topographic gravimetric effects in earth sciences review of origin significance and implications abstract we present a comprehensive view of the origin significance and implications of topographic effects in gravimetry these are gravitational effects of topographic masses that are present in any observable quantity of the earth s gravitational field in most gravimetric applications and their computational realizations when topography is not the focus of the study these effects need to be properly treated as corrections reductions some of them might not be obvious or intuitive and may remain misunderstood and mistreated first we look at topographic effects in geodesy and focus on those that affect the determination of the geoid from terrestrial gravity data we review the origin and role of both the direct and indirect the primary and secondary topographic effects then we review the bouguer concept in geophysical applications finally we take a look at the topographic effect induced by the deformation of the topographic surface and its importance in the interpretation of observed spatiotemporal gravity changes we illustrate the sizes and shapes spatial properties of these effects discuss their relevance and impacts in the areas of geodesy geophysical structural studies exploration and prospection and in geodynamics with a focus on volcano geodesy

volcano monitoring by microgravity and energy budget analysis microgravity monitoring of active volcanoes can provide evidence of sub surface mass and or density changes that precede eruptions if in addition precursory increases in thermal emissions are observed an integrated mechanistic model for volcanic activity may be developed with the potential for forecasting eruptions crater lake volcanoes provide an interesting target for such studies since thermal output can be monitored simply through lake water calotimetry here we summarize 10 years of gravity and thermal data from poas volcano costa rica mass energy balance calculations demonstrate that in the steady state the large thermal inertia of the crater lake acts as a buffer to short term changes in the energy input from the cooling magma feeder pipe since february 1986 it is postulated that there has been gradual emplacement of a shallow magma intrusion associated with vesiculation and gas loss to the surface this follows from unambiguous gravity increases constrained by elevation control that are coincident in time with a period of long term increased energy input to the crater lake progressive reduction of the lake volume by evaporation seepage culminated in an april 1989 ash eruption providing a good documented record of combined gravity and thermodynamic precursors to volcanic activity

temporal gravity and height changes of the yellowstone caldera 1977 1994 this paper describes the longest record of gravity measurements in the area of the yellowstone caldera wyoming the temporal gravity changes at the 12 gal 10 8 ms 2 precision level are compared with changes in heights from leveling and gps the gravity field decreased across the caldera from 1977 to 1983 during the uplift and attained a maximum decrease of up to 60 2 gal along the caldera axis the gravity field then reversed polarity to increasing values of up to 60 12 gal between 1986 and 1993 the ratio between height and gravity changes varied during the entire time but converged over the latter period following the free air gravity gradient general ground deformation deduced from leveling showed caldera wide uplift of 15 mm a during the period of gravity decrease then from leveling and gps subsidence of 25 mm a during the gravity increase

nitrogen isotopic composition of ammoniated phyllosilicates case studies from precambrian metamorphosed sedimentary rocks ammonium concentrations in phyllosilicates from archean and proterozoic schists and carbonates were evaluated by fourier transform infrared microspectrometry aftir the y 15 nair values of structural nitrogen in these phases were subsequently measured by laser mass spectrometry a rapid estimate of the concentration of nh4 in biotite by aftir allows the preselection of the samples to be analyzed for their isotopic composition micas from 1 90 2 09 ga metasediments from finland and from 1 025 1 500 ga biotite schists from the moine succession in scotland have high concentrations of structural ammonium between 176 and 1549 ppm suggestive of a biological origin for the nitrogen the heavy nitrogen isotopic signatures y 15 n 4 9x to 19 7x of structural nh4 in these micas are considered consistent with biological denitrification in operation at the time of sedimentation evidence for denitrification in the mesoproterozoic is in agreement with geological and geochemical data for abundant free oxygen in the atmosphere facilitating the stability of marine no3 sequences of early archean ca 3 8 ga garnet mica schists from the isua supracrustal belt isb in southern west greenland contain biotite rich in nh4 between 233 and 512 ppm and nitrogen isotopic signatures y 15 n 1 9x to 5 9x which possibly point to an early evolution of ammonium assimilation and or nitrogen fixation this result appears to be consistent with molecular phylogenetic studies in the bacterial and archaeal domains which suggest that nitrogen fixation and ammonium assimilation were metabolic features of the last common ancestor lca of all organisms d 2004 elsevier b v all rights reserved

insights on the march 1998 eruption at piton de la fournaise volcano la reunion from microgravity monitoring we investigate the temporal gravity changes associated with one of the major recent eruptions at piton de la fournaise volcano march 1998 that occurred after an unusual five year quiet period and initiated a new eruptive cycle repeated microgravity surveys allowed us to measure residual gravity changes up to 100 gal within the enclos fouque caldera for four months before the start of the eruption we first analyzed the temporal gravity changes and the height changes also measured at the gravity benchmarks on the basis of an intrusive dyke model previously proposed for this eruption from insar and tilt data this analysis reveals that such simple model finite rectangular shaped tensile dislocation cannot fit both gravity and geodetic data and leads us to propose a dual source gravity model for this eruption the gravity data inversion using a genetic algorithm search method allows us to quantify the mass change produced by the intrusive dyke 3 9 to 8 7 109kg and to suggest an additional mass increase at sea level depth 4 6 to 7 2 1010kg we interpret the latter as the effect of magma ascent into a reservoir that occurred within the four months before the eruption we suggest that high concentrations of gas content in the magma reservoir account for a higher compressibility of the intruded magma and produce significant mass change with moderate surface deformation the 1996 seismic crisis interpreted as an upward migration of magmatic fluids into a reservoir located at sea level might support such a hypothesis

spatiotemporal gravity variations to look deep into the southern flank of etna volcano 1 a 14 year long microgravity data set october 1994 to september 2007 collected along a 24 km east west trending profile of 19 stations was analyzed to detect underground mass redistributions related to the volcanic activity involving the southern flank of mt etna italy a multiresolution wavelet analysis was applied to separate the volcano related anomalies from the unwanted components the residual image having both spatial extension and temporal duration evidenced two complete gravity increase decrease cycles mainly affecting the central and eastern stations of the profile the first gravity increase early 1995 to the end of 1996 and decrease end of 1996 to late in 1998 cycle reached a maximum amplitude of approximately 90 gal the second gravity increase mid 1999 to mid 2000 and decrease mid 2000 to early 2004 cycle attained an amplitude of about 80 gal after about 5 years of a persistent negative gravity anomaly a new semicycle started at the end of 2006 and continued during the last survey carried out in september 2007 the density changes modeled over time since 1994 using a quadratic programming algorithm are mainly located at a depth of 2 4 km bsl in a region recognized to be a preferential pathway of magma rising and an intermediate zone of magma storage withdrawal the computed positive mass variations of about 105 109 kg were interpreted as magma accumulation while negative mass changes of about 120 109 kg were associated with either magma drainage or opening of new voids by tectonic stresses within a source volume where tensional earthquakes occurred

viscoelastic modeling of deformation and gravity changes induced by pressurized magmatic sources abstract gravity and height changes which reflect magma accumulation in subsurface chambers are evaluated using analytical and numerical models in order to investigate their relationships and temporal evolutions the analysis focuses mainly on the exploration of the time dependent response of gravity and height changes to the pressurization of ellipsoidal magmatic chambers in viscoelastic media firstly the validation of the numerical finite element results is performed by comparison with analytical solutions which are devised for a simple spherical source embedded in a homogeneous viscoelastic half space medium then the effect of several model parameters on time dependent height and gravity changes is investigated thanks to the flexibility of the numerical method in handling complex configurations both homogeneous and viscoelastic shell models reveal significantly different amplitudes in the ratio between gravity and height changes depending on geometry factors and medium rheology the results show that these factors also influence the relaxation characteristic times of the investigated geophysical changes overall these temporal patterns are compatible with time dependent height and gravity changes observed on etna volcano during the 1994 1997 inflation period by modeling the viscoelastic response of a pressurized prolate magmatic source a general agreement between computed and observed geophysical variations is achieved

