rare earth elements ree and low sr and pb content the ba la 47 72 and pb la 0 7 1 5 ratios are high incompatible element ratios are variable and ree patterns cross one another the 87sr 86sr ratio 0 70365 0 00003 is the highest value obtained from the aleutian islands also 206pb 204pb 18 91 0 02 207pb 204pb 15 60 0 02 and 208pb 204pb 38 51 0 04 ratios are among the most radiogenic values known whereas the 143nd 144nd ratio 0 51297 0 00003 is among the lowest measured low abundances of incompatible elements high ba la and pb la ratios uniform sr nd and pb isotope ratios and high eruptive temperatures 1160 c suggest that basalt erupted at seguam ascends through extended subarc lithosphere without extensive chemical exchange with the upper mantle or lower crust partial melting of geochemically distinct portions of an isotopically uniform source region best explains observed geochemical characteristics trace element abundances rule out an eclogite source and suggest instead a peridotite dominated source with 5 10 of a subducted sediment component this peridotite may reside in the mantle wedge or in the amlia fracture zone afz of the pacific plate that was subducted beneath seguam 1 ma in addition the afz possibly enhanced the subduction of terrigenous sediment into the source region beneath seguam and this extra terrigenous component may explain the ba la pb la and sr nd and pb isotope ratios the distinctive composition of seguam basalt reflects a complex set of physical conditions including fracture zone subduction and intraarc extension that affected both the source region and thermo chemical history of magma ascent local structural and tectonic factors impact profoundly the nature of island arc magma sources and processes models that propose a common parental arc magma type or common processes on a global or arcwide scale are too generalized to explain the diversity actually observed in the aleutian arc

magmatic evolution and ascent history of the aries micaceous kimberlite central kimberley basin western australia evidence from zoned phlogopite phenocrysts and uv laser 40ar 39ar analysis of phlogopite biotite the neoproterozoic aries kimberlite was emplaced in the central kimberley basin western australia as a n nne trending series of three diatremes infilled by lithic rich kimberlite breccias the breccias are intruded by hypabyssal macrocrystic phlogopite kimberlite dykes that exhibit differentiation to a minor high na si olivine phlogopite richterite kimberlite and late stage macrocrystic serpentine diopside ultramafic dykes mineralogical and geochemical evidence suggests that the high na si olivine phlogopite richterite kimberlite was derived from the macrocrystic phlogopite kimberlite as a residual liquid following extended phlogopite crystallization and the assimilation of country rock sandstone and that the macrocrystic serpentine diopside ultramafic dykes formed as mafic cumulates from a macrocrystic phlogopite kimberlite chemical zonation of phlogopite biotite phenocrysts indicates a complex magmatic history for the aries kimberlite with the early inheritance of a range of high ti phlogopite biotite xenocrysts from metasomatized mantle lithologies followed by the crystallization of a population of high cr phlogopite phenocrysts within the spinel facies lithospheric mantle a further one to two phlogopite biotite overgrowth rims of distinct composition formed on the phlogopite phenocrysts at higher levels during ascent to the surface ultra violet laser 40ar 39ar dating of mica grain rims yielded a kimberlite eruption age of 815 4 4 3 ma 95 confidence 40ar 39ar laser profiling of one high ti phlogopite biotite macrocryst revealed a radiogenic 40ar diffusive loss profile from which a kimberlite magma ascent duration from the spinel facies lithospheric mantle was estimated assuming an average kimberlite magma temperature of 1000 c yielding a value of 0 23 2 32 days for the north extension lobe of the aries kimberlite

a temporal record of magma accumulation and evolution beneath nevado de toluca mexico preserved in plagioclase phenocrysts plagioclase crystals from the 8 km 10 5 ka upper toluca pumice utp eruption from nevado detoluca provide a detailed temporal record of pre eruptive magmatic processes the crystals display a range of textures and major and trace element concentrations a distinct feature of the crystals is the presence of several sharp increases in mgo feo andtio2 which occur at some of the numerous resorption horizons and coincide with increases in xan and in some cases ce and la these abrupt compositional peaks and the associated textural variations reflect recharge events of more mafic melt three distinct recharge events can be recognized the general compositional trends suggest that crystallization occurred within a common chamber however the crystal cores display a range of textures and a wide range of compositions suggesting that they are relics of earlier crystallization episodes within the upper crust the temporal record of sr and ba melt contents recorded by the crystals calculated using partition coefficients fluctuates significantly within single crystals overall two trends of sr ba variation in the melt are apparent the first trend involves decreasing sr and slightly increasing ba consistent with plagioclase crystallization the second trend involves an increase in both sr and ba that is not consistent with crystallization of plagioclase alone this trend is ascribed to chemical variations within the deeper magma reservoirs from which the various magma batches entering the utp shallow reservoir were ultimately sourced the magmatic system under nevado de toluca was open and received intermittent but relatively small pulses of magma from a deeper source dacite was the predominant recharge composition although some pulses were distinctly more mafic and hotter these processes led to the accumulation of a large volume of dacitic magma in the upper crust one of the more mafic pulses appears to have triggered the eruption

