Science.gov

Sample records for magma

  1. 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.

  2. 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.

  3. 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)

  4. Magma chambers

    NASA Technical Reports Server (NTRS)

    Marsh, Bruce D.

    1989-01-01

    Recent observational and theoretical investigations of terrestrial magma chambers (MCs) are reviewed. Consideration is given to the evidence for MCs with active convection and crystal sorting, problems of direct MC detection, theoretical models of MC cooling, the rheology and dynamics of solidification fronts, crystal capture and differentiation, convection with solidification, MC wall flows, and MC roof melting. Diagrams, graphs, and a list of problems requiring further research are provided.

  5. Magma energy extraction

    SciTech Connect

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

    1987-01-01

    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.

  6. 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.

  7. Watching magma from space

    USGS Publications Warehouse

    Lu, Zhong; Wicks, Charles W., Jr.; 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. 

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. 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

  16. 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

  17. 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.

  18. 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…

  19. Superheat in magma oceans

    NASA Technical Reports Server (NTRS)

    Jakes, Petr

    1992-01-01

    The existence of 'totally molten' planets implies the existence of a superheat (excess of heat) in the magma reservoirs since the heat buffer (i.e., presence of crystals having high latent heat of fusion) does not exist in a large, completely molten reservoir. Any addition of impacting material results in increase of the temperature of the melt and under favorable circumstances heat is stored. The behavior of superheat melts is little understood; therefore, we experimentally examined properties and behavior of excess heat melts at atmospheric pressures and inert gas atmosphere. Highly siliceous melts (70 percent SiO2) were chosen for the experiments because of the possibility of quenching such melts into glasses, the slow rate of reaction in highly siliceous composition, and the fact that such melts are present in terrestrial impact craters and impact-generated glasses. Results from the investigation are presented.

  20. Heat transfer in magma in situ

    SciTech Connect

    Dunn, J.C.; Carrigan, C.R.; Wemple, R.P.

    1983-12-16

    Heat transfer rates in a basaltic magma were measured under typical magma chamber conditions and a numerical model of the experiment was used to estimate magma viscosity. The results are of value for assessing methods of thermal energy extraction from magma bodies in the upper crust as well as for modeling the evolutionary track of these systems. 13 references, 3 figures.

  1. 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.

  2. Parsing Aleutian Arc Magma Compositions

    NASA Astrophysics Data System (ADS)

    Nye, C. J.

    2011-12-01

    The first-order subdivision of Aleutian arc magma compositions is based on SiO2, and the second-order subdivision is usually based on the change of FeOt/MgO as a function of SiO2, resulting in the additional twofold subdivision into (TH) and calcalkaline (CA) magmas. However, additional robust compositional variations exist. The two most important of these are (1) variation of the calcium number [Ca#; Ca/(Na+Ca)] as a function of SiO2, and (2) the Rate of Incompatible Trace-element Enrichment (RITE) at individual volcanic centers. Additionally, the data show that the low FeOt/MgO of CA andesite and dacite is more controlled by MgO excess than FeOt depletion. The Ca# of andesites and dacites is strongly bimodal. The low-Ca# group is "calc-alkalic", while the high-Ca# group is "calcic", using Peacock (1931) criteria. A continuum of Ca#s exists, but lavas intermediate between high-Ca# and low-Ca# are much less abundant. Ca#s merge below about 55% SiO2, and have a simple normal distribution. RITE, with rare but important exceptions, is generally constant at the temporal and spatial scale of a single volcano. Among high-RITE magmas LILE, LREE, HFSE, and Th increase ~3.5-fold, and HREE increase ~2.5-fold from basalt or basaltic-andesite through andesite to dacite. There is no strong indication that RITE is silica-dependant. High-RITE magmas develop a strong negative Eu anomaly, and are qualitatively compatible with an origin primarily involving fractionation of plagioclase-dominated mineral assemblages. Low-RITE magmas, in contrast, have nearly invariant REE and HFSE, and LILE and Th increase merely 1.5-fold over the same silica range. Low-RITE magmas are not compatible with fractionation of a plagioclase-dominant mineral assemblage. Alternative qualitatively plausible explanations (needing rigorous evaluation) include fractionation of an ultramafic mineral assemblage (Alaskan-type mafic-ultramafic bodies may be a model; see USGS Prof Paper 1564); that low-RITE basaltic

  3. 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.

  4. 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.

  5. 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.

  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. Magma rheology variation in sheet intrusions (Invited)

    NASA Astrophysics Data System (ADS)

    Magee, C.; O'Driscoll, B.; Petronis, M. S.; Stevenson, C.

    2013-12-01

    The rheology of magma fundamentally controls igneous intrusion style as well as the explosivity and type of volcanic eruptions. Importantly, the dynamic interplay between the viscosity of magma and other processes active during intrusion (e.g., crystallisation, magma mixing, assimilation of crystal mushes and/or xenolith entrainment) will likely bear an influence on the temporal variation of magma rheology. Constraining the timing of rheological changes during magma transit therefore plays an important role in understanding the nuances of volcanic systems. However, the rheological evolution of actively emplacing igneous intrusions cannot be directly studied. While significant advances have been made via experimental modelling and analysis of lava flows, how these findings relate to intruding magma remains unclear. This has led to an increasing number of studies that analyse various characteristics of fully crystallised intrusions in an attempt to ';back-out' the rheological conditions governing emplacement. For example, it has long been known that crystallinity affects the rheology and, consequently, the velocity of intruding magma. This means that quantitative textural analysis of crystal populations (e.g., crystal size distribution; CSD) used to elucidate crystallinity at different stages of emplacement can provide insights into magma rheology. Similarly, methods that measure flow-related fabrics (e.g., anisotropy of magnetic susceptibility; AMS) can be used to discern velocity profiles, a potential proxy for the magma rheology. To illustrate these ideas, we present an integrated AMS and petrological study of several sheet intrusions located within the Ardnamurchan Central Complex, NW Scotland. We focus on the entrainment and transport dynamics of gabbroic inclusions that were infiltrated by the host magma upon entrainment. Importantly, groundmass magnetic fabrics within and external to these inclusions are coaxial. This implies that a deviatoric stress was

  8. Magma chamber paradox: decompression upon replenishment

    NASA Astrophysics Data System (ADS)

    Papale, Paolo; Longo, Antonella; Montagna, Chiara Paola

    2013-04-01

    The invasion of active magma chambers by fresh magma of deeper provenance is invariably assumed to cause chamber pressurization. Pressure increase thus stands as an intuitive consequence of magma chamber replenishment. However, new numerical simulations demonstrate that pressure evolution is highly non-linear, and that decompression dominates when large density contrasts exist between injected and resident magmas. This apparent paradox originates from the compressible nature of volatile-rich magma and the dynamics of convection associated with injections of buoyant magma. While decompression can dominate in a shallow chamber, pressure increase develops in the connected deep regions of magma provenance. These results contradict classical views adopted to interpret observations at active as well as fossil magma chambers, and demonstrate that a simple reliance on intuition is insufficient: what may be perceived as a paradox - magma chamber decompression upon replenishment - is instead likely, and rooted in the complex physics that governs the multiphase, multi-component dynamics of magma transport in geometrically composite, spatially extended magmatic systems.

  9. Numerical simulation of magma chamber dynamics.

    NASA Astrophysics Data System (ADS)

    Longo, Antonella; Papale, Paolo; Montagna, Chiara Paola; Vassalli, Melissa; Giudice, Salvatore; Cassioli, Andrea

    2010-05-01

    Magma chambers are characterized by periodic arrivals of deep magma batches that give origin to complex patterns of magma convection and mixing, and modify the distribution of physical quantities inside the chamber. We simulate the transient, 2D, multi-component homogeneous dynamics in geometrically complex dyke+chamber systems, by means of GALES, a finite element parallel C++ code solving mass, momentum and energy equations for multi-component homogeneous gas-liquid (± crystals) mixtures in compressible-to-incompressible flow conditions. Code validation analysis includes several cases from the classical engineering literature, corresponding to a variety of subsonic to supersonic gas-liquid flow regimes (see http://www.pi.ingv.it/~longo/gales/gales.html). The model allows specification of the composition of the different magmas in the domain, in terms of ten major oxides plus the two volatile species H2O and CO2. Gas-liquid thermodynamics are modeled by using the compositional dependent, non-ideal model in Papale et al. (Chem.. Geol., 2006). Magma properties are defined in terms of local pressure, temperature, and composition including volatiles. Several applications are performed within domains characterized by the presence of one or more magma chambers and one or more dykes, with different geometries and characteristic size from hundreds of m to several km. In most simulations an initial compositional interface is placed at the top of a feeding dyke, or at larger depth, with the deeper magma having a lower density as a consequence of larger volatile content. The numerical results show complex patterns of magma refilling in the chamber, with alternating phases of magma ingression and magma sinking from the chamber into the feeding dyke. Intense mixing takes place in feeding dykes, so that the new magma entering the chamber is always a mixture of the deep and the initially resident magma. Buoyant plume rise occurs through the formation of complex convective

  10. Formation of crustal magma chambers in Iceland

    SciTech Connect

    Gudmundsson, A.

    1986-02-01

    Formation of crustal magma chambers in Iceland may be facilitated by the occurrence of stress barriers that lead to formation of thick sills. Such sills absorb the magma of all dikes that enter them and may evolve into magma chambers. Ideal sites for stress barriers, and hence for magma chambers, are rock formations where individual layers have different elastic properties. The rocks formed during the Pleistocene have notably different elastic properties, and when buried in the volcanic zones, they form more promising sites for magma chambers than the Tertiary rocks. This may explain why the number of magma chambers, indicated by the number of corresponding central volcanoes, during the late Pleistocene (i.e., during the past 0.7 m.y.) appears to be proportionally greater than the number of chambers (i.e., central volcanoes) active during Tertiary time.

  11. 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.

  12. 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.

  13. Replenishment of magma chambers by light inputs

    NASA Astrophysics Data System (ADS)

    Huppert, Herbert E.; Sparks, R. Stephen J.; Whitehead, John A.; Hallworth, Mark A.

    1986-05-01

    Magma chambers, particularly those of basaltic composition, are often replenished by an influx of magma whose density is less than that of the resident magma. This paper describes the fundamental fluid mechanics involved in the replenishment by light inputs. If ρ denotes the uniform density of the resident magma and ρ — Δρ that of the input, the situation is described by the reduced gravity g' = gΔρ/ρ, the volume flux Q, and the viscosities of the resident and input magmas νe and νi, respectively. The (nondimensional) Reynolds numbers, Ree = (g'Q3)1/5/νe and Rei = (g'Q3)1/5/νi and chamber geometry then completely specify the system. For sufficiently low values of the two Reynolds numbers (each less than approximately 10), the input rises as a laminar conduit. For larger values of the Reynolds numbers, the conduit may break down and exhibit either a varicose or a meander instability and entrain some resident magma. At still larger Reynolds numbers, the flow will become quite unsteady and finally turbulent. The values of the Reynolds numbers at which these transitions occur have been documented by a series of experiments with water, glycerine, and corn syrup. If the input rises as a turbulent plume, significant entrainment of the resident magma can take place. The final spatial distribution of the mixed magma depends on the geometry of the chamber. If the chamber is much wider than it is high, the mixed magma forms a compositionally stratified region between the roof and a sharp front above uncontaminated magma. In the other geometrical extreme, the input magma is mixed with almost all of the resident magma. If the density of the resident magma is already stratified, the input plume may penetrate only part way into the chamber, even though its initial density is less than that of the lowest density resident magma. The plume will then intrude horizontally and form a hybrid layer at an intermediate depth. This provides a mechanism for preventing even

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. Magma energy research project, FY80 annual progress report

    NASA Astrophysics Data System (ADS)

    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.

  20. 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.

  1. 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

  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 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

  4. 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.

  5. 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.

  6. 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.

  7. The Effects of Preeruptive Magma Viscosity on Eruption Styles and Magma Eruption Rates

    NASA Astrophysics Data System (ADS)

    Tomiya, A.; Koyaguchi, T.; Kozono, T.; Takeuchi, S.

    2014-12-01

    We have collected data on magma eruption rate, which is one of the most fundamental parameters for a volcanic eruption. There are several compilations on eruption rates, for example, for Plinian eruptions (Carey and Sigurdsson, 1989), basaltic eruptions (Wadge, 1981), lava dome eruptions (Newhall and Melson, 1983), and all combined (Tomiya and Koyaguchi, 1998; Pyle, 2000). However, they did not quantitatively discuss the effects of magma viscosity, which must control eruption rates. Here, we discuss the effects of magma viscosity on eruption rates, by using 'preeruptive magma viscosities', which are important measures of magma eruptibility (Takeuchi, 2011). Preeruptive magma viscosity is the viscosity of magma (melt, dissolved water, and crystals) in the magma chamber at the preeruptive conditions, and can be approximately obtained only by the bulk rock SiO2 and phenocryst content, using an empirical formula (Takeuchi, 2010). We have found some interesting relationships, such as (1) eruption styles and rates are correlated to preeruptive magma viscosity but not correlated to bulk rock composition, and (2) the gap (ratio) in eruption rates between explosive and effusive phases in a series of eruptions is proportional to preeruptive magma viscosity. We also propose, by combining (1) and (2), that (3) the radius (or width) of volcanic conduit is positively correlated with preeruptive magma viscosity. Our data also show that the eruptive magmas are divided into two types. One is the low-viscosity type (basalt ~ phenocryst-poor andesite), characterized by lava flow and sub-Plinian eruptions. The other is the high-viscosity type (phenocryst-rich andesite ~ rhyolite), characterized by lava dome and Plinian eruptions. The boundary is at about 104 Pa s. These two types may be closely linked to the magma generation processes (fractional/batch crystallization vs. extraction from a mushy magma chamber).

  8. Reconstructing magma reservoir dynamics from field evidence

    NASA Astrophysics Data System (ADS)

    Verberne, R.; Muntener, O.; Ulmer, P.

    2013-12-01

    Reconstructing the dynamics within magma reservoirs during and after emplacement greatly enhance our understanding of their formation and evolution. By determining the length and timescales over which magma remains mobile within magma reservoirs, fluxes of magma that is possibly extractable can be quantified, providing a link between plutonic and volcanic systems, and constraints on the likelihood of a pluton feeding volcanic eruptions. However, the general absence of marker beds and uncertainties regarding at which crystal fractions super-solidus foliation patterns are recorded make it difficult to reconstruct and quantify deformation inside plutons, especially the deformation that occurred at low crystal fractions. Here we present a case study of the Listino Ring Structure (LRS) of the Adamello Batholith in N-Italy, a 300-500 m-wide semi-circular zone of intensely foliated tonalite containing abundant evidence for magmatic deformation and magma mingling (Brack, 1984). The differences in the interaction between felsic and mafic magmas recorded in the form of mafic dikes, sheets and enclaves can be used to determine spatial and/or temporal differences of magma rheology during evolution of the reservoir. Detailed field mapping shows a clear difference in intrusion style between the southern and eastern sides of the LRS, as mafic magma intrudes into different felsic host magmas. An attempt is made to quantify these differences in terms of the physical state of the host magmas, using a variety of analyses pertaining to the breakup of mafic dikes into enclaves, the assimilation of phenocrysts from the host magma by the mafic magma, and the back-veining of mafic dikes and enclaves. The common component of these analyses is a parametrization of the phase petrology of the magmas as a function of temperature, which allows for the determination of melt fraction and composition at super-solidus conditions, from which physical properties such as density and viscosity can be

  9. Evidence for seismogenic fracture of silicic magma.

    PubMed

    Tuffen, Hugh; Smith, Rosanna; Sammonds, Peter R

    2008-05-22

    It has long been assumed that seismogenic faulting is confined to cool, brittle rocks, with a temperature upper limit of approximately 600 degrees C (ref. 1). This thinking underpins our understanding of volcanic earthquakes, which are assumed to occur in cold rocks surrounding moving magma. However, the recent discovery of abundant brittle-ductile fault textures in silicic lavas has led to the counter-intuitive hypothesis that seismic events may be triggered by fracture and faulting within the erupting magma itself. This hypothesis is supported by recent observations of growing lava domes, where microearthquake swarms have coincided with the emplacement of gouge-covered lava spines, leading to models of seismogenic stick-slip along shallow shear zones in the magma. But can fracturing or faulting in high-temperature, eruptible magma really generate measurable seismic events? Here we deform high-temperature silica-rich magmas under simulated volcanic conditions in order to test the hypothesis that high-temperature magma fracture is seismogenic. The acoustic emissions recorded during experiments show that seismogenic rupture may occur in both crystal-rich and crystal-free silicic magmas at eruptive temperatures, extending the range of known conditions for seismogenic faulting. PMID:18497823

  10. Numerical modeling of bubble dynamics in magmas

    NASA Astrophysics Data System (ADS)

    Huber, Christian; Su, Yanqing; Parmigiani, Andrea

    2014-05-01

    Understanding the complex non-linear physics that governs volcanic eruptions is contingent on our ability to characterize the dynamics of bubbles and its effect on the ascending magma. The exsolution and migration of bubbles has also a great impact on the heat and mass transport in and out of magma bodies stored at shallow depths in the crust. Multiphase systems like magmas are by definition heterogeneous at small scales. Although mixture theory or homogenization methods are convenient to represent multiphase systems as a homogeneous equivalent media, these approaches do not inform us on possible feedbacks at the pore-scale and can be significantly misleading. In this presentation, we discuss the development and application of bubble-scale multiphase flow modeling to address the following questions : How do bubbles impact heat and mass transport in magma chambers ? How efficient are chemical exchanges between the melt and bubbles during magma decompression? What is the role of hydrodynamic interactions on the deformation of bubbles while the magma is sheared? Addressing these questions requires powerful numerical methods that accurately model the balance between viscous, capillary and pressure stresses. We discuss how these bubble-scale models can provide important constraints on the dynamics of magmas stored at shallow depth or ascending to the surface during an eruption.

  11. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    2004-01-01

    The research described in this progress report involved the study of petrological, geochemical, and volcanic processes that occur on the Moon and the SNC meteorite parent body, generally accepted to be Mars. The link between these studies is that they focus on two terrestrial-type parent bodies somewhat smaller than earth, and the fact that they focus on the types of magmas (magma compositions) present, the role of volatiles in magmatic processes, and on processes of magma evolution on these planets. We are also interested in how these processes and magma types varied over time.In earlier work on the A15 green and A17 orange lunar glasses, we discovered a variety of metal blebs. Some of these Fe-Ni metal blebs occur in the glass; others (in A17) were found in olivine phenocrysts that we find make up about 2 vol 96 of the orange glass magma. The importance of these metal spheres is that they fix the oxidation state of the parent magma during the eruption, and also indicate changes during the eruption . They also yield important information about the composition of the gas phase present, the gas that drove the lunar fire-fountaining. During the tenure of this grant, we have continued to work on the remaining questions regarding the origin and evolution of the gas phase in lunar basaltic magmas, what they indicate about the lunar interior, and how the gas affects volcanic eruptions. Work on Martian magmas petrogenesis questions during the tenure of this grant has resulted in advances in our methods of evaluating magmatic oxidation state variations in Mars and some new insights into the compositional variations that existed in the SNC magmas over time . Additionally, Minitti has continued to work on the problem of possible shock effects on the abundance and distribution of water in Mars minerals.

  12. 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

  13. Volatiles Which Increase Magma Viscosity

    NASA Astrophysics Data System (ADS)

    Webb, S.

    2015-12-01

    The standard model of an erupting volcano is one in which the viscosity of a decompressing magma increases as the volatiles leave the melt structure to form bubbles. It has now been observed that the addition of the "volatiles" P, Cl and F result in an increase in silicate melt viscosity. This observation would mean that the viscosity of selected degassing magmas would decrease rather than increase. Here we look at P, Cl and F as three volatiles which increase viscosity through different structural mechanisms. In all three cases the volatiles increase the viscosity of peralkaline composition melts, but appear to always decrease the viscosity of peraluminous melts. Phosphorus causes the melt to unmix into a Na-P rich phase and a Na-poor silicate phase. Thus as the network modifying Na (or Ca) are removed to the phosphorus-rich melt, the matrix melt viscosity increases. With increasing amounts of added phosphorus (at network modifying Na ~ P) the addition of further phosphorus causes a decrease in viscosity. The addition of chlorine to Fe-free aluminosilicate melts results in an increase in viscosity. NMR data on these glass indicates that the chlorine sits in salt-like structures surrounded by Na and/or Ca. Such structures would remove network-modifying atoms from the melt structure and thus result in an increase in viscosity. The NMR spectra of fluorine-bearing glasses shows that F takes up at least 5 different structural positions in peralkaline composition melts. Three of these positions should result in a decrease in viscosity due to the removal of bridging oxygens. Two of the structural positons of F, however, should result in an increase in viscosity as they require the removal of network-modifying atoms from the melt structure (with one of the structures being that observed for Cl). This would imply that increasing amounts of F might result in an increase in viscosity. This proposed increase in viscosity with increasing F has now been experimentally confirmed.

  14. Process for forming hydrogen and other fuels utilizing magma

    DOEpatents

    Galt, John K.; Gerlach, Terrence M.; Modreski, Peter J.; Northrup, Jr., Clyde J. M.

    1978-01-01

    The disclosure relates to a method for extracting hydrogen from magma and water by injecting water from above the earth's surface into a pocket of magma and extracting hydrogen produced by the water-magma reaction from the vicinity of the magma.

  15. Magma Energy Overview and Status Report

    SciTech Connect

    Dunn, James C.

    1989-03-21

    Up to 500,000 Quads of thermal energy are believed to be contained in crustal magma bodies within the U.S. at temperatures in excess of 600 C and at depths less than 10 km. Scientific feasibility of utilizing this energy resource was concluded after a seven-year study that culminated in successful energy extraction experiments in molten rock at Kilauea Iki lava lake. The current DOE program is developing technology to experimentally extract energy from a silicic magma body so that engineering feasibility of the magma energy concept can be evaluated. At this point, significant progress has been achieved in three areas: Geophysics and site selection. Energy Extraction Processes, and Geochemistry/Materials. Future activities will be focused by drilling and evaluating a deep exploratory well in Long Valley caldera where active magma is expected.

  16. 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.

  17. Rheology of Halogen-Rich Magmas

    NASA Astrophysics Data System (ADS)

    Webb, S. L.

    2010-12-01

    The degassing of magma as it rises through the volcanic conduit to the surface affects the viscosity and rate of movement of the magma. While the production of bubbles in the magma decreases the density of the magma and thus increases its rate of ascent, the loss of volatiles from the magma, in general, results in an increase in the viscosity. This is the ideal scenario for the deformation rate of the magma crossing the relaxation timescale of the increasingly viscous magma which can result in the shattering of the magma in its unrelaxed (glassy) state; which results in an explosive eruption and pyroclastic flow. The effect of the volatiles H2O and F on magma viscosity and relaxation timescale have been extensively studied; with 1 mol% F2O-1 or H2O causing a 4 to 5 order of magnitude decrease in viscosity at ca. 800 C. Early determinations of the effect of chlorine on melt viscosity, however, indicated that chlorine increases the viscosity of Al-bearing melts (but decreases the viscosity of Al-free synthetic melts). Thus the degassing of chlorine would result in a decrease in magma viscosity and a distancing of the physical condition of the magma from the shattering of the magma as it rises to the surface. The viscosity of chlorine-bearing peralkaline Na2O-CaO-Al2O3-SiO2 melts has been investigated using micro-penetration techniques in the 108 - 1013 Pa s viscosity range. The presence of 0.5 mol% (0.6 wt%) Cl2O-1 increases viscosity by 0.5 log10 units. A similar amount of H2O or F2O-1 would decrease viscosity by 2.5 orders of magnitude in this viscosity range. More information about the relative solubility of Cl, F and H2O as a function of composition, temperature and pressure is needed before one can model the relative effects of degassing volatiles on the rheology of magmas. Very little is known about the structural role of chlorine in silicate melts. NMR studies of Na2O-CaO-Al2O3-SiO2 glasses have shown that chlorine does not bond to Al (in contrast to fluorine

  18. Rates of Magma Transfer in the Crust: Insights into Magma Reservoir Recharge and Pluton Growth

    NASA Astrophysics Data System (ADS)

    Menand, T.; Annen, C.; De Saint Blanquat, M.

    2014-12-01

    Plutons have long been viewed as crystallized remnants of large magma reservoirs, a concept now challenged by high precision geochronological data coupled with thermal models. Similarly, the classical view of silicic eruptions fed by long-lived magma reservoirs that slowly differentiate between mafic recharges is being questioned by petrological and geophysical studies. In both cases, a key and yet unresolved issue is the rate of magma transfer in the crust. Here, we use thermal analysis of magma transport to calculate the minimum rate of magma transfer through dykes. We find that unless the crust is exceptionally hot the recharge of magma reservoirs requires a magma supply rate of at least ~ 0.01 km3/yr, much higher than the long-term growth rate of plutons, which demonstrates unequivocally that igneous bodies must grow incrementally. This analysis argues also for magma reservoirs being short-lived and erupting rapidly after a recharge of already differentiated magma. These findings have strong implications for the monitoring of dormant volcanic systems, and raise questions on our ability to interpret geodetic surface signals related to incipient eruptions.

  19. 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

  20. Silicic magma generation at Askja volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Sigmarsson, O.

    2009-04-01

    Rate of magma differentiation is an important parameter for hazard assessment at active volcanoes. However, estimates of these rates depend on proper understanding of the underlying magmatic processes and magma generation. Differences in isotope ratios of O, Th and B between silicic and in contemporaneous basaltic magmas have been used to emphasize their origin by partial melting of hydrothermally altered metabasaltic crust in the rift-zones favoured by a strong geothermal gradient. An alternative model for the origin of silicic magmas in the Iceland has been proposed based on U-series results. Young mantle-derived mafic protolith is thought to be metasomatized and partially melted to form the silicic end-member. However, this model underestimates the compositional variations of the hydrothermally-altered basaltic crust. New data on U-Th disequilibria and O-isotopes in basalts and dacites from Askja volcano reveal a strong correlation between (230Th/232Th) and delta 18O. The 1875 AD dacite has the lowest Th- and O isotope ratios (0.94 and -0.24 per mille, respectively) whereas tephra of evolved basaltic composition, erupted 2 months earlier, has significantly higher values (1.03 and 2.8 per mille, respectively). Highest values are observed in the most recent basalts (erupted in 1920 and 1961) inside the Askja caldera complex and out on the associated fissure swarm (Sveinagja basalt). This correlation also holds for older magma such as an early Holocene dacites, which eruption may have been provoked by rapid glacier thinning. Silicic magmas at Askja volcano thus bear geochemical signatures that are best explained by partial melting of extensively hydrothermally altered crust and that the silicic magma source has remained constant during the Holocene at least. Once these silicic magmas are formed they appear to erupt rapidly rather than mixing and mingling with the incoming basalt heat-source that explains lack of icelandites and the bi-modal volcanism at Askja

  1. Describing the chemical character of a magma

    NASA Astrophysics Data System (ADS)

    Duley, Soma; Vigneresse, Jean-Louis; Chattaraj, Pratim K.

    2010-05-01

    We introduce the concepts of hard-soft acid-base (HSAB) and derive parameters to characterize a magma that consists either of a solid rock, a melt or its exsolved gaseous phase. Those parameters are the electronegativity, hardness, electrophilicity, polarisability and optical basicity. They determine the chemical reactivity of each component individually, or its equivalence in the case of a complex system of elements or oxides. This results from equalization methods or from direct computation through density functional theory (DFT). Those global parameters help in characterizing magma, provide insights into the reactivity of the melt or its fluid phase when in contact with another magma, or when considering the affinity of each component for metals. In particular, the description leads to a better understanding on the mechanisms that control metal segregation and transportation during igneous activity. The trends observed during magma evolution, whether they follow a mafic or a felsic trend are also observed using these parameters and can be interpreted as approaching a greater stability. Nevertheless, the trend for felsic magma occurs at constant electrophilicity toward a silica pole of great hardness. Conversely, mafic magmas evolve at a constant hardness and decreasing electrophilicity

  2. 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].

  3. Final report - Magma Energy Research Project

    SciTech Connect

    Colp, J.L.

    1982-10-01

    Scientific feasibility was demonstrated for the concept of magma energy extraction. The US magma resource is estimated at 50,000 to 500,000 quads of energy - a 700- to 7000-yr supply at the current US total energy use rate of 75 quads per year. Existing geophysical exploration systems are believed capable of locating and defining magma bodies and were demonstrated over a known shallow buried molten-rock body. Drilling rigs that can drill to the depths required to tap magma are currently available and experimental boreholes were drilled well into buried molten rock at temperatures up to 1100/sup 0/C. Engineering materials compatible with the buried magma environment are available and their performances were demonstrated in analog laboratory experiments. Studies show that energy can be extracted at attractive rates from magma resources in all petrologic compositions and physical configurations. Downhole heat extraction equipment was designed, built, and demonstrated successfully in buried molten rock and in the very hot margins surrounding it. Two methods of generating gaseous fuels in the high-temperature magmatic environment - generation of H/sub 2/ by the interaction of water with the ferrous iron and H/sub 2/, CH/sub 4/, and CO generation by the conversion of water-biomass mixtures - have been investigated and show promise.

  4. Magma reservoir systems inferred from tilt patterns

    NASA Astrophysics Data System (ADS)

    Schimozuru, D.

    1981-09-01

    Inflation patterns based on water-tube tiltmeter and levelling observation show different features for Krafla Volcano in Iceland and Kilauea Volcano in Hawaii. Monotonous sawtooth shape inflation is observed at Krafla, while inflation curves at Kileauea are more or less complicated. The difference was attributed to differences in the system of magma reservoir for the two volcanoes. By using the electrical equivalent of a magma reservoir and volcanic conduit as a capacitor and a resistor, an electrical oseillator was considered to be a possible model for a magma reservoir system. In the case of Krafla, the magma reservoir system is replaced with one electric oscillator called «Single system» or «Icelandic type» system. The complicated inflation pattern of Kilauea was interpreted as the assembly of a main magma reservoir and the group of surrounding small reservoirs. The equivalent electric analogue is the composite parallel and serial connection of a single oscillator which generates irregular output voltage during a charging process. The proposed magma reservoir system of Kilauea is called «Multi-coupled system» or «Hawaiian type system» which also help in interpreting the wondering of the uplift center and tidal phenomena of the Halemaumau lava lake.

  5. Hydroxyl speciation in felsic magmas

    NASA Astrophysics Data System (ADS)

    Malfait, Wim J.; Xue, Xianyu

    2014-09-01

    The hydroxyl speciation of hydrous, metaluminous potassium and calcium aluminosilicate glasses was investigated by 27Al-1H cross polarization and quantitative 1H MAS NMR spectroscopy. Al-OH is present in both the potassium and the calcium aluminosilicate glasses and its 1H NMR partial spectrum was derived from the 27Al-1H cross polarization data. For the calcium aluminosilicate glasses, the abundance of Al-OH could not be determined because of the low spectral resolution. For the potassium aluminosilicate glasses, the fraction of Al-OH was quantified by fitting its partial spectrum to the quantitative 1H NMR spectra. The degree of aluminum avoidance and the relative tendency for Si-O-Si, Si-O-Al and Al-O-Al bonds to hydrolyze were derived from the measured species abundances. Compared to the sodium, lithium and calcium systems, potassium aluminosilicate glasses display a much stronger degree of aluminum avoidance and a stronger tendency for the Al-O-Al linkages to hydrolyze. Combining our results with those for sodium aluminosilicate glasses (Malfait and Xue, 2010a), we predict that the hydroxyl groups in rhyolitic and phonolitic magmas are predominantly present as Si-OH (84-89% and 68-78%, respectively), but with a significant fraction of Al-OH (11-16% and 22-32%, respectively). For both rhyolitic and phonolitic melts, the AlOH/(AlOH + SiOH) ratio is likely smaller than the Al/(Al + Si) ratio for the lower end of the natural temperature range but may approach the Al/(Al + Si) ratio at higher temperatures.

  6. Emplacement-related layering in magma slurries

    NASA Astrophysics Data System (ADS)

    Petford, N.

    2009-04-01

    Textures and structures such as layering, grading and foliations preserved in igneous rocks offer a glimpse into the magma emplacement process. However, despite recent advances, a full and proper understanding of the fluid dynamics of congested fluid-particle mixtures during shear remains elusive. This is a shame as without recourse to such fundamental understanding, the interpretation of structural field data in the context of magma flow remains problematic. One way to gain insight into the process is to treat flowing magma as a dynamic material with a rheology similar to sheared, congested slurries. The idea that dense magma equates to a high temperature slurry is an attractive one, and opens up a way to examine the emplacement process that does not rely on equilibrium thermodynamics as a final explanation for commonly observed igneous structures. Using the Basement Sill, Antarctica, as a world class example of a magmatic slurry, shearing at high Peclet (Pe) number where particle diffusion is negligible has the potential to impart a rich diversity of structures including layering, grading and flow segregation. Work to model numerically the flow of the Basement Sill slurry using a range of theoretical and experimentally-derived non-Newtonian magma rheologies will be presented and assessed. A key impilcation is that in addition to more classical explanations such as compaction and gravitational settling, igneous layering can also arise spontaneously during shear associated with the ascent and emplacement of congested magma. A final aspect of the emplacement model considers the irregular geometry of the Basement Sill boundaries. Movement of magma along these boundaries results in the formation of local eddies and fluid swirl/back-flow that add additional complexity to macroscopic flow field.

  7. Radiographic visualization of magma dynamics in an erupting volcano.

    PubMed

    Tanaka, Hiroyuki K M; Kusagaya, Taro; Shinohara, Hiroshi

    2014-01-01

    Radiographic imaging of magma dynamics in a volcanic conduit provides detailed information about ascent and descent of magma, the magma flow rate, the conduit diameter and inflation and deflation of magma due to volatile expansion and release. Here we report the first radiographic observation of the ascent and descent of magma along a conduit utilizing atmospheric (cosmic ray) muons (muography) with dynamic radiographic imaging. Time sequential radiographic images show that the top of the magma column ascends right beneath the crater floor through which the eruption column was observed. In addition to the visualization of this magma inflation, we report a sequence of images that show magma descending. We further propose that the monitoring of temporal variations in the gas volume fraction of magma as well as its position in a conduit can be used to support existing eruption prediction procedures. PMID:24614612

  8. Radiographic visualization of magma dynamics in an erupting volcano

    PubMed Central

    Tanaka, Hiroyuki K. M.; Kusagaya, Taro; Shinohara, Hiroshi

    2014-01-01

    Radiographic imaging of magma dynamics in a volcanic conduit provides detailed information about ascent and descent of magma, the magma flow rate, the conduit diameter and inflation and deflation of magma due to volatile expansion and release. Here we report the first radiographic observation of the ascent and descent of magma along a conduit utilizing atmospheric (cosmic ray) muons (muography) with dynamic radiographic imaging. Time sequential radiographic images show that the top of the magma column ascends right beneath the crater floor through which the eruption column was observed. In addition to the visualization of this magma inflation, we report a sequence of images that show magma descending. We further propose that the monitoring of temporal variations in the gas volume fraction of magma as well as its position in a conduit can be used to support existing eruption prediction procedures. PMID:24614612

  9. Rapid Crystallization of the Bishop Magma

    NASA Astrophysics Data System (ADS)

    Gualda, G. A.; Anderson, A. T.; Sutton, S. R.

    2007-12-01

    Substantial effort has been made to understand the longevity of rhyolitic magmas, and particular attention has been paid to the systems in the Long Valley area (California). Recent geochronological data suggest discrete magma bodies that existed for hundreds of thousands of years. Zircon crystallization ages for the Bishop Tuff span 100-200 ka, and were interpreted to reflect slow crystallization of a liquid-rich magma. Here we use the diffusional relaxation of Ti zoning in quartz to investigate the longevity of the Bishop magma. We have used such an approach to show the short timescales of crystallization of Ti-rich rims on quartz from early- erupted Bishop Tuff. We have now recognized Ti-rich cores in quartz that can be used to derive the timescales of their crystallization. We studied four samples of the early-erupted Bishop. Hand-picked crystals were mounted on glass slides and polished. Cathodoluminescence (CL) images were obtained using the electron microprobe at the University of Chicago. Ti zoning was documented using the GeoSoilEnviroCARS x-ray microprobe at the Advanced Photon Source (Argonne National Lab). Quartz crystals in all 4 samples include up to 3 Ti-bearing zones: a central core (50-100 μm in diameter, ca. 50 ppm Ti), a volumetrically predominant interior (~40 ppm Ti), and in some crystals a 50-100 μm thick rim (50 ppm Ti). Maximum estimates of core residence times were calculated using a 1D diffusion model, as the time needed to smooth an infinitely steep profile to fit the observed profile. Surprisingly, even for the largest crystals studied - ca. 2 mm in diameter - core residence times are less than 1 ka. Calculated growth rates imply that even cm-sized crystals crystallized in less than 10 ka. Crystal size distribution data show that crystals larger than 3 mm are exceedingly rare, such that the important inference is that the bulk of the crystallization of the early-erupted Bishop magma occurred in only a few thousand years. This timescale

  10. 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

  11. 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

  12. Magma production and migration within the moon

    NASA Technical Reports Server (NTRS)

    Turcotte, D. L.; Ahern, J. L.

    1978-01-01

    Partial melting is likely to have occurred throughout much of the moon due to heating during accretion and the volumetric heating of radioactive isotopes. Important problems that have received relatively little attention concern the migration of the resulting magmas to form surface or near surface volcanic rock. In the paper the basic mechanism for the migration of the magma through the lunar asthenosphere is considered. A porous flow model is proposed. The magma behaves like a liquid flowing through a porous matrix. The volume fraction of liquid present determines the saturated porosity. The differential buoyancy of the magma drives it upwards. It is shown that the per cent partial melt in the lunar interior will only slightly exceed that required to provide interconnecting porosity. Assuming that the radioactive isotopes are preferentially segregated into the magma, the time dependence of the partial melting of the lunar interior is found. It is shown that the total degree of partial melting of the deep lunar interior is likely to be between five and ten per cent.

  13. Magma fragmentation speed: an experimental determination

    NASA Astrophysics Data System (ADS)

    Spieler, O.; Dingwell, D. B.; Alidibirov, M.

    2004-01-01

    The propagation speed of a fragmentation front, combined with the ascent velocity of magma is, in all likelihood, a controlling factor in the dynamics of explosive volcanic eruptions. Direct measurement of the 'fragmentation speed' in natural systems appears to be impossible at present. Fortunately, laboratory experiments can provide information on the propagation speed of the fragmentation front. Here we present the results of fragmentation speed determinations using a so-called 'fragmentation bomb'. These are, to the best of our knowledge, the first in situ fragmentation speed determinations performed on magma. Natural magma samples (Merapi basaltic andesite, Mount St. Helens dacite and Unzen dacite) have been investigated in the temperature range of 20-950°C and at pressures up to 25 MPa. Two techniques have been employed. Firstly, in experiments at 20°C, dynamic pressure transducers were placed above and below the magma samples and the fragmentation speed of the magma sample was derived from an analysis of the decompression curves. Secondly, at elevated temperatures, an alternative technique was introduced and successfully employed. This involved the severing via fragmentation of conducting wires placed within the samples at various heights. Fragmentation speeds are very low, falling in the range of 2-70 m/s and increasing with an increase in the magnitude of the decompression step responsible for the fragmentation. The first high-temperature determination seems consistent with low-temperature results. Implications for explosive volcanism are discussed briefly.

  14. Crystallization kinetics in magmas during decompression

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Many variables play a role during magma crystallization at depth or in a volcanic conduit, and through experimentally derived constraints we can better understand pre- and syn-eruptive magma crystallization behavior. The thermodynamic properties of magmas have been extensively investigated as a function of T, P, fO2 and magma composition [1], and this allows estimation of the stability of equilibrium phases and physical parameters (e.g., density, viscosity). However, many natural igneous rocks contain geochemical, mineralogical and textural evidence of disequilibrium, suggesting that magmas frequently follow non-equilibrium, time-dependent pathways that are recorded in the geochemical and petrographic characteristics of the rocks. There are currently no suitable theoretical models capable of calculating nucleation and growth rates in disequilibrium conditions without experimental constraints. The aim of this contribution is provide quantitative data on growth and nucleation rates of feldspar crystals in silicate melts obtained through decompression experiments, in order to determine the magma evolution in pre- and sin-eruptive conditions. Decompression is one of the main processes that induce the crystallization of feldspar during the magma ascent in the volcanic conduit. Decompression experiments have been carried out on trachytic and basaltic melts to investigate crystallization kinetics of feldspar as a function of the effect of the degassing, undercooling and time on nucleation and crystal growth process [2; 3]. Furthermore, feldspar is the main crystals phase present in magmas, and its abundance can strongly vary with small changes in pressure, temperature and water content in the melt, implying appreciable variations in the textures and in the crystallization kinetics. Crystallization kinetics of trachytic melts show that long experiment durations involve more nucleation events of alkali feldspar than short experiment durations [2]. This is an important

  15. Can basal magma oceans generate magnetic fields?

    NASA Astrophysics Data System (ADS)

    Stegman, D. R.; Ziegler, L. B.; Davies, C.

    2015-12-01

    Earth's magnetic field is very old, with recent data now showing the field possibly extended back to 4.1 billion years ago (Tarduno et al., Science, 2015). Yet, based upon our current knowledge there are difficulties in sustained a core dynamo over most of Earth's history. Moreover, recent estimates of thermal and electrical conductivity of liquid iron at core conditions from mineral physics experiments indicate that adiabatic heat flux is approximately 15 TW, nearly 3 times larger than previously thought, exacerbating difficulties for driving a core dynamo by convective core cooling alone throughout Earth history. A long-lived basal magma ocean in the lowermost mantle has been proposed to exist in the early Earth, surviving perhaps into the Archean. While the modern, solid lower mantle is an electromagnetic insulator, electrical conductivities of silicate melts are known to be higher, though as yet they are unconstrained for lowermost mantle conditions. Here we explore the geomagnetic consequences of a basal magma ocean layer for a range of possible electrical conductivities. For the highest electrical conductivities considered, we find a basal magma ocean could be a primary dynamo source region. This would suggest the proposed three magnetic eras observed in paleomagnetic data originate from distinct sources for dynamo generation: from 4.5-2.45 Ga within a basal magma ocean, from 2.25-0.4 Ga within a superadiabatically cooled liquid core, and from 0.4-present within a quasi-adiabatic core that includes a solidifying inner core. We have extended this work by developing a new code, Dynamantle, which is a model with an entropy-based approach, similar to those commonly used in core dynamics models. We present new results using this code to assess the conditions under which basal magma oceans can generate positive ohmic dissipation. This is more generally useful than just considering the early Earth, but also for many silicate exoplanets in which basal magma oceans

  16. 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

    Understanding the processes that affect the rate of liquid state homogenization provides fundamental clues on the otherwise inaccessible subsurface dynamics of magmatic plumbing systems. Compositional heterogeneities detected in the matrix of magmatic rocks represent the arrested state of a chemical equilibration. Magmatic homogenization has been divided into a) the mechanical interaction of magma batches (mingling) and b) the diffusive equilibration of compositional gradients, where diffusive equilibration is exponentially enhanced by progressive mechanical interaction [1]. The mechanical interaction between two distinct batches of magma has commonly been attributed to shear and folding movements between two liquids of distinct viscosities. A mode of mechanical interaction scarcely invoked is the advection of mafic material into a felsic one through bubble motion. Yet, experiments with analogue materials demonstrated that bubble ascent has the potential to enhance the fluid mechanical component of magma mixing [2]. Here, we present preliminary results from bubble-advection experiments. For the first time, experiments of this kind were performed using natural materials at magmatic temperatures. Cylinders of Snake River Plain (SRP) basalt were drilled with a cavity of defined volume and placed underneath cylinders of SRP rhyolite. Upon melting, the gas pocket, or bubble trapped within the cavity, rose into the rhyolite, so entraining a layer of basalt. Successive iterations of the same experiment at progressive intervals ensured a time series of magmatic interaction caused by bubble segregation. Variations in initial bubble size allowed the tracking of bubble volume to advected material ratio at defined viscosity contrast. The resulting plume-like structures that the advected basalt formed within the rhyolite were characterized by microCT and subsequent high-resolution EMP analyses. The mass of advected material per bubble correlated positively with bubble size. The

  17. Evolution and Consequences of Magma Ocean Solidifcation

    NASA Astrophysics Data System (ADS)

    Maurice, Maxime; Tosi, Nicola; Ana-Catalina, Plesa; Breuer, Doris

    2015-04-01

    The various and intense energy sources involved in the early stages of planetary formation, such as kinetic energy of accretion, decay of short-lived radiogenics, release of gravitational potential energy upon core formation, and tidal effects, are thought to have caused partial or possibly entire melting of the mantle of terrestrial planets and moons [Elkins-Tanton2012]. Global or local liquid magma oceans could thus have formed, whose solidification upon planetary cooling could have exerted a significant impact on the differentiation and subsequent evolution of the interior of terrestrial bodies. The solidification of such magma oceans likely proceeds from the bottom upwards because of the steeper slope of the mantle adiabat with respect to the slope of the solidus, and controls the initial compositional stratification of the solid mantle, which, in turn, can play an important role in shaping the earliest forms of mantle convection and surface tectonics. We investigate the thermal evolution of a whole-mantle magma ocean using the finite-volume code Gaia [Huettig2013]. We run two-dimensional simulations of magma ocean cooling and crystallization and investigate in particular the conditions for which the onset of solid-state thermal convection is possible before mantle solidification has completed. We assume an adiabatic temperature profile in the magma ocean and various cooling rates of the surface temperature according to coupled magma ocean-atmosphere models [Lebrun2013]. Upon reaching a critical melt fraction that marks the formation of the so-called rheological front, [Solomatov2007], we self-consistently solve with Gaia the conservation equations of solid-state mantle convection in the partially molten domain assuming a viscosity strongly dependent on temperature and melt content. By varying the reference Rayleigh number and the magma ocean cooling rate, we show that, even for a surface temperature decreasing very rapidly at a rate of 1000 K/Myr, a

  18. Timing of Magma Mixing Prior to the 2011 Eruption of Shinmoedake, Japan: On the Relationship Between Magma Injection, Magma Mixing, and Eruption Triggering

    NASA Astrophysics Data System (ADS)

    Tomiya, A.; Miyagi, I.; Saito, G.; Geshi, N.

    2013-12-01

    Various petrological evidences indicate magma mixing often preceded volcanic eruptions. Magma injection into the associated magma chambers also often occurs prior to eruptions as evidenced by inflation of a volcanic edifice. However, the relationship between magma injection, magma mixing, and eruption triggering is unclear because injection does not necessarily cause instantaneous mixing if the injected magma is sufficiently denser than the pre-existing magma and has formed stable stratified layers. To investigate the relationship, we estimated the timing of magma mixing prior to the 2011 sub-Plinian eruptions of Shinmoedake volcano, Kirishima volcanic group, Japan, on the basis of chemical zoning observed in magnetite phenocrysts and numerical diffusion modeling. We compared the timing with that of volcanic inflation/deflation processes. The eruptive products are comprised mainly of phenocryst-rich (28 vol%) gray pumice (SiO2 = 57 wt%) with minor amount of white pumice (SiO2 = 62 wt%). We recognized two magmatic end members, low-T dacitic magma and high-T mafic magma (basalt or basaltic andesite), and hybrid andesitic magma on the basis of our petrologic studies. Gray pumice is comprised mainly of the hybrid andesitic magma. White pumice is comprised mainly of the low-T dacitic magma with mixing of small volume of the hybrid andesitic magma. Most of the magnetite phenocrysts (type-A1) were crystallized in the hybrid andesitic magma. Their zoning profiles showed considerable increase in Mg and Al contents toward the rims of the phenocrysts, due to mixing with the high-T mafic magma. We calculated the time for diffusion to form these zoning profiles to be only 0.4 to 3 days. The short time scale suggests that the mixing of high-T magma triggered the sub-Plinian eruptions. This mixing process was not accompanied by a significant change in the volume of the magma chamber because no significant crustal deformation was observed several days prior to the eruptions (Japan

  19. Unusual Iron Redox Systematics of Martian Magmas

    SciTech Connect

    Danielson, L.; Righter, K.; Pando, K.; Morris, R.V.; Graff, T.; Agresti, D.; Martin, A.; Sutton, S.; Newville, M.; Lanzirotti, A.

    2012-03-26

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite. Morris et al. proposed that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks. Magnetite stability in terrestrial magmas is well understood, as are the stabilities of FeO and Fe{sub 2}O{sub 3} in terrestrial magmas. In order to better understand the variation of FeO and Fe{sub 2}O{sub 3}, and the stability of magnetite (and other FeO-bearing phases) in martian magmas, we have undertaken an experimental study with two emphases. First, we determine the FeO and Fe{sub 2}O{sub 3} contents of super- and sub-liquidus glasses from a shergottite bulk composition at 1 bar to 4 GPa, and variable fO{sub 2}. Second, we document the stability of magnetite with temperature and fO{sub 2} in a shergottite bulk composition.

  20. Petrology and Physics of Magma Ocean Crystallization

    NASA Technical Reports Server (NTRS)

    Elkins-Tanton, Linda T.; Parmentier, E. M.; Hess, P. C.

    2003-01-01

    Early Mars is thought to have been melted significantly by the conversion of kinetic energy to heat during accretion of planetesimals. The processes of solidification of a magma ocean determine initial planetary compositional differentiation and the stability of the resulting mantle density profile. The stability and compositional heterogeneity of the mantle have significance for magmatic source regions, convective instability, and magnetic field generation. Significant progress on the dynamical problem of magma ocean crystallization has been made by a number of workers. The work done under the 2003 MFRP grant further explored the implications of early physical processes on compositional heterogeneity in Mars. Our goals were to connect early physical processes in Mars evolution with the present planet's most ancient observable characteristics, including the early, strong magnetic field, the crustal dichotomy, and the compositional characteristics of the SNC meteorite's source regions as well as their formation as isotopically distinct compositions early in Mars's evolution. We had already established a possible relationship between the major element compositions of SNC meteorite sources and processes of Martian magma ocean crystallization and overturn, and under this grant extended the analysis to the crucial trace element and isotopic SNC signatures. This study then demonstrated the ability to create and end the magnetic field through magma ocean cumulate overturn and subsequent cooling, as well as the feasibility of creating a compositionally- and volumetrically-consistent crustal dichotomy through mode-1 overturn and simultaneous adiabatic melting.

  1. 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.

  2. Isotopic zonations in silicic magma chambers

    SciTech Connect

    Johnson, C.M. )

    1989-12-01

    Many ash-flow tuffs are zoned in radiogenic isotope ratios, indicating that roofward assimilation of crust occurs in ash-flow magma chambers prior to eruption. Cases where relatively well constrained calculations may be made regarding the percentage of assimilation in the roof zone indicate that the percentage of assimilation often exceeds the percentage of phenocrysts in the tuffs. This relation, in addition to the fact that assimilation gradients are opposite to that of the percentage of phenocrysts, suggests that assimilation and crystallization in the silicic roof zones of crustal magma chambers are separated in time and space, and that these processes are best modeled as two-component mixing; true assimilation-fractional crystallization is probably restricted to the lower mafic parts. Most phenocrysts in the silicic upper parts of magma chambers crystallized after assimilation, providing minimum estimates of time between assimilation and eruption (1-100 yr). Preservation of monotonic isotopic gradients suggests that convection is minor in the upper parts of silicic magma chambers during the late stages of evolution.

  3. Frozen magma lenses below the oceanic crust.

    PubMed

    Nedimović, Mladen R; Carbotte, Suzanne M; Harding, Alistair J; Detrick, Robert S; Canales, J Pablo; Diebold, John B; Kent, Graham M; Tischer, Michael; Babcock, Jeffrey M

    2005-08-25

    The Earth's oceanic crust crystallizes from magmatic systems generated at mid-ocean ridges. Whereas a single magma body residing within the mid-crust is thought to be responsible for the generation of the upper oceanic crust, it remains unclear if the lower crust is formed from the same magma body, or if it mainly crystallizes from magma lenses located at the base of the crust. Thermal modelling, tomography, compliance and wide-angle seismic studies, supported by geological evidence, suggest the presence of gabbroic-melt accumulations within the Moho transition zone in the vicinity of fast- to intermediate-spreading centres. Until now, however, no reflection images have been obtained of such a structure within the Moho transition zone. Here we show images of groups of Moho transition zone reflection events that resulted from the analysis of approximately 1,500 km of multichannel seismic data collected across the intermediate-spreading-rate Juan de Fuca ridge. From our observations we suggest that gabbro lenses and melt accumulations embedded within dunite or residual mantle peridotite are the most probable cause for the observed reflectivity, thus providing support for the hypothesis that the crust is generated from multiple magma bodies. PMID:16121179

  4. Loki Patera: A Magma Sea Story

    NASA Technical Reports Server (NTRS)

    Veeder, G. J.; Matson, D. L.; Rathbun, A. G.

    2005-01-01

    We consider Loki Patera on Io as the surface expression of a large uniform body of magma. Our model of the Loki magma sea is some 200 km across; larger than a lake but smaller than an ocean. The depth of the magma sea is unknown, but assumed to be deep enough that bottom effects can be ignored. Edge effects at the shore line can be ignored to first order for most of the interior area. In particular, we take the dark material within Loki Patera as a thin solidified lava crust whose hydrostatic shape follows Io's isostatic surface (approx. 1815 km radius of curvature). The dark surface of Loki appears to be very smooth on both regional and local (subresolution) scales. The thermal contrast between the low and high albedo areas within Loki is consistent with the observed global correlation. The composition of the model magma sea is basaltic and saturated with dissolved SO2 at depth. Its average, almost isothermal, temperature is at the liquidus for basalt. Additional information is included in the original extended abstract.

  5. 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.

  6. Iron Redox Systematics of Martian Magmas

    NASA Technical Reports Server (NTRS)

    Righter, K.; Danielson, L.; Martin, A.; Pando, K.; Sutton, S.; Newville, M.

    2011-01-01

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite [1]. Morris et al. [1] propose that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks [2,3]. Magnetite stability in terrestrial magmas is well understood, as are the stability of FeO and Fe2O3 in terrestrial magmas [4,5]. In order to better understand the variation of FeO and Fe2O3, and the stability of magnetite (and other FeO-bearing phases) in martian magmas we have undertaken an experimental study with two emphases. First we document the stability of magnetite with temperature and fO2 in a shergottite bulk composition. Second, we determine the FeO and Fe2O3 contents of the same shergottite bulk composition at 1 bar and variable fO2 at 1250 C, and at variable pressure. These two goals will help define not only magnetite stability, but pyroxene-melt equilibria that are also dependent upon fO2.

  7. Unusual Iron Redox Systematics of Martian Magmas

    NASA Technical Reports Server (NTRS)

    Danielson, L.; Righter, K.; Pando, K.; Morris, R. V.; Graff, T.; Agresti, D.; Martin, A.; Sutton, S.; Newville, M.; Lanzirotti, A.

    2012-01-01

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite. Morris et al. proposed that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks. Magnetite stability in terrestrial magmas is well understood, as are the stabilities of FeO and Fe2O3 in terrestrial magmas. In order to better understand the variation of FeO and Fe2O3, and the stability of magnetite (and other FeO-bearing phases) in martian magmas, we have undertaken an experimental study with two emphases. First, we determine the FeO and Fe2O3 contents of super- and sub-liquidus glasses from a shergottite bulk composition at 1 bar to 4 GPa, and variable fO2. Second, we document the stability of magnetite with temperature and fO2 in a shergottite bulk composition.

  8. The rheology of two-phase magmas

    NASA Astrophysics Data System (ADS)

    Llewellin, E. W.; Mader, H. M.; Mueller, S.

    2012-12-01

    Great advances in our understanding of the rheology of two-phase magmatic suspensions (magma with either bubbles or crystals in it) have been made in recent years. These advances are based on laboratory experiments with both magma and analogue materials, and on analytical and numerical modelling. The current state-of-the-art is the culmination of scores of studies undertaken by scores of research groups and presented in scores of publications. Consequently, whilst it is possible to construct a sophisticated rheological description of a two-phase magma based on a few easily-measured properties (melt composition, crystal/vesicle volume fraction, CSD/VSD, etc.) the task of determining how best to do this is daunting to the non-specialist. We present a straightforward, practical, algorithmic approach to determining the rheology of two-phase magma to the degree of sophistication appropriate to most modelling applications. The approach is based on a broad synthesis of the literature, on new experimental data, and on new theoretical analysis.

  9. 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

  10. Shallow crystallization of Kilauean olivines: Magma density and picritic eruptions

    SciTech Connect

    Anderson, A.T. Jr.; Brown, G.G. . Dept. of the Geophysical Sciences)

    1992-01-01

    Of 35 analyzed glass inclusions in olivine phenocrysts from the 1959 Kilauea Iki eruption, 23 formed at pressures less than 1 Kbar, 10 between 1 and 2 Kbar and 2 at pressures greater than 2 Kbar. The surprisingly topheavy distribution of formation pressures suggests that the 1959 magma rose rapidly to the upper parts of Kilauea's summit magma storage reservoir where cooling and crystallization dominantly occurred. The implication that the parental magma was buoyant relative to preexisting resident magma is consistent with an expected preeruptive bulk CO[sub 2] content of 0.3wt.% and petrographic evidence for turbulent mixing between parental and preexisting magma. That the 1959 magma was rich not only in crystals but also in gas, as evidenced by its high lava fountains, suggests that the storage time in the summit reservoir was too short for either crystals or gas to be lost. Therefore, the 1959 Kilauean magma probably is a near-parental magma that rose and formed a gas- and crystal-rich cap at the top of Kilauea's summit magma storage reservoir. Whether parental magma rises to the top or ponds at the base of the summit reservoir depends mainly on reservoir pressure and magma gas content. Consequently, it seems likely that the eruptive and degassing behavior of Kilauea is regulated in part by an interplay between the CO[sub 2] content of parental magma and the pressure at the base of the summit storage reservoir.

  11. Numerical simulation of magma energy extraction

    SciTech Connect

    Hickox, C.E.

    1991-01-01

    The Magma Energy Program is a speculative endeavor regarding practical utility of electrical power production from the thermal energy which reside in magma. The systematic investigation has identified an number of research areas which have application to the utilization of magma energy and to the field of geothermal energy. Eight topics were identified which involve thermal processes and which are areas for the application of the techniques of numerical simulation. These areas are: (1) two-phase flow of the working fluid in the wellbore, (2) thermodynamic cycles for the production of electrical power, (3) optimization of the entire system, (4) solidification and fracturing of the magma caused by the energy extraction process, (5) heat transfer and fluid flow within an open, direct-contact, heat-exchanger, (6) thermal convection in the overlying geothermal region, (7) thermal convection within the magma body, and (8) induced natural convection near the thermal energy extraction device. Modeling issues have been identified which will require systematic investigation in order to develop the most appropriate strategies for numerical simulation. It appears that numerical simulations will be of ever increasing importance to the study of geothermal processes as the size and complexity of the systems of interest increase. It is anticipated that, in the future, greater emphasis will be placed on the numerical simulation of large-scale, three-dimensional, transient, mixed convection in viscous flows and porous media. Increased computational capabilities, e.g.; massively parallel computers, will allow for the detailed study of specific processes in fractured media, non-Darcy effects in porous media, and non-Newtonian effects. 23 refs., 13 figs., 1 tab.