ammonium partitioning and nitrogen isotope fractionation among coexisting micas during high temperature fluid rock interactions examples from the new england appalachians abstract despite recent advances in the field of n isotope geochemistry our understanding of the behavior of this element in the solid earth remains limited by a lack of fundamental information regarding the partitioning of ammonium and isotopic fractionation of n among coexisting mineral and fluid phases study of n behavior in regionally metamorphosed rocks provides the opportunity to assess intermineral nh 4 partitioning and n isotope fractionation among coexisting micas during metamorphism and affords an application of the n system as a tracer of high t fluid rock interactions analyzed mica samples range in 15 n air from 3 3 to 11 9 and contain 9 to 1820 ppm n the outcrop at townshend dam vermont allows examination of n behavior across strike on a relatively small scale and samples from western maine demonstrate the effect of varying metamorphic conditions on n behavior in metapelites 15 n bt w mica 15 n biotite 15 n white mica ranges from 0 9 to 2 7 for all samples from both suites mean 0 36 with 1 0 79 with samples containing a separate paragonite white mica phase showing the greatest range 0 12 to 1 02 mean 0 58 1 1 03 thirteen samples containing only na poor muscovite six from townshend dam seven from western maine have mean 15 n bt w mica of 0 07 1 0 41 in both suites biotite nearly always contains more n than coexisting white mica but n w mica n bt also shows some significant scatter mean n w mica n bt 0 46 with 1 0 34 the thirteen samples containing only a na poor muscovitic white mica phase have mean n w mica n bt 0 39 with 1 0 26 similar to that reported by others for other metamorphic suites containing only muscovite as the white mica phase there is no obvious suggestion of equilibrium n isotopic fractionation among coexisting micas at epidote amphibolite to amphibolite facies metamorphic conditions although nh 4 appears to partition systematically among coexisting biotite and white mica significant scatter in both 15 n bt w mica and nh 4 partitioning conceivably the result of differential closure to exchange during cooling or of retrograde replacements could however obscure observation of small equilibrium intermica fractionations related to the characteristics of the interlayer sites in which nh 4 resides samples most unlike the mean in both 15 n bt w mica and n w mica n bt contain abundant chlorite some of which is likely retrograde based on petrographic observations chl chl bt 0 3 thus retrograde replacement of biotite by chlorite may have been accompanied by fluid mineral n isotope exchange perhaps involving the production of fine grained retrograde n bearing white mica observed petrographically for some samples it is also possible that sampling at scales greater than those of n isotope equilibrium domains e g across fine interlayers results in some scatter because of varying relative modal proportions of the two micas in adjacent fine interlayers although further investigation of the extent of retrograde reequilibration of mica n systematics is warranted the observed lack of systematic n isotope fractionation among coexisting micas and the reasonably systematic nh 4 partitioning data for these phases provide important preliminary constraints for attempts to model n isotope behavior in fluid rock systems these results and other attempts to calibrate n isotope fractionation through field studies point to the conspicuous lack of experimentally determined mica fluid n isotope fractionation factors

transitions between explosive and effusive eruptions of silicic magmas water rich silicic magmas may erupt explosively giving rise to massive columns of fragmented ash1 5 or effusively as viscous bubbly lavas to form lava domes6 8 complex cycles of explosive and effusive eruptions are often observed8 12 although these two eruption mechanisms have been modelled independently1 8 the conditions under which a volcano exhibits a particular style of eruption are not known and the transitions between eruption styles are poorly understood by modelling the ascent of magma along a permeable conduit we show here that for small magma chamber overpressures the style of eruption explosive or effusive is dependent on the magma flow rate we also identify a critical overpressure above which only explosive eruptions occur complex eruption sequences follow naturally for example if a shallow magmatic system is supplied with magma at an intermediate flow rate the eruption will be slow and effusive until the chamber over pressure becomes too large an explosive eruption then relieves the overpressure and an effusive eruption style resumes we suggest that monitoring of temporal variations in chamber overpressure for example by measuring ground deformation can be used to assess whether a passively effusing volcano has the potential to erupt explosively

the 15 september 1991 pyroclastic flows at unzen volcano japan a flow model for associated ash cloud surges large scale collapse of a dacite dome in the late afternoon of 15 september 1991 generated a series of pyroclastic flow events at unzen volcano pyroclastic flows with a volume of 1 106 m3 as dre descended the northeastern slope of the volcano changing their courses to the southeast due to topographic control after they exited a narrow gorge an ash cloud surge rushed straight ahead detaching the main body of the flow that turned and followed the topographic lows to the east the surge swept the kita kamikoba area which had been devastated by the previous pyroclastic flow events and transported a car as far as 120 m following detachment the surge lost its force after it moved several hundred meters but maintained a high temperature the deposits consist of a bottom layer of better sorted ash unit 1 a thick layer of block and ash unit 2 and a thin top layer of fall out ash unit 3 unit 2 overlies unit 1 with an erosional contact the upper part of unit 2 grades into better sorted ash at distal block and ash flow deposits the bottom part of unit 2 also consists of better sorted ash and the contact with the unit 1 deposits becomes ambiguous video footage of cascading pyroclastic flows during the 1991 1995 eruption traveling over surfaces without any topographic barriers revealed that lobes of ash cloud protruded intermittently from the moving head and sides and that these lobes surged ahead on the ground surface this fact together with the inspection by helicopter shortly after the events suggests that the protruded lobes consisted of better sorted ash and resulted in the deposits of unit 1 the highest ash cloud plume at the oshigadani valley exit and the thickest deposition of fall out ash over kita kamikoba and ohnokoba indicate that abundant ash was also produced when the flow passed through a narrow gorge in the model presented here the ash clouds from the pyroclastic flows were composed of a basal turbulent current of high concentration main body an overriding and intermediate fluidization zone and an overlying dilute cloud release of pressurized gas in lava block pores due to collisions among blocks and the resulting upward current caused a zone of fluidization just above the main body the mixture of gas and ash sorted in the fluidization zone moved ahead and to the side of the main body as a gravitational current where the ash was deposited as surge deposits the main body which had high internal friction and shear near its base then overran the surge deposits partially eroding them when the upward current of gas fluidization waned better sorted ash suspended in the fluidization zone was deposited on block and ash deposits in the distal places of block and ash deposits unit 2 probably was deposited in non turbulent fashion without any erosion of the underlying layer unit 1

elastic model for the gravity and elevation changes before the 2001 eruption of etna volcano for 5 months before the 2001 mt etna eruption a progressive gravity decrease was measured along a profile of stations on the southern slope of the volcano between january and july 2001 the amplitude of the change reached 80 gal while the wavelength of the anomaly was of the order of 15 km elevation changes observed through gps measurements during a period encompassing the 5 month gravity decrease remained within 4 6 cm over the entire volcano and within 2 4 cm in the zone covered by the microgravity profile we review both gravity and elevation changes by a model assuming the formation of new cracks uniformly distributed in a rectangular prism the inversion problem was formulated following a global optimization approach based on the use of genetic algorithms although it is possible to explain the observed gravity changes by means of the proposed analytical formulation the results show that calculated elevation changes are significantly higher than those observed two alternative hypotheses are proposed to account for this apparent discrepancy 1 that the assumptions behind the analytical formulation used to invert the data are fallacious at etna and thus numerical models should be utilized 2 that a second process enabling a considerable mass decrease to occur without deformation acted together with the formation of new cracks in the source volume

stable isotopic composition of upper oceanic crust formed at a fast spreading ridge odp site 801 1 odp legs 129 and 185 sampled the upper 474 m of 170 ma ocean crust in the western pacific in order to investigate alteration processes in fast spread crust and to determine inputs to subduction fourteen composite bulk samples of altered upper oceanic crust from site 801 have 18o 8 7 25 7 d 69 4 to 90 4 and 13c 2 7 to 1 8 the intensity of alteration and the amount of sediment within the basement decrease with depth leading to corresponding decreases in 18o and d a super composite constructed to estimate the bulk composition of the upper crust has 18o 12 0 d 87 0 and 13c 0 7 compared to core descriptions and geophysical logs the super composite contains too much 18o rich sediment 18o 25 7 and a corrected 18o value of 10 8 is more reasonable for the upper crust at site 801 these values are higher than those for other bulk upper oceanic basement sections 18o 8 0 10 0 and result in part from 1 intense low temperature 100 c hydrothermal alteration of the upper 100 m of tholeiitic basement at site 801 that may not be representative of material subducting in the western pacific and 2 an aging effect whereby progressive addition of 18o rich secondary carbonate in veins and breccia cements contributed to the high bulk 18o of this old upper crustal section

kinetic nitrogen isotope fractionation associated with thermal decomposition of nh3 experimental results and potential applications to trace the origin of n2 in natural gas and hydrothermal systems abstract ammonia nh3 is the major intermediate phase in the pathway of nitrogen n transfer from the fixed n phases e g in crustal material to free n2 e g in natural gas reservoirs and volcanic gases yet the n isotopic behavior during these n cycling processes remains poorly known in an attempt to contribute to the understanding of n cycling using n isotopes we carried out laboratory experiments to investigate the n isotopic effect associated with thermal decomposition of ammonia 2nh3 n2 3h2 pure nh3 with initial 15 n nh 3 of 2 relative to air standard was sealed into quartz tubes and thermally decomposed at 600 700 or 800 c from 2 hours to 500 days with the progress of the reaction the 15n of the remaining nh3 and the accumulated n2 increased from 2 to 35 and from 20 to 2 respectively the differences of the n isotope fractionations at the three temperatures are not significant modeling using the rayleigh distillation model yielded similar kinetic n isotope fractionation factors n 2 nh 3 of 0 983 0 002 for 600 700 and 800 c applied to geological settings this significant isotope discrimination 17 associated with partial decomposition of nh3 nh4 from crustal sources 15naverage 6 3 can produce mantle like i e 5 or even lower 15n values of n2 this may explain the large variation of 15n 20 to 30 of n2 in natural gas reservoirs it can also possibly explain the extreme 15n depletion of n2 in some volcanic gases this possibility has to be carefully considered when using n isotopes to trace geological n cycling across subduction zones by analysis of volcanic n2

hazard assessment during caldera unrest at the campi flegrei italy a contribution from gravity height gradients hazard assessment and risk mitigation at restless calderas is only possible with adequate geophysical monitoring we show here how detailed long term micro gravity and deformation surveys may contribute to hazard assessment at the campi flegrei caldera cfc in italy by evaluating gravity height change g h gradients obtained during ground inflation and deflation between 1981 and 2001 such gradients provide a framework from which to assess the likelihood and type of volcanic eruptions our new analysis of unrest at the cfc allows us to separate noise during the gravity survey from the signal of deep seated magmatic processes this facilitates identification of the dynamics within the magma reservoir beneath the cfc we found that magma replenishment during rapid uplift between 1982 and 1984 was insufficient probably by one to two orders of magnitude to trigger an eruption similar to the 1538 monte nuovo eruption the most recent volcanic eruption within the cfc furthermore our interpretation of g h gradients for the ongoing period of deflation since 1984 suggests that eruptive volcanic activity is not imminent short periods of minor inflation associated with large gravity changes since 1981 are interpreted to reflect noise which to some degree is probably due to sub surface mass density changes within shallow hydrothermal systems beneath the cfc indicating no risk of eruptive volcanic activity we propose that monitoring g h gradients at restless calderas is essential as a caldera develops from a state of unrest to a state where volcanic eruptions have to be anticipated adoption of this method for the several tens of restless calderas world wide will provide early warning of changes in or increase of activity at these supervolcanoes