laser interference and nomarski interference imaging of zoning profiles in plagioclase phenocrysts from the may 18 1980 eruption of mount st helens washington

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

weathering and mineralogical evolution in a high alpine soil chronosequence a combined approach using sem edx cathodoluminescence and nomarski dic microscopy abstract physical and chemical weathering of primary minerals of granitic till in the proglacial area of morteratsch switzerland was investigated using cathodoluminescence cl nomarski differential interference contrast dic microscopy and scanning electron microscope sem edx the investigated time span ranges from 0 to 140 years of sediment exposure for the very early stage of weathering or soil formation only little information is available the main aim of our investigation was consequently to see whether weathering of primary minerals can be detected in such a short time span using for the first time for soils well established methods as cl and nomarski dic microscopy in geo and material science such for that purpose the fine earth fraction o si in quartz that start to break and to transform into free radicals k feldspar and plagioclase contain fe when using fe3 as reference point 680 700 nm to standardise the cl spectra the al o al defects of k feldspar exhibit a relative decrease with time this was not the case for plagioclase the cl measurements showed that the investigated apatite contained ree rare earth elements in the crystal structure however none of the other techniques dic sem edx was helpful in detecting any specific weathering features for apatite in the time span of 140 years epidote weathering was evidenced using xrd in a previous investigation and here using dic microscopy morphologic changes several mineral changes could be traced within a very short weathering sequence using the applied techniques these changes include physical e g biotite chemical or crystal structure k feldspar biotite features such an analytical combination is promising therefore for the detection of chemical physical and mineralogical characteristics and changes in very young glacial sediments

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

volcanological evolution of the rivi capo volcanic complex at salina aeolian islands magma storage processes and ascent dynamics lava flows and pyroclastic deposits from strombolian fallout related to the activity of the rivi and capo volcanoes which are representative of early subaerial volcanoes on salina aeolian islands have been investigated through a geological petrological approach our geological field survey shows that rivi and capo volcanoes are part of a single n50 e aligned volcanic complex here named rivi capo volcanic complex rcvc stratigraphically specific rock sampling has allowed reconstruction of the magma feeding processes through time whole rock major element compositions together with core to rim profiles of plagioclase and clinopyroxene crystals show a general evolution toward more basic compositions through the three formations constituting the capo volcano and within the rivi center melts simulations and mass balance modeling suggest that the rcvc rocks are the result of fractional crystallization of plagioclase clinopyroxene and olivine ca 45 of solid removed from a primary magma in addition to fractional crystallization continuous recharge and mixing with more basic magma coming from deeper parts of the magmatic plumbing system contributed to the final volcanic rock compositions our textural and microanalytical data on plagioclase and clinopyroxene crystals allow the definition of a multilevel magmatic storage system with reservoirs at 20 and 3 km below sea level when processes of magma differentiation ascent and storage are considered together with the stratigraphic position of each sample a history of continuous modification of the rcvc plumbing system can be constructed volcanism may have been characterized by fissure type eruptions during the early stages lower capo lower rivi and middle capo formations gradually changing later to central type volcanism upper capo and upper rivi formations