  12. 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.

  13. Deep magma transport at Kilauea volcano, Hawaii

    USGS Publications Warehouse

    Wright, T.L.; Klein, F.W.

    2006-01-01

    The shallow part of Kilauea's magma system is conceptually well-understood. Long-period and short-period (brittle-failure) earthquake swarms outline a near-vertical magma transport path beneath Kilauea's summit to 20 km depth. A gravity high centered above the magma transport path demonstrates that Kilauea's shallow magma system, established early in the volcano's history, has remained fixed in place. Low seismicity at 4-7 km outlines a storage region from which magma is supplied for eruptions and intrusions. Brittle-failure earthquake swarms shallower than 5 km beneath the rift zones accompany dike emplacement. Sparse earthquakes extend to a decollement at 10-12 km along which the south flank of Kilauea is sliding seaward. This zone below 5 km can sustain aseismic magma transport, consistent with recent tomographic studies. Long-period earthquake clusters deeper than 40 km occur parallel to and offshore of Kilauea's south coast, defining the deepest seismic response to magma transport from the Hawaiian hot spot. A path connecting the shallow and deep long-period earthquakes is defined by mainshock-aftershock locations of brittle-failure earthquakes unique to Kilauea whose hypocenters are deeper than 25 km with magnitudes from 4.4 to 5.2. Separation of deep and shallow long-period clusters occurs as the shallow plumbing moves with the volcanic edifice, while the deep plumbing is centered over the hotspot. Recent GPS data agrees with the volcano-propagation vector from Kauai to Maui, suggesting that Pacific plate motion, azimuth 293.5?? and rate of 7.4 cm/yr, has been constant over Kilauea's lifetime. However, volcano propagation on the island of Hawaii, azimuth 325??, rate 13 cm/yr, requires southwesterly migration of the locus of melting within the broad hotspot. Deep, long-period earthquakes lie west of the extrapolated position of Kilauea backward in time along a plate-motion vector, requiring southwesterly migration of Kilauea's magma source. Assumed ages of 0

  14. Outgassing of silicic magma through bubble and fracture networks (Invited)

    NASA Astrophysics Data System (ADS)

    Okumura, S.; Nakamura, M.; Uesugi, K.

    2013-12-01

    Outgassing of magma is a fundamental process that controls the style and explosivity of volcanic eruptions. Vesiculation during the ascent and decompression of magma results in the formation of bubble networks within the magma. The permeable gas escape through the bubble networks is an efficient way to induce the outgassing of silicic magma (Eichelberger et al., 1986). To understand magma ascent dynamics and predict the style and explosivity of eruptions, it is necessary to constrain the rate of magma outgassing as the magma ascends in a volcanic conduit. However, the gas permeability of natural samples should not be considered, because it reflects complicated processes involving vesiculation, deformation, outgassing, and compaction. Experimental studies have demonstrated that vesiculation and compaction processes show hysteresis behavior (Okumura et al., 2013). Thus, we have performed experiments to simulate magma decompression and the deformation of vesicular magmas (e.g., Okumura et al., 2009, 2012). A series of decompression and deformation experiments indicates that the gas permeability is less than the order of 10-15 m2 for isotropic vesiculation at vesicularity <60-80 vol%. When magma ascent is simulated with shear deformation, the gas permeability is much greater than that observed under isotropic conditions. Akin to bubble networks, permeable networks consisting of shear-induced brittle fractures are thought to be efficient outgassing pathways (Gonnermann and Manga, 2003). Our recent experiments demonstrated that fractured magma has a higher gas permeability than vesicular magma at least at vesicularities <~40 vol%. This indicates that fracture networks in magma become efficient parts for the outgassing. However, as shear fracturing results from high strain rates in highly viscous magma, outgassing via fracture networks can be enhanced in localized shear zones and shallow parts of the conduit. The permeable bubble and fracture networks are preferentially

  15. Magma energy: the ultimate heat source for geothermal fields

    SciTech Connect

    Hardee, H.C.

    1982-07-01

    A scientific feasibility study, funded by DOE/Basic Energy Sciences, of extracting energy directly from buried magma sources is discussed. This study has examined the problems of locating and drilling into the magma and then extracting useful quantities of energy from the magma. Theoretical calculations with supporting laboratory and field measurements have been used to show that there are no theoretical or physical barriers that prevent the direct extraction of energy from magma. As a result of this study it has been concluded that magma energy utilization is scientifically feasible.

  16. Magma Dynamics in Dome-Building Volcanoes

    NASA Astrophysics Data System (ADS)

    Kendrick, J. E.; Lavallée, Y.; Hornby, A. J.; Schaefer, L. N.; Oommen, T.; Di Toro, G.; Hirose, T.

    2014-12-01

    The frequent and, as yet, unpredictable transition from effusive to explosive volcanic behaviour is common to active composite volcanoes, yet our understanding of the processes which control this evolution is poor. The rheology of magma, dictated by its composition, porosity and crystal content, is integral to eruption behaviour and during ascent magma behaves in an increasingly rock-like manner. This behaviour, on short timescales in the upper conduit, provides exceptionally dynamic conditions that favour strain localisation and failure. Seismicity released by this process can be mimicked by damage accumulation that releases acoustic signals on the laboratory scale, showing that the failure of magma is intrinsically strain-rate dependent. This character aids the development of shear zones in the conduit, which commonly fracture seismogenically, producing fault surfaces that control the last hundreds of meters of ascent by frictional slip. High-velocity rotary shear (HVR) experiments demonstrate that at ambient temperatures, gouge behaves according to Byerlee's rule at low slip velocities. At rock-rock interfaces, mechanical work induces comminution of asperities and heating which, if sufficient, may induce melting and formation of pseudotachylyte. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The bulk composition, mineralogy and glass content of the magma all influence frictional behaviour, which supersedes buoyancy as the controlling factor in magma ascent. In the conduit of dome-building volcanoes, the fracture and slip processes are further complicated: slip-rate along the conduit margin fluctuates. The shear-thinning frictional melt yields a tendency for extremely unstable slip thanks to its pivotal position with regard to the glass transition. This thermo-kinetic transition bestows the viscoelastic melt with the ability to either flow or

  17. Fractionation of a Basal Magma Ocean

    NASA Astrophysics Data System (ADS)

    Laneuville, M.; Hernlund, J. W.; Labrosse, S.

    2014-12-01

    Earth's magnetic field is thought to be sustained by dynamo action in a convecting metallic outer core since at least 3.45 Ga (Tarduno et al., 2010). Convection induces an isentropic temperature gradient that drains 13±3 TW of heat from the core by thermal conduction (de Koker et al., 2012; Pozzo et al., 2012; Gomi et al., 2013), and suggests that Earth's core has cooled by ˜1,000 K or more since Earth's formation (Gomi et al., 2013). However, models of Earth's initial thermal evolution following a giant-impact predict rapid cooling to the mantle melting temperature (e.g., Solomatov, 2007). In order to understand how the core could have retained enough heat to explain the age of the geodynamo, we relax a key assumption of the basal magma ocean model of (Labrosse et al., 2007) to allow for the possibility that the magma is stably stratified. Recent giant impact simulations suggest extensive core-mantle mixing (Saitoh and Makino, 2013), which could have produced such a large stratified magma layer at the core-mantle boundary. In the presence of a stable density gradient, heat transfer through the basal magma ocean occurs through conduction and therefore delays heat loss from the core. Partitioning of iron in the liquid phase upon crystallization changes the density profile and triggers convection in the upper part of the basal magma ocean. Our hypothesis suggests that early core cooling is dominated by the diffusion timescale through the basal magma ocean, and predicts a delayed onset of the geodynamo (i.e, during the late Headean/early Archean). This model can therefore be falsified if the existence of a geomagnetic field can be inferred from magnetization of inclusions in Hadean zircons. N. de Koker et al., Proc. Natl. Acad. Sci. 190, 4070-4073 (2012).H. Gomi et al., Phys. Earth Planet. Inter. 224, 88-103 (2013).S. Labrosse et al., Nature 450, 866-869 (2007).M. Pozzo et al., Nature 485, 355-358 (2012).T. Saitoh and J. Makino. Astrophys. J. 768, 44 (2013).V

  18. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    2000-01-01

    The research described in this progress report involved the study of petrological, geochemical and volcanic processes that occur on the Moon and the SNC parent body, generally accepted to be Mars. The link between these studies is that they focus on two terrestrial-type parent bodies somewhat smaller than earth, and the fact that they focus on the role of volatiles in magmatic processes and on processes of magma evolution on these planets. The work on the lunar volcanic glasses has resulted in some exciting new discoveries over the years of this grant. During the tenure of the present grant, we discovered a variety of metal blebs in the A17 orange glass. Some of these Fe-Ni metal blebs occur in the glass; others were found in olivine phenocrysts which we find make up about 2 vol % of the orange glass magma. The importance of these metal spheres is that they fix the oxidation state of the parent magma during the eruption, and also indicate changes during the eruption. They also yield important information about the composition of the gas phase present, the gas which drove the lunar fire-fountaining. In an Undergraduate senior thesis project, Nora Klein discovered a melt inclusion that remained in a glassy state in one of the olivine phenocrysts. Analyses of this inclusion gave additional information on the CO2, CO and S contents of the orange glass magma prior to its reaching the lunar surface. The composition of lunar volcanic gases has long been one of the puzzles of lunar magmatic processes. One of the more exciting findings in our research over the past year has been the study of magmatic processes linking the SNC meteorite source magma composition with the andesitic composition rocks found at the Pathfinder site. In this project, graduate student Michelle Minitti showed that there was a clear petrologic link between these two magma types via fractional removal of crystals from the SNC parent melt, but the process only worked if there was at least 1 wt

  19. Magma Piracy in the Southern Mariana Backarc

    NASA Astrophysics Data System (ADS)

    Becker, N. C.; Fryer, P.; Martinez, F.; Stern, R. J.; Bloomer, S. H.

    2001-12-01

    Since 1997 the southern Mariana convergent margin system has been mapped with Hydrosweep, MR-1, and SeaBeam swath sonar systems on five cruises resulting in 168,500 km2 of bathymetry data and 186,800 km2 of sidescan data, revealing anomalous processes relative to the rest of the Mariana region. Most of the Mariana Arc is characterized by arc volcanism dominated by large, central volcanoes located at the boundary between a backarc basin with slow-spreading ridge morphology and a nonaccretionary forearc composed of Eocene volcanic arc rocks But southwest of Tracey Seamount, the southernmost large central arc volcano, the character of the arc and backarc changes dramatically. The arc volcanoes become small or nonexistent, but those that do occur lie along relict spreading fabric within the backarc basin. Furthermore, the spreading center appears to have an inflated, fast-spreading morphology, including dueling propagator fabric, and this southern backarc basin forms a shallow plateau overall. The spreading center then becomes less well-defined west of 143oE, and the volcanism appears to cease altogether west of 142oE in an area of amagmatic rifting, an observation supported by earthquake focal mechanisms and magnetics. The inflated morphology of the spreading axis, along with the absence or reduced size of nearby arc volcanoes suggests that arc magmas have been entrained into the backarc-spreading magmatic system. This "magma piracy" would result in arc magma being erupted at the backarc spreading center, therefore the backarc crust would be formed in part from arc magmas. Dredge samples from along the active ridge show compositions consistent with this suggestion. We suggest that this magma piracy has dominated the southern backarc basin for at least the last 3 m.y. since the robust spreading began. We suggest that the apparently higher magma production rate and the hybridized crust could account for the shallowness of the basin, as the more evolved arc-lavas would

  20. Volcanic conduit failure as a trigger to magma fragmentation

    NASA Astrophysics Data System (ADS)

    Lavallée, Y.; Benson, P. M.; Heap, M. J.; Flaws, A.; Hess, K.-U.; Dingwell, D. B.

    2012-01-01

    In the assessment of volcanic risk, it is often assumed that magma ascending at a slow rate will erupt effusively, whereas magma ascending at fast rate will lead to an explosive eruption. Mechanistically viewed, this assessment is supported by the notion that the viscoelastic nature of magma (i.e., the ability of magma to relax at an applied strain rate), linked via the gradient of flow pressure (related to discharge rate), controls the eruption style. In such an analysis, the physical interactions between the magma and the conduit wall are commonly, to a first order, neglected. Yet, during ascent, magma must force its way through the volcanic edifice/structure, whose presence and form may greatly affect the stress field through which the magma is trying to ascend. Here, we demonstrate that fracturing of the conduit wall via flow pressure releases an elastic shock resulting in fracturing of the viscous magma itself. We find that magma fragmentation occurred at strain rates seven orders of magnitude slower than theoretically anticipated from the applied axial strain rate. Our conclusion, that the discharge rate cannot provide a reliable indication of ascending magma rheology without knowledge of conduit wall stability, has important ramifications for volcanic hazard assessment. New numerical simulations are now needed in order to integrate magma/conduit interaction into eruption models.

  1. Magma oceanography. I - Thermal evolution. [of lunar surface

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.; Longhi, J.

    1977-01-01

    Fractional crystallization and flotation of cumulate plagioclase in a cooling 'magma ocean' provides the simplest explanation for early emplacement of a thick feldspar-rich lunar crust. The complementary mafic cumulates resulting from the differentiation of such a magma ocean have been identified as the ultimate source of mare basalt liquids on the basis or rare-earth abundance patterns and experimental petrology studies. A study is conducted concerning the thermal evolution of the early differentiation processes. A range of models of increasing sophistication are considered. The models developed contain the essence of the energetics and the time scale for magma ocean differentiation. Attention is given to constraints on a magma ocean, modeling procedures, single-component magma oceans, fractionating magma oceans, and evolving magma oceans.

  2. Magma transport and storage at Kilauea volcano, HI

    NASA Astrophysics Data System (ADS)

    Wright, T. L.

    2010-12-01

    Thomas L. Wright and Fred W. Klein (USGS, Johns Hopkins University, Baltimore, MD 21218, Menlo Park, CA 94025; 410-516-7040, 650-329-4794) Seismic and deformation data between 1950 and the beginning of the Mauna Ulu eruption of 1969-1974 indicate (1) that summit inflation and deflation cycles are best matched by a magma reservoir beneath Kilauea's summit consisting of concatenated vertical plugs and (2) that magmas erupted at Kilauea's summit are also present beneath the east rift zone where they can cool and fractionate. Three "olivine-controlled" magmas fractionated by removal of olivine only and distinguished from each other by their major-oxide chemistry were erupted at Kilauea's summit within Halemaumau crater in 1952, 1961 and 1967-68. From 1955 to 1969, these three magmas were mixed with fractionated magmas stored beneath Kilauea's east rift zone to form "hybrid" eruptions. Two eruptions important to our interpretation occurred on the lower east rift zone 1n 1955 and 1960. Published mixing calculations show that the 1952 magma mixed with the fractionated 1955 magma in the latter part of the 1955 eruption and that the 1961 magma was intruded in 1955 to become the parent for fractionated magma later erupted in 1977 from the rift zone. The 1960 eruption began with magma hybridized in 1955, then was successively mixed with the remaining 1952 magma, 1961 magma and the 1967-68 magma. The latter two summit magmas were identified in hybrid eruptions from 1961-1965 and also as parents for fractionated magma present in fractionated and hybrid rift eruptions of 1968-69. The mixing in this period demonstrates that the 1952, 1961 and 1967-68 summit magmas appear in that order in hybrid eruptions on the east rift zone before they are erupted at the summit, traveled within the rift without appreciable cooling or mixing with each other, and were identified as eruption components for up to ~ 10 years. Volume calculations indicate that these magmas were stored prior to

  3. The location and timing of magma degassing during Plinian eruptions

    NASA Astrophysics Data System (ADS)

    Giachetti, T.; Gonnermann, H. M.

    2014-12-01

    Water is the most abundant volatile species in explosively erupting silicic magmas and significantly affects magma viscosity, magma fragmentation and the dynamics of the eruption column. The effect that water has on these eruption processes can be modulated by outgassing degassing from a permeable magma. The magnitude, rate and timing of outgassing during magma ascent, in particular in relation to fragmentation, remains a subject of debate. Here we constrain how much, how fast and where the erupting magma lost its water during the 1060 CE Plinian phase of the Glass Mountain eruption of Medicine Lake Volcano, California. Using thermogravimetric analysis coupled with numerical modeling, we show that the magma lost >90% of its initial water upon eruption. Textural analyses of natural pumices, together with numerical modeling of magma ascent and degassing, indicate that 65-90% of the water exsolved before fragmentation, but very little was able to outgas before fragmentation. The magma attained permeability only within about 1 to 10 seconds before fragmenting and during that time interval permeable gas flow resulted in only a modest amount of gas flux from the un-fragmented magma. Instead, most of the water is lost shortly after fragmentation, because gas can escape rapidly from lapilli-size pyroclasts. This results in an efficient rarefaction of the gas-pyroclast mixture above the fragmentation level, indicating that the development of magma permeability and ensuing permeable outgassing are a necessary condition for sustain explosive eruptions of silicic magma. Magma permeability is thus a double-edged sword, it facilitates both, the effusive and the explosive eruption of silicic magma.

  4. Short-lived radioactivity and magma genesis.

    PubMed

    Gill, J; Condomines, M

    1992-09-01

    Short-lived decay products of uranium and thorium have half-lives and chemistries sensitive to the processes and time scales of magma genesis, including partial melting in the mantle and magmatic differentiation in the crust. Radioactive disequilibrium between (238)U, (230)Th, and (226)Ra is widespread in volcanic rocks. These disequilibria and the isotopic composition of thorium depend especially on the extent and rate of melting as well as the presence and composition of vapor during melting. The duration of mantle melting may be several hundred millennia, whereas ascent times are a few decades to thousands of years. Differentiation of most magmas commonly occurs within a few millennia, but felsic ones can be tens of millennia old upon eruption. PMID:17738278

  5. Magma ocean formation due to giant impacts

    NASA Technical Reports Server (NTRS)

    Tonks, W. B.; Melosh, H. J.

    1993-01-01

    The thermal effects of giant impacts are studied by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths. Additionally, the effects of the planet's initial temperature on the generated melt volume are examined. The shock pressure required to completely melt the material is determined using the Hugoniot curve plotted in pressure-entropy space. Once the melting pressure is known, an impact melting model is used to estimate the radial distance melting occurred from the impact site. The melt region's geometry then determines the associated melt volume. The model is also used to estimate the partial melt volume. Magma ocean depths resulting from both excavated and retained melt are calculated, and the melt fraction not excavated during the formation of the crater is estimated. The fraction of a planet melted by the initial shock wave is also estimated using the model.

  6. 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.

  7. Yamato 980459: Crystallization of Martian Magnesian Magma

    NASA Technical Reports Server (NTRS)

    Koizumi, E.; Mikouchi, T.; McKay, G.; Monkawa, A.; Chokai, J.; Miyamoto, M.

    2004-01-01

    Recently, several basaltic shergottites have been found that include magnesian olivines as a major minerals. These have been called olivinephyric shergottites. Yamato 980459, which is a new martian meteorite recovered from the Antarctica by the Japanese Antarctic expedition, is one of them. This meteorite is different from other olivine-phyric shergottites in several key features and will give us important clues to understand crystallization of martian meteorites and the evolution of Martian magma.

  8. Magma Suspension As a Complex Fluid

    NASA Astrophysics Data System (ADS)

    Kurokawa, A.; Kurita, K.

    2012-12-01

    Magma is essentially a multiphase suspension of solid crystals, gaseous bubbles and silicate liquid. As for non-linear properties of magma two aspects have been focused for controlling factors in magma flow instability: the existence of the yield stress and the multiplicity in the relation between driving pressure and flow rate. The emergence of the yield stress in a suspension system has been experimentally investigated by using PNIPAM aqueous suspension as an analogue of magma (Kurokawa et al, EGU 2012-4105-2,2012). In this presentation we focus on the other aspect, the multiplicity in the rheological relationship. We investigate its physical origin of the rheology and its role in generating pressure oscillation associated with tube flow of suspension based on the PNIPAM analogue material. PNIPAM is a polymer gel and undergoes volumetric phase change at the temperature around 35 degree C: below this temperature the gel phase absorbs water and swells while over this temperature, it expels water and shrinks. Due to this property, the volume fraction of gel phase systematically changes with temperature. This makes it possible to observe the change of rheology continuously associated with the change of the fraction of solid phase. By series of rheological measurements PNIPAM aqueous suspension has been revealed to exhibit peculiar ageing effect, which is well known for complex suspension fluid. This ageing effect is responsible for generating the yield stress and the multiplicity. The multiplicity; coexistence of several flow rates at a certain pressure drives jumping between low and high flow rates, which causes oscillatory behavior of flow. We report experimental support of this model by demonstrating pressure oscillation in tube flow of PNIPAM aqueous suspension.

  9. Permeable Gas Flow Influences Magma Fragmentation Speed.

    NASA Astrophysics Data System (ADS)

    Richard, D.; Scheu, B.; Spieler, O.; Dingwell, D.

    2008-12-01

    Highly viscous magmas undergo fragmentation in order to produce the pyroclastic deposits that we observe, but the mechanisms involved remain unclear. The overpressure required to initiate fragmentation depends on a number of physical parameters, such as the magma's vesicularity, permeability, tensile strength and textural properties. It is clear that these same parameters control also the speed at which a fragmentation front travels through magma when fragmentation occurs. Recent mathematical models of fragmentation processes consider most of these factors, but permeable gas flow has not yet been included in these models. However, it has been shown that permeable gas flow through a porous rock during a sudden decompression event increases the fragmentation threshold. Fragmentation experiments on natural samples from Bezymianny (Russia), Colima (Mexico), Krakatau (Indonesia) and Augustine (USA) volcanoes confirm these results and suggest in addition that high permeable flow rates may increase the speed of fragmentation. Permeability from the investigated samples ranges from as low as 5 x 10-14 to higher than 9 x 10- 12 m2 and open porosity ranges from 16 % to 48 %. Experiments were performed for each sample series at applied pressures up to 35 MPa. Our results indicate that the rate of increase of fragmentation speed is higher when the permeability is above 10-12 m2. We confirm that it is necessary to include the influence of permeable flow on fragmentation dynamics.

  10. Magma-assisted rifting in Ethiopia.

    PubMed

    Kendall, J-M; Stuart, G W; Ebinger, C J; Bastow, I D; Keir, D

    2005-01-13

    The rifting of continents and evolution of ocean basins is a fundamental component of plate tectonics, yet the process of continental break-up remains controversial. Plate driving forces have been estimated to be as much as an order of magnitude smaller than those required to rupture thick continental lithosphere. However, Buck has proposed that lithospheric heating by mantle upwelling and related magma production could promote lithospheric rupture at much lower stresses. Such models of mechanical versus magma-assisted extension can be tested, because they predict different temporal and spatial patterns of crustal and upper-mantle structure. Changes in plate deformation produce strain-enhanced crystal alignment and increased melt production within the upper mantle, both of which can cause seismic anisotropy. The Northern Ethiopian Rift is an ideal place to test break-up models because it formed in cratonic lithosphere with minor far-field plate stresses. Here we present evidence of seismic anisotropy in the upper mantle of this rift zone using observations of shear-wave splitting. Our observations, together with recent geological data, indicate a strong component of melt-induced anisotropy with only minor crustal stretching, supporting the magma-assisted rifting model in this area of initially cold, thick continental lithosphere. PMID:15650736

  11. Volatile content of Hawaiian magmas and volcanic vigor

    NASA Astrophysics Data System (ADS)

    Blaser, A. P.; Gonnermann, H. M.; Ferguson, D. J.; Plank, T. A.; Hauri, E. H.; Houghton, B. F.; Swanson, D. A.

    2014-12-01

    We test the hypothesis that magma supply to Kīlauea volcano, Hawai'i may be affected by magma volatile content. We find that volatile content and magma flow from deep source to Kīlauea's summit reservoirs are non-linearly related. For example, a 25-30% change in volatiles leads to a near two-fold increase in magma supply. Hawaiian volcanism provides an opportunity to develop and test hypotheses concerning dynamic and geochemical behavior of hot spot volcanism on different time scales. The Pu'u 'Ō'ō-Kupaianaha eruption (1983-present) is thought to be fed by essentially unfettered magma flow from the asthenosphere into a network of magma reservoirs at approximately 1-4 km below Kīlauea's summit, and from there into Kīlauea's east rift zone, where it erupts. Because Kīlauea's magma becomes saturated in CO2 at about 40 km depth, most CO2 is thought to escape buoyantly from the magma, before entering the east rift zone, and instead is emitted at the summit. Between 2003 and 2006 Kīlauea's summit inflated at unusually high rates and concurrently CO2emissions doubled. This may reflect a change in the balance between magma supply to the summit and outflow to the east rift zone. It remains unknown what caused this surge in magma supply or what controls magma supply to Hawaiian volcanoes in general. We have modeled two-phase magma flow, coupled with H2O-CO2 solubility, to investigate the effect of changes in volatile content on the flow of magma through Kīlauea's magmatic plumbing system. We assume an invariant magma transport capacity from source to vent over the time period of interest. Therefore, changes in magma flow rate are a consequence of changes in magma-static and dynamic pressure throughout Kīlauea's plumbing system. We use measured summit deformation and CO2 emissions as observational constraints, and find from a systematic parameter analysis that even modest increases in volatiles reduce magma-static pressures sufficiently to generate a 'surge' in

  12. Emplacement of magma in sedimentary basins

    NASA Astrophysics Data System (ADS)

    Malthe-Sorenssen, A.; Planke, S.

    2002-12-01

    Sheet-like intrusive complexes are commonly present in sedimentary basins on rifted volcanic margins. Such sill complexes have important impact on petroleum maturation, migration and trapping. We are currently completing an integrated seismic, field and theoretical study on the petroleum implications of sill intrusions. One aspect of this study has been to get new understanding of the magma emplacement processes based on integrated numerical modeling and geophysical/geological mapping activities. Extensive sill complexes have been identified and mapped in the NE Atlantic and Karoo basins based on seismic, borehole, remote sensing and field data. Early Tertiary intrusive complexes are present in the Voring and More basins offshore mid-Norway. Similar sill complexes are exposed onshore in Cretaceous to Permian age sedimentary sequences on the conjugate central-east Greenland margin. A voluminous Jurassic age intrusive complex is well exposed in the Permian to Jurassic Karoo basin as the erosionally strong dolerites form an impressive mountainous landscape in large parts of South Africa. The sheet intrusions are found at paleodepths of 0-6 km. Deep intrusions are generally long and smooth, whereas shallow intrusions are rough, transgressive and commonly saucer-shaped. Saucer-shaped intrusions are present in unstructured basin segments. The diameter of the saucers increases with depth. Structured basin segments are characterized by a variety of sill complex geometries. The intrusions generally mimic the basin structure. In nature, magma is emplaced in internally pressurized, planar cracks. The emplacement process is controlled by the local stress field and complex interactions of buoyancy forces, host rock resistance to fracture, elastic deformation of country rock, magma hydrostatic pressure and fluctuating magma pressure, magma viscosity and weight of overburden. We have developed a discrete element model to study the emplacement process. Results from the modeling

  13. Geochemical Evidence for a Terrestrial Magma Ocean

    NASA Technical Reports Server (NTRS)

    Agee, Carl B.

    1999-01-01

    The aftermath of phase separation and crystal-liquid fractionation in a magma ocean should leave a planet geochemically differentiated. Subsequent convective and other mixing processes may operate over time to obscure geochemical evidence of magma ocean differentiation. On the other hand, core formation is probably the most permanent, irreversible part of planetary differentiation. Hence the geochemical traces of core separation should be the most distinct remnants left behind in the mantle and crust, In the case of the Earth, core formation apparently coincided with a magma ocean that extended to a depth of approximately 1000 km. Evidence for this is found in high pressure element partitioning behavior of Ni and Co between liquid silicate and liquid iron alloy, and with the Ni-Co ratio and the abundance of Ni and Co in the Earth's upper mantle. A terrestrial magma ocean with a depth of 1000 km will solidify from the bottom up and first crystallize in the perovskite stability field. The largest effect of perovskite fractionation on major element distribution is to decrease the Si-Mg ratio in the silicate liquid and increase the Si-Mg ratio in the crystalline cumulate. Therefore, if a magma ocean with perovskite fractionation existed, then one could expect to observe an upper mantle with a lower than chondritic Si-Mg ratio. This is indeed observed in modern upper mantle peridotites. Although more experimental work is needed to fully understand the high-pressure behavior of trace element partitioning, it is likely that Hf is more compatible than Lu in perovskite-silicate liquid pairs. Thus, perovskite fractionation produces a molten mantle with a higher than chondritic Lu-Hf ratio. Arndt and Blichert-Toft measured Hf isotope compositions of Barberton komatiites that seem to require a source region with a long-lived, high Lu-Hf ratio. It is plausible that that these Barberton komatiites were generated within the majorite stability field by remelting a perovskite

  14. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Renggli, C. J.; Perugini, D.; De Campos, C. P.; Hess, K.-U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2015-08-01

    In order to explore the materials' complexity induced by bubbles rising through mixing magmas, bubble-advection experiments have been performed, employing natural silicate melts at magmatic temperatures. A cylinder of basaltic glass was placed below a cylinder of rhyolitic glass. Upon melting, bubbles formed from interstitial air. During the course of the experimental runs, those bubbles rose via buoyancy forces into the rhyolitic melt, thereby entraining tails of basaltic liquid. In the experimental run products, these plume-like filaments of advected basalt within rhyolite were clearly visible and were characterised by microCT and high-resolution EMP analyses. The entrained filaments of mafic material have been hybridised. Their post-experimental compositions range from the originally basaltic composition through andesitic to rhyolitic composition. Rheological modelling of the compositions of these hybridised filaments yield viscosities up to 2 orders of magnitude lower than that of the host rhyolitic liquid. Importantly, such lowered viscosities inside the filaments implies that rising bubbles can ascend more efficiently through pre-existing filaments that have been generated by earlier ascending bubbles. MicroCT imaging of the run products provides textural confirmation of the phenomenon of bubbles trailing one another through filaments. This phenomenon enhances the relevance of bubble advection in magma mixing scenarios, implying as it does so, an acceleration of bubble ascent due to the decreased viscous resistance facing bubbles inside filaments and yielding enhanced mass flux of mafic melt into felsic melt via entrainment. In magma mixing events involving melts of high volatile content, bubbles may be an essential catalyst for magma mixing. Moreover, the reduced viscosity contrast within filaments implies repeated replenishment of filaments with fresh end-member melt. As a result, complex compositional gradients and therefore diffusion systematics can be

  15. Long-term evolution of erupted magma chemistry

    NASA Astrophysics Data System (ADS)

    Caricchi, L.; Simpson, G.

    2014-12-01

    Magmatic reservoirs that feed explosive volcanic activity at the surface are constructed by the periodic injection of magma into the upper crust. The long-term magma flux controls the thermal evolution of these magmatic reservoirs and therefore the possibility of accumulating eruptible magma in the plumbing system of volcanoes. Magma flux, in combination with the periodicity of magma injection, regulates the frequency and magnitude of volcanic eruptions. We combined thermal and mechanical modelling with Monte Carlo simulations to compute the temporal evolution of the chemistry of eruptible magma (<50 vol. % crystals) in systems growing at different characteristic magma fluxes. We simulated the periodic injection of andesitic magma in the upper crust and trace the volume and chemistry of the eruptible magma together with the evolution of the overpressure within the reservoir. Eruptions are prescribed to occur once overpressure reached critical values (1-40 MPa). The calculations show that eruptions of rhyolitic compositions are rare and can only occur after a stage of prolonged thermal maturation of a magmatic reservoir (lasting a few hundredths of thousands of years). Additionally, eruptions of chemically evolved rocks are restricted to a specific range of physical conditions. Interestingly, the probability of eruptions of rhyolitic compositions increases substantially once the injection of magma into the magmatic reservoir ceases, which would imply that rhyolitic eruptions (not produced by partial melting of continental crust) are most likely to occur during the waning (not waxing) stages of magmatic activity.

  16. Modeling of Magma Dynamics Based on Two-Fluid Hydrodynamics

    NASA Astrophysics Data System (ADS)

    Perepechko, Y. V.; Sorokin, K.

    2012-12-01

    Multi-velocity multi-porous models are often used as a hydrodynamic basis to describe dynamics of fluid-magma systems. These models cover such problems as fast acoustic processes or large-scaled dynamics of magma systems having non-compressible magma. Nonlinear dynamics of magma as multiphase compressible medium has not been studied sufficiently. In this work we study nonlinear thermodynamically consistent two-liquid model of magma system dynamics, based on conservation law method. The model is restricted by short times of local heat balance between phases. Pressure balance between phases is absent. Two-fluid magma model have various rheological properties of the composing phases: viscous liquid and viscoelastic Maxwell medium. The dynamics of magna flows have been studied for two types of magma systems: magma channels and intraplate intermediate magma chambers. Numerical problem of the dynamics for such media is solved using the control volume method ensuring physical correctness of the solution. The solutions are successfully verified for benchmark one-velocity models. In this work we give the results of numerical modeling using CVM for a number of non-stationary problems of nonlinear liquid filtering through granulated medium in magma channels and problems two-liquid system convection in intraplate magma chambers for various parameters. In the last case the convection regimes vary depending on non-dimensional Rayleigh and Darcy numbers and the parameter field, where compressibility effects appear, is located. The given model can be used as a hydrodynamic basis to model the evolution of magma, fluid-magma systems to study thermo-acoustic influence on hydrodynamic flows in such systems. This work was financially supported by the Russian Foundation for Basic Research, Grant #12-05-00625.

  17. Oxidized sulfur-rich mafic magma at Mount Pinatubo, Philippines

    USGS Publications Warehouse

    de Hoog, J.C.M.; Hattori, K.H.; Hoblitt, R.P.

    2004-01-01

    Basaltic fragments enclosed in andesitic dome lavas and pyroclastic flows erupted during the early stages of the 1991 eruption of Mount Pinatubo, Philippines, contain amphiboles that crystallized during the injection of mafic magma into a dacitic magma body. The amphiboles contain abundant melt inclusions, which recorded the mixing of andesitic melt in the mafic magma and rhyolitic melt in the dacitic magma. The least evolved melt inclusions have high sulfur contents (up to 1,700 ppm) mostly as SO42, which suggests an oxidized state of the magma (NNO + 1.4). The intrinsically oxidized nature of the mafic magma is confirmed by spinel-olivine oxygen barometry. The value is comparable to that of the dacitic magma (NNO + 1.6). Hence, models invoking mixing as a means of releasing sulfur from the melt are not applicable to Pinatubo. Instead, the oxidized state of the dacitic magma likely reflects that of parental mafic magma and the source region in the sub-arc mantle. Our results fit a model in which long-lived SO2 discharge from underplated mafic magma accumulated in the overlying dacitic magma and immiscible aqueous fluids. The fluids were the most likely source of sulfur that was released into the atmosphere during the cataclysmic eruption. The concurrence of highly oxidized basaltic magma and disproportionate sulfur output during the 1991 Mt. Pinatubo eruption suggests that oxidized mafic melt is an efficient medium for transferring sulfur from the mantle to shallow crustal levels and the atmosphere. As it can carry large amounts of sulfur, effectively scavenge sulfides from the source mantle and discharge SO2 during ascent, oxidized mafic magma forms arc volcanoes with high sulfur fluxes, and potentially contributes to the formation of metallic sulfide deposits. ?? Springer-Verlag 2003.

  18. Magma deformation and emplacement in rhyolitic dykes

    NASA Astrophysics Data System (ADS)

    McGowan, Ellen; Tuffen, Hugh; James, Mike; Wynn, Peter

    2016-04-01

    Silicic eruption mechanisms are determined by the rheological and degassing behaviour of highly-viscous magma ascending within shallow dykes and conduits. However, we have little knowledge of how magmatic behaviour shifts during eruptions as dykes and conduits evolve. To address this we have analysed the micro- to macro-scale textures in shallow, dissected rhyolitic dykes at the Tertiary Húsafell central volcano in west Iceland. Dyke intrusion at ~3 Ma was associated with the emplacement of subaerial rhyolitic pyroclastic deposits following caldera formation[1]. The dykes are dissected to ~500 m depth, 2-3 m wide, and crop out in two stream valleys with 5-30 m-long exposures. Dykes intrude diverse country rock types, including a welded ignimbrite, basaltic lavas, and glacial conglomerate. Each of the six studied dykes is broadly similar, exhibiting obsidian margins and microcrystalline cores. Dykes within pre-fractured lava are surrounded by external tuffisite vein networks, which are absent from dykes within conglomerate, whereas dykes failed to penetrate the ignimbrite. Obsidian at dyke margins comprises layers of discrete colour. These display dramatic thickness variations and collapsed bubble structures, and are locally separated by zones of welded, brecciated and flow-banded obsidian. We use textural associations to present a detailed model of dyke emplacement and evolution. Dykes initially propagated with the passage of fragmented, gas-charged magma and generation of external tuffisite veins, whose distribution was strongly influenced by pre-existing fractures in the country rock. External tuffisites retained permeability throughout dyke emplacement due to their high lithic content. The geochemically homogenous dykes then evolved via incremental magma emplacement, with shear deformation localised along emplacement boundary layers. Shear zones migrated between different boundary layers, and bubble deformation promoted magma mobility. Brittle

  19. Viscosity of Campi Flregrei (Italy) magmas

    NASA Astrophysics Data System (ADS)

    Misiti, Valeria; Vetere, Francesco; Scarlato, Piergiorgio; Behrens, Harald; Mangiacapra, Annarita; Freda, Carmela

    2010-05-01

    Viscosity is an important factor governing both intrusive and volcanic processes. The most important parameters governing silicate melts viscosity are bulk composition of melt and temperature. Pressure has only minor effect at crustal depths, whereas crystals and bubbles have significant influence. Among compositional parameters, the water content is critical above all in terms of rheological behaviour of melts and explosive style of an eruption. Consequently, without an appropriate knowledge of magma viscosity depending on the amount of dissolved volatiles, it is not possible to model the processes (i.e., magma ascent, fragmentation, and dispersion) required to predict realistic volcanic scenarios and thus forecast volcanic hazards. The Campi Flegrei are a large volcanic complex (~150 km2) located west of the city of Naples, Italy, that has been the site of volcanic activity for more than 60 ka and represents a potential volcanic hazard owing to the large local population. In the frame of a INGV-DPC (Department of Civil Protection) project devoted to design a multidisciplinary system for short-term volcano hazard evaluation, we performed viscosity measurements, under dry and hydrous conditions, of primitive melt compositions representative of two Campi Flegrei eruptions (Minopoli-shoshonite and Fondo Riccio-latite). Viscosity of the two melts have been investigated in the high temperature/low viscosity range at atmospheric pressure in dry samples and at 0.5 GPa in runs having water content from nominally anhydrous to about 3 wt%. Data in the low temperature/high viscosity range were obtained near the glass transition temperature at atmospheric pressure on samples whose water contents vary from 0.3 up to 2.43 wt%. The combination of high- and low-viscosity data permits a general description of the viscosity as a function of temperature and water content using a modified Tamman-Vogel-Fulcher equation. logν = a+ --b--+ --d--×exp(g × w-) (T - c) (T - e) T (1) where

  20. 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.

  1. 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

  2. Magma degassing during eruption through water-saturated porous rocks

    NASA Astrophysics Data System (ADS)

    Melnik, O. E.; Afanasyev, A. A.; Zarin, G. A.

    2016-05-01

    In the case of extrusive eruption, we consider the problem on magma degassing which rises in a volcano conduit crossing porous water-saturated rocks. We show that the intensity of outflow of volcanic gases into the rocks is comparable to the intensity of their transport with the rising magma. The magma degassing in the rocks substantially affects the eruption dynamics, in particular, the duration of the periods of eruptive activity.

  3. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Daniele, M.; Renggli, C.; Perugini, D.; De Campos, C.; Hess, K. U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2014-12-01

    Rising bubbles may significantly affect magma mixing paths as has been demonstrated by analogue experiments in the past. Here, bubble-advection experiments are performed for the first time employing natural materials at magmatic temperatures. Cylinders of basaltic glass were placed below cylinders of rhyolite glass. Upon melting, interstitial air formed bubbles that rose into the rhyolite melt, thereby entraining tails of basaltic liquid. The formation of plume-like filaments of advected basalt within the rhyolite was characterized by microCT and subsequent high-resolution EMP analyses. Melt entrainment by bubble ascent appears as efficient mechanism to mingle contrasting melt compositions. MicroCT imaging shows bubbles trailing each other and trails of multiple bubbles having converged. Rheological modelling of the filaments yields viscosities of up to 2 orders of magnitude lower than for the surrounding rhyolitic liquid. Such a viscosity contrast implies that subsequent bubbles rising are likely to follow the same pathways that previously ascending bubbles have generated. Filaments formed by multiple bubbles would thus experience episodic replenishment with mafic material. Fundamental implications for the concept of bubble advection in magma mixing are thus a) an acceleration of mixing because of decreased viscous resistance for bubbles inside filaments and b) non-conventional diffusion systematics because of intermittent supply of mafic material (instead of a single pulse) inside a filament. Inside these filaments, the mafic material was variably hybridised to andesitic through rhyolitic composition. Compositional profiles alone are ambiguous, however, to determine whether single or multiple bubbles were involved during formation of a filament. Statistical analysis, employing concentration variance as measure of homogenisation, demonstrates that also filaments appearing as single-bubble filaments are likely to have experienced multiple bubbles passing through

  4. 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

  5. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    1998-01-01

    The research described in this progress report involved the study of petrological, geochemical and volcanic processes that occur on the Moon and the SNC parent body, generally accepted to be Mars. The link between these studies is that they focus on two terrestrial-type parent bodies somewhat smaller than earth, and the fact that they focus on the role of volatiles in magmatic processes and on processes of magma evolution on these planets. The work on the lunar volcanic glasses has resulted in some exciting new discoveries over the years of this grant. We discovered small metal blebs initially in the Al5 green glass, and determined the significant importance of this metal in fixing the oxidation state of the parent magma (Fogel and Rutherford, 1995). More recently, we discovered a variety of metal blebs in the Al7 orange glass. Some of these Fe-Ni metal blebs were in the glass; others were in olivine phenocrysts. The importance of these metal spheres is that they fix the oxidation state of the parent magma during the eruption, and also indicate changes during the eruption (Weitz et al., 1997) They also yield important information about the composition of the gas phase present, the gas which drove the lunar fire-fountaining. One of the more exciting and controversial findings in our research over the past year has been the possible fractionation of H from D during shock (experimental) of hornblende bearing samples (Minitti et al., 1997). This research is directed at explaining some of the low H2O and high D/H observed in hydrous phases in the SNC meteorites.

  6. Coupled effect of magma degassing and rheology on silicic volcanism

    NASA Astrophysics Data System (ADS)

    Okumura, Satoshi; Nakamura, Michihiko; Uesugi, Kentaro; Nakano, Tsukasa; Fujioka, Takuma

    2013-01-01

    Explosive volcanism such as the 1991 Mt. Pinatubo, Philippines, and the 2008 Mt. Chaitén, Chile, eruptions is caused by violent vesiculation of hydrous magma. However, gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit. This makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common. Here, we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation X-ray radiography and computed tomography. We observed, for the first time in situ, that the shear localization caused magma fracturing and formed a slip plane, and thus inhibited deformation and outgassing elsewhere. We also observed the compaction of vesicular magma into a dense "lava" as a result of outgassing when shear localization did not occur. In a natural setting, shear localizes along the edges of a volcanic conduit, where the strain rate is high, causing a highly permeable fracturing layer to form at the conduit's edge and leaving less-sheared and less-outgassed magma at its center. The less-outgassed magma in the center may ascend rapidly and cause explosive volcanism. Non-explosive lava effusion may occur only when shear localization does not occur effectively. This new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity (pyroclastic obsidian and highly vesiculated pumice).

  7. Selection of promising sites for magma energy experiments

    SciTech Connect

    Carson, C.C.

    1985-01-01

    The Long Valley and Coso Hot Springs areas of California have been identified as the most promising sites for conducting a magma energy extraction experiment. These two locations were selected from among the potential sites on the basis of several factors that are critical to the success of the proposed long-term energy extraction experiment. These factors include the likelihood of the existence of shallow magma targets as well as several other drilling, energy extraction and programmatic considerations. As the magma energy extraction program continues, these sites will be analyzed in detail so that one can be selected as the site for the planned magma experiment.

  8. Dynamics and evolution of a magma ocean

    NASA Technical Reports Server (NTRS)

    Stevenson, D. J.

    1992-01-01

    The prevailing view of very large impacts during earth accretion suggests an initial state for earth evolution that was totally molten or nearly so. The problem confronted is to understand the evolution from this state to an almost completely solidified mantle. Two crucial questions are asked by the author: (1) is the resulting endstate of magma ocean freezing compatible with geological record, inferred mantle structure and evidence from geochemistry; and (2) does the freezing event leave a signature that can be discerned in the present earth. The emphasis on this keynote introduction will be to set the stage for the more detailed analyses to follow and to clarify the crucial questions and uncertainties.

  9. Special Relativity Derived from Spacetime Magma

    PubMed Central

    Greensite, Fred

    2014-01-01

    We present a derivation of relativistic spacetime largely untethered from specific physical considerations, in constrast to the many physically-based derivations that have appeared in the last few decades. The argument proceeds from the inherent magma (groupoid) existing on the union of spacetime frame components and Euclidean which is consistent with an “inversion symmetry” constraint from which the Minkowski norm results. In this context, the latter is also characterized as one member of a class of “inverse norms” which play major roles with respect to various unital -algebras more generally. PMID:24959889

  10. Special relativity derived from spacetime magma.

    PubMed

    Greensite, Fred

    2014-01-01

    We present a derivation of relativistic spacetime largely untethered from specific physical considerations, in constrast to the many physically-based derivations that have appeared in the last few decades. The argument proceeds from the inherent magma (groupoid) existing on the union of spacetime frame components [Formula: see text] and Euclidean [Formula: see text] which is consistent with an "inversion symmetry" constraint from which the Minkowski norm results. In this context, the latter is also characterized as one member of a class of "inverse norms" which play major roles with respect to various unital [Formula: see text]-algebras more generally. PMID:24959889

  11. Asteroid differentiation - Pyroclastic volcanism to magma oceans

    NASA Technical Reports Server (NTRS)

    Taylor, G. J.; Keil, Klaus; Mccoy, Timothy; Haack, Henning; Scott, Edward R. D.

    1993-01-01

    A summary is presented of theoretical and speculative research on the physics of igneous processes involved in asteroid differentiation. Partial melting processes, melt migration, and their products are discussed and explosive volcanism is described. Evidence for the existence of asteroidal magma oceans is considered and processes which may have occurred in these oceans are examined. Synthesis and inferences of asteroid heat sources are discussed under the assumption that asteroids are heated mainly by internal processes and that the role of impact heating is small. Inferences of these results for earth-forming planetesimals are suggested.

  12. Role of Yield Stress in Magma Rheology

    NASA Astrophysics Data System (ADS)

    Kurokawa, A.; Di Giuseppe, E.; Davaille, A.; Kurita, K.

    2012-04-01

    Magmas are essentially multiphase material composed of solid crystals, gaseous bubbles and silicate liquids. They exhibit various types of drastic change in rheology with variation of mutual volumetric fractions of the components. The nature of this variable rheology is a key factor in controlling dynamics of flowing magma through a conduit. Particularly the existence of yield stress in flowing magma is expected to control the wall friction and formation of density waves. As the volumetric fraction of solid phase increases yield stress emerges above the critical fraction. Several previous studies have been conducted to clarify this critical value of magmatic fluid both in numerical simulations and laboratory experiments ([Lejeune and Pascal, 1995], [Saar and Manga 2001], [Ishibashi and Sato 2010]). The obtained values range from 13.3 to 40 vol%, which display wide variation and associated change in rheology has not been clarified well. In this presentation we report physical mechanism of emergence of yield stress in suspension as well as the associated change in the rheology based on laboratory experiments using analog material. We utilized thermogel aqueous suspension as an analog material of multiphase magma. Thermogel, which is a commercial name for poly(N-isopropyl acrylamide) (PNIPAM) undergoes volumetric phase change at the temperature around 35C:below this temperature the gel phase absorbs water and swells while below this it expels water and its volume shrinks. Because of this the volumetric fraction of gel phase systematically changes with temperature and the concentration of gel powder. The viscosity measured at lower stress drastically decreases across this phase change with increasing temperature while the viscosity at higher stress does not exhibit large change across the transition. We have performed a series of rheological measurements focusing on the emergence of yield stress on this aqueous suspension. Since the definition of yield stress is not

  13. Magma hybridisation at Soufriere Hills Volcano, Montserrat

    NASA Astrophysics Data System (ADS)

    Humphreys, Madeleine; Edmonds, Marie; Christopher, Thomas; Hards, Vicky

    2010-05-01

    Arc volcanoes commonly show evidence of mingling between mafic and silicic magma. For example, the Soufrière Hills Volcano, Montserrat typically erupts andesitic magma containing basaltic to basaltic-andesite inclusions. However, the andesite also contains a wide variety of phenocryst textures as well as strongly zoned microlites, suggesting that more intimate physical mixing also occurs. Analysis of minor elements in both phenocrysts and microlites allows the discrimination of different crystal populations, and provides insight into their origins. Microlites of plagioclase and orthopyroxene are chemically distinct from the phenocrysts, being enriched in Fe and Mg, and Al and Ca respectively. However, they are indistinguishable from the compositions of these phases in the mafic inclusions. Microlite compositions also give anomalously high temperatures using standard geothermometry techniques, similar to those of the mafic inclusions. Compositions of clinopyroxene from overgrowth rims on quartz and orthopyroxene and coarse-grained breakdown rims on hornblende, are identical to those from the mafic inclusions, indicating that these rims form during interaction with mafic magma. We infer that the inclusions disaggregated under conditions of high shear stress during ascent in the conduit, transferring mafic material into the andesite groundmass. This implies that the mafic component of the system is greater than previously determined from the volume proportion of mafic enclaves. The presence of mafic-derived microlites in the andesite groundmass also means that care must be taken when using this as a starting material for phase equilibrium experiments. Melt inclusions and matrix glasses in the erupted include an anomalously K2O-rich population which overlaps with residual (high-K2O, high-TiO2) mafic inclusion glass. These glasses represent the effects of physical mixing with mafic magma, both during ascent and by diffusive exchange during the formation of mafic

  14. 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.

  15. Magma chamber dynamics constrained by crystal isotope stratigraphy

    NASA Astrophysics Data System (ADS)

    Davidson, J. P.; Tepley, F. J., III; Hora, J. M.

    2003-04-01

    The architecture of subvolcanic magma plumbing systems controls the thermal regime transited by magmas in the lithosphere, and consequently influences the rates and processes by which magmas evolve. The resolution of current geophysical methods is unable to accurately define the shapes, sizes and crystallinity of small magma bodies. Exhumed fossil magma chambers may provide terminal or cumulative plumbing system assemblies but cannot provide snapshots of the system at a given time, and fail to identify ephemeral components such as dikes, which may open and close to transport magma. Petrographically-constrained in situ analysis of the components of volcanic rocks, including crystal isotope stratigraphy, has recently proved an important new approach to constraining the dynamics of magma storage systems. Core-to-rim decreases in 87Sr/86Sr accompanied by increases in Sr concentration for single plagioclase crystals seen at volcanoes such as El Chichon, Mexico, are explained by frequent recharge of a storage reservoir(s). The fact that high 87Sr/86Sr values are restricted to cores suggests that contamination occurs at the initial stages of injection and contact between magma and the crust. This in turn suggests that crystallization occurs at the margins of the magma body where the thermal gradient is strongest, volatiles are concentrated and epitaxial crystallization is promoted. The crystallized boundary zone then isolates the magma and prevents subsequent recharge magma from interacting directly with the crust. In cases such as Ngauruhoe volcano, New Zealand, 87Sr/86Sr increases from core-to-rim of plagioclase crystals suggest that the magma was not completely isolated from a crustal contaminant. In either case, changes in Sr isotope ratio are correlated with punctuated textural evidence for disequilibrium events, underscoring the importance of recharge. Recharge disaggregates and remobilizes much of the material crystallized from earlier events. Petrographic and

  16. Magma volumes and storage in the middle crust

    NASA Astrophysics Data System (ADS)

    Memeti, V.; Barnes, C. G.; Paterson, S. R.

    2015-12-01

    Quantifying magma volumes in magma plumbing systems is mostly done through geophysical means or based on volcanic eruptions. Detailed studies of plutons, however, are useful in revealing depths and evolving volumes of stored magmas over variable lifetimes of magma systems. Knowledge of the location, volume, and longevity of stored magma is critical for understanding where in the crust magmas attain their chemical signature, how these systems physically behave and how source, storage levels, and volcanoes are connected. Detailed field mapping, combined with single mineral geochemistry and geochronology of plutons, allow estimates of size and longevity of melt-interconnected magma batches that existed during the construction of magma storage sites. The Tuolumne intrusive complex (TIC) recorded a 10 myr magmatic history. Detailed maps of the major units in different parts of the TIC indicate overall smaller scale (cm- to <1 km) compositional variation in the oldest, outer Kuna Crest unit and mainly larger scale (>10 km) changes in the younger Half Dome and Cathedral Peak units. Mineral-scale trace element data from hornblende of granodiorites to gabbros from the Kuna Crest lobe show distinct hornblende compositions and zoning patterns. Mixed hornblende populations occur only at the transition to the main TIC. This compositional heterogeneity in the first 1-2 myr points to low volume magmatism resulting in smaller, discrete and not chemically interacting magma bodies. Trace element and Sr- and Pb-isotope data from growth zones of K-feldspar phenocrysts from the two younger granodiorites indicate complex mineral zoning, but general isotopic overlap, suggesting in-situ, inter-unit mixing and fractionation. This is supported by hybrid zones between units, mixing of zircon, hornblende, and K-feldspar populations and late leucogranites. Thus, magma body sizes increased later resulting in overall more homogeneous, but complexly mixing magma mushes that fractionated locally.

  17. Thermal and mechanical constraints on mixing between mafic and silicic magmas

    NASA Astrophysics Data System (ADS)

    Sparks, R. S. J.; Marshall, L. A.

    1986-09-01

    When magmas of different temperature and composition are intimately mingled together, transfer of heat results in substantial changes in the rheological properties of the magmas. Since thermal diffusion rates are orders of magnitude faster than chemical diffusion rates, mixing magmas will come nearly to the same temperature before complete homogenization of the magmas can occur by diffusion and shearing. The ability of magmas to mix thus depends on their physical properties after thermal equilibration. Calculations are presented on how the viscosity and crystal content of mafic and silicic magmas vary as a function of their initial temperatures and the proportion of mafic magma in the mixture. Three physical situations can be identified: (a) where the mafic magma remains less viscous than the silicic magma; (b) where the mafic magma becomes more viscous than the silicic magma due to crystallization; and (c) where the mafic magma is effectively solid due to its high crystal content. In the last situation it is proposed that complete mixing cannot take place, but the mafic magma is dispersed as solid xenoliths or inclusions within the silicic magma. Xenolith or inclusion formation occurs when there is a large temperature difference between the magmas or a large proportion of silicic magma. Complete hybridization can only occur when the magmas both behave as liquids at the same temperature. A diagram is constructed that shows the fields where the mafic magma becomes a solid or remains a fluid on a plot of the proportion of mafic magma against the composition of the mafic magma. Where there is a large proportion of silicic magma, complete hybridization can only occur with evolved mafic magmas (andesitic magmas). An example of this compositional selectivity is described from St. Kilda, Scotland where silicic magmas have only hybridized with highly evolved theoleiitic andesite magmas, although the silicic magma is intimately intermingled with more mafic magmas in net

  18. Magma chambers: Formation, local stresses, excess pressures, and compartments

    NASA Astrophysics Data System (ADS)

    Gudmundsson, Agust

    2012-09-01

    An existing magma chamber is normally a necessary condition for the generation of a large volcanic edifice. Most magma chambers form through repeated magma injections, commonly sills, and gradually expand and change their shapes. Highly irregular magma-chamber shapes are thermo-mechanically unstable; common long-term equilibrium shapes are comparatively smooth and approximate those of ellipsoids of revolution. Some chambers, particularly small and sill-like, may be totally molten. Most chambers, however, are only partially molten, the main part of the chamber being crystal mush, a porous material. During an eruption, magma is drawn from the crystal mush towards a molten zone beneath the lower end of the feeder dyke. Magma transport to the feeder dyke, however, depends on the chamber's internal structure; in particular on whether the chamber contains pressure compartments that are, to a degree, isolated from other compartments. It is only during large drops in the hydraulic potential beneath the feeder dyke that other compartments become likely to supply magma to the erupting compartment, thereby contributing to its excess pressure (the pressure needed to rupture a magma chamber) and the duration of the eruption. Simple analytical models suggest that during a typical eruption, the excess-pressure in the chamber decreases exponentially. This result applies to a magma chamber that (a) is homogeneous and totally fluid (contains no compartments), (b) is not subject to significant replenishment (inflow of new magma into the chamber) during the eruption, and (c) contains magma where exsolution of gas has no significant effect on the excess pressure. For a chamber consisting of pressure compartments, the exponential excess-pressure decline applies primarily to a single erupting compartment. When more than one compartment contributes magma to the eruption, the excess pressure may decline much more slowly and irregularly. Excess pressure is normally similar to the in

  19. Comparison of Magma Residence, Magma Ascent and Magma-Hydrothermal Interaction at EPR 9°N and Endeavour Segment

    NASA Astrophysics Data System (ADS)

    Michael, P. J.; Gill, J. B.; Ramos, F. C.

    2010-12-01

    We compare magmas’ temperatures (Mg#s), their degree of crustal assimilation (“excess” Chlorine) and their residence depth and ascent speed (dissolved CO2 content) at similar scales, using new data for Endeavour and new and published [1] data for EPR 9°N. We relate differences between the two segments to other differences, e.g., depth and width of the AMC reflector. Cl in glasses, and Cl/K or Cl/Nb ratios, are indicators of magma’s interaction with altered crust, probably at the roof of the AMC [1,2]. An excess Cl (in ppm) value for each glass can be calculated by subtracting mantle-derived Cl from measured Cl. At 9°N, excess Cl is negatively correlated with Mg#. Mg# is lower and excess Cl is higher off-axis (up to 4 km). At a given Mg#, Cl is higher off-axis [1]. Endeavour magmas on-axis have lower Mg# than EPR, while their ranges are similar off-axis. At Endeavour, there is no good correlation of excess Cl with Mg#, although glasses with high Mg# are found mostly on-axis. There is no trend of Mg# or excess Cl with distance from the axis. Excess Cl is similar on-axis between the two ridges. At both ridges, assimilation has a stochastic distribution, such that high- and low-Cl glasses are found in most locations. Because CO2 exsolution and bubble formation is slow compared to magma ascent and surface flow, many glasses are oversaturated compared to their eruption depth. Dissolved CO2 contents thus provide information about the duration of a magma’s transit between its last stopping point and final lava emplacement. If magma erupts and cools quickly, its dissolved CO2 should correspond to its last resting point, possibly the AMC. At EPR 9°N, maximum CO2 contents would be in equilibrium at the AMC roof, while minimum CO2 contents are nearly in equilibrium with collection depths. Glasses have high CO2 on-axis and low CO2 off-axis, and there is a negative correlation between CO2 and distance off-axis [1]. This is partly due to post-eruptive flow away from

  20. Zircons reveal magma fluxes in the Earth's crust.

    PubMed

    Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

    2014-07-24

    Magma fluxes regulate the planetary thermal budget, the growth of continents and the frequency and magnitude of volcanic eruptions, and play a part in the genesis and size of magmatic ore deposits. However, because a large fraction of the magma produced on the Earth does not erupt at the surface, determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large-scale geological processes. Here we show that age distributions of zircons, a mineral often present in crustal magmatic rocks, in combination with thermal modelling, provide an accurate means of retrieving magma fluxes. The characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the Earth's crust. Our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems. Analysis of existing age population data sets using our method suggests that porphyry-type deposits, plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes. We anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions, and to determine the main factors controlling the distribution of resources on our planet. PMID:25056063

  1. Post-Emplacement Behaviour of Magma Reservoirs

    NASA Astrophysics Data System (ADS)

    Roman, A. M.; Jaupart, C. P.