volcanic eruption prediction magma chamber physics from gravity and deformation measurements one of the greatest remaining problems in modern volcanology is the process by which volcanic eruptions are triggered it is generally accepted that eruptions are preceded by magma intrusion sigurdsson and sparks 1978 the degree of interaction between previously ponded magma in a chamber and newly intruded magma determines the nature and rate of eruption and also the chemistry of erupted lavas and shallow dykes here we investigate the physics of this interaction volcano monitoring at its most effective is a synergy between basic science and risk assessment while hazard mitigation depends on reliable interpretation of eruption precursors the simple and much used mogi model relates ground deformation h to changes in magma chamber volume gravity changes g combined with ground deformation provide information on magma chamber mass changes our new models predict how the g h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity thus by simultaneous measurement of deformation and gravity at a few key stations magma chamber processes can be identified prior to the onset of conventional eruption precursors

inversion for sources of crustal deformation and gravity change at the yellowstone caldera the 3100 km2 yellowstone caldera yellowstone national park was formed in the latest of three explosive eruptions of rhyolites and ash flow tuffs totalling 3700 km3 at 2 1 2 and 0 6 m y before present its youthful volcanic history widespread hydrothermal activity intense seismicity and extremely high heat flow in excess of 30 times the continental average marks the yellowstone volcanic system as a giant caldera at unrest orthometric height increases of the caldera of up to 76 cm measured from precise leveling surveys from 1923 to 1975 1977 were inverted to determine volume expansion source models for the caldera wide deformation for the 1923 to 1977 uplift episode two regions of expansion were found 1 in the northern part of the caldera near the sour creek resurgent dome of 0 37 km3 and 2 in the southern part of the caldera near the mallard lake resurgent dome of 0 41 km3 both bodies occur in the upper crust from near surface depths to 6 0 km but the largest volume expansions were found in the 3 0 6 0 tan depth range the southern caldera source volume near the mallard lake dome may extend down to 9 0 km the data are however unable to resolve if these two resurgent domes separated laterally by 40 km are connected prom 1976 to 1987 nearly simultaneous measurements of elevation and gravity changes were made on a profile across the northern caldera during a period of net uplift models of the temporal gravity variation infer that the volume increase for the northern caldera source must lie above 9 0 km and involved a density perturbation greater than 0 002 g cm3 the modeled volumetric sources are in the same general locations as bodies of low p wave velocities high seismic attenuation and large negative bouguer gravity anomalies in view of the intense quaternary volcanism the anomalously high heat flow and the correlation of the source volumes with the regional geophysical anomalies it is likely that the modeled volumetric increases were caused by migration of magmas and or the introduction of large volumes of hydrothermal fluids into the upper crust

on the relative importance of self gravitation and elasticity in modeling volcanic ground deformation and gravity changes 1 elastic half space models widely used to interpret displacements and gravity data in active volcanic areas usually compute the displacement response to dilatational sources that simulate a change in pressure of the magma chamber elastic gravitational models allow the computation of gravity deformation and gravitational potential changes due to pressurized magma cavities and intruding masses together this type of model takes into account the mass interaction with the self gravitation of the earth through coupling between model equations we perform a dimensional analysis of the elastic gravitational model estimating the magnitude of intrusion mass and coupling effects at the space scale associated with volcano monitoring we show that the intrusion mass cannot be neglected in the interpretation of gravity changes while displacements are primarily caused by pressurization therefore the intrusion of mass together with the associated pressurization of the magma chamber produces distinctive changes in gravity that could be used to interpret gravity changes without ground deformation and vice versa depending on what type of source plays the main role in the intrusion process theoretical experiments indicate that mass and self gravitation could produce changes in the magnitude and pattern of predicted gravity that may be above microgravity accuracy application of the elastic gravitational model to interpret geodetic precursors observed at mayon volcano philippines prior to the eruption of 2001 shows that inversions increase in precision by using this model therefore our elastic gravitational model is a refinement of purely elastic models and can better interpret gravity and deformation changes in active volcanic zones

anomalous nitrogen isotopes in ultrahigh pressure metamorphic rocks from the sulu orogenic belt effect of abiotic nitrogen reduction during fluid rock interaction modern nitrogen n fixation is primarily mediated by biological processes however in the early earth where biological activity was absent or limited abiotic n reduction in hydrothermal systems is thought to be a key process to transform atmospheric n2 and nox to ammonium an essential nutrient to support the emergence of life and also an n form that can be incorporated into rocks surprisingly evidence for abiotic n reduction in the rock record has not been clearly identified in this study we reported anomalously low n isotope compositions n15 values as low as 15 8 15 8 of mica samples in ultrahigh pressure metamorphic rocks from the donghai area in the sulu orogenic belt eastern china compared with mica samples with typical crustal n15 values 3 9 3 9 in similar metamorphic rocks from the western dabie orogen the 15n depleted mica samples from the sulu orogen are characterized by significant n enrichment 10 times higher and extreme 18o depletion o18 values as low as 9 9 these features can be best explained by assimilation of n from a source characterized by extremely low n15 values less than 16 16 the extremely low n15 value would be produced by abiotic n reduction during reaction of a meteoric hydrothermal fluid with crustal rocks before subduction this observation provides a clue to the occurrence of abiotic n reduction in continental supracrustal rocks and infer that abiotic n reduction process could be a fundamental process driving the geological n cycling in early earth

gravity changes as a precursor to volcanic eruption at poas volcano costa rica monitoring of gravity changes at active volcanoes has considerable potential for understanding magma chamber dynamics and for detecting eruptive precursors the technique essentially aims to identify changes in sub surface mass or density corresponding to departures from the free air gradient fag or bouguer corrected terrain corrected fag bcfag respectively1 2 such gravity changes of the order of 10 100 gal have been reported previously through eruptive periods3 6 here we present a ten year data set measured at poas volcano costa rica in which gravity increases in 1987 1989 relative to both the fag and the bcfag preceded the ash cloud eruptions of april may 1989 these results constitute the first unambiguous detection of gravity changes as a precursor to eruption and we interpret them in terms of the intrusion of an ascending relatively dense magma body

nitrogen and argon isotopic signatures in graphite from the 3 8 ga old isua supracrustal belt southern west greenland abstract the problems involved with the interpretation of carbon isotopes as indicators for early life in highly metamorphosed early archean rocks have prompted the search for additional chemical and isotopic biomarkers here we report an attempt to identify the origin of carbonaceous matter in the 3 8 ga old isua supracrustal belt in southern west greenland by measuring the concentration and isotopic composition of a trapped nitrogen component stepped combustion pyrolysis mass spectrometry of carbonaceous matter in several rock samples revealed three different reservoirs of trapped nitrogen 1 nitrogen associated with a very small amount of reactive carbonaceous material 2 nitrogen intercalated in graphite correlated with intercalated radiogenic argon 3 nitrogen strongly retained at defects or chemically bound in the graphite structure the 15n of nitrogen associated with reactive carbonaceous matter ca 6 overlaps with that of average phanerozoic sedimentary organic matter and is believed to be part of nonindigenous postmetamorphic biologic material in situ raman spectroscopy confirmed the high degree of crystallinity of the metamorphosed indigenous carbonaceous material and this material is further referred to as graphite graphite interpreted as epigenetic associated with mg mn siderite in metacarbonates contains a very small strongly retained nitrogen component with a low 15n ratio 3 to 1 this range overlaps with values that are typically found in archean kerogens but also those of a metamorphically emplaced inorganic basaltic source geological constraints suggest that this graphite incorporated nitrogen from surrounding metabasaltic rocks graphite interpreted as syngenetic and biogenic found in a turbidite deposit is relatively similar to this mg mn siderite derived graphite based on degree of graphite crystallinity amount of trapped radiogenic argon low nitrogen concentration and 15n signature we conclude that nitrogen concentration and its isotope ratio in graphite cannot be used conclusively as a biomarker in these rocks from the highly metamorphosed isua supracrustal belt

numerical evidence enabling reconciliation gravity and height changes in volcanic areas s u m m a r y gravity and height changes reflecting magma accumulation in subsurface chambers are evaluated using finite element models in order to resolve controversial relationships observed in some volcanic areas when significant gravity changes occur without any significant deformation or vice versa it is often difficult if not impossible to jointly explain the observations using the popular mogi model here we explore whether these discrepancies can be explained by magma compressibility and source geometry effects compression of resident magma and expansion of the chamber wall act concurrently to accommodate newly added magma gravityheight ratios are found to mainly depend on i geometry of the sources which control the volume expansion of the chamber ii magma compressibility which affects the contraction of the magma resident in the chamber and iii depth of the sources our numerical results show that when magma compressibility and non spherical sources are taken into account significant gravity variations can indeed be successfully reconciled with negligible height changes this may be the case at etna volcano where gravity changes about 40 gal without any significant deformation below 5 cm were observed during the 1994 1995 inflation period the numerical results point to the accumulation of a 1 4 1010 kg mass into an elongated source simulating a shallow storage region supplying the summit craters

