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Sample records for active magma chamber

  1. Mush Column Magma Chambers

    NASA Astrophysics Data System (ADS)

    Marsh, B. D.

    2002-12-01

    Magma chambers are a necessary concept in understanding the chemical and physical evolution of magma. The concept may well be similar to a transfer function in circuit or time series analysis. It does what needs to be done to transform source magma into eruptible magma. In gravity and geodetic interpretations the causative body is (usually of necessity) geometrically simple and of limited vertical extent; it is clearly difficult to `see' through the uppermost manifestation of the concentrated magma. The presence of plutons in the upper crust has reinforced the view that magma chambers are large pots of magma, but as in the physical representation of a transfer function, actual magma chambers are clearly distinct from virtual magma chambers. Two key features to understanding magmatic systems are that they are vertically integrated over large distances (e.g., 30-100 km), and that all local magmatic processes are controlled by solidification fronts. Heat transfer considerations show that any viable volcanic system must be supported by a vertically extensive plumbing system. Field and geophysical studies point to a common theme of an interconnected stack of sill-like structures extending to great depth. This is a magmatic Mush Column. The large-scale (10s of km) structure resembles the vertical structure inferred at large volcanic centers like Hawaii (e.g., Ryan et al.), and the fine scale (10s to 100s of m) structure is exemplified by ophiolites and deeply eroded sill complexes like the Ferrar dolerites of the McMurdo Dry Valleys, Antarctica. The local length scales of the sill reservoirs and interconnecting conduits produce a rich spectrum of crystallization environments with distinct solidification time scales. Extensive horizontal and vertical mushy walls provide conditions conducive to specific processes of differentiation from solidification front instability to sidewall porous flow and wall rock slumping. The size, strength, and time series of eruptive behavior

  2. On the Interaction of a Vigorous Hydrothermal System with an Active Magma Chamber: The Puna Magma Chamber, Kilauea East Rift, Hawaii

    NASA Astrophysics Data System (ADS)

    Gregory, R. T.; Marsh, B. D.; Teplow, W.; Fournelle, J.

    2009-12-01

    The extent of the interaction between hydrothermal systems and active magma chambers has long been of fundamental interest to the development of ore deposits, cooling of magma chambers, and dehydration of the subducting lithosphere. As volatiles build up in the residual magma in the trailing edge of magmatic solidification fronts, is it possible that volatiles are transferred from the active magma to the hydrothermal system and vice versa? Does the external fracture front associated with vigorous hydrothermal systems sometimes propagate into the solidification front, facilitating volatile exchange? Or is the magma always sealed at temperatures above some critical level related to rock strength and overpressure? The degree of hydrothermal interaction in igneous systems is generally gauged in post mortem studies of δ18O and δD, where it has been assumed that a fracture front develops about the magma collapsing inward with cooling. H.P. Taylor and D. Norton's (1979; J. Petrol.)seminal work inferred that rocks are sealed with approach to the solidus and there is little to no direct interaction with external volatiles in the active magma. In active lava lakes a fracture front develops in response to thermal contraction of the newly formed rock once the temperature drops to ~950°C (Peck and Kinoshita,1976;USGS PP935A); rainfall driven hydrothermal systems flash to steam near the 100 °C isotherm in the solidified lake and have little effect on the cooling history (Peck et al., 1977; AJS). Lava lakes are fully degassed magmas and until the recent discovery of the Puna Magma Chamber (Teplow et al., 2008; AGU) no active magma was known at sufficiently great pressure to contain original volatiles. During the course of routine drilling of an injection well at the Puna Geothermal Venture (PGV) well-field, Big Island, Hawaii, a 75-meter interval of diorite containing brown glass inclusions was penetrated at a depth of 2415 m, continued drilling to 2488 m encountered a melt

  3. Simulation of Layered Magma Chambers.

    ERIC Educational Resources Information Center

    Cawthorn, Richard Grant

    1991-01-01

    The principles of magma addition and liquid layering in magma chambers can be demonstrated by dissolving colored crystals. The concepts of density stratification and apparent lack of mixing of miscible liquids is convincingly illustrated with hydrous solutions at room temperature. The behavior of interstitial liquids in "cumulus" piles can be…

  4. A model to forecast magma chamber rupture

    NASA Astrophysics Data System (ADS)

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2016-04-01

    An understanding of the amount of magma available to supply any given eruption is useful for determining the potential eruption magnitude and duration. Geodetic measurements and inversion techniques are often used to constrain volume changes within magma chambers, as well as constrain location and depth, but such models are incapable of calculating total magma storage. For example, during the 2012 unrest period at Santorini volcano, approximately 0.021 km3 of new magma entered a shallow chamber residing at around 4 km below the surface. This type of event is not unusual, and is in fact a necessary condition for the formation of a long-lived shallow chamber. The period of unrest ended without culminating in eruption, i.e the amount of magma which entered the chamber was insufficient to break the chamber and force magma further towards the surface. Using continuum-mechanics and fracture-mechanics principles, we present a model to calculate the amount of magma contained at shallow depth beneath active volcanoes. Here we discuss our model in the context of Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011-2012 unrest period, that the measured 0.02% increase in volume of Santorini's shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano.

  5. Thermomechanics of shallow magma chamber pressurization: Implications for the assessment of ground deformation data at active volcanoes

    NASA Astrophysics Data System (ADS)

    Gregg, P. M.; de Silva, S. L.; Grosfils, E. B.

    2013-12-01

    In this study, we utilize thermomechanical models to investigate how magma chambers overpressurize as the result of either magmatic recharge or volatile exsolution. By implementing an adaptive reservoir boundary condition we are able to track how overpressure dissipates as the magma chamber expands to accommodate internal volume changes. We find that the size of the reservoir greatly impacts the resultant magma chamber overpressure. In particular, overpressure estimates for small to moderate-sized reservoirs (1-10 km3) are up to 70% lower than previous analytical predictions. We apply our models to Santorini volcano in Greece where recent seismic activity and ground deformation observations suggested the potential for eruption. The incorporation of an adaptive boundary condition reproduces Mogi flux estimates and suggests that the magma reservoir present at Santorini may be quite large. Furthermore, model results suggest that if the magma chamber is >100 km3, overpressures generated due to the high magma flux may not exceed the strength of the host rock, thus requiring an additional triggering mechanism for eruption. Although the adaptive boundary condition approach does not calculate the internal evolution of the magma reservoir, it represents a fundamental step forward from elastic Mogi models and fixed boundary solutions on which future investigations of the evolution of the magma can be built.

  6. Magma chamber dynamics and Vesuvius eruption forecasting

    NASA Astrophysics Data System (ADS)

    Dobran, F.

    2003-04-01

    Magma is continuously or periodically refilling an active volcano and its eruption depends on the mechanical, fluid, thermal, and chemical aspects of the magma storage region and its surroundings. A cyclically loaded and unloaded system can fail from a weakness in the system or its surroundings, and the fluctuating stresses can produce system failures at stress levels that are considerably below the yield strength of the material. Magma in a fractured rock system within a volcano is unstable and propagates toward the surface with the rate depending on the state of the system defined by the inertia, gravity, friction, and permeability parameters of magma and its source region. Cyclic loading and unloading of magma from a reservoir caused by small- or medium-scale eruptions of Vesuvius can produce catastrophic plinian eruptions because of the structural failure of the system and the quiescent periods between these eruptions increase with time until the next eruption cycle which will be plinian or subplinian and will occur with a very high probability this century. Such a system behavior is predicted by a Global Volcanic Simulator of Vesuvius developed for simulating different eruption scenarios for the purpose of urban planning the territory, reducing the number of people residing too close to the cone of the volcano, and providing safety to those beyond about 5 km radius of the crater. The magma chamber model of the simulator employs a thermomechanical model that includes magma inflow and outflow from the chamber, heat and mass transfer between the chamber and its surroundings, and thermoelastoplastic deformation of the shell surrounding the magma source region. These magma chamber, magma ascent, and pyroclastic dispersion models and Vesuvius eruption forecasting are described in Dobran, F., VOLCANIC PROCESSES, Kluwer Academic/Plenum Publishers, 2001, 590 pp.

  7. Processes active in mafic magma chambers: The example of Kilauea Iki Lava Lake, Hawaii

    USGS Publications Warehouse

    Helz, R.T.

    2009-01-01

    Kilauea Iki lava lake formed in 1959 as a closed chamber of 40??million m3 of picritic magma. Repeated drilling and sampling of the lake allows recognition of processes of magmatic differentiation, and places time restrictions on the periods when they operated. This paper focuses on evidence for the occurrence of lateral convection in the olivine-depleted layer, and constraints on the timing of this process, as documented by chemical, petrographic and thermal data on drill core from the lake. Lateral convection appears to have occurred in two distinct layers within the most olivine-poor part of the lake, created a slightly olivine-enriched septum in the center of the olivine-depleted section. A critical marker for this process is the occurrence of loose clusters of augite microphenocrysts, which are confined to the upper half of the olivine-poor zone. This process, which took place between late 1962 and mid-1964, is inferred to be double-diffusive convection. Both this convection and a process of buoyant upwelling of minimum-density liquid from deep within the lake (Helz, R.T., Kirschenbaum H. and Marinenko, J.W., 1989. Diapiric melt transfer: a quick, efficient process of igneous differentiation: Geological Society of America Bulletin, v. 101, 578-594) result from the fact that melt density in Kilauea Iki compositions decreases as olivine and augite crystallize, above the incoming of plagioclase. The resulting density vs. depth profile creates (1) a region of gravitationally stable melt at the top of the chamber (the locus of double-diffusive convection) and (2) a region of gravitationally unstable melt at the base of the melt column (the source of upwelling minimum-density melt, Helz, R.T., Kirschenbaum H. and Marinenko, J.W., 1989. Diapiric melt transfer: a quick, efficient process of igneous differentiation: Geological Society of America Bulletin, v. 101, 578-594). By contrast the variation of melt density with temperature for the 1965 Makaopuhi lava lake does

  8. Basaltic injections into floored silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Wiebe, R. A.

    Recent studies have provided compelling evidence that many large accumulations of silicic volcanic rocks erupted from long-lasting, floored chambers of silicic magma that were repeatedly injected by basaltic magma. These basaltic infusions are commonly thought to play an important role in the evolution of the silicic systems: they have been proposed as a cause for explosive silicic eruptions [Sparks and Sigurdsson, 1977], compositional variation in ash-flow sheets [Smith, 1979], mafic magmatic inclusions in silicic volcanic rocks [Bacon, 1986], and mixing of mafic and silicic magmas [Anderson, 1976; Eichelberger, 1978]. If, as seems likely, floored silicic magma chambers have frequently been invaded by basalt, then plutonic bodies should provide records of these events. Although plutonic evidence for mixing and commingling of mafic and silicic magmas has been recognized for many years, it has been established only recently that some intrusive complex originated through multiple basaltic injections into floored chambers of silicic magma [e.g., Wiebe, 1974; Michael, 1991; Chapman and Rhodes, 1992].

  9. Convective Regimes in Crystallizing Basaltic Magma Chambers

    NASA Astrophysics Data System (ADS)

    Gilbert, A. J.; Neufeld, J. A.; Holness, M. B.

    2015-12-01

    Cooling through the chamber walls drives crystallisation in crustal magma chambers, resulting in a cumulate pile on the floor and mushy regions at the walls and roof. The liquid in many magma chambers, either the bulk magma or the interstitial liquid in the mushy regions, may convect, driven either thermally, due to cooling, or compositionally, due to fractional crystallization. We have constructed a regime diagram of the possible convective modes in a system containing a basal mushy layer. These modes depend on the large-scale buoyancy forcing characterised by a global Rayleigh number and the proportion of the chamber height constituting the basal mushy region. We have tested this regime diagram using an analogue experimental system composed of a fluid layer overlying a pile of almost neutrally buoyant inert particles. Convection in this system is driven thermally, simulating magma convection above and within a porous cumulate pile. We observe a range of possible convective regimes, enabling us to produce a regime diagram. In addition to modes characterised by convection of the bulk and interstitial fluid, we also observe a series of regimes where the crystal pile is mobilised by fluid motions. These regimes feature saltation and scouring of the crystal pile by convection in the bulk fluid at moderate Rayleigh numbers, and large crystal-rich fountains at high Rayleigh numbers. For even larger Rayleigh numbers the entire crystal pile is mobilised in what we call the snowglobe regime. The observed mobilisation regimes may be applicable to basaltic magma chambers. Plagioclase in basal cumulates crystallised from a dense magma may be a result of crystal mobilisation from a plagioclase-rich roof mush. Compositional convection within such a mush could result in disaggregation, enabling the buoyant plagioclase to be entrained in relatively dense descending liquid plumes and brought to the floor. The phenocryst load in porphyritic lavas is often interpreted as a

  10. Magma Chambers, Thermal Energy, and the Unsuccessful Search for a Magma Chamber Thermostat

    NASA Astrophysics Data System (ADS)

    Glazner, A. F.

    2015-12-01

    Although the traditional concept that plutons are the frozen corpses of huge, highly liquid magma chambers ("big red blobs") is losing favor, the related notion that magma bodies can spend long periods of time (~106years) in a mushy, highly crystalline state is widely accepted. However, analysis of the thermal balance of magmatic systems indicates that it is difficult to maintain a significant portion in a simmering, mushy state, whether or not the system is eutectic-like. Magma bodies cool primarily by loss of heat to the Earth's surface. The balance between cooling via energy loss to the surface and heating via magma accretion can be denoted as M = ρLa/q, where ρ is magma density, L is latent heat of crystallization, a is the vertical rate of magma accretion, and q is surface heat flux. If M>1, then magma accretion outpaces cooling and a magma chamber forms. For reasonable values of ρ, L, and q, the rate of accretion amust be > ~15 mm/yr to form a persistent volume above the solidus. This rate is extremely high, an order of magnitude faster than estimated pluton-filling rates, and would produce a body 10 km thick in 700 ka, an order of magnitude faster than geochronology indicates. Regardless of the rate of magma supply, the proportion of crystals in the system must vary dramatically with depth at any given time owing to transfer of heat. Mechanical stirring (e.g., by convection) could serve to homogenize crystal content in a magma body, but this is unachievable in crystal-rich, locked-up magma. Without convection the lower part of the magma body becomes much hotter than the top—a process familiar to anyone who has scorched a pot of oatmeal. Thermal models that succeed in producing persistent, large bodies of magma rely on scenarios that are unrealistic (e.g., omitting heat loss to the planet's surface), self-fulfilling prophecies (e.g., setting unnaturally high temperatures as fixed boundary conditions), or physically unreasonable (e.g., magma is intruded

  11. Layer Formation in Convective Magma Chambers

    NASA Astrophysics Data System (ADS)

    Höink, T.; Schmalzl, J.; Hansen, U.

    2004-12-01

    The dynamics of a convective magma chamber is crucially influenced by the competetion between sedimentation and convective suspension of crystals. Crystal settling combined with the crystal's density contribution is a possible mechanism leading to differentiation and layer formation. Here we address the question whether crystals can remain suspended or whether they are able to dynamically form a layered structure within the convective lifetime of a magma chamber. We employ an existing numerical method that, by means of a finite volume scheme, discretizes the equations for thermally driven convection in an infinite Prandtl-number Boussinesq fluid in Cartesian geometry. We implement a newly developed settling algorithm for the numerical study of finite-sized-particle settling in a non-dilute convective suspension. Our approach considers a consistent settling velocity and the density contribution due to particle mass. The buoyancy ratio B, which is the ratio of the density variation due to crystal mass to the thermal density variation, is varied for five different Rayleigh numbers, covering a range of four orders of magnitude. We find B to be a critical parameter and its critical value to depend on the Rayleigh number. For subcritical values we observe that the presence of a crystal phase reduces convective vigor and most crystals stay suspended. When a critical buoyancy ratio is exceeded, the presence of crystals can significantly alter convective motion. For all investigated Rayleigh numbers we find a critical buoyancy ratio, above which layering can be achieved from an initially unstratified fluid. Most of the crystal mass collects in the dynamically created bottom layer, even for cases where the average settling velocity is three orders of magnitude smaller than the root mean square convective velocity. The time it takes a crystal to travel across the height of the cell with the full settling velocity in the absence of a thermal gradient defines the settling

  12. Evaluating volumes for magma chambers and magma withdrawn for caldera collapse

    NASA Astrophysics Data System (ADS)

    Geshi, Nobuo; Ruch, Joel; Acocella, Valerio

    2014-06-01

    We develop an analytical model to infer the total volume of a magma chamber associated with caldera collapse and the critical volume of magma that must be withdrawn to induce caldera collapse. The diameter of caldera border fault, depth to the magma chamber, and volumes of magma erupted before the onset of collapse and of entire eruption are compiled for 14 representative calderas. The volume of erupted magma at the onset of collapse aligns between the total erupted volume of the other representative caldera-forming eruptions and the volume of eruptions without collapse during the post-caldera stage, correlating with the structural diameter of the calderas. The total volume of magma chamber is evaluated using a piston-cylinder collapse model, in which the competition between the decompression inside magma chamber and friction along the caldera fault controls the collapse. Estimated volumes of the magma chambers associated with caldera collapse are 3-10 km3 for Vesuvius 79 A.D. to 3000-10 500 km3 for Long Valley, correlating with the cube of caldera diameters. The estimated volumes of magma chamber are always larger than the total volume of erupted magma for caldera formation, suggesting that the magma chambers are never completely emptied by the caldera-forming eruptions. The minimum volumes of erupted magma to trigger collapse are calculated from the correlation between the caldera diameters and the evaluated volume of magma chambers. The minimum eruptive volume for the collapse correlates with the square of the caldera radius r and the square of the depth to the magma chamber h, and inversely correlates with the bulk modulus of magma, which is mainly controlled by the bubble fraction in the magma. A bubble fraction between 5 and 10% at the onset of collapse may explain the distribution of the erupted volumes at the onset of collapse of the calderas in nature.

  13. Discovery of a magma chamber and faults beneath a Mid-Atlantic Ridge hydrothermal field.

    PubMed

    Singh, Satish C; Crawford, Wayne C; Carton, Hélène; Seher, Tim; Combier, Violaine; Cannat, Mathilde; Pablo Canales, Juan; Düsünür, Doga; Escartin, Javier; Miranda, J Miguel

    2006-08-31

    Crust at slow-spreading ridges is formed by a combination of magmatic and tectonic processes, with magmatic accretion possibly involving short-lived crustal magma chambers. The reflections of seismic waves from crustal magma chambers have been observed beneath intermediate and fast-spreading centres, but it has been difficult to image such magma chambers beneath slow-spreading centres, owing to rough seafloor topography and associated seafloor scattering. In the absence of any images of magma chambers or of subsurface near-axis faults, it has been difficult to characterize the interplay of magmatic and tectonic processes in crustal accretion and hydrothermal circulation at slow-spreading ridges. Here we report the presence of a crustal magma chamber beneath the slow-spreading Lucky Strike segment of the Mid-Atlantic Ridge. The reflection from the top of the magma chamber, centred beneath the Lucky Strike volcano and hydrothermal field, is approximately 3 km beneath the sea floor, 3-4 km wide and extends up to 7 km along-axis. We suggest that this magma chamber provides the heat for the active hydrothermal vent field above it. We also observe axial valley bounding faults that seem to penetrate down to the magma chamber depth as well as a set of inward-dipping faults cutting through the volcanic edifice, suggesting continuous interactions between tectonic and magmatic processes.

  14. Discovery of a magma chamber and faults beneath a Mid-Atlantic Ridge hydrothermal field.

    PubMed

    Singh, Satish C; Crawford, Wayne C; Carton, Hélène; Seher, Tim; Combier, Violaine; Cannat, Mathilde; Pablo Canales, Juan; Düsünür, Doga; Escartin, Javier; Miranda, J Miguel

    2006-08-31

    Crust at slow-spreading ridges is formed by a combination of magmatic and tectonic processes, with magmatic accretion possibly involving short-lived crustal magma chambers. The reflections of seismic waves from crustal magma chambers have been observed beneath intermediate and fast-spreading centres, but it has been difficult to image such magma chambers beneath slow-spreading centres, owing to rough seafloor topography and associated seafloor scattering. In the absence of any images of magma chambers or of subsurface near-axis faults, it has been difficult to characterize the interplay of magmatic and tectonic processes in crustal accretion and hydrothermal circulation at slow-spreading ridges. Here we report the presence of a crustal magma chamber beneath the slow-spreading Lucky Strike segment of the Mid-Atlantic Ridge. The reflection from the top of the magma chamber, centred beneath the Lucky Strike volcano and hydrothermal field, is approximately 3 km beneath the sea floor, 3-4 km wide and extends up to 7 km along-axis. We suggest that this magma chamber provides the heat for the active hydrothermal vent field above it. We also observe axial valley bounding faults that seem to penetrate down to the magma chamber depth as well as a set of inward-dipping faults cutting through the volcanic edifice, suggesting continuous interactions between tectonic and magmatic processes. PMID:16943836

  15. The Growth of Magma Bodies by Amalgamation of Discrete Sheet Intrusions: Implications for the Formation of Magma Chambers

    NASA Astrophysics Data System (ADS)

    Annen, C.

    2007-12-01

    the assembly of plutons over millions years, an active magma chamber only represents a small part of the total intruded volume. The formation of the magma chamber occurs at a late stage in the growth of the pluton unless transient accelerations of the emplacement rate affect the pluton assembly.

  16. The relative roles of boundary layer fractionation and homogeneous fractionation in cooling basaltic magma chambers

    NASA Astrophysics Data System (ADS)

    Kuritani, Takeshi

    2009-06-01

    In a cooling magma chamber, magmatic differentiation can proceed both by fractionation of crystals from the main molten part of the magma body (homogeneous fractionation) and by mixing of the main magma with fractionated melt derived from low-temperature mush zones (boundary layer fractionation). In this study, the relative roles of boundary layer fractionation and homogeneous fractionation in basaltic magma bodies were examined using a thermodynamics-based mass balance model. Model calculations show that boundary layer fractionation cannot be a dominant fractionation mechanism when magma chambers are located at low pressures (< ~ 50 MPa) or when magmas are less hydrous (< ~ 1 wt.%), such as mid-ocean ridge basalt and intraplate basalt, because of the low efficiency of melt transport from the mush zones to the main magma. Therefore, magmas evolve principally by homogeneous fractionation. If crystal-melt separation does not occur effectively in the main magma, the magma becomes crystal-rich in the early stages of magmatic evolution. On the other hand, boundary layer fractionation can occur effectively when magmas are hydrous (> ~ 2 wt.%), such as arc basalt, and the magma chambers are located at depth (> ~ 100 MPa). Because the melt derived from mush zones is enriched in alkalis and H 2O, crystallization from the main magma is suppressed by mixing with the mush melt as a consequence of depression of the liquidus temperature. Therefore, homogeneous fractionation is more effectively suppressed in magma chambers in which boundary layer fractionation is more active. If magmatic differentiation proceeds primarily by boundary layer fractionation, magmas can remain free of crystals for long periods during magmatic evolution.

  17. Location and Pressures Change Prediction of Bromo Volcano Magma Chamber Using Inversion Scheme

    NASA Astrophysics Data System (ADS)

    Kumalasari, Ratih; Srigutomo, Wahyu

    2016-08-01

    Bromo volcano is one of active volcanoes in Indonesia. It has erupted at least 50 times since 1775 and has been monitored by Global Positioning System (GPS) since 1989. We applied the Levenberg-Marquardt inversion scheme to estimate the physical parameters contributing to the surface deformation. Physical parameters obtained by the inversion scheme such as magma chamber location and volume change are useful in monitoring and predicting the activity of Bromo volcano. From our calculation it is revealed that the depth of the magma chamber d = 6307.6 m, radius of magma chamber α = 1098.6 m and pressure change ΔP ≈ 1.0 MPa.

  18. Geologic evidence for a magma chamber beneath Newberry Volcano, Oregon

    SciTech Connect

    Macleod, N.S.; Sherrod, D.R.

    1988-09-10

    At Newberry Volcano, central Oregon, more than 0.5 m.y. of magmatic activity, including caldera collapse and renewed caldera-filling volcanism, has created a structural and thermal chimney that channels magma ascent. Holocene rhyolitic eruptions (1) have been confined mainly within the caldera in an area 5 km in diameter, (2) have been very similar in chemical composition, phenocryst mineralogy, and eruptive style, and (3) have occurred as recently as 1300 years ago, with repose periods of 2000--3000 years between eruptions. Holocene basaltic andesite eruptions are widespread on the flanks but are excluded from the area of rhyolitic volcanism. Basaltic andesite in fissures at the edge of the rhyolite area has silicic inclusions and shows mixed basalt-rhyolite magma relations. These geologic relations and the high geothermal gradient that characterizes the lower part of a drill hole in the caldera (U.S. Geological Survey Newberry 2) indicate that a rhyolitic magma chamber has existed beneath the caldera throughout the Holocene. Its longevity probably is a result of intermittent underplating by basaltic magma.

  19. Physical constraints of the evolution of felsic magma chambers: implications for the evolution of granite magmas

    NASA Astrophysics Data System (ADS)

    Bea, F.

    2012-04-01

    Igneous petrologist working on mafic magmas generally agree that magmas are stored and frac-tionated in crustal reservoirs called magma chambers. The current fashion among granite petrologist, on the other hand, is to minimize the importance of such reservoirs assuming that the huge granite bodies found in many crustal segments grew incrementally, due to the sequential addition of small magma batches. This idea is mostly based on the existence of cryptic contacts and isotope heterogenities inside a single pluton. However, these features can be as well explained by the crystallization dynamics of a viscous magma filling a km sized magma chamber, which is additionally consistent with field evidence. Magma chambers are transient structures that change by loosing and replenishment of magma and volatiles, that but also evolve as a whole due to the crystallization dynamics induced by cooling. The evolution of a given magma chamber depends on the ratios between (1) the rates of magma extraction/replenishment and (2) heat loss. To understand the complexity of magma chamber evolution, here we studied the evolution of an isolated magma chamber (no extraction/replenishment) during cooling, by coupling an internally consistent rheological dataset with the laws of fluids dynamics and heat transfer. Without regional stress, the evolution of the magma is dominated by top-down convection due to negative density gradient in the upper part of the body caused by crystallization. If the melt density is so low that permits fast melt-crystal segregation, the above-described mechanism is inhibited, and melt diapirs formed in the lower crystallizing zone can detach and ascend through the magma chamber producing so differentiation. Convective heat-loss leads most of the magma chamber to critical crystallinity in a few thousands years, which stops all magmatic dynamics except residual melt extraction due either to gravity-driven compaction, which produces short-range differentiation series

  20. Forecasting magma-chamber rupture at Santorini volcano, Greece

    NASA Astrophysics Data System (ADS)

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-10-01

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011-2012 unrest period, that the measured 0.02% increase in volume of Santorini’s shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano.

  1. Forecasting magma-chamber rupture at Santorini volcano, Greece.

    PubMed

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-10-28

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011-2012 unrest period, that the measured 0.02% increase in volume of Santorini's shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano.

  2. Forecasting magma-chamber rupture at Santorini volcano, Greece

    PubMed Central

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-01-01

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011–2012 unrest period, that the measured 0.02% increase in volume of Santorini’s shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano. PMID:26507183

  3. Forecasting magma-chamber rupture at Santorini volcano, Greece.

    PubMed

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-01-01

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011-2012 unrest period, that the measured 0.02% increase in volume of Santorini's shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano. PMID:26507183

  4. Evidence for magma mixing within the Laacher See magma chamber (East Eifel, Germany)

    USGS Publications Warehouse

    Worner, G.; Wright, T.L.

    1984-01-01

    The final pyroclastic products of the late Quaternary phonolitic Laacher See volcano (East Eifel, W.-Germany) range from feldspar-rich gray phonolite to dark olivine-bearing rocks with variable amounts of feldspar and Al-augite megacrysts. Petrographically and chemically homogeneous clasts occur along with composite lapilli spanning the compositional range from phonolite (MgO 0.9%) to mafic hybrid rock (MgO 7.0%) for all major and trace elements. Both a basanitic and a phonolitic phenocryst paragenesis occur within individual clasts. The phonolite-derived phenocrysts are characterized by glass inclusions of evolved composition, rare inverse zoning and strong resorption indicating disequilibrium with the mafic hybrid matrix. Basanitic (magnesian) clinopyroxene and olivine, in contrast, show skeletal (normally zoned) overgrowths indicative of post-mixing crystallization. In accord with petrographical and other chemical evidence, mass balance calculations suggest mixing of an evolved Laacher See phonolite containing variable amounts of mineral cumulates and a megacryst-bearing basanite magma. Magma mixing occurred just prior to eruption (hours) of the lowermost magma layer of the Laacher See magma chamber but did not trigger the volcanic activity. ?? 1984.

  5. Modeling the Temporal Evolution of the Magma Chamber at Mount Hood (Oregon, USA)

    NASA Astrophysics Data System (ADS)

    Degruyter, W.; Huber, C.; Cooper, K. M.; Kent, A. J.

    2014-12-01

    The evolution of shallow magma reservoirs is complex as new mass is added intermittently and phase proportions (crystals, melt and bubbles) vary because of cooling or mass removal (eruptions). One requirement for eruptions to occur is that the crystal content during storage is low enough (< 0.4-0.6) such that the magma is mobile. Thermal modeling and geochemical data suggest these chambers are mobile only a very small fraction of their lifetime. Data from uranium-series disequilibria, crystal size distributions, and zoning of trace elements in crystals collected at Mount Hood (Oregon, USA) provide constraints on the thermal evolution of this system over the past 21 kyrs years and suggest <10% of this time the magma was mobile. This system also produced at least 3 significant eruptions over the last 10 kyrs based on the stratigraphic record (~220 and ~1500, and ~7700 years ago). Here we investigate the physical conditions of an open-system magma chamber that are in agreement with the thermal history inferred from the crystal record and with the eruption sequence. What are the magma recharge fluxes that are required to keep a system such as Mount Hood active but predominantly crystal-rich over the last 21 kyrs and what combination of processes produces the observed eruption frequency? To answer these questions we use an idealized magma chamber model to solve for the evolution of the thermodynamical state of the chamber (pressure, temperature, gas and crystal content) as new magma is injected into the chamber. Heat is lost to the surrounding colder crust, which responds visco-elastically to the pressure accumulated during recharge and volatile exsolution. If the crystal volume fraction is lower than 0.5 and chamber overpressure reaches 20 MPa we assume an eruption occurs. We analyze what type of injection (constant, periodic, magma lensing), injection rate, and magma chamber volume yields trends consistent with the timescales found at Mount Hood.

  6. A simplified model to tie magma chamber evolution to eruption frequency

    NASA Astrophysics Data System (ADS)

    Degruyter, W.; Huber, C.

    2013-12-01

    Whether a magma body is able to produce eruptions and at what frequency remains a challenging problem in volcanology as it involves the non-linear interplay of different processes acting over different time scales. Due to their complexity they are often considered independently in spite of their coupled nature. Here we consider a simplified model that focuses on the evolution of the thermodynamical state of the chamber (pressure, temperature, gas and crystal content) as new magma is injected into the chamber. The crust heats up in contact with the magma chamber and is allowed to respond visco-elastically to the stress accumulated during recharge and volatile exsolution. The magma is considered eruptible if the crystal volume fraction is smaller than 0.5. If a critical overpressure is reached mass is released from the magma chamber in the form of dikes until the lithostatic pressure is recovered. Using scaling of dike propagation and thermal viability arguments, we assess whether the released mass can reach the surface or remains intruded in the crust. Our model also includes passive degassing, which is parameterized as a multiphase porous flow model that becomes active when the crystal fraction exceeds 0.5 and the fluid volume fraction of exsolved volatiles exceeds 0.2 (percolation threshold). Using this model, we study the effect of various scenarios for the magma recharge on the periodicity of eruptions, the volume of magma erupted (and its gas and crystal content), and whether the magma in the reservoir is headed to form eruptions or plutons. These recharge scenarios include (i) constant injection, (ii) periodic injection, and (iii) magmatic lensing through which magma chamber overpressure increases injection rate due to dike focusing. The modularity and the simplicity of the model allow for rapid calculations and offer the flexibility to add different and sometimes competing processes and test their influence on the evolution of the magma reservoir.

  7. Magma-driven subcritical crack growth and implications for dike initiation from a magma chamber

    NASA Astrophysics Data System (ADS)

    Chen, Zuan; Jin, Z.-H.

    2006-10-01

    The purpose of this paper is to explore a viscoelastic energy dissipation theory for subcritical dike growth from a magma chamber. The theoretical relationship between the dike growth velocity and dike length is established using the viscoelastic subcritical crack growth theory proposed by the first author and the solutions of stress intensity factor at the crack tip derived by a perturbation method. Effects of magma chamber over-pressure, buoyancy and viscoelastic properties of the host rock on the subcritical growth rate are included in the model. The numerical results indicate that the viscous energy dissipation of the host rock could allow a short dike to slowly grow on the order of 10-7-10-5 m/s under modest over-pressure and to accelerate when the stress intensity factor increases close to the fracture toughness, followed by the unstable dike propagation. The proposed theory provides a reasonable understanding of dike initiation process from a magma chamber.

  8. Seismic Structure of the Endeavour Segment, Juan de Fuca Ridge: Correlations of Crustal Magma Chamber Properties With Seismicity, Faulting, and Hydrothermal Activity

    NASA Astrophysics Data System (ADS)

    van Ark, E. M.; Detrick, R. S.; Canales, J. P.; Carbotte, S. M.; Diebold, J. B.; Harding, A.; Kent, G.; Nedimovic, M. R.; Wilcock, W. S.

    2003-12-01

    Multichannel seismic reflection data collected in July 2002 at the RIDGE2000 Integrated Studies Site at the Endeavour segment, Juan de Fuca Ridge show a high-amplitude, mid-crustal reflector underlying all of the known hydrothermal vent fields at this segment. This reflector, which has been identified with a crustal magma body [Detrick et al., 2002], is found at a two-way travel time of 0.85-1.5 s (1.9-4.0 km) below the seafloor and extends approximately 25 km along axis although it is only 1-2 km wide on the cross-axis lines. The reflector is shallowest (2.5 km depth on the along-axis line) beneath the central, elevated part of the Endeavour segment and deepens toward the segment ends, with a maximum depth of 4 km. The cross axis lines show the mid-crustal reflector dipping from 9 to 50? to the east with the shallowest depths under the ridge axis and greater depths under the eastern flank of the ridge. The amplitude-offset behavior of this mid-crustal axial reflector is consistent with a negative impedance contrast, indicating the presence of melt or a crystallizing mush. We have constructed partial offset stacks at 2-3 km offset to examine the variation of melt-mush content of the axial magma chamber along axis. We see a decrease in P-wave amplitudes with increasing offset for the mid-crustal reflector beneath the Mothra and Main Endeavour vent fields and between the Salty Dawg and Sasquatch vent fields, indicating the presence of a melt-rich body. Beneath the High Rise, Salty Dawg, and Sasquatch vent fields P-wave amplitudes vary little with offset suggesting the presence of a more mush-rich magma chamber. Hypocenters of well-located microseismicity in this region [Wilcock et al., 2002] have been projected onto the along-axis and cross-axis seismic lines, revealing that most axial earthquakes are concentrated in a depth range of 1.5 - 2.7 km, just above the axial magma chamber. In general, seismicity is distributed diffusely within this zone indicating thermal

  9. Efficiency of differentiation in the Skaergaard magma chamber

    NASA Astrophysics Data System (ADS)

    Tegner, C.; Lesher, C. E.; Holness, M. B.; Jakobsen, J. K.; Salmonsen, L.; Humphreys, M.; Thy, P.

    2011-12-01

    Although it is largely agreed that crystallization occurs inwardly in crystal mushes along the margins of magma chambers, the efficiency and mechanisms of differentiation are not well constrained. The fractionation paradigm hinges on mass exchange between the crystal mush and the main magma reservoir resulting in coarse-grained, refractory (cumulate) rocks of primary crystals, and complementary enrichment of incompatible elements in the main reservoir of magma. Diffusion, convection, liquid immiscibility and compaction have been proposed as mechanisms driving this mass exchange. Here we examine the efficiency of differentiation in basaltic crystal mushes in different regions of the Skaergaard magma chamber. The contents of incompatible elements such as phosphorus and calculated residual porosities are high in the lowermost cumulate rocks of the floor (47-30%) and decrease upsection, persisting at low values in the uppermost two-thirds of the floor rock stratigraphy (~5% residual porosity). The residual porosity is intermediate at the walls (~15%) and highest and more variable at the roof (10-100%). This is best explained by compaction and expulsion of interstitial liquid from the accumulating crystal mush at the floor and the inefficiency of these processes elsewhere in the intrusion. In addition, the roof data imply upwards infiltration of interstitial liquid. Remarkably uniform residual porosity of ~15% for cumulates formed along the walls suggest that their preservation is related to the rheological properties of the mush, i.e. at ≤ 15% porosity the mush is rigid enough to adhere to the wall, while at higher porosity it is easily swept away. We conclude that the efficiency of compaction and differentiation can be extremely variable along the margins of magma chambers. This should be taken into account in models of magma chamber evolution.

  10. Finite difference seismic modeling of axial magma chambers

    SciTech Connect

    Swift, S.A.; Dougherty, M.E.; Stephen, R.A. )

    1990-11-01

    The authors tested the feasibility of using finite difference methods to model seismic propagation at {approximately}10 Hx through a two-dimensional representation of an axial magma chamber with a thin, liquid lid. This technique produces time series of displacement or pressure at seafloor receivers to mimic a seismic refraction experiment and snapshots of P and S energy propagation. The results indicate that the implementation is stable for models with sharp velocity contrasts and complex geometries. The authors observe a high-energy, downward-traveling shear phase, observable only with borehole receivers, that would be useful in studying the nature and shape of magma chambers. The ability of finite difference methods to model high-order wave phenomena makes this method ideal for testing velocity models of spreading axes and for planning near-axis drilling of the East Pacific Rise in order to optimize the benefits from shear wave imaging of sub-axis structure.

  11. The influence of magma viscosity on convection within a magma chamber

    NASA Astrophysics Data System (ADS)

    Schubert, M.; Driesner, T.; Ulmer, P.

    2012-12-01

    Magmatic-hydrothermal ore deposits are the most important sources of metals like Cu, Mo, W and Sn and a major resource for Au. It is well accepted that they are formed by the release of magmatic fluids from a batholith-sized magma body. Traditionally, it has been assumed that crystallization-induced volatile saturation (called "second boiling") is the main mechanism for fluid release, typically operating over thousands to tens of thousands of years (Candela, 1991). From an analysis of alteration halo geometries caused by magmatic fluids, Cathles and Shannon (2007) suggested much shorter timescales in the order of hundreds of years. Such rapid release of fluids cannot be explained by second boiling as the rate of solidification scales with the slow conduction of heat away from the system. However, rapid fluid release is possible if convection is assumed within the magma chamber. The magma would degas in the upper part of the magma chamber and volatile poor magma would sink down again. Such, the rates of degassing can be much higher than due to cooling only. We developed a convection model using Navier-Stokes equations provided by the computational fluid dynamics platform OpenFOAM that gives the possibility to use externally derived meshes with complex (natural) geometries. We implemented a temperature, pressure, composition and crystal fraction dependent viscosity (Ardia et al., 2008; Giordano et al., 2008; Moore et al., 1998) and a temperature, pressure, composition dependent density (Lange1994). We found that the new viscosity and density models strongly affect convection within the magma chamber. The dependence of viscosity on crystal fraction has a particularly strong effect as the steep viscosity increase at the critical crystal fraction leads to steep decrease of convection velocity. As the magma chamber is cooling from outside to inside a purely conductive layer is developing along the edges of the magma chamber. Convection continues in the inner part of the

  12. Modeling the compositional evolution of recharging, evacuating, and fractionating (REFC) magma chambers: Implications for differentiation of arc magmas

    NASA Astrophysics Data System (ADS)

    Lee, Cin-Ty A.; Lee, Tien Chang; Wu, Chi-Tang

    2014-10-01

    Equations are presented to describe the compositional evolution of magma chambers undergoing simultaneous recharge (R), evacuation (E), and fractional crystallization (FC). Constant mass magma chambers undergoing REFC will eventually approach a steady state composition due to the “buffering” effect of recharging magma. Steady state composition is attained after ∼3/(Dαx + αe) overturns of the magma chamber, where D is the bulk solid/melt partition coefficient for the element of interest and αx and αe are the proportions of crystallization and eruption/evacuation relative to the recharge rate. Steady state composition is given by Cre/(Dαx + αe). For low evacuation rates, steady state concentration and the time to reach steady state scale inversely with D. Compatible (D > 1) elements reach steady state faster than incompatible (D < 1) elements. Thus, magma chambers undergoing REFC will eventually evolve towards high incompatible element enrichments for a given depletion in a compatible element compared to magma chambers undergoing pure fractional crystallization. For example, REFC magma chambers will evolve to high incompatible element concentrations for a given MgO content compared to fractional crystallization. Not accounting for REFC will lead to over-estimation of the incompatible element content of primary magmas. Furthermore, unlike fractional crystallization alone, REFC can efficiently fractionate highly incompatible element ratios because the fractionation effect scales with the ratio of bulk D's. By contrast, in pure fractional crystallization, ratios fractionate according to the arithmetic difference between the bulk D's. The compositional impact of REFC should be most pronounced for magma chambers that are long-lived, have low rates of eruption/evacuation, and/or are characterized by high recharge rates relative to the mass of the magma chamber. The first two conditions are likely favored in deep crustal magma chambers where confining pressures

  13. Buoyancy-driven convection and mixing in magma chambers - the case of Phlegraean Fields caldera

    NASA Astrophysics Data System (ADS)

    Montagna, Chiara P.; Longo, Antonella; Bagagli, Matteo; Papale, Paolo

    2016-04-01

    Ascent of primitive magmas from depth into shallow, partially degassed reservoirs is commonly assumed to be a viable eruption trigger. At Phlegraean Fields (Southern Italy), processes of convection and mixing have been identified as taking an active part both in pre- and syn-eruptive stages in many eruptions of different size. We performed numerical simulations of magma chamber replenishment referring to an archetypal case whereby a shallow, small magma chamber containing degassed phonolite is invaded by volatile-rich shoshonitic magma coming from a deeper, larger reservoir. The system evolution is solely driven by buoyancy, as the magma entering the shallower chamber is less dense than the degassed, resident phonolite. The evolution in space and time of physical quantities such as pressure, gas content and density is highly heterogeneous; nonetheless, an overall decreasing exponential trend in time can be observed and characterizes the whole process. The same exponentially decreasing trend can be observed in the amplitude of the ground deformation signals (seismicity over the whole frequency spectrum) calculated from the results of the magmatic dynamics. Exponential decay in the efficiency of the mixing process has been also observed experimentally, albeit on much smaller length and time scales (Morgavi et al., Contrib. Min. Petr. 2013). Depending on the initial and boundary conditions explored, such as chamber geometry or density contrast, the time constant thus the duration of the process can vary. Independently, the evolution of pressure in the magmatic system also depends on the initial and boundary conditions, leading either to eruption-favourable conditions or not. Relating the time scales for convective processes to be effective with their outcomes in terms of stresses at the chamber boundaries can substantially improve our ability to forecast eruptions at volcanoes worldwide.

  14. Magma Chamber Dynamics Recorded by Mineral Disequilibrium. Evidences and Questions.

    NASA Astrophysics Data System (ADS)

    Wagner, C.; Deloule, E.

    2004-05-01

    Clinopyroxenes (cpx) are one of the phases commonly used for tracing shallow-level processes in magma reservoirs. They are likely phases to constrain and record the magmatic evolution, as they are liquidus phases over a wide range of temperature and composition, and incorporate trace elements in sufficient amounts to be analysed. We discuss here the potentiality and limits for reconstructing magma chamber dynamics from a study of disequilibrium cpx assemblages from alkaline rocks from North Morocco. Cpx are Al-rich diopside and salite enriched in incompatible elements. Salite and diopside occur indifferently as resorbed cores or rims, and their respective composition is identical in both cases. The Al distribution between octahedral and tetrahedral sites shows that cores and rims follow a trend of low-pressure origin. This supports shallow-level crystallization for all cpx, including the cores, which then do not represent xenocrysts extracted from the wall-rock during ascent. The heterogeneous cpx population may result from : 1) a thermally and compositionally zoned reservoir in which salite crystallized from the mush layer (T = 950oC) and diopside from the main magma body (T = 1150oC). Residence times of 1 to 15 years have been estimated for cores and rims respectively, constraining the movement of the cpx in and out of the mush layer. 2) mixing processes: as both diopside and salite cores are present, mixing must have occurred subsequent the crystallization of both types of cpx in their respective magmas. Oscillatory zoning of diopsidic and salitic compositions suggests repeated mixing episodes (up to four cycles of crystallization interrupted by episodes of mixing between more or less evolved melts). Different scenarii will be proposed. Particularly, we discuss the importance of crystal-chemical controls (crystal lattice model) and liquid composition/structure on partitioning of some elements (HFSE, REE, Sr) between cpx and melt for using with confidence the cpx

  15. Snapshots from deep magma chambers: decoding field observations

    NASA Astrophysics Data System (ADS)

    De Campos, Cristina P.

    2014-05-01

    During the post-orogenic stage of a Neoproterozoic orogen (Araçuaí-West Congo), inversely zoned calc-alkaline to alkaline plutonic structures intruded previous geologic units. Structural measurements, mapping of flow patterns and additional geochemical and isotopic data point towards different compositional domains which have been generated during a time span between 20 to 30 Ma. The result from decades of mapping revealed the architecture of ca. 10 large plutons in more détail. This work will focus on the dynamics of magmatic interaction for six different plutons ranging from c.20 to 200 km2 in outcropping area. Conclusions are based on already published and new unpublished data aiming the state of the art. In the silica-richer structures concentric fragmented and folded layers of granite in a K-basaltic matrix contrast with predominant more homogeneous K-basaltic to gabbroic regions. These may be separated by stretched filament regions (magmatic shear zones) where mixing has been enhanced resulting in hybrid compositions. Locally sharp and pillow-like contacts between granitic and K-basaltic rocks depict a frozen-in situation of different intrusive episodes. In the silica-poorer plutonic bodies gradational contacts are more frequent and may be the result of convection enhanced diffusion. For all plutons, however, mostly sub-vertical internal contacts between most- and least-differentiated rocks suggest generation from predominat large magma bodies of variable composition which crystallized while crossing the middle to lower crust (< 25 km depth). They have been catch in the act on their way up. Accordingly mushroom- to funnel-like magma-chambers and/or conduits could register snapshots of the interaction dynamics between granitic and noritic/dioritic or syeno-monzonitic and gabbroic magmas. Different compositional domains within different plutons suggest distinct kinematics. Nevertheless all studied plutons provide outstanding evidence for mixing, not only

  16. A model for the origin of large silicic magma chambers: precursors of caldera-forming eruptions

    SciTech Connect

    Jellinek, A. Mark; DePaolo, Donald J.

    2002-01-02

    The relatively low rates of magma production in island arcs and continental extensional settings require that the volume of silicic magma involved in large catastrophic caldera-forming (CCF) eruptions must accumulate over periods of 10(5) to 10(6) years. We address the question of why buoyant and otherwise eruptible high silica magma should accumulate for long times in shallow chambers rather than erupt more continuously as magma is supplied from greater depths. Our hypothesis is that the viscoelastic behavior of magma chamber wall rocks may prevent an accumulation of overpressure sufficient to generate rhyolite dikes that can propagate to the surface and cause an eruption. The critical overpressure required for eruption is based on the model of Rubin (1995a). An approximate analytical model is used to evaluate the controls on magma overpressure for a continuously or episodically replenished spherical magma chamber contained in wall rocks with a Maxwell viscoelastic rheology. The governing parameters are the long-term magma supply, the magma chamber volume, and the effective viscosity of the wall rocks. The long-term magma supply, a parameter that is not typically incorporated into dike formation models, can be constrained from observations and melt generation models. For effective wall-rock viscosities in the range 10(18) to 10(20) Pa s(-1), dynamical regimes are identified that lead to the suppression of dikes capable of propagating to the surface. Frequent small eruptions that relieve magma chamber overpressure are favored when the chamber volume is small relative to the magma supply and when the wall rocks are cool. Magma storage, leading to conditions suitable for a CCF eruption, is favored for larger magma chambers (>10(2) km(3)) with warm wall rocks that have a low effective viscosity. Magma storage is further enhanced by regional tectonic extension, high magma crystal contents, and if the effective wall-rock viscosity is lowered by microfracturing, fluid

  17. Stoping of chamber margins into mafic intrusions: Magma mingling at Soufriere Hills volcano, Montserrat

    NASA Astrophysics Data System (ADS)

    Genareau, Kimberly; Clarke, Amanda B.

    2010-05-01

    . This range safely brackets the temperature required for quartz precipitation at equivalent pressures (less than 825 ° C). Within the groundmass, no pyroxene microlites are visible, suggesting a crystallization pressure of more than 100 MPa, based upon decompression experiments on a representative magma. Additionally, plagioclase phenocrysts show no obvious zoning in their anorthite compositions as would result from ascent through the conduit. SEM X-ray element maps reveal percolation of calcium-rich melt into the margins of zone A, suggesting sustained contact between this silicic inclusion and the intruding mafic magma that resulted in isolation and heating of a stoped chamber margin. The characteristics of this single tephra sample suggest that magma mingling at Soufrière Hills may not only result from disaggregation of mafic inclusions during transport through the conduit, but also from stoping of the crystallized chamber margins into the intruding mafic magma. The more mafic portions of the erupted clast display high vesicularity, indicating that a volatile-rich portion of the mafic intrusion (perhaps a foam layer at the mafic/resident magma interface) ascended or convected into the chamber and incorporated portions of the chamber margins 37-78 days prior to the July 2003 dome collapse. Although initial examination of the tephra in hand sample shows evidence of oxidation typically attributed to sustained residence in the lava dome, in some cases this oxidation may actually result from heating within the system prior to ascent through the conduit. Thus, effects of mafic magma intrusion at Soufrière Hills may not only involve heating of the resident magma, but also disaggregation and incorporation of stoped chamber margins, indicating another possible method of magma mingling at this active volcano.

  18. Utilising Geological Field Measurements and Historic Eruption Volumes to Estimate the Volume of Santorini's Magma Chamber

    NASA Astrophysics Data System (ADS)

    Browning, J.; Drymoni, K.; Gudmundsson, A.

    2015-12-01

    An understanding of the amount of magma available to supply any given eruption is useful for determining the potential eruption magnitude and duration. Geodetic measurements and inversion techniques are often used to constrain volume changes within magma chambers, as well as constrain location and depth, but such models are incapable of calculating total magma storage. For example, during the 2012 unrest period at Santorini volcano, approximately 0.021 km3 of new magma entered a shallow chamber residing at around 4 km below the surface. This type of event is not unusual, and is in fact a necessary condition for the formation of a long-lived shallow chamber, of which Santorini must possess. The period of unrest ended without culminating in eruption, i.e the amount of magma which entered the chamber was insufficient to break the chamber and force magma further towards the surface. We combine previously published data on the volume of recent eruptions at Santorini together with geodetic measurements. Measurements of dykes within the caldera wall provide an estimate of the volume of magma transported during eruptions, assuming the dyke does not become arrested. When the combined volume of a dyke and eruption are known (Ve) they can be used to estimate using fracture mechanics principles and poro-elastic constraints the size of an underlying shallow magma chamber. We present field measurements of dykes within Santorini caldera and provide an analytical method to estimate the volume of magma contained underneath Santorini caldera. In addition we postulate the potential volume of magma required as input from deeper sources to switch the shallow magma chamber from an equilibrium setting to one where the pressure inside the chamber exceeds the surrounding host rocks tensile strength, a condition necessary to form a dyke and a possible eruption.

  19. Time Evolution of Thermo-Mechanically and Chemically Coupled Magma Chambers

    NASA Astrophysics Data System (ADS)

    Ozimek, C.; Karlstrom, L.; Erickson, B. A.

    2015-12-01

    Complexity in the volcanic eruption cycle reflects time variation both of magma inputs to the crustal plumbing system and of crustal melt storage zones (magma chambers). These data include timing and volumes of eruptions, as well as erupted compositions. Thus models must take into account the coupled nature of physical attributes. Here we combine a thermo-mechanical model for magma chamber growth and pressurization with a chemical model for evolving chamber compositions, in the limit of rapid mixing, to study controls on eruption cycles and compositions through time. We solve for the mechanical evolution of a 1D magma chamber containing melt, crystals and bubbles, in a thermally evolving and viscoelastic crust. This pressure and temperature evolution constrains the input values of a chemical box model (Lee et al., 2013) that accounts for recharge, eruption, assimilation and fractional crystallization (REAFC) within the chamber. We plan to study the influence of melt supply, input composition, and chamber depth eruptive fluxes and compositions. Ultimately we will explore multiple chambers coupled by elastic-walled dikes. We expect that this framework will facilitate self-consistent inversion of long-term eruptive histories in terms of magma transport physics. Lee, C.-T. A., Lee, T.-C., Wu, C.-T., 2013. Modeling the compositional evolution of recharging, evacuating, and fractionating (REFC) magma chambers: Implications for differentiationof arc magmas. Geochemica Cosmochimica Acta, http://dx.doi.org/10.1016/j.gca.2013.08.009.

  20. Upward migration of Vesuvius magma chamber over the past 20,000 years.

    PubMed

    Scaillet, B; Pichavant, M; Cioni, R

    2008-09-11

    Forecasting future eruptions of Vesuvius is an important challenge for volcanologists, as its reawakening could threaten the lives of 700,000 people living near the volcano. Critical to the evaluation of hazards associated with the next eruption is the estimation of the depth of the magma reservoir, one of the main parameters controlling magma properties and eruptive style. Petrological studies have indicated that during past activity, magma chambers were at depths between 3 and 16 km (refs 3-7). Geophysical surveys have imaged some levels of seismic attenuation, the shallowest of which lies at 8-9 km depth, and these have been tentatively interpreted as levels of preferential magma accumulation. By using experimental phase equilibria, carried out on material from four main explosive events at Vesuvius, we show here that the reservoirs that fed the eruptive activity migrated from 7-8 km to 3-4 km depth between the ad 79 (Pompeii) and ad 472 (Pollena) events. If data from the Pomici di Base event 18.5 kyr ago and the 1944 Vesuvius eruption are included, the total upward migration of the reservoir amounts to 9-11 km. The change of preferential magma ponding levels in the upper crust can be attributed to differences in the volatile content and buoyancy of ascending magmas, as well as to changes in local stress field following either caldera formation or volcano spreading. Reservoir migration, and the possible influence on feeding rates, should be integrated into the parameters used for defining expected eruptive scenarios at Vesuvius.

  1. Styles of zoning in central Andean ignimbrites - Insights into magma chamber processes

    NASA Technical Reports Server (NTRS)

    De Silva, S. L.

    1991-01-01

    Data are presented showing that calc-alkaline high-K ignimbrites from the Altiplano-Puna Volcanic Complex of the Central Volcanic Zone of the Andes, showing a variety of compositional zonations. The characteristics of the juvenile material from the zoned and heterogenous ignimbrites suggest that crystallization of the observed phenocrysts occurred in prezoned magma chambers consisting of two or more layers. It is suggested that the width/height ratio of a magma chamber plays a critical role in the control of the style of zonation that may develop in a closed magma chamber.

  2. A Ground Deformation Monitoring Approach to Understanding Magma Chamber Systems and Eruptive Cycles of Mount Cameroon

    NASA Astrophysics Data System (ADS)

    Riley, S.; Clarke, A.

    2005-05-01

    Mount Cameroon is a 13,400ft basanite volcano on the passive margin of West Africa. It has erupted seven times in the past century making it one of the most active volcanoes in Africa. Most recently Mount Cameroon erupted in 1999 and 2000 first issuing strombolian explosions from vents near the summit, and later erupting effusively from a fissure running southwest from the summit (Suh et al., 2003). Prior to 2004, the only monitoring equipment on Mount Cameroon was a small seismometer network installed following the 1982 eruption. By 1999 only a single seismometer in the network was functional. Seismic activity did not rise above background levels until the few days immediately preceding the eruption. In an effort to raise awareness of the volcano's condition and provide a more efficient warning of impending eruptions we have begun constructing a ground deformation network on Mount Cameroon. The new network currently consists of two Applied Geomechanics 711-2A(4X) biaxial tiltmeters capable of resolving 0.1 microradians of tilt. One station is located approximately 500 m from the 2000 summit vent, and the other is approximately 1km away from the central fissure approximately 5km southwest of the 2000 summit vent. Three primary processes could precede eruptions at Mt. Cameroon, offering the opportunity for detection and prediction by our network. These processes are magma chamber pressurization, magma ascent via a central conduit, and/or propagation of magma along the central fissure. Magma chamber location, if a significant chamber exists, is poorly constrained, however, previous petrologic studies on Mount Cameroon (Suh et al., 2003; Fitton et al., 1983) suggest Mount Cameroon magmas originate at a depth less than 40km. Published seismic data (Ambeh, 1989) contains evidence of magmatic activity and possible chambers at depths ranging from 10km to 70km. Preliminary calculations using a simple Mogi model suggest deformation caused by pressurization of a large

  3. Convective melting in a magma chamber: theory and numerical experiment.

    NASA Astrophysics Data System (ADS)

    Simakin, A.

    2012-04-01

    We present results of the numerical modeling of convective melting in a magma chamber in 2D. Model was pointed on the silicic system approximated with Qz-Fsp binary undersaturated with water. Viscosity was calculated as a function of the melt composition, temperature and crystal content and comprises for the pure melt 104.5-105.5 Pas. Lower boundary was taken thermally insulated in majority of the runs. Size of FEM (bilinear elements) grid for velocity is 25x25 cm and for the integration of the density term 8x8 cm. Melting of the chamber roof proceeds with the heat supply due to the chaotic thermo-compositional convection and conductive heat loose into melted substrate. We compare our numerical data with existing semi-analytical models. Theoretical studies of the assimilation rates in the magma chambers usually use theoretical semi-analytical model by Huppert and Sparks (1988) (e.g., Snyder, 2000). We find that this model has strong points: 1) Independence of the melting rate on the sill thickness (Ra>>Rac) 2) Independence of the convective heat transfer on the roof temperature 3) Determination of the exponential thermal boundary layer ahead of the melting front and weak points: 1) Ignoring the possibility of the crystallization without melting regime for narrow sills and dykes. 2)Neglecting of two-phase character of convection. 3)Ignoring of the strong viscosity variation near the melting front. Independence of convective flux from the sill size (at Ra>>Rac) allows reducing of computational domain to the geologically small size (10-15 m). Concept of exponential thermal boundary layer is also rather important. Length scale (L0) of this layer is related to the melting rate and thermal diffusivity coefficient kT as L0=kT/um and at the melting rate 10 m/yr becomes about 2 m. Such small scale implies that convective melting is very effective (small conductive heat loss) and part of the numerical domain filled with roof rocks can be taken small. In the H&S model

  4. Geophysical Evidence for the Locations, Shapes and Sizes, and Internal Structures of Magma Chambers beneath Regions of Quaternary Volcanism

    NASA Astrophysics Data System (ADS)

    Iyer, H. M.

    1984-04-01

    delineating magma chambers with minimum horizontal and vertical dimensions of about 6 km. This technique has been used successfully to detect low-velocity anomalies, interpreted as magma bodies in the volume range 103-106 km3, in several volcanic centres in the U.S.A. and in Mt Etna, Sicily. Velocity models developed using teleseismic residuals of the Cascades volcanoes of Oregon and California, and Kilauea volcano, Hawaii, do not show appreciable storage of magma in the crust. However, regional models imply that large volumes of parental magma may be present in the upper mantle of these regions. In some volcanic centres, teleseismic delays are accompanied by P-wave attenuation, and linear inversion of spectral data have enabled computation of three-dimensional Q-models for these areas. The use of gravity data for magma chamber studies is illustrated by a study in the Geysers-Clear Lake volcanic field in California, where a strong gravity low has been modelled as a low-density body in the upper crust. This body is approximately in the same location as the low-velocity body delineated with teleseismic delays, and is interpreted as a magma body. In Yellowstone National Park, magnetic field data have been used to map the depth to the Curie isotherm, and the results show that high temperatures may be present at shallow depths beneath the Yellowstone caldera. The main application of electrical techniques in magma-related studies has been to understand the deep structure of continental rifts. Electromagnetic studies in several rift zones of the world provide constraints on the thermal structure and magma storage beneath these regions. Geophysical tools commonly used in resource exploration and earth-structure studies are also suited for the detection of magma chambers. Active seismic techniques, with controlled sources, and passive seismic techniques, with local and regional earthquakes and teleseisms, can be used to detect the drastic changes in velocity and attenuation that occur

  5. Isotopic constraints on open system evolution of the Laacher See magma chamber (Eifel, West Germany)

    NASA Astrophysics Data System (ADS)

    Wörner, G.; Staudigel, H.; Zindler, A.

    1985-09-01

    The Laacher See phonolite tephra sequence (11,000 years B.P.) of the Quaternary East Eifel volcanic field (West Germany) represents an inverted, chemically zoned magma column. Mafic and differentiated phonolites, respectively, represent the lowermost and uppermost erupted portion of the Laacher See magma chamber. Sr and Nd isotopic compositions of whole rocks, matrices and phenocrysts have been analyzed in order to provide constraints for open versus closed system evolution of the Laacher See magma chamber. 87Sr/ 86Sr isotope ratios of mafic phonolites and their phenocrysts are slightly more radiogenic than parental East Eifel basanite magmas. Bulk rock samples show a drastic increase in 87Sr/ 86Sr from mafic towards the most differentiated compositions that were erupted from the top of the magma chamber. Glass matrix separates show a parallel, but less pronounced, increase in 87Sr/ 86Sr . Phenocrysts, in contrast, show a narrow range in 87Sr/ 86Sr with a slight, but significant, increase towards the top of the magma chamber. Phenocrysts from the uppermost portion of the magma column were not in isotopic (or chemical) equilibrium with their host matrices. 143Nd/ 144Nd isotope ratios for whole rocks, matrices, and phenocrysts fall within a restricted range similar to that of East Eifel mafic magmas. A representative suite of crustal rocks (lower crustal granulites, quartzo-feldspathic gneisses, mica schists, Devonian slates and graywacke) was also analyzed in order to permit an evaluation of possible assimilation models. Our results are consistent with chemical evolution of the zoned Laacher See magma chamber mainly through crystal fractionation accompanied by minor amounts of assimilation. Slight contamination of the magma system may have involved (a) the assimilation of gneisses (?) and mica schists during the initial stage of magma chamber evolution (basanite-mafic phonolite), (b) combined assimilation-fractional crystallization (AFC) concurrent with the second

  6. Isotopic Studies of processes in mafic magma chambers: III. The Muskox intrusion, Northwest Territories, Canada

    NASA Astrophysics Data System (ADS)

    Stewart, Brian W.; DePaolo, Donald J.

    We report the results of a neodymium and strontium isotopic investigation of magma sources and magma chamber processes in the Proterozoic Muskox layered mafic intrusion. Our internal Sm-Nd isochron age of 1258±40 Ma from a two-pyroxene gabbro agrees well with previous U-Pb age determinations for the Muskox intrusion and Mackenzie igneous events. The preservation of a pre-Muskox Sm-Nd isochron age in a sample of stoped wall rock has allowed us to place constraints on the duration of the Muskox magma system; models for diffusive equilibration suggest a time scale of 103-104 years for crystallization of the upper 10% of the magma chamber. The liquids injected into the magma chamber had ɛNd(1258 Ma) values in the range of -3 to +1, indicating that they were derived from an undepleted mantle source. Large differences in 87Sr/86Sr and 143Nd/144Nd between the Muskox parent magma and a zone of wall rock-derived silicic magma that existed at the roof of the chamber make these isotopes sensitive indicators of interaction between the components of the system. Modeling of isotopic variations within individual cyclic units (where each cyclic unit represents crystallization of a single influx of magma into the chamber) suggests that the rate of assimilation of silicic wall rock by mafic magma was <5% of the crystallization rate, in spite of the proximity of the basaltic liquid to the overlying molten wall rock. We attribute this lack of significant assimilation to large differences in buoyancy and viscosity between mafic and silicic magmas. Variations in 87Sr/86Sr and 143Nd/144Nd among cyclic units within the layered series most likely resulted from mixing between mafic magma and molten silicic wall rock during injection of new magma pulses, or from variations in the magma source feeding the Muskox intrusion. We suggest that the successive cyclic units moved toward more evolved compositions as the vigor of the magmatic system decreased, allowing increased mixing between new

  7. Magma mixing and degassing processes in the magma chamber of Gorely volcano (Kamchatka): evidence from whole-rock and olivine chemistry.

    NASA Astrophysics Data System (ADS)

    Gavrilenko, M.; Ozerov, A.; Kyle, P. R.; Carr, M. J.; Nikulin, A.

    2015-12-01

    Gorely is a shield-type volcano in southern Kamchatka currently in an eruptive phase [1] with prior eruptions recorded in 1980 and 1984 [4]. It is comprised of three main structural units: ancient (middle Pleistocene) edifice called 'Old-Gorely' volcano; thick ignimbrite complex, associated with a caldera forming eruption (40 ka); modern edifice named 'Young Gorely' growing inside the caldera [6]. Gorely lavas consist of a suite of compositions ranging from basalt to rhyolite (calk-alkaline series).In this study we describe the mixing processes in magma chamber [2] based on analysis of whole-rock and mineralogical data in an attempt to compare the magma evolution pathways for 'Old Gorely' and Young Gorely volcanoes. Our results indicate that fractional crystallization (FC) is the dominant process for 'Old Gorely' magmas, while 'Young Gorely' magmas are the result of mixing of primitive and evolved magmas in Gorely magma chamber], which is located at depth range from 2 to 10 km below the volcano edifice [6]. We present results of olivine high-precision electron microprobe data analysis (20kV, 300 nA) [7], alongside traditional methods (WR diagrams, mineral zonation) to demonstrate the difference between 'Old' (FC) and 'Young' (mixing) Gorely magmas. We estimated magma H2O (~3 wt.%) content for Gorely magma using independent methods: 1) using THI [8]; 2) using ΔT Ol-Pl [3]; 3) using Ol-Sp temperatures [9]. Additionally, calculations of [4] and analysis of olivine chemistry allow us to describe water content changes during magma evolution. We show that degassing (H2O removal) is necessary for strong plagioclase fractionation, which is observed in Gorely evolved lavas (less than 5 wt.% of MgO). [1] Aiuppa et al. (2012), GRL. 39(6): p.L06307. [2] Gorbach & Portnyagin (2011) Petrology, 19(2): p.134-166. [3] Danyushevsky (2001) JVGR, 110(3-4): p.265-280. [4] Kirsanov & Melekescev (1991) Active volcanoes of Kamchatka, v.2: p.294-317. [5] Mironov & Portnyagin (2011

  8. A practical petrological method for the determination of volume proportions of magma chamber refilling

    NASA Astrophysics Data System (ADS)

    Bindeman, Ilya N.

    1993-05-01

    A method is described for determining the proportion of the volume of a magma chamber refilled by new pulses of hot primitive melts. This method is based on the changes is crystal contents and in phenocryst zoning resulting from temperature equilibration. Study of phenocryst zoning and the composition of interstitial glasses from various chilled magmatic inclusions and mafic bands in hybrid rocks supports the idea that equilibration of temperatures between two magmas is reached before their physical mixing. If the magmas are genetically related (for example magma-fractionate and initial hot melt), this leads to equilibration of the compositions of residual melts and phenocrysts rims. Intervals of reverse zoning in minerals, resulting from temperature increases, and intervals of normal zoning, caused by cooling, along with the changes in modal mineral contents enable estimation of the amounts of released and adsorbed heat and, therefore, assessment of the proportion of the volume of each magma. Application of the method to some hybrid volcanic series of the Kurile-Kamchatka island arc shows that the proportion of mafic magma intruded into a siliceous magma chamber reservoir never exceeds 10% of the volume of the host magma, based upon thermal considerations. However, the observed degree of compositional mingling requres 25-50% of the mafic end-member. It is shown that this contradiction is related to flotation of vesiculated magmatic inclusions towards the chamber roof, where they become concentrated near the exit and are further mingled with the host during the eruption (forced convection).

  9. A model for eruption frequency of upper crustal silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Degruyter, W.; Huber, C.

    2014-10-01

    Whether a magma body is able to produce eruptions and at what frequency remains a challenging problem in volcanology as it involves the nonlinear interplay of different processes acting over different time scales. Due to their complexity these are often considered independently in spite of their coupled nature. Here we consider an idealized model that focuses on the evolution of the thermodynamic state of the chamber (pressure, temperature, gas and crystal content) as new magma is injected into the chamber. The magma chamber cools in contact with the crust, which responds viscoelastically to the pressure accumulated during recharge and volatile exsolution. The magma is considered eruptible if the crystal volume fraction is smaller than 0.5. If a critical overpressure is reached, mass is released from the magma chamber until the lithostatic pressure is recovered. The setup of the model allows for rapid calculations that provide the opportunity to test the influence of competing processes on the evolution of the magma reservoir. We show how the frequency of eruptions depends on the timescale of injection, cooling, and viscous relaxation and develop a scaling law that relates these timescales to the eruption frequency. Based on these timescales we place different eruption triggering mechanisms (second boiling, mass injection, and buoyancy) in a coherent framework and evaluate the conditions needed to grow large magma reservoirs.

  10. Building a large magma chamber at Mount Mazama, Crater Lake, Oregon

    NASA Astrophysics Data System (ADS)

    Wright, H. M.; Karlstrom, L.; Bacon, C. R.

    2012-12-01

    Crater Lake caldera, Oregon, a structure produced by the 50 km3 eruption of Mount Mazama ~7.7 ka, is one of only three identified Quaternary calderas in the Cascades volcanic chain (Hildreth 2007). What were the conditions necessary to build a large volume magma chamber capable of producing this caldera-forming eruption at Mount Mazama? Using the well-documented >400,000 year volcanic history at Mazama (Bacon and Lanphere 2006), an approximation of vent locations for each eruptive unit (Bacon 2008), and a compilation of over 900 whole-rock compositions from Mount Mazama and regional volcanic rocks, we examine questions of magma chamber assembly in an active volcanic arc. These questions include: (1) is magmatic input approximately constant in composition between Mazama and regional monogenetic volcanic centers? (2) how did melt evolution differ in the two cases (Mazama vs. regional volcanism)? (3) is there spatiotemporal evidence in eruption data (including eruptive volume and chemistry) for a growing magma chamber at depth? and (4) does stability of that chamber require pre-warming of the surrounding country rock? An assumption of approximately constant major-element composition magmatic input is consistent with observed compositional overlap between basaltic to basaltic andesitic eruptive products at Mount Mazama and its vicinity (within 15 km of the volcano). MELTS modeling (Ghiorso and Sack 1995) from an initial composition of magnesian basaltic andesite of monogenetic Red Cone (erupted at a distance of ~8 km from the climactic vent) is consistent with water-saturated magmatic evolution at relatively shallow depths (<500 MPa, with the caveat that shallow pressure calibration data are largely lacking from MELTS models). Within this pressure range, differences in whole-rock compositions indicate that regional magmatic rocks evolved at shallower depths and/or drier conditions than those at the Mazama center. Observations of eruptive ages, compositions, vent

  11. Caldera subsidence and magma chamber depth of the Olympus Mons volcano, Mars

    NASA Technical Reports Server (NTRS)

    Zuber, M. T.; Mouginis-Mark, P. J.

    1992-01-01

    An axisymmetric finite element model is constructed to calculate elastic stresses in a volcanic edifice to examine the relationship between surface tectonism, caldera subsidence, and the physical characteristics of Olympus Mons' magmatic reservoir. Model results indicate that the surface stress state is not strongly sensitive to the aspect ratio or pressure distribution of the magma chamber, or to the contrast in stiffness between the magma chamber and surroundings, but is strongly dependent on the depth and width of the chamber. A gross similarity is suggested between the configurations of the magmatic plumbing systems of Olympus Mons and several well-studied terrestrial volcanoes such as the Hawaiian shields.

  12. 3D Visualization of "Frozen" Dynamic Magma Chambers in the Duluth Complex, Northeastern Minnesota

    NASA Astrophysics Data System (ADS)

    Peterson, D. M.; Hauck, S. A.

    2005-12-01

    The Mesoproterozoic Duluth Complex and associated intrusions of the Midcontinent Rift in northeastern Minnesota constitute one of the largest, semi-continuous, mafic intrusive complexes in the world, second only to the Bushveld Complex of South Africa. These rocks cover an arcuate area of over 5,000 square kilometers and give rise to two strong gravity anomalies (+50 & +70 mgal) that imply intrusive roots to more than 13 km depth. The geometry of three large mafic intrusions within the Duluth Complex have been modeled by the integration of field mapping and drill hole data with maps of gravity and magnetic anomalies. The igneous bodies include the South Kawishiwi, Partridge River, and Bald Eagle intrusions that collectively outcrop over an area of > 800 square kilometers. The South Kawishiwi and Partridge River intrusions host several billion tons of low-grade Cu-Ni-PGE mineralization near their base, while the geophysical expressions of the Bald Eagle intrusion have the same shape and dimensions as the "bulls eye" pattern of low velocity seismic reflection anomalies along the East Pacific Rise. These anomalies are interpreted to define regions of melt concentrations, i.e., active magma chambers. This suggests that the funnel-shaped Bald Eagle intrusion could be an example of a "frozen" dynamic magma chamber. In support of this analogy we note that the magmatic systems of intracontinental rifts, mid-ocean ridges, extensional regimes in back-arc environments, and ophiolites have a common characteristic: the emplacement of magma in extensional environments, and the common products in all four are varieties of layered intrusions, dikes and sills, and overlying volcanic rocks. 3D visualization of these intrusions is integral to the understanding of the Duluth Complex magmatic system and associated mineralization, and can be used as a proxy for study of similar systems, such as the Antarctic Ferrar dolerites, worldwide.

  13. A numerical method for investigating crystal settling in convecting magma chambers

    NASA Astrophysics Data System (ADS)

    Verhoeven, J.; Schmalzl, J.

    2009-12-01

    Magma chambers can be considered as thermochemically driven convection systems. We present a new numerical method that describes the movement of crystallized minerals in terms of active spherical particles in a convecting magma that is represented by an infinite Prandtl number fluid. The main part focuses on the results we obtained. A finite volume thermochemical convection model for two and three dimensions and a discrete element method, which is used to model granular material, are combined. The new model is validated with floating experiments using particles of different densities and an investigation of single and multiparticle settling velocities. The resulting velocities are compared with theoretical predictions by Stokes's law and a hindered settling function for the multiparticle system. Two fundamental convection regimes are identified in the parameter space that is spanned by the Rayleigh number and the chemical Rayleigh number, which is a measure for the density of the particles. We define the T regime that is dominated by thermal convection. Here the thermal driving force is strong enough to keep all particles in suspension. As the particles get denser, they start settling to the ground, which results in a C regime. The C regime is characterized by the existence of a sediment layer with particle-rich material and a suspension layer with few particles. It is shown that the presence of particles can reduce the vigor of thermal convection. In the frame of a parameter study we discuss the change between the regimes that is systematically investigated. We show that the so-called TC transition fits a power law. Furthermore, we investigate the settling behavior of the particles in vigorous thermal convection, which can be linked to crystal settling in magma chambers. We develop an analytical settling law that describes the number of settled particles against time and show that the results fit the observations from numerical and laboratory experiments.

  14. Shallow magma chamber under the Wudalianchi Volcanic Field unveiled by seismic imaging with dense array

    NASA Astrophysics Data System (ADS)

    Li, Zhiwei; Ni, Sidao; Zhang, Baolong; Bao, Feng; Zhang, Senqi; Deng, Yang; Yuen, David A.

    2016-05-01

    The Wudalianchi Volcano Field (WDF) is a typical intraplate volcano in northeast China with generation mechanism not yet well understood. As its last eruption was around 300 years ago, the present risk for volcano eruption is of particular public interest. We have carried out a high-resolution ambient noise tomography to investigate the location of magma chambers beneath the volcanic cones with a dense seismic array of 43 seismometers and ~ 6 km spatial interval. Significant low-velocity anomalies up to 10% are found at 7-13 km depth under the Weishan volcano, consistent with the pronounced high electrical-conductivity anomalies from previous magnetotelluric survey. We propose these extremely low velocity anomalies can be interpreted as partial melting in a shallow magma chamber with volume at least 200 km3 which may be responsible for most of the recent volcanic eruptions in WDF. Therefore, this magma chamber may pose a serious hazard for northeast China.

  15. Effects of crustal-scale mechanical layering on magma chamber failure and magma propagation within the Venusian lithosphere

    NASA Astrophysics Data System (ADS)

    Le Corvec, Nicolas; McGovern, Patrick J.; Grosfils, Eric B.; Galgana, Gerald

    2015-07-01

    Understanding the connection between shallow subsurface magmatism and related surface expressions provides first-order insight into the volcanic and tectonic processes that shape a planet's evolution. When assessing the role of flexure, previous investigations assumed homogeneous host rock, but planetary lithospheres typically include crust and mantle material, and the mechanical response of a layered lithosphere subjected to flexure may influence both shallow magma reservoir failure and intrusion propagation. To assess the formation of giant radial dike systems, such as those observed on Venus, we create axisymmetric elastic finite element models of a spherical reservoir centered at the contact between stiff, dense mantle overlain by softer, lighter crust. We analyze magma chamber stability, overpressure at rupture, and resulting intrusion types for three distinct environments: lithostatic, upward flexure, and downward flexure. In the lithostatic case, reservoir failure at the crust-mantle contact favors lateral sill injection. In the flexure cases, we observe that failure location depends upon the crust/lithosphere thickness ratio and, at times, will favor radial dike intrusion. Specifically, upward flexure can promote the formation of giant radiating dike swarms, a scenario consistent with a plume-derived origin. Our results present a mechanical explanation for giant radial dike swarm formation, showing that both the stability of magma chambers on Venus and the type of intrusions that form are influenced by lithospheric layering. Furthermore, where dike swarms occur, our approach provides a powerful new way to constrain local crust/mantle layering characteristics within the lithosphere at the time the swarm was forming.