    2015-12-01

    For common crustal structures and melt compositions, basalts are buoyant in the lower crust and negatively buoyant in the upper crust. Intrusion and storage can occur at a depth or an interface where the density of magma becomes larger than that of the overlying rocks. After emplacement, magma density typically increases due to the formation of dense minerals. Fully solidified mafic bodies have bulk densities between 3000-3100 kg m-3 which are much higher than those of the continental rocks they intruded. This negative density contrast is much stronger than the positive one that drove magma ascent. We investigate the dynamical consequences of this marked buoyancy reversal using 3D laboratory experiments on viscous fluids and 2D numerical calculations with complex crustal rheologies. Material is emplaced at a density interface, such that its density is between those of the upper and lower layers. Its bulk density increases as temperature decreases and eventually exceeds that of the lower layer. We observe that the intrusion tends to spread laterally in an initial phase and to sag, and in some cases sink, in a later phase when its density exceeds that of the host. We identified two distinct instability modes. One consists of a single diapiric-like sinker and the other takes the form of spectacular nearly axisymmetric Rayleigh-Taylor-type downwellings. An intermediate mode consists of several long wavelength blobs which disrupt the initial symmetrical arrangement. The transition between the two modes is mainly determined by the aspect ratio of the intrusion at the onset of instability. Sagging can lead to full-fledged sinking to the base of the crust depending mainly on the temperature of country rocks. This proceeds over timescales that are relevant for true magmatic systems (in a range of a few kyr to a few Myr). At shallow crustal depths, cold temperatures and stiff country rocks are able to withstand the load of a large and dense intrusion. Significant post

  2. Experimental Constraints on a Vesta Magma Ocean

    NASA Technical Reports Server (NTRS)

    Hoff, C.; Jones, J. H.; Le, L.

    2014-01-01

    A magma ocean model was devised to relate eucrites (basalts) and diogenites (orthopyroxenites), which are found mixed together as clasts in a suite of polymict breccias known as howardites. The intimate association of eucritic and diogenitic clasts in howardites argues strongly that these three classes of achondritic meteorites all originated from the same planetoid. Reflectance spectral evidence (including that from the DAWN mission) has long suggested that Vesta is indeed the Eucrite Parent Body. Specifically, the magma ocean model was generated as follows: (i) the bulk Vesta composition was taken to be 0.3 CV chondrite + 0.7 L chondrite but using only 10% of the Na2O from this mixture; (ii) this composition is allowed to crystallize at 500 bar until approx. 80% of the system is solid olivine + low-Ca pyroxene; (iii) the remaining 20% liquid crystallizes at one bar from 1250C to 1110C, a temperature slightly above the eucrite solidus. All crystallization calculations were performed using MELTS. In this model, diogenites are produced by cocrystallization of olivine and pyroxene in the >1250C temperature regime, with Main Group eucrite liquids being generated in the 1300-1250C temperature interval. Low-Ca pyroxene reappears at 1210C in the one-bar calculations and fractionates the residual liquid to produce evolved eucrite compositions (Stannern Trend). We have attempted to experimentally reproduce the <1250C portion of the MELTS Vesta magma ocean. In the MELTS calculation, the change from 500 bar to one bar results in a shift of the olivine:low-Ca pyroxene boundary so that the 1250C liquid is now in the olivine field and, consequently, olivine should be the first-crystallizing phase, followed by low-Ca pyroxene at 1210C, and plagioclase at 1170C. Because at one bar the olivine:low-Ca pyroxene boundary is a peritectic, fractional crystallization of the 1210C liquid proceeds with only pyroxene crystallization until plagioclase appears. Thus, the predictions of the

  3. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Renggli, C.; Perugini, D.; De Campos, C. P.; Hess, K.-U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2015-04-01

    That rising bubbles may significantly affect magma mixing paths has already been demon strated by analogue experiments. Here, for the first time, bubble-advection experiments are performed employing volcanic melts at magmatic temperatures. Cylinders of basaltic glass were placed below cylinders of rhyolite glass. Upon melting, interstitial air formed bubbles that rose into the rhyolite melt, thereby entraining tails of basaltic liquid. The formation of plume-like filaments of advected basalt within the rhyolite was characterized by microCT and subsequent high-resolution EMP analyses. Melt entrainment by bubble ascent appears to be an efficient mechanism for mingling volcanic melts of highly contrasting compositions and properties. MicroCT imaging reveals bubbles trailing each other and multiple filaments coalescing into bigger ones. Rheological modelling of the filaments yields viscosities of up to 2 orders of magnitude lower than for the surrounding rhyolitic liquid. Such a viscosity contrast implies that bubbles rising successively are likely to follow this pathway of low resistance that previously ascending bubbles have generated. Filaments formed by multiple bubbles would thus experience episodic replenishment with mafic material. Inevitable implications for the concept of bubble advection in magma mixing include thereby both an acceleration of mixing because of decreased viscous resistance for bubbles inside filaments and non-conventional diffusion systematics because of intermittent supply of mafic material (instead of a single pulse) inside a material. Inside the filaments, the mafic material was variably hybridised to andesitic through rhyolitic composition. Compositional profiles alone are ambiguous, however, to determine whether single or multiple bubbles were involved during formation of a filament. Statistical analysis, employing concentration variance as measure of homogenisation, demonstrates that also filaments appearing as single-bubble filaments

  4. Mesoscale pervasive felsic magma migration: alternatives to dyking

    NASA Astrophysics Data System (ADS)

    Weinberg, Roberto F.

    1999-03-01

    This paper reviews the literature on dyking as a mechanism of felsic magma extraction from a source and transport to shallower crustal levels, and review the recent literature suggesting a range of alternative mechanisms of magma migration in hot crustal zones which produce mesoscale pervasive granite sheet intrusions. Recent papers have strongly favoured dyking as the main mechanism controlling magma migration. However, the initiation of dykes from a felsic magma source is fraught with difficulties, even when magma is immediately available for transportation, as in magma chambers. Within a partially molten source, magma may reside in a range of structures with a wide range of shapes, sizes and degrees of connectivity. Whereas the growth of individual dykes within a partially molten zone, and the self-propagation of large dykes into subsolidus crust, have both been studied in some detail, little attention has been given to the crucial intermediate step of the growth of a dyke network capable of producing wide crustal scale dykes. The rarity of granite dyke swarms suggests that, if dyking is the preferred mechanism of magma transport, felsic magma sources produce only few major transporting dykes during their lifetime. Alternatively, dyking is not an important mechanism. The parameters controlling the volume of the catchment drained by one such dyke, as well as other basic geometrical parameters controlling the structure of the dyke network within the source, are unknown. The ability of dyking to drain a partially molten source depends crucially on these variables and particularly on the horizontal permeability of the source. The slow velocity of viscous felsic magmas traveling in rock pores implies that magma drained during dyking is mostly that previously extracted from the pores, and resident in irregular magma bodies or dyke networks. The observation that large volumes of buoyant magma are commonly present in migmatite zones, and that dyking in these zones plays

  5. Magma energy exploratory well Long Valley caldera, Mono County, California

    SciTech Connect

    Bender-Lamb, S.

    1991-04-01

    Intensive study of Long Valley over the past 15 years indicates evidence for magma at depths accessible to drilling. The Department of Energy's Magma Energy Extraction Program is currently drilling a 20,000 foot exploratory well into the Long Valley caldera. The purpose of this program is to determine the feasibility of producing electrical power from magma. If the magma energy experiment is successful, the Long Valley caldera could hypothetically supply the electrical power needs of California for 100 years at present power consumption rates. The paper describes calderas, the potential of geothermal energy, Long Valley geology, the Long Valley magma energy exploratory well, the four phases of the exploratory well drilling program, and Phase 1 results.

  6. 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.

  7. Factors controlling the structures of magma chambers in basaltic volcanoes

    NASA Technical Reports Server (NTRS)

    Wilson, L.; Head, James W.

    1991-01-01

    The depths, vertical extents, and lateral extents of magma chambers and their formation are discussed. The depth to the center of a magma chamber is most probably determined by the density structure of the lithosphere; this process is explained. It is commonly assumed that magma chambers grow until the stress on the roof, floor, and side-wall boundaries exceed the strength of the wall rocks. Attempts to grow further lead to dike propagation events which reduce the stresses below the critical values of rock failure. The tensile or compressive failure of the walls is discussed with respect to magma migration. The later growth of magma chambers is accomplished by lateral dike injection into the country rocks. The factors controlling the patterns of growth and cooling of such dikes are briefly mentioned.

  8. Fate of a perched crystal layer in a magma ocean

    NASA Technical Reports Server (NTRS)

    Morse, S. A.

    1992-01-01

    The pressure gradients and liquid compressibilities of deep magma oceans should sustain the internal flotation of native crystals owing to a density crossover between crystal and liquid. Olivine at upper mantle depths near 250 km is considered. The behavior of a perched crystal layer is part of the general question concerning the fate of any transient crystal carried away from a cooling surface, whether this be a planetary surface or the roof of an intrusive magma body. For magma bodies thicker than a few hundred meters at modest crustal depths, the major cooling surface is the roof even when most solidification occurs at the floor. Importation of cool surroundings must also be invoked for the generation of a perched crystal layer in a magma ocean, but in this case the perched layer is deeply embedded in the hot part of the magma body, and far away from any cooling surface. Other aspects of this study are presented.

  9. 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

  10. Fractionation products of basaltic komatiite magmas at lower crustal pressures: implications for genesis of silicic magmas in the Archean

    NASA Astrophysics Data System (ADS)

    Mandler, B. E.; Grove, T. L.

    2015-12-01

    Hypotheses for the origin of crustal silicic magmas include both partial melting of basalts and fractional crystallization of mantle-derived melts[1]. Both are recognized as important processes in modern environments. When it comes to Archean rocks, however, partial melting hypotheses dominate the literature. Tonalite-trondhjemite-granodiorite (TTG)-type silicic magmas, ubiquitous in the Archean, are widely thought to be produced by partial melting of subducted, delaminated or otherwise deeply buried hydrated basalts[2]. The potential for a fractional crystallization origin for TTG-type magmas remains largely unexplored. To rectify this asymmetry in approaches to modern vs. ancient rocks, we have performed experiments at high pressures and temperatures to closely simulate fractional crystallization of a basaltic komatiite magma in the lowermost crust. These represent the first experimental determinations of the fractionation products of komatiite-type magmas at elevated pressures. The aim is to test the possibility of a genetic link between basaltic komatiites and TTGs, which are both magmas found predominantly in Archean terranes and less so in modern environments. We will present the 12-kbar fractionation paths of both Al-depleted and Al-undepleted basaltic komatiite magmas, and discuss their implications for the relative importance of magmatic fractionation vs. partial melting in producing more evolved, silicic magmas in the Archean. [1] Annen et al., J. Petrol., 47, 505-539, 2006. [2] Moyen J-F. & Martin H., Lithos, 148, 312-336, 2012.

  11. 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.

  12. Session 6: Magma Energy: Engineering Feasibility of Energy Extraction from Magma Bodies

    SciTech Connect

    Traeger, R.K.

    1983-12-01

    Extensive quantities of high-quality energy are estimated to be available from molten magma bodies existing within 10 Km of the US continent's surface. A five-year study sponsored by DOE/BES demonstrated that extraction of energy from these melts was scientifically feasible. The next stage of assessment is to evaluate the engineering feasibility of energy extraction and provide a preliminary economic evaluation. Should the second step demonstrate engineering feasibility, the third step would include detailed economic, market and commercialization endeavors. Evaluation of the engineering feasibility will be initiated in FY 84 in a program supported by DOE/GHTD and managed by Dave Allen. The project will be managed by Sandia Labs in James Kelsey's Geothermal Technology Development Division. The project will continue to draw on expertise throughout the country, especially the scientific base established in the previous BES Magma Energy Program.

  13. Chemical diffusion during isobaric degassing of magma

    NASA Astrophysics Data System (ADS)

    von Aulock, Felix W.; Kennedy, Ben M.; Lavallée, Yan; Henton-de Angelis, Sarah; Oze, Christopher; Morgan, Daniel J.; Clesham, Steve

    2014-05-01

    During ascent of magma, volatiles exsolve and bubbles form. Volatiles can either escape through a permeable network of bubbles in an open system or be trapped in non-connected pores during closed system degassing. Geochemical studies have shown that in most cases both- open system and closed system degassing take place at the same time. During cooling of the melt, diffusion slows down and eventually diffusional gradients get frozen in, preserving a history of degassing and rehydration during bubble growth, bubble collapse and crystal growth. We present data from experiments in which natural obsidian was degassed at atmospheric pressures at 950ºC over timescales of 3-24h. During bubble growth, a skin formed, at the outer edge of the sample, effectively prohibiting any degassing of its interior. Diffusion gradients were measured across the glass surrounding vesicles, and across this impermeable skin. Water contents were analyzed with synchrotron sourced Fourier transform infrared spectroscopy and several major, minor and trace elements were mapped using synchrotron sourced X-ray fluorescence spectroscopy. The samples show a dimpled surface, as well as signs of oxidation and growth of submicroscopic crystals. Water contents around bubbles decrease in simple heating experiments (from ~0.13 wt. % down to ~0.1 wt. %), whereas slight rehydration of the vesicle wall can be observed when a second, cooler step at 850ºC follows the initial 950ºC. Water gradients towards the outside of the sample decrease linearly to a minimum of ~0.045 wt. %, far below the solubility of water in melts at these temperatures. We mapped the distribution of K, Ca, Fe, Ti, Mn, Rb, Sr, Y and Zr. Especially the trace elements show a decrease towards the outside of the sample, whereas K, Fe, Ca and Ti generally do not show significant partitioning between melt and gas/crystal phase. Several effects could attribute to the distribution of these elements, such as the crystal growth and exchange with

  14. The three stages of magma ocean cooling

    NASA Technical Reports Server (NTRS)

    Warren, Paul H.

    1992-01-01

    Models of magma ocean (MO) cooling and crystallization can provide important constraints on MO plausibility for a given planet, on the origin of long term, stable crusts, and even on the origin of the solar system. Assuming the MO is initially extensive enough to have a mostly molten surface, its first stage of cooling is an era of radiative heat loss from the surface, with extremely rapid convection below, and no conductive layer in between. The development of the chill crust starts the second stage of MO cooling. Heat loss is now limited by conduction through the crust. The third stage of cooling starts when the near surface MO evolves compositionally to the point of saturation with feldspar. At this point, the cooling rate again precipitously diminishes, the rate of crustal thickness growth as a function of temperature suddenly increases. More work on incorporating chemical constraints into the evolving physical models of MO solidification would be worthwhile.

  15. Magma ocean formation due to giant impacts

    NASA Technical Reports Server (NTRS)

    Tonks, W. B.; Melosh, H. J.

    1992-01-01

    The effect of giant impacts on the initial chemical and thermal states of the terrestrial planets is just now being explored. A large high speed impact creates an approximately hemispherical melt region with a radius that depends on the projectile's radius and impact speed. It is shown that giant impacts on large planets can create large, intact melt regions containing melt volumes up to a few times the volume of the projectile. These large melt regions are not created on asteroid sized bodies. If extruded to the surface, these regions contain enough melt to create a magma ocean of considerable depth, depending on the impact speed, projectile radius, and gravity of the target planet.

  16. Electromagnetic Imaging of Crustal Magma Chambers

    NASA Astrophysics Data System (ADS)

    Constable, S.; Li, Y.; Key, K.

    2006-12-01

    In February/March 2004 we carried out a combined magnetotelluric (MT) and controlled source electromagnetic (CSEM) study of the mid-ocean ridge in the Pacific Ocean at 9°--10° North latitude. A 40-kilometer line of 22 seafloor electromagnetic recorders at 9°30' collected data from 27 kilometers of deep-towed CSEM transmission at 2~Hz, with a source dipole moment of 22~kAm. In order to obtain a first-order image of the information contained in the CSEM data we computed an apparent resistivity psuedosection based on signal amplitudes. This generates a spectacular image of a 10-kilometer wide, 20~Ømegam magma chamber embedded in a 500~Ømegam crust, along with pockets of melt or brine offset to the east of the ridge. We used the pseudosection to guide trial-and-error forward modeling using a newly developed 2D unstructured finite element code which allows seafloor bathymetry to be accurately meshed. The more rigorous modeling results in a good fit to the data from a much narrower 20~Ømegam `mush' zone only 2.5~km wide, capped by a 600-m thick 5~Ømegam melt lens. Unlike the pseudosection, the forward model requires a conductive (5~Ømegam) tent which extends from the melt lens to within about 100~m of the seafloor, probably corresponding to a zone of hydrothermal circulation. This is in contrast to earlier results from the slow-spreading, deeper magma chamber at the Valu Fa Ridge in the Lau Basin, where a large, asymmetric conductivity anomaly in the upper crust suggests that hydrothermal fluids extend 10~km west of the ridge axis.

  17. Limits to magma mixing based on chemistry and mineralogy of pumice fragments erupted from a chemically zoned magma body

    SciTech Connect

    Vogel, T.A.; Ryerson, F.J.; Noble, D.C.; Younker, L.W.

    1987-09-01

    The chemical variation among pumice fragments from the Pahute Mesa Member of the Thirsty Canyon Tuff (Black Mountain volcanic center, southwestern Nevada) is consistent with magma withdrawal from a chemically zoned magma body. The top of this magma body contained little chemical variations, the lowest concentration of light REEs, and the highest concentrations of SiO/sub 2/, heavy REEs, and Th. The pumice fragments derived from the top of the magma body contain nearly pure ferrohedenbergite and fayalite. The next discrete zone in the magma body contained lower SiO/sub 2/, heavy REEs, and Th concentrations, and very high concentrations of light REEs. The lowest erupted layer contained relatively low concentrations of SiO/sub 2/, Th, and light and heavy REEs. Pumice fragments with polymodal disequilibrium phenocryst populations are a priori evidence of magma mixing. The magma mixing process is constrained by: the systematic vertical distribution of chemically distinct pumice fragments throughout the ash-flow sheet; the presence of disequilibrium phenocrysts within some pumice fragments in all but the lowermost part of the sheet; and the presence of compositionally uniform glass in most pumice fragments, including those with widely varying phenocryst compositions. Negligible mixing occurred at the top of the magma body; limited mixing occurred in the second and third layers. Because mixing did not destroy the original layering, the amount of guest magma must have been small. In order for unzoned disequilibrium phenocrysts to not become zoned, they must have been preserved in the magma body only a short time. And yet, in order to produce the homogeneous liquid that surrounds these phenocrysts, mechanical mixing must have been very efficient. 44 references.

  18. 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.

  19. 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

  20. MAGMA: analysis of two-channel microarrays made easy.

    PubMed

    Rehrauer, Hubert; Zoller, Stefan; Schlapbach, Ralph

    2007-07-01

    The web application MAGMA provides a simple and intuitive interface to identify differentially expressed genes from two-channel microarray data. While the underlying algorithms are not superior to those of similar web applications, MAGMA is particularly user friendly and can be used without prior training. The user interface guides the novice user through the most typical microarray analysis workflow consisting of data upload, annotation, normalization and statistical analysis. It automatically generates R-scripts that document MAGMA's entire data processing steps, thereby allowing the user to regenerate all results in his local R installation. The implementation of MAGMA follows the model-view-controller design pattern that strictly separates the R-based statistical data processing, the web-representation and the application logic. This modular design makes the application flexible and easily extendible by experts in one of the fields: statistical microarray analysis, web design or software development. State-of-the-art Java Server Faces technology was used to generate the web interface and to perform user input processing. MAGMA's object-oriented modular framework makes it easily extendible and applicable to other fields and demonstrates that modern Java technology is also suitable for rather small and concise academic projects. MAGMA is freely available at www.magma-fgcz.uzh.ch. PMID:17517778

  1. 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

  2. Persistent multitiered magma plumbing beneath Katla volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Budd, David A.; Troll, Valentin R.; Dahren, Börje; Burchardt, Steffi

    2016-03-01

    Recent seismic unrest and a persistent Holocene eruption record at Katla volcano, Iceland indicate that a near-future eruption is possible. Previous petrological investigations suggest that Katla is supplied by a simple plumbing system that delivers magma directly from depth, while seismic and geodetic data also point toward the existence of upper-crustal magma storage. To characterize Katla's recent plumbing system, we established mineral-melt equilibrium crystallization pressures from four age-constrained Katla tephras spanning from 8 kyr BP to 1918. The results point to persistent shallow- (≤8 km depth) as well as deep-crustal (ca. 10 - 25 km depth) magma storage beneath Katla throughout the last 8 kyr. The presence of multiple magma storage regions implies that mafic magma from the deeper reservoir system may become gas-rich during ascent and storage in the shallow crust and erupt explosively. Alternatively, it might intersect evolved magma pockets in the shallow-level storage region, and so increase the potential for explosive mixed-magma ash eruptions.

  3. 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

    Until recently, igneous bodies (plutons and magma chambers) were commonly considered to be approximately spherical bodies, rapidly emplaced into the crust. However, field, structural, geophysical, and geochronological studies indicate that many plutons are low aspect-ratio tabular bodies (sills) that are formed by the amalgamation of successive discrete magma pulses. The thermal evolution of an igneous body that grows by accretion of thin magma sheets is fundamentally different from the evolution of a rapidly emplaced magma sphere or of a single thick magma sill. In thin sheet intrusions, the heat loss is through the walls of the sheets and the temperatures within the intrusions do not depend on the volumes injected but on the one-dimension sheets emplacement rate. The first sheets injected in a cold crust rapidly cool down and solidify. The ability of successive intrusions to stay at high temperature and eventually build up a long-lived magma chamber is controlled by the emplacement rate. Heat transfer modeling applied in the context of a volcanic arc shows that average emplacement rates of at least several centimeters per year and an incubation time of tens thousands of years are needed for a persistent magma chamber to form. During the incubation time, the intrusions solidify and when a chamber of high melt fraction magma eventually grows, the volume of eruptible magma only form a small part of the total intruded volume. The emplacement rate of plutons is controversial. Geochronological data suggest that some plutons may be emplaced over millions years. For a pluton that is assembled at a slow rate of a few millimeters per year, millions of years are needed, over which kilometric thicknesses are intruded, before a volume of magma larger than the size of a single intrusion becomes mobile and eruptible. In many cases, volcanic products may come from a deep source without being associated with a long-lived upper crust magma chamber. If volcanism is associated with

  4. 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.

  5. Diatexite Deformation and Magma Extraction on Kangaroo Island, South Australia

    NASA Astrophysics Data System (ADS)

    Hasalova, P.; Weinberg, R. F.; Ward, L.; Fanning, C. M.

    2012-12-01

    Migmatite terranes are structurally complex. We have investigated the relationships between deformation and magma extraction in migmatites formed during the Delamerian orogeny on Kangaroo Island. Several phases of deformation occurred in the presence of melt (D1-D4) and we describe how magma segregation, accumulation and extraction changes with deformation style. During an early upright folding event (D2), magma was channelled towards the hinge of antiforms. Funnel-shaped networks of leucosomes form a root that link towards a central axial planar channel, marking the main magma extraction paths. Extraction was associated with limb collapse, and antiformal hinge disruption. During a later deformation phase (D4), diatexites were sheared so that schollen were disaggregated into smaller blocks and schlieren, and deformed into asymmetric, sigmoidal shapes. Foliations in the magmatic matrix and schollen asymmetry indicate dextral shearing. During flow, magma accumulated in shear planes, indicating a dilational component during shearing (transtension) and on strain shadows of schollen. As deformation waned (post-D4), magma extraction from these diatexites gave rise to steeply dipping, funnel-shaped channels, similar to those developed during folding. The funnel-shape networks are interpreted as magma extraction networks and indicate magma flow direction. Structures developed during this phase are comparable with those developed during dewatering of soft sediments. The magmatic rocks from migmatites formed early, during folding, and formed late after deformation waned were dated. Both have two monazite (U-Pb, SHRIMP) age groups of ~490Ma and ~505-520Ma. The older sample has a well-defined peak at 505-510Ma and trails into the younger ages. The younger sample has the opposite, with few old spots and a well-defined young peak at ~490Ma. The age range indicates the duration of anatexis, and well-defined peaks are interpreted to mark the age of individual magma batch

  6. Mechanisms for the generation of compositional heterogeneities in magma chambers

    NASA Technical Reports Server (NTRS)

    Trial, Alain F.; Spera, Frank J.

    1990-01-01

    The two main hypotheses concerning the origin of compositional heterogeneities in magma chambers are discussed: (1) models in which the development of compositional zonation is simultaneous with the birth and growth of the magma body and (2) models in which zonation develops within an initially homogeneous batch of magma. The paper presents an overview of the geological possibilities and evaluates them on the basis of current research. Calculations are presented for boundary-layer flow in isothermal ternary component systems, and it is demonstrated that multicomponent diffusion effects may be very significant, as was earlier suggested by Trial and Spera (1988).

  7. Thermal evolution and chemical differentiation of the terrestrial magma ocean

    NASA Technical Reports Server (NTRS)

    Abe, Y.

    1992-01-01

    The release of gravitational energy resulted in global melting and formation of a magma ocean during accretion of the Earth. Although it is believed that the formation of the magma ocean resulted in gravitational differentiation of melt and solid, the differentiation might be disturbed by the following processes: (1) convective mixing; (2) cooling and solidification; and (3) growth of the earth, which results in secular increase of pressure, and stirring by planetesimal impacts. The purpose of this study is to investigate the differentiation processes of the terrestrial magma ocean by taking into account various disturbing processes.

  8. Magma energy extraction - Annual Report for FY88

    SciTech Connect

    Dunn, J.C.

    1989-08-01

    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 50,000 to 500,000 Quads. The objective of the Magma Energy Extraction Program is to determine engineering feasibility of locating, accessing and utilizing magma as a viable energy resource. Engineering feasibility will depend on size and depth of the resource; extraction rates; and material life times. 11 refs., 29 figs., 1 tab.

  9. How do crystal-rich magmas outgas?

    NASA Astrophysics Data System (ADS)

    Oppenheimer, Julie; Cashman, Katharine V.; Rust, Alison C.; Sandnes, Bjornar

    2014-05-01

    Crystals can occupy ~0 to 100% of the total magma volume, but their role in outgassing remains poorly understood. In particular, the upper half of this spectrum - when the particles touch - involves complex flow behaviours that inevitably affect the geometry and rate of gas migration. We use analogue experiments to examine the role of high particle concentrations on outgassing mechanisms. Mixtures of sugar syrup and glass beads are squeezed between two glass plates to allow observations in 2D. The experiments are performed horizontally, so buoyancy does not intervene, and the suspensions are allowed to expand laterally. Gas flow regimes are mapped out for two sets of experiments: foams generated by chemical reactions, and single air bubbles injected into the particle suspension. Chemically induced bubble nucleation and growth throughout the suspension gradually generated a foam and allowed observations of bubble growth and migration as the foam developed. High particle fractions, close to the random maximum packing, reduced foam expansion (i.e. promoted outgassing). In the early phases of the experiments, they caused a flushing of bubbles from the system which did not occur at low crystal contents. High particle fractions also led to melt segregation and phase re-arrangements, eventually focusing gas escape through connected channels. A more in-depth study of particle-bubble interactions was carried out for single bubbles expanding in a mush. These show a clear change in behaviour close to the limit for loose maximum packing of dry beads, determined experimentally. At concentrations below loose packing, gas expands in a fingering pattern, characterized by a steady advance of widening lobes. This transits to a 'pseudo-fracturing' regime at or near loose packing, whereby gas advances at a point, often in an episodic manner, and outgases with little to no bulk expansion. However, before they can degas, pseudo-fractures typically build up larger internal gas pressures

  10. Assembly of a zoned volcanic magma chamber from multiple magma batches: The Cerberean Cauldron, Marysville Igneous Complex, Australia

    NASA Astrophysics Data System (ADS)

    Clemens, J. D.; Birch, W. D.

    2012-12-01

    The Late Devonian (374 Ma) Cerberean Cauldron forms the northern part of the Marysville Igneous Complex, in Central Victoria, Australia, filled with around 900 km3 of intra-caldera ignimbrites. The basal volcanic formation is the rhyolitic high-Al Rubicon Ignimbrite, overlain by a larger volume of crystal-rich rhyolitic low-Al Rubicon Ignimbrite, which grades upward into the voluminous, rhyodacitic Lake Mountain Ignimbrite. The rocks are S-type in character, with initial 87Sr/86Sr around 0.709 to 0.710 and ɛNdt varying from - 4.7 to - 6.0, suggesting metagreywacke protoliths. The chemistry of the volcanic rocks is incompatible with formation by a differentiation mechanism. Experimentally determined phase relations of a low-Al Rubicon Ignimbrite and a Lake Mountain Ignimbrite show that early crystallisation of the Lake Mountain magma began at > 450 MPa and at > 875 °C (possibly up to 940 °C), with an initial magma H2O content of 4.1 to 5.3 wt.%. In the pre-eruption magma chamber, the Rubicon Ignimbrite magma had a temperature of ≥ 780 °C and contained ≥ 4 wt.% H2O. Each formation, and indeed smaller volumes of rock, appears to have been produced by partial melting of slightly contrasting greywackes in a protolith with spatial variations in its chemistry and mineralogy, with the magma delivered in batches to a high-level chamber. The Rubicon Ignimbrite magmas underwent some internal differentiation, probably by crystal settling, prior to eruption, and variations in the Lake Mountain Ignimbrite are most probably due to small but variable degrees of peritectic phase entrainment. The limited gradation between the Rubicon Ignimbrite and Lake Mountain Ignimbrite is due to minor, pre-eruption mixing across the magma interface. Such limited mixing between individual magma batches appears typical of anatectic granitic magmas.

  11. Implications of magma transfer between multiple reservoirs on eruption cycling.

    PubMed

    Elsworth, Derek; Mattioli, Glen; Taron, Joshua; Voight, Barry; Herd, Richard

    2008-10-10

    Volcanic eruptions are episodic despite being supplied by melt at a nearly constant rate. We used histories of magma efflux and surface deformation to geodetically image magma transfer within the deep crustal plumbing of the Soufrière Hills volcano on Montserrat, West Indies. For three cycles of effusion followed by discrete pauses, supply of the system from the deep crust and mantle was continuous. During periods of reinitiated high surface efflux, magma rose quickly and synchronously from a deflating mid-crustal reservoir (at about 12 kilometers) augmented from depth. During repose, the lower reservoir refilled from the deep supply, with only minor discharge transiting the upper chamber to surface. These observations are consistent with a model involving the continuous supply of magma from the deep crust and mantle into a voluminous and compliant mid-crustal reservoir, episodically valved below a shallow reservoir (at about 6 kilometers). PMID:18845752

  12. Time scales of crystal mixing in magma mushes

    NASA Astrophysics Data System (ADS)

    Schleicher, Jillian M.; Bergantz, George W.; Breidenthal, Robert E.; Burgisser, Alain

    2016-02-01

    Magma mixing is widely recognized as a means of producing compositional diversity and preconditioning magmas for eruption. However, the processes and associated time scales that produce the commonly observed expressions of magma mixing are poorly understood, especially under crystal-rich conditions. Here we introduce and exemplify a parameterized method to predict the characteristic mixing time of crystals in a crystal-rich magma mush that is subject to open-system reintrusion events. Our approach includes novel numerical simulations that resolve multiphase particle-fluid interactions. It also quantifies the crystal mixing by calculating both the local and system-wide progressive loss of the spatial correlation of individual crystals throughout the mixing region. Both inertial and viscous time scales for bulk mixing are introduced. Estimated mixing times are compared to natural examples and the time for basaltic mush systems to become well mixed can be on the order of 10 days.

  13. 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

  14. Preliminary considerations for extraction of thermal energy from magma

    SciTech Connect

    Hickox, C.E.; Dunn, J.C.

    1985-01-01

    Simplified mathematical models are developed to describe the extraction of thermal energy from magma based on the concept of a counterflow heat exchanger inserted into the magma body. Analytical solutions are used to investigate influence of the basic variables on electric power production. Calculations confirm that the proper heat exchanger flow path is down the annulus with hot fluid returning to the surface through the central core. The core must be insulated from the annulus to achieve acceptable wellhead temperatures, but this insulation thickness can be quite small. The insulation is effective in maintaining the colder annular flow below expected formation temperatures so that a net heat gain from the formation above a magma body is predicted. The analyses show that optimum flow rates exist that maximize electric power production. These optimum flow rates are functions of the heat transfer coefficients that describe magma energy extraction. 15 refs., 3 figs.

  15. The Role of Magma Mixing in Creating Magmatic Diversity

    NASA Astrophysics Data System (ADS)

    Davidson, J. P.; Collins, S.; Morgan, D. J.

    2012-12-01

    Most magmas derived from the mantle are fundamentally basaltic. An assessment of actual magmatic rock compositions erupted at the earth's surface, however, shows greater diversity. While still strongly dominated by basalts, magmatic rock compositions extend to far more differentiated (higher SiO2, LREE enriched) compositions. Magmatic diversity is generated by differentiation processes, including crystal fractionation/ accumulation, crustal contamination and magma mixing. Among these, magma mixing is arguably inevitable in magma systems that deliver magmas from source-to-surface, since magmas will tend to multiply re-occupy plumbing systems. A given mantle-derived magma type will mix with any residual magmas (and crystals) in the system, and with any partial melts of the wallrock which are generated as it is repeatedly flushed through the system. Evidence for magma mixing can be read from the petrography (identification of crystals derived from different magmas), a technique which is now well-developed and supplemented by isotopic fingerprinting (1,2) As a means of creating diversity, mixing is inevitably not efficient as its tendency is to blend towards a common composition (i.e. converging on homogeneity rather than diversity). It may be surprising then that many systems do not tend to homogenise with time, meaning that the timescales of mixing episodes and eruption must be similar to external magma contributions of distinct composition (recharge?). Indeed recharge and mixing/ contamination may well be related. As a result, the consequences of magma mixing may well bear on eruption triggering. When two magmas mix, volatile exsolution may be triggered by retrograde boiling, with crystallisation of anhydrous phase(s) in either of the magmas (3) or volatiles may be generated by thermal breakdown of a hydrous phase in one of the magmas (4). The generation of gas pressures in this way probably leads to geophysical signals too (small earthquakes). Recent work pulling

  16. Magma Dynamics at Yucca Mountain, Nevada

    SciTech Connect

    D. Krier

    2005-08-29

    Small-volume basaltic volcanic activity at Yucca Mountain has been identified as one of the potential events that could lead to release of radioactive material from the U.S. Department of Energy (DOE) designated nuclear waste repository at Yucca Mountain. Release of material could occur indirectly as a result of magmatic dike intrusion into the repository (with no associated surface eruption) by changing groundwater flow paths, or as a result of an eruption (dike intrusion of the repository drifts, followed by surface eruption of contaminated ash) or volcanic ejection of material onto the Earth's surface and the redistribution of contaminated volcanic tephra. Either release method includes interaction between emplacement drifts and a magmatic dike or conduit, and natural (geologic) processes that might interrupt or halt igneous activity. This analysis provides summary information on two approaches to evaluate effects of disruption at the repository by basaltic igneous activity: (1) descriptions of the physical geometry of ascending basaltic dikes and their interaction with silicic host rocks similar in composition to the repository host rocks; and (2) a summary of calculations developed to quantify the response of emplacement drifts that have been flooded with magma and repressurized following blockage of an eruptive conduit. The purpose of these analyses is to explore the potential consequences that could occur during the full duration of an igneous event.

  17. CONDITIONS LEADING TO SUDDEN RELEASE OF MAGMA PRESSURE

    SciTech Connect

    B. Damjanac; E.S. Gaffney

    2005-08-26

    Buildup of magmatic pressures in a volcanic system can arise from a variety of mechanisms. Numerical models of the response of volcanic structures to buildup of pressures in magma in dikes and conduits provide estimates of the pressures needed to reopen blocked volcanic vents. They also can bound the magnitude of sudden pressure drops in a dike or conduit due to such reopening. Three scenarios are considered: a dike that is sheared off by covolcanic normal faulting, a scoria cone over a conduit that is blocked by in-falling scoria and some length of solidified magma, and a lava flow whose feed has partially solidified due to an interruption of magma supply from below. For faulting, it is found that magma would be able to follow the fault to a new surface eruption. A small increase in magma pressure over that needed to maintain flow prior to faulting is required to open the new path, and the magma pressure needed to maintain flow is lower but still greater than for the original dike. The magma pressure needed to overcome the other types of blockages depends on the details of the blockage. For example, for a scoria cone, it depends on the depth of the slumped scoria and on the depth to which the magma has solidified in the conduit. In general, failure of the blockage is expected to occur by radial hydrofracture just below the blocked length of conduit at magma pressures of 10 MPa or less, resulting in radial dikes. However, this conclusion is based on the assumption that the fluid magma has direct access to the rock surrounding the conduit. If, on the other hand, there is a zone of solidified basalt, still hot enough to deform plastically, surrounding the molten magma in the conduit, this could prevent breakout of a hydrofracture and allow higher pressures to build up. In such cases, pressures could build high enough to deform the overlying strata (scoria cone or lava flow). Models of such deformations suggest the possibility of more violent eruptions resulting from

  18. The role of turbulence in explosive magma-water mixing

    NASA Astrophysics Data System (ADS)

    Mastin, L. G.; Walder, J. S.; Stern, L. A.

    2003-12-01

    Juvenile tephra from explosive hydromagmatic eruptions differs from that of dry magmatic eruptions by its fine average grain size and highly variable vesicularity. These characteristics are generally interpreted to indicate that fragmentation, which occurs in dry magmas by bubble growth, is supplemented in hydromagmatic eruptions by quench-fracturing. Quench fragmentation is thought to accelerate heat transfer to water, driving violent steam expansion and increasing eruptive violence. Although some observed hydromagmatic events (e.g. at Surtsey) are indeed violent, others (e.g. quiescent entry of lava into the ocean at Kilauea) are not. We suggest that the violence of magma-water mixing and the grain size and dispersal of hydromagmatic tephras are controlled largely by the turbulence of magma-water mixing. At Surtsey, fine-grained, widely dispersed hydromagmatic tephras were produced primarily during continuous uprush events in which turbulent jets of magma and gas passed through shallow water (Thorarinsson, 1967). During Kilauea's current eruption, videos show generation of fine-grained tephras when turbulent jets of magma, steam, and seawater exited through skylights at the coastline. Turbulence intensity, or the fraction of total jet kinetic energy contained in fine-scale turbulent velocity oscillations, has long been known to control the scale of atomization in spray nozzles and the rate of heat transfer and chemical reaction in fuel injectors. We hypothesize that turbulence intensity also influences grain size and heat transfer rate in magma-water mixing, though such processes are complicated by boiling (in water) and quench fracturing (in magma). We are testing this hypothesis in experiments involving turbulent injection of water (a magma analog) into liquid nitrogen (a water analog). We also suggest that turbulent mixing influences relative proportions of magma and water in hydromagmatic eruptions. Empirical studies indicate that pressure-neutral turbulent

  19. Seismic Tremors and Three-Dimensional Magma Wagging

    NASA Astrophysics Data System (ADS)

    Liao, Y.; Bercovici, D.

    2015-12-01

    Seismic tremor is a feature shared by many silicic volcanoes and is a precursor of volcanic eruption. Many of the characteristics of tremors, including their frequency band from 0.5 Hz to 7 Hz, are common for volcanoes with very different geophysical and geochemical properties. The ubiquitous characteristics of tremor imply that it results from some generation mechanism that is common to all volcanoes, instead of being unique to each volcano. Here we present new analysis on the magma-wagging mechanism that has been proposed to generate tremor. The model is based on the suggestion given by previous work (Jellinek & Bercovici 2011; Bercovici et.al. 2013) that the magma column is surrounded by a compressible, bubble-rich foam annulus while rising inside the volcanic conduit, and that the lateral oscillation of the magma inside the annulus causes observable tremor. Unlike the previous two-dimensional wagging model where the displacement of the magma column is restricted to one vertical plane, the three-dimensional model we employ allows the magma column to bend in different directions and has angular motion as well. Our preliminary results show that, without damping from viscous deformation of the magma column, the system retains angular momentum and develops elliptical motion (i.e., the horizontal displacement traces an ellipse). In this ''inviscid'' limit, the magma column can also develop instabilities with higher frequencies than what is found in the original two-dimensional model. Lateral motion can also be out of phase for various depths in the magma column leading to a coiled wagging motion. For the viscous-magma model, we predict a similar damping rate for the uncoiled magma column as in the two-dimensional model, and faster damping for the coiled magma column. The higher damping thus requires the existence of a forcing mechanism to sustain the oscillation, for example the gas-driven Bernoulli effect proposed by Bercovici et al (2013). Finally, using our new 3

  20. Crystallization and saturation front propagation in silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Lake, Ethan T.

    2013-12-01

    The cooling and crystallization style of silicic magma bodies in the upper crust falls on a continuum between whole-chamber processes of convection, crystal settling, and cumulate formation and interface-driven processes of conduction and crystallization front migration. In the end-member case of vigorous convection and crystal settling, volatile saturation advances downward from the roof and upward from the floor throughout the chamber. In the end-member case of stagnant magma bodies, volatile saturation occurs along an inward propagating front from all sides of the chamber. Ambient thermal gradient primarily controls the propagation rate; warm (⩾40 °C/km) geothermal gradients lead to thick (1200+ m) crystal mush zones and slow crystallization front propagation. Cold (<40 °C/km) geothermal gradients lead to rapid crystallization front propagation and thin (<1000 m) mush zones. Magma chamber geometry also exerts a first-order control on propagation rates; bodies with high surface to magma volume ratio and large Earth-surface-parallel faces exhibit more rapid propagation and thinner mush zones. Crystallization front propagation occurs at speeds of greater than 10 cm/yr (rhyolitic magma; 1 km thick sill geometry in a 20 °C/km geotherm), far faster than diffusion of volatiles in magma and faster than bubbles can nucleate, grow, and ascend through the chamber. Numerical simulations indicate saturation front propagation is determined primarily by pressure and magma crystallization rate; above certain initial water contents (4.4 wt.% in a dacite) the mobile magma is volatile-rich enough above 10 km depth to always contains a saturation front. Saturation fronts propagate down from the magma chamber roof at lower water contents (3.3 wt.% in a dacite at 5 km depth), creating an upper saturated interface for most common (4-6 wt.%) magma water contents. This upper interface promotes the production of a fluid pocket underneath the apex of the magma chamber. If the fluid

  1. Diatexite Deformation and Magma Extraction on Kangaroo Island, South Australia

    NASA Astrophysics Data System (ADS)

    Hasalova, Pavlina; Weinberg, Roberto; Ward, Lindsay; Fanning, Mark

    2013-04-01

    Migmatite terranes are structurally complex because of strong rheological contrast between layers with different melt contents and because of magma migration leading to volume changes. Migmatite deformation is intimately linked with magma extraction and the origin of granitoids. We investigate here the relationships between an evolving deformation and magma extraction in migmatites formed during the ca. 500Ma Delamerian orogeny, exposed on Kangaroo Island, South Australia. Here, several phases of deformation occurred in the presence of melt. During an early upright, non-cylindrical folding event, magma was channeled towards the hinge zones of antiforms. Funnel-shaped networks of leucosomes form a root zone that link up towards a central axial planar channel, forming the main magma extraction paths during folding. Extraction was associated with fold limb collapse, and antiformal hinge disruption by magma accumulation and transfer. During a later deformation phase, melt-rich diatexites were deformed, and schollen were disaggregated into smaller blocks and schlieren, and deformed into asymmetric, sigmoidal shapes indicative of dextral shearing flow. During flow, magma accumulated preferentially along shear planes, indicating a dilatational component during shearing (transtension) and in strain shadows of schollen. As deformation waned, magma extraction from these diatexites gave rise to N-trending, steeply dipping, funnel-shaped channels not associated to any deformational feature. The funnel-shape of these structures indicates the direction of magma flow. Structures developed during this phase are comparable with those formed during dewatering of soft sediments. Despite a high degree of complexity, magma migration and extraction features record distinct responses to the evolving deformation which can be used to understand deformation, and nature and direction of melt extraction. The oldest and youngest magmatic rocks from migmatites were dated (U-Pb monazite, SHRIMP

  2. Low-(18)O Silicic Magmas: Why Are They So Rare?

    SciTech Connect

    Balsley, S.D.; Gregory, R.T.

    1998-10-15

    LOW-180 silicic magmas are reported from only a small number of localities (e.g., Yellowstone and Iceland), yet petrologic evidence points to upper crustal assimilation coupled with fractional crystallization (AFC) during magma genesis for nearly all silicic magmas. The rarity of 10W-l `O magmas in intracontinental caldera settings is remarkable given the evidence of intense 10W-l*O meteoric hydrothermal alteration in the subvolcanic remnants of larger caldera systems. In the Platoro caldera complex, regional ignimbrites (150-1000 km3) have plagioclase 6180 values of 6.8 + 0.1%., whereas the Middle Tuff, a small-volume (est. 50-100 km3) post-caldera collapse pyroclastic sequence, has plagioclase 8]80 values between 5.5 and 6.8%o. On average, the plagioclase phenocrysts from the Middle Tuff are depleted by only 0.3%0 relative to those in the regional tuffs. At Yellowstone, small-volume post-caldera collapse intracaldera rhyolites are up to 5.5%o depleted relative to the regional ignimbrites. Two important differences between the Middle Tuff and the Yellowstone 10W-180 rhyolites elucidate the problem. Middle Tuff magmas reached water saturation and erupted explosively, whereas most of the 10W-l 80 Yellowstone rhyolites erupted effusively as domes or flows, and are nearly devoid of hydrous phenocrysts. Comparing the two eruptive types indicates that assimilation of 10W-180 material, combined with fractional crystallization, drives silicic melts to water oversaturation. Water saturated magmas either erupt explosively or quench as subsurface porphyrins bejiire the magmatic 180 can be dramatically lowered. Partial melting of low- 180 subvolcanic rocks by near-anhydrous magmas at Yellowstone produced small- volume, 10W-180 magmas directly, thereby circumventing the water saturation barrier encountered through normal AFC processes.

  3. Solidification of basaltic magma during flow in a dike.

    USGS Publications Warehouse

    Delaney, P.T.; Pollard, D.D.

    1982-01-01

    A model for time-dependent unsteady heat transfer from magma flowing in a dyke is developed. The ratio of solidification T to magma T is the most important parameter. Observations of volcanic fissure eruptions and study of dykes near Ship Rock, New Mexico, show that the low T at dyke margins and the rapidly advancing solidification front predicted by the model are qualitatively correct.-M.S.

  4. Experimental Fractional Crystallization of the Lunar Magma Ocean

    NASA Technical Reports Server (NTRS)

    Rapp, J. F.; Draper, D. S.

    2012-01-01

    The current paradigm for lunar evolution is of crystallization of a global scale magma ocean, giving rise to the anorthositic crust and mafic cumulate interior. It is thought that all other lunar rocks have arisen from this differentiated interior. However, until recently this paradigm has remained untested experimentally. Presented here are the first experimental results of fractional crystallization of a Lunar Magma Ocean (LMO) using the Taylor Whole Moon (TWM) bulk lunar composition [1].

  5. Magma plumbing system of the Aso-3 large pyroclastic eruption cycle at Aso volcano, Southwest Japan: Petrological constraint on the formation of a compositionally stratified magma chamber

    NASA Astrophysics Data System (ADS)

    Kaneko, Katsuya; Inoue, Kazuhisa; Koyaguchi, Takehiro; Yoshikawa, Masako; Shibata, Tomoyuki; Takahashi, Toshiro; Furukawa, Kuniyuki

    2015-09-01

    Aso volcano has the largest caldera (18 × 25 km in diameter) in the southwestern Japan Island Arc, and it formed as the result of four large (VEI = 6-7) pyroclastic-eruption cycles. We study the penultimate large eruption cycle, the Aso-3 cycle, which occurred 123 ka with an ejecta volume of more than 150 km3. The processes in the pre-eruptive magma chamber and the magma genesis of the Aso-3 cycle were inferred from geological data, phenocryst chemistry, and whole-rock chemical and Sr-, Nd-, and Pb isotopic analyses of juvenile clasts. The geological and petrological data indicate that the pre-eruptive magma chamber was stratified compositionally into three layers: from top to bottom, silicic, intermediate, and mafic magma layers. The three magma layers had a uniform isotope composition, suggesting that all the magmas were generated from a single source. The silicic and intermediate magmas were not generated from the mafic magma by fractional crystallization. The silicic magma has higher Ni content (compatible element) than the mafic magma. This suggests that these magmas were produced by partial melting of the same mafic crust but with differing amounts of partial melting: the silicic magma was produced by a low degree of partial melting of the source rock without fractional crystallization, and the mafic magma was produced by a large degree of partial melting followed by fractional crystallization. The intermediate magma compositions plot on the tie line between the silicic magma and the melt of the mafic magma in variation diagrams, and the intermediate magma has phenocrysts whose compositions are identical with those in the silicic magma. This observation indicates that, before the Aso-3 eruption cycle, a two-layer stratified magma chamber of the silicic and mafic magmas was formed as a result of melting of the mafic crust, which was followed by formation of the intermediate layer as a result of interfacial mixing between the silicic magma and the melt of

  6. The Rheology of Three-Phase Basaltic Magma

    NASA Astrophysics Data System (ADS)

    Llewellin, E. W.; Truby, J.; Mueller, S. P.; Mader, H. M.

    2014-12-01

    The transport of magma is controlled by its rheology which, in turn, is a function of its crystal and bubble content. We develop the first empirically-validated model for the rheology of a three-phase magma (i.e. one containing both bubbles and crystals). The model is valid at low bubble capillary number (where bubble deformation is small) which is typical of basaltic magma. We adopt an 'effective-medium' approach in which the bubbly melt is treated as a continuous medium which suspends the crystals. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and crystal suspension rheology, which are taken from the literature. The model is validated against new analogue experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction (0 ≤ Фp ≤0.5) and bubble volume fraction (0 ≤ Фb ≤ 0.3). Consistent with model predictions, experimental results demonstrate that, at low capillarity, bubble growth in a crystal-poor magma increases its viscosity, whilst bubble growth in a crystal-rich magma decreases its viscosity. The validity range of the model makes it particularly applicable to the transport of magma in the sub-volcanic plumbing system. The model is trivially extended to account for variations in crystal shape, and for the high capillarity regime; these extended models await experimental validation.

  7. Crystallization and Cooling of a Deep Silicate Magma Ocean

    NASA Astrophysics Data System (ADS)

    Bower, Dan; Wolf, Aaron

    2016-04-01

    Impact and accretion simulations of terrestrial planet formation suggest that giant impacts are both common and expected to produce extensive melting. The moon-forming impact, for example, likely melted the majority of Earth's mantle to produce a global magma ocean that subsequently cooled and crystallised. Understanding the cooling process is critical to determining magma ocean lifetimes and recognising possible remnant signatures of the magma ocean in present-day mantle heterogeneities. Modelling this evolution is challenging, however, due to the vastly different timescales and lengthscales associated with turbulent convection (magma ocean) and viscous creep (present-day mantle), in addition to uncertainties in material properties and chemical partitioning. We consider a simplified spherically-symmetric (1-D) magma ocean to investigate both its evolving structure and cooling timescale. Extending the work of Abe (1993), mixing-length theory is employed to determine convective heat transport, producing a high resolution model that parameterises the ultra-thin boundary layer (few cms) at the surface of the magma ocean. The thermodynamics of mantle melting are represented using a pseudo-one-component model, which retains the simplicity of a standard one-component model while introducing a finite temperature interval for melting. This model is used to determine the cooling timescale for a variety of plausible thermodynamic models, with special emphasis on comparing the center-outwards vs bottom-up cooling scenarios that arise from the assumed EOS.

  8. The effects of Venus' thermal structure on buoyant magma ascent

    NASA Technical Reports Server (NTRS)

    Sakimoto, S. E. H.; Zuber, M. T.

    1992-01-01

    The recent Magellan images have revealed a broad spatial distribution of surface volcanism on Venus. Previous work in modeling the ascent of magma on both Venus and Earth has indicated that the planetary thermal structure significantly influences the magmatic cooling rates and thus the amount of magma that can be transported to the surface before solidification. In order to understand which aspects of the thermal structure have the greatest influence on the cooling of ascending magma, we have constructed magma cooling curves for both plutonic and crack buoyant ascent mechanisms, and evaluated the curves for variations in the planetary mantle temperature, thermal gradient curvature with depth, surface temperature gradient, and surface temperature. The planetary thermal structure is modeled as T/T(sub 0) = 1-tau(1-Z/Z(sub 0)(exp n), where T is the temperature, T(sub 0) is the source depth temperature, tau = 1-(T(sub s)/T(sub 0)) where T(sub s) is the planetary surface temperature, Z is the depth, Z(sub 0) is the source depth, and n is a constant that controls thermal gradient curvature with depth. The equation is used both for mathematical convenience and flexibility, as well as its fit to the thermal gradients predicted by the cooling half-space models. We assume a constant velocity buoyant ascent, body-averaged magma temperatures and properties, an initially crystal-free magma, and the same liquidus and solidus for both Venus and Earth.

  9. Dynamically-induced structures formation in congested magma

    NASA Astrophysics Data System (ADS)

    Petford, N.

    2008-12-01

    Crystal fabrics preserved in igneous rocks offer a glimpse into the magma emplacement process. Detailed field mapping, in combination with AMS studies, seem to provide the best available data for unravelling intrusion architecture on the decimetre scale. However, a full and proper understanding of the fluid dynamics of congested fluid-particle mixtures during shear remains elusive. This is a shame as without recourse to such fundamental understanding, the interpretation of structural field data in the context of magma flow remains problematic. One way to gain insight into the process is to treat flowing magma as a dynamic material with a rheology similar to sheared, congested slurries. The fancy that dense magma equates to a high temperature slurry is an attractive one, and opens up a way to examine the emplacement process that does not rely exclusively on equilibrium thermodynamics as a final explanation of commonly observed igneous structures. Instead, using examples from mafic rocks where cooling has been rapid, the idea is put forward that in high Peclet number suspensions (where particle diffusion is negligible), shearing and non- Newtonian behaviour imparts a rich diversity of structures including layering, grading and flow segregation. Key to understanding the rheology, hence flow dynamics of congested magma, is the particle microstructure, a still poorly known essence of suspension flows. Where magma transport is continental in scale and long lived (e.g. Large Igneous Provinces), rotation of the earth may in theory endow a small but potentially measurable imprint on the preserved flow fabric.

  10. Experimental Magma Mixing and Mingling in Volcanic Environments

    NASA Astrophysics Data System (ADS)

    Morgavi, D.; Laumonier, M.; Petrelli, M.; Perugini, D.

    2015-12-01

    Magma mixing and mingling features are commonly observed in both plutonic and volcanic environments. Major occurrences are represented by hybrid products, enclaves and crystals in disequilibrium with the melt. According to present knowledge the complete mixing of magmas in crustal reservoirs (leading to the production of hybrids) requires a low viscosity contrast between the two end-members (0.5 log unit). On another hand, recent experimental and field works have shown that (1) crystal-free magmas with viscosity difference of 3 orders of magnitude produced mingling and mixing features at higher deformation conditions (strain and strain rate) and (2) these features are found in volcanic products out of the above mentioned rheological window. In this study, we performed magma mixing experiments, to test the effects of chaotic deformation of a two component system at volcanic conditions and strain rates comparable to natural magmatic systems (volcanic conduits and lava flows): in the ChaOtic Magma Mixing Apparatus (COMMA) installed at the University of Perugia, a synthetic haplotonalite and a natural basalt from Santorini volcano were juxtaposed and chaotically mixed for several hours at ~1140°C with a moderate strain rate of ~5.10-3. The textural and geochemical (electronic microprobe, laser ablation mass spectrometry) features developed during the experiments show the development of complex patterns with high inter-exchange between both magmas. Our results show how chaotic convection extends the mixing capacities at moderate strain rate.

  11. Geophysical and geochemical evolution of the lunar magma ocean

    NASA Technical Reports Server (NTRS)

    Herbert, F.; Drake, M. J.; Sonett, C. P.

    1978-01-01

    There is increasing evidence that at least the outer few hundred kilometers of the moon were melted immediately following accretion. This paper studies the evolution of this lunar magma ocean. The long time scale for solidification leads to the inference that the plagioclase-rich (ANT) lunar crust began forming, perhaps preceded by local accumulations termed 'rockbergs', at the very beginning of the magma ocean epoch. In this view the cooling and solidification of the magma ocean was primarily controlled by the rate at which heat could be conducted across the floating ANT crust. Thus the thickness of the crust was the factor controlling the lunar solidification time. Heat arising from enthalpy of crystallization was transported in the magma by convection. Mixing length theory is used to deduce the principal flow velocity (typically several cm/s) during convection. The magma ocean is deduced to have been turbulent down to a characteristic length scale of the order of 100 m, and to have overturned on a time scale of the order of 1 yr for most of the magma ocean epoch.

  12. Thermal and mechanical controls on magma supply and volcanic deformation

    NASA Astrophysics Data System (ADS)

    Hickey, James; Gottsmann, Jo; Nakamichi, Haruhisa; Iguchi, Masato

    2016-04-01

    Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rock. Geodetic models aimed at constraining source processes consequently require the implementation of realistic mechanical and thermal rock properties. However, most generic models ignore this requirement and employ oversimplified mechanical assumptions without regard for thermal effects. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that despite on-going eruptions magma is accumulating faster than it can be ejected, and the current uplift is approaching the level inferred prior to the 1914 Plinian eruption. Our results from inverse and forward numerical models are consistent with petrological constraints and highlight how the location, volume, and rate of magma supply, 0.014 km3/yr, are thermomechanically controlled. Magma storage conditions coincide with estimates for the caldera-forming reservoir ˜29,000 years ago, and the inferred magma supply rate indicates a ˜130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide.

  13. 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.

  14. Effects of shallow subvolcanic magma storage regions on magma evolution and eruptions dynamics of small mafic centers

    NASA Astrophysics Data System (ADS)

    Cashman, K. V.; Wallace, P. J.; McKay, D.; Ruscitto, D. M.