widening of the krafla fissure swarm during the 1975 1981 volcano tectonic episode frequent distance measurements across the krafla fissure swarm north iceland recorded the extension accompanying the sequence of rifting events which started in december 1975 and lasted for 6 years an 80 to 90 km long section of the fissure swarm extended during this sequence of rifting and volcanic events maximum widening of about 8 m occurred 10 to 12 km north of leirhnjukur which is located above the center of the krafla magma reservoir from that location the amount of widening decreased north wards and is estimated to exceed 2 m where the seismicity indicated the northern termination of the present rifting off the north coast about 70 km north of leirhnjukur the amount of widening also decreased southwards and approached zero at 15 to 20 km south of leirhnjukur the ground deformation associated with these rifting events can be summarised as a narrow strip 1 to 2 km wide along the fissure swarm is heavily fractured with numerous open cracks parallel to the fissure swarm this fractured strip has subsided 2 to 3 m relative to its flanks the flanks of the fractured zone have been uplifted relative to regions farther away the uplift is not well constrained but tilt observations at several locations indicate about 1 m uplift the flanks of the rift zone have contracted perpendicular to the fissure swarm the maximum contractional strain exceeds 300 mm per km the amount of areal expansion windening of the fissure swarm times the length of the fractured zone associated with these rifting events is estimated to be about 0 30 km2 for individual events the area of expansion has been roungly proportional to the volume of subsidence above the krafla magma reservoir if the width of a new dike is equal widening of surface fissures the ratio of the subsidence volume to the area of expansion for the best observed events indicated a height of a new dike system as 2 4 to 2 8 km this ratio is significantly less for events of large lava production but even during these events the majority of magma leaving the krafla reservoir was apparently emplaced in subsurface fissures

gravity height correlations for unrest at calderas abstract calderas represent the sites of the world s most serious volcanic hazards although eruptions are not frequent at such structures on the scale of human lifetimes there are nevertheless often physical changes at calderas that are measurable over periods of years or decades such calderas are said to be in a state of unrest and it is by studying the nature of this unrest that we may begin to understand the dynamics of eruption precursors here we review combined gravity and elevation data from several restless calderas and present new data on their characteristic signatures during periods of inflation and deflation we find that unless the bouguer gravity anomaly at a caldera is extremely small the free air gradient used to correct gravity data for observed elevation changes must be the measured or calculated gradient and not the theoretical gradient use of which may introduce significant errors in general there are two models that fit most of the available data the first involves a mogi type point source and the second is a bouguer type infinite horizontal plane source the density of the deforming material usually a magma chamber is calculated from the gravity and ground deformation data and the best fitting model is to a first approximation the one producing the most realistic density no realistic density is obtained where there are real density changes or where the data do not fit the point source or slab model we find that a point source model fits most of the available data and that most data are for periods of caldera inflation the limited examples of deflation from large silicic calderas indicate that the amount of mass loss or magma drainage is usually much less than the mass gain during the preceding magma intrusion in contrast deflationary events at basaltic calderas formed in extensional tectonic environments are associated with more significant mass loss as magma is injected into the associated fissure swarms

interpretation of 1992 1994 gravity changes around mayon volcano philippines using point sources significant gravity changes observed around the mayon volcano philippines between 1992 and 1994 at 26 stations are interpreted in terms of an increase of mass and pressure changes at several point sources modelled using a fast inversion process this inversion approach attempts to fit gravity and elevation changes by combining a random search for the positions of the sources and a linear least squares fit for the incremental mass pressure and possible common regional values for gravity or elevation changes some stabilizer terms are included in the misfit function models with one and two sources were tested against the observed changes at mayon models with only one source give a best fit for a shallow source with a positive mass increment horizontally displaced far from the summit the study using two sources gives a best fit that is similar to the one source model but in addition indicates anomalous behavior at stations in the sw neglecting the stations located southward from a local fracture the best fitting model suggests one central positive mass change source which is likely to be an intrusion of about 0 5 mu with a depth of about 5 km beneath the volcano standard deviation for the residuals ranges from 7 8 gal for one source models to 6 7 gal for models with two sources both of the cases are below the error value of 9 4 gal estimated for the gravity data so that it is not possible to discriminate between both possible interpretations without additional information

distribution of ammonium in minerals of metamorphic and granitic rocks abstract sixty nine analyses are given for nh4 in minerals of metamorphic and granitic rocks mostly from the ryoke belt japan the distribution of nh4 in coexisting minerals is quite systematic suggesting that nh4 is one of the stable geochemical components in high temperature processes biotite has the highest content of nh4 followed by muscovite k feldspar and plagioclase pure quartz is almost free from nh4 calcic plagioclase contains less nh4 than does sodic plagioclase the partition coefficients d pl bi d kf bi and d kf bi are on the average 0 11 0 38 and 0 43 respectively the fractionation of nh4 in these minerals is quite similar to that of rb but much smaller than that of cs distribution of nh4 as well as those of rb and cs appears to be explained by its ionic radius and the shortest cation o distances in alkali positions of minerals

oxygen and hydrogen isotope geochemistry of gneisses associated with ultrahigh pressure eclogites at shuanghe in the dabie mountains the oxygen and hydrogen isotope compositions of minerals and whole rock were determined for two types of gneiss biotite gneiss and granitic gneiss associated with ultrahigh pressure uhp eclogites in the shuanghe district of the eastern dabie mountains there are significant differences in 18o between the two gneisses the uhp biotite gneiss varying from 4 3 to 10 6 similar to the associated eclogites whereas the non uhp granitic gneiss ranges only from 3 8 to 1 2 the d values are similar in the two gneisses with 37 to 64 for epidote zoisite 92 to 83 for amphibole and 63 to 109 for biotite phengite hydrogen isotope disequilibrium among the coexisting hydroxyl bearing minerals is ascribed to retrograde exchange subsequent to amphibolite facies metamorphism oxygen isotopic equilibrium has been preserved among various minerals in both gneisses regardless of the large variation in rock 18o oxygen isotopic geothermometers yield different but regular temperatures corresponding to the closure temperatures of oxygen diffusion in the minerals the metamorphic temperatures of both eclogite facies and amphibolite facies have been recovered in mineral pairs from the biotite gneiss the isotopic temperatures for the granitic gneiss are mostly in accordance with amphibolite facies metamorphism however high temperatures of 550 to 650 c are obtained from those minerals resistant to retrograde oxygen isotope exchange implying that the granitic gneiss may have experienced higher temperature metamorphism than expected from petrologic thermometers the 18o depletion of both gneisses is interpreted to result from meteoric hydrothermal exchange before during plate subduction therefore the measured 18o values of the gneisses reflect the oxygen isotope compositions of their protoliths prior to the uhp metamorphism it is inferred that the uhp unit is in foreign contact with the non uhp unit like a tectonic melange but both of them experienced the two common stages of geodynamic evolution 1 18o depletion prior to the uhp metamorphism 2 uplifting since the amphibolite facies metamorphism

unusually low δ18o ultra high pressure metamorphic rocks from the sulu terrain eastern china eclogite and quartzite interlayers containing ultra high pressure uhp metamorphic mineral assemblages occur at qinglongshan in the sulu terrain eastern china these rocks exhibit some of the most negative oxygen isotope compositions that have ever been reported for metamorphic rocks the 18 value of minerals in eclogite ranges from 10 4 to 9 0 o and in quartzite ranges from 10 2 to 7 3 near isotopic equilibrium between minerals and rocks suggests that these rocks must have acquired such low oxygen isotope compositions before the uhp metamorphism through near surface meteoric water rock interactions the rocks were then subducted to a great depth during continent continent collision forming uhp minerals with concomitant local oxygen isotope redistribution it is significant that the rocks have retained such negative oxygen isotope compositions despite subduction into the upper mantle