postseismic deformation associated with the 1992 m ω 7 3 landers earthquake southern california following the 1992 m 7 3 landers earthquake a linear array of 10 geodetic monuments at roughly 5 km spacing was established across the emerson fault segment of the landers rupture the array trends perpendicular to the local strike of the fault segment and extends about 30 km on either side of it the array was surveyed by global positioning system 0 034 0 048 0 381 1 27 1 88 2 60 and 3 42 years after the landers earthquake to measure both the spatial and temporal character of the postearthquake relaxation the temporal behavior is described roughly by a short term decay time 84 23 days exponential relaxation superimposed upon an apparently linear trend because the linear trend represents motions much more rapid than the observed preseismic motions we attribute that trend to a slower decay time greater than 5 years postseismic relaxation the curvature of which cannot be resolved in the short run 3 4 years of postseismic data about 100 mm of right lateral displacement and 50 mm of fault normal displacement accumulated across the geodetic array in the 3 4 year interval covered by the postseismic surveys those displacements are attributed to postseismic right lateral slip in the depth interval 10 to 30 km on the downward extension of the rupture trace the right lateral slip amounted to about 1 m directly beneath the geodetic array and the fault normal displacement is apparently primarily a consequence of the curvature of the rupture these conclusions are based upon dislocation models fit to the observed deformation however no dislocation model was found with rms residuals as small as the expected observational error

sieve textured plagioclase in dacitic magma interference imaging results the dacite of the pebble creek formation mount meager bc canada is an extraordinary occurrence of lavas containing coarse sieve textured plagioclase phenocrysts that appear to have reacted extensively with the melt we record this unusual occurrence of a naturally reacted crystal melt pair utilizing nomarski differential interference contrast ndic imaging and electron microprobe data hieroglyphic textures are common in plagioclase of this study and appear to represent older plagioclase remnants in sharp contact with new plagioclase forming a palimpsest texture outlining the occurrence of previous pools of melt throughout the processes affecting the phenocrysts capillaries of liquid remained open to the external melt

variations in fault slip and strain accumulation at parkfield california initial results using two color geodimeter measurements 1984 1988 repeated length measurements of several geodetic baselines near parkfield california have revealed significant variations in the local rates of shallow fault slip and strain this network of baselines surveyed several times each week straddles the san andreas fault in the transition zone between the creeping section to the northwest and the locked section to the southeast the length measurements characterized by a precision approaching 0 1 ppm reveal large fluctuations in the rates of baseline extension principal mode analysis of the length change data indicates that the two largest components of the signal are 1 secular extensions and contractions consistent with surface slip on the main strand of the san andreas fault and 2 a large seasonal oscillation with no obvious spatial coherence on most of these baselines the second component appears to be in phase with seasonal rainfall when data from the baselines with the largest amplitude of the seasonal signal are excluded the remaining data can be modeled in terms of both spatial and temporal variations in surface slip variations in the components of the changes in uniform strain and the possible displacement of the central monument in this radial network in parameterizing this model the spatial variation of slip beneath the near surface is reflected by changes in shear strain although the computed secular shear is highly dependent upon the specified parameterization of surface slip the data are consistent with the hypothesis that slip at intermediate depths lags behind the surface slip rate however the range in models that fit the data does not necessarily imply that there is a deficit in slip at depth relative to the surface comparison of the inferred values of surface slip from the model with the observed fault slip measured by very short baseline creep meters indicates close agreement in secular rates but the short term variations observed with the creep meters are either highly attenuated or nonexistent in the modeled slip since the modeled slip is a spatial average which smooths out possible short wavelength variations in the surface slip for which the creep instruments are most sensitive an interesting conclusion from the two color data is that surface slip on the san andreas fault appears to be spread over a 2 km wide zone on the south flank of middle mountain but is confined to a very narrow zone to the south as the fault passes through the center of the network this conclusion is dependent upon the assumption that a few critical monuments are stable and track tectonic displacements in the long term finally the largest observed strain change is an extensional strain coincident with the kettleman hills earthquake m5 5 in august 1985

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

present day crustal deformation along the magallanes fagnano fault system in tierra del fuego from repeated gps observations summary the present day deformation of the earth crust in the argentine part of tierra del fuego main island southernmost south america is here investigated based on repeated geodetic gps observations the island is traversed by the active transform boundary between the south american and scotia tectonic plates represented by the magallanes fagnano fault system since 1993 a regional network comprising to date 29 gps sites has been observed almost every year the complete set of accumulated observations was processed using the bernese gps software and state of the art processing strategies and models the utilization of homogeneous gps products resulting from a reprocessing of the global igs network warrants a stable realization of a global reference frame for each gps site 3 d positions and linear velocities with error estimates were obtained a strain analysis of the horizontal velocity components revealed the zones of major deformation activity a 30 km wide deformation belt centred on the main trace of the fault system was identified this belt is bordered to the north south america and south scotia by geodynamically stable zones which move horizontally with a relative average velocity of 4 4 0 6 east and 0 3 0 4 north mm a 1 within the deformation belt a maximum strain rate in the order of 0 25 strain per year has been detected a pronounced change in the deformation style from transtension east to transpression west is observed the area of predominating shortening of the crust coincides with a local rotation minimum and relative uplift throughout the period covered by the gps observations the displacements and deformations occurred to be linear with time