    2009-12-01

    The existence of shallow subvolcanic dike and sill complexes has long been recognized in field investigations of mafic cinder cones and shield volcanoes. Evidence that these subvolcanic storage regions develop during (rather than separate from) eruptive activity comes from detailed studies of tephra deposits and lava flows produced during cinder cone eruptions. These deposits show both the variable volatile contents of olivine-hosted melt inclusions and pervasive microphenocryst crystallization, both of which indicate temporary magma storage at shallow levels prior to eruption. The consequences of such shallow magma storage for both eruption dynamics and syn-eruptive magma evolution have not previously been considered. Here we use both physical (density, crystallinity) and compositional (bulk, melt inclusion) data from the 1943-1952 eruption of Parícutin, Mexico to examine the impact of shallow pre-eruptive storage on both the eruption process and on the dramatic evolution in magma composition first described by Wilcox (1954). We supplement these observations with data from recent (1500-2000 ybp) mafic cinder cone eruptions in central Oregon. Our data show that shallow subvolcanic storage of magma permits pre-eruptive degassing and crystallization, which, in turn, are responsible for the (typically) wide density range of basaltic scoria observed in cinder cone activity. As pre-eruptive gas loss will diminish the volatiles available to fuel explosive activity, we further speculate that the ease of syn-eruptive dike and sill formation, which is likely to be controlled by both the rate of magma supply and the specific tectonic setting, may modulate the explosive potential of cinder cone eruptions. Additionally, all of the deposits that we have studied have a range in bulk composition, with the earliest tephra the most mafic and the latest lava the most silicic of the eruptive sequence. This observation suggests that an additional consequence of shallow magma storage

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    The rheology of magmas controls not only eruption dynamics but also the rate of transport of magmas through the crust and to a large extent the rate of magma differentiation and degassing. Magma bodies stalled in the upper crust are known to spend most of their lifespan above the solidus at a high crystal content (Cooper and Kent, 2014; Huber et al., 2009), where the probability of melt extraction (crystal fractionation) is the greatest (Dufek and Bachmann, 2010). In this study, we explore a new theoretical framework to study the viscosity of crystal bearing magmas. Since the seminal work of A. Einstein and W. Sutherland in the early 20th century, it has been shown theoretically and tested experimentally that a simple self-similar behavior exist between the relative viscosity of dilute (low crystal content) suspensions and the particle volume fraction. The self-similar nature of that relationship is quickly lost as we consider crystal fractions beyond a few volume percent. We propose that the relative viscosity of crystal-bearing magmas can be fully described by two state variables, the intrinsic viscosity and the crowding factor (a measure of the packing threshold in the suspension). These two state variables can be measured experimentally under different conditions, which allows us to develop closure relationships in terms of the applied shear stress and the crystal shape and size distributions. We build these closure equations from the extensive literature on the rheology of synthetic suspensions, where the nature of the particle shape and size distributions is better constrained and apply the newly developed model to published experiments on crystal-bearing magmas. We find that we recover a self-similar behavior (unique rheology curve) up to the packing threshold and show that the commonly reported break in slope between the relative viscosity and crystal volume fraction around the expected packing threshold is most likely caused by a sudden change in the state

  16. When Magma Might but Doesn't Erupt

    NASA Astrophysics Data System (ADS)

    Newhall, C.

    2008-12-01

    If we define failed eruptions as those in which magma seemingly comes close to erupting but doesn't, 3 main variants are seen: (1) where volcanoes exhibit only fumarolic changes (strong steaming, sometimes but not always with high SO2 emission or fumarole temperatures) without notable other unrest (e.g,, Baker 1975; Fourpeaked 2006; Kudriavy, Satsuma-Iwojima, and Momotombo); (2) where seismic swarms, inflation, and other evidence of stress buildup simply stop, abruptly or slowly (e.g., Akutan 1996, Iliamna 1996); and (3) where unrest culminates in phreatic explosions (e.g., Soufrière Guadeloupe 1976, Bulusan-1980'-2000's, Canlaon 1990's-2000's, Iwo-Jima 2001, Huila 2007) A special case of (2) and (3) is when swarms of high-frequency earthquakes under or just off volcano flanks (distal volcano-tectonic earthquakes or DVT's) dominate seismicity (e.g., Tacana 1986, Guagua Pichincha 1998-99 during its phreatic phase); Another category, where deep LP earthquakes and/or deep-focus inflation stop after little or no shallow unrest (e.g., Three Sisters, Fuji), should not be called "failed" because magma isn't (yet) close to erupting. Unrest with or without eruption is especially common at large magma-hydrothermal systems beneath calderas (e.g., Rabaul 1982-84; Campi Flegrei 1969-70, 1982-85, 2004-06; Long Valley 1979-present). These are large, metastable systems that can buffer small incoming intrusions. Unrest is often prolonged. At Rabaul unrest died back but then resurged and magma finally erupted in 1994. At Campi Flegrei and Long Valley, unrest still occurs intermittently as of 2008. Most failed eruptions involve magma intrusion and/or acceleration of magma convection in a conduit; a few may involve late-stage second boiling. The final step to magmatic eruption can be aborted by (a) loss of driving force (gas pressure, magma supply) or (b) a physical barrier (solid; viscous or low-density magma). Degassing diminishes driving force AND increases viscosity - a double

  17. Crystallization and Cooling of a Deep Silicate Magma Ocean

    NASA Astrophysics Data System (ADS)

    Wolf, A. S.; Bower, D. J.

    2015-12-01

    Impact and accretion simulations of terrestrial planet formation suggest that giant impacts are both common and expected to produce extensive melting. The moon-forming impact, for example, likely melted the majority of Earth's mantle to produce a global magma ocean that subsequently cooled and crystallized (e.g. Nakajima and Stevenson, 2015). Understanding the cooling process is critical to determining magma ocean lifetimes and recognizing possible remnant signatures of the magma ocean in present-day mantle heterogeneities (i.e. Labrosse et al., 2007). Modeling this evolution is challenging, however, due to the vastly different timescales and lengthscales associated with turbulent convection (magma ocean) and viscous creep (present-day mantle), in addition to uncertainties in material properties and chemical partitioning. We consider a simplified spherically-symmetric (1-D) magma ocean to investigate both its evolving structure and cooling timescale. Extending the work of Abe (1993), mixing-length theory is employed to determine convective heat transport, producing a high resolution model that captures the ultra-thin boundary layer (few cms) at the surface of the magma ocean. The thermodynamics of mantle melting are represented using a pseudo-one-component model, which retains the simplicity of a standard one-component model while introducing a finite temperature interval for melting (important for multi-component systems). We derive a new high P-T equation of state (EOS) formulation designed to capture the energetics and physical properties of the partially molten system using parameters that are readily interpreted in the context of magma ocean crystallization. This model is used to determine the cooling timescale for a variety of plausible thermodynamic models, with special emphasis on comparing the center-outwards vs bottom-up cooling scenarios that arise from the assumed EOS (e.g., Mosenfelder et al., 2009; Stixrude et al., 2009).

  18. 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.

  19. Experimental constraints on the outgassing dynamics of basaltic magmas

    NASA Astrophysics Data System (ADS)

    Pioli, L.; Bonadonna, C.; Azzopardi, B. J.; Phillips, J. C.; Ripepe, M.

    2012-03-01

    The dynamics of separated two-phase flow of basaltic magmas in cylindrical conduits has been explored combining large-scale experiments and theoretical studies. Experiments consisted of the continuous injection of air into water or glucose syrup in a 0.24 m diameter, 6.5 m long bubble column. The model calculates vesicularity and pressure gradient for a range of gas superficial velocities (volume flow rates/pipe area, 10-2-102 m/s), conduit diameters (100-2 m), and magma viscosities (3-300 Pa s). The model is calibrated with the experimental results to extrapolate key flow parameters such as Co (distribution parameter) and Froude number, which control the maximum vesicularity of the magma in the column, and the gas rise speed of gas slugs. It predicts that magma vesicularity increases with increasing gas volume flow rate and decreases with increasing conduit diameter, until a threshold value (45 vol.%), which characterizes churn and annular flow regimes. Transition to annular flow regimes is expected to occur at minimum gas volume flow rates of 103-104 m3/s. The vertical pressure gradient decreases with increasing gas flow rates and is controlled by magma vesicularity (in bubbly flows) or the length and spacing of gas slugs. This study also shows that until conditions for separated flow are met, increases in magma viscosity favor stability of slug flow over bubbly flow but suggests coexistence between gas slugs and small bubbles, which contribute to a small fraction of the total gas outflux. Gas flow promotes effective convection of the liquid, favoring magma homogeneity and stable conditions.

  20. 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.

  1. 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.

  2. Magma storage prior to the 1912 eruption at Novarupta, Alaska

    USGS Publications Warehouse

    Hammer, J.E.; Rutherford, M.J.; Hildreth, W.

    2002-01-01

    New analytical and experimental data constrain the storage and equilibration conditions of the magmas erupted in 1912 from Novarupta in the 20th century's largest volcanic event. Phase relations at H2O+CO2 fluid saturation were determined for an andesite (58.7 wt% SiO2) and a dacite (67.7 wt%) from the compositional extremes of intermediate magmas erupted. The phase assemblages, matrix melt composition and modes of natural andesite were reproduced experimentally under H2O-saturated conditions (i.e., PH2O=PTOT) in a negatively sloping region in T-P space from 930 ??C/100 MPa to 960 ??C/75 MPa with fO2???N NO + 1. The H2O-saturated equilibration conditions of the dacite are constrained to a T-P region from 850 ??C/ 50 MPa to 880 ??C/25 MPa. If H2O-saturated, these magmas equilibrated at (and above) the level where coerupted rhyolite equilibrated (???100 MPa), suggesting that the andesite-dacite magma reservoir was displaced laterally rather than vertically from the rhyolite magma body. Natural mineral and melt compositions of intermediate magmas were also reproduced experimentally under saturation conditions with a mixed (H2O + CO2) fluid for the same range in PH2O. Thus, a storage model in which vertically stratified mafic to silicic intermediate magmas underlay H2O-saturated rhyolite is consistent with experimental findings only if the intermediates have XH2Ofl=0.7 and 0.9 for the extreme compositions, respectively. Disequilibrium features in natural pumice and scoria include pristine minerals existing outside their stability fields, and compositional zoning of titanomagnetite in contact with ilmenite. Variable rates of chemical equilibration which would eliminate these features constrain the apparent thermal excursion and re-distribution of minerals to the time scale of days.

  3. 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

  4. Insights Into Earthquake Nucleation and Fault Evolution Within Magma

    NASA Astrophysics Data System (ADS)

    Tuffen, H.; Sturton, S.; Dingwell, D. B.

    2004-05-01

    Volcanoes erupting highly viscous magma generate an exceptionally large amount of seismic energy per unit volume. Seismicity is unlike that generated on most tectonic faults, being characterised by repeated small events (Mw < 3) with identical waveforms and short inter-event times (from days to less than a second). Events occur in swarms with typical durations of hours to weeks and have anomalously low frequency content (dominant energy in the 1-3 Hz range). They also show no S-wave arrivals and occur within a small volume typically < 2 km from the surface. New field evidence suggests that these earthquakes may occur on small faults that nucleate by shear fracture of magma during conduit flow (Tuffen et al. Geology 31:1089-1092, 2003). Shear fracture occurs due to stress accumulation when strain rates are too high for purely viscous flow. The anastomosing fracture networks generated share many characteristics with "tectonic" pseudotachylites, including injection veins and evidence for fluidisation. Fracture networks evolve with continued slip into near-planar faults up to five metres in length that are rotated parallel to the magma flow direction. Cataclasite on fault planes bears the textural hallmarks of frictional stick-slip behaviour, with localised grain size reduction, slip localisation, and Riedel shear zones. Eventually, cohesive viscous deformation occurs due to frictional heating and strain rate decrease and completely heals the faults. This forms flow banding in obsidian, which is a kind of high-temperature pseudotachylite. This new evidence may help to explain some properties of the low-frequency earthquakes that occur during eruptions of high-viscosity magma: a) The short inter-event time may be due to high strain rates (10-6 to 10-2 s-1 are typical of eruptions of silicic magma). b) Similar events may be generated by multiple slip pulses on fault planes. c) The seismogenic lifetime of faults may be limited by the high temperature of the faulting

  5. Carbon dioxide in magmas and implications for hydrothermal systems

    USGS Publications Warehouse

    Lowenstern, J. B.

    2001-01-01

    This review focuses on the solubility, origin, abundance, and degassing of carbon dioxide (CO2) in magma-hydrothermal systems, with applications for those workers interested in intrusion-related deposits of gold and other metals. The solubility of CO2 increases with pressure and magma alkalinity. Its solubility is low relative to that of H2O, so that fluids exsolved deep in the crust tend to have high CO2/H2O compared with fluids evolved closer to the surface. Similarly, CO2/H2O will typically decrease during progressive decompression- or crystallization-induced degassing. The temperature dependence of solubility is a function of the speciation of CO2, which dissolves in molecular form in rhyolites (retrograde temperature solubility), but exists as dissolved carbonate groups in basalts (prograde). Magnesite and dolomite are stable under a relatively wide range of mantle conditions, but melt just above the solidus, thereby contributing CO2 to mantle magmas. Graphite, diamond, and a free CO2-bearing fluid may be the primary carbon-bearing phases in other mantle source regions. Growing evidence suggests that most CO2 is contributed to arc magmas via recycling of subducted oceanic crust and its overlying sediment blanket. Additional carbon can be added to magmas during magma-wallrock interactions in the crust. Studies of fluid and melt inclusions from intrusive and extrusive igneous rocks yield ample evidence that many magmas are vapor saturated as deep as the mid crust (10-15 km) and that CO2 is an appreciable part of the exsolved vapor. Such is the case in both basaltic and some silicic magmas. Under most conditions, the presence of a CO2-bearing vapor does not hinder, and in fact may promote, the ascent and eruption of the host magma. Carbonic fluids are poorly miscible with aqueous fluids, particularly at high temperature and low pressure, so that the presence of CO2 can induce immiscibility both within the magmatic volatile phase and in hydrothermal systems

  6. Eddy Flow during Magma Emplacement: The Basemelt Sill, Antarctica

    NASA Astrophysics Data System (ADS)

    Petford, N.; Mirhadizadeh, S.

    2014-12-01

    The McMurdo Dry Valleys magmatic system, Antarctica, forms part of the Ferrar dolerite Large Igneous Province. Comprising a vertical stack of interconnected sills, the complex provides a world-class example of pervasive lateral magma flow on a continental scale. The lowermost intrusion (Basement Sill) offers detailed sections through the now frozen particle macrostructure of a congested magma slurry1. Image-based numerical modelling where the intrusion geometry defines its own unique finite element mesh allows simulations of the flow regime to be made that incorporate realistic magma particle size and flow geometries obtained directly from field measurements. One testable outcome relates to the origin of rhythmic layering where analytical results imply the sheared suspension intersects the phase space for particle Reynolds and Peclet number flow characteristic of macroscopic structures formation2. Another relates to potentially novel crystal-liquid segregation due to the formation of eddies locally at undulating contacts at the floor and roof of the intrusion. The eddies are transient and mechanical in origin, unrelated to well-known fluid dynamical effects around obstacles where flow is turbulent. Numerical particle tracing reveals that these low Re number eddies can both trap (remove) and eject particles back into the magma at a later time according to their mass density. This trapping mechanism has potential to develop local variations in structure (layering) and magma chemistry that may otherwise not occur where the contact between magma and country rock is linear. Simulations indicate that eddy formation is best developed where magma viscosity is in the range 1-102 Pa s. Higher viscosities (> 103 Pa s) tend to dampen the effect implying eddy development is most likely a transient feature. However, it is nice to think that something as simple as a bumpy contact could impart physical and by implication chemical diversity in igneous rocks. 1Marsh, D.B. (2004), A

  7. Magma Plumbing beneath Askja Volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Greenfield, T. S.; White, R. S.

    2013-12-01

    Through a combination of accurate earthquake locations and tomography we have imaged the melt feeding network beneath Askja, a large central volcano, in the Northern Volcanic Zone, Iceland. We have deployed and operated a dense network of 3-component, broadband seismometers around the volcano since 2006 and have recorded a large number of events (on the order of 150 a day). The majority of these are due to an extensive geothermal area within the caldera and tectonically induced earthquakes to the northeast which are not related to the magma plumbing system. More intriguing are the less numerous deeper earthquakes situated in three distinct areas within the volcanic system. These have a lower frequency content to the shallower events which may be the result of highly attenuating lower crust. The deep earthquakes extend from 12-25 km depth, significantly below a well defined brittle-ductile boundary at 8-9 km. These earthquakes indicate the presence of melt moving or degassing at depth as only high strain rates or increased pore fluid pressures would cause brittle fracture in what is normally an aseismic region in the ductile zone. To image the structure beneath Askja, local and regional earthquakes have been used as sources to solve for the velocity structure beneath the volcano. Travel-time tables were created using a finite difference technique and the residuals were used to solve simultaneously for both the earthquake locations and velocity structure. Results showed a pronounced low-velocity anomaly beneath the caldera at a depth of ~5 km. The anomaly is ~10% slower than the initial best fitting 1D model and has a Vp/Vs ratio higher than the surrounding crust, suggesting the presence of increased temperature or partial melt. The body is unlikely to be entirely melt as S-waves are still detected at stations directly above the anomaly. This low-velocity body is slightly deeper than the depth range suggested by InSAR and GPS studies of a deflating source beneath

  8. Oxygen Isotope Trajectories of Crystallizing Arc Magmas

    NASA Astrophysics Data System (ADS)

    Bucholz, C. E.; Jagoutz, O. E.; VanTongeren, J. A.; Wang, Z.

    2014-12-01

    Oxygen isotopes are essential to quantify mantle-derived versus 'recycled' crustal contributions to arc magmas. High δ18O values in igneous rocks (i.e., δ18OSMOW > ~5.7) are generally used to identify supra-crustal inputs, but a melt can also become enriched in 18O due to magmatic differentiation [1,2]. To assess magmatic δ18O values of plutonic rocks, δ18Ozircon values, which are resilient to secondary alteration, are often used. Thus, to disentangle the effects of assimilation versus fractionation, both the absolute increase in melt δ18O due to differentiation and ∆18O(WR-zircon) must be determined. However, existing constraints on the effect of magmatic fractionation on melt δ18O are model-based [2] and calculated relationships between WR SiO2, δ18Ozircon, and δ18Omelt do not incorporate complex melt SiO2, H2O, and temperature (T) relationships [3]. To build upon these initial constraints, we combine the first high-precision δ18O data set on natural samples documenting changes in δ18O melt values with increasing extent of differentiation and modeling which incorporates experimentally constrained melt SiO2, H2O, and T relationships. We analyzed 55 mineral separates with infrared laser-fluorination [4] across large fractionation intervals of two well-studied cumulate sequences: (I) a relatively dry (~1 wt.% H2O initial) tholeiitic sequence (analyzed minerals include plag, opx, cpx, & Fe-rich ol) from the Bushveld Complex and (II) a hydrous high-K sequence (analyzed minerals include ol, cpx, bt, fsp, & qtz) from the Dariv paleoarc in Mongolia. Our results indicate that multiple per mil increases in melt δ18O can occur during magmatic fractionation that in detail depend strongly on melt composition and T. Calculated relationships between WR SiO2 and δ18Ozircon for experimental melt compositions show that wet, 'cool' and dry, 'hot' melts are characterized by larger and smaller ∆18O (melt-zircon) fractionations, respectively. Applying our results to

  9. Magmas, Mushes and Mobility: Thermal Histories of Magma Reservoirs from Combined U-Series and Diffusion Ages

    NASA Astrophysics Data System (ADS)

    Cooper, K. M.; Rubin, A. E.; Schrecengost, K.; Kent, A. J.; Huber, C.

    2014-12-01

    The thermal conditions of magma storage control many aspects of the dynamics of a magma reservoir system. For example, the temperature of magma storage directly relates to the crystallinity, and magmas stored at relatively low temperatures in a crystal mush (more than 40-50% crystalline) must be remobilized (e.g., by heating) before they can be erupted. A better understanding of the duration of magma storage at largely-liquid vs. largely-solid conditions is thus critical to understanding crustal magmatic processes such as magma mixing and for quantifying the hazard potential of a given volcano. Although mineral thermometry reflects the conditions of crystal growth or equilibration, these may not correspond to the thermal conditions of crystal storage. The duration of crystal storage at high temperatures can be quantified by comparing U-series crystal ages with the time scales over which disequilibrium trace-element profiles in the same crystals would be erased by diffusion. In the case of Mount Hood, OR, such a comparison for the two most recent eruptions shows that <12% of the total lifetime of plagioclase crystals (minimum 21 kyr) was spent at temperatures high enough that the magma would be easily mobilized. Partial data sets for other systems suggest such behavior is common, although the diffusion and U-series ages in these cases are from different samples and may not be directly comparable. We will present preliminary data combining U-series dating and diffusion timescales on the same samples for other volcanic systems (e.g., Lassen Volcanic Center, Mount St. Helens, Okataina Volcanic Center, New Zealand). Combining these data with numerical models offers additional insights into the controls on the conditions of storage. In addition, extension of this approach to combining U-Th ages with time scales of Li diffusion in zircon offers a promising new method to quantify thermal histories of silicic reservoir systems.

  10. Understanding which parameters control shallow ascent of silicic effusive magma

    NASA Astrophysics Data System (ADS)

    Thomas, Mark E.; Neuberg, Jurgen W.

    2014-11-01

    estimation of the magma ascent rate is key to predicting volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. Linking potential changes of 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 Soufrière 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. We show that variability in the rate of low frequency seismicity, assumed to correlate directly with the rate of magma movement, can be used as an indicator for changes in ascent rate and, therefore, eruptive activity. The results indicate that conduit diameter and excess pressure in the magma chamber are amongst the dominant controlling variables, but the single most important parameter is the volatile content (assumed as only water). Modeling this parameter in the range of reported values causes changes in the calculated ascent velocities of up to 800%.

  11. Implications of magma chamber dynamics for Soret-related fractionation

    NASA Astrophysics Data System (ADS)

    Carrigan, Charles R.; Cygan, Randall T.

    1986-10-01

    Convection of silicate melts in magma chambers is considered as a possible mechanism for producing significant or, at least, detectable chemical fractionation by the Soret effect. Thermal boundary layer analyses show that Soret fractionation would be, at best, an extremely weak process in evolving magmatic systems. For very large amplitude thermally driven convection at horizontal chamber margins, both the magnitude of the temperature gradient and the time scale for residence of magma in the unstable thermal boundary layer are entirely inappropriate for chemical fractionation of the magma at levels comparable to those obtained in laboratory experiments (5-60%). For a typical convecting body a relative concentration enhancement of 0.04% is obtained as an estimate of the upper limit of Soret fractionation. Even if exceedingly large temperature gradients (of the order of 104 °C/m) in a transient thermal regime are attained by compositionally driven convection, the magma residence time in the thermal boundary layer is so brief (100 s) that much less chemical fractionation results (0.002%). For convection near vertical margins a kinematic model of a countercurrent flow regime provides estimates of chemical separation produced by the thermogravitational fractionation mechanism. Incorporating a range of physical and chemical parameters that characterize magma chamber convection, steady state values of concentration enhancement are even smaller than for fractionation near horizontal boundaries.

  12. Progressive mixed-magma recharging of Izu-Oshima volcano, Japan: A guide to magma chamber volume

    NASA Astrophysics Data System (ADS)

    Ishizuka, Osamu; Taylor, Rex N.; Geshi, Nobuo; Oikawa, Teruki; Kawanabe, Yoshihisa; Ogitsu, Itaru

    2015-11-01

    To discover how magmas move and interact beneath an arc we have examined the temporal and spatial evolution of the largest Izu-Bonin frontal arc volcano Izu-Oshima and the adjacent Izu-Tobu field of backarc volcanoes. Extensive 14C ages and geochemical analysis of subaerial satellite cones as well as other effusives has enabled us to construct a well-constrained ∼ 14 ka record of Izu-Oshima volcanism. The geochemistry of Izu-Oshima is found to change systematically through the last 14 000 yr. Ba/La, Pb/Ce, 87Sr/86Sr, 143Nd/144Nd and 206Pb/204Pb all decrease between 10 ka and 5 ka before increasing between 5 ka and the present, while La/Yb and Nb/Zr show the reverse. These changes in composition match the addition of Izu-Tobu (backarc) magma to the Izu-Oshima plumbing system with a maximum of a 40% Izu-Tobu at around 5 ka. Progressive but asymptotically declining changes in composition through the 10-5 ka period are found to fit a model where pre-mixed magma is episodically added to, and mixed with, a chamber beneath Izu-Oshima. The 5-0 ka period reverses this trend, but is again progressive and declining, suggesting a switch to a progressive influx of pure Izu-Oshima frontal arc magma. Combining flux and eruption volume estimates with the observed geochemical mixing rates indicates that the accessible melt volume of the Izu-Oshima magma system is ∼ 16 km3. Interaction and pre-mixing between the fluid-dominated frontal arc melt and the sediment-bearing backarc magmas must occur at deeper levels within the arc crust. This deep reservoir receives a continuous feed from the frontal arc mantle, but may periodically intercept rising magmas from the backarc source to produce episodes of magma mixing on timescales of ∼ 5000 yr. This study demonstrates that interaction between frontal arc and backarc magma needs to be considered to achieve better understanding of material transfers and elemental budgets at subduction zones.

  13. Phenomena associated with magma expansion into a drift

    SciTech Connect

    Gaffney, E. S.

    2002-01-01

    One of the significant threats to the proposed Yucca Mountain nuclear waste repository has been identified as the possibility of intersection of the underground structure by a basaltic intrusion. Based on the geology of the region, it is assumed that such an intrusion would consist of an alkali basalt similar to the nearby Lathrop Wells cone, which has been dated at about 78 ka. The threat of radioactive release may be either from eruption through the surface above the repository of basalt that had been contaminated or from migration through ground water of radionucleides released as a result of damage to waste packages that interact with the magma. As part of our study of these threats, we are analyzing the phenomena associated with magma expansion into drifts in tuff. The early phenomena of the encounter of volatile-rich basaltic magma with a drift are discussed here.

  14. Flow patterns of magma in dikes, Makhtesh Ramon, Israel

    SciTech Connect

    Baer, G.; Reches, Z.

    1987-06-01

    Directions of magma flow were measured in a system of radial dikes in Makhtesh Ramon, Israel. The flow directions were determined from field observations of segments, fingers, grooves, and groove molds of the dikes. The study indicates that the mean axis of magma flow is subhorizontal toward the north, in agreement with the direction of divergence of the radial dike system. Two modes of flow were observed: (1) regular, bedding-parallel flow in the well-stratified rock units and (2) irregular, meandering flow in the massive rock units. It is suggested that corrugated dike walls in well-stratified host rocks cause magma channelization, and random or self-generated restrictions in massive host rocks cause the apparent meanders. Furthermore, the major lithologic boundaries in the host units strongly affect segmentation of the dikes.

  15. Origin of silicic magma in Iceland revealed by Th isotopes

    SciTech Connect

    Sigmarsson, O.; Condomines, M. ); Hemond, C. ); Fourcade, S. ); Oskarsson, N. )

    1991-06-01

    Th, Sr, Nd, and O isotopes have been determined in a suite of volcanic rocks from Hekla and in a few samples from Askja and Krafla volcanic centers in Iceland. Although {sup 87}Sr/{sup 86}Sr and {sup 143}Nd/{sup 144}Nd ratios are nearly the same for all compositions at Hekla, the ({sup 230}Th/{sup 232}Th) ratios differ and thus clearly show that the silicic rocks cannot be derived from fractional crystallization of a more primitive magma. Similar results are obtained for the Krafla and Askja volcanic centers, where the {delta}{sup 18}O values are much lower in the silicic magma than in the mafic magma. These data suggest that large volumes of silicic rocks in central volcanoes of the neovolcanic zones in Iceland are produced by partial melting of the underlying crust.

  16. Magma storage in a strike-slip caldera

    PubMed Central

    Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.

    2016-01-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions. PMID:27447932

  17. The magma ocean as an impediment to lunar plate tectonics

    NASA Technical Reports Server (NTRS)

    Warren, Paul H.

    1993-01-01

    The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the magma ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the magma ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the magma ocean.

  18. Complexities in Shallow Magma Transport at Kilauea (Invited)

    NASA Astrophysics Data System (ADS)

    Swanson, D. A.

    2013-12-01

    The standard model of Kilauea's shallow plumbing system includes magma storage under the caldera and conduits in the southwest rift zone (SWRZ) and the east rift zone (ERZ). As a field geologist, I find that seemingly aberrant locations and trends of some eruptive vents indicate complexities in shallow magma transport not addressed by the standard model. This model is not wrong but instead incomplete, because it does not account for the development of offshoots from the main plumbing. These offshoots supply magma to the surface at places that tell us much about the complicated stress system within the volcano. Perhaps most readily grasped are fissures peripheral to the north and south sides of the caldera. Somehow magma can apparently be injected into caldera-bounding faults from the summit reservoir complex, but the process and pathways are unclear. Of more importance is the presence of fissures with ENE trends on the east side of the caldera, including Kilauea Iki. Is this a rift zone that forms an acute angle with the ERZ? I think there is another explanation: the main part of the ERZ has migrated ~5 km SSE during the past few tens of thousands of years owing to seaward movement of the south flank, but older parts of the rift zone can be reactivated. The fissures east of the caldera have the ERZ trend and may record such reactivation; this interpretation includes the location of the largest eruption (15th century) known from Kilauea. Whether or not this interpretation has validity, the question remains: what changes in the plumbing system allow magma to erupt east of the caldera? The SWRZ can be divided into two sections, the SWRZ proper and the seismically active part (SASWRZ) southeast of the SWRZ. The total width of both sections is ~4 km. The SWRZ might be migrating SSE, as is the ERZ. Fissures in the SWRZ proper trend SW. Fissures in the SASWRZ, however, have ENE trends like that of the ERZ, although, because of en echelon offsets, the fissure zone itself

  19. The magma ocean as an impediment to lunar plate tectonics

    NASA Astrophysics Data System (ADS)

    Warren, P. H.

    1993-03-01

    The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the magma ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the magma ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the magma ocean.

  20. Deep-level magma ascent rates at Mt. Etna (Italy)

    NASA Astrophysics Data System (ADS)

    Armienti, P.; Perinelli, C.; Putirka, K. D.

    2012-12-01

    Deep-level ascent rates are related to the triggering mechanisms of volcanic eruptions. Recent models and experimental studies have focused on the very shallow parts of magma plumbing systems, mostly the upper few km, and have thus far emphasized that volatile contents and volatile exsolution, are key to understanding eruption dynamics and its fingerprint in the rock texture. Massive volatile loss induces a dramatic change in the liquidus temperature, thus producing observable effects on the rates of nucleation and growth of minerals . Volatile saturation, however, may well occur at greater depths, which means that initial stages of magma ascent may be triggered by events taking place at much greater depths than those recorded by melt inclusions, likely captured at shallow levels. We present a method to evaluate ascent rates deep in a volcano plumbing system, discussing the implications for magma dehydration and using Mt. Etna as case a study. We investigate the deeper levels of magma transport by presenting detailed P-T paths for Etnean magmas, and combining these with Crystal Size Distribution (CSD)-derived cooling rates. The key to this analysis is the recognition that the slope of a P-T path, as determined from mineral-melt thermobarometry, is a result of magma cooling rate, which is in turn a function of magma ascent via the effect of pressure on volatile solubility. We also rely on a thermodynamic treatment of exsolution of non-ideal H2O-CO2 mixtures, based on the Kerric & Jacobs (1981) model, and the simplified solubility model of CO2 (Spera & Bergman, 1980) and H2O (Nicholls, 1980), recalibrated with experimental and melt inclusions data from Mt. Etna. Our modeling is able to decipher magma ascent velocity, v (dH/dt; H = depth, t = time), from ascent rate (dP/dt), and rate of cooling (dT/dt), where ρ is magma density, P is pressure, T is temperature and g is the acceleration of gravity. This equation for v provides a key to investigating the relationships

  1. Magma storage in a strike-slip caldera

    NASA Astrophysics Data System (ADS)

    Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.

    2016-07-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions.

  2. Iron Redox Systematics of Shergottites and Martian Magmas

    NASA Technical Reports Server (NTRS)

    Righter, Kevin; Danielson, L. R.; Martin, A. M.; Newville, M.; Choi, Y.

    2010-01-01

    Martian meteorites record a range of oxygen fugacities from near the IW buffer to above FMQ buffer [1]. In terrestrial magmas, Fe(3+)/ SigmaFe for this fO2 range are between 0 and 0.25 [2]. Such variation will affect the stability of oxides, pyroxenes, and how the melt equilibrates with volatile species. An understanding of the variation of Fe(3+)/SigmaFe for martian magmas is lacking, and previous work has been on FeO-poor and Al2O3-rich terrestrial basalts. We have initiated a study of the iron redox systematics of martian magmas to better understand FeO and Fe2O3 stability, the stability of magnetite, and the low Ca/high Ca pyroxene [3] ratios observed at the surface.

  3. Magma storage in a strike-slip caldera.

    PubMed

    Saxby, J; Gottsmann, J; Cashman, K; Gutiérrez, E

    2016-01-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions. PMID:27447932

  4. The variation of magma discharge during basaltic eruptions

    NASA Astrophysics Data System (ADS)

    Wadge, G.

    1981-12-01

    The rate at which basaltic magma is discharged varies substantially during many eruptions. An individual eruption has an eruption rate ( Qe), the volumetric rate of discharge averaged over the whole or a major part of an eruption, and an effusion rate ( Qf), the volumetric flux rate at any given time. In many examples Qf soon reaches a maximum value after a short period of waxing flow, partly because of magmatic expansion, and then falls more slowly in the later parts of the eruption. The release of elastic strain energy from stored magma and the sub-volcanic reservoir during eruption can produce an exponential form of such waning flow. Comparison of the eruption rates of the historic eruptions of Mauna Loa, Kilauea and Etna shows that for each volcano there is a trend of decreasing Qe with increasing duration of eruption. This relationship is not predicted by a simple elastic model of magma release. Two additional processes are invoked to explain the eruptive histories of these volcanoes: modification of the eruptive conduits, and the continued supply of magma from depth during eruption. Conduits evolving from dikes to plugs by wall-rock erosion or freezing of magma can result in increased early values of Qf and the maintenance of very low values of Qf values for long periods later in the eruption. Discharge variations during three specific eruptions are discussed in detail. Paricutin (1943-1952) had exponentially waning flow, with a time constant of about three years, that is consistent with a deep reservoir. The waning flow of Hekla's 1947-1948 eruption showed some of the characteristics of conduit modification, whilst the 1959 Kilauea Iki eruption is interpreted in terms of a closed system with varying magma rheology.

  5. Cooling magma model for deep volcanic long-period earthquakes

    NASA Astrophysics Data System (ADS)

    Aso, Naofumi; Tsai, Victor C.

    2014-11-01

    Deep long-period events (DLP events) or deep low-frequency earthquakes (deep LFEs) are deep earthquakes that radiate low-frequency seismic waves. While tectonic deep LFEs on plate boundaries are thought to be slip events, there have only been a limited number of studies on the physical mechanism of volcanic DLP events around the Moho (crust-mantle boundary) beneath volcanoes. One reasonable mechanism capable of producing their initial fractures is the effect of thermal stresses. Since ascending magma diapirs tend to stagnate near the Moho, where the vertical gradient of density is high, we suggest that cooling magma may play an important role in volcanic DLP event occurrence. Assuming an initial thermal perturbation of 400°C within a tabular magma of half width 41 m or a cylindrical magma of 74 m radius, thermal strain rates within the intruded magma are higher than tectonic strain rates of ~ 10-14 s-1 and produce a total strain of 2 × 10-4. Shear brittle fractures generated by the thermal strains can produce a compensated linear vector dipole mechanism as observed and potentially also explain the harmonic seismic waveforms from an excited resonance. In our model, we predict correlation between the particular shape of the cluster and the orientation of focal mechanisms, which is partly supported by observations of Aso and Ide (2014). To assess the generality of our cooling magma model as a cause for volcanic DLP events, additional work on relocations and focal mechanisms is essential and would be important to understanding the physical processes causing volcanic DLP events.

  6. Failed magmatic eruptions: Late-stage cessation of magma ascent

    USGS Publications Warehouse

    Moran, S.C.; Newhall, C.; Roman, D.C.

    2011-01-01

    When a volcano becomes restless, a primary question is whether the unrest will lead to an eruption. Here we recognize four possible outcomes of a magmatic intrusion: "deep intrusion", "shallow intrusion", "sluggish/viscous magmatic eruption", and "rapid, often explosive magmatic eruption". We define "failed eruptions" as instances in which magma reaches but does not pass the "shallow intrusion" stage, i. e., when magma gets close to, but does not reach, the surface. Competing factors act to promote or hinder the eventual eruption of a magma intrusion. Fresh intrusion from depth, high magma gas content, rapid ascent rates that leave little time for enroute degassing, opening of pathways, and sudden decompression near the surface all act to promote eruption, whereas decreased magma supply from depth, slow ascent, significant enroute degassing and associated increases in viscosity, and impingement on structural barriers all act to hinder eruption. All of these factors interact in complex ways with variable results, but often cause magma to stall at some depth before reaching the surface. Although certain precursory phenomena, such as rapidly escalating seismic swarms or rates of degassing or deformation, are good indicators that an eruption is likely, such phenomena have also been observed in association with intrusions that have ultimately failed to erupt. A perpetual difficulty with quantifying the probability of eruption is a lack of data, particularly on instances of failed eruptions. This difficulty is being addressed in part through the WOVOdat database. Papers in this volume will be an additional resource for scientists grappling with the issue of whether or not an episode of unrest will lead to a magmatic eruption.

  7. Shallow Magma Ocean on Vesta and Implications for the HEDs

    NASA Astrophysics Data System (ADS)

    Neumann, Wladimir; Breuer, Doris; Spohn, Tilman

    2014-05-01

    The asteroid 4 Vesta is widely held as a differentiated object and as the parent body of the HED meteorites. However, the origin of the HEDs, which is closely linked to the differentiation processes, is still a subject of debate. In particular, various differentiation scenarios have been proposed (e.g. partial melt[1] and residual melt[2,3] scenario) to explain the process of HEDs' formation. Here we present results of numerical calculations of the early thermo-chemical evolution of Vesta, placing constraints on the possible differentiation scenario and on the occurrence and depth of the Vestan mantle magma ocean. We use a numerical heat conduction code[4] that considers accretion, compaction, melting, associated changes of the material properties, partitioning of 26Al, advective heat transport, differentiation by porous flow, and effective cooling of a magma ocean by convection. We show that partitioning of 26Al and its transport with the silicate melt is crucial for the formation of a magma ocean. Previous models that neglect this effect[5,6,7] infer a whole-mantle magma ocean beneath a solid crust. We show that in contrast to these models a deep magma ocean does not form if partitioning of 26Al is considered: Radioactive nuclides are enriched in the melt and relocated towards the surface. Due to the over-production of the radiogenic heat in a shallow layer, the melt fraction increases rapidly above a critical melting threshold (here we assume 50 % of melt) for which the rheology is dominated by the liquid phase, i.e. a magma ocean forms. For formation times of Vesta

  8. Lunar Magma Ocean Crystallization: Constraints from Fractional Crystallization Experiments

    NASA Technical Reports Server (NTRS)

    Rapp, J. F.; Draper, D. S.

    2015-01-01

    The currently accepted paradigm of lunar formation is that of accretion from the ejecta of a giant impact, followed by crystallization of a global scale magma ocean. This model accounts for the formation of the anorthosite highlands crust, which is globally distributed and old, and the formation of the younger mare basalts which are derived from a source region that has experienced plagioclase extraction. Several attempts at modelling the crystallization of such a lunar magma ocean (LMO) have been made, but our ever-increasing knowledge of the lunar samples and surface have raised as many questions as these models have answered. Geodynamic models of lunar accretion suggest that shortly following accretion the bulk of the lunar mass was hot, likely at least above the solidus]. Models of LMO crystallization that assume a deep magma ocean are therefore geodynamically favorable, but they have been difficult to reconcile with a thick plagioclase-rich crust. A refractory element enriched bulk composition, a shallow magma ocean, or a combination of the two have been suggested as a way to produce enough plagioclase to account for the assumed thickness of the crust. Recently however, geophysical data from the GRAIL mission have indicated that the lunar anorthositic crust is not as thick as was initially estimated, which allows for both a deeper magma ocean and a bulk composition more similar to the terrestrial upper mantle. We report on experimental simulations of the fractional crystallization of a deep (approximately 100km) LMO with a terrestrial upper mantle-like (LPUM) bulk composition. Our experimental results will help to define the composition of the lunar crust and mantle cumulates, and allow us to consider important questions such as source regions of the mare basalts and Mg-suite, the role of mantle overturn after magma ocean crystallization and the nature of KREEP

  9. Gas transport through magma near the percolation threshold (Invited)

    NASA Astrophysics Data System (ADS)

    Llewellin, E. W.; Blower, J.; Leslie, D.

    2009-12-01

    Explosive silicic eruptions may simultaneously produce both tube pumice - containing highly-elongate vesicles - and pumice containing sub-spherical vesicles. This has been cited as evidence for strain localization within the volcanic conduit: in a relatively-undeformed axial ‘plug’ bubbles are spherical (regime 1) whilst near the conduit margin rapidly-shearing magma bears elongate bubbles (regime 2). Published numerical studies support this model and indicate that bubbly-magma rheology or viscous heating may be responsible for strain localization. The difference in bubble morphology in these two regimes has important consequences for magma permeability. We present the results of fluid dynamic simulations which quantify the anisotropy of permeability in regime 2 as a function of gas volume fraction and bubble aspect ratio. In this regime, we find that vertical permeability may be many times greater than radial permeability, and that permeability anisotropy is most pronounced near the percolation threshold. We further use a network model to quantify the development of permeability in regime 1. In the case where the predominantly vertical expansion of the magma is slow compared with bubble relaxation time, we find that permeability is, again, anisotropic, but that radial permeability dominates. This effect is also most pronounced near the percolation threshold, and percolation is expected to occur radially before vertical percolation occurs. Our findings imply that gas transport in regime 1 is predominantly radial, whilst vertical gas transport is favoured in regime 2. Consequently, near the percolation threshold, conditions are appropriate for effective degassing of the central magma plug as gas permeates radially to the conduit margin and then vertically upwards. Repeated cycles of percolation, radial gas loss and densification may degas the central magma plug without the development of large gas volume fractions.

  10. Silicic magma entering a basaltic magma chamber: eruptive dynamics and magma mixing — an example from Salina (Aeolian islands, Southern Tyrrhenian Sea)

    NASA Astrophysics Data System (ADS)

    Calanchi, Natale; de Rosa, Rosanna; Mazzuoli, Roberto; Rossi, Pierluigi; Santacroce, Roberto; Ventura, Guido

    1993-09-01

    The Pollara tuff-ring resulted from two explosive eruptions whose deposits are separated by a paleosol 13 Ka old. The oldest deposits (LPP, about 0.2 km3) consist of three main fall units (A, B, C) deposited from a subplinian column whose height (7 14 km) increased with time from A to C, as a consequence of the increased magma discharge rate during the eruption (1 8x106 kg/s). A highly variable juvenile population characterizes the eruption. Black, dense, highly porphyritic, mafic ejecta (SiO2=50 55%) almost exclusively form A deposits, whereas grey, mildly vesiculated, mildly porphyritic pumice (SiO2=56 67%) and white, highly vesiculated, nearly aphyric pumice (SiO2=66 71%) predominate in B and C respectively. Mafic cumulates are abundant in A, while crystalline lithic ejecta first appear in B and increase upward. The LPP result from the emptying of an unusual and unstable, compositionally zoned, shallow magma chamber in which high density mafic melts capped low density salic ones. Evidence of the existence of a short crystal fractionation series is found in the mafic rocks; the andesitic pumice results from complete blending between rhyolitic and variously fractionated mafic melts (salic component up to 60 wt%), whereas bulk dacitic compositions mainly result from the presence of mafic xenocrysts within rhyolitic glasses. Viscosity and composition-mixing diagrams show that blended liquids formed when the visosities of the two end members had close values. The following model is suggested: 1. A rhyolitic magma rising through the metamorphic basement enterrd a mafic magma chamber whose souter portions were occupied by a highly viscous, mafic crystal mush. 2. Under the pressure of the rhyolitic body the nearly rigid mush was pushed upwards and mafic melts were squeezed against the walls of the chamber, beginning roof fracturing and mingling with silicic melts. 3. When the equilibrium temperature was reached between mafic and silicic melts, blended liquids rapidly

  11. Determining the Magma Genesis of Mo Porphyry Deposits

    NASA Astrophysics Data System (ADS)

    Gaynor, S.; Coleman, D. S.; Rosera, J.

    2015-12-01

    The high flux of magma associated with super eruptions is hypothesized to rebuild the deep crust, altering the source(s) of subsequent magmatism. Climax-type Mo deposits are commonly generated immediately after eruption of large ignimbrites within a volcanic field, and provide an opportunity to understand the evolution of magma sources following high flux events. The Questa caldera of the Latir volcanic field, NM exposes a 10 Ma long record of pre-, syn- and post-ignimbrite intrusive and extrusive rocks, and hosts the Questa Climax-type Mo deposit. New detailed geochronology and geochemistry from Questa (including extensive sampling of subsurface rocks in the mine) permit detailed reconstruction of the temporal evolution of magma sources through the waxing and waning stages of super eruption magmatism. Comparison of chemical and isotopic data waxing, ignimbrite, Mo-mineralizing and waning stage magmas reveals several patterns. Waxing and waning magmas (waxing: 29-25.7 Ma; waning: 24.5-19 Ma) have intermediate trace elements and radiogenic isotopes relative to other magmatism (87Sr/86Sri=0.7050 to 0.7070, ɛNd=-5.2 to -7.2). Ignimbrite magmatism (25.5 Ma) is depleted in incompatible elements, enriched in MREE and HREE's and has more evolved radiogenic isotopes (87Sr/86Sri=0.7095, ɛNd=-8.0). Molybdenum mineralizing magmas (24.9-24.5 Ma), are enriched in incompatible elements, depleted in MREE and HREE's and have distinct radiogenic isotopes (87Sr/86Sri=0.7055 to 0.7075, ɛNd=-4.2 to -5.7). We suggest the lower crustal source of magmas changed during ignimbrite generation, and as a result, subsequent mineralizing magmas incorporated more juvenile, mafic components. This mantle influence is the metallogenesis for Climax-type deposits and indicates that deep crustal hybridization, rather than upper crustal differentiation, is pivotal in their generation. These results indicate that a lower crustal source of magmatism for a volcanic field is altered due to super

  12. Magma generation on Mars: Estimated volumes through time

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Schneid, B.

    1991-01-01

    Images of volcanoes and lava flows, chemical analysis by the Viking landers, and studies of meteorites show that volcanism has played an important role in the evolution of Mars. Photogeologic mapping suggests that half of Mars' surface is covered with volcanic materials. Here, researchers present results from new mappings, including estimates of volcanic deposit thicknesses based on partly buried and buried impact craters using the technique of DeHon. The researchers infer the volumes of possible associated plutonic rocks and derive the volumes of magmas on Mars generated in its post-crustal formation history. Also considered is the amount of juvenile water that might have exsolved from the magma through time.

  13. Magmas and reservoirs beneath the Rabaul caldera (Papua New Guinea)

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    The area of Rabaul (Papua New Guinea) consists of at least seven - possibly nine - nested-calderas that have formed over the past 200 ky. The last caldera-forming eruption occurred 1400 y BP, and produced about 10 km3 of crystal-poor, two-pyroxene dacite. Since then, five effusive and explosive eruptive episodes have occurred from volcanic centres along the caldera rim. The most recent of these was preceded by decade-long unrest (starting in 1971) until the simultaneous eruption of Vulcan and Tavurvur, two vents on opposite sides of the caldera in 1994. Most eruptive products are andesitic in composition and show clear signs of mixing/mingling between a basalt and a high-K2O dacite. The hybridization is in the form of banded pumices, quenched mafic enclaves, and hybrid bulk rock compositions. In addition, the 1400 y BP caldera-related products show the presence of a third mixing component; a low-K2O rhyodacitic melt or magma. Geochemical modeling considering major and trace elements and volatile contents shows that the high-K2O dacitic magma can be generated by fractional crystallization of the basaltic magma at shallow depths (~7 km, 200 MPa) and under relatively dry conditions (≤3 wt% H2O). The low-K2O rhyodacitic melt can either be explained by extended crystallization at low temperatures (e.g. in the presence of Sanidine) or the presence of an additional, unrelated magma. Our working model is therefore that basalts ascend to shallow crustal levels before intruding a main silicic reservoir beneath the Rabaul caldera. Storage depths and temperatures estimated from volatile contents, mineral-melt equilibria and rock densities suggest that basalts ascend from ~20 km (~600 MPa) to ~7 km (200 MPa) and cool from ~1150-1100°C before intruding a dacitic magma reservoir at ~950°C. Depending on the state of the reservoir and the volumes of basalt injected, the replenishing magma may either trigger an eruption or cool and crystallize. We use evidence from major and

  14. On the cooling of a deep terrestrial magma ocean

    NASA Astrophysics Data System (ADS)

    Monteux, J.; Andrault, D.; Samuel, H.

    2016-08-01

    Several episodes of complete melting have probably occurred during the first stages of the Earth's evolution. We have developed a numerical model to monitor the thermal and melt fraction evolutions of a cooling and crystallizing magma ocean from an initially fully molten mantle. For this purpose, we numerically solve the heat equation in 1D spherical geometry, accounting for turbulent heat transfer, and integrating recent and strong experimental constraints from mineral physics. We have explored different initial magma ocean viscosities, compositions, thermal boundary layer thicknesses and initial core temperatures. We show that the cooling of a thick terrestrial magma ocean is a fast process, with the entire mantle becoming significantly more viscous within 20 kyr. Due to the slope difference between the adiabats and the melting curves, the solidification of the molten mantle occurs from the bottom up. In the meantime, a crust forms due to the high surface radiative heat flow, the last drop of fully molten silicate is restricted to the upper mantle. Among the studied parameters, the magma ocean lifetime is primarily governed by its viscosity. Depending on the thermal boundary layer thickness at the core-mantle boundary, the thermal coupling between the core and magma ocean can either insulate the core during the magma ocean solidification and favor a hot core or drain the heat out of the core simultaneously with the cooling of the magma ocean. Reasonable thickness for the thermal boundary layer, however, suggests rapid core cooling until the core-mantle boundary temperature results in a sluggish lowermost mantle. Once the crystallization of the lowermost mantle becomes significant, the efficiency of the core heat loss decreases. Since a hotter liquidus favors crystallization at hotter temperatures, a hotter deep mantle liquidus favors heat retention within the core. In the context of an initially fully molten mantle, it is difficult to envision the formation of a

  15. Magma dynamics above the Karoo plume, South Africa

    NASA Astrophysics Data System (ADS)

    Ferre, Eric; Geissman, John; Stephanie, Maes; Aneesa, Gillum; Julian, Marsh

    2015-04-01

    Mantle plumes produce voluminous amounts of magma (106 km3) during a short period of time (106 years). The heat input of such plumes into sedimentary basins has been proposed as a significant factor in several global climatic crises. Indeed heat transfer through conductive and advective processes is likely to bake organic matter-rich sediments, which in turn may release greenhouse gases (CO2 and CH4). One of the yet poorly understood aspects of this model is the regional pattern of magma flow. The objective of this study is to constrain magma dynamics in the Karoo Large Igneous Province (LIP) intruded in a continental basin of South Africa. Magnetic fabrics provide an efficient and accurate mean to determine magma flow direction in gabbroic rocks. The anisotropy of magnetic susceptibility (AMS) is particularly suited for this type of study. A previous study had shown that the AMS fabric is a reliable proxy for magma flow as long as samples are collected from the upper chilled margin of a sill. The central part is more complex due to interference caused by thermal convection. Oriented core samples were collected from 30 different sills and yielded 1598 specimens for AMS measurements. The low-field magnetic susceptibility Km ranges widely from about 100 to 20,000 . 10-6 [SI], while the degree of anisotropy P' ranges from 1.01 to 1.10. Thermomagnetic experiments reveal that the main magnetic carrier is titanomagnetite with variable ulvöspinel content. This is confirmed by measurement of hysteresis properties that also indicate that titanomagnetite in general has a pseudo-single domain grain size. The results of this study clearly indicate that magma flow followed a main NW-SE direction in the studied area. The AMS directional data is consistent with the nearly horizontal attitude of the sill in 23 out of 30 cases, with subvertical K3 axes. In 5 out of 30 sills, K3 axes are subhorizontal, characterized by scattered directional data and are considered anomalous AMS

  16. Output rate of magma from active central volcanoes

    NASA Technical Reports Server (NTRS)

    Wadge, G.

    1980-01-01

    For part of their historic records, nine of the most active volcanoes on earth have each erupted magma at a nearly constant rate. These output rates are very similar and range from 0.69 to 0.26 cu m/s. The volcanoes discussed - Kilauea, Mauna Loa, Fuego, Santiaguito, Nyamuragira, Hekla, Piton de la Fournaise, Vesuvius and Etna - represent almost the whole spectrum of plate tectonic settings of volcanism. A common mechanism of buoyantly rising magma-filled cracks in the upper crust may contribute to the observed restricted range of the rates of output.

  17. The Relationship Between Amphibole Cumulates and Adakite Magma

    NASA Astrophysics Data System (ADS)

    Rooney, T. O.

    2009-12-01

    Amphibole, while uncommon as a primary fractioning phase is increasingly recognized as a key constituent in the petrogenesis of arc magmas. Fractional crystallization of water-saturated arc magmas in the lower crust can yield substantial volumes amphibole cumulates that, depending on the pressure of crystallization, may also contain garnet. Fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production adakite magmas. The origin of adakites, defined by their heavy REE and Y depletion and Sr enrichments, have vigorously debated since their re-discovery in Panama two decades ago. In addition to widespread modern adakitic volcanism, the Panamanian portion of the Central American Arc preserves the magmatic record of arc development in close spatial association with younger magmatism. Late-Oligocene hypabyssal crystal-rich andesites from Cerro Patacon are preserved near the Panama Canal region. These contain nodules of amphibole cumulates, and may be used to examine the amphibole-fractionation model for adakite origin. The cumulate nodules are ~6 cm in diameter and are almost entirely composed of 5-10mm amphibole crystals (dominantly ferri-tschermakite), and are accompanied in the host andesites by amphibole phenocrysts, antecrysts and megacryts. Cerro Patacon andesites have REE concentrations that plot at the most depleted end of the array defined by similarly differentiated (58-60% SiO2) Central American Arc magmas, and exhibit a distinctive depletion in the middle REE. These geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the Cerro Patacon andesite. Sr/Y which is used as a geochemical tool for discriminating adakites from other arc magams, is transitional in the Cerro Patcon andesites. However La/Yb is within the range for ‘normal’ arc magmas and shows that amphibole fractionation alone is insufficient to generate adakite magmas - some garnet

  18. Magma mingling in the panozero sanukitoid intrusion, baltic shield

    NASA Astrophysics Data System (ADS)

    Rollinson, H.

    2003-04-01

    The 2.7 Ga Panozero pluton is a composite intrusion comprising magmas of sanukitoid affinity, intrusive into the ca. 2.75 Ga Segozero greenstone belt in western Karelia in the Baltic Shield. The intrusion is predominantly a monzonite, is elliptical in form (9 x 6 km) and is undeformed. Along the eastern margin of the intrusion a wide variety of cogenetic magmas have been mapped ranging in composition from biotite-hornblendites, through monzo-gabbro and monzonite to quartz-monzonite. The contact relationships between the different phases of the intrusion are complex and imply magma mingling and incomplete mixing between magma types. The monzogabbros show a gradational relationship with the monzodiorites, but occur as inclusions within, and contain inclusions of, the monzonite implying two coexisting melts. Similar relationships exist between the monzonite and quartz monzonite and in places there is a gneissose banding of the darker phase within the lighter phase. The quartz-syenite is intrusive into all earlier phases, although the latest phase is hornblendite. This is present as net veining in gabbro and as irregular veins, dykes and as irregularly shaped xenoliths in monzonite, quartz monzonite and syenite. The irregular form and deformed state of the hornblendite inclusions within the earlier magmas implies that the hornblendite was emplaced whilst the host magma was hot. Also developed along the eastern margin of the intrusion are breccia pipes. These are found in the monzodiorites, monzonites and in quartz monzonites. They contain elliptical fragments up to 20 cm long of hornblendite, tremolitite, epidotised amphibolite and in the monzodiorite euhedral feldspars with felsic reaction rims. The matrix of the breccias is often very similar to the composition of their host rock. Many of the fragments are thought to be derived from the adjacent greenstone belt. However, metabasaltic rocks are not recorded from this part of the greenstone belt and so may be derived

  19. Do Plinian Eruptions of Mafic Magma Require Fast Ascent Rates?

    NASA Astrophysics Data System (ADS)

    Szramek, L. A.; Gardner, J. E.

    2008-12-01

    Although rare, mafic magma is known to erupt explosively in Plinian fashion. Given that models for such eruptions often invoke high viscosities as pre-requisite, mafic magmas erupting explosively seems to pose a quandary. One possibility is that such magmas can erupt explosively, if they ascend towards the surface very fast, creating conditions that lead to explosive degassing and fragmentation. In order to estimate how fast mafic magma ascends in such eruptions, we are carrying out series of isothermal decompression experiments to examine groundmass textures in natural samples from such eruptions to infer ascent rates. One eruption we are examining is the 122 B.C. Plinian eruption of hawaiite from Mt Etna. Prior work suggests that this magma was stored at 1025°C and 75 MPa before erupting. We find that the groundmass has a total crystallinity of 58 vol.%, consisting of 34 vol.% pyroxene, 20 vol.% plagioclase, and 4 vol.% Fe- Ti oxides. The area number densities are on the order of 3-7 x 10-2μm-2. Thus far, we have been unable to mimic its groundmass textures with either the single-step or multi-step decompression experiments, in which pressure dropped from 75 MPa to 13 MPa at rates ranging from 0.18 to 0.001 MPa s -1. Although the slowest decompression produced the correct groundmass assemblage and total crystallinity it has twice the plagioclase and far too little pyroxene. In addition, area number densities are 1-2 orders of magnitude less. Additionally, hopper shaped plagioclase is observed in all but the slowest experiment, whereas the natural sample contains only tabular to acicular plagioclase. Our results suggest that the textures of the hawaiite scoria cannot be explained by rapid ascent alone. One possibility is that the magma stalled and slowly crystallized prior to eruption. The additional microlites would have increased the viscosity of the melt, allowing the mafic magma to erupt in a Plinian style. In order to further test the rapid ascent model for

  20. Magmatic Water Contents in Mariana and Izu Arc Magmas

    NASA Astrophysics Data System (ADS)

    Parman, S.; Grove, T.; Plank, T.