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

influence of lateral particle advection and organic matter degradation on sediment accumulation and stable nitrogen isotope ratios along a productivity gradient in the canary islands region abstract we compare total and biogenic particle fluxes and stable nitrogen isotope ratios 15n at three mooring sites along a productivity gradient in the canary islands region with surface sediment accumulation rates and sedimentary 15n higher particle fluxes and sediment accumulation rates and lower 15n were observed in the upwelling influenced eastern boundary region ebc compared to the oligotrophic sites north of gran canaria european station for time series in the ocean canary islands estoc and north of la palma lp the impact of organic matter degradation and lateral particle advection on sediment accumulation was quantified with respect to the multi year flux record at the estoc remineralisation of organic matter in the water column and at the sediment surface resulted in an organic carbon preservation of about 0 8 and total nitrogen preservation of about 0 4 of the estimated export production higher total and carbonate fluxes and accumulation rates in the lower traps and surface sediment compared to the upper traps indicated that at least 50 of the particulate matter at the estoc was derived from allochthonous sources low 15n values in the lower traps of the estoc and lp point to a source region influenced by coastal upwelling we conclude from this study that the reconstruction of export production or nutrient regimes from sedimentary records in regions with strong productivity gradients might be biased due to the mixture of particles originating from autochthonous and allochthonous sources this could result in an imprint of high productivity signatures on sedimentation processes in oligotrophic regions

magma movements in etna volcano associated with the major 1991 1993 lava eruption evidence from gravity and deformation the 1991 1993 eruption was probably the largest on mt etna for 300 years since then the volcano has entered an unusually quiescent period a comprehensive record of gravity and ground deformation changes presented here bracket this eruption and give valuable insight into magma movements before during and after the eruption the gravity and deformation changes observed before the eruption 1990 1991 record the intrusion of magma into the summit feeder and the sse trending fracture system which had recently been active in 1978 1979 1983 and 1989 creating the feeder dyke for the 1991 1993 eruption in the summit region gravity changes between 1992 and 1993 spanning the end of the eruption reflect the withdrawal of magma from the conduit followed more recently 1993 1994 by the re filling of magma in the conduit up to pre eruption levels in contrast in the vicinity of the fracture zone gravity has remained at the 1991 1992 level indicating that no withdrawal has occurred here rather magma has solidified in the fracture system and sealed it such that the 1993 1994 increase in magma level in the conduit was not accompanied by further intrusion into the flanks mass calculations suggest that a volume of at least 107 m3 of magma has solidified within the southeastern flank of the volcano

multiparameter monitoring of fogo island cape verde for volcanic risk mitigation fogo island in the cape verde archipelago north atlantic is a stratovolcano of nearly conical shape that rises 2829 m above sea level and v6000 m above the surrounding seafloor with a population of 40 000 the island has known intense historical volcanic activity since ad 1500 with an average interval between eruptions of the order of 20 years twentieth century rates were more subdued with only two flank eruptions in 1951 and 1995 following the 1995 eruption increased awareness of the volcanic hazard affecting the population of the island led to the deployment of the permanent vigil network seismographic stations both broadband and short period tiltmeters and a co2 sensor where installed in fogo together with a telemetry infrastructure to allow remote real time monitoring a broadband seismographic station was installed in neighbour brava island the operation of the network was complemented by the introduction of routine geodetic and microgravity surveying and the operation of an automatic meteorological station in this paper we describe the methodology adopted to monitor the volcanic activity combining real time data analysis volcanotectonic and volcanic earthquakes volcanic tremor and tilt with repeated surveying at intervals of several months gps microgravity examples of data from the first years of operation are presented in particular the data pertaining to a period of anomalous activity in september october 2000 are discussed in the context of the risk mitigation strategy currently being developed

post eruptive gravity changes from 1990 to 1996 at krafla volcano iceland the 1975 1984 krafla rifting episode was a major lava and dyke producing event associated with the release of extensional strain accumulated over more than 200 years at the divergent plate boundary in north iceland the present work provides a unique example of gravity decreases and increases sustained over a long period following a major eruptive episode at a rift volcano after height correction persistent net gravity decreases over the source of observed mogi type deflation occur with gravity increases occurring further away from this centre of deformation gravity decreases are interpreted in terms of drainage from a shallow magma chamber the net gravity decreases require that at least 4 1010 kg of magma must have been drained during the 6 year observation period assuming a density of 2700 kg m 3 this magma would occupy 1 5 107 m3 and by analogy with results obtained for kilauea this implies a magma chamber volume change of 4 1 106 m3 this is consistent with the chamber volume change deduced from ground deformation data assuming a poisson s ratio of 0 25 and a mogi source net gravity increases are more spatially extensive and are most likely caused by migration of the steam water interface and or closure of micro fractures in lavas above the magma chamber during post eruptive cooling and contraction we present a model for the krafla magma chamber in which a cooling contracting and draining magma body causes subsidence at the surface these results contrast with observations from the askja caldera iceland where post eruptive deflation has been shown to be accompanied by negligible net gravity changes above the mogi type source in the caldera long term post eruptive deflation and magma drainage have not been observed at subduction related volcanoes this may be a function of a difference in magma viscosity

isotopic variations of the fixed nitrogen in metamorphic rocks the content and isotopic composition of fixed nitrogen nh 4 n in metasedimentary rocks phyllites mica schists and gneisses from prograde metamorphic zones in the erzgebirge saxon ore mountains g d r were measured and show that the nitrogen content decreases and 15n increases with increasing metamorphic grade the geochemical and isotopic behaviour of nitrogen during contact metamorphism was investigated in a mica schist profile through the contact aureole of a granitic pluton the nitrogen concentrations of the wall rocks decrease towards the contact whereas the 15n values become higher various model experiments were carried out in the laboratory to explain the changes observed in the rock samples the nitrogen isotope fractionation factor was determined for the isotopic exchange in the system ammonium sulphate ammonia at 250 c 1 0143 0 0012 and 350 c 1 0128 0 0006 in accordance with the model experiments the conclusion seems warranted that the change in nitrogen content and its isotopic composition in rocks during metamorphic processes depend mainly on the metamorphic temperature

two types of volcanic tremor changed with eruption style during 1986 izu oshima eruption volcanic tremor provides clues to magma migration pathways so that tremor source location is expected to be an efficient tool for tracking dynamic behavior of magma in evolution of eruptive activity however clear evidence which connects between temporal variation in volcanic tremor and evolution of eruption style is still lacking we have analyzed volcanic tremors occurred during 1986 izu oshima eruption using recently digitized data the results present a clear link between eruption styles waveform variations and source locations of the tremors moreover precursory activity of the tremors that indicates injection of magma below fissures has been clarified 5 days prior to the fissure eruptions this demonstrates predominance of tremor activity as an adaptive monitoring tool in volcanic eruption

detecting volcanic eruption precursors a new method using gravity and deformation measurements abstract one of the fundamental questions in modern volcanology is the manner in which a volcanic eruption is triggered the intrusion of fresh magma into a reservoir is thought to be a key component the amount by which previously ponded reservoir magma interacts with a newly intruded magma will determine the nature and rate of eruption as well as the chemistry of erupted lavas and shallow dykes the physics of this interaction can be investigated through a conventional monitoring procedure that incorporates the simple and much used mogi model relating ground deformation most simply represented by h to changes in volume of a magma reservoir gravity changes g combined with ground deformation provide information on magma reservoir mass changes our models predict how during inflation the observed g h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity calderas in a state of unrest and large composite volcanoes are the targets for the methods proposed here and are exemplified by campi flegrei rabaul krafla and long valley we show here how the simultaneous measurement of deformation and gravity at only a few key stations can identify important precursory processes within a magma reservoir prior to the onset of more conventional eruption precursors

the origin and response of zircon in eclogite to metamorphism during the multi stage evolution of the huwan shear zone china insights from lu hf and u pb isotopic and trace element geochemistry abstract the huwan shear zone hsz is an eclogite bearing transpressive wrench zone located along the shangdan suture that juxtaposes the paleozoic qinling and mesozoic hong an dabie orogenic terrains the region preserves a complex history that bridges the gap between adjacent orogenic terrains simultaneous in situ trace element u th pb and lu hf isotope analysis of zircon grains from samples of the xiongdian and sujiahe eclogite identify a late carboniferous to early permian period of high pressure metamorphism ca 283 to 306 ma zircon grains are observed to respond to metamorphic overprint via a two stage process 1 an initial prograde stage of fluid catalyzed interface coupled dissolution reprecipitation involving exsolution of a non ideal solid solution thorite thsio 4 end member and loss of highly incompatible components lree and pb 2 a second stage of coupled zircon dissolution coarsening and new rim growth in equilibrium with garnet at high pressure conditions we identify proterozoic whole rock sm nd and zircon grain lu hf isotopic evidence which challenges the traditional interpretation that the xiongdian and sujiahe eclogite formed in response to early paleozoic mantle melting and oceanic crust generation we argue the huwan shear zone contains no conclusive evidence of early middle paleozoic oceanic crust but rather proterozoic crustal components analogous to those found in the northern qinling terrain and associated with formation of the shangdan suture we present a simpler geodynamic model involving continuous convergence and accretion of terrains onto the southern margin of the north china block during the paleozoic qinling and mesozoic dabie orogenies

strain at radially fractured centers on venus 1 radially fractured centers rfcs on venus are distinctive 100 km long radiating systems of graben fissures and fractures arranged around a central topographic high we use cycle 1 and cycle 3 magellan images to determine the depths and wall dip angles of several large radial graben using two different methods at four rfcs becuma mons didilia corona h uraru corona and pavlova corona we record graben depths of 0 3 0 9 km and mean wall dip angles of about 36 which we interpret as a primary talus slope rather than a fault plane using the calculated depths and a more realistic fault dip of 60 we find extension of between 0 5 and 1 km on graben between about 5 and 10 km wide we use this extension to estimate the hoop strain at each rfc maximum measured strains on the flanks are typically between 1 and 4 and may be up to 7 toward the center we conclude that this strain is too large to be explained by current plume related uplift models and also by magma chamber inflation we conclude that dikes are probably responsible for the majority of the strain at the large radial graben