experimental study of plagioclase rim growth around anorthite seed crystals in rhyodacitic melt the purpose of this study was to replicate experimentally the growth of new rims around highly anorthitic plagioclase core phenocrysts analogous to the incorporation of xenocrysts into a silicic magma body through magma mixing aniakchak rhyodacite forms the bulk starting composition and phase equilibria experiments constrained the pre eruption magma conditions to be 110 mpa and 870 880 c the experimental runs were seeded with great sitkin anorthite an 9 1 9 5 crystals new rim growth of an 2 8 3 8 plagioclase occurred at rates between 3 5 0 3 x 10 1 0 to 60 6 20 0 x 10 1 0 cm s at pressures and temperatures from 50 to 150 mpa and 825 to 880 c the values in parentheses are 1 standard deviation microlite crystallization an 2 7 4 1 occurred in all experiments within the plagioclase stability field and their growth rates varied from 4 4 1 3 x 10 1 0 to 65 7 10 1 x 10 1 0 cm s the rim and microlite growth rates are similar to one another within each experiment and microlite number density n v is correlated approximately inversely with rim growth rates microlite crystallinities increased from 4 2 to 49 7 vol as a function of increasing t e f f up to 95 c the results indicate growth dominated crystallization at low t e f f and nucleation dominated crystallization at high t e f f in agreement with previous studies assuming the experiments apply to nature the rim growth rates can provide a minimum estimate on how fast magma mixing can occur rims that are 10 to 100 m wide can grow in 10 days to 4 months recording fast mixing timescales as long as eruption occurs shortly after mixing the growth rate estimates presented here generally agree with those derived from sodic rims growing around anorthite cores after mixing between basalt and andesite prior to the 1996 eruption of karymsky volcano kamchatka

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

crystal residence times from trace element zoning in plagioclase reveal changes in magma transfer dynamics at mt etna during the last 400 years abstract trace element zoning in plagioclase of selected alkaline lavas from the historic 1607 1892 ad and recent 1983 2013 ad activity of mt etna volcano has been used to explore the possible role that volcano tectonics exert on magma transfer dynamics the observed textural characteristics of crystals include near equilibrium textures i e oscillatory zoning and textures with variable extent of disequilibrium patchy zoning coarse sieve textures and dissolved cores historic crystals exhibit lower k concentrations at lower anorthite contents a feature in agreement with the general more potassic character of the recent lavas if compared to the historic products historic plagioclases have statistically higher ba and lower sr concentrations than the recent crystals which result in different sr ba ratios for the two suites of plagioclase variations in the anorthite content along core to rim profiles obtained on crystals with different types of textures for both the historic and recent eruptive periods were evaluated particularly versus sr ba at comparable average an contents crystals characterized by oscillatory zoning which are representative of near equilibrium crystallization from the magma display distinct sr ba ratios we suggest that these features are primarily related to recharge of a new geochemically distinct magma into the storage and transport system of the volcano in addition to distinct trace element and textural characteristics of plagioclase sr diffusion modeling for plagioclase suggests that residence times are generally shorter for crystals found in recently erupted lavas 25 77 years average 43 years compared to those of the historic products 43 163 years average 99 years shorter residences times correlate with gradual increases in eruption volume and eruption frequency rates through time we attribute these features to an increasing influence since the 17th century of extensional tectonic structures within the upper 10 km of the etnean crust which have promoted shorter residence times and higher eruption frequency