  16. Why does the Size of the Laacher See Magma Chamber and its Caldera Size not go together? - New Findings with regard to Active Tectonics in the East Eifel Volcanic Field

    NASA Astrophysics Data System (ADS)

    Schreiber, Ulrich; Berberich, Gabriele

    2013-04-01

    The East Eifel's early Cenozoic tectonic development is characterized by a main stress field trending in NW-SE direction, causing a re-organisation of postvariscan dextral strike-slip faults in approximately 105° direction, the formation of the tectonic depression of the Neuwieder Basin and small-scale transtension zones. The 105° trending strike-slip faults are staggered in equidistant intervals of several kilometers. This system continues from the Eifel to the North into the Ruhr Carboniferous, where it has been recognized due to the extensive underground coal mining first (Loos et al. 1999). Our recent research on analyses of tectonics in quarries, quartz/ore-dykes, mapping of minerals springs and gas analyses, has revealed a prominent 105° trending strike-slip fault cutting the South of Laacher See ("Laacher See Strike-slip Fault"). Within the Laacher See caldera, the "Laacher See Strike-slip Fault" can be tracked by a wide mofette zone that was mapped with a self-propelled submarine. At present, the "Laacher See Strike-slip Fault" can be tracked from Holzmühlheim in the West, Spessart, Wehrer Kessel, Laacher See, Plaidt to Bad Ems and furthermore to the South-East. Along this direction five intersections points of the "Laacher See Strike-slip Fault" with the Lahn River are documented, creating small-scale mofette fields in the Lahn River. In the Neuwied Basin, near Plaidt, the "Laacher See Strike-slip Fault" is intersected by the NW-SE-trending Ochtendung Fault. Regional strike-slip faults in combination with block rotation and uplift could have provided the voids for the magma chambers of the Wehrer Kessel and the Laacher See Caldera. Holohan et al. (2005) showed in analogue models that regional strike-slip regimes (including Riedel shears, chamber-localised graben fault, and a partial Y-shear) play a decisive role for caldera formation. In the East Eifel tectonic movement rates of active faults are approx. 1 mm/year (Meyer & Stets 2002, Cambell et al

  17. Bubble-crystal aggregates promote magma chamber overturn in arc crust

    NASA Astrophysics Data System (ADS)

    Edmonds, M.; Woods, A. W.; Humphreys, M.

    2014-12-01

    Bubble nucleation in melts occurs preferentially on the surfaces of crystals. Of all phases in oxidized melts, magnetite is most favorable for the heterogeneous nucleation of bubbles owing to the high wetting angles at the bubble-crystal-melt interface. Preservation of such relationships in erupted rocks however, is rare owing to overprinting by decompression-induced degassing, shear and bubble detachment during magma ascent. We present evidence from basaltic enclaves preserved in andesite lavas from Soufriere Hills Volcano, Montserrat, for a spatial association between magnetite and bubbles that we propose is a relict of the bubble nucleation process at depth. The existence of bubble-crystal aggregates means that magnetite crystals will tend to sink more slowly, and bubbles will rise less fast than for the case of single crystals and bubbles. The behavior of bubble-crystal aggregates will be dependent on their bulk density, which depends on the relative proportion by mass of the magnetite and the bubble and the pressure. In deeper chambers, the smaller mass of exsolved volatiles leads to the prediction that many of the bubble-crystal aggregates are dense and so fall to base of the chamber (and the bubbles are wholly or partially resorbed). In shallower chambers, however, the larger volume and mass of exsolved volatiles would tend to promote buoyant aggregate formation. The presence of the aggregates has implications for the mixing/mingling process when mafic magmas underplate crystal-rich evolved magma bodies in the arc crust. For shallow magma chambers the buoyancy of the aggregates in the underplating mafic magma will either cause vapor accumulation at the magma interface and the formation of mafic inclusions rich in magnetite; or the enhanced density of the aggregates may promote magma chamber overturn and mixing of mafic magmas into the andesites bodies. Both processes may be important over different spatial and time-scales. The overturn mechanism may explain

  18. Growing magma chambers control the distribution of small-scale flood basalts.

    PubMed

    Yu, Xun; Chen, Li-Hui; Zeng, Gang

    2015-01-01

    Small-scale continental flood basalts are a global phenomenon characterized by regular spatio-temporal distributions. However, no genetic mechanism has been proposed to explain the visible but overlooked distribution patterns of these continental basaltic volcanism. Here we present a case study from eastern China, combining major and trace element analyses with Ar-Ar and K-Ar dating to show that the spatio-temporal distribution of small-scale flood basalts is controlled by the growth of long-lived magma chambers. Evolved basalts (SiO2 > 47.5 wt.%) from Xinchang-Shengzhou, a small-scale Cenozoic flood basalt field in Zhejiang province, eastern China, show a northward younging trend over the period 9.4-3.0 Ma. With northward migration, the magmas evolved only slightly ((Na2O + K2O)/MgO = 0.40-0.66; TiO2/MgO = 0.23-0.35) during about 6 Myr (9.4-3.3 Ma). When the flood basalts reached the northern end of the province, the magmas evolved rapidly (3.3-3.0 Ma) through a broad range of compositions ((Na2O + K2O)/MgO = 0.60-1.28; TiO2/MgO = 0.30-0.57). The distribution and two-stage compositional evolution of the migrating flood basalts record continuous magma replenishment that buffered against magmatic evolution and induced magma chamber growth. Our results demonstrate that the magma replenishment-magma chamber growth model explains the spatio-temporal distribution of small-scale flood basalts. PMID:26581905

  19. Growing magma chambers control the distribution of small-scale flood basalts

    PubMed Central

    Yu, Xun; Chen, Li-Hui; Zeng, Gang

    2015-01-01

    Small-scale continental flood basalts are a global phenomenon characterized by regular spatio-temporal distributions. However, no genetic mechanism has been proposed to explain the visible but overlooked distribution patterns of these continental basaltic volcanism. Here we present a case study from eastern China, combining major and trace element analyses with Ar–Ar and K–Ar dating to show that the spatio-temporal distribution of small-scale flood basalts is controlled by the growth of long-lived magma chambers. Evolved basalts (SiO2 > 47.5 wt.%) from Xinchang–Shengzhou, a small-scale Cenozoic flood basalt field in Zhejiang province, eastern China, show a northward younging trend over the period 9.4–3.0 Ma. With northward migration, the magmas evolved only slightly ((Na2O + K2O)/MgO = 0.40–0.66; TiO2/MgO = 0.23–0.35) during about 6 Myr (9.4–3.3 Ma). When the flood basalts reached the northern end of the province, the magmas evolved rapidly (3.3–3.0 Ma) through a broad range of compositions ((Na2O + K2O)/MgO = 0.60–1.28; TiO2/MgO = 0.30–0.57). The distribution and two-stage compositional evolution of the migrating flood basalts record continuous magma replenishment that buffered against magmatic evolution and induced magma chamber growth. Our results demonstrate that the magma replenishment–magma chamber growth model explains the spatio-temporal distribution of small-scale flood basalts. PMID:26581905

  20. The origin of a zoned ignimbrite: Insights into the Campanian Ignimbrite magma chamber (Campi Flegrei, Italy)

    NASA Astrophysics Data System (ADS)

    Forni, Francesca; Bachmann, Olivier; Mollo, Silvio; De Astis, Gianfilippo; Gelman, Sarah E.; Ellis, Ben S.

    2016-09-01

    Caldera-forming eruptions, during which large volumes of magma are explosively evacuated into the atmosphere from shallow crustal reservoirs, are one of the most hazardous natural events on Earth. The Campanian Ignimbrite (CI; Campi Flegrei, Italy) represents a classical example of such events, producing a voluminous pyroclastic sequence of trachytic to phonolitic magma that covered several thousands of squared kilometers in the south-central Italy around 39 ka ago. The CI deposits are known for their remarkable geochemical gradients, attributed to eruption from a vertically zoned magma chamber. We investigate the relationships between such chemical zoning and the crystallinity variations observed within the CI pyroclastic sequence by combining bulk-rock data with detailed analyses of crystals and matrix glass from well-characterized stratigraphic units. Using geothermometers and hygrometers specifically calibrated for alkaline magmas, we reconstruct the reservoir storage conditions, revealing the presence of gradients in temperature and magma water content. In particular, we observe a decrease in crystallinity and temperature and an increase in magma evolution and water content from the bottom to the top of the magma chamber. We interpret these features as the result of protracted fractional crystallization leading to the formation of a cumulate crystal mush at the base of the eruptible reservoir, from which highly evolved, crystal-poor, water-rich and relatively cold melts were separated. The extracted melts, forming a buoyant, easily eruptible cap at the top of the magma chamber, fed the initial phases of the eruption, until caldera collapse and eruption of the deeper more crystalline part of the system. This late-erupted, crystal-rich material represents remobilized portions of the cumulate crystal mush, partly melted following hotter recharge. Our interpretation is supported by: 1) the positive bulk-rock Eu anomalies and the high Ba and Sr contents observed in

  1. Pre-eruptive magmatic processes re-timed using a non-isothermal approach to magma chamber dynamics

    NASA Astrophysics Data System (ADS)

    Petrone, Chiara Maria; Bugatti, Giuseppe; Braschi, Eleonora; Tommasini, Simone

    2016-10-01

    Constraining the timescales of pre-eruptive magmatic processes in active volcanic systems is paramount to understand magma chamber dynamics and the triggers for volcanic eruptions. Temporal information of magmatic processes is locked within the chemical zoning profiles of crystals but can be accessed by means of elemental diffusion chronometry. Mineral compositional zoning testifies to the occurrence of substantial temperature differences within magma chambers, which often bias the estimated timescales in the case of multi-stage zoned minerals. Here we propose a new Non-Isothermal Diffusion Incremental Step model to take into account the non-isothermal nature of pre-eruptive processes, deconstructing the main core-rim diffusion profiles of multi-zoned crystals into different isothermal steps. The Non-Isothermal Diffusion Incremental Step model represents a significant improvement in the reconstruction of crystal lifetime histories. Unravelling stepwise timescales at contrasting temperatures provides a novel approach to constraining pre-eruptive magmatic processes and greatly increases our understanding of magma chamber dynamics.

  2. Petrology of the zoned calcalkaline magma chamber of Mount Mazama, Crater Lake, Oregon

    USGS Publications Warehouse

    Druitt, T.H.; Bacon, C.R.

    1989-01-01

    Evolution of the magma chamber at Mount Mazama involved repeated recharge by two types of andesite (high-Sr and low-Sr), crystal fractionation, crystal accumulation, assimilation, and magma mixing (Bacon and Druitt 1988). This paper addresses the modal compositions, textures, mineral chemistry and magmatic temperatures of (i) products of the 6845??50 BP climactic eruption, (ii) blocks of partially fused granitoid wallrock found in the ejecta, and (iii) preclimactic rhyodacitic lavas leaked from the chamber in late Pleistocene and early Holocene time. Immediately prior to the climactic eruption the chamber contained ??? 40 km3 of rhyodacite (10 vol% plag + opx + aug + hb + mt + ilm, ???880?? C) overlying high-Sr andesite and cumulus-crystal mush (28-51 vol% plag + hb ?? opx ?? aug + mt ?? ilm, 880?? to ???950?? C), which in turn overlay low-Sr crystal mush (50-66 vol% plag + opx + aug ?? hb ?? ol + mt + ilm, 890?? to ???950??? C). Despite the well known compositional gap in the ejecta, no thermal discontinuity existed in the chamber. Pre-eruptive water contents of pore liquids in most high-Sr and low-Sr mushes were 4-6 wt%, but on average the high-Sr mushes were slightly richer in water. Although parental magmas of the crystal mushes were andesitic, xenocrysts of bytownite and Ni-rich magnesian olivine in some scoriae record the one-time injection of basalt into the chamber. Textures in ol-bearing scoriae preserve evidence for the reactions ol + liq = opx and ol + aug + liq(+ plag?) = hb, which occurred in andesitic liquids at Mount Mazama. Strontium abundances in plagioclase phenocrysts constrain the petrogenesis of preclimactic and climactic rhyodacites. Phenocryst cores derived from high-Sr and low-Sr magmas have different Sr contents which can be resolved by microprobe. Partition coefficients for plagioclase in andesitic to rhyolitic glasses range from 2 to 7, and increase as glass %SiO2 increases. Evolved Pleistocene rhyodacites (???30-25,000 BP) and

  3. Coupled evolution of magma chambers and flow in conduits during large volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Karlstrom, L.; Manga, M.; Rudolph, M. L.

    2010-12-01

    The largest silicic and mafic volcanic eruptions in the geologic record, Supervolcano and Large Igneous Province (LIP) eruptions, are distinguished by differences in surface emplacement mode, geologic context, magma volatile content, viscosity, and reservoir depth. However, these large eruptions also share several common features. Individual eruptions of both types emplace roughly the same total volume (10^3 - 10^4 km^3) of remarkably homogeneous magma that likely comes from a single reservoir. In addition, they both release large quantities of volatiles, and hence individual eruptions may significantly perturb global climate. We have developed a model that couples conduit flow and magma chamber deformation, allowing us to study both eruption types. Steady, one-dimensional multiphase flow of magma containing crystals, exsolved water, and CO_2 in a cylindrical conduit is coupled to pressure evolution within an ellipsoidal magma chamber beneath a free surface. LIP eruptions are characterized by gas-driven flow of mafic lava that may be sustained past the cessation of chamber overpressure, much like a siphon. Eruptions cease when the yield strength of the country rocks is reached and the (generally Moho-level) chamber or the conduit implodes, resulting in steady discharge and atmospheric volatile loading. In contrast, more shallow silicic lavas such as the Fish Canyon Tuff erupt through rapid mobilization of a long-lived crystal-rich mush. The crystal-rich mush is a yield strength fluid, which we model using the von Mises criterion for mobilization. If the trigger for mobilization of the mush leads directly to eruption, time-progressive yielding due to mass removal results in a fluid magma chamber that grows as the eruption proceeds, until free-surface stresses induce roof collapse and caldera formation. Chamber pressure evolution may be buffered by the mobilization of the mush, maintaining overpressure and high discharge throughout the eruption. This model suggests

  4. Gabbroic xenoliths from the northern Gorda Ridge: implications for magma chamber processes under slow spreading centers

    USGS Publications Warehouse

    Davis, A.S.; Clague, D.A.

    1990-01-01

    Abundant gabbroic xenoliths in porphyritic pillow basalt were dredged from the northern Gorda Ridge. The host lava is a moderately fractionated, normal mid-ocean ridge basalt with a heterogeneous glass rind (Mg numbers 56-60). Other lavas in the vicinity range from near primary (Mg number 69) to fractionated (Mg number 56). On the basis of textures and mineral compositions, the xenoliths are divided into five types. The xenoliths are not cognate to the host lava, but they are genetically related. Chemistry of mineral phases in conjunction with textural features suggests that the xenoliths formed in different parts of a convecting magma chamber that underwent a period of closed system fractionation. The chamber was filled with a large proportion of crystalline mush when new, more primitive, and less dense magma was injected and mixed incompletely with the contents in the chamber, forming the hybrid host lava. -from Authors

  5. Numerical modelling by the Stokes--DEM coupled simulation for a roof at hot magma chamber

    NASA Astrophysics Data System (ADS)

    Furuichi, M.; Nishiura, D.

    2014-12-01

    The dynamics of a granular media has been suggested to play an important role in a reheated magma chamber by a hot intrusion (e.g. Burgisser and Bergantz, 2011). Although several mechanisms, such as Rayleigh Taylor instability, unzipping, and rhythmic convection (e.g. Shibano et.al. 2012, 2013), have been proposed for characterizing upward migration process in a crystalline magma chamber, their contributions in the long geodynamical time scale are not clear yet. Thus we perform numerical simulations to investigate the thermal evolution of the magma chamber with basal intrusion in three dimensions. In order to solve high-viscosity fluid and particle dynamics for modelling a melt--crystal jammed state of the magma, we have developed a coupled Stokes--DEM simulation code with two key techniques: formulation of particle motion without inertia and semi-implicit treatment of particle motion in the fluid equation (Furuichi and Nishiura 2014). Our simulation can successfully handle sinking particles in a high-viscosity fluid. We examine different types of the granular media heated from the bottom with varying parameters. We especially focus on pattern of the settling particles against the melt density contrast between upper and lower region.

  6. Inverse solution for crystal fractionation in a periodically tapped magma chamber, Sierrita porphyry copper deposit, Arizona

    SciTech Connect

    Anthony, E.Y.; Titley, S.R.

    1985-01-01

    Inversion techniques have been used to simultaneously solve for the initial concentrations, distribution coefficients, and degrees of crystallization for a suite of Laramide rocks related to subduction and porphyry copper mineralization. The suite includes diorite, andesite, and granodiorite. The granodiorite has differentiated in place to a granite core and it is this granite which immediately precedes mineralization. To perform the inversion one must verify that the rocks are genetically related by crystallization or melting. Their comagmatic nature is suggested by the similarity throughout the suite in the ratios of incompatible elements and in the few available isotopic determinations. The geochemical path of crystallization is indicated by the decrease in compatible elements and increase in incompatible elements. Inversion of the trace element data yields high initial concentrations for elements such as Ba and Ce and low concentrations for the transition metals, which is consistent with crustal melting. Thus, there was s substantial magma chamber at depth from which the more felsic liquids the authors sample have separated. The residence time of this chamber was not less than 6 million years. Such a prolonged history has been observed in other porphyry systems for which 10 million years of igneous activity and 2 million years of intermittent mineralization are recorded.

  7. The effect of pressurized magma chamber growth on melt migration and pre-caldera vent locations through time at Mount Mazama, Crater Lake, Oregon

    NASA Astrophysics Data System (ADS)

    Karlstrom, Leif; Wright, Heather M.; Bacon, Charles R.

    2015-02-01

    The pattern of eruptions at long-lived volcanic centers provides a window into the co-evolution of crustal magma transport, tectonic stresses, and unsteady magma generation at depth. Mount Mazama in the Oregon Cascades has seen variable activity over the last 400 ky, including the 50 km3 climactic eruption at ca. 7.7 ka that produced Crater Lake caldera. The physical mechanisms responsible for the assembly of silicic magma reservoirs that are the precursors to caldera-forming eruptions are poorly understood. Here we argue that the spatial and temporal distribution of geographically clustered volcanic vents near Mazama reflects the development of a centralized magma chamber that fed the climactic eruption. Time-averaged eruption rates at Mount Mazama imply an order of magnitude increase in deep magma influx prior to the caldera-forming event, suggesting that unsteady mantle melting triggered a chamber growth episode that culminated in caldera formation. We model magma chamber-dike interactions over ∼50 ky preceding the climactic eruption to fit the observed distribution of surface eruptive vents in space and time, as well as petrologically estimated deep influx rates. Best fitting models predict an expanding zone of dike capture caused by a growing, oblate spheroidal magma chamber with 10-30 MPa of overpressure. This growing zone of chamber influence causes closest approaching regional mafic vent locations as well as more compositionally evolved Mazama eruptions to migrate away from the climactic eruptive center, returning as observed to the center after the chamber drains during the caldera-forming eruption.

  8. Systematic tapping of independent magma chambers during the 1 Ma Kidnappers supereruption

    NASA Astrophysics Data System (ADS)

    Cooper, George F.; Wilson, Colin J. N.; Millet, Marc-Alban; Baker, Joel A.; Smith, Euan G. C.

    2012-01-01

    was tectonic triggering and linkage of eruptions. Our results show that supereruptions can be generated by near simultaneous multiple eruptions from independent magma chambers rather than the evacuation of a large single unitary magma chamber.

  9. The Development of a Restless Rhyolite Magma Chamber at Laguna del Maule, Chile

    NASA Astrophysics Data System (ADS)

    Andersen, N.; Singer, B. S.; Jicha, B. R.; Fierstein, J.; Vazquez, J. A.

    2013-12-01

    lower silica rhyolite (72-74%) than the majority erupted during phase 1 (75-76%) but a smaller range of compositions overall as andesite and rhyodacite eruptions become rare and peripheral. The two phases are also distinguished by a small, but consistent, shift in REE contents. Phase 1 is marked by lower REE contents, but higher Ce/Sm ratios. The chemical trends are temporally, rather than spatially, correlated reflecting the evolution of an integrated magma body rather than local vagaries in magmatic process. Early eruptions in both phases 1 and 2 are characterized by elevated two-oxide temperatures, the presence of trace pyrrhotite, and Ta contents 2-3 times greater than subsequent eruptions, an enrichment of similar magnitude to that observed in the early Bishop Tuff. The intrusion of basalt to the base of the magma chamber could provide a source of heat and volatiles catalyzing the crystallization of Fe-sulfide and roofward diffusion of Ta. Such events have been followed by periods of heightened volcanic activity and produced an increasing rate of silicic magma generation. If the current unrest is indicative of basaltic intrusion, it could foreshadow continuing silicic volcanism at LdM, potentially leading to a catastrophic caldera forming eruption.

  10. Water content variability in Ignimbrite Campana melts. New insights on magma chamber history

    NASA Astrophysics Data System (ADS)

    Marianelli, P.; Proto, M.; Sbrana, A.

    2003-04-01

    The Ignimbrite Campana (39 ka) represents the most powerful eruption characterizing the volcanic history of the Campi Flegrei caldera. The study is based on melt inclusions investigations in phenocrysts of juvenile pumice from the fallout unit and from the Breccia Museo Unit. The aim of this work is the determination of both the chemical composition and the pre-eruptive volatile content of Ignimbrite Campana magmas. Glass compositions fall in the trachyte field close to the trachyte-phonolite boundary, similarly to the others Ignimbrite Campana products. FTIR analyses on double-polished melt inclusions were carried out in order to investigate H_2O and CO_2 contents. CO_2 was below detection limit. Melt inclusions from Breccia Museo products and from the fallout layer show a very large range of H_2O contents with a mode of 2--4wt% and higher values of about 5--6%wt%. The variability of water content is independent of the evolutive degree of the melt (CaO=2.5--1.5wt%), and therefore cannot be ascribed to differentiation processes. Minimum pressures of crystallization are estimated assuming saturation conditions for the trapped melts and using the H_2O solubility model of Carroll and Blank (1997). Most of crystallization pressures are in the range 20--60 MPa, whereas a few values are between 100 and 150 MPa. We suggest that the higher values could indicate the pressure of crystallization in a magma chamber, located at a depth of about 4.5--6 Km. The abundance of melt inclusions with lower water content could testify an abrupt change in pre-eruptive conditions of the Ignimbrite Campana magma chamber, such as degassing due to magma rising or opening and decompression of the magma chamber. References Carroll M.R. and Blank J.G. (1997): The solubility of H_2O in phonolitic melts. American Mineralogist, 82: 549--556.

  11. From Magma Chamber to Tephra- what can volcanic titanite tell us about pre-eruptive processes?

    NASA Astrophysics Data System (ADS)

    Iddon, Fiona; McLeod, Graham; Dempster, Tim; Walshaw, Richard; Everard, Lucie

    2014-05-01

    Large volume, apparently homogenous, crystal rich pyroclastic deposits, or so called 'monotonous intermediates' are often considered to represent erupted batholiths. Their formation and life-cycle can be preceded and eruptions triggered by highly complex magma chamber processes, with multiple periods of recharge, mixing and thermal oscillations [1]. This information is difficult to observe, even at the crystal scale due to fragmentation or re-equilibration with subsequent recharge events. Titanite is a geochemically robust mineral that acts as a reservoir for trace elements, in particular the HFSEs and REEs. This ability to act as a primary control on the trace element budget of a melt [2], coupled with its refractory nature, allows titanite to preserve compositional zoning, proven to act as a reliable record of magma chamber conditions even in long-lived plutons [3]. This study extends the use of titanite to volcanic rocks via a coupled micro-textural and geochemical study of titanites from the Fish Canyon Tuff, Colorado. Regarded as the largest ever recorded pyroclastic deposit, it is thought that the batholith-sized magma chamber cooled to a rigid crystalline mush prior to thermal rejuvenation via underplating mafic magma [1]. It is additionally suggested this may have acted as a trigger for the eruption [1]. Results have shown the titanites to possess trace element zoning reflecting changes in melt composition and chamber conditions. Dissolution horizons and inclusion suites additionally provide evidence for multiple changes in temperature and oxygen fugacity aiding the interpretation of pre-eruptive processes. The study is ongoing with investigation of titanite from the Cerro Galan Ignimbrite, Argentina. The deposit again is suggested to have undergone a complex magma chamber growth and recharge history, with further proposals of multiple magma storage locations at different crustal levels [4]. The crystal zoning may provide further evidence for this, however

  12. The effect of pressurized magma chamber growth on melt migration and pre-caldera vent locations through time at Mount Mazama, Crater Lake, Oregon

    USGS Publications Warehouse

    Karlstrom, Leif; Wright, Heather M.; Bacon, Charles R.

    2015-01-01

    The pattern of eruptions at long-lived volcanic centers provides a window into the co-evolution of crustal magma transport, tectonic stresses, and unsteady magma generation at depth. Mount Mazama in the Oregon Cascades has seen variable activity over the last 400 ky, including the 50 km3 climactic eruption at ca. 7.7 ka that produced Crater Lake caldera. The physical mechanisms responsible for the assembly of silicic magma reservoirs that are the precursors to caldera-forming eruptions are poorly understood. Here we argue that the spatial and temporal distribution of geographically clustered volcanic vents near Mazama reflects the development of a centralized magma chamber that fed the climactic eruption. Time-averaged eruption rates at Mount Mazama imply an order of magnitude increase in deep magma influx prior to the caldera-forming event, suggesting that unsteady mantle melting triggered a chamber growth episode that culminated in caldera formation. We model magma chamber–dike interactions over ∼50 ky preceding the climactic eruption to fit the observed distribution of surface eruptive vents in space and time, as well as petrologically estimated deep influx rates. Best fitting models predict an expanding zone of dike capture caused by a growing, oblate spheroidal magma chamber with 10–30 MPa of overpressure. This growing zone of chamber influence causes closest approaching regional mafic vent locations as well as more compositionally evolved Mazama eruptions to migrate away from the climactic eruptive center, returning as observed to the center after the chamber drains during the caldera-forming eruption.

  13. Ardnamurchan 3D cone-sheet architecture explained by a single elongate magma chamber.

    PubMed

    Burchardt, Steffi; Troll, Valentin R; Mathieu, Lucie; Emeleus, Henry C; Donaldson, Colin H

    2013-01-01

    The Palaeogene Ardnamurchan central igneous complex, NW Scotland, was a defining place for the development of the classic concepts of cone-sheet and ring-dyke emplacement and has thus fundamentally influenced our thinking on subvolcanic structures. We have used the available structural information on Ardnamurchan to project the underlying three-dimensional (3D) cone-sheet structure. Here we show that a single elongate magma chamber likely acted as the source of the cone-sheet swarm(s) instead of the traditionally accepted model of three successive centres. This proposal is supported by the ridge-like morphology of the Ardnamurchan volcano and is consistent with the depth and elongation of the gravity anomaly underlying the peninsula. Our model challenges the traditional model of cone-sheet emplacement at Ardnamurchan that involves successive but independent centres in favour of a more dynamical one that involves a single, but elongate and progressively evolving magma chamber system. PMID:24100542

  14. Ardnamurchan 3D cone-sheet architecture explained by a single elongate magma chamber

    PubMed Central

    Burchardt, Steffi; Troll, Valentin R.; Mathieu, Lucie; Emeleus, Henry C.; Donaldson, Colin H.

    2013-01-01

    The Palaeogene Ardnamurchan central igneous complex, NW Scotland, was a defining place for the development of the classic concepts of cone-sheet and ring-dyke emplacement and has thus fundamentally influenced our thinking on subvolcanic structures. We have used the available structural information on Ardnamurchan to project the underlying three-dimensional (3D) cone-sheet structure. Here we show that a single elongate magma chamber likely acted as the source of the cone-sheet swarm(s) instead of the traditionally accepted model of three successive centres. This proposal is supported by the ridge-like morphology of the Ardnamurchan volcano and is consistent with the depth and elongation of the gravity anomaly underlying the peninsula. Our model challenges the traditional model of cone-sheet emplacement at Ardnamurchan that involves successive but independent centres in favour of a more dynamical one that involves a single, but elongate and progressively evolving magma chamber system. PMID:24100542

  15. The impact of rapid recharge events on the evolution of magma chambers: Case studies of Santorini Volcano (Greece) and Volcan Quizapu (Chile)

    NASA Astrophysics Data System (ADS)

    Degruyter, Wim; Huber, Christian; Bachmann, Olivier; Cooper, Kari; Kent, Adam

    2016-04-01

    Magma reservoirs in the crust are thought to be dominantly formed by episodic recharge events at rates that are much larger than the long-term average magma inflow rates. Hence, a better understanding of the evolution of a magma reservoir requires elucidating the mass change, pressurization, heating, deformation and the potential for an eruption associated with different recharge scenarios. Most importantly, the bifurcation in behavior between a recharge event that leads to eruption and one that will grow the chamber requires quantification for better volcanic hazard assessment. We use a numerical model to determine the change in pressure, temperature and volume of a magma chamber as it is exposed to a recharge event. The model is applied to the well-studied volcanic systems of Santorini Volcano (Greece) and Volcan Quizapu (Chile). We establish the rates and the duration of magma recharge events that will lead to an eruption. In doing so, we demonstrate the importance of the state of the magma chamber prior to the recharge event, i.e. its size and exsolved volatile content, on the subsequent evolution of the reservoir. In the case of Santorini, the model successfully reproduces the main features of the Minoan eruption and Nea Kameni activity, providing volume estimates for the active part of the current subvolcanic reservoir as well as information regarding the presence of exsolved volatiles. For Quizapu, we suggest that the change in eruptive style, from an effusive outpouring of lava in 1846-1847 to an explosive Plinian eruption in 1932, was controlled by a shift in the state of the magma chamber induced by the first eruption. These case studies show that thermo-mechanical models offer a new framework to integrate the historic eruption record with geodetic measurements and provide a context to understand the past, present and future of active volcanic centers.

  16. MORB differentiation: In situ crystallization in replenished-tapped magma chambers

    NASA Astrophysics Data System (ADS)

    Coogan, L. A.; O'Hara, M. J.

    2015-06-01

    The differentiation of mid-ocean ridge basalt (MORB) is investigated with a focus on intermediate- to fast-spreading ridges and two recently proposed differentiation mechanisms: (i) differentiation in replenished-tapped-crystallizing (RTX) magma chambers, and (ii) chromatographic element separation during melt-rock reaction in the lower crust. There is compelling evidence in the petrology and geochemistry of MORB indicating that magma chambers at mid-ocean ridges behave as open systems, as required on thermal grounds in locations where a steady-state magma chamber exists. It has recently been suggested that the commonly observed over-enrichment of more-to-less incompatible elements during MORB differentiation can be explained by such an RTX model. However, the petrology of samples from the lower oceanic crust suggests an alternative mechanism could produce this over-enrichment. Clinopyroxene crystals in oceanic gabbros are commonly strongly zoned in incompatible elements with crystal rims apparently having grown from melts with very high incompatible element abundances. Elevated Zr/LREE in clinopyroxene rims, which has been interpreted as indicating growth from a melt in which these elements had been fractionated from one another by melt-rock reaction (chromatographic separation), is shown to be more simply explained by post-crystallization diffusive fractionation. However, the high incompatible element abundances in crystal rims demonstrates that the interstitial melt in crystal mush zones becomes highly differentiated. Disaggregation of such mush zones is indicated by the crystal cargo of MORB and must be accompanied by the return of interstitial melt to the eruptible reservoir - a form of in situ crystallization. Both a magma chamber undergoing closed system in situ crystallization, and a RTX magma chamber in which crystallization occurs in situ, are shown to be capable of reproducing the differentiation trends observed in MORB. Simple stochastic models of the

  17. Compositional evolution of the zoned calcalkaline magma chamber of Mount Mazama, Crater Lake, Oregon

    USGS Publications Warehouse

    Bacon, C.R.; Druitt, T.H.

    1988-01-01

    The climactic eruption of Mount Mazama has long been recognized as a classic example of rapid eruption of a substantial fraction of a zoned magma body. Increased knowledge of eruptive history and new chemical analyses of ???350 wholerock and glass samples of the climactic ejecta, preclimactic rhyodacite flows and their inclusions, postcaldera lavas, and lavas of nearby monogenetic vents are used here to infer processes of chemical evolution of this late Pleistocene - Holocene magmatic system. The 6845??50 BP climactic eruption vented ???50 km3 of magma to form: (1) rhyodacite fall deposit; (2) welded rhyodacite ignimbrite; and (3) lithic breccia and zoned ignimbrite, these during collapse of Crater Lake caldera. Climactic ejecta were dominantly homogeneous rhyodacite (70.4??0.3% SiO2), followed by subordinate andesite and cumulate scoriae (48-61% SiO2). The gap in wholerock composition reflects mainly a step in crystal content because glass compositions are virtually continuous. Two types of scoriae are distinguished by different LREE, Rb, Th, and Zr, but principally by a twofold contrast in Sr content: High-Sr (HSr) and low-Sr (LSr) scoriae. HSr scoriae were erupted first. Trace element abundances indicate that HSr and LSr scoriae had different calcalkaline andesite parents; basalt was parental to some mafic cumulate scoriae. Parental magma compositions reconstructed from scoria wholerock and glass data are similar to those of inclusions in preclimactic rhyodacites and of aphyric lavas of nearby monogenetic vents. Preclimactic rhyodacite flows and their magmatic inclusions give insight into evolution of the climactic chamber. Evolved rhyodacite flows containing LSr andesite inclusions were emplaced between ???30000 and ???25000 BP. At 7015??45 BP, the Llao Rock vent produced a zoned rhyodacite pumice fall, then rhyodacite lava with HSr andesite inclusions. The Cleetwood rhyodacite flow, emplaced immediately before the climactic eruption and compositionally

  18. Effect of stress fields on magma chamber stability and the formation of collapse calderas

    NASA Astrophysics Data System (ADS)

    Bosworth, William; Burke, Kevin; Strecker, Manfred

    2003-08-01

    The summits of many of the Earth's and other planets' larger volcanoes are occupied by calderas that formed by collapse into an evacuating, underlying magma chamber. These collapse calderas are typically several tens of square kilometers in area and are commonly elliptical in shape. We show that the long axes of late Quaternary collapse calderas in the Kenya rift valley, the western Basin and Range province, the Snake River-Yellowstone Plateau, and the Iceland rift zone are parallel to the upper crustal minimum horizontal stress direction (Sh) as determined by independent criteria. We suggest that circular magma chambers beneath these volcanoes became elliptical by stress-induced spalling of their chamber walls, by a mechanism that is analogous to the formation of breakouts in boreholes and tunnels. In breakouts, the hole becomes elongate parallel to the far-field minimum stress. In the Kenya rift, Late Pleistocene caldera collapse was accompanied by a 45° rotation of Sh and an increase in the magnitude of the maximum horizontal stress (SH). The breakout model predicts increasingly unstable caldera walls under these conditions, a possible explanation for the sudden appearance of so many collapse events in a volcanic setting that had never experienced them before. This mechanism of stress change-induced collapse may have played a role in other caldera settings.

  19. Imaging shallow magma chambers at Alaskan volcanoes with ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Haney, M. M.; Prejean, S. G.

    2009-05-01

    Ambient noise tomography/inversion (ANT) is an emerging technique in seismology with the ability to provide 3D images of subsurface volcanic structure using relatively sparse seismic networks. The method relies on the principle that the cross-correlation of noise recordings at two different seismic stations reproduces an experiment in which one of the stations acts as an active source. Ambient seismic noise in the frequency band from 0.1 to 1 Hz is mostly composed of fundamental mode surface waves, of both Love and Rayleigh type. As a result, noise cross-correlations are sensitive to shear-wave structure and complement compressional-wave images computed from phase arrivals of local earthquakes. At Okmok volcano in the Aleutian islands, a 3D image constructed from 40 days of noise recordings in 2005 on a 12 station network clearly shows two low velocity zones (LVZs) centered about the 10-km-wide caldera: a shallow zone in the upper 1-2 km and a deeper zone between 4-4.5 km. The shallow LVZ is interpreted to be weak, poorly-consolidated material within the caldera; the deeper LVZ is indicative of the shallow magma chamber at Okmok. That the chamber is imaged as an LVZ in 2005 points to it remaining in a molten state throughout the time period between the 1997 and 2008 eruptions. The existence of a shallow chamber at Okmok is consistent with independent studies based on GPS, InSAR, and petrologic data. A 3D image has also been determined for the Katmai group of volcanoes along the Alaska peninsula from 60 days of continuous recordings in 2005 and 2006. An LVZ at Katmai Pass, previously known from local earthquake tomography (LET), is evident in the 3D shear-wave velocity model at depths down to 2 km BSL. That the LVZ exists in compressional-wave velocity models suggests it is a shallow magma storage area for Trident volcano. In contrast, low shear-wave velocity under Martin volcano is likely fluid-related, given the lack of low compressional-wave velocities in images

  20. The origin of a zoned ignimbrite: insights into the Campanian Ignimbrite magma chamber (Campi Flegrei, Italy)

    NASA Astrophysics Data System (ADS)

    Forni, Francesca; Bachmann, Olivier; Mollo, Silvio; De Astis, Gianfilippo

    2016-04-01

    The Campanian Ignimbrite (CI; Campi Flegrei, Italy), dated at 39 ka, is a widespread pyroclastic sequence emplaced during a cataclysmic caldera-forming eruption fed by trachytic to phonolitic magmas. The CI pyroclastic sequence is famous for its remarkable geochemical gradients,attributed to the presence of a vertically zoned magma chamber. Combining bulk-rock data with detailed phenocrysts and matrix glass analyses from well characterized stratigraphic units, we investigate the relatioships between such chemical zoning and the crystallinity variations observed along the CI pyroclastic sequence. Using geothermometers and hygrometers specifically calibrated for alkaline magmas, we reconstruct the reservoir storage conditions, revealing the presence of gradients in temperature and magma water content. In particular, we observe an increase in crystallinity and temperature and a decrease in magma evolution and water content from the bottom to the top of the sequence. We interpret these features as the result of protracted fractional crystallization leading to the formation of a cumulate crystal mush at the base of the eruptible reservoir, from which highly evolved, crystal-poor, water-rich and relatively cold melts were separated. The extracted melts, forming a buoyant, easily eruptible cap at the top of the magma chamber, fed the initial phases of the eruption, until caldera collapse and eruption of the deeper, more crystalline part of the system. This late-erupted, crystal-rich material, represents remobilized portions of the cumulate crystal mush, rejuvenated after mafic recharge. Our interpretation is supported by: 1) the bulk-rock positive Eu anomalies and the high Ba and Sr contents observed in the crystal-rich units, implying feldspar accumulation; 2) the positive Eu anomalies in the matrix glass of the crystal-rich units, testifying to the presence of liquid derived from partial melting of low temperature mineral phases within the crystal mush (feldspars and

  1. Ore formation in porphyry-type deposits during incrementally built magma chamber and fluid sparging

    NASA Astrophysics Data System (ADS)

    Vigneresse, J. L.; Bachmann, O.; Huber, C.; Parmigiani, A.; Dufek, J.; Campos, E.

    2012-04-01

    Porphyry-type mineralizations are commonly associated with an underlying magma chamber from which a volatile phase exsolves from the crystallizing magma. We suggest a model of fluid sparging during multiple successive intrusions yielding metals concentration within the gas phase. Metals enrichment by 3-4 orders of magnitude takes place during the magmatic stage prior to hydrothermal effects, resulting from a competition between diffusion and advection of the volatile phase. The model explains why a single intrusion is not efficient enough to lead to economically viable ore deposit, though it also involves a gas phase percolating within a crystalline mush. During multiple intrusions, metals segregate from the new melt to the gas phase by diffusion, as long as the gas has not overcome a critical saturation level (about 20 % gas). Adding gas exsolved, about 4 % at each new magma recharge, overcomes this level. Then, the diffusion process switches toward advection, since the bubbles get interconnected, enhancing the transport of a gas phase enriched in metals. Once advected, the enriched gas phase turns into hydrothermal circulation during which metals condensate. Two non-dimensional numbers, Péclet and Stefan numbers, respectively rule diffusion and advection of elements while heat is lost through cooling. The model also examines the total duration of the process that re-establishes after 4-6 recharges in magma. It also provides an explanation why intrusions are barren or enriched, although they result from similar conditions of magma genesis. Development of a zoned alteration pattern may serve as a guide for prospection.

  2. Magma Accumulation throughout the Antilles ArcCrust: Insights from Integrating Petrology, Tomography and Chamber Growth Modelling

    NASA Astrophysics Data System (ADS)

    Annen, C.; Melekhova, E.; Paulatto, M.; Blundy, J.; Minshull, T. A.; Sparks, S. S.

    2012-12-01

    Magmas stall at several levels within the crust, from the Moho to the Earth's surface, where volcanic edifices can be considered as the ultimate stage of magmatic products accumulation. Crustal growth and differentiation are determined by the rate at which magmas transfer and accumulate within the crust. At each level, emplacement rates control the magma thermal evolution and its ability to form magma reservoirs. Tomography experiments reveal a seismic low velocity volume at depth 5-8 km beneath Soufrière Hills, the currently active volcano of Montserrat. We numerically simulated the accumulation of andesitic sills at different rates and produced synthetic velocity images that were compared with Soufrière Hills tomography. Fits were found for magma chambers that grew over more than 4000 yrs up to 100,000 yrs by accretion of sills at rates of at least 25 mm/yr corresponding to volumetric fluxes of the order 10-3km3/yr. The crystal residence times inferred from diffusion profiles are less than 320 yrs (Zellmer et al, 2003a) but our results favour an older chamber, which suggests that only the most recently emplaced magma is erupting. In contrast, U-Th ages are more than 350,000 yrs and much older than the shallow chamber, which can be explained by protracted magma residence in deep hot zones (Zellmer et al, 2003b). Because of the absence of large volumes of cumulates in the upper crust, most magma differentiation is likely to happen in deep hot zones at the base or within the lower crust. Petrological experiment data obtained by melting a basalt from St Vincent were integrated in deep hot zone numerical simulations. The distribution of melt fractions in a hot zone depends both on the initial H2O content of the parental basalt and on the maturity of the hot zone. We estimated the distribution of melt fractions of St Vincent volcanic products using the rock concentration in incompatible elements. This distribution fits modelled distributions if the melt was produced

  3. Diamond-bearing Rocks among Mantle Xenoliths in Kimberlites as Indicatory for the Chambers of Diamond-parental Carbonatite Magma

    NASA Astrophysics Data System (ADS)

    Litvin, Yuriy; Kuzyura, Anastasia

    2014-05-01

    may originate and evolve by: (1) metasomatic-magmatic stage resulted in partial carbonatization of mantle peridotite under attack of K-CO2-bearing metasomatic agents and generation of carbonate melts; (2) dissolving-magmatic stage when major and accessory minerals of peridotite host-rock, volatiles and carbon dissolve in carbonate melt whereas insoluble sulphide phases penetrate into melts; eventually, completely miscible peridotite-carbonatite-carbon magma parental for diamond and paragenetic minerals (hosting xenogenetic sulphide minerals and melts) are formed; (3) fraction-crystallization stage (in chamber consolidated into a self-dependent body) during natural cooling of parental magma up to solidus temperature; the cooling activates physicochemical control that is created by PT-phase relations for the parental magma composition, i.e., syngenesis phase diagram on a representative polythermal section of peridotite-eclogite-carbonatite-diamond system at 7 GPa under conditions of fractional crystallization (Litvin, 2013). Parental carbonatite melts, while compositionally evolve under fractional crystallization, are physicochemically capable to form diamond and sequentially minerals of peridotitic and eclogitic parageneses (presented as primary inclusions in diamonds). Paragenetic peridotite-eclogite transition in the course of ultrabasic-basic fractional evolution of parental melts is revealed in physicochemical experiments as the effect of 'peridotite-to-eclogite' tonnel (Litvin, 2013). Diamond-bearing peridotite and eclogite rocks and intimate mineral intergrowths with diamond are also formed in the chambers of diamond-parental carbonatite magmas under these physicochemical conditions. Diamond-free rocks among mantle xenoliths in kimberlites represent samples of the enclosing host-rocks for the chambers of diamond-parental carbonatite magma. Support: grant of the RF President #MK-1386.2013.5, RFBR grants 12-05-33044, 13-05-00835 and 14-05-00537.

  4. Geyser's magma chamber, California: constraints from gravity data, density measurements, and well information

    USGS Publications Warehouse

    Blakely, Richard J.; Stanley, W.D.; ,

    1993-01-01

    A new crustal model based on isostatic residual gravity, geologic mapping, well information, and density measurements shows that the high-gradient parts of the residual gravity anomaly can be explained in terms of lithologic variations within the upper 7 km of the crust, consistent with the upper-crustal framework of the area. This conclusion does not rule out the presence of a magma chamber at lower crustal depths; the broad aspects of the gravity anomaly support the presence of low-density partial melting at 15 to 20 km depth, consistent with magnetotelluric soundings and other geophysical measurements.

  5. The buoyancy of large siliceous magma chambers is sufficient to initiate supereruptions

    NASA Astrophysics Data System (ADS)

    Malfait, W.; Sanchez-Valle, C.; Seifert, R.; Petitgirard, S.; Perrillat, J.; Ota, T.; Nakamura, E.; Lerch, P.; Mezouar, M.

    2012-12-01

    The geological record shows abundant evidence for rare, but extremely large caldera-forming eruptions of siliceous magmas that dwarf all historical volcanic episodes in erupted volume [1] and environmental impact [2, 3]. Because of the large size of the magma chambers that feed these eruptions, the overpressure generated by magma recharge is insufficient to fracture the cap rock and trigger an eruption [4]. For these thick magma chambers, the buoyancy of the magma potentially creates a sufficient overpressure capable of fracturing the cap rock, but the lack of data on the density of rhyolite melts precludes the appropriate estimation of the overpressure and the role of buoyancy in initiating supervolcano eruptions. The density of rhyolite melts has not been determined at super-liquidus temperatures or elevated pressures because traditional techniques, including Archimedean methods, sink/float experiments and acoustic measurements, are limited by the high melt viscosity. Here, we measured the density of rhyolitic/granitic melts with 0, 4.5 and 7.7 wt% of dissolved water at geologically relevant conditions: 0.9 to 3.6 GPa, 1270 to 1950 K. High pressure and temperature conditions were generated in a Paris-Edinburgh large volume press. Before and after each density measurement, the molten state of the sample was verified by X-ray diffraction. The density of the melt (ρPT) was determined from the X-ray attenuation coefficient of the sample, determined in situ (μPT) and at room conditions (μ0), and the density at room conditions (ρ0): ρPT=ρ0.(μPT/μ0). The acquired data were combined with available ambient pressure data on super-cooled liquids [5, 6] to derive a third order Birch-Murnaghan equation of state that accurately predicts the density of rhyolite melts as a function of pressure, temperature and water content, and the partial molar volume of dissolved water. Application of the melt equation of state to calculate the overpressure at the roof of supervolcano

  6. Conditions of deep magma chamber beneath Fuji volcano estimated from high- P experiments

    NASA Astrophysics Data System (ADS)

    Asano, K.; Takahashi, E.; Hamada, M.; Ushioda, M.; Suzuki, T.

    2012-12-01

    Fuji volcano, the largest in volume and eruption rate in Japan, is located at the center of Honshu, where North America, Eurasia and Philippine Sea plates meets. Because of the significance of Fuji volcano both in tectonic settings and potential volcanic hazard (particularly after the M9 earthquake in 2011), precise knowledge on its magma feeding system is essentially important. Composition of magma erupted from Fuji volcano in the last 100ky is predominantly basalt (SiO2=50-52wt%, FeO/MgO=1.5-3.0). Total lack of silica-rich magma (basaltic andesite and andesite) which are always present in other nearby volcanoes (e.g., Hakone, Izu-Oshima, see Fig.1) is an important petrologic feature of Fuji volcano. Purpose of this study is to constrain the depth of magma chamber of Fuji volcano and explain its silica-nonenrichment trend. High pressure melting experiments were carried out using two IHPVs at the Magma Factory, Tokyo Institute of Technology (SMC-5000 and SMC-8600, Tomiya et al., 2010). Basalt scoria Tr-1 which represents the final ejecta of Hoei eruption in AD1707, was adopted as a starting material. At 4kbar, temperature conditions were 1050, 1100 and 1150C, and H2O contents were 1.3, 2.7 and 4.7 wt.%, respectively. At 7kbar, temperature conditions were 1075, 1100 and 1125C, and H2O contents were 1.0, 1.1, 3.6 and 6.3wt.%, respectively. The fO2 was controlled at NNO buffer. At 4kbar, crystallization sequence at 3 wt% H2O is magnetite, plagioclase, clinopyroxene and finally orthopyroxene. At 7 kbar, and ~3 wt% H2O, the three minerals (opx, cpx, pl) appears simultaneously near the liquidus. Compositional trend of melt at 4 kbar and 7 kbar are shown with arrows in Fig.1. Because of the dominant crystallization of silica-rich opx at 7 kbar, composition of melt stays in the range SiO2=50-52wt% as predicted by Fujii (2007). Absence of silica-rich rocks in Fuji volcano may be explained by the tectonic setting of the volcano. Because Fuji volcano locates on the plate

  7. Evidence for a Dying Magma Chamber at Rábida Island, Galápagos

    NASA Astrophysics Data System (ADS)

    Bercovici, H.; Geist, D.; Harpp, K. S.; Almeida, M.

    2015-12-01

    Rábida Island in the Galapagos has experienced both explosive and effusive volcanism. It is located to the east of the most active volcanoes of the Galapagos, and previously determined ages range from 0.9 to 1.1 Ma. An unusually curved escarpment cuts the western sector of the island, which might be part of a caldera wall, although its radius of curvature is much greater than that of the island. Lavas range from basalt to rhyolite, and there are also several intermediate compositions, which are unique in the archipelago. A welded ignimbrite crops out in northeast sector, the only such deposit known in the entire region. The volumetric proportion of evolved rocks is unusually high; 25% of the rocks in our comprehensive sample set are intermediate to felsic. The siliceous rocks occur in two clusters in the southern and southwestern sections of the island, suggesting two separate sources. The intermediate rocks are concentrated in the center and northwestern parts of the island. Despite these foci of more siliceous lavas, basalt is the most widespread rock type across the island. It is notable that Rabida is immediately east of Volcan Alcedo, which is the only active Galápagos volcano that has also erupted rhyolite, and south of Santiago Island, which erupted the trachyte dome observed by Charles Darwin in 1835. These observations, in conjunction with the cumulate xenoliths observed in Rábida explosive deposits, are consistent with the evolved rocks resulting from fractional crystallization of a dying magma chamber, as the volcano is carried away from the hotspot.

  8. P-SV conversions at a shallow boundary beneath Campi Flegrei caldera (Italy) - evidence for the magma chamber

    SciTech Connect

    Ferrucci, F.; Hirn, A.; De Natale, G.; Virieux, J.; Mirabile, L. Inst. de Physique du Globe, Paris Osservatorio Vesuviano, Naples CNRS, Inst. de Geodynamique, Valbonne Ist. Universitario Navale, Naples )

    1992-10-01

    Seismograms from an active seismic experiment carried out at Campi Flegrei caldera (near Naples, Italy), show a large-amplitude SV-polarized shear wave, following by less than 1.5-s P waves reflected at wide angle from a deep crustal interface. Early arriving SV-polarized waves, with the same delay to direct P waves, are also observed in seismograms from a regional 280 km-deep, magnitude 5.1 earthquake. Such short delays of S to P waves are consistent with a P-SV conversion on transmission occurring at a shallow boundary beneath the receivers. The large amplitude of the converted-SV phase, along with that the P waves are near vertical, requires a boundary separating a very low rigidity layer from the upper caldera fill. The converted phases are interpreted as a seismic marker of a magma chamber. The top of this magma chamber is located slightly deeper than the deepest earthquakes observed during the 1982-1984 unrest of Campi Flegrei. 8 refs.

  9. Drilling through the largest magma chamber on Earth: Bushveld Igneous Complex Drilling Project (BICDP)

    NASA Astrophysics Data System (ADS)

    Trumbull, R. B.; Ashwal, L. D.; Webb, S. J.; Veksler, I. V.

    2015-05-01

    A scientific drilling project in the Bushveld Igneous Complex in South Africa has been proposed to contribute to the following scientific topics of the International Continental Drilling Program (ICDP): large igneous provinces and mantle plumes, natural resources, volcanic systems and thermal regimes, and deep life. An interdisciplinary team of researchers from eight countries met in Johannesburg to exchange ideas about the scientific objectives and a drilling strategy to achieve them. The workshop identified drilling targets in each of the three main lobes of the Bushveld Complex, which will integrate existing drill cores with new boreholes to establish permanently curated and accessible reference profiles of the Bushveld Complex. Coordinated studies of this material will address fundamental questions related to the origin and evolution of parental Bushveld magma(s), the magma chamber processes that caused layering and ore formation, and the role of crust vs. mantle in the genesis of Bushveld granites and felsic volcanic units. Other objectives are to study geophysical and geodynamic aspects of the Bushveld intrusion, including crustal stresses and thermal gradient, and to determine the nature of deep groundwater systems and the biology of subsurface microbial communities.

  10. Depth and Pressures of Crystallization of Magma Chambers beneath Hawai'ian Volcanoes

    NASA Astrophysics Data System (ADS)

    Ditkof, J.

    2010-12-01

    The Hawai’ian Emperor Seamount Chain was formed by a mantle plume beginning about 80 Ma. The crust is raised by the plume while continuous eruptions form islands. As the islands begin to slide off the plume, they fall back to the sea floor, becoming a seamount. There are currently more than 80 undersea volcanoes stretching from the Aleutian Trench to the newly formed Loi’hi seamount. There are currently eight major islands which make up the state of Hawai’i. Seismic and other geophysical data have been used previously to determine the depth of magma chambers beneath Hawai’ian Volcanoes. Yang et al (1996) created a method in which three equations are used to calculate liquid compositions along the olivine-plagioclase-clinopyroxene coetectic. I used chemical analyses of glasses, which represent quenched liquid compositions, to calculate the pressure and temperature at which these liquids crystallize the minerals olivine, plagioclase, and clinopyroxene. The depth of crystallization can be calculated from these pressures. I then filtered the data, removing any classes that contained excess aluminum or water. Plotting the results for the filtered data set in CoPlot yields similar trends for all of the Hawai’ian Volcanoes in plots of CaO versus MgO, P versus MgO, T versus MgO, and depth versus MgO. The results agree with geophysical data, showing that the magma chambers lie at shallow depths, less than 10km at a pressure of about 1kilobar. Knowledge of the depths of chambers and pressures of crystallization is important for a number of reasons including understanding the chemical composition of molten rock that is flowing within the chamber and predicting when an eruption will occur.

  11. Geophysical study of a magma chamber near Mussau Island, Papua New Guinea

    USGS Publications Warehouse

    Dadisman, Shawn V.; Marlow, M. S.

    1988-01-01

    Analysis of a 24-channel seismic-reflection data collected near Mussau Island, Papua New Guinea, shows a high-amplitude, negative-polarity reflection that we believe is from the top of a magma chamber.  The reflecting horizon lies at a depth of about 4.4 s subbottom and can be traced laterally for 2.6 km.  On shot gathers, the reflection demonstrates normal moveout appropriate for an in-place event.  The frequency spectrum of the reflection shows a decrease in high-frequency content when compared to the sea floor reflection, as would be expected for a deep subsurface event.  The polarity of the reflection event is negative, suggesting that the reflection horizon is the top of a low-velocity zone.  Magnetic data indicate that the ridge containing the reflecting horizon is magnetic, and the geology of Massau Island suggests that the ridge is volcanic in its origin.  We speculate that the high-amplitude reflection is from the top of a magma chamber some 7-11 km deep.

  12. Reintrusion of silicic magma chambers by mafic dike complex: evidence from the northern Semail ophiolite

    SciTech Connect

    Stakes, D.S.; Shervais, J.; Ressetar, R.

    1985-01-01

    Late plagiogranite bodies in the Semail ophiolite have been previously suggested to represent late stage fractionates within an episodic spreading center magma chamber or the roots of seamount chains. Field and lab observations suggest that these late silicic magma chambers represent zones of repeated injection by dikes of intermediate to mafic composition. Multiple generations of intrusion, partial resorption and reintrusion are preserved in the plagiogranite as 1) relict phantom xenoliths, 2) angular xenoliths with quartz-rich margins, 3) deformed fine-grained dikes with distinct chilled margins, and 4) planes of rectangular blocks with cuspate margins or ellipsoids of similar fine grained mafic materials. The blocks and ellipsoids are actually dismembered mafic dikes that chilled by intruding a cooler silicic liquid and were either thermally fractured or pinched out. All of the dikes are hydrothermally altered to assemblages including amph., qtz., epi., preh., and chl. and are enriched in delta/sup 18/O. Extremely altered diabase from a copper sulfide-bearing normal fault is isotopically depleted (delta/sup 18/0=2.0 per mil) suggesting that such deep faults are high temperature hydrothermal conduits. Malachite and amphibole bearing veins along the margins of the plagiogranite suggest a genetic relationship between the silicic intrusions, the multiple diking events and copper sulfide deposition.

  13. Deciphering the thermal and mixing history of the Pleistocene rhyolite magma chamber at Augustine Volcano

    NASA Astrophysics Data System (ADS)

    Nadeau, P. A.; Webster, J. D.; Mandeville, C. W.; Monteleone, B.; Shimizu, N.; Goldoff, B. A.

    2015-12-01

    Recent activity at Augustine Volcano, located in Cook Inlet, Alaska, has been dominated by intermediate composition lavas and relatively small explosions. Earlier in Augustine's history, however, a thick (~30 m) rhyolite fall was erupted ca. 25 ka, containing at least three distinct rhyolite lithologies. Numerous studies have documented evidence of magma mixing in the more recently-erupted material. Here we attempt to evaluate similar mixing events that may have affected the 25 ka rhyolitic magma prior to its eruption. Basaltic to basaltic-andesitic deposits are found interbedded with the rhyolite at Augustine, so at least two magmas were present in Augustine's plumbing system at the same or nearly the same time. Hints at interactions between two or more magmas are also evident on a smaller scale. Xenocrysts of olivine and clinopyroxene are present in the rhyolite, each with mafic melt inclusions. Additionally, two of the three rhyolitic lithologies studied contain high-aluminum amphiboles that are compositionally similar to amphiboles from mafic enclaves entrained during the 2006 eruption and thus may be xenocrystic. To further investigate possible heating by secondary melts and the history of mixing, we use the titanium-in-quartz geothermometer (TitaniQ) on chemical zonation in quartz phenocrysts. We find that most quartz has a distinct 3-zone pattern, though one lithology also contains some complex zoning patterns in phenocryst cores, perhaps suggesting a xenocrystic origin. Additionally, we examine relationships between trace elements in the silicate melt inclusions from a variety of phenocryst types to determine if there is evidence for input of additional magma of different compositions. Finally, we apply results of a preliminary investigation of the mineralogy of a high-phosphorus dacite that stratigraphically overlies the rhyolite to assess their similarity and the degree of mixing, if any, that may have led to the transition from rhyolitic to dacitic magma.

  14. Modelling Of Hindered Crystal Settling-Floating Process In A Magma Chamber

    NASA Astrophysics Data System (ADS)

    Berres, S.; Forien, M.; Bagdassarov, N. S.; Dingwell, D. B.

    2011-12-01

    In interior of magma chamber during the fractional crystallisation, the separation of the minerals can be done by a simple density contrast. The denser minerals sank to the bottom of magma chamber and can formed, later, a cumulate layer. In order to better understand the relations between cumulus texture and evolution of the chemical composition at grain boundaries during the crystal-melt settling-floating process, a series of centrifuge experiments have been carried out. The experiments were conducted in a centrifuging furnace at 1235°C under atmospheric pressure during 6 hours and with an acceleration range between 1g to 1000g of partially molten gabbro samples with the grain size 100μm. Crystals during the centrifuging process have been segregated according to their buoyancy: plagioclase crystals floated to the top and magnetite crystals sank to the bottom of container. The chemical evolution of melt, vertical and horizontal distribution of crystals and melt in the experiments at 100g and 200g is similar. The segregation realized in experiments at 500g and 1000g revealed much worse separation of heavy and light crystals and the melt phase. The vertical evolution of the major and trace elements in the melt phase shows that close to the cumulate layer (between 0 to 2 mm from the bottom) the variation of these elements depends on the distance from the container wall, and becomes constant in the interior of sample. The horizontal evolution shows some variations which appear close to the walls of the capsule and which are due to the wall effect during the centrifuging runs. In order to describe the compaction evolution with time, a numerical modelling of the sedimentation process of the crystals has been build and then compared with the centrifuge modelling. The numerical and centrifuge modelling results agree quite well: the stratification of the compacted layer in the runs is reproduced in numerical models. The settling model of a concentrated suspension can

  15. The response of visco-elastic crust and mantle to the inflation/deflation of magma chamber

    NASA Astrophysics Data System (ADS)

    Yamasaki, T.

    2015-12-01

    It is important to quantitatively evaluate how magmatic activities at depth are reflected in geodetically (GPS and/or InSAR) observed surface deformation in order to distinguish magma-induced crustal deformation. This study employs 3-D finite element model to examine response of the linear Maxwell visco-elastic crust and mantle to a development of sill. Models with instantaneous and/or time-dependent inflation/deflation of sill at various depths in the crust have predicted geodetically detectable surface deformation, providing important constraints on spatio-temporal-scale of magmatic activities. Instantaneous inflation of sill in the crust causes the surface uplift. The amplitude and wavelength of the uplift are amplified for shallower and deeper inflations, respectively. The inflation occurred over a greater horizontal extent intensify both the amplitude and wavelength. The inflation-induced surface uplift would however abate with time by visco-elastic relaxation. Any signature of sill would disappear in ~ 50 - 100 times Maxwell relaxation time of the crust unless the inflation occurred within the uppermost layer that effectively acts as elastic layer. Time-dependent inflation accompanies with visco-elastic relaxation, and the inflation having occurred over the time-scale of ~ 50 - 100 times crustal relaxation time would provide insignificant signature at the surface, which in turn tells us that crustal deformation would reflect the development of magma chamber only if it has occurred in that time-scale. This study also has found that an ascent of magma into shallower depth may be recognised by an observation such that a horizontal extent over which the surface uplift is progressively intensified focusses into a narrower region.

  16. Non-traditional stable isotope behaviors in immiscible silica-melts in a mafic magma chamber

    PubMed Central

    Zhu, Dan; Bao, Huiming; Liu, Yun

    2015-01-01

    Non-traditional stable isotopes have increasingly been applied to studies of igneous processes including planetary differentiation. Equilibrium isotope fractionation of these elements in silicates is expected to be negligible at magmatic temperatures (δ57Fe difference often less than 0.2 per mil). However, an increasing number of data has revealed a puzzling observation, e.g., the δ57Fe for silicic magmas ranges from 0‰ up to 0.6‰, with the most positive δ57Fe almost exclusively found in A-type granitoids. Several interpretations have been proposed by different research groups, but these have so far failed to explain some aspects of the observations. Here we propose a dynamic, diffusion-induced isotope fractionation model that assumes Si-melts are growing and ascending immiscibly in a Fe-rich bulk magma chamber. Our model offers predictions on the behavior of non-traditional stable isotope such as Fe, Mg, Si, and Li that are consistent with observations from many A-type granitoids, especially those associated with layered intrusions. Diffusion-induced isotope fractionation may be more commonly preserved in magmatic rocks than was originally predicted. PMID:26620121

  17. Non-traditional stable isotope behaviors in immiscible silica-melts in a mafic magma chamber.

    PubMed

    Zhu, Dan; Bao, Huiming; Liu, Yun

    2015-01-01

    Non-traditional stable isotopes have increasingly been applied to studies of igneous processes including planetary differentiation. Equilibrium isotope fractionation of these elements in silicates is expected to be negligible at magmatic temperatures (δ(57)Fe difference often less than 0.2 per mil). However, an increasing number of data has revealed a puzzling observation, e.g., the δ(57)Fe for silicic magmas ranges from 0‰ up to 0.6‰, with the most positive δ(57)Fe almost exclusively found in A-type granitoids. Several interpretations have been proposed by different research groups, but these have so far failed to explain some aspects of the observations. Here we propose a dynamic, diffusion-induced isotope fractionation model that assumes Si-melts are growing and ascending immiscibly in a Fe-rich bulk magma chamber. Our model offers predictions on the behavior of non-traditional stable isotope such as Fe, Mg, Si, and Li that are consistent with observations from many A-type granitoids, especially those associated with layered intrusions. Diffusion-induced isotope fractionation may be more commonly preserved in magmatic rocks than was originally predicted. PMID:26620121

  18. Non-traditional stable isotope behaviors in immiscible silica-melts in a mafic magma chamber.

    PubMed

    Zhu, Dan; Bao, Huiming; Liu, Yun

    2015-12-01

    Non-traditional stable isotopes have increasingly been applied to studies of igneous processes including planetary differentiation. Equilibrium isotope fractionation of these elements in silicates is expected to be negligible at magmatic temperatures (δ(57)Fe difference often less than 0.2 per mil). However, an increasing number of data has revealed a puzzling observation, e.g., the δ(57)Fe for silicic magmas ranges from 0‰ up to 0.6‰, with the most positive δ(57)Fe almost exclusively found in A-type granitoids. Several interpretations have been proposed by different research groups, but these have so far failed to explain some aspects of the observations. Here we propose a dynamic, diffusion-induced isotope fractionation model that assumes Si-melts are growing and ascending immiscibly in a Fe-rich bulk magma chamber. Our model offers predictions on the behavior of non-traditional stable isotope such as Fe, Mg, Si, and Li that are consistent with observations from many A-type granitoids, especially those associated with layered intrusions. Diffusion-induced isotope fractionation may be more commonly preserved in magmatic rocks than was originally predicted.

  19. Non-traditional stable isotope behaviors in immiscible silica-melts in a mafic magma chamber

    NASA Astrophysics Data System (ADS)

    Zhu, Dan; Bao, Huiming; Liu, Yun

    2015-12-01

    Non-traditional stable isotopes have increasingly been applied to studies of igneous processes including planetary differentiation. Equilibrium isotope fractionation of these elements in silicates is expected to be negligible at magmatic temperatures (δ57Fe difference often less than 0.2 per mil). However, an increasing number of data has revealed a puzzling observation, e.g., the δ57Fe for silicic magmas ranges from 0‰ up to 0.6‰, with the most positive δ57Fe almost exclusively found in A-type granitoids. Several interpretations have been proposed by different research groups, but these have so far failed to explain some aspects of the observations. Here we propose a dynamic, diffusion-induced isotope fractionation model that assumes Si-melts are growing and ascending immiscibly in a Fe-rich bulk magma chamber. Our model offers predictions on the behavior of non-traditional stable isotope such as Fe, Mg, Si, and Li that are consistent with observations from many A-type granitoids, especially those associated with layered intrusions. Diffusion-induced isotope fractionation may be more commonly preserved in magmatic rocks than was originally predicted.

  20. Quaternary volcanics from the Broken Top volcano area, Oregon High Cascades: Varied low pressure processes in calc-alkaline magma chambers

    SciTech Connect

    Webster, J.R. . Div. of Science and Math)

    1992-01-01

    Broken Top (BT) is a Quaternary composite volcano in the central Oregon High Cascades. Volcanics in the vicinity of BT range from basalt to rhyodacite with a paucity of andesite. Most pre- and syn-BT lavas were generated through low pressure crystal fractionation (CF) in small, short-lived chambers. Mixing superimposed on CF generally involved magmas with minimal compositional differences. Lavas erupted from BT are dominantly phenocryst-rich bas. andesite which exhibits evidence for a mixing origin. Whole-rock and phenocryst compositions suggest mixing between basalt and andesite. The andesite can be explained by low pressure CF of the basalt. Latest BT activity consisted of bas. andesite, dacite, and rhyodacite lavas which were generated through CF. During BT activity, andesite was produced by CF during rapid sidewall crystallization and ponded at the top of the chamber. Mixing most likely took place during eruptive events, but evidence for a persistent presence of mixed (hybrid) magma in the chamber suggests incomplete evacuation of mixed magma. With time, the andesite layer became less significant due to decreasing rates of sidewall crystallization and/or frequent eruption/replenishment, more widespread crystal settling resulted in eruption of CF-generated bas. andesite and low-Si dacite. Rapid crystallization of dacitic magma followed by buoyant segregation yielded rhyodacite. These processes operating during the latest stages of the BT activity were likely similar to those operating in the short-lived chambers. Paucity of CF-generated andesite is explained by: (1) low density crust which retards andesite ascent, and (2) rapid crystallization over the dacite range. While significant amounts of andesite were produced in the longer-lived BT system, it rarely erupted unmixed.

  1. Field And Structural Constraints On Batholith Growth, Mush Deformation, And The Size Of A Magma Chamber

    NASA Astrophysics Data System (ADS)

    Yoshinobu, A. S.; Coint, N.; Barnes, C. G.; Leopold, M. B.

    2012-12-01

    Much like the mid-ocean ridge and ophiolite communities, geologists working on arc plutonic rocks are faced with a fascinating problem: What mechanisms attend the assembly of batholiths from what may be small, even ephemeral magma increments emplaced into a mush or solid rock? Field and structural observations from the Wooley Creek batholith (WCB), CA, provide a glimpse of the structural complexity of batholith assembly and point to a conclusion that magma homogenization by repeated injection and then "mushification" may occur at low melt fractions in a reasonably large magma chamber. The tilted WCB exposes 9 km of structural relief and is divided into three units: a lower (650 MPa contact aureole pressures) biotite-hornblende-two pyroxene gabbro to tonalite, a central biotite-hornblende quartz-diorite to tonalite with numerous swarms of mingled microgranitoid enclaves and syn-plutonic intrusions, and an upper unit (300 MPa) that is zoned upward from biotite-hornblende tonalite to biotite-hornblende granodiorite and granite (Coint et al., 2012, EGU Abs.; in review, Geol.). Five upper unit samples yield preliminary CA-ID-TIMS U/Pb ages of 158.25 Ma with uncertainties from 0.16 to 0.95 Ma (K. Chamberlain, in prog.). The WCB is moderately to strongly discordant to host rock structure and existing gravity data and regional structural relations indicate a minimum thickness of > 3 km. A narrow contact aureole is variably developed, particularly in the structurally deepest exposures. Quantifying displacement of the metamorphic host rocks during batholith growth is hampered because host rocks are largely serpentine-matrix mélange and chert argillite with little structural coherency. Field relations in the host rocks indicate that both elastic (diking) and inelastic (creep, folding) deformation facilitated space for the WCB. Internal features include variations in texture, crystal size, fabric development, and multiple generations of co-magmatic gabbro, diorite, qtz

  2. Magma dynamics at the base of an evolving mafic magma chamber: Incompatible element evidence from the Partridge River intrusion, Duluth Complex, Minnesota, USA

    NASA Astrophysics Data System (ADS)

    Chalokwu, Christopher I.; Ariskin, Alexei A.; Koptev-Dvornikov, Evgeny V.

    1996-12-01

    A characteristic feature of the Partridge River intrusion of the Keweenawan Duluth Complex is the approximately fivefold to ninefold increase in the concentrations of incompatible elements in the lower zone compared with cumulates stratigraphically higher. The concentrations of incompatible elements decrease from the lower zone upward to steady state values, which is ascribed to variations in the proportions of trapped liquid rather than variable degrees of fractional crystallization of a single parental magma. The calculated average composition of trapped liquid using our algorithm is similar to typical Keweenawan low-alumina, high Tisbnd P basalts associated with the Duluth Complex but is different from the leading edge ferrodioritic liquid quenched in the chilled margin of the intrusion. This difference suggests that the chilled margin does not represent the original (parental) magma composition from which the whole intrusion solidified, and that the enrichment of incompatible elements may be related to the local flotation of magmatic suspensions. To test the latter hypothesis numerically, we have used heat-mass transfer models, assuming a sheet-like magma chamber, to calculate the parameters of the model that best reproduce the observed distribution of incompatible elements in a mush zone at the base of the Partridge River intrusion. The results indicate that a mush zone enriched in the incompatible elements is produced if the velocity of movement of the lower solidification front into the magma body was less than the floating velocity of the bulk crystal mush. The dynamic parameters that best reproduce the observed distribution of incompatible elements include a magma emplacement pressure of 2 kbar, critical crystallinities of 50-68% in the mush zone from which the liquid is being expelled, and an emplacement temperature of ˜ 1160°C for the initial magma.

  3. Deducing the magma chamber processes of middle Eocene volcanics, Sivas and Tokat regions; NE Turkey: Insights from clinopyroxene chemistry

    NASA Astrophysics Data System (ADS)

    Göçmengil, Gönenç; Karacık, Zekiye; Genç, Ş. Can; Prelevic, Dejan

    2016-04-01

    Middle Eocene Tokat and Sivas volcanic successions occur within the İzmir-Ankara-Erzincan suture zone. Different models are suggested for the development of the middle Eocene volcanism such as post-collisional, delamination and slab-breakoff models as well as the arc magmatism. In both areas, volcanic units cover all the basement units with a regional disconformity and comprise lavas spanning a compositional range from mainly basalt-basaltic andesite to a lesser amount trachyte. Here, we report mineral chemistry of different basaltic lavas through transect from northern continent (Tokat region, Pontides) to southern continent (Sivas region, Kırşehir block) to deduce the characteristics of the magma chamber processes which are active during the middle Eocene. Basaltic lavas include olivine bearing basalts (Ol-basalt: ± olivine + clinopyroxene + plagioclase); amphibole bearing basaltic andesite (Amp-basaltic andesite: amphibole + clinopyroxene + plagioclase ± biotite) and pyroxene bearing basaltic andesite (Px-basaltic andesite: clinopyroxene + plagioclase). Microlitic, glomeroporphyric and pilotaxitic texture are common. Clinopyroxene phenocrystals (macro ≥ 750 μm and micro ≤300 μm) are common in all three lava series which are investigated by transecting core to rim compositional profiles. They are generally augite and diopside; euhedral to subhedral in shape with oscillatory, normal and reverse zoning patterns. Also, all clinopyroxene phenocrystals are marked by moderately high Mg# (for Ol-basalt: 67-91; avg. 80; Amp-basaltic andesite: 76-83, avg: 80; Px -basaltic andesite 68-95, avg: 81). In Ol-basalt, clinopyroxene phenocrystals show normal zonation (high Mg# cores and low Mg# rims). In Amp-basaltic andesite, clinopyroxenes are generally homogenous in composition with minor variation of Mg# towards the rims. On the contrary, in Px-basaltic andesite, clinopyroxene macro phenocrystals show reverse zonation with the core with low Mg# and the rims with

  4. High-Mg adakitic rocks and their complementary cumulates formed by crystal fractionation of hydrous mafic magmas in a continental crustal magma chamber

    NASA Astrophysics Data System (ADS)

    Ma, Qiang; Xu, Yi-Gang; Zheng, Jian-Ping; Sun, Min; Griffin, William L.; Wei, Ying; Ma, Liang; Yu, Xiaolu

    2016-09-01

    Understanding how adakitic magmas form is important for understanding the formation of the continental crust. Generating such high-Sr/Y rocks by crystal fractionation of basalts/basaltic andesites in magma chambers has been proposed in a wide range of tectonic settings. However, the complementary cumulates predicted by this scenario have rarely been observed. The late Triassic (~ 227 Ma) Ningcheng complex from the North China Craton is composed of a websterite - (Ol -/Hbl-) pyroxenite - gabbro unit and a quartz-diorite unit. They are interpreted as the products (cumulates and derivative melts, respectively) of fractionation from hydrous mafic magmas at mid- to lower-crustal pressures (4.9 ~ 8.3 kbar). The quartz diorites are high-Mg intermediate rocks with moderate SiO2 (57.0 ~ 62.9 wt%), high Mg# (> 49) and adakitic trace element signatures, such as high Sr (≥ 636 ppm) and light rare earth elements (REEs), low Y (≤ 17 ppm) and heavy REEs (Yb ≤ 1.8 ppm), lack of obvious Eu anomalies, and high Sr/Y (≥ 31) and La/Yb (≥ 24)). These adakitic signatures reflect differentiation of hydrous mantle-derived magmas in the deep crust, leaving behind a plagioclase-free residual solid assemblage in the early stages, which is represented by the coeval websterite-pyroxenite complex. This study therefore not only demonstrates that hydrous crystal fractionation is an important mechanism to form adakitic rocks, but also presents an example of a preserved fractionating system, i.e. high-Sr/Y rocks and their complementary cumulates. A geochemical comparison is made between representative adakitic rocks formed by fractionation of hydrous magmas and Archean TTGs. It is suggested that crystal fractionation is an efficient process for making Phanerozoic high Sr/Y rocks but was not responsible for the formation of Archean granitoids.

  5. Dynamics of exploding magma chambers: Implications for K-T volcanism and mass extinctions

    NASA Technical Reports Server (NTRS)

    Rice, A. R.

    1988-01-01

    Although it is well known that unconfined chemical explosives may yield pressures to several megabars on detonation in air, the explosive literature has yet to be accessed by some contributors to the volcanological literature who've indicated that pressures in excess of the overburden and/or tensile cannot be obtained. Idealized ballistic assessments of pressures internal to volcanoes yield pressures in the hundreds of kilobar range upon correction by addition of friction, etc. Previous assessments of exploding magma chamber pressure have been made from the characteristics of the Mt. St. Helens explosion. A variety of methods yield pressures of similar value: at least hundreds of kilobars. Such results are consistent with free energy requirements for quench supersaturation explosion, a process occurring in solidifying industrial melts. Several reviews of geochemical literature emphasize the carbon event at the Cretaceous-Tertiary (K-T) boundary as being an indicator of a massive dump of CO2 derived from the mantle and entering the atmosphere by extensive global volcanism. Oxygen isotope data indicates extreme warming at the end of the Cretaceous which is consistent with a greenhouse effect attending the CO2 event. Reaction rate equations for the quench supersaturation explosion mechanism indicated, are consistent with the rise in pressure to 30 kbar on solidification of magmatic melts, these pressures limited by the strength of the experimental apparatus.

  6. Fluid inclusions in apatite from Jacupiranga calcite carbonatites: Evidence for a fluid-stratified carbonatite magma chamber

    NASA Astrophysics Data System (ADS)

    Costanzo, Alessandra; Moore, Kathryn Ruth; Wall, Frances; Feely, Martin

    2006-10-01

    Carbonatites of the Jacupiranga alkaline-carbonatite complex in São Paulo State, Brazil, were used to investigate mineral-fluid interaction in a carbonatite magma chamber because apatite showed a marked discontinuity between primary fluid inclusion-rich cores and fluid inclusion-poor rims. Sylvite and burbankite, apatite, pyrite, chalcopyrite and ilmenite are the common phases occurring as trapped solids within primary fluid inclusions and reflect the general assemblage of the carbonatite. The apatite cores had higher Sr and REE concentrations than apatite rims, due to the presence of fluid inclusions into which these elements partitioned. A positive cerium anomaly was observed in both the core and rim of apatite crystals because oxidised Ce 4+ partitioned into the magma. The combined evidence from apatite chemistry, fluid inclusion distribution and fluid composition was used to test the hypotheses that the limit of fluid inclusion occurrence within apatite crystals arises from: (1) generation of a separate fluid phase; (2) utilization of all available fluid during the first stage of crystallization; (3) removal of crystals from fluid-rich magma to fluid-poor magma; (4) an increase in the growth rate of apatite; or (5) escape of the fluids from the rim of the apatite after crystallization. The findings are consistent with fractionation and crystal settling of a carbonatite assemblage in a fluid-stratified magma chamber. Secondary fluid inclusions were trapped during a hydrothermal event that precipitated an assemblage of anhedral crystals: strontianite, carbocernaite, barytocalcite, barite and norsethite, pyrophanite, magnesian siderite and baddeleyite, ancylite-(Ce), monazite-(Ce) and allanite. The Sr- and REE-rich nature of the secondary assemblage, and lack of a positive cerium anomaly indicate that hydrothermal fluids have a similar source to the primary magma and are related to a later carbonatite intrusion.