continuous monitoring of surface deformation at long valley caldera california with gps continuous global positioning system gps measurements at long valley caldera an active volcanic region in east central california have been made on the south side of the resurgent dome since early 1993 a site on the north side of the dome was added in late 1994 special adaptations for autonomous operation in remote regions and enhanced vertical precision were made the data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber measurement precisions 1 standard error for absolute position coordinates i e relative to a global reference frame are 3 4 mm north 5 6 mm east and 10 12 mm vertical using 24 hour solutions corresponding velocity uncertainties for a 12 month period are about 2 mm yr in the horizontal components and 3 4 mm yr in the vertical component high precision can also be achieved for relative position coordinates on short 10 km baselines using broadcast ephemerides and observing times as short as 3 hours even when data are processed rapidly on site comparison of baseline length changes across the resurgent dome between the two gps sites and corresponding two color electronic distance measurements indicates similar extension rates within error 2 mm yr once we account for a random walk noise component in both systems that may reflect spurious monument motion both data sets suggest a pause in deformation for a 3 5 month period in mid 1995 when the extension rate across the dome decreased essentially to zero three dimensional positioning data from the two gps stations suggest a depth 5 8 1 6 km and location west side of the resurgent dome of a major inflation center in agreement with other geodetic techniques near the top of a magma chamber inferred from seismic data gps systems similar to those installed at long valley can provide a practical method for near real time monitoring and hazard assessment on many active volcanoes

combining relative and absolute gravity measurements to enhance volcano monitoring to achieve a balance between uncertainty and efficiency in gravity measurements we have investigated the applicability of combined measurements of absolute and relative gravity as a hybrid method for volcano monitoring between 2007 and 2009 three hybrid gravity surveys were conducted at mt etna volcano in june 2007 july 2008 and july 2009 absolute gravity data were collected with two absolute gravimeters which represent the state of the art in recent advances in ballistic gravimeter technology 1 the commercial instrument fg5 238 and 2 the prototype instrument imgc 02 we carried out several field surveys and confirmed that both the absolute gravimeters can still achieve a 10 gal or better uncertainty even when they are operated in severe environmental conditions the use of absolute gravimeters in a field survey of the summit area of mt etna is unprecedented the annual changes of the gravity measured over 2007 2008 and 2008 2009 provide unequivocal evidence that during the 2007 2009 period two main phenomena of subsurface mass redistribution occurred in distinct sectors of the volcano accompanying different eruptive episodes from 2007 to 2008 a gravity change of 60 gal was concentrated around the north east rift this coincided with a zone affected by strong extensional tectonics and hence might have been related to the opening of new voids between 2008 and 2009 a north south elongate feature with a maximum gravity change of 80 gal was identified in the summit craters area this is interpreted to indicate recharge of a deep intermediate magma storage zone which could have occurred when the 2008 2009 eruption was still ongoing

tertiary coastal dunes of the eucla basin australia abstract on the northeast margin of the nullarbor plain in western south australia there is preserved an assemblage of coastal aeolian landforms that includes coastal dune dune ridge and possible beach ridge one of these landforms is the ooldea range a 650 km long coastal dune that lies 25 300 km from the present coast these landforms are believed to have formed at the end of the eocene after maximum marine transgression in the eucla basin the ooldea barton and paling ranges formed in a tectonically stable region of topographically subdued terrain their orientation and position may be related in part to crustal fractures that were active during initial break up of australia and antarctica the large quantities of sand required for their construction were supplied to the coast by rivers which drained a hinterland of various suitable source rocks growth may have begun as chains of barrier islands which amalgamated to form large coast parallel dunes during progradation these coastal dunes provide evidence about climate at and after the time of their formation their formation indicates an atmospheric circulation of at least moderate intensity and prevailing winds with a major westerly component this occurred at a time when the climate is likely to have been temperate if the interpretation of the dunes age is correct they may be viewed as landforms bearing testimony to the global change in climate which occurred at the end of the eocene their excellent preservation in the landscape today some 34 37 million years after formation is remarkable implied is a degree of aridity for much of the remainder of the cainozoic this appears to have been more significant in the nullarbor plain region than in the southeastern part of australia other factors responsible for their preservation are likely to include vegetation cover the permeability of their quartz sands subsequent history of sea level and hydrodynamics of the basin

nitrogen cycling during the cretaceous cenomanian turonian oceanic anoxic event ii low 15n values ranging from 1 2 to 3 9 and atomic carbon nitrogen c n ratios of 25 50 are characteristic of black shales deposited during the cenomanian turonian boundary interval and oceanic anoxic event ii oae ii an observed antithetic relationship between c n ratios and 15n could suggest a predominance of terrestrially derived organic matter or a diagenetic control on 15n variability shifting bulk 15n values lower however hydrogen indices hi generally 450 and a positive correlation of hi with c n mitigates against a significant terrestrial organic matter fraction high c n values are likely the result preferential degradation of labile n rich compounds during early diagenesis and loss of n as ammonium from sediments through time a hypothetical model that considers the degradation of a 15n enriched labile protein fraction yields only small 1 2 negative shifts in 15n however 15n depletion during diagenesis is contrary to normal isotope kinetics which should result in 15n enrichment of bulk organic matter therefore we conclude that the bulk 15n values in this study reflect primary changes in the nitrogen cycle the 15n data support the hypothesis of expanded nitrogen fixation driven by upwelling of nutrient nitrogen poor phosphorus replete waters during oae ii and from the mid cenomanian to santonian at demerara rise the low 15n values which are significantly lower than bulk 15n values in modern regions where nitrogen fixation is known to be important probably result from a more significant fraction of dissolved inorganic nitrogen being produced by nitrogen fixation during the peak of oae ii a marked shift to lower 15n values is observed this shift possibly reflects greater utilization of 15n depleted ammonium during a chemocline upward excursion cue dominance of low 15n values from other periods of more widespread marine anoxia is likely the result of similar processes

remnants of premetamorphic fluid and oxygen isotopic signatures in eclogites and garnet clinopyroxenite from the dabie sulu terranes eastern china a combined oxygen isotope and fluid inclusion study has been carried out on high and ultrahigh pressure metamorphic hp uhpm eclogites and garnet clinopyroxenite from the dabie sulu terranes in eastern china coesite bearing eclogites garnet clinopyroxenite and quartz eclogites have a wide range in whole rock 18ovsmow from 0 to 11 the high t oxygen isotope fractionations preserved between quartz and garnet preclude significant retrograde isotope exchange during exhumation and the wide range in whole rock oxygen isotope composition is thought to be a presubduction signature of the precursors aqueous fluids with variable salinities and gas species n2 co2 or ch4 rich are trapped as primary inclusions in garnet omphacite and epidote and in quartz blebs enclosed within eclogitic minerals in high 18o hp uhpm rocks from hujialin and shima high salinity brine and or n2 inclusions occur in garnet porphyroblasts which also contain inclusions of coesite cl rich blue amphibole and dolomite in contrast in low 18o eclogites from qinglongshan and huangzhen the cl concentrations in amphibole are very low 0 2 wt and low salinity aqueous inclusions occur in quartz inclusions in epidote porphyroblasts and in epidote cores these low salinity fluid inclusions are believed to be remnants of meteoric water although the fluid composition was modified during pre and syn peak hp uhpm eclogites at houshuichegou and hetang contain ch4 rich fluid inclusions coexisting with high salinity brine inclusions methane was probably formed under the influence of co2 rich aqueous fluids during serpentinisation of mantle derived peridotites prior to or during plate subduction remnants of premetamorphic low to high salinity aqueous fluid with minor n2 and or other gas species preserved in the dabie sulu hp uhpm eclogites and garnet clinopyroxenite indicate a great diversity of initial fluid composition in the precursors implying very limited fluid rock interaction during syn and post peak hp uhpm

precambrian ammonium biogeochemistry a study of the moine metasediments scotland abstract the content and isotopic composition of ammoniacal nitrogen have been determined in a suite of amphibolite facies metasediments of precambrian age whole rock samples and mica separates from the moine succession proterozoic of scotland were analysed by a combination of capacitance manometry and static vacuum mass spectrometry prior to the analyses the presence of the ammonium ion was confirmed by obtaining infrared ir absorption spectra from the micas principally biotites whole rock ammonium contents are high for amphibolite facies metasediments 140 422 ppm the ammonium ion was not detected in the ir absorption spectra of biotites from one schist however this sample contains neither garnet nor white mica for most of the samples the 15n values are very positive between 12 4 and 16 6 with one sample having a lower value of 8 4 the major variations between samples can be interpreted in terms of original sedimentary features for the ammonium bearing samples muscovites have concentrations between 365 and 633 ppm biotites between 845 and 1739 ppm for individual samples nh4 mu nh4 bi varies between 0 31 and 0 43 a much narrower range than has been reported previously there are no significant or consistent differences in 15n between co existing biotite and white mica nor between the 15n values of the mineral separates and their respective whole rock values the latter suggests minimal selective partitioning of isotopes between micas and plagioclase feldspar the only other potential host for ammonium in the rocks assuming that the ammonium has been derived from organic matter originally present at the time of deposition and by comparison with previous studies it can be inferred that the original 15n value of the moine sediments was somewhere between 5 and 10 similar to recent sediments this suggests that the nitrogen cycle in the proterozoic shelf sea from which the moine sediments were deposited was broadly similar to the present day overall the study underlines how under developed the n system is compared to other stable isotope systems notably c and s and we use the opportunity to highlight some areas that could be developed in the future however one aspect is clear future ammonium studies of metamorphic rocks will need to be performed at high resolution visible scale of heterogeneity with strong mineralogical petrological and field controls