the interplay between crystallization replenishment and hybridization in large felsic magma chambers abstract while hybridized granitoid magmas are readily identifiable the mechanisms of hybridization in large crustal magma chambers are so not clearly understood characteristic features of hybrid granitoids are 1 both the granitoid and included enclaves are commonly hybrids as shown by mineralogy geochemistry and isotopes 2 mixing seen in zoned plutons and synplutonic dykes and enclaves occurred early 3 zoned plagioclase phenocrysts commonly show very complex life histories of growth and dissolution 4 mafic end members in hybrids are commonly fractionated magmas and 5 stratification in subvolcanic granitoid magma chambers is not uncommon and stratification has been identified in some deeper level plutons hybridization must overcome the tendency to form a stable stratification of dense mafic magma underlying less dense felsic magma experimental work with magma analogues and theoretical considerations reveal very severe thermal rheological and dynamical limitations on mixing only very similar composition temperature magmas are likely to mix to homogeneity and only moderately silicic hybrids are likely to be produced however impossibly silicic hybrids do exist synchronous interactive fractional crystallization and hybridization may provide a mechanism for hybridization of magmas in the following manner a mafic magma intrudes into the base of a stratified felsic magma and is cooled against it crystallization of the upper boundary layer of the mafic magma yields an eventually buoyant residual melt that overturns and mixes with an adjacent stratum of the felsic magma chamber subsequently melt released by crystallization pf this now hybrid zone mixes with adjacent more felsic zones thus a suite of hybrid magmas are progressively formed density inhibitions are overcome by the generation of relatively low density residual melts as crystallization proceeds later injections are preserved as dykes and enclaves composed of hybrid magma in this process only physically adjacent and dynamically thermally similar magmas directly interact and so may mix to homogeneity finally not simply felsic and mafic endmembers mix but a whole suite of intermediate endmembers participate ranging from relatively mafic through to felsic pairs of magmas direct mixing between the primary magmas only occurs at the beginning

detection of crustal deformation from the landers earthquake sequence using continuous geodetic measurements the measurement of crustal motions in technically active regions is being performed increasingly by the satellite based global positioning system gps 1 2 which offers considerable advantages over conventional geodetic techniques3 4 continuously operating gps arrays with ground based receivers spaced tens of kilometres apart have been established in central japan5 6 and southern california to monitor the spatial and temporal details of crustal deformation here we report the first measurements for a major earthquake by a continuously operating gps network the permanent gps geodetic array pgga 7 9 in southern california the landers magnitude afw of 7 3 and big bear mw 6 2 earthquakes of 28 june 1992 were monitored by daily observations ten weeks of measurements centred on the earthquake events indicate significant coseismic motion at all pgga sites significant post seismic motion at one site for two weeks after the earthquakes and no significant preseismic motion these measurements demonstrate the potential of gps monitoring for precise detection of precursory and aftershock seismic deformation in the near and far field

rapid resolution of crustal motion at short ranges with the global positioning system on the basis of the analysis of global positioning system gps data collected at the u s geological survey kennedy ranch house alinement array near parkfield california in november 1990 and february 1991 we assess the temporal resolution of crustal deformation for gps receiver systems operating as strain meters and provide guidelines for achieving millimeter level precision with short range kinematic type gps measurements site occupation of about one half hour is sufficient for day to day repeatability of submillimeter precision in relative position during good satellite geometry signal multipath effects which dominate dispersive baseline errors are essentially averaged out and need not be modeled however as occupation times decrease baseline solutions are increasingly sensitive to multipath effects which together with nondispersive receiver measurement noise are of millimeter to centimeter magnitude in epoch by epoch solutions on repeatedly monitored baselines we can account for both of these noise sources separately the mostly random receiver noise is effectively suppressed by low pass filters with corner frequencies of about 20 mhz the multipath noise is filtered using the fact that it essentially repeats from day to day residual errors in filtered 1 s epoch by epoch solutions are below 2 mm during periods of good satellite geometry hence for a continuously monitored baseline actual deformation in excess of this threshold can be detected with a time lag comparable to the group delay of the low pass filter i e typically within a minute in terms of strain along a typical short baseline of 1 km sampled once per second we can detect 1 2 s in l min with multipath modeling without multipath modeling it takes 10 min to resolve the same magnitude of deformation in 30 min we can detect 0 1 s independent of multipath modeling these results have important implications for kinematic type gps surveys for millimeter level precision without impractical multipath modeling it is necessary to occupy a site during good satellite geometry for a period longer than that of the multipath signature our experience in both benign and difficult multipath environments indicates that approximately 10 min are sufficient the measurements at the kennedy ranch house alinement array suggest that this segment of the san andreas fault appears to be virtually locked at the surface during the 3 month period between the two surveys