    2002-05-01

    We estimate the magmatic water content of magmas from the Mariana-Izu arc system using experimental phase equilibria. Our goal is to produce primary H2O estimates for Mariana-Izu magmas to compare with along-arc variations in the trace element and isotopic compositions of the magmas. Such correlations can be used to quantify the chemical inputs into the sub-arc mantle wedge from the subducting Pacific plate. The experiments are performed in externally heated, gas-pressure vessels. H2O-saturatation is maintained throughout the experiment, as well as an fO2 at the Ni-NiO buffer. The experimental melts contain between 5.5 and 6.2 wt.% H2O. The observed LLD for Pagan island in the Mariana arc falls midway between the hydrous 200 MPa LLD and an anhydrous LLD modeled using the MELTS program [Ghiorso and Sack, 1995], suggesting an initial H2O content of ~3 wt.%. This in good agreement with the H2O content (2.7 wt.%, Plank, unpub. data) of an olivine-hosted melt inclusion contained in the Pagan samples. Experiments at lower H2O contents are being conducted to verify this estimate. The LLD for Hachijo-jima in the Izu arc follows the 200 MPa, H2O saturated LLD fairly well, though there is significant scatter in the natural sample compositions, likely due to plagioclase accumulation. Thus our preliminary results indicate higher H2O contents in the Hachijo-jima magmas (5-7 wt.%) relative to the Pagan magmas. The compositions of minerals in the mafic Pagan sample (PAF3b; Woodhead, 1989) indicate a history of mixing. Relative to the hydrous experiments, olivine (ol) phenocrysts in the sample have higher Mg#s (0.867 vs. 0.809), while plag phenocrysts have lower anorthite (An) contents (0.889 vs. 0.946). The lower An contents are consistent with the lower estimated H2O contents in the Pagan magmas relative to the experiments, while the higher ol Mg# indicates that even the most mafic Pagan sample is fractionated or a mixed magma. Glomerocrysts in the sample contain ol with lower

  1. Imaging magma plumbing beneath Askja volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Greenfield, Tim; White, Robert S.

    2015-04-01

    Volcanoes during repose periods are not commonly monitored by dense instrumentation networks and so activity during periods of unrest is difficult to put in context. We have operated a dense seismic network of 3-component, broadband instruments around Askja, a large central volcano in the Northern Volcanic Zone, Iceland, since 2006. Askja last erupted in 1961, with a relatively small basaltic lava flow. Since 1975 the central caldera has been subsiding and there has been no indication of volcanic activity. Despite this, Askja has been one of the more seismically active volcanoes in Iceland. The majority of these events are due to an extensive geothermal area within the caldera and tectonically induced earthquakes to the northeast which are not related to the magma plumbing system. More intriguing are the less numerous deeper earthquakes at 12-24km depth, situated in three distinct areas within the volcanic system. These earthquakes often show a frequency content which is lower than the shallower activity, but they still show strong P and S wave arrivals indicative of brittle failure, despite their location being well below the brittle-ductile boundary, which, in Askja is ~7km bsl. These earthquakes indicate the presence of melt moving or degassing at depth while the volcano is not inflating, as only high strain rates or increased pore fluid pressures would cause brittle fracture in what is normally an aseismic region in the ductile zone. The lower frequency content must be the result of a slower source time function as earthquakes which are both high frequency and low frequency come from the same cluster, thereby discounting a highly attenuating lower crust. To image the plumbing system beneath Askja, local and regional earthquakes have been used as sources to solve for the velocity structure beneath the volcano. Travel-time tables were created using a finite difference technique and the residuals were used to solve simultaneously for both the earthquake locations

  2. Supervolcano eruptions driven by melt buoyancy in large silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Malfait, Wim J.; Seifert, Rita; Petitgirard, Sylvain; Perrillat, Jean-Philippe; Mezouar, Mohamed; Ota, Tsutomu; Nakamura, Eizo; Lerch, Philippe; Sanchez-Valle, Carmen

    2014-02-01

    Super-eruptions that dwarf all historical volcanic episodes in erupted volume and environmental impact are abundant in the geological record. Such eruptions of silica-rich magmas form large calderas. The mechanisms that trigger these super-eruptions are elusive because the processes occurring in conventional volcanic systems cannot simply be scaled up to the much larger magma chambers beneath supervolcanoes. Over-pressurization of the magma reservoir, caused by magma recharge, is a common trigger for smaller eruptions, but is insufficient to generate eruptions from large supervolcano magma chambers. Magma buoyancy can potentially create sufficient overpressure, but the efficiency of this trigger mechanism has not been tested. Here we use synchrotron measurements of X-ray absorption to determine the density of silica-rich magmas at pressures and temperatures of up to 3.6GPa and 1,950K, respectively. We combine our results with existing measurements of silica-rich magma density at ambient pressures to show that magma buoyancy can generate an overpressure on the roof of a large supervolcano magma chamber that exceeds the critical overpressure of 10-40MPa required to induce dyke propagation, even when the magma is undersaturated in volatiles. We conclude that magma buoyancy alone is a viable mechanism to trigger a super-eruption, although magma recharge and mush rejuvenation, volatile saturation or tectonic stress may have been important during specific eruptions.

  3. Multiple Use of Magma Pathways: Mechanism for Hybridization

    NASA Astrophysics Data System (ADS)

    Hasalova, P.; Weinberg, R. F.; Reichardt, H.

    2010-12-01

    In the Karakoram Shear Zone, Ladakh, NW India, Miocene leucogranitic dykes form an extensive, varied and complex network, linking the Pangong Range anatectic terrane with leucogranites of the Karakoram Batholith. Water-fluxed Miocene anatexis occurs at upper amphibolite conditions, and was contemporaneous with shearing. The network is characterized by continuous and interconnected leucosomes and dykes, with only rare cross-cutting relationships, forming dyke swarms and more chaotic injection complexes where magmatic rocks cover up to 50% of the outcrop area. Despite this volume of magma, the system was always controlled by solid framework suggesting that it did not flow en masse and that the magma network was not all liquid simultaneously. Leucogranites in this network, carry an isotopic signature intermediate between the two main anatectic rocks in the source, suggesting efficient homogenization of the magmatic products. This meso- to macroscale complex network is also reflected at microscale. Microstructural observations indicate that these magmatic rocks consist dominantly of Qtz, Plg and Kfs in two very distinct appearances, as large irregularly-shaped grains with cuspate boundaries, or/and as fine-grained minerals with lobate boundaries. These two show intimate spatial relationship with fine-grained material forming semi- to continuous corridors to wide channels that links together and form an extensive network branching around large grains. We suggest, that the large minerals represent early formed solid granitic framework that was later invaded by a new melt batch that exploits microfractures in between and through the framework forming crystals giving rise to this interconnected network. The presence of later crystallized melt and its interaction with the solid rock was inferred from the following microstructures: (i) narrow, tortuous corridors of fine-grained minerals cutting across or lining the boundaries of larger grains, interpreted to be remnants of

  4. Magma supply rates inferred from cinder cone volumes

    NASA Astrophysics Data System (ADS)

    Bemis, K. G.; Borgia, A.; Neri, M.; Kervyn, M.

    2010-12-01

    Revisiting the question of how cinder cones grow suggests the possibility of inferring magma supply rates from cinder cones sizes. We start with a conceptual model of cinder cone growth: (1) Eruption volume flux increases rapidly and then decreases exponentially. (2) Cinder cones get steeper during the initiation of the eruption and then maintain a constant steepness. (3) The initial basal diameter varies with volume flux into the cone. Based on these constraints, we propose a general form for the relationship between cinder cone volume and magma supply rate: V = Q(exp(-t/b)/b - exp(-t/a)/a), where V is volume (in m3), Q is the maximum potential magma flux (in m3/s), t is time (in s), a is a damping factor (in s) controlling the decline in volume flux, and b is a factor controlling the initial increase in volume flux. Then we use the data available on the growth of cinder cones from four modern eruptions to show the relevance of our model and to constrain the supply curves. All four modern cones (Paricutin, Mexico which erupted 1943-1974; Tolbachik, Kamchatka which erupted in 1975-1976; Cono del Laghetto, Mount Etna, Italy which formed in 2001; and a small cone on the summit of Oldoinyo Lengai, Tanzania, which formed during the 2007 eruption) show the basic growth pattern: initial rapid growth followed by declining growth (Figure 1). The regression results yeild the following magma supply rates: The southern Tolbachik cones have the largest predicted magma supply at ~100 m3/s. Paricutin and Laghetto are around 9 m3/s. The Oldoinyo Lengai cone has a magma supply of ~0.5 m3/s. The northern Tolbachik cone has the lowest magma supply of ~0.1 m3/s. In contrast, the damping factor a is generally on the order of 107 (it varies from 8 x 106 at southern Tolbachik to 4 x 107 at northern Tolbachik). The parameter b controlling the initial increase is generally small (<1). The predicted magma supply does not seem to be very sensitive to either parameter. Thus we suggest that

  5. Water-saturated magmas in the Panama Canal region: a precursor to adakite-like magma generation?

    NASA Astrophysics Data System (ADS)

    Rooney, Tyrone O.; Franceschi, Pastora; Hall, Chris M.

    2011-03-01

    Amphibole, while uncommon as a phenocryst in arc lavas, is increasingly recognized as a key constituent in the petrogenesis of arc magmas. Fractional crystallization of water-saturated arc magmas in the lower crust can yield substantial volumes of amphibole cumulates that, depending on the pressure of crystallization, may also contain garnet. Fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production of magmas that contain an adakitic signature. This study examines newly dated Late-Oligocene (25.37 ± 0.13 Ma) hypabyssal amphibole-rich andesites from Cerro Patacon in the Panama Canal region. These andesites contain nodules of amphibole cumulates that are ~4-6 cm in diameter and are almost entirely composed of 5-10-mm amphibole crystals (dominantly ferri-tschermakite). Geochemical variations, optical and chemical zoning of the Cerro Patacon amphiboles are consistent with their evolution in a crystal mush environment that had at least one recharge event prior to entrainment in the host andesite. Amphiboles hosted within the cumulate nodules differ from those hosted in the Cerro Patacon andesite and contain consistently higher values of Ti. We suggest these nodules represent the early stages of fractionation from a water-saturated magma. Cerro Patacon andesites have REE concentrations that plot at the most depleted end of Central American Arc magmas and exhibit a distinctive depletion in the middle REE. These geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the Cerro Patacon andesite, consistent with the petrographic evidence. Fractionation of water-saturated magmas is a mechanism by which adakitic compositions may be produced, and the Cerro Patacon andesites do exhibit adakite-like geochemical characteristics (e.g., elevated Sr/Y; 28-34). However, the relatively elevated concentrations of Y and HREE indicate garnet was not stable in the fractionating

  6. Magma energy research project: state-of-the-project report, October 1, 1978

    SciTech Connect

    Colp, J.L.; Traeger, R.K.

    1980-02-01

    The feasibility of extracting energy from magma bodies is investigated. The work done in FY 76, 77, and 78 in the following tasks are summarized; resource location and definition, source tapping, magma characterization and materials compatibility, and energy extraction. (MHR)

  7. Evolution of magma feeding system in Kumanodake agglutinate activity, Zao Volcano, northeastern Japan

    NASA Astrophysics Data System (ADS)

    Takebe, Yoshinori; Ban, Masao

    2015-10-01

    The Kumanodake agglutinate of Zao Volcano in northeastern Japan consists of pyroclastic surge layers accumulated during the early part of the newest stage of activity (ca. 33 ka to present). Our petrologic study of this agglutinate based on systematically collected samples aims to reveal the evolution of magma feeding system. To understand the magma evolution, we have examined samples from the agglutinate by using petrologic data including, petrography, analysis of minerals (plagioclase, pyroxene, and olivine), glass compositions, and whole rock major element and trace element (Ba, Sr, Cr, Ni, V, Rb, Zr, Nb, and Y) compositions. Agglutinate are mixed, medium-K, calc-alkaline olv-cpx-opx basaltic andesite (55.2-56.2% SiO2). Results show that the magma feeding system comprised a shallow felsic chamber injected by mafic magma from depth. The felsic magma (59-62% SiO2, 950-990 °C), which was stored at a shallower depth, had orthopyroxene (Mg# = 60-69), clinopyroxene (Mg# = 65-71), and low-An plagioclase (Anca. 58-70). The mafic magma is further divisible into two types: less-differentiated and more-differentiated, designed respectively as an initial mafic magma-1 and a second mafic magma-2. The original mafic magma-1 was olivine (Fo~ 84) basalt (ca. 48-51% SiO2, 1110-1140 °C). The second mafic magma-2, stored occasionally at 4-6 km depth, was basalt (1070-1110 °C) having Foca. 80 olivine and high-An (Anca. 90) plagioclase phenocrysts. These two magmas mixed (first mixing) to form hybrid mafic magma. The forced injections of the hybrid mafic magmas activated the felsic magma, and these two were mixed (second mixing) shortly before eruptions. The explosivity is inferred to have increased over time because the abundance of large scoria increased. Furthermore, the erupted magma composition became more mafic, which reflects increased percentage of the hybrid mafic magma involved in the second mixing. At the beginning of activity, the mafic magma also acted as a heat

  8. Crystallization of Magma. CEGS Programs Publication Number 14.

    ERIC Educational Resources Information Center

    Berry, R. W.

    Crystallization of Magma is one of a series of single-topic problem modules intended for use in undergraduate geology and earth science courses. Through problems and observations based on two sets of experiments, this module leads to an understanding of how an igneous rock can form from molten material. Environmental factors responsible for…

  9. Degassing of rhyolitic magma during ascent and emplacement

    SciTech Connect

    Westrich, H.R.; Stockman, H.W.; Eichelberger, J.

    1988-06-10

    The degassing history of a rhyolitic igneous system was documented from analyses of drill core samples through the extrusive and intrusive portions of Obsidian Dome and of surface samples of associated tephra. The initial volatile composition of the Inyo magma was estimated to be 4.0 wt % H/sub 2/O, 500 ppm F, 800 ppm Cl, and 80 ppm S. Retained volatile contents of glassy and crystalline samples reflect the effects of decompression and second boiling. Decompression is rapid and involves loss of water-rich fluid until a close approach to lithostatic equilibrium is achieved. Second boiling is a slower process and produces a chlorine-rich fluid, some of which can be trapped during development of extremely fine crystallization textures. Nearly complete dewatering during decompression of surface-extruded magma strongly undercools the system (..delta..Tapprox. =175 /sup 0/C), suppressing crystallization and yielding glassy rhyolitic lava. Partial degassing of shallowly intruded magma permits pervasive crystallization even at high cooling rates. The subvolcanic intrusive regime is the zone of maximum volatile release because second boiling is incomplete in extrusives, and volatile-bearing crystalline phases are stable in magma crystallized at greater depth. copyright Amierican Geophysical Union 1988

  10. 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.

  11. Loki Patera as the Surface of a Magma Sea

    NASA Technical Reports Server (NTRS)

    Matson, D. L.; Davies, A. G.; Veeder, G. J.; Rathbun, J. A.; Johnson, T. V.

    2004-01-01

    Inspired by the finding of Schubert et al that Io's figure is consistent with a hydrostatic shape, we explore the consequences of modeling Loki Patera as the surface of a large magma sea. This model is attractive because of its sheer simplicity and its usefulness in interpreting and predicting observations. Here, we report on that work.

  12. 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.

  13. Insights into high temperature tensional fracturing in silicic magma

    NASA Astrophysics Data System (ADS)

    Lamb, Oliver; Lavallée, Yan; De Angelis, Silvio; Hornby, Adrian

    2015-04-01

    During dome-forming eruptions, the rapid transition from effusive to explosive activity is a direct consequence of strain localisation in magma. A deformation mechanism map of magma subjected to strain localisation will help develop accurate numerical models, which, coupled to an understanding of the mechanics driving the monitored geophysical signals precursor to failure, will enhance eruption forecasts. Here we present our work where seismic data is combined with experimental work to give insights into high temperature tensional fracturing in magma. The seismic data is derived from multiple recent dome-forming eruptions including Unzen (Japan), Volcán de Colima (Mexico) and Mt. St. Helens (USA). For the analysis we implemented various methods to study temporal variations in seismicity, such as: automatic event detection, statistical analysis of time-series, waveform correlation, and singular value decomposition. Preliminary results have highlighted various processes during dome formation such as: sub-weekly cycles, clusters during spine extrusion, and variations in precursors to dome extrusion. In our experiments, samples from the above volcanoes were placed under tensional conditions at high temperatures and acoustic emissions were recorded. The data is analysed and compared to the natural seismic data so that constraints may be placed on the conditions of the natural seismogenic sources. Using a combination of field and experimental data promises a greater understanding of the processes affecting the rise of magma during an eruption. This will help with the challenge of forecasting and hazard mitigation during dome-forming eruptions worldwide.

  14. 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.

  15. The crystal's view of upper-crustal magma reservoirs

    NASA Astrophysics Data System (ADS)

    Cooper, K. M.; Kent, A. J.; Huber, C.; Stelten, M. E.; Rubin, A. E.; Schrecengost, K.

    2015-12-01

    Upper-crustal magma reservoirs are important sites of magma mixing, crustal refining, and magma storage. Crystals residing in these reservoirs have been shown to represent valuable archives of the chemical and physical evolution of reservoirs, and the time scales of this evolution. This presentation addresses the question of "What do crystals "see" and record about processes within the upper crust? And how is that view similar or different between plutonic and volcanic records?" Three general observations emerge from study of the ages of crystals, combined with crystal-scale geochemical data: 1) Patterns of isotopic and trace-element data over time in zircon crystals from a given magmatic system (e.g., Yellowstone, WY, and Taupo Volcanic Zone, New Zealand) can show systematic changes in the degree of heterogeneity, consistent with extraction of melts from a long-lived (up to 100s of kyr), heterogeneous crystal mush and in some cases continued crystallization and homogenization of the magma during a short period (< a few kyr) preceding eruption. 2) Thermal histories of magma storage derived from crystal records also show that the vast majority of time recorded by major phases was spent in storage as a crystal mush, perhaps at near-solidus conditions. 3) Comparison of ages of accessory phases in both plutonic blocks and host magmas that brought them to the surface do not show a consistent relationship between the two. In some cases, zircons from plutonic blocks have age spectra much older than zircon in the host magma. In other cases, host and plutonic block zircons have similar age spectra and chemical characteristics, suggesting a closer genetic connection between the two. These observations suggest that crystals in plutonic bodies, if examined at similar spatial and temporal scales to those in volcanic rocks, would show records that are highly heterogeneous in chemistry and age on the scale of a pluton or a lobe of a pluton, but that local regions of limited

  16. Magma Plumbing and Emplacement Mechanisms within Sedimentary Basins

    NASA Astrophysics Data System (ADS)

    Schofield, Nick; Magee, Craig; Holford, Simon; Jackson, Christopher

    2013-04-01

    In recent years our understanding of sub-volcanic magmatic plumbing systems has been revolutionised by the study of hydrocarbon industry 3D seismic reflection datasets from offshore sedimentary basins. In particular, 3D seismic reflection data has provided important insights into sheet intrusion geometry and emplacement mechanisms as well as linkages and magma flow between multiple intrusions within sill-complexes. However, even high-quality 3D seismic reflection datasets have a limit to what they can resolve; thus, to allow a better understanding of detailed emplacement mechanisms and to test the validity of subsurface-based interpretations, it is critical to bridge the resolution gap that exists between seismic and outcrop datasets. Magmatic sheet (sill) intrusions contribute significantly to the upper crustal magma transport network. The emplacement mechanism of the magmatic sheets controls the final geometry of the intrusions and the characteristics of host rock deformation. Previous observations have highlighted the preponderance of brittle structures (e.g. intrusive steps and broken brides) associated with shallow-level sheet intrusions. However, recent studies have suggested that non-brittle host rock behaviour also occurs, particularly related to the formation of magma fingers during shallow-level sill intrusion. Importantly, these structures can provide insights into emplacement style and magma flow directions. Here, we examine both brittle and non-brittle intrusion mechanisms and structures using both field- and 3D seismic-based observations from a series of widespread and variable magmatic systems. Non-brittle emplacement (i.e. magma finger and lobe development) appears to be primarily associated with viscous flow of the host rock during intrusion and is therefore intimately linked to the contemporaneous host rock rheology as well as magma dynamics. Purely brittle and non-brittle emplacement processes are found to be end members with many intrusions

  17. 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

  18. Seismic tremors and magma wagging during explosive volcanism.

    PubMed

    Jellinek, A Mark; Bercovici, David

    2011-02-24

    Volcanic tremor is a ubiquitous feature of explosive eruptions. This oscillation persists for minutes to weeks and is characterized by a remarkably narrow band of frequencies from about 0.5 Hz to 7 Hz (refs 1-4). Before major eruptions, tremor can occur in concert with increased gas flux and related ground deformation. Volcanic tremor is thus of particular value for eruption forecasting. Most models for volcanic tremor rely on specific properties of the geometry, structure and constitution of volcanic conduits as well as the gas content of the erupting magma. Because neither the initial structure nor the evolution of the magma-conduit system will be the same from one volcano to the next, it is surprising that tremor characteristics are so consistent among different volcanoes. Indeed, this universality of tremor properties remains a major enigma. Here we employ the contemporary view that silicic magma rises in the conduit as a columnar plug surrounded by a highly vesicular annulus of sheared bubbles. We demonstrate that, for most geologically relevant conditions, the magma column will oscillate or 'wag' against the restoring 'gas-spring' force of the annulus at observed tremor frequencies. In contrast to previous models, the magma-wagging oscillation is relatively insensitive to the conduit structure and geometry, which explains the narrow band of tremor frequencies observed around the world. Moreover, the model predicts that as an eruption proceeds there will be an upward drift in both the maximum frequency and the total signal frequency bandwidth, the nature of which depends on the explosivity of the eruption, as is often observed. PMID:21350484

  19. 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].

  20. Magma Reservoirs Feeding Giant Radiating Dike Swarms: Insights from Venus

    NASA Technical Reports Server (NTRS)

    Grosfils, E. B.; Ernst, R. E.

    2003-01-01

    Evidence of lateral dike propagation from shallow magma reservoirs is quite common on the terrestrial planets, and examination of the giant radiating dike swarm population on Venus continues to provide new insight into the way these complex magmatic systems form and evolve. For example, it is becoming clear that many swarms are an amalgamation of multiple discrete phases of dike intrusion. This is not surprising in and of itself, as on Earth there is clear evidence that formation of both magma reservoirs and individual giant radiating dikes often involves periodic magma injection. Similarly, giant radiating swarms on Earth can contain temporally discrete subswarms defined on the basis of geometry, crosscutting relationships, and geochemical or paleomagnetic signatures. The Venus data are important, however, because erosion, sedimentation, plate tectonic disruption, etc. on Earth have destroyed most giant radiating dike swarm's source regions, and thus we remain uncertain about the geometry and temporal evolution of the magma sources from which the dikes are fed. Are the reservoirs which feed the dikes large or small, and what are the implications for how the dikes themselves form? Does each subswarm originate from a single, periodically reactivated reservoir, or do subswarms emerge from multiple discrete geographic foci? If the latter, are these discrete foci located at the margins of a single large magma body, or do multiple smaller reservoirs define the character of the magmatic center as a whole? Similarly, does the locus of magmatic activity change with time, or are all the foci active simultaneously? Careful study of giant radiating dike swarms on Venus is yielding the data necessary to address these questions and constrain future modeling efforts. Here, using giant radiating dike swarms from the Nemesis Tessera (V14) and Carson (V43) quadrangles as examples, we illustrate some of the dike swarm focal region diversity observed on Venus and briefly explore some

  1. A young solidification age for the lunar magma ocean

    NASA Astrophysics Data System (ADS)

    Gaffney, Amy M.; Borg, Lars E.

    2014-09-01

    The time at which the lunar magma ocean solidified can be determined from the Lu-Hf isotope systematics of lunar rocks derived from magma sources that formed during crystallization of the lunar magma ocean. The final magma ocean crystallization product, termed urKREEP, is enriched in incompatible elements including K, REE and P. We have determined the initial Hf isotopic compositions of four samples, two KREEP basalts and two Mg-suite norites. The incompatible trace element compositions of these samples are controlled by an urKREEP component, and therefore the initial Hf isotopic compositions of these samples represent the Hf isotopic evolution of urKREEP. In order to correct the effects of neutron irradiation on the Hf isotopic compositions of these samples, we have developed a model that uses the stable Hf and Sm isotopic compositions measured on an irradiated sample to determine and correct for the thermal and epithermal neutron fluence that has modified the Hf isotopic composition of the sample. We use our corrected results to calculate a 176Lu-176Hf urKREEP model age of 4353 ± 37 Ma and the 176Lu/177Hf of urKREEP to be 0.0153 ± 0.0033. The Lu-Hf model age is concordant with the re-calculated Sm-Nd urKREEP model age of 4389 ± 45 Ma, and we take the average of these ages, 4368 ± 29 Ma, to represent the time at which urKREEP formed. This age is concordant with the age of the most reliably dated ferroan noritic anorthosite as well as 142Nd model ages for the formation or re-equilibration of mare basalt sources. Taken together, these ages indicate that the Moon experienced a widespread, large-scale magmatic event around 4370 Ma, most plausibly attributed to solidification of the lunar magma ocean.

  2. Tracking the changing oxidation state of Erebus magmas, from mantle to surface, driven by magma ascent and degassing

    NASA Astrophysics Data System (ADS)

    Moussallam, Yves; Oppenheimer, Clive; Scaillet, Bruno; Gaillard, Fabrice; Kyle, Philip; Peters, Nial; Hartley, Margaret; Berlo, Kim; Donovan, Amy

    2014-05-01

    The conventional view holds that the oxidation state of a mantle-derived degassed magma reflects its source. During magma ascent and degassing the oxidation state is thought to follow a redox buffer. While this view has been challenged by petrological data, geochemical models and volcanic gas measurements, the fingerprints of such redox changes and their driving forces have not hitherto been captured by an integrated study. Here, we track the redox evolution of an alkaline magmatic suite at Erebus volcano, Antarctica, from the mantle to the surface, using X-ray absorption near-edge structure (XANES) spectroscopy at the iron and sulphur K-edges. We find that strong reduction of Fe and S dissolved in the melt accompanies magma ascent. Using a model of gas-melt chemical equilibria, we show that sulphur degassing is the driving force behind this evolutionary trend, which spans a wide compositional and depth range. Our results explain puzzling shifts in the oxidation state of gases emitted from Erebus volcano, and indicate that, where sulphur degassing occurs, the oxidation states of degassed volcanic rocks may not reflect their mantle source or co-eruptive gas phase. This calls for caution when inferring the oxidation state of the upper mantle from extrusive rocks and a possible re-assessment of the contribution of volcanic degassing to the early Earth's atmosphere and oceans. The relationship between magma redox conditions and pressure (depth) emphasises the value of measuring redox couples in gases emitted from volcanoes for the purposes of operational forecasting.

  3. 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

  4. Nd isotopic gradients in upper crustal magma chambers: Evidence for in situ magma-wall-rock interaction

    SciTech Connect

    Farmer, G.L.; Tegtmeyer, K.J.

    1990-01-01

    Multiple Nd isotopic analyses were obtained for one metaluminous and two peralkaline Tertiary rhyolitic ash-flow tuffs in the Great Basin to determine whether upper crustal silici magmas chemically evolve under closed- or open-system conditions. All the ash-flow tuffs analyzed show significant internal Nd isotopic variations. The largest variations occur within the peralkaline Double-H Mountains Tuff ({epsilon}{sub Nd} = +2.0 to +6.4) at the McDermitt volcanic field in north-central Nevada, and the smallest within the metaluminous Topopah Spring Tuff ({epsilon}{sub Nd} = {minus}10.6 to {minus}11.7) at the southwestern Nevada volcanic field. In all cases the isotopic variation are correlated with magmatic Nd contents, even though the Nd concentrations decreased roofward for the metaluminous rhyolite and increased for the peralkaline rhyolites. The consistent positive correlation between [Nd] and {epsilon}{sub Nd} provides strong evidence for in situ open-system addition of low {epsilon}{sub Nd} wall-rock material to the silicic magmas during their residence in the upper crust. The proportion of wall-rock Nd required to produce the isotopic zonations is small (1 to 15 mol%) for both the peralkaline and metaluminous rhyolites. All levels of the parental magmas sampled by the ash-flow tuffs, and not just magma occupying the roof zone, were open to wall-rock interaction. These results suggest that upper crustal silicic magma bodies evolve under open-system conditions and the effects of such processes should be addressed in models for their chemical differentiation.

  5. Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 1. Intereruption deformation, 1997–2008

    USGS Publications Warehouse

    Lu, Zhong; Dzurisin, Daniel; Biggs, Juliet; Wicks, Charles, Jr.; McNutt, Steve

    2010-01-01

    Starting soon after the 1997 eruption at Okmok volcano and continuing until the start of the 2008 eruption, magma accumulated in a storage zone centered ~3.5 km beneath the caldera floor at a rate that varied with time. A Mogi-type point pressure source or finite sphere with a radius of 1 km provides an adequate fit to the deformation field portrayed in time-sequential interferometric synthetic aperture radar images. From the end of the 1997 eruption through summer 2004, magma storage increased by 3.2–4.5 × 107 m3, which corresponds to 75–85% of the magma volume erupted in 1997. Thereafter, the average magma supply rate decreased such that by 10 July 2008, 2 days before the start of the 2008 eruption, magma storage had increased by 3.7–5.2 × 107 m3 or 85–100% of the 1997 eruption volume. We propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region. Eventually the effects of continuing magma supply and vesiculation of stored magma caused a critical pressure threshold to be exceeded, triggering the 2008 eruption. A similar pattern of initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption. In both cases, withdrawal of magma during the eruptions depressurized the shallow storage zone, causing significant volcano-wide subsidence and initiating a new intereruption deformation cycle.

  6. Terrestrial magma ocean and core segregation in the earth

    NASA Technical Reports Server (NTRS)

    Ohtani, Eiji; Yurimoto, Naoyoshi

    1992-01-01

    According to the recent theories of formation of the earth, the outer layer of the proto-earth was molten and the terrestrial magma ocean was formed when its radius exceeded 3000 km. Core formation should have started in this magma ocean stage, since segregation of metallic iron occurs effectively by melting of the proto-earth. Therefore, interactions between magma, mantle minerals, and metallic iron in the magma ocean stage controlled the geochemistry of the mantle and core. We have studied the partitioning behaviors of elements into the silicate melt, high pressure minerals, and metallic iron under the deep upper mantle and lower mantle conditions. We employed the multi-anvil apparatus for preparing the equilibrating samples in the ranges from 16 to 27 GPa and 1700-2400 C. Both the electron probe microanalyzer (EPMA) and the Secondary Ion Mass spectrometer (SIMS) were used for analyzing the run products. We obtained the partition coefficients of various trace elements between majorite, Mg-perovskite, and liquid, and magnesiowustite, Mg-perovskite, and metallic iron. The examples of the partition coefficients of some key elements are summarized in figures, together with the previous data. We may be able to assess the origin of the mantle abundances of the elements such as transition metals by using the partitioning data obtained above. The mantle abundances of some transition metals expected by the core-mantle equilibrium under the lower mantle conditions cannot explain the observed abundance of some elements such as Mn and Ge in the mantle. Estimations of the densities of the ultrabasic magma Mg-perovskite at high pressure suggest existence of a density crossover in the deep lower mantle; flotation of Mg-perovskite occurs in the deep magma ocean under the lower mantle conditions. The observed depletion of some transition metals such as V, Cr, Mn, Fe, Co, and Ni in the mantle may be explained by the two stage process, the core-mantle equilibrium under the lower

  7. Experimental constraints on the deformation and breakup of injected magma

    NASA Astrophysics Data System (ADS)

    Hodge, Kirsten F.; Carazzo, Guillaume; Jellinek, A. Mark

    2012-04-01

    The injection, breakup and stirring of dikes entering convecting silicic magma chambers can govern how they grow and differentiate, as well as influence their potential for eruption at the surface. Enclaves observed in plutons may preserve a record of this process and, thus, identifying and understanding the physical processes underlying their formation is a crucial issue in volcanology. We use laboratory experiments and scaling theory to investigate the mechanical and rheological conditions leading to the deformation and breakup of analog crystal-rich dikes injected as discrete plumes that descend into an underlying imposed shear flow. To scale the experiments and map the results across a wide range of natural conditions we define the ratio S of the timescale for the growth of a gravitational Rayleigh-Taylor (R-T) instability of the sheared, injected material to the timescale for settling through the fluid layer and the ratio Y of the timescales for shearing and lateral disaggregation of the particle-fluid mixture (yielding). At low S (< 3) and high Y (> 40), descending plumes are stretched and tilted before undergoing R-T instability, forming drips with a wavelength that is comparable to the initial diameter of the injection. At low Y (< 40) and S values that increase from ∼ 3 as Y → 0, an injection yields in tension before a R-T instability can grow, forming discrete particle-fluid blobs that are much smaller than the initial injection diameter and separated by thin filaments of the original mixture. At high S (> 3) and high Y (> 40), injections remain intact as they settle through the layer and pond at the floor. Applied to magma chambers, our results do not support the production of a continuum of enclave sizes. Indeed, from scaling analyses we expect the two breakup regimes to form distinct size populations: Whereas enclaves formed in the R-T regime will be comparable to the injection size, those formed in the tension regime will be much smaller. We show

  8. Magma-tectonic interaction and the eruption of silicic batholiths

    NASA Astrophysics Data System (ADS)

    Gottsmann, J.; Lavallée, Y.; Martí, J.; Aguirre-Díaz, G.

    2009-07-01

    Due to its unfavorable rheology, magma with crystallinity exceeding about 50 vol.% and effective viscosity > 10 6 Pa s is generally perceived to stall in the Earth's crust rather than to erupt. There is, however, irrefutable evidence for colossal eruption of batholithic magma bodies and here we analyze four examples from Spain, Mexico, USA and the Central Andes. These silicic caldera-forming eruptions generated deposits characterized by i) ignimbrites containing crystal-rich pumice, ii) co-ignimbritic lag breccias and iii) the absence of initial fall-out. The field evidence is inconsistent with most caldera-forming deposits, which are underlain by initial fall-out indicating deposition from a sustained eruption column before the actual collapse sequence. In contrast, the documented examples suggest early deep-level fragmentation at the onset of eruption and repeated column collapse generating eruption volumes on the order of hundreds of cubic kilometers almost exclusively in the form of ignimbrites. These examples challenge our understanding of magma eruptability and eruption initiation processes. In this paper, we present an analysis of eruption promoters from geologic, theoretical and experimental considerations. Assessing relevant dynamics and timescales for failure of crystal-melt mush we propose a framework to explain eruption of batholithic magma bodies that primarily involves an external trigger by near-field seismicity and crustal failure. Strain rate analysis for dynamic and static stressing, chamber roof collapse and rapid decompression indicates that large "solid-like" silicic reservoirs may undergo catastrophic failure leading to deep-level fragmentation of batholithic magma at approximately 2 orders of magnitude lower strain rates than those characteristic for failure of crystal-poor magmas or pure melt. Eruption triggers can thus include either amplified pressure transients in the liquid phase during seismic shaking of a crystal-melt mush

  9. Differentiation of Vesta: Implications for a shallow magma ocean

    NASA Astrophysics Data System (ADS)

    Neumann, Wladimir; Breuer, Doris; Spohn, Tilman

    2014-06-01

    The Dawn mission confirms earlier predictions that the asteroid 4 Vesta is differentiated with an iron-rich core, a silicate mantle and a basaltic crust, and supports the conjecture of Vesta being the parent body of the HED meteorites. To better understand its early evolution, we perform numerical calculations of the thermo-chemical evolution adopting new data obtained by the Dawn mission such as mass, bulk density and size of the asteroid. We have expanded the thermo-chemical evolution model of Neumann et al. (2012) that includes accretion, compaction, melting and the associated changes of the material properties and the partitioning of incompatible elements such as the radioactive heat sources, advective heat transport, and differentiation by porous flow, to further consider convection and the associated effective cooling in a potential magma ocean. Depending on the melt fraction, the heat transport by melt segregation is modelled either by assuming melt flow in a porous medium or by simulating vigorous convection and heat flux of a magma ocean with a high effective thermal conductivity. Our results show that partitioning of 26Al and its transport with the silicate melt is crucial for the formation of a global and deep magma ocean. Due to the enrichment of 26Al in the liquid phase and its accumulation in the sub-surface (for formation times t0<1.5 Ma), a thin shallow magma ocean with a thickness of 1 to a few tens of km forms - its thickness depends on the viscosity of silicate melt. The lifetime of the shallow magma ocean is O(104)-O(106) years and convection in this layer is accompanied by the extrusion of 26Al at the surface, resulting in the formation of a basaltic crust. The interior differentiates from the outside inwards with a mantle that is depleted in 26Al and core formation is completed within ˜0.3 Ma. The lower mantle experiences a maximal melt fraction of 45% suggesting a harzburgitic to dunitic composition. Our results support the formation of non

  10. Shallow axial magma chamber at the slow-spreading Erta Ale Ridge

    NASA Astrophysics Data System (ADS)

    Pagli, Carolina; Wright, Tim J.; Ebinger, Cynthia J.; Yun, Sang-Ho; Cann, Johnson R.; Barnie, Talfan; Ayele, Atalay

    2012-04-01

    The existence of elongated, shallow magma chambers beneath the axes of fast-spreading mid-ocean ridges is well established. Yet, at slow-spreading ridges such shallow and elongated magma chambers are much less evident. Simple thermal models therefore predict that spreading velocity and magma supply may provide the main controls on magma-chamber depth and morphology. Here we use interferometric synthetic aperture radar data to investigate the dynamics of the magma chamber beneath the slow-spreading Erta Ale segment of the Ethiopian Rift. We show that an eruption from Alu-Dalafilla in November 2008 was sourced from a shallow, 1km deep, elongated magma chamber that is divided into two segments. The eruption was probably triggered by a small influx of magma into the northern segment. Both segments of the magma chamber fed the main eruption through a connecting dyke and both segments have been refilling rapidly since the eruption ended. Our results support the presence of independent sources of magma supply to segmented chambers located along the axes of spreading centres. However, the existence of a shallow, elongated axial chamber at Erta Ale indicates that spreading rate and magma supply may not be the only controls on magma-chamber characteristics.

  11. Oxygen fugacity of basaltic magmas and the role of gas-forming elements

    NASA Technical Reports Server (NTRS)

    Sato, M.

    1978-01-01

    It is suggested that major variations in the relative oxygen fugacity of a basaltic magma are caused primarily by gas-forming elements, especially carbon and hydrogen. According to this theory, carbon, present in the source region of a basaltic magma, reduces the host magma during ascent, as isothermally carbon becomes more reducing with decreasing pressure. For an anhydrous magma such as lunar basalts, this reduction continues through the extrusive phase and the relative oxygen fugacity decreases rapidly until buffered by the precipitation of a metallic phase. For hydrous magmas such as terrestrial basalts, reduction by carbon is eventually superceded by oxidation due to loss of H2 generated by the reaction of C with H2O and by thermal dissociation of H2O. The relative oxygen fugacity of a hydrous magma initially decreases as a magma ascends from the source region and then increases until magnetite crystallization curbs the rising trend of the relative oxygen fugacity.

  12. A magma ocean and the Earth's internal water budget

    NASA Technical Reports Server (NTRS)

    Ahrens, Thomas J.

    1992-01-01

    There are lines of evidence which relate bounds on the primordial water content of the Earth's mantle to a magma ocean and the accompanying Earth accretion process. We assume initially (before a magma ocean could form) that as the Earth accreted, it grew from volatile- (H2O, CO2, NH3, CH4, SO2, plus noble) gas-rich planetesimals, which accreted to form an initial 'primitive accretion core' (PAC). The PAC retained the initial complement of planetesimal gaseous components. Shock wave experiments in which both solid, and more recently, the gaseous components of materials such as serpentine and the Murchison meteorite have demonstrated that planetesimal infall velocities of less than 0.5 km/sec, induce shock pressures of less than 0.5 GPa and result in virtually complete retention of planetary gases.

  13. 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.

  14. Degassing during magma ascent in the Mule Creek vent (USA)

    USGS Publications Warehouse

    Stasiuk, M.V.; Barclay, J.; Carroll, M.R.; Jaupart, Claude; Ratte, J.C.; Sparks, R.S.J.; Tait, S.R.

    1996-01-01

    The structures and textures of the rhyolite in the Mule Creek vent (New Mexico, USA) indicate mechanisms by which volatiles escape from silicic magma during eruption. The vent outcrop is a 300-m-high canyon wall comprising a section through the top of a feeder conduit, vent and the base of an extrusive lava dome. Field relations show that eruption began with an explosive phase and ended with lava extrusion. Analyses of glass inclusions in quartz phenocrysts from the lava indicate that the magma had a pre-eruptive dissolved water content of 2.5-3.0 wt% and, during eruption, the magma would have been water-saturated over the vertical extent of the present outcrop. However, the vesicularity of the rhyolite is substantially lower than that predicted from closed-system models of vesiculation under equilibrium conditions. At a given elevation in the vent, the volume fraction of primary vesicles in the rhyolite increases from zero close to the vent margin to values of 20-40 vol.% in the central part. In the centre the vesicularity increases upward from approximately 20 vol.% at 300 m below the canyon rim to approximately 40 vol.% at 200 m, above which it shows little increase. To account for the discrepancy between observed vesicularity and measured water content, we conclude that gas escaped during ascent, probably beginning at depths greater than exposed, by flow through the vesicular magma. Gas escape was most efficient near the vent margin, and we postulate that this is due both to the slow ascent of magma there, giving the most time for gas to escape, and to shear, favouring bubble coalescence. Such shear-related permeability in erupting magma is supported by the preserved distribution of textures and vesicularity in the rhyolite: Vesicles are flattened and overlapping near the dense margins and become progressively more isolated and less deformed toward the porous centre. Local zones have textures which suggest the coalescence of bubbles to form permeable

  15. The variation of magma discharge during basaltic eruptions

    NASA Astrophysics Data System (ADS)

    Wadge, G.

    The different types of magmatic flow in basaltic eruptions are discussed, and processes explaining the eruptive history of specific volcanoes are investigated. The effusion rate curve is divided into waxing and waning flow parts, and the ideal, elastic response of the reservoir in the waning phase is analytically shown. Historical eruption rates of Mauna Loa, Kilauea, and Etna are presented, demonstrating that for each volcano there is a trend of decreasing rate with increasing duration of eruption, a relationship not predicted by a simple elastic model of magma release. The eruptive histories of these volcanoes is explained by the processes of modification of the eruptive conduits and the continued supply of magma from depth during eruption. Discharge variations from Paricutin, Hekla, and Kilauea Iki are discussed in detail.

  16. Magma zonation - Effects of chemical buoyancy and diffusion

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    Numerical simulations and scale analysis are used to assess the viability of the marginal box-filling mechanism for producing compositional zonation in magma bodies. Scale analysis and two-dimensional numerical experiments both show that box-filling occurs provided a critical ratio of compositional-to-thermal buoyancy is exceeded. This critical ratio depends on the ratio of thermal-to-chemical diffusivity; application of this result to magma bodies suggests that box-filling may occur for components with relatively high-chemical diffusivities such as water. However, box-filling will not produce significant zonation for components with small chemical diffusivities, such as silica, unless diffusive coupling increases silica diffusivity.

  17. Symmetries and nonlocal conservation laws of the general magma equation

    NASA Astrophysics Data System (ADS)

    Khamitova, Raisa

    2009-11-01

    In this paper the general magma equation modelling a melt flow in the Earth's mantle is discussed. Applying the new theorem on nonlocal conservation laws [Ibragimov NH. A new conservation theorem. J Math Anal Appl 2007;333(1):311-28] and using the symmetries of the model equation nonlocal conservation laws are computed. In accordance with Ibragimov [Ibragimov NH. Quasi-self-adjoint differential equations. Preprint in Archives of ALGA, vol. 4, BTH, Karlskrona, Sweden: Alga Publications; 2007. p. 55-60, ISSN: 1652-4934] it is shown that the general magma equation is quasi-self-adjoint for arbitrary m and n and self-adjoint for n = -m. These important properties are used for deriving local conservation laws.

  18. Origin of high-alumina basalt, andesite, and dacite magmas

    USGS Publications Warehouse

    Hamilton, W.

    1964-01-01

    The typical volcanic rocks of most island arcs and eugeosynclines, and of some continental environments, are basalt, andesite, and dacite, of high alumina content. The high-alumina basalt differs from tholeiitic basalt primarily in having a greater content of the components of calcic plagioclase. Laboratory data indicate that in the upper mantle, below the level at which the basaltic component of mantle rock is transformed by pressure to eclogite or pyroxenite, the entire basaltic portion probably is melted within a narrow temperature range, but that above the level of that transformation plagioclase is melted selectively before pyroxene over a wide temperature range. The broad spectrum of high-alumina magmas may represent widely varying degrees of partial melting above the transformation level, whereas narrow-spectrum tholeiite magma may represent more complete melting beneath it.

  19. Origin of High-Alumina Basalt, Andesite, and Dacite Magmas.

    PubMed

    Hamilton, W

    1964-10-30

    The typical volcanic rocks of most island arcs and eugeosynclines, and of some continental environments, are basalt, andesite, and dacite, of high alumina content. The high-alumina basalt differs from tholeiitic basalt primarily in having a greater content of the components of calcic plagioclase. Laboratory data indicate that in the upper mantle, below the level at which the basaltic component of mantle rock is transformed by pressure to eclogite or pyroxenite, the entire basaltic portion probably is melted within a narrow temperature range, but that above the level of that transformation plagioclase is melted selectively before pyroxene over a wide temperature range. The broad spectrum of high-alumina magmas may represent widely varying degrees of partial melting above the transformation level, whereas narrow-spectrum tholeiite magma may represent more complete melting beneath it. PMID:17794034

  20. Sulfate Saturated Hydrous Magmas Associated with Hydrothermal Gold Ores

    NASA Astrophysics Data System (ADS)

    Chambefort, I.; Dilles, J. H.; Kent, A. J.

    2007-12-01

    Hydrothermal ore deposits associated with arc magmatism represent important sulfur anomalies. During degassing of magmatic systems the volatile may transport metals and sulfur and produce deposits. The ultimate origin of the magma-derived sulfur is still uncertain. The Yanacocha high-sulfidation epithermal Au deposit, Peru, is hosted by a Miocene volcanic succession (ca. 16 to 8 Ma). Magmatic rocks are highly oxidized >NNO+2 and show a range of composition from andesite to dacite. Two populations of amphibole occur in the Yanacocha dacitic ignimbrite deposits (~7 and 12 wt% Al2O3). Low Al amphiboles crystallized at ~ 1.5-2 kbar and 800°C (Plag-Hb thermobarometry) in equilibrium with plagioclase and pyroxene. High Al amphiboles only contain inclusions of anhydrite associated with apatite (up to 1.2 wt% SO3), and have a higher Cr2O3 content (up to 1000 ppm). We estimate these amphiboles form near the magma's liquidus at P(H2O)> 3kbar and 950 to 1000°C of a basaltic, basaltic andesite ascending magma. Low Al amphibole presents an REE pattern with negative anomalies in Sr, Ti and Eu, characteristic of plagioclase and titanite fractionation in the magma. High Al amphiboles are less enriched in REE and have no Sr, Ti, or Eu anomaly. Rare crystals of high Al amphibole display a low Al rim marked by higher REE contents compared to the core and a negative Eu anomaly. Magmatic sulfate occurrences have been discovered through the 8 m.y. volcanic sequence. Rounded anhydrite crystals are found included within clinopyroxene and both high and low Al amphibole. The rare high Al amphiboles (from the sample RC6) contain up to ~10 vol.%, ~5-80 micrometer-long anhydrite as irregularly shaped (amoeboid) blebs that do not show crystallographic forms and do not follow host cleavages. Extremely rare sulfide inclusions are found in plagioclase (Brennecka, 2006). The major and trace element contents of Yanacocha magmatic anhydrite have been analyzed by electron microprobe and LA

  1. Magmas and magmatic rocks: An introduction to igneous petrology

    SciTech Connect

    Middlemost, E.A.K.

    1986-01-01

    This book melds traditional igneous petrology with the emerging science of planetary petrology to provide an account of current ideas on active magmatic and volcanic processes, drawing examples from all igneous provinces of the world as well as from the moon and planets. It reviews the history and development of concepts fundamental to modern igneous petrology and includes indepth sections on magmas, magnetic differentiation and volcanology.

  2. Experiments on the rheology of vesicle-bearing magmas

    NASA Astrophysics Data System (ADS)

    Vona, Alessandro; Ryan, Amy G.; Russell, James K.; Romano, Claudia

    2016-04-01

    We present a series of high temperature uniaxial deformation experiments designed to investigate the effect of bubbles on the magma bulk viscosity. Starting materials having variable vesicularity (φ = 0 - 66%) were synthesized by high-temperature foaming (T = 900 - 1050 ° C and P = 1 bar) of cores of natural rhyolitic obsidian from Hrafntinnuhryggur, Krafla, Iceland. These cores were subsequently deformed using a high-temperature uniaxial press at dry atmospheric conditions. Each experiment involved deforming vesicle-bearing cores isothermally (T = 750 ° C), at constant displacement rates (strain rates between 0.5-1 x 10‑4 s‑1), and to total strains (ɛ) of 10-40%. The viscosity of the bubble-free melt (η0) was measured by micropenetration and parallel plate methods and establishes a baseline for comparing data derived from experiments on vesicle rich cores. At the experimental conditions, the presence of vesicles has a major impact on the rheological response, producing a marked decrease of bulk viscosity (maximum decrease of 2 log units Pa s) that is best described by a two-parameter empirical equation: log ηBulk = log η0 - 1.47 * [φ/(1-φ)]0.48. Our model provides a means to compare the diverse behaviour of vesicle-bearing melts reported in the literature and reflecting material properties (e.g., analogue vs. natural), geometry and distribution of pores (e.g. foamed/natural vs. unconsolidated/sintered materials), and flow regime. Lastly, we apply principles of Maxwell relaxation theory, combined with our parameterization of bubble-melt rheology, to map the potential onset of non-Newtonian behaviour (strain localization) in vesiculated magmas and lavas as a function of melt viscosity, vesicularity, strain rate, and geological condition. Increasing vesicularity in magmas can initiate non-Newtonian behaviour at constant strain rates. Lower melt viscosity sustains homogeneous Newtonian flow in vesiculated magmas even at relatively high strain rates.

  3. Slab melting and magma generation beneath the southern Cascade Arc

    NASA Astrophysics Data System (ADS)

    Walowski, K. J.; Wallace, P. J.; Clynne, M. A.

    2014-12-01

    Magma formation in subduction zones is interpreted to be caused by flux melting of the mantle wedge by fluids derived from dehydration of the downgoing oceanic lithosphere. In the Cascade Arc and other hot-slab subduction zones, however, most dehydration reactions occur beneath the forearc, necessitating a closer investigation of magma generation processes in this setting. Recent work combining 2-D steady state thermal models and the hydrogen isotope composition of olivine-hosted melt inclusions from the Lassen segment of the Cascades (Walowski et al., 2014; in review) has shown that partial melting of the subducted basaltic crust may be a key part of the subduction component in hot arcs. In this model, fluids from the slab interior (hydrated upper mantle) rise through the slab and cause flux-melting of the already dehydrated MORB volcanics in the upper oceanic crust. In the Shasta and Lassen segments of the southern Cascades, support for this interpretation comes from primitive magmas that have MORB-like Sr isotope compositions that correlate with subduction component tracers (H2O/Ce, Sr/P) (Grove et al. 2002, Borg et al. 2002). In addition, mass balance calculations of the composition of subduction components show ratios of trace elements to H2O that are at the high end of the global arc array (Ruscitto et al. 2012), consistent with the role of a slab-derived melt. Melting of the subducted basaltic crust should contribute a hydrous dacitic or rhyolitic melt (e.g. Jego and Dasgupta, 2013) to the mantle wedge rather than an H2O-rich aqueous fluid. We are using pHMELTS and pMELTS to model the reaction of hydrous slab melts with mantle peridotite as the melts rise through the inverted thermal gradient in the mantle wedge. The results of the modeling will be useful for understanding magma generation processes in arcs that are associated with subduction of relatively young oceanic lithosphere.

  4. Origin of picritic green glass magmas by polybaric fractional fusion

    NASA Technical Reports Server (NTRS)

    Longhi, John

    1992-01-01

    A preliminary presentation is given of a model which explains the picritic lunar mare green glass compositions as composites or magmas derived by polybaric fractional melting. The model accommodates changes in source composition and solidus temperature. As in the Klein and Langmuir model, the final compositions of the melts signify only average depths of melting. The onset of melting is deeper, final segregation is shallower.

  5. Dynamic Heating and Decompression Experiments on Dacite and Rhyolite Magmas

    NASA Astrophysics Data System (ADS)

    Andrews, B. J.; Waters, L.; Grocke, S. B.

    2015-12-01

    Mineral reaction rims, zoned crystals, and myriad growth or dissolution textures provide evidence for changes in magma pressure, temperature, or composition. Quantifying the magnitudes, timescales and length scales of those variations is a fundamental challenge of volcanology and igneous petrology; experiments provide quantitative insights into how magmas react to changes in pressure and temperature that can be used to address that challenge. We use single-step and dynamic experiments conducted in cold seal pressure vessels to study the responses of dacite and rhyolite magmas to heating and decompression events. During single-step decompression (or heating) experiments, conditions are changed nearly instantaneously from the initial to final state in one step, or several smaller steps, whereas "dynamic experiments" have continuous variation in pressure and/or temperature. These two types of experiments yield useful and complementary information describing crystal nucleation, growth, and reaction rates in response to changing (as opposed to steady state) conditions. Here we discuss isothermal decompression experiments that show substantial path-dependence for runs with equivalent time-averaged decompression rates as slow as 0.27 MPa/h for >500 h. Continuous decompression experiments often contain fewer but larger plagioclase crystals than are present in single-step runs, and those new crystals often show complex growth textures. Our results suggest that even slow changes in storage conditions can disrupt melt structure and greatly retard nucleation provided the changes are steady. We hypothesize that if the decompression path remains steady and continuous (absent a stall on and/or rapid decompression), the magma can remain in a growth-dominated regime even though it is far from equilibrium.

  6. MAGMA: Generalized Gene-Set Analysis of GWAS Data

    PubMed Central

    de Leeuw, Christiaan A.; Mooij, Joris M.; Heskes, Tom; Posthuma, Danielle

    2015-01-01

    By aggregating data for complex traits in a biologically meaningful way, gene and gene-set analysis constitute a valuable addition to single-marker analysis. However, although various methods for gene and gene-set analysis currently exist, they generally suffer from a number of issues. Statistical power for most methods is strongly affected by linkage disequilibrium between markers, multi-marker associations are often hard to detect, and the reliance on permutation to compute p-values tends to make the analysis computationally very expensive. To address these issues we have developed MAGMA, a novel tool for gene and gene-set analysis. The gene analysis is based on a multiple regression model, to provide better statistical performance. The gene-set analysis is built as a separate layer around the gene analysis for additional flexibility. This gene-set analysis also uses a regression structure to allow generalization to analysis of continuous properties of genes and simultaneous analysis of multiple gene sets and other gene properties. Simulations and an analysis of Crohn’s Disease data are used to evaluate the performance of MAGMA and to compare it to a number of other gene and gene-set analysis tools. The results show that MAGMA has significantly more power than other tools for both the gene and the gene-set analysis, identifying more genes and gene sets associated with Crohn’s Disease while maintaining a correct type 1 error rate. Moreover, the MAGMA analysis of the Crohn’s Disease data was found to be considerably faster as well. PMID:25885710

  7. Density of phonolitic magmas and time scales of crystal fractionation in magma chambers

    NASA Astrophysics Data System (ADS)

    Seifert, R.; Malfait, W. J.; Petitgirard, S.; Sanchez-Valle, C.

    2013-11-01

    Understanding magmatic processes and their evolution in the Earth's interior requires a better knowledge of silicate melts and their physical properties. Among them, density is one of the most important to constrain the residence or ascent time of magma in the upper mantle and crust. However, the volumetric properties of volatile-bearing and highly polymerized silicate melts are still poorly constrained due to scarce experimental data. In this study, the density of dry and hydrous (4.35 wt% H2O) phonolitic melt was measured in situ using the X-ray absorption method in a Paris-Edinburgh press at 0.73-3.1 GPa and 1484-1855 K. Calculated melt densities range from 2.49±0.02 to 2.66±0.03 g/cm and from 2.31±0.02 to 2.52±0.02 g/cm for the dry and hydrous compositions at depths of 30 to 100 km. The results are used to calibrate the equation of state (EoS) of phonolitic liquids for crustal and upper mantle conditions and to derive the partial molar volume of water: a least-squares fit of the P-T-ρ data to a third-order Birch-Murnaghan EoS yields: V0=28.10-0.74+0.10 cm/mol, KT=14.6-3.0+3.2 GPa, K‧=8.9-2.6+3.3 and α=47-30+28×10-6/K for the dry melts and V0=20.6-0.8+7.5 cm/mol, KT=4.6-3.0+2.3 GPa, K‧=5.5-0.5+6.1 and α=135-115+114×10-6/K for the hydrous component at 1673 K. Combined with literature data, our EoS for water indicates that V does not depend strongly on the silicate liquid composition at the investigated conditions.

  8. Does temperature increase or decrease in adiabatic decompression of magma?

    NASA Astrophysics Data System (ADS)

    Kilinc, A. I.; Ghiorso, M. S.; Khan, T.

    2011-12-01

    We have modeled adiabatic decompression of an andesitic and a basaltic magma as an isentropic process using the Melts algorithm. Our modeling shows that during adiabatic decompression temperature of andesitic magma increases but temperature of basaltic magma decreases. In an isentropic process entropy is constant so change of temperature with pressure can be written as dT/dP=T (dV/dT)/Cp where T (dV/dT)/Cp is generally positive. If delta P is negative so is delta T. In general, in the absence of phase change, we expect the temperature to decrease with adiabatic decompression. The effect of crystallization is to turn a more entropic phase (liquid) into a less entropic phase (solid), which must be compensated by raising the temperature. If during adiabatic decompression there is small amount or no crystallization, T (dV/dT)/Cp effect which lowers the temperature overwhelms the small amount of crystallization, which raises the temperature, and overall system temperature decreases.

  9. Magma mixing due to disruption of a compositional interface

    SciTech Connect

    Flood, T.P.; Schuraytz, B.C.; Vogel, T.A.

    1986-07-15

    The chemical compositions of glassy pumices are used to investigate the relationship between two ash-flow sheets that were erupted from the same volcanic center. The first ash-flow sheet, the large volume (>1200 km{sup 3}) Topopah Spring Member, represents an eruption from a magma body that contained a sharp compositional interface between a high-silica rhyolite and a lower-silica quartz latite. The second ash-flow sheet is the smaller volume (<40 km{sup 3}) Pah Canyon Member. It represents an eruption of a relatively homogenous magma that is intermediate in composition to the compositions of the Topopah Spring Member. Mixing of the quartz latite and rhyolite magmas to produce the Pah Canyon Member is evaluated using variation diagrams of the major and trace elements, ratio-ratio plots, and least-squares multiple linear regression. The latter includes two independent tests, one using the major elements, and the other using selected trace elements. Fractional crystallization of the quartz latite to produce the Pah Canyon Member is evaluated using multiple linear regression with both the major elements and selected trace elements.

  10. Concentration variance decay during magma mixing: a volcanic chronometer

    NASA Astrophysics Data System (ADS)

    Perugini, Diego; de Campos, Cristina P.; Petrelli, Maurizio; Dingwell, Donald B.