interactions between volcanism rifting and subsidence implications of intracaldera palaeoshorelines at taupo volcano new zealand at taupo volcano new zealand a major young caldera system is superposed on the taupo fault belt a zone of late quaternary extensional normal faulting accompanying rifting palaeoshorelines formed at 26 5 and 1 8 ka around intracaldera lake taupo highlight contrasts between short term vertical deformation patterns detected by geodetic and lake levelling surveys and longer term trends recorded by the warped and offset palaeoshoreline levels rifting is apparently occurring without the accumulation of long term vertical offsets and net subsidence on adjacent normal faults of the taupo fault belt geomorphic and stratigraphic data indicate that much vertical deformation is episodic and closely related to major volcanic eruptions at other times compensation is occurring possibly by magma accumulation in the crust however periods of caldera unrest at taupo may reflect regional rifting processes made manifest by the presence of the lake rather than magmatic processes alone

residual gravity changes and eruption magnitudes abstract research during the last four decades has demonstrated that systematic temporal gravity changes are associated with eruptive activity these gravity changes are caused by the free air effect of elevation changes induced by magma bodies and by mass redistributions where gravity change data are accompanied by concurrent elevation control observed gravity changes can be corrected for the free air effect giving residual gravity changes residual gravity changes reflect only mass redistributions at most volcanoes residual gravity changes can be accounted for by the addition of mass during pre eruption time and by the removal or addition of mass during post eruption time at explosive volcanoes however the data show mass must be removed from near surface magma systems during preeruptive time the only reasonable mechanism acounting for these negative pre eruption mass redistributions is displacing dense country rock or magma with gas bubbles in vesiculated magma application of gauss theorem to areal residual gravity changes and an assumed density for the displaced material give an estimate of the volume of exsolved gas contained within the magma body the kinetic energy released in explosive magmatic eruptions to a first approximation is caused by the explosive expansion of exsolved and dissolved gases contained within magma if the density and temperature of magma and if the amount pressure and composition of volatiles contained in magma bodies are known or assumed then the kinetic energy released by explosive gas decompression can be computed or estimated using simple thermodynamic relationships kinetic energy estimates for explosive magmatic eruptions computed from muzzle velocities and computed for isothermal and adiabatic gas decompression using assumed volatile contents pressures and temperatures give similar results minimum pre eruption exsolved volatile contents estimated from negative pre eruption mass deficits and assumed magma densities temperatures and pressures were used to compute predicted kinetic energies for five eruption gravity change sequences at pacaya mihara usu and mt st helens volcanoes although the data are too few to be conclusive they do indicate the possibility of forecasting eruption magnitudes at some volcanoes using precursory gravity changes

ammonium concentration and nitrogen isotope composition in metasedimentary rocks from different tectonometamorphic units of the european variscan belt the content and isotopic composition of ammonium nh4 were measured by using kjeldahl distillation for 63 samples of predominantly metasedimentary rocks from two different geological settings of the european variscides i e the erzgebirge and the zone of erbendorf vohenstrauss in germany the studied erzgebirge schists represent an early paleozoic passive margin sequence that reappears in different deep subducted metamorphic units this allows an efficient examination of nitrogen loss and isotope fractionation during prograde metamorphism ammonium is found to be progressively depleted accompanied by a shift in 15n from the low grade units 2 kbar 300 c with 638 124 ppm and 15n 2 2 0 6 to the garnet phyllite unit 9 kbar 470 c with 621 190 ppm and 15n 3 5 0 9 the mica schist eclogite unit 12 kbar 550 c with 394 113 ppm and 15n 3 9 0 8 and to the gneiss eclogite unit 12 kbar 730 c with 99 32 ppm and 15n 7 7 2 0 using equilibrium models for rayleigh distillation and batch volatilization suggest that the nitrogen depletion took place by ammonia release only for the mica schists this isotope fractionation can be explained by the loss of molecular nitrogen in comparison with the early paleozoic schists the proterozoic ortho and paragneisses of the erzgebirge gneiss unit 6 8 kbar 650 c contain significantly lower amounts of ammonium 70 ppm and reach relatively low 15n values 2 5 to 3 6 the paragneisses from the zone of erbendorf vohenstrauss zev sampled from the ktb pilot hole represents a separate tectonometamorphic unit that has undergone polyphase metamorphic conditions with the major imprint being amphibolite facies 7 kbar 650 700 c the metagraywackes have nh4 contents of 80 ppm and 15n of approximately 6 gneisses in the vicinity of a late cataclastic shear zone at 2000 m depth are characterized by a shift in nh4 250 ppm and 15n up to 12 which suggest late fluid rock interactions with a nitrogen and 15n enriched fluid

petrogenesis of uhp metamorphic rocks from qinglongshan southern sulu east central china abstract five kinds of uhp metamorphic rocks including eclogite orthogneiss paragneiss schist and quartzite are exposed in the qinglongshan roadcut southern sulu orogenic belt of eastern central china they comprise metamorphic supracrustal rocks with bimodal volcanic characteristics and continental affinity and granitic intrusive associations the preservation of coesite inclusions and or its pseudomorphs in eclogite and other rocks indicate that they have been subjected to in situ uhp metamorphism four stages of metamorphism were recognized by combining petrographic observations and compositions of minerals from various uhp rocks prograde epidote amphibolite facies uhp coesite eclogite facies post uhp quartz eclogite facies and retrograde amphibolite facies assemblages delineate an inferred p t path with a clockwise trajectory and a retrograde event characterized by the coupling of decompression with a temperature decrease garnet porphyroblasts in uhp eclogites display a complex growth zoning and mineral distribution and record a crucial segment of the prograde and retrograde metamorphic evolution the preservation of growth zoning in eclogitic and gneissic garnets suggests that the uhp rocks had a short residence time before retrograde metamorphism and a very high uplift rate in order to preserve the prograde growth zoning

modelling gravity variations consistent with ground deformation in the campi flegrei caldera italy abstract in recent years 1970 72 and 1982 84 two inflation episodes took place in the campi flegrei caldera italy characterized by significant ground uplift and gravity variations an elastic half space model with vertical density stratification is employed to compute the displacement field and the gravity variations produced by the deformation of buried layers following the inflation of a spherically symmetric deformation source contributions to gravity variations are produced by dilation contraction of the medium by the displacements of density interfaces the free surface and subsurface layers and of source boundaries and possibly by new mass input from remote distances into the source volume three cases were examined in detail in case i the magma chamber is identified as the deformation source and volume and pressure increase in the magma chamber is due to input of new magma from remote distances in case ii deformation is due to magma differentiation within the magma chamber deformation source with constant mass in case iii the geothermal system is identified as the deformation source and a pressure increase possibly driven by the exsolution of high temperature and high pressure volatiles in the magma chamber is assumed to play a dominant role from the comparison between measured and computed gravity residuals free air corrected gravity variations we can assess that in case i an inflation source with constant density would predict gravity residuals compatible with observations whereas an expansion at constant mass case ii would predict gravity residuals much lower than observed the resolving power of gravity data however prevents accurate assessment of the density of the emplaced material in case iii the pervasive density increase of the geothermal fluids induced by pressure increase is assumed to be the main source of gravity variations the average porosity value required for this model to match both the ground deformation and the gravity residuals is found to be 10 a value which is compatible with measured porosity values at campi flegrei in deep wells the subsidence phases following both inflation episodes and the gravity residuals during subsidence lead us to consider case iii as more plausible even if a suitable combination of cases i and iii cannot be discarded

nitrogen isotope compositions of metasedimentary rocks in the catalina schist california implications for metamorphic devolatilization history abstract in the catalina schist subduction zone metamorphic complex california metasedimentary rocks show a decrease in n concentration and an increase in 15nair with increasing metamorphic grade lowest grade lawsonite albite rocks contain 632 185 ppm n with 15 n 1 9 0 6 whereas highgrade amphibolite equivalents contain 138 76 ppm n with 15 n 4 3 0 8 loss of n accompanied devolatilization reactions that evolved h2o rich c o h s n fluids through consumption of chlorite and phengitic white mica and production of mineral assemblages containing muscovite biotite garnet and kyanite whole rock n concentrations of up to 200 ppm in veins and pegmatites produced during high p t metamorphism reflect the redistribution of n during devolatilization and partial melting of the metasedimentary rocks bulk fluid rock n isotope fractionations 15n 15nfluid 15nrock of 1 5 1 were calculated with the rayleigh distillation equation taking into account variability in rock composition by comparison of samples with similar k2o concentrations these fractionations are similar to but slightly lower than published calculated fractionations for n2 nh4 exchange at the temperature range of 350 600 c over which most of the devolatilization occurred in the catalina schist approximately 3 4 to 2 25 the n systematics appear to be explained by n2 nh4 exchange and a devolatilization process intermediate in behavior to batch volatilization and rayleigh distillation the observed shifts in n concentration and 15n cannot be explained by nh3 nh4 exchange at these temperatures using the equilibrium models the distillation devolatilization process implicated in this study may govern the behavior of other trace elements partitioned into hydrous fluids during devolatilization e g b cs u similarity of the calculated fluid 15n 1 5 to 5 5 with compositions of natural gases inferred to be derived from metasedimentary sources indicates the possibility of using n as a tracer of large scale volatile transport