  7. Surface displacements resulting from magma-chamber roof subsidence, with application to the 2014-2015 Bardarbunga-Holuhraun volcanotectonic episode in Iceland

    NASA Astrophysics Data System (ADS)

    Browning, John; Gudmundsson, Agust

    2015-12-01

    The conditions which lead to caldera collapse are still poorly constrained. As there have only been four, possibly five, well-documented caldera forming events in the past century, the geodetic signals produced during chamber roof subsidence, or chamber volume reduction (shrinkage) in general, are not well documented or understood. In particular, when two or more geodetic sources are operating and providing signals at the same time, it is important to be able to estimate the likely contribution of each. Simultaneous activities of different geodetic sources are common and include pressure changes in magma chambers/reservoirs occurring at the same time as dyke emplacement. Here we present results from numerical models designed to simulate the subsidence of a magma-chamber roof, either directly (chamber shrinkage) or through ring-fault displacement, and the induced surface deformation and crustal stresses. We consider chamber depths at 3 km, 5 km, and 7 km below the crustal surface, using both non-layered (isotropic) and layered (anisotropic) crustal models. We also model the effects of a caldera lake and of a thick ice cover (ice sheet) on top of the caldera. The results suggest that magma-chamber roof subsidences between 20 m and 100 m generate large (tens of centimetres) vertical and, in particular, horizontal displacements at the surfaces of the ice and the crust out to distances of up to tens of kilometres from the caldera/chamber centre. Crustal layering tends to reduce, but increasing chamber depth to enlarge, the horizontal and vertical surface displacements. Applying the results to the ice subsidence in the Bardarbunga Caldera during the 2014-2015 Bardarbunga-Holuhraun volcanotectonic episode indicates that the modelled ice displacements are less than those geodetically measured. Also, the geodetically measured crustal displacements are less than expected for a 60 m chamber-roof subsidence. The modelling results thus suggest that only part of the ice

  8. Direct evidence for the origin of low-18O silicic magmas: quenched samples of a magma chamber's partially-fused granitoid walls, Crater Lake, Oregon

    USGS Publications Warehouse

    Bacon, C.R.; Adami, L.H.; Lanphere, M.A.

    1989-01-01

    Partially fused granitoid blocks were ejected in the climactic eruption of Mount Mazama, which was accompanied by collapse of Crater Lake caldera. Quartz, plagioclase, and glass in the granitoids have much lower ??18O values (-3.4 to +4.9???) than any fresh lavas of Mount Mazama and the surrounding region (+5.8 to +7.0???). Oxygen isotope fractionation between phases in granitoids is consistent with equilibrium at T ??? 900??C following subsolidus exchange with hydrothermal fluids of meteoric origin. Assimilation of ??? 10-20% of material similar to these granitoids can account for the O and Sr isotopic compositions of lavas and juvenile pyroclasts derived from the climactic magma chamber, many of which have ??18O values ??? 0.5??? or more lower than comparable lavas of Mount Mazama. The O isotope data provide the only clear evidence for such assimilation because the mineralogy and chemical and radiogenic isotopic compositions of the granitoids (dominantly granodiorite) are similar to those of erupted juvenile magmas. The granitoid blocks from Crater Lake serve as direct evidence for the origin of 18O depletion in large, shallow silicic magma bodies. ?? 1989.

  9. Xenoliths from Late Cretaceous seamounts in the Central Pacific: Cumulates of fractionating alkalic basalt magma chambers

    SciTech Connect

    Davis, A.S.; Friesen, W.B.; Pickthorn, L.; Pringle, M.S.; Clague, D.A. )

    1990-06-01

    Abundant xenoliths in alkalic basalt were recovered from two Late Cretaceous seamounts in the Central Pacific. One seamount, located in the Phoenix archipelago (lat 0{degree}22'5, long 176{degree}05'W), is dated by {sup 40}Ar/{sup 39}Ar techniques as 65 Ma. The other seamount, located in the northern Line Islands (lat 15{degree}39'N, long 170{degree}23'W), is dated as 70 Ma. Host lavas are basanite and differentiated alkalic basalt. Mafic xenolith assemblages consist of clinopyroxene with variable amounts of amphibole and mica. Intermediate assemblages have abundant feldspar in addition to the mafic minerals. Rare felsic xenoliths consist of two or more feldspars. Variable amounts of apatite, titanite, and magnetite are poikilitically enclosed in mafic phases, and minor feldspathoids are present in some xenoliths. Most xenoliths are holocrystalline with fine- to medium-grained, equigranular cumulus texture, but two xenoliths have a seriate, interlocking crystal framework in a small amount of glassy to microcrystalline matrix. Clinopyroxene in the holocrystalline samples is partially replaced by amphibole. In a few samples, extensive replacement of clinopyroxene by rounded amphibole grains results in a nearly granoblastic texture. Clinopyroxene compositions range from diopside to ferrosalite and are essentially Cr-free but generally have high Ti and Al contents. Cr-rich diopside and Al-augite, characteristic of mantle clinopyroxene, are absent. Feldspars include plagioclase, anorthoclase, and sanidine. Mineral compositions of xenoliths are similar to those of phenocrysts in the host lavas, indicating that these xenoliths are not metasomatized mantle material, but rather are cumulates from fractionating alkalic basalt magma chambers.

  10. Linking Plagioclase Zoning Patterns to Active Magma Processes

    NASA Astrophysics Data System (ADS)

    Izbekov, P. E.; Nicolaysen, K. P.; Neill, O. K.; Shcherbakov, V.; Plechov, P.; Eichelberger, J. C.

    2015-12-01

    Plagioclase, one of the most common and abundant mineral phases in volcanic products, will vary in composition in response to changes in temperature, pressure, composition of the ambient silicate melt, and melt H2O concentration. Changes in these parameters may cause dissolution or growth of plagioclase crystals, forming characteristic textural and compositional variations (zoning patterns), the complete core-to-rim sequence of which describes events experienced by an individual crystal from its nucleation to the last moments of its growth. Plagioclase crystals in a typical volcanic rock may look drastically dissimilar despite their spatial proximity and the fact that they have erupted together. Although they shared last moments of their growth during magma ascent and eruption, their prior experiences could be very different, as plagioclase crystals often come from different domains of the same magma system. Distinguishing similar zoning patterns, correlating them across the entire population of plagioclase crystals, and linking these patterns to specific perturbations in the magmatic system may provide additional perspective on the variety, extent, and timing of magma processes at active volcanic systems. Examples of magma processes, which may be distinguished based on plagioclase zoning patterns, include (1) cooling due to heat loss, (2) heating and/or pressure build up due to an input of new magmatic material, (3) pressure drop in response to magma system depressurization, and (4) crystal transfer between different magma domains/bodies. This review will include contrasting examples of zoning patters from recent eruptions of Karymsky, Bezymianny, and Tolbachik Volcanoes in Kamchatka, Augustine and Cleveland Volcanoes in Alaska, as well as from the drilling into an active magma body at Krafla, Iceland.

  11. Forward and Inverse Modeling of Magma Chamber Dynamics and Crystal Zoning Provides Insights into Rates and Processes Leading to Eruption

    NASA Astrophysics Data System (ADS)

    Costa Rodriguez, F.; Bouvet de Maisonneuve, C.; Degruyter, W.; Huber, C.

    2014-12-01

    Chemical and textural features of crystals provide unique constrains on the processes and rates that occur during the growth, replenishment and eruption of magma reservoirs. Recent studies that use different methods have highlighted that many eruptions are issued from reservoirs that may grow for up to hundreds of thousands years (e.g, U-Th series of mineral separates, zircon dating). In contrast, the effect of new magma injections (recharges) can influence the thermodynamic state of reservoirs on a much shorter scale. In extreme cases it can lead to remobilization of magmas over months (for small reservoirs) to thousands of years (for larger systems). Modeling of mineral zoning provides a lower bound estimate for the timescales associated with magma recharge because (a) they do not record dissolution/resorbtion of phases and (b) they only record the time at which a crystal reacts to a thermodynamic change, which does not necessarily equate with the timing of an intrusion. In open system reservoirs, magmas may experience significant thermal and compositional fluctuations over time, and so far, only simple cooling scenarios [1] have been considered. In particular, under what conditions does a recharge lead to an eruption? Can large recharge events be mostly recycled and partially involved in later eruptions? Here we combine new forward models of magma chamber replenishment and evolution [2] that track the thermodynamic evolution of shallow resevoir with crystal zoning models. We explore several scenarios of magma reservoir growth and evolution and compare them to the time scales obtained from the crystal zoning (e.g. thermal history and boundary condition changes with time). Inverse modeling of natural crystal zoning profiles from the silicic eruptions of Rabaul caldera in 1994 and 2006 allows us to distinguish between scenarios where inputs of fresh magma leads to eruption and recharges that are accommodated by the reservoir over longer time scales and are

  12. Subsidence of ash-flow calderas: Relation to caldera size and magma-chamber geometry

    USGS Publications Warehouse

    Lipman, P.W.

    1997-01-01

    Diverse subsidence geometries and collapse processes for ash-flow calderas are inferred to reflect varying sizes, roof geometries, and depths of the source magma chambers, in combination with prior volcanic and regional tectonic influences. Based largely on a review of features at eroded pre-Quaternary calderas, a continuum of geometries and subsidence styles is inferred to exist, in both island-arc and continental settings, between small funnel calderas and larger plate (piston) subsidences bounded by arcuate faults. Within most ring-fault calderas, the subsided block is variably disrupted, due to differential movement during ash-flow eruptions and postcollapse magmatism, but highly chaotic piecemeal subsidence appears to be uncommon for large-diameter calderas. Small-scale downsag structures and accompanying extensional fractures develop along margins of most calderas during early stages of subsidence, but downsag is dominant only at calderas that have not subsided deeply. Calderas that are loci for multicyclic ash-flow eruption and subsidence cycles have the most complex internal structures. Large calderas have flared inner topographic walls due to landsliding of unstable slopes, and the resulting slide debris can constitute large proportions of caldera fill. Because the slide debris is concentrated near caldera walls, models from geophysical data can suggest a funnel geometry, even for large plate-subsidence calderas bounded by ring faults. Simple geometric models indicate that many large calderas have subsided 3-5 km, greater than the depth of most naturally exposed sections of intracaldera deposits. Many ring-fault platesubsidence calderas and intrusive ring complexes have been recognized in the western U.S., Japan, and elsewhere, but no well-documented examples of exposed eroded calderas have large-scale funnel geometry or chaotically disrupted caldera floors. Reported ignimbrite "shields" in the central Andes, where large-volume ash-flows are inferred to

  13. Magma chamber recharging and tectonic influence on reservoirs: The 1986 eruption of Izu-Oshima

    NASA Astrophysics Data System (ADS)

    Linde, Alan T.; Kamigaichi, Osamu; Churei, Masaaki; Kanjo, Kenji; Sacks, Selwyn

    2016-02-01

    Although analytical expressions for deformation due to simple reservoirs and planar dikes have been in use for decades, seldom are there sufficient data to provide well-constrained detailed models of volcanic activity. Deformation due to the eruption of Miharayama, Izu-Oshima, Japan, in November 1986 was captured by a wider array of monitoring than usual at that time. Here we show that the first eruptive stage requires a shallow non-spherical source, extended perpendicular to the axis of maximum tectonic tension, together with a deeper reservoir. The shallow reservoir was partially recharged, from a deeper reservoir, during the eruption, with a magma ascent rate of ~ 10 km/day; this has important implications for estimation of reservoir gas content. Precursory changes starting 2 h before the second phase require dike propagation from at least 10 km depth. Surface elevation changes are indicative of a long sub-surface dike. A model incorporating dikes and a deep (10 km) reservoir, extended in the same direction as the dikes, provides a very good match to the data. Such reservoir geometry may explain why the eruption was unexpected.

  14. There's more than one way to build a caldera magma chamber: Evidence from volcanic-plutonic relationships at three faulted Rio-Grande-rift calderas

    NASA Astrophysics Data System (ADS)

    Zimmerer, M. J.; McIntosh, W. C.

    2011-12-01

    The temporal and chemical relationships of volcanic and plutonic rocks of the Questa (NM), Mt. Aetna (CO), and Organ caldera (NM) complexes were investigated to establish the origin of these silicic magmas. Rio Grande Rift faulting at these systems has exposed both intracaldera sequences and subvolcanic plutons. Ar/Ar and U/Pb ages reveal the timing of volcanic activity and pluton emplacement and cooling. We observe a link between ignimbrite zoning patterns and the temporal-chemical relationship of volcanic and plutonic rocks. The Questa caldera erupted the high-SiO2 peralkaline Amalia Tuff (AT) at 25.4 Ma. Volumetrically minor phases of two resurgent plutons and a ring dike are compositionally similar to the AT. The age of the ring dike (25.4 Ma) is indistinguishable to AT, suggesting that the peralkaline intrusions are nonerupted AT. The remaining pluton ages are 100 ka to 6.1 Ma younger than AT and are too young to be the AT residual crystal mush. The Mt. Princeton batholith and nested Mt. Aetna caldera are interpreted to be the sources for the 37.3 Ma, low-SiO2 rhyolitic Wall Mountain Tuff (WMT) and the 34.3 Ma, dacitic Badger Creek Tuff (BCT). U/Pb and Ar/Ar ages of Mt. Princeton batholith (36.5 to 35.1 Ma) indicate that it was emplaced and rapidly cooled during the interval between the WMT and BCT eruptions, and that any WMT age intrusions are now eroded. During the eruption of the BCT, the fully crystallized Mt. Princeton batholith collapsed into the Mt. Aetna caldera. Intrusions along the margins of the Mt. Aetna caldera are compositionally identical the BCT and contain zircons 100 to 500 ka older than the tuff, suggesting that the BCT magma chamber was incrementally emplaced prior to caldera eruption. The Organ caldera complex erupted three ignimbrites: a basal high-silica 36.5 Ma rhyolite, a middle intermediate-silica 36.2 Ma rhyolite, and an upper 36.0 Ma low-silica rhyolite. The intracaldera sequence is intruded by the Organ Needle pluton. U/Pb zircon

  15. Conductive heat transfer from an isothermal magma chamber and its application to the measured heat flow distribution from mount hood, Oregon

    USGS Publications Warehouse

    Nathenson, Menuel; Tilling, Robert I.; ,

    1993-01-01

    A steady-state solution for heat transfer from an isothermal, spherical magma chamber, with an imposed regional geothermal gradient far from the chamber, is developed. The extensive published heat-flow data set for Mount Hood, Oregon, is dominated by conductive heat transfer in the deeper parts of most drill holes and provides an ideal application of such a model. Magma-chamber volumes or depths needed to match the distribution of heat-flow data are larger or shallower than those inferred from geologic evidence.

  16. Shallow Chamber & Conduit Behavior of Silicic Magma: A Thermo- and Fluid- Dynamic Parameterization Model of Physical Deformation as Constrained by Geodetic Observations: Case Study; Soufriere Hills Volcano, Montserrat

    NASA Astrophysics Data System (ADS)

    Gunn de Rosas, C. L.

    2013-12-01

    The Soufrière Hills Volcano, Montserrat (SHV) is an active, mainly andesitic and well-studied stratovolcano situated at the northern end of the Lesser Antilles Arc subduction zone in the Caribbean Sea. The goal of our research is to create a high resolution 3D subsurface model of the shallow and deeper aspects of the magma storage and plumbing system at SHV. Our model will integrate inversions using continuous and campaign geodetic observations at SHV from 1995 to the present as well as local seismic records taken at various unrest intervals to construct a best-fit geometry, pressure point source and inflation rate and magnitude. We will also incorporate a heterogeneous media in the crust and use the most contemporary understanding of deep crustal- or even mantle-depth 'hot-zone' genesis and chemical evolution of silicic and intermediate magmas to inform the character of the deep edifice influx. Our heat transfer model will be constructed with a modified 'thin shell' enveloping the magma chamber to simulate the insulating or conducting influence of heat-altered chamber boundary conditions. The final forward model should elucidate observational data preceding and proceeding unrest events, the behavioral suite of magma transport in the subsurface environment and the feedback mechanisms that may contribute to eruption triggering. Preliminary hypotheses suggest wet, low-viscosity residual melts derived from 'hot zones' will ascend rapidly to shallower stall-points and that their products (eventually erupted lavas as well as stalled plutonic masses) will experience and display two discrete periods of shallow evolution; a rapid depressurization crystallization event followed by a slower conduction-controlled heat transfer and cooling crystallization. These events have particular implications for shallow magma behaviors, notably inflation, compressibility and pressure values. Visualization of the model with its inversion constraints will be affected with Com

  17. The Atlantis Bank gabbro-suite was not a "normal" magma-chamber that produced basalts

    NASA Astrophysics Data System (ADS)

    Kvassnes, A. J.; Dick, H. J. B.; Grove, T. L.

    2003-04-01

    The differentiation of the basalts sampled at Atlantis II Fracture Zone, South-West Indian Ridge, is not the result of simple fractionation of gabbroic mineral-assemblages like those recovered from the adjacent Atlantis Bank and ODP Hole 735B. Large mineral data sets for the gabbros (Dick, et al 2002) are now available for analysis and comparison to spatially associated basalts. We have used Melts and pMelts (Ghiorso and Sack, 1995) to estimate the fractional crystallization trend gabbros from a primitive mantle melt or of the AII F.Z. MORB. Thermodynamic models (Grove et al (1992), Putirka (1999)) were also used to model the glasses hypothetical mafic and felsic mineral equilibrium-compositions. Our results show that while the basalts suggest 30-50% crystallization, the gabbros indicate 35-90% crystallization of a primary melt. It is therefore unlikely that the gabbros sampled from Atlantis Bank are the fossil magma-chambers that expelled melts that formed the spatially associated basalts. The models also show that the most primitive gabbros have elevated clinopyroxene Mg#s (Mg/(Mg+Fe)) relative to the coexisting plagioclase An%. This was unexpected, as the clinopyroxene frequently occurs as oikocrysts surrounding the plagioclase and encloses rounded olivine chadacrysts, indicating that the clinopyroxene precipitated late. Elthon (1992) noted the same problem for Cayman Trough gabbros; suggesting that this was the result of intermediate pressure fractionation. In our models, pressure does have some effect up to 5kbar, but is not enough to explain the discrepancy. We propose a model where melts are modified in a porous network or mush. Plagioclase-olivine networks form by accumulation of buoyant glomerocrysts and then work as filters as new melts pass through. Dissolution of the minerals would make the new melt appear to be more primitive with regards to increased Mg#s, as the dissolution happens fast without complete internal re-equilibration with the gabbro

  18. The Torres del Paine intrusion as a model for a shallow magma chamber

    NASA Astrophysics Data System (ADS)

    Baumgartner, Lukas; Bodner, Robert; Leuthold, Julien; Muntener, Othmar; Putlitz, Benita; Vennemann, Torsten

    2014-05-01

    The shallow magmatic Torres del Paine Intrusive Complex (TPIC) belongs to a series of sub-volcanic and plutonic igneous bodies in Southern Chile and Argentina. This trench-parallel belt is located in a transitional position between the Patagonia Batholith in the West, and the alkaline Cenozoic plateau lavas in the East. While volumetrically small amounts of magmatism started around 28 my ago in the Torres del Paine area, and a second period occurred between 17-16 Ma, it peaked with the TPIC 12.59-12.43 Ma ago. The spectacular cliffs of the Torres del Paine National park provide a unique opportunity to study the evolution of a very shallow magma chamber and the interaction with its host rocks. Intrusion depth can be estimated based on contact metamorphic assemblages and granite solidus thermobarometry to 750±250 bars, corresponding to an intrusion depth of ca. 3km, ca. 500m above the base of the intrusion. Hornblende thermobarometry in mafic rocks agrees well with these estimates (Leuthold et al., 2014). The TPIC is composed of a granitic laccolith emplaced over 90ka (Michel et al., 2008) in 3 major, several 100m thick sheets, forming an overall thickness of nearly 2 km. Contacts are sharp between sheets, with the oldest sheet on the top and the youngest on the bottom (Michel et al., 2008). The granitic laccolith is under-plated by a ca. 400m thick mafic laccolith, built up over ca. 50ka (Leuthold et al. 2012), constructed from the bottom up. Granitic and mafic sheets are themselves composed of multiple metric to decametric pulses, mostly with ductile contacts between them, resulting in outcrop patterns resembling braided stream sediments. The contact of the TPIC with the Cretaceous flysch sediments document intrusion mechanism. Pre-existing sub-horizontal fold axes are rotated in the roof of the TPIC, clearly demonstrating ballooning of the roof; no ballooning was observed in the footwall of the intrusion. Extension during ballooning of the roof is indicated by

  19. The Ignimbrite Campana Magma Chamber: Pre-eruptive P-t-x Conditions From Melt Inclusion Data

    NASA Astrophysics Data System (ADS)

    Marianelli, P.; Proto, M.; Sbrana, A.

    The Ignimbrite Campana (36 ka) represents the most powerful eruption characterizing the volcanic history of the Campi Flegrei caldera. The eruption was fed by a stratified magma chamber (Civetta et al., 1997). This study, based on melt inclusion investigations in phenocrysts of pumice, is aimed to better constrain depth, thermal conditions and composition of magmas hosted in the magma chamber. Samples from the Breccia Museo products (proximal deposits of the Ignimbrite Campana) were selected, due to their sin-eruptive and sin-depositional quenching. On the basis of melt inclusions investigations important informations about crystallization conditions (P, T, X) and volatile contents have been obtained. Glass compositions fall in the trachyte field close to the trachyte-phonolite boundary, similarly to the others Ignimbrite Campana products. The temperature of homogenization ranges between 850 and 1135°C. These values of temperature, that can be assumed as crystallization temperatures, correlate to the host crystal compositions with the highest one corresponding to melt inclusions trapped in less Fe-rich pyroxene. FTIR analyses on double -polished melt inclusions were carried out in order to investigate H2O and CO2 contents. Preliminary results indicate values of H2O that range from about 2 up to 8.0wt%, whereas CO2 was not detected. Lowest values of H2O (modal value = 2- 3wt%) correspond to the melt inclusions from layers at the top of the Breccia Museo (pumice flow deposits). Minimum pressures of crystallization are estimated in the range 100-200 MPa, assuming saturation conditions for the trapped melts and calculating the solubility of H2O in trachytic magmas according to the model of Moore et al. (1998). References Civetta L., Orsi G., Pappalardo L., Fisher R.V., Heiken G., Ort M. (1997): Geochemical zoning, mingling, eruptive dynamics and depositional processes ­ the Campanian Ignimbrite, Campi Flegrei caldera, Italy. J. Volcanol. Geoth. Res., 75: 183

  20. Constraints from sill intrusions and their deeper source magma chambers (seismic high velocity bodies) on the origins of volcanic rifted margins

    NASA Astrophysics Data System (ADS)

    Rohrman, M.

    2015-12-01

    Volcanic rifted margins are characterized by massive igneous activity originating from the rift margin, characterized by seaward dipping reflectors. These consist of basalt flows and associated magmatic products, from deep magma chambers imaged on seismic data as High Velocity Bodies (HVB) with seismic velocities between 7 and 7.5 km/s. The relationship between rifting and decompression melting have been well quantified, using the HVB's as constraints on magmatic production to match extension models. Crucial in this approach are the relationship between extension and mantle plumes, with HVB's generated by mantle plumes often indicative of velocities between 7.5 - 7.8 km/s. Here I address information that can be obtained from sill complexes in sedimentary basins associated with rifting, representing the earliest phase of magmatism. I use a simple crustal scale hydrostatic model for dikes while incorporating the presence of sills by calculating magmatic overpressures from differences in pressure gradients. It transpires that the presence of sills as observed on seismic reflection and outcrop data, can be predicted. Modelling further suggests that the source of these sill complexes are large magma chambers at or near the Moho, and equate to HVB's observed on seismic data. Utilizing simple mass balance calculations, the ratio of cumulate thickness (from HVB thickness) and expelled melt (from accumulated sill thicknesses) can be related to MgO content in expelled liquids, primary magma and cumulates. Higher MgO content translates in higher seismic velocities. Thus, HVB velocity can subsequently be used to discriminate between mantle plume, or shallow rift related melting. The theory is applied to various basins bordering the northern North Atlantic (Vøring Basin, Jameson Land Basin and Rockall Basin) and South Atlantic rifts (Namibia), associated with the Paleocene/Eocene Iceland mantle plume and the Early Cretaceous Tristan da Cunha mantle plume magmatism respectively.

  1. Open magma chamber processes in the formation of the Permian Baima mafic-ultramafic layered intrusion, SW China

    NASA Astrophysics Data System (ADS)

    Liu, Ping-Ping; Zhou, Mei-Fu; Wang, Christina Yan; Xing, Chang-Ming; Gao, Jian-Feng

    2014-01-01

    The Baima mafic-ultramafic layered intrusion of the 260-Ma Emeishan Large Igneous Province (ELIP) hosts the second largest Fe-Ti-(V) oxide deposit in the Panxi region, SW China. It is a ~ 1600-m-thick layered body intruded by slightly younger syenitic and granitic plutons. The intrusion includes the Lower and Upper Zones. Troctolite and olivine pyroxenite of the Lower Zone contains conformable oxide ore layers, whereas the Upper Zone consists of olivine gabbro and gabbro with abundant apatite in the higher level. The crystallization order of the silicates in the Baima intrusion is olivine → plagioclase → clinopyroxene. Fe-Ti oxides (titanomagnetite and ilmenite) crystallized after olivine, and possibly plagioclase. The oxide ores in the Lower Zone show slightly LREE enriched patterns with (La/Yb)N values between 2.0 and 6.4, and positive Eu anomalies (Eu/Eu*) of 1.0 to 2.7. In contrast, olivine gabbros in the Lower Zone display stronger LREE enrichments (La/YbN = 7.7-14.0) and positive Eu anomalies (Eu/Eu* = 2.8-3.3). Gabbros in the Upper Zone have REE profiles characterized by intermediate LREE enrichments with (La/Yb)N values of 3.2 to 11.2 and positive Eu anomalies of 2.1 to 3.0. Primitive mantle-normalized trace element patterns are characterized by negative La-Ce, Th, Sm and positive Nb-Ta, Ba and Ti anomalies in oxide ores and negative Th-U, Zr-Hf and positive Ba, Sr and Ti anomalies in olivine gabbro and gabbro. Fo of olivine and An of plagioclase remain roughly constant from 0 to ~ 90 m in the Lower Zone, indicating that the magma chamber was continuously filled by compositionally similar magmas during the initial stage. Three magma replenishments occurred afterwards in the upper part of the Lower Zone and the Upper Zone based on compositional reversals of plagioclase, olivine and Sr isotope. Mass balance calculations show that the Baima parental magma can produce all oxide ores under closed system conditions. A wide range of An values of plagioclase

  2. The Ioko-Dovyren layered massif (Southern Siberia, Russia): 1. Internal structure, magma compositions, and fingerprints of open magma chamber behavior

    NASA Astrophysics Data System (ADS)

    Ariskin, Alexey; Danyushevsky, Leonid; Nikolaev, Georgy

    2013-04-01

    YDM cumulates. Estimates for Ol-gabbronorites and Pl-dunites from ultramafic sills result in more evolved magma containing Ol~Fo85 at T~1190oC. Both geochemical and cumulate structure of YDM is indicative of a significant amount of mafic melts to be extracted from the original cumulate piles, followed by their expulsion from the magma staging chamber. Fingerprints of such an open-system behavior are recorded in (1) strong depletion in incompatible elements of the bulk YDM composition with respect to parental magmas, (2) a complimentary "over-enrichment" with Ol cumulates and sulfides, (3) insignificant variations of Ol composition throughout the Layered Series, and (4) the absence of the Upper Border Series as a marginal compositional reversal. This research was supported by AngloAmerican, BHP Billiton and Votorantim Metais through AMIRA project P962, by the Australian Research Council funding to the CODES, and the Russian Foundation for Basic Research (projects 08-05-00194a, 11-05-00268a). [1] Ariskin et al. (2013) Geochem. Intern. [2] Ariskin et al. (2012)Abs. 12th Intern. Ni-Cu-(PGE) symp. (China)

  3. Comagmatic granophyric granite in the Fish Canyon Tuff, Colorado: Implications for magma-chamber processes during a large ash-flow eruption

    USGS Publications Warehouse

    Lipman, P.; Dungan, M.; Bachmann, Olivier

    1997-01-01

    The 27.8 Ma Fish Canyon Tuff, a vast ash-flow sheet (??5000 km3) of uniform phenocryst-rich dacite, is representative of "monotonous intermediate" eruptions from a magma chamber that lacked compositional gradients. Sparse small fragments of comagmatic granophyre in late-erupted tuff and postcaldera lava, having mineral compositions indistinguishable from phenocrysts in the tuff and precaldera lava-like rocks, record complex events in the Fish Canyon chamber just prior to eruption. Sanidine phenocrysts in the granophyre preserve zoning evidence of mingling with andesitic magma, then shattering by decompression and volatile loss accompanying early Fish Canyon eruptions before overgrowth by granophyre. The textural and chemical disequilibria indicate that the eruption resulted from batholith-scale remobilization of a shallow subvolcanic chamber, contrary to previous interpretations of magma storage and phenocryst growth in the lower crust.

  4. Zircon crytallization and recycling in the magma chamber of the rhyolitic Kos Plateau Tuff (Aegean arc)

    USGS Publications Warehouse

    Bachman, O.; Charlier, B.L.A.; Lowenstern, J. B.

    2007-01-01

    In contrast to most large-volume silicic magmas in continental arcs, which are thought to evolve as open systems with significant assimilation of preexisting crust, the Kos Plateau Miff magma formed dominantly by crystal fractionation of mafic parents. Deposits from this ??? 60 km3 pyroclastic eruption (the largest known in the Aegean arc) lack xenocrystic zircons [secondary ion mass spectrometry (SIMS) U-Pb ages on zircon cores never older than 500 ka] and display Sr-Nd whole-rock isotopic ratios within the range of European mantle in an area with exposed Paleozoic and Tertiary continental crust; this evidence implies a nearly closed-system chemical differentiation. Consequently, the age range provided by zircon SIMS U-Th-Pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus. The age distribution from 160 ka (age of eruption by sanidine 40Ar/39Ar dating; Smith et al., 1996) to ca. 500 ka combined with textural characteristics (high crystal content, corrosion of most anhydrous phenocrysts, but stability of hydrous phases) suggest (1) a protracted residence in the crust as a crystal mush and (2) rejuvenation (reduced crystallization and even partial resorption of minerals) prior to eruption probably induced by new influx of heat (and volatiles). This extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned Aegean microplate acts as a refractory container for magmas in the dying Aegean subduction zone (continent-continent subduction). ?? 2007 Geological Society of America.

  5. Zircon crystallization and recycling in the magma chamber of the rhyolitic Kos Plateau Tuff (Aegean arc)

    USGS Publications Warehouse

    Bachman, O.; Charlier, B.L.A.; Lowenstern, J. B.

    2007-01-01

    In contrast to most large-volume silicic magmas in continental arcs, which are thought to evolve as open systems with significant assimilation of preexisting crust, the Kos Plateau Tuff magma formed dominantly by crystal fractionation of mafic parents. Deposits from this ~60 km3 pyroclastic eruption (the largest known in the Aegean arc) lack xenocrystic zircons [secondary ion mass spectrometry (SIMS) U-Pb ages on zircon cores never older than 500 ka] and display Sr-Nd whole-rock isotopic ratios within the range of European mantle in an area with exposed Paleozoic and Tertiary continental crust; this evidence implies a nearly closed-system chemical differentiation. Consequently, the age range provided by zircon SIMS U-Th-Pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus. The age distribution from 160 ka (age of eruption by sanidine 40Ar/39Ar dating; Smith et al., 1996) to ca. 500 ka combined with textural characteristics (high crystal content, corrosion of most anhydrous phenocrysts, but stability of hydrous phases) suggest (1) a protracted residence in the crust as a crystal mush and (2) rejuvenation (reduced crystallization and even partial resorption of minerals) prior to eruption probably induced by new influx of heat (and volatiles). This extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned Aegean microplate acts as a refractory container for magmas in the dying Aegean subduction zone (continent-continent subduction).

  6. Mineral disequilibrium in lavas explained by convective self-mixing in open magma chambers.

    PubMed

    Couch, S; Sparks, R S; Carroll, M R

    2001-06-28

    Characteristic features of many porphyritic andesite and dacite lavas are that they are rich in crystals and display a range of disequilibrium features, including reversely zoned crystals, resorption surfaces, wide ranges of mineral compositions and minerals which are not in equilibrium with the surrounding rock matrix. These features are often interpreted as evidence of the mixing of magmas of contrasting composition, temperature and origin. Here, however, we propose that such features can also be caused by convection within a magma body with a single composition, that is heated from below and cooled from above. We describe petrological observations of andesite lava erupted at the Soufrière Hills volcano, Montserrat, which indicate a heating event and the intermingling of crystals that have very different thermal histories. We present experimental data on a representative groundmass composition of this lava, which indicate that it is difficult to explain the calcic compositions of plagioclase overgrowth rims and microphenocrysts unless parts of the magma were at temperatures much higher than the inferred average temperature. The concept of convective self-mixing allows us to explain the occurrence of compositions of minerals that apparently cannot coexist under equilibrium conditions.

  7. Mineral disequilibrium in lavas explained by convective self-mixing in open magma chambers.

    PubMed

    Couch, S; Sparks, R S; Carroll, M R

    2001-06-28

    Characteristic features of many porphyritic andesite and dacite lavas are that they are rich in crystals and display a range of disequilibrium features, including reversely zoned crystals, resorption surfaces, wide ranges of mineral compositions and minerals which are not in equilibrium with the surrounding rock matrix. These features are often interpreted as evidence of the mixing of magmas of contrasting composition, temperature and origin. Here, however, we propose that such features can also be caused by convection within a magma body with a single composition, that is heated from below and cooled from above. We describe petrological observations of andesite lava erupted at the Soufrière Hills volcano, Montserrat, which indicate a heating event and the intermingling of crystals that have very different thermal histories. We present experimental data on a representative groundmass composition of this lava, which indicate that it is difficult to explain the calcic compositions of plagioclase overgrowth rims and microphenocrysts unless parts of the magma were at temperatures much higher than the inferred average temperature. The concept of convective self-mixing allows us to explain the occurrence of compositions of minerals that apparently cannot coexist under equilibrium conditions. PMID:11429601

  8. Carbonate-derived CO 2 purging magma at depth: Influence on the eruptive activity of Somma-Vesuvius, Italy

    NASA Astrophysics Data System (ADS)

    Dallai, Luigi; Cioni, Raffaello; Boschi, Chiara; D'Oriano, Claudia

    2011-10-01

    Mafic phenocrysts from selected products of the last 4 ka volcanic activity at Mt. Vesuvius were investigated for their chemical and O-isotope composition, as a proxy for primary magmas feeding the system. 18O/ 16O ratios of studied Mg-rich olivines suggest that near-primary shoshonitic to tephritic melts experienced a flux of sedimentary carbonate-derived CO 2, representing the early process of magma contamination in the roots of the volcanic structure. Bulk carbonate assimilation (physical digestion) mainly occurred in the shallow crust, strongly influencing magma chamber evolution. On a petrological and geochemical basis the effects of bulk sedimentary carbonate digestion on the chemical composition of the near-primary melts are resolved from those of carbonate-released CO 2 fluxed into magma. An important outcome of this process lies in the effect of external CO 2 in changing the overall volatile solubility of the magma, enhancing the ability of Vesuvius mafic magmas to rapidly rise and explosively erupt at the surface.

  9. Investigation of MAGMA chambers in the Western Great Basin. Final report, 9 June 1982-31 October 1985

    SciTech Connect

    Peppin, W.A.

    1986-02-10

    This report summarizes efforts made by the Seismological Laboratory toward the detection and delineation of shallow crustal zones in the western Great Basin, and toward the development of methods to accomplish such detection. The work centers around the recently-active volcanic center near Long Valley, California. The work effort is broken down into three tasks: (1) network operations, (2) data analysis and interpretation, and (3) the study of shallow crustal amomalies (magma bodies). Section (1) describes the efforts made to record thousand of earthquakes near the Long Valley caldera, and focusses on the results obtained for the November 1984 round Valley earthquake. Section (2) describes the major effort of this contract, which was to quantify the large volume of seismic data being recorded as it pertains to the goals of this contract. Efforts described herein include (1) analysis of earthquake focal mechanisms, and (2) the classification, categorization, and interpretation of unusual seismic phases in terms of reflections and refractions from shallow-crustal anomalous zones. Section (3) summarizes the status of our research to date on the locations of magma bodies, with particular emphasis on a location corresponding to the map location of the south end of Hilton Creek fault. Five lines of independent evidence suggest that magma might be associated with this spot. Finally, new evidence on the large magma bodies within the Long Valley caldera, of interest to the DOE deep drilling project, is presented.

  10. Characteristics of calderas and major ignimbrites in the western Great Basin, USA: Phenocryst-rich rhyolites and voluminous zoned magma chambers

    NASA Astrophysics Data System (ADS)

    Henry, C. D.; John, D. A.

    2012-12-01

    Synthesis of the at least 37 major, mid-Cenozoic ignimbrites (~34-19 Ma; 100's to >1000 km3) and their known or suspected calderas of the western Great Basin (WGB; ignimbrite flareup) challenge two common but partly controversial views about caldera activity: (1) major ignimbrites and/or supervolcanoes (≥1000 km3) are predominantly either sparsely porphyritic, high- to low-Si rhyolite or abundantly porphyritic dacite, and (2) caldera magma chambers are small and completely evacuated during ignimbrite eruption. In the WGB, high-Si, phenocryst-rich (20-50 %) and phenocryst-poor (<15 %) rhyolites are equally abundant and voluminous; only one unit is phenocryst-rich dacite. Phenocryst-rich and probably relatively low-T rhyolite magmas have no trouble erupting as voluminous ignimbrites. Both rhyolite types are commonly normally zoned upward to trachydacite, although several thick (2.5-4 km) intracaldera ignimbrites consist entirely of crystal-rich rhyolite (77-72% SiO2; e.g., 34.0 Ma Caetano Tuff, 25.3 Ma upper tuff of Poco Canyon). All well-studied calderas show abundant post-collapse magmatism expressed as resurgent intrusions (both porphyritic hypabyssal rocks and granitoids), ring-fracture intrusions, and/or intracaldera lavas that are closely related temporally (~0 to 0.5 Ma younger) to caldera formation. The post-collapse rocks are typically less evolved but compositionally continuous with the caldera-forming ignimbrites. Therefore in the WGB, erupted caldera-forming tuffs commonly were the upper parts of large magma chambers that retained considerable volumes of generally less-evolved magma after ignimbrite eruption. Many ignimbrites flowed great distances (≥200 km) from source, mostly because they were channelized into broad paleovalleys that drained westward toward the Pacific Ocean. Several phenocryst-poor and definitely or probably high-T rhyolites are especially widespread and flowed both westward and eastward across a regional and possibly high

  11. On the anatomy of magma chamber and caldera collapse: The example of trachy-phonolitic explosive eruptions of the Roman Province (central Italy)

    NASA Astrophysics Data System (ADS)

    Palladino, Danilo M.; Gaeta, Mario; Giaccio, Biagio; Sottili, Gianluca

    2014-06-01

    Textural and compositional features of pyroclastic products erupted during caldera-forming events often reveal the tapping of different portions of variably zoned magma chambers due to changing geometries of the conduit/vent systems. Here we report on ultrapotassic trachytic-phonolitic explosive eruptions of the Roman Province (central Italy), which show remarkable changes of textural features and glass compositions in the juvenile material, even if the bulk chemical composition is essentially constant. In each example, the lower eruption sequence contains whitish, crystal-poor (leucite-free), highly vesicular pumice, emplaced by early Plinian fallout and/or pyroclastic currents; upsection, the eruption sequence contains black, low porphyritic (sanidine + leucite-bearing), moderately vesicular, scoria or spatter, emplaced by major pyroclastic flows (red tuff with black scoria) and associated co-ignimbrite, coarse lithic-rich breccias. This suggests a shift from a central feeder conduit, tapping the central part of the magma chamber, to a ring fracture vent system, tapping the peripheral portions of the magma chamber, during caldera collapse. Key features of these evacuating magma chambers are the thermal and volatile concentration (Xvol) gradients that produce the observed textural and compositional spectrum of trachy-phonolitic rock types. In particular, the degrees of freedom during the crystallization of these ultrapotassic magmas are increased by the variation of the leucite stability field at different PH2O conditions. Both leucite-free and leucite-bearing differentiated ultrapotassic rock types can be produced in the course of individual eruptions, as a result of pre-eruptive conditions in the feeder magma, with no need to invoke different differentiation suites related to mantle source heterogeneities of parental magmas.

  12. Structural reconstruction and zonation of a tilted mid-crustal magma chamber: the felsic Chemehuevi Mountains plutonic suite

    SciTech Connect

    John, B.E.

    1988-07-01

    Structural relief resulting from middle Tertiary extensional deformation in the Chemehuevi Mountains of California exposes a unique cross section through an extensive (> 280 km/sup 2/) calc-alkalic, compositionally zoned, sill-like granitic intrusion of Late Cretaceous age. Minimum estimates for emplacement pressure, 4 to 6 kbar, imply that the Chemehuevi Mountains plutonic suite was initially intruded at mid-crustal depths and has undergone 10/sup 0/ to 15/sup 0/ of post emplacement tilting, tectonic denudation, and erosion. Reconstruction of the pre-Tertiary (pre-tilt) configuration suggests that this metaluminous to peraluminous granitic suite exhibits crude normal, vertical, and temporal zonation from granodiorite to granite. The zonation involves a decrease in age and an increase in silica away from the walls and roof, the youngest and most evolved members being concentrated toward the center and floor of the intrusion. The lower part of the intrusion had a flat floor, which was penetrated by at least three feeder dikes providing magma to the chamber. Structural reconstruction indicates that the roof is less than 1 km above the exposed top of the intrusion. The magma apparently ponded along the contact between undeformed Proterozoic basement above and subhorizontally foliated mylonitic gneisses below. This reconstruction provides opportunity to observe crosscutting relations between different types of mid-crustal structures (thick mylonitic shear zones, granitic intrusions, and temporally unrelated detachment faults), the geometry of which emphasizes the need for careful evaluation of seismic reflection profiles across complexly deformed and intruded continental crust.

  13. Magma chamber evolution: implication for the generation of continental crust: A case study in Kekeli batholith, North Qilian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Huang, H.; Niu, Y.

    2013-12-01

    plus minor other felsic minerals (Kfs, Qtz). The charnockite sample QL10-26 has the highest TiO2, pyroxene with Amp reaction rims and the most radiogenic WR-Hf (ɛHf(t) = 26) and therefore represent the most primitive mafic endmember. The leucogranite samples have the lowest ɛHf(t) and ɛNd(t) and thus represent the crustal endmember. Other samples with intermediate composition between these two endmembers also have the intermediate isotopic compositions in between. The various zircon types with complex internal structures present in most samples reflect complex source materials. All these observations are consistent with the scenario that the mantle-derived basaltic magmas interacted with granitic magmas derived from the lower crust. Considering the petrotectonic associations, it is probable that the Kekeli Batholith may represent a fossil magma chamber that crystallized at the base of a continental arc crust associated with a subduction zone. Schmitz, M.D., Vervoort, J.D., Bowring, S.A., Patchett, P.J., 2004. Decoupling of the Lu-Hf and Sm-Nd isotope systems during the evolution of granulitic lower crust beneath southern Africa. Geology 32, 405.

  14. New structural limits on magma chamber locations at the Valley of Ten Thousand Smokes, Katmai National Park, Alaska

    SciTech Connect

    Wallmann, P.C.; Pollard, D.D. ); Hildreth, W. ); Eichelberger, J.C. )

    1990-12-01

    New structural data from the Novarupta basin, Katmai National Park, Alaska, site of the largest volcanic eruption of this century (1912), provide limits for the location of magma chambers associated with this eruption. To investigate the subsurface structure of the 1912 vents, and to support an interdisciplinary study of this young volcanic system, a project of geologic mapping of surficial and bedrock structures in the vent region of the 1912 eruption has been undertaken. Landslide scarps, arcuate grabens, a monoclinal fold, and truncated ridges circumscribe the Novarupta basin, marking the inferred outer rim of the vent. A set of radial fissures crosses the southern margin of the basin, striking {approximately}140{degree}, subparallel to the dominant bedrock joint set. These fissures and joints, along with the local plate-motion vector and the inferred regional stress orientation, are consistent with a feeder dike propagating from a reservoir beneath Trident volcano to the eruptive vent.

  15. Effects of magma and conduit conditions on transitions between effusive and explosive activity: a numerical modeling approach

    NASA Astrophysics Data System (ADS)

    Carr, B. B.; De'Michieli Vitturi, M.; Clarke, A. B.; Voight, B.

    2013-12-01

    Transitions between effusive and explosive eruptions, common at silicic volcanoes, can occur between distinct eruptive episodes or can occur as changes between effusive and explosive phases within a single episode. The precise causes of these transitions are difficult to determine due to the multitude of mechanisms and variables that can influence fragmentation thresholds. Numerical modeling of magma ascent within a volcanic conduit allows the influence of key variables to be extensively tested. We study the effect of different variables on the mass eruption rate at the vent using a conservative, 1-D, two-phase, steady-state model that allows for lateral gas loss at shallow depths. Several fragmentation criteria are also tested. We are able to generate a number of regime diagrams for a variety of magma and conduit conditions that constrain transitions from effusive to explosive episodes. We show that a transition to explosive activity can occur without changes in the bulk chemistry, crystal volume fraction, or gas mass fraction of the magma. Eruptive style can be controlled by the pressure gradient within the conduit caused by either overpressure in the chamber or varying lava dome size at the vent. Specific results are sensitive to both magma temperature and conduit geometry. It is important that these variables are well constrained when applying this model to different volcanic systems. We apply our model to the recent activity at Merapi Volcano in Indonesia. We constrain model input and output parameters using current petrologic, seismic, and geodetic studies of the Merapi system, and vary critical parameters over reasonable ranges as documented in the literature. Our model is able to reproduce eruption rates observed during both the 2006 effusive and 2010 explosive/effusive eruptions. Our modeling suggests that a combination of chamber overpressure, increased volatile content, and decreased crystal content due to the voluminous injection of new magma into the

  16. Spatial distribution of the b value under the Popocatepetl volcano and its relation with the structure of the magma chamber

    NASA Astrophysics Data System (ADS)

    Garza-Girón, R.; Zuniga, R. R.

    2014-12-01

    The spatial distribution of the b value under volcanoes and other tectonic environments is not uniform but it rather shows pockets of anomalies related to different phenomena. We analyzed the frequency-magnitude distribution of the 2191 best located volcano-tectonic events with MD ≥ 2.1 under the Popocatepetl volcano and performed 2D and 3D maps using a griding technique. For the 3D mapping we used samples of 100 events within spherical volumes with radii ≤ 3 km. Also, only volumes with σ ≤ 0.3 were taken into account. Three main anomalies with b ≥ 2.2 were detected within a normal crust (b ≤ 1.6). The first anomaly is observed north of the crater summit at depths 4-8 km and comprises a volume of approximately 15 km3. The second lies slightly to the E and SE of the crater at depths between 2 and 5 km, and the third and latter anomaly is located SE of the summit at depths of 6-12 km and spans over a volume of 40 km3 (or greater). In any case, we interpret our high b values anomalies as regions were high pore pressures (low effective stresses), high thermal gradients and/or high heterogeneity take place due to the presence of a magmatic body nearby. Whilst we cannot know with certainty if the source of the anomaly located N of the crater is a dyke complex or a shallow magma chamber, we infer that the shallowest volume mapped is related to Popocatepetl's plumbing system. The greatest anomalous volume located at the SE is thought to represent the main shallow magma chamber, since it is located at depths similar to those found in other volcanoes in the world and correlates with previous geophysical studies carried out at Popocatepetl.

  17. {sup 226}Ra and {sup 231}Pa systematics of axial MORB, crustal residence ages, and magma chamber characteristics at 9--10{degree}N East Pacific Rise

    SciTech Connect

    Goldstein, S.J.; Murrell, M.T.; Perfit, M.R.; Batiza, R.; Fornari, D.J.

    1994-06-01

    Mass spectrometric measurements of {sup 30}Th-22{sup 226}Ra and {sup 235}-U{sup 231}Pa disequilibria for axial basalts are used to determine crustal residence ages for MORB magma and investigate the temporal and spatial characteristics of axial magma chambers (AMC) at 9--10{degrees}N East Pacific Rise (EPR). Relative crustal residence ages can be calculated from variations in {sup 226}Ra/{sup 230}Th and {sup 231}Pa/{sup 235}U activity ratios for axial lavas, if (1) mantle sources and melting are uniform, and mantle transfer times are constant or rapid for axial N-MORB, and (2) {sup 231}Pa/{sup 235}U and {sup 226}Ra/{sup 230}Th in the melt are unaffected by shallow level fractional crystallization. Uniform Th, Sr, and Nd isotopic systematics and incompatible element ratios for N-MORB along the 9--10{degrees}N segment indicate that mantle sources and transfer times are similar. In addition, estimated bulk solid/melt partition coefficients for U, Th, and Pa are small, hence effects of fractional crystallization on {sup 231}Pa/{sup 235}U ratios for the melt are expected to be negligible. However, fractional crystallization of plagioclase in the AMC would lower {sup 226}Ra/{sup 230}Th ratios in the melt and produce a positive bias in {sup 226}Ra crustal residence ages for fractionated lavas.

  18. Volatile and trace element composition of melt inclusions from the Lower Bandelier Tuff - implications for magma chamber processes and eruptive style

    SciTech Connect

    Dunbar, N.W.; Hervig, R.L. |

    1992-10-01

    The preeruptive volatile gradient that was present in the magma which produced the Lower Bandelier Tuff (LBT) is determined on the basis of an analysis of the H{sub 2}O, Cl, and F contents of melt inclusions (MIs) in LBT phenocrysts. The trace element contents of bulk pumice and MIs are measured in order to facilitate interpretation of the pristine nature of the MIs. The data show that there was a large gradient in the H2O content (hence density) of the magma between an H2O-saturated cap and the body of the chamber. The trace element analysis of the MIs and bulk rocks show that after the water gradient evolved, the chamber underwent about 40 percent eutectic fractional crystallization and was then intruded by a second rhyolitic magma at some time prior to eruption. 75 refs.

  19. Designing an Active Target Test Projection Chamber

    NASA Astrophysics Data System (ADS)

    Koci, James; Tan Ahn Collaboration, Dr.; Nicolas Dixneuf Collaboration

    2015-10-01

    The development of instrumentation in nuclear physics is crucial for advancing our ability to measure the properties of exotic nuclei. One limitation of the use of exotic nuclei in experiment is their very low production intensities. Recently, detectors, called active-target dectectors, have been developed to address this issue. Active-target detectors use a gas medium to image charged-particle tracks that are emitted in nuclear reactions. Last semester, I designed a vacuum chamber to be used in developing Micro-Pattern Gas detectors that will upgrade the capabilities of an active-target detector called the Prototype AT-TPC. With the exterior of the chamber complete, I have now been using an electric field modeling program, Garfield, developed by CERN to design a field cage to be placed within the vacuum chamber. The field cage will be a box-like apparatus consisting of two parallel metal plates connected with a resistor chain and attached to wires wrapped between them. The cage will provide a uniform electric field within the chamber to drift electrons from nuclear reactions down to the detector in the bottom of the chamber. These signals are then amplified by a proportional counter, and the data is sent to a computer. For the long term, we would like to incorporate a Micro-Pattern Gas Detectors in the interior of the chamber and eventually use the AT-TPC to examine various nuclei. Dr. Ahn is my advising professor.

  20. Numerical Modeling of Surface Deformation due to Magma Chamber Inflation/Deflation in a Heterogeneous Viscoelastic Half-space

    NASA Astrophysics Data System (ADS)

    Dichter, M.; Roy, M.

    2015-12-01

    Interpreting surface deformation patterns in terms of deeper processes in regions of active magmatism is challenging and inherently non-unique. This study focuses on interpreting the unusual sombrero-shaped pattern of surface deformation in the Altiplano Puna region of South America, which has previously been modeled as the effect of an upwelling diapir of material in the lower crust. Our goal is to investigate other possible interpretations of the surface deformation feature using a suite of viscoelastic models with varying material heterogeneity. We use the finite-element code PyLith to study surface deformation due to a buried time-varying (periodic) overpressure source, a magma body, at depth within a viscoelastic half-space. In our models, the magma-body is a penny-shaped crack, with a cylindrical region above the crack that is weak relative to the surrounding material. We initially consider a magma body within a homogeneous viscoelastic half-space to determine the effect of the free surface upon deformation above and beneath the source region. We observe a complex depth-dependent phase relationship between stress and strain for elements that fall between the ground surface and the roof of the magma body. Next, we consider a volume of weak material (faster relaxation time relative to background) that is distributed with varying geometry around the magma body. We investigate how surface deformation is governed by the spatial distribution of the weak material and its rheologic parameters. We are able to reproduce a "sombrero" pattern of surface velocities for a range of models with material heterogeneity. The wavelength of the sombrero pattern is primarily controlled by the extent of the heterogeneous region, modulated by flexural effects. Our results also suggest an "optimum overpressure forcing frequency" where the lifetime of the sombrero pattern (a transient phenomenon due to the periodic nature of the overpressure forcing) reaches a maximum. Through further

  1. Depth of origin of magma in eruptions

    PubMed Central

    Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

    2013-01-01

    Many volcanic hazard factors - such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses - relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11–15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011–2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide. PMID:24067336

  2. Depth of origin of magma in eruptions.

    PubMed

    Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

    2013-01-01

    Many volcanic hazard factors--such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses--relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11-15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011-2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide. PMID:24067336

  3. Depth of origin of magma in eruptions.

    PubMed

    Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

    2013-09-26

    Many volcanic hazard factors--such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses--relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11-15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011-2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide.

  4. Evidences for disruption of a crystallizing front in a magma chamber during caldera collapse: an example from the Breccia Museo unit (Campanian Ignimbrite eruption, Italy)

    NASA Astrophysics Data System (ADS)

    Fulignati, P.; Marianelli, P.; Proto, M.; Sbrana, A.

    2004-05-01

    This work is focused on juvenile components and some cognate xenoliths of the Breccia Museo (BM) unit. The BM is a coarse-grained proximal unit of the caldera-forming phase of the Ignimbrite Campana (IC) eruption, southern Italy. The BM products show some peculiar characteristics that distinguish them from the other IC deposits. In particular, different types of pumice fragments constitute the juvenile fraction and their crystal contents are remarkably higher than the other IC units. Slightly porphyritic and highly porphyritic trachytic to phonolitic pumices were distinguished in each sample and investigated separately for mineralogy, matrix glass composition, melt and fluid inclusion studies. Most feldspar crystals may have formed at the margins of the magma chamber and the crystal content of both types of pumice fragments can be ascribed to variable entrainment of these crystals (from the solidification front) by the melt. Variably porphyritic (<5 to 30 vol% phenocrysts) pumice and completely crystallized nodules may represent samples of progressively crystallized magma at the chamber walls. Crystallization temperatures of magmas and xenoliths were estimated using two independent methods: a two-feldspar geothermometer and the homogenization temperatures of melt and fluid inclusions in clinopyroxene and K-feldspar. The decrease in the estimated crystallization temperatures from the melt (980-850°C) to the nodules (840-820°C) is consistent with a model of decreasing temperature at a magma chamber solidification front. The study of xenoliths revealed that exsolution of a hypersaline aqueous fluid phase occurred at the peripheral parts of the magma chamber.

  5. The convective liquidus in a solidifying magma chamber - A fluid dynamic investigation

    NASA Technical Reports Server (NTRS)

    Brandeis, Genevieve; Marsh, Bruce D.

    1989-01-01

    An experimental study of the solidification of a layer of paraffin cooled from above is reported. When the fluid is superheated, convection sets in at the beginning of cooling but rapidly decreases in intensity. Once the layer has lost its superheat, convection ceases and further cooling is by conduction. The interior temperature then remains constant until encountered by the upper crust. The convective liquidus is defined as the temperature threshold below which convection is very weak or nonexistent. In natural basaltic systems the convective liquidus, although strictly unknown, may be very close to the true liquidus. Rapid convection may therefore not be a dominant process during the crystallization of many magmna chambers; instead, convection is part of an overall intimate balance between phase equilibria, crystal growth, and heat transfer.

  6. Volcanic facies and mineral chemistry of Tertiary volcanics in the northern part of the Eastern Pontides, northeast Turkey: implications for pre-eruptive crystallization conditions and magma chamber processes

    NASA Astrophysics Data System (ADS)

    Yücel, Cem; Arslan, Mehmet; Temizel, İrfan; Abdioğlu, Emel

    2014-06-01

    temperature ranging from 970 to 978 °C at pressure ranging from 8.70 to 9.00 kbar with water content ranging from 8.04 to 8.64 wt.% and oxygen fugacity ranging from 10-8.75 to 10-8.87 (ΔNNO+2). Brown mica thermobarometric data show that Eocene volcanics were characterized by relatively high oxygen fugacity varying from 10-10.32 to 10-12.37 (HM) at temperature ranging from 858 to 953 °C and pressure ranging from 1.08 to 1.41 kbar. Miocene volcanics were crystallized at highly oxidized conditions, which are characterized by high oxygen fugacity of 10-12.0 (HM) at temperature of 875 °C and pressure of 2.09 kbar. The wide range of obtained temperatures for clinopyroxenes of the suites denotes that the equilibration of clinopyroxene crystals initiates from depth until close to the surface before magma eruption. The compositional variations, resorbed core and reverse zoning patterns in clinopyroxene phenocrysts, as well as variable pressures of crystallization, further indicate that the magmas that formed the suites were polybaric in origins and were composite products of more than one petrogenetic stage. The observed range of phenocryst assemblage and different compositional trends possibly originated from fractionation of magmas with different initial water contents under variable pressures of crystallization. The repeated occurrence of magmas from different suites during a single period of activity suggests that the magmatic system consists of several conduit systems and that magma reservoirs are dispersed at different levels of crustal magma chambers.

  7. Geochemical investigation of a semi-continuous extrusive basaltic section from the Deccan Volcanic Province, India: implications for the mantle and magma chamber processes

    NASA Astrophysics Data System (ADS)

    Vijaya Kumar, Kopparapu; Chavan, Chakradhar; Sawant, Sariput; Naga Raju, K.; Kanakdande, Prachiti; Patode, Sangita; Deshpande, Krishna; Krishnamacharyulu, S. K. G.; Vaideswaran, T.; Balaram, V.

    2010-06-01

    Spatial and temporal variations in the geochemistry of an extrusive basaltic section of Deccan traps record progressive changes in mantle melting and crustal filtration and are relevant to understand continental flood basalt (CFB) magmatism. In the present work we have carried out detailed field, petrographic, density and magnetic susceptibility, and geochemical investigations on a small, semi-continuous extrusive section in the eastern Deccan Volcanic Province (DVP) to understand the role of shallow magma chambers in CFB magmatism. Four formations, Ajanta, Chikhli, Buldhana and Karanja crop out in the Gangakhed-Ambajogai area with increasing elevation. Our studies indicate that: (1) the Karanja Formation represents a major magma addition, as indicated by abrupt change in texture, increases in MgO, CaO, Ni, Cr, and Sr, and drastic decreases in Al2O3, Na2O, K2O, Rb, Ba, REE, bulk-rock density and magnetic susceptibility; (2) assimilation fractional crystallization, crystal-laden magmas, and accessory cumulus phases influence the trace element chemistry of Deccan basalts; (3) the predicted cumulate sequence of olivine gabbro-leucogabbro-oxide-apatite gabbro is supported by the observed layered series in a shallow magma chamber within the DVP; (4) the initial magma was saturated with olivine, plagioclase, and augite, and final the pressure of equilibration for the Gangakhed-Ambajogai section basalts is ~2 kbar (~6 km depth); (5) petrophysical parameters act as proxies for magmatic processes; (6) a small layer of oxide-rich basalts may represent the latest erupted pulse in a given magmatic cycle in the DVP; (7) parental basalts to some of the red boles, considered as formation boundaries, might represent small degree partial melts of the mantle; (8) SW Deccan basaltic-types continue into the eastern DVP; and (9) in addition to the magma chamber processes, dynamic melting of the mantle may have controlled DVP geochemistry. The present study underscores the importance of

  8. Crustal structure of Axial Volcano on the Juan de Fuca Ridge, from seafloor depths to the bottom of the magma chamber, using Elastic Full Waveform Inversion.

    NASA Astrophysics Data System (ADS)

    Arnulf, Adrien; Harding, Alistair; Kent, Graham

    2013-04-01

    Axial volcano is located at 46˚N, 130˚W at the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg seamount chain. It is the most recent eruptive center of the Cobb hotspot, which last erupted in 2011. The volcano rises ~700 m above the adjacent ridge axis and its summit features a 8-km-long, U-shaped caldera with an opening to the southeast where there is an active hydrothermal field and very young lava flows. Located at the junction of a mid-ocean ridge and a volcanic hotspot, Axial volcano is atypical and its internal structure remains poorly understood. Here, we present results from an elastic full waveform inversion (FWI) along multiple seismic lines that span the whole volcano. We have used a multi-stage FWI, inverting successively wide-angle reflections and refractions arrivals from downward extrapolated streamer data, then windowed short offset reflections from the underlying magma chamber. Our final models show fine scale velocity structures with spatial resolutions of tens of meters. Our results indicate that Layer 2A thickness is extremely heterogeneous (350-900 m) within the volcano with abrupt vertical offsets of >300 m at the caldera walls, consistent with faulting of a geologically defined Layer 2A. Interestingly, Layer 2A appears to be extremely thin beneath the active hydrothermal field, where sheeted dikes might lay <100 m beneath the seafloor. On the other hand, the ever-dropping floor of the caldera appears to be a perfect trap for the ponding of lava flows: the thickness of the lava flows increase gradually to the northwest reaching ~450 m at end of the caldera. Surface velocities are low and exhibit limited variation over the whole volcano suggesting relative recent formation, as layer 2A velocity increases rapidly with age at slightly greater depths. Crustal aging (increase in layer 2A velocity with age) appears to be controlled by pipe-like pattern of focused hydrothermal mineralization. Finally, RTM images reveal a large melt

  9. The cogenetic organ cauldron and batholith, south central New Mexico: Evolution of a large-volume ash flow cauldron and its source magma chamber

    NASA Astrophysics Data System (ADS)

    Seager, William R.; McCurry, Michael

    1988-05-01

    The Organ cauldron and its underlying plutonic roots are exposed through a vertical section 5-6 km thick in the Organ Mountains of south central New Mexico. Emplaced within a 1 m.y. time span at 33.7-32.8 Ma, both cauldron fill tuffs and lavas, as well as the underlying Organ batholith, document emplacement of a chemically and mineralogically zoned magma chamber at shallow depths. The tuffs, as much as 3.0 km thick near the center of the cauldron, show rather simple normal chemical and mineralogical gradients which indicate zoning in the magma chamber from aphyric rhyolite (77% SiO2) at the top to crystal-rich rhyolite (68% SiO2) at deeper levels. Lava flows, more than 0.3 km thick, overlie the tuffs and apparently represent still deeper, more mafic (68-61% SiO2), crystal-rich parts of the erupted magma volume. The oldest phase of the batholith may also be compositionally zoned from quartz syenite (68% SiO2) at the top to monzodiorite (55% SiO2) at the lowest exposed level. This phase of the batholith, which forms both a concordant floor beneath the volcanic roof and a thick dikelike body along part of the cauldron margin, may be the undrained residue of the magma chamber whose silicic cap was erupted as tuffs and lavas. Small bodies of fine-grained, porphyritic alkali feldspar granite at the top of the batholith may represent undrained remnants of the silicic cap. Diapirlike intrusions of the deeper, more mafic parts of the batholith into higher more silicic parts may be related to eruption mechanisms. Three younger plutonic phases of the batholith seemingly represent three stages of silicic core magma generation and intrusion during the progressive crystallization and differentiation of the batholith. Major normal faults which offset cauldron fill and are invaded by plutonic rocks suggest the cauldron evolved in a regional extensional stress field.

  10. Paragenesis of Diamond and Minerals of Peridotites and Carbonatites in the Mantle Magma Chambers Based on Experiments Data

    NASA Astrophysics Data System (ADS)

    Kuzyura, Anastasia; Simonova, Dariya; Litvin, Yury

    2014-05-01

    It is considered that role of carbonate melts is important in processes of mantle metasomatism; according to other representations, it is also assumed that they could be formed at partial melting of carbonated peridotite. Dissolving of peridotite minerals and carbon in carbonate melts are responsible for formation of completely miscible carbonate-silicate-carbon magmas parental for diamonds. It can be expected that such carbonate magmas are capable to assimilate an form parental magama "chambers" within the hosting mantle peridotite. While natural cooling of the chambers dissolved in carbonate melts components of the peridotite crystallize forming minerals similar to these of the host mantle peridotite. The recrystallized peridotite minerals are fragmentarily included hermetically within growing diamonds and occur as syngenetic inclusions in them. Therefore experimental modeling of origin of the upper mantle carbonate-silicate diamond-forming melts, their consolidations in the magmatic chambers and evolutions at conditions of equilibrium and fractional crystallization are especially significant for understanding of processes of deep magmatic petrology and genetic mineralogy, including genesis of diamond. In the study at 6 GPa model approximations of mineral phases, significant in compositions of probable metasomatic agents, the upper mantle peridotites, and also syngenetic inclusions in diamonds were used: starting mixtures were model peridotite with composition Ol48Opx16Cpx16Grt20, close to model compositions of the primitive mantle and real mantle xenolithes, as well as multicomponent carbonate (CaCO3)20(Na2CO3)20(FeCO3)20(Na2CO3)20(K2CO3)20 modeling carbonatite inclusions in natural diamonds. Spectral pure graphite was used as a source of carbon in the system. Pressure and temperature were reached using apparatus of toroidal type 'anvil-with-hole'. Electron microprobe and SEM researches were carried out on the polished surfaces with carbon covering at IEM RAS

  11. Magnetic fabric and emplacement mechanisms in a co-mingled mafic and felsic magma chamber: the Espinharas granite (Borborema Province, NE Brasil)

    NASA Astrophysics Data System (ADS)

    Viegas, G.; Gouveia, F.; Archanjo, C.; Hollanda, M.

    2013-12-01

    crystallization of the granite and are younger than the main metamorphic event in the Seridó Belt (~ 575 Ma). These data suggest that the magnetic fabric of the Espinharas granite records the high-temperature deformation observed in the Seridó Belt. This deformation was active during a prolonged time range (~ 100 Ma) in a hybrid magmatic chamber emplaced in the middle- to shallow continental crust. These conditions indicate that the Patos shear zone controlled the development of the magmatic- to solid-state fabric of the Espinharas granite, highlighting the contribution of strain partitioning in the mechanical mingling of magmas in the continental crust.

  12. An investigation of caldera-forming magma chambers using the timing of ignimbrite eruptions and pluton emplacement at the Mt. Aetna caldera complex

    NASA Astrophysics Data System (ADS)

    Zimmerer, Matthew J.; McIntosh, William C.

    2012-11-01

    The temporal and chemical relationships of volcanic and plutonic rocks exposed at the Mt. Aetna caldera complex, central Colorado, provide insight into the emplacement history of pre-, syn-, and postcaldera plutons and the origin of caldera-related silicic magmas. 40Ar/39Ar sanidine ages indicate the rhyolitic Wall Mountain Tuff erupted at 37.3 Ma. LA-ICP-MS U/Pb zircon ages of the compositionally zoned Mt. Princeton batholith, which has been interpreted by several previous studies to be the nonerupted, less-fractionated residuum of the Wall Mountain Tuff magma chamber, indicate that it was emplaced between 35.9 and 35.2 Ma during postcaldera magmatism. Nested within the Mt. Princeton batholith is the Mt. Aetna caldera. The dacitic Badger Creek Tuff erupted at 34.3 Ma during Mt. Aetna caldera collapse. The Badger Creek Tuff is deposited on some of the Mt. Princeton intrusive units, demonstrating that the Wall Mountain Tuff caldera was obliterated during exhumation and erosion prior to 34.3 Ma. Shortly after the Mt. Aetna caldera collapse, the intracaldera ignimbrite and caldera ring faults were intruded by magma that is compositionally and temporally similar to the Badger Creek Tuff, suggesting that these intrusions represent a nonerupted, geochemically equivalent portion of the magma chamber. Emplacement of postcaldera luecogranites at ~ 31 Ma caused localized thermal resetting of biotite and K-feldspar in older, adjacent intrusions. Most samples contain antecrystic zircon. Antecrystic zircon populations range from 38.8 to 33.6 Ma, indicating that open system magmatic processes operated throughout the history of the caldera complex. The temporal, chemical, and spatial relationships of plutonic and volcanic rocks at the Mt. Aetna caldera complex indicate that the majority of the exposed plutons were emplaced during pre- and/or postcaldera magmatism. None of the exposed plutons represent the less-fractionated, mafic residuum of either caldera-forming magma

  13. Magma chamber history related to the shield building stage of Piton des Neiges volcano, La Réunion Island

    NASA Astrophysics Data System (ADS)

    Berthod, Carole; Michon, Laurent; Famin, Vincent; Bascou, Jérôme; Bachelery, Patrick

    2016-04-01

    Piton des Neiges volcano (La Réunion hotspot) experienced a long-lasting shield building stage before entering its degenerative stage 0.4 my ago. The deep edifice incision due to the intense tropical erosion allowed the description for several decades of a layered gabbroic complex interpreted as a piece of magma chamber, which has been tectonically displaced (Chevallier & Vatin-Perignon, 1982; Upton & Wadsworth, 1972). Here, we combine field investigations, petrographic, mineralogical, geochemical and anisotropy of magnetic susceptibility (AMS) studies to constrain the spatial distribution of the plutonic complex, to identify the physical and chemical processes and to integrate this complex in the evolution of Piton des Neiges (PdN). Field investigations allowed us to discover three additional massifs of gabbro and peridotite along the Mât River. The four massifs are overlaid by a pile of basic sills and a breccia interpreted as a debris avalanche deposit. Albeit spatially disconnected, the massifs show a relatively constant dip of the magnetic foliation toward the current summit of the volcano (i.e. toward the SSE). The two massifs cropping in the upper Mât River are exclusively composed of massive dunite and wherlite units with a cumulate texture and no visible dynamic structures. The two massifs located in the lower Mât River are made of olivine-gabbro, ferrogabbro and gabbro showing numerous flow structures and synmagmatic faults that indicates instabilities which trend NNW-SSE. Minerals (olivine, clinopyroxene and oxide) present primitive compositions in the two upper massifs and slightly differentiated ones in the lower massif. Given the consistency of our dataset, we propose that the four massifs correspond to outcrops of a unique chemically stratified magma chamber, whose center would have been located about 4 km North of the current summit of PdN. The existence of an initial PdN, North of the current edifice, is supported by morphological

  14. Hydrothermal processes above the Yellowstone magma chamber: Large hydrothermal systems and large hydrothermal explosions

    USGS Publications Warehouse

    Morgan, L.A.; Shanks, W.C. Pat; Pierce, K.L.

    2009-01-01

    Hydrothermal explosions are violent and dramatic events resulting in the rapid ejection of boiling water, steam, mud, and rock fragments from source craters that range from a few meters up to more than 2 km in diameter; associated breccia can be emplaced as much as 3 to 4 km from the largest craters. Hydrothermal explosions occur where shallow interconnected reservoirs of steam- and liquid-saturated fluids with temperatures at or near the boiling curve underlie thermal fields. Sudden reduction in confi ning pressure causes fluids to fl ash to steam, resulting in signifi cant expansion, rock fragmentation, and debris ejection. In Yellowstone, hydrothermal explosions are a potentially signifi cant hazard for visitors and facilities and can damage or even destroy thermal features. The breccia deposits and associated craters formed from hydrothermal explosions are mapped as mostly Holocene (the Mary Bay deposit is older) units throughout Yellowstone National Park (YNP) and are spatially related to within the 0.64-Ma Yellowstone caldera and along the active Norris-Mammoth tectonic corridor. In Yellowstone, at least 20 large (>100 m in diameter) hydrothermal explosion craters have been identifi ed; the scale of the individual associated events dwarfs similar features in geothermal areas elsewhere in the world. Large hydrothermal explosions in Yellowstone have occurred over the past 16 ka averaging ??1 every 700 yr; similar events are likely in the future. Our studies of large hydrothermal explosion events indicate: (1) none are directly associated with eruptive volcanic or shallow intrusive events; (2) several historical explosions have been triggered by seismic events; (3) lithic clasts and comingled matrix material that form hydrothermal explosion deposits are extensively altered, indicating that explosions occur in areas subjected to intense hydrothermal processes; (4) many lithic clasts contained in explosion breccia deposits preserve evidence of repeated fracturing

  15. From a long-lived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemistry of zircon crystals at Bajo de la Alumbrera (NW Argentina)

    NASA Astrophysics Data System (ADS)

    Buret, Yannick; von Quadt, Albrecht; Heinrich, Christoph; Selby, David; Wälle, Markus; Peytcheva, Irena

    2016-09-01

    The formation of world class porphyry copper deposits reflect magmatic processes that take place in a deeper and much larger underlying magmatic system, which provides the source of porphyry magmas, as well as metal and sulphur-charged mineralising fluids. Reading the geochemical record of this large magmatic source region, as well as constraining the time-scales for creating a much smaller porphyry copper deposit, are critical in order to fully understand and quantify the processes that lead to metal concentration within these valuable mineral deposits. This study focuses on the Bajo de la Alumbrera porphyry copper deposit in Northwest Argentina. The deposit is centred on a dacitic porphyry intrusive stock that was mineralised by several pulses of porphyry magma emplacement and hydrothermal fluid injections. To constrain the duration of ore formation, we dated zircons from four porphyry intrusions, including pre-, syn- and post-mineralisation porphyries based on intersection relations between successive intrusion and vein generations, using high precision CA-ID-TIMS. Based on the youngest assemblages of zircon grains, which overlap within analytical error, all four intrusions were emplaced within 29 ka, which places an upper limit on the total duration of hydrothermal mineralisation. Re/Os dating of hydrothermal molybdenite fully overlaps with this high-precision age bracket. However, all four porphyries contain zircon antecrysts which record protracted zircon crystallisation during the ∼200 ka preceding the emplacement of the porphyries. Zircon trace element variations, Ti-in-zircon temperatures, and Hf isotopic compositions indicate that the four porphyry magmas record a common geochemical and thermal history, and that the four intrusions were derived from the same upper-crustal magma chamber. Trace element zoning within single zircon crystals confirms a fractional crystallisation trend dominated by titanite and apatite crystallisation. However, zircon

  16. Samail Ophiolite plutonic suite: Field relations, phase variation, cryptic variation and layering, and a model of a spreading ridge magma chamber

    NASA Astrophysics Data System (ADS)

    Pallister, J. S.; Hopson, C. A.

    1981-04-01

    Geologic mapping of an intact plutonic sequence within the Samail ophiolite in the Ibra area, southeastern Oman Mountains, reveals stratigraphic, structural, and petrologic details of oceanic layer 3. Four measured stratigraphic sections, each spaced about 5 km apart across the southern flank of Jabal Dimh, define a time-transgressive progression within the ophiolite and reveal geometric and petrologic features of a spreading-ridge magma chamber. The sections show the following vertical sequence: (1) dunite (chr-ol cumulates ± harzburgite xenoliths) 0-200 m thick, grading up from a transition zone with harzburgite tectonite, (2) interlayered wehrlite-melagabbro-gabbro (cpx-ol and ol-cpx-pl cumulates) 0-100 m thick, (3) layered gabbro (chiefly ol-cpx-pl cumulates but including recurrent intervals of cumulus wehrlite and melagabbro) 2.6-5.5 km thick, (4) planar laminated nonlayered gabbro (chiefly ol-cpx-pl cumulates) 100-400 m thick, (5) hypidiomorphic (ol)-hb-cpx gabbro (high-level gabbro) 200-800 m thick, (6) small, discontinous diorite to plagiogranite bodies at or near the top of the gabbro. Cumulus textures (adcumulus > mesocumulus), planar lamination, and cumulus layering (phase, ratio, and grain size layers at mm to 10-m scale, commonly graded) within this sequence show that crystals accumulated from the base of the magma chamber upward to within a few hundred meters of the top; downward solidification from the roof was minor. Cyclicity within the cumulus sequence is represented by the recurrence of olivine-rich intervals (melagabbo and wehrlite) up to high stratigraphic levels and by hundreds of phase-graded layers (ol-rich at the bases to pl-rich at the tops), individually up to 5 m thick. Limited cryptic variation relative to closed-system layered intrusions and the limited range in solid-solution components of olivine (Fo69-90), plagioclase (An62-95) and clinopyroxene (En40-54, Fs4-16, Wo37-49) from the cumulus suite require replenishment of the magma

  17. The eruption of the Breccia Museo (Campi Flegrei, Italy): Fractional crystallization processes in a shallow, zoned magma chamber and implications for the eruptive dynamics

    NASA Astrophysics Data System (ADS)

    Melluso, Leone; Morra, Vincenzo; Perrotta, Annamaria; Scarpati, Claudio; Adabbo, Mariarosaria

    1995-11-01

    The Breccia Museo Member (BMM) was formed by an explosive eruption that occurred in the SW sector of Campi Flegrei about 20 ka ago. The eruptive sequence consists of the Lower Pumice Flow Unit and the overlying Upper Pumice Flow Unit with its associated lithic Breccia Unit. Interlayered with the Breccia Unit is a welded deposit that mainly consists of spatter clasts (Spatter Unit). The products of this eruption range in composition from trachytic to trachyphonolitic with K 2O decreasing from 9.5 to 7 wt.%; Na 2O correspondingly increases from 2.6 to 7.2 wt.% with increasing differentiation (Nb from 23 to 122 ppm). The phenocrysts are mostly sanidine (Or 88-63) with subordinate plagioclase (An 33-27), clinopyroxene (Ca 47Mg 44Fe 9 to Ca 46Mg 35Fe 19), biotite, titanomagnetite, and apatite. The observed major- and trace-element variations are fully consistent with about 80% fractional crystallization of a sanidine-dominated assemblage starting from the least differentiated trachytes. The compositions of the erupted products are compatible with the progressive tapping of a shallow magma chamber that was thermally and chemically zoned. The incompatible trace elements indicate a slightly different magma composition with respect to trachytes of the Campi Flegrei mainland. The geochemical stratigraphy suggests that after an early eruptive phase during which the upper, most differentiated level of the magma chamber was tapped, the sudden collapse of the roof of the reservoir triggered drainage of the remaining magma, which ranged in composition from trachyte to trachyphonolite, and formed the Breccia Unit and the Upper Pumice Flow Unit. The strongly differentiated trachyphonolite composition of the spatter clasts also suggests that they likely originated from the uppermost part of the reservoir soon after the eruption of Lower Pumice Flow Unit and the collapse of the chamber roof. This is in agreement with the eruptive model proposed by Perrotta and Scarpati (1994).