    2015-09-01

    The mixing of magmas is a common phenomenon in explosive eruptions. Concentration variance is a useful metric of this process and its decay (CVD) with time is an inevitable consequence during the progress of magma mixing. In order to calibrate this petrological/volcanological clock we have performed a time-series of high temperature experiments of magma mixing. The results of these experiments demonstrate that compositional variance decays exponentially with time. With this calibration the CVD rate (CVD-R) becomes a new geochronometer for the time lapse from initiation of mixing to eruption. The resultant novel technique is fully independent of the typically unknown advective history of mixing - a notorious uncertainty which plagues the application of many diffusional analyses of magmatic history. Using the calibrated CVD-R technique we have obtained mingling-to-eruption times for three explosive volcanic eruptions from Campi Flegrei (Italy) in the range of tens of minutes. These in turn imply ascent velocities of 5-8 meters per second. We anticipate the routine application of the CVD-R geochronometer to the eruptive products of active volcanoes in future in order to constrain typical “mixing to eruption” time lapses such that monitoring activities can be targeted at relevant timescales and signals during volcanic unrest.

  11. The chlorine isotope fingerprint of the lunar magma ocean

    PubMed Central

    Boyce, Jeremy W.; Treiman, Allan H.; Guan, Yunbin; Ma, Chi; Eiler, John M.; Gross, Juliane; Greenwood, James P.; Stolper, Edward M.

    2015-01-01

    The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free (“dry”) Moon. We have analyzed abundances and isotopic compositions of Cl and H in lunar mare basalts, and find little evidence that anhydrous lava outgassing was important in generating chlorine isotope anomalies, because 37Cl/35Cl ratios are not related to Cl abundance, H abundance, or D/H ratios in a manner consistent with the lava-outgassing hypothesis. Instead, 37Cl/35Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high 37Cl/35Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar magma ocean. These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar magma ocean early in the Moon’s history. Chlorine isotope variability is therefore an indicator of planetary magma ocean degassing, an important stage in the formation of terrestrial planets. PMID:26601265

  12. Concentration variance decay during magma mixing: a volcanic chronometer

    PubMed Central

    Perugini, Diego; De Campos, Cristina P.; Petrelli, Maurizio; Dingwell, Donald B.

    2015-01-01

    The mixing of magmas is a common phenomenon in explosive eruptions. Concentration variance is a useful metric of this process and its decay (CVD) with time is an inevitable consequence during the progress of magma mixing. In order to calibrate this petrological/volcanological clock we have performed a time-series of high temperature experiments of magma mixing. The results of these experiments demonstrate that compositional variance decays exponentially with time. With this calibration the CVD rate (CVD-R) becomes a new geochronometer for the time lapse from initiation of mixing to eruption. The resultant novel technique is fully independent of the typically unknown advective history of mixing – a notorious uncertainty which plagues the application of many diffusional analyses of magmatic history. Using the calibrated CVD-R technique we have obtained mingling-to-eruption times for three explosive volcanic eruptions from Campi Flegrei (Italy) in the range of tens of minutes. These in turn imply ascent velocities of 5-8 meters per second. We anticipate the routine application of the CVD-R geochronometer to the eruptive products of active volcanoes in future in order to constrain typical “mixing to eruption” time lapses such that monitoring activities can be targeted at relevant timescales and signals during volcanic unrest. PMID:26387555

  13. Dropping stones in magma oceans - Effects of early lunar cratering

    NASA Technical Reports Server (NTRS)

    Hartmann, W. K.

    1980-01-01

    A new methodology is used to calculate the accumulation rate of megaregolith materials for two models of early lunar cratering, both with and without episodes of late cataclysmic cratering. Results show that the pulverization of early rock layers was an important process competing with the formation of a coherent rock lithosphere at the surface of the hypothetical lunar magma ocean. If a magma ocean existed, then its initial cooling was marked by a period of pre-lithospheric chaos in which impacts punched through the initially thin rocky skin, mixing rock fragments with splashed magma. Furthermore, the results show that intense brecciation and pulverization of rock materials must have occurred to a depth of at least tens of kilometers in the first few hundred years of lunar history regardless of whether a 'terminal lunar cataclysm' occurred around 4.0 G.y. ago. The predicted pattern of brecciation and the ages of surviving rock fragments is similar to that actually observed among lunar samples. More reliable dating of basin-forming events and models of rock exhumation and survival are needed in order to understand better the relation between the early intense bombardment of the moon and the samples collected on the moon today.

  14. Deep degassing and the eruptibility of flood basalt magmas

    NASA Astrophysics Data System (ADS)

    Black, B. A.; Manga, M.

    2015-12-01

    Individual flood basalt lavas often exceed 103 km3 in volume, and many such lavas erupt during emplacement of flood basalt provinces. The large volume of individual flood basalt lavas demands correspondingly large magma reservoirs within or at the base of the crust. To erupt, some fraction of this magma must become buoyant and overpressure must be sufficient to encourage failure and dike propagation. Because the overpressure associated with a new injection of magma is inversely proportional to the total reservoir volume, buoyancy overpressure has been proposed as a trigger for flood basalt eruptions. To test this hypothesis, we develop a new one-dimensional model for buoyancy overpressure-driven eruptions that combines volatile exsolution, bubble growth and rise, assimilation, and permeable fluid escape through the surrounding country rocks. Degassing during emplacement of flood basalt provinces may have major environmental repercussions. We investigate the temporal evolution of permeable degassing through the crust and degassing during eruptive episodes. We find that assimilation of volatile-rich country rocks strongly enhances flood basalt eruptibility, implying that the eruptive dynamics of flood basalts may be intertwined with their climatic consequences.

  15. Concentration variance decay during magma mixing: a volcanic chronometer.

    PubMed

    Perugini, Diego; De Campos, Cristina P; Petrelli, Maurizio; Dingwell, Donald B

    2015-01-01

    The mixing of magmas is a common phenomenon in explosive eruptions. Concentration variance is a useful metric of this process and its decay (CVD) with time is an inevitable consequence during the progress of magma mixing. In order to calibrate this petrological/volcanological clock we have performed a time-series of high temperature experiments of magma mixing. The results of these experiments demonstrate that compositional variance decays exponentially with time. With this calibration the CVD rate (CVD-R) becomes a new geochronometer for the time lapse from initiation of mixing to eruption. The resultant novel technique is fully independent of the typically unknown advective history of mixing - a notorious uncertainty which plagues the application of many diffusional analyses of magmatic history. Using the calibrated CVD-R technique we have obtained mingling-to-eruption times for three explosive volcanic eruptions from Campi Flegrei (Italy) in the range of tens of minutes. These in turn imply ascent velocities of 5-8 meters per second. We anticipate the routine application of the CVD-R geochronometer to the eruptive products of active volcanoes in future in order to constrain typical "mixing to eruption" time lapses such that monitoring activities can be targeted at relevant timescales and signals during volcanic unrest. PMID:26387555

  16. Viscosity of bubble- and crystal- bearing magmas: Analogue results

    NASA Astrophysics Data System (ADS)

    Namiki, A.; Manga, M.

    2006-12-01

    Natural magmas often include both phenocrysts and bubbles. Such magmas can be regarded as suspensions including particles and bubbles and should have a viscosity different from the particle- and bubble- free melt. Viscosity is one of the key physical properties that affects eruption dynamics and magma flow. To understand the relation between the viscosity and the volume fraction of bubbles and particles, we directly measure the viscosity of suspensions with both particles and bubbles. Measurements are performed with the 4 degree cone-and-plate type rheometer (Thermo HAAKE Rheoscope 1), which allows us to observe the samples in situ during the measurement. The suspending fluid is corn syrup whose viscosity is 1.7 Pa·s at 23 °C. Particles are Techpolymer (polymethylmethacrylate) 40 μm diameter spheres. Bubbles are made by dissolving baking soda and citric acid; reaction between them generates carbon dioxide. No surfactant is added. The Peclet number is sufficiently large that Brownian motion does not influence our results. The measured viscosity for the suspensions with particles, and with both particles and bubbles, show strong shear thinning. The measured viscosities during increasing and decreasing shear rate differ from each other, indicating that the microstructure is modified by flow. When the deformation of bubbles is not significant, the measured viscosity with bubbles is higher than that without bubbles, and vice versa.

  17. Concentration variance decay during magma mixing: a volcanic chronometer

    NASA Astrophysics Data System (ADS)

    Perugini, D.; De Campos, C. P.; Petrelli, M.; Dingwell, D. B.

    2015-12-01

    The mixing of magmas is a common phenomenon in explosive eruptions. Concentration variance is a useful metric of this process and its decay (CVD) with time is an inevitable consequence during the progress of magma mixing. In order to calibrate this petrological/volcanological clock we have performed a time-series of high temperature experiments of magma mixing. The results of these experiments demonstrate that compositional variance decays exponentially with time. With this calibration the CVD rate (CVD-R) becomes a new geochronometer for the time lapse from initiation of mixing to eruption. The resultant novel technique is fully independent of the typically unknown advective history of mixing - a notorious uncertainty which plagues the application of many diffusional analyses of magmatic history. Using the calibrated CVD-R technique we have obtained mingling-to-eruption times for three explosive volcanic eruptions from Campi Flegrei (Italy) in the range of tens of minutes. These in turn imply ascent velocities of 5-8 meters per second. We anticipate the routine application of the CVD-R geochronometer to the eruptive products of active volcanoes in future in order to constrain typical "mixing to eruption" time lapses such that monitoring activities can be targeted at relevant timescales and signals during volcanic unrest.

  18. Magma ascent pathways associated with large mountains on Io

    NASA Astrophysics Data System (ADS)

    McGovern, Patrick J.; Kirchoff, Michelle R.; White, Oliver L.; Schenk, Paul M.

    2016-07-01

    While Jupiter's moon Io is the most volcanically active body in the Solar System, the largest mountains seen on Io are created by tectonic forces rather than volcanic construction. Pervasive compression, primarily brought about by subsidence induced by sustained volcanic resurfacing, creates the mountains, but at the same time inhibits magma ascent in vertical conduits (dikes). We superpose stress solutions for subsidence, along with thermal stress, (both from the "crustal conveyor belt" process of resurfacing) in Io's lithosphere with stresses from Io mountain-sized loads (in a shallow spherical shell solution) in order to evaluate magma ascent pathways. We use stress orientation (least compressive stress horizontal) and stress gradient (compression decreasing upwards) criteria to identify ascent pathways through the lithosphere. There are several configurations for which viable ascent paths transit nearly the entire lithosphere, arriving at the base of the mountain, where magma can be transported through thrust faults or perhaps thermally eroded flank sections. The latter is consistent with observations of some Io paterae in close contact with mountains.

  19. The chlorine isotope fingerprint of the lunar magma ocean.

    PubMed

    Boyce, Jeremy W; Treiman, Allan H; Guan, Yunbin; Ma, Chi; Eiler, John M; Gross, Juliane; Greenwood, James P; Stolper, Edward M

    2015-09-01

    The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free ("dry") Moon. We have analyzed abundances and isotopic compositions of Cl and H in lunar mare basalts, and find little evidence that anhydrous lava outgassing was important in generating chlorine isotope anomalies, because (37)Cl/(35)Cl ratios are not related to Cl abundance, H abundance, or D/H ratios in a manner consistent with the lava-outgassing hypothesis. Instead, (37)Cl/(35)Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high (37)Cl/(35)Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar magma ocean. These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar magma ocean early in the Moon's history. Chlorine isotope variability is therefore an indicator of planetary magma ocean degassing, an important stage in the formation of terrestrial planets. PMID:26601265

  20. Automatic Compound Annotation from Mass Spectrometry Data Using MAGMa

    PubMed Central

    Ridder, Lars; van der Hooft, Justin J. J.; Verhoeven, Stefan

    2014-01-01

    The MAGMa software for automatic annotation of mass spectrometry based fragmentation data was applied to 16 MS/MS datasets of the CASMI 2013 contest. Eight solutions were submitted in category 1 (molecular formula assignments) and twelve in category 2 (molecular structure assignment). The MS/MS peaks of each challenge were matched with in silico generated substructures of candidate molecules from PubChem, resulting in penalty scores that were used for candidate ranking. In 6 of the 12 submitted solutions in category 2, the correct chemical structure obtained the best score, whereas 3 molecules were ranked outside the top 5. All top ranked molecular formulas submitted in category 1 were correct. In addition, we present MAGMa results generated retrospectively for the remaining challenges. Successful application of the MAGMa algorithm required inclusion of the relevant candidate molecules, application of the appropriate mass tolerance and a sufficient degree of in silico fragmentation of the candidate molecules. Furthermore, the effect of the exhaustiveness of the candidate lists and limitations of substructure based scoring are discussed. PMID:26819876

  1. Buffered and unbuffered dike emplacement on Earth and Venus - Implications for magma reservoir size, depth, and rate of magma replenishment

    NASA Technical Reports Server (NTRS)

    Parfitt, E. A.; Head, J. W., III

    1993-01-01

    Models of the emplacement of lateral dikes from magma chambers under constant (buffered) driving pressure conditions and declining (unbuffered) driving pressure conditions indicate that the two pressure scenarios lead to distinctly different styles of dike emplacement. In the unbuffered case, the lengths and widths of laterally emplaced dikes will be severely limited and the dike lengths will be highly dependent on chamber size; this dependence suggests that average dike length can be used to infer the dimensions of the source magma reservoir. On Earth, the characteristics of many mafic-dike swarms suggest that they were emplaced in buffered conditions (e.g., the Mackenzie dike swarm in Canada and some dikes within the Scottish Tertiary). On Venus, the distinctive radial fractures and graben surrounding circular to oval features and edifices on many size scales and extending for hundreds to over a thousand km are candidates for dike emplacement in buffered conditions.

  2. 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

  3. 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.

  4. Timescales for permeability reduction and strength recovery in densifying magma

    NASA Astrophysics Data System (ADS)

    Heap, M. J.; Farquharson, J. I.; Wadsworth, F. B.; Kolzenburg, S.; Russell, J. K.

    2015-11-01

    Transitions between effusive and explosive behaviour are routine for many active volcanoes. The permeability of the system, thought to help regulate eruption style, is likely therefore in a state of constant change. Viscous densification of conduit magma during effusive periods, resulting in physical and textural property modifications, may reduce permeability to that preparatory for an explosive eruption. We present here a study designed to estimate timescales of permeability reduction and strength recovery during viscous magma densification by coupling measurements of permeability and strength (using samples from a suite of variably welded, yet compositionally identical, volcanic deposits) with a rheological model for viscous compaction and a micromechanical model, respectively. Bayesian Information Criterion analysis confirms that our porosity-permeability data are best described by two power laws that intersect at a porosity of 0.155 (the "changepoint" porosity). Above and below this changepoint, the permeability-porosity relationship has a power law exponent of 8.8 and 1.0, respectively. Quantitative pore size analysis and micromechanical modelling highlight that the high exponent above the changepoint is due to the closure of wide (∼200-300 μm) inter-granular flow channels during viscous densification and that, below the changepoint, the fluid pathway is restricted to narrow (∼50 μm) channels. The large number of such narrow channels allows porosity loss without considerable permeability reduction, explaining the switch to a lower exponent. Using these data, our modelling predicts a permeability reduction of four orders of magnitude (for volcanically relevant temperatures and depths) and a strength increase of a factor of six on the order of days to weeks. This discrepancy suggests that, while the viscous densification of conduit magma will inhibit outgassing efficiency over time, the regions of the conduit prone to fracturing, such as the margins, will

  5. Geochemical evidences of magma dynamics at Campi Flegrei (Italy)

    NASA Astrophysics Data System (ADS)

    Caliro, S.; Chiodini, G.; Paonita, A.

    2014-05-01

    Campi Flegrei caldera, within the Neapolitan area of Italy, is potentially one of the most dangerous volcanoes in the world, and during the last decade it has shown clear signs of reactivation, marked by the onset of uplift and changes in the geochemistry of gas emissions. We describe a 30-year-long data set of the CO2-He-Ar-N2 compositions of fumarolic emissions from La Solfatara crater, which is located in the center of the caldera. The data display continuous decreases in both the N2/He and N2/CO2 ratios since 1985, paralleled by an increase in He/CO2. These variations cannot be explained by either processes of boiling/condensation in the local hydrothermal system or with changes in the mixing proportions between a magmatic vapor and hydrothermal fluids. We applied the magma degassing model of Nuccio and Paonita (2001, Earth Planet. Sci. Lett. 193, 467-481) using the most recent inert-gas solubilities in order to interpret these peculiar features in accordance with petrologic constraints derived from the ranges of the melt compositions and reservoir pressures at Campi Flegrei. The model simulations for mafic melts (trachybasalt and shoshonite) show a remarkably good agreement with the measured data. Both decompressive degassing of an ascending magma and mixing between magmatic fluids exsolved at various levels along the ascent path can explain the long-term geochemical changes. Recalling that (i) a sill-like reservoir of gases at a depth of 3-4 km seems to be the main source of ground inflation and (ii) there is petrologic and geophysical evidence for a reservoir of magma at about 8 km below Campi Flegrei, we suggest that the most-intense episodes of inflation occur when the gas supply to the sill-like reservoir comes from the 8 km-deep magma, although fluids exsolved by magma bodies at shallower depths also contribute to the gas budget. Our work highlights that, in caldera systems where the presence of hydrothermal aquifers commonly masks the magmatic signature

  6. The non-isothermal rheology of low viscosity magmas.

    NASA Astrophysics Data System (ADS)

    Kolzenburg, Stephan; Giordano, Daniele; Dingwell, Donald B.

    2016-04-01

    Accurate prediction of the run-out distance of lava flows, as well as the understanding of magma migration in shallow dyke systems is hampered by an incomplete understanding of the transient, sub-liquidus rheology of crystallizing melts. This sets significant limits to physical property based modelling of lava flow (especially flow width, length and advancement rate) and magma migration behaviour and the resulting accuracy of volcanic hazard assessment The importance of the dynamic rheology of a lava / magma on its emplacement style becomes especially apparent in towards later stages of flow and dyke emplacement, where the melt builds increasing resistance to flow, entering rheologic regimes that determine the halting of lava flows and sealing of dykes. Thermal gradients between the interior of a melt body and the contact with air or the substratum govern these rheologic transitions that give origin to flow directing or impeding features like levees, tubes and chilled margins. Besides the critical importance of non-isothermal and sub-liquidus processes for the understanding of natural systems, accurate rheologic data at these conditions are scarce and studies capturing the transient rheological evolution of lavas at conditions encountered during emplacement virtually absent. We describe the rheologic evolution of a series of natural, re-melted lava samples during transient and non-equilibrium crystallization conditions characteristic of lava flows and shallow magmatic systems in nature. The sample suite spans from foidites to basalts; the dominant compositions producing low viscosity lava flows. Our data show that all melts undergo one or more change zones in effective viscosity when subjected to sub liquidus temperatures. The apparent viscosity of the liquid-crystal suspension increases drastically from the theoretical temperature-viscosity relationship of a pure liquid once cooled below the liquidus temperature. We find that: 1) Both cooling rate and shear rate

  7. The Yellowstone magma reservoir is 50% larger than previously imaged

    NASA Astrophysics Data System (ADS)

    Farrell, J.; Smith, R. B.; Husen, S.

    2013-12-01

    Earlier tomographic studies of the Yellowstone crustal magma system have revealed a low P-wave crustal anomaly beneath the 0.64 Ma Yellowstone caldera that has been interpreted to be the magma reservoir of partial melt that provides the thermal energy for Yellowstone's youthful volcanic and hydrothermal systems. The Yellowstone seismic network has evolved over the last decade into a modern real-time volcano monitoring system that consists of 36 short-period, broadband, and borehole seismometers that cover the entire Yellowstone volcanic field and surrounding tectonic areas. Until recently, limited seismograph coverage did not provide for adequate resolution of the velocity structure northeast of the caldera, an area of the largest negative Bouguer gravity field of -60 mGal whose 3D density model reveals a shallow, low density body that extends ~20 km northeast of the caldera. Recent upgrades to the Yellowstone Seismic Network (YSN), including the addition of nine 3-component and broadband seismic stations providing much better ray coverage of the entire Yellowstone area with greater bandwidth data. This allows much-expanded and improved resolution coverage of the Yellowstone crustal velocity structure. We have compiled waveforms for the Yellowstone earthquake catalog from 1984-2011 with 45,643 earthquakes and 1,159,724 waveforms to analyze P-wave arrival times with an automatic picker based on an adaptive high-fidelity human mimicking algorithm. Our analysis reduced the data to the 4,520 best-located earthquakes with 48,622 P-wave arrival times to invert for the velocity structure. The resulting 3D P-wave model reveals a low Vp body (up to -7% ΔVp) that is interpreted to be the Yellowstone crustal magma reservoir and is ~50% larger than previously imaged. It extends as an oblong shaped anomalous body ~90 km NE-SW, ~20 km NE of the 0.64 Ma caldera, and up to 30 km wide and markedly shallowing from 15 km depth beneath the caldera to less than ~2 km deep northeast of

  8. Reconciling Volatile Outputs with Heat Flow and Magma Intrusion Rates at the Yellowstone Magma-Hydrothermal System

    NASA Astrophysics Data System (ADS)

    Lowenstern, J. B.; Hurwitz, S.

    2012-12-01

    The Yellowstone hydrothermal system releases hundreds of millions of liters of water on a daily basis. Gigawatts of heat and kilotons of magmatic volatiles (CO2, S, Cl, F and He) are discharged by these waters. By quantifying the relative contributions of crustal, meteoric, and mantle-derived components, we can estimate the rate at which magma is fed to the crust from below (1). Combining isotopic studies with mass discharge rates of geothermal gases and aqueous dissolved solids, we recognize that over 20,000 tons of CO2 is released from basaltic magmas ponding beneath any silicic magma reservoir in the mid to shallow crust (1,2). In contrast, silicic magma provides significantly less volatiles than what emerges from the hydrothermal system. Estimates of heat flow range from ~3 to 8 GW (1,3,4), derived from satellite, surface geophysics and geochemical methods. Such values, combined with estimates from gas flux, imply prolific basalt intrusion rates between 0.05 and 0.3 cubic kilometers per year (1). Over the history of the Yellowstone Plateau Volcanic Field, a picture emerges where the lower crust is converted from Precambrian metasediments and silicic intrusions into a thick gabbroic batholith similar to that envisioned by some to reside beneath the Snake River Plain along the ancestral track of the Yellowstone Hot Spot (5). (1) Lowenstern and Hurwitz, 2008, Elements 4: 35-40. (2) Werner and Brantley, 2003, G-Cubed 4;7: 1061 (3) Vaughan and others, 2012, JVGR 233-234: 72-89. (4) Hurwitz and others, in press, JGR (5) Shervais and others, 2006, Geology 34:365-368.

  9. Sediment-enriched adakitic magmas from the Daisen volcanic field, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Feineman, Maureen; Moriguti, Takuya; Yokoyama, Tetsuya; Terui, Sakiko; Nakamura, Eizo

    2013-08-01

    The Quaternary Southwest Japan Arc is a product of subduction of the hot, young Philippine Sea Plate beneath the Eurasian Continental Plate. The magmas erupted from the Southwest Japan Arc belong to a category of magmas commonly referred to as "adakites" or "adakitic magmas". These magmas show trace element evidence for interaction with garnet at depth, and may be associated with partial melting of subducted altered oceanic crust. Also found throughout the southern Sea of Japan region are alkali basalts with little apparent connection to the subduction zone. We have determined major element, trace element, and Sr, Nd, Pb, and U-Th isotopic compositions for a bimodal suite of lavas erupted at the Daisen volcanic field in the Southwest Japan Arc. These magmas consist of mildly alkaline basalts and a calcalkaline intermediate suite, separated by a ˜10 wt.% silica gap. The intermediate magmas show trace element and isotopic evidence for interaction with garnet, consistent with partial melting of the hot, young (˜20 Ma) Philippine Sea Plate. The Daisen intermediate magmas are distinct from other adakitic magmas in their radiogenic isotopic characteristics, consistent with a significant contribution (˜25%) from subducted Nankai Trough sediments. Our data suggest that the basalts erupted at the Daisen volcanic field are not parental to the intermediate magmas, and contain a small contribution of EM1-like mantle common in Sea of Japan alkali basalts but not apparent in the Daisen intermediate magmas.

  10. The Perils of Partition: Difficulties in Retrieving Magma Compositions from Chemically Equilibrated Basaltic Meteorites

    NASA Technical Reports Server (NTRS)

    Treiman, Allan H.

    1996-01-01

    The chemical compositions of magmas can be derived from the compositions of their equilibrium minerals through mineral/magma partition coefficients. This method cannot be applied safely to basaltic rocks, either solidified lavas or cumulates, which have chemically equilibrated or partially equilibrated at subsolidus temperatures, i.e., in the absence of magma. Applying mineral/ melt partition coefficients to mineral compositions from such rocks will typically yield 'magma compositions' that are strongly fractionated and unreasonably enriched in incompatible elements (e.g., REE's). In the absence of magma, incompatible elements must go somewhere; they are forced into minerals (e.g., pyroxenes, plagioclase) at abundance levels far beyond those established during normal mineral/magma equilibria. Further, using mineral/magma partition coefficients with such rocks may suggest that different minerals equilibrated with different magmas, and the fractionation sequence of those melts (i.e., enrichment in incompatible elements) may not be consistent with independent constraints on the order of crystallization. Subsolidus equilibration is a reasonable cause for incompatible- element-enriched minerals in some eucrites, diogenites, and martian meteorites and offers a simple alternative to petrogenetic schemes involving highly fractionated magmas or magma infiltration metasomatism.

  11. Origin of magmas in subduction zones: a review of experimental studies

    PubMed Central

    Kushiro, Ikuo

    2007-01-01

    Studies of the origin of magmas in subduction zones, particularly in the Japanese island arc, have been significantly advanced by petrological, geochemical, geophysical and experimental studies during last 50 years. Kuno’s original model1) for magma generation in the Japanese island arc, that tholeiite magmas are formed at relatively shallow levels in the mantle on the Pacific Ocean side whereas alkali basalt magmas are formed in deeper levels on the Japan Sea side, stimulated subsequent studies, particularly high-pressure experimental studies in which the author participated. Recent seismic tomographic studies of regions beneath the Japanese island arc demonstrate that seismic low-velocity zones where primary magmas are formed have finger-like shapes and rise obliquely from the Japan Sea side toward the Pacific Ocean side. Based on experimental studies, it is suggested that the compositions of primary magmas depend mainly on the H2O content and degree of melting in the melting zones, and that primary tholeiite magmas are formed by 10–25% melting of the source mantle containing less than 0.2 wt.% H2O. High-alumina basalt and alkali basalt magmas are formed by smaller degrees of melting of similar mantle, whereas primary boninite magmas are formed by more than 20% melting of the source mantle with more than 0.2 wt.% H2O, and finally, high-magnesia andesite magmas are formed by smaller degrees of melting of similar mantle. PMID:24019580

  12. Origin of magmas in subduction zones: a review of experimental studies.

    PubMed

    Kushiro, Ikuo

    2007-02-01

    Studies of the origin of magmas in subduction zones, particularly in the Japanese island arc, have been significantly advanced by petrological, geochemical, geophysical and experimental studies during last 50 years. Kuno's original model(1)) for magma generation in the Japanese island arc, that tholeiite magmas are formed at relatively shallow levels in the mantle on the Pacific Ocean side whereas alkali basalt magmas are formed in deeper levels on the Japan Sea side, stimulated subsequent studies, particularly high-pressure experimental studies in which the author participated. Recent seismic tomographic studies of regions beneath the Japanese island arc demonstrate that seismic low-velocity zones where primary magmas are formed have finger-like shapes and rise obliquely from the Japan Sea side toward the Pacific Ocean side. Based on experimental studies, it is suggested that the compositions of primary magmas depend mainly on the H2O content and degree of melting in the melting zones, and that primary tholeiite magmas are formed by 10-25% melting of the source mantle containing less than 0.2 wt.% H2O. High-alumina basalt and alkali basalt magmas are formed by smaller degrees of melting of similar mantle, whereas primary boninite magmas are formed by more than 20% melting of the source mantle with more than 0.2 wt.% H2O, and finally, high-magnesia andesite magmas are formed by smaller degrees of melting of similar mantle. PMID:24019580

  13. Controls on the explosivity of scoria cone eruptions: Magma segregation at conduit junctions

    NASA Astrophysics Data System (ADS)

    Pioli, L.; Azzopardi, B. J.; Cashman, K. V.

    2009-10-01

    Violent strombolian (transitional) eruptions are common in mafic arc settings and are characterized by simultaneous explosive activity from scoria cone vents and lava effusion from lateral vents. This dual activity requires magma from the feeder conduit to split into vertical and lateral branches somewhere near the base of the scoria cone. Additionally, if the flow is separated, gas and liquid (+ crystals) components of the magma may be partitioned unevenly between the two branches. Because flow separation requires bubbles to move independently of the liquid over time scales of magma ascent separation is promoted by low magma viscosities and by high magma H 2O content (i.e. sufficiently deep bubble nucleation to allow organization of the gas and liquid phases during magma ascent). Numerical modeling shows that magma and gas distribution between vertical and horizontal branches of a T-junction is controlled by the mass flow rate and the geometry of the system, as well as by magma viscosity. Specifically, we find that mass eruption rates (MERs) between 10 3 and 10 5 kg/s allow the gas phase to concentrate within the central conduit, significantly increasing explosivity of the eruption. Lower MERs produce either strombolian or effusive eruption styles, while MER > 10 5 kg/s prohibit both gas segregation and lateral magma transport, creating explosive eruptions that are not accompanied by effusive activity. These bracketing MER constraints on eruptive transitions are consistent with field observations from recent eruptions of hydrous mafic magmas.

  14. 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.

  15. An empirical scaling of shear-induced outgassing during magma ascent: Intermittent magma ascent causes effective outgassing

    NASA Astrophysics Data System (ADS)

    Namiki, Atsuko

    2012-11-01

    Outgassing, which changes the distribution of volcanic gases in magmas, is one of the most important processes to determine the eruption styles. Shear deformation of ascending bubbly magmas at the vicinity of the volcanic conduit wall has been considered as an efficient mechanism of outgassing. On the other hand, seismological observations of volcanic eruptions reveal the gas bursting associated with long-period (LP) earthquakes and tremors, suggesting the existence of a large void space in the conduit. However both, the quantitative features of shear-induced outgassing and a mechanism to make a large void space, have still remain unknown. Here I perform a series of model experiments in which shear localization of syrup foam causes outgassing by making large bubbles or a crack-like void space, likely a gas bursting source. There is a critical strain, γ, above which outgassing occurs depending on the Capillary number, Ca, γ>1 for Ca<1 and γ>Ca-1 for Ca≥1. The width of the region in which outgassing occurs is described as a function of γ0.48Ca0.24. Outgassing occurs efficiently at the very beginning of the deformation, suggesting that intermittent magma ascent causes effective outgassing such that the eruption style becomes effusive. This hypothesis is consistent with the fact that cyclic activity has been observed during effusive dome eruptions.

  16. Eruptive dynamics during magma decompression: a laboratory approach

    NASA Astrophysics Data System (ADS)

    Spina, L.; Cimarelli, C.; Scheu, B.; Wadsworth, F.; Dingwell, D. B.

    2013-12-01

    A variety of eruptive styles characterizes the activity of a given volcano. Indeed, eruptive styles can range from effusive phenomena to explosive eruptions, with related implications for hazard management. Rapid changes in eruptive style can occur during an ongoing eruption. These changes are, amongst other, related to variations in the magma ascent rate, a key parameter affecting the eruptive style. Ascent rate is in turn dependent on several factors such as the pressure in the magma chamber, the physical properties of the magma and the rate at which these properties change. According to the high number of involved parameters, laboratory decompression experiments are the best way to achieve quantitative information on the interplay of each of those factors and the related impact on the eruption style, i.e. by analyzing the flow and deformation behavior of the transparent volatile-bearing analogue fluid. We carried out decompression experiments following different decompression paths and using silicone oil as an analogue for the melt, with which we can simulate a range of melt viscosity values. For a set of experiments we added rigid particles to simulate the presence of crystals in the magma. The pure liquid or suspension was mounted into a transparent autoclave and pressurized to different final pressures. Then the sample was saturated with argon for a fixed amount of time. The decompression path consists of a slow decompression from the initial pressure to the atmospheric condition. Alternatively, samples were decompressed almost instantaneously, after established steps of slow decompression. The decompression path was monitored with pressure transducers and a high-speed video camera. Image analysis of the videos gives quantitative information on the bubble distribution with respect to depth in the liquid, pressure and time of nucleation and on their characteristics and behavior during the ongoing magma ascent. Furthermore, we also monitored the evolution of

  17. The role of bubble ascent in magma mixing

    NASA Astrophysics Data System (ADS)

    Wiesmaier, Sebastian; Morgavi, Daniele; Perugini, Diego; De Campos, Cristina; Hess, Kai-Uwe; Lavallée, Yan; Dingwell, Donald B.

    2013-04-01

    Understanding the processes that affect the rate of liquid state homogenization provides fundamental clues on the otherwise inaccessible subsurface dynamics of magmatic plumbing systems. Compositional heterogeneities detected in the matrix of magmatic rocks represent the arrested state of a chemical equilibration. Magmatic homogenization is divided into a) the mechanical interaction of magma batches (mingling) and b) the diffusive equilibration of compositional gradients, where diffusive equilibration is exponentially enhanced by progressive mechanical interaction [1]. The mechanical interaction between two distinct batches of magma has commonly been attributed to shear and folding movements between two distinct liquids. A mode of mechanical interaction scarcely invoked is the advection of mafic material into a felsic one through bubble motion. Yet, experiments with analogue materials demonstrated that bubble ascent has the potential to enhance the fluid mechanical component of magma mixing [2]. Here, we present preliminary results from bubble-advection experiments. For the first time, experiments of this kind were performed using natural materials at magmatic temperatures. Cylinders of Snake River Plain (SRP) basalt were drilled with a cavity of defined volume and placed underneath cylinders of SRP rhyolite. Upon melting, the gas pocket (=bubble) trapped within the cavity, rose into the rhyolite, and thus entraining a portion of basaltic material in the shape of a plume trail. These plume-like structures that the advected basalt formed within the rhyolite were characterized by microCT and subsequent high-resolution EMP analyses. Single protruding filaments at its bottom end show a composite structure of many smaller plume tails, which may indicate the opening of a preferential pathway for bubbles after a first bubble has passed. The diffusional gradient around the plume tail showed a progressive evolution of equilibration from bottom to top of the plume tail

  18. Petrologic Insights into Magma System Response to Edifice Collapse

    NASA Astrophysics Data System (ADS)

    Shipman, J. S.; Izbekov, P. E.; Gavrilenko, M.

    2011-12-01

    In order to understand eruptive behavior at volcanic centers and to improve models for monitoring and prediction of volcanic eruptions, it is important to constrain magma storage conditions and transport in the system. Here the post-collapse eruptive behavior at Bezymianny and Shiveluch volcanoes, (Kamchatka Peninsula, Russia) are each compared to the well-known sequence at Mount St. Helens, Washington, USA (from 1956, 1964, and 1980, respectively). The magma system responds to rapid unloading of overburden pressure, due to edifice collapse, with a violent large-scale paroxysmal eruption. This reflects the amplitude of the triggering decompression event with later dome-building and explosive activity due to the reduction of vent elevation. The massive unloading events and post-collapse eruptive chronologies, provides a unique opportunity for comparison of the sources driving the catastrophic eruptions and eruptive style transitions. Analytical techniques employed included X-ray fluorescence spectroscopy, electron probe micro-analyses, Fe-Ti oxide and two-pyroxene geothermometry, X-ray elemental mapping, and a novel image processing technique. Presented here are results from petrological investigations into the temporal variations of whole-rock geochemistry, geothermometry, mineral modal abundances and textures. Bezymianny is becoming more mafic over time from 61.0 to 57.3 wt.% SiO2 (1956 and 2010). Pre-eruptive magma temperatures increased from 950oC to 1050oC from 1956 to 2006. Plagioclase and amphibole disequilibrium textures are observed throughout the time series and rare mafic enclaves exist. The whole-rock chemical trend at Shiveluch shows a subtle, yet reversed trend from 60.6 to 64.2 wt.% SiO2 (1964 and 2007). Two-pyroxene geothermometry yields ~950oC+30oC (2001-2007) and is consistent with data from the 2001 -2004 eruption, of 834-978oC+60oC. Mafic enclaves occurred throughout the entire period of eruptive activity at Shiveluch. In contrast to both

  19. 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.

  20. 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

  1. The dynamics of magma transport and eruption processes: An overview of recent developments

    SciTech Connect

    Carrigan, C.R. ); Eichelberger, J.C.; Stockman, H.W. )

    1990-05-01

    The transport of magma in the Earth's crust and its eruption onto the surface can be strongly affected by seemingly subtle details of mass and heat transfer that are often overlooked. In particular, model calculations indicate that the multiphase nature of magma will exert a significant influence. The dynamics of flowing magma may be further enriched by chemical heterogeneity. A variety of studies indicate that a heterogeneous magma can be self-lubricating if viscous segregation of its components occurs. Subtle modifications of dike geometry and boundary conditions can also significantly affect magma transport in thermally unfavorable regimes. Nearer to the surface, changes with time in the permeability of vent boundaries that control leakage of the vapor phase have been linked to the normal progression from explosive, ash producing events to more effusive ones that form lava domes. In this review we attempt to integrate a variety of effects into a coherent view of magma transport and eruption. 16 refs., 8 figs.

  2. 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.

  3. 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.

  4. Lithological controls on shallow-level magma emplacement (Invited)

    NASA Astrophysics Data System (ADS)

    Magee, C.; Jackson, C. A.; Schofield, N.; Briggs, F.

    2013-12-01

    The emplacement of magma within the upper crust requires space to be generated by the deformation or assimilation of the host rock. Intrusion morphologies, magma reservoir locations and the architecture of interconnecting magma conduits are therefore strongly influenced by the behaviour of the host rock during emplacement. Importantly, monitoring host rock deformation affects (e.g., surface uplift) can provide invaluable insights into the potential timing, location and magnitude of future volcanic eruptions. This has led to significant advances in the inversion of host rock deformation patterns, acquired from geophysical and geodetic data, to elucidate sub-volcanic plumbing systems. However, the link between the shape and size of intrusion and the style and magnitude of the ground deformation is non-unique. While numerical and physical models have been developed to test plausible intrusion-deformation scenarios, they cannot explicitly incorporate complex host rock stratigraphies, temperature-driven intrusion-host rock interactions or brittle faulting. We advocate that three-dimensional seismic reflection data, which provide unparalleled images of entire volcanic plumbing systems, can be used to enhance our understanding of the intrusive networks and to test hypotheses concerning syn-emplacement host rock deformation. We use 3D seismic reflection data from the Exmouth Sub-basin, offshore NW Australia, to examine the link between a saucer-shaped sill and an overlying, dome-shaped fold developed at the contemporaneous palaeosurface. Our results highlight a disparity in size (e.g., areal coverage, thickness/amplitude) between the sill and fold, which we attribute to the initial accommodation of magma by fluid expulsion from the poorly consolidated claystone host rock, prior to a period of (forced) folding. This is supported by field observations, which indicate ';triggered' or ';thermal' fluidisation of the host rock may occur during sill emplacement. In such cases

  5. Rheological flow laws for multiphase magmas: An empirical approach

    NASA Astrophysics Data System (ADS)

    Pistone, Mattia; Cordonnier, Benoît; Ulmer, Peter; Caricchi, Luca

    2016-07-01

    The physical properties of magmas play a fundamental role in controlling the eruptive dynamics of volcanoes. Magmas are multiphase mixtures of crystals and gas bubbles suspended in a silicate melt and, to date, no flow laws describe their rheological behaviour. In this study we present a set of equations quantifying the flow of high-viscosity (> 105 Pa·s) silica-rich multiphase magmas, containing both crystals (24-65 vol.%) and gas bubbles (9-12 vol.%). Flow laws were obtained using deformation experiments performed at high temperature (673-1023 K) and pressure (200-250 MPa) over a range of strain-rates (5 · 10- 6 s- 1 to 4 · 10- 3 s- 1), conditions that are relevant for volcanic conduit processes of silica-rich systems ranging from crystal-rich lava domes to crystal-poor obsidian flows. We propose flow laws in which stress exponent, activation energy, and pre-exponential factor depend on a parameter that includes the volume fraction of weak phases (i.e. melt and gas bubbles) present in the magma. The bubble volume fraction has opposing effects depending on the relative crystal volume fraction: at low crystallinity bubble deformation generates gas connectivity and permeability pathways, whereas at high crystallinity bubbles do not connect and act as "lubricant" objects during strain localisation within shear bands. We show that such difference in the evolution of texture is mainly controlled by the strain-rate (i.e. the local stress within shear bands) at which the experiments are performed, and affect the empirical parameters used for the flow laws. At low crystallinity (< 44 vol.%) we observe an increase of viscosity with increasing strain-rate, while at high crystallinity (> 44 vol.%) the viscosity decreases with increasing strain-rate. Because these behaviours are also associated with modifications of sample textures during the experiment and, thus, are not purely the result of different deformation rates, we refer to "apparent shear-thickening" and

  6. Volcanic gas emissions: constraining magma degassing and volatile sources (Invited)

    NASA Astrophysics Data System (ADS)

    Fischer, T. P.; de Moor, M. J.

    2013-12-01

    Approximately 70 volcanoes erupt per year and about 500 emit gases through vents or hydrothermal systems. The global volcanic sulfur flux is dominated by passively degassing volcanoes and only 1-10% of the total SO2 flux is emitted during eruptions [1, 2] - likely also the case for other volatiles. Magmas lose their volatiles during ascent from the mantle and magma with 7 wt% water will become saturated at 15-17 km depth [3]. Volcanic eruptions commonly release more gas into the atmosphere than could have been dissolved in the erupted magma, first recognized by Rose [4]. Volcanic gases provide information on magmatic volatiles. Sampling of high temperature (> 400°C) volcanic gases emitted from crater fumaroles provide complete information on gas chemistry and isotopic ratios that are generally unaffected by low-temperature processes [5]. Complete gas compositions can be evaluated for equilibrium and corrected for modifications due to atmospheric contamination to obtain near-pristine magmatic gas compositions. In cases where gas and magma have been evaluated for fO2 both generally agree. Oxygen fugacities calculated using gas equilibria (H2/H2O; CO2/CO) show that the highest temperature (>800C) gases from rifts (Erta Ale) are close to QFM, arc volcanoes record oxygen fugacities above QFM (ΔQFM +6 to +8 based on H2O/H2; +0.2 to +3.7 based on CO2/CO) consistent with a more oxidized nature of the subarc-mantle. H-based gas equilibria show significantly higher oxygen fugacities than C-based values. This may be related to surfical water in the system or oxidation of H, which can be tracked by stable isotopes. H2O/CO2 values vary between arcs where Kuriles, Japan and Kamchatka show higher ratios (40 to 800) than Cascades, Central America, S. America, Java, and Aeolian (1 to 70). Erta Ale gases have H2O/CO2 of 3. Order of magnitude changes in H2O/CO2 ratios (2 to 20) due to magma degassing have been unequivocally documented by Gerlach [6] at Kilauea. H2O/CO2 ratios in

  7. 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

  8. Continental mantle signature of Bushveld magmas and coeval diamonds.

    PubMed

    Richardson, Stephen H; Shirey, Steven B

    2008-06-12

    The emplacement of the 2.05-billion-year-old Bushveld complex, the world's largest layered intrusion and platinum-group element (PGE) repository, is a singular event in the history of the Kaapvaal craton of southern Africa, one of Earth's earliest surviving continental nuclei. In the prevailing model for the complex's mineralization, the radiogenic strontium and osmium isotope signatures of Bushveld PGE ores are attributed to continental crustal contamination of the host magmas. The scale of the intrusion and lateral homogeneity of the PGE-enriched layers, however, have long been problematical for the crustal contamination model, given the typically heterogeneous nature of continental crust. Furthermore, the distribution of Bushveld magmatism matches that of seismically anomalous underlying mantle, implying significant interaction before emplacement in the crust. Mineral samples of the ancient 200-km-deep craton keel, encapsulated in macrodiamonds and entrained by proximal kimberlites, reveal the nature of continental mantle potentially incorporated by Bushveld magmas. Here we show that sulphide inclusions in approximately 2-billion-year-old diamonds from the 0.5-billion-year-old Venetia and 1.2-billion-year-old Premier kimberlites (on opposite sides of the complex) have initial osmium isotope ratios even more radiogenic than those of Bushveld sulphide ore minerals. Sulphide Re-Os and silicate Sm-Nd and Rb-Sr isotope compositions indicate that continental mantle harzburgite and eclogite components, in addition to the original convecting mantle magma, most probably contributed to the genesis of both the diamonds and the Bushveld complex. Coeval diamonds provide key evidence that the main source of Bushveld PGEs is the mantle rather than the crust. PMID:18548068

  9. A Primordial and Complicated Ocean of Magma on Mars

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2006-03-01

    It seems almost certain that the Moon was surrounded by an ocean of magma when it formed. This important idea has been applied to the other terrestrial planets and even to asteroids. Linda (Lindy) Elkins-Tanton and colleagues Mark Parmentier, Paul Hess, and Sarah Zaranek at Brown University, and Lars Borg and David Draper (University of New Mexico) have examined the chemical and physical consequences of magma ocean crystallization on Mars. Elkins-Tanton has focused on the fate of the pile of crystals created during solidification of a magma ocean over a thousand kilometers thick. Crystallization causes the minerals that form first to lie beneath those formed later. The deepest minerals are also less dense than the overlying minerals. This is an unstable situation: the low-density rocks would have a tendency to rise while the high-density rocks would have a tendency to sink. Although we think of rocks as solid and hard, when hot and under pressure, they flow like liquids. They do not flow fast, but they do flow like ultra-gooey liquids (about a factor of 100 million billion times gooier than ketchup at room temperature). Thus, the heavy layers sink and the light layers rise, producing a complicated Martian mantle with chemical characteristics like those cosmochemists infer from studies of Martian meteorites. The sinking of relatively cool rocks from the top of the crystallized pile cools the boundary between the metallic core and the mantle, causing motions inside the core to produce the early, strong magnetic field of Mars.

  10. Role of magma-water interaction in very large explosive eruptions

    SciTech Connect

    Valentine, G.A.

    1993-11-01

    An important class of explosive eruptions, involving large-scale magma-water interaction during the discharge of hundreds to thousands of cubic kilometers of magma, is discussed. Geologic evidence for such eruptions is summarized. Case studies from New Zealand, Australia, England, and the western United States are described, focusing on inferred eruption dynamics. Several critical problems that need theoretical and experimental research are identified. These include rates at which water can flow into a volcanic vent or plumbing system, entrainment of water by explosive eruptions through lakes and seas, effects of magma properties and gas bubbles on magma-water interaction, and hazards associated with the eruptions.

  11. Self-Potential Changes Caused by Magma Ascent and Degassing

    NASA Astrophysics Data System (ADS)

    Ishido, T.

    2009-12-01

    The self-potential (SP) distributions have similar features on a number of volcanoes: SP first decreases several hundred millivolts to more than one volts as one climbs the slopes of the volcano, then rapidly recovers to the level measured on the flank of volcano as the summit crater is approached. Consequently, the entire SP profile along a survey line starting from the foot, passing near the summit and reaching the foot on the opposite side often has the shape of the letter "W". Numerical simulations by Ishido (2004; see, Geophys. Res. Lett., doi:10.1029/2004GL020409) showed that the primary cause of the "W"-shaped SP distribution is a combination of the electrokinetic drag current associated with the downward liquid flow in the unsaturated and underlying saturated layers and the presence of a shallow conductor near the volcano summit. If the shallow conductor contacts a deep conductive layer, this conductive structure provides a current path between the low-potential shallow and high-potential deep regions, resulting in substantial increase in SP around the summit. The calculated amplitude of high SP around the summit is sensitive to the conductivity structure, which is thought to change over time due to volcanic activities such as magma ascent, degassing, development of hydrothermal convection, etc. Evolution of high SP near the summit crater due to ascent of magma and associated degassing is expected to be largely affected by the continuity of the pre-existing conductive structure between the near surface and deep regions. In the present study, the effects of high temperature acidic gas emanated from magma into surrounding country rocks are discussed based upon the results of numerical simulation. In case that the permeability of the country rock is relatively high, the volcanic gas diffuses into the country rock over a substantial distance, creates a dry-out region adjacent to the volcanic conduit where magma is ascending and condenses into acidic water in

  12. Magma ascent pathways associated with large mountains on Io

    NASA Astrophysics Data System (ADS)

    McGovern, P. J.; Kirchoff, M. R.; White, O. L.; Schenk, P.

    2013-12-01

    While Jupiter's moon Io is the most volcanically active body in the solar system, the largest mountains seen on Io are created by tectonic forces rather than volcanic construction. Pervasive compression, brought about by subsidence induced by sustained volcanic resurfacing and aided by thermal stress, creates the mountains, but at the same time inhibits magma ascent in vertical conduits (dikes). We superpose stress solutions for subsidence and thermal stress (from the 'crustal conveyor belt' resurfacing) in Io's lithosphere with stresses from Io mountain-sized loads (in a shallow spherical shell solution) in order to evaluate magma ascent pathways. We use stress orientation (least compressive stress horizontal) and stress gradient (compression decreasing upwards) criteria to identify ascent pathways through the lithosphere. For nominal 'conveyor belt' stress states, the ascent criteria are satisfied only in a narrow (5 km or so), roughly mid-lithosphere band. Superposed stresses from loading of a 150-km wide mountain (comparable to Boösaule Mons) on a lithosphere with thickness Te = 50 km results in a thickening of the ascent-favorable (AF) zone beneath the center of the edifice, with a total thickness of 38 km for an 18 km tall (post-flexure) edifice. Most of the thickening is upward, although some is downward. Widening the edifice to 200 km produces a 'U-shaped' AF zone, thin and depressed at r = 0 but intersecting the surface at distances of about 20 to 40 km from the center. Increasing edifice width increases the radial distance at which the AF zone intersects the surface. Thinner lithospheres create generally thinner AF zones, and U-shaped AF zones for narrower edifices. There are several configurations for which viable ascent paths transit nearly the entire lithosphere, arriving at the base of the mountain, where magma can be transported through thrust faults or perhaps thermally erode flank sections, the latter consistent with observations of paterae in

  13. Granite magma formation, transport and emplacement in the Earth's crust.

    PubMed

    Petford, N; Cruden, A R; McCaffrey, K J; Vigneresse, J L

    2000-12-01

    The origin of granites was once a question solely for petrologists and geochemists. But in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation, transport and emplacement of silica-rich melts in the continental crust. Accepted petrological models are being questioned, either because they require unrealistic rheological behaviours of rocks and magmas, or because they do not satisfactorily explain the available structural or geophysical data. Provided flow is continuous, mechanical considerations suggest that--far from being geologically sluggish--granite magmatism is a rapid, dynamic process operating at timescales of < or = 100,000 years, irrespective of tectonic setting. PMID:11130061

  14. Evidence for magma oceans on asteroids, the moon, and Earth

    NASA Technical Reports Server (NTRS)

    Taylor, G. Jeffrey; Norman, Marc D.

    1992-01-01

    There are sound theoretical reasons to suspect that the terrestrial planets melted when they formed. For Earth, the reasons stem largely from the hypothesis that the moon formed as a result of the impact of a Mars-sized planetesimal with the still accreting Earth. Such a monumental event would have led to widespread heating of the Earth and the materials from which the moon was made. In addition, formation of a dense atmosphere on the Earth (and possibly the Moon) would have led to retention of accretional heat and, thus, widespread melting. In other words, contemporary theory suggests that the primitive Moon and terrestrial planets had magma oceans.

  15. Numerical Simulation of Plagioclase Growth During Magma Storage and Ascent

    NASA Astrophysics Data System (ADS)

    Melnik, O. E.; Gorokhova, N. V.; Plechov, P.

    2012-12-01

    A mathematical model of plagioclase growth from a magmatic melt is developed. Plagioclase is one of the main rock-forming minerals. Plagioclase is composed of molecules of two types: anorthite and albite. Crystallization occurs as a result of component (albite and anorthite) diffusion to the boundary of the growing crystal and opposite diffusion of residual melt components. The model is based on multicomponent diffusion equations with the real dependencies between crystal and melt compositions, pressure and temperature. Mass conservation is applied as a boundary condition on a crystal-melt interface. Crystal growth rate depends on local magma undercooling in the vicinity of the crystal. We assume that the growth is in 1D and that the crystal is located in a cell with symmetry (no mass flux) conditions on the cell boundaries. Diffusion of components within the crystal is negligibly slow. Based on this model variation of plagioclase composition with respect of monotonic cooling or pressure drop is studied. It is shown that due to interplay between diffusion of melt components to crystal-melt interface and crystal growth rate crystal composition can vary in a non-monotonic way in response to linear decrease in temperature. A condition of presence of plagioclase zonation is obtained as a result of parametric studies. A growth of rims on plagioclase crystals related to magma ascent during dome building eruptions on Bezymianny volcano (Kamchatka) is simulated. Bezymianny Volcano supplies material to the Earth surface about every half a year. Eruptions of 2000, 2006 and 2007 were selected to determine the magma ascent conditions as the most typical for the last activity cycle. The role of initial conditions, crystal growth rate, the ratio between anorthite and albite diffusion rates and ascent conditions on the rim composition is investigated. The ascent conditions of magma for Bezymianny Volcano eruptions were reconstructed. Simulations suggest ascent from a pressure of

  16. Element variations in rhyolitic magma resulting from gas transport

    NASA Astrophysics Data System (ADS)

    Berlo, K.; Tuffen, H.; Smith, V. C.; Castro, J. M.; Pyle, D. M.; Mather, T. A.; Geraki, K.

    2013-11-01

    Tuffisite veins are glass-filled fractures formed when magma fragments during degassing within the conduit. These veins form transient channels through which exsolved gases can escape from magma. The purpose of this study is to determine the extent to which chemical heterogeneity within the melt results from gas transport, and assess how this can be used to study magma degassing. Two tuffisite veins from contrasting rhyolitic eruptions at Torfajökull (Iceland) and Chaitén (Chile) were studied in detail. The tuffisite vein from Torfajökull is from a shallow dissected conduit (∼70 ka) that fed a degassed lava flow, while the sample from Chaitén was a bomb ejected during the waning phases of Plinian activity in May 2008. The results of detailed in situ chemical analyses (synchrotron XRF, FTIR, LA-ICP-MS) show that in both veins larger vesiculated fragments are enriched in volatile elements (Torfajökull: H, Li, Cl; Chaitén: Li, Cl, Cu, Zn, As, Sn, Sb) compared to the host, while the surrounding smaller particles are depleted in the Torfajökull vein (Li, Cl, Zn, Br, Rb, Pb), but enriched in the Chaitén vein (K, Cu, Zn, As, Mo, Sb, Pb). The lifespans of both veins and the fluxes of gas and particles through them can be estimated using diffusion profiles and enrichment factors. The Torfajökull vein had a longer lifespan (∼a day) and low particle velocities (∼cm/s), while the Chaitén vein was shorter lived (<1 h) with a high gas velocity (∼m/s). These differences are consistent with the contrasting eruption mechanisms (effusive vs. explosive). The amount of magma that degassed through the Chaitén vein is more than ten times the volume of the vein itself, requiring the vein to tap into pre-exsolved gas pockets. This study highlights that tuffisite veins are highly efficient gas pathways and thereby impart chemical diversity in volatile elements on the melt.

  17. Melt inclusions in veins: linking magmas and porphyry Cu deposits.

    PubMed

    Harris, Anthony C; Kamenetsky, Vadim S; White, Noel C; van Achterbergh, Esmé; Ryan, Chris G

    2003-12-19

    At a porphyry copper-gold deposit in Bajo de la Alumbrera, Argentina, silicate-melt inclusions coexist with hypersaline liquid- and vapor-rich inclusions in the earliest magmatic-hydrothermal quartz veins. Copper concentrations of the hypersaline liquid and vapor inclusions reached maxima of 10.0 weight % (wt %) and 4.5 wt %, respectively. These unusually copper-rich inclusions are considered to be the most primitive ore fluid found thus far. Their preservation with coexisting melt allows for the direct quantification of important oreforming processes, including determination of bulk partition coefficients of metals from magma into ore-forming magmatic volatile phases. PMID:14684818

  18. Long-Term Volumetric Eruption Rates and Magma Budgets

    SciTech Connect

    Scott M. White Dept. Geological Sciences University of South Carolina Columbia, SC 29208; Joy A. Crisp Jet Propulsion Laboratory, California Institute of Technology Pasadena, CA 91109; Frank J. Spera Dept. Earth Science University of California, Santa Barbara Santa Barbara, CA 93106

    2005-01-01

    A global compilation of 170 time-averaged volumetric volcanic output rates (Qe) is evaluated in terms of composition and petrotectonic setting to advance the understanding of long-term rates of magma generation and eruption on Earth. Repose periods between successive eruptions at a given site and intrusive:extrusive ratios were compiled for selected volcanic centers where long-term (>104 years) data were available. More silicic compositions, rhyolites and andesites, have a more limited range of eruption rates than basalts. Even when high Qe values contributed by flood basalts (9 ± 2 Å~ 10-1 km3/yr) are removed, there is a trend in decreasing average Qe with lava composition from basaltic eruptions (2.6 ± 1.0 Å~ 10-2 km3/yr) to andesites (2.3 ± 0.8 Å~ 10-3 km3/yr) and rhyolites (4.0 ± 1.4 Å~ 10-3 km3/yr). This trend is also seen in the difference between oceanic and continental settings, as eruptions on oceanic crust tend to be predominately basaltic. All of the volcanoes occurring in oceanic settings fail to have statistically different mean Qe and have an overall average of 2.8 ± 0.4 Å~ 10-2 km3/yr, excluding flood basalts. Likewise, all of the volcanoes on continental crust also fail to have statistically different mean Qe and have an overall average of 4.4 ± 0.8 Å~ 10-3 km3/yr. Flood basalts also form a distinctive class with an average Qe nearly two orders of magnitude higher than any other class. However, we have found no systematic evidence linking increased intrusive:extrusive ratios with lower volcanic rates. A simple heat balance analysis suggests that the preponderance of volcanic systems must be open magmatic systems with respect to heat and matter transport in order to maintain eruptible magma at shallow depth throughout the observed lifetime of the volcano. The empirical upper limit of Å`10-2 km3/yr for magma eruption rate in systems with relatively high intrusive:extrusive ratios may be a consequence of the fundamental parameters

  19. MAGMIX: a basic program to calculate viscosities of interacting magmas of differing composition, temperature, and water content

    USGS Publications Warehouse

    Frost, T.P.; Lindsay, J.R.

    1988-01-01

    MAGMIX is a BASIC program designed to predict viscosities at thermal equilibrium of interacting magmas of differing compositions, initial temperatures, crystallinities, crystal sizes, and water content for any mixing proportion between end members. From the viscosities of the end members at thermal equilibrium, it is possible to predict the styles of magma interaction expected for different initial conditions. The program is designed for modeling the type of magma interaction between hypersthenenormative magmas at upper crustal conditions. Utilization of the program to model magma interaction at pressures higher than 200 MPa would require modification of the program to account for the effects of pressure on heat of fusion and magma density. ?? 1988.