relative and absolute sea level rise in western canada and northwestern united states from a combined tide gauge gps analysis 1 empirical studies and climate models suggest large variations of absolute sea level asl changes between oceanic basins such potential variations raise concern on the applicability of global mean asl predictions to specific regions and on estimates of relative sea level rsl hazards we address this issue for the western canada and northwestern united states coastline by estimating the 20th century asl rate using a combination of 34 colocated tide gauge and global positioning system gps stations the tide gauge data are quality controlled and corrected for spatially and temporally correlated sea level transients in order to derive robust rsl trends and standard errors reference frame and other gps specific issues are considered as part of the error budget in absolute gps vertical velocities our combined tide gauge gps analysis aligned to the international terrestrial reference frame 2000 indicates a northeast pacific asl rise of 1 8 0 2 mm a through the 20th century which is similar to accepted rates for the global eustatic mean for the period 1993 2003 we find a regional asl rate of 4 4 0 5 mm a consistent with satellite altimetry on the basis of the intergovernment panel on climate change assessment report 4 mean scenario and our assessment of coastal motions from gps and tide gauge data we derive a map of predicted 21st century rsl rise in western canada and the northwestern united states variations in coastal uplift strongly affect spatial rsl patterns subsidence of southern puget sound may significantly increase rsl rise in the seattle tacoma metropolitan area conversely tectonic uplift along parts of the outer west coast may reduce future rsl rise by up to 50 100

gps measurement of postseismic deformation following the 1999 chi chi taiwan earthquake 1 in the 15 month period september 1999 to december 2000 after the 1999 chi chi taiwan earthquake mw 7 6 about 80 campaign surveyed gps stations in central taiwan were occupied up to seven times furthermore seven continuous gps stations were put into operation in the epicentral region mostly within three weeks after the main shock gps data from these near field stations and some pre existing far field stations were utilized to study the postseismic deformation following the chi chi earthquake the postseismic displacements of the gps stations were approximated by a combination of an exponential transient decay function with a relaxation time of 86 days and a postseismic linear rate change stations on the hanging wall displayed west northwesterly horizontal displacements of up to 252 mm and uplift as large as 229 mm postseismic displacements are much larger to the south near the epicenter of chi chi main shock than in the north where the maximum coseismic displacement occurred stations on the footwall show only small displacements the postseismic gps data were inverted to infer the deeper fault geometry and afterslip distribution based on a four segment fault model with its shallow part constrained by coseismic fault geometry deduced from gps and seismological studies the optimal model requires the lower fault segment to be a horizontal plane at a depth of 10 4 km consistent with a model based on gps data taken during the first three months after the main shock and other geological or geophysical studies the maximum afterslip 459 mm occurs in the hypocentral region and in the northern part of the decollement slip of about 430 mm also occurs in the southern part of the decollement the afterslip moment inferred from 15 months of gps data is 4 7 1019 n m approximately 2 3 times the seismic moment released by aftershocks this implies that a major part of the postseismic deformation is aseismic

anorthite calibrated backscattered electron profiles trace elements and growth textures in feldspars from the teide pico viejo volcanic complex tenerife abstract magma chamber dynamics at the phonolitic to basanitic teide pico viejo volcanic complex on tenerife canary islands have been investigated using feldspar zonation and chemistry backscattered electron image grey value profiles obtained by electron microprobe and calibrated on anorthite content allow the investigation of much better spatially resolved zonation profiles than quantitative point analysis alone on the basis of these zonation patterns and trace element analyses by electron microprobe magma chamber processes such as magma recharge and mingling as well as whole chamber overturn events can be identified and characterized in more detail samples from all investigated eruption centres contain feldspars which have experienced growth in a deep reservoir followed by ascent resorption and growth of mantles in more shallow levels in the crust just prior to eruption two pico viejo samples exhibit feldspars with a characteristic drop in anorthite content which is not accompanied by resorption trace element behaviour in these samples shows that cores and mantles have grown from the same magma reservoir the conclusion from these data is that there occurred complete overturn events in layered magma chambers presumably induced by cold plumes from the cupola layers a mass balance calculation shows that the proportions of the layers are 75 wt lower part and 25 wt cupola layer correlations between zonation patterns of single crystals in different rocks show that the teide magma chambers are larger and chemically buffered compared with the smaller pico viejo system feldspars from pico viejo exhibit rather complex anorthite profiles and more frequently display disturbances likely to be caused by arrival of new magma batches