glacial interglacial changes in the isotopes of nitrate from the greenland ice sheet project 2 gisp2 ice core received 3 march 2005 revised 23 september 2005 accepted 26 october 2005 published 24 december 2005 1 the 15 n 14 n and 18 o 16 o ratios of nitrate in the greenland ice sheet project 2 gisp2 summit greenland ice core are much higher in ice from the last glacial period than in the pre industrial holocene despite the lack of a significant glacial interglacial change in nitrate concentration while both the 15 n 14 n and 18 o 16 o records are anticorrelated with snow accumulation rate neither is satisfactorily explained by accumulation changes or post depositional processes the similarity in the glacial interglacial change in 15 n 14 n from several different greenland ice cores and the large amplitude of this change relative to observed seasonal variation raise the possibility that the isotopes of nitrate in ice cores indicate a large scale glacial interglacial change in the isotopic composition of atmospheric nox the glacial interglacial change in 18 o 16 oi s best explained by a greater contribution of hno3 production from hydrolysis of n2o5 which has implications for reconstruction of past atmospheric oxidant levels although isotope effects associated with nox photochemistry and nitrate scavenging have not been fully characterized the 15 n 14 n data may indicate glacial interglacial changes in the relative contributions from different natural sources of nox on a hemispheric or global scale

nitrogen isotope record of fluid rock interactions in the skiddaw aureole and granite english lake district the skiddaw granite and its contact metamorphic aureole in the english lake district provide an excellent opportunity to test the capability of the n isotope system to trace devolatilization and large scale transfer of crustal fluids in the aureole skiddaw group metasedimentary rocks with relatively uniform lithology and major element compositions show a dramatic decrease in n content toward the granite contact from or 800 ppm at distances 2 5 km from the contact to 1 5 km these rocks have extremely uniform delta 15 n air near 3 7 per mil whereas closer to the contact or 1 km delta 15 n is shifted to higher values up to 8 7 per mil the coupled decreases in n content and increases in delta 15 n are compatible with the removal of n having low delta 15 n in fluids during continuous prograde devolatilization reactions involving the break down of white mica and the stabilization of biotite cordierite and andalusite bearing assemblages in the same metasedimentary rocks the lack of obvious trends in major element concentrations including sio 2 tio 2 sio 2 al 2 o 3 and the ratios of other major oxides to tio 2 and al 2 o 3 with distance from the granitic contact is consistent with minimal change in major element composition during the contact metamorphism ratios of whole rock n b rb and ba concentrations to whole rock k 2 o content are believed to reflect the differing fluid mica partitioning and involving varying relative proportions of white mica and biotite of these trace elements during devolatilization reactions greisenized skiddaw granite from a borehole is enriched in n range of 17 225 ppm for whole rocks and white mica separates relative to the unaltered granite whole rock 30 ppm and has delta 15 n of 1 0 to 4 8 per mil the n concentrations and delta 15 n of the wall rocks and greisenized granites combined with c isotopic data carbonate and carbonaceous matter for the same rocks are consistent with the mobilization of fluids having low delta 15 n and delta 13 c pdb values from the devolatilized aureole into the cooling intrusive body such transport is consistent with the predictions of recent theoretical models of late stage hydrothermal evolution in cooling intrusive systems

reply to comment by d carbone and d patane on multidisciplinary investigation on a lava fountain preceding a flank eruption the 10 may 2008 etna case

deaths and injuries in the eruption of galeras volcano colombia 14 january 1993 abstract six volcanologists and three tourists were killed in the crater of galeras volcano colombia when it erupted without warning the scientists were attending the united nations international decade for natural disaster reduction workshop which had been convened to improve monitoring research and disaster mitigation at galeras at the time the most active and one of the most hazardous volcanoes in south america information on the events surrounding the eruption was obtained by sending a questionnaire to twelve scientists who had been inside the caldera at the time of the eruption or who had assisted in the search and rescue operation the autopsy reports on the five corpses and the few pieces of equipment and clothing retrieved from the crater area were also studied the main causes of death and injury were the forces at the eruptive vent and the bombardment by hot rocks ejected in the first 15 min of the eruption ranging from blocks over 1 m in size to pea sized lapilli which fell last some conclusions can be drawn for the future safety of volcanologists working in craters at high altitude hard hats would protect against concussion from blows to the head during escape from the danger area and a lightweight heat resistant and water repellent coverall would limit the skin burns and the risk of clothing being ignited from contact with incandescent falling ejecta the coverall could also be life saving by protecting immobilised casualties from hypothermia due to the rain and wind whilst waiting to be rescued especially as the volcanic activity cloud cover or nightfall could curtail rescue efforts work in hazardous craters should be strictly limited to essential tasks and periods of good visibility and a climbing team should leave the area at least four hours before nightfall in case rescue is needed tourists must be warned against visiting active crater areas

effects of volatiles on mixing in calc alkaline magma systems the intimate mixing between different magmas of disparate densities characteristic of some calc alkaline magma systems is explained by a new mechanism involving the emplacement of a layer of wet undersaturated mafic magma at the base of a magma chamber containing more differentiated magma turbulent transfer of heat between the mafic magma and the overlying magma leads to crystallization and exsolution of volatiles in the lower layer for an initial water content of a few per cent the bulk density of the mafic magma can become equal to that of the overlying magma causing overturning and intimate mixing of the magmas the mechanism is most probable in the low pressure environment of a high level magma chamber

preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis abstract the carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments in order to reconstruct past environmental changes from sedimentary organic matter it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments in a series of oxic and anoxic incubation experiments we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation the decomposition rates determined with a double exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions however under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions within three months of incubation the 13c of bulk organic matter decreased by 1 6 with respect to the initial value the depletion can be attributed to the selective preservation of 13c depleted organic compounds during anoxic decay the 15n values continuously decreased to about 3 below the initial value the decrease probably results from bacterial growth adding 15n depleted biomass to the residual material in the oxic experiment 15n values increased by more then 3 before decreasing to a value indistinguishable from the initial isotopic composition the dissimilarity between oxic and anoxic conditions may be attributed to differences in the type timing and degree of microbial activity and preferential degradation in agreement with the anoxic incubation experiments sediments from eutrophic lake lugano are on average depleted in 13c 1 5 and 15n 1 2 with respect to sinking particulate organic matter collected during a long term sediment trap study

tectonic driving of neoproterozoic glaciations evidence from extreme oxygen isotope signature of meteoric water in granite abstract the global context of glaciation in the neoproterozoic has been hypothesized to result from the massive reorganization of the earth s land and ocean systems due to breakup and dispersal of the supercontinent rodinia at about 750 ma this hypothesis gains support from unusually light o isotope records of hydrothermally altered rocks in a rift tectonic zone at that time which is indicative of interaction with meteoric water of low mean annual temperature and thus tectonic driving of cold paleoclimate at the time of hydrothermal alteration very negative 18 o values of 14 4 to 10 0 are found for garnet from neoproterozoic granite in south china which are the lightest o isotope record so far reported for minerals from igneous rocks negative d values of 129 to 109 are obtained for garnet magnetite and zircon thus high t meteoric hydrothermal alteration occurred during magma emplacement shrimp u pb dating for magmatic and hydrothermal zircons yields two groups of ages at 782 3 ma and 748 3 ma respectively responsible for granite crystallization and hydrothermal alteration the garnet is in o isotope disequilibrium with zircon indicating differential effects of subsolidus hydrothermal alteration on the minerals of different o diffusion rates occurrence of the unusually negative 18 o granite at mid low paleolatitudes provides a geochemical proxy for a cold paleoclimate at 748 3 ma possibly a continental glaciation corresponding to the kaigas iceage it suggests a tectonic link to the climatic effect of uplifted rift flanks due to the rodinia breakup at about 750 ma and thus the ice fire interaction by syn rift magmatism of low 18 o imprints in association with the mantle event of asthenospheric upwelling hence the tectonic driving is evident for regional glaciations in supercontinental rift basins

nitrogen isotope tracers of high temperature fluid rock interactions case study of the catalina schist california abstract nitrogen isotope data for metasomatized rocks veins and pegmatites in the catalina schist subduction zone metamorphic complex allow futher characterization of complex high p t metasomatic proceses and evaluation of the scales of isotopic equilibration and fluid transport during subduction zone metamorphism throughout the catalina schist n resides predominantly as nh4 in white mica which occurs in nearly all bulk compositions i e metasedimentary metamafic and to a lesser extent metaultramafic melange at all grades within each metamorphic unit of the catalina schist ranging in grade from lawsonite albite to amphibolite facies 15n values of mica in metasomatized metamafic and metaultramafic rocks are consistent with the metasomatic addition of n from nearby devolatilizing metasedimentary rocks into the initially n poor mafic and ultramafic rocks within each unit uniformity of mica 15n in metasomatized rocks relative to the 15n of metasedimentary rocks in the same unit implies mixing of n from nearby heterogeneous metasedimentary sources perhaps producing fluids with unifrom 15n at up to the kilometer scale however the trend in 15n of metasedimentary sources with increasing metamorphic grade is inconsistent with larger scale up temperature transfer of fluid in this case n2 bearing in the catalina schist paleosubduction zone such flow at scales of up to tens of kilometers has been inferred through previous oxygen isotope study nitrogen isotope compositions are instead believed to have been controlled at a more local scale than the o isotope systematics due to the more rock dominated fluid rock mass balance for n the 15n of muscovite in leucosomes and pegmatites in amphibolite grade metasedimentary exposures matches that of muscovite in metasedimentary hosts implying minimal n isotope fractionation during migmatization processes and possible transfer of metasedimentary n isotope signatures in silicate melts these results illustrate the potential of the n isotope system to yield valuable information regarding fluid rock interactions in the crust and mantle the data for the catalina schist demonstrate the ability of n isotopes to trace the transfer of sediment derived c o h s n fluids and silicate melts and show the expected benefit of the n isotope system in having a differing fluid rock mass balance relative to the more commonly used stable isotope systems that can yield unique constraints in quantitative models of crustal fluid processes