  20. Budget of shallow magma plumbing system at Asama Volcano, Japan, revealed by ground deformation and volcanic gas studies

    NASA Astrophysics Data System (ADS)

    Kazahaya, Ryunosuke; Aoki, Yosuke; Shinohara, Hiroshi

    2015-05-01

    Multiple cycles of the intensive volcanic gas discharge and ground deformation (inflation and deflation) were observed at Asama Volcano, Japan, from 2000 to 2011. Magma budget of the shallow magma plumbing system was estimated on the basis of the volcanic gas emission rates and ground deformation data. Recent inflations observed in 2004 and 2008 were modeled as a dike intrusion to 2-3 km west of Asama Volcano. Previous studies proposed that magma ascends from a midcrustal magma reservoir to the dike and reaches the surface via a sinuous conduit which connects the dike to the summit. The intensive volcanic sulfur dioxide discharge of up to 4600 t/d at the volcano was modeled by magma convective degassing through this magma pathway. The volcano deflates as shrinkage of the magma in a reservoir by volcanic gas discharge. We estimated the volume change of the dike modeled based on the GPS observations, the volume decrease of the magma by the volcanic gas discharge, and the amount of degassed magma produced to calculate the magma budget. The results show that the volume decrease of the magma by the volcanic gas discharge was larger than the volume change of the dike during the inflation periods. This indicates that a significant volume of magma at least more than 2 times larger than the volume change of the dike was supplied from the midcrustal magma reservoir to the dike. The volume decrease of the dike was comparable with the volume decrease of the magma by the volcanic gas discharge during the deflation periods. The long-term deflation trend of the dike and the volume of degassed magma (108-9 m3) suggest that the degassed magma produced is not stored in the dike and the magma is mainly supplied from the midcrustal magma reservoir. In both periods, the volume of degassed magma produced was 1 order of magnitude larger than the volume change of the dike. This indicates that the actual volume of the magma supplied from the midcrustal magma reservoir is up to 1 order of

  1. Boron isotope fractionation in magma via crustal carbonate dissolution

    PubMed Central

    Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela

    2016-01-01

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to −41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle. PMID:27488228

  2. Boron isotope fractionation in magma via crustal carbonate dissolution.

    PubMed

    Deegan, Frances M; Troll, Valentin R; Whitehouse, Martin J; Jolis, Ester M; Freda, Carmela

    2016-01-01

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ(11)B values down to -41.5‰, reflecting preferential partitioning of (10)B into the assimilating melt. Loss of (11)B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports (11)B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ(11)B melt values in arc magmas could flag shallow-level additions to the subduction cycle. PMID:27488228

  3. Experimental study of lunar and SNC (Mars) magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    1994-01-01

    The overall objectives of this research were to evaluate the role of C-O-S-Cl degassing processes in explaining vesiculation, oxidation state and fire-fountaining of lunar magmas by analysis of individual lunar glass spherules, and by experimental determination of equilibrium abundances and diffusion rates of C, S and Cl melt species in lunar glass compositions; and to determine possible primitive SNC magma compositions and the mineralogy of the mantle from which they were derived, and to evaluate P, T, XH2O etc. conditions at which they crystallize to form the SNC meteorites. After funding for one year, a project on the A15 volcanic green glass has been completed to the point of writing a first manuscript. Carbon-oxygen species C-O and CO2 are below detection limits (20 ppm) in these glasses, but there is up to 500 ppm S with concentrations both increasing and decreasing toward the spherule margins. Calculations and modeling indicate that C species could have been present in the volcanic gases, however. In a second project, experiments with low PH2O have resulted in refined estimates of the early intercumulus melt composition in the Chassigny meteorite which is generally accepted as a sample from Mars.

  4. Boron isotope fractionation in magma via crustal carbonate dissolution

    NASA Astrophysics Data System (ADS)

    Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela

    2016-08-01

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to ‑41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

  5. Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas

    SciTech Connect

    Singer, B.S.; O'Neil, J.R. ); Brophy, J.G. )

    1992-04-01

    The first measurement of {sup 18}O/{sup 16}O ratios of plagioclase, clinopyroxene, orthopyroxene, and titanomagnetite phenocrysts from modern Aleutian island-arc lavas provides new insight and independent constraints on magma sources and intracrustal processes. Basalts are heterogeneous on the scale of the entire arc and individual volcanic centers. Combined with Sr isotope and trace element data {delta}{sup 18}O{sub plag} values suggest a variable magma source characterized by differences in the mantle wedge or the subducted sediment component along the volcanic front. Seven tholeiitic basalt to rhyodacite lavas from the Seguam volcanic center have nearly identical {delta}{sup 18}O{sub plag} values of 6.0{per thousand} {plus minus} 0.2{per thousand}, reflecting extensive closed-system plagioclase-dominated crystal fractionation. Oxygen isotope thermometry and pyroxene and oxide equilibria indicate that differentiation occurred between 1,150 {plus minus} 100C (basalt) and 950 {plus minus} 100C (rhyodacite). In contrast, {delta}{sup 18}O{sub plag} values of 12 calc-alkalic basaltic andesites and andesites from the smaller Kanaga volcanic center span a broader range of 5.9{per thousand}-6.6{per thousand}, and consist of mostly higher values. Isotopic disequilibrium in the Kanaga system is manifest in two ways: two types of basaltic inclusions with contrasting {delta}{sup 18}O values occur in one andesite, and in two other andesites plagioclase-titanomagnetite and clinopyroxene-titanomagnetite oxygen isotope temperatures are inconsistent.

  6. Heat capacity, configurational heat capacity and fragility of hydrous magmas

    NASA Astrophysics Data System (ADS)

    Di Genova, D.; Romano, C.; Giordano, D.; Alletti, M.

    2014-10-01

    The glassy and liquid heat capacities of four series of dry and hydrous natural glasses and magma as a function of temperature and water content (up to 19.9 mol%) were investigated using differential scanning calorimetry (DSC). The analyzed compositions are basalt, latite, trachyte and pantellerite. The results of this study indicate that the measured heat capacity of glasses (Cpg) is a linear function of composition and is well reproduced by the empirical model of Richet (1987). For the investigated glasses, the partial molar heat capacity of water can be considered as independent of composition, in agreement with Bouhifd et al. (2006). For hydrous liquids, the heat capacity (Cpliq) decreases nonlinearly with increasing water content. Previously published models, combined with the partial molar heat capacity of water from the literature, are not able to reproduce our experimental data in a satisfactory way. We estimated the partial molar heat capacity of water (CpH2O) in hydrous magma over a broad compositional range. The proposed value is 41 ± 3 J mol-1 K-1. Water strongly affects the configurational heat capacity at the glass transition temperature [Cpconf (Tg)]. An increases of Cpconf (Tg) with water content was measured for the polymerized liquids (trachyte and pantellerite), while the opposite behavior was observed for the most depolymerized liquids (basalt and latite). Structural and rheological implications of this behavior are discussed in light of the presented results.

  7. Numerical Simulations of Multicomponent Convection in a volatile-rich Replenished Magma Chamber

    NASA Astrophysics Data System (ADS)

    Longo, A.; Vassalli, M.; Papale, P.

    2005-12-01

    The dynamics of multicomponent convection in a volatile-rich magma chamber have been studied by means of numerical simulations. The investigated system is an elliptic chamber with 4 km horizontal and 2 km vertical axes, replenished from below with new magma. Magma volatiles are H2O and CO2. The composition and volatile content of magma initially present in the chamber are uniform or stratified. The input magma is equal to or different from the resident magma in terms of liquid composition and volatile content, and enters the chamber on its axis at a constant velocity of 1 cm/s over 200 m of width. Numerical simulations are carried out by using the recently developed numerical code GALES (Longo at al., 2005). GALES is a finite element algorithm that solves the 2D, transient, multicomponent dynamics of compressible to incompressible homogeneous flows. The conservation equations for mass, momentum, energy and composition are discretized in time and space with Galerkin least-squares and discontinuity-capturing stabilizing techniques. The code is previously validated on several test cases spanning a wide range of flow conditions in terms of Mach, Reynolds, Prandtl and Schmidt numbers. Constitutive equations for magma properties employ recent viscosity measurements and parameterizations, as well as non-ideal multicomponent thermodynamic modeling. The numerical results show the complex dynamics of convection triggered by magma replenishment, displaying the formation and evolution of rising plumes and vortexes. Cases of injection of magma having the same composition and volatile content of resident magma do not produce convection in the examined range of conditions, resulting in accumulation of new magma around the inlet area and progressive decrease of the gas volume fraction over the entire magma chamber. On the contrary, the ingression of CO2-rich magma is a very efficient mean of producing large-scale convection. CO2 contents increasing to a few wt% correspond to

  8. A complex magma mixing origin for rocks erupted in 1915, Lassen Peak, California

    USGS Publications Warehouse

    Clynne, M.A.

    1999-01-01

    The eruption of Lassen Peak in May 1915 produced four volcanic rock types within 3 days, and in the following order: (1) hybrid black dacite lava containing (2) undercooled andesitic inclusions, (3) compositionally banded pumice with dark andesite and light dacite bands, and (4) unbanded light dacite. All types represent stages of a complex mixing process between basaltic andesite and dacite that was interrupted by the eruption. They contain disequilibrium phenocryst assemblages characterized by the co-existence of magnesian olivine and quartz and by reacted and unreacted phenocrysts derived from the dacite. The petrography and crystal chemistry of the phenocrysts and the variation in rock compositions indicate that basaltic andesite intruded dacite magma and partially hybridized with it. Phenocrysts from the dacite magma were reacted. Cooling, cyrstallization, and vesiculation of the hybrid andesite magma converted it to a layer of mafic foam. The decreased density of the andesite magma destabilized and disrupted the foam. Blobs of foam rose into and were further cooled by the overlying dacite magma, forming the andesitic inclusions. Disaggregation of andesitic inclusions in the host dacite produced the black dacite and light dacite magmas. Formation of foam was a dynamic process. Removal of foam propagated the foam layer downward into the hybrid andesite magma. Eventually the thermal and compositional contrasts between the hybrid andesite and black dacite magmas were reduced. Then, they mixed directly, forming the dark andesite magma. About 40-50% andesitic inclusions were disaggregated into the host dacite to produce the hybrid black dacite. Thus, disaggregation of inclusions into small fragments and individual crystals can be an efficient magma-mixing process. Disaggregation of undercooled inclusions carrying reacted host-magma phenocrysts produces co-existing reacted and unreacted phenocrysts populations.

  9. 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.

  10. Isotopic evidence of source variations in commingled magma systems: Colorado River extensional corridor, Arizona and Nevada

    SciTech Connect

    Metcalf, R.V.; Smith, E.I.; Martin, M.W. . Dept. of Geoscience); Gonzales, D.A.; Walker, J.D. . Isotope Geochronology Lab.)

    1993-04-01

    Mixing of mantle derived mafic and crustal derived felsic magmas is a major Province-wide process forming Tertiary intermediate magmas within the Basin and Range. Major variations in magma sources, however, may exist in temporally and spatially related systems. Such variations are exemplified by two closely spaced plutons within the northern Colorado River extensional corridor. The 15.96 Ma Mt. Perkins pluton (MPP) was emplaced in three major phases: phase 1 (oldest) gabbro; phase 2 quartz diorite to hornblende granodiorite; and phase 3 biotite granodiorite ([+-]hbld). Phases 2 and 3 contain mafic microgranitoid enclaves (MME) that exhibit evidence of magma mingling. Combined data from phase 2 and 3 rocks, including MMW, shows positive [sup 87]Sr/[sup 86]Sr and negative [var epsilon]Nd correlations vs. SiO[sub 2] (50--72 wt %). Phase 2 rocks, which plot between phase 2 MME and MME-free phase 3 granodiorite, represent hybrid magmas formed by mixing of mantle and crustal derived magmas. Phase 1 gabbro falls off isotope-SiO[sub 2] trends and represents a separate mantle derived magma. The 13.2 Ma Wilson Ridge pluton (WRP), <20 km north of MPP, is cogenetic with the river Mountains volcano (RMV). In WRP an early diorite was intruded by a suite of monzodiorite to quartz monzonite. The monzodiorite portion contains MME and mafic schlieren representing mingled and mixed mafic magmas. The WRP and MPP represent two closely spaced isotopically distinct and separate magma systems. There are five magma sources. The two felsic mixing end members represent two different crustal magma sources. Two mantle sources are presented by MPP phase 1 gabbro and phase 2 MME, reflecting lithospheric and asthenospheric components, respectively. The latter represents the oldest reported Tertiary asthenospheric component within the region. A single lithospheric mantle source, different from the MPP gabbro, is indicated for the mafic mixing end member in the WRP-RMV suite.

  11. Analysis of magma-thermal conversion of biomass to gaseous fuel

    SciTech Connect

    Gerlach, T.M.

    1982-02-01

    A wide range of magma types and pluton geometries believed to occur within the upper 10 km of the crust provide suitable sources of thermal energy for conversion of water-biomass mixtures to higher quality gaseous fuel. Gaseous fuel can be generated within a magma body, within the hot subsolidus margins of a magma body, or within surface reaction vessels heated by thermal energy derived from a magma body. The composition, amount, and energy content of the fuel gases generated from water-biomass mixtures are not sensitive to the type, age, depth, or temperature of a magma body thermal source. The amount and energy content of the generated fuel is almost entirely a function of the proportion of biomass in the starting mixture. CH/sub 4/ is the main gas that can be generated in important quantities by magma thermal energy under most circumstances. CO is never an important fuel product, and H/sub 2/ generation is very limited. The rates at which gaseous fuels can be generated are strongly dependent on magma type. Fuel generation rates for basaltic magmas are at least 2 to 3 times those for andesitic magmas and 5 to 6 times those for rhyolitic magmas. The highest fuel generation rates, for any particular magma body, will be achieved at the lowest possible reaction vessel operating temperature that does not cause graphite deposition from the water-biomass starting mixture. The energy content of the biomass-derived fuels is considerably greater than that consumed in the generation and refinement process.

  12. Geodesy - the key for constraining rates of magma supply, storage, and eruption

    NASA Astrophysics Data System (ADS)

    Poland, Michael; Anderson, Kyle

    2016-04-01

    Volcanology is an inherently interdisciplinary science that requires joint analysis of diverse physical and chemical datasets to infer subsurface processes from surface observations. Among the diversity of data that can be collected, however, geodetic data are critical for elucidating the main elements of a magmatic plumbing system because of their sensitivity to subsurface changes in volume and mass. In particular, geodesy plays a key role in determining rates of magma supply, storage, and eruption. For example, surface displacements are critical for estimating the volume changes and locations of subsurface magma storage zones, and remotely sensed radar data make it possible to place significant bounds on eruptive volumes. Combining these measurements with geochemical indicators of magma composition and volatile content enables modeling of magma fluxes throughout a volcano's plumbing system, from source to surface. We combined geodetic data (particularly InSAR) with prior geochemical constraints and measured gas emissions from Kīlauea Volcano, Hawai`i, to develop a probabilistic model that relates magma supply, storage, and eruption over time. We found that the magma supply rate to Kīlauea during 2006 was 35-100% greater than during 2000-2001, with coincident increased rates of subsurface magma storage and eruption at the surface. By 2012, this surge in supply had ended, and supply rates were below those of 2000-2001; magma storage and eruption rates were similarly reduced. These results demonstrate the connection between magma supply, storage, and eruption, and the overall importance of magma supply with respect to volcanic hazards at Kīlauea and similar volcanoes. Our model also confirms the importance of geodetic data in modeling these parameters - rates of storage and eruption are, in some cases, almost uniquely constrained by geodesy. Future modeling efforts along these lines should also seek to incorporate gravity data, to better determine magma

  13. Early magma ocean and core formation on Vesta

    NASA Astrophysics Data System (ADS)

    Neumann, Wladimir; Breuer, Doris; Spohn, Tilman

    2013-04-01

    The Dawn mission confirms predictions that the asteroid 4 Vesta is differentiated in an iron rich core, a silicate mantle and a basaltic crust, supports its identification as the parent body of the HEDs and provides revised values of e.g. the mass, the bulk density and the dimensions of the asteroid 4 Vesta. Although no distinct volcanic regions have been identified, resurfacing by igneous processes distinguishes Vesta from asteroids like Ceres with its primitive surface, or Lutetia, which retained its primordial surface composition (and may still be partially differentiated[1]). Vesta's core radius is estimated to be 107-113 km[2] (derived from the mass concentration towards the centre). We performed numerical calculations of the thermo-chemical evolution of Vesta adopting the new data obtained by the Dawn mission (mass, bulk density, radius). We have expanded the thermo-chemical evolution model of [3], which includes accretion, compaction, melting, associated changes of the material properties, advective heat transport and differentiation by porous flow, by considering convection and thus effective cooling in a magma ocean to analyse its formation and evolution on Vesta. For melt fractions below the rheologically critical melt fraction (RCMF) of ?50% the heat transport by melt segregation is modeled assuming melt flow in porous media and by supplementing the energy balance equation with additional advection terms. Above the RCMF the effective thermal conductivity keff is computed from the convective heat flux in the soft turbulence regime[4]. The parameter keff mimics the vigorous convection and heat flux of the magma ocean with a low viscosity. It amounts to O(106) W m-1K-1 and substitutes the thermal conductivity in the energy balance equation. We consider both instantaneous and continuous accretion (assuming late runaway material accumulation). In particular, we compare the evolution scenarios arising from the instantaneous accretion of Vesta at different

  14. 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

  15. Syneruptive deep magma transfer and shallow magma remobilization during the 2011 eruption of Shinmoe-dake, Japan—Constraints from melt inclusions and phase equilibria experiments

    NASA Astrophysics Data System (ADS)

    Suzuki, Yuki; Yasuda, Atsushi; Hokanishi, Natsumi; Kaneko, Takayuki; Nakada, Setsuya; Fujii, Toshitsugu

    2013-05-01

    The 2011 Shinmoe-dake eruption started with a phreatomagmatic eruption (Jan 19), followed by climax sub-Plinian events and subsequent explosions (Jan 26-28), lava accumulation in the crater (end of January), and vulcanian eruptions (February-April). We have studied a suite of ejecta to investigate the magmatic system beneath the volcano and remobilization processes in the silicic magma mush. Most of the ejecta, including brown and gray colored pumice clasts (Jan 26-28), ballistically ejected dense lava (Feb 1), and juvenile particles in ash from the phreatomagmatic and vulcanian events are magma mixing products (SiO2 = 57-58 wt.%; 960-980 °C). Mixing occurred between silicic andesite (SA) and basaltic andesite (BA) magmas at a fixed ratio (40%-30% SA and 60%-70% BA). The SA magma had SiO2 = 62-63 wt.% and a temperature of 870 °C, and contains 43 vol.% phenocrysts of pyroxene, plagioclase, and Fe-Ti oxide. The BA magma had SiO2 = 55 wt.% and a temperature of 1030 °C, and contains 9 vol.% phenocrysts of olivine and plagioclase. The SA magma partly erupted without mixing as white parts of pumices and juvenile particles. The two magmatic end-members crystallized at different depths, requiring the presence of two separate magma reservoirs; shallower SA reservoir and deeper BA reservoir. An experimental study reveals that the SA magma had been stored at a pressure of 125 MPa, corresponding to a depth of 5 km. The textures and forms of phenocrysts from the BA magma indicate rapid crystallization directly related to the 2011 eruptive activity. The wide range of H2O contents of olivine melt inclusions (5.5-1.6 wt.%) indicates that rapid crystallization was induced by decompression, with olivine crystallization first (≤ 250 MPa), followed by plagioclase addition. The limited occurrence of olivine melt inclusions trapped at depths of < 5 km is consistent with the proposed magma system model, because olivine crystallization ceased after magma mixing. Our petrological

  16. Fractionation and magma mixing within intruding dike swarm: evidence from the Miocene Shitara-Otoge igneous complex, central Japan

    NASA Astrophysics Data System (ADS)

    Geshi, Nobuo

    2000-05-01

    The analysis of intrusion pattern and petrological character of the central dike swarm in the Miocene igneous complex of the Shitara district, central Japan clarified that magma mixing between a strongly differentiated magma and a less-differentiated magma occurred within a dike swarm. The dike rocks have a wide compositional variation ranging from 5.5 to 0.7 wt.% MgO. They are divided into P1- and P2-types. The P2-type rocks provide many lines of evidence for magma mixing such as reversely zoned phenocrysts, bimodal composition distribution, and dissolution texture, whereas P1-type rocks do not. Phenocryst compositions of P2-type suggest that the magma mixing occurred between a less-fractionated phenocryst-poor magma and a strongly fractionated crystal-rich magma. Concentration ratios among incompatible elements show that the mixing end components were derived from a similar parental magma common to P1-type by fractional crystallization in a near closed system. The dikes with evidence for the magma mixing (P2-type) are distributed only in the southern marginal part of the dike swarm, whereas P1-type dikes do not show any such localization. The distribution and the intrusion direction of the dikes indicate a nearly horizontal outward flow of magmas in the southern part of the dike swarm and accompanied magma mixing in the dike during intrusion. The fractionated end component is inferred to be a product of crystal fractionation within small and ephemeral magma pockets in the dike swarm. Magma mixing is thought to have occurred when a newly intruded dike ruptured the magma reservoir. The frequency of magma mixing was controlled mainly by competition between the lifetime of ephemeral magma reservoir and frequency of dike intrusions. The condition of magma mixing was satisfied only in the southern part of the dike swarm affected by the preceding volcanic activities.

  17. Homogeneous crystal-rich vs. zoned crystal-poor ignimbrites: how much strain accumulates in large magma reservoirs between a new magma recharge and eruption? (Invited)

    NASA Astrophysics Data System (ADS)

    Huber, C.; Bachmann, O.; Dufek, J.; Manga, M.

    2010-12-01

    Silicic volcanic fields often display two different types of deposits: (1) crystal-rich dacitic magmas that display a striking homogeneity at the hand-sample scale and (2 dominantly crystal-poor, rhyolitic magmas that commonly grade into more mafic and more crystal-rich magmas towards the end of the eruption. An well-documented example of this dichotomy is the Central San Juan Volcanic Field (Colorado, USA), where, from the 9 major ignimbrites erupted during the climactic stage (~28.6 to 26.9 Ma), 4 occur as zoned crystal-poor to crystal-rich units and the remaining 5 form crystal-rich homogeneous deposits (make sure you explain what zoned means). In this presentation, we discuss different thermal and mechanical processes that influence the homogeneity of magmas as they evolve in shallow reservoirs. For magma bodies that are able to convect, we discuss the effect of stirring and introduce a new metric for their homogeneity for time-dependent convection. We show that the strain accumulated during 5-10 convective overturns is necessary to homogenize a magma to the hand-sample scale. In contrast, crystal-rich magmas do not experience any/enough stirring as they reach a rigid mush state. For these magmas, we discuss the effect of latent heat buffering as an agent for homogenization of temperature and crystallinity near the solidus. In order to become eruptible again, a crystal mush requires a reactivation event usually, usually attributed to the injection of new, hotter magma. We show that the time required to reactivate a mush, in every relevant case, greatly exceeds the time required to accumulate 5-10 overturns for the part of the mush that is able to convect. This difference in time-scales explains why reactivated mushes are inherently homogenous when they erupt. On the other hand, dominantly crystal-poor magmas do not need to be reactivated. Their homogeneity is governed by the competition between the time between the introduction of heterogeneities (for example

  18. Timescales of quartz crystallization and the longevity of the Bishop giant magma body.

    PubMed

    Gualda, Guilherme A R; Pamukcu, Ayla S; Ghiorso, Mark S; Anderson, Alfred T; Sutton, Stephen R; Rivers, Mark L

    2012-01-01

    Supereruptions violently transfer huge amounts (100 s-1000 s km(3)) of magma to the surface in a matter of days and testify to the existence of giant pools of magma at depth. The longevity of these giant magma bodies is of significant scientific and societal interest. Radiometric data on whole rocks, glasses, feldspar and zircon crystals have been used to suggest that the Bishop Tuff giant magma body, which erupted ~760,000 years ago and created the Long Valley caldera (California), was long-lived (>100,000 years) and evolved rather slowly. In this work, we present four lines of evidence to constrain the timescales of crystallization of the Bishop magma body: (1) quartz residence times based on diffusional relaxation of Ti profiles, (2) quartz residence times based on the kinetics of faceting of melt inclusions, (3) quartz and feldspar crystallization times derived using quartz+feldspar crystal size distributions, and (4) timescales of cooling and crystallization based on thermodynamic and heat flow modeling. All of our estimates suggest quartz crystallization on timescales of <10,000 years, more typically within 500-3,000 years before eruption. We conclude that large-volume, crystal-poor magma bodies are ephemeral features that, once established, evolve on millennial timescales. We also suggest that zircon crystals, rather than recording the timescales of crystallization of a large pool of crystal-poor magma, record the extended periods of time necessary for maturation of the crust and establishment of these giant magma bodies. PMID:22666359

  19. Modeling Io volcanism: Maximum volcanic temperatures, depths of melting and magma composition

    NASA Technical Reports Server (NTRS)

    Crumpler, L. S.; Strom, R. G.

    1984-01-01

    Interim results of thermal and structural modeling of volcanism on Io were presented. The final results of the modeling are summarized. The basic analysis is an evaluation of the magma trigger mechanism for initiating and maintaining eruptions. Secondary aspects include models of the mechanical mode of magma emplacement, interactions with a sulphur-rich upper crust, and more speculative implications for Io's volcanism.

  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. Zircon reveals protracted magma storage and recycling beneath Mount St. Helens

    USGS Publications Warehouse

    Claiborne, L.L.; Miller, C.F.; Flanagan, D.M.; Clynne, M.A.; Wooden, J.L.

    2010-01-01

    Current data and models for Mount St. Helens volcano (Washington, United States) suggest relatively rapid transport from magma genesis to eruption, with no evidence for protracted storage or recycling of magmas. However, we show here that complex zircon age populations extending back hundreds of thousands of years from eruption age indicate that magmas regularly stall in the crust, cool and crystallize beneath the volcano, and are then rejuvenated and incorporated by hotter, young magmas on their way to the surface. Estimated dissolution times suggest that entrained zircon generally resided in rejuvenating magmas for no more than about a century. Zircon elemental compositions reflect the increasing influence of mafic input into the system through time, recording growth from hotter, less evolved magmas tens of thousands of years prior to the appearance of mafic magmas at the surface, or changes in whole-rock geochemistry and petrology, and providing a new, time-correlated record of this evolution independent of the eruption history. Zircon data thus reveal the history of the hidden, long-lived intrusive portion of the Mount St. Helens system, where melt and crystals are stored for as long as hundreds of thousands of years and interact with fresh influxes of magmas that traverse the intrusive reservoir before erupting. ?? 2010 Geological Society of America.

  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. 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.

  4. 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

  5. Complex interaction of aluminous metasedimentary xenoliths and siliceous magma; an example from Mt. Amiata (Central Italy)

    NASA Astrophysics Data System (ADS)

    van Bergen, Manfred J.; Barton, Michael

    1984-12-01

    Aluminous, silica-deficient metasedimentary xenoliths in siliceous lavas of Mt. Amiata have preserved composite zoning-patterns indicative for complex processes of magma-rock interaction. Petrographic observations and small-scale mineralogical and chemical differences between up to five distinct zones (including the core and envelope of lava) provide evidence that: 1. Partial melt formed in and extracted from the xenoliths was more mafic than the host magma and had a Mg/Fe ratio higher than that of the restite, at least during the peak of thermometamorphism. 2. Liquid-state interdiffusion occurred at the interface between partial melt and the enclosing magma. 3. Certain mineral phases in the restite (notably, hercynitic spinel) became unstable in the presence of a siliceous liquid. Quartz-poor muscovite-biotite schists are considered to be the most likely parent rocks and it is believed that release of volatiles from decomposing micas played a significant role in the high-temperature metamorphic evolution of the xenoliths and their interaction with the magma. The conditions favourable for assimilation were enhanced by injection of mafic magma into the magma chamber. Although this concurrent operation of magma-mixing precludes a quantitative estimate of contamination from the wall-rocks (which was probably of minor importance) the present example indicates that dry acid magma may potentially become more mafic by interaction with partially melted hydrous rocks.

  6. 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.

  7. Timescales of Quartz Crystallization and the Longevity of the Bishop Giant Magma Body

    SciTech Connect

    Gualda, Guilherme A.R.; Pamukcu, Ayla S.; Ghiorso, Mark S.; Anderson, Jr. , Alfred T.; Sutton, Stephen R.; Rivers, Mark L.

    2013-04-08

    Supereruptions violently transfer huge amounts (100 s-1000 s km{sup 3}) of magma to the surface in a matter of days and testify to the existence of giant pools of magma at depth. The longevity of these giant magma bodies is of significant scientific and societal interest. Radiometric data on whole rocks, glasses, feldspar and zircon crystals have been used to suggest that the Bishop Tuff giant magma body, which erupted {approx}760,000 years ago and created the Long Valley caldera (California), was long-lived (>100,000 years) and evolved rather slowly. In this work, we present four lines of evidence to constrain the timescales of crystallization of the Bishop magma body: (1) quartz residence times based on diffusional relaxation of Ti profiles, (2) quartz residence times based on the kinetics of faceting of melt inclusions, (3) quartz and feldspar crystallization times derived using quartz+feldspar crystal size distributions, and (4) timescales of cooling and crystallization based on thermodynamic and heat flow modeling. All of our estimates suggest quartz crystallization on timescales of <10,000 years, more typically within 500-3,000 years before eruption. We conclude that large-volume, crystal-poor magma bodies are ephemeral features that, once established, evolve on millennial timescales. We also suggest that zircon crystals, rather than recording the timescales of crystallization of a large pool of crystal-poor magma, record the extended periods of time necessary for maturation of the crust and establishment of these giant magma bodies.

  8. 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

  9. Textural and chemical consequences of interaction between hydrous mafic and felsic magmas: an experimental study

    NASA Astrophysics Data System (ADS)

    Pistone, Mattia; Blundy, Jonathan D.; Brooker, Richard A.

    2016-01-01

    Mantle-derived, hydrous mafic magmas are often invoked as a mechanism to transfer heat, mass and volatiles to felsic plutons in the Earth's crust. Field observations suggest that mafic, water-rich magmas often intrude viscous felsic crystal-rich mushes. This scenario can advect water from the crystallising mafic magma to the felsic magma, leading to an increase in melt fraction in the felsic mush and subsequent mobilisation, at the same time as the mafic magma becomes quenched through a combination of cooling and water loss. To investigate such a scenario, we conducted experiments on a water-undersaturated (4 wt% H2O in the interstitial melt) dacitic crystal mush (50-80 vol% quartz crystals) subject to volatile supply from a water-saturated (≥6 wt% H2O) andesite magma at 950 °C and 4 kbar. Our experimental run products show unidirectional solidification textures (i.e. comb layering) as crystals nucleate at the mafic-felsic interface and grow into the mafic end-member. This process is driven by isothermal and isobaric undercooling resulting from a change in liquidus temperature as water migrates from the mafic to the felsic magma. We refer to this process as "chemical quenching" and suggest that some textures associated with natural mafic-felsic interactions are not simply cooling-driven in origin, but can be caused by exsolution of volatiles adjacent to an interface, whether a water-undersaturated felsic magma (as in our experiments) or a fracture.

  10. The Paradox of Consistency in the Major Element Compositions of Mauna Loa Magmas Over Time

    NASA Astrophysics Data System (ADS)

    Rhodes, J. M.

    2013-12-01

    The vast majority of Mauna Loa lavas plot on well-defined olivine-control trends. When normalized to a constant MgO content (16%) their major element compositions (SiO2 = 48.86 +/- 0.30; Al2O3 = 10.58 +/- 0.17; FeO = 9.83 +/- 0.23; CaO = 8.31 +/- 0.19 (all at 1 sigma)) have remained remarkably constant for over 600 ka. This observation is distinctly at odds with what we think we know about melting processes and source components in the Hawaiian plume. Given a 9-10 cm/yr northwesterly movement of the Pacific plate, Mauna Loa will have traversed about two thirds of the plume melting zone (~ 60 km) over 600 ka. It should, therefore, have sampled magmas of varying compositions produced by melting at different temperatures and depths within the plume. Additionally, in contrast with the major elements, the isotopic ratios of these lavas over 600 ka are highly variable (Sr and Pb 39% and Pb 43% of the entire range for Hawaiian shield lavas). This implies varying contributions of plume (Loihi) and recycled crustal (Koolau) components which should also strongly influence the major element compositions of the magmas. What is the explanation for this paradox? Two ubiquitous processes, one deep the other shallow, are thought to be responsible. First, diverse magma compositions are produced, as anticipated, by melting at varying T and P, and from mixtures of different source components. On ascent, these melts react with overlying depleted harzburgite residue produced by prior melting in the plume. The resulting magma composition will reflect the depth at which it finally segregates from this residue. The silica geobarometer indicates that this depth is relatively shallow (~45 - 60 km), resulting in comparatively uniform high SiO2 and other major element constituents of the parental magmas. Secondly, these parental magmas mix into a magma reservoir at shallow levels within the volcano. This reservoir magma is 'perched' at the end of the olivine-control trend at the pigeonite

  11. The Parent Magmas of the Cumulate Eucrites: A Mass Balance Approach

    NASA Technical Reports Server (NTRS)

    Treiman, Allan H.

    1996-01-01

    The cumulate eucrite meteorites are gabbros that are related to the eucrite basalt meteorites. The eucrite basalts are relatively primitive (nearly flat REE patterns with La approx. 8-30 x CI), but the parent magmas of the cumulate eucrites have been inferred as extremely evolved (La to greater than 100 x CI). This inference has been based on mineral/magma partitioning, and on mass balance considering the cumulate eucrites as adcumulates of plagioclase + pigeonite only; both approaches have been criticized as inappropriate. Here, mass balance including magma + equilibrium pigeonite + equilibrium plagiociase is used to test a simple model for the cumulate eucrites: that they formed from known eucritic magma types, that they consisted only of magma + crystals in chemical equilibrium with the magma, and that they were closed to chemical exchange after the accumulation of crystals. This model is tested for major and Rare Earth Elements (REE). The cumulate eucrites Serra de Mage and Moore County are consistent, in both REE and major elements, with formation by this simple model from a eucrite magma with a composition similar to the Nuevo Laredo meteorite: Serra de Mage as 14% magma, 47.5% pigeonite, and 38.5% plagioclase; Moore County as 35% magma, 37.5% pigeonite, and 27.5% plagioclase. These results are insensitive to the choice of mineral/magma partition coefficients. Results for the Moama cumulate eucrite are strongly dependent on choice of partition coefficients; for one reasonable choice, Moama's composition can be modeled as 4% Nuevo Laredo magma, 60% pigeonite, and 36% plagioclase. Selection of parent magma composition relies heavily on major elements; the REE cannot uniquely indicate a parent magma among the eucrite basalts. The major element composition of Y-791195 can be fit adequately as a simple cumulate from any basaltic eucrite composition. However, Y-791195 has LREE abundances and La/Lu too low to be accommodated within the model using any basaltic

  12. Changes in the Soufriere Hills Volcano, Montserrat, magma system 2003 - 2010

    NASA Astrophysics Data System (ADS)

    Sacks, S. I.; Linde, A. T.

    2011-12-01

    The structure of the magma system beneath the Soufriere Hills Volcano has been determined in many studies, e.g. Hautmann et al, 2010. A large magma chamber at about 11 km depth feeds a smaller one at about 5 km depth, which in turn couples to a dike topped by a ~1 km long conduit to the surface. Data from a network of four borehole dilatometers has shown significant changes in the hydraulic and gas coupling between the units. The strain ratios between the strain data at different sites allows a fairly confident assessment of where in the magma system the pressure changes occur. The major dome collapse on 13th July 2003 involved pressure change in the upper magma chamber only. The 5 following vulcanian explosions in three days, were confined to the conduit, as expected for fragmentation events. However, in the hour following the explosion on the 15th, there was an indication of a gas infusion into the dike from the magma chambers. The March 2004 event (Linde et al, 2010) started with a gas infusion into the dike from the upper magma chamber, that took less than two minutes, indicating that a gas path, not controlled by the highly viscous magma, had developed. All later vulcanian explosions in 2008, 2009, 2010, show large gas overpressure in the conduit, ~10x larger than for the July 2003 events. The deformation in December 2008, shows that both magma chambers and the dike are coupled. The high gas pressure detected before the 3 December explosion is consistent with the unusual lack of erupted pumice. It seems clear that all units are not permanently coupled together. Recent long-term inflation is dominated by the deeper magma chamber. Dome collapses, 2003 and 2006, affect the upper magma chamber. Since 2004, a fast gas path developed between the upper magma chamber and the dike. By 2008, this fast path extended to the deeper magma chamber as well. We conjecture that the enhanced magma flow rate, and therefore shear deformation rate, due to the five vulcanian

  13. 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

  14. Forcing of seismic waves travelling through a bubbly magma

    NASA Astrophysics Data System (ADS)

    Kurzon, I.; Lyakhovsky, V.; Lensky, N. G.; Navon, O.

    2005-12-01

    The idea of amplification of seismic waves in magma was first introduced by Lensky et al. (2002) who examined the compressibility and the effective bulk viscosity of a bubbly suspension that expands due to the growth of gas bubbles in a supersaturated melt. At the initial stages of growth, when diffusion is efficient and viscous resistance of the melt controls expansion, bulk viscosity is negative. Only later, when growth decelerates, it turns positive. Bulk viscosity is negative whenever the conversion rate of potential chemical energy of dissolved volatiles into expansion work is higher than the rate of dissipation of kinetic energy to heat. They suggested that when bulk viscosity is negative, part of the excess energy in the system may be converted into seismic energy resulting in the amplification of seismic waves. We have studied this possibility by examining the dynamics of pressure waves in an expanding bubbly magma. The integration of pressure oscillations with bubble growth dynamics was carried-out by following the path laid by Commander and Prosperetti (1989). They developed a wave equation for bubbly suspensions and showed that the introduction of bubbles can be accounted for by an additional term, the second time-derivative of the gas volume fraction. Combining their equation with the bubble growth model (Navon & Lyakhovsky, 1998), we now solve for the amplitude of pressure oscillations in the suspension. The expansion of the additional term leads to a wave equation which includes additional terms for damping and forcing. We solved this equation for the initial stage, following pressure drop, when growth is controlled by the viscous resistance of the melt. We used typical conditions and properties of magma in a conduit below a dome. The results show that in this case, forcing overcomes damping and the amplitude of the pressure waves increases with time. A numerical model is constructed to follow the evolution of the pressure waves during the full course

  15. Two-phase Damage Models of Magma Fracturing

    NASA Astrophysics Data System (ADS)

    Cai, Z.; Bercovici, D.

    2011-12-01

    Damage and fracturing in two-phase and porous flows are relevant for geological process such as magma-fracturing during melt migration and hydro-fracturing of crustal rocks for carbon sequestration and shale-gas recovery. These fracturing processes are associated with the propagation of a pore-generating damage front ahead of high-pressure fluid injection. We therefore examine the propagation of porous flow in a damageable matrix by applying the two-phase theory for compaction and damage proposed by Bercovici et al. [2001]; Bercovici and Ricard [2003]. The movement of the fluid and the solid is governed by the two phase flow laws, while damage (void generation and microcracking) is treated by considering the generation of interfacial surface energy by deformational work. Calculations of one dimensional (1-D) flow of fluid migrating buoyantly through compacting and damageable matrix show that damage is mitigated in steady-state largely because of pressure loss at the fluid front. However, in time-dependent flows, linear stability analysis shows that the propagation velocity of porosity waves is strongly dependent on damage. In the damage-free case porosity waves are dispersive in that wave-speed decreases with wavenumber (inverse wavelength); however with damage the dispersion flattens and beyond a critical damage reverses (the wave speed increases with wave number). Since normal dispersive behavior balances breaking in the nonlinear wave case, such reversed dispersion implies that damage has a profound effect in the nonlinear limit by facilitating wave front steepening and high-speed shocks. Nonlinear solitary wave solutions are obtained numerically and show that the transmission of porosity waves induce high stress and damage that can push the damage front forward. With damage the porosity waves sharpen and calculations suggest that they can transform from shape-conserving solitary waves into faster shock waves, which is also predicted by the linear theory. Such

  16. The timescales of magma evolution at mid-ocean ridges

    NASA Astrophysics Data System (ADS)

    Brandl, Philipp A.; Regelous, Marcel; Beier, Christoph; O'Neill, Hugh St. C.; Nebel, Oliver; Haase, Karsten M.

    2016-01-01

    Oceanic crust is continuously created at mid-ocean ridges by decompression melting of the upper mantle as it upwells due to plate separation. Decades of research on active spreading ridges have led to a growing understanding of the complex magmatic, tectonic and hydrothermal processes linked to the formation of new oceanic igneous crust. However, less is known about the timescales of magmatic processes at mid-ocean ridges, including melting in and melt extraction from the mantle, fractional crystallisation, crustal assimilation and/or magma mixing. In this paper, we review the timescales of magmatic processes by integrating radiometric dating, chemical and petrological observations of mid-ocean ridge basalts (MORBs) and geophysical models. These different lines of evidence suggest that melt extraction and migration, and crystallisation and mixing processes occur over timescales of 1 to 10,000 a. High-resolution geochemical stratigraphic profiles of the oceanic crust using drill-core samples further show that at fast-spreading ridges, adjacent flow units may differ in age by only a few 100 a. We use existing chemical data and new major- and trace-element analyses of fresh MORB glasses from drill-cores in ancient Atlantic and Pacific crust, together with model stratigraphic ages to investigate how lava chemistry changes over 10 to 100 ka periods, the timescale of crustal accretion at spreading ridges which is recorded in the basalt stratigraphy in drilled sections through the oceanic crust. We show that drilled MORBs have compositions that are similar to those of young MORB glasses dredged from active spreading ridges (lavas that will eventually be preserved in the lowermost part of the extrusive section covered by younger flows), showing that the dredged samples are indeed representative of the bulk oceanic crust. Model stratigraphic ages calculated for individual flows in boreholes, together with the geochemical stratigraphy of the drilled sections, show that at

  17. Source component mixing in the regions of arc magma generation

    NASA Astrophysics Data System (ADS)

    Arculus, Richard J.; Powell, Roger

    1986-05-01

    Most recent workers attribute the main features of island arc basalt geochemistry to variable contributions of at least two source components. The major source appears to be the peridotitic wedge of upper mantle overlying the subducted slab, but the nature of the second component and the processes by which the sources become mixed during genesis of arc magmas are in dispute. A metasomatic addition to the wedge resulting from devolatilization in the slab is the simplest explanation of the marked enrichment of the alkali and alkaline earth elements with respect to the rare earths in island arc basalts, together with the variably developed trends in Pb, Sr, and Nd isotopic data toward sedimentary contaminants. However, lack of the correlations between relative degrees of trace element fractionation and radiogenic isotopic ratios expected of such processes requires a more complex explanation. Alternative models that suggest that all of the characteristics of island arc basalts can be accounted for by melting of an intraoceanic, hot spot type of mantle source also face specific difficulties, particularly with regard to the strong depletions of trace high-field-strength elements in arc compared with hot spot magmas. A possible resolution of these specific geochemical difficulties may lie in dynamic transport processes within the wedge linked with the slab through coupled drag, and the marked depression of mantle isotherms in subduction zones. Inefficient escape of melts and subsequent repeated freezing within the overturning wedge can lead to local mineralogic and geochemical heterogeneity of the peridotite overlying the slab. Fluids released from the slab may infiltrate the heterogeneous wedge and preferentially scavenge the alkalis and alkaline earths with respect to the rare earths and high field strength elements from locally enriched portions of the wedge. Incorporation of such metasomatic fluids in renewed melting at shallower but hotter levels within the wedge can

  18. Slab melting and magma formation beneath the southern Cascade arc

    NASA Astrophysics Data System (ADS)

    Walowski, K. J.; Wallace, P. J.; Clynne, M. A.; Rasmussen, D. J.; Weis, D.

    2016-07-01

    The processes that drive magma formation beneath the Cascade arc and other warm-slab subduction zones have been debated because young oceanic crust is predicted to largely dehydrate beneath the forearc during subduction. In addition, geochemical variability along strike in the Cascades has led to contrasting interpretations about the role of volatiles in magma generation. Here, we focus on the Lassen segment of the Cascade arc, where previous work has demonstrated across-arc geochemical variations related to subduction enrichment, and H-isotope data suggest that H2O in basaltic magmas is derived from the final breakdown of chlorite in the mantle portion of the slab. We use naturally glassy, olivine-hosted melt inclusions (MI) from the tephra deposits of eight primitive (MgO > 7 wt%) basaltic cinder cones to quantify the pre-eruptive volatile contents of mantle-derived melts in this region. The melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), suggesting extensive dehydration of the downgoing plate prior to reaching sub-arc depths and little input of slab-derived B into the mantle wedge. However, correlations of volatile and trace element ratios (H2O/Ce, Cl/Nb, Sr/Nd) in the melt inclusions demonstrate that geochemical variability is the result of variable addition of a hydrous subduction component to the mantle wedge. Furthermore, correlations between subduction component tracers and radiogenic isotope ratios show that the subduction component has less radiogenic Sr and Pb than the Lassen sub-arc mantle, which can be explained by melting of subducted Gorda MORB beneath the arc. Agreement between pMELTS melting models and melt inclusion volatile, major, and trace element data suggests that hydrous slab melt addition to the mantle wedge can produce the range in primitive compositions erupted in the Lassen region. Our results provide further evidence that chlorite-derived fluids from the mantle portion of the

  19. The magma budget of Volcan Arenal, Costa Rica from 1968 to 1980

    NASA Technical Reports Server (NTRS)

    Wadge, G.

    1983-01-01

    The magma volume emitted by Volcan Arenal, Costa Rica, has been calculated to be 304 x 10 to the 6th cu m. A near-continuous rise from very deep within the crust is proposed as an explanation for Arenal's magma supply, and the long-term seismic pattern is interpreted as individual batches of magma using previously fractured pathways. During a break in activity (1973) the effusion site moved from Crater A to Crater C, approximately 400 m higher. It is maintained that the steady downward tilting of the volcano's summit was caused by the loading of the volcano's western side by about 19 x 10 to the 6th cu m of lava. Also noted is the abrupt decrease in effusion rate compatible with the increased magmatic head needed to reach Crater C. It is concluded that the constancy of magma composition and effusion rate from 1974 to 1980 indicates a homogeneous magma reservoir.

  20. Degassing-induced crystallization of basaltic magma and effects on lava rheology

    USGS Publications Warehouse

    Lipman, P.W.; Banks, N.G.; Rhodes, J.M.

    1985-01-01

    During the north-east rift eruption of Mauna Loa volcano, Hawaii, on 25 March-14 April 1984 (Fig. 1), microphenocryst contents of erupted lava increased from 0.5 to 30% without concurrent change in either bulk magma composition or eruption temperature (1,140 ?? 3 ??C). The crystallization of the microphenocrysts is interpreted here as being due to undercooling of the magma 20-30 ??C below its liquidas; the undercooling probably resulted from separation and release of volatiles as the magma migrated 12 km from the primary summit reservoir to the eruption site on the north-east rift zone. Such crystallization of magma during an eruption has not been documented previously. The undercooling and crystallization increased the effective viscosity of the magma, leading to decreased eruption rates and stagnation of the lava flow. ?? 1985 Nature Publishing Group.

  1. Evidence for crustal recycling during the Archean: The parental magmas of the stillwater complex

    NASA Technical Reports Server (NTRS)

    Mccallum, I. S.

    1988-01-01

    The petrology and geochemistry of the Stillwater Complex, an Archean (2.7 Ga) layered mafic intrusion in the Beartooth Mountains of Montana is discussed. Efforts to reconstruct the compositions of possible parental magmas and thereby place some constraints on the composition and history of their mantle source regions was studied. A high-Mg andesite or boninite magma best matches the crystallization sequences and mineral compositions of Stillwater cumulates, and represents either a primary magma composition or a secondary magma formed, for example, by assimilation of crustal material by a very Mg-rich melt such as komatiite. Isotopic data do not support the extensive amounts of assimilation required by the komatiite parent hypothesis, and it is argued that the Stillwater magma was generated from a mantle source that had been enriched by recycling and homogenization of older crustal material over a large area.

  2. The Effect of Thermal Cycling on Crystal-Liquid Separation During Lunar Magma Ocean Differentiation

    NASA Technical Reports Server (NTRS)

    Mills, Ryan D.

    2013-01-01

    Differentiation of magma oceans likely involves a mixture of fractional and equilibrium crystallization [1]. The existence of: 1) large volumes of anorthosite in the lunar highlands and 2) the incompatible- rich (KREEP) reservoir suggests that fractional crystallization may have dominated during differentiation of the Moon. For this to have occurred, crystal fractionation must have been remarkably efficient. Several authors [e.g. 2, 3] have hypothesized that equilibrium crystallization would have dominated early in differentiation of magma oceans because of crystal entrainment during turbulent convection. However, recent numerical modeling [4] suggests that crystal settling could have occurred throughout the entire solidification history of the lunar magma ocean if crystals were large and crystal fraction was low. These results indicate that the crystal size distribution could have played an important role in differentiation of the lunar magma ocean. Here, I suggest that thermal cycling from tidal heating during lunar magma ocean crystallization caused crystals to coarsen, leading to efficient crystal-liquid separation.

  3. 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.

  4. Linking magma composition with volcano size and eruptive style in basaltic monogenetic systems

    NASA Astrophysics Data System (ADS)

    Smith, I. E.; McGee, L. E.; Cronin, S. J.

    2012-12-01

    Magma composition, volcano size and eruptive style (together with vent locations) are the definitive parameters of basaltic monogenetic systems. These variables are not independent, but the relationships between them are complex. Monogenetic volcano fields that episodically erupt small-volume, discrete magma batches such as the Auckland Volcanic Field (AVF, northern New Zealand), typically represent primary mantle melts variably modified by near source processes. In such cases, where the volume of magma is small, eruption styles are strongly controlled by the interaction of magma with the surficial environment and this is determined by both magma volume and its rise rate. The magmatic compositional extremes of primitive magmas in the AVF define a spectrum ranging from strongly silica-undersaturated nephelinite to sub-alkalic basalt. Nephelinites are low SiO2 (~40 wt.%), highly incompatible-element enriched compositions, representing very low degrees of partial melting (<2%) in the asthenospheric mantle. Higher SiO2 (~48 wt.%) sub-alkalic compositions have lower incompatible element contents representing higher degrees of melting (~<5%) at slightly shallower depths. Geochemical modeling indicates that all of these magmas are sourced within the same general mantle region at depths of 80-70 km. The two compositional extremes also define extremes in volume of magma and ultimately magma flux at the surface. The surficial environment of the AVF is characterized by highly water saturated sediments of variable competency and many pressurized aquifer systems. Where there is a combination of small volumes and low flux rates, environmental factors dominate and phreatomagmatic explosive eruptions ensue, forming tuff cones, rings and maars. Larger volumes and flux rates result in dry eruptions forming cinder cones and lava fields. Thus at a fundamental level defining magma source characteristics and temporal or spatial variation in these (such as cyclic or evolutionary trends

  5. 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.

  6. Does Cooling Magma Drive Deep Low-Frequency Earthquakes?

    NASA Astrophysics Data System (ADS)

    Aso, N.; Ide, S.; Tsai, V. C.

    2013-12-01

    = Introduction = One major type of deep low-frequency earthquakes (LFEs) is tectonic LFEs that locate around plate boundaries, and are thought to be slip events. Another type of LFEs is volcanic LFEs that locate around the Moho mostly beneath active or Quaternary volcanoes, and their physical mechanism is not well established. We recently suggested that the volcanic LFEs in eastern Shimane can be interpreted as a resonant oscillation within an old magma conduit of 1600 m in length, which produces a focal mechanism that is equivalent to a compensated linear vector dipole (CLVD) oriented in the direction of the conduit [Aso et al., in prep. for re-submission]. However, a remaining question is what excites the resonance. In the present study, we suggest that cooling magma acts as a trigger for the resonant oscillation of volcanic LFEs, with the idea that thermal contraction of magma produces an anisotropic strain rate and the resulting brittle failure would trigger oscillation. To verify this, we calculated strain rates produced by this effect both analytically and numerically. = Model Setting and Method = We set the initial extent of magma as a 1600-m-long 400-m-wide pipe as is inferred from the distribution of hypocenters in eastern Shimane. The initial perturbation is set to be 400 K uniformly within the pipe. Thermal strain rate is calculated using the thermal stress potential of Timoshenko and Goodier [1970]. First, we estimated the strain rate without the effect of latent heat release. Assuming a cuboid pipe, it can be solved easily analytically. Next, to account for latent heat release, we use the enthalpy method [Eyres et al., 1946] to numerically solve the problem, assuming a cylindrical pipe. = Results = For the case without latent heat release, the strain rate remains higher than than 10-14/s for 600 years at the center of the pipe. For the case with latent heat release, although the latent heat delays the thermal evolution and decreases the strain rate, it

  7. Mafic intrusion remobilising silicic magma under El Hierro, Canary Islands

    NASA Astrophysics Data System (ADS)

    Sigmarsson, O.; Laporte, D.; Marti, J.; Devouard, B.; Cluzel, N.

    2012-04-01

    The 2011 submarine eruption at El Hierro, Canary Islands, has produced volcanic bombs that degas at sea surface, boil seawater and sink when cooled and degassed. At the beginning of the eruption white coloured pumices enveloped in darker coloured spatters floated on land. These composite pumices show evidence of magma mingling with folds and undulations of the darker coloured magma within the white pumice suggesting magma mingling in a viscous regime. The white pumice is highly vesicular and resembles foam. Most of the vesicular structure is made of tightly packed, polygonal bubbles of uniform size (˜ 100 μm), suggesting a single event of homogeneous bubble nucleation. An earlier event of heterogeneous bubble nucleation is indicated by the presence of a few large bubbles developed around tiny quartz crystals. Both the darker and lighter coloured pumices are almost aphyric. A few olivine crystals with perfect euhedral morphology occur within the darker part. Rare olivines of same composition are also found in the white pumice glass but then display somewhat rounded outlines and hopper-type structure. Melt inclusions in olivines of the darker pumice are of the same composition as the enveloping mafic glass, whereas olivines in the mixing boundary layer have melt inclusions of less mafic composition. The whole-rock composition and slightly more evolved glass composition are of basanitc and alkali rhyolitic composition (at the limit of the trachyte field) according to the TAS classification. Such rhyolitic compositions are rare in the Canaries. Analyses of residual volatile concentration in the glasses show that the silicic glass is highly degassed (F: 511 ±222; Cl: 202 ±58; S: below detection limit; values in ppm,1SD, n=10), whereas the basanitic glass still has very high halogene concentrations (F: 1354 ±151; Cl: 1026 ±47; S: 362 ±29; 1SD, n=10). In-situ analysis of trace element compositions of the dark glasses reveal typical basanitic compositions with

  8. Compositional dependence of sulfur speciation in Terrestrial and Martian magmas

    NASA Astrophysics Data System (ADS)

    Nash, William; Wood, Bernard; Smythe, Duane

    2016-04-01

    The capacity of magmas to transport sulfur from mantle to crust strongly influences a planet's surface chemistry. Sulfur is perhaps exceptional among the elements in the diversity of it's chemical speciation, exhibiting four redox species at geologically relevant conditions: sulfide (2-), elemental sulfur (0), sulfite (4+) and sulphate (6+). Furthermore, the solubility of sulfur in a magma (and hence the magma's capacity for delivering mantle-derived sulfur to the crust) depends critically on it's oxidation state. Our aim with this experimental study was to quantitatively determine the chemical speciation of sulfur within several common magmas, as a function of oxygen fugacity (fO2). We have performed a series of experiments on six sulfur-bearing silicate melts, which together represent a broad range of naturally occurring compositions: two putative Martian basalts, two terrestrial MORBs (one primitive, one evolved), an andesite, and a dacite. These melts were equilibrated together (at one-atmosphere pressure, 1300°C) with various CO-CO2-SO2 gas mixtures, which imposed a range of fO2s. This range spanned -2 to +1.6 log units (relative to the Quartz-Fayalite-Magnetite or QFM buffer), and the step-size was 0.25 log units. The quenched glasses were analyzed by X-ray Absorption Spectroscopy (specifically XANES) at the Diamond synchrotron (UK), and the spectra obtained were used to determine the species of sulfur present in each glass. The chemical composition of each glass (including their sulfur contents) was characterized by electron-probe microanalysis. Despite the generally low concentrations of sulfur in our glasses (never exceeding 0.24 wt%), we have clearly resolved the crossover between reduced (S2-) and oxidized (S6+) species for three of our basalts. The other three melts yielded more noisy XANES spectra, and as a result their redox crossovers are visible, but less clearly resolved. For every melt composition, the redox crossover is a continuous (though

  9. Steady-state magma discharge at Etna 1971-81

    NASA Technical Reports Server (NTRS)

    Wadge, G.; Guest, J. E.

    1981-01-01

    Throughout the past decade Mount Etna has been in almost continuous activity and even during periods of repose incandescent lava has often been visible in at least one of the summit vents. Using observations by Italian, British and French volcanological teams, the volumes of lava produced by each eruption from 1971 to July 1981 have been estimated. The computed output of magma for this period approximates to a rate of 0.7 cu m/s. This is compared with the output rate estimates for Etna's historic past. The steady-state nature of the output during the past decade has implications for the interpretation of the volcano's internal plumbing and the petrology of its lavas, and the assumption that this state will be maintained allows a discussion of the timing and magnitude of future eruptions.

  10. The lunar magma ocean - A transient lunar phenomenon

    NASA Technical Reports Server (NTRS)

    Minear, J. W.

    1980-01-01

    The time required for the solidification of a lunar magma ocean is considered. In the absence of a thermal boundary crust, heat loss is by radiation and the ocean will solidify in a few decades. However, only a few millimeters of crust would effectively limit radiation. The current investigation has the objective to present estimates of conduction boundary (crust) thickness based on several models of the mechanism of crustal formation. Three different models for estimating conduction boundary layer thickness are discussed. They are based on the formation of a chill margin, a plagioclase flotation layer, and a layer which is continually destroyed by meteorite impacts and regrows by conductive heat loss. Based on these models, the maximum solidification time for a 200 km thick ocean is about 100 million years. A more probable solidification time based on a plagioclase flotation crust model is about 60 million years.

  11. 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

  12. Constraints from melt inclusions on depths of magma residence at intermediate magma supply along the Galápagos Spreading Center

    NASA Astrophysics Data System (ADS)

    Colman, Alice; Sinton, John M.; Wanless, V. Dorsey

    2015-02-01

    Shallow, seismically imaged melt lenses are a ubiquitous feature of mid-ocean ridges with high magma supply; melt lenses deepen and become less continuous along axis as the rate of magma supply decreases. Despite compelling petrologic evidence for evolution of magma within the crust prior to eruption at lower magma supply, melt lenses are rarely detected along ridge segments with rates of magma supply less than 0.3 ×106m3 /yr /km, and the depths of sub-axial magma reservoirs are therefore poorly known. We use ion microprobe measurements of H2O and CO2 concentrations of olivine-hosted melt inclusions to calculate vapor saturation pressures that constrain crystallization depths at two locations along the Galápagos Spreading Center (94.2°W and 95°W). These sites were chosen to examine crystallization pressures in the presence (94.2°W) and absence (95°W) of a seismically imaged melt lens. At 95°W, where magma supply is too low to sustain a seismically resolvable melt lens, samples were selected from each of the three most recent eruptive units, allowing us to document temporal variations in vapor saturation pressures and the depth of magma residence at this location. Clusters in melt inclusion entrapment depths for these eruptions range from 3.0 to 3.4 km below the seafloor, indicating that magmas at 95°W resided at a narrow range of mid-crustal depths prior to eruption, generally consistent with the global trend of increasing melt lens depth with decreasing rate of magma supply. A discrepancy between seismic data and the peak in melt inclusion entrapment depths at 94.2°W may reflect temporal variability of magmatic systems at this location. This study demonstrates the potential for using measurements of the concentrations of H2O and CO2 in olivine-hosted melt inclusions to determine the depths of crustal magmatic systems that feed mid-ocean ridge eruptions, even in locations where seismic studies have not detected melt lenses.