  18. The effects of depth-dependent crustal viscosity variation on visco-elastic response to inflation/deflation of magma chamber

    NASA Astrophysics Data System (ADS)

    Yamasaki, Tadashi

    2016-04-01

    Development of the satellite observations (GPS and/or InSAR) has allowed us to precisely measure surface deformation. However any geodetic observation by itself does not tell us a mechanism of the deformation. All we can do the most is to compare such an observation to some quantitative predictions, only from which we can deduce a possible deformation mechanism. We therefore need to understand characteristic deformation pattern for a given source mechanism. This study particularly pays attention to magmatic activity in depth as the source, aiming to distinguish magma-induced crustal deformation by better knowing how the activity can be reflected in geodetically observable surface deformation. A parallelized 3-D finite element code, OREGANO_VE [e.g., Yamasaki and Houseman, 2015, J. Geodyn., 88, 80-89], is used to solve the linear Maxwell visco-elastic response to an applied internal inflation/deflation of magma chamber. The rectangular finite element model is composed with a visco-elastic layer overlaid by an elastic layer with thickness of H, and the visco-elastic layer extends over the rest of crust and the uppermost mantle. The visco-elastic crust has a depth-dependent viscosity (DDV) as an exponential function of depth due to temperature-dependent viscosity: hc = h0 exp[c(1 - z/L0)], where h0 is the viscosity at the bottom of the crust, c is a constant; c > 0 for DDV model and c = 0 for uniform viscosity (UNV) model, z is the depth, and L0 is a reference length-scale. The visco-elastic mantle has a spatially uniform viscosity hm. The inflation and/or deflation of sill-like magma chamber is implemented by using the split node method developed by Melosh and Raefsky [1981, Bull. Seism. Soc. Am., 71, 1391-1400]. UNV model with c = 0 employed in this study shows that the inflation-induced surface uplift would abate with time by visco-elastic relaxation. The post-inflation subsidence would erase the uplift in ~ 50 - 100 times Maxwell relaxation time of the crust

  19. A non-traditional isotope study of plagiogranite and rhyo-dacite suites: insights into mid ocean ridge magma chamber processes (Invited)

    NASA Astrophysics Data System (ADS)

    Lundstrom, C.; Huggett, N.; Perfit, M. R.; Zambardi, T.

    2013-12-01

    The eruption of silicic volcanic rocks in the mid-ocean ridge environment, although rare, provides an important observation for understanding MOR magma chamber processes. Although axially erupted MORB are quite homogeneous geochemically, this likely reflects mixing and reaction from the magma lens axis at only slightly variable temperature. Differentiation occurs along the colder 'wings' of the magma lens and rhyo-dacite suites show mixing trends with normal MORB. Both plagiogranites in ophiolites and erupted rhyodacites provide evidence of extensive magma evolution at MORs. Yet, whether silicic eruptives in MOR environments are equivalent to plagiogranites is unknown. Here we compare the non-traditional isotope ratios of Fe and Si in a plagiogranite suite from Troodos (Cyprus) with rhyo-dacite suites from the Galapagos Spreading Center, the Juan de Fuca-Blanco ridge-transform intersection [RTI], and the 9°N EPR overlapping spreading center [OSC]) to shed light on the origin of oceanic silicic rocks. Within the eastern Troodos Ophiolite we collected 14 samples from a 700m transect from gabbros through to plagiogranites (which immediately transition to sheeted dikes). Indeed, Troodos geologic maps show plagiogranites ubiquitously occur at the upper gabbro-sheeted dike contact. Silica content ranges from ~45 wt. % in the gabbros to 75 wt. % in the most evolved plagiogranites. Notably, iron ratios increase (become heavier) with increasing, up-section distance from the gabbros (d56Fe ranges from -0.05 to 0.40). This spatial pattern is consistent with the prediction of thermal diffusion occurring within a temperature gradient in a MOR magma lens although other explanations are possible. Because there is a spatial progression in SiO2 from gabbro to plagiogranite, these isotope ratios also increase with SiO2. Notably, within the 3 silicic MOR systems, d56Fe and d30Si exhibit the same relationship becoming isotopically heavier with increasing silica content (d30Si ranges

  20. Construction of the Vinalhaven Intrusive Complex, Maine, USA: the Plutonic Record of Evolving Magma Chambers Affected by Multiple Episodes of Replenishment, Rejuvenation, Crystal Accumulation and Eruption

    NASA Astrophysics Data System (ADS)

    Wiebe, R. A.; Hawkins, D. P.

    2004-12-01

    Increasingly, the plutonic roots of volcanic systems can be shown to contain temporal records of events inferred from the study of volcanic rocks. The Vinalhaven intrusive complex preserves evidence for multiple episodes of silicic and mafic replenishments, rejuvenation of granite, and probable eruptive events over a nominal time-span of 1.7 Ma (Hawkins and Wiebe, this volume). The complex is about 12 km in diameter and consists mainly of cg granite, a thick section of arcuate, inward-dipping gabbro-diorite sheets in the southeastern half of the complex, and a circular core of fg granite. Field relations demonstrate that the base of the intrusion is along the southeastern margin of the complex, and the top is along the northwestern margin where it intrudes coeval volcanic rocks. Aphyric basaltic and granitic dikes fed this essentially bimodal intrusion. When basaltic dikes intersected a silicic chamber, basalt spread across a floor of silicic crystal mush to form gabbro-diorite sheets in granite. Several extensive layers of angular blocks of country rock occur within the mafic rocks. Granitic dikes and the fg granitic core of the complex have sharp to gradational contacts with cg granite, and, locally, both granites are intimately mixed and commingled. These relations indicate that new silicic injections mixed into partly crystallized resident magma. Several irregular bodies of porphyry (0.2 to 0.5 km in average dimension) intrude cg granite with sharp, gradational, or commingled contacts. The porphyry has 5 to 40% corroded phenocrysts, identical in composition to crystals in the granite, and a variably quenched matrix. Some of these bodies formed when late injections of basalt remelted largely solid portions of cg granite. New silicic input may have contributed to other porphyry bodies. The matrix probably quenched because of a sudden decrease in pressure, possibly due to eruption of magma from the chamber. The cg granite and inter-layered mafic rocks preserve a

  1. Unraveling the Eyjafjallajökull 2010 plumbing system and magma chamber dynamics through high-resolution geochemical investigations

    NASA Astrophysics Data System (ADS)

    Laeger, Kathrin; Petrelli, Maurizio; Andronico, Daniele; Scarlato, Piergiorgio; Cimarelli, Corrado; Misiti, Valeria; del Bello, Elisabetta; Perugini, Diego

    2016-04-01

    The April-May 2010 eruption of the Eyjafjallajökull volcano (EFJ, Iceland) was triggered by an intrusion of fresh magma coming from deeper portions of the crust migrating into shallower depth of 3-6 km in the magmatic system. Here, we present new EMPA and LA-ICP-MS analyses on groundmass glasses of ash particles erupted between 18 and 22 May 2010, the last days of the eruption. The glasses define two well separated groups. The first group is basaltic in composition with SiO2 ranging from 49.98 to 51.76 wt.% and a total alkali content (Na2O + K2O) in the range between 4.63 and 5.17 wt.%. The second group ranges between trachyandesitic and rhyolitic compositions with SiO2 ranging between 57.13 to 70.38 wt.% and a total alkali content from 7.21 to 10.90 wt.%. Least square modelling after Störmer and Nicholls (1978) discriminates best the origin of the basaltic glass by both fractional crystallization of a more primitive basalt or mixing of a basalt and a felsic magma. Furthermore, this model proves that the trachyandesitic range is the result of mixing of trachyandesite and trachyte magma. Magma mixing modeling after Langmuir (1978) and element concentration histograms indicate a probable incomplete magma mixing as the main process forming the great compositional variability observed in the erupted products. Finally, we estimated mixing end-members of intermediate (~59 wt.% SiO2) and felsic composition (~66-68 wt.% SiO2) with a felsic melt-proportion of 0.35-0.47. In the 90s, recorded seismicity and ground deformation indicated intrusions at shallow depth under the EFJ edifice probably forming separated sills. Therefore, the origin of the trachyandesite is presumably to find in a discrete magma batch that generated years before eruption. The rhyolite composition can be considered as the residual melt that remained in the plumbing system of EFJ since the last eruption in 1821-23. We suggest that these different magma batches formed the plumbing system of EFJ and have

  2. Sequential Notch activation regulates ventricular chamber development

    PubMed Central

    D'Amato, Gaetano; Luxán, Guillermo; del Monte-Nieto, Gonzalo; Martínez-Poveda, Beatriz; Torroja, Carlos; Walter, Wencke; Bochter, Matthew S.; Benedito, Rui; Cole, Susan; Martinez, Fernando; Hadjantonakis, Anna-Katerina; Uemura, Akiyoshi; Jiménez-Borreguero, Luis J.; de la Pompa, José Luis

    2016-01-01

    Ventricular chambers are essential for the rhythmic contraction and relaxation occurring in every heartbeat throughout life. Congenital abnormalities in ventricular chamber formation cause severe human heart defects. How the early trabecular meshwork of myocardial fibres forms and subsequently develops into mature chambers is poorly understood. We show that Notch signalling first connects chamber endocardium and myocardium to sustain trabeculation, and later coordinates ventricular patterning and compaction with coronary vessel development to generate the mature chamber, through a temporal sequence of ligand signalling determined by the glycosyltransferase manic fringe (MFng). Early endocardial expression of MFng promotes Dll4–Notch1 signalling, which induces trabeculation in the developing ventricle. Ventricular maturation and compaction require MFng and Dll4 downregulation in the endocardium, which allows myocardial Jag1 and Jag2 signalling to Notch1 in this tissue. Perturbation of this signalling equilibrium severely disrupts heart chamber formation. Our results open a new research avenue into the pathogenesis of cardiomyopathies. PMID:26641715

  3. Oxygen isotopes reveal crustal contamination and a large, still partially molten magma chamber in Chaîne des Puys (French Massif Central)

    NASA Astrophysics Data System (ADS)

    France, Lydéric; Demacon, Mickael; Gurenko, Andrey A.; Briot, Danielle

    2016-09-01

    The two main magmatic properties associated with explosive eruptions are high viscosity of silica-rich magmas and/or high volatile contents. Magmatic processes responsible for the genesis of such magmas are differentiation through crystallization, and crustal contamination (or assimilation) as this process has the potential to enhance crystallization and add volatiles to the initial budget. In the Chaîne des Puy series (French Massif Central), silica- and H2O-rich magmas were only emitted during the most recent eruptions (ca. 6-15 ka). Here, we use in situ measurements of oxygen isotopes in zircons from two of the main trachytic eruptions from the Chaîne des Puys to track the crustal contamination component in a sequence that was previously presented as an archetypal fractional crystallization series. Zircons from Sarcoui volcano and Puy de Dôme display homogeneous oxygen isotope compositions with δ18O = 5.6 ± 0.25‰ and 5.6 ± 0.3‰, respectively, and have therefore crystallized from homogeneous melts with δ18Omelt = 7.1 ± 0.3‰. Compared to mantle derived melts resulting from pure fractional crystallization (δ18Odif.mant. = 6.4 ± 0.4‰), those δ18Omelt values are enriched in 18O and support a significant role of crustal contamination in the genesis of silica-rich melts in the Chaîne des Puys. Assimilation-fractional-crystallization models highlight that the degree of contamination was probably restricted to 5.5-9.5% with Rcrystallization/Rassimilation varying between 8 and 14. The very strong intra-site homogeneity of the isotopic data highlights that magmas were well homogenized before eruption, and consequently that crustal contamination was not the trigger of silica-rich eruptions in the Chaîne des Puys. The exceptionally strong inter-site homogeneity of the isotopic data brings to light that Sarcoui volcano and Puy de Dôme were fed by a single large magma chamber. Our results, together with recent thermo-kinetic models and an experimental

  4. Incremental assembly and prolonged consolidation of Cordilleran magma chambers--Evidence from the Southern Rocky Mountain volcanic field

    USGS Publications Warehouse

    Lipman, Peter W.

    2007-01-01

    Plutons thus provide an integrated record of prolonged magmatic evolution, while volcanism offers snapshots of conditions at early stages. Growth of subvolcanic batholiths involved sustained multistage open-system processes. These commonly involved ignimbrite eruptions at times of peak power input, but assembly and consolidation processes continued at diminishing rates long after peak volcanism. Some evidence cited for early incremental pluton assembly more likely records late events during or after volcanism. Contrasts between relatively primitive arc systems dominated by andesitic compositions and small upper-crustal plutons versus more silicic volcanic fields and associated batholiths probably reflect intertwined contrasts in crustal thickness and magmatic power input. Lower power input would lead to a Cascade- or Aleutian-type arc system, where intermediate-composition magma erupts directly from middle- and lower-crustal storage without development of large shallow plutons. Andean and southern Rocky Mountain–type systems begin similarly with intermediate-composition volcanism, but increasing magma production, perhaps triggered by abrupt changes in plate boundaries, leads to development of larger upper-crustal reservoirs, more silicic compositions, large ignimbrites, and batholiths. Lack of geophysical evidence for voluminous eruptible magma beneath young calderas suggests that near-solidus plutons can be rejuvenated rapidly by high-temperature mafic recharge, potentially causing large explosive eruptions with only brief precursors.

  5. Quartz Crystallization in the Youngest Toba Tuff Magma Chamber and its Remnants: A Complex Lineage Uncovered by CL Zoning

    NASA Astrophysics Data System (ADS)

    Barbee, O. A.; Chesner, C. A.; Reid, M. R.

    2014-12-01

    The giant >2800 km3 Youngest Toba Tuff (YTT) and its post-caldera, crystal-rich rhyolitic lava domes share identical compositions (69-76 wt. % SiO2), mineralogies, mineral textures, and zircon and allanite U-Th ages (Barbee et al., 2014). To further understand the genetic relation between the YTT and the domes, we conducted an extensive in-situ cathodoluminescence (CL) study on serial slices of their unusual ≤2 cm, euhedral quartz crystals. Several important magma processes are recorded by CL zoning of Toba quartz, including (1) episodes of undercooling and irregular crystal growth (skeletal and dendritic zones, melt entrapment, growth embayments), (2) crystal dissolution (rounded cores and truncated zones), (3) quartz clustering (synneusis, parallel growth or twinning), and (4) fluctuating magma conditions and dynamics (contrasts in CL intensity). The associated features (1-3) are defined by growth zone configurations, whereas distinct cores, mantles, rims, and oscillatory zones mainly represent differences in trace element concentrations (4). Nearly all magma compositions are dominated by quartz with continuous subtle core to rim oscillatory zoning, while mid- to lower-SiO2 samples contain the largest proportion of crystals with bright interior and rim zones consistent with crystal settling into a high-T environment or injection of hotter magma. The diversity of near-rim zoning patterns and CL boundary sharpness in single samples indicates coalescence of quartz with dissimilar, late-stage histories; however, interior zoning patterns broadly correlate with low- and high-SiO2 bulk magma compositions similarly for the YTT and lava domes. Although a second generation of quartz crystallization is apparent in the groundmass of the lavas, its occurrence is not visually evident on the majority of dome (or recycled-YTT) phenocrysts. Processes promoting cluster formation appear important for quartz growth at Toba and may be related to those responsible in plutonic

  6. Glass and mineral analyses from first deposits of Peach Spring Supereruption (SW USA) illuminate initial tapping of a zoned magma chamber

    NASA Astrophysics Data System (ADS)

    Mccracken, R. G.; Miller, C. F.; Buesch, D.; Gualda, G. A.; Covey, A.

    2012-12-01

    The Peach Spring supereruption (18.78±0.02 Ma) was sourced from Silver Creek caldera in the southern Black Mountains, Arizona (Ferguson et al. in press). The resulting ignimbrite, the Peach Spring Tuff (PST), blanketed >32,000 km2 of Arizona, California, and Nevada (Buesch, 1993). Underlying the ignimbrite is a thin (≤ 1m thick) basal layered deposit that consists of texturally distinct layers 1a-e (Valentine et al. 1989) and is present up to ~100 km from the source caldera. Basal layered deposits contain the first material erupted during the PST supereruption, preceding the main eruption event. Petrography and geochemistry of minerals and pumice clasts from basal layered deposits collected ~15-100 km from the caldera, combined with a survey of glass and crystal compositions from both outflow and basal deposits, permit (1) comparisons with the overlying ignimbrite, and (2) insights into the initial stages of the supereruption and extraction of magma from the chamber. Pumice clasts from a pumice-rich layer (1a2) of the basal deposit were characterized by LA-ICPMS and SEM. Unaltered glass has a uniform high-Si rhyolite composition (76.7% SiO2, 13.0% Al2O3, 3.6% Na2O, 5.3% K2O, 0.6% FeO, <0.1% MgO, 0.6% CaO, 0.1% TiO2). Mildly altered glass is similar but has lower Na2O and higher K2O. Pumice clasts are relatively crystal poor (<10% phenocrysts) with an assemblage dominated by sanidine (~Or55Ab43An2), with lesser plagioclase (~Ab73An19Or8), minor hornblende and biotite, and accessory magnetite, sphene, zircon, chevkinite, and apatite; no quartz was identified. Initial LA-ICPMS results for glass reveal REE patterns with large negative Gd (0.21: i.e. U-shaped REE pattern) and Eu (0.31) anomalies, very low Ba and Sr (≤10 ppm), and high Rb (~250 ppm). These compositions are essentially identical to those of the most common pumice from distal outflow ignimbrite, but very different from crystal-rich (>30%) trachyte pumice that dominates the intracaldera fill and is

  7. Dominica Pumiceous Eruptions: Reconstruction of Dynamics and Timescales of Magma Chamber Processes from Crystal Record and Diffusion Modelling.

    NASA Astrophysics Data System (ADS)

    Solaro, C.; Boudon, G.; Balcone Boissard, H.; Martel, C.; Morgan, D. J.

    2015-12-01

    In the last 50ky, Dominica Island (Lesser Antilles Arc) has experienced three major pumiceous ignimbritic eruptions: Layou (~50ka), Roseau (~30ka), and Rosalie (~20ka). These eruptions emitted magma volumes one order of magnitude larger (tens of km3 DRE/eruption) than those of the neighboring islands of Martinique and Guadeloupe (<1 km3/eruption). Reservoir processes and pre-eruptive magma dynamics of these eruptions are still poorly constrained. Our study focuses on the basal Plinian fallout deposit of these three eruptions. We studied the crystal assemblage and performed a detailed analysis of chemical zoning patterns, textures and composition variations on orthopyroxene crystals (12-16% total crystal content). A system analysis approach is conducted to unravel crystals' remobilization processes in the reservoir before eruption. Timescales of these processes have been calculated performing Fe2+-Mg interdiffusion modelling on selected orthopyroxenes by intercalibration of high resolution BSE images with EPMA analyses. Results suggest the existence of a main magmatic environment, containing approximately 80-85% of the total orthopyroxene amount. The remnant 15-20% orthopyroxenes exhibit clear zoning with normal, reverse and double zoning for Layou and Rosalie eruptions and almost reverse and double zoning for Roseau. They display cyclic interaction with smaller magmatic environments of an either more or less evolved composition. Mobilization of crystals in between these different environments causes the simple or double normal and reverse zoning in crystals. In order to constrain timescales of reservoir processes, diffusion has been modelled along the a- and b-axis on zoned orthopyroxenes of Layou and Roseau eruptions at 850°C. For both eruptions, dating of diffusion kinetics on crystal zoning provides comparable timescale distributions of ~3-4 years before each eruption. This suggests magma remobilization of about 3 years prior each eruption, likely acting as a

  8. Trace element evidence for anatexis at oceanic magma chamber roofs and the role of partial melts for contamination of fresh MORB

    NASA Astrophysics Data System (ADS)

    Fischer, Lennart A.; Erdmann, Martin; France, Lydéric; Wolff, Paul E.; Deloule, Etienne; Zhang, Chao; Godard, Marguerite; Koepke, Jürgen

    2016-09-01

    At oceanic spreading centers, interactions between magma and hydrothermal convecting systems trigger major physical, thermal, and chemical exchanges. The two-pyroxene hornfels recovered from the base of the sheeted dike sequence at Integrated Ocean Drilling Program (IODP) Site 1256 (equatorial Eastern Pacific) are interpreted as a conducting boundary layer between the underlying axial melt lens and the hydrothermally cooled sheeted dikes. They are cut by numerous small, felsic veins, which were recently interpreted as a product of hydrous partial melting of sheeted dikes. Here, we present trace element compositions of products (melts and residues) of hydrous partial melting experiments using basalts and hornfels from IODP Site 1256 as starting material. The experimental products generated between 910 °C and 970 °C match the natural lithologies from Site 1256 in terms of major and trace element compositions. The compositions of the anatectic melts correspond to the compositions of the felsic veins, while the residual minerals match the compositions of the two-pyroxene hornfels, evidencing that hydrous partial melting is an important magmatic process in the gabbro/dike transition of fast-spreading mid-oceanic ridges. Our results complement previous experimental studies on anatectic processes occurring at the roof of the magma chambers from fast-spreading mid-ocean ridges. Moreover, calculations of mixing and assimilation fractional crystallization using the experimental partial melts as contaminant/assimilant showed that anatectic melts can only be a minor contributor to the contamination process.

  9. How caldera collapse shapes the shallow emplacement and transfer of magma in active volcanoes

    NASA Astrophysics Data System (ADS)

    Corbi, F.; Rivalta, E.; Pinel, V.; Maccaferri, F.; Bagnardi, M.; Acocella, V.

    2015-12-01

    Calderas are topographic depressions formed by the collapse of a partly drained magma reservoir. At volcanic edifices with calderas, eruptive fissures can circumscribe the outer caldera rim, be oriented radially and/or align with the regional tectonic stress field. Constraining the mechanisms that govern this spatial arrangement is fundamental to understand the dynamics of shallow magma storage and transport and evaluate volcanic hazard. Here we show with numerical models that the previously unappreciated unloading effect of caldera formation may contribute significantly to the stress budget of a volcano. We first test this hypothesis against the ideal case of Fernandina, Galápagos, where previous models only partly explained the peculiar pattern of circumferential and radial eruptive fissures and the geometry of the intrusions determined by inverting the deformation data. We show that by taking into account the decompression due to the caldera formation, the modeled edifice stress field is consistent with all the observations. We then develop a general model for the stress state at volcanic edifices with calderas based on the competition of caldera decompression, magma buoyancy forces and tectonic stresses. These factors control: 1) the shallow accumulation of magma in stacked sills, consistently with observations; 2) the conditions for the development of circumferential and/or radial eruptive fissures, as observed on active volcanoes. This top-down control exerted by changes in the distribution of mass at the surface allows better understanding of how shallow magma is transferred at active calderas, contributing to forecasting the location and type of opening fissures.

  10. The 2006-2009 activity of the Ubinas volcano (Peru): Petrology of the 2006 eruptive products and insights into genesis of andesite magmas, magma recharge and plumbing system

    NASA Astrophysics Data System (ADS)

    Rivera, Marco; Thouret, Jean-Claude; Samaniego, Pablo; Le Pennec, Jean-Luc

    2014-01-01

    Following a fumarolic episode that started six months earlier, the most recent eruptive activity of the Ubinas volcano (south Peru) began on 27 March 2006, intensified between April and October 2006 and slowly declined until December 2009. The chronology of the explosive episode and the extent and composition of the erupted material are documented with an emphasis on ballistic ejecta. A petrological study of the juvenile products allows us to infer the magmatic processes related to the 2006-2009 eruptions of the andesitic Ubinas volcano. The juvenile magma erupted during the 2006 activity shows a homogeneous bulk-rock andesitic composition (56.7-57.6 wt.% SiO2), which belongs to a medium- to high-K calc-alkaline series. The mineral assemblage of the ballistic blocks and tephra consists of plagioclase > two-pyroxenes > Fe-Ti oxide and rare olivine and amphibole set in a groundmass of the same minerals with a dacitic composition (66-67 wt.% SiO2). Thermo-barometric data, based on two-pyroxene and amphibole stability, records a magma temperature of 998 ± 14 °C and a pressure of 476 ± 36 MPa. Widespread mineralogical and textural features point to a disequilibrium process in the erupted andesite magma. These features include inversely zoned "sieve textures" in plagioclase, inversely zoned clinopyroxene, and olivine crystals with reaction and thin overgrowth rims. They indicate that the pre-eruptive magmatic processes were dominated by recharge of a hotter mafic magma into a shallow reservoir, where magma mingling occurred and triggered the eruption. Prior to 2006, a probable recharge of a mafic magma produced strong convection and partial homogenization in the reservoir, as well as a pressure increase and higher magma ascent rate after four years of fumarolic activity. Mafic magmas do not prevail in the Ubinas pre-historical lavas and tephras. However, mafic andesites have been erupted during historical times (e.g. AD 1667 and 2006-2009 vulcanian eruptions). Hence

  11. Down Hole Variation in the Chemistry of Gabbroic Rocks From Atlantis Bank, ODP Hole 1105A, Southwest Indian Ridge: Magma Chamber Processes

    NASA Astrophysics Data System (ADS)

    Banerji, D.; Casey, J. F.

    2001-12-01

    Geochemical studies on cored sections have been conducted on gabbroic rocks recovered from ODP Leg 179 Hole 1105A. Hole 1105A was drilled on the Atlantis Bank through the same gabbroic massif cored at Hole 735B (Leg 118 and 176). Both holes are located along the Atlantis II Transform, Southwest Indian Ridge. Hole 1105A is offset 1.2 Km from Hole 735B, the deepest hole ever drilled in to the plutonic foundation of the oceanic crust. Preliminary shipboard magnetic, resistivity, lithologic and geochemical data suggest a possible correlation of lithostratigraphic units identified in both holes. Four major rock types have been identified in the cored section of Hole 1105A. They are the gabbros, olivine gabbros, oxide olivine gabbros and the oxide gabbros. The cored section is divided into 4 major units based on the presence and absence of oxide minerals in the gabbroic rocks. The major rock types are distinguished on the basis of the presence of cumulus phases olivine, clinopyroxene, plagioclase. Whole rock Mg numbers range from 83.5 to 19.6 indicating extensive fractionation of magma. The oxide free gabbroic rocks have a very low abundance of incompatible elements like P2O5, TiO2, Zr and LREE indicating that they crystallized as adcumulates or mesocumulates with little to no trapped melt retained. The oxide gabbro layers have a higher abundance of Fe2O3 and TiO2.Textural variation is observed with changes in Mg number down hole. Clinopyroxenes show a wide range of composition, Mg number ranging from 50.86-83.78. The mineral chemistry matches closely with the whole rock data and shows down hole cryptic chemical variation. Variations in Mg numbers of CPX occur on thin section scale as well as in meter scales. Down hole cryptic chemical variations suggest periodic replenishment of the magma chamber, fractionation and magma mixing. The bulk rock major, trace, REE and the mineral chemistry suggest that gabbroic rocks formed as cumulates with low to negligible trap melt and

  12. Interpretation of trace element and isotope features of basalts: relevance of field relations, petrology, major element data, phase equilibria, and magma chamber modeling in basalt petrogenesis

    NASA Astrophysics Data System (ADS)

    O'Hara, M. J.; Herzberg, C.

    2002-06-01

    explain the chemical variation between fertile and residual peridotite in natural ultramafic rock suites. The subtleties of magma chamber partial crystallization processes can produce an astounding array of "pseudospidergrams," a small selection of which have been explored here. Major modification of the trace element geochemistry and trace element ratios, even those of the highly incompatible elements, must always be entertained whenever the evidence suggests the possibility of partial crystallization. At one extreme, periodically recharged, periodically tapped magma chambers might undergo partial crystallization by ˜95% consolidation of a succession of small packets of the magma. Refluxing of the 5% residual melts from such a process into the main body of melt would lead to eventual discrimination between highly incompatible elements in that residual liquid comparable with that otherwise achieved by 0.1 to 0.3% liquid extraction in equilibrium partial melting. Great caution needs to be exercised in attempting the reconstruction of more primitive compositions by addition of troctolite, gabbro, and olivine to apparently primitive lava compositions. Special attention is focussed on the phase equilibria involving olivine, plagioclase (i.e., troctolite), and liquid because a high proportion of erupted basalts carry these two phases as phenocrysts, yet the equilibria are restricted to crustal pressures and are only encountered by wide ranges of basaltic compositions at pressures less than 0.5 GPa. The mere presence of plagioclase phenocrysts may be sufficient to disqualify candidate primitive magmas. Determination of the actual contributions of crustal processes to petrogenesis requires a return to detailed field, experimental, and forensic petrologic studies of individual erupted basalt flows; of a multitude of cumulate gabbros and their contacts; and of upper-mantle outcrops.

  13. Apollo 11 prime crew during manned altitude chamber test activity

    NASA Technical Reports Server (NTRS)

    1969-01-01

    Interior view of the chamber in the Kennedy Space Center's Operations Building showing Apollo Spacecraft 107 Command Module during manned altitude chamber test activity. The prime crew of the Apollo 11 lunar landing mission is Astronauts Neil A. Armstrong, commander; Michael Collins, command module pilot; and Edwin E. Aldrin Jr., lunar module pilot.

  14. Discharge Chamber Primary Electron Modeling Activities in Three-Dimensions

    NASA Technical Reports Server (NTRS)

    Steuber, Thomas J.

    2004-01-01

    Designing discharge chambers for ion thrusters involves many geometric configuration decisions. Various decisions will impact discharge chamber performance with respect to propellant utilization efficiency, ion production costs, and grid lifetime. These hardware design decisions can benefit from the assistance of computational modeling. Computational modeling for discharge chambers has been limited to two-dimensional codes that leveraged symmetry for interpretation into three-dimensional analysis. This paper presents model development activities towards a three-dimensional discharge chamber simulation to aid discharge chamber design decisions. Specifically, of the many geometric configuration decisions toward attainment of a worthy discharge chamber, this paper focuses on addressing magnetic circuit considerations with a three-dimensional discharge chamber simulation as a tool. With this tool, candidate discharge chamber magnetic circuit designs can be analyzed computationally to gain insight into factors that may influence discharge chamber performance such as: primary electron loss width in magnetic cusps, cathode tip position with respect to the low magnetic field volume, definition of a low magnetic field region, and maintenance of a low magnetic field region across the grid span. Corroborating experimental data will be obtained from mockup hardware tests. Initially, simulated candidate magnetic circuit designs will resemble previous successful thruster designs. To provide opportunity to improve beyond previous performance benchmarks, off-design modifications will be simulated and experimentally tested.

  15. Multiple plagioclase crystal populations identified by crystal size distribution and in situ chemical data: Implications for timescales of magma chamber processes associated with the 1915 eruption of Lassen Peak, CA

    USGS Publications Warehouse

    Salisbury, M.J.; Bohrson, W.A.; Clynne, M.A.; Ramos, F.C.; Hoskin, P.

    2008-01-01

    Products of the 1915 Lassen Peak eruption reveal evidence for a magma recharge-magma mixing event that may have catalyzed the eruption and from which four compositional members were identified: light dacite, black dacite, andesitic inclusion, and dark andesite. Crystal size distribution, textural, and in situ chemical (major and trace element and Sr isotope) data for plagioclase from these compositional products define three crystal populations that have distinct origins: phenocrysts (long axis > 0??5 mm) that typically have core An contents between 34 and 36 mol %, microphenocrysts (long axis between 0??1 and 0??5 mm) that have core An contents of 66-69, and microlites (long axis < 0??1 mm) with variable An core contents from 64 to 52. Phenocrysts are interpreted to form in an isolated dacitic magma chamber that experienced slow cooling. Based on textural, compositional, and isotopic data for the magma represented by the dacitic component, magma recharge was not an important process until just prior to the 1915 eruption. Average residence times for phenocrysts are in the range of centuries to millennia. Microphenocrysts formed in a hybrid layer that resulted from mixing between end-member reservoir dacite and recharge magma of basaltic andesite composition. High thermal contrast between the two end-member magmas led to relatively high degrees of undercooling, which resulted in faster crystal growth rates and acicular and swallowtail crystal habits. Some plagioclase phenocrysts from the dacitic chamber were incorporated into the hybrid layer and underwent dissolution-precipitation, seen in both crystal textures and rim compositions. Average microphenocryst residence times are of the order of months. Microlites may have formed in response to decompression and/ or syn-eruptive degassing as magma ascended from the chamber through the volcanic conduit. Chemical distinctions in plagioclase microlite An contents reveal that melt of the dark andesite was more mafic than

  16. Abrupt magma chamber contraction and microseismicity at Campi Flegrei, Italy: Cause and effect determined from strainmeters and tiltmeters

    NASA Astrophysics Data System (ADS)

    Amoruso, Antonella; Crescentini, Luca; Scarpa, Roberto; Bilham, Roger; Linde, Alan T.; Sacks, I. Selwyn

    2015-08-01

    In March 2010 two borehole strainmeters and three Michelson tiltmeters within the Campi Flegrei volcanic system, Italy, registered an abrupt deformation signal that was followed 20 min later by seismic slip on a pair of onshore normal faults. We demonstrate that the observed strain changes were caused by a small but rapid volume decrease in a previously identified offshore ellipsoidal magma source or part of it. Although the total deflation was below the detectability of interferometric synthetic aperture radar and GPS, deflation observed rates were briefly 2 orders of magnitude more rapid than decadal inflation rates. We conclude that this high dilatational contraction rate was responsible for triggering seismicity and that this process may be responsible for the normal faulting often observed in the Campi Flegrei region. Our study quantifies the crucial role played by a transient, minor reduction in dilatational stress, in triggering slip on a fault near critical failure. Our subsurface measurements of strain and tilt registered anomalous deformation three sigma above background noise levels 17 min before the onset of microseismicity suggesting strain measurements have potential utility as an early warning system for the city of Naples.

  17. A Dual-Porosity, In Situ Crystallisation Model For Fast-Spreading Mid-Ocean Ridge Magma Chambers Based Upon Direct Observation From Hess Deep

    NASA Astrophysics Data System (ADS)

    MacLeod, C. J.; Lissenberg, C. J.

    2014-12-01

    We propose a revised magma chamber model for fast-spreading mid-ocean ridges based upon a synthesis of new data from a complete section of lower crust from the East Pacific Rise, reconstructed from samples collected from the Hess Deep rift valley during cruise JC21. Our investigation includes detailed sampling across critical transitions in the upper part of the plutonic section, including the inferred axial melt lens (AML) within the dyke-gabbro transition. We find that an overall petrological progression, from troctolite and primitive gabbro at the base up into evolved (oxide) gabbro and gabbronorite at the top of the lower crustal section, is mirrored by a progressive upward chemical fractionation as recorded in bulk rock and mineral compositions. Crystallographic preferred orientations measured using EBSD show that the downward increase in deformation of mush required in crystal subsidence models is not observed. Together these observations are consistent only with a model in which crystallisation of upward migrating evolving melts occurs in situ in the lower crust. Over-enrichment in incompatible trace element concentrations and ratios above that possible by fractional crystallisation is ubiquitous. This implies redistribution of incompatible trace elements in the lower crust by low porosity, near-pervasive reactive porous flow of interstitial melt moving continuously upward through the mush pile. Mass balance calculations reveal a significant proportion of this trace element enriched melt is trapped at mid-crustal levels. Mineral compositions in the upper third to half of the plutonic section are too evolved to represent the crystal residues of MORB. Erupted MORB therefore must be fed from melts sourced in the deeper part of the crystal mush pile, and which must ascend rapidly without significant modification in the upper plutonics or AML. From physical models of mush processes we posit that primitive melts are transported through transient, high porosity

  18. How caldera collapse shapes the shallow emplacement and transfer of magma in active volcanoes

    NASA Astrophysics Data System (ADS)

    Corbi, Fabio; Rivalta, Eleonora; Pinel, Virginie; Maccaferri, Francesco; Bagnardi, Marco; Acocella, Valerio

    2016-04-01

    Calderas are topographic depressions formed by the collapse of a partly drained magma reservoir. At volcanic edifices with calderas, eruptive fissures can circumscribe the outer caldera rim, be oriented radially and/or align with the regional tectonic stress field. Constraining the mechanisms that govern this spatial arrangement is fundamental to understand the dynamics of shallow magma storage and transport and evaluate volcanic hazard. Here we use numerical models to show that the previously unappreciated unloading effect of caldera formation may contribute significantly to the stress budget of a volcano. We first test this hypothesis against the ideal case of Fernandina, Galápagos, where previous models only partly explained the peculiar pattern of circumferential and radial eruptive fissures and the geometry of the intrusions determined by inverting the deformation data. We show that by taking into account the decompression due to the caldera formation, the modeled edifice stress field is consistent with all the observation. We then develop a general model for the stress state at volcanic edifices with calderas based on the competition of caldera decompression, magma buoyancy forces and tectonic stresses. These factors control the shallow accumulation of magma in stacked sills, consistently with observations as well as the conditions for the development of circumferential and/or radial eruptive fissures, as observed on active volcanoes. This top-down control exerted by changes in the distribution of mass at the surface allows better understanding of how shallow magma is transferred at active calderas, contributing to forecasting the location and type of opening fissures.

  19. Magma storage depths beneath an active rift volcano in Afar (Dabbahu), constrained by melt inclusion analyses, seismicity and Interferometric Synthetic Aperture Radar (INSAR)

    NASA Astrophysics Data System (ADS)

    Field, L.; Blundy, J.; Wright, T. J.; Yirgu, G.; Afar Consortium

    2010-12-01

    Dabbahu volcano is located at the northern end of the active Manda Hararo rift segment in western Afar, Ethiopia. In 2005 a major rifting episode began in the segment, which has been modelled as basalt dyke injections (1). Seismic activity, inflation and deflation have been recorded at the volcano. The aim of this research is to provide an insight into the history and evolution of a silicic magmatic centre in the rift, and to contribute to the wider aims of the NERC Afar Consortium to track the creation, migration, evolution and emplacement of magma from the asthenosphere to the crust. The volatile contents of rare melt inclusions trapped within phenocrysts of alkali feldspar, clinopyroxene and olivine from Dabbahu have been studied using secondary ion mass spectrometry. The host lavas are mildly peralkaline obsidians, which, based on field evidence and preliminary results from 40Ar-39Ar dating, represent the youngest samples on the volcano (<4 ka). Whilst the obsidian and pumice groundmass glasses are largely degassed, the H2O contents of the analysed inclusions are up to 5.8 wt%. CO2 contents are generally low; <462 ppm in the alkali feldspar-hosted inclusions, but higher values (up to 1457 ppm) have been found in the clinopyroxene-hosted inclusions. The pressure (and depth) of pre-eruptive magma storage beneath Dabbahu has been constrained using H2O and CO2 data, which suggest shallow magma storage at depths of ~1 - 5 km below the surface. These depths are consistent with observations from recorded seismicity and InSAR at Dabbahu. Seismicity has been recorded from deformation caused by deflation of the magma chamber following the 2005 dyke emplacement event (Oct 2005 - Apr 2006)(2) and InSAR has monitored deflation and subsequent steady inflation after this event. We show that melt inclusions accurately record a stable, shallow magma chamber as corroborated by remote sensing and geophysical observations at Dabbahu volcano. 1 Ayele et al. 2009 ‘September 2005

  20. Linking enclave formation to magma rheology

    NASA Astrophysics Data System (ADS)

    Hodge, K. F.; Jellinek, A. M.

    2012-10-01

    Magmatic enclaves record the history of deformation and disaggregation (i.e., fragmentation) of relatively hot, compositionally more mafic magmas injected into actively convecting silicic magma chambers through dikes. Enclave size distributions may provide crucial clues for understanding the nature of this mechanical mixing process. Accordingly, we conduct a comprehensive field study to measure enclave size distributions in six Cascade lava flows. Using results from recent fluid dynamics experiments along with thermodynamic and modeling constraints on key physical properties of the injected and host magmas (i.e., temperature, density and effective viscosity), we use the size distributions of enclaves to characterize the magmatic flow regime governing enclave formation. Scaling arguments suggest that the viscous stresses related to magma chamber flow acting against the yield strength of a crystallizing injected magma control the breakup of 1 m-wide mafic dikes into millimeter- to centimeter-scale enclaves. Our data analysis identifies a characteristic length scale of breakup that constrains the yield strength of the injected magmas in a more restrictive way than existing empirical models for yield strength based on crystal content. In all six lava flows, we show that the progressive fragmentation of the injected magma is self-similar and characterized by a fractal dimensionDf ˜ 2, which is comparable to previous studies on enclaves. We also find a small but statistically significant dependence of Df on the effective viscosity ratio between host and enclave magmas, such that large variations in effective viscosity enhance breakup. This work demonstrates that field observations of enclave size distributions can reliably constrain the rheological and flow conditions in which enclaves form.

  1. Echo-resonance and hydraulic perturbations in magma cavities: application to the volcanic tremor of Etna (Italy) in relation to its eruptive activity

    NASA Astrophysics Data System (ADS)

    Montalto, A.; Longo, V.; Patanè, G.

    1995-08-01

    A study is presented of spectral features of volcanic tremor recorded at Mount Etna (Sicily, Italy) following the methods of analysis suggested by the resonant scattering formalism of Gaunaurd and Überall (1978, 1979a, 1979b) and the model for hydraulic origin of Seidl et al. (1981). The periods investigated include summit and flank eruptions that occurred between 1984 and 1993. Recordings from a permanent station located near the top of the volcano were used, and the temporal patterns associated with (a) the average spacing (bar Δ ) between consecutive spectral peaks in the frequency range 1 6 Hz, (b) the spectral shape and (c) the overall spectral amplitude were analyzed. bar Δ values are thought to depend on the physical properties of magma, such as its density, which, in turn, is controlled by the degree of gas exsolution. Variations in the spectral shape are tentatively attributed to changes in the geometrical scattering from the boundary of resonant conduits and magma batches. Finally, the overall amplitude at the station should essentially reflect the state of turbulence of magma within the superficial ascending path. A limit in the application of the resonant scattering formalism to the study of volcanic tremor is given by the fact that the fundamental modes and integer harmonics are difficult to identify in the frequency spectra, as tremor sources are likely within cavities of very complex geometry, rather than in spherical or cylindrical chambers, as expected by theory. This study gives evidence of some correlations between the analyzed temporal patterns and the major events in the volcanic activity, related to both lava flow and explosions at the summit vents. In particular, relatively high values of bar Δ have been attained during the SE crater eruption of 1984, the complex eruptive phases of September October 1989 and the 1991 1993 flank eruption, suggesting the presence of a relatively dense magma for all of these events. Conversely, very low

  2. Magma movements and Iceland's next eruptions (Invited)

    NASA Astrophysics Data System (ADS)

    Sigmundsson, F.; Ofeigsson, B.; Hreinsdottir, S.; Hensch, M.; Gudmundsson, G.; Vogfjord, K. S.; Roberts, M. J.; Geirsson, H.; La Femina, P. C.; Hooper, A. J.; Sturkell, E. C.; Einarsson, P.; Gudmundsson, M. T.; Brandsdottir, B.; Loughlin, S. C.; Team, F.

    2013-12-01

    Iceland, created by hotspot-ridge interaction, is characterized by higher magmatic input and more complicated plate boundary structure than other parts of the Mid-Atlantic rift system. It has 30+ volcanic systems, where 20 confirmed eruptions have occurred in the last 40 years, the most recent at Eyjafjallajökull in 2010 and Grimsvotn in 2011. Likely candidates for the next eruption include the four most active volcanoes in Iceland (Hekla, Katla, Grimsvotn, and Bardarbunga) and other areas of volcanic unrest (Askja region, the Krisuvik area). Present volcano monitoring and research, including the FUTUREVOLC project, aims at providing warnings of impending eruptions and their character. Earthquake monitoring and deformation studies have hereto provided the most relevant information. Hekla continuously accumulates magma at a rate of about 0.003-0.02 km3/yr, according to GPS and InSAR studies, in a magma chamber placed below 14 km depth. A sequence of M0.4-1 earthquakes early this year stands out from otherwise mostly aseismic character of Hekla during repose periods. The Hekla magma chamber does not fail at a constant amount of magma volume, rather a clear pattern is observed with eruption size scaling with the length of the preceding period of dormancy. The ice capped Katla volcano shows unusual annual deformation pattern, seismic activity, and hydrological variations depending on time of year, presumably related to ice load and water pressure variations. It may be in a critical stage and renewed inflow of magma may quickly move the volcano towards failure. Bardarbunga had major earthquake and magma transfer activity in 1996, and has been the site of deep low-frequency earthquakes. Grímsvötn volcano is the only volcano with a shallow magma chamber with ongoing confirmed recharging, and failure criteria closest to 'expected'. A large eruption occurred in 2011 compared to much smaller eruption in 2004. However, the amount of erupted magma did not scale with the

  3. Insights into the Geochemical Evolution of the Youngest Toba Tuff Magma Chamber using Zircon-hosted Melt Inclusion

    NASA Astrophysics Data System (ADS)

    Lerner, A. H.; Kent, A. J.

    2015-12-01

    Zircon crystals can provide multidimensional insights into magmatic evolution. We combine zircon U-Th dating and trace element chemistry, with zircon-hosted melt inclusion compositions and volatile abundances to investigate the magmatic evolution preceding the 74 ka Youngest Toba Tuff (YTT) eruption. Zircon have U-Th crystallization ages spanning from eruption age to > 375 ka, reinforcing earlier findings that the YTT system was long-lived. A progressive increase of U in zircon (from < 500 to ~1500 ppm) indicates that the YTT system, or a portion of it, became highly fractionated between 130-200 ka. A possible lull in zircon crystallization is contemporaneous with a previously recognized increase in chemical diversity of allanite ~110-130 ka, suggesting a period of enhanced thermal input into the system. We identify two main populations of zircon-hosted melt inclusions. A low-MgO type is more evolved (> 280 ppm Rb, ~125 ppm Ba, 25-30 ppm Sr, < 0.03 wt% MgO) and has high water contents (3.8-5.7 wt% H2O), consistent with formation and storage in a highly fractionated crystal mush ~ 4-9 km deep. A high-MgO type (250-260 ppm Rb, 160-450 ppm Ba, 35-55 ppm Sr, 0.04-0.07 wt% MgO) has compositions similar to matrix glasses, and is typically less hydrous (0.5-3.5 wt% H2O), suggesting storage and degassing in a somewhat more primitive melt < 3 km deep. Melt inclusions dated via U-Th measurements of surrounding zircon zones, show no clear temporal differences between the two MgO populations. Rather, melt inclusions entrapped throughout the entire YTT history have relatively invariant major element chemistries, and have no temporal trends in volatile abundances. Zircon-hosted melt inclusions (particularly the low-MgO type) of many ages occur within sealed reentrant melt-channels. A number of zircon grains have actively open melt channels rimmed with 1-3 μm of low-U zircon growth. These dissolution/regrowth features are texturally similar to dissolution zones with high

  4. Inverse differentiation pathway by multiple mafic magma refilling in the last magmatic activity of Nisyros Volcano, Greece

    NASA Astrophysics Data System (ADS)

    Braschi, Eleonora; Francalanci, Lorella; Vougioukalakis, Georges E.

    2012-07-01

    Based on detailed field, petrographic, chemical, and isotopic data, this paper shows that the youngest magmas of the active Nisyros volcano (South Aegean Arc, Greece) are an example of transition from rhyolitic to less evolved magmas by multiple refilling with mafic melts, triggering complex magma interaction processes. The final magmatic activity of Nisyros was characterized by sub-Plinian caldera-forming eruption (40 ka), emplacing the Upper Pumice (UP) rhyolitic deposits, followed by the extrusion of rhyodacitic post-caldera domes (about 31-10 ka). The latter are rich in magmatic enclaves with textural and compositional (basaltic-andesite to andesite) characteristics that reveal they are quenched portions of mafic magmas included in a cooler more evolved melt. Dome-lavas have different chemical, isotopic, and mineralogical characteristics from the enclaves. The latter have lower 87Sr/86Sr and higher 143Nd/144Nd values than dome-lavas. Silica contents and 87Sr/86Sr values decrease with time among dome-lavas and enclaves. Micro-scale mingling processes caused by enclave crumbling and by widespread mineral exchanges increase from the oldest to the youngest domes, together with enclave content. We demonstrate that the dome-lavas are multi-component magmas formed by progressive mingling/mixing processes between a rhyolitic component ( post-UP) and the enclave-forming mafic magmas refilling the felsic reservoir (from 15 wt.% to 40 wt.% of mafic component with time). We recognize that only the more evolved enclave magmas contribute to this process, in which recycling of cumulate plagioclase crystals is also involved. The post-UP end-member derives by fractional crystallization from the magmas leftover after the previous UP eruptions. The enclave magma differentiation develops mainly by fractional crystallization associated with multiple mixing with mafic melts changing their composition with time. A time-related picture of the relationships between dome-lavas and

  5. Bubble plumes generated during recharge of basaltic magma reservoirs

    NASA Astrophysics Data System (ADS)

    Phillips, Jeremy C.; Woods, Andrew W.

    2001-03-01

    CO 2 is relatively insoluble in basaltic magma at low crustal pressures. It therefore exists as a gas phase in the form of bubbles in shallow crustal reservoirs. Over time these bubbles may separate gravitationally from the magma in the chamber. As a result, any new magma which recharges the chamber from deeper in the crust may be more bubble-rich and hence of lower density than the magma in the chamber. Using scaling arguments, we show that for typical recharge fluxes, such a source of low-viscosity, bubble-rich basalt may generate a turbulent bubble plume within the chamber. We also show that the bubbles are typically sufficiently small to have a low Reynolds number and to remain in the flow. We then present a series of analogue laboratory experiments which identify that the motion of such a turbulent bubble-driven line plume is well described by the classical theory of buoyant plumes. Using the classical plume theory we then examine the effect of the return flow associated with such bubble plumes on the mixing and redistribution of bubbles within the chamber. Using this model, we show that a relatively deep bubbly layer of magma may form below a thin foam layer at the roof. If, as an eruption proceeds, there is a continuing influx at the base of the chamber, then our model suggests that the bubble content of the bubbly layer may gradually increase. This may lead to a transition from lava flow activity to more explosive fire-fountaining activity. The foam layer at the top of the chamber may provide a flux for the continual outgassing from the flanks of the volcano [Ryan, Am. Geophys. Union Geophys. Monogr. 91 (1990)] and if it deepens sufficiently it may contribute to the eruptive activity [Vergniolle and Jaupart, J. Geophys. Res. 95 (1990) 2793-3001].

  6. Evidence of varying magma chambers and magmatic evolutionary histories for the Table Mountain Formation in the Carson-Iceberg Wilderness region, Sonora Pass, California

    NASA Astrophysics Data System (ADS)

    Asami, R.; Putirka, K. D.; Pluhar, C. J.; Farner, M. J.; Torrez, G.; Shrum, B. L.; Jones, S.

    2012-12-01

    The Sonora Pass- Dardanelles region in the Carson- Iceberg Wilderness area is located in the central Sierra Nevada and home to the type section for latites (Slemmons, 1953), a volcanic rock that contains high potassium, clinopyroxene, and plagioclase phenocysts. Latite lavas and tuffs exposed in the Sonora Pass region originated from the sources in the eastern Sierra Nevada (Noble et al., 1974) where lavas flowed toward California's Great Valley, and were emplaced in stream valleys along the way, which are now inverted to form "table mountains", ergo the name "Table Mountain Latite" (TML) (Slemmons, 1966). Similarly high-K volcanic rocks of the same age are exposed at Grouse Meadows, which is just north of the Walker Lane Caldera east of Sonora Pass, and at the type section, between Red Peak and Bald Peak west of Sonora Pass. Latites lavas and tuffs in all three regions were analyzed for major oxides and trace elements with X-ray fluorescence spectrometry at California State University, Fresno. Analysis of three locations of (TML) at the type section show that they (Ransome, 1898), may have a different magmatic evolutionary history compared to other latites, exposed at Sonora Pass and Grouse Meadows, as the latter two show similar major oxide and trace element compositions. Most compelling is the contrast in the behavior of Al2O3 and CaO at the type section. Variation diagrams show that at the type section Al2O3 and CaO enrichment decreases with increasing amounts of MgO as fractional crystallization occurs. Conversely, at Sonora Peak and Grouse Meadows, CaO and Al2O3 concentrations mostly increase as MgO decreases with fractional crystallization. This contrasts shows that plagioclase was a major fractioning phase at the type section, but not at the other two localities. This suggests that the lava flows at the type section were erupted from a distinct set of magma chambers and vents that underwent a very distinct magmatic evolutionary history, perhaps involving

  7. Imaging of Lower-crustal Magma Chambers at an Ultraslow Spreading Ridge Segment using Elastic Waveform Inversion of a Sparse OBS Dataset

    NASA Astrophysics Data System (ADS)

    Jian, H.; Singh, S. C.; Chen, Y. J.; Li, J.

    2014-12-01

    The existence of axial magma chambers (AMC) is indicative of the magmatic crustal accretion at Mid-Ocean Ridges. They have been extensively imaged with seismic reflection data (e.g. multichannel seismic data), showing that the depth of the top reflector increases from 1 km to ~3 km below the seafloor, when the spreading rate decreases from fast to slow spreading. Under the ultraslow spreading environment, we have previously reported the discovery of a large lower-crustal low-velocity zone at the Southwest Indian Ridge at 50°28'E from 3-D travel time tomography of refraction data registered by an ocean bottom seismometer (OBS) array. These results suggest the presence of partial melt within the lower crust (>4 km bsf). Here we further improve the resolution of the AMC image by employing a 2-D time-domain elastic full waveform inversion (FWI) method. The FWI gives a higher resolution than travel time tomography as it utilizes amplitude information and does not require the high-frequency approximation used in travel time tomography. The non-linearity of the FWI is overcome by using the tomographic results as a starting model. We have selected a 70-km long profile running across the ridge axis around the segment center, where 340 shots spaced at ~220 m were recorded on 3 OBSs. The small number of OBS poses serious challenge for the success of the full waveform inversionFWI. In order to examine the resolvability of this sparse OBS dataset, we first performed FWI over a sparse synthetic data set. We find that the FWI of these this sparse dataset is capable of retrieving an isolated lower-crustal AMC anomaly beneath the ridge axis, although the resulting velocity anomaly is smeared out, particularly along the lateral direction. For the real-data inversion, the starting model was built from the 3-D travel time tomography. The inverted results clearly show the sharp boundary of the top of the low velocity zone, suggesting that the low velocity zone indeed corresponds to

  8. Endocytic activity of Sertoli cells grown in bicameral culture chambers

    SciTech Connect

    Dai, R.X.; Djakiew, D.; Dym, M.

    1987-07-01

    Immature rat Sertoli cells were cultured for 7 to 14 days on Millipore filters impregnated with a reconstituted basement membrane extract in dual-environment (bicameral) culture chambers. Electron microscopy of the cultured cells revealed the presence of rod-shaped mitochondria, Golgi apparatus, rough endoplasmic reticulum, and Sertoli-Sertoli tight junctions, typical of these cells in vivo. The endocytic activity of both the apical and basal surfaces of the Sertoli cells was examined by either adding alpha 2-macroglobulin (alpha 2-M) conjugated to 20 nm gold particles to the apical chamber or by adding /sup 125/I labeled alpha 2-M to the basal chamber. During endocytosis from the apical surface of Sertoli cells, the alpha 2-M-gold particles were bound initially to coated pits and then internalized into coated vesicles within 5 minutes. After 10 minutes, the alpha 2-M-gold was found in multi-vesicular bodies (MVBs) and by 30 minutes it was present in the lysosomes. The proportion of alpha 2-M-gold found within endocytic cell organelles after 1 hour of uptake was used to estimate the approximate time that this ligand spent in each type of organelle. The alpha 2-M-gold was present in coated pits, coated vesicles, multivesicular bodies, and lysosomes for approximately 3, 11, 22, and 24 minutes, respectively. This indicates that the initial stages of endocytosis are rapid, whereas MVBs and lysosomes are relatively long-lived.

  9. pXRF quantitative analysis of the Otowi Member of the Bandelier Tuff: Generating large, robust data sets to decipher trace element zonation in large silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Van Hoose, A. E.; Wolff, J.; Conrey, R.

    2013-12-01

    similar trace element zonation. The eruption culminated in caldera collapse after transitioning from a single central vent to ring fracture vents. Ignimbrites deposited at this time have lithic breccias and chaotic geochemical profiles. The geochemical discrepancy between early and late deposits warrants detailed, high-resolution sampling and analysis in order to fully understand the dynamics behind zonation processes. Samples were collected from locations that circumvent the caldera and prepared and analyzed in the field and the laboratory with the pXRF. Approximately 2,000 pumice samples will complete this unprecedented data set, allowing detailed reconstruction of trace element zonation around all sides of the Valles Caldera. These data are then used to constrain models of magma chamber processes that produce trace element zonation and how it is preserved in the deposits after a catastrophic, caldera-forming eruption.

  10. Magma energy

    SciTech Connect

    Dunn, J.C.

    1987-01-01

    The thermal energy contained in magmatic systems represents a huge potential resource. In the US, useful energy contained in molten and partially-molten magma within the upper 10 km of the crust has been estimated at 5 to 50 x 10/sup 22/ J (50,000 to 500,000 Quads). The objective of the Magma Energy Extraction Program is to determine the engineering feasibility of locating, accessing, and utilizing magma as a viable energy resource. This program follows the DOE/OBES-funded Magma Energy Research Project that concluded scientific feasibility of the magma energy concept. A primary long-range goal of this program is to conduct an energy extraction experiment directly in a molten, crustal magma body. Critical to determining engineering feasibility are several key technology tasks: (1) Geophysics - to obtain detailed definition of potential magma targets, (2) Geochemistry/Materials - to characterize the magma environment and select compatible engineering materials, (3) Drilling - to develop drilling and completion techniques for entry into a magma body, and (4) Energy Extraction - to develop heat extraction technology.

  11. Magma Fragmentation

    NASA Astrophysics Data System (ADS)

    Gonnermann, Helge M.

    2015-05-01

    Magma fragmentation is the breakup of a continuous volume of molten rock into discrete pieces, called pyroclasts. Because magma contains bubbles of compressible magmatic volatiles, decompression of low-viscosity magma leads to rapid expansion. The magma is torn into fragments, as it is stretched into hydrodynamically unstable sheets and filaments. If the magma is highly viscous, resistance to bubble growth will instead lead to excess gas pressure and the magma will deform viscoelastically by fracturing like a glassy solid, resulting in the formation of a violently expanding gas-pyroclast mixture. In either case, fragmentation represents the conversion of potential energy into the surface energy of the newly created fragments and the kinetic energy of the expanding gas-pyroclast mixture. If magma comes into contact with external water, the conversion of thermal energy will vaporize water and quench magma at the melt-water interface, thus creating dynamic stresses that cause fragmentation and the release of kinetic energy. Lastly, shear deformation of highly viscous magma may cause brittle fractures and release seismic energy.

  12. Cloud Chamber Activities for the High School Classroom.

    ERIC Educational Resources Information Center

    Perry, John Timothy; Sankey, Mary Ann

    1995-01-01

    Presents the idea that cloud chambers can be used by students as an experimental tool enabling them to conduct their own investigations on radiation. Provides detail regarding the construction of a cloud chamber and suggestions for student assignments that involve the cloud chamber. (DDR)

  13. Magma energy

    SciTech Connect

    Hardee, H.C.

    1985-01-01

    The paper briefly describes the potential magma resources in the US and worldwide, and possible ways of exploiting this resource. Two target sites for field experiments to characterize magma targets are identified: Long Valley Caldera and Coso Hot Springs. 11 refs. (ACR)

  14. Mass flux measurements at active lava lakes: Implications for magma recycling

    NASA Astrophysics Data System (ADS)

    Harris, Andrew J. L.; Flynn, Luke P.; Rothery, David A.; Oppenheimer, Clive; Sherman, Sarah B.

    1999-04-01

    Remotely sensed and field data can be used to estimate heat and mass fluxes at active lava lakes. Here we use a three thermal component pixel model with three bands of Landsat thematic mapper (TM) data to constrain the thermal structure of, and flux from, active lava lakes. Our approach considers that a subpixel lake is surrounded by ground at ambient temperatures and that the surface of the lake is composed of crusted and/or molten material. We then use TM band 6 (10.42-12.42 μm) with bands 3 (0.63-0.69 μm) or 4 (0.76-0.90 μm) and 5 (1.55-1.75 μm) or 7 (2.08-2.35 μm), along with field data (e.g., lava lake area), to place limits on the size and temperature of each thermal component. Previous attempts to achieve this have used two bands of TM data with a two-component thermal model. Using our model results with further field data (e.g., petrological data) for lava lakes at Erebus, Erta 'Ale, and Pu'u 'O'o, we calculate combined radiative and convective fluxes of 11-20, 14-27 and 368-373 MW, respectively. These yield mass fluxes, of 30-76, 44-104 and 1553-2079 kg s-1, respectively. We also identify a hot volcanic feature at Nyiragongo during 1987 from which a combined radiative and convective flux of 0.2-0.6 MW implies a mass flux of 1-2 kg s-1. We use our mass flux estimates to constrain circulation rates in each reservoir-conduit-lake system and consider four models whereby circulation results in intrusion within or beneath the volcano (leading to endogenous or cryptic growth) and/or magma mixing in the reservoir (leading to recycling). We suggest that the presence of lava lakes does not necessarily imply endogenous or cryptic growth: lava lakes could be symptomatic of magma recycling in supraliquidus reservoirs.

  15. Numerical modelling of triple-junction tectonics at Karlıova, Eastern Turkey, with implications for regional magma transport

    NASA Astrophysics Data System (ADS)

    Karaoğlu, Özgür; Browning, John; Bazargan, Mohsen; Gudmundsson, Agust

    2016-10-01

    Few places on Earth are as tectonically active as the Karlıova region of eastern Turkey. In this region, complex interactions between the Arabian, Eurasian and Anatolian plates occur at the Karlıova Triple Junction (KTJ). The relationship between tectonics and magma propagation in triple-junction tectonic settings is poorly understood. Here we present new field and numerical results on the mechanism of magma propagation at the KTJ. We explore the effects of crustal heterogeneity and anisotropy, in particular the geometry and mechanical properties of many faults and layers, on magma propagation paths under a variety of tectonic loadings. We propose that two major volcanic centres in the area, the Turnadağ volcano and the Varto caldera, are both fed by comparatively shallow magma chambers at depths of about 8 km, which, in turn, are fed by a single, much larger and deeper reservoir at about 15-18 km depth. By contrast, the nearby Özenç volcanic area is fed directly by the deeper reservoir. We present a series of two-dimensional and three-dimensional numerical models showing that the present tectonic stresses encourage magma-chamber rupture and dyke injection. The results show that inversion tectonics encourages the formation of magma paths as potential feeder dykes. Our three-dimensional models allow us to explore the local stresses induced by complex loading conditions at the Karlıova triple junction, using an approach that can in future be applied to other similar tectonic regions. The numerical results indicate a great complexity in the potential magma (dyke) paths, resulting from local stresses generated by interaction between mechanical layers, major faults, and magma chambers. In particular, the results suggest three main controls on magma path formation and eventual eruptions at KTJ: (1) the geometry and attitude of the associated faults; (2) the heterogeneity and anisotropy of the crust; and (3) mechanical (stress) interactions between deep and shallow

  16. Magma-tectonic interactions in an area of active extension; a review of recent observations, models and interpretations from Iceland

    NASA Astrophysics Data System (ADS)

    Pedersen, Rikke; Sigmundsson, Freysteinn; Drouin, Vincent; Rafn Heimisson, Elías; Parks, Michelle; Dumont, Stéphanie; Árnadóttir, Þóra; Masterlark, Timothy; Ófeigsson, Benedíkt G.; Jónsdóttir, Kristín; Hooper, Andrew

    2016-04-01

    The geological setting of Iceland provides rich opportunities of studying magma-tectonic interactions, as it constitutes Earth's largest part of the mid-oceanic ridge system exposed above sea level. A series of volcanic and seismic zones accommodate the ~2 cm/year spreading between the North-American and Eurasian plates, and the Icelandic hot-spot conveniently provides the means of exposing this oceanic crust-forming setting above sea-level. Both extinct and active plumbing system structures can be studied in Iceland, as the deeply eroded tertiary areas provide views into the structures of extinct volcanic systems, and active processes can be inferred on in the many active volcanic systems. A variety of volcanic and tectonic processes cause the Icelandic crust to deform continuously, and the availability of contemporaneous measurements of crustal deformation and seismicity provide a powerful data set, when trying to obtain insight into the processes working at depth, such as magma migration through the uppermost lithosphere, magma induced host rock deformation and volcanic eruption locations and styles. The inferences geodetic and seismic datasets allow on the active plate spreading processes and subsurface magma movements in Iceland will be reviewed, in particular in relation to the Northern Volcanic Zone (NVZ). There the three phases of a rifting cycle (rifting, post-rifting, inter-rifting) have been observed. The NVZ is an extensional rift segment, bounded to the south by the Icelandic mantle plume, and to the north by the Tjörnes transform zone. The NVZ has typically been divided into five partly overlapping en-echelon fissure swarms, each with a central main volcanic production area. Most recently, additional insight into controlling factors during active rifting has been provided by the Bárðarbunga activity in 2014-2015 that included a major rifting event, the largest effusive eruption in Iceland since 1783, and a gradual caldera collapse. It is evident

  17. Is magma cooling responsible for the periodic activity of Soufrière Hills volcano, Montserrat, West Indies?

    NASA Astrophysics Data System (ADS)

    Caricchi, Luca; Simpson, Guy; Chelle-Michou, Cyril; Neuberg, Jürgen

    2016-04-01

    After 400 years of quiescence, Soufrière Hills volcano on Montserrat (SHV) started erupting in 1995. Ongoing deformation and sulphur dioxide emission demonstrate that this volcanic systems is still restless, however, after 5 years of inactivity it remains unclear whether magma extrusion will restart. Also, if such periodically observed activity at SHV will restart, can we use past monitoring data to attempt to forecast the reawakening of this volcano? Cooling of volatile saturated magma leads to crystallisation, the formation of gas bubbles and expansion. Such volumetric variations are not only potentially responsible for deformation signals observed at the surface (Caricchi et al., 2014), but also lead to pressurisation of the magmatic reservoir and eventually renewed magma extrusion (Tait et al., 1989). We postulate that volcanic activity observed at SHM over the last 20 years could be essentially the result of the unavoidable progressive cooling of a magmatic body, which was probably assembled over thousands of years and experienced internal segregation of eruptible lenses of magma (Christopher et al., 2015). To test this hypothesis, we performed thermal modelling to test if the cooling of a shallow magma body emplaced since 1990 could account for the monitoring signals observed at SHV. The results show that progressive cooling of a 4km3 volume of melt could explain the deformation rate currently observed. Using the deformation rate obtained from the modelling for the first 15 years of cooling, a reservoir volume of about 13 km3 (Paulatto et al., 2012) and a critical value of overpressure of 10 MPa, it would have taken approximately only 3 years to pressurise the reservoir to the critical pressure and restart magma extrusion. This is in agreement with the time interval between previous pauses at SHV before 2010. Considering the current deformation rates, we speculate that magma extrusion could restart in 6-8 years after the end of the last event in 2010, hence

  18. Gravity fluctuations induced by magma convection at Kilauea Volcano, Hawai'i

    USGS Publications Warehouse

    Carbone, Daniele; Poland, Michael P.

    2012-01-01

    Convection in magma chambers is thought to play a key role in the activity of persistently active volcanoes, but has only been inferred indirectly from geochemical observations or simulated numerically. Continuous microgravity measurements, which track changes in subsurface mass distribution over time, provide a potential method for characterizing convection in magma reservoirs. We recorded gravity oscillations with a period of ~150 s at two continuous gravity stations at the summit of Kīlauea Volcano, Hawai‘i. The oscillations are not related to inertial accelerations caused by seismic activity, but instead indicate variations in subsurface mass. Source modeling suggests that the oscillations are caused by density inversions in a magma reservoir located ~1 km beneath the east margin of Halema‘uma‘u Crater in Kīlauea Caldera—a location of known magma storage.

  19. Rapid heterogeneous assembly of multiple magma reservoirs prior to Yellowstone supereruptions.

    PubMed

    Wotzlaw, Jörn-Frederik; Bindeman, Ilya N; Stern, Richard A; D'Abzac, Francois-Xavier; Schaltegger, Urs

    2015-09-10

    Large-volume caldera-forming eruptions of silicic magmas are an important feature of continental volcanism. The timescales and mechanisms of assembly of the magma reservoirs that feed such eruptions as well as the durations and physical conditions of upper-crustal storage remain highly debated topics in volcanology. Here we explore a comprehensive data set of isotopic (O, Hf) and chemical proxies in precisely U-Pb dated zircon crystals from all caldera-forming eruptions of Yellowstone supervolcano. Analysed zircons record rapid assembly of multiple magma reservoirs by repeated injections of isotopically heterogeneous magma batches and short pre-eruption storage times of 10(3) to 10(4) years. Decoupled oxygen-hafnium isotope systematics suggest a complex source for these magmas involving variable amounts of differentiated mantle-derived melt, Archean crust and hydrothermally altered shallow-crustal rocks. These data demonstrate that complex magma reservoirs with multiple sub-chambers are a common feature of rift- and hotspot related supervolcanoes. The short duration of reservoir assembly documents rapid crustal remelting and two to three orders of magnitude higher magma production rates beneath Yellowstone compared to continental arc volcanoes. The short pre-eruption storage times further suggest that the detection of voluminous reservoirs of eruptible magma beneath active supervolcanoes may only be possible prior to an impending eruption.

  20. Rapid heterogeneous assembly of multiple magma reservoirs prior to Yellowstone supereruptions

    PubMed Central

    Wotzlaw, Jörn-Frederik; Bindeman, Ilya N.; Stern, Richard A.; D’Abzac, Francois-Xavier; Schaltegger, Urs

    2015-01-01

    Large-volume caldera-forming eruptions of silicic magmas are an important feature of continental volcanism. The timescales and mechanisms of assembly of the magma reservoirs that feed such eruptions as well as the durations and physical conditions of upper-crustal storage remain highly debated topics in volcanology. Here we explore a comprehensive data set of isotopic (O, Hf) and chemical proxies in precisely U-Pb dated zircon crystals from all caldera-forming eruptions of Yellowstone supervolcano. Analysed zircons record rapid assembly of multiple magma reservoirs by repeated injections of isotopically heterogeneous magma batches and short pre-eruption storage times of 103 to 104 years. Decoupled oxygen-hafnium isotope systematics suggest a complex source for these magmas involving variable amounts of differentiated mantle-derived melt, Archean crust and hydrothermally altered shallow-crustal rocks. These data demonstrate that complex magma reservoirs with multiple sub-chambers are a common feature of rift- and hotspot related supervolcanoes. The short duration of reservoir assembly documents rapid crustal remelting and two to three orders of magnitude higher magma production rates beneath Yellowstone compared to continental arc volcanoes. The short pre-eruption storage times further suggest that the detection of voluminous reservoirs of eruptible magma beneath active supervolcanoes may only be possible prior to an impending eruption. PMID:26356304

  1. Rapid heterogeneous assembly of multiple magma reservoirs prior to Yellowstone supereruptions

    NASA Astrophysics Data System (ADS)

    Wotzlaw, Jörn-Frederik; Bindeman, Ilya N.; Stern, Richard A.; D'Abzac, Francois-Xavier; Schaltegger, Urs

    2015-09-01

    Large-volume caldera-forming eruptions of silicic magmas are an important feature of continental volcanism. The timescales and mechanisms of assembly of the magma reservoirs that feed such eruptions as well as the durations and physical conditions of upper-crustal storage remain highly debated topics in volcanology. Here we explore a comprehensive data set of isotopic (O, Hf) and chemical proxies in precisely U-Pb dated zircon crystals from all caldera-forming eruptions of Yellowstone supervolcano. Analysed zircons record rapid assembly of multiple magma reservoirs by repeated injections of isotopically heterogeneous magma batches and short pre-eruption storage times of 103 to 104 years. Decoupled oxygen-hafnium isotope systematics suggest a complex source for these magmas involving variable amounts of differentiated mantle-derived melt, Archean crust and hydrothermally altered shallow-crustal rocks. These data demonstrate that complex magma reservoirs with multiple sub-chambers are a common feature of rift- and hotspot related supervolcanoes. The short duration of reservoir assembly documents rapid crustal remelting and two to three orders of magnitude higher magma production rates beneath Yellowstone compared to continental arc volcanoes. The short pre-eruption storage times further suggest that the detection of voluminous reservoirs of eruptible magma beneath active supervolcanoes may only be possible prior to an impending eruption.

  2. Rapid heterogeneous assembly of multiple magma reservoirs prior to Yellowstone supereruptions.

    PubMed

    Wotzlaw, Jörn-Frederik; Bindeman, Ilya N; Stern, Richard A; D'Abzac, Francois-Xavier; Schaltegger, Urs

    2015-01-01

    Large-volume caldera-forming eruptions of silicic magmas are an important feature of continental volcanism. The timescales and mechanisms of assembly of the magma reservoirs that feed such eruptions as well as the durations and physical conditions of upper-crustal storage remain highly debated topics in volcanology. Here we explore a comprehensive data set of isotopic (O, Hf) and chemical proxies in precisely U-Pb dated zircon crystals from all caldera-forming eruptions of Yellowstone supervolcano. Analysed zircons record rapid assembly of multiple magma reservoirs by repeated injections of isotopically heterogeneous magma batches and short pre-eruption storage times of 10(3) to 10(4) years. Decoupled oxygen-hafnium isotope systematics suggest a complex source for these magmas involving variable amounts of differentiated mantle-derived melt, Archean crust and hydrothermally altered shallow-crustal rocks. These data demonstrate that complex magma reservoirs with multiple sub-chambers are a common feature of rift- and hotspot related supervolcanoes. The short duration of reservoir assembly documents rapid crustal remelting and two to three orders of magnitude higher magma production rates beneath Yellowstone compared to continental arc volcanoes. The short pre-eruption storage times further suggest that the detection of voluminous reservoirs of eruptible magma beneath active supervolcanoes may only be possible prior to an impending eruption. PMID:26356304

  3. Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

    USGS Publications Warehouse

    Matthews, Naomi E.; Vazquez, Jorge A.; Calvert, Andrew T.

    2015-01-01

    The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff. Tephra from the Lava Creek eruption is a key Quaternary chronostratigraphic marker, in particular for dating the deposition of mid Pleistocene glacial and pluvial deposits in western North America. To resolve the timing of eruption and crystallization history for the Lava Creek magma, we performed (1) 40Ar/39Ar dating of single sanidine crystals to delimit eruption age and (2) ion microprobe U-Pb and trace-element analyses of the crystal faces and interiors of single zircons to date the interval of zircon crystallization and characterize magmatic evolution. Sanidines from the two informal members composing Lava Creek Tuff yield a preferred 40Ar/39Ar isochron date of 631.3 ± 4.3 ka. Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 626.5 ± 5.8 ka, and have trace element concentrations that vary with the eruptive stratigraphy. Zircon interiors yield a mean 206Pb/238U date of 659.8 ± 5.5 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high U concentration cores that likely grew from highly evolved melt. The occurrence of distal Lava Creek tephra in stratigraphic sequences marking the Marine Isotope Stage 16–15 transition supports the apparent eruption age of ∼631 ka. The combined results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103−104 year interval before eruption.

  4. Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

    NASA Astrophysics Data System (ADS)

    Matthews, Naomi E.; Vazquez, Jorge A.; Calvert, Andrew T.

    2015-09-01

    The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff. Tephra from the Lava Creek eruption is a key Quaternary chronostratigraphic marker, in particular for dating the deposition of mid Pleistocene glacial and pluvial deposits in western North America. To resolve the timing of eruption and crystallization history for the Lava Creek magma, we performed (1) 40Ar/39Ar dating of single sanidine crystals to delimit eruption age and (2) ion microprobe U-Pb and trace-element analyses of the crystal faces and interiors of single zircons to date the interval of zircon crystallization and characterize magmatic evolution. Sanidines from the two informal members composing Lava Creek Tuff yield a preferred 40Ar/39Ar isochron date of 631.3 ± 4.3 ka. Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 626.5 ± 5.8 ka, and have trace element concentrations that vary with the eruptive stratigraphy. Zircon interiors yield a mean 206Pb/238U date of 659.8 ± 5.5 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high U concentration cores that likely grew from highly evolved melt. The occurrence of distal Lava Creek tephra in stratigraphic sequences marking the Marine Isotope Stage 16-15 transition supports the apparent eruption age of ˜631 ka. The combined results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103-104 year interval before eruption.

  5. Deformation of Grímsvötn volcano, Iceland, 1992-2014: Constraints on magma flow in relation to eruptions in 1998, 2004 and 2011

    NASA Astrophysics Data System (ADS)

    Sigmundsson, Freysteinn; Hreinsdottir, Sigrun; Sturkell, Erik; Ofeigsson, Benedikt; Einarsson, Pall; Roberts, Matthew; Grapenthin, Ronni; Villemin, Thierry; Arnadottir, Thora; Geirsson, Halldor

    2014-05-01

    A time series of ground deformation at Grímsvötn volcano, Iceland from 1992 to 2014 reveals deformation due to plate movements, glacial-isostatic uplift in response to the melting of the Vatnajökull ice cap, annual changes due to snow loading and magma movements. GPS measurements have been made at one nunatak, conducted intermittently since 1992 and continuously since 2004. During this period eruptions have occurred at Grímsvötn in 1998, 2004 and 2011. The component of displacement related to magma movements is obtained after the time series are corrected for signals due to other processes. Uplift and displacement away from the caldera occurs between eruptions at a rate of few cm/yr, interrupted by sudden co-eruptive subsidence and displacement towards the caldera (up to half a meter). This inflation/deflation pattern suggests deformation driven by pressure change in an upper crustal magma chamber, similar to other highly active calderas in Iceland such as Askja and Krafla. A simple model of pressure change variation in a magma chamber at shallow depth, with variable inflow between eruptions and outflow during eruptions can explain the observed deformation pattern. The erupted volume of magma in the 2011 eruption is about 10 times larger than the inferred co-eruptive volume change, attributed to compressibility of magma in the chamber. The magma compressibility is inferred to have remained constant during the 2011 eruption, as about constant scale factor is found during that eruption between eruption rate and displacement rate. This scale factor is, however, about five times lower for the 2004 eruption. This difference implies higher compressibility of magma in the shallow Grímsvötn magma chamber during the 2011 eruption compared to 2004, assuming the active part of the Grimsvötn magma plumbing system remained the same in both eruptions.

  6. Differentiation mechanism of frontal-arc basalt magmas

    NASA Astrophysics Data System (ADS)

    Kuritani, T.; Yoshida, T.; Kimura, J.; Hirahara, Y.; Takahashi, T.

    2012-04-01

    In a cooling magma chamber, magmatic differentiation can proceed both by fractionation of crystals from the main molten part of the magma body (homogeneous fractionation) and by mixing of the main magma with fractionated melt derived from low-temperature mush zones (boundary layer fractionation) (Jaupart and Tait, 1995, and references therein). The geochemical path caused by boundary layer fractionation can be fairly different from a path resulting from homogeneous fractionation (e.g., Langmuir, 1989). Therefore, it is important to understand the relative contributions of these fractionation mechanisms in magma chambers. Kuritani (2009) examined the relative roles of the two fractionation mechanisms in cooling basaltic magma chambers using a thermodynamics-based mass balance model. However, the basaltic magmas examined in the work were alkali-rich (Na2O+K2O > 4 wt.%). In this study, to explore differentiation mechanisms of frontal-arc basalt magmas that are volumetrically much more important than rear-arc alkali basalt magmas, the relative roles of the two fractionation mechanisms are examined for low-K tholetiitic basalt magma from Iwate Volcano, NE Japan arc, using the same mass balance model. First, the water content and the temperature of the Iwate magma were estimated. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78-81) correlates positively with the An content of coexisting plagioclase phenocrysts (An85-92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase. It is inferred from these observations that the phenocrysts with variable compositions were derived from a common magma with variable temperature in a magma chamber, and the plagioclase phenocrysts were all derived from mushy boundary layers along the walls of the magma chamber. By

  7. Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

    NASA Astrophysics Data System (ADS)

    Vazquez, J. A.; Matthews, N. E.; Calvert, A. T.

    2015-12-01

    The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff (LCT). Tephra from the eruption blanketed much of the western United States, and is a key Quaternary chronostratigraphic marker, in particular for dating deposition of mid-Pleistocene glacial and pluvial deposits in western North America. We performed 40Ar/39Ar dating of single sanidines to delimit eruption age, and ion microprobe U-Pb and trace-element analyses of crystal faces on single zircons to characterize magmatic evolution and date near-eruption crystallization, as well as analyses of crystal interiors to date the interval of zircon crystallization. Sanidines from the two LCT members A and B yield an 40Ar/39Ar isochron date of 631 ± 4 ka (2σ). Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 627 ± 6 ka (2σ) and have trace element concentrations that vary with eruptive stratigraphy. Zircon interiors yield a weighted mean 206Pb/238U date of 660 ± 6 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high-U concentrations and dark cathodoluminescence (CL) cores. These crystals with high-U cores are possibly sourced from 'defrosting' of melt-impregnated margins of the growing subvolcanic reservoir. LCT sanidines mirror the variation of zircon composition within the eruptive stratigraphy, with crystals from upper LCT-A and basal LCT-B having bright-CL rims with high Ba concentrations, suggesting late crystallization after addition of less evolved silicic magma. The occurrence of distal LCT in stratigraphic sequences marking the Marine Isotope Stage 16-15 transition supports the apparent eruption age of ca. 631 ka. These results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103-104 year interval

  8. Stability of rift axis magma reservoirs: Spatial and temporal evolution of magma supply in the Dabbahu rift segment (Afar, Ethiopia) over the past 30 kyr

    NASA Astrophysics Data System (ADS)

    Medynski, S.; Pik, R.; Burnard, P.; Vye-Brown, C.; France, L.; Schimmelpfennig, I.; Whaler, K.; Johnson, N.; Benedetti, L.; Ayelew, D.; Yirgu, G.

    2015-01-01

    Unravelling the volcanic history of the Dabbahu/Manda Hararo rift segment in the Afar depression (Ethiopia) using a combination of cosmogenic (36Cl and 3He) surface exposure dating of basaltic lava-flows, field observations, geological mapping and geochemistry, we show in this paper that magmatic activity in this rift segment alternates between two distinct magma chambers. Recent activity in the Dabbahu rift (notably the 2005-2010 dyking crises) has been fed by a seismically well-identified magma reservoir within the rift axis, and we show here that this magma body has been active over the last 30 kyr. However, in addition to this axial magma reservoir, we highlight in this paper the importance of a second, distinct magma reservoir, located 15 km west of the current axis, which has been the principal focus of magma accumulation from 15 ka to the subrecent. Magma supply to the axial reservoir substantially decreased between 20 ka and the present day, while the flank reservoir appears to have been regularly supplied with magma since 15 ka ago, resulting in less variably differentiated lavas. The trace element characteristics of magmas from both reservoirs were generated by variable degrees of partial melting of a single homogeneous mantle source, but their respective magmas evolved separately in distinct crustal plumbing systems. Magmatism in the Dabbahu/Manda Hararo rift segment is not focussed within the current axial depression but instead is spread out over at least 15 km on the western flank. This is consistent with magneto-telluric observations which show that two magma bodies are present below the segment, with the main accumulation of magma currently located below the western flank, precisely where the most voluminous recent (<15 ka) flank volcanism is observed at the surface. Applying these observations to slow spreading mid-ocean ridges indicates that magma bodies likely have a lifetime of a least 20 ka, and that the continuity of magmatic activity is

  9. Megacrystals track magma convection between reservoir and surface

    NASA Astrophysics Data System (ADS)

    Moussallam, Yves; Oppenheimer, Clive; Scaillet, Bruno; Buisman, Iris; Kimball, Christine; Dunbar, Nelia; Burgisser, Alain; Ian Schipper, C.; Andújar, Joan; Kyle, Philip

    2015-03-01

    Active volcanoes are typically fed by magmatic reservoirs situated within the upper crust. The development of thermal and/or compositional gradients in such magma chambers may lead to vigorous convection as inferred from theoretical models and evidence for magma mixing recorded in volcanic rocks. Bi-directional flow is also inferred to prevail in the conduits of numerous persistently-active volcanoes based on observed gas and thermal emissions at the surface, as well as experiments with analogue models. However, more direct evidence for such exchange flows has hitherto been lacking. Here, we analyse the remarkable oscillatory zoning of anorthoclase feldspar megacrystals erupted from the lava lake of Erebus volcano, Antarctica. A comprehensive approach, combining phase equilibria, solubility experiments and melt inclusion and textural analyses shows that the chemical profiles are best explained as a result of multiple episodes of magma transport between a deeper reservoir and the lava lake at the surface. Individual crystals have repeatedly travelled up-and-down the plumbing system, over distances of up to several kilometers, presumably as a consequence of entrainment in the bulk magma flow. Our findings thus corroborate the model of bi-directional flow in magmatic conduits. They also imply contrasting flow regimes in reservoir and conduit, with vigorous convection in the former (regular convective cycles of ∼150 days at a speed of ∼0.5 mm s-1) and more complex cycles of exchange flow and re-entrainment in the latter. We estimate that typical, 1-cm-wide crystals should be at least 14 years old, and can record several (from 1 to 3) complete cycles between the reservoir and the lava lake via the conduit. This persistent recycling of phonolitic magma is likely sustained by CO2 fluxing, suggesting that accumulation of mafic magma in the lower crust is volumetrically more significant than that of evolved magma within the edifice.

  10. Note: A single-chamber tool for plasma activation and surface functionalization in microfabrication

    SciTech Connect

    Bowman, Adam J.; Scherrer, Joseph R.; Reiserer, Ronald S.

    2015-06-15

    We present a simple apparatus for improved surface modification of polydimethylsiloxane (PDMS) microfluidic devices. A single treatment chamber for plasma activation and chemical/physical vapor deposition steps minimizes the time-dependent degradation of surface activation that is inherent in multi-chamber techniques. Contamination and deposition irregularities are also minimized by conducting plasma activation and treatment phases in the same vacuum environment. An inductively coupled plasma driver allows for interchangeable treatment chambers. Atomic force microscopy confirms that silane deposition on PDMS gives much better surface quality than standard deposition methods, which yield a higher local roughness and pronounced irregularities in the surface.

  11. Note: A single-chamber tool for plasma activation and surface functionalization in microfabrication

    PubMed Central

    Bowman, Adam J.; Scherrer, Joseph R.; Reiserer, Ronald S.

    2015-01-01

    We present a simple apparatus for improved surface modification of polydimethylsiloxane (PDMS) microfluidic devices. A single treatment chamber for plasma activation and chemical/physical vapor deposition steps minimizes the time-dependent degradation of surface activation that is inherent in multi-chamber techniques. Contamination and deposition irregularities are also minimized by conducting plasma activation and treatment phases in the same vacuum environment. An inductively coupled plasma driver allows for interchangeable treatment chambers. Atomic force microscopy confirms that silane deposition on PDMS gives much better surface quality than standard deposition methods, which yield a higher local roughness and pronounced irregularities in the surface. PMID:26133881

  12. Role of large flank-collapse events on magma evolution of volcanoes. Insights from the Lesser Antilles Arc

    NASA Astrophysics Data System (ADS)

    Boudon, G.; Villemant, B.; Le Friant, A.; Paterne, M.; Cortijo, E.

    2012-12-01

    Flank-collapse events are now recognized as common process of destruction of volcanoes. They can occur several times on a volcanic edifice and may involve a large range of volume of material from km3 to thousands of km3. Large flank-collapse events may have significant effects on magma eruption and evolution. The load exerted by the volcanic edifice on the plumbing system and the magma chamber acts as a density filter for magma ascent. Magmas denser than the density threshold are stored within the magma chamber where they differentiate and thus become less dense with time which favours their eruption. When a flank-collapse event occurs the edifice load suddenly decreases which decreases the density threshold allowing denser magmas to ascend and erupt. Thus construction and destruction of volcanic edifices may control both differentiation and eruptive processes. In the Lesser Antilles Arc, a large number of flank-collapse events have been identified. Here, we show that some of the largest events are correlated to significant variations in erupted magma compositions and eruptive styles. On Montagne Pelée, after the 32 kys old flank-collapse event, the magma production rate is sustained during several thousand years: basic and dense magmas were emitted through open-vent eruptions that generated abundant scoria flows. The pre-flank collapse activity produced significantly more acidic magmas. The rapid building of a new cone after the flank collapse progressively increased the load and the density threshold, leading to a decrease in magma production rate and a change in the magma composition of the erupted products. They are more acidic and less dense and thus generate plinian and dome-forming eruptions up to present. On the contrary, at Soufrière Volcanic Centre of St Lucia and at Pitons du Carbet in Martinique, the flank collapses have an opposite effect: in both cases, more acidic magmas erupted after the flank collapse events. These magmas are highly crystallized

  13. The link between multistep magma ascent and eruption intensity: examples from the recent activity of Piton de la Fournaise (La Réunion Island).

    NASA Astrophysics Data System (ADS)

    Di Muro, Andrea

    2014-05-01

    Caldera collapses represent catastrophic events, which induce drastic modification in a volcano plumbing system and can result in major and fast evolution of the system dynamics. At Piton de la Fournaise (PdF) volcano, the 2007 eruptive sequence extruded the largest lava volume (240 Mm3) since at least 3 centuries, provoking the collapse of a small (1 km wide; 340 m deep) summit caldera. In about 35 days, the 2007 major eruption generated i) the greatest lava output rate, ii) the strongest lava fountaining activity (> 200 m high), iii) the largest SO2 volume (> 230 kt) ever documented at PdF. This event ended a 9 year-long period (1998-2007) of continuous edifice inflation and sustained eruptive activity (3 eruptions per year on average). Unexpectedly and in spite of the large volume of magma erupted in 2007, volcano unrest and eruptive activity resumed quickly in 2008, soon after caldera collapse, and produced several closely spaced intracaldera eruptions and shallow intrusions. The post-2007 activity is associated with a trend of continuous volcano deflation and consists in small-volume (<3 Mm3) weak (< 20 m high fountains; strombolian activity) summit/proximal eruptions of moderate/low MgO magmas and frequent shallow magma intrusions. Non-eruptive tremor and increase in SO2 emissions were interpreted as evidences of magma intrusions at shallow depth (< 2.0 km) preceding the eruptions. The 2007-2011 phase of activity represents an ideal case-study to analyze the influence of magma ascent kinetics on the evolution of volcano dynamics at a persistently active basaltic volcano. In order to track magma storage and ascent, we compare geochemical data on fast quenched glasses (melt inclusions, Pele's hairs, coarse ash fragments produced by lava-sea water interaction, glassy crust of lavas, high-temperature lavas quenched in water, matrix glasses) with the geophysical record of volcano unrest. Petro-chemical data suggest that the shallow PdF plumbing system is formed by

  14. The Magma Transport System of the Mono Craters, California

    NASA Astrophysics Data System (ADS)

    Johnson, M. R.; Putirka, K. D.

    2013-12-01

    The Mono Craters are a series of 28 volcanic domes, coulees, and craters, just 16 km north of Long Valley. The magmatic products of the Mono Craters include mostly small magmatic bodies, sills, and dikes set in a transtensional tectonic setting. New high-density sampling of the domes reveals a wider range of magma compositions than heretofore recognized, and thus reveals what is likely a more complex magmatic system, involving a greater number of batches of magma and a more complex magma storage/delivery system. Here, we present a model for the magma plumbing system based on space-composition patterns and preliminary estimates of crystallization temperatures and pressures based on olivine-, feldspar- and clinopyroxene-liquid equilibria. Whole rock analyses show three compositionally distinct batches of magma within the Mono Craters proper: a felsic (73-78.4% SiO2), intermediate (64.4-68% SiO2) and mafic (52.7-61% SiO2) group. The Mono Lake Islands (Paoha and Negit) fall into the intermediate group, but contain distinctly lower TiO2 and Fe2O3 at a given SiO2 compared to all other Mono Craters; on this basis, we surmise that the Paoha and Negit eruptions represent a distinct episode of magmatism that is not directly related to the magmatic activity that created the Mono Craters proper. The discontinuous nature of the three groups indicates that magma mixing, while evident to some degree within and between certain domes, did not encompass the entire range of compositions at any given time. The three groups, however, do form a rough linear trend, and some subsets of domes have compositions that fall on distinctly linear (if still discontinuous) trends that cannot be reproduced by fractional crystallization, but rather are indicative of magma mixing. Our high-density sampling also reveals interesting geographical patterns: for example, felsic magmas erupt throughout the entire Mono Craters chain, erupting at a wide range of temperatures, ranging from 650-995°C, but

  15. Shallow lateral magma migration or not during the Bárðarbunga 2014 activity and preceding the Flæðahraun eruption: the geochemical perspective.

    NASA Astrophysics Data System (ADS)

    Sigmarsson, Olgeir

    2015-04-01

    Basaltic fissure eruptions several tens of km away from central volcanoes in Iceland are interpreted to reflect either lateral magma migration from a shallow magma chamber beneath the central volcano, or vertical dyke propagation from deep magma reservoir underlying large part of the fissure swarm. During the Krafla Fires (1975-1984) basalts emitted within the caldera of the central volcano and far away out on the fissure swarm have different composition. During the subglacial eruption at Gjálp (1996), halfway between Grímsvötn and Bárdarbunga, the erupted magma had identical isotope ratios as that of the former but different from that of the latter, despite earthquake originating at Bárdarbunga and propagation towards the eruption site at Gjálp. These geochemical fingerprints have been taken to indicate that lateral magma migration over tens of km was an unlikely process. The spectacular lateral migration of seismicity from 16 August to 29 August and associated ground deformation has been interpreted to reflect a lateral dyke injection over 45 km, from a shallow magma chamber beneath the Bárðarbunga central volcano to the eruption site forming the new Flæðahraun (Sigmundsson et al., 2015). The isotope ratio of Sr in Flæðahraun is identical to that of Holocene lavas and tephra produced at the Bárdarbunga Volcanic System confirming uniform Sr isotope ratios at a given volcanic system in Iceland. Thermodynamic equlibrium between mineral and magmatic liquid indicate that the first Flæðahraun olivine tholeiite originated from more than 10 km depth at a temperature of approximately 1180 °C. Basalt this hot is not likely to have been stored in a superficial magma chamber before migrating laterally at shallow depth over 40 km beneath a glacier covered surface. Basalts crystallizing at variable depth should have different trace element composition caused by evolving crystallizing mineral assemblage, where plagioclase proportions should increase with

  16. Magma Differentiation in the Plumbing System of an Alkaline Ocean Island Volcano (Fuerteventura, Canary Island).

    NASA Astrophysics Data System (ADS)

    Tornare, E.; Bussy, F.; Pilet, S.

    2014-12-01

    Magma differentiation and mixing are generally regarded as taking place in magma chambers, sills or reservoirs, while magma stagnates before continuing to ascent or erupt. Here we consider differentiation to occur during magma rise in vertical dykes, as documented in the PX1 pluton, Fuerteventura, which is part of the root-zone of an eroded ocean island volcano. PX1 is a vertically layered cumulative body composed of meter to decameter-wide bands of clinopyroxenites and gabbros, surrounded by a very high-grade contact aureole (ca. 1000°C, Hobson et al., 1998). Many clinopyroxenites are characterized by a coarse-grained texture and complexly zoned clinopyroxene crystals. Resorption features and reverse zoning observed in rims are evidence for successive pulses. Percolation of high temperature basaltic melts through the accumulating crystal-rich mush would generate the complexly zoned clinopyroxenes and lead to crystal coarsening. We interpret these coarse-grained clinopyroxenites as crystal-rich magma channels, through which sustained magma fluxes travelled to the surface over a long period of time, thus generating the contact aureole. On the other hand, gabbro bands are interpreted as sluggish magma pulses emplaced in a cooler environment during the waning stages of magmatic activity. We thus propose a model of magma differentiation by dynamic fractionation in dykes throughout magma ascent in the plumbing system of basaltic volcanoes. This model assumes fractional crystallization of continuously rising magmas in vertical channels all along their way to the surface through phenocryst accumulation and crystal-melt interaction processes.

  17. Arrayed lipid bilayer chambers allow single-molecule analysis of membrane transporter activity.

    PubMed

    Watanabe, Rikiya; Soga, Naoki; Fujita, Daishi; Tabata, Kazuhito V; Yamauchi, Lisa; Hyeon Kim, Soo; Asanuma, Daisuke; Kamiya, Mako; Urano, Yasuteru; Suga, Hiroaki; Noji, Hiroyuki

    2014-07-24

    Nano- to micron-size reaction chamber arrays (femtolitre chamber arrays) have facilitated the development of sensitive and quantitative biological assays, such as single-molecule enzymatic assays, digital PCR and digital ELISA. However, the versatility of femtolitre chamber arrays is limited to reactions that occur in aqueous solutions. Here we report an arrayed lipid bilayer chamber system (ALBiC) that contains sub-million femtolitre chambers, each sealed with a stable 4-μm-diameter lipid bilayer membrane. When reconstituted with a limiting amount of the membrane transporter proteins α-hemolysin or F0F1-ATP synthase, the chambers within the ALBiC exhibit stochastic and quantized transporting activities. This demonstrates that the single-molecule analysis of passive and active membrane transport is achievable with the ALBiC system. This new platform broadens the versatility of femtolitre chamber arrays and paves the way for novel applications aimed at furthering our mechanistic understanding of membrane proteins' function.

  18. Arrayed lipid bilayer chambers allow single-molecule analysis of membrane transporter activity

    PubMed Central

    Watanabe, Rikiya; Soga, Naoki; Fujita, Daishi; Tabata, Kazuhito V.; Yamauchi, Lisa; Hyeon Kim, Soo; Asanuma, Daisuke; Kamiya, Mako; Urano, Yasuteru; Suga, Hiroaki; Noji, Hiroyuki

    2014-01-01

    Nano- to micron-size reaction chamber arrays (femtolitre chamber arrays) have facilitated the development of sensitive and quantitative biological assays, such as single-molecule enzymatic assays, digital PCR and digital ELISA. However, the versatility of femtolitre chamber arrays is limited to reactions that occur in aqueous solutions. Here we report an arrayed lipid bilayer chamber system (ALBiC) that contains sub-million femtolitre chambers, each sealed with a stable 4-μm-diameter lipid bilayer membrane. When reconstituted with a limiting amount of the membrane transporter proteins α-hemolysin or F0F1-ATP synthase, the chambers within the ALBiC exhibit stochastic and quantized transporting activities. This demonstrates that the single-molecule analysis of passive and active membrane transport is achievable with the ALBiC system. This new platform broadens the versatility of femtolitre chamber arrays and paves the way for novel applications aimed at furthering our mechanistic understanding of membrane proteins’ function. PMID:25058452

  19. Higher sympathetic nerve activity during ventricular (VVI) than during dual-chamber (DDD) pacing

    NASA Technical Reports Server (NTRS)

    Taylor, J. A.; Morillo, C. A.; Eckberg, D. L.; Ellenbogen, K. A.

    1996-01-01

    OBJECTIVES: We determined the short-term effects of single-chamber ventricular pacing and dual-chamber atrioventricular (AV) pacing on directly measured sympathetic nerve activity. BACKGROUND: Dual-chamber AV cardiac pacing results in greater cardiac output and lower systemic vascular resistance than does single-chamber ventricular pacing. However, it is unclear whether these hemodynamic advantages result in less sympathetic nervous system outflow. METHODS: In 13 patients with a dual-chamber pacemaker, we recorded the electrocardiogram, noninvasive arterial pressure (Finapres), respiration and muscle sympathetic nerve activity (microneurography) during 3 min of underlying basal heart rate and 3 min of ventricular and AV pacing at rates of 60 and 100 beats/min. RESULTS: Arterial pressure was lowest and muscle sympathetic nerve activity was highest at the underlying basal heart rate. Arterial pressure increased with cardiac pacing and was greater with AV than with ventricular pacing (change in mean blood pressure +/- SE: 10 +/- 3 vs. 2 +/- 2 mm Hg at 60 beats/min; 21 +/- 5 vs. 14 +/- 2 mm Hg at 100 beats/min; p < 0.05). Sympathetic nerve activity decreased with cardiac pacing and the decline was greater with AV than with ventricular pacing (60 beats/min -40 +/- 11% vs. -17 +/- 7%; 100 beats/min -60 +/- 9% vs. -48 +/- 10%; p < 0.05). Although most patients showed a strong inverse relation between arterial pressure and muscle sympathetic nerve activity, three patients with severe left ventricular dysfunction (ejection fraction < or = 30%) showed no relation between arterial pressure and sympathetic activity. CONCLUSIONS: Short-term AV pacing results in lower sympathetic nerve activity and higher arterial pressure than does ventricular pacing, indicating that cardiac pacing mode may influence sympathetic outflow simply through arterial baroreflex mechanisms. We speculate that the greater incidence of adverse outcomes in patients treated with single-chamber ventricular

  20. Storage and interaction of compositionally heterogeneous magmas from the 1986 eruption of Augustine Volcano, Alaska

    USGS Publications Warehouse

    Roman, D.C.; Cashman, K.V.; Gardner, C.A.; Wallace, P.J.; Donovan, J.J.

    2006-01-01

    Compositional heterogeneity (56-64 wt% SiO2 whole-rock) in samples of tephra and lava from the 1986 eruption of Augustine Volcano, Alaska, raises questions about the physical nature of magma storage and interaction beneath this young and frequently active volcano. To determine conditions of magma storage and evolutionary histories of compositionally distinct magmas, we investigate physical and chemical characteristics of andesitic and dacitic magmas feeding the 1986 eruption. We calculate equilibrium temperatures and oxygen fugacities from Fe-Ti oxide compositions and find a continuous range in temperature from 877 to 947??C and high oxygen fugacities (??NNO=1-2) for all magmas. Melt inclusions in pyroxene phenocrysts analyzed by Fourier-transform infrared spectroscopy and electron probe microanalysis are dacitic to rhyolitic and have water contents ranging from <1 to ???7 wt%. Matrix glass compositions are rhyolitic and remarkably similar (???75.9-76.6 wt% SiO2) in all samples. All samples have ???25% phenocrysts, but lower-silica samples have much higher microlite contents than higher-silica samples. Continuous ranges in temperature and whole-rock composition, as well as linear trends in Harker diagrams and disequilibrium mineral textures, indicate that the 1986 magmas are the product of mixing between dacitic magma and a hotter, more mafic magma. The dacitic endmember is probably residual magma from the previous (1976) eruption of Augustine, and we interpret the mafic endmember to have been intruded from depth. Mixing appears to have continued as magmas ascended towards the vent. We suggest that the physical structure of the magma storage system beneath Augustine contributed to the sustained compositional heterogeneity of this eruption, which is best explained by magma storage and interaction in a vertically extensive system of interconnected dikes rather than a single coherent magma chamber and/or conduit. The typically short repose period (???10 years) between

  1. Magmatic (silicates/saline/sulfur-rich/CO2) immiscibility and zirconium and rare-earth element enrichment from alkaline magma chamber margins : Evidence from Ponza Island, Pontine Archipelago, Italy

    USGS Publications Warehouse

    Belkin, H.E.; de Vivo, B.; Lima, A.; Torok, K.

    1996-01-01

    Fluid inclusions were measured from a feldspathoid-bearing syenite xenolith entrained in trachyte from Ponza, one of the islands of the Pontine Archipelago, located in the Gulf of Gaeta, Italy. The feldspathoid-bearing syenite consists mainly of potassium feldspar, clinopyroxene, amphibole, biotite, titanite, manganoan magnetite, apatite with minor nosean, Na-rich feldspar, pyrrhotite, and rare cheralite. Baddeleyite and zirkelite occur associated with manganoan magnetite. Detailed electron-microprobe analysis reveals enrichments in REE, Y, Nb, U, Th as well as Cl and F in appropriate phases. Fluid inclusions observed in potassium feldspar are either silicate-melt or aqueous inclusions. The aqueous inclusions can be further classified as. (1) one-phase vapor, (2) two-phase (V + L) inclusions, vapor-rich inclusions with a small amount of CO2 in most cases; homogenization of the inclusions always occurred in the vapor phase between 359 and 424??C, salinities vary from 2.9 to 8.5 wt. % NaCl equivalent; and. (3) three-phase and multiphase inclusions (hypersaline/sulfur-rich aqueous inclusions sometimes with up to 8 or more solid phases). Daughter minerals dissolve on heating before vapor/liquid homogenization. Standardless quantitative scanning electron microscope X-ray fluorescence analysis has tentatively identified the following chloride and sulfate daughter crystals; halite, sylvite, glauberite. arcanite, anhydrite, and thenardite. Melting of the daughter crystals occurs between 459 and 536??C (54 to 65 wt. % NaCI equivalent) whereas total homogenization is between 640 and 755??C. The occurrence of silicate-melt inclusions and high-temperature, solute-rich aqueous inclusions suggests that the druse or miarolitic texture of the xenolith is late-stage magmatic. The xenolith from Ponza represents a portion of the peripheral magma chamber wall that has recorded the magmatic/hydrothermal transition and the passage of high solute fluids enriched in chlorides, sulfur, and

  2. Mesozoic igneous activity in the southern Cordillera of North America: Implications for tectonics and magma genesis

    SciTech Connect

    Asmerom, Y.

    1988-01-01

    A representative section in Santa Rita Mountains is dated using the zircon U-Th-Pb isotopic method. The oldest unit, the lower member of the Mt. Wrightson Formation, is concordantly dated at 210 {plus minus} 3 Ma. Initial basaltic andesite to andesite volcanism was followed by deposition of red beds and associated volcanic rocks that are dated at 200 Ma. Felsic volcanism and eolian sand deposition may have spanned from 190 to 170 Ma. The Piper Gulch Granodiorite, representing the earliest Mesozoic intrusive equivalent, gives concordant dates of 188 {plus minus}2 Ma. A second cycle of andesite and rhyolitic volcanism and sedimentation is dated at 151 {plus minus} 5 Ma using the whole-rock Rb-Sr isotopic method. The Hovatter Volcanics in the Little Harquahala Mountains, southwestern Arizona is dated at 165 Ma. Whole-rock Rb-Sr isotopic method on the same rocks gives a coherent reset isochron of 70 {plus minus} 3 Ma. A new stratigraphic correlation is proposed based on the dating data. This part of the Cordillera was an uplifted arc terrane during the Early Mesozoic and may have provided volcanic detritus to the Late Triassic Chinle Formation in the Colorado Plateau. The second part deals with magma evolution and crust modification during arc magmatism. Rocks in southeastern Arizona have {sub Nd} values of {minus}3.4 to {minus}6.4, while rocks to the west have {sub Nd} values ranging from {minus}8.5 to {minus}9.2. Combined REE and isotopic data indicate that assimilation of lower crust by mantle melts followed by fractional crystallization took place.

  3. Grain-scale processes in actively deforming magma mushes: New insights from electron backscatter diffraction (EBSD) analysis of biotite schlieren in the Jizera granite, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Žák, Jiří; Verner, Kryštof; Týcová, Patricie

    2008-12-01

    In the porphyritic Jizera granite, Bohemian Massif, three distinct types of lattice-preferred orientations of biotite grains were revealed in schlieren-delineated magmatic structures using the electron backscatter diffraction (EBSD) method. (1) Biotite basal planes (001) reorient from schlieren-subparallel near the schlieren base to schlieren-perpendicular in the upper part of the schlieren. Both orientations share subhorizontal ˜N-S to ˜NNE-SSW-trending a axes. (2) In some domains, the a axes are steep and at a high angle to the schlieren plane while the c axes plunge shallowly and rotate around an ill-defined a axis. (3) In other domains, the EBSD coincides with background magnetic fabric of the host granite revealed using the anisotropy of magnetic susceptibility (AMS) method: that is, the a axes plunge shallowly to the SE or NW while the c axes are subhorizontal and cluster around the ˜NE-SW trend. These multiple biotite orientations in the schlieren are interpreted to reflect (1) velocity-gradient in laminar magma flow along channel-like conduits, localized within the high-strength host phenocryst framework, (2) grain-scale gravity-driven constrictional deformation of the magma mush, and (3) overprinting background (tectonic?) deformation transmitted across large parts of the magma chamber prior to its final crystallization. The grain-scale mechanisms of biotite fabric acquisition in the schlieren presumably involved rotation of biotite crystals during flow, with the biotite alignment reflecting the flow geometry and kinematics, replaced after flow cessation by melt-aided grain-boundary sliding of those biotite crystals still enclosed in melt pockets within otherwise static, highly crystallized magma mush. The latter process was sufficient to reorient biotite grains but not to cause destruction of the schlieren. Using the Jizera granite as a case example, we argue that the lattice-preferred orientation of mineral grains in mafic schlieren is highly

  4. Evaluating the Controls on Magma Ascent Rates Through Numerical Modelling

    NASA Astrophysics Data System (ADS)

    Thomas, M. E.; Neuberg, J. W.

    2015-12-01

    The estimation of the magma ascent rate is a key factor in predicting styles of volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. The ability to link potential changes in such parameters to monitoring data is an essential step to be able to use these data as a predictive tool. We present the results of a suite of conduit flow models that assess the influence of individual model parameters such as the magmatic water content, temperature or bulk magma composition on the magma flow in the conduit during an extrusive dome eruption. By systematically varying these parameters we assess their relative importance to changes in ascent rate. The results indicate that potential changes to conduit geometry and excess pressure in the magma chamber are amongst the dominant controlling variables that effect ascent rate, but the single most important parameter is the volatile content (assumed in this case as only water). Modelling this parameter across a range of reported values causes changes in the calculated ascent velocities of up to 800%, triggering fluctuations in ascent rates that span the potential threshold between effusive and explosive eruptions.

  5. History of the bubble chamber and related active- and internal-target nuclear tracking detectors

    NASA Astrophysics Data System (ADS)

    Becchetti, F. D.

    2015-06-01

    Donald Glaser, 1960 Nobel laureate in Physics, recently passed away (2013), as have many of his colleagues who were involved with the early development of bubble chambers at the University of Michigan. In this paper I will review those early years and the subsequent wide-spread application of active-target (AT) bubble chambers that dominated high-energy physics (HEP) research for over thirty years. Some of the related, but more modern nuclear tracking detectors being used in HEP, neutrino astrophysics and dark-matter searches also will be discussed.

  6. Gridded ionization chamber for detection of x-ray wave activity in tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Goldman, M. A.; Hill, K. W.; Moshey, E. A.; Sauthoff, N. R.; von Goeler, S.

    1985-03-01

    In order to carry out x-ray observations of magnetohydrodynamic wave activity of the plasma during DD and DT (deuterium-beam-heated deuterium and tritium plasmas, respectively) operation of the Tokamak Fusion Test Reactor (TFTR), we will need detectors not susceptible to nuclear radiation damage. We have investigated the use of gridded ionization chambers as fast nondamageable x-ray detectors. A prototype chamber is described which was tested on the PDX tokamak. These tests and laboratory tests with a pulsed x-ray source suggest that the detector has sufficient sensitivity and speed for the required measurements.

  7. Gridded ionization chamber for detecion of x-ray wave activity in tokamak plasmas

    SciTech Connect

    Goldman, M.A.; Hill, K.W.; Moshey, E.A.; Sauthoff, N.R.; von Goeler, S.

    1982-11-01

    In order to carry out X-ray observations of magnetohydrodynamic wave activity of the plasma during DD and DT (deuterium-beam-heated deuterium and tritium plasmas, respectively) operation of the Tokamak Fusion Test Reactor (TFTR), we will need detectors not susceptible to nuclear radiation damage. We have investigated the use of gridded ionization chambers as fast nondamageable X-ray detectors. A prototype chamber is described, which was tested on the PDX tokamak. These tests and laboratory tests with a pulsed X-ray source suggest that the detector has sufficient sensitivity and speed for the required measurements.

  8. Rift initiation with volatiles and magma

    NASA Astrophysics Data System (ADS)

    Ebinger, Cynthia; Muirhead, James; Roecker, Steve; Tiberi, Christel; Muzuka, Alfred; Ferdinand, Rrichard; Mulibo, Gabrile; Kianji, Gladys

    2015-04-01

    Rift initiation in cratonic lithosphere remains an outstanding problem in continental tectonics, but strain and magmatism patterns in youthful sectors of the East African rift provide new insights. Few teleseisms occur in the Eastern rift arm of the East African rift system, except the southernmost sector in northern Tanzania where extension occurs in Archaean lithosphere. The change in seismic energy release occurs over a narrow along-axis zone, and between sectors with and without volcanoes in the central rift valley. Are these differences in strain behavior indicative of along-strike variations in a) rheology; b) strain transfer from border faults to magma intrusion zones; c) dike vs fault slip; and/or d) shallow vs deep magma chambers? We present time-space relations of seismicity recorded on a 38-station array spanning the Kenya-Tanzania border, focal mechanisms for the largest events during those time periods, and compare these to longer-term strain patterns. Lower crustal seismicity occurs along the rift length, including sectors on and off craton, and those with and without central rift valley volcanoes, and we see no clear along-strike variation in seismogenic layer thickness. One explanation for widespread lower crustal seismicity is high gas pressures and volatile migration from active metasomatism of upper mantle and magma degassing, consistent with very high volatile flux along fault zones, and widespread metasomatism of xenoliths. Volatile release and migration may be critical to strength reduction of initially cold, strong cratonic lithosphere. Seismicity patterns indicate strain (and fluid?) transfer from the Manyara border fault to Gelai shield volcano (faulting, diking) via Oldoinyo Lengai volcano. Our focal mechanisms and Global CMTs from an intense fault-dike episode (2007) show a local, temporally stable, rotation from ~E-W extension to NE-SE extension in this linkage zone, consistent with longer term patterns recorded in vent and eruptive

  9. Long-distance lateral magma transport from intra-oceanic island arc volcanoes

    NASA Astrophysics Data System (ADS)

    Ishizuka, O.; Geshi, N.; Kawanabe, Y.; Ogitsu, I.; Tuzino, T.; Nakano, S.; Arai, K.; Sakamoto, I.; Taylor, R. N.; Sano, K.; Yamamoto, T.

    2011-12-01

    Long-distance lateral magma transport in oceanic island arc volcanoes is emerging as a common phenomenon where the regional stress regime is favorable. It should also be recognized as an important factor in the construction and growth of island arcs. In this contribution, we report on recent investigations into the magma plumbing of Izu-Oshima volcano: an active basaltic volcano with an extensive fissure system. Geophysical observations in the Izu-Bonin intra-oceanic island arc indicate that magma is transported long distances laterally from the main basaltic composite volcano. When Miyakejima erupted in 2000, seismic activity migrated about 30km northwestward from the volcanic centre (Geshi et al., 2002). This event is interpreted to reflect northwestward dike injection and propagation from Miyakejima, transporting magma at a depth range between 12 and 20km (Kodaira et al., 2002). We demonstrated that long-distance lateral magma transport also occurred at the Nishiyama volcano on Hachijojima Island using petrological, geochemical and structural studies of satellite vents (Ishizuka et al., 2008). Nishiyama provided evidence for two types of magma transport. In the first type, primitive magma moved laterally NNW for at least 20km in the middle to lower crust (10-20km deep). The other type is characterized by magmas that have experienced differentiation in a shallow magma chamber beneath Nishiyama and have been transported short distances (<5km). The long-distance magma transport seems to be controlled by a regional extensional stress regime, while short distance transport may be controlled by local stress regime affected by the load generated by the main volcanic edifice. Izu-Oshima volcano comprises numerous, subparallel NW-SE trending submarine ridges extending up to 22 km to the NW and SE from the summit of Izu-Oshima. A recent diving survey has revealed that: 1) NW-SE trending ridges are fissures which erupted basaltic spatter and lava flows. 2) Basaltic

  10. The 1998-2002 activity of Piton de la Fournaise, Réunion island: lessons in magma supply and transfers

    NASA Astrophysics Data System (ADS)

    Semet, M. P.; Joron, J.-L.; Staudacher, T.

    2003-04-01

    In March 1998, Piton de la Fournaise, one of the most frequently active aerial volcanoes on earth, awoke after an unusually long sleep of almost 6 years. This eruption, which was also preceded and accompanied by uncommon patterns of seismicity and deformation (Staudacher et al., 1998), lasted about six months and was followed to the end of 2002 by 9 eruptive episodes of about one week to a little more than a month duration. In these episodes, seismicity and deformations were those more customarily observed. The total amount of erupted magma over this 5 year period amounts to ca. 120 Mm3, which yields an average production rate close to 0.3 m3/s. Suites of lava samples were regularly obtained for each of these episodes, often as water-quenched molten lava, and examined in the laboratory for their petrography and geochemistry. Two subtly differing magmas were erupted in the 1998 episode from two locations. The voluminous lavas vented North of the central cone (Kapor and related vents) were of the ordinary Steady State Basalts (SSB) type modeled by Albarède et al. (1997) yet showed minor but significant evolution through the six months of eruption. Those vented to the South of the cone (Hudson crater) were apparently fed directly and rapidly from depths ca. 15 km, the crust-upper-mantle boundary under Réunion. Hudson samples are of a type observed mostly in peripheral vents but rarely in central eruptions. They are characterized by major and trace element signatures indicating enhanced clinopyroxene fractionation (a high pressure fractionating phase) relative to SSB. In the subsequent 9 eruptions, lavas were again of the SSB kindred, sometimes rich (50 modal %) in cumulative xenocrystic olivine (e.g. June 2001 and January, 2002). Significant chemical differences with the Kapor trend indicate that they were not fed from the same reservoir nor were they akin to Hudson samples. Glass analyses in the quenched post-1998 samples have an almost invariable composition

  11. Energy extraction from crustal magma bodies

    SciTech Connect

    Dunn, J.C.

    1982-01-01

    An open heat exchanger system for extracting thermal energy directly from shallow crustal magma bodies is described. The concept relies on natural properties of magma to create a permeable, solidified region surrounding a borehole drilled into the magma chamber. The region is fractured, possessing large surface area, and is sealed from the overburden. Energy is extracted by circulating a fluid through the system. Thermal stress analysis shows that such a fractured region can be developed at depths up to 10 km. An open heat exchanger experiment conducted in the partial melt zone of Kilauea Iki lava lake demonstrated the validity of this concept. Effective heat transfer surface area an order of magnitude greater than the borehole area was established during a two-day test period. The open heat exchanger concept greatly extends the number of magma systems that can be economically developed to produce energy.

  12. Thermal stress fracturing of magma simulant materials

    SciTech Connect

    Wemple, R.P.; Longcope, D.B.

    1986-10-01

    Direct contact heat exchanger concepts for the extraction of energy from magma chambers are being studied as part of the DOE-funded Magma Energy Research Program at Sandia National Laboratories. These concepts require the solidification of molten material by a coolant circulated through a borehole drilled into the magma and subsequent fracture of the solid either as a natural consequence of thermal stress or by deliberate design (intentional flaws, high pressure, etc.). This report summarizes the results of several thermal stress fracturing experiments performed in the laboratory and compares the results with an analysis developed for use as a predictive tool. Information gained from this test series has been the basis for additional work now under way to simulate magma melt solidification processes.

  13. Volcanology: Look up for magma insights

    USGS Publications Warehouse

    Segall, Paul; Anderson, Kyle

    2014-01-01

    Volcanic plumes can be hazardous to aircraft. A correlation between plume height and ground deformation during an eruption of Grímsvötn Volcano, Iceland, allows us to peer into the properties of the magma chamber and may improve eruption forecasts.

  14. Neutron-induced nucleation inside bubble chambers using Freon 115 as the active medium

    NASA Astrophysics Data System (ADS)

    Ghilea, M. C.; Meyerhofer, D. D.; Sangster, T. C.

    2011-08-01

    Neutron imaging is used in inertial confinement fusion (ICF) experiments to measure the core symmetry of imploded targets. Liquid bubble chambers have the potential to obtain higher resolution images of the targets for a shorter source-target distance than typical scintillator arrays. Due to the fact that nucleation models used in gel detectors research cannot always give correct estimates for the neutron-induced bubble density inside a liquid bubble chamber, an improved theoretical model to describe the mechanism of bubble formation for Freon 115 as the active medium has been developed. It shows that the size of the critical radius for the nucleation process determines the mechanism of bubble formation and the sensitivity of the active medium to the 14.1-MeV incident neutrons resulting from ICF implosions. The bubble-growth mechanism is driven by the excitation of the medium electronic levels and not by electrons ejected from the medium's atoms as happens for the bubble chambers used to detect charged particles. The model accurately predicts the neutron-induced bubble density measured on OMEGA with both liquid bubble chambers and gel detectors.

  15. Recent volcanic history of Irazu volcano, Costa Rica: alternation and mixing of two magma batches, and pervasive mixing

    USGS Publications Warehouse

    Alvarado, Guillermo E.; Carr, Michael J.; Turrin, Brent D.; Swisher, Carl C.; Schmincke, Hans-Ulrich; Hudnut, Kenneth W.

    2006-01-01

    40Ar/39Ar dates, field observations, and geochemical data are reported for Irazú volcano, Costa Rica. Volcanism dates back to at least 854 ka, but has been episodic with lava shield construction peaks at ca. 570 ka and 136–0 ka. The recent volcanic record on Irazú volcano comprises lava flows and a variety of Strombolian and phreatomagmatic deposits, with a long-term trend toward more hydrovolcanic deposits. Banded scorias and hybridized rocks reflect ubiquitous magma mixing and commingling. Two distinct magma batches have been identified. One magma type or batch, Haya, includes basalt with higher high field strength (HFS) and rare-earth element contents, suggesting a lower degree melt of a subduction modified mantle source. The second batch, Sapper, has greater enrichment of large ion lithophile elements (LILE) relative to HFS elements and rare-earth elements, suggesting a higher subduction signature. The recent volcanic history at Irazú records two and one half sequences of the following pattern: eruptions of the Haya batch; eruptions of the Sapper batch; and finally, an unusually clear unconformity, indicating a pause in eruptions. In the last two sequences, strongly hybridized magma erupted after the eruption of the Haya batch. The continuing presence of two distinct magma batches requires two active magma chambers. The common occurrence of hybrids is evidence for a small, nearer to the surface chamber for mixing the two batches. Estimated pre-eruptive temperatures based on two-pyroxene geothermometry range from ∼1000–1176 °C in basalts to 922 °C in hornblende andesites. Crystallization occurred mainly between 4.6 and 3 kb as measured by different geobarometers. Hybridized rocks show intermediate pressures and temperatures. High silica magma occurs in very small volumes as banded scorias but not as lava flows. Although eruptions at Irazú are not often very explosive, the pervasiveness of magma mixing presents the danger of larger, more explosive

  16. Effect of Grain Size on Bacterial Penetration, Reproduction, and Metabolic Activity in Porous Glass Bead Chambers

    PubMed Central

    Sharma, Pramod K.; McInerney, Michael J.

    1994-01-01

    We determined the effects of grain size and nutritional conditions on the penetration rate and metabolic activity of Escherichia coli strains in anaerobic, nutrient-saturated chambers packed with different sizes of glass beads (diameters, 116 to 767 μm) under static conditions. The chambers had nearly equal porosities (38%) but different calculated pore sizes (range, 10 to 65 μm). Motile strains always penetrated faster than nonmotile strains, and nutrient conditions that resulted in faster growth rates (fermentative conditions versus nitrate-respiring conditions) resulted in faster penetration rates for both motile and nonmotile strains for all of the bead sizes tested. The penetration rate of nonmotile strains increased linearly when bead size was increased, while the penetration rate of motile strains became independent of the bead size when beads having diameters of 398 μm or greater were used. The rate of H2 production and the final amount of H2 produced decreased when bead size was decreased. However, the final protein concentrations were similar in chambers packed with 116-, 192-, and 281-μm beads and were only slightly higher in chambers packed with 398- and 767-μm beads. Our data indicated that conditions that favored faster growth rates also resulted in faster penetration times and that the lower penetration rates observed in chambers packed with small beads were due to restriction of bacterial activity in the small pores. The large increases in the final amount of hydrogen produced without corresponding increases in the final amount of protein made indicated that metabolism became uncoupled from cell mass biosynthesis as bead size increased, suggesting that pore size influenced the efficiency of substrate utilization. PMID:16349250

  17. Numerical Simulations of the Incremental Intrusion of Granitic Magma into Continental Crust

    NASA Astrophysics Data System (ADS)

    Cao, W.; Kaus, B. J.; Paterson, S. R.

    2012-12-01

    We have employed the visco-elasto-plastic Finite-Element & Marker-in-cell code, MILAMIN_VEP, to carry out a 2D modeling study of the incremental intrusion of granitic magma into continental crust. Algorithms of multiple pulses of magma and pseudo-diking are implemented into the code. New magma of an initial circular shape is regularly replenished at "magma source" regions at sub-crustal depths. Pseudo-dikes of rectangular shapes are added at location where the maximum differential stress along the melt-solid interface is greater than an assigned tensile strength of the surrounding solid host rock. Preliminary results show that when diking and multiple pulses of magma are included, later pulses of magma rise higher and faster and even reach the Earth's surface in some cases by taking advantage of the pre-heated low-viscosity pathways created by earlier dikes and pulses of magma. Host rocks display bedding rotation, and downward flow at two sides of a growing magma chamber but show discordantly truncation when magma ascend through the weak channels made by dikes. The effect of the thermal structure of the crust was tested as well. In a cold crust, "diking" is critical in breaking the high-viscosity crust, guiding the direction of magma rising, and facilitating later magma pulses to form chambers. In a warmer crust, magma rises in the form of diapirs, after which dikes take over in transporting later pulses of magma to the surface. The simulations also suggest that a magma chamber incrementally constructed by multiple magma bathes is a very dynamic environment featuring intra-chamber convection and recycling previous batches of magma. In simulations without diking and multiple pulses, magma is unable to reach the shallow crust. Instead, it is stuck in the middle crust, as the viscosity of the upper crust is too large to permit rapid motion, and at the same time magma-induced stresses are insufficient to deform the upper crust in a plastic manner. Intra

  18. Magma mixing in a zoned alkalic intrusion

    SciTech Connect

    Price, J.G.; Henry, C.D.; Barker, D.S.; Rubin, J.N.

    1985-01-01

    The Marble Canyon stock is unique among the alkalic intrusions of the Trans-Pecos magmatic province in being zoned from a critically silica-undersaturated rim of alkali gabbro (AG) to a silica-oversaturated core of quartz syenite (QS). Hybrid rocks of intermediate chemical and mineralogical compositions occur between the rim and core. Nepheline-syenite dikes occur only within the AG. Silica-rich dikes of quartz trachyte, pegmatite, and aplite cut the AG, QS, and hybrid rocks. Thermodynamic calculations of silica activity in the magmas illustrate the presence of two trends with decreasing temperature: a silica-poor trend from AG to nepheline syenite and a silica-rich trend from hybrid rocks to QS. Least-square modeling of rock and mineral compositions suggests 1) the nepheline syenites were derived by crystal-liquid fractionation from nearly solidified AG at the rim of the stock, 2) AG magma farther from the rim mixed with a small proportion of granitic magma, and 3) the mixture then differentiated to produce the hybrid rocks and QS. Zirconium dioxide inclusions in plagioclase crystals of the hybrid rocks and QS indicate that the AG magma contained some crystals before it mixed with the granitic magma. Two origins for the granitic magma are possible: 1) a late-stage differentiate of a mantle-derived hypersthene-normative magma and 2) melting of crustal material by the AG magma. Recognition of magma mixing might not have been possible if the AG had been hypersthene-normative.

  19. Evaluation of radioisotope tracer and activation analysis techniques for contamination monitoring in space environment simulation chambers

    NASA Technical Reports Server (NTRS)

    Smathers, J. B.; Kuykendall, W. E., Jr.; Wright, R. E., Jr.; Marshall, J. R.

    1973-01-01

    Radioisotope measurement techniques and neutron activation analysis are evaluated for use in identifying and locating contamination sources in space environment simulation chambers. The alpha range method allows the determination of total contaminant concentration in vapor state and condensate state. A Cf-252 neutron activation analysis system for detecting oils and greases tagged with stable elements is described. While neutron activation analysis of tagged contaminants offers specificity, an on-site system is extremely costly to implement and provides only marginal detection sensitivity under even the most favorable conditions.

  20. Calibration and efficiency curve of SANAEM ionization chamber for activity measurements.

    PubMed

    Yeltepe, Emin; Kossert, Karsten; Dirican, Abdullah; Nähle, Ole; Niedergesäß, Christiane; Kemal Şahin, Namik

    2016-03-01

    A commercially available Fidelis ionization chamber was calibrated and assessed in PTB with activity standard solutions. The long-term stability and linearity of the system was checked. Energy-dependent efficiency curves for photons and beta particles were determined, using an iterative method in Excel™, to enable calibration factors to be calculated for radionuclides which were not used in the calibration. Relative deviations between experimental and calculated radionuclide efficiencies are of the order of 1% for most photon emitters and below 5% for pure beta emitters. The system will enable TAEK-SANAEM to provide traceable activity measurements.

  1. Magma Energy Extraction

    SciTech Connect

    Dunn, J.C.; Ortega, A.; Hickox, C.E.; Chu, T.Y.; Wemple, R.P.; Boehm, R.F.

    1987-01-20

    The rate at which energy can be extracted from crustal magma bodies has an important influence on the economic viability of the magma energy concept. Open heat exchanger systems where fluid is circulated through solidified magma offer the promise of high energy extraction rates. This concept was successfully demonstrated during experiments in the molten zone of Kilauea Iki lava lake. Ongoing research is directed at developing a fundamental understanding of the establishment and long term operation of open systems in a crustal magma body. These studies show that magma solidifying around a cooled borehole will be extensively fractured and form a permeable medium through which fluid can be circulated. Numerical modeling of the complete magma energy extraction process predicts that high quality thermal energy can be delivered to the wellhead at rates that will produce from 25 to 30 MW electric. 10 figs., 10 refs.

  2. Volatiles in pantellerite magmas: A case study of the Green Tuff Plinian eruption (Island of Pantelleria, Italy)

    NASA Astrophysics Data System (ADS)

    Lanzo, Giovanni; Landi, Patrizia; Rotolo, Silvio G.

    2013-07-01

    The Green Tuff (GT) Plinian eruption, the largest in magnitude at Pantelleria, erupted 3 to 7 km3 DRE of pantellerite magma and a small volume of trachyte. Fifty-nine anorthoclase-hosted melt inclusions from the two basal pumice members were analyzed by FT-IR spectroscopy in order to assess the pre-eruptive H2O content in the pantellerite melt. Microanalytical methods were used to determine major element, Cl, F and S contents. Melt inclusions and glassy groundmasses have a nearly homogeneous pantelleritic composition (peralkaline index = 1.9-2.2) and variable water contents ranging from 1.4 to as high as 4.2 wt %, i.e. much higher than the 1.4 wt % of earlier published studies. The chlorine content is constant at about 1 wt %. Combined Cl and H2O data were used to estimate a confining pressure of about 50 MPa (depth around 2-3 km) for the GT magma chamber. The chamber was characterized by a compositional zoning with a dominant pantellerite overlying a trachyte magma. Soon after the GT eruption, intra-caldera volcanism was dominated by the eruption of voluminous trachyte lava flows, while pantellerite melt production resumed after about 20 ka with numerous low-volume, mildly explosive (Strombolian) to effusive eruptions. Comparison with data from the literature reveals that, despite the different explosivity, the post-caldera Strombolian eruptions and the GT Plinian eruption were fed by pantelleritic magmas with similar water contents. Chlorine and CO2 contents suggest that the young magma reservoirs feeding the Strombolian to effusive activity were deeper (h ≥ 4.5 km) than the much larger (based on erupted volumes) magma chamber which fed the GT eruption.

  3. Pre-eruption recharge of the Bishop magma system

    USGS Publications Warehouse

    Wark, D.A.; Hildreth, W.; Spear, F.S.; Cherniak, D.J.; Watson, E.B.

    2007-01-01

    The 650 km3 rhyolitic Bishop Tuff (eastern California, USA), which is stratigraphically zoned with respect to temperatures of mineral equilibration, reflects a corresponding thermal gradient in the source magma chamber. Consistent with previous work, application of the new TitaniQ (Ti-in-quartz) thermometer to quartz phenocryst rims documents an ???100 ??C temperature increase with chamber depth at the time of eruption. Application of TitaniQ to quartz phenocryst cores, however, reveals lower temperatures and an earlier gradient that was less steep, with temperature increasing with depth by only ???30 ??C. In many late-erupted crystals, sharp boundaries that separate low-temperature cores from high-temperature rims cut internal cathodoluminescent growth zoning, indicating partial phenocryst dissolution prior to crystallization of the high-temperature rims. Rimward jumps in Ti concentration across these boundaries are too abrupt (e.g., 40 ppm across a distance of <10 ??m) to have survived magmatic temperatures for more than ???100 yr. We interpret these observations to indicate heating-induced partial dissolution of quartz, followed by growth of high-temperature rims (made possible by lowering of water activity due to addition of CO2) within 100 yr of the climactic 760 ka eruption. Hot mafic melts injected into deeper parts of the magma system were the likely source of heat and CO2, raising the possibility that eruption and caldera collapse owe their origin to a recharge event. ?? 2007 Geological Society of America.

  4. Fundamental changes in the activity of the natrocarbonatite volcano Oldoinyo Lengai, Tanzania. I. New magma composition during the 2007-2008 explosive eruptions

    NASA Astrophysics Data System (ADS)

    Keller, Jörg; Klaudius, Jurgis; Kervyn, Matthieu; Ernst, Gerald G. J.; Mattsson, Hannes B.

    2010-10-01

    With a paroxysmal ash eruption on 4 September 2007 and the highly explosive activity continuing in 2008, Oldoinyo Lengai (OL) has dramatically changed its behavior, crater morphology, and magma composition after 25 years of quiet extrusion of fluid natrocarbonatite lava. This explosive activity resembles the explosive phases of 1917, 1940-1941, and 1966-1967, which were characterized by mixed ashes with dominantly nephelinitic and natrocarbonatitic components. Ash and lapilli from the 2007-2008 explosive phase were collected on the slopes of OL as well as on the active cinder cone, which now occupies the entire north crater having buried completely all earlier natrocarbonatite features. The lapilli and ash samples comprise nepheline, wollastonite, combeite, Na-åkermanite, Ti-andradite, resorbed pyroxene and Fe-Ti oxides, and a Na-Ca carbonate phase with high but varying phosphorus contents which is similar, but not identical, to the common gregoryite phenocrysts in natrocarbonatite. Lapilli from the active cone best characterize the erupted material as carbonated combeite-wollastonite-melilite nephelinite. The juvenile components represent a fundamentally new magma composition for OL, containing 25-30 wt.% SiO2, with 7-11 wt.% CO2, high alkalies (Na2O 15-19%, K2O 4-5%), and trace-element signatures reminiscent of natrocarbonatite enrichments. These data define an intermediate composition between natrocarbonatite and nephelinite, with about one third natrocarbonatite and two thirds nephelinite component. The data are consistent with a model in which the carbonated silicate magma has evolved from the common combeite-wollastonite nephelinite (CWN) of OL by enrichment of CO2 and alkalies and is close to the liquid immiscible separation of natrocarbonatite from carbonated nephelinite. Material ejected in April/May 2008 indicates reversion to a more common CWN composition.

  5. Using a combined population-based and kinetic modelling approach to assess timescales and durations of magma migration activities prior to the 1669 flank eruption of Mt. Etna

    NASA Astrophysics Data System (ADS)

    Kahl, M.; Morgan, D. J.; Viccaro, M.; Dingwell, D. B.

    2015-12-01

    The March-July eruption of Mt. Etna in 1669 is ranked as one of the most destructive and voluminous eruptions of Etna volcano in historical times. To assess threats from future eruptions, a better understanding of how and over what timescales magma moved underground prior to and during the 1669 eruption is required. We present a combined population based and kinetic modelling approach [1-2] applied to 185 olivine crystals that erupted during the 1669 eruption. By means of this approach we provide, for the first time, a dynamic picture of magma mixing and magma migration activity prior to and during the 1669 flank eruption of Etna volcano. Following the work of [3] we have studied 10 basaltic lava samples (five SET1 and five SET2 samples) that were erupted from different fissures that opened between 950 and 700 m a.s.l. Following previous work [1-2] we were able to classify different populations of olivine based on their overall core and rim compositional record and the prevalent zoning type (i.e. normal vs. reverse). The core plateau compositions of the SET1 and SET2 olivines range from Fo70 up to Fo83 with a single peak at Fo75-76. The rims differ significantly and can be distinguished into two different groups. Olivine rims from the SET1 samples are generally more evolved and range from Fo50 to Fo64 with a maximum at Fo55-57. SET2 olivine rims vary between Fo65-75 with a peak at Fo69. SET1 and SET2 olivines display normal zonation with cores at Fo75-76 and diverging rim records (Fo55-57 and Fo65-75). The diverging core and rim compositions recorded in the SET1 and SET2 olivines can be attributed to magma evolution possibly in three different magmatic environments (MEs): M1 (=Fo75-76), M2 (=Fo69) and M3 (=Fo55-57) with magma transfer and mixing amongst them. The MEs established in this study differ slightly from those identified in previous works [1-2]. We note the relative lack of olivines with Fo-rich core and rim compositions indicating a major mafic magma

  6. IN VITRO STUDY OF THE PULP CHAMBER TEMPERATURE RISE DURING LIGHT-ACTIVATED BLEACHING

    PubMed Central

    Carrasco, Thaise Graciele; Carrasco-Guerisoli, Laise Daniela; Fröner, Izabel Cristina

    2008-01-01

    This study evaluated in vitro the pulp chamber temperature rise induced by the light-activated dental bleaching technique using different light sources. The root portions of 78 extracted sound human mandibular incisors were sectioned approximately 2 mm below the cementoenamel junction. The root cavities of the crowns were enlarged to facilitate the correct placing of the sensor into the pulp chamber. Half of specimens (n=39) was assigned to receive a 35% hydrogen peroxide gel on the buccal surface and the other halt (n=39) not to receive the bleaching agent. Three groups (n=13) were formed for each condition (bleach or no bleach) according to the use of 3 light sources recommended for dental bleaching: a light-emitting diode (LED)-laser system, a LED unit and a conventional halogen light. The light sources were positioned perpendicular to the buccal surface at a distance of 5 mm and activated during 30 s. The differences between the initial and the highest temperature readings for each specimen were obtained, and, from the temperature changes, the means for each specimen and each group were calculated. The values of temperature rise were compared using Kruskal-Wallis test at 1% significance level. Temperature rise varied significantly depending on the light-curing unit, with statistically significant differences (p<0.01) among the groups. When the bleaching agent was not applied, the halogen light induced the highest temperature rise (2.38±0.66°C). The LED unit produced the lowest temperature increase (0.29±0.13°C); but there was no significant difference between LED unit and LED-laser system (0.35±0.15°C) (p>0.01). When the bleaching agent was applied, there were significant differences among groups (p<0.01): halogen light induced the highest temperature rise (1.41±0.64°C), and LED-laser system the lowest (0.33±0.12°C); however, there was no difference between LED-laser system and LED unit (0.44±0.11°C). LED and LED-laser system did not differ

  7. Magma accumulation or second boiling - Investigating the ongoing deformation field at Montserrat, West Indies

    NASA Astrophysics Data System (ADS)

    Collinson, Amy; Neuberg, Jurgen; Pascal, Karen

    2016-04-01

    For over 20 years, Soufriere Hills Volcano, Montserrat has been in a state of volcanic unrest. Intermittent periods of dome building have been punctuated by explosive eruptions and dome collapse events, endangering the lives of the inhabitants of the island. The last episode of active magma extrusion was in February 2010, and the last explosive event (ash venting) in March 2012. Despite a lack of eruptive activity recently, the volcano continues to emit significant volumes of SO2 and shows an ongoing trend of island inflation. Through the aid of three-dimensional numerical modelling, using a finite element method, we explore the potential sources of the ongoing island inflation. We consider both magmatic (dykes and chamber) and tectonic sources. Whilst a magmatic source suggests the possibility for further eruption, a tectonic source may indicate cessation of volcanic activity. We show that a magmatic source is the most likely scenario, and illustrate the effect of different sources (shapes, characters and depths) on the surface displacement. Furthermore, through the inclusion of topographic data, we investigate how the topography may affect the displacement pattern at the surface. We investigate the conflicting scenarios of magma chamber resupply versus second boiling - crystallisation-induced degassing. Based on numerical modelling results, we suggest the required pressurisation is too high for crystallisation-induced degassing to be the dominant process - thereby suggesting magma accumulation may be ongoing. However, we show that second boiling may be a contributing factor, particularly when taking into account the local tectonics and regional stretching.

  8. Water content of primitive low-K tholeiitic basalt magma from Iwate Volcano, NE Japan arc: implications for differentiation mechanism of frontal-arc basalt magmas

    NASA Astrophysics Data System (ADS)

    Kuritani, Takeshi; Yoshida, Takeyoshi; Kimura, Jun-Ichi; Hirahara, Yuka; Takahashi, Toshiro

    2014-02-01

    The water content of low-K tholeiitic basalt magma from Iwate volcano, which is located on the volcanic front of the NE Japan arc, was estimated using multi-component thermodynamic models. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78-85) correlates positively with the An content of coexisting plagioclase phenocrysts (An85-92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase phenocrysts. It is inferred from these observations that the phenocrysts with variable compositions were primarily derived from mushy boundary layers along the walls of a magma chamber. By using thermodynamic calculations with the observed petrological features of the lavas, the water content of the Iwate magma was estimated to be 4-5 wt.%. The high water content of the magma supports the recent consensus that frontal-arc magmas are remarkably hydrous. Using the estimated water content of the Iwate magma, the water content and temperature of the source mantle were estimated. Given that the Iwate magma was derived from a primary magma solely by olivine fractionation, the water content and temperature were estimated to be ~0.7 wt.% and ~1,310 °C, respectively. Differentiation mechanisms of low-K frontal-arc basalt magmas were also examined by application of a thermodynamics-based mass balance model to the Iwate magma. It is suggested that magmatic differentiation proceeds primarily through fractionation of crystals from the main molten part of a magma chamber when it is located at <~200 MPa, whereas magma evolves through a convective melt exchange between the main magma and mushy boundary layers when the magma body is located at >~200 MPa.

  9. Water content of primitive low-K tholeiitic basalt magma from Iwate Volcano, NE Japan arc: implications for differentiation mechanism of frontal-arc basalt magmas

    NASA Astrophysics Data System (ADS)

    Kuritani, Takeshi; Yoshida, Takeyoshi; Kimura, Jun-Ichi; Hirahara, Yuka; Takahashi, Toshiro

    2013-03-01

    The water content of low-K tholeiitic basalt magma from Iwate volcano, which is located on the volcanic front of the NE Japan arc, was estimated using multi-component thermodynamic models. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78-85) correlates positively with the An content of coexisting plagioclase phenocrysts (An85-92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase phenocrysts. It is inferred from these observations that the phenocrysts with variable compositions were primarily derived from mushy boundary layers along the walls of a magma chamber. By using thermodynamic calculations with the observed petrological features of the lavas, the water content of the Iwate magma was estimated to be 4-5 wt.%. The high water content of the magma supports the recent consensus that frontal-arc magmas are remarkably hydrous. Using the estimated water content of the Iwate magma, the water content and temperature of the source mantle were estimated. Given that the Iwate magma was derived from a primary magma solely by olivine fractionation, the water content and temperature were estimated to be ~0.7 wt.% and ~1,310 °C, respectively. Differentiation mechanisms of low-K frontal-arc basalt magmas were also examined by application of a thermodynamics-based mass balance model to the Iwate magma. It is suggested that magmatic differentiation proceeds primarily through fractionation of crystals from the main molten part of a magma chamber when it is located at <~200 MPa, whereas magma evolves through a convective melt exchange between the main magma and mushy boundary layers when the magma body is located at >~200 MPa.

  10. Magma, crust and water fluid. From the imbalance of their interaction to the modeling of volcanic eruption

    NASA Astrophysics Data System (ADS)

    Nechayev, A.

    2012-12-01

    The work describes a simple physical model that provides a theoretical justification for a single origin of the different types of volcanic eruptions. The leading mechanism of this model is that a vertical column of magma under certain conditions starts to be erupted by the critical action of water vapor fluid contained by the crust under high pressure and high temperature. This fundamental mechanism of imbalance between liquid and gas was first described as a mechanism of geyser eruption (Nechayev 2012a). A generalization of this mechanism in case of volcanic eruptions is developed in (Nechayev 2012b). We assume that the acceleration of magma and its eruption results from a pressure difference between magma and fluid in the contact zone at depths exceeding 1 km. Water vapor as a fluid can be found in the subduction zones where the oceanic crust with the sedimentary layer saturated by water is pushing under the continental crust delivering water fluid in the zone of active volcanism. Water vapor fluid in the supercritical state behaves as an ideal gas. The greater the volume of fluid the smaller the decrease of its pressure during the expansion. If the fluid penetrates the magma conduit and its volume exceeds a certain critical value, the fluid starts to push magma as a piston. The critical volume is equal to γSH, where γ is the adiabatic coefficient of water vapor (γ=1,4), S is the section of the magmatic conduit, H is the bedding depth of fluid layer. The greater the volume of superheated water fluid and the distance separating it from the magma chamber, the higher may be the eruption power. During volcanic eruption the fluid does work and expands, its pressure and density decrease, the eruption ends. To be repeated and to form a stratovolcano the eruption need some time to restore the critical volume of the fluid. This can occur due to the diffusion of fluid from the periphery. Perhaps it is just the fluid diffusion time which determines the interval between

  11. Bakeout Chamber Within Vacuum Chamber

    NASA Technical Reports Server (NTRS)

    Taylor, Daniel M.; Soules, David M.; Barengoltz, Jack B.

    1995-01-01

    Vacuum-bakeout apparatus for decontaminating and measuring outgassing from pieces of equipment constructed by mounting bakeout chamber within conventional vacuum chamber. Upgrade cost effective: fabrication and installation of bakeout chamber simple, installation performed quickly and without major changes in older vacuum chamber, and provides quantitative data on outgassing from pieces of equipment placed in bakeout chamber.

  12. Intrusion of granitic magma into the continental crust facilitated by magma pulsing and dike-diapir interactions: Numerical simulations

    NASA Astrophysics Data System (ADS)

    Cao, Wenrong; Kaus, Boris J. P.; Paterson, Scott

    2016-06-01

    We conducted a 2-D thermomechanical modeling study of intrusion of granitic magma into the continental crust to explore the roles of multiple pulsing and dike-diapir interactions in the presence of visco-elasto-plastic rheology. Multiple pulsing is simulated by replenishing source regions with new pulses of magma at a certain temporal frequency. Parameterized "pseudo-dike zones" above magma pulses are included. Simulation results show that both diking and pulsing are crucial factors facilitating the magma ascent and emplacement. Multiple pulses keep the magmatic system from freezing and facilitate the initiation of pseudo-dike zones, which in turn heat the host rock roof, lower its viscosity, and create pathways for later ascending pulses of magma. Without diking, magma cannot penetrate the highly viscous upper crust. Without multiple pulsing, a single magma body solidifies quickly and it cannot ascent over a long distance. Our results shed light on the incremental growth of magma chambers, recycling of continental crust, and evolution of a continental arc such as the Sierra Nevada arc in California.

  13. Magma Storage Conditions, Eruption Initiation and Magma Evolution Over Time: Investigating the Eruptions of Organ Caldera, Southern NM

    NASA Astrophysics Data System (ADS)

    Lente, J. L.; Johnson, E. R.

    2015-12-01

    The Organ caldera in southern New Mexico formed ~36 Ma from a series of three explosive, voluminous eruptions. The volcanic deposits are now exposed in the Organ Mountains and have a combined thickness of nearly 3 km and an estimated volume between 500 and1000 km3 (Seager & McCurry, 1988). This research uses analyses of quartz-hosted melt inclusions from the first- and last-erupted units to study the storage and differentiation of the magma body prior-to and during the initial eruption, as well as changes in the magma chamber over time as the eruptions progressed and ultimately ceased. Previous work suggests the Organ magma chamber was compositionally stratified (Seager, 1981) erupting top-down and tapping less-evolved magmas over time. However, preliminary results suggest a more complex system; possibly a convecting, homogenized magma chamber or a series of dykes and sills. Results obtained using FTIR analyses of H2O and CO2 in melt inclusions have shown variable volatile contents from the first erupted unit (~2.3 to 6.8 weight percent H2O, 0-118 ppm CO2). Using these values, saturation pressures of 45 to 266 MPa were calculated, indicating a minimum pressure at which the melt inclusion was trapped. These pressures suggest magma storage depths for the first erupted magmas of ~2 to 9 km (with most inclusions trapped between 4 and 8 km) which is inconsistent with the initial eruption coming from the top of a normally stratified chamber. The large variation in volatile contents and storage depths can have many explanations, such as degassing and shallow crystallization during ascent, or perhaps a more complex, elongate magma storage system. These possibilities, and whether or not magma mixing/rejuvenation triggered the initial eruption, will be explored with the acquisition of major and trace element compositions of melt inclusions. Additionally, analyses of melt inclusions from the last erupted ignimbrite, which erupted ~0.5 Ma after the first eruption, will enable

  14. Variation of spectral response curves of GaAs photocathodes in activation chamber

    NASA Astrophysics Data System (ADS)

    Zou, Jijun; Chang, Benkang; Yang, Zhi; Wang, Hui; Gao, Pin

    2006-09-01

    The spectral response curves of reflection-mode GaAs (100) photocathodes are measured in activation chamber by multi-information measurement system at RT, and by applying quantum efficiency formula, the variation of spectral response curves have been studied. Reflection-mode GaAs photocathodes materials are grown over GaAs wafer (100) by MBE with p-type beryllium doping, doping concentration is 1×10 19 cm -3 and the active layer thickness is 1.6μm. During the high-temperature activation process, the spectral response curves varied with activation time are measured. After the low-temperature activation, the photocathode is illuminated by a white light source, and the spectral response curves varied with illumination time are measured every other hour. Experimental results of both high-temperature and low-temperature activations show that the spectral response curve shape of photocathodes is a function of time. We use traditional quantum efficiency formulas of photocathodes, in which only the Γ photoemission is considered, to fit experimental spectral response curves, and find the theoretical curves are not in agreement with the experimental curves, the reason is other valley and hot-electron yields are necessary to be included in yields of reflection-mode photocathodes. Based on the two-minima diffusion model and the fit of escape probability, we modified the quantum efficiency formula of reflection-mode photocathodes, the modified formula can be used to explain the variation of yield curves of reflection-mode photocathodes very well.

  15. Surface deformation versus eruption rates of the two Eyjafjallajökull 2010 eruptions; implications for the magma plumbing system and origin of melts

    NASA Astrophysics Data System (ADS)

    Pedersen, R.; Sigmundsson, F.; Hreinsdottir, S.; Arnadottir, T.; Hoskuldsson, A.; Gudmundsson, M. T.; Magnusson, E.

    2010-12-01

    Repeated geodetic measurements reveal how active volcanoes deform at the surface, and data inversion facilitates inferences about the related volume changes of underlying deformation sources. During an eruption, drainage from a shallow magma chamber can lead to direct correlation between magma flow rate and deformation rates, as observed previously in Iceland. In the simplest case, a constant scale factor relates magma flow rates, deformation rates on the surface, and inferred volume contraction of subsurface sources. The scale factor will depend on magma source geometry, compressibility of residing magma and rheological properties of the crustal rocks. During the two eruptions of the Eyjafjallajökull volcano, Iceland, in 2010 an entirely different behaviour was observed. This behaviour may be related to the rather unique plumbing system of this particular Icelandic volcano, which appears to have no shallow magma chamber. For the initial flank eruption, where olivine basalt were erupted during a period of about 3 weeks, the average eruption rate was comparable to the inferred flow rate during formation of a pre-eruptive network of intrusions. Detailed GPS and InSAR measurements have revealed a model for the subsurface magma plumbing system active prior to and during the events with multiple sills around 5 km depth. Such intrusions have occurred intermittently in this particular volcano for the past 18 years. During the subsequent explosive trachy-andesitic summit eruption, the relation between deformation rate and magma flow rate is more complex. A large discrepancy exists between the inferred erupted volume and the computed volume change based on the associated surface deformation. When recalculated to dense rock equivalent, the inferred volume change responsible for the main deformation is about one order of magnitude smaller than the sum of mapped erupted volumes. Furthermore, the spatial pattern of the deformation is complex, and not directly related to the

  16. Evolution of Large Venusian Volcanoes: Insights from Coupled Models of Lithospheric Flexure and Magma Reservoir Pressurization

    NASA Astrophysics Data System (ADS)

    Galgana, G. A.; McGovern, P. J.; Grosfils, E. B.

    2009-12-01

    Many large volcanic edifices on Venus exhibit surficial evidence of subsurface magma transport and storage: summit caldera faults indicating collapse into a magma chamber, and radial grabens indicating radiating dikes (although uplift may also produce the latter). These tectonic features reflect interactions between local magma-induced stresses and broader-scale stresses resulting from flexure of the lithosphere beneath the edifice load. Here, we explore the relationship between magma movement in the lithosphere and the flexural stress state via axisymmetric finite element models of the Venusian lithosphere. The lithosphere, modeled as an elastic material of thickness Te, is overlain with a conical edifice and embedded with an inflating, hence overpressured, spherical magma reservoir that perturbs the surrounding region. The volcanic edifice acts as a continuous gravitational load, flexing the lithosphere. The resulting flexural stress state beneath the edifice is characterized by high differential stresses, extensional in the upper part of the lithosphere and compressional in the lower part. These two distinct regions are separated by a neutral plane, a region characterized by relatively low differential stresses and least compressive principal stress (σ3) oriented out of the model plane. We examine models with different reservoir depths and analyze the orientation patterns of maximum stresses along the magma chamber wall. For a given chamber model, we increase the overpressure until one of the normal stresses at some point on the wall satisfies the failure criterion (here taken to be 0 MPa, the onset of the tensile regime). We find that reservoirs situated in the lower (extensional) lithosphere fail at the bottom; such a chamber is unstable, because it would not collect magma but rather expel it downward. Thus, we conclude magma chamber formation in the lower lithosphere is unlikely. In contrast, failure promoting lateral sill formation occurs near the reservoir

  17. Magma mixing enhanced by bubble ascent

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Perugini, D.; De Campos, C. P.; Hess, K.; Lavallee, Y.; Dingwell, D. B.

    2012-12-01

    progressive loss of advected basalt during bubble motion was quantified by microCT for defined viscosity couples. The diffusional gradient around the plume tail showed a progressive evolution of equilibration from bottom to top of the plume tail. A future aim is to compute the impact of bubble motion on the efficiency of magma mixing in dependence of volatile solubilities and pressure and viscosity variations. This has implications for the capacity of magma to produce bubbles in e.g. stratified magma chambers. [1] De Campos, C., D. Perugini, W. Ertel-Ingrisch, D. Dingwell, and G. Poli (2011), Enhancement of magma mixing efficiency by chaotic dynamics: an experimental study, Contrib. Mineral. Petrol., 161(6), 863-881. [2] Thomas, N., S. Tait, and T. Koyaguchi (1993), Mixing of stratified liquids by the motion of gas bubbles: application to magma mixing, Earth Planet. Sci. Lett., 115(1-4), 161-175.

  18. An Active Target-Time Projection Chamber (AT-TPC) for reaccelerated beams

    NASA Astrophysics Data System (ADS)

    Beceiro-Novo, Saul; Ahn, T.; Abu-Nimeh, F.; Bazin, D.; Bradt, J.; Chajecki, Z.; Fritsch, A.; Kohley, Z.; Kolata, J. J.; Lynch, W.; Mittig, W.; Suzuki, D.; Usher, N.

    2014-09-01

    Reaccelerated radioactive beams near the Coulomb barrier, which will soon be available from the ReA3 accelerator at NSCL, will open up new opportunities for the study of nuclear structure near the driplines. Since these beams can only be produced at modest intensities, efficient techniques must be used for measurement. The Active Target- Time Projection Chamber (AT-TPC), which was developed at MSU, solves this problem by providing the increased luminosity of a thick target while maintaining a good energy resolution by tracking the reaction vertex over an essentially 4 π solid angle. The AT-TPC and similar detectors allow us to take full advantage of the radioactive ion beams at present and future nuclear physics facilities to explore the frontier of rare isotopes where much of the spectroscopic information is unknown. We used a prototype of the AT-TPC to study resonances in light nuclei, and some illustrative results will be shown. The AT-TPC technology will be presented together with new experimental results and the commissioning of the detector and its 10240 electronic channels. Reaccelerated radioactive beams near the Coulomb barrier, which will soon be available from the ReA3 accelerator at NSCL, will open up new opportunities for the study of nuclear structure near the driplines. Since these beams can only be produced at modest intensities, efficient techniques must be used for measurement. The Active Target- Time Projection Chamber (AT-TPC), which was developed at MSU, solves this problem by providing the increased luminosity of a thick target while maintaining a good energy resolution by tracking the reaction vertex over an essentially 4 π solid angle. The AT-TPC and similar detectors allow us to take full advantage of the radioactive ion beams at present and future nuclear physics facilities to explore the frontier of rare isotopes where much of the spectroscopic information is unknown. We used a prototype of the AT-TPC to study resonances in light nuclei

  19. Magma evolution at mount vulture (Southern Italy)

    NASA Astrophysics Data System (ADS)

    de Fino, M.; La Volpe, L.; Piccarreta, G.

    1982-06-01

    The Vulture complex is made up of foiditic, tephritic, phonolitic-trachytic and phonolitic products. New rock analyses have been performed in order to ascertain whether the various rock types derive from a unique parental magma and, if so, to define its nature. The data presented support that the Vulture suite originated from a foiditic melt which had differentiated at low pressures. The main process determining the foidite → → tephrite → phonolitic trachyte evolution seems to be the crystal fractionation of mainly clinopyroxenes, and opaques, with the contribution of plagioclases and haüyne too in the tephrite → trachyte evolution. Additionary role must have been played by a mixing of melts at different evolution stages occurred in a shallow seated magma chamber.

  20. Crystallization kinetics in magmas during decompression

    NASA Astrophysics Data System (ADS)

    Arzilli, Fabio; Burton, Mike; Carroll, Michael R.

    2016-04-01

    aspect to understand magma evolution in the magma chamber and in the conduit, which in turn has strong effects on magma rheology. The onset of the crystallization process in basaltic melts during experiments was characterized by an initial nucleation event within the first hour of the experiment, which produced the largest amount of plagioclase [3]. This nucleation event, at short experimental duration, can produce a dramatic change in crystal number density and crystal fraction, triggering a significant textural evolution in only 1 h. The obtained results show that crystallization kinetics are strictly related to undercooling, time, final pressure, superheating and water content in the melt. Here we show that a small decrease in pressure could induce a dramatic increase of crystallinity in few hours, in natural systems this may affect the magma rheology and eruptive dynamics on very short time scales. References: [1] Ghiorso MS (1997) Thermodynamic models of igneous. Annu Rev Earth Planet Sci 25:221-241. [2] Arzilli F, Carroll MR (2013) Crystallization kinetics of alkali feldspars in cooling and decompression-induced crystallization experiments in trachytic melt. Contrib Mineral Petrol 166:1011-1027. [3] Arzilli F, Agostini C, Landi P, Fortunati A, Mancini L, Carroll MR (2015) Plagioclase nucleation and growth kinetics in a hydrous basaltic melt by decompression experiments. Contrib Mineral Petrol 170:55.

  1. Watching magma from space

    USGS Publications Warehouse

    Lu, Zhong; Wicks, Charles W.; Dzurisin, Daniel; Thatcher, Wayne R.; Freymueller, Jeffrey T.; McNutt, Stephen R.; Mann, Dorte

    2000-01-01

    Westdahl is a broad shield volcano at the western end of Unimak Island in the Aleutian chain. It has apparently been dormant since a 1991-92 eruption and seismicity levels have been low. However, satellite radar imaging shows that in the years following 1992 the upper flanks of Westdahl have risen several centimeters, probably from the influx of new magma deep below its summit. Until now, deep magma reservoirs have been difficult to detect beneath most volcanoes. But using space geodetic technologies, specifically interferometric synthetic aperture radar (InSAR), we have discovered a deep magmatic source beneath Westdahl. 

  2. A new analogue experiment on the vesiculation and fragmentation of magma during Plinian-style eruptions

    NASA Astrophysics Data System (ADS)

    Taddeucci, J.; Spieler, O.; Ichihara, M.; Dingwell, D.; Scarlato, P.

    2003-04-01

    The exsolution and expansion of volatiles dissolved in magmas are well acknowledged as the main driving force for Plinian-style volcanic eruptions. However, it is still unclear whether magma fragmentation during such activity results from the strain induced by gas expansion within individual bubbles, or from the strain that expansion and acceleration impose to the whole batch of exsolving magma. In order to experimentally investigate these processes, we present a new set-up for shock-tube experiments involving the exsolution and expansion of a volatile phase within a viscoelastic medium. The experimental set-up consists of a high-pressure Plexiglas chamber (volume in the order of 10 cm3, pressure up to 20 MPa) containing an argon-saturated polymer (commercial name: Silly Putty\\copy) sample, and a large volume (order of 105 cm3) steel tank at atmospheric pressure. Sudden decompression of the chamber causes argon exsolution, bubble growth, and expansion and flow of the sample, possibly followed by its fragmentation. Pre-experiment measurements include rheological characterization of the polymer at ambient conditions, and with different amounts of dissolved argon, performed under pressure in the chamber using a modified falling sphere method. During the experiments still-camera images record the expansion velocity of the foam and its fragmentation, pressure transducers record the pressure profiles at the bottom and above the sample, while porosity, morphology, and vesicle size distribution characterize the recovered fragments. By measuring the size distribution of the vesicles and the velocity profile of the flowing sample we may be able to put constraints both on the elongational strain rates of the sample and on the strain rates on bubble walls. Moreover, we aim at providing a phenomenological characterization of the range of processes involved in the flow and fragmentation of a vesicular, viscoelastic medium, by varying the following experimental conditions: argon

  3. Dynamics of an open basaltic magma system: The 2008 activity of the Halema‘uma‘u Overlook vent, Kīlauea Caldera

    USGS Publications Warehouse

    Eychenne, Julia; Houghton, Bruce; Swanson, Don; Carey, Rebecca; Swavely, Lauren

    2015-01-01

    On March 19, 2008 a small explosive event accompanied the opening of a 35-m-wide vent (Overlook vent) on the southeast wall of Halema‘uma‘u Crater in Kīlauea Caldera, initiating an eruptive period that extends to the time of writing. The peak of activity, in 2008, consisted of alternating background open-system outgassing and spattering punctuated by sudden, short-lived weak explosions, triggered by collapses of the walls of the vent and conduit. Near-daily sampling of the tephra from this open system, along with exceptionally detailed observations, allow us to study the dynamics of the activity during two eruptive sequences in late 2008. Each sequence includes background activity preceding and following one or more explosions in September and October 2008 respectively. Componentry analyses were performed for daily samples to characterise the diversity of the ejecta. Nine categories of pyroclasts were identified in all the samples, including wall-rock fragments. The six categories of juvenile clasts can be grouped in three classes based on vesicularity: (1) poorly, (2) uniformly highly to extremely, and (3) heterogeneously highly vesicular. The wall-rock and juvenile clasts show dissimilar grainsize distributions, reflecting different fragmentation mechanisms. The wall-rock particles formed by failure of the vent and conduit walls above the magma free surface and were then passively entrained in the eruptive plume. The juvenile componentry reveals consistent contrasts in degassing and fragmentation processes before, during and after the explosive events. We infer a crude ‘layering’ developed in the shallow melt, in terms of both rheology and bubble and volatile contents, beneath a convecting free surface during background activity. A tens-of-centimetres thick viscoelastic surface layer was effectively outgassed and relatively cool, while at depths of less than 100 m, the melt remained slightly supersaturated in volatiles and actively vesiculating

  4. Dynamics of an open basaltic magma system: The 2008 activity of the Halema'uma'u Overlook vent, Kīlauea Caldera

    NASA Astrophysics Data System (ADS)

    Eychenne, Julia; Houghton, Bruce F.; Swanson, Donald A.; Carey, Rebecca J.; Swavely, Lauren

    2015-01-01

    On March 19, 2008 a small explosive event accompanied the opening of a 35-m-wide vent (Overlook vent) on the southeast wall of Halema'uma'u Crater in Kīlauea Caldera, initiating an eruptive period that extends to the time of writing. The peak of activity, in 2008, consisted of alternating background open-system outgassing and spattering punctuated by sudden, short-lived weak explosions, triggered by collapses of the walls of the vent and conduit. Near-daily sampling of the tephra from this open system, along with exceptionally detailed observations, allow us to study the dynamics of the activity during two eruptive sequences in late 2008. Each sequence includes background activity preceding and following one or more explosions in September and October 2008 respectively. Componentry analyses were performed for daily samples to characterise the diversity of the ejecta. Nine categories of pyroclasts were identified in all the samples, including wall-rock fragments. The six categories of juvenile clasts can be grouped in three classes based on vesicularity: (1) poorly, (2) uniformly highly to extremely, and (3) heterogeneously highly vesicular. The wall-rock and juvenile clasts show dissimilar grainsize distributions, reflecting different fragmentation mechanisms. The wall-rock particles formed by failure of the vent and conduit walls above the magma free surface and were then passively entrained in the eruptive plume. The juvenile componentry reveals consistent contrasts in degassing and fragmentation processes before, during and after the explosive events. We infer a crude 'layering' developed in the shallow melt, in terms of both rheology and bubble and volatile contents, beneath a convecting free surface during background activity. A tens-of-centimetres thick viscoelastic surface layer was effectively outgassed and relatively cool, while at depths of less than 100 m, the melt remained slightly supersaturated in volatiles and actively vesiculating. Decoupled metre

  5. Long-term Rates of Mafic Magma Emplacement and Implications for Heat Advection

    NASA Astrophysics Data System (ADS)

    White, S. M.; Spera, F. J.; Crisp, J. A.

    2003-12-01

    Rates of magmatism (magma emplacement rate) including both volcanic products and intrusive bodies were obtained for terrestrial petrotectonic systems where reliable volumes can be estimated and geochronological data exist. Approximately 50 estimates of magma emplacement rates have been extracted from the literature published between 1982 and 2003 for persistent basaltic systems with durations from 1 ka to ~5 Ma. Although the volcanic output is highly episodic, the data indicate that the mass output rate at individual hotspot volcanoes is on the order of 10-3 km3/yr when averaged over several thousand years. This differs from the estimated output rates of large igneous provinces, such as continental flood basalts and oceanic plateaus, which have maximal output rates on the order of 1 km3/yr per province. For globally averaged mid-ocean ridges, the total volcanic emplacement rate is only 10-6 km3/yr/100 km of ridge. Ratios of intrusive to extrusive emplacement are subject to much uncertainty, but generally lie in the range 6:1 to 10:1 for most crustal mafic magma systems. Recent seismic, geodetic, and gravity work suggests that there may be large regions of underplating and storage in subcrustal magma chambers in areas of basaltic volcanism previously not widely considered in intrusive volume estimates that may increase most of these ratios to 10:1. Rates of magmatism may be translated into excess heat flows for specific magmatic provinces to obtain estimates of advected heat transport via magmatism at regional scales over magmatic province timescales. For mafic eruption rate V and an intrusive/extrusive ratio of R, the volumetric rate of magma flow into the crust is RV. The excess heat power (J/yr) associated with magma transport from mantle to crust is RVρ δ T [Cp + δ h/(Tliquidus-Tsolidus)] where δ T is the temperature difference between the magma and host crust, δ h is the enthalpy of crystallization (250-400 kJ/kg dependent on magma composition), ρ is

  6. Self Sealing Magmas

    NASA Astrophysics Data System (ADS)

    von Aulock, Felix W.; Wadsworth, Fabian B.; Kennedy, Ben M.; Lavallee, Yan

    2015-04-01

    During ascent of magma, pressure decreases and bubbles form. If the volume increases more rapidly than the relaxation timescale, the magma fragments catastrophically. If a permeable network forms, the magma degasses non-violently. This process is generally assumed to be unidirectional, however, recent studies have shown how shear and compaction can drive self sealing. Here, we additionally constrain skin formation during degassing and sintering. We heated natural samples of obsidian in a dry atmosphere and monitored foaming and impermeable skin formation. We suggest a model for skin formation that is controlled by diffusional loss of water and bubble collapse at free surfaces. We heated synthetic glass beads in a hydrous atmosphere to measure the timescale of viscous sintering. The beads sinter at drastically shorter timescales as water vapour rehydrates an otherwise degassed melt, reducing viscosity and glass transition temperatures. Both processes can produce dense inhomogeneities within the timescales of magma ascent and effectively disturb permeabilities and form barriers, particularly at the margins of the conduit, where strain localisation takes place. Localised ash in failure zones (i.e. Tuffisite) then becomes associated with water vapour fluxes and alow rapid rehydration and sintering. When measuring permeabilities in laboratory and field, and when discussing shallow degassing in volcanoes, local barriers for degassing should be taken into account. Highlighting the processes that lead to the formation of such dense skins and sintered infills of cavities can help understanding the bulk permeabilities of volcanic systems.

  7. Magma energy for power generation

    SciTech Connect

    Dunn, J.C.

    1987-01-01

    Thermal energy contained in crustal magma bodies represents a large potential resource for the US and magma generated power could become a viable alternative in the future. Engineering feasibility of the magma energy concept is being investigated as part of the Department of Energy's Geothermal Program. This current project follows a seven-year Magma Energy Research Project where scientific feasibility of the concept was concluded.

  8. Magma energy: a feasible alternative

    SciTech Connect

    Colp, J.L.

    1980-03-01

    A short review of the work performed by Sandia Laboratories in connection with its Magma Energy Research Project is provided. Results to date suggest that boreholes will remain stable down to magma depths and engineering materials can survive the downhole environments. Energy extraction rates are encouraging. Geophysical sensing systems and interpretation methods require improvement, however, to clearly define a buried magma source.

  9. Exposure chamber

    DOEpatents

    Moss, Owen R.; Briant, James K.

    1983-01-01

    An exposure chamber includes an imperforate casing having a fluid inlet at the top and an outlet at the bottom. A single vertical series of imperforate trays is provided. Each tray is spaced on all sides from the chamber walls. Baffles adjacent some of the trays restrict and direct the flow to give partial flow back and forth across the chambers and downward flow past the lowermost pan adjacent a central plane of the chamber.

  10. Draining mafic magma from conduits during Strombolian eruption

    NASA Astrophysics Data System (ADS)

    Wadsworth, F. B.; Kennedy, B.; Branney, M. J.; Vasseur, J.; von Aulock, F. W.; Lavallée, Y.; Kueppers, U.

    2014-12-01

    During and following eruption, mafic magmas can readily drain downward in conduits, dykes and lakes producing complex and coincident up-flow and down-flow textures. This process can occur at the top of the plumbing system if the magma outgases as slugs or through porous foam, causing the uppermost magma surface to descend and the magma to densify. In this scenario the draining volume is limited by the gas volume outgassed. Additionally, magma can undergo wholesale backflow when the pressure at the base of the conduit or feeder dyke exceeds the driving pressure in the chamber beneath. This second scenario will continue until pressure equilibrium is established. These two scenarios may occur coincidently as local draining of uppermost conduit magma by outgassing can lead to wholesale backflow because the densification of magma is an effective way to modify the vertical pressure profile in a conduit. In the rare case where conduits are preserved in cross section, the textural record of draining is often complex and great care should be taken in interpreting bimodal kinematic trends in detail. Lateral cooling into country rock leads to lateral profiles of physical and flow properties and, ultimately, outgassing potential, and exploration of such profiles elucidates the complexity involved. We present evidence from Red Crater volcano, New Zealand, and La Palma, Canary Islands, where we show that at least one draining phase followed initial ascent and eruption. We provide a rheological model approach to understand gravitational draining velocities and therefore, the timescales of up- and down-flow cycles predicted. These timescales can be compared with observed geophysical signals at monitored mafic volcanoes worldwide. Finally, we discuss the implications of shallow magma draining for edifice stability, eruption longevity and magma-groundwater interaction.

  11. Design and performance of an ionisation chamber for the measurement of low alpha-activities

    NASA Astrophysics Data System (ADS)

    Hartmann, A.; Hutsch, J.; Krüger, F.; Sobiella, M.; Wilsenach, H.; Zuber, K.

    2016-04-01

    A new ionisation chamber for alpha-spectroscopy has been built from radio-pure materials for the purpose of investigating long lived alpha-decays. The measurement makes use of pulse shape analysis to discriminate between signal and background events. The design and performance of the chamber is described in this paper. A background rate of (10.9 ± 0.6) counts per day in the energy region of 1-9 MeV was achieved with a run period of 30.8 days. The background is dominantly produced by radon daughters.

  12. Origin of compositional heterogeneities in tuffs of the Timber Mountain Group: The relationship between magma batches and magma transfer and emplacment in an extenional enviroment

    SciTech Connect

    Cambray, F.W.; Vogel, T.A.

    1995-08-10

    Compositionally zoned ash flow sheets provide convincing evidence for chemically zoned magma bodies. Most workers have assumed that the high-silica portions of these magma bodies evolved largely by differentiation processes that occurred within the magma chamber. However, chemical heterogeneities within some ash flow sheets are not consistent with these diferentiation processes. The chemical variation of pumice fragments in the large volume (>1200 km{sup 3}), Rainier Mesa ash flow sheet ranges from 55 to 76.3% silica. These pumice fragments occur in three distinct chemical groups. A low- and high-silica group is separated by a compositional gap at about 72% silica, and within the high-silica group there are two distinct populations based on trace element variations. There is little overlap between populations. These three magma types have been resident in same magma chamber at the same time and cannot be produced by any differentiation process of a single magma body. They must reflect discrete magma batches generated in the source area. Furthermore, the lower silica portion (<72% SiO{sub 2}) of the Rainer Mesa ash flow sheet is chemically distinct from the lower silica portion of the overlying Ammonia Tanks ash flow sheet, even though they erupted within 200,000 years of each other. These ash flow sheets from the SW Nevada volcanic field are associated in time and place with Basin and Range extension, and all models for extension involve detachment surfaces that extend to great depth. A model for the relationship of these compositional heterogeneities and the regional extension involves (1) the generation of magma batches by either continuous melting of the source at different temperatures, or by melting of different sources, (2) the use of faults (shears) as conduits for transport of magma, and (3) the use of a dilatant releasing step on a detachment as storage chamber for the magma. 80 refs., 12 figs., 1 tab.

  13. Enhanced desalination performance of membrane capacitive deionization cells by packing the flow chamber with granular activated carbon.

    PubMed

    Bian, Yanhong; Yang, Xufei; Liang, Peng; Jiang, Yong; Zhang, Changyong; Huang, Xia

    2015-11-15

    A new design of membrane capacitive deionization (MCDI) cell was constructed by packing the cell's flow chamber with granular activated carbon (GAC). The GAC packed-MCDI (GAC-MCDI) delivered higher (1.2-2.5 times) desalination rates than the regular MCDI at all test NaCl concentrations (∼ 100-1000 mg/L). The greatest performance enhancement by packed GAC was observed when treating saline water with an initial NaCl concentration of 100 mg/L. Several different GAC materials were tested and they all exhibited similar enhancement effects. Comparatively, packing the MCDI's flow chamber with glass beads (GB; non-conductive) and graphite granules (GG; conductive but with lower specific surface area than GAC) resulted in inferior desalination performance. Electrochemical impedance spectroscopy (EIS) analysis showed that the GAC-MCDI had considerably smaller internal resistance than the regular MCDI (∼ 19.2 ± 1.2 Ω versus ∼ 1222 ± 15 Ω at 100 mg/L NaCl). The packed GAC also decreased the ionic resistance across the flow chamber (∼ 1.49 ± 0.05 Ω versus ∼ 1130 ± 12 Ω at 100 mg/L NaCl). The electric double layer (EDL) formed on the GAC surface was considered to store salt ions during electrosorption, and facilitate the ion transport in the flow chamber because of the higher ion conductivity in the EDLs than in the bulk solution, thereby enhancing the MCDI's desalination rate.

  14. Barometry of lavas from the 1951 eruption of Fogo, Cape Verde Islands: Implications for historic and prehistoric magma plumbing systems

    NASA Astrophysics Data System (ADS)

    Hildner, Elliot; Klügel, Andreas; Hansteen, Thor H.

    2012-03-01

    Fogo is one of the most active oceanic volcanoes in the world. The island was affected by a prehistoric giant lateral collapse that decapitated the summit of the former Monte Amarelo volcano. Subsequent volcanism has partly filled the collapse scar and built up the present-day Cha das Caldeiras plain and the Pico do Fogo stratovolcano. We have conducted a thermobarometric study of historic and prehistoric, basanitic to tephritic rocks in order to gain insight into Fogo's magma plumbing system and the impact of the collapse event on fractionation depths. A main focus was the penultimate 1951 eruption, which produced basanites to tephrites (5.0-8.2 wt.% MgO) at two sites south and northwest of Pico do Fogo. Clinopyroxene-melt barometry of phenocrysts yields a well-confined pressure range of 480-650 MPa for the final crystallization level. Microthermometric data of CO2-dominated fluid inclusions in olivine and clinopyroxene phenocrysts yield systematically lower pressures of 250-430 MPa. Inclusions in cumulate xenoliths yield pressures of 100-290 MPa. The combined data indicate pre-eruptive magma storage in the uppermost mantle between 17 and 22 km depth and syn-eruptive short-term magma stalling within the lower crust at 8-13 km depth. The lower pressures revealed by fluid inclusions in xenoliths may indicate that they originate from pre-1951 magma pulses that stalled and crystallized at variable levels in the crust. There is, however, no petrologic evidence for persistent crustal magma chambers. Clinopyroxene-melt barometric data of other historic and prehistoric eruptions indicate that magma storage and differentiation occurred in the uppermost mantle at pressures between 420 and 870 MPa (15-30 km depth) throughout the subaerial evolution of Fogo. Our data indicate that fractionation depths decreased significantly during a period of about 100 ka representing a strong growth phase of Fogo edifice leading up to the giant Monte Amarelo flank collapse at 123-62 ka

  15. Comparative Magma Oceanography

    NASA Technical Reports Server (NTRS)

    Jones, John H.

    1999-01-01

    The question of whether the Earth ever passed through a magma ocean stop is of considerable interest. Geochemical evidence strongly suggests that the Moon had a magma ocean and the evidence is mounting that the same was true for Mars. Analyses of mar (SNC) meteorites have yielded insights into the differentiation history of Mars, and consequently, it is interesting to compare that planet to the Earth. Three primary features of An contrast strongly to those of the Earth: (1) the extremely ancient ages of the martian core, mantle, and crust (approx. 4.55 b.y.); (2) the highly depleted nature of the martian mantle; and (3) the extreme ranges of Nd isotopic compositions that arise within the crust and depleted mantle.

  16. The Surtsey Magma Series

    PubMed Central

    Ian Schipper, C.; Jakobsson, Sveinn P.; White, James D.L.; Michael Palin, J.; Bush-Marcinowski, Tim

    2015-01-01

    The volcanic island of Surtsey (Vestmannaeyjar, Iceland) is the product of a 3.5-year-long eruption that began in November 1963. Observations of magma-water interaction during pyroclastic episodes made Surtsey the type example of shallow-to-emergent phreatomagmatic eruptions. Here, in part to mark the 50th anniversary of this canonical eruption, we present previously unpublished major-element whole-rock compositions, and new major and trace-element compositions of sideromelane glasses in tephra collected by observers and retrieved from the 1979 drill core. Compositions became progressively more primitive as the eruption progressed, with abrupt changes corresponding to shifts between the eruption’s four edifices. Trace-element ratios indicate that the chemical variation is best explained by mixing of different proportions of depleted ridge-like basalt, with ponded, enriched alkalic basalt similar to that of Iceland’s Eastern Volcanic Zone; however, the systematic offset of Surtsey compositions to lower Nb/Zr than other Vestmannaeyjar lavas indicates that these mixing end members are as-yet poorly contained by compositions in the literature. As the southwestern-most volcano in the Vestmannaeyjar, the geochemistry of the Surtsey Magma Series exemplifies processes occurring within ephemeral magma bodies on the extreme leading edge of a propagating off-axis rift in the vicinity of the Iceland plume. PMID:26112644

  17. The Surtsey Magma Series

    NASA Astrophysics Data System (ADS)

    Ian Schipper, C.; Jakobsson, Sveinn P.; White, James D. L.; Michael Palin, J.; Bush-Marcinowski, Tim

    2015-06-01

    The volcanic island of Surtsey (Vestmannaeyjar, Iceland) is the product of a 3.5-year-long eruption that began in November 1963. Observations of magma-water interaction during pyroclastic episodes made Surtsey the type example of shallow-to-emergent phreatomagmatic eruptions. Here, in part to mark the 50th anniversary of this canonical eruption, we present previously unpublished major-element whole-rock compositions, and new major and trace-element compositions of sideromelane glasses in tephra collected by observers and retrieved from the 1979 drill core. Compositions became progressively more primitive as the eruption progressed, with abrupt changes corresponding to shifts between the eruption’s four edifices. Trace-element ratios indicate that the chemical variation is best explained by mixing of different proportions of depleted ridge-like basalt, with ponded, enriched alkalic basalt similar to that of Iceland’s Eastern Volcanic Zone; however, the systematic offset of Surtsey compositions to lower Nb/Zr than other Vestmannaeyjar lavas indicates that these mixing end members are as-yet poorly contained by compositions in the literature. As the southwestern-most volcano in the Vestmannaeyjar, the geochemistry of the Surtsey Magma Series exemplifies processes occurring within ephemeral magma bodies on the extreme leading edge of a propagating off-axis rift in the vicinity of the Iceland plume.

  18. The Surtsey Magma Series.

    PubMed

    Schipper, C Ian; Jakobsson, Sveinn P; White, James D L; Michael Palin, J; Bush-Marcinowski, Tim

    2015-06-26

    The volcanic island of Surtsey (Vestmannaeyjar, Iceland) is the product of a 3.5-year-long eruption that began in November 1963. Observations of magma-water interaction during pyroclastic episodes made Surtsey the type example of shallow-to-emergent phreatomagmatic eruptions. Here, in part to mark the 50(th) anniversary of this canonical eruption, we present previously unpublished major-element whole-rock compositions, and new major and trace-element compositions of sideromelane glasses in tephra collected by observers and retrieved from the 1979 drill core. Compositions became progressively more primitive as the eruption progressed, with abrupt changes corresponding to shifts between the eruption's four edifices. Trace-element ratios indicate that the chemical variation is best explained by mixing of different proportions of depleted ridge-like basalt, with ponded, enriched alkalic basalt similar to that of Iceland's Eastern Volcanic Zone; however, the systematic offset of Surtsey compositions to lower Nb/Zr than other Vestmannaeyjar lavas indicates that these mixing end members are as-yet poorly contained by compositions in the literature. As the southwestern-most volcano in the Vestmannaeyjar, the geochemistry of the Surtsey Magma Series exemplifies processes occurring within ephemeral magma bodies on the extreme leading edge of a propagating off-axis rift in the vicinity of the Iceland plume.

  19. Calderas and magma reservoirs

    NASA Astrophysics Data System (ADS)

    Cashman, Katharine; Giordano, Guido

    2015-04-01

    Large caldera-forming eruptions have long been a focus of both petrological and volcanological studies; traditionally, both have assumed that eruptible magma is stored within a single long-lived melt body. Over the past decade, however, advances in analytical techniques have provided new views of magma storage regions, many of which provide evidence of multiple melt lenses feeding a single eruption, and/or rapid pre-eruptive assembly of large volumes of melt. These new petrological views of magmatic systems have not yet been fully integrated into volcanological perspectives of caldera-forming eruptions. We discuss the implications of syn-eruptive melt extraction from complex, rather than simple, reservoirs and its potential control over eruption size and style, and caldera collapse timing and style. Implications extend to monitoring of volcanic unrest and eruption progress under conditions where successive melt lenses may be tapped. We conclude that emerging views of complex magma reservoir configurations provide exciting opportunities for re-examining volcanological concepts of caldera-forming systems

  20. The Surtsey Magma Series.

    PubMed

    Schipper, C Ian; Jakobsson, Sveinn P; White, James D L; Michael Palin, J; Bush-Marcinowski, Tim

    2015-01-01

    The volcanic island of Surtsey (Vestmannaeyjar, Iceland) is the product of a 3.5-year-long eruption that began in November 1963. Observations of magma-water interaction during pyroclastic episodes made Surtsey the type example of shallow-to-emergent phreatomagmatic eruptions. Here, in part to mark the 50(th) anniversary of this canonical eruption, we present previously unpublished major-element whole-rock compositions, and new major and trace-element compositions of sideromelane glasses in tephra collected by observers and retrieved from the 1979 drill core. Compositions became progressively more primitive as the eruption progressed, with abrupt changes corresponding to shifts between the eruption's four edifices. Trace-element ratios indicate that the chemical variation is best explained by mixing of different proportions of depleted ridge-like basalt, with ponded, enriched alkalic basalt similar to that of Iceland's Eastern Volcanic Zone; however, the systematic offset of Surtsey compositions to lower Nb/Zr than other Vestmannaeyjar lavas indicates that these mixing end members are as-yet poorly contained by compositions in the literature. As the southwestern-most volcano in the Vestmannaeyjar, the geochemistry of the Surtsey Magma Series exemplifies processes occurring within ephemeral magma bodies on the extreme leading edge of a propagating off-axis rift in the vicinity of the Iceland plume. PMID:26112644

  1. Lunar magma transport phenomena

    NASA Technical Reports Server (NTRS)

    Spera, Frank J.

    1992-01-01

    An outline of magma transport theory relevant to the evolution of a possible Lunar Magma Ocean and the origin and transport history of the later phase of mare basaltic volcanism is presented. A simple model is proposed to evaluate the extent of fractionation as magma traverses the cold lunar lithosphere. If Apollo green glasses are primitive and have not undergone significant fractionation en route to the surface, then mean ascent rates of 10 m/s and cracks of widths greater than 40 m are indicated. Lunar tephra and vesiculated basalts suggest that a volatile component plays a role in eruption dynamics. The predominant vapor species appear to be CO CO2, and COS. Near the lunar surface, the vapor fraction expands enormously and vapor internal energy is converted to mixture kinetic energy with the concomitant high-speed ejection of vapor and pyroclasts to form lunary fire fountain deposits such as the Apollo 17 orange and black glasses and Apollo 15 green glass.

  2. Middle Triassic magma mixing in an active continental margin: Evidence from mafic enclaves and host granites from the Dewulu pluton in West Qinling, central China

    NASA Astrophysics Data System (ADS)

    Huang, X.; Mo, X.; Yu, X.

    2015-12-01

    The Qinling-Dabie-Sulu orogen was formed through the collision of the North and South China blocks, but the precise timing of the closure of the Paleo-Tethys ocean between the two blocks remains debated. Large volumes of Triassic granites associated with mafic microgranular enclaves (MMEs) were emplaced in the Qinling terrane. This paper presents field observations, petrography, geochronology and geochemistry of the MMEs and their host granites from the Dewulu pluton in West Qinling. The host rocks comprise granodiorite and granodioritic porphyry, and the The MMEs range in composition from gabbroic diorite to diorite. Zircon LA-ICP-MS U-Pb ages suggest that the granites and MMEs were coeval at ca. 245 Ma. The granites are relatively enriched in LILE and depleted in HFSE, and have evolved Sr-Nd-Pb and zircon Hf isotopic compositions [initial 87Sr/86Sr = 0.7070-0.7076, ɛNd(t) = -7.5 to -6.8, ɛHf(t) = -8.2 to -4.2], indicative of an origin from the amphibolitic lower crust. The near-primitive gabbro-dioritic MMEs bear a remarkable geochemical resemblance to the high-magnesium andesite (HMA), such as moderate SiO2 (~55 wt.%), low FeOT/MgO (~0.75), high Cr (268-308 ppm) and MgO (8.58-8.77 wt.%) with Mg# of ~70. Additionally, they exhibit lower initial 87Sr/86Sr, higher ɛNd(t) and ɛHf(t), and more radiogenic Pb isotopes than the dioritic MMEs which share similar isotopic compositions with the granites. These features, together with the presence of the specific minerals in the MMEs (e.g., felsic xenocrysts and acicular apatite), point to mixing process between the lower crust-derived magmas and the melts produced by the reaction of the subducting sediment-derived components and the overlying mantle. Taking into account the regional occurrence of synchronous plutonic-volcanic complexes (250-234 Ma) ranging from basaltic to granitic variants, we suggest that the Dewulu pluton formed in an active continental margin in response to the local extension triggered by the

  3. Direct Observation of Rhyolite Magma by Drilling: The Proposed Krafla Magma Drilling Project

    NASA Astrophysics Data System (ADS)

    Eichelberger, J. C.; Sigmundsson, F.; Papale, P.; Markusson, S.; Loughlin, S.

    2014-12-01

    Remarkably, drilling in Landsvirkjun Co.'s geothermal field in Krafla Caldera, Iceland has encountered rhyolite magma or hypersolidus rhyolite at 2.1-2.5 km depth in 3 wells distributed over 3.5 km2, including Iceland Deep Drilling Program's IDDP-1 (Mortensen, 2012). Krafla's most recent rifting and eruption (basalt) episode was 1975-1984; deformation since that time has been simple decay. Apparently rhyolite magma was either emplaced during that episode without itself erupting or quietly evolved in situ within 2-3 decades. Analysis of drill cuttings containing quenched melt from IDDP-1 yielded unprecedented petrologic data (Zierenberg et al, 2012). But interpreting active processes of heat and mass transfer requires knowing spatial variations in physical and chemical characteristics at the margin of the magma body, and that requires retrieving core - a not-inconceivable task. Core quenched in situ in melt up to 1150oC was recovered from Kilauea Iki lava lake, Hawaii by the Magma Energy Project >30 years ago. The site from which IDDP-1 was drilled, and perhaps IDDP-1 itself, may be available to attempt the first-ever coring of rhyolite magma, now proposed as the Krafla Magma Drilling Project (KMDP). KMDP would also include geophysical and geochemical experiments to measure the response of the magma/hydrothermal system to fluid injection and flow tests. Fundamental results will reveal the behavior of magma in the upper crust and coupling between magma and the hydrothermal system. Extreme, sustained thermal power output during flow tests of IDDP-1 suggests operation of a Kilauea-Iki-like freeze-fracture-flow boundary propagating into the magma and mining its latent heat of crystallization (Carrigan et al, EGU, 2014). Such an ultra-hot Enhanced Geothermal System (EGS) might be developable beneath this and other magma-heated conventional hydrothermal systems. Additionally, intra-caldera intrusions like Krafla's are believed to produce the unrest that is so troubling in

  4. Smog Chamber Investigation on the Iron-Catalyzed Activation of Chloride from Modeled Saltpans

    NASA Astrophysics Data System (ADS)

    Wittmer, Julian; Bleicher, Sergej; Oeste <, Franz Dietrich; Zetzsch, Cornelius

    2014-05-01

    Halogen activation on sea spray aerosols and other halide surfaces and thus the formation of reactive halogen species (RHS), influencing trace and greenhouse gases, has become an important topic of research in recent years. In this context the chloride and bromide activation, in particular the formation of RHS by photochemically induced halogen release from (sea) salt surface and reactions with ozone (O3) and nitrogen oxides (NOx), came into focus [1,2]. Our studies concentrate on the quantification of atomic chlorine (Cl), bromine (Br) and hydroxyl (OH) radicals in the gas phase above lab-models of salt pans, enriched in iron(III) chloride (FeCl3), that are exposed to simulated sunlight in a smog chamber. The applied radical clock method [3] results in time profiles and source strengths for Cl, Br and OH, which are combined with the various compositions of humidified salts. In particular, the influence of bromine, sulfate, oxalate, and catechol on the FeCl3 enriched salt is investigated. Comparable investigations only exist for the aqueous phase chemistry of FeCl3 (e.g. [4]). Driven by the photolytic reduction from Fe(III) to Fe(II), an enormous amount of chlorine atoms (>107 cm-3) could be detected for sodium chloride (NaCl) salt pans with low addition of FeCl3 (0.5 - 2 wt%), even in an O3 and NOx free environment. The Cl2 source strength reaches a maximum of 8×1011 Cl2 molecules per cm3 within the first hour of the experiment, corresponding to a Cl2 mixing ratio of 30 ppbv at standard pressure. These concentrations exceeded the release above pure NaCl samples by a factor of 1000. A crucial factor for the Cl2 release is the pH and thus the formation of iron(III) complexes on the salt crystals that differ in their sensitivity for photolysis. Whereas the presence of sodium bromide normally strengthens the chlorine release, a suppression accompanied by strong bromine activation (>1010 cm-3) could be observed for iron enriched samples. Furthermore, the addition of

  5. Comparative Magma Oceanography

    NASA Technical Reports Server (NTRS)

    Jones, J. H.

    1999-01-01

    The question of whether the Earth ever passed through a magma ocean stage is of considerable interest. Geochemical evidence strongly suggests that the Moon had a magma ocean and the evidence is mounting that the same was true for Mars. Analyses of martian (SNC) meteorites have yielded insights into the differentiation history of Mars, and consequently, it is interesting to compare that planet to the Earth. Three primary features of Mars contrast strongly to those of the Earth: (i) the extremely ancient ages of the martian core, mantle, and crust (about 4.55 b.y.); (ii) the highly depleted nature of the martian mantle; and (iii) the extreme ranges of Nd isotopic compositions that arise within the crust and depleted mantle. The easiest way to explain the ages and diverse isotopic compositions of martian basalts is to postulate that Mars had an early magma ocean. Cumulates of this magma ocean were later remelted to form the SNC meteorite suite and some of these melts assimilated crustal materials enriched in incompatible elements. The REE pattern of the crust assimilated by these SNC magmas was LREE enriched. If this pattern is typical of the crust as a whole, the martian crust is probably similar in composition to melts generated by small degrees of partial melting (about 5%) of a primitive source. Higher degrees of partial melting would cause the crustal LREE pattern to be essentially flat. In the context of a magma ocean model, where large degrees of partial melting presumably prevailed, the crust would have to be dominated by late-stage, LREE-enriched residual liquids. Regardless of the exact physical setting, Nd and W isotopic evidence indicates that martian geochemical reservoirs must have formed early and that they have not been efficiently remixed since. The important point is that in both the Moon and Mars we see evidence of a magma ocean phase and that we recognize it as such. Several lines of theoretical inference point to an early Earth that was also hot

  6. Geology of magma systems: background and review

    SciTech Connect

    Peterfreund, A.R.

    1981-03-01

    A review of basic concepts and current models of igneous geology is presented. Emphasis is centered on studies of magma generation, ascent, emplacement, evolution, and surface or near-surface activity. An indexed reference list is also provided to facilitate future investigations.

  7. Abrupt transition from fractional crystallization to magma mixing at Gorely volcano (Kamchatka) after caldera collapse

    NASA Astrophysics Data System (ADS)

    Gavrilenko, Maxim; Ozerov, Alexey; Kyle, Philip R.; Carr, Michael J.; Nikulin, Alex; Vidito, Christopher; Danyushevsky, Leonid

    2016-07-01

    A series of large caldera-forming eruptions (361-38 ka) transformed Gorely volcano, southern Kamchatka Peninsula, from a shield-type system dominated by fractional crystallization processes to a composite volcanic center, exhibiting geochemical evidence of magma mixing. Old Gorely, an early shield volcano (700-361 ka), was followed by Young Gorely eruptions. Calc-alkaline high magnesium basalt to rhyolite lavas have been erupted from Gorely volcano since the Pleistocene. Fractional crystallization dominated evolution of the Old Gorely magmas, whereas magma mixing is more prominent in the Young Gorely eruptive products. The role of recharge-evacuation processes in Gorely magma evolution is negligible (a closed magmatic system); however, crustal rock assimilation plays a significant role for the evolved magmas. Most Gorely magmas differentiate in a shallow magmatic system at pressures up to 300 MPa, ˜3 wt% H2O, and oxygen fugacity of ˜QFM + 1.5 log units. Magma temperatures of 1123-1218 °C were measured using aluminum distribution between olivine and spinel in Old and Young Gorely basalts. The crystallization sequence of major minerals for Old Gorely was as follows: olivine and spinel (Ol + Sp) for mafic compositions (more than 5 wt% of MgO); clinopyroxene and plagioclase crystallized at ˜5 wt% of MgO (Ol + Cpx + Plag) and magnetite at ˜3.5 wt% of MgO (Ol + Cpx + Plag + Mt). We show that the shallow magma chamber evolution of Old Gorely occurs under conditions of decompression and degassing. We find that the caldera-forming eruption(s) modified the magma plumbing geometry. This led to a change in the dominant magma evolution process from fractional crystallization to magma mixing. We further suggest that disruption of the magma chamber and accompanying change in differentiation process have the potential to transform a shield volcanic system to that of composite cone on a global scale.

  8. Comment on 'volume of magma accumulation or withdrawal estimated from surface uplift or subsidence, with application to the 1960 collapse of Kilauea volcano' by P.T. Delaney and D.F. McTigue

    USGS Publications Warehouse

    Johnson, Daniel J.; Sigmundsson, F.; Delaney, P.T.

    2000-01-01

    In volcanoes that store a significant quantity of magma within a subsurface summit reservoir, such as Kilauea, bulk compression of stored magma is an important mode of deformation. Accumulation of magma is also accompanied by crustal deformation, usually manifested at the surface as uplift. These two modes of deformation - bulk compression of resident magma and deformation of the volcanic edifice - act in concert to accommodate the volume of newly added magma. During deflation, the processes reverse and reservoir magma undergoes bulk decompression, the chamber contracts, and the ground surface subsides. Because magma compression plays a role in creating subsurface volume of accommodate magma, magma budget estimates that are derived from surface uplift observations without consideration of magma compression will underestimate actual magma volume changes.

  9. Petrological constrains of magma feeding system of Bezymyanny volcano (Kamchatka)

    NASA Astrophysics Data System (ADS)

    Plechov, P.; Shcherbakov, V. D.; Izbekov, P. E.

    2010-12-01

    Bezymyanny volcano is located in Central Kamchatka Depression and is in continuous eruption since 1956. Last decade is characterized by frequent (2 times per year) significant explosive events accompanied by extrusive dome growth. Composition of erupted lavas was changed gradually from hornblende-rich andesites (in wt%: SiO2 60-61, MgO 2.5-2.7, K2O 1.3) to two-pyroxene andesites (in wt%: SiO2 56-57, MgO 3.8-4.1, K2O 1.1) during last 54 years. We estimated PT-conditions of Bezymyanny magma chamber for 1956 from phenocrysts assemblage as 890±20°C and 600±200 MPa [1], whereas for 2000-2007 Bezymyanny magma chamber temperature and pressure were estimated as ~940°C and 77 - 87 MPa, respectively [2]. We suggest that temperature increased and lava compositions changed due to often influx of new magma portions since 1956. Changes in pressure of magma chamber can be explained by initiation of a new shallow magmatic chamber, which could have been formed after 1956. Harzburgite xenoliths in lavas first occurred in 2007-2009 eruption products and were described by authors. Primary assemblage consists of olivine (Fo87.2-91.0), orthopyroxene(En89.7-91.6Fs8.4-9.4Wo0-0.9) and Cr-spinel (Cr#=0.46-0.58). Equilibrium temperature for the assemblage is estimated as 950±40°C, ΔlogQFM =+2.1 and degree of mantle melting is 20-30%. We suggest that xenoliths represent fragments of lithosphere mantle, which were trapped by primitive magmas of Bezymyanny volcano during ascent. Occurrence of these xenoliths argued for the rapid penetration of xenolith-bearing magmas from mantle level to the shallow magma chamber during the last few years. [1] Plechov P. et al.(2008). Petrology:16:1:19-35. [2] Shcherbakov et al. (2010)CMP,accepted.

  10. Magma energy: engineering feasibility of energy extraction from magma bodies

    SciTech Connect

    Traeger, R.K.

    1983-12-01

    A research program was carried out from 1975 to 1982 to evaluate the scientific feasibility of extracting energy from magma, i.e., to determine if there were any fundamental scientific roadblocks to tapping molten magma bodies at depth. The next stage of the program is to evaluate the engineering feasibility of extracting energy from magma bodies and to provide insight into system economics. This report summarizes the plans, schedules and estimated costs for the engineering feasibility study. Tentative tasks and schedules are presented for discussion and critique. A bibliography of past publications on magma energy is appended for further reference. 69 references.

  11. Exposure chamber

    DOEpatents

    Moss, Owen R.

    1980-01-01

    A chamber for exposing animals, plants, or materials to air containing gases or aerosols is so constructed that catch pans for animal excrement, for example, serve to aid the uniform distribution of air throughout the chamber instead of constituting obstacles as has been the case in prior animal exposure chambers. The chamber comprises the usual imperforate top, bottom and side walls. Within the chamber, cages and their associated pans are arranged in two columns. The pans are spaced horizontally from the walls of the chamber in all directions. Corresponding pans of the two columns are also spaced horizontally from each other. Preferably the pans of one column are also spaced vertically from corresponding pans of the other column. Air is introduced into the top of the chamber and withdrawn from the bottom. The general flow of air is therefore vertical. The effect of the horizontal pans is based on the fact that a gas flowing past the edge of a flat plate that is perpendicular to the flow forms a wave on the upstream side of the plate. Air flows downwardly between the chamber walls and the outer edges of the pan. It also flows downwardly between the inner edges of the pans of the two columns. It has been found that when the air carries aerosol particles, these particles are substantially uniformly distributed throughout the chamber.

  12. Along-strike magma mixing beneath mid-ocean ridges - Effects on isotopic ratios

    NASA Technical Reports Server (NTRS)

    Kenyon, P. M.; Turcotte, D. L.

    1987-01-01

    The effects of mixing processes on the isotopic variability of midocean ridge basalts are studied. The processes considered are porous flow dispersion and convective mixing in magma chambers. Porous flow dispersion is capable of mixing magmas over distances of only a few tens of meters. Convective mixing, on the other hand, is found to produce continuous magma chambers, where mixing is limited by convective processes, and for discontinuous chambers, where mixing is limited by chamber size. Preliminary comparison of the calculations with observations along the midocean ridges shows that the calculations are consistent with the existence of a correlation between bathymetry and isotopic ratio at long, but not at short, wavelengths. They are also capable of explaining a decrease in isotopic variability with increasing spreading rate.

  13. Basaltic calderas: Collapse dynamics, edifice deformation, and variations of magma withdrawal

    NASA Astrophysics Data System (ADS)

    Michon, Laurent; Massin, FréDéRick; Famin, Vincent; Ferrazzini, ValéRie; Roult, GenevièVe

    2011-03-01

    The incremental caldera collapses of Fernandina (1968), Miyakejima (2000), and Piton de la Fournaise (2007) are analyzed in order to understand the collapse dynamics in basaltic setting and the associated edifice deformation. For each caldera, the collapse dynamics is assessed through the evolution of the (1) time interval T between two successive collapse increments, (2) amount of vertical displacement during each collapse increment, and (3) magma outflow rate during the whole collapse caldera process. We show from the evolution of T that Piton de la Fournaise and Fernandina were characterized by a similar collapse dynamics, despite large differences in the caldera geometry and the duration of the whole collapse caldera process. This evolution significantly differs from that of Miyakejima where T strongly fluctuated throughout the whole collapse process. Quantification of the piston vertical displacements enables us to determine the magma outflow rates between each collapse increment. Displacement data (tiltmeter and/or GPS) for Piton de la Fournaise and Miyakejima are used to constrain the edifice overall deformation and the edifice deformation rates. These data reveal that both volcanoes experienced edifice inflation once the piston collapsed into the magma chamber. Such a deformation, which lasts during the first collapse increments only, is interpreted as the result of larger volume of piston intruded in the magma chamber than magma withdrawn before each collapse increment. Once the effect of the collapsing rock column vanishes, edifice deflates. We also determine for each caldera the critical amount of magma evacuated before collapse initiation and compare it to analog models. The significant differences between models and nature are explained by the occurrence of preexisting weak zones in nature, i.e., the ring faults, that are not taken into account in analog models. Finally, we show that T at Piton de la Fournaise and Fernandina was equally controlled by

  14. FEM-based linear inverse modeling using a 3D source array to image magma chambers with free geometry. Application to InSAR data from Rabaul Caldera (PNG).

    NASA Astrophysics Data System (ADS)

    Ronchin, Erika; Masterlark, Timothy; Dawson, John; Saunders, Steve; Martí Molist, Joan

    2015-04-01

    In this study, we present a method to fully integrate a family of finite element models (FEMs) into the regularized linear inversion of InSAR data collected at Rabaul caldera (PNG) between February 2007 and December 2010. During this period the caldera experienced a long-term steady subsidence that characterized surface movement both inside the caldera and outside, on its western side. The inversion is based on an array of FEM sources in the sense that the Green's function matrix is a library of forward numerical displacement solutions generated by the sources of an array common to all FEMs. Each entry of the library is the LOS surface displacement generated by injecting a unity mass of fluid, of known density and bulk modulus, into a different source cavity of the array for each FEM. By using FEMs, we are taking advantage of their capability of including topography and heterogeneous distribution of elastic material properties. All FEMs of the family share the same mesh in which only one source is activated at the time by removing the corresponding elements and applying the unity fluid flux. The domain therefore only needs to be discretized once. This precludes remeshing for each activated source, thus reducing computational requirements, often a downside of FEM-based inversions. Without imposing an a-priori source, the method allows us to identify, from a least-squares standpoint, a complex distribution of fluid flux (or change in pressure) with a 3D free geometry within the source array, as dictated by the data. The results of applying the proposed inversion to Rabaul InSAR data show a shallow magmatic system under the caldera made of two interconnected lobes located at the two opposite sides of the caldera. These lobes could be consistent with feeding reservoirs of the ongoing Tavuvur volcano eruption of andesitic products, on the eastern side, and of the past Vulcan volcano eruptions of more evolved materials, on the western side. The interconnection and

  15. Dynamic mixing in magma bodies - Theory, simulations, and implications

    NASA Technical Reports Server (NTRS)

    Oldenburg, Curtis M.; Spera, Frank J.; Yuen, David A.; Sewell, Granville

    1989-01-01

    The magma-mixing process is different from the mantle mixing process in that the mixing components of magma are dynamically active, with the melt density depending strongly on composition. This paper describes simulations of time-dependent variable-viscosity double-diffusive convection which were carried out to investigate quantitatively the mixing dynamics of magma in melt-dominated magma bodies. Results show that the dynamics of double-diffusive convection can impart complex patterns of composition, through time and space. The mixing time depends nonlinearly on many factors, including heat flux driving convection, the rate of diffusion of chemical species, the relative importance of thermal and chemical buoyancy, the viscosities of the mixing components, and the shape of the magma body.

  16. Wire chamber

    DOEpatents

    Atac, Muzaffer

    1989-01-01

    A wire chamber or proportional counter device, such as Geiger-Mueller tube or drift chamber, improved with a gas mixture providing a stable drift velocity while eliminating wire aging caused by prior art gas mixtures. The new gas mixture is comprised of equal parts argon and ethane gas and having approximately 0.25% isopropyl alcohol vapor.

  17. Evolution of large Venusian volcanoes: Insights from coupled models of lithospheric flexure and magma reservoir pressurization

    NASA Astrophysics Data System (ADS)

    Galgana, Gerald A.; McGovern, Patrick J.; Grosfils, Eric B.

    2011-03-01

    The growth and evolution of large volcanic edifices on Venus should reflect interactions between local magma reservoir-induced stresses and broader-scale stresses resulting from flexure of the lithosphere beneath the edifice load. Here, we explore the relationship between magma movement in the lithosphere and the flexural stress state via static, gravitationally loaded, axisymmetric finite element models. We find that reservoirs situated in the lower (extensional) lithosphere fail at the bottom and are therefore not viable long-term conduits for upward magma transport. Furthermore, for high-stress conditions (e.g., large edifices or thin lithospheres), chambers in the lowermost lithosphere exceed the failure criterion even before pressurization and are therefore unstable. In contrast, magma chambers located in the upper (compressional) lithosphere fail at or somewhat above the reservoir midsection, promoting lateral sill injection; continued failure in this mode would tend to produce oblate magma chambers with zones of intrusion at their margins. Reservoirs near the flexural neutral plane require the greatest overpressure to reach failure, emplacing cone sheets that transition to sills further from the chamber. The out-of-plane orientation of principal extensional stresses in the flexed lower lithosphere predicts the presence of radial dikes that are likely the main conduits for any subsequent magma ascent from the mantle melt source region. Our results also explain how the evolving stress state in the lithosphere tends to redirect magma passage over time: magma ascending into the lithosphere beneath the edifice is diverted to lateral sills in the upper lithosphere, inhibiting summit eruptions and possibly shifting eruption locations to the lower flanks at and beyond the distal margins of an oblate chamber or sill complex. We apply these results to interpret the observed structure and tectonism of Sapas Mons, Venus, in terms of flexurally controlled intrusive

  18. Focal Mechanisms for Local Earthquakes within a Rapidly Deforming Rhyolitic Magma System, Laguna del Maule, Chile

    NASA Astrophysics Data System (ADS)

    Peterson, D. E.; Keranen, K. M.; Cardona, C.; Thurber, C. H.; Singer, B. S.

    2015-12-01

    Large shallow rhyolitic magma systems like the one underlying the Laguna del Maule Volcanic Field (LdM) atop the Southern Andes, Chile, that comprises the largest concentration of rhyolitic lava and tephra younger than 20 ka at earth's surface, are capable of producing modest to very large explosive eruptions. Moreover, LdM is currently exhibiting magma migration, reservoir growth, and crustal deformation at rates higher than any volcano that is not actively erupting. The long-term build-up of a large silicic magmatic system toward an eruption has yet to be monitored, therefore, precursory phenomena are poorly understood. In January of 2015, 12 broadband, 3-component seismometers were installed at LdM to detect local microearthquakes and tele-seismic events with the goals of determining the migration paths of fluids as well as the boundaries of the magma chamber beneath LdM. These stations complement the 6 permanent stations installed by the Southern Andes Volcano Observatory in 2011. Focal mechanisms were calculated using FOCMEC (Snoke et al., 1984) and P-wave first motions for local events occurring between January and March of 2015 using these 18 broadband stations. Results from six of the largest local events indicate a mixture of normal and reverse faulting at shallow (<10 km) depths surrounding the lake. This may be associated with the opening of fractures to accommodate rising magma in the subsurface and/or stresses induced by the rapid deformation. Two of these events occurred near the center of maximum deformation where seismic swarms have previously been identified. Focal mechanisms from smaller magnitude events will be calculated to better delineate subsurface structure. Source mechanisms will be refined using P-S amplitude ratios and full waveform inversion.

  19. IONIZATION CHAMBER

    DOEpatents

    Redman, W.C.; Shonka, F.R.

    1958-02-18

    This patent describes a novel ionization chamber which is well suited to measuring the radioactivity of the various portions of a wire as the wire is moved at a uniform speed, in order to produce the neutron flux traverse pattern of a reactor in which the wire was previously exposed to neutron radiation. The ionization chamber of the present invention is characterized by the construction wherein the wire is passed through a tubular, straight electrode and radiation shielding material is disposed along the wire except at an intermediate, narrow area where the second electrode of the chamber is located.

  20. Method and apparatus for active control of combustion rate through modulation of heat transfer from the combustion chamber wall

    SciTech Connect

    Roberts, Jr., Charles E.; Chadwell, Christopher J.

    2004-09-21

    The flame propagation rate resulting from a combustion event in the combustion chamber of an internal combustion engine is controlled by modulation of the heat transfer from the combustion flame to the combustion chamber walls. In one embodiment, heat transfer from the combustion flame to the combustion chamber walls is mechanically modulated by a movable member that is inserted into, or withdrawn from, the combustion chamber thereby changing the shape of the combustion chamber and the combustion chamber wall surface area. In another embodiment, heat transfer from the combustion flame to the combustion chamber walls is modulated by cooling the surface of a portion of the combustion chamber wall that is in close proximity to the area of the combustion chamber where flame speed control is desired.

  1. Crustal Magma Evolution: the View from the Chemistry of Large Central Andean Ignimbrites

    NASA Astrophysics Data System (ADS)

    Kay, S. M.; Coira, B.

    2006-12-01

    Voluminous andesitic to rhyodacitic ignimbritic fields linked to giant calderas are distinctive features of the Neogene magmatic record of the central Andean Altiplano-Puna plateau. These magmas evolved in a thickened backarc crust of an active subduction regime at a compressional margin. Their chemistry reflects the thermo-mechanical conditions that control the generation of large crustal magma systems, and tracks changes in a crust subjected to thickening, flow and delamination. Correlations with high resolution geophysical images help to decipher magma generation and eruption processes. A compilation of some 400 published and new chemical analyses allows a view of the spatial-temporal crustal evolution of large complexes in the Puna (22° -28°S) over the last 12 Ma. Data are from the 11-10 Ma Granada and Pairique, 9 to 8 Ma Vilama, 6.8 to 6.5 Ma Coranzulí, 6.7-6.1 Ma Panizos, 5.3-4 Ma Toconao, 4.2-3.8 Ma Atana, and 1.3 Ma Purico complexes in the north, the 12-10 Ma Aguas Calientes complex in the central Puna and the 5.1-3.6 Ma Laguna Amarga/Verde and 6.4 2.2 Ma Cerro Galan complexes in the south. A notable older to younger chemical trend that is seen is for La/Yb (40 to 10) and Sm/Yb (7.5 to 2) ratios to decrease without a corresponding pattern in Eu anomalies. This trend suggests a change from garnet to amphibole as a controlling residual phase at depth followed by feldspar fractionation at higher levels, possibly in magmas chambers near 20 km imaged by seismic data. Xenocrysts in mafic andesitic lavas could be phenocrysts from magmas at this level. A correlated temporal change to lower Al/(K+Na+Ca) and ^8^7Sr/^86Sr ratios and increasing epsilon Nd in the northern Puna requires a changing source linked to an evolving crust. Other patterns are better linked to regional basement differences and variability in the mantle-derived mafic magmas that supply the heat for melting.

  2. Evolution of a Chemically Zoned Magma Body: Black Mountain Volcanic Center, southwestern Nevada

    NASA Astrophysics Data System (ADS)

    Vogel, Thomas A.; Noble, Donald C.; Younker, Leland W.

    1989-05-01

    Rocks of the Black Mountain volcanic center consist of four ash flow sheets and units of lava that underlie, interfinger with, and overlie the sheets. Rocks from the center represent three magma types. Magma type c was present through the history of the center, whereas types a and b were available after the eruption of the Rocket Wash Member, during the eruptions of the Pahute Mesa and Trail Ridge members. The magma types are defined by trace element ratios; for example, magma types a, b, and c have La/Th values of 1.0-3.5, >7.5, and 3.5-7.5. Silica contents in the magma types a, b, and c range from 71.5 to 74.1, from 65.8 to 69.2, and from 55.6 to 73.8 wt %, respectively. The stratigraphic distribution of chemically distinct pumice fragments within the ash flow sheets is used to show that magma type a was located in the uppermost part of the chamber and was underlain successively by magma types b and c. Because pumice fragments that belong to all three magma types occur in individual cooling units, a zoned magma body must have existed during this period. Magma mixing is indicated by the disequilibrium phenocrysts which are common in pumice fragments from all magma types; however, this mixing did not destroy the original zoning of the upper part of the magma body. Most of the chemical variation of magma type c is consistent with fractionation of feldspar, olivine, and pyroxene, but abundant disequilibrium, mafic phenocrysts indicate that magma replenishment and mixing were common. Magma type b had much higher La/Th and light rare earth element (LREE)/heavy rare earth element values and must have originated independently from magma type c. Most likely the two types were derived from different source material. The low La/Th values of magma type a can be explained by separation of a phenocryst assemblage containing both a LREE-bearing phase and zircon from either magma types b or c, or possibly by the partial melting of source material containing these phases.

  3. Magma heating by decompression-driven crystallization beneath andesite volcanoes.

    PubMed

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

    2006-09-01

    Explosive volcanic eruptions are driven by exsolution of H2O-rich vapour from silicic magma. Eruption dynamics involve a complex interplay between nucleation and growth of vapour bubbles and crystallization, generating highly nonlinear variation in the physical properties of magma as it ascends beneath a volcano. This makes explosive volcanism difficult to model and, ultimately, to predict. A key unknown is the temperature variation in magma rising through the sub-volcanic system, as it loses gas and crystallizes en route. Thermodynamic modelling of magma that degasses, but does not crystallize, indicates that both cooling and heating are possible. Hitherto it has not been possible to evaluate such alternatives because of the difficulty of tracking temperature variations in moving magma several kilometres below the surface. Here we extend recent work on glassy melt inclusions trapped in plagioclase crystals to develop a method for tracking pressure-temperature-crystallinity paths in magma beneath two active andesite volcanoes. We use dissolved H2O in melt inclusions to constrain the pressure of H2O at the time an inclusion became sealed, incompatible trace element concentrations to calculate the corresponding magma crystallinity and plagioclase-melt geothermometry to determine the temperature. These data are allied to ilmenite-magnetite geothermometry to show that the temperature of ascending magma increases by up to 100 degrees C, owing to the release of latent heat of crystallization. This heating can account for several common textural features of andesitic magmas, which might otherwise be erroneously attributed to pre-eruptive magma mixing.

  4. Magma heating by decompression-driven crystallization beneath andesite volcanoes.

    PubMed

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

    2006-09-01

    Explosive volcanic eruptions are driven by exsolution of H2O-rich vapour from silicic magma. Eruption dynamics involve a complex interplay between nucleation and growth of vapour bubbles and crystallization, generating highly nonlinear variation in the physical properties of magma as it ascends beneath a volcano. This makes explosive volcanism difficult to model and, ultimately, to predict. A key unknown is the temperature variation in magma rising through the sub-volcanic system, as it loses gas and crystallizes en route. Thermodynamic modelling of magma that degasses, but does not crystallize, indicates that both cooling and heating are possible. Hitherto it has not been possible to evaluate such alternatives because of the difficulty of tracking temperature variations in moving magma several kilometres below the surface. Here we extend recent work on glassy melt inclusions trapped in plagioclase crystals to develop a method for tracking pressure-temperature-crystallinity paths in magma beneath two active andesite volcanoes. We use dissolved H2O in melt inclusions to constrain the pressure of H2O at the time an inclusion became sealed, incompatible trace element concentrations to calculate the corresponding magma crystallinity and plagioclase-melt geothermometry to determine the temperature. These data are allied to ilmenite-magnetite geothermometry to show that the temperature of ascending magma increases by up to 100 degrees C, owing to the release of latent heat of crystallization. This heating can account for several common textural features of andesitic magmas, which might otherwise be erroneously attributed to pre-eruptive magma mixing. PMID:16957729

  5. Magma Migration Through the Continental Crust - 3-D Seismic and Thermo-mechanical Constraints on Sites of Crustal Contamination

    NASA Astrophysics Data System (ADS)

    Wilson, M.; Wheeler, W.

    2002-12-01

    Current understanding of the processes and pathways by which magma travels from its mantle source, through the crust to the Earth's surface is limited by the lack of continuously exposed sections through "fossil" magmatic systems. We report results from a 50 x 30 km 3-D seismic reflection survey of part of the Voring rifted continental margin of Norway which provide the first detailed images of an entire crustal magmatic plumbing system, from a Moho-level magma chamber, through complexes of sills and dykes in the mid to upper crust, to lavas and vent fields extruded at the early Tertiary paleosurface. The Voring margin of Norway formed during a period of Late Cretaceous to early Tertiary (Eocene) continental break-up when Greenland rifted away from Eurasia, resulting in the opening the NE Atlantic Ocean. Rifting was accompanied by widespread magmatic activity, inferred to be related to the impingement of the Iceland mantle plume on the base of the continental lithosphere. Regionally, magma migration occurred in at least two pulses: 62-59 Ma (main initial phase) and 57-54 Ma (continental break-up phase). Wide-angle seismic experiments indicate the presence of a laccolith-like "high-velocity body" (HVB) in the lower crust beneath most of the outer Voring Basin with P-wave velocities (Vp 7.1-7.4 km/s) characteristic of basaltic igneous rocks, overlying typical mantle rocks with Vp of over 8 km/s. The HVB locally reaches 8 km thickness and at break-up (54 Ma) measured 300 km x 500 km - corresponding to a volume of 450,000 cubic km of basaltic magma. It is interpreted as a magmatic underplate formed over a period of several million years as rising basaltic magmas ponded at the Moho at their level of neutral buoyancy. A laterally extensive sill complex (1000 m thick) occurs at the interface between thinned crystalline basement and the overlying Mesozoic sedimentary sequence. This is interpreted as one of the main intra-crustal magma storage reservoirs and is the most

  6. Interaction of model F-bearing silicic melt with chloride fluid, uraninite, and columbite at 750°C and 1000-2000 bar and its implications for estimation of the ore-forming capability of the upper crustal magma chamber beneath the Strel'tsovka caldera, eastern Transbaikalia

    NASA Astrophysics Data System (ADS)

    Redkin, A. F.; Velichkin, V. I.; Aleshin, A. P.; Borodulin, G. P.

    2009-08-01

    total uranium resources of the deposits localized in the Strel’tsovka caldera. Thus, the upper crustal silicic magma chamber hardly was a source of uranium for Mo-U deposits of the Strel’tsovka ore field.

  7. Regulatory, Land Ownership, and Water Availability Factors for a Magma Well: Long Valley Caldera and Coso Hot Springs, California

    SciTech Connect

    Blackett, Robert

    1985-09-01

    The U.S. Department of Energy is currently engaged in a program to demonstrate the engineering feasibility of extracting thermal energy from high-level molten magma bodies. The program is being carried out under the direction of Sandia National Laboratories where a number of individual projects support the overall program. The existing program elements include (1) high-temperature materials compatibility testing; (2) studies of properties of melts of various compositions; and (3) the investigation of the economics of a magma energy extraction system. Another element of the program is being conducted with the cooperation of the U.S. Geological Survey, and involves locating and outlining magma bodies at selected sites using various geophysical techniques. The ultimate goal here will be to define the limits of a magma body as a drilling target. During an earlier phase of the program, more than twenty candidate study sites considered were evaluated based upon: (1) the likelihood of the presence of a shallow magma chamber, (2) the accessibility of the site, and (3) physical and institutional constraints associated with each site with respect to performing long-term experiments. From these early phase activities, the number of candidate sites were eventually narrowed to just 2. The sites currently under consideration are Coso Hot Springs and the Long Valley caldera (Figure 1). This report describes certain attributes of these sites in order to help identify potential problems related to: (1) state and federal regulations pertaining to geothermal development; (2) land ownership; and (3) water resource availability. The information sources used in this study were mainly maps, publications, and informative documents gathered from the California Division of Oil and Gas and the U.S. Department of the Interior. Environmental studies completed for the entire Long Valley caldera study area, and for portions of the Coso Hot Springs study area were also used for reference.

  8. Geophysical observations of Kilauea Volcano, Hawaii, 2. Constraints on the magma supply during November 1975-September 1977

    USGS Publications Warehouse

    Dzurisin, D.; Anderson, L.A.; Eaton, G.P.; Koyanagi, R.Y.; Lipman, P.W.; Lockwood, J.P.; Okamura, R.T.; Puniwai, G.S.; Sako, M.K.; Yamashita, K.M.

    1980-01-01

    Following a 22-month hiatus in eruptive activity, Kilauea volcano extruded roughly 35 ?? 106 m3 of tholeiitic basalt from vents along its middle east rift zone during 13 September-1 October, 1977. The lengthy prelude to this eruption began with a magnitude 7.2 earthquake on 29 November, 1975, and included rapid summit deflation episodes in June, July, and August 1976 and February 1977. Synthesis of seismic, geodetic, gravimetric, and electrical self-potential observations suggests the following model for this atypical Kilauea eruptive cycle. Rapid summit deflation initiated by the November 1975 earthquake reflected substantial migration of magma from beneath the summit region of Kilauea into the east and southwest rift zones. Simultaneous leveling and microgravity observations suggest that 40-90 ?? 106 m3 of void space was created within the summit magma chamber as a result of the earthquake. If this volume was filled by magma from depth before the east rift zone intrusive event of June 1976, the average rate of supply was 6-13 ?? 106 m3/month, a rate that is consistent with the value of 9 ?? 106 m3/month suggested from observations of long-duration Kilauea eruptions. Essentially zero net vertical change was recorded at the summit during the 15-month period beginning with the June 1976 intrusion and ending with the September 1977 eruption. This fact suggests that most magma supplied from depth during this interval was eventually delivered to the east rift zone, at least in part during four rapid summit deflation episodes. Microearthquake epicenters migrated downrift to the middle east rift zone for the first time during the later stages of the February 1977 intrusion, an occurrence presumably reflecting movement of magma into the eventual eruptive zone. This observation was confirmed by tilt surveys in May 1977 that revealed a major inflation center roughly 30 km east of the summit in an area of anomalous steaming and forest kill first noted in March 1976. ?? 1980.

  9. Oxygen isotope study of the Long Valley magma system, California: isotope thermometry and convection in large silicic magma bodies

    NASA Astrophysics Data System (ADS)

    Bindeman, Ilya; Valley, John

    2002-07-01

    Products of voluminous pyroclastic eruptions with eruptive draw-down of several kilometers provide a snap-shot view of batholith-scale magma chambers, and quench pre-eruptive isotopic fractionations (i.e., temperatures) between minerals. We report analyses of oxygen isotope ratio in individual quartz phenocrysts and concentrates of magnetite, pyroxene, and zircon from individual pumice clasts of ignimbrite and fall units of caldera-forming 0.76 Ma Bishop Tuff (BT), pre-caldera Glass Mountain (2.1-0.78 Ma), and post-caldera rhyolites (0.65-0.04 Ma) to characterize the long-lived, batholith-scale magma chamber beneath Long Valley Caldera in California. Values of δ18O show a subtle 1‰ decrease from the oldest Glass Mountain lavas to the youngest post-caldera rhyolites. Older Glass Mountain lavas exhibit larger ( 1‰) variability of δ18O(quartz). The youngest domes of Glass Mountain are similar to BT in δ18O(quartz) values and reflect convective homogenization during formation of BT magma chamber surrounded by extremely heterogeneous country rocks (ranging from 2 to +29‰). Oxygen isotope thermometry of BT confirms a temperature gradient between "Late" (815 °C) and "Early" (715 °C) BT. The δ18O(quartz) values of "Early" and "Late" BT are +8.33 and 8.21‰, consistent with a constant δ18O(melt)=7.8+/-0.1‰ and 100 °C temperature difference. Zircon-melt saturation equilibria gives a similar temperature range. Values of δ18O(quartz) for different stratigraphic units of BT, and in pumice clasts ranging in pre-eruptive depths from 6 to 11 km (based on melt inclusions), and document vertical and lateral homogeneity of δ18O(melt). Worldwide, five other large-volume rhyolites, Lava Creek, Lower Bandelier, Fish Canyon, Cerro Galan, and Toba, exhibit equal δ18O(melt) values of earlier and later erupted portions in each of the these climactic caldera-forming eruptions. We interpret the large-scale δ18O homogeneity of BT and other large magma chambers as evidence

  10. The rheology of crystal-rich magmas (Kuno Award Lecture)

    NASA Astrophysics Data System (ADS)

    Huber, Christian; Aldin Faroughi, Salah; Degruyter, Wim

    2016-04-01

    of dispersion of the magma (change in the state variables caused by either shear localization or crystal breakage). We argue that the model we propose is a first step to go beyond fitting experimental data and towards building a predictive rheology model for crystal-bearing magmas. Cooper, K.M., and Kent, A.J.R. (2014) Rapid remobilization of magmatic crystals kept in cold storage. Nature, 506(7489), 480-483. Dufek, J., and Bachmann, O. (2010) Quantum magmatism: Magmatic compositional gaps generated by melt-crystal dynamics. Geology, 38(8), 687-690. Huber, C., Bachmann, O., and Manga, M. (2009) Homogenization processes in silicic magma chambers by stirring and mushification (latent heat buffering). Earth and Planetary Science Letters, 283(1-4), 38-47.

  11. Io: Loki Patera as a Magma Sea

    NASA Technical Reports Server (NTRS)

    Matson, Dennis L.; Davies, Ashley Gerard; Veeder, Glenn J.; Rathbun, Julie A.; Johnson, Torrence V.; Castillo, Julie C.

    2006-01-01

    We develop a physical model for Loki Patera as a magma sea. We calculate the total volume of magma moving through the Loki Patera volcanic system every resurfacing cycle (approx.540 days) and the resulting variation in thermal emission. The rate of magma solidification at times reaches 3 x 10(exp 6) kg per second, with a total solidified volume averaging 100 cu km per year. A simulation of gas physical chemistry evolution yields the crust porosity profile and the timescale when it will become dense enough to founder in a manner consistent with observations. The Loki Patera surface temperature distribution shows that different areas are at different life cycle stages. On a regional scale, however, there can be coordinated activity, indicated by the wave of thermal change which progresses from Loki Patera's SW quadrant toward the NE at a rate of approx.1 km per day. Using the observed surface temperature distribution, we test several mechanisms for resurfacing Loki Patera, finding that resurfacing with lava flows is not realistic. Only the crustal foundering process is consistent with observations. These tests also discovered that sinking crust has a 'heat deficit' which promotes the solidification of additional magma onto the sinking plate ("bulking up"). In the limiting case, the mass of sinking material can increase to a mass of approx.3 times that of the foundering plate. With all this solid matter sinking, there is a compensating upward motion in the liquid magma. This can be in excess of 2 m per year. In this manner, solid-liquid convection is occurring in the sea.

  12. Search for α-Cluster Structure in Exotic Nuclei with the Prototype Active-Target Time-Projection Chamber

    NASA Astrophysics Data System (ADS)

    Fritsch, A.; Ayyad, Y.; Bazin, D.; Beceiro-Novo, S.; Bradt, J.; Carpenter, L.; Cortesi, M.; Mittig, W.; Suzuki, D.; Ahn, T.; Kolata, J. J.; Becchetti, F. D.; Howard, A. M.

    2016-03-01

    Some exotic nuclei appear to exhibit α-cluster structure. While various theoretical models currently describe such clustering, more experimental data are needed to constrain model predictions. The Prototype Active-Target Time-Projection Chamber (PAT-TPC) has low-energy thresholds for charged-particle decay and a high luminosity due to its thick gaseous active target volume, making it well-suited to search for low-energy α-cluster reactions. Radioactive-ion beams produced by the TwinSol facility at the University of Notre Dame were delivered to the PAT-TPC to study nuclei including 14C and 14O via α-resonant scattering. Differential cross sections and excitation functions were measured. Preliminary results from our recent experiments will be presented. This work is supported by the U.S. National Science Foundation.

  13. Degassing of the 1912 Katmai magmas

    NASA Astrophysics Data System (ADS)

    Westrich, H. R.; Eichelberger, J. C.; Hervig, R. L.

    1991-08-01

    Pre- and post-eruptive H2O, F, Cl, and S contents of the three 1912 Katmai magmas were inferred from analyses of melt inclusions and matrix glasses in tephra samples. With increasing silica content (andesite⇒rhyolite), pre-emptive melt H2O increases from ≥1.0 to 3.8 wt.%, Cl increases slightly from 1700 to 1900 ppm, S decreases from 170 to ≤65 ppm, and F remains constant at 550 ppm. These variations are not consistent with a simple crystal fractionation relationship. For plausible chamber depths, the magmas were vapor undersaturated during storage and fragmented during the last few hundred meters of ascent, consistent with geologic evidence for excavation of the vent funnel within the upper 1 km. Vitrophyres of welded intravent fallback tephra ejected late in the eruption show that extensive degassing and complete welding could take place in less than the 60-hour eruptive period. Release of HCl was twice that of the 1980 eruption of Mount St. Helens while H2SO4 output was comparable to that of the 3.5 ka Santorini eruption. Significant retention of Cl and F, which would be released along with residual H2O during high-temperature devitrification, may explain the important vapor transport that occurred in the Valley of Ten Thousand Smokes fumaroles following emplacement of the ignimbrite.

  14. Magma Beneath Yellowstone National park.

    PubMed

    Eaton, G P; Christiansen, R L; Iyer, H M; Pitt, A D; Mabey, D R; Blank, H R; Zietz, I; Gettings, M E

    1975-05-23

    The Yellowstone plateau volcanic field is less than 2 million years old, lies in a region of intense tectonic and hydrothermal activity, and probably has the potential for further volcanic activity. The youngest of three volcanic cycles in the field climaxed 600,000 years ago with a voluminous ashflow eruption and the collapse of two contiguous cauldron blocks. Doming 150,000 years ago, followed by voluminous rhyolitic extrusions as recently as 70,000 years ago, and high convective heat flow at present indicate that the latest phase of volcanism may represent a new magmatic insurgence. These observations, coupled with (i) localized postglacial arcuate faulting beyond the northeast margin of the Yellowstone caldera, (ii) a major gravity low with steep bounding gradients and an amplitude regionally atypical for the elevation of the plateau, (iii) an aeromagnetic low reflecting extensive hydrothermal alteration and possibly indicating the presence of shallow material above its Curie temperature, (iv) only minor shallow seismicity within the caldera (in contrast to a high level of activity in some areas immediately outside), (v) attenuation and change of character of seismic waves crossing the caldera area, and (vi) a strong azimuthal pattern of teleseismic P-wave delays, strongly suggest that a body composed at least partly of magma underlies the region of the rhyolite plateau, including the Tertiary volcanics immediately to its northeast. The Yellowstone field represents the active end of a system of similar volcanic foci that has migrated progressively northeastward for 15 million years along the trace of the eastern Snake River Plain (8). Regional aeromagnetic patterns suggest that this course was guided by the structure of the Precambrian basement. If, as suggested by several investigators (24), the Yellowstone magma body marks a contemporary deep mantle plume, this plume, in its motion relative to the North American plate, would appear to be "navigating" along a

  15. Magma Beneath Yellowstone National park.

    PubMed

    Eaton, G P; Christiansen, R L; Iyer, H M; Pitt, A D; Mabey, D R; Blank, H R; Zietz, I; Gettings, M E

    1975-05-23

    The Yellowstone plateau volcanic field is less than 2 million years old, lies in a region of intense tectonic and hydrothermal activity, and probably has the potential for further volcanic activity. The youngest of three volcanic cycles in the field climaxed 600,000 years ago with a voluminous ashflow eruption and the collapse of two contiguous cauldron blocks. Doming 150,000 years ago, followed by voluminous rhyolitic extrusions as recently as 70,000 years ago, and high convective heat flow at present indicate that the latest phase of volcanism may represent a new magmatic insurgence. These observations, coupled with (i) localized postglacial arcuate faulting beyond the northeast margin of the Yellowstone caldera, (ii) a major gravity low with steep bounding gradients and an amplitude regionally atypical for the elevation of the plateau, (iii) an aeromagnetic low reflecting extensive hydrothermal alteration and possibly indicating the presence of shallow material above its Curie temperature, (iv) only minor shallow seismicity within the caldera (in contrast to a high level of activity in some areas immediately outside), (v) attenuation and change of character of seismic waves crossing the caldera area, and (vi) a strong azimuthal pattern of teleseismic P-wave delays, strongly suggest that a body composed at least partly of magma underlies the region of the rhyolite plateau, including the Tertiary volcanics immediately to its northeast. The Yellowstone field represents the active end of a system of similar volcanic foci that has migrated progressively northeastward for 15 million years along the trace of the eastern Snake River Plain (8). Regional aeromagnetic patterns suggest that this course was guided by the structure of the Precambrian basement. If, as suggested by several investigators (24), the Yellowstone magma body marks a contemporary deep mantle plume, this plume, in its motion relative to the North American plate, would appear to be "navigating" along a

  16. Magma beneath Yellowstone National Park

    USGS Publications Warehouse

    Eaton, G.P.; Christiansen, R.L.; Iyer, H.M.; Pitt, A.M.; Mabey, D.R.; Blank, H.R.; Zietz, I.; Gettings, M.E.

    1975-01-01

    The Yellowstone plateau volcanic field is less than 2 million years old, lies in a region of intense tectonic and hydrothermal activity, and probably has the potential for further volcanic activity. The youngest of three volcanic cycles in the field climaxed 600,000 years ago with a voluminous ashflow eruption and the collapse of two contiguous cauldron blocks. Doming 150,000 years ago, followed by voluminous rhyolitic extrusions as recently as 70,000 years ago, and high convective heat flow at present indicate that the latest phase of volcanism may represent a new magmatic insurgence. These observations, coupled with (i) localized postglacial arcuate faulting beyond the northeast margin of the Yellowstone caldera, (ii) a major gravity low with steep bounding gradients and an amplitude regionally atypical for the elevation of the plateau, (iii) an aeromagnetic low reflecting extensive hydrothermal alteration and possibly indicating the presence of shallow material above its Curie temperature, (iv) only minor shallow seismicity within the caldera (in contrast to a high level of activity in some areas immediately outside), (v) attenuation and change of character of seismic waves crossing the caldera area, and (vi) a strong azimuthal pattern of teleseismic P-wave delays, strongly suggest that a body composed at least partly of magma underlies the region of the rhyolite plateau, including the Tertiary volcanics immediately to its northeast. The Yellowstone field represents the active end of a system of similar volcanic foci that has migrated progressively northeastward for 15 million years along the trace of the eastern Snake River Plain (8). Regional aeromagnetic patterns suggest that this course was guided by the structure of the Precambrian basement. If, as suggested by several investigators (24), the Yellowstone magma body marks a contemporary deep mantle plume, this plume, in its motion relative to the North American plate, would appear to be "navigating" along a

  17. Ionization chamber

    DOEpatents

    Walenta, Albert H.

    1981-01-01

    An ionization chamber has separate drift and detection regions electrically isolated from each other by a fine wire grid. A relatively weak electric field can be maintained in the drift region when the grid and another electrode in the chamber are connected to a high voltage source. A much stronger electric field can be provided in the detection region by connecting wire electrodes therein to another high voltage source. The detection region can thus be operated in a proportional mode when a suitable gas is contained in the chamber. High resolution output pulse waveforms are provided across a resistor connected to the detection region anode, after ionizing radiation enters the drift region and ionize the gas.

  18. Ionization chamber

    DOEpatents

    Walenta, A.H.

    An ionization chamber is described which has separate drift and detection regions electrically isolated from each other by a fine wire grid. A relatively weak electric field can be maintained in the drift region when the grid and another electrode in the chamber are connected to a high voltage source. A much stronger electric field can be provided in the detection region by connecting wire electrodes therein to another high voltage source. The detection region can thus be operated in a proportional mode when a suitable gas is contained in the chamber. High resolution output pulse waveforms are provided across a resistor connected to the detection region anode, after ionizing radiation enters the drift region and ionizes the gas.

  19. The intrusion of new magma triggered the 2011-2012 unrest at Santorini: evidence from noble-gas isotopes

    NASA Astrophysics Data System (ADS)

    Rizzo, A.; Barberi, F.; Carapezza, M.; Di Piazza, A.; Francalanci, L.; Sortino, F.; D'Alessandro, W.

    2013-12-01

    Santorini is one of the most famous active volcanoes of the world for its catastrophic explosive eruption that occurred during the Minoan civilization. Since then the Kameni eruptive centers that formed within the caldera erupted repeatedly until 1950. In 2011-2012 the volcano has been characterized by a seismic unrest, that was unprecedented at Santorini at least since the 1950 eruption, and that led to fear for an imminent eruption. Because more than 100,000 visitors are present on the island during the tourist season, and considering the eruptive potential of Santorini, it is crucial to evaluate the hazard of this volcano, which depends on the type of magma actually present in the volcanic system. With the aim to address this question, this research shows the first comparison between noble-gas isotope composition of the present fumarolic gases with that of fluid inclusions hosted in enclaves contained in the 1570 and 1925 AD dacitic magmas erupted at Nea Kameni. These enclaves are a portion of mafic magma batches that replenished the shallow chamber of the plumbing system hosting cooler and more silicic melts. Their Sr-Nd isotope ratios are quite similar to those measured in the host dacitic rocks, implying a common parental magma. Therefore, the analyzed enclaves may be considered representative of the historic magma erupted at Nea Kameni which could be still present in the volcano plumbing system feeding the crater fumaroles. The 3He/4He ratios of enclaves, once corrected for air contamination (3.1-3.6 Ra), partially overlap those of the gases (3.5-4.0 Ra) collected from Nea and Palea Kameni. The range of 3He/4He ratios (3.1-4.0 Ra) is appreciably lower than typical arc volcanoes (R/Ra ~7-8), implying that a contamination by 4He-rich fluids occurred either directly in the mantle and/or in the plumbing system. Comparison of 3He/4He and 4He/40Ar* ratios measured in enclaves with those of gases, as well as long-term monitoring of R/Ra in the latters, coherently

  20. Pyroclast texture and chemical composition of the 2007-2008 explosive eruption at Oldoinyo Lengai, Tanzania: Evidence for magma mixing

    NASA Astrophysics Data System (ADS)

    Bosshard, S. A.; Mattsson, H. B.

    2012-12-01

    The last explosive eruption of Oldoinyo Lengai in northern Tanzania started on the night from the 3rd to 4th September 2007 and lasted until April 2008. This eruption terminated 25 years of effusive natrocarbonatitic activity and was at times highly explosive with an eruption plume that reached up to 15 km into the atmosphere. We sampled tephra fallout on September 7th (i.e. on the third day of eruption) with additional samples from the 24th. During fieldwork in May 2011 we measured 140 profiles for their dominating grain size and collected representative samples. The tephra layers show variable grain-sizes from fine ash (< 1mm) to fine lapilli (2-30 mm). Most locations revealed three distinct layers with different dominating grain sizes, but especially on the western flank of the volcano, where the tephra deposits were thicker overall (due to the wind direction during the eruption), up to seven layers with alternating grain-sizes were visible. All pyroclasts are well-rounded with euhedral silicate minerals (commonly nepheline, pyroxene, garnet, wollastonite) in the center, surrounded by a moderately vesiculated melt film. The first tephra fallout contains variable amounts of silicate fragments, natrocarbonatite droplets and a mixture between the two magmas. These deposits are interpreted to reflect incomplete mixing between a natrocarbonatitic and a nephelinitic magma. Tephra collected two weeks later (24th September 2007) have a composition that is consistent with being a hybrid between a nephelinite and a natrocarbonatite. The natrocarbonatitic magma is completely assimilated into the new hybrid magma (tephra of natrocarbonatitic composition is no longer observed). It has previously been suggested that CO2, which exsolved from the natrocarbonatite melt during mixing with more silicic, nephelinitic melt is the driving force for these violent explosive, mixed eruptions. Our data support this hypothesis based on CO2 content, which decreases towards the end of the

  1. Genesis of basalt magmas and their derivatives under the Izu Islands, Japan, inferred from Sr/Ca-Ba/Ca systematics

    NASA Astrophysics Data System (ADS)

    Onuma, Naoki; Hirano, Masataka; Isshiki, Naoki

    1983-10-01

    The Sr/Ca-Ba/Ca systematics defined for a series of volcanic rocks provided by volcanoes of the Izu Islands, Japan, have cast a new light on the origin and evolution of basalt magmas and their derivatives: (1) The mantle material in the source region of primary basalt magmas beneath the Izu Islands shows a chondritic value of Sr/Ca and Ba/Ca ratios. (2) Both the tholeiite magma and the high-alumina/calc-alkali basalt magma are primary with higher degrees (15-20% for the former) and lower degrees (8-11% for the latter) of partial melting of a common mantle material. (3) The primary basalt magmas evolve independently via crystal fractionation process in respective magma chambers at shallower depths each providing a series of andesite and dacite magmas corresponding to respective primary basalt magmas. (4) The crystal fractionation process in magma chamber is controlled mainly by plagioclase and clinopyroxene crystallization in terms of the alkaline earth elements. The plagioclase/clinopyroxene ratio decreases during crystal fractionation process. The chemical environments of magma chambers are similar to each other in the tholeiite series and in the high-alumina basalt/calc-alkali rock series. (5) The end products provided by the crystal fractionation process lie within Bowen's petrogeny's residua system, making a thin, silicic crust under the volcanic islands near the Izu Peninsula. The calc-alkali rhyolites in these islands are derived from the thin silicic crust via melting process by the heat of intruded primary basalt magmas. (6) The regional distribution of degree of partial melting indicates variations from 15 to 20% along the volcanic front and from 8 to 11% in the region behind it. The fact suggests that an interaction between the mantle wedge under the Philippine Sea Plate and the subducting slab of the Pacific Plate beneath the Izu Islands is different from place to place, with respect to temperature distribution and/or water supply from the subducting

  2. Crustal Assimilation and Magma Recharge in the Recent Mt. Etna Magma Plumbing System: Evidence from In Situ Plagioclase Textural and Compositional Data

    NASA Astrophysics Data System (ADS)

    Pitcher, B. W.; Bohrson, W. A.; Viccaro, M.

    2011-12-01

    Mt. Etna is Europe's largest and most active volcano, and as a result of its proximity to populated areas, understanding the structure of its magma plumbing system and the nature of its magmatic processes is essential for better predicting eruptive hazards. The aim of this study is to document core to rim textural, chemical, and isotopic variations in plagioclase, in order to investigate the physical characteristics of the subvolcanic magma system and processes by which magmas evolve. Nomarski Differential Interference Contrast (NDIC) imaging was used to characterize the complex textures of plagioclase crystals in six trachybasaltic samples from eruption years 1974, 1981, 2001, and 2004. Approximately 30 NDIC images per sample revealed 6 textural categories defined by combinations of monotonous, oscillatory, sieve, and patchy zoning. Core to rim electron microprobe analyses carried out at distinct textural boundaries revealed variable anorthite (An) (mol %) values ranging from 92 to 44. In most phenocrysts, An decreases non-monotonically from core to rim, and simple correlations among An, FeO (wt. %), textural type, and eruption year are lacking, indicating intricate crystallization histories that likely reflect changing magma chamber conditions. Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICPMS) 87Sr/86Sr analyses were performed on cores and rims of selected crystals from each textural type within each sample. Phenocryst 87Sr/86Sr values ranged from ~0.70300 to 0.70370 (±.00002), and were significantly lower than preliminary groundmass 87Sr/86Sr values, which ranged from ~0.70466 to 0.70498. Whole-rock 87Sr/86Sr values are between groundmass and crystal values. The Δ87Sr/86Sr within each crystal, defined as rim minus core, varied from -0.00030 to +0.00011; while most crystals exhibit a core to rim increase, some showed a decrease and some had constant 87Sr/86Sr. The prevalence of core to rim increases, combined with whole rock and preliminary

  3. Tracking dynamics of magma migration in open-conduit systems

    NASA Astrophysics Data System (ADS)

    Valade, Sébastien; Lacanna, Giorgio; Coppola, Diego; Laiolo, Marco; Pistolesi, Marco; Donne, Dario Delle; Genco, Riccardo; Marchetti, Emanuele; Ulivieri, Giacomo; Allocca, Carmine; Cigolini, Corrado; Nishimura, Takeshi; Poggi, Pasquale; Ripepe, Maurizio

    2016-11-01

    Open-conduit volcanic systems are typically characterized by unsealed volcanic conduits feeding permanent or quasi-permanent volcanic activity. This persistent activity limits our ability to read changes in the monitored parameters, making the assessment of possible eruptive crises more difficult. We show how an integrated approach to monitoring can solve this problem, opening a new way to data interpretation. The increasing rate of explosive transients, tremor amplitude, thermal emissions of ejected tephra, and rise of the very-long-period (VLP) seismic source towards the surface are interpreted as indicating an upward migration of the magma column in response to an increased magma input rate. During the 2014 flank eruption of Stromboli, this magma input preceded the effusive eruption by several months. When the new lateral effusive vent opened on the Sciara del Fuoco slope, the effusion was accompanied by a large ground deflation, a deepening of the VLP seismic source, and the cessation of summit explosive activity. Such observations suggest the drainage of a superficial magma reservoir confined between the crater terrace and the effusive vent. We show how this model successfully reproduces the measured rate of effusion, the observed rate of ground deflation, and the deepening of the VLP seismic source. This study also demonstrates the ability of the geophysical network to detect superficial magma recharge within an open-conduit system and to track magma drainage during the effusive crisis, with a great impact on hazard assessment.

  4. Magma storage under Iceland's Eastern Volcanic Zone

    NASA Astrophysics Data System (ADS)

    Maclennan, J.; Neave, D.; Hartley, M. E.; Edmonds, M.; Thordarson, T.; Morgan, D. J.

    2014-12-01

    The Eastern Volcanic Zone (EVZ) of Iceland is defined by a number of volcanic systems and large basaltic eruptions occur both through central volcanoes (e.g. Grímsvötn) and on associated fissure rows (e.g. Laki, Eldgjá). We have collected a large quantity of micro-analytical data from a number of EVZ eruptions, with the aim of identifying common processes that occur in the premonitory stages of significant volcanic events. Here, we focus on the AD 1783 Laki event, the early postglacial Saksunarvatn tephra and the sub-glacially erupted Skuggafjöll tindar and for each of these eruptions we have >100 olivine-hosted or plagioclase-hosted melt inclusion analyses for major, trace and volatile elements. These large datasets are vital for understanding the history of melt evolution in the plumbing system of basaltic volcanoes. Diverse trace element compositions in melt inclusions hosted in primitive macrocrysts (i.e. Fo>84, An>84) indicate that the mantle melts supplied to the plumbing system of EVZ eruptions are highly variable in composition. Concurrent mixing and crystallisation of these melts occurs in crustal magma bodies. The levels of the deepest of these magma bodies are not well constrained by EVZ petrology, with only a handful of high-CO2 melt inclusions from Laki providing evidence for magma supply from >5 kbar. In contrast, the volatile contents of melt inclusions in evolved macrocrysts, which are close to equilibrium with the carrier liquids, indicate that final depths of inclusion entrapment are 0.5-2 kbar. The major element composition of the matrix glasses shows that the final pressure of equilibration between the melt and its macrocryst phases also occurred at 0.5-2 kbar. The relationship between these pressures and seismic/geodetic estimates of chamber depths needs to be carefully evaluated. The melt inclusion and macrocryst compositional record indicates that injection of porphyritic, gas-rich primitive melt into evolved/enriched and degassed shallow

  5. The Topopah Spring Tuff: Evidence for dynamic withdrawal from a layered magma body

    SciTech Connect

    Schuraytz, B.C.; Vogel, T.A.; Younker, L.W.

    1987-08-15

    The Topopah Spring Tuff is a classic example of a compositionally zoned ash-flow sheet resulting from eruption of a compositionally zoned magma body. Geochemical and petrographic analyses of whole-rock tuff samples indicate that the base of the ash-flow sheet and the dominant volume of erupted material consist of crystal-poor high-silica rhyolite, with a gradational transition into overlying crystal-rich quartz latite. Major and trace element analyses of glassy pumices and microprobe analyses of their oxide and silicate phenocrysts provide closer approximations to the chemical and thermal gradients within the magma body. The gradients inferred from these data indicate that the transition from high-silica rhyolitic to quartz latitic magma was abrupt, rather than gradational, with a distinct liquid-liquid interface separating the contrasting magmas. Observations are consistent with fluid dynamic models in which the angular velocity field developed near the entrance region of the vents results in simultaneous withdrawal of magma from a continually greater lateral and vertical extent within the chamber. The abrupt transition to chemically variable pumices, dominated by those of quartz latitic composition, implies that the interface between the magma layers remained relatively stable until drawdown breached the interface and preferentially erupted higher temperature, more mafic magma along with subordinate amounts of the incompletely exhausted high-silica rhyolitic magma.

  6. Long-period (12sec) Volcanic Tremor Observed at Usu 2000 Eruption: Seismological Detection of a Deep Magma Plumbing system

    NASA Astrophysics Data System (ADS)

    KAWAKATSU, H.; YAMAMOTO, M.

    2001-12-01

    Mt. Usu is a dacitic stratovolcano located in southwestern Hokkaido, Japan, and has erupted repeatedly (in 1910, 1943-45, and 1977-78). In the end of March 2000, after twenty some years of quiescence, Usu volcano began its activity with an intensive earthquake swarm. After several days of the earthquake swarm, on March 31, 2000, the eruption began at the northwest foot of the volcano. We have installed five broadband seismometers around the volcano, and detected long period (12 sec) tremors (hereafter called LPTs) which are continually emitted from the volcano. Although these LPTs are continually observed at an interval of a few minutes, there exist no corresponding surface activities such as eruptions. The source of these LPTs are located relatively deep at a depth of 5 km, and their amplitude variation well correlates with the uplift rate of the eruption area. We thus attribute these LPTs to the flow induced vibration of a magma chamber and its outlet located around the source region of the LPTs. The estimated moment tensor for LPTs shows a reversed polarity for the isotropic and CLVD components. This is consistent with a combination of a deflating spherical source and an inflating crack which opens northwestern direction toward the eruption site. The volumetric magma flow rate may be estimated from the observed RMS amplitude of LPT through a seismic moment rate, and turns out to be around 3*E5 m3 per day. Geodetic observations report the volume change of the order of 107 m3 within the first few days. It appears that the volume flow rate estimated from LPTs is about one order of magnitude smaller than that of the actual flow rate. This may be reasonable if we consider that through seismic waves we are observing a fluctuating part of the magma flow. This may be the first seismological detection of dynamics of a main magma plumbing system beneath volcanos directly related to eruption activities.

  7. Melt inclusion evidence of second immiscibility within a magma derived non-silicate phase (Mt Vesuvius)

    NASA Astrophysics Data System (ADS)

    Fulignati, P.; Kamenetsky, V.; Marianelli, P.; Sbrana, A.

    2003-04-01

    Processes of melt immiscibility occurring during late magmatic differentiation play important role in the generation of many magmatic-hydrothermal ore deposits and may activate and control the style of volcanic eruptions. The exsolution of a non-silicate, volatile-rich phase from the phonolitic magma occurred at the peripheral parts of the 79AD Vesuvius magma chamber. The results of our work suggest that this immiscible phase can further experience another unmixing event that occurs in essentially "post-magmatic" environment. Heating/cooling experiments were carried out on the cogenetic multiphase (clear daughter crystals + vapour bubble(s) + interstial liquid) inclusions, hosted in K-feldspar of cognate felsic xenoliths, representative of rocks in the peripheral parts of the magma chamber. During heating, solid phases begin to dissolve at about 150^oC and melt completely at 530^oC. These low temperatures of melting argue for a non-silicate composition of daughter minerals, and thus bulk inclusion content. The remaining vapour bubble dissolves at 880^oC. During subsequent cooling, vapour bubble nucleates at 785^oC and increases in size. Unmixing of at least two melt phases occurs instantaneously at 500^oC in all studied inclusions. Globules of one melt float freely in the matrix of another melt, change their shape and size, coalesce and split apart continuously down to 100--150^oC. The movements of globules slow down with decreasing temperature until final solidification at 40--50^oC. The similarity of observed phase transformations inside inclusions suggests their homogeneous trapping at magmatic temperatures. By analogy with results of the study of xenoliths from the Vesuvius 472AD eruption (Fulignati et al., 2001) we interpret unmixed phases as globules of the Na-K chloride melt set in the matrix of Ca-carbonate melt. We infer that immiscibility between low viscosity, highly fugitive non-silicate melts may significantly influence partitioning of metals

  8. Anti-HIV-1 activity of flavonoid myricetin on HIV-1 infection in a dual-chamber in vitro model.

    PubMed

    Pasetto, Silvana; Pardi, Vanessa; Murata, Ramiro Mendonça

    2014-01-01

    HIV infection by sexual transmission remains an enormous global health concern. More than 1 million new infections among women occur annually. Microbicides represent a promising prevention strategy that women can easily control. Among emerging therapies, natural small molecules such as flavonoids are an important source of new active substances. In this study we report the in vitro cytotoxicity and anti-HIV-1 and microbicide activity of the following flavonoids: Myricetin, Quercetin and Pinocembrin. Cytotoxicity tests were conducted on TZM-bl, HeLa, PBMC, and H9 cell cultures using 0.01-100 µM concentrations. Myricetin presented the lowest toxic effect, with Quercetin and Pinocembrin relatively more toxic. The anti-HIV-1 activity was tested with TZM-bl cell plus HIV-1 BaL (R5 tropic), H9 and PBMC cells plus HIV-1 MN (X4 tropic), and the dual tropic (X4R5) HIV-1 89.6. All flavonoids showed anti-HIV activity, although Myricetin was more effective than Quercetin or Pinocembrin. In TZM-bl cells, Myricetin inhibited ≥90% of HIV-1 BaL infection. The results were confirmed by quantification of HIV-1 p24 antigen in supernatant from H9 and PBMC cells following flavonoid treatment. In H9 and PBMC cells infected by HIV-1 MN and HIV-1 89.6, Myricetin showed more than 80% anti-HIV activity. Quercetin and Pinocembrin presented modest anti-HIV activity in all experiments. Myricetin activity was tested against HIV-RT and inhibited the enzyme by 49%. Microbicide activities were evaluated using a dual-chamber female genital tract model. In the in vitro microbicide activity model, Myricetin showed promising results against different strains of HIV-1 while also showing insignificant cytotoxic effects. Further studies of Myricetin should be performed to identify its molecular targets in order to provide a solid biological foundation for translational research.

  9. Anti-HIV-1 Activity of Flavonoid Myricetin on HIV-1 Infection in a Dual-Chamber In Vitro Model

    PubMed Central

    Pasetto, Silvana; Pardi, Vanessa; Murata, Ramiro Mendonça

    2014-01-01

    HIV infection by sexual transmission remains an enormous global health concern. More than 1 million new infections among women occur annually. Microbicides represent a promising prevention strategy that women can easily control. Among emerging therapies, natural small molecules such as flavonoids are an important source of new active substances. In this study we report the in vitro cytotoxicity and anti-HIV-1 and microbicide activity of the following flavonoids: Myricetin, Quercetin and Pinocembrin. Cytotoxicity tests were conducted on TZM-bl, HeLa, PBMC, and H9 cell cultures using 0.01–100 µM concentrations. Myricetin presented the lowest toxic effect, with Quercetin and Pinocembrin relatively more toxic. The anti-HIV-1 activity was tested with TZM-bl cell plus HIV-1 BaL (R5 tropic), H9 and PBMC cells plus HIV-1 MN (X4 tropic), and the dual tropic (X4R5) HIV-1 89.6. All flavonoids showed anti-HIV activity, although Myricetin was more effective than Quercetin or Pinocembrin. In TZM-bl cells, Myricetin inhibited ≥90% of HIV-1 BaL infection. The results were confirmed by quantification of HIV-1 p24 antigen in supernatant from H9 and PBMC cells following flavonoid treatment. In H9 and PBMC cells infected by HIV-1 MN and HIV-1 89.6, Myricetin showed more than 80% anti-HIV activity. Quercetin and Pinocembrin presented modest anti-HIV activity in all experiments. Myricetin activity was tested against HIV-RT and inhibited the enzyme by 49%. Microbicide activities were evaluated using a dual-chamber female genital tract model. In the in vitro microbicide activity model, Myricetin showed promising results against different strains of HIV-1 while also showing insignificant cytotoxic effects. Further studies of Myricetin should be performed to identify its molecular targets in order to provide a solid biological foundation for translational research. PMID:25546350

  10. Giant plagioclase growth during storage of basaltic magma in Emeishan Large Igneous Province, SW China

    NASA Astrophysics Data System (ADS)

    Cheng, Li-Lu; Yang, Zong-Feng; Zeng, Ling; Wang, Yu; Luo, Zhao-Hua

    2014-02-01

    Giant plagioclase basalts (GPBs) reflect the storage of flood basalt magma in subvolcanic magma chambers at crustal depths. In this study of the Late Permian Emeishan large igneous province in southwest China, we focus on understanding the plumbing system and ascent of large-volume basaltic magma. We report a quantitative textural analysis and bulk-rock geochemical composition of clustered touching crystals (CT-type) and single isolated crystal (SI-type) GPB samples from 5- to 240-m-thick flows in the Daqiao section. Both types of GPBs are evolved (<6 MgO wt%), but have high Ti/Y ratios (>500) and high total FeO content (11.5-15.2 wt%). The mineral chemistry of the two types of plagioclase displays a small range of anorthite content (<5 mol%), which is consistent with their unzoned characteristics. The two types of GPBs have S-type crystal size distributions but have quite different slopes, intercepts, and characteristic lengths. The characteristic lengths of the five flows are 1.54, 2.99, 1.70, 3.22, and 1.86 mm, respectively. For plagioclase growth rates of 10-11 to 10-10 mm/s, steady-state magma chamber models with simple continuous crystal growth suggest that CT-type plagioclase megacrysts have the residence time of about 500-6,000 years, whereas the residence time for SI-type plagioclase is significantly longer, about 1,000-10,000 years. By combining field geology, quantitative textural data with geochemistry, we suggest that CT- and SI-type crystals grew and were coarsened in the outer part and inner part of a magma chamber, respectively. Magma evolution during storage is controlled by crystallization, crystal growth, and magma mixing, and pulsating eruptions occur in response to the continuous supply of hot magma.

  11. Composition and origin of basaltic magma of the Hawaiian Islands

    USGS Publications Warehouse

    Powers, H.A.

    1955-01-01

    Silica-saturated basaltic magma is the source of the voluminous lava flows, erupted frequently and rapidly in the primitive shield-building stage of activity, that form the bulk of each Hawaiian volcano. This magma may be available in batches that differ slightly in free silica content from batch to batch both at the same and at different volcanoes; differentiation by fractionation of olivine does not occur within this primitive magma. Silica-deficient basaltic magma, enriched in alkali, is the source of commonly porphyritic lava flows erupted less frequently and in relatively negligible volume during a declining and decadent stage of activity at some Hawaiian volcanoes. Differentiation by fractionation of olivine, plagioclase and augite is evident among these lavas, but does not account for the silica deficiency or the alkali enrichment. Most of the data of Hawaiian volcanism and petrology can be explained by a hypothesis that batches of magma are melted from crystalline paridotite by a recurrent process (distortion of the equatorial bulge by forced and free nutational stresses) that accomplishes the melting only of the plagioclase and pyroxene component but not the excess olivine and more refractory components within a zone of fixed and limited depth. Eruption exhausts the supply of meltable magma under a given locality and, in the absence of more violent melting processes, leaves a stratum of crystalline refractory components. ?? 1955.

  12. Thermal and rheological controls on magma migration in dikes: Examples from the east rift zone of Kilauea volcano, Hawaii

    NASA Technical Reports Server (NTRS)

    Parfitt, E. A.; Wilson, L.; Pinkerton, H.

    1993-01-01

    Long-lived eruptions from basaltic volcanoes involving episodic or steady activity indicate that a delicate balance has been struck between the rate of magma cooling in the dike system feeding the vent and the rate of magma supply to the dike system from a reservoir. We describe some key factors, involving the relationships between magma temperature, magma rheology, and dike geometry that control the nature of such eruptions.

  13. Quantifying magma segregation in dykes

    NASA Astrophysics Data System (ADS)

    Yamato, P.; Duretz, T.; May, D. A.; Tartèse, R.

    2015-10-01

    The dynamics of magma flow is highly affected by the presence of a crystalline load. During magma ascent, it has been demonstrated that crystal-melt segregation constitutes a viable mechanism for magmatic differentiation. Moreover, crystal-melt segregation during magma transport has important implications not only in terms of magma rheology, but also in terms of differentiation of the continental crust. However, the influences of the crystal volume percentage (φ), of their geometry, their size and their density on crystal-melt segregation are still not well constrained. To address these issues, we performed a parametric study using 2D direct numerical simulations, which model the ascension of a crystal-bearing magma in a vertical dyke. Using these models, we have characterised the amount of segregation as a function of different physical properties including φ, the density contrast between crystals and the melt phase (Δρ), the size of the crystals (Ac) and their aspect ratio (R). Results show that small values of R do not affect the segregation. In this case, the amount of segregation depends upon four parameters. Segregation is highest when Δρ and Ac are large, and lowest for large pressure gradient (Pd) and/or large values of dyke width (Wd). These four parameters can be combined into a single one, the Snumber, which can be used to quantify the amount of segregation occurring during magma ascent. Based on systematic numerical modelling and dimensional analysis, we provide a first order scaling law which allows quantification of the segregation for an arbitrary Snumber and φ, encompassing a wide range of typical parameters encountered in terrestrial magmatic systems. Although developed in a simplified system, this study has strong implications regarding our understanding of crystal segregation processes during magma transport. Our first order scaling law allows to immediately determine the amount of crystal-melt segregation occurring in any given magmatic

  14. Making room for magma beneath the Jemez Mountains volcanic field: implications for chemical diversity and caldera formation

    NASA Astrophysics Data System (ADS)

    Brunstad, K. A.; Wolff, J. A.; Watkinson, A.; Gardner, J. N.

    2006-12-01

    The Miocene-Quaternary Jemez Mountains volcanic field (JMVF), the site of the Valles caldera, lies at the intersection of the Jemez lineament, which marks the site of a Proterozoic suture zone, and the Cenozoic Rio Grande rift. The JMVF has a history of volcanism reaching back more than 20 Myr prior to the caldera-forming eruption of the Bandelier Tuff, involving magma compositions ranging from nephelinite to high-silica rhyolite. This longevity of volcanism, despite significant westward movement of the North American continent, indicates that the controls on the location of the JMVF volcanism reside within the lithosphere. The geochemical evolution of continental magmatic systems must be considered in the light of the "space problem" of crustal magma chambers. Significantly, the present geometry of seismic attenuation zones beneath the JMVF may be predicted on the basis of tectonic patterns that existed during the initiation of the volcanic field in the mid-Miocene. We integrate regional structural, tectonic and geophysical data to construct a model for the emplacement and chemical diversification of magmas erupted throughout the history of the JMVF. In addition, we use this approach to develop a new model for the Valles caldera. Reactivation of Laramide thrust faults and transtensional movement on the Jemez lineament during rift-related extension produce low-pressure zones at bends in shear zones were magma could be emplaced. The bends in the shear zones are located at structural triple points representing rheologically stronger and weaker material. The existence of this rheologic variability produces an asymmetry during simple shear deformation in which the stronger material is displaced towards the weaker along one boundary and visa versa along the other. This process creates fragile dilational, low-pressure zones into which magma can be emplaced. Magma chamber shape was controlled by syn-magmatic opening of a tensional-shear fracture or fracture network

  15. Intercomparison of active, passive and continuous instruments for radon and radon progeny measurements in the EML chamber and test facility

    SciTech Connect

    Scarpitta, S.C.; Tu, K.W.; Fisenne, I.M.; Cavallo, A.; Perry, P.

    1996-10-01

    Results are presented from the Fifth Intercomparison of Active, Passive and Continuous Instruments for Radon and Radon Progeny Measurements conducted in the EML radon exposure and test facility in May 1996. In total, thirty-four government, private and academic facilities participated in the exercise with over 170 passive and electronic devices exposed in the EML test chamber. During the first week of the exercise, passive and continuous measuring devices were exposed (usually in quadruplicate) to about 1,280 Bq m{sup {minus}3} {sup 222}Rn for 1--7 days. Radon progeny measurements were made during the second week of the exercise. The results indicate that all of the tested devices that measure radon gas performed well and fulfill their intended purpose. The grand mean (GM) ratio of the participants` reported values to the EML values, for all four radon device categories, was 0.99 {plus_minus} 0.08. Eighty-five percent of all the radon measuring devices that were exposed in the EML radon test chamber were within {plus_minus}1 standard deviation (SD) of the EML reference values. For the most part, radon progeny measurements were also quite good as compared to the EML values. The GM ratio for the 10 continuous PAEC instruments was 0.90 {plus_minus} 0.12 with 75% of the devices within 1 SD of the EML reference values. Most of the continuous and integrating electronic instruments used for measuring the PAEC underestimated the EML values by about 10--15% probably because the concentration of particles onto which the radon progeny were attached was low (1,200--3,800 particles cm{sup {minus}3}). The equilibrium factor at that particle concentration level was 0.10--0.22.

  16. Modelling the petrogenesis of high Rb/Sr silicic magmas

    USGS Publications Warehouse

    Halliday, A.N.; Davidson, J.P.; Hildreth, W.; Holden, P.

    1991-01-01

    Rhyolites can be highly evolved with Sr contents as low as 0.1 ppm and Rb Sr > 2,000. In contrast, granite batholiths are commonly comprised of rocks with Rb Sr 100. Mass-balance modelling of source compositions, differentiation and contamination using the trace-element geochemistry of granites are therefore commonly in error because of the failure to account for evolved differentiates that may have been erupted from the system. Rhyolitic magmas with very low Sr concentrations (???1 ppm) cannot be explained by any partial melting models involving typical crustal source compositions. The only plausible mechanism for the production of such rhyolites is Rayleigh fractional crystallization involving substantial volumes of cumulates. A variety of methods for modelling the differentiation of magmas with extremely high Rb/Sr is discussed. In each case it is concluded that the bulk partition coefficients for Sr have to be large. In the simplest models, the bulk DSr of the most evolved types is modelled as > 50. Evidence from phenocryst/glass/whole-rock concentrations supports high Sr partition coefficients in feldspars from high silica rhyolites. However, the low modal abundance of plagioclase commonly observed in such rocks is difficult to reconcile with such simple fractionation models of the observed trace-element trends. In certain cases, this may be because the apparent trace-element trend defined by the suite of cognetic rhyolites is the product of different batches of magma with separate differentiation histories accumulating in the magma chamber roof zone. ?? 1991.

  17. Intercomparison of active, passive and continuous instruments for radon and radon progeny measurements in the EML chamber and test facility

    SciTech Connect

    George, A.C.; Knutson, E.O.; Tu, K.W.; Fisenne, I.M.

    1995-12-01

    The results from the May 1995 Intercomparison of Active, Passive and Continuous Instruments for Radon and Radon Progeny Measurement conducted in the EML radon exposure and test facility are presented. Represented were 13 participants that measure radon with open faced and diffusion barrier activated carbon collectors, 10 with nuclear alpha track detectors, 9 with short-term and long-term electret/ionization chambers, and 13 with active and passive commercial electronic continuous monitors. For radon progeny, there were four participants that came in person to take part in the grab sampling methodology for measuring individual radon progeny and the potential alpha energy concentration (PAEC). There were 11 participants with continuous and integrating commercial electronic instruments that are used for measuring the PAEC. The results indicate that all the tested instruments that measure radon fulfill their intended purpose. All instruments and methods used for grab sampling for radon progeny did very well. However, most of the continuous and integrating electronic instruments used for measuring the PAEC or working level appear to underestimate the potential risk from radon progeny when the concentration of particles onto which the radon progeny are attached is <5,000 cm{sup -3}.

  18. A refined model for Kilauea's magma plumbing system

    NASA Astrophysics Data System (ADS)

    Poland, M. P.; Miklius, A.; Montgomery-Brown, E. D.

    2011-12-01

    Studies of the magma plumbing system of Kilauea have benefitted from the volcano's frequent eruptive activity, ease of access, and particularly the century-long observational record made possible by the Hawaiian Volcano Observatory. The explosion of geophysical data, especially seismic and geodetic, collected since the first model of Kilauea's magmatic system was published in 1960 allows for a detailed characterization of Kilauea's magma storage areas and transport pathways. Using geological, geochemical, and geophysical observations, we propose a detailed model of Kilauea's magma plumbing that we hope will provide a refined framework for studies of Kilauea's eruptive and intrusive activity. Kilauea's summit region is underlain by two persistently active, hydraulically linked magma storage areas. The larger reservoir is centered at ~3 km depth beneath the south caldera and is connected to Kilauea's two rift zones, which radiate from the summit to the east and southwest. All magma that enters the Kilauea edifice passes through this primary storage area before intrusion or eruption. During periods of increased magma storage at the summit, as was the case during 2003-2007, uplift may occur above temporary magma storage volumes, for instance, at the intersection of the summit and east rift zone at ~3 km depth, and within the southwest rift zone at ~2 km depth. The east rift zone is the longer and more active of Kilauea's two rift zones and apparently receives more magma from the summit. Small, isolated pods of magma exist within both rift zones, as indicated by deformation measurements, seismicity, petrologic data, and geothermal drilling results. These magma bodies are probably relicts of past intrusions and eruptions and can be highly differentiated. Within the deeper part of the rift zones, between about 3 km and 9 km depth, magma accumulation is hypothesized based on surface deformation indicative of deep rift opening. There is no direct evidence for magma within

  19. Water In The Lunar Mantle: Results From Magma Ocean Modeling

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, Linda

    2010-05-01

    The Moon is posited to have formed by reconsolidation of materials produced during a giant impact with the Earth. The young Moon appears to have experienced a magma ocean of some depth. The hypothetical energetics of such an impact and cooling process, combined with the low oxygen activity implied by lunar petrology, has lead investigators to believe that the Moon was free of water. Recent results, however, indicate that lunar volcanic glasses produced by fire fountaining contain small amounts of water (Saal et al., 2008). The volcanic glasses are reported to contain 4 to 46 ppm water, thought to be the remnant after degassing an original minimum 260 ppm. Lunar sample suites indicate fractional crystallization of a lunar magma ocean, including efficient flotation of anorthite to its surface, unimpeded by high crystal fractions or crystal networks. Modeling lunar magma ocean solidification including a small amount of initial water produces predictions for the locations and quantities of water that should be found in the lunar interior, and water that would have been degassed. Compositions of mineral phases are calculated in equilibrium with the magma ocean liquid composition at that stage of solidification, using experimentally-determined KDs for major elements and partition coefficients for hydroxyl and trace elements; for methods see Elkins-Tanton (2008). Water and all other incompatible elements are progressively enriched in the evolving magma ocean liquids as solidification progresses. Progressive enrichment of water in magma ocean liquids produces increasing water contents in solidifying cumulate minerals. Between 0.2 and 1% of the magma ocean liquid water content will be incorporated into solidifying cumulates, enhanced by trapped interstitial liquids. Upon later melting about 99% of cumulate source region water moves into the melt phase. Finally, upon eruption, Saal et al. (2008) estimate that 98% of magmatic water is degassed. Fractional solidification of

  20. Chapter 9 The magma feeding system of Somma-Vesuvius (Italy) strato-volcano: new inferences from a review of geochemical and Sr, Nd, Pb and O isotope data

    USGS Publications Warehouse

    Piochi, M.; de Vivo, B.; Ayuso, R.A.

    2006-01-01

    A large database of major, trace and isotope (Sr, Nd, Pb, O) data exists for rocks produced by the volcanic activity of Somma-Vesuvius volcano. Variation diagrams strongly suggest a major role for evolutionary processes such as fractional crystallization, contamination, crystal trapping and magma maxing, occurring after magma genesis in the mantle. Most mafic magmas are enriched in LILE (Light Ion Lithophile Elements; K. Rb, Ba), REE (Ce, Sm) and Y, show small Nb-Ta negative anomalies, and have values of Nb/Zr at about 0.15. Enrichments in LILE, REE, Nb and Ta do not correlate with Sr isotope values or degree of both K enrichment and silica undersaturation. The results indicate mantle source heterogeneity produced by slab-derived components beneath the volcano. However, the Sr isotope values of Somma-Vesuvius increase from 0.7071 up to 0.7081 with transport through the uppermost 11-12 km of the crust. The Sr isotope variation suggests that the crustal component affected the magmas during ascent through the lithosphere to the surface. Our new geochemical assessment based on chemical, isotopic and fluid inclusion data points to the existence of three main levels of magma storage. Two of the levels are deep and may represent long-lived reservoirs; the uppermost crustal level probably coincides with the volcanic conduit. The deeper level of magma storage is deeper than 12 km and fed the 1944 AD eruption. The intermediate level coincides with the seismic discontinuity detected by Zollo et al. (1996) at about 8 km. This intermediate level supplies magmas with 87Sr/86Sr values between 0.7071 and 0.7074, and ??O18<8% that typically erupted both during interplinian (i.e. 1906 AD) and sub-plinian (472 AD, 1631 AD) events. The shallowest level of magma storage at about 5 km was the site of magma chambers for the Pompei and Avellino plinian eruptions. New investigations are necessary to verify the proposed magma feeding system. ?? 2006 Elsevier B.V. All rights reserved.

  1. The Prototype Active-Target Time-Projection Chamber used with TwinSol radioactive-ion beams

    NASA Astrophysics Data System (ADS)

    Ahn, T.; Bardayan, D. W.; Bazin, D.; Beceiro Novo, S.; Becchetti, F. D.; Bradt, J.; Brodeur, M.; Carpenter, L.; Chajecki, Z.; Cortesi, M.; Fritsch, A.; Hall, M. R.; Hall, O.; Jensen, L.; Kolata, J. J.; Lynch, W.; Mittig, W.; O'Malley, P.; Suzuki, D.

    2016-06-01

    The study of low-energy reactions with radioactive-ion beams has been greatly enhanced by the recent use of active-target detectors, which have high efficiency and low thresholds to detect low-energy charged-particle decays. Both of these features have been used in experiments with the Prototype Active-Target Time-Projection Chamber to study α -cluster structure in unstable nuclei and 3-body charged-particle decays after implantation. Predicted α -cluster structures in 14 C were probed using resonant α scattering and the nature of the 3- α breakup of the 02+ Hoyle state in 12 C after the beta decay of 12 N and 12 B was studied. These experiments used in-flight radioactive-ion beams that were produced using the dual superconducting solenoid magnets TwinSol at the University of Notre Dame. Preliminary results from these experiments as well as the development of future radioactive beams to be used in conjunction with the PAT-TPC are presented.

  2. Mare basalt magma source region and mare basalt magma genesis

    SciTech Connect

    Binder, A.B.

    1982-11-15

    Given the available data, we find that the wide range of mare basaltic material characteristics can be explained by a model in which: (1) The mare basalt magma source region lies between the crust-mantle boundary and a maximum depth of 200 km and consists of a relatively uniform peridotite containing 73--80% olivine, 11--14% pyroxene, 4--8% plagioclase, 0.2--9% ilmenite and 1--1.5% chromite. (2) The source region consists of two or more density-graded rhythmic bands, whose compositions grade from that of the very low TiO/sub 2/ magma source regions (0.2% ilmenite) to that of the very high TiO/sub 2/ magma source regions (9% ilmenite). These density-graded bands are proposed to have formed as co-crystallizing olivine, pyroxene, plagioclase, ilmenite, and chromite settled out of a convecting magma (which was also parental to the crust) in which these crystals were suspended. Since the settling rates of the different minerals were governed by Stoke's law, the heavier minerals settled out more rapidly and therefore earlier than the lighter minerals. Thus the crystal assemblages deposited nearest the descending side of each convection cell were enriched in heavy ilmenite and chromite with respect to lighter olivine and pyroxene and very much lighter plagioclase. The reverse being the case for those units deposited near the ascending sides of the convection cells.

  3. Activated carbons from end-products of tree nut and tree fruit production as sorbents for removing methyl bromide in ventilation effluent from postharvest chamber fumigation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    End-products of tree nuts and tree fruits grown in California, USA were evaluated for the ability to remove methyl bromide from the ventilation effluent of postharvest chamber fumigations. Activated carbon sorbents from walnut and almond shells as well as peach and prune pits were prepared using dif...

  4. The chemical and isotopic differentiation of an epizonal magma body: Organ Needle pluton, New Mexico

    USGS Publications Warehouse

    Verplanck, P.L.; Farmer, G.L.; McCurry, M.; Mertzman, S.A.

    1999-01-01

    Major and trace element, and Nd and Sr isotopic compositions of whole rocks and mineral separates from the Oligocene, alkaline Organ Needle pluton (ONP), southern New Mexico, constrain models for the differentiation of the magma body parental to this compositionally zoned and layered epizonal intrusive body. The data reveal that the pluton is rimmed by lower ??(Nd) (~-5) and higher 87Sr/86Sr (~0.7085) syenitic rocks than those in its interior (??(Nd) ~ 2, 87Sr/86Sr ~0.7060) and that the bulk compositions of the marginal rocks become more felsic with decreasing structural depth. At the deepest exposed levels of the pluton, the ??(Nd)~-5 lithology is a compositionally heterogeneous inequigranular syenite. Modal, compositional and isotopic data from separates of rare earth element (REE)-bearing major and accesory mineral phases (hornblende, titanite, apatite, zircon) demonstrate that this decoupling of trace and major elements in the inequigranular syenite results from accumulation of light REE (LREE)-bearing minerals that were evidently separated from silicic magmas as the latter rose along the sides of the magma chamber. Chemical and isotopic data for microgranular mafic enclaves, as well as for restite xenoliths of Precambrian granite wall rock, indicate that the isotopic distinction between the marginal and interior facies of the ONP probably reflects assimilation of the wall rock by ??(Nd) ~-2 mafic magmas near the base of the magma system. Fractional crystallization and crystal liquid separation of the crystally contaminated magma at the base and along the margins of the chamber generated the highly silicic magmas that ultimately pooled at the chamber top.

  5. 238U sbnd 230Th sbnd 226Ra disequilibria in young Mount St. Helens rocks: time constraint for magma formation and crystallization

    NASA Astrophysics Data System (ADS)

    Volpe, Alan M.; Hammond, Paul E.

    1991-12-01

    We use 238U-series nuclides and 230Th/ 232Th ratios measured by mass spectrometry to constrain processes and time scales of calc-alkaline magma genesis at Mount St. Helens, Washington. Olivine basalt, pyroxene andesites and dacites that erupted 10-2 ka ago show 3-14% ( 230Th) sbnd ( 238U) and 6-54% 226Ra sbnd 230Th disequilibria. Mineral phases exhibit robust ( 226Ra) sbnd ( 230Th) fractionation. Plagioclase has large 65-280% ( 226Ra) excesses, and magnetite has large 65% ( 226Ra) deficits relative to ( 230Th). Calculated partition coefficients for Ba, Th, and U in mineral-groundmass pairs, except Ba in plagioclase, are low (⩽ 0.04). Correlation between ( 226Ra/ 230Th ) activity ratios and rm/BaTh element ratios in the minerals suggests that 226Ra partitions similar to Ba during crystallization. Internal ( 230Th) sbnd ( 238U) isochrons for 1982 summit and East Dome dacites and Goat Rocks and Kalama andesites show that closed Th sbnd U system fractionation occurred 2-6 ka ago. Apparent internal isochrons for Castle Creek basalt (34 ka) and andesite (27 ka) suggest longer magma chamber residence times and mixing of old crystals and young melt. Mineral ( 226Ra) sbnd ( 230Th) disequilibrium on Ba-normalized internal isochron diagrams suggests average magma chamber residence times of 500-3000 years. In addition, radioactive ( 226Ra/ 230Th ) heterogeneity between minerals and groundmass or whole rock is evidence for open-system Ra sbnd Th behavior. This heterogeneity suggests there has been recent, post-crystallization, changes in melt chemical composition that affected 226Ra more than 230Th. Clearly, magma fractionation, residence and transport of crystal-melt before eruption of chemically diverse lavas at Mount St. Helens occurs over geologically short periods.

  6. Fluid-mechanical models of crack propagation and their application to magma transport in dykes

    NASA Astrophysics Data System (ADS)

    Lister, John R.; Kerr, Ross C.

    1991-06-01

    The ubiquity of dykes in the Earth's crust is evidence that the transport of magma by fluid-induced fracture of the lithosphere is an important phenomenon. Magma fracture transports melt vertically from regions of production in the mantle to surface eruptions or near-surface magma chambers and then laterally from the magma chambers in dykes and sills. In order to investigate the mechanics of magma fracture, the driving and resisting pressures in a propagating dyke are estimated and the dominant physical balances between these pressures are described. It is shown that the transport of magma in feeder dykes is characterized by a local balance between buoyancy forces and viscous pressure drop, that elastic forces play a secondary role except near the dyke tip and that the influence of the fracture resistance of crustal rocks on dyke propagation is negligible. The local nature of the force balance implies that the local density difference controls the height of magma ascent rather than the total hydrostatic head and hence that magma is emplaced at its level of neutral buoyancy (LNB) in the crust. There is a small overshoot beyond this level which is calculated to be typically a few kilometres. Magma accumulating at the LNB will be intruded in lateral dykes and sills which are directed along the LNB by buoyancy forces since the magma is in gravitational equilibrium at this level. Laboratory analogue experiments demonstrate the physical principle of buoyancy-controlled propagation to and along the LNB. The equations governing the dynamics of magma fracture are solved for the cases of lithospheric ascent and of lateral intrusion. Volatiles are predicted to be exsolved from the melt at the tips of extending fractures due to the generation of low pressures by viscous flow into the tip. Chilling of magma at the edges of a dyke inhibits cross-stream propagation and concentrates the downstream flow into a wider dyke. The family of theoretical solutions in different geometries

  7. Fusion studies with low-intensity radioactive ion beams using an active-target time projection chamber

    NASA Astrophysics Data System (ADS)

    Kolata, J. J.; Howard, A. M.; Mittig, W.; Ahn, T.; Bazin, D.; Becchetti, F. D.; Beceiro-Novo, S.; Chajecki, Z.; Febbrarro, M.; Fritsch, A.; Lynch, W. G.; Roberts, A.; Shore, A.; Torres-Isea, R. O.

    2016-09-01

    The total fusion excitation function for 10Be+40Ar has been measured over the center-of-momentum (c.m.) energy range from 12 to 24 MeV using a time-projection chamber (TPC). The main purpose of this experiment, which was carried out in a single run of duration 90 h using a ≈100 particle per second (pps) 10Be beam, was to demonstrate the capability of an active-target TPC to determine fusion excitation functions for extremely weak radioactive ion beams. Cross sections as low as 12 mb were measured with acceptable (50%) statistical accuracy. It also proved to be possible to separate events in which charged particles were emitted from the fusion residue from those in which only neutrons were evaporated. The method permits simultaneous measurement of incomplete fusion, break-up, scattering, and transfer reactions, and therefore fully exploits the opportunities presented by the very exotic beams that will be available from the new generation of radioactive beam facilities.

  8. Evidence for dynamic withdrawal from a layered magma body: The Topopah Spring Tuff, southwestern Nevada

    SciTech Connect

    Schuraytz, B. C.; Vogel, T. A.; Younker, L. W.

    1989-05-10

    The Topopah Spring Tuff is a classic example of a compositionally zoned ash flow sheet resulting from eruption of a compositionally zoned magma body. Geochemical and petrographic analyses of whole rock tuff samples indicate that the base of the ash flow sheet and the predominant volume of erupted material consist of crystal-poor high-silica rhyolite, with agradational transition into overlying crystal-rich quartz latite. However, major and trace element analyses of glassy pumice lumps and microprobe analyses of their silicate and oxide phenocrysts provide closer approximations of the chemical and thermal gradients within the magma body. The gradients inferred from these data indicate that the transition from high-silica rhyolitic to quartz latitic magma within the chamber was abrupt, rather than gradational, with a distinct liquid-liquid interface separating the contrasting magma layers. Compositionally and texturally distinct pumice lumps are present throughout the ash flow sheet. The degree of heterogeneity within and among pumice lumps increases with stratigraphic height, becoming most pronounced in the uppermost quartz latite, where the chemical variability among pumice lumps is as great as that of the entire ash flow sheet. These observations are consistent with fluid dynamic models in which the velocity field developed near the entrance region of the vent(s) results in simultaneous withdrawal of magma from all points of a continuously expanding lateral and vertical region within the chamber. The abrupt transition to chemically bimodal pumice types near the top of the ash flowsheet, dominated by those of quartz latitic composition, implies that the interface between the magma layers remained relatively stable until drawdown breached the interface and preferentially erupted hotter, more mafic magma along with lesser amounts of remaining high-silica rhyolitic magma.

  9. Magma Systems Formation and Crustal Accretion in Intermediate-rate Spreading Ridges of the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Dubinin, E. P.; Galushkin, Y. I.; Sveshnikov, A. A.; Grokholsky, A.

    2008-12-01

    Fast spreading mid-ocean ridges (MOR) are known to be characterized by well-developed axial rises with axial magma chambers (AMC) in the crust, whereas slow spreading centers with deep rift valleys are devoid of AMC. An AMC disappears when spreading rate is about 4-5 cm/year. Approximately the same spreading rate is marked by axial morphology transition from axial rises to rift valleys. This transition was thoroughly analyzed for South-East Indian intermediate spreading ridge. Typical patterns of bathymetric profiles across the rift axis with transitional morphology were revealed. Dimensions and relative position of profile constituents change regularly with morphology turning from axial rises to rift valleys. A non-steady thermal model of spreading with periodic axial intrusions allows an explanation of location, size and shape of the crust and mantle magma chambers. This model also permits us to analyze changes in parameters including spreading rate, temperature and composition of the mantle and crust rocks. In the axial zones of intermediate spreading ridges with higher mantle temperature (e.g., under the influence of mantle plumes or hot spots), the modeling confirms an occurrence of the zones with higher melt concentration (magma chambers) at two levels: at depth ~2 km and more in the crust and just below the Moho boundary in the mantle. In the axial zones of intermediate spreading ridges with lower mantle temperature, a quasi steady-state magma chamber in the crust does not exist, but here, formation of the short-living magma chambers in the crust is possible. Difference in location depth, shape and sizes of magma chambers in spreading ridges result in considerable differences in rheologic behavior and accretion mechanisms of the crust and therefore in relief and deep structure of the crust. The steady-state crust magma chambers in the fast spreading ridges or in the intermediate spreading ridges with higher mantle temperature secure a differentiation of

  10. Electrical Properties of Hydrous Magmas

    NASA Astrophysics Data System (ADS)

    Laumonier, M.; Sifre, D.; Gaillard, F.

    2013-12-01

    Volatiles strongly affect physical and chemical properties of magmas which are major vectors of mass and heat transfer in the Earth's. In subduction zones, hydrated melts prevail during the entire course of differentiation from basalts, andesites, dacites to rhyolites. Several electrical surveys obtained by magneto telluric investigations are currently deployed at subduction zones. The electrical conductivity of hydrous melts is however poorly constrained: so far only three studies have experimentally addressed this topic. Here, we show in situ electrical impedance of natural dacites, andesites (from Uturuncu Volcano, Bolivia) and basaltic magmas obtained with a 4-wire set up in a piston cylinder and internally heated pressure vessel. The range of temperature (500 to 1300°C), pressure (0.3 to 2 Gpa), and the various water contents and crystal fractions covers the respective ranges occurring at natural conditions. First results show that the conductivity increases with the temperature, the melt fraction, and a slightly decreases with the pressure and the crystal fraction. The compilation of these results with previous studies (rhyolitic, phonolitic and basaltic compositions) will lead to a general model of the electrical properties of magmas. Such a model will help in (i) interpreting the electrical signature of natural magmas and (ii) constraining their conditions (chemical composition, temperature, pressure, water content, melt fraction) from the source to the storage location.

  11. A conceptual model of Kilauea's magma plumbing system

    NASA Astrophysics Data System (ADS)

    Poland, M. P.; Miklius, A.; Montgomery-Brown, E. K.

    2013-12-01

    The current magma plumbing system of Kilauea Volcano, Hawai`i, is routinely described as consisting of a conduit that extends upward from mantle depths and feeds a magma storage reservoir beneath the summit caldera. From the summit reservoir, rift zones radiate to the east and southwest. Geological and geophysical observations, however, suggest a more complex picture. Models of the summit magma storage area include at least three discrete reservoirs. The largest is centered at ~3 km depth beneath the southern part of the caldera and serves as the main storage volume for the volcano. A smaller body lies 1-2 km beneath the east margin of Halema`uma`u Crater and presumably feeds the summit eruptive vent (active since 2008). Magma is also occasionally stored beneath the southeast part of the caldera near Keanakāko`i Crater, where the east rift zone intersects the summit. The reservoirs are interconnected, but the level of connectivity appears to vary according to pressurization of the magma plumbing system. Kilauea's rift zone system extends both to the east and southwest as paired shallow and deeper sections. The deeper rift zones (~3-km depth) are connected to the south caldera reservoir and, along with the Koa`e fault system, represent the structural boundaries of Kilauea's mobile south flank. Both trend southward near the summit before bending into east/northeast- and southwest-directed orientations, which may reflect southward migration of the rift zones over time due to seaward motion of the volcano's south flank (originally proposed by Swanson et al., 1976). Isolated pods of magma (relict from past intrusions) are scattered along the rift zone trends, and molten cores allow for rapid transport of magma between the summit and distal eruption/intrusion sites portions. The shallow rift zones (~1-km depth) are connected to the summit magma system via the Halema`uma`u reservoir and probably represent the former locations of the main rift systems. While this model is

  12. Chamber propagation

    SciTech Connect

    Langdon, B.

    1991-01-16

    Propagation of a heavy ion beam to the target appears possible under conditions thought to be realizable by several reactor designs. Beam quality at the lens is believed to provide adequate intensity at the target -- but the beam must pass through chamber debris and its self fields along the way. This paper reviews present consensus on propagation modes and presents recent results on the effects of photoionization of the beam ions by thermal x-rays from the heated target. Ballistic propagation through very low densities is a conservative mode. The more-speculative self-pinched mode, at 1 to 10 Torr, offers reactor advantages and is being re-examined by others. 13 refs.

  13. Chamber transport

    SciTech Connect

    OLSON,CRAIG L.

    2000-05-17

    Heavy ion beam transport through the containment chamber plays a crucial role in all heavy ion fusion (HIF) scenarios. Here, several parameters are used to characterize the operating space for HIF beams; transport modes are assessed in relation to evolving target/accelerator requirements; results of recent relevant experiments and simulations of HIF transport are summarized; and relevant instabilities are reviewed. All transport options still exist, including (1) vacuum ballistic transport, (2) neutralized ballistic transport, and (3) channel-like transport. Presently, the European HIF program favors vacuum ballistic transport, while the US HIF program favors neutralized ballistic transport with channel-like transport as an alternate approach. Further transport research is needed to clearly guide selection of the most attractive, integrated HIF system.

  14. Magma Genesis of Sakurajima, the Quaternary post- Aira caldera volcano, southern Kyushu Island, Japan

    NASA Astrophysics Data System (ADS)

    Shibata, T.; Suzuki, J.; Yoshikawa, M.; Kobayashi, T.; Miki, D.; Takemura, K.

    2012-12-01

    Sakurajima volcano is the Quaternary post-caldera volcano of Aira caldera, which was caused by the eruption of huge amount of silicic pyroclastics, situated on Ryukyu arc, southern Kyushu Island, Japan. This volcano is quite active, so it can be considered that the preparation of next caldera-forming eruption with huge amount of silicic magma is proceeding. It is, therefore, expected that the investigation of magma genesis of Sakurajima volcano give us information for the mechanism generating huge amount of silicic magma, which cause the caldera formation. We analyzed major and trace elements with Sr, Nd and Pb isotopic compositions of volcanic rocks from Sakurajima volcano. We sampled (ol) - opx - cpx - pl andesite and dacite from almost all the volcanic units defined by Fukuyama and Ono (1981). In addition to Sakurajima samples, we also studied basaltic rocks erupted at pre-caldera stage of the Aira caldera to estimate the primary magma of Sakurajima volcano. Major and trace element variations generally show linear trends on the Harker diagrams, with the exception of P2O5 and TiO2. Based on the trend of P2O5 vs.SiO2, we divided studied samples low-P (P2O5 < 0.15 wt. %) and high-P (P2O5 > 0.15 wt. %) groups and these groups also display two distinct trends on TiO2-SiO2 diagram. The composition of trace elements shows typical island arc character as depletion of Nb and enrichments of Rb, K and Pb, suggesting addition of aqueous fluids to the mantle wedge. The Zr and Nb concentrations make a liner trend (Zr/Nb = 27) and this trend across from tend of MORB (Zr/Nb = 35) to that of crustal materials (Zr/Nb=17). The Sr, Nd and Pb isotopic compositions broadly plot to on the mixing curve connecting MORB-type mantle and sediments of the Philippine Sea Plate, indicating that the primary magma was generated by partial melting of MORB-type mantle wedge, which was hydrated with fluids derived from the subducted Philippine Sea sediments. But we found that our data plot apart

  15. Prolonged, episodic evacuation of discrete magma bodies at the onset of the Huckleberry Ridge Tuff supereruption

    NASA Astrophysics Data System (ADS)

    Myers, M.; Wallace, P. J.; Wilson, C. J. N.; Morter, B. K.; Swallow, E. J.

    2015-12-01

    Integration of geochemical data with time breaks inferred from physical characteristics in early-erupted fall deposits shed light on the triggering mechanisms and initial episodic behavior1 of the Huckleberry Ridge Tuff (HRT: 2500 km3) supereruption2. In each layer sampled in the basal 2 m of fall deposits at Mount Everts, wide H2O variations (1.0-4.7 wt.%) in co-erupted, fully enclosed, quartz-hosted rhyolitic melt inclusions (MI) imply <1 day to a week of diffusive loss. These data indicate highly variable and surprisingly slow ascent conditions during the opening stages of the eruption. The second largest Quaternary eruption on Earth2 started hesitatingly, with magma slowly ascending to feed periodic explosive activity, with time breaks manifested by contemporaneous reworking in the fall deposits1. Importantly, this behavior requires low degrees of overpressure in the feeding magma body to permit such slow ascent4, and we thus propose that external rather than internal (i.e. chamber overpressure) controls were central to initiation of the HRT eruption. In addition, multi-variant cluster analysis on trace elements for all MI reveals that the fall deposit contains six statistically distinct host-quartz populations. CO2 vs. restored H2O data show that the first erupted, most evolved compositions crystallized deeper (150-200 MPa), whereas the later-erupted, least evolved compositions crystallized shallower (100-140 MPa). This diversity indicates that the quartz populations represent magma bodies that were spatially separated to some extent during crystallization and evolution from a chemically similar parent. However, trace element analysis of reentrants and co-erupted obsidian clasts, which represent the compositions of melts at the time of eruption, although clustered, have values that correspond to only three of the six quartz populations. Taken all together, we conclude that the HRT eruption onset saw several vents active simultaneously and sequentially

  16. Volcano seismicity and ground deformation unveil the gravity-driven magma discharge dynamics of a volcanic eruption.

    PubMed

    Ripepe, Maurizio; Donne, Dario Delle; Genco, Riccardo; Maggio, Giuseppe; Pistolesi, Marco; Marchetti, Emanuele; Lacanna, Giorgio; Ulivieri, Giacomo; Poggi, Pasquale

    2015-01-01

    Effusive eruptions are explained as the mechanism by which volcanoes restore the equilibrium perturbed by magma rising in a chamber deep in the crust. Seismic, ground deformation and topographic measurements are compared with effusion rate during the 2007 Stromboli eruption, drawing an eruptive scenario that shifts our attention from the interior of the crust to the surface. The eruption is modelled as a gravity-driven drainage of magma stored in the volcanic edifice with a minor contribution of magma supplied at a steady rate from a deep reservoir. Here we show that the discharge rate can be predicted by the contraction of the volcano edifice and that the very-long-period seismicity migrates downwards, tracking the residual volume of magma in the shallow reservoir. Gravity-driven magma discharge dynamics explain the initially high discharge rates observed during eruptive crises and greatly influence our ability to predict the evolution of effusive eruptions.

  17. Volcano seismicity and ground deformation unveil the gravity-driven magma discharge dynamics of a volcanic eruption.

    PubMed

    Ripepe, Maurizio; Donne, Dario Delle; Genco, Riccardo; Maggio, Giuseppe; Pistolesi, Marco; Marchetti, Emanuele; Lacanna, Giorgio; Ulivieri, Giacomo; Poggi, Pasquale

    2015-01-01

    Effusive eruptions are explained as the mechanism by which volcanoes restore the equilibrium perturbed by magma rising in a chamber deep in the crust. Seismic, ground deformation and topographic measurements are compared with effusion rate during the 2007 Stromboli eruption, drawing an eruptive scenario that shifts our attention from the interior of the crust to the surface. The eruption is modelled as a gravity-driven drainage of magma stored in the volcanic edifice with a minor contribution of magma supplied at a steady rate from a deep reservoir. Here we show that the discharge rate can be predicted by the contraction of the volcano edifice and that the very-long-period seismicity migrates downwards, tracking the residual volume of magma in the shallow reservoir. Gravity-driven magma discharge dynamics explain the initially high discharge rates observed during eruptive crises and greatly influence our ability to predict the evolution of effusive eruptions. PMID:25980642

  18. Revealing magma degassing below closed-conduit active volcanoes: Geochemical features of volcanic rocks versus fumarolic fluids at Vulcano (Aeolian Islands, Italy)

    NASA Astrophysics Data System (ADS)

    Mandarano, Michela; Paonita, Antonio; Martelli, Mauro; Viccaro, Marco; Nicotra, Eugenio; Millar, Ian L.

    2016-04-01

    The elemental and isotopic compositions of noble gases (He, Ne, and Ar) in olivine- and clinopyroxene-hosted fluid inclusions have been measured for rocks at various degrees of evolution and belonging to high-K calcalkaline-shoshonitic and shoshonitic-potassic series in order to cover the entire volcanological history of Vulcano Island (Italy). The major- and trace-element concentrations and the Sr- and Pb-isotope compositions for whole rocks were integrated with data obtained from the fluid inclusions. 3He/4He in fluid inclusions is within the range of 3.30 and 5.94 R/Ra, being lower than the theoretical value for the deep magmatic source expected for Vulcano Island (6.0-6.2 R/Ra). 3He/4He of the magmatic source is almost constant throughout the volcanic history of Vulcano. Integration of the He- and Sr-isotope systematics leads to the conclusion that a decrease in the He-isotope ratio of the rocks is mainly due to the assimilation of 10-25% of a crustal component similar to the Calabrian basement. 3He/4He shows a negative correlation with Sr isotopes except for the last-erupted Vulcanello latites (Punta del Roveto), which have anomalously high He isotope ratios. This anomaly has been attributed to a flushing process by fluids coming from the deepest reservoirs, since an input of deep magmatic volatiles with high 3He/4He values increases the He-isotope ratio without changing 87Sr/86Sr. A comparison of the He-isotope ratios between fluid inclusions and fumarolic gases shows that only the basalts of La Sommata and the latites of Vulcanello have comparable values. Taking into account that the latites of Vulcanello relate to one of the most-recent eruptions at Vulcano (in the 17th century), we infer that the most probable magma which actually feeds the fumarolic emissions is a latitic body that ponded at about 3-3.5 km of depth and is flushed by fluids coming from a deeper and basic magma.

  19. Modelling of a magma energy geothermal power plant

    SciTech Connect

    Boehm, R.F.; Berg, D.L.; Jr.; Ortega, A.

    1987-01-01

    We are currently investigating the engineering feasibility of drilling into an active magma body at a depth of roughly 5 km from the earth's surface, establishing a downhole heat exchange region, and extracting thermal energy from the magma body by circulating fluid through this heat exchange region. In the present paper, we evaluate the overall thermodynamic performance of various conceptual magma energy systems in which energy is added as heat to the fluid within the magma region and is converted to useful work in a power conversion cycle at the surface. Unusually high return temperatures and pressures may be available at the wellhead of such a circulating well. Cycles investigated here are an open Rankine power system in which steam from the magma well is circulated directly through a power conversion cycle and a closed Rankine cycle where the heated fluid from downhole is circulated through an aboveground heat exchanger to heat the cycle fluid. The downhole heat exchange region is established during the drilling process. As drilling proceeds into the magma, a solidified layer forms about the drilling tube due to heat exchange to the fluid. This solidified layer thermally fractures because of large temperature gradients between the cooled inner region and the heated outer region, thereby opening secondary flow paths. Two models of the downhole behavior have been used. In the simplest approach, denoted as the ''infinite area model,'' the water entering the pipe to return to the surface is assumed to be always at the temperature of the magma, independent of mass flow rate and other parameters. The other model is more detatiled and the fractured heat exchange region is modelled as a cylindrical porous layer through which fluid flows vertically. The net power and the performance aspects for the systems are investigated in terms of various parameters, including the characteristics of the downhole heat transfer.

  20. Ion chamber based neutron detectors

    DOEpatents

    Derzon, Mark S; Galambos, Paul C; Renzi, Ronald F

    2014-12-16

    A neutron detector with monolithically integrated readout circuitry, including: a bonded semiconductor die; an ion chamber formed in the bonded semiconductor die; a first electrode and a second electrode formed in the ion chamber; a neutron absorbing material filling the ion chamber; and the readout circuitry which is electrically coupled to the first and second electrodes. The bonded semiconductor die includes an etched semiconductor substrate bonded to an active semiconductor substrate. The readout circuitry is formed in a portion of the active semiconductor substrate. The ion chamber has a substantially planar first surface on which the first electrode is formed and a substantially planar second surface, parallel to the first surface, on which the second electrode is formed. The distance between the first electrode and the second electrode may be equal to or less than the 50% attenuation length for neutrons in the neutron absorbing material filling the ion chamber.

  1. Reconstructing Magma Degassing and Fragmentation: The 1060 CE Plinian Eruption of Medicine Lake Volcano, California

    NASA Astrophysics Data System (ADS)

    Giachetti, T.; Gonnermann, H. M.; Crozier, J.

    2015-12-01

    Magma fragmentation during explosive volcanic eruptions occurs when the bubble overpressure exceeds some threshold. Because bubble coalescence and ensuing permeable outgassing allow partial release of bubble overpressure, high magma permeabil
ity is thought to adversely affect magma fragmentation and the ability of magma to erupt explosively. We used the Plinian phase of the 1060 CE Glass Mountain eruption of Medicine Lake Volcano, California, to show that this is not necessarily the case. We performed numerical modeling of eruptive magma ascent and bubble growth to predict the development of magma porosity, permeability, and the built-up of gas pressure inside bubbles. We explicitly took into account permeable outgassing in the model. We used the measured porosity and permeability of the Plinian pyroclasts, together with percolation modeling, to reconstruct the conditions for magma degassing and fragmentation. Our results show that the porosity and permeability of pyroclasts coincide with the conditions required for fragmentation of the erupting magma. The onset of fragmentation occurs when the decompression rate reaches about 2 MPa.s-1, corresponding to a constant melt viscosity of ˜107 Pa.s and a magma porosity of approximately 0.75, conditions met for a mass discharge rate of about 107 kg.s-1, a cross sectional area of about 2,000 m2, and at a depth of approximately 1 km. Pyroclasts formed from magma that fragmented over a depth range of several tens of meters, probably reflecting some degree of lateral variability in magma porosity in the conduit. The model also indicates that, even if the magma was highly permeable at the onset of fragmentation, permeable outgassing did not affect fragmentation. The transition to an effusive activity and the emission of obsidian after the Plinian phase of the Glass Mountain eruption is most probably due to a decrease in decompression rate.

  2. Variations in magma supply and magma partitioning: the role of tectonic settings

    NASA Astrophysics Data System (ADS)

    Takada, Akira

    1999-11-01

    Magma supply rates for 200 years at Krafla and Lakagigar, Iceland, and those for 150 years at Kilauea and Mauna Loa, Hawaii, are estimated roughly, based on their geophysical and geological observations. A diagram that relates erupted volumes to eruption intervals at volcanoes under various tectonic settings is represented. These results lead to a new model that a large volume (1-10 km 3) of magma is supplied intermittently at a long interval (10 2-10 4 years) beneath volcanoes in rift zones, while magma is supplied continuously with oscillations or fluctuations beneath intraplate volcanoes. Chemical data such as the MgO wt.% of lava may be one indicator in evaluating the magma supply rates of Hawaiian volcanoes. Systematic variation with time in magma partitioning within a volcano or to the surface is obtained in comparisons between among migration patterns of eruption sites, cumulative supplied volumes, and the volume ratios of erupted to supplied magma at Krafla and Kilauea. The variations suggest that a magma plumbing system may act under self-control (regulating) system through stress as one system. In response to a change in magma supply rate, the system partitions magma horizontally into dikes or vertically toward the surface. A large magma supply rate promotes the vertical extent of a crack to result in an eruption with a large volume ratio of erupted to supplied magma. This tendency is supported by field observations of flood basalts. The partitioned magma as dike intrusions suppresses magma supply partially in the shallow crust. Using analog experiments on liquid-filled cracks in gelatin, this paper demonstrates fundamental processes for magma partitioning on the effect of magma supply and stress change by the partitioned magma. A dynamical system of two differential equations on magma supply rate and stress around a magma plumbing system is proposed, to understand the qualitative variations in magma supply rate imposed by tectonic settings.

  3. Origin of crystal-poor, differentiated magmas: insights from thermal gradient experiments

    NASA Astrophysics Data System (ADS)

    Masotta, Matteo; Freda, Carmela; Gaeta, Mario

    2012-01-01

    Crystal-poor, differentiated magmas are commonly erupted from shallow, thermally zoned magma chambers. In order to constrain the origin of these magmas, we have experimentally investigated crystallization, differentiation and crystal-melt separation in presence of a thermal gradient. Experiments have been designed taking advantage of the innate temperature gradient of the piston cylinder apparatus and carried out on a phonolitic system at 0.3 GPa and temperature ranging from 1,050 to 800°C. Crystallization degree and melt composition in experimental products vary as a function of the temperature gradient. In particular, melt composition differentiates from tephri-phonolite (starting material) to phonolite moving from the hotter, glassy zone ( T ≤ 1,050°C) towards the cooler, heterogeneously crystallized zone ( T ≤ 900°C) of the charge. The heterogeneously crystallized zone is made up of: (1) a crystal-rich, mushy region (crystallinity >30 vol%), (2) a rigid crystal framework (crystallinity ≤80 vol%) and (3) glassy belts of phonolitic glass at the top. Thermal gradient experiments picture crystallization, differentiation and crystal-melt separation processes occurring in a thermally zoned environment and reveal that relatively large volumes of crystal-poor melt (glassy belts) can originate as a consequence of the instability and collapse of the rigid crystal framework. Analogously, in thermally zoned magma chambers, the development and collapse of a solidification front may represent the controlling mechanism originating large volumes of crystal-poor, differentiated magmas.

  4. Impermeable high-porosity magmas

    NASA Astrophysics Data System (ADS)

    Heap, Michael; Vona, Alessandro; Kolzenburg, Stephan; Ryan, Amy; Russell, Kelly

    2016-04-01

    Magma vesiculation (i.e., porosity increase) is the consequence of decompression-driven volatile release during ascent and/or heating. The ease at which these exsolved volatiles can escape is thought to strongly impact volcanic explosivity. Permeability is usually considered to increase as a function of porosity. High and low porosity are typically associated with high and low permeability, respectively. Here we present permeability experiments on foamed natural rhyolitic melts containing total porosities from 0.12 to 0.65; we compliment these data with measurements on synthetic foamed glasses (prepared by FOAMGLAS®) that contain a total porosity of 0.9. The rhyolitic melts (from Krafla, Iceland: Tg = 690 °C) were kept at atmospheric pressure and 1000 °C for 0.5, 1, 2, and 4 hours, followed by quenching. The four experiments yielded total porosities of 0.12, 0.44, 0.51, and 0.65, respectively. The permeability of these samples was then measured using a steady-state, benchtop permeameter under a confining pressure of 1 MPa. The permeability of the foamed samples containing a porosity of 0.12 and 0.44 were not measurable in our system, meaning their permeabilities are lower than ~10-18 m2. The permeability of the samples containing a porosity of 0.51 and 0.65 were 8.7 × 10-15 and 1.0 × 10-15 m2, respectively. Both types of FOAMGLAS® - containing a porosity of 0.9 - also have permeabilities lower than ~10-18 m2. Our study highlights that highly porous magmas are not necessarily permeable due to the absence of a connected network of pores. These data suggest that (1) the percolation threshold for magma requires further thought and, (2) that the liberation of exsolved volatiles will require the fracturing of bubble walls to connect the network of pores within the magma.

  5. Modeling magma flow in volcanic conduit with non-equilibrium crystallization

    NASA Astrophysics Data System (ADS)

    Yulia, Tsvetkova

    2010-05-01

    Modeling magma flow in volcanic conduit including with non -equilibrium crystallization There is a set of models of magma flow in volcanic conduits which predicts oscillations in magma discharge during extrusion of lava domes. These models neglect heating of surrounding rocks and use 1D approximation of the flow in the conduit. Here magma flow is investigated with an account of heat exchange between surrounding rocks and magma and different dependences viscosity on temperature and crystal concentration. Stick-slip conditions were applied at the wall. The flow is assumed to be quasi-static and quasi 1D. Only vertical component of velocity vector is present, thus, we do not consider horizontal momentum balance. At the top of the conduit the pressure is assumed to be fixed, chamber pressure changes according with magma influx and outflux. First set of simulation was made for the viscosity that depends on cross-section average crystal concentration and parabolic velocity profile. In earlier models that account for crystal growth kinetics the temperature was allowed to change only due to the release of latent heat of crystallization. Heat transfer leads to cooling of the outer parts of the conduit leading to high crystal contents and high magma viscosities. Changes in viscosity result in changes in discharge rate. For the non-isothermal case there is no motion during most part of the cycle and a portion of magma solidifies at the top of the conduit forming a plug. During repose period chamber pressure is growing due to influx of fresh magma, and magma discharge rate starts to increase. Influx of hot magma into the conduit leads to decrease in friction resulting in a jump in discharge rate that lead to depressurization of magma chamber. Discharge rate decreases and magma solidifies again. For isothermal model with the same parameters discharge rate monotonically tends to the value of Qin. Simulation reveal that crystal content changes significantly across the conduit

  6. Partially molten magma ocean model

    SciTech Connect

    Shirley, D.N.

    1983-02-15

    The properties of the lunar crust and upper mantle can be explained if the outer 300-400 km of the moon was initially only partially molten rather than fully molten. The top of the partially molten region contained about 20% melt and decreased to 0% at 300-400 km depth. Nuclei of anorthositic crust formed over localized bodies of magma segregated from the partial melt, then grew peripherally until they coverd the moon. Throughout most of its growth period the anorthosite crust floated on a layer of magma a few km thick. The thickness of this layer is regulated by the opposing forces of loss of material by fractional crystallization and addition of magma from the partial melt below. Concentrations of Sr, Eu, and Sm in pristine ferroan anorthosites are found to be consistent with this model, as are trends for the ferroan anorthosites and Mg-rich suites on a diagram of An in plagioclase vs. mg in mafics. Clustering of Eu, Sr, and mg values found among pristine ferroan anorthosites are predicted by this model.

  7. Evidence for variations in magma production along oceanic spreading centers - A critical appraisal

    NASA Technical Reports Server (NTRS)

    Karson, J. A.; Elthon, D.

    1987-01-01

    Recent geologic, geophysical, and geochemical studies of the oceanic lithosphere near fracture zones have resulted in the proposal that the 'magma budget,' defined as the amount of magma delivered to magma chambers or conduits beneath a spreading center for a given amount of spreading, decreases as fracture zones are approached. Seismic reflection and refraction studies indicate that the crust becomes anomalously thin near fracture zones, but reference must be made to the boundary between residual upper mantle peridotites and overlying cumulate rocks in order to assess potential variations in the magma budget. The position of this interface, however, generally is not constrained by geophysical studies. Geochemical variations in basaltic glasses collected near fracture zones are consistent with a decrease in partial melting as fracture zones are approached, but they could also be produced by variations in open-system magmatic processes with no change in the extent of partial melting. Although a decrease in the magma budget as fracture zones are approached is consistent with these data, so are alternative models that incorporate a constant magma budget.

  8. Implications of Viscosity-Contrast for Co-Extruding Two-Component Magmas, Triggering Eruptions and Forming Layered Domes

    NASA Astrophysics Data System (ADS)

    Carrigan, C. R.; Clarke, S. M.

    2004-12-01

    Polymer co-extrusion experiments represent excellent dynamical analogies with two-magma transport and the effusion of composite lava domes. They demonstrate that the co-extrusion of magmas having different viscosity can explain not only the observed normal zoning in magma dikes and conduits but also the compositional layering observed in effused lava domes. New results indicate that dike and conduit zoning along with dome layering are strongly dependent on the viscosity contrast between the flowing magmas. Realistic models of magma storage and dike formation show that co-extrusion of magmas is both more readily explained and energetically preferred over serial intrusion processes. Co-extrusion during the formation of dikes may play an important role in triggering larger volcanic eruptions. Lubrication of the flow by a typically, more mafic, lower-viscosity component allows a more viscous but also more highly volatile-charged magma to be transported greater distances upward in the dike resulting in exsolution of a gas phase and the formation of a magma foam. Transition to a foam lowers the bulk density of the magma enabling dikes to propagate greater vertical distances for a given back pressure. Our new results suggest that a dike propagating across a sloping magma-chamber roof intersecting both "wet" silicic and relatively "dry" mafic layers has the greatest probability of reaching the surface in the dike segment where the magmas flow co-extrusively. Thus, bimodal eruptive compositions are dynamically preferred in such a petrologically common magmatic regime. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

  9. The Sense of Magma Flow in Neogene Dike Intrusions from East Iceland (Invited)

    NASA Astrophysics Data System (ADS)

    Riishuus, M. S.; Eriksson, P. I.; Elming, S.

    2013-12-01

    flow and paleo-stress resolved on the dikes are determined in 13 of 24 dikes. The magma flow is for nine dikes interpreted as sub-horizontal and northward directed away from the central volcano, and found vertical in three cases. The preferentially sub-horizontal magma flow in the Álftafjördur swarm suggests that dike propagation in this type of Icelandic volcanic systems originate in shallow crustal magma chambers. The regional tectonic paleo-stress field is deduced to cause oblique spreading across the Álftafjördur dike swarm and govern a sub-horizontal dextral shear component on the dike planes during propagation. Limitations of the applied magnetic fabric analysis will be discussed.

  10. Modeling the Daly Gap: The Influence of Latent Heat Production in Controlling Magma Extraction and Eruption

    NASA Astrophysics Data System (ADS)

    Nelson, B. K.; Ghiorso, M. S.; Bachmann, O.; Dufek, J.

    2011-12-01

    A century-old issue in volcanology is the origin of the gap in chemical compositions observed in magmatic series on ocean islands and arcs - the "Daly Gap". If the gap forms during differentiation from a mafic parent, models that predict the dynamics of magma extraction as a function of chemical composition must simulate a process that results in volumetrically biased, bimodal compositions of erupted magmas. The probability of magma extraction is controlled by magma dynamical processes, which have a complex response to magmatic heat evolution. Heat loss from the magmatic system is far from a simple, monotonic function of time. It is modified by the crystallization sequence, chamber margin heat flux, and is buffered by latent heat production. We use chemical and thermal calculations of MELTS (Ghiorso & Sack, 1995) as input to the physical model of QUANTUM (Dufek & Bachmann, 2010) to predict crystallinity windows of most probable magma extraction. We modeled two case studies: volcanism on Tenerife, Canary Islands, and the Campanian Ignimbrite (CI) of Campi Flegrei, Italy. Both preserve a basanitic to phonolitic lineage and have comparable total alkali concentrations; however, CI has high and Tenerife has low K2O/Na2O. Modeled thermal histories of differentiation for the two sequences contrast strongly. In Tenerife, the rate of latent heat production is almost always greater than sensible heat production, with spikes in the ratio of latent to sensible heats of up to 40 associated with the appearance of Fe-Ti oxides at near 50% crystallization. This punctuated heat production must cause magma temperature change to stall or slow in time. The extended time spent at ≈50% crystallinity, associated with dynamical processes that enhance melt extraction near 50% crystallinity, suggests the magma composition at this interval should be common. In Tenerife, the modeled composition coincides with that of the first peak in the bimodal frequency-composition distribution. In our

  11. A cellular automaton to model magma/crust interactions and volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Sanchez, L.; Shcherbakov, R.

    2012-12-01

    Volcanic eruptions are the outcomes of complex dynamical interactions between magma and the Earth's crust and are characterized by non-trivial temporal correlations. It is of major importance to study the processes involved in magma ascent within the crust which can lead to a better under-standing of the failure mechanism that leads to an eruption. In a previous study, we showed that the interevent time distributions of volcanic eruptions were characterized by a universal behavior, independent of the type of volcanism and geographical location. The distribution for interevent times between successive eruptions were shown to deviate from the simple Poisson statistics. Instead, occurrence of volcanic eruptions can be modeled by a log-normal distribution. In the present work, we investigate the interactions between the magma and the host rock at the microscopic level using a cellular automaton approach. We consider a two-dimensional system on a rectangular lattice consisting of the magma chamber and the overlying crust. The magma particles coming from the chamber rise through the crust by damaging it to its failure point, and eventually reach the surface resulting in an eruption. While not damaged by magma, the crust can heal with time and fractures will close. The amount of damage that a particle can afflict on a crustal site and the healing capability of the crust are two model parameters and mimic various crustal settings. We consider two different definitions of the eruption sizes: i) only the magma in the vertical fractures directly under the eruption point is considered to define the eruption; ii) the entire fracture network (vertical and horizontal) filled with magma and connected to the eruption point is considered to define the eruption. In order to investigate further what controls the explosivity of eruptions, we introduce a binary system to model the magma and dissolved gases: magma and dissolved gases which are characterized by dierent damage capacities

  12. Geophysical observations of Kilauea Volcano, Hawaii, 2. Constraints on the magma supply during November 1975 September 1977

    NASA Astrophysics Data System (ADS)

    Dzurisin, Daniel; Anderson, Lennart A.; Eaton, Gordon P.; Koyanagi, Robert Y.; Lipman, Peter W.; Lockwood, John P.; Okamura, Reginald T.; Puniwai, Gary S.; Sako, Maurice K.; Yamashita, Kenneth M.

    1980-05-01

    Following a 22-month hiatus in eruptive activity, Kilauea volcano extruded roughly 35 × 10 6m3 of tholeiitic basalt from vents along its middle east rift zone during 13 September-1 October, 1977. The lengthy prelude to this eruption began with a magnitude 7.2 earthquake on 29 November, 1975, and included rapid summit deflation episodes in June, July, and August 1976 and February 1977. Synthesis of seismic, geodetic, gravimetric, and electrical self-potential observations suggests the following model for this atypical Kilauea eruptive cycle. Rapid summit deflation initiated by the November 1975 earthquake reflected substantial migration of magma from beneath the summit region of Kilauea into the east and southwest rift zones. Simultaneous leveling and microgravity observations suggest that 40-90 × 10 6 m 3 of void space was created within the summit magma chamber as a result of the earthquake. If this volume was filled by magma from depth before the east rift zone intrusive event of June 1976, the average rate of supply was 6-13 × 10 6 m 3/month, a rate that is consistent with the value of 9 × 10 6 m 3/month suggested from observations of long-duration Kilauea eruptions. Essentially zero net vertical change was recorded at the summit during the 15-month period beginning with the June 1976 intrusion and ending with the September 1977 eruption. This fact suggests that most magma supplied from depth during this interval was eventually delivered to the east rift zone, at least in part during four rapid summit deflation episodes. Microearthquake epicenters migrated downrift to the middle east rift zone for the first time during the later stages of the February 1977 intrusion, an occurrence presumably reflecting movement of magma into the eventual eruptive zone. This observation was confirmed by tilt surveys in May 1977 that revealed a major inflation center roughly 30 km east of the summit in an area of anomalous steaming and forest kill first noted in March 1976.

  13. Dike injection and magma mixing in Kenya rift volcanoes

    NASA Astrophysics Data System (ADS)

    Anthony, E. Y.; Espejel, V.; Biggs, J.

    2009-12-01

    A nexus of volcanoes in the rift graben at approximately the latitude of Nairobi consist of central vent trachyte, phonolite, and peralkaline rhyolite and cinder cone and fissure-fed flows of basalt to benmoreite. The volcanoes are referred to as the Central Kenya Peralkaline Province (CKPP, Macdonald and Scaillet, 2006, Lithos 91, 59-73) and formed by a combination of processes including fractional crystallization, magma mixing, and volatile transport (Ren et al., 2006, Lithos 91, 109-124; Macdonald et al., 2008, JPet 49, 1515-1547). This presentation focuses on magma mixing for trachytes and phonolites for Suswa rocks, which are the southernmost part of the CKPP. We also explore the contribution of magma process studies to the interpretation of recent geodetic data, which indicate inflation/deflation of up to 21 cm for Kenyan volcanoes from 1997 to present (Biggs et al., 2009, Geology, in press). Incontrovertible evidence for magma mixing is found in field evidence, where a basaltic trachyandesite ash horizon is found interbedded with syncaldera trachyte (Skilling, 1993, J. Geol. Society London 150, 885-896), hand-specimen and thin-section petrography, and disequilibrium mineral chemistry. Precaldera lavas contain a homogeneous group of anorthoclase crystals with An content 6% or less. Syncaldera samples contain this same group and two other populations: polysynthetic twinned labradorite and andesine and anorthoclase with An content of 17%. Textures for all three groups indicate disequilibrium. Postcaldera flows contain the high and low An anorthoclase populations but lack the polysynthetic twinned labradorite and andesine. These observations suggest a model of injection of mafic magmas via diking into shallow trachtytic magma systems. Recent geodetic studies of dike injection and subsequent seismic/volcanic activity in both Ethiopia and Lengai point to the ongoing importance of these processes to rift evolution in East Africa.

  14. Shallow magma targets in the western US

    SciTech Connect

    Hardee, H.C.

    1984-10-01

    Within the next few years a hole will be drilled into a shallow magma body in the western US for the purpose of evaluating the engineering feasibility of magma energy. This paper examines potential drilling sites for these engineering feasibility experiments. Target sites high on the list are ones that currently exhibit good geophysical and geological data for shallow magma and also have reasonable operational requirements. Top ranked sites for the first magma energy well are Long Valley, CA, and Coso/Indian Wells, CA. Kilauea, HI, also in the top group, is an attractive site for some limited field experiments. A number of additional sites offer promise as eventual magma energy sites, but sparsity of geophysical data presently prevents these sites from being considered for the first magma energy well.

  15. ARE the Merensky Reef and Massive Chromitites of the Bushveld Complex Formed from Crystal Slurries or Superheated Magmas?

    NASA Astrophysics Data System (ADS)

    Latypov, R.; Chistyakova, S.

    2014-12-01

    Many recent models attribute the origin of the Merensky Reef and massive chromitites of the Bushveld Complex, South Africa to replenishment of a magma chamber by phenocryst-rich magmas (crystal slurries). In particular, the emplacement of chromite-rich slurries from the staging chamber is currently thought to be responsible for the formation of massive chromitites of the Bushveld Complex. There are, however, first-order observations that are not compatible with this popular idea. One of the key features of the Merensky Reef and almost all layers of massive chromitites is their close association with so-called potholes, the circular to elliptical depressions with gently to steeply inclined sidewalls that are transgressive relative to their footwall rocks. Portions of magmatic stratigraphy are totally absent from the footwall rocks in pothole areas. Here we summarize abundant field evidence from several localities of the Eastern and Western Bushveld Complex that provide strong support to an idea that these portions of footwall rocks were thermally and partly mechanically eroded away by new magma pulses refilling the chamber. To be able to erode the footwall rocks so effectively, the new magmas must have been superheated upon emplacement into the chamber (no phenocrysts in the magmas). Otherwise the phenocrysts will immediately settle to the floor of the chamber to form a blanket protecting footwall rocks from the thermal erosion. The geological observations thus suggest that the origin of the Merensky Reef and massive chromitites must be tackled in the frame of the models that involve the emplacement of superheated, rather than phenocryst-laden magmas. The important lesson to be drawn from this study is that the field observations are still one of the primary tools for the rigorous testing of our hypotheses in modern igneous/ore petrology.

  16. Short-lived decay series disequilibria in the natrocarbonatite lavas of Oldoinyo Lengai, Tanzania: constraints on the timing of magma genesis

    NASA Astrophysics Data System (ADS)

    Pyle, D. M.; Dawson, J. B.; Ivanovich, M.

    1991-08-01

    The 1988 natrocarbonatite lavas from Oldoinyo Lengai volcano, Tanzania have been analysed for 232Th, 230Th, 228Th, 238U, 228Ra/ 226Ra. These lavas are unique, in showing disequilibria between 228Th/ 232Th, and between 228Ra and 232Th. Aa and pahoehoe lavas have a mean ( 228Th 232Th) activity ratio of 5.5 ± 0.6 , and one lava has ( 228Ra/ 226Ra) = 0.11 ± 0.01 . The lavas have ( 230Th/ 238U) ˜ 0.1-0.2 , and [ UTh] weight ratios of 2.0-3.2. Late-stage samples, extruded from the lavas on cooling and interpreted as extreme fractionates of the original lavas are highly enriched in U and Ra relative to Th. These samples have measured [ UTh] weight ratios of 5.6-6.4, and a calculated ( 228Ra/ 232Th) activity ratio of 108 ± 5 . Disequilibria between 238U&z.sbnd; 230Th&z.sbnd; 226Ra are consistent with an origin by immiscibility of 4-22wt% natrocarbonatite from nephelinite magma. Disequilibria between 232Th&z.sbnd; 228Ra&z.sbnd; 228Th are consistent with either of two endmember models: (1) instantaneous separation of magma at depth, with eruption 20 ± 1 years later; (2) recharging of a steady-state magma chamber below Oldoinyo Lengai with a maximum volume of 1.5 ± 0.2 × 10 7 m 3 of carbonatite, and a mean magma residence time of 81 ± 9 years. The total time between natrocarbonatite generation and eruption is between 20 and 81 years.

  17. National Ignition Facility Target Chamber

    SciTech Connect

    Wavrik, R W; Cox, J R; Fleming, P J

    2000-10-05

    On June 11, 1999 the Department of Energy dedicated the single largest piece of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) in Livermore, California. The ten (10) meter diameter aluminum target high vacuum chamber will serve as the working end of the largest laser in the world. The output of 192 laser beams will converge at the precise center of the chamber. The laser beams will enter the chamber in two by two arrays to illuminate 10 millimeter long gold cylinders called hohlraums enclosing 2 millimeter capsule containing deuterium, tritium and isotopes of hydrogen. The two isotopes will fuse, thereby creating temperatures and pressures resembling those found only inside stars and in detonated nuclear weapons, but on a minute scale. The NIF Project will serve as an essential facility to insure safety and reliability of our nation's nuclear arsenal as well as demonstrating inertial fusion's contribution to creating electrical power. The paper will discuss the requirements that had to be addressed during the design, fabrication and testing of the target chamber. A team from Sandia National Laboratories (SNL) and LLNL with input from industry performed the configuration and basic design of the target chamber. The method of fabrication and construction of the aluminum target chamber was devised by Pitt-Des Moines, Inc. (PDM). PDM also participated in the design of the chamber in areas such as the Target Chamber Realignment and Adjustment System, which would allow realignment of the sphere laser beams in the event of earth settlement or movement from a seismic event. During the fabrication of the target chamber the sphericity tolerances had to be addressed for the individual plates. Procedures were developed for forming, edge preparation and welding of individual plates. Construction plans were developed to allow the field construction of the target chamber to occur parallel to other NIF construction activities. This was

  18. Magma evolution and the formation of porphyry Cu Au ore fluids: evidence from silicate and sulfide melt inclusions

    NASA Astrophysics Data System (ADS)

    Halter, Werner E.; Heinrich, Christoph A.; Pettke, Thomas

    2005-03-01

    Silicate and sulfide melt inclusions from the andesitic Farallón Negro Volcanic Complex in NW Argentina were analyzed by laser ablation ICPMS to track the behavior of Cu and Au during magma evolution, and to identify the processes in the source of fluids responsible for porphyry-Cu-Au mineralization at the 600 Mt Bajo de la Alumbrera deposit. The combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle-derived mafic magma that contained approximately 6 wt.% H2O and 200 ppm Cu. This magma and a rhyodacitic magma mixed in an upper-crustal magma chamber, feeding the volcanic systems and associated subvolcanic intrusions over 2.6 million years. Generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps: (1) Generation of a sulfide melt upon magma mixing in some parts of the magma chamber. (2) Partitioning of Cu and Au into the sulfide melt (enrichment factor of 10,000 for Cu) leading to Cu and Au concentrations of several wt.% or ppm, respectively. (3) A change in the tectonic regime from local extension to compression at the end of protracted volcanism. (4) Intrusion of a dacitic magma stock from the upper part of the layered magma chamber. (5) Volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber, generating a fluid with a Cu/Au ratio equal to that of the precursor sulfide. (6) Focused fluid transport and precipitation of the two metals in the porphyry, yielding an ore body containing Au and Cu in the proportions dictated by the magmatic fluid source. The Cu/S ratio in the sulfide melt inclusions requires that approximately 4,000 ppm sulfur is extracted from the andesitic magma upon mixing. This exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source

  19. Portable Hyperbaric Chamber

    NASA Technical Reports Server (NTRS)

    Schneider, William C. (Inventor); Locke, James P. (Inventor); DeLaFuente, Horacio (Inventor)

    2001-01-01

    A portable, collapsible hyperbaric chamber was developed. A toroidal inflatable skeleton provides initial structural support for the chamber, allowing the attendant and/or patient to enter the chamber. Oval hatches mate against bulkhead rings, and the hyperbaric chamber is pressurized. The hatches seal against an o-ring, and the internal pressure of the chamber provides the required pressure against the hatch to maintain an airtight seal. In the preferred embodiment, the hyperbaric chamber has an airlock to allow the attendant to enter and exit the patient chamber during treatment. Visual communication is provided through portholes in the patient and/or airlock chamber. Life monitoring and support systems are in communication with the interior of the hyperbaric chamber and/or airlock chamber through conduits and/or sealed feed-through connectors into the hyperbaric chamber.

  20. Recent progress in magma energy extraction

    SciTech Connect

    Ortega, A.; Dunn, J.C.; Chu, T.Y.; Wemple, R.P.; Hickox, C.E.

    1987-01-01

    Ongoing research in the area of Magma Energy Extraction is directed at developing a fundamental understanding of the establishment and long term operation of an open, direct-contact heat exchanger in a crustal magma body. The energy extraction rate has a direct influence on the economic viability of the concept. An open heat exchanger, in which fluid is circulated through the interconnecting fissures and fractures in the solidified region around drilling tubing, offers the promise of very high rates of heat transfer. This paper discusses recent research in five areas: (1) fundamental mechanisms of solidifying and thermally fracturing magma; (2) convective heat transfer in the internally fractured solidified magma; (3) convective flow in the molten magma and heat transfer from the magma to the cooled heat exchanger protruding into it; (4) numerical simulation of the overall energy extraction process; and (5) the thermodynamics of energy conversion in a magma power plant at the surface. The studies show that an open heat exchanger can be formed by solidifying magma around a cooled borehole and that the resulting mass will be extensively fractured by thermally-induced stresses. Numerical models indicate that high quality thermal energy can be delivered at the wellhead at nominal rates from 25 to 30 MW electric. It is shown that optimum well circulation rates can be found that depend on the heat transfer characteristics of the magma heat exchanger and the thermodynamic power conversion efficiencies of the surface plant.

  1. The Relationship Between Amphibole Cumulates and Adakite Magma

    NASA Astrophysics Data System (ADS)

    Rooney, T. O.

    2009-12-01

    fractionation is needed. New 39Ar/40Ar ages (~25-26 Ma) for these andesites show that they are among the earliest products of the Central American Arc in Panama. During this initial stage of activity, the lithospheric thickness of the arc may have been insufficient to stabilize garnet and the magmas were dominated by amphibole fractionation. Changing lithospheric conditions during the Pliocene-Quaternary may have led to the stabilization of garnet in these same water-saturated andesites, producing the modern adakite magmas of the Panama Arc.

  2. Combined effect of permeability and crystallization on the explosive eruption of basaltic magma

    NASA Astrophysics Data System (ADS)

    Moitra, P.; Gonnermann, H. M.; Houghton, B. F.; Crozier, J.

    2015-12-01

    Plinian eruptions are the most dangerous style of eruptive activity of basaltic magma. In this study, we focus on the two best studied Plinian eruptions of basaltic magma at Mt. Tarawera, New Zealand (1886 CE) and Mt. Etna, Italy (122 BCE). We measured and analyzed the porosity-permeability relationships of the pyroclasts from both eruptions. We then used numerical modeling to assess the relative importance of two competing processes during eruptive magma ascent, which are the syneruptive crystallization that increases viscosity, potentially increasing bubble overpressure, and the open-system degassing of the permeable magma that allows the pressurized gas to escape, potentially reducing bubble overpressure. We find that the onset of crystallization is likely to have occurred prior to the onset of magma percolation. The orders of magnitude increase in magma viscosity due to the nucleation and growth of microlites had the combined effect of rapidly increasing the decompression rate, due to viscous pressure losses associated with magma flow within the volcanic conduit, and decreasing the rates of bubble growth, thus building up large overpressures inside bubbles. Although measured permeabilities of the studied pyroclasts are 1-2 orders of magnitude higher than their silicic counterpart, our model results show that crystallization and subsequent increase in viscosity are likely to surpass the effect of open-system gas loss, thus increasing bubble overpressure, required for explosive magma fragmentation.

  3. Geochemical characteristics of hydrous basaltic magmas due to assimilation and fractional crystallization: the Ikoma gabbroic complex, southwest Japan

    NASA Astrophysics Data System (ADS)

    Koizumi, N.; Okudaira, T.; Ogawa, D.; Yamashita, K.; Suda, Y.

    2016-02-01

    To clarify the processes that occur in hydrous basaltic magma chambers, we have undertaken detailed petrological and geochemical analyses of mafic and intermediate rocks from the Ikoma gabbroic complex, southwest Japan. The complex consists mainly of hornblende gabbros, hornblende gabbronorites, and hornblende leucogabbros. The hornblende leucogabbros are characterized by low TiO2 and high CaO contents, whereas the hornblende gabbronorites have high TiO2 and low CaO contents. The initial 87Sr/86Sr ratios (SrI) of the hornblende gabbronorites and hornblende gabbros are higher than those of the hornblende leucogabbros and plagioclase, and they may have resulted from a higher degree of assimilation of metasediments. The geochemical features of the hornblende leucogabbros and hornblende gabbronorites can be explained by accumulation of plagioclase and ilmenite, respectively, in a hybrid magma that formed by chemical interaction between mafic magma and metasediment, whereas the hornblende gabbros were produced by a high degree of crustal assimilation and fractional crystallization of this hybrid magma. As a result of the density differences between crystals and melt, the Ikoma gabbroic rocks formed by the accumulation of plagioclase in the middle of the magma chamber and by the accumulation of ilmenite in the bottom of the chamber. Taking into account the subsequent assimilation and fractional crystallization, our observations suggest an enriched mantle (SrI = ~0.7071) as the source material for the Ikoma gabbros.

  4. Geochemical characteristics of hydrous basaltic magmas due to assimilation and fractional crystallization: the Ikoma gabbroic complex, southwest Japan

    NASA Astrophysics Data System (ADS)

    Koizumi, N.; Okudaira, T.; Ogawa, D.; Yamashita, K.; Suda, Y.

    2016-10-01

    To clarify the processes that occur in hydrous basaltic magma chambers, we have undertaken detailed petrological and geochemical analyses of mafic and intermediate rocks from the Ikoma gabbroic complex, southwest Japan. The complex consists mainly of hornblende gabbros, hornblende gabbronorites, and hornblende leucogabbros. The hornblende leucogabbros are characterized by low TiO2 and high CaO contents, whereas the hornblende gabbronorites have high TiO2 and low CaO contents. The initial 87Sr/86Sr ratios (SrI) of the hornblende gabbronorites and hornblende gabbros are higher than those of the hornblende leucogabbros and plagioclase, and they may have resulted from a higher degree of assimilation of metasediments. The geochemical features of the hornblende leucogabbros and hornblende gabbronorites can be explained by accumulation of plagioclase and ilmenite, respectively, in a hybrid magma that formed by chemical interaction between mafic magma and metasediment, whereas the hornblende gabbros were produced by a high degree of crustal assimilation and fractional crystallization of this hybrid magma. As a result of the density differences between crystals and melt, the Ikoma gabbroic rocks formed by the accumulation of plagioclase in the middle of the magma chamber and by the accumulation of ilmenite in the bottom of the chamber. Taking into account the subsequent assimilation and fractional crystallization, our observations suggest an enriched mantle (SrI = ~0.7071) as the source material for the Ikoma gabbros.

  5. Petrogenesis of the Elephant Moraine A79001 meteorite Multiple magma pulses on the shergottite parent body

    NASA Technical Reports Server (NTRS)

    Mcsween, H. Y., Jr.; Jarosewich, E.

    1983-01-01

    The EETA 79001 achondrite consists of two distinct igneous lithologies joined along a planar, non-brecciated contact. Both are basaltic rocks composed primarily of pigeonite, augite, and maskelynite, but one contains zoned megacrysts of olivine, orthopyroxene, and chromite that represent disaggregated xenoliths of harzburzite. Both lithologies probably formed from successive volcanic flows or multiple injections of magma into a small, shallow chamber. Many similarities between the two virtually synchronous magmas suggest that they are related. Possible mechanisms to explain their differences involve varying degrees of assimilation, fractionation from similar parental magmas, or partial melting of a similar source peridotite; of these, assimilation of the observed megacryst assemblage seems most plausible. However, some isotopic contamination may be required in any of these petrogenetic models. The meteorite has suffered extensive shock metamorphism and localized melting during a large impact event that probably excavated and liberated it from its parent body.

  6. Electricity generation using chocolate industry wastewater and its treatment in activated sludge based microbial fuel cell and analysis of developed microbial community in the anode chamber.

    PubMed

    Patil, Sunil A; Surakasi, Venkata Prasad; Koul, Sandeep; Ijmulwar, Shrikant; Vivek, Amar; Shouche, Y S; Kapadnis, B P

    2009-11-01

    Feasibility of using chocolate industry wastewater as a substrate for electricity generation using activated sludge as a source of microorganisms was investigated in two-chambered microbial fuel cell. The maximum current generated with membrane and salt bridge MFCs was 3.02 and 2.3 A/m(2), respectively, at 100 ohms external resistance, whereas the maximum current generated in glucose powered MFC was 3.1 A/m(2). The use of chocolate industry wastewater in cathode chamber was promising with 4.1 mA current output. Significant reduction in COD, BOD, total solids and total dissolved solids of wastewater by 75%, 65%, 68%, 50%, respectively, indicated effective wastewater treatment in batch experiments. The 16S rDNA analysis of anode biofilm and suspended cells revealed predominance of beta-Proteobacteria clones with 50.6% followed by unclassified bacteria (9.9%), alpha-Proteobacteria (9.1%), other Proteobacteria (9%), Planctomycetes (5.8%), Firmicutes (4.9%), Nitrospora (3.3%), Spirochaetes (3.3%), Bacteroides (2.4%) and gamma-Proteobacteria (0.8%). Diverse bacterial groups represented as members of the anode chamber community.

  7. Formation of redox gradients during magma-magma mixing

    NASA Astrophysics Data System (ADS)

    Ruprecht, P.; Fiege, A.; Simon, A. C.

    2015-12-01

    Magma-mixing is a key process that controls mass transfer in magmatic systems. The variations in melt compositions near the magma-magma interface potentially change the Fe oxidation state [1] and, thus, affect the solubility and transport of metals. To test this hypothesis, diffusion-couple experiments were performed at 1000 °C, 150 MPa and QFM+4. Synthesized crystal-bearing cylinders of hydrous dacite and hydrous basaltic andesite were equilibrated for up to 80 h. The run products show that mafic components (Fe, Mg, etc.) were transported from the andesite into the dacite, while Si, Na and K diffused from the dacite into the andesite. A crystal dissolution sequence in the order of cpx, opx, plag, and spl/il was observed for the andesite. We combined μ-XANES spectroscopy at Fe K-edge [2] with two-oxide oxybarometry [3] to measure redox profiles within our experiments. Here, fO2 decreased towards the interface within the dacite and increased towards the interface within the andesite. This discontinuous fO2 evolution, with a sharp redox gradient of ~1.8 log fO2 units at the interface was maintained throughout the time-series despite the externally imposed fO2 of the vessel. We propose a combination of two mechanisms that create and sustain this redox gradient: 1) The dissolution of cpx and opx in the andesite mainly introduced Fe2+ into the melt, which diffused towards the dacite, lowering Fe3+/SFe near the interface. 2) Charge balance calculations in the melt during diffusive exchange suggest net positive charge excess in the andesite near the interface (i.e., oxidation) and net negative charge excess in the dacite near the interface (i.e., reduction). We suggest that this (metastable) redox layer can help to explain the contrasting Au/Cu ratios observed for arc-related porphyry-type ore deposits. [1] Moretti (2005), Ann. Geophys. 48, 583-608. [2] Cottrell et al. (2009), Chem. Geol. 268, 167-179. [3] Ghiorso and Evans (2008), Am. J. Sci. 308, 957-1039.

  8. Origin of Aphyric Phonolitic Magmas: Natural Evidences and Experimental Constraints

    NASA Astrophysics Data System (ADS)

    Masotta, M.; Freda, C.; Gaeta, M.

    2010-12-01

    Large explosive phonolitic eruptions are commonly characterised by aphyric juvenile eruptive products. Taking into account the low density contrast among phonolitic composition and settling phases (i.e., feldspar and leucite), the almost complete lack of crystals in these differentiated compositions rises the question of which process could produce such an efficient crystal-melt separation. Seeking for an answer, we have investigated crystallization in presence of a thermal gradient as a possible mechanism for crystal-melt separation, considering both chemical and physical effects acting on a variably crystallized system. Using a natural tephri-phonolitic composition as starting material (M.te Aguzzo scoria cone, Sabatini Volcanic District, Central Italy), we have reproduced thermal gradient-driven crystallization in order to simulate the crystallization process in a thermally zoned magma chamber. Crystallization degree (paragenesis made of clinopyroxene±feldspars±leucite) as well as melt composition varies along the thermal gradient. In particular, melt composition ranges from the tephri-phonolitic starting composition at the bottom of the charge (hottest and aphyric zone) to phonolitic at the top (cooler and heterogeneously-crystallised zone). Backscattered images of experimental products clearly evidence: i) the aphyric tephri-phonolitic melt region at the bottom of the charge; ii) a drop-shaped crystal clustering in the middle zone; and iii) large aphyric belt and pockets (up to 100 µm wide) of phonolitic melt, with large deformed-shaped sanidine occurring at their margin, at the charge top region. The latter two features, resulting from solid-melt displacements, suggest that the segregation of phonolitic melt can be related to crystal sinking and compaction. On the other hand, the compositional variability of the melt along the thermal gradient is directly related to the crystallization degree, indicating that chemical diffusion and thermal migration have

  9. Why do Martian Magmas erupt?

    NASA Astrophysics Data System (ADS)

    Balta, J. B.; McSween, H. Y.

    2011-12-01

    Eruption of silicate lava, whether on Earth or another planet, requires that at some depth the melt has lower density than the surrounding rocks. As the densities of silicate liquids change during crystallization, whether a particular silicate liquid will erupt or be trapped at a level of neutral buoyancy is a complex yet fundamental issue for planetary dynamics. In general, 3 factors drive surface eruptions: inherent buoyancy relative to mantle phases, compositional evolution, and volatile contents. These factors manifest on Earth as terrestrial basalts commonly have compositions close to a density minimum [1]. Recent work has produced estimates of Martian parental magma compositions [2-5] based on shergottite meteorites and from Gusev crater. Using the MELTS algorithm [6] and other density calibrations, we simulated evolution of these liquids, focusing on density changes. For much of the crystallization path, density is controlled by FeO. All of the liquids begin with ρ ~ 2.8 g/cc at 1 bar, and the evolution of liquid density is controlled by the liquidus phases. At low pressures, olivine is the liquidus phase for each melt, and as FeO is not incompatible in olivine, olivine crystallization decreases liquid density, increasing buoyancy with crystallization. However, FeO is incompatible in pyroxene, and thus liquids crystallizing pyroxene become denser and less buoyant with crystallization, producing liquids with densities up to and above 3.0 g/cc. As the olivine-pyroxene saturation relationship is affected by pressure and chemistry, the identity of the liquidus phase and density evolution will vary between magmas. Without spreading centers, Mars has no location where the mantle approaches the surface, and it is likely that any magma which is denser than the crust will stall below or within that crust. The crystallization path of a liquid is a function of pressure, with pyroxene crystallizing first at P > 10 kbar (~80 km depth), close to the base of the Martian

  10. Taxonomy Of Magma Mixing I: Magma Mixing Metrics And The Thermochemistry Of Magma Hybridization Illuminated With A Toy Model

    NASA Astrophysics Data System (ADS)

    Spera, F. J.; Bohrson, W. A.; Schmidt, J.

    2013-12-01

    The rock record preserves abundant evidence of magma mixing in the form of mafic enclaves and mixed pumice in volcanic eruptions, syn-plutonic mafic or silicic dikes and intrusive complexes, replenishment events recorded in cumulates from layered intrusions, and crystal scale heterogeneity in phenocrysts and cumulate minerals. These evidently show that magma mixing in conjunction with crystallization (perfect fractional or incremental batch) is a first-order petrogenetic process. Magma mixing (sensu lato) occurs across a spectrum of mixed states from magma mingling to complete blending. The degree of mixing is quantified (Oldenburg et al, 1989) using two measures: the statistics of the segregation length scales (scale of segregation, L*) and the spatial contrast in composition (C) relative to the mean C (intensity of segregation, I). Mingling of dissimilar magmas produces a heterogeneous mixture containing discrete regions of end member melts and populations of crystals with L* = finite and I > 0. When L*→∞ and I→0 , the mixing magmas become hybridized and can be studied thermodynamically. Such hybrid magma is a multiphase equilibrium mixture of homogeneous melt, unzoned crystals and possible bubbles of a supercritical fluid. Here, we use a toy model to elucidate the principles of magma hybridization in a binary system (components A and B with pure crystals of α or β phase) with simple thermodynamics to build an outcome taxonomy. This binary system is not unlike the system Anorthite-Diopside, the classic low-pressure model basalt system. In the toy model, there are seven parameters describing the phase equilibria (eutectic T and X, specific heat, melting T and fusion enthalpies of α and β crystals) and five variables describing the magma mixing conditions: end member bulk compositions, temperatures and fraction of resident magma (M) that blends with recharge (R) magma to form a single equilibrium hybrid magma. There are 24 possible initial states when M

  11. Explosive eruption of rhyodacitic magma at the Cordón-Caulle volcanic complex, southern Chile

    NASA Astrophysics Data System (ADS)

    Castro, J. M.; Schipper, C.

    2011-12-01

    After lying dormant for decades, the Cordón-Caulle volcanic complex (CCVC) reactivated again on 4 June, 2011 with an explosive eruption that produced a sustained vertical ash column reaching roughly 14,000 m a.s.l. This explosive phase produced a tephra plume that dispersed E-SE across the Chilean Patagonia into Argentina, and within a week encircled the globe prompting widespread disruption to air traffic and several airport closures. After about 3 weeks of fluctuating explosive activity, a lava flow began effusing from the same vent as the initial activity. We analyzed pumice and ash samples of the Plinian fall from 4 June for their major and trace element makeup, mineralogical characteristics, and 3D textural relationships within pyroclasts. The light beige, phenocryst-poor (<5 vol%) pumice contains plagioclase (~1mm) as its primary phase, and magnetite, orthopyroxene and clinopyroxene in sub-equal amounts. The crystals often form intergrowth clusters but may also be found separate and enclosed in highly vesicular microlite-free glass. As shown by XRF analyses on bulk pumice and ash samples collected from two localities southeast of the vent, the current eruptives comprise the following (in wt.%): SiO2 = 69.6, TiO2 = 0.70, Al2O3 = 14.3, Fe2O3 = 4.56, MnO = 0.11, MgO = 0.54, CaO = 2.3, Na2O = 5.14, K2O = 2.75, P2O5 = 0.11; and, (in ppm): Cr = 6.7, Ni = 2.3, Rb = 70.3, Sr = 163.3, Y = 51.7, Zr = 328, Ba = 702, Pb = 23.7. Interestingly, these compositions are virtually identical to those of magma erupted during 1960 and closely resemble rhyodacite erupted in 1921 from nearby vents. The primary difference between the present eruption and its recent predecessors is the much greater eruptive vigour of the current phase. Another distinction between the present and past historical eruptions is the presence of conspicuous mafic-felsic mingling textures in a small percentage (~0.5 vol%) of the current pumice. Textural and chemical analyses of the mafic blobs are

  12. Pressures of Partial Crystallization of Magmas from the Juan de Fuca Ridge: Implications for Crustal Accretion

    NASA Astrophysics Data System (ADS)

    Scott, J. L.; Barton, M.

    2010-12-01

    Plate spreading at the mid-ocean ridges is accompanied by intrusion of dikes and eruption of lava along the ridge axis. It has been suggested that the depth of magma chambers that feed the flows and dikes is related to the rate of spreading. As part of a larger effort to examine this hypothesis, we determined the depths of magma chambers beneath the intermediate spreading Juan de Fuca Ridge (JdF) which extends from the Blanco fracture zone at about 44.5 degrees North to the Triple junction of the JdF, Nootka Fault, and the Socanco fracture zone at 48.7 degrees North. Pressures of partial crystallization were determined by comparing the compositions of natural liquids (glasses) with those of experimental liquids in equilibrium with olivine, plagioclase, and clinopyroxene at different pressures and temperatures using the method described by Kelley and Barton (2008). Chemical analyses mid-ocean ridge basalts glasses sampled from along the JdF were used as liquid compositions. Samples with anomalous chemical compositions and samples that yielded pressures associated with unrealistically large uncertainties were filtered out of the database. The calculated pressures for the remaining 533 samples were used to calculate the depths of partial crystallization and to identify the likely location of magma chambers. Preliminary results indicate that the pressure of partial crystallization decreases from 2 to 1±0.5 kbars from the Blanco fracture zone to the north along the Cleft segment of the ridge. Calculated pressures remain approximately constant at 0.87±0.53 kbars along ridge segments to the north of the Cleft. These low pressures for the remaining segments of the ridge are interpreted to indicate magma chambers at depths of 1.3-4.9 km and agree reasonably well with the depths of seismically imaged tops of axial magma chambers (2-3 km) (Canales et al 2009). The higher pressures obtained for lavas erupted along the Cleft segment of the JdF agree very well with recent

  13. Magma Energy Research Project, FY80 annual progress report

    SciTech Connect

    Colp, J.L.

    1982-04-01

    The technical feasibility of extracting energy from magma bodies is explored. Five aspects of the project are studied: resource location and definition, source tapping, magma characterization, magma/material compatibility, and energy extraction.

  14. Interaction between two contrasting magmas in the Albtal pluton (Schwarzwald, SW Germany): textural and mineral-chemical evidence

    NASA Astrophysics Data System (ADS)

    Michel, Lorenz; Wenzel, Thomas; Markl, Gregor

    2016-07-01

    The magmatic evolution of the Variscan Albtal pluton, Schwarzwald, SW Germany, is explored using detailed textural observations and the chemical composition of plagioclase and biotite in both granite and its mafic magmatic enclaves (MMEs). MMEs probably formed in a two-step process. First, mafic magma intruded a granitic magma chamber and created a boundary layer, which received thermal and compositional input from the mafic magma. This is indicated by corroded "granitic" quartz crystals and by large "granitic" plagioclase xenocrysts, which contain zones of higher anorthite and partly crystallized from a melt of higher Sr content. Texturally, different plagioclase types (e.g. zoned and inclusion-rich types) correspond to different degrees of overprint most likely caused by a thermal and compositional gradient in the boundary layer. The intrusion of a second mafic magma batch into the boundary layer is recorded by a thin An50 zone along plagioclase rims that crystallized from a melt enriched in Sr. Most probably, the second mafic intrusion caused disruption of the boundary layer, dispersal of the hybrid magma in the granite magma and formation of the enclaves. Rapid thermal quenching of the MMEs in the granite magma is manifested by An30 overgrowths on large plagioclase grains that contain needle apatites. Our results demonstrate the importance of microtextural investigations for the reconstruction of possible mixing end members in the formation of granites.

  15. On depressurization of volcanic magma reservoirs by passive degassing

    NASA Astrophysics Data System (ADS)

    Girona, Társilo; Costa, Fidel; Newhall, Chris; Taisne, Benoit

    2014-12-01

    Many active volcanoes around the world alternate episodes of unrest and mildly explosive eruptions with quiescent periods dominated by abundant but passive gas emissions. These are the so-called persistently degassing volcanoes, and well-known examples are Mayon (Philippines) and Etna (Italy). Here, we develop a new lumped-parameter model to investigate by how much the gas released during quiescence can decrease the pressure within persistently degassing volcanoes. Our model is driven by the gas fluxes measured with monitoring systems and takes into account the size of the conduit and reservoir, the viscoelastic response of the crust, the magma density change, the bubble exsolution and expansion at depth, and the hydraulic connectivity between reservoirs and deeper magma sources. A key new finding is that, for a vast majority of scenarios, passive degassing reduces the pressure of shallow magma reservoirs by several MPa in only a few months or years, that is, within the intereruptive timescales of persistently degassing volcanoes. Degassing-induced depressurization could be responsible for the subsidence observed at some volcanoes during quiescence (e.g., at Satsuma-Iwojima and Asama, in Japan; Masaya, in Nicaragua; and Llaima, in Chile), and could play a crucial role in the onset and development of the physical processes which may in turn culminate in new unrest episodes and eruptions. For example, degassing-induced depressurization could promote magma replenishment, induce massive and sudden gas exsolution at depth, and trigger the collapse of the crater floor and reservoir roof.

  16. Degassing and microlite crystallization of basaltic andesite magma erupting at Arenal Volcano, Costa Rica

    NASA Astrophysics Data System (ADS)

    Szramek, Lindsay; Gardner, James E.; Larsen, Jessica

    2006-09-01

    Volcanoes can erupt explosively in Plinian style or effusively as lava flows. Most models for such ranges in activity are based on silicic magma, which may not be appropriate for less viscous basic magma. Although basic magma erupting at Arenal volcano has not varied significantly in bulk composition, the volcano has exhibited a full range in eruptive style, from Plinian activity in 1968 to Strombolian bursts to lava flows. We examined groundmass textures of samples erupted over that range of activity to investigate the controls on the variability. Microlite textures in lavas collected both hot (rapid quenched) and cold show that most samples have textures that are overprinted by crystallization as a result of cooling. Despite that overprint, microlites in the Plinian sample have unique crystal morphologies and vesicles that are much smaller and more spherical than those in the other samples. We interpret those differences as recording a change in degassing style as a result of changing ascent rate in the conduit. To constrain the potential changes in ascent rate, a limited number of decompression experiments were run at rates from 0.0013 to 0.25 MPa/s. Crystal textures and morphologies vary greatly as decompression rates change, and compared to our observed differences in the natural groundmass, it appears that magma erupted in the Plinian event decompressed between 0.0013 and 0.025 MPa/s, whereas magma erupted in non-Plinian events decompressed slower than 0.0013 MPa/s. The change in eruptive style from explosive Plinian to lava effusion thus resulted from an order of magnitude decrease in magma ascent rate. Plinian magma probably rose too quickly to allow bubbles to coalesce and allow the magma to degas efficiently, whereas at other times magma rose more slowly, which allowed bubbles to coalesce and gas to escape leading to less explosive activity.

  17. Magma-water interactions in subaqueous and emergent basaltic

    NASA Astrophysics Data System (ADS)

    Kokelaar, Peter

    1986-10-01

    -explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material, water, and steam. The water gets into the vent by flooding across or through the top of the tephra pile, and violent explosions cease when this access is sealed. The eruptions during emergence of Surtsey and Capelinhos typify the distinctive explosive activity, the style and controls of which are different from those of maar volcanoes.

  18. Unravelling Magma Interaction Phenomena in Volcanic and Plutonic Environments: Analogies and Differences

    NASA Astrophysics Data System (ADS)

    Poli, G.; Perugini, D.

    2003-04-01

    The interaction between magmas is considered more and more to be one of the main mechanisms acting within magma chambers. The coexistence of at least two magmas of different composition and temperature is inherent in these models, and commingling and mixing occur both in the volcanic and plutonic environments, not only on a local scale, but even to produce large batches of magma. Geochemical and thermodynamical aspects of this mechanism have been studied in case histories from petrographical, geochemical, and isotopic point of view in order to define analogies and differences of the effects of magma interaction phenomena in the volcanic and the plutonic environment. Magma interaction has been pointed out using detailed petrographical and mineralogical observations coupled with image analysis. Structures produced by magma mixing processes can be divided into four main groups: i) enclaves, ii) fluidal structures, iii) fragmented dykes and basic septa, iv) mineralogical phase showing chemical-physical disequilibrium. Such structures can be found in both volcanic and plutonic environments although some are more common in the volcanic environment, and vice versa. For instance enclaves are ubiquitous in plutonites and volcanites whereas fluidal structures are more common in the volcanic than the plutonic environment; fragmented dikes and basic septa are almost exclusively a prerogative of plutonic bodies. Besides, whatever is the environment evidence are ubiquitous that physicochemical changes induced disequilibrium phenomena in mineralogical phases that reacted very differently in response to the imposed changes and they now coexist at short distance even in the same thin section. These occurrences can be explained considering the relative time scales on which magma interaction processes can operate in the plutonic and the volcanic environment. For instance the homogenisation by chemical diffusion of elongated fluidal structures requires much less time with respect to

  19. Magma ocean: Mechanisms of formation

    NASA Technical Reports Server (NTRS)

    Kaula, W. M.

    1992-01-01

    The thermal state of the Earth at the time relevant to formation of a magma ocean was dominated by the great impact that created the Moon. As shown in computer experiments, the iron in the impacting bodies quickly sank to the core of the proto-Earth, while a significant fraction of silicates was pushed far enough out beyond the geosynchronous limit to constitute the main material of the Moon. Most of any atmosphere would have been pushed aside, rather than being expelled in the impact. However, the energy remaining in the material not going to the core or expelled was still sufficient to raise its temperature some 1000's of degrees, enough to vaporize silicates and to generate a strong 'planetary wind': a hydrodynamic expansion carrying with it virtually all volatiles plus appreciable silicates. This expansion was violent and uneven in its most energetic stage, but probably the resulting magma ocean was global. The duration, until cooling, was sufficient for silicates to condense to melt and the duration was probably short. Comparison of the Earth and Venus indicates that the great impact was extraordinarily effective in removing volatiles from the proto-Earth; in particular, the enormous differences in primordial inert gases between the planets demand a catastrophic difference in origin circumstances. On the other hand, the comparison limits the amount of silicates lost by the Earth to a rather minor fraction; most of that expelled in the wind must have condensed soon enough for the silicate to fall back to Earth or be swept up by the proto-Moon. So the Earth was left with a magma ocean. The question is whether sufficient water was retained to constitute a steam atmosphere. Probably not, but unknowns affecting this question are the efficiencies of outgassing in great impacts and in subsequent convective churnings deep in the mantle. During the stage when mantle convection is turbulent, an appreciable fraction of volatiles were also retained at depth, perhaps in

  20. Gas-driven filter pressing in magmas

    USGS Publications Warehouse

    Sisson, T.W.; Bacon, C.R.

    1999-01-01

    Most silicic and some mafic magmas expand via second boiling if they crystallize at depths of about 10 km or less. The buildup of gas pressure due to second boiling can be relieved by expulsion of melt out of the region of crystallization, and this process of gas-driven filter pressing assists the crystallization differentiation of magmas. For gas-driven filter pressing to be effective, the region of crystallization must inflate slowly relative to buildup of pressure and expulsion of melt These conditions are satisfied in undercooled magmatic inclusions and in thin sheets of primitive magma underplating cooler magma reservoirs. Gas-driven filter pressing thereby adds fractionated melt to magma bodies. Gas-driven filter pressing is probably the dominant process by which highly evolved melts segregate from crystal mush to form aplitic dikes in granitic plutons; this process could also account for the production of voluminous, crystal-poor rhyolites.

  1. More Evidence for Multiple Meteorite Magmas

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2009-02-01

    Cosmochemists have identified six main compositional types of magma that formed inside asteroids during the first 100 million years of Solar System history. These magmas vary in their chemical and mineralogical make up, but all have in common low concentrations of sodium and other volatile elements. Our low-sodium-magma diet has now changed. Two groups of researchers have identified a new type of asteroidal magma that is rich in sodium and appears to have formed by partial melting of previously unmelted, volatile-rich chondritic rock. The teams, one led by James Day (University of Maryland) and the other by Chip Shearer (University of New Mexico), studied two meteorites found in Antarctica, named Graves Nunatak 06128 and 06129, using a battery of cosmochemical techniques. These studies show that an even wider variety of magmas was produced inside asteroids than we had thought, shedding light on the melting histories and formation of asteroids.

  2. Chemical versus temporal controls on the evolution of tholeiitic and calc-alkaline magmas at two volcanoes in the Alaska-Aleutian arc

    USGS Publications Warehouse

    George, R.; Turner, S.; Hawkesworth, C.; Bacon, C.R.; Nye, C.; Stelling, P.; Dreher, S.

    2004-01-01

    The Alaska-Aleutian island arc is well known for erupting both tholeiitic and calc-alkaline magmas. To investigate the relative roles of chemical and temporal controls in generating these contrasting liquid lines of descent we have undertaken a detailed study of tholeiitic lavas from Akutan volcano in the oceanic A1eutian arc and calc-alkaline products from Aniakchak volcano on the continental A1askan Peninsula. The differences do not appear to be linked to parental magma composition. The Akutan lavas can be explained by closed-system magmatic evolution, whereas curvilinear trace element trends and a large range in 87 Sr/86 Sr isotope ratios in the Aniakchak data appear to require the combined effects of fractional crystallization, assimilation and magma mixing. Both magmatic suites preserve a similar range in 226 Ra-230 Th disequilibria, which suggests that the time scale of crustal residence of magmas beneath both these volcanoes was similar, and of the order of several thousand years. This is consistent with numerical estimates of the time scales for crystallization caused by cooling in convecting crustal magma chambers. During that time interval the tholeiitic Akutan magmas underwent restricted, closed-system, compositional evolution. In contrast, the calc-alkaline magmas beneath Aniakchak volcano underwent significant open-system compositional evolution. Combining these results with data from other studies we suggest that differentiation is faster in calc-alkaline and potassic magma series than in tholeiitic series, owing to a combination of greater extents of assimilation, magma mixing and cooling.

  3. Forecasting the failure of heterogeneous magmas

    NASA Astrophysics Data System (ADS)

    Vasseur, J.; Wadsworth, F. B.; Lavallée, Y.; Bell, A. F.; Main, I. G.; Dingwell, D. B.

    2015-12-01

    Eruption prediction is a long-sought-after goal of volcanology. Yet applying existing techniques retrospectively (hindcasting), we fail to predict events more often than we success. As much of the seismicity associated with intermediate to silicic volcanic eruptions comes from the brittle response of the ascending magma itself, we clearly require a good understanding of the parameters that control the ability to forecast magma failure itself. Here, we present suites of controlled experiments at magmatic temperatures using a range of synthetic magmas to investigate the control of microstructures on the efficacy of forecast models for material failure. We find that the failure of magmas with very little microstructural heterogeneity - such as melts - is very challenging to predict; whereas, the failure of very heterogeneous magmas is always well-predicted. To shed further light on this issue, we provide a scaling law based on the relationship between the microstructural heterogeneity in a magma and the error in the prediction of its failure time. We propose this method be used to elucidate the variable success rate of predicting volcanic predictions. We discuss this scaling in the context of the birth, life and death of structural heterogeneity during magma ascent with specific emphasis on obsidian-forming eruptions such as Chaitèn, 2008. During such eruptions, the repetitive creation and destruction of fractures filled with granular magma, which are thought to be the in situ remnants of seismogenic fracturing itself, are expressions of the life-cycle of heterogeneity in an otherwise coherent, melt-rich magma. We conclude that the next generation of failure forecast tools available to monitoring teams should incorporate some acknowledgment of the magma microstructure and not be solely based on the geophysical signals prior to eruption.

  4. Degassing during quiescence as a trigger of magma ascent and volcanic eruptions

    PubMed Central

    Girona, Társilo; Costa, Fidel; Schubert, Gerald

    2015-01-01

    Understanding the mechanisms that control the start-up of volcanic unrest is crucial to improve the forecasting of eruptions at active volcanoes. Among the most active volcanoes in the world are the so-called persistently degassing ones (e.g., Etna, Italy; Merapi, Indonesia), which emit massive amounts of gas during quiescence (several kilotonnes per day) and erupt every few months or years. The hyperactivity of these volcanoes results from frequent pressurizations of the shallow magma plumbing system, which in most cases are thought to occur by the ascent of magma from deep to shallow reservoirs. However, the driving force that causes magma ascent from depth remains unknown. Here we demonstrate that magma ascent can be triggered by the passive release of gas during quiescence, which induces the opening of pathways connecting deep and shallow magma reservoirs. This top-down mechanism for volcanic eruptions contrasts with the more common bottom-up mechanisms in which magma ascent is only driven by processes occurring at depth. A cause-effect relationship between passive degassing and magma ascent can explain the fact that repose times are typically much longer than unrest times preceding eruptions, and may account for the so frequent unrest episodes of persistently degassing volcanoes. PMID:26666396

  5. Degassing during quiescence as a trigger of magma ascent and volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Girona, Társilo; Costa, Fidel; Schubert, Gerald

    2015-12-01

    Understanding the mechanisms that control the start-up of volcanic unrest is crucial to improve the forecasting of eruptions at active volcanoes. Among the most active volcanoes in the world are the so-called persistently degassing ones (e.g., Etna, Italy; Merapi, Indonesia), which emit massive amounts of gas during quiescence (several kilotonnes per day) and erupt every few months or years. The hyperactivity of these volcanoes results from frequent pressurizations of the shallow magma plumbing system, which in most cases are thought to occur by the ascent of magma from deep to shallow reservoirs. However, the driving force that causes magma ascent from depth remains unknown. Here we demonstrate that magma ascent can be triggered by the passive release of gas during quiescence, which induces the opening of pathways connecting deep and shallow magma reservoirs. This top-down mechanism for volcanic eruptions contrasts with the more common bottom-up mechanisms in which magma ascent is only driven by processes occurring at depth. A cause-effect relationship between passive degassing and magma ascent can explain the fact that repose times are typically much longer than unrest times preceding eruptions, and may account for the so frequent unrest episodes of persistently degassing volcanoes.

  6. Locating the depth of magma supply for volcanic eruptions, insights from Mt. Cameroon

    PubMed Central

    Geiger, Harri; Barker, Abigail K.; Troll, Valentin R.

    2016-01-01

    Mt. Cameroon is one of the most active volcanoes in Africa and poses a possible threat to about half a million people in the area, yet knowledge of the volcano’s underlying magma supply system is sparse. To characterize Mt. Cameroon’s magma plumbing system, we employed mineral-melt equilibrium thermobarometry on the products of the volcano’s two most recent eruptions of 1999 and 2000. Our results suggest pre-eruptive magma storage between 20 and 39 km beneath Mt. Cameroon, which corresponds to the Moho level and below. Additionally, the 1999 eruption products reveal several shallow magma pockets between 3 and 12 km depth, which are not detected in the 2000 lavas. This implies that small-volume magma batches actively migrate through the plumbing system during repose intervals. Evolving and migrating magma parcels potentially cause temporary unrest and short-lived explosive outbursts, and may be remobilized during major eruptions that are fed from sub-Moho magma reservoirs. PMID:27713494

  7. Locating the depth of magma supply for volcanic eruptions, insights from Mt. Cameroon

    NASA Astrophysics Data System (ADS)

    Geiger, Harri; Barker, Abigail K.; Troll, Valentin R.

    2016-10-01

    Mt. Cameroon is one of the most active volcanoes in Africa and poses a possible threat to about half a million people in the area, yet knowledge of the volcano’s underlying magma supply system is sparse. To characterize Mt. Cameroon’s magma plumbing system, we employed mineral-melt equilibrium thermobarometry on the products of the volcano’s two most recent eruptions of 1999 and 2000. Our results suggest pre-eruptive magma storage between 20 and 39 km beneath Mt. Cameroon, which corresponds to the Moho level and below. Additionally, the 1999 eruption products reveal several shallow magma pockets between 3 and 12 km depth, which are not detected in the 2000 lavas. This implies that small-volume magma batches actively migrate through the plumbing system during repose intervals. Evolving and migrating magma parcels potentially cause temporary unrest and short-lived explosive outbursts, and may be remobilized during major eruptions that are fed from sub-Moho magma reservoirs.

  8. Degassing during quiescence as a trigger of magma ascent and volcanic eruptions.

    PubMed

    Girona, Társilo; Costa, Fidel; Schubert, Gerald

    2015-01-01

    Understanding the mechanisms that control the start-up of volcanic unrest is crucial to improve the forecasting of eruptions at active volcanoes. Among the most active volcanoes in the world are the so-called persistently degassing ones (e.g., Etna, Italy; Merapi, Indonesia), which emit massive amounts of gas during quiescence (several kilotonnes per day) and erupt every few months or years. The hyperactivity of these volcanoes results from frequent pressurizations of the shallow magma plumbing system, which in most cases are thought to occur by the ascent of magma from deep to shallow reservoirs. However, the driving force that causes magma ascent from depth remains unknown. Here we demonstrate that magma ascent can be triggered by the passive release of gas during quiescence, which induces the opening of pathways connecting deep and shallow magma reservoirs. This top-down mechanism for volcanic eruptions contrasts with the more common bottom-up mechanisms in which magma ascent is only driven by processes occurring at depth. A cause-effect relationship between passive degassing and magma ascent can explain the fact that repose times are typically much longer than unrest times preceding eruptions, and may account for the so frequent unrest episodes of persistently degassing volcanoes. PMID:26666396

  9. Rheology of phonolitic magmas - the case of the Erebus lava lake

    NASA Astrophysics Data System (ADS)

    Le Losq, Charles; Neuville, Daniel R.; Moretti, Roberto; Kyle, Philip R.; Oppenheimer, Clive

    2015-02-01

    Long-lived active lava lakes are comparatively rare and are typically associated with low-viscosity basaltic magmas. Erebus volcano, Antarctica, is unique today in hosting a phonolitic lava lake. Phonolitic magmas can erupt explosively, as in the 79 CE Plinian eruption of Vesuvius volcano, Italy, and it is therefore important to understand their physical properties. The phonolite at Erebus has slightly higher silica content than that at Vesuvius yet its present activity is predominantly non-explosive. As a contribution to understanding such contrasting eruptive behaviour, we focus on the rheological differences between these comparable magmas. In particular, we evaluate the viscosity of the Erebus phonolite magma by integrating new experimental data within a theoretical and empirical framework. The resulting model enables estimation of the Erebus melt viscosity as a function of temperature, crystal and water concentrations, with an uncertainty of, at most, ± 0.45 log (Pa s). Using reported ranges for these parameters, we predict that the magma viscosity in the upper region of the plumbing system of Erebus ranges between 105 and 107 Pas. This is substantially higher than has been hitherto considered with significant implications for modelling the dynamics of the lava lake, conduit and magma reservoir system. Our analysis highlights the generic challenges encountered in calculation of magma viscosity and presents an approach that can be applied to other cases.

  10. Degassing during quiescence as a trigger of magma ascent and volcanic eruptions.

    PubMed

    Girona, Társilo; Costa, Fidel; Schubert, Gerald

    2015-12-15

    Understanding the mechanisms that control the start-up of volcanic unrest is crucial to improve the forecasting of eruptions at active volcanoes. Among the most active volcanoes in the world are the so-called persistently degassing ones (e.g., Etna, Italy; Merapi, Indonesia), which emit massive amounts of gas during quiescence (several kilotonnes per day) and erupt every few months or years. The hyperactivity of these volcanoes results from frequent pressurizations of the shallow magma plumbing system, which in most cases are thought to occur by the ascent of magma from deep to shallow reservoirs. However, the driving force that causes magma ascent from depth remains unknown. Here we demonstrate that magma ascent can be triggered by the passive release of gas during quiescence, which induces the opening of pathways connecting deep and shallow magma reservoirs. This top-down mechanism for volcanic eruptions contrasts with the more common bottom-up mechanisms in which magma ascent is only driven by processes occurring at depth. A cause-effect relationship between passive degassing and magma ascent can explain the fact that repose times are typically much longer than unrest times preceding eruptions, and may account for the so frequent unrest episodes of persistently degassing volcanoes.

  11. Combined magnetotelluric and petrologic constrains for the nature of the magma storage system beneath the Ciomadul volcano (SE Carpathians)

    NASA Astrophysics Data System (ADS)

    Novák, A.; Harangi, Sz.; Kiss, B.; Szarka, L.; Molnár, Cs.

    2012-04-01

    The Ciomadul volcano is the youngest in the Carpathian-Pannonian region (eastern-central Europe) and there are indications that magma could still reside at the depth. Therefore, we performed a magnetotelluric investigation with the aim to detect a still hot magma reservoir. The results were compared with those coming from the petrological investigations. The Ciomadul volcanic complex contains a central amalgamated set of lava domes and a few peripheral domes with two explosion craters in the central zone. Geologically the domes were built by effusion of high viscosity dacite magma. Lava dome collapses resulted in volcanoclastic deposits (block-and ash flow deposits). The magmatic activity could have been connected to the seismically powerful region of the nearby Vrancea zone. Twelve long period magnetotelluric (MT) soundings were carried out to aim of define to electric resistivity distribution of the volcanic system and find correlation with the petrologic model to confirm the hot magma chamber beneath the region. At each MT site, the horizontal components of the magnetic and the electric fields were observed between the 0.00006-4 Hz frequency range. The vertical component of the magnetic field was also recorded to analyze the lateral conductivity inhomogenities under the subsurface. Soundings were located in non systematic grid and we selected several profiles which may represent the resistivity distribution of subsurface and cross-sections were applied as well. At started by dimensionality analysis and decomposition parameters the most part of the measuring are multi-dimensional. Traditional MT interpretation - 1D, 2D inversion and modeling - was carried out taking into account the decomposition results. 3D interpretation is not realized because of weak resolution of the data and large memory requirement. Both the local 1D inversion and the 2D inversion along the profiles defined a low resistivity zones at about 2 km depth which in continuation at depth with a

  12. Extensive, water-rich magma reservoir beneath southern Montserrat

    NASA Astrophysics Data System (ADS)

    Edmonds, M.; Kohn, S. C.; Hauri, E. H.; Humphreys, M. C. S.; Cassidy, M.

    2016-05-01

    South Soufrière Hills and Soufrière Hills volcanoes are 2 km apart at the southern end of the island of Montserrat, West Indies. Their magmas are distinct geochemically, despite these volcanoes having been active contemporaneously at 131-129 ka. We use the water content of pyroxenes and melt inclusion data to reconstruct the bulk water contents of magmas and their depth of storage prior to eruption. Pyroxenes contain up to 281 ppm H2O, with significant variability between crystals and from core to rim in individual crystals. The Al content of the enstatites from Soufrière Hills Volcano (SHV) is used to constrain melt-pyroxene partitioning for H2O. The SHV enstatite cores record melt water contents of 6-9 wt%. Pyroxene and melt inclusion water concentration pairs from South Soufriere Hills basalts independently constrain pyroxene-melt partitioning of water and produces a comparable range in melt water concentrations. Melt inclusions recorded in plagioclase and in pyroxene contain up to 6.3 wt% H2O. When combined with realistic melt CO2 contents, the depth of magma storage for both volcanoes ranges from 5 to 16 km. The data are consistent with a vertically protracted crystal mush in the upper crust beneath the southern part of Montserrat which contains heterogeneous bodies of eruptible magma. The high water contents of the magmas suggest that they contain a high proportion of exsolved fluids, which has implications for the rheology of the mush and timescales for mush reorganisation prior to eruption. A depletion in water in the outer 50-100 μm of a subset of pyroxenes from pumices from a Vulcanian explosion at Soufrière Hills in 2003 is consistent with diffusive loss of hydrogen during magma ascent over 5-13 h. These timescales are similar to the mean time periods between explosions in 1997 and in 2003, raising the possibility that the driving force for this repetitive explosive behaviour lies not in the shallow system, but in the deeper parts of a vertically

  13. A mantle-driven surge in magma supply to Kīlauea Volcano during 2003--2007

    USGS Publications Warehouse

    Poland, Michael P.; Miklius, Asta; Sutton, A. Jeff; Thornber, Carl R.

    2012-01-01

    The eruptive activity of a volcano is fundamentally controlled by the rate of magma supply. At Kīlauea Volcano, Hawai‘i, the rate of magma rising from a source within Earth’s mantle, through the Hawaiian hotspot, was thought to have been relatively steady in recent decades. Here we show that the magma supply to Kīlauea at least doubled during 2003–2007, resulting in dramatic changes in eruptive activity and the formation of new eruptive vents. An initial indication of the surge in supply was an increase in CO2 emissions during 2003–2004, combined with the onset of inflation of Kīlauea’s summit, measured using the Global Positioning System and interferometric synthetic aperture radar. Inflation was not limited to the summit magma reservoirs, but was recorded as far as 50 km from the summit, implying the existence of a connected magma system over that distance. We also record increases in SO2 emissions, heightened seismicity, and compositional and temperature variations in erupted lavas. The increase in the volume of magma passing through and stored within Kīlauea, coupled with increased CO2 emissions, indicate a mantle source for the magma surge. We suggest that magma supply from the Hawaiian hotspot can vary over timescales of years, and that CO2 emissions could be a valuable aid for assessing variations in magma supply at Kīlauea and other volcanoes.

  14. A decadal view of magma fragmentation

    NASA Astrophysics Data System (ADS)

    Cashman, K. V.; Rust, A.

    2010-12-01

    preservation. These pyroclasts also have uniformly high permeabilities, high pore connectivity, and simple porous pathways, all of which suggest that ease of gas escape also contributed to clast preservation. By extension, parts of the magma that were not well connected fragment to ash, thus the fine ash produced by explosive activity defines the efficiency of fragmentation. Rapid decompression of porous samples in the laboratory generates fragments with power law size distributions that reflect both the ΔP of fragmentation and the sample porosity. TGSDs of pyroclastic fall deposits show that fragmentation efficiency is typically high (> 50%) in silicic eruptions. Moreover, a comparison of vesicle size distributions with the TGSD for the 1980 Mount St. Helens deposit shows similar power law exponents for vesicles in pumice and ash component of the fall deposit. In contrast, the fragmentation efficiency is negligible (< 5%) in mafic eruptions, consistent with low power law exponents in scoria, and suggest that exponential, rather than power law, fits are more appropriate for mafic tephra deposits. A primary challenge for the future is integration of these observational and experimental data into numerical models of magma ascent and eruption.

  15. Testing a New Method for Imaging Crustal Magma Bodies: A Pilot Study at Newberry Volcano, Central OR

    NASA Astrophysics Data System (ADS)

    Beachly, M. W.; Hooft, E. E.; Toomey, D. R.; Waite, G. P.; Durant, D. T.

    2010-12-01

    Magmatic systems are often imaged using delay time seismic tomography, though a known limitation is that wavefront healing limits the ability of transmitted waves to detect small, low-velocity regions such as magma chambers. Crustal magma chambers have been successfully identified using secondary arrivals, including both P and S wave reflections and conversions. Such secondary phases are often recorded by marine seismic experiments owing to the density and quality of airgun data, which improves the identification of coherent arrivals. In 2008 we conducted a pilot study at Newberry volcano to test a new method of detecting secondary arrivals in a terrestrial setting. Our experimental geometry used a line of densely spaced (~300 m), three-component seismometers to record a shot-of-opportunity from the High Lave Plains Experiment. An ideal study would record several shots, however, data from this single event proves the concept. As part of our study, we also reanalyze all existing seismic data from Newberry volcano to obtain a tomographic image of the velocity structure to 6 km depth. Newberry is a lone shield volcano in central Oregon, located 40 km east of the Cascade axis. Newberry eruptions are silicic within the central caldera and mafic on its periphery suggesting a central silicic magma storage system, possibly located at upper crustal depths. The system may still be active with a recent eruption ~1300 years ago, and a central drill hole temperature of 256° C at only 932 m depth. A low-velocity anomaly previously imaged at 3-5 km beneath the caldera indicates either a magma body or a fractured pluton. Our tomographic study combines our 2008 seismic data with profile and array data collected in the 1980s by the USGS. In total, the inversion includes 16 active sources and 322 receivers yielding 1007 P-wave first arrivals. Beneath the caldera ring faults we image a high-velocity ring-like anomaly extending to 2 km depth. This anomaly is inferred to be near

  16. Subsurface magma pathways inferred from statistical analysis of volcanic vent distribution and numerical model of magma ascent

    NASA Astrophysics Data System (ADS)

    Germa, Aurelie; Connor, Laura; Connor, Chuck; Malservisi, Rocco

    2015-04-01

    One challenge of volcanic hazard assessment in distributed volcanic fields (large number of small-volume basaltic volcanoes along with one or more silicic central volcanoes) is to constrain the location of future activity. Although the extent of the source of melts at depth can be known using geophysical methods or the location of past eruptive vents, the location of preferential pathways and zones of higher magma flux are still unobserved. How does the spatial distribution of eruptive vents at the surface reveal the location of magma sources or focusing? When this distribution is investigated, the location of central polygenetic edifices as well as clusters of monogenetic volcanoes denote zones of high magma flux and recurrence rate, whereas areas of dispersed monogenetic vents represent zones of lower flux. Additionally, central polygenetic edifices, acting as magma filters, prevent dense mafic magmas from reaching the surface close to their central silicic system. Subsequently, the spatial distribution of mafic monogenetic vents may provide clues to the subsurface structure of a volcanic field, such as the location of magma sources, preferential magma pathways, and flux distribution across the field. Gathering such data is of highly importance in improving the assessment of volcanic hazards. We are developing a modeling framework that compares output of statistical models of vent distribution with outputs form numerical models of subsurface magma transport. Geologic data observed at the Earth's surface are used to develop statistical models of spatial intensity (vents per unit area), volume intensity (erupted volume per unit area) and volume-flux intensity (erupted volume per unit time and area). Outputs are in the form of probability density functions assumed to represent volcanic flow output at the surface. These are then compared to outputs from conceptual models of the subsurface processes of magma storage and transport. These models are using Darcy's law

  17. Sloshing of a bubbly magma reservoir as a mechanism of triggered eruptions

    NASA Astrophysics Data System (ADS)

    Namiki, Atsuko; Rivalta, Eleonora; Woith, Heiko; Walter, Thomas R.

    2016-06-01

    Large earthquakes sometimes activate volcanoes both in the near field as well as in the far field. One possible explanation is that shaking may increase the mobility of the volcanic gases stored in magma reservoirs and conduits. Here experimentally and theoretically we investigate how sloshing, the oscillatory motion of fluids contained in a shaking tank, may affect the presence and stability of bubbles and foams, with important implications for magma conduits and reservoirs. We adopt this concept from engineering: severe earthquakes are known to induce sloshing and damage petroleum tanks. Sloshing occurs in a partially filled tank or a fully filled tank with density-stratified fluids. These conditions are met at open summit conduits or at sealed magma reservoirs where a bubbly magma layer overlays a newly injected denser magma layer. We conducted sloshing experiments by shaking a rectangular tank partially filled with liquids, bubbly fluids (foams) and fully filled with density-stratified fluids; i.e., a foam layer overlying a liquid layer. In experiments with foams, we find that foam collapse occurs for oscillations near the resonance frequency of the fluid layer. Low viscosity and large bubble size favor foam collapse during sloshing. In the layered case, the collapsed foam mixes with the underlying liquid layer. Based on scaling considerations, we constrain the conditions for the occurrence of foam collapse in natural magma reservoirs. We find that seismic waves with lower frequencies < 1 Hz, usually excited by large earthquakes, can resonate with magma reservoirs whose width is > 0.5 m. Strong ground motion > 0.1 m s- 1 can excite sloshing with sufficient amplitude to collapse a magma foam in an open conduit or a foam overlying basaltic magma in a closed magma reservoir. The gas released from the collapsed foam may infiltrate the rock or diffuse through pores, enhancing heat transfer, or may generate a gas slug to cause a magmatic eruption. The overturn in the

  18. Time to Solidify an Ocean of Magma

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2009-03-01

    Cosmochemists are reasonably sure that a global ocean of magma surrounded the Moon when it formed. This was a monumentally important event in lunar history, forming the primary feldspar-rich crust of the lunar highlands and setting the stage for subsequent melting inside the Moon to make additional crustal rocks. Numerous questions remain about the complex array of processes that could have operated in such a huge amount of magma, and about how long it took to solidify the magma ocean. Alex Nemchin and colleagues at Curtin University of Technology (Australia), Westfailische Wilhelms-Universitat (Munster, Germany), and the Johnson Space Center (Houston, Texas, USA) dated a half-millimeter grain of the mineral zircon (ZrSiO4) in an impact melt breccia from the Apollo 17 landing site. They used an ion microprobe to measure the concentrations of lead and uranium isotopes in the crystal, finding that one portion of the grain recorded an age of 4.417 ± 0.006 billion years. Because zircon does not crystallize until more than 95% of the magma ocean has crystallized, this age effectively marks the end of magma ocean crystallization. Magma ocean cooling and crystallization began soon after the Moon-forming giant impact. Other isotopic studies show that this monumental event occurred 4.517 billion years ago. Thus, the difference between the two ages means that the magma ocean took 100 million years to solidify.

  19. Mushy magma processes in the Tuolumne intrusive complex, Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Memeti, V.; Paterson, S. R.

    2012-12-01

    whole rock data. 4) Single mineral geochemistry suggests that this increased heterogeneity in the interior of the complex is likely caused by the presence of mixed mineral populations that acquired their compositional zoning in magmas different than the one they most recently crystallized in. 5) Mixed mineral populations have also been found in places of local magma mixing (e.g., tubes and troughs), and 6) oscillatory trace element zoning in K-feldspar phenocrysts most likely represents magma replenishment. All of these phenomena suggest a fairly dynamic environment of magma replenishment, magmatic erosion and extensive mixing at the locus of chamber growth. Magma replenishment subsided after episodic flare-ups and the magma mush dominantly underwent fractional crystallization and magmatic fabric formation during waning stages, when it was capable of preserving the evidence at map to crystal scale, lacking any later overprint by mixing. Fractionation related evidence is apparent in the presence of 1) map to outcrop scale leucogranite lenses and dikes in all major Tuolumne units (including the Johnson Peak granite itself), 2) the concentric compositional zonation of magmatic lobes (e.g., southern Half Dome lobe), 3) local crystal accumulations and widespread schlieren, and 4) fractionation related single mineral element zoning.

  20. Thermodynamics and Phase Equilibria of Concurrent Assimilation and Fractional Crystallization (AFC) in Crustal Magma Bodies

    NASA Astrophysics Data System (ADS)

    Creamer, J. B.; Spera, F. J.; Bohrson, W. A.; Ghiorso, M. S.

    2009-12-01

    Mafic magmas generated by partial melting of mantle peridotites, eclogites or clinopyroxenites are hotter than, compositionally distinct from and have higher liquidus temperatures than the crustal rocks through which they ascend or are emplaced. The low thermal conductivity of crystalline and molten silicates implies that steep thermal gradients along the margins of propagating melt-filled fractures and stagnant magma bodies can develop and lead to crustal anatexis especially at depths >~10 km. Small differences in ambient deviatoric stresses within the crust can lead to the percolation of anatectic melts into adjacent magma. The magnitude of contamination is strongly dependant upon permeability which in turn depends upon the square of the volume fraction of anatectic melt, itself controlled by local phase equilibria. From the thermochemical vantage, AFC processes may be quantified using the Magma Chamber Simulator (MCS) by studying the variables that define the extent of AFC: thermal interaction mass ratio (ratio of pristine magma mass to mass of wallrock), bulk composition (including volatiles) of pristine magma and wallrock, the mean pressure and prevailing oxygen fugacity at which AFC occurs. Here we present MCS phase equilibria and major element solutions for a number of scenarios in which the sensible variables defining the extent of assimilation have been systematically varied. In particular, initial magma and wallrock temperatures, relative masses of wallrock and magma, oxygen fugacity and the mean pressure of AFC interaction are defined. The sub-systems are then allowed to proceed towards thermodynamic (thermal and chemical potential) equilibrium. Incremental enthalpy changes associated with magma cooling and crystallization are transferred to wallrock where heating and possible partial melting can occur. Fractional crystallization occurs in the magma and once the wallrock temperature exceeds its solidus, equilibrium melting in wallrock is enabled. When

  1. Deep Magma Accumulation at Nyamulagira Volcano in 2011 Detected by GNSS Observations

    NASA Astrophysics Data System (ADS)

    Ji, K. H.; Stamps, D. S.; Geirsson, H.; Mashagiro, N.; Syauswa, M.; Kafudu, B.; Subira, J.; d'Oreye, N.

    2015-12-01

    The Virunga Volcanic Province of the Democratic Republic of Congo is at very high natural risk due to active volcanism. A Global Navigation Satellite System network, KivuGNet (Kivu Geodetic Network), has operated since 2009 for monitoring and research of the deformation of Nyamulagira and Nyiragongo volcanoes as well as tectonic deformation in the region. We detected an inflationary signal from the position time series observed in the network using our detection method, which is a combination of Kalman filtering and principal component analysis. The inflation occurred in October 2010 and lasted for about 6 months prior to the 2011 eruption at Nyamulagira volcano. The pre-eruptive inflationary signal is much weaker than the co-eruptive signal, but our method successfully detected the signal. The maximum horizontal and vertical displacements observed are ~14 mm and ~10 mm, respectively. A Mogi point source at a depth > 10 km can explain the displacement field suggesting a relatively deep source for the magma chamber. Continuous monitoring of the volcanic activity is essential for understanding the eruption cycle and assessing potential volcanic hazards.

  2. Probing Io's putative global magma ocean through FUV auroral spot morphology

    NASA Astrophysics Data System (ADS)

    Roth, Lorenz

    2013-10-01

    Whether Io possesses a magma ocean or not is a central issue for understanding the most volcanically active body in our solar system and is a long standing ques