  13. Dynamics of magma ascent through the Sierra Nevada, California

    SciTech Connect

    Kovach, L.A.

    1984-01-01

    A 9 m.y. old alkali basalt intrudes the Red Lake pluton, approx.90 m.y. old granodiorite of the Huntington Lake quadrangle in the Sierra Nevada, California. The basaltic neck, standing 5 meters above the floor of the Big Creek drainage (approx. 25 meters in diameter), appears to have been the feeder for the flows that cap Chinese Peak (approx. 1 km to the south). The surrounding Red Lake granodiorite was partially fused during the intrusive process. Ten meters of the fused rock is now exposed surrounding the basaltic neck. Thermal models indicate that magma must have flowed through the pipe for approx. 1000 years to produce the extensive melting of the country rock. The basalt was probably intruded at a temperature of 900/sup 0/C, ultramafic nodules indicate its mantle origin. Surrounding the inner basaltic core is a region of basalt interlayered with granitic melt and xenoliths, which formed due to interaction of the basalt and partially molten wall rock during magma ascent. The partially fused granodiorite wall rock contains 40-45% melt at the contact, decreasing to 20% melt 10 meters from the contact. The glass composition (approx.73%-approx.75% SiO/sub 2/, 5% K/sub 2/O) suggests invariant melting. Data on Rb, Sr, and Sr isotopic composition of the glass, residual crystals, and whole rocks are used to model chemical and isotopic equilibration of silicic liquids with their residual crystals. In comparison to the granodiorite, the glass is enriched in Rb (approx.250 ppm), depleted in Sr (approx.135 ppm), permitting the construction of an apparent isochron 11.0 +/- 2.7 m.y.

  14. Two-phase damage models of magma-fracturing

    NASA Astrophysics Data System (ADS)

    Cai, Zhengyu; Bercovici, David

    2013-04-01

    Damage and fracturing in two-phase and porous flows are relevant for geological process such as magma-fracturing during melt migration, which is associated with the propagation of a pore-generating damage front ahead of high-pressure fluid injection. We therefore examine the propagation of porous flow in a damageable matrix by applying the two-phase theory for compaction and damage proposed by Bercovici et al. (2001a) and Bercovici and Ricard (2003). The movement of the fluid and the solid is governed by the two-phase flow laws, while damage (void generation and microcracking) is treated by considering the generation of interfacial surface energy by deformational work. Calculations of one-dimensional (1-D) flow of fluid migrating buoyantly through compacting and damageable matrix show that damage is mitigated in steady-state largely because of the loss of the velocity gradient at the fluid front. However, in time-dependent flows, linear stability analysis shows that the propagation velocity of porosity waves is strongly dependent on damage. In the damage-free case porosity waves are dispersive in that wave-speed decreases with wavenumber (inverse wavelength); however with damage the dispersion flattens and beyond a critical damage reverses (the wave speed increases with wavenumber). Since normal dispersive behavior balances breaking in the nonlinear wave case, such reversed dispersion implies that damage has a profound effect in the nonlinear limit by facilitating wave front steepening and higher wave velocities. Nonlinear solitary wave solutions are obtained numerically and show that the transmission of porosity waves induces high stress and damage that can push the damage front forward. With damage the porosity waves sharpen and calculations suggest that they can transform from shape-conserving solitary waves into faster high amplitude waves, which is also predicted by the linear theory. Such pulse-like sharper waves may prove effective at promoting fluid

  15. Experimental modelling of ground deformation associated with shallow magma intrusions

    NASA Astrophysics Data System (ADS)

    Galland, Olivier

    2012-02-01

    Active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems. The analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems. Nevertheless, these analyses usually take into account simplistic shapes (sphere, dykes, sills) and the results cannot be verified as the modelled systems are buried. In this paper, I present new results from experimental models of magma intrusion, in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored. The models consisted of a molten vegetable oil, simulating low viscosity magma, injected into cohesive fine-grained silica flour, simulating the brittle upper crust; oil injection resulted is sheet intrusions (dykes, sills and cone sheets). The initial topography in the models was flat. While the oil was intruding, the surface of the models slightly lifted up to form a smooth relief, which was mapped through time. After an initial symmetrical development, the uplifted area developed asymmetrically; at the end of the experiments, the oil always erupted at the steepest edge of the uplifted area. After the experiment, the oil solidified, the intrusion was excavated and the shape of its top surface mapped. The comparison between the uplifted zone and the underlying intrusions showed that (1) the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions, (2) the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion, and (3) the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil. The experimental results also suggest that complex intrusion shapes (inclined sheet, cone sheet, complex sill) may have to be considered more systematically in the analyses of ground deformation patterns on volcanoes.

  16. Experimental modelling of ground deformation associated with shallow magma intrusions

    NASA Astrophysics Data System (ADS)

    Galland, O.

    2012-04-01

    Active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems. The analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems. Nevertheless, these analyses usually take into account simplistic shapes (sphere, dykes, sills) and the results cannot be verified as the modelled systems are buried. In this contribution, I will present new results from experimental models of magma intrusion, in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored in 3D. The models consisted of a molten vegetable oil, simulating low viscosity magma, injected into cohesive fine-grained silica flour, simulating the brittle upper crust; oil injection resulted is sheet intrusions (dykes, sills and cone sheets). The initial topography in the models was flat. While the oil was intruding, the surface of the models slightly lifted up to form a smooth relief, which was mapped through time. After an initial symmetrical development, the uplifted area developed asymmetrically; at the end of the experiments, the oil always erupted at the steepest edge of the uplifted area. After the experiment, the oil solidified, the intrusion was excavated and the shape of its top surface mapped. The comparison between the uplifted zone and the underlying intrusions showed that (1) the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions, (2) the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion, and (3) the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil. The experimental results also suggest that complex intrusion shapes (inclined sheet, cone sheet, complex sill) may have to be considered more systematically in analyses of ground deformation patterns on volcanoes.

  17. Deciphering magma histories through phosphorus zoning in olivine

    NASA Astrophysics Data System (ADS)

    Ersoy, Ö.; Nikogosian, I.; Mason, P. R. D.; van Bergen, M.

    2015-12-01

    Since olivine is usually the first major phase to crystallize from basaltic magma, its primary chemistry is a sensitive tracer of the early evolution of volcanic systems. However, fast diffusion and homogenization under magmatic conditions frequently modifies the original composition of olivine, which hampers the reconstruction of cooling histories and magma evolution from the chemistry and zoning patterns of phenocrysts in erupted products. Phosphorous is a notable exception due to its sluggish diffusion in olivine crystals and silicate melts, as igneous olivines almost always display complex zoning patterns. Phosphorus zoning in olivine has been linked either to crystallization rate variations and diffusion controlled growth or to strong compositional controls on melt-mineral partitioning. We illuminate the versatility of P-in-olivine with a comprehensive EPMA and LA-ICPMS dataset on olivines from Italian potassium rich mafic lavas and the primitive melt inclusions (MI) that they host. The olivines are characterized by P concentrations from limit of quantification (22 ppm) to 435 ppm P with MIs containing up to 2.2 wt.% P2O5. High resolution (1-2 μm per pixel) element maps show both fine oscillatory and large scale sector zoning in P, which is uncorrelated with zoning in any other element. The MIs are virtually always surrounded by P-depleted zones that are also depleted in Cr and enriched in Al and Ti, which we attribute to a combination of supply-limited slow growth and melt compositional controls on partitioning behavior imposed by the boundary layer. We demonstrate that P zoning carries valuable information on the nature and timing of magmatic events such as mingling/mixing, wall-rock assimilation and subsequent re-equilibration processes. P-in-olivine is most promising to distinguish multiple generations of MIs, as a guide to study their mode of entrapment and to disclose the origin of primary heterogeneities.

  18. Magma genesis in the lesser Antilles island arc

    NASA Astrophysics Data System (ADS)

    Hawkesworth, C. J.; Powell, M.

    1980-12-01

    143Nd/ 144Nd, 87Sr/ 86Sr and REE results are reported on volcanic rocks from the islands of Dominica and St. Kitts in the Lesser Antilles. Particular attention is given to the lavas and xenoliths of the Foundland (basalt-andesite) and the Plat Pays (andesite-dacite) volcanic centres on Dominica. Combined major and trace element [ 2] and isotope results suggest that the bulk of the andesites and dacites on Dominica, and by analogy in the rest of the arc, are produced by fractional crystallisation of basaltic magma. The differences in the erupted products of the two volcanoes do not appear to be related to any significant differences in the source rocks of the magmas. Along the arc 87Sr/ 86Sr ratios range from 0.7037 on St. Kitts, to 0.7041-0.7047 on Dominica, and 0.7039-0.7058 on Grenada [ 5], and these are accompanied by a parallel increase in K, Sr, Ba and the light REE's. Moreover, compared with LIL-element-enriched and -depleted rocks from MOR and intraplate environments, the basic rocks from the Lesser Antilles are preferentially enriched in alkaline elements (K, Ba, Rb, Sr) relative to less mobile elements such as the rare earths. 143Nd/ 144Nd varies from 0.51308 on St. Kitts, to 0.51286 on Dominica, and 0.51264-0.51308 on Grenada [ 5], and all these samples have relatively high 87Sr/ 86Sr ratios compared with the main trend of Nd and Sr isotopes for most mantle-derived volcanic rocks. Alkaline elements and 87Sr appear to have been introduced from the subducted ocean crust, but the results on other, less mobile elements are more ambiguous — island arc tholeiites (as on St. Kitts) do not appear to contain significant amounts of REE's, Zr, Y, etc., from the subducted oceanic crust, but such a contribution may be present in more LIL-element-enriched calc-alkaline rock types.

  19. Mechanisms 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. P.; Humphreys, M. C. S.; Thy, P.

    2012-04-01

    The Skaergaard intrusion is a superb natural laboratory for studying mechanisms of magma chamber differentiation. The magnificent exposures and new systematic sample sets of rocks that solidified inwards from the roof, walls and floor of the chamber provide means to test the relative roles of crystal settling, diffusion, convection, liquid immiscibility and compaction in different regions of the chamber and in opposite positions relative to gravity. Examination of the melt inclusions and interstitial pockets has demonstrated that a large portion of intrusion crystallized from an emulsified magma chamber composed of immiscible silica- and iron-rich melts. The similarity of ratios of elements with opposite partitioning between the immiscible melts (e.g. P and Rb) in wall, floor and roof rocks, however, indicate that large-scale separation did not occur. Yet, on a smaller scale of metres to hundred of metres and close to the interface between the roof and floor rocks (the Sandwich Horizon), irregular layers and pods of granophyre hosted by extremely iron-rich cumulates point to some separation of the two liquid phases. Similar proportions of the primocryst (cumulus) minerals in roof, wall and floor rocks indicate that crystal settling was not an important mechanism. Likewise, the lack of fractionation of elements with different behavior indicate that diffusion and fluid-driven metasomatism played relatively minor roles. Compositional convection and/or compaction within the solidifying crystal mush boundary layer are likely the most important mechanisms. A correlation of low trapped liquid fractions (calculated from strongly incompatible elements) in floor rocks with high fractionation density (the density difference between the crystal framework and the liquid) indicate that compaction is the dominating process in expelling evolved liquid from the crystal mush layer. This is supported by high and variable trapped liquid contents in the roof rocks, where gravity

  20. Eruption Depths, Magma Storage and Magma Degassing at Sumisu Caldera, Izu-Bonin Arc: Evidence from Glasses and Melt Inclusions

    NASA Astrophysics Data System (ADS)

    Johnson, E. R.

    2015-12-01

    Island arc volcanoes can become submarine during cataclysmal caldera collapse. The passage of a volcanic vent from atmospheric to under water environment involves complex modifications of the eruption style and subsequent transport of the pyroclasts. Here, we use FTIR measurements of the volatile contents of glass and melt inclusions in the juvenile pumice clasts in the Sumisu basin and its surroundings (Izu-Bonin arc) to investigate changes in eruption depths, magma storage and degassing over time. This study is based on legacy cores from ODP 126, where numerous unconsolidated (<65 ka), extremely thick (few m to >250 m), massive to normally graded pumice lapilli-tuffs were recovered over four cores (788C, 790A, 790B and 791A). Glass and clast geochemistry indicate the submarine Sumisu caldera as the source of several of these pumice lapilli-tuffs. Glass chips and melt inclusions from these samples were analyzed using FTIR for H2O and CO2 contents. Glass chips record variable H2O contents; most chips contain 0.6-1.6 wt% H2O, corresponding to eruption depths of 320-2100 mbsl. Variations in glass H2O and pressure estimates suggest that edifice collapse occurred prior-to or during eruption of the oldest of these samples, and that the edifice may have subsequently grown over time. Sanidine-hosted melt inclusions from two units record variably degassed but H2O-rich melts (1.1-5.6 wt% H2O). The lowest H2O contents overlap with glass chips, consistent with degassing and crystallization of melts until eruption, and the highest H2O contents suggest that large amounts of degassing accompanied likely explosive eruptions. Most inclusions, from both units, contain 2-4 wt% H2O, which further indicates that the magmas crystallized at pressures of ~50-100 MPa, or depths ~400-2800 m below the seafloor. Further glass and melt inclusion analyses, including major element compositions, will elucidate changes in magma storage, degassing and evolution over time.

  1. Mid-Miocene Rhyolite Sequence, Highland Range, NV: Record of Magma Evolution and Eruption From the Searchlight Pluton Magma Chamber

    NASA Astrophysics Data System (ADS)

    Colombini, L. L.; Gualda, G. A.; Miller, C. F.; Faulds, J.; Miller, J.; Wooden, J.; Mazdab, F.

    2008-12-01

    The Highland Range in southern Nevada contains a ~3 km-thick sequence of pre- to synextensional volcanic rock that records both large-magnitude Miocene extension and the evolution of large magma system. The volcanic sequence and probable source pluton are both well-exposed in a steeply W-tilted fault block (Faulds et al. 2002). A km-thick sequence of rhyolite in the southeast part of the range was emplaced above a thick section of trachyandesite and trachydacite at 16.2-16.0 Ma (SHRIMP zircon U-Pb, biotite Ar/Ar; Faulds et al 2002, J Miller et al 2007, new data). The lower half of the sequence comprises low-SiO2 rhyolite lavas (plag + biotite + cpx phenocrysts), which abruptly give way to tuffs and inter-fingered lavas (qtz + san + plag + bio + cpx + sphene) that mark a transition to a more explosive period of eruption of more evolved rhyolite plus active mafic input. Throughout the rhyolite sequence, mafic enclaves are abundant, changing from brittle fragments (lithics) in the lower lavas to quenched, crenulate-bordered magmatic enclaves in upper lavas and tuffs. Xenocrysts of reacted olivine, pyroxene, and plagioclase are evident in some rhyolites. The uppermost unit of the sequence is a quartz + sanidine-bearing lava that is heavily contaminated on all scales by mafic enclaves, lithics, and xenocrysts. Basaltic trachyandesite overlies this upper rhyolite. SHRIMP analysis of Ti and other trace elements in zircon from two samples near the top of the sequence documents strongly fluctuating T (720-920 C) and evolution of melt compositions; for the most part, rims grew at lower T from more evolved melt. Zr-in-sphene thermometry indicates that these phenocrysts grew at the lower temperatures recorded by the zircon rims. The rhyolite sequence appears to have erupted from the middle granite zone of the nearby Searchlight pluton, which is the same age and similarly evolved toward highly silicic compositions, records co-injection of mafic magma, and overlies slightly

  2. ULF Oscillations in Magma in the Period of seismic Event Preparation

    NASA Astrophysics Data System (ADS)

    Kopytenko, Yu. A.; Nikitina, L. V.

    2003-04-01

    ULF OSCILLATIONS IN MAGMA IN THE PERIOD OF SEISMIC EVENT PREPARATION Yu.A.Kopytenko, L.V.Nikitina SPbF IZMIRAN, Muchnoi per.2, p/b 188, St-Petersburg, Russia, 191023 lida@mail.spbnit.ru Magma movements in volcanic center are activated in the period of the seismic event preparation. Hydrodynamic processes in the moving magma can lead to appearance of waves and vortices in the flow. In this work different sources of ULF pulsations in magma are considered. The electromagnetic emission induced by ULF pulsations in magma is estimated. An initial source of magma is at the depth about 100km. When volcano activity increases magma moves upward to the Earth surface by volcano channels, filling intermediate volcano reservoirs. Magma is a two-phase liquid (liquid with gas). If volcanic activity increases some bubbles of gas in magma are floating up to its surface. Bubbles of gas disturb the magma surface and support the oscillations on this surface. The magnetic fields induced by this oscillations are about 0.01-0.1 nT if we assume that a conductivity of hot magma is about 0.01 Sm/m. The second cause of the ULF movements in magma is connected with vortex structures that appear in magma flow under the action of Coriolys force. Corresponding quasiconstant magnetic fields are about 0.2nT. The describing mechanism allows to explain some features of electromagnetic emissions in the period of the Earthquake preparation: the increase of the electromagnetic emission about 1.5-2 months before the earthquake and a sharp decrease of emission about 1.5 - 2 days before the earthquake. It's considered a spreading of the variable electromagnetic fields from the source to the Earth surface. It's shown that at the distance about 100 km from the source the magnetic field decreases to 0.05-0.1 nT. Gradient of the magnetic field is about 1-5pT/km that is in accordance with the measured data.

  3. 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

  4. Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption

    PubMed Central

    Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P.; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

    2016-01-01

    Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common. PMID:27558276

  5. 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.

  6. 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

  7. Explosive volcanism may not be an inevitable consequence of magma fragmentation.

    PubMed

    Gonnermann, Helge M; Manga, Michael

    2003-11-27

    The fragmentation of magma, containing abundant gas bubbles, is thought to be the defining characteristic of explosive eruptions. When viscous stresses associated with the growth of bubbles and the flow of the ascending magma exceed the strength of the melt, the magma breaks into disconnected fragments suspended within an expanding gas phase. Although repeated effusive and explosive eruptions for individual volcanoes are common, the dynamics governing the transition between explosive and effusive eruptions remain unclear. Magmas for both types of eruptions originate from sources with similar volatile content, yet effusive lavas erupt considerably more degassed than their explosive counterparts. One mechanism for degassing during magma ascent, consistent with observations, is the generation of intermittent permeable fracture networks generated by non-explosive fragmentation near the conduit walls. Here we show that such fragmentation can occur by viscous shear in both effusive and explosive eruptions. Moreover, we suggest that such fragmentation may be important for magma degassing and the inhibition of explosive behaviour. This implies that, contrary to conventional views, explosive volcanism is not an inevitable consequence of magma fragmentation. PMID:14647379

  8. 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.

  9. 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.

  10. 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.

  11. Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption.

    PubMed

    Di Vito, Mauro A; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

    2016-01-01

    Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common. PMID:27558276

  12. A damage model for volcanic edifices: Implications for edifice strength, magma pressure, and eruptive processes

    NASA Astrophysics Data System (ADS)

    Carrier, Aurore; Got, Jean-Luc; Peltier, Aline; Ferrazzini, Valérie; Staudacher, Thomas; Kowalski, Philippe; Boissier, Patrice

    2015-01-01

    Monitoring of large basaltic volcanoes, such as Piton de la Fournaise (La Réunion Island, France), has revealed preeruptive accelerations in surface displacements and seismicity rate over a period of between 1 h and several weeks before magma reaches the surface. Such eruptions are attributed to ruptures of pressurized magma reservoirs. Elastic models used to describe surface deformation would assume that accelerations in surface deformation are due to increases in reservoir pressure. This assumption requires changes in magma or pressure conditions at the base of the magma feeding system that are unrealistic over the observed timescale. Another possible cause for these accelerations is magma pressure in the reservoir weakening the volcanic edifice. In the present study, we modeled such weakening by progressive damage to an initially elastic edifice. We used an incremental damage model, with seismicity as a damage variable with daily increments. Elastic moduli decrease linearly with each damage increment. Applied to an initially elastic edifice with constant pressure at the base of the system, this damage model reproduces surface displacement accelerations quite well when damage is sufficient. Process dynamics is controlled by the damage parameter, taken as the ratio between the incremental rupture surface and the surface to be ruptured. In this case, edifice strength and magma reservoir pressure decrease with decreasing elastic moduli, whereas surface displacement accelerates. We discuss the consequences of pressure decreases in magma reservoirs.

  13. 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

  14. Upper mantle magma storage and transport under a Canarian shield-volcano, Teno, Tenerife (Spain)

    NASA Astrophysics Data System (ADS)

    Longpré, Marc-Antoine; Troll, Valentin R.; Hansteen, Thor H.

    2008-08-01

    We use clinopyroxene-liquid thermobarometry, aided by petrography and mineral major element chemistry, to reconstruct the magma plumbing system of the late Miocene, largely mafic Teno shield-volcano on the island of Tenerife. Outer rims of clinopyroxene and olivine phenocrysts show patterns best explained by decompression-induced crystallization upon rapid ascent of magmas from depth. The last equilibrium crystallization of clinopyroxene occurred in the uppermost mantle, from ˜20 to 45 km depth. We propose that flexural stresses or, alternatively, thermomechanical contrasts create a magma trap that largely confines magma storage to an interval roughly coinciding with the Moho at ˜15 km and the base of the long-term elastic lithosphere at ˜40 km below sea level. Evidence for shallow magma storage is restricted to the occurrence of a thick vitric tuff of trachytic composition emplaced before the Teno shield-volcano suffered large-scale flank collapses. The scenario developed in this study may help shed light on some unresolved issues of magma supply to intraplate oceanic volcanoes characterized by relatively low magma fluxes, such as those of the Canary, Madeira and Cape Verde archipelagoes, as well as Hawaiian volcanoes in their postshield stage. The data presented also support the importance of progressive magmatic underplating in the Canary Islands.

  15. Stable isotope relations in an open magma system, Laacher See, Eifel (FRG)

    NASA Astrophysics Data System (ADS)

    Wörner, G.; Harmon, R. S.; Hoefs, J.

    1987-03-01

    18O/16O and D/H ratios have been measured for matrix glasses and phenocrysts from the zoned phonolitic Laacher See tephra sequence (11000 y.b.p., East Eifel volcanic field, FRG) to study open-system behaviour of the associated magma system. Mineral and glass δ 18O values appear to be largely undisturbed by low-temperature, secondary alteration, record isotopic equilibrium and confirm previous conclusions, based on radiogenic isotope evidence, of early, small-scale crustal assimilation during differentiation of parental magmas in a crustal magma chamber. One sanidine-glass pair possibly documents the late stage influx of meteoric fluids into the topmost magma layer prior to eruption. A sealing carapace of chilled magma, which itself was strongly contaminated, prevented large-scale fluid exchange up to the point prior to eruption when this carapace was fractured and meteoric water gained access to parts of the magma system. D/H measurements of various glass types (glass inclusions, dense and pumiceous glass) and amphiboles gave conflicting results suggesting a combination of degassing, volatile exchange with country rocks and hydration. Stable isotope ratios for primitive parental magmas ( δ 18O=+5.5 to 7.0‰) and mantle megacrysts ( δ 18O=+ 5.5 to +6.0‰, δD=-21 to -38‰, for amphiboles and phlogopite, resp.) suggest a rather variable fluid composition for the sub-Eifel mantle.

  16. The Campi Flegrei Deep Drilling Project `CFDDP': Understanding the Magma-Aquifers Interaction at Large Calderas

    NASA Astrophysics Data System (ADS)

    de Natale, G.; Troise, C.; Sacchi, M.

    2007-05-01

    Campi Flegrei caldera is a good example of the most explosive volcanism on the Earth, a potential source of global catastrophes. Alike several similar volcanic areas (Yellowstone and Long Valley, USA; Santorini, Greece; Iwo Jima, Japan, etc.) its volcanic activity, i.e. eruptions and unrests, is dominated by physical mechanisms involving the strict interaction between shallow magma sources and geothermal systems. Furthermore, just like similar areas, it should be characterised by very large shallow magma chambers, filled by residual magma left after the ignimbritic caldera forming eruptions. However, neither the physical mechanisms of magma-water interaction, nor the evidence for such large magma chamber, have been ever clear enough to be used for detailed volcanological interpretation and eruption forecast. The CFDDP project aims to understand, for the first time, the location and rehology of large residual magma chambers and the mechanisms of interaction between magma and aquifer systems to generate eruptions and unrests. CFDDP is then structured as a large multidisciplinary project, with a main volcanological aim and with a further goal to launch a geothermal energy exploitation project in the area. A larger goal of the CFDDP project is to establish at Campi Flegrei, a densely urbanised area in a developed western country, a natural laboratory to study volcanic risk, environmental issues, monitoring technologies, geothermal energy exploitation.

  17. 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.

  18. Explosive style, magma degassing and evolution in the Chaimilla eruption, Villarrica volcano, Southern Andes

    NASA Astrophysics Data System (ADS)

    Pioli, L.; Scalisi, L.; Costantini, L.; Di Muro, A.; Bonadonna, C.; Clavero, J.

    2015-11-01

    Villarrica (Chile) is a basaltic stratovolcano, currently in an open-conduit condition. It now has relatively frequent Strombolian and effusive eruptions, but it had large explosive eruptions in prehistoric times. Among them, the most recent eruption was Chaimilla, which occurred about 3100 years ago and produced deposits that indicate complex, multiphase eruptive dynamics. Significant differences in mineralogy and glass compositions of the erupted scoria suggest the eruption was fed by two distinct magma batches with similar bulk compositions but distinct crystallization and degassing histories. The lower sequence scoria has a complex crystal assemblage with several crystal populations produced by mixing between a relatively degassed magma containing Fo75-79 olivine, normally or reversely zoned plagioclase (An70-94) and augite (type 1 magma), and a subordinate volume of more-primitive and more volatile-rich magma rising from depth (type 2 magma) and carrying normally zoned plagioclase and higher-Mg (Fo81-85) olivine crystals. Type 2 magma was the main component emitted during the larger and more explosive eruptive phase that deposited the upper sequence. The Chaimilla eruption occurred under closed-vent conditions and was fed by water-rich magmas. When compared with the petrological features of the magma currently erupted at Villarrica, which has slightly more-evolved bulk compositions, lower crystal content and lower water content, these results suggest that the evolution in eruptive style of the volcano from highly explosive to a lava lake/Strombolian activity corresponds to significant changes in the shallow plumbing system (which is now at much shallower depths); these plumbing-system changes were not associated with significant changes in the parental magma compositions.

  19. On the role of diapirism in the, segregation, ascent and final emplacement of granitoid magmas

    NASA Astrophysics Data System (ADS)

    Bateman, Roger

    1984-12-01

    Only bodies of magma with a high crystal content and partially molten (crustal) country rocks can ascend as diapirs; once such an envelope is pierced, the diapiric ascent of the pluton is arrested by the high viscosity of a solid aureole. Deformation by shortening of the carapace of these bodies may lead to the expulsion of a magma with a relatively low crystal content, which may then continue ascent via fractures and dykes. The details of the mechanisms of granitoid magma segregation are still unknown, but it appears that many magmas hegin their ascent through the crust as mushes with at least 50% melt, and that such magmas are rheologically able to ascend through a thickness of crust. This ascent mechanism explains the dearth of structures attributable to the ascent of granitoids, in contrast to the abundance of structures that developed during their final emplacement. When a magma becomes too crystalline (melt < 25%) to continue its ascent via dykes, it is immobilised. At approximately this stage, a hydrous magma may become saturated with water and release fluids into the aureole, making it particularly susceptible to deformation. Magma that continues to arrive at this level is also immobilised, and the pluton grows as a ballooning diapir. These characteristically deform themselves and their aureoles by bulk shortening. Magmas that are able to ascend to shallow depths, largely by virtue of lower water contents and higher initial temperatures, tend to become finally accommodated by such brittle processes as stoping and cauldron subsidence. High level intrusions lend to be tabular, are also fed by dykes or conduits, and assemble in tabular batholiths.

  20. 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

  1. The parent magma of the Nakhla (SNC) meteorite: Reconciliation of composition estimates from magmatic inclusions and element partitioning

    NASA Technical Reports Server (NTRS)

    Treiman, A. H.

    1993-01-01

    The composition of the parent magma of the Nakhla meteorite was difficult to determine, because it is accumulate rock, enriched in olivine and augite relative to a basalt magma. A parent magma composition is estimated from electron microprobe area analyses of magmatic inclusions in olivine. This composition is consistent with an independent estimate based on the same inclusions, and with chemical equilibria with the cores of Nakhla's augites. This composition reconciles most of the previous estimates of Nakhla's magma composition, and obviates the need for complex magmatic processes. Inconsistency between this composition and those calculated previously suggests that magma flowed through and crystallized into Nakhla as it cooled.

  2. The parent magma of xenoliths in shergottite EETA79001: Bulk and trace element composition inferred from magmatic inclusions

    NASA Technical Reports Server (NTRS)

    Treiman, Allan H.; Lindstrom, David J.; Martinez, Rene R.

    1994-01-01

    The SNC meteorites are samples of the Martian crust, so inferences about their origins and parent magmas are of wide planetologic significance. The EETA79001 shergottite, a basalt, contains xenoliths of pyroxene-olivine cumulate rocks which are possibly related to the ALHA77005 and LEW88516 SNC lherzolites. Olivines in the xenoliths contain magmatic inclusions, relics of magma trapped within the growing crystals. The magmatic inclusions allow a parent magma composition to be retrieved; it is similar to the composition reconstructed from xenolith pyroxenes by element distribution coefficients. The xenolith parent magma is similar but not identical to parent magmas for the shergottite lherzolites.

  3. A dynamic balance between magma supply and eruption rate at Kilauea volcano, Hawaii

    USGS Publications Warehouse

    Denlinger, R.P.

    1997-01-01

    The dynamic balance between magma supply and vent output at Kilauea volcano is used to estimate both the volume of magma stored within Kilauea volcano and its magma supply rate. Throughout most of 1991 a linear decline in volume flux from the Kupaianaha vent on Kilauea's east rift zone was associated with a parabolic variation in the elevation of Kilauea's summit as vent output initially exceeded then lagged behind the magma supply to the volcano. The correspondence between summit elevation and tilt established with over 30 years of data provided daily estimates of summit elevation in terms of summit tilt. The minimum in the parabolic variation in summit tilt and elevation (or zero elevation change) occurs when the magma supply to the reservoir from below the volcano equals the magma output from the reservoir to the surface, so that the magma supply rate is given by vent flux on that day. The measurements of vent flux and tilt establish that the magma supply rate to Kilauea volcano on June 19, 1991, was 217,000 ?? 10,000 m3/d (or 0.079 ?? 0.004 km3/yr). This is close to the average eruptive rate of 0.08 km3/yr between 1958 and 1984. In addition, the predictable response of summit elevation and tilt to each east rift zone eruption near Puu Oo since 1983 shows that summit deformation is also a measure of magma reservoir pressure. Given this, the correlation between the elevation of the Puu Oo lava lake (4 km uprift of Kupaianaha and 18 km from the summit) and summit tilt provides an estimate for magma pressure changes corresponding to summit tilt changes. The ratio of the change in volume to the change in reservoir pressure (dV/dP) during vent activity may be determined by dividing the ratio of volume erupted to change in summit tilt (dV/dtilt) by the ratio of pressure change to change in summit tilt (dP/dtilt). This measure of dV/dP, when combined with laboratory measurements of the bulk modulus of tholeitic melt, provides an estimate of 240 ?? 50 km3 for the volume

  4. 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.

  5. Magma flow and interaction with waste packages in a geologic repository at Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Marsh, Bruce D.; Coleman, Neil M.

    2009-05-01

    The likelihood that a nuclear waste repository at Yucca Mountain could be intersected by igneous activity is very low, but its potential consequences are nevertheless important to performance assessments. An ongoing critical area of concern is the nature and magnitude of the thermal interaction of magma with tunnel walls, high-level nuclear waste packages, and waste forms. Previous assessments consider a variety of dynamic scenarios, but large uncertainties remain in understanding the rheological nature of the magma likely to be involved and its behavior within a repository drift. Here we specifically address the issue of magma rheology during degassing, cooling, and solidification as basaltic magma approaches Earth's surface and enters a drift. Magma containing significant amounts (> ~ 2 wt.%) of dissolved water (Wet Magma), as is anticipated for this region, at or near its liquidus temperature and saturated with water at 200 MPa is at a temperature near or below the 1-atm solidus temperature. Isentropic ascent from this near liquidus temperature promotes extensive solidification and/or glassification. Exsolving water with approach to the surface promotes rapid vesiculation leading to fragmentation and tephra production. With continued ascent the still water-saturated magma traverses the solidification phase field and undergoes a combination of rapid crystallization and quenching, becoming a glassy highly viscous (~ 10 8 Pa s) mass of greatly reduced mobility. This immobility is reflected in the high effective viscosity regulating flows from nearby cinder cones associated with wet basalt. This also matches well with the experimentally determined rheology of dry basalt glass. This rheology greatly restricts the mobility of basalt within repository drifts, amounting to < 10 m per day. Magma in this state quenches rapidly (~ 10 cm/min) on waste packages. Wet basalt is explosive, but relatively immobile as lava. Dry Magma is not explosive, but highly mobile as lava

  6. FY 1984 and FY 1985 geochemistry and materials studies in support of the Magma Energy Extraction Program

    SciTech Connect

    Westrich, H.R.; Weirick, L.J.; Cygan, R.T.; Reece, M.; Hlava, P.F.; Stockman, H.W.; Gerlach, T.M.

    1986-04-01

    Geochemistry and materials studies are being performed in support of the Magma Energy Extraction Program. The work is largely restricted to: (1) characterizing magmatic environments at sites of interest, (2) testing engineering materials in laboratory simulated magmatic environments, (3) investigating chemical mass transport effects inherent in designs for direct contact heat exchangers, and (4) evaluating degassing hazards associated with drilling into and extracting energy from shallow magma. Magma characterization studies have been completed for shallow magma at Long Valley, Coso volcanic field, and Kilauea volcano. The behavior of 17 commercially available materials has been examined in rhyolite magma at 850/sup 0/C and 200 MPa for periods up to seven days. Analysis of reaction products from materials tests to date indicate that oxidation is the main corrosion problem for most alloys in rhyolitic magma. Considerations of corrosion resistance, high-temperature strength, and cost indicate nickel-base superalloys offer the most promise as candidates for use in rhyolitic magma.

  7. Experimental interaction of magma and “dirty” coolants

    NASA Astrophysics Data System (ADS)

    Schipper, C. Ian; White, James D. L.; Zimanowski, Bernd; Büttner, Ralf; Sonder, Ingo; Schmid, Andrea

    2011-03-01

    The presence of water at volcanic vents can have dramatic effects on fragmentation and eruption dynamics, but little is known about how the presence of particulate matter in external water will further alter eruptions. Volcanic edifices are inherently “dirty” places, where particulate matter of multiple origins and grainsizes typically abounds. We present the results of experiments designed to simulate non-explosive interactions between molten basalt and various “coolants,” ranging from homogeneous suspensions of 0 to 30 mass% bentonite clay in pure water, to heterogeneous and/or stratified suspensions including bentonite, sand, synthetic glass beads and/or naturally-sorted pumice. Four types of data are used to characterise the interactions: (1) visual/video observations; (2) grainsize and morphology of resulting particles; (3) heat-transfer data from a network of eight thermocouples; and (4) acoustic data from three force sensors. In homogeneous coolants with <~10% bentonite, heat transfer is by convection, and the melt is efficiently fragmented into blocky particles through multiple thermal granulation events which produce associated acoustic signals. For all coolants with >~20% sediment, heat transfer is by forced convection and conduction, and thermal granulation is less efficient, resulting in fewer blocky particles, larger grainsizes, and weaker acoustic signals. Many particles are droplet-shaped or/and “vesicular,” containing bubbles filled with coolant. Both of these particle types indicate significant hydrodynamic magma-coolant mingling, and many of them are rewelded into compound particles. The addition of coarse material to heterogeneous suspensions further slows heat transfer thus reducing thermal granulation, and variable interlocking of large particles prevents efficient hydrodynamic mingling. This results primarily in rewelded melt piles and inefficient distribution of melt and heat throughout the coolant volume. Our results indicate

  8. NVP melt/magma viscosity: insight on Mercury lava flows

    NASA Astrophysics Data System (ADS)

    Rossi, Stefano; Morgavi, Daniele; Namur, Olivier; Vetere, Francesco; Perugini, Diego; Mancinelli, Paolo; Pauselli, Cristina

    2016-04-01

    After more than four years of orbiting Mercury, NASA's MESSENGER spacecraft came to an end in late April 2015. MESSENGER has provided many new and surprising results. This session will again highlight the latest results on Mercury based on MESSENGER observations or updated modelling. The session will further address instrument calibration and science performance both retrospective on MESSENGER and on the ESA/JAXA BepiColombo mission. Papers covering additional themes related to Mercury are also welcomed. Please be aware that this session will be held as a PICO session. This will allow an intensive exchange of expertise and experience between the individual instruments and mission. NVP melt/magma viscosity: insight on Mercury lava flows S. Rossi1, D. Morgavi1, O. Namur2, D. Perugini1, F.Vetere1, P. Mancinelli1 and C. Pauselli1 1 Dipartimento di Fisica e Geologia, Università di Perugia, piazza Università 1, 06123 Perugia, Italy 2 Uni Hannover Institut für Mineralogie, Leibniz Universität Hannover, Callinstraβe 3, 30167 Hannover, Germany In this contribution we report new measurements of viscosity of synthetic komatitic melts, used the behaviour of silicate melts erupted at the surface of Mercury. Composition of Mercurian surface magmas was calculated using the most recent maps produced from MESSENGER XRS data (Weider et al., 2015). We focused on the northern hemisphere (Northern Volcanic Province, NVP, the largest lava flow on Mercury and possibly in the Solar System) for which the spatial resolution of MESSENGER measurements is high and individual maps of Mg/Si, Ca/Si, Al/Si and S/Si were combined. The experimental starting material contains high Na2O content (≈7 wt.%) that strongly influences viscosity. High temperature viscosity measurements were carried out at 1 atm using a concentric cylinder apparatus equipped with an Anton Paar RheolabQC viscometer head at the Department of Physics and Geology (PVRG_lab) at the University of Perugia (Perugia, Italy

  9. Apatite: a new redox proxy for silicic magmas?

    NASA Astrophysics Data System (ADS)

    Miles, Andrew; Graham, Colin; Hawkesworth, Chris; Gillespie, Martin; Bromiley, Geoff; Hinton, Richard

    2015-04-01

    The oxidation states of magmas provide valuable information about the release and speciation of volatile elements during volcanic eruptions, metallogenesis, source rock compositions, open system magmatic processes, tectonic settings and potentially titanium (Ti) activity in chemical systems used for Ti-dependent geothermometers and geobarometers. In this presentation we explore the use of Mn in apatite as an oxybarometer in intermediate and silicic igneous rocks. Increased Mn concentrations in apatite in granitic rocks from the zoned Criffell granitic pluton (southern Scotland) correlate with decreasing Fe2O3 (Fe3+) and Mn in the whole-rock and likely reflect increased Mn2+/Mn3+and greater compatibility of Mn2+ relative to Mn3+ in apatite under reduced conditions. Fe3+/Fe2+ ratios in biotites have previously been used to calculate oxygen fugacities (fO2) in the outer zone granodiorites and inner zone granites where redox conditions have been shown to change from close to the magnetite-hematite buffer to close to the nickel-nickel oxide buffer respectively[1]. This trend is apparent in apatite Mn concentrations from a range of intermediate to silicic volcanic rocks that exhibit varying redox states and are shown to vary linearly and negatively with log fO2, such that logfO2=-0.0022(±0.0003)Mn(ppm)-9.75(±0.46) Variations in the Mn concentration of apatites appear to be largely independent of differences in the Mn concentration of the melt. Apatite Mn concentrations may therefore provide an independent oxybarometer that is amenable to experimental calibration, with major relevance to studies on detrital mineral suites, particularly those containing a record of early Earth redox conditions, and on the climatic impact of historic volcanic eruptions[2]. [1] Stephens, W. E., Whitley, J. E., Thirlwall, M. F. and Halliday, A. N. (1985) The Criffell zoned pluton: correlated behaviour of rare earth element abundances with isotopic systems. Contributions to Mineralogy and

  10. Seismic tomography reveals magma chamber location beneath Uturuncu volcano (Bolivia)

    NASA Astrophysics Data System (ADS)

    Kukarina, Ekaterina; West, Michael; Koulakov, Ivan

    2014-05-01

    Uturuncu volcano belongs to the Altiplano-Puna Volcanic Complex in the central Andes, the product of an ignimbrite ''flare-up''. The region has been the site of large-scale silicic magmatism since 10 Ma, producing 10 major eruptive calderas and edifices, some of which are multiple-eruption resurgent complexes as large as the Yellowstone or Long Valley caldera. Satellite measurements show that the hill has been rising more than half an inch a year for almost 20 years, suggesting that the Uturuncu volcano, which has erupted last time more than 300,000 years ago, is steadily inflating, which makes it fertile ground for study. In 2009 an international multidisciplinary team formed a project called PLUTONS to study Uturuncu. Under this project a 100 km wide seismic network was set around the volcano by seismologists from University of Alaska Fairbanks. Local seismicity is well distributed and provides constraints on the shallow crust. Ray paths from earthquakes in the subducting slab complement this with steep ray paths that sample the deeper crust. Together the shallow and deep earthquakes provide strong 3D coverage of Uturuncu and the surrounding region. To study the deformation source beneath the volcano we performed simultaneous tomographic inversion for the Vp and Vs anomalies and source locations, using the non-linear passive source tomographic code, LOTOS. We estimated both P and S wave velocity structures beneath the entire Uturuncu volcano by using arrival times of P and S waves from more than 600 events registered by 33 stations. To show the reliability of the results, we performed a number of different tests, including checkerboard synthetic tests and tests with odd/even data. Obtained Vp/Vs ratio distribution shows increased values beneath the south Uturuncu, at a depth of about 15 km. We suggest the high ratio anomaly is caused by partial melt, presented in expanding magma chamber, responsible for the volcano inflation. The resulting Vp, Vs and the ratio

  11. 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.

  12. Magma-poor and magma-rich segments along the hyperextended, pre-Caledonian passive margin of Baltica

    NASA Astrophysics Data System (ADS)

    Andersen, Torgeir B.; Alsaif, Manar; Corfu, Fernando; Jakob, Johannes; Planke, Sverre; Tegner, Christian

    2015-04-01

    The Scandinavian Caledonides constitute a more than 1850 km long 'Himalayan-type' orogen, formed by collision between Baltica-Avalonia and Laurentia. Subduction-related magmatism in the Iapetus ended at ~430 Ma and continental convergence continued for ~30 Myr until ~400 Ma. The collision produced a thick orogenic wedge comprising the stacked remnants of the rifted to hyperextended passive Baltican margin (Andersen et al. 2012), as well as suspect, composite and outboard terranes, which were successively emplaced as large-scale nappe complexes onto Baltica during the Scandian collision (see Corfu et al. 2014 for a recent review). Large parts (~800 km) of the mountain-belt in central Scandinavia, particularly in the Särv and Seve Nappes and their counterparts in Troms, are characterised by spectacular dyke complexes emplaced into continental sediments (e.g. Svenningsen 2001, Hollocher et al. 2007). These constitute a magma-rich segment formed along the margin of Baltica or within hyperextended continental slivers outboard of Baltica. The intensity of the pre-Caledonian magmatism is comparable to that of the present NE-Atlantic and other volcanic passive margins. The volumes and available U-Pb ages of 610-597 Ma (Baird et al. 2014 and refs therein) suggest that the magmatism was short lived, intense and therefore compatible with a large igneous province (LIP). By analogy with present-day margins this LIP may have been associated with continental break-up and onset of sea-floor spreading. The remnants of the passive margin both north and south of the magma-rich segment have different architectures, and are almost devoid of rift/drift related magmatic rocks. Instead, these magma-poor segments are dominated by heterogeneous sediment-filled basins characterised by the abundant presence of solitary bodies of variably altered mantle peridotites, also commonly present as detrital serpentinites. These basins are interpreted to have formed by hyperextension. We suggest that

  13. Eruption of Deep Mushy Magma from the Searchlight Magma System, Southern Nevada (USA): a Crystal Size Distribution and Geochemical Analysis

    NASA Astrophysics Data System (ADS)

    Bazar, D.; Miller, J.; Miller, C.; Dodge, M.; Hodge, K.; Faulds, J.

    2006-12-01

    The Miocene Searchlight pluton and overlying volcanic rocks are exposed in the Eldorado Mountains of southern Nevada within the Colorado River Extensional Corridor. Steep tilting of the pluton and its cover provides an exceptional opportunity to study the magmatic plumbing system from bottom to top, including possible eruptions of magma from the Searchlight magma system. The pluton is approximately 10 km thick and divided into three compositionally distinct units that solidified in monotonic fashion: a 2 km thick upper fine-grained quartz monzonite (solidification front), a 6 km thick lower, more mafic quartz monzonite (cumulate), and a 2 km thick middle granite (extracted melt) [ref]. In addition, near E-W-striking rhyolite and trachydacite porphyry dikes intrude the upper quartz monzonite unit (but not the lower or middle units), and identical trachydacite porphyries (locally > 45 vol. % crystals) occur as irregular pods and masses in the roof area. The trachydacite porphyries superficially resemble trachydacite lavas in part of the overlying volcanic section. Ion probe zircon ages are identical within error for the upper unit, the lower unit, and the trachydacite dikes and pods (206Pb/238U age for samples of each ranging from 16.6±0.3 Ma to 16.9±0.2 Ma 2σ). Ages for the middle granite unit and rhyolite dikes are consistently younger (15.8-16.0 Ma). Crystal size distribution (CSD) analysis on plagioclase has been undertaken on samples from the upper Searchlight and overlying volcanic rocks in order to establish and corroborate linkages between the volcanic and intrusive units and to better understand the growth and solidification history of the Searchlight magma system. The CSD's for the intermediate porphyry dikes and pods that intrude upper Searchlight pluton are identical to trachydacite lava flows and domes erupted onto Proterozoic gneiss and earlier lava flows that comprise the roof of the pluton. The CSD's for these rocks are distinctly concave up and

  14. Organization of volcanic plumbing through magmatic lensing by magma chambers and volcanic loads

    NASA Astrophysics Data System (ADS)

    Karlstrom, Leif; Dufek, Josef; Manga, Michael

    2009-10-01

    The development of discrete volcanic centers reflects a focusing of magma ascending from the source region to the surface. We suggest that this organization occurs via mechanical interactions between magma chambers, volcanic edifices, and dikes and that the stresses generated by these features may localize crustal magma transport before the first eruption occurs. We develop a model for the focusing or "lensing" of rising dikes by magma chambers beneath a free surface, and we show that chambers strongly modulate dike focusing by volcanic edifices. We find that the combined mechanical effects of chambers, edifice loading, and dike propagation are strongly coupled. Chambers deeper than ˜20 km below the surface with magmatic overpressure in the range of 20-100 MPa should dominate dike focusing, while more shallow systems are affected by both edifice and chamber focusing.

  15. 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.

  16. Sensitivity of seafloor bathymetry to climate-driven fluctuations in mid-ocean ridge magma supply.

    PubMed

    Olive, J-A; Behn, M D; Ito, G; Buck, W R; Escartín, J; Howell, S

    2015-10-16

    Recent studies have proposed that the bathymetric fabric of the seafloor formed at mid-ocean ridges records rapid (23,000 to 100,000 years) fluctuations in ridge magma supply caused by sealevel changes that modulate melt production in the underlying mantle. Using quantitative models of faulting and magma emplacement, we demonstrate that, in fact, seafloor-shaping processes act as a low-pass filter on variations in magma supply, strongly damping fluctuations shorter than about 100,000 years. We show that the systematic decrease in dominant seafloor wavelengths with increasing spreading rate is best explained by a model of fault growth and abandonment under a steady magma input. This provides a robust framework for deciphering the footprint of mantle melting in the fabric of abyssal hills, the most common topographic feature on Earth. PMID:26472905

  17. Magma Reservoir Processes Revealed by Geochemistry of the Ongoing East Rift Zone Eruption, Kilauea Volcano, Hawaii

    NASA Astrophysics Data System (ADS)

    Thornber, C. R.

    2002-12-01

    Geochemical data were examined for a suite of 1,000 near-vent lava samples from the Pu`u `O`o-Kupaianaha eruption of Kilauea, collected from January 1983 through October 2001. Bulk lava and glass compositions reveal short- and long-term changes in pre-eruptive magma conditions that can be correlated with changes in edifice deformation, shallow magma transfer and eruptive behavior. Two decades of eruption on Kilauea's east rift zone has yielded ~2 km3 of lava, 97% of which is sparsely olivine-phyric with an MgO range of 6.8 to 9.6 wt%. During separate brief intervals of low-volume, fissure eruption (episodes 1 to 3 and 54), isolated rift-zone reservoirs with lower-MgO and olv-cpx-plg-phryic magma were incorporated by more mafic magma immediately prior to eruption. During prolonged, near-continuous eruption(e.g.,episodes 48-53 and most of 55), steady-state effusion is marked by cyclic variations in olivine-saturated magma chemistry. Bulk lava MgO and eruption temperature vary in cycles of monthly to bi-annual frequency, while olivine-incompatible elements vary inversely to these cycles. However, MgO-normalized values and ratios of highly to moderately incompatible elements (HINCE/MINCE), which nullify olivine fractionation effects, reveal cycles in magma chemistry that occur prior to olivine crystallization over the magmatic temperature range that is tapped by this eruption (1205-1155°C). These short-term cycles are superimposed on a long-term decrease of HINCE/MINCE, which is widely thought to reflect a 20-year change in mantle-source conditions. While HINCE/MINCE variation in primitive recharge magma cannot be ruled out, the short-term fluctuations of this signature may require unreasonably complex mantle variations. Alternatively, the correspondence of HINCE/MINCE cycles with edifice deformation and eruptive behavior suggests that the long-term evolving magmatic condition is a result of prolonged succession of short-term shallow magmatic events. The consistent

  18. Magma degassing triggered by static decompression at Kīlauea Volcano, Hawai‘i

    USGS Publications Warehouse

    Poland, Michael P.; Jeff, Sutton A.; Gerlach, Terrence M.

    2009-01-01

    During mid-June 2007, the summit of Kīlauea Volcano, Hawai‘i, deflated rapidly as magma drained from the subsurface to feed an east rift zone intrusion and eruption. Coincident with the deflation, summit SO2 emission rates rose by a factor of four before decaying to background levels over several weeks. We propose that SO2 release was triggered by static decompression caused by magma withdrawal from Kīlauea's shallow summit reservoir. Models of the deflation suggest a pressure drop of 0.5–3 MPa, which is sufficient to trigger exsolution of the observed excess SO2 from a relatively small volume of magma at the modeled source depth beneath Kīlauea's summit. Static decompression may also explain other episodes of deflation accompanied by heightened gas emission, including the precursory phases of Kīlauea's 2008 summit eruption. Hazards associated with unexpected volcanic gas emission argue for increased awareness of magma reservoir pressure fluctuations.

  19. The Lunar Magma Ocean: Reconciling the Solidification Process with Lunar Petrology and Geochronology

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, L. T.; Burgess, S.; Yin, Q.-Z.

    2011-03-01

    Detailed physical and chemical models of fractional solidification of the lunar magma ocean offer solutions to both basalt and picritic glass source region compositions and depths, and to the wide span of ages of highlands materials.

  20. Sensitivity of seafloor bathymetry to climate-driven fluctuations in mid-ocean ridge magma supply

    NASA Astrophysics Data System (ADS)

    Olive, J.-A.; Behn, M. D.; Ito, G.; Buck, W. R.; Escartín, J.; Howell, S.

    2015-10-01

    Recent studies have proposed that the bathymetric fabric of the seafloor formed at mid-ocean ridges records rapid (23,000 to 100,000 years) fluctuations in ridge magma supply caused by sealevel changes that modulate melt production in the underlying mantle. Using quantitative models of faulting and magma emplacement, we demonstrate that, in fact, seafloor-shaping processes act as a low-pass filter on variations in magma supply, strongly damping fluctuations shorter than about 100,000 years. We show that the systematic decrease in dominant seafloor wavelengths with increasing spreading rate is best explained by a model of fault growth and abandonment under a steady magma input. This provides a robust framework for deciphering the footprint of mantle melting in the fabric of abyssal hills, the most common topographic feature on Earth.

  1. 75 FR 28778 - Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan, Pinal County, AZ

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-24

    ... Natural Resources Conservation Service Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan, Pinal County, AZ AGENCY: Natural Resources Conservation Service. ACTION: Notice of a Finding of No...; the Council on Environmental Quality Regulations (40 CFR part 1500); and the Natural...

  2. Eruption vs. storage: Key thermomechanical controls on the production of large silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Jellinek, M.; Depaolo, D.

    2008-12-01

    The production of large-volume silicic magma chambers in the mid to upper crust is enigmatic: Why would buoyant and otherwise eruptible magma remain ponded at depth rather than drain to the surface roughly at the rate at which it is produced? One way that the rise and eruption of this magma can be checked is if the nucleation and/or propagation of dikes to the surface is suppressed. Additionally, if the average rate at which heat is carried in to the chamber by basaltic or silicic replenishments is insufficiently large relative to the rate of internal crystallization, the magma may become overly crystal rich and effectively "uneruptible". Bearing in mind these two mechanisms favoring chamber growth we will simple models to discuss three issues that ultimately govern whether buoyant magma becomes stored in a high-level magma chamber or erupts at the surface: 1) The long-term average supply of magma to the chamber; 2) the thermal structure, mechanical strength and background stress regime of the crust; and 3) the volume and shape of the magma chamber. For a given chamber volume, shape and cooling rate, the magma supply to a volcanic/plutonic system governs both the mean crystal content and the maximum average chamber overpressure available to propagate dikes to the surface. Whether such an overpressure can drive dike formation and propagation to the surface or lead to magma storage depends on the strength and thermal regime of surrounding crust, which depends, in turn, on their initial thermo-mechanical state and subsequent history of magmatism. In principle, even if a magmatic system is in a regime that favors eruption a very high magma supply (greater than the rates of eruption and crystallization) can ensure that magma accumulate in the crust. Thus, the most import parameter in the problem that must be constrained carefully is the magma supply. The long term magma supply is controlled primarily by the heat transfer properties of underlying mantle convection and

  3. Evidence for the reversal of gradients in the uppermost parts of silicic magma reservoirs

    USGS Publications Warehouse

    Duffield, W.A.; Ruiz, J.

    1992-01-01

    Evidence from large-volume ignimbrites indicates that the source-magma reservoirs for most of these voluminous silicic pyroclastic deposits contained monotonic vertical chemical gradients at the time of eruption. However, gradients from a large-volume magma reservoir that produced a group of penecontemporaneous silicic lava domes, but no ignimbrite, show a reversal of the usual ignimbrite pattern. This reversal originated by modification of the usual pattern through minor assimilation of partially melted roof rocks. Eruptions that produced these domes apparently just tapped the uppermost part of their source reservoir. They thereby provide a high-resolution instantaneous view of this variably contaminated part of the magma system. The long-standing paradigm for monotonic zoning in large-volume reservoirs of silicic magma may require modification. -from Authors

  4. Evolution of a terrestrial magma ocean: Thermodynamics, kinetics, rheology, convection, differentiation

    NASA Technical Reports Server (NTRS)

    Solomatov, V. S.; Stevenson, D. J.

    1992-01-01

    The evolution of an initially totally molten magma ocean is constrained on the basis of analysis of various physical problems in the magma ocean. First of all an equilibrium thermodynamics of the magma ocean is developed in the melting temperature range. The equilibrium thermodynamical parameters are found as functions only of temperature and pressure and are used in the subsequent models of kinetics and convection. Kinematic processes determine the crystal size and also determine a non-equilibrium thermodynamics of the system. Rheology controls all dynamical regimes of the magma ocean. The thermal convection models for different rheological laws are developed for both the laminar convection and for turbulent convection in the case of equilibrium thermodynamics of the multiphase system. The evolution is estimated on the basis of all the above analysis.

  5. Derivation of primary magmas and melting of crustal materials on Venus - Some preliminary petrogenetic considerations

    NASA Technical Reports Server (NTRS)

    Hess, Paul C.; Head, James W.

    1990-01-01

    As an aid to understanding crustal formation and evolution processes on Venus, a general paradigm is developed for the derivation of primary magmas, and the range of possibilities of conditions for remelting of crustal materials and the evolution of the products of remelting. The present knowledge of the bulk and surface composition is used as a basis. A wide range of magma types is possible for the range of conditions of derivation of primary magmas and crustal remelting and no magma type can be arbitrarily excluded from consideration on Venus. The composition of Venus and the nature of source materials for melting, the melting of mantle material peridotites, and the melting of basalts including tholeiites and modified basalts are discussed. Magmatic differentiation is considered, and a comparison to terrestrial magmatic environments is conducted. It is concluded the magnetic and volcanic activity on Venus could be very similar to that on the earth, although eruption styles are expected to vary due to environmental conditions.

  6. 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

  7. Magma to Microbe: Modeling Hydrothermal Processes at Ocean Spreading Centers

    NASA Astrophysics Data System (ADS)

    Lowell, Robert P.; Seewald, Jeffrey S.; Metaxas, Anna; Perfit, Michael R.

    Hydrothermal systems at oceanic spreading centers reflect the complex interactions among transport, cooling and crystallization of magma, fluid circulation in the crust, tectonic processes, water-rock interaction, and the utilization of hydrothermal fluids as a metabolic energy source by microbial and macro-biological ecosystems. The development of mathematical and numerical models that address these complex linkages is a fundamental part the RIDGE 2000 program that attempts to quantify and model the transfer of heat and chemicals from "mantle to microbes" at oceanic ridges. This volume presents the first "state of the art" picture of model development in this context. The most outstanding feature of this volume is its emphasis on mathematical and numerical modeling of a broad array of hydrothermal processes associated with oceanic spreading centers. By examining the state of model development in one volume, both cross-fertilization of ideas and integration across the disparate disciplines that study seafloor hydrothermal systems is facilitated. Students and scientists with an interest in oceanic spreading centers in general and more specifically in ridge hydrothermal processes will find this volume to be an up-to-date and indispensable resource.

  8. Are Ferroan Anorthosites Direct Products of the Lunar Magma Ocean?

    NASA Technical Reports Server (NTRS)

    Neal, C. R.; Draper, D. S.

    2016-01-01

    According to Lunar Magma Ocean (LMO) theory, lunar samples that fall into the ferroan anorthosite (FAN) category represent the only samples we have of of the primordial crust of the Moon. Modeling indicates that plagioclase crystallizes after >70% LMO crystallization and formed a flotation crust, depending upon starting composition. The FAN group of highlands materials has been subdivided into mafic-magnesian, mafic-ferroan, anorthositic- sodic, and anorthositic-ferroan, although it is not clear how these subgroups are related. Recent radiogenic isotope work has suggested the range in FAN ages and isotopic systematics